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The Permian Fengcheng Formation (P1f.) in the Hashan area, situated on the southwestern margin of the Junggar Basin, has witnessed a remarkable breakthrough in shale oil exploration in recent years with nearly 789 million tons of shale oil resources. As a unique set of mixed sedimentary shales, the Fengcheng Formation in the Hashan area is characterized by mixed sedimentation of terrigenous siliciclastic sediments, authigenic minerals, and tuffaceous materials. However, the understanding of pore characteristics in the mixed sedimentary reservoir still remains limited, prohibiting accurate estimation of the oil content and insights into oil mobility. Scanning electron microscopy (SEM), X-ray diffraction (XRD), mercury injection capillary pressure (MICP), nuclear magnetic resonance (NMR), X-Ray Computer Tomography (X-CT), and geochemical analysis were performed to investigate the pore size distribution and main controlling factors of the mixed sedimentary reservoir. Results showed that the main pore types in the mixed sedimentary reservoir are intergranular pores and dissolution pores. The pores of the P1f. mixed shales in the Hashan area were classified into II-micropores (< 25 nm), I-micropores (25–100 nm), mesopores (100–1000 nm) and macropores (> 1000 nm). In general, the mixed sedimentary rocks of P1f. formation feature few macropores but a large number of micropores and mesopores. The CS exhibits the most favourable physical properties among all lithofacies. It is concluded that the abundance and maturity of organic matter, mineral composition, sedimentary structure, and diagenesis of reservoir together impact the pore structure in the mixed sedimentary reservoirs. The maturity of organic matter and the content of tuffaceous minerals are the most significant in influencing the pore structure of P1f. shales. Overall, the pore structure of complex lithologic reservoir formed by mixed deposition and its influence on physical properties are studied, and the characteristics of the microscopic pore-throat system of the dominant lithofacies in the Hashan area are clarified, which is of great significance as a guide for the exploration and development of mixed sedimentary reservoirs in continental shale oil in China. [ABSTRACT FROM AUTHOR]

Although significant amounts of methane are present in anthracite coal seams, coalbed methane resources cannot be extracted effectively and quickly. This study mainly focused on investigating the pore system and methane adsorption capacity to clarify the storage of coalbed methane. Anthracite coal samples from the Anzenan coalbed methane block in China were collected, and pore characterization methods (low-pressure N2 adsorption, mercury injection experiments, and scanning electron microscopy (SEM) observations) and methane isothermal adsorption experiments were conducted. The results showed that few mesopores and nanoscale macropores were present in the anthracite coal samples. The volume of the 2-300 nm pores in these coal samples obtained from the N2 adsorption experiment was lower than 0.01 cm3/g. SEM observations also revealed that only a small number of mesopores and nanoscale macropores could be seen, and most of these pores were isolated. In terms of the methane isothermal adsorption data, it was found these anthracite coals have a large methane adsorption capacity, and the Langmuir volume ranges from 19.5 to 28.4 cm3/g, with an average of 22.2 cm3/g. With increasing ash yield, the Langmuir volume decreased linearly, indicating that methane molecules were mainly adsorbed in the organic matter of coal. As methane is mainly adsorbed in the micropores of coal organic matter and there are few mesopores and nanoscale macropores in the organic pores in coal, there are not enough tunnels to transport the adsorbed methane molecules to the outside. Thus, it is difficult to extract coalbed methane from anthracite. This study reveals the impact of pore system limitations on the storage and extraction of coalbed methane in anthracite coal. The findings can be applied to the extraction of coalbed methane from anthracite coal seams worldwide. [ABSTRACT FROM AUTHOR]

In order to understand pore evolution in relation to sedimentary facies, a study has been conducted on the Chang 6 reservoir in Western Ordos Basin. Tight reservoir space comprises primary intergranular pores with an average original porosity is 36.29%, and secondary pores related to feldspar dissolution. Reservoir porosity is 8.03–11.43% and permeability is 0.12 × 10−3–1.31 × 10−3 μm2. Cementation and mechanical compaction are the main reasons for the quality of the reservoir. Dissolution of feldspar grains improved the reservoir quality. The reservoir has undergone four evolutionary stages: ① Syn-sedimentary compaction which decreased the porosity by 21.27%, to an average remaining porosity was 15.12%. ② Early diagenetic cementation which decreased the porosity by 6.23% to an average residual porosity was 8.89%. ③ Early stage of mesodiagenesis: involving dissolution and formation of micro-fractures that led to an increase in porosity by 5.47% resulting in an average porosity of 14.36%. ④ Compaction and cementation during the late mesodiagenetic stage resulting in an average porosity of 10.87%. Quantitative calculations reveal an average reservoir porosity is 10.68% with an error of 1.75%. The results contribute to a better understanding of the main controlling factors and pore evolution characteristics of tight reservoir development. [ABSTRACT FROM AUTHOR]

Salix sand barriers have been widely used in arid and semi‐arid regions of northern China as an environmentally friendly approach to control wind erosion. However, the inherent variability in length and thickness of Salix branches complicates achieving the desired fence porosity, typically resulting in an error of approximately 10% or more. This defect affects the fence's wind protection, thereby limiting their broader application. To address these challenges, we conducted a field experiment in the Hobq Desert, where we established Salix fences with porosities of 23%, 37%, and 44%, and measured the airflow velocities around these fences. The results indicated that the fence with 37% porosity exhibited the most effective sheltering effect, providing a protection distance up to 7.14 times of the fence height. A total of 44% porosity fences are also reasonably effective for practical purposes. On the other end of the spectrum, fences with 23% porosity demonstrated a better sediment interception than its high porosity peers, achieving an interception rate of 81.46%. Therefore, we conclude that organic fences made from Salix branches can serve as efficient windbreaks. Our findings provide foundational data for the application of organic fences in arid and semi‐arid regions of northern China, and potentially similar environments globally. [ABSTRACT FROM AUTHOR]

Marine–continental transitional shale has become a new field for shale gas exploration and development in recent years. Its reservoir characteristics analysis lags significantly behind that of marine shale, which restricts the theoretical research on the accumulation of marine–continental transitional shale and the progress of exploration and development. The shale pore system is complex and has strong heterogeneity, which restricts the fine evaluation and optimization of the reservoir. Based on nitrogen adsorption–desorption experiments, the morphology and structural characteristics of coal-bearing shale pores were analyzed, and then the micro-pore structure heterogeneity was quantitatively characterized based on fractal theory and nitrogen adsorption–desorption data, and the relationship between pore structure parameters and their influence on fractal characteristics were discussed. The hysteresis loop of nitrogen desorption isotherm mainly belongs to type B, indicating ink bottle, flat plate, and slit are the main pore shapes. The pore size distribution curves are left unimodal or multimodal, with the main peak around 4 nm and 20–60 nm. Smaller pores develop a larger specific surface area, resulting in a high value of fractal dimension (2.564 to 2.677). The rougher the pore surface and the larger the specific surface area provide an adequate adsorption site for shale gas adsorption and aggregation. Thus, fractal characteristics conduced to understand the pore structure, heterogeneity, and gas-bearing property of coal-bearing shale. [ABSTRACT FROM AUTHOR]

The porosity characteristics of coal seams serve as a pivotal factor in assessing the development potential of coalbed methane (CBM) resources, significantly influencing the adsorption and permeability capabilities of coal reservoirs, as well as the accumulation, entrapment, and preservation of CBM. In this study, we focused on the coal seams of the Xishanyao Formation in the western part of the southern Junggar Basin (NW China). By leveraging the complementarity of nuclear magnetic resonance (NMR), low-temperature liquid nitrogen experiments, and high-pressure mercury intrusion porosimetry (MIP) in spatial exploration range and precision, we conducted a comprehensive analysis to achieve a fine description of porosity characteristics. Furthermore, we explored the coal petrology factors controlling the pore characteristics of the Xishanyao Formation, aiming to provide geological evidence for the selection of favorable areas and the development potential evaluation of CBM in the study area. The results indicate the following: (1) The total pore volume of the coal samples is 6.318 × 10−3 cm3/g on average, and the micropore volume accounts for a relatively high proportion (averaging 44.17%), followed by the fine pores (averaging 39.41%). The average porosity is approximately 3.87%, indicating good gas storage and connectivity of the coal seams, albeit with some heterogeneity. The coal reservoir is dominated by micropores and fine pores with diameters less than 100 nm, and the pore structure is characterized by low pore volume and high pore area. (2) The pore structure is influenced by both the coalification degree and the coal maceral. Within the range of low coalification, porosity increases with the increase in coalification degree. Building upon this, an increase in the vitrinite content promotes the development of micropores and fine pores, while an increase in the inertinite content promotes the development of meso–macropores. The clay mineral content exhibits a negative correlation with the adsorption pore volume ratio and a positive correlation with the seepage pore volume ratio. [ABSTRACT FROM AUTHOR]

