P I P E R O T A T I O N E F F E C T S

THE EFFECT OF pipe rotation on veloc-ity profile and pressure drop is calculatedin concentric and eccentric annulus, dur-ing the axial flow of non-Newtonian fluid.The calculations are applied to the designof hole-cleaning during drilling andcementing. The calculations are validat-ed by comparison with measured values.

In the absence of reliable calculations,one can only guess the impact of piperotation on hole-cleaning. This workgives an engineer the tool to design forimproved hole-cleaning and hence helpsave time and money during well con-struction and production.

The drilling community has generallyrealized the usefulness of pipe rotationto clean the hole both during drilling andcementing. However, no method wasavailable to quantify the effect of piperotation on hole cleaning. This isbecause the calculation of velocity profileand pressure drop for non-Newtonianfluid is not straightforward.

Pipe rotation is more important in aneccentric annulus to remove the drill cut-tings and the gelled drilling fluid from thenarrow annulus. This is because, in aneccentric annulus, the fluid flows prefer-entially through the wider annulus.

The pipe rotation speed, ie, the RPM,equired to remove the gelled drilling fluidand the drill cuttings in various annulusconfigurations and eccentricities arepresented. The results discussed in thispaper can be applied for effective hole-cleaning during drilling and cementing.This should save nonproductive timeduring drilling and cementing and alsononproduction time by reducing remedi-al and intervention costs during well pro-duction.

Pipe Rotation and Hole Cleaning inEccentric Annulus (IADC/SPE 99150) KRavi, T Hemphill, Halliburton.

R I S K - B A S E D R E L I A B I L I T Y

Rotary Steerable directional drilling andlogging assemblies in use today deliversignificant value to operators throughimproved drilling efficiency, precise wellplacement and effective formation evalu-ation. System failure is often associatedwith a high cost and a high pain factor.

This paper describes a rigorous risk-based approach to quantify and improvethe reliability and performance of direc-tional drilling bottomhole assemblies.

Extensive field data gathered whiledrilling 15 million ft of hole drilledbetween 2003 and 2005 have been usedto drive a reliability-centered design andmaintenance program with the objectiveof improving drilling performance,improving system reliability, increasingaverage rates of penetration and reduc-ing nonproductive time.

All aspects of service delivery are con-sidered, including mechanical and elec-trical system component performance,repair and maintenance procedures, jobdesign and field operating practice.

The approach has yielded measurableimprovements in rotary steerable andlogging while drilling bottom hole assem-bly reliability and performance.

Industry metrics such as mean timebetween failure, feet drilled per circulat-ing hour, feet drilled between failure, fail-ure-free runs and operating efficiency

66 D R I L L I N G C O N T R A C T O R January/February 2006

Advances allow drillers to reach further

IADC/SPE DRILLING CONFERENCE: ERD & PERFORMANCE METRICS

98150: Extensive field data gathered between 2003 and 2005 drove a reliability-centered design andmaintenance program, which has yielded measurable improvements in rotary steerable and loggingwhile drilling bottomhole assembly reliability and performance.

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(ratio of nonproductive time to operatingtime) are analyzed, benchmarking cur-rent performance and setting perform-ance expectations for existing and futuredownhole systems.

The industry has a need to standardizethe method of evaluating downholedrilling system performance and tounderstand and quantify the benefitsand risks associated with the applicationof a specific downhole system in a givendownhole environment.

This paper proposes such a standardapproach.

Risk-Based Reliability EngineeringEnables Improved Rotary SteerableSystem Performance and Defines NewIndustry Performance Metric(IADC/SPE 98150) PA Wand, I Silvester,M Bible, Schlumberger.

S A K H A L I N B I T D E S I G N S

Six of the ten longest reach wells in theworld have been drilled in Chayvo fieldon Sakhalin Island. Significant learningshave been gained from these wells andwill be applied to the remaining wells toreduce cost and risk. The learnings arediscussed in this paper.

The evolution of Sakhalin bit designswas driven by a variety of factors. Initialbit design focused on steerability andROP. Intermediate bit designs reducedoverall drill string torque by reducingmicro tortuosity and bit torque. Currentbit designs use extended gauge lengthsto reduce bit darting and excessive vibra-tions in hard stringers while maintainingaggressive cutting structures.

