Maximising the Dynamic CO₂ storage Capacity through the Optimisation of CO₂ Injection and Brine Production Rates

CO₂ storage capacity in saline aquifers can dramatically be reduced by pressure build up due to the CO₂ injection process. In this paper, a novel optimisation strategy that maximises the CO₂ storage capacity utilisation and net profits before tax is presented in a scenario of simultaneous CO₂ injection and brine production to help control pressure build up and increase the effective storage capacity. The strategy is tested at the region surrounding the Forties and Nelson fields, assuming both as pure saline aquifer traps. The optimisation was performed considering constraints such that the CO₂ plume distribution does not migrate outside the license boundaries, the fracture pressure is not reached within the reservoir, and the CO₂ injection and brine production rates occur within feasible limits. The problem was first formulated analytically with the aid of surrogate models, and then optimised using the SIMPLEX and Generalized Reduced Gradient methods. Results for the Forties and Nelson fields show that by allowing five brine production wells producing up to 2.2 MMtonnes/year, the CO₂ storage capacity increased between 112-145% compared to the case where no brine production is practiced.