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DRAFT

CONTROL OF CORROSION AND SCALING IN GEOTHERMAL SYSTEMS

Project coordinated by BRGM (1. Ignatiadis)

BP 6009,45060 Orléans Cedex 2, France

Contract Nos:

JOU2-CT92-0108 and CIPD-CT93-0314

Final Report Covering the period from

December 1 st 1992 to July 31 st, 1996

Research funded in part by

THE EUROPEAN COMMISSION

in the framework of the JOULE Programme

Subprogramme ADVANCED FUEL TECHNOLOGIES: EARTH SCIENCES

Date: November 20th. 1996

Control of corrosion and scaling in geothermal systems

PRESENTATION OF THE FINAL REPORT OF THE CONTRACTORS by 1. IGNATlADlS (coordinator) and A. ABOU AKAR

(BRGMIDRIGGP)

JOULE II Project, contract Nos. JOU2-CT92-0108 and CIPD-CT93-0314 Title: Control of corrosion and scalUig in geothemal systems

FOREWORD

This final report presents the scientific contributions of al1 the partners in the Joule 2 programme, contract Nos. JOU2-CT92-0108 and CIPD-CT93-0314 (entitled Control of corrosion and scaliig in geothermal systems). The partners are BRGM, CEBELCOR, CPERI, CPR, and ICEHT, the research groups that have been involved in the project from the beginning of the programme (December 1, 1992), and BBPDICM, CAEL, CRIC, ICPE C-60 and ICVL, the groups from Central and Eastern European countries who joined the project in 1994.

In this report, the research groups put together their work in a unique contribution as an integrated work. The work done has been classified according to the 6 main themes of the project as defied by the contractors and European Experts at Udine in July 1994 (corrosion prevention, corrosion studies, scale formation and modelling, scale prevention, corrosion and scaling in diphasic flow conditions and corrosion and scaling monitoring). This classification was proposed in order to facilitate the presentation of this report. Nevertheless, abstract, introduction and conclusion specific to each contractor were maintained just as it is. Let's specify that some articles can deal with two or more themes.

This report was presented at the final meeting that takes place in Paris, France, on July 19, 1996, a day after the 7th biannual meeting and repoa presentation which was held in the same venue as the fmal meeting.The officia1 end of the programme is July 31, 1996. The outline adopted for this report is as follows:

Abstract (related to each partner contribution) A i of the research: context and general objectives, particular objectives of each group The body of the report, made up of al1 the scientific contributions grouped by themes. This part describe work performed, results and discussion Preliminary conclusions (related to each partner contribution) General conclusion and future developments References List of publications and patents related to the project (1993-1996) Figures

The 10 partners of the programme are:

1. BRGM, Research Division, Department of Geotechnical Engineering and Minera1 Technology (DRIGGP), Orleans, France 1. Ignatiadis, A. Abou Akar, M. Amalhay, C. Cotiche and H. Lesueur

2. CEBELCOR, Centre Belge de 1'Etude de la Corrosion, Bmssels, Belgium A. Pourbaix and A. Singh

EEC-DG XII-Joule Programme-contract Nos JOU2-CT92-0708 and CIPD-CT93-0314 - final report 1


3. Chemical Process Engineering Research Institute (CPERI), Thessaloniki, Greece A. Karabelas, N. Andritsos, M. Kostoglou, S.V. Paras and N.A. Vlachos

4. Consorzio Pisa Ricerche, Centro TEA (CPR), Pisa, Italy P. Andreussi, R. Corsi, M. Guidi, L. Marini, G. Mura, A. Paglianti, A. Pasqualeîti, E. Piciocchi, F. Prosperi, F. Sabatelli and E. Viviani.

5 Institute of Chemical Engineering and High Temperature Chemical Processes and the Department of Chemical Engineering, University of Patras, Greece P. G. Koutsoukos, N.G. Harmandas and P. Klepetsanis.

6. Bioactive and Biocompatible Polymers Department of the Petm-Poni Institute of Macromolecular Chemistry (BBPDICM), Iasi, Romania A. Carpov, G.C. Chitanu, 1. L. Zaharia and A. G. Anghelescu-Dogam.

7. Computer Aided Electrochemistry Laboratory (CAEL) of the "Politechnica" University of Bucharest, Romania V. Cotarta, G.H. Juncu, B. Petrescu, F. Stan and F.M.G. Tomescu.

8. Central Research Institute for Chemistry (CRIC), Budapest, Hungary E. Kalman, 1. Bako, 1. Felhosi, F. H. Karman, 1. Lukoviks, G. Palinkas, G. Patzay, G. Stahl and J. Telegdi.

9. Electrochemical Technologies and Active Anticorrosive Protection Laboratory of the Research and Design Institute for Electrical Engineering (ICPE C-60), Bucharest, Romania 1. Lingvay, D. Badea, M. Chefneux, R. Cindea, C. Ionescu, C. Pacala, P. Paraian, C. Rata, V. Stanciu and F. Stoian.

10. Institute of Chemistry (ICVL), Vilnius, Lithuania. E. Juzeliunas, M. Samuleviciene, K. Leinartas, D. Vibalyte, A. Sidavicius, P. Miecinskas and V. Noskovas.

2 EEC-DG XII-Joule Programme-contract Nos JOU2-CT92-0708 and CIPD-CT93-0374 - final report


1. ABSTRACT

The BRGM contribution to the European Union CO-financed research programme aims to eliminate the problerns due to corrosion and scaling in low enthalpy geothermal systems in order to ensure their financial profitability. It focuses on solving real problems encountered during exploitation of geothermal resources. In this perspective the fields studied are the low enthalpy Dogger aquifer of the Paris basin. The results can be summarized as follow: In order to monitor the corrosion rate of carbon steel (used for pipes and casings) and to maintain the effectiveness of a treatment by a corrosion inhibitor in a given geothermal plant, several different methods must be used, each having its own limitations, its advantages and disadvantages. The work done has contributed to the adaptation and the use of three type of methods for geothermai applications. The influence of some exploitation conditions on corrosion and scaliig in geothermal wells is reported. The corrosivity of a geothermal fluid was assessed with respect to various materials at two flowrates, in the presence and absence of corrosion inhibitor (quatemary ammonium salt). The behaviour of a carbon steel in the absence and in the presence of various corrosion inhibitors in partially reconstituted, actual and modified geothermal water is examined in order to optimize their use in low enthalpy geothermal systems. The influence of some physico-chemicai parameters known to be determinant in the process of carbon steel corrosion and its inhibition such as s a l i t y , hydrogen sulfide concentration and geothermal fluid flowrate in the casings have also been studied in a naturai geothermal water. The determination of the influence of these physico-chemical parameters on the effectiveness of an inhibitor, enable us to predict the order of magnitude of the concentration necessary of inhibitor for an optimum effectiveness as a function of the composition of the fluid of each well. Another main part of the work performed is iron sulfide formation and inhibition studies. Experiments were done in order to better understand its precipitation kinetics. Results of analyses done at the end of the kinetics experiments and those of the fluids at the production wellhead were used to identify which iron sulfide controls the solubility of iron and sulfide in the geothermal environment. Machawite is this iron sulfide, despite the presence of other ones in the deposits. Electrochemical techniques were used to monitor the behavior of carbon steel during the crystallization of corrosion deposits in the presence of corrosion inhibitors. By combining the results with mineralogical analyses of the scale, we have shown that the crystallization of amorphous iron sulfide into mackinawite is accompanied by an increase in the corrosion rate due to the transfer of cathodic sites from the surface of the metal to that of the scale. A comparative study of the effectiveness of various surfactants in inhibiting iron sulfide precipitation in a natural geothermal environment have been realized. Its objective is to better understand the mechanisms controllmg the action of these inhibitors and compare their effectiveness to those of other molecules or formulae which are synthesized and provided by the BBPDICM. In general, al1 the additives tested in this experimental investigation did not prove to have any scaling inhibition effectiveness with respect to iron sulfide formation. The behaviour of some non metallic materials in actual and treated geothermal environment have been characterized. This study shows that knowledge of the behaviour of nonmetallic materiais in the field of low enthalpy geothermal energy is limited. Scientific results are rare as scientists are currently concentrating their efforts on the battle against steel casing corrosion. After briefly describing the context in which these materials are used, this study l i ts the principal characteristics of the nonmetallic materials which can be used in geothermal activities and gives the main results gathered from the Dogger exploitation in the Paris Basin. On the topic of modelliig corrosion and scalmg phenomena on the walls of steel casing in geothermal wells a digital mode1 that enables the simulation of these phenomena is proposed.



Considering the complexity of the real phenomena, certain simplivig hypotheses were included in the model. The amount of mackinawite (the main scale constituant) precipitated is calculated using the solubility product, Ks or according kinetic considerations. The model also (i) simulates the precipitation of five other mineral species, (ii) offers the possibility of adjusting the flowrate of the geothermal water in the well, and (iii) takes into account the presence of a well-bottom treatment tube (WBTT) when calculating the head loss. The environmental impact of a perforation in the casing of a well exploiting the water of the Dogger was studied. When localiied, corrosion can lead to perforations in the casing, thereby increasing the risk of contamination by geothermal fluids of freshwater aquifers (Albian, Challc) traversed by the wells. After examination of the various water-migration possibilities with one or two casing perforations in a production or injection well, the different detection methods for perforations are discussed in terms of their limitations and accuracy. In al1 case, a logging tool is necessary to confirm the existence of a perforation and to locate its depth.

The work performed by the CEBELCOR refers to the preparation of potential-pH equilibrium diagrams, to the effects of oxidants and to the study of corrosion processes and to electrochemical systems for monitoring corrosion.

The general aim of the work performed by the CPERI is to contribute to a better understandiig of the complicated phenomena of scale formation and corrosion in geothermal systems. The work deals specifically with three different areas: the formation and inhibition of deposits, stabiiity of colloidal systems and two-phase flow characteristics encountered in geothermal installations. The data on iron (II) sulfide scale formation show that appreciable mass of relatively strongly adhering amorphous deposits develops only within a narrow pH range. For al1 additives tested, a small inhibition action was found for the Fe,S system, while for the CaC03 system at intermediate supersaturation ratios almost complete scale inhibition was obtained. New data are obtained in the so called "st~atifiedlatomisation" two-phase flow regirne are helpful for the development of generalized correlations of engineering interest. The latter are aimed at predicting gas phase velocity distribution, shear stress at the liquidlwall interface, and pressure &op. As regards stability and coagulation of colloidal dispersions, a new computer code was developed for predicting phenomena occurring simultaneously along the flow path of a supersaturated geothermal fluid, i.e. particle nucleation, growth and coagulation as well as particle deposition and wall crystallization. The system PbS-water (typical of geothermal fluids) was used for case study. Other important phenomena, relating to colloidal particle coagulation, were also theoretically studied, such as the effects of particle surface roughness and of its dynamics on repulsive forces resisting coagulation.

The development of a process for eliminating chlorides by washing geothermal s t e m and the identification of the interactions between diphasic flow conditions and corrosion and scaling are the main objectives of CPR within the Work Programme. With respect to these objectives, the activities described in the present report allowed the following major results to be obtained: 1. Design of a full-scale sbuctured column for s t em washing. The column will be constructed and

tested in the near future by ENEL at Larderello Geothermal Field. 2. Development of GEA (Geothermal Equilibria Assessment) code. This code allows the computation

of vapour-liquid equilibria in geothennal equipment and represents a significant extension and completion of the Drop Code developed in the previous programme (JOUG-0005-C).

3. Analysis of field data on the efficiency of chloride abatement in existing facilities. This activiiy has been canied out in cooperation with ENEL.



4. Development of a dry process for chloride abatement. This process should allow a significant increase of power production in geothermal plants.

5. Analysis of diphasic flow conditions and in particular, of annular flow in geothermal wells. This analysis lead to the development of a vertical upward flow version of the HORF (Horizontal Flow) Code, developed in the previous programme. This code, named VEA (Vertical Annular), has been used to test the feasibility of s t em washing operations conducted directly in the well.

The mechanism of iron (II) sulfide precipitation was studied by ICEMTCP using spontaneous precipitation experiments at temperature, pH and salinity conditions simulating scaling conditions in geothermal wells in which this type of deposits are found. Spontaneous precipitation occurred only in solutions supersaturated with respect to amorphous FeS which was the initially forming phase in acidic solutions (pH 5.5-6.5). In neutral or slightly alkaline solutions mackinawite was formed. The effect of salinity at 80°C was found to iduence both the threshold limit for precipitation and the nature of the precipitating phase. In high salinity aqueous media in the presence of oxidizing ions (Cl-, NO3-) the formation of pyrite was favoured. In al1 cases the dependence of the rates of iron sulfides formation on the relative solution supersaturation yielded a high apparent order (n = 1-9) suggesting a surface controlled process. The experiments of iron sulfide precipitation done at geothermal wells showed a similar mechanism. The additives tested faiied to show satisfactory inhibition with respect to iron sulfide formation except for ATP 6.2 which showed significant inhibition of the rates of crystallization in natural geothermal brines. The water-soluble additives tested (commercial and BBPDICM preparations) with the exception of Nomst 491@, showed however inhibition with respect to calcium carbonate scale formation which for concentrations ranging from 0.05-10 ppm was between 15-100%. Both AC and DC electrochemical evaluation of commercial products and compounds prepared by BBPDICM showed that only the former products Solamine 12g8, Nomst 4918 and Aquaprox MDC 1 3 0 0 ~ gave significant reduction of the corrosion rates of carbon steel in NaCl containing media.

The results conceming the synthesis of maleic copolymers and the derivatives and the activity of these products as scale and101 corrosion inhibitors investigated by BRGM, ICEIHT, CPERI and ICPE C-60 are presented by BBPDICM. It was synthesized several maleic anhydride binary or temary copolymers with methyl methacrylate or N-vinylpyrrolidone as well as salts, monoesters, monoamides and derivatives containing heterocyclic or aromatic amines. Some maleic copolymers, especially the ones containing N-vinylpyrrolidone as comonomer exhibited a good ability to inhibit the calcium carbonate precipitation or even the iron sulfide precipitation. Some of them reduce also the corrosion of mild steel in some cases but in this regard the results are not yet conclusive. It could be observed a certain relationship between chemical structure of maleic copolymers and their effect as scalelcorrosion inhibitors. Some maleic copolymers or their derivatives exhibited at the same time good properties as scale and corrosion inhibitors. The "ortho effect" stated for anticorrosion activity of aromatic amines was identified also by the maleic copolymer derivatives of these products.

The first aim of the work done by the CAEL was to mode1 the corrosion processes in large volumes (reservoirs) using multigrid and finite element methods, in order to simulate the distribution of current and potential field, for an optimum position of anode in cathodic protection. The important aspect are: (i) the influence of the distance between the liquid superior level and the electrode on the potential distribution and wall current values, (ii) the laboratory study conceming the cathodic protection of metals (alloys) in geothermal water in the absence of extemal current sources, and (iii) the corrosion monitoring system based on multi-electrode. The second aim of the work was to determine the influence of ions (Cl-, HS-), pH, and inhibitors on the corrosion process: a very



contradictory behaviour of the steel in contact with brine, which contain H2S and CO2 was observed. The attack was not uniform corrosion in an electrochemical sense, although it may have been uniform on a microscopic scale. On the other site an oscillatory domain is identified during Fe anodic polarisation, which is strongly influenced by some critical values of the parameters mentionned above. The last aim of the work is to model and simulate the periodic oscillations, that occur at the anodic polarisation of Fe electrodes in geothermal water with high Cl- content. Another aspect of this aim is the using of the integral method to calculate the Tafel kinetic corrosion parameters @,, b,) and corrosion current (I,,,), in the geothermal water.

New simulation algorithm and computer program was developed by CRIC for the equilibrium scale formation of calcite: - in water at any desired temperature, pressure. The simulation method based on the Pitzer activity

coefficient calculation. - in multicomponent (13 ionic species) water at any desired temperature, pressure. The simulation

method based on the Pitzer activity coefficient calculation. New simulation algorithm and computer program was developed for the equilibrium determination of the bubble point using gas separation data in thermal water wells at any desired temperature, pressure. The simulation method is based on the Kocsis method. Were developed an equilibrium simulation algorithm and a computer program for the determination of the partial pressures of the dissolved gases (CO2, CH4, and N2 ) and, using detemined CO2 partial pressures, for the determination of the CaC03 scale formation in Na-K-Mg-Ca-H-Ba-Sr-Cl-Br-S04-OH-HC03-CO3- CO2-H20 system along the well between the bubble point and the well head. New small scale test reactor was developed for the investigation of calcite scaliig in water at 20-600°C and 1-8 bar. New pilot plant device was developed to investigate the scaliig processes in various model solutions at 20-800°C and 1-4 bar. The correlation between the molecular structure and corrosion/scaling inhibitor efficiency was investigated. Chemicals used as corrosion inhibitor were prepared in our laboratory. Based on the ability of derivatives of natural amino acids to inhibit corrosion and presumed their scale inhibiting properties experiments were designed to evaluate their effects on corrosion of mild steel and on scale formation. Various N-acylamino acids were synthetized and their inhibiting capacity was tested by using potentiostatic method. The inhibiting efficiencies varied between 36 and 61%. The electronic properties obtained by using the AMI quantum chemical approach, were correlated with experimental efficiencies and the best multiple correlation coefficient obtained was equal to 0.80. Due to these prelimiiary results, N-acylamino acids may form charge transfer complexes with the iron atoms on the metal surface. A stochastic mathematical model was developed for a statistical description of corrosion process of metals and for inhibition of corrosion by an adsorption mechanism. Based on the model, the dissolution of metals and the efficiency of inhibitors can be studied by computer simulation.

The corrosion process and scaling from the geothermal systems of Romania were studied by ICPE- C60 theoretically and experimentally. Also, it was conceived, designed and tested an equipment with its specific elements destined for active anticorrosive protection of the extemal sides of the metallic installations in direct contact with the soi1 as so as of the intemal sides of some bulky equipments in direct contact with the geothermal fluid. To choose the adequate inhibitors and their optimal doses (from technical and economical point of view), the kinetic parameters of the corrosion reactions to the interfaces carbon steel R37lgeothermal fluid, were detemined from 14 wells. These corrosion rates are influenced by the ionic content of geothennal fluids, especially of Cl-, S042- and S2-. Maleic polyelectrolytes having different structures were studied and the conclusion is that they can be utilized as inhibitors with cumulated effect



(corrosion and scaling). The result of these determinations indicates that many studied substances had a pronounced effect of inhibition. These depending of the lateral groups from the structure of the polyelectrolytes, operating through the altering of the transfer coefficient a (implicitly the Tafel slope), or by braking the anodic and101 cathodic reaction of the charge transfer. It was also studied and conceived an automated system of dosing and injection of the inhibitors having an optimal concentration (technico-economical) for the geothermal welis. For this purpose, it was conceived and realized a multifunctional transducer which collects (in situ) fiom the geothermal water the parameters; corrosion, scale and temperature. The experimental results of this device are detailed, described for geothermal waters having Ca2+ and HC03-.

The results of iron and carbon steel corrosion investigations in geothermal fluids Vidmantai 1 and Vidmantai 2 (Lithuania) are summarized by the ICVL. The fluid content was determined by means of atomic-absorption spectroscopy, ion chromatography and other analytical methods. Corrosion rates were estirnated taking volkammetric measurements. Cathodic and anodic Tafel slopes, the polarisation resistance and the corrosion rate were determined in the fluid as functions of electrode rotation, the immersion t h e , temperature and the amount of chloride. This has been done in naturally aerated solutions as well as in the N2 and CO2 atmosphere. Formation of oxide-layer on carbon steel during the corrosion process have been studied. X-ray photoelectron spectroscopy and surface etching with ionized argon were used for this purpose. The influence of oxide layer on kinetics of corrosion process was discussed. The results of iron corrosion investigations by electrochemical quartz crystal micro-gravimetry (EQCM) are also reported. The EQCM data were analysed in terms of oxide layer formation, precipitation of scarcely soluble compounds on the electrode, and iron corrosive dissolution. The investigations in synthesised solutions were conducted as well.



TABLE OF CONTENTS

1 . Introduction . Aim of the research .....................................................

2 . Work performed. results and discussion ..............................................

2.1. Corrosion prevention ....................................................................... 2.2. Corrosion studies ............................................................................ 2.3. Scale formation and modelling ............................................................ 2.4. Scale prevention ............................................................................. 2.5. Corrosion and scalig in diphasic flow conditions .................................... 2.6. Corrosion and scaiiig monitoring ........................................................

3 . Preliminary conclusions ..................................................................

4 . General conclusion and future objectives .............................................

5 . References ..................................................................................

6 . List of publications related to the project (1993-1996) .............................

7 . Annexes: (figures) .........................................................................

8 EEC-DG XII-Joule Programme-contract Nos JOU2-CT92-0108 and CIPD-CT93-0314 . final report


1. INTRODUCTION - AIM OF THE RESEARCH

The aim of the programme is to resolve the problems caused by corrosion and scaliig in the exploitation of low and high enthalpy geothermal systems. The increased costs resulting from these problems decrease the profitability of the projects and, in certain cases, can be inimical to the development of the uses of geothemal energy. The geothermal plants most concerned are those currently operating in the Paris Basin in France, at Larderello in Italy, in Greece, and those in the planning stage in these and other countries. The mechanisms of corrosion and the formation of scale encountered are similar, even when the geothermal fluids have different physico-chemical characteristics. Very few European research centres are currently working on these highly specific and complex aspects of corrosion in deoxygenated media in France, Italy and Greece. Since the energetic (or economic) value of the resource is low, it is necessary to develop processes that are both very efficient and inexpensive.

The immediate objectives of the programme are to detemine the conditions under which corrosion takes place and which lead to the formation and growth of scale (iron sulfide, calcium carbonate, silica, lead sulfide), and to develop predictive models. This will lead to the design of processes for industrial application to control corrosion and scaliig, using corrosion and crystal growth inhibitors, vapour-cleaning systems and treatment of condensates before injection. The work programme is carried out by the following groups:

Bureau de Recherches Géologiques et Minières, Direction de la Recherche, Research Division, Département Géomatériaux et Géoprocédés, Department of Geotechnical Engineering and Minera1 Technology, (BRGM, Dr. 1. Ignatiadis, Coordinator) Orleans, France; Centre Belge de 1'Etude de la Corrosion (CEBELCOR, Dr. Pourbaix) Bmsseis, Belgium; Chemical Process Engineering Research Institute (CPERI, Prof. A. Karabelas) Thessaloniki, Greece; Consorzio Pisa Ricerche, Centro TEA (CPR, Prof. P. Andreussi) Pisa, Italy, and Institute of Chemical Engineering and High Temperature Chemical Processes (ICEIHTCP, Prof. P. Koutsoukos) Patras, Greece.

