Oil Shale Resources Research Articles

Shale Oil–Water Two-Phase Flow Simulation Based on Pore Network Modeling

Abstract With the growing significance of shale oil in the realm of oil and gas resources, there has been a heightened focus on the impact of the indeterminate oil–water two-phase flow behavior in shale reservoirs on the effective exploitation of shale oil. The utilization of FIB–SEM scanning on shale samples enables the establishment of the real pore network structure and facilitates the analysis of pore type, pore throat size and connectivity of shale reservoirs through the implementation of two-dimensional slices. Subsequently, the gridded connectivity-based pore network model is utilized to conduct oil–water two-phase flow simulation, wherein the L–S and N–S mathematical models are incorporated to quantitatively examine the correlation between the displacement pressure and wettability and the recovery degree and remaining oil, as well as the impact of throat size on pressure loss. The research findings indicate the emergence of five distinctive pore types in shale reservoirs, namely intergranular pores, dissolution pores, intercrystalline pores, intracrystalline pores, and microfractures. In shale reservoirs with poor connectivity, a significant quantity of nanometer-scale pores are generated, wherein the seepage capacity is primarily influenced by the size and connectivity of pore throats. The smaller the throat size is, the greater the displacement pressure will be and the greater the pressure drop will be after the throat is passed through. To prevent fingering and excessive pressure drop, it is necessary to maintain reasonable control over the displacement pressure. The displacement efficiency is optimal when the wall surface is in a water-wet state. Therefore, enhancing the wettability of the surface can facilitate the efficient recovery of the remaining oil in the microscopic pore throats. The research findings offer valuable theoretical insights for the efficient exploitation of shale oil resources.

Characteristics and genesis of tuffaceous shale oil lithofacies:A case study of Lucaogou Formation in Santanghu Basin

Lucaogou Formation in the Santanghu Basin is a special lacustrine fine-grained sedimentary deposits rich in volcanic debris and carbonate, with abundant shale oil resources. However, understanding of shale oil characteristics and genesis remains unclear. Lithofacies, sedimentary environment, and formation mechanisms of tuffaceous shale oil are investigated based on core and thin section observations, X-ray diffraction, field emission SEM and geochemical analysis. Results show that three mixed lithofacies types are developed in Lucaogou Formation: blocky tuff, laminated tuffaceous dolomite, and laminated dolomitic tuff. These lithofacies types are characterized by high content of felsic and dolostone, widespread organic matter, and low clay content. Formation of tuffaceous shale oil sweet spots is primarily influenced by four factors: inputting of volcanic ash as a high-quality source rocks and reservoirs provides good material basis; devitrification of volcanic glass, calcitization, and dissolution are crucial for formation of reservoirs; expulsion of source rocks with high-abundance organic matter expulsion facilitates migration and accumulation of hydrocarbon in adjacent reservoirs; fracture development improves reservoir permeability to form highly productive sweet spots. By analyzing characteristics and genesis of tuffaceous shale oil, the main controlling factors of reservoir physical property and oil saturation are clarified, which is of great significance for selection of shale oil exploration zones.

Shale oil potential and mobility in low- to medium-maturity lacustrine shales: A case study of the Yanchang Formation shale in southeast Ordos Basin, China

Oil mobility is essential for the evaluation of shale oil resources, yet there has been limited research conducted on the oil mobility of low- to medium-maturity lacustrine shale. This study integrates multiple methodologies such as organic geochemistry, mineralogy, oil-kerogen adsorption-swelling experiments, and in-situ conversion process (ICP) models to evaluate the mobility and potential for shale oil in the lacustrine shale of the Yanchang Formation in the Yaoqu 1 (YQ1) well situated in the southeastern region of the Ordos Basin. The Chang 7 shales are categorized as highly favorable source rocks, nonetheless, the oil contained within these layers predominantly exists in an adsorbed-swelling state, resulting in limited mobility as indicated by the oil saturation index, a modified oversaturation index, and production index. Therefore, the utilization of existing conventional techniques for shale oil exploitation is not viable for the Chang 7 shale characterized by low to medium maturity in the study area. Nevertheless, during the ICP, the quantity and mobility of oil within the Chang 7 shales exhibit a substantial increase as temperature rises. Moreover, once the Chang 7 type II shales reach a maturity level of around 0.91%Ro, they demonstrate noteworthy prospects for shale oil production. The findings of this study serve as a valuable reference for guiding the advancement of in-situ conversion process technology in the study area, while also offering substantial evidence for addressing the intricate challenge of crude oil mobility in low- to medium-maturity lacustrine shale reservoirs.

