Influence of the deep petroleum transformation on the CO2 budget of the atmosphere

Influence of the deep petroleum transformation on the CO2 budget of the atmosphere Aleksandr Y. Serovaiskii Doctoral Thesis 2018 KTH Royal Institute of Technology School of Industrial Engineering and Management Department of Energy Technology SE-100 44 Stockholm, Sweden

ISBN 978-91-7729-811-3 TRITA-ITM-AVL 2018:21 © Aleksandr Serovaiskii Stockholm 2018 [email protected] Academic thesis, which with the approval of Royal Institute of Technology (KTH), will be presented in fulfilment of the requirements for the Degree of Doctor of Philosophy, Public defence is in Room Brinellsalen, at KTH Royal Institute of Technology, Stockholm, at 13:00, on the 14th of June 2018.

Doctoral Thesis by Aleksandr Y. Serovaiskii | ii

Abstract Petroleum is an important component of the Earth’s crust and a necessary agent in human life. Due to fossil fuels usage in human activities, the carbon dioxide budget of the atmosphere is growing on the 4-5 GtC/year. However, could CO2 be generated from the “natural burning” of petroleum, resulting from the involvement of petroleum in subduction? During subduction, petroleum deposits, accumulated in the subducting slab, submerge down to the mantle and occur in the area with the extreme thermobaric conditions. As a result, hydrocarbons undergo high temperature and pressure and can be transformed into the oxidized form of carbon (such as CO2 and carbonates).

The purpose of the present study is to investigate the role of petroleum in the deep processes of the Earth and explore, whether there is any influence from these processes on the carbon dioxide budget of the atmosphere.

In the current thesis, the results of the experimental work are presented, which model the behavior of the petroleum hydrocarbons in the thermobaric conditions and surrounding environment of the lower part of the Earth's crust and upper mantle in the depth range of 20-300 km (320-2,000 °C, 0.7-9.5 GPa). High-pressure, high-temperature experiments were carried out, using diamond anvil cells and a Toroid-type large reactive volume unit. The stability and possible transformations of hydrocarbon systems at the presence of slab and mantle surrounding, and fate of carbon, submerged down into the Earth's interiors in the form of hydrocarbon during subduction, was investigated.

The obtained experimental results demonstrate the chemical transformation of petroleum during subduction. It was discovered, that CO2 was not formed from hydrocarbons during subduction. Hydrocarbons could react with the surrounding mantle and slab and transform into more sustainable compounds at thermobaric and Redox conditions, corresponding with the Earth’s deep interior. However, this process does not have any significant influence on the carbon dioxide budget of the atmosphere.

Keywords Petroleum, hydrocarbons, carbon dioxide, subduction, the upper mantle, the Earth’s crust, Redox, high pressure, high temperature, toroid-type large reactive volume unit, diamond anvil cells, chromatography, Raman spectroscopy, Mössbauer spectroscopy.

Doctoral Thesis by Aleksandr Y. Serovaiskii | iv

Preface The present thesis is devoted to the transformation of

hydrocarbon systems during subduction. This thesis is divided into four chapters. The introduction provides a brief overview of the current

investigation dealing with the global carbon cycle, the carbon dioxide budget of the atmosphere, subduction as a part of the deep carbon cycle, and the petroleum implication in the subduction. The main purpose and the research questions of the current investigation are also presented in Chapter 1.

Chapter 2 explains the choice of the high-pressure high-temperature methods used in the work and describes in detail the experimental procedure that was performed, including a discussion on the complications with the Raman spectroscopy analysis of hydrocarbon mixtures.

Chapter 3 presents the experimental investigation of the complex hydrocarbon mixture behavior under the Earth’s crust thermobaric conditions and in the oxidative surrounding. The chapter focuses on the crustal depth range of the possible petroleum accumulations occurrence by modeling relevant pressure and temperature.

Chapter 4 describes the transformation of petroleum during subduction. The influence of the hydrocarbon systems transformation on the CO2 budget of the atmosphere was investigated by modeling the chemical behavior of hydrocarbon systems in the thermobaric conditions and surrounding, corresponding to the deep interior. A hypothesis about the possible transformation of petroleum into CO2 during subduction was tested experimentally.

Doctoral Thesis by Aleksandr Y. Serovaiskii | vi

Acknowledgements

First, I would like to express my the greatest gratitude to my main supervisor, Professor Vladimir Kutcherov, who provided me with the opportunity to study at KTH, who supported and encouraged my studying and always helped with any kind of the encountered problem.

Thanks to him, I got great scientific experience and broadened my knowledge in many fields of science. I am sincerely grateful to my supervisor for his motivation and inspiration. I am sure that I made my decision to become a scientist becoming acquainted with Professor Kutcherov.

I am thankful to all my project colleagues, Anton, Elena and Daniil, who spent a lot of their time helping me with the experimental procedures.

I thank the physics department at Gubkin University, Moscow, Russia, where the main part of my experiments was carried out. Special thanks to Professor Aleksey Chernoutsan, for his help and support.

Many thanks to my colleagues from BGI Bayerisches Geoinstitut, Bayreuth, Germany, and especially to Leonid Dubrovinsky, for providing me with an opportunity to obtain great experience in high-pressure research and work with such a high-skilled team.

I would like to express my sincere gratitude to my parents and friends, who supported and motivated me during the entire period of my studying. Special thanks are to my mother and father for their constant belief in me.

Finally, I would like to express my heartfelt gratitude to my fiancée Elizaveta for her permanent support and encouragement during the entire period of my studying

Financial support was granted by Russian Global Education Program (GEP) and Sloan Foundation through the Deep Carbon Observatory.

Stockholm, June 2018 Aleksandr Yu. Serovaiskii

Doctoral Thesis by Aleksandr Y. Serovaiskii | viii

List of appended papers Paper A A. Serovaiskii, E. Mukhina, L. Dubrovinsky, A. Kolesnikov, C. McCammon, G. Aprillis, I. Kupenko, A. Chumakov, M. Hanfland and V. Kutcherov Fate of hydrocarbons in iron-bearing mineral environments during subduction, Geology, submitted. Paper B A. Serovaiskii, A. Kolesnikov, V. Kutcherov, Formation of complex hydrocarbon systems from methane at upper mantle thermobaric conditions, Organic Geochemistry, submitted Paper C A. Serovaiskii, A. Kolesnikov, L. Dubrovinky, V. Kutcherov, Stability of a petroleum-like hydrocarbon mixture at thermobaric conditions that correspond to depths of 50 km, Scientific Reports, accepted Paper D A.Yu. Serovaiskii, A.Yu. Kolesnikov, E.D. Mukhina, V.G. Kutcherov, The photochemical reaction of hydrocarbons under extreme thermobaric conditions, Journal of Physics: Conf. Series, 950 (042056), 2017, doi :10.1088/1742-6596/950/4/042056

Related publications V.G. Kutcherov, A.Yu. Kolesnikov, E.D. Mukhina, A.Yu.

Serovaisky, Teaching aid “High-pressure high-temperature experimental studies”, Gubkin Russian State University of Oil and Gas (National Research University), 2016;

D. Kudryavtsev, A. Serovaiskii, E. Mukhina, A. Kolesnikov, B.

Gasharova, V. Kutcherov, L. S. Dubrovinsky, Raman and IR Spectroscopy Studies on Propane at Pressures of Up to 40 GPa, The Journal of Physical Chemistry A, 121 (32), 2017, doi: 10.1021/acs.jpca.7b05492

A. Serovaiskii, A. Kolesnikov, V. Kutcherov, Formation iron

hydride and iron carbide from petroleum under ultra-high thermobaric conditions, Geochemistry International, submitted

Doctoral Thesis by Aleksandr Y. Serovaiskii | x

Authors’ contributions The main purpose and the research questions of the manuscript were developed by Aleksandr Serovaiskii under the guidance of the main supervisor associate Professor Vladimir Kutcherov. A. Serovaiskii carried out all experiments and data analysis described in the present thesis. A. Serovaiskii wrote all texts for all appended papers, and as the corresponding author for all the papers, prepared and revised the texts for publication after the co-authors’ advise and comments.

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Definition of critical terms and nomenclature Petroleum – a complex mixture of naturally occurring hydrocarbon compounds found in rock. Petroleum can range from solid to gas, but the term is generally used to refer to liquid crude oil. Subduction – occurs along a tectonic boundary, where one tectonic plate sinks under an opposite one into the Earth’s mantle. Part of the plate sunk into the mantle is a subducting slab. Redox conditions – conditions, specified by the tendency of the environment to be oxidized or reduced. pT parameters, thermobaric conditions – pressure (GPa) and temperature (°C) List of abbreviations DAC – diamond anvil cell LRV – large reactive volume FID – flame ionization detector C – carbon CO2 – carbon dioxide CH4 – methane Fe2O3 – iron oxide (III) FeHx – variety of iron hydrides with different chemical structure. Fe7C3, Fe3C, Fe5C2 – crystal modifications of iron carbide. fcc - face-centered cubic phase fO2 – oxygen fugacity List of notations V – volume m – mass ρ – density M – molar mass n – amount of substance P – pressure T – temperature 2θ – diffraction angle

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Content Abstract........................................................................................ ii

Preface ........................................................................................ iv

Acknowledgements .................................................................... vi

List of appended papers .......................................................... viii

Authors’ contributions ................................................................ x

Definition of critical terms and nomenclature ......................... xii

Content...................................................................................... xiv

Chapter 1. Introduction ............................................................... 1

1.1. Distribution of Carbon in the Earth ...................................... 1

1.2. Carbon dioxide budget of the atmosphere ........................... 2

1.3. Subduction as a part the Deep carbon cycle ....................... 6

1.4. The main purpose, the research questions and the structure

of the dissertation ...................................................................... 9

