Abstract: Oil and Gas Pool-Forming Dynamics in the North Shelf Basins, South China Sea

WU PEIKANG, WEILIN ZHU, MINGBI LI

Basins in the study area experienced three developing stages: lacustrine sedimentation in the rifting stage (E₁-E₃²), bay sedimentation in the transitive stage (E₃³-N₁¹) and open sea sedimentation in the postrifting stage (N₁²-Q). The lacustrine petroleum supersystem (LPSS) consists of the lacustrine source rocks, bay tidal sand-body reservoir and open sea regional caprocks, and is present mainly in the Beibuwan basin and Zhu 1 and Zhu 2 depressions of Pearl River Mouth basin; In parts of the area where very thick Neogene sediments were deposited, the mature source rocks due to the high geothermal gradient (greater than 42 degreesC/km) and marine turbidite make up the marine petroleum surpersystem (MPSS).

The LPSS contains a series of petroleum systems which appear to be controlled by the half graben and its combination, pods of active source rocks developed locally (1-8 X 10³km²), and isolated and low-strength (pressure coefficient greater than 1.5) pressure systems; the discovered oil and gas are in and near it. The MPSS mainly occurs in the Yinggehai-Qiongdongnan basins and Zhu 2 depression; its overpressure systems are large (2-10 X 10⁴km²), and there is high strength (pressure coefficient greater than 2.2). In Yinggehai basin large mud diapirs(up to 10 km high) developed. Diagentic events, fluid inclusion, and organic geochemical analyses, DST, and RFT indicate that expulsions of overpressure systems are in not less than 4 stages; especially the hydrocabon-related two stages of expulsions are closely related to the regional structural movements, and the pathways of hydrocarbon thermal fluid flow are markedly controlled by the patterns of carrier systems in which the fault nets and sand-body frameworks are most important.

AAPG Search and Discovery Article #90942©1997 AAPG International Conference and Exhibition, Vienna, Austria