The wellhead is the point at which a well intersects the surface of the earth. At this point, a production pipe comes to the surface, where water intakes and a pump are located. After completion of work on the device of the water source, metal pipes are installed, the diameter of which is 12.7; 14.6 or 16.8 cm (these parameters are specified in GOSTs, where information about casing pipes is provided). But if other sizes are used, this indicates that the pipes are not drilling. Plastic pipes can be laid inside to ensure that the produced water is environmentally friendly.
When plastic pipes are installed
The wellhead is sometimes arranged using only plastic elements. Which is true if the depth does not exceed 50 m. Such products have a service life of about half a century, and they are not afraid of corrosion, they are not covered by microorganisms, and sediment does not appear inside. The pipes are highly resistant to chemicals andresistance to rock settlement or soil freezing.
The material for such pipes is polyethylene, and some products also have a thread. PVC pipes are almost never found and are not used, as they are made to order and connected by soldering, which increases the cost of well construction.
Mouth design
The wellhead must be designed for year-round use. Therefore, the arrangement of this part of the water source is one of the important stages in creating a water supply system for a house or even a village. Initially, a head should be installed at the mouth, which is a large metal pipe. The rest of the work on the arrangement of this part of the well can be carried out after drilling is completed or later.
The wellhead is arranged using some components, namely:
- large capacity;
- steel pipe;
- submersible pump;
- automatic equipment;
- connectors.
Pumping equipment will be located in the tank. This part of the well is called the caisson. It will border on the ground surface at the top point. This is a head, it is needed to control the operation of the water supply system. The node is located at the wellhead.
Expert advice
It is important to determine the right amount of such additional elements:
- pipes;
- valves;
- fittings.
The caisson must be steel or plastic witha good layer of insulation and anti-corrosion coating. And the correct installation allows you to protect the water supply system from freezing when the temperature drops.
Device Features
The wellhead is arranged by removing the soil around the metal pipe. After that, the caisson descends to the depth. First, a head should be installed on the wellhead - a pipe with a diameter that will be greater than the diameter of the first casing pipe. The base of the cap will need to be cemented.
When drilling a well that will be operated all year round, a caisson should be installed. Pumping equipment will be located in the tank. A caisson is something like a large barrel of 2 m. The diameter is 1 m. This device is installed on the head, while the container must be on the soil freezing line. Soil must be removed around the steel pipe, and the caisson must then be lowered.
In the bottom of the caisson, you need to make a hole with a diameter equal to the diameter of the head. Both elements are connected by welding. It will be necessary to install pumping equipment in the caisson, then communications are connected, power supply is connected.
The cover of the caisson will have to block access to the source. As a result, you will get a manhole that provides access to the well. When choosing a caisson, you can purchase both ground and underground chambers. On dry soils, it is recommended to use underground chambers. Aboveground caissons will be relevant in other cases.
Toppart of the casing pipe must be designed in a certain way so that surface water and dirt do not get inside. You also need to make sure that the pressure line does not freeze, because it will have to be serviced by cleaning, and repairs will also be required from time to time.
Head at the mouth
The outlet pipe must have a head with a diameter larger than that of the upper casing. This part of the well not only prevents pollution, but also to hold the submersible pump, undergoes pressure from inside and outside. Headers can be made from:
- cast iron;
- plastic;
- steel.
The second ones are designed for shallow wells and differ in quality and type of connecting fitting. Steel heads can withstand a load of up to 0.5 tons, while plastic heads can withstand about one centner.
The head of the mouth provides for the presence of fasteners, a cover, a flange (made of steel or plastic). The knot also consists of a carabiner, as well as a rubber ring. The outer cover has not only terminals, but also external eyebolts that are welded on, and one of them is from the inside.
About pressure
One of the operations in the construction of a well is a development operation in order to create conditions for the flow of oil. At the same time, the density of the clay solution gradually decreases - it is diluted with water, and the hydrostatic pressure of the liquid column decreases. Manipulations continue until the mud is replaced.
When the pressure at the wellhead decreases bythe last oil from the reservoir begins to flow through the perforations into the wellbore, displacing water, coming to the surface. In order to make the process safe and controlled, the mouth is closed with a lid. This requirement is especially important to meet at high reservoir pressures. The cover is bolted to the casing flange. A production string of pipes is passed through the cover into the well, while pipes and valves are attached from the outside. The knot is called a Christmas tree. And the outlet fitting in this system plays the role of a corridor through which oil is taken from the well. If the oil well head pressure is insufficient, compression is performed by compressors to increase absorption and reduce plant investment.
Features of the piping of the mouth
The wellhead control equipment is mounted on the drill string to control the flow of gas and liquid. This also prevents the risk of formation fluid blowout from the wellbore.
Wellhead piping involves screwing a wellhead head to the top drill pipe (it can be swivel or fixed type). The head is connected to the steel manifold with movable swivel elbows using quick couplings. The manifold is fixed to the drilling rig by means of supports, which eliminates the vibration of the pipeline.
Performing sealing
Wellhead sealing is carried out after shutdowndrilling. Next, you need to achieve the exit of the pipe coupling to the line of the wrench dies, while the winch brake is fixed, and the pumps stop. The end valve must be opened and the position of the valves on the throttling unit must be checked. They need to be opened. The wellhead equipment provides for the screwing of a ball valve. The winch brake must be fixed. The tool is insured by the elevator. The preventer at this stage should be closed, as well as the ball valve. The flow line valve must be closed. It is important to monitor the pressure.
