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eISSN: 2572-8466

Applied Biotechnology & Bioengineering

Review Article Volume 2 Issue 4

Effect of non-hydrocarbon components on gas compressibility factor values and correlations

Hamada GM

Petroleum Engineering Department, Universiti Technologi Petronas, Malaysia

Correspondence: GM Hamada, Petroleum Engineering Department, Faculty of Geosciences and Petroleum Engineering, Universiti Technologi Petronas, Malaysia

Received: October 24, 2016 | Published: March 6, 2017

Citation: Hamada GM. Effect of non-hydrocarbon components on gas compressibility factor values and correlations. J Appl Biotechnol Bioeng. 2017;2(4):124-134. DOI: 10.15406/jabb.2017.02.00036

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Abstract

Gas compressibility factor is necessary in most natural gas engineering calculations. The most common sources of z-factor values are experimental measurements, equation of state and empirical correlations. There are more than twenty correlations available with two variables for calculating the z-factor from fitting Standing-Katz chart values in EOS or through fitting technique. The theory of corresponding states dictates that the Z-factor can be uniquely defined as function of reduced pressure and temperature. Natural gases frequently contain material other than hydrocarbon components, such as nitrogen, carbon dioxide and hydrogen sulfide. Hydrocarbon gases are classified as sweet or sour depending on the hydrogen sulfide content. Both sweet and sour gases may contain nitrogen, carbon dioxide or both. The compositions of most natural gases are hydrocarbon of the same family (paraffin hydrocarbons), so the correlation of this type is possible but containing non-hydrocarbon on the gases, make the prediction difficult. This paper focuses on evaluating the correlations which calculate gas compressibility factor for natural gas reservoirs contains non-hydrocarbon components. It is found that gas pseudo-critical temperature decreases with the increase of N2 and H2S. Also, it is observed that in the tested gas reservoirs which contain C7+ by Stewart Mixing Rules and Kay’s there are some deviation on z factor between two methods that became negligible by using the correction method for non-hydrocarbon.

Keywords: mole fraction (H2S+CO2), mole fraction of H2S, temperature, pressure, impurities

Abbreviations

Pc, critical pressure; Ppr, pseudo-reduced pressure; Ppc, pseudo critical pressure; P’pc, corrected pseudo critical pressure; Tc, critical temperature; Tpr, pseudo reduced temperature; Tpc, pseudo-critical temperature; T’pc, corrected pseudo critical temperature; Ɛ, pseudo-critical temperature adjustment factor; CO2, carbon dioxide; SK, standing and Katz; DK, dranchuk- abou- kassem; SBV, stewart-burkhardt-voo

Introduction

Gas compressibility factor is involved in calculating gas properties such as formation volume factor, density, compressibility and viscosity. All these properties are necessary in the oil and gas industry for evaluating newly discovered gas reservoirs, calculating initial gas reserves, predicting future gas production and designing production tubing and pipelines. The accurate measurement of natural gas related fluids is difficult. The compressibility factor is a ubiquitous concept in measurement. It arises in many industry practices and standard. The industry standard is to measure gas properties, pressure-volume-temperature in the laboratory using reservoir samples. The drawback is that these isothermally measured PVT data is applicable at measures pressure and reservoir temperature. Calculation Methods such as correlations and equation of state are used to predict properties at other pressure and temperature. Also, laboratory analyses for PVT behavior are sometimes expensive and time consuming. Correlations, which are used to predict gas compressibility factor, are much easier and faster than equation of state. Natural gases frequently contain material other than hydrocarbon components, such as nitrogen, carbon dioxide and hydrogen sulfide. Hydrocarbon gases are classified as sweet or sour depending on the hydrogen sulfide content. Both sweet and sour gases may contain nitrogen, carbon dioxide or both. Sometimes these correlations have comparable accuracy to equation of state. Predicting compressibility factor for gas containing non-hydrocarbon (impurities) is much difficult than that for sweet gas. The compositions of most natural gases are hydrocarbon of the same family (paraffin hydrocarbons), so the correlation of this type is possible but containing non-hydrocarbon on the gases, make the prediction difficult. Therefore, several attempts have been made to predict compressibility factor for sweet gases, Wichert and Aziz and Carr-Kobayashi-Burrows presented correction for the presences of hydrogen sulfide and carbon dioxide for determining the compressibility factor. The objective of this study is evaluating the pervious correlations which calculate gas compressibility factor for gases contain non-hydrocarbon component and observe the effect of these component on Z factor.1-5,8

Correlation

The most common method is to use one of the forms of the principle of corresponding states. In this form, gas compressibility factor is expressed as function of pseudo-reduced pressure and temperature (Ppr, Tpr). Compressibility factors are function of composition as well as temperature and pressure. Standing and Katz (SK) presented a chart for determining gas compressibility factor based on the principle of corresponding states. The SK chart was prepared for binary mixture of low molecular weight sweet gases. Several mathematical expressions fitting the SK chart have been proposed to calculate the gas compressibility factor. Dranchuk- Abou- Kassem (DK) correlation is the most accurate representation of SK chart. When dealing with gas mixture, the gas mixture is critical pressure (Ppc) and temperature (Tpc) are required. Critical properties of natural gas are calculated from either gas composition or gas gravity. Several Mixing rules have been proposed to calculate mixture critical properties of natural gases. Among these methods, Kay’s mixing rule and stewart-Burkhardt-Voo (SBV) are the most widely used. Kay’s mixing rule is simple and provides an accurate determination of gas compressibility factor for sweet gases of low molecular weight. Satter and Campbell evaluated several mixing rules for calculating properties of natural gases.6-8 They concluded that Stewart-Burkhardt-Voo rule known as SBV provided the most satisfactory results especially for gases of high molecular weight. Sutton studied the performance of several mixing rule for calculating compressibility factor for gas condensates that contain a large amount of heptanes plus fraction. Sutton modified SBV mixing rule to account for the presence of heptanes plus in the natural gases. Standard laboratory analysis gives composition of natural gases through hexane and lump components heavier than hexane in heptane plus fraction known as C7+ critical properties of pure components are well documents as shown Table 1. The critical properties of the C7+, fraction are calculated from correlations using molecular weight and specific gravity of the heptanes plus. Standing presented correlation of pseudo critical properties to gas gravity based on low molecular weight which are:

P pc =70651.7 γ g 11.1 γ g 2 MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGWj0Jf9crFfpeea0xh9v8qiW7rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaqcfaOaamiuam aaBaaabaGaamiCaiaadogaaeqaaiabg2da9iaaiEdacaaIWaGaaGOn aiabgkHiTiaaiwdacaaIXaGaaiOlaiaaiEdacqaHZoWzdaWgaaqaai aadEgaaeqaaiabgkHiTiaaigdacaaIXaGaaiOlaiaaigdacqaHZoWz daqhaaqaaiaadEgaaeaacaaIYaaaaaaa@4C78@ (1)

T pc =187+330 γ g 71.5 γ g MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGWj0Jf9crFfpeea0xh9v8qiW7rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaqcfaOaamivam aaBaaabaGaamiCaiaadogaaeqaaiabg2da9iaaigdacaaI4aGaaG4n aiabgUcaRiaaiodacaaIZaGaaGimaiabeo7aNnaaBaaabaGaam4zaa qabaGaeyOeI0IaaG4naiaaigdacaGGUaGaaGynaiabeo7aNnaaDaaa baGaam4zaaqaaaaaaaa@4B09@ (2)

Component

Molecular weight

Critical pressure (Psia)

Critical Temperature(Ro)

H2S

34.08

1300

672.45

CO2

44.01

1071

547.45

N2

28.01

493

227.27

C1

16.04

667.8

343.04

C2

30.07

707.8

549.76

C3

44.01

616.3

665.68

i-C4

58.12

529.1

734.65

n-C4

58.12

550.7

765.32

i-C5

72.15

490.4

828.77

n-C5

72.15

488.6

845.37

C6

86.18

436.9

913.37

Table 1 Physical Properties of defined component.

