Vapor-Liquid Equilibria for Natural Gas-Crude Oil Mixtures C. H. ROLAND Phillips Petroleum Company, Bartlesville, Oklu.
A consistent set of equilibrium constants and related phase data were obtained for a mixture of League City natural gas and Billings crude oil for pressures from lo00 to 10,000 pounds per square inch and at temperatures of 120" and 200" F. Data were also obtained for miscellaneous mixtures of the oil and gas, and were compared to the data for the fixed-composition mixture. The effect of composition upon the equilibria is noted, and through
two experiments in which the composition is varied b3 removal from the system of a liquid phase at a higher pressure the effect of a particular composition change ib determined. The composition change appears to affect the component characteristic of the heptanes and heavier component but not the equilibrium constants. Colored hydrocarbon fractions were show-n to be present in the vapor phase at high pressures.
V
indicated a reversal in the curvature of the equilibrium consteiit lines similar to that shown in the plots of Webber. That such reversal of curvature was not present in the distillate systems may be attributed to the fact that, for the distillate mixtures, thc temperature of the determinations was much nearer the critical ternperatures of the mixtures. The data obtained in the experimental work of this paper may be divided into three groups. I n the first, gas and crude oil were combined in various proportions to produce miscellaneous mixtures. The equilibrium data were then determined for these mixtures. I n the second group the gas and oil were combined in tl fixed ratio, and the equilibrium data were determined for varioub pressures from 1000 to 10,000 pounds per square inch. I n the third group a vapor phase was removed from one of the equilibria of the second group and used as a system a t a lower pressure for which the equilibrium constants and related phase data w ~ r o drtermined. In addition to the equilibrium constant data, particular attc.11tion was given to the specific gravity and molecular weight of the heptanes and heavier fractions. I n the phase equilibria at high pressures such as are encountered in reservoir studies, thc equilibrium constant of the hept,anes and heavier fraction is of prim(. importance and in many cases is the determining factor in a calculation. The significant variations of the molecular weight arid specific gravities are important in hclping to select the c o r r w value for the heptanes and heavier constant.
APOR-liquid equilibrium constants and related data have been determined for mixtures of a natural gas and crude oil at 120' and 200" F. for pressures from 1000-10,000 pounds per square inch. These data are useful to those engaged in process design and reservoir engineering for predicting phase relations. The range of tempcratures and pressures studied include those which represent the initial conditions existing in most of the known oil and gas producing reservoirs. Several investigators have reported vapor-liquid equilibrium constants for multicomponent hydrocarbon mixtures with a wide range of volatility such as occur in natural gas and crude oil separations. Kat2 and Hachmuth (8) presented data for pressures to 3000 pounds per square inch a t 40°, 120°, and 200" F., determined with natural gas and Oklahoma City Wilcox crude oil mixtures. These data were extrapolated in the published article to a convergence pressure of 5000 pounds per square inch. Webber (6) published equilibrium constant data for hydrorarbons in absorption oil at 33 O, 100 and 180O F. and pressures from 100 to 5000 pounds per square inch. These mixtures were made up synthetically by adding the pure hydrocarbons to the absorption oil. The varying amounts of hydrocarbons used affected the equilibrium constants and thus indicated how important were the relative amounts of hydrocarbons present at pressures above 1000 pounds. Roland, Smith, and Kaveler (3) published equilibrium constant data for Gulf Coast distillate-natural gas mixtures at 40", 120°, and 200" F. for pressures from 200 to 4000 pounds per square inch. Measurements were made at, pressures both above and below the limit for existence of a two-phase condition, and the determinations established with a reasonable degree of certainty the existence of a convergence pressure (pressure at which the equilibrium constants appear to converge to unity for certain mixtures). Eilerts and Smith (I) includedsomeequilibrium constant data obtained in a study of separator gas-liquid hydrocarbon mixtures from a distillate well. These data were obtained at 3192 pounds per square inch pressure and 228' F. for various mixtures of separator gas and liquid. They show a considerable variation of the equilibrium constant yith the ratio of gas to liquid in the mixture. Standing and Katz (4) published equilibrium constant data, for four different mixtures of natural gas and crude oils at 35 O to 250 O F. from 100 to 8220 pounds per square inch. Their measurements included the phase densities under the equilibrium conditions; these data assist in determining whether the increase in pressure on the system produces a bubble point or a dew point. At high pressures their equilibrium constant data as plotted against pressure on logarithmic paper O,
EXPERIMENTAL DETAILS
The apparatus included an equilibrium cell, constant-temperature bath, gages, hand-operated mercury pump, volumetric mercury-displacement pump, and analytical apparatus. The equilibrium cell was of the rocking-bomb type. The analytical equipment included two sets of low-temperature fractionating columns; a balance, pycnometers, and cryoscopic molecular weight apparatus were used to study the heptanes and heavier fractions. CRUDEOIL AND NATURAL GAS. The crude oil used in making up the equilibrium samples wm a pipe line oil from the Wilcox formation near Billings, Okla., in Noble county. A commercial preparation (Tretolite) was added to the oil to assist in removing the water. The percentage of Tretolite was very small and was assumed to have no effect on the equilibria. Thirty gallons of this oil were thoroughly agitated in a drum. From this drum 23 quart cans were filled and sealed so that a fresh can of oil would be available for each charge of the equilibrium cell. Table I gives a fractional analysis of the oil and Figure 1 shows a distillation chart. 930