Chapter 2. Methodology of the experimental study of

hydrocarbons under extreme thermobaric conditions. .......... 11

2.1. High-pressure experimental techniques ............................ 11

2.2. Diamond anvil cells ........................................................... 14

2.2.1. Experiments with the synthetic petroleum ................... 14

2.2.2. Raman spectroscopy application in DAC experiments

with complex hydrocarbon systems ...................................... 17

2.2.3. Modeling of the hydrocarbons-iron bearing minerals

interaction during subduction ................................................ 18

2.2.4. Mössbauer spectroscopy analysis of the reaction

products ............................................................................... 19

2.3. Toroid-type LRV unit ......................................................... 21

2.3.1. Calibration of the Toroid-type LRV unit ....................... 22

xv | Doctoral Thesis by Aleksandr Y. Serovaiskii

2.3.2. Investigation of the C-O-H fluid under the thermobaric

conditions, corresponding to upper mantle, using the Toroid-

type Large Reaction Volume unit ......................................... 25

2.3.3. Gas chromatography analysis of the gaseous product 26

2.3.4. Raman spectroscopy analysis of the solid products ... 27

Chapter 3. Petroleum in the lower part of the Earth’s crust. . 28

3.1. Thermal stability of the model hydrocarbon system. ......... 28

3.2. Oxidative resistance of the hydrocarbon system at the

Earth’s crust thermobaric conditions. ....................................... 31

3.3. Impact to the concept of the abiogenic deep genesis of

hydrocarbons .......................................................................... 34

Chapter 4. Contribution of hydrocarbons in the subduction

and its influence on the CO2 budget of the atmosphere ........ 36

4.1. Chemical transformations of hydrocarbons during

subduction. .............................................................................. 36

4.2. Behavior of methane under the thermobaric conditions,

corresponding to upper mantle. ............................................... 41

4.3. The role of petroleum in the processes in the Earth’s

mantle. .................................................................................... 48

Chapter 5. Conclusions and future work ................................ 51

Chapter 6. Summary of appended papers .............................. 54

References .............................................................................. 56

Doctoral Thesis by Aleksandr Y. Serovaiskii | 1

Chapter 1. Introduction The present thesis is aimed at investigating the transformation of petroleum during the subduction and to examine the possible influence of this process on the carbon dioxide emissions to the atmosphere. The description of the global carbon cycle and the subduction is presented in the introduction. The emphasis is placed on the CO2 budget in the atmosphere and the possible influence of the Earth’s interior processes on the amount of CO2 in the atmosphere. The main part of the dissertation focuses on the modeling of petroleum transformation in the abyssal processes and aims to determine the possible contribution to the atmospheric carbon dioxide budget.

1.1. Distribution of Carbon in the Earth Carbon is the sixth element in the Mendeleev’ periodic table,

and its importance for the life on the Earth is known since antiquity. Carbon is an abundant element in the Universe (the fourth by mass after hydrogen, helium, and oxygen), and it is the essential part of every living thing on our planet. Due to its atomic structure, carbon possesses unique physical and chemical properties, that leads to the ability to form different substances, which can exist in a wide range of pressures and temperatures.

A significant part of the Earth's carbon is stored in the core (20-80*1023 g of C 1) in the form of metal carbides, mostly Fe and Ni. This carbon is isolated and it is not connected with the surface of the Earth and the Earth’s atmosphere. The amount of carbon in the mantle varies according to the depth. It concentration can reach 0.5% (0.8-12.5*1023 g of C 1). Carbon in the mantle is presented in the form of carbonates, carbides, pure carbon (diamond and crystalline graphite), and light hydrocarbons (mostly methane). In the crust the main forms of carbon are carbonates, and a wide variety of hydrocarbons exist in petroleum deposits and organic substances. The mass of the remaining hydrocarbons, which can still be extracted and burned is not precisely known, however, it is 5–10 times bigger than the current amount of carbon in the atmosphere.


1.2. Carbon dioxide budget of the atmosphere Carbon substances occurring in the atmosphere (mostly

carbon dioxide and methane) are connected to the surface processes through the global carbon cycle. The global (short-term) carbon cycle is a complex of processes that lead to the carbon interchange between the carbon storages in the Earth’s atmosphere, the terrestrial biosphere and the global ocean.

Almost all organisms on the Earth absorb oxygen during breathing and release carbon dioxide (CO2) as a product of their life. During photosynthesis terrestrial and marine plants absorb CO2 and produce carbohydrates, emitting O2 in the atmosphere (1.1). CO2 reacts with water under the ultraviolet light of the sun due to chlorophyll in terrestrial and water-inhabiting plants. Thanks to this process the amount of CO2 in the atmosphere decreases and the amount of O2 increases; this process leads to the availability of a balanced composition of the atmosphere.

(1.1)

Global carbon cycle has been altered significantly during the

lifetime of the Earth. The concentration of carbon substances in the atmosphere storages has not been constant. Comparing the present concentration of carbon dioxide in the atmosphere with its concentration 420,000 years ago (which has been calculated, using ice record data 2), it was found that the concentration of CO2 is 100 ppm higher in the present-day atmosphere 3.

The investigation of the carbon dioxide budget of the atmosphere became an important topic when scientists realized the increasing amount of CO2 (Figure 1.1) in the atmosphere, its possible connection to the anthropogenic activities 4 and its influence on the global climate change 5. During the last 70 years the amount of CO2 in the atmosphere has grown drastically (from 320 ppm in 1960 to 408 ppm in 2018, Figure 1.2 6). Scientific knowledge about the global carbon cycle increased, especially by the investigation and quantification of the terrestrial processes, connected to the anthropogenic activity. The industrialization, in particular, has led to the misbalance between the CO2 emission to the atmosphere and


absorption of the atmospheric CO2 by the surface. It is strongly considered that due to human activity (mostly by burning fossil fuels and cement production, but also from deforestation and other land-use-changing activities 7) the atmospheric carbon amount increases annually by 4.4±0.1 GtC/year (Figure 1.3 8).

Figure 1.1. The atmospheric CO2 growth rate (a); CO2 emissions from

human activity (b) 4.


Figure 1.2. Surface average atmospheric CO2 concentration by Mauna

Loa Laboratory, from 1960 to 2018 6. The red curve - the carbon dioxide data, measured as the mole fraction in dry air; the black curve represents the seasonally corrected data.


Figure 1.3. The representative scheme of the disproportion of the

global (short-term) carbon cycle caused by anthropogenic activities 8. The arrows demonstrate emissions from fossil fuels and industry and the absorption of carbon by the ocean and land reservoirs. All data are in units of GtC year-1.

The main upstream and downstream flows of carbon with the quantitative estimations are presented in Figure 1.3. Today approximately 9 Gt/year are emitted into the atmosphere from fossil fuel consumption and cement manufacturing. Part of these emissions is absorbed by plants and oceans, and another part is accumulated in the atmosphere. The amount of the remaining carbon dioxide in the atmosphere is about 4-5 Gt/year.


However, it might be one more source of carbon dioxide in the Earth’s interior. This source is connected to the subduction of the lithosphere plates.

1.3. Subduction as a part the Deep carbon cycle The Deep Carbon Cycle (or Long-term Global Carbon cycle) is

connected to the cycling of carbon from the mantle to the atmosphere and the Earth’s crust and, on the contrary, from the atmosphere and the crust into the mantle 9. It is mostly caused by the constant movement of the lithosphere plates. The main reason for this process is the transportation of heat from the central part of the Earth by very viscous magma. The downstream of carbon in the deep carbon cycle appears due to subduction when the oceanic plate is submerging under the continental plate. Ultimately, the upstream of this cycle is connected to volcanism and metamorphic outgassing to the atmosphere, when mostly carbon dioxide is realized to the atmosphere 10.

During subduction all carbon in the form of carbonates 11, 12, organic material of sediments 13, graphite 11 submerges into the mantle – the area with extremely high pressure and temperature. This flux is estimated to 2.4-6.6*1013 g of C per year (Figure 1.4) 1, 14. During this process carbon from the subducting slab gets into the mantle and develops into CO2 and CH4 fluids or gas 15, 16, diamond 13,

17, or carbonated silicate melts 15. The total budget of the Earth’s crust is estimated as 1.4*1022 g of C, the total budget of upper mantle is 0.8-12.5*1023 g of C 1. The subsequent fate of the submerged carbon can be the following: by convection flows in the mantle these carbon substances can be transported to the mantle-crust boundary and through arch volcanos and degassing it is released into the atmosphere in the form of CO2 and methane. Part of this carbon flux is accumulated in the lithospheric plate. The estimation of the carbon upstream is 1.4-6.6*1013 g of C per year (Figure 1.4). During the lifetime period of the Earth existence, subduction processes potentially could transfer the entire carbon from the surface to the Earth’s interior 9, 18, 19.


Figure 1.4. Major fluxes of carbon in the Earth’s interior, enrolled in the

Deep carbon cycle (adopted from 20). Data in parentheses are given from 1.

The role of carbonates and organic carbon, their concentration, solubility in the mantle at different depths, phase transitions at various thermobaric conditions have been well estimated during the last ten years 21-23. However, petroleum as a carbon-containing material within subducting slabs was not really considered to take part in subduction in particular, or in the entire deep carbon cycle in general. However, hydrocarbons may not only occur in the Earth’s crust but also in the entire depth range of the mantle up to the mantle-core boundary 24. Petroleum components were detected as inclusions in diamonds and igneous rocks 25, that also demonstrates their occurrence in the mantle.

Numerous giant petroleum deposits are located close to subduction zones 26, and there is no reason to exclude the hydrocarbons involvement in subduction (Figure 1.5). In the case of subducting organic sediments and carbonates carbon dioxide is considered to be the major gaseous product (together with carbonates, melted in the mantle) 10. The most oxidized form of carbon (CO2 or carbonates) is the preliminary state in the upper mantle due to its Redox characteristics. 27.


