To understand what downhole is, you need to have a general idea of the process, design components, their functions.
This technology is very often used, as wells are used in various areas. This is a geological working, in which the length is greater than the diameter. Often such a system of artificial type, including several components, is created to extract water.
Design Features
Before you deal with the face, you need to find out where it is located. The well is a geological working. Its components:
- mouth - the very beginning;
- wall - the surface inside, has the shape of a cylinder;
- trunk - all space inside;
- bottom hole.
In general, the well includes the following elements:
- Direction. This is the first part of the mouth, which includes loose rocks, they are easily eroded. To strengthen, they make a wide well to the layer where the harder rocks are. Usually it is about 4 to 8 m. A pipe is placed in the hole, and the gap is poured with concrete.
- Conductor. This is the partwhich follows the direction. The conductor is reinforced with a casing, which consists of many smaller ones. The space between it and the cement is also filled with cement.
- Intermediate column. The section that passes through the direction, and the conductor, to cover the weak or difficult layers, as well as those that are not planned to be developed further. If the well is very deep, then there may be several intermediate columns.
- Production column. This is a section from the bottom to the mouth. It is through it that the material is transported.
- Slaughter. This is the last zone of the well. It is intended to extract the product from the layers. The reservoir itself has an upper and lower boundary (roof and sole).
These are the main components without which there is no well.
Slaughter functions
Design of well bottoms is one of the main components of drilling. It performs the following functions:
- Maintains the mechanical strength of the productive layer, due to which the required downhole equipment can be loaded.
- Maintains sufficient hydraulic permeability of the pre-slaughter mechanism.
- Gives access to other productive type reservoirs that were not originally intended to be exploited.
- The ability to influence various adjacent layers or individual sections of the productive layer.
- Maintaining the drainage of the entire reservoir in use.
Since the development conditions can be different, the design of the bottomhole of the well can be sever altypes: open, filtered, perforated, overlapped.
Open face
The bottomhole of an open type is equipped so that the production string reaches the beginning of the layer used. In this state, it is fixed with cement. After that, the layer is cut with equipment with a smaller diameter. The barrel will remain open.
This construction can be used in the following cases:
- clarified the exact boundaries of the layer used;
- layer thickness is small;
- layer includes rocks that will not collapse;
- formation is homogeneous and does not include clay mass that can collapse due to swelling;
- no need to act on hotel sublayers.
The open face has the highest efficiency of the hydrodynamic type compared to other types of structures. That is why the hydrodynamic drilling coefficients of other types are measured relative to the open hole, which is taken as one.
The downside is that there is no way to develop separate zones of the reservoir or separately influence them. In addition, there is a possibility of a layer collapse during pumping, due to the fact that the pressure inside it decreases. Therefore, open-hole wells are rarely used - in about 5% of cases.
Hole covered by perforated production string liner
If it is planned to use this type of bottomhole, then the well is deepened to the bottom of the selected layer and fixedproduction string with drilled perforation, which is located at the level of the productive formation. After that, it is cemented to the point where the used layer begins.
The perforated area will remain open. This option does not have such disadvantages as a decrease in the working diameter, the risk of rock collapse. This method of well bottoming is used in the same cases as the open type.
Backhole with filter
If a bottom hole with a filter is selected, then the casing string is placed up to the upper edge of the used interlayer and filled with cement. A filter is placed into the reservoir along it, which has holes in the form of a circle or a slot. The sections between the filter and the pipe are closed with an oil seal.
Barriers of various designs are suitable. For example, they use these:
- Ring filter. It includes rings worn on a perforated tube. Between them there are tapes of such thickness that the required gap is formed, which is necessary for filtration.
- Gravel filter. These are 2 perforated tubes of concentric type. Between them is gravel 0.5-0.6 cm in size. It is he who is the filter element.
- Sintered metal filter. These are rings made of ceramic shot, which is baked under high pressure. The product is put on a perforated tube.
The last type of filter is the most efficient, as the hydrodynamic resistance is low and has good cleaning ability.
In general, filter faces are used to protectof the extracted product from sand impurities during the development of layers where such formations can be.
Perforated bottom hole
This design option is considered the most common. It has the following advantages:
- Easy to install.
