Gels for CO₂ geo-storage and conformance control: A systemic review of behavior and performance

Carbon capture and storage (CCS) remains one of the most feasible techniques for the control of Greenhouse gas emission levels. However, there will always be risks attached to the subsurface injection of CO₂. These could be in the form of leakages from the injection wellbore due to completion failure; escape of the injected CO₂ to neighboring aquifers due to the heterogeneous or fractured nature of the storage site; or seepage at the surface due to inadequacy of the sealing cap rock. While all these may occur, the most cost-effective and timely way to reduce the risk of leakages is by plugging the pathways. This is done using either traditional Cementous materials or more augmented sealants like organic gels and resins. A lot of studies in the literature have described this collection of materials within the context of CO₂ conformance control. So also, there are reviews on the classification and description of these chemicals. This review provides a more systemic evaluation of these classes of chemicals. This is by providing critical analyses of how external factors like CO₂, pH, brine salinity and hardness, rock mineralogy, pressure, temperature, and injectivity could affect the performance of different sealants that can be utilized. Based on these assessments, best practices for the application of the sealants, both at the testing stage in the laboratory and the pilot stage and field deployment, are suggested.