Carbon dioxide wettability of South West Hub sandstone, Western Australia: Implications for carbon geo-storage

•Wettability is very sensitive to organic matter even for minute amount.•Organic matter (except kerogen) can be removed from the sample using organic solvents.•Sample cleaning is of particular importance in contact angle characterization.•Increase in CO2 wettability may affect residual trapping capacities. CO2-rock wettability is a key factor which determines the fluid dynamics and CO2 geo-storage capacity. However, the full understanding of real reservoir CO2-wettability is yet to be gained. We thus systematically analysed the wettability of CO2/brine/South West Hub sandstones at various pressures (0.1 MPa, 5 MPa, 10 MPa, 15 MPa, and 20 MPa) at 334 K. A new procedure based on organic carbon isotope tracking (δ13Corg) was proposed to eliminate the effect of artificial organic matter introduced by drilling mud penetration. The results indicate that the advancing (θa) and receding (θr) water contact angles for the CO2/brine/South West Hub sandstone system increase with increase in pressure (ranging from 71° to 118° and 66° to 111°). It can thus be suggested that the system is weakly water-wet to intermediate-wet. When the samples were treated with dichloromethane, a slight decline in organic content was observed leading to slight decrease in water contact angles (i.e. TOC decreased from 0.019% to 0.003% for core C, and the corresponding θa and θr decreased from 118° and 111° to 110° and 104°, respectively, at 20 MPa and 334 K). This wettability analysis demonstrates that (a) of the contact angle is very sensitive to the amount of organic matter and therefore care should be taken to remove artificial organic matter from the sample, and that (b) this condition prevails in a real proposed CO2-storage site. This analysis thus has important implications for assessing the feasibility of long-term CO2 storage and enabling large-scale industrial carbon geological storage projects.