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Conduction heating and convection heating are the two main methods of in-situ oil shale extraction. The efficiency of heat injection and transfer, oil and gas transportation and production during in-situ oil shale extraction is directly controlled by shale structure and permeability. In this paper, pyrolysis tests of conduction-heated and convection-heated oil shale were carried out, micro-CT scans of the pyrolyzed oil shale were performed, and systematic comparisons of the differences in the pore structure of oil shale under the two heating modes were carried out, and the seepage-heat transfer simulation of oil shale at the fine-scale was realized by interfacing Avizo with the multi-field coupled finite element software Comsol. The results of the study show: the original oil shale sample produces a large number of irregular pores at different scales after conduction and convection heating, resulting in a significant increase in the representative elementary volume, which are 3.5 times higher than the original state. After conduction heating and convection heating, the porosity of oil shale increases by 2.96 and 3.15 times compared to the original state, respectively. The pore size distribution of oil shale in the original state ranges from 5 μm to 320 μm, which dramatically expands to 5–1400 μm when heated by conduction and convection, demonstrating that small-scale pores connect to form large-scale pores. In the original state, the percentage of oil shale pore shape factor of 0.0625 was as high as 29 %, the percentage of oil shale pore shape factor in the range of 0.005–0.032 was significantly increased by conductive heating treatment, and the percentage of pore shape factor in the range of 0.005–0.02 was slightly increased by the convective heating effect at the same temperature. The permeability and maximum heat transfer rate of oil shale after convective heating increased by 5.51 and 6.17 times, respectively, compared with conduction heating, and the pore-fracture connectivity of oil shale after convective heating was greatly improved compared with that of conduction heating, which reduced the emergence of dead-end fractures and isolated fractures, and improved the seepage capacity and heat transfer capacity of oil shale. • The pyrolysis tests of conduction-heated and convection-heated oil shale were carried out. • The differences in the pore structure of oil shale under the two heating modes were analyzed. • The seepage-heat transfer simulation of oil shale at the fine-scale was realized. [ABSTRACT FROM AUTHOR]

High-temperature H2O and CO2 can improve the pyrolysis behavior of oil shale. Therefore, in this paper, Jimusar oil shale was selected as the research object and the effect of the reaction atmosphere (H2O, CO2, and N2) on its pyrolysis behavior, pyrolysate distribution, and pyrolysis oil quality was fully compared and studied. The results showed that compared with the N2 atmosphere, the presence of H2O and CO2 both increased the weight loss and weight loss rate during pyrolysis of oil shale and the existence of H2O advanced the initial precipitation temperature of volatiles by 17°C. The comprehensive release characteristic indices of volatiles during pyrolysis of oil shale in the CO2 and H2O atmospheres increased by 49.34% and 114.35%, respectively, which significantly improved its pyrolysis reactivity. Both H2O and CO2 atmospheres improved the pyrolysis oil yield of oil shale, and the pyrolysis oil yield in the H2O atmosphere performed better than that in the CO2 atmosphere. Especially, the H2O atmosphere could increase the pyrolysis oil yield by 41.42%. The existence of CO2 prevented methyl radicals from accepting hydrogen radicals during pyrolysis and reduced the alkane yield, while CO2 participated in the addition reaction of alkane, which increased the alkene yield. High-temperature H2O provided more hydrogen source, which increased the alkane yield and inhibited the alkene formation. Both H2O and CO2 atmospheres promoted the cracking of polycyclic aromatics and increased the yield of small-molecular aromatics in the pyrolysis oil. During the pyrolysis process of oil shale, CO2 and H2O underwent reforming reaction with the heavy oil, which increased the light component fraction, thereby increasing the H/C ratio of pyrolysis oil. Thus, the existence of H2O and CO2 atmospheres improved the quality of pyrolysis oil and the effect of H2O was better than CO2. The H2O and CO2 atmosphere promoted the formation of a well-developed pore structure, which was conducive to mass and heat transfer during pyrolysis of oil shale. [ABSTRACT FROM AUTHOR]

