Developing deep coal resources is often hindered by technical challenges and low chemical reactivity. Underground coal gasification, a key approach for exploiting medium to deep coal seams, suffers from low reaction efficiency. In this study, the regulatory mechanism of supercritical CO2 pre-treatment on gasification performance was investigated using multi-scale characterization. Results show that supercritical CO2 exposure transformed the coal surface from dense to loose, prompting the development of numerous multi-scale pores and fractures. Specifically, the micropore volume and specific surface area increased from 0.0364 cm3/g and 168.231 m2/g to 0.0365 cm3/g and 169.455 m2/g, respectively. Similarly, the mesopore volume and specific surface area rose from 0.0190 cm3/g and 3.717 m2/g to 0.0198 cm3/g and 4.113 m2/g. During high-temperature simulated gasification, the raw and modified coal exhibited similar initial weight loss (9.19% and 9.38%, respectively). However, during the medium-temperature pyrolysis stage (200–600 °C), the modified coal showed a higher cumulative weight loss (23.68%) than the raw coal (17.02%). Consequently, the residual carbon rate at 1000 °C decreased from 18.06% to 15.84%, indicating that supercritical CO2 modification promotes earlier volatile release and more complete gasification. Microscopic chemical evolution analysis indicated that the oxygen-containing functional groups were removed in the sequence: carboxyl group–ether bond/hydroxyl group–carbonyl group. The total content of these functional groups in the modified coal increased from 26.18% at 25 °C to 48.50% at 550 °C, before dropping to 34.24% at 600 °C. Concurrently, the proportion of aromatic carbon (C–C/C=C) reached 80.37%, notably higher than that of the raw coal (55.21%). In summary, supercritical CO2 promotes volatile release, lowers gasification activation energy, and enhances overall reactivity. This is achieved through the synergistic regulation of pore structure, surface oxygenated intermediates, and carbon skeleton reorganization, establishing a cohesive “pore–surface–chemical state” regulatory framework.

To investigate the heterogeneous characteristics of the shale pore size distribution (PSD) of the Daanzhai Member in the Ziliujing Formation in the Sichuan Basin and its influencing factors, an analysis of its shale components, pore structure, and morphology was conducted. The analysis methods included the determination of total organic carbon (TOC), field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), LP-CO2GA, and LT-N2GA. The heterogeneity of the PSD was further analyzed via multifractal theory. The results indicate that the PSDs of both micropores and mesopores in shale exhibit multifractal features. The heterogeneity of mesopores is higher than that of micropores, but the pore connectivity is lower in mesopores than in micropores. Additionally, the degree of dispersion is higher in mesopores than in micropores. The PSD of micropores is influenced mainly by pores in the range of 0.30~0.70 nm in diameter. The distribution of mesopores is significantly affected by pores within the range of 2~10 nm in diameter. The pore connectivity and heterogeneity of mesopores are influenced primarily by the specific surface area (SSA) of the shale. In the case of micropores, both the SSA and pore volume (PV) contribute to the pore connectivity and heterogeneity. The effects of the rock components on the pore heterogeneity and connectivity vary significantly, with mineral components being the primary factors influencing pore heterogeneity. Compared with those of the mature Bakken Formation and the overmature Wufeng–Longmaxi Formation, the shale of the high-maturity Daanzhai Member has higher small-scale pore heterogeneity but weaker mesopore heterogeneity.

To enhance biogenic coalbed methane production, it is imperative to comprehend the processes by which methane is generated when microbes decompose coal in perched water zones situated in steeply inclined fire zones. Low-rank coal from Fukang mining was used to simulate biogenic gas production and investigate methane generation in perched water zones in steeply inclined coal fire zones. This study integrated characterization techniques, multifractal theory, and field data. Microbial activity increased oxygen-containing functional groups, reduced aromatic rings, and disrupted aliphatic clusters in samples. Aromatic nucleus interlayer spacing expanded; microcrystalline stacking, extensibility, and aromatic layers decreased. Coal structure degraded as microbes targeted aromatic then aliphatic carbon. Increased pore and fracture density enhanced pore connectivity (H) and reduced pore heterogeneity (triangle alpha), while pore types remained unchanged. Methane production via microbial degradation follows acetate and hydrogenotrophic pathways. Methane rates were affected by perched water zone distance, coal seam salinity, and pH.

