1995 j Assessment of the Pvt Correlations for Predicting the Properties of Kuwaiti Crude Oils

PETROLEUM SCIENCE & ENGINEERING

ELSEVIER Journal of Petroleum Science and Engineering 13 ( 1995) 219-232

Assessment of the PVT correlations for predicting the properties of Kuwaiti crude oils

Adel M. Elsharkawy, Ahmed A. Elgibaly, Abbas A. Alikhan Petroleum Engineering Department, Kuwait University, P.O. Box 5969 &fat 13060, Kuwait

Received 30 September 1994; accepted 8 March 1995

Abstract

Several correlations have been proposed for determining PVT properties. Limitations concerning the validity of these corre-

lations for different types of hydrocarbon systems, accuracy, range of applicability, corrections for non-hydrocarbons contents, etc., have been controversial.

Because crude oils from different regions have different properties, it is recommended to assess the accuracy of the available

correlations. The present study is concerned with the assessment of these correlations for a variety of oils from Kuwaiti fields. The study

evaluated recently developed correlations in the Middle East region and the Arabian Gulf as well as those most often used. The limitations of these correlations have been analyzed. Forty-four individual crude oil samples from Kuwaiti oil fields were used

in this study. Corrections due to the presence of non-hydrocarbon gases, adjustment to oil composition, and correction of gas gravity to common separation conditions were taken into consideration. It was found that Standing’s correlation showed the best accuracy for predicting the bubble-point pressure among all others, though such accuracy is beyond desirable engineering limits.

All the correlations examined in the present study showed a comparable accuracy in predicting OFVF at the bubble point with

Al-Marhoun’s correlation having the least deviation.

1. Introduction

The accurate determination of the PVT properties of

the reservoir fluid, such as bubblepoint pressure, solu-

tion GOR and oil FVF, is necessary for the formation

evaluation of hydrocarbon reserves, reservoir perform-

ance, production operations and the design of produc-

tion facilities. Although these PVT properties can be

measured in the laboratory using collected bottom-hole

samples, it may occasionally be required to make predictions with only data on reservoir pressure,

temperature, gas gravity and oil API gravity available.

Several correlations have been developed in the lit-

erature to estimate reservoir fluid properties. The most

0920.4105/95/$09.50 0 1995 Elsevier Science B.V. All rights reserved SSDlO920-4105(9S)OOO12-7

commonly used correlations are those given by Stand-

ing (1947, 1962, 1977). Standing’s correlations are based on solution gas-

oil ratio, gas gravity, oil API gravity and reservoir temperature. Twenty-two different crude oil and gas mixtures from California were used in developing his

correlation. He reported an average relative error of

4.8% for the bubblepoint pressure and an average rel-

ative error of 1.7% for the formation volume factor.

The ranges of the data used in developing Standing’s correlation are given in Table 1.

Lasater ( 1958) developed a correlation for the bubblepoint pressure based on Henry’s law. He correlated mole fraction of gas in solution to a bubblepoint pressure factor. Lasater’s correlation is based on I 37 inde-

220 A.M. Elsharkawy et al. /Journal oj’Petroleum Science and Engineering 13 (1995) 219-232

pendent crude oil and gas mixtures from Canada, western and Mid-Continental US and South America.

Lasater reported an average error of 3.8% for his correlation. The ranges of data used in Lasater’s correla-

tion are also given in Table 1.

Vasquez and Beggs ( 1980) developed a PVT correlation based on 600 PVT laboratory analyses from

different oil fields representing a wide variety of loca- tions in the world. Their correlation is unique in covering a wide range of crude oils with different physical

and chemical characters. This, in the meantime, repre- sents a weakness in the Vasquez and Beggs correlation because the composition of crude oil (classified as par-

affinic, naphthenic or aromatic) and the concentration

of non-hydrocarbon gases vary with each location. Fur-

thermore, they found that separation conditions affect

gas gravity which is a strong correlating parameter in their correlation. For this reason, they recommended

adjusting the gas gravity to a separator pressure of 100 psi. Vasquez and Beggs presented two correlations;

one for crudes having API gravity higher than 30 and another for crudes having API gravity equal or less than

30. Their correlation has an average error of 4.7% for the formation volume factor. It is important to note that

they reported the average temperature rather than the

temperature range used in developing their correlation.

