Determination of Water in Oil Emulsions by a Microwave Resonance Procedure Daryl A. Doughty Bartlesville Energy Research Center, Energy Research and Development Administration, Bartlesville, Oklahoma 74003
A mlcrowave resonance procedure was developed for the rapid semimicro quantitative determlnatlon of water In oil emulsions. The apparatus operates at a frequency of 9510 MHz in the X-band microwave region. The procedure Is based on the large differences in dielectric properties between water and oil and can be used to determine water content from 0 to 100 %. The measurement requires only 0.2 cm3 of sample and takes only 2 to 3 min per sample. The preclsion Is variable, depending on water content, and ranges from f0.5% at low water content to f3.7% for samples containlng 75 to 80% water.
The Energy Research and Development Administration (ERDA) together with industry is investigating methods for the enhanced recovery of oil (I). Of the several methods possible for enhanced oil recovery, water-miscible flooding using surfactants (also called micellar flooding) appears to have the most wide-spread application (2). As a result of the application of this recovery technique, fluids produced by oil wells will be variable mixtures of oil, water (brine), surfactants, and cosurfactants along with other more minor constituents. Laboratory investigations of these complex mixtures are required before field trials to determine the most effective and economical injection fluid characteristics. Out of these investigations arose the need for a method of determining water in oil-water emulsions that would be applicable to small samples. Several different methods are available for the determination of water in petroleum or petroleum produds. Standard methods for use in the laboratory are centrifugation, distillation, and Karl Fischer titration (3). The first two have the disadvantage of requiring larger samples of 20 t o 50 cm3 volume. Although the centrifuge method normally requires little sample treatment, its use on the microemulsion systems investigated in this research would require the use of demulsifying agents. Thus, for our purposes, both centrifugation and distillation procedures would require more extensive sample treatment. Karl Fischer titration requires a much smaller sample volume than the other two methods and also would be faster because it requires less sample handling. However, all three of these methods result in sample destruction, a disadvantage if additional analysis of the sample is required and only limited sample is available. Nondestructive methods for the determination of water in oils generally rely on the large differences in dielectric properties between water and oil (4). Water has a dielectric constant of -80 compared to -2.3 for most crude oils (refined, nonaromatic oils have dielectric constants in the range 1.9-2.0.) Many of the references on methods using dielectric constant measurements report the use of a resonant circuit consisting of an inductance in parallel with a capacitance cell. Changes in the dielectric properties of the sample cause corresponding changes in the cell capacitance, affecting the circuit’s resonant frequency. Some methods use a capacitance bridge to measure changes in the sample cell capacitance. Several instruments based on these methods have been de690
ANALYTICAL CHEMISTRY, VOL. 49, NO. 6, MAY 1977
veloped for continuous monitoring of wellhead oil in the field for water content ( 4 ) . These capacitance cell methods have two disadvantages for our requirements. They also require a larger sample (10 cm3 or more) to fill the cell, and sample conductivity limits their usefulness to emulsion systems that are oil-external, generally containing less than 50% water (5). The method developed and described in this paper also uses the difference in dielectric properties between water and oil. However, the apparatus operates at much higher frequencies in the microwave region (specifically 9510 MHz) and the sample is inserted into a resonance cavity. The required sample volume is much smaller (approximately 0.2 cm3), and the apparatus does not appear to be directly affected by sample conductivity. Thus, i t is useful on emulsions containing up t o 100% water; however, precision is reduced a t water contents above 50%.