The Lower Cambrian shale gas in the western Hubei area, South China has a great resource prospect, but the gas-in-place (GIP) content in different sedimentary facies varies widely, and the relevant mechanism has been not well understood. In the present study, two sets of the Lower Cambrian shale samples from theWells YD4 and YD5 in the western Hubei area, representing the deep-water shelf facies and shallowwater platform facies, respectively, were investigated on the differences of pore types, pore structure and methane adsorption capacity between them, and the main controlling factor and mechanism of their methane adsorption capacities and GIP contents were discussed. The results show that the organic matter (OM) pores in the YD4 shale samples are dominant, while the inorganic mineral (IM) pores in the YD5 shale samples are primary, with underdeveloped OM pores. The pore specific surface area (SSA) and pore volume (PV) of the YD4 shale samples are mainly from micropores and mesopores, respectively, while those of the YD5 shale samples are mainly from micropores and macropores, respectively. The methane adsorption capacity of the YD4 shale samples is significantly higher than that of the YD5 shale samples, with a maximum absolute adsorption capacity of 3.13 cm3/g and 1.31 cm3/g in average, respectively. Compared with the shallow-water platform shale, the deep-water shelf shale has a higher TOC content, a better kerogen type and more developed OM pores, which is the main mechanism for its higher adsorption capacity. The GIP content models based on two samples with a similar TOC content selected respectively from theWells YD4 and YD5 further indicate that the GIP content of the deep-water shelf shale is mainly 3-4 m3/t within a depth range of 1000e4000 m, with shale gas exploration and development potential, while the shallow-water platform shale has normally a GIP content of <1 m3/t, with little shale gas potential. Considering the geological and geochemical conditions of shale gas formation and preservation, the deep-water shelf facies is the most favorable target for the Lower Cambrian shale gas exploration and development in the western Hubei area, South China. [ABSTRACT FROM AUTHOR]

Pore‐throat structure is a key factor that influences the storage and fluid flow capacity of tight sandstone reservoirs. Taking the tight sandstone reservoir of Xu2 Fm in Zhongba area as an example, the reservoir quality, pore‐throat type and pore size distribution of tight sandstone in the study area were described by casting thin section, scanning electron microscope and high‐pressure mercury injection test. In order to quantitatively characterize the complexity and heterogeneity of pore‐throat structure, fractal analysis was performed using mercury saturation and pore size data. This study mainly reveals the relationship between the geometric shape characteristics and fractal dimension of the binary pore structure of ultra‐low permeability tight sandstone and clarifies the influence of different scale pore throats on reservoir physical properties. The results indicate that the physical properties of the reservoir in the study area are poor, the pores are mainly intergranular pores and dissolution pores, the throat is flake and necked and the pore size distribution range is large. The fractal curve obtained by the mercury saturation method shows a significant turning point, and the pore‐throat system is divided into two types: small‐scale and large‐scale. The fractal dimension of large‐scale pore throat is greater than the three‐dimensional Euclidean space dimension, which does not conform to the fractal theory. The fractal dimension of small‐scale pore throat is closely related to the pore‐throat structure and has obvious fractal characteristics. The geometric shape of binary pore‐throat structure in tight sandstone is the main factor affecting the difference of fractal dimension. The development of small pores in sandstone is positively correlated with the total porosity, but its contribution to permeability is relatively low. The physical properties of tight sandstone are mainly controlled by the development degree of large‐scale pore throat. [ABSTRACT FROM AUTHOR]

Characterizing the microscopic pore systems in shale reservoirs is crucial for understanding their impact on shale oil and gas enrichment. Although significant strides have been made in understanding the pore structure characteristics, research on pore structures related to small-scale sedimentary structures remains limited. This study investigated the multi-scale nanopore structure characterization and its coupling relationship with sedimentary structures using comprehensive analyses of cores, field-emission scanning electron microscopy, and gas (CO2 and N2) physisorption quantification from the Upper Cretaceous Qingshankou Formation, Southern Songliao Basin, NE China. Three lithofacies were identified based on sedimentary structures: wavy laminated shale, horizontally laminated shale, and homogeneously laminated shale. Both organic and inorganic pores (interparticle pores and intraparticle pores) are generally present in shale samples. The pore size distribution displays a multi-peak pattern, with mesopores contributing to approximately 57% of the total pore volume, micropores contributing to about 31%, and macropores accounting for a small portion of the total pore volume. The pore evolution of different lithofacies shales varies due to the influence of clay minerals, quartz content, and total organic carbon (TOC) content, resulting in the substantial heterogeneity and complex pore structure characteristics of existing reservoirs. Additionally, wavy laminated shales are more favorable to lacustrine shale exploration than other lithofacies. This study offers an enhanced methodology for determining which lithofacies may be most advantageous for future shale oil exploitation. [ABSTRACT FROM AUTHOR]

The study of deep shale gas (>3500 m) has become a new research hotspot in the field of shale gas research in China. In this study, 16 representative deep shale samples were selected from different layers of the Wufeng–Longmaxi Formation in the Z-3 well in the western Chongqing area to conduct low-field nuclear magnetic resonance (NMR) tests, field-emission scanning electron microscopy (FE-SEM) observation, and fractal modeling. By comparing the differences in pore structure and their influencing factors in representative samples from different layers, the particularities of high-quality reservoirs have been revealed. The results show that the Z-3 well shales mainly develop micropores and mesopores, with pore sizes of 1 nm–200 nm. The fractal dimensions of bound fluid pores D1 (1.6895–2.3821) and fractal dimension of movable fluid pores D2 (2.9914–2.9996) were obtained from T2 spectra and linear fitting, and the pores were divided into three sections based on the NMR fractal characteristics. TOC content was one of the major factors affecting the gas content in the study area. The shale samples in the bottom S1l1-1 sub-layer with a higher TOC content have larger porosity and permeability, leading to enhanced homogeneity of the pore structure and favorable conditions for shale gas adsorption. A comparative understanding of the particularities of pore structure and influencing factors in high-quality reservoirs with higher gas content will provide the scientific basis for further exploration and exploitation of the Wufeng–Longmaxi Formation deep shale reservoirs in the western Chongqing area. [ABSTRACT FROM AUTHOR]

This study delves into the micro-occurrence states and enrichment mechanisms of residual oil, pivotal for advancing the production from tight sandstone reservoirs, particularly from the Chang 8 Member of the Upper Triassic Yanchang Formation, Ordos Basin. Through an analysis of 23 core samples, employing high-pressure mercury injection, field emission scanning electron microscopy, thin section, and X-ray diffraction techniques, distinct reservoir types were categorized. The utilization of environmental scanning electron microscope, multi-solvent continuous extraction, and an oil components separation system facilitated an intricate analysis of residual oil micro-occurrence states and their subsequent effects on porosity and permeability reduction across varying reservoir types. The findings accentuate the integral role of reservoir type in determining residual oil distribution within tight sandstone reservoirs. Favorable pore throat sorting and connectivity in specified reservoir types are identified as conducive to residual oil enrichment with a higher concentration of light components. In contrast, elevated carbonatite and clay content in other reservoir types leads to adsorption of heavy components, disrupting pore throat connectivity, and impeding crude oil filling. The varied interactions between oil and rock, oil–oil, and pore throat sealing significantly impact the distribution of oil components of residual oil, culminating in a notable reduction of porosity and permeability by 2.63% and 0.197 mD, with corresponding reduction rates of 27.19% and 46.69%, respectively. The insights derived from this study furnish a theoretical foundation for augmenting tight oil recovery and comprehending the enrichment mechanism of residual oil driven by the heterogeneity of tight sandstone reservoirs. [ABSTRACT FROM AUTHOR]

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This study employs similar simulation testing and discrete element simulation coupling to analyze the failure and deformation processes of a model coal seam's roof. The caving area of the overburden rock is divided into three zones: the delamination fracture zone, broken fracture zone, and compaction zone. The caving and fracture zones' heights are approximately 110 m above the coal seam, with a maximum subsidence of 11 m. The delamination fracture zone's porosity range is between 0.2 and 0.3, while the remainder of the roof predominantly exhibits a porosity of less than 0.1. In addition, the numerical model's stress analysis revealed that the overburden rock's displacement zone forms an 'arch-beam' structure starting from 160 m, with the maximum and minimum stress values decreasing as the distance of advancement increases. In the stress beam interval of the overburden rock, the maximum value changes periodically as the advancement distance increases. Based on a comparative analysis between observable data from on-site work and numerical simulation results, the stress data from the numerical simulation are essentially consistent with the actual results detected on-site, indicating the validity of the numerical simulation results. [ABSTRACT FROM AUTHOR]

