Contact angle measurements of CO2–water–quartz/calcite systems in the perspective of carbon sequestration

This work presents contact angle measurements for CO2–water–quartz/calcite systems at general sequestration pressure and temperature conditions (200–3000 psig and 77–122 °F). The effect of drop volume, repeated exposure of the substrates to dense water saturated CO2, pressure and temperature on the contact angles is examined. In the 1st measurement cycle, the contact angles for the quartz substrate varied from 46 to 48° and 47 to 46° for gaseous (water saturated) CO2 and liquid (water saturated) CO2 respectively, at 77 °F. For calcite substrate, these values varied from 45 to 48° and 42 to 40°, respectively. Remarkably, this work highlights a characteristic permanent shift in the contact angle data with repeated exposure to dense, water saturated, CO2. The contact angle data trends after repeated exposure to the dense, water saturated CO2 varied from 89 to 91° and 85 to 80° for the quartz substrate for gaseous (water saturated) CO2 and liquid (water saturated) CO2 respectively, at 77 °F. For calcite substrates, these values varied from 60 to 59° and 54 to 48°, respectively. This important observation has serious implications towards the design and safety issues, as a permanent positive contact angle shift indicates lower CO2 retention capabilities of sequestration sites due to a reduction in the capillary pressure. It is further confirmed that the permanent shift in the contact angle is due to surface phenomena. With an increase in temperature (from 77 to 122 °F), the contact angle shift is reduced from about 45° to about 20° for quartz substrates. Other observations in the contact angle data with respect to pressure are in good agreement with the trends reported in the literature.

► Remarkable positive contact angle shift upon the repeated exposure to the dense water saturated CO2 for quartz and calcite substrates is discovered.
► The positive contact angle shift upon repeated exposure to the dense water saturated CO2 is confirmed due to a surface phenomenon for quartz substrate.
► Observed data trends indicate lower sealing capacities of CO2 sequestration sites than usually assumed.
► For quartz substrate, the shift in the contact angle with repeated exposure to the dense water saturated CO2 reduced with an increase in temperature.