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Improved Frac Efficiency Using FocusShot Perforating Hydraulic Fracturing Journal Page 1 of 9
ImprovedFracEfficiencyUsingFocusShotPerforating
Authors:LarryAlbertandGreggFrasure,Allied-HorizontalWirelineServices
INTRODUCTION
Thispaperwillpresentanewconcept(FocusShot)inperforatinggundesigntailoredspecificallyforfracturingoperations(Sites,USPatent9,145,763B1).Currentperforatinggunsshootjetsperpendiculartothegunbody(andcasing),thuscreatingholesinthecasingandtunnelsthroughthecementedannulusandformation,Figure1.Theseperforatingtunnelsareusuallyevenlyspacedalongtheaxisofthecasingandcanbephasedinmanyconfigurations,themostpopularbeing0°,0-180°and60°.FocusShotconfiguresthegunassemblysothatshapedchargesdisplacedfromcenterareorientedbacktothemid-pointoftheperforatinggunassembly(orientationangleincreasesasdisplacementincreases),thusconvergingtheexplosiveenergyandtheperforatingtunnelsonasingleplaneatthecenteroftheperforatedinterval,Figure2.Withtheexceptionofmodifyingthechargecarriertoholdchargesatanangle,theconvergingFocusShotgun-stringusesthesamecomponentsasaconventionalperforatingassembly.Theconvergingshotconfigurationworkswithmostgunsizes,lengths,shotdensitiesandcanberunin0°,0-180°and60°phasing.Inthispaper,wewillreviewthebackgroundforhorizontalwellperforating,reviewthedesignandtestingoftheFocusShottechnologyandthenpresentfieldtestresultsthatdemonstratethevalueforFracoptimization.
BACKGROUND
Perforatingcementedcasingswithexplosiveshapedchargeshasbeenemployedfordecades.
Overthepastfiftyyears,thetechnologyhasadvancedanddevelopedinresponsetoindustrydemandsfordifferentproductstosolvereservoirandcompletiondesignissues.TheconceptofexplosiveshapedchargeperforatingoriginatedinWorldWarIIwiththebazookadesign.
Figure1–ConventionalPerforating
Figure2–FocusShot(Converging)Perforating
Improved Frac Efficiency Using FocusShot Perforating Hydraulic Fracturing Journal Page 2 of 9
Anexplosiveshapedchargeutilizespowderedexplosivescompressedbehindametalliner(powderedorsolid)intoacase,Figure3.Whentheshapedchargeisdetonated,theexplosioncausesthemetallinertocollapsefromthecenterandflowatextremelyhighvelocitiesperpendiculartothechargecasesurface.Thisjetofhighvelocitymetalcreatesahole(perforation)intheguncarrier,casing,cementannulusandtunnelsintotherockformation.Perforatinggunsaredesignedtocarrymultipleshapedchargesconfiguredinvariableshotdensitiesandphasingdependentupontheapplication.Thedesignoftheshapedchargewilldeterminethediameteroftheentryholeinthecasing,depthofpenetrationintotherockformationandshapeoftheperforationtunnel.
PERFORATINGFORFRACTURING
Muchhasbeenwrittenaboutperforatingforfracturingoptimization(Willingham,etal.1993)includingtheselectionofEHD(entryholediameter),phasing(azimuthaldistributionofchargesaroundthecarrier),shotdensity(perforationsperfoot)andlengthofperforationinterval(cluster)(vandeKetterij,dePater1997).Ithasbeenproventhatperforationdesignhasasubstantialimpactonfracturingefficiencyandperformance(BehrmannandNolte1998).Theperforationsaretheconduitforthefracturingfluidtoexitthesteelcasingandapplypressuretotherockformation.Theidealperforationwouldhavesufficientfrictionandpressuredroptoinsurefluidisevenlydistributedtoeachperforationinthecluster/stage,andcreatetheleastamountoftortuosityinthefracturepath.TheseidealperforationswouldallowtheimmediateinitiationofasingletransversefractureatthePreferredFracturePlane(PFP)ateachperforationclusterwithinastage,Figure4.Itisundesirableformultiplefracturestobe
initiatedintheproximityoftheperforationinterval(cluster),orforaxialfracturingtooccur(Daneshy2014).Multiplefracturesand/or,axialfracturingcanrobenergyfromthefluid,reducefracturewidth,reducethelengthofthefractureandrestricttheplacementofproppantintotheformation.Restrictionsonfluidflowoutsideoftheperforationcanresultinascreen-out.Thiswastrueforverticalwells,butisprovingtobeevenmorecriticalforhorizontalwellcompletions.Foroptimalhorizontalwellcompletions,weprefersingletransversefracturesinitiatedateachclusterwithinthestage,withmaximumlength,Figure5.