October, 1945
INDUSTRIAL A N D ENGINEERING CHEMISTRY
931
volume of the li uid phase e ual to the desired volume of sample wouyd be availahe below the intake to the liquid-phase eduction tube. This would ensure -Charging Materiala-an adequate amount of liquid sample being taken since Billings -Natural amComBosite Composition8 during the sampling, the mercury level would rise and Hydrocarbon crudeoil No.7 No. 8a No.8ab NO.1 No.2d No.3' finally cover the entrance to the eduction tube. Methane 91.150 91.136 91.419 81.113 81.107 81.358 The cell was evacuated with a Hyvac pump. The Ethane 0:642 4.368 4.392 4.386 3.896 8.914 3.909 Propane 1.142 2.047 2.059 1.990 1.948 1.958 1,897 desired quantity of gas to be added to the equilibrium Butanes 4.413 1.288 1.283 1.251 1.629 1.628 1.600 cell was measured in an auxiliary cell. The compressiPentanes 6.054 0.513 0 493 0.459 1.123 1.106 1.075 bility of this gas was previously determined so that Hexanes 8.535 0,317 0.290 0.270 1.222 1.197 1.179 HeDtanes and 79.794 0,317 0.347 0.225 9.089 9.091 8.982 the volume a t a desired temperature and pressure would heavier be known. The gas was then displaced with mercury E gr. a$ 60° F. 0,8285 0.735 0.753 0.8268 0.8i68 0.8268 into the equilibrium cell. 200.8 105 107 ... '198 198 198 d o l . weight 39.6 39.6 39.6 A.P.I. ravityat 39.3 61.0 56.4 The crude oil was measured in a graduate a t 60' F. 60' 5. and added to the smaller auxiliary cell from which it was displaced with mercury into the equilibrium a Cylinder HQOlT'afterremoving liquid at 32O F. and 19001b./sq. in. gage. cell, care being taken to use a fresh quart b Cylinder H9017 after removing more liquid resulting from pressure drop to 1060 lb./sq. in. gage at 75O F can of crude oil each time the equilibrium cell was Applies to 120' F. damples at presaurea of 3666.5581,6831,6580,7940.9374 lb./aq. . charged. in. abs. After charging the equilibrium cell with the re uid Applies to 200' F. esmply at reasurea of 1600, 1907,2500,3560,3792,4957,5737, 6740 7470 7965 8078 Ib./sq. in. I&. site quantities' of gas and liquid the cell was rocled e AppliG to 2dOO F. samples at preasurea of lO47,5402,79051b./sq. in. ab*. for 10 or 15 minutes to bring the contents to equilibrium. The cell was then fixed in an upright position, and the sample valves were connected to the sampling - lines. The volumetric mercury pump was connected to the bottom of The gas was obtained from the Lobit No. 2 well, League City, the cell and used to maintain the pressure constant during the Texas. This gas was chosen because it was accessible, similar in withdrawal of vapor or liquid from the cell. Each valve was composition to other natural gwes, and available at a Well head opened slightly. and material was removed from the cell until it was assured t&t ohly the desired phase was being obtained. Samples pressure high enough to fill the gas storage cylinders to 2000 were then displaced into the analytical columns. Records were pounds per square inch gage pressure. The cming-head gas from this well was passed through chaccoalinto the cylinders to remove the heavier constituents. The gas w&9 further denuded of its detachable glass trap through which the e uiEbrium sample was r d to remove the heavier components%efore condensing the heavier constituents by cooling the cylinders in a crushed ice i hter COm onents in the kettles cooled with li uid nitrogen. bath, inverting, m d draining the condensed liquid from each T k s procezre prevented the heavier materials %om pluggmg cylinder. This procedure was assumed to give a supply of gas which would not undergo retrograde condensation upon further In aome cases, particularly the equilibria at higher pressures, i t was pressure and' hence be Of constant during neoeasary to rook the cell when adding the liquid 80 that the pressure during use. Frequent checks of the gas cylinders during and following solution of the 0-w could be kept below thg upper pressure limit of the the run a t 120' F. showed the cylinder to be free of liquid hydrogages. carbons. During the 200' F. run a small amount of liquid was found in one cylinder after three doterminations had been made; the gas was reanalyzed and the analyses were only slightly different. Both analyses are recorded in Table I. PROCEDURE. Previous experience in the determination of equilibrium constants for the gas distillate and other crude oil systems indicated that the equilibrium cell might be charged with liquid and gas to some high pressure and samples be removed at several pressures until one or another of the phases was depleted. At this point more liquid or gas could be added to restore the depleted phase and additional samples be taken. The composite composition could be calculated, and any change in the value of the equilibrium as a result of change in cell composition could be correlated with the change in one of the other variables. A group of equilibrium points were determined in this way. Although this method accelerated the experimental work, the data showed more variation than was anticipated, and correlation was made impossible. It was therefore decided to determine the equilibrium constants for a constant-composition system. This system would be made up each time by adding gas and crudo oil in the mole ratio of 8.086 to 1. A typical experimental run involved the following procedure:
TABLE I. ANALYSISOF OIL AND GAS
.
