Friction forces key to preventing pipe bucklingF R I C T I O N A N D B U C K L I N G

WE KNOW THAT pipe buckles withfriction. In conventional analysis, theonly possibility for buckling is to have aninitial non-zero lateral displacement, sothat the axial force contribution mayexceed the fully mobilized friction force.This initial displacement cannot normal-ly be accurately estimated, so the forceneeded to buckle pipe with sliding fric-tion is essentially unknown.

A cylindrical pipe has another possiblemode of lateral displacement. Instead ofsliding, the pipe can roll. In this case, thefriction force developed is static friction.Static friction may take on any valuebetween zero and the peak static frictionvalue, where the value of the static fric-tion is usually determined from a bal-ance of known forces in the problem ofinterest. Here, the magnitude of the stat-ic friction is determined from a balanceof torsional forces on the pipe. The keyfact is that the friction force developsgradually, so we may determine a criticalbuckling force in the traditional sense.

The introduction of axial torque addsfurther complications to the bucklinganalysis.

This paper develops a comprehensivemodel for pipe with axial forces andtorque, and then develops the criticalbuckling loads for two cases of primaryinterest. Several sample calculations areperformed to illustrate the importance offriction forces in the stability of tubingand seafloor flowlines.

The Effect of Friction on Initial Buck-ling of Tubing and Flowlines (IADC/SPE99099) RF Mitchell, Halliburton.

W O R L D R E C O R D A T V I S U N D

Statoil ASA’s Visund project is operatedfrom a floating installation located in theTampen area of the Norwegian NorthSea. The Visund field has been developedthrough 16 subsea completed wells overthe past six years. Recently, Statoil ASAset a world record for drilling the longestreach well off a floating installation.Visund’s well A 6HT2 was drilled to ameasured depth of 9,082m, 822m longerthan the Visund A 22 well, which previ-ously held the record. In addition to set-ting a world record, well A 6HT2 was fin-ished ahead of plan, within budget and

set a Visund record for the fastest spudto total depth well with an average rateof penetration of 102m/day.

Compared with the A 22 well, a key tech-nology used on A 6HT2 was a full-length,intermediate-sized 5 7/8-in drill string.Well A 22 used a conventional tapereddrill string with several drillpipe sizes.Some of the achievements noted with theintermediate-sized pipe were improved

ease of running and handling time,reduced handling tool inventory andmaintenance, reduced surface pumppressure and maintenance, reduced drillstring weight and a large cost benefitfrom improved drilling speed.

Achieving this record reach has enabledStatoil ASA to hit targets from the float-ing installation that were previouslythought unreachable.

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99172: At Statoil ASA’s Visund field in the Tampen area of the Norwegian North Sea, a full-length,intermdediate-sized 5 7/8-in. drill string was used. Improved ease of running and handling time wereamong the achievements noted.

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This paper will present a case historyuse of 5 7/8-in drill pipe and chronicle themany improvements it allowed so aworld record reach could be made. Anovel method for ECD reduction in thetroublesome 8 1/2-in hole section willalso be presented.

Achieving Statoil Visund's WorldRecord Reach With Intermediate SizeDrillpipe A Case History (IADC/SPE99172) WA Ogilvie, RB Chandler, ADevlin, Grant Prideco; HJ Kile, K Rolfsen,Statoil; O Eilertsen, Odfjell Drilling.

S T R E S S R E L I E F B E N E F I T S

The fatigue performance of HWDP anddrill collars cut with and without pinstress relief grooves and API borebackboxes were evaluated using Finite Ele-ment Analysis (FEA) and a strain lifeprediction model. Both NC38 and 6 5/8-in.(6 5/8 FH) HWDP were modeled in vari-ous hole curvatures and while buckled instraight hole sections of various holediameters. Similarly, NC 38 and 8-in(NC56 and 6 5/8 REG) drill collars wereevaluated.

The results of the analyses show thatstress relief features improve fatigue lifesignificantly and should be included onall HWDP and drill collar componentswith NC38 and larger connection types.Additionally, heavyweight drill pipe isproven more fatigue-resistant than com-parably sized drill collar alternatives.

