Coal Properties and Coalbed Methane Potential in the Southern Part of the Upper Silesian Coal Basin, Poland

Abstract

The area studied covers unmined Pennsylvanian Ćwiklice and Dankowice coal deposits located in the southern part of the Upper Silesian Coal Basin, Poland. The geological structure of the area clearly affects the current distribution of methane. The content of methane is lower in coal seams lying within porous and permeable sandstones (Łaziska sandstones), whereas it is higher in seams that occur in sequences (Mudstone Series) where impermeable shales and mudstones occur. Due to the previous attempts to extract methane from boreholes, this area, characterized by a dense network of exploratory and prospecting drillings, is worth analyzing with regard to the conditions of methane occurrence in terms of extraction possibilities. Using contour maps, cross-sections and profiles, the variability of methane content and resources, as well as the moisture and ash content of coal seams, were analyzed. Methane content isolines are parallel to the boundary between the Cracow Sandstone Series and the Mudstone Series and to main faults. Coal moisture contents clearly reduce methane contents. A high methane content >8 m3/t coaldaf is typical for coal seams in which moisture contents do not exceed 5%. High- and medium-volatile bituminous coal in the area is characterized by low methane saturation, though saturation increases with depth. Coal permeability is variable (from 0.2 to more than 100 mD), but, below a depth of 1200 m, a clear trend of decreasing permeability with depth is evident. From the point of view of coalbed methane (CBM) recovery, relatively low coal permeabilities and methane saturation levels could make CBM output problematic in the studied area. Methane production will be more probable as a result of demethanation of the Dankowice 1 deposit, where coal mining is planned. This will result in the emission of methane into the atmosphere from ventilation shafts and methane drainage stations. Therefore, effective use of the gas captured by the methane drainage station is highly desirable for environmental and economic reasons.