Holger Kinzel

Fatigue Life Evaluation: A Key to Avoid Drillpipe Failure Due to Die-marks

Slips and tongs produce permanent marks on pipe body and tool joints. Such marks develop high stress concentration that reduces strength of pipes. The remaining strength of pipes often falls below the pipe stresses which can lead to tubular failure. Slim pipes are most susceptables to failure due to die-marks. In many instances, slim pipes are handled using double elevator system to reduce pipe failure. In this paper, results of a recent study of various die-mark related failures of drill pipes under different loading conditions, with particular emphasis on fatigue damage are presented. Stress concentration due to die-marks is characterised by finite element analyses as a function of mark sizes to cover various gripping systems available in the market. Then a methodology is presented for the prediction of failure due to cumulative fatigue damage. Effect of stress concentration arising from die-marks is taken into account in the analysis. Results of this study suggest that the effect of stress concentration on the cumulative fatigue damage may be significant depending on particular gripping system in use. In most cases, the fatigue life evaluation based on conventional assumption of smooth pipe surface is found to be very unsafe. Thus, a new approach is proposed in this paper for prediction of true safe life of marked drillpipes against fatigue failure. Fatigue damage results are presented in graphical forms. Calculation of cumulative fatigue damage of drillpipes used in a number of drilling events is then presented systematically in tabular form to assist drilling engineers in the evaluation of actual remaining fatigue life of drillpipes for the target drilling event using a particular gripping system.

Evaluation of Real-Time Torque-Turn Charts With Application to Intelligent Make-Up

A wide spectrum of power tongs can accommodate the increasing interest in mechanized operations at the rig floor. The importance of a torque-turn recording has been stated in many papers as a good control method for the make-up process, and the reliability of a drill string can be improved using feed back of make-up recordings. State-of-the-art devices not only allow the precise mechanized make-up of connections, but they also provide sufficient data to analyze the quality of the connection make-up. The motivation behind the research performed is the desire to make use of the data that are already provided to increases the lifetime of the connections and the reduction of drill string failures, especially for drilling under extreme downhole conditions like HPHT or deep water. This paper presents a new algorithm to evaluate the slope of the torque-turn recordings and to extract information that can be used to predict the quality of the process, with application to extreme drilling situations. This work is based on more than 300 make-up and break-out laboratory tests.Copyright

Field Test of a Downhole-Activated Centralizer To Reduce Casing Drag

A good cementation is based on an adequate centralization. Conventional bow-type centralizers create a drag force, which is not acceptable under certain conditions. The downhole-activated centralizer (DAC{trademark}) was developed for use in highly inclined wells and whenever restrictions in the wellbore like close tolerance wellheads have to be passed. It can be released by external hydraulic pressure, by temperature or by a chemical reaction. The first downhole-activated centralizers with pressure released locking mechanism were field tested in two wells offshore Italy. These field tests proved the function and the effectiveness of the downhole-activated centralizers under operational conditions.