Evolution of Shale Pore During Tectonic Uplift: A Case Study of Silurian Shallow Shales From Wufeng-Longmaxi Formations in the Taiyang–Haiba Area

Abstract

Taking shallow shales (buried depth less than 2000 m) from the Wufeng Formation –Long1₁ submember in the Taiyang–Haiba area of Zhaotong in the Sichuan Basin as the focus, this study integrates field-emission scanning electron microscopy (FE-SEM), mercury intrusion porosimetry (MIP), and low-temperature N₂/CO₂ adsorption to characterise pore structures. By comparing the pore structures of shales at various burial depths, we investigate the evolution of pore systems during tectonic uplift. The results indicate that micropores and mesopores hosted in organic matter dominate the shallow Longmaxi Formation shale, contributing nearly all adsorption gas storage space and a large portion of free gas capacity. Although mesopores exhibit more complex surface morphologies and spatial configurations than micropores, micropores display stronger heterogeneity. Organic matter exerts a primary control on pore development, while carbonate and clay minerals influence meso- and macropore structures. During tectonic uplift, favourable preservation conditions persist, and a dynamic balance between pore fluid escape and the rate of overburden erosion ensures that pore structure and morphology remain essentially unaffected. This research provides a solid foundation for understanding the effects of tectonic uplift on shale pore systems and holds significant theoretical and practical implications for shale gas exploration and development.