drillbotics 2017

FACULTYOFSCIENCEANDTECHNOLOGY

Drillbotics2017

Studyprogram/specialization:

PetroleumEngineering–DrillingandWellEngineering

FallSemester,2016

Writers:

ErikAndreasLøken,PatrickHarris,OleAndréHjelm,SimenJøsangNilsen,AlexanderTrulsen

FacultySupervisor:DanSui

ExternalSupervisor:RobertEwald,InternationalResearchInstituteofStavanger(IRIS)

Title:

Drillbotics2017:RigDesignPrinciplesandDecemberUpdate2016/2017

Keywords:

• RigDesign

• AutonomousDrilling

• Drillbotics

• DrillingControl

• DrillingPerformance

• Autonomouscontrolsystems

Numberofpages:48(+appendix)

Stavanger,2016-12-31

UniversityofStavanger,2016-12-31

II

Contents:

Summary VI

1. ProblemDescription 1

2. Rig-andControlSystemArchitecture 22.1RigSystems 22.2ControlPrinciples 3

3. Rigdesign 53.1DrillStringCalculations 53.1.1PreliminaryMetallurgicalConsiderationsforTorque 53.1.2DrillString–Twist-Off 63.1.3MaximumAllowableOverpull 73.1.4MaximumAllowableWOB 73.2Bottom-HoleAssemblyDesignandConceptualization 83.2.1BasisofDesign 83.2.2BHAManufacturing 113.3CirculationSystem 123.3.1 Pump 123.3.2 RotaryUnion 133.3.3 Multi-TieredFiltrationSystem 143.3.3.1 DesignPrinciples 143.3.3.2 DesignConsiderations 143.3.3.3 ProposedLayout 153.3.3.4 FlowProfiles 163.3.3.5 Tank3initialMinimumStartupVolume 163.3.3.6 CirculationSystemAdvantagesandDisadvantages 173.4PowerTransmission 183.5HoistingSystem 193.5.1 HoistingSystemPrinciples 193.5.2 HoistingSystemComponents 203.6ConstructionofFramework 223.7TorqueSensing 233.7.1 DesignPrinciples 233.7.2 SystemAdvantagesandDisadvantages 243.8PressureSensing 253.9AnalogueInfraredElevationSensing 263.10LoadCellForceSensing 27

4. SystemCalibrationandDetectionofDrillingDeterioration 294.1CalibrationinSteadyStateConditions 294.1.1SteadyStatePumpPressure(sameasDrillbotics2016,UniversityofStavanger) 294.1.2SteadyStateTorqueCalibration 304.1.3SteadyStateDrillStringVerticalityandWOBCalibration 304.2CalibrationinTransientConditions 31


III

4.3DetectionofaDeteriorationinDrillingConditions(sameasDrillbotics2016,Universityof

Stavanger) 31

5. ControlStrategies:DownholeDrillingProblems 325.1LiteratureReview 325.2NormalDrillingState(sameasinDrillbotics2016,UniversityofStavanger) 325.2.2 OffBottomCalibration 325.2.3 ResumeDrilling 335.2.4 ManagementofROPinanUnknownFormation 335.2.5 ManagementofROPinaKnownFormation 335.2.6 ManagementofDrillingParametersBetweenSoftandHardFormations 335.2.7 ManagementofDrillingParametersBetweenHardandSoftFormations 345.2.8 ManagementofanIncliningDrillString 345.2.9 EndofDrilling 345.3DeterioratedDrillingState(sameasinDrillbotics2016,UniversityofStavanger) 355.3.1 ManagementofPoorROPPerformance 355.3.2 ManagementofDrillString-vibrations 355.4CatastrophicDrillingState 355.4.1 StuckPipe–DifferentialSticking 355.4.2 StuckPipe–KeySeating 365.4.3 StuckPipe–Pack-off 365.4.4 DrillingFluids–BitBalling 375.4.5 DrillingFluids–ProgressiveGels 375.4.6 Drillstring–Stick/Slip 385.4.7 Drillstring–Twist-off 38

6. DatahandlingandDisplay(sameasDrillbotics2016,UniversityofStavanger) 39

7. EstimatedCosts 43

References 48

Appendix1 iCalculationofDrill-stringTwist-offTimeandAnglevs.OperationalTorque i


IV

Figurelist:Figure1:DepictionoftheproposedPhase-1design.............................................................................2

Figure 2:Outlineof the three-tiered control hierarchywhere each tier requires faster responsetimes,with theStrategicdecisioncontrollerbeing theslowestandthe response time in thehoisting-,powertransmission-andcirculationsystemsthefastest.............................................4

Figure3:Drill-stringtwistanglevs.torqueforanaluminiumpipe......................................................6

Figure4:Drill-stringtwist-offtimevs.operationaltorqueforanAluminiumpipe.............................7

Figure5:ProposedBHAdesigndepictingtheindividualcomponentsandtheirdimensions..............9

Figure6:TypicalBHAdesignsforverticalwells...................................................................................10

Figure7:CAD-sketchoftheproposedBHA-design.............................................................................11

Figure8:Outlineofthecirculationsystem..........................................................................................12

Figure 9: TheDeublin rotary union is assembled on top of the hollow shaftmotor using closingstoppers.AD6075-201DeublinCartridgewillbeinstalledwiththerotaryunion....................13

Figure10:CAD-sketchofthemulti-tieredfiltrationsystem............................................................14

Figure11:Birds-eyeviewofproposeddrillingfluidcirculationsystem.............................................15

Figure12:Drillingfluidcirculationsystemflow-pathandproposedlayout.......................................16

Figure 13: CAD depiction of how the brushless motor will be mounted on the top-drive plateattachedtotheactuatorsandhowtherotaryunionwillbefitted............................................18

Figure14:Outlineofthehoistingsystemandasimplifiedsketchshowinghowoff-setdetectionwillcorrectdrill-stringinclination.......................................................................................................19

Figure15:NEMA23StepperMotor......................................................................................................20

Figure16:HucoBrake(FSB015)withastatictorqueof1.69Nmforeachbrake................................20

Figure17:C-beamLinearactuatorbundleequippedwithaNEMA23Steppermotor.......................20

Figure18:ForsentekFNZtri-axialloadcell(x,y,z:0-100N).................................................................20

Figure19:Electricalconfigurationforthethreesteppermotorscontrollingtheactuators..............21

Figure20:Outlineoftheframeworkofthedrillingmachine.............................................................22

Figure21:Bracketsandlockablejointswillpreventtheconstructionfromcreeping.......................22

Figure22:TorqueSensorprovidedbyTorqueandMoreGMBH,modifiedtoprovideasamplingrateof2000HzandsupportingintegrationintoMatlabandMatlabSimulink..................................23


V

Figure23:TheGemsanaloguepressuresensorhasaresponsetimeof1ms,andanaccuracyofwithin0.25%.............................................................................................................................................25

Figure24:Depictionoftheproposedsharpdistancesensor.Thesensorwillneedanamplifier,astheoutputvoltagewilldecreaseasthedistanceincreases..............................................................26

Figure25:0-100NFNZcustomtri-axialloadcellsbyForsentekprovidingananalogueratedoutput1.0mV/Vandhysteresisof±0.2%oftheratedoutput............................................................27

Figure23:Illustrationofhowcalibrationwillbeconducted;acylinderwillbeplacedinsidethewatercontainerandpumppressurewillberecordedatdifferentbitdepths.....................................29

Figure24:Depictionofhowtorquewillbemeasuredinthecalibrationphasetoensurenodamagetotheequipmentandconfiguration............................................................................................30

Figure 25: Illustration of how the forcemeasurements obtained from the tri-axial load cells areinterpretedinthereal-timecontrollerbeforecommandsareissuedtoeachactuatortoreachazero-offsetstate...........................................................................................................................30

Figure26:Definitionofthefounderpoint,sothatadeteriorationintheDrillingconditionsmaybedetected........................................................................................................................................31

Figure30:Depictionofthe#ofinstructionsthatcanbecarriedoutwithvariousloopdurations...39

Figure31:IllustrationofhowPCandPLCwillco-operateinthehierarchicalcontrolsystem...........40


VI

SummaryTheautonomousdrillingrigisdesignedinaccordancewiththeguidelinesandconstraintsthataredefined

bytheDrillboticsCommitteeoftheDrillbotics2017Competition,hostedbySPE.Thecompetitioninvolves

designingandbuildingasmall-scaleautonomousdrillingrig,whichiscapableofdrillingthroughan

unknownrocksampleof0.6mheightinthefastestperiodoftime.

Thedrillingmachineisdimensionedtofullyexploit,yetnotexceedthestrengthoftheweakest

component:thealuminumdrillpipe.Themechanicalpropertiesofthealuminumpipethusdefinethe

drillingmachine´smaximumoperatingcapabilities,i.e.theRPMmax,ROPmaxandWOBmax.Tosuccessfully

achievetherequiredobjectiveandavoidanydrillingincidence,forinstancedamagetoequipment,akey

elementinthedesignprocesshasbeentobuildanaccuratesystem,whichiscapableofquickdetection

andadaptationtovariousdrillingscenarios.

Athree-tieredhierarchicalcontrolsystemwasdesignedbytheUniversityofStavanger(UiS)inthe

Drillbotics2016competitiontobalancethenecessityforfastresponsetime,sufficientmodelanddata

analysisandgooddecisionmaking.Byhavingdeterministicmachinesperformthemostcomplexanalysis

andcomputationsthatarenottimecriticalandcreatelook-uptableswhichcanbeaccessedand

interpolatedfrombynon-deterministicreal-timecontrollers,thedrillingmachinecanrespondtochanges

indrillingconditionsandimplementcountermeasurestooptimizethedrillingprocess.Pleasenotethat

sections4.1.1,4.3,5.2,5.3and6arethesameasthosepresentedinPhase1bytheUiSintheDrillbotics

2016competition,whichwillpossiblyberevisedinthelatephasesoftwarearchitecturedesignand

implementation.Inthisreport,wefocusmoreontheworkregardingthemechanicaldesign,

components´selectionduetothesafewindowoperations,realtimedataacquisitionandmodellingand

simulations.

Inthefirstphasedesign,ahollowshaftpowertransmissionsystem,whichprovidesrotationalvelocityis

designed.Throughtheuseofabrushlessmotorratherthanasteppermotor,vibrationswhichoriginate

fromthetopdriveandfurtherpropagatedownthedrillstringwillbekepttoaminimum,evenathigh

RPM.Inaddition,advancednon-contacttorquesensingequipmentallowsfordirecttorque

measurementsonthedrillstring,permittingthedrillingmachinetooperateclosetoitsfullpotential.

Threeactuators,individuallycontrolledandconnectedtothetop-driveofthedrillstringusingtri-axial

loadcellswillallowforaccurateWOBontotheformation,andensureverticalityofthedrillstringthrough

off-setdetectiononallthreeaxes.Thecirculationsystememploysathree-tieredbucketcollectionsolids

removalconcept.Ashaker-stylesystemwasconsidered,butnotutilized,sinceagel-basedsystemwillnot

berun.Thedrillingfluidwilllikelybeanoilbasedfluidbasedonitslubricityandeffectivenessinreal-

worldapplications.Regardingthedrillingoftherocksample;afullypackedbottomholeassemblyhas


VII

beenselectedbasedontherecommendationsoflastyear´sUiSentryandgoodindustrypractice.Thisis

toensurethewellisdrilledwiththemostpossiblecontroloverdeviationandtoachievethemostvertical

well-pathpossible.Anassessmentofthetotalcosttobuildtherig,andthepowerconsumptionrequired

torunit,isapproximatelyUS$9.800and1.6kW.


