Best Practices SILDRIL.pdf

M-I SWACO R&E 5950 North Course Drive

Houston, TX 77072 Tel: 281-561-1440

www.miswaco.com

This report is being made available to you with the understanding that it contains CONFIDENTIAL

information, which must not be used by, or distributed to, anyone outside of your organization.

M-I SWACO Global Best Practice

SILDRIL

Revision 4

Best Practices - SILDRIL

of 33 Revision 4 CONFIDENTIAL

Contents 1 Introduction .......................................................................................................................................................................... 6

2 System Description .............................................................................................................................................................. 6

2.1 Fluid Design ........................................................................................................................................................ 6

2.2 Shale Inhibition Mechanism ........................................................................................................................... 7

2.3 Mechanism for wellbore stability / shale inhibition ................................................................................ 8

2.4 Comparative Inhibition Performance .......................................................................................................... 9

2.5 SILDRIL the IFE Fluid ............................................................................................................................................. 9

3 Product Selection and Description .................................................................................................................................. 10

3.1 General Formulation: ............................................................................................................................................ 10

3.2 Products ................................................................................................................................................................ 11

3.2.1 Primary Shale Inhibitor – SILDRIL (sodium silicate) ............................................................................................. 11

3.2.2 Secondary Shale Inhibitor – Potassium Salt – KCl or K2CO3 or K2SO4 or K-52 ................................................... 11

3.2.3 Sodium Chloride Alternative for Drilling Salt Formations ...................................................................................... 12

3.2.4 Potassium Chloride, Sodium Chloride, MEG (Monoethylene glycol), and DEG (Diethylene glycol) for gas hydrate suppression for Deepwater Application .................................................................................................................. 12

3.2.5 Viscosifier – Xanthan Gum Biopolymer ................................................................................................................ 12

3.2.6 Fluid Loss Additives – Polyanionic Cellulose and/or Starch ................................................................................. 12

3.2.7 Lubricity Additives – SIL-LUBE™, BLACK FURY™, DRIL-FREE™, ................................................................... 12

3.2.8 Fluid Loss and Lubricity Additive – GLYDRIL MC™ ............................................................................................. 12

3.2.9 Microfracture Sealant ............................................................................................................................................ 12

3.2.10 Thinners ................................................................................................................................................................ 12

3.2.11 High Temperature Additives ................................................................................................................................. 12

3.3 Fluid Formulation and Properties .......................................................................................................................... 13

3.4 Mixing Recommendations .................................................................................................................................... 13

3.5 Toxicity and Environmental Issues ....................................................................................................................... 13

3.5.1 Physiolgical and Environmental Effects of Sodium Silicate .................................................................................. 13



3.5.2 pH Effects ............................................................................................................................................................. 14

3.5.3 Environmental Approval ........................................................................................................................................ 14

3.6 Engineering and Maintenance Recommendations .............................................................................................. 14

4 Silicate Determination ....................................................................................................................................................... 15

4.1 Four methods are used to determine the silicate concentration in the system. .................................................... 15

The HACH SiO2 Test Kit is a self-contained kit, which is easy to use. The TITRATION METHOD provides a more accurate determination. ....................................................................................................................................................... 15

4.2 HACH TEST PROCEDURE FOR SOLUBLE SILICA ANALYSIS ........................................................................ 15

4.2.1 Analytical Procedure for the High Range Kit (0-800 mg/L SiO2) ........................................................................... 15

4.2.2 Analytical Procedure for the Medium Range Kit (0-40 mg/L SiO2) ....................................................................... 16

4.2.3 CALIBRATION CURVE - HACH Test ................................................................................................................... 17

4.3 STANDARD TITRATION METHOD FOR DIRECT SILICATE ANALYSIS ........................................................... 17

4.3.1 Equipment. ............................................................................................................................................................ 17

4.3.2 Reagents .............................................................................................................................................................. 18

4.3.3 Procedure. ............................................................................................................................................................ 18

4.3.4 SILDRIL Determination ......................................................................................................................................... 18

4.3.5 Silica (SiO2) Content ............................................................................................................................................. 18

4.3.6 Calculations .......................................................................................................................................................... 18

4.4 FIELD TITRATION METHOD FOR PRODUCT ANALSIS - RECOMMENDED ................................................... 19

4.4.1 Equipment. ............................................................................................................................................................ 19

4.4.2 Reagents .............................................................................................................................................................. 19

4.4.3 Procedure. ............................................................................................................................................................ 19

4.4.4 SILDRIL Determination ......................................................................................................................................... 19

4.4.5 Silica (SiO2) Content ............................................................................................................................................. 19

4.4.6 Calibration Curve .................................................................................................................................................. 20

4.5 SILDRIL CONCENTRATION USING ALKALINITY MEASUREMENT ................................................................. 20

4.5.1 Procedure ............................................................................................................................................................. 20

4.5.2 Field Measurement ............................................................................................................................................... 20

4.5.3 CALIBRATION CURVE – Pf, Mf ............................................................................................................................ 20



4.6 pH ......................................................................................................................................................................... 21

4.6.1 CALIBRATION CURVE - pH vs. %v/v SILDRIL.................................................................................................... 21

5 Fluid Properties .................................................................................................................................................................. 21

5.1 Optimum Silicate Concentration ........................................................................................................................... 21

5.2 Mud Weight ........................................................................................................................................................... 22

5.3 Rheology ............................................................................................................................................................... 22

5.4 Filtration Control ................................................................................................................................................... 22

5.5 Alkalinity ................................................................................................................................................................ 22

5.6 pH ......................................................................................................................................................................... 22

5.7 MBT ...................................................................................................................................................................... 23

5.8 Hardness .............................................................................................................................................................. 23

5.9 Silicate Solubility ................................................................................................................................................... 23

5.10 Lubricity ................................................................................................................................................................ 23

6 System Maintenance & Recommended Practices .......................................................................................................... 24

6.1 Recommended treatment ..................................................................................................................................... 24

6.2 Depletion rates ...................................................................................................................................................... 24

7 Contamination .................................................................................................................................................................... 25

7.1 Drill Solids ............................................................................................................................................................. 25

7.2 Cement Contamination ......................................................................................................................................... 25

7.3 Seawater ............................................................................................................................................................... 25

7.4 Acid Gases ........................................................................................................................................................... 25

7.5 Bacterial Degradation ........................................................................................................................................... 25

8 Corrosion Control .............................................................................................................................................................. 26

9 Engineering Guidelines ..................................................................................................................................................... 26

9.1 Hole Cleaning Recommendations ........................................................................................................................ 26

9.2 Wiper Trips ........................................................................................................................................................... 27

9.3 Circulating the Hole Clean prior to Trips ............................................................................................................... 27

9.4 Torque and Drag Considerations .......................................................................................................................... 27

9.5 Solids Maintenance .............................................................................................................................................. 27



9.6 Cementing ............................................................................................................................................................ 27

9.7 Lost Circulation ..................................................................................................................................................... 28

9.8 Bit Balling .............................................................................................................................................................. 28

9.9 Accretion ............................................................................................................................................................... 28

9.10 Formation Damage ............................................................................................................................................... 28

9.11 Waste Management .............................................................................................................................................. 29

9.12 Compatibility Issues with Logging Tools ............................................................................................................... 29

9.13 Mud Logging and Lithology Interpretation ............................................................................................................ 29

9.14 System Limitations ................................................................................................................................................ 29

9.15 Logistics ................................................................................................................................................................ 29

9.16 SILDRIL Application at Higher Temperatures to 350ºF ........................................................................................ 29

10 Ten Key Issues that are Crucial when using a SILDRIL Fluid ....................................................................................... 29

10.1 MUD WEIGHT ...................................................................................................................................................... 29

10.2 HOLE CLEANING – MUD RHEOLOGY ............................................................................................................... 30

10.3 HOLE CLEANING - DRILLING PRACTICES ....................................................................................................... 30

10.4 WIPER TRIPS ...................................................................................................................................................... 30

10.5 SILICATE CONCENTRATION ............................................................................................................................. 30

10.6 CIRCULATING THE HOLE CLEAN PRIOR TO TRIPS........................................................................................ 30

10.7 SOLIDS CONTROL .............................................................................................................................................. 30

10.8 LOGISTICS ........................................................................................................................................................... 31

10.9 SILICATE SYSTEM DESIGN – SILDRIL .............................................................................................................. 31

10.10 LUBRICITY ........................................................................................................................................................... 31

11 Technical Support .............................................................................................................................................................. 31

12 Appendicies ........................................................................................................................................................................ 32



1 Introduction

Silicate technology was introduced to the drilling industry in the 1930’s by Garrison and Vietti to drill troublesome red beds in West Texas. Over 100 wells were drilled with this simple system composed of gel and sodium silicate (better known as “water glass”). The technology was briefly revived by Darley in the early 1960’s (3 wells). One of the mud engineers on the silicate wells in the 1930’s was Orien Van Dyke who later became Vice-President of Magcobar in the 1950’s. The following is an excerpt from a memo he wrote to the Oklahoma City Magcobar manager in 1956:

”The principle of silicate mud is to provide a liquid phase that prevents the hydrous disintegration of water-sensitive shales. The liquid phase of silicate mud is far more effective in preventing disintegration than any of the variety of muds that we are currently using to retard disintegration and dispersion. When drilling with a silicate mud, the cuttings arrive at the surface unaltered, showing definite marks of the bit. Experience in more than 100 wells has confirmed that by using a mud that prevents the disintegration of the formation drilled, the hole stays to gauge even through soft water-reactive shales, which with conventional muds would be enlarged, often resulting in sloughing and heaving. Where high pressures are associated with the troublesome shale, it is necessary to carry sufficient weight to balance the pressures; otherwise, caving would result even with the protective silicate muds. It appears that the improvements that have been made in drilling muds and drilling practice during the past few years have eliminated the necessity for using silicate muds. We still think of them as being an “ace in the hole” should our best conventional practice fail to handle troublesome conditions that might be encountered.”

