Qualifying Drillstring Components for Deep Drilling
Authors: Hill T.H. , Money R.C. , Palmer C.R. 
Published: December 2007

Deep, hard, or directional drilling imposes extraordinary stresses on drillstring components. Because of theadditional economic risks of deep drilling, the inspection and acceptance of drillstring components should be based ontheir compliance with API and user standards. Inspection procedures that provide the highest probability of finding procedures that provide the highest probability of finding and eliminating unacceptable components should be used. Often, too much reliance is placed on a "report" or"certification" that the drill string components have been"inspected, "The operator assumes that because the material has been inspected, it is suitable for the intended service. This paper addresses three areas in which the above approach may lead to trouble.Widespread, established practices have resulted insome applicable API guidelines being unintentionally ignored by users and inspection companies.API standards for used drillpipe do not address someitems of concern to operators engaged in deep or critical drilling.Inspection companies frequently do not followsimple quality control steps that can markedly improve theresults of their work.

Examples of shortcomings in current industry practicesare given. Corrective actions implemented by several companies in the last 12 to 18 months are also given. A hand-held calculator program that will aid in evaluating the wear limits on rotary shouldered connections isprovided in the Appendix. provided in the Appendix. Drillstring Failures

Examples of drillstring failures are well documented inliterature. 1 Unfortunately, they are also all too familiarto most drilling engineers and operations managers fromfirsth and experience. Common in-service failures include the following.Fatigue cracks can be induced by cyclic loading inhigh-stress areas of connections and drillpipe tubes(Fig. 1).Washouts caused by leaking drilling mud can erodemetal and enlarge the leak (Fig. 2). Leaks may occur fora variety of reasons, but the most common causes are fatigue cracks, inadequate makeup torque, shoulder sealdamage, or excessive or improper refacing of the shoulders.Tensile breaks occur when the load-carrying capacityof a member is exceeded. This occurs most frequentlyin the tube body (Fig. 3) or in the pin of a connection.Torsional failures occur when the torque applied indrilling exceeds the capacity of a drillstring componentto resist torque.

Fig. 4 is an example of a torsional failurein a drillpipe box. Drillpipe failures occur for a variety of reasons. Broadly speaking, these can be grouped into three categories. If a failure occurs eitherthe drill string was designedincorrectly-e.g., the weight and grade were inadequatefor the application;the drillstring was misused-e.g., connections were over torqued during rig floor makeup;ordefective components were accepted and runbecause of inadequate inspection, poor-quality inspection, or poor definition of the standards of acceptance.

It has been our experience that persons responsible for drilling wells are much more familiar with the design and proper use of drill strings than they are with inspection proper use of drill strings than they are with inspection processes and acceptance standards for those strings. In processes and acceptance standards for those strings. In the hope of helping to correct this situation, the remainder of this paper addresses some problems and solutions inthe area of drillstring inspection.

Drillstring Inspection

There seems to be a pervasive attitude among drillingpeople that inspection is someone else's problem. Few oil people that inspection is someone else's problem. Few oil companies would write the following clause into theirday-rate drilling contract.

The drilling contractor shall decide well location, well depth, directional program, mud program, logging program, casing and cementing program, and whether the well will be completed or abandoned. Contractor shall provide a report certifying that allthe above was done correctly.

On the other hand, most companies do not hesitate todelegate the inspection and acceptance of their drillstring components to their contractor or inspection company. It is still common practice to accept an inspection "report"as proof that the components have been inspected. Frequently, when failures occur, the corrective measure maybe to change inspection companies and to repeat the cycle, without any technical involvement in the inspection process. Our message is that the operator can often process. Our message is that the operator can often substantially reduce his economic exposure to drillstring failuresby becoming involved in the inspection process.

JPT

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