Figure 1.5. Petroleum fields (red circles), located close to subduction

zones.

Therefore, during subduction petroleum hydrocarbons may chemically behave in a similar way and be transformed into carbon dioxide too. The Earth’s interior could behave as the so-called “the natural furnace”, consuming and burning fossil fuels by itself and transforming them into CO2. According to this hypothesis, the behavior of hydrocarbons in the subduction slab and under thermobaric conditions, corresponding to the mantle, is of great interest.

There is no accurate information of the real amount of petroleum in the Earth’s crust. Petroleum geologists discover new petroleum deposits all over the world. Moreover, during the last several decades, several giant ultradeep petroleum deposits have been discovered in the various petroleum regions 25, 28. These deposits occur deeper than the main zone of the petroleum generation, the so-called the “oil window” – the depth limit down to 6-8 km 29-31. Due to the depth, the reservoir pressure of such deep deposits should be higher, and the reserves of these deposits may be huge. Therefore, the amount of petroleum, submerged down to the mantle during subduction, is not estimated, but potentially it may be enormous.

A decline of the world petroleum consumption is considered in the near future due to high prices, ecological reasons and the development of sustainable energy 32. Due to significant emissions


of carbon dioxide to the atmosphere, human society does it best to decrease the consumption of fossil fuels and replacing them with environmentally friendly energy sources, such as solar and wind energy. However, even if the fossil fuels consumption decrease, petroleum reservoirs will be kept in the Earth’s crust and potentially they may be “burned” naturally in the Earth’s interior during subduction.

To summarize, petroleum as the present-day major source of energy on the Earth plays a significant role in the global short-term carbon cycle and its contribution to the global climate change causes no doubt. Fossil fuel consumption by human society drastically increases the CO2 budget in the atmosphere. However, there may be another one fossil fuel consumer, the so-called “natural furnace”, which constantly has been transforming petroleum into CO2 during subduction since the formation of the Earth.

Therefore, the volume of petroleum in the crust may be highly underestimated, since petroleum, accumulated in the subducting slab, submerges down to the mantle during subduction, it can potentially be transformed into CO2. This contribution to the atmosphere budget of carbon dioxide may be significant.

The understanding of the petroleum transformation during subduction and its potential role in the deep processes of the Earth may provide detailed information about its possible influence on the global short-term carbon cycle and the atmosphere budget of CO2.

1.4. The main purpose, the research questions and

the structure of the dissertation The main purpose of this study is to investigate the

transformation of petroleum hydrocarbons during subduction experimentally, as well as to answer the question how this process may influence the carbon dioxide budget in the atmosphere. In particular, the present thesis is devoted to the investigation of the possible CO2 formation from petroleum hydrocarbons during subduction, that potentially may have an essential impact on the atmosphere budget of carbon dioxide.

The dissertation is designed to cover this purpose through the following research questions:

Research question group 1: The methodology of the high- pressure high-temperature research. What are the main techniques


for the high- pressure high-temperature experiments? What are the main benefits, drawbacks, and limitations of the techniques?

Chapter 2, appended Paper D and the Methods part of appended Papers A and B are focused on these research questions.

Research question group 2: What is the thermobaric limit of the existence of hydrocarbons in the Earth’s crust? According to the Earth’s crust pressure and temperature, how deep may petroleum deposits occur in the Earth’s crust? How should the known experimental techniques be improved to answer these questions?

Chapter 3 and the appended Papers С and D are devoted to answering these research questions.

Research question group 3: What happens with petroleum during subduction? Do hydrocarbons transform into CO2 in Redox and thermobaric conditions of the subducting slab and the upper mantle?

Paragraph 4.1 of Chapter 4 and the appended Paper A are devoted to answering these research questions.

Research questions group 4: Does CH4 transform into CO2 in the C-O-H fluid under upper mantle thermobaric conditions? What other hydrocarbons can also exist in the C-O-H fluid under upper mantle thermobaric conditions? How does temperature influence on the composition of hydrocarbon systems in the C-O-H fluid?

Paragraph 4.2 of Chapter 4 and the appended Paper B aim to answer these research questions.


Chapter 2. Methodology of the experimental study of hydrocarbons under extreme thermobaric conditions.

The current investigation is based on the complex experimental work; two different high-pressure techniques were involved in the research – diamond anvil cells and Toroid-type Large Reactive Volume unit. The experiments included all the required preparations, pressure and temperature calibration of the equipment and complex analysis of the products. The method development and its improvement were one of the major purposes of the research, that is reflected in the appended papers A, B and D. The experimental high-pressure methods were improved, according to the special aspects of hydrocarbon investigation. It allowed combining up-to-date high-pressure methods with the most effective analytical tools for hydrocarbon systems. The incorporation of several experimental and analytical techniques increased the accuracy and validity of the results.

2.1. High-pressure experimental techniques High-pressure investigations are widely spread among

several fields of science, such as fundamental physics, material science, geology, and geochemistry. In fundamental physics, for example, the physical properties and chemical structure of the compounds at different thermobaric conditions have been investigated, new phases and new phase transitions were determined at these conditions 33-40. Condensed matter physics actively employ extremely high pressures for the synthesis of new materials 41. High-pressure technique is widely used in geoscience to model extreme thermobaric conditions of the Earth’s interior and the thermobaric conditions of other planets. Such experiments have led to the discovery of the chemical composition of the different layers of the Earth and also the physical and chemical properties of the Earth interior components 42, 43.

At present, the most popular and important high-pressure techniques for the investigation of behavior and properties of substances and modelling of the physical and chemical processes of the Earth’s interior include:

Autoclaves. They are mostly used for crustal pressure modelling (< 1 GPa). Externally heated autoclaves are limited to 900


°C, the temperature in the internally heated autoclaves can reach 1,500 °C 44, 45.

The piston-cylinder apparatus (Figure 2.1) is mostly used for the experiments under the conditions of the Earth’s upper mantle. The pressure range is limited by the tensile strength of the vessel and can reach 6 GPa. The maximum temperature, which can be reached in the piston cylinder experiments, is 1,700 °C 46, 47.

The multianvil press (Figure 2.1), for experiments in the deep upper mantle, the transition zone, and the lower mantle conditions. The sample can be pressurized up to 25 GPa and heated up to 3,000 °C 48, 49.

Toroid-type large reactive volume (LRV) unit (Figure 2.2), for experiments at the thermobaric conditions, corresponding to the upper mantle. The sample can be pressurized from 2 to 8 GPa and heated up to 1,400 °C 50, 51.

The diamond anvil cell (DAC; Figure 2.1), which gives the possibility to reach pressures higher than those in the center of the Earth. The most significant advantage of this technique is that the diamond anvil cells allow direct observation and in situ measurements of the sample at temperature and pressure, by optical inspection under a microscope and by various spectroscopic and diffraction techniques. Due to this, it is often used at rather low pressures as well. Both external resistive heating and laser heating are possible. The pressure can vary from up to 300 GPa and even higher. The temperature >5,000 °C can be reached in the DAC experiments by laser heating 52.


Figure 2.1. Devices for high-pressure experiments.

Figure 2.2. Toroid-type large reactive volume (LRV) unit, Gubkin

Russian State University of Oil and Gas (National Research University) 34.

In the current study, DAC and the Toroid-type LRV unit were used. The application of two different types of high-pressure tools increased the reliability of the experiments. Both methods have their own benefits and disadvantages, and they were taken into consideration during the research design. In case of DAC, the great advantages of this method are the opportunity to carry out in situ spectroscopy analysis (appended papers A, C, D) and extremely high-temperature heating (up to 2,300 K, appended paper A). The disadvantage of this method is the small volume of the cell (~3.4*10-

7 cm3), that is not crucial due to the high sensitivity of the analytical


methods applied (Mossbauer spectroscopy). In case of the Toroid-type LRV unit, the volume of the sample (~0.3 cm3) is an important aspect of the experiment for further gas chromatography analysis, which is efficient for complex hydrocarbon mixtures and can be carried out ex situ.

2.2. Diamond anvil cells During the last half of the century, DACs have become the

most successful and widely used technique for creating high pressure (from 0.1 GPa up to 300 GPa and higher). Because of its small size, extreme hardness and transparency, and the possibility to be employed in common with most analytical tools. DACs have become the most universal method in high-pressure experiments. The common characteristic for all the diamond anvil cells is the employment of two diamonds of the same size, but with the opposite configuration. The metal gasket (steel, rhenium, and beryllium) is placed between the sharp sides of diamonds with the polished culets. The hole is drilled in the indentation of the gasket, and the sample is loaded into this hole. The metal gasket serves as a pressure medium in high-pressure experiments. Due to this design, little out pressure is necessary to create extremely high inner pressure. The important feature of the DAC experiments is the transmitting of pressure in all dimensions inside the sample volume. If the sample is solid, pressure transmitting media are usually utilized to create a hydrostatic effect in the sample volume around the cell 53.

2.2.1. Experiments with the synthetic petroleum

The purpose of this part of the current research was to investigate the behavior of petroleum at the Earth’s crust thermobaric conditions with the pressure range 0.7-1.4 GPa, temperature range 320-450 °C. These thermobaric conditions are not so convenient for DAC experiments, due to low pressure and relatively high uncertainty of the method for such pressure interval. However, in situ analysis by means of Raman spectroscopy, which is very sensitive to any changes in the composition of the hydrocarbon mixture, was the important characteristic for our task. To cope with high-pressure uncertainty two different internal standards with a known correlation of the physical property at different pressures were added in the sample


– ruby (Cr-doped Al2O3) and Sm:YAG (Sm-doped Y3Al5O12) 54, 55. The fluorescence shift of these compounds, excited by the laser and detected by the Raman spectroscopy, depended on the pressure and temperature in the sample. Due to this combined measurement, the pressure uncertainty was decreased to ±0.1 GPa.

