Petroleum System and Hydrocarbon Accumulation Characteristics in the Wenchang and Enping Formations in the Huizhou Sag, Pearl River Mouth Basin, China

Abstract

Conventional oil and gas reservoirs are in the Oligocene and later formations in the Huizhou Sag, Pearl River Mouth Basin, South China, and oil & gas were generated by the source rocks in the Eocene Wenchang and Eocene-Oligocene Enping Formations. However, exploration paradigm shift has been made in the Sag with the depletion of conventional reservoirs and recent oil and gas discoveries in the Wenchang and Enping Formations, and Wenchang and Enping become the new targets of exploration. With more detailed researches to evaluate the exploration potential in the two conventional source rock formations, basic factors of the petroleum system are analyzed based on seismic data, well drilling, and lab measurements. We used sequence stratigraphy and statistics to research thickness trend of source rock. Different from discontinuous distribution of lake basin during the Wenchang formation deposition suggested by predecessors, as the major source rock in the Wenchang Formation, SQ2 whose dominant facies are deep lakes and shallow lakes is present widely with thickness varies from 200 meters to 1000 meters, and the thickest source rocks locate in the Huixi, Luxi and Huidong half-grabens. Both the Wenchang and Enping formations contain multiple source rock-reservoirseal combinations. We conduct a detailed study on the petroleum system in the deeper reservoir-cap combinations in the Huizhou Sag. The study results in the hydrocarbon generation and migration timing. Reservoirs are classified based on the multi-stage structural movements and multi-stage hydrocarbon generations. We address the controlling effect of the structure evolution on hydrocarbon accumulation. Finally, we build a relationship between reservoir quality and structural units in the study area, and helps reduce the risks of the exploration and production in the Huizhou Sag.