Chemical Reactions of Portland Cement with Aqueous CO₂ and Their Impacts on Cement’s Mechanical Properties under Geologic CO₂ Sequestration Conditions

Abstract

To provide information on wellbore cement integrity in the application of geologic CO2 sequestration (GCS), chemical and mechanical alterations were analyzed for cement paste samples reacted for 10 days under GCS conditions. The reactions were at 95 °C and had 100 bar of either N2 (control condition) or CO2 contacting the reaction brine solution with an ionic strength of 0.5 M adjusted by NaCl. Chemical analyses showed that the 3.0 cm × 1.1 cm × 0.3 cm samples were significantly attacked by aqueous CO2 and developed layer structures with a total attacked depth of 1220 μm. Microscale mechanical property analyses showed that the hardness and indentation modulus of the carbonated layer were 2-3 times greater than for the intact cement, but those in the portlandite-dissolved region decreased by ∼50%. The strength and elastic modulus of the bulk cement samples were reduced by 93% and 84%, respectively. The properties of the microscale regions, layer structure, microcracks, and swelling of the outer layers combined to affect the overall mechanical properties. These findings improve understanding of wellbore integrity from both chemical and mechanical viewpoints and can be utilized to improve the safety and efficiency of CO2 storage.

Permeability Evolution of a Cemented Volcanic Ash During Carbonation and CO2 Depressurization

“…In contrast, Fabbri et al () observed a porous region developing within the reaction front of samples carbonated ( T = 90 °C, P p = 28 MPa) without confinement, and speculated that this region included a population of microcracks that seeded larger fractures when samples were brought to failure under deviatoric stress. Their proposal is consistent with the microfractures imaged by Li et al (), who inferred a correlation of such defects with a measured decrease in both the modulus of rupture and the elastic modulus after carbonation of unconfined samples. Similarly, Rochelle and Milodowski () observed an enhanced porosity and microfractures ahead of the CaCO 3 phase (i.e., in the less carbonated zone) for both cement in laboratory experiments and C‐S‐H‐bearing rocks in nature.…”

Effects of sulfate and magnesium on cement degradation under geologic CO2 sequestration conditions

“…However, their effects on cement degradation under relevant GCS conditions (i.e., under high temperature and high CO2 pressure in brines with high salinity) are not well understood. To our knowledge, only recently, Li et al, 2015a, Li et al, 2015b reported the effects of sulfate ions on newly hardened cement under 95 °C and ∼100 atm CO2 condition. In their study, Li et al, 2015a, Li et al, 2015b proposed that the presence of sulfate could protect cement from CO2 attack through sulfate adsorption and/or coating of gypsum on calcite (CaCO3) grains in carbonated layer.…”

“…To our knowledge, only recently, Li et al, 2015a, Li et al, 2015b reported the effects of sulfate ions on newly hardened cement under 95 °C and ∼100 atm CO2 condition. In their study, Li et al, 2015a, Li et al, 2015b proposed that the presence of sulfate could protect cement from CO2 attack through sulfate adsorption and/or coating of gypsum on calcite (CaCO3) grains in carbonated layer. However, gypsum was not directly detected in their experiments.…”

“…In previous studies of cement degradation under relevant GCS conditions, layered structures were observed to have formed in the reacted cement samples (Kutchko et al, 2007, Kutchko et al, 2008, Kutchko et al, 2009, Duguid, 2009, Duguid and Scherer, 2010, Jacquemet et al, 2012, Carey, 2013, Li et al, 2015a, Li et al, 2015b and atmospheric pressurecondition (50 °C and 1 atm of air) were examined using optical microscopy. For cement samples reacted in different brine solutions (Table 1) under atmospheric pressure, only a thin white layer was observed outside the cement rim ( Fig.…”

Sustainability: GEOC’s Perspective

“…Geologic formations proposed for long term (over 1000 years) storage for CO 2 include sandstone reservoirs overlaid with low-permeability caprock. Understanding mineral dissolution and precipitation triggered by the injection of large volumes of CO 2 is critical to these efforts (17)(18)(19)(20). Similarly, CO 2 is expected to dissolve and acidify groundwater, potentially causing mineral dissolution and development of fractures (e.g.…”