Rods Specifically for PCP Applications
By Franklin L. Foster, Ph.D.
based on a presentation by Brian George, RG Industies Ltd.
The change from reciprocal pumps to progressing cavity pumps (PCP) means a rethinking of equipment design. One area where this has happened is with regard to sucker rods. In the reciprocal pumps, the rod string connects the beam head at the surface with the pump down hole. For this application, maximum tensile strength is needed to support heavy straight lifting loads.
The progressing cavity pump, on the other hand, requires rotary power where torque is the main resistance challenge. New designs to meet this challenge led to what are better termed "drive rods". With the new designs came other advantages. Of particular interest were the couplings which join one rod length to another to stretch deep underground. What was achieved was a stronger coupling which, at the same time, had a slimmer profile, allowing better flow-by, and reduced flow and pressure losses (a key factor in PCP applications).
These innovative designs lead to drive rods with less metal fatigue (and therefore less maintenance cost), improved well production, and even less wear and tear on tubing. In short, the design modifications produced a new species of rods which should be used in all PCP applications.