At geologic CO2 sequestration (GCS) sites, the Portland cement used in building and decommissioning CO2 injection wells can deteriorate as a result of extensive reactions with injected CO2. Characteristically, a carbonated layer forms, which could partially reduce CO2 attack by clogging pores in the cement. We conducted high temperature/pressure experiments using Portland cement samples and quantified the chemical reactions that occurred as well as the samples’ change in strength and hardness after 10 days of reaction. Under our experimental conditions (95 oC, 100 bar, and 0.5 M of NaCl solution), the carbonated layer lost its protective efficiency and a wide and weak portlandite-depleted zone formed inside of the carbonated zone, significantly reducing the samples’ strength. To further investigate the mechanisms by which this portlandite-depleted zone forms, we set up a one-dimensional CrunchFlow continuum model that successfully reproduced our main observations. Most importantly, defects in the carbonated layer can open pathways for CO2 to continuously penetrate into the cement and widen the portlandite-depleted zone. This finding suggests that any strategies that help form a less defective carbonated layer would decrease cement deterioration. This study advances our understanding of cement deterioration and provides insights for more robust cementing of wells.

Experimental and modeling investigations of Portland cement deterioration under geologic CO2 sequestration conditions

251st National Meeting (2016)

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