Kerogen Pyrolysis Research Articles

Feasibility and recovery efficiency of in-situ shale oil conversion in fractured reservoirs via steam heating: Based on a coupled thermo-flow-chemical model

Shale oil is a type of liquid hydrocarbon obtained through the pyrolysis of organic matter such as kerogen in oil shale reservoirs. Effective extraction of shale oil can significantly alleviate the pressure on oil supply. Among the various methods proposed for shale oil extraction, in-situ conversion of shale oil through high-temperature steam heating is a promising technique. This study employs a newly developed thermo-flow-chemical numerical simulator to establish a heterogeneous geological model and provides a detailed description of the evolution of different components within the shale oil reservoir during the in-situ conversion process. Additionally, the study thoroughly analyzes the role of high-permeability channels, such as fractures, in fluid transport and heat transfer during this process. In comparison with homogeneous reservoirs, fractures play a controlling role in the transport of steam. After injection, steam forms a preferential transport path between the heating well and the production well through the fractures. Subsequent injected steam will preferentially travel through this path, leading to faster heating of the reservoir. However, the uneven distribution of fractures may result in incomplete pyrolysis of the organic matter within the reservoir. Additionally, we found that the producing pressure and the steam injection rate significantly affect the pyrolysis of kerogen and the production of oil and gas. Both excessively low producing pressure and excessively high steam injection rate are detrimental to shale oil extraction. Based on these findings, this study aims to develop more rational heating strategies for reservoirs with different characteristics.

Geochemical Characteristics and Origin of Natural Gas in the Middle of Shuntuoguole Low Uplift, Tarim Basin: Evidence from Natural Gas Composition and Isotopes

Multiple types of reservoirs, including volatile oil reservoirs, condensate gas reservoirs, and dry gas reservoirs, have been discovered in ultra-deep layers buried at depths greater than 7500 m. Understanding the genetic types of natural gas is of utmost importance in evaluating oil and gas exploration potential. The cumulative proved reserves of the super deep layer in the Shuntuoguole low uplift area of the Tarim Basin exceed 1 × 108 t (oil equivalent). The origin, source, and accumulation characteristics of natural gas still remain a subject of controversy. By analyzing the composition and carbon isotope of natural gas, a detailed investigation was conducted to examine the unique geochemical and reservoir formation characteristics of the Ordovician ultra-deep natural gas within different fault zones in the middle region of the Shuntuoguole low uplift. It was determined that most of the natural gas in this area is displaying a characteristic of wet gas with a drying coefficient ranging from 0.41 to 0.99. The carbon isotope composition of methane in the gas reservoir shows relatively light values, ranging from −49.4‰ to −42‰. The carbon and hydrogen isotopes of the components are distributed in a positive order. The natural gas is oil type gas, which is derived from marine sapropelic organic matter and has a good correspondence with the lower Yuertusi formation. The maturity of natural gas in Shunbei No. 1 and No. 5 fault zones is about 1.0%, which is the associated gas of normal crude oil, while the maturity of No. 4 and No. 8 fault zones is higher than 1.0%, which is the mixture of kerogen pyrolysis gas and crude oil pyrolysis gas. The variations in the drying coefficient and carbon isotope composition of the natural gas provide evidence for the migration patterns within the Shuntuoguole low uplift central region. It indicates that the Shunbei No. 5 and No. 8 fault zones have likely migrated from south to north, while the No. 4 fault zone has migrated from the middle to both the north and south sides. These migration patterns are primarily controlled by high and steep strike-slip faults, which facilitate the vertical migration of natural gas along fault planes. Consequently, the gas accumulates in fractured and vuggy reservoirs within the Ordovician formation.

Study on pyrolysis characteristics of Gonghe oil shale using Py-GC/MS under different atmospheres

ABSTRACT Taking Gonghe oil shale as raw material, the rapid pyrolysis experiment was carried out using the Py-GC/MS device under different atmospheres. The effects of different pyrolysis atmospheres on the rapid pyrolysis products of Gonghe oil shale were studied. The results show that the H2 atmosphere can not only increase the content of saturated hydrocarbons and reduce the content of unsaturated hydrocarbons but also reduce the content of oxygen-containing heterocyclic compounds. This may be because more H free radicals under the H2 atmosphere are produced to react with the free radical fragments formed by kerogen decomposition. The coupling between H free radicals and free radical fragments can prevent the polymerization among macromolecular free radicals and inhibit the generation of heavy byproducts, which can promote the kerogen pyrolysis and increase the release of volatile matter. In addition, the pyrolysis atmosphere is conducive to the deoxygenation of oxygen-containing heterocyclic compounds to a certain extent.