Glaso ( 1980) developed correlations for calculating

the bubblepoint pressure and the oil formation volume factor, OFVF. A total of 45 oil samples mostly from

the North Sea region were used in his correlation. He

presented an adjustment to the API gravity term when his correlation is used with oils of different composi-

tions. The adjustment of API gravity is a function of residual oil gravity and dead oil viscosity from a differential test. Glaso reported that his correlations give an average error of 1.28% for bubblepoint pressure

and - 0.43% for OFVF. Al-Marhoun ( 1988, , 1992) developed correlations

for calculating the bubblepoint pressure and OFVF. He

used 69 bottom-hole samples collected from the Middle East. As shown in Table I, Al-Marhoun’s correlations have the advantage of covering a wide range of non- hydrocarbon gases. He reported an average error of 0.03% for bubblepoint pressure and - 0.01% for the oil formation volume factor.

Dokla and Osman ( 1992) presented correlations for bubblepoint pressure and oil formation volume factor. Fifty data points from UAE reservoirs were used in

their correlation. They showed an average error of

0.45% for bubblepoint pressure and 0.023% for oil formation volume factor.

Labedi ( 1990) developed correlations for oil for-

mation volume factor, density and compressibility. His

correlations are based on pressure and temperature of

the first stage separator, total GOR, gas gravity, oil API and reservoir temperature. Labedi’s correlation for

OFVF is based on 128 oil samples collected from Afri- can countries, mostly from Libya. He reported an aver-

age error of 0.003% and a standard deviation of 2.96% for the OFVF.

Ostermann et al. (1983) evaluated the Standing,

Lasater, Vasquez and Beggs, and Glass correlations for their accuracy in predicting PVT properties for the

“Alaskan crudes”. They used PVT results of eight

samples from flash and differential separation in their

evaluation. Ostermann et al. found that Glaso’s correlation for bubblepoint pressure and Standing’s correlation for oil FVF are the most accurate.

Suttan and Farshad (1990) studied Standing’s and Glaso’s correlations for their ranges of accuracy in esti- mating the PVT correlations of the “Gulf of Mexico

crudes” . They used 3 1 different crude oil/gas systems

and adjusted differential PVT data to represent flash data for the correlations used in their study. Suttan and

Farshad found that Glaso’s correlation is better than

Standing’s correlation but the accuracy is undesirable.

The presence of non-hydrocarbon gas in surface-

produced gas has a significant effect on the prediction of bubblepoint pressure from PVTcorrelations. Lasater

reported that the estimated bubblepoint pressure decreases as the CO, content increases, while Glase, reported the opposite effect. Jacobson (1967) and Glaso found that bubblepoint pressure increases with

increasing N2 content but decreases with increasing H,S content.

Although each of the afored-mentioned correlations was developed for crude oils of a specific region, some

authors claim that their correlations adequately fit ran- dom PVT data and can be applied to crude oils from other geological areas. Most engineers prefer Stan- ding’s correlation for low API crudes and Lasater’s correlation for high API crudes.

Glaso tried to extend his correlation to oils with different paraffinity. His correlation became of limited use because residual API gravity and dead oil viscosity from differential tests may not be available. It is impor-

A.M. Elsharkawy et al. /Journal of Petroleum Science and Engineering 13 (1995) 219-232 221

Table 1 Data ranges for published PVT correlations and present study

Standing

(1947)

Lasater

(1958)

Vasquez and Beggs

( 1980)

YAW 5 30 YAM ’ 30

Glaso

( 1980)

Al-Marhoun Dokla and Labedi Present study (1988) Osman (1990)

(1992)

Bubblepoint 130-7000 48-5680 154572 156055 165-7142 130-3573 590-4640 3x7-4375 pressure (psia)

Bubblepoint 908-48,800 335-39,670 105-71,931 105-42,288 1152- 908-24.954 4 120- 2:! 14-30555

pressure (Kpa) 49,880 32,406

Temperature (“F) 100-258 82-272 162” 180 80-280 74240 190-275 loo-306 130-250

Temperature (“C) 38-125 28-133 72” 82” 27-138 23-l 15 88-135 38-152 55-121

FVF, RBISTB 1.024-2.15 - 1.042-1.545 1.028-2.226 1.032-2.588 1.032-1.997 1.216-2.493 1.040- 1,057-l .770

(m3/Stdm7) 3.092

Solution GOR 20- 1425 3-2905 O-831 O-2199 90-2637 26-1602 181-2266 13-3533 34-1400

