Study on Borehole Trajectory Deviation Characteristics and Influencing Factors in Three-Soft Coal Seams

The three-soft coal seam, characterized by its soft and fractured lithology, is prone to significant drilling trajectory deviation during construction, severely compromising gas drainage efficiency and posing potential safety hazards. In order to clarify the variation law of the drilling trajectory of the three-soft coal seam, this paper takes the 14205 working face of a mine in Guizhou Province as the engineering background, monitors and analyzes the drilling inclination and the change in the inclination, and then studies the influencing factors of the drilling deviation. During on-site drilling and coring operations and data monitoring, the formation lithology and fragmentation conditions were clarified, and the trajectories of gas drainage drilling holes at 15°, 30°, 45°, 60°, 75°, and 90° were obtained. It was observed that when the hole inclination is 15° or 90°, the change Δ value of the hole inclination is close to 0°. When the hole inclination is 30° or 75°, the change Δ value of the hole inclination is close to 2.5°. When the hole inclination is 45° or 60°, the change Δ value of the borehole inclination angle is close to 4.5°. The curve of the change Δ value of the borehole inclination angle and the borehole inclination angle was obtained by calculation and fitting, and the whole presents a quadratic function distribution. It was inferred that when the inclination angle of the borehole is 50°, the change Δ value of the inclination angle of the borehole reaches the maximum value, which is close to 5°, that is, the deflection of the gas drainage borehole is the largest. With the help of this curve, the deflection was predicted, controlled, and reduced. The AHP analysis model was used to rank the importance of the influencing factors of the borehole trajectory, and it was clear that the main controlling factor of the borehole deflection is the geological factor. This study provides a basis for obtaining the drilling deflection law and determining the appropriate drilling deflection control and correction technology.