Limitations to Storage Pressure in Finite Saline Aquifers and the Effect of CO2 Solubility on Storage Pressure

Abstract

Abstract CO2 storage in aquifers is an attractive option for reducing CO2 emissions into the atmosphere. The successful example of CO2 storage in the Sleipner injection project proves that large volumes of CO2 can be stored in a water-bearing subsurface formation. In general, most of the injected CO2 will displace water and will accumulate as free gas at the crest of the aquifer. On the other hand, CO2 is also soluble in water. Therefore, the aquifer or depleted reservoir will eventually be saturated with CO2. The present paper explores various aspects of the solution process, based on numerical simulation studies for a Norwegian type of open aquifer storage location and other types of storage structures. The case studies indicate that only in the long term (> 1000 yrs), solubility may offer a storage mechanism for most of the CO2 stored in depleted fields. This is due to the accumulation of CO2 in the gas phase, which has a limited contact area with the water phase. However, if injection strategies focus on exposing the injected CO2 to as much "fresh water" as possible (i.e. through extended and dispersed migration paths) the amount of CO2 in the free gas phase can be reduced significantly and within a shorter time. It is commonly believed that all CO2 will eventually disappear because it will dissolve in water. We agree with the fact that all CO2 will dissolve if there is enough water, but when a lot of material (CO2) is added to the system, this will affect fluid volumes and pressures in the total storage system. By studying a practical, real storage location, we try to find out some of the pressure effects of CO2 solubility on the total storage capacity of the selected storage site.