Purpose: The aim of this study was to investigate the clinical and multi-slice spiral computed tomography angiography (MSCTA) characteristics for the diagnosis of infected AAA. Methods: This retrospective comparative study included patients who were diagnosed with AAA at our hospital between January 2014 and May 2023. Results: A total of 40 patients were included, comprising 20 with infected AAA and 20 with non-infected AAA. Patients with infected AAA were more likely to be younger (62.9 ± 10.1 vs. 70.0 ± 4.4 years, P = 0.007) and to present with fever [7 (35%) vs. 1 (5%), P = 0.026], pain [15 (75%) vs. 2 (10%), P < 0.001], higher C-reactive protein levels (60.4 ± 57.0 vs. 4.1 ± 2.9 mg/l, P = 0.005), and higher erythrocyte sedimentation rates (47.7 ± 23.4 vs. 15.2 ± 8.3 mm/h, P < 0.001) compared to those with non-infected AAA. Moreover, those with infected AAA exhibited significantly more eccentric saccular morphology [17 (85%) vs. 1 (5%), P = 0.002], a smaller longitudinal-transverse ratio (1.12 ± 0.33 vs. 2.33 ± 0.54, P = 0.001), thicker peri-aneurysmal soft tissue (2.29 ± 1.48 vs. 0.73 ± 0.55 cm, P < 0.001), more lobulated margins [18 (90%) vs. 1 (5%), P = 0.001], lower aortic calcification scores (49 vs. 56, P < 0.001), more pneumatosis [6 (30%) vs. 0 (0%), P = 0.014], more ruptures [15 (75%) vs. 5 (20%), P = 0.002], more blurred peri-abdominal aortic fat spaces [16 (80%) vs. 2 (10%), P = 0.001], more adjacent bone destruction [5 (25%) vs. 0 (0%), P = 0.025], more involvement of the psoas major muscle [8 (40%) vs. 1 (5%), P = 0.005], more lymphadenectasis [8 (40%) vs. 1 (5%), P = 0.020], and less tortuous aortas [2 (10%) vs. 9 (45%), P = 0.034] compared with those with non-infected AAA. Conclusion: The clinical manifestations and MSCTA characteristics may differ between infected and non-infected AAA. [ABSTRACT FROM AUTHOR]

The seepage of gas-liquid two-phase flow in fracture is a commonly found phenomenon in nature. To reveal the underlying mechanism and the critical condition of the chaos occurrence, a stochastic gas-liquid two-phase flow seepage model is established, and then investigated through a numerical simulation and a horizontal Hele-Shaw experiment. The numerical simulation and laboratory experiment results show that the seepage chaos of gas-liquid two-phase flow takes place when the relative saturation is in the range of gas relative saturation 44%-70%, and the occurrence probability can be expressed in polynomials. The chaos probability exceeds 80% when the relative saturation of gas is 47%-65%, and the chaos probability is 100% when the relative gas saturation is 57%-60%. It is found that the stochastic variation of gas connection cluster and the compressibility of gas lead to a remarkable change of pressure gradient of the gas-liquid flow both in magnitude and direction. Therefore, the turbulent flow is formed, the kinetic energy of fluid transport decreases gradually, and the flow is stopped at last. [ABSTRACT FROM AUTHOR]

The in situ heating technology for mining oil shale through steam injection involves creating interconnected horizontal fractures in the orebody. The authors use meter-scale oil shale as the experimental object to create a unified, integral sample containing oil shale, a filling body, and a rigid pressure chamber containing drilled holes as well as temperature and pressure sensors. A 1000 ton large press was used to apply load to the sample, and water pumps and steam boilers were used to comparatively analyze the processes of in situ hydraulic fracturing and high-temperature steam fracturing. The results showed that the starting pressure for hydraulic fracturing was only 0.34 times lower than the in situ stress, it featured rapid fracture propagation, with a synchronous pressure response between the boreholes as well as a short connection time for the group wells. Furthermore, the horizontal cracks were more easily formed than vertical cracks in layered rock masses. Moreover, high-temperature steam fracturing was required to overcome the constraints imposed by the superposition of the formation and thermal stresses. The fracturing pressure was 1.2 times higher than the in situ stress and fracture propagation was slow, with a negligibly small pressure response between the boreholes and a long connection time for the group wells. For this heterogeneous shale with obvious bedding plane structure, the influence of the thermal stress on the fracture-inducing stress of the orebody was much stronger than that of its own tensile strength. Finally, an appropriate fracturing technology for group wells should be selected according to the rated pressure of the steam boiler. • The process of in situ hydraulic fracturing and high-temperature steam fracturing for meter-scale oil shale was analyzed. • The mechanism of in situ high-temperature steam fracturing was explained. • The characteristics of the two fracturing methods were compared. [ABSTRACT FROM AUTHOR]

