Evaluation of Source Rocks Based on Geology, Geochemistry and Seismology: A Case Study of the Second Member of the Liushagang Formation in the Wushi West Sag

In light of the relatively low degree of exploration, limited drilling activities, and scarce indicators of source rocks in the West Sag of Wushi, a comprehensive study was conducted to analyze the distribution and potential of source rocks within the second member of the Liushagang Formation. This study integrated geological, geochemical, and seismic data alongside thermal simulation experiments for hydrocarbon generation.

The findings indicate that: (1) The activity of sag-controlling faults, base subsidence, and sedimentary infill in the West Sag of Wushi exhibit a positive correlation with the paleo-productivity values of source rocks identified in drilled wells. (2) The paleo-productivity values for source rocks from the second member of the Liushagang Formation in this region range from 200 to 771 gC/m²·a. Three types of source rocks have been identified—medium quality, good quality, and high quality—with respective volumes measuring 10.1 km³, 13.3 km³, and 16.4 km³. Notably, high-quality shale serves as the primary mechanism for hydrocarbon supply and is predominantly located at the center of the sag. (3) The bottom hydrocarbon generation conversion rates for medium-quality, good-quality, and high-quality source rocks within this formation are recorded at 70%, 80%, and 85% respectively; corresponding hydrocarbon generation amounts are estimated at 3.0×10⁷ t, 8.6×10⁷ t, and 5.1×10⁸ t respectively. These results suggest that this area has undergone significant hydrocarbon generation processes while demonstrating considerable potential for future hydrocarbon production.