VIII

Nomenclature(common)''(-Confinedcompressivestrength

)*+,-Bitdiameter

ID-Internaldiameter

OD-Outsidediameter

12-Young’smodulus

3-Force

345,6754-Lateralforcetodestabilizethestructure

38+64)-Maximumallowableaxialforceondrill-pipe

F*+,-Forcebetweenthebitandtheformation

G-Shearmodulus

g–Gravitationalacceleration

=-Bucklingeffectivelengthfactor

4-Lengthofdrill-pipe

>(1-MechanicalSpecificEnergy

?@-Bucklingcriticalload

7@A-Distancefromthecenterofrotationtothecenterofgravity

74-Distancefromthecenterofrotationtothepointofapplicationofthelateralforce

B'(-Uniaxialcompressivestrength

C*+,-rateofpenetration

DEF-Weightonbit

GHIJ −Ultimatestrength

GLM −Ultimateshearstrength

GLNO −Shearyieldpoint

GNO −Tensileyieldstrength

τHIJ −Maxtorque

τQRSTUIVST −Tolerabletorqueasafunctionoftheresponsetoavoidexceedingtheyieldtorque


IX

τNWTSX −Yieldtorque

θIZ[ST −Angle

µVWQ/UR^_ −Coefficientoffriction

ρ −Density

ωVWQ −Bitangularvelocity


X

Abbreviations(common)ROP–Rateofpenetration

WOB–Weightonbit

RPM–Revolutionsperminute

ID–Innerdiameter

OD–Outerdiameter

SPE–SocietyofPetroleumEngineers

DSATS–DrillingSystemsAutomationTechnicalSection(SectionoftheSPE)

UiS–UniversityofStavanger

WBM–WaterBasedMud

OBM–OilBasedMud

PV–PlasticViscosity

SF–SafetyFactor

YS–YieldStrength

USS–UltimateShearStress

UTS–UltimateTensileStrength

UCS–UniaxialCompressiveStrength

TFA–TotalFlowArea

BHA–Bottom-HoleAssembly

TD–TotalDepth

DP–DrillPipe

HWDP–Heavy-WeightDrillPipe

SPP–StandPipePressure

MSE–MechanicalSpecificEnergy

CCS–ConfinedCompressiveStrength

MAOP–MaximumAllowableOver-Pull

RO–RatedOutput

SNR–Signal-to-NoiseRatio


1

1. ProblemDescriptionTheteamwilldesignandbuildanautonomousdrillingmachine,whichphysicallyimitatesthe

functionalityoffull-scalerigmachinery.Arocksamplemeasuring12”widthx12”lengthx24”height

(30cmx30cmx60cm),istobedrilledasverticallyaspossible,asquicklyaspossible.Therock

samplewillbe“manufacturedusingcement,varyingsoilsamplesandpossiblyothermaterialsnot

typicallyencounteredduringregulardrilling.Allsimulatedformationsmaynotbeparalleltoeach

other(e.g.formationdip)”1.Atimeconstrainttopenetratetherocksampleissettoamaximumof

twohours(120minutes),i.e.aminimumrateofpenetration(ROP)of0.5cm/min.Therocksample

shallbedrilledusingaPDCmicro-bitwithanouterdiameter(OD)of1.125”(28.575mm),braced

cutterswithacutterbackrakeangleof20degrees,acutterdiameterof0.529”(13.4366mm)andtwo

nozzles.Thenozzleseachare2.35mmindiameteri.e.atotalflowarea(TFA)of8.6747mm2.

Thedrillstringiscomprisedofasinglealuminumtubeof36”(914.4mm)length,withanODofbc”

(9.525mm)andawallthicknessof0.016”(0.4064mm),i.e.aninnerdiameter(ID)of8.7122mm.In

designingthebottomholeassembly(BHA),stabilizersarepermitted.Stabilizersshallhowevernot

exceedatotallengthof3.5”(88.9mm),andmaynotbeusedinamattertostiffenthedrillstring.

Sensorscanbeapplied,bothonthedrillingrigandthedrillstring,butarenotpermittedtologthe

rocksample(providedbytheDSATS).Thedrillingrigwillworkautonomously,meaningcalibration,

drillingandproblemhandlingistobefullyautomatedwithouthumaninteraction.Thisappliesto

bothsensors,motors,pumps,etc.2Allremoteoperationand/orinterventionisprohibited.

Thepowerconsumptionislimitedto2.5horsepower3(1.8643kilowatts).Thisistoincludeallthe

componentsandmonitoringsystemsinplace.Theofficialguidelinesalsoencourageallteamsto

spendlessthanUS$10,000.ExceedingthisbudgetlimitmayleadtopenaltiesfromtheDSATS

committee.

Differingfromcompetitionsinpreviousyears,thereisnolimitontheweightonbit(WOB)thatcan

beapplied.

1DrillboticsGuidelines;InternationalUniversityCompetition2016-20172Aseriesofsetabortcriteriainourcontrolsystemwillbespecifiedinthefinalreport,toensurethesafetyofbothpersonnelandequipment(resemblingarealdrillingsituation).3 The official guidelines for Drillbotics 2017 states that the total power consumption is not to exceed 25horsepower(18.643kw).Asthisistentimeshigherthaninpreviousyears,weassessthattheintendedpowerconsumptionislimitedto2.5horsepower.


2

2. Rig-andControlSystemArchitecture

2.1RigSystems

Therigisconstructedfocusingonmobility,ratherthanthemachinebeingpurelystationary.To

ensurethestabilityoftherig,high-qualitystrutprofilesareutilized,connectedbybracketsand

lockablejoints.TherigismountedonheavyliftingwheelsasdepictedinFigure1.

Ahollowshaftpowertransmissionsystemhasbeenchosentoprovidetherequiredrotational

velocitytopenetratetherocksample.Thebrushlesshollowshaftmotorallowsforcirculation

throughthemotorandisconnecteddirectlyontopofthetop-driveusingarotaryunion.Therotary

unionisattachedontopofthemotor,ratherthanbeneath,toovercomethechallengewithsmall-

Figure1:Thedrillingmachinewillbemobile,withanapproximateheightof2.5m.Acrylicplasticsheetswillprotectpersonnelandequipment,andisinstalledtoallowforusingbothoilbased-andwaterbaseddrillingfluidsfortesting.Pleasenotethatwiring,hoses,andseveralcomponentsarenotincludedinthisfigure.


3

scalerotaryunionsproducinghighamountsofviscousfrictionwhenperforminginlow-pressure

conditionsathighRPMbeneaththemotor.

ForthedrillingtobeperformedasverticallyaspossibleandwithanaccurateWOBatalltimes,three

actuatorsareconnectedtothesteelplatewherethetopdriveismounted.Theactuatorsare

connectedtotheframeofthedrillingrigconstitutethehoistingsystemofthemachine.Thehoisting

systemwillprovideuswiththeWOBneededtoeffectivelypenetratetherocksample,thus

controllingthespeedofbitelevationandROP.Thedecisiontoutilizethreeactuatorsinthehoisting

systemallowsthedrillingmachinetocounteractforcesinthex,y,z-directionsactingfromthe

formationonthebitwhiledrilling.Bymonitoringandadjustingtheelevationofeachindividual

actuator,drillstringverticalitythroughouttheentireoperationisachieved.Tomeasuretheseforces,

notlimitedtothoseactinginthez-direction,tri-axialloadcellsareappliedbetweeneachactuator

andthetopdrive-plateinwhichthetopdriveismountedto.Byusingreal-timecontrollers,the

drillingrigcandetectandcorrectforanoffsetindrill-stringverticalityifsaidforcesactingfromthe

formationtothebitcreateaninclinationinthedrillstring.

Theproposedcirculationsystemenablesdrilledcuttingstobetransportedawayfromthebitto

surface,whilstthebiggestsolidsarefilteredoutusingamulti-tieredfiltrationscreensystem.Anoil

basedmud(OBM)isproposedasthefinaldrillingfluid,howeverwaterbasedmud(WBM)willalso

betestedtocomparedifferencesinbehaviorandadvantageswhenoperatingasmall-scalerig.

2.2ControlPrinciples

Giventhecomplexityofasystemoperatingautonomously,thecontrolsystemisratheradvanced.

Thedrillingrigneedsnotonlytoexecuteapre-setdrillingstrategy,butadapttoseveraldifferent

scenariosandconditions.Figure2depictsasimpleoutlineoftheproposedcontrolhierarchy

intendedtodetect,interpretandadapttothesevariousdrillingconditions.Themostcomplex

functions,whicharenottime-criticaltocarryout,willbeprocessedbythestrategicdecision

controller.Suchfunctionsaredrill-offtestingtodetermineinitialvalueswherenoWOBisappliedto

theformation,excessivevibrationinthedrillstring,damagetotherigetc.Thestrategicdecision

controllercanbeallowedtooperateslowerthanthereal-timedecisioncontrollerandmaybe

subjecttoanon-deterministiclatencywhichminimizestheriskoftwisting-offthedrillstringor

damagingequipment.


4

Figure2:Outlineofthethree-

tieredcontrolhierarchywhere

eachtierrequiresfasterresponse

times,withtheStrategicdecision

controllerbeingtheslowestand

theresponsetimeinthehoisting-,

powertransmission-and

circulationsystemsthefastest.

Thereal-timedecisioncontrollerontheotherhand,hastoexecutecommandsoflesscomplexity

withadeterministic4latencyandcriticallooptimestoavoiddamagetothedrillstring.Thehoisting,

powertransmissionandcirculationsystemsallneedtobeacceleratedanddecelerateddependingon

thevariousconditionsencountered.Theindividualsystemcontrollersneedtooperatewiththe

fastestresponsetimestocarryoutcommandsinstructedbythereal-timecontroller.

Thevarioussensors(loadcells,torquesensor,pressuresensor,heightsensor)needtoprovidehigh

enoughsamplingratestothereal-timedecisioncontroller.Thisissothatthelooptimesofthe

controlsystemsdonotexceedthoserequiredtohandleaworst-casescenariowithouttwistingoff

thedrillstring.

4Inadeterministicsystem,theoutput(futurestate)canbepredictedwith100%certainty.Inacriticalsystemsuchasthereal-timecontroller,repeatability,constantlooptimesandconstantoutputsisanecessity.


5

3. Rigdesign

3.1DrillStringCalculations

Thestrengthofthedrillstringislimitedbythatoftheweakestcomponent;whichisthealuminumdrill

pipe(DP),specifiedtobeusedinthecompetitionguidelines.Metallurgicalcalculationswillbeapplied

witha1.1(or10%)safetyfactor,toallowfordeficienciesinpipestrengthandlongerthanexpected

looptimestoceaserotationswhenproblemsareencountered.Pleasenotethatcalculationswillbe

coveredmoreindepthinlatermonthlyreports,aswehaveyettoconductdestructivetestingofthe

drillstring,bothwithandwithoutfluidcirculation.

3.1 .1PreliminaryMetallurgicalConsiderationsforTorque

Aluminuminitspurestformhasayieldstrength(YS)of34MPaandaUltimateTensileStrength(UTS)

of89MPa.Theassumptionismade(Sheasbyet.Al.,2001).

2dHIJ = 89>?5

B4,+h5,6dℎ657d,76dd = 0.65l2(HIJ = 57>?5

Wewillassumea(3no1.1

Therefore,themaximumtorquethatcanbeappliedbeforethepipeshearsis:

qrHIJ =B((7

s32()R

v − )Wv) = 3.01hx = y. z{|}~�ÄÅÇÉ

Maximumapplicabletorquethatcanbeappliedbeforethepipeyieldsis:

qrNWTSX = 2?7s32()R

v − )Wv) = 1.73hx = Ñ. Öz|}~�ÄÅÇÉ

Therefore,withtheSFinplace,therigneedstoprovideaminimumtorqueof1.57mNinorderto

workatthemaximumoperatinglimit.Thesefiguresassumeapurealuminum,andthatthereareno

impuritieswithinthemetal.CertainAlalloysmaystrengthenorweakenthepropertiesshown

above.


