Influence factors analysis of a flexible gel sealing material for coal-bed methane drainage boreholes

Coal-bed methane (CBM) hazards are among the principal hazards in a coal mine, causing events such as coal and gas outbursts, and gas explosions. CBM drainage in underground coal mines plays a fundamental role in preventing coal mine accidents and ensuring safe production in coal mines. The effective sealing of boreholes is regarded as an important measure in the guarantee of efficient CBM drainage. Aiming at the shortcomings of conventional sealants (their poor stability, low permeability, and low adaptability), a flexible gel (FG) that adapts to borehole deformation and has preferable sealing performance was developed. In this study, the development method and the effect of the application of the FG were introduced, the effect of stirring status and the ratio of FG material to water on the water retention, hydrophobicity, and permeability of the FG were investigated; the sealing mechanism of the FG was proposed and the relationship between the stirring status, the ratio of FG material to water and its sealing effect were discussed. The results reveal that: (1) the viscosity of FG increases with time at low stirring speeds (600 rpm and below) and then reaches a constant viscosity. On the other hand, at high stirring speeds (800 rpm and above), the viscosity of FG first increases, then decreases, and finally reaches a constant viscosity. (2) The FG contains many hydrophobic groups and the surface has a protective layer structure: the main mechanisms in its borehole sealing role are the borehole deformation adaptability, high permeability, preferable water retention, and hydrophobicity. (3) The higher the ratio of material to water in the FG, the lower the hydrophobicity and permeability, and the better the water retention of the FG. (4) Once sufficiently stirred, FG has the lowest permeability, and the best water retention and hydrophobicity: excessively stirred FG is the next best option, and insufficiently stirred FG has the poorest water retention and hydrophobicity, but the greatest permeability. (5) To ensure good sealing performance, sufficiently stirred FG, with a lower ratio of material to water, is selected as the sealing material.