Pore Structure Heterogeneity of Deep Marine Shale in Complex Tectonic Zones and Its Implications for Shale Gas Exploration

Deep Wufeng-Longmaxi marine shale has abundant natural gas resources, but its complex tectonic characteristics lead to strong reservoir heterogeneity, limiting large-scale shale gas development. Herein, to clarify the effects of tectonism on shale pore structure characteristics and reservoir quality in different tectonic regions, typical shale samples from high-steep anticline (HSA) and broad-gentle syncline (BGS) were collected and analyzed through field emission scanning electron microscopy (FE-SEM), gas adsorption, high-pressure mercury injection, and field gas desorption. The results show that under stable tectonic conditions, BGS-shale develops lots of organic matter (OM) pores, and mesopores provide the main pore volume, accounting for over 75%. Deformed and damaged by tectonic extrusion, the HSA-shale is mainly composed of interparticle (InterP) pores and intraparticle (IntraP) pores, with mesopores and micropores accounting for 38.97-47.69% and 37.79-51.28% of total pore volume. Benefiting from increased microfractures and dissolution pores, the macropore volume of HSA-shale is similar to that of BGS-shale. Under good preservation and high pressure coefficient, BGS-shale has a larger pore volume, pore surface area, and porosity to store abundant shale gas, which is conducive to a high shale gas yield. However, the HSA-shale has lower shale gas storage capacity and yield because its porosity, pore volume, and pore surface area are reduced with worse preservation condition. Therefore, in complex tectonic zones, the deep BGS-shale is more favorable for shale gas development than HSA-shale.