Advances in Drillpipe Fatigue Management

Abstract

Abstract Recent improvements in manufacturing quality control have dramatically reduced drillpipe failures caused by insufficient material properties. However, preventable fatigue-induced failures continue to occur at a high frequency. Increased drilling activity, rising rig spread rates and the technically challenging nature of today's ultra deep and extended reach wells dictate the need for an effective drill pipe fatigue management system. This paper discusses the cumulative fatigue damage approach as applied to drill pipe and presents a field-implemented fatigue management strategy that can significantly improve the overall fatigue performance of the drill string. Drill pipe fatigue analysis has been approached through both total fatigue life and fracture mechanics models. The fracture mechanics model was used to develop the concept of comparative fatigue design introduced in a previous paper (IADC/SPE 87188). Comparative fatigue design allows for a quantitative comparison of drill string design and well bore geometry alternatives based on normalized fatigue crack propagation and various known well bore parameters like dogleg severity, hanging tension, drill pipe size, hole size, etc. However, this "snapshot" technique only provides an insight into the fatigue performance of the drill pipe under one set of operating conditions. A joint of drill pipe experiences substantial variations in loading conditions at different depths along the well bore trajectory. Hence the comparative fatigue design technique was further refined to consider all significant operating conditions and allow quantitative comparison of cumulative drill pipe fatigue damage. The cumulative fatigue damage technique has been successfully applied as a design tool to compare different drill string configurations, well bore trajectories and drilling operations. This technique can also be applied in calculating relative fatigue damage within different well bore sections and the entire well bore, thus identifying sections of the drill string that will accumulate maximum fatigue damage after a series of operations. Sections of drill pipe may then be repositioned within the string or pulled and reinspected to minimize the risk of fatigue-induced failures.