EXPERIMENTAL Apparatus. Figure 1 illustrates the principal parts of the system. The adjustable resonant cavity was made from a Hewlett-Packard model X920A adjustable short. The short was modified in two particulars. The regular knob on the short was replaced by a precision calibrated knob, arbitrarily provided with 100 divisions, together with a fixed index mark attached to the short’s body. Next, a sample tube hole was drilled across the wide dimension of the short. The location of this hole was such as to position the sample in a region of maximum electric field inside the cavity. The size of this hole must be such as to prevent excessive sideways movement of the sample tube. Figure 2 is a schematic representation of the cavity, showing the location of the sample tube and the relative positions of the electric and magnetic fields inside the cavity at resonance. The opening at the left end is for coupling the cavity to the waveguide. Also shown is the electric field variation along the sample tube axis and the longitudinal axis of the cavity. The cavity as set up operates in the mode of resonance referred to as the Telozmode (6). Turning the knob changes the length of the cavity causing resonance to occur at different wavelengths and frequencies. Changing the dielectric properties of the medium inside the cavity also affects the resonance conditions. The resonant frequency is mainly dependent on the dielectric constant of the medium and the sharpness of the resonance is dependent on the dielectric loss of the medium which affects the Q of the cavity (7). Together the dielectric constant and the dielectric loss determine the complex dielectric constant. During operation at a fixed frequency, a change in the dielectric medium can be counteracted by changing the length of the cavity to reestablish resonance. The cavity is attached to the waveguide from the bridge with an adjustable iris in between. The iris provides for maximizing coupling between the waveguide and cavity. Also contained in the waveguide between the bridge and the cavity (not shown in Figure 1) is a Hewlett-Packard model X532B wavemeter to monitor the cavity resonance frequency. Water has both a high dielectric constant and a high dielectric loss at X-band frequencies. It would cause large changes in cavity resonant frequency and cavity Q if present in appreciable amounts. Therefore, to be useful in measuring water content in samples of high water content and to restrict changes in resonance conditions to manageable proportions, a small diameter sample tube is used and its position carefully chosen to minimize these changes, yet still permit a reasonable difference in response to samples of similar yet different water content. With the sample tubes used, the change in the length of the cavity going from a
60 H r
Klystron Power Supply
Sweep G e nerotor
1
Adjustoble resono n t c a v i t y with s a m p l e
Flgwre 1. Block diagram of apparatus for determination of water in
oillwater emulsions
The klystron power supply provides smooth dc fiiament voltage, a regulated positive voltage to the klystron resonator, and a regulated, variable, negative voltage to the klystron reflector. The power supply control must be such that the filament supply comes on first, then the reflector supply, and then the resonator supply. The klystron frequency is partly controlled by variations in the reflector voltage. The 60-Hz sweep generator supplies a fixed voltage sweep signal to the oscilloscope X axis and a variable voltage sweep signal to the reflector of the klystron through the klystron power supply. This sweep signal applied to the reflector of the klystron causes the klystron's power output to sweep through a band of frequencies whose width is controlled by the sweep amplitude. The oscilloscope thus displays a signal whose vertical component is related to the microwave power incident on the cavity and whose horizontal component is related to the frequency of the microwaves. The sweep generator also has a phasing control on the oscilloscopesweep signal for proper display of the signal. The sample tubes used were precision quartz tubes obtained from Wilmad Glass Co., Inc. (Part No. 705-PQ). The tubes were long enough to be cut in half and, by sealing the upper half on one end, to make two short tubes from each regular tube. A Karl Fischer titration (KFT) apparatus was constructed and used as the primary standard method for water determination (3).
t
t
EY! Ey
I
b
position
Figure 2. Schematic representation of the cavity showing the relative positions of sample tube and electric and magnetic fields at resonance
sample containing no water to one of all water is 0.045 inch for a cavity 1.70 inches long. At the sample tube position (see Figure 2), the antinode of the electric field shifts by only 0.034 inch with this change. This would result in less than a 1% change in the electric field strength experienced by the sample if the field amplitude were not also affected by changes in the cavity Q value. Because this shift in the antinode is a regular function of the cavity adjustment to achieve resonance, a calibration against standards would adequately account for its effect even if it were larger. The microwave bridge is a Varian Associates X-band bridge. It has a tuning knob for varying the klystron frequency and an attenuator for varying the microwave power incident on the cavity. The klystron arm of the bridge also contains an isolator which attenuates reflected microwave power and prevents it from causing frequency shifts in the klystron output. The bridge itself is a hybrid tee containing four arms. When microwave power from the klystron reaches the hybrid tee it divides, one half going to an arm containing a resistive load which absorbs essentially all the power, the other half going to the arm containing the wavemeter and the cavity together with the iris. If the iris cavity is properly adjusted far resonance, all this power is absorbed by the cavity and the bridge is balanced. The crystal detector located in the remaining arm of the bridge, whose output is fed to the 'l axis of the oscilloscope, would show no response under this condition. If the iris cavity is off resonance, not all the microwave power incident on the cavity is absorbed; part is reflected. When this reflected power reaches the tee it divides, half going back toward the klystron where it is absorbed by the isolator, the other half going into the arm containing the crystal detector whose output is related to the microwave power incident on the crystal detector. The crystal detector has provisions for optimum matching to the bridge.
Reagents. Delaware-Childers crude oil (Delaware-Childers field, Northeast Oklahoma) was used for the crude oil emulsion systems. Stoddard solvent was used as a refined oil for the rest of the emulsion systems. One crude oil emulsion system was prepared using Amoco H-4447-1sulfonate with ethoxylated alcohol cosurfactant. All other emulsion systems were prepared using Petronate TRS-1OB (Witco Chemical, Sonneborn Division), a sodium sulfonate, as surfactant in conjunction with various alcohols as cosurfactants. Alcohols used were isopropyl alcohol, isobutyl alcohol, tert-butyl alcohol, and tert-amyl alcohol. All alcohols were reagent grade. The TRS-lOB/alcohol blends were prepared in the ratio 2 parts TRS-1OB :1 part alcohol by weight. Various concentrations of brine were used as the aqueous phases in the emulsion systems. Most brines contained only reagent grade sodium chloride in distilled water with some brines containing in addition s m d concentrations of Ca2+(aq) (50 ppm) and Mg2+ (as) (10 ppm). Stabilized Karl Fischer Reagent (Matheson Coleman and Bell) was used for the Karl Fischer titrations. Emulsion Preparation. Two parameters were used to control the water content of the emulsions used in this research once the oil, surfactant, and cosurfactant were selected: (a) the relative proportion of surfactant/cosurfactant blend added to a 50/50 mixture by volume of the oil and aqueous phase-more surfactant/cosurfactant leads to greater water content in the emulsion; (b) the salt content of the brine used as the aqueous phase-greater salt concentration leads to decreasing water content in the emulsion. The actual salt content of the water taken up in the emulsions was not determined and may not be simply related to the salt content of the aqueous phase used to prepare the emulsions. Procedure for HzODetermination. Sufficient sample to be tested is transferred to the sample tube so that the sample extends above and below the openings in the cavity when the tube is placed in the cavity. The precise volume of the sample is not critical if the above precaution is satisfied. With the sample tubes used in this investigation (Wilmad No. 705-PQ), 0.2-cm3sample volume was more than sufficient. Figure 3 represents the oscilloscope display typical for an emulsion sample of low water content. The display is the microwave power reflected from the cavity and appearing in the detector arm of the bridge. The dip is that portion of the power absorbed by the cavity centered about the resonant frequency of the cavity (8). A perfect cavity of infinite Q would absorb power only at one frequency, Le., the dip would have no width. Because the cavity is not perfect and has a finite Q, the dip has a measurable width related to the Q of the cavity-the lower the Q, the greater the width of the dip. If the cavity absorbed no power, the display would follow the dashed part of the curve in the central region and would be the power mode of the klystron, representing the klystron's power output as a function of frequency. If the sweep amplitude is large enough, several power ANALYTICAL CHEMISTRY, VOL. 49, NO. 6, M A Y 1977
691
Typical oscilloscope display of klystron power mode with cavity resonance absorption dip superimposed Figure 3.
