The wellhead arrangement of a typical sucker-rod pumped well is shown in Figure 2-45. The polished rod, the uppermost part of the rod string, reciprocates with the movement of the walking beam that is transmitted to the rods by the wireline hanger. The polished rod moves inside the tubing head, on top of which a pumping tee is installed, which leads the fluids produced by the pump into the flowline. Usually, the flowline and the casing vent line are connected with a short pipe section, enabling the gas that separates in the casing-tubing annulus to be led to the flow-line. A check valve is installed on this line to prevent the fluids already produced to flow back to the well. Above the pumping tee, a stuffing box is installed to eliminate leaking of well fluids into the atmosphere.

Figure 2-45

The polished rod is a solid steel rod available in different standard sizes and lengths and equipped with proper connections on both ends. Since it carries the greatest pumping loads, the polished rod must be stronger than any rod in the string. Its size is selected, therefore, to be larger than the size of the top rod section. In addition to transmitting the pumping movement to the rods, the polished rod's other function is to permit a seal to be formed against the leaking of well fluids. For this reason, its outside surface is polished, which enables a leak-free seal in the stuffing box. Abrasive action and corrosion...