Coalbed methane (CBM) resources are abundant along the southern margin of the Junggar Basin. However, the complex geological characteristics of coal reservoirs render traditional logging methods designed for nearhorizontal coal seams unsuitable for use in steep coal reservoirs, thereby hindering their efficient development. A comprehensive evaluation method that incorporates geological characteristics, core analysis, and well logging data is proposed for steep coal reservoirs in the Baiyanghe area in the southern margin of the Junggar Basin. A standard for coal reservoir logging evaluation and high-production well identification was developed by combining volume models and multi-parameter quantitative identification. The results showed that the neutron density intersection method was more accurate than single-density logging. Tectonic coal has a slightly higher density, lower acoustic time-lag values, and borehole diameter curves with diameter expansion and high fragmentation. Logging identification criteria for the macroscopic coal petrology types were established using compensated neutrons, acoustic time lags, and borehole diameter curves. The key indicators of high-production CBM wells include negative anomalies, higher average compensated neutron values, and smaller diameter logging amplitude differences. Using logging data and combining linear multiple regression and double lateral models, a logging evaluation model was developed to assess the coal components, gas content, and reservoir properties. This approach facilitates the identification of high-production areas and provides a foundation for accurate CBM development. The proposed method is expected to be particularly useful in evaluating unconventional gas reservoirs under complex geological conditions.

Objective To explore the enrichment conditions and main controlling factors of shale gas in the Lower Wuerhe Formation of the Permian System in the Junggar Basin, the Lower Wuerhe Formation in the Dongdaohaizi Sag was selected as the research object. Methods Based on the data of outcrop, core, well logging, well-calibrated seismic reflections and the technologies of total organic carbon (TOC) content determination, whole-rock X-ray diffraction, gas adsorption (N2, CO2), the distribution characteristics, organic matter development characteristics, reservoir characteristics, and gas bearing characteristics of the Lower Wuerhe Formation shale were studied. Results The results show that: (1) The organic matter of the Lower Wuerhe Formation shale is dominated by Ⅱ2 and Ⅲ types and shows an average TOC content of 1.58%. The average vitrinite reflectance (Ro) of organic matter is 1.46%, which indicates the mature stage. The average thickness of the source rock is 75 m. Summarily, the source rock is good and has a high gas potential. The basin simulation results show an average shale gas content of 1.89 m3/t in the Lower Wuerhe Formation. (2) The pores and microfractures in shale reservoirs are highly developed, and gas is primarily adsorbed in micropores and mesopores. The average porosity and permeability are 6.10% and 0.27×10-3 μm2 respectively, which are favourable for shale gas accumulation. (3) The shale has a high clay mineral content, with an average of 29.6%, providing a significant specific surface area and enhancing the gas adsorption capacity of the shale. Additionally, the average brittle mineral content is 50.9%, indicating good frackability. (4) Moreover, the shale reservoir exhibits a relatively large pressure coefficient of 1.58, indicating the favourable conservation conditions. The analysis of the regional tectonic-sedimentary environment and geochemical parameters indicates that the main factors controlling shale gas accumulation in the Lower Wuerhe Formation of the Dongdaohaizi Sag are geochemical parameters and preservation conditions. The key factors influencing shale gas accumulation include the high thermal evolution maturity of organic matter, large shale thickness, high TOC content, and good preservation conditions. These conditions suggest that the favourable area for shale gas exploration and development in the Dongdaohaizi Sag is located in the northeastern slope area of the sag's abdomen. Conclusion The results of this research reveal the enrichment conditions and main controlling factors of shale gas in the Lower Wuerhe Formation in the Dongdaohaizi Sag, which has reference value for deep oil and gas exploration in the abdominal area of the Junggar Basin.

