Improved carbonation resistance and durability of Saudi Class G oil well cement sheath in CO2 rich environments using laponite

Abstract

The physical properties of the oil well cement are significantly changing after reacting with CO2-saturated brine. In this study, the effect of incorporating the laponite on the properties of the Saudi Class G cement for applications of CO2 sequestration at conditions of 130 °C and 1500 psi was evaluated.Cement slurries with different laponite concentration were prepared in this work, the first slurry is the base cement which has no laponite, while other three slurries were prepared with 0.1, 0.3, and 0.5% by weigh of cement (BWOC) of the laponite. The cement samples were characterized using the X-ray diffraction analysis after cured at 75 °C for 24 h inside a water bath. After that the samples were submerged into high-pressure high-temperature reaction chamber and reacted with CO2-saturated 0.5 M NaCl brine at 130 °C and 1500 psi for 10 days. Then the change in the cement samples properties was investigated.After 10 days of carbonation, addition of 0.3% BWOC of the laponite decreased the carbonation depth by 27.0%; the micro-computerized tomography scan technique also confirmed this reduction in the carbonation depth. The compressive and tensile strengths for the samples prepared with 0.3% BWOC of the laponite were 12.5% and 20.1% greater than these for the base cement, respectively. Incorporating 0.3% of the laponite to the cement slurry maintained the matrix permeability 50.0% lower than the permeability of the sample without laponite. The ability of the laponite to reduce the portlandite concentration and the permeability of the cement considerably contributed to improve the carbonation resistance for the cement; addition of laponite also reduced calcium leaching as confirmed by the microscopic images.