Exploration of CO2-Sensitive Chemicals as Potential Sealing Agents for Subsurface CO2 Storage

Abstract

Pre-existing and induced leakage pathways in subsurface CO2 storage reservoirs pose a threat to long-term CO2 storage. A potential preventative solution to CO2 escape is the use of CO2-sensitive chemicals. These chemicals change from liquid to solid or solid-like state upon contact with CO2, and create an in-situ barrier to flow. This study explores CO2-sensitive materials and the mechanisms by which they can seal the leakage routes in subsurface CO2 storage sites. In this article we surveyed a wide range of reactions that are influenced or triggered by CO2, whose products may potentially seal geological formations. We classified these reactions based on their sealing mechanisms into two categories. First group of reactions produce solids or gels, which completely fill the pore space and plug the hosting porous/fractured medium. Second group of reactions involves suspensions of CO2-sensitive particles. These particles may grow or aggregate upon contact with CO2, and eventually block the hosting pores/fractures. CO 2 triggers gelation through various mechanisms. It is known to crosslink molecules with amino groups on their side chains, even at high pressures and temperatures. At room temperature, CO2 triggers the gelation of aliphatic amines. Furthermore, CO2 triggers other gelation reactions by creating an acidic environment or decreasing the solubility of water-soluble polymers. The other sealing mechanism induced by CO2 is salt precipitation. Solid formation through this mechanism is the result of mineral carbonation and eventual formation of insoluble salts. The third mechanism of solid formation is resin solidification after the initial aqueous compound is exposed to high concentrations of CO2. Finally, some polymeric particles swell or aggregate upon contact with CO2. As these particles grow in size due to the aforementioned mechanisms, they block the flow pathways inside the pores and fractures. This study provides a list of candidate chemicals that may be used as preventative sealing agents in subsurface CO2 reservoirs. It also highlights their limitations and the lack of knowledge on their performance in terms of reaction viability and seal stability and durability at elevated temperatures, pressures, and salinities.