The pore structure of shale is a key factor affecting the occurrence and flow of shale gas, and fractal dimensions can be used to quantitatively describe the complexity of the shale pore structure. In this study, the Leping Formation shale in the Junlian block of the southern Sichuan Basin was investigated. The pore structure characteristics of this shale were examined via low-pressure CO2 adsorption (LP-CO2A) and low-temperature N2 adsorption (LT-N2A) methods via field emission scanning electron microscopy (FE-SEM), shale geochemistry, and mineral composition analysis. Pore fractal dimensions were calculated via the Frenkel-Halsey-Hill (FHH) model, and the relationships among the fractal dimensions, shale composition (total organic carbon (TOC), quartz, and clay mineral contents), and pore structure were discussed. The results revealed that the TOC contents of the Leping Formation shale in the study area were high and ranged from 0.9% to 4.48%, with an average of 2.25%. The quartz contents were 17.2% to 60.1%, and the clay mineral contents were 33.8% to 67.2%. On the basis of the FE-SEM and N2 adsorption-desorption curve analyses, the pore types of the Leping Formation shale were complex and significantly variable in terms of the scale and development of organic pores, intragranular pores, and microfractures. The pore morphologies were mostly narrow slit-type flat pores and four-sided open or cone-type flat pores. The pore size distribution exhibited a multimodal pattern. The pore type was mainly mesopores, followed by micropores and minimal macropores. The specific surface area (SSA) of micropores accounted for more than 78% of the total SSA. The fractal dimension D 1 of the shale ranged from 2.262 to 2.618 (with a mean of 2.519), and the fractal dimension D 2 ranged from 2.662 to 2.843 (with a mean of 2.739). D 2 was greater than D 1, indicating that the internal structure of the pores was significantly more complex than that of the surface. The TOC and clay mineral contents were positively correlated with the Brunauer-Emmett-Teller (BET) SSA and the Barret-Joyner-Halenda (BJH) PV, whereas the quartz content was negatively correlated with the BET SSA and BJH PV. The considered fractal dimensions were positively correlated with the TOC content, clay mineral content, BET SSA, and BJH PV but negatively correlated with the quartz content and average pore diameter. The complexity and heterogeneity of the pore structure of the studied shale were quantitatively evaluated through fractal dimension analysis; thus, this approach can be applied in studies of the characteristics of the shale pore structure distribution and reservoir evaluation.

The SX area of the Ordos Basin in China is characterized by small thickness and considerable lateral variation of the reservoir, and high heterogeneity. It is difficult to identify gas and water by conventional P-wave seismic data without fully utilizing reservoir P-wave and S-wave information. Therefore, this study forms a series of seismic fluid detection technologies based on multi-wave seismic data, including the multi-wave “bright spot” feature analysis, multi-wave amplitude ratio technique, multi-wave amplitude versus offset analysis, multi-wave matched compression correlation analysis, and multi-wave pre-stack simultaneous inversion. The combined application of P- and S-waves facilitates visualized identification of fluids and improves the success rate of seismic prediction of underground gas-bearing features. The multi-wave interpretation technology series for low-permeability lithological gas reservoirs formed in this area has achieved a transformation from qualitative interpretation to quantitative prediction, and from lithological identification to fluid detection. These technologies have achieved significant geological results in the SX area.

Tuff reservoirs,as a type of tight oil and gas reservoir,are significantly influenced by their micro and nano-pores in terms of hydrocarbon storage.To understand the pore structure and heterogeneity characteristics of tuff reservoirs in the Perm-ian Section 2 Feng in Hashan area,Junggar Basin,six tuff samples from Well Ha 11 in Hashan area were selected.These samples underwent total organic carbon(TOC)content measurement,whole rock mineral composition analysis,and character-ization of pore structure through CO2 and N2 adsorption experiments.Using multifractal theory,the pore heterogeneity and con-nectivity were analyzed.The results show that the average TOC content of the tuff samples is 0.931%,and the mineral compo-nents are mainly feldspar,quartz,clay minerals,and dolomite.Micropores are mainly developed in the 0.33-0.38,0.50-0.68,and 0.72-0.86 nm pore size ranges,while meso-macropores are mainly developed in the 2.94-16.09 nm range.The generalized fractal dimension Dq decreases with increasing q,and the singular fractal spectrum shows a convex asymmetric parabola.The pores in tuff reservoirs have multifractal characteristics.Micropores(0-2 nm)have smaller width of the singular spectrum(Δα)values and larger Hurst index(H)values,while meso-macropores(2-100 nm)have larger Δα values and smaller Hurst index(H)values,indicating that micropores have better homogeneity and connectivity.The heterogeneity of meso-macropores is affected by the pore volume.With the increase in pore volume,pore heterogeneity increases,and connectivity decreases.TOC content and mineral composition have different effects on pore heterogeneity and connectivity.An increase in TOC content improves the connectivity of meso-macropores.An increase in plagioclase content increases the heterogeneity of meso-macropores.An increase in clay mineral content increases the heterogeneity of micropores,while an increase in dolomite and calcite content reduces the heterogeneity of meso-macropores.