Rotary steerable reliability is importantbecause trips for tool replacement takeup to 6 days. Rotary steerable systemswere improved by evaluating failures,redesigning downhole components andimplementing an aggressive incentivecontract based on run time. Also, byusing downhole vibration measurementtools, we calibrated our understanding ofdrill string vibrations leading toincreased rotary steerable life and ROP.

Initial wells required extensive back-reaming to make connections and trips.The drill team modified bit designs, BHAconfigurations and operations practicesto minimize the amount of backreamingand achieve One Pass Trippable Hole.

Torque reduction became a concernwhen torque on the second well was sohigh we could not drill out the 9 5/8-in.casing shoe. Many different torquereduction solutions were evaluated

including mud systems, mud additives,mechanical torque reduction compo-nents and drill pipe design. A combina-tion of these solutions reduced torque by30 percent.

The 13 5/8-in. casing, 9 5/8-in. casing,and 7-in. liners were floated on the firstwells. Evaluation of casing running fric-tion factors allowed us to convert the 135/8-in. and 7-in. to conventional mud-filled casing running operations.

Initial completions were cased, cementedand perforated on coiled tubing toachieve a low skin completion with zonalisolation. After experiencing problemswith production liner cementing andcoiled tubing perforating, the team decid-ed to attempt alternative completionmethods. The current completion beingevaluated for reservoir performanceincorporates standalone screens andpredrilled liner isolated by swell packers.

The Next Generation of SakhalinExtended Reach Drilling (IADC/SPE99131) RA Viktorin, JR McDermott, RERush, JH Schamp, ExxonMobil.

R I N G H O R N E D E V E L O P M E N T

Ringhorne platform in the Norwegianpart of the North Sea is a challengingextended reach development, with 24wells planned from the centrally locatedplatform. The platform was designed todrill to 7 accumulations within 8 km withtarget TVDs ranging from 1,750 m to2,000 m. The multiple separate reser-voirs were insufficiently sized by them-selves to support a standalone develop-ment.

The field development as of June 2005 ison its 18th well and most challengingwell to date: 7,600m MD at 1,796m TVD,VS/TVD (seabed) = 4.3. The Ringhornedevelopment was made possible by usinga combination of the latest drilling tech-nologies for extended reach drilling.

During the project-planning phase, 2 keyissues related to drilling were identifiedand stewarded at a project managementteam level. The key issues involveddrilling operations and drilling accuracy.For drilling operations, feasibility forextended reach casing installations, abil-ity to drill long horizontal 8 1/2-in. holesections due to tight margins (ie lostreturns), ability to drill deep 17 1/2-in.hole sections and ability to directionallydrill 24-in. hole sections were identified.For drilling accuracy, concern centeredaround sufficient well placement notbeing possible due to surveying uncer-

tainty. This talk will highlight some of thekey drilling technologies used and thestructured approach applied during fielddevelopment to gain experience usingthese.

In the second part of the talk, the paperwill address key observations concern-ing how many large-scale developmentprojects have fundamentally shiftedmore of the development risk towardsdrilling, particularly in extended reachprograms. As such, by now relying onmore complex and higher-risk welldesigns to achieve development objec-tives, how did the Ringhorne drill teameffectively communicate risks to theclient, ie subsurface development teamand senior management.

The talk will conclude with providing anupdate on the ongoing D&C campaignand challenges ahead as extended reachprograms in general become ever morecomplex.

Ringhorne Development TechnologiesApplied in Extended Reach Drilling:Successes, Failures, and Communicat-ing Risks (IADC/SPE 99124) NNMusaeus, ExxonMobil.

R E C O R D E R D W E L L

Description: Case history from a worldrecord ERD well drilled in the North Seafrom the Visund floating platform. Thewell was originally planned as a separatecostly subsea development, but a newstudy showed that this well could bedrilled from the existing Visund floatingplatform using existing subsea systems.

Application: ERD wells drilled from afloating rig. What is possible for subseadevelopment in the future.

Results, observation, conclusion: Well34/8 A 6T2H reached a TD of 9,082m/29,796 ft. Horizontal reach 7484m/24553 ft, world record from a floatinginstallation. Water depth 335 mMSL/1,100 ft.

Low friction/torque, optimal well profile,good hole-cleaning with 180 string RPM.

DIACS completion in an ERD well. Evenlonger well can be drilled from subsealocations in the future. Optimal pre-plan-ning phase with use of all service compa-nies involved and optimal teamwork inthe subsurface team using 3D visualiza-tion tools.