modes centered about different frequencies would be displayed. During initial setup of the apparatus, the klystron tuning, reflector voltage, and the sweep amplitude are adjusted to display the largest power mode and center it in the oscilloscope display. The height of the power mode display is controlled by the klystron attenuator and the oscilloscope vertical gain. To minimize the chance of sample heating microwave power incident on the cavity was set at about 18 db below 0.25 watt, or approximately 0.004 ,watt. Figure 3 depicts what can be considered the optimum display for making measurements. After this initial setup, hardly any adjustment of klystron tuning, reflector voltage, or sweep amplitude need be made on a routine basis. Only two adjustments are necessary for making measurements on different samples once the initial setup is made. These are illustrated with the solid curve in Figure 3. With the sample in the cavity, the calibrated knob on the cavity is adjusted to display the resonance dip superimposed on the power mode display. The dip is roughly centered. The adjustable iris is then adjusted to maximize the depth of the dip (on samples of high water content, a dip may be barely discernible-only a flattening of the top of the power mode.) There is a slight interaction of these two controls; a touch-up adjustment of each may be required. At the end of the adjustments,the dip should have the maximum possible depth for the sample and the crests of the power mode on each side of the dip should lie on the same horizontal line of the oscilloscopescale as displayed in Figure 3. This arbitrary criterion permits an easily recognizable feature for standardizingresonance settings. It also seems to lead to a satisfactorily constant resonance frequency for different samples. The measurement recorded is the scale reading on the calibrated knob of the cavity opposite the index mark. This scale reading is identified by the label VS for variable short. To eliminate the influence of possible long-term instrument drift, all samples were referenced to the VS reading for the pure oil, and the data plotted on the graph of Figure 4 are AVS vs. volume percent water where AVS = VS,,, - VSsamp~e.
RESULTS AND DISCUSSION The data obtained in establishing the relationship between the variable short cavity setting and water content of microemulsions is presented in Figure 4. The variable short settings for all samples were referenced to that, of the respective pure oil, either Stoddard solvent or Delaware-Childers crude oil, as mentioned previously. The pure oils were found to contain very little water as indicated by Karl Fischer titration; less than 0.04% by volume. The variable short setting of Delaware-Childers oil is lower by 2.39 units than that of referenced to Stoddard solvent. This means that AVSH,~ Delaware-Childers oil would be 2.39 units less than AVSH~O referenced to Stoddard solvent. Data for Delaware-Childers oil samples were therefore corrected according to the following equation:
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WATER, volume percent Figure 4.
Standard curve showing relationship between cavity setting
(AVS) and water content for various oillwater microemulsions. The solid curve is the least squares fit. The dashed curves are the 95% confidence limits. Open symbols represent measurements on individual samples. Solid symbols represent averaged measurements on 14
samples-the error bars, expressed as a variation in water content, are at the 95% confidence level. Circles (0,0 )emulsions containing Stoddard’s solvent with fefibutyl alcohol. Triangles (A,A)emulsions m) containing Stoddard’ssolvent with ferkamyl alcohol. Squares (0, emulsions containing Delaware-Childers crude oil with various alcohols Table I. Equation Constants for Best Fit
c, c 2
c 3 c 4
Sa
2,5934 -1.7308 X -8.6375 X l o - ’ 1.0862 X 1.387
a S is expressed as a deviation in AVS assuming the water percentages to be exact.