Microwave heating of oil shale based on multiphysics field coupling: Positioning of the waveguide

Microwave heating has proven widespread applications in oil shale pyrolysis; however, the impact of waveguide port positioning on the microwave reactor's thermal performance remains underexplored. This work establishes a 3D coupled model that incorporates electromagnetic, thermochemical, and fluid dynamics effects employing multiphysics modeling methodology. The thermochemical characteristics of an oil shale sample under microwave irradiation are quantified for a broad range of waveguide port positions, specified via Latin hypercube sampling, which ensures the randomness of the port coordinates. The cavity field strength exhibits markedly high sensitivity to the waveguide positioning: the standard deviation of the cavity-averaged electromagnetic intensities for all considered positions is found to be 30.42% greater compare to the associated mean. The best port position yields a temperature rising rate an order of magnitude higher than the worst positioning, for which kerogen pyrolysis does not appear to be even activated in the same initial stage. The ranking of waveguide positions identified based on the temperature rising rate aligns well with the analysis of microwave utilization efficiency. The study offers insights for optimized microwave reactor design with enhanced oil shale thermal treatment.

Fluid inclusion records of oil-cracked wet gas in Permian carbonate reservoirs from the Eastern Sichuan Basin, China

Oil-cracked gas is an important gas resource in petroliferous basins. In theory, oil-cracked gas should be rich in C2+ (i.e., wet gas). However, gas reservoirs of oil cracking origin in the Sichuan Basin (South China) are mainly composed of dry gas. Fluid inclusions record hydrocarbon generation and evolution. Obviously, identifying wet gas inclusions is the key to solving the above controversy. Here, we calibrate the Raman spectroscopic detection limits of ethane and propane (0.007 and 0.016 MPa, respectively) and demonstrate that Raman spectroscopy is a powerful method to identify C2+-bearing inclusions. Based on this technique, C1–C2–C3-bearing wet gas inclusions (C1/ƩCi = 0.90–0.93) are identified in calcite cements of the Permian Changxing Formation carbonate reservoir in the Eastern Sichuan Basin. These inclusions are direct geological evidence of oil-cracked gas because the calcite cement precipitated after the formation of pyrobitumen. Furthermore, reconstruction of the temperature-pressure-composition evolutions of calcite-hosted (Changxing Formation) and quartz-hosted gas inclusions in the Ordovician Wufeng–Silurian Longmaxi Formation black shale indicates that high pressure can effectively retard the cracking of C2+ gas hydrocarbons. Differences in gas composition and δ13CCH4 signature between reservoir gas and inclusion gas lead us to conclude that large-scale oil cracking occurred during the Early–Middle Jurassic in the Permian Changxing carbonate reservoir. Nevertheless, oil-cracked gas escaped during the evolution of the paleo-gas reservoir. Formation of the current dry gas reservoir can be attributed to the continuous mixing of late-stage kerogen pyrolysis gas.

Performance Prediction and Heating Parameter Optimization of Organic-Rich Shale In Situ Conversion Based on Numerical Simulation and Artificial Intelligence Algorithms.

In situ conversion technology is a green and effective way to realize the development of organic-rich shale. Supercritical CO2 can be used as a good heating medium for shale in situ conversion. Numerical simulation is an important means to explore the shale in situ conversion process, but it requires a lot of time and computational cost for in situ conversion simulation under different working conditions. Therefore, a computational framework for rapid prediction of shale in situ conversion development performance and heating parameter optimization is proposed by coupling artificial neural network (ANN) and particle swarm optimization (PSO). The results indicated that kerogen pyrolysis and hydrocarbon product release mainly occurred within 2 years of shale in situ conversion. The production curves of pyrolysis hydrocarbon obviously slowed after in situ conversion for 2 years. The database was constructed by a large number of in situ conversion simulations, and Pearson correlation analysis and the random forest method were adopted to obtain seven main controlling factors affecting reservoir temperature and hydrocarbon production. The determination coefficient of the obtained ANN-based prediction models is higher than 97%, and the mean square error (MSE) is lower than 0.3%. The basic reservoir case can choose to inject 350-450 °C supercritical CO2 (Sc-CO2) fluid with a rate of 600 m3/day to obtain a more promising development effect. The heating parameter optimization for three typical reservoir cases using PSO was performed, and reasonable injection temperature and injection rate were obtained. It realized accurate development prediction and rapid heating parameter optimization, which helps the effective application of shale in situ conversion development design.

