Pore Structure Evolution’s Reaction to Late-Stage Tectonic Uplift in Organic-Rich Marine Shale Reservoirs

An important scientific question in comprehending the dynamic adjustment and accumulation mechanisms of shale gas is the effect of late-stage tectonic uplift on the shale pore structure. It has a direct impact on how well shale gas exploration and development work in China’s structurally complicated Sichuan Basin. This study aims to reveal the rebound evolution patterns and characteristics of shale pores at different scales under the influence of the most recent tectonic uplift. To achieve this, we conducted triaxial creep experiments to investigate the compression recovery behavior of shale under varying confining pressures. Shale samples were subjected to low-pressure CO2/N2 adsorption studies and high-pressure mercury intrusion both prior to and during creep testing. Combined with the fractal theory, these methods revealed the evolution patterns of shale pore structures across different scales. Key findings reveal a bimodal pore size distribution in the Longmaxi Formation shale. Micropores contribute 60.25% to 81.52% of the specific surface area, while mesopores account for 51.02% to 70.03% of the pore volume. Under deep burial, macropores and mesopores tend to transform into micropores, enhancing the adsorbed gas storage. Micropore evolution is jointly influenced by clay minerals and total organic carbon (TOC), whereas mesopores correlate strongly with the TOC and quartz. Macropore development is governed by brittle minerals, such as quartz and calcite. This study presents a conceptual model of multiscale pore rebound under a tectonic uplift, highlighting the complex interactions between the mineral composition and mechanical behavior.