Abandoned Mine Methane in Germany - Gas Potential Assessment and Drilling Experiences

摘要

In the German Renewable Energy Law (EEG), coal mine methane is included giving a warranty of fixed revenues for power generated from this source of energy. The increased planning security led to the issuance of approximately 70 exploration or production licenses covering almost the entire abandoned mining area in the German Ruhr District. The first projects of Abandoned Mine Methane (AMM) production utilized already installed degasification pipes in shafts as a readily available and economical way of gas supply for the modular CHP plants. However, the number of shafts with existing installations usable for this purpose was limited and by no means sufficient to allow for an optimal exploitation of the potential of the deposit. Therefore, the option of drilling production wells into old mine workings became of interest at a fairly early stage. Due to the complexity of geological and mining related factors, the companies were faced with a number of technical problems and risks in the planning and realization of such drillholes. Since AMM wells are targeted at mine workings within the fractured and loosened rock mass and the cleated host rock, risks and costs have to be carefully considered due to the challenges resulting from drilling under these conditions.