Experimental Study of Well Cement Carbonation under Geological Storage Conditions

Abstract

Batch experiments were carried out to examine the carbonation reaction of neat cement and two cement-fly ash admixtures (poz mix and lightweight) in 0.5 M NaCl solution at 53°C and 10 MPa CO 2 . The reactions were monitored for 3, 7, 14, 28, and 84 days. The major cation contents of the solutions were determined. Detailed characterization of cement samples was performed using SEM&EDS and EPMA. Density, porosity and air permeability were also determined in cement samples. Complete carbonation was achieved within 28 days in poz mix and 7 days in lightweight samples, while carbonation in neat cement is limited to about 200 microns after 84 days of reaction. A carbonation zone and a porous transition zone were observed in partially carbonated samples. These reaction zones can be delineated by the elemental profiles, which show Na enrichment and Cl depletion in carbonated cement. The carbonation zone is dominated by calcium aluminosilicates. Micro-analytical techniques show that some of these phases are compositionally similar to zeolites. Calcium carbonate formed in the carbonation zone and outgrowth of well-formed crystals was also observed. Near the surface, a region leached of calcium carbonate developed. Carbonation causes very little change in both the porosity and permeability in the neat cement sample. An increase in the porosity was measured in fully carbonated poz mix cement; however, the permeability remained essentially unchanged. For the lightweight cement, the permeability increased from 0.16 to 1.1 mD after 84 days of reaction, suggesting that carbonation results in the degradation of lightweight cement under the experimental conditions. The integrity of lightweight cement could be compromised if it is in contact with a considerable volume of CO 2 -rich brine that is not previously equilibrated with carbonate minerals.

A review on cement degradation under CO 2 -rich environment of sequestration projects

“…2 due to the low quantity of CaCO3 and pozzolanic reaction of Fly Ash with portlandite. Zhang and Talman, (2014) carried out a series of experiments on three different cement samples consisting of neat class G cement, pozzolanic cement (fly ash with 2% of bentonite) and light weight sample (fly ash with 1% of sodium metasilicate). Water to bulk ratio of the first two cement samples was 0.554, while it was 1.130 for the lightweight cement.…”

Zeolite and fly ash in the composition of oil well cement: Evaluation of degradation by CO2 under geological storage condition

“…Cement pastes, class G or class H, usually used in the insulation between well drilling and steel casing should ensure complete sealing and maintain the integrity of the well structure for long periods of time to avoid CO 2 escape routes (Bai et al, 2016;Cailly et al, 2005;Scherer et al, 2005). However, class G or class H cements are chemically unstable in CO 2 -rich environments due to the occurrence of chemical reactions in which some components of the hardened cement paste react with carbonic acid causing degradation at a quite accelerated level (Abid et al, 2015;Bagheri et al, 2018;Bai et al, 2016;Barlet-Gou� edard et al, 2007;Bertos et al, 2004;Bjørge et al, 2019;Carey et al, 2010;Huet et al, 2011;Kutchko et al, 2008Kutchko et al, , 2009Lesti et al, 2013;Matteo et al, 2018;Omosebi et al, 2016;Yang et al, 2016;Zhang and Talman, 2014). Several factors influence the degradation of cement paste, such as pressure and temperature, which change with well depth.…”

“…Kutchko et al (2009) observed that despite the CO 2 penetration layer for cement with the addition of fly ash being superior when compared to cement without addition of pozzolan, the alteration of the cement properties was unexpressive. Zhang and Talman (2014) also studied the carbonation reaction of cement class G with pozzolanic material using two mixtures of cement/fly ash in saline solution with 0.5 M NaCl at 53 � C and 10 MPa, with reaction periods of 3, 7, 14, 28 and 84 days. The results of the degradation tests indicated that pozzolanic material could be useful in cement reinforcement, improving resistance to CO 2 acid attack.…”

Carbonate geochemistry and its role in geologic carbon storage

“…When exposed to CO 2 -rich environments, pozzolanic cements do not react to the characteristic orange layer reaction front consistently observed on pristine cements [157,168]. They tend to uniformly carbonate and at higher rates than pristine cement [169,170]. This behaviour has been attributed to a higher penetration rate of the CO 2 into the pozzolanic cements [149], and to the lower content of portlandite limiting the carbonation reactions.…”

“…Despite such differences, pozzolanic cements appear to conserve permeability below 200 μD, as recommended by the American Petroleum Institute. Only in Zhang and Talman [170] did a lightweight cement rapidly increased its permeability up to 1000 μD. Overall, pozzolanic cements are more rapidly carbonated, which might indicate a lower resistance to chemical aggression compared to pristine cement.…”