The possibilities for developing the use of geothermal energy in other European countries (Hungary, Romania, Lithuania, etc.) led us to propose an extension of the programme to allow the association of new research partners. This extention was prompted by the European Union programme for "Cooperation in Science and Technology with Central and Eastern European Countries, 1993". The additional work programme is carried out by the following groups:

Bioactive and Biocompatible Polymers Department of the Petni-Poni Institute of Macro- molecular Chemistry (BBPDICM, Prof. A. Carpov), Iasi, Romnia, Computer Aided Electrochemistry Laboratory (CAEL, Dr. V. Cotarta) of the "Politechnica" University of Bucharest, Romania, Central Research Institute for Chemistry (CRIC, Prof. E. Kalrnan), Budapest, Hungary, Electrochemical Technologies and Active Anticorrosive Protection Laboratory of the Research and Design Institute for Electrical Engineering (ICPE C-60, Dr. 1. Lingvay), Bucharest, Romania, Institute of Chemistry (ICVL, Dr. E. Juzeliunas), Vilnius, Lithuania.

The aims and deliverables for the laboratories of the European Union are defined in the initial work programme. The general objectives, particular objectives and deliverables for laboratories in Central and Eastern European countries are defined in the additional and specific work programme.



BRGM The BRGM contribution to the European Cornmunity co-financed research programme Joule contract noJOU2-CT92-0108 aims to eliminate the problems due to corrosion and scaling in the exploitation of low enthalpy geothermal systems in order to ensure their financial profitability. It focuses on solving real problems encountered during exploitation of geothermal resources. In this perspective the fields studied are the low enthalpy Dogger aquifer of the Paris basin (41 doublets in operation representing a thermal power of more than 350 MW). The research programme aims on the one hand, on the theoretical level, to develop understanding of the reaction mechanisms which control corrosion (of carbon steel) and scaling, and on the other hand, on the technological level, it aims to improve the solutions currently employed and to develop new, less costly and101 more reliable solutions. This contribution deals with the following topics: (i) development of the metrology associated with the monitoring of corrosion and scalig, (ii) selection of the most efficient products for inhibiting corrosion or crystal growth with a view to

their optimal use withii current and future operations, (iii)establishment of the kinetics of the formation and growth of the scale most frequently

encountered, with the development of appropriate numerical simulation codes. The calculation code will enable modelling of corrosion-scaling phenomena in low enthalpy geothermal systems,

(iv) establishment of a general methodology for detecting and assessing perforations in casings of wells exploiting geothermal waters,

(v) study of corrosion and scaling phenomena in diphasic flow conditions.

CEBELCOR The feeling of CEBELCOR is that his previous work on the E-pH diagrams has provided a much stronger confidence in the data and in the resulting diagrams, and an detailed consciousness on what is still uncertain (stoichiometric coefficients, data for some iron sulfides, metastability, aging). E-pH equilibrium diagrams are a solid support to the interpretation of field data and of lab experiments. The limitations of these diagrams due to kinetic aspects have been clarified and appear as marginal: field observations, lab experiments and measurements in other disciplines (oil and gas, marine) show that most of the reactions of these systems S-H20 and Fe-S-H20 are rather reversible, at least much more than generally considered before. The experiments conducted in double-cells clearly indicate the activity of local corrosion cells. These cells may become interesting sensors for the study or detection of corrosion in H2S media. The results of the lab tests have shown the importance of catalysis of electrochemical reactions that have a l i i t e d driving force. This has opened a field for research that is not yet completed. The work of Cebelcor is concemed with. (i) influence of oxidants and corrosion process in both S and Cl environments (also localised

corrosion and corrosion under deposits), (ii) E p H diagrams for Fe-S-H20 systems, (iii) development of electrochemical systems for the determination of corrosion modes and rates.

CPEIU The formation of hard and tenacious scales in both the surface and the subsurface equipment, as well as the corrosion of metallic surfaces have inevitably severe adverse consequences on the operation and the economics of a geothennal installation. The general objectives of the present research programme are, first, to expand our knowledge of the mechanisms which control scaling and corrosion phenomena and, second, to improve the currently employed techniques or to develop new ones in an effort to alleviate these problems. The particular objectives of thii part of the project, as outlined in the original work programme, are: (i) to elucidate the mechanisms of sulfide scale formation (notably of iron sulfide), (ii) to assess the efficiency of organic additives to inhibit scale deposition.

10 EEC-DG Xll-Joule Programme-contract Nos JOU2-CT92-0108 and CIPD-CT93-0314 - final report


(iii) to study theoretically the coagulation process and use the results in modelling efforts. More precisely, to realise a computer code capable of predicting the evolution along the pipe of the colloidal particle distribution and of deposit formation,

(iv) to study the local characteristics of two-phase flows affecting corrosion and scaling phenomena,

CPR The main objective of the present programme is the analysis and solution of corrosion problems created by the presence of hydrochloric acid in superheated geothermal steam. Part of the programme represents the continuation of a previous EU funded programme (JOUG-0005-C). In particular, this is the case for the following items: (i) design of a structured packing column for steam washing, (ii) development of a computer code for the assessment of vapour-liquid equilibrium in geothennal

systems, (iii) analysis of field data relative to chloride abatement. New objectives of the present programme are the following: (iv) development of a dry process for steam washiig, (v) analysis of diphasic flow conditions in geothermal wells and of their relevance with respect to

corrosion problems. Not al1 these objectives were stated in details in the original work programme, and also, it was expected to perfonn an experimental activity with regard to point (v) which has not been possible due to the larger priorities and more consistent fund allocation received by the other parts of the programme. Major deliverables completed in the course of the project can be grouped as follows: (i) wet processes for HCl abatement, (ii) dry Process for HC1 abatement, (iii) computation of vapour-liquid equilibria in geothermal equipment.

ICEIHTCP The problems of corrosion and scaling, often coupled, constitute a serious impediment in the utiliiation of geothermal energy which is based in handliig geothermal fluids of various chemical compositions. The process of scale formation is a heterogeneous process including various steps as development of supersaturation, diffusion of the growth units of the salts forming through the bulk fluid onto the heterogeneous surface (e.g. pipe walls or valves or suspended particles), followed by surface diffusion to the active sites, dehydration and finally integration into the growing crystal. The slowest of the above stages is the rate determinmg step. It is therefore necessary, for each salt forming, to understand the mechanism of formation by studying the conditions (e.g. temperature, ionic strength, supersaturation etc.) and measuring the kinetics of precipitation. Analysis of the kinetics results leads to conclusions regardiig the mechanism of scale formation and to suggestions as to how to reduce these phenomena. Phase characterization is another important issue since a number of iron sulfides are known and may be formed in geothermal fluids. Scale formation is very often related with corrosion of metallic parts which are in contact with the aqueous media. Corrosion is another severe problem which seems to affect seriously the installations of geothennal energy utilization. Carbon steel is a material commonly used in the geothermal installations because it is inexpensive and of interest for its mechanical characteristics. Unfortunately, carbon steel is sensitive to corrosion in the geothermal environment. Geothermal waters are characterized by the relatively high fluid temperature and salinity, which in addition to the presence of H2S and CO2 compose a very corrosive aqueous environment. The objectives of the ICEIHT group in the frame of this project are the following: (i) construction and development of a computer based automatic titrator system for the

investigation of iron sulfide formation in aqueous systems at 25"C,

EEC-DG XII-Joule Programme-contract Nos JOU2-CT92-0708 and CIPD-CT93-0314 - final report 1 1


(ii) investigation of spontaneous iron sulfide scale formation (and particle size distribution) in supersa-turated aqueous solutions at 25°C and 80°C under sustained (only for 25°C) and variable solution supersaturation. The effect of pH, ionic strength and presence of foreign ions will be studied,

(i) study of the inhibiting properties of various organic additives on iron sulfide scale formation at 80°C in high salinity supersaturated solutions in the laboratory and in real geothermal fluid,

(iv) inhibition of calcium carbonate scale formation by water soluble polymers prepared by BBPDICM and by commercially available corrosion inhibitors;

(v) preparation of synthetic pyrite crystals from amorphous FeS suspensions and study of amorphous FeS particle transformation to pyrite,

(vi) electrochemical investigations of the corrosion of carbon steel in Cl- and HS- containing media, and of the anti-corrosive properties of the additives prepared by BBPDICM and already used commercial corrosion inhibitors in Cl- containing media.

BBPDICM The BBPDICM contribution was the obtaining of new maleic copolymers and maleic copolymer derivatives, the objectives of the research programme were: (i) to develop new types of scale inhibitors for geothermal waters, eventually corrosion inhibitors. (ii) to study the correlation between the chemical structure, composition and physico-chemical

properties of polyelectrolytes and their inhibiting effect on the precipitation of carbonates or other insoluble salts that produce scale in geothermal systems.

CAEL The anti-corrosion protection of large volume tanks where electrolyte solutions are stored still constitutes an important element inîluencing the cost of such units. The anti-corrosion can be realised by applying different methods. The inner wall surface can be diversely coated, corrosion inhibitors can be added to the electrolyte itself, and fmally, electrochemical protection can be used: cathodic protection without or with extemal current source, and anodic protection. The high Cl' contents in the chemical composition of geothermal water and its temperature drastically l i t the efficiency of protection methods. The cathodic protection with extemal current source supposes solving a field problem in an electrically conductive medium, described by Laplace's equation. The cathodic protection of steel structures using dummy anodes with no extemal current source is a common corrosion protection procedure used in ship buildimg. The aims of this study was: (i) to model the corrosion processes in large volumes using multigrid and fuiite element methods,

in order to simulate the distribution of current and potential field, for an optimum position of anode in cathodic protection. The corrosion monitoring system was based on multi-electrode.

(ii) to determine the iduence of Cl-, HS-, pH and inhibitors on the corrosion process (corrosion rate, uniform corrosion, pitting corrosion, formation, porosity and breakdown of scale).

(iii) to model and simule the periodic oscillations, that occur at the anodic polarisation of Fe electrodes in geothermal water with high Cl- content and to calculate the kinetic corrosion parameters ba, bc and Icor, in the geothermal water.

CRIC The aim of the programme is to resolve the problems caused by corrosion and scaling in the exploitation of low and high enthalpy geothermal systems. In low temperature systems, often referred to as "hydrothermal" or "direct use", scaling apparently plays a less important role. It is well known that Hungary has the second biggest resource in the world of low enthalpy hot water and this type of energy should be used in the near future to a higher degree. The research



programme which aimed the understanding of the corrosion and scale controlling mechanisms in geothermal field was: (i) to develop mathematical models for:

- inhibition of mineral scaling and metal corrosion in geothermal wells; - scaling mode1 which includes equilibrium thermodynamic relationships, temperature,

pressure, water composition; - stochastic description of metal corrosion including adsorption kinetics of inhibitor molecules;

(ii) to establish of empirical relationships between kinetic and thermodynamical parameters of the processes based on laboratory experiments;

(iii) to develope new type of anti scale and anti corrosion agents for use in geothermal systems based on systematic studies of correlations between the reactivity and structure for newly synthetized molecules;

ICPE-CO0 The purpose of this programme is both the theoretical study of the corrosion mechanism and of scale forming in geothermal systems with various physical and chemical characteristics and to test technical solutions for scales decreasing and elmination. The geothermal systems in exploitation in Romania consists principally of: (i) drilling well -at different depths- catching source, (ii) vessel, degassing tank, usually positioned next to the well, (iii) transport pipes to user, (iv) users equipments, principally heat exchangers, (v) pipes for the transport of the exhausted geothermal water from user to soi1 reinsertion well, (vi) buffer vessel for exhausted geothermal water, and (vii) reinsertion well. The principal areas affected by electrochemical corrosion are the wells (outsidelinside), the transport pipes (outsidelinside), the inside of regulation and flowrate measurement units, the degassing vessel inside, the heat exchanger, etc ... Conceming the scales forming the most exposed areas are: the head of catchiig well (to 100-150 m depth), the transport pipes and the heat exchangers. The objectives are: (i) to design, build and test a prototype for active cathodic protection with potentiostatic control

for exterior corrosion metallground) of collecting/transport pipes, (ii) to determinate the kinetic parameters of corrosion in geothermal systems exploited in Romania,

and elsewhere if requested; (iii) to develop corrosion inhibitor (possibly includiig crystal growth properties, accordingly to the

proposa1 of Pr. A. Carpov from BBPDICM), the effectiveness of the inhibitor will be d e t e ~ i n e d by ICPE-C6O or by other partners.

ICVL The task of ICVL group in the frame of the programme was the corrosion investigations of iron and carbon steel in geothermal fluid of the West Lithuania aquifers. The fluids are from Cambrian aquifer and has temperature of about 800C. The next task of the work was an investigation of oxide- layer formation on carbon steel and on iron taking place during the corrosion process in the geothermal environment. X-ray photoelectron spectroscopy (XPS) simultaneously with the etchimg of samples surfaces with ionised argon as well as electrochemical quartz crystal microgravimetry (EQCM) were used for this purpose. The attention was focused on: (i) Tafel slopes, polarization resistance and corrosion rates of iron and carbon steel in the

geothermal environment of Vidmantai 1 and Vidmantai 2, (ii) influence of the liquid flow rate on the parameters mentioned above by means of a rotating disc

electrode, (iii) influence on the corrosion rate of temperature, exposure time, chloride, CO2 and air

atmosphere, (iv) influence of the above factors on interphase layer formation.


Control of corrosion and scaling in geothermal sysrems

2. WORK PERFORMED, RESULTS AND DISCUSSION

2.1. Corrosion prevention

BRGM The behaviour of a carbon steel in the absence and in the presence of various corrosion inhibitors in partially reconstituted, actual and modified geothermal water is examineci in order to optimize their use in low enthalpy geothermal systems. The influence of some physico-chemical parameters known to be determinant in the process of carbon steel corrosion and its inhibition such as salinity, hydrogen sulfide concentration and geothermal fluid flowrate in the casings have also been studied in a natural geothermal water. The determination of the influence of these physico-chemical parameters on the effectiveness of an inhibitor, enable us to predict the order of magnitude of the concentration necessary of inhibitor for an optimum effectiveness as a function of the composition of the fluid of each well. It would thus be possible to ensure that the inhibitor is sufficiently effective at economically supportable concentrations. Finally, we evaluate the adsorption-desorption kinetics of inhibitors in order to see whether or not its action is immediate or not and to determine how long the inhibitor remains effective after treaiment has ceased.

In reconstituted geothermai water, the inhibitors were tested using various stationary and transitory electrochemical techniques and a precise experimental protocol (Amalhay, 1994; Arfaoui, 1995; Amalhay and Ignatiadis, 1994b; Ignatiadis and Amalhay, 1995). By combining and comparing results gathered using theses techniques, we were able to determine the mechanisms goveming the action of the inhibitors and determine their effectiveness. It was clear that scale plays a preponderant role in the evolution of the corrosion.

In actuai geothermal water, a fwst comparative study (long-term) of the carbon steel corrosion rate in untreated and treated geothermal waters using coupons have been realized (Ignatiadis et al., 1995). This study allows us to verify and extrapolate the results obtained during short- and medium- term periods of immersion by electrochemical tests and to provide more precise information on actual carbon steel behaviour and on how inhibitors work. Gravimetric tests carried out on corrosion coupons immersed 65 days in an untreated geothermal fluid from Melun 1'Almont enabled us to estimate the average corrosion rate to be 1.21 mmlyear. The corrosion is not absolutely uniform and is very great because of the presence of scale on coupons and of the absence of treatment with inhibitor. Gravimetric tests carried out concurrently at the Villeneuve La Garenne (non treated fluid) and la Courneuve Nord (treated fluid) sites enabled us to show that inhibitors act by slowing down crystal growth. The corrosion rate was more than 10 times lower in a treated fluid than in a non treated fluid. These in situ tests enabled us to validate results gathered using electrochemical methods concerning not only the evolution of the morphology of the scale as a function of time and of the injection of corrosion inhibitor, but also the effectiveness of the inhibitor. A second comparative study of the effectiveness of various additives in inhibiting carbon steel corrosion in a natural geothermal water by using rapid electrochemical tests have been realized (Amalhay 1994; Amalhay et al., 1994d; Cotiche 1994; Amalhay and Ignatiadis, 1995a, 1995~). In order to rapidly determine the mode of action and the effectiveness of some corrosion inhibitors in reducing corrosion rate, we developped and carried out a series of rapid and successive tests using stationary and transitory electrochemical techniques. These techniques consist in electrochemical monitoring, for short periods of around three and a half hours, of the response of carbon steel electrodes. The electrodes are immersed from the start in a natural geothermal water treated with 10 mg/l of each inhibitor. these compounds cannot be recommended for use as scale formation inhibitors. Several compounds are recommended for use as corrosion inhibitor at low concentrations (economically feasible). In the natural fluid, scale plays a preponderant role in the evolution of the



corrosion, where the study of the cathodic slopes of the Tafel lines, shows that the cathodic reaction probably occurs entirely on the scale and controls the kinetics of the corrosion reactions. Without treatment, the large decrease in the corrosion rate of steel which was seen during the first 20 hours of immersion is due to the formation of amorphous iron sulfide which temporarily protects the metal.

In modüied geothermal waters, fwstly was studied the iduence on the electrochemical behaviour of carbon steel of the immersion t h e , the rotating speed and the concentration of corrosion inhibitor in a degassed geothermal solution, where only the Cl- play a preponderant role (Amalhay and Ignatiadis, 1994a; Amalhay et al., 1995a). The results prove that the temporal evolution of the corrosion of steel is essentially linked to the physico-chemical properties of the layer of scale. Secondly, electrochemical measurements were done to determine the corrosion rate of the carbon steel in a natural geothermal water as a function of immersion time, electrode rotating speed, flowrate, HS-, Cl- and inhibitor content in the water (Amalhay, 1994; Amalhay et al., 1994e; Amalhay and Ignatiadis, 1996a). HS- causes significant changes in the electrochemical behaviour of carbon steel as indicated by an increase in corrosion potential and current. During the first 6 hours of immersion, we distinguished three stages of carbon steel behaviour in water with various HS- contents. When inhibitor is added, the diffusion of HS- towards the metallic surface, and thus the cathodic reaction which takes place on the scale, seem to be limited, but the inhibitor nevertheless infiuences the anodic reaction as there is an increase in the corrosion potential and a notable decrease in the corrosion rate. The behaviour of the metal can again be separated into three stages. An increase in Cl- content from 0.2 to 0.5 M causes a slight increase in corrosion potential for three different flowrates (13.5, 21, 30 1.h-1) with and without inhibitor. Without inhibitor, the flowrate seems to primarily affect the stationary electrode. With inhibitor, corrosion potential and anodic Tafel constants increase with increasing flowrate at 0.2 and 0.5 M NaCl. The increase in flowrate therefore facilitates the anodic action of the inhibitor, probably by reducing the thickness of the scale and thereby facilitating access to the metallic surface.

Electrochemical techniques were used to monitor the behavior of carbon steel during the crystallization of conosion deposits. Corrosion inhibitors were tested at different concentrations on site in order to compare their effectiveness in reducing the corrosion rate (Amalhay and Ignatiadis, 1995b). By combining results of electrochemical measurements and mineralogical analyses of the scale, we have shown that the crystallization of amorphous iron sulfide into mackinawite is accompanied by an increase in the corrosion rate due to the transfer of cathodic sites from the surface of the metal to that of the scale (Ignatiadis and Amalhay, 1996a, 1996b; Amaihay and Ignatiadis, 1996b). Al1 of the inhibitors tested significantly reduce the corrosion rate of carbon steel and delay the crystallisation of mackinawite from amorphous iron sulfide.

The behaviour of some non metallic materials in actual and treated geothermal environment have been characterized (Corton, 1994, Lesueur, 1994). This study shows that knowledge of the behaviour of nonmetallic materials in the field of low enthalpy geothermal energy is limited, for example, to the analysis of nonmetallic elements already installed on wells or to the "views" of companies providing services in the field of geothermal energy. Scientific results are rare as scientists are currently concentrating their efforts on the battle against steel casing corrosion. After briefly describing the context in which these materials are used, this study lists the principal characteristics of the nonmetallic materials which can be used in geothermal activities and gives the main results gathered from the Dogger exploitation in the Paris Basin.

CPR The design of a structured packhg column for steam washing was a continuation of the previous programme (JOUG-0005-C) and has been made on the basis of a set of specific data relative to HC1


Conrrol of corrosion and scaling in geothermal sysrems

absorption in alkali solutions. The process operates at relatively low s tem velocity (< 7 mis), and consequently low droplet entrainment. The large interfacial surface needed for HCl absorption was provided by the stmctured packing. On the basis of this work, a full scale washiig column has been designed and will be constmcted and tested in the near future at Larderello field. Specific support from EC under THERMIE programme was obtained for this project.

The results of the conventional washing processes adopted at Larderello field have been published in the open literature by Paglianti et al., (1996) and represent a useful tool for any possible improvement of these processes in particular for analysis of steam washing equipment. On the basis of the results obtained it is possible to evaluate the contribution to s tem washiig due to the different apparatuses present in the plant, liquid injection section, mixer, primary separator, demister.

This activity conceming the dry abatement of HCl has started with a thermodynamic analysis of gas-solid reactions between HC1 and various possible solid sorbents. On the basis of the results obtained, the kinetics of the chemical reaction between HCl and sodium bicarbonate and carbonate has been studied in a differential reactor. The kinetic study demonstrated the feasibility of dry sorption of HC1 and allowed the p r e l i i a r y design of the main reactor. The cost of this abatement method is such that its installation would allow consistent savings in the energy losses due to s t e m desuperheating. However, it is recommended that the process be analysed in a pilot plant reactor before any field applications.

ICEIHTCP Experimental details of electrochemical measurements The electrochemical investigation of carbon steel corrosion in NaCl containing aqueous media was done in the presence and absence of sulfide ions and in the presence of additives to be tested. Testing of additives regarding their corrosion inhibiting properties was also done in real geothermal water. Electrochemical investigation included DC (open circuit potential (OCP) measurement vs. time and Potentiodynarnic scans (Log(1) vs. Applied potential)) and AC (impedance spectroscopy: measurements of impedance vs. frequency) measurements. The following water-soluble compounds were examined with respect to their potential as corrosion inhibitors for carbon steel: 1. Organophosphoms compounds: ENTMP,NTMP and HEDP, 2. Commercial products: Solamine 129, Nomst 491 and Aquaprox MDC 1300. 3. Polymeric additives (prepared by BBPDICM) and, 4. Organic compounds: Picric Acid, Sodium Oxalate, Sodium Benzoate and p-~ydrbxy Benzoic

Acid. Presence of atmospheric oxygen and sulfides in the working solutions proved to enhance the corrosion of carbon steel. Presence of amorphous FeS leads to protection against corrosion due to a non porous solid layer that adheres on the carbon steel surface. Concerning corrosion inhibition, only the commercial products showed a satisfactory behavior. Solamine 129 showed the best behavior in sodium chloride aqueous media and in real geothermal fluid. Al1 the other additives tested either they did not affect the corrosion of carbon steel, or they enhanced the corrosion process.

