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

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 (δ¹³C_org) was proposed to eliminate the effect of artificial organic matter introduced by drilling mud penetration. The results indicate that the advancing (θ_a) and receding (θ_r) 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 θ_a and θ_r 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.