Oil Shale In Situ Production Using a Novel Flow-Heat Coupling Approach.

Oil shale development, a significant global energy concern, involves the pyrolysis of kerogen, a process that can heat and contaminate groundwater with pyrolysis products. To address these challenges, this study introduces the ambient-temperature gas in situ heating (ATGIH) method as an alternative to traditional techniques. The ATGIH method establishes a low-temperature gas barrier to prevent water infiltration into the production zone by placing heating holes between the injection and production wells. The effectiveness of the ATGIH method in mitigating groundwater contamination during oil shale development is demonstrated through thermochemically coupled reservoir simulations. The study further discusses how gas injection enhances the flowability of mobile oil and gas phases into production wells and how controlling the Dykstra-Parsons coefficient, a measure of heterogeneity, can mitigate gravity segregation and aggregate viscous fingering issues. Our results show that well spacing is a critical factor in designing oil shale development, with a larger spacing resulting in higher energy efficiency but lower oil recovery rates. Furthermore, the study reveals that porosity decreases while permeability increases during pyrolysis due to thermal cracking and pore structure changes. It also highlights that heterogeneity-induced issues can be alleviated by increasing the correlation length to make the system more homogeneous. Therefore, the ATGIH method represents a key innovation in oil shale development, offering a solution that mitigates groundwater contamination while improving the energy efficiency.

Composition of Hydrocarbon Gases Formed by Dry Pysolysis of Domanik Shale Kerogen after Hydrothermal Experiment

The composition of hydrocarbon gases formed by pyrolysis of residual Domanik shale kerogen at 800°C, preceded by hydrothermal treatment at 250–375°С, was studied by pyrolytic gas chromatography. Starting from the autoclave temperature of 320–325°C, the hydrothermal treatment of the shale affects the kerogen structures responsible for the formation of C2+ gases in pyrolysis at 800°C. An increase in the temperature of the shale hydrothermal treatment leads to a monotonic increase in the С1/С2+ ratio in the products of the residual kerogen pyrolysis at 800°C. The methane yield at 800°C does not correlate with the content of alkyl structures, determined in kerogen by IR spectroscopy, and the yield of С2+ gases linearly correlates with the content of alkyl structures.

ReaxFF Molecular Dynamics Study on the Microscopic Mechanism for Kerogen Pyrolysis.

Kerogen is mainly composed of carbon, hydrogen, and oxygen, which are the main components of crude oil and gas. The pyrolysis of kerogen is an efficient method to generate clean energy. In the present work, the pyrolysis reaction process of three types of kerogen is simulated using ReaxFF molecular dynamics (MD) methods to study the microscopic mechanism and the distribution of products. The results indicated that the pyrolysis products of the three types of kerogen significantly depend on the molecular structures, temperature, and reaction time. As the temperature increases, the gaseous hydrocarbon and the light and heavy oil fractions decreased, where small molecular fragments polymerized to form new molecular fragments. For an isothermal temperature, with the reaction proceeding, some component polymerization of the pyrolyzed fragments occurred, resulting in the generation of new light oils and heavy oils. Moreover, quantum chemical analysis was employed to reveal the kerogen pyrolysis mechanism. First, the weak bonds such as C-O, C-N, and C-S structures were decomposed to generate large carbon and some heavy shale oil fragments. Second, the cycloalkanes and long-chain alkanes were decomposed to generate a large amount of light shale oil and gaseous hydrocarbons. Finally, the decomposition of C═C in the aromatic ring, the secondary decomposition of light and heavy shale oils, and the further decomposition of short-chain alkanes occurred. In addition, the production of hydrogen (H2) occurred at the late stage of the pyrolysis reaction. Hydrogen radicals were formed by the decomposition of C-H bonds and subsequently collided with each other, resulting in the formation of H2 molecules. The pyrolysis and chemical analysis of kerogen can clearly determine the type and content of hydrocarbon substances, providing scientific data for exploration, development, and utilization of shale gas and shale oil.

