Pathway System And Hydrocarbon Migration And Accumulation Of Hexiwu Buried-hill Zone In Jizhong Depression

The Hexiwu buried hill belt in Jizhong depression is rich in oil and gas resources.However,due to the lack of systematic reservoir formation mechanism research,the main controlling factors of reservoir formation and the law of oil and gas accumulation are unclear,which seriously hinders the process of oil and gas exploration.Taking the conduit system as the research object,this study analyzes the characteristics of unconformity,fault and inner reservoir fracture of buried hill zone and establishes the oil and gas conduit framework by using geological,geochemical,seismic,drilling and logging data.On this basis,the dominant migration pathways and favorable accumulation area of oil and gas are determined by means of numerical simulation and physical simulation.By dissecting typical oil and gas reservoirs,the main controlling factors and enrichment rules of oil and gas accumulation are summarized,and the corresponding oil and gas accumulation model is established to guide the next oil and gas exploration.The results show that there are 4 types of unconformity contact relationship,3 types of lithologic configuration and 2 types of migration channels on the top of the Ordovician in the Hexiwu buried hill zone,forming 4 types of oil and gas migration and accumulation.The vertical seepage zone and horizontal undercurrent zone in the semi weathered rock layer are the main channels of oil and gas migration.On the plane,the area of Caojiawu liuqiying Yongqing is the dominant direction of oil and gas migration and accumulation through unconformity.To some extent,the shape of oil source faults control the migration and accumulation of oil and gas in the northern part of buried hill belt.The activity characteristics of oil source faults are segmented in space and staged in time.The characteristics of fault activity affect the sealing and the way of oil and gas filling.The early generation and expulsion of oil and gas are consistent with fault activity,oil and gas are filled in the form of "seismic pump".The later fault tends to be static,oil and gas are filled in the form of steady-state seepage.At least three high angle fractures are developed in the buried hill belt,which are mainly NE-SW trending.The formation process of vein body in fracture is accompanied by the activity of hydrocarbon fluid,indicating that fracture is an important channel for hydrocarbon migration.The degree of fracture development has obvious coupling relationship with the physical and petroliferous properties of the reservoir,indicating that the fracture development and distribution area in the inner reservoir is the favorable zone for oil and gas migration and accumulation.The reservoir forming in the study area are mainly controlled by the differences of source rock hydrocarbon generation characteristics,reservoir characteristics and conduit system,and there are two kinds of accumulation models as a whole,namely,double depression multi direction hydrocarbon supply-fault and fracture conduit-multi layer accumulation reservoir model represented by Yangshuiwu buried hill in the north and single depression multi direction hydrocarbon supply-unconformity and karst fracture cave conduit-top accumulation model represented by Yongqing-Liuqiying buried hill in the south.The structural highs on the path of oil-gas dominant migration are favorable areas for oil-gas accumulation.Zhongchakou buried hill,south of Yangshuiwu buried hill and Bieguzhuang buried hill are potential targets for next oil-gas exploration.