In order to clarify the pore structure and fractal characteristics of the deep continental shale of the Lower Wuerhe Forma-tion in the central Junggar Basin,the Lower Wuerhe Formation shale in the Dongdaohaizi Sag was taken as the research object.On the basis of an in-depth analysis of shale minerals and geochemical characteristics,the pore structure characteristics of the Lower Wuerhe Formation shale were quantitatively characterized by using field emission scanning electron microscopy and low-temperature N2 adsorption experiments.The fractal dimension of shale pores was calculated based on the FHH model,and the rela-tionships among TOC content,mineral composition,pore structure parameters,fractal dimension,and its geological significance were revealed.The results show that the Lower Wuerhe Formation shale mainly develops inorganic pores and micro-fractures,and the pore size distribution is multi-peak type,mostly parallel plate or narrow slit pores.The pore development of shale is controlled by TOC and the content of quartz,feldspar,and clay minerals,which results in significant differences and strong heterogeneity among pore structures.Shale pores of the Lower Wuerhe Formation in the study area have double fractal characteristics,in which the surface fractal dimension D1 varies from 2.452 2 to 2.594 8,with an average value of 2.540 9.The fractal dimension D2 of the structure ranges from 2.604 5 to 2.774 8,with an average of 2.705 6.TOC is negatively correlated with fractal dimension,while pore structure parameters(specific surface area and pore volume)and mineral composition(quartz,feldspar,and clay mineral con-tent)are positively correlated with fractal dimension.An increase in the content of brittle minerals such as quartz,feldspar and clay minerals contributes to the development of micro-and nano-scale pores and micro-fractures.This results in an increase in specific surface area,pore volume,and fractal dimension.As pore heterogeneity strengthens,the complexity of the pore structure also in-creases.

Coal and shale reservoirs are characterized by low porosity, low permeability, and complex pore structure, which are the limiting factors for dual gas production. Studying the pore structure of shale and coal informs gas migration, adsorption mechanisms, and storage modes, guiding the assessment of reservoir quality and development plans, crucial for dual gas recovery and underground H2 and CO2 storage. Hence, in this study, we aimed to comparatively analyze the pore structures of different rock types. Gas adsorption and field-emission scanning electron microscope coupled with multiple fractal theory analyses were performed to characterize the porosity and pore structure of the over-mature Longmaxi Formation (Lower Silurian system) and coal of the Benxi Formation (Upper Carboniferous system). The organic pores in coal were more developed than in shale. Micropores provided pore volume and specific surface area in coal, whereas meso-macropores were dominant in shale. Micropores and meso-macropores exhibited multifractal pore-size distributions in coal and shale. Micropores had higher connectivity but lower heterogeneity than meso-macropores. The permeability, connectivity, and heterogeneity of coal rock were related to vitrinite reflectance, ash content, and moisture content, respectively, whereas the permeability, connectivity, and heterogeneity of shale were influenced by total organic carbon content and mineral composition. In the shale of the Longmaxi Formation, gas molecules were predominantly adsorbed in microscopic pores, whereas in the coal of the Benxi Formation, they were primarily free, with a few in microscopic pores. Desorption of adsorbed gas into free gas in the microcavities of coal beds was key to coal bed methane development, whereas migration of shale gas from the matrix reservoir space to natural or engineered fracturing was controlled by pore connectivity. Thus, the study reveals the differences between coal and shale rocks that impact gas distribution and emphasize the importance of pore evaluation for effective development and storage strategies in both reservoirs. Collectively, this research has important implications for future dual-gas and tri-gas co-extraction and selection layers as well as underground hydrogen storage.

