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Energies 2016, 9(4), 249; doi:10.3390/en9040249

Rock-Breaking Properties of Multi-Nozzle Bits for Tree-Type Drilling in Underground Coal Mines

1,2
,
1,2
,
1,2,* , 1,2
and
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1
State Key Laboratory of Coal Mine Disaster Dynamics and Control, Chongqing University, Chongqing 400044, China
2
National & Local Joint Engineering Laboratory of Gas Drainage in Complex Coal Seam, Chongqing University, Chongqing 400044, China
*
Author to whom correspondence should be addressed.
Academic Editor: Vasily Novozhilov
Received: 16 February 2016 / Revised: 22 March 2016 / Accepted: 23 March 2016 / Published: 30 March 2016
View Full-Text   |   Download PDF [7305 KB, uploaded 30 March 2016]   |  

Abstract

Tree-type drilling is a new technique for drilling radial tree-type boreholes in coal seams in underground mines using water jets to break the coal. The aim is to drain gas from the coal seams in larger quantities and from larger areas than can be done by conventional gas drainage using single boreholes. The self-propelled drill bit is the most important component for this technique. The bit generates a self-propelling force to move forward, break coal, and form a borehole. This paper investigates the relationships between the physical parameters of the forward nozzles in the bit and the diameter and shape of the borehole drilled. The effect of different physical parameters on the rock-breaking efficiency is studied by conducting drilling experiments. The results show that the size, orientation and number of the nozzles significantly affect the rock-breaking efficiency of the bit. To obtain a better rock-breaking efficiency under the experimental conditions used for this paper, the axial angle for forward nozzles should be 15°, the radial angle 90°, and nozzles should be arranged 2.1 mm from the center of a 12 mm drill bit. The experimental results provide a reference for the design of multi-nozzle bits for many applications such as radial jet drilling (RJD) and bent pipe cleaning. View Full-Text
Keywords: coalbed methane (CBM) drainage; tree-type drilling; water jet; multi-nozzle bits; rock-breaking properties coalbed methane (CBM) drainage; tree-type drilling; water jet; multi-nozzle bits; rock-breaking properties
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Lu, Y.; Xiao, S.; Ge, Z.; Zhou, Z.; Deng, K. Rock-Breaking Properties of Multi-Nozzle Bits for Tree-Type Drilling in Underground Coal Mines. Energies 2016, 9, 249.

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