Enhanced Gas Recovery, Challenges Shown at the Example of three Gas Fields

Abstract

Abstract CO2-EOR has been used successfully to recover incremental oil after water flooding. In the USA, more than 260,000 bbl/d are produced by using this EOR method. CO2 Enhanced Gas Recovery (CO2-EGR) has also been proposed, however, only small scale projects have been performed until know. In this paper, the challenges of CO2-EGR are addressed at the example of three fields. The Hoeflein Field (Austria) contains gas condensate with a maximum liquid drop out of 4 %. The simulation results show that CO2 injection can recover incremental condensate. However, owing to the shape of the reservoir, CO2 will break through early. Hence, gas recovery will be reduced compared with conventional gas production. The second field which was investigated is located in Pakistan. This field is an elongated field. The production wells are distributed over the full length of the field. CO2 injection can increase recovery (0.2 % maximum) only, if the surface facilities are able to handle high CO2 contents in the produced gas (more than 50 %). The Schoenkirchen Uebertief Field (Austria) is a deep (5700 mSS), elongated structure. The production wells are located at one end of the structure. To recover incremental gas, good well placement and gas injection later in the lifetime of the field is required, about 1.5 % additional gas compared with depletion drive can be expected. The example cases of CO2-EGR show that even for almost ideal reservoir structures (elongated with wells at one end and injection at the other end), limited potential for CO2-EGR exists. To increase gas production compared with depletion, a good well placement and knowledge of the structure accordingly is required, the production facilities have to be able to handle high CO2 contents and CO2 injection should commence later in the life-time of the field to avoid trapping of hydrocarbon gas in unswept areas at high pressures.