What is a Rod Pumping Unit and How Does It Work?

1. Interpretation of rod pumping unit

Rod pumping unit is a kind of machinery and equipment for oil extraction. Use pressure to get the oil out of the well. When the rod pumping unit is upstroke, the tubing elastically contracts and moves upwards, driving the mechanical plug-removing oil extractor to move upwards, hitting the sliding sleeve, and generating vibration. At the same time, the positive check valve is closed and the variable-diameter piston assembly blocks oil. When the rod pumping unit is the downstroke, the tubing elastically stretches and moves downwards, driving the mechanical plug-removing oil extractor to move downwards and hitting the sliding sleeve to generate vibration. At the same time, the reverse check valve is partially closed, and the reducing piston assembly still blocks the annular oil passage of the oil sleeve, so that the area under the reverse check valve forms a high-pressure area. This movement produces a reverse impact on the oil flow channels in the formation.

2. Why is it best to use variable speed transmission for rod pumping units?

Common rod pumping units, namely beam rod pumping units, are traditional pumping equipment widely used in oil fields and are usually driven directly by ordinary AC asynchronous motors. The crank belt drives the sucker rod with a counterweight and balanced weight and drives the downhole sucker pump to make a fixed period of up and down reciprocating movement to send downhole oil to the surface. In one stroke, as the sucker rod rises/falls, the motor works in the electric/generating state. During the ascent process, the motor absorbs energy from the power grid and runs electrically; during the descending process, the loaded nature of the motor is a potential load, and the negative pressure in the underground makes the motor in a power generation state, which converts mechanical energy into electrical energy and feeds it back to the power grid.

However, the conditions of downhole oil layers are particularly complex, with rich oil wells and poor oil wells, and thin oil wells, and heavy oil wells. The constant speed application problem is obvious. If these are aside, as far as the rod pumping unit oil pump itself is concerned, the gap leakage between the worn piston and the bushing is a difficult problem to solve. Moreover, changing formation factors such as sand, wax, water, gas, and other complex conditions in the oil also have a great impact on the amount of oil pumped out per stroke. It can be seen that only the speed control drive can achieve the best control.

After the introduction of speed-regulating transmission, the stroke frequency of the rod pumping unit and the speed of the up and down strokes can be adjusted according to the downhole state, which can increase the pump's full coefficient and reduce the pump's leakage to obtain the maximum oil output. In particular, the use of frequency conversion speed regulation has no start-up shock, and can solve the problems of low power factor caused by conservative selection and long lines. It can save energy and increase efficiency while increasing the life of the whole machine.