Organic-rich shales present significant potential for underground hydrogen storage, yet our understanding of the interactions of H₂ with CH₄ and CO₂ in kerogen-hosted nanopores remain insufficient. This study constructs and validates macromolecular models of high-maturity and overmature kerogens via combining solid-state carbon-13 nuclear magnetic resonance spectroscopy, Fourier-transform infrared spectroscopy, and X-ray photoelectron spectroscopy. Grand canonical Monte Carlo and molecular dynamics simulations are performed, which reveal that kerogen maturity controls the competitive adsorption and diffusion of methane/hydrogen and carbon dioxide/hydrogen mixtures by regulating nanopore structure and surface chemical heterogeneity. Compared with high-maturity kerogen, overmature kerogen shows stronger confinement and a more pronounced near-surface enrichment of CH₄ and especially CO₂, which reduces the effective storage space available for H₂. Mechanistically, CH₄/H₂ competition is driven by van der Waals interactions, whereas CO₂/H₂ competition is dominated by stronger electrostatic and inductive interactions, establishing a thermodynamic affinity order. The radial distribution functions and interaction energies are measured, which confirm that CH₄ and CO₂ monopolize high-energy surface sites, relegating H₂ to a weakly adsorbed, bulk-like state. Although H₂ exhibits the weakest adsorption affinity, its high mobility suggests a stronger migration tendency and potential leakage risk, which should be considered when evaluating long-term containment security during underground hydrogen storage. Overall, this study reveals that maturity-controlled coupling exists between kerogen structure, competitive adsorption and gas transport, providing molecular-scale insights into hydrogen storage security, injectivity, leakage risk, and recovery in organic-rich shale reservoirs.

Studies on shale reservoir spaces mostly focus on matrix pores, as manifested by a lack of studies on microfractures’ role and on the quantitative characterization of multi-scale pore-fracture structures as a whole. This study delves into the shales of varying lithofacies from the Jurassic Lianggaoshan Formation, northeastern Sichuan Basin, using field emission scanning electron microscopy (FE-SEM) aided by a random forest algorithm for image processing, and achieves the automatic identification and quantitative characterization of organic and inorganic pores and fractures in the shales. Furthermore, by combining the large field-of-view (FoV) image stitching for SEM (SEM-Maps), we comprehensively characterize the distribution characteristics of multi-scale pores and fractures in the shales. The results indicate that the random forest model can effectively distinguish organic and inorganic pores and fractures. The SEM-Maps images at the FoV scale of 300 μm × 300 μm are representative and can exclude the effects of heterogeneity. In addition, the shales with various lithofacies exhibit significantly different characteristics of pore-fracture structures. In detail, the medium-high organic matter lamellar felsic shales have a total pore-fracture areal porosity of up to 2. 66%, significantly higher than that of low-organic-matter laminated felsic shales (1. 66%) and low-organic-matter massive silty to fine-grained sandstones (0. 99%). In contrast, the shales with various lithofacies exhibit similar distributions of pore and micro-fracture scales, with the pore scales primarily falling in the range of 20 to 1000 nm, and the microfracture scales predominantly between 200 nm and 5000 nm. Calculations based on single-component pore-fracture development coefficients, indicate that clay minerals are easier to form pores and fractures compared with felsic minerals in the Lianggaoshan Formation. This study not only reveals the differences in the multi-scale pore-fracture structures of shales with various lithofacies in the Lianggaoshan Formation, but also identifies the shale lithofacies with a high pore-fracture areal porosity and favorable pore-fracture types. These findings provide an important scientific basis for the precise assessment of sweet spots and efficient shale oil development.

