川南地区海相层系成储模式和油气勘探潜力OA

Although marine sequences in the southern Sichuan are generally gas-bearing,hydrocarbon exploration discoveries remain disproportionate to the region's resource potential compared with other zones in the basin.The key constraints are the poorly understood primary controlling factors governing reservoir formation and the unclear distribution patterns of large-scale reservoirs.Based on the latest exploration progress and integrating extensive field outcrop analyses,core testing data,and seismic interpretation,this study systematically evaluated the reservoir formation models and exploration potential of key marine sequences in the southern Sichuan Basin from the perspective of tectono-sedimentary differentiation.As indicated by the research results,although the southern Sichuan Basin shared the same evolutionary stages and cycles as the entire Sichuan Basin,it was relatively weakly affected by marginal tectonic stresses of the basin owing to its distal position relative to the Longmenshan tectonic belt and the Dabashan-Micangshan tectonic belt.Consequently,its sedimentary infill and evolution were governed by a dynamic regime of weak extension and weak compression.The differentiation features of the region are summarized as follows:rift-controlled differentiation during the Sinian(Ediacaran)-Early Cambrian,uplift-depression differentiation during the Middle-Late Cambrian to Silurian,reactivation-induced differentiation during the Early-Middle Permian,and paleogeomorphic differentiation during the Late Permian-Middle Triassic;since the Late Triassic,the region has been dominated by tectonic overprinting.Governed by this weak-differentiation dynamic background,three reservoir formation models were identified.First,the"dual-facies and pressure-field"relay reservoir formation model involves three key elements:sedimentary facies,diagenetic facies,and pressure field.In terms of reservoir-space architecture and evolution,sedimentary facies create the environment conducive to enrichment of dissolution-prone minerals,and sufficient mineral transformation provides the basis for porosity enhancement;diagenetic facies furnishes conditions favorable for diagenetic porosity modification,which in combination with widespread penecontemporaneous dissolution improve reservoir space;the pressure field sustains reservoir effectiveness with a stable overpressure system ensuring long-term capacity.The"facies-dissolution-fault"composite reservoir formation model includes three essential elements:favorable facies belts,dissolution-driven porosity enhancement,and interlayer faults.Favorable facies belts provide the fundamental framework that controls accumulation units at the macroscopic scale;dissolution-driven porosity enhancement is the key shaping reservoir architecture at the regional scale;interlayer faults spatially govern hydrocarbon enrichment,with platform margins or platform slope-break zones being optimal locations.While the"depositional-diagenetic"dual-phase superimposed reservoir formation model consists of sedimentary facies and diagenetic facies.Original high-energy facies belts underpin the development of large-scale high-quality reservoirs;tectonic uplifting-induced zoned karstification during the penecontemporaneous stage,is critical for the quality grading and spatial localization of large-scale,high-quality reservoirs;the superposition of early favorable sedimentary facies belts and penecontemporaneous diagenetic facies belts formed a dual-phase superimposed zone that ultimately controls the distribution of large-scale,high-quality reservoirs.Under the combined control of the four types of sedimentary differentiation and the three reservoir formation models,four types of hydrocarbon reservoirs were identified in the study area:near-source shoal-facies,laterally juxtaposed dolomite,facies-dissolution-fault composite,and marlstone oil and gas reservoirs.These reservoir types are systematically distributed across multiple stratigraphic horizons,defining a vertically stacked,multi-target exploration framework for the marine successions in the southern Sichuan Basin.In addition,the principal stratigraphic intervals associated with each reservoir formation and accumulation type were analyzed,and favorable exploration zones were identified.