Influence of Lamina Types and Combinations of Deep Marine Shale on Reservoir Quality in Zigong Block of Southern Sichuan Basin

Abstract

The influence of the type of lamina and its combination on the reservoir quality in deep-sea shales of the Zigong Block in the southern Sichuan Basin was investigated. The shale reservoirs in the Wufeng and Longmaxi Formations were characterized in detail by employing a variety of advanced techniques such as full-scale thin section imaging, micro-X-ray fluorescence spectroscopy (Micro-XRF), field emission scanning electron microscopy, and a quantitative mineral evaluation system (QEMSCAN). This study systematically analyzed the structural characteristics of different types of lamina and their effects on the reservoir porosity, permeability, and gas content. The findings reveal that the type and combination of laminae significantly affect the reservoir quality of shale. Among the identified combinations, the “authigenic quartz–organic matter + carbonate + felsic–carbonate” lamina combination demonstrates the most favorable characteristics, with higher organic content, brittle mineral content, and porosity, making it the optimal “sweet spot” for shale gas development. This research provides crucial theoretical insights into the formation mechanisms of deep marine shale gas reservoirs and supports further advancements in shale gas exploration and development.