In the late 1980’s Conoco/DuPont introduced a modern silicate inhibitive fluid design with a shale inhibitive product blend of potassium silicate, potassium carbonate, and a polyvinyl alcohol polymer. The blend was marketed as WBS100. This inhibition technology was based on research developed by a DuPont surface and colloid chemist, Jim Wingrave. The WBS technology was the first system to use polymer and silicate technology to drill troublesome shales. Conoco drilled over 10 wells using WBS100 (later referred to as WBS200) beginning in 1986 in Texas, Louisiana, Wyoming, California, onshore Holland, as well as the North Sea.

Polymer technology, fine screen shaker equipment design, the technical requirement to drill troublesome reactive formations more effectively, and environmental regulations provided the impetus for the development of more improved water base fluid design. Silicate technology provided one of these water base solutions.

With the re-introduction of silicate technology to the industry, service companies began marketing inhibitive silicate systems to the industry in the mid-1990’s. M-I SWACO introduced SILDRIL in 1998-99 with successful wells in the UK, Germany, Australia, India, and Norway. In 2001 M-I SWACO acquired BW Mud UK. BW had drilled numerous wells in the UK since 1994 using shale inhibitive silicate technology. From 1994 to 2011 over 1000 wells have been drilled by M-I SWACO using the highly inhibitive silicate water base fluid.. Silicates have been used to drill hole sizes from 26” to 6”. The majority of the wells drilled have been vertical (55%). 30% have been drilled at high angle, and 35º-70º with 15 % greater than 70º.

2 System Description

2.1 Fluid Design SILDRIL is an inhibitive mud system formulated with a soluble silicate for maximum shale inhibition. The system has been developed to drill water-sensitive, reactive shales and dispersible chalk and illite formations. The degree of inhibition provided by the SILDRIL system truly approaches the level of an oil base system.



The system can be engineered with monovalent salts and a GLYDRIL polyglycol to enhance filtration control and lubrication of the fluid. The polyglycol also improves temperature stability.

The SILDRIL drilling fluid system is a water base fluid which has been developed to provide a drilling fluid to drill in areas where wellbore stability is a problem and an invert emulsion fluid normally would be used. Formations like micro-fractured shales and chalks or formations with interbedded dispersive clays like illite are applications where a SILDRIL system should be considered. The system is designed using conventional polymers for rheology (xanthan gums) and filtration (starches and PACs).

2.2 Shale Inhibition Mechanism In a SILDRIL fluid the silicate monomers form three-dimensional polymeric structures. Gelation (polymerization) and intermolecular condensation of silicate polymers occurs. The silicate polymer has functional reactive –Si-OH groups which can, via hydrogen bonding, adsorb on the surface of the shale structure providing an effective barrier to water inbibition resulting in a highly inhibitive mechanism for shale inhibition.



2.3 Mechanism for wellbore stability / shale inhibition Attraction occurs between polymerized silicate species and the shale surface via hydrogen bonding of the surface hydroxyl groups and bridging via mono- and divalent cations. Induced by pressure and temperature, physical bonding can occur between the silicate and shale silanol groups by condensation reactions. Thereby, the silicate filter cake / membrane becomes a part of the shale structure and effectively seals the formation wellbore. Oil-base muds provide highly effective shale inhibition through osmotic control of water flows through a near perfect ion exclusion membrane. This membrane appears to be located at the surface of the shale. The osmotic membrane formed via silicate polymerization appears to be generated within the shale. This silicate osmotic membrane is slightly leaky with some potassium and/or sodium ions migrating through the clay film. The fluid transport is controlled by the salinity imbalance across the osmotic membrane. To prevent destabilizing osmotic water flow from the mud into the shale, the water activity of the silicate-base fluid should be lower or at least equal to the shale activity. A lower water activity forces a flow from the shale through the osmotic membrane. It has been postulated that the resulting dehydration and pore-pressure decrease may help to stabilize the shale. The inhibition efficiency of a drilling fluid, or in this case, a silicate-base drilling fluid can be evaluated by recovery tests in the laboratory. Such tests have shown, that the optimum silicate concentration in a drilling fluid is around 4-6 percent active silicate

SILICATE INTERACTION WITH FORMATION AND

DRILL SOLID SURFACES

..... . .

. .. . ..

.

...

..

.. ..

..

. . ..

. .

.... Si

Ho

H o

Si

PHYSICAL

&CHEMICAL

BARRIER

TOINVASION

CLAY PLATELETS

NON-CLAY PARTICLES

FILTER CAKE DEPOSITION



2.4 Comparative Inhibition Performance The following chart provides a relative comparison of the inhibition properties of the various water base inhibitive systems compared with an invert emulsion oil mud system. The greater percent recovery indicates a more inhibitive fluid. The light tan bar represents swelling or reactive shales and the brown bar highly dispersive shales. In summary, the silicate (SILDRIL) fluids demonstrate a degree of inhibition comparable to an oil base fluid – the last column on the right.

2.5 SILDRIL the IFE Fluid With proper solid maintenance engineering, dilution rates of silicate fluids are comparable to an oil base system. The silicate system is an environmentally benign fluid with numerous HS&E advantages. Soluble

0

10

20

30

40

50

60

70

80

90

100

Shale Recovery - %

REACTIVE SHALES (HIGH SMECTITE CONTENT) DISPERSIVE CLAYS



silicate can be disposed with negligible environmental impact. Soluble silicates are safe, non-toxic and have a GRAS rating. Silicates are non-volitile. Soluble silicates have agricultural applications including the use of potassium silicate as a fertilizer and there are numerous environmental sound disposal options for silicate base fluids.

Environmental compliance, however, of SILDRIL is dependent on governmental regulatory requirements, but generally speaking, the shale inhibition efficiency results in a low environmental impact of the SILDRIL system which makes it an excellent candidate as an ideal “IFE Fluid.”

3 Product Selection and Description The SILDRIL Sytem must be made up with fresh water treated with soda ash and caustic to remove all divalent ions (Mg++ and Ca++); these ions will precipitate the silicate if left in the make-up water. Sea water can only be used if treated with soda ash and caustic prior to mixing; if treated sea water is used, the hardness concentration must be checked to ensure it is zero before mixing the SILDRIL fluid. The following is a typical formulation for an inhibitive SILDRIL fluid. However, the formulation needs to be tailored to the application. This will be determined by hole size, shale/formation reactivity, drilling rate, rig and solids control equipment limitations, fluid loss requirements, hole angle, and temperature requirements.

3.1 General Formulation:

Table 1. Basic Formulation – Primary Products

BASIC FORMULATION CONCENTRATION

Sodium or Potassium Hydroxide 0.25-0.5 ppb

Sodium or Potassium Carbonate 1.0-5.0 ppb

DUOVIS or FLO-VIS Plus or SUPRAVIS 0.5-2.5 ppb

POLYPAC UL or POLYPAC ELV 2.0-6.0 ppb

DUALFLO or POLYSAL or FLO-TROL 2.0-6.0 ppb

SILDRIL L or SILDRIL K (liquid) 4-14%v/v

or SILDRIL D or SILDRIL K (dry) 15-60 ppb

KCl 3-15%w/w

Barite or Calcium Carbonate As required for density



Table 2. Contingency Products

All special application formulations must be pilot tested before recommending to a client.

PRODUCT FUNCTION CONCENTRATION

Sodium Chloride Salinity 3-15%w/w

GLYDRIL MC Fluid Loss, Lubricity 3.0-5.0%

RESINEX HTHP Application >250ºF 0.5-2.5 ppb

CALOVIS FL HTHP Application >250ºF 2.0-4.0 ppb

DURALON HTHP Application >250ºF 2.0-4.0 ppb

POROSEAL Microfracture Sealant 5-7%v/v

ASPHASOL Microfracture Sealant 4-8 ppb

SIL-LUBE Lubricity 2-3%v/v

BLACK FURY Lubricity 2-3%v/v

G SEAL PLUS LPM, LCM 15-30 ppb

All Conventional LCM LCM As per product recommendation

IDCAP D Encapsulator 1-2 ppb

3.2 Products

3.2.1 Primary Shale Inhibitor – SILDRIL (sodium silicate) SILDRIL utilizes unique silicate chemistry and the potassium ion to stabilize the wellbore and maintain the integrity of the drill cuttings.

The SILDRIL system can use either or both sodium silicate and potassium silicate. Sodium silicate is available both as a liquid product (SILDRIL L) and a dry product (SILDRIL D). SILDRIL L and SILDRIL D require a potassium salt for optimum inhibition performance. Potassium silicate (SILDRIL K) is an alternative silicate product that can be used without a potassium salt to provide superior inhibition performance. SILDRIL K is available both as a liquid and a solid.

Selection of product is dependent on cost, application, logistic considerations, and environmental requirements.

