System response as a function of relative permeability in geologic CO2 sequestration

Abstract:

Within the portfolio of risk assessment strategies for carbon capture and sequestration projects, numerical modeling and simulation is frequently utilized for predicting CO₂ storage capacity, leakage potential, and geomechanical reservoir integrity. In numerical CO₂ injection models, one commonly used approach for simulating the effects of relative permeability (k_rel) is to apply the van Genuchten (1980) model to the wetting phase and the Corey (1954) model to the non-wetting phase. In this formulation, wetting phase permeability decay is controlled by a phase interference parameter (m), and non-wetting phase permeability decay is controlled by irreducible non-wetting phase saturation (S_gr). Although k_rel is a well-known phenomenon, there exists much uncertainty in parameterizing k_rel models and little is known about the influence of parameter space on reservoir performance. This work presents results from a numerical modeling experiment designed to isolate the effects of variability in k_rel parameters, m and S_gr. A series of CO₂ injection simulations is performed for 399 unique combinations of m and S_gr, which vary systematically over a range of 0.1 – 0.99 and 0.01 – 0.50, respectively. CO₂ is injected at modest 2.78 kg/s for 10 years into a radially symmetric grid using a beta version of TOUGH3/ECO2N, and all reservoir properties remain constant across the ensemble of 399 simulations. Results from this work show the injection pressure response ranging from ~10 MPa to >60 MPa, where the high end of this range is focused on a narrow portion of the parameter space corresponding to m < 0.3 for all S_gr. Additionally, the maximum CO₂ plume radius (defined as CO₂ saturation > 0.01) ranges from 550 m to 1250 m, where the high end of this range corresponds with low m and low S_gr. Although the model geometry is quite simple, these results demonstrate enormous variability in the both injection pressure and CO₂ plume dimension solely as a function of k_rel.