Hydrocarbon generation potential and oil source comparison of source rocks in the central and western regions of Xihu Depression

Abstract

Objective The Xihu Depression, located in eastern China, is a significant area for oil and gas exploration. While previous studies have focused on deep strata, such as the Pinghu Formation, little research has been conducted on the middle and shallow strata, including the Huagang Formation. Recent findings suggest that these shallow and middle strata have hydrocarbon accumulation potential, but their hydrocarbon-generating capacity and the source of crude oil in the Xihu Depression remain uncertain. Methods To address these gaps, we collected 203 source rock samples from 13 drilling boreholes in the western slope zone and central inversion tectonic zone of the Xihu Depression. These samples spanned from the Eocene Baoshi Formation to the Miocene Longjing Formation. Geochemical tests and analysis were conducted to assess the hydrocarbon potential and biomarker characteristics of the source rocks. Results The results indicate that coal and carbonaceous mudstone in the Xihu Depression have excellent hydrocarbon generation potential, while the hydrocarbon generation potential of mudstone varies. Deep layer source rocks are evaluated as good or excellent sources of hydrocarbons, while the middle and shallow layers are considered poor sources. The organic matter in the source rocks mainly consists of types Ⅱ2-Ⅲ, and the thermal evolution stage can be divided into a hydrocarbon generation stage (Ro>0.6%) and a large hydrocarbon expulsion stage (Ro>0.8%).Comparing the biomarkers of crude oil and different types of source rocks, we found that the argillaceous source rock in the study area is the primary source of crude oil. Conclusion This research provides valuable guidance for future oil and gas exploration in the Xihu Depression.

Keywords

• source rock
• hydrocarbon generation potential
• geochemical feature
• biomarker
• xihu depression