Seismic prediction of Permian volcanic rock reservoirs in Southwest Sichuan Basin

Abstract The study aims to analyze Permian volcanic reservoirs (VResr) in the Chengdu Janyang area in the southwestern part of the Sichuan Basin through seismic prediction (SP) techniques in order to identify and predict VResr. The study integrated geological, logging and seismic data to construct a system for identifying eruption patterns and seismic characteristics of volcanic rocks (VR). Through detailed analyses of the VRs in the Chengdu Janyang area, the distribution range was determined, and the seismic phase models of VRs in different phase zones were established, and a phase-controlled quantitative study of the VResr was carried out. The Permian VRs in Southwest Sichuan are primarily classified into three phases: spatial, overflow, and sedimentary, with rock types comprising tuffs, basalts, and volcanoclastic lavas. Based on the seismic reflection characteristics, the VRs were classified into type I eruptive phases, type II eruptive phases, mobile phases, volcanic sedimentary phases, and non-volcanic normal sedimentary phases. The formation of VResr was influenced by a variety of factors, including petrography and fluid-modifying effects, among which petrography is the distribution of Permian VResr. High-quality VResr are predominantly found in the Chengdu–Jianyang–Santai area. These pore-type reservoirs have a porosity of 9–13%, with the core area reaching up to 11%, and are mainly formed by volcanoclastic lava. The reservoirs are continuously distributed in the plane and generally exceed 120 m in thickness, making this region the most promising for current volcanic oil and gas exploration. The study not only enriches the knowledge system of SP of Permian VResr in the southwestern part of the Sichuan Basin but also provides a scientific basis and direction guidance for oil and gas exploration. The experimental testing has clarified the next favorable exploration zone for VRs in the Jinyang area, offering precise technical guidance for their development.