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8/15/2019 Sutton Z Factor Paper SPE-14265-MS
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.,
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.
.
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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
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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
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COMPRESSIBILITY FACTORS FOR HIGH MOLECULAR WEIGHT RESERVOIR GASES
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.
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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.
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COMPRESSIBILITY FACTORS FOR HIGH MOLECULAR WEIGHT RESERVOIR GASES
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,
Society of Petroleum Engineers of AIME,
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
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SPE 14265
STATISTICAL ACCURACY OF
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