While many studies have examined the role of biochar in carbon (C) accrual in short-term scale, few have explored the decadal scale influences of biochar on non-biochar C, e.g., native soil organic C (SOC) and added substrate. To address this knowledge gap, soils were collected from decade-old biochar field trials located in the United Kingdom (Cambisol) and China (Fluvisol), with each site having had three application rates (25–30, 50–60 and 75–100 Mg ha−1) of biochar plus an unamended Control, applied once in 2009. We assessed physicochemical and microbial properties associated with sucrose (representing the rhizodeposits) mineralization and the priming effect (PE) on native SOC. Here, we showed both soils amended with biochar at the middle application rate (50 Mg ha−1 biochar in Cambisol and 60 Mg ha−1 biochar in Fluvisol) resulted in greater substrate mineralization. The enhanced accessibility and availability of sucrose to microorganisms, particularly fast-growing bacterial genera like Arenimonas, Spingomonas, and Paenibacillus (r-strategists belonging to the Proteobacteria and Firmicutes phyla, respectively), can be attributed to the improved physicochemical properties of the soil, including pH, porosity, and pore connectivity, as revealed by synchrotron-based micro-CT. Random forest analysis also confirmed the contribution of the microbial diversity and physical properties such as porosity on sucrose mineralization. Biochar at the middle application rate, however, resulted in the lowest PE (0.3 and 0.4 mg of CO2-C g soil−1 in Cambisol and Fluvisol, respectively) after 53 days of incubation. This result might be associated with the fact that the biochar promoted large aggregates formation, which enclosed native SOC in soil macro-aggregates (2–0.25 mm). Our study revealed a diverging pattern between substrate mineralization and SOC priming linked to the biochar application rate. This suggests distinct mechanisms, biophysical and physicochemical, driving the mineralization of non-biochar carbon in a field where biochar was applied a decade before. Highlights: The application of biochar at a moderate rate (50–60 Mg ha−1) resulted in increased labile C mineralization and decreased priming of native SOC. Biochar amendments led to the reconfiguration of physicochemical properties, including pH, porosity, and the formation of aggregates. Modified microbial community structure towards more r-strategists caused greater sucrose mineralization. Biochar incorporation rate governed the C dynamics via (biophysical vs physicochemical mechanisms) in long-term biochar amended fields. [ABSTRACT FROM AUTHOR]

Acidified CO2 fracturing is a viable method for increasing production in deep, tight sandstone reservoirs. However, the potential mechanism of changes in pore structure and mechanical properties of sandstone under acidified CO2 supercritical composite is not clear. Understanding this mechanism is important for the study of crack initiation and extension in tight sandstone reservoirs. This study utilizes sandstone samples from the Xujiahe Formation reservoir in Rongchang District as experimental specimens. The primary focus is to analyze the changes in pore structure and mechanical properties of these samples after acidification–supercritical CO2 composite action. Nuclear magnetic resonance (NMR) and uniaxial compression tests are employed as the main investigative techniques. The results show that there was a physicochemical synergy between the acidification–supercritical CO2 composite effect; the crack initial stress, damage stress, and peak stress of the sandstone after 16 MPa supercritical CO2 acidification treatment were reduced by 20%, 49.5%, and 49.8%, respectively; the crack volumetric strain accelerated and the sandstone evolved from brittle to ductile damage; and the larger pore space and microcracks of the sandstone increased significantly after the treatment, which can be attributed to the gradual dissolution of intergranular cement leading to the formation of new pores connected to the existing pore network. The change mechanism of sandstone after acidification–supercritical CO2 compound treatment is also proposed. [ABSTRACT FROM AUTHOR]

Porosity is a pivotal factor affecting the capacity for storage and extraction in shale reservoirs. The paucity of labeled data in conventional well logs interpretation and supervised learning models leads to inadequate generalization and diminished prediction accuracy, thus limiting their effectiveness in precise porosity evaluation. This study introduces a contrastive learning – convolutional neural network (CL-CNN) framework that utilizes CL for pretraining on a vast array of unlabeled data, followed by fine-tuning using a traditional CNN on a curated set of labeled data. Applied to the Subei Basin in Eastern China, the framework was tested on 130 labeled data and 2576 unlabeled data points from well H1. The results indicate that the CL-CNN framework outperforms traditional CNN-based supervised learning and other machine learning models in terms of prediction accuracy for the dataset under consideration. Furthermore, it demonstrates the potential for extensive porosity assessment across different logged depths. Due to its efficacy and ease of use, the proposed framework is versatile enough for application in reservoir evaluation, engineering development, and related fields. The innovative contribution of this research is encapsulated in its unique methodology and procedural steps for the accurate prediction of shale reservoir porosity, thus significantly enriching the existing body of knowledge in this domain. [ABSTRACT FROM AUTHOR]

The surface subsidence caused by coal mining in the aeolian sand area of China northwest has seriously affected the soil pore structure and distribution of water and nutrients. In this study, three sample areas (one unexploited area RF, one edge subsidence area MF, and one dynamic subsidence area DF) were set at Dafanpu Coal Mine. The soil moisture content (SMC) and soil organic matter (SOM) content were measured at depths of 0–60 cm for each sampling point. The spatial variability of SMC and SOM in both vertical and horizontal dimensions was examined. Based on computed tomography (CT) technology, the true pore structure of typical soil samples at different depths was scanned, and three-dimensional reconstruction and analysis of soil pores were carried out using Amira Avizo software. The correlation between SMC, SOM content and soil pore parameters was presented, and the influence mechanism of soil pore change on water and nutrient variation in subsidence area was revealed. The results show that the SMC and SOM contents in the subsidence area at a depth of 0–60 cm are lower than those in the unexploited area. The mining-induced subsidence exacerbates the spatial heterogeneity of the horizontal distribution of SMC and SOM content. The variation coefficients of SMC and SOM content increase by 35.77% to 39.56% and 33.29% to 42.74%. The mining-induced subsidence increases the number and porosity of soil pores, particularly the number and porosity of macropores. The connectivity of soil pores in subsidence areas MF and DF is increased by 61.57% and 18.51%, respectively. The SMC and SOM content exhibit significant negative correlations with soil porosity and pore connectivity (P ≤ 0.05). The augmentation of soil porosity and pore connectivity in subsidence areas caused by coal mining are significant factors contributing to the variations in SMC and SOM content. [ABSTRACT FROM AUTHOR]

The fractured-vuggy carbonate oil resources in the western basin of China are extremely rich. The connectivity of carbonate reservoirs is complex, and there is still a lack of clear understanding of the development and topological structure of the pore space in fractured-vuggy reservoirs. Thus, effective prediction of fractured-vuggy reservoirs is difficult. In view of this, this work employs adaptive point cloud technology to reproduce the shape and capture the characteristics of a fractured-vuggy reservoir. To identify the complex connectivity among pores, fractures, and vugs, a simplified one-dimensional connectivity model is established by using the meshless connection element method (CEM). Considering that different types of connection units have different flow characteristics, a sequential coupling calculation method that can efficiently calculate reservoir pressure and saturation is developed. By automatic history matching, the dynamic production data is fitted in real-time, and the characteristic parameters of the connection unit are inverted. Simulation results show that the three-dimensional connectivity model of the fractured-vuggy reservoir built in this work is as close as 90% of the fine grid model, while the dynamic simulation efficiency is much higher with good accuracy. [ABSTRACT FROM AUTHOR]

Low-contrast oil reservoirs have a complicated origin story that frequently results from the interaction of several different factors. The low-contrast oil reservoirs in the Daqing Oilfield's SaPu intercalation in the Longxi Region are the main subjects of this study. This work investigates the petrophysical origins of these low-resistivity oil reservoirs through a series of carefully planned petrophysical experiments. The results showed that the main determinants of the low-contrast oil reservoirs in the SaPu intercalation were the conductivity of clay minerals and a high irreducible water saturation. A low clay conductivity had a significant effect, resulting in a significant reduction in the formation resistivity, even in circumstances with a low porosity and a low formation-water salinity. Moreover, the results from the NMR tests revealed that the irreducible water saturation in the core samples primarily ranged from 0.6 to 0.8, suggesting a significant prevalence. This work provides strong petrophysical indices for evaluating low-resistivity oil reservoirs in the SaPu intercalation and useful information for the petrophysical evaluation of similar reservoirs. [ABSTRACT FROM AUTHOR]

Paleo-oil reservoir is of great importance to understand hydrocarbon enrichment mechanism and hydrocarbon exploration potential, but is yet poorly investigated in Kuqa Depression. The occurrence of the paleo-oil reservoir in Dabei area was proved by quantitative grain fluorescence (QGF) and fluid inclusion petrography. Development history of the paleo-oil reservoir was reconstructed through: (1) oil-source correlation; (2) time coupling of source rock maturation, porosity evolution and migration pathways. The impact of paleo-oil reservoir on tight-gas accumulation was consequently discussed. Results suggest that considerable oil was accumulated in the K1bs reservoir with paleo oil-water contact in Dabei 2 Well and Dabei 201 Well at 5 800 and 6 040 m, respectively. Crude oil was primarily sourced from Triassic source rocks with Jurassic source rocks of secondary importance, which was at oil generation window (0.7%–1.1% Ro) during 9–6 and 7.5–5 Ma, respectively. The occurrence of K1bs tight reservoir (porosity < 12%) was about 25 Ma, while faults and associated fractures at Kelasue structural belt were developed approximately from 8 to 3.5 Ma. Therefore, the tight oil accumulation was formed during 8–5 Ma. The paleo-oil reservoir in Dabei 1 gas field was destroyed by the evaporation fractionation in later stage. [ABSTRACT FROM AUTHOR]

This study investigated the influence of movable oil on the pore structure of various shale types, analyzing 19 shale samples from Well X in the Mahu Sag of the Junggar Basin. Initially, X-ray diffraction (XRD) analysis classified the shale samples. Subsequently, the geochemical properties and pore structures of the samples, both pre and post oil Soxhlet extraction, were comparatively analyzed through Total Organic Carbon (TOC) content measurement, Rock-Eval pyrolysis, and nitrogen adsorption experiments. Additionally, fractal theory quantitatively described the impact of movable oil on the pore structure of different shale types. Results indicated higher movable oil content in siliceous shale compared to calcareous shale. Oil extraction led to a significant increase in specific surface area and pore volume in all samples, particularly in siliceous shale. Calcareous shale predominantly displays H2–H3 type hysteresis loops, indicating a uniform pore structure with ink-bottle-shaped pores. Conversely, siliceous shale exhibited diverse hysteresis loops, reflecting its complex pore structure. The fractal dimension in calcareous shale correlated primarily with pore structure, exhibiting no significant correlation with TOC content before or after oil extraction. Conversely, the fractal dimension changes in siliceous shale samples do not have a clear correlation with either TOC content or pore structure, suggesting variations may result from both TOC and pore structure. [ABSTRACT FROM AUTHOR]