Exploration and Development of Shale Oil in China: State, Challenges, and Prospects

Abstract —This article presents the latest state of exploration and development of shale oil of continental lacustrine formations in the main basins of China, summarizes the main theoretical considerations and key technologies for exploration and development, and suggests prospects for exploration and development of shale oil in China. It is believed that the exploration and development of oil in shale formations rich in organic matter of types I and II of medium and high maturity are key to the breakthrough of production of 10 million tons in China. This will play an important role in China’s stable oil production at the level of 200 million tons per year in the future. The efficient development of medium- and low- maturity shale oil resources can be significantly improved and lead to serious changes in oil production only after new breakthroughs in the theory and technology of shale deposits.

Fates of pyrolysis oil components in the non-isothermal propped fractures during oil shale in situ pyrolysis exploitation

In situ pyrolysis by heating the reservoir is an effective method to convert oil shale resources to liquid oil. However, in the in situ non-isothermal reservoir during artificial heating, pyrolysis oil components experience extremely complex processes from generation to recovery, including phase transition, component separation, migration, secondary cracking, etc. These processes determine the in situ pyrolysis exploitation efficiency. In this study, pore-scale experiments of distribution, migration, and recovery were performed in a non-isothermal propped fracture. Results showed that pyrolysis oil flowed in a mixed state of multi-components through continuous oil channels below 260 °C, and the continuous oil channels narrowed with the improvement of temperature; while the separation of the light and heavy components occurred at higher temperatures. The fates and recovery mechanism of pyrolysis oil components were revealed under different temperatures, results indicated that the distribution and migration characteristics contributed to the lightness of the produced oil, and might induce the blockage of the in situ reservoir. The obtained results can provide preferences for predicting and adjusting the status of in situ pyrolysis exploitation.

Understanding pore space and oil content of liquid-rich shale in the southern Bohai Sea, China

The commercial production of shale oil in onshore Bohai Bay Basin has become a reality, but the potential of offshore shale oil is still unclear. The Bohai Sea, the leading crude oil-producing area in China in 2022, has great potential of shale oil resources, but the shale properties have not been comprehensively studied. The southern Bohai Sea, including the Huanghekou and southwestern Bozhong Sags, was selected. The study was performed on three layers: the third member of Shahejie Formation, first and second members of Shahejie Formation (as a whole), and the third member of Dongying Formation. Twenty-one shale core samples from nine wells, for the first time, were analyzed for sedimentary structure, lithology, pore space, composition of the thermally hydrocarbons and oil content. The content of minerals, pore sizes, and composition of the thermally hydrocarbons were compared with those of shales from other regions of China. The potentially producible oil generated in the organic-rich laminae was found to be accumulated in the silt-grained laminae through micromigration. Mixed and siliceous shale were the main lithofacies. Mineral overgrowths and solid bitumen reduce the volume of former intergranular pores. Honeycomb-like OM pores in samples with higher maturity (Ro > 1.1%) substantially increased pore connectivity from FIB-SEM image datasets. The retained oil was mainly distributed in pores with widths larger than 4 nm. The composition of the thermally hydrocarbons in samples stored at ambient conditions was governed by the maturity and concentration of the OM. Light hydrocarbons, even gaseous hydrocarbons are still retained in the shale with lower maturity and higher TOC for strong sorption of OM. The oil content is 0.50–23.41 mg/g after Rock-Eval S1 correction, with an average of 6.27 mg/g. While average oil content is 1.38 mg/g without correction. Finally, the optimal production intervals for Well B4 and Well B8 were determined. This study provides data and suggestions for the exploration of shale oil resources in the southern Bohai Sea.