BBPDICM (see scale prevention)

CAEL For the CAEL group, the objective was to mode1 the corrosion processes in large volumes (resewoirs) using multigrid and f&te element methods, in order to simulate the distribution of



the bulky equipments-in contact with the geothermal electrolyle to be achieved through cathodic current injection potentiostatically controlled. The design has at basis a theoretical calculation of the current and potentiel distributions at the metal surface. The calculation is absolutely necessary for the correct dimensioning of each element of the system. According with the obtained data, it was designed each element: anode placement, anode diensioning, electronic schemes of the potentiostatic rectifier, placement and conception of the reference electrode. Two potentiostatic equipments destined for anticorrosive protection of outside structures as so as for the inside structures of the bulky equipments too, specifically for the geothermal systems. The proposed system ensure the active anticorrosive protection systems throught current injection potentiostatically controlled. The injection is realised versus active anodes which can be inert and101 consurnable, specialized. The important elements- (specialiied sensors) were concepted and made for a long working period in the specific mediums for which they were created. The proposed equipments and systems follow to be tested both in situ of the geothermal systems in operating, and in the ICPE S.A. specialized laboratories for the fiability test. As result of the tests in laboratory the tested equipments respects the national prescriptions (STAS) and the international ones (CE1 and ISO), and also the specific parameters for functioning given by project. For the operating geothermal systems these equipments continue to work and there is no technical problem with them so far. It was studied the possibilities of application of the active anticorrosive protection in some metallic subassemblies from geothermal systems. Thus, there were identified: (i) the extemal sides of the metallic structures which are in direct contact with the soil; (ii) the interna1 sides of some bulky equipments. These parts can be protected through the injection of cathodic current method. The system proposed by us for these surfaces is a complex one, with automatic injection of current in closed-loop, controlled by the output signal given by an adequate sensor. The equipments achieved were tested in laboratory and we have obtained good results. We also continue to test these equipments on a geothermal system from Romania-Bihor district. At this moment we are working to elaborate the documentation of these equipments according to international prescriptions ISO-9000.

Another part of the work done deals with the shidy of the anticorrosive efficiency of some polyelectrolytes with anti-scaling effect, synthesized by BBPDICM. It becomes necessary to conceive new inhibilors with cumulative effect (corrosion and scaliig) and to determine of the optimal conditions for dosing these inhibitors. Experiments were realized for 21 maleic polyelectrolytes:

a) It was studied the effect of 13 polyelectrolytes at 0.1-30 ppm addition in synthetic geothermal water at 60°C in order to select a commercial cheaply formula, with a cumulated effect of the corrosion and the scale inhibition. From the analyses of the experimental results it is estirnated that a part of the studied polyelectrolytes solutions presents a pronounced inhibitory effect. These solutions can present a practical interest for a simultaneous inhibition both of steel corrosion and of scaling. Another part of the presented formula have a reduced anticorrosive efficiency or even nul.

b) It was studied the effect of some polyelectrolytes (copolymers of maleic acid with triethanolamine) at 0.1-30 ppm addition in synthetic geothermal water at 50°C, with the sarne objective as in a). The corrosion inhibition effect was sîudied with polarization curves. The results are: (i) the AV.128.72 polyelectrolyte in large domains of concentration decreases the corrosion rate in geothermal waters (1116) and has a mixed effect: reduce both the partial anodic and cathodic current, (ii) the AV.127.71 polyelectrolyte presents a smaller inhibition effect and influences only the partial anodic process.

c) The inhibition of corrosion effect was tested for carbon steel R 37 in synthetic geothermal water at 60°C with some polyelectrolytes - copolymers of maleic acid, N-vinilpyrolidone with piperazine



and its derivatives. The tests were realized through the methods of steady state polarization curves and impedance spectroscopy in a.c.-impedance analyses. By analyzing the data it results that: - the polyelectrolytes copolymers of maleic acid and N-vinilpirolidone with piperazine and its

derivates, are mixed inhibitors if their structures have lateral aminic groups. In absence of lateral amino groups the polyelectrolytes reduce the rate of pure charge transfer only for the cathodic reactions;

- the tested electrolytes have a fast effect so only 1 hour after the addition of inhibitors the corrosion rate is reduced about 2 to 4 times;

- maximum inhibition effect is achieved with APAEP-1 which has a combined action.

d) The study of geothermal water corrosiveness with polyelectrolyte addition: copolymers of maleic acid with aromatical amines: it can be observed that many polyelectrolytes present the antiscaling effect and the inhibition of corrosion too. Through the determination of the acting mechanism, in correlation with the stmctural formula and the composition of the polyelectrolytes, we consider that it can be conceived new structures of polyelectrolytes with a great anticorrosive effect.

The corrosion reaction from the interface metallsynthetic geothermal water were studied in the presence and absence of 21 different maleic polyelectrolytes. Most of them have a great anticorrosive effect. Il was establiihed that in concordance with the molecular structure and the content of functional groups, the polyelectrolytes acting anodic, cathodic or mixed either through the braking of the charge transfert or the modification of the transfer coefficient. A maximum anticorrosive effect was obtained with the polyelectrolytes having mix action respectively of those which operate both kinetically and adsorption (alter the transfer coefficient).

2.2. Corrosion studies

BRGM (see corrosion prevention)

CEBELCOR Potential-pH equiiibrium diagrams for the system S-H20 were prepared for temperatures from O to 150°C. Consistent thermodynamic data were obtained from Shock (1988), Shock and Helgeson (1988) for these temperatures. The data were reviewed in comparison with earlier data from other sources, and an extensive publication was prepared using the data selected (Pourbaix and Pourbaix, 1990; 1992). This publication includes equilibrium diagrams for the system S-H20 at 25, 50, 100 and 150°C, for a total dissolved sulfur concentration of 1 molell, considering sulfur, sulfides, thiosulfates, tetrathionates and sulfites on the one hand, and hydrosulfites, sulfites and dithionates on the other hand. Al1 calculations for 0°C and for other sulfur concentrations are also repoaed. A theoretical analysis of the effect of access of oxygen is also presented.

Equilibrium diagrams for the system S-H20 for sulfur concentrations of 0.1 and 0.001 molell, corresponding to solutions in equilibrium with partial pressures of H2S of about 1 and 0.01 bar respectively, were calculated (Singh and Pourbaix, 1996a). Diagrams were calculated for the system Fe-S-H20 at 25"C, for these two sulfur concentrations. Equations are given for other sulfur concentrations. Two data are missing for higher temperatures: the free energies of formation of mackinawite FeS0,943 and of sulfide S2-. As soon as such data are available, an additional publication will be prepared with equilibrium diagrams up to 150 or 200°C.

From this work (Singh and Pourbaix, 1996a), mackinawite appears as metastable versus pyrrhotite. Mackinawite may be obtained by reduction of ferrous ion, while pyrrhotite may be formed by



oxidation of ferrous ion. The lower the dissolved sulfur concentration, the larger the corrosion region where Fe2+ is stable. The area of stability of magnetite is small when maghemite is considered as the hydrated ferric oxide, and is even smaller or non-existent when hematite or goethite are considered. Other iron sulfides (troilite, greigite) were not considered in this work, because the prime interest in geothermy is on pyrrhotite and mackinawite. The E-pH equilibrium diagrams are useful for the interpretation of laboratory experiments and of field data.

Another part of the work done deals with the effect of trace amounts of oxidants on the corrosion of C-steel in H2S environment. The theoretical analysis (Pourbaix and Pourbaix, 1990; 1992) suggests that, if the oxidation of H2S solutions leads to thiosulfate or tetrathionate, there will be a pH decrease, while if the oxidation leads to elemental sulfur, there will be no pH change. Quantified examples are given for solutions in equilibrium with 1 bar H2S and with occasional or permanent exposure to a partial pressure of 0.01 bar Oz. Experiments were conducted to indicate the redox potential and pH of H2S solutions exposed to either air (po2 = 0.2 bar) or H2S (pHzs = 1 bar). The tests were made in NaCl 0.35M, representative of the Dogger geothermal water. Gold and platinum were used as redox electrode. Typical results are shown in figure 1 (annex). The correspondence between the Eredox changes and the pH changes is shown in figure 2 (annex). The potentials and pH, when plotted in a E-pH diagram for the system S-H20 (Singh and Pourbaix, 1996a), correspond to the oxidation of H2S into elemental S for the small plateau at O mVshe of figure 1, and then to the oxidation of H2S into SzO3-- for the rest of the plateau around + 100 mVshe (fig. 1 and 2). These data suggest that both reactions (oxidation of H2S to S and to S2O3-- can indeed proceed and that acidification can occur when the latter takes place.

Concerning the study of the corrosion process in sulfide and chloride environment, the approach was to conduct corrosion experiments combined with electrochemical measurements in order to interpret the results and identify the reactions taking place. Experiments were conducted also in a double-compartment corrosion cell, to simulate several factors that could induce localised corrosion: crevice, scratching, depletion in H2S (Singh and Pourbaix, 1996b). The methods were found satisfactory, although collection of corrosion products for analysis was not easily feasible. The major conclusions of this study are:

- the electrochemical conditions for iron and carbon steel in H2S saturated solutions lie well below the water-hydrogen equilibrium potential, in a region of stability of iron sulfide, not far from a corrosion area;

- rnackinawite, pyrrhotite, and perhaps troilite can form in these conditions. Pyrite is not stable, unless slight aeration;

- a slight acidification can significantly increase the corrosion, for a given sulfide concentration; - the presence of chioride has apparently no influence on the electrochemical conditions of plain

iron surface in H2S solutions; - however, hydrolysis of ferrous iron in the presence of chioride could produce some acidification,

with increased corrosion as a result. This mechanism may be iiiited to the initiation step. During the propagation step, anodic surfaces see a higher pH;

- in the complete absence of oxygen, the driving force between cathodic and anodic surfaces is small;

- still, anodic corrosion current densities are high when the anode is the H2S depleted surface. This tends to support the idea that H2S depletion is part of the mechanism of localised corrosion in sulfide solutions;

- the transformation of ferrous ions into pyrrhotite is an oxidation reaction, while the transformation of ferrous ions into mackinawite is a reduction reaction. This may suggest that pyrrhotite could preferably form by precipitation of dissolved ferrous ions when a reduction


Control of corrosion and scaling-in geothermal systems

reaction is available and that mackinawite could preferably form when an oxidation reaction is available. Application of this for the control of deposits in geothermy could be investigated;

- the rate of the cathodic reaction (mainly hydrogen evolution) is probably much influenced by the sulfur compound present: pyrite, troilite, the non-stoichiometric iron sulfides or elemental sulfur. Measurement of the kinetics is accessible through experimental techniques derived from the methods used here;

- it is probable that large current densities are due to the fact that some species act as catalysts for the corrosion reaction or for the hydrogen evolution reaction. Catalysts for non reversible reactions are reversible redox systems of which the equilibrium potential is between the equilibrium potential of the reduction reaction and the equilibrium potential of the oxidation reaction. Two types of catalysts must be considered in geothermal systems: non stoichiometric iron sulfides, and bacteria;

- non stoichiometric iron sulfides are present in geothennai wells: pyrrhotite FeSl+, and mack'iawite FeSI,. In given conditions (sulfide concentration, pH), the redox system mackinawite-pyrrhotite or the transformation of mackinawite with different values of x may act as a catalyst for the corrosion of iron with reduction of water into hydrogen;

- the same concept may be extended to the action of bacteria: thanks to specific enzymes, bacteria are reversible systems and they act as catalysts for reactions of which the equilibrium potential of the oxidation partial reaction and the equilibrium potential of the reduction partial reduction are lower and higher than the range of potential in which the bacteria can grow;

- inhibition of corrosion in geothermal conditions is govemed by the electrochemistry of the system: the conditions in operation correspond to the formation of iron sulfides (possibly pyrrhotite and mackinawite), with a possible general corrosion because the region of stability of Fe2+ is not far from the actual conditions, and with a possible corrosion under deposits. F i i g amines are effective to control H2S corrosion, especially in the absence of deposits. A combination of acid treatment to prevent deposits and of f W i g amines is sometimes used in the oil and gas indusm. Another possibility is to increase pH with neutraluig inhibitors;

ICErnCP see corrosion prevention

CAEL The objective was to study the corrosion processes due to the presence of HS- and Cl- anions. A very contradictory behaviour of the steel in contact with brine, which contain H2S and CO2 was observed. The attack was not uniform corrosion in an electrochemical sense, although it may have been uniform on a rnicroscopic scale. In any case an important conclusion for practical applications, since in constmction of tube for geothermal water transport, is that it must be assumed that H2S can increase the severity of corrosion, even when present in small amounts. It was attempting to conclude that the lack of reproducibility and the high corrosion rates indicated by the polarisation resistance resulted from defects in these films. On the other site an osciilatory domain is identified during Fe anodic polarisation, which is strongly influenced by some critical parameter values: Cl-, HS-, inhibitor concentration and pH value. A scanning rate over 1 mVlsec in lmear voltamrnetry can by-pass the oscillatory domain. From this point of view, the current oscillations on Fe electrodes in geothermal water of high Cl- and HS- anion contents can be considered as a non- stationary process.

The other deliverable was focused on the determination of the kinetic parameters of corrosion in the range of oscillating current. Modelling and simulating the periodic oscillations, that occur at the anodic polarisation of Fe electrodes in geothermal water with high Cl- content are the aims of this study. One supposes that the occurrence of the oscillations is due to the kinetic steps only. The



mathematical mode1 consists of a two-diensionai ODE system. Non-Langmuir isotherm was found to be essential for producing the lirnit cycle. Oniy local fit between experiment and theory is obtained. Another aspect of this work is the using of the integral method to calculate the kinetic corrosion parameters b,, b, and I,,,, in the geothermal water. The mathematical theory of a two- parameter method, based on an integral formula, for analysing polarisation curves is applied and the roots of the non-linear system of two equations are solved. The experimental applications concerns the behaviour of ARMCO iron in geothermal water with sulfur and CO2 contents.

ICPE-C6O The purpose of this work is the study of the corrosion mechanism a t the metdgeothermai water interface, the experimental determination of the corrosion rate, respective of the kinetic parameters of the iron dissolution electrochemical process, data which are absolutely necessary for the design of the mechanical assemblies and for choosing the proper inhibitor.

For the detennination of the corrosion risk and also of the proper inhibitors to preventing it, the corrosivity of fourteen geothermal fluids from Bihor basin - Romania were investigated through the method of steady state polarisation curves. The tests were made for five different temperatures in the range of 30 to 90°C. Ten types of geothermal waters having chlorosodic character, with diverse contents of Ca+ and HC03-, waters at which the contents of S04" is smaller than 17 mg11 were investigated through the method of steady state polarization curves; and four geothermal waters with a great content of S042- andlor S2-. The results are: - in chlorosodic geothermal waters, with a low content of S042-, the corrosion rate is primarily

determined by the concentration of Cl-; - lg j o = f(lg [Cl-]) is a liiear function (deduced from the graphic representation), but there are two

different zones, respectively for Cl- concentration lower and higher than 15 mgll; each of these zones having its own type of mechanism;

- for these waters the corrosion rate, in the range of 30 to 95"C, is decreasing with the increasing of the temperature;

- in geothermal waters which have content of S04" and101 S2-, the control of the reaction is pure kinetical, the l i t stage being the pure charge transfer. Differently of the geothemal waters from the first category, at these ones the corrosion rate is increasing with the increasing of temperature.

ICVL The unique geothermal anomaly in Lithuania and its vicinity is situated in the area of the West Latvia, the West Lithuania and the Kaliigrad Region of Russia. The West-Lithuanian Geothermal Anomaly (WLGA) is the most intensive and has the biggest area. The average temperature gradient in the WLGA is ascertained as 40-5O0C/lan, while it is usually oniy 20-3O0C/km in the surroundiig regions. Klaipeda, Silute, Palanga, Gargzdai and several smaller towns are situated in this region and can be considered as the potential users of the geothermal energy for district heating and other applications. The two most promising aquifers in the geothermal fields have been discovered during the geological exploration and geothermal interpretation. The first aquifer is located at the depth of 700-1100 m in the MiddleILower Devonian geological formation and is characterised by low temperature (30-40°C). Aquifers, situated in the MiddleILower Cambrian geological formations at the depth of 1700-2200 m., are more suitable for geothermal utilisation. A temperature range of 60- 95°C has been measured in these aquifers. The isotherm of 80 and 60°C covers respectively an area of 2400 and 6000 Id. Despite sufficiently generous investigations dealing with utilisation of geothermal energy in Lithuania, no corrosion investigations in geothermal environment have been carried out until recently. These investigations were conducted in the current work. To better understand the corrosion behaviour of iron, it is very important to study the oxide layer formation as a function of various factors. XPS and EQCM were used for this purpose in the work presented.



Working electrodes for voltammetric measurements were made of pure iron (ARMCO, 99.9) and of carbon steel Ct 3 which is widely used for manufacturing the pipes. The iron and steel sarnple were pressed into Teflon jackets and had the geometric area of 1 cm2. The rotating disc electrode was prepared in the same manner. The reference electrode was a KC1 saturated calomel one (SCE) placed into separate vesse1 and connected with the investigating solution through the electrochemical key fdled with the same solution.

The measurements were taken in a special glass ceIl for electrochemical investigations. The ce11 made it possible to thermostat the solution and to have a necessary atmosphere. Voltammetric dependencies were obtained under conditions of pulse and stationary potentiostatic polarisation as well as at a liiear potential sweep. The distribution of the elements in the steel surface layers was investigated by X-ray photoelectron spectroscopy (XPS) and a special electrochemical ce11 was designed for EQCM measurements.

To simulate the hydrodynamic conditions in a pipe, the rotating disc electrode was used. It is well known that liquid moves parallel to the electrode surface in the layers close to them when the electrode rotation is applied, so the geothermal fluid flow in the pipes may be simulated. Besides, the influence of difision processes on corrosion kinetics may be studied as well. The corrosion behaviour of iron and carbon steel was studied (under laboratory conditions) in the geothermal fluids of Iridmntai 1 and Vidmntai 2 . The following conclusions may to be drawn accordiig to the data obtained: - the corrosion rate decreases with the immersion time of iron in the solution; -the cathodic Tafel slopes and corrosion current densities are much higher when the rotation of

electrode is applied; -the anodic Tafel slopes vary not much as a function of immersion t h e and electrode rotation

frequency and has the value in the range of about 80 - 100 mV; -the positive open circuit potential shift, i.e. intensifyiig of cathode process proceeds when

electrode rotation is switched on; - deaeration of the solution leads to decrease in the corrosion rate. To the greatest degree this is

noticeable in the first hour of immersion and especially when electrode rotation is applied. After two hours immersion the decrease in the corrosion current in deaerated solution is insignificant. The corrosion current density depends from the electrode rotation in deaerated fluid the same as in the aerated one;

- the rises of temperature from 20 to 80°C cause decrease in corrosion rate of about 1.5 - 3 times depending on the immersion time. Much pronounced decrease was determined in an unstirred solution in which the same rising of temperature results in increase of jc about 10 times;

-saturation of geothermal fluid with CO2 causes a slight rise of corrosion rate after 1 h of immersion in the solution;

- corrosion process inhibition is obsewed when increasing the chloride concentration in the sulfate solution (pH 3) to the value like in the real geothermal fluid (100 g/l). The lower concentrations of chloride, viz. 10 and 50 g/l, hiiders the process only at the beginning of immersion;

- the approximate value of the limiting corrosion rate in the naturally aerated system under study has been calculated. This value was equal to 1.52 mA/cm2.

The formation of oxide layer on iron surface was studied by XPS using surface etchimg with ionised argon. The formation of the layer at initial stages of corrosion was investigated by EQCM. Following conclusions can be drown: - the thickness of oxide layer growth with the exposure time in the solution. The thickness is very

similar in the cases of aerated, deaerated and CO2-saturated solutions; - the rise of the temperature from 20 to 80°C causes developing of more thick layer;

24 EEC-DG XII-Joule Programme-contract Nos JOU2-CT92-0708 and CIPD-CT93-0314 - final repori


-the electrode mass growth was detected by EQCM in the first stages of corrosion. The effect was attributed to the surface blocking by scarcely soluble compounds. The interphase layer should be sufficient compact otherwise it could not affect a q u m oscillation frequency;

- the most thick layer at the beginning of corrosion develops in the naturally aerated solution. The layer developed in the CO2 saturated fluid is significant th i ie r ;

- the corrosion rate calculated from mass gain data at the initial stages of corrosion is extremely high for the naturally aerated solutions. Three main reasons can be presumed to explain such a result: i) an high initial electrode activity; ii) a thii depletion layer with pH gradient at the first stages, consequently, high reduction rate of depolarisers; iii) a precipitation of solution components simultaneously with corrosion products precipitation.

2.3. Scale formation and modelling

BRGM Experiments were done in order to better understand iron sulfide precipitation kinetics (Peyrot, 1993; Ignatiadis, 1993a, 1993b; Peyrot et al., 1995). Results of analyses done at the end of the kinetics experiments and those of the fluids at the production wellhead were used to identify which iron sulfide controls the solubility of iron and sulfide in the geothermal environment (Ignatiadis and Peyrot, 1994). Mackinawite is this iron sulfide, despite the presence of pyrite, pyrrhotite, greigite and marcasite in the deposits on filters. The origin of the iron (from both the resemoir and corrosion) and of the dissolved sulfides (from both the resemoir and current bacterial activiîy), and the influence of these species on scaling processes are discussed (Amalhay et al., 1994b, 1994c, 1995b; Ignatiadis, 1994a; Gauthier and Ignatiadis, 1994; Ignatiadis et al., 1996, 1997). A model of scaling regulation (control) is proposed, suggesting that the formation of scale is controlled by the diffusion of anions (sulfide, hydrocarbonate, chloride) through the scale (Amalhay et al., 1994b, 1994c, 1995b).

Concerning the development of the MODEP computation code, the aim was to propose a digital model that enables the simulation of corrosion and scaling phenomena on steel casing walls (Abou Akar and Ignatiadis, 1994, 1995). Considering the complexity of the real phenomena, certain simpliQimg hypotheses were included in the model (Abou Akar, 1994a, 1994b; Abou Akar and Ignatiadis, 1994, 1995). The simulation of casing corrosion is based on application of the Volmer- Heyrovski reactive mechanism. The calculations take into account Fick's diffusion laws, the variation of the thickness of the diffusion layer due to scale growth, and the porosity of the scale (assumed initially to be made up of mackinawite Fel+,S, the main scale constituant) (Abou Akar and Boens 1995a, 1995b, 1996; Boens, 1995). The amount of mackinawite precipitated is calculated using the solubility product, K, or accordiig to kinetic considerations. The model simulates also the precipitation of other minera1 species (commonly encountered in scale in geothermal wells in the Paris basin, i.e. pyrrhotite Fe,.,S, siderite FeC03, goethite FeOOH, calcite CaC03 and amorphous silica SiOz) according to thermodynamic considerations and offers the possibility of adjusting the flowrate of the geothermal water in the well and takes into account the presence of a well-bottom treatment tube (WBTT) when calculating the head loss (Abou Akar et al., 1996). The transfer onto PC of the VAX Fortran code (Abou Akar et al., 1995b, 1996; Battaglia, 1995) has a numerous advantages: a faster computation speed, autonomous operation, demonstration possibilities outside the office, and a direct link with graphic packages. Simulation of the behaviour of geothermal fluids using the MODEP code has enabled the study of the evolution of the major parameters as a function of the exploitation duration and well depth. The results has revealed (Abou Akar and Boens, 1995a, 1995b, 1996; Abou Akar et al., 1996):

EEC-DG XII-Joule Programme-contract Nos JOU2-CT92-0708 and CIPD-CT93-0374 - final repori 25


- the establishment of different kinetic regimes as a function of diffusion length; - the calculation of chemical species concentrations on casing walls; - that the well is subjected to high corrosion at the beginning of its life. Inhibitor treatments must

therefore be applied as soon as water flows through the well; - that because of the simulation method chosen (increasing thickness of protector scale), the

corrosion rate falls rapidly with time at the beginning of simulation. This reduction in corrosion becomes less marked when the scale is sufficiently thick. In addition, corrosion rates calculated are similar to those experimentally measured;

- a good correlation between the evolution of iron content (fluid vein and wall) and that of pH and sulfide content, and also between the evolution of casing diameter and production flowrate;

- the effect that the slightest variation in pH has on evolution of the corrosion rate of the casing.

