Determination of the CO2 storage capacity of the Utsira formation

Abstract

Abstract As the storage capacity especially in the shallower region is critically dependent on the phase behaviour of CO2 a modelling of the geothermal gradient with emphasis on the Miocene and Pliocene strata where CO2 may accumulate was performed. The geothermal model included the transient temperature changes due the long glacial cycles because they have a penetration depth that affects the Utsira formation. The results showed that CO2 can be stored in dense phase up to a depth of approximately 500 m below mean sea level (MSL) which is significantly shallower than previously suggested. If a significant fraction of any closed aquifer shall be utilised for storage the pressure has to be controlled by production of water out of the aquifer to avoid pressure build up that could jeopardize the integrity of the sealing rock. The storage capacity of the Utsira formation was studied both by static volume estimates and by reservoir simulation of injection with up to 210 injection wells distributed over the whole formation. In simulation of several 300 years injection scenarios it was demonstrated that 7% of the pore volume corresponding 40 Gtonne (Gt) CO2, could be utilised for storage while pressure control and CO2 break-through control in the production wells was observed. The optimal filling will depend of the number of wells and is accordingly a result of an economic optimisation. The simulation results indicate that a cost effective utilisation of the reservoir could be in the range of 20 to 60 Gt.