This ensures that AVSH,~ referenced to Delaware-Childers oil is the same as AVSH~O referenced to Stoddard solvent, with samples between the pure crude oil and pure water being corrected in proportion to the ratio of their AVS values to that of water. This correction was used instead of one based on the volume fraction of water because both oils gave data following the same trend in their relationship between AVS and water content. The assumption was made that any difference between the two data sets varied according to that same trend. As Figure 4 shows, there is no simple relationship between AVS and water content even though it is reproducible. The solid curve through the data of Figure 4 was obtained by a least-squares computer program fitting to an equation of the type
y
=
clx+ c2x2+ c3x3+ . . .
with AVS = y and % HzO = X . The program also calculated the standard deviation of the data relative to the curve. A best fit was obtained for an equation containing four constants which are listed in Table I along with the standard deviation for this curve. The dashed curves represent the 95% confidence limits for the fit. T o establish the source(s) of the scatter in the data, selected emulsion systems were prepared, and 14 samples of each
Table 11. Data Obtained in Establishment of Measurement Variability Sample H2O
Stoddard solventa D.C. oila
Meanvariable short setting, VS, arbitrary units 95.29 f 203.86 c 201.47 i 100.41 c 121.51 t 139.30 * 167.56 f 109.86 f 132.39 f 161.44 i 137.63 f 120.37 c 108.06 i 105.44 fi 102.82 i
Vol % H,O from least squares fit 100.0 i 1.5 0.0 i 0.6
Mean vol % H 2 0 by KFT 100.00 i 0.44
0.70 0.65 1.05 0.41 0.57 0.78 0.43 0.45 0.75 0.46 0.69 0.71 0.57 0.80 1.45
--_._
0.0 i 0.6 91.00 f 0.11 93.3 f 2.2 50.33 t 0.40 49.9 f 1.8 32.6 i 1.0 32.50 i 0.55 15.7 c 0.7 14.89 t 0.16 70.82 i 0.62 72.1 c 3.7 37.18 f 0.29 38.2 f 1 . 3 18.94 f 0.13 18.8 i 0.8 31.74 i 0.48 33.2 i 1.1 50.8 t 1.9 52.60 i 0.26 77.84 i 0.36 76.8 i 3.7 83.27 ~t 0.42 83.8 f 3.1 89.2 * 2.6 90.25 i 0.51 a h->an VS setting based on fewer samples (five for Stoddard solvent; three for D.C. oil). --Jwever, sample tubes used were selected t o cover range of variability expected as mentioned in the text. D4B1 D5Em D6Cm D7Eu D8C1 DlOAm DllFu DC44.5/10m DC46/8m DC46/81 DC47/61 DC49/21
system were analyzed, each sample in a different sample tube. A set of 28 sample tubes was available and on the basis of instrument response to a pure substance placed in each of the sample tubes, these tubes had been categorized as giving a high, intermediate, or low response. The 1.4 sample tubes were selected taking half of each of the three categories (plus or minus one tube in case the category had an odd number). Thus each emulsion was analyzed in 8: set of sample tubes having as representative a response as possible. The emulsion samples themselves were drawn from the upper, middle, or lower regions of the microemulsion layer on a rotating basis as fresh samples were placed in the tubes. This gave a check on the degree of homogeneity of the emulsion as a source of variability. The results of this analysis are summarized in Table 11. The measure of dispersion reported in the table is the standard deviation. The water content of each of these emulsions was determined by Karl Fischer titration of two to three samples from each emulsion. These data are also plotted in Figure 4. The error bars represent the combined dispersions in AVS and % H20 for each emulsion expressed as variation in % H2Q a t the 95% confldence level. Only one of the samples (DC49/21) gave much indication of inhomogeneity of the emulsion layer. This accounts for the much larger deviation in % as shown in Table 11. Without sample DC49/21 the average standard deviation (S,) for the samples listed in Table I1 is 0.64 with a standard deviation of 0.18. The three “pure” substances listed thus appear to give a typical instrument response compared to the emulsions. This indicates that the variability in % is