Characterizing the near-bottom dispersion of drilling mud on three offshore banks

The fate of discharged drilling muds is an ongoing issue for offshore petroleum operators, regulators, the fishing industry and environmentalists. The problem is compounded by difficulties in measuring transient mud concentrations and in relating experience gained at one location to locations with different oceanographic characteristics. We use the benthic boundary layer transport model (bblt) and a simple bulk release discharge scenario, together with measured currents and hindcast waves, as the basis for characterizing the near-bottom dispersion of drilling mud at three locations in Atlantic Canada: the Northeast Peak of Georges Bank, the North Triumph site on Sable Island Bank, and the Hibernia site on the Grand Bank. While the three locations have similar water depths (65-85 m), we find dramatic differences in the drift, dispersion and potential near-bottom concentrations. The drift rates and effective diffusivities are greatest at Northeast Peak and least at Hibernia. The variations in the near-bottom concentrations, which cover five orders of magnitude, can be explained by a simple scaling argument that accounts for the differences in vertical distribution and effective diffusivity.