Origin of Crude Oil and Relation with Hydrocarbon Migration and Accumulation in South Turgai Basin
Great numbers of crude samples in South Turgai basin were analyzed in organic geochemistry.Its oil-gas migration and accumulation features were discussed according to the structural characteristics in this basin.On the basis of their biomarker compounds and carbon isotope,the oils could be divided into Type-A,Type-B and Type-C.According to the differences between their biomarker and maturity,Type-B oil is then sub-divided into two types of B1 and B2.The source rocks in this basin include two kinds of lacustrine and coal-measure ones.Type-A oil comes mainly from lacustrine source rocks of Karagansay formation,Type-B1 oil mainly from lacustrine source rocks of Doshan formation,part of it from Karagansay formation,and Type-B2 oil is mainly from Doshan formation,mixed with some oil generated from source rocks of Aybelin formation of Lower Jurassic.Type-C oil comes from Aybelin formation.The hydrocarbon migration of this basin is in lateral way mainly along sand body,basement unconformity and fault.The great fault communicating the deep source rocks becomes major channel for hydrocarbon migration from the deep to the shallow.Large amounts of oil and gas have been found on both sides of the Karatau strike-slip fault in Aryskum sag,but there are still greater petroleum exploration potentials.