Model of gaseous hydrocarbon generation in the Miocene strata of the Polish part of the Carpathian Foredeep

Abstract

The ITI modelling demonstrated that the autochthonous Miocene strata located in the outer Miocene basin of the Carpathian Foredeep, north of the present edge of the Carpathian overthrust have generated only the microbial gas. In the part of the Miocene basin covered recently by the Carpathian overthrust the low-temperature thermogenic gases were generated down to 7,000 of meters depth. Finally, in the hypothetical zone ojthe Lower Miocene molasse located recently at depth intervaI 7,500-11,000 meters only the high-temperature thermogenic gases could be formed. Alternatively, at the site of the Lower Miocene molasse the depression filled with Upper Carboniferous coal-bearing formation may occur. Therefore, at depth beneath 7,500 meters, i.e. beneath the Carpathian overthrust the gas deposits can be expected. The maximum yield of the microbial methane generation within the autochthonous Miocene calculated for depth interval 900 to 1,500 meters is about 5 cubic meters per cubic meter of source rock. It is possible that the generation process of microbial methane still continues. Accumulation of microbial methane within the autochthonous Miocene strata was facilitated by high sedimentation rate and rhythmic and cyclic deposition of clays and sands. .