sutton z factor paper spe-14265-ms

8/15/2019 Sutton Z Factor Paper SPE-14265-MS

1/16

.,

SPE

SPE 14265

Compressibility Factors for High-Molecular-Weight

Reservoir Gases

by R.P. Sutton, Marathon OilCo.

SPE Membar

Copyriiht 19S5, Societyof Petroleum Engineers

Thispapar

was

prepared for presentationat the 60th AnnualTechnical Conference and Exhibitionof the .S@ety of Petroleum Engineera heldin Las

Vagaa, NV September 22-25, 1985.

This papa was selected for presentation by an SPE Program Committee followingreview of informationcontained in an abstract aubmiltadby the

author(a).Contentsof the paper, as presented, have notbeen reviewed by the Society of Petroleum Engineersand are subjectto correctionby the

author(s).The material, as presented,doas notneceaaarilyreflect anypositionofthe Societyof PetroleumEngineers, itsofficers,or members. Papers

presentad at SPE meetings are subjectto publicationreview by Editorial Commifteeaof the Society of Petroleum Engineers. Permissionto copyis

restrictedtoan abatract of notmore than300 words.Illustrationsmaynotbe copied.The abatractshouldcontainconspicuousacknowledgmentofwhere

and by whom the papar ia preaentad. Write Publication Manager, SPE, P.O. Box 633836, Richardson,TX 75063-3836. Telex, 730989 SPEDAL.

kBSTRACT

resulting pressure

drop from flow through pipe, static

pressure

gradiente in

gae

wells, and reeervoir

This paper examines the

effect of

high

performance.

Ideally,

gae PVT

properties are

concentrations of

the heptanes-plus

fraction in

determined

from laboratory

etudiee

designed to

natural

gases on the

calculation

of gas

duplicate

conditions of interest.

However, quite

compreeaibility (Z) factors.

Laboratory meaeured gae

often

experimental data ie unavailable, or

PVT

compositions and Z factore are ueed to evaluate the

properties muet be evaluated at conditions different

accuracy of

the

Standing-Katz

chart.

It

was

from those examined by the laboratory etudies. In

determined that the chart itself provides eatiefactory theee casea, PVT properties must be determined from

sccuracy; however, Kay’e molar average combination correlation.

Probably

the most widely

rulee or

accepted

comparable

gravity

relationships for

correlation

for natural

gas

mixtures ie

the

18 (SK) z factor chart.

calculating pseudo-critical pressure and temperature

Standing-Katz

reeult in unsatisfactory Z factore for high molecular

@e~Qht reeervoir gasee.

The contribution of thie

..-

The SK chart wae developed using data for binary

paper

are

two-fold.

Firet,

mixtures or met”nanewith pr~p=nz,

seudo-critical

“

.

new

.Fhqa

=....-.

. .

LWCZW, and

property

- gae gravity relationehipe are developed,

natural gaees having a wide range of composition.

3

snd

second,

alternate

methode

for

calculating

None of the gas mixturee had molecular weights in

pseudo-critical

properties

from

composition

are

excese of 40.

The SK chart is actually a modification

established.

By utilizing either of theee methods to

and exteneion of

a generalized Z

factor

chart

Holcomb1 2 (BH) and is

alculate pseudo-critical preeaure

and temperature,

developed by Brown and

the

overall accuracy of Z factors

from

the

identical to the BH chart at reduced preesuree less

Standing-Katz chart is increased almost three-fold.

than 4. Above thie value, the BH chart wae found to

be consistently inaccurate; therefore, Standing and

Katz used data from 16 natural gaa mixtures, along

INTRODUCTION

with methane Z factors ae a guide, to extend the chart

to re~ueed ~i~8S.u?~S ef

~~-

~in~~

the SK chart

.1:-I.