The previous correlation work only when there no non-hydrocarbon gases present on the gases. Sutton developed the following correlation work with high molecular weight of gases.

P pc =756.8131.0 γ g 3.6 γ g 2 MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGWj0Jf9crFfpeea0xh9v8qiW7rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaqcfaOaamiuam aaBaaabaGaamiCaiaadogaaeqaaiabg2da9iaaiEdacaaI1aGaaGOn aiaac6cacaaI4aGaeyOeI0IaaGymaiaaiodacaaIXaGaaiOlaiaaic dacqaHZoWzdaWgaaqaaiaadEgaaeqaaiabgkHiTiaaiodacaGGUaGa aGOnaiabeo7aNnaaDaaabaGaam4zaaqaaiaaikdaaaaaaa@4DEF@ (3)

T pc =169.2+349.5 γ g 74.0 γ g 2 MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGWj0Jf9crFfpeea0xh9v8qiW7rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaqcfaOaamivam aaBaaabaGaamiCaiaadogaaeqaaiabg2da9iaaigdacaaI2aGaaGyo aiaac6cacaaIYaGaey4kaSIaaG4maiaaisdacaaI5aGaaiOlaiaaiw dacqaHZoWzdaWgaaqaaiaadEgaaeqaaiabgkHiTiaaiEdacaaI0aGa aiOlaiaaicdacqaHZoWzdaqhaaqaaiaadEgaaeaacaaIYaaaaaaa@4EAC@ (4)

The gases which Suttton used to develop previous correlation were sweet gases with minor amount of carbon dioxide and nitrogen and no hydrogen sulfide. Then, Elsharkawy AM et al. 1 developed Sutton correlation but will cover heavier hydrocarbons and minor of hydrogen sulfide.

P pc =787.06147.34 γ g 7.916 γ g 2 MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGWj0Jf9crFfpeea0xh9v8qiW7rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaqcfaOaamiuam aaBaaabaGaamiCaiaadogaaeqaaiabg2da9iaaiEdacaaI4aGaaG4n aiaac6cacaaIWaGaaGOnaiabgkHiTiaaigdacaaI0aGaaG4naiaac6 cacaaIZaGaaGinaiabeo7aNnaaBaaabaGaam4zaaqabaGaeyOeI0Ia aG4naiaac6cacaaI5aGaaGymaiaaiAdacqaHZoWzdaqhaaqaaiaadE gaaeaacaaIYaaaaaaa@50F5@ (6)

T pc =149.18+345.14 γ g 66.976 γ g 2 MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGWj0Jf9crFfpeea0xh9v8qiW7rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaqcfaOaamivam aaBaaabaGaamiCaiaadogaaeqaaiabg2da9iaaigdacaaI0aGaaGyo aiaac6cacaaIXaGaaGioaiabgUcaRiaaiodacaaI0aGaaGynaiaac6 cacaaIXaGaaGinaiabeo7aNnaaBaaabaGaam4zaaqabaGaeyOeI0Ia aGOnaiaaiAdacaGGUaGaaGyoaiaaiEdacaaI2aGaeq4SdC2aa0baae aacaWGNbaabaGaaGOmaaaaaaa@51AC@ (7)

Methods of Calculating the Pseudo-critical Gas Properties

The pseudo-critical properties provide a mean to correlate the physical properties of mixtures with principle of the corresponding states. The principle of corresponding states suggests that pure but similar gases have the same gas deviation or Z factor at the same values of reduced pressure and temperature. The mixture of chemically similar gases can be correlated with reduced temperature and reduced pressure.9,10 There are several methods which are:

  1. Mixing Rules developed by Stewart et al and Kay’s requires the gas composition to be known.
  2. Estimating pseudo-critical properties when the gas composition is not known, developed by Sutton.

The theory corresponding states dictates that the Z-factor can be uniquely defined as function of reduced pressure and temperature. The reduce pressure and temperatures are:

T pr = P P pc P pr = T T pc MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGWj0Jf9crFfpeea0xh9v8qiW7rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGceaqabeaajuaGca WGubWaaSbaaeaacaWGWbGaamOCaaqabaGaeyypa0ZaaSaaaeaacaWG qbaabaGaamiuamaaBaaabaGaamiCaiaadogaaeqaaaaaaOqaaKqbak aadcfadaWgaaqaaiaadchacaWGYbaabeaacqGH9aqpdaWcaaqaaiaa dsfadaWgaaqaaaqabaaabaGaamivamaaBaaabaGaamiCaiaadogaae qaaaaaaaaa@48A1@ (7)

The values of pseudo-critical pressure and temperature can be estimated from the following equations if the composition of the gas and the critical properties of the individual component are known (kay):

T pc = i=1 n P ci y i P pc = i=1 n T ci y i MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGWj0Jf9crFfpeea0xh9v8qiW7rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGceaqabeaajuaGca WGubWaaSbaaeaacaWGWbGaam4yaaqabaGaeyypa0ZaaabCaeaacaWG qbWaaSbaaeaacaWGJbGaamyAaaqabaGaamyEamaaBaaabaGaamyAaa qabaaabaGaamyAaiabg2da9iaaigdaaeaacaWGUbaacqGHris5aaGc baqcfaOaamiuamaaBaaabaGaamiCaiaadogaaeqaaiabg2da9maaqa habaGaamivamaaBaaabaGaam4yaiaadMgaaeqaaaqaaiaadMgacqGH 9aqpcaaIXaaabaGaamOBaaGaeyyeIuoacaWG5bWaaSbaaeaacaWGPb aabeaaaaaa@5638@ (8)

Procedures for Stewart Mixing Rules

  1. Estimate the boiling temperature of the C7+ fraction.
  2. T bc7+ = (4.5579 M C7+ 0.15178 γ C7+ 0.15427 ) 3 MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGWj0Jf9crFfpeea0xh9v8qiW7rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaqcfaOaamivam aaBaaabaGaamOyaiaadogacaaI3aGaey4kaScabeaacqGH9aqpcaGG OaGaaGinaiaac6cacaaI1aGaaGynaiaaiEdacaaI5aGaamytamaaDa aabaGaam4qaiaaiEdacqGHRaWkaeaacaaIWaGaaiOlaiaaigdacaaI 1aGaaGymaiaaiEdacaaI4aaaaiabeo7aNnaaDaaabaGaam4qaiaaiE dacqGHRaWkaeaacaaIWaGaaiOlaiaaigdacaaI1aGaaGinaiaaikda caaI3aaaaiaacMcadaahaaqabeaacaaIZaaaaaaa@5689@ (9)

