directional drilling

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Dr.WillardH.(Bill)Wattenburg

DirectionalDrilling

DownHoleDirectionalDrillingToolswhoseangularpositioncanbecontrolledandmeasuredfromthewellhead.

Dr.BillWattenburg

Manypeople have askedme to explain the downhole directional drilling tools patented in 1995 and 1997, patent numbers5,445,230and5,673,765(licensedtoSperrySun,partofDresserIndustries,laterpurchasedbyHalliburton).www.google.com/patents?id=1z8aAAAAEBAJwww.google.com/patents?id=QfkiAAAAEBAJ

The1997 patent isan improvementon the1995design tomake the tool moreuseful forsmallboredrilling,down to2 inchdiameterflexiblecoileddrillpipe.The1997designhasthesamemainfeatures,butsomewhatsimplifiedfromthestandpointofmanufacturing(inotherwordswhatIlearnedafternineprototypesandfieldtestinginHouston).

Seethelastsectionbelowforthehistoryofthisadventure.

OverviewofDesign.SeeFigure1and2below.

Themainhousingandoperationalactionof thisdirectionaldrillingtool is shown in theFigures1and 2below. Anydeviceinstalled inadrill pipe (string), such as this directional drilling device, is called a tool or a sub. The numbers in the texthenceforthrefertospecificcomponentsofthetoolaslabeledinFigures1and2.

ReferringtoFigures1and2below,themainhousingofthetoolconsistsofanuppercylinder 1 inwhicha lowercylinder2slidesandrotates.Theupperdrillpipe3isrigidlyattachedtotheuppercylinder1atasmallfixedbendangle4(Xdegrees).

The lowerdrill string 5 is rigidlyattachedtothelowercylinder2atthesameangle4(Xdegrees)astheupperdrillpipe3.InFigure 1 below, the effective bendangle6betweenthecenterlineofthedrillpipe3andthecenterlineofthedrillpipe5canthusbechanged fromzero degrees to 2times X degrees by rotating thelowercylinder2insideofandwithrespecttotheuppercylinder1.

Pressurizedmudfluid20whichdrivesthedrillingmotor30(mudmotor)flowsdowninsidethedrillpipe3throughthedirectionaldrillingtooltothedrillpipe5connectedtothemudmotor30andthenoutontotheannulus21ofthewellbore.

Themainoperationalmodeofthistoolthatallowsdrillersatthewellheadtochangethebendangleinthedownholedrillpipeisthefollowing:Theeffectivebendangleinthedrillpipeischangedeachtimeuppercylinder1israisedashortdistanceupfromlowercylinder2whichisconnectedtotheheavymudmotoranddrillbit.Thisreleasesaninternalrotationallockingmechanismthat lockscylinder1andcylinder2when theyareclosed together. When thedrillstring is loweredagainat thewellhead, cylinder2ispushedbackupinsidecylinder1.Ascylinder2comesbackupintocylinder1,aninternalratchetingmechanismcausescylinder2torotateafixedamount (say,45degrees). Thischangestheeffectivebendangle in thedrillstringbyoneincrement(45degrees)asitpassesthroughthenestedcylinders1and2ofthistool.Oncethedrillstringisloweredinplaceat



thewellhead,mudpressureisbroughtuptodrillinglevelsanddrillingcommenceswiththenewbendangleforthedrillingbit.

The ratchet movement to changeangular position is accomplishedwhen cylinder 1 is raised only about 6 inches and thenloweredbackoncylinder2.Thisupanddownactiontochangethebendangledownholeisveryeasyfordrillerstoexecuteatthewellhead.Theysimplyshutoffallmudfluidpressureintheannulusofthedrillstringtostopdrillingandeliminatefluidpressureinthetool.Thentheyraisethedrillstringashortdistancetochangethebendanglebyoneincrement(45degrees).Thisnewbendangleislockedinbyloweringthedrillstringwhichclosesupcylinders1and2(cylinder2fullyinsidecylinder1).Whencylinders1and2areclosedtogetherinthedrillingmode,thecylindersarelockedinafixedrotationalpositionwithrespecttoeachothersothatthebendangledoesnotchangeduringdrillingoperations.