The mechanism of H2O in the superheated steam affecting pyrolysis of the kaolinite-associated kerogen

In this work, ReaxFF molecular dynamics (MD) simulation was adopted to investigate the effect of superheated steam on the conversion of the kaolinite-associated Barkol kerogen (BLK) and reveal the corresponding mechanism. The ReaxFF simulated weight loss rate (DTG) and release tendency of H2O, H2 and CO2 for BLK and the kaolinite-associated BLK agreed well with the results of Py-MS experiments. H-rich rate, double bond equivalents (DBEs), and hydrocarbon content were adopted to assess the quality of C5-C40, and configurations of C40+ were extracted to investigate the characteristics of residues. And the H2Osteam- and kaolinite-involved (steam refers to the superheated steam) reactions were analyzed. The results indicate that B- and L-acid sites of kaolinite co-catalyzed decomposition of BLK into heavy oil and shale gas in the kaolinite-pyrolysis system, and in steam/kaolinite-pyrolysis system, H2Osteam further promoted decomposition of BLK into higher quality shale oil, especially for C5-C13 components, remaining higher aromatic and porous residues. And this enhanced effect of H2Osteam is attributed to kaolinite and the induced decomposition of H2Osteam molecules and their participation as reactants in reactions in two aspects: i) interaction between kaolinite and H2Osteam, on one hand, inhibited formation of L-acids and facilitated generation of B-acids to catalyze carbocation ion reactions process, further weakened dehydrogenation of organics catalyzed by L-acid sites, and enhanced cracking of residues catalyzed by B-acaid sites, on the other hand, promoted decomposition of H2Osteam molecules to form H-rich environment and further weakened dehydrogenation of organics; ii) attacking Car directly, H2Osteam promoted shedding of alkyl side chains and ring-opening of aromatics to increase the –CH2– content in shale oil. This paper provides theoretical guidance for further understanding mechanism of H2Osteam on pyrolysis of kaolinite-associated kerogen and corresponding catalyst development and preparation.

Effect of methanol on the pyrolysis behaviour of kerogen by ReaxFF molecular dynamics simulations

ABSTRACTA series of molecular dynamics simulations were performed using the ReaxFF reactive force field to investigate the pyrolysis of Longkou oil shale kerogen in the presence of methanol. The roles of methanol in kerogen pyrolysis were deeply explored to reveal the microscopic mechanism of methanolysis by analyzing the distribution of products, the consumption of methanol, and the formation processes of typical products at different temperatures. The results demonstrate that the yield of shale oil in the presence of methanol is consistently higher than that of kerogen direct pyrolysis at the same temperature, which is consistent with the trend of oil yield with temperature reported by previous methanolysis experiments. Methanol supplies a large number of small radicals under the pyrolysis condition, which can facilitate the breakage of weak bonds and take part in the formation of products through combining with the radical fragments generated by the pyrolysis of kerogen. This study will provide theoretical guidance for understanding the methanolysis process of oil shale.

Natural and laboratory-induced maturation of kerogen from the Vaca Muerta Formation: A comparison study

Artificial maturation of kerogen is a widely used technique to assess the hydrocarbon potential of shale rocks and to observe thermal transformations of organic matter in the laboratory. However, the degree of reproducibility of natural geological transformation at the molecular level is still not fully established. In the present work, a set of kerogens isolated from Vaca Muerta Formation core samples at varying levels of thermal maturity were studied. Another set of samples was obtained by anhydrous pyrolysis of kerogen in a closed system. Molecular structures measured by solid-state techniques (13C NMR, XPS and FTIR) were compared in natural and artificially matured samples at equivalent levels of thermal maturation. We observed that heating in an anhydrous closed system accurately reproduces most of the molecular structural changes observed during natural thermal maturation, with exceptions related to the branching degree and oxygen containing groups. The evolution of some parameters, such as N and S content, are highly variable in the natural samples because of differences in their deposition environments. In these cases, artificial thermal maturation changes are smaller and follow more clearly defined trends because variables other than thermal changes are not present. This is the first work comparing natural and artificial thermal maturation in the Vaca Muerta Formation and add valuable data regarding the limitation of artificial maturation that can be extrapolated to other formations.

