Evaluation of CO2 attack in wellbore class G cement: influence of epoxy resins, composites and minerals as additives

Carbon dioxide (CO2) injection into geological formations is pointed out as one of the most effective alternatives to reduce anthropogenic CO2 emissions to the atmosphere. To promote long‐term CO2 storage, wellbore integrity is a critical issue to be considered. Portland cement is commonly used for cementing wells, and considered chemically unstable in CO2‐rich media. In this context, this study investigated the CO2 chemical resistance of class G Portland cement modified with novel additives (epoxy resins, epoxy–clay composites, and clay minerals) at 1 and 2.5 wt% contents. Reaction times of 7 and 30 days of exposure to CO2 in supercritical conditions were evaluated. Samples were characterized by mechanical compression tests and phenolphthalein indicator as well as field emission scanning electron microscopy in order to determine the depth of carbonation in cement. Our results indicate that although there is slight reduction in the initial compressive strength, the addition of tested additives to cement paste offers improvements in terms of chemical resistance. The optimum content of different additives was 1 wt% in order to maintain compressive strength properties and improve chemical resistance to CO2. The best result was achieved with an epoxy resin blend as an additive, decreasing carbonation by up to 60% (7 days of exposure to CO2) and 52% (30 days of exposure to CO2). Addition of montmorillonite to the epoxy blend tends to improve chemical resistance of cement paste when compared to the neat epoxy blend. © 2019 Society of Chemical Industry and John Wiley & Sons, Ltd.