Analysis the Effect of Microsilica Addition on the Compressive Strength of Cement Slurry Under CO₂ Storage Well

Abstract

Ensuring long-term well integrity in CO₂ storage applications is critical to the success of CCUS projects, particularly during early cement hydration when the risk of gas migration is highest. Silica fume or microsilica is known to improve cement durability under CO₂ exposure, but its influence on early-age mechanical performance without direct CO₂ contact remains underexplored. This study evaluates the effect of microsilica additions at 3%, 6%, and 9% BWOC on the performance of Class G cement slurry, focusing on compressive strength, thickening time, fluid loss, and rheological behavior. Laboratory tests were conducted according to API RP 10B, simulating bottom-hole conditions at 60 °C for circulating and 80 °C for static. Results show that increased microsilica content enhances compressive strength from 5807 psi to 7264.5 psi and reduces thickening time from 3.52 to 2.27 hours. The 9% BWOC formulation achieved the lowest fluid loss 40 mL/30 min, highest yield point 22.03 lbf/100 ft², and improved suspension capacity, while maintaining pumpable viscosity. These improvements support better early zonal isolation and reduce the risk of gas migration. In conclusion, the 9% BWOC microsilica formulation is recommended as the optimal design for CO₂ well cementing, offering enhanced early mechanical integrity and potential long-term resistance to carbonation.