The influence of methyl orange on the CO2-brine wettability of organic-acid-aged calcite samples: Implications for CO2 geo-storage

The underground storage of CO2 in a depleted carbonate formation is a suitable method for limiting its anthropogenic release and minimize global warming. The rock wettability is an essential factor controlling the mechanisms of CO2 trapping and its containment safety in the geo-storage formation. The geo-storage rock contains innate organic acids which alters the wettability of the rock surface from the hydrophilic condition to the hydrophobic state, thus reduce the CO2 storage capacity. In this study, methyl orange which is a toxic dye that is generally released into environment was used as wettability modifier to change the wettability of stearic acid aged calcite (oil wet) to water wet. This study uses the contact angle technique (sessile drop method) to examine the effects of various concentration of methyl orange (10-100 mg/L) on the wettability of the CO2/brine/stearic-acid aged calcite system under geo-storage conditions (i.e., temperatures of 25 and 50 degrees C and pressures of 5-20 MPa). The results indicate that the advancing and receding contact angles (q a and qr) of the organic-acid contaminated rock surface were drastically reduced upon exposure to methyl orange, attaining the minimum values of 62 degrees and 58 degrees respectively, in the presence of 100 mg/L methyl orange at 20 MPa and 50 degrees C. Thus, the present results suggest that rather than discharging methyl orange into the environment, it could be injected into underground reservoirs in order to reduce the level of environmental pollution and at the same time increase the CO2 storage capacity of carbonate formations.