Natural petroleum demonstrated strong luminescence at Raman spectra because of the asphaltenes and resins, therefore, it was replaced by an artificially synthesized mixture of about 40 hydrocarbons of linear, branched and cyclic structure (paraffins, naphtenes and aromatic hydrocarbons), similar to gas condensate. This mixture demonstrated clear Raman spectra.

As usual for DAC experiments, two diamonds with the opposite configuration (the culet diameter was 250 µm) and with the steel gasket (or rhenium in the case with the hydrocarbons-Fe2O3 mixture) were used in the experiment (Figure 2.3). The hole was drilled in the indentation of the gasket, and the liquid hydrocarbon mixture (or the mixture hydrocarbons-Fe2O3) was loaded in this hole. Liquid sample served as a pressure medium.

Figure 2.3. Diamond anvil cell scheme.

External electrical heating with Pt resistive heater allowed to generate the required range of temperatures (up to 450 °C). The temperature was measured by the Pt-Pt/Rh thermocouple (Figure 2.4). However, such method had several limitations 56, 57, such as oxidation and graphitization of diamonds and the uncertainty of the temperature, connected with the high thermal conductivity of the diamond. The first problem was solved by directing the Ar-H2 gas flow to the diamonds, that protected the diamonds and the gasket


from oxidation (Figure 2.5). The temperature uncertainty was decreased by mounting the thermocouple directly on the surface of the diamond (Figure 2.4). Another significant problem was to maintain constant pressure during heating, since the external resistive heater drastically increased the temperature of the DAC body, that led to the extension of the screws and decreasing the pressure. Regular control of the pressure by measurement of the ruby and Sm:YAG Raman shifts 2-3 times per hour and correction of the pressure solved this issue. The experimental design of the DAC, used in the current experiments, is presented in Figure 2.5.

Figure 2.4. The DAC body with Pt heater and thermocouple (left) and

thermocouple on the surface of the diamond (right).


Figure 2.5. The experimental design of the DAC: 1 – microscope, 2-

DAC, 3 – Pt heater, 4 – Ar-H2 flow, 5 – Pt-Pt/Rh thermocouple.

The temperature was increased with the speed of 50-60°C with regular pressure correcting by employing DAC screws. When the required temperature was reached, it was kept for several hours (from three to twelve hours). Then the cell was quenched with the same speed and pressure correcting.

2.2.2. Raman spectroscopy application in DAC experiments

with complex hydrocarbon systems

The method of Raman spectroscopy has become a basic analytical technique for DAC experiments because of the high sensitivity to hydrocarbon samples and low requirements for the diamonds quality. A green Ar+-laser (514.5 nm), equipped with the LabRam spectrometer (2 cm-1 spectral resolution) was employed for the in situ analysis (power from 0.001-0.6 W). Raman spectra of the hydrocarbon mixture were made before and after the heating under the required experimental pressure and ambient temperature. After that, two spectra were compared.


It has been considered, that the influence of the Raman laser is typically inconspicuous. However, in the experiments with the model petroleum the photochemical effect on the hydrocarbon reactivity was detected 58 (appended paper D). It was discovered, that at high pressure and temperature the relatively high power (0.5W and higher) of the Raman laser could activate the cracking reactions. As a result, the strong luminescence appeared in the Raman spectra, that blocked the Raman peaks of the source hydrocarbons. Moreover, a black opaque spot was detected by optical observations in the sample at the focal point of the laser. This phenomenon may be explained by the photochemical transformation of the hydrocarbons into heavy resins. The similar effect was detected by 59 in the experiments with pure methane, that was explained by the formation of ultra-dispersive diamonds.

This photochemical effect of the Raman laser was investigated during the current research, and the correlation between the laser power, temperature, and pressure of the hydrocarbon mixture was found (described in the appended paper D). As an improvement for the current experiments, the Raman analysis of the sample was carried out at ambient temperature before and after the heating, and the pressure and temperature control and correction in DAC during the resistive heating was made by the significant decreasing of the laser power (down to 0.1 W) and extending the time exposure of the measurement.

2.2.3. Modeling of the hydrocarbons-iron bearing

minerals interaction during subduction For this part of the research, a mixture of the hydrocarbon

system and powdered iron bearing material was loaded in DAC. 57Fe0.94O, ferropericlase or pyroxene-like glass (Mg0.91Fe0.09)(Si0.91Al0.09)O3 were used as iron bearing materials, natural Astrakhan crude oil or paraffin oil (n-alkanes C15-C40) were taken as the hydrocarbon systems. It was discovered during the experiment, that the composition of the hydrocarbon system did not influence on the chemical reaction pathway and the composition of the products. Therefore, paraffin oil with a clear Raman spectrum allowed to detect the chemical transformations of hydrocarbons, while experiments with the crude oil represented the natural hydrocarbon system of the subducting slab.


The sample was heated in the portable laser heating setup with two optical fiber-based lasers (50 and 100 W, Figure 2.6) 60. Ruby chips, placed inside the cell, served as a pressure sensor. Temperature measurements in the laser-heating experiments was an important and complicated issue 61. The temperature at the surface of the sample was determined from the spectrum of radiation, emitted by the heated sample, by means of multi-wavelength spectroradiometry. The thermal spectrum was recorded over a wide range of the visible and near-infrared region (600-900 nm), and then fitted to the Planck function. However, knowledge of the pressure and temperature dependence of the emissivity is very limited, therefore, the uncertainties of such measurements were estimated to ±100 °C. Temperature gradients, that could be significant in the laser-heated DAC experiments 60, 62, were considered in the experiment by the constant movement of the laser spot over the entire hole of the DAC.

Figure 2.6. Double-sided laser heating experimental setup

After the heating, the sample was analyzed by means of Raman and Mössbauer spectroscopy.

2.2.4. Mössbauer spectroscopy analysis of the reaction

products

The Mössbauer effect can be explained as the recoilless emission and absorption of X-rays by specific nuclei in a solid


sample63. The interactions between the nucleus and the atomic electrons depend strongly on the electronic, chemical and magnetic state of the atom. Information from these hyperfine interactions is provided by the hyperfine parameters, which can be determined experimentally from the line positions in a Mössbauer spectrum 64.

A Mössbauer apparatus is relatively simple and can be divided into three parts - the source, the sample (absorber) and the detector (Fig. 2.7). Since most source radiation is monochromatic, energy is generally varied using the Doppler effect by moving the source relative to the sample (or vice versa), hence the source is commonly mounted on a drive system. Gamma rays that do not interact with the sample pass through and are recorded by the detector, while those absorbed are re-emitted in a different direction and not recorded by the detector; hence the resulting Mössbauer spectrum shows dips instead of peaks. The energy scale of the resulting spectrum is typically expressed in mm/s for source velocities used to probe hyperfine interactions in 57Fe.

Figure 2.7. The scheme of a Mössbauer spectrometer, resulting to the

Mössbauer spectrum 64.

Conventional Mössbauer spectroscopy with a 57Co point source was used for the current investigation. The isomer shift and the velocity scale were calibrated relatively to α-Fe. Transmission Mössbauer spectra were fitted to Lorentzian line-shapes by MossA software, that allowed to analyze Mössbauer spectra 65.

The more detailed description of the Mössbauer spectroscopy and the examples of Mössbauer spectra, collected after the quenching of the sample, are presented in the appended paper A. Experimental points are shown by dots, fits by red lines, residuals are shown above each spectrum, and percentage sections indicate the relative amount of each component.


2.3. Toroid-type LRV unit The greatest advantage of the Toroid-type LRV unit is the

amount of the sample, used in the experiment (0.3 cm3), that allows employing the gas chromatography analytical method, which is one of the most effective analytical tools for complex hydrocarbon mixtures and inorganic gaseous mixtures. Due to the relatively large volume of the cell and high sensitivity of the gas chromatography, components of the products mixture can be detected on trace level. However, the most important issue of using this method is the loading of gaseous samples in the cell.

In the Toroid-type LRV unit (Figure 2.8) experiments were carried out in the metal (steel, copper, gold-covered) thin-wall cylindrical cells, mounted in the ceramic high pressure chamber of toroid shape 66. This high pressure technique allowed to pressurize the sample up to 8 GPa with the resistive heating up to 1,800 K. The cell with the sample was placed in the ceramic container, that served as a pressure medium; at high pressure the material of the chamber collapsed and behaved as a pseudo-fluid, equally distributing the pressure on the cylindrical surface of the cell. Two resistive heaters, made of the mixture C-Al2O3 (1:4 mas.), were placed in the hole of the container on the top and bottom face of the cell. When the electrical current flowed through the heaters, their temperature increased due to the electrical resistance of the heaters, leading to the heating of the cell between the heaters. For additional conductivity metal discs were placed between the heater and the cell. Then the container with the cell was mounted between two tungsten carbide matrices and then all this sample assembly was placed in the toroid unit between two puassons and then pressurized. When the experimental pressure was reached, the heating was turned on. Temperature and pressure in the cell were measured by using calibration curves, made by phase transitions of reference compounds.


Figure 2.8. A – Toroid-type LRV unit, b – tungsten carbide matrices, c

– toroid-shape ceramic container, Cgr

-Al2O

3 heater, steel

cylindrical cell, d – the scheme of the sample assembly.

