四川盆地北部二叠系吴家坪组页岩岩相分异规律及其勘探开发启示OA

The exploration and development of shale gas in the Permian Wujiaping Formation of the northern Sichuan Basin are currently in a critical transition period from point-scale breakthrough to areal expansion.Due to the complex paleogeomorphology of the Kaijiang-Liangping trough,the reservoir heterogeneity is extremely strong.As a result,the lithofacies differentiation patterns and the coupling mechanisms between reservoir properties and engineering mechanics remain poorly understood,which severely restricts the large-scale,areal development of shale gas in this region.Taking the third Member of the Wujiaping Formation as the research object,this paper systematically investigates fine classification,characterization,differentiation mechanisms,and geological-engineering compatibility of shale lithofacies by means of of experimental methods such as core observation,whole-rock X-ray diffraction,X-ray fluorescence(XRF)core scanning,scanning electron microscopy(SEM),and triaxial rock mechanical tests comprehensively.The following results are obtained.First,the third Member of the Wujiaping Formation can be classified into three core lithofacies,namely siliceous,mixed,and calcareous shale lithofacies.These lithofacies exhibit significant gradational differences in mineral composition,organic matter enrichment,pore structure,physical properties,and mechanical characteristics.Second,the differential paleogeomorphology of the trough during the deposition is the dominant controlling factor for lithofacies differentiation,while sea-level fluctuation serves as a secondary controlling factor,and their coupling governs the lateral differentiation and vertical variation of the lithofacies.Third,based on the coupled relationship of"paleogeomorphology controlling lithofacies,lithofacies controlling reservoir quality,and lithofacies controlling engineering performance",Type-I favorable zones for large-scale productivity construction and Type-II favorable zones for potential expansion are defined,and correspondingly,differentiated fracturing stimulation techniques and tiered exploration and development strategies are determined for distinct zones.In conclusion,this study improves the lithofacies-based geological theory for the Wujiaping Formation shale gas,establishes an exploration evaluation and engineering development system tailored to complex thin-interbedded reservoirs,and provides important theoretical support and technical guidance for the transition from point-scale breakthrough to large-scale areal expansion of shale gas in the study area.