Abstract
Geologic storage of carbon dioxide (CO2) is considered a viable strategy for significantly reducing anthropogenic CO2 emissions into the atmosphere; however, understanding the flow mechanisms in various geological formations is essential for safe storage using this technique. This study presents, for the first time, a two-phase (CO2 and brine) flow visualization under reservoir conditions (10 MPa, 50 °C) for a highly heterogeneous conglomerate core obtained from a real CO2 storage site. Rock heterogeneity and the porosity variation characteristics were evaluated using X-ray computed tomography (CT). Multiphase flow tests with an in-situ imaging technology revealed three distinct CO2 saturation distributions (from homogeneous to non-uniform) dependent on compositional complexity. Dense discontinuity networks within clasts provided well-connected pathways for CO2 flow, potentially helping to reduce overpressure. Two flow tests, one under capillary-dominated conditions and the other in a transition regime between the capillary and viscous limits, indicated that greater injection rates (potential causes of reservoir overpressure) could be significantly reduced without substantially altering the total stored CO2 mass. Finally, the capillary storage capacity of the reservoir was calculated. Capacity ranged between 0.5 and 4.5%, depending on the initial CO2 saturation.
Highlights
Geologic storage of carbon dioxide (CO2) is considered a viable strategy for significantly reducing anthropogenic CO2 emissions into the atmosphere; understanding the flow mechanisms in various geological formations is essential for safe storage using this technique
This study presents, for the first time, a two-phase flow visualization under reservoir conditions for a highly heterogeneous conglomerate core that has been obtained from the real CO2 storage site
In South Korea, a conglomerate formation is being tested for geologic CO2 storage
Summary
Geologic storage of carbon dioxide (CO2) is considered a viable strategy for significantly reducing anthropogenic CO2 emissions into the atmosphere; understanding the flow mechanisms in various geological formations is essential for safe storage using this technique. Released carbon dioxide (CO2) is considered to be a major deriver behind climate change, and as such geologic CO2 storage is considered a key technology in climate change mitigation strategies[1,2] Both industry and research communities are currently evaluating the safety and feasibility of long-term CO2 sequestration, and a number of pilot- and demonstration-scale projects have been conducted as a part of this effort to test, monitor, and verify technologies in various subsurface geological environments[3,4,5]. Previous research related to geologic CO2 storage has until now focused on evaluating sandstone formations, as their relatively high porosity and permeability suggest greater economic viability than other rock formations For this reason, the reservoir lithology of most pilot-scale (e.g., Frio, Nagaoka, Ketzin and Otway) and demonstration- or commercial-scale projects (e.g., MGSC Decatur, Sleipner, Snøhvit, In Sala and Gorgon) has been sandstone[3,5]. This plot reveals the injectivity at Janggi falls between 0.1 and 1 darcy-meter, similar to the estimated injectivities at the Nagaoka and In Salah sites
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