Source rock evaluation within a sequence stratigraphic framework of the Palaeogene Liushagang Formation in the Fushan Depression, South China Sea

The Fushan Depression is one of the prolific hydrocarbon-bearing depressions in the Beibuwan Basin, South China Sea. In this study, a total of 133 mudstone samples, 18 well-logging curves, and 12 seismic sections were analysed to investigate the geochemical features and spatial distribution of effective source rocks of the Palaeogene Liushagang Formation within a sequence stratigraphic geochemical framework. The results suggest that depositional centres of mudstones northward migrated from the central Huangtong Sag during the Liushagang period. Good hydrocarbon generation potential source rocks containing Type II kerogen occur in the transgressive systems tract (TST)-highstand systems tract (HST) of lower Liushagang sequence (SQls3), the middle Liushagang sequence (SQls2), and the lowstand systems tract (LST)-TST of upper Liushagang sequence (SQls1). The occurrence of effective source rock kitchens, which are mainly controlled by the thermal maturity is distributed in the strip-shaped area of SQls3 sequence, the whole Huangtong Sag of SQls2 sequence, and the central and northern part of Huangtong Sag of SQls1 sequence, respectively. Fewer hydrocarbon accumulations were found in the southern slope due to the relatively deeper hydrocarbon generation threshold depth and to the limited occurrence of effective source rock kitchens.

Automated summary

This study investigates the geochemical features and spatial distribution of effective source rocks in the Fushan Depression using mudstone samples, well-logging curves, and seismic sections. The results show that the good hydrocarbon generation potential source rocks are mainly distributed in different systems tracts and their occurrence is controlled by thermal maturity. The southern slope has fewer hydrocarbon accumulations.