The igneous reservoir has become an important exploration target for increasing reserves and production of oil and gas in the Junggar Basin. However, igneous reservoir exploration is restricted because the seismic exploration of high-quality igneous reservoirs is difficult and the anisotropy induced by high-angle fractures cannot be neglected. To implement the characterization of igneous reservoirs, we first study the correlation between anisotropy parameters and physical properties of igneous rock, and we propose a 5D facies-driven inversion method based on rock physics, which means we employ 3D seismic data at different incidence angles and azimuths to implement the estimation of a hydrocarbon reservoir constrained by the igneous rock facies. We also present an anisotropic igneous rock-physics model, in which micro-petrophysical characteristics, strong heterogeneity of skeleton minerals, and pore structures are considered. As a reasonable initial model is important for seismic inversion, we propose a facies-driven modelling seismic inversion method in which we use facies obtained on the basis of the difference between rock composition, reservoir physical parameters, and elastic parameters of different lithofacies igneous rocks to constrain the seismic inversion. Finally, we present a step seismic inversion method of using seismic data to estimate multi-parameters of horizontal transversely isotropic media. Therefore, the comprehensive processes of rock-physics modelling, inversion model establishment, and reservoir prediction of high-quality igneous rocks are proposed in this study, which demonstrates effective application for igneous reservoirs in China. [ABSTRACT FROM AUTHOR]

To further clarify the optimal target layer in the horizontal section of Wufeng–Longmaxi shale, we selected 126 shale samples from the Wufeng–Longmaxi Formations (Long111 to Long114 and Long12 submember) as the primary study objects from the perspective of the microscopic pore structure. We conducted this experimental study on the pore structure of shale samples according to various methods, including low-temperature nitrogen adsorption and carbon dioxide adsorption experiments, atomic force microscopy, and nano-computed tomography scanning. We calculated the fractal dimensions of samples at different horizons through the study of the characteristics of adsorption–desorption isotherms using the Frenkel–Halsey–Hill model. These results indicated that the shale samples had a complex pore structure (with a higher fractal dimension). The fractal dimensions were positively correlated with the specific surface area and total organic carbon content of the shale samples, weakly positively correlated with the micropore pore volume, and negatively correlated with the average pore radius. The samples from the Wufeng Formation and the Long111 and Long112 submembers had large fractal dimensions, whereas the samples from Long12 had the smallest fractal dimension. The pores of the shale samples generally were type H2/3, which were characterized by wedge, tabular, and ink-bottle shapes. Only three H3-type pore samples corresponded to the three smallest fractal dimension values. The Wufeng Formation's Long 111 and Long 112 layers should be the target layers for horizontal wells. In this study, we identified the optimal target layer of the horizontal shale profile of Wufeng–Longmaxi Formation, which holds great significance for shale oil and gas development in this formation. [ABSTRACT FROM AUTHOR]

Superficial weathering in the form of granular disaggregation, powdering and flaking on stone surface is one of the most serious damages to stone heritages, since the surface carries most of the artistic, historical information. The determination of the thickness of the superficially weathered layer of historical stones is critical to their conservation. However, the methodology for quantitative analyses of such thickness remains very limited. In this study, we carefully study the vapor absorption and pore structure evolution of historical sandstones from Guanzhong area with respect to their weathering. We find out that the thickness of superficial weathered layer of Guanzhong sandstones can be derived by following the changes in vapor absorption or pore structure. Such data achieved from various methods developed in this work are consistent with each other and in good agreement with the results obtained by using current techniques such as drilling resistance measurement, the Ruxton method and ultrasonic testing. Among all methods used, pore size distribution analysis requires less sample preparation and measures the thickness of superficial weathered layer of Guanzhong sandstones around 7 mm. [ABSTRACT FROM AUTHOR]

The lithofacies types, pore structure differences, and main controlling factors on the shale reservoirs are vital problems that need to be addressed in the process of shale oil exploration and development. This study explores the Luohe oilfield in the southern Ordos Basin, which is composed of organic-rich shale in the Chang 7 member, to clarify the reservoir properties and analyze major factors affecting the reservoir quality. The shale reservoir can be divided into five lithofacies using ternary diagrams of TOC, argillaceous minerals, and siliceous minerals: high organic-rich siliceous shale (HOSS), high organic-rich argillaceous shale (HOAS), medium organic-rich siliceous shale (MOSS), medium organic-rich argillaceous shale (MOAS), and low organic-rich shale (LOS). The type of organic matter in the studied samples is mainly Type I kerogen and Type II kerogen, predominantly Type II1 kerogen. The kerogen mostly lie within the mature zone in the study area. Various types of pores have been identified in the studied shale: intergranular pores, intragranular pores, intercrystalline pores, organic matter pores, and seams around organic matter. The pores are commonly nanoscale to micrometer in scale, with diameters ranging from 10 nm to several microns. The S1 content in shale is positively correlated with the macropore content, indicating that macropores in shale are the main effective oil storage spaces and are important for oil-bearing reservoirs. There is a good positive relationship between the macropore volume of shale and the content of organic matter. Organic matter in the shale can be beneficial for generating organic matter pores, dissolution pores, and seams at organic matter edge, resulting in better physical properties of shale reservoirs. There is a negative relationship between the quartz/feldspar content and macropores content, indicating that quartz and feldspar are detrimental for the macropore volume development. The lithofacies type is one of the important factors controlling the macropore volume. MOAS and HOAS are favorable lithofacies for the development of macropores. The findings of this study can be utilized for hydrocarbon exploration and development in the lacustrine shale formation of the Ordos Basin and other similar basins. [ABSTRACT FROM AUTHOR]

Tight oil has become one of the important energy sources for increasing reserves and production in China's oil and gas field. Chang 8 Member of Ordos Basin shows great exploration potential, and the classification and evaluation of tight reservoirs are critical to reservoir optimization and reserve evaluation. However, the classification and evaluation of tight reservoirs in Chang 8 Member of Ordos Basin have not been unified. Therefore, on the basis of previous research results, this paper systematically studied the petrological characteristics, physical properties and microscopic pore throat structure characteristics of tight sandstone reservoirs by means of rock slice observation, overburden porosity and permeability test and high-pressure mercury injection test. On this basis, the weight coefficient of the correlation between the key parameters and the oil-bearing property of the reservoir is determined by screening the key parameters, and the mathematical model of reservoir classification evaluation is established by using the analytic hierarchy process. The research results show that the reservoir composition maturity of Chang 8 Member in Ordos basin is medium, and the lithology is mainly lithic arkose and feldspathic lithic sandstone. The physical property of Chang 8 reservoir is poor, and it belongs to low porosity, low permeability ultra-low permeability reservoir as a whole. The reservoir space is dominated by intergranular pores and dissolution pores, and micro fractures are developed locally. The pore throat structure of the reservoir is fine, and the pore type is smaller than 10 μm, and the throat and micro throat are dominant with 0.2 μm. Considering porosity, permeability, displacement pressure, average pore throat radius and other parameters comprehensively, normalize each parameter, and determine the weight of each parameter according to its correlation with oil saturation. The reservoir classification and evaluation model were established by using the analytic hierarchy process (AHP), and the reservoir quality index (RMI) is used to classify the reservoirs of Chang 8 Member in Ordos Basin into 4 types. This study can provide a basis for efficient exploration and development of tight oil. [ABSTRACT FROM AUTHOR]

CO2 injection in coal seams, which is a significant initiative to mitigate environmental problems caused by greenhouse gases, often leads a sequence of changes in the physical properties of coal reservoirs. To look into how the pore structure changes in the process of CO2 sequestration, we selected fresh coal from Huoerxinhe coal mine in China as the object. Then, acid treatment and SC-CO2 extraction were used to dissolve Organic and inorganic components in coal. Thus, by using SEM, LTGA-N2 apparatus and XRD, the characteristics of pore parameter and fractal dimension variation were discussed. The research results show that, the APS of samples THF, HCL-HF and Y-C increase, while the total PV decreases and the pore connectivity deteriorates. The pore connectivity of Samples THF and HCL-HF is improved (THF-C, HCL-HF-C), but the total pore volume continuously reduces. In addition, solvents treatment and SC-CO2 extraction mainly act on the microporous fraction. After solvents pretreatment, the changes in the pore size distribution curves are mainly manifested in the reduction of number of micropores, especially in the micropores around 3–4 nm. There is a small increase in micropores for samples Y-C and HCL-HF-C, with the pore size mainly concentrated around 4 nm, while the pores of the sample THF-C mainly show an increase within the scope of 3–16 nm. Generally, solvent pretreatment and SC-CO2 extraction help to simplify pore structure. However, the sample HCL-HF-C shows opposite change characteristics. In a short period of time, the larger pore fractal dimension, the less beneficial it is to the flow of CO2, while pore fractal dimension becomes progressively less useful in assessing pore connectivity with increasing time. [ABSTRACT FROM AUTHOR]

The Chang 7 member of the Triassic Yanchang Formation in the Ordos Basin is a significant continent shale oil reservoir in China. Therefore, conducting an in-depth investigation into the pore structure and fluid mobility characteristics of the Chang 7 shale oil reservoir holds immense importance for advancing shale oil exploration. This study conducts a detailed analysis of the pore structures and their impact on fluid mobility of the Chang 7 shale oil reservoir using multiple methodologies, i.e., a cast thin section, scanning electron microscopy (SEM), X-ray diffraction (XRD), high-pressure mercury injection (HPMI), low-temperature nitrogen adsorption (LTNA), and nuclear magnetic resonance (NMR). The results show that the sandstone in the Yanwumao area of the Chang 7 shale oil reservoir consists mainly of lithic arkose and feldspathic litharenite, which can be classified into three lithofacies (massive fine-grained sandstone (Sfm), silt-fine sandstone with graded bedding (Sfgb), and silt-fine sandstone with parallel bedding (Sfp)). Moreover, three pore structures (Type I, II, and III), and four pore spaces (nanopores, micropores, mesopores, and macropores) can be characterized. Pore structure Type I, characterized by large pores, exhibits bimodal pore diameter curves, resulting in the highest levels of movable fluid saturation (MFS) and movable fluid porosity (MFP). Pore structure Type II demonstrates unimodal pore structures, indicating robust connectivity, and higher MFS and MFP. Pore structure Type III primarily consists of dissolved and intercrystalline pores with smaller pore radii, a weaker pore configuration relationship, and the least fluid mobility. Furthermore, a correlation analysis suggests that the pore structure significantly impacts the fluid flowability in the reservoir. Favorable petrophysical properties and large pores enhance fluid flowability. Micropores and mesopores with high fractal dimensions have a greater impact on reservoir fluid mobility compared to macropores and nanopores. Mesopores mainly control MFS and MFP, while micropores govern the shift from bound fluid to movable fluid states. Among the lithofacies types, the Sfm lithofacies exhibit the highest fluid mobility due to their significant proportion of macropores and mesopores, whereas the Sfgb lithofacies have lower values because they contain an abundance of micropores. The Sfp lithofacies also dominate macropores and mesopores, resulting in medium fluid mobility levels. This study combines lithofacies types, micro-reservoir pore structure characteristics, and mobile fluid occurrence characteristics to better understand the dominant reservoir distribution characteristics of the Chang 7 shale oil reservoirs in the Ordos Basin and provide theoretical information for further optimization of production strategies. [ABSTRACT FROM AUTHOR]

Against the backdrop of the national strategic goals of carbon peaking and carbon neutrality, the imperative for China's low-carbon new energy transformation is evident. Emerging as an efficient and clean new energy source, the coal-based "three gases" (coalbed methane, tight sandstone gas, and shale gas) have gained prominence. Nevertheless, the current exploration of the coal-based "three gases" is limited to individual reservoirs, posing challenges to achieving overall extraction efficiency. The primary obstacle lies in the conspicuous disparities in gas content among different reservoirs, with the causes of such disparities remaining elusive. To address this issue, this study focused on the Permian Longtan Formation (coal, shale, and tight sandstone) in the southeastern Sichuan Basin. Through a comparative analysis of the mineral composition, organic geochemical features, and pore structure characteristics, this study aimed to delineate reservoir variations and establish a foundation for the simultaneous exploration and exploitation of the coal-based "three gases". The research findings revealed that the differences in reservoir characteristics account for the variations in gas content among coal, shale, and tight sandstone. The mineral composition of the rock formations in the study area primarily consists of quartz, feldspar, clay minerals, pyrite, calcite, and dolomite. By comparison, the coal samples from the four major coal seams in the study area exhibited relatively large pore sizes, which are favorable for gas accumulation. [ABSTRACT FROM AUTHOR]

Tight glutenite reservoirs characterization and effective hydrocarbon-bearing formation identification faced great challenge due to ultra-low porosity, ultra-low permeability and complicated pore structure. Fracturing fracture-building technique always needed to obtain deliverability because of poor natural productive capacity. Pore structure characterization and friability prediction were essential in improving such type of reservoir evaluation. In this study, fractured tight glutenite reservoirs in Permian Jiamuhe Formation that located in northwest margin of Junggar Basin, northwest China, were chosen as an example, and 25 typical core samples were drilled and simultaneously applied for mercury injection capillary pressure (MICP), nuclear magnetic resonance (NMR) and whole-rock mineral X-ray diffraction experiments. A novel method of synthetizing pseudo-pore-throat radius (Rc) distribution from porosity frequency spectra was established to characterize fractured formation pore structure. Quartz and calcite were considered as the fragile mineral, and rock mineral component ratio method was used to predict brittleness index. Meanwhile, the statistical model raised by Jin et al. (SPE J 20:518–526, 2015) was used to predict two types of fracture toughness. And then, brittleness index and fracture toughness were combined to characterize tight glutenite reservoirs friability. Combining with maximal pore-throat radius (Rmax, reflected rock pore structure) and friability, our target formations were classified into four clusters. In addition, relationships among pore structure, friability and daily hydrocarbon production per meter (DI) were analyzed, and a model to predict DI from well-logging data was established. Comparison of predicted DI with the extracted results from drill stem test (DST) data illustrated the reliability of our raised models. This would be valuable in determining optimal hydrocarbon production intervals and formulating reasonable developed plans. [ABSTRACT FROM AUTHOR]

Introduction: This study investigates the key controlling factors of the occurrence state of deep coalbed methane (CBM). CBM is an abundant energy resource in China, particularly in deep coal seams. However, the exploration and development of deep CBM face numerous challenges, and the understanding of the controlling factors of its occurrence state is still limited. Methods: The study reveals that deep CBM primarily exists in the form of adsorbed gas and free gas within the pore-fracture system of coal. Factors such as formation temperature, formation pressure, pore structure, and water saturation collectively influence the occurrence state of deep CBM. By employing the Simplified Local Density (SLD) model and molecular simulation methods. Results and discussion: This study examines the impact of two external geological control factors (formation temperature, formation pressure) and three internal geological control factors (pore size, water saturation, Specific surface area) on deep CBM and establishes a theoretical model for gas content. Finally, the relationship between the adsorbed gas, free gas, total gas content, and burial depth is calculated using the model, uncovering the primary factors controlling the occurrence state of deep CBM. This research is of significant importance in providing key parameters for gas content in deep coal and optimizing deep CBM exploration. [ABSTRACT FROM AUTHOR]

Ultra-low permeability argillaceous sandstone reservoirs have become a significant focus for exploration and development. Saturation is a crucial parameter in evaluating such reservoirs. Due to the low porosity, low permeability, complex pore structure, and strong heterogeneity in ultra-low permeability argillaceous sandstone reservoirs, traditional evaluation methods are unable to achieve the required level of interpretation accuracy. To improve the accuracy of gas saturation calculations in ultra-low permeability argillaceous sandstone gas reservoirs, the conductivity characteristics of the ultra-low permeability argillaceous sandstone gas reservoirs in the Huangliu Formation in the Dongfang area, China, were analyzed through rock physics experimental data and geological information. The results revealed the clay content in the study area to range from 6% to 33.4%. Influenced by burial depth and temperature, kaolinite and montmorillonite transform into illite and chlorite, and the cation exchange capacity is not correlated with the clay content. This suggests that the effects of cation-attached conductivity can be ignored. The regional variation in rock electrical parameters is significant. When the lithology coefficient is a = 1, the consolidation index m varies between 1.25 and 1.75. When the lithology coefficient is b = 1, the saturation index n varies between 1.6 and 1.96. Under the influence of high temperature and pressure, the reservoirs in the study area exhibit two distinct characteristics on the capillary pressure curve, fractal dimension, and effective porosity index intersection diagram, (1) In Class I reservoirs, there is a strong correlation between the formation factor and natural gamma, as well as porosity, and a logarithmic relationship between the saturation exponent and the formation factor; and (2) in Class II reservoirs, there is a strong power-law relationship between the formation factor and porosity, as well as a logarithmic relationship between the saturation exponent and formation factor. Based on experimental and logging data, reservoir classification was conducted using core-scale logging and principal component analysis. Additionally, a saturation interpretation model was developed using multivariate regression, based on rock electrical parameters. The actual application results demonstrate that compared to the fixed rock resistivity saturation model, this model has reduced the average absolute error by 5.9%. The calculated values are consistent with the gas saturation analysis of the core at the pure gas section as determined by cable testing sampling. This model meets the requirements of practical production. The study of this interpretation method is of great significance for the formulation of development plans for ultra-low permeability offshore argillaceous sandstone gas reservoirs. [ABSTRACT FROM AUTHOR]

