Introduction

The weight of the sucker-rod string is distributed along its length, and any section has to carry at least the weight of the rods below it. This fact suggests that the ideal sucker-rod string would be a continuous taper from top to bottom. Since such a shape is practically impossible to achieve, one tries to approach the ideal construction by designing tapered strings with sections of increasing diameters toward the surface. For lower depths, straight rod strings made up from one rod size only are also used, but deeper wells inevitably require the application of tapered strings.

In order to simplify the identification of strings made up of different rods, tapered strings are designated using standard API code numbers. The taper code system is different for the coupled (conventional) and the continuous rod types. For coupled rods with a ?? increment in available rod sizes, the first numeral of the code refers to the largest rod size; the second numeral refers to the smallest rod size in the string; both are expressed in eights of an inch. For example, a three-taper string composed of 1 ?, ??, and ? rods is designated with the code 86. The continuous rod sizes are available in increments, and their code is expressed in sixteenths of an inch, omitting the first numeral 1. Thus, a rod string made up of 1 ?, , and ?? continuous rods is designated as...