I AllliOb

PUBLICATIONS

NBSIR 83-1683

DIELECTRIC MEASUREMENTS OF OIL

SHALE AS FUNCTIONS OF

TEMPERATURE AND FREQUENCY

Ramon L. Jesch

Robert H. McLaughlin

National Bureau of Standards

U.S. Department of Commerce

Boulder, Colorado 80303

January 1983

Or e-RjnJAif'iS UrEART

NBSIR 83-1683

DIELECTRIC MEASUREMENTS OF OIL

SHALE AS FUNCTIONS OF

TEMPERATURE AND FREQUENCY

Ramon L Jesch

Robert H. McLaughlin

Electromagnetic Fields Division

National Engineering Laboratory

National Bureau of Standards

U.S. Department of Commerce

Boulder, Colorado 80303

January 1983

U.S. DEPARTMENT OF COMMERCE, Malcolm Baldrige. Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

C.O

PREFACE

This final report on Dielectric Measurements of Oil Shale as Functions of

Temperature and Frequency terminates a two-year investigation on the

Development of High Frequency Electromagnetic Mapping (HFEM) Technology funded

by the U.S. Department of Energy, Laramie Energy Technology Center, Laramie,

Wyoming. The contract was awarded to the Electromagnetic Fields Division of

the National Bureau of Standards in 1980 for continuation of oil shale work

started under Purchase Order No. DE-AP22-80PC10236 in 1979.
CONTENTS

Page

Preface i 1. INTRODUCTION 1 2. SAMPLE HOLDER CHARACTERIZATION 3

2.1 Dielectric Samples 3

2.1.1 Preparation of Samples and Sample Holder 3

2.2 Measurement Procedure and Results of Standard Samples 5 3. OIL SHALE MEASUREMENTS 8

3.1

Oil Shale Samples 8

3.1.1 Measurement Results of A-1 Oil Shale Samples 11

3.1.2 Measurement Results of Additional Oil Shale Samples 15

3. 1.2.1 Measurement Conditions 15

3. 1.2. 2 Preparation of Oil Shale Samples 16

3. 1.2. 3 Measurement Results 17

3.1.3 Gas and Liquid Sample Collection 27

4. DATA SUMMARY 30

5. CONCLUSIONS 30

6. ACKNOWLEDGMENT 31

7. REFERENCES 31

IV
DIELECTRIC MEASUREMENTS OF OIL SHALE AS

FUNCTIONS OF TEMPERATURE AND FREQUENCY

Ramon L. Jesch

Robert H. McLaughlin

Electromagnetic Fields Division

National Bureau of Standards

Boulder, Colorado 80303

A high-temperature sample holder designed by the National

Bureau of Standards was used to determine the dielectric properties of approximately 40 oil shale samples as functions of

temperature and frequency. A description of the sample holder

characterization is given along with the measurement procedure and

the sample preparation. Experimental results are given for different oil shale samples, varying in yield from 0.024 L/kg (6

gal/ton) to 0.338 L/kg (81 gal/ton), that were measured at room temperature (25®C) up to 500°C and within the frequency range of 5 - 1000 MHz.

Key words: dielectric properties, dielectric constant, electromagnetic, high-temperature sample holder, oil shale.

1. INTRODUCTION

In response to a request from the Department of Energy (DOE), the

National Bureau of Standards (NBS), in 1979, undertook a program to develop

the technology to utilize High Frequency Electromagnetic Mapping (HFEM) techniques for evaluating rubblized oil shale in the cold retort state in the

modified in situ process. This technology development should also be applicable for using HFEM techniques for diagnosing, monitoring, controlling and

evaluating modified in situ retorts after they are ignited. The modified in

situ retorting process appears to offer significant environmental and economic

advantages compared to surface retorting methods. Developmental work is

needed to formulate optimum techniques for preparing modified in situ

retorts. The efficiency of the prepared retort is governed, among other

things, by porosity distribution, void ratio and its distribution and rubble

size within the retort. There is presently no economical method of measuring

the physical state of a cold retort, and, therefore, there is no way to predict the efficiency of the retort prior to its ignition. One possible technique for economically determining the physical state of the retort is by HFE‘! techniques.

1
The work performed during the period October 1979 to September 1980 was reported in the NBS Final Report SR-723-2-81, "Dielectric Properties of Oil

Shale as a Function of Frequency" which contained the results of measurements

the National Bureau of Standards made of ten half-core oil shale samples to

determine their electromagnetic (EM) properties of permittivity (dielectric

and attenuation constants) as a function of frequency. The samples were furnished by the Laramie Energy Technology Center (LETC), Laramie, Wyoming, and were taken from a core which was drilled between Occidental's retorts #7 and

#8 near Rifle, Colorado. The measurements were taken within the frequency

range of 1 - 2000 MHz at various frequency intervals. The use of EM properties of permittivity to characterize oil shale for el ectromagnetical ly mapping

a retort is one possible technique being considered by the DOE for determining

the physical state of a retort prior to its ignition.

The work performed during the period October 1980 to September 1981 was reported in the NBS Final Report SR-723-8-82, "Development of High Frequency

Electromagnetic Mapping (HFEM) Technology" which was later published as DOE

publication D0E/LC/10417-T1 . This report described the baseline data work

required to design a high-temperature sample holder and experiments for determining the EM properties of oil shale samples at elevated temperatures (200-

500°C). A section was devoted to the theoretical approach for modeling EM

sensing techniques for oil shale retorts. The retort was assumed to be a spheroid with an average dielectric constant and numerical results were

presented. Finally, the measurement results were given for the spent and raw shale samples that were obtained from portions of the ten half-core samples

plus the results of the EM transmission measurements taken on oil shale

samples at the LETC in Laramie, Wyoming.

This report covers the work performed from October 1981 to September

1982, validating the accuracy of the high-temperature sample holder at

elevated temperatures up to 500°C. Measurement results are given for approximately 40 oil shale samples that were measured in the high-temperature sample

holder at room temperature and up to 500®C and