... ...
m
a
~
~
~
-
The temperature and pressure of the desired equilibrium were selected. The approximate volume of the liquid phase which would be present in the cell a t the selected conditions was computed from previous data for the phase density or, if necessary, by the use of generalized correlations available in the literature. With this information the mercury level in the cell was adjusted so that a sufficient
Figure 1. Distillations of Heptanes and Heavier Fractions
~
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
932
Vol. 37, No. 10
SO 4.0
3.0
2.0
g
1.0 0,s u) 0.8 Q
t-
z
0 0.7 0
0.6 Y
0.5
3
K
04
m d
3
0.3
O
w
0.2
ai
1
Y I
NATURAL GAS
a BILLINGS CRUDE O I L 2OO0F,
0
CONSTANT COMPOSITION
P MISC. MIXTURES
0
MISC. M I X T U R E S
0
DATA OF KAT2
a
HACHMUTH
0.006 0.005
0
0.004
EQUILIBRIA DERIVED FROM
5
6
f
8 910
P R E S S U R E IN THOUSANDS R bl.A,
Figure 2.
Vapor-Liquid Equilibrium Constants for Natural Gas and Billings Crude Oil at 120° F.
1
2
0.004
PRESSURE IN THOUSANDS P.S.I.A.
Figure 3. Vapor-Liquid Equilibrium Constants for Natural Gas and Billings Crude Oil at 20O0 F.
INDUSTRIAL AND ENGINEERING CHEMISTRY
October, 1945
933
TABLE 11. PHASE ANALYSES AND EOTJILIBRITJM CONSTANTS FOB MISCELLANEOUS MIXTURES OF NATURAL GASAND BILLINQSCRUDEOIL
Lb.Q, 120° Liquid 50.464 4.034 2.662 3.463 3.083 3.596 a2.688 207 0.8326 0.1492 21.8 1.174
F.
6173 Lb., 120° 89.532 58.807 Ethane 4.186 4.616 1.942 2.748 Propene 1.367 2.448 Butanes 0.687 1.674 Pentanes 0.108 1.843 Hexanes 1.778 27.964 Heptanes and heavier 148 254 Mol. wt. 0.7805 0.8687 8 gr. at 60° F. 0.758 0.1339 Mop,, sampled 66.770 17.94 Co sam led 0.979 1.785 z hP~JNRT 6 Pressure in pounds per square inch.
F.
Methane Ethane Propane Butanes Pentanes Hexanes H e tanee and heavier Aol. weight 8 gr. a t 60° F. Mags sampled Cc Sam led z LP ~ ~ N R T
.
3201 Vapor 91.266 3.500 1.484 1.221 0.750 0.667 1.222 116 0.7633 1.1181 107.8 0.796
Methane
6040 Lb.. 120° F. Vapor Liquid K 59.366 1.480 88 7 0.9.m 3: 9% 4.814 0.730 2.621 1.914 0.568 1.380 2.428 0.438 0.786 1.797 0.842 0.692 2.026 0.0908 27.461 2.492 136 227 . e * 0.7749 0.8469 0.4140 0.8495 62.8 47.800 0.968 1.496
K 1.809 0.867 o.ma 0.362 0.244 0.168 0.0374
... ...
... ... ... ...
... ...
