High Viscosity Land Based Oil Flow Model

Highly viscous oil does not behave the same as other regular liquid hydrocarbon mixtures. To evaluate the effects of a potential land-based blowout on the surrounding environment, RPS implemented a multi-step approach to simulate the trajectory and fate of high viscosity oil downslope flow. If spilled on land, initially warm oil cools and tends to gel, implying a non-Newtonian flow. To predict the behavior of high viscosity oil as it flows downslope, spreads and cools, RPS developed a new unique land-based spill model. The behavior of highly viscous crude oil has many similarities to volcanic lava flows, particularly the stark changes in oil viscosity and shear stress as the fluid cools. This study describes a “lava” flow numerical model developed to simulate the response of high viscosity oils. The viscous flow model is based on the lava model of Griffiths (2000) which simulates the unconfined motion of a Bingham fluid down a plane of constant slope. The model allows all physical and chemical parameters to vary continuously downslope. The lateral flow is assumed to cease when the cross-slope pressure gradient is balanced by the basal-yield stress also giving the height of the flow (H) on the center line of the flow as a function of shear stress. For oil flow motion the downslope pressure gradient must be greater than the oil shear stress and hence there is a critical height, based on the local oil shear stress and slope, below which there will be no downslope motion. An atmospheric heat transfer equation was applied to the oil surface as the surface boundary condition. The model was applied to a hypothetical on land release of highly viscous oil in a one-dimensional, downslope form, where the ground slope was assumed constant along the flow path. As the oil progresses downslope, its temperature was updated each time step in each cell and used to calculate new oil properties for density, specific heat, viscosity, and shear stress. The model results provide information about the rate and total distance travelled and time for the downslope flow to stop.