Abstract:

During the construction of underground extraction boreholes, trajectory deviation is common, prone to blind gas extraction areas and produces gas extraction blank zones. In order to ensure that gas extraction achieves the expected results, the 15121 bottom pumping lane, 15124 low level lane and 15124 return air lane of Xinjing mine in Shanxi province were taken as the background of the project. We tested the deviation of borehole drilling through the seam and along the seam respectively, calculated the three-dimensional trajectory of the drill holes by using the mean angle full distance method, established the three-dimensional trajectory of the drill holes and the three-dimensional layer relationship of coal rock based on the geological information of coal seam assignment, realized the visualization of the trajectories of the drill holes, analyzed the factors affecting the deviation of the drill holes and the experimental fitting data, and came up with a characteristic of the deviation of the boreholes. The research findings suggest that cross-layer boreholes initially exhibit deviation within fine sandstone layers, with the deviation intensifying notably within the coal seam segment, reaching a maximum deviation of up to 0.52 meters within this section. In the case of in-seam drilling, greater drilling depth results in larger vertical deviations, with an average vertical offset of 1.37 meters at a depth of 40 meters when the opening angles of boreholes are similar. Overall, low-angle boreholes are more susceptible to gravity-induced deviations, leading to a higher likelihood of trajectory deflection, while high-angle boreholes tend to exhibit vertical deviations, albeit with a smaller overall deviation compared to low-angle boreholes. In the horizontal direction, borehole spacing is reduced by 0.68 meters for bottom drainage galleries, 0.28 meters for lower position galleries, and 0.54 meters for return airways. The research results effectively guide the design of subsequent gas extraction drilling trajectories under the same geological conditions, provide theoretical support for controlling and eliminating the blind zone of gas extraction, and improve the efficiency and effectiveness of gas extraction.

Key words: gas extraction, cross-seam borehole drilling, in-seam borehole drilling, three-dimensional trajectory, deviation characteristic, hole parameter guidance