2.3.1. Calibration of the Toroid-type LRV unit

To control pressure and temperature inside the cell during the experiment traditional methods (thermocouple, manometer) could not be applied. However, the automatic controlling system of the Toroid-type LRV unit provided the pressure of lubricant oil in the hydraulic system during the experiment, and these data was converted into the pressure in the cell, using calibration curves. The temperature of the cell could not be measured directly, however, the electrical resistance of the assemblage was detected during the experiment, and this data were converted into the temperature of the cell. To do these procedures, reference substances were used 67,

68. These substances (Tables 2.1 and 2.2) change their physical properties abruptly at relevant pressure and temperature, allowing to use their physical anomaly for the calibration. The described calibration method provides uncertainties of ±0.5 GPa for pressure and ±50 °C for temperature.

During the pressure calibration, a paper disk was placed between one of the resistive heaters and the cell (Fig. 2.9a). The reference compound (Table 2.1) was loaded into the small hole in the center of the paper disk so that the electrical current would flow only through this hole. For pressure calibration, the temperature had to be kept constant during the calibration experiment (ambient


temperature), and the pressure had to be continuously growing until the phase transition. When assemblage was mounted in the LRV unit, the electrical current with low power (4-6 W) was switched on. Such power would not heat the cell; however, it would be enough to detect the phase transition of the reference compound. When the required pressure was reached, the electrical resistance of the assemblage was abruptly changed. It meant that the phase transition had taken place. The example of this phenomena for Bi is presented in Figure 2.10. This metal has two phase transitions: at 2.6 GPa and 7.7 GPa. During the first phase transition (at 39-40 atm in the hydraulic system) the electrical resistance abruptly increases. After the first transitions, the electrical resistance of Bi smoothly decreases. At 115 atm, the small drop of the resistance can be detected, therefore, the pressure of 7.7 GPa has been reached.

Figure 2.9. The assemblage of the Toroid-type LRV unit for pressure

calibration (a) and temperature calibration (b).

In case of temperature calibration, the procedure was similar, however, instead of a small hole in the paper disc, a thin disc of a reference compound (Table 2.2) was placed on the whole area between the heater and the cell (Fig. 2.9b), so the electrical current would flow through the entire area of the disk. For temperature calibration, the pressure in the cell had to be kept constant during the calibration experiment, and the temperature was continuously growing until the phase transition. When the required pressure in the cell was reached, the heating was switched on. The power was being increased constantly with the speed ~1.5W/s. When the required temperature was reached, the electrical resistance of the assemblage was abruptly changed. It meant, that the phase transition had taken place. The example of this phenomena for Pb is presented in Figure 2.10. This metal has a phase transition at 510 °C and 2.6 GPa. When the required temperature is reached, the abrupt drop of the electrical resistance is detected.


Table 2.1. Reference compounds for pressure calibration67, 68.

Compound Phase transition

T, °C P, GPa

PbSe 20 4.3

PbTe 20 5.0

Bi 20 2.6

20 7.7

Ce 20 0.8 Table 2.2. Reference compounds for temperature calibration67, 68.

Compound Phase transition

T, °C P, GPa

Pb 790 8.0

510 2.6

Sn 310 2.6

Ti 80 2.6

830 2.6

Ti 760 8.0

Cu 1170 2.6

Figure 2.10. Phase transition of the reference compounds during

calibration: Bi at the pressure calibration (left) and Pb at the temperature calibration (right).

Calibration procedures were carried out for different reference compounds, and the data obtained were assembled in calibration curves. The calibration curves for pressure and temperature are shown in the Figure 2.11. These plots represent the


dependence of the pressure in the hydraulic system in the LRV unit and the pressure in the cell (left plot) and the dependence of the electrical power on the temperature in the cell (right plot).

Figure 2.11. Pressure (left) and temperature (right) calibration of the LRV

unit. 2.3.2. Investigation of the C-O-H fluid under the thermobaric

conditions, corresponding to upper mantle, using the Toroid-type Large Reaction Volume unit

To check the possible formation of CO2 from hydrocarbons in the upper mantle and its abundance in the C-O-H fluid 69, 70, methane with water were investigated in the LRV unit under the thermobaric conditions, corresponding to the upper mantle . As it was mentioned above, experimental investigation of gaseous samples was a great issue for the LRV unit. In case of the current research, the solution was the in situ synthesis of methane from Al4C3 and water 71. The mixture of Al4C3-H2O (water in the excess amount) was loaded into the steel cell. The synthesis of methane was carried out at 2 GPa and 200 °C for 30 minutes (2.1): Al4C3 + 6H2O → 3CH4 + 2Al2O3 (2.1)

The chromatography analysis of the gaseous products demonstrated the formation of a mixture, consisted of 99.26 % of methane (with the impurities of ethane – 0.11%, propane – 0.35%, and n-butane – 0.05%), and the solid products consisted only of Al2O3, which meant, that the entire Al4C3 had transformed into Al2O3. Therefore, this experiment was used as the first step of the current investigation of modeling C-O-H fluid in the upper mantle thermobaric conditions, all the investigations of the C-O-H fluid in the research were started from the in situ synthesis of methane. After 30 minutes of synthesis, the thermobaric conditions were increased, according to the requirement, and the modeled C-O-H system was kept at the constant thermobaric conditions during the


exposure time. After the heating was finished, the electricity was turned off, and the cell was quenched. The cell was depressurized only after the assemblage was quenched down to ambient temperature.

2.3.3. Gas chromatography analysis of the gaseous product

The gaseous chemical products were analyzed by means of the Gas chromatograph Chromatek-5000. This chromatograph allowed to separate and analyze complex light mixtures, consisting of hydrocarbons and inorganic gases. The chromatograph was equipped with the Agilent GS-GasPro capillary column (60m length) and two flame ionization detectors: detector I for hydrocarbons and detector II for inorganic components (CO2 in particular).

After the cell with the reaction products was extracted from the assemblage, it was placed in the sealed device, that was designed for gas products recovering. It allowed opening the cell in the sealed zone, connected with the chromatograph, by going down the sharp steel stock, making the hole in the cell (Figure 2.12). After this procedure, the gaseous products of the reaction were recovered from the cell in the sealed zone without any loss. For the additional extraction the sealed device was heated at 45-50°C. In ten minutes after recovering, the gaseous product was sent to the chromatograph by the carrier gas (He), and in 50 minutes the chromatogram of the light products was obtained. Data, obtained from the detectors, were processed to graphical chromatograms due to the Chromatek Analytic 2.6 software, also providing the relative of the content of each component.

CO2 content in the product mixture was estimated in relation to the carbon dioxide content in the air. The calibration chromatogram was made before each measurement. The data obtained from the calibration measurement was subtracted from the products measurement curve artificially. This procedure was important because of the constant amount of CO2 and CH4 in the air.


Figure 2.12. Sealed device for gaseous products recovering.

2.3.4. Raman spectroscopy analysis of the solid products

After the chromatography analysis, the solid products were recovered from the cell and analyzed by means of Raman spectroscopy. The solid sample was intimately distributed on the surface of a glass plate. A He-Ne laser (wavelength 632.8 nm, power 2 mW), equipped with the LabRam spectrometer (a spectral resolution of 2 cm-1) was employed to analyze the solid product. The solid sample from the cell was tested in several different zones on the glass plate to obtain the reliable results.


Chapter 3. Petroleum in the lower part of the Earth’s crust.

One of the research questions of the current study (see paragraph 1.4) was the investigation of the depth limit of the petroleum stability in the Earth’s crust, that may have significant value for the understanding of the abyssal Earth’s processes and the global carbon cycles.

Numerous theoretical and experimental investigations were devoted to the studying of the thermal stability and behavior of individual hydrocarbons and hydrocarbon mixtures at high temperature, corresponding to the Earth’s interior, particularly the Earth’s crust 72, 73. As an output, it has been considered that the depth limit for petroleum existence in the Earth’s crust is 6-8 km (so called the “oil window”). At a deeper level hydrocarbons would decompose to methane or inorganic substances 29. However, several giant ultra-deep petroleum deposits have been discovered recently in various crude oil fields worldwide at a deeper level of the Earth’s crust (10 km and deeper) 25, 28. These petroleum deposits are located deeper than the “oil window” and the petroleum in those deposits is stable at the corresponding thermobaric conditions. Therefore, it is perfectly reasonable to expect petroleum deposits at a deeper level of the Earth’s crust, down to the crust-mantle boundary. In case this hypothesis is correct, the hydrocarbon budget of the Earth’s crust may be underestimated, and the involvement of petroleum in the subduction can be taken into consideration.

3.1. Thermal stability of the model hydrocarbon system.

High temperature seems to be crucial for hydrocarbons existence in the lower part of the Earth’s crust. Until recently, most investigations drew the conclusion that only the natural gas deposits could occur at depth layers with temperatures higher than 170-180 °C. These conclusions were found on the theoretical calculations 73. However, in the another theoretical model 72 reservoir pressure was taken into account, and it was demonstrated, that petroleum could be thermally stable at temperatures up to 240-260 °C. Therefore, high pressure could significantly increase the temperature limit of hydrocarbon stability.


Experimental investigations of the behavior of the individual hydrocarbons at high temperatures are presented in works 74-76. These experiments demonstrate the formation of complex hydrocarbon mixtures at the temperatures up to 450 °С. Moreover, it was shown experimentally, that high pressure (up to 1.5 GPa) hinders the decomposition of hydrocarbons 75. Besides the influence of high pressure, it was discovered, that the thermal stability of the complex hydrocarbon mixtures was higher than the stability of individual hydrocarbons. This phenomenon can be explained by the inhibition effect of hydrocarbons of different classes on each other 77.

The investigation of crude oil at high temperatures, carried out by 78, 79, demonstrated the hydrocarbon decomposition, starting from 600 K at a pressure range of 30-150 MPa. However, such pressures are significantly lower, than natural pressure, corresponding to the experimental temperature, according to geotherms 80, 81. The results of the crude oil investigation at extreme pressures up to 2 GPa and temperatures up to 450 K 35, 82, demonstrated the remaining of the chemical composition of the hydrocarbon system at the examined thermobaric range.

