SPE 68230 A New Correlation for Gas-condensate Dewpoint Pressure Prediction A.A. Humoud, SPE, Saudi Aramco, and M.A. Al-Marhoun, SPE, King Fahd U. of Petroleum and Minerals
Copyright 2001, Society of Petroleum Engineers Inc. This paper was prepared for presentation at the 2001 SPE Middle East Oil Show held in Bahrain, 17–20 March 2001. This paper was selected for presentation by an SPE Program Committee following review of information contained in an abstract submitted by the author(s). Contents of the paper, as presented, have not been reviewed by the Society of Petroleum Engineers and are subject to correction by the author(s). The material, as presented, does not necessarily reflect any position of the Society of Petroleum Engineers, its officers, or members. Papers presented at SPE meetings are subject to publication review by Editorial Committees of the Society of Petroleum Engineers. Electronic Electronic reproduction, distribution, or storage of any part of this paper for commercial purposes without the written consent of the Society of Petroleum Engineers is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 300 words; illustrations may not be copied. The abstract must contain conspicuous acknowledgment acknowledgment of where and by whom the paper was presented. Write Librarian, SPE, P.O. Box 833836, Richardson, TX 75083-3836, 75083-3836, U.S.A., fax 01-972-952-9435.
Abstract The paper presents a new empirical correlation to predict the dewpoint pressure of gas-condensate fluids from readily available field data. The new correlation relates the dewpoint pressure of a gas-condensate fluid directly to its reservoir temperature, pseudoreduced pressure and temperature, primary separator gas-oil ratio, the primary separator pressure and temperature, and relative densities of separator gas and heptanes-plus fraction. The correlation was developed based on field and laboratory PVT analysis data of several gascondensate fluid samples representing different gas reservoirs in the Middle East. Additional data sets, not included in the development of this correlation, were used to validate the new model’s accuracy. Based on the error statistical analysis results, the new model outperforms the existing correlations.
Introduction The dewpoint of a gas-condensate fluid occurs when a gas mixture containing heavy hydrocarbons is depressured until a liquid is formed. The dewpoint is defined by a substantial amount of gas phase that exists in equilibrium with an infinitesimal amount of liquid phase. The determination of gas-condensate dewpoint pressure is essential for fluid characterization, gas reservoir performance calculations, and for the design of production systems. Traditionally, the dewpoint pressure of a gas-condensate fluid is experimentally determined in the laboratory in a process called constant mass expansion (CME) test using a visual window-type PVT cell. The laboratory measurement of the dewpoint pressure provides the most accurate and reliable determination. However, due to the following economical and technical reasons, quite often this information cannot be obtained from laboratory measurements: (1) the laboratory
analysis can be expensive and cumbersome, (2) inability to obtain a representative sample, (3) sample volume is insufficient to obtain complete analysis, and (4) laboratory analyses are in error. In this case, the dewpoint pressure values can be predicted from empirically derived correlations. The dewpoint pressure correlations, proposed in the literature, are considered very limited. In addition, these correlations were developed based on gas-condensate fluid samples obtained from certain reservoirs of specific regions in the world. Due to varying compositions of gas-condensate fluids from reservoirs of different regions, different empirical correlations may not provide good predictions of dewpoint pressures when they are applied to gas-condensate fluids behaving differently from the fluids based on which they were developed. Most of these empirical correlations are strongly relating the dewpoint pressure to the gas-condensate fluid composition. Therefore, there is a great interest to evaluate the accuracy of these empirical correlations in predicting the dewpoint pressures of the Middle East gas-condensate fluids. This paper presents a new empirical correlation for predicting dewpoint pressure of gas-condensate systems exclusively for the Middle East gas-condensate fluids using multiple linear/nonlinear regression procedures. In addition, the accuracy of some empirically derived dewpoint pressure correlations was evaluated to determine their applicability for the gas-condensate fluids prevailing in the M iddle East.
