Pressure-derived storage efficiency for open saline aquifer CO 2 storage

Abstract

Various approaches are used at the preliminary stage (before flow modelling studies) to evaluate the resources of saline aquifers for storing CO 2 . The two approaches used most commonly are the volumetric ‘open aquifer’ and ‘closed aquifer’ approaches, which provide the end members for the resources of a given aquifer store. We propose a novel approach based on extending the analytical aquifer methods, which have been routinely used for decades in the oil and gas industry, to CO 2 saline aquifer storage. The CO 2 storage resource is derived from the pore volume liberated by pressurization to accommodate CO 2 in the store, which is the sum of: (i) the volume of the store obtained by compression; and (ii) the volume of water outflow towards the regional aquifer. It enables the CO 2 storage resources and storage efficiencies for pressure-limited stores (meaning when the resource is not even more limited by CO 2 migration issues) to be estimated. Formalism is presented, as well as implications and limitations of the method. With this method, storage efficiencies are directly connected to closed store efficiencies that are corrected for the water outflux and pressure dissipation from the CO 2 store into the regional aquifer, reconciling the ‘closed’ and ‘open’ approaches. We present an application to the Havnsø saline aquifer structure in order to highlight the consequences of the CO 2 storage resource evaluation and also of appraisal and development phases.