Citation

Zhang J, Zhai C, Zhong C, Xu J, Sun Y. Safety Sci. 2019; 115: 141-153.

Copyright

(Copyright © 2019, Elsevier Publishing)

DOI

10.1016/j.ssci.2019.02.007

PMID

unavailable

Abstract

As an unavoidable hazard threatening the mining safety and an important energy resources for human society and environmental protection, coalbed methane (CBM) extraction is proved to be of great importance pre mining. The method of upward borehole extraction is commonly used for underground gas extraction, however, some limitations of the traditional sealing methods and materials always make poor sealing results and extraction efficiency. In this paper, a method of upward borehole self-sealing technology using drill cuttings has been proposed. The sealing failure of the upward boreholes has been investigated and three potential leakage paths for air have also been studied, such as the defects of the sealing material, the channels between materials and the borehole walls, and the cracks around the borehole. An experimental system was been established to simulate upward borehole self-sealing technology, and some critical parameters, like particle size distribution (PSD) and the motion of drill cuttings within the borehole, were investigated. The PSD results indicated that huge amount of small scale particles could be compacted to be dense with low porosity; the motion of particles results shown that the cracks around the boreholes could be occupied by different scales of particles due to the large initial velocity; the angle of repose for accumulated particles increased as the increasing particle volume, blocking the contact interface by some water-coal fines. A field application was carried out in the No. 8 coal mine in Pingdingshan, China, and the high concentration of extracted CBM verified the feasibility of upward borehole self-sealing technology, in which these boreholes could be sealed by cuttings by preventing the three potential leakage paths, and the concentration variances indicated that the effective sealing duration could be recognized. The laboratory and field results all prove that the method of upward borehole self-sealing using drill cuttings could be helpful to improve CBM extraction efficiency and might be a potential and promising technology in the future.

Language: en

Keywords

Coal methane extraction; Drill cuttings; Mining safety; Particle size distribution; Potential leakage paths; Upward borehole self-sealing