N2 + CO2 + NaCl brine interfacial tensions and contact angles on quartz at CO2 storage site conditions in the Gippsland Basin, Victoria/Australia

Abstract

Carbon geo-sequestration (CGS) has been identified as an important method to reduce carbon dioxide (CO2) emissions to the atmosphere thus mitigating global warming. In CGS, the CO2 captured from large point source emitters is injected into hydrocarbon reservoirs for enhanced oil and gas recovery or into deep saline aquifers for storage. In this context the State of Victoria (southeast Australia) is reviewing the suitability of Victorian sedimentary basins as CO2 sinks. The main focus is on the Gippsland basin, which has been positively evaluated from a geological point of view. Now it is necessary to assess the storage capacity of the formation and thus the intimately related fluid–fluid–rock properties. We therefore conducted interfacial tension and contact angle measurements at the prevailing storage conditions (13 MPa, 333 K); as a result, we show that CO2 has a relatively high water contact angle (θ=47°), while lower θ values were measured for N2 (θ=40.6°=47°) and for a 50 mol% CO2+50 mol% N2 mixture (θ=33.9°). Consequently all systems were weakly water-wet. This implies that residual and structural trapping capacities are reduced; however, both mechanisms should work adequately. Specifically, we predict that a CO2 column height of ~698 m can be permanently immobilized beneath the caprock.