In the current research, the behavior of the petroleum was examined at the temperature range 320-450 °C and pressure range 0.7-1.4 GPa (Table 3.1), that correspond to depths of 20-50 km 80. The details of the experimental setup and related procedures are described in Chapter 2 of the present thesis and in Paper C. The experiments demonstrated the thermal stability of the hydrocarbon system at relevant thermobaric conditions and exposure times (Figure 3.1). The model petroleum, which had a composition typical for natural gas condensates kept its composition in all series of experiments. The representative peaks of the hydrocarbons in the spectra kept their Raman shift, shape, and intensity; no new peaks appeared after heating. Increasing the time of the heating from 3 to 12 hours (experiment 3, Table 3.1) did not influence on the stability of the petroleum.


Table 3.1. Conditions of the experiments with the model petroleum.

Exp. Sample Pressure, GPa(±0.1)

Temperature, °C (±10)

Corresponding depth, km

Exposure time, hours

1 Model petroleum

0.7 320 20-30 3

2 Model petroleum

1.2 420 30-40 3

3 Model petroleum

1.4 450 40-50 12

4 Model petroleum

+ Fe2O3

1.4 450 40-50 12


Figure 3.1. Raman spectra of the model petroleum at relevant pressure

and ambient temperature before heating (the red curve) and after heating (the black curve): a) at 0.7 GPa and 320 °C, 3 hours, b) at 1.2 GPa and 420 °C, 3 hours, c) at 1.4 GPa and 450 °C, 12 hours.

3.2. Oxidative resistance of the hydrocarbon system at the Earth’s crust thermobaric conditions.

The second part of the experiments with the model petroleum behavior at the thermobaric conditions, corresponding to the Earth crust, was devoted to the hydrocarbons oxidation resistance

c

a b


and their possibility to chemically interact with the oxidative surrounding minerals. Iron compounds seem to control the oxygen fugacity inside the Earth due to its abundance and chemical properties 83. Therefore, in the current research Fe2O3

was employed to model the oxidative surrounding of the Earth’s crust as the potential component with the highest oxidative characteristic 84, that could behave as an oxidizer in the presence of hydrocarbons.

A finely ground Fe2O3 powder (99% reached 57Fe) was mixed with the model petroleum and loaded in DAC. The cell was pressurized up to 1.4 GPa and then resistively heated at 450 °C, like in the previous part of the research. The Mössbauer spectra of the sample were registered at ambient temperature, both before and after the 12 hours of heating (Figure 3.2). No new iron compounds appeared in the Mössbauer spectra after the experiment, and the only sextet of Fe2O3 was registered in both spectra. Therefore, the iron oxide did not take part in any chemical reaction with the hydrocarbons during the 12 hours of heating.


Figure 3.2. The Mössbauer spectra of the mixture hydrocarbons-Fe2O3

at 1.4 GPa and ambient temperature before the heating (a) and after the heating at 450 °C for 12 hours (b).

Despite the “oil window” depth limit of 8 km for the petroleum occurrence, the results of the current research claim, that petroleum can be stable at the thermobaric conditions of depths down to 50 km. The exposure time of 12 hours cannot be directly compared to the life scale of the Earth, however, the kinetic investigations of the hydrocarbons’ transformations during thermal cracking suppose the most significant changes in composition during the first 20 hours of heating in the 1000 hours experiment72. Thus, the experimental results regarding the stability of hydrocarbon systems can be extrapolated for a significantly longer period of time (up to years).

The oxidizing resistance of the hydrocarbon system was examined in the modeled solid mineral surrounding of the crust. Fe2O3, as the hypothetic component of the Earth’s crust, did not chemically interact with hydrocarbons. It is not possible to draw a conclusion about the equilibrium in the system hydrocarbons-

a

b


Fe2O3, however, the oxygen fugacity of the crust is substantially lower, than the fO2 of Fe2O3. Thus, it is expected that the solid surroundings of the crust will not influence on the stability of the petroleum.

3.3. Impact to the concept of the abiogenic deep genesis of hydrocarbons

The data obtained not only experimentally explain the existence of discovered ultra-deep hydrocarbon deposits at depths of 11-12 km, but also extend the possible occurrence of petroleum through the entire depth range of the crust down to the crust-mantle frontier. The possible source of the deep petroleum deposits may be the hydrocarbon fluid from the mantle 85. The existence of hydrocarbon systems in the lower part of the Earth’s crust may be the evidence of the abyssal abiogenic petroleum formation concept 25.

According to this concept, hydrocarbons are considered a product of the chemical reaction between inorganic compounds (donors of carbon – carbonates, CO2, iron carbides, pure carbon and donors of hydrogen – water, hydroxyl groups of minerals, iron hydride) in the upper mantle. These compounds occur in the mantle in solid state or in melted (fluid) condition. In the thermodynamically appropriate thermobaric conditions and Redox surroundings, hydrocarbon fluid is generated from the donors of carbon and hydrogen 50: nCaCO3 + (9n + 3)FeO + (2n + 1)H2O → nCa(OH)2 + + (3n + 1)Fe3O4 + C𝑛H2n+2 (3.1) CaCO3 + 12FeO + 2H2O → CaO + 4Fe3O4 + CH4 (3.2) Migrating to the Earth’s crust through deep faults, the hydrocarbon fluid forms petroleum deposits in any kind of rock (crystalline, igneous, sediment rocks) and on any depth of the crust (Figure 3.3).


Figure 3.3. Formation of hydrocarbon deposits in the Earth’s crust,

according to the abiogenic hydrocarbon formation concept (modified from 25).

Because of the closeness to the mantle source for the deep petroleum deposits, the field pressure and reserves can be significantly higher in such accumulations. Although these deposits are unattainable for the human exploration (at least not in the near future), they can actively take part in the subduction. According to the results obtained, the volume of the petroleum, accumulated in the crust, can be significantly larger than currently estimated nowadays, and the petroleum impact in the subducting carbon material may be essential.


Chapter 4. Contribution of hydrocarbons in the subduction and its influence on the CO2 budget of the atmosphere

The volume of petroleum in the Earth’s crust can be significantly larger than currently estimated nowadays (see Chapter 3). Therefore, petroleum involvement in the subduction processes may have a significantly greater effect on the carbon processes on the Earth. During subduction petroleum, accumulated in the subducting slab, will submerge down in the mantle and undergo extreme thermobaric conditions, and in the mantle surroundings, with high oxygen fugacity petroleum hydrocarbons may transform into oxidized forms of carbon. These processes may lead to the formation of a great amount of carbon dioxide, that will contribute to the atmosphere budget of CO2 through mantle degassing and arch volcano eruptions. This contribution may be significant, due to potential occurrence of petroleum in the entire depth range of the Earth’s crust.

The most important purpose of the present research was to model the petroleum behavior during subduction. The current chapter provides the results of the experimental modeling of the hydrocarbons behavior during subduction and the possible formation of CO2 from hydrocarbons in the mantle.

4.1. Chemical transformations of hydrocarbons during subduction.

Iron substances are expected to control oxygen fugacity due to

variable valence states and their abundance in the mantle 83. Petroleum hydrocarbons as reducing agents, submerging in the mantle within the subduction slab, may chemically interact with iron-containing oxidizers 83. As a result, carbon should be transformed into the more oxidized form (possibly CO2). Thus, to investigate this process, the chemical interaction of hydrocarbon systems and iron-bearing minerals of subducting slab and mantle surrounding was examined at the thermobaric conditions, corresponding to the depth down to 300 km.

As a source of hydrocarbons paraffin oil (99,9% purity, paraffins of C15-C40) and natural crude oil (Korchaginskoe deposit, Astrakhan region) were used in the experiments.


Pyroxene-like glass with a composition (Mg0.91Fe0.09)(Si0.91Al0.09)O3, wüstite Fe0.94O, and ferropericlase (Mg0.8Fe0.2)O were employed in the experiments as iron-bearing minerals of subducting slab and mantle surroundings, representing a wide range of oxygen fugacity. The mixture iron substance-hydrocarbon system was loaded in DAC and pressurized up to the required pressure. The behavior of hydrocarbons in the presence of iron compounds was investigated in the thermobaric range 2.6-9.5 GPa and 1,000-2,000 K (Table 4.1 and appended paper A). The sample was heated by two opposite lasers several times in each series of experiments.

The results of the experiments are presented in Table 4.1 and Figure 4.1. When the temperature reached 1,350(±100) K (pressure from 2.6(±0.2) to 6.9(±0.2) GPa, corresponding to depths of 80-200 km), hydrocarbons reacted with iron-bearing minerals from the slab or mantle and formed iron hydride. At higher pressure (from 7.4(±0.2) to 9.5(±0.2) GPa, corresponding to depths from 210 to 290 km), iron carbide was originated.

Moreover, it was detected, that methane, graphite, aromatic hydrocarbons and water were formed from the paraffin oil (Figure 4.2) 86, 87.


Figure 4.1. The results of the interaction of hydrocarbon systems and

iron-bearing compounds, according to the Earth’s geotherms. Diamonds –(Mg0.8Fe0.2)O + petroleum, squares – Fe0.94O + paraffin oil, circles (Mg0.91Fe0.09)(Si0.91Al0.09)O3 + paraffin oil; open symbols – no reaction, shaded grey – iron hydride is present in the run product, shaded black – iron carbide and iron hydride are present in the run product. Blue solid line – cold geotherm of the subduction slab, red solid line – hot geotherm of the subduction slab 88, black solid line – the Earth’s geotherm 80, black dashed line – melting curve of γ-FeHx

89.