(SCF/STB)

Solution GOR 3-254 O-517 O-148 O-392 16470 5-285 32-403 2-680 6-250

(m’/Stdm’)

Tank-oil gravity 16.5-63.8 17.9-51.1 15.3-30.0 30.6-59.5 22.3-48.1 19.40-44.6 2840.3 32.2-48 20-45

(“API)

Gas gravity 0.59-0.95 0.574-1.223 0.511-1.351 0.530-1.259 0,650-l ,276 0.752-1.367 0.798-1.290 0.698- 0.663- 1.064

(air= 1) I.473

CO2 in surface < 1% 0 _ _ 0.00-16.38 0.37-8.9 - 0.0-6.9

gases (mol%)

Nz in surface 0 0 0.00-3.89 0.1-1.85 - 0.0-4.4

gases (mol%)

H2S in surface 0 0 _ 0.00-16.13 O-6.02 - 0.0-2.44

gases (mol%)

“Average temperature

-: Unavailable data.

tant to mention that the number of separation stages

and conditions affect the input data into any PVT correlation.

Before a given PVT correlation is selected for use in

reservoir calculations, it is necessary to examine the

range of data, covered by such a correlation, the composition of oil and gas used in developing the correlation, and compare these data with the reservoir under

study. The objective of the present study is to examine the

PVT correlations available in the literature, especially the recently developed correlations for oils in the Mid-

dle East, to assess their accuracy for predicting the PVT properties of the Kuwaiti crudes.

2. The present study

Seventy-four measured PVT data points, representing 44 different crude oil/gas systems from Kuwaiti

oil fields, were utilized in the present study. The bub-

blepoint pressure, bubblepoint oil FVF, solution GOR,

gas gravity and oil API were measured by flash and

differential separation for 30 crude oil/gas mixtures.

PVTdata for the remaining 14 mixtures were measured

by differential separation only, Also, dead oil viscosity

by differential separation and concentration of non-

hydrocarbon gases for the 44 crude oil/gas systems,

were available in the present study (see Table 4 in

Appendix D) . It is worthy to note that these mixtures

represent samples from fields in the west, south and

southeast of Kuwait.

Crude oils from the west Kuwaiti field used in this

study are characterized by high API gravity (37-43”).

The surface gas contains O-4.4% N,, 26.9% CO, and

O-2.5% H,S. South and southeast Kuwaiti fields are

characterized by medium gravity crude oils (2O-

35”API), and surface gas contains very small amounts

of N2 and COZ, O-l% and o-0.68%, respectively, with

A.M. Elsharkawy et al. /Journal of Petroleum Science and Engineering 13 (199.5’) 219-232

1 10 100 1000

Flash GOR, m3/Std ,3

Fig, 1, Flash versus differential GOR for Kuwaiti crudes.

1.800

1.600

Bobdaa 1.057

1.000 1.200 1.400 1.600 1.800 2.000

Flash OFVF, m3/Std m3

Fig. 2. Flash versus differential OFVF for Kuwaiti crudes.

Table 2

Statistical accuracy of bubblepoint pressure calculations for the Kuwaiti crude oils

Standing Lasater Vasquez-Beggs Glaso Dokla-Osman Al-Marhoun

Average error (%) 7.032 1.32 15.21 27.52 -6.3 9.96

Average absolute error (%) 10.85 14.01 16.4 27.66 16.86 22.64 Standard deviation 14.66 17.96 21.87 35.02 20.43 28.42

A.M. Elsharkawy et al. /Journal of Petroleum Science and Engineering I3 (1995) 219-232 223

Experimental bubblepoint pressure, Kpa

0 YXM IWOO ,5wo 2woo 25wo 300 35~

Experimental Bubblepoint Pressure, psi

Fig. 3. Crossplot for bubblepoint pressure.

