Estimation of CO2 storage capacities in saline aquifers using material balance

Estimating CO₂ storage capacities is crucial in developing carbon capture and storage projects. Material balance equation (MBE) methods, widely employed for oil and gas reserve estimation, offer a direct approach to estimating CO₂ storage capacities. However, previous MBE methods rely on an original fluid in-place volume calculated using volumetric methods to estimate CO₂ storage capacities, lacking validation for accuracy. It is essential to accurately estimate the original fluid in-place volume, representing the pore volume, as it substantially influences CO₂ storage capacity. This study presents a refined MBE method that ensures accurate estimates of CO₂ storage capacities by validating the original fluid in-place volumes in saline aquifers. The accuracy of this method was evaluated by comparing it with a commercial reservoir simulator for a synthetic aquifer example and the Sleipner L9 model. In the synthetic aquifer example, the relative error in CO₂ storage capacity estimation with the proposed MBE method was only 2.09%, even when short-term (1-year) injection data were utilized. The proposed MBE method demonstrates consistent accuracy in estimating CO₂ storage capacities under different aquifer properties, operating conditions, and MBE-related conditions. The proposed MBE method also accurately estimated the CO₂ storage capacity in the Sleipner L9 model, achieving a relative error of 3.47%.