A parametric analysis of capillary pressure effects during the carbon sequestration injection process in a sandstone reservoir

Geological Carbon Sequestration (GCS) is considered as a key method for mitigating the adverse effects of steadily increasing atmospheric CO2 concentrations. Numerical simulation is one technique for better understanding the injection, migration and leakage of supercritical CO2 (scCO2) during GCS. At the field scale, capillary pressure (Pcap) is an important factor governing the subsurface movement of scCO2. Constitutive models of Pcap as a function of wetting phase saturation (Sw) are essential to field-scale GCS simulations; however, such Pcap models are based on core-scale laboratory measurements. As a result, there exists uncertainty in the application of laboratory-measured Pcap models to field-scale GCS simulations. In this study, a parametric analysis of commonly used van Genucthen Pcap model is undertaken to quantify the effects of variability in the model parameter space. The study focuses on two parameters: the non-wetting phase entry pressure (P0) and the pore-size distribution index (λ), the latter of which controls curvature of the Pcap model. A two-dimensional parameter space is selected that covers a wide range of laboratory-scale Pcap measurements in the scCO2-brine system, and scCO2 injection processes are modeled within a homogeneous sandstone reservoir over the complete parameter space. Simulation results demonstrate how changes in the Pcap model parameters influence scCO2 migration within the storage reservoir. Maximum injection pressure is largely insensitive to variability of Pcap model parameters; however, vertical scCO2 migration is strongly controlled by Pcap model parameter selection. Since vertical scCO2 migration is the key point to estimate scCO2 leakage risk through caprock sealing, these results illustrate the importance of Pcap model parameter selection in field-scale numerical models of GCS.