224 A.M. Elsharkawy et al. /Journal ofPetroleum Science and Engineering 13 (1995) 219-232

-15 -5 5 15 25 J5

(b)

Rclativc Error %

a: Standing Correlation

Rclativc Error %

b: Laster Correlation

-__-

Cc) 10 -

.___._ _ 7

i 5-

/&.

_--

1 -1

o- -- _----_I

20

s 10

0

-10 0 10 20 30 40 50 0 20 40 60

Relative Error % Relative Error %

C: Vasquez and Beggs Correlation d: Glaso Correlation

I

-33 -10 10 xl 50

Rclativc Error %

.zDoklaand OsmanCorrdacion

IS

a I ”

/

/ \

1 1 I 1 I I

-Xl -10 10 30 50 70

Relative Error %

f AI-Marholm Comlation.

Fig. 4. Error distribution for bubblepoint pressure.

Table 3

A.M. Elsharkawy et al. /Journal of Petroleum Science und Engineering 13 (1995) 219-232 22s

Statistical accuracy of OFVF calculations for the Kuwaiti crude oils

Standing Labedi Vasquez-Beggs Glas0 Dokla-Osman A-Marhoun

Average error (%) 1.20 1.21 0.42 - I .31 0.60 - 0.26

Average absolute error (%) 3.17 3.11 3.41 3.19 3.38 2.12

Standard deviation 4.23 4.16 4.59 4.19 4.68 3.78

no H,S. Flash PVTdata were plotted versus differential

data for GOR as shown in Fig. 1 and for OFVF as shown in Fig. 2. These figures were used to adjust differential PVT data to represent flash for the few

mixtures that were not measured by flash separation.

The ranges of the data used in developing the seven

correlations examined in this study are compiled in Table 1. It is clear that these correlations have some

limitations, in that their data ranges do not cover the

properties of the Kuwaiti crudes. The Standing, Dokla

and Osman, Al-Marhoun, and Labedi correlations do

not cover the gas gravity range of the Kuwaiti crudes, while the Vasquez and Beggs, Al-Marhoun, and Dokla

and Osman correlations have limitations on the temperature range used in developing their correlations.

Finally, Dokla and Osman, and Labedi covered a nar- row range of tank-oil API in developing their correla-

tions.

3. Results and discussion

The prediction of the bubblepoint pressures were

made using the Standing, Lasater, Vasquez and Beggs, Glaso, Dokla and Osman, and Al-Marhoun correlations. The equations used in predicting bubblepoint

pressures are given in Appendix A. The separator pres-

sure and temperature were used to adjust the gas gravity

for the Vasquez and Beggs correlation. The API gravity and dead oil viscosity from differential tests were used to adjust the API gravity term as recommended by

Glaso. It was found that adjusting the API gravity for Glaso’s correlation did not improve its prediction capa- bility of the bubblepoint pressure. Therefore, it was

decided not to adjust the API gravity used in Glass’s

correlation in the present study. This is in agreement with the findings of Suttan and Farshad who computed a correction multiplier of 0.94 for the Gulf of Mexico crudes and reported that the use of this correction decreases the accuracy of Glaso’s correlation.

The estimated bubblepoint pressures were corrected for the presence of non-hydrocarbon gases for all correlations except those given by Dokla and Osman, and Al-Marhoun. The equations used in correcting the bub-

blepoint pressures are given in Appendix B. The deci-

sion not to correct the bubblepoint pressure estimated from the Al-Marhoun, and Dokla and Osman correla-

tions is based on the fact that the crude oils used in

those correlations contained non-hydrocarbon gases in concentrations similar to those measured for the

Kuwaiti crudes. Predictions of the bubblepoint oil FVF

were made using the Standing, Labedi, Vasquez and Beggs, Glass, Dokla and Osman, and Al-Marhoun cor-

relations. (The equations are reported in appendix C.)

4. Accuracy of the correlations

The accuracy of each correlation was determined by

studying the statistical errors (Walpole and Myers, 1985). The error analysis comprises the average per-

cent relative error, average absolute relative error and

standard deviation. The accuracies of the correlations were also checked by crossplots of experimental versus

estimated PVT parameters and plots of error distribution histograms with overlaid normal distribution

curve.

It is important to note that the average percent relative error can be misleading if the data points distribute

equally on both sides of the unite slope line. In such case, the average percent relative error can be very low but the calculated and measured values can be very different.