Currently, there are more than 200 types of seismic attributes extracted from seismic data, the high-dimensional features of the data have become increasingly obvious. Although the increasing number of seismic attribute parameters is beneficial for researchers to understand seismic data, the massive amount of data also leads to redundancy and makes it difficult to further explore deeper buried information in seismic attributes, thereby reducing the accuracy of reservoir prediction. Manifold learning projects high-dimensional data into low-dimensional space by maintaining the local structure of the data, and mines and discovers the inherent characteristics and regularities hidden in the data. It is a new field of seismic attribute optimization research. This study is based on the application of manifold learning algorithms from cognitive science technology, comparing the advantages and disadvantages of the Isometric Mapping (ISOMAP) and Multidimensional Scaling (MDS) for extracting seismic attribute features, reducing the dimensionality of seismic attributes and optimizing the attributes. Both theoretical model analysis and practical application show that manifold learning has better clustering analysis ability and feature extraction performance in dealing with nonlinear problems, Seismic attributes extracted by ISOMAP are more accurate than those extracted by MDS in characterizing the distribution characteristics of favorable reservoirs, which provide powerful tools for subsequent reservoir characterization, sweet spot identification, and seismic interpretation.

Accurate description of micro and nano pores in coal reservoir plays an important role in evaluating the reservoir and gas production capacity of coalbed methane, we used 6 continuous samples of high rank coal in Daning-Jixian area on the eastern margin of Ordos Basin as the research object, and combined with high pressure mercury injection, low temperature N2 adsorption and low pressure CO2 adsorption experiments to characterize the pore structure characteristics. The aim of this study is to have an in-depth understanding of the full-size pore size distribution and explore the influencing factors of coal reservoir pore structure. The results show that the pore volume and specific surface area of coal sample in the study area have obvious differences with the pore size distribution, and the contribution rate of coal sample micropores to pore volume and specific surface area is significant, especially the diameter less than 1.5 nm micropore provides storage space for most of the adsorptive gas. The contribution of mesoporous and macroporous to pore volume and surface area is relatively small, which is not conducive to coalbed methane seepage. The vitrinite content of coal samples in the study area is positively correlated with pore volume and specific surface area, which contributes significantly to pore development. The relationship between inertinite content and pore volume and surface area is not obvious. With the increase of Mad, more adsorption pores are developed in coal samples, and pore volume and specific surface area are negatively correlated with Ad, indicating that the increase of Ad will lead to the decrease of pore volume and specific surface area.

To study the influence of coal metamorphism on the pore system development characteristics of deep coal reservoirs, coal samples of different ranks were collected as research objects. Based on maceral identification and industrial analysis, the pore structure of the coal samples of different ranks was characterized on multiple scales by combining low-pressure CO2 adsorption (L -PA), low-temperature N2 adsorption (L -TA) and high -pressure mercury intrusion porosimetry (MIP) experiments. In this paper, the distribution and variation in pores in coal samples of different ranks were investigated, the relationship between the pore structure characteristics and coal metamorphism was examined, and the influence of coal metamorphism on the pore structure was analysed. CH4 isothermal adsorption experiments of the coal samples of different ranks were conducted to reveal the relationship between the Langmuir parameters and Ro,max. According to the shape of the hysteresis loop of the nitrogen adsorption-desorption curves, the pores in the low-rank coal samples mainly included slit pores and cylindrical pores, while those in the medium- and high -rank coal samples mainly included slit pores, semiclosed wedge pores and ink-bottle pores. There were significant differences in the pore structures of the coal samples of different ranks. With increasing metamorphism, the pore volume (PV) and specific surface area (SSA) first decreased and then increased according to a U-shaped trend, reaching minimum values at a Ro,max of 1.7 %. According to the characterization results of the coal sample pore diameter, the pore size distribution (PSD) type was mainly the unimodal micropore-dominated type. Coal micropores with pore diameters smaller than 1.5 nm largely contributed to the SSA and PV. In addition, the coal rank linearly increased with increasing Langmuir volume (VL), while the Langmuir pressure (PL) first decreased and then increased, indicating that the CH4 adsorption capacity increased with increasing metamorphism.

页岩储层孔隙结构作为页岩气的赋存与运移空间,决定着页岩气的赋存状态与含气量多少,因此研究页岩储层的孔隙结构就尤为重要.通过对近十年页岩储层孔隙结构研究的方法理论进行归纳整理,并对影响页岩储层孔隙结构的因素进行分析,以期能为我国页岩气勘探开发事业提供帮助.