Table 4.1. Initial conditions and results of experiments.

Exp. System P,

(±0.2) GPa

T, (±100)

K

Composition of the products mixture (%)

1 Paraffin oil + pyroxene-like

glass (Mg0.91Fe0.09)(Si0.91Al0.09)O3

2.6 1500

pyroxene glass (81.7)

FeHx (18.3)


glass (Mg0.91Fe0.09)(Si0.91Al0.09)O3

4.5 1800


FeHx (33.6)

3

Crude oil + ferropericlase (Mg0.8Fe0.2)O

6.9 1800

new Fe2+ component (26.1)

FeHx (53.1)

α-Fe (20.8)

4 Paraffin oil + Fe0.94O 7.5 1600

Fe0.94O (15.7)

FeHx (11.7)

Fe7C3a (19.2)

Fe7C3b (44.6)

5 Paraffin oil + ferropericlase

(Mg0.75Fe0.25)O 7.4 1800

ferropericlase (53.4)

FeHx (19.2)

Fe7C3 (19.3)

α-Fe (8.1)


glass (Mg0.91Fe0.09)(Si0.91Al0.09)O3

8.8 2000


new Fe3+ component (12.9)

FeHx (36.5)

Fe7C3 (25.6)


7 Crude oil + ferropericlase

(Mg0.8Fe0.2)O 9.5 1700

ferropericlase (39.8)

FeHx (24.9)

Fe7C3a (22.0)

Fe7C3b (11.8)

α-Fe (1.5)

Figure 4.2. Formation of graphite, methane, aromatic hydrocarbons and

water in the chemical reaction of paraffin oil + ferropericlase (7.4(0.2) GPa), detected by means of Raman spectroscopy. Left spectrum: black curve – before heating, blue curve – after laser heating at 1,200(±100) K, right spectrum: orange

curve – after laser heating at 1,200(±100) K, dark blue curve

– after laser heating at 1,600(±100) K.

The experiments were carried out in the wide thermobaric range, corresponding to the upper mantle conditions, in wide range of oxygen fugacity, and with different hydrocarbon systems, however, instead of this, methane, graphite and iron carbide were formed. Iron carbides were expected to exist in the deeper layers of mantle 1, 83, however, according to the experimental results, they may exist in the mantle at depths from 210 km and deeper.


However, the amount of iron carbide decreased with increasing temperature, while the amount of iron hydride was growing, which means, that part of iron carbide(s) may be transformed into hydride due to high temperature, and iron carbide can be stable in cold zones of the upper mantle (appended paper A).

Petroleum hydrocarbons do not transform into carbon dioxide directly during subduction, however, methane, originated in the upper mantle from the subducted petroleum (appended paper A), can shift the equilibrium of the C-O-H fluid to the additional formation of CO2, therefore, this process should be investigated.

4.2. Behavior of methane under the thermobaric conditions, corresponding to upper mantle.

C-O-H fluid in the mantle is represented by water and carbon compounds, mostly CO2 and CH4 90. It was discovered by the experimental investigation recently, that methane could be transformed into heavier hydrocarbons (up to n-butane) in the upper mantle 62. However, the detection of hydrocarbons, heavier than butane, was limited by the response characteristic of the Raman spectrometer. Moreover, CO2 was not observed in the products mixture, that might be also caused by the limitation of the analytical equipment resolution.

Investigations of the formation of hydrocarbon systems from inorganic compounds (CaCO3-H2O-FeO) at the thermobaric conditions, corresponding to the upper mantle, were carried out both in DAC 91, 92 and in the high-pressure chamber KONAK 37, 50. The hydrocarbon systems, generated in the experiments, consisted of different hydrocarbons from methane and up to C11. CO2 was not detected in the product mixture, methane was the major product of the abiogenic hydrocarbon synthesis.

Therefore, a significant volume of methane can be generated due to the abiogenic synthesis in the upper mantle, besides the formation from petroleum during subduction. The purpose of the current part of the research was to model the C-O-H fluid and to evaluate the possibility of methane to be transformed into carbon dioxide and heavier hydrocarbons. Methane occurred in the mantle by different pathways, such as the decomposition of petroleum during subduction (appended paper A), may shift the equilibrium in the C-O-H fluid between CH4 and CO2, as far as carbon dioxide is considered to be the main carbon volatile at the upper mantle 83.


The experiments were carried out using a novel technique for such purposes – Toroid-type LRV unit with the gas chromatography analysis (see Chapter 2 and appended paper B). The methane behavior was investigated at the thermobaric conditions corresponding to the upper mantle conditions on the depth down to 70-80 km. It was discovered, that in colder zones of upper mantle (850(±25) K and 2.5(±0.2) GPa) the complex hydrocarbon mixture was formed from methane. The hydrocarbon mixture consisted of saturated linear, branched and cyclic hydrocarbons up to C7 and benzene (Figure 4.3) with trace amounts of unsaturated hydrocarbons (olefins and alkynes), which could be intermediate compounds of the methane transformation. The solid products mixture consisted only of Al2O3 (Figure 4.4). In warmer zones of upper mantle (1,000(±25) K and 2.5(±0.2) GPa) hydrocarbon mixture consisted of the light saturated hydrocarbons up to C5 (Figure 4.5). Solid products contained pure graphite (D and G bands of graphite, 1,325 and 1,581 cm-1 93).


Figure 4.3. Gas chromatogram of the hydrocarbon mixture, synthesized

from methane at 850(±25) K and 2.5(±0.2) GPa.


Figure 4.4. Raman spectra of the sample before heating at ambient

conditions (black curve), the solid products, formed after heating at 850(±25) K and 2.5(±0.2) GPa at ambient conditions (red curve), and the solid products, formed after heating at 1,000(±25) K and 2.5(±0.2) GPa, at ambient conditions (blue curve).


Figure 4.5. Gas chromatogram of the hydrocarbon mixture, synthesized

from methane at 1,000(±25) K and 2.5(±0.2) GPa.

During the investigation of the C-O-H fluid in the thermobaric conditions, corresponding to upper mantle conditions, it was discovered, that complex hydrocarbon mixture was formed from methane. New classes of hydrocarbons (branched paraffins, naphthenic and aromatic hydrocarbons) with all the existent isomers were presented in the product mixture. The possible chemical pathways of the formation of heavier hydrocarbons from methane are presented in figure 4.6. The main directions of the reactions are the growth of the carbon-carbon bonds, isomerization and cyclization via the radical mechanism 94. In the modeled C-O-H fluid methane is evolved into more oxidized forms of heavier hydrocarbons and graphite, however, it is not oxidized to CO2. This fact is evidenced by data, obtained from FID 2 of the chromatograph (Figure 4.7).


Figure 4.6. Formation of heavy hydrocarbons from methane in modeled

C-O-H fluid under the thermobaric conditions, corresponding to upper mantle. Solid brown arrow – reactions with the growth of the carbon-carbon chain, blue dashed line – isomerization of the synthesized hydrocarbon, red dashed line – dehydrogenation with the formation of the cycle chain or aromatic chain (appended paper B).


Figure 4.7. Chromatogram of the gaseous products of methane

transformation under the thermobaric conditions, corresponding to upper mantle: black curve – calibration curve of the air in the lab, red curve – heating at 850(±25) K and 2.5(±0.2) GPa, and the solid products, blue curve – heating at 1,000(±25) K and 2.5(±0.2) GPa.

According to the results obtained, at 2.5 GPa the temperature limit for heavier hydrocarbons C5+ is between 850K and 1,000K. It is not still clear, what the depth limits of the thermobaric stability zone are for complex hydrocarbons mixtures. However, at higher pressures, the temperature limit for heavier hydrocarbons C5+ may be higher. As a result, it is expected that the existence of complex hydrocarbon mixtures is not limited by the depth of 70-80 km, but it is governed by the still unknown pressure-temperature correlation in the mantle.


4.3. The role of petroleum in the processes in the Earth’s mantle.

The experiments, described in the current chapter, demonstrate the complex involvement of the crustal hydrocarbon deposits in the abyssal processes. As it was presented in Chapter 3, the hydrocarbon budget of the Earth’s crust is potentially much higher, than it was evaluated. The ultradeep petroleum deposits are considered to be unrecoverable, however, they are actively involved in subduction. Thus, during subduction huge amounts of hydrocarbons is submerged in the mantle, and it should be taken into consideration in the downstream of the deep carbon cycle.

When petroleum reaches the mantle, it does not decompose to CO2, as expected, according to the behavior of organic sediments 13, 22. Hydrocarbons remain in the slab, but they transform into a more sustainable form, mostly aromatics and methane. Besides, graphite is formed in the system. At higher temperatures (correlated with pressure) methane predominates in the hydrocarbon system.

Methane, generated from petroleum during subduction, contributes to the methane budget of the upper mantle. The performed experiments, simulating the C-O-H model, presume, that the chemical transformations of methane at the thermobaric conditions, corresponding to the upper depth border of the abiogenic hydrocarbons formation zone (70-80 km) 80, 81, led to the formation of the complex hydrocarbon mixture. It was strongly considered that methane and carbon dioxide were the predominant carbon components in the upper mantle fluids, and because of this hypothesis only methane 13, 70 and sometimes methane with ethane 95 were taken into consideration in the C-O-H model as hydrocarbons, occurring in the mantle. Moreover, CO2 was considered as the most abundant carbon-containing volatile in mantle 96. However, the experiments carried out on the C-O-H fluid modeling in the Toroid-type LRV unit assume the absence of carbon dioxide in the products mixture. The experimental results suggest that about 25% of methane could be transformed into heavier hydrocarbons at the thermobaric conditions of the upper mantle (Figure 4.8). Therefore, it is expected, that complex hydrocarbon mixtures may exist in the upper mantle and should be included in the C-O-H fluid modeling. Moreover, the complex hydrocarbon mixtures, generated in the upper mantle from methane, can migrate


to the Earth’s crust through deep faults 25 or in subduction zones along the weakened surface of the slab 97 and contribute to petroleum deposits.

