Role and impact of CO 2–rock interactions during CO 2 storage in sedimentary rocks

Abstract

Before implementing CO 2 storage on a large scale its viability regarding injectivity, containment and long-term safety for both humans and environment is crucial. Assessing CO 2–rock interactions is an important part of that as these potentially affect physical properties through highly coupled processes. Increased understanding of the physical impact of injected CO 2 during recent years including buoyancy driven two-phase flow and convective mixing elucidated potential CO 2 pathways and indicated where and when CO 2–rock interactions are potentially occurring. Several areas of interactions can be defined: (1) interactions during the injection phase and in the near well environment, (2) long-term reservoir and cap rock interactions, (3) CO 2–rock interactions along leakage pathways (well, cap rock and fault), (4) CO 2–rock interactions causing potable aquifer contamination as a consequence of leakage, (5) water–rock interactions caused by aquifer contamination through the CO 2 induced displacement of brines and finally engineered CO 2–rock interactions (6). The driving processes of CO 2–rock interactions are discussed as well as their potential impact in terms of changing physical parameters. This includes dissolution of CO 2 in brines, acid induced reactions, reactions due to brine concentration, clay desiccation, pure CO 2–rock interactions and reactions induced by other gases than CO 2. Based on each interaction environment the main aspects that are possibly affecting the safety and/or feasibility of the CO 2 storage scheme are reviewed and identified. Then the methodologies for assessing CO 2–rock interactions are discussed. High priority research topics include the impact of other gaseous compounds in the CO 2 stream on rock and cement materials, the reactivity of dry CO 2 in the absence of water, how CO 2 induced precipitation reactions affect the pore space evolution and thus the physical properties and the need for the development of coupled flow, geochemical and geomechanical models.