3.2.2 Secondary Shale Inhibitor – Potassium Salt – KCl or K2CO3 or K2SO4 or K-52 The SILDRIL system requires the potassium ion for optimum inhibition performance when drilling swelling smectite shale formations. Potassium chloride is the most common inorganic salt normally used in the SILDRIL system with the concentration normally varying from 3-15 w/w%, depending on individual drilling requirements. Potassium carbonate, or potassium sulfate, as well as K-52™ (potassium acetate) can also be used as alternative salts to provide a chloride-free fluid for environmental and logging applications. Potassium nitrate is not a viable option because of safety issues. Typical treatment concentration with potassium carbonate is from 5-30 lb/bbl (15-90 kg/m3). Potassium sulfate treatment is typically 20-40 lb/bbl (60-120 kg/m3). Treatment concentration with potassium nitrate (if used) is from 15-30 lb/bbl (45-90 kg/m3). K-52 is 2-4 lb/bbl (6-12 kg/m3). The salt composition is dependent on individual well requirements and formation characteristics.



3.2.3 Sodium Chloride Alternative for Drilling Salt Formations Sodium chloride is primarily used from 30-50 lb/bbl (90-150 kg/m3) to saturate the system for drilling salt/shale formations and to alleviate potential accretion problems.

3.2.4 Potassium Chloride, Sodium Chloride, MEG (Monoethylene glycol), and DEG (Diethylene glycol) for gas hydrate suppression for Deepwater Application

Potassium chloride, sodium chloride, MEG, and DEG are compatible with the SILDRIL system to provide gas hydrate inhibition. WHyP software can be used to provide an estimate of the concentration(s) required to meet the water depth and seabed temperature parameters.

3.2.5 Viscosifier – Xanthan Gum Biopolymer The system is designed for use with all Xanthan Gum polymers to provide optimum Low-Shear-Rate Viscosity (LSRV) for superior hole cleaning, wellbore stability, and optimum hydraulics. Yield Point and Low-Shear-Rate values should be designed to ensure proper hole cleaning. High, flat, fragile gel strengths are maintained to ensure solids suspension. LSRV values are recommended based on well geometry and hole angle. Please refer to “Best Practices for Hole Cleaning” for optimum fluid performance.

3.2.6 Fluid Loss Additives – Polyanionic Cellulose and/or Starch Filtration control is readily maintained with all conventional filtration control polymers – POLYPAC™ R, POLYPAC™ UL, POLYPAC™ ELV, POLY-SAL™, POLY-SAL HT™, FLO-TROL™, DUAL-FLO™, DUAL-FLO HT™, FLO-PLEX™, HIBTROL™, and THERMPAC UL™. Selection of fluid loss products is dependent on performance and temperature requirements, logistics, and cost considerations.

3.2.7 Lubricity Additives – SIL-LUBE™, BLACK FURY™, DRIL-FREE™, ... Some conventional water-soluble lubricants are not effective in silicate systems. SIL-LUBE™, BLACK FURY™, DRIL-FREE™, SILDRIL EPL™, BW Polylube, G SEAL™ and Radiagreen SL (Oleon) have all been used successfully in the SILDRIL system. SIL-LUBE™ has been developed solely for use in the SILDRIL system. All lubricants should be pilot tested before addition to the active system.

3.2.8 Fluid Loss and Lubricity Additive – GLYDRIL MC™ GLYDRIL MC™ or GLYDRIL GP™ can also be used to improve the lubricity and filtration property of the SILDRIL system. GLYDRIL MC™ can provide lubrication, fluid loss control, and improved thermal stability to the SILDRIL system.

3.2.9 Microfracture Sealant ASPHASOL™ or ASPHASOL SUPREME™ and POROSEAL™ are compatible with SILDRIL and can be used as a microfracture sealant.

3.2.10 Thinners Conventional anionic thinners are not recommended for use with a silicate-base system. The addition of water, KCl brine, and/or a silicate/KCl/polymer premix is recommended to control and reduce the viscosity.

3.2.11 High Temperature Additives SILDRIL fluids have been successfully run to 350ºF (177ºC) bottom hole temperature. To engineer the fluid design for BHT temperature greater than 275ºF (135ºC) synthetic polymers can be used for rheology and filtration control. CALOVIS FL can be used for this application. It is mandatory to minimize low gravity solids to achieve acceptable rheology parameters. The maximum density for a high temperature SILDRIL fluid is 15.0 ppg. When tripping at the high temperatures, it is recommended to spot a weighted (barite or hematite) SILDRIL/polymer pill (drill solids-free) across the high temperature open hole interval to minimize adverse gelation effects. All high temperature formulations must be pilot tested prior to use.



3.3 Fluid Formulation and Properties The non-dispersed SILDRIL system is designed with relatively few products, thus providing a great deal of flexibility. Premium grade Xanthan Gums are recommended to obtain the rheology specifications and all POLYPAC products, starch additives, as well as modified starch products, can be utilized in the fluid to maintain filtration control. The system is compatible with a wide variety of supplemental additives, that may be required for special applications.

SILDRIL should not be engineered as a bentonite-base fluid. 1-3 lb/bbl M-I GEL (3-9 kg/m3) can be used in the laboratory formulation to stabilize the filtration and rheology properties. The normal incorporation of colloidal and silt-sized particles during the drilling process will provide adequate solids for filtration control. Treatments with M-I GEL are not recommended.

3.4 Mixing Recommendations The pH of the system is higher than conventional non-dispersed polymer fluids, ranging from 11.0 to 12.5. It is important to understand that the high pH and alkalinity values are attributed to the alkaline silicate anion and not a hydroxyl anion. A decrease in the pH or alkalinity is normally the result of the depletion of silicate (via polymerization, precipitation, and adsorption). The pH, alkalinities, and silicate analysis are used to monitor treatment requirements during drilling. The use of caustic is not recommended to control the pH of the system. Caustic and soda ash, or potassium hydroxide and potassium carbonate, or TKPP are used to treat pre-mix water prior to the addition of polymer additives to remove hardness. Soda ash or potassium carbonate is used to treat cement contamination.

The silicate anion and polymeric species will precipitate if divalent or trivalent cations are present. Therefore, the concentration of silicate will deplete in the presence of calcium or magnesium ions. Therefore, drillwater is recommended when formulating the system. Seawater may be used if it is pre-treated with caustic soda or caustic potash and soda ash or potassium carbonate or TKPP. Divalent ions generated during the drilling process (e.g. anhydrite) will react with the silicate, thereby increasing the concentration required to maintain inhibition performance. The reaction with divalent ions is normally not detrimental to the rheology or fluid-loss performance.

The concentration of the silicate can be readily monitored using a standard quantitative test for the silicate ion. pH and alkalinity are also used to monitor the active concentration of silicate in the fluid.

SILDRIL L, SILDRIL D, SILDRIL K, and SILDRIL 2L, all can be added directly to the system or used in premixes to maintain the desired concentration. The recommended active concentration is 6-15% by volume of the liquid product and 3-8% by weight of the dry product. The working concentration will be determined by the reactivity of the formation. A combination of silicate products can be used and will be determined by the requirements of the drilling program. Concentrated polymer premixes are the recommended procedure for maintenance during drilling to minimize system dilution.

3.5 Toxicity and Environmental Issues The silicate system is an environmentally benign fluid with numerous HS&E advantages. Soluble silicate can be disposed with negligible environmental impact. Soluble silicates are safe, non-toxic and have a GRAS rating. Silicates are non-volitile. Soluble silicates have agricultural applications including the use of potassium silicate as a fertilizer and there are numerous environmental sound disposal options for silicate base fluids.

Environmental compliance, however, of SILDRIL is dependent on governmental regulatory requirements, but generally speaking, the shale inhibition efficiency results in a low environmental impact of the SILDRIL system.

3.5.1 Physiolgical and Environmental Effects of Sodium Silicate

Sodium silicate adds silicate anions, together with sodium and hydroxyl ions, to water.



Silica is found to some extent in all natural waters and is believed to be ecologically harmless. The charged, polymeric nature of the silica found in synthetic silicate solutions is responsible for its reaction with metals and corrosion inhibition properties.

The sodium content of water will increase slightly with sodium silicate addition. This issue has been raised as a concern in some instances. At the highest dosages recommended for potable water treatment (24 mg SiO2/L), SILDRIL (sodium silicate) will contribute less than 5.6 mg Na/L to the water.

Furthermore, when using N silicate at normal maintenance dosages of 4-12mg SiO2/L, the sodium contribution is 0.9-2.8 mg Na/L, respectively. When other sodium silicates are used, the sodium contribution will be different depending on the weight ratio of SiO2/Na2O. If no sodium addition is tolerable, potassium silicates offer an alternative. Neither sodium nor potassium silicate corrosion inhibitors contribute phosphorus or metals such as zinc to the ecosystem. These are concerns with other corrosion inhibitors, especially phosphorus-based types.

3.5.2 pH Effects Sodium silicates are alkaline chemicals. Treating water at typical levels of 4-24 mg SiO2/L may raise the water pH anywhere from 0.1 to 2.0 pH units or more. The actual pH increase will depend on overall water quality and silicate dosage.

3.5.3 Environmental Approval The use of sodium silicates for the control of corrosion in municipal water systems is approved by the American Water Works Association and the American National Standards Institute (refer to ANSI/AWWA Standard B404). Sodium silicate also has Food and Drug Administration (FDA) unpublished “generally recognized as safe” (GRAS) status as a corrosion preventative in water (at levels below 100 mg/L). The U.S. Environmental Protection Agency (EPA) recognizes that silicate inhibitors may be effective in controlling corrosion of lead and copper in potable water systems.

