Publications

Effect of exposure environment on the interactions between acid gas (H2S and CO2) and pozzolan-amended wellbore cement under acid gas co-sequestration conditions

Publication Information:

Zhang, L., D.A. Dzombak, D.V. Nakles, S.B. Hawthorne, D.J. Miller, B. Kutchko, C. Lopano, and B. Strazisar, “Effect of exposure environment on the interactions between acid gas (H2S and CO2) and pozzolan-amended wellbore cement under acid gas co-sequestration conditions,” 27, 309-318, 2014.

Year: 2014

Topics:

Laboratory experiments were conducted to determine the effect of exposure environment on the integrity of pozzolan-amended Class H cement under geologic acid gas co-sequestration conditions. Cement was exposed to two potential subsurface storage environments: (1) a supercritical mixture of CO2/H2S and (2) a CO2/H2S saturated brine. Results show that cement alteration is dependent on the amount of pozzolan addition. The alteration rate and mechanism also differ for the two exposure scenarios. Cement containing 35% pozzolan amounts by volume (hereafter referred to as 35 vol% pozzolan cement) exposed to the aqueous environment was more vulnerable to alteration, compared with the same pozzolan content cement exposed to a supercritical mixture of CO2/H2S (21 mol% H2S). Specifically, 35 vol% pozzolan cement exposed to the aqueous environment exhibited a higher level of mineral dissolution (e.g., C-S-H, 3CaO·SiO2, 2CaO·SiO2, etc.) and a higher degree of sulfur alteration than the same pozzolan content samples exposed to the supercritical mixture of CO2–H2S (21 mol% H2S). Different from the 35 vol% pozzolan cement, the cement containing 65% pozzolan by volume (hereafter referred to as 65 vol% pozzolan cement) was more susceptible to alteration in the supercritical CO2/H2S (21 mol% H2S) environment, compared with the same pozzolan content cement exposed to the aqueous environment. Increasing the H2S mol% in the supercritical phase from 21 mol% to 40 mol% increased the alteration of cement exposed to both exposure environments. The 65 vol% pozzolan cement was more resistant to H2S and CO2 alteration than the 35 vol% pozzolan cement if the H2S content was high (i.e., 40 mol%), while the 35 vol% pozzolan cement was more resistant to H2S and CO2 alteration than the 65 vol% pozzolan cement if the H2S content was relatively low (i.e., 21 mol%). It was observed that while the two related exposure environments resulted in different degrees of cement alteration, the exposure environments did not result in the formation of different minerals.

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