Mechanisms for mechanical trapping of geologically sequestered carbon dioxide

Abstract

Carbon dioxide (CO 2 ) sequestration in subsurface reservoirs is important for limiting atmospheric CO 2 concentrations. However, a complete physical picture able to predict the structure developing within the porous medium is lacking. We investigate theoretically reactive transport in the long-time evolution of carbon in the brine–rock environment. As CO 2 is injected into a brine–rock environment, a carbonate-rich region is created amid brine. Within the carbonate-rich region minerals dissolve and migrate from regions of high-to-low concentration, along with other dissolved carbonate species. This causes mineral precipitation at the interface between the two regions. We argue that precipitation in a small layer reduces diffusivity, and eventually causes mechanical trapping of the CO 2 . Consequently, only a small fraction of the CO 2 is converted to solid mineral; the remainder either dissolves in water or is trapped in its original form. We also study the case of a pure CO 2 bubble surrounded by brine and suggest a mechanism that may lead to a carbonate-encrusted bubble owing to structural diffusion.