This study investigates the microscopic structural changes and the evolution of physical properties in typical shale samples from three wells in southwestern China during water–rock interactions. Using scanning electron microscopy (SEM), nuclear magnetic resonance (NMR), and other techniques, we analyzed the changes in pore structure, mineral dissolution behavior, and fracture propagation in shale samples of different types (organic-rich, mixed, and inorganic) during water immersion. The results show that water–rock interaction significantly affects the porosity, fracture width, and physical properties of shale. As the reaction time increases, the pore volume and number of pores generally increase in all shale types, with significant fracture propagation. Furthermore, fracture width changes exhibit varying trends depending on the reaction depth. NMR T2 spectrum analysis indicates that water–rock interaction not only influences the expansion of microfractures but also shows different responses in organic and inorganic pores. SEM images further reveal the impact of water–rock interaction on mineral dissolution, particularly during the early stages, where the dissolution of minerals significantly alters the pore structure. Overall, water–rock interaction plays a crucial role in the development of shale gas reservoirs, providing valuable data and theoretical support for future shale gas extraction.

Low permeability oil reservoirs hold an important position in the global oil resource reserves. They boast abundant reserves and serve as one of the crucial sources for crude oil reserve replacement in China and even the world. The mechanisms for improving the oil recovery rate in high-oil-bearing reservoirs include improving fluid properties, enhancing displacement efficiency, etc. However, their development is quite challenging, requiring continuous exploration and innovation in development technologies. This study addresses the unclear distribution patterns of microbial communities and the incomplete understanding of microbial enhanced oil recovery (MEOR) mechanisms in low permeability reservoirs. Utilizing high-throughput genomics and functional gene analysis techniques, combined with laboratory and field data, the study investigates the distribution and growth patterns of microbial communities in a low permeability reservoir, exemplified by the S169 block. Additionally, the potential of MEOR to enhance oil recovery and its underlying mechanisms are explored. The results indicate that microbial communities in low permeability reservoirs exhibit strong heterogeneity, with their distribution closely correlated to geological factors such as reservoir permeability and porosity. The diversity of microbial communities is positively correlated with oil recovery efficiency, and highly active microbial populations promote the production of metabolites that enhance oil recovery. The metabolic products of microorganisms help reduce the interfacial tension between oil and water, improve the fluidity of oil, and enhance the recovery rate. In addition, the structural changes in microbial communities are closely related to factors such as the permeability and porosity of reservoirs. This study provides a theoretical basis for the optimization of microbial enhanced oil recovery (MEOR) technology.

Clay content is a critical geological parameter influencing the pore structure, compaction sensitivity, and flow capacity of sandstone reservoirs. In this study, representative Tertiary sandstones from a major sedimentary basin in western China were selected, covering natural and synthetic core samples with clay contents ranging from 20% to 70%. Utilizing a self-developed apparatus capable of both static and dynamic compaction experiments, we systematically performed staged static loading and gas–water two-phase displacement tests. This enabled us to obtain comprehensive datasets on porosity, permeability, pressure response, and two-phase flow characteristics under various clay content, confining pressure, and gas drive rate conditions. Results demonstrate that high clay content leads to pronounced pore structure compaction and substantially greater permeability reductions compared to low-clay reservoirs, indicating heightened stress sensitivity. The synergy between gas drive rate and confining pressure regulates intralayer water production efficiency: initially, increased gas drive enhances mobile water production, but efficiency drops sharply at late stages due to pore contraction and increased bound water. As confining pressure increases, the mixed-flow region for two-phase flow shrinks, with water permeability decreasing sharply and gas permeability increasing, revealing the dynamic fluid transport and productivity decline mechanisms controlled by effective stress. The research deepens understanding of compaction–flow mechanisms in clay-rich sandstones, offering bases for evaluating reservoir stress sensitivity and supporting efficient, sustainable gas reservoir development, which increasingly helps offset global energy shortages.

This study addresses the impact of rock physical property differences on the displacement efficiency during the multi-cycle gas–water mutual drive process in water-driven gas storage reservoirs. Utilizing multi-cycle gas–water displacement core experiments and high-pressure nuclear magnetic resonance (NMR) technology, we systematically investigate the relationship between rock physical properties and gas–water flow dynamics. By measuring and dynamically monitoring changes in gas–water distribution within the core, we focus on the effects of differences in permeability, porosity, and pore structure on the non-uniformity and displacement efficiency during the gas–water mutual drive process. The results demonstrate that rock heterogeneity significantly reduces the displacement efficiency, particularly in low-permeability layers where pore structure heterogeneity exacerbates the uneven flow of gas and water, leading to a notable decline in displacement efficiency. Moreover, the impact of micropore structure on displacement efficiency has also been validated. These findings provide important experimental data and theoretical foundations for evaluating and demonstrating the gas–water mutual drive efficiency in water-driven gas storage reservoirs, which is crucial for enhancing gas storage recovery and long-term stability.