Figure2showstheupper3andlower5fixedbendsectionsorientedinthesamedirection(zerodegreesnetbendangleforthedrillpipe).Inthisorientationthecylindricaltoolisnothingmorethanasmalloffset7orkinkinthedrillpipe.Thecenterline8oftheupperdrillsection3andthecenterline9ofthelowerdrillpipesection5areparallelwithanoffsetofdistance7.Thedrillbitisnowpointedstraightdownwithnoeffectiveangulardeviation.

However,whentheupperandlowerfixedbendsections3and5areorientedinoppositedirections,asinFigure1,theeffectivebendangle6 inthedrillpipepassingthroughthetool is maximumat 2 timesthefixedbendangleofXdegrees. Continuedrotationofthecylindersanother180degreeswithrespecttoeachotherbringstheeffectivedrillstringbendanglebacktozerodegreesasshowninFigure2.

MajorProblems:

1) The twocylinder housingwantstoblowapart.

The two cylinder housingdescribed so far is totallyimpractical in a down hole toolthat carries highly pressurizedfluid such as the mud fluid in a drill string at thousandsof psi. It isobvious that thecylinders1and 2 will experience enormoushydraulic force to push themapart. Internal lockingmechanisms strong enough tohold them together arecumbersome.Anyfailureofsucha lockingmechanismmeans thatthe lower drill string and thedrilling motor and bit are lostwhen cylinder 2 is blown out ofcylinder 1 down hole. That iswhytheindustryhadabandoneddownhole drilling tools that usedconcentric cylinders as for themainhousingofthetools.

2) How to confirm the downholebendangleattopside?

There must be some way for drillers at top side to measureandconfirmthebendangleinthedrill string down hole, no matterhoweasyitistochangethebendangle.

Solutions:

Within the cylindrical housings 1and 2 of this directional drillingtool, there are two mainsubassemblies that solve the two show stopper problems 1)and2)above.

Problem 1) wassolvedwith athird cylinder 10 inside the twooutsidehousingcylinders1and2. Third cylinder 10 carries the

pressurizedmudfluid20throughthecenterofthetool.Theinternalcavitiesoftheoutertwocylinders1and2aresealedbysealpositions12and13withtheinnerthirdcylinder10.Thisconfigurationmakesahydrauliccylinder11thatclosesthetwooutercylinders1and2onthemselvesratherthanexpandsthemapartwhenmudpressure20isappliedinsidetheassembly.

ThethirdcylinderideawastheEurekamomentforme(thirdprototype,oneyeartoolate)thatmanyothershadmissedfordecades.Thisiswhatmadeaworkingcylindricaltoolpossible.

Myfirstworkingprototypewith the third internalcylinder10wasshippedto theirmain testing lab inHouston. Ididnot tell theDresserengineersaboutthethirdinternalcylinder10.TheythoughtmydevicewasstillanordinarydualcylindertoolandthatIhadbuiltanordinary(thelatest)illfatedcylinderlockingmechanisminsidetokeepthecylindersfromexplodingapartunderhighinternalpressure.Toteasethem,Istartedthetestwiththecylinders1and2extendedfullyapart.Wheninternalmudpressurereachedamere10psi,thetool(cylinders1and2)actuallyclosedonitself.Thecylinders1and2stayedclosedwhenthe



internalmudfluid20pressurereached500psi.Theengineersinattendancewereinabsolutedisbelief.Irememberoneoftheseniorengineersstormingoutofthetestinglabshoutingthisisagoddamnfraud.Buttheboss,Exec.VPJimBryan,wasthere.(HewastheonewhogotmeintothisprojectwhenhebetmethatIcouldnotbuildadownholedirectiondrillingtoolthatcouldbecontrolledfromthewellhead.WewereinLondonin1991helpingtheKuwaitOilCompanyputouttheir500oilwellfires.SeeHistorysectionbelow.)

JimBryan looked around and ordered the test technicians to raise themud fluid pressure tomax, about 6000 psi. Othercompanyengineerswereleavingthetestingfloor.Theywerecertainthatmy10inchdiametertoolwasgoingtoblowapartwithpiecesflyingoutthewalls.Theybelievedthatthetwonestedcylinderstheycouldseeontheoutsidewereexperiencing150,000lbsofforcetoblowthemapart.Iwentoverandleanedonthetoolasthepressurecameup.JimBryanlookedathisassistantandannounced:Idontknowwhatthiscleverbastardhasdone,butgivehimthemoneytobuildoneofthesethatwecanputdownholeanddosomerealdrilling.Ifitworkslikethis,givehimsomemoremoney.

