Characteristics and Hydrocarbon Generation Potential of Permian Source Rocks in the Yining Sag, Ili Basin, Western China

This study is based on field observations and sample collections from the Panjinbulak, Qiongbulak, and Qunjisayi outcrops in the Yining Sag of the Ili Basin. Using organic geochemical analysis methods, the characteristics and hydrocarbon generation potential of the Permian Xiaoshansayi Formation (P2x) and Tamqisayi Formation (P2t) source rocks in the Yining Sag were compared and analyzed. The results indicate that the Permian source rocks in the Yining Sag of the Ili Basin exhibit high organic matter abundance and good types, among which the P2t source rocks are overall superior to the P2x. The P2t source rocks in the Panjinbulak outcrop section on the northern margin are dominated by Type II1-II2 kerogen, while those in the Qunjisayi and Qiongbulak outcrop sections on the southern margin show a transition to Type II2-III kerogen. The maturity of Permian source rocks presents a pattern of “higher in the south and lower in the north”, and all have reached the hydrocarbon-generation threshold. The northern margin is in the oil window, mainly dominated by oil generation; the southeastern margin has higher maturity, mainly producing oil/condensate gas. The Permian source rocks were deposited in a saline-reducing environment, with mixed input of aquatic organisms and terrestrial plants. During the deposition of P2t source rocks in the northern margin, the water salinity was higher, and plankton such as cyanobacteria made prominent contributions. The P2t source rocks in the Panjinbulak outcrop section on the northern margin have relatively better organic matter abundance and type, making it the main hydrocarbon-generation-potential area. The source rocks in the Qunjisayi outcrop section on the southeastern margin are slightly poorer, but their maturity is higher, currently in the main oil window, representing a secondary hydrocarbon-generation-potential area.