  3. Estimate the pseudo-critical pressure of the C7+ fraction.
  4. P pcC7+ =exp[ 8.3634 0.0566 γ C7+ ( 0.24244+ 2.2898 γ c7+ + 0.11857 γ C7+ 2 ) T bC7+ 1000 + ( 1.4685+ 3.648 γ C7+ + 0.47227 γ c7+ 2 ) T bC7+ 2 10 7 ( 0.42019+ 1.6977 γ C7+ 2 ) T bC7+ 3 10 10 ] MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGWj0Jf9crFfpeea0xh9v8qiW7rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaqcfaOaamiuam aaBaaabaGaamiCaiaadogacaWGdbGaaG4naiabgUcaRaqabaGaeyyp a0JaciyzaiaacIhacaGGWbWaamWaaqaabeqaaiaaiIdacaGGUaGaaG 4maiaaiAdacaaIZaGaaGinaiabgkHiTmaalaaabaGaaGimaiaac6ca caaIWaGaaGynaiaaiAdacaaI2aaabaGaeq4SdC2aaSbaaeaacaWGdb GaaG4naiabgUcaRaqabaaaaiabgkHiTmaabmaabaGaaGimaiaac6ca caaIYaGaaGinaiaaikdacaaI0aGaaGinaiabgUcaRmaalaaabaGaaG Omaiaac6cacaaIYaGaaGioaiaaiMdacaaI4aaabaGaeq4SdC2aaSba aeaacaWGJbGaaG4naiabgUcaRaqabaaaaiabgUcaRmaalaaabaGaaG imaiaac6cacaaIXaGaaGymaiaaiIdacaaI1aGaaG4naaqaaiabeo7a NnaaDaaabaGaam4qaiaaiEdacqGHRaWkaeaacaaIYaaaaaaaaiaawI cacaGLPaaadaWcaaqaaiaadsfadaWgaaqaaiaadkgacaWGdbGaaG4n aiabgUcaRaqabaaabaGaaGymaiaaicdacaaIWaGaaGimaaaacqGHRa WkaeaadaqadaqaaiaaigdacaGGUaGaaGinaiaaiAdacaaI4aGaaGyn aiabgUcaRmaalaaabaGaaG4maiaac6cacaaI2aGaaGinaiaaiIdaae aacqaHZoWzdaWgaaqaaiaadoeacaaI3aGaey4kaScabeaaaaGaey4k aSYaaSaaaeaacaaIWaGaaiOlaiaaisdacaaI3aGaaGOmaiaaikdaca aI3aaabaGaeq4SdC2aa0baaeaacaWGJbGaaG4naiabgUcaRaqaaiaa ikdaaaaaaaGaayjkaiaawMcaamaalaaabaGaamivamaaBaaabaGaam OyaiaadoeacaaI3aGaey4kaScabeaadaahaaqabeaacaaIYaaaaaqa aiaaigdacaaIWaWaaWbaaeqabaGaaG4naaaaaaGaeyOeI0YaaeWaae aacaaIWaGaaiOlaiaaisdacaaIYaGaaGimaiaaigdacaaI5aGaey4k aSYaaSaaaeaacaaIXaGaaiOlaiaaiAdacaaI5aGaaG4naiaaiEdaae aacqaHZoWzdaqhaaqaaiaadoeacaaI3aGaey4kaScabaGaaGOmaaaa aaaacaGLOaGaayzkaaWaaSaaaeaacaWGubWaa0baaeaacaWGIbGaam 4qaiaaiEdacqGHRaWkaeaacaaIZaaaaaqaaiaaigdacaaIWaWaaWba aeqabaGaaGymaiaaicdaaaaaaaaacaGLBbGaayzxaaaaaa@B1B4@  (10)

  5. Estimate the pseudo-critical temperature of the C7+ fraction.
  6. T pcC7+ =( 341.7+811 γ C7+ )+(0.4244+0.1174 γ C7+ ) T bC7+ +(0.46693.2623 γ C7+ ) 10 5 T bC7+ MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGWj0Jf9crFfpeea0xh9v8qiW7rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaqcfaOaamivam aaBaaabaGaamiCaiaadogacaWGdbGaaG4naiabgUcaRaqabaGaeyyp a0ZaaeWaaeaacaaIZaGaaGinaiaaigdacaGGUaGaaG4naiabgUcaRi aaiIdacaaIXaGaaGymaiabeo7aNnaaBaaabaGaam4qaiaaiEdacqGH RaWkaeqaaaGaayjkaiaawMcaaiabgUcaRiaacIcacaaIWaGaaiOlai aaisdacaaIYaGaaGinaiaaisdacqGHRaWkcaaIWaGaaiOlaiaaigda caaIXaGaaG4naiaaisdacqaHZoWzdaWgaaqaaiaadoeacaaI3aGaey 4kaScabeaacaGGPaGaamivamaaBaaabaGaamOyaiaadoeacaaI3aGa ey4kaScabeaacqGHRaWkcaGGOaGaaGimaiaac6cacaaI0aGaaGOnai aaiAdacaaI5aGaeyOeI0IaaG4maiaac6cacaaIYaGaaGOnaiaaikda caaIZaGaeq4SdC2aaSbaaeaacaWGdbGaaG4naiabgUcaRaqabaGaai ykamaalaaabaGaaGymaiaaicdadaahaaqabeaacaaI1aaaaaqaaiaa dsfadaWgaaqaaiaadkgacaWGdbGaaG4naiabgUcaRaqabaaaaaaa@7699@ (11)

  7. Determine the correction factor Fj,ξj and ξk for high- molecular weight component using Sutton’s method.
  8. F j = 1 3 ( y T c P c ) C7+ + 2 3 ( y 2 T c P c ) C7+ MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGWj0Jf9crFfpeea0xh9v8qiW7rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaqcfaOaamOram aaBaaabaGaamOAaaqabaGaeyypa0ZaaSaaaeaacaaIXaaabaGaaG4m aaaadaqadaqaamaalaaabaGaamyEaiaadsfadaWgaaqaaiaadogaae qaaaqaaiaadcfadaWgaaqaaiaadogaaeqaaaaaaiaawIcacaGLPaaa daWgaaqaaiaadoeacaaI3aGaey4kaScabeaacqGHRaWkdaWcaaqaai aaikdaaeaacaaIZaaaamaabmaabaWaaSaaaeaacaWG5bWaaWbaaeqa baGaaGOmaaaacaWGubWaaSbaaeaacaWGJbaabeaaaeaacaWGqbWaaS baaeaacaWGJbaabeaaaaaacaGLOaGaayzkaaWaaSbaaeaacaWGdbGa aG4naiabgUcaRaqabaaaaa@520D@ (12)

    ξ j =0.6081 F j +1.1325 F j 2 14.004 F j y C7+ +64.434 F j y C7+ 2 MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGWj0Jf9crFfpeea0xh9v8qiW7rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaqcfaOaeqOVdG 3aaSbaaeaacaWGQbaabeaacqGH9aqpcaaIWaGaaiOlaiaaiAdacaaI WaGaaGioaiaaigdacaWGgbWaaSbaaeaacaWGQbaabeaacqGHRaWkca aIXaGaaiOlaiaaigdacaaIZaGaaGOmaiaaiwdacaWGgbWaa0baaeaa caWGQbaabaGaaGOmaaaacqGHsislcaaIXaGaaGinaiaac6cacaaIWa GaaGimaiaaisdacaWGgbWaaSbaaeaacaWGQbaabeaacaWG5bWaaSba aeaacaWGdbGaaG4naiabgUcaRaqabaGaey4kaSIaaGOnaiaaisdaca GGUaGaaGinaiaaiodacaaI0aGaamOramaaBaaabaGaamOAaaqabaGa amyEamaaDaaabaGaam4qaiaaiEdacqGHRaWkaeaacaaIYaaaaaaa@60A2@ (13)

