1、UnconventionalReservoirStimulationR.D.BarreeBarree&AssociatesLLCHowDoWeOptimizeStimulationDesigns?Experience Ourpersonalobservations Ourpasthistory OurexpectationsofwhatwillbesuccessfulDiagnostics Pumpintests Fracturemapping Tracers(chemicalandRA)Reservoircharacterization Loganalysis CorestudiesMode
2、ls Fracturegeometry LEFM,planar,2D,3D,coupled,sheardecoupled?Reservoirproduction singlephase,multiphase,transient,infiniteacting,isotropic,Darcy?Are these transferable from conventional to unconventional?20092009WhatAreUnconventionalReservoirs?Tightandultratightgassands Permlessthanwhat?0.01md?Compo
3、sedof Fluvialchannelsandlenticularsands AnisotropicanddiscontinuousbodiesGasshales Whatisashale,anyway?Typicallylessthan2030%clay Maybequartziticorcarbonaceous Finegrained,smallporesize,highTOC?Whatistheproductionmechanism?Darcyslawforfreegasflow?Diffusionfromkerogen?Howdoweestimategascontentandreco
4、veryCoalbedMethane Wetordrycoals?Whatisthepermeabilityofthecleatsystem?Whatcontrolsgascontentandrecovery?Desorptionisotherm?Dewateringorrateofpressuredecline?2009PuzzlesforUnconventionalReservoirDevelopment PayidentificationandGasInPlace Porosity,saturation,TOC,desorptionisotherm,netpay,drainagearea
5、,aspectratio Permeability PorosityandSwrelations,stressdependence,effectsoffractures,capillaryeffects(permjail?)Stimulationdesign fracgeometryProductionforecastingandEURApplyingpressurediagnosticsManagingstimulationdamagePerforating2009GasStoragev.FracPlacementandProduction Logs(DTCstepout)helpshowg
6、asandTOCcontent Areasofhighgascontentmaynotbeproductive Gasistherebecauseitistrapped Gasmaybeathighpressure,increasingfracgradient Highstressandno“natural”fracturesmeansnofracplacementorproduction Howdoweidentifybestfracplacementtocontactstoredgas?2009LogDerivedKHRarelyWorksinUnconventionalReservoir
7、s Porositydoesnotcorrelatewelltopermeability Poresizeandsizedistributionareneeded Saturation(orresistivity)maybemisleading Distributionofphases,wettability,claymorphology(notvolume)maybeimportant Small,sparsenaturalfracturescontributetoeffectivepermeabilityintightrock2009GasRecoveryMechanismsinCoal2
8、009PorosityofCoalsMacropores(500 Angstroms)Space within cleats and natural fractures primarily determines the storage capacity for water considered to vary between 1-5%Micropores(8 to 20 Angstroms)Capillaries and cavities of molecular dimensions in the coal matrixEssential for gas storage in the ads
9、orbed stateGas is adsorbed on particle surface98%of methane is typically adsorbed in the microporesStorage capacity is equivalent to 20%porosity sandstone of 100%gas saturation the same depth 1 lb of sample Fruitland coal has an estimated internal surface area of325,000 to 1,000,000sqft A very large
10、 volume of methane can be stored in the micropores of coaldespite low porosity in the cleat system.2009TypicalSizeDistributioninCoalPorosity2009Gas Storage&Transportation Mechanism inCoals(contd.)2009Saturation vs UndersaturationPermeability Change withShrinkageMatrix shrinkage:Coal matrix shrinks a
11、sgases desorb and thiscauses an enlargementof the adjacent cleatspacing increasedpermeability Effect increases withadsorbate affinity forcoals(i.e.effect is morefor the desorption ofCO2 than for methane)20092009ShaleGasProductionFollowsaSimilarModel2009ShaleGasContent:FreeandAdsorbedGas2009EffectofS
12、wofEffectiveGasPermeabilityforLowPermSystems2009QHPbL=Flow rate(bbl/day)Height of fracture(ft)Pressure differential(psi)Fracture aperture(in)Length of fracture(ft)Fluid viscosity(cp)FlowThroughSmoothSurfacedFracture,TheCubicLawEquation6 HPb32009EffectofFracturesonSystemPermeabilityforParallelFlowAss
13、umed Fracture Aperture=0.001”Matrix Perm2009CorePermeabilityChangeswithStressCycling2009UnproppedFractureConductivityLosswithStressWhatKindofFracDoWeNeed?SingleplanarfracLimitedsurfaceareaAllflowpassesthroughasmallchannelRequireshighconductivityProductiondependentonfracconductivityandreservoirperm C
14、omplex(shear)fracturenetwork Largesurfaceareaexposed Maynotbeabletoconnectanddrainentirenetwork(loadrecoveryexperience)Fractureconductivitymaybelessimportant(exceptnearthewell,butmustbemeasurable)Productiondependentoneffectivesurfacearea(diffusiondominated)20092009ComplexFractureNetworkorSimplePlana
15、rFrac?SPE 90051,Fisher et al,20042009SimpleModelforComplexTransverseFractures2009IncreaseinExposedFormationAreawithMultipleFractures2009EstimatingEURandProductionDeclineCurveAnalysis Producedatcapacity ProducedatconstantBHP Drainageareamustremainconstant Onlyvalidinboundarydominatedflow(whenisthat?)