Review of Literature
1
In 1947, Sage and Olds studied experimentally the behavior of five paired samples of oil and gas obtained from wells in San Joacuin fields in California. Their investigations resulted in developing a rough correlation relating the retrograde dewpoint pressure to the gas-oil ratio, temperature and stocktank API oil gravity. The results of this correlation were presented in tabulated and graphical forms. This correlation is applicable only for gas-oil ratio of 15,000-40,000 scf/STB, for o o o temperature of 100-220 F, and for API oil gravity of 52 -64 . 2 In 1952, Organick and Golding presented a correlation to predict saturation pressures, which could be a dewpoint or a bubble point pressure, for gas-condensate and volatile oil reservoir fluids. Saturation pressure is related directly to the chemical composition of the mixtures with the aid of twogeneralized composition characteristics: (1) the molal average o boilin boiling g point point ( B ) in R, and (2) the modified average
2
A.A. HUMOUD, M.A. AL-MARHOUN
equivalent molecular weight (Wm). These parameters can be calculated from the composition of the gas mixture. The correlation was given in the form of 14 working charts, and on each chart the saturation pressure is plotted against temperature. Each chart is for a specific value of W m and gives a set of curves representing different values of B . 3 In 1967, Nemeth and Kennedy developed a correlation in the form of an equation, which relates the dewpoint pressure of a gas-condensate fluid to its chemical composition, temperature and characteristics of C 7+. The final form of the equation contains eleven constants; See the Appendix. The dewpoint pressure and temperature ranges varied from 1,270o 10,790 psi, and 40-320 F respectively. The average absolute error for the 579 experimental data points used to develop this correlation was found to be 7.4%. 4 In 1996, Potsch and Braeuer presented a graphical method for determining the dewpoint pressure as a backup for the laboratory visual reading of dewpoint pressure during a CME test. The key idea of this method is to plot the number of moles, calculated as a function of single-phase compressibility factor (Z-factor), versus pressure. Above dewpoint pressure, the plot yields a straight line, and below dewpoint pressure the plot shows a curve. The point of intersection marks the dewpoint pressure.
Data Acquisition Seventy-four (74) data sets, representing different gascondensate fluids of the Middle East, were acquired and made available for this research. Each data set included field production data, fluid compositional data, and the results of CME test. The field production data included the reservoir pressure and temperature, the operating pressure and temperature of the primary separator, the primary separator gas-oil ratio, the separator gas specific gravity and the heptanes-plus specific gravity. The results of compositional analysis were utilized to estimate the pseudocritical properties of the gas-condensate fluids. All the dewpoint pressure values used in this study were experimentally determined from the CME tests performed on the gas-condensate fluids. Table 1 lists the ranges of main parameters of the Middle East gas-condensate fluids. Wide ranges of dewpoint pressure, temperature and gas-oil ratio were covered. Lean and rich gases with high concentration of acid gas were also covered in this study.
SPE 68230
variables was based on the pressure and temperature conditions, while the second type of independent variables was related to the gas-condensate fluid composition. Several models were mathematically formulated with different sets of parameters, expressed in different forms of linear, logarithmic and power relationships. The relationships of these parameters, on the individual and combined basis, to the dewpoint pressure were investigated. Based on of 2 coefficient of determination ( r ) and the t -test results, the most important parameters were selected and the least important ones were excluded from the correlation. The best model that fits the seventy-four (74) experimental data points was found to be;
Pd = ƒ (TR , R SP , PSP , TSP , Ppr , Tpr , γ gSP , γ C7 + ) …………...(1) where γ C7 + = heptanes-plus specific gravity (water = 1.0)
γ gSP = primary separator gas specific gravity (air = 1.0) Ppr PSP RSP Tpr TSP TR
= = = = = =
pseudoreduced pressure primary separator pressure (psia) primary separator gas-oil ratio (scf/SP bbl) pseudoreduced temperature o primary separator temperature ( R) o reservoir temperature ( R)
The following equation has been found to be the best form that minimizes the deviation from measured data: ln(Pd ) = β 0 + β1 ln(TR ) + β 2 ln(R m ) + β 3 ln( PSP ⋅ TSP )
+
β4 Tpr
+
β5 Ppr
+
β6 ………………………....(2) γ C 7 +
where β0 = 43.777183 β1 = -3.594131 β2 = -0.247436 β3 = -0.053527 β4 = -4.291404 β5 = -3.698703 β6 = -4.590091
Development of Correlation Multiple least-square linear/nonlinear regression was utilized to develop this new dewpoint pressure correlation. Statistical regression programs were developed to build the models, investigate the behavior of many regression models and evaluate each combination of the dependent variable with the independent variables. The first step in developing the correlation was to select the parameters that are anticipated to influence the dewpoint pressure behavior. Two types of independent variables were used to develop the new model. The first type of independent
