The impact of boundary conditions on CO2 storage capacity estimation in aquifers

The boundary conditions of a proposed CO2 storage reservoir form a key parameter for capacity estimation, in both static and dynamic calculations. Common static methods in use represent end-members - open or entirely closed aquifers. Although static methods can semi-quantitatively estimate capacities (i.e. higher in open systems vs. closed) they do not account for a heterogeneous pressure distribution, which may be a limiting factor in exploitable storage resource. Dynamic flow simulations can account for higher near-well pressures, and when pressure is considered as a percentage of the fracture pressure, the particular susceptibility of shallow structures to pressure build-up is highlighted. Furthermore, dynamic simulations allow for the construction of more realistic geological models, such as very large aquifers, reservoirs with discontinuous boundaries, and low permeability (as opposed to impermeable) boundaries and seals. Application of these techniques to a case study region of the Bunter Sandstone indicates that the closed system assumption is highly conservative, and that at regional scales, heterogeneous caprocks and discontinuous boundaries allow aquifers to behave more like an open system. (C) 2011 Published by Elsevier Ltd.