..-l.--.,l=

w~+mhr hvdrnca~b~n ga Se S KIOr lIla ll~

n~gu ~v~=~...-r-%-=..-..._ --

appeared in the literature in 1941, equatione of state

encountered in the petroleum industry can be grouped

have been developed which effectively reproduce afid

into two general categories. Natural gaees in the extend the chart aa ehown by the Dranchuk and

Eiret category contain relatively high concentration

Abou-Kaseem method 5 in Fige. 1A and lB. Thie chart

of ethane and propane typically ae the result of a low

correlate Z factor ae a function of peeudo-reduced

pressure flash with crude oil, while gasee in the

preeaure and temperature:

second category are gae-condeneatee and derive their

~igh molecular

weight from the quantity of

z

=f(Ppr, Tpr) . . . . . . . . . . . . . .(1)

leptanes-plue present. This paper is concerned with

latter category of gaeee.

where the peeudo-reduced pressure and temperature are

defined

relative to pseudo-critical pressure

and

The calculation of natural gas volume, density,

temperature.

Dr viscosity at elevated pressuree and temperature

requires

..

values of Z factor.

Tbeee quantities are

‘pr

=P/Ppc . . . . . . . . . . . . . . . .(2)

necessary for the evaluation of gae reeerves, the

‘pr

=T/Tpc . . . . . . . . . . . . . . . .(3)

:.,..----:--”

references and

IiLUWLLaLLU~L at

end cf paper.

.


2/16

. .

2

COMPRESSIBILITY FACTORS FOR HIGH MOLECULAR WEIGHT RESERVOIR GASES

SPE 1426

W.S b=gis for a generalized Z factor chart comes

adjusting pseudo-critical properties.

A total o

from van der Waals’ principle of corresponding states

1,085 Z factors from 9i gas mixttire~Were tltiiiZSd E

rhich says

that

two

Sa ibSt t 3 ikC~S a t

-n--nspfi~ing

develo~ the adjustment parameters. The ranges of dat

“..-

:onditions,

referenced to some basic properties such

used In

the development of the method

and th

Is

critical pressure and

temperature,

will have

equations are detailed below:

similar physical properties.

Therefore, if the

xinciple could be applied without error, all gases

Pressure, psia

154 to 7,026

rould have the same Z factor at the same reduced

Temperature, “F

40

to

300

>ressure and temperature.

However,

the principle of

Carbon Dioxide, mole Z

O to 54.46

‘~rresp??ding ‘tates :s ‘ot ‘Xact aa ‘hem by

Hydrogen Sulfide, mole %

O to 73.85

?lg. 2, but when applled to gasea having a similar

:hemical structure,

such as the paraffin hydrocarbons

c s IZO.(AO.9 -

A1.6) + 15.(B005 - B4) . . (6)

present in light natural gas mixtures, it providea a

correlating method with suitable accuracy

for many

engineering calculations.

T’ =TPC-E . . . . . . . . . . . . . . .(7)

pc

The SK chart effectively provides a corresponding

]tatea average Z factor correlation for natural gases.

P;c =

P

Pc”T;c/(Tpc +B”(l-B)E) . ...”(8)

in independent confirmation of the chart’s accuracy

:ss

.-nnrt.d by Matthews et

-F----

al.14

The average

Values from Eqs. 7 and 8 are then used t

~bsolute error for 231 data points from 29 different

caiculate

pseudo-rediiced

........_

pa=..u.c

=.m,

temperatur

gases was 1.2% with a maximum error of 6.7Z. The data

for

use with

SK chart. The

average

absolut

lsed in that study encompassed the following ranges of

error in calculated Z factor from the Wichert an

?alues:

Aziz

method was reported to be

0.97% with

maximum error of 6.59%.

This method waa used t

Pressure, psia

15 to 8,220 adjust

the pseudo-critical properties of

gase

Temperature, ‘F

20 to 280

containing carbon dioxide for

Gas Gravity, (air=l)

all furthe

0.591 to 1.074 calculations performed for this paper.

Nitrogen, mole %

o to 7.5

Carbon Dioxide, mole %

O to 1.8

To date,

similar work for heavy hydrocarbo

gases has not appeared in the literature, althoug

Roberts et al,15 showed that the chemical nature (i.e

The

principle of

corresponding states, as

?roposed by van der Waals, applies to single component

paraffinic, naphthenic,

or aromatic) of the heav

~ases, but subsequent work by Kay12 extended it to fraction in the gas affects the accuracy of the

oixtures. For gas mixtures, pseudo-criticai pressiire fsctcr .s....

