Microstructural modeling on cement mechanical properties under carbonation reactions and its implications to well integrity

CO 2 geological storage involves the CO 2 injection into subsurface reservoirs through wells. Cementing is a critical component of well construction and is necessary for mechanical integrity as well as hydraulic sealing of wells. The injected CO 2 can react with the hydrated materials in the cementing. This chemical process, often called carbonation reactions, can have a significant impact on the microstructure, mechanical properties and durability of the well cementing. However, there is no published work that focuses on the changes in the microstructure and mechanical properties of cement caused by carbonation reactions and its implications to well integrity at a large scale. This study aims to solve this multiscale challenge of well integrity during CO 2 geological storage. First, an image processing technique was developed to capture the changes in cement 3D microstructure due to carbonation and bicarbonation processes. Second, we perform simulation steps to calculate the cement mechanical properties under various levels of carbonation reactions and validate the simulation results with laboratory experiments. The simulation results show that carbonation and bicarbonation processes lead to a non-trivial evolution of the constitutive relationship. Third, the microstructure simulation provides input to a multistage finite element model to evaluate the well stability. The results indicate that the carbonation process can adversely impact the well stability as it may induce tensile failure and damage to the cement. This work shows that advanced numerical models are powerful tools to ensure the cement integrity of CO 2 storage projects.