Geochemical characteristics and, origin of heavy oil in the periphery of Wenchang-B depression in Zhu III Sub-basin, Pearl River Mouth Basin, China

Heavy oil reservoirs have been discovered in the periphery of Wenchang-B depression in Zhu III sub-basin, but there is no relevant research on the geochemical characteristics and genesis of heavy oil. The characteristics of source rocks and crude oil were analyzed by various geochemical experiments. The results indicated that: (1) Second member of the Wenchang Formation (WC2) source rock has the largest hydrocarbon generation potential, WC1 and EP source rocks have similar characteristics, but EP source rocks have low maturity and Pr/nC(17) greater than one; (2) Its heavy oil-density ranges from 0.91-0.97 g/cm(3), with low sulfur content. The saturated hydrocarbon content in well Q4 is high, whereas it has low the non-hydrocarbon content. The carbon isotope values range from -28.2 parts per thousand and -25.4 parts per thousand. Combined with the biomarker characteristics, the source of heave oil corresponds to WC2 and WC1 source rocks. Hence, there are two origins of heavy oil in the Wenchang-B depression, low-mature heavy crude oil (well Q4), and biodegradable heavy oil (well Q1). Clarifying the origin and source of heavy oil can provide more references for exploration and development.