Fiberglass Sucker Rod Design Considerations
Authors: Reynolds M.M. 
Published: March 2010

Artificial lift systems using fiberglass sucker rods were initially developed in 1973, as a means of reducing steel rod failures in sour and very corrosive pumping wells. It soon became apparent that fiberglass had other advantages over steel rods, such as:increased production due to pump overtravel;reduced surface pumping system stresses; anddecreased lifting costs.

After some initial problems with rod quality control, poor string design, and misapplications. Fiber glass systems have become a reliable method of artificial lift. Fiberglass systems have become more widely used recently due to low capital cost requirements and lower operating costs, compared to other lift systems. However, a more rigorous design procedure must be used compared to steel sucker rod systems. An optimum procedure utilized by Petro-Canada is outlined in this paper.

Petro-Canada's experiences with fiberglass systems are Discussed, including the use of a specially designed pumping unit made to maximize fiberglass rod benefits in a "total system" design approach. This pumping unit was the first of its type to be operated in Canada.

Introduction

The use of fiberglass sucker rods in pumping oil wells was pioneered in West Texas in the early 1970s(l). While the rods were initially developed to reduce corrosion related failures, the light weight and elastic properties of fiberglass were identified as a solution to increasing fluid production rates in beam pumping wells, without upgrading the surface lift equipment.

The first generation of fiberglass rods were manufactured between 1975 and 1978. These rods were highly susceptible to failure and, as a result, were not widely used. The two main problems with these early rods were: rod body breaks and end fitting pinch-off of the metal pins(2). The rod body breaks resulted mainly from looping or knotting of the glass fibers during manufacturing, causing a weak point that failed under stress. Improved processes developed to maintain the glass fibers in tension during manufacturing overcame this problem. The end-fitting pinch-offs were eliminated by re-designing the pin to better distribute the load into the rod and by improved epoxy application between the metal and fiberglass. These second generation rods began to appear in 1979 and have proven to be reliable in the field.

Other major problems with the installation of early fiberglass rods included poor string design and misapplication(3,2) Many premature failures were caused by the overloading of the fiberglass rods. This overloading resulted primarily from inaccuracies in the calculation of the system stresses. These inaccuracies were due to the modification of the empirical API technique, which had been developed for steel rods, to handle fiberglass systems(4). It was not until development of a computer program from first principles of Hooke's Law that system stresses could be satisfactorily estimated.

Advantages of Fiberglass Over Steel Sucker Rods

Reduced Corrosion Failures

In pumping wells where numerous steel rod failures were attributed to corrosive conditions, it seemed logical that the use of a non-metallic material in the sucker rods could reduce the number of failures.