Shale Exploitation Research Articles

Kinetics study on supercritical water conversion of low-maturity shale for hydrogen-rich hydrocarbon gas generation

Supercritical water (SCW) has gained substantial interest for shale exploitation due to its high conversion efficiency. To quantify the generated gases and the mutual conversion of gases on reaction of shale in SCW, experiments were carried out in batch reactor at 400–600°C and residence time up to 480 min. The products are classified as residual solids, liquid intermediates and gases. Experimental results show that the generated gases are mainly C1, C2, C3 alkanes, H2 and CO2. The concentrations of C1 and C2 alkanes decrease with temperature and residence time but the other three are the opposite. A kinetic model of shale-intermediates-gases reaction is developed. This model can characterize the gas generation features of shale and SCW resulting from chemical reactions, and can quantitatively describe the mutual conversion between gases. The calculated results demonstrate well applicative for predicting gas concentration at various residence time within an acceptable deviation. The reaction process can be divided into three stages: pyrolysis of organic matter to generate intermediates, hydrolysis reaction and alkyl thermal cracking of intermediates to generate gases, mutual conversion between the generated gases. Reactions among gases involve methanation reaction, water-gas shift reaction and hydrocarbon gas decomposition. This study provides a potential kinetic model for the gas generation characteristics of reaction with shale and supercritical water.

Fracture propagation and evaluation of dual wells, multi-fracturing, and split-time in Fuyu oil shale

Reservoir stimulation is crucial for in-situ exploitation, it can promote a fracture network and increase the heat transfer area. Therefore, it directly affects heat injection and products transportation efficiencies. Conventional reservoir stimulation techniques, such as hydraulic fracturing are widely used. However, hydraulic fracturing in a vertical well tends to generate simple fractures that are unfavorable for heat transfer, and real-time fracture propagation is difficult to monitor, thus failing to precisely control the hydraulic fracturing scale. In addition, there are few qualitative and quantitative criteria in reservoir-scale fracture evaluations for interpreting the overall hydraulic fracturing effect. Consequently, in this study, dual wells, multi-fracturing, and split-time technology (DMS) were designed and conducted based on microseismic monitoring in field experiment to find real-time fracture propagation. Furthermore, based on Hugot's research on connecting microseismic events by spatiotemporal sequences, we proposed a step index and path intensity considering microseismic event intensities to evaluate the effect on hydraulic fracturing. The results showed that a three-dimensional fracturing zone with a 60 × 30 × 8 m length, width, and height was generated at a 476–484 m depth, which corresponded to the designed hydraulic fracturing and facilitated heat transfer and product migration. Higher pump pressure and rate harmed hydraulic fracturing, blocking proppant migration during which the FK1-4 coefficient of viscosity reached 70 N⋅s/m2, 1.4 times greater than that of FK1-2 and FK1-5 according to Poiseuille's law. The hydraulic fracturing effect in FK1-4 was superior than that in FK1-2 and FK1-5. This study serves as a reference for monitoring oil shale exploitation via in-situ pyrolysis.

STUDYING 18-9 STAINLESS STEEL UNDER THE SAME CONDITIONS OF OIL SHALE HYDROPYROLYSIS AND PREDICTING THE SUITABLE STEEL TO BE USED DURING THIS REACTION

Hydrogen incinerates in most compounds and element due to its small size, so when it is used in oil shale exploitation, it may react with the elements making up the reactor and the steel enclosure forming the exploitation assembly. In this work we will treat an 18-9 stainless steel under the same hydropyrolysis conditions as the Tarfaya oil shale (Morocco) and predict which elements of the steel will not be affected by hydrogen.The advantage of treating oil shale with hydrogen is that it increases the oil yield compared with pyrolysis, and it also makes these oils lighter, as well as forming numerous hydrides with the mineral matrix, which are also fuels.After treating 18-9 stainless steel and using analytical techniques, we selected the elements iron β and nickel, which do not undergo alteration in the presence of hydrogen. The analytical techniques used in this work are thermogravimetry using the Red-Croft balance(A.Attaoui :2022) where we carried out the hydrotreatment, calorimetry (DCA) as an amplified calorimetric differential linked to the balance, morphology carried out by SEM (scanning electron microscope) and which is coupled with dispersive X-rays.

