DEEPWATER GRAVITY FLOW DEPOSITIONAL SYSTEM IN QIONGDONGNAN BASIN, SOUTH CHINA SEA

The global oil and gas exploration has gradually entered the exploration stage of deep strata (>4500m) and deep water (>300m) with continuous development of conventional oil and gas resources in the middle and shallow strata. The continental margin basin of the northern South China Sea is rich in oil and gas resources. As one of the most important oil and gas bearing basins in the northern South China Sea, Qiongdongnan Basin is currently the main block for deep-water oil and gas exploration in China. Based on seismic data, drilling data and logging data, the gravity flow sedimentary system was studied by seismic sedimentology in Qiongdongnan Basin.

Gravity flow deposits have been widely developed in Qiongdongnan Basin, mainly in the form of turbid water channel and submarine fan. Turbid water channel is easy to be identified in seismic profile with the characteristics of strong amplitude and good local continuity. Because the irregular surface of overlapping fans will produce multiple reflections and overlapping hyperbolic reflections, most fans show a mound-shaped seismic geometry, with lateral pinchout, lower overshoot or upper overshoot above the sequence boundary, showing a wedge-shaped oblique configuration along the fan direction and a thinning trend away from the provenance. The Red River submarine fan and the Central Canyon are mainly developed in the basin. The former spans Yinggehai Basin and Qiongdongnan Basin. The latter is a long-distance turbid water channel running through the whole Qiongdongnan Basin, showing east-west distribution. The description and analysis of gravity flow depositional system are of great significance for oil and gas exploration in deep water area.