6

3.1.2DrillString–Twist-Off

Duringdrilling,wherestick-slipconditionsprevail,anysuddenstopinrotationmaytwistthedrillpipe

toitsshearpointiflooptimesarenotsufficienttoceaserotation.

WeknowtheshearmodulusofAluminumis64GPa.

ThetorquegeneratedbythetwistingoftheDPisgiven:

qrNWTSX = Üáàâ,ℎ6,5 = Ñ. z{|}

Where: Üá = äãv()R

v − )Wv),whichisthesecondmomentofarea

à = 91.44@h

Theconsiderationmustalsobemadefordrillstringtwist-offasafunctionoftwistangleandalsoasa

functionoftime.Theresultsofthesecalculationsareshownbelow.Thecalculationsforthesetwo

resultscanbeseenintheappendix.5

Figure3:Drill-stringtwistanglevs.torqueforanaluminiumpipe

5See“Twist-off–AluminiumPipe”forfullcalculationsandpresentationofresults.


7

Figure4:Drill-stringtwist-offtimevs.operationaltorqueforanAluminiumpipe

3.1.3MaximumAllowableOverpull

MaximumAllowableOverpull(MAOP)canbedeterminedbyknowingthetensilestrengthoftheDP,

settinganappropriateSFof1.1:

3NWTSX = s4)R

ç − )Wç 2( = 395x ≅ 40=A = {èêë~�ÄÅÇÉ

Thismeanstheentirestringweightcannotexceed36kg.

Note:Buoyancyhasnotbeentakenintoaccountinthesecalculations.

3.1.4MaximumAllowableWOB

MAOPcanbedeterminedbyknowingthepointatwhichtheDPwillbuckleandapplyingaSFtoprevent

thisfromhappening.Then,we’llneedtocalculatetherelationshipbetweenWOBandtorqueatthe

bitandfindthemaximumallowableWOBforagivenUCS(rockstrength).

'7+,+@54Fí@=4+ìA3n7@6 = (sç1NÜî)(=à)ç

= yïÑ}ñ�óóòô, yõ}ú~ùû�óë

Hence,theWOBmax(applyingSF=1.1)=182Npinned,22Nswaying(WOBinterval=2kgto18kg)


8

Thekvaluevariesfrom0.7to2.0,i.e.Oneendpinnedthroughtooneendswaying.EyforAlis69GPa.

In our case, we have the DP pinned to the BHA and the TD, but we need to account for lateral

movementwhendrillingcommences. Gooddrillingpracticescanminimize thiseffect,byensuring

maximumRPMandflowrate,combinedwithalowWOBareappliedbeforecommencingdrilling.

3.2Bottom-HoleAssemblyDesignandConceptualization

3.2.1BasisofDesign

Itisuncommonforadrillbittodrillastraightandtrueverticalholewithoutsomeassistancefrom

thebottom-holeassembly(BHA)above.Inparticular;BHA’scanbedesignedtoachievenumerous

desiredwellpaths.

InthecaseoftheDrillbotics2017venture,theguidelineshavestipulatedthatasmall-scaledrilling

rigbebuiltinordertodrillaverticalwellina30x30x60(cm)sampleofrockasquicklyaspossible.

Inpreviousyears,somesuccesshasbeenfoundinusingwhatisknowninindustryasa“pendulum

assembly”(discussedfurtherbelow).Whilethisdesignisoftensuccessfullyimplementedinreal-life

surfaceholesections,particularlywherelowweightonbit(WOB)isrequired,onthescalein

questionfortheDrillboticsRig,highWOB,completewithanimproperrigdesignhasbeenshownto

leadtoissueswithlateralandtorsionaldrillstringvibrations,amongotherdownholeissues.

Anotherissuethispresentsisthepossibilityofadeviatedwellboresection.Thisisbecausehigh

WOBactingononestabilizercanhaveabucklingeffectonthestringabove.Wherethisisapparent,

tri-axialloadingisincreasedonthedrillstringandbit,whichresultsinsub-optimaldrilling

parametersandcanultimatelyleadtoproblems.

Thedrillstringdesignwhichisbeingproposedisoutlinedonthenextpage(seeFigure5andsketch

provided)andhasbeendesignedinaccordancewiththeguidelinesprovidedinSections4.6–4.9in

theDrillboticsGuidelines2017document6.

6DrillboticsGuidelines;InternationalUniversityCompetition2016-2017


9

87 654321

Figure5:ProposedBHAdesigndepictingtheindividualcomponentsandtheirdimensions.

Thereasonofafully-packeddrillingassemblyhasbeenchosenoverapendulumassemblyisoutlined

below(SeeFigure6).Apackedassemblyisineffect,astiffdrillingassemblywhichusuallyconsistsof

twoormorestabilizers(orreamers,dependingonthescenario),drillcollarsandHWDP.The

purposeofthisdesignistoallowfortheminimumpossiblerateofchangeindeviationofthewell

path.Atypicalpacked-assemblyhasbeenshownbelow,ontherighthandsideofFigure6.

Pendulumassemblies(asexemplifiedbythesketchshownonthelefthandsideofFigure6),are

typicallydesignedforwellboresectionswherethenaturaltendencyoftheformationhasthebit

driftingawayfromvertical.Apendulumassembly,thankstotheunsupportedsectionofthedrill

collarwillswingtotheleftorrightofthelowsideoftheholeandcanusuallycorrectnatural

deviationsinthewellpath.ForthecaseoftheDrillboticsproject,itisassumedthataformation


10

samplewillnotpresenttheusuallarge-scaleformationinconsistenciesoveralongenoughperiodto

needtocorrectfornaturalwellboredriftandhencetheselectionofthepacked-assembly.

Figure6:TypicalBHAdesignsforverticalwells

(DrillingEngineering-HeriotWattUniversity,2005)

Oneofthebiggesthindrancesofdrillingperformancesinpreviousyears,hasbeentheissuescaused

duetostringvibrations.PendulumassemblieshavebeenshownintheDrillboticsarena(andinreal-

lifesituations)tocausesignificantvibrationswhenimproperparametersareappliedtothedrillbit.

Thedrill stringvibratesasa resultof loadexcitationsappliedatvarious locationsand frequencies.

Potentialexcitationsourcesare:

• Massimbalance

• Misalignmentorkinks/bendsinthestring

• Cuttingactionofthebit


11

• Friction factor between bit and borehole (which can beminimizedwith a lubricated fluid

system)

Assuming the above excitation sources have been accounted for and with minimal stick-slip, the

pendulumassemblyisstillthemostlikelyofthetwopossibledesignstoexperiencelateralvibrations.

Thesecanbebroughtonduetoeitherthebucklingeffectofthestring,ortheunrestrainednatureof

thedrill collarsabove thebottom-most stabilizeras stringdrillsdeeper (SchlumbergerDrillingand

Measurements,2010).

Furtherconsiderationswithregardstovibrationsandstabilizerplacement/drillcollarlengthswillbe

made when the Drillbotics Rig and its associated ancillary equipment is fully constructed and

optimizationtestingbegins.Furtherinformationonthedrillstringbasisofdesignwillbeprovidedin

theforthcomingBachelor’sDegreeThesisforthisproject,throughtheUniversityofStavangerandin

anyotherfuturereportsonthetopic.

3.2.2BHAManufacturing

The BHA components are intended to be fabricated from steel using a lathe and CNC machine,

availabletostudentsattheUniversityofStavanger.Eachcomponentwillalsobemanufacturedwith

theappropriatethreadprofiletomatchthenext joint. Aconsignmentofextra3/8”NPTPinxBox

connectionswillbeorderedasbackup.

Figure7:CAD-sketchoftheproposedBHA-design.


12

3.3CirculationSystem

Totransportoutcuttings,lubricateandcoolthedrillstringandwellbore,acommonfluidcirculation

systemisused.InthebuildingandtestingstageofthedrillrigWBMorOBMwillbeusedasthe

circulatingfluid.Itislikelythatasimpleoilbaseddrillingfluidwillbetestedandusedforthe

Drillboticscompetition.AspartoftheBSc-thesis,adiscussionofadvantagesanddisadvantagesusing

bothOBMandWBMinsmall-scalerigswillbepresentedbasedonresultsfromtestsrunwiththe

builtrig.

Figure8:Outlineofthecirculationsystem.

3.3.1 Pump

Whenchoosingapumpthereareseveraldifferentparameterswhichneedtobetakenintoaccount.

Theseare;fluidtype,pressurerange,flowvelocity,handlingofparticles,physicalpropertiesofthe

typeofpumpandtemperaturerange,etc.Assumingawaterbasedmud,theflowvelocityneedsto


13

begreaterthanorequalto0.5m/s,basedonpreliminarycalculationsandassumptionsforour

proposedcirculationsystem.Thisgivesaminimumflowrateof8.82l/min,andfurtherimpliesthat

thepumpshouldbeabletoprovidepressureheadofatleast2.26bar.Forourpurpose,wehave

decidedtogowiththeITTFlojetElectricPump.Thispumpispoweredbya12vDCoutput,and

providesaflowrateofupto18,5l/min,hasacutoutpressureof3.1bar(45PSI)andcanhandle

liquidtemperaturesofupto54˚C.AGemsPressuresensorsupporting0-10barwillbeinstalledto

ensurethatpressureinthecirculationsystemdonotexceedthewantedparameters.

3.3.2 RotaryUnion

Arotaryunionisadevicethatprovidesasealbetweenastationarysupplypassageandarotating

parttopermittheflowofafluidintoand/oroutoftherotatingpart.Inourcasetherubberhose

fromthemotortotherotaryunionisthestationarypart.Whilethedrillstringistherotatingpart.

TherotaryunionthatwillbeusedforthissystemisaDeublin3/8”NPTRH(D55-000-001).This

rotaryunionhasalowtorqueratingandcanhandlebothWBMandOBM.

Figure9:TheDeublinrotaryunionisassembledontopofthehollowshaftmotorusingclosingstoppers.AD6075-201DeublinCartridgewillbeinstalledwiththerotaryunion.


14

3.3.3 Multi-TieredFiltrationSystem

Figure10:CAD-sketchofthemulti-tieredfiltrationsystem

thatwillallowforremovingsolidsbothinWBMandOBM.

3.3.3.1 DesignPrinciples

Thefiltrationsystemisamulti-tieredfiltrationscreensystemtoremovebiggestsolids,asfluidflows

fromonebuckettoanother.Meshscreenswereinitiallyconsideredtobeusedforsolidscontrol.

Thismayormaynotbetrialed,asitmightbemoreappropriateforagelledfluidsystem(whichthis

projectwillnotbeincorporating).Forthetimebeing,thedesignonthenextpagewillassumeuseof

themeshscreens,butmaybeomittedinfuturedesignworkdependingontheresultsofthe

practicaltests,whenbuilt.Fluidwillbepumpedfromthelastbucketbackthroughthesystem.

3.3.3.2 DesignConsiderations

Thedrilledholevolumeisknown,sothescreensizeswillbedesignedtoaccommodateforthevolume

drilled,plussomeextraamountsoasnottoclogupthescreens.Assumeamudweight(MW)of0.7

specificgravity(SG),andacuttingsdensityof2.6SG(averageforlimestone–sandstone).


