Characteristics of Jiufotang source rock and its relationship to hydrocarbon enrichment, southern Songliao Basin

Source rock and crude oil samples from the Jiufotang Formation in the Zhangwu and Changtu depressions in the southern Songliao Basin were analysed for TOC content, pyrolysis yield, rock group composition, carbon isotope and biomarkers. The oil in the Zhangwu Depression was mainly sourced from the lower part of Jiufotang Formation, while that in the Changtu Depression mainly derived from the upper part of Jiufotang Formation. The Jiufotang source rocks in other depressions with industrial oil and gas discoveries in the study area were also studied, indicating that the Jiufotang source rocks were the main source rocks in the region, with high abundance, multiple types, and low evolution degree. The source rock distribution has a good relationship with the degree of hydrocarbon enrichment. Various factors such as structural evolution of the depression, sedimentary environment, burial depth, and later-stage preservation conditions result in more hydrocarbon production in the lower part of Jiufotang Formation relative to those in the upper part. Maturity is an important factor affecting source rocks. The development and distribution of high-quality source rocks in the Jiufotang Formation were determined. Finding a good source and reservoir configuration and appropriate near-source traps lead to favorable exploration directions in the southern Songliao Basin.