The study investigated the relationship between the temperature field distribution and fracture connectivity of oil shale heated by water vapor using infrared thermal imaging experiment. High temperature triaxial permeability testing system was then used to study the permeability of oil shale containing single penetrating fracture under the condition of water vapor heating. Finally, micro CT imaging and hot stage microscope imaging experiments were conducted to study the microstructure characteristics of oil shale at different temperatures. It was observed that when the oil shale was heated by water vapor, fractures became the main flow channels, and the connectivity of fractures affected the heating area of oil shale. The magnitude of fracture permeability of oil shale decreased from 10−15 m2 at 25 °C to 10−17 m2 at 350 °C. When the temperature was higher than 350 °C, the permeability of oil shale increased rapidly and recovered to the order of 10−15 m2 after 500 °C. The micro-fractures had little contribution to permeability in the temperature range of 25 °C–350 °C. The decrease in the permeability in this temperature range was caused by the closure of the single penetrating fracture. When the temperature reached 400 °C, some new penetrating fractures appeared. This resulted in the increase in permeability. • Fractures constitute the main channels for fluid flow in oil shale. • The distribution of fractures determines the range of oil shale heated by superheated water vapor. • The threshold temperature of permeability of fractured oil shale was 350 °C. • The influence of fracture evolution on oil shale permeability was analyzed. [ABSTRACT FROM AUTHOR]

The stability of the casing is a crucial prerequisite for implementing the in situ high-temperature steam injection method in oil shale reservoirs. In order to address the issues of substantial expansion, concentrated thermal stresses, and susceptibility to damage observed in traditional straight casings under high temperatures, this paper proposes the utilization of a corrugated casing structure. In this regard, to investigate the impact of the shape and structure of the wellbore casing on its mechanical properties, identical corrugated and straight casings were selected and studied. Uniaxial compression and tensile tests were conducted on the casings, along with coordination deformation experiments between the casing and cement sheath under varying temperatures. Numerical simulations were employed to obtain the deformation characteristics of the corrugated and straight casings under axial compression and tension loads, as well as the stress distribution on the outer casing wall. The results showed that when subjected to the same amount of deformation under axial loading, the corrugated casing experienced lower compressive and tensile loads compared to the straight casing. Moreover, under the sole constraint of cement sheath, increasing the temperature led to lower vertical strains (perpendicular to the ground) at all measuring points of the corrugated casing as compared to the corresponding strains in the straight casing. Numerical simulations revealed that, under the same temperatures, the deformation at the interface between the corrugated casing and the cement sheath was smaller, while the vertical stress at the interface of the corrugated casing was also lower than the straight casing. Overall, the corrugated casing, with its corrugated structure that enabled micro-deformation, effectively mitigated the axial deformation of the casing caused by thermal expansion. Consequently, the corrugated casing reduced the extrusion of wellbore casing on the cement sheath, thereby preserving the integrity and stability of the wellbore cementing structure. [ABSTRACT FROM AUTHOR]

• The progress of oil shale in-situ conversion technology is reviewed extensively. • Pores/fractures formed in oil shale pyrolysis constitute a channel for fluid flow. • Oil shale in-situ steam injection technology is proposed. • The principles of effective pyrolysis energy of oil shale are proposed. Oil shale is an important strategic resource with tremendous reserve. In-situ retorting is the only technology available to achieve large-scale industrial exploitation. This paper systematically introduces the intensive researches conducted by Zhao's team on oil shale retorting, as well as the progress of oil shale in-situ conversion technology in the world. The oil shale deposit in sedimentary strata with hidden layering, and the kerogen in oil shale is dispersed in flat strips that ranges from a few to tens of microns in size. A large amount of micro-scale pores and fractures are formed along the bedding in oil shale during the in-situ pyrolysis process, which creates connected channels and enhances the effectiveness of thermal fluid injection and the yield of pyrolysis products. Back to 2005, Zhao's team invented the oil shale in-situ retorting technology by injecting superheated steam, and related technical advantages are analyzed in detail. The principles of effective pyrolysis energy of oil shale are proposed so as to evaluate development stage of the reserve, meantime, the advantages of steam as a heat carrier fluid are specified by comparing the effective injection energy of steam and other gases. Furthermore, the scientific, technical, industrial advances of latest developments, including electric heating, fluid injection heating, combustion, and radiant heating in oil shale in-situ conversion technology are reviewed in detail. By comparing with the advantages and disadvantages of various technical solutions, the directions in which several key problems should be solved were pointed out. [ABSTRACT FROM AUTHOR]