The mass gas-oil ratio (Rm) is defined as: Rm =
R SP ⋅ γ gSP
γ C7 +
………………………………………..(3)
The pseudoreduced pressure and temperature are defined as:
SPE 68230
Ppr = Tpr =
A NEW CORRELATION FOR GAS-CONDENSATE DEWPOINT PRESSURE PREDICTION
PR Ppc TR Tpc
………………………………………………..(4) ……………………………………………….(5)
where PR
= reservoir pressure (psia)
For known gas mixture composition, the pseudocritical pressure (Ppc) in psia and the pseudocritical temperature (Tpc) o 5 in R are estimated using Kay’s mixing rules defined as:
3
New Correlation for Pseudocritical Properties. The pseudocritical pressure and temperature of a gas-condensate fluid can be estimated using some empirical relationships based on the reservoir gas gravity, such as Standing’s correlation presented in the Appendix, if the composition is not available. For accuracy purposes, a new correlation has been developed in this research for estimation of pseudocritical properties of the Middle East gas-condensate fluids. Using linear least-squares regression, the new relationships as function of reservoir gas specific gravity ( γ gR ) are:
n
Ppc = ∑ yi ⋅ Pci ……………………………………...…..(6)
Ppc = 694.5 − 55.3γ gR ……………………………....…..(8)
i =1 n
Tpc = ∑ yi ⋅ Tci ………………...………………………..(7) i =1
where Pci
= critical pressure of component Ci
Tci
= critical temperature of component Ci
yi
= mole fraction component i in the gas mixture
Correlation Error Analysis. The new correlation, given in Eq. 2, was developed with a correlation coefficient ( r ) of 0.9479, which indicates that about 95% of the data variation in the dewpoint pressure (dependent variable) can be explained by the model. The average absolute relative error was 4.33% and the error standard deviation was 3.34%. The error distribution of this new correlation is presented in Fig. 1 as average absolute relative error versus data frequency. It indicates that approximately 65% of the predicted dewpoint pressures fall within 5% average absolute error, and about 95% of the data points are within 10% error. The model’s accuracy for all the data points used to develop this correlation is 15%. Sensitivity of New Model. The influence of the individual independent variables on the dewpoint pressure was tested. In this sensitivity test, the variation in the dewpoint pressure is observed by varying an independent variable over the practical range while holding the other variables constant at minimum, average and maximum values. Figure 2 shows that dewpoint pressure is very sensitive to the reservoir temperature when other variables are held at minimum values. It is also observed that the sensitivity of the model is reduced as the values of other variables increase. The influence of the reservoir temperature becomes much less significant when other variables are at their maximum values. Figure 3 illustrates that the model is more sensitive to low values of gas-oil ratio than to high values. It is also noticed that the influence of the gas-oil ratio on the model is decreasing with decreasing the values of other variables.
Tpc = 208.5 + 213.7 γ gR …....…………………………....(9) Using the correlation given in equations 8 and 9, the average absolute errors were found to be 1.8% and 1.0% in predicting the pseudocritical temperature and pressure respectively compared to the Kay’s mixing method (equations 6 and 7). Based on the estimated pseudocritical properties using equations 8 and 9, the new model in Eq. 2 predicted the dewpoint pressures with an average absolute error of 6.4%, as compared to 13% using Standing’s correlation.
Comparison of Correlations The data sets used to develop the new correlation were utilized to evaluate the accuracy of two existing dewpoint pressure correlations: (1) the Organick and Golding correlation, and (2) the Nemeth and Kennedy correlation. Both statistical and graphical means were used in this co mparative evaluation. Statistical Error Analysis. Table 2 lists three statistical error parameters that are used to evaluate the two existing correlations in comparison with the newly developed correlation. The parameters include the average absolute relative error ( E a), the maximum relative error ( E max ), and the standard deviation error (s). Table 2 shows that using the Organick and Golding correlation to predict the dewpoint pressures of the Middle East gas-condensate fluids resulted in an average absolute error of 32.6%, and a maximum relative error of 53.4%. This indicates that the accuracy of this correlation is unsatisfactory. Table 2 shows also that the accuracy of the Nemeth and Kennedy correlation is better than the Organick and Golding correlation. The average absolute error in the dewpoint pressure predictions was 11.64%, and the maximum relative error was 37.4%. The newly developed correlation predicted the dewpoint pressures with an average absolute error of 4.33%, and a maximum relative error of 15.1%. Therefore, the new correlation outperforms the existing correlations.