    ξ K = ( T c P c ) C7+ ( 0.3129 y C7+ 4.8156 y C7+ 2 +27.3751 y C7+ 3 ) MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGWj0Jf9crFfpeea0xh9v8qiW7rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaqcfaOaeqOVdG 3aaSbaaeaacaWGlbaabeaacqGH9aqpdaqadaqaamaalaaabaGaamiv amaaBaaabaGaam4yaaqabaaabaWaaOaaaeaacaWGqbWaaSbaaeaaca WGJbaabeaaaeqaaaaaaiaawIcacaGLPaaadaWgaaqaaiaadoeacaaI 3aGaey4kaScabeaadaqadaqaaiaaicdacaGGUaGaaG4maiaaigdaca aIYaGaaGyoaiaadMhadaWgaaqaaiaadoeacaaI3aGaey4kaScabeaa cqGHsislcaaI0aGaaiOlaiaaiIdacaaIXaGaaGynaiaaiAdacaWG5b Waa0baaeaacaWGdbGaaG4naiabgUcaRaqaaiaaikdaaaGaey4kaSIa aGOmaiaaiEdacaGGUaGaaG4maiaaiEdacaaI1aGaaGymaiaadMhada qhaaqaaiaadoeacaaI3aGaey4kaScabaGaaG4maaaaaiaawIcacaGL Paaaaaa@61AB@ (12)

  9. Obtain the critical pressure and temperature of the remaining component from Table 1.
  10. Determine the pseudo-critical pressure and temperature of the gas
  11. Calculate the parameters J and K
  12. J= 1 3 i=1 nc ( y T c P c ) i + 2 3 [ i=1 nc ( y T c P c ) i ] 2 MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGWj0Jf9crFfpeea0xh9v8qiW7rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaqcfaOaamOsai abg2da9maalaaabaGaaGymaaqaaiaaiodaaaWaaabCaeaadaqadaqa amaalaaabaGaamyEaiaadsfadaWgaaqaaiaadogaaeqaaaqaaiaadc fadaWgaaqaaiaadogaaeqaaaaaaiaawIcacaGLPaaadaWgaaqaaiaa dMgaaeqaaaqaaiaadMgacqGH9aqpcaaIXaaabaGaamOBaiaadogaai abggHiLdGaey4kaSYaaSaaaeaacaaIYaaabaGaaG4maaaadaWadaqa amaaqahabaWaaeWaaeaacaWG5bWaaOaaaeaadaWcaaqaaiaadsfada WgaaqaaiaadogaaeqaaaqaaiaadcfadaWgaaqaaiaadogaaeqaaaaa aeqaaaGaayjkaiaawMcaamaaBaaabaGaamyAaaqabaaabaGaamyAai abg2da9iaaigdaaeaacaWGUbGaam4yaaGaeyyeIuoaaiaawUfacaGL DbaadaahaaqabeaacaaIYaaaaaaa@5D71@ and K= i=1 nc ( y T c P c ) i MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGWj0Jf9crFfpeea0xh9v8qiW7rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaqcfaOaam4sai abg2da9maaqahabaWaaeWaaeaadaWcaaqaaiaadMhacaWGubWaaSba aeaacaWGJbaabeaaaeaadaGcaaqaaiaadcfadaWgaaqaaiaadogaae qaaaqabaaaaaGaayjkaiaawMcaaaqaaiaadMgacqGH9aqpcaaIXaaa baGaamOBaiaadogaaiabggHiLdWaaSbaaeaacaWGPbaabeaaaaa@4895@ (13)

  13. Correct the parameters J and K for the C7+ fraction.
  14. J ' =J ξ j K ' =K ξ K MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGWj0Jf9crFfpeea0xh9v8qiW7rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGceaqabeaajuaGca WGkbWaaWbaaeqabaGaai4jaaaacqGH9aqpcaWGkbGaeyOeI0IaeqOV dG3aaSbaaeaacaWGQbaabeaaaOqaaKqbakaadUeadaahaaqabeaaca GGNaaaaiabg2da9iaadUeacqGHsislcqaH+oaEdaWgaaqaaiaadUea aeqaaaaaaa@4779@ (14)

  15. Calculate the pseudo-critical temperature and pressure
  16. T pc = K 2' J ' P pc = T pc J ' MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGWj0Jf9crFfpeea0xh9v8qiW7rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGceaqabeaajuaGca WGubWaaSbaaeaacaWGWbGaam4yaaqabaGaeyypa0ZaaSaaaeaacaWG lbWaaWbaaeqabaGaaGOmaiaacEcaaaaabaGaamOsamaaCaaabeqaai aacEcaaaaaaaGcbaqcfaOaamiuamaaDaaabaGaamiCaiaadogaaeaa aaGaeyypa0ZaaSaaaeaacaWGubWaaSbaaeaacaWGWbGaam4yaaqaba aabaGaamOsamaaCaaabeqaaiaacEcaaaaaaaaaaa@4973@ (15)

  17. Calculated the Pseudo-reduced pressure and temperature by using equation7
  18. Finding z factor from Standing & Katz compressibility factors Figure 1.
Figure 1 Standing and Katz Compressibility Factors Chart 3.

Procedures for Sutton’s correlations of sweet gas

  1. Estimate the gas gravity of the mixture
  2. Calculate the pseudo-critical pressure and temperature for the hydrocarbon component by using the following equation:

P pch =756.8131.0 γ h 3.6 γ h 2 T pch =169.2+349.5 γ h 74.0 γ h 2 MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGWj0Jf9crFfpeea0xh9v8qiW7rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGceaqabeaajuaGca WGqbWaaSbaaeaacaWGWbGaam4yaiaadIgaaeqaaiabg2da9iaaiEda caaI1aGaaGOnaiaac6cacaaI4aGaeyOeI0IaaGymaiaaiodacaaIXa GaaiOlaiaaicdacqaHZoWzdaWgaaqaaiaadIgaaeqaaiabgkHiTiaa iodacaGGUaGaaGOnaiabeo7aNnaaDaaabaGaamiAaaqaaiaaikdaaa aakeaajuaGcaWGubWaaSbaaeaacaWGWbGaam4yaiaadIgaaeqaaiab g2da9iaaigdacaaI2aGaaGyoaiaac6cacaaIYaGaey4kaSIaaG4mai aaisdacaaI5aGaaiOlaiaaiwdacqaHZoWzdaWgaaqaaiaadIgaaeqa aiabgkHiTiaaiEdacaaI0aGaaiOlaiaaicdacqaHZoWzdaqhaaqaai aadIgaaeaacaaIYaaaaaaaaa@6683@ (16)

  1. Ignore the nitrogen contamination, then

P pc = P pch T pc = T pch MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGWj0Jf9crFfpeea0xh9v8qiW7rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGceaqabeaajuaGca WGqbWaaSbaaeaacaWGWbGaam4yaaqabaGaeyypa0JaamiuamaaBaaa baGaamiCaiaadogacaWGObaabeaaaOqaaKqbakaadsfadaWgaaqaai aadchacaWGJbaabeaacqGH9aqpcaWGubWaaSbaaeaacaWGWbGaam4y aiaadIgaaeqaaaaaaa@486E@ (17)

  1. Calculated the Pseudo-reduced pressure and temperature from equation 7.
  2. Finding z factor from Standing & Katz compressibility factors chart.

