Enhanced Formation Conditions of the Large-Scale Volcanic Reservoir in the BZ8-3S Large Volcanic Structure in Bozhong Sag,Bohai Bay Basin

Zhou Jiaxiong; Xu Chunqiang; Huang Zhi; Shan Xuanlong; Zhang Jiangtao; Yi Jian

doi:10.3799/dqkx.2024.026

Abstract：In order to solve the problem of finding large-scale volcanic reservoirs in the Mesozoic of Bozhong Depression,Bohai Bay Basin,this paper takes BZ8-3S large volcanic trap and BZ8-3S-A high-yield volcanic exploration well drilled in this structure as the research object,and studies the lithology,lithofacies and reservoir characteristics of volcanic rocks in this structure in detail.The development conditions of the large volcanic trap model reservoir close to the source rock are discussed and the development model of the reservoir is established.The results show that the BZ8-3S structure is composed of several large and medium-sized acid lava volcanic structures and mainly develops three lithological lithofacies,namely porous rhyolite of the upper subfacies of the intermediate effusive facies,massive rhyolite of the lower subfacies and the crypto-explosive breccia subfacies of the volcanic vent facies,forming three types of volcanic reservoirs:high porosity and low permeability,medium porosity and low porosity and low permeability.The medium and large acid lavas with multiple eruption centres,rich upper subfacies of the effusive facies,as well as the upper subfacies of the effusive facies and the crypto-explosive breccia subfacies developed near the source facies of the volcanic mechanism are the basis for the formation of regular model volcanic rock reservoirs.Weathering promoted the formation of pores and fractures in the upper subfacies of the intermediate effusive facies and the crypto-explosive breccia subfacies,improved reservoir physical properties and was key to the formation of favourable reservoirs in the weathered crust.Tectonism transformed the massive lava of the lower subfacies of the effusive facies and formed the fracture and dissolution pore development zone in the parent rock of the lower part of the weathered crust,which formed the weathered crust-internal two-layer reservoir structure.Based on BZ8-3S,the reservoir development model of large-scale volcanic structure is established,which is based on the favourable lithology and lithofacies of large acid lava volcanic institutions and is controlled by weathering and tectonic transformation.