Multilayer accumulation conditions and key technologies for exploration and development of the West Sichuan gas field in Sichuan Basin
Sichuan Basin has abundant oil-gas resources.Several hydrocarbon accumulation systems develop vertically from marine to terrestrial facies.In recent years,significant oil-gas exploration achievements have made in multiple strata of the West Sichuan gas field.To deepen the understanding of hydrocarbon enrichment regularities,guide the exploration and development practice,and fur-ther expand achievements in oil-gas production,this paper reviews the exploration and development history of the West Sichuan gas field and systematically analyzes the hydrocarbon accumulation conditions.The results show as follows.There are many sets of high-quality source rocks in western Sichuan depression,which provide sufficient material conditions.The development of tidal flat dolo-mite pore reservoir in the Member 4 of Middle Triassic Leikoupo Formation in western Sichuan area can expand marine exploration field from high-energy reef-beach and karst to confined platform tidal-flat dolomites,and enrich the types of marine oil-gas explora-tion.The superposed high-energy sandbodies widely developed at mouth bar and underwater distributary channel in the Member 2 of Upper Triassic Xujiahe Formation form a complete source-reservoir assemblage with inner source rocks or underlying Xiaotangzi For-mation source rocks.The high-energy sandbodies widely developed at fan delta and braided river delta underwater distributary chan-nels in Shaximiao Formation form a complete source-reservoir assemblage with source rocks of the Member 5 of Xujiahe Formation.The direct and relay through-source faults developed from Permian to Triassic Leikoupo Formation,the network micro-faults and fractures developed in Leikoupo Formation,the fault-fracture-sandbody transport system developed in Xujiahe Formation,and the fault-sandbody transport system developed in Shaximiao Formation in western Sichuan area are all efficient oil-gas transport systems,which ensure the efficient migration and accumulation of natural gas.The fine techniques of ultra-deep tidal-flat thin interbedded res-ervoir prediction are established,and the techniques of thin reservoir prediction and middle-small fracture space characterization for the Member 2 of Xujiahe Formation are formed,thus achieving fine reservoir characterization and supporting the implementation of horizontal wells.The development goals of high yield with fewer wells and effective use of reserves have been realized through well-matched development plan and research on drilling and completion technology.In western Sichuan area,the development and produc-tion of tidal-flat dolomite gas reservoirs in the ultra-deep complex structural belt,the efficient development of Xujiahe Formation,and the exploration breakthrough of Shaximiao Formation tight sandstone promote the process of exploration and development as well as the innovations of method and technology in relevant fields.
Leikoupo FormationXujiahe FormationShaximiao Formationaccumulation conditionWest Sichuan gas field
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