characteristic of the sample environment during a measurement and not the sample itself. Part of this variability is associated with instrument stability and warmup characteristics. A sealed sample of the pure oil was measured a t the beginning and end and several times during a run of samples as a check on instrument characteristics. A typical variation in VS from beginning to end would be 0.2 to 0.3 unit. This can be considered a measure of the instrument stability and reproducibility including effects caused by insertion and removal of sample tubes. Comparing this to the average standard deviation mentioned above (0.64 f 0.18 unit), it is evident that the major portion of the deviation arises not from the instrument but from the sample tubes. In Figure 4, the error bars on the points plotted from data in Table I1 generally appear representative of the overall data variability. The average standard deviation (expressed as a variation in AVS) for the points plotted from data in Table I1 is 1.03 compared to the value of 1.387 obtained from the curve fitting program for all the points. Most of this variation
Table 111. Results of Water Determination in Emulsions Containing a Different Surfactant /Cosurfactant Vol % H,O Vol % H,O from curve by KFT Sample A m 54.0 A 84.7 i 0.3 53.3 * 1.9 72.7 f 1.1 39.5 t 1.6 47.2 B*O. C
83.4 f 64.2 f 81.6 i 56.0 ?r 88.1 i 60.3 f 85.7 i 53.2 i: 97.2 t 84.0 * 43.4 f 40.8 i 30.0 I 23.9 ?r 16.8 i 13.1 f
D* E
F* G H*
I J*
K L* M N*
0
P*
Q
R* A
A
;fL cc DD EE
FF GG “U ”M 11U
IIL
0.0 0.1 0.1 0.3 0.6 0.4 0.0 0.9 0.1 0.1 0.4 0.6 0.1 0.0 0.2 0.1
~ 92.1 ~ f 0.0 99.4 i 1.0 92.5 i 86.7 i 78.8 t 68.0 ?r 55.5 i 44.4 i 15.2 t 55.1 0.0 f 86.2 t
0.4 2.3
0.1 0.5 0.4 0.0 0.0 0.0 0.0 0.0
51.3 t: 32.4 c 48.9 f 26.9 f 58.9 i 29.6 f 54.9 i 25.1 i 80.7 t 52.2 i 19.4 i 18.1 t 12.8 f 9.8 i 6.9 t 5.2 *
1.7 1.0 1.6 0.9 2.4 1.0 1.8 1.2 3.4 1.8
0.8 0.9 0.6 0.6 0.5 0.5
67.2 i 3.4 85.9 i 3.6 68.3 f 3.6 56.4 c 4.5 45.7 i 1.7 35.2 f 1.2 26.5 c 0.9 20.0 i 0.8 6.2 i 0.6 26.2 ?: 0.9 0.0 i 0.6 55.4 i 2.2
51.9 38.4 49.3 30.7 60.7 36.4 57.4 32.0 76.5 53.0 21.0 22.5 13.9 11.9 7.5 6.6 78.3 84.2 71.8 62.6 46.7 35.6 25.2 18.3 6.3 25.0 0.06 55.3
The sample designations with an asterisk contained Stoddard’s solvent as the oil component. All others contained Delaware-Childers crude oil. The subscripted letter refers to the level of the sampled portion of the microemulsion layer: U, upper; M, middle; L, lower portion of the layer. a
arises from VS measurements and, as previously discussed, the sample tubes appear to be responsible for the major share of the VS variation. Table I11 gives the results obtained for the determination of water in emulsions prepared using a different surfactant/cosurfactant blend with different brine concentrations and with Stoddard’s solvent or Delaware-Childers crude oil. A correction factor, based on the sample tube used, was m value for the applied to each sample in obtaining the A sample. The volume percent water obtained using the method ANALYTICAL CHEMISTRY, VOL. 49, NO. 6, MAY 1977
693
is compared to that obtained using Karl Fischer titration. The measure of dispersion is the standard deviation. The values obtained for the emulsions containing Delaware-Childers oil agree within the 95% confidence limits, and the differences are sometimes positive, sometimes negative. The values obtained for the emulsions containing Stoddard’s solvent, however, are significantly different in many cases and are consistently lower for the method compared to the K F T results. The actual emulsion is a complex system containing several components in addition to the oil and water which are known to affect the dielectric properties of water in solutions (9). The salt and alcohol may be of particular significance in this regard. When the emulsions were prepared, there existed either an excess oil layer, an excess aqueous layer, or both in equilibrium with the emulsion layer, depending on the initial composition (IO). What portions of the alcohol