The reservoirs of ultra-deep and low-permeability sandstones typically exhibit characteristics of lithological tightness and poor physical properties. Fractures control the oil and gas content as well as the productivity of such reservoirs. However, the distribution of fractures is complex, exhibiting strong heterogeneity. Therefore, a systematic study on reservoir fracture modeling can provide geological foundations for the development of such reservoirs. Due to the considerable burial depth of these reservoirs, conventional methods relying solely on seismic information have limited reliability, and the established discrete network models of fractures are often less dependable. In this paper, taking the X gas reservoir in a basin in western China as an example, we discuss a fracture modeling method based on the integration of geological information to enhance the efficiency and accuracy of fracture modeling. The modeling method primarily involves the use of deterministic methods to obtain large-scale fractures, while random simulation is employed for small and medium-scale fractures. The fracture development control factors and seismic attribute information are integrated using permanence of ratios (PR) model to establish a fracture development probability field model. Subsequently, the geometric parameters of fractures and the fracture density model are used as input parameters to generate a discrete network model of small and medium-scale fractures using a object-based modeling method. Finally, based on the fracture equivalent property model and verified through geological understanding, analysis of production dynamics, and numerical simulation of the gas reservoir, it is demonstrated that the fracture model established using the proposed method aligns with geological understanding and exhibits high reliability. [ABSTRACT FROM AUTHOR]

With the continuous growth in global energy demand, research and development of unconventional oil and gas reservoirs have become crucial in the field of energy. This study focuses on the Chang 3 reservoir of the Yanchang Formation in the Ordos Basin, Weibei Oilfield, China. This reservoir is a typical tight sandstone reservoir, and its microscopic pore structure and displacement mechanism are essential for the efficient development of tight oil. However, the reservoir faces challenges such as complex microscopic pore structures and unclear displacement mechanisms, which hinder the efficient development of tight oil. In light of these challenges, through various studies including core observation, high-pressure mercury injection tests, water flooding experiments, oil-water two-phase relative permeability measurements, and stress sensitivity experiments, it was found that the Chang 3 reservoir exhibits strong microscopic heterogeneity. The pore-throat distribution characteristics mainly present two types: single peak and double peak, with the double peak type being predominant. The reservoir was classified and evaluated based on these characteristics. The improved injection ratio and properties enhance oil displacement efficiency, but an increase in irreducible water saturation has a negative impact on efficiency. The stress sensitivity of the reservoir fluctuates between weak and strong, with permeability being sensitive to net confining pressure. It is recommended to pay particular attention to the stress-sensitivity characteristics during reservoir development. The research results provide a scientific basis for the optimized development of tight oil reservoirs in this region, promote the sustainable development of unconventional oil and gas resources, and have significant theoretical and practical implications. [ABSTRACT FROM AUTHOR]

Deep low-rank coalbed methane (CBM) resources are numerous and widely distributed in China, although their exploration remains in its infancy. In this work, gas adsorption (N2/CO2), mercury intrusion porosimetry, and 3D CT reconstruction were performed on five coal samples of deep and shallow low-rank coal from northeast China to analyze their pore structure. The impact of the features in the pore structure at full scale on the capacity for methane adsorption and seepage is discussed. The results indicate that there are significant differences between deep low-rank coal and shallow low-rank coal in terms of porosity, permeability, composition, and adsorption capacity. The full-scale pore distribution was dispersed over a broad range and exhibited a multi-peak distribution, with the majority of the peak concentrations occurring between 0.45–0.7 nm and 3–4 nm. Mesopores are prevalent in shallow coal rock, whereas micropores are the most numerous in deep coal rock. The primary contributors to the specific surface area of both deep and superficial coal rock are micropores. Three-dimensional CT reconstruction can characterize pores with pore size greater than 1 μm, while the dominating equivalent pore diameters (Deq) range from 1 to 10 μm. More mini-scale pores and fissures are observed in deep coal rock, while shallow coal rock processes greater total and connection porosity. Multifractal features are prevalent in the fractal qualities of all the numbered samples. An enhancement in pore structure heterogeneity occurs with increasing pore size. The pore structure of deep coal rock is more heterogeneous. Furthermore, methane adsorption capacity is favorably connected with D1 (0.4 nm < pore diameter ≤ 2 nm), D2 (2 nm < pore diameter ≤ 5 nm), micropore volume, and specific surface area and negatively correlated with D3 (5 nm < pore diameter ≤ 50 nm), showing that methane adsorption capability is primarily controlled by micropores and mesopores. Methane seepage capacity is favorably connected with the pore volume and connected porosity of macropores and negatively correlated with D4 (pore diameter > 50 nm), indicating that the macropores are the primary factor influencing methane seepage capacity. [ABSTRACT FROM AUTHOR]

The Middle and Upper Permian Dalong and Gufeng Formations in South China have recently been considered as potential gas-producing shales. However, their pore structure characteristics remain poorly understood. To investigate the pore structure and fractal characteristics of the pores in these two formations, a suite of shale samples from the Dalong and Gufeng Formations in the western Hubei Province, South China were analyzed by multiple techniques, namely, TOC content, X-ray diffraction (XRD) mineralogy analysis, optical microscopy observations, major elemental analysis, field emission-scanning electron microscopy (FE-SEM), and low-pressure gas adsorption measurements (N2 and CO2). The identified major shale lithofacies include siliceous mudstone, carbonaceous mudstone, argillaceous-siliceous mixed mudstone, and calcareous-siliceous mixed mudstone. SEM images show that the dominant pore types include the pores between brittle minerals, slit-shaped pores between clay sheets, and secondary organic matter (OM) pores within solid bitumen. The pore size distribution is dominated by micropores and mesopores (<30 nm), which are the major contributors to total pore volume and surface area for the Dalong and Gufeng Formations. Based on the Frenkel–Halsey–Hill (FHH) method, fractal dimensions (D1, D2) calculated from the nitrogen adsorption data have a range of from 2.489 to 2.772 (D1) and from 2.658 to 2.963 (D2), and are higher in the Gufeng Formation (average TOC = 8.3 wt.%) due to a higher TOC content comparing to the Dalong Formation (average TOC = 6.2 wt.%). The pore development and fractal characteristics are primarily controlled by organic matter (OM), carbonate minerals, and clay minerals for both the Dalong and Gufeng Formations. Shale samples with high TOC content, low carbonate content, and high clay content tend to develop more heterogeneous micropores and mesopores, which is ascribed to the generation of clay-related and OM-hosted pores, along with the destruction of primary pores by pore-filling carbonate cements. [ABSTRACT FROM AUTHOR]

Early freezing of concrete is common in the construction of water conservancy projects in northern China. Early freezing damage induces the deterioration of the mechanical properties of concrete structures, which seriously affects the safety, stability, and service life of engineering structures. Through a laboratory uniaxial compression test and a computed tomography (CT) test, the influence law of freezing time and freezing temperature on the mechanical properties of concrete is analyzed herein. The three-dimensional pore structure of concrete at different freezing times is reconstructed. The pore distribution and pore structure characteristic parameters of concrete at different freezing times are studied. The correlation between mechanical properties and the pore structure of early frozen concrete is determined. The results show that with the delay of freezing time, the porosity of concrete test blocks increases first and then decreases. The average pore surface area primarily decreases and then increases. The average pore diameter increases with the trend of a quadratic parabola. The average pore form factor primarily decreases, then increases, and then decreases. The average pore surface area has the best correlation with the compressive strength and elastic modulus of early frozen concrete. The outcomes suggest that the average pore surface area should be preferred when constructing the mesoscopic damage index of early frozen concrete. Relevant results provide support for revealing the macro and micro damage mechanisms of early frozen concrete. [ABSTRACT FROM AUTHOR]

The Qinghai–Tibet Plateau is the main permafrost area in China. Concrete structures constructed on permafrost are affected by the early negative-temperature environment. In particular, the negative-temperature environment seriously affects the strength growth process and the frost resistance of concrete (FRC). Therefore, this study considered the influence of the gas content, water–binder ratio (w/b), age, and other factors on the strength variation law and FRC under −3 °C curing conditions. Nuclear magnetic resonance (NMR) was used to analyze the pore structure of concrete before and after freeze–thaw cycles (FTCs). The results showed that the compressive strength of the concrete (CSC) under −3 °C curing was only 57.8–86.4% of that cured under standard conditions. The CSC under −3 °C curing showed an obvious age-lag phenomenon. The FRC under −3 °C curing was much lower than that under standard curing. The porosity of the concrete under −3 °C curing was greater, with a higher percentage of harmful and multi-harmful pores than that under standard curing. The concrete properties deteriorated primarily because curing at −3 °C hindered the hydration reaction compared with standard methods. This hindrance resulted in diminished hydration development, weakening the concrete's structural integrity. Under both curing conditions, when the gas content was between 3.2% and 3.8%, the frost resistance was the best. This is because a gas content within this range effectively enhances the internal pore structure, therefore relieving the swelling pressure caused by FTCs. Based on the freeze–thaw damage (FTD) model proposed by previous authors, a new model for the CSC under −3 °C curing reaching that of the concrete under standard curing for 28 d was established in this study. This advanced model was capable of accurately assessing the FTD of concrete structures in permafrost regions. Finally, the life expectancy of concrete in Northwest China was predicted. The life of the concrete reached 46.9 years under standard curing, while the longest life of the concrete under −3 °C curing was only 12.9 years. Therefore, attention should be paid to constructing and curing concrete structures in cold environments. [ABSTRACT FROM AUTHOR]