.,.
6678 Lb., 120° F. 87.332 64.072 1.363 0.806 3.486 4.327 0.796 1.980 2.486 0.688 1.605 2.337 0.641 0.968 1.772 0.421 0.860 2.018 0.166 3.790 22.988 164 264 0.7918 0.8602 0.9104 0.8017 m.38 83.7 1.178 1.919
1.522 0.907 0.707 0.669 0.437 0.276
... ... ... ... ...
0.0636
.
... ... ... ...
..a
the small neck leading to the kettle of the column. At the end of ampling, the trap was heated to drive all components more volatile than heptane into the kettle of the analytical column. Analysis of the sample was carried throu h the hexane?, and the residue of heptanes and heavier was con8ensed and weighed.
---IHATERlAL BALANCE BASED ON METHANE AND HEPTANES HEAVIER, 0
0 2 .
__
,I
I
6153 Lb., 120° F. -Vapor Liquid R 87.442 62.971 1.388 0.966 3.080 1.661 0.667 1.636 2.482 0.618 1.170 2.090 0.660 1.020 2.170 0.470 4.191 24.760 0.169 132 196.6 0.7722 0.8293 0.1981 0.3921 43.97 40.91 0.974 1.383 7968 Lb., 120° F. 84.596 68.642 1.230 0.976 3.918 4.010 0.868 1.933 2.220 1.629 1.989 0.818 0,732 1.037 1.416 0.662 1.037 1.665 0.302 6.851 20.063 171 229 0.8041 0.8666 0.6896 0.3171 46.20 80.9 1.372 1.998
...
6163 Lb., 120° F. Vapor Liquid 86.746 62.298 3.294 3.468 1.713 2.228 1.626 2.505 1.172 2.181 1.041 2.646 4.610 24.676 196.6 130 0.7787 0.831jl 0.3044 0.2443 21.32 26.03 0.927 1.413
... ... ... ... ...
9695 82.112 4.208 2.034 1.734 1.220 1.111 7.682 186.6 0.8206 0.7012 62.41 1.862
i:%
... ... ... ...
K 1.382 0.950 0.769 0.609 0.637 0.894 0.188
... ... ... ... ...
Lb.. 120° F. 69.451 1.182 3.972 0.944 2.059 0.988 2.061 0.841 1.621 0.755 1.879 0.692 18. 968 0.400 280 0.8807 0.2475 23.06 2.322
...
4 . .
... ... ...
The molecular weight was determined by the cryoscopic method, using benzene saturated with water. Standardization of molecular weight determinations was carried out against ure isooctane. The density of the residue was determined in cali!rated pycnometers, and the remaining residue ww sealed in bottles and retained for further examination. EQUILIBRIUM CONSTANT DATA The data determined at 120’ F. for miscellaneous mixtures of natural gas and Billings crude oil are recorded in Tqble 11. Theae constants and the other recorded phase data show that variables other than temperature, pressure, and general type of systezni.e., distillate or crude oil systems-are important in determining the value of the constant. These variables are the relative m o u n t s of each component present in the mixture. I n this connection the term “component” refers to each individud chemical component and, when used in this sense, the effect of the mixture of components commonly reported as heptanes and heavier may be properly understood. Many investigators have pointed out that by the phase rule there are (n 2) variables besides temperature and pressure to be satisfied before a two-phase multicomponent system with n components is fixed. To fix all these variables would be virtually impossible in a practical problem; therefore it is desirable t o find the minimum number of general properties that may be determined and readily measured in order t o fix the equilibria with a reasonable degree of accuracy. The first problem was to obtain a consistent set of equilibria for a system with a fixed composition. Accordingly, for each equilibrium, gas and oil having the compositions and properties given in Table I were combined in the ratio of 8.086 moles of gas per mole of oil. The equilibria determined for this constant composition system are recorded in Table 111 for 120° and 200’ F. Plot8 of the equilibrium constants and related data were prepared to inspect the consistency of the data so that possible errors might be eliminated. Figures 2 and 3 were prepared from equilibrium constant data. Curves were drawn through the data for the fixed composition system beginning at 3000 pounds per square inch absolute for the 120’ F. isotherm and 10oO pounds for the 200’ F. isotherm. Those values found to be inconsistent were considered from the standpoint of whether the errors were introduced in charging the equilibrium cell, sampling, or analyzing. The related phase data
