Effects of Sulfate during CO2 Attack on Portland Cement and Their Impacts on Mechanical Properties under Geologic CO2 Sequestration Conditions.
To investigate the effects of sulfate on CO2 attack on wellbore cement (i.e., chemical and mechanical alterations) during geologic CO2 sequestration (GCS), we reacted cement samples in brine with 0.05 M sulfate and 0.4 M NaCl at 95 °C under 100 bar of either N2 or supercritical CO2. The results were compared to those obtained from systems without additional sulfate at the same temperature, pressure, salinity, and initial brine pHs. After 10 reaction days, chemical analyses using scanning electron microscopy with a backscattered electron detector (SEM-BSE) and inductively coupled plasma optical emission spectrometry (ICP-OES) showed that the CO2 attack in the presence of additional sulfate was much less severe than that in the system without additional sulfate. The results from three-point bending tests also indicated that sulfate significantly mitigated the deterioration of the cement's strength and elastic modulus. In all our systems, typical sulfate attacks on cement via formation of ettringite were not observed. The protective effects of sulfate on cement against CO2 attack resulted from sulfate adsorption, coating of CaSO4 on the CaCO3 grains in the carbonated layer, or both, which inhibited dissolution of CaCO3. Findings from this study provide new, important information for understanding the integrity of wellbores at GCS sites and thus promote safer GCS operations.
†Department of Energy, Environmental and Chemical Engineering, Washington University, St. Louis, Missouri 63130, United States.
Qingyun
Q
Li
‡Department of Civil and Environmental Engineering, Yonsei University, Seoul 120-749, Republic of Korea.
Yun Mook
YM
Lim
†Department of Energy, Environmental and Chemical Engineering, Washington University, St. Louis, Missouri 63130, United States.
Young-Shin
YS
Jun
D002245:Carbon Dioxide / Q000737:chemistry*; D057965:Carbon Sequestration; D003252:Construction Materials / Q000032:analysis*; D055119:Elastic Modulus; D055593:Geological Phenomena; D006244:Hardness; D006863:Hydrogen-Ion Concentration; D055595:Mechanical Phenomena; D008855:Microscopy, Electron, Scanning; D013431:Sulfates / Q000737:chemistry*; D014961:X-Ray Diffraction
D013431:Sulfates; D002245:Carbon Dioxide