Lecture note on PROPERTIES OF DRY GASES.pdf

Lecture: 14
RESERVOIR ROCK AND FLUID PROPERTIES (PME 1110) PROPERTIES OF DRY GASES

1. Lecture: 14
RESERVOIR ROCK AND FLUID PROPERTIES
(PME 1110)PROPERTIES OF DRY GASES
DEPARTMENT OF PETROLEUM ENGINEERING
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2. Viscosity of Gas Mixtures (Cont.)
•Ifthecompositionofthe
gasisunavailable,Figure
6-8canbeusedtoobtain
viscositiesofmixturesof
hydrocarbongasesatone
atmospherepressure.
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3. The Coefficient of Viscosity of Gas (Cont.)
EXAMPLE6-10:UseFigure6-8toreworkExample6-9.
Step1:calculatethespecificgravityofthegas.
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4. The Coefficient of Viscosity of Gas (Cont.)
Step2:
Determineviscosity
?5
=0.0125cpat200°F
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5. Gas Viscosity at High Pressure
•Inmostinstances,thepetroleumengineeris
concernedwiththeviscosityofgasesat
higherpressures
•Thetheoremofcorrespondingstateshasbeen
usedtodevelopagasviscositycorrelation.
•Drygases,wetgases,andgasesseparated
fromblackoilsnormallyhavespecific
gravitieswhichliewithintherangeofFigure
6-9.
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6. Gas Viscosity at High Pressure (Cont.)
•Retrogradegasesandgasesassociatedwithvolatileoilsgenerallyhavespecific
gravitiesgreaterthan1.0.Figures6-10through6-12canbeusedtoobtainviscosity
ratiosforthesegases.
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7. Gas Viscosity at High Pressure (Cont.)
EXAMPLE6-11
Calculateavalueofviscosityforthedrygaswithaspecificgravityof0.818at
reservoirtemperatureof220°Fandreservoirpressureof2100psig.
Solution
Step1:Determineavalueofgasviscosityatoneatmosphere.
WeKnow
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8. Gas Viscosity at High Pressure (Cont.)
Step2:Determineavalueofviscosityratio
Step3:Calculategasviscosity
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9. Heating Value
•Theheatingvalueofagasisthequantityofheatproducedwhenthegasisburned
completelytocarbondioxideandwater.Heatingvalueusuallyisexpressedas
Britishthermalunitsperstandardcubicfootofgas,BTU/scf.
•Wetheatingvaluemeansthatthegasissaturatedwithwatervaporpriorto
combustion,about1.75volumepercent.
•Dryheatingvaluemeanshatthegascontainsnowatervaporpriortocombustion.
Sometimes,thetermbonedryisused.
•Grossheatingvalueistheheatproducedincompletecombustionunderconstant
pressurewiththecombustionproductscooledtostandardconditionsandthewater
inthecombustionproductscondensedtotheliquidstate.
•Netheatingvalueisdefinedsimilarly,exceptthewaterofcombustionremains
vaporatstandardconditions.
•Thedifferencebetweennetandgrossheatingvaluesistheheatofvaporizationof
thewaterofcombustion.
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10. Heating Value (Cont.)
EXAMPLE6—12
Calculatethegrossheatingvalueofaseparatorgasofcompositiongivenbelow.
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11. Heating Value (Cont.)
Step1:Calculategrossheatingvalueofidealgasandcompressibilityfactorofthe
gasatstandardconditions.
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12. Heating Value (Cont.)
Step2:Calculategrossheatingvalueofthegasasarealgas
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13. Joule-Thomson Effect
•Temperaturechangesaspressureisreducedwhenaflowingstreamofgaspasses
throughathrottle,i.e.,avalve,choke,orperforationsincasing.Thisiscalledthe
Joule-Thomsoneffect.Thechangeintemperatureisdirectlyrelatedtothe
attractionofthemoleculesforeachother.
•Forasystemwithadiabaticpressurechange,thatis,noheatentersorleavesthe
system,andforasmallpressurechange,thetemperaturechangeis
•ThetermCpistheheatcapacityofthegasatconstantpressure;itisrelatedtothe
energyrequiredtoovercomemolecularattractionasthegasexpandsduetoheating
atconstantpressure.
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14. Joule-Thomson Effect (Cont.)
•Thecompressibilityequationofstate
•Combinationoftwogives:
•ThetermsV,T,z,andCparealwayspositive.Thus,thedirectionofthechangein
temperaturedependsonthesignofboththetermandthederivative,
!?
!?
?
•Petroleumengineersusuallydealwithsituationsinwhichpressuredecreases.Flow
ofgasthroughrestrictionssuchasavalveorchokeorthroughperforationsatthe
bottomofthewellareexamples.Therefore,thevalueof intheequationis
alwaysnegative
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15. Joule-Thomson Effect (Cont.)
•Atmoderatepressure,forexample,valuesof
pseudoreducedpressurelessthanabout6.0,z-
factorincreasesastemperatureincreasesat
constantpressure.Thatis,atpseudoreduced
pressureslessthanabout6.0,thederivativeofz-
factorwithrespecttoTispositive.
•Useofanegativevalueof andapositive
valueof
!?
!?
?
intheequationcausestobe
negative.Thatis,temperaturedecreasesas
pressuredecreases.
•Thegreatesttemperaturedecreaseoccurswhen
thepressuredecreasestartsatvaluesbetween
1500and2000psia.Thisisobservedasgasflows
throughthesurfacechokeatcommonsurface
conditions.
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16. Joule-Thomson Effect (Cont.)
•Athighpressure(forinstance,at
pseudoreducedpressuresgreaterthanaboutz-
factordecreasesastemperatureincreases.
Undertheseconditions,thederivativeofz-
factorwithrespecttoTisnegative.
•Thus,theequationindicatesthattemperature
increasesaspressuredecreases.
•Thissituationoccurswhenhigh-pressuregas
expandsthroughperforationsinthecasingina
deepgaswell.
•Temperaturesurveysinthewellshow"hot
spots"wherethegreatestamountofgasis
enteringthewellbore.
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17. Reference
•McCainJr,WilliamD."Propertiesofpetroleumfluids."–2
nd
Edition-Chapter6
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18. Thank You
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