Vertical Equilibrium Models with Variable Density for CO2 Sequestration

In geological sequestration of CO2, computer simulations are used to understand and analyse the injection and storage processes. There is a particular interest in developing simplified modelling tools specifically adapted to model and analyse CO2 storage scenarios. One family of such models is based on the assumption of vertical equilibrium (VE), which considerably reduces computational requirements compared with conventional approaches. The use of such models for large-scale simulation of CO2 storage has been investigated in recent years. So far, most work on VE models for CO2 storage has either assumed incompressible CO2, or only considered lateral variations in CO2 density. In our present work, we have extended the VE framework to permit the full modelling of CO2 compressibility in the VE setting, including vertical density changes. We have: * Derived the upscaled VE equations with compressibility, and investigated the resulting effects; * quantifid the importance of such effects depending on local temperature and pressure conditions; * compared different models (incompressible, laterally compressible and fully compressible) in the simulation of some sample scenarios. * Discussed practical computational aspects and proposed some quick approximations.