A hydraulic drive with self-oscillating operation for reciprocating downhole pump

Rod pumps (pumping units) are widely used for pumping products from production wells. Their simplicity and low cost are undoubted advantages. However, when operating in inclined wells, these pumps are susceptible to accidents caused by friction forces between the rod string and oil well tubing in the contact zone, particularly when the well axis is bent. The rod and rope drive for the plunger pump is suitable for use in wells with a slight inclination of up to 15°, but it is not suitable for use in deviated wells. The article aims to evaluate the feasibility of discontinuing the use of the rod drive in deep well plunger pumps and to suggest an alternative solution. One of the options considered is a self-oscillating hydraulic drive with a spool switch located inside the piston of the drive hydraulic cylinder. This drive provides the large rod displacement necessary to operate a plunger well pump. To supply the working fluid to the distributor, a hollow rod is used. The rod is pressurized with a pressure higher than the downhole pressure from the pump located on the surface near the wellhead through the oil well tubing. A piston switch with an original design is proposed, which provides a self-oscillating mode of the drive and allows for changing the oscillation period. The methods for changing the oscillation period are briefly discussed. A mathematical model of the hydraulic drive is compiled, and the dynamic and power characteristics are determined. The design is developed, and a mockup of the drive and a bench for testing are created. The test results confirm the theoretical characteristics and reliability of the drive. The use of a self-oscillating hydraulic drive for plunger well pumps enables their application in wells of any curvature.