Oil and gas industries need special equipment. For the organization of the working cycle, a downhole motor (VZD ) is often used. He is involved in the production of liquid and gaseous, as well as solid minerals, and can also be used in the process of repairing existing wells.
Special equipment has a number of special technical characteristics. In order for the unit to fully fulfill the functions assigned to it, it must be correctly selected in accordance with existing operating conditions. For this, it is necessary to understand the design structure of the PDA, as well as the rules for its application at various objects.
general characteristics
A downhole screw motor is used in the mining industry for drilling deep, directional, horizontal and vertical wells. It allows you to drill plugs of sand, salt deposits, cement bridges.
So that the engine can perform its functions, it has a certain torque. Depending on its technical characteristics, equipment can destroy rocks at the required speed. This ensures high efficiency of the technological cycle.
The diameter of the IDC can be from 54 to 230 mm. Strong but flexible teeth are used in the design. This allows you to provide high rigidity to the bending structure, to reduce the leakage of liquids during their pumping.
The production of downhole screw motors began in 1962. It was released by the American manufacturer Dyna-Drill. It was a single screw pump. A similar design was invented in 1930 by the French engineer Muano.
The characteristics of the first VZD were slightly different from modern units. It provided effective directional drilling. At the same time, its speed was 200 rpm. In 1966, a unit was created by domestic technologists, which was distinguished by a low speed. He was able to adjust the speed from 100 to 200 rpm.
Over time, the device improved. There are many varieties of such equipment. They are used in various mining industries. To ensure proper drilling in various conditions, the design and principle of operation of the IDP may differ slightly. However, the main principle of operation remains the same for all varieties.
Design
The design of the equipment shown may vary slightly. For example, consider the device of a downhole motor DR 95. This device is a symmetrical rotary equipment. When it is used, gearing is oblique. The mechanism is driven by the pressure of the supplied fluid.
The design consists of an engine assembly as well as a working part. The first element of the system is the main power component. It is from its characteristics that the operational features of the equipment depend. These include power, efficiency, torque, and rotor speed.
The motor unit consists of a stator (housing) and an elastomeric insert with a thread. The rotor hooks on it. Under fluid pressure, rotation begins. The elastic shell divides the chamber into two cavities. It is made of durable rubber, resistant to wear. When abrasive particles get on the surface of the material, it does not collapse.
The performance of a downhole screw motor is influenced by many factors. The design rotor has the form of a drill. Its coating is very durable, made of alloy steel. The number of teeth on the rotor is one less than that of the stator. The motor unit has a certain gear tension. It depends on the characteristics of the working fluid, operating temperature, etc.
The working bodies are represented by a spindle unit and an angle adjuster. The first of them transmits torque to the working tool. It is subjected to significant axial loads. The spindle unit has a housing and two supports. A shaft is mounted on them. A node can be open or closed.
Operating principle
The principle of operation of a downhole screw motor is determined by the design features. These are volumetric rotary machines. The stator of their engine with cavities is adjacent to the low and high pressure chambers. The rotor screw is leading. Through it, torque is transmitted to the actuator.
Locking screws are called follower members. They seal the engine. By means of contactors, liquid from the high-pressure chamber is prevented from entering the low-pressure compartment.
The fluid circulates inside the structure through the working bodies. This movement is possible due to the pressure drop. In this case, a rotor torque occurs. The screw elements of the working bodies are mutually closed. They separate the high and low pressure areas.
Therefore, the principle of operation of a downhole screw motor is similar to the operation of piston types of equipment. Separated gateways are created in the working bodies of the VZD. For this, the number of stator teeth is determined to be larger by one than that of the rotor (internal element). The length of the working bodies cannot be less than the pitch of the helical surface of the outer element. This determines the normal functioning of the system. Moreover, the ratio of the steps of the outer and inner surfaces of the screw is proportional to the ratio of the number of teeth. Their profiles are characterized by a mutually flexible shape. This allows them to be in continuous contact in any area of the clutch.
Multiplicity is one of the main parameters of the equipment. Domestic production units have multi-working working bodies. Foreign companies manufacture the presented engines with one or more rotor starts.
Classification
In accordance with various factors, there is a classification of downhole screw motors. According to the sign of application, there are three main categories of SAC:
- Units for drilling in the vertical direction. They have direct execution. The outer diameter of such units is from 172 to 240 mm.
- Equipment for horizontal and directional drilling. Such engines have a curved layout. The diameter can range from 76 to 240 mm.
- Devices for repair work. They have direct execution. The outer diameter is from 43 to 127 mm.
Power units can have an active part up to 550 cm long. The downhole screw motor 105, 127, 88, 76, 43 mm can have a direct design. Instruments with the ability to adjust the angle of inclination are also available. This also allows for inclined or horizontal drilling. Power units are used to create a vertical well. Their outer diameter, power should be greater. The dimensions of the diameter for such units can not be less than 178 mm.
The simplest and most inexpensive varieties of the equipment are VZD for well repair. These are reliable units equipped with a torsion transmission, rubber-metal bearings.
Drilling equipment is additionally equipped with emergency components. This eliminates the need to leave parts on the face in the event of a breakdown. Spindle compartments of engines for inclined and horizontal drilling incorporate radial carbide bearings. Their bearings have a high load capacity.
Sludge traps, calibrators, centralizers, check valves and overflow valves can be added to the design of the VZD. Also, the package may include various spare parts.
Number of sections
A downhole motor may have one, two or three sections. This determines the design and operation features of the device. Single-section varieties are indicated by the letter "D". They consist of a spindle section and a motor. Also in the design there is an overflow valve.
Single-section designs are of direct design and are most often used for well repair. Due to the features of the mechanism, the use of special seals drilling is possible with pressure drops on the bit up to 8-10 MPa. Single-section designs are made in our country and abroad. They are widely used in modern mining industry.