A Study on the Pore Structure and NMR Fractal Characteristics of Continental Shale in the Funing Formation of the Gaoyou Sag, Subei Basin

The continental shale oil resource in China exhibits significant potential and serves as a crucial strategic alternative to the country’s conventional oil and gas reserves. The efficacy of shale oil exploration and production is heavily contingent upon the heterogeneity of the pore structure within the reservoir. However, there remains a scarcity of research pertaining to the pore structure of continental shale and the factors that influence it. The objective of this study is to provide a quantitative characterization of the heterogeneity exhibited by the continental shale of the Funing Formation in the Gaoyou Sag. In this study, the research focus is directed toward the continental shale of the Funing Formation located in the Gaoyou Sag of the Subei Basin. This paper examines the correlation between the fractal dimension of nuclear magnetic resonance (NMR) and various factors including the total organic carbon (TOC), mineral composition, geochemical parameters, and physical properties, utilizing the principles of fractal dimension theory. The findings indicate that the primary pore types observed in the Funing Formation continental shale are inorganic matrix pores, which encompass dissolution pores, clay mineral intergranular pores, and a limited number of pyrite intergranular pores. By employing a relaxation time cutoff, the NMR fractal dimension can be categorized into two distinct dimensions: the bound-fluid-pore fractal dimension (0.5795~1.3813) and the movable-fluid-pore fractal dimension (2.9592~2.9793). The correlation between mineral composition and the fractal dimension indicates a negative relationship between the fractal dimensions of bound-fluid pores and movable-fluid pores and the content of quartz. The correlation between clay minerals and the fractal dimension indicates a significant negative relationship between the fractal dimensions of bound-fluid pores and movable-fluid pores with illite. There exists a negative correlation between the pore fractal dimension of bound fluid and the content of organic matter, whereas a positive correlation is observed between the pore fractal dimension of mobile fluid and the content of organic matter. The range of maturity of organic matter within the Funing Formation exhibits a relatively limited span, as indicated by the vitrinite reflectance (Ro) values falling between 0.8% and 0.9%. This narrow range of maturity does not exert a substantial influence on the two fractal dimensions. The NMR fractal dimension exhibits a negative correlation with permeability in relation to reservoir physical properties, while the bound-fluid-pore fractal dimension demonstrates a negative correlation with the total porosity. The findings suggest that the NMR fractal dimension can serve as a valuable indicator for evaluating the physical characteristics of reservoirs. The present study successfully examined the pore structure of continental shale through the utilization of nuclear magnetic resonance technology. This innovative technique provides a novel avenue for the assessment of continental shale reservoirs and the investigation of pore heterogeneity on a global scale.

Study on the mechanical properties of sandstone-shale composite continental shale gas based on the discrete element method

China has abundant continental shale oil resources, and multiple shale oil exploration and development demonstration zones have been established, making it a key field for oil and gas exploration and development. However, drilling and fracturing treatment often encounter vertically interlaced and superimposed sandstone and shale reservoirs, which significantly affect the stability of the reservoir and the propagation of fractures. Therefore, it is of great significance to study the rock mechanics characteristics of sandstone-shale composite. Using the orthogonal experimental method for microscale parameter calibration, this study established the relationship between the macroscopic and microscopic parameters of sandstone-shale in the parallel bond model. The results of the orthogonal experimental scheme were analyzed using multi-factor variance analysis and linear regression analysis to determine the influence and ranking of each microscale parameter on the macroscopic parameters. Based on the results of uniaxial and triaxial compression experiments, the particle flow simulation of sandstone-shale composite rock samples was studied using the discrete element method. The study investigated the influence of the thickness ratio, combination form, and confining pressure of sandstone-shale on the mechanical properties of composite rock samples. The results showed that: (1) Under uniaxial loading conditions, for the combination form of sandstone on top and shale on the bottom (M-S type), the peak stress of the composite rock sample increased first and then decreased and then increased again with the increase of the thickness of sandstone; for the combination form of shale on top and sandstone on the bottom (S-M type), the peak stress of the composite sample decreased first and then increased and then decreased again with the increase of the thickness of shale. (2) After applying confining pressure, the compressive strength of the M-S type composite sample decreased with the increase of the thickness ratio of sandstone, while the compressive strength of the S-M type composite sample increased with the increase of the thickness ratio of shale as well as the compressive strength of the composite sample was lower than that of any complete rock sample. (3) Under uniaxial loading, the fracture mode of the composite sample was related to the combination form and the thickness ratio of different lithologies. For the M-S type sample, when the thickness ratio of sandstone was <30%, the sample was mainly fractured by tension, and when the thickness ratio of sandstone was >30%, it was mainly fractured by shear mode. For the S-M type sample, when the thickness ratio of shale was <70%, the sample had the most internal shear cracks, and when the thickness ratio of shale was >70%, it had the most tension cracks.

