Determination of Rod Guide Erodible Wear Volume

Rod guides used to centralize sucker rods inside tubing have evolved dramatically over the past 20 years. The primary function of a rod guide is to extend the life of the production equipment by preventing metal-to-metal contact. Basically, the portion of a rod guide between the largest O.D. on the rod string and the I.D. of the tubing is all that can prevent the damaging metal-to-metal contact. This protective volume of the rod guide is often referred to as erodible wear volume (EWV). It is an important indicator of rod guide performance. A properly designed sucker rod string with strategically located rod guides can be economically justified in many situations. One way to evaluate the investment is by the amount of EWV. Unfortunately, EVW can be defined in a variety of ways and a lack of standardization creates confusion when attempts are made to compare the EWV of one rod guide with that of another. The definition of EWV has evolved since it was first introduced in 1986. The original definition, which will be referred to as Gross EWV, is the amount of rod guide material outside the O.D. of the sucker rod coupling. It is a simple, easy to measure index. Consequently, it is not prone to measurement or calculation errors. However, Gross EWV neglects the effects of rod guide geometry. Initially this was not a problem because the geometry of the few rod guides on the market were very similar. Therefore, Gross EWV did an adequate job as an indicator. The more recent definition, which will be referred to as Net EWV, is the amount of rod guide material that will erode before the sucker rod coupling contacts the tubing. Net EWV is a more difficult concept and prone to errors in measurement. It is virtually impossible to calculate without sophisticated computer modeling software. However, Net EWV does account for rod guide geometry. It is more representative of true protection and it is a concept that needs to be developed in light of all the new rod guides that are evolving today. The primary objective of this paper is to compare Gross and Net EWV and to suggest industry standards for measuring both. Unless standards are adopted, EWV as an index will continue to be confusing to the industry. One important point to remember is that no definition of EWV really means anything unless the rod string is continuously rotated and the rod guides wear evenly.