Simulation of CO2 Migration for the Planning of Well Test Configurations at the South West Hub Project, Western Australia

Abstract

Containment of injected CO2 at the South West Hub project in Western Australia is dependent on non-structural trapping mechanisms in the 1500 m thick Wonnerup Member of the Lesueur Sandstone due to uncertainties regarding the sealing character of the ∼600 m thick overlying Yalgorup Member. Therefore, vertical migration distance and sweep efficiency and their impact on residual saturation and CO2 dissolution need to be properly assessed through reservoir simulations. We find that conventional Darcy-flow reservoir simulations result in significantly different predictions of plume migration compared to invasion percolation modelling when injecting at the base of the Wonnerup Member. If numerical predictions of the fate of injected CO2 are sensitive to the choice of model, care must be taken when selecting the methodology. One way to validate simulation predictions at a scale appropriate to the modelling is the use of well tests. In the Wonnerup Member a vertical migration test is recommended for consideration to confirm whether conventional reservoir simulations or percolation invasion modelling accurately predict the CO2 migration processes at the site. This test would involve a small injection of CO2 that is allowed to migrate upwards. The migration would be monitored with repeat pulsed neutron logging. This represents a new kind of test unique to the situation for the South West Hub site.