Characteristics Of Source Rocks And Hydrocarbon Generation Evolution Of The Third Member Of Shahejie Formation In Laizhouwan Sag

The Laizhouwan Sag is an important hydrocarbon-bearing area with great potential for oil and gas exploration in the Bohai Bay Depression.Due to the lack of drilling core in regional wells and shallow drilling depth,the source rock is still controversial.Whether the third member of the Shahejie Formation(E2s3)can be regard as good source rocks like the neighbouring regions is still unclear.By the geochemical analysis,the evaluation and hydrocarbon generation evolution of the source rocks of E2s3 were studied combined with basin modeling.Through comprehensive analysis of total organic carbon(TOC),chloroform asphalt A,total hydrocarbon content and hydrocarbon generation potential,it is concluded that the source rock has a relatively high organic matter abundance,which is good source rock.Through the comprehensive analysis of pyrolysis parameters of source rock,kerogen element,kerogen microscopy,the ratio of Pr/Ph,Pr/C17,Ph/C18,(C21+C22)/(C28+C29),the sterane C27-C29 content relationship,C31-C35 liters of hono,and gamma wax,it is concluded that the type of source rock is type II,which varies slightly with the change of the regional sedimentary facies Through the comprehensive analysis of the vitrinite reflectance(Ro),the highest pyrolysis temperature,the type of sterane,the sterane-C29-20S/(20S+20R),and the sterane-C29-??/(??+??),the homohopane 22S/(S+R),the Tm/Ts,the moretane/hopance ratio and the hopance content distribution maps,it is concluded that the maturity of the source rock ranges from low to medium.Based on the calculation of denudation amount and the determination of paleotemperature parameters,the thermal evolution of source rocks is modeled with BasinMod software.It is found that the hydrocarbon evolution degrees of different tectonic units are not the same in different tectonic periods.The tectonic evolution of the Laizhouwan Sag is divided into three stages,which are the early fault depression stage,the medium stage strike-slip stage and the late activation stage.During the fault depression stage,the source rock of E2s3 is thicker with higher maturityin the northern steep zone and northern low-lying near the sag sedimentary center.During the strike-slip period,affected by the strike-slip fault,the strata of E2s1,E2s2 and E2 d were deposited thickly in the whole depression,and the sedimentary center migrated to the northeast of the depression,where the hydrocarbon evolution conditions were better.During the final stage,due to the influence of neotectonic movement,the entire sag underwent rapid subsidence with the sedimentary center migrated to the north,which made the sedimentary strata become thicker in the northern low-lying and northern steep slope zone.Therefore,source rocks of the northern low-lying and northern steep slope zone have the best conditions for hydrocarbon evolution.