Development of Titanium Drill Pipe for Short Radius Drilling

摘要

A need exists for drill pipe that offers improved reliability andextended life in reentry drilling programs where the radius ofcurvature is less than 60 ft (I.e., >95-deg/100 ft). Steel,aluminum, and composite drill pipe traditionally utilized inthese short radius drilling operations often exhibit abbreviatedlives stemming from fatigue, wear, and/or physical damage.With an elastic modulus of approximately 17 msi, titaniumpipe offers enhanced flexibility and reduced fiber stressescompared to steel pipe when rotated in holes of highcurvature. Utilization of the most widely used titanium alloy,Ti-6Al-4V, offers a high nominal yield strength of 120 ksiwith a density 56% that of steel. Combined with goodcorrosion and fatigue resistance in drilling and downhole fluidenvironments, this titanium alloy is a lightweight, highlyflexible, robust, and fatigue-resistant drill pipe material.A practical and cost-optimized Ti drill pipe joint designconsists of a seamless Ti-6Al-4V alloy pipe body, which isproduced in standard API sizes and Range 2 and 3 lengths, towhich steel tool joints are mechanically attached to the upsetends. The steel tool joints offer the advantages of lower tooljoint costs, standard drill pipe make/break connectionbehavior, the option for tool joint hardbanding, andelimination of welded joints.Successful development of titanium drill pipe assemblies forshort-radius drilling included appropriate conditioning of theOD and ID pipe body surfaces to maximize fatigue life,optimizing the pipe end upsetting procedure, establishing thetool joint-to-pipe attachment methodology, and design andtesting of a high-integrity tool joint-to-pipe connection andtool joint for optimum fatigue performance. This paperoverviews these developments and the laboratory test resultsused to establish critical performance behavior andrequirements for 2-7/8 in. OD titanium drill pipe for shortradiusdrilling. An update on recent field experience withtitanium drill pipe utilization in various short radius drillingprograms is provided as well.