- High quality insulation.
- There is the possibility of further development of other layers.
- It is possible to influence adjacent layers.
- The cross section of the well remains unchanged for a long time.
To make a perforated face, you need to drill a hole from the selected mark. Before the installation site of the casing, everything is examined using special equipment. As a result, you can make marks of the aquifer, and the result will be as accurate as possible.
When the pipe is lowered, it is cemented from the bottom to certain marks, and also perforated in the area of the formation being used.
Cleaning: hydraulic method
An important work operation is cleaning the bottom of a well during its drilling. In this case, it is required to remove the slag, transporting it to the top. If you do not do this, then the accumulated masses will interfere with further deepening. And if there are too many of them, they can provoke sticking of the drill, which will lead to an accident and destruction of the bottom of the well.
It is important to consider cleaning methods as well. It is carried out in different ways. One of them is hydraulic. That is, flushing the bottom of the well. This is the most common option.
He suggestsdownhole fluid use. Usually they use industrial water, special means - saline, clay and clay-free, aerated. In addition, natural solutions are used. They are formed directly in the process of downhole well during its drilling.
If the rocks are weakly stable, then clay solutions are used during the rotation of the drill. They perform the following functions:
- Fix the rock in the walls of the well due to claying and the formation of increased hydrostatic pressure at the bottom of the well.
- Temporarily isolate the aquifer.
- Keep loose rock particles in suspension when fluid stops circulating.
- Reduce fluid loss when supposed to pass through water-absorbing layers.
- Significantly improve the conditions for cleaning the face and transporting cuttings.
Aerated type liquids are used. This is necessary to reduce the hydrostatic pressure at the bottom of the well and the penetration of fluid into the layers. At the same time, aquifers are less clogged, and fluid loss is reduced.
Direct flush pattern
Direct flushing is very simple, but has a number of disadvantages. This includes increased fluid costs, especially if the well diameter is large.
Due to the fact that you need to have a significant speed of the ascending jet, which ensures the removal of sludge. In addition, the increase in the likelihood of an accident due to collapses of the walls, which are made of unstablebreed.
Reverse flush pattern
Backwashing is carried out due to the fact that liquid is pumped in or it is pumped out by a special pump. Vacuum, centrifugal, piston, water jet type equipment or airlifts are used. With this method of flushing, the circulation of the solution is local or downhole, complete or not.
Such a scheme has the following advantages:
- increases the speed of the ascending jet and at the same time the liquid flow is small;
- It is possible to transport the masses without a drilling tool.
These nuances must be taken into account.
Cleaning: pneumatic method
In this cleaning method, air or gas is used instead of a solution. The latter is used during drilling of wells with oil. It is also used in gas-bearing regions. This is due to the fact that it is forbidden to use air there, as this can lead to a fire. For example, exhaust gases from internal combustion engines can be used.
But air blowing is the more common method. It is used even more often than washing. Benefits include:
- no solution required;
- no special fluid cleaning equipment needed;
- can be drilled in non-water-bearing areas, as well as in places with permafrost;
- drilling speed is getting faster;
- hygienic conditions for the brigade are better, especially in winter.
But thisThe method also has disadvantages. The main thing is that if water enters the well, accidents can be provoked. For example, a small influx of water causes the sludge to turn into a dough-like mass that adheres to the equipment. In more difficult cases, the drilling depth is reduced.
Cleaning: mechanical method
This method involves screw and impact methods. And so are the types of drilling, and at the same time cleaning. Both methods are equally popular.
In the first case, a special screw conveyor is used, which is a hollow tube with a spiral belt. During its friction, the rock is destroyed and rises up due to the movement of the apparatus.
In the impact method, after the destruction of the rock by a drilling rig, special mechanisms are used that are lowered into the well and transport cuttings from it. Such equipment is called a bailer. It rises to the surface a large number of times and dumps the collected material, which has a suspended state. To do this, they pour a little solution into the well.
Cleaning: combined method
Combined cleaning method involves a combination of hydraulic or pneumatic method with a mechanical one. This option is considered more efficient. It is often used when wells are column-shaped or have a large diameter.
