Research on comprehensive CBM extraction technology and its applications in China's coal mines

One of the primary concerns regarding coal and coalbed methane (CBM) extraction in China is coal mining safety. Based on coal-seam geology and the conditions of CBM occurrence, effective CBM extraction methods should be selected. Comprehensive CBM extraction is achieved by CBM extraction before mining, during mining, and after mining. The methods used for CBM extraction before mining include original coal-seam CBM extraction and pressure-relief coal-seam CBM extraction. The extraction effect is assessed in terms of the residual coal-seam CBM pressure and content. The method used for CBM extraction during coal-seam mining should be selected according to workface ventilation, for which the workface CBM extraction rate is an assessment indicator. CBM extraction after coal-seam mining is performed to extract CBM from sealed goafs and the top fracture zone, which can improve a mine's CBM extraction rate. For comprehensive CBM extraction technology, the mine total return-air CBM volume percentage and the rate of mine CBM extraction are used to measure the effect of comprehensive gas extraction from mines. Herein, the application of various technological approaches to the comprehensive extraction of CBM in coal mining is discussed using the example of the Qinan Coal Mine in the Huaibei mining area, where CBM extraction efforts are notably effective. Recent CBM extraction data and actual outcomes from several mines in China with high levels of CBM are analyzed in detail, with a discussion of existing problems and the presentation of new solutions for CBM extraction. Moreover, this article considers problems such as poor borehole sealing quality, low permeability of coal seams and difficulty in drilling soft coal seams to have restricted the further increase in coal mine gas extraction to a certain extent. (C) 2014 Elsevier B.V. All rights reserved.