This is a simple model and certain phenomena are not taken into account. Nevertheless, this model could be improved by taking into consideration the reduction of chemical species other than H+such as HS- and HC03-. However, cemin phenomena are difficult to model: - the possible precipitation or redissolution within the pores of the scale, which leads to a variation

in porosity with time; - the appearance of additional cathodic sites, where the protons would be reduced (the electrons

produced during oxidation of iron can move around in the scale as it is conductive). It is no longer sufficient to only study the metal surface. The scale must be subdivided into thin layers (choice of the thickness of the layers, calculation of the total intensiiy of the corrosion current). The numerous problems to be overcome increase the calculation time considerably.

Certain phenomena are very diicult to model, such as the frequency of corrosion pitting at a given point of the casing. At the most, quantification of the influence of certain physical parameters on the probability of the appearance of pitting corrosion can be attempted. Even the proposed version of the code isn't capable of simulating the totality of real phenomena, it can nevertheless be used to calculate trends that result from variations in the major parameters of the aquifer and101 the casing. Results will be compared with corrosion measurements in the near future to provide an indication of the gap with reality and to enable calibration.

CEBELCOR See corrosion studies

CPERI Iron Sulfide Scaie Formation A detailed description of the experimental set-up and procedures is given in Andritsos and Karabelas (1991). The pH of the fmal solution was controlled by injecting reagent grade nitric acid into the ferrous Stream. The test section consists of four to six tubular segments, each accomodating two replaceable pairs of semiannular coupons, forming a pipe section with a uniform inner diameter of 13 mm. The test coupons were made of 316L stainless steel, titanium and teflon, materials used in geothermal applications. Crystalline reagent grade ferrous ammonium sulfate and sodium suphide were used for the preparation of the ferrous and sulfide solutions, respectively. The crystal structure of the deposits was established by X-ray diffraction and the morphology of the deposits was examined by SEM. The particle size and the morphology of buk precipitated FexS particles were examined by dynamic light scattering (DLS) respectively in a Brookhaven Instruments Co. unit and by SEM.

As has been observed with other sulfide systems, the deposited mass increases linearly with time in the pH range where measurable deposits are formed, at least for the period of these tests (3-5



hours). Appreciable deposition for a certain set of experimental conditions (constant concentration, temperature and velocity) occurs withii a fairly narrow range of pH values (Andritsos and Karabelas, 1995). At pH values less than 5.8 the mass of the deposits is extremely small and cannot be weighed. With increasing pH the deposition rate increases rather sharply and then declines after reaching a maximum at a value of pH between 6.2 and 6.5. Qualitatively, this behaviour is similar to what is observed in other sulfide systems such as PbS (Andritsos and Karabelas, 1991). For scale formation to occur, a critical value of the supersaturation ratio, Sc, should be exceeded, a characteristic common to other sulfide systems (PbS and CdS). With increasing supersaturation above Sc, the measured deposition rate rises significantly reaching a maximum value. At even greater S values, spontaneous bulk precipitation occurs instantly with mixing of the two reagent streams. In fact, Ricard (1989) reports that for the FeS system in the pH range of 7 to 9, bulk precipitation is almost complete within 0.26 s after mixiig the reagent streams. The sulfide particles formed in the bulk (with size of order 100 nm) could be deposited on the pipe surface, but simple calculations with accepted correlations (e.g. those suggested by Papavergos and Hedley, 1984) show that the convective transport rate of the particles is two orders of magnitude smaller than that of individual ions. The black colour of the deposits at pH < 6.7 turns reddish-brown after several hours of air exposure. XRD examination of both black and reddish-brown deposits did not reveal any crystalline phase other than elemental sulfur (a-S). Analysis of the deposits by EDS has shown qualitatively that the major constituents of the deposits were iron and sulfur. In most cases, however, more sulfur than iron was detected on an atomic basis. The above observation is further supported by three other observations: (1) The concentration of iron measured in filtrates (using 25- nm membranes) corresponds to 30-50% of the initial [FeIt. (2) Runs with a ratio [SItl[Felt of about two shows that the deposition rate is quite close to that for equimolar concentrations. Morphologically, at short tirnes isolated amo~phous semi-spherical particles are observed on any substrate. Their size is less than 200 nm. With t h e , a rather finniy adhering layer forms. Ricard (1989) suggested that in the precipitation of FeSx the first precipitate has a Fe(SH)z composition, forming through a fast and a slow process. It is not unliiely that the bubble-like protmsions seen on the sulfide layers are due to the release of H2S. This observation, combined with the above mentioned ratio Fe:S- 1:2, strongly supporLs the suggestion of Ricard for the Fe,S formation mechanism. An increase of the temperature of the liquid increases significantly the deposit formation rate. The estimated activation energy (-23 Wlmol) is relatively close to that expected for a diffusion-controlled process, i.e. -20 Wlmol (Mullii, 1993). The deposition rate increases with increasing flow velocity, suggesting that the formation of deposits may be controlled by the convective mass transport of the scale-building ions from the fluid bulk to the substrate. However, at higher velocities it seems that the deposition rate remains constant with increasing velocity. Although no definite explanation can be offered at the moment for this behaviour, it is probable that at higher velocities the deposition process is controlled by a surface reaction mechanism.

Cornputer Simulation of Scale Formation and of Coiioidal Parücie Coagulation Simulation of Particle size Distribution and Scaling Along a Pipeline The simulation of precipitation and scale formation in pipe flow of sparingly soluble salts, developed in this programme (Kostoglou et al., 1995), is shown to produce physically realistic results. State of the art models are used to represent the individual processes involved (nucleation, particle growth, coagulation) and no arbitrary parameters are introduced. To cope with unavailable data, the PbS surface energy is estimated by means of turbidity data obtained for the specific system in a parallel experimental activity. Regarding the formulation, a rather comprehensive population balance is employed for the solid phase (PbS) in connection with mass balance for the ionic species. The predictions are quite encouraging, reproducing the bell-shaped deposition versus pH curves obtained in the laboratory. The peak value of the deposition rate is also predicted quite satisfactorily. Additionally, the computations display trends of particle size distributions, affected by the


Control o f corrosion and scaling in geothermal systerns

interaction of various mechanisms, which are physically realistic, in a quantitative and qualitative sense. On the basis of the above results, it appears that by employing this simulation scheme one can scale up with confidence to larger pipe sizes and different tïow rates encountered in geothermal plants. Also the model can be easily extended to other similar systems of sparingly soluble salts.

Effect of Roughness on Repulsive Forces between Colloidal Particles Particular attention is paid in this project to colloidal particle coagulation, which (if enhanced) greatly affects both scaling and brine treatment processes due to particle size enlargement. To irnprove physical understandiig as well as modeling particle coagulation and particulate fouling, a theoretical siudy was completed on the effect of particle surface microroughness on electrostatic repulsive forces between particles. The latter represent a major force resisting particle coagulation. A simple model of rough surfaces is proposed, which allows computation of the repulsive energy of interaction as well as an estimation of the tangential forces developing between these surfaces. The influence of some key model parameters (such as roughness parameters, distance between surfaces and electrical double layer thickness) on the repulsion energy are examined. The results of the simple model can be generaliied at least qualitatively, for arbitrary rough surfaces.

Effect of Suvace Dynamics on Repulsive Forces This part of the study is concerned with surface dynamics of colloidal particles when they approach each other, which is of sig~ficance in relation to colloidal particle stability and coagulation. More specifically work is summarized on double layer repulsive forces between colloidal surfaces approaching each other with finite velocity. The classical theory of colloidal interactions tacitly assumes that the approach velocity is either infhitely small or infinitely large. In this work the above assumption is relaxed and the theory is extended for intermediate values of the approach velocity. Two models of the colloidal surface are considered; Stem layer and dissociation of surface groups. For the linear problem (small surface potential) closed form expressions have been developed for the repulsion force. Numerical results are presented which tend to agree qualitatively with experimental observations.

ICEIHTCP For the investigation of iron sulfide formation in aqueous systems at 25'C, a computer based automatic titrator system was constmcted. This unit based on a 386DX IBM compatible PC was developed for the control of experimental variables. The master variable chosen for monitoring the process of FeS precipitation was the solution pH. Specific software was wntten for monitoring pH and maintaining it constant at a preset value. This was realized through an appropriate expansion card which provided capability of PC-pH meter communication and control of an external stepper motor for driving a pair of mechanically coupled syringes. Data from each experiment is recorded on the disk for further treatment.

Precipitatr'on Experiments The spontaneous precipitation expenments in supersaturated aqueous solutions were done in a 200 ml, double walled glass reactor thermostated at 25°C. The supersaturated working solutions were prepared by mixiig equal volumes of solutions of the ions composing the salt studied. Experiments were done at both variable and constant supersaturation for iron sulfide and calcium carbonate, in the presence and absence of inert electrolytes and101 additives to be tested as potential precipitation inhibitors. Seeded growth experiments were also done for the calcium carbonate system. The additives tested @repared by BBPDICM), were salts of maleic anhydrite copolymers with various groups as N-Vinyl Pyrrolidone, Vinyl Acetate, Styrene and Methyl Methacrylate, with code names AP 28.52.1, AP 28.2, AS 11.2 and AV 142.1. Commercial additive codes were Solamine 129, Aquaprox MDC 1300 and Nomst 491.



The spontaneous iron suljïde scale formation in supersaturated aqueous solutions ut high temperature was investigated. A high temperature high pressure benchtop reactor (Parr Instruments) was used for this type of experiments at 8OoC, having an effective volume of 300 ml. Al1 experiments were done at variable solution supersahiration in the absence and presence of various foreign ions and water soluble polymers to be tested as crystallization inhibitors. Experiments were also done under real conditions in the geothennal site of Melun YAlmont (Paris, France), for testing of the various additives. Particle size evolution measurements were done under the same experimental conditions at both 25 and 80°C, by transferring unfiltered aliquots of the work'ig solution in a laser particle counter during the precipitation experiments.

The driving force for the precipitation of a solid phase is the difference between the chemical potentials in the supersaturated solution, p,, and at equilibrium, b, respectively:

A v = b - ~ s Kietics data from experiments were fitted to the semi-empirical equation

R, = k,o "' where Rp is the measured rate of precipitation, kg the reaction constant, m the apparent order of precipitation and CJ the relative supersaturation with respect to the solid phase fonning defied as

Inhibition effectiveness tests were carried out at a fned supersaturation level so that the rates measured could be directly compared. The relative inhibition was defined as

R.I.% = (Ro -.%O x IO0

%, Ri are the precipitation rates measured in absence and in presence of additive respectively.

Iron sulfide precipitation was found to occur spontaneously in supersaturated aqueous solutions. The point where precipitation starts depends on the pH, temperature and saliity of the supersaturated solution. At low temperature (25°C) only iron monosulfides can be directly precipitated, regardless of the solution salinity. In neutral or slightly alkaliie solutions the phase forming is mackinawite. In slightly acidic solutions amorphous FeS precipitates. At elevated temperature (80°C) under low salinity conditions the spontaneously precipitating phase is amorphous FeS. In slightly acidic, s a l i e solutions supersaturated with respect to amorphous FeS, the same phase was found fonning while at lower supersaturations pyrite precipitates. Precipitation of pyrite is enhanced by the presence of oxidiuing ions such as Cl- and NO3-. The highest precipitation rates were observed in NaCl solutions. From the kinetic analysis it may be assumed that in al1 cases iron sulfide precipitation is a surface controlled process. It was also found that iron sulfide particles exhibit enhanced aggregation during precipitation in aqueous solutions. Synthetic pyrite can be produced via the thermo- dynamically unstable precursor solid phase amorphous FeS, by ripening at elevated temperature for extended time periods. The product was found to consist of uniformly sized (lpm) sphemiiitic crystallites, having a specific surface area of 6 ml g-'. Testing of various polymer compounds as potential scalig inhibitors gave ambiguous results. While in laboratory experiments many of them exhibited inhibition properties, in on-site experiments only ATP 6.2 @repared by BBPDICM) gave satisfying results.

Polymeric additives (BBPDICM products), derivatives of maleic anhydrite showed very good behavior in most cases as scale inhibitors in the calcium carbonate system. Reduction up to 100% in the crystallization rates was obtained at very low additive concentrations especially for seeded growth experiments, indicating blocking of the active growth sites by copolymer molecules. Among



the commercial products tested only AQUAPROX MDC 1300 was found to be effective at very low concentrations. Solamine 129 and Norust 491 did not exhibit an equal effectiveness.

CRIC in Hungarian geothermal wells the scaling is mainly due to calcite precipitation and a suitable description and modeiiig of these rather complicated scaling processes have an economical importance. Computer-assisted calculations are increasingly used in the prediction of scaliig and corrosion (Haarberg, 1989; Plummer and Busenberg, 1982; Hamie, 1984). A great advantage is the ability to simulate the effects of changes in brine variables, such as temperature and composition, and the probable result on scaling and corrosion. It is necessary to estimate scaling and corrosion rates at various points in a geothermal power plant. Input data are based on the brine chemistry and flow and the computational model provides the following parameters: flow rate, temperature and velocity at certain distance from the bottom of the production well through the plant to the waste injection system.

in our research we started a step by step construction of a simulating tool to describe these processes. The first step in this development is the equiiibrium description of the scaling of calcite and the other important scaling components and the determination of the bubble point. We have developed an equilibrium model algorithm and program of 15 component by the simplification of the Haarberg model (1989) in order to describe the equilibrium solubility of calcium carbonate, calcium sulfate, barium sulfate and strontium sulfate thermal water system under various carbon dioxide pressure, temperature and concentration of the 15 components. Formulating a model for an aqueous electrolyte system the following set of equations is to be solved:

material balances electroneutrality balances phase equilibria equations reaction equilibria equations

For the Na-K-Mg-Ca-H-Ba-Sr-Cl-Br-S04-OH-HC03-CO3-O-O system the following equations are valid:

The vapour-liquid equilibrium for the CO2 the carbon dioxide hydrolysis . the HC03- dissociation the H20 dissociation the calcium, barium and strontium solubility the electroneutrality balance . the total allcdinity the mass balances for carbon dioxide and as well for the calcium, barium, strontium and sulfate ions

The carbonate system at a fmed CO2 partial pressure (or fmed pH) can be described by the five equilibrium equations of the CO2-H20-Ca2+ system. However the fixed CO2-partial pressure model has serious limitations: the CO2-pressure maybe unknown and during the possible precipitation or dissolution the carbonate equilibrium system changes, which results in alteration of the CO2-partial pressure. To elimmate these limitations the mass balance for CO2 may be used. To solving the given equilibrium problem we used the strategy developed by Haarberg (1989). Fust we solved the equations of the carbonate system, by calculating the equilibrium state before precipitation or dissolution and by determining some solid phase which could be included or taken out. The equilibrium composition after precipitation or dissolution is fially calculated. This set of equations may be solved by the method of Haarberg (1989) by combining and reducing into two equations in two unknowns. The resulting non-iimear equations can then be solved for m,,



and for mHol by a regular Newton-Raphson solver in two variables. The solution of this system

using activities instead of concentration requires an iteration algorithm. The input data may be the total alkalinity-CO2 pressure, or the total alkalinity-pH values. We constmcted a solution algorithm and a prograrn for both the mT-pCol and for the mT-pH input cases.

From the calcite dissolution equations (for a CaC03-CO2-H20 system) it is quite clear that removal of CO2 from the solution into a steam phase during flashing leads to calcite supersaturation even though the concomitant temperature drop itself leads increase in calcite saturation. Smce most reservoir fluids are close to saturation with calcite, carbonate scaling the precipitation is possible for al1 geothermal wells inside the well between the bubble point depth and the production casing. The solubility of calcium carbonate minerals in aqueous solution at any particnlar temperature increases with increasing partial pressure of CO2. Boiling leads to strong reduction in CO2 partial pressure due to effective transfer of CO2 into the steam phase. The presence of other gases in the geothermal fluid, especially if they are less soluble in water then CO2 will enhance degassing of the CO2 during boilimg . In the next step we combined this algorithm with the earlier developed multicomponent equilibrium solubility algorithm. The basic idea of this combination is the fact that scaling starts only above the bubble point, so we have to describe the precipitation and dissolution processes betweeu the bubble point depth and the well head. Using the available gas separation and chemical analysis data for a given well one can determine the bubble point pressure (and the partial pressures of the three gas components). Moving in the direction upward of the well head it is possible to determine the new gas pressures, temperature the liquidlgas phase ratio at this new depth value. In our simulation mode1 we used a method similar to the Kocsis method [Kocsis, 19761 for the determination of the equilibrium gas pressures and temperature between the bubble point and well head depths.

The small laboratory reactor was constmcted in order to make pre-investigations before constmction of a semi-plant scale equipment. It was necessary to determine the residence times which are needed to reach the equilibrium. This small reactor is also suitable for static experiments conceming the investigations of precipitation-dissolution processes of the main scale developer CaC03 and other compounds.

2.4. Scale prevention

BRGM A comparative study of the effectiveness of various surfactants in inhibiting iron sulfide precipitation in a natural geothennal environment have been realiied (Harmandas et al., 1996). The objective of this study is to try to understand bener the mechanisms controlling the action of these inhibitors and compare their effectiveness to those of other molecules or fonnulae which have not been marketed and are synthesized and provided by the group of Prof. A. Carpov (BBPDICM, Iasi, Romania). In general, al1 the additives tested in this experimental investigation did not prove to have any scaliig inhibition effectiveness. Yet, we can see that in some cases, some of the compounds accelerated the formation of iron sulfide precipitate. Considering that the concentration used (5 mg/l) was in the s m e order of magnitude as Fez+ concentration, these compounds cannot be recommended for use as scale formation inhibitors.

CPERI The scale inhibition studies were conducted in the previously described set-up with the addition of a second test section following the first one. The inhibitor solution was introduced after the first test



attained with the same maleic copolymer. BBPDICM think that is the first step to obtain a multifunctional agent for geothermal water treatment.

ICPE-CO0 (see corrosion prevention)

2.5. Corrosion and scaling in diphasic flow conditions

BRGM The study of corrosion and scaling in diphasic flow conditions was undertaken on an artesian production well of the Chelles geothermal station (France), which was operating without treatment with additives injected at the bottom of the well (Abou Akx, 1993; Abou Akar and Lafforgue, 1994). Corrosion at the surface has been under study at this location for several years. In 1992, an auxiliary injection tube was put down the well to a depth of 150 metres. Fitted with coupon-holders, corrosion coupons were placed at three depths: 150 m (monophase zone), 60 m (bubbling point) and 4 m (biphase zone). Measurement of the rate of corrosion shows a slight increase with the degassing of the fluid. Examination of polished sections with a metallographic microscope shows that the products of corrosion are made up of iron oxides and oxy-hydroxides containing a mackinawite residue. These products initially take the form of the coupon and at the surface growth of iron sulfides with mainly pyrrhotite can be obsewed, in places associated with carbonates or diluted in a siliceous matrix. It has not been possible to demonstrate any correlation between this deposition on one hand (nature and proportion) and on the other, the transition from the monophase to the biphase zone.

CPERI The velocity measurements were carried out in a horizontal flow loop (using Laser Doppler Anemometry, LDA), where air-water two-phase flow developed in a 50.8 mm i.d. pipe (Paras and Karabelas, 1991). Regardiig the she'ar stress experiments, measurements were carried out at nearly atmospheric pressure, in a newly constmcted horizontal flow loop, where two-phase flow developed in a 24 mm i.d Plexiglas tube with a 5 m long straight section. Liquid-to-wall shear stress, at various pipe circumferential locations was measured using the electrodifîusion technique. A schematic layout of the flow loop, as well as the description of the electrochemical technique are presented in more detail elsewhere (Vlachos et al, 1996). This setup is of smaller scale than the existing 50.8 mm i.d. pipe loop in order to better control the conditions of the electrochemical system and to reduce the volume of the photo-sensitive liquid inventory and of the possibly required nitrogen gas. At relatively small liquid flow rates (compared to s t e m or gas ihroughput), and for gas velocity above 10m/s, the so-called "stratifiedlatomisation" flow (da) regime prevails. The main features of this regime are the appearance of disturbance waves, with a characteristic frequency 1-10 Hz, the liquid droplets entrained in the gas phase and the drastic change of the average gaslliquid interface profile from flat to concave. Conclusions are reported for the gas phase flow field and for the liquid layer characteristics.

The new LDA data in the gas phase of sla flow are assessed in connection with already reported data of wavy liquid layer characteristics obtained in the same experimental set-up, under the same conditions, and found to be consistent. The tirne average velocity profiles on the vertical symmetry plane display a maximum generally below the middle (or center) of the gas space coordinate y/(D- hW). On the contrary, the axial velocity profiles on the horizontal symmetry plane (Le. 90" to the vertical) clearly exhibit a "moustache" shape, with a local minimum at the pipe center, and two



(symmetrically spaced) maxima. These trends are in general agreement with those observed in the data by Dykhno et al (1994), strongly suggesting the presence of secondary flow currents. Regardmg the structure of such secondary currents, the new data seem to be in agreement with the observations made by Flores et al (1995), i.e. of two large counter-rotating vortices with respect to the vertical symmetry plane. Well-hown forms of the turbulent velocity profile seem to be quite satisfactory for correlating the data, not only at the pipe top but also in the lower strata of gas phase if the equivalent roughness of the wavy interface is properly taken into account. The infiuence of large waves is quite significant near the gaslliquid interface, as expected. An interesting fmding of this study (obtained from the velocity spectra) is that the influence of large waves may extend up to the pipe top (even at distance from the wall y - lmm), probably through the secondary motion in the gas core.

Special attention is paid to the lateral distribution of the liquid-to-wall shear stress by making measurements at various circumferential locations. An important result regarding the local time- averaged shear stress is that a significant lateral variation exists, associated with the decreasing liquid film thichess, away from the bottom of the pipe. Only in the case of relatively low superficial velocities (UG< 15m/s), the mean shear stress is roughly constant up to 45", where an adequate liquid film exists. Beyond that lateral position, shear stress tends to decrease as the film thickness decreases to reach, at the angle q of the triple-point (solid/gas/liquid), the value of the gas- to-wall shear stress. By taking into account the correct shape of the gaslliquid interface and having the ability to calculate accurately a circurnferentially averaged shear stress value, improved estimates of the interfacial friction factor fi are obtained. To estimate fi, film thichess, pressure drop and shear stress measurements (or respective correlations) are required. For the computational procedure the gas-liquid interface is considered to be concave, and not flat for reasons pointed out earlier. The complete procedure is described elsewhere (Vlachos et al., 1996).