16、MaterialBalanceReservoirfluidsinphaseequilibriumAccuratefluidpropertiesandproductiondataReservoirsaturationsareuniformthroughoutReservoirpressurecanberepresentedbyasingleaveragevalue(whatisit?)RateTransientAnalysisHomogeneous,isotropicreservoirSinglePhaseflowing(waterandcondensateimmobile)Isothermal
17、,laminarflow(negligiblenonDarcyeffects)Gasmaterialbalanceisvalid(noactivewaterdrive)SPE 78695,Cox et al(tDA)pssctAtpss=r(tDA)pss=Where-()+WL=2009EstablishingtimetoPss/BDF ByusingthefollowingequationareasonablereLestimatecanbemade:0.006328k2e4AWW L162009HowLongUntilDeclineCurvesareValid?4 days 1 mont
18、h2009EvaluationofTechniquesforReserveForecasting EclipseSimulationCase:channelflowDrainage Area 160 acresModel ParametersFormation Top,ftInitial Reservoir Pressure,psi10,0005,000Net Pay,ft40Gas Specific GravityEffective Gas Perm.MdFracture Half Length,ftFracture Conductivity,md-ft0.650.05200500600 f
19、tOGIP4.1 BcfRec.1.9 Bcf after 30 yearsEUR 2.8 Bcf after 81 yearsSimulation Controls Flowing tubing pressure of 100 Psia Economic limit 30 mcfpd and/or 30 years Single layer systemsGas Rate(Mscf/D)Gas Rate(Mscf/D)P/Z(psia)2009100010000100Jan-02Jan-03Jan-04Jan-05Jan-06Jan-07Jan-08Jan-09Exponential,Di=
20、1.18,EUR=448 MMscfHyperbolic b=1.75,Di=3.03,EUR=1,720 MMscfHarmonic b=1.0,Di=2.39,EUR=942 MMscf180 Days of ProductionSimulation Data10001001000010Jan-02Jan-04Jan-06Jan-08Jan-10Jan-12Jan-14Jan-16Jan-18Time to Pseudo-Steady StateDecline Estimate after Reaching Pseudo-Steady StateSimulation DataExponen
21、tial,Di=0.033 EUR=2,367 MMscf0600050004000300020001000050010001500200025003000350040004500Gp(MMscf)P/ZMaterial Balance-Simulation Case 2Initial PressureSimulation Average Pressure7-day final shut-in pressure1-day final shut-in presure Hyperbolic exponent 1(still transient)Time BDF 5450 days Exponent
22、ial declineUnder-predicts EUR at 180 days over-predicts EUR after BDF SI required to reach avg.press(P/z)100 yrsEUR results after 180 days of productionPwD or PwD1/PwDPwD or PwD1/PwDGas in Place=0.68 BCF-Equivalent Area 27 acres-180 Days0.00.51.01.52.52.03.000.020.040.060.080.10.120.140.16QDASimulat
23、ionAnalytical0.11101000.010.000001 0.000010.00010.0010.010.1110100tDASimulation PwDSimulation PwDAnalytical PwDAnalytical PwDFinite Conductivity Fracture in 18.6 to 1 Rectangular Boundary Post BDFGas in Place=4.06 BCF-Equivalent Area 160 acres-Post BDF0.00.51.01.52.52.03.000.020.040.060.080.120090.1
24、20.140.16QDASimulationAnalytical0.11101000.010.000001 0.000010.00010.0010.010.1110100TDASimulation PwDSimulation PwDAnalytical PwDAnalytical PwDInfinite Conductivity Fracture in 3.1 to 1 Rectangular Boundary at 180 DaysWith transient analysis,you know when BDF occurs2009EstimatingReserves Inunconven
25、tionalreservoirsitcantakeyearstoestablishboundarydominatedflow Anaccuratepressurebuildupformaterialbalance(P/z)cantakeyears Doreservoirscontrolledbydesorptioneverbehaveasvolumetricsystems?Onlyratetransientanalysiscangiveinsightsinto:Drainageaspectratio Transientflowregimes Effectivenessofstimulation
26、2009PressureDiagnostics Gfunctionandloglogflowregimeplotsforconventionalandunconventionalreservoirs Doesinjectedfluid(water)enterporesforcoalandshaletoestablishareservoirpressuretransient?Canwediagnosefracturesystemextentorconductivityfromfalloffbehavior?Gfunctionina“Shale”thatlookslikeareservoirGoh
27、Win Pumping Diagnostic Analysis ToolkitMinifrac-G Function1020304050607080G(Time)200985009750950092509000875010500102501000010750A0120010008006004002001800160014002000D(0.002,0)(m=48.16)(34.1,1642)(Y=0)Bottom Hole Calc Pressure(psi)Smoothed Pressure(psi)1st Derivative(psi)G*dP/dG(psi)AADD2112End of