3.6 Engineering and Maintenance Recommendations Primary inhibition is normally achieved with the maintenance of 3-6% active silicate. SILDRIL L is 41-46% active with a 2.6-2.8 silicate ratio (SiO2:Na2O).

SILDRIL 2L is 43-48% active with a 2.0 silicate ratio. SILDRIL K is 38-45% active with a 2.8-3.6 silicate ratio.

The recommended treatment concentration for SILDRIL L and SILDRIL 2L is 6-12% by volume. A Potassium salt is required for optimum silicate performance.

SILDRIL D is 80% active. The recommended treatment level is 10-20 lb/bbl (30-60 kg/m3). The dry product can be added directly to the active system and can be used for maintenance with SILDRIL L.

The recommended concentration for SILDRIL K is 6-12% by volume. Additional potassium salts are not required but may be used for highly reactive smectite formations

The dry and liquid products can be used separately or together.

General inhibition is dependent on formation composition and chemistry. The SILDRIL System is designed to provide maximum chemical stabilization of the formation and cuttings in a water-base fluid.

It is critical to maintain the active silicate concentration in the recommended range (4-6%) with the addition of SILDRIL L, D, 2L or K / KCl Brine / Polymer premixes or by the direct addition of product. During drilling, the ”in” and “out” silicate concentrations should be monitored regularly to determine both the rate of depletion and to regulate treatment requirements.



To ensure optimum product concentration and inhibition, the silicate and potassium ion concentrations must be monitored. Silicate is monitored via pH, alkalinity, and a quantitative silicate test. Potassium ion is also monitored via one of several analytical tests (Centrifuge Method or Potassium Strips). Analytical determinations should be correlated with mathematical calculations of the product concentrations to quantify depletion rates and to determine maintenance requirements.

A properly treated SILDRIL system will result in excellent cuttings integrity, gauge hole, and minimum dilution.

4 Silicate Determination An accurate silicate determination and correlation with the alkalinity values and the pH are keys to properly maintaining the required concentration of SILDRIL. It is important to construct calibration curves of the specific SILDRIL product initially when arriving on location. This is mandatory because of the range of SILDRIL products as well as the various suppliers. Calibration curves should be established with the product on location prior to the beginning of drilling. Concentration standards with the product on site should be for the range recommended in the mud program. The monitoring of silicate in the fluid is the most important engineering requirement to correctly assess the inhibition performance of the fluid.

4.1 Four methods are used to determine the silicate concentration in the system. a) HACH SiO2 Test Kit

b) TITRATION METHOD

c) ALKALINITY VALUES - Pm and Pf

d) pH

The HACH SiO2 Test Kit is a self-contained kit, which is easy to use. The TITRATION METHOD provides a more accurate determination.

4.2 HACH TEST PROCEDURE FOR SOLUBLE SILICA ANALYSIS Hach SiO2 Test Kit ((0-40 mg/L SiO2))(0-800 mg/l SiO2)Model SI-5 (Catalog No. 14554-00).

This test kit is complete with instructions and chemical reagents to test the filtrate for silicate.

The Hach Kit is available in two ranges:

Medium Range (0-40 mg/L SiO2)

High Range (0-800 mg/L SiO2)

The high range is recommended to minimize the dilution requirement of the filtrate sample.

The mud filtrate will require dilution to be in the proper range for analysis of the SILDRIL filtrate sample. The filtrate will typically require a dilution of 1:250 for the High Range Kit. The Medium Range Kit mg/l) will require a 1:2000 dilution. The filtrate sample is diluted with de-ionized water. It is important to check the de-ionized water used in the analysis to ensure that the hardness is less than 25 mg/L.

WARNING: The chemicals in this kit may be hazardous to the health and safety of the user if inappropriately handled. Please read all warnings before performing the test and use appropriate safety equipment.

4.2.1 Analytical Procedure for the High Range Kit (0-800 mg/L SiO2) 1. One milliliter of the diluted sample is used for analysis and added to the square sample bottle.



2. The mixing bottle is filled to the 20 ml mark with deionised water. Swirl to mix. 3. Using this diluted water sample fill both sample tubes to the 5 ml mark. 4. Use the clippers to open one Molybdate Reagent Powder Pillow and one Acid Reagent Powder

Pillow. Add the contents of both pillows to one of the tubes. Swirl to dissolve. 5. Allow the sample to stand for ten minutes to allow color development. If silica or phosphate is

present in the sample, a yellow color will develop. 6. Use the clippers to open one Citric Acid Powder Pillow. Add the contents of the powder pillow to the

same sample tube. Swirl to mix and allow the solution to stand for two minutes. The citric acid will destroy the yellow color due to phosphate.

7. Use the clippers to open one Silica 3 Reagent Powder Pillow. Add the contents of this pillow to the same tube and swirl to mix.

8. Allow 5 minutes for color development. If silica is present, a blue color will develop. 9. Insert the tube of prepared sample into the right top opening of the color comparator. 10. Insert the tube of untreated water into the left top opening of the color comparator. 11. Hold the comparator up to a light source. 12. Rotate the disc to obtain a color match. 13. To obtain the mg/L silica concentration, multiply the reading obtained in Step 12 by 20. 14. Correct for the original dilution.

The result is reported in grams per liter (kg/m3) of SiO2.

Use the reading obtained in Step 12 to prepare a calibration curve from the series of standard solutions. Use this curve to extrapolate the % SILDRIL.

4.2.2 Analytical Procedure for the Medium Range Kit (0-40 mg/L SiO2) 1. Five milliliter of the diluted sample is used for analysis and added to the square sample bottle. 2. Use the clippers to open one Molybdate Reagent Powder Pillow and one Acid Reagent Powder Pillow. Add the contents of both pillows to one of the tubes. Swirl to dissolve. 3. Allow the sample to stand for ten minutes to allow color development. If silica or phosphate is present in the sample, a yellow color will develop. 4. Use the clippers to open one Citric Acid Powder Pillow. Add the contents of the powder pillow to the same sample tube. Swirl to mix and allow the solution to stand for two minutes. The citric acid will destroy the yellow color due to phosphate. 5. Use the clippers to open one Silica 3 Reagent Powder Pillow. Add the contents of this pillow to the same tube and swirl to mix. 6. Allow 5 minutes for color development. If silica is present, a blue color will develop. 7. Insert the tube of prepared sample into the right top opening of the color comparator. 8. Insert the tube of untreated water into the left top opening of the color comparator. 9. Hold the comparator up to a light source. 10. Rotate the disc to obtain a color match. 11. Read the mg/L silica (SiO2) through the scale window.

Use the reading obtained in Step 10 to prepare a calibration curve from the series of standard solutions. Use this curve to extrapolate the % SILDRIL



4.2.3 CALIBRATION CURVE - HACH Test DIAL READING vs. %v/v SILDRIL

This graph should be used as an example. The dial readings vs %v/v SILDRIL should be established at the rig with the product on the rig and the test kit being used.

4.3 STANDARD TITRATION METHOD FOR DIRECT SILICATE ANALYSIS Due to the affinity of SiO2 to glass, the titration should be carried out in plastic beakers. If this not possible, the beakers must be washed out thoroughly after use. This procedure describes the method for determining Silica (SiO2), by titration.

The test is in two stages:

The first determines the Sodium Oxide (Na2O) alkalinity, which is due in part to the molar ratio of Na2O to SiO2 present in the Silicate product.

The second to determine Silica. The Silica is reacted with Sodium Fluoride, which is then titrated with strong acid.

Technical Reference.

SPE 35059. Silica Based Drilling Fluids: Competent, Cost-effective and Benign Solutions to Wellbore Stability Problems (E. van Oort et al, 1996).

4.3.1 Equipment. pH meter with Calomel electrode

0

100

200

300

400

500

600

700

800

900

0 2 4 6 8 10 12 14 16

DIA

L R

EAD

ING

% SILDRIL L v/v

CALIBRATION CURVE - HACH TEST (example)



Balance, accurate to 0.1g Stirrer c/w small stir bar Pipettes, 5 ml & 2 ml

Beakers, 100 ml

4.3.2 Reagents De-mineralized Water Hydrochloric Acid, 0.2N Hydrochloric Acid, 2.0N Methyl Red Indicator Solution Sodium Fluoride, reagent grade pH buffers, pH 4 & 10

4.3.3 Procedure.

A blank titration is first performed to compensate for silicate present in the reagents.

Pipette 5 ml de-mineralized water into a small beaker and add 1 drop of Methyl Red.

Add 0.2N Hydrochloric Acid until the color first changes to pink.

Add 1 gram Sodium Fluoride. The color changes to yellow.

Titrate with 2.0 N Hydrochloric Acid to a pink color change at pH = 6.0.

Record the amount of acid used (Volume A).

4.3.4 SILDRIL Determination

Ensure the pH meter is calibrated.

Pipette 5 ml of de-mineralized water into a small beaker and add 1 drop of methyl red indicator.

Set the beaker on a stirrer, and insert the pH electrode. The indicator solution is used as a guide, but accurate measurements are against the pH value.

Add a few drops of 0.2N Hydrochloric Acid, until the color is pink.

Pipette 1 ml of filtrate into this beaker. The color changes to yellow.

Titrate with 0.2N Hydrochloric Acid to pH 5.5, where the color change to pink is noted.

Record the milliliters of acid used (Volume B).

4.3.5 Silica (SiO2) Content

To the sample titrated above, add 1gram of Sodium Fluoride. The color changes to yellow. The pH will increase to 8 -9.