15

3.3.3.3 ProposedLayout

• HoleVolume:3.847l10üvcubicmetres=

384cm3

• Maximumpossibleflowrate=9litersper

minute(LPM)=9000cm3/min(Assumed!–

basedonpumpspecs)

• Initialvolumeintank3=22.5LPM

• AreaofRock=900cm3

• Rockvoldrilled=384cm3

• Maxallowableflowrate=9000cm3/min

Minimumrequiredmeshareasandboxlengthsfortheentiredurationofdrilling:

• H1 = Öï†|

• °h+ì1 = Ñ¢ï†|{

• °,n,541 = 180 + °7n@= = Ñï¢ï†|{

• à1 = {y†|

• §1 = z. y•(5ddíh+ìA7íì − noo5,40@h)

• ¶2 = õï†|

• °h+ì2 = yyÖ†|{

• °,n,542 = 225 + °,n,541 = Ñ{ïÖ†|{

• à2 = 36@h, §2 = è. z•(5ddíh+ìA7íì − noo5,30@h)

• ¶3 = {ï†|

• °h+ì3 = {ïï†|{

• °,n,543 = 300 + °,n,542 = ÑèïÖ†|{

• à3 = õï†|

• §3 = ¢. ß•, ®ℎ+@ℎ®+44ì66),n*6+ì@765d6),n22.5à

Figure11:Birds-eyeviewofproposeddrillingfluidcirculationsystem.


16

3.3.3.4 FlowProfiles

Thedashedlinesresembleadivider,whichwillhaveanoffbottomclearanceof10-15cm.Thishas

beenproposedbytheteamforgoodsolidscontrol.Thedividerswillbesecuredateachcornerofthe

boxtothefloorofthebox.

Figure12:Drillingfluidcirculationsystemflow-pathandproposedlayout

3.3.3.5 Tank3initialMinimumStartupVolume

OneneedstocalculatetheinitialvolumeatcommencementofdrillingthatwillbecontainedinTank

3,whichwearecallingthesuctiontank.

Thefollowingassumptionsaremade:

• Thewellwillbedrilledintwohours(worstcasescenario)

• Themaximumpossibleflowrateis9LPM=150cu.cm/s

• Totalfluidvolumepumpedoverthecourseofdrillingis1080Lifdrillingtakestwohours

Onealsoneedstoknowthe“filluprate”oftank3andunderstandhowmanylitresperminuteare

comingbackfromthewellintotank3.Alsoneedtoknowhowlongitwilltakeforfirstfluidtoflow

backoncedrillingcommences.

• TimetofillTank1=47seconds



17


• Totaltime,on-bottomtosuctiontank,firstfluid~=2minutes,30seconds

Thefinaltankwillrequireaninitialstartupvolumeof22.5literstoallowforfullcirculation.

3.3.3.6 CirculationSystemAdvantagesandDisadvantages

Advantages:

• Smoothfluidoverflowfromrocktocollectionpitsonallaxesoftheareaoftherock

• “Screeningup”(ie.Goingfromameshscreenwithmoreopenflowvolume,toonewithless

openflowvolume)willallowforexcellentsolidscontrol

• Eachtankisdesignedsoasnotto“runout”ofcleanfluidfromthesuctiontankatanyone

time.

• Settingtheoverflowslotsflushwiththemaxheightofthenexttankandinsertingadividerin

eachtank(dottedlinesonslideprevious)allowstimeforgravityseparationofdrilledsolids

• Optimization:

• Increase the mesh areas with shallow pit heights to avoid unwanted spillage of

“unclean”fluidintothenextpit.

• Runpressuredrop calculations to knowexact flow rates and then tweakonce the

systemiscompletelybuilt

Disadvantages:

• Reliesheavilyonthecalculationsbeingaccurateforcirculationvolumes,pumppressuresand

ROP’s.I.e.Alotofassumptionshavebeenmade.Thiscanhoweverbeavoidedbystarting

withdoubletherequiredfluidvolume.

• Potentialforspillageof“unclean”fluidfromonepittoanotherifdrilledmudis“spitting”out

ofthewellbore


18

3.4 PowerTransmission

PoweristransmittedtothedrillbitviaaAPM-HE09ACHhollowshaftbrushlessmotorproviding2.86

ratedtorqueduringoperationsfrom0to3000rpm.Themotordraws900Wattfromthegridrequiring

130 Volt DC. Since the grid in Norway is 230 Volt AC, the current needs to go through a power

supply/converterviaacontrollertothemotor.Themotorisboltedtothetopplatewith4machine

screwswhichensuresasolidandstableplatform.Amaximumof37kgaxialloadcanbehandledbefore

strainingthemotor,whichismorethanthemaximumWOBthedrillstringcanhandle.Furthermore,

the drill sting and fluid system is connected to the hollow shaft with six M5 machine screws to

connection,machinedbytheteaminalathe.Theconnectionisafunnel-shapedpieceofmetalwitha

flangedepictedinthefigurebelow.

Advantages:

• Rigidandsoliddesign

• Allowsforflowthroughthemotor

• HighRPMsallowingforincreasedROP

• HighWOBsupported

• Assessedtoproducelessvibrationthanasteppermotor,whichisidealforourpurpose

• Allowsthemountingofaferro-magneticsteelshaftthroughthemotor,sothattorquecanbe

measuredunderthemotor(ratherthanmeasuringthecountertorqueinthemotor)

Disadvantages:

• Vibrationscanpropagatefromthemotorthroughtothetopplateandinterferewiththeload

cellsorthetorquesensor

Figure13:CADdepictionofhowthebrushlessmotorwillbemountedonthetop-driveplateattachedtotheactuatorsandhowtherotaryunionwillbefitted.


19

3.5 HoistingSystem

3.5.1 HoistingSystemPrinciples

TheeffectiveROPreliesheavilyonhowmuchWOBwecanapplytotheformation.Sincethereisno

limitthisyearonmaximumWOB,thealuminumdrillstringcriticalbucklingforce(CBF)determines

themaximumWOBourhoistingsystemwillprovide(CBFmax=182Npinned,22Nswaying).Through

continuoustorquemeasurement,anddatacollectionfromtheloadcellsinthez-direction,the

systemisabletooperateclosetothemaximumCBF.Byusingananalogueinfraredheightsensor

(0.2to1.5mdistance),therigisallowedtooperatewithhigherRPMsandROPsinthetop-andmid

sectionoftherock,beforeloweringtheROPintheend-phaseofthedrillingoperation.The

estimatedweightofthemovingplatform,includingthehollowshaftmotor,swivel,topplate,the

drillstring,BHAandsensorsareestimatedtobe25kg,wellbelowthemaximumaxialloadof37kg

thetopdrivemotorcanprovide.

Tocounteractapossibleinclinationofthedrillstring,threeactuators–eachconnectedtothetop-

driveplatethroughtri-axialloadcellssupporting0-100Noneachx-,y-,z-axis,areutilized.Through

initialsystemcalibrationandtestingwithoutapplyingaforceontotheformation,thestrategic

decisioncontrollerestablishesasetofinitialvaluesdefiningaperfectlyleveledtop-plateresembling

averticaldrillstring.Ifanoff-setisdetectedinthex-,y-directions,thereal-timecontrollerwillfeed

theproperactuatorswithcommandstore-establishasituationofforceequilibriumbetweenthe

loadcells,thusallowingtocontinuedrillingwithaverticaldrillstring.Testingwiththecompletedrig

willdeterminewhetherthisoperationcanbedonewhiledrillingorwhetheronewillneedtotripout

ofthewell,adjustandcommencedrilling.Thethreesteppermotors(oneforeachactuator)will

provideenoughtorqueandliftpowertotripinandoutwithhighenoughspeeds.

Figure14:Outlineofthehoistingsystemandasimplifiedsketchshowinghowoff-setdetectionwillcorrectdrill-stringinclination


20

3.5.2 HoistingSystemComponents

Thehoistingsystemisrequiredtorespondquicklyandpreciselytoascenariowherethedrillstring

startstodeviatefrombeingcompletelyvertical.Therefore,eachactuatorisequippedwitha

NEMA232,80Asteppermotor,eachwithastepangleof1.8andatorqueof1.236Nmgivingthe

hoistingsystematotaltorqueof3.71Nm.Todecelerateandholdinertialloads,eachsteppermotor

isequippedwithaHucoBrakeFSB015,supportingastatictorqueof1.69Nm(totalof5.07Nm).

Astherocksampletobedrilledhasanestimated

heightof0.6m,thechosenactuatorshaveatravel

lengthof0.9m,allowingforfullypenetratingthe

rocksampleaswellastrippinginandoutofthe

holeifrequired,tolevelthetopplateand

commencedrillingvertically.C-beamLinear

actuatorbundles(1000mm)areused.TwoC-

beamriserplatesareusedtoconnecteachofthe

actuatorstotheloadcellsattachedonthetop-

plate.

TonotonlymeasureWOB-forcesandhookloadinthez-direction,it

wasdecidedtousetri-axialloadcells.TheFNZload-cellsprovidedby

Forsenteksupport0-100Nonallthreeaxes.Theuseofthreeload

cellsthusallowsforatotalof300NintheZ-direction,andsimilarin

thex-andy-direction(theseforcesareestimatedtonotbenearlyas

highasinthez-direction).Withanestimatedmaximumweightof

25kg(approx.245N),thereshouldbenoriskofdamagingtheload

cells.Giventhatthereal-timecontrollersystemneedstohavea

deterministiclatency,andfairlyquickloop-timestobeabletoreact

quickenough,loadcellswithahysteresisof+-0.2%oftherated

Fx

Fy

Fz

Figure15:NEMA23StepperMotor Figure16:HucoBrake(FSB015)withastatictorqueof1.69Nmforeachbrake.

Figure17:C-beamLinearactuatorbundleequippedwithaNEMA23Steppermotor.

Figure18:ForsentekFNZtri-axialloadcell(x,y,z:0-100N).


21

output(1.0mV/V)havebeenchosen.Theloadcellsanaloguesignaloutputwillbeconnectedtoan

analogueamplifierandrunthroughanArduinoDue32-bitmicrocontroller(actingasananalogue

digitalconverter)beforeprocessedbythereal-timecontroller.ByusingArduinos,processingisdone

withlowenoughlooptimes,allowingustooperatewithhigherRPMsandROPsduringthedrilling

operation.ThreeArduinoDueswillbeused:oneforthepowertransmissionsystem,oneforthe

hoistingsystemandoneforthepump.

Figure19depictshowtheelectricalsystemwillbeconfiguredforthesteppermotors.

ThethreeHucoBrakes(oneforeachmotor)willalsorequiresimilarelectricalconfigurations.The

ArduinoDuemicrocontrollerswillbepoweredusingaUSB-hub,astheseonlyrequire10Woftotal

powertorun.

Advantages:

• AccurateandpreciseWOB,withafastresponsesystemifneededtochangeWOBrapidly

• Systemcanhandleandcorrectaninclinationofthedrillstringthusensuringverticaldrilling

• AllowsforhighRPMandROPs

• Fastresponsetimestoreal-timecontrollerreducingriskoftwist-offscenario

• Combinedwiththeferro-magnetictorquesensor,thedesignallowsdrillingoperationsfully

exploitingthecapabilitiesoftherig,ratherthanoperatingwithveryhighsafetyfactorsdueto

slowresponsetimeandlongloopdurations

• Singlecomponentseasytoassembleandconnect,chosencomponentsalsoallowfortweaking

ifdesign-alterationsarerequired

• Cantripinandoutofthewellifthisisrequiredtobalancethetopplate

Figure19:Electricalconfigurationforthethreesteppermotorscontrollingtheactuators.


22

Disadvantages:

• Advancedcontrolsystemandprogramming

• Duetohighsamplingrates,somecomponentsmightbeexposedtodamageifamajorleakage

inthecirculationsystemoccurs.

