Reservoir characteristics and controlling factors of the Middle Jurassic carbonate reservoir in the Buqu For-mation,Southern Qiangtang Depression
Based on field profiles,drilling,and core data,this study explores the characteristics and con-trolling factors of the Middle Jurassic Buqu Formation carbonate reservoir using methods such as core observation,conventional and cast thin section identification,scanning electron microscopy,cathodolu-minescence,mercury intrusion,and porosity and permeability testing.The results indicate that the car-bonate reservoir rocks of the Middle Jurassic Buqu Formation in the South Qiangtang Depression are mainly composed of bright crystal oolitic limestone,grain dolomite,(residual)grain dolomite,and bio-clastic limestone.The storage space mainly consists of intragranular dissolution pores,mold pores,in-tergranular pores,intergranular dissolution pores,non fabric selective dissolution pores,and cracks.The physical properties of reservoirs with different rock types vary significantly,with dolomite reser-voirs having better physical properties than transitional rocks and limestone,mainly belonging to classⅡ-Ⅲ reservoirs.Sedimentary facies and diagenesis are the controlling factors for favorable reservoirs.The material basis for the development of favorable reservoirs is formed by the sedimentation of carbon-ate platform margin shoals and intra platform shoals.Dolomitization,dissolution,and pressure dissolu-tion are key factors for the formation of favorable reservoirs.Thorough dolomitization has a significant promoting effect on the increase of reservoir porosity.Fine crystalline self formed dolomite has the best physical properties.The various fractures generated by tectonic fracturing are beneficial for the migra-tion of dissolution fluids and effectively improve reservoir properties.This result provides geological ba-sis for the next step of oil and gas exploration in the study area.
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