Numerical simulation and optimization study of In-Situ Heating for three-dimensional oil shale exploitation with different well patterns

In order to explore a three-dimensional shale well network model with low power consumption and high oil production rate, this study employed Ansys Fluent numerical simulation software to analyze cumulative oil production volume, annual oil production volume, heating rate factor, and unit volume power consumption for seven well network models. The results indicate that during the in-situ heating and extraction process of oil shale, all seven different well network models undergo direct in-situ pyrolysis without a preheating period. With an increasing number of heating wells, Model VII reaches its peak annual oil production volume at day 360, and the heating rate factor peaks at 3.696 on day 540. This is a 5.68-fold increase compared to Model I's peak heating rate factor. The slope of the cumulative oil production volume over time is the highest, indicating the fastest heating rate, and complete pyrolysis is achieved by day 780. However, throughout the entire in-situ heating process of oil shale, Model VI exhibits the lowest unit volume power consumption at 814.87 Kw/m3, with the highest energy utilization efficiency. This represents a significant reduction of 41.93% in unit volume power consumption compared to the other six well network models. The exploration results of these different well network models provide robust technical support for subsequent in-situ oil shale extraction field experiments.

The investigation on shale mechanical characteristics and brittleness evaluation

Rock mechanical property is significant for shale gas development and exploitation. Shale compressive strength, tensile strength, elastic deformation and so on, are necessary parameters for drilling, completion and fracturing work in shale formation. Among all these shale mechanical parameters, brittleness is a tricky and significant rock property, which has been widely used to hydraulic fracturing design. Currently, although so many works have been conducted to investigate shale brittleness, there is no precise definition of brittleness. In particular, there is no consensus on which method is the most reliable for shale brittleness evaluation. It is vital to figure out how to evaluate shale brittleness in a reliable method. Thus, this paper presents an experimental study on shale mechanical properties, analyzing mechanical features in stress strain curve, relation between mineral content and strength, mechanical parameters at varying confined stress. Based on shale mechanical characteristics and its brittle exhibition, stress strain curve from triaxial compression test is divided into 3 stages, namely, elastic stage, plastic stage and post peak stage. In combined with brittle characteristics in 3 stages of axial and radial stress–strain curves, a new brittleness index has been established for assessing shale brittleness. In order to prove the applicability of new brittleness index, its result is compared with shale failure sample after triaxial test and existing brittleness indexes based on mineral content, elastic deformation, energy, stress and strain, showing a good consistency and proving its practicability. Based on this brittleness index, influence factors of shale brittleness have been discussed. It is shown that elastic module is the most important factor of shale brittleness. Bedding plane makes shale brittleness have strong anisotropy. Brittleness is not only relied on its structure and mineral (like bedding plane, silicate and clay mineral content), but is also highly affected by external stress. Large confined pressure is able to impair shale brittleness. Outcome in this study can offer theoretical guidance for shale exploitation.

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.

Numerical Study on Enhanced Heat Transfer of Downhole Slotted-Type Heaters for In Situ Oil Shale Exploitation.

In order to improve the flow state of the heater shell side and enhance the performance evaluation of the heater, this paper proposes a perforated plate-type heater model. Based on Fluent, numerical studies are conducted on the heat transfer performance and shell-side fluid flow characteristics of a perforated plate-type heater. The variations of the heat transfer factor Nu, friction factor f, and evaluation parameter Nu/f1/3 are analyzed for different helix angles β and ratios of the long and short semiaxes of the circular holes on the heating plate under different Reynolds numbers Re. The results reveal that under the same shell-side Reynolds number Re, the heat transfer factor Nu shows an increasing trend with the increase in the proportion of the helix angle β. The heat transfer factor Nu for the heating plate with the hole shape ratio a/b = 1 does not exhibit significant improvement compared to hole shape ratios a/b = 0.8 and a/b = 0.6, but it increases by 4.87 to 7.07% compared to the hole shape ratio a/b = 0.4 in the perforated plate-type heater. On the other hand, the friction factor f decreases as the helix angle β and the ratio of hole shapes on the heating plate increase. The lowest friction factor f is observed for the helix angle β of 25° and the hole shape ratio a/b = 1 in the perforated plate-type heater. When the helix angle β is 25° and the hole shape ratio is a/b = 1, the evaluation parameter Nu/f1/3 reaches its highest value, indicating the optimal overall performance of the perforated plate-type heater.

