Research on trajectory control of dual-power composite directional drilling in underground coal mine

Drilling trajectory control is one of the key technologies to achieve safe and efficient composite directional drilling. Due to the different force conditions of drilling tools in the hole and the composition of the analysis model, the existing trajectory control theory of composite directional drilling in the field of surface oil and gas drilling cannot be directly applied to the coal mine. Based on the analysis of the technical characteristics of dual-power composite directional drilling in coal mines, structural bend angle of screw motor and rotary centrifugal force are treated equivalently. The dual-power composite directional drilling trajectory control model is established based on the quasi-dynamic principle to analyze the influence law of structural bend angle of screw motor, weight on bite and borehole diameter expansion rate on the trajectory control. The results show that increasing structural bend angle of screw motor is conducive to increasing the build-up rate of the sliding deflection, and is not conducive to the control of rotary angle holding trajectory. Increasing the weight on bit is not conducive to improving the build-up rate of the sliding deflection, and is conducive to the control of rotary angle holding trajectory. Increasing the expansion rate of borehole diameter is not conducive to improving the build-up rate of the sliding deflection, and has little effect on the control of rotary angle holding trajectory. Based on the analysis of the influence law of drilling trajectory control, a dual-power composite directional drilling trajectory control method is proposed, and different parameter setting suggestions are given. The structural bend angle of screw motor is generally 1.25°, and can be set to 1.5° when the drilling tool grade is large. In the context of the safety of the drilling tool, the weight on bit can be increased appropriately, and the weight on bit setting should not be too large when drilling in coal-measure strata with low consistent coefficient. The rotary speed is generally 40-60 r/min, the borehole diameter expansion rate is generally 4%-6%, and the proportion of rotary angle holding section is no less than 80%. The dual-power composite directional drilling trajectory control method is used in the test of super-deep directional long drilling for gas extraction above 3 000 m in the large area of Baode Coal Mine. The results show that the drilling efficiency is high, the drilling trajectory control capability is strong, which meet the requirements of efficient drilling in deep holes.