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Abstract:
Methane (CH4) hydrates are considered as a player in the field of energy supply and – if applied as such – as a possible sink for the greenhouse gas carbon dioxide (CO2). Next to the more conventional production methods depressurization and thermal stimulation, an extraction of CH4 by means of CO2 injection is investigated. The method is based on the chemical potential gradient between the CH4 hydrate phase and the injected CO2 phase. Results from small-scale laboratory experiments on the replacement method indicate recovery ratios of up to 66% CH4 but also encounter major discrepancies in conversion rates. So far it has not been demonstrated with certainty that the process rates are sufficient for an energy and cost effective production of CH4 with a concurrent sequestration of CO2.
In a co-operation of GFZ and GEOMAR we used LARS (Large Scale Reservoir Simulator) to investigate the CO2-CH4-replacement method combined with thermal stimulation. LARS accommodates a sample volume of 210 l and allows for the simulation of in situ conditions typically found in gas hydrate reservoirs. Based on the sample size, diverse transport mechanisms could be simulated, which are assumed to significantly alter process yields. Temperature and pressure data complemented by a high resolution electrical resistivity tomography (ERT), gas
chromatography, and flow measurements serve to interpret the experiments. In two experiments 50 kg heated CO2 was injected into sediments with CH4 hydrate saturations of 50%. While
in the first experiment the CO2 was injected discontinuously in a so called “huff’n puff” manner, the second experiment saw a continuous injection. Conditions within LARS were set to 13 MPa and 8°C, which allow for stability of pure CO2 and CH4 hydrates as well as mixed hydrates. The CO2 was heated and entered the sediment sample with temperatures of approximately 30° C. In this presentation we will discuss the results from the largescale experiments and compare them with data from small-scale experiments.