Fracture Modeling of Shale Oil and Gas Reservoirs in Texas

Formation fracturing is the method of choice for developing shale oil and gas reservoirs that constitute a gigantic resource in the U.S.A. and many other countries but are characterized by a low permeability in the nano-Darcy range. The oil production of Texas has increased by about 5 million B/D in 15 years as a result of shale exploitation by massive multistage hydraulic fracturing. The mathematical modeling of this fracturing process is complex and can be approached in several ways. This paper first gives a concise description of the fracturing process as carried out in Texas. Included are the ranges of the key reservoir properties, as well as the injection fluid volumes and pressure, the composition of the injected fluid, proppant type, and volume, and other relevant data. Also included are the number of fracture stages, methods of zonal isolation, and diagnostic techniques used. An important variable considered is flowback, in particular, fluid retention and oil and gas production. High-salinity water production is discussed. Given the above variables, the currently used fracture simulators are briefly considered and compared, both the geomechanics-based and fracture-propagation-based. No single simulator can model the complete process. The directions currently being followed are briefly described. Also discussed is the simulation of the re-fracturing process and its range of success in increasing oil recovery from about the original ~5% to ~8%. Future processes such as plasma fracturing are mentioned, and their future applicability is discussed for further increasing oil recovery.

Experimental study of hydraulic fracturing initiation and propagation from perforated wellbore in oil shale formation

Perforation hydraulic fracturing is essential in developing unconventional oil and gas resources. This study scales the critical parameters to simulate operations at the field scale, using a true triaxial hydraulic fracturing experimental system to mimic actual far-field stress conditions. The research simulates various scenarios of perforation and fracturing fluid parameters, which significantly influence fracture propagation behaviour and fracture network morphology. The results showed that the initiation pressure required for fracturing with perforation is 20.91% lower than that of open-hole fracturing. Multiple fractures, including bedding and branch fractures, exhibit cross-propagation behaviour, forming barrier-type morphology. Induced by perforation, hydraulic fracture initiation and propagation occur along the direction of maximum geo-stress, but unreasonable orientation and reduction in perforation length can also increase initiation pressure. The flow rate and viscosity of fracturing fluid are positively proportional to the initiation pressure. A high flow rate of 100 mL/min facilitates the generation of bedding fractures, enhances the bedding fractures connectivity and increases fracture network complexity. However, the increase in viscosity forces hydraulic fracture to penetrate the bedding plane directly and diminishes the complexity of the fracture network. Compared to the pressure build-up phase, fluctuations in the fracturing curve during the propagation phase are significantly related to the complexity of the fracture network. Small-scale structural surfaces developed within the strata can become part of the hydraulic fractures and increase the fracture network complexity. Additionally, the hydraulic fractures are captured and hindered by large-scale structural surfaces, forming a single fracture morphology. The findings significantly aid in predicting fracture propagation and fracture network morphology in oil shale exploitation.

Advancements and Environmental Implications in Oil Shale Exploration and Processing

This comprehensive review presents a holistic examination of oil shale as a significant energy resource, focusing on its global reserves, extraction technologies, chemical characteristics, economic considerations, and environmental implications. Oil shale, boasting reserves equivalent to approximately 6 trillion barrels of shale oil worldwide, holds substantial potential to augment the global energy supply. Key extraction methods analyzed include surface mining, modified in situ, and true in situ conversion processes, each exhibiting distinct operational parameters and efficiencies. The review further delves into the chemical aspects of oil shale retorting and pyrolysis, highlighting the critical role of variables such as retorting temperature, residence time, particle size, and heating rate in determining the yield and composition of shale oil and byproducts. Economic analyses reveal that capital and operating costs, which vary according to the specific extraction and processing technologies implemented, are crucial in appraising the economic feasibility of oil shale projects. Lastly, the review acknowledges the potential environmental hazards linked with oil shale development, such as groundwater contamination and harmful emissions. It emphasizes the importance of rigorous monitoring programs, environmental impact assessments, sustainable technologies, and innovative strategies like co-combustion and comprehensive utilization systems in mitigating such impacts. The review underlines the need for a balanced approach that harmonizes technological advancement, economic viability, and environmental sustainability in oil shale exploitation.

Erosion characteristics and simulation charts of sand fracturing casing perforation

Large-scale sand fracturing is a necessary means in the efficient exploitation of shale gas/oil. However, in the process of fracturing operation, the sand carrying fluid and proppant easily causes scouring and wear to production strings, especially the casing perforation system, which damage the wellbore integrity and deformation to affect the subsequent fracturing. For this problem, taking the actual construction conditions and perforation technology of an oilfield in western China as an example, the structural parameters of the downhole string were measured and the wall thickness reduction model of casing perforation suitable for large-displacement sand fracturing in horizontal well section was established. With software ANSYS-FLUENT, the casing perforation erosion under the conditions of different displacements, sand content and perforation sand-passing quantity in the process of sand fracturing was simulated and calculated. The influences of three parameters on perforation erosion and expansion were analyzed and the prediction chart of the influences of three main control factors on perforation erosion and expansion was established. The perforation erosion images after fracturing construction were obtained with the downhole eagle perforation logging technology. The logging chart results were compared with the downhole eagle perforation data. The error between the established numerical simulation calculation charts and the real logging data was about 5%, indicating that the simulation charts were the valuable reference.