.I-,tIag~e~ by nc. mnre than 2.2%.

Therefore

md temperature are used in place of critical pressure

the effects of the quantity, and not necessarily th

and temperature. The pseudo-critical valuea have no

nature of the heavy fraction, must be ascertained.

physical significance,

but merely provide a means of

correlating mixture

properties

applicable to

corresponding states principles. Kay proposed that

LABORATORY PVT DATA

>seudo-critical pressure

and

temperature

could be

:alculated using simple mole average relationships.

To determine the accuracy of Z factors calculate

by the traditional method (i.e. Ksy’s combinatio

P

=xyi.P . . . . . . . . . . . . . . . . . (4)

pc

cl

rules and the SK chart) and to arrive at

a mor

accurate method, a data bank of laboratory measure

T

=Zyi.T , . . . . . . . . . . . . . . . . (5)

pc

cl

natural gas

compositions and

PVT properties wa

created. The data included 634 compositions from 27

For

low

molecular

weight, homologous

gas

individual PVT reports. A total of 1,761 single phas

mixtures,

Kay suggested that the error in pseudo-

2 factors covering a wide range of pressures an

:ritical properties determined from Eqs. 4 and 5 is on

temperatures were provided by the reports. Th

:he order of 2% to 3X. However, for gas mixtures

producing areas repreaented by the data and th

vhose components differ greatly in molecular weight or

distribution of the reports within each area i

:hemical nature, the pseudo-critical pressure

and provided below:

temperature from these equations, when used with a

generalized compressibility factor chart, can lead to Location PVT Reports Total Compositions

inaccurate Z factors. These errors can become greater

Gulf of Mexico

112

290

:han tolerable for normal engineering calculation. Louisiana

85

131

Texas 53 98

Natural gaaes

often contain nitrogen,

carbon

Mississippi

6

6

,,

llOXidE il.d / Oi h y~~s~e l?

sulfide which can affect the

Wyoming 1

6

~ccuracy of

calculated Z factors.

Additionally,

Other 18 i03

~uantities

of high molecular weight hydrocarbons,

Total

m

m

?hich are usually lumped together and reported as

Ieptanes-plus,

can be present

in the gas which can

None of the gases contained hydrogen sulfide, but th

significantly

affect the accuracy of calculated Z

samplea did contain varied amounts of carbon dioxid

Factors.

and nitrogen.

Eighty-six compositions (14% of th

total) contained concentrations

Wiehert and Aziz24

of carbon dioxid

have examined the effects of

greater than 5%. ‘“””

he ranges of data covered by th

:arbon dioxide and hydrogen sulfide on the calculation

reports is aa follows:

>f gas Z factor and have proposed methods Eor suitably

.-


3/16

SPE 14265

R. P. SUTTON

3

pressure, psia

200 to

Temperature, “F

100 to

Compressibility Factor

0.748 to

Gas Gravity, (air=l)

0.571 to

Carbon Dioxide, mole %

0.01 to

Nitrogen, mole %

o to

Heptanes-plus, mole %

0.02 to

12,500

360

2.147

1.679

11.86

2.86

14.27

;oUPONENT CRITICAL PROPERTIES

The critical pressure and temperature for the

mre components norm lly present in natural gases are

movided in Table 1.

?

‘he critical pr’’pertig::o:~

~eptanes-plus fraction must be estimated.

Las reviewed various methoas for eaLCU~~....=-----

-..+:+:..-V-l.soaf

.ee-Kess~ej sure >

:ritical pr

and temperature and recommended the

correlations (Eqs. 9 and 10).

From the

:urrent study,

Table 2 provides a comparison of the

radiations in accuracy

of the calculated Z factor

4,13,14,19

ming different methods

to characterize the

Leptanes-plus

fraction.