-
Figure 4. Phase Distribution at Equilibrium Pressure and Temperature
934
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INDUSTRIAL A N D ENGINEERING CHEMISTRY
Vol. 37, No. 10
~~~~
TABLE111. PHASEANALYSSAAND
Methane Ethane Propane Butanes Pentanes Hexanes Heptanes, and heavier Mol. weight Sp. gr. at 60' F. Moles sampled Cc. sampled 2 PV/NRT
-
Methane Ethane Propane Butanes Pentanes Hexanes Heptanes and heavier Mol. weight S gr at60OF. M o t s sampled Co. sampled Z = PV/NRT Methane Ethane Propane Butanes Pentanes Hexanes Heptanes and heavier Mol. weight Sp. gr. at 60' F. Moles sampled Co. sampled Z PV/NRT
-
Methane Ethane Propane Butanes Pentanes Hexanes Heptanes, and heavier Mol. weight S gr.at6OPF. Moks sampled Cc. sampled 2 = PV/NRT Methane Ethane Propane Butanes Pentanes Hexanes Heptanes and heavier Mol. weight S gr a t 6 0 ° F . M o t s sampled Cc. Sam led z = P+/NRT Methane Ethane Propane Butanes Pentanes Hexahes HeDtanes and heavier Mol. weight S gr at60'F. M o f e s ssmpled Co Sam led z L P$/NRT
Vapor 90,658 3.790 1.584 1.281 0.697 0.630 1.360 124 0.7588 1.0561 99.95 0.868
3566 Lb.5, 120' F. Liquid K 52.792 1.717 0.838 4.521 0.557 2.846 2.924 0.438 2.565 0.272 0.198 3.186 31.166 222.8 0.8361 0.2813 36.28 1.183
CONSTANTS FOR A CONSTANT-COMPOSITION MIXTUREOF NATUHAL GAS AND BILLINGS CRUDEO I L
EQUILIBRIUM
0.0436
... ... ... ... ...
Vapor 87.393 4.129 1.727 1.417 0.929 0.981
5581 Lb., 120' F. Liquid K 63.119 1.383 4.127 0.990 0.750 2.300 2.224 0.637 1.812 0.512 0.440 2.226
3.424 148 0.7821 0.8987 64.41 1.027
24.190 228.5 0.8451 0.3462 38.45 1.592
5831 Lb., 120° F. Vapor Liquid K 87.684 64.370 1.362 3.971 0.961 4.131 1.770 2.267 0.781 1.446 2.130 0.679 0.948 1.727 0.549 1.105 2.141 0.516 3.076 146 0.7844 0.8970
0.142
... ... ... ... ...
... ...
23.234 228 0.8464 0.3826
0.132
... ... ... ... ...
... ...
6580 Lb., 120' F. Vapor Liquid K 86.443 96.903 1.289 3.938 4.077 0.960 1.818 2.244 0.805 1.494 2.027 0.735 0.815 1.568 0.518 0.902 1.949 0.462 4.590 21.233 159 243 0.7698 0.8499 0.6947 0.3694 47.59 37.94 1.158 1.737
0.218
... .... .. ... ,..
7940 Lb., 120" F. 70.913 1.190 84.253 0.980 3.931 4.013 2.115 0.860 1,820 0.810 1.548 1.912 0.756 1.076 1.423 1.666 0.736 1.226
9374 Lb.. 120" F. 72.723 1.132 82.358 3.979 0.993 3.952 1.854 2.044 0.905 1.806 0.892 1.616 1.119 1.350 0.828 1.274 1.560 0.818
4725 Lb.b, 120' F. 88.681 59.116 1.500 ' 0.919 3.826 4.164 0.684 1.680 2.455 0.591 1.408 2.384 0.443 0.873 1.969 0.361 0.883 2.447
6752 Lb.6, 120' F. 85.833 68.529 1.268 3.835 4.101 0.942 0.806 1.780 2.226 1.509 1.967 0.773 1.011 1.566 0.652 1.867 0.617 1.145
6.147 173 0.8077 0.9547 64.8 1.385
7.827 193 0.8238 0.9535 66.12 1.668
2.649 133.5 0.7714 0.9459 71.80 0.921
4.887 156 0.7933 0,7933 53.53 1.172
17.950 240.8 0.8547 0.3682 35.21 1.950
0.342
... ...
... ... ...
1047 Lb., 200' F. 20.640 4.437 91.570 2,906 1.407 4.488 2.456 0.715 1.755 3.274 0.362 1.186 0.171 0.607 3.545 0.0721 0.386 5.352 0.409
...
:
0 ik46 220.63 1.077
61.828 208.7 0.8346 0.1560 37.63 0,. 572
0.00662
... .., ... ... ...
l6nO
91.560 4.013 1.714 1.165 0.594 0.450 0.504 110
0.7447 0.7579 192.07 0.917
16.538 270 0.8710 0.3838 36.39 2.282
0.473
... ... ... ...
