Environmental Monitoring and Modeling of Drilling Discharges at a Location with Vulnerable Seabed Fauna: Comparison between Field Measurements and Model Simulations

Offshore drilling activities were carried out by Statoil at the Hyme field, located in the Norwegian Sea, in an area with vulnerable seabed fauna. Cold water corals (Lophelia) were identified in vicinity of the drilling well location. Drilling activities in sensitive areas requires that the operator perform an assessment of potential impact or risk of drilling discharges prior to the drilling operation. The risk assessment is an input to the planning of the drilling operation with regards to minimize negative impacts on corals or other vulnerable fauna present. In addition, environmental monitoring during the drilling operation is undertaken in such areas, to document and, if possible, prevent potential impacts on the seabed fauna. The monitoring program at the Hyme field included measurements of ocean currents, temperature, salinity, turbidity and sedimentation of particles at the drilling location during the drilling operation. After drilling, the environmental risk assessment was updated with actual current data and high resolution discharge data for the whole discharge period. The results from the field measurements were used for validation of model simulations of dispersion and deposition of discharged drilling particles, in order to predict actual exposure and consequently potential effects or risk to the corals. In the present paper a comparison between model simulations and field measurements is presented. The model predicted particle exposure concentrations and burial of corals will be verified against turbidity measurements in the water column and particle sedimentation measurements at different distances from the discharge points. A high level accuracy in the model simulations, as basis for assessment of potential impacts to biota, is of high importance. This enables the operator to evaluate alternatives with regards to drilling discharge solutions (discharge point etc.) with lowest impact on environmental resources at the drilling site prior to drilling. A high level of accuracy is also important in the validation of the simulation.