survey
Pumping unit is the main equipment in oil production, the number of which is more than 100000. The total installed capacity of the motor is 35 million KW, and the annual power consumption is more than 10 billion kwh. The power consumption of pumping units accounts for about 40% of the total electricity consumption in the oilfield. The operation efficiency is very low, the average operating efficiency is only 25%, the power factor is low and the waste of electric energy is large. Therefore, the energy saving potential of pumping unit is very huge, and the petroleum industry is also the key industry to promote "energy saving of motor system".
Several advantages of frequency conversion of pumping unit
1. Greatly improve the power factor (0.25 ~ 0.5, increase more than 0.9). The power supply current is reduced, so the load of power grid and transformer is reduced.
2. Dynamic adjustment of extraction speed can save energy and increase crude oil production.
3. To achieve real "soft start" on the motor gearbox pumping unit, avoid excessive mechanical impact, prolong the service life of the equipment.
Load analysis of pumping unit
1. The beam pumping unit is widely used in China
1) The ground part is composed of motor, reducer and four connecting rods;
2) Downhole part: oil well pump (suction valve, pump barrel, plunger and drain valve), which is suspended at the lower end of the casing;
3) Sucker rod string: the middle part connecting the surface pumping unit and the downhole oil pump
2. The motor load of the pumping unit changes periodically. When it starts, the load is large and the starting torque is required to be large. When the load rate is very high, it is only about 30% at normal load rate. The load curve of the motor has two peaks, which are the "dead point" of the up and down stroke of the pumping unit. Under the condition of unbalancing, the load of up stroke and down stroke is extremely unbalanced. In the up stroke, it is necessary to lift the rod string and liquid column, and the motor needs to pay a lot of energy. In the down stroke, the rod string works on the motor to make the motor in the state of power generation. Usually, a balance weight is added to the crank of the pumping unit to eliminate the load imbalance between the upper and lower strokes. However, the impact current of the counterweight is 5 times of that of the pumping unit at each stroke, which may result in the unbalance of the counterweight. Adjusting the balance weight can reduce the impact current, which is 1.5 times of the normal working current. Load characteristics: it runs at constant speed. Due to the counterweight, it has variable torque and variable power. The load has two power generation states in a cycle, with large starting torque and large inertia. The common problems of pumping units used in domestic oilfields are: long running time, low efficiency, large energy consumption, inconvenient adjustment of stroke and stroke, and space-time pumping phenomenon.
Difficulties in the transformation of traditional pumping unit frequency converter
A lot of attempts have been made to transform the frequency conversion energy saving of oil engine, but they are not very successful
1) In a working cycle, the pumping unit has two power generation states. Especially when the counterweight is unbalanced, the "pumping voltage" is very high. The problem can not be completely solved by increasing the electrolytic capacitor at DC side of frequency converter and reducing the braking resistance value. Moreover, with the change of oil layer, "pump up voltage" is also changing.
2) The pumping unit needs a large starting torque to start. If the parameters of frequency converter are not set properly, it is easy to cause over-current or unable to start.
3) The change of oil level and oil concentration is seldom considered in the design of frequency conversion and energy-saving transformation. In terms of increasing yield, the effect is not good.
Solution
For the problems existing in the frequency conversion transformation of pumping units, our company proposes the following solutions:
1) Frequency conversion speed regulation technology is adopted to match the motor speed with the pumping unit load. In the early stage of the well, due to the large amount of oil, the frequency converter was operated to 65Hz, the motor speed was increased by 30%, the oil recovery rate was increased by 20% compared with the power frequency, and the work efficiency was increased by 1.2 times. In the middle and later stage of the well, the oil volume is reduced, the speed and stroke are reduced, and the motor speed is reduced by 30% when the general frequency is between 35 Hz and 40Hz. The power saving rate can reach 25%, and the power factor is improved.
2) Dynamic adjustment of the stroke frequency of the pumping unit, with the oil well pumping from the shallow to the deep, the oil quantity gradually decreases, the pump fullness is insufficient, and the pump efficiency decreases. When the oil supply capacity of the oil well is less than the displacement of the oil pump, the phenomenon of pump evacuation and liquid hammer will occur. By reducing the frequency, the motor speed decreases and the fullness increases, not only the energy is saved, but also the crude oil production is increased.
3) Dynamic adjustment of the speed of the up and down stroke of the pumping unit, properly reducing the down stroke speed, increasing the filling degree of the pump, and properly increasing the up stroke speed, can reduce the leakage coefficient in the lifting process, make the pumping unit work in a better operation state, and effectively improve the crude oil production per unit time.
4) It is necessary to solve the problem fundamentally, such as large starting torque, low load in operation and high impulse current. Increase the number of motor poles or speed ratio of reducer to increase the output torque. The frequency converter operates normally for 80 ~ 90hz. This is also conducive to reducing the energy in the power generation state and reducing the "pumping voltage".
5) Treatment of renewable energy
Increase the capacity of filter capacitor at DC side of frequency converter; reduce the value of braking resistance to improve the power consumption of braking system; or directly use feedback braking to reduce energy loss; when generating power, the frequency increases.
6) Air defense pumping, increase production. Dynamic adjustment of pumping unit stroke frequency and up and down stroke speed. Motor speed, motor output power, real-time detection value, motor output power greater than standard value. On the other hand, it decelerates to realize closed-loop control.
