Geological Storage of CO₂ to Reduce Greenhouse Gases

With heightened concerns on CO₂ emissions from pulverized-coal power plants, there has been major emphasis in recent years on the development of safe and economical Geological Carbon Sequestration (GCS) technology for mitigation of Greenhouse Gases (GHG) and carbon footprint. Although being one of the most promising technologies to address global-warming due to anthropogenic CO₂ emissions, the detailed multiphase fluid dynamics and processes of GCS are not fully understood because various mechanisms of GCS have large variations in spatial scales from nanometers to hundreds of kilometers and in temporal scales from milliseconds to hundreds of years. As a result, there remain many uncertainties in determining the sequestration capacity of the formation/reservoir and the safety of sequestered CO₂ due to leakage. These uncertainties arise due to lack of information about the detailed interior geometry of the formation and the heterogeneity in its geological properties such as permeability and porosity which influence the sequestration capacity and plume migration. Furthermore, the sequestration efficiency is highly dependent on the CO₂ injection strategy which includes injection rate, injection pressure, type of injection well employed and its orientation etc. The goal of GCS is to maximize the sequestration capacity and minimize the plume migration by optimizing the GCS operation before proceeding with its large-scale deployment. In this paper, first the basic fluid dynamics and trapping mechanisms for CO₂ sequestration are briefly discussed including the spatial and temporal scales at which various mechanisms occur. Then a couple of examples of numerical simulations of industrial scale projects are presented to demonstrate the ability of currently available simulation codes to provide reasonable estimates of the plume migration in a reservoir.