Oil shale is a critical strategic energy with huge reserve. The research and development of an economically feasible in-situ retorting technology for oil and gas extraction from oil shale is of great significance. Thus, this paper experimentally studied the large oil-shale samples pyrolysis by in-situ superheated steam injection (MTI) implemented from 2014 to 2016. The structure of the large-scale in-situ pyrolysis test system, the experimental procedure, and the results are presented here. The steam fracturing-connection was used during the initial stage, and the pressure of the superheated steam for fracturing was ~2 times higher than the strata stress. The variation of temperature and pressure during pyrolysis was controlled by the variation in steam seepage. The operating steam pressure during pyrolysis was lower than 1/4 of the strata stress. The energy utilization of the superheated steam for the pyrolysis reaction was 42.7%. The average temperature of the fluid that was discharged from the production wells was around 170 °C, which can be recycled to achieve a heat-utilization coefficient of 13.19% in commercial operations. The oil-recovery rate in the pyrolysis area exceeded 95%, and the overall oil-recovery rate reached up to 70.7% of the tested large oil-shale samples. The gas production rate and the effective energy rate of the injected steam are correlated with an exponential function. Our pilot tests indicate that the in-situ retorting technology of oil shale by MTI shows great potential for commercial operation in oil-shale formation. • A new oil shale in-situ retorting technology, MTI technology, is proposed. • This is the first pilot test on large-scale oil-shale pyrolysis by in-situ superheated steam injection throughout the world. • The operating pressure of steam during pyrolysis is lower than 1/4 of the strata stress. • The oil-recovery rate in the pyrolysis area can exceed 95%, and the overall oil-recovery rate reaches up to 70.7%. [ABSTRACT FROM AUTHOR]

It is well known that underground in situ pyrolysis technology for oil shale production is a promising field. In the in situ modification mining process, the permeability property of a shale matrix has a great effect on the transport capacity of pyrolytic products. For oil shale undergoing pyrolysis, the changes of internal structure (fracture and pore space) have a considerable influence on the permeability network which further affects the migration of hydrocarbon products. In this study, based on an oil shale retorting experiment performed under different temperatures (20 °C, 100 °C, 200 °C, 300 °C, 325 °C, 350 °C, 375 °C, 400 °C, 425 °C, 450 °C, 475 °C, 500 °C, 525 °C, 550 °C, 575 °C, 600 °C), an investigation on the distribution characteristics of the fractures was conducted using micro-CT technology. Meanwhile, mercury injection porosimetry was used to characterize the pore structure of the oil shale samples under different temperatures. Finally, a fracture-pore dual medium model was constructed to calculate the percolation probability to quantitatively describe the permeability variation of oil shale with temperature. The test results indicated that the higher the temperature, the larger were the pore spaces. The increase in pore volume due to pyrolysis temperatures mainly affected the pores ranging from 10 nm to 100 nm and occurred in the specific temperature range (400 °C to 425 °C). Additionally, CT images show that the fracture morphology varied with increasing temperature and the number and length of fractures at different temperatures were in great accordance with the fractal law statistically. On the other hand, simulation of the percolation probabilities discovered that in a single pore media model over the whole range of tested temperatures they were too low to exceed the threshold. In contrast, in the dual medium model, the theoretical threshold of 31.16% was exceeded when the temperature reached 350 °C. Moreover, the results demonstrated that fractures dominated the seepage channel and had more significant effects on the permeability of oil shale. What has been done in this study will provide some guidance for the in situ fluidization mining of oil shale. [ABSTRACT FROM AUTHOR]

