Performance of lightweight cement pastes under CO2 storage conditions

CHRISTIAN MARCELO MARTIN; TERESA M. PIQUE; JEAN MICHEL PEREIRA; DIEGO GUILLERMO MANZANAL

Lyon

Conferencia; 16th International Conference on Greenhouse Gas Control Technologies GHGT-16; 2022

The deployment of CO2 underground storage is advancing fast, and the technology previously used to inject and extract different fluids to or from the formations should be evaluated considering the presence of this fluid in a supercritical state. For underground CO2 storage, injection wells are cemented to isolate formations and protect the casing, using cement paste to fill the annular space between the casing and the borehole. Before hardening, the paste exerts pressure on the formations proportional to its specific weight, which cannot be higher than the formation's fracture gradient nor lower than its pore pressure. Therefore, the weight of the cementing pastes must be constantly controlled. As a solution for lowering pastes' density without compromising their mechanical properties, the addition of hollow glass microspheres (HGMS) has been considered. These consist of low-density micrometric hollow spheres with high crush strength. HGMS have been widely used for cementing underground wells. Nevertheless, the durability of the cement paste admixed with hollow glass microspheres has not been studied under a supercritical CO2 saturated atmosphere. The cement sheath must grant isolation of the formation throughout the CO2 storage project; therefore, its durability should be granted.In this work, we intend to study the performance of cement pastes lightened with HGMS to determine whether their properties would be affected when in contact with supercritical CO2. For this purpose, it is important to assess the interaction between HGMS and cement paste to determine its initial properties. In previous research, the chemical and mechanical interactions between these two materials were already studied, confirming their compatibility and the development of a chemical reaction between the HGMS and the cement paste. Consequently, HGMS modified the composition of cement paste, particularly the amount of calcium hydroxide and calcium silicate hydrate. In addition, in the presence of supercritical CO2, the cement paste undergoes specific changes in its chemical composition, which are also related to the dissolution of calcium hydroxide and calcium silicate hydrate. Research has already been carried out to understand the implications of this exposure, verifying the effect on the physicochemical properties of cement pastes. As carbonation progresses, variations in the physical and chemical properties of the cement can be seen.Nevertheless, the interaction between a cement paste lightened with HGMS and supercritical CO2 has not been evaluated yet. To this end, cement pastes with and without HGMS were subjected to a carbon dioxide-saturated atmosphere under 20 MPa and 90ºC for 60 days. The pastes' chemical composition and compressive strength were measured before and after the carbonation. Furthermore, the carbonation front was visually determined using microscopy images.It was determined that adding HGMS to the cement pastes affects the carbonation mechanisms of cement pastes. The presence of HGMS noticeably modified both chemical and mechanical properties of cement pastes under a supercritical CO2 atmosphere, even the advancement of the carbonation front was modified by its addition. These observations could be related to the chemical interaction between HGMS and cement paste, which, in the presence of supercritical CO2, eases the advancement of the carbonation front and the induced effects on pastes' properties given the unconnected porous structure provided by the hollow spheres. Therefore, special attention should be paid when cementing CO2 injection wells with lightened admixtures that can react with cement hydration products.