Conversely, in drill collars, most of thebending occurs in the highly stressedconnection. When possible, replacingdrill collars with heavy weight drill pipeand eliminating tapered drill collarstrings is recommended. The fatiguebenefit of stress relief features on HWDPand drill collars decreases as doglegseverity increases or as the hole size inwhich the components are buckledincreases. Although this is true, thestress relief features still provide a sig-nificant improvement in fatigue life.

The Effect of Stress Relief Features onHWDP and Drill Collars: Are SRFs Nec-essary, and When Are They Most Bene-ficial? (IADC/SPE 98992) SE Ellis, THHill Associates.

L I N E R S I N T R O U B L E Z O N E S

This paper will present rotary linerdrilling trial results for Shell where anexpandable liner hanger system wasused to drill new hole. The technical con-siderations reviewed are liner connec-

tions, liner hanger and packer reliability,torque and drag, and equivalent circulat-ing densities (ECD). Results have beenincorporated into future trials.

Running liners across depleted or trou-ble formations in deepwater Gulf of Mex-ico is challenging. Traditionally, linerrunning operations across these forma-tions are subject to significant losses orborehole stability issues that increasethe difficulty of getting the liner to bot-tom. Drilling the liner through the trou-ble zone may reduce these risks. Howev-er, some of these practices also have lim-itations.

In some instances, a mud motor is run,but these are ineffective in low flowratesituations (ECD limitation). Alternative-ly, the liner maybe drilled in rotary modebut often requires a liner top cementsqueeze for zonal isolation, or a two-tripsystem to run a packer element. Theseinefficiencies may be reduced by utilizinga one-trip expandable liner system.

Discussion of the trial results covers thefirst liner drilling attempt, which result-ed in a premature liner release. From thelessons learned, a bypass well wasdrilled, and a second liner drilling trialresulted in successfully drilling new hole.

The liner hanger setting was successful,and the packer held to a positive and anegative test.

Rotary liner drilling trial presentedresults test provide further evidence thatit is feasible to successfully drill a linerthrough difficult formations.

Rotary Liner Drilling Application inDeepwater Gulf of Mexico (IADC/SPE99065) JF Mota, DB Campo, J Menezes,Shell; PE Smith, AT Jackson, Hallibur-ton.

I N T E G R A T E D F E A M O D E L I N GDownhole measurement systems havereached an impressive level of accuracyand reliability. The predictive behavioraspect of complete drilling systems,whether it’s vibrational or directional,has not, until recently, received the samefocus, however. Additionally, cuttingstructure optimization tends to be con-fined to: 1) rock strength/type and 2)drive mechanism. These issues have sig-nificant cost implications for the opera-tor but in both cases require complexmodeling. A system approach is requiredto achieve true optimization of these twohistorically separate areas of drillstringdesign.

Currently available drillstring analysisprograms are run from PCs. RAM capa-bilities limit modeling to only the BHAportion of a drillstring. For the same rea-son, bit effect factors that significantlyinfluence drillstring behavior are at bestassumed.

By utilizing a suite of Finite ElementAnalysis (FEA) based programs, four-dimensional, time-based simulations ofthe drilling process are possible.

The system generates the behavior of theentire drillstring, from the cutting edgeof the bit to surface. The modeling accu-rately predicts the vibrations and accel-erations often seen to have detrimentaleffects on directional control, tool relia-bility, drillstring integrity and drillingperformance. This ability to pinpoint thesource and effects of torsional, axial andlateral oscillations enables users to qual-ify design changes to the drillstring con-figuration and optimize parameters priorto drilling a well. This paper describesIntegrated FEA Modeling and descriptiveresults that have been achieved throughits use.

Integrated FEA Modeling Offers Sys-tem Approach to Drillstring Optimiza-tion (IADC/SPE 99018) H Aslaksen,Smith Bits; LC Paez, UT Tran, MAnnand, Smith International Inc; RGDuncan, Smith Bits. �

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99065: In rotary liner drilling trials for Shell, anexpandable liner hanger system was used todrill new holes. Test results showed it’s feasi-ble to successfully drill a liner through difficultformations.

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