Significance: Subsea developments incombination with ERD wells canincrease oil production and lower totaldevelopment cost.

IADC/SPE DRILLING CONFERENCE: ERD & PERFORMANCE METRICS

January/February 2006 D R I L L I N G C O N T R A C T O R 67

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World Record ERD Well Drilled From aFloating Installation in the North Sea(IADC/ SPE 98945) A Hjelle, TG Teige, KRolfsen, KJ Hanken, S Hernes, Statoil; YHuelvan, Schlumberger.

3 D D R I L L S T R I N G M E C H A N I C S

With well trajectories becoming morecomplex, drillstring composition beingunconventional and the material beingused to its operating limit, the necessityto have a tool that realistically predictsforces, bending moment and contactloads along the wellbore is essential. Theconventional soft string model gives agood approximation of forces and con-tact loads in the drillstring for verysmooth trajectories but is inappropriatewhen the trajectory becomes tortuous orcomplex.

An advanced numerical method hasbeen applied to address the 3D mechan-ical problem of a complete drill stringmoving and freely rotating inside awellbore: computation of the unknowncontacts between the drillstring and thewellbore. As this new model does notuse the time-consuming finite elementanalysis, it can be used in real-timedrilling operation at the rig to monitortorque and& drag. For the first time, itis even possible to perform simultane-ously a torque and drag and directionalanalysis while drilling.

The power of a 3D visualization of thedrillstring deformed inside the wellboreenables to localize easily contact loadson any drill string component, from thedrilling bit (including side force at the bitand tilt) to the top drive or rotary table(hook load and rotary torque at surface),facilitating drilling problems analysis.

This paper will describe the fundamen-tals of the model developed and show thedifferences between the conventionalsoft string model and the new model interms of tension, torque, bendingmoment and contact points between thedrillstring and the wellbore.

With the help of the 3D visualizationsofware, this paper will show the caseswhere the drill pipe contacts the highside of the borehole, or goes up to theright or the left side of the boreholedepending on the right or left turn rate ofthe well trajectory.

This new model should improve signif-icantly the torque and drag calcula-tions and the understanding of thedrillstring contributions to overalldrilling performance.

Advancements in 3D Drillstringmechanics: From the Bit to the Top-drive (IADC/SPE 98965) S Menand, HSellami, M Tijani, Paris School of Mines;DC Dupuis, Pride Forasol; C Simon,Drillscan.

F O R M A T I O N A N I S O T R O P Y

Interbedded formations are a majorcause of borehole tortuosity. In somefields, shale formations have a tendency

to cause wellbore deviations to unde-sired directions.

The formation anisotropy modifies therock bit and the bit string interactions.Those interactions have to be under-stood to eliminate tortuosity. A programhas been carried out using drilling bits indifferent formations (hard/soft, soft/hardwith different interface angles).

Coupling a 3D rock bit model with a 3DBHA model enables prediction of theoccurrence of tortuosity at a small andlarge scales and to evaluate the responseof all directional drilling systems. Devia-tions caused by formation anisotropiesare separated into two phenomena.

An initial deviation is caused by therock bit interaction. The experimentaland theoretical results explain how thegauge length, bit profile and dip anglecan affect the amplitude of this devia-tion. A second deviation is generatedwhen the different stabilizers are slid-ing through the initial one. They can beamplified or attenuated according todrilling system used. The number ofstabilizers and their positions, BHAcharacteristics and bit steer abilityaffect on these deviations.

A post analysis of some real drillingcases, showed that, for a given drillingconditions including the formationsanisotropies, it is possible to select thebest drilling system minimizing the welltortuosity.

Effect of Formations Anisotropy onDirectional Tendencies of DrillingSystems (IADC/SPE 98865) R Boualleg,H Sellami, S Menand, Paris School ofMines; C Simon, Drillscan. �

68 D R I L L I N G C O N T R A C T O R January/February 2006

IADC/SPE DRILLING CONFERENCE: ERD & PERFORMANCE METRICS

98965: An advanced numerical method hasbeen applied to address the 3D mechanicalproblem of a complete drill string moving andfreely rotating inside a wellbore — computa-tion of the unknown contacts between the drilstring and the wellbore.

98865: Coupling a 3D rock bit model with a 3DBHA model allows prediction of the occurrenceof tortuosity and to evaluate, feet by feet, theresponse of all directional drilling systems.

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