Titrate with 2.0N Hydrochloric acid to pH 6.0. Record the milliliters acid used (Volume C).

4.3.6 Calculations

Alkalinity: For a 1 ml sample: mg/l Na2O = 31,000 x Volume B x 0.2, where Volume B is the volume of 0.2N Hydrochloric Acid used Silicate (SiO2) For a 1 ml sample: mg/l SiO2 = 15,000 x N x (Volume C – Volume A) or g/l SiO2 = 15 x N x (Volume C – Volume A), where Volume C is the volume of 2.0N Hydrochloric Acid used in the titration, Volume A is the volume of acid used in the blank correction ( typically < 0.1 ml), and N is the normality of the acid ( 2N).



To convert g/l SiO2 to % v/v silicate in the SILDRIL system: % volume silicate = g/l SiO2 x 0.2237, where the SG of Silicate is 1.475, with an SiO2 activity of 30.3% by wt.

4.4 FIELD TITRATION METHOD FOR PRODUCT ANALSIS - RECOMMENDED

4.4.1 Equipment. pH meter with Calomel electrode Balance, accurate to 0.1g Stirrer c/w small stir bar Pipettes, 5 ml & 2 ml

Beakers, 100 ml

4.4.2 Reagents De-mineralized Water Hydrochloric Acid, 0.2N Hydrochloric Acid, 2.0N Methyl Red Indicator Solution Sodium Fluoride, reagent grade pH buffers, pH 4 & 10

4.4.3 Procedure.

A blank titration is first performed to compensate for silicate present in the reagents.

Pipette 5 ml de-mineralized water into a small beaker and add 1 drop of Methyl Red.

Add 0.2N Hydrochloric Acid until the color first changes to pink.

Add 1 gram Sodium Fluoride. The color changes to yellow.

Titrate with 2.0 N Hydrochloric Acid to a pink color change at pH = 6.0.

Record the amount of acid used (Volume A).

4.4.4 SILDRIL Determination

Ensure the pH meter is calibrated.

Pipette 5 ml of de-mineralized water into a small beaker and add 1 drop of methyl red indicator.

Set the beaker on a stirrer, and insert the pH electrode. The indicator solution is used as a guide, but accurate measurements are against the pH value.

Add a few drops of 0.2N Hydrochloric Acid, until the color is pink.

Pipette 1 ml of filtrate into this beaker. The color changes to yellow.

Titrate with 0.2N Hydrochloric Acid to pH 5.5, where the color change to pink is noted.

Record the milliliters of acid used (Volume B).

4.4.5 Silica (SiO2) Content

To the sample titrated above, add 1gram of Sodium Fluoride. The color changes to yellow. The pH will increase to 8 -9.

Titrate with 2.0N Hydrochloric acid to pH 6.0. Record the milliliters acid used (Volume C).



4.4.6 Calibration Curve Prepare a calibration curve from a series of SILDRIL standards. Graph (Volume C- Volume A) vs SILDRIL concentration. Use this curve for determining the concentration of SILDRIL in the system.

4.5 SILDRIL CONCENTRATION USING ALKALINITY MEASUREMENT The alkalinity measurements can be used to accurately monitor the product concentration.

4.5.1 Procedure Preparate a series of standard concentration (ppb or v/v%). Obtain values for alkalinity Pf. and Mf for the standard solutions.

4.5.2 Field Measurement The Pm value of the fluid is indicative of the tolal silicate product in the mud, soluble and insoluble. The Pf and Mf are measured on the API filtrate and are indicative of the dissolved silicate in the fluid

4.5.3 CALIBRATION CURVE – Pf, Mf ml 0.02 N H2SO4 vs. %v/v SILDRIL

0

5

10

15

20

25

30

35

40

0 2 4 6 8 10 12 14

Alk

alin

ity

wit

h .

02

N H

2SO

4

Volume % SILDRIL L

Alkalinity Values for Calibration of SILDRIL L Concentration

Pf Mf



4.6 pH The pH can be used to track the relative silicate concentration but it should only be considered a coarse indicator of the rel,ative concentration because it is a non-linear relationship.

4.6.1 CALIBRATION CURVE - pH vs. %v/v SILDRIL

5 Fluid Properties

5.1 Optimum Silicate Concentration Effective SILDRIL concentration is dependent on the reactivity and dispersibility of the shale, the hole size drilled, and the ROP. Intermittant gyp and calcite stringers can be problematic and cause depletion of the silicate.

It is important to ensure that the silicate concentration is maintained during drilling. The silicate concentration, pH, Pm, and Pf are all closely monitored to ensure an adequate silicate concentration for optimum inhibition. Because silicate inhibition is a sacrificial process, maintenance of the silicate concentration is a key to optimizing inhibition performance. Silicate depletion is accelerated with the introduction of divalent ions (calcium and magnesium). The use of seawater during drilling is not recommended (for example, to clean the shaker screens). If seawater is used to build volume, the calcium and magnesium ions should be treated out prior to mixing with SILDRIL. The divalent ions precipitate the silicate and increase the maintenance requirement for silicate. The divalent silicate does not adversely affect the rheology. If concentrated premixes are mixed onshore, then the mud should be checked at the plant and at the rig to ensure that the transport tanks are not contaminated with seawater. It is important to handle the fluid as if it is an OBM to ensure no contamination occurs during transport. If anhydrite or calcium or magnesium formations are encountered during drilling then additional silicate will be required to maintain the performance of the system; if massive anhydrite is encountered then the addition of silicate should be stopped and allowed to deplete to prevent unnecessaty cost. After drilling cement it will be necessary to replenish silicate removed by calcium ion from the cement.

9.8

10

10.2

10.4

10.6

10.8

11

11.2

11.4

11.6

11.8

0 5 10 15

pH

Volume % SILDRIL L



GLYDRIL MC does not enhance the inhibition performance of the SILDRIL system but it is compatible and will improve the filtration, lubricity, and temperature stability of the system. Inhibitive polymers, such as PHPA, and amines are compatible but also do not enhance the inhibitive performance of the SILDRIL system.

5.2 Mud Weight The mud weight is a key design parameter. The mud weight must be adequate to compensate for the pore pressure and mechanical wellbore stability. This is particularly critical in high angle wells or in areas where tectonic stress is a major factor.

5.3 Rheology Proper rheology is extremely important. The system uses biopolymers to provide optimum low-shear-rate-viscosity (LSRV) for superior hole cleaning, wellbore stability and optimum hydraulics. The inhibitive, non-dispersed silicate fluid maintains the integrity of the cuttings and the rheology must provide efficient transport in the annulus and effective removal at the shale shakers and centrifuges. The rule-of-thumb for 6 RPM and 3 RPM values is typically the hole size in inches. Elevated flat gel strengths are important to ensure suspension of solids. The shear thinning rheology provided by the biopolymer results in optimum hydraulics (low ECDs and annulus pressures) and efficient separation of the solids by the removal equipment. The use of high density-viscous sweeps should only be used as a diagnostic tool to ensure adequate hole cleaning.

5.4 Filtration Control The filtration parameters should be designed as you would any conventional polymer base drilling fluid. PACs and starches are used to control the API fluid loss. A single product or combination of products can be used to achieve the desired target. Low viscosity or ultra low viscosity PACs are recommended to minimize viscosity effects to the fluid. The low viscosity from the low molecular weight PAC additives allows better performance from the shear thinning xanthan polymer.

5.5 Alkalinity Soluble silicates are alkaline and possess strong buffering characteristics. The pH of a soluble silicate is determined by the molar ratio and concentration. Commercial strength solutions have pH values in the range 10.9-13.5.

The large buffering capacity of soluble silicates is confirmed by their pH stability when neutralized, until the alkali has almost completely disappeared. Soluble silicates have similar buffering capacity to caustic soda, but are effective in a lower, more desirable range. Buffering range narrows and buffering pH falls as the molar ratio is increased.

Na2SiO3 + H2O + H2SO4 Si(OH)4 + Na2SO4

Pm and Pf are used in drilling fluid analysis to provide an analysis of the soluble and insoluble alkaline components of the mud. The chemistry of the silicate ion is similar to a carbonate or phosphate and can be similarly quantitatively analyzed using field Pm and Pf information.

5.6 pH The pH decreases during the silicate inhibition process and effective inhibition performance requires maintaining the silicate concentration. Inhibition is a sacrificial process, as the silicate reacts with the shale and clay surfaces of the wellbore and drill cuttings. Maintenance of pH must be with the addition of SILDRIL product or concentrated polymer/salt/silicate premix. Caustic addition is not used to maintain the pH.

The pH is also a useful tool for tracking silicate concentration, but it is the least sensitive because of the buffering effect of the silicate ion.



5.7 MBT A primary indicator of inhibition performance is the Methylene Blue Test. The Methylene Blue Test is the only direct measurement of the reactive solids in the fluid and, therefore, is the best mud parameter to monitor relative inhibition performance.

MBT Trend Curve from a SILDRIL Well

5.8 Hardness The silicate anion precipitates in the presence of divalent and trivalent ions. Consequently, the total hardness of the SILDRIL system is zero. Total hardness or calcium in the fluid indicates the silicate is depleted.

5.9 Silicate Solubility The solubility of powdered or granular silicate in water is initially dependent on the molar ratio of the silicate and the water temperature.

