A new approach to the analysis of drillstring fatigue behavior

This paper presents a method for determining the fatigue behavior of drillstring (DS) components under given environmental conditions. Over the past few years, field data for DS failures have been gathered from certain wells drilled in Italy and West and North Africa. Fatigue phenomena were identified as the main cause of most of such failures. Among the several factors that can affect DS-element fatigue resistance are tensile load, makeup torque, material properties, corrosive environment, abrasive wear, and so on. However, simply on the basis of the existing guidelines, it is difficult to define the real cause of a failure under given operating conditions. A comparative study of full-scale fatigue-test results and field data suggests a new approach for the analysis of some of the drilling technology factors that can affect the DS fatigue behavior.