Gazonośność złoża węgla kamiennego Łęczna w Lubelskim Zagłębiu Węglowym

Andrzej Różkowski, Marek Sosnowski




The paper deals with the results of the research on gas content of the hard coal deposit situated in the region of Łęczna, within the central part of the Lublin Coal Basin. The research has been made by direct and indirect methods in bore holes. The studies comprised also a wide range of laboratory examinations.
The direct methods comprised: 1 – logging using drill mud methanometer, 2 – sampling using gas-tight sampler GC-1 and Johnstone's sampler, 3 – sampling coal seams and degassing in laboratories. The indirect methods concerned a complex of logging measuring methods. The examination of reservoir properties of rocks have been made in the laboratories.
The deposit series of the mine field Łęczna is related to the Westphalian formations developed the in the claystone-siltstone-sandstone facies. The overburden of the deposit consists of a 700 m thick complex .of carbonate rocks, Jurassic and Cretaceous in age.
The results of the logging measurements and of the gas logging have proved the lack of gas in the Mesozoic formations. This phenomenon is emphasized also by the values of characteristic hydrochemical coefficients.
The gas content of the Carboniferous has been explained in the section of the Westphalian and of the underlying Namurian deposits. Sandstones and siltstones are here the potential water-gas reservoirs of the productive Carboniferous. In the Westphalian formations their thickness ranges from 0,2 to 15,0 m. Effective porosity of the sandstones is from 5,65 to 20,20%, 9,2% on the average. Permeability of these rocks ranges from 0,063 to 326 mdc, mainly, however, it does not exceed several mdc. The Namurian formations underlying the deposit series are characterized by considerably better parameters.
The complex research works did not demonstrate the presence of free gas in the section of the deposit series. Methane zone has been observed to occur below, within the Namurian formations.
The results of the degassing process of coals from the Westphalian and Namurian formations have proved the occurrence of the sorbed gas – methane.
Analysing the gas content of the coal seams in the deposit series we can observe the following regularities: almost all the seams are gaseous; maximum gas content is related to the strongly carbonized seams of coal of type 34; and gas content increases with the depth.
The gas content of coals (determined in m3 of CH4/ton of pure carbon substance) ranges from 0,128 to 2,58. According to the obligatory regulations this gas content corresponds to the I and II categories of gas danger. Gas found to occur in the Westphalian formations originated due to the coalification and metamorphism of organic substance. Additional research of the gas content of this deposit is required, particularly as concerns quantitative relations.


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