Based on the high-precision microcomputed tomography (micro-CT) technology, the evolution of the μm-scale pore structure and connectivity of lignite during pyrolysis from room temperature to 600°C was studied. The results show that the pore connectivity of lignite increases with the increase of temperature, and the change of pore structure can be divided into four stages: the first stage is from room temperature to 100°C, characterized by generation and connection of small-diameter pores. The second stage is 100–200°C, characterized by rapid expansion and interconnection of pores due to the thermal cracking. The third stage is from 200°C to 450°C, characterized by the slow evolution of pore structure for pyrolysis. The fourth stage is from 450°C to 600°C, characterized by pore interconnection for pyrolysis. 200°C is the temperature at which the μm-scale pore structure of lignite changes dramatically. During the whole pyrolysis process from room temperature to 600°C, the pore quantity of lignite is mainly from the pores of a diameter of 0.65–3 μm. At 200°C and above, the pore volume of lignite is mainly from the pores with a diameter larger than 100 μm, but they are few. These research results have important theoretical reference values for the upgrading and pyrolysis of lignite. [ABSTRACT FROM AUTHOR]

The process of in-situ oil shale extraction via convection heating is accompanied by complex solid–fluid-thermal-mass transfer multi-field coupling effects. As the fluid temperature increases, thermal cracking and pyrolysis occur within the oil shale, forming a highly permeable and porous structure, resulting in the oil shale being subjected to complex stress field changes. This paper, set against the background of the in-situ oil shale extraction process using steam injection, conducts uniaxial compression tests on oil shale under different bedding directions under the real-time action of high-temperature steam. Combined with micro-CT, XRD and XPS analysis of oil shale, the characteristics of anisotropic evolution of compressive strength of oil shale under the real-time action of high-temperature steam and the internal mechanisms occurring are clarified. As the steam temperature increases, the compressive strength and elastic modulus of oil shale in different bedding directions show a trend of decreasing and then increasing, reaching their lowest values at a steam temperature of 400 °C. The rate of change in compressive strength of oil shale perpendicular and parallel to the bedding direction differs significantly at different pyrolysis stages. When the steam temperature exceeds 400 °C, the rate of increase in compressive strength of oil shale in the vertical bedding direction is significantly higher than in the parallel bedding direction. At high temperatures, the fracturing of oil shale is primarily along the bedding planes, while the development of interlayer fractures is relatively slow, resulting in higher strength of oil shale in the vertical bedding direction. The failure characteristics of oil shale perpendicular to the bedding direction transition from brittle shear fracturing to semi-brittle shear fracturing and then to plastic deformation, eventually returning to semi-brittle shear fracturing. In contrast, the failure characteristics of oil shale parallel to the bedding direction transition from brittle shear fracturing through semi-brittle shear fracturing to plastic deformation. During pyrolysis process, the content of clay minerals inside the oil shale does not change significantly, but the change in non-clay minerals is most pronounced. When the temperature exceeds 400 °C, the diffraction-peak intensity of pyrite suddenly decreases or even disappears, the diffraction-peak intensity of kaolinite gradually decreases, and the content changes of elements such as C, O, Al, Si are also more noticeable. The transformation of internal mineral composition in oil shale (e.g., the conversion of kaolinite to metakaolinite) is the fundamental reason for the strength increase of oil shale at temperatures above 400 °C. [ABSTRACT FROM AUTHOR]

In the convection heating technology for shale oil recovery, steam is used as a transmission medium to pyrolyze oil shale. An experiment was designed to pyrolyze oil shale via steam injection in a large reactor. The samples of oil shale and semi-coke were obtained at different pyrolysis temperatures, and the pore-fracture structure of the samples was studied. The results showed that the average pore diameter and median pore diameter increased by about 10 times when the steam temperature increased from 314 °C to 555 °C. After completion of the steam pyrolysis, we observed that the internal fractures of oil shale were mainly microfractures. At the pyrolysis temperature of 555 °C, the number of microfractures in oil shale was more than 50 times compared with those observed at normal temperature. The micro-CT results indicated that the porosity of oil shale reached 15% after pyrolysis with high-temperature steam. At this porosity, the oil content of samples after pyrolysis was 0.05–0.22%, and the internal organic matter was completely pyrolyzed. Finally, the bedding planes of rock mass exhibited significant ruptures when the oil shale was pyrolyzed with high-temperature steam, thus providing proper channels for steam injection and flows of oil and gas. • An experiment of oil shale pyrolysis by steam injection in a long reactor was designed. • The internal fractures of oil shale after steam pyrolysis were mainly microfractures. • The number of microfractures in oil shale at 555 ℃ was over 50 times higher than that at normal temperature. • The organic matter retained in the dead-end pores was fully pyrolyzed by superheated steam. [ABSTRACT FROM AUTHOR]

