Hysteretic enhancement of carbon dioxide trapping in deep aquifers

The sequestration of supercritical carbon dioxide in saline aquifers has been proposed to mitigate global climate change. An important issue is whether it escapes to the atmosphere: chemical retention, for instance, is permanent in well chosen aquifers. The effects of chemical reactions may take time, so one needs short-term containment techniques such as CO2 capillary retention enhanced by permeability hysteresis during water imbibition. This retention is predicted in a class of permeability models for the capillary-dominated regime. Here, we use high-quality laboratory-measured permeabilities as well as exact analytic solutions and accurate simulation techniques to quantify the amount of carbon dioxide that can be trapped. This study on one-dimensional, vertically upward flow demonstrates that under ideal conditions, all of the carbon dioxide is immobilized permanently. This is achieved by a trapping shock due to switching under hysteresis from CO2 to chase-brine injection. This shock is peculiar: it possesses a very small amplitude but a large speed, making it difficult to simulate and detect.