Characteristics Of Hydrocarbon Accumulation And Main Controlling Factors Of EK₂ In Cangdong Sag

The Cangdong Sag has great potential for petroleum exploration,and the EK2 is the main source of hydrocarbons.Due to the different structures and depositional conditions,the accumulation conditions of different structural zones in the sag are different,and the characteristics of accumulation and main controlling factors also need to be studied systematically.Based on seismic,drilling,logging and analysis testing data,this paper uses petroleum geology,organic geochemistry,and basin simulation techniques to comprehensively and systematically analyze the accumulation conditions of the Cangdong Sag,and conducted in-depth analysis of the hydrocarbons transport system and migration mechanism.After understanding the hydrocarbon generation time,migration,accumulation regularity,and accumulation period,the typical reservoirs are analyzed,and the hydrocarbon accumulation model is summarized.Finally,the regularity of hydrocarbons accumulation are sorted out,and the main controlling factors are refined.The results show that the EK2 of Cangdong Sag has good condition of hydrocarbon accumulation,but there are differences in different structural zones:There are the best source rocks in the low part of Kongxi slope and Nanpi slope;The reservoir in Nanpi slope is beneficial for oil storage;The traps in the northern part of the study area are structural trap related to faults,and the closed area of the trap is small.The traps in the southern part of the study area are structural-lithologic trap and lithologic trap.Hydrocarbon pathway system mainly includes faults,sand body and their combinations.The structural inversion zone is mainly a complex pathway system of fault-sand combination.Hydrocarbon migrate laterally in the sand in NanPi slope.Hydrocarbon migration is affected by different dynamics.Overpressure is not developed in the study area,and only small overpressures develop in parts of the lower part of the slope.The shale oil distribution area uses the source-storage pressure difference as the hydrocarbon migration and movement force,and the conventional reservoir distribution area is mainly composed of buoyancy.Combining sources,pathway systems,migration characteristics,accumulation periods,and deep anatomy of typical reservoirs,three hydrocarbon accumulation models are established:"buoyancy and pressure drive?falut and sand control in mid-low part+source-reservoir pressure difference drive?unibody source-reservoir in high part"conventional and shale oil accumulation models in structural reversal zone;"source-reservoir pressure difference drive?unibody source-reservoir in low part+buoyancy drive?sandbody transport?mudstone cover"conventional and shale oil accumulation models in Nanpi slope;"falut and sandbody transport?buoyancy drive?mudstone cover" oil accumulation models in Shenvsi.The hydrocarbon in the EK2 is mainly distributed in the structural uplift area.The hydrocarbon distribution in the EK2 is complementary to the EK1.Hydrocarbon accumulation is controlled by multiple factors together:structural characteristic affects the distribution pattern of hydrocarbon;sedimentary facies and hydrocarbon generation center affect the scale of hydrocarbon distribution;the transport system controls the migration and accumulation of hydrocarbon.