5. Accuracy of bubblepoint pressure correlations

Table 2 presents the errors and standard deviations for the six correlations used in this study. It is clear from this table, that Standing’s correlation shows the

226 A.M. Elsharkawy et al. /Journal of Petroleum Science and Engineering 13 (1995) 219-232

2.000

1.900

1.600

1.700

1.600

1.500

1.400

1.300

1.200

(Q 1.100

1.000

1.900

1.600

1.700

1600

1.500

1.400

1.300

,200

(d)

1.100

1000

1900

1.900

1.700

1.600

1.500

1.400

1.300

1.200

1.100

@I 1.000

2.000

1.900

1.600

1.700

1.600

1.500

1400

1.300

1.200

(e> '.'O"

1000

1900'

1 BOO

I 700

1600

1500

1.400

1300

1.200

1.100

Cc) 1.000

: 1.900

1.600

1.700

1.600

1.500

I.400

1.300

1.206

1.100

Cal l.ooa

Correlations a. 1 Standing b. Labcdi- C. Vasquez-Beggs l- d. Glas$

: Dokla-Osman Al-Marhoun

I

I.600 1.100 1.260 1.300 1.400 1.500 1.600 I.700 1.606 ,.900 r600

Experimental OFVF, m3/Std m3

Fig. 5. Crossplot for bubblepoint OFVF.

A.M. Elsharkawy ef al. /Journal ofPefroieum Science and Engineering 13 (1995) 219-232

40

30

i 2o B 6 10

0

20

0

20

s

P s 10

E

.! !I (4

Relative Error %

a: Standing Correlation b: Labedi Correlation

-5 0 5 10 15

Relative Error %

c: Vasquez and Beggs Correlation

-10 -5 0 5 10 15 -5 0 5 10 15 Relative Error % Relative Error %

e: DoWa and Oman Correlation

20

c 5 = 10 s

6

0

20

0

25

-a -3 2 7 12 1;

Relative Error %

Relative Error %

d: Glaso Correlation

L fi Al-Marhoun Cordation

Fig. 6. Error distribution for bubblepoint OFVF


lowest errors and standard deviation followed by the

Lasater, and Dokla and Osman correlations, while the

Glaso, Vasquez and Beggs, and Al-Marhoun correlations show poor accuracy.

Crossplots of the bubblepoint pressures are pre-

sented in Fig. 3. These plots are grouped in one figure

with shifted vertical scales for the purpose of compar- ison. This figure demonstrates that the Standing and

Lasater correlations depicted closer scatter to the unite

slope line of perfect correlation than the others. The

Dokla and Osman, and Al-Marhoun correlations show wide scatter around the 45” line. The Glaso and Vas-

quez and Beggs correlations revealed their overesti-

mation. Error distribution plots are presented in Fig. 4. These

plots illustrated that Standing’s correlation has the

smallest relative error range, from - 15 to 35%, followed by Lasater’s correlation with relative error range

from - 20 to 50%, and having mean values about 7%

and 9%, respectively. In addition, the Vasquez and Beggs, and Glass correlations show wider error range

and peaks at 15% and 30%, respectively. This indicates a high overestimation and stronger positive skewed

error distribution than the others. In conclusions all six

correlations failed to predict acceptable bubble-point

pressures for the Kuwaiti crudes.

6. Accuracy of oil FVF correlations

Table 3 presents the errors and standard deviation

for the calculated OFVF. Al-Marhoun’s correlation

shows the smallest average relative error, average abso-

lute error, and standard deviation followed closely by

the others.

Crossplots of bubblepoint OFVF (Fig. 5) illustrate that all the correlations have a scatter around the perfect correlation line. However, Al-Marhoun’s correlation shows closer scatter to the perfect correlation line than

the others. Error distribution plots presented in Fig. 6 reveals

that Al-Marhoun’s correlation has the smallest error

range and the normal curve peak is close to zero. The other correlations show comparable error ranges and skewness.

