Deepwater and Ultra-Deepwater Blowout and Offshore Spill Model
Sim, Lawrence; Graham, James; Rose, Kelly
To assist with risk assessment to prevent future hydrocarbon spills and provide a comprehensive tool for response planning, we have developed an integrated water column modeling system for simulating offshore oil spills resulting from deepwater (>500ft) and ultra-deepwater (>5,000ft) blowouts. The water column modeling system is comprised of multiple models for the plume phase, the advection and diffusion dominated transport phase, an intermediary model between the two, and other models for handling the physical properties of oil/gas and the weathering of crude oil.
The plume model simulates the buoyant jets and plumes emerging from a deepwater blowout source using Lagrangian control-volume analysis to track the movement and shape of the plume as it travels through the water column. The control-volumes are driven by buoyancy and the entrainment of ambient seawater, taking into account the ambient conditions, droplet sizes, gas bubbles, and gas hydrates. A newly developed jet coefficient and a 3-phase approach to droplet terminal velocities allow the model to balance between jet-like and plume-like behavior. The plume model performed capably when validated against the North Sea field experiments, and the use of the jet coefficient has provided improved simulations.
Once reaching a terminal level, the intermediary model converts the control-volumes into Lagrangian parcel elements based on a probability density surface created from a moving oil concentration centroid, allowing for skewed and non-normal distribution of crude concentrations and droplet sizes. From there, the transport and weathering model takes over to simulate the final fate and distribution of oil, accounting for non-surfacing plumes and control volume sources. The development of this modeling system from the ground up has allowed for the adaptation of the entire system towards ultra-deepwater blowouts instead of simply assigning a deepwater plume model to a traditional oil spill process model.
AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013