...
Lh.. ZOOo E". ~. 28.879 3.170 1.203 3.336 0.588 2.914 3.378 0.345 0.188 3.163 0.085 5.281 53.050 208 0.8364 0.1702 31.58 0.672
0.0095
... ... ... ... ...
3560 Lb., 201)"F. 89,919 49.043 1.833 3.846 4.163 0.924 1.721 2.708 0.836 1.300 2.806 0.463 0.791 2.407 0.329 0.654 3.155 0.207
3792 Lb.. 200' F. 89.703 51.425 1.744 0.952 3.853 4.047 2.583 0.674 1.741 0.513 1.303 2.538 2.210 0.357 0.790 0.230 0.652 2.836
1.768 121 0.7568 0.7409 83.41 0.906
1.957 128 0.7638 0,9449 101.24 0.919
36.719 217 0.8394 0.2258 32.92 1.172
0.050
... ...
... ....
...
34.362 214 0.8379 0.2911 40.35 1.188
0.057
... .,.
...
... ...
5402 Lb., 200" F. 87.750 61.270 1.432' 3.880 3.898 0.996 1.781 2.072 0.860 1.372 2.092 0.656 0.876 1.645 0.532 0,841 2.078 0.405
5737 Lb., 200' F. 63.185 1.376 86.970 0,962 3.861 4.012 0.756 1,730 2.289 2.127 0.721 1.533 1.707 0.534 0.912 0.485 0.969 1.998
3.500 26.946 143.7 225 0.7807 0.8436 0,6876 0.4663 65.80 55.50 1.170 1.453
4.025 149.3 0.7859 0.6934 57.64 1.079
0.130
... ... ... ... ...
24.685 230 0.8471 0.5052 61.19 1.570
'
0.163
... ... ...
... ...
27.465 203 0.8359 0.3438 37.95 1.340
0.0965
... ...
... ... ...
1907 Lb.. ZOOo F. ............ 33.335 2.740' 91.307 3.992 3.634 1.098 2.918 0,578 1.687 1.152 3.289 0.350 3.203 0.196 0.629 4.184 0.110 0.461 0.773 114 o:ii52 151.84 0.913
49.437 210 0.8340 0.1490 28.71 0.830
0.0156
... ... ... ... ...
3792 Lb.. 200' F. 89.878 3.846 1.730 1.293 0.813 0.696
... ...
1.744 128 0.7640 0.7327
... ...
... ... ... ... ... ...
... *..
... ...
... ... ... ... ... ... ... *.. ... ... ... ...
5.902 159.1 0.7943 0.5595 43.04 1.172
20.762 233.5 0.8458 0.3962 43.67 1.680
0.284
... ...
... ... ...
8a78 Lb., 200' F. 83.317 71.871 1.159 0.983 3.898 3.965 0.868 1.833 2.110 0.818 1.482 1.811 0.736 1.099 1.494 1.176 1.551. 0.758
7.169 181 0.8138 0.8616 66.60 1.382
7.337 180 0.8123 0.6792 52.23 1.385
7.195 179 0.8081 0.4844 39.45 1.488
... ... ...
... ...
13.197 239.7 0.8504 0.5235 49.70 1.712
served to assist in this consideration and in constructing the equilibrium constant lines as drawn. The equilibrium constants of methane and of heptanes and heavier for the miscellaneousmixtures of League City natural gas and Billings crude oil were added to the 120' F. isotherm. The variations of the constants for the miscellaneous mixtures show a definite effect of composition on
0.556
... ... ... ... ...
... ... ... ... , ..
2500 Lb., 200' F. 91.108 39.956 2.280 3.977 3.933 1.011 1.693 3.010 0.563 1.199 3.071 0.390 2.787 0.228 0.635 0.501 3.907 0.128 0.886
116 0.7501 0.844 133.01 0.890
43.337 211.5 0.8383 0.3507 55.65 0.898
0.4204
... ... ... ... ...
4957 Lb.. ZOOo F. 88.333 59.384 1.487 3.961 4.104 0,965 1.912 2.426 0.788 1.417 2.248 0.630 0.903 1.838 0.491 0.922 2.241 0.411 2.555 142.5 0.7764 0.5571 48.73 0.978
27.758 227.5 0.8452 0.2509 30.85 1.378
0.0921
...
.. .. .. ... ...
6.688 172.5 0.8035 0.8507 65.29 1.297
17.938 241.5 0.8498 0.3774 38.79 .1.736
0.373
... ... ... ... ...
