四川盆地合川区块沙溪庙组天然气成藏特征及有利区分布OA

In recent years,several old wells in Hechuan block of Sichuan Basin have tested commercial gas flow in Shaximiao Formation,demonstrating significant exploration potential.In order to further clarify the characteristics of natural gas accumulation in Shaximiao Formation of this block and lay the foundation for subsequent exploration and evaluation,geological conditions of accumulation in Shaximiao Formation of Hechuan block are studied based on logging,seismic data and related research on transition zone in central Sichuan Basin-western Sichuan Basin.By analyzing gas-producing wells and gas-logging display wells,natural gas migration and accumulation patterns are clarified,and favorable accumulation areas are preliminary identified.The results show that,the first member of Shaximiao Formation exhibits limited areal distribution of single-stage distributary channel sand bodies,but verti-cally developing multi-stages sand bodies with large range of superposition,which is conductive to multi-layers and large-scale accumulation.The underlying Xujiahe Formation and Lower Jurassic source rocks have large thickness,entering the mature stage and providing favorable hydrocarbon generation conditions.Hechuan block of the first member of Shaximiao Formation exhibits three-dimensional accumulation characteristics,with 2 types of vertical source-reservoir connecting faults.Type ① faults are composed of reverse faults extending from Xujiahe Formation to Lower Jurassic and normal faults extending from Lower Jurassic to Shaximiao Formation.Type ② faults are nor-mal faults extending from Lower Jurassic to Shaximiao Formation.Areally,there are 2 types of migration and accu-mulation patterns of natural gas including channel-along enrichment and cross-channel enrichment.The develop-ment of along-channel enrichment pattern,with a distance to source fault of<15 km and reservoir porosity>9%,is used as the evaluation criterion for Class I favorable accumulation areas.S2-2,S3-2 and S4-1 channels are identi-fied as the most favorable,representing the key target layers for further exploration and development.The research provides theoretical guidance for subsequent exploration and evaluation in Hechuan block.