SILDRIL D (dry sodium silicate, 2.6-2.8 molar ratio) would have a solubility between the 2.0 and 3.3 molar ratio silicates. In addition to these two factors, the dissolution rate is influenced by particle size, particle structure, and the degree of hydration of the product. The addition of salts as well as the addition of polymers further complicates the question of solubility. A saturated salt solution has a theoretical Aw (water activity) according to the following graph.

In order to ascertain the solubility, pilot tests on the field fluid will provide the most definitive answer. Additions of the dry silicate to the saturated salt slurry to determine how much free water is available from the slurry for solubilization, in conjunction with increasing the temperature will provide a guideline for field treatment. If additional silicate is required for improving the chemical shale stabilization, then liquid silicate or pre-hydrated dry silicate can be added to the drilling fluid. It will be extremely important with the saturated salt slurry to ensure that a critical solids concentration does not have an adverse effect on the fluid viscosity

5.10 Lubricity Lubricity is a primary concern with all water-base muds. The coefficient of friction of the silicate fluid is slightly higher than conventional water-base polymer fluids based on laboratory data. However, no field problems

0

10

20

30

40

50

1650 1750 1850 1950 2050 2150 2250

Depth (meters)

MB

T (

kg

/m3

be

nto

nit

e

eq

uiv

ale

nt)



have been identified related to a higher coefficient of friction, or hole angle. Twenty-eight per cent (28%) of SILDRIL experience had hole angles from 35º-65º, and sixteen per cent (16%) of the wells have been 35º-65º.

6 System Maintenance & Recommended Practices

6.1 Recommended treatment General inhibition is dependent on formation composition and chemistry. The SILDRIL System is designed to provide maximum chemical stabilization of the formation and cuttings in a water base fluid. Recommended treatment for a reactive “gumbo” shale (CECSHALE = 20-30 meq/100g) is significantly different to a low reactivity gas shale (CECSHALE = 2-5 meq/100g). The general recommendation for a highly reactive shale generally encountered in offshore North Sea or the Gulf of Mexico is 4-6% active silicate concentration which is equivalent to 8-10v/v% SILDRIL L (43-45% active). For a gas shale (example Marcellus or Fayetteville) the concentration of silicate required is significantly less, 1-3% active silicate.

A properly treated SILDRIL system will result in excellent cuttings integrity, gauge hole, and minimum dilution.

Two other major drilling parameters play an important role in determining the recommended treatment of silicate: Wellbore Geometry and Drilling rate. For a 17½” hole thr treatment requirement will be roughly twice the concentration required for a 12¼” hole. Similarly high rates of penetration will require an increased silicate concentration level.

These three factors must be included in the Drilling Fluid Program to ensure that proper execution of inhibition performance is obtained.

Shale compositional analysis provides useful information in the planning of the Drilling Fluid program. It can be used to provide the initial estimate for effective silicate treatment and maintenance.

Other factors which determine required silicate treatment are use of hole openers, backreaming, drilling anhydrite or formations with soluble divalent ions, and contamination with seawater or green cement.

6.2 Depletion rates Depletion rates are directly related to the operations reviewed in the previous section.

Formation reactivity

Wellbore Geometry

Rate of Penetration

Seawater or cement contamination

0

50

100

1 2 3 4 5 6 7 8

% S

ha

le R

ec

ove

ry

% Active Silicate with 10 ppb KCl

TYPICAL INHIBITION PERFORMANCE FOR A MODERATELT REACTIVE SHALE (CEC = 20-25meq/100g)



Calcium-bearing formations

Use of hole openers

Backreaming

To properly engineer the maintenance for a silicate system, the use of concentrated (2X) polymer/salt/silicate premixes are recommended. The silicate chemistry provides low dilution rates (1.25-2 times the volume of hole drilled) which is comparable to NAF fluids. As a result maintenance with the equivalent formulation of the fluid is not effective to maintain nominal system volume. The use of a concentrated premix is also an effective way to deal with contaminants and excessive depletion.

7 Contamination

7.1 Drill Solids The inhibition performance of the SILDRIL System contributes to optimum performance from the solids control equipment. Solids removal is enhanced as a consequence of the large inhibited cuttings that are generated with the inhibitive fluid, and the shear-thinning nature of the Xanthan rheology.

7.2 Cement Contamination Silicate depletes in the presence of calcium ions. It is, therefore, recommended to pre-treat the system prior to drilling out cement.

Soda ash (or potassium carbonate) is added to the SILDRIL mud prior to drilling out the cement. pH from the cement is not detrimental to the system and it is recommended not to use sodium bicarbonate or citric acid. The carbonate ion will compete with silicate, removing the calcium ion, minimizing SILDRIL depletion. Prior to drilling the next interval it will be necessary to restore the system to the required SILDRIL concentration correcting for silicate lost during cementing.

7.3 Seawater Seawater can be problematic engineering the SILDRIL system. The Ca++ and Mg++ ions will deplete active silicate from the system. Seawater will reduce the effective silicate concentration approximately 3-5 lb/bbl (9-15 kg/m3). If seawater is used, it is necessary to treat out the hardness with 0.5 lb/bbl NaOH or KOH and 1.0-2.0 lb/bbl soda ash or potassium carbonate.

It is preferable to make up the system with drill water. The drill water should be checked for hardness. Treat as required to remove hardness.

If SILDRIL volumes are pre-mixed onshore and transported offshore, boat tanks should be checked to ensure that the tanks do not contain any seawater or mud to contaminate the SILDRIL system.

7.4 Acid Gases The high pH and buffering capacity of a silicate fluid provides an excellent water base solution to drill formations where acid gas may be present.

7.5 Bacterial Degradation If the Sildril system is stored for any length of time, conventional treatment of M-I Cide is recommended, as for any conventional water-base polymer mud.



8 Corrosion Control Soluble silicates are economical, effective, and environmentally responsible chemicals which have been used for more than 70 years to protect metals from the corrosive effects of water. They are classified as corrosion inhibitors because they can deposit protective films onto various metal surfaces, isolating the metal from any further corrosive attack, and because they raise the water pH which can make it less corrosive to metals. Silicates do not contribute zinc or phosphorous to treated water.

Soluble sodium silicates are industrial corrosion inhibitors. Silicates reduce corrosion by adsorption onto a range of metallic and non-metallic surfaces. In the water industry, additions of silicate to potable water help prevent the corrosion of the distribution pipe network. Similarly, one of the functions of silicate in detergent formulations is to reduce the corrosion to machine parts and, in machine dishwashing, to ceramics, porcelain, and glassware.

9 Health and Safety Soluble silicates are well-established industrial chemicals that have been used in a variety of environmentally sensitive and health sensitive applications such as water treatment, soil remediation, and manufacturing of soaps. Silicates have been classified as GRAS or Generally Recognized As Safe by the FDA. It is the designation given to substances that are considered safe for direct or indirect additives to foods and in many industries is considered a blanket statement of the harmless and nontoxic nature of a substance. The main hazard associated with soluble silicates derives from their alkalinity. Both sodium and potassium silicate products can range from moderately to strongly alkaline. A similar level of safety and handling precautions should be exercised when working with silicates as with working with any other alkaline chemicals. Silicate may cause mild skin and eye irritation depending on the degree of alkalinity. It is recommended that personal protective equipment (PPE) and protective clothing be worn based on the degree of alkalinity handled. The inherent alkalinity of silicate drilling fluids has meant that biocides are generally not added to the drilling fluid. Furthermore, soluble silicates are established corrosion inhibitors thus eliminating the need to add corrosion inhibitors to the fluid. The removal of biocides and corrosion inhibitors contributes to a reduction in mud costs and complements the health safety and environmental benefits. Soluble silicates are odorless, inorganic chemicals that produce no unpleasant fumes or VOC emissions. Because of this, the silicate base fluid does not exhibit the distinctive odor associated with petroleum and synthetic drilling fluids. Silicate drilling fluids are also not as slick as oil muds. This helps reducing slipping and falling hazards on an operating rig. The non-flammable nature of silicates further reduces the safety concerns associated with somedrilling muds and makes silicate fluids less of a hazard to work with.

10 Engineering Guidelines

10.1 Hole Cleaning Recommendations Controlled ROP, optimum circulation rates, maximum pipe rotation, proper mud rheology – all these factors are critical to ensure effective and efficient drill solids removal from the wellbore in vertical and especially in high angle wellbores. In high performance inhibitive fluids, the engineering of solids removal becomes even more critical. Planning, monitoring, and engineering solids removal plays an important role in the success of the well. Virtual Hydraulics provides key information on the hydraulics and hole cleaning efficiency. Torque and drag monitoring is an important tool to diagnose the formation of cuttings beds in high angle wells. Visual observation at the shale shakers is the final key that provides an evaluation of the end result.



10.2 Wiper Trips The silicate fluid will provide a gauge hole and wiper trips may be required. The prudent use of wiper trips is important to facilitate cuttings transport and to ensure the caliper of the wellbore. This is especially important when using a stiff BHA. Monitor overpull on trips for indications of inadequate hole cleaning or tight hole. If overpull is a major problem, then consideration should also be given to a change in the BHA assembly

10.3 Circulating the Hole Clean prior to Trips Before pulling out of the hole it is critical to ensure that the cuttings have been efficiently removed from the wellbore. This is especially important because of the gauge wellbore and the larger cuttings typically obtained with silicate fluids. The circulation time can be determined based on hole cleaning algorithms, but the ultimate decision should be the observation at the shaker. If any over-pull is observed on a trip, it is recommended to trip 3 stands back in the hole and continue to circulate. This process should be repeated until overpull is acceptable and tripping can proceed. Backreaming is not recommended.