-
7965 Lb., 200' F. 1.090 83.180 76.346 0.978 3.907 3.987 0.909 1.874 2.061 0.910 1.551 1.704 0.842 1.057 1.255 0.755 1.095 1.450
0.415
0.236
7470 Lb., 200' F. 84.119 71.051 1.184 0.951 3.774 3.968 1.831 2.104 0.869 0.794 1.465 1.845 0.717 1.032 1.440 0.640 1.091 1.654
7905 Lb., 200' F. 71.990 1.159 83.465 0.971 3.879 3.996 2.139 0.866 1,852 1.726 0.867 1.496 0.797 1.059 1.330 1.080 1.532 0.705 17.286 247 0.8608 0..2524 27.28 1.932
19.745 228 0.8452 0.4726 46.74 1.720
17.200 253 0.8586 0.1797 19.23 1.955
0.418
...
... ... ...
a Pressure in pounds per square inch. b Equilibria determined with 9374lb./sq. in. abs. vapor phase as a system.
...
the system. The equilibrium constants as originally determined by Kata and Hachmuth (8) for an Oklahoma City Wilcox crude oil and natural gas were also added to both the 120 O and 200 F. isotherms for comparison. The plot in Figure 4 of the mole fractionof vapor in the equilibrium cell at vhrious pressures shows that 120" and 200" F. were
INDUSTRIAL A N D E N G I N E E R I N G CHEMISTRY
October, 1945
935
and in Figure 6, t i n a function of each other. Within the accuracy of the data it does not appear t h a t temperature effect on these two properties may be established. These data are particularly useful in defining the accuracy of the heptanes and heavier equilibrium constant and for the i m p li c a t i o n they may extend to reservoir studies showing, for example, that very heavy crude oil may have been in the vapor phase at one time or another. This is ill u s t r a t e d by the vapor phase anallysis in Table I11 for the sample a t 8078 pounds and 200 O F. Figure 5. Molecular Weights and Specific Gravities of Heptanes and Heavier Fractions The vaDor - -Dhase contains 7.195 mole per cent of heptanes and heavier, which is 43y0 by weight, TABLEIV. PROPORTION OF CELL CONTENTS IN VAPORPHASE and has a molecular weight of 181 and specific gravity of 0.8138. A T VARIOUS PRESSURES AND TEMPERATURES This vapor phase could, upon pressure reduction, form a liquid Preaaure, Mole Fraation Vapor" by: phase similar in composition to the composite analyses of many Lh./Sq. In. Temp., Heptanea and producing crude-oil reservoirs during the period of initial diAbs. * F. Methane balance heavier balaooe covery and development. 120 0.748 3566 120 0.741 5581 I n Figure 7 the compressibility of each phase is shown as com120 0.718 5831 120 0.727 0580 puted from the displaced volumes, a direct measurement. The 0.765 120 7940 mole quantity of each sample is an indirect measurement partly 0.871 , 120 9374 0.853 200 1047 dependent upon the molecular weights of the heptanes and heav0.832 1600 200 0.825 1907 200 ier fractions which were determined by the cryoscopic method. 0.804 2500 200 These data aid in deciding whether a liquid phase sample may 0.784 3560 200 0,776 3792 200 have been contaminated with some gas phase during displace0.761 200 4957 0.758 200 6402 ment of the sample. The ratio of vapor to liquid compressibility, 0.754 5737 multiplied by the ratio of mole fraction of vapor to mole frar0,818 6740 0.770 200 7470 tion of liquid from Figure 4 gives the ratio of vapor volume to 0.795 200 7905 0.697 200 7965 liquid volume in the system at a given pressure and temperature.
t%
8078 4725s 6752)
--
200 120 120
-
-
0.807 0.788 0.800 Xn)/(Yn
-
Mole fraation vapor (Zn x$ where Z n mole fraction oomponent in composite Yn Imole fraction component in vapor phase X n mole fraotion component in liquid phase b Derived system.
a
TABLE V. 'EXAMINATION OF HEPTANESAND HEAVIER FRACTIONR Vapor Phsse at 9374 Lb.0 and 120D ~. F. --. 193 0.8238 62.0 0.789 0.879
100' F. 130: F.
0.29 0.148
F.
