The Source Rock And Hydrocarbon Generation Of Bayindulan South Subsag

Bayindulan south subsag is located in the south of the Bayindulan sag.It is a typical oil-rich depression with good source rock and early hydrocarbon generation.Compared with other oil-rich sags in Erlian Basin,Bayindulan sag has obvious characteristics of immature oil.It is necessary to make a fine evaluation of the source rock to further clarify the exploration potential of South subsag.In this paper,the geochemical characteristics,logging analysis and sedimentary environment are combined to identify the organic facies of the source rock;a total of 15 exploration wells are described to analyze the vertical and lateral variation of the oil-prone source rock,and the spatial distribution characteristics of the oil-prone source rock are obtained.The previous thermal evolution history recovery in the study area is of low accuracy.Using vitrinite reflectance,biomarker parameters,rock pyrolysis data to indicate the hydrocarbon generation threshold.The effect of the paleo surface temperature,paleo geothermal gradient and denudation thickness are comprehensively considered to simulate the thermal evolution history of each single well,which can demarcate the maturity and conversion rate of the source rock more precisely.The results show that there are one set of effective source rocks in South subsag,K1bt1 and K1 ba formation,which are uninterrupted vertically.The main source rocks in both K1bt1 and K1 ba are organic facies C source rocks.The initial hydrogen index of the source rocks is 600mg/g TOC-650mg/g TOC on average,and the main TOC is 2%-4%.The thickness of organic facies C source rocks in the K1 ba formation is 150-300 m,while that in the K1bt1 formation is 200m-450 m.The vitrinite reflectance in K1bt1 formation is 0.65%-0.76%,and that of the K1ba4 formation is 0.65%-0.85%.Most of the crude oil found in the south subsag shows the characteristics of immature oil,and a small amount of mature oil is also distributed.The maturity of Ba?structural belt is a little higher than that of Ba?structural belt as a whole.The main reason for the formation of immature oil is that oil parent material is good,and the C-phase source rock reaches the threshold of hydrocarbon generation and expulsion earlier.The "special lithologic section"(dolomitic mudstone)in K1ba-K1bt1 source rock is widely exist.It is distributed in the Ba?structural belt,the middle trough and the west slopes.Oil source correlation and oil family division show that the crude oil in the Bayindulan south subsag belongs to the same oil family.The difference of crude oil properties is mainly caused by maturity.Oil accumulation shows highly charged of near source focus.At present,the amount of oil and gas resources found is about 1/4 of the amount of hydrocarbon expulsion,and the western slope area still has great resource potential.