Shale Oil Resource Potential of Es₃^L Sub-Member of Bonan Sag, Bohai Bay Basin, Eastern China

Following shale gas, shale oil has become another highlight in unconventional hydrocarbon exploration and development. A large amount of shale oil has been produced from a host of marine shale in North America in recent years. In China, lacustrine shale, as the main source rock of conventional oil and gas, should also have abundant oil retained in place. In this study, geochemical and geologic characteristics of lacustrine shale from Es₃^L sub-member in Bonan sag were characterized by using total organic carbon (TOC), Rock-Eval pyrolysis, X-ray diffraction, and ∆log R method. The results show that the Es₃^L sub-member shale have TOC contents ranging from 0.5 wt.% to 9.3 wt.%, with an average of 2.9 wt.%. The organic matter is predominantly Type Ⅰ kerogen, with minor amounts of Type Ⅱ₁ kerogen. The temperature of maximum yield of pyrolysate (T_max) values ranges from 424 to 447 ℃, with an average of 440 ℃, and vitrinite reflectance (Ro%) ranges from 0.7% to 0.9%, indicating most of shales are thermally mature. The dominant minerals of Es₃^L shale in Bonan sag are carbonates (including calcite and dolomite), averaging 51.82 wt.%, and the second minerals are clay (mostly are montmorillonite-illite-mixed layer and illite) and quartz, averaging about 18 wt.%. Finally, its shale oil resources were evaluated by using the volumetric method, and the evaluation result shows that the shale oil resource is up to 5.94 billion tons, and mostly Class Ⅰ resource. Therefore, the exploration of the lacustrine shale oil of Es₃^L in Bonan sag should be strengthened.