Simulation of subsurface mechanical dispersion (SSMD) of oil by a water jet

Abstract

This study explores the formation of oil droplets (dispersion) using a water jet, labeled herein subsurface mechanical dispersion (SSMD), as an alternative to chemical dispersants for mitigating impacts from subsea oil releases. Utilizing Reynolds-Averaged Navier-Stokes (RANS) and Mixture equations (a multiphase model to calculate the oil volume fraction) within the CFD model Fluent, both small-scale (a 1.0 mm oil orifice diameter and 0.17 mm water jet orifice diameter) and large-scale simulations (oil diameter = 0.5 m and water diameter = 0.05 m) were conducted. Four metrics were used to evaluate the dispersion potential: spatial spread of the oil; the maximum stable diameter of oil droplets, D95; and two metrics that depend on the product of the energy dissipation rate and the holdup (ratio of oil volume to total volume in each cell). The spreading and distribution of oil was quantified in the whole domain of the corresponding simulation. The remaining metrics were evaluated in both the area at the intersection of the oil plume and the water jet, and along the main trajectory of flow. For the small-scale experiment, the simulation results showed good agreement with laboratory observations in terms of oil plume deflection and droplet sizes. At the large-scale, the simulations suggested that SSMD reduced the D95 by 40 % and 80 % for water flow rates that are 17 % and 55 % of the oil rate, respectively. The results suggest that a water jet, at a sufficiently large flowrate, could be a viable technology for initial dispersion of oil spill during response. Further research, including experimental validation and detailed simulations, is needed to ascertain the full potential of SSMD, especially for oil releases containing gas.