Innovative Design and Numerical Simulation Research of Downhole Electrical Heaters for In-Situ Oil Shale Exploitation

Summary To improve the overall performance of continuous spiral baffle heating systems, we propose in this paper two different structural models of electric heaters for in-situ shale oil wells. The models are simulated using Fluent software to investigate the flow and heat-transfer characteristics under different mass flow rates. The variation in heat-transfer coefficient, pressure drop, and overall performance of the heating plate under different gas mass flow rates and heights of heating and shielding plates are analyzed. The performance of the two different heater structures is compared with Wang’s laboratory experiment. The results show that Model I of the heating system has the best overall performance when the gas mass flow rate is between 9.74×10−3 kg/s and 1.624×10−2 kg/s, and the height of the heating and shielding plates is 35 mm at a mass flow rate of 9.74×10–3 kg/s. Wang’s pressure drop (ΔP) is more than 2.48 times higher than that of Model I and more than 6.49 times higher than that of Model II, while the heat-transfer coefficient (h) of both Model I and Model II is increased by more than 15% compared to Wang’s experiment. The overall performance (g) of Model II is increased by more than 5.7 times compared to Wang’s experiment, and the overall performance (g) of Model II is increased by more than 1.68 times compared to Model I. These results provide a theoretical basis for optimizing the design of continuous spiral baffle heating systems.

Ecological Restoration and Transformation of Maoming Oil Shale Mining Area: Experience and Inspirations

Oil shale is a kind of unconventional energy resource with abundant reserves, but its exploitation has a continuous negative impact on the environment, which has hindered the research and exploitation of oil shale under the international environmental consensus on issues such as climate change. Therefore, more attention should be paid to environmental problems as the side effect of oil shale exploitation. With the combination of field research, literature collection, and tracking survey, the oil shale open-pit exploitation and management process in Maoming, Guangdong, China, has been investigated, and its development and transformation model has been subsequently refined and summarized. The research results show that Maoming oil shale open-pit mine area has gone through four main stages: pre-exploitation stage, large-scale utilization stage, restoration stage, and green development stage. Through the management of mine pit treatment, vegetation restoration, ecological park construction, and tourism resource development, the abandoned open-pit mine has been transformed into an ecological park combining ecosystem, tourism, and cultural resources. In this process, this area has achieved the transformation from rough resource extraction to environment-friendly sustainable growth in its development mode. As a successful case of open-pit mine management in the world, the ecological restoration experience in Maoming can function as a reference for the smooth development and transformation of other oil shale mines in developing countries.

Geomechanical brittleness index prediction for the Marcellus shale exploiting well-log attributes

Geomechanical brittleness of tight formations calculated from Poisson's Ratio with Young's Modulus requires laboratory testing of cores and/or estimation from shear wave acoustic logs. In shale exploitation budgets are not available to provide those measurements in many wells and it is desirable to estimate a geomechanical brittleness index (BIg) from a basic, often limited, suite of available well logs. BIg helps field operators to select the most prospective sections of tight rocks that are likely to benefit most from fracture stimulation. A machine-learning (ML) approach that combines a few recorded well logs with derivative and volatility attributes calculated from that recorded data is applied to two wellbores that penetrate the Middle Devonian formations (Appalachian Basin). This technique is novel as it has not been previously applied to predict BIg. The results demonstrate that ML models involving just two or three recorded well logs plus selected attributes as input variables provide BIg predictions that are as accurate as ML models that involve three and five recorded well logs as input variables, respectively. Moreover, the ML models involving attributes are as generalizable as ML models based only on multiple recorded well logs when applying models trained with data from one well to predict BIg from well log data in another nearby well. Extreme gradient boosting and elastic net models provide the lowest BIg prediction errors when the trained models are applied to log data from another well. Feature importance analysis identifies that the recorded compression sonic log, bulk density and gamma ray, in that order, are the most influential features in the BIg prediction models applied to the two Marcellus Shale wells. However, two of calculated well-log attributes (moving averages of the well-log derivative and volatility) are particularly effective at improving the BIg predictions when used in combination with just those three recorded well logs. The technique is worth testing in other shale basins.

