超深层页岩烃类微运移特征与成藏模式OA

The hydrocarbon accumulation patterns of ultra-deep,marine shale in the northeastern Sichuan Basin remain unclear.Taking the Permian Dalong Formation in Well Tiebei 1 L-HF in the Puguang area,northeastern Sichuan Basin,as an example,this study integrated petro-mineralogical,geochemical,and micro-scale characterization techniques to systematically reveal the enrichment mechanisms of primary organic matter and the reservoir-forming conditions of shale and establish the hydrocarbon micro-migration and accumulation model.The main findings are obtained in three aspects.First,three core lithofacies,i.e.siliceous,calcareous and mixed shales,are identified vertically in the Dalong Formation.Siliceous shale,dominated by sapropelinite,possesses the optimal primary hydrocarbon-generating potential.Mixed shale exhibits the TOC(average 9.31％)exceeding that of the siliceous shale(average 6.85％),indicating that the current organic matter distribution is controlled by late-stage hydrocarbon redistribution rather than solely by primary deposition.Second,a multi-scale cross-lithofacies composite pore-fracture system is identified.Siliceous shale provides basic storage space of hydrocarbon and horizontal transport;calcareous shale contains fractures in calcite veins,which act as migration"transfer stations"of hydrocarbon;and mixed shale develops tectonic tensile fractures and dissolution pores.Together,these elements support fluid conduction in ultra-deep settings.Third,the micro-migration mechanism of"in-source enrichment and lithofacies-controlled migration"is confirmed for ultra-deep shale hydrocarbons.Within an overpressure compartment,driven by hydrocarbon generation-induced overpressure,hydrocarbons undergo stepwise micro-migration along the siliceous shale(source)→ calcareous shale(conduit)→ mixed shale(sink)path,inducing short-distance fractionation and redistribution of components.