3.6 ConstructionofFramework

Toensurestabilityofthemobilerig,high-gradealuminiumstrut

profilesaretobeused.BoschRexrothStrutProfiles90x90L/

45x45Lareevaluatedtogiveusthebestoverallstability,

defendingthehighcostofthesecomponents.90x90LStrut

Profileswillbeusedinthelowersectionsoftherigsupportingthe

overlyingconstruction.45x45Lstrutprofileswillbeusedinthe

uppersectionoftherigandtoconnecttablestoeachside,in

whichthepump,computer(inclmonitors)andelectricalcontrol

systemwillbemountedon.

With90x90and45x45brackets,andlockable45x45joints,theconstructionwillnotbeexposedto

creepovertime,whichoftencanbeseeninsmall-scalerigsandbuildswhereunder-dimensioned

strutprofilesareutilizedwithoutproperjointsconnectingthem.

Themainconstructionrigwillbemountedonlifting

wheels,alsoprovidedbyBoschRexroth

(3842547890).Theyallowformovementoftherig,

andcanbede-attachedatthescenewherethe

drillingwillbeconductedtoavoidmovementand

instabilitywhendrilling.Acrylicplasticsheetswill

beboughtatBiltema,andmountingtablesare

providedbytheUniversity.Theacrylicplasticsheets

willallowforsafedrilling,infrontofanaudience,

andwillalsoprotecttheelectricalcomponents

wiredandconnectedoutsideoftherig.

Figure20:Outlineoftheframeworkofthedrillingmachine.

Figure21:Bracketsandlockablejointswillpreventtheconstructionfromcreeping.


23

3.7 TorqueSensing

3.7.1 DesignPrinciples

Thetorquesensorisadeviceformeasuringandrecordingthetorqueonarotatingsystem.The

sensorwillnotmeasurethetorquecomingfromthemotor,butonlytheactualDP-torque.This

allowsustooperateclosetomaximummechanicalpropertiesofthedrillstring.

Sincethetorquesensorcanonlymeasuretorqueinaferro-magneticshaft,wewillinstalla

ferromagneticDPwithanequalODandIDasouraluminumdrillpipe.Thiswillbeattachedbetween

thehollowshaftmotorandtheAlshaft.ThetorquesensorprovidedbyTAMwillprovideadigital

samplingrateof2000Hz(i.e.2000samples/second).Thisconfigurationwillallowustooperatewith

RPMs>300revolutionsperminuteofthedrillstring.Thetorquesensorisdeliveredwithsoftware

thatcanbeintegratedintoMatlabandMatlabSimulink,thusmakingassemblyandintegrationinto

thecontrolsystemsimple.

Theferromagneticsteelshaftwillbemadeinalathe,whereoneendhasaflangewhichwillbe

attachedtothemotorshaftwithsixscrews,withasealbetweentheflangeandtheshaft.Thetorque

sensorwillbeinstalledasshowninfigure22.AstheODandIDwillbeequaltothatoftheDP,and

Figure22:TorqueSensorprovidedbyTorqueandMoreGMBH,modifiedtoprovideasamplingrateof2000HzandsupportingintegrationintoMatlabandMatlabSimulink.


24

thetorquesensorisfittedtoourintendedferromagneticshaft,thedistancebetweenthesteelshaft

andthetorquesensorwillbelessthan2mm(whichisaworkingrequirementforthetorquesensor).

3.7.2 SystemAdvantagesandDisadvantages

Advantages:

• Out-of-the-boxmeasurementsimmediately

• Non-Contact,allowingforsomevibrationinthedrillstringwithoutdamagingthetorquesensor

• WorksonanyFerromagneticobject/shaftmakingthesensorsuitabletomosttorque-

measurement-purposes

• Noshaftmagnetizationrequired

• Anyshaftsize(>5mmdiameter),noupperlimit

• Reliableperformance

• Notaffectedbyover-load

• Notdamagedbymagneticstrayfield

• Insensitivetowater,oilanddust

• Insensitivetoair-gapchanges

• Insensitivetoshaftspeed

• +5Voltanaloguesignaloutput

• USBserialdigitalcommunicationwithPC

• Automaticandmanualinitialization

• Bi-directionalmeasurementrange

• Built-indataloggerandsignalfilter

• Verywiderangeofmaterialwhereitcanbeused

Disadvantages:

• Samplingfrequencyislimitedto10000Hzrawdata,2000Hzafterfiltering(toensureahigh

enoughsignaloutputtoovercomesignalnoise)

• RPMlimitations

• Equipmentisexpensive,evenwiththespecialpriceTAMGMBHofferedtotheUniversity,and

maybetooexpensiveforlow-costrigs.Itdoeshoweverfitwellintoourbudget,sinceaccurate

torquesensingisoneofourhighestprioritiestoavoidatwistoffsituation


25

3.8 PressureSensing

Asseeninsection3.1.1Pump,basedonpreliminarycalculationsandassumptions,thepumpshould

beabletooperatewithapressureheadofatleast2.26bar.Withtheproposeddesign,thepumphas

acutoutpressureof3.1bar,andinordertonotsustaindamagetothepumpandotherequipment,

itisthereforeanecessitytoincludeapressuresensorinthecontrolsystem.Forthispurpose,we

plantouseaGemsSensorsPressureSensorthatmeasures0-10bar.

Thepressuresensorhasan

analogueoutputof4-20mAand

runsonasupplyvoltageof10-

30Vdc.Althoughwedonot

plantooperatewithdifferent

pressuresandflowvelocities,

thepressuresensorisa

necessityininitialcalibration

andthetestoffphasebefore

drillingcanbegin,todetectany

leakorsystemfaultthatcan

effectthedrillingoperation.

Advantages:

• Easytofitintotherigdesignandoperate

• Canuseexistingmicrocontrollers(ArduinoDue)todoanaloguedigitalconvertingoftheoutput

signal

• Highaccuracyandresponsetime

• GoodexperienceinpreviousUiS-projects

• Operatesatmosttemperatureranges

Disadvantages:

• Expensiveduetoitshighaccuracyandperformance

• Signalneedstobeconverted

Figure23:TheGemsanaloguepressuresensorhasaresponsetimeof1ms,andanaccuracyofwithin0.25%.


26

3.9 AnalogueInfraredElevationSensing

IntheDrillbotics2016competition,theUiS-righadnocapabilitytodeterminetheelevationofthebit

accuratelyatalltimes.ToallowforhigherROPduringdrilling,andasatooltoincreaseaccuracyin

calibrationanddrillofftesting,ananalogueinfraredheightsensorisproposedinourphase1design.

TheSharpdistancesensor(GP2Y0A02YK0F)providesdistancemeasuringbetween20-150cmwhich

ishighlyacceptableforthedesignandcontrolsystem.Therockistobedrilled0.6m,andthe

additionaldistanceallowsforaccuracyiftrippinginandoutofthewell.Thedistancesensorwillbe

fittedbeneaththetopplate(wherethetopdriveismounted),andwillreceiveareflectionoffofthe

platethatlaysontopoftherocksampletopreventspillage.Thedistancesensorhasananalogue

outputvoltageof0.4to2.45Vandshouldnotrequireanadditionalamplifier.

Advantages:

• Easytofit

• Infraredsensingischeapcomparedtoalaserandprovidesenoughaccuracy

• Allowsforelevationmeasurementsthroughouttheentiredrillingoperation

• IntegrateswellwiththeArduinomicrocontrollers

Disadvantages:

• Reflectorcanbesoiledbydrillingfluid(WBMorOBM)ifaleakoccurs,possiblyrenderingthe

sensorinaccurateintheend-phaseofthedrilling

Figure24:Depictionoftheproposedsharpdistancesensor.Thesensorwillneedanamplifier,astheoutputvoltagewilldecreaseasthedistanceincreases.


27

3.10 LoadCellForceSensingThetotalweightoftheassemblyisestimatedtobelessthan25kg(approx.245.2N).Givena

perfectlyverticaldrillstring,withzeroforcesactinginthex-,y-directionsandaperfectweight

distributionbetweenthethreeloadcells,eachloadcellwillneedtosupport82Ninthez-direction.If

asafetyfactor(SF)of1.2ischosen:

x6@6dd5784n5)@5©5@+,8+ìá − )+76@,+nì = 1.2 ∗ 82x = 98.4x

Forthispurpose,ourproposedloadcellseachsupport100Nonthez-axis.

Ifthedrillstringbeginstoincline,i.e.fromadipinthelayeredrockformation,forceswillactonthe

bitbothinthex-,andy-direction,whichlikelywillpropagateupthedrillstringtothetop-driveplate.

Onasmall-scalerigwithafixeddrillstringandBHA,itmightbedifficulttoachieveaperfectly

verticaldrillingoperationintheeventofinclination.Ourproposedsolutiontoensureverticaldrilling

istousethreeactuatorsinourhoistingsystem,eachconnectedtoourtopassemblyusingtri-axial

loadcells.

WerecommendtouseanalogueloadcellsthatcanbeconnecteddirectlytotheArduinoDue

microcontroller(thatalsoworksasananaloguedigitalconverter),asthiswillgreatlysimplifyour

controlsystemandlowerthelooptimes.Ifi.e.loadcellswithadigitalUSB-outputhadbeenchosen,

estimatedlooptimeswouldlikelybehigher,asthesignalwouldhavetogothroughthePCbefore

processedbytheArduinoDueratherthandirectlytotheArduinoDue.Forthisreason,FNZAnalogue

Tri-axialloadcells(0-100Nloadcapacity)areproposedinourdesign.Theloadcellshaveacapacity

of0-100Noneachaxis,workwithasafeoverloadof150%oftheirfullscale(FS)capacityandhavea

lowhysteresisofonly0.2%ofitsratedoutput(RO).WithaROofonly1.0mV/V,anamplifierwillbe

necessarytoenhancethesignal.

Figure25:0-100NFNZcustomtri-axialloadcellsbyForsentekprovidingananalogueratedoutput1.0mV/Vandhysteresisof±ï. y%oftheratedoutput.


28

Advantages:

• Tri-axialforcemeasurementshighlyincreaseouroperationalcapability

• Asufficientlyhighloadcapacityoneachaxisandasafeoverloadof150%ofFSreducesrisk

ofdamagetothesensors

• AnalogueconnectivitylowerslooptimesastheycanbeconnecteddirectlytotheArduino

Due

• Lowhysteresisensuresaccuracyinforcemeasurements

• Lowprofileandweight

• Easytoinstallbetweensteel-plateandactuators

• FNZloadcellcheapcomparedtosimilarproducts

Disadvantages:

• Multi-axisloadcellsareexpensivecomparedtosingle-point

o Priceallowsforlessexperimentationwithhighloadsapplied

• Ananaloguesignal,beingtransmittedoverlongdistances,isexposedtonoiseaddingup–

degradingthesignal-to-noiseratio

Solution:Tocircumventreceivingatoolowsignal-to-noiseratio(SNR),weintendtopositionthe

ArduinoDuesonthetopplate,nexttothemotor,inasealedcontainer.Thisreducesthetravel

lengthoftheanaloguesignalfromapproximately2.5mtolessthan0.5m,whichgreatlyshould

enhanceourSNR


29

4. SystemCalibrationandDetectionofDrillingDeteriorationAsdiscussedinsection3RigDesign,itisvitaltoknowtheindividualcomponents´andthesystem

responsetime,sothatrapidchangesinthedrillingconditionscanbedetectedandhandledwithout

riskingtwistoffoftheDPordamagetothedrillingmachine.Theresponsetimeofthesystem

dependsontheloopdurationofthecontrollerbutitalsodependsonitsmechanicalinertiaand

friction.Itisthereforevitaltocalibratetheactualresponseofthesystemtodifferentconditions.