Experimental and mechanistic study on isothermal oxidative pyrolysis of oil shale

The reasonable introduction of oxygen to the in situ conversion process of oil shale can effectively reduce energy consumption. However, current studies on oxidative pyrolysis often proceed under non-isothermal conditions with sharp fluctuations in temperature which hinders the accurate determination of the reaction process and the corresponding temperature in the system. In this work, we study the isothermal oxidative pyrolysis behavior of two oil shales differing in total organic carbon (TOC) at constant temperatures. The results indicated that with the increase in reaction temperature, low-temperature oxidative pyrolysis (LTOP) and high-temperature oxidative pyrolysis (HTOP) can be distinguished, where the transition temperature is approximately 340 ℃. During the LTOP, kerogen undergoes low-temperature oxidation, including oxygen addition, isomerization, and decomposition reactions. As for the HTOP, high-temperature oxidation coexists with the pyrolysis of kerogen and the subsequent coke oxidation. The pyrolysis reaction gradually dominates the entire reaction with increasing temperature. Accordingly, a temperature-dependent reaction model of oxidative pyrolysis of oil shale in isothermal conditions was validated and the real-time change in the reaction rates was obtained. Also, oil shale with a higher TOC has a more intense reaction and a higher transition temperature of HTOP and LTOP. This work provides a theoretical basis for the further application of oxidative pyrolysis in oil shale exploitation.

Study on the kinetic-guided pyrolysis of oil shale kerogen catalyzed by needle-like NiFe-LDH

An in-depth understanding of the thermo-physicochemical behavior of kerogen catalytic pyrolysis is helpful to realize the efficient utilization of oil shale. In this work, the pyrolysis behavior of Barkol Kerogen and its product distribution were investigated by dry distilled experiment with needle-like NiFe-LDH as Catalyst, which was designed based on the kinetic experiments. As a result, NiFe-LDH has low-temperature and high-efficiency pyrolysis catalytic activity in the oil shale recovery and product selectivity. The initial pyrolysis catalytic temperature of kerogen was advanced to 250 °C, and the optimum pyrolysis temperature was decreased by 42.02 °C. The catalytic pyrolysis temperature was selected as 400 °C because of the maximum temperature weight loss in thermal analysis. NiFe-LDH not only increased the oil yield of kerogen by 5.18% and alkane selectivity by 2.62% but also reduced the content of heteroatomic hydrocarbon by 6.46%. Simultaneously, according to the change of activation energy during thermal analysis and the results of pyrolysis experiment, the catalytic pyrolysis process was speculatively divided into three possible stages. This resolution is helpful to understand the catalytic effect of NiFe-LDH on kerogen. Thus, NiFe-LDH plays a distinct role in the catalytic pyrolysis of kerogen and its kinetic regulation.

Average molecular structure model of shale kerogen: Experimental characterization, structural reconstruction, and pyrolysis analysis

Shale can be both a source rock and a reservoir rock, which is a typical self-generating and self-storing type of oil accumulation. Its main organic component is kerogen. Using molecular dynamics (MD), a realistic kerogen molecular structure model is an alternative to experimental and analytical-only approaches for studying shale organic matter's microscopic properties. Therefore, it is useful to establish an average molecular structure model for shale kerogen. Moreover, the pyrolysis mechanism of shale kerogen is of great significance for developing and utilizing shale mineral resources. In this study, geochemical and spectroscopic measurements such as the elemental analysis, 13C nuclear magnetic resonance spectroscopy (13C NMR), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) were used to obtain information about the carbon skeleton, aliphatic structures, and aromatic structures of the kerogen. Following information analysis and molecular fragment splicing, a 2D molecular structure model of kerogen from the Nanpu shale, with the chemical formula C199H240O20N6S2 and molecular weight of 3096 Daltons was constructed. After that, the accuracy of the 2D structure was verified by comparing the 13C NMR spectra simulated by the 2D structure to the experimental spectra. Using MD simulation, based on the kerogen density, 10 2D structures are then combined to create a realistic 3D molecular structure model of kerogen. Finally, pyrolysis analysis was performed based on the established 3D molecular structure model of kerogen to determine the effect of temperature on pyrolysis. Using the advantages of various technologies, this study not only provides a systematic method for establishing a realistic 3D molecular structure model of kerogen but also contributes to in-depth research on the reaction mechanism of kerogen pyrolysis, providing a reliable foundation for future research on the properties of shale at the molecular scale.

