In water well engineering, the traditional pipes used to build wells are mainly cast iron pipes, steel pipes and concrete pipes. These pipes have serious corrosion and aging problems, which have been difficult to solve. Compared with traditional well pipes, polyvinyl chloride PVC-U pipes have uniform performance, strong corrosion resistance, light weight, abrasion resistance and biological inertness, low water flow resistance, long service life, simple and rapid installation, and low cost And other distinctive features.

1 Well completion process
1.1 Preparation for well completion
(1) Correct the hole depth. After the drilling is completed, the hole depth is corrected, and the steel ruler is used to accurately measure all the drilling tools raised from the hole. The hole depth error shall not be greater than 2.
(2) Test hole. After the hole is drilled, test the hole in time to check whether the diameter of the hole meets the requirements, whether the hole is vertical and round, to ensure the smooth installation of the well pipe and the uniform thickness of the gravel. It is advisable to use a steel hole tester to test holes. The length of the hole tester is 20-30 times the diameter of the hole, and the diameter is 20mm-30mm smaller than the diameter of the hole.
Impact drilling test hole: The hole tester is connected to the end of the drill wire rope, and the hole tester can smoothly go to the bottom of the manhole. Drilling: fL I~P qualified.
Rotary drilling test hole: The hole tester is connected with the drill rod to drill the hole. While running the drilling tool, rotate the drill rod manually, and if it goes down to the bottom of the hole smoothly without any resistance, the drilling meets the requirements. Otherwise, put forward the drill bit to repair the hole until the drilling meets the requirements.
(3) Piping. According to the stratum profile divided by drilling and hydrological logging, the location of the filter pipe and the filling location of different specifications of filter materials are determined, and the actual structure of the well is compiled. The filter tube and filter material should be selected according to the aquifer particle screening data. If the prepared filter tube and filter material specifications do not match the screening data, the filter tube and filter material that meet the requirements should be replaced.
When piping, check the quality of the well pipe, carefully check the fit of the threads, and clean the threads; use a steel ruler to measure the length of each well pipe. And use a marker to number the upper and lower pipes on the well pipe according to the actual well structure drawing.
(4) Drill hole cleaning. Before the well pipe is installed, the hole depth and diameter should be accurately measured, and the hole should be cleaned. The percussion drilling hole is used to draw out the drill cuttings and thick mud that settled at the bottom of the hole with a suction tube. After the rotary drilling hole is tested, the drilling tool should be lowered to the bottom of the hole again, and the mud pump should be activated to flush the cuttings deposited at the bottom of the hole out of the hole, and the mud should be thinned out.
1.2 Well pipe installation
(1) The bottom of the sedimentation tube must be set up at the bottom. The bottom of the tube should be processed with a PVC-U board with a thickness of 20mm~30mm or made of other materials that can ensure the bottom of the seal. The bottom of the tube and the precipitation tube can be connected by plastic welding, epoxy resin bonding, mechanical riveting, etc., but it must be ensured The connection is firm and reliable.
(2) The method of direct lifting and one-off pipe down is adopted. When running down the pipe, the well pipe may float before the water filter pipe enters the water (due to the low pipe density, PVc-u well pipe density: 1.35 ~ 1.45g/cm.) sinking is difficult, you can take the well Water is injected into the pipe to increase its weight and help it sink.
(3) Set up a centralizer. In order to locate the well pipe in the center of the borehole and ensure the uniform thickness of the gravel packing, centralizers must be installed at the appropriate positions of the water filter pipe and the well wall pipe when installing the well pipe. The number of centralizers per well shall not be less than 3 (configured according to the actual well depth). The distance between centralizers is generally 30m~50m, and the diameter of centralizers is 50mm~60mm smaller than the borehole diameter. The centralizer can be made of wood, PVC—U board length should not be less than
600mm, thickness 30mm~50mm. 4 pieces of wood centralizers should be evenly distributed along the circumference of the pipe and tied firmly with iron wires; 3 pieces of UPVC centralizers should be evenly distributed along the circumference of the pipe, which can be bonded by adhesive or tied by iron wires.
Whether it is wire binding or adhesive bonding, it should be ensured that the supporting device is firm and reliable.
(4) The well pipe adopts press-formed thread. When lowering the tube, after twisting the thread to the end by hand, you must use hemp rope and wooden sticks or V-belt and wooden sticks to further tighten it.
(5) The lowering speed in the manhole under the well pipe should be uniform and slow. If you encounter obstacles during the down-pipe process, you should find the cause in time. Solutions such as moving up and down and turning the well pipe slightly clockwise, etc. can be taken, without piercing. If the treatment is invalid, the well pipe should be removed from the hole in time. It is strictly forbidden to knock with metal utensils during the lowering process.
(6) The well pipe must be lowered to the bottom of the hole, and pipe hanging is strictly prohibited. After the well pipe goes down to the bottom of the well, a spirit level should be used to measure the verticality of the well pipe and the levelness of the wellhead, and check the size of the exposed ground as required. When all the requirements are met, fix the well pipe mouth, and use the drilling rig hoist to apply tension to the well pipe (natural hanging state) before enclosing the filter material.
1.3 Gravel filling
(1) Filter material selection. The quality and specifications of the filter material should be carefully checked before gravel filling (the quality and specifications of the filter material shall be implemented in accordance with the relevant technical specifications), and the filter material that does not meet the requirements shall not be filled in the manhole. The filter media containing more soil impurities should be rinsed with water before being used. Measure the number of filter materials stored on site and calculate whether the number of filter materials meets the design requirements. The filter material preparation should be sufficient.