In order to better simulate the porous media with different pore distribution characteristics, this paper introduced a pore distribution factor m (m represents the randomly generated pore volume in the site percolation model, which is expressed by the number of sites)into the classic site percolation model. On this basis, the influence of pore distribution characteristics of two-dimensional (2D) and three-dimensional (3D) porous media on the percolation threshold is studied using numerical simulations. The study found that, when the porosity is the same, larger the value of m , smaller the number of pores in both the simulated 2D and 3D porous media. The decrease in the number of pores leads to the changes in the pore volume distribution characteristics. The shape of each pore, generated using the simulation in this paper, is random, due to which, larger the value of m is, easier it is for pores to merge to form larger pore clusters, which result in a reduction in the percolation threshold. The percolation threshold of 2D (lattice type: square) and 3D (lattice type: simple cubic) site percolation models decreases with the increase in the value of m. When the value of m is unity, the percolation thresholds of 2D and 3D porous media are found to be 59.27% and 31.16%, respectively, which are in agreement with the existing research results. When the value of m increases to 40, the percolation thresholds of 2D and 3D porous media decrease to 38.38% and 8.65%, respectively. Therefore, the pore connectivity of porous media is determined by the porosity and the pore distribution characteristics, whereas the pore connectivity of porous media can be misjudged if only porosity is taken into account. • A new filling method different from RSA is proposed. • We presented an extension of the classic site percolation theory. • The pore connectivity depends on porosity and pore distribution characteristics. • The percolation threshold is affected by pore distribution characteristics. [ABSTRACT FROM AUTHOR]

In the process of pyrolyzing oil shale using water vapor as a heat carrier fluid, the internal structure of rock mass is subject to complex changes. Studies on the permeability of oil shale pyrolysis by high-temperature water vapor are of great importance to the design of oil shale mining technology by convection heating. In this paper, the permeability of oil shale samples after water vapor pyrolysis was studied using permeability tests and flow field simulations. The permeability of oil shale was compared and analyzed in the direct mode of retorting. The results can be summarized as follows. First, when the pyrolysis temperature increased from 20 °C to 382 °C, the increasing rate of permeability was relatively low. At temperatures between 382 °C and 555 °C, the permeability increased significantly with increasing pyrolysis temperature. Second, when the water vapor temperature was 314 °C, there was no broad range of seepage pathways in the sample, and the flow field distribution was relatively limited. At water vapor temperatures of 534 °C and 555 °C, the streamline distribution in the sample was tight, and the permeability of oil shale was high. Third, the permeability of oil shale in the convection heating mode was significantly higher than that in the direct mode of retorting. At temperatures between 314 °C and 382 °C, the difference in permeability between the two modes was more prominent. Finally, the results of the permeability test and the results of the seepage field simulation were combined to explain the permeability evolution law and thermal cracking characteristics of oil shale heated by high-temperature water vapor. [ABSTRACT FROM AUTHOR]

Both physical and chemical cross-linking methods can improve the mechanical properties of hydrogel by increasing the cross-link density. In this study, a series of polyvinyl alcohol/polyacrylamide-co-polyacrylic acid (PVA/PAM-co-PAA)-based hydrogels were prepared by using Fe3+ as physical cross-linking agent and N,N'-methylenebisacrylamide (MBA) as chemical cross-linking agent. The stress relaxation experiments of PVA/PAM-co-PAA-based hydrogels and nonlinear fitting analysis were performed to study the effects of cross-linking methods on stress relaxation behavior of hydrogels. Furthermore, the four-element generalized Maxwell model succeeded in simulating stress relaxation behavior of hydrogels. When Fe3+ was used as the cross-linking agent of Fe3+/PVA/PAM-co-PAA hydrogel, it took a long time of 199.9 s when the structural units began to move. However, when MBA was used as the cross-linking agent of PVA/PAM-MBA-PAA hydrogel, the time was shortened significantly. Compared with PVA/PAM-co-PAA hydrogel, the initial and equilibrium stress of Fe3+/PVA/PAM-co-PAA and PVA/PAM-MBA-PAA hydrogel significantly increased. When Fe3+ and MBA were used as the cross-linking agent of Fe3+/PVA/PAM-MBA-PAA hydrogel together, the network structure became looser. The initial and equilibrium stress were 0.04 and 0.015 MPa, respectively. [ABSTRACT FROM AUTHOR]

