Lithofacies characteristics and controlling on volcanic reservoirs in the basement: A case study of the offshore Bohai Bay Basin, Eastern China

Volcanic rocks are important, but special reservoirs, for hydrocarbon exploration. Volcanic lithofacies play an important role in reservoir development, but the understanding of the relationship between lithofacies and reservoirs is still limited, especially for volcanic basements. In this paper, we characterized the intermediate-basic lithofacies features and discuss the relationship between lithofacies and reservoirs in the offshore Bohai Bay Basin. The results show that there developed volcanic conduit, eruptive (basic and neutral), explosive, and volcanogenic sedimentary facies in the study area. Among them, the explosive and eruptive facies are dominant. Different lithofacies present diverse well-logging and seismic responses, and the basic-eruptive (basalt), neutral-eruptive (andesite), explosive, and volcanogenic sedimentary facies are distributed from the bottom to top orderly fashion. This vertical superposition pattern represents a volcanic eruption process that has resulted in eruptive facies being more developed than explosive facies. The pores (intershard, dissolution, and devitrified pores) and tectonic fractures are the predominant spaces for explosive and neutral-eruptive facies (andesite), respectively. The lithofacies control the development of the primary spaces, fractures, and the diagenesis processes, leading to explosive and neutral-eruptive facies being the dominant facies for reservoir development. The understanding of high-quality reservoirs in the volcanic buried hills is not only controlled by weathering but also dominant lithofacies that will guide the volcanic exploration globally.