Graphite Composite Tape in Beam-Pumped Oil Wells
Authors: Hensley H.N. , Tanner C.J. 
Published: December 2007

A continuous, reelable graphite composite tape is being developed as an alternative to jointed sucker rods for use in beam pumped oil wells. Four units have been tested in wells. The composite tape is composed of graphite fibers, glass fabric, Kevlar fibers and vinylester resin. Graphite fibers have a high modulus of elasticity and provide the longitudinal stiffness needed to operate the downhole pump, while allowing a thin cross section flexible enough to be wound onto small diameter reels. This advanced graphite composite is the first practical, lightweight, reelable alternative to jointed sucker rods.

Introduction

The dominant method of producing oil from nonflowing wells is with sucker rod operated lift pumps. Over 400,000 wells are pumped in the United States with this type of system. New installations each year range from 10,000 to 30,000. More statistics can be found in Reference 1. The reason for this wide usage is that sucker rod pumping systems are simple, reliable and cost effective.

Steel sucker rods are formed in 25 foot sections with upset and threaded male ends (pins). They are joined together with steel sleeves (boxes) as they are lowered into the tubing. Several grades of steel are available and are selected depending on the strength and corrosion resistance required for the particular well. Dimensions and other features are controlled by the American Petroleum Institute Specifications. Fiberglass sucker rods are also available. They are made in lengths up to 37.5 feet but still require steel couplings for joining. The pin ends are bonded to the pultruded fiberglass body sections. Reference 2.

Conventional sucker rods are adversely affected by corrosion and by stresses induced through improper handling and cycling under high load ranges. Sucker rods, and the procedures for handling them in the field, have reached a high degree of development. Only very modest further improvements can be expected. Still, there is widespread interest in reducing rod string failures due to fatigue, corrosion, wear, and coupling failures. Well service equipment remains cumbersome, expensive and dangerous. With stable oil prices and increasing secondary recovery projects, lease operating expenses have taken on a new priority with significant consideration being given to developing priority with significant consideration being given to developing more efficient lift systems in terms of BPD/HP.

In response to the need for a lightweight, strong rod string which is not affected by corrosion, the aerospace industry was accessed in the search for a new material exemplifying the above characteristics. It was also determined that the box/pin connection was critical in maintaining the integrity of all conventional sucker rod strings, yet failures in these box/pin connections accounted for over 50 percent of all rod string failures. Thus, the elimination of couplings was mandated. Advance graphite composite materials offer substantial weight savings, remain free from corrosion, have a high modulus of elasticity, are sufficiently stiff for use in pumping, and have enough flexibility to be wound on a small reel in pumping, and have enough flexibility to be wound on a small reel in continuous lengths.

A fully developed advanced composite ribbon rod system has proven to be a viable, both technically and economically, alternative to jointed sucker rods and could play an important role in solving some of the nagging problems inherent in current sucker rod designs.