CPR The GEA ( G e o t h e d Eqdibn Assessment) Code represents a consistent extension and completion of the DROP code developed to determine the liquid composition at dew point of geothermal steam. The GEA code is able to predict the equilibrium composition found in the heat exchange equipment of a geothermal power plant and in particular in the Direct Contact Condenser - Cooling Tower system. The code also considers the oxidation of H,S due to dissolved oxygen and for this reason can be extremely useful in order to determine the effect of HC1 in the H2S partitioning between non-condensable gases and the circulating liquid.

Direct injection of an alkaline solution in the well (stem washing in the weii) allows, in principle, protection of well casing in al1 the cases in which a corrosive condensate may form in the well. The theoretical investigation conducted in this part of the project demonstrated the feasibility of this process, in particular with regard to the phenomenon of well flooding and the identification of the liquid flowrate which allows good protection of pipe wall at an acceptable increase of pressure losses. In order to determine the pressure losses and the flow structure in the well with respect to liquid partition between the wall layer and the entrained droplets, a new model has been developed in order to evaluate liquid deposition at the wall. This model, along with other correlations developed in the past in this laboratory or available in the open literature is the central block of the vertical annular flow version of the HORF code named VEA (Vertical Annular). The HORF code has been developed in the past to predict the flow structure in the transportation in long pipelines of geothermal fluids. The model devëloped in the present research was proven to predict accurately the measurements of liquid entrainment rates, liquid deposition rates and pressure drops available in the literature. The resuits obtained with respect ;O the irocess of steam &whing in the well suggest that also in this case a direct application of this technique is feasible.



2.6. Corrosion and scaling monitoring

BRGM In order to monitor the corrosion rate of carbon steel (used for pipes and casings) and to maintain the effectiveness of a treatment by a corrosion inhibitor in a given geothermal plant, several different methods must be used, each having its own limitations, its advantages and disadvantages. The work done has contributed to the adaptation and the use of three types of methods for geothermal applications (Ignatiadis et al., 1994a, 1994b, 1994c, 1994d). The results obtained by al1 of these methods enable us to evaluate corrosion rates in cells (with partially reconstiiuted or actual geothermal water), in pipes and casings in geothermal plants. To determine the decrease in casing thickness by measurement of the iron flux emanating from the production well, it is necessary to know the iron content of the reservoir fluid and the amount of scale deposited by the rising fluid on the well walls. The physico-chemical fluid data gathered at production wellheads and from the Well Bottom Treatment Tubes (WBTTs) or from the down hole sampler PRINPIMO (Lesueur et al., 1996) allow the calculation of corrosion rates. Measurements of weight loss of metal coupons immersed in the fluid at the surface for various lengths of time are converted into thichess loss. Measurement of the polarisation resistance of a metal sample immersed in the fluid makes it possible to determine the aggressivity of the fluid (generalised corrosion) with respect to the sample. Work towards the design and test of an on-line probe has been carried out. The use of a suitable electrochemical equipment, allow us to determine the type of corrosion observed in the presence of an inhibitor and on the influence of certain chemical components of the fluid on the corrosion.

The influence of some exploitation conditions on corrosion and scaling in geothermal wells is reported (Amalhay et al., 1994a; Ignatiadis et al., 1997). The corrosivity of a geothermal fluid was assessed with respect to various materials at two flowrates, 0.3 and 3 m/s, in the presence and absence of an corrosion inhibitor (quatemary ammonium salt type). The procedure for measuring corrosion rates included both weight loss and electrochemical methods. The scale produced under the same conditions was characterized by classical chemical analysis, X-ray diffractometry, scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (EDS). The experiments show that carbon steel samples suffer fairly general corrosion. The corrosion rate and scale thichess decrease as a function of the fluid flowrate. The inhibitor considerably reduces both corrosion rate and scale thickness (Amalhay and Ignatiadis, 1993; Amalhay et al., 1994a; Ignatiadis et al., 1997). Concentration of chloride ions at the metallscale interface in the presence of the inhibitor is considerably reduced compared to that measured in absence of inhibitor. Mineralogical analysis showed that the scale is composed of more than 70% iron sulfides (mainly as mackinawite) and that the S/Fe ratio in the scale increases as a function of length of exposure. In an attempt to understand the mechanisms of formation of iron suIfide scale, we used several techniques to analyze scale formed on samples of carbon steel immerged in geothermal water for relatively long periods of t h e . SEM studies of polished sections of carbon steel after long immersion times showed that the scale is made up of two distinct layers having different compositions. The inner layer is made up primarily of iron oxi-hydroxide (FeO-OH), of iron hydro-oxichloride and of iron chloride. This layer is thii and adheres well to the metal. Small heterogeneities of iron sulfides and iron carbonates are sometimes present in this first layer. The outer layer is much thicker-up to, or even more than, 1 millimetre thick. This layer is formed essentially of a mixture of iron sulfides. This layer is soft, brittle and does not adhere well to the metal. When the hydrogen sulfide content is low, the scale has this two-layer structure, but the inner layer of iron hydroxide is very thick and in the outer layer, the iron sulfides are made up mainly of pyrite. The lower the hydrogen sulfide concentration of the fluid, the richer the scale formed on the carbon steel coupons coming from the various



CAEL Specific tools (two specialised softwares) to be used for experimental measurements or interpretation of experimental data were developed: (i) a program (TAFEL II) for computation of corrosion rate and polarisation resistance by using the integral method (distributed to the Greek's partner of the contract); (ii) another program (LEAC) for experimental data acquisition, to assist the matrix electrode system via a multiplexing hardware system. It allows the measurement of the current distribution andlor open circuit electrode potential.

The matrix electrode (multi-electrode) is an extension of usual single-electrode electrochemical systems. It is particularly suited for corrosion monitoring in actual or micro-pilot systems. This matrix electrode:

can be used in studying the infiuence of flowing corrosion inhibitors over plane electrodes; is a very flexible system, since it is computer assisted; can be integrated in so called virtual instruments and can be operated in the frame of object type graphical programs; reduces the measuring errors currently present in surface manufacturing by virtue of its very matrix structure; can be used in electrochemical system with or without extemal current source; is a monitoring system and as such it cannot be used properly in investigating surface phenomena associated with the first polarisation cycle;

The system can be easily developed and oriented toward different data acquisition boards since a large part of it (electrode, multiplexor, software) is designed by LEAC;

A muitiplexer board was designed to connect the matrix electrode to the data acquisition card. The set of electric information produced by the matrix electrode is received by the data acquisition system (BP 100 board) via the multiplexor system. The electrical information is presented either directly or suitably amplified to the A/D board, where the continuously varying data are converted into digital (discrete varying) data, which is in tum presented to the PC computing system. This process is controlled by a dedicated software package LEAC which exchanges information with the matrix electrode. The experimental date can be either processed in real time or stored in view of subsequent processing using commercial software packages compatible with ASCII data files. The post-processing used in our study of corrosion processes was done on the ORIGIN software package.

ICPE-CO0 The possibiüty for automatic dosing (in closed-loop) of the inhibitors in geothemal systems was examined. Geothennal well operators are interested in correctly dosing the corrosion and101 scaling inhibitors in such quantities, so to obtained the best result for the technical and economical parameters. The quantity of inhibitor requested depends of some physico-chemical parameters, which are variable intime. It is better to dose the inhibitor in a controlled automatised process. This means that finally if there is not enough inhibitor, the purpose of dimiishiig both the scale and the corrosion is not fulfilled, or if it is too much the cost is to high. Conceming the work performed:

a) It has been studied the constmction of the actuator for automatically dosing the inhibilor. In order to obtain the best technico-economical effect for the inhibitor dosage, the electrical motor must be of a special design and type, so to provide constant speed at constant torque, in large range of speed (1110 ratio). The purnp driven by the electrical motor must be of a high pressure value (300 atm) and controlled debit function of the motor speed. b) it has been studied, conceived, designed and executed a multifunctional transducer device capable to collect information about scaliig and corrosion rate and temperature and to transform these parameters in electric signals. In order to use this information it has been conceived an intelligent

EEC-DG XII-Joule Programme-contracf Nos JOU2-CT92-0108 and CIPD-CT93-0314 - final report 37


system that collects, transmits, processes the information and decides the dosage of the inhibitor by means of an actuator. By monitoring these parameters we can obtain the automatic dosage required for the geothemal water. c) It was experimentally demonstrated the possibility of monitoring the scaling rate by measuring the impedance of some special designed electrodes. It was designed, built and tested the proper device. Considering the ideas presented previously, the multifunctional transducer can give at its output a signal which is substantial sufficient to control an automatic injection system of inhibitor. It was studied the automatic dosing possibiliiy in optimal quantities (from technico-economical point of view) of the inhibitors in geothermal systems. So it was designed an automatic system controlled by computer through the electrical signal given by a multifunctional sensor for corrosion, scale and temperature. This signal controls the actuator (the assembly motor-purnp) which inject the inhibitor inside the geothermal well. Also, it is realized and tested a multifunctional transducer. From its experimentations it results that for the carbonates scales, the impedance variation at 100 Hz of the transducer is about 200 n / m d , respectively 0.2 Q/pm.

38 EEC-DG XI/-Joule Programme-contract Nos JOU2-CT92-0708 and CIPD-CT93-0314 - final report


3. PRELlMlNARY CONCLUSIONS

BRGM The objectives of the BRGM were to eliminate the problems due to corrosion and scaliig in the exploitation of low enthalpy geothennal systems in order to ensure their financial profitability. The research programme aimed on the one hand, on the theoretical level, to develop understanding of the reaction mechanisms which control corrosion (of carbon steel) and scaling, and on the other hand, on the technological level, it aimed to improve the solutions currently employed and to develop new, less costly andlor more reliable solutions. The work carried out in the framework of this project allow us to:

Develop a metrology associated with the monitoring of corrosion and scalmg; Select the most efficient products for inhibiting corrosion or crystal growth with a view to their optimal use within current and future operations; Establish the kinetics of the formation and growth of the scale most frequently encountered, with the development of appropriate numerical simulation codes. The calculation code enable modelling of corrosion-deposition phenomena in low enthalpy geothermal systems; Establish a general methodology for detecting and assessing perforations in casings of wells exploiting geothermal waters.

Seven main studies were carried out: (i) to monitor, study and model the corrosion and scaling phenomena, and (ii) to determine the optimal conditions for the elmination of the causes of corrosion and scaling: 1) In order to monitor the corrosion rate of carbon steel, several methods have been used and

adapted for geothermal applications: chernical analysis, weight loss of coupons and measurement of the polarisation resistance. Each of these methods have its own limitations, its advantages and disadvantages.

2) The influence of some exploitation conditions (iibitor, flowrate, material) on corrosion and scaling in geothermal wells have been examined: the corrosion rate and scale thickness decrease as a function of the fluid flowrate. The inhibitor considerably reduces both corrosion rate and scale thickness. The scale is composed of -70% iron sulfides (mainly as mackinawite).

3) The behaviour of a carbon steel in the absence and in the presence of various corrosion inhibitors in reconstituted, actual and modified geothermal water in order to optimize their use in low enthalpy geothermal systems has been studied. The influence of some physico-chemical parameters such as saliity, hydrogen sulfide concentration and flowrate have also been studied. This enable us to adjust (for each fluid composition) the concentration of the inhibitor for an optimum effectiveness.

4) Experiments were done to understand iron sulfide precipitation kinetics. Mackinawite is the one which controls the solubility of iron and sulfide in the geothermal environment. A model of scaling regulation is proposed, suggesting that the formation of scale is controlled by the diffusion of anions through the scale. Crystalliiation of amorphous iron sulfide into mackinawite is accompanied by an increase in the corrosion rate. Al1 of the inhibitors tested, except those prepared by BBPDICM, significantly reduce the corrosion rate of carbon steel and delay the crystaiiiiation of mackinawite from amorphous iron sulfide. A comparative study of the effectiveness of various surfactants in inhibiting iron sulfide precipitation have been realized. In general, al1 the additives tested did not prove to have any scaling inhibition effectiveness.

5) The behaviour of some nonmetallic materiab in actual and treated geothermal environment have been characterized. After briefly describing the context in which these materials are used, this study lists the principal characteristics of the nonmetallic materials which can be used in geothermal activities and gives the main results gathered from the Dogger exploitation in the Paris Basin.

EEC-DG XII-Joule Programme-contract Nos JOUZ-CT92-0108 and CIPD-CT93-0314 - final report 39


6) A digital model (MODEP) that enables the modelling of corrosion and scaling phenomena on the casing walls is proposed. Simulation of corrosion is based on the Volmer-Heyrovski reactive mechanism and takes acconnt Fick's diffusion laws, the diffusion layer and the scale porosity. The model (i) simulates the precipitation of mackiiawite and other mineral species, (ii) adjusts the flowrate in the well, and (iii) takes into account the presence of a well-bottom treatrnent tube. Although the MODEP code has never claimed to be capable of simulating the totality of real phenomena, it can nevertheless be used to calculate trends that result from variations in the major parameters of the aquifer and101 the casing.

7) The environmental impact of a perforation in the casing of a well exploiting the water of the Dogger was examined. When localized, corrosion can lead to perforations in the casing, thereby increasing the risk of contamination by geothermal fluids of freshwater aquifers traversed by the wells. After examination of the various water-migration possibilities with one or two casing perforations in a production or injection well, the different detection methods for perforations are discnssed in terms of their limitations and accuracy.

These results were presented at the partners periodic meetings to which CEC experts are invited and in seven biannual reports. BRGM annual reports and some study reports have been sent to experts in order to spread the information. Several publications in international meetings have been made.

CEBELCOR E p H equilibrium diagram contribute to the correct understandimg of the reactions that are possible and of those that must not be considered, in given conditions of pH, potential, sulfur and iron concentrations. They provide also a trustable guide for extrapolation and prediction of phenomena in modified conditions. They clearly show the combinations of anodic and cathodic reactions that rnust be considered simultaneonsly. The nature of possible corrosion products is indicated also, and this is a support to the analysis of deposits and scale. Again, diagrams suggest modifications of operating conditions that would decrease the amount of deposits formed. Of course, specific inhibitors for crystal growth need other siudies, conducted by other groups. The use of two-compartment corrosion cells appears promising for the detection of corrosion processes, includ'mg localised corrosion. The principle of these cells has been described. Three draft papers have resulted from this research programme: one is almost ready for being submitted, probably to Corrosion Science. Data for mackinawite at higher temperature would strongly add to the interest of this paper. A second draft paper (on experimental work) is now being cornplemented by addition of surface and deposits analysis and would then be an interesting contribution to corrosion in sulfide media. When these papers will be ready, they will be presented also in corrosion congresses. It is important to indicate that this programme induced a close collaboration between BRGM, Cebelcor and Dr. Amaihay, throngh a post doc position of the latter at Cebelcor, within the "Research in Bmssels" programme of the "Région de Bmxelles-Capitale".

CPERI Three main studies were carried out: (i) iron snlfide scale formation, (ii) two phase flow, and (iii) simulation of particle size distribution and scaliig along a pipeline. The data show that deposits form essentially oniy within a narrow pH range, which is associated with the solubility of the amorphous Fe,S. At relatively large supersaturation ratios precipitation in the bulk solution occnrs immediately after mixing of the two reagent streams, thus depleting the solution of ions needed for wall crystallization. One may conclude that a small reduction of pH of the brine can be beneficial, not oniy by converting a supersaiurated solution to an undersaturated one, but also by decreasing the supersaturation ratio below its critical value. On the other hand, a small increase of pH can alter the spontaneous precipitation propensity of a brine, promoting instantaneons bulk precipitation. The relatively small size of the precipitated particles may suggest



the use of a flocculating agent in the clarification system. The experimental work regardimg scale inhibition deals with the effects of several additives on the scale formation of Fe,S and CaC03 systems. A small inhibition action was found for the iron sulfide system at an additive concentration of 10 mgll. On the other hand, for intermediate CaC03 supersaturation ratios almost complete scale inhibition was obtained with al1 additives, while at higher ratios crystal distortion occurred, resulting in weakly cohesive deposits, but not in a significant reduction of the scale formation rate.

At relatively small liquid flow rates (compared to s tem or gas throughput), and for gas velocity above 10m/s, the sa-called "stratified/atomization" flow regime prevails. The main features of this regime are the appearance of disturbance waves, with a characteristic frequency 1-10 Hz, the liquid droplets entrained in the gas phase and the drastic change of the average gaslliquid interface profile from flat ta concave.

The simulation of precipitation and scale formation in pipe flow of sparingly soluble salts, presented here, is shown to produce physically realistic results. State of the art models are used to represent the individual processes involved (nucleation, particle growth, coagulation) and no arbitrary parameters are introduced. The predictions are quite encouraging, reproducing the bell-shaped deposition versus pH curves obtained in the laboratory. The peak value of the deposition rate is also predicted quite satisfactorily. Additionally, the computations display trends of particle size distributions, affected by the interaction of various mechanisms. Particular attention is paid in this project ta colloidal particle coagulation, which (if enhaced) greatly affects both scdmg and brine treatment processes due ta particle size enlargement. A theoretical study was completed on the effect of particle surface microroughness on electrostatic repulsive forces between particles. A simple mode1 of rough surfaces is proposed, which allows computation of the repulsive energy of interaction as well as an estimation of the tangential forces developing between these surfaces.

CPR Al1 the activities carried out in the course of the present research programme arrived ta a firm conclusion and the major results obtained can be used for a more efficient and clean exploitation of geothermal energy. Future work can obviously be dedicated ta an improved lmowledge of the processes and methods investigated in this project, but present results can be immediately transferred to field operations.

ICEIHTCP Iran sulfide precipitation is a process controlled by a surface diffusion mechanism regardless of the environment in which it occurs. The finally forming phase depends on various physicochemical parameters in the working solution. Metastable phases form initially, converting gradually to stable ones. Polymeric products were tested but showed little effectiveness regardiig inhibition of iron sulfide formation, especially under real conditions, while for the calcium carbonate system they even caused complete inhibition of precipitation. Corrosion of carbon steel specimens occurs rapidly in aerated saline solutions. Corrosion is also enhanced in the presence of sulfides while it is retarded by the presence of amorphous iron monosulfide in the working solution. Commercial products used in French geothermal wells exhibited good inhibiting properties regarding corrosion, but maleic anhydrite copolymers gave poor results. It has ta be pointed out that in both cases of solid formation and corrosion, the fuial additive testing should be done with experiments at the specific geothermal site they are going to be used in order ta draw decisive results.



BBPDICM BBPDICM appreciates that this research must be continued because maleic copolymers are not only usefui for geothennal waters but also in other industrial domains or in environmental protection. BBPDICM intends to contact the Programme EUREKA, if this programme is still interested in geothermal studies, with the aim to test our products in different countries interested in the exploitation of geothermal water containing calcium and magnesium bicarbonates. In the same time the collaboration with ICEIHT Patras will be continued in the future on a biiateral basis. The laboratory synthesis of its products could be scaled up in the small or medium sized production units without great diff~culties in Romania or abroad. The maleic polyelectrolytes are versatile products. They can be applied in a large number of research domains in the following programmes: - environment - as water and waste water treatment or sludge, etc, - agriculture - as soi1 conditioners, etc, - industrial technologies - as filtration aids, etc, - biomedicine - as formulation aids for dmg delivery systems, inhibitors for calcification of artificial

organs or implants. Concerning his intentions to publish, BBPDICM thinks that the following results could be published, of course with the agreement and in collaboration with our colleagues: - inhibition of FeS precipitation with maleic polyelectrolytes (this effect is not yet cited in literature), - inhibition of CaC03 precipitation in geothennal systems with various maleic polyelectrolytes (new

products with a such effect), - review papers conceming polymeric antiscalants and anticorrosion agents, - piperazine derivatives of maleic copolymers as corrosion inhibitors, - aromatic amine derivatives of maleic copolymers as corrosion inhibitors, - romanian patent applications regard'ig the synthesis of various derivatives of maleic copolymers, - european patent applications (with the help of Our colleagues and EU) concerning inhibition of FeS

precipitation or inhibition of corrosion with maleic polyelectrolytes.

CAEL For the CAEL group, the work performed in this programme allowed the following points:

purchase of research equipment, computing equipment and associated software at the current European level; international contacts with suitable partners in the area of corrosion and scaling; marketing studies regarding the implementation of anti-corrosion protection and anti-scaling methods in geothermal wells of the Bihor-Romania area; preparation of two papers to be published, the first concerning the cathodic protection of tanks with external current source and the second dealiig with the validation of an integral method of computing the corrosion rate.

CRIC An equilibrium model and a related computer programme was developed to simulate the solubility of calcite in water. The first model is based on the simultaneous resolution of the material balances, electroneutrality, phase equilibria and reaction equilibria equations via Newton-Raphson method. Using this model one can calculate the equilibrium concentration values for the Ca2+, H+, OH-, HC03-, CO3" ions, and the H ~ C O ~ * as well as the pH, the alkalinity and the total carbonate at any temperature and CO2 pressure using the Davies and Pitzer activity calculation methods. A small laboratory scale reactor was developed first to test the predictions and for the future experiments. The predicted results fitted well the data measured and given in the literature. The developed model is a suitable basis for the simulation of solubilities of multicomponent geothermal and thermal water including the Na-K-Mg-Ca-H-Ba-Sr-Cl-Br-S04-OH-HC03-CO3-CO2-H20 system.



An equilibrium model and a related computer code was developed in the second step by modifying the Haarberg model maarberg, 19891 to simulate the equilibrium scale formation in thermal water. The model is based on the simultaneous solution of the material balances, electroneutrality, phase equilibria and reaction equilibria equations via Newton-Raphson method. Using the model one can calculate the equilibrium concentration values for the Ca2+, Ba2+, Sr2+, Mg2+, H+, Na+, K+, OH-, Cl-, B r , HCOy, C032-, S042- ions, and the H2C03* as well as the pH, the alkalinity and the total carbonate at any temperature and CO2 pressure using the Davies and Pitzer activity calculation methods. The predicted results fitted the literature data well. The developed model is a suitable basis for the simulation of multicomponent geothermal and thermal water solubilities includiig the Na-K- Mg-Ca-H-Ba-Sr-Cl-Br-S04-OH-HC03-CO3-CO2-HO system. An equilibrium simulation algorithm and a computer program were developed for the determination of the bubble point pressures in a thermal or geothermal well. The developed program computes the bubble point using the measured gas separation and other data. The computed bubble point depth and pressures were compared with the measured values and a suitable coincidence was found.

N-substituted (acylated, hydroxymethylated, carboxymethylated) amino acids reduced the corrosion mild steel up to 85% in test water. The presence of a more hydrophobie moiety enhanced the acylamino acid's corrosion inhibition activity.' N-carboxymethylated amino acids are effective scale control agents and may reduce the corrosion inhibition at the same t h e . This property of inhibitors could be a consequence of the electronwithdrawing properties and inductive effects. Actually, inhibitory efficiency depends upon a combination of intramolecular, steric and electronic activities. SFM images gave a detailed information on the surface morphology due to the corrosion with or without inhibitors. Our prel imiry results indicate the imporîance of the ELUMO. Efficiency increases with decreasing values of ELUMO. The results seem to indicate, that charge transfer from the metal surface to the inhibitor takes place during the adsorption. The continuation of this investigations is in progress. Comparing simulated and experimentally deterniined fractional coverages a very simple model was found for interaction adsorbed species in order to make a distinguition between the adsorption mechanisms of Langmuir and Frumkin type. The results got by CRIC were already included at several international conferences by the coworkers and the publication of the results has also been started. The accumulated results will also be distributed among Hungarian specialists dealing with geothermal systems. The CRIC is going to organize the industrial production of newly developed chemicals and introduce the new product at Hungarian geothermal wells.

