Effects of thermal shocks on integrity of existing and newly-designed sealants for CCS applications

Abstract

Sealants that can guarantee long-term wellbore sealing integrity are of great significance to the safe and sustainable storage of CO2 in carbon capture and storage (CCS). In this study, we investigate how abrupt cyclic thermal shocks affect the integrity of four sealants of different compositions. These sealants include two reference OPC-based blends (S1 and S2), one newly-designed OPC-based blend that contains CO2-sequestering additives (S3), and one calcium aluminate cement (CAC)-based blend designed for CCS applications (S4). We have measured the thermal properties of these samples, followed by quenching and flow-through experiments to apply strong cyclic thermal shocks on samples of the four sealants, where we heated the samples to 120 °C, and quenched them in, or flowed through water of 20 °C. Using X-ray tomography (32 µm/voxel) before and after the experiment showed that both S1, S2 (reference OPC-based) and S4 (CAC-based) broke after thermal-shocking experiments. Cracks and new voids developed in the samples. Post-treatment strength testing shows that thermal shocks reduce the unconfined compressive strength of these three sealants. This implies that these compositions may not be optimal materials for long-term wellbore sealing during CO2 injection and storage afterward. For all these three sealant compositions, quenching resulted in a greater reduction in strength (by 53 % on average) than flow-through experiments (by 29 % on average). On the contrary, we have not observed any cracks after either quenching or flow-through experiments in S3 sealant (OPC with CO2-sequestering additives). We attribute the intactness of this sealant after thermal shocks to its higher thermal diffusivity than the other three sealants. Heat transfers more rapidly in this sealant and the associated thermal stresses are mild and insufficient to cause any damage to its integrity, which makes this sealant a good candidate for wellbore sealing material that can effectively withstand strong thermal shocks encountered during CCS, though further studies are required.