CFD simulation on turbidity current processes of the recovered turbidites in western Qiongdongnan Basin, South China Sea

Abstract

Turbidity currents are major agents of sediment transport on land, in lakes, seas and oceans. Especially, they dominate volumetrically the most significant clastic accumulations in the deep sea, and can become many of the world's most important hydrocarbon reservoirs. Recently, 6 boreholes in western Qiongdongnan Basin, South China Sea, have revealed turbidity current deposits as good reservoirs. However, their several potential provenances are argued, which is essential to illustrate their sedimentary processes as well as to evaluate their reservoir qualities. On the other hand, the numerical simulation has been developing rapidly in last several years, which offers insights into the turbitity current behaviours because geologically significant turbidity currrents are impractical to directly investigate owing to their large scale and often destructive nature. Meanwhile, the interpretation of turbidite system based on high-resolution 3D seismic data has also been discussed by extensive literatures and industrial development, which makes it possible to be compared with the simulation results. In this study, after the paleotophography was acquired via the back-stripping on Well A in Ledong sag, western Qiongdongnan basin, and the crossing seismic profile, the numerical model was built on the basis of this back-stripped profile. After defining various turbidity current initial boundary conditions, including grain size, velocity, sediment concentration and so on, the structures and behaviors of turbidity currents were investigated via numerical simulation software FLUENT. Finally, the performance of the simulated turbidity deposits was compared with the interpreted sedimentary bodies based on 3D seismic data and the potential provenances of turbidites revealed by Well A were discussed in details. The simulation results indicated that a sedimentary body developed faraway from its source with an average grain size of 0.1mm (sand), which concides with the cores in Well A and indicates the turbidites should be transported from Vietnam instead of Hainan Island.