and salt are retained in these excess phases and what portions retained in the emulsions are not known. However, the variation in water content of the emulsions is a regular function of the compositional variation during preparation. A reasonable assumption would seem to be an equally regular variation in the salt and alcohol content of the emulsions accompanies the variation in water content. The effects of these variations in salt and alcohol content are implicitly contained in the relationship between AVS and water content shown in Figure 4. The complex nature of the emulsions makes it virtually impossible to isolate the effects of variations in salt and alcohol content from that of the changing water content. The major advantages of this method of water determination in oil emulsions are the rapidity and simplicity of the measurement, the small sample size required, and the nondestructive nature of the method. Each measurement including placing the sample in the sample tube requires only 2 to 3 min with no involved sample processing required. The lack of a simple relationship between AVS and water content makes preparation of a standard curve more difficult as many more standards must be measured to establish the shape of the curve. Also, as the results indicate, the curve presented in this paper does not appear to be entirely general. A standard curve prepared for each system of interest would improve the reliability and probably increase the precision of the measurements.
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ANALYTICAL CHEMISTRY, VOL. 49, NO. 6, MAY 1977
The method as described can be applied to samples over the entire range of water content. However, the precision is reduced on samples of high water content above 40%. If samples are measured which contain a limited amount of water, the sensitivity and precision could be increased by using a larger diameter sample tube. The larger cavity filling factor resulting from the larger tube would increase the AVS value for a given sample. Also, larger diameter sample tubes of greater precision can be obtained than the ones used in this investigation, particularly if glass tubes are used instead of quartz. Although the results of this investigation have been confined t o the determination of water in oil/water microemulsions, the method would appear to be applicable to the determination of water in other materials either solid (powdered) or liquid as long as an appreciable difference existed in the dielectric properties of water and the material of interest.
ACKNOWLEDGMENT I wish to thank P. B. Lorenz of the Center for his many helpful suggestions in preparing the emulsion systems used in this research.
LITERATURE CITED (1) National Plan for Energy Research, Development, and Demonstration: C r e a m Energy choices for the F W e , Vol. 1, (ERDA48), Energy Research and Development Administration, Washington, D.C., 1975. (2) W. B. Gogarty, J. Pet. Techno/.(Jan.) 93-102 (1976). (3) ASTM test method designations D 98 (centrifugation), D 95 (distillation), and D 1744 (Karl Flscher Titration) in “1975 Annual Book of ASTM Standards”, American Society for Testing and Materials, Philadelphia, Pa., 1975. (4) W. J. Warren, J . Pet. Techno/., 1207-1212 (1962). (5) R. S. Wood, Oil Gas J . (Dec. 8), 102-107 (1958). (6) F. A. Nelson, “Instrumentation of EPR” in Varlan Associates, “NMR and EPR Spectroscopy”, Pergamon Press, New York, N.Y., 1960. (7) C. P. Smyth, “Dielectric Beehavior and Structure”, McGraw-Hill, New York, N.Y., 1955. (8) W. C. Lockhart and R. C. Jones, “EPR Spectrometers: Operating Fundamentals” in Varian Associates, “NMR and EPR Spectroscopy”, Pergamon Press, New York, N.Y., 1960. (9) J. B. Hasted and S. H. M. El Sabeh, Trans Faraday Soc., 49, 1003-101 1 (1953). (10) R. N. Healy, R. L. Reed, and D. G. Stenmark, SOC.Pet. Eng. J . (June) 147-160 (1976).
RECEIVED for review November 11,1976. Accepted January 17, 1977. Mention of brand names does not imply endorsement by ERDA.
