A novel sealing material and a bag-grouting sealing method for underground CBM drainage in China

Abstract

Coalbed methane (CBM) is not only a hazard to underground coal mines and atmospheric environment, but also an unconventional natural gas. The effect of underground CBM drainage is influenced markedly by borehole sealing quality. This research focused on a novel sealing material and a bag-grouting sealing method for CBM drainage. First, based on leakages of underground CBM drainage borehole, a material with dual expansion sources (DE) was proposed. Then, the expansion ratios (by rubber bag method) and the expansion pressures (under small swelling) of a modified cement (MC) and the DE were tested. Next, a bag-grouting sealing method, characterized by a bag-grouting sealing device, was proposed. Slurry can be grouted into the bag-grouting sealing device continuously, then the borehole can be sealed tightly. Finally, engineering test was performed at No.2 coal mine in Huangling mining area. Laboratory test results show that the DE expands fast at initial hydration stage, then continues to expand slowly. Especially, the expansion ratios of the DE are more than 60%, however, the MC tends to shrink after initial expansion. Besides, the expansion pressures of the DE are above 1.3 MPa, which are much greater than those of the MC. Engineering test results show that the effect of the DE and the bag-grouting sealing method is preferable to that of the MC and the traditional “two sealing and one grouting” method. The average methane concentration of the boreholes, sealed by the bag-grouting sealing method with the DE as sealing material, is 40% within 90 days. Besides, the concentration does not decrease drastically.