Perspectives of Machine Learning Development on Kerogen Molecular Model Reconstruction and Shale Oil/Gas Exploitation

The shale revolution has provided abundant shale oil/gas resources for the world, but the efficient, sustainable, and environmentally friendly exploitation of shale oil/gas is still challenging. Kerogen is the primary hydrocarbon source of shale oil/gas. The research on the kerogen chemo-mechanical properties significantly influences the development of shale oil/gas extraction technology. Rapid reconstruction of the kerogen molecular models is the most effective way to study the generation mechanism of shale oil/gas from the bottom-up molecular level. However, due to the combinatorial explosion problem, the reconstruction complexity of kerogen increases sharply because of the kerogen’s characteristics of complex origin, large molecular weight, and diverse functional groups. The traditional kerogen molecular reconstruction methods require professionals to comprehensively analyze various experimental information to approximate the actual kerogen molecular models through trial-and-error. So, the traditional methods are time and material-consuming and extremely inefficient. These shortcomings make researchers spend too much strength on the reconstruction of kerogen molecular models and cannot focus on the study of kerogen chemo-mechanical properties. For the past few years, state-of-the-art machine learning (ML) methods have been applied to intelligently reconstruct the kerogen molecular models through high-throughput and predict shale oil/gas production mechanisms. Although the current work is still in the infancy stage, ML methods are believed to be the most promising way to solve the drawbacks of traditional methods and reconstruct kerogen in reliable and large molecular weight. Hence, mechano-energetics is proposed to study the efficient development and utilization of energy based on mechanics and ML. This paper briefly reviews the development history of kerogen molecular model reconstruction methods and the research of ML in the fields of kerogen reconstruction and shale oil/gas exploitation. Some recommendations for further ML-based work are also suggested. We are convinced that the ML methods will accelerate the research of kerogen and promote the significant development of unconventional oil/gas exploitation technologies.

Numerical simulation and thermo-hydro-mechanical coupling model of in situ mining of low-mature organic-rich shale by convection heating

The in situ efficient exploitation of low-mature organic-rich shale resources is critical for alleviating the current oil shortage. Convection heating is the most critical and feasible method for in situ retortion of shale. In this study, a thermo-hydro-mechanical coupling mathematical model for in situ exploitation of shale by convection heating is developed. The dynamic distribution of the temperature, seepage, and stress fields during the in situ heat injection of shale and the coupling effect between multiple physical fields are studied. When the operation time increases from 1 to 2.5 years, the temperature of most shale formations between heat injection and production wells increases significantly (from less than 400 to 500 °C), which is a period of significant production of shale oil and pyrolysis gas. The fluid pore pressure gradually decreases from the peak point of the heat injection well to the surrounding. Compared with shale formation, bedrock permeability is poor, pore pressure increases slowly, and a lag phenomenon exists. The pore pressure difference between bedrock and shale is minimal by 1 year. When the heat injection time is 2.5 years, the permeability coefficient of shale formation in the area from the heat injection well to the production wells increases nearly 100 times the initial permeability coefficient. With increasing formation temperature, the vertical stress gradually evolves from compressive stress to tensile stress. Meanwhile, the action area of tensile stress expands outward with time with the heat injection well as the center. In general, increasing tensile stress enlarges the pore volume. It extends the fracture width, creating favorable conditions for the injection of high-temperature fluids and the production of oil and gas. Cited as: Zhao, J., Wang, L., Liu, S., Kang, Z., Yang, D., Zhao, Y. Numerical simulation and thermo-hydro-mechanical coupling model of in situ mining of low-mature organic-rich shale by convection heating. Advances in Geo-Energy Research, 2022, 6(6): 502-514. https://doi.org/10.46690/ager.2022.06.07

Optimization Design and Analysis of Bionic Friction Reducing Nozzle in Oil Shale High-Pressure Jet Mining

