Bonding performance of cement sealants designed for CCS applications

Sealant/casing bond integrity is considered an important performance characteristic of sub-sea wells repurposed for Carbon Capture and Storage (CCS) operations, yet there is still lack of general agreement on how this should be assessed. This study presents an investigation into the shear bond performance of four cementitious sealants that are intended for use in the plugging of CCS wells. To this end, a series of samples designed as miniature versions of a plugged well-bore, comprising an outer cylindrical steel casing and an internal cement plug, were configured. These sealant/steel samples were then cured at elevated temperatures and pressure to simulate subterranean conditions, before undergoing a push-out shear-bond test. Bond strength was found to be directly influenced by the type of sealant and the condition of the sealant/casing interface observed after testing. Factors affecting bond integrity are discussed for each sealant in light of the results of shear-bond and compressive strength tests, as well as the condition of the sealant/casing interface.