Mitigation and evaluation of the impact of a sandstone channel on a longwall face.

Activities are described which were carried out between October 2011 and February 2012 at a longwall coal mine in Pennsylvania, USA, to improve face conditions and the safety of underground personnel during mining of a 457 m wide longwall panel. The safety concerns were related to adverse face conditions encountered during mining of the preceding panel, with many of the problems attributed to a thick and massive sandstone channel. Following geologic and geotechnical evaluations, it was recommended that four hydraulic fracturing holes should be drilled along the centre access of the sandstone channel to reduce pressure and improve face conditions. The average fracture initiation pressure was about 34.5 MPa and the average shut-in pressure was 3.45 MPa, indicating the formation of horizontal pancake fractures. The effectiveness of the hydraulic fracturing programme was monitored using longwall visual analysis software to track the face pressure and cavity formation index along the longwall face. The longwall face entered the western edge of the sandstone channel in mid-December 2011 and cleared the eastern edge on 3 February 2012. The results of a monitoring programme indicated that three additional holes may be needed to fill the gaps, or that water could be pumped into each hole to propagate the pancake fractures to enable them to overlap each other. The latter, more cost-effective method will be employed for the next panel.
Activities are described which were carried out between October 2011 and February 2012 at a longwall coal mine in Pennsylvania, USA, to improve face conditions and the safety of underground personnel during mining of a 457 m wide longwall panel. The safety concerns were related to adverse face conditions encountered during mining of the preceding panel, with many of the problems attributed to a thick and massive sandstone channel. Following geologic and geotechnical evaluations, it was recommended that four hydraulic fracturing holes should be drilled along the centre access of the sandstone channel to reduce pressure and improve face conditions. The average fracture initiation pressure was about 34.5 MPa and the average shut-in pressure was 3.45 MPa, indicating the formation of horizontal pancake fractures. The effectiveness of the hydraulic fracturing programme was monitored using longwall visual analysis software to track the face pressure and cavity formation index along the longwall face. The longwall face entered the western edge of the sandstone channel in mid-December 2011 and cleared the eastern edge on 3 February 2012. The results of a monitoring programme indicated that three additional holes may be needed to fill the gaps, or that water could be pumped into each hole to propagate the pancake fractures to enable them to overlap each other. The latter, more cost-effective method will be employed for the next panel.