Procedures for Sutton’s correlations of Sour gas

  1. Determine the gravity of the hydrocarbon components of the Mixture
  2. γ h = γ w 1.1767 y H2S 1.5196 y co2 0.9672 y N2 0.6220 y H2O 1 y H2S y Co2 y N2 y H2O MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGWj0Jf9crFfpeea0xh9v8qiW7rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaqcfaOaeq4SdC 2aaSbaaeaacaWGObaabeaacqGH9aqpdaWcaaqaaiabeo7aNnaaBaaa baGaam4DaaqabaGaeyOeI0IaaGymaiaac6cacaaIXaGaaG4naiaaiA dacaaI3aGaamyEamaaBaaabaGaamisaiaaikdacaWGtbaabeaacqGH sislcaaIXaGaaiOlaiaaiwdacaaIXaGaaGyoaiaaiAdacaWG5bWaaS baaeaacaWGJbGaam4BaiaaikdaaeqaaiabgkHiTiaaicdacaGGUaGa aGyoaiaaiAdacaaI3aGaaGOmaiaadMhadaWgaaqaaiaad6eacaaIYa aabeaacqGHsislcaaIWaGaaiOlaiaaiAdacaaIYaGaaGOmaiaaicda caWG5bWaaSbaaeaacaWGibGaaGOmaiaad+eaaeqaaaqaaiaaigdacq GHsislcaWG5bWaaSbaaeaacaWGibGaaGOmaiaadofaaeqaaiabgkHi TiaadMhadaWgaaqaaiaadoeacaWGVbGaaGOmaaqabaGaeyOeI0Iaam yEamaaBaaabaGaamOtaiaaikdaaeqaaiabgkHiTiaadMhadaWgaaqa aiaadIeacaaIYaGaam4taaqabaaaaaaa@7387@  (18)

  3. Calculate the pseudo-critical pressure and temperature for the hydrocarbon component by using the following equations.
  4. P pch =756.8131.0 γ h 3.6 γ h 2 T pch =169.2+349.5 γ h 74.0 γ h 2 MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGWj0Jf9crFfpeea0xh9v8qiW7rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGceaqabeaajuaGca WGqbWaaSbaaeaacaWGWbGaam4yaiaadIgaaeqaaiabg2da9iaaiEda caaI1aGaaGOnaiaac6cacaaI4aGaeyOeI0IaaGymaiaaiodacaaIXa GaaiOlaiaaicdacqaHZoWzdaWgaaqaaiaadIgaaeqaaiabgkHiTiaa iodacaGGUaGaaGOnaiabeo7aNnaaDaaabaGaamiAaaqaaiaaikdaaa aakeaajuaGcaWGubWaaSbaaeaacaWGWbGaam4yaiaadIgaaeqaaiab g2da9iaaigdacaaI2aGaaGyoaiaac6cacaaIYaGaey4kaSIaaG4mai aaisdacaaI5aGaaiOlaiaaiwdacqaHZoWzdaWgaaqaaiaadIgaaeqa aiabgkHiTiaaiEdacaaI0aGaaiOlaiaaicdacqaHZoWzdaqhaaqaai aadIgaaeaacaaIYaaaaaaaaa@6683@ (19)

  5. Calculate the Pesudo-critical properties of the total mixture.
  6. P pc =(1 y H2S y CO2 y N2 y H2O ) P pch +1,306 y H2S +1,071 y CO2 +493.1 y N2 +3200.1 y H20 T pc =(1 y H2S y CO2 y N2 y H2O ) T pch +672.35 y H2S +547.58 y CO2 +227.16 y N2 +1164.9 y H20 MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGWj0Jf9crFfpeea0xh9v8qiW7rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGceaqabeaajuaGca WGqbWaaSbaaeaacaWGWbGaam4yaaqabaGaeyypa0Jaaiikaiaaigda cqGHsislcaWG5bWaaSbaaeaacaWGibGaaGOmaiaadofaaeqaaiabgk HiTiaadMhadaWgaaqaaiaadoeacaWGpbGaaGOmaaqabaGaeyOeI0Ia amyEamaaBaaabaGaamOtaiaaikdaaeqaaiabgkHiTiaadMhadaWgaa qaaiaadIeacaaIYaGaam4taaqabaGaaiykaiaadcfadaWgaaqaaiaa dchacaWGJbGaamiAaaqabaGaey4kaSIaaGymaiaacYcacaaIZaGaaG imaiaaiAdacaWG5bWaaSbaaeaacaWGibGaaGOmaiaadofaaeqaaaqa aiabgUcaRiaaigdacaGGSaGaaGimaiaaiEdacaaIXaGaamyEamaaBa aabaGaam4qaiaad+eacaaIYaaabeaacqGHRaWkcaaI0aGaaGyoaiaa iodacaGGUaGaaGymaiaadMhadaWgaaqaaiaad6eacaaIYaaabeaacq GHRaWkcaaIZaGaaGOmaiaaicdacaaIWaGaaiOlaiaaigdacaWG5bWa aSbaaeaacaWGibGaaGOmaiaaicdaaeqaaaqaaiaadsfadaWgaaqaai aadchacaWGJbaabeaacqGH9aqpcaGGOaGaaGymaiabgkHiTiaadMha daWgaaqaaiaadIeacaaIYaGaam4uaaqabaGaeyOeI0IaamyEamaaBa aabaGaam4qaiaad+eacaaIYaaabeaacqGHsislcaWG5bWaaSbaaeaa caWGobGaaGOmaaqabaGaeyOeI0IaamyEamaaBaaabaGaamisaiaaik dacaWGpbaabeaacaGGPaGaamivamaaBaaabaGaamiCaiaadogacaWG ObaabeaacqGHRaWkcaaI2aGaaG4naiaaikdacaGGUaGaaG4maiaaiw dacaWG5bWaaSbaaeaacaWGibGaaGOmaiaadofaaeqaaaGcbaqcfaOa ey4kaSIaaGynaiaaisdacaaI3aGaaiOlaiaaiwdacaaI4aGaamyEam aaBaaabaGaam4qaiaad+eacaaIYaaabeaacqGHRaWkcaaIYaGaaGOm aiaaiEdacaGGUaGaaGymaiaaiAdacaWG5bWaaSbaaeaacaWGobGaaG OmaaqabaGaey4kaSIaaGymaiaaigdacaaI2aGaaGinaiaac6cacaaI 5aGaamyEamaaBaaabaGaamisaiaaikdacaaIWaaabeaaaaaa@B053@ (20)

Methods of Correction the Pseudo-critical Gas Properties for H2S and CO2 contamination.

Natural gases, which contain H2S and CO2 frequently, exhibit different compressibility factor behavior than do sweet gases. Wichert and Aziz developed a simple, easy to use calculation procedure to account for these differences.

Wichert-Aziz Correction Method

This method permits the use of the standing-Katz chart, by using a pseudo-critical temperature adjustment factor, which is function of the concentration of CO2 and H2S in the sour gas. The following Wichert and Aziz correlation is also can obtain from Figure 2:

ξ=120( A 0.9 A 1.6 )+15( B 0.5 B 4 ) MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGWj0Jf9crFfpeea0xh9v8qiW7rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaqcfaOaeqOVdG Naeyypa0JaaGymaiaaikdacaaIWaWaaeWaaeaacaWGbbWaaWbaaeqa baGaaGimaiaac6cacaaI5aaaaiabgkHiTiaadgeadaahaaqabeaaca aIXaGaaiOlaiaaiAdaaaaacaGLOaGaayzkaaGaey4kaSIaaGymaiaa iwdadaqadaqaaiaadkeadaahaaqabeaacaaIWaGaaiOlaiaaiwdaaa GaeyOeI0IaamOqamaaCaaabeqaaiaaisdaaaaacaGLOaGaayzkaaaa aa@4FBE@  (20)

Figure 2 Show the pseudo-critical property correction for H2S and CO2 3.

