1 、Double-Tube Directional Drilling Process for Soft and Broken Coal and Rock Strata

This process is mainly applied to the drilling of soft and broken coal seams in underground coal mines, effectively solving the problems of hole formation and hole protection. The drilling rig is equipped with two sets of tool strings: drill pipes and external casings. During the drilling process, the drill pipes advance while the casings remain stationary (water enters simultaneously through the center of the drill pipes and the annulus between the drill pipes and the casings). After reaching the designed hole depth, the central drill pipes are withdrawn, leaving the hole - protecting casings in the hole. After the screen pipes are lowered through the entire length of the casing, the casing is withdrawn. This realizes the installation of screen pipes with hole protection for the entire length of the directional long borehole, ensuring the successful formation of the directional long borehole and improving the utilization rate of gas extraction from the borehole.

2、Applicable Conditions

(1) It is mainly used for drilling in soft and broken coal and rock strata in underground coal mines, effectively solving the problems of hole formation and hole protection.

(2) The firmness coefficient of the coal and rock strata, f ≤ 10.

3 、Process Technical Parameters

(1) Drilling depth: ≥ 1000m;

(2) Borehole trajectory deviation: ± 0.5°;

(3) Final hole offset: left - right ≤ 2m, up - down ≤ 1m;

(4) Measurement accuracy of borehole inclination: ± 0.1°;

(5) Measurement accuracy of borehole azimuth: ± 0.3°;

4 、Process Advantages

(1) With the protection of the external casing, the directional drilling efficiency in soft coal seams is high. The use of an automatic drill pipe loading device significantly reduces the labor intensity.

(2) The double - wall hole - protecting drilling method with water intake through the annulus between the double walls avoids downhole accidents caused by hole collapse.

(3) It has a high hole formation rate for soft and broken coal and rock masses, effectively increasing the drilling depth to meet the drilling requirements.

(4) After the drilling is completed, under the protection of the external casing, screen pipes that meet the extraction requirements can be installed throughout the entire borehole, improving the gas extraction effect.