Migration and accumulation of crude oils in the Qionghai Uplift, Pearl River Mouth Basin, Offshore South China Sea

摘要

The crude oils migration and accumulation of the Qionghai (QH) Uplift in the Zhu Ⅲ Super-depression was investigated from the perspective of oil source and migration conduit using gas chromatography-mass spectrometry (GC-MS), stable carbon isotope, quantitative grain fluorescence (QGF) analysis and basin simu- lation methods. The results on the oil-source correlation showed that oil origins of the five typical reservoirs were very complicated. Crude oils of the eastern and western parts of the QH Uplift were from the Wenchang A sag and the Wenchang B sag, respectively, whereas oil sources of the central part of the QH Uplift were from both the Wenchang A and B sags. The research on the migration conduit showed that structure ridge, fault and connectivity sand body jointly controlled crude oil migration and accumulation in the study area. Under the control of structure ridges and well-connected sand bodies, crude oils accumulated at a low-magnitude folding structure forming the WC13-1, WC13-2 and QH18-1 reservoirs, whereas the sealed fault played an important role in forming the WC8-3 and WC13-6 reservoirs. Combing the differences in oil origins and crude oils migration conduits, we finally identified two types of crude oils migration and accumulation modes from the Wenchang Sag to the QH Uplift. One was a gentle-slope long-distance migration and accumulation model, which was developed from the Wenchang A sag to the QH Uplift. The other was a steep-slope short-distance migration and accumulation model, which was developed from the Wenchang B sag to the QH Uplift. This study could provide guidance for exploring the petroleum potential and prospecting promising zones in the South China Sea.