The role of particle aggregation in size-dependent deposition of drill mud

Petroleum exploration on continental shelves raises concerns over potential impacts it may have on ecologically sensitive and valuable fishing grounds. Several studies demonstrate that drill mud discharged from platforms exhibit negative impacts on surrounding benthic communities. However, the dispersal and deposition mechanisms of such mud are poorly understood. This study investigates the evolution of disaggregated particle size distributions of bentonite enriched water-based drill mud in a suspension flowing over a flat sand bed using a laboratory flume. Observed size-specific decay rates of suspended sediment concentrations indicate that suspended grains deposit as single grains and flocs. A simple model that considers deposition of particles by gravitational settling of single grains and flocs yields estimates of decay rates in good agreement with the measurements. The proposed model provides a grain size-specific analysis of parameters characteristic of a poorly sorted aging suspension that have previously been undocumented.