Capillary Pressure–Saturation Relations for Supercritical CO2 and Brine in Limestone/Dolomite Sands: Implications for Geologic Carbon Sequestration in Carbonate Reservoirs

In geologic carbon sequestration, capillary pressure (P c)–saturation (S w) relations are needed to predict reservoir processes. Capillarity and its hysteresis have been extensively studied in oil–water and gas–water systems, but few measurements have been reported for supercritical (sc) CO2–water....

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Bibliographic Details
Published in:Environmental science & technology 2015-06, Vol.49 (12), p.7208-7217
Main Authors: Wang, Shibo, Tokunaga, Tetsu K
Format: Article
Language:English
Subjects:
Calcium Carbonate - chemistry
Carbon Dioxide - chemistry
Carbon Sequestration
Geological Phenomena
Magnesium - chemistry
Porosity
Pressure
Salts - chemistry
Temperature
Time Factors
Wettability
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Summary:In geologic carbon sequestration, capillary pressure (P c)–saturation (S w) relations are needed to predict reservoir processes. Capillarity and its hysteresis have been extensively studied in oil–water and gas–water systems, but few measurements have been reported for supercritical (sc) CO2–water. Here, P c–S w relations of scCO2 displacing brine (drainage), and brine rewetting (imbibition) were studied to understand CO2 transport and trapping behavior under reservoir conditions. Hysteretic drainage and imbibition P c–S w curves were measured in limestone sands at 45 °C under elevated pressures (8.5 and 12.0 MPa) for scCO2–brine, and in limestone and dolomite sands at 23 °C (0.1 MPa) for air–brine using a new computer programmed porous plate apparatus. scCO2–brine drainage and imbibition curves shifted to lower P c relative to predictions based on interfacial tension, and therefore deviated from capillary scaling predictions for hydrophilic interactions. Fitting universal scaled drainage and imbibition curves show that wettability alteration resulted from scCO2 exposure over the course of months-long experiments. Residual trapping of the nonwetting phases was determined at P c = 0 during imbibition. Amounts of trapped scCO2 were significantly larger than for those for air, and increased with pressure (depth), initial scCO2 saturation, and time. These results have important implications for scCO2 distribution, trapping, and leakage potential.
ISSN:0013-936X
1520-5851
DOI:10.1021/acs.est.5b00826