Nowadays, it has become a reality to use small and medium-sized horizontal directional drilling rigs to lay pipelines in hard rock formations. The following will discuss the equipment requirements and selection of using small and medium-sized horizontal directional drilling rigs to lay pipelines in hard rock formations.
Drill bit: Although the drill bit is small, it is extremely critical. All other drilling equipment is based on matching with the drill bit. Three common types of drill bits:
(1) Inclined palm face bit: cheap, suitable for pilot hole drilling in soft formations;
(2) Cone bits: moderately priced, in a variety of forms and suitable for a variety of formations, with good milling resistance and high strength, making them the most efficient bit choice for drilling in hard rock formations.
(3) Diamond drill bits: expensive, using homogeneous hard rock formations and some igneous rocks. The use of diamond drill bits in conglomerate and pebble formations will greatly shorten the lifespan. It is recommended not to use them in such formations;
Screw motor: The screw motor is driven by the mud to drive the drill bit to cut the rock and realize directional drilling. Efficient drilling can be achieved by selecting an effective combination of bit size, pump volume, and bit unit area load.
Drill rod: Drill pipe is the key medium for transmitting torque, thrust, backing force and mud. The proper diameter of the drill rod can ensure the transmission of sufficient torque and thrust to ensure the drilling of the rock formation. The inner diameter of the drill pipe needs to meet the mud volume requirements of the drive screw motor and the drill bit.
Drilling rig: drilling into the formation to determine the bottom hole assembly, so as to determine the size of the required rig.
Reamer: The pressure per unit area acting on the drilled section is not less than: 6.895Mpa, and the speed should be 40-90 rpm. The final hole diameter of the small drill is 250-305mm. Medium-sized: 445-660mm. Of course, as the length of the traverse increases, the requirements for expanding the drill rig with the same diameter are higher.
In hard rock formations, it is more economical to use small rock drilling equipment to complete pilot hole drilling and to use medium-sized drills for reaming.