While in large dogleg sections of horizontal wells, steel drill pipe with high stiffness goes through such complex trajectory which makes it subjected to the high tensile-compressive alternating stress in the drilling process. This could lead to the drill pipe failure very quickly due to the fatigue fracture. Additionally, the drilling fluid with corrosive medium may accelerate the process of fatigue failure. Titanium drill pipe with stronger corrosion resistance, lighter weight and better flexibility may help prolong the fatigue life of drill pipe in these extreme situations. Therefore, a series of experimental tests were conducted to investigate the mechanical properties and fatigue performances of titanium alloy drill pipe, including hardness tensile and, impact testing, hard testing as well as rotary fatigue experimental test. Then based on these resultant parameters obtained from experiments a finite element model incorporating the stress and dynamic fatigue development was established to analyze the service life of drill pipe in the practical field of horizontal drilling at large doglegs. Our results show that titanium alloys have higher strength and lower percentage elongation but only half the elastic modulus of carbon steel. The corrosion fatigue experiments indicate that the fatigue life of titanium alloy samples is almost twice longer than that of G105 steel in practical drilling mud at large doglegs. Using this methodology, operators can make precise economic assessments on the optimization of drill string assembly at doglegs.

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