Effect of Three-Phase Relative Permeability on Field-Scale Carbon Dioxide Storage and Oil Recovery

Oranan Ariyarit , Ann Muggeridge, Vinicius Luiz Santos Silva, Nopparit Somboonkittichai, Nattaphon Temkiatvises, Martin J. Blunt

Currently, the vast majority of subsurface carbon dioxide storage occurs in mature oil fields, where sequestration is combined with enhanced oil recovery. When carbon dioxide is injected below the minimum miscibility pressure, three-phase flow occurs. We study the sensitivity of assumptions made in the assignment of three-phase relative permeabilities on predicted oil recovery and carbon dioxide storage for a three-dimensional reservoir models. We investigate saturation paths, time to water breakthrough, oil recovery and gas storage in weakly water-wet and strongly oil-wet reservoirs, using representative two-phase relative permeabilities. Different interpolation methods to determine the three-phase relative permeabilities are used to assess the impact on reservoir performance. In particular, we show how a physically-consistent characterization of the gas relative permeability has a critical impact on predicted performance. Using saturation-weighted interpolation on the gas relative permeability between gas/oil and gas/water endpoints, where gas is not the most non-wetting phase in the presence of mobile water, has a major impact on CO2 storage: compared to a traditional model using only the gas/oil relative permeability 10% more CO2 is stored, while the oil recovery is 5% lower. This work stresses the necessity of having accurate measurements of relative permeability when assessing CO2 storage in oil fields, and the importance of allowing all three relative permeabilities to vary as a function of two independent saturations.