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 degrees 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 degrees and 47 to 46 degrees for gaseous (water saturated) CO2 and liquid (water saturated) CO2 respectively, at 77 degrees F. For calcite substrate, these values varied from 45 to 48 degrees and 42 to 40 degrees, 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 degrees and 85 to 80 degrees for the quartz substrate for gaseous (water saturated) CO2 and liquid (water saturated) CO2 respectively, at 77 degrees F. For calcite substrates, these values varied from 60 to 59 degrees and 54 to 48 degrees, 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 degrees F), the contact angle shift is reduced from about 45 degrees to about 20 degrees 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. (C) 2011 Elsevier Ltd. All rights reserved.