Numerical Simulation Analysis of Wellbore Integrity and Casing Damage in High-Temperature Injection and Production of Shale Oil

Shale oil represents a relatively new form of unconventional oil and gas resource, and the extensive exploration and development of shale oil resources carry significant implications for China’s oil and gas supply and demand dynamics. At present, within the realm of low-maturity shale oil extraction technologies, the reservoir must be subjected to elevated temperatures ranging between 400 to 60 °C. Prolonged exposure of wellbores to such high temperatures can result in a substantial decrease in cement strength, the formation of microcracks due to cement cracking, and damage stemming from thermal stresses on the casing. Casing damage stands out as a prominent factor contributing to wellbore integrity failures and well shutdowns within the context of shale oil development. Given the limited natural energy reservoirs of shale oil formations, it becomes necessary to supplement the reservoir’s energy during the development process. Furthermore, shale oil exhibits high viscosity and poor flowability, and conventional water injection methods yield limited efficacy. This situation can induce significant shifts in the stress field and rock mechanical parameters, potentially activating specific formations and complicating the load dynamics on the casing. Consequently, the risk of failure increases. In light of these considerations, this study uses numerical simulations to study the integrity of high-temperature injection and production wellbores in shale oil and aims to encompass a comprehensive evaluation and analysis of the principal factors that influence casing damage, the fluctuations in thermal stress, and the yield strength of various steel grades of casings exposed to alternating stress conditions. Subsequently, this paper developed a model for simulating the temperature and pressure within shale oil and steam injection wellbores to support engineering design analysis. The research results indicate that the application of pre-stress results in a significant increase in stress at the casing pipe head while causing a noticeable decrease in stress within the pipe wall. When N80 casing is used, the entire casing experiences thermal stresses surpassing the casing’s yield limit. Stress concentration may arise at both ends of the external seal, potentially leading to casing contraction, shear failure, and, under non-uniform stress conditions, casing bending deformation. The temperature of steam injection significantly influences the temperature field of the casing wall, with stress values experiencing a marked reduction when the steam injection temperature decreases from 350 °C to 200 °C, underscoring the substantial impact of temperature on casing thermal stress. As the steam injection process advances along with injection-production cycles, shear stresses at the interface can exceed the bond strength, resulting in relative slippage between the cement and the casing. The bonding force between the wellbore and the cement primarily depends on the interface’s friction, particularly in the context of friction during wellhead lifting. This study endeavors to determine rational injection and production parameters under varying conditions, optimize completion methods, reduce casing damage, and extend the casing’s operational life; it aims to offer critical technical support for the safe and efficient development of shale oil resources.

Optimal parameter adjustment of catalytic combustion heaters for oil shale in-situ conversion of low calorific value gases

Oil shale resources are huge, and in order to develop and utilize them rationally, it is crucial to research heaters suitable for downhole in-situ conversion mining. Compared with the problems of short life and multi-stage energy utilization of downhole electric heaters, combustion heaters have advantages such as high thermal efficiency and low cost. The heater uses low calorific value industrial waste gas as the fuel for gas injection, which reduces carbon emissions and environmental pollution and saves gas injection costs. In this paper, we propose to apply catalytic combustion of low calorific value industrial waste gas to generate high temperature exhaust gas suitable for mining, and establish the relationship between gas injection flow rate, combustion chamber parameters and gas injection duration by mathematical methods. The effect of the downhole high-pressure environment on the catalytic combustion characteristics of low calorific gas was simulated and the formula for calculating the content of low calorific gas in the exhaust gas was modified. The results show that the determination of the relational equation solves the problem of excessive axial volume in the design process of downhole heaters. Under high pressure conditions downhole, the exhaust gas temperature and low calorific gas conversion rate are significantly improved. The catalyst ignition temperature ranged from 973 K to 1073 K. Increasing the downhole pressure to 5 MPa increased the conversion of low calorific value gas from 74.56% to 88.22%. The gas injection rate and calorific value range can be calculated by correcting the equation for the content of low calorific gas in the exhaust gas. The conclusion of the study provides a reference basis for the selection of catalytic combustion process parameters for low calorific industrial waste gas, and also provides an important theoretical basis for the construction of the downhole test prototype.