ICPECOO It was studied the possibilities to control the corrosion and scaling in romanian geothermal systems. Regarding the problem of corrosion Our research takes in consideration both the method of active protection, through the injection of cathodic current in potentiostatic regirne and that of the corrosion inhibitors. From our works has resulted that the method of active protection is suitable in good technico-economical conditions only for the protection of extemal sides of the system (metallground interface) and also, of the intemal sides of some bulky equipments (metallgeothemal fluid interface) as: degassing tanks, buffer vessel, etc.. . Are presented the aspects regarding the conception-electrical and electrochemical diiensioning of a active anticotrosive protection systems (current distribution, the positioning of injection anodes, etc.) and also their constmction and their functional test. To h o w the exactly corrosiveness of the geothermal water respectively of its origin, were determined the kinetical parameters of the corrosion reactions to the R 37 steel/geothermal fluid interface from 14 representative wells which operating in correlation with the mineralogical structure of these.



The conclusions of these works show that in geothermal fluid without S2- and with a small content of S042-, the corrosion is determined primarily by the concentration of Cl-. For these geothermal waters, in the range of temperature 30-95"C, the corrosion is increasing with the temperature decreasing so, the damages caused by them are more important on the "cool" side of the equipments (the output of the heat exchanger, the recirculation pipes, buffer vessels, etc...). In the geothermal fluids having a small content of Cl- and an important one of S2- and S042- the corrosion is determined by these concentrations and increases with temperature increasing. The most corrosive geothermal fluids are those which have a high content of Cl-, SOd2- respectively S2-. To have a simultaneous supervision of corrosion and scaling, it was studied the anticorrosive action of some maleic polyelectrolytes having a wellknown antiscaling effect. Thus, it was determined the corrosion for carbon steel R37 in direct contact wilh synthetic geothermal water in the presence and also the absence of some polyelectrolyte additions (0.1-30 ppm) which have different structure. From Our determinations was resulted that dependig of their structure and composition the maleic polyelectrolytes can present a pronounced inhibition effect. They act through the braking of the charge transfer reactions (anodics and101 cathodics) and through the modifying of the transfer coefficient a. From our determination it results that the maximum inhibition effect of the corrosion and scaling too, is usually obtained for an optimal concentration of inhibitor, concentration with depend both the geothermal temperature and chemical composition. In this context it was conceived an automatic system (controlled in closed loop by a computer) of injection and dosing dependig of the momentary values of the corrosion, scaling and temperature. In the system conceived by us the adjustments is executed taking in consideration the above mentionned parameters detected by a multifunctional transducer designed, built and tested by us. From these determinations the conclusion is that the carbonate scale resulting from the geothermai fluid of the well no 4159 - Oradea has the resistivity of about 120 Qm, so the impedance variation (to a signal at 100 Hz) of the transducer is about 0.20 R/pm - signal which is enough big to be processed in the automatic system proposed.

ICVL Corrosion of iron and carbon steel in the geothermal fluids of Vidmntai 1 and Vidmntai 2 was studied under laboratory conditions. The following conclusions can be made: - the corrosion rate decreases with the immersion time of iron in the solution; - the corrosion current density is much'higher when the rotation of electrode is applied; - deaeration of the solution leads to decrease in the corrosion rate, especially when electrode

rotation is applied. After two hours immersion the decrease in the corrosion current in deaerated solution is insig~ficant;

-the rises of temperature from 20 to 80°C cause decrease in corrosion rate depending on the immersion t h e . Much pronounced decrease was determined in an unstirred solution;

-saturation of geothermal fluid with CO2 causes a slight rise of corrosion rate after 1 h of immersion;

- corrosion process inhibition is observed when increasing the chloride concentration in the sulfate solution (pH 3) to the value l i e in the real geothermal fluid (100 g/l);

- the corrosion rate in the naturally aerated system reached a limited value (- 1.52 mA/cm2); Conceming the formation of oxide layer on iron surface, the following conclusions can be drown: - the thickness of oxide layer growth with the exposure time in the solution. The thichess is very

similar in the cases of aerated, deaerated and COTsaturated solutions; - the rise of the temperature from 20 to 80°C causes developing of more thick layer; - the most thick layer at the beginning of corrosion develops in the naturally aerated solution. The

layer developed in the CO2 saturated fluid is sig~ficant thiier.



4. GENERAL CONCLUSION AND FUTURE OBJECTIVES

The work carried out for the project has provided us with a better understandiig of the corrosion- scaliig that has taken place and represents a marked progress in each of the six following topics: corrosion prevention, corrosion studies, scale formation and modelling, scale prevention, corrosion and scaliig in diphasic flow conditions and corrosion and scaling monitoring.

The prevention of corrosion in low-enthalpy geothermal systems was the main concern of the contracting parties in this project: much of the study was devoted to testing the effectiveness of corrosion inKibitors, their conditions of use and their adaptation to geothermal fluids with different physico-chemical characteristics. A wide range of inhibitors, both commercially avaiiable and synthesized by certain partners, were exchanged between the contracting parties and tested under geothermal field conditions as well as in the laboratory. The electrochemical approach (measurement of impedance and polarization resistance) was the main tool adopted for these studies. The prevention of corrosion is also expressed by other studies as the cathodic protection and anodic protection of the surface distribution network. Monitoring the effectiveness of the inhibitor treatment by adapting existing methods to geothermal fluids, as discussed in the chapter on "corrosion scaling and monitoring", enables the early detection of anomalies so that they can be remedied. Some of the methodologies, such as mild acidification (injecting an acidhhibitor mixture down the well in order to dissolve the scaling), inhibitor concentration and injection frequency, are now applied to certain geothermal operations in the Paris Basin. Non-metallic materials were also considered, and a study was made of their behavior under geothermal conditions. Where high enthalpy is concemed, studies continued on the process of s tem washing (for HCl abatement); this was begun under the Joule 1 contract; on the basis of this work, a full scale washing column has been designed and will be constmcted and tested in the near future at the Larderello field. The feasibility of a dry process (dry abatement of HC1) was also examined and a reactor for this study is now being designed.

Corrosion studies (reaction mechanisms, effect of fluid composition, etc.) were the second most important element of the project. The work was based on constmcting Eh-pH equilibrium diagrams of the S-H20 and Fe-S-H20 systems. The presence of trace amounts of oxidiziig agents and chloride ions, and their effect on corrosion and on the formation, nature and development of scaling, were also studied when drawing up these diagrams. Studies in reconstituted, real and modified geothermal media (both with and without the presence of an inhibitor) have made it possible to (a) assess the effect of different parameters (pH, Oz, CO2, H2S, T, salinity, flowrate, effective protection of corrosion products, etc.) on the variation of the corrosion rate, and (b) determine the kinetic parameters of the corrosion reaction.

The third objective concerned the study and modeiiig of scaling. Scaliig experiments were run, both in the presence and absence of an inhibitor, in reconstituted and real (and modified) geothermal media in order to study the formation rate, size, morphology and composition of scaling in relation to the principal physico-chemical parameters of the fluid. This study led to the formulation of a mechanism for their growth and effective protection relative to theu steel support. New calculation codes, suitable for both high and low enthalpy, were written for modeliig the scaling phenomena. The MODEP code (dedicated to low enthalpy) proposed in the Fia1 Report of the Joule 1 project has been greatly improved. Today it includes Fick's laws of distribution, kinetic and thermodynamic criteria and the precipitation of several mineral species. In addition to the formation of scaliig, the MODEP code also simulates the corrosion of casings (a deliverable that was not initially planned, but which turned out to be required for the studies). Further improvement of this mode1 is the basis of a proposa1 to the European Union as part of the INCO COPERNICUS work programme in 1996. A second code simulates the coagulation of colloidal PbS particles in the fluid vein (nucleation, growth, distribution) and the eventual formation of scaling on the casing wall. The dynamics of the



particles, their roughness and their mutual repulsive forces are al1 taken into consideration by the model. A fia1 model simulates the precipitation and deposition of CaC03 on the walls of high- enthalpy wells, a phenomenon that occurs between the bubble point and the well head. This code calculates the bubble point and the partial gas pressures after degassing. The codes have been tested and the results are satisfactory.

The prevention of scaling, which was considered as the fourth most important topic, was carried out at the same time as the corrosion prevention studies. It appears that the good corrosion inibitors are often poor scaling inhibitors and that a good CaC03 scaliig inhibitor is much less efficient in inhibiting the deposition of mackinawite. The once again shows the necessity of adapting each inhibitor to a specific fluid accordiig to the desired final result.

Study of corrosion and scaling in diphasic flow conditions or, more generally, the two-phase flow studies comprised the fifth objective of the study. The velocity measurements were carried out in a horizontal flow loop, where air-water two-phase flow developed in a 50.8 mm i.d. pipe. Regarding the shear stress experiments, measurements were carried out at nearly atmospheric pressure, in a newly constmcted horizontal flow loop. Liquid-to-wall shear stress, at various pipe circumferential locations was measured using the electrodiffusion technique. At relatively small liquid flow rates, and for gas velocity above IOmIs, the so-called "stratifiedlatomisation" flow (da) regime prevails. The main features of this regime are the appearance of disturbance waves, the liquid droplets entrained in the gas phase and the drastic change of the average gaslliquid interface profile from flat to concave. The study of corrosion and scaliig in diphasic flow conditions was undertaken on an artesian production well, which was operating without treatment with additives. An auxiliary injection tube was put down the well. Fitted with coupon-holders, corrosion coupons were placed at three depths: 150 m (monophase zone), 60 rn (bubbling point) and 4 m (biphase zone). Measurement of the rate of corrosion shows a slight increase with the degassing of the fluid. The products of corrosion are examined by using metallographic microscope. Concerning stearn washing in the well, direct injection of an alkaline solution in the well allows protection of well casing in al1 the cases in which a corrosive condensate may form in the well. The theoretical investigation conducted demonstrated the feasibility of this process, in particular with regard to the phenomenon of well flooding and the identification of the liquid flowrate which allows good protection of pipe wall at an acceptable increase of pressure losses.

The last aims of this study was "corrosion and scaliig monitoring". In order to monitor the corrosion rate of carbon steel and to maintain the effectiveness of a treatment by a corrosion inhibitor in a given geothermal plant, several different methods must be used, each having its own limitations, its advantages and disadvantages. The work done has contributed to the adaptation and the use of three type of methods for geothermal applications. These methodes included chemical analysis, weight loss and electrochemical methods. A methodology for the detection and assessment of perforations in well casings was carried out: wells often penetrate fresh water aquifers which are used as a drinking water resource in the Paris region. Following localized or prolonged corrosion of the casing by the geothermal fluid, the casing may be pierced. Dependiig on the existence or absence of dual completion in the area of the perforation, the geothermal fluid may enter into the water from the adjacent aquifer, thus creating the risk of pollution of the water. M e r examination of the various water-migration possibilities with one or two casing perforations in a production or injection well, the different detection methods for perforations are discussed in terms of their limitations and accuracy. In al1 cases, a logging tool is necessary to confirm the existence of a perforation and to locate its depth. Conceming scale monitoring, the scale removed from the well or deposited on steel coupons was characterized by classical chemical analysis, metallographic microscopy of polished sections, X-ray



diffractometry, scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (EDS). The experjments show that carbon steel samples suffer fairly general corrosion. The corrosion rate and scale thickness decrease as a function of the fluid flowrate. The inhibitor considerably reduces both corrosion rate and scale thickness. Electrochemical methods for the surveillance and investigation of corrosion modes and corrosion rates in geothermal applications derive directly form the study reported above (2nd theme). Two specific tools was developed in order to be used for experimental measurements or interpretation of experimental data: TAFEL II is a program for computation of corrosion rate and polarisation resistance by using the integral method. LEAC is a program for experimental data acquisition, to assist the matrix electrode system via a multiplexing hardware system. It allows the measurement of the current distribution andlor open circuit electrode potential. It was studied the automatic dosing possibiity in optimal quantities of the inhibitors in geothennal systems. So it was designed an automatic system controlled by computer through the electrical signal given by a multifunctional sensor for corrosion, scale and temperature. This signal controls the actuator (the assembly motor-pump) which inject the inhibitor inside the geothemal well.



5. REFERENCES

ABDUL-AHAD P.G., AL MADFAI S.H.F. (1989) - Corrosion, 45, 978. ABOU AKAR A. (1993) - Study of the corrosion in the diphasic and monophasic zones in an artesian well. First six-monthly report of the JOULE ïI programme (contract no JOU2-CT92-0108, BRGMICCE DG XII), "Control of corrosion and scaling phenomena in geothermal systems", September 93, Patras, Greece, pp. 125-169. ABOU AKAR A. (1994a) - Modelling of deposition phenomena in low enthalpy geothemal wells. Third six-monthly report of the JOULE II programme (contract no JOU2-CT92-0108, BRGMICCE DG XII), "Control of corrosion and scaling phenomena in geothermal systems", July 94, Udine, Italy, pp. 51-67. ABOU AKAR A. (1994b) - Modelling of deposition phenomena in low enthalpy geothermal wells. Fourth six-monthly report of the JOULE II programme (contract no JOU2-CT92-0108, BRGMICCE DG XII), "Control of corrosion and scaling phenomena in geothennal systems", December 94, Budapest, Hungary, pp. 75-90. ABOU AKAR A., IGNATIADIS 1. (1994) - A new mode1 for uon sulphide deposition in geothermal wells. In: Proceediigs of the International Symposium, Geothermics 94 in Europe, from Research to Development, BRGM (ed), Orléans, France, 8-9 Febmary 1994, pp. 215- 222 ABOU AKAR A., IGNATIADIS I., LESUEUR H., LONGIN G. (1994a) - Risque de pollution des nappes d'eau douce du fait des exploitations géothermales de l'aquifère du Dogger du Bassin parisien. 4. Méthodologie de détection des percements intervenus sur le tubage d'un puits géothermique. Convention Ademe-BRGM 2 07 0028. Rap. BRGM R 38035,47 p., 10 tabl., 2 ann. ABOU AKAR A., IGNATIADIS I., LESUEUR H. (1994b). Methods for detecting perforations in casings of wells exploiting geothermal fluids. Second six-monthly report of the JOULE II programme (contract no JOU2-CT92-0108, BRGMICCE DG XII) "Control of corrosion and scaling phenomena in geothermal systems", February 1994, Paris, France, pp. 103-132. ABOU AKAR A., LAFFORGUE M. (1994). Etude de la corrosion par coupons en acier au carbone placés en zones monophasique et diphasique sur la centrale géothermique de Chelles (Seine-et- Marne). Rap. BRGM R 37832 GGP-DR-94, 91p. ABOU AKAR A., BOENS P. (1995a) - Modélisation des phénomènes de corrosion-dépôts sur les parois des tubages en acier des exploitations géothermales. 1. Proposition d'un modèle de simulation des phénomènes de corrosion-dépôts. Rap. BRGM R 38612 GGP DR 95, 50p. ABOU AKAR A., BOENS P. (1995b) - Modelling of corrosion and scaling phenomena in low enthalpy geothermal wells. Sixth six-monthly report of the JOULE II programme (contract no JOU2- CT92-0108, BRGMICCE DG XII), "Control of corrosion and scaling phenomena in geothermal systems", December 95, Thessaloniki, Greece, pp. 87-1 18. ABOU AKAR A., IGNATIADIS 1. (1995) - Modelling of the deposition phenomena in geothermal wells in the Paris basin. In: Proceedigs of the World Geothermal Congress, 1995, Florence, Italy, 18-31 May 1995 (International Geothermal Association, Inc., Auckland, New Zeland, 1995, Volumes 1 to 5), 4, pp. 2491-2496. ABOU AKAR A., IGNATIADIS I., LESUEUR H. (1995a). Methods for detecting perforations in casings of wells exploiting geothermal fluids. In: Proceedings of the World Geotherrnal Congress, 1995, Florence, Italy, 18-31 May 1995 (International Geothermal Association, Inc., Auckland, New Zeland, 1995, Volumes 1 to 5), 4, pp. 2397-2402. ABOU AKAR A., BATTAGLIA D., LESUEUR H. (1995b) - Modelling of corrosion and scaling phenomena: transfer of the modep code under windows. Sixth six-monthly report of the JOULE II programme (contract no JOU2-CT92-0108, BRGMICCE DG XII), "Control of corrosion and scaling phenomena in geothemal systems", pp. 119-127, December 95, Thessaloniki, Greece.



ABOU AKAR A., BOENS P. (1996) - Modelling of corrosion and scaling phenomena in low enthalpy geothermal wells. In: Proceedings of EUROCORR196, Nice (France), Septembre 1996, pp. XV P2-11 XV P2-4. ABOU AKAR A., BOENS P., BATTAGLIA D., LESUEUR H. (1996) - Modelling of corrosion and scaling phenomena in low enthalpy geothermal wells. Seventh six-monthly report of the JOULE II programme (contract no JOU2-CT92-0108, BRGMICCE DG XII), "Control of corrosion and scaling phenomena in geothennal systems" , Juiy 18, 1996, Paris, France, pp. 71-126. ALLEN, CRENSHAW J.L., MERWIN H.E. (1914) - Amer. J. Sci., 38, p. 393. AMALHAY M., IGNATIADIS 1. (1993) - Laboratory studies and field tests in a geothermal environment to measure carbon steel corrosion rates using electro-chemical methods and to determine the influence of fluid composition, the presence of an inhibitor and of scale. First six- monthly report of the JOULE II programme (contract no JOU2-CT92-0108, BRGMICCE DG XII), "Control of corrosion and scaling phenomena in geothermal systems", September 93, Patras, Greece, pp. 5-58. AMALHAY M. (1994) - Contribution à l'étude des phénomènes de corrosion-dépôt et de leur inhibition dans les tubages en acier au carbone des puits géothermiques. Thèse d'université. Université de Provence Aix Marseille 1, BRGMIDRIGGP. Décembre 1994,216 p. AMALHAY M., IGNATIADIS 1. (1994a) - Laboratory studies and field tests in a geothermal environment to measure carbon steel corrosion rates using electro-chemicai methods and to determine the influence of fluid composition, the presence of an inhibitor and of scaie. Second six- monthly report of the JOULE II programme (contract no JOU2-CT92-0108, BRGMlCCE DG XII), "Control of corrosion and scaling phenomena in geothermal systems", Febmary 1994, Paris, France, pp. 7-55. AMALHAY M., IGNATIADIS 1. (1994b) - The influence of some physico-chemical parameters and exploitation conditions on corrosion and scaling in geothermal wells in the Paris basin. Second six-monthly report of the JOULE II programme (contract no JOU2-CT92-0108, BRGMICCE DG XII), "Control of corrosion and scaling phenomena in geothermal systems", Febmary 1994, Paris, France, pp. 73-85. AMALHAY M., GAUTHIER B., IGNATIADIS 1. (1994a) - The influence of some physico- chemical parameters and exploitation conditions on corrosion and scaling in geothermal wells in the Paris Basin. h: Proceediigs of the International Symposium, Geothennics 94 in Europe, from Research to Development, BRGM (ed), Orléans, France, 8-9 Febmary 1994, pp. 233-240. AMALHAY M., ABOU AKAR A., IGNATIADIS 1. (1994b) - Study of the deposition phenomena in geothermal wells in the Paris Basin. In: Proceedings of the International Symposium, Geothermics 94 in Europe, from Research to Development, BRGM (ed), Orléans, France, 8-9 Febmary 1994, pp.223-232. AMALHAY M., ABOU AKAR A., IGNATIADIS 1. (1994~) - Study of the deposition phenomena in geothermal wells in the Paris basin. Second six-monthly report of the JOULE II programme (contract no JOU2-CT92-0108, BRGMICCE DG XII), "Control of corrosion and scaling phenomena in geothermal systems", Febmary 1994, Paris, France, pp. 87-101. AMALHAY M., COTICHE C., IGNATIADIS 1. (1994d) - Study of the behaviour of a carbon steel in a real and treated geothermal environment. Third six-monthly report of the JOULE II programme (contract no JOU2-CT92-0108, BRGMICCE DG XII), "Control of corrosion and scaling phenomena in geothermal systems", July 94, Udine, Italy, pp. 7-49. AMALHAY M., JACQUIOT F., IGNATIADIS 1. (1994e) - Study of the behaviour of a carbon steel in a natural or modified and treated geothermal environment. Fourth six-monthly report of the JOULE II programme (contract no JOU2-CT92-0108, BRGMICCE DG XQ, "Control of corrosion and scaling phenomena in geothermal systems", December 94, Budapest, Hungary, pp. 31-74.



AMALHAY M., IGNATIADIS 1. (1995a) - Comparative study of the effectiveness of various organic surfactants in inhibiting carbon steel corrosion in a natural geothermal environment by using rapid electrochemical tests. Fifth six-monthly report of the JOULE II programme (contract no JOU2-CT92-0108, BRGMICCE DG XII), "Control of corrosion and scaling phenomena in geothermal systems", May 20, 1995, Pise, Italy, pp. 31-46. AMALHAY M., IGNATIADIS 1. (1995b) - Influence of iron sulfide scale on the corrosion of carbon steel in geothermal installations. Fifth six-monthly report of the JOULE II programme (contract no JOU2-CT92-0108, BRGMICCE DG XII), "Control of corrosion and scaling phenomena in geothermal systems", May 20, 1995, Pise, Italy, pp. 47-74. AMALHAY M., IGNATIADIS 1. (1995~) - Comparative study of the effectiveness of various organic surfactants in inhibiting carbon steel corrosion in a natural geothermal environment. In: Ann. Univ. Ferrara, Proceedings of the 8th European Symposium on Corrosion Inhibitors (8 SEIC) 18th-22nd September, 1995, Ferrara, Italy, no special, Sez. V, suppl. nolO, pp. 1355-1366. AMALHAY M., COTICHE C . , IGNATIADIS I.(1995a) - Study of the electrochemical behaviour of a carbon steel in a real and treated geothermal environment. In: Proceedmgs of the World Geothermal Congress, 1995, Florence, Italy, 18-31 May 1995 (International Geothermal Association, Inc., Auckland, New Zeland, 1995, Volumes 1 to 5), 4, pp. 2369-2374. AMALHAY M., ABOU AKAR A., IGNATIADIS 1. (1995b) - Overview of the deposition phenomena in geothermal wells in the Paris Basin. In: Proceedimgs of the World Geothermal Congress, 1995, Florence, Italy, 18-31 May 1995 (International Geothermal Association, Inc., Auckland, New Zeland, 1995, Volumes 1 to 5), 4, pp. 2497-2502. AMALHAY M., IGNATIADIS 1. (1996a) - Study of the behaviour of a carbon steel in a natural or modified and treated geothermal environment. In: Proceedimgs of EUROCORR'96, Nice (France), septembre 1996, pp. II P15-l1iI P15-4. AMALHAY M., IGNATIADIS 1. (1996b) - Application de la diffractométrie des rayons X à l'étude électrochiiique de la corrosion de l'acier au carbone en milieu géothermal réel et traité. Journal de physique IV, colloque C4, vol. 6, pp. 913-920. ANDRITSOS N., KARABELAS A.J. (1991) - Crystallization and deposit formation of lead sulfide from aqueous solutions 1. Deposition rates. J. Colloid Inte@ace Sci. 145, 158-169. ARFAOUI S. (1995) - Etude comparative de l'action de différents inhibiteurs de corrosion sur le comportement électroch'iique d'un acier au carbone dans un fluide géothermal reconstitué, Rapport de stage d'ingéniorat ENSEEG, 57p. BATES R. G. (1967) - pH Determination (Wiley New York), p. 479. BATTAGLIA D. (1995) - Modélisation des phénomènes de corrosion-dépôts dans les tubages des puits géothermaux. Rapport de stage d'ingénieur EEIRE, 58p. BERNER R.A. (1967) - Am. J. Science 265, p. 773. BOENS P. (1995) - Modélisation des phénomènes de corrosion-dépôts sur les parois des tubages des puits géothermiques, Rapport de stage d'ingéniorat ENSEEG, 44p. CORTON S. (1994) - Comportement des matériaux non-métalliques dans une eau géothermale contenant des additifs de limitation de son pouvoir corrosif. Rapport de stage d'ingéniorat (2ème année) de 1'Ecole Supérieure d'Energie et des Matériaux (ESEM), soutenu le 15 décembre 1994. BRGMIDRIGGP. Septembre 1994, 52 p. COTARTA I.V. (1994) - Anode dissolution of Iron in Geothermal water with Cl- and H S Contents, in the fouah JOU2-CT92-0108 periodic report, p.197; COTARTA V. (1994) - in the 4th periodic report, p.197; COTICHE C. (1994) - Etude du comportement électrochimique d'un acier au carbone dans un fluide géothermal réel et traité. Rapport de stage d'ingéniorat (3ème année) de 1'Ecole Nationale Supérieure de Chimie de Toulouse, soutenu le 22 juin 1994. BRGMIDRIGGP. Juin 1994, 50 p.