The Lee-Kessler equations

}how a

slight improvement in calculated Z factor

:ompared with the results obtained using the other

correlations.

Based these findings and Whitson’s

recommendation, the Lee-Kessler equations were used

?or further calculations.

PC

n

I)ww l-f -

= exp t?.mk -

v.”av”, ,

(0,24244 + 2.2898/Y +

0.11857/Y2)0

0.47227/Y2)-

10-10.Tb3]

0-3.Tb +

o-7.Tb2 -

. . . . .

1.4685 + 3.648/Y +

(0.42019 + 1.6977/Y2)”

. . . . . . . . .

(9)

Tc = 341.7 + 811oY + (0.4244 + 0.1174.y).Tb +

(0.4669 - 3.2623”Y)”105/Tb . . . . . . (10)

The

Lee-Kessler equations

correlate

critical

c..-.*:--of hoiIio.gp~int and specific

>roperties &s a .“&L&.&W..

~ravity; however, laboratory reports normally provide

mly the specific gravity and moiecuiar weight of the

nitson22 has provided an

~~titF .~S pl ’U8

f~=~~~on

~quation suitable for estimating the boiling point

:rom specific gravity and molecular weight.

Tb = (4.5579°M0”15178@”15427)3 . . . . . . (11)

CALCULATION METHOD AND RESULTS

Numerical representation of the SK chart for

:omputer calculations is ffered by many investigators

is reviewed by Takacs.

2f

T e most recent methods

~tilize equations of state5~6~8,9 that offer increased

~ccuracy while significantly extending the range of

the SK chart. Each of these equations of state offer

:omparable accuracy over its range of applicability.

3ased on results presented by Takacs, the Dranchuk and

ibou-Kassem

correlation was selected

for

the

waluation presented in this paper.

This correlation

is an 11 constant,

generalized Starling equation of

~tate as given by Eq. 12.

Z = 1 + (Al + A2/Tr + A3/Tr3 + A41Tr4 +

A5/Tr5)Pr + (A6 + A7/Tr + A8/Tr2)Pr2 -

2)Pr5 + Alo(l + A11Pr2)o

(A7/Tr + A81Tr

(pr2/Tr3)exp(-A11Pr2) . . . . . . . . . . (12)

where

Pr = 0.27[Pr/(Z*Tr)] . . . . . . . . . . . . (13)

The constants, Al - All,

in Eq. 12 are as follows:

‘1

.

= 0,3265

A, = -0.7361

A2 =

-1.0700

A8 =

0.1844

A3 = -0.5339

%

= 0.1056

A4 =

0.01569

Alo

= 0.6134

A5 = -0.05165

Al1

= 0.7210

n


4/16

4


SPE 14265

~ calculated Z factor iS obtalP.-

-d by utilizing Eqs.

~ and 15 to determine pseudo-critical pressure and

mperature.

This is evident in Figs. 9 and 10 where

rerage absolute

error in

calculated Z factor is

duced to 1.20%.

In 1959, Stewart, Burkhardt

and Voo20 (SBV)

lveloped and compared 21 different sets of mixing

ties for determining pseudo-critical pressure and

xnperature.

Overall,

they found the best method for

Ilculating pseudo-critical constants is given by the

)iiowlng equations:

J = l/3Zyi”(Tc/Pc)i +

(2/3).[Eyi”(Tc/Pc)~”5]2 _ . . . . . . (16)

K=~yi.(Tc/Pc0”5)i . . . . . . . . . . . (17)

Tpc

=K2/J . . . . . . . . . . . . . . .(18)

Ppc

=Tpc/J . . . . . . . . . . . . . .

.(19)

These equations are essentially

-qu~.:=~ep.~Q ~’e

>mbination rules proposed by Joffe

16.

In 1949 but are

~:;;}?nally ‘impler.” ln 1963’ ‘atter andevaluated 8 different combination rules and

Included that the SBV rules provide more satisfactory

?Sults

over more

complicated

rules

utilizing

iditional correlating parameters. Both Stewart et

1. and Satter and Campbell noted a decrease in the

>thod’S

accuracy

when carbon dioxide or hydrogen

llfide are present in the gas.

