Reasons for plugging artesian wells and methods of its implementation. How to choose a material, the sequence of works when cementing a mine. Backfilling of an artesian well is a set of measures carried out after drilling a mine and during the elimination of sources of this type. The procedure is performed to prevent contamination of the aquifer. You can find out how to properly carry out the work in our article.
What is artesian well plugging?
Artesian wells are considered valuable sources of drinking water and are a strategic reserve of the country. Structures of this type are subject to mandatory cementing to maintain the purity of the deep aquifer, which is carried out according to the well plugging project. A thick sanitary layer reduces the rate of penetration of dirty water underground, and until it reaches the aquifer, all pathogenic microorganisms will die.
Shafts with a typical device are subject to revision: this is a small-diameter mine, the walls of which are reinforced with a casing. Adjacent elements of the barrel are connected by threaded connection, welding or clamps. There is a filter at the bottom of the source. There are wells in which the piezometric level (head) of water rises more than 1.5 m above the surface and less than 1.5 m.
Backfilling is carried out in two cases: to abandon a well or to prevent dirt from entering the underground layers through the gap between the casing and the ground. The procedure is similar in both cases - the voids are filled with special mixtures. Only for liquidation, the solution is poured into the casing, and for strengthening - around it.
With the help of grouting, only artesian wells are decommissioned. Other types of sources are closed in this way only in special cases.
Reinforcement plugging is also performed to protect the joints between the casing sections. In artesian wells, a large mechanical load is applied to the wellbore, which can damage the shaft or the joints of the wellbore. In this case, liquid from the upper aquifers or poorly treated rainwater will begin to flow through the cracks. To avoid trouble, the entire space near the joints is filled with cement or clay mortar. The formed shell, in addition, reliably protects the artificial shaft from aggressive groundwater.
Firming tamponing can be done in different ways:
- Straight … The mixture is poured between the casing and the ground. It descends on its own and fills all the voids.
- Back … The solution is poured into the well, and then pressure is created in it, squeezing it out into the space between the pipe and the ground.
- Multi-stage … The voids are filled simultaneously with the drilling of the wellbore, each section is processed separately.
The advantages and disadvantages of each method are shown in the table:
|Straight||No special equipment required, easy to carry out||It is impossible to control the pouring process, the mixture does not seep to a great depth|
|Back||The voids are reliably sealed, but not throughout the depth of the mine||Special expensive equipment is required|
|Multi-stage||The voids are closed throughout the depth of the mine||Terms of work are significantly increased|
Reasons and scheme of well plugging
Liquidation plugging of wells is performed using special solutions that are fed into the mine through pipes. It is carried out for the following reasons:
- The debit of the source has decreased, and its operation is impossible.
- Other sources of water supply have appeared.
- Defects of the trunk were revealed that cannot be eliminated.
- Deterioration in water quality.
The aquifer can be contaminated with bacteria and chemicals that penetrate deep underground with rainwater. In most cases, they remain in the upper water, which is bounded above and below by waterproof clay layers. The soil itself also traps dirt. But if there is only one aquifer in a given area, dirty water can penetrate to it, even if it is far from the surface. Therefore, it is recommended to drill an artesian well to the greatest possible depth. If chemical elements or harmful bacteria are found, the source will have to be eliminated using plugging.
In some cases, temporary plugging is performed. It is used if an artesian well is being tested or repaired, in which it is necessary to free a part of the well from water. It is placed for a limited period of time. Temporary plugging devices can be hydraulic, pneumatic and mechanical. The simplest design is mechanical, consisting of a rubber nozzle and a rigid rod. When the central part rotates, the size of the nozzle increases, and it tightly clogs the opening.
Sometimes it is necessary to reduce the depth of the excavation in order to start pumping liquid from another aquifer. In this case, partial cementing is carried out, cutting off the lower part of the shaft.
The schematic diagram of the liquidation of an artesian well is as follows:
- Submitting a source owner's statement or a prescription from the relevant services to local authorities.
- Coordination of the procedure with the sanitary and epidemiological service.
- Development of a project of work.
- Cementing the mine in accordance with the main rule for liquidation of wells, which consists in partial or complete filling of the wellbore above the aquifer with a special solution.
- Drawing up an act on the performance of work and transferring it to government agencies after the end of the work.
- A plate is left on the conserved source indicating its depth and the number of the artesian well.
How to grout a well
Grouting refers to complex work performed with the help of special equipment. However, there are simple cementing methods that the owners of the source can do with minimal drilling and mine development experience. Let's consider the sequence of backfilling during liquidation of an artesian well and strengthening of the borehole walls.
