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.