CO [ subscript 2 ] migration in saline aquifers . Part 2 . Capillary and solubility trapping

Article is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use. The MIT Faculty has made this article openly available. Please share how this access benefits you. Your story matters. The large-scale injection of carbon dioxide (CO 2) into saline aquifers is a promising tool for reducing atmospheric CO 2 emissions to mitigate climate change. An accurate assessment of the post-injection migration and trapping of the buoyant plume of CO 2 is essential for estimates of storage capacity and security, but these physical processes are not fully understood. In Part 1 of this series, we presented a complete solution to a theoretical model for the migration and capillary trapping of a plume of CO 2 in a confined, sloping aquifer with a natural groundwater through-flow. Here, we incorporate solubility trapping, where CO 2 from the buoyant plume dissolves into the ambient brine via convective mixing. We develop semi-analytical solutions to the model in two limiting cases: when the water beneath the plume saturates with dissolved CO 2 very slowly or very quickly ('instantaneously') relative to plume motion. We show that solubility trapping can greatly slow the speed at which the plume advances, and we derive an explicit analytical expression for the position of the nose of the plume as a function of time. We then study the competition between capillary and solubility trapping, and the impact of solubility trapping on the storage efficiency, a macroscopic measure of plume migration. We show that solubility trapping can increase the storage efficiency by several-fold, even when the fraction of CO 2 trapped by solubility trapping is small. 1. Introduction Mitigation of climate change will necessitate a reduction in atmospheric carbon dioxide (CO 2) emissions; however, electric power generation is a primary source of CO 2 emissions, and demand for electric power is expected to rise steadily for the foreseeable future. The global transition to a low-carbon energy infrastructure will take tens to hundreds of years. One promising tool for reducing CO 2 emissions during this transitional period is the large-scale injection of CO 2 into deep saline aquifers (Bachu, At typical aquifer conditions, CO 2 is less dense and less viscous than the ambient groundwater, making it buoyant and mobile. As a result, a primary concern is the