In order to study the environmental impact of the drilling fluid’s discharge on the surrounding sea area, a numerical model is established based on the development of an oil field in South China Sea. The Galerkin finite element method is adopted to discrete the governing equations with the hydrodynamic and sediment transport module. To prove the reliability of this model, the simulated tide level and current are validated with the field test data through a comparison. Afterward, the verified model is used to optimize the key numerical parameter in the diffusion process of the drilling fluid’s discharge and the suitable calculation coefficient is chosen for the targeted field in South China Sea. According to the calibrated settling velocity of the sediment, the influence area of the drilling fluid’s discharge is calculated under the conventional conditions. The furthest distance in excess of the primary standard (10 mg/L) and the recovery time are also analyzed as well. The study shows that the numerical results of tide level and current are in good agreement with the field test data and the established model is proved to be accurate and reasonable. When the mean settling velocity of the solid-phase particle is 1.00×10~(-5) m/s in the drilling fluid, the simulated concentrations of the suspended solids are more consistent with the field monitoring results. Under the conventional condition, the optimized calculation shows that the area of the suspended solids concentration in excess of the primary standard is mainly distributed in the surface and middle layer of the water column. As for the influence area in excess of the tertiary standard (100 mg/L), it only exists in the surface layer and is very small, whereas there is no area in excess of the quaternary standard (150 mg/L). In addition, the furthest distance in excess of the primary standard is about 1.30 kilometers and the recovery time of the water quality is around 0.5 hours.
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