Improving class G cement carbonation resistance for applications of geologic carbon sequestration using synthetic polypropylene fiber

Abstract

The hydrated products of Class G cement drastically change after exposure to CO2-saturated brine, compromising the cement physical properties, especially, the compressive and tensile strengths. In this study, the effect of different concentrations of the synthetic polypropylene fiber (PPF) on the cement matrix strength retrogression resistance under the carbonation process was evaluated. Four cement slurries with 0%, 0.125%, 0.25%, and 0.375% by weight of cement (BWOC) of the PPF were prepared and tested for the change in their compressive and tensile strengths and permeability after reacting with CO2-saturated 0.5 M NaCl brine at 130 °C and 10 MPa for 10 and 20 days. The results of this study revealed that incorporating 0.125% BWOC of the PPF decreased the portlandite concentration as well as considerably decreased the cement permeability, therefore, enhanced the cement carbonation resistance as indicated by the reduction in the carbonation depth and carbonation rate. Incorporation of 0.125% BWOC of PPF enhanced the strength retrogression resistance of the cement against CO2-saturated brine. After 20 days of carbonation, the compressive and tensile strengths of the cement samples incorporating 0.125% BWOC of PPF are 50.6% and 27.4% greater than the base cement, respectively. The carbonation rate inside the samples with 0.125% BWOC of the PPF is 31.0% less than that inside the base cement. Cement sample with PPF of 0.125% BWOC has the lowest permeability among all evaluated samples.