4.1CalibrationinSteadyStateConditions

Thestrategicdecisioncontrollerisnotrequiredtobeasfastasthereal-timecontrollers,sothiscanbe

non-deterministicwithvaryinglatencies.ThecalibrationneedstoprovidevaluesforzeroWOBapplied

totheformation,pumppressure,torque,drillstringverticalityandhook-load.

4.1.1SteadyStatePumpPressure(sameasDrillbotics2016,Universityof

Stavanger)7

AstheprovidedpressurebythecirculatingsystemdoesnotprovideacontributiontotheROP,but

simplyremovescuttingsandhelppreventastuck-pipesituation,wewillnotcontrolthepumpmotor

speed.Thepumpspeedvariesasafunctionofthepumppressure.Hence,ifthecirculation

conditionschange,thepumppressurewillchangeandsowillthemotorspeeduntilonereachesa

newsteadystatecondition.Therearetwopossiblereasonsforthechangesincirculationconditions.

Thefirstoneisachangeofthehydrostaticpressureatthepumpoutlet.Thehighestelevationpoint

ofthehoseconnectedtotheswivelchangesasthetop-driveisraisedorlowered.Thesecondfactor

influencingthepressurelossisthetransportofcuttingsoutoftheborehole.

Wedonotreallyneedtoknowtheexactpumppressureaslongastheconditionsarenormal.Butwe

doneedtoknowwhenthepumppressurestartstogetabnormal,suchasifthereisapack-off

(overpressure)orifthedrill-pipesarebroken(under-pressure).Forthatreason,weplantocalibrate

the

7DrillBotics2016-UiS-PhaseI-v0.5

Figure26:Illustrationofhowcalibrationwillbeconducted;acylinderwillbeplacedinsidethewatercontainerandpumppressurewillberecordedatdifferentbitdepths.


30

expectedrangeofnormalpressures.Theprocedurewillconsistinputtingacylinderinsidethewater

containerandrecordthepumppressureatdifferentbitdepths.Thenwewillfillthecylinderwith

sandandwewillrepeattheprocedureatdifferentspeedsandrecordthecorrespondingpressure

variations(seeFigure30).Afterseveralexperiments,weshouldhavenormalpumppressure

variationsasafunctionofthetop-driveelevationwhichcanthenbeusedtoautomaticallydetect

obstructionsordrill-pipewashouts.

4.1.2SteadyStateTorqueCalibration

Aswethisyearhavedecidedonusinganon-contactferromagnetictorque

sensor,ratherthanhavingthetop-drivemotorismountedintoafree

rotatinggimbalwhichhasanarmthatpressesagainsttwoloadcells,steady

statetorquewillnotbeaffectedbyfrictioninthebearingsofpower

transmissionshaft.

Thissystemdesignallowsustocalibratetorquemeasurement,byhavingthe

motorcontrollermaintainingdifferenttorquesandspeedswithoutapplying

WOBontotheformation.Inthatwaywewillobtainaconversiontableof

themeasuredtorqueasafunctionofthepowertransmissionspeed,from

whichtherealtimecontrollercaninterpolateduringtheactualdrilling

operation.

4.1.3SteadyStateDrillStringVerticalityandWOBCalibration

Thetri-axialloadcellsmeasurethehookloadinthez-direction,andthecalibrationofthehookload

measurementisstraightforward,astheweightsthatareattachedtothepowertransmissionshaft

areknown.Toensurethat

thedrillstringremains

vertical,asetofvalues

definingaperfectlyleveled

topplate(i.e.azero-

inclinationofthedrillstring)

willbedetermined.This

Figure27:Depictionofhowtorquewillbemeasuredinthecalibrationphasetoensurenodamagetotheequipmentandconfiguration.

Figure28:Illustrationofhowtheforcemeasurementsobtainedfromthetri-axialloadcellsareinterpretedinthereal-timecontrollerbeforecommandsareissuedtoeachactuatortoreachazero-offsetstate.


31

shouldbedonewiththepowertransmissionsystemoperatingatdifferenttorquesandspeeds,as

rotationfromthepowertransmissionshaftlikelywillexertforcesinthex-andy-directions.By

measuringtheseforceswhilemaintainingrotation,onecandeterminezerooff-setvalues,thus

allowingoff-setdetectionwhiledrillingthroughtherocksamplethatcanbecompensatedfor.

4.2 CalibrationinTransientConditionsItisimportanttoknowthedynamicresponseofthesystematvariousrotationalandaxial

speeds.HowweplantoobtainthisinformationwillbeoutlinedintheDrillboticsJanuaryUpdate

2017.

4.3 DetectionofaDeteriorationinDrillingConditions(sameasDrillbotics2016,

UniversityofStavanger)8

Inidealconditions,theROPvarieslinearlywithWOBandRPM.However,ifthemaximumdepthof

cutisreached,theROPwillnotincreasewhenaddingmoreweight:thereisnotanymorealinear

response.Similarly,iftherearefineparticlesaccumulatingaroundthecutters,thebitwillnotwork

ideallyandtheresponsetochangesinRPMorWOBwillnotbelinear.Finally,iftherearevibrations

atthebit,theenergyprovidedtothebitwillnotbesolelyusedtodrilltheboreholeandtherefore

thelinearitydependenceoftheROPtoWOBandRPMwillnotberespected.Thepointbywhichthe

linearityislost,isoftencalledthefounderpoint.

Sothenon-linearityoftheROPasafunctionofthevariationsofWOBandRPMcanbeagoodindication

thatthedrillingconditionsarenotoptimal.Forthatreason,automaticsweepsofWOBandautomatic

sweepsofRPMwillbeperformedwhentheROPseemstobestable(ifitisnotstable,thenitishard

toconcludeanything).Incaseofnon-linearbehavior,thedrillingparameterswillbechangedtoensure

thatthebitworksingoodconditions.


Figure29:Definitionofthefounderpoint,sothatadeteriorationintheDrillingconditionsmaybedetected.


32

5. ControlStrategies:DownholeDrillingProblems

5.1LiteratureReview

Oneofthekeycriteriaofthisprojectisthatdrillingshouldbecompleteautomated.Thismeanswe

havewhatisineffecta“pluginandplay”systemwhichdrillsthewelltoplan.Thesystem,asapart

oftheautomationprocess,needstobeabletodiagnoseanumberoflikelydrillingproblems,andbe

abletorespondaccordinglytokeepdrillingontrackandwithoutanydamagetothedrillstring,orrig

components.Thereareanumberofdrillingrelatedissueswhichmaybeencounteredinthisproject,

whichhavebeenoutlinedbelow.

Note:Nomentionwillbemadeatpresentontheprogramming language,oranyoftheupperand

lower limitsondrillingparameterswhichwillbeusedtobe indicativeofdownhole issues. Further

discussionaroundtheseaspectsof thecontrol systemsandprogrammingdesignwill follow indue

course.Thissectionaimsonlytoprovideanoverviewofthemostlikelydrillingscenariosandhowone

mightreactinareal-lifesituation.Commentshavebeenmadewhereappropriateonhowtheseissues

maybeapplicabletotheDrillboticsRig.

5.2 NormalDrillingState(sameasinDrillbotics2016,UniversityofStavanger)9

5.2.1 BottomHoleTagging

Inaninitialunspecifiedstate,thesystemdoesnotknowwhetheritisonbottomornotanditdoes

notknowwhereisthetopoftheblock.Forthatreason,itstartstoraisetheblockforaminimum

distanceanduntilthehookloadhasstabilizedinordertoensurethatitisoffbottom.Thenitmoves

downwarduntilthehookloadstartstodecrease:thiselevationisrecordedasthetopoftheblock.

Duringthisoperation,thepumpandthetop-driveareoff.

Comment:IntheDrillbotics2017-design,ananalogueheightsensorwillbeusedinsteadfor

continuousmeasurementofdrillbitposition.ThisisdonetoallowforhigherROPsinthetop-and

mid-sectionoftherock(byknownthebitelevationrelativetotherock)andfordisplaypurposes.

5.2.2 OffBottomCalibration

Thisprocedureisusedwhenthesystemisuncelebratedbutaftertaggingthebottomhole.With

rotationandpumpingoff,thecontrolsystemraisesthedrill-stringforaminimumdistancetoensure



33

thatthebitisoffbottom.Thenitstartsthepumpingandwaituntilthepressurehasstabilized:this

willbethereferencepressure.Afterward,itstartstherotationbyincrementalsteps.Foreachstep,

thesystemwaitsforastabletorqueandrecordstheperiodandamplitudeoftheoscillations

generatedbytherotationalspeedstepchangesinordertogatherinformationaboutthenatural

resonancefrequenciesofthedrill-string.Theoffbottomtopofstringforceisalsorecordedasa

referencevalue.

5.2.3 ResumeDrilling

Whenthetopoftherockisknownandthesystemhasbeencalibrated,drillingcanstart.Ifthebitis

onbottom,thedrill-stringisraisedforashortdistance.Ifthereisnocirculation,thenthepumpis

started.Iftherotationisoff,thetop-driveisrampeduptoamiddlerangespeedthatdoesnot

correspondtoanaturalresonancefrequencyofthedrill-string.Thenthedrill-stringisloweredtothe

lastknowntopholeataspeedthatiscompatiblewiththereactiontimeofthecontrolsystemfor

handlinglargevariationofformationstrength.

5.2.4 ManagementofROPinanUnknownFormation

Whenstartingdrillinginanunknownformation,theWOBisincreasedaslinearlyaspossiblewhile

theROPisrecorded.However,theWOBshallneverexceedthemaximumallowableWOBtohandle

rapidchangeofformationstrength.ThelinearityoftheROPvsWOBcurveisanalysedtodetermine

theformationstrength.ThentheRPMischangedtoavaluethatincreasesROP,yetissafefor

handlingsuddenstick-slipconditions.

5.2.5 ManagementofROPinaKnownFormation

Whentheformationstrengthhasbeenestimated,theWOBislinearlyincreasedandthendecreased

witharelativelysmallvariationtoverifythattheROPstillvarylinearlywiththeWOB.Ifthelinearity

factorhaschanged,thenitisanewformation.Ifthevariationisnotlinear,thenthebitdoesnot

workingoodconditions.Alternatively,theRPMislinearlyincreasedandthendecreasedwitha

relativelysmallvariationtoverifythattheROPstillvarylinearlywiththeRPM.Ifthevariationisnot

linear,thenthebitdoesnotworkingoodconditions.

5.2.6 ManagementofDrillingParametersBetweenSoftandHardFormations

IftheROPreducesdrastically,wearedrillingfromasofttoahardformationandthereisariskfor

drill-stringvibrations.TheWOBandtheRPMarechangedtominimizetheriskofdrill-string


34

vibrations.WhentheROPhasstabilized,wehavepassedthetransitionzoneandanewformation

canbeinvestigated.

5.2.7 ManagementofDrillingParametersBetweenHardandSoftFormations

IftheROPincreases,wearedrillingfromahardtosoftformationandthereisariskfordrill-string

vibrations.TheWOBandtheRPMarechangedtominimizetheriskofdrill-stringvibrations.When

theROPhasstabilized,wehavepassedthetransitionzoneandanewformationcanbeinvestigated

asexplainedin6.1.4.