Comparing Figs. 4 and 6, it is obvious that the bubblepoint OFVF correlations showed better accuracy than the bubblepoint pressure correlations, because by

nature of their values, bubble-point OFVFs have a nar-

row range of values compared to their absolute values. This is very different from the values of bubble-point

pressures which have a wide range compared to their possible absolute values. From this observation it can

be seen that it is highly possible that the bubble-point OFVF correlations would give the estimates that are

much closer to the measured values than those given

by the bubble-point pressure correlations and all relative errors calculated for the bubble-point OFVF esti-

mation can be much lower than those for the bubble-point pressure estimation.

7. Conclusions

The objectives of the present study are to character- ize the Kuwaiti crude oils and study the recently devel-

oped correlations in the area and those most often used.

It also aims at assessing the accuracy of these correlations for their applicability in predicting the PVTprop- erties of the Kuwaiti crudes.

Although Standing’s correlation was developed

from Californian crudes and Lasater’s correlation from

North and South American crudes, and both contained essentially no non-hydrocarbon gases, they yield the

least errors for the bubblepoint pressures, but such

errors are unacceptable. All the OFVF correlations studied showed a very

close range of accuracy. The Al-Marhoun, and Dokla and Osman correlations (although developed for Mid-

dle East and UAE crudes, respectively, with identical

ranges of non-hydrocarbon gases and API gravity, and

sometimes produced from the same formation) did not

satisfactorily estimate the bubblepoint pressure for the

Kuwaiti crudes. Because all published correlations con- sidered in this study failed to give satisfactory predictions, it is recommended that a correlation for bubble point pressure and bubble point OFVF be developed

for the Kuwaiti crudes.

8. Nomenclature

B ob

B,’ YAP1

Oil FVF at bubble point pressure, RB / STB [ res m3/stock-tank m3] Correlating number for calculating Bob Tank oil gravity (“API)

A.M. Elsharkawy et al. /Journal of Petroleum Science and Engineering 13 (1995) 2 I9-232 229

YiPI

* YAPIcon

YAPIcon

Residual oil API from differential separation

Corrected residual oil API from differential separation

Corrected tank oil API from flash separation

Total gas specific gravity (air = 1 .O)

Total gas specific gravity from separator condition of 100 psi Tank oil specific gravity (water = 1 .O)

Effective tank oil molecular weight Reservoir pressure, Psia [ kPa] Bubble point pressure, Psia [ kPa]

Correlating number for bubble point

Bubble point pressure factor

Separator pressure, Psia [ kPa]

Solution GOR, SCF/STB [ Std m3/ stock-tank m”]

Reservoir temperature, “F [“Cl

Reservoir temperature “R [“K] Dead oil viscosity at reservoir temperature, cP [ mPa.s] Mole fraction of gas

9. SI metric conversion factors

“API= 141.5/( 131.5+ y,,) = gm/cm3 bbl x 1.589 873 E - 01 =m3

DegreeF (“F-32)/1.8 =“C Degree R “F + 460 =“R

psia X 6.894 757 EOO = kPa SCF/STB Y 1.801 175 E - 01 = Stdm3/m3

Acknowledgements

The authors would like to thank the Ministry of Oil and the Kuwait Oil Company (KOC) for providing the information used in the present study.

Appendix A

Bubblepoint pressure correlations

Standing

P, = 18.2 [ (R”)o.“3antilog

(0.00091?-O.O125y,,,) - 1.41

Lasater

p b

= W(T+459.67)

Yg

M,=725.32143- 16.03333YApI+0.09524$.p1

p,=O.38418- 1.20081Y,+9.64868Y;

Vasquez and Beggs

Cl& P,= (- antilog - c3YAPI ) I/c2

Ygs T+ 459.67

YAPI 2 3o

C, = 27.64 c, = 1.0937

C,= 11.172

YAP1 > 30

C, = 56.06 C,= 1.1870

c3 = 10.393

G Las@

Pb = antilog [ 1.7669 + 1.7447 log p;

-0.30218(logp,‘)*]

where:

pb’ = ($8190.172

YS ‘YAP1 - 0.989

L YAPIcom = antilog[ up&]

a=3.184(10-“)T3.44

b= [ 10.213(logT) -36.4471-l

Y~PIcolT YAPIcorr

=-

YiPI YAP1


Al-Marhoun

P, = 5.38088

X 10-3~0.715082 - 1.877840 5 7,

7.1437 Y”

1.32657 T,

Dokla and Osman

P, = 0.836386

X ~~4y,l.0104Y~107YY'~,0.Y52S84~7Z4047

Appendix B

Effect of Non-hydrocarbon gases

Glas#

Nitrogen:

C,,= l.O+ [( -2.65x 10-4y,,I+5.5x 10-3)T

+(0.0931yA,,+0.8295)]Y,,,2+[(1.954

X lo-“$$p)T+ (O.O27y,,,-2.366)] (YN2)2

where Y,, is the mole fraction of nitrogen. Carbon dioxide:

C co2 = 1.0 - 693.8Yco2T - ‘.s33

where Y,,, is the mole fraction of C02. Hydrogen sulfide:

c H2S= l.O- (0.9035 +0.0015y,&Y,,,

+".019(45-~,4PI)(yH2S)2

C= 15.85 +2.86N,,-0.,07T

Appendix C

OFVF correlations

Standing

Vasquez and Beggs

B,,b=1.0+C,R,+C2(T-60)(T)

+C R (T-60)(+ 3 s

%

API I 30 API> 30 C1 =4.677x 1O-4 C, =4.670x 1O-4 c, = 1.751 x 1o-s c,= 1.100x 1o-s c,= -1.8106X 1o-8 c3 = 1.337 x lo9

Glas@

B,, = 1 .O + antilog

[ -6.58511+2.9132910gB~b-0.27683(logB,’,)2]

where:

B,‘b = R,( yg/y,)o.526 + 0.968T

Al-Marhoun

B,, = 0.497069 + 0.862963 X lo- 3T, + 0.182594

X 10-2F+0.318099x 10-5F2

where:

F= ~0.742390 .323294 -1.202040 s g Yo

Dokla and Osman

B,,=0.431935 X 10-l $0.156667

x 10p2T,+0.139775

X 10-2F+0.380525

x lo-‘F2

where:

Table 4

A.M. Elsharkawy et al. /Journal of Petroleum Science and Engineering I3 (1995) 219-232 231

Fluid property of the Kuwaiti crudes

No. Bubble point pressure Bubble point oil FVF Solution GOR Tank oil gravity Reservoir temp. Non-hydrocarbon gases

(Kpa) (m3/Std m3) (Std m3/Stock m’) (“C)

Flash Diff. Flash Diff. Nz (%) CO> (%) H,O(%)