Previouswork(Daneshy1973,2009,2014)demonstratedthatthestateofstressina
Figure3–ExplosiveShapedCharge
Figure4–TransverseFracture
Improved Frac Efficiency Using FocusShot Perforating Hydraulic Fracturing Journal Page 3 of 9
boreholeprovidesanaturaltendencyforlongitudinal(axial)fractureinitiation.AccordingtoDaneshy,thisisageometricaleffectandindependentofin-situstressorientation.Becauselongitudinalfracturesarenotperpendiculartotheminimumhorizontalstress,theyneedhigherinitialpressuretoextend.Conventionalperforatingadoptedfromverticalwellcompletionsdoesnotpromotetransversefractureinitiationregardlessofspacingbetweenperforations,orphasingaroundthecasing.Theaxialdistributionofperpendicularperforationtunnelscancreatemultiplefracturesandnarrowpathswithconsiderableturbulenceatthewellbore,resultinginhighwellborepressure.Theresultcanbereducedfracturelengths,higherpumppressures,obstructedproppantpathatthewellboreandpotentialforscreen-outs.
AccordingtoDaneshy(2009),abettermethodforperforatingwouldbetoalignallperforationsineachclusterinasingleplaneperpendiculartotheboreholeaxis,Figure6.Figure6(a)showsa
spiralpeforatingpatterncreatedbya60°phasegunassembly.Figure6(b)showsthoseperforationscollapsedtoasingleplane.Unfortunately,withaperforatinggunassemblyitisimpossibletoaligntheshapedchargesto
perforatethecasingonasingleplane.Explosiveshapedchargesmustbeaxiallydisplacedalongtheguncarrierduetospacelimitationsinsidethegunbodyandtoeliminateexplosiveinterference,thusexplosiveshapedchargeperforationsareaxiallydisplacedalongthecasingcircumference.Whileitisimpossibletoalignalltheexplosiveshapedchargestoasingleplaneinsideaperforatinggunbody,analternativewasproposed(Sites2012).Bychangingtheanglefortheperforatingchargesinsidethegunbodytoorienteachoftheperforationsbacktothecenterofthegunassemby,theperforationenergyandtunnelscanbeconvergedtoasingleplane,Figure7.Theperforatingtunnelswillconvergeatadistancefromthecasingdependinguponshaped
Figure5–StageFracturing
Figure6–PerforationGeometry
Figure7–FocusShot60°Phasing
Improved Frac Efficiency Using FocusShot Perforating Hydraulic Fracturing Journal Page 4 of 9
geometricorientationandtargetpenetration(i.e.deeppenetratingchargessetatahigheralignmentanglewillconvergedeeperintothereservoirrock).
DEVELOPMENTANDBALLISTICTESTING
Totesttheperformanceoftheconverging(FocusShot)concept,aseriesofballistictestswereperformedinconcretetargetsatashapedchargeperforatingtestingfacility.Thetestsweredesignedtoevaluategunstability,chargeperformance(interference),targetpenetration,casingintegrityandperforationexitholediameters.Thetestwassetuptoshootaseriesofoneandtwoft.long,3.125in.ODperforatinggunsloadedwithstandardshapedchargesalignedatvaryingangles,Figure8,intofiveft.
diameterflowerpotconcretetargetswith4.5in.ODcasingcentered,Figure9.TheFocusShot(converging)configurationwastestedagainstconventionalloadanddownshot,Figure10.
