Geological characteristics and exploration of continental fault-block shale oil reservoirs in the Subei Basin

Continental faulted basins in eastern China contain multiple suites of significantly thick lacustrine organic-rich shales of the Mesozoic and Cenozoic, thus boasting abundant shale oil resources. However, these organic-rich shales are extensively dissected by faults, resulting in multiple isolated fault blocks. This is a big difference compared with the shale strata in North America in continuous and stable distribution, and poses the challenge to obtain stable commercial oil flow in exploration. Based on the investigation and comprehensive assessment of the lithology, and quality of source rocks and reservoir of shales in the 2^nd member of the Funing Formation (also referred to as the Fu 2 Member) in the Gaoyou Sag, Subei Basin, we hold that three suites of thick target intervals are developed in the Fu 2 Member, which can be explored and exploited as a whole. Given the current geological conditions of the target intervals, faults, and fault blocks in the Fu 2 Member, we propose an idea for fault-block shale oil reservoir exploration, that is, to have long laterals landed within a single or across multiple target intervals within a single or multiple fault blocks. Considering the correlation between fault throw and target interval thickness, we divided the fault-block shale oil reservoirs into three types for exploration, that is, the continuous and stable reservoir, reservoir dissected by micro-faults, and the reservoir spanning multiple fault blocks with multiple sweet spots. It has been verified through practical exploration that all these exploration targets can yield stable commercial oil flow. The study results have expanded the exploration targets and reservoir types for continental shale oil in China, thus serving as a significant reference for shale oil exploration in continental faulted basins.