oa Development of Storage Coefficients for Carbon Dioxide Storage in Deep Saline Formations

The aim of this study was to define a series of storage coefficients, which can be applied to regional calculations to provide more realistic estimates. Coefficients were considered and derived principally for Deep Saline Formations (DSF), reflecting the large storage potential but associated inherent complexity and uncertainty. <br> The study has successfully built upon earlier work by both the CSLF and US DOE, confirming the similarities of the two methodologies and more importantly, establishing an ease of comparison of storage coefficients employed and resources calculated for deep saline formations. <br> Due to the limited amount of data available from real-world CO2 injection projects, focus was kept to the use of modelling simulations to derive storage coefficients. The alternative numerical modelling approach was employed with input parameters derived from global hydrocarbon reservoir data. The modelling work showed the relative influence of various parameters on the efficiency of storage, and allowed the derivation of probabilistic ranges of storage coefficients for calculation of effective storage resource at both site-specific and formation levels. <br> ‘Open’ systems form the majority cases for DSF storage and have relatively consistent geological properties and may be largely un-faulted and fluid and pressure communication across the formation will be strong. <br> However, ‘closed’ or ‘semi-closed’ systems may also exist, where lateral flow boundaries such as faults can restrict fluid movement. CO2 injection would result in pressure increase, limiting effective storage capacity to the volume created by both the compressibility of the formation and existing pore fluids, and the limit of pressure increase before physical damage to the system. A series of equations derived from US DOE methodology; enable the storage coefficient to be defined as the fraction of total pore volume that will be accessible to CO2, based on volumetric changes caused by compressibility. <br> Heterogeneous models were developed using statistical distributions from the Average Global Database for the various lithologies, depositional environments and structures, to derive ranges of storage capacity coefficients. The resulting values for storage coefficient ranged from 4% to 17% with an 80% confidence interval. Structural setting was found the exert the largest influence of any parameter on the results, with storage coefficients for effective resource exceeding 25% in some cases. <br> The study provides a series of storage coefficients that can be used for assessment of CO2 storage resources in deep saline formations.