CO2–Brine Contact Angle Measurements on Navajo, Nugget, Bentheimer, Bandera Brown, Berea, and Mt. Simon Sandstones

In this study, contact angles were measured for CO2 bubbles on six different sandstones (Navajo, Nugget, Bentheimer, Bandera Brown, Berea, and Mt. Simon) that could potentially represent properties of CO2 storage depositional environments. The impacts of pressure and temperature were studied by focusing on the CO2 phase behavior in three different scenarios: gaseous, liquid, and supercritical conditions. Despite controlling the sample preparation and cleanliness, CO2-brine equilibration conditions, and pressure and temperature, there were inconsistencies in contact angle trends that could largely be attributed to natural sample heterogeneity resulting from localized variations in topography, surface roughness, and mineral composition across the surface. Despite these variations, the analysis of 298 measurements from this study showed that 81% of the contact angles were <40 degrees, representing strongly water-wet to (moderately) water-wet behaviors. Also, 17.3% of the measurements were between 40 degrees and 60 degrees (weakly water-wet) and primarily belonged to small CO2 bubbles (<500 mu m) that were heavily impacted by localized surface heterogeneity in natural sandstone samples. In addition, only 1.7% of the measurements had angles greater than 60 degrees and could be classified as no longer water-wet, but these measurements occurred on extremely small bubbles (100-200 mu m) that were very dependent on localized surface heterogeneity. While some of the detailed physics of the CO2/brine/sandstone interface is still poorly understood, from an application standpoint, the sandstones of this study were best characterized as strongly water-wet to (moderately) water-wet.