Figure 4.8. The product mixture after the heating of methane for 4

hours: a – complex hydrocarbon mixture, formed at 850(±25) K and 2.5(±0.2) GPa, b – complex hydrocarbon mixture, formed at 1,000(±25) K and 2.5(±0.2) GPa.

During subduction, in the depth range of 90-200 km (pressure range 2.6 GPa-6.9 GPa) iron hydride (FeHx) is formed from the reaction between natural hydrocarbons and iron-bearing minerals at the thermobaric conditions, corresponding to subducting slabs. The results obtained demonstrate that iron hydride can be stable in the wide range of oxygen fugacity due to its formation even in the excess amount of iron oxide/ferropericlase. Iron hydride has a relatively low melting temperature 89; however, the density of FeHx is much higher, than the density of the surrounding rocks (~ 7.3-7.5 g/cm3 98 against 3.3 g/cm3 at 200 km 99). Therefore, iron hydride may generate a single phase, that could migrate deeper into the mantle or up to the mantle-crust boundary, transporting the source of hydrogen.

From the depth of 200-210 km and down to 300 km (pressure range 7.4 GPa-9.5 GPa) iron carbide (Fe7C3) is formed, because of the chemical interaction between hydrocarbons and iron compounds. Investigations of iron carbide demonstrated its stability at thermobaric conditions up to 4,100 K and 250 GPa 100-

102. Iron carbides were considered to be a component of the lower mantle 15 and the Earth’s core 43, however, the current research supposes their occurrence in the upper mantle too. By convection flows, iron carbide may be transported to the mantle zones with


appropriate thermobaric conditions for the abiogenic synthesis of hydrocarbons and serve as a donor of carbon in the hydrocarbons formation.

Summarizing, it is possible to conclude, that petroleum hydrocarbons involved in subduction, do not have any significant influence on the CO2 budget of the atmosphere 8. The increasing amount of the remaining carbon dioxide in the atmosphere (4-5 Gt/year, see chapter 1) is caused by the human activity only. However, the involvement of petroleum in subduction may have contributed to the CH4 budget of the atmosphere, since CH4 is an important product of the petroleum decomposition during subduction.


Chapter 5. Conclusions and future work To summarize all the knowledge discovered during the

current investigation, these statements are provided to answer the main research questions, presented in the Introduction chapter of the present thesis.

1. Modeled petroleum demonstrates its stability at the thermobaric conditions, corresponding to the Earth’s crust (320-450 °C, 0.7-1.4 GPa). The oxidized surroundings do not have any influence on the stability of the hydrocarbon mixture. Therefore, petroleum accumulations may exist in the entire depth range of the Earth’s crust, and the petroleum budget of the crust may be significantly larger than currently expected nowadays.

2. Raman laser radiation can initiate the chemical transformations in the hydrocarbon mixture under high pressure. Temperature influence on the hydrocarbon mixture is significant in these photochemical reactions, however, the influence increases with the higher pressure in DAC. The photochemical reactions of the hydrocarbons start instantaneously, and the exposure time does not make any additional influence. The Raman spectroscopy method may be limited in the application of complex hydrocarbon mixtures at extreme thermobaric conditions.

3. During subduction, petroleum hydrocarbons react with the iron-bearing surrounding of the slab and mantle and form iron hydrides from the depth of 100-120 km (2.6 GPa). From the depth of 210 km (7.4 GPa) the mixture of iron carbide and iron hydride is formed. These substances may be stable in the upper mantle and take part in the abyssal processes, such as elemental cycles and abiogenic hydrocarbons formation. Complementary to iron carbide, carbon from the hydrocarbons transforms into graphite and methane. Moreover, part of the hydrocarbons remains in the mixture, paraffin hydrocarbons transform into aromatic ones and methane. CO2 is not formed from petroleum hydrocarbons in Redox and thermobaric conditions of the subducting slab and the upper mantle.

4. Methane transforms into the heavier hydrocarbons in the modeled C-O-H fluid under the thermobaric conditions, corresponding to the upper mantle. Complex hydrocarbon mixture (up to C7) is formed from methane in colder zones of the upper mantle. The hydrocarbon mixture consists of linear and branched paraffins, naphtenes and aromatic hydrocarbons. Unsaturated


hydrocarbons seem to be intermediate products of the methane transformation. CO2 is not formed in C-O-H fluid under pressure and temperature, corresponding to the upper mantle thermobaric conditions. In the warmer zones of the upper mantle the hydrocarbon mixture, formed from methane, only consists of light hydrocarbons (up to C5).

5. It is proposed, that petroleum hydrocarbons are actively involved in subduction. During subduction carbon from petroleum hydrocarbons transforms to iron carbide, that can be transported to the mantle zones with appropriate thermobaric conditions and become a carbon donor for the abiogenic hydrocarbon synthesis. Iron hydride, due to very high density, can form a single phase, that may sink to greater depths, transporting hydrogen and reduced iron.

In summary, the current investigation proposes that

petroleum hydrocarbons, accumulated in the crust, are actively involved in the deep carbon processes. The possible existence of petroleum deposits in the entire depth range of the crust and, therefore, larger volume of petroleum, subducted in the mantle, supposes the significant impact of hydrocarbons in the deep carbon cycle, that must be taken into consideration. However, this fundamental process of the Earth does not lead to the formation of CO2. Instead, petroleum hydrocarbons decompose to the simpler compounds, which can become intermediates in the abyssal abiogenic hydrocarbon formation process, contributing to crustal petroleum accumulations.

Future investigation will be focused on the following issues: • Investigation of the C-O-H fluid at the thermobaric conditions, corresponding to the deeper mantle layers. • Investigation of the ethane, propane and butane behavior under the thermobaric conditions, corresponding to the upper mantle, and their influence on the C-O-H fluid. • Quantitative estimation of the possible amount of petroleum in the crust, that submerges into the mantle during subduction per year/century/million years. • The influence of mantle-derived minerals – the possible catalysts, on the behavior of hydrocarbons at the upper mantle thermobaric conditions.


• Investigation of the deep hydrocarbon cycle influence on the methane emissions in the atmosphere. • Testing the hypothesis, that iron carbide can be a carbon donor in the abiogenic deep genesis of hydrocarbons.


Chapter 6. Summary of appended papers This thesis is based on four journal papers. These papers are

summarized in this chapter. Paper A. Fate of hydrocarbons in iron-bearing mineral

environments during subduction. The investigation of the possible transformations of

hydrocarbons in the presence of iron-bearing rock-forming material of the subducting slab and upper mantle surroundings. The chemical reactions in the system hydrocarbons mixture - iron substances were investigated in the range of thermobaric conditions corresponding to the depth down to 290 km (2.6-9.5 GPa, 1200-2300 K). The experimental procedure and analysis techniques are fully described in the paper. The result of the research demonstrates that iron hydride (FeHx) and iron carbide (Fe7C3) may be formed in consequence of the chemical interaction between petroleum hydrocarbons and the rock-forming iron compounds under the mantle thermobaric conditions at the depth of 200-290 km. These substances may be present in the mantle and take part in the abyssal hydrocarbons formation. In addition, it was demonstrated, that the hydrocarbon - iron-bearing mineral chemical interaction does not lead to the formation of carbon dioxide.

Paper B. Formation of complex hydrocarbon systems from

methane at upper mantle thermobaric conditions. The presented investigation was focused on the methane

transformations at thermobaric conditions, corresponding to the depth of 70-80 km (850-1,000K, 2.5 GPa), using a novel technique for such purposes – Toroid-type LRV unit. Due to this method the chemical products of the methane transformations were investigated by means of gas chromatography, that allowed detecting heavy normal and iso-paraffins, naphtenes and aromatic hydrocarbons in the reaction products and the absence of CO2 in the products mixture. The results obtained broad knowledge about the behavior of hydrocarbons under the thermobaric conditions, corresponding to the upper mantle, and suggest possible chemical pathways of the abyssal abiogenic hydrocarbons formation.

Paper C. Stability of a petroleum-like hydrocarbon mixture at

thermobaric conditions corresponding to depths of 50 km.


The paper is aimed at experimental investigation of the thermal and Redox stability of the complex hydrocarbon mixture at thermobaric conditions, corresponding to depth down to 50 km (up to 450ºC and 1.4 GPa). It was discovered that the complex hydrocarbon mixture, similar to natural petroleum, kept its chemical composition at the pressure and temperature of the Earth’s crust. It was also shown, that hydrocarbons did not undergo a reaction with the iron-bearing oxidizer in a modeled highly oxidative environment. The research explains the existence of ultra-deep crude oil deposits and demonstrates the possibility of the petroleum existence in the entire depth range of the Earth’s crust.

Paper D. The photochemical reaction of hydrocarbons under

extreme thermobaric conditions. This publication is focused on the photochemical effect of

Raman spectroscopy on the hydrocarbon systems at extreme pressure and temperature. During the Raman laser irradiation hydrocarbons can react under specific thermobaric conditions. Particularly, the strong luminescence signal and disappearance of the Raman peaks of hydrocarbons was detected. This photochemical effect was investigated in the pressure range 0.7-12 GPa and the temperature range from the ambient conditions to 450°C, while the power of laser from 0.05 W to 1.2 W was used in the experiments. The initiation of the photochemical reaction in the complex hydrocarbon system depends on the pressure, temperature, and laser power. However, the key factor in this phenomenon is the pressure.


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Influence of the deep petroleum transformation on the CO2 budget of the atmosphere

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