Experimental Study of Stability and Integrity of Cement in Wellbores Used for CO2 Storage

This paper examines the results obtained from several sets of experimental work conducted on cement deterioration in environments similar to those found in CO2 injection and storage projects. In order to investigate various changes in macroscopic and microscopic properties and behaviour of cement in presence of sulphate ions and CO2, several sets of experiments were conducted. The study consisted of preparing and investigating the behaviour of several hundred samples of cement in presence of various concentrations of sulphate, from 0.1 wt% up to 6%, as well as CO2 at 15,160 kPa and 55 degrees C. The effect of sulphate ions on cement was studied at 30 degrees C, 55 degrees C and 75 degrees C. The two common classes of cement of Type 10 and Class G were tested during this study. A total of 300 identical cubic and 400 identical cylindrical samples were tested. The change in permeability, compressive strength, and shear and hydraulic bonding strength for these samples were monitored after 2, 4, 6, 8, 10 and 12 months. Laboratory results showed that sulphate ions and CO2 improve the performance of cement during the first few months. However, the effect is reversed under prolonged experiments. The highest reduction in performance was observed for hydraulic shear bonding, which indicates that the highest risk of CO2 leakage is through pathways between the cement and casing.