Numerical simulation of sedimentation in the Central Canyon of Lingshui area, Qiongdongnan Basin

Abstract

Deepwater canyon is now the focus of the research field of offshore oil and gas exploration.In the Qiongdongnan Basin of the northwestern South China Sea, several deepwater exploration boreholes have been deployed in the Central Canyon to reveal the lithologic hydrocarbon reservoir of sediment infill therein.However, due to the relatively limited number of these boreholes, the large distance between each borehole, as well as the low resolution of seismic data, the issues regarding the superposition relationship between different sandstone bodies within the canyon, their contact relationship with boundaries, and sedimentary evolution remain poorly understood, which severely hinder the delicate characterization of reservoir physical properties.This study investigates the Lingshui area of the Central Canyon from the perspective of numerical simulation of sedimentation.Geological and mathematical models are established based on the specific geological observations.The hydrodynamic simulation software ANSYS FLUENT is used for the forward modeling of multiple sedimentary stages and sandstone bodies with different initial conditions (e.g., provenance and inlet velocity) to reveal the geometry of modeled turbidite sedimentation, including the horizontal and vertical distribution patterns of sandstone bodies.The simulation results show that: Within the straight section of the canyon, the flow rate and intensity of the turbidity current gradually decrease due to the effect of substrate friction; Relatively coarse and fine particles can be deposited on the substrate and suspended along with the vortex at the head of the turbidity flow, respectively; Within the narrow section of the canyon, the turbulence of the head of the turbidity flow is strong enough to erode the canyon wall and also shift the strike of the canyon.Suspended particles can be affected by centrifugation force to form the overflow sedimentation; In addition, the results show a vertical heterogeneity of sandstone bodies distributed within the canyon: sandstone bodies are usually interlayered by mudstone that features a small thickness and poor lateral continuity.A comparison with the available seismic and borehole data shows the validity of the obtained simulation results.This study attempts to reveal the hydrodynamic processes in terms of different sedimentary stages and sandstone bodies, and then to predict the configuration of sandstone bodies that provides a favorable basis for reservoir prediction.

Keywords

• qiongdongnan basin
• lingshui area
• central canyon
• numerical simulation
• sedimentary hydrodynamics