Casing string

A casing string for a well is used during its drilling. The tasks of this element are to restrain the soil from shedding inside. 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 string. What you can learn more about 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. It will have the diameter and the size of the hole.

How to choose the diameter

The diameter of the casing string influences well productivity. The larger this parameter, the more water can be obtained. To reduce the flow rate, you should determine the smallest diameter that will be able to meet the needs of the family in the water. These parameters are necessary for the correct choice of casing.

The peak consumption of water for a country house or cottage can be determined by calculating the number of points of consumption. It can be a kitchen, a watering site, a washing machine and a bathroom. In this scenario, the peak consumption of water will be approximately 3 m ³ / h. If it is a house or a cottage, this parameter will vary from 4 to 8 m ³ / h.

Calculating the diameter

Calculation of casing strings must be carried out, trying to calculate the diameter, which will depend on the submersible pumping equipment used. If the column is located in the country, where the water flow 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 pump diameter should be 102 mm. Sometimes it happens that the aquifer has a higher dynamic or static water level, in which case the pump in the pipe must hang.

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. Due to the fact that the casing string has standard dimensions, it is necessary to select the parameters closest to the calculated ones. For example, to 87 mm, the most suitable are 89, 108 or 114 mm.

Under the chosen diameter, it will be necessary to equip the well, this option will be considered the most economical. If you chose a 102-mm pump, then calculations for it must be made according to the above described procedure. To this parameter should be added 4 and 8 mm, which will get 114 mm.

Selecting casing pipes for this case, you can prefer 114 mm, but experts recommend buying pipes with a stock in diameter, eventually you can get a casing, the diameter of which varies from 127 to 133 mm.

Casing cementation

Cementing of casing strings can be carried out according to one of several schemes. The first is called a straight line and involves pumping the mixture inside the column to the shoe. The solution enters the annular space and is filled from the bottom up. The second scheme is called reverse and differs by feeding the mixture from the surface. The injected composition is moved from top to bottom.

If it is an industrial scale, then the first method is most often used. In this case, the cementing is carried out in one step, during which the volume of the solution is forced through immediately. When the casing string is of an impressive length, two-stage cementing is used. The front of the work in this case is divided into intervals performed by the equipment alternately.

An additional method of cementation is the cuff, which is used when it is necessary to protect part of the trunk from penetrating 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 to a separate group.

Preparation of cementing equipment

The following equipment may be required for cementing the column:

• Cementing devices;
• Cement-mixing equipment;
• Cementing head;
• Filling plugs.

Cementing aggregates are required to prepare the cement and push the solution into the well under pressure. Cement mixing machines are used for the same purposes, but the cementing head is needed for washing the trunk and cementing the walls.

Traffic jams are used if you want to resort to a two-stage cementing. Sometimes for the work required also small equipment, namely:

• Flexible metal hoses;
• High pressure cranes;
• Devices for distribution of solution.

What are the objectives of cementing?

Cementing is performed to displace the drilling fluid from the annulus. The grouting solution rises to a certain height, which is prescribed in the preliminary calculations. Cementing technology provides:

• Displacement of the washing liquid;
• Protection of the solution against ingress of washing liquid;
• Filling with a solution of the interval of the trunk along its entire length;
• Excellent adhesion of cement stone to the walls of the well.

If the casing string of the well is cemented well, this will increase the durability of the deep structures and the production time, as well as operation.

Casing run: preparation

A few days prior to the descent of the casing, it is necessary to deliver it to the drilling rig. Unloading should be carried out by special rolling or by means of a truck crane. It is strictly forbidden to discharge casing pipes when unloading.

When inspecting before beginning installation, the pipes should be checked for deformation of the couplings, curvature, stratification of the material, the presence of notches and chopped ends. Pipes should be checked for ovality, and then laid on the bridge in the order of descent. Casing run-off should be carried out after the numbering of the elements, as well as measuring with steel tape measure.

Preparation of the trunk

In order to avoid complications during the descent of the column, it is necessary to prepare a wellbore. The types and scope of work will depend on the condition of the trunk, the extent of the open part and the complexity of the geological section. It is necessary to determine the intervals where difficulties are noted when the tool is lowered. This can be the formation of ledges, the zone of narrowing of the trunk and areas of inflection.

Prior to equalizing the properties of the drilling fluid, the well must be rinsed. The duration of this process should be two cycles or more. Finally, graphite or oil is added to the washing liquid to facilitate the descent of the casing.

Casing run

At the next stage, the casing is lowered into the well, using centralizers, scrapers and turbulators. During the descent, it is important to monitor the compliance with the order of the column, taking into account the plan for the strength groups of steel and the thickness of the pipe walls.

In the well, first comes the bottom of the casing, which includes a shoe. Elements of the bottom of the column must be treated using a hardening grease based on epoxy resin. The use of a check valve in this case is mandatory, which is true if there are gas displays in the well.

Pipes are delivered to the well mouth in order of priority, and they are pre-engineered prior to building. The rigid cylindrical template must enter the pipe on the side of the coupling. Descending the casing, it is necessary to keep track of stackable pipes, indicating the number of the element, the strength group of the steel, the length of the pipe, and the wall thickness. It is important to note the final length of the pipe and its total mass.

Conclusion

Casing pipes are made of different materials, such as plastic, wooden, metal and asbestos-cement products. Plastic elements have recently gained popularity, this is supported by high performance characteristics.