Reservoir Formation Mechanism And Enrichment Modes Of Shale Oil And Gas In The Western Liaohe Depression

The western sag of Liaohe is one of the oil-rich sags in the Bohai Bay Basin,an important petroleum-bearing basin in China.It is currently an important area of shale oil and gas exploration and development in China.Aiming at the characteristics of controlled sedimentation of the lake basin structure in the western sag,the thesis analyzes the transformation law of subsidence-depositional migration in the rift lake basin in the western sag of the Liaohe.Besides,this paper discusses the control effect of the structure and sedimentation on the formation and distribution of shale oil and gas,improves the continental shale the classification method.In addition we analyze the main controlling factors of hydrocarbon accumulation,and reveal the formation mechanism of shale oil and gas in the western sag.So that the paper establishes the shale oil and gas enrichment model in the western sag.The following understandings have been made:The Sha 3 and Sha 4 members are the most promising layers for the formation of shale oil and gas in the western sag of the Liaohe depression.The faulting activities during the same depositional period have obviously controlled the deposition and shale distribution.The formation and distribution of shale are obviously different.The difference in fault activity in the western sag controls the sedimentation,which is manifested in the weaker fault activity of the Sha 4 in the western sag and shallower water in the same sedimentary body.The fault does not control the distribution of strata,and the paleomorphology and provenance control the distribution of shale,which mainly forms dolomitic shale,calcite shale and clay shale.The high carbonate content is the result of the semi-closed and brackish water bay controlling the mineral composition of the shale.The third phase of the Shahejie fault has strong activity and obvious segmentation,and the co-sedimentary water body is deeper.The northwest to southeast direction obviously migrated,and the semi-deep lake-deep lake facies also migrated synchronously,It is mainly felsic shale,with brittle minerals such as quartz and feldspar in the shale successively developing from the center to the edge of the lake basin While the clay mineral content gradually decreased,the shale sedimentary profile showed a wedge shape thinning westward.The Sha 3 and Sha 4 members have favorable conditions for the formation of shale oil and gas,and the sedimentation controls the shale organic geochemistry and reservoir physical conditions.The sedimentary environment restricts the distribution of shale organic matter types and abundance,and forms the distribution characteristics of the ring-shaped organic matter around the center of the deep lake on the plane,and the organic matter abundance changes accordingly.The continuous process of subsidence promotes the continuous occurrence of diagenesis and produces good shale reservoir physical properties,which provides good conditions for the formation and preservation of shale oil and gas.The shales of the Sha3 and Sha4 can be divided into continuous,intermittent,and dispersive texture structures,which represent the characteristics of organic matter occurrence in different depositional environments.The history of thermal evolution controls the formation and distribution of shale oil and gas,leading to differences in the production of source rocks in the southern and northern parts of the Western Sag.The research reveals the change rule of shale oil and gas in the western sag,and clarifies the oil and gas distribution pattern of "North Oil and South Gas" in the plane and "Down Gas and Up Oil" in the vertical direction.The carbonate rock mineral content has a positive effect on the formation of shale oil.The carbonate rock content has a positive correlation with the shale oil content,and has the effect of accelerating low-maturity organic matter to accelerate oil generation.Subsidence-deposition center transfer controls the formation and distribution of shale oil and gas.Inherited lacustrine sedimentation makes Sha 4 and Sha 3 have similar organic matter types,but later subsidence migration controls the migration of thermal evolution maturity centers.Although the fourth member of Shahejie Formation is older than that of the third member,the migration of the sedimentation-sediment center leads to a higher maturity of the latter.This establishes shale oil enrichment models for Sha 4 and shale gas enrichment models for Sha 3 respectively.The conclusions of the study provide important guidance for shale oil and gas evaluation and exploration in the western sag of the Liaohe depression,which can be extended to other basins(sags)in eastern China and can also be referenced for other continental basins.