Petrological Characteristics and Hydrocarbon Generation of Carbonate Source Rocks of the Permian Taiyuan Formation in Central and Eastern Ordos Basin, China

In order to evaluate the hydrocarbon generation potential and effectiveness of the carbonate source rock from the Lower Permian Taiyuan Formation of the Upper Paleozoic gas reservoirs in the central and eastern Ordos Basin, 87 core samples from the formation were analyzed through the comprehensive application of core observation, thin section analysis, lithofacies division, and organic geochemistry experiments. The results show that the carbonate source rocks of the Taiyuan Formation comprise four lithofacies types with type I–II kerogen: laminar argillaceous micritic limestone, massive micrite, massive bioclastic micritic limestone, and massive algae-clotted limestone. Among them, laminar argillaceous micritic limestone and massive micrite are favorable lithofacies for high-quality source rocks, with a TOC distribution range of 0.99% to 6.07% (average 2.56%) and 0.24% to 8.27% (average 1.77%), respectively. Hydrous gold tube pyrolysis showed that the samples of laminar argillaceous micritic limestone and massive micrite attained a peak yield of nearly 115.0 mL/g TOC (heating rate 2 °C/h) and 101.4 mL/g TOC (heating rate 2 °C/h), respectively, for C1–5 compounds. Due to the higher maturity of the samples, the hydrocarbon gases were dominated by residual kerogen pyrolysis gases and lacked liquid hydrocarbon cracking gas. Furthermore, the carbonate source rocks had weak methane absorption ability, with a maximum adsorption capacity of only about 0.15 cm3/g. In addition, the hydrocarbon gas generation of carbonate source rocks of the Taiyuan Formation was far greater than 0.2 mL/g rock, which is the lower limit standard for effective gas source rock. Therefore, the carbonate source rocks of the Taiyuan Formation should be regarded as important gas source rocks in subsequent explorations of the central and eastern Ordos Basin.

Heat-Induced Pore Structure Evolution in the Triassic Chang 7 Shale, Ordos Basin, China: Experimental Simulation of In Situ Conversion Process

The reservoir properties of low–medium-maturity shale undergo complex changes during the in situ conversion process (ICP). The experiments were performed at high temperature (up to 450 °C), high pressure (30 MPa), and a low heating rate (0.4 °C/h) on low–medium-maturity shale samples of the Chang 7 Member shale in the southern Ordos Basin. The changes in the shale composition, pore structure, and reservoir properties during the ICP were quantitatively characterized by X-ray diffraction (XRD), microscopic observation, vitrinite reflectance (Ro), scanning electron microscopy (SEM), and reservoir physical property measurements. The results showed that a sharp change occurred in mineral and maceral composition, pore structure, porosity, and permeability at a temperature threshold of 350 °C. In the case of a temperature > 350 °C, pyrite, K-feldspar, ankerite, and siderite were almost completely decomposed, and organic matter (OM) was cracked into large quantities of oil and gas. Furthermore, a three-scale millimeter–micrometer–nanometer pore–fracture network was formed along the shale bedding, between OM and mineral particles and within OM, respectively. During the ICP, porosity and permeability showed a substantial improvement, with porosity increasing by approximately 10-times and permeability by 2- to 4-orders of magnitude. Kerogen pyrolysis, clay–mineral transformation, unstable mineral dissolution, and thermal stress were the main mechanisms for the substantial improvement in the reservoir’s physical properties. This study is expected to provide a basis for formulating a heating procedure and constructing a numerical model of reservoir properties for the ICP field pilot in the Chang 7 shale of the Ordos Basin.

