MODELLING THE DISPERSION OF PRODUCED WATER DISCHARGES

Abstract

The ability of two state-of-the-art dispersion models (MUDMAP and the OOC model) to predict the fate of produced formation water (PFW) discharged by offshore petroleum platforms was examined. This was achieved by comparing model predictions with measurements made in the field. The models predicted peak concentrations of tracer PFW constituents (benzene and toluene) to typically within a factor of 2 and location to within 200 metres of the field observations. The models showed that water currents actively transport PFW plumes. Therefore, plume position is largely governed by local tide and wind conditions. Alteration in current strength over the tidal cycle was also shown to cause significant variation in plume concentration. Further, tidal oscillation may cause discharged PFW to pass more than once through a given area ('second dosing'). Once validated, these models can be used to greatly improve estimation of the potential ecological impacts of PFW plumes. This is achieved by using these models to investigate the range of potential PFW dispersion patterns possible for a region around the platform. Collectively, these simulations provide measures of best case and worst case scenarios which can be used for understanding potential ecological impacts. Further, the models can readily estimate the influence of changing discharge practices, such as: altering pipe width and/or depth, improving oil reduction prior to release, increasing discharge volumes, etc. Such features are essential for decision support to platform managers in their efforts to minimise the environmental impacts of offshore platform operations.