Pore Genesis and Organic–Inorganic Synergistic Evolution of Lacustrine Organic-Rich Shales

Lacustrine shale reservoirs exhibit complex pore structures and strong heterogeneity, which exert a critical control on hydrocarbon storage and fluid flow. Although numerous studies have independently investigated organic matter–hosted pores and inorganic mineral pores, the coupled evolution of organic matter and inorganic minerals—and its influence on pore development across different thermal maturity stages—remains insufficiently understood. In this study, shale samples from the Qingshankou Formation in the Gulong Sag, spanning a range of thermal maturities, were analyzed using field-emission scanning electron microscopy (FE-SEM) combined with quantitative pore characterization techniques. The results indicate that pore formation and evolution in lacustrine shale are fundamentally governed by the coupled evolution of organic matter and inorganic minerals. Organic matter–clay composite pores are closely associated with organic matter thermal cracking and clay mineral transformation processes, and their development is primarily controlled by thermal maturity and clay mineral content. Organic matter–hosted pores are mainly influenced by organic matter type, abundance, and maturity, while inorganic minerals—particularly pyrite and clay minerals—can significantly promote organic matter cracking. Interparticle pores are closely related to the abundance of felsic minerals and thermal maturity; however, organic acid dissolution and ion precipitation during clay mineral transformation may partially or completely occlude these pores. In addition, organic acid dissolution capacity (controlled by total organic carbon content, soluble mineral content, and vitrinite reflectance Ro) and clay mineral transformation processes (controlled by clay content and Ro) further regulate intraparticle pore development by influencing dissolution pores and clay intercrystalline pores, respectively. These findings provide important insights into the genesis and evolutionary mechanisms of pores in lacustrine shale reservoirs.