Coal gas outbursts (especially CO2) present a high risk in mining of lignite in the Velenje Coal Mine, located in the Velenje Basin in northern Slovenia. A programme of monitoring geochemical parameters was set up to help understand the behaviour of the coalbed gas distribution in advance of the working face using mass spectrometric methods to study its composition and origin. Coalbed gas samples from four different excavation fields (G2/C and K.-130/A from the north and south Preloge mining area and K.-5/A and K.-50/C from the Pesje mining area), which were operational between the years 2010 and 2011 were investigated. The major gas components are CO2 and methane. Temporal changes in chemical and isotopic composition of free seam gases were observed within boreholes as a function of the advancement of the working face. The study also revealed that at a distance of around 120 m from the working face, the influence of coal exploitation by the Velenje Longwall Mining Method causes coalbed gas to migrate. At a distance of 70 m the lignite structure is crushed causing desorption of fixed CO2 from the coal. Differences in coalbed gas composition at the longwall panels which underlie the unmined area or under previously mined areas were found. A high CDMI index with values up to 95.6% was typical for areas of pre-mined excavation fields (South Preloge K.-130/A and Pesje area K.-5/A), while in excavation fields with no previous mining activity (North Preloge G2/C and Pesje area K.-50/C) up to 61.9 vol % of CH4 was detected. The concentration measurements and isotopic studies revealed endogenic CO2 (including CO2 originating from dissolution of carbonates) with d13CCO2 values ranging from -7.0‰ to 5.5‰, microbial methane and CO2 with values ranging from -70.4‰ to -50‰ for methane and from -11.0‰ to -7.0‰ for CO2. Higher d13CCH4 values ranging from -50‰ to -19.8‰ could be attributed to so -called secondary processes influencing the d13CCH4 value, such as migration due to lignite excavation (escape of isotopically lighter methane ). In excavation fields (G2/C and K.-50/C) with no-premining activity higher d13CCH4 could also be explained by migration of methane from deeper strata. The d13CCH4 value also depended on the depth of the excavation field; at shallower levels of the excavation field (K.-5/A) lower d13CCH4 was traced indicating microbial gas, while at deeper levels higher d13CCH4 values were found.
B.03 Paper at an international scientific conferenceCOBISS.SI-ID: 26647335
In the contribution is explained that coal rema the most important enery source of 21. century as well as the most important energent in Slovenia.
B.03 Paper at an international scientific conferenceCOBISS.SI-ID: 9002663
In report we present concentrations (CO2, CH4, N2, Ar) and isotopic composition of carbon in carbon dioxide and methane at excavation fields Preloge and Pesje. Measured parameters were determined with methods of mass spectrometry and isotope mass spectrometry and represent the basis for improvement the database and further interpretation of coalbed gases at excavation fields.
F.16 Improvements to an existing information system/databasesCOBISS.SI-ID: 26988071