Occurrence Types of Chlorite and Their Association with Reservoir Quality in Emeishan Basalts

Volcanic reservoirs are critical deep hydrocarbon exploration targets, but the complex relationship between chlorite occurrence types and reservoir quality in mafic volcanic successions remains poorly constrained. This study investigates Emeishan basalts from Well A (southwestern Sichuan Basin) using integrated geochemical, mineralogical, and petrophysical methods. Four chlorite occurrence types are identified, with distinct Fe/(Fe+Mg) compositional variations. A three-stage alteration sequence is delineated, and a ~3 m thick tight barrier layer formed by dense matrix replacement and pervasive amygdale-filling chlorite vertically compartmentalizes the reservoir. Chlorite exerts context-dependent effects: matrix replacement and pseudomorphic chlorite generally are preferentially associated with intervals exhibiting higher porosity; fracture-filling and amygdale-filling chlorite commonly occur in intervals characterized by reduced porosity and permeability. This study proposes an occurrence-based framework for interpreting reservoir heterogeneity in mafic volcanic rocks, providing practical reference for volcanic reservoir evaluation.