陆相湖盆细粒浊流沉积序列及对页岩油类型划分的意义:以松辽盆地白垩系青山口组为例OA

As one of the core dynamic mechanisms for the transport of fine-grained sediments in the deep-water environment of continental lacustrine basins,the meticulous characterization and genetic ana-lysis of the sedimentary sequences of fine-grained turbidite deposits constitute a key entry point for revealing the shale oil accumulation mechanism and improving the classification system of shale oil types.Taking the Member 1 of the Upper Cretaceous Qingshankou Formation in the Changling sag of the Songliao Basin as the research object,a total of nine sedimentary units have been identified based on the data from three full-core drilling wells,and the Markov chain method was adopted to analyze the turbidite sedimen-tary sequences,which reveals the transition laws of turbidite events from initiation,high-energy transpor-tation to terminal attenuation in the prodelta-semi-deep lake-deep lake sedimentary environments.Based on the actual geological data of the study area,the sedimentary characteristics of fine-grained turbidite currents in continental lacustrine basins were characterized,and a sedimentary sequence model for fine-grained turbidite deposits in continental lacustrine basins is established,among which the fine-grained turbidite deposits are composed of Units T1 to T7 that clearly reflect the high-energy to low-energy sedimen-tary evolution laws of turbidites.Synthesizing such parameters as lithologic assemblages,sedimentary structures and sand-to-shale ratio,a classification scheme for shale oil types in the study area is proposed.The characteristics of different shale oil types are significantly controlled by the fine-grained turbidite deposits:the interbedded type is governed by proximal turbidite deposits,with sandstone and siltstone interbeds providing high-quality reservoir spaces for shale oil;the laminated type is associated with distal turbidite deposits,dominated by high-frequency thin-bedded silty mudstones and shales and possessing favorable reservoir physical properties and brittleness;the massive type is related to the combined effects of terminal turbidite deposits and lacustrine still-water deposits in the lacustrine basin,with relatively poor reservoir physical properties and brittleness.