1 17535

2 16645

3 15590

4 12706

5 13323

6 15241

7 10994

8 12535

9 2171

10 5069

11 4637

12 25618

13 18186

14 15652

15 17193

16 12878

17 16481

18 18111

19 10062

20 15138

21 15823

22 10912

23 11419

24 11521

25 11110

26 13131

27 13309

28 13199

29 18734

30 16439

31 19727

32 29331

33 17981

34 15617

35 11179

36 12672

37 19536

38 22741

39 19042

40 9007

41 17741

42 29968

43 13665

44 19625

I .704

1.664

1.634

1.383

1.385

1.510

1.292

I .368

1.057

1.138

1.127

1.533

I.416

1.338

1.355

1.243

1.350

1.273

1.020

1.243

1.342

I.238

1.270

1.269

1.226

I.227

1.330

1.199

1.325

1.969

1.936

1.859

1.519

1.522

I.681

1.399

1.500

1.076

1.178

1.149

1.671

1.454

1.369

1.438

1.279

I.437

1.493

1.197

1.280

1.407

1.235

I.311

1.289

1.267

1.323

1.332

1.289

I.411

I .470

1.590

1.710

1.470

1.320

I.240

1.300

1.530

1.610

1.450

1.250

1.450

1.770

1.260

1.520

183.6

169.9

157.4

89.6

88.0

126.3

80.9

104.7

6.1

31.0

24.6

180.4

111.8

98.0

112.2

70.9

99.0

135.0

42.6

75.9

98.8

69.5

82.8

88.2

54.0

82.8

90.7

67.0

128.2

246.5 0.814 115.6

232.4 0.812 121.1

209. I 0.818 121.1

127.5 0.828 120.6

118.1 0.823 116.7

192.5 0.838 95.6

104.7 0.836 104.4

130.9 0.822 116.7

6.9 0.920 71.1

40.2 0.910 81.1

29.4 0.917 81.1

213.4 0.852 85.6

133.7 0.861 87.2

115.2 0.872 76.7

129.5 0.874 81.7

79.1 0.906 80.0

127.9 0.73 82.2

138.6 0.869 80.0

54.7 0.930 73.9

89.4 0.904 80.0

117.4 0.883 81.1

86.4 0.872 54.4

98.3 0.856 56. I

94.4 0.859 56.7

72.7 0.872 55.6

103.7 0.859 55.6

107.7 0.862 57.2

108.1 0.873 57.2

129.8 0.887 73.9

132.7 0.880 78.9

175.6 0.890 95.6

249.3 0.860 94.4

131.8 0.870 88.9

95.8 0.890 78.9

57.9 0.920 78.9

83.9 0.906 76.7

157.6 0.860 82.2

185.0 0.860 89.4

125.4 0.890 98.9

63.8 0.900 77.8

134.5 0.860 77.8

236.9 0.860 93.9

79.1 0.910 77.8

151.0 0.860 88.9

0.20 3.63 0.16

0.16 3.92 1.66

0.29 3.67 2.44

0.21 2.09 0.20

0.18 2.12 0.11

0.00 3.91 1.37

0.13 2.35 0.06

0.78 2.09 0.84

4.40 4.4 1 0.00

0.49 6.90 1.21

0.67 6.80 0.82

0.03 0.63 0.00

0.39 0.68 0.00

0.32 0.39 0.00

0.30 0.30 0.00

0.35 0.43 0.00

0.40 0.45 0.00

0.48 0.42 0.00

0.83 0.43 0.00

0.52 0.15 ~3.00

0.29 0.4 1 0.00

1.310 0.68 0.00

I .030 0.15 IO.00

1.300 0.33 Il.00

0.710 2.83 0.00

0.00 2.81 0.00

1.650 0.92 0.00

0.760 0.28 0.00

1.70 2.70 0.00


404020 - 0.882605 F+.773572$. ‘yo

Labedi

Appendix D

Fluid property of the Kuwaiti crudes

The fluid properties of the Kuwaiti crudes are listed

in Table 4.

References

Standing, M.B., 1977. Volumetric and Phase Behavior of Oil Field

Hydrocarbon Systems. SPE. Richardson, Tex., 124.

Suttan, R.P. and Farshad, F.F., 1990. Evaluation of empirically

derived PVT properties for Gulf of Mexico crude oils. SPE Res.

Eng., (Feb.): 79-86.

Al-Marhoun, M.A., 1988. PVT Correlations for Middle East crude Vasquez, M.E. and Beggs, H.D., 1980. Correlations for fluid physical

oils. J. Pet. Technol., (May): 650-666; Trans. AIME, 285. property prediction. J. Pet. Technol., (June): 968-970.

Al-Marhoun, M.A., 1992. New correlation for formation volume Walpole, R.E. and Myers, R.H., 1985. Probability and Statistics for

factors of oil and gas mixtures. J. Can. Pet. Technol., 31(3): 22- Engineers and Scientists. McMillan Publishing Inc Co., New

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Dokla, M.E. and Osman, M.E., 1992. Correlation of PVT properties

for UAE crudes. SPE Form. Eval., (March): 4146.

Glaso, O., 1980. Generalized pressure-volume-temperature corre-

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Jacobson, H.A., 1967. The effect of nitrogen on reservoir fluid sat-

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Labedi, R., 1990. Use of production data to estimate volume factor

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Lasater, J.A., 1958. Bubble point pressure correlation. Trans. AIME,

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Ostermann, R.D., Ehlig-Economides,C.A. and Owalabi, O.O., 1983.

Correlations for the reservoir fluid properties of Alaskan crudes.

SPE 11703, presented at 1983 SPE Calif. Reg. Meet., Ventura,

Calif., March 23-25.

Standing, M.B., 1947. A pressure-volume-temperature correlation

for mixtures of California oils and gases. Drill. Prod. Prac. API,

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Standing, M.B., 1962. Oil-system correlations. In: T.C. Frick (Edi-

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1995 j Assessment of the Pvt Correlations for Predicting the Properties of Kuwaiti Crude Oils

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