To elucidate the role of effective pore preservation in controlling shale gas enrichment and high yield. This study focuses on fine-grained sedimentary shale of the Qiongzhusi Formation in Sichuan Basin, sampled from different tectonic settings. Rock facies were classified based on total organic carbon (TOC) measurements, X-ray diffraction (XRD), and cast thin section observations. The same lithofacies shale was selected for multi-scale pore characterization and field emission scanning electron microscopy (FE–SEM) to identify pore types and pore structures. By integrating actual drilling and logging data, paleopressure reconstruction via methane inclusion Raman spectroscopy, and burial history analysis of gas reservoirs, the preservation conditions of gas reservoirs are clarified. This study systematically reveals the mechanisms of shale pore preservation at different tectonic settings under the coupled effects of mineral composition, sealing systems, and fluid overpressure. A conceptual model for pore preservation in the Qiongzhusi Formation shales is further proposed. The results show that the deep shelf shales within the rift trough is characterized by high TOC, a rigid mineral skeleton, and overpressure storage. These shales develop an organic–inorganic composite pore network, exhibiting significantly higher pore volume and gas yield compared to shales outside the trough. At the trough margin, a semi-closed system with plastic mineral framework and moderate overpressure supports medium porosity. In contrast, shales outside the rift trough exhibit the weakest pore preservation capacity due to an open system, normal pressure, and plastic mineral framework. This study proposes a ternary synergistic pore preservation model of “rigid skeleton–closed system–hydrocarbon fluid overpressure”, which provides critical geological insight for the exploration and development of deep fine-grained sedimentary shale gas.

Organic matter is the basis of shale gas generation, and the study of Quaternary Pleistocene climate change in the Qaidam Basin and its effect on organic matter enrichment is crucial for the exploration and development of biogenic gas in the Qaidam Basin. In this paper, the Quaternary shale in the Qaidam Basin is taken as the research object, and Quaternary Pleistocene climate change is clarified in terms of paleo-moisture and paleo-temperature through organic carbon analysis and main and trace element experiments. Then, the influence of climate change on organic matter enrichment is analyzed from two perspectives: biological productivity and organic matter preservation. Finally, the Quaternary Pleistocene organic matter depositional pattern of the Qaidam Basin is established. The results show that (1) in the early-middle Quaternary Pleistocene, the climate was cool and humid, the herbaceous plants were luxuriant, and rich in cellulose, hemicellulose, sugar, starch and pectin, which improved the biological productivity of the surface layer of the water column. The amount of precipitation was high, and the stratification of the water column was good. The strong stratification of the water column also enhanced the reduction level of the lower layer of the water column, which is favorable for the preservation of the organic matter deposited from the upper layer and thus favors the enrichment of sedimentary organic matter. Additionally, relatively low temperatures inhibit the activities of methanogenic bacteria, which is also conducive to the preservation of organic matter. (2) In the late Pleistocene, under the Neotectonic Movement, the Tibetan Plateau uplifted, the climate became arid, and the temperature increased, leading to an increase in the proportion of woody plants and a decrease in the amount of nutrients available to methanogenic bacteria, decreasing the biological productivity of the surface layer of the water column. On the other hand, the stratification of the water column was weakened. The mixing of oxygen-rich water in the upper layer and oxygen-poor water in the lower layer results in the level of reduction of the lower layer of the water column being significantly lowered. The sedimentary organic matter that settled from the upper layer was easily destroyed, which was unfavorable for the preservation of sedimentary organic matter. Additionally, when the temperature was relatively high, methanogenic bacteria consumed a large amount of organic matter, which was also unfavorable for the preservation of organic matter. The research results have important theoretical and practical significance for the exploration and development of biogenic gas in the study area.

