Development and Application of Water Sealing Technology for Gas Drainage Boreholes

Abstract

The poor sealing effect of gas extraction boreholes causes low efficiency of gas extraction. As a consequence, the requirements of coal mine safety production are often not attained. The sealing effect of boreholes depends not only on the sealing material itself but also on the combination degree between the material and the hole wall and the structural change characteristics of the material during operation. Our theoretical analysis shows that the amount of liquid leakage increases with the gap width Δ h in a cubic law, decreases with the sealing hole viscosity in a hyperbolic form, increases linearly with the diameter of the borehole, and increases with the eccentricity in a quadratic function. We have developed a PD sealing material that has good compactness and sealing effects, excellent water retention performance, and an expansion rate of 1.29. The material can generate secondary expansion through microscopic development, which is beneficial to improve the quality of the sealing hole. HV-CMC has good stability in plugging mucus. In addition, the manual pump has been redeveloped to be portable and also to overcome the blockage of the suction valve of the original device. In addition, the auxiliary device for drilling and sealing has been invented. The field application demonstrates that the gas concentration and flow pressure difference of the new sealing borehole can be maintained at a high level in a short period of time and then decrease slowly with time. The resulting improved sealing effect demonstrates that our new approach has important theoretical and practical significance for mine gas drainage.

Study on Effective Extraction Radius of Directional Long Borehole and Analysis of the Influence Mechanism

“…As is evident from Figure 8, under the negative pressures of orifice of 27, 33, and 40 kPa, with the increase in extraction time, (1) the increase in the effective extraction radius increases with an increase in the negative pressure of the orifice, and (2) the negative pressure of the orifice and the effective extraction radius of the borehole depth of 430 m are in line with the linear relationship. The fitting degree is greater than 0.950, the slope is the largest at 180 days, and the maximum slope is 0.15 (see Table 5).…”

Morphological characteristics and permeability evolution of deep mine gas drainage boreholes

“…Unloading is a deep mine gas disaster management technology. Hydraulic punching is a tectonic coal unloading extraction gas effective technique, and its role is mainly reflected in the following three aspects (Wu et al, 2002;Wang et al, 2013;Jiang et al, 2018;Liu and Liu, 2019;He et al, 2021): 1) high-pressure water is used to break the coal body, forming a certain range of pressure relief area around the hole, in which the permeability increases substantially, so as to achieves the purpose of gas extraction; 2) wetting coal reduces its elastic potential energy; and 3) water lock reduces gas desorption speed. The pore shape is a key influencing factor in the design of gas drainage.…”

Industrial Preparation of Self-Lubricating Polyurethane via Direct Fluorination with Gaseous Fluorine

“…Benefiting from tailored hard and soft segments, polyurethane (PU) presents an excellent combination of stiffness, elasticity, and abrasion resistance and thus is widely used as a sealing material to produce transport belt, bearing, valve seals, O-rings in aircraft, and marine industry. − However, the friction coefficient is high with poor self-lubrication, so that in large sealing devices running under high frequency, huge stress followed by a sharp increase in friction heat often causes serious damage of the PU material. , Therefore, it is critical to reduce the friction coefficient for high-performance PU sealing materials.…”