Energy Reports (Nov 2021)
Material optimization of drill pipe in complex wellbore environments by comparing fatigue life and cost
Abstract
The fatigue life of drill pipe is a vital factor affecting the drilling process and safety, while severe fatigue failure of drill pipe under the condition of high temperature containing hydrogen sulfide have been reported frequently in recent years. Hence, a systematic methodology was proposed to investigate the fatigue behavior of different drill pipe under multi-factor environment. The present work aims to characterize the fatigue life and mechanism of G105, S135, V150 as well as the titanium alloy drill pipe. The hardness and tensile tests were initially performed to determine the material characterization of the different drill pipe. Then, a fatigue experimental system was specifically designed based on the experimental conditions to evaluate the fatigue property of the drill pipes. Experimental results reveal that in the air, drill pipe’s fatigue life could be longer with the increasing steel grade while in drilling mud, the fatigue performance of titanium alloy drill pipe is the best. The results of sensitivity analysis demonstrate that the coupling factor of H2S mud with temperature showed the greatest influence on the fatigue properties, followed by the single factor of H2S mud and the temperature respectively. The sensitivity to temperature and mud coupling factors is: V150 (65.2%) > S135 (58.1%) > Ti (51.6%) > G105 (40.3%). The sensitivity for H2S mud is: V150 (59.8%) > S135 (51.6%) > G105 (29.7%) > Ti (21.7%). The order of sensitivity to temperature is as follows: Ti (6.5%) > S135 (6.3%) > G105 (2.5%) > V150 (1.5%). The mechanisms underlying fatigue fracture were explored. Finally, according to the experimental results, the economical practicality of different drill pipes is analyzed and compared. The work presented in this paper can provide a technological basis for fatigue theory and service conditions of drill pipes.