Figs. 11 and 12 show the increased accuracy in

~lculated Z factors

as a result of using the SBV

lles as opposed to the results obtained from using

my’s combination rules (Figs. 7 and 8).

The average

>solute error amounts to 1.31%.

However,

the errors

re

still

larger

than

those obtained from the

>eudo-critical property -

gas gravity relationships.

~oking at Figs.

13 and 14, it can be seen that there

s an increasing deviation at the end points

xresponding to gases

with

high

heptanes-plus

mcentrations. Therefore,

substantial improvement in

~lcuiated z factcrs C.s?lbe

cbtained by minimizing

lese deviations. This is best accomplished utilizing

mpirically derived adjustment factors applied to the

W “J” and “K” terms.

J’=J-EJ . . . . . . . . . . . . . . . .(20)

K’=K-cK . . . . . . . . . . . . . . . .(21)

The terms,

CJ and CK,

were derived using multiple

zgression analyses resulting in Eqs.

23 and 24.

sptanes-plus concentrations of up tn 14.27% were used

n the

development of

these

equations so

the

ijustment parameters should be suitable for all

sses.

FJ = (i/3)”iy”(Tci’Pc)]C7++

(2/3)-[Y-(Tc/Pc)0”5]:7+ . . . . . . . . (22)

‘J =

0.6081.FJ + 1.1325.FJ2 -

14.004.FJyC7+ + 64.434.FJy~7+ . . . . . (23)

EK .

(Tc/Pc0”5)

~7+”[0.3129”yC7+ -

4.8156*y 7+ +

27.3751”y~7+] . . . . . . . . . . . . (24)

The pseudo-critical pressure and temperature are

:alculated from Eqs.

18 and 19 using the adjusted

Values,

J’ and K’.

The adjusted pseudo-critical

constants

are plotted againat the “inferred”

pseudo-critical values in Figa. 15 and 16. The

sverage

absolute

error

of

these

adjusted pseudo-

:ritical pressures and temperatures amounted to 1.24%

.-

and i.72z, respectively.

Mere importantly} subsequent

calculations

of z factors evidence the increased

sccuracy of the modified SBV method as shown in Figs.

17 and 18 where the average absolute error i

:alculated Z factor is reduced to 0.95%.

Table 3 provides a summary of the accuracy of the

calculated Z factors for the different combination

rules over several ranges of

gas gravity. The

nodified SBV method consistently yields more accurate

results for the higher specific gravity reservoir

gases.

CONCLUSIONS

As a result of the work performed for this paper,

the following has been concluded:

1.

Significant improvements in

the

accuracy of

calculated Z factors from the Standing-Katz chart can

be obtained,

particularly for high molecular weight

reservoir gases.

The improvement is the result of

newly defined methods for calculating pseudo-critical

pressure and temperature.

2. Pseudo-critical

property -

gas

gravity

relationships are established which are suitable fo

all reservoir gases and provide more accurate results

than those offered from relationships derived with

Kay’s rules.

3. The Stewart, Burkhardt, and Voo (SBV) combination

rules, together

with empirical

adjustment factor

related to the

presence of

heptanes-plus,

significantly improve the acd~racy ef calculated Z

factor.

Overall, this method provides results almost

three times more accurate than those obtained using

Kay’s combination rules. For high molecular weight

reservoir gases (i.e.yg > 1.25), the modified SBV

rules give Z factors over eight times more accurate.

4.

Kay’s

combination rules

should not be used t

determine the pseudo-critical pressure and temperature

for reservoir gases with specific gravities greater

than about 0.75. This method consistently results i

underpredicted Z factors with errors ranging as high

as 15%.

5.

The Lee-Kessler equations

should be used t

calculate the critical pressure and temperature fo

the heptanes-plus fraction.

6. The Wichert and Aziz method should be used t

adjust pseudo-critical pze s’urs

and

temperature fo

the presence of carbon dioxide in the gas mixture.


5/16

SPE 14265

R. P. SUTTON

5

NOMENCLATURE

A.