Where the pseudo-critical temperature, T’pc and pressure P’pc , adjusted for CO2 and H2S contamination are :

T pc ' = T pc ξ P pc ' = T pc ' P pc [ T pc +B(1B)ξ ] MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGWj0Jf9crFfpeea0xh9v8qiW7rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGceaqabeaajuaGca WGubWaa0baaeaacaWGWbGaam4yaaqaaiaacEcaaaGaeyypa0Jaamiv amaaBaaabaGaamiCaiaadogaaeqaaiabgkHiTiabe67a4bGcbaqcfa OaamiuamaaDaaabaGaamiCaiaadogaaeaacaGGNaaaaiabg2da9maa laaabaGaamivamaaDaaabaGaamiCaiaadogaaeaacaGGNaaaaiaadc fadaWgaaqaaiaadchacaWGJbaabeaaaeaadaWadaqaaiaadsfadaWg aaqaaiaadchacaWGJbaabeaacqGHRaWkcaWGcbGaaiikaiaaigdacq GHsislcaWGcbGaaiykaiabe67a4bGaay5waiaaw2faaaaaaaaa@5A2C@ (21)

Where,
A: Sum of the mole fractions of H2S and CO2 in the gas mixture
B: Mole fraction of H2S in the gas mixture.

Methods of Correction the Pseudo-critical Gas Properties for N2 and H2O vapor contamination

Carr-Kobayashi and Burrows developed a simple procedure to adjust the pseudo-critical properties of natural gases when non-hydrocarbon components are present.

Carr-Kobayashi and Burrows Correction Method

The procedures to obtain the correction are following:

  1. Known the specific gravity of the natural gas, calculate the pseudo-critical temperature and pressure from Figure 3 or by the following equation:

T pc =168+325 γ g 12.5 γ g 2 P pc =677+15 γ g 37.5 γ g 2 MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGWj0Jf9crFfpeea0xh9v8qiW7rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGceaqabeaajuaGca WGubWaaSbaaeaacaWGWbGaam4yaaqabaGaeyypa0JaaGymaiaaiAda caaI4aGaey4kaSIaaG4maiaaikdacaaI1aGaeq4SdC2aaSbaaeaaca WGNbaabeaacqGHsislcaaIXaGaaGOmaiaac6cacaaI1aGaeq4SdC2a a0baaeaacaWGNbaabaGaaGOmaaaaaOqaaKqbakaadcfadaWgaaqaai aadchacaWGJbaabeaacqGH9aqpcaaI2aGaaG4naiaaiEdacqGHRaWk caaIXaGaaGynaiabeo7aNnaaBaaabaGaam4zaaqabaGaeyOeI0IaaG 4maiaaiEdacaGGUaGaaGynaiabeo7aNnaaDaaabaGaam4zaaqaaiaa ikdaaaaaaaa@5EDA@ (22)

Figure 3 Show the pseudo-critical property of natural gases 3.
  1. Calculate the corrections for nitrogen and water vapor.

T = pc,cor 246.1 y N2 +400 y H2O P pc,cor =162.0 y N2 +1270 y H2O MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGWj0Jf9crFfpeea0xh9v8qiW7rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGceaqabeaajuaGca WGubWaaSraaeaacaWGWbGaam4yaiaacYcacaWGJbGaam4Baiaadkha aeqaaiabg2da9iabgkHiTiaaikdacaaI0aGaaGOnaiaac6cacaaIXa GaamyEamaaBaaabaGaamOtaiaaikdaaeqaaiabgUcaRiaaisdacaaI WaGaaGimaiaadMhadaWgaaqaaiaadIeacaaIYaGaam4taaqabaaake aajuaGcaWGqbWaaSbaaeaacaWGWbGaam4yaiaacYcacaWGJbGaam4B aiaadkhaaeqaaiabg2da9iabgkHiTiaaigdacaaI2aGaaGOmaiaac6 cacaaIWaGaamyEamaaBaaabaGaamOtaiaaikdaaeqaaiabgUcaRiaa igdacaaIYaGaaG4naiaaicdacaWG5bWaaSbaaeaacaWGibGaaGOmai aad+eaaeqaaaaaaa@6451@  (23)

  1. Calculate the pseudo-critical temperature and pressure for nitrogen and water vapor.
  2. T pc '' = T pc ' (227.2) y N2 (1,165) y H2O ( 1 y N2 y H2O ) + T pc,cor P pc '' = P pc ' (493.1) y N2 (3,200) y H2O ( 1 y N2 y H2O ) + P pc,cor MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGWj0Jf9crFfpeea0xh9v8qiW7rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGceaqabeaajuaGca WGubWaa0baaeaacaWGWbGaam4yaaqaaiaacEcacaGGNaaaaiabg2da 9maalaaabaGaamivamaaDaaabaGaamiCaiaadogaaeaacaGGNaaaai abgkHiTiaacIcacaaIYaGaaGOmaiaaiEdacaGGUaGaaGOmaiaacMca caWG5bWaaSbaaeaacaWGobGaaGOmaaqabaGaeyOeI0Iaaiikaiaaig dacaGGSaGaaGymaiaaiAdacaaI1aGaaiykaiaadMhadaWgaaqaaiaa dIeacaaIYaGaam4taaqabaaabaWaaeWaaeaacaaIXaGaeyOeI0Iaam yEamaaBaaabaGaamOtaiaaikdaaeqaaiabgkHiTiaadMhadaWgaaqa aiaadIeacaaIYaGaam4taaqabaaacaGLOaGaayzkaaaaaiabgUcaRi aadsfadaWgaaqaaiaadchacaWGJbGaaiilaiaadogacaWGVbGaamOC aaqabaaakeaajuaGcaWGqbWaa0baaeaacaWGWbGaam4yaaqaaiaacE cacaGGNaaaaiabg2da9maalaaabaGaamiuamaaDaaabaGaamiCaiaa dogaaeaacaGGNaaaaiabgkHiTiaacIcacaaI0aGaaGyoaiaaiodaca GGUaGaaGymaiaacMcacaWG5bWaaSbaaeaacaWGobGaaGOmaaqabaGa eyOeI0IaaiikaiaaiodacaGGSaGaaGOmaiaaicdacaaIWaGaaiykai aadMhadaWgaaqaaiaadIeacaaIYaGaam4taaqabaaabaWaaeWaaeaa caaIXaGaeyOeI0IaamyEamaaBaaabaGaamOtaiaaikdaaeqaaiabgk HiTiaadMhadaWgaaqaaiaadIeacaaIYaGaam4taaqabaaacaGLOaGa ayzkaaaaaiabgUcaRiaadcfadaWgaaqaaiaadchacaWGJbGaaiilai aadogacaWGVbGaamOCaaqabaaaaaa@91BE@  (24)

    Where, T’Pc and P’pc are the pseudo-critical temperature and pressure corrected for H2S and CO2 with wichert and Aziz correlation.

