Hydrocarbon generation and expulsion characteristics of Eocene source rocks in the Huilu area, northern Pearl River Mouth basin, South China Sea: Implications for tight oil potential

In recent years, new oil reservoirs have been discovered in the Eocene tight sandstone of the Huilu area, northern part of the Pearl River Mouth basin, South China Sea, indicating good prospects for tight oil exploration in the area. Exploration has shown that the Huilu area contains two main sets of source rocks: the Eocene Wenchang (E(2)w) and Enping (E(2)e) formations. To satisfy the requirements for further exploration in the Huilu area, particularly for tight oil in Eocene sand reservoirs, it is necessary to re-examine and analyze the hydrocarbon generation and expulsion characteristics. Based on mass balance, this study investigated the hydrocarbon generation and expulsion characteristics as well as the tight oil resource potential using geological and geochemical data and a modified conceptual model for generation and expulsion. The results show that the threshold and peak expulsion of the E(2)w source rocks are at 0.6% vitrinite reflectance and 0.9% vitrinite reflectance, respectively. There were five hydrocarbon expulsion centers, located in the western, eastern, and northern Huizhou Sag and the southern and northern Lufeng Sag. The hydrocarbon yields attributed to E(2)w source rocks are 2.4 x 10(11) tons and 1.6 x 10(11) tons, respectively, with an expulsion efficiency of 65%. The E(2)e source rock threshold and peak expulsion are at 0.65% vitrinite reflectance and 0.93% vitrinite reflectance, respectively, with hydrocarbon expulsion centers located in the centers of the Huizhou and Lufeng sags. The yields attributed to E2e source rocks are 11 x 10(11) tons and 0.2 x 10(11) tons, respectively, with an expulsion efficiency of 20%. Using an accumulation coefficient of 7%-13%, the Eocene tight reservoirs could contain approximately 13 x 10(10) tons to 23 x 10(10) tons, with an average of 1.8 x 10(10) tons, of in-place tight oil resources (highest recoverable coefficient can reach 17-18%), indicating that there is significant tight oil potential in the Eocene strata of the Huilu area. (C) 2016 Elsevier Ltd. All rights reserved.