Permeability improvements of an outburst‐prone coal seam by means of presplitting and blasting with multiple deep boreholes

Abstract

Coalbed methane, which is a significant potential unconventional source of energy, exhibits considerable challenges in the implementation of the exploration and production process, especially the degasification in low permeability of coal seams with high gas concentrations. Due to the difficulties in gas extraction, long mining period and low extraction concentration in soft and outburst coal seams, the permeability improvement method using presplitting and blasting technology with multiple boreholes has been proposed and applied to improve the permeability of soft coal seam, which is achieved by optimizing the inseam distribution of generated fractures through multiple control boreholes. Research results showed that the permeability improved by presplitting and blasting with deep boreholes is 2.5 times higher than that of the original coal seam. Within 6 days of extraction, the average extraction concentration and pure volume of the extraction borehole were 40.13% and 0.113 m3/min, respectively, which are 2.9 times and 4.1 times higher than the original data, respectively. Likewise, the average extraction concentration and purity of the extraction hole were 21.75% and 0.063 m3/min after being extracted within 14 days, which is twice and three times higher than that of the original average extraction concentration and purity volume, respectively. Besides, proposed technology has a little influence on the methane concentration of the coal seam 70 m ahead of the heading face. The research results promote the prevention and control of coal‐gas outburst in low permeability and high gas concentration coal seams.

A Study on Cut Blasting with Large Diameter Charges in Hard Rock Roadways

“…To investigate the formation of the stress wave and the intensity of the stress field, three-dimensional numerical models of wedge cut blasting for two charge diameters were established by a solid element of eight nodes in ANSYS/LS-DYNA [37]. As shown in Figure 3, for both numerical models, the size of the rock mass is 4000 mm × 3000 mm × 3000 mm with six cut holes symmetrically arranged on the left and right sides of the model; the cut hole angle is 77°, the cut hole top space is 1500 mm, the cut hole bottom space is 300 mm, the cut hole space is 500 mm, the cut hole depth is 2600 mm, and the charge length is 1320 mm.…”

Characteristics of in situ stress and its influence on coalbed methane development: A case study in the eastern part of the southern Junggar Basin, NW China

“…In other words, the pore-fracture system varies with the change of in situ stress regime, along with K of coal reservoirs. 9,48 The permeability mainly includes matrix permeability and fracture system permeability, and the latter is the main factor that controls the percolation conditions of the coal reservoirs in the actual formation conditions, with the former almost negligible. 49 In general, paleo-tectonic stress fields determined the formation, distribution, and development degree of natural fractures, whereas the current stress regime can control opening/ closing of pore-fracture systems, and it then influences the permeability of the coal reservoirs.…”

Stress Relief and Stimulation of Coal Reservoir by Hydraulic Slotting

“…To improve the efficiency of gas extraction, experts and scholars at home and abroad have been putting lots of effort in permeability improvement in the coal reservoir. e widely applied techniques to improve the permeability of the coal seam include deep-hole split blasting [6][7][8], hydraulic slotting [9][10][11][12], hydraulic fracturing [13,14], hydraulic flushing [15][16][17], CO 2 fracturing [18][19][20], and gas injection [21,22]. Different techniques are all able to create a large number of fractures, forming a network of fractures that can promote the gas migration.…”