HYDRAULIC PARAMETER UPSCALING AND SENSITIVITY IN GEOLOGIC CARBON SEQUESTRATION SIMULATIONS
Numerical simulations are widely used in feasibility studies for GCS. Storage potentials and efficiencies of the GCS process must first be assessed before reactive transport simulation can be evaluated. Accurate estimates of hydraulic parameters are needed as inputs for these simulations. However, only few experimental values are available for CO2 – brine systems. Sensitivity and scaling analyses were conducted using the STOMP numerical code (PNNL, US Department of Energy) for supercritical CO2 injected into a model confined deep saline aquifer. The influence of hydraulic parameters, i.e. intrinsic permeability (k), porosity, pore compressibility, and capillary pressure – saturation / relative permeability parameters on CO2 injection rates and costs were evaluated and the parameters were ranked based on normalized coefficients of variation. The two most influential parameters were intrinsic permeability k and the van Genuchten m value (which is related to the pore-size distribution). The porosity, mostly used in CO2 storage capacity calculations, ranked fifth out of the seven parameters investigated.
Scale effects were investigated by comparing point and height- averaged van Genuchten capillary pressure-saturation parameters. The point parameters reduced the cost of the injections significantly relative to the average parameters.
Findings highlight the need for accurate estimates of capillary pressure – saturation / relative permeability parameters for CO2 – brine systems at reservoir-relevant scales for GCS simulations, in addition to porosity and intrinsic permeability.