[Introduction]
As a new technology in engineering field, underground directional drilling technology of coal mine has been widely used in borehole drilling in gas drainage, water hazard control, geological exploration and accurate drilling fields. ZDY12000LD directional drilling rig, mud pulse transmission MWD system, assorted drilling tools and combined directional drilling technique are developed to solve current technical limitation of direction drilling. The whole set of equipment appears significant advantages. These advantages include enlarged power, high borehole accident handing capacity and high wireless MWD accuracy. Meanwhile, less drilling cutting and small borehole curvature are expected to generate by combined directional drilling technique. The ZDY12000LD drilling rig have completed the ultra-long directional drilling along the coal seam with the main hole depth of 3353m in Baode coal mine, which has once again set a new world record of directional drilling in China.


[Components of directional drilling system]
1.Drilling rig
ZDY12000LD is a directional drilling rig with high rotary torque (the rated torque is 12000N.m), low rotary speed (range from 50r/m to 150r/m). The rig is capable for precise directional drilling operations with borehole depths of up to 1500m by using a downhole motor. It is suitable to drill large diameter underground borehole. The application of the rig includes directional drilling operations for gas drainage, water detection/drainage, grout injection, exploration of geological structure, detection of seam thickness, water injection in seam, etc. Technical parameters are listed in following table.



Some special features/benefits on the rig are:
(1) Magnificent power and drill ability
As far as we know, ZDY12000LD drill rig has the highest rated torque in underground series drill rigs. Magnificent torque not only lead to the strong borehole drilling ability but also can maintain outstanding ability to avoid downhole accident. It can meet the requirement of rotary drilling technique, downhole motor drilling technique and integrated drilling technique (mix rotary drilling with downhole drilling) with relative high drilling efficiency.
(2) Advanced hydraulic system
With the use of high quality hydraulic components(Rexroth and Sauer), the rig has a reliable hydraulic. Chuck and clamp can be operated independently which lead to flexible and reliable control. Drill rod deployed handle are special designed to protect drill rod screws during connect and discharge process. Linkage system and optimized pressure/flow rate control lead to simple operation.

2. Mud pump crawler
BLY390/12 mud pump crawler is a hydraulic pump crawler with large flow rate (the max flow rate is 390l/min) and high mud pressure (rated pressure is 12Mpa). The rig can maintain enough flow rate under high pressure work situation. It can supply enough hydraulic fluid power for downhole motor operation and drill cut remove to meet the requirement of long depth directional borehole drilling.





3. Downhole assembly
Typical downhole assembly include several drill tools packages:
(1) Φ98mm directional drill bit, Φ73mm downhole motor, cable transmission MWD system and Φ73mm cable-transmission drill rod. The assembly is suitable for long distance directional borehole drilling in coal seam.
(2) Φ98mm directional drill bit, Φ73mm downhole motor, mud pulse transmission MWD system and Φ73mm cable-free drill rod. The assembly is suitable for long distance directional borehole drilling in coal seam.
(3) Φ120mm directional drill bit, Φ89mm downhole motor, cable transmission MWD system and Φ89mm cable-transmission drill rod. The assembly is suitable to drill pilot hole for long distance directional borehole drilling in roof and coal seam.
(4) Φ98mm-Φ120mm reamer drill bit, and Φ73mm cable-transmission drill rod/Φ73mm cable-free drill rod. These tools are used to expand borehole for large diameter directional borehole drilling in coal seam.
(5) Φ120mm-Φ153mm reamer drill bit, Φ89mm cable-transmission drill rod/Φ89mm cable-free drill rod. These tools are used to expand borehole for large diameter directional borehole drilling in roof.
(6) Φ133mm-Φ98mm-Φ82mm fishing drill bit, Φ102mm fishing string. These tools are used to fish Φ73mm downhole assembly.
(7) Φ146mm-Φ120mm-Φ100mm fishing drill bit, Φ127mm fishing string. These tools are used to fish Φ73mm downhole assembly.


[Technical specification]



[Patent certificate]



[Application]                    
                                               Four world records have been set one after another with the deepest borehole of 3353m

1.Baode coal mine, Shenhua Group, China
Xi'an Research Institute started drilling construction from No.27 roadway of No.1 intake airflow roadway in No.5 panel of Baode coal mine, taking 21 days to drill through the working face of the second panel and successfully connected with the No.2 return air roadway of the third lower panel on the opposite side. The depth of the main hole is 3353m, the total footage is 4428m, the hole diameter is 120mm, the top and bottom branches are explored 13 times, the error of the target coordinate of the drilling through the roadway is less than 0.15%, and the average daily gas drainage volume is more than 5000m³ at present.
     
This drilling broke the world record for the hole depth of the 2570m ultra-long directional borehole created by CCTEG Xi'an in Baode Mine in early 2019. The drilling project successfully achieved a significant increase in drilling depth and achieved ultra-long-distance high-precision mid-targets, mainly due to CCTEG Xi'an's continuous innovation in downhole directional drilling technology and equipment development. The institute has developed a super-long directional hole sliding drilling drag reduction process and a composite drilling trajectory control method for underground coal mines, which greatly improved the downhole drilling capability and drilling efficiency. The ZDY15000LD directional drilling equipment, the YHD3-3000 mud pulse wireless measurement while drilling system and the large through-hole high-strength cableless directional drilling tool, which are independently developed by CCTEG Xi'an, are applied to realize the measurement of the pressure pulse signal in the wireless while drilling. Deep and stable transmission. In addition, CCTEG Xi'an has also applied industrially to the newly developed underground cleaning fluid circulation system for underground coal mines, solving the problem of large water consumption and large discharge volume of ultra-long hole construction. This realizes the leap of directional drilling flushing fluid from "open" to "closed" circulation, which promotes the development of green drilling technology and equipment in coal mines.

The successful implementation of 3353m ultra-long directional drilling along the coal seam is a new milestone in the development of underground directional drilling technology and equipment, marking that China has reached the international leading level in the field of underground directional drilling, which is of great significance to promote the advance control of gas in large areas of coal seam, the replacement of tunnel engineering with holes, the prevention and control of water disasters and geological exploration and other technological progress.


2.Baode coal mine, Shenhua Group, China
New record of underground sub-horizontal in-seam directional drilling has been accomplished by Xi'an Research Institute of CCTEG in Baode Coal Mine. The maximum drilling depth reached 2311 meters. The borehole has 15 sidetracks. Borehole direction was controlled accurately and the trajectory extended inside coal seams. Tremendous high gas drainage efficiency is expected to be achieved.
                                                                                       Borehole trajectory of in-seam directional drilling


3.Sihe coal mine, Jincheng Mineral Group, China
In-site experiment of integrated underground directional drilling equipment and technology has been accomplished in Sihe coal mine (5301 working face). Two long distance boreholes have been drilled. Borehole 1# has maximum depth of 1881m which we believe is the deepest coal mine underground directional borehole. The hole has 11 sidetracks (branches), 7 of them are drilled to detected roof and the rest are drilled to detected floor. Detail track of the borehole can be found in figure 3. Average daily drilling depth reached as high as 210m. 180m average daily drilling depth was maintained even after the borehole depth exceed 1000m. The fact shows that relative high drilling efficiency has been achieved.