1、Process Flow of High-pressure Nitrogen Directional Drilling

Gas drilling is an underbalanced drilling technology that runs with the compressed gas as both the circulating medium and the energy to crush the rocks. The air screw motor is used to drive the drill bit to rotate and break the coal seam (rock formation) with the compressed nitrogen as a medium. Since the high-pressure nitrogen (outlet flow rate of 600-900m3/h and outlet pressure of 2MPa) is used as the circulating medium, which completely eliminates the chip hold down effect at the bottom, and greatly improves the mechanical drilling speed, the high-pressure nitrogen drilling has a high mechanical drilling speed, which is generally 3-8 times that of the drilling process using the conventional drilling fluids.

2、Application Conditions

（1）It is mainly used for drilling in soft and fractured coal seams in the underground coal mines, which can greatly enhance the drilling efficiency and effectively solve the hole forming problems.

（2）The firmness coefficient f of the coal seam shall be ≤1.

3、Technical Parameters of Process

（1）Drilling Depth: ≥1,000m;

（2）Deviation of Drilling Trajectory: ±0.5°;

（3）Ending Offset: ≤2m horizontally, and ≤1m vertically;

（4）Measurement Accuracy of Drilling Angle: ±0.1°;

（5）Measurement Accuracy of Drilling Azimuth: ±0.3°;

4、Process Advantages

（1）Since the high-pressure nitrogen (2MPa) is used as the circulating medium to completely eliminates the chip hold down effect at the bottom and greatly improve the mechanical drilling speed, the high-pressure nitrogen drilling has a high mechanical drilling speed, which is generally 3-8 times that of the drilling process using the conventional drilling fluids.

（2）Using high nitrogen drilling technique can easily pass through abnormal formations.Sinca there is no liquid phase in gas drilling,it will not involve the problem of hydration instability in shaft lining.

（3）High nitrogen drilling is highly safe.Under normal supporting and monitoring means,harmful gas pollution and natural gas deflagration will not occur.