Selection of materials for grouting
Filling a well with water begins with determining the material for creating a working mixture and calculating its amount. The choice of components depends on the composition of the soil, and the amount is determined by the volume of the space to be filled.
Pay attention to these points:
- Sand and cement slurry is suitable only for wells drilled in clay layers. The base should be cement grade 400 or higher. It allows you to prepare a liquid mixture that can be easily pumped through hoses. Crushed stone or gravel can be added to increase the strength of the cork. Cement is not used in mines made in loose soils, because the expense will be very high.
- When plugging in porous soils, asbestos, paper and fibrous substances are used.
- For work with loose soils, various fillers and foaming agents are added to the cement to increase the tightness.
- Under certain conditions, clay is used for these purposes, which is prepared in a special way.
Step-by-step instructions for well abandonment
In artesian wells, water comes to the surface under soil pressure. Before starting work, eliminate the spontaneous flow of water by welding a 1 m long elbow to the head. If an increase in the height of the trunk does not help, for plugging use special devices for killing mines - fountain equipment, a pump for pumping liquid solutions, a bailer. All equipment can be rented, but you still need to have experience with it.
The grouting is performed as follows:
- Attach the flowering equipment to the end of the casing.
- Connect it with a hose to the injection pump. The power of the device must exceed the pressure of the water column.
- Prepare a weighted clay mortar.
- Turn on the pump and pump the mixture into the well. It will block the flow of water to the surface.
- Dismantle the fountain equipment.
- Prepare the cement mix.
- Lower the column pipe into the wellbore and pump the prepared solution into it. Instead of cement, the well can be plugged with clay, which is lowered with a bailer.
- If there is no fountain apparatus, the flow of water can be stopped using a mud pump. Install the pipe string into the shaft 1-1.5 m above the bottom and pump in a weighted clay slurry through it.
If the water pressure in the well is low and the liquid does not come out, do the following:
- Clean out debris from the well using special tools such as a bailer. Flush the shaft with a disinfectant. For this purpose, chlorinated water will be needed, the volume of which is equal to three times the volume of the trunk.
- Pour sand into the well above the filter level.
- Prepare the clay or grout for grouting using a concrete mixer. For the procedure, use a viscous clay with a sand content of 5-6%.
- Make balls from it, which are a few millimeters less than the diameter of the hole.
- Dry the workpieces.
- Throw the balls into the barrel one at a time at intervals of 2-3 seconds.
- Clay periodically tamp with a special tool. For a good result, create a layer 1, 5-2 m higher than the filter.
- Fill the entire space of the well to the top with cement mortar.
Clay cylinders made on a press can be used for liquidation of wells. Clay is lowered to the bottom of the well with a thief with a piston. Instead, it is allowed to use a special pipe, which is installed in the well and fixed in the middle of the opening.
The process is carried out as follows:
- Lower the shell with a clay cylinder to a height of 1.5 m from the bottom.
- Squeeze the soil out of the thief with the piston.
- Raise the instrument to the surface.
- Tamp the clay with a special tool.
- Repeat the operation so that a layer of soil of the specified height is formed above the filter.
If it is necessary to move to another aquifer, an artesian well may be partially plugged. To do this, lower a pipe with a smaller diameter into the trunk and create a cement plug with a height of 7-10 m.
Strengthening the walls of the well
To strengthen the walls of an artesian well, the gaps between the casing and the soil are cemented using a special technology called backfilling.
The work is performed in the following sequence:
- Prepare a pump that is capable of pumping liquid mixtures under high pressure to the bottom of the well.
- Install a special shoe in the casing to ensure that the solution is supplied to the gap between it and the ground. He will not let the solution into the well. Connect the device to the pump using special pipes.
- Prepare a grouting solution. For this purpose, gypsum-alumina expanding cement is used, which differs from traditional Portland cement in its ability to expand and fill all voids and cracks.
- Switch on the pump. The semi-liquid mixture will begin to flow into the annulus from below, squeezing out the rest of the soil onto the surface and filling all the cracks.
- After filling the entire space, remove the shoe from the barrel.
What is well plugging - watch the video:
Tamping allows you to maintain the purity of the water in the source. However, the procedure for strengthening the walls of a mine or its liquidation is very complex and time consuming, therefore it is necessary to take it seriously and not deviate from the abandonment plugging project. Responsible work, because errors in its implementation cannot be corrected.