Mechanism Of Oil And Gas Migration And Accumulation In The Paleozoic-Proterozoic Of Shuguang Area,Western Sag In Liaohe Depression

The Shuguang buried hills in the western sag of the Liaohe Depression are rich in hydrocarbon resources.However,the lack of systematic research on hydrocarbon migration and accumulation mechanisms and the poor understanding of hydrocarbon migration and accumulation patterns have seriously hindered the process of hydrocarbon exploration.In this study,we analyzed the hydrocarbon formation conditions of the Paleozoic and Proterozoic buried hills by using geological,geochemical,seismic,drilling and logging data.The source of crude oil is defined by oil-source comparison.The distribution characteristics of faults in different active stages and their transport and sealing effects on oil and gas are analyzed.The fluid potential and tectonic ridge simulation software were used to analyze the dominant migration paths of oil and gas.On the basis of this,various methods were used to trace the migration paths of oil and gas,and the relationship between abnormal Formation pressure and oil and gas accumulation was discussed.Finally,the process of hydrocarbon migration and accumulation is summarized and the model of hydrocarbon migration and accumulation in different subduction zones is established to guide for predicting favorable reservoir areas.The results of the study show that the Shuguang Paleozoic-Proterozoic oil and gas mainly originate from the hydrocarbon source rocks in the Chenjia sub-sag and the fourth member of Shahejie Formation of the Low buried hills,and the source of oil and gas is single;the types of crude oil are mainly classified into normal crude oil and biodegraded crude oil according to the degree of biodegradation;three stages of fractures are developed in the Shuguang buried hills,and the overall north-east spreading is dominant,with the Yanshan Movement A-maku west-drop reverse fault in the early stage,the Movement B-maku west-drop positive fault in the middle stage,and the Xishan east-drop positive fault in the late stage.On the whole,the dip and distance of the Xishan stage faults are large,and they are migration faults,while the dip and distance of the Yanshan Movement stage faults are relatively small,and they are mainly closed faults.The nearnortheast-oriented Xishan Movement stage east-falling reverse fault and unconformity surface are the main migration channels of oil and gas,and oil and gas migrated in parallel along the structural ridge.The migration path is perpendicular to the main fault strike,mainly from the low part of the slope to the high part,from the low buried hill to the middle and high buried hill along the southeast to northwest.The Chenjia sub-sag and the low part of the low buried hills,the fourth member of Shahejie Formation hydrocarbon source rocks are mainly transported from the low part of the low subduction mountain to the high part of the low buried hills.The hydrocarbon source rocks of the Chenjia subsag and the low buried hills of the fourth member of the Shahejie Formation reached the peak of hydrocarbon production at the end of the Dongying Formation period,which is the main reservoir formation period.The reservoir formation in the Shuguang PaleozoicProterozoic buried hills is controlled by the oil source and migration conditions and has different accumulation characteristics.The low buried hills are in-source + adjacent source-fault vertical and lateral migration-weak anomalous low pressure to normal pressure accumulation mode;the middle buried hills are near source-high angle fault vertical and unconformity lateral migration-low pressure to normal pressure accumulation mode;the high buried hills is distant source-high angle fault vertical and unconformable lateral migration-normal pressure accumulation mode.