Monte Carlo Mixing Zone Study of Sediment Transport in an Offshore Environment

Development of offshore oil and gas wells often includes the discharge of drilling muds and cuttings into the ocean. Modeling the resulting sediment plume trajectory and sediment deposition on the ocean bottom is useful for evaluating environmental impacts resulting from offshore drilling. A case study is presented based on a drilling muds and cuttings discharge from an offshore oil platform. CORMIX mixing zone modeling software was used to model plume sediment transport, suspended solids concentrations, and bottom deposition. CORMIX can simulate sediments as either dredge sediments or drilling muds and cuttings. Outfall configurations can be single port, multiport, surface, or above surface discharges. For drilling muds and cuttings, CORMIX supports modeling of up to 10 custom particle size classes, including particle fall velocities. Data for the case study were obtained from a field study conducted in the Gulf of Guinea. Drilling muds and cuttings were discharged on the surface from an offshore platform in about 46 m of water. Availability of ambient and discharge data from the project site was limited. In the absence of detailed ambient current speed, direction, and depth data for the site, a statistically-based, Monte Carlo time series was developed. Nine sediment particle sizes and their corresponding fall velocities were specified. The CORMIX model simulated discharges over a period of several days. Multiple CORMIX simulations for different discharge durations and ambient time series data, were input to the CorPlot post-processing tool to simulate sediment transport and bottom deposition. Graphical visualization of the sediment deposition is presented.