The casing for the well is used during its drilling. The objectives of this element are to restrain soil from shedding inward. Install the column in the hole that is initially drilled.
At the final stage, concrete is poured into the space between the well wall and the casing. What you can learn more below. Further installation of the equipment is accompanied by the installation of devices in the casing, which should be selected taking into account the conditions of the project. The diameter and size of the hole will be written in it.
How to choose a diameter
Casing diameters affect well productivity. The larger this parameter, the greater the volume of water that can be obtained. To reduce consumption, you should determine the smallest diameter that will be able to meet the water needs of the family. These parameters are necessary for the correct selection of casing pipes.
The peak water flow rate for a country house or cottage can be determined by calculating the number of consumption points. It can be a kitchen, watering the plot, a washing machine and a bathroom. In this situation, the peak water consumption will be approximately 3 m 3 / h. If we are talking about a house or a cottage, then this parameter will vary from 4 to 8 m 3 / h.
Diameter calculation
Calculation of casing strings is necessary, trying to calculate the diameter, which will depend on the used submersible pumping equipment. If the column is located in the country, where the water consumption is approximately 3 m 3 / h, then a 75 mm pump should be used. If the flow rate is increased to 8 m 3 / h, then the diameter of the pump should be 102 mm. Sometimes it happens that the aquifer is characterized by an increased dynamic or static water level, in which case the pump must hang in the pipe.
The choice of pipe diameter for a 75 mm pump should be as follows: 75 + 4 + 8 = 87. Where 4 is the gap between the column and the equipment, while 8 is the pipe wall thickness. For the reason that the casing string has standard sizes, it is necessary to select the parameters that are closest to the calculated ones. For example, 89, 108 or 114 mm are most suitable for 87 mm.
Under the selected diameter, it will be necessary to equip the well, this option will be considered the most economical. If you have chosen a 102-mm pump, then calculations for it must be done according to the method described above. 4 and 8 mm should be added to this parameter, which will make 114 mm.
Choosing casing pipes for this case, you can prefer 114 mm, but experts recommend purchasing pipes with a margin in diameter, as a result, you can purchase a casing, the diameter of which varies from 127 to 133 mm.
Casing Cementing
Cementing casing can be carried out according to one of several schemes. The first is called straight and involves the injection of the mixture into the column with passage to the shoe. The solution enters the annulus and is filled from bottom to top. The second scheme is called reverse and differs by the flow of the mixture from the surface. The injected composition moves from top to bottom.
When it comes to industrial scale, the first method is most often used. In this case, cementing is carried out in one step, during which the volume of the solution is forced through immediately. When the casing has an impressive length, resort to two-stage cementing. The front of work in this case is divided into intervals performed using the equipment in turn.
An additional method of cementing is the cuff, which is used if necessary to protect part of the barrel from the penetration of the solution. The cuff isolates the area located in the interval of the reservoir. There are ways to fill the solution with secret columns and sections, which are allocated in a separate group.
Cementing equipment preparation
The following equipment may be required for cementing the column:
- cementing devices;
- cement mixing equipment;
- cementing head;
- filling plugs.
Cementing aggregates are required for the preparation of cement and forcing the mortar into the well under pressure. Cement-mixing machines are used for the same purposes, but the cementing head is needed to flush the barrel and cement the walls.
Jams are used if you want to resort to two-stage cementing. Sometimes, small equipment is also required for work, namely:
- flexible metal hoses;
- high pressure valves;
- devices for distributing the solution.
What are the goals of cementing?
Cementing is performed to displace drilling fluid from the annulus. The grouting mortar rises to a certain height, which is prescribed in preliminary calculations. Cementing technology provides:
- displacement of flushing fluid;
- protection of solution from hit of washing liquid;
- filling with the solution the interval of the trunk along its entire length;
- excellent adhesion of cement stone to the walls of the well.
If the casing of the well is cemented in a quality manner, this will increase the durability of the deep structures and the production and operational life.
Casing Descent: Preparation
A few days before the casing descent, it must be delivered to the rig. Unloading should be carried out on special rolls or using a truck crane. It is strictly forbidden to drop casing pipes when unloading.
When inspecting before installing the pipe, you should check for deformation of the couplings, curvature, delamination of the material, the presence of nicks and cut ends. The pipes should be checked for ovality and then laid on the bridge in the order of descent. Casing descent should be carried out after numbering the elements, as well as measuring with steel tape.
Barrel preparation
In order to eliminate complications during the descent of the column, it is necessary to prepare the wellbore. The types and volume of work will depend on the condition of the trunk, the length of the open part and the complexity of the geological section. It is necessary to determine the intervals where difficulties are noted during the descent of the tool. This may be the formation of ledges, zones of narrowing of the trunk and areas of inflection.
Before aligning the properties of the flushing fluid, the well must be flushed. The duration of this process should be two cycles or more. Finally, graphite or oil is added to the flushing fluid to facilitate casing descent.
Casing descent
At the next stage, the casing is lowered into the well; for this, centralizers, scrapers and turbulators are used. During the descent, it is important to monitor compliance with the order of manning the column, taking into account the plan for the groups of steel strength and pipe wall thickness.
The bottom of the casing, which includes the shoe, first goes into the well. Elements of the bottom of the column must be processed using hardening grease based on epoxy resin. The use of a check valve in this case is necessary, which is true if there are gas manifestations in the well.
Pipes are delivered to the wellhead in order of priority, and they are patterned before building up. A rigid cylindrical template must enter the pipe from the coupling side. When lowering the casing, it is necessary to keep records of stacked pipes, indicating the element number, steel strength group, pipe length, wall thickness. It is important to note the final length of the pipe and its total mass.
Conclusion
Pipes of different materials are used as casing strings; these can be plastic, wood, metal and asbestos-cement products. Plastic elements have recently gained popularity, this contributes to high performance.