B=

J=

K=

M=

P=

Pc =

PCC7+ =

Ppc =

‘pr =

T=

Tb =

Tc =

~cc7+ =

Tpc =

‘pr =

Yi =

YL.7+=

z=

E=

Y=

Yg =

P= =

Ei =

E=

lE/=

u=

mole fraction (C02 + H2S)

mole fraction H2S

SBV parameter, Tpc/Ppc, “R/psia

SBV parameter, Tpc/Ppc0”,5,0R/psia0”5

molecular weight, lb-mole

pressure, psia

critical pressure, psia

critical pressure of heptanes-plus fraction,

psia

pseudo-critical pressure, psia

pseudo-reduced pressure

temperature,

“R (“F + 459.47)

normal boiling point temperature, “R

critical temperature, “R

critical temperature of heptanes-plus

fraction, “R

pseudo-critical temperature, ‘R

pseudo-reduced temperature

mole fraction of component “it

mole fraction of the heptanes-plus component

compressibility factor

adjustment factor

specific gravity, (water=l)

gas specific gravity, (air=l)

reduced density

calculated - measured

measured

x 100, percent error

ns

average percent error

+,

average absolute percent error

[=%0”5

n = number of observations

standard deviation

(absolute standard

deviation determined

using absolute error and

average absolute error)

aCKNOWLEDGEMENTS

The author would like to thank the management of

4arathon Oil Company for permission to publish this

>aper.

John Neal with Weatheriy ‘~b~rat~iie~, Ific.

should be recognized for contributing a significant

?ortion of the laboratory data.

Finally, the author

.. ...

-- _,

?OUld LLK6? ~0 CkItiIIK ~Oiig k@~.~G~L

ad Ecb P~rsQns for

:heir technical support

and

help

during the

undertaking of this project.

U FERENCES

1.

Brown, G.G.: “The Compressibility of

I- Pure Gases,” Pet. Eng. (Jan.,

2. Brown, G.G. and Holcomb, D.E.:

“The

Gases, Part

940) 21-24.

Compressibility of Gases, Part 11 - Gaseous

Mixtures,” Pet. Eng. (Feb., 1940) 23-26.

?

Rv.wll

-.

“ . . . .

G.G,, Katz, D.L., Oberfell, G.G., and

Alden,’R,C. : Natural Gasoline and The

Volatile Hydrocarbons, Natural Gas. ASSOC. of

America,

Tulsa, OK (1948) Chapts. 2 and 4.

4. Cavett, R.H.: “Physical Data for Distillation

Calculations - Vapor- Liquid Equilibria,”

Proc. 27th Mid-Year Meeting, API, San

Fransico, CA (1962) 351-366.

5.

Dranchuk, P.M., Purvis, R.A. and Robinson, D.B.:

“Computer Calculation of Natural Gas

Compressibility Factors Using the Standing

and Katz Correlations,” Institute of Petroleum

Technical Series, No. IP74-008 (1974) 1-13.

6.

Dranchuk, P.M. and Abou-Kassem, J.H.:

“Calculation of Z Factors For Natural Gases

Using Equations of State,” J. Cdn. Pet. Tech.

(July-Sept., 1975) 34-36.

7. Engineering Da tiEmit, 9th EditiC t,GES

Processors Suppliers Assn., Tulsa, OK (1972)

Sec. 16.

8.

Hall, K.R. and Yarborough, L.:

“A New Equation

of State for Z-Factor Calculations,” Oil and

Gas J. (June 18, 1973) 82-85, 90, 92.

9.

Hall, K.R. and Yarborough, L.:

“How to Solve

Equation of State for Z-Factors,” Oil and Gas

J. (Feb. 18, 1974) 86-88.

—

10.

Joffe. J.: “Commessibilities of Gas Mixtures.”

Ind. Eng.

Chern.(July, 1947) 837-838. -

11.

Katz, D.L., Cornell, D., Kobayashi, R.,

Poettmann, F.H., Vary, J.A., Elenbaas, J.R.,

and Weinaug, C.F.:

Handbook of Natural Gas

Engineering, McGraw-Hill Book Co., NY (1959).