Mobility is a crucial metric for assessing sweet spots of continental shale oil. However, due to the complexity of shale oil reservoirs characteristics and the lack of systematic analyses of factors influencing mobility, the difference in shale oil mobility under multiple lithofacies control remains unclear, causing significant challenges for mobility evaluation and sweet spot prediction. This study examines continental shales of the Fengcheng Formation in the Mahu Sag, employing scanning electron microscopy (SEM), nitrogen adsorption (NA), nuclear magnetic resonance (NMR), spontaneous imbibition (SI), and contact angle measurements (CAM) to investigate the pore structure, connectivity, and wettability properties of different lithofacies shale. Quantitative analyses of shale movable oil content and saturation were conducted using multistep temperature pyrolysis (MTP) and NMR centrifugation techniques. Furthermore, the influence of reservoir characteristics, geochemical characteristics, and lamination development on shale oil mobility were discussed. Results indicate that larger pore diameter, higher imbibition slopes, and lower fractal dimensions of movable fluid pores (D₂) correspond to higher movable oil saturation. Organic matter exerts a dual effect on shale movable oil content. When the TOC is below a threshold, the movable oil content gradually increases with TOC. Laminations exhibit favorable reservoir properties and light oil enrichment, enhancing shale oil mobility. Massive siltstone (MS) develops interconnected intergranular pores with the best pore structure and connectivity, the lowest D₂ values, and the highest shale oil mobility. Laminated felsic shale (LFS) and laminated calcareous shale (LCS) exhibit moderate mobility, where the development of microfractures enhances fluid flow by connecting isolated pores into pore-fracture networks. In contrast, massive felsic shale (MFS) and bedded felsic shale (BFS) primarily develop intragranular dissolution pores with more complex structures and poorer connectivity, resulting in weaker mobility. A more accurate approach for assessing shale oil mobility has been presented, taking into account both total oil content and movable oil saturation. More importantly, this study establishes a comprehensive conceptual model illustrating the potential relationships among shale lithofacies, reservoir characteristics, and movable oil flow space in the study area. This research not only provides a systematic approach for assessing shale oil mobility but also deepens the understanding of flow mechanisms of continental shale oil, offering theoretical guidance for optimizing sweet spots in the Fengcheng Formation shale oil reservoirs of the Mahu Sag.

The Qiongzhusi Formation, following the Wufeng-Longmaxi formations, has been recognized as a promising target for future shale gas exploration and exploitation in the Sichuan Basin. Presently, notable achievements have been made in shale gas exploration in wells Z201 and WY1, drilled at the center and margin of the Deyang-Anyue aulacogen, respectively. However, there is a lack of clear understanding of the Qiongzhusi Formation shale reservoirs occurring in the aulacogen. Focusing on wells Z201 and WY1, coupled with other data on shale gas exploration and exploitation, we systematically analyze the mineral and organic geochemical characteristics, reservoir and storage space characteristics, and gas-bearing properties of each shale in the Qiongzhusi Formationin the study area. Key findings are outlined as follows. (1)The Qiongzhusi Formation shales in the study area can be divided into eight layers, predominantlycomposed of brittle minerals overall. This formation generally exhibits total organic carbon (TOC) content exceeding 1 %, suggesting high-quality source rocks. Furthermore, the TOC content is higher within the aulacogen than on its margin, indicating favorable gas generation conditions. aulacogen (2)Both organic and inorganic pores are found in the Qiongzhusi Formation shales, more prevalent within the aulacogen, contributing to extremely high gas content. Black shale reservoirs in layers 1, 3, 5, and 7 exhibit high quality, especially the layer 5. (3)The quality of shale reservoirs in the Qiongzhusi Formation is governed by the Deyang-Anyue aulacogen. Specifically, reservoirs encountered in drilling well Z201, situated within the aulacogen, exhibit superior characteristics compared to those in well WY1 located at the margin. (4)The degree of organic matter evolution in the Qiongzhusi Formation shales is significantly influenced by the Leshan-Longnvsi paleo-uplift. The organic matter generally tends to be less mature within than outside. The moderate-degree organic matter evolution within the paleo-uplift creates conditions favorable to large-scale gas enrichment. Therefore, high-quality Qiongzhusi Formation shale reservoirs are identified as a major successor play for future shale gas exploration and exploitation.