# Development and Application of Unesaled borehole Leakage Detection Device Based on Flow Method
###### Abstract  
Poor sealing of gas extraction boreholes is one key to restrict gas extraction efficiency. In this paper, a novel borehole sealed quality detection device for the gas extraction of a coal mine is developed based on the theory of air leakage. By comparing the amount of gas extracted at different test points, it is possible to determine whether there is air leakage around the borehole, and the specific leakage position and leakage amount. Moreover, this device has the advantages of simple operation and a short test period. Based on the above analysis, a corresponding air leakage disposal method was proposed to handle the leaky boreholes. Field tests showed that the air-gas mixture flow in the test borehole was reduced by a factor of approximately 1.55 and the concentration of pure seam gas was increased approximately six times after the disposal of the air leaks. The combination of the leakage disposal method and the leakage detection device can accurately seal the borehole at the position of the leak, thus effectively ensuring the effectiveness of gas extraction from the borehole. The findings have important implications for improving the efficiency of gas extraction in coal mining operations. Keywords:gas extraction; borehole sealing quality; unsealed borehole leakage detection; leakage disposal technique; extraction efficiency +
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the borehole well, and support the borehole after the slurry is consolidated. However, there are also problems such as high cost, complicated operation, and grout pressure being limited by the strength of the bag. Considering that the sealing quality of boreholes can be better guaranteed with the pressure sealing method under different conditions, most coal mines adopt the \"two plugging and one injection\" method of pressure sealing [17; 18; 19]. However, no matter which sealing method is used, air leakage will occur in the actual extraction process [20; 21]. In general, the causes of unsealed borehole leakage are mainly reflected in the following aspects. First of all, when the sealing length is insufficient, the sealing section of the borehole may be in the range of the pressure relief area, which is an area of more developed cracks, permeability, and proneness to air leakage [22; 23; 24; 25; 26]. Secondly, when the sealing material is deformed or destroyed under the action of borehole deformation and its own gravity, there will be leakage from the sealing material itself or the contact surface between the material and the borehole wall [27; 28]. Moreover, under the mutual superposition of double fracture area of the roadway fracture area and the fracture area around the borehole, the fractures around the borehole are developed and penetrated into each other, forming a macroscopic air leakage channel, thus affecting the sealing quality of the borehole [29]. The detection of leaky boreholes is a prerequisite for the disposal of air leaks and the improvement in the quality of borehole sealing. This has also been studied extensively by a number of scholars. [PERSON] et al. [22], [PERSON] et al. [26], [PERSON] et al. [30], and [PERSON] et al. [31] revealed the effect of sealing depth, extraction negative pressure, borehole diameter, and coal permeability on the quality of borehole sealing by establishing different borehole leakage models. [PERSON] [32], [PERSON] et al. [33], and [PERSON] et al. [34] developed the air leakage detection device for gas extraction boreholes based on the distribution law and changes in gas concentration and extraction negative pressure in leaky boreholes, and the sealing quality of gas extraction boreholes was determined by detecting the gas sample parameters of different borehole depths. [PERSON] et al. [35] and [PERSON] et al. [36] injected tracer gas into the borehole, and then used the tracer gas concentration sensor to detect the tracer gas concentration in the extracted gas, so as to judge the sealing quality of the extraction borehole.