Reservoir simulation study of CO2 storage and CO2 -EGR in the Atzbach–Schwanenstadt gas field in Austria

Abstract

The Atzbach–Schwanenstadt gas field has been investigated in the CASTOR project with respect to its suitability for safe, long-term underground CO2 storage. Storage capacity of the reservoir has been estimated to 14.5 million tonnes of CO2. Potential nearby CO2 sources emit together about 300 000 tonnes of CO2 per year. Assuming that reservoir would be filled up until its initial reservoir pressure the available storage capacity would be sufficient to store all CO2 produced during the next 48 years. Results from the reservoir simulation of the storage showed that during 30 years of injection 8.2 million tonnes of CO2 could be stored. A CO2-EGR effort in the field could in theory increase gas production and therefore enlarge the available storage capacity for CO2. However, none of the conducted reservoir simulations could prove that CO2 injection would enhance gas recovery at the Atzbach–Schwanenstadt field. CO2 breakthrough to the production wells is very quick and occurs almost immediately after start of injection. The fraction of CO2 in produced gas increases rapidly and this limits production of the clean gas. Compared to the simulation with no CO2 injection, EGR cases give lower production of the clean gas. Therefore use of CO2 for the enhanced gas recovery is not recommended for the Atzbach–Schwanenstadt field. The long-term storage simulation shows that reservoir pressure stabilizes shortly after injection stops. During the period of 1500 years after the end of injection only 10% of injected CO2 will dissolve in the immobile reservoir water. In a scenario of potential leakage four abandoned wells were selected to mimic leaking wells. Simulation results show that if CO2 reaches the abandoned wells, and this would lead to leakage, as much as 5.6% of injected CO2 could escape from the reservoir during a period of 1500 years.