Characterization of pozzolan-amended wellbore cement exposed to CO2 and H2S gas mixtures under geologic carbon storage conditions

Publication Information:

Zhang, L., D.A. Dzombak, D.V. Nakles, S.B. Hawthorne, D.J. Miller, B.G. Kutchko, C.L. Lopano, and B.R. Strazisar, “Characterization of pozzolan-amended wellbore cement exposed to CO2 and H2S gas mixtures under geologic carbon storage conditions,” International Journal of Greenhouse Gas Control 19, 358-368, 2013.

Year: 2013


Capture and subsurface co-sequestration of acid gas (a mixture of CO2 and H2S) is a geologic sequestration approach that can reduce the emission of both CO2 and sulfur-containing “sour” gas. To investigate the effects of co-sequestration on pozzolan-amended wellbore cement, samples were mixed, cured and exposed to mixtures of H2S and CO2 under geologic sequestration conditions (50 °C, 15.1 MPa) for various periods of time. The resulting samples were characterized using microscopy, X-ray diffraction, and microhardness testing. These analyses showed significant alteration at the surfaces of pozzolan-amended cement samples after 28 days of exposure to 21 mole% H2S in a mixture with CO2. Results of samples exposed for 28 days also revealed that the samples with higher pozzolan amount (65% pozzolan by volume) allowed faster CO2 and H2S penetrations than those with lower pozzolan amount (35% pozzolan by volume). Analyses showed that there was formation of carbonate species in the interior “core” region of pozzolan-amended cement samples with 65 vol% pozzolan after 28 days of exposure, which was not the case for the samples with 35 vol% pozzolan. In addition, the microhardness test results showed that the rim region of the 35 vol% pozzolan samples exhibited a higher microhardness than that of the core region for the same sample, whereas the different regions of the 65 vol% pozzolan samples exhibited similar microhardness values. In summary, the pozzolan-amended cement samples with 35 vol% pozzolan exhibited better H2S-resisting performance than the samples with 65 vol% pozzolan.

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