Figure8–FocusShotLoad
Figure10–BallisticsTest
Figure9–ConcreteFlowerpotTarget
Improved Frac Efficiency Using FocusShot Perforating Hydraulic Fracturing Journal Page 5 of 9
ItwasnotedduringandafterthetestdetonationsthattheconcretetargetsintheFocusShotconfigurationsweremorecompletelybrokenatintersectionoftheperforationtunnels,indicatingthepoweroftheconvergingenergy.
Infigure11theconvergingperforationtunnelscanbetracedinthetesttargetfromthecasingexitpointtotheedgeoftheremainingtarget.
Table1summarizestheresultsofthetests.Allshotswerethroughthetargetsanditwasnotedthataschargeangleincreased,sodidEHD.
Figure11–FocusShot(Converging)TestTarget
Table1–FocusShotTestData
Improved Frac Efficiency Using FocusShot Perforating Hydraulic Fracturing Journal Page 6 of 9
FIELDTESTRESULTS
AfieldtestwassetuptoevaluateconventionalversusFocusShotonaMarcellusprojectinPennsylvania.Thiswasahorizontalwellpadwithtwo~4,050ft.laterals;750ft.spaced;~5,100ft.TVD;drilledinthesamenortheastdirection.Thefracdesign(water,proppant,chemicals)andstagelengthwerecomparablebetweenwells.Eachstagewasperforatedwith5clustersusing3.125in.6spf(12holes)60°phasedperforatinggunswithstandard“goodHole”charges.TheConventionalwellwasperforatedwithconventionalgunsandtheFocusShotwithconverging.Ingeneral,theFocusShotwelltreatedwithlowerpressureandhighersandvolumes.
Figure12comparestwoofthestagesforpressure,rateandproppantconcentration.WiththeFocusShotperforations,thepressurebuild-upindicatestheprobablecreationofasingletransversefracture.Atpumprates>90bpm(barrelsperminute)thepressureremainedconstantasproppantconcentrationswereincreasedwellabovethetargetlevel.TheConventionalwellshowsanerratichigh-pressureresponse,likelyindicatingtheproductionofmultipleand/oraxialfractures.The90bpmtargetpumpratecouldnotbeachievedandproppantconcentrationwaswellshortofthetarget.Inthisstage,proppantdisplacementwascurtailedandfellwellshortofdesign.TheaveragetreatingpressurefortheFocusShotwellwas-6%,or340psilower,Figure13,thantheConventionalwell.
AnX-Y-Zplot,Figure14,comparesallstagesformaximumpressure(Yaxis),sandvolume(Xaxis)andfrictionreducervolume(Zaxis).Mostofthe
FocusShotstagestrendtothelowerrightportionofthegraph(lowertreatingpressuresandhighersandvolumes).ThesetreatmentprofileswouldsuggestthattheFocusShotperforationsweremoreeffectiveintheinitiationofsingletransversefracturesatclusterdepthsandallowedhighersandvolumestopumpatlowerpressures(acharacteristicofidealperforations).
Betterfracturingtreatmentsshouldresultinbetterproduction.Thefirst31daysonthetwowellsshowsapproximately9%betterproductionfromtheFocusShotwell,Figure15.