4
A.A. HUMOUD, M.A. AL-MARHOUN
Graphical Error Analysis. Two graphical analysis techniques were considered in this study for comparative evaluation of the existing correlations with the new correlation. These techniques included the crossplot and the parameter grouping analysis. Crossplots. The crossplots of estimated versus experimental values of the dewpoint pressures are shown in Fig. 4 through 6. For the purpose of accuracy analysis, both zero-error line or o the 45 line and the + 10% error variance are drawn on these plots. The crossplot of Organick and Golding, presented in Fig. 4, shows that the majority of data points are widely scattered o and highly deviated from the 45 line. The crossplot also reveals that this correlation always underestimates the dewpoint pressures compared to the experimental values. The crossplot of Nemeth and Kennedy correlation, presented in Fig. 5, shows that the correlation dewpoint pressure predictions were within + 10% error variance for dewpoint pressures less than 5500 psia. However, the correlation had the tendency to underestimate the dewpoint pressures at pressures higher than 5500 psia with increasing the deviation as the dewpoint pressure increases. The crossplot of the newly developed correlation, presented in Fig. 6, shows clearly that the majority of the data points fall within +10% error variance. It is also observed from this crossplot that the data points are well scattered o closely around the 45 line. Overall, The newly developed correlation showed a better prediction accuracy and a better error scatter in the data points than the other two existing correlations. Parameter Grouping Analysis. The degree of error randomness or error distribution with the change in any parameter was tested by plotting the average absolute error versus groups of a variable. Figure 7, is a plot of average absolute error grouped by the dewpoint pressure. The plot shows that both existing correlations are influenced by the dewpoint pressure with increasing the average absolute error as the dewpoint pressure increases. However, the new correlation is showing a random average absolute error over different ranges of dewpoint pressure. Figure 8, is a plot of average absolute error grouped by the reservoir temperature. The Organick and Golding correlation shows a random error distribution with the change in reservoir temperature. On the other hand, the Nemeth and Kennedy correlation is strongly influenced by the change in reservoir temperature with decreasing the average absolute error as the reservoir temperature increases. The correlation showed a o constant E a at temperatures greater than 250 F. The plot shows also that the error in the new correlation is not influenced by the change in reservoir temperature. The least error occurred at o temperature range of 200-250 F.
SPE 68230
sets for the Middle East gas-condensate fluids that were not used in the development of the new correlation. The new correlation was also compared against the two existing correlations. Table 3 summarizes the results of error analyses of the three correlations. The table shows that the Organick and Golding correlation has the highest average absolute and maximum relative errors. The Nemeth and Kennedy correlation shows a better accuracy than the Organick and Golding correlation. The accuracy of the new correlation was tested using two different methods for estimation of pseudocritical pressure and temperature, based on the available fluid composition (Eqs. 6 and 7) and the gas specific gravity correlation (Eqs. 8 and 9) for unknown fluid composition. The predictions of the new correlation for the dewpoint pressure were found within less than 4% average absolute error, and with a maximum relative error of less than 10% as shown in Table 3.
Conclusions 1. 2.
3.
4.
5.
6.
A new empirical correlation to predict the gascondensate dewpoint pressure has been developed. The developmental approach of this new correlation is based on some readily available gas-condensate properties and parameters. Most of these parameters were not considered in the existing correlations. Comparative evaluation of existing correlations was made using statistical and graphical error analyses. It showed that the new correlation outperforms the existing correlations. The empirical correlation developed in this study was validated by data, which were not used in the development of this correlation, and the model provided a better accuracy than the existing correlations. The new correlation is considered more relevant and applicable to the Middle East gas-condensate properties and conditions than the existing correlations since the new model has been developed based on a large number of data sets for the Middle East gas-condensate fluid samples. New correlations to estimate pseudocritical properties as a function of gas relative density were developed based on Middle East gas-condensate data. Higher accuracies were obtained when these correlations are used instead of Standing’s ones.
Nomenclature E a E max γapi
= = =
average absolute percent relative error maximum absolute percent relative error stock tank oil gravity, oAPI
Validation of New Correlation
γ C7 +
=
specific gravity of heptanes-plus fraction
In order to examine the applicability and reliability of the newly developed correlation, it was validated using 20 data
γ gs
=
(water = 1.0) average specific gravity of surface separator
SPE 68230
A NEW CORRELATION FOR GAS-CONDENSATE DEWPOINT PRESSURE PREDICTION
γgR
=
gas (air = 1.0) reservoir gas specific gravity (air = 1.0)
γgSP
=
specific gravity of gas fro m primary
2.
