PESA ETSIG/CSIRO CCS Knowledge Transfer Series: Installment 4

For the successful implementation and regulation of CO₂ geological storage operations, it is important to establish a reliable definition, classification, and estimation of storage resources.  For this purpose, the Society of Petroleum Engineers (SPE) released the CO₂ Storage Resources Management System (SRMS) following the concept of its industry-standard Petroleum Resources Management System (PRMS). The SRMS considers both technical and commercial factors and the major storage resource classes with increasing data knowledge and chance of commerciality are: Inaccessible Storage Resources, Prospective Storage Resources, Contingent Storage Resources, Capacity, and Stored. The volumetric estimation of storage resources involves the interpretation of the subsurface which has an inherent degree of uncertainty. Fundamental for elevating storage resources to a storage capacity is the evaluation of containment of the stored CO₂ and, most importantly, injectivity considerations. Here, bigger is not necessarily better. Rather the capacity of a commercial CO₂ storage operation needs to be sufficient to accept the planned volume of CO₂ with emphasis on injection efficiency, safety and economics. Hence, actual injection or formation tests and containment assessment must provide a high confidence in the commercial injectability of the characterised geologic formation. Injectivity is constrained by the allowable bottom hole pressure, which should be safely below the reservoir fracture pressure or the pressure capable to activate any faults in the vicinity of the storage complex. Storage capacity could be increased, at a cost, by managing reservoir pressure through water production wells. Other than in petroleum operations, where production wells are generally completed at the top of the reservoir for production efficiency, CO₂ injectors placed at the bottom or at the downdip portion of the storage complex may be the most efficient strategy for achieving maximum storage capacity.