    1. If there is no H2S or CO2 in the gas mixture, then T p = T pc MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGWj0Jf9crFfpeea0xh9v8qiW7rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaqcfaieaaaaaa aaa8qacaWGubGaaiygG8aadaWgaaqaa8qacaWGWbaapaqabaWdbiab g2da9iaadsfapaWaaSbaaeaapeGaamiCaiaadogaa8aabeaaaaa@3FAA@  and P pc = P pc MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGWj0Jf9crFfpeea0xh9v8qiW7rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaqcfaieaaaaaa aaa8qacaWGqbGaaiygG8aadaWgaaqaa8qacaWGWbGaam4yaaWdaeqa a8qacqGH9aqpcaWGqbWdamaaBaaabaWdbiaadchacaWGJbaapaqaba aaaa@408A@

Result and discussion

The data are analyzed and Stewart method and Kay’s mixing rules for predicting pseudo-reduce pressure and temperatures are used for these data with knowing composition. Moreover, according to present of non-hydrocarbon on the data I used the correction methods which are Wichert- Aziz and Carr-Kobayashi and Burrows. The data of three reservoirs (A,B,C) with water vapor, carbon dioxide and hydrogen sulfide but with light molecular weight while ,the others (D,E,F) have C7+ and without water vapor are shown in Table 2, so I used Stewart Mixing Rules and Kays, The calculation and result for six reservoir are appear in Tables 3-14. From calculation, it is found that gas pseudo-critical temperature decrease with increase of N2 as shown in Figure 4. Moreover, pseudo-critical temperature with increasing H2S is decreases with limitation as shown in Figure 5 then slightly increase with increase temperature maybe it related to the behavior of H2S in reservoir. In addition, gas pseudo-critical pressure increase with increase N2 and H2S as shown in Figure 5 & 8. Also, it is observed that in the tested gas reservoirs which contain C7+ by Stewart Mixing Rules and Kay’s there are some deviation on z factor between two methods that became negligible by using the correction method for non-hydrocarbon as shown in Figure 8 and Table 10 &14. It is obvious from the error of Z factor calculated by Stewart for reservoirs D, E and F (Table 10) is lower than Z error for reservoirs A, B and C (Table 6) with Kay’s technique, therefore it is recommended to adopt Stewart Mixing Rules to solve the problem on non-hydrocarbon impurities in natural gas behavior and more specifically Z factor

A

B

C

D

E

F

Pressure(psia)

6000

5200

5000

4010

2640

2748

Temperature (Ro)

673.8

657.6

657.6

711.6

672

690

C1

59.59

69.14

71.32

57.95

61.83

40

C2

0.02

2.27

0.1

12.59

7.7

11.93

C3

0.01

1.96

0

7.94

7.63

14

i-C4

0

0.46

0

1.13

1.73

4.7

n-C4

0

1.46

0

3.16

4.38

7.37

i-C5

0

0

0

1.42

2.38

2.38

n-C5

0

0

0

2.01

2.6

5.6

C6

0

0

0

2.18

4.34

7.54

C7+

0

0

0

4.54

6.87

5.93

CO2

12.59

7.9

9.05

3.9

0.3

0.34

N2

11.95

0.1

6.35

0.2

0.24

0.21

H2S

12.09

13.03

9.44

2.98

0

0

H2O

3.75

3.68

3.74

0

0

0

Table 2 Six different reservoir in Abu-Dhabi.

Component

Yi

Mi

YiMi

Tci

YiTci

Pci

YiPci

CO2

0.1259

44

5.5396

547.6

68.94284

1071

134.8389

N2

0.1198

28

3.3544

239.3

28.66814

507.5

60.7985

H2S

0.1209

34

4.1106

672.35

81.28712

1306

157.8954

H20

0.0375

18

0.675

1164.85

43.68188

3200.1

120.0038

C1

0.5956

16

9.5296

343

204.2908

666.4

396.9078

C2

0.0002

30

0.006

549.6

0.10992

706.5

0.1413

C3

0.0001

45

0.0045

665.7

0.06657

616

0.0616

i-C4

0

58

0

734.1

0

527.9

0

n-C4

0

58

0

765.3

0

550.6

0

Total

1

23.2197

427.0473

870.6473

Table 3 Reservoir A using Kay’s Rule at P=6000psi and T=673.8Ro.

Component

Yi

Mi

YiMi

Tci

YiTci

Pci

YiPci

CO2

0.079

44

3.476

547.6

43.2604

1071

84.609

N2

0.001

28

0.028

239.3

0.2393

507.5

0.5075

H2S

0.1303

34

4.4302

672.35

87.60721

1306

170.1718

H20

0.0368

18

0.6624

1164.85

42.86648

3200.1

117.7637

C1

0.6914

16

11.0624

343

237.1502

666.4

460.749

C2

0.0227

30

0.681

549.6

12.47592

706.5

16.03755

C3

0.0196

45

0.882

665.7

13.04772

616

12.0736

i-C4

0.0046

58

0.2668

734.1

3.37686

527.9

2.42834

n-C4

0.0146

58

0.8468

765.3

11.17338

550.6

8.03876

Total

1

22.3356

451.1975

872.3792

Table 4 Reservoir B using Kay’s Rule at P=5200psi and T=657.6Ro.

Component

Yi

Mi

YiMi

Tci

YiTci

Pci

YiPci

CO2

0.0905

44

3.982

547.6

49.5578

1071

96.9255

N2

0.0635

28

1.778

239.3

15.19555

507.5

32.22625

H2S

0.0944

34

3.2096

672.35

63.46984

1306

123.2864

H20

0.0374

18

0.6732

1164.85

43.56539

3200.1

119.6837

C1

0.7132

16

11.4112

343

244.6276

666.4

475.2765

C2

0.001

30

0.03

549.6

0.5496

706.5

0.7065

C3

0

45

0

665.7

0

616

0

i-C4

0

58

0

734.1

0

527.9

0

C5

0

72

0

828.77

0

490.4

0

Total

1

21.084

416.9658

848.1049

Table 5 Reservoir C using Kay’s Rule at P=5000psi and T=657.6 Ro.

A

B

C

PPc

870.647

872.379

848.105

TPc

427.047

451.197

416.966

PPr

6.891

5.961

5.895

TPr

1.578

1.457

1.577

Z

0.928

0.848

0.872

Tpc'

400.563

426.246

394.149

Ppc'

811.305

819.004

797.964

Tp''

376.709

412.673

373.208

PP''

778.462

774.854

756.788

Tr

1.789

1.594

1.762

Pr

7.708

6.711

6.607

z

1.004

0.92

0.946

(Z- Error)

0.0089

0.0065

0.0178

Table 6 Properties and Compressibility factor for the three Reservoirs.

Component

Yi

Mi

yiMi

Tci (R)

Pci (psia)

yiTci/Pci

yiTci/Pci

yiTci/√Pci

N2

0.002

28.01

0.06

227.16

493.1

0

0

0.02

CH4

0.5795

16.04

9.3

343

666.4

0.3

0.42

7.7

C2H6

0.1259

30.07

3.79

549.59

706.5

0.1

0.11

2.6

C3H8

0.0794

44.1

3.5

665.73

616

0.09

0.08

2.13

i-C4H10

0.0113

58.12

0.66

734.13

527.9

0.02

0.01

0.36

n-C4H10

0.0316

58.12

1.84

765.29

550.6

0.04

0.04

1.03

i-C5H12

0.0142

72.15

1.02

828.77

490.4

0.02

0.02

0.53

n-C5H12

0.0201

72.15

1.45

845.47

488.6

0.03

0.03

0.77

C6H14

0.0218

86.18

1.88

913.27

436.9

0.05

0.03

0.95

C7+

0.0454

114.23

5.19

1005.3

375.5

0.12

0.07

2.36

CO2

0.039

44.01

1.72

547.45

1071

0.02

0.03

0.65

H2S

0.0298

34

1.01

672.35

1306

0.02

0.02

0.55

1

30.39

0.8

0.86

19.66

Table 7 Reservoir D using Stewart Mixing Rules.

