Natural gas fields are located at great depths within the Earth's crust due to burial and thermal maturation processes
Geological literature establishes that natural gas fields and deep coal-rock gas deposits are located at great burial depths and formed through thermal maturation and subsidence processes.
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Pore Diagenetic Evolution and Its Coupling Relationship with Natural Gas Accumulation in Tight Sandstone Reservoirs of the Second Member of the Xujiahe Formation, Xinchang Area, Western Sichuan. 2025. https://doi.org/10.3390/min15101052
By employing thin section analysis, scanning electron microscopy (SEM), homogenization temperatures of fluid inclusions, and carbon–oxygen isotope analysis of carbonate cements, this study conducted a temporal-quantitative investigation into the porosity evolution of relatively high-quality reservoirs in the Second Member of the Xujiahe Formation (Xu-2 Member) in the Xinchang area of western Sichuan. The analysis focused on quantifying porosity loss due to compaction, cementation, and porosity enhancement from dissolution. Results indicate that compaction exerted the most significant impact on reservoir quality in the Xu-2 Member, causing over 70% of total porosity loss. Cementation processes, including carbonate cements, silica cements, and authigenic chlorite, further degraded reservoir properties. Authigenic chlorite precipitated earliest at burial depths of 600–800 m, while authigenic quartz and carbonate cements persistently affected the reservoir at depths of 2000–5000 m, reducing porosity by at least 10% (up to 21%). Dissolution processes initiated at approximately 3500 m burial depth, generating secondary porosity of ≥2%, with a maximum increase of 16%. Integrating these findings with the natural gas accumulation history, the coupling relationship between pore evolution and gas accumulation was elucidated. The study reveals that reservoir tightness in the Xu-2 Member developed at burial depths of 4050–5300 m, with large-scale gas accumulation predominantly occurring prior to reservoir densification. The findings provide critical guidance for identifying high-quality tight sandstone reservoirs and optimizing exploration targets in the Xu-2 Member of the Xinchang area, Western Sichuan Basin, thereby supporting efficient development of regional tight gas resources.
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Deep Coal-rock Gas in China: A Review of Distribution, Geological Characteristics, and Its Enrichment Conditions.. 2025. https://doi.org/10.1021/acsomega.5c02056
Deep coal-rocks in China are widely distributed and characterized by greater thickness, and coal-rock methane (CRM) resource potentials have been suggested to be huge. In recent years, the exploration and development of deep CRM have achieved major breakthroughs, attracting widespread attention. Based on recently published data, this paper systematically summarizes the exploration and development history, geological and distribution characteristics of the coal-rocks, and the main controlling factors of deep CRM enrichment in China. Deep CRM is mainly widely distributed in the northern and southwestern areas of China and primarily developed in three sets of strata: the Carboniferous, Permian, and Jurassic systems. Deep coal-rocks exhibit high total organic carbon contents, with organic matter types mainly classified as types II<sub>2</sub> and III, generally in the mature to highly mature stages, demonstrating strong gas generation capacity. The maceral composition is dominated by vitrinite, and the industrial composition is primarily fixed carbon, which is classified as high-quality coal. The distribution of sedimentary facies, high thermal evolution degree, development of pores and microfractures, and favorable preservation conditions are significant factors contributing to the high CRM content. The primary occurrence states of deep CRM consist of adsorbed and free states. Under geological conditions, the adsorbed CRM content is mainly controlled by temperature, showing a clear negative correlation, while the reservoir pressure has a lesser impact on CRM content. Based on the analysis of the controlling factors for the enrichment and high production of deep CRM in China, it is concluded that CRM reservoirs can be classified into two accumulation models: self-sourcing and self-reservoiring and endogenous sourcing with external reservoiring.
Formation conditions of natural gas fields in the lacustrine basin in eastern China: Insights into the first discovery within the Bohai Bay Basin. 2023. https://doi.org/10.3389/feart.2022.1002581
The hydrocarbon source of Bohai Bay Basin is dominated by oil-prone kerogens of type II 2 -II 1 within semi-deep and deep lacustrine facies. In the Neogene period, faults were well-developed via significant structural activity. The Bohai Sea is generally considered to have no geological basis for the formation of large natural gas fields. Through analogous analysis of domestic and international gas fields, the key geological factors that restrict formation in continental rift lacustrine basins were studied, including gas source, preservation conditions, and reservoirs. A natural gas enrichment and accumulation model within a petroliferous basin is presented. The model indicates that rapid subsidence and high-intensity gas generation within petroliferous sags during the late stages were main contributors to natural gas field formation. Archean metamorphic buried hill reservoirs and thick, overpressure mudstone with strong vertical sealing ability provided favorable storage space and preservation, respectively. Using the model, an integrated Archaean metamorphic buried hill condensate gas reservoir, Bozhong 19–6, was discovered in the Bohai Bay Basin. The natural gas reserves are about 450×10 9 m 3 , equivalent to oil production of 800 ×10 6 m 3 , and signify a breakthrough in natural gas exploration of continental rift lacustrine basins in China.
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