DUPIN P., VILOVIA-VERA D. A., DE SAVIGNAC LATTES A., HAICOUR P. (1980) - Proc. 5th European Corrosion Inhibitors (Ferrara, 1980), p. 301. DYKHNO L.A, WILLIAMS L.R., HANRATTY T.J. (1994) - Maps of mean gas velocity for stratified flows with and without atomization. Int. J. Multiphme Flow 20, 4, 691-702. FLORES A.G., CROWE K.E., GRIFFITH P. (1995) - Gas-phase secondary flow in horizontal, stratified and annular two-phase flow. Int. J. Multiphase Flow 21, 2, 207-221. FRANSON M.A.H. (Ed.) (1981) - Standard Methods for the Examination of Water and Wastewater 15th edition (American Public Health Organization, Washington DC), p. 447. GAUTHIER B., IGNATIADIS 1. (1994) - Relation between MglCa ratio and sulfide concentration in geothermal fluids at wellheads in the Paris basin. Use of their variation versus time and flowrate to distinct cunent from ancient bacterial activity in the wells-reservoir system. In: Proceediigs of the International Symposium, Geothennics 94 in Europe, from Research to Development, BRGM (ed), Orléans, France, 8-9 Febniary 1994, pp. 249-256. GAYRAL L., MASBERNAT L., SUZANNE C. (1979) - Mean velocities and Reynolds stresses in CO-curent gas-liquid stratified charnel flow. Two-phase Mornenturn, Heat and Mass transfer in Chernical, Process and Energy Engineering System. Durst, Tsiklauri & Afgan 2, 921-931. GOLDHABER, STANTON M.R. (1987) - Geol. Soc. Amer. Abstr. Prog. 19, p. 678. GROWCOCK F.B. (1989) - Corrosion, 45, 1003. GROWCOCK F.B., FREINER W.W., ANDREOZZI A. (1989) - Corrosion, 45, 1007. HAARBERG T. (1989) - Mimera1 Deposition During Oil Recovery.An Equilibrium Mode1 PhD Thesis. University of Trondheim, Norway, 1989. HARMANDAS N.G., IGNATIADIS I., KOUTSOUKOS P.G. (1996) - Comparative study of the effectiveness of various organic surfactants in inhibiting iron sulfide precipitation in a natural geothemal environment. Seventh six-monthly report of the JOULE il programme (contract no JOU2-CT92-0108, BRGMICCE DG XII), "Control of corrosion and scaling phenomena in geothemal systems" , July 18, 1996, Paris, France, pp.53-62. HARVIE E.C., MOELLER N., WEARE J.H. (1984) - The Prediction of Mineral Solubilities in Natural Waters: The Na-K-Mg-Ca-H-Cl-SO~-OH-HCO3-CO3-CO2-H20 System to High IONC Strengths at 25 OC , Geochiiica and Cosmochimica Acta, Vol. 86, pp 723-751. IGNATIADIS 1. (1993a) - Experimental concentration versus time curves for the iron (II) sulphide precipiiation reaction in partly reconstituted geothermal fluids in the presence and absence of surfactant additive and their interpretation. First six-monthly report of the JOULE II programme (contract no JOU2-CT92-0108, BRGMICCE DG XII), "Control of corrosion and scaling phenomena in geothermal systems", September 93, Patras, Greece, pp. 59-106. IGNATIADIS 1. (1993b) - Estimation of the solubility product of the iron sulphide controlling the solubility of iron and sulphides dissolved in geothermal fluids from production weliheads in the Paris Basin. Fust six-monthly report of the JOULE II programme (contract no JOU2-CT92-0108, BRGMICCE DG XII), "Control of corrosion and scaling phenomena in geothermal systems", September 93, Patras, Greece, pp. 107-124. IGNATIADIS 1. (1994) - Origins of the increased dissolved sulphide concentrations noted in geothemal fluids at production wellheads in the south and east of the Paris basin. In: Proceediigs of the International Symposium, Geothemics 94 in Europe, from Research to Development, BRGM (ed), Orléans, France, 8-9 Febmary 1994, pp. 241-248. IGNATIADIS I., ABOU AKAR A., AMALHAY M., BRAY Ph., LESUEUR H., LONGIN G. (1994a) - Recommandations relatives au suivi de l'efficacité des traitements pai inhibiteur de corrosion en géothermie basse énergie. Convention Ademe-BRGM 3 07 0001. Rap. BRGM R 38123, 89 p, 9 fig., 13 tabl., 3 am. IGNATIADIS I., ABOU AKAR A., AMALHAY M. (1994b) - Methods for monitoring corrosion and the efficiency of treatment by corrosion inhibitor on the geothemal projects of the Paris basin.


Control of corrosion and scaling in geothermal sysrems

Second six-monthly report of the JOULE II programme (contract no JOU2-CT92-0108, BRGMICCE DG XII), "Control of corrosion and scaling phenomena in geothermal systems", Febmary 1994, Paris, France, pp. 57-72. IGNATIADIS I., ABOU AKAR A., AMALHAY M. (1994~) - Methods for monitoring corrosion and the efficiency of treatment by corrosion inhibitor on the geothermal projects of the Paris basin. In: Proceedings of the International Symposium, Geothermics 94 in Europe, from Research to Development, BRGM (ed), Orléans, France, 8-9 Febmary 1994, pp. 257-266. IGNATIADIS I., ABOU AKAR A., AMALHAY M. (1994d) - Monitoring of corrosion and the efficiency of treatment by corrosion inhibitor on the geothermal projects of the Paris Bassin. In: Proceediigs du 2ème Colloque Européen "Corrosion dans les Usines Chimiques et Parachiiiques, Grenoble 21-22 Septembre 1994, CEFRACOR (ed), Paris, France, Section C2 P15-1 - P15-8. IGNATIADIS I., PEYROT N. (1994) - Estimation of the solubility product of the iron sulphide controlliig Fez+ and S2- solubilities in geothermal waters. Poster presentation in the 8th European Union of Geosciences, 9-13 April 1995, Strasbourg, France, 9-30 April 1995. In: Proceediigs of EUG8, Terra abstracts, Abstract supplement Nol , to Terra nova, Vol. 7, 1995, p. 322. IGNATIADIS I., AMALHAY M. (1995) - Comparative study of the effectiveness of various organic surfactants in inhibiting carbon steel corrosion in a partial reconstituted geothermal environment. Sixth six-monthly report of the JOULE II programme (contract no JOU2-CT92-0108, BRGMICCE DG XII), "Control of corrosion and scaling phenomena in geothermal systems", December 15, 1995, Thessaloniki, Greece, pp. 47-86. IGNATIADIS I., AMALHAY M., COTICHE C. (1995) - Comparative study (long-term) of the carbon steel corrosion rate in untreated and treated geothermal fluids using coupons. Sixth six- monthly report of the JOULE II programme (contract no JOU2-CT92-0108, BRGMICCE DG XII), "Control of corrosion and scaliig phenomena in geothermal systems", December 15, 1995, Thessaloniki, Greece, pp. 33-46. IGNATIADIS I., ABOU AKAR A., COTICHE C. (1996) - Analysis and consequences of bacterial proliferation in casings and resewoirs of geothermal doublets of the Paris basin. In: Proceedings of EUROCORR'96, Nice (France), Septembre 1996, pp. V P l - IN Pl-4. IGNATIADIS I., AMALHAY M. (1996a) - The effect of iron sulfide deposits on corrosion of carbon steel in a natural and treated geothennal water using electrochemical techniques and X-ray diffractometry. In: Proceediigs of EUROCORR'96, Nice (France), Septembre 1996, pp. II P21- 1/11 P21-4. IGNATIADIS I., AMALHAY M. (19960) - Identification of the role of iron sulfide deposits on corrosion of carbon steel in untreated and treated geothermal environment thought electrochemical techniques and X-ray diffractometry. In: Proceediigs of the 47th Annual Meeting of the International Society of Electrochemistry, September 1-6, 1996, Veszprém and Balatonfüred (Hungary), pp. P6a-10. IGNATIADIS I., AMALHAY M., ABOU AKAR A., COTICHE C. (1997) - Analyse et conséquences de la prolifération bactérienne sur les tubages et dans le réservoir @roche ou lointain) des doublets géothermiques du bassin de Paris. Ecole thématique CNRS "Biodétérioration des matériaux". Saint Avit devialard, 30 septembre - 6 octobre 1995. Editions de la Physique, Les Ulis. Biodétériotation des matériaux. L'article de 26 pages sera publié en 1997 dans le livre de l'école thématique. KALMAN E., VARHEGYI B., BAKO I., FELHOSI 1. KARMAN F.H, SHABAN A. J. (1994) - Electrochemical Society, Vol. 141, p. 3357. KARABASH A. G. (1953) - Zhur. Anal. Khim. 8, p. 140. KLEPETSANIS P.G., IGNATIADIS 1. (1996) - Comparative study of the effectiveness of various organic additives in inhibiting carbon steel corrosion in a natural geothermal environment by using rapid electrochemical tests. Seventh six-monthly report of the JOULE II programme (contract no



JOU2-CT92-0108, BRGMICCE DG XII), "Control of corrosion and scaliig phenomena in geothermal systems", July 18, 1996, Paris, France, pp.33-51. KOROLEV, S.V. KOZERENKO (1965) - Proc. Acad. Sci. USSR, 165, p. 194. KOCSIS 3. (1976) - Dissertation, TU of Budapest, Budapest. JELLINEK A. (1968) - In: Inorganic Sulfur Chemistry (G.Nickless ed) Elsevier, Amsterdam, p.715 LESUEUR H. (1994) - Behaviour of non metallic materials in geothermal fluids containing corrosion limiting additives. Fourth six-monthly report of the JOULE ii programme (contract no JOU2-CT92-0108, BRGMICCE DG XII), "Control of corrosion and scaling phenomena in geothermal systems", December 94, Budapest, Hungary, pp. 91-1 18. LESUEUR H., ABOU AKAR A., IGNATIADIS I., FOUCHER J.C. (1996) - Irnprovement of the prinpimo down-hole fluid sampler. Seventh six-monthly report of the JOULE II programme (contract no JOU2-CT92-0108, BRGMICCE DG XII), "Control of corrosion and scaling phenomena in geothermal systems", July 18, 1996, Paris, France, pp.63-70. LIU S.T., NANCOLLAS G.H. (1973) - J.Colloid and Interface Science, Vo1.44, p. 422. LUKOVITS I., KALMAN E., PALINKAS G. (1995) - Corrosion. Vo1.51, No.3, 201. MANSFELD F., SHM H., GREENE H., TSAI C.H. (1993) - "Analysis of EIS Data for Comrnon Corrosion Processes", Electrochemical Impedance: Analysis and Interpretation, ASTM STP 1188, J.R. Scully, D.C. Silverman, M.W. Kendig, Eds., American Society for Testing and Materials, Phiiadelphia, 33. MORSE J.W., ARAKAKI T. (1993) - Geoch. Cosmoch. Acta 57, p. 3635. MORSE J.W., MILLER0 F.J., CORNWELL J.C., RICKARD D. (1987) - Earth Science Reviews 24, 1. MULLIN J.W. (1993 ) -Crystallization. Buttenvorth-Heinemann, 2nd ed., Oxford. NATHAN C.C. (1973) - "Corrosion Inhibitors", ed. NACE, p. 20. PAPAVERGOS P.G., HEDLEY A.B. (1984) - Particle deposition behaviour from turbulent flows. Chern. Eng. Res. Dev. 62, 275-295. PAPELIS C., HAYES K.F., LECKIE J.O. (1988) - Tech. Report No 306, Stanford Univ., p.130. PETRESCU B., COTARTA V. (1996) - Design of a computer asisted system for corrossion tests, seventh report. PEYROT N. (1993) - Contribution à l'étude de la cinétique de formation des sulfures de fer en solutions géothennales reconstituées. Rapport de stage de DEA de Cinétique Chimique Appliquée, Université d'Orléans-BRGM, 28 juin 1993,48 p. PEYROT N., IGNATIADIS I., AMALHAY M. ABOU AKAR A. (1995) - Experimental concentration versus t h e curves for the iron (ii) sulphide precipitation reaction in partly reconstituted geothermal waters and their interpretation. Poster presentation in the 8th European Union of Geosciences, 9-13 April 1995, Strasbourg, France, 9-30 April 1995. In: Proceediigs of EUG8, Terra abstracts, Abstract supplement Nol , to Terra nova, Vol. 7, 1995, p.72. PLUMMER L.N., BUSENBERG E. (1982) - The Solubilities of Calcite and Vaterite in H20-CO2 Solutions Between O and 90 "C and an Evaluation of the Aqueous Mode1 for the System CaC03- H20-C02, Geochimica and Cosmochimica Acta, Vol. 46, pp 101 1-1040. POURBAIX M., POURBAIX A. (1990, 1992) - Potential-pH diagrams for the system S-H20, from 25 to 150 OC. Influence of access of oxygen in sulfide solutions, Rapports Techniques CEBELCOR, vol. 159, RT.299 (1990). Also in: Geochiiica and Cosmochimica Acta, vol 56, p. 3157-3178 (1992). POWER H.A. (1976) - Fine, Minerals Sci. Eng. 8, p. 106. RICKARD D. (1989) - Experimental concentration-time curves for the iron (II) sulfide precipitation process in aqueous solutions and their interpretation. Chem. Geol. 78, 315-324. SARDISCO J.B., PITTS R.E. (1965) - Corrosion, Vol. 21, p. 245. SARDISCO J.B., PITTS R.E. (1965) - Corrosion, Vol. 21, p. 350.

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SCHOONEN M.A.A., BARNES H.L. (1991) - Geoch. Cosmoch. Acta 55, p. 1495. SCHOONEN M.A.A., BARNES H. L. (1991) - Geoch. Cosmoch. Acta 55, p. 1505. SHOCK E.L. (1988) - Persona1 communication, 16.7.88. SHOCK E.L., HELGESON H.C. (1988) - Calculation of the Thennodynamic and Transport Properties of Aqueous Species at High Pressures and Temperatures. Correlation Algorithms for Ionic Species and Equation of State Predictions to 5 KB and 1000 OC. Geochiica and Cosmochirnica Acta, vol. 52, p. 2009-2036. SHOESMITH D.W., TAYLOR P., BAILEY M.G., OWEN D.G. (1980) - J. Electrochemical Society, Vol. 127, p. 1007. SINGH A.K., POURBAIX A. (1996a) - E-pH diagrams for the Fe-S-Hz0 system", to be published. SINGH A.K., POURBAIX A. (1996b) - Corrosion of carbon steel in the presence of sulfides and chlorides. Report on experiments conducted. Draft to be submitted for publication at a later date. Intemal Cebelcor report (1996). SMITH R.M., MARTELL A.E. (1976) - Critical Stability Constants V.4-Inorganic Complexes (Plenum Press New York - London), p. 257. SWEENEY R.E., KAPLAN I.R. (1973) - Econ.Geo1. 68, p. 618. TAYLOR, RUMMERY T.E., OWEN D.C. (1979) - J. Inorg. Nucl. Chem. 41, p. 595. WARD C. (1970) - Rev. Pure Appl. Chem. 20, p. 175. WEIJNEN M.P.C, VAN ROSMALEN G.M. (1984) - Industrial Crystallization 84, edited by S.J.Jancic and E.J.de Jong, Elsevier Science Publishers B.V., Amsterdam.



6. List of publications related to the project (1993-1996)

BRGM ABOU AKAR A., BOENS P. (1996) - Modelling of corrosion and scaling phenomena in low enthalpy geothermal wells. In: Proceedings of EUROCORR'96, Nice (France), septembre 1996, pp. XV P2-11 XV P2-4. ABOU AKAR A., BOENS P. (1995) - Modélisation des phénomènes de corrosion-dépôts sur les parois des tubages en acier des exploitations géothermales. 1. Proposition d'un modèle de simulation des phénomènes de corrosion-dépôts. Rap. BRGM R 38612 GGP DR 95, 5@. ABOU AKAR A., IGNATIADIS I., LESUEUR H. (1995). Methods for detecting perforations in casings of wells exploiting geothermal fluids. In: Proceediigs of the World Geothermal Congress, 1995, Florence, Italy, 18-31 May 1995 (International Geothermal Association, Inc., Auckland, New Zeland, 1995, Volumes 1 to 5), 4, pp. 2397-2402. ABOU AKAR A., IGNATIADIS 1. (1995) - Modelling of the deposition phenomena in geothermal wells in the Paris basin. In: Proceediigs of the World Geothermal Congress, 1995, Florence, Italy, 18-31 May 1995 (International Geothermal Association, Inc., Auckland, New Zeland, 1995, Volumes 1 to 5), 4, pp. 2491-2496. ABOU AKAR A., IGNATIADIS I., LESUEUR H., LONGIN G. (1994) - Risque de pollution des nappes d'eau douce du fait des exploitations géothermales de l'aquifère du Dogger du Bassin parisien. 4. Méthodologie de détection des percements intervenus sur le tubage d'un puits géothermique. Convention Ademe-BRGM 2 07 0028. Rap. BRGM R 38035,47 p., 10 tabl., 2 ann. ABOU AKAR A., IGNATIADIS 1. (1994)- A new mode1 for iron sulfide deposition in geothermal wells. In: Proceedings of the International Symposium, Geothermics 94 in Europe, from Research to Development, BRGM (ed), Orléans, France, 8-9 February 1994, pp. 215- 222 ABOU AKAR A., LAFFORGUE M. (1994). Etude de la corrosion par coupons en acier au carbone placés en zones monophasique et diphasique sur la centrale géothermique de Chelles (Seine-et- Marne). Rap. BRGM R 37832 GGP-DR-94,91p. AMALHAY M., IGNATIADIS 1. (1996) - Application de la difîractométrie des rayons X à l'étude électrochimique de la corrosion de l'acier au carbone en milieu géothermal réel et traité. Journal de physique IV, colloque C4, vol. 6, pp. 913-920. AMALHAY M., IGNATIADIS 1. (1996) - Study of the behaviour of a carbon steel in a natural or modified and treated geothermal environment. In: Proceedings of EUROCORR196, Nice (France), septembre 1996, pp. II P15-ILI P15-4. AMALHAY M., IGNATIADIS 1. (1995) - Comparative study of the effectiveness of various organic surfactants in inhibiting carbon steel corrosion in a natural geothermal environment. In: Ann. Univ. Ferrara, Proceediigs of the 8th European Symposium on Corrosion Inhibitors (8 SEIC) 18th-22nd September, 1995, Ferrara, Italy, no special, Sez. V, suppl. nOIO, pp. 1355-1366. AMALHAY M., COTICHE C., IGNATIADIS 1.(1995) - Study of the electrochemical behaviour of a carbon steel in a real and treated geothermal environment. In: Proceedings of the World Geothermal Congress, 1995, Florence, Italy, 18-31 May 1995 (International Geothermal Association, Inc., Auckland, New Zeland, 1995, Volumes 1 to 5), 4, pp. 2369-2374. AMALHAY M., ABOU AKAR A., IGNATIADIS 1. (1995) - Overview of the deposition phenomena in geothermal wells in the Paris Basin. In: Proceediigs of the World Geothermal Congress, 1995, Florence, Italy, 18-31 May 1995 (International Geothermal Association, Inc., Auckland, New Zeland, 1995, Volumes 1 to 5), 4, pp. 2497-2502. AMALHAY M. (1994) - Contribution à l'étude des phénomènes de corrosion-dépôt et de leur inhibition dans les tubages en acier au carbone des puits géothermiques. Thèse d'université. Université de Provence Aix Marseille 1, BRGMIDRIGGP. Décembre 1994, 216 p.



