Defining the Brittle Failure Envelopes of Individual Reaction Zones Observed in CO2-Exposed Wellbore Cement

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• 作者：Suzanne J. T. Hangx ; Arjan van der Linden ; Fons Marcelis ; Emilia Liteanu
• 刊名：Environmental Science & Technology
• 出版年：2016
• 出版时间：January 19, 2016
• 年：2016
• 卷：50
• 期：2
• 页码：1031-1038
• 全文大小：409K
• ISSN：1520-5851

文摘

To predict the behavior of the cement sheath after CO₂ injection and the potential for leakage pathways, it is key to understand how the mechanical properties of the cement evolves with CO₂ exposure time. We performed scratch-hardness tests on hardened samples of class G cement before and after CO₂ exposure. The cement was exposed to CO₂-rich fluid for one to six months at 65 °C and 8 MPa P_total. Detailed SEM-EDX analyses showed reaction zones similar to those previously reported in the literature: (1) an outer-reacted, porous silica-rich zone; (2) a dense, carbonated zone; and (3) a more porous, Ca-depleted inner zone. The quantitative mechanical data (brittle compressive strength and friction coefficient) obtained for each of the zones suggest that the heterogeneity of reacted cement leads to a wide range of brittle strength values in any of the reaction zones, with only a rough dependence on exposure time. However, the data can be used to guide numerical modeling efforts needed to assess the impact of reaction-induced mechanical failure of wellbore cement by coupling sensitivity analysis and mechanical predictions.