10.4 Torque and Drag Considerations The coefficient of friction of the silicate fluid is slightly higher than conventional water-base polymer fluids based on laboratory data. No field problems have been identified related to higher coefficient of friction. Field data based or torque versus depth curves also indicate that field lubricity is not a problem. M-I SWACO has several lubricant products for use in the silicate system when required. One of these products has been used on a horizontal well using SILDRIL with a resultant torque reduction in the field of 35%. An effective lubricant is an important consideration when planning for a high angle well. It is important to note that high angle wells, including horizontal wells, have been drilled with silicates without lubricant additives without any abnormal torque and drag. SIL-LUBE, SILDRIL EPL, DRIL-FREE, GLYDRIL MC, Finagreen SL (Radiagreen SL), and Black Fury have all been used successfully in the SILDRIL System.

10.5 Solids Maintenance Optimum solids removal and minimum system dilution are characteristic of the silicate fluid. It is important to ensure that the solids process system is designed and sized to obtain the benefits of the high performance inhibitive system. Rig equipment limitations (pump prcess rate and shaker process capacity) will dramatically limit the performance of the fluid.

The key to solids removal is the primary process equipment – the shale shaker system. An adequate number of high performance shale shakers to process the required flow rates and to handle the required rheology is essential for optimum removal performance of the system. With highly inhibitive water base fluids efficient removal of the solids at the shakers decreases the necessity for extensive downstream centrifuge equipment.

The combination of a high performance water base mud, efficient primary solids removal, and de-watering equipment provide the ultimate solution to minimize the environmental impact.

10.6 Cementing Silicate depletes in the presence of calcium ions. It is, therefore, recommended to pre-treat the system prior to drilling out cement.

SODA ASH (or potassium carbonate) is added to the SILDRIL mud prior to drilling out the cement. pH from the cement is not detrimental to the system and it is recommended not to use sodium bicarbonate or citric acid. The carbonate ion will compete with silicate, removing the calcium ion, minimizing SILDRIL depletion. Prior to drilling the next interval it will be necessary to restore the system to the required SILDRIL concentration correcting for silicate lost during cementing.

Cement spacers and procedures are the same as any non-dispersed polymer system. It is recommended to use large volume spacers to isolate the SILDRIL fluid from the cement to minimize depletion of SILDRIL during the cementing procedure. Drilling hard cement is not a problem. “Green” cement will deplete the silicate concentration but will not adversely affect the rheology; it may cause a slight increase in the fluid loss.



After completing the cement job, it will be necessary to restore the rheology and fluid-loss specification with the addition of DUO-VIS and FLO-TROL and/or PAC, respectively.

The gauge wellbore and the compatible chemistry provide the conditions for excellent cement bond logs.

10.7 Lost Circulation Lost circulation can be a problem for all fluid systems. The shear-thinning rheology of the SILDRIL system minimizes pressure losses and provides a minimum ECD for optimum hydraulics minimizing lost circulation risks. The rheology, annular velocity, pipe rotation, etc. must provide good cuttings transport to minimize risk, especially in high angle wells.

If lost circulation does occur, remedial loss circulation procedures are the same as any water-base mud system. Pre-mix blends of conventional materials and polymers plugs (FORM-A-BLOK, FORM-A-SET and FORM-A-PLUG) are compatible with SILDRIL.

Silicate products have been available as a lost circulation additive for over twenty years and the controlled chemistry of the SILDRIL system can minimize potential lost circulation risks/problems.

10.8 Bit Balling Bit balling is indicative of poor shale inhibition. The level of treatment is not adequate to properly prevent hydration of the shale and the solids are gummy and sticky and will adhere to bottom hole assemblies (stabilizers and tool joints) and bits with poor hydraulics. The solution is simply to increase the level of treatment with silicate or potassium ion or both.

10.9 Accretion Accretion can occur with high silicate concentrations if the hydraulics of the fluid is inadequate to prevent the solids from adhering to the BHA or bit. Increased flow and smaller nozzles provide improved hydraulics to alleviate accretion. Lubricants can also be used.

10.10 Formation Damage Concern over formation damage has been a major stumbling block in the more widespread use of silicate-base fluids. Silicates polymerize in the presence of salts and a lower pH - a process that depends on silicate concentration and ion type. The physical adsorption of the polymers to the formation surface raises the risk of blocking pore spaces, thus potentially reducing the rock permeability. Conversely, the highly inhibitive silicate fluid stabilizes clays, reduces swelling, clay hydration and fines migration.

Before any system can be used as a drill-in fluid, it is necessary to determine through laboratory tests the effect of the silicate chemistry on the production rock. The effect of silicate chemistry on filtrate and solids invasion into rock pore structure must be evaluated to determine potential formation damage.

It is recommended to use a particle size distribution of bridging solids in the drill-in fluid to match the highest rock permeability. This ensures proper bridging of the larger size pores, which are the main oil producers. OPTIBRIDGE can be used to provide the optimum particle size distribution. Also, during the drilling process both drill solids and calcium carbonate will be ground to the smaller size necessary to seal the smaller pore spaces.

Looking at the depth of mud invasion into pore space, the silicate fluid causes most of the damage in the first five millimeters of the core section. The shallow damage will be cleaned during the production process and, therefore will have negligible effect on production.

SILDRIL has been used successfully to drill the reservoir when the completion practice is to run casing and perforate. The characteristic shallow damage is an advantage of the silicate system.



10.11 Waste Management

10.12 Compatibility Issues with Logging Tools Ensure the logging tools have been dressed with the proper elastomers and seals as required. HNBR (Hydrogenated Nitrile Butadiene) elastomers are recommended for silicate environments. . Testing has shown that Viton will crack and split. It is therefore recommended that Viton seals are replaced whenever they are in contact with silicate fluids. Nitrile rubbers have been found to be the most resistant. However, it should be noted that there are a number of nitrile based compounds. For silicates a highly saturated nitrile is preferrred, although if abrasion resistance is also required a carboxylated nitrile may more suitable.

In the field, and from experience, the inspection frequency may also need to be increased as an integral component of any preventative maintenance program. Silicate fluids tend to precipitate (due to water evaporation) and become attached to metal parts. Silicates are industrial corrosion inhibitors. After use the tools must be thoroughly flushed with fresh water. Sea water or hard water must not be used to wash the tools.

10.13 Mud Logging and Lithology Interpretation One of the primary advantages of the SILDRIL system is improved lithology interpretation. Operators have been able to better define formations because of the improvement in cuttings integrity.

10.14 System Limitations The SILDRIL system is limited to densities less than 14.0 ppg. This is due to the fact that the silicate component and the barite both compete for the free water in the system. Dense fluids will require higher dilution rates to maintain manageable viscosities. The silicate concentration can also be decreased at the higher density to help maintain fluid properties. SILDRIL is a non-dispersed inhibitive system and the use of deflocculants is not an option.

10.15 Logistics An adequate inventory of silicate is essential. Because silicate is used up in the drilling process and whole mud losses can occur from poor solids removal equipment or potential lost circulation, it is important to have inventory both onshore and offshore. The silicate system is especially useful to control shale and wellbore stability in the 17½,“ and 16” intervals. Large volumes are required to maintain these hole sections and the use of concentrated premixes (mixed onshore) minimize handling and mixing requirements on the rig. SILDRIL is also excellent for drilling troublesome 12¼” intervals but logistics in the smaller hole sections is not as critical.

10.16 SILDRIL Application at Higher Temperatures to 350ºF SILDRIL has been used on numerous wells at temperatures from 250º-350ºF. Design of these fluids requires formulation with high temperature polymers such as GLYDRIL MC, RESINEX, DURALON, and CALOVIS FL. Formulations for a high temperature application must be rigorously laboratory tested to ensure field engineering performance. Dilution rates for high temperature applications will be higher than the conventional applications. Excellent solids maintenance is mandatory for good performance.

11 Ten Key Issues that are Crucial when using a SILDRIL Fluid

11.1 MUD WEIGHT The mud weight is a key design parameter. The mud weight must be adequate to compensate for the pore pressure and the mechanical wellbore stability. This is particularly critical in high angle wells or in areas where tectonic stress is a key factor.



11.2 HOLE CLEANING – MUD RHEOLOGY Proper rheology is extremely important. The system uses biopolymers to provide optimum low-shear-rate-viscosity (LSRV) for superior hole cleaning, wellbore stability and optimum hydraulics. The inhibitive, non-dispersed silicate fluid maintains the integrity of the cuttings and the LSRV values are maintained higher than conventional polymer fluids to provide adequate hole cleaning performance. Elevated flat, fragile gel strengths are important to ensure suspension of solids. Proper rheology is even more critical in high angle wells to prevent the formation of cuttings beds and the degradation of the large, inhibited cuttings. The use of high density-viscous sweeps should only be used to ensure adequate hole cleaning; proper rheology is the key to efficient solids removal.

11.3 HOLE CLEANING - DRILLING PRACTICES Controlled ROP, maximum circulation rates, maximum pipe rotation, and LSRV mud rheology – all of these factors are critical to ensure drill solids removal from the wellbore in vertical and especially in a high angle wellbore. This is critical because of the improved cuttings integrity.

11.4 WIPER TRIPS The silicate fluid will provide a gauge hole and, therefore, it is important to utilize wiper trips. The prudent use of wiper trips is important to facilitate cuttings transport and to ensure the calliper of the wellbore. This is especially important when using a stiff BHA. Monitor over-pull on trips for indications of inadequate hole cleaning or tight hole. If over-pull is a major problem, then consideration should also be given to a change in the BHA assembly.

