Theoretical Test Case of the Injection of 100,000 t of CO₂ into the Altmark Depleted Gas Field

Abstract

CLEAN was a scientific programme in support of a pilot Enhanced Gas Recovery (EGR) project and it was planned to inject nearly 100,000 t of carbon dioxide (CO₂) into the Altmark natural gas field. Due to delays in the permitting process, injection did not occur within the time frame of the project. Therefore a test case was studied of the theoretical injection of CO₂.

Modelling CO₂ injection in the Altensalzwedel segment of the Altmark depleted gas field shows that effective injection can be carried out at a tubing head pressure as low as 3.5 MPa and at tubing head temperature of 10 °C.

The history matching of the simulation model and the injection prediction were successfully conducted with a volume ratio of injected CO₂ to the gas in place of approximately 0.06 which did not show any enhancement in the gas recovery (no EGR effect). Within the pilot project period of 2 years there would be no CO₂ arrival at the production well located at about 1,600 m from the injector. Penetration of the CO₂ into the reservoir was maximum approximately 800 m and minimum around 250 m depending on the permeability of the formation layer. The gas mixing zone reaches the observation well which is located at about 660 m from the injector already before 1 year of injection.

Under the simulated conditions direct monitoring of the CO₂ front with active seismic measurements will not be feasible as the reservoir layers are too thin and the effects of CO₂ gas replacing reservoir gas are too small. Seismic monitoring has to concentrate on the detection of possible leakages in shallower aquifers where larger velocity and density changes would occur.