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EN
During drilling wellbores from the surface to recover methane from post-extraction gobs, attention should be paid to using appropriate rigs. Rigs with optimum technological parameters, adjusted to the geological setting, design of wellbore and technology of drilling, allow for high drilling rates and a considerably lower cost of realization to be obtained. The rig to be used for drilling production wells can be correctly selected using the multicriteria optimization method with synthetic evaluation measure of its technological parameters. For this purpose, the technological parameters of rigs available on the Polish market for the realization of normal diameter wells with percussion-rotary method to a depth of 500 m and 1000 m were reviewed. Taking into account the geological build of the Upper Silesian area and the design of the producing well used for the production of methane from past-extraction gobs, eight evaluation criteria and their weights (W) were selected. On this basis the technical parameters of rigs to be used for drilling wells to a depth of 500 m and 1000 m were reviewed with the multicriteria method. This created the basis for selecting dedicated rigs with optimum technological parameters for drilling normal diameter wells to a depth of 500 m and 1000 m.
EN
Lignite opencast extraction can be performed after prior dewatering of the rock mass. Most frequently it is realized with large-diameter dewatering wells which have been mostly drilled with the invert mud rotary method and airlift. This method allows for quick drilling in lithologically diversifi ed aquifers, minimizing the negative impact of mud on the near-well zone. When drilling in dewatered carbonate rocks with the stone runs or well developed karst the effi ciency of this method considerably decreases. The technical and technological aspects of use of downhole hammers for drilling large-diameter dewatering wells in diffi cult geological conditions are discussed in the paper. Thanksto the use of this method for drilling wells in ‘Bełchatów’ Lignite Mine the drilling rate could be increased and the number of complications and drilling failures lowered.
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