5.2.8 ManagementofanIncliningDrillString

Comment:IntheDrillbotics2017-design,thissectionisnewasweintendtouseathree-actuator

hoistingsystemandtri-axialloadcellstohandleaninclinationofthedrillstring.Thesystemwill,

dependingonsuccessintesting,maintaintheRPMbutthesystemwilltripoutofthewell.The

actuatorswillbecorrectedinaccordancewitheachother,toachieveastateofalineartopplate

(fullyhorizontal)resemblingacompletelyverticaldrillstring.TheRPMwillbeincreasedtoahigher

RPMthanthatwhichleadtoaninclination,WOBwillbemaintained.Onewillattempttotripback

intothewell,ifdrillingcancontinuewithoutarepeatedinclinationofthedrillstring,drilling

continues.IftheDPagainbeginstoincline,resettoazero-offsetinthetopplateposition(vertical

drillstring)andattemptwithahigherRPMandhigherWOB.Testingwilldeterminehowthefinal

commandwillbe.

5.2.9 EndofDrilling

Comment:Byusingtheanalogueheightsensor,theROPwillbeloweredforthelast0.03m(3cm)of

therocksample,i.e.a57cmhasbeendrilledand3cmremains.TheROPwillbeheldconstantuntil

reaching0.6mbitdepthintotherocksamplebeforetherigwilltripoutofthewellandWOBand

RPMwillbeadjustedto0.


35

5.3 DeterioratedDrillingState(sameasinDrillbotics2016,Universityof

Stavanger)10

5.3.1 ManagementofPoorROPPerformance

IfthevariationofROPasafunctionofWOBorRPMisnotlinearthenthebitisnotworkingin

optimalconditions.Thatcanbeduetobottomholeballing,bitdullingorvibrations(Dupriest&

Koederitz,2005).IfitwastheWOBthatcausedthenon-linearity,thentheWOBisdecreasedlinearly

untilthelinearityconditionisreached.IfitwastheRPM,thentop-drivespeedisdecreasedlinearly

untilthelinearityconditionissatisfied.

5.3.2 ManagementofDrillString-vibrations

Ifthetorquestartstofluctuateabovereasonablemargins,thedrill-stringispickedoffbottom.Ifthe

oscillations do not stop after a short moment, the top-drive rotation is ramped down to 0. The

combinationofWOBandRPMthatcausedthevibrationisrecordedforthecurrentformationrock

andwillnotbeusedanymoreuntilanewformationrockisdrilled.AnewcombinationofWOB/RPM

ischosenamongstthosethatarepossibleanddrillingisresumed.

5.4 CatastrophicDrillingState

5.4.1 StuckPipe–DifferentialSticking

Problemdefinition

The drill string becomes stuck due to a high differential pressure between the drill string and the

formation.Thinkoftheboreholeasavacuumcleaner,andthedrillpipebeingsuckedintoit.

Diagnostics

UsuallyasharporgradualdropinROPcombinedwithaproportionalincreaseintorque.Thisismost

clearlyseenwhenrotatingthestringoff-bottom,whereatorqueincreaseisindicativeofdifferential

sticking.CuttingsizeswillalsovaryandSPPshouldincrease.

Solutions

Inourcase,thisishighlyunlikelytooccur,ifevenimpossible.



36

5.4.2 StuckPipe–KeySeating

Problemdefinition

Thedrillstringbecomesstuckduetoastringbucklingcreatingsomethingofakeyholemicro-borehole

adjacenttotheactualborehole.Thiscausessectionsofthepipetobecomeimmobileandisusually

causedbytoomuchWOBorpoordirectionalcontrol

Diagnostics

Immobiledrillstring.SteepdropinROP,combinedwithahightorqueincrease.Needtobecareful

hereaspipe-whirlcaneasilyfollow.

Solutions

This can bemitigated by knowing definitively themaximumbuckling force, applying a SF and not

exceedingthisvalue.

Determine the stuck point of the drill pipe, by converting the string elongation to stuck point

downhole,proceedtopulltomaximumallowableoverpullandattempttoestablishstringrotation.If

unsuccessful,proceedtojar,butdoNOTdosowithstringrotation.Pumpingalubricantdownhole

canalsoassistwithfreeingthepipe,sincethecoefficientoffrictionisreduced.

5.4.3 StuckPipe–Pack-off

Problemdefinition

Thedrillstringbecomesstuckduetopoorboreholequalityeffectivelyblockingupthehole.Whether

thisisdoneatsomepointuptheholeordownattheBHAlevel,itisusuallythecuttingsfallingback

downthatcausethis.

Diagnostics

Nocirculationislikelytobepossible,andtherewillbeasevereincreaseinSPP.Rotationislikelyto

bedifficultandhightorquewillbeagoodindicationofthis

Solutions

DONOT JAR INTOTIGHTHOLE. Attempt topickupoff bottomand circulate clean. Important to

establishifpipemovementispossibleupordown.Fromhere,itisusuallyadvisabletoalterthefluid

propertiestoremovethecuttings.High-viscositysweepscanbehelpfulhere,allthewhileattempting

torestorerotationandcirculation.JarinthedirectionthepipeisNOTstuck.


37

5.4.4 DrillingFluids–BitBalling

Problemdefinition

Theblockingofdrillbitnozzlesandgradualcollectionofmud/rockdepositsonthedrillbitblades,

makingdrillingimpossible.

Diagnostics

Sharp increase inSPP,withadrop in torquecanbeseen. Lookout for largecollectionsofgumbo

comingovertheshakers. Mudparametersalmostguaranteedtobeoutofspec. Verycommonin

shalyformationswherenoshaleinhibitorisused(KCl,PAC,KOH-etc.)

Solutions

Inalmostallcasesthebitneedstobepulledandcleaned.Mitigatingactionscanbetakeninourcase.

Since there is every possibility of encountering a swelling clay, ~3-4% KCl should be added to the

systemifaWBMisused.UsingOBMwilllikelyeliminatethisproblemaltogether.

Whencomingbacktobottominanysituationoncedrillinghascommenced,lowWOB,highRPMand

fulldrillingflowrateneedtobeused.

We’llneedtoprogramthesystemtomakeawipertrip(non-rotationaltriptosurfaceandback)every

x-millimetreswithnoflow–essentialforgoodholecleaning.

5.4.5 DrillingFluids–ProgressiveGels

Problemdefinition

The long-term increase inmudPVasa resultofdrilledsolidsbecomingcolloidaloveranextended

periodoftime.MorecommoninWBM.

Diagnostics

AnydecentMudManwillbeabletospotthis,sincehis10and30mingelrheologytestsshouldpick

upthefactthatPVisrising.Ontherigfloor,thedrillerwillseeagradualSPPincreaseandoveralong

period,themudwillstarttolooklikeathickcustard.

Solutions

Decentshakersandacentrifugeusuallysolvethisproblembeforehand.Dumpingadilutingisthemost

immediatesolutionafterthefact.Inourcase,theuseofameshscreenwillbecriticaltoensuringtiny


38

drilledsolidstonotbecomecolloidaltooearly.Attachingaconventionalkitchenfilteraroundthefluid

collectionbucketcanhelpwiththis,combinedwithatieredbucketcollection/separationsystem.

5.4.6 Drillstring–Stick/Slip

Problemdefinition

Thestickingof thedrillbit followedby the release fromrock“slipping”once the torquereachesa

certainpoint.Thisoccurserraticallywhendrillingcertainrockswithcertainparameters.

Diagnostics

TypicallyoccurswhendrillingsoftrockwithahighWOBandlowRPM.Thedepthofcutwillincrease

(inlayman'sterms,thismeanthebitistakingabiggerbite)andthetorsionalforceslikelytoincrease.

Solutions

Whenthesediagnosticsarespotted,back-offWOBsignificantly,keepRPMsteady.Ifnochange,back

offRPM.Pickupoffbottom,gobackdrillingandbedthebitwithaverylowWOBandRPM,fullflow

rate.Graduallystageupparameters.

5.4.7 Drillstring–Twist-off

Problemdefinition

Acompleteshearingofthedrillpipeatsomepointalongthestringcausedbyexcessivestringtorque.

This iswhathappenswhen stick-slip isn’t broughtunder control, orwhen thedriller is notpaying

attention.

Diagnostics

Likelywhenstick-slipisbecomingaproblem.TypicallyoccurswhendrillingsoftrockwithahighWOB

andlowRPM.Thedepthofcutwillincrease(inlayman'sterms,thismeanthebitistakingabigger

bitethanusual)andthetorsionalforceslikelytoincrease.

Solutions

Fishing!

Whenthesediagnosticsarespotted,back-offWOBsignificantly,keepRPMsteady.Ifnochange,back

offRPM.Pickupoffbottom,gobackdrillingandbedthebitwithaverylowWOBandRPM,fullflow

rate.Graduallystageupparameters.


39

6. DatahandlingandDisplay(sameasDrillbotics2016,Universityof

Stavanger)11

Lastyear’sdesigniskeptfordatahandlinganddisplay.

Thecontrolloopdurationshallbeasshortaspossibleinordertohavethebestpossiblechancesto

control,intime,quicktransitions,likewhenthebitstopsrotatinginastick-slipsituationorwhen

reachingahardformationafterdrillinginasoftone.TheOmronPLChasacommonprocessingtime

of0.4msand,intheworstcase,instructionexecutiontimeis0.41μs.Table1showsthenumberof

PLCinstructionsthatcanbeusedfordifferentPLCloopdurations.

Figure30:Depictionofthe#ofinstructionsthatcanbecarriedoutwithvariousloopdurations.

Astheloopdurationshouldbekeptbelow20ms,andifpossiblecloserto10ms,thePLCprogram

shouldnotexceed3000to4000instructions.Yetthereisaneedtoperformrelativelyheavy

computationslikedrill-stringvibrationcalculations.Sothemostcomplexcalculationsshallbe

performedonthePCside.ButthePCisnotadeterministicmachineandresponsetimecannotbe

guaranteed.TodealwiththevariablelatencyproblemofthecommunicationbetweenthePCand

thePLC,itisproposedtoprecompute,onthePCside,look-uptablesthatarevalidforawiderange

ofparametersandletthePLCinterpolatewithintheselook-uptablesofthevaluesthatareneeded

tocontrolthedrillingprocess.Inthatway,wecankeeptheprogramexecutiononthePCtobenon-

deterministic,whilethePLCprogramcanbekeptasshortaspossibletominimizetheloopduration.

Asimilarmethodhasbeendescribedin(Cayeux,2012).



40

Figure31:Illustrationofhowthedatahandlingisperformedinthehierarchicalcontrolsystem

Themodelsusedtogeneratethelook-uptableshavetobecalibratedwiththeactualrecorded

values.Forthatreasonacalibrationprocessmonitorsthesensorvaluesandextractcalibration

parametersthatareusedwhilecomputingthelook-uptables.

ThesensorvaluesacquiredbythePLCarepushedtothePCsidewhereadataacquisitionservice

collectsthedatausingforinstanceOPC(OLEforProcessControl).OnthePCside,thesensorvalues

arepropagatedtothegraphicaluserinterface(GUI),theprocessgeneratingthelook-uptablesanda

processwhichtakescareofthecalibrations.Thecalibrationresultsarefeedbackintothelook-up

tablegenerationprocess.Figure36showsablockdiagramofthemaincomponentsandthedata

flowbetweeneachoftheprocesses.AlltheresultsgeneratedbytheprocessesrunningonthePC

sideareloggedintoASCIIfiles.

TheGUIhasfivefunctions:

• Configurethesystem

• Setupoftheinitialstate

• Calibratetherigperformance

• Controltheexecution

• Displayinformationduringadrillingsequence

Theconfigurationshallcoverthefollowingsubjects:

• Descriptionofthephysicalproperties(density,Youngandshearmoduli,ultimatestrength)

andgeometricaldimensionsofthedrill-string(OD,ID,length,nozzlediameters,pressureloss

coefficientofswivel,etc.).