2) Thesecondessential component in the tool isan internal pressurereliefvalve25 thatsolvesproblem2. Thisvalve isuniqueinthatitopenswidelyshortlyaftertheopeningthresholdpressureisreached.Thisuniquepressurereliefvalveinlinewith themud fluidpathwaymade it possible tomeasure the bend angle in the tool downhole. This pressure relief valve isdesignedtoopenatpresetlowpressurescorrespondingtotherelativeangles(ratchetpositions)ofthedrillstringdownholethataresetbytheupanddownmotionofthedrillstringasdescribedabove.

Whenthereliefvalve25opens,itallowsinitialmudfluid20toflowatthewellheadtopside.Thepressurewhenmudfluidflowfirst begins at topside is easilymeasured. There are eight preset pressure relief valve thresholds. These eight pressurethresholdscorrespondtotheeightangularpositionsofthedrillstringthatcanbesetbythetooldownhole. Thesepressurethresholdswhenmudflowfirstbeginstoflowareclearsignalsatthewellhead(topside)thatmeasuretheeffectivedrillangleofthe tool down hole. Operators only need to note the pressure atwhichmud flow first begins as they bring up themud fluidpressure(eventuallytothousandsofpsi)tobegindrillingafterpickingupthedrillstringandsettingitbackdowntosetanewdrillbitangle.

Itookprototype#6toHoustontodemonstratethistopsidedrillanglemeasuringschemewiththevariablepressurereliefvalve.AsIwasbraggingaboutthesuccessfultest,thecompanyengineersinformedmethatpressurereliefvalvesofanysortareforbiddeninadownholedrillpipe.Theyjustknewtheyhadmewithanothergotcha.Anyexperiencedvalvedesignerwouldhaveknownwhy. Anormalspring loadedpressure relief valveonlyopensasmall amount such that thehighvelocity flowthroughthevalvecreatesapressuredropthatkeepsthevalveopen.Thiscreatesalargeflowrestrictionthatisintolerableinadrillstring.Worseyet,thenarrowfluidpassagewayatthevalveseatisrapidlyerodedbyhighvelocitymudfluidsuchthatthevalveiseatenaway.(IwasonedepressedpersonontheflightbackfromHouston.HowcouldIhavebeensostupidasnottohaverealizedthatflawinmydesign?)

AchievingtheopenwidelyvalvefeaturewasmysecondEurekamoment.ThiswassimplyanecessitythatIhadtoinventorgiveup.

Again,theinternalthirdcylinder10schemesavedme.Itletmedesignanotherhydrauliccylinderassemblybetweenthethirdcylinder10andtheupper outercylinder1 thatsupports therelief valveplunger. Thiscylindermechanismpushesthevalveheadbackandwidelyopensthevalveafterthevalvefirstopensandgivesaclearsignalofthedrillbitangletothetopside.(Thedetailsofthisvalvedesignarefullyexplainedingreatdetailinthepatentspecifications.)

Idemonstratedprototype#7withtheopenswidelyreliefvalveinthetestlabatHouston.Whentheflowrateatfullmudfluidpressurewasnotdecreasedwithmyvalveinthedrillpipeannulus,Igotthesamereaction.Thecompanyengineerwhoproudlytoldmeearlierthatreliefvalvesarenotpossibleindrillpipesdemandedthatmyprototypebetakenapartbeforehiseyes.HewassurethatsomehowIhadlockedtheinternalreliefvalvewidelyopenbeforethetest.Imadehimasmallwagerthathewouldfindthevalvenormallyclosedundernopressure.Ofcourse,hecouldnotseehoworwhyitworkedunderrealpressurewhenthetoolhousingwasclosed.Hepaidforthesteakdinnerthatnightwhilebuggingmeforhowitworked. I toldhimIwouldsendhimacopyofthepatentdisclosureandapplicationsohecouldseeitfirsthand.

ExecVPJimBryancametoseemydesigntestedonemoretimewithbothoftheshowstopperproblemsovercome.Heagreedtobuyalicenseforthepatentsandpayforallmyexpensesoverthelastfouryears.ButneveragainwillIshootmymouthoffabouthoweasysomethingwillbe.ThatiswhatIhaddonein1991.IhadconfidentlytoldJimBryan,whenwegettheseoilwell fires inKuwaitoutIwilldesignadownholedirectionaldrillingtool foryou thatyoucancontrol fromthewellhead.

