Executive summary

The Rotaqua KFT has contracted the University of Miskolc Faculty of Earth Science and Engineering to prepare a summary document about the Mecsek coalbed methane potential. The company owns the exploration license, which consists of three blocks, a total extension of 416,9, with expiry dates in 2008 and 2009.

The Mecsek is the largest hard coal complex in Hungary, several underground and open pit mines were operated from 1782 until today. Three main mine complexes worked: Pécs-Hosszúhetény, Komló, Szászvár, with annual production rate of 2,5-4 million tons, 0,7 M t in 2003. The explored but undeveloped coal resource amounts to 980 million tons.

The coal-bearing sequence is of Lower Jurassic age, it forms a complex faulted syncline-anticline fold structure, with eastward plunge, between Triassic footwall and Middle-Jurassic hanging wall sedimentary formations, hosting several Cretaceous alkali basalt sills, dikes. Young Neogene covering sequence consists of rhyolite tuffs, andesite, marine sediments. The latest intense structural movements (overthrust, faults) are dated to Late Pliocene. The coal-bearing series is 120 to 1000 m thick, with 36 coal seams in three seam-groups.

The coal is high volatile A bituminous rank, high ash, medium- high sulfur quality, with maximum vitrinite reflection values of 1,6. The coal rank gradient is discordant to stratigraphy, reflecting the definite role of tectonic deformation in the coal maturation. Magmatic emplacement have also evidently contributed to increased coalification locally.

The coal seams have produced gas outbursts and explosions since the early stages of mining from the 19th century. Pre-production gas drainage has become a routine safety measure. The released gas was collected, exhausted and used for heating. Coalbed methane potential was realized in the late 1980s. The first resource estimates have shown 118 BCM (cca 3.3 TCF) in-place gas. USGS – HGS joint research in 2002 has verified the gas potential of the coalfield, agreed with the earlier critical evaluation of the previous exploration programme, and provided an estimate of in-place resources between 1-4 TCF gas. With our present estimation the Mecsek CBM recoverable gas resource (28.5 BCM) is larger than the combined recent available gas resource of Hungary.

A CBM exploration programme was carried out in 1993-1994, drilling four boreholes in the different parts of the coalfield. The programme was unsuccessful. Subsequent evaluation revealed significant errors and difficulties in most significant steps of the execution (drilling, sampling, perforation, injection, hole completion), as well as underlined the complex and low-permeability nature of the coal.
Parallel basic research programmes have shown that cca 90 % of the gas is not physically adsorbed, rather stored in the internal coal structure. Tests have shown that nitrogen or carbon dioxide can be efficient elution gases to mobilize the methane. It was also shown that methanol or similar fluids efficiently disaggregate the internal coal structure and increase the desorption of gas. It was also concluded that physical impact may provide the necessary energy to expel the methane from the internal coal structure.
Our review has verified the potential of the Mecsek Mountains for methane exploration. It is also pointed out that the new exploration programme should be preceded by a detailed structural re-interpretation and careful drill-site selection in order to find places of increased permeability.
The Mecsek Mountains, the largest CBM occurrence in Hungary