The connectivity of the internal pores and fractures in oil shale is the critical factor in determining the success of the insitu pyrolysis of the oil shale with superheated steam. In this paper, using a self-developed superheated steam pyrolysis experimental system, oil shale samples were subjected to pyrolysis experiments at different steam temperatures. Then, the oil shale samples were scanned with high-precision micro-CT equipment to obtain the three-dimensional digital core of oil shale (DCOS). Based on the three-dimensional site percolation theory and renormalization group algorithm, the pore and fracture connectivity characteristics of the DCOSs were studied. The results show that when the steam temperature reached the pyrolysis temperature for oil shale, a series of pores was formed during the pyrolysis process. These pores gradually connected the adjacent fracture and subsequently formed a massive pore-fracture cluster. However, from room temperature to 555 °C, there were always parts with porosity less than 5% in the DCOSs perpendicular to the direction of the sedimentary bedding, forming the bottleneck of the seepage passage. This occurrence is the main reason that the permeability of the oil shale perpendicular to the direction of the sedimentary bedding is far lower than that parallel to the direction of the sedimentary bedding. [ABSTRACT FROM AUTHOR]

• Internal structure of oil shale pyrolysis with injection steam under in situ condition was studied. • Porosity of oil shale along bedding planes is 12.77 times that of natural oil shale. • Internal fractures of pyrolytic oil shale were mainly dominated by microcracks. • The proportion of pyrolytic orebody with permeability ranging from 1.8 × 10−3 nm2 to 3.0 × 10−3 nm2 was 63.51%. • Oil shale is transformed from dense rock to porous medium under the effect of superheated steam. In the in situ pyrolysis of oil shale (OS) with superheated steam (SS), the internal pores and fractures of the OS act as channels for the migration of steam and locations for heat exchange. After a laboratory test of the in situ pyrolysis of OS with SS, 30 OS samples located in different zones between the injection and production wells were collected. The main parameters of pore and fracture structures inside OS samples were investigated. The results first showed that in each position along the bedding planes, the effective porosity was greater than 19.41%. The internal OS fractures were mainly dominated by microfractures, with lengths between 100 µm and 500 µm. The average pore diameter of the orebody was between 52.77 nm and 69.01 nm, and the aperture of the microfractures was between 59.31 µm and 68.85 µm. Then, in the position near the roof bedrock perpendicular to the bedding directions (BD), the effective porosity and pore diameter of the orebody were small. Only a few cracks were observed in the rock mass, and the distribution of the pore groups in the 3D space was fragmented and had poor connectivity. Finally, in the whole studied OS orebody, the proportion of ore layers with permeabilities ranging from 1.8 × 10−17 m2 to 3.0 × 10−17 m2 was 63.51%, which proved that the connectivity of the pores and fractures in the large area was superior to other areas. [ABSTRACT FROM AUTHOR]

