Long‐term wellbore integrity is crucial to prevent leakage of CO2 and to ensure performance and safety of carbon geologic storage. One of the concerns is the degradation of Portland cement due to its exposure to CO2. In this study, Portland cement paste composed of three reinforced‐epoxy resins (talc, agalmatolite, and montmorillonite clay as filler) was compared to unmodified cement paste with respect to CO2 resistance. CO2 degradation experiments were conducted with aqueous CO2 at elevated pressure (50 bar) and temperature (70°C) in order to mimic wellbore conditions. Epoxy cement composites were characterized by phenolphthalein test, field emission scanning electron microscopy, Fourier transform infrared spectroscopy, and mechanical compression test. The preparation method of the composites is the parameter likely to affect the CO2 resistance than curing conditions (natural and thermal). Addition of up to 5% of montmorillonite clay reinforced‐epoxy resins provides an improvement in CO2 resistance over unmodified Portland cement paste, showing to be a promising alternative to obtain suitable materials for use in wellbores in CO2 sequestration reservoirs. POLYM. COMPOS., 39:E2234–E2244, 2018. © 2017 Society of Plastics Engineers
Carbon dioxide (CO 2 ) injection into geological formations is pointed out as one of the most effective alternatives to reduce anthropogenic CO 2 emissions to the atmosphere. To promote long-term CO 2 storage, wellbore integrity is a critical issue to be considered. Portland cement is commonly used for cementing wells, and considered chemically unstable in CO 2 -rich media. In this context, this study investigated the CO 2 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 CO 2 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 CO 2 . The best result was achieved with an epoxy resin blend as an additive, decreasing carbonation by up to 60% (7 days of exposure to CO 2 ) and 52% (30 days of exposure to CO 2 ).
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