Figure12–StageFracturingData
Improved Frac Efficiency Using FocusShot Perforating Hydraulic Fracturing Journal Page 7 of 9
Figure13–AverageTreatingPressureperWellandMaximumTreatingPressureperStage
*FRVol.=BubbleSize
Figure14–MaximumPressurevs.SandVolumeandFrictionReducer
Improved Frac Efficiency Using FocusShot Perforating Hydraulic Fracturing Journal Page 8 of 9
SUMMARYANDCONCLUSIONS
Anewperforatingtechniquehasbeendevelopedforhorizontalwellcompletions.Thisperforatingdesignutilizesangledshapedchargeconfigurationstoconvergeperforationtunnelsandenergyatthecenteroftheperforatinggun/cluster.Thistechniqueconvergestheperforatingtunnelsonasingleplaneperpendiculartothecasingaxisatafixeddistancefromthecasingoutsidediameter.Itisproposedthatconvergingperforatingwillbemoreeffectivefortheinitiationoftransversefracturesatthecenteroftheperforationclusters.Ifthenewdesigncanreducethepropensityforperforationstocreateaxialandmultiplefractures,thenmoreeffectivestimulationsandbetterproductionwillresult.
FieldtestresultsindicatethatFocusShotisaneffectivemethodtoperforatehorizontalwellstooptimizefracturingandimproveproduction.FocusShothasthepotentialtoreducetreatingpressuresandincreaseproppantdeliverytothereservoir.Todate,therehavebeenseveralhundredFocusShotstagescompletedinMarcellus,Utica,Woodford,HuntonandEagleFordwellswithoutasingleoccurrenceofascreen-out.
REFERENCES:
1. Behrmann,L.A.,andNolte,K.G.(1998):PerforatingRequirementsforFractureStimulations,SPE39453,presentedatInternationalSymposiumonFormationDamageinLafayette,LA,February18-19,1998.
2. Daneshy,A.A.(1973):AStudyofInclinedHydraulicFractures,SPEJournal,Vol.13,Number2,April1973,pp.61-68.
3. Daneshy,A.A.(2009):Horizontal-WellFracturing:WhyIsItDifferent?,SPEJournal,Vol.1,Number3,September2009,pp.30-35
4. Daneshy,A.A.(2014):FractureInitiationandExtensioninCementedCasedHorizontalWells,HydraulicFracturingJournal,July2014,pp.16-22.
5. Sites,J.(2015):UnitedStatesPatent9,145,763B1,filedMay15,2012,issuedSeptember29,2015
6. vandeKetterij,R.G.,anddePater,C.J.(1997):ImpactofPerforationsonHydraulicFractureTortuosity,SPE56193,presentedatEuropeanFormationDamageConferenceinTheHague,June2-3,1997.
Figure15–31DaysProduction(BOE)
Improved Frac Efficiency Using FocusShot Perforating Hydraulic Fracturing Journal Page 9 of 9
7. Willingham,J.D.,Tan,H.C.andNorman,L.R.(1993):PerforationFrictionPressureofFracturingFluidSlurries,SPE25891,presentedatRockyMountainRegional/LowPermeabilityReservoirsSymposiuminDenver,CO,April12-14,1993.
BIOGRAPHY:
Larry Albert is a BSc graduate of Oklahoma City University. He joined Gearhart Industries in January 1977 as an open-hole field engineer. After Halliburton acquired Gearhart in 1988, he held key management assignments at corporate and field locations around the globe. Prior to leaving Halliburton, he was Senior Director of Wireline Operations. In May 2010, Allied Wireline Services was formed and he served as President and CEO until Allied merged with Horizontal Wireline in 2014. He is currently Vice-Chairman and member of the Board for Allied-Horizontal Wireline Services, one of the largest independent wireline services companies.
Larry has been a member of SPWLA since 1977 and has held officer level positions in chapters around the globe. As a member of SPE since 1984, he has published technical papers and been an active speaker and contributor. He is also a member of API, AADE and AESC.
Gregg Frasure joined Welltec in 2005 as a Field Engineer. He spent 8 years with Welltec holding various positions in operations and sales. Prior to leaving Welltec, Gregg was Account Manager for the GOM helping drive opportunities in the riserless sub-sea intervention market. In 2013, he joined Superior Energy Services in Business Development. In 2014, he joined Horizontal Wireline Services as Sales Manager, after merging with Allied Wireline he became VP of Northern Sales.
Gregg is a member of SPE and has published two technical papers on wireline deployed intervention technologies. He is a graduate of Texas Tech University.