Abstract:  The exploration potential of Mesozoic volcanic rocks in Liaodong Bay depression of Bohai Bay basin is great, but the development law of high-quality volcanic rocks reservoir is not well understood. Aiming at the difficulty of exploring the genesis of favorable reservoirs of Mesozoic volcanic rocks, the reservoir space types, physical properties, pore microstructure, and other characteristics of Mesozoic volcanic rocks in  Jinzhou 25-A structure area in Bohai Sea are studied by a comprehensive application of drilling data, thin section, and physical property data, and the conditions and reservoir development model of high-quality volcanic rocks are analyzed and discussed. The results show that the Mesozoic volcanic rocks in Jinzhou 25-A structure area are mainly composed of trachyandesite and andesite in the lower subfacies of the intermediate-acid overflow facies, and a small amount of basalt in the basic overflow facies. Favorable reservoirs are mainly developed in trachyandesite and trachyte of the intermediate-acid overflow facies. The reservoir space is dominated by secondary origin, which mainly develops matrix pores, intracrystalline pores and fractures. Some intergranular pores can also be seen in the breccia on top of volcanic rocks. The average porosity and permeability of the reservoir are 20.3% and 0.209 mD respectively. It belongs to the high porosity and low permeability reservoir. Thick weathering crust is often developed on the top of volcanic rock mass after a long time weathering and denudation. At the same time, the inner reservoir of secondary weathering crust between eruptive units is also developed in the mother rock zone. The effective fracture direction is mainly NEE-SWW and NS direction, which creates good conditions for the formation of favorable reservoirs. Therefore, this paper established a volcanic rock regular model reservoir development model of “weathering as the main control, thick weathering crust reservoir developed on the top of volcanic rock, and secondary thin weathering crust inside reservoir developed on the top of eruption unit”.

Key words:  , Bohai Bay basin, Liaodongwan sag, Jinzhou 25-A structure area, Mesozoic, volcanic reservoir, weathering crust, development model