Heavy oil reservoirs can be found in many locations around the world, such as Canada, Venezuela, United States and Brazil. When in-situ oil viscosity is prohibitively high to allow recovery by conventional methods, additional techniques are used, such as hot water or steam injection. As water exchanges heat with the surroundings, a temperature gradient is established inside the reservoir, which results in a spatial variation of physical properties, especially viscosity. This leads to different mechanisms for fluid flow and trapping. A typical feature of heavy oil immiscible displacements is early breakthrough due to water fingering, which leads to very poor sweep efficiencies. However, physical experiments and field results have demonstrated that additional mechanisms may play a role in heavy oil immiscible displacements, such as capillary imbibition and oil stripping due to high shear flows.
In this paper, a series of numerical experiments are performed to evaluate secondary imbibition at different viscosity ratios and injection rates using a Finite Volume approach to solve the Navier–Stokes equations at the pore-scale, and the Volume of Fluid method to properly capture interfaces. The simulations are performed in a 2-dimensional, water-wet, digital porous medium with complex geometry including dead end pores.
The operating conditions and the associated complex topology allow evaluation of the typical pore-scale events in a secondary imbibition process, such as oil ganglion mobilization, break-up and coalescence, micro-fingering due to capillary imbibition and oil stripping in high shear flows. Thus the main production mechanisms observed in a heavy oil immiscible displacement are successfully reproduced.