When oil shale is pyrolyzed with high-temperature water vapor as a heat carrier fluid, the water vapor will participate in the pyrolysis reaction of organic matter, to change the release characteristics of oil and gas products. Based on the self-designed long reaction system of oil shale pyrolysis by injecting water vapor, this paper deeply studies the quantitative law of water vapor temperature and reaction distance on oil upgrading, compares the quality of shale oil using different pyrolysis methods, and reveals the mechanism of upgrading of oil shale pyrolysis by injecting water vapor. The change of heteroatom and light component contents of shale oil can indicate the change in shale oil quality. The relationship between the two indexes and the reaction distance follows the Boltzmann distribution, and the relationship is called the modification distance. When the injection temperature is 450 °C, the modification distance of shale oil is 1400 mm. When the injection temperature reaches 500 °C, the modification distance extends to 2600 mm. Moreover, when the temperature of the water vapor is low, the reaction intensity is low, the upgrading level is low, and the modification distance is short. However, when the temperature of the water vapor is high, the shale oil's rapid hydro-upgrading distance increases, and the upgrading degree is also enhanced. To make oil shale fully pyrolyzed and form shale oil with good quality, the injection temperature should be at least 500 °C. In that case, the reaction distance of 2600 mm is the threshold distance of oil upgrading. The light component content in the shale oil obtained by the pyrolysis of oil shale with water vapor can be two times that obtained by direct distillation and three times that of crude oil. • The effects of temperature and reaction distance on the upgrading and modification of shale oil were revealed. • The threshold distance of oil upgrading was obtained. • The technical advantages of oil shale pyrolysis by water vapor injection were explained. [ABSTRACT FROM AUTHOR]

The technology of oil shale pyrolysis by water vapor injection uses high-temperature steam as a heat carrier to heat oil shale. Water vapor not only plays the role of transferring and exchanging heat, but it also chemically reacts with organic matter and some oil and gas products, altering the generation characteristics of oil and gas products. In this paper, we developed a long reaction distance test system for oil shale pyrolysis by water vapor injection and obtained the effects of heat injection temperature and time on the quality of oil and gas products. First, the results showed that with increasing pyrolysis temperature, the hydrogen content in the gas components gradually increased and then tended to be stable. In the process of heat injection temperature, increasing from 330 °C to 475 °C, the hydrogen content increased from 1.05% to 66.64%. High hydrogen concentration was mainly due to the reaction of water vapor with carbon residues, water vapor conversion reactions, and steam gasification reactions of hydrocarbon gases. Then, for shale oil, when the injection temperature was higher than 500 °C, the content of light components in shale oil remained at high levels, but the content of heteroatomic compounds was very little and the quality of shale oil was good. Next, when the injection temperature was controlled to 555 °C and the pyrolysis time was increased from 0 h to 4 h, the hydrogen content in the gas products increased first and then decreased, but the heteroatomic contents in the shale oil products increased first and then decreased. When the pyrolysis time was 2.5 h, the hydrogen content peaked, reaching 87.6%. When the pyrolysis time was 2 h, the content of heteroatoms peaked and reached 8.22%. Overall, when the injection temperature was 555 °C and the injection time reached 3 h, the shale oil formed through oil shale cracking presented higher quality. • The relationship between steam temperature and quality of hydrocarbon was obtained. • The oil shale pyrolysis process in a long-distance reactor was analyzed. • The reasonable conditions for oil shale pyrolysis by water vapor injection were obtained. [ABSTRACT FROM AUTHOR]

The evolution of pore structure during in situ underground exploitation of oil shale directly affects the diffusion and permeability of pyrolysis products. In this study, on the basis of mineral analysis and thermogravimetric results, in combination with the low-pressure nitrogen adsorption (LPNA) and mercury intrusion porosimetry (MIP) technique, the evolution of pore structure from 23 to 650 °C is quantitatively analyzed by simulating in situ pyrolysis under pressure and temperature conditions. Furthermore, based on the experimental results, we analyze the mechanism of pore structure evolution. The results show the following: (1) The organic matter of Fushun oil shale has a degradation stage in the temperature range of 350–540 °C, and there is no obvious temperature gradient between decomposition of kerogen and the secondary decomposition of bitumen. The thermal response mechanisms of organic matter and minerals are different in each temperature stage, and influence the change of pore structure. (2) Significant changes occur in pore shape at 350 °C, where thermal decomposition of kerogen begins. The ink-bottle pores are dominant when the temperature is less than 350 °C, whereas slit pores dominate when the temperature is greater than 350 °C. (3) The change in pore structure of oil shale is much less significant from 23 to 350 °C. The pore volume, porosity, and specific surface area (SSA) of samples increase rapidly with temperature varying from 350 to 600 °C. The variation of each parameter is dissimilated from 600 to 650 °C: the porosity and pore volume increases with a small gradient from 600 to 650 °C, and SSA decreases significantly. (4) The lithostatic pressure does not cause change in the evolution discipline of the pore structure, but the inhibitory effect on the pore development is significant. [ABSTRACT FROM AUTHOR]