Geological setting, occurrences, extent, quality and reserves of coal seams in the Mura Formation of the Mura-Zala Basin in NE Slovenia are presented in the paper. The Mura-Zala Basin consists of antiforms and sinforms bounded by normal and reverse faults. It is filled in its deepest parts by more than 4000 m of clastic sediments from the late lower Miocene upwards. It represents one of the western basins of the Pannonian Basin System. The coal-bearing Mura Formation is of the Pontian age. It is more than 1000 m thick and consists of marls, silts and sands, and of numerous (10–30) beds of brown coal which are relatively thin. The coal-bearing depositional system is clearly paralic. Original peat-lands developed in freshwater environments while bulk sedimentation in-between (according to paleontological investigations of the Ostracoda microfauna) took place under influence of brackish waters. Well ascertained coal beds are only those in a restricted area (ca. 60 km2) between Lendava (Slovenia) and Mursko Središće (Croatia), where the coal beds dip almost from the surface (under 10–20 m of Quaternary gravel) downwards to depths of not more than 400 m. The whole coal-bearing bed-set in the Lendava area is about 130 m thick but contains only three coal seams which are generally 1.0–2.2 m thick. At the “as received basis” (25–30 % moisture content, 15–20 % ash yield), the net calorific value of the Lendava coal reaches ca. 14.5 MJ/kg, and the average sulphur content is ca. 1.6 %. The Mursko Središće coal is of a similar quality. Tectonic structure of coal beds is simple and uniform. In the Ormož-Selnica Antiform (which continues to the Budafa – Lovászi Antiform in Hungary), strata inclination follows gentle flanks of this antiform and similar is true for other sinforms and antiforms throughout the Mura-Zala Basin. Coal beds in the broader area of NE Slovenia (ca 1000 km2) are not explored enough. They were encountered by almost all deep oil, gas, and hydrogeological wells but these wells were not core-drilled. The existing data are originating only from master-logs and geophysical logs, by which, coal thicknesses are most probably exaggerated – telling us about thicknesses of single coal beds of 4 metres and even more. Therefore, realistically speaking, if analogy with the Lendava coal-bearing area is taken into consideration, and taking into account that the coal seams thicker than 1 m are in total 5 m thick, than the total coal resources (at the 1.3 t/m3 density) in the entire NE Slovenia amount to around 6500 Mt. In terms of energy, at calorific value of coal of 14.5 MJ/kg, it represents nearly 1014 MJ of energy stored.
COBISS.SI-ID: 1916245
During excavation of lignite in the Velenje Coal Mine coalmine, seam problems with gas outbursts occur. Geochemical investigations are designed to help predict, prevent, and manage coal mine gas outbursts and to study their origin and mechanisms. However, geochemical studies of the coalbed gases in the Velenje basin have been initiated since year 2000. Temporal changes in chemical and isotopic composition of “free” seam gases were observed as a function of the advancement of the working face –120/B, G2/C and –50/B within boreholes jpk-28/10, jpk-30/10, jpk-31/10, jpk-22/09 and jpk- 23/09. Mass spectrometry and isotope mass spectrometry methods were used to determine gas composition and perform gas characterization. Coalbed gases in the Velenje basin are highly variable in both their concentrations and stable isotope composition. Major gas components are CO2 and methane. Concentrations and isotopic studies revealed several genetic types of coalbed gases: endogenic CO2 (including CO2 originating from dissolution of carbonates), microbial methane and CO2.
COBISS.SI-ID: 25317159
Laboratory study of adsorption-desorption characteristics of various lignite lithotypes is very important for prevention of coal dust and gas outbursts that represent a dangerous and unpredictable phenomenon in underground mining of the Velenje lignite. The performed study consists of adsorption investigations carried out in the geotechnical laboratory of the Velenje Coal Mine (VCM). Lignite samples contained in the reaction cell were exposed for a limited time to a gas pressure of up to 100 bar. The measurements were performed on an updated instrument according to the improved volumetric gas sampling method. The gas was sampled from the reaction cell during the sorption simulation. Updating of the instrument affected positively the data quality. The performed three sets of measurements led to results that were crucial for further research. In the experiment, the amount of adsorbed and desorbed gas was calculated from the pressure difference in the known cell volume. The obtained results could permit the risk assessment of possible coal dust and gas outbursts. The performed tests shall enable a more exact determination and understanding of gas effects, possibly add some new knowledge to understanding of the dangerous phenomena, maybe also improve their prediction and lead to better safety in mining.
COBISS.SI-ID: 950878