Modelling Carbon Dioxide Sequestration in Geological Formations
Overwhelming scientific evidence suggests that climate change is an unequivocal reality which could pose a serious global threat (IPCC, 2001 & Stern, 2006). This demands an urgent global response in implementing a portfolio of climate change mitigation options. Although a wide range of mitigation options exist, some possess less risk and technical potential than others. Carbon dioxide capture and storage (CCS) in geological media is a supply-side approach to addressing the climate change problem that has been surrounded by concerns over security of storage since its inception.
In order for geological storage of CO2 to become accepted as an effective climate change mitigation option, the mechanisms and physics associated with flows governing the long term distribution of immiscible CO2 within the subsurface should be understood. Thus we develop a model to describe gravity driven flow within homogenous permeable layers which possess distinct density contrasts. This is an analogue to post injection migration of supercritical CO2 within formations possessing oil and formation water or gas and formation water.
A simplified analytical solution which ignores viscosity contrasts and assumes a homogenous, isotropic formation was developed. Some new laboratory experiments utilizing a Hele-Shaw cell were also conducted, in order to test the theoretical model. The laboratory experiments were performed with and without the inclusion of porous media for different density ratios and height variations. The model predictions were found to be consistent with the self similar analytical solutions under symmetrical conditions.
In concluding, we briefly consider how these results can be applied to characteristics plots which explore the self-similar dynamics of supercritical CO2 migration within oil and gas reservoirs, over timescales of 10-1000 years subsequent to injection. These plots form a simplified computational tool which can be utilized in the initial appraisal stages of potential geological storage sites.