Torque and Drag Modeling for Horizontal Openhole Completions
Authors: Denney Dennis 
Published: February 2015

This article, written by Technology Editor Dennis Denney, contains highlights of paper SPE 97079, "Torque and Drag Modeling for Horizontal Openhole Completions," by R. Rezvani, Halliburton/Sperry Sun, and B. Techentien, Halliburton Energy Services Inc., prepared for the 2005 SPE Annual Technical Conference and Exhibition, Dallas, 9–12 October.
With horizontal openhole sections being drilled to lengths that exceed 20,000 ft, placement of the completion string (CS) to planned total depth (TD) may not be possible if the proposed drilling plan is not studied carefully. It is important to model the well before attempting to run the planned completion to deter-mine whether the CS can withstand the strains (tension, compression, and torque) of installation, as well as whether the upper CS has sufficient weight to push the lower CS to TD.

Introduction
Frictional drag can prevent installation of a CS to TD of a well. This situation can be especially critical in an open-hole horizontal well with the additional challenges inherent in gravel-pack assemblies. Because of the increased costs and risks in these well scenarios, accurate assessment of the stresses to which the CS could be subjected during installation is critical.
The technique that is detailed in the full-length paper provides the completion designer with an additional tool in designing a CS that can withstand the downhole stresses encountered during its running. For example, if the modeling process indicates that the CS will not withstand the stresses of installation without failing from tensile loading, buckling from the compression load, or failing from rotational torque, a different well plan must be devised.
The operator then must formulate a new configuration, which then can be assessed with the torque and drag models for primary assessing of the capabilities of the new configuration.
Recent technological advances in drilling have resulted in new drilling and measurement equipment for both offshore and onshore drilling. Major changes in the drilling sector have resulted from the following.The advent of rotary-steerable systems and integration of computer and information technology into the down-hole drilling processes.Larger and stronger drilling rigs.High-pressure/high-temperature measurement-while-drilling tools with an increased array of improved sensors.
Real-time data can be transmitted from downhole to surface and from the rigsite to the office. These capabilities have improved drilling efficiency such that many of the wells being drilled and completed today could not have been developed and/or financed before these advances.
Rotary-steerable systems have enabled drilling wells deeper and to greater horizontal lengths, as well as enabling wells to reach reservoirs that previously were not accessible. These advantages improve the overall economics of the projects.
By design, downhole completion hardware is not as rugged as drillpipe or drilling assemblies. The new wellbores enabled by the advances in drilling technology can induce loads and stresses not experienced before and that must be evaluated and understood fully before designing the CS.
The drillstring can be rotated to TD, and casing strings are floated to TD. However, the CS cannot be rotated or floated.