Component

Yi

Mi

yiMi

Tci (R)

Pci (psia)

yiTci/Pci

yiTci/Pci

yiTci/√Pci

N2

0.0024

28.01

0.07

227.16

493.1

0

0

0.02

CH4

0.6183

16.04

9.92

343

666.4

0.32

0.44

8.22

C2H6

0.077

30.07

2.32

549.59

706.5

0.06

0.07

1.59

C3H8

0.0763

44.1

3.36

665.73

616

0.08

0.08

2.05

i-C4H10

0.0173

58.12

1.01

734.13

527.9

0.02

0.02

0.55

n-C4H10

0.0438

58.12

2.55

765.29

550.6

0.06

0.05

1.43

i-C5H12

0.0238

72.15

1.72

828.77

490.4

0.04

0.03

0.89

n-C5H12

0.026

72.15

1.88

845.47

488.6

0.04

0.03

0.99

C6H14

0.0434

86.18

3.74

913.27

436.9

0.09

0.06

1.9

C7+

0.0687

114.23

7.85

1005.3

375.5

0.18

0.11

3.56

CO2

0.003

44.01

0.13

547.45

1071

0

0

0.05

1

34.4

0.91

0.91

21.26

Table 8 Reservoir E using Stewart Mixing Rules.

Component

Yi

Mi

yiMi

Tci (R)

Pci (psia)

yiTci/Pci

yiTci/Pci

yiTci/√Pci

N2

0

28.01

0.06

227.16

493.1

0

0

0.02

CH4

0.4

16.04

6.42

343

666.4

0.21

0.29

5.31

C2H6

0.12

30.07

3.59

549.59

706.5

0.09

0.11

2.47

C3H8

0.14

44.1

6.17

665.73

616

0.15

0.15

3.76

i-C4H10

0.05

58.12

2.73

734.13

527.9

0.07

0.06

1.5

n-C4H10

0.07

58.12

4.28

765.29

550.6

0.1

0.09

2.4

i-C5H12

0.02

72.15

1.72

828.77

490.4

0.04

0.03

0.89

n-C5H12

0.06

72.15

4.04

845.47

488.6

0.1

0.07

2.14

C6H14

0.08

86.18

6.5

913.27

436.9

0.16

0.11

3.29

C7+

0.06

114.23

6.77

1005.3

375.5

0.16

0.1

3.08

CO2

0

44.01

0.15

547.45

1071

0

0

0.06

1

42.43

1.07

0.99

24.92

Table 9 Reservoir F using Stewart Mixing Rule.

D

E

F

Fj

0.044

0.07

0.059

Ej

0.007

0.002

0.004

Ek

0.355

0.397

0.38

J

0.762

0.851

1.017

K

19.66

21.256

24.924

J'

0.756

0.849

1.013

K'

19.305

20.859

24.544

Tpc

493.256

512.496

594.9

Ppc

652.851

603.662

587.495

Tpc'

481.534

511.864

594.193

Ppc'

636.898

602.917

586.797

Tp''

493.263

511.958

594.448

PP''

653.206

602.792

586.654

Tr

1.478

1.313

1.161

Pr

6.296

4.379

4.684

Z

0.874

0.69

0.666

Z-Error %

0.0023

0.0056

0.0102

Table 10 Properties and Compressibility factor for the three Reservoirs.

Component

yi

Mi

Tci (R)

Pci (psia)

yiTci

yiPci

N2

0.002

28

227.2

493.1

0.5

1

CH4

0.58

16

343

666.4

198.8

386.2

C2H6

0.126

30.1

549.6

706.5

69.2

88.9

C3H8

0.079

44.1

665.7

616

52.9

48.9

i-C4H10

0.011

58.1

734.1

527.9

8.3

6

n-C4H10

0.032

58.1

765.3

550.6

24.2

17.4

i-C5H12

0.014

72.2

828.8

490.4

11.8

7

n-C5H12

0.02

72.2

845.5

488.6

17

9.8

C6H14

0.022

86.2

913.3

436.9

19.9

9.5

C7+

0.045

114.2

1005.3

375.5

45.6

17

CO2

0.039

44

547.5

1071

21.4

41.8

H2S

0.03

34

672.4

1306

20

38.9

1

8097.5

7728.9

489.5

672.4

Table 11 Reservoir D using Kay’s Mixing Rules.

Component

yi

Mi

Tci (R)

Pci (psia)

yiTci

yiPci

N2

0.0024

28

227.2

493.1

0.5

1.2

CH4

0.6183

16

343

666.4

212.1

412

C2H6

0.077

30.1

549.6

706.5

42.3

54.4

C3H8

0.0763

44.1

665.7

616

50.8

47

i-C4H10

0.0173

58.1

734.1

527.9

12.7

9.1

n-C4H10

0.0438

58.1

765.3

550.6

33.5

24.1

i-C5H12

0.0238

72.2

828.8

490.4

19.7

11.7

n-C5H12

0.026

72.2

845.5

488.6

22

12.7

C6H14

0.0434

86.2

913.3

436.9

39.6

19

C7+

0.0687

114.2

1005.3

375.5

69.1

25.8

CO2

0.003

44

547.5

1071

1.6

3.2

1

7425.2

6422.9

504

620.2

Table 12 Reservoir E using Kay’s Mixing Rules.

Component

yi

Mi

Tci (R)

Pci (psia)

yiTci

yiPci

N2

0.0021

28

227.2

493.1

0.5

1

CH4

0.4

16

343

666.4

137.2

266.6

C2H6

0.1193

30.1

549.6

706.5

65.6

84.3

C3H8

0.14

44.1

665.7

616

93.2

86.2

i-C4H10

0.047

58.1

734.1

527.9

34.5

24.8

n-C4H10

0.0737

58.1

765.3

550.6

56.4

40.6

i-C5H12

0.0238

72.2

828.8

490.4

19.7

11.7

n-C5H12

0.056

72.2

845.5

488.6

47.3

27.4

C6H14

0.0754

86.2

913.3

436.9

68.9

32.9

C7+

0.0593

114.2

1005.3

375.5

59.6

22.3

CO2

0.0034

44

547.5

1071

1.9

3.6

1

6877.7

5351.9

584.8

601.4

Table 13 Reservoir F using Kay’s Mixing Rules.

D

E

F

Tpc

489.453

504.005

584.759

Ppc

672.432

620.215

601.395

Tpc'

477.731

503.373

584.052

Ppc'

655.874

619.437

600.668

Tp''

477.741

503.446

584.759

PP''

655.876

619.352

601.395

Tr

1.49

1.335

1.181

Pr

6.114

4.263

4.576

Z

0.865

0.691

0.663

Table 14 Properties and Compressibility factor for the three Reservoirs.

Figure 4 Show the mole percent of nitrogen verses pseudo-critical temperature.
Figure 5 Show the mole percent of H2S verses pseudo-critical temperature.
Figure 6 Show the mole percent of nitrogen verses pseudo-critical Pressure.
Figure 7 Show the Z-factor verses pseudo-reduce temperature & pressure.
Figure 8 Z-factor obtained from Stewart & Kay and correction with impurities verses pseudo-critical temperature& pressure.

Conclusion

Natural gases, which contain H2S and CO2 frequently, exhibit different compressibility factor behavior than do sweet gases. Wichert and Aziz & Carr-Kobayashi and Burrows developed a simple procedure to account for these differences and adjust the pseudo-critical properties of natural gases. During this study, I observe that pseudo-critical temperature decreases if the mole percent of N2 increase. While, pseudo-critical pressure was increase with increasing the percentage of nitrogen. Also, the z factor increases with increasing pseudo- reduce pressure and temperature. In addition, pseudo-critical temperature decreases if the mole percent of H2S increase. I also notice that when I calculate the z-factor for reservoirs which contain C7+ by Stewart Mixing Rules and Kay’s there are some deviation on z factor between two methods but it reduce when I used the correction method for non-hydrocarbon and it is recommended to use Stewart Mixing Rules to investigate the impact of non-hydrocarbon impurities on natural gas properties.

Acknowledgements

None.

Conflict of interest

The author declares no conflict of interest.

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