Organick, E.I. and Golding, B.H.: “Prediction of Saturation Pressures for Condensate-Gas and VolatileOil Mixtures,” Trans., AIME (1952) Vol. 195, 135-148. Nemeth, L.K. and Kennedy, H.T.: “A Correlation of Dewpoint Pressure With Fluid Composition and Temperature,” paper SPE 1477 presented at SPE 41st Annual Fall Meeting held in Dallas, Tex., 1966. Potsch, K.T. and Braeuer, L., “A Novel Graphical Method for Determining Dewpoint Pressures of Gas Condensates,” Paper SPE 36919, presented at the 1996 SPE European Conference held in Italy, October 22-24, 1996. Sutton, R.P., “Compressibility Factors of HighMolecular-Weight Reservoir Gases,” Paper SPE 14265, presented at the 1985 SPE Annual Technical Conference and Exhibition, Las Vegas, Sept. 22-25, 1985. Ahmed, T.: Hydrocarbon Phase Behavior, Vol. 7, Gulf Publishing Company: Houston, 1989.
3.
separator (air = 1.0) MC7+ Pd Ppc Pci Ppr PSP Rm RSP 2
r r s T
= = = = = = = =
the molecular weight of heptanes plus dewpoint pressure, psia pseudocritical pressure, psia critical pressure of component ci pseudoreduced pressure of the gas mixture primary separator pressure (psig) mass gas-oil ratio, defined by Eq. 3 producing gas-oil ratio from primary separator (scf/STB) coefficient of determination correlation coefficient standard deviation o temperature, R
= = = =
Pd = A1[ y CO 2 + y H 2S + y C 6 + 2(y C3 + y C 4 ) + 0.4 y C1 + 0.2 y N 2 ]
+ A 2 γ C 7 + +
A 3 y C1 y C1 + 0.002
+ A9 [ Tci Tpc Tpr
M C7 +
γ C7 + + 0.001 = = =
TSP TR yi
= = =
yCi
=
6.
SI Metric Conversion Factors 141.5/(131.5+ γapi) bbl x 1.589 873 3 fto x 2.831 685 ( F + 40)/1.8 – 40 psi x 6.894 757
]2 + A10 [
γ C7 + + 0.001
M C7 +
γ C 7 + + 0.001
]3 + A11
critical temperature of component i o pseudocritical temperature, R pseudoreduced temperature of the gas mixture o primary separator temperature ( R) o reservoir temperature ( R) mole fraction of component i in the gas mixture mole fraction of component Ci in gas mixture
= γo (unit-less) 3 E + 01 = m 3 E – 02 = om = C E + 00 = kPa
Appendix – Correlations Nemeth and Kenndy dewpoint pressure correlation:
primary separator reservoir gas methane, ethane,… property of heptanes plus fraction mass dewpoint pseudocritical pseudoreduced
Sage, B.H. and Olds, R.H.: “Volumetric Behavior of Oil and Gas from Several San Joaquin Valley Fields,” Trans., AIME (1947) Vol. 170, 156-173.
3
Where A1 = -2.0623054 -3 A3 = -4.4670559 x 10 -2 A5 = 3.2673714 x 10 -5 A7 = 7.4299951 x 10 -4 A9 = 6.2476497 x 10 A11 = 1.0746622 x 10
A2 = 6.6259728 -4 A4 = 1.0448346 x 10 -3 A6 = -3.6453277 x 10 -1 A8 = -1.1381195 x 10 -6 A10 = -1.0716866 x 10
Standing pseudocritical properties correlation:
References 1.
5.
A 8 M C7 +
Subscript
SP R g C1,C2,… C7+ m d pc pr
4.
