Source Rock And Petroleum Accumulation In Jiergalangtu Sag,Erlia Basin

This paper is mainly based on the analysis of a large number of data in Jirgalangtu sag,the evaluation of single well source rocks,the fine characterization of the thickness of different types of organic source rocks,the determination of the thermal history of source kitchen,the prediction of hydrocarbon expulsion properties and expulsion intensity of different organic facies source rocks at different maturity stages,and the inference of the nature of source rocks according to the physical and geochemical characteristics of oil and gas.The relationship between the discovered oil and gas reservoirs and hydrocarbon source kitchen is discussed and the favorable exploration areas are predicted.The effective source rocks in Jirgalangtu sag are located in the K₁bt₁ and K₁ba.The typical exploration wells in Jirgalantu sag are quantitatively evaluated by improved log R source rock logging evaluation technology.The results show that the main source rocks of K₁bt₁ and K₁ba in the Jirgalantu sag are C facies,in which organo-facies C1source rocks are developed in the lower part of the K₁bt₁ and organo-facies C2 and D/E source rocks are developed in the K₁ba.Source rocks are mainly developed in the deep-lying deposits of the central and western sags,and gradually thinned to the margin of the sag.The source rocks of the K₁bt₁ and K₁ba belong to a set of source rocks,mainly organo-facies C source rocks of lacustrine algae,and the macerals are mainly sapropelic formations.Crude oil is basically derived from the lacustrine source rocks of freshwater-brackish water,reflecting the characteristics of a single oil source.According to API,viscosity and sterane parameters of crude oil,the oil groups in Jirgalangtu sag are classified.The results show that crude oil can be divided into three types:primary heavy oil generated by organo-facies C1 source rocks in immature-low maturity stage,medium-light oil produced by organo-facies C2 source rocks and organo-facies D/E source rocks in mature stage,and biodegradable oil,which is secondary change of the first two types of crude oil.Crude oils of different origins are mainly controlled by organic facies types and maturity of source rocks.The API of crude oil varies greatly and distributes in the range from 5 to 40degrees.The farther away from the source kitchen,the smaller the API of crude oil and the lower the maturity.The distribution of oil and gas reservoirs is controlled by source kitchen.Oil and gas accumulate in the slope zone near the source kitchen,showing the characteristics of accumulation near the source kitchen.The favorable exploration areas are located in the slope zone and its surrounding areas of the two oil-rich sags in the central and western regions.