Hydrocarbon source potential evaluation insight into source rocks—A case study of the first member of the Paleogene Shahejie Formation, Nanpu Sag, NE China

The features of source rock hydrocarbon generation, expulsion, and retention are essential factors in petroleum resource potential evaluation. In this study, the improved hydrocarbon generation potential evaluation method was used to quantify the characteristics of the source rocks of the first member of the Paleogene Shahejie Formation (Es1) in the Nanpu Sag, Bohai Bay Basin, NE China. Based on the geological and geochemical data for the source rocks, the favorable exploration areas were predicted and the resource potential was evaluated. Our results show that Es1 is a set of high-quality source rocks with desirable geological (maximum thickness > 600 m) and geochemical (average total organic carbon content of 1.44%; dominantly type II kerogen; mature stage) characteristics. The improved hydrocarbon generation potential model shows that the hydrocarbon expulsion threshold is located at Ro=1.0%. The maximum hydrocarbon generation potential (Qg), hydrocarbon expulsion potential (Qe), hydrocarbon retention potential (Qs), and efficient hydrocarbon retention potential (Qse) are 549.31, 162.20, 387.11, and 287.11 mg HC/g TOC, respectively. The maximum hydrocarbon generation, expulsion, retention, and effective retention intensities are 250×104, 70×104, 180×104, and 150×104 t/km2, respectively. These parameters reach the highest value in the Linque and Caofeidian Sub-sag. The resource potential of the retention shale oil, the movable shale oil, and the conventional and the tight petroleum resources are 1.99×108, 4.38×108, and 1.37×108 t oil equivalent, respectively. This study offers a fresh and plain but operable workflow for resource evaluation, which can be applied in other petroliferous basins with low degree of exploration.