(2) Gravel filling. According to the characteristics of UPVC well pipes, the gravel filling method should adopt the flushing gravel filling method. According to the actual situation of the well site, the pumpless gravel packing method or air compressor reverse circulation flushing gravel packing method can also be adopted. The gravel should be filled continuously and evenly around the well pipe from the wellhead, and should not be filled from a single direction. The filling speed must not be too fast. During the gravel filling process, the position of the filter material surface in N:fL should be checked regularly. If blockage or "bridging" is found, measures should be taken to eliminate the gravel before filling. After the filter material is filled to the predetermined position, the surface of the filter material should be measured again before the water stop or external sealing of the pipe
If there is a sinking position, it should be filled to the predetermined position.
Wash the gravel. After running the pipe, lower the drill pipe from the inside of the pipe to a distance of lm~2m from the bottom of the well pipe, and take measures to close the pipe mouth, and start the water pump to inject water from the drill pipe into the well pipe. The amount of water injection shall be subject to not flushing out the filter material. After the annulus outside the pipe returned water, gravel filling began. During the gravel filling process, the flushing fluid should always be circulated and the pump should not be stopped midway.
No pump to fill gravel. Gravel packing H~: The liquid in fL should always keep overflowing from the well nozzle. If the overflow is interrupted, measures must be taken to refill the gravel until the well pipe mouth resumes overflow.
The air compressor washes the gravel in reverse circulation. The orifice should be connected to the water source when filling gravel. The flushing fluid should always circulate over the hole.
1.4 Waterstop and sealing
(1) Water stop material. Waterstop materials should meet the requirements of relevant regulations, and high-quality clay balls or cement slurry should be used. Generally, high-quality clay balls are preferred for permanent water stop. When a well is formed in a high-pressure artesian zone or there are special requirements for water stopping, cement slurry or colloidal cement slurry should be used for permanent water stopping.
(2) Clay balls stop water. The clay ball is made of high-quality clay, the diameter of the clay ball is 20mm~30mm. Let it cool and dry before use until the surface is slightly dry and the inside is moist and soft. When using clay balls to stop water, the clay balls should be filled continuously and evenly around the well pipe from the wellhead, and should not be filled from a single direction, and the speed of putting the clay balls should not be too fast. During the process of putting the clay ball, the position of the clay sphere in the hole should be detected regularly. If blockage is found, measures should be taken to eliminate it before throwing the clay earth. ’
(3) Cement slurry to stop water. When using cement slurry to stop water, it is advisable to use ordinary Portland cement or aluminum sulfate geological prospecting cement of 32.5Mpa or more. Concentrated quick-drying cement should not be used. In order to prevent the water chemical reaction heat generated by the cement slurry from affecting the UPVC well pipe If the strength is affected, 2-9 bentonite should be added to the cement slurry to eliminate the heat generated by water chemistry.
After the clay ball is filled to the predetermined position, the position of the clay sphere should be measured again before the clay backfilling and sealing outside the pipe. If there is sinking, it should be filled to the predetermined position and backfilled with clay. If you want to check the water stop effect, you can do it before backfilling.
1.5 Well wash
Well washing should be carried out after gravel filling and water-stopping clay is backfilled to the ground level, 24 hours after the procedures are completed. According to the characteristics of UPVC well pipes, sodium pyrophosphate or compressed air should be used for well washing. Pistons can also be used to wash wells.
(1) Sodium pyrophosphate washes wells. Sodium pyrophosphate or sodium hexametaphosphate should be cleaned according to relevant specifications. In order to achieve a good well cleaning effect, before cleaning the well, the mud used for drilling and the mud on the hole wall should be tested indoors, the medicament should be dosed according to the test results, and the well should be pumped and washed regularly.
(2) The compressed air well flushing shall be carried out in accordance with the relevant prescribed procedures. In order to reduce the pressure difference between the inside and outside of the well pipe, the air injection speed should be controlled.
(3) Piston washes well. If a piston is used to clean the well, the following requirements should be met: the diameter of the piston should be 20mm~30mm smaller than the inner diameter of the well tube (the steel platen should be 50mm~60mm smaller than the inner diameter of the well tube), and the length of the piston should be 80mm~100mm. The lifting speed of the piston should not be too fast, and should be controlled between 0.4 and 0.8 m/s. When using steel wire rope weighted drill rods to drive pistons to wash wells, elastic centralizers must be installed on the weighted drill rods to prevent damage to UPVC well pipes. The well is cleaned from top to bottom step by step, and the piston cannot stay in the hole for a long time.

2 Problems and countermeasures in construction
(1) Existing problems. When there is no seat at the bottom of the well during construction, the water level in the pipe will drop after the well is washed, and the mud and filter material outside the well pipe will sink and drive the lower well pipe to sink. The upper well pipe cannot follow the pressure of the backfill at the same time. When sinking, the well pipe is prone to be disconnected, causing waste wells.
(2) Countermeasures. First of all, try to place the well pipe at the bottom of the well. After the well pipe is down to the bottom of the well, the well pipe can be lifted by lm~2m again, and then the well pipe can be quickly dropped to the bottom of the well after aggravating, so that the well pipe can be seated at the bottom of the well several times . In addition, when the well pipe is installed, 4 holes can be drilled at the 1:1 position of the well pipe and anchored with screws, so that no disconnection occurs when the well pipe sinks. After the well is washed, the filter material and the backfill can be solidified. The well maintenance was successful.

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