Geometric heterogeneities in tight reservoir rocks saturated with a fluid mixture may exhibit different scale distribution characteristics. Conventional models of rock physics based on poroelasticity, which usually consider single‐scale pore structure and fluid patches, are inadequate for describing elastic wave responses. A major challenge is to establish the relationship between the wave response at different spatial scales and frequencies. To address this problem, three sets of observational data over a wide frequency range were obtained from a tight oil reservoir in the Ordos Basin, China. Ultrasonic measurements were made on eight sandstone samples at partial oil‐water saturation at 0.55 MHz. Data from six borehole measurements and seismic profiles were acquired and analyzed at about 10 kHz and 30 Hz, respectively. Analysis of the cast thin sections shows that dissolution pores and microcracks generally develop, with fractal dimensions of the pores ranging from 2.45 to 2.67 for the samples with porosities between 5.1% and 10.2%. Compressional wave velocity and attenuation were estimated from the observed data. The results show that the velocity dispersion from seismic to ultrasonic frequencies is 10.02%, mostly occurring between sonic and ultrasonic frequencies. The attenuation is stronger at higher oil saturation. The relationships between velocity, attenuation, and wavelength were established and can be used for further forward modeling and seismic interpretation studies. A partial saturation model has been derived based on effective differential medium theory and a double double‐porosity model, assuming that the medium contains fractal cracks and fluid patches. The effects of scale and saturation on wave responses are prevalent. Modeling results consistent with observed data show that the radii of cracks and fluid patches range from 0.1 μm to 2.8 mm, affecting ultrasonic, acoustic, and seismic attenuation. The multiscale data and proposed model quantify the relationship between fracture and fluid distributions and attenuation and could be useful for upscaling to the reservoir scale. The study helps improve the understanding of seismic wave propagation in partially saturated rocks, which has potential applications in seismic exploration, hydrocarbon production in reservoirs, and CO2 sequestration in aquifers. Plain Language Summary: The physical properties of the rock and fluid can be inferred from the measured elastic wave responses and energy dissipation characteristics. However, the effects of heterogeneities of different sizes and at different frequencies can hinder studies to quantify wave responses in a partially saturated porous medium, which are usually based on laboratory measurements. A major problem is the difference between observed frequencies and scales: megahertz in the laboratory, 10 of kilohertz in the borehole scale, and hertz in the seismic exploration scale. In this work, the frequency‐ and saturation‐dependent compressional velocity and attenuation are investigated using three geophysical data sets from the same tight reservoirs. A strong velocity dispersion over the measured frequency range is observed. The stronger attenuation at partial saturation may be caused by the multiscale heterogeneities of the pore structure and fluid patch distribution. A fractal poroelasticity model is developed by gradually inserting inclusions of different sizes with compliant pores and liquid patches into a homogeneous host skeleton. The wave responses are significantly affected by scale distribution and saturation. The proposed model, verified by the measured data, can be useful in interpreting the anelasticity of tight heterogeneous reservoirs in a broadband range. Key Points: We investigate how fluid saturation affects wave attenuation and dispersion over a wide frequency range in tight sandstone layersA partial saturation model describes the fractal properties of the layersThe size of the cracks and fluid patches are determined by applying the fractal model to the multiscale data [ABSTRACT FROM AUTHOR]

Carbonisation is one of the important methods to improve the utilisation of coal. The structural composition of coal plays an important role in coal carbonisation. This work used small-angle X-ray scattering (SAXS) to investigate the pore structure of three kinds of raw coals with different carbon content derived from Xingtai City, Hebei Province, China. The structures of the corresponding cokes obtained through carbonisation at 1200°C were investigated by elemental analysis and SAXS. In addition, the gasification reaction of the three cokes (C1, C2, C3) with CO2 were studied by thermogravimetric analysis. The SAXS results indicate that the surface fractal dimension increases while the pore size decreases, and the pore distribution became wider after carbonisation. In addition, all coals and cokes present a positive deviation from Porod's law, indicating that there is a micro-fluctuation of electron density in the samples. Besides, it exhibites a negative correlation has been found between the degree of deviation from Porod's law and the carbon content. The gasification reactivity of cokes C1 and C3 in CO2 are higher than that of C2, indicating that the pore structures affect the gas reactivity of the three different metamorphic degree cokes in CO2. [ABSTRACT FROM AUTHOR]

Carbonate rock is a critical reservoir for China's onshore oil and gas exploration. Carbonate reservoirs in different regions significantly differ in sedimentary and diagenesis processes and factors affecting their petrophysical and seismic rock physics properties. Therefore, it is critical to analyze the corresponding properties of carbonate rocks in different regions. Based on systematic petrological, rock microstructure, physical property, and seismic elastic characteristic measurements of deep carbonate reservoir samples in the Tarim Basin, the variation laws and influencing factors of the samples' physical and seismic elastic properties are analyzed. Based on these measurements, the variation patterns and influencing factors of petrophysical and seismic rock properties of rock samples are analyzed. The results show that the carbonate pore structure controls the overall variations of petrophysical and seismic rock physical properties of carbonate samples, and it is challenging to build a simple statistical model of porosity—permeability, porosity—velocity, and density—velocity. P- and S-velocities correlate well, and the P-and S-velocity ratio is a good index for rock typing. For tight carbonate samples, apparent velocity dispersion at a seismic exploration frequency band (5–200 Hz) can be observed, and the pore structure controls the velocity dispersion and attenuation features. Carbonate samples with crack-dissolution pores show moderately stronger velocity dispersion than samples with dissolution and microcrack pores. The pore aspect ratio and the frame flexibility factor (γ) calculated from the seismic rock physics model correlate well with pore structure parameters, such as the characteristic ratio surface. The pore aspect ratio and frame flexibility factor can be used to quantitatively characterize the changes in the pore structure of tight carbonate samples, reflecting the pore structure effects on the elastic wave velocity. This study's results can provide a basis for rock-typing carbonate reservoirs, lithology, and hydrocarbon detection of relevant reservoirs. [ABSTRACT FROM AUTHOR]

The effect of the attack by chemical contaminants on the microstructure of loess and the resultant changes in shear strength properties threaten the safety of engineering projects in Northwest (NW) China. The aim of this study was to investigate the microscopic mechanisms of the variation in shear strength of acid- and alkali-contaminated loess. Intact loess samples were immersed in acid and alkali solutions of various concentrations, and triaxial shear, scanning electron microscopy (SEM), and mercury intrusion porosimetry (MIP) measurements were then conducted to assess the effects of acid and alkali contamination on the shear strength and microstructure of loess. The results indicated that the shear properties (stress‒strain behavior, failure strength and cohesion) of loess deteriorated under acid contamination but were improved under alkali contamination. The structural damage (particle fragmentation, cement dissolution, and pore expansion) in acid-contaminated loess intensified with increasing acid concentration. In contrast, structural improvement occurred in alkali-contaminated loess because new cementation balanced local damage and enhanced the degree of structural connection. In acid-contaminated loess, the diffuse double layer (DDL) thinned, the calcium carbonate content rapidly decreased, and the liquid limit (LL) and plastic limit (PL) declined, while in alkali-contaminated loess, these parameters were improved. A series of physicochemical reactions (mineral dissolution, ion exchange, and particle and pore structure adjustment) in the presence of acid and alkali contamination drove the observed structural variation in loess. This comprehensive effect resulted in either loess shear strength enhancement or reduction, depending on whether damage to the original structure or formation of a new structure dominated, respectively. These findings contribute to a deeper understanding of the response of intact loess under various hydrochemical conditions, which has important practical significance for elucidating the disaster mechanism of loess slopes and facilitating ecological environment protection in acid–alkali-polluted areas. [ABSTRACT FROM AUTHOR]

Tight gas sandstone reservoirs play an important role in the field of exploration and development of unconventional oil/gas resources. However, these reservoirs typically exhibit low-porosity and poor-permeability, with pore structures of strong heterogeneity comprising connected and isolated pores. The traditional rock physics models (such as the Gassmann model) are established under the assumption of fully connected pores, which cannot reasonably describe the complexity in tight reservoirs. In this regard, this work proposes a rock physics modeling approach aimed at tight sandstone reservoirs based on a reformulated Xu–White model. Specifically, the differential effective medium model and Xu–White model are combined to analyze the influences of isolated pores on the dry rock skeleton. To characterize the general effects due to the different pore types on rock elastic moduli, the volume content of connected pores is defined as a pore-connectivity parameter. The simulated annealing algorithm is applied to invert the parameter, which is treated as a weighting coefficient for correcting the wet rock elastic moduli, thereby improving the precision of rock physics modeling. The proposed approach is tested and verified by using the log data of the work area of Sichuan Basin, West China. The result shows that, compared with the conventional method, the P- and S-wave velocities predicted by the proposed method are consistent with the log data. In addition to the inversion results of the conventional petrophysical parameters, the inverted pore-connectivity parameter can be a good auxiliary attribute that assists locating potential targets for tight gas sandstone reservoirs. [ABSTRACT FROM AUTHOR]