Sectional downhole screw motors for drilling wells may have certain design features. Their use is considered more appropriate. Single-section varieties significantly lose their energy characteristics during wear of screw pairs.
Multisectional types of equipment are more popular today. Due to the features of their design, the load on the working pairs is reduced. Drilling fluid consumption is also reduced. Depending on their class in the designation there are 2 letters. Engines of the DS type can be used for drilling inclined and vertical tunnels for various purposes. Their drilling fluid cannot have a temperature above 373 K.
The DG series has a shorter length. The necessary power and resource provides a two-step power section. In such designs, various mechanisms of curvature of the housing are used. Can be equipped with centering devices.
The DO series is represented by rejectors. They have a hard curve sub. The angle of curvature of the spindle section is unregulated. It is used to create inclined tunnels. Devices of the “DR” type have a curvature angle regulator.
Turboprop Varieties
A relatively new kind of equipment are turbine-screw downhole motors . They are characterized by high resistance and high energy efficiency. This variety of units is sometimes referred to as a gear turbodrill class.
The screw pair has the function of a reducer and a stabilizer. This allows you to optimize the work of the bit under load. The design of turbine-screw varieties is highly complex. When you create it requires a lot of material. Therefore, the cost of the equipment presented remains high. However, its working life exceeds the usual varieties of CDP.
The screw pair of the presented units can be mounted above the turbine section or between it and the spindle compartment. The first option is simpler. The unit includes in this case only one connection node. The second version of the screw pair is less reliable due to its complexity. Here it is necessary to create two rotary junction nodes.
PDC characteristics
Features of drilling with downhole helical motors determine their characteristics. They must be taken into account for the correct selection of drilling parameters. Stable drilling conditions must be maintained throughout the entire production process. Today, the HPAs are being improved in accordance with the existing requirements of mining companies.
Equipment performance is constantly improving. This allows you to correctly apply new technologies in the mining industry. In the modern world, adjustable pump drives have been used. Drilling can be carried out in inclined and horizontal directions. A continuous pipe method is also used. To ensure high productivity of new processes, equipment characteristics are examined in various ways.
During the development of the drilling program, bench tests of the PDW are performed. This allows you to identify their actual operating parameters. This entails additional costs for the manufacturer. However, the equipment is used more efficiently. Production cycles are organized harmoniously. By the pressure that is present in the riser, you can control the load of the bit. This entails an increase in drilling efficiency.
Downhole helical motors for drilling wells can have static or dynamic characteristics. In the first case, the dependence between the observed variables in steady states is reflected. Dynamic characteristics reflect the ratio of indicators in transient modes. They are caused by the inertia of the observed processes.
Bench and load characteristics
Drilling with downhole helical motors requires compliance with the rules and regulations established by the equipment manufacturer. They are determined using bench or load characteristics. In the first case, torque functions are tested in production. The load characteristics are determined after bench tests for specific well creation conditions.
With increasing torque, a certain pressure drop is created. This indicator increases linearly. The speed at the beginning of the test decreases slightly. When approaching a complete stop, the drop occurs abruptly. The curves of general efficiency and power are extreme.
Testing is performed in four main modes (optimal, idle, extreme and braking). The operating mode of the VZD in the study in the conditions of production are extreme conditions. In accordance with this mode, the passport data of the equipment are indicated.
It is considered optimal if the unit is used in modes that are shifted to the left of extreme operating conditions. Torque in this case will be less important. Under extreme operating conditions, the most effective rock breakdowns are determined. The boundary of this mode passes near the zone of stability of the device. With a further increase in load, drilling with downhole motors stops. There is a braking mode.
Operational Features
Based on the results of testing the characteristics of the equipment, the rules for operating downhole screw motors are established. In the cold period, the mechanism is heated by steam or hot water. The flushing fluid must have a certain level of viscosity and density. There should not be sand in it.
When the device is lowered to a depth of 10-15 m, you need to turn on the pump, flush the well zone. The engine does not turn off at this moment. If the bit is new, it is necessary to run it in with a small axial load.
The tool is fed into the well smoothly. There should be no jerking. Periodically, the rotation of the VZD is performed. In this case, it is necessary to correctly set the flow rate of the flushing fluid. For this, it is necessary to take into account the features of cleaning the face.
In the process, the working pair gradually wears out. To ensure high efficiency when operating a downhole motor , it is necessary to increase the flushing flow. It should be 20-25% higher at the end of the work compared to the initial level.
To prevent sludge from accumulating in the engine, it is necessary to flush the well before increasing the capacity or raising it when replacing the bit. Only after this the tool rises above the bottom zone by 10-12 m. After that, you can stop the pump, open the valve.
Also, during the operation of the equipment, it is necessary to check its operation. The engine is sent for maintenance at a set frequency. With a decrease in its power and operational characteristics, the equipment is sent for repair. This procedure is also necessary when increasing the spindle clearance. Also, the engine maintenance procedure is carried out in case of contamination or inability to start over the well.
Finally
The downhole motor must have a certain flow rate of the washing liquid. The more blades the rotor has, the greater the amount of flushing required during operation of the equipment. However, this also leads to increased wear on the unit.
When there is no load on the equipment (when rising from the well), the pressure inside drops. If the rotor is suspended, bring the equipment harder. This requires a huge amount of energy.
When the load on the CDW increases, a drop in pressure is observed at the start of the procedure. However, it is restored when the rotor is untwisted.
When operating the unit, the maximum permissible pressure in the working unit must be taken into account. If the established line is exceeded, the elastomer is deformed. Torque will be lost. In this case, the work will not be able to move forward, and the working fluid will flow idle through the engine.
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