Depositional system and hydrocarbon accumulation in Gubei slope zone, Zhanhua Depression, Bohai Bay Basin, eastern China

Abstract

The Zhanhua Depression is a hydrocarbon-rich, fault-generated depression in Bohai Bay Basin, eastern China. Gubei slope zone, located in eastern Zhanhua Depression, is an important oil production region. Drilling cores, logging data, and 3D seismic data were used to identify several depositional system infilling the slope zone, including braided-delta, sublacustrine fans, and deep/semi-deep lake fine-grained deposits and turbidite, all of which are associated with a lacustrine succession belonging to the 3rd member of Shahejie Formation (Es3). Sedimentary rock of Es3 are composed of mudstone, silty mudstone, fine sandstone, coarse sandstones, and conglomeratic sandstones with various structures including massive bedding, parallel bedding, scour-fill structures, graded bedding, and deformed structures. Sandstone distributed in braided-delta front subfacies, lacustrine fans and some turbidite are favorable reservoir facies. Fault system was an important hydrocarbon migration pathway and sometimes a sealing geologic unit, which played an important role in the formation of commercial oil reservoirs in Gubei slope zone. The commercial oil reservoir is dominantly distributed in ridge-like structures in Gubei slope zone, which give an inspiration that ridge-like structure was probably a very favorable area for hydrocarbon exploration in continental basin slope zone.