AMALHAY M., GAUTHIER B., IGNATIADIS 1. (1994a) - The influence of some physico- chemical parameters and exploitation conditions on corrosion and scaliig in geothermal wells in the Paris Basin. In: Proceedings of the International Symposium, Geothermics 94 in Europe, from Research to Development, BRGM (ed), Orléans, France, 8-9 Febmary 1994, pp. 233-240. AMALHAY M., ABOU AKAR A., IGNATIADIS 1. (1994b) - Study of the deposition phenomena in geothermal wells in the Paris Basin. In: Proceediigs of the International Symposium, Geothermics 94 in Europe, from Research to Development, BRGM (ed), Orléans, France, 8-9 Febmary 1994, pp.223-232. AMALHAY M., IGNATIADIS 1. (1993) - Etude du comportement de l'acier au carbone API K55 dans le fluide géothennal dégazé. Rapport BRGM n0R37868 IRG SGN 93, 39 p. AMALHAY M., IGNATIADIS 1. (1993) - The effects of some physico-chernical characteristics and exploitation conditions on corrosion and scaling in geothermal wells in the Paris bassin. PEH 93, (Physique en Herbe), Paris, France, 6-12 Juin 1993. Proceediigs, pp. 45-47. ARFAOUI S. (1995) - Etude comparative de l'action de différents inhibiteurs de corrosion sur le comportement électrochiiique d'un acier au carbone dans un fluide géothermal reconstitué, Rapport de stage d'ingéniorat ENSEEG, 57p. BATTAGLIA D. (1995) - Modélisation des phénomènes de corrosion-dépôts dans les tubages des puits géothermaux. Rapport de stage d'ingénieur EEIRE, 58p. BOENS P. (1995) - Modélisation des phénomènes de corrosion-dépôts sur les parois des tubages des puits géothermiques, Rapport de stage d'ingéniorat ENSEEG, 44p. BRAY P., LESUEUR H., IGNATIADIS I., BOISDET A. (1993) - Instrumentation et télégestion du réservoir géothermique du Dogger du bassin de Paris. Rapport BRGM n0R37868 IRG SCiN 93, 66 p, 4 Volumes. CORTON S. (1994) - Comportement des matériaux non-métalliques dans une eau géothemale contenant des additifs de limitation de son pouvoir corrosif. Rapport de stage d'ingéniorat (2ème année) de 1'Ecole Supérieure dlEnergie et des Matériaux (ESEM), soutenu le 15 décembre 1994. BRGMIDRIGGP. Septembre 1994, 52 p. COTICHE C. (1994) - Etude du comportement électrochimique d'un acier au carbone dans un fluide géothermal réel et traité. Rapport de stage d'ingéniorat (3ème année) de 1'Ecole Nationale Supérieure de Chimie de Toulouse (ENSCT), soutenu le 22 juin 1994. BRGMIDRIGGP. Juin 1994, 50 p. DETOC-KARIMI S., IGNATIADIS 1. (1994) - Sélection et optimisation des méthodes d'analyse des espèces du soufre produites lors de l'oxydation du sulfure d'hydrogène des fluides géothermaux. In: Proceediigs of the First International Research Symposium on "Water treatment by-products". Communication orale N028-1, Poitiers, France, 29-30 Septembre 1994. DETOC-KARIMI S., IGNATIADIS 1. (1994) - Kinetics of oxidation of hydrogen sulfide by hydrogen peroxide in actual geothermal fluids. In: Proceedings of the First International Research Symposium on "Water treatment by-products". Communication orale No28-2, Poitiers, France, 29- 30 Septembre 1994. DEZAIACOMO 0. (1994) - Produits de corrosion en milieu géothermal réel : nature, formation, croissance et influence sur la corrosion de l'acier au carbone. Rapport de stage de fin de Maîtrise de C h i e (Université d'Orléans) soutenu le 29 juin 1994. BRGMIDRIGGP. Juin 1994, 52 p. DRIEUX J.J., ROQUE C., IGNATIADIS I., JULIEN E., GIROU A. (1996) - Proposition d'une sonde de contrôle des phénomènes de dépôt-corrosion. Pilotage de l'injection d'un inhibiteur dans un puits géothermique. In: Proceedings du colloque "Journées Information Eaux (JIE-96), Poitiers, Septembre 1996 (France) pp. P18-11P18-4. DRIEUX J.J., JULIEN E., GIROU A., IGNATIADIS I., ROQUE C. (1996) - Electrochemical device for the prevention of corrosion-scaliig phenomena in geothermal installations. In: Proceedings of EUROCORR196, Nice (France), septembre 1996, pp. II OR15-ID1 OR15-4.



GAUTHIER B., IGNATIADIS 1. (1994) - Relation between MglCa ratio and sulfide concentration in geothermal fluids at wellheads in the Paris basin. Use of their variation versus time and flowrate to distinct current from ancient bacterial activity in the wells-resewoir system. In: Proceedings of the International Symposium, Geothermics 94 in Europe, from Research to Development, BRGM (ed), Orléans, France, 8-9 Febmary 1994, pp. 249-256. IGNATIADIS I., AMALHAY M., ABOU AKAR A., COTICHE C. (1997) - Analyse et conséquences de la prolifération bactérienne sur les tubages et dans le réservoir (proche ou lointain) des doublets géothermiques du bassin de Paris. Ecole thématique CNRS "Biodétérioration des matériaux". Saint Avit devialard, 30 septembre - 6 octobre 1995. Editions de la Physique, Les Ulis. Biodétériotation des matériaux. L'article de 26 pages sera publié en 1997 dans le livre de l'école thématique. IGNATIADIS I., AMALHAY M. (1996) - Identification of the role of iron sulfide deposits on corrosion of carbon steel in untreated and treated geothermal environment thought electrochemical techniques and X-ray diffractometry. In: Proceediigs of the 47th Annual Meeting of the International Society of Electrochemistry, September 1-6, 1996, Veszprém and Balatonfüred (Hungary), pp. P6a-10. IGNATIADIS I., ABOU AKAR A., COTICHE C. (1996) - Analysis and consequences of bacterial proliferation in casings and reservoirs of geothermal doublets of the Paris basin. In: Proceedings of EUROCORR'96, Nice (France), Septembre 1996, pp. V P l - I N Pl-4. IGNATIADIS I., AMALHAY M. (1996) - The effect of iron sulfide deposits on corrosion of carbon steel in a natural and treated geothermal water using electrochemical techniques and X-ray diffractometry. In: Proceedings of EUROCORR'96, Nice (France), Septembre 1996, pp. II P21- 1/11 P21-4. IGNATIADIS I., CHERADAME J.M., DAUMAS S. (1996) - Comparative tests to determine the effectiveness of various bactericides on sulfate reducing bacteria in geothermal fluids. In: Proceedings of EUROCORR'96, Nice (France), Septembre 1996, pp. V OR8-1N ORS-4. IGNATIADIS 1. (1994) - Origins of the increased dissolved sulfide concentrations noted in geothermal fluids at production wellheads in the south and east of the Paris basin. In: Proceediigs of the International Symposium, Geothermics 94 in Europe, from Research to Development, BRGM (ed), Orléans, France, 8-9 Febmary 1994, pp. 241-248. IGNATIADIS 1. (1994) - Problèmes de matériaux dans l'exploitation de la ressource géothermique du bassin parisien : historique, études et perspectives. In: Proceedings of the European Technology Forum (Les entretiens de la Technologie). Communication orale, Atelier Matériaux-Energie. Palais de Congrès, Paris, France, 15-16 Mars 1994. IGNATIADIS I., LE DINH BA0 B. (1994) - Laboratory studies and field tests in a geothermal environment for the determination of anti-corrosion properties of silica füms deposited on carbon steel. In: Proceedimgs of the International Symposium, Geothermics 94 in Europe, from Research to Development, BRGM (ed), Orléans, France, 8-9 Febmary 1994, pp. 189-198. IGNATIADIS I., ABOU AKAR A., AMALHAY M., BRAY Ph., LESUEUR H., LONGIN G. (1994a) - Recommandations relatives au suivi de l'efficacité des traitements par inhibiteur de corrosion en géothermie basse énergie. Convention Ademe-BRGM 3 07 0001. Rap. BRGM R 38123, 89 p, 9 fig., 13 tabl., 3 ann. IGNATIADIS I., ABOU AKAR A., AMALHAY M. (1994b) - Methods for monitoring corrosion and the eficiency of treatment by corrosion inhibitor on the geothermal projects of the Paris basin. In: Proceedimgs of the International Symposium, Geothedcs 94 in Europe, from Research to Development, BRGM (ed), Orléans, France, 8-9 Febmary 1994, pp. 257-266. IGNATIADIS I., ABOU AKAR A., AMALHAY M. (1994~) - Monitoring of corrosion and the efficiency of treatment by corrosion inhibitor on the geothermal projects of the Paris Bassin. In:

EEC-DG XII-Joule Programme-contract Nos JOU2-CT92-0708 and CIPD-CT93-03 74 - final report 57

Control of corrosion and scalingin geothermal systems

Proceedings du 2ème Colloque Européen "Corrosion dans les Usines Chimiques et Parachiimiques, Grenoble 21-22 Septembre 1994, CEFRACOR (ed), Paris, France, Section C2 P15-1 - P15-8. IGNATIADIS I., PEYROT N. (1994) - Estimation of the solubility product of the iron sulfide controlling Fe2+ and ~ 2 - solubilities in geothermal waters. Poster presentation in the 8th European Union of Geosciences, 9-13 April 1995, Strasbourg, France, 9-30 April 1995. In: Proceedigs of EUG8, Terra abstracts, Abstract supplement Nol , to Terra nova, Vol. 7, 1995, p. 322. IGNATIADIS I., AMALHAY M., CHERADAME J.M. (1993) - Etude des dégradations des para- mètres hydrodynamiques des puits de Coulommiers, phase Ji. Note technique no 93CFG378, 35p. JACQUIOT F. (1994) - Etude du comportement électrochimique d'un acier au carbone dans un fluide géothermal réel ou modifié et traité. Rapport de stage d'ingéniorat (Teme année) de 1'Ecole Nationale Supérieure d'Electrochimie et d'Electrométallurgie de Grenoble (ENSEEG), soutenu le 21 décembre 1994. BRGMIDRIGGP. Juin 1994,66 p. PEYROT N., IGNATIADIS I., AMALHAY M. ABOU AKAR A. (1995) - Experimental concentration versus time curves for the iron (ii) sulfide precipitation reaction in partly reconstituted geothermal waters and their interpretation. Poster presentation in the 8th European Union of Geosciences, 9-13 April 1995, Strasbourg, France, 9-30 April 1995. In: Proceedigs of EUG8, Terra abstracts, Abstract supplement Nol, to Terra nova, Vol. 7, 1995, p.72. PEYROT N. (1993) - Contribution à i'étude de la cinétique de formation des sulfures de fer en solutions géothermales reconstituées. Rapport de stage de DEA de Cinétique Chimique Appliquée, Université d'Orléans-BRGM, 28 juin 1993, 48 p.

CEBELCOR SINGH A.K., POURBAIX A. (1996a) - E-pH diagrams for the Fe-S-Hz0 system", to be published. SINGH A.K., POURBAIX A. (1996b) - Corrosion of carbon steel in the presence of sulfides and chlorides. Report on experiments conducted. Draft to be submitted for publication at a later date. Interna1 Cebelcor report (1996). AMALHAY M., POURBAIX A. (1997) - Contribution à l'étude de la corrosion localisée du fer et de l'acier à 13% Cr en milieu H2S. Rapports Techniques de Cebelcor. AMALHAY M., POURBAE A. (1997) - Contribution to the study of localized corrosion of iron and 13%Cr stainless steel in H2S environment. To be submitted to Corrosion Science.

CPERI ANDRITSOS N., KARABELAS A.J. (1995) - An experimental study of sulfide scale formation in pipes. In: Proceedings of the WORLD GEOTHERMAL CONGRESS 1995, ed. E. Barbier et. al., Florence, Italy, 18-31 May, 1995. pp. 2469-2474. KOSTOGLOU M., KARABELAS A.J. (1994) - Evaluation of zero order methods for simulating particle coagulation. J. Colloid Inte@ace Sei. 163, pp. 420-431. KOSTOGLOU M., ANDRITSOS N., KARABELAS A.J. (1995) - Flow of supersaturated solutions in pipes. Modelig bulk precipitation and scale formation. Chem. Engng Comm. 133, 107-131. PARAS S.V., KARABELAS A.J. (1992) - Measurements of local velocities inside thin liquid films in horizontal two-phase flow. Experiments in Fluidr 13, 190-198. PARAS S.V., VLACHOS N.A., KARABELAS A.J. (1994) - Liquid layer characteristics in stratified-atomization flow. Int. J. Multiphase Flow 20, 5, 939-956. PARAS S.V., VLACHOS N.A., KARABELAS A.J. (1996) - LDA measurements of local velocities in horizontal Stratifiedlatomization Two-phase Flow. In: Proceedigs of the International Congress of Chemical & Process Engineering, Praha, Chech Republic, August 25-39, 1996. VLACHOS N.A., PARAS S.V., KARABELAS A.J. (1994) - Liquid-to-Wall Shear Stress Distribution in Stratifiedlatomization Flow. Accepted for publication Int. J. Multiphme Flow, 1996.

58 EEC-DG Xll-Joule Programme-contract Nos JOU2-CT92-0108 and CIPD-CT93-0314 - final report

Control o f corrosion and scaling in geotherrnal systems

CPR ANDREUSSI P., MINERVINI A., PAGLIANTI A., SABATELLI F. (1994) - Two-Phase Flow of Brine in Long Pipelines: Analysis of Field Experiments. Geothermics, 23, p. 33-41, JOUG-0005-C. ANDREUSSI P., PAGLIANTI A., PASQUALETTI A.(1995) - Design of an Absorption Column for Steam Washing, Proc. World Geothermal Congress, Firenze. MARINI L., GUIDI M., ANDREUSSI P., CORSI R. (1994) - The Computation of Dew Point and Liquid Composition of Geothermal Steam", Geothermics, 23, p. 233-255, JOUG-0005-C. NARDINI G., PAGLIANTI A., VIVIANI E. (1993) - Abatement of Hydrogen Chloride in Structured Packiigs. In Proc. Geothermal Resources Council, S. Francisco, p. 387-393, JOUG- 0005-C. NARDINI G., PAGLIANTI A., TRAVERSARI F., MONDELLO B. (1994) - An Analysis on the Efficiency of Vane Type Demisters. In Geothermal Resources Council, Salt Lake, p. 543-548, JOUG-0005-C. PAGLIANTI A., VIVIANI E., BRUNAZZI E., SABATELLI F. (1996) - A Simple Method to Compute Hydrogen Chloride Abatement in Geothermal Power Plants", Geothermics, 25, p. 37-62. SOLDATI A., ANDREUSSI P. (1995) - On the Development of a Mechanistic Mode1 for Vertical Amular Two Phase Flow, Proc. Second Italian Conference on Chernical and process Engineering, Florence, May 15-17. SOLDATI A., ANDREUSSI P. (1996) - The Influence of Coalescence on Droplet Transfer in Vertical Annular Flow, Chem. Engng. Sci., 51, p. 353-363. VIVIANI E., PAGLIANTI A., SABATELLI F., TARQUIN1 B. (1995) - Abatement of Hydrogen Chloride in Geothermal Power Plants", In Proc. World Geothermal Congress Firenze, p. 2421- 2426.

ICEIHTCP Andritsos N., Kontopoulou M., Karabelas A.J., Koutsoukos P.G. (1997) - Calcium carbonate deposit formation under isothermal conditions. Can J. Chem. Eng. In Press. Harmandas N., Koutsoukos P.G. (1997) - The formation of iron (ii) sulfides in aqueous solutions. J.Crysta1 Growth, In Press. Klepetsanis P.G., Lampeas N., Kioupis N., Koutsoukos P.G. (1995) - The effect of mineral deposits on stainless steel. In: Minera1 Scale Formation and Inhibition, Ed. Z. Amjad, Plenum Press, New York, 1995, pp. 131-144. Klepetsanis P.G., Drakia P., Koutsoukos P.G. (1995) - The calcite-hydroxyapatite system. Crystal growth studies in aqueous solutions. In: Minera1 Scale Formation and Inhibition, Ed. Z. Amjad, Plenum Press, New York, 1995, pp. 251-260. Kobotiatis L., Tsikrikas Ch., Koutsoukos P.G. (1995) - Investigation of the corrosion of Al-7075 in NaCl. Effect of the oxalate anions. Corrosion, vol. 51, pp. 19-29. Kobotiatis L., Kioupis N., Koutsoukos P.G. (1997) - The electronic properties of the passive films grown on AA7075 in solutions containing oxalate and chromate. Corrosion, In Press. Lampeas N., Koutsoukos P.G. (1994) - The importance of the solution pH in the corrosion of aluminium in aqueous chloride media. Corrosion Science, vol. 36, pp. 1011-1025. Malollari 1. Xh., Klepetsanis P.G., Koutsoukos P.G. (1995) - Precipitation of strontium sulfate in aqueous solutions at 25°C. J. Cystal growth, vol. 155, pp. 240-246. Sabbides Th.G., Koutsoukos P.G. (1993) - The crystallization of calcium carbonate in artificial seawater; role of the substrate, Journal of Crystal Growth, vol. 133, pp. 13-22. Sabbides Th.G., Koutsoukos P.G. (1995) - The dissolution of calcium carbonate in the presence of magnesium and inorganic orthophosphate. In: Minera1 Scale Formation and Inhibition, Ed. Z. Amjad, Plenum press, New York, 1995, pp. 73-86.


Control o f corrosion and scaling in geothermal systerns

Sabbides Th.G., Koutsoukos P.G. (1996) - The effect of surface pretreatrnent with inorganic orthophosphate in the dissolution of calcium carbonate. J. Cqstal Growth, vol. 165, pp. 268-272. Symeopoulos B.D., Koutsoukos P.G. (1993) - Radioanalytical monitoring of the formation of barium sulfate in aqueous solution. J.Radioanalytical and Nuclear Chemistry, vol. 173, pp. 23-26. Symeopoulos B.D., Koutsoukos P.G. (1993) - The use of radioanalytical methods in nucleation and crystal growth studies: the barium sulfate system. Appl. Radiat. Isot., vol. 44, pp. 894-896.

BBPDICM Chitanu G.C., Anghelescu-Dogam A.G, Carpov A. (1994) - Chemical reactions on maleic Anhydride Copolymers. Semiamidation. IXfi Session of Scientific Communications "Progress in the Polymer Science" at the Days of the Romanian Academy in Iasi, October 6-9, 1994, Iasi (Romania). Chitanu G.C., Lingvay I., Zaharia I.L., Anghelescu-Dogam A.G., Carpov A. (1995) - Some Data Concerning the Anticorrosion Activity of Maleic Polyelectrolytes. First International Symposium on Polyelectrolytes, Polyelectrolytes, Potsdam '95, September 18-22, 1995, Potsdam (Gemany). Chitanu G.C., Ligvay I., Anghelescu-Dogam A.G., Zaharia I.L. (1995) - Maleic derivatives for antocorrosion treatment in geothermal systems. Xfi Session of Scientific Communications "Progress in the Polymer Science" at the Days of the Romanian Academy in Iasi , October 5-7, 1995, Iasi (Romania). Lingvay I., Chitanu G.C., Pacala C., Carpov A. (1994) - Contributions to prevent the corrosion and the depositions in freezers with sea water. Proceedings of International Conference on UK Corrosion and EUROCORR '94, Bournemouth, UK. Lingvay I., Carpov A., Pacala C., Chitanu G.C., Rata C. (1994) - Studies concerning the control of corrosion and scale in heat exchangers with untreated water. 7th Conference on Physical Chemistry, September 21-23, 1994, Bucharest (Rornania). Zaharia I.L., Chitanu G.C., Holerca M.N. (1994) - Analysis and Characterisation of some Derivatives of Maleic Anhydride Copolymers. IXh Session of Scientific Communications "Progress in thePolymer Science" at the Days of the Romanian Academy in Iasi, October 6-9, 1994, Iasi (Romania).

Patent Applications: Chitanu G.C., Zaharia I.L., Carpov A. (1994) - Process of obtaining ester derivatives from maleic anhydride copolymers - Appl. no. C 1366/12.08. 1994. Chitanu G.C., Zaharia I.L., Anghelescu-Dogam A., Carpov A. (1994) - Process of obtaining some maleic anhydride-methylmethacrylate copolymers or terpolymers - Appl. no. C 1709/25.10.1994. Chitanu G.C., Zaharia I.L., Anghelescu-Dogam A.G., Carpov A. (1995) - Process of synthesis of some inorganic salts of maleic copolymers and terpolymers - Appl. no. 95-0030817.02.1995. Chitanu G.C., Anghelescu-Dogam A.G., Carpov A. (1996) - Process of obtaining some maleic anhydride-N-vinyl-pyrrolidone copolymers and terpolymers - Appl. no. C/01004/06.05.1996. Chitanu G.C., Zaharia I.L., Anghelescu-Dogam A.G., Carpov A. (1996) - Process of synyhesis of some organic salts of some copolymers with carboxylic groups - Appl. no. C/01060/23.05.1996.

CAEL Caire J.P., Juncu Gh., Cotarta V., (1996) - A cylindrical tanks inner cathodicaly protected with extemal current source. Oral commu~cation to "Electrochemistry a Frontier Field of Theoretical and Practical Interest" - 31 October - 3 November 1996, Cluj Napoca - Romania. Cotaaa V., Juncu Gh. (1997) - A kinetic corrosion parameters in geotermal water solving with integral method, submitted to Revue Roumaine de Chimie. Juncu Gh., Cotarta V., Caire J.P. (1997) - A numeric mode1 of cyliidric tank cathodically protected, submitted to J. Appl. Electochemistty.



Juncu Gh., Cotarta V., Caire J.P. (1997) - Modélisation numérique de la protection cathodique de réservoirs cylindriques. Accepted as oral communication to "Journée d'Electrochiiie 1997", Montréal, Canada, 2-5 juillet 1997. Petrescu, B., Cotarta V., Bouteillon J. (1996) - A computer asisted electrochemistry methods environement. Oral communication to "Electrochemistry a Frontier Field of Theoretical and Practical Interest" - 31 October - 3 November 1996, Cluj Napoca - Rornania.

CRIC: KALMAN E., VARHEGYI B., BAKO I., FELHOSI 1. KARMAN F.H, SHABAN A. J. (1994) - Corrosion inhibition by l-hydroxy-ethane-1.1-diphosphonic acid. An electrochemical impedance spectroscopy study. J.Electrochemical Society, Vol. 141, pp. 3357-3360. KALMAN E., LUKOVITS I., PALINKAS G. (1995) - A simple mode1 of synergism of corrosion inhibitors. ACHModels in Chemistry, vol 132, pp. 527-537.

ICPE-CO0 see BBPDICM

ICVL Juzeliunas E., Samueleviciene M., Leinartas K., Virbalyte D. (1995) - Peculiarities of iron corrosion in geothermal fluid from west-Lituanian aquifers. In: Lietuvos mokslas ir pramone. Extended abstracts of the conference, part: Inorganic Chemistry and Technology. Kaunas. Technologija, pp. 23-27. Juzeliunas E., Samueleviciene M., Sudavicius A., Leinartas K., Virbalyte D. (1995) - Corrosion of iron and oxide layer formation in geoîhemal fluid from west-Lituanian aquifers. In: National Lituanian Conference "Chemistry 95", Book of Abstracts, Vilnius, pp.94-95. Juzeliunas E., Samueleviciene M., Leinartas K., Virbalyte D., Radeckas B. (1995) - Laboratory studies of iron corrosion in geoîhermal fluid from west-Lituanian aquifers. Chemijia OSSN 0235- 7216) 2, pp.25-32. Juzeliunas E., Kaiiiuskas P., Miecinskas P. (1996) - J. Electrochem. SOC. 143, p. 1513. Juzeliunas E., Samueleviciene M., Sudavicius A., Leinartas K., Virbalyte D. (1996) - Laboratory studies of iron corrosion and oxide layer formation in geothermal fluid from west-Limanian aquifers. Chemijia (ISSN 0235-7216) 1, pp.8-18. Juzeliunas E., Leinartas K., Samueleviciene M., Miecinskas P. (1997) - EQCM study of iron corrosion in geothermal fluid from west-Lituanian aquifers. Chemijia (ISSN 0235-7216) (accepted).



7. ANNEXES (Figures)

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Figure 1: Redox potential (on Au) versus time. under N2, H2S and air. (in 0.35 M NaCI)

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Figure 2: Redox potential (on Pt) and pH versus time. under air and H2S (in 0.35M NaCI)

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6 2 EEC-DG XII-Joule Programme-contract Nos JOU2-CT92-0108 and CIPD-CT93-0314 - final report

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