Szkoła Eksploatacji Podziemnej

The main problem of most of the coal mines in the Upper Silesia Coal Basin (Poland) is related to their high methane content. Most of the remaining hard coal mines have high methane hazards, which must be addressed for operational safety reasons (Krause, 2005; Krause and Skiba, 2014).
The high methane content of the GZW mines and problems related to hard coal mining technology directly threaten work and human safety, which has been observed more and more often in the last 20 years. The methane hazard in hard coal mines determines the increase in coal mining costs related to the financial outlays incurred to prevent and combat this hazard. High costs are generated by the need to carry out methane drainage (Jureczka, 2017).
On the other hand, methane captured by methane drainage systems can be a carrier of clean energy, covering the costs associated with methane drainage and even bringing additional profits (Karacan et al., 2011; Flores et al., 2019; Zhang et al., 2022). Recently, attempts have been made to capture methane from the surface by drilling holes and fracturing coal seams (Jureczka, 2017; Jureczka and Hadro, 2022).
In our study, we evaluate the efficiency of new drainage technology with the application of the long-reach directional drilling boreholes network drilled above the exploited coal seam in one of the multi-seam hard coal mines in USCB, Poland (Leśniak et al., 2022). To address the aim of the study, numerical modelling was used, combining geomechanics with reservoir fluid flow models constructed in the framework of 3D structural models including both the architecture and the properties of the rocks occurring in the study area.
To employ the method of effective coupling between geomechanical and flow simulations and concerning the influence of geomechanical state variations upon the transport properties of rocks within the model region, flow and geomechanical simulations were performed for several selected time steps. The results of geomechanical simulations provided deformation and stress distributions which were quantified and converted to find permeability modifications with the use of Kozeny-Carman (Bear, 1972) and Shi and Duruncan (Shi & Durucan, 2005) models.
The simulation model of the 501 coal seam and its surroundings was calibrated achieving a satisfactory match with the historical data related to the coal production from the C lot of the seam including schedule and measurement data. The calibrated model of the 501 coal seam and its surroundings was used to simulate a hypothetical scenario that did not apply directional boreholes for methane drainage to compare it with the real case implementing those boreholes.
. The fundamental results of that simulation in terms of (i) total gas production by the ventilation system, (ii) total methane production by the ventilation system, (iii) total gas production by the standard drainage borehole system, and (iv) total methane production by the standard drainage borehole system, and the results for the volume of methane left in the C lot of the 501 coal seam led to the conclusion that the application of the long-reach directional boreholes significantly (by ca. 52%) decreases the methane content in the ventilation gas and notably (by ca. 48%) reduces the methane content in the coal matrix of the excavated coal seam thus proves the effectiveness of methane drainage by the long-reach directional boreholes.
Conducted sensitivity analysis of geological and structure parameters and their influence for their relative modifications by 10% upon the above 4 significant methane drainage effectiveness criteria allow to draw conclusions referring to the estimates of the methane available to the drainage process and, consequently, drainage requirements.
The analysis of the technological parameters of the methane drainage strategy brought up the conclusion that the closer the trajectories to the 501 seam, the larger the methane total production and the higher the recovery of the methane originally adsorbed in the C lot of the 501 seams.