Depletion of shallow depth reservoirs has driven the industry towards drilling of ultra-deep HPHT wells to reach unexploited reserves. Drilling such challenging wells is the most compelling reason for drilling companies to look for alternative drill pipes that meet their requirements. Currently, with the emergence of light-weight drill pipes, a thorough study of their advantages and disadvantages compared with conventional drill pipes is needed. Weight of drillstring, dynamic load at the surface and produced surge and swab pressures can be considered as the most significant parameters during tripping operations in ultra-deep wells. The deeper the well the more crucial becomes the management of the dynamic load. In this study the main focus is on the comparison of dynamic load along four different drillstrings in deep and ultra-deep vertical wells: Steel Drillpipe (SDP), Aluminum Drillpipe (ADP), Titanium Drillpipe (TDP) and Composite Drillpipe (CDP). A new approach for calculation of the dynamic load based on a semi-analytical solution of the wave equation has been developed. According to our calculation, the string made of SDP produces the highest dynamic load among those studied. It is shown that vibration along the composite drillstring lasts a much shorter time than vibration along the other types of drillstring. In other words, the impact of fluid damping is more effective on the composite drillstring than the others. Investigation of different slips removal velocity profiles reveals that an optimum slips removal velocity profile can reduce the magnitude of the produced dynamic load coming from the subsequent downward motion. This paper can help drilling engineers design an optimal drillstring for ultra-deep wells as well as optimal tripping velocity profiles.

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