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.