Main equipment and equipment Ingersoll Rand VHP750 air compressor, rated displacement 212m3/min, pressure 138MPa, power 224kW; XY-1000 drilling rig; BW-150 mud pump; SG18 rig; LZ-500 Turntable; J-150 type DTH hammer; 89mm drill pipe; duct type is 322W-11MPa.
Design principle of well structure and drilling parameters: Due to the characteristics of air drilling itself, when designing the well structure, it is important to ensure that there should be no major changes in the return air velocity in the entire well, especially on the upper part of the well. The return wind speed cannot be much lower than the return air velocity on the bottom of the well. Otherwise, the wind speed will drop and the cuttings will not be able to discharge the wellhead. Water well structure: about 2,000 meters from the Quaternary to the rock, the diameter of the well is 170mm; the steel perforated pipe is drilled into the hole, and then the J-150 type DTH hammer is used to drill the final hole. Drilling parameters: speed 3040r / min, drilling pressure 220kN.
The construction method uses the J-150 type DTH hammer to drill into the Quaternary to the bedrock, and drills about 2m into the rock. The 170mm three-wing drill bit is used to ream the hole. When the hole is reamed, the mud is used as the flushing liquid, and the hole is recirculated to the end. After reaming, insert a 165mm steel grommet. Then use a J-150 type DTH hammer to drill into the final hole. After the pumping test is finished, below the stable water level, you can enter the corresponding deep well pump.
Several problems should be paid attention to during construction. (1) Steel perforated pipe is welded to the hole. No leakage welding or blisters are allowed. The bottom of the pipe is wrapped with hemp rope to prevent water from immersing in the hole.
(2) Wells should be designed according to the conditions of groundwater. The Quaternary gravel layer water well or the main aquifer is the water well of the fracture zone. Generally, the well formation process is: the downhole pipe (solid pipe and flower pipe) is put into the filter material to stop the water and wash the well pumping test. Since the aquifer in the area is in the interbedded layer of the relatively complete bedrock, the well wall is stable, and the well pipe does not need to be installed in the well.
(3) When drilling to 20m (after seeing the water outlet for 4m at the beginning), when the new drilling is started, the down-the-hole hammer is prone to non-operation.
Form of expression: The pointer of the air pressure gauge of the air supply rises rapidly from 05MPa, and reaches 1112MPa in an instant. Due to the leakage of small gas volume, the pointer of the pressure gauge returns to 0809MPa, and the pointer of the tachometer is between 8001000r/min. Explain that the downhole hammer airway is blocked (generally, the downhole hammer itself can be eliminated). This is similar to the domestic 2W-9/7 air compressor. 2W-9/7 air compressor, when the air circuit is blocked, the diesel engine speed and pressure reach the maximum value instantaneously (speed 1450r/min, pressure 72105Pa, At this time, the exhaust volume is the largest), then the speed drops back to 700800r/min, and the pressure range is (5672) 105Pa. The difference is that the 2W-9/7 type air compressor uses a load regulator to adjust the diesel engine speed, while Ingersoll Rand The VHP750 air compressor uses a sensor to adjust the speed of the diesel engine. When the air circuit is blocked, the speed of the diesel engine is controlled by the sensor, and the speed and pressure are not up to the rated value.
Analysis of the cause: After the end of the drilling, the slag discharge time is short, the rock powder is not fully removed, and the bottom of the drill bit is used as the interface after the wind is stopped, and the interface (hole wall and drill pipe annular gap) is mixed. Fluid (water, mud, cuttings, etc.), from the basic principle of hydrostatics (P = P0 + gh), there is a role of liquid pressure; inside the interface (deep hole hammer cavity) is a compressed gas. When the wind stops, the check valve is closed. Due to the action of the check valve, the pressure inside the drill pipe is P0, which is obviously smaller than the pressure of the cavity of the downhole hammer. Due to the compressibility of the air and the limitation of the sealing performance of the check valve manufacturing process, the pressure outside the interface is greater than the pressure within the interface, and the internal and external pressure difference is negative, causing the rock powder to flow back and block the air passage, causing the down-the-hole hammer to not work. . When the dry hole is drilled, it is not easy for the cuttings to block the air passage of the downhole hammer.
Treatment method: At this time, the drill should not be blindly lifted to check the down-the-hole hammer, thereby increasing the auxiliary time and reducing the time of pure drilling. Instead, the drill pipe should be lifted with 12 single roots, forks and forks, and drilled while the air is being supplied. With a slight lower pier, the rock powder can be washed out of the airway. At this point, the gauge pointer drops rapidly and the tachometer pointer rises rapidly. Then, the hammer of the down-the-hole hammer is dropped into the bottom of the well, and the hammer of the down-the-hole hammer starts to work. At this time, the pressure gauge and the tachometer are stable at normal values. If the above method does not work, it may be that the rock powder is seriously blocking the drill bit, or the upper check valve of the down-the-hole hammer is broken, or the rock powder lining (mud ring) is formed outside the drill pipe, or the well wall collapses, and the drill should be checked. .
Conclusion The use of pneumatic down-the-hole hammer drilling method to construct the water supply well has the advantages of fast drilling speed (efficiency of 22m/h), no need for special well washing, simple well-forming technology and large water output. However, the drilling depth is limited by the performance of the air compressor, the depth of the underground aquifer and the amount of water. Therefore, when the underground aquifer is buried deep, it is generally not suitable to use the pneumatic down-the-hole hammer drilling method to construct the water supply well, but the conventional drilling method should be used.
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