Gulong shale oil enrichment mechanism and orderly distribution of conventional– unconventional oils in the Cretaceous Qingshankou Formation, Songliao Basin, NE China

Through the study of organic matter enrichment, hydrocarbon generation and accumulation process of black shale of the Cretaceous Qingshankou Formation in the Songliao Basin, the enrichment mechanism of Gulong shale oil and the distribution of conventional–unconventional oil are revealed. The Songliao Basin is a huge interior lake basin formed in the Early Cretaceous under the control of the subduction and retreat of the western Pacific plate and the massive horizontal displacement of the Tanlu Fault Zone in Northeast China. During the deposition of the Qingshankou Formation, strong terrestrial hydrological cycle led to the lake level rise of the ancient Songliao Basin and the input of a large amount of nutrients, resulting in planktonic bacteria and algae flourish. Intermittent seawater intrusion events promoted the formation of salinization stratification and anoxic environment in the lake, which were beneficial to the enrichment of organic matters. Biomarkers analysis confirms that the biogenic organic matter of planktonic bacteria and algae modified by microorganisms plays an important role in the formation of high-quality source rocks with high oil generation capability. There are four favorable conditions for the enrichment of light shale oil in the Qingshankou Formation of the Gulong Sag, Songliao Basin: the moderate organic matter abundance and high oil potential provide sufficient material basis for oil enrichment; high degree of thermal evolution makes shale oil have high GOR and good mobility; low hydrocarbon expulsion efficiency leads to a high content of retained hydrocarbons in the source rock; and the confinement effect of intra-layer cement in the high maturity stage induces the efficient accumulation of light shale oil. The restoration of hydrocarbon accumulation process suggests that liquid hydrocarbons generated in the early (low–medium maturity) stage of the Qingshankou Formation source rocks accumulated in placanticline and slope after long-distance secondary migration, forming high-quality conventional and tight oil reservoirs. Light oil generated in the late (medium–high maturity) stage accumulated in situ, forming about 15 billion tons of Gulong shale oil resources, which finally enabled the orderly distribution of conventional–unconventional oils that are contiguous horizontally and superposed vertically within the basin, showing a complete pattern of “whole petroleum system” with conventional oil, tight oil and shale oil in sequence.

Numerical simulation of hydraulic fracture extension patterns at the interface of coal-measure composite rock mass with Cohesive Zone Model

This study presents the development of a numerical computational model for hydraulic fracturing of coal-measure rock mass. The model is based on the B-K hybrid fracture energy criterion and is implemented using the extended finite element method (XFEM) and cohesive zone model (CZM) in the ABAQUS software. The study took into account the elastic-plastic damage properties of the coal-measure rock mass, as well as the combined effects of tensile and shear damage during the start and expansion of hydraulic fractures. The expansion trajectories and fracture morphology of hydraulic fractures at the interface of coal-measure rock mass under different lithological combinations (lithological strength differences) and ground stress conditions are revealed, and the main controlling factors affecting the expansion across the bedding are clarified. The study provides valuable insights into the management of hydraulic fracturing in the challenging context of hard roof coal mines, the stimulation of coal-measure gas co-production reservoirs, and the development of effective fracturing stimulation strategies for shale oil reservoirs interlayered with thin sandstone, and it can promote the development of industrial production technology for coal-measure gas and shale oil and gas resources, and is beneficial to increase the proportion of clean energy in China's energy consumption structure, and thus promoting a further reduction in the carbon emissions from energy consumption.

