Geochemical characteristics of crude oil and oil-source analysis in Nai 1 block for Naiman depression,Kailu Basin

Based on systematic analysis of group compositions,saturated hydrocarbon GC-MS for source rocks and crude oil in Nai 1 block,the geochemical characteristics and oil-source correlation were studied.The follwing are the characteristics of crude oil and lower Jiufotang formation source rocks: The distribution of alkane is complete,possessing double peaks which are nC23 and C17 respectively.Content of phytane is obviously higher than pristane w(Pr)/w(Ph)=0.36-0.53.For sterane series,the content of regular sterane,distributing in the shape of V,is also obviously higher than the counterpart of pregnane and rearranged sterane.Besides,the value of the parameters of C29w(20S)/w(20S+20R) and w(ββ)/w(αα+ββ) are respectively 0.27-0.49 and 0.23-0.39.The terpane series is characterized by major part of C30Hopane,relatively higher content of tricyclic diterpane and gammacerane but lower content of rearranged sterane,w(Ts)w(Tm).The values of C31w(22S)/w(22S+22R) and C32w(22S)/w(22S+22R) are respectively 0.51-0.57 and 0.48-0.59.All of these characteristics mentioned above show that the crude oil in research area mainly origins from strong reducing environment of salt-water deep lacustrine facies.Parent materials come from both lower aquatic plants and terrestrial higher plants.Maturity of crude oil is low and mainly distributes from lower to middle stage.The crude oil in Nai 1 block is mainly from lower Jiufotang formation in Lower Cretaceous.