In China's cold region water conservancy and hydropower projects, the contact interface between the dam and the reservoir bank rock is prone to cracking under external loading and freeze–thaw action, which may lead to dam-bank failure and damage and cause engineering disasters. The NMR (Nuclear Magnetic Resonance) tests and uniaxial compression tests of concrete, sandstone, and sandstone-concrete composite after different numbers of freeze–thaw cycles were carried out to analyze the pore structure development and uniaxial compression mechanical properties of the three types of specimens under different numbers of freeze–thaw cycles. The results show that freeze–thaw cycling promotes the development of pores in sandstone and concrete, and sandstone is more sensitive to low-temperature freeze–thaw than concrete. The UCS (uniaxial compressive strength) of the sandstone-concrete binary changed in a V-shaped with the increase of the dip angle of the cemented interface, and the angle had no obvious effect on the microscopic pores. The freeze–thaw effect on the deterioration of the microscopic pore structure and mechanical properties of the sandstone-concrete binary has a similar effect pattern, in which the deterioration rate of porosity and compressive strength is faster in the early freeze–thaw period, slower in the middle period, and increases in the later period compared with the middle period, but the increase is smaller than that in the early period of freeze–thaw. In addition, the relationship between the porosity and UCS of the sandstone-concrete binary under the freeze–thaw cycle environment is a quadratic parabola. [ABSTRACT FROM AUTHOR]

The fluid flow behavior, generally referred to as seepage, could determine the hydrocarbon and brine movement behavior. Movable fluid property, as one of the vital parameters for seepage characteristic evaluation, was generally used for tight oil reservoirs' fluid flow ability assessment. The nuclear magnetic resonance technique was used to experiment with movable fluid percentage and movable fluid porosity, which can provide a realistic assessment of the amount of fluid that can flow in the porous media. Other techniques were also used to analyze the main factors in regulating the differences in movable fluid parameters. However, the research about fluid flow behavior was generally based on traditional methods, while the seepage characteristics from the pore-scale view are still a myth. To promote this process, in this study, core samples obtained from the Chang 7 reservoir of the Triassic Yanchang Formation in the Longdong region of Ordos Basin, China, were tested. The results show that the average movable fluid percentage and average movable fluid porosity of the total 16 core samples are 36.01% and 2.77%, respectively. The movable fluid exists mainly in the midlarge pores with the corresponding T 2 relaxation time over 10 ms. T 2 distributions mainly present four typical patterns: (1) bimodal distribution with similar amplitudes of the two peaks (occupying 6.25%), (2) bimodal distribution with higher right peak and lower left peak (occupying 18.75%), (3) bimodal distribution with higher left peak and lower right peak (occupying 56.25%), and (4) unimodal distribution (occupying 18.75%). Pore structure heterogeneity is closely related to the movable fluid parameters; the movable fluid parameters exhibit a relatively good correlation with core throat radius as well as permeability. There is an obvious difference between the movable fluid parameters and the microscopic characteristic factors in tight oil reservoirs due to the difference in physical properties, clay mineral content, microcracks, and pore structure characteristics. This research has provided a new perspective for the movable fluid property evaluation, and the relevant results can give some advice for the oil field development. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The interaction between shale and various fluids is crucial as it modifies pore structures, which govern the effective development of shale gas and the geological storage of carbon dioxide in shale formations. In this study, samples from the Longmaxi Formation shale in Sichuan Basin of China were exposed to different fluids, including 6 MPa CO2, 12 MPa CO2, 6 MPa CO2+brine, and 12 MPa CO2+brine, at 45 °C for 100 days. Various methods, including X-ray diffraction (XRD), X-ray fluorescence (XRF), field-emission scanning electron microscopy (FESEM), and the low-pressure gas adsorption (N2) test, were adopted to evaluate chemical and structural changes during the exposure process. After being treated with supercritical CO2+brine and subcritical CO2+brine, the shale underwent significant changes in its major element composition. The content of Ca, Al, and K in shale saturated with supercritical CO2+brine decreased from 13.00% to 10.34%, from 3.65% to 3.36%, and from 1.56% to 1.37%, respectively. Meanwhile, the content of Si and Na in the same shale increased slightly after saturation. The amount of quartz and dolomite increased, while the levels of clay and calcite slightly decreased. The surface of the shale sample became rougher and small bumps and cracks appeared after saturation with different fluids, as shown by the FESEM analysis results. Furthermore, the changes in both the total pore volume and pore size followed a similar pattern to the alterations in the specific surface areas. The highest level of variation occurred with the shale that was saturated with 12 MPa of CO2, indicating that gas pressure and CO2 phase state have a significant influence on the shale's pore structure. In addition, the distribution of pore sizes showed a bias towards larger sizes across all diameters; this suggests that the reaction resulted in a decrease in the number of micropores. This also highlights that the impact of varying fluid saturation was primarily focused on micropores and macropores. The results of this study provided experimental evidence to further test the mechanisms and permeability of geological storage of CO2 in organic-rich self-sourced shale. [ABSTRACT FROM AUTHOR]

The genetic types and evolution characteristics of pores are the important basis for evaluating the quality of unconventional shale reservoirs. In this paper, taking the Lower Cambrian Marine shales in southern China as an example, the microscopic pore structure, genetic types and evolutionary characteristics of shales are systematically studied. The results show that circular and oval organic pores with good connectivity and non-fixed inorganic pores with poor connectivity are mainly developed in marine shale. The marine shales mostly have laminar sedimentary structures, the thickness of which is several millimeters to several centimeters. Siliceous laminae, clay laminae, organic laminae and carbonate laminae were identified. Lamination can also be retained in oxygen-rich environments with rapid sediment inflow, which may be related to high turbidity fluid. The Lower Paleozoic marine shales in southern China have experienced a complex tectonic-thermal evolution history, which aggravated the complex distribution of laminar structures. Some shale sections show very low resistivity, and resistivity has a significant negative correlation with TOC content. Organic matter is the main factor that causes the extremely low resistivity of shale. This study is of great significance to accelerate the process of Marine shale exploration and development. [ABSTRACT FROM AUTHOR]

Lithofacies and micropore characteristics of shale reservoir directly affect the exploration and development of natural gas. To determine the development potential of shales of the Longmaxi Formation in the Western Hunan‐Hubei Region, the lithofacies types and micropore structure characteristics of the Longmaxi Formation shales have been systematically studied in this paper, based on ordinary thin sections, argon ion polishing–scanning electron microscopy, physical property testing, x‐ray diffraction whole‐rock and clay mineral analysis, isothermal nitrogen, and carbon dioxide adsorptions. According to the principle of 'laminar structure + total organic carbon (TOC) + mineral composition of felsic, clay, and carbonate minerals', eight types of shale lithofacies were identified. The effective porosity of the Longmaxi shale ranges from 1.8% to 14.4%, with a peak range from 3% to 6%, while the permeability ranges from 0.001 to 1.27 mD, with an average of 0.106 mD. Combined with the isothermal adsorption experiments, the proportion of mesopores is the largest in the Longmaxi shale, followed by macropores and micropores. Moreover, the pore diameters of mesopores are concentrated between 3 and 10 nm, while those of micropores are concentrated between 0.4 and 0.9 nm. The pore volume of shale is most developed when the content of brittle felsic minerals is 50% ~ 75% and the content of clay minerals is 25% ~ 50%, and the TOC content is positively correlated with the pore volume and specific surface area. There are significant differences in the pore development characteristics of different lithofacies. The shale reservoir space analysis indicates that micropores are controlled by TOC content and clay minerals, while the macropores are controlled by depositional intergranular pores, TOC content, and felsic content, as well as diagenetic pyrite mould pores, microfractures pores, and intercrystalline pores. On the other hand, mesopores are related to a mix of depositional and diagenetic factors with dominant contribution of intergranular pores, intercrystalline pores, organic pores, and intergranular shrinkage fractures pores. It is found that the pore development of massive organic‐rich siliceous shale lithofacies has the best reservoir quality, including well‐connected intergranular pores, intercrystalline pores, organic pores, and shrinkage fractures. Therefore, the massive organic‐rich siliceous shale lithofacies is the dominant fine‐grained reservoir lithofacies in the studied area. Based on understating the pore characteristics of different lithofacies, this study can provide a scientific basis for the prediction of favourable sweet spots of shale gas reservoir in the Longmaxi Formation, western Hunan‐Hubei Region. [ABSTRACT FROM AUTHOR]

As underground engineering extends into the western and deeper regions of China, more and more Luohe Formation sandstone layers will be encountered, which have weak cementation and high water content. It is a significant challenge to apply the open TBM, and the support system is crucial in determining whether TBM can excavate quickly and safely. Therefore, in order to optimize the support scheme, this paper analyzes the pore structure and porosity through CT scanning, the results indicate that the volume percentage of pores ≥34 μm is 2.3% and 1.5%, respectively, the large pore apertures are predominant, the surrounding rock has strong permeability, and there is a high risk of rock burst and roof collapse accidents, hence requiring reinforced support measures. On this basis, numerical simulations were conducted to evaluate the support effectiveness. The results show that replacing the "bolt + mesh" with a "bolt + cable + mesh + steel belt", and replacing the top three bolts with 7.3 m anchor cables, can better control the deformation and provide sufficient thrust force for the TBM, ensuring excavation speed. After the implementation of this scheme at the Kekegai coal mine in Shaanxi, China, the TBM excavation speed increased by 70%, from the previous 10 m/day to 17 m/d, significantly reducing the project duration and construction costs. [ABSTRACT FROM AUTHOR]