The casing for a well is used during its drilling. The tasks of this element are to contain the shedding of the soil inward. Install the string in the hole that is originally drilled.
At the final stage, concrete is poured into the space between the borehole wall and the casing string. Which you can find out more about below. Further installation of the equipment is accompanied by the installation of devices in the casing, which must be selected taking into account the conditions of the project. It will contain the diameter and size of the hole.
How to choose the diameter
Casing string diameters affect well performance. The higher this parameter, the more water can be obtained. To reduce consumption, it is necessary to determine the smallest diameter that will be able to meet the needs of the family in water. These parameters are necessary for the correct choice of casing pipes.
Peak water consumption for a country house or cottage can be determined by calculating the number of points of consumption. It can be a kitchen, watering the plot, a washing machine and a bathroom. In this scenario, the peak water consumption will be approximately 3 m3/h. If we are talking about a house or a cottage, then this parameter will vary from 4 to 8 m3/h.
Calculation of 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 a country house where the water consumption is approximately 3 m3/h, then a 75 mm pump should be used. If the flow rate is increased to 8 m3/h, then the pump diameter 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 clearance between the column and the equipment, while 8 is the wall thickness of the pipe. Due to the fact that the casing has standard dimensions, it is necessary to select parameters that are closest to the calculated ones. For example, 89, 108 or 114 mm are most suitable for 87 mm.
It will be necessary to equip a well for the selected diameter, 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 method described above. Add 4 and 8 mm to this parameter, which will give you 114 mm.
When choosing casing pipes for this case, you can prefer 114 mm, however, experts recommend purchasing pipes with a margin in diameter, as a result, you can purchasecasing, the diameter of which varies from 127 to 133 mm.
Casing pipe cementing
Cementing casing strings can be carried out according to one of several schemes. The first is called direct and involves the injection of the mixture into the column with the passage to the shoe. The solution enters the annulus and is filled from the bottom up. The second scheme is called reverse and is distinguished by the supply of the mixture from the surface. The uploaded 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 pressed 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 collar, which is used when it is necessary to protect part of the trunk from the penetration of the solution. The cuff isolates the area located in the interval of the productive formation. There are ways to fill secret columns and sections with mortar, which are allocated to a separate group.
Preparation of equipment for cementing
The following equipment may be required for column cementing work:
- cementing devices;
- cement mixing equipment;
- cementing head;
- fill plugs.
Cementing units are required to prepare the cement and push the slurry into the well under pressure. Cement-mixing machines are used for the same purposes, but the cementing head is needed for washing the hole and cementing the walls.
Plugs 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 taps;
- devices for solution distribution.
What are the goals of cementing
Cementing is done to displace drilling fluid from the annulus. The cement slurry rises to a certain height, which is specified in the preliminary calculations. Cementing technology provides:
- displacement of flushing fluid;
- protection of the solution from ingress of flushing fluid;
- filling the interval of the trunk with mortar along its entire length;
- excellent adhesion of cement stone to borehole walls.
If the well casing is well cemented, this will increase the durability of deep structures and the life of production, as well as operation.
Casing run: preparation
A few days before the casing is run, it must be delivered to the rig. Unloading should be carried out according to special rollsor with a crane. It is strictly forbidden to dump casing pipes during unloading.
When inspecting before starting the installation of the pipe, check for deformation of the couplings, curvature, delamination of the material, the presence of nicks and cut ends. The pipes must be checked for ovality and then laid on the bridge in order of running sequence. Casing strings should be run after the numbering of the elements, as well as measuring with a steel tape measure.
Preparing the stem
In order to avoid complications when running the string, it is necessary to prepare the wellbore. The types and scope of work will depend on the condition of the wellbore, the length of the open section and the complexity of the geological section. It is necessary to determine the intervals where difficulties are noted when lowering the tool. These can be ledge formations, narrowing zones of the trunk and inflection areas.
Before leveling 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 drilling fluid to ease the running of the casing.
Casing run
At the next stage, the casing string is lowered into the well; for this, centralizers, scrapers and turbulators are used. During descent, it is important to monitor compliance with the order of completing the string, taking into account the plan for steel strength groups and pipe wall thickness.
The bottom of the casing, which includes the shoe, goes into the well first. Bottom elementsparts of the column must be treated using a hardening lubricant based on epoxy resin. The use of a check valve in this case is mandatory, which is true if there are gas shows in the well.
Pipes are delivered to the wellhead in order of priority, and before building them they are templated. A rigid cylindrical template should enter the pipe from the side of the coupling. When lowering the casing, it is necessary to keep a record of the pipes being built up, 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 weight.
Conclusion
Pipes made of different materials are used as casing strings, these can be plastic, wood, metal and asbestos-cement products. Plastic elements have recently been gaining popularity, this is facilitated by high performance.
