Modeling Subsurface Dispersant Applications for Response Planning and Preparation

Abstract

ABSTRACT The increase in oil and gas development activity at increasing water depths has highlighted the need for modeling tools to evaluate the unique aspects of accidental deepwater releases, one aspect being the need to assess the impact of subsurface dispersant application to a deepwater blowout. In response to this need, the effect of subsurface dispersant application has been implemented within RPS ASA's blowout model OILMAPDeep. OILMAPDeep was developed to simulate deepwater blowout releases; it predicts the evolution and characteristics of the subsurface plume and estimates the oil droplet size distribution associated with the release. The droplet size distribution dictates the vertical transport of oil within the water column, and impacts the relative volume anticipated to either surface or remain trapped in the water column. Droplet sizes are primarily a function of the energy of the release and the oil-water interfacial tension. The energy of the release is characterized by a reference velocity, typically the exit velocity, and the oil-water interfacial tension as a function of the oil properties. Dispersants mixed with oil reduce the oil-water interfacial tension, which in turn reduces the droplet sizes associated with treated releases serving to delay or eliminate surfacing oil. The present model implementation takes advantage of recent studies that have quantitatively assessed the relationship between the dispersant to oil ratio and surface tension. Here we present a background of the OILMAPDeep module, the governing physical processes of droplet formation, and the relationship between dispersant-to-oil ratio (DOR) and droplet size formation as characterized in the model. A description of the model implementation including model inputs and outputs are provided. Furthermore a set of scenarios are presented that demonstrate the model's capabilities for planning and preparing response activities in the event of a potential oil well blowout. This paper shows how the implementation of subsurface dispersant application within OILMAPDeep provides an effective means of evaluating potential response activities associated with subsurface dispersant application to a deepwater blowout. This includes evaluating the effect of subsurface dispersant application on droplet size distribution, and the ultimate impact on the timing, location and the relative volume of surfacing oil.