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TheoryGasChokesGasBeanChokeThebeanchokeisusedformeasurementswhenconditionsrequiremorerobustequipment.Forexample,ifsandisbeingproduced,orificeplateswillbeerodedveryquicklyandabeanchoke,whichismuchmorerobust,ispreferable.

Abeanchokeisbasicallya6"tubewithaknowninternaldiameter.

Beanchokesrequirecriticalflowtobevalid.Thismeanstheupstreampressuremustbeatleasttwicethedownstreampressure.Ifthisconditionfails,thenflowratesfromthebeanchokeequationsarenolongervalid.Theoperatorshouldbevigilantandreadytochangetoasmallerchokewhenthisconditionoccurs.However,ifoperationsdofallbelowcriticalflow,FieldNoteshassomeprovisionstocalculatereasonablyaccurateflowrates.

Beanchokes(sometimesjustcalledchokes)arefoundinseveralplaces.Abeanchokecanbeplacednearthewellheadtolimitproductionfromoneparticularwell.Itcanlimitproductionintoaseparator.Itcanbefoundinamanifoldbetweentwopiecesofproductionequipment.Beanchokescanbeeasilychangedout.Thisisveryusefulwhenencounteringsandproblems.

BeanChokeEquationTheequationisidenticaltothatforaCriticalFlowProver.However,the"C"coefficientsaredifferent.

where

qg=gasrate(mscf/day)C=chokecoefficient

P=upstreampressure(psia)

G=specificGravityofGas

T=Temperature(R)

ValuesforC(BeanChoke)ChokeSize(inches) C

0 0

0.0625 0.88

0.09375 2.74

0.125 6.25

0.188 14.44

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0.250 26.51

0.313 43.64

0.375 61.21

0.438 85.13

0.500 112.72

0.625 179.74

0.750 260.99

1 468.99

1.25 737.86

1.5 1067.39

1.75 1457.56

2 1908.38

2.25 2419.85

2.5 2991.98

2.75 3624.75

3 4318.17

Source:Diehl,JohnC.,NaturalGasHandbook:MetricMetalWorks,Erie,Pa.,1927.p.94

GasAdjustableChokeTheadjustablechokeisanadjustablevalvewhichiscalibrated(in1/64ofaninch)toshowthesizeofthevalveopening.Simplyturningthevalvehandlecanincreasetheopeningfrom0(shutin)tothemaximum.Thecalculationofflowratesfromthechokesettingsisapproximateandcanbeobtainedfromthefollowingequationsandcoefficients.

AdjustableChokeEquationTheequationfortheadjustablechokeisasimplifiedversionofthatusedforthebeanchokeorthecriticalflowprover.Becauseflowratemeasurementswhenusingadjustablechokesareonlyapproximate,acomplexequationisnotjustified.TheequationusedinFieldNotes,andthecorrespondingcoefficientsareshownbelow:

Q=FlowrateinMMscf/dC=Chokecoefficient,assumingcriticalflowconditions.P=Upstreampressure(psia)

ValuesofCfortheAdjustableChoke

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NominalSize(Inches) BoreDiameter(inches) Coefficient

1/8 0.1250 0.347

9/64 0.1406 0.444

5/32 0.1563 0.553

11/64 0.1719 0.674

3/16 0.1875 0.802

13/64 0.2031 0.956

7/32 0.2188 1.116

15/64 0.2344 1.288

1/4 0.250 1.470

17/64 0.2656 1.667

9/32 0.2813 1.885

19/64 0.2969 2.110

5/16 0.3125 2.340

21/64 0.3281 2.601

11/32 0.3438 2.866

23/64 0.3594 3.144

3/8 0.3750 3.400

25/64 0.3906 3.740

13/32 0.4063 4.063

27/64 0.4219 4.394

7/16 0.4375 4.730

29/64 0.4531 5.101

15/32 0.4688 5.474

31/64 0.4844 5.862

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1/2 0.5000 6.260

9/16 0.5525 8.010

5/8 0.6250 9.980

11/16 0.6875 12.176

3/4 0.7500 14.49

64/64 1.0000 25.76

72/64 1.125 32.6025

5/4 1.250 40.459

11/8 1.375 49.048

3/2 1.500 58.463

7/4 1.750 79.770

128/64 2.000 104.382

9/4 2.250 132.298

5/2 2.500 163.518

11/4 2.750 198.042

192.64 3.000 235.869

Thistablecomesfromacommonlyusedadjustablechokemeter.Thecoefficientsareessentiallyequivalenttothoseofthebeanchoke.Becausethemachiningstandardsmaybedifferentamongthemanufacturers,usersshouldconsultthemanufacturerfortheexactcoefficientoftheiradjustablechoke.

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