Abstract - Carbon dioxide sequestration in deep geological formations has been proposed as a way of reducing greenhouse gas emissions and helping to mitigate global warming. Fault rocks may affect the efficiency of the CO2 sequestration process by compartmentalizing the storage formations due to reduced permeabilities and higher capillary pressures compared to the host rocks. Previous work investigating the influence of fault rock properties on CO2 sequestration has suggested that when two-phase fault rock properties (capillary pressure and relative permeability functions) are taken into account, many more wells or much lower injection rates are required to prevent pressure during injection reaching values high enough to cause hydrofracturing and CO2 leakage, compared to models containing only single-phase fault rock properties. In the present work we present flow simulation models indicating that overpressuring of the storage formations is not solely dependent on the incorporation of two-phase fault rock properties, but is caused by the creation of a CO2 plug which eliminates the possibility of pressure equilibration across the fault in the water-leg. This plug is associated with the across-fault juxtaposition geometry and hence with the displacement of the fault and thickness of the storage aquifer. Using idealized 2D, 2-phase flow simulation models, the relationship between pressure compartmentalization, two–phase fault rock properties and fault displacement is mapped out for a particular thickness aquifer. The results provide insights into the combination of circumstances likely to result in high pressurizations during a CO2 sequestration programme.
Abstract of talk given to:
Irish Geological Research Meeting, University of Ulster, March 2013.