Introduction

The individual components of a sucker-rod pumping system can be divided in two major groups: surface and downhole equipment. The main elements of a common installation are shown in Figure 2-1.

Figure 2-1

The surface equipment includes:

• The prime mover that provides the driving power to the system and can be an electric motor or a gas engine.

• The gear reducer or gearbox reduces the high rotational speed of the prime mover to the required pumping speed and, at the same time, increases the torque available at its slow speed shaft.

• The pumping unit, a mechanical linkage that transforms the rotary motion of the gear reducer into the reciprocating motion required to operate the downhole pump. Its main element is the walking beam, which works on the principle of a mechanical lever.

• The polished rod connects the walking beam to the sucker-rod string and ensures a sealing surface at the wellhead to keep well fluids within the well.

• The wellhead assembly contains a stuffing box that seals on the polished rod and a pumping tee to lead well fluids into the flowline. The casing-tubing annulus is usually connected, through a check valve, to the flowline.

The downhole equipment includes:

• The rod string composed of sucker rods, run inside the tubing string of the well. The rod string provides the mechanical link between the surface drive and the subsurface pump.

• The pump plunger, the moving part of a usual sucker-rod pump is directly connected to the rod string. It houses...