Scaling behavior of convective mixing, with application to geological storage of CO₂

CO 2 storage in deep saline aquifers is considered a possible option for mitigation of greenhouse gas emissions from anthropogenic sources. Understanding of the underlying mechanisms, such as convective mixing, that affect the long‐term fate of the injected CO 2 in deep saline aquifers, is of prime importance. We present scaling analysis of the convective mixing of CO 2 in saline aquifers based on direct numerical simulations. The convective mixing of CO 2 in aquifers is studied, and three mixing periods are identified. It is found that, for Rayleigh numbers less than 600, mixing can be approximated by a scaling relationship for the Sherwood number, which is proportional to Ra 1/2 . Furthermore, it is shown that the onset of natural convection follows t Dc ∼Ra −2 and the wavelengths of the initial convective instabilities are proportional to Ra. Such findings give insight into understanding the mixing mechanisms and long term fate of the injected CO 2 for large scale geological sequestration in deep saline aquifers. In addition, a criterion is developed that provides the appropriate numerical mesh resolution required for accurate modeling of convective mixing of CO 2 in deep saline aquifers.