Western Australia basalt-CO₂-brine wettability at geo-storage conditions

CO₂ geo-storage is a technique, where millions of tonnes of CO₂ are stored in underground formations every year for permanent immobilization to reduce greenhouse gas emissions. Among promising geo-storage formations, basalt is attracting keen interest from researchers and industry. However, the literature severely lacks information on the wetting behaviour of basaltic rocks at geo-storage conditions.

To enable a more general statement of basalt-scCO₂-brine contact angles, the wettability of a basalt from Western Australia was compared with a similar rock type from Iceland. This study reports the advancing and receding contact angles for a basalt-scCO₂-brine system at pressures ranging from 0.1 to 20 MPa and temperatures of 298 and 323 K, respectively. Based on the experimental data, the amount of CO₂, expressed by the column height, which could be safely trapped beneath the basalt was then calculated.

The basalt was initially water-wet but with increasing pressure, it was converted sequentially from a water-wet to an intermediate-wet and then finally into a completely CO₂-wet template at pressures exceeding 15 MPa and 323 K. Under those experimental conditions, found in the field at depths below 1500 m, injected supercritical CO₂ into a porous basalt reservoir is assumed to flow freely in lateral and vertical directions and is less impeded by capillary/residual trapping, potentially leading to CO₂ leakage. It is suggested that the injection depth should not be chosen too deep to avoid increased free CO₂ plume mobility. It is found from CO₂ column height calculations that at 800 m depth (a minimum requirement to keep CO₂ supercritical), the height of the CO₂ column that can be safely trapped below the cap rock, was still 100 m but shrank to nil at ≥1500 m.