川中‒蜀南地区茅口组岩溶储层油气成藏条件与有利区带预测OA北大核心CSTPCD

Early exploration of Maokou Formation in Sichuan Basin was always focused on southern and eastern ar-eas with high-steep structural zone and fracture-developed zones.In recent years,re-examination of old wells re-veals widespread active oil and gas shows in non-structural highs,especially slope-synclinal area in central-south-ern Sichuan Basin,but without clear understanding of distribution and development pattern of reservoirs in slope-synclinal area,and undetermined exploration direction of karst reservoirs in regional Maokou Formation.Karst res-ervoirs of Maokou Formation in central-southern Sichuan Basin are studied by using core analysis,CT imaging,log-ging and seismic data.The results show 2 sets of high-energy grain shoal bodies developed in Maokou Formation.Grain shoals of Mao2b sub-member of lower Maokou Formation develop a new type of karst reservoir,i.e.,porous-vuggy,controlled by horizontal undercurrent belts.Together with fractured-vuggy karst reservoirs developed in Mao2a sub-member to Mao3 member of upper Maokou Formation,they constitute effective karst reservoirs in Maok-ou Formation of central-southern Sichuan Basin.Karst reservoirs in Maokou Formation have experienced 3 stages of oil and gas charging process,with characteristics of large-area accumulation of"early large-scale enrichment and late differential adjustment in current anticline structural area,and in-situ preservation in slope-syncline area".Combined with paleomorphology of key accumulation periods,grain shoals and present structure,2 favorable explo-ration plays are finally optimized in Maokou Formation near Weiyuan-Gulin.Meanwhile,exploration targets are sug-gested to be expanded from only traditional fractured-vuggy karst reservoirs in upper Maokou Formation to both up-per and lower Maokou reservoirs,especially structural-stable syncline area with fractures not well-developed.The newly discovered porous-vuggy carbonate reservoirs are new field for oil and gas exploration in Maokou Formation.This study provides new ideas for oil and gas exploration in Maokou Formation of Sichuan Basin.