• Descriptionofthefluidproperties(density,viscosity).


41

• Descriptionofthelimitsoftherigcomponents,e.g.maxmotorspeed,gearratio,max

torque,threadedshaftpitchanddiameter,maxhoistingdistance.

Theinitialstatesetupisbasicallyreducedtoenteringthecurrentelevationofthemovingtable.

Thecalibrationoftherigperformanceshalladdressthefollowingtopics:

• Offbottomtorqueasafunctionofrotationalvelocity

• Timingforfaststopofthedrill-stringrotationasafunctionofrotationalvelocityincluding

theeffectsofthePLClooptimeandinertiaofthesystem

• Offbottomhookload

• Timingforfaststopofthehoistingsystemasafunctionofloweringandraisingspeed

includingtheeffectsofthePLClooptimeandinertiaofthesystem

• Offbottompumppressureandexpectedstandardvariations

Thecontroloftheexecutionhasonlytwobuttons:StartandStop.Thesystemshallstopbyitself

whenthedrillingoftheblockisfinished,neverthelessthereisastopbuttonontheGUIthatcanbe

usedincaseofmalfunctioning.Inaddition,incaseofemergency,thereisaphysicalbuttonthatcut

theelectricalpoweronthewholerig(seesection3.7).

Thefollowinginformationwillbedisplayedonthescreen:

• Time-based

• Bit-depthandbottomholedepth

• MovingtablespeedandmaximumallowableROP

• WOBandmaximumallowableWOB

• Top-drivespeedandmaximumallowablespeed

• Top-drivetorqueandmaximumallowabletorque

• Pumppressureandminimum/maximumtolerances

• EstimatedformationUCSanduncertainty

• EstimatedlinearityofWOB/ROPandRPM/ROPrelationships

• Estimatedstick-sliplevelandmaximumallowablevalue


42

• Depth-based

• FormationUCSanduncertainty

• AllowableROP,WOB,top-drivespeedandtorque

• EstimatedandobservedcombinationofWOB/RPMthatcausestick-slip

• State-based

• Currentmode:bottomholetagging,normaldrilling,hardnesstransition,WOB

linearitytesting,RPMlinearitytesting,etc.

• Alarms:pack-off,twist-off,pipewashout

• DetailedinformationoncurrentWOBlinearitytest

• DetailedinformationoncurrentRPMlinearitytest

Automaticsnapshotsofthescreenwillbetakenatregularintervalsinordertodocumentwhat

happenedduringtheexperiment.


43

7. EstimatedCostsTheDrillboticscompetitionallowsforamaximumbudgetofUS$10,000.Exceedingthisbudgetmay

leadtopenaltiesfromtheDrillboticsCommittee.Inthebudget,thetotalexpectedcostsincluding

thoseforself-manufacturingarelisted.Somecomponents,suchasacrylicplasticcovers,lifting

wheels,BoschRexroth90x90Lstrutprofilesetc.arenotvitaltothedrillingriganditsperformance,

butareincludedtoallowforamobilerigfordisplayandrecruitmentpurposesattheuniversity.

ComponentsallowingthemobiledesignareestimatedcostingUS$1672.

Thus,theexpectedbudgetfortheautonomousdrillingrigdoesnotexceedUS$10,000

ThecostofthedrillingrigiscoveredbytheUniversityofStavanger–DepartmentofPetroleum

Technology.TheworkshopsattheUniversity(machinerylabanddrillingfluidlabs)willbeusedfor

self-manufacturinganddesigningsomeofthecomponents.Inaddition,LabE351willbeusedforthe

actualassemblyandbuilding,andtesting.

PowerTransmissionSystem

(PTS):

Supplier Amount: SUM(USD) Totalcost,PTS

(USD):

US$2176

Totalcost,PTS

(NOK):18974

HollowShaftmotor(APM-

HE09ACH)

MotionControl

Products

1 1476

Rearshaft(M5TapPCD50) MotionControl

Products

1 Estimate200USD

DriverController(suitableto

theAPM-HE09ACH)

MotionControl

Products

1 Estimate300USD

PowerSupplytoAPM-

HE09ACH

MotionControl

Products

1 Estimate200USD

HoistingSystem(HS): Supplier Amount: SUM(USD) Totalcost,HS

(USD):

US$947

Totalcost,HS

(NOK):8258

C-BeamLinearActuator

Bundle(1000mmincldriver)

Ooznest 3 567

NEMA23Drivers Ooznest 3 0(includedinactuator

bundle)

C-Beam™RiserPlates(2pcs) Ooznest 3 26

HucoBrakeM.1704.2321 RSComponentsAS 3 354


44

CirculationSystem(CS): Supplier Amount: SUM(USD) Totalcost,CS

(USD):

US$559

Totalcost,CS

(NOK):4874

ITTFlojetElectricPump

(R4300143A)

RSComponentsAS 1 293

GemsPressureSensor10bar

(3100B0010G01B000)

RSComponentsAS 1 116

Hoses,valves,screws,

conections

RSComponents 150

TorqueSensor: Supplier Amount: SUM(USD) Totalcost

(USD):

US$3335

Totalcost(NOK):

29080

TorqueActive3Advanced

(2000hz,10mmOD)

TorqueandMore

GMBH

1 3335

Loadcells: Supplier Amount: SUM(USD) Totalcost

(USD):

US$1173

Totalcost(NOK):

10228

FNZ0-100NTri-axial Forsentek 3 960

Loadcellamplifiers RSOnline 3 Estimated69

ArduinoDueAT91SAM3X8E

84MHzclockspeed

RSOnline 3 144


45

Constructionofframe: Supplier Amount: SUM(USD) Totalcost

(USD):2392

Totalcost(NOK):

20858

Strutprofiles,90x90L BoschRexroth 15 946

Strutprofiles,45x45L BoschRexroth 12 204

Brackets(90x90)incl

fasteningset

BoschRexroth 24 292

Brackets(45x45),standard BoschRexroth 20 84

T-boltM8x30 BoschRexroth 100 57

FlangnutM8 BoschRexroth 100 14

Joint45x45lockable BoschRexroth 4 132

Cableduct45*45mm

2000mm

BoschRexroth 1 25

Devidingstrip3000mm

BoschRexroth 1 6

Wheels-lifting

BoschRexroth 4 364

Screwonplate

BoschRexroth 4 168

Solidrubberwheelswith

lock

BoschRexroth 2 46

Cap90x90 BoschRexroth 20 54

Rotaryunion: Supplier Amount: SUM(USD) Totalcost

(USD):163

Totalcost(NOK):

1421

Rotor3/8"NPTRHD55-000-

001

HNCGroup 1 120

Sealingstopper,D55-617 HNCGroup 3 11

DeublinCartidge,D6075-201 HNCGroup 1 32


46

Otherelectricalcomponents Supplier Amount: SUM(USD) Totalcost

(USD):546

Totalcost(NOK):

4761

USB3.0HUBpowersupplier

toArduinoDue

microcontrollers

UniversityofStavanger

–oldstock

1 0(estimatedvalue=29)

Computer(i5processing

unit)incl.2monitors

UniversityofStavanger

–oldstock

1 0(estimatedvalue=287)

Powersupplierto3stepper

motors(actuator)andHuco

brakes

RSOnline 1 0(estimatedvalue=230)

Selfmanufacturing: Supplier Amount: SUM(USD) Totalcost

(USD):0

Totalcost(NOK):

0

BHAassemblyincl3

stabilizers(totallengthof

stabilizers<3,5”)

Universityof

Stavanger,machinelab

0

Mudfluidforcirculation Universityof

Stavanger,Drillfluid

lab

0

Torque-sensingbracket Universityof

Stavanger,machinelab

0

Othercomponents: Supplier Amount: SUM(USD) Totalcost

(USD):153

Totalcost(NOK):

1334

Additionalscrewsinclself

locking

Biltema 20

Heatsinks ClaesOhlson 20

Connectors Jernia 10

Riseracrylicplastic

manufactured+acrylicplast

coverscoveringthestrut

profiles

Biltema 1+12 70

Top-plateforrocksampleto

reducespillage

- 1 -

Emergencytopbutton Eaton 1 33


47

Mountingtables UniversityofStavanger 2 -

Totalcostformobilerig: USD: 11444 NOK: 99789.39

- USD1672onlyvitalformobilitypurposes

Totalcostfor

stationaryrig:

USD:9,772 NOK:85,209.9


48

References

1. DrillingEngineering-HeriotWattUniversity.(2005).DrillingEngineering.InDrillingEngineering(p.S.3P.20).Edinburgh:HeriotWattUniversity.

2. SchlumbergerDrillingandMeasurements.(2010).DrillstringVibrationsandVibrationModelling.RetrievedDecember9,2016,fromhttps://www.slb.com/~/media/Files/drilling/brochures/drilling_opt/drillstring_vib_br.pdf

3. Sheasbyet.al.(2001).Introduction-Aluminium,itsproperties,alloysandfinishes.RetrievedDecember11,2016,fromhttp://www.asminternational.org/documents/10192/1849770/06945G_Sample.pdf/9c7a7f57-5508-43fa-9d8f-3e5a2dc57ec7

4. SocietyofPetroleumEngineers,DSATS.(2016).DrillboticsGuidelinesInternationalUniversityCompetition2016-2017.December01,2016,fromhttps://drillbotics.mst.edu/wp-content/uploads/sites/20/2016/09/2017-drillbotics-guidelines.pdf

5. Alani,Akisanmi,McTiernan.(2015/2016).Drillbotics2016:RigDesignPrinciples.AvailablefromAssociateProfessorDanSuiattheUniversityofStavanger,Norway


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Appendix1

CalculationofDrill-stringTwist-offTimeandAnglevs.OperationalTorqueclearallclc

%Twist-offAluminiumpipe

OD=9.525;%[mm]ID=8.7122;%[mm]

C1=10^(-3);

OD=OD*C1;%[m]ID=ID*C1;%[m]

L=36;%[inch]L=L*0.0254;%[m]

%TheshearmodulusG=24;%[GPa]G=G*10^9;%[Pa]

%CalculatingthepolarmomentofinertiaJ=(pi/32)*((OD^4-ID^4));%[m^4]

%Axialyieldstressy_axial=95*10^6;%[Pa]

%conversionfromaxialyieldtoshearyieldC2=0.55;%Thisisanempiricalvalueobtainedbyexperimentalresults.

%Shearyieldstressy_shear=y_axial*C2;%|Pa]?=[N/m^2]?


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%Maximumallowedtorque

T_max=(y_shear*J)/OD;%[N*m]

%definingatorquevector

T=0:0.01:T_max;

fori=1:length(T);

%Twist-offangle

ang(i)=[(T(i)*L)/(J*G)]*(180/pi);%[degrees]

%Fromthispointwecalculatetheresponsetimeofthetorquesensor.rmp=1000;

dps=rmp*(360/60);%[degrees/second]

%Twist-offtimet(i)=ang(i)/dps;%[s]

end

figure(1)plot(T,ang)title('Twistangle')xlabel('Torque[Nm]')ylabel('Angle[degrees]')

%FromthispointweconsidertheoperationwhereweapplyWOBandtorqueon


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%thebittobeabletodrillthroughtherock.

%OperationaltorquevaluesT_op=0:0.01:T_max;

dT=T_max-T_op;

fori=1:length(dT);dang(i)=[(dT(i)*L)/(J*G)]*(180/pi);%[degrees]dt(i)=dang(i)/dps;%[s]dt(i)=dt(i)*1000;%[ms]end

figure(2)plot(T_op,dt)title('Twist-offtimeinoperation')xlabel('Operationtorque[Nm]')ylabel('Twist-offtime[ms]')

drillbotics 2017

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