Many examples of reaction-diffusion processes are encountered in enhanced heavy oil recovery applications. A typical instance of such a process is when a chemical diffuses through a fluid column and then undergoes reaction with another chemical species. The reaction products further diffuse through the porous media. The challenges involved in modeling these processes are accurate representation of the propagation of the reaction front which is very localized and accurate depiction of diffusion which is one of the main transport mechanisms. We evaluate a simulation model for the displacement of carbon dioxide in a simultaneous injection of carbon dioxide and elemental sodium in a heavy oil reservoir. The main objective of using sodium in this process is the highly exothermic reaction of sodium with the in-situ water that results in the liberation of heat that in turn reduces the oil viscosity. Another important advantage of this process is the formation of sodium hydroxide that reduces the interfacial tension at the bitumen interface.

The modeling of the mechanism of transport of sodium to the reaction interface through diffusion and the subsequent displacement of the reaction zone was attempted using the commercial software STARS™. When sodium suspended in liquid carbon dioxide is injected into the reservoir, it has to diffuse through the carrier phase and then interact with water. This mechanism has to be adequately captured at the scale of the simulation grid blocks. A random walk diffusion algorithm with reactive dissipation is implemented to more accurately represent reaction/diffusion processes and to study their scaling characteristics.

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