History:

IgotinvolvedinthisprojecttodesignandbuildadownholedirectionaldrillingtoolbecauseIshotmymouthofftoafamousdrillerwhileworkingontheKuwaitoilwellfiresinApril1991(seeKuwaitoilwellfiressectionatwww.wattenburg.us).JimBryanwastheexecutivevicepresidentofDresserIndustries,amajorinternationaloilwellsupplyandservicecompany.HecametohelpwiththeKuwaitoilwellfires.HisvastexperienceinthedrillingbusinessandhisknowledgeoftheoilwellequipmentthatweweretryingtorescueinKuwaitwasinvaluable.Andhewasagreatguyasafriendandmentor.

Onenightoverdinner,Iaskedhimwhatsortoftechnologyhedreamedabouthavingforhisdrillingoperations.Hetoldmeaboutthegreatcostanddifficultyofchangingthedirectionthatadrillbitgoesdowninawellhole.Heexplainedhowthedrillerhadtopulluptheentiredrillpipe(tripthestring)toinsertabendangleinthedrillpipe(abentsub)justbeforethedrillbitsothatthedrillbitwouldbegindrillingatanangleinsteadofstraightdown.Thenwhenthedrillbithaddrilledfarenoughinanewdirection, thedrillerhadtotrip thestringagaintoreplacethebentsubwithanotheroneofadifferentangle (orastraight ). Pullingouttheentiredrillpipe(trippingthestring)forawellthatcouldbe5000ftdeepwasverycostlyandtimeconsuming.Hetoldmethateverydrillerdreamedofhavingatoolinthedrillpipefardownholethatcouldchangethedrillinganglewithouthavingtotripthestringeachtime.Andthetoolhadtobeadjustablefromthewellheadandthetoolhadtotellthedrillerattopsidewhatthedownholeangleofthetoolwasatanytime.

I thought about the drilling problem for a few minutes. I told him about some of the exotic things we had designed forundergroundnuclear testingover theyearsat theLawrenceLivermoreNationalLaboratory. I toldhim that I thoughtwhathewantedwouldnotbedifficultwhenIhadtime.

JimBryan calmly tookoutapieceofpaper fromhiscoatpocketandspenta fewminuteswritingoutsomething forme. Hehandedittome.Itwasahandwrittencheckfor$50,000drawnonaHoustonbank.Theconditionswere:ThischeckcanbecashedbyDr.BillWattenburgwhenhedeliverstoDresserIndustriesanoperationaldownholedirectionaldrillingtoolthatcanbe



programmedatthewellheadwithinonehourtochangethedrillbitdirectiondownholewithouttrippingthestringandthetoolsuccessfullyoperatesformorethan100hoursatadepthof1000feetormore.Ismiled.IwasconfidentthatIwouldneedonlyafewweekswhenIgotbacktotheLivermoreLabtocollectthis$50,000.

Thusbegananadventureinfrustrationthateventuallyrequiredninedifferentprototypes,sixdifferenttestsinHouston,andoverhalfofmytimefor thenext threeyearsbefore Iwonthebet. Bythat timeIhadexpendedmany timesthe$50,000outofpocket.Fortunatelyforme,thefinaltoolthatIdeliveredworkedfarbetterthanJimBryanoranyofhiscompanyengineershadexpected.Andtheywereveryinterestedinsomefeaturesofmytoolthatcouldbeusedinotherdownholetools,suchasthewaythecylindersofthehousingcloseunderpressureandtheopenswidelypressurereliefvalve..

JimBryanofferedtolicensethepatentsonthedesign.Iwasdelightedtoturnaloserintoadecentprofitandleaveitwiththem.ItookalumpsumpaymentforanonexclusivelicenseofthepatentsandmovedontootherproblemsforwhichIcouldoffersomeexpertise.

Beforethisadventurewasover,Ilearnedthatwhenevertheoldtimersinanyfieldhavenotsolvedaveryseriousandexpensiveproblemintheirbusiness,itisnotnecessarilybecausetheyareincompetent.Youwillhavetoworkprettyhardtobeatthemattheirowngame.

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