139 78
Mol. weight 8 gr. at 60° F. Zevapd. at 580' F. Sp. gr. at 60° F. Sp. gr. of realdue at BO0 F. V i s c o a ~ ; ~oenti~~
.
above the critical temperature of the constant composition mixture. As the mole fraction vaporized for this plot was computed (Table IV) by both a methane and a heptanes and heavier balance, the few points not on the curve indicate an error in some of the mole percentages of methane or of heptanes and heavier. The extrapolated portions of the curves at the higher pressures are based in part on a study of both the variation in the phase compositions and the equilibrium constants with pressure. From this extrapolation it appears that the cell contents were all vapor at approximately 9200 pounds per square inch absolute for 200 "*F. and 10,500pounds for 120' F. I n Figure 5 the molecular weight and specific gravity of the heptanes and heavier fraction arc) shown as a function of pressure,
Liquid Phaseb
at 6752 Lb. and 120° F. 22' 846 49.3 0.801 0.886
Viscosity, Saybolt sea. loOD F. 130'
Liquid Phase at 9374 Lb. and 120° F.
Billings Crude Oil
270 0.8710 39.0 0.804 0.916
200.8 0.8285 56.0 0.791 0.886
0.76O 0.197
1.80 0.65
0.454 0.203
8510 98
832 299
210 101
Conradson carbon of 580° F. residue 0.64 (mixture) Appearanoe at Light red brown Chunks of war, BlaFk. Dark room temp. & yellowish dark yellowVI~COUS oryetals, wax ish brown 4 Preaaure in pounds per square inoh absolute. b Li uid phase obtained by reducing pressure on 9374 psia vapor phase. e D&oult to obtain duplioate results-wax may not have melted.
INDUSTRIAL AND ENGINEERING CHEMISTRY
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Vol. 37, No. 10
so0
280
IeO'F. 0 8OdF.
260-
+ X
OHARQINQ OIL OR OAS EQUILIBRIA DERIVED FROM 9374 P.9.l.A. VAPOR AT 120'F. YISC. M IXTURES AT 120%
U
0.4 0
0
Figure 6. Relation of Specific Gravity to Molecular Weight for Heptanes and Heavier Fractions
The determinations for the fixed composition mixture were considered to be a consistent set of equilibria. It was therefore decided t o alter the constant composition system by removing at some high pressure the liquid phase from the system and then, by lowering the pressure of the remaining vapor phase and taking advantage of the retrograde condensation, to form a new vaporliquid equilibrium. Accordingly, two sets of equilibria were measured in which the 9374 pound-120' F. equilibrium liquid phase was removed. The pressure was lowered to 6752 and 4725 pounds per square inch absolute, respectively, and the equilibrium data were measured. Significant changes were noted in the molecular weights, specific gravities, and other properties of the heptanes and heavier fractions as listed in Table V. At 4728 pounds pressure the liquid phase of the derived system had a molecular weight about 18 points lower than the smoothed value of 220 for the parent system at the same pressure, The equilibrium constants were, however, not significantly different from those of the parent system at a corresponding pressure. This suggested that the characteristic of the heptanes and heavier fraction was not so important at these equilibrium conditions. A study of the phase compositions showed that the distribution of the components was not materially changed by removing the liquid phase at 9374 pounds per square inch absolute, although the molecular weight of the heptanes and heavier fraction was changed.
VAPOR AT IEO'F. f LIQUID AT 12O'F. f f EQUILIBRIA DERIVED FROM 9374 RS.1.A. VAPOR I
I
1
Figure 7.
3 4 S 6 7 e 9 1 RESSURE I N THOUSANDS RSlA.
0
1
1
Compressibility, Z = PVINRT, of Equilibrium Phases
A phenomenon encountered in all high-pressure vapor phase samples was the appearance of colored hydrocarbons. A t very high pressures the condensed liquid in the analytical fractionating column kettles was like a light lube oil in color. The material was colored as it came from the equilibrium cell, and the degree of color which i t showed was roughly an indication of the pressure of the equilibrium-the higher the pressure the darker the liquid. ACKNOWLEDGMENT
The author wishes to acknowledge the heIpful suggestions of W. S. Walls and D. L. Kata of the University of Michigan, the precise analytical work of Dan E. Smith and Donald R. Douslin, the assistance of many other members of the Research Departr ment, and the permission of the Phillips Petroleum Company to publish this work. LITERATURE CITED (1)
Eilerts, Kenneth, and Smith, R. V., U. S. Bur. Mines. Rept. Investigation 3642 (1942).
. , Kats. D. L.. and Hachmuth. K. H..IND.ENQ.CHEU.,29, 1072
(2)
(1937).
(3) Roland, C.H., Smith, D. E., and Kaveler, H. H., OiZ Gas J., 39 (46), 128 (1941).
B..and Ksta, D. L., Tram. Am. Inst. M i ~ i m gMet. Enpu., 155,232 (1944). (6) .Webber, C. E.,Ibid., 141,192 (1941).
(4) Standing, M.
