Reservoir Inclination and Permeability Effects on CO2 Plume Migration - A Numerical Simulation Study

Abstract Reservoir inclination and permeability are two key variables during the injection and later lateral migration of CO2. These two factors will control the lateral extent of the plume, CO2 dissolution, residual trapping and the pressure build up within the reservoir. The goal of this paper is to use reservoir simulation to illustrate the effects of reservoir inclination and permeability on the lateral propagation of CO2 in inclined reservoirs during and after injection. A homogeneous 100 m thick reservoir is modeled in five inclinations (0 °, 0.5 °, 1 °, 2 ° and 4 °) and with two types of reservoirs with porosities and permeabilities of 20%/100md and 25%/400md. Three CO2 injection scenarios were considered, 1, 3 and 5 MMTPA. The numerical simulation of the injection and later lateral migration is performed for 1000 years to assess CO2 saturation, CO2 dissolution, residual trapping and pressure build up within the reservoir. The main effect on CO2 saturation caused by permeability differences is that the 20% porosity 100md reservoir shows a wide invasion zone of CO2 around the injection well, whereas the 25% porosity 400md reservoir shows a narrower CO2 invasion zone and a much faster vertical migration. Complete vertical migration in the better reservoir can take a few years, whereas in the lower permeability reservoir it takes decades. This observation applies to all inclinations. Reservoir quality and inclination also affect CO2 dissolution and residual trapping. Residual trapping is almost double in the lower porosity/permeability reservoir than in the higher porosity/permeability reservoir. The opposite is true for dissolution, since there is more propagation in the higher porosity/permeability reservoir, it is exposed to more formation water, doubling its dissolution compared with the lower porosity/permeability reservoir. Higher reservoir inclinations have more dissolution. Pressure build up is proportional to the amount of CO2 injected and the buildup is greater in the lower porosity/permeability reservoir than in the higher porosity/permeability reservoir. The difference in pressure build up between the two reservoirs in the 1 MMTPA case is 20 psi, 80 psi in the 3 MMTPA case and 100 psi in the 5 MMTPA case.