Methods of hydraulic fracturing of poorly caving roof and coal seams to eliminate dynamic phenomena in coal mines

Abstract

The paper demonstrates the need to develop methods of managing poorly caving roofs in the stoping and development faces as well as the ways of intensifying the degassing process of unrelieved coal seams to improve the technical and economic performance and safety of operation. Methods of the directional hydraulic fracturing (DHF) of the roof and the interval hydraulic fracturing (IHF) of the coal seam are suggested to eliminate the dynamic phenomena in coal mines as well as technological charts of their implementation. The DHF method consists in creating an initiating slot in the borehole walls, which acts as a stress concentrator, followed by its sealing with an insulating device, i.e. a packer. When a fluid is injected into this slot, the tensile stresses are created in the borehole walls and the fracture is forced to develop in a predetermined direction. The IHF method of the coal seam from the development workings using non-cased degassing holes of large and variable diameter consists in creation of transverse hydraulic fractures in the hole relative to its axis and increasing its gas recovery by an order of magnitude. This is achieved by using a double-sided packer with elastically expanding elements and a valve installed between them. Additional tangential stresses created in the borehole walls ensure the development of inelastic strain zone, leading to the formation of transverse cracks in the borehole. The results of numerical modeling of the stress-and-strain state of the rocks near the borehole where packer seals are installed using the finite element method are presented in the paper. Techniques and means to monitor the processes of hydraulic impact on the coal-rock massif are shown.