+ A 4 T + A 5 ( y C7 + M C 7 + ) +
A 6 ( y C 7 + M C7 + ) 2 + A 7 ( y C7 + M C 7 + )3 +
5
Ppc = 706 − 51.7 γ gR − 11.1γ gR
2
Tpc = 187 + 330γ gR − 71.5γ gR
2
6
6
A.A. HUMOUD, M.A. AL-MARHOUN
Table 1: Ranges of Gas-condensate Fluid Data
Parameter
Minimum
SPE 68230
Table 2: Statistical Accuracy of Dewpoint Pressure Correlations for Model Development Data
Maximum Correlation
Pd (psia)
2700
7465
TR ( F)
o
100
310
PSP (psia)
60
1215
3,400
150,000
TSP ( F)
70
190
APIC7+
42
56
γgR
0.7089
1.466
γgSP
0.66
0.82
CO2 (mole %)
0.12
3.93
H2S (mole %)
0.0
9.32
C1 (mole %)
57.7
83.9
C7+ (mole %)
0.53
13.0
RSP (scf/SP bbl) o
Organick and Golding
Organick and Golding
E max (%)
s (%)
32.56
53.38
13.50
Nemeth and Kenndey
11.64
37.40
9.83
This study
4.33
15.10
3.34
Table 3: Statistical Accuracy of Dewpoint Pressure Correlations for Model Validation Data
Correlation
E a (%)
E a (%)
E max (%)
s (%)
35.43
44.83
9.95
Nemeth and Kenndey
11.29
20.83
5.97
This study (1)
3.72
9.41
2.37
This study (2)
3.35
9.05
2.49
Notes: (1) The pseudocritical properties were estimated based on the gas-condensate fluid composition using Kay’s method (Eqs. 6 and 7). (2) The pseudocritical properties were estimated using new correlation (Eqs. 8 and 9).
SPE 68230
A NEW CORRELATION FOR GAS-CONDENSATE DEWPOINT PRESSURE PREDICTION
8000
100
Minimum Values
90
Maximum Values
7000
80
) % ( y c n e u q e r F a t a D
7
Average Values
) a i s p ( 6000 e r u s s e r P 5000 t n i o p w e D 4000
70 60 50 40 30 20
3000
10 2000
0 1
2
3
4
5
6
7
8
9
10 11 12
50
13 14 15
100
150
200
250
Reservoir Temperature
Average Absolute Error (%)
300
350
(oF)
Figure 2: Sensitivity of new mo del to reservoir temperature
Figure 1: New m odel error distribution
8000
+10%
Minimum Values
11000
) a i s p ( e r u s s e r P t n i o p w e D d e t a m i t s E
Maximum Values Average Values
) a i s 9000 p ( e r u s s e r 7000 P t n i o p w 5000 e D
3000
6000
5000
4000
3000
2000
1000 4 ,000
7000
14,000
24,000
34,000
44,000
54,000
Gas Oil-Ratio (scf/SP bbl)
Figure 3: Sensitivity of new model to gas-oil ratio
2000
3000
4000
5000
6000
7000
8000
Experimental Dewpoint Pressure (psia)
Figure 4: Crossplot of Organick and Golding correlation
8
A.A. HUMOUD, M.A. AL-MARHOUN
8000
8000
+10%
+10%
) a i s p ( e r u s s e r P t n i o p w e D d e t a m i t s E
SPE 68230
) a i s p ( e r u s s e r P t n i o p w e D d e t a m i t s E
7000
6000
5000
4000
3000
7000
6000
5000
4000
3000
2000
2000
2000
3000
4000
5000
6000
7000
8000
2000
3000
4000
5000
7000
8000
Experimental Dewpoint Pressure (psia)
Experimental Dewpoint Pressure (psia)
Figure 5: Crossplot of Nemeth and Kennedy correlation
Figure 6: Crossplot of new correlation
50
45
This Study 45
This Study 40
Nemeth & Kennedy
Nemeth and Kennedy
Organick & Golding 40
) % ( r o r r E e t u l o s b A e g a r e v A
6000
) % ( r o r r E e t u l o s b A e g a r e v A
35 30
25 20
15
Organick and Golding 35
30
25
20
15
10
10
5
5
0 4000
5000
6000
7000
8000
0 100
< 4000 (6)*
4000 -5000
(16 )
5000 -6000
6000 -7000
(31 ) (15 ) Dewpoint Pressure (psia)
> 7000 (6)
Figure 7: Accuracy of Correlations for ranges of dewpoint pressures (* number of data points)
< 150 (8 )*
150
150 -200
200
200 -250
250
250 -300
(8 ) (17 ) (31 ) Reservoir Temperature (oF)
300
> 300 (10 )
Figure 8: Accuracy of Correlations for ranges of reservoir temperature (* number of data points)
