Development Characteristics and Controlling Factors of Inorganic Pores in Qiongzhusi Formation Shales from Different...

The Deyang-Anyue rift trough is a key target for Lower Cambrian Qiongzhusi shale gas exploration in the Sichuan Basin, yet inorganic pore heterogeneity across structural positions remains poorly constrained. Shales from the fifth sublayer in intratrough and trough-margin settings were analyzed using an integrated large-scale Mosaic scanning electron microscopy (LAM-SEM)advanced mineral identification and characterization system (AMICS) workflow, enabling pixel-scale mineral-pore registration and quantitative characterization of inorganic pore types, area fraction, size distribution, and morphology. Intratrough shales, mainly organic-rich to organic-moderate quartz-rich felsic shales, exhibit low inorganic pore area fractions but larger average pore sizes with predominantly unimodal distributions. Their pores are elongated and irregular, showing high eccentricity and low circularity, and are mainly feldspar-hosted dissolution pores. In contrast, trough-margin shales display higher inorganic pore area fractions, smaller pore sizes, and particularly locally multimodal size distributions in organic-lean feldspar-rich shales. These pores are more equant and smoother, characterized by lower eccentricity and higher circularity. Mineral composition and TOC jointly control inorganic pore structures: quartz content is positively correlated with pore size, whereas feldspar content shows a negative correlation. Easily soluble minerals are positively correlated with pore circularity, whereas clay minerals show a negative correlation. In addition, TOC promotes heterogeneous dissolution, leading to decreased circularity and increased eccentricity. These findings reveal two contrasting inorganic pore development patterns within the rift trough and provide new insights into pore evolution mechanisms and reservoir quality variations in deeply buried marine shales, offering a basis for deep marine shale reservoir evaluation and exploration target optimization.