12.

Kay, W.B.: “Density of Hydrocarbon Gases and

Vapors at High Temperature and Pressure,” Ind.

Eng.

Chem. (Sept.,

1936) 1014-1019. —

13.

Kessler, M.G. and Lee, B.I.: “Improve Prediction

of Enthalpy of Fractions,” Hyd. Proc. (March,

1976) 153-158.


6/16

A


SPE 14265

. .

.

).

Matthews, T.A.,

Roland, C.H., and Katz~ D.L.:

“High Pressure Gas

Measurement,” Petrol.

Refiner (June, 1942) 58-70.

j. Roberts, D.S., Clark, C.R.~ and swift) ‘“:

“PVT

Behavior for Mixtures of Methane, Propane, and

0. u“dr~~grbQns3VS

Sot. Pet. En- (Sept.,

; 6?) 338-342.

~.

SAS User’s Guide: statistics, SAS ~n~~i~~te

Inc., Cary, North Carolina (1982) 15-35.

7. Satter, A. and Campbell, J.M.:

“Non-Ideal

Behavior of Gases and Their Mixtures,” SM.

Pet. Eng.

J. (Dec.j 1963) 333-347.

1. Standing, M.B. and Katz, D.L.:

“Density of

Natural Gases,” Trans. AIME (1942) Vol. 146,

140-149, Phase Behavior SPE Reprint Series No.

15 (1980) 119-128.

3.

Standing, M.B.: Volumetric and Phase Behavior of

Oil Field Hydrocarbon Systems, 9th printing,

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Dallas, TX (1981).

.

iABLE 1

20.

Stewart, W.F., Burkhardt, S.F., and

VO08 ‘“:

“Prediction of Pseudocritical Parameters for

4ixtures,”paper presented at the AIChE

Meeting, Kansas City, MO (May 18, 1959).

21.

Takacs, G.:

“Comparisons Made for Computer

Z-Factor Calculations,” Oil and Gas J. (Dec.

20, ‘--e’ “ ‘L

Y/OJ

U4-UU.

22.

Whitson, C.H. and Torp, S.B.:

“Evaluating

Cofistan~Vc~uw Depletion Data~” J. _Pet.

~ (March, 1983) 610-620.

~~.

Whitmni C H. :

“Effect of Physical Properties

Estimation on Equation-of-State Predictions,t;

paper SPE 11200 presented at the 57th Annual

Fall Technical Conference and Exhibition, New

Orleans, LA (Sept. 26-29, 1982).

24.

Wichert, E. and Aziz, K.:

Sour Gases,” Hyd. PrOc.

~~g-~~~e

S1 Metric Conversion Factors

‘tCalculateZ’s for

(May, 1972)

degree F (°F-32)/l.8 = “C

psi x 6.894 757 E+OO = kPa

Component

Carbon Dioxide

Nitrogen

Methane

Ethane

Propane

Isobutane

n-Butane

Isopentane

n-Pentane

Hexane

Air

PHYSICAL PROPERTIES

OF

DEFINED COMPONENTS

Critical

Molecular Weight

Pressure, psia Temperature,

“R

44.010

28.013

16.043

30.070

44.097

58.124

58.124

72.151

72.151

86.178

28.964

1,071.0

493.0

667.8

707.8

616.3

529.1

550.7

490.4

488.6

436.9

---

TABLE 2

EFFECT OF HEPTANES-PLUS CHARACTERIZATION

STATISTICAL ACCURACY OF COMPRESSIBILITY FACTOR

Average % Error

Standard Deviation

Average Absolute %

Standard Deviation

547.57

227.27

343.04

549.76

665.68

734.65

765.32

828.77

845.37

913.37

---

ON THE

CALCULATIONS

Critical Property Correlation

Matthews,

Roland & Katz

-2.40

Cavett

-2.31

Lee-Kessler

-2.29

3.77 3.58

3.58

Error

2.90

2.80

2.78

3.41

3.21

3.21


7/16

SPE 14265

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