11.5 SILICATE CONCENTRATION It is important to ensure that the silicate concentration is maintained during drilling. The silicate concentration, pH, Pm, and Pf are all closely monitored to ensure an adequate silicate concentration for optimum inhibition. Because silicate inhibition is a sacrificial process, maintenance of the silicate concentration is a key to optimizing inhibition. Silicate depletion is accelerated with the introduction of divalent ions (calcium and magnesium). The use of seawater during drilling is not recommended (for example, to clean the shaker screens). If seawater is used to build volume the calcium and magnesium ions should be treated out prior to mixing with the silicate. The divalent ions precipitate the silicate and increase the maintenance requirement for silicate. The silicate does not adversely affect the rheology. If concentrated premixes are mixed onshore, then the mud should be checked at the plant and at the rig to ensure that the transport tanks are not contaminated with seawater. It is important to handle the fluid as if it is an OBM to ensure no contamination occurs during transport. If anhydrite or calcium or magnesium formations are encountered during drilling then additional silicate will be required to maintain the system; if massive anhydrite is encountered then the system should be converted to a conventional polymer fluid. After drilling cement it will be necessary to replenish silicate removed by calcium ion from the cement.

11.6 CIRCULATING THE HOLE CLEAN PRIOR TO TRIPS. Before pulling out of the hole it is critical to remove all the cuttings from the wellbore. This is especially important because of the gauge wellbore and larger cuttings typically obtained with silicate fluids. The circulation time can be determined based on hole cleaning algorithms, but the ultimate observation is at the shaker. If any over-pull is observed on a trip, then additional circulation time and/or wiper trips are recommended.

11.7 SOLIDS CONTROL Optimum solids removal and minimum system dilution are characteristic of the silicate fluid. It is important to ensure that the solids removal system is properly designed and sized to ensure optimum performance. The key with regard to solids removal is the primary solids removal equipment – the shale shaker system. An adequate number of high performance shale shakers to process the required flow rates and to handle the required rheology is mandatory. The minimum dilution requirements of the silicate system make it the number one choice when logistics and environmental discharge are a primary concern.



11.8 LOGISTICS An adequate inventory of silicate is essential. Because silicate is used up in the drilling process and whole mud losses can occur from poor solids removal equipment or potential lost circulation, it is important to have inventory both onshore and offshore. The use of premixes is also important to the successful offshore application of the silicate system. The silicate system is especially useful to control shale and wellbore stability in the 17½“ and 16” intervals. Large volumes are required to maintain these hole sections and the use of concentrated premixes (mixed onshore) minimize handling and mixing requirements on the rig.

11.9 SILICATE SYSTEM DESIGN – SILDRIL SILDRIL uses a unique “2.6” silicate to provide optimized inhibition performance. SILDRIL is maintained based on the silicate concentration analysis. A decrease in pH is indicative of silicate ion depletion and SILDRIL addition is necessitated. Caustic is not used to control the pH. Biopolymers are used to control the rheology profile and PAC (preferably UL and ELV) and/or starch polymers are used to control fluid loss. Bentonite is not recommended to control rheology or filtration properties.

11.10 LUBRICITY The coefficient of friction of the silicate fluid is slightly higher than conventional water-base polymer fluids based on laboratory data. No field problems have been identified related to higher coefficient of friction. It is important to note that conventional lubricants are ineffective in silicate systems. M-I has two alternative lubricant products for use in the silicate system when required. One of these products has been used on a horizontal well using SILDRIL with a resultant torque reduction in the field of 35%. An effective lubricant is an important consideration when planning for a high angle well. It is important to note that high angle wells, Including horizontal wells, have been drilled with silicates without lubricant without any abnormal torque and drag.

12 Technical Support Any questions regarding product usage and treatment fo the xxx system should be directed to the Project Engineer or Technical Services in Houston:

Name Stan Alford Title Global Senior Technical Service Engineer [email protected] +1 281 919- 5141

Name Steve Smith Title Global Senior Technical Service Engineer [email protected] +1 281 433-5318

Name Arne Asko Title Technical Service Manager Eastern Hemisphere [email protected] +1 123 456 7891

mailto:[email protected]





13 Appendicies

References

1. Wingrave, J.A., Kubena, E., Jr., Douty, C.F., Whitfill, D.L. and Cords, D.P.: “New

Chemical Package Produces an Improved Shale Inhibitive Water-Based Drilling

Fluid System,” SPE 16687, 1987 SPE Technical Conference, Dallas, Sept 27-30, 1987.

2. Alford, S.: “North Sea Field Application of an Environmentally Responsible Water-

Base Shale Stabilizing System,” SPE/IADC 21936, 1991 SPE/IADC Drilling Conference, Amsterdam, Mar 11-14, 1991.

3. van Oort, E., Ripley, D., Ward, I., Chapman, J., Williamson, R. and Aston, M.: “Silicate-Based Drilling Fluids: Competent, Cost-Effective and Benign Solutions to

Wellbore Stability Problems,” SPE/IADC 35059, 1996 SPE/IADC Drilling Conference, New Orleans, Mar 12-15, 1996.

4. Bailey, L., Craster, B., Sawdon, C., Brady, M. and Cliffe, S.: “New Insight into the Mechanisms of Shale Inhibition Using Water Based Silicate Drilling Fluids,”

SPE/IADC 39401, 1996 SPE/IADC Drilling Conference, Dallas, Mar 3-6, 1996.

5. Alford, S., Dzialowski, A., Jiang, P. and Ullmann, H.: “Research into Lubricity, Formation Damage Promises to Expand Applications for Silicate Drilling Fluids,”

SPE/IADC 67737, 2001 SPE/IADC Drilling Conference, Amsterdam, Feb 27 – Mar 1,

2001.

6. Sorić, T., Marinescu, P., and Huelke R.: “Silicate-Based Drilling Fluids Deliver Optimum Shale Inhibition and Wellbore Stability,” SPE/IADC 87133, 2004 SPE/IADC

Drilling Technology Conference, Dallas, Mar 2-4, 2004.

7. Essawy, W., Hamzah, R., Malik, M.M., Knox, D., Monem, M. and Oswald, R.: “Novel Application of Sodium Silicate Fluids Achieves Significant Improvement of the

Drilling Efficiency and Reduce the Overall Well Costs by Resolving Borehole Stability Problems in East Africa Shale,” SPE/IADC 88008, 2004 Asia Pacific Drilling

Technology Conference, Kuala Lumpur, Sept 13-15, 2004.

8. Aston, M.S., Alberty, M.W., McLean, M.R., de Jong, H.J. and Armagost, K.: “Drilling

Fluids for Wellbore Strengthening,” IADC/SPE 87130, 2004 IADC/SPE Drilling

Conference, Dallas, Mar 2-4, 2004.



9. 11. Alford, S. E., Aston, M., Asko, A., Campbell, M., Kvalvaag, E., “Silicate-Based Fluid, Mud Recovery System Combine to Stabilize Surface Formations of Azeri

Wells,” SPE/IADC 92769, 2005 SPE Annual Technical Conference, Amsterdam, The Netherlands, 23-25 February 2005.

10. McDonald, M., Barr, K., Dubberley, S. R., and Wadsworth, G. “Use of Silicate-Based Fluids to Mitigate Metal Corrosion,” 2007 SPE International Symposium On Oilfield

Chemistry, Houston, Texas, Feb. 28-Mar. 2, 2007.

11. Alford, S. E., Asko, A., Stave, R., Aston, M. S., Kvalvaag. E., “Riserless Mud Recovery System and High Performance Inhibitive Fluid Successfully Stabilize West Azeri Surface Formation,” 2005 Offshore Mediterranean Conference, March 16-18.

12. McDonald, M., Reifsnyder, R., Sidorkiewicz, V., and LaPlant, D., “Silicate Based Drilling Fluids: A Highly Inhibitive Mud System Offering HS&E Benefits Over Traditional Oil Based Muds,” AADE-02-DFWM-HO-29, AADE 2002 Technology Conference, April 2-3, 2002, Houston, Texas.

13. Boyd, J. P., McGinness, T., Galal, M., and Bruton, J., “Sodium Silicate Fluids Improve Drilling

Efficiency and Reduce Costs by Resolving Borehole Stability Problems in the Atoka Shale, AADE-02-DFWM-HO-35, AADE 2002 Technology Conference, April 2-3, 2002, Houston, Texas.

14. Oswald, R., Iskander, G., Monem, M. R., Chaudry, I., “Design and Application of World’s First

High Temperature Silicate Mud System for Highly Reactive Ranikot Shales in Sawan Field,” SPE Paper for Pakistan Conference.

15. Ward, I., Chapman, J. W., Williamson, R., “Silicate Based Muds: Chemical Optimisation Based on Field Experience,” SPE 37266, 1997 SPE International Symposium On Oilfield Chemistry, Houston, Texas, Feb. 18-21, 1997.

16. Schlemmer, R, Friedheim, Growcock, F. B., Bloys, J. B., and Polnaszek, S., “Membrane Efficiency in Shale – An Empirical Evaluation of Drilling Fluid

Chemistries and Implications for Fluid Design,” IADC/SPE 74557, 2002 SPE Drilling

Conference, Dallas, Texas, 26-28 February 2002.

Best Practices SILDRIL.pdf

Documents

Transcript of Best Practices SILDRIL.pdf