(2014023) THE ULTIMATE ROD STRING DESIGN PROCEDURE
Available sucker-rod strong design models calculate rod taper lengths that ensure proper operation without premature fatigue failures. Their common design problems are (a) defining the principle of taper length determination, and (b) calculating the true mechanical stresses along the string. The universally accepted principle of taper length calculations is to province the same level of safety against fatigue failure in each taper section. Mechanical loads and stresses, not he other hand, are found form highly approximate calculations in most of the design procedures. These loads, therefore, can greatly deviate from the true mechanical loads that would be measured in the rod string run in the well. The paper discusses the development of a novel procedure that estimates rods loads from the predictive solution of the damped wave equation when designing the rod string. Since loads calculated that way very accurately imitate actual loads the most important limitation of previous rod string design procedures is eliminated. Strings designed using the proposed model, therefore, have a much enhanced safety against fatigue failures as compared to previous designs.