Natural Gas Accumulation and exploration potential of permian Volcanic Rocks in Southwest Sichuan Basin

Abstract

To figure out gas enrichment laws in Permian volcanic rocks, Sichuan Basin, an association among reservoir-forming elements was explored to analyze forming modes and point out exploration prospects in accordance with reservoir characteristics, gas source conditions, and fault elongation in Zhougongshan and Jianyang areas. Results show that there mostly exist porous volcaniclastic rock and lava reservoirs of explosive facies. In Jianyang with Lower Cambrian Qiongzhusi Formation as the principal source rock, early faults offered pathways to assemble ample initial oil and gas. Following an increase of burial depth, oil started cracking vastly to create oil-cracked gas. These elements constitute one reservoir-forming mode of Cambrian hydrocarbon supply–fault transporting–in-situ cracking in Jianyang. While in Zhougongshan with Lower Permian Maokou 1 Member as the main source, active faults during hydrocarbon generation and expulsion acted on trap preservation. Late kerogen-cracked gas gathered at structural highs far from giant faults. Thus, the other mode exhibited in Zhougongshan is Permian hydrocarbon supply–fault adjustment–effective trap accumulation. Reservoir-forming conditions in volcanic rocks present certain disparity among all kinds of tectonic settings inside the basin, giving rise to various volcanic gas reservoirs developed. The Permian volcanic rocks are expected to be a major domain for reserve and production increase in Sichuan Basin.