The borehole hydraulic mining method has unique advantages for underground oil shale exploitation. Breaking rock with a high-pressure water jet is a crucial step to ensure the smooth implementation of borehole hydraulic mining in oil shale. The hydraulic performance of the nozzle determines the efficiency and quality of high-pressure water jet technology. To obtain a superior hydraulic performance nozzle, based on the bionic non-smooth theory, a circular groove was selected as the bionic unit to design a bionic straight cone nozzle. The structural parameters of the circular groove include the groove depth, width, and slot pitch. The optimization objective was to minimize the pressure drop, where the fluid has the least resistance. A genetic algorithm was used to optimize the structural parameters of the circular grooves in the inlet and outlet sections of the bionic straight cone nozzle. The optimal structural parameters of the nozzle were as follows: the inlet diameter was 15 mm, the inlet length was 20 mm, the outlet diameter was 4 mm, the length-to-diameter ratio was 3, and the contraction angle was 30°. In addition, in the inlet section, the groove width, slot pitch, and groove depth were 3.9 mm, 5.2 mm, and 5.5 mm, respectively, and the number of circular grooves was 2. Moreover, in the outlet section, the groove width, slot pitch, and groove depth were 2.25 mm, 3 mm, and 5.5 mm, respectively, and the number of circular grooves was 2. The CFD numerical simulation results showed that under the same numerical simulation conditions, compared with the conventional straight cone nozzle, the bionic straight cone nozzle velocity increase rate could reach 13.45%. The research results can provide scientific and valuable references for borehole hydraulic mining of high-pressure water jets in oil shale drilling.

Study on Pyrolysis-Mechanics-Seepage Behavior of Oil Shale in a Closed System Subject to Real-Time Temperature Variations.

In situ mining is a practical and feasible technology for extracting oil shale. However, the extracted oil shale is subject to formation stress. This study systematically investigates the pyrolysis–mechanics–seepage problems of oil shale exploitation, which are subject to thermomechanical coupling using a thermal simulation experimental device representing a closed system, high-temperature rock mechanics testing system, and high-temperature triaxial permeability testing device. The results reveal the following. (i) The yield of gaseous hydrocarbon in the closed system increases throughout the pyrolysis reaction. Due to secondary cracking, the production of light and heavy hydrocarbon components first increases, and then decreases during the pyrolysis reaction. The parallel first-order reaction kinetic model shows a good fit with the pyrolysis and hydrocarbon generation processes of oil shale. With increasing temperature, the hydrocarbon generation conversion rate gradually increases, and the uniaxial compressive strength of oil shale was found to initially decrease and then increase. The compressive strength was the lowest at 400 °C, and the conversion rate of hydrocarbon formation gradually increased. The transformation of kaolinite into metakaolinite at high temperatures is the primary reason for the increase in compressive strength of oil shale at 400–600 °C. (ii) When the temperature is between 20 and 400 °C, the magnitude of oil shale permeability under stress is small (~10−2 md). When the temperature exceeds 400 °C, the permeability of the oil shale is large, and it decreases approximately linearly with increasing pore pressure, which is attributed to the joint action of the gas slippage effect, adsorption effect, and effective stress. The results of this research provide a basis for high efficiency in situ exploitation of oil shale.

Dispersion Stability of Graphene Oxide in Extreme Environments and Its Applications in Shale Exploitation

Dispersion Stability of Graphene Oxide in Extreme Environments and Its Applications in Shale Exploitation

Real-time monitoring of the oil shale pyrolysis process using a bionic electronic nose

Accurate and rapid prediction of thermal maturity during oil shale exploitation is important to optimize pyrolysis processes and decrease production costs. Then, a bionic electronic nose (BEN) was used for the first time for the real-time monitoring of the oil shale pyrolysis process. The results show that the calculated Easy%Ro change, unlike that of the measured vitrinite reflectance (%Ro), was small (±0.004) in decomposition stages (dewatering, hydrocarbon generation stage and inorganic matter decomposition) at the different heating rate. This time–temperature-related parameter made it a perfect intermediary to associate the thermal maturation process with the BEN signal during oil shale pyrolysis. The monitoring of the pyrolysis process of oil shale in real time was divided into two steps: 1) qualitatively checking whether the oil shale had entered the hydrocarbon generation stage, and 2) when entering this stage, quantitatively predicting the Easy%Ro evolution. Combined with different feature extraction methods, a support vector machine (SVM) as a classifier was used to complete the first step, which had the best recognition rate of 91.13%. For the second step, random forest (RF) was applied to quantitatively measure the Easy%Ro values, with an R2 reaching 0.95. During the verification stage, the established integration model was used to recognize a heating rate, which, between the trained heating rate in the algorithm model, performed much better in the first step (SVM, 92.96%) than in the second step (RF, 0.57), and those results were given in 38 to 125 s. Thus, the BEN technique can be applied in the real-time detection of oil shale exploration.