Rod Guide Theory, Spacing Methodology, And Field Application

A major maintenance expense for rod pumped wells is sucker rod induced wear on the tubing string. In most cases this wear is due to 1) deviated wellbores, 2) rod buckling on the downstroke and/or, 3) tubing buckling on the upstroke due to unanchored tubing. In order to address these problems operators frequently rely on rules of thumb gained after years of trial and error experience. This paper describes a systematic approach for predicting when rod/tubing wear is significant and offers recommendations to help reduce its detrimental effects. The deviated wellbore calculations are performed using a rod by rod force balance that considers deviation survey data. The rod buckling portion is based on static load tests of three rod sizes equipped with up to four guides per rod. The test results are compared to Euler's column buckling equations for different l/r (length/radius of gyration) ratios in an effort to determine a predictive equation. Tubing effects are considered using the methods proposed by Lubinski. Field verification tests were performed since 1991 for several rod strings equipped with rod guides in different producing environments. Also, a computer design program was developed and used to deliver this technology to the field.