The detection and up-picking pf the seismic events are critical for seismic dat analysis and interpretation. Events picking can be used for sequence stratigraphic analysi reservoir feature extraction, the determining of the subsequent reflection interface, th improving of the SNR and the storage prediction. The research of the events picking i very significant for the seismic exploration. In order to overcome the existing event picking methods have the same sensitivity to noise. we propose a non-classical receptiv field visual cognitive method for the events picking up. Vision is an important functiona organ for human beings to obseve and recognize the world. About 80% of th information obtained by human beings from the outside world comes from the visua system. which fully shows that visual information is huge. and also shows that huma beings have a high utilization rate of visual information. How to transfer some typica information processing mechanism and target recognition function of human vision t machine is one of the most important and urgent tasks in the field of computer vision an artificial intelligence. The introduction of computer vision technology into geophysica prospecting is still in its infancy in the field of seismic exploration, our research fill th blank of this field, where the use of visual features to improve the seismic data processin and rapid realization of oil and gas exploration, will become the vane of the futur direction of research and development. As a basic research work in the crossing field. this paper has made a breakthrough i the research methods and ideas, and the research content can be summarized as th following four aspects:1. The proposed method implements the function of environmental suppression an spatial enhancement of the bio-visual primary visual cortex. which is applies to th pre-stack seismic data, as pre-stack seismic data contains abundant information such a amplitude and frequency to reflect tiny structures of the formation. 2. The seismic data is preprocessed to obtain the wavelet fusion of the envelope peal instantaneous frequency (EPIF) and the slant stack peak amplitude (SSPA), which can maximum the limit to provide optimal quality data. 3. An adaptive Gabor filter direction selection method is proposed to provide a reliabl angle range and improve the recognition rate of filter decomposition. In addition. b adopting an anisotropic environmental suppression method, our method can detect edg variability more accurately than the isotropic method. 4. With the enhanced contour aggregation. cocircular constraint is adopted and combine with the characteristics of low curvature and continuous changing curvature, which i unique to the seismic events. to establish a consistent spatial structure perception model The events picked by our method is more continuous and accurate than the existin methods. and doesn't require human interaction, which is beneficial for subsequent seismic interpretation and reservoir prediction.

鄂尔多斯盆地延长组长7黑色页岩分布面积广、厚度大、有机质含量高,具有广阔的页岩油勘探前景.在大量岩心、薄片和地化数据分析的基础上,对长7黑色页岩的岩相类型、地质特征与分布规律进行剖析,利用微量元素指标对其形成期古环境和页岩成因机制进行研究.按照"有机质丰度—岩矿组成—沉积构造"分类标准,将长7划分出3类岩相,其中长73底部发育极富有机质纹层状页岩,向长72过渡为富有机质纹层状黏土/粉砂质页岩,长71发育贫有机质块状粉砂质泥岩.自长73到长71,随着湖盆萎缩和三角洲推进,黏土矿物、有机质和黄铁矿含量以及纹层发育程度逐渐降低.亚热带温暖潮湿气候和长期稳定的深水湖泊环境为藻类大规模发育创造了条件.微量元素研究表明,长73极富有机质页岩形成于湖盆生产力极高、水体缺氧甚至硫化的强还原环境,因受火山活动和湖底热液的影响而富含胶磷矿和Ni、Cu、Mo等营养元素,是国内罕见的富铀页岩.结合古地貌、气候、水文条件综合分析,认为长7黑色页岩的成因机制为强烈构造运动下火山活动、热液活动叠加拗陷湖盆的水体分层模式.

Fluid mobility refers to the ratio of the effective permeability to the fluid viscosity of a fluid, and it reflects the interaction of permeability and fluid viscosity in the rock matrix of a reservoir. Studies have focused mainly on mobility attributes calculation and seldom dealt with mobility effects on the seismic responses of reservoirs and the inversion method based on petrophysical model. It is noted that there is a correspondence between mobility and dispersion and attenuation of the White's layered patchy-saturated model. On the basis of White's theory, we firstly employ numerical simulation to investigate mobility effects on seismic dispersion and attenuation for two typical sandstone reservoirs at two gas saturations. Secondly, we propose a method to inverse mobility value using P-waves dispersion data by particle swarm optimization. Finally, case studies of mobility inversion using core data from the Sulige gas field are given to verify the effectiveness and accuracy of our proposed method. The results show perceptible mobility effects on P-wave dispersion and attenuation. In general, mobility has a notable effect on seismic responses of unconsolidated sandstone reservoirs with large porosity and low gas saturation. Inversions on core data show the method is reliable, stable and convergent, and the inverted results are of high precision. All these theoretical findings would provide the basis and new technical ideas for mobility prediction.

