In some regions, the sedimentary basins contain deep saline formations that are highly faulted and compartmentalized, allowing for very little or no formation fluid communication with the surrounding formations. The injection volume in such compartmentalized hydrogeologic systems would be limited by the pressure buildup in the reservoir. This pressure buildup could greatly reduce the total CO2 storage resource/capacity. The effective storage resource would be limited to the volume created by the compressibility of the pores and formation fluids and the maximum pressure buildup that the formation could sustain without damage. The volume that would be available to store CO2 in this case could be expressed with the following mathematical expressions developed independently by both Zhou and others (2008) and DOE in the Carbon Sequestration Atlas II of the United States and Canada (2008).
Mathematically, compressibility (c) is defined as: