Study on the geo-chemical characteristics and the oil source of Chang 10 member oil in Ansai oilfield

Based on the analysis of the geo-chemical characteristics of the oil samples collected from Chang 10 member of G52 well in Ansai oilfield,the distribution characteristic of the biomarkers and the oil source of the samples are systematically studied.The results show that n-alkane of the oil samples is characterized by unimodal distribution without even or odd n-alkanes predominance,and main carbon peak is at nC21.The distribution C27∶C28∶C29 ααα20R steranes presents L shaped,and ββ-steranes has high abundance.The abundance of tricyclic terpane is medium,and Ts,C29Ts and 18a(H)-rearranged hopanes have higher abundance and lower gammacerane index.The lower abundance of C31-C35 homohopanes indicates that the oil has high maturity.The compositions and parameters of the biomarkers indicate that the mature crude oil is generated from the lacustrine source rock mainly enclusing lower hydrobionts and lacustrine algaes under the environments of fresh-brackish lacustrine.According to the comparison of the distribution and related parameters of the biomarkers in Chang 10 crude oil with those in the hydrocarbon source rock of Chang 6-Chang 9,it is shown that the characteristics of the biomarkers in Chang 10 crude oil is similar to those in Chang 9 hydrocarbon source rock,so it is held that the Chang 10 crude oil is mainly from the Chang 9 hydrocarbon source rock.