Tectono-Stratigraphic Evolution of the Deepwater Qiongdongnan Basin, Northwestern South China Sea: The Emerging Prolific Gas Province

Abstract

The deepwater Qiongdongnan Basin, northwestern South China Sea was located to the east of collision zone of Eurasia Plate and Indian Plate, and to the west of Pacific Ocean Plate. From early Tertiary, it evolved through the intra-continental rifting and sea-floor spreading, and formed the deepwater marginal basin. With recent multi-TCF gas discoveries, the deepwater basin is emerging as the prolific gas province. Integrated with gravity and magnetic survey data, 3D seismic data of about 20,000 square kilometers, and several regional exploration wells, the mantle-crust structure and tectono-stratigraphic evolution were analyzed in order to define controls on the petroleum system elements. The deepwater area of the basin has shallower Moho depth as of 15–25km than the shallow water area, indicating the uplift of mantle and severe extension of crust during the continental rifting. The magnetic data showed active magmatic intrusion and volcanism at the eastern basin. The deepwater basin underwent the Paleogene syn-rift episode, the Early-Middle Miocene early post-rift episode and late post-rift episode since Late Miocene. Normal Faulting was intensely active in syn-rift episode, and generally terminated in middle Miocene. The shelf-slope break was formed at the northern rift margin by the re-activities of bounding faults. The basin initially rifted in Eocene with lacustrine sediments, and coastal plain developed in Early Oligocene and then marine environment gradually dominated the basin. High-resolution well paleontological analysis confirmed that the slope were formed since Middle Miocene. The bathyal environment developed below the slope to the ocean plain. In late post-rift episode, the deepwater basin had the distinct tectono-stratigraphic characteristics between the western and eastern portions. The western portion was affected by the Red River Fault with hugely thick progradational slope sediments. And the eastern portion was affected by the severe subsidence and overlapped by the Xisha Trough to form ultra-deepwater. The confirmed primary petroleum system elements were the source rocks of coaly coastal plain mudstones in the syn-rift episode, the reservoirs of post-rift channel turbidite sandstones, and the vertical hydrocarbon migration through faults and “heat flow zones” especially in the western subbasin. The syn-rift submarine fan play remains much potential to drill in the near future.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015