Modelling Produced Water Transport and Mixing with a Lagrangian Particle Model

Offshore petroleum production usually involves large volumes of produced water, which are continuously discharged back to the sea. While the water will pass through a separation process prior to discharge, small amounts of hydrocarbons from the reservoir will remain, and these residual components may pose a risk to the marine environment. Assessment of environmental impact from produced water discharges is typically performed with numerical models, which simulate the transport and dilution of the produced water plume in order to predict environmental concentration of the residual chemical constituents.

Using a Lagrangian particle model, we investigate the effects of flow field resolution and sub-grid turbulent mixing parametrisation on produced water dispersion. We consider a simplified produced water discharge, modelled as a non-degradable tracer, discharged from a point source off the coast of mid-Norway, and advected with ocean model currents at two different resolutions (800 m and 4 km), during two different seasons (winter and spring).

The reconstructed tracer concentrations from the Lagrangian model are compared with predictions from an Eulerian grid model. In general, the models are in reasonable agreement, with the Lagrangian predictions tending to drift further from the Eulerian over time. We find a significant difference in tracer distribution and concentrations between the two model resolutions, and to a lesser extent between seasons; additionally, the 800 m model has less mixing towards the coast than the 4 km in the spring scenario.