The oil field, as a special industry, has its own unique background. The application of the medium frequency converter in the oil field is mainly focused on beam-type pumping unit control (commonly known as “bread machineâ€), electric submersible pump control, injection well control, and oil and gas gathering and transmission control. Wait a few occasions. This article mainly introduces the application of Taiwan billion inverter on beam pumping unit.
First, the working principle of bread machine
Figure 1 physical diagram of beam pumping unit
At present, in the field of oil pumping equipment, the use of beam type Shantou pumping unit is the most common application, the largest number, but the traditional steamed bread machine generally has a large starting impact, running power consumption, large horsepower car, low efficiency Many problems, in addition to the complex well conditions, the phenomenon of heavy oil, wax deposition, and Shaka are frequent, and broken rods, burning motors and other phenomena often occur, there is no reliable protection function for the motor, and the amount of equipment maintenance is large. Therefore, it is urgently needed. Some pumping unit equipment was modified.
When the hoe machine is working, the load acting on the donkey head is changed. On the upstroke, the head of the donkey needs to lift the sucker rod and the liquid column. Under the condition that the pumping unit is not balanced, the motor must pay a lot of energy. On the down stroke, the pump rod turns to work on the motor, leaving the motor in generator operation. When the pumping unit is not in balance, the load on the upper and lower strokes is extremely uneven, which will seriously affect the efficiency and life of the four-bar linkage mechanism, the reduction gear box and the electric motor of the pumping unit, and deteriorate the working conditions of the sucker rod, increasing the Its number of breaks. In order to eliminate these disadvantages, a balance weight is generally added to the tail or the crank of the pumping unit or both, as shown in FIG. 1 . In this way, in the lower stroke of the hanging point, the balance weight should be lifted from a low position to a high position to increase the potential energy of the counterweight. In order to raise the balance weight, in addition to relying on the bit energy released by the drop of the sucker rod, the motor must also pay a part of the energy. On the upstroke, the counterweight falls from a high position, releasing the stored bit energy during the down stroke, helping the motor to raise the sucker rod and the liquid column and reducing the amount of energy the motor needs to give in the upstroke. At present, more beam pumping units are used, and the working method of adding balance weights is adopted. Therefore, in a working cycle of a pumping unit, there are two motor operating states and two generator operating states. When the balance weight adjustment is good, both the generator operating time and the energy generated are small.
The frequency conversion of beam pumping unit mainly has the following three aspects
(1) The power factor is greatly improved (from the original 0.25-0.5 to 0.9 or more), which greatly reduces the power supply current, thereby reducing the burden on the power grid and the transformer, reducing the line loss, and eliminating the need for a large number of "Expenditure. This is mainly concentrated on occasions where the power supply enterprises require higher quality of the power grid. In order to avoid a decline in the quality of the power grid, variable frequency control is required. Its main purpose is to reduce the influence of the working process of the pumping unit on the power grid. In the early stage, due to freshly mined and large oil storage, the frequency converter was operated to 65HZ, the frequency was increased by 1/3, the corresponding motor speed was increased by 30%, and the amount of oil used was also increased accordingly. Its comprehensive oil recovery rate was comparable to In the case of frequency, more than 20% of oil is recovered, and the work efficiency is increased by 1.2 times, which is very popular with oil field oil refiners.
(2) Frequency conversion with energy saving as the first goal. This is more common, on the one hand, oil field pumping units to overcome the large starting torque, the use of the motor is far greater than the actual power required, the working efficiency of the motor is generally 20% to 30%, the maximum will not exceed 50% The motor is often in a light load state, causing waste of resources. On the other hand, the continuous change of the pumping unit's working conditions depends on the state under the ground. If it is always at the power frequency, it will also cause a waste of electrical energy. In order to save energy and improve the efficiency of the motor, frequency conversion must be carried out. In the middle and later wells, due to the reduction of well reserves, if the motor is still running frequently, it will certainly waste energy and cause unnecessary losses. Therefore, we adopt a way to reduce the speed, reduce the stroke, and generally run the frequency of the inverter to 35-40Hz. Between these, the motor speed drops by 30%, and the general load of the oil extraction equipment is lighter, the energy saving rate can reach about 25%, and the power factor is increased, which reduces the reactive power loss.
(3) The inverter has a soft start/soft stop function. When the motor starts, it reduces the mechanical impact on the sucker rod and protects the motor and protects the motor against heavy oil, wax, sand, and other effective areas. Mechanical equipment, reduce maintenance, prevent broken rods, the inverter can reliably protect against over-voltage, under-voltage, overload, short circuit and motor stall. It has good performance in prolonging the life of the motor and reducing the wear of mechanical equipment. effect.
Thanks to the realization of a true "soft start", excessive mechanical shocks are avoided for motors, gearboxes and pumping units, which greatly extends the service life of the equipment, reduces the production stoppage time, and increases the production efficiency. To improve the quality of the power grid and energy saving for the purpose of frequency conversion. This situation combines the advantages of the above two transformations and is an important direction of development in the application.
Third, the pumping machine technology development
The first generation: The first main motor of the pumping unit is mainly used to start the three-phase asynchronous motor. The disadvantage of the three-phase asynchronous motor starting operation is that there is no speed regulation function, and only one constant speed is maintained, which seriously affects the oil production. This unprotected pumping motor control mode has already withdrawn from the stage of history.
The second generation: Since the DC motor was introduced, it also accelerated the application of DC motors on pumping units, thus replacing the use of asynchronous motors. The method of using DC speed regulation is obviously superior to the three-phase asynchronous motor, and the oil production is also much higher. However, the cost of the DC motor is relatively high, and its speed regulation performance is not very satisfactory.
The third generation: the use of variable-speed motor speed control, is to change the motor pole pairs to achieve the purpose of speed, often using 4/8/32 pole multi-speed motor. However, the device is more complicated, the space is also relatively large, the equipment life is short, and the stability is not very good.
The fourth generation: frequency conversion speed control technology, because the frequency conversion speed regulation technology has already become the energy conservation and the effective measure which enhances the product benefit quality, the oil field medium frequency changer application has already been very widespread in the beam pumping unit. Because the types and conditions of oil wells vary greatly, downhole oil seepage and seepage are changing every moment. The load change of the pumping unit is irregular, so the variable frequency speed regulation technology is adopted to adapt the movement law of the pumping unit to the changing working conditions of the oil well, thereby achieving the improvement of the efficiency of the pumping system and achieving the purpose of energy saving and production increase. The application of the frequency converter in the oil field boring machine is illustrated below. A few applications are briefly discussed.
V. Summary
In short, frequency conversion speed control technology as a high and new technology, basic technology and energy-saving technology, its application has penetrated into the various sectors of the oil industry.