28、PDLClosureTime3.7212.02BHCP102169822SP102189827DP447.7841.6FE66.3486.507 days of falloff with apossible closure at G12101001000PostClosureReservoirTransientina“Shale”TestGohWin Pumping Diagnostic Analysis ToolkitMinifrac-Log Log234567 8 9234567 8 9234567 8 9234567 8 9234560.11Time(0=9.216667)2009324
29、45298761032100 987651000A01030205040B(0.87,59.96)(m=0.5)(673.3,1668)(Y=20.33)(576.9,359.7)(m=-0.502)(1430,228.1)(Y=106.6)Delta Bottom Hole Calc Pressure(psi)Delta Smoothed Pressure(psi)Smoothed Adaptive 1st Derivative(psi/min)Adaptive DTdDP/dDT(psi)AABABH ISIP=10664 psi11ClosureTime173.62DBHCP841.7D
30、SP837.0FE86.502009CoalInjectionTest:Isthisafracturetest?2009CoalInjectionGFunctionInterpretationBottom Hole ISIP 7216 psi(0.91 psi/ft)Closure Pressure 5939 psi(0.75 psi/ft)2009CoalInjectionLogLogPlot2009SimulationofRadialInjectionintoReservoir(constperm)2009RadialInjectionSimulationGFunction2009Radi
31、alInjectionSimulationLogLog23:585/16/200700:005/17/200700:0200:0400:0600:0800:10 2009 00:125/17/2007Time150050004500400035003000250020005500A0.03.02.52.01.51.00.53.5BBH Gauge Pressure(psi)Clean Rate(bpm)AB21CoalInjection:BHGaugeISIPGohWin Pumping Diagnostic Analysis ToolkitJob DataMinifrac Events123
32、StartShut InStopTime5/17/2007 00:00:095/17/2007 00:05:145/17/2007 08:07:01BGP319149362604CR2.5280.1180.050(ISIP=4839)ISIP=1.14 psi/ftEarlytimeGfunctioninadeepcoalGohWin Pumping Diagnostic Analysis ToolkitMinifrac-G Function0.51.01.52.02009 2.5G(Time)340044004200400038003600500048004600A0500400300200
33、100800700600D(0.0023,0)(0.3993,535.7)(m=1349.4)(Y=0)BH Gauge Pressure(psi)Smoothed Pressure(psi)1st Derivative(psi)G*dP/dG(psi)AADD11ClosureTime BGP0.24 4473SP DP FE4532 365.1 11.71First closure at 1 psi/ftLatetimeGfunctionfordeepcoalGohWin Pumping Diagnostic Analysis ToolkitMinifrac-G Function51015
34、202009G(Time)25002750375035003250400047505000A0100200300040030050045006004250700800D(0.002,0)(m=83.89)(6.388,535.7)(Y=0)BH Gauge Pressure(psi)Smoothed Pressure(psi)1st Derivative(psi)G*dP/dG(psi)AADD11ClosureTime BGP5.90 3220SP3225DP FE1619 75.8210100 2009LogLogFlowRegimePlotforDeepCoalGohWin Pumpin
35、g Diagnostic Analysis ToolkitMinifrac-Log Log2345678 922345678 9 23413 4 5 6 7 8 9Time(0=5.233333)32100.1432100 987654321000 98765(m=0)(m=-0.184)Delta Bottom Hole Calc Pressure(psi)Delta Smoothed Pressure(psi)1st Derivative(psi/min)DTdDP/dDT(psi)BH ISIP=4839 psi1Closure1Time DBHCP DSP FE44.05 1619 1
36、615 75.82No definablereservoir transientflow regimes2009PressureDiagnosticsinUnconventionalReservoirs Informationmaybehiddeninthedetails Someshowreservoirtransientbehaviorandsomedont Someshowextendedfracture/fissuretransientswithnoactualclosureafterdaysoffalloff Workisneededtocorrelatethesesignature
37、stoproductionresponse ThetestsmaysuggestwhenshearenhancedfracturingiswarrantedandwhenfractureconductivityisrequiredConclusions Conventionalandunconventionalreservoirsmayhaveverydifferentstimulationneeds Subtletiesofpressurediagnosticsneedtobelinkedtowellperformanceforunconventionalreservoirs Weneedt
38、oacceptthatunconventionalreservoirdeliverabilityisnotcontrolledbymatrixproperties(althoughstorageis)Weneedtodefineanddifferentiatewhenexposedsurfaceareaismoreimportantthanconductivity Fluid,proppant,rate,andvolumeofdesignmustbebasedonaspecificstimulationgoal Weneedtobetterunderstandandaccountfortimedependenceofdamageandconductivity WeneedtoappreciatethetimedependenceandimportanceofdrainageareaandaspectratioonEURandstimulationeconomics 2009