Gas Desorption Characteristics of the Chang 7 Member Shale in the Triassic Yanchang Formation, Yan’an Area, Ordos Basin

In the Yan’an area of the Ordos Basin, the lithological heterogeneity of Chang 7 Member shale is extremely strong. In addition, sandy laminae is highly developed within the Chang 7 Member shale system. In order to explore the gas generation and migration processes of Chang 7 Member shale, geochemical characteristics of desorption gas are comprehensively compared and analyzed. In this study, rock crushing experiments were carried out to obtain shale samples, and desorption experiments were carried out to obtain shale samples and sandy laminated shale samples. For the crushing gas and desorption gas, the volume contents of different gas components were obtained using gas chromatography experiments. The rock crushing experiments revealed that the average volume percentage of CH4 in Chang 7 Member shale is 61.93%, the average volume percentage of C2H6 and C3H8 is 29.53%, and the average volume percentage of other gases is relatively small. The shale gas in Chang 7 Member is wet gas; the gas is kerogen pyrolysis gas. Most of the shale gas hosting in Chang 7 Member shale is adsorbed gas. Porosity, permeability and organic matter content are the main geological factors controlling gas migration and gas hosting. Shale with a higher porosity, good permeability and a low organic matter content is conducive to gas migration. The shale gas in Chang 7 Member shale contains CH4, C2H6, C3H8, iC4H10, nC4H10, iC5H12, nC5H12, CO2 and N2. N2 migrates more easily than CH4, and CH4 migrates more easily than CO2. For hydrocarbon gases, gas components with small molecular diameters are easier to migrate. The desorption characteristics of shale might provide clues for guiding hydrocarbon exploration in the study area. The sandy laminated shale with a higher gas content may be the “sweet spot” of shale gas targets. In Chang 7 Member, the locations hosting both shale oil and CH4 may be the most favorable targets for shale oil production.

Mechanism and reservoir simulation study of the autothermic pyrolysis in-situ conversion process for oil shale recovery

The autothermic pyrolysis in-situ conversion process (ATS) consumes latent heat of residual organic matter after kerogen pyrolysis by oxidation reaction, and it has the advantages of low development cost and exploitation of deep oil shale resources. However, the heating mechanism and the characteristic of different reaction zones are still unclear. In this study, an ATS numerical simulation model was proposed for the development of oil shale, which considers the pyrolysis of kerogen, high-temperature oxidation, and low-temperature oxidation. Based on the above model, the mechanism of the ATS was analyzed and the effects of preheating temperature, O2 content, and injection rate on recovery factor and energy efficiency were studied. The results showed that the ATS in the formation can be divided into five characteristic zones by evolution of the oil and O2 distribution, and the solid organic matter, including residue zone, autothermic zone, pyrolysis zone, preheating zone, and original zone. Energy efficiency was much higher for the ATS than for the high-temperature nitrogen injection in-situ conversion process (HNICP). There is a threshold value of the preheating temperature, the oil content, and the injection rate during the ATS, which is 400 °C, 0.18, and 1100 m3/day, respectively, in this study.

Highly efficient catalytic pyrolysis of oil shale by CaCl2 in subcritical water

An innovative method combining CaCl2 with subcritical water is proposed for in-situ mining of oil shale. The catalytic hydrothermal pyrolysis of block Huadian oil shale was carried out at 350 °C to evaluate the feasibility and reaction mechanism of this method. After adding CaCl2, the time required for kerogen pyrolysis was shortened from 70 to 40 h, while the maximum expelled oil yield increased from 19.14% to 21.96%. This excellent catalytic activity indicated that CaCl2 was transported into shale matrix by subcritical water to catalyze the pyrolysis of kerogen. It was found that the C–O bonds in kerogen were first broken and then the whole decomposition of kerogen initiated. The compositional analysis of residual kerogen indicated that CaCl2 could facilitate the transportation of hydrogen from subcritical water to kerogen, thereby inhibiting the excessive condensation of kerogen to improve its oil-generating potential. The macromolecular compounds in expelled oil would undergo a secondary cracking reaction. Besides, CaCl2 could also promote the re-cracking and discharge of residual bitumen in oil shale matrix. These findings demonstrated that combining CaCl2 and subcritical water enabled efficient pyrolysis of block oil shale and provided a novel technique for in-situ mining of oil shale.