Status and Progress of Enhanced Oil Recovery Technology in Shale Reservoirs

With the continuous exploitation of domestic conventional oil and gas resources, it is urgent to form a new strategic successor force for stable crude oil production, and China's shale oil and gas resources are abundant and rank in the forefront of the world. At present, various cutting-edge technologies such as CO2 gas injection throughput, horizontal well segmented fracturing technology, and horizontal well synchronous fracturing technology have been applied to the on-site exploitation of shale oil, and numerical simulation methods for shale oil exploitation in various ways are also actively explored. Starting from comparing the current situation of shale oil exploitation at home and abroad and clarifying various development methods and means, this paper summarizes the field application and indoor scientific research of enhanced oil recovery technology in shale oil reservoirs at home and abroad, compares and analyzes the advantages and disadvantages of various methods, and expounds the development trend of shale oil enhanced oil recovery.

The autothermic pyrolysis in-situ conversion process for oil shale recovery: Effect of gas injection parameters

The scale benefit exploitation of oil shale is of great significance to alleviate the current world energy shortage. The autothermic pyrolysis in-situ conversion process (ATS) method shows the feasibility and broad prospects of in-situ efficient utilization of oil shale resources (Guo et al., 2022) [29]. This study conducts in-situ pyrolysis of oil shale by ATS method with oxygen content and injection gas flow as experimental parameters, further clarifying the energy efficiency mechanism and influence characteristics of oxygen injection amount on the in-situ autothermic pyrolysis. The results showed that the in-situ self-pyrolysis reaction can be successfully triggered at 300 °C under the injection parameters of 12,16,21% oxygen content and 3,5,7 L/min injection gas flow rate. However, neither too low nor too high oxygen injection amount can achieve a good in-situ conversion effect. Within the range of parameters considered in this study, the optimal combination of oxygen injection parameters for in-situ pyrolysis of oil shale by the ATS method is 16% oxygen content and 5 L/min injection gas flow. The recovery rate of its cracked oil is 67.1%, and its energy efficiency is as high as 3.46, which is 6.78 times the energy efficiency of in-situ high-temperature nitrogen pyrolysis, realizing the benefits of the transformation of oil shale resources. Meanwhile, according to the apparent optical characteristics of the sample after the experiment and the evolution of the material components in each reaction region, the in-situ autothermic pyrolysis has a significant regional fingering feature. It is hoped that this study will provide reliable data support for the large-scale application of the ATS method.

NMR and CT characterizing the influence of O2 in air injection performance in shale oil cores

BackgroundThe primary objective of this paper is to evaluate the performance of extracting shale oil resources by air injection experiments. In this paper, the shale cores were acquired from Xinjiang Permian Lucaogou formation, with an average porosity of 14% and an average permeability of 0.3mD. 2) Method: The remaining oil distribution and mobilization of oil saturation was characterized by online NMR spectra and X-ray CT scanner. Nitrogen, 8% oxygen of air and 16% oxygen of air injection were evaluated for their enhanced shale oil recovery performance. 3) Significant findings: With the increase of oxygen concentration in the air, a higher oil recovery factor was yielded. Under different O2 concentration, oil recovery factor by nitrogen drive is 45.31%, and the highest (16% oxygen) is 69.81%. Most of hydrocarbons were produced from the 1～5 μ m pore size. Approximately 50% of oil was recovered by the first 0.6 PV of air injection. Oil recovery efficiency is remarkably declined for successive 0.6 PV of air injection. From the CT images of air injection into the fractured shale cores, air injection has the potential to recover incremental oil in the presence of fractures.

