Determining CO₂/brine relative permeability and capillary threshold pressures for reservoir rocks and caprocks: Recommendations for development of standard laboratory protocols

Important parameters for the determination of fluid transport in reservoir rocks are capillary pressures and relative permeabilities for the CO ₂/brine system. These factors influence the plume migration, residual CO₂ trapping and CO₂ dissolution in the reservoir brines. CO₂-brine relative permeabilities for different rock types are rare in public literature and usually adapted from mathematical relations or from more recent experimental data. The experimental data vary greatly in saturation and relative permeability endpoints, between 10 and 100%. It is necessary to reduce the uncertainty in the data range, since these parameters are sensitive and indispensable for the numerical simulation of the evolution of a CO ₂ plume in the subsurface. The petrophysical properties of caprocks are the limiting factor to the amount of CO₂ stored in potential storage sites. The caprock sealing capacity is determined by the capillary pressure (or column height) at which the trapped fluid starts leaking through a caprock. These rocks have high capillary threshold pressures, which, combined with wettability and interfacial tension (IFT) , determine the final column height that a seal can hold. Those three factors - capillary pressure, wettability and IFT - play an important role in the geological storage of CO₂ in controlling the potential of CO₂ moving through the seal. The capillary threshold pressures need to be determined accurately to estimate brine displacement in caprocks and hence the onset of viscous flow or leakage to the surface. Within the framework of the Carbon Capture Project (CCP3), we plan to establish standard experimental protocols with academic and/or commercial laboratories.