Geological setting, occurences, 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
Stable isotopes of carbon were used to trace organic and inorganic carbon cycles and biogeochemical processes, especially methanogenesis within different geologic substrates of the Pliocene lignite-bearing Velenje Basin in northern Slovenia. Lithotypes of lignite, coalbed gases, calcified woods (xylites), carbonate-rich sediments, and groundwaters were investigated. Carbon isotope (δ13C) values of the different lignite lithotypes ranged from − 28.1 to − 23.0‰, with the variability likely a function of the original isotopic heterogeneity of the source plant materials and subsequent biogeochemical processes (i.e. gelification, fusinitization, mineralization of organic matter) during the early stage of biomass accumulation and diagenesis. In the lignite seam, CO2 and CH4 were the major gas components with small amounts of N2. The carbon isotope values of CO2 (δ13CCO2) and CH4 (δ13CCH4) were highly variable, ranging from − 9.7 to 0.6‰ and − 70.5 to − 34.2‰, respectively. Carbon dioxide is likely sourced from a mixture of in situ microbial activity and external CO2, while CH4 is dominantly sourced from microbial methanogenesis, with possible addition of thermogenic gas from deeper formations, and the influence of microbial oxidation of methane. Calcified xylites enriched with 13C (δ13C values up to 16.7‰) indicate that microbial methanogenesis was active during formation of the basin. The δ13CDIC values (from − 17.4 to − 3.2‰) of groundwaters recharging the basin from the Triassic aquifer are consistent with degradation of organic matter and dissolution of dolomite. Groundwaters from the Pliocene sandy and Lithothamnium carbonate aquifers have δ13CDIC values (from − 9.1 to 0.2‰) suggestive of degradation of organic matter and enrichment via microbial reduction of CO2.
COBISS.SI-ID: 24995623
Thematics of this paper is similar to that already published in RMZ Journal - described above under 2. The aim was to present this research work and the results also to the international scientific community dealing with gasses in coal. Extanded is consideration of the state of the art (references), and much broader discussion on especially origin of gasses and processes of therir formation. To our opinion, this study contributed significantly to the world-wide studies of gasses in low rank coals. Namely, for low rank coals, i.e. lignites and brown coals, less such studies exist. The reason is that in general lignites are less gass-bearing than bituminous (hard) coals, that lignites are mostly exploited on the surface (not underground as Velenje), and, finally, that the greatly prevailing world production of coals is bituminous (hard) coal, it is ) 80 %, whereas brown coal and/or lignite represents only ( 20 %.
COBISS.SI-ID: 27862823
This study, dealing with possibilities for energy exploitation of landfill gasses in Slovenia was not a direct object of our project but is connected with it indirectly. Our mining and geotechnology profession is now already for a considerable time (last 15 years or so) interested in so called waste material mining and manegement from different aspects: restoration of waste material dumping zones, protection of environment (especialy waters), extraction of beneficial substances etc. Capture of gas from decaying organic matter, which is gathered and deposited to more and more extent separately in the last 10 years, is also an activity how to use landfill material-s potential. For our project it is welcome and important that we have contacts with this field of gas capture and usage in the sense of exchange of information, results, knowledge and analytical equipment.
COBISS.SI-ID: 1097566