As an unconventional oil/gas resource, shale oil is rich in reserves, widely-distributed, and has great potential for the exploration and development. It has become the focus and hotspot of the oil and gas industries in the recent years. However, shale oil reservoirs are characterized by diverse mineral components, low porosity and low permeability, complex structures, and strong heterogeneities, which are significantly different from the conventional oil and gas resources. In this study, ten tight sandstone samples from the Chang 7 oil-layer group of Mesozoic Yanchang Formation in Ordos Basin are selected. The mineral components of each sample are obtained by the X-ray diffraction analysis. P- and S-wave velocities and inverse quality factors are computed based on the ultrasonic experimental tests under different confining pressures and fluid saturation conditions. The porosities with respect to the varying pressure are also obtained based on the experimental measurements, after which the microcrack porosity of each sample is estimated by the linear extrapolation and incorporated into the EIAS (Equivalent Inclusion-Average Stress) model. The corresponding microcrack aspect ratios and microcrack densities are obtained to analyze the effect of pore-microcrack properties on wave attenuation. The results show that the correlations between total porosity, microcrack aspect ratio and microcrack density, and the variation of attenuation (the difference between the attenuation at each confining pressure and that at the highest confining pressure) in the tight sandstones are significantly better than the correlations between those and attenuation. It is revealed that the tight sandstone samples have a triple-porosity structure of microcrack inclusions, intrapore clay inclusions, and intergranular pores according to the thin section analysis. Therefore, this study introduces a triple-porosity structure model to quantitatively estimate the clay content in each sample, and then analyzes the relations between the intrapore clay content, total clay content and P-wave attenuation. The results show that the intrapore clay content (rather than the total clay content) is one of the main factors that dominate the magnitude of P-wave attenuation in the shale oil reservoirs. This study can provide theoretical supports for the analysis of attenuation characteristics, the construction of rock physics models, and the studies on seismic exploration methods for shale oil reservoirs.

The pore-fracture structure of deep coal reservoirs is of great significance to the evaluation, exploration and development of deep coalbed methane (CBM) resource potential. However, investigations on the pore-fracture structure of coals have mainly focused on micro/nanopores, while the contribution of microfractures to the activity of coal reservoir pore systems has not received sufficient attention. This study considers the coal rock of the Benxi Formation in the Daning-Jixian Block on the eastern margin of the Ordos Basin as the research object. Based on the coal quality parameters of coal rock, FE-SEM, the gas adsorption method, the high-pressure mercury injection method and micro-CT scanning are used to quantitatively characterize nanoscale pores and micron-scale fractures in deep coal reservoirs and comprehensively evaluate the pore-fracture structure characteristics at different scales. Combined with physical characteristics such as porosity and permeability, the influence of different scales of pore fractures on the occurrence and seepage of deep CBM is discussed. The results show that based on a variety of pore characterization methods, the pore-fracture volume distribution of deep coal reservoirs can be quantitatively characterized at full scale. The pore-fracture volume distribution type is mainly bimodal type, presenting a bimodal state of coexistence of micropores and microfractures, mainly concentrated in the range of 0.3-1.5 nm and >1000 μm. Among these elements, the volumes of micropores (<2 nm), mesopores (2-50 nm), macropores (50 nm-10 μm) and microfractures (>10 μm) account for 78.0%, 6.8%, 2.1% and 13.1% of the total pore volume, respectively. The coal rocks of the Benxi Formation mainly contain organic matter (OM) pores, inorganic pores and microfractures. The OM pores are diverse in shape, mainly circular, elliptical and wedge-shaped. The pore diameter of intragranular pores is small, between 20-50 nm, while the pore diameter of intergranular pores is large, generally greater than 300 nm. The microfractures are mainly distributed at the edge of OM and inside clay minerals, which exhibit slender stripes or serrated curves. Based on a full-scale pore-fracture splicing calculation, the total permeability of the coal rocks of the Benxi Formation (the sum of pore permeability and fracture permeability) is 5.77~28.22 mD. These microfractures are interconnected and distributed in a three-dimensional network structure with strong connectivity. The permeability is mainly provided by microcracks with a pore diameter of >100 μm, accounting for approximately 95% of the total permeability. Micropores in deep coal reservoirs provide a large adsorption space for adsorbed gas, while microcracks enhance the permeability of deep CBM.