Present-day in-situ stress prediction in the Duvernay shale of Simonette Block, Western Canada Sedimentary Basin

The Duvernay Formation of Simonette Block is rich in shale oil and gas resources. The present-day in-situ stress field is a crucial parameter during the exploration and development in this block, a better understanding of which can assist with drilling and completion engineering, fracturing stimulation, and well deployment. In this study, the present-day in-situ stress in the Duvernay shale is predicted and analyzed based on well calculations and geomechanical modeling. The findings indicate that, I, NE-SW-trending is the dominant S Hmax orientation. The S Hmax and S hmin are the maximum and minimum principal stress, indicating that the Duvernay shale of Simonette Block is under a strike-slip faulting stress regime. II, The present-day in-situ stress in the Duvernay shale is heterogeneously distributed, which is controlled by lithology difference, fault development, and distribution. High stress values in the upper shale member D layer are mainly in the northwestern and central parts of Simonette Block. III, The present-day differential stress in the Duvernay shale mainly ranges from 15 MPa to 30 MPa. Bedding-parallel fractures are relatively developed, aiding in the creation of complex fracture networks. The results are expected to offer geological references for further development of shale oil and gas in the Simonette Block.

Microscopic oil occurrence in high-maturity lacustrine shales: Qingshankou Formation, Gulong Sag, Songliao Basin

Occurrence and mobility of shale oil are prerequisites for evaluating shale oil reserves and prioritizing exploration targets, particularly for heterogeneous lacustrine shales. The Qingshankou Formation in the Gulong Sag, Songliao Basin is a classic lacustrine pure shale reservoir that contains abundant shale oil resources. The predicted geological reserves of the shale are 1.268 × 109 t. In this study, field emission scanning electron microscope (FE-SEM), the modular automated processing system (MAPS), pyrolysis-gas chromatography (Py-GC), low-pressure nitrogen gas adsorption (LPNA), Soxhlet extraction, pyrolysis, and 2-D nuclear magnetic resonance (NMR) were integrated to describe the shale oil components, microscopic occurrence, mobility, and the effective pore size distribution. Meanwhile, the related controlling factors are discussed.The shale oil in the Qingshankou Fm exists dominantly in the matrix pores of the clay minerals, with small amounts distributed in the intergranular pores of terrigenous clastic grains, intercrystalline pores of pyrite, intragranular pores of ostracod shells, and micro-fractures. Shale oil is distributed in the pore spaces of variable sizes in different lithofacies. The clay mineral-laminated shales are characterized by the broadest range of pore size and largest volume of pore spaces with shale oil distribution, while the ostracod-laminated shales have limited pore spaces retaining oil. Furthermore, the proposed integrated analysis evaluates the shale oil molecules existing in two states: movable, and adsorbed oil, respectively. The result illustrates that movable oil takes up 30.6%–79.4% of the total residual oil. TOC, mineral composition, and pore structures of the shale joint together to control the states and mobility of the shale oil. TOC values are positively correlated with the quantities of shale oil regardless of the state of oil. The mineral components significantly impact the state of shale oil. Noticeable differences in the states of oil were observed following the changing types of minerals, possibly due to their difference in adsorption capacity and wettability. Clay minerals attract more adsorbed oil than movable oil. Felsic minerals generally decrease the occurrence of total and adsorbed oil. Carbonate plays a positive role in hydrocarbon retention of all the shale oil states. As for the pore structure, the average pore size exerts a critical impact on the total, movable, and adsorbed oil content. The total pore volume and specific surface area of shales play a principal role in controlling the total yields and amounts of adsorbed oil. This research improves the understanding of the occurrence characteristics and enrichment mechanisms of shale oil in terrestrial pure shales and provides a reference for locating favorable shale oil exploration areas.

Organic matter enrichment mechanism in saline lacustrine basins: A review

Organic‐rich shale in saline lacustrine basins holds significant importance as a source rock for conventional hydrocarbon exploration and has emerged as a prominent target for unconventional hydrocarbon exploration and development in recent years. Based on saline lacustrine basins, this paper provides a summary of the organic matter enrichment mechanisms in saline lacustrine basins, considering sedimentary characteristics, biological activities, factors for the organic matter enrichment and consumption, and hydrocarbon generation. The implications for these factors are discussed in relation to the distribution prediction of high‐quality lacustrine shale district settings and the exploration and development of shale oil. Saline lacustrine basins undergo distinct evolutionary stages, each corresponding to different sedimentary stages involving carbonate minerals, sulphate minerals, and alkaline minerals. Moreover, these basins exhibit diverse biological types and experience extensive biological activities. The prosperity of organisms and the accumulation of sedimentary organic matter are ensured by halophilic organisms. Organic matter enrichment in saline lacustrine basins is influenced by two main aspects: the primary productivity of organic matter, which is promoted by the proliferation of halophilic organisms, and the efficient preservation of organic matter facilitated by the strong reducing environment resulting from promoted water salinity stratification. The organic matter consumption in saline lacustrine basins involves bacterial sulphate reduction (BSR) in the early stages, thermochemical sulphate reduction (TSR) in the late stages, and dilution of salt minerals with higher depositional rates. of the presence of salt beds and saline minerals positively influences hydrocarbon generation and expulsion in organic‐rich shale within saline lacustrine deposition. Consequently, continental saline lacustrine basins in China offer favourable conditions for the formation of organic‐rich shale and present broad prospects for the exploration of shale oil and gas resources.

A Method for the Modified Estimation of Oil Shale Mineable Reserves for Shale Oil Projects: A Case Study

The amount if oil shale resources throughout the world has been roughly estimated in accordance with various resource estimation methods. However, in some instances, detailed and comprehensive supporting methodologies for the estimation of commercial shale oil reserves have not been presented. The goal of this study is to develop a comprehensive method for the modified estimation of oil shale mineable reserves for shale oil projects. The methodology characterises oil shale according to its calorific value, oil content, conditional organic mass, and ash content by utilising a Monte Carlo simulation. Based on the results of the case study, the developed method proposes considering the relationships of the in situ oil shale grade and tonnage material (oil shale + limestone) to the oil retorting feed material grade and tonnage by taking into account the retorting plant oil recovery. For this purpose, a Monte Carlo stochastic modelling algorithm was developed. Based on the data analysis, a modifying factor to convert mineral reserves to petroleum reserves was produced. The results of this study are useful for feasibility studies that estimate oil shale reserves in relation to justifying their utilisation fields. Some oil shale deposits have good potential for development but need to be re-estimated in accordance with the most sophisticated extraction and processing technologies.

The shale oil potential of Permian Lucaogou shales (Southeastern Junggar Basin) evaluated by a new quantitative index based on geochemometric methods

The decline of conventional petroleum resources has shifted attention to the exploration of shale oil resources. The shale oil potential of organic-rich shales is a critical focus, which is controlled by organic matter (OM) abundance, thermal maturity, kerogen type, and thickness. However, some commonly-used indicators to characterize the shale oil potential often yield inconsistent results. Hence, to precisely assess the shale oil potential, in this study, combined with the rock-eval pyrolysis, organic petrography, total organic carbon (TOC) content, organic elements, vitrinite reflectance (Ro, %), and gas chromatography-mass spectrometry (GC-MS), a new evaluation index for shale oil potential (SOPI) was proposed to evaluate the shales of Permian Lucaogou Formation in southeastern Junggar basin. Several geochemometric methods including principal component analysis (PCA), grey correlation analysis (GCA), hierarchical cluster analysis (HCA), and analytical hierarchy process (AHP) were used to calculate the SOPI. PCA serves to transform multiple shale oil evaluation metrics into a few integrated metrics (main principal component, PC) that reflect the practical geological significance (OM abundance, kerogen type, thermal maturity, and dark mudstone thickness). Then, the weights of these PC with practical geological significance were determined by GCA. Based on this, SOPI was obtained by which the quality of Permian Lucaogou shales in different areas was quantitatively determined. The SOPI values were examined by the HCA, which indicates a high coincidence rate of 89.4%. The AHP method also confirmed the credibility of the weights obtained from GCA with a good result of the consistency test. The results of shale oil potential evaluation based on the SOPI are consistent with the previous unilateral shale oil evaluation based on uni- and bivariate evaluation parameters, the distribution characteristics of shale oil resources volume, and the lithological distribution proposed by previous research. The comprehensive analysis suggests that, in the six areas of the southeastern Junggar Basin, the Qitai area exhibits the highest shale oil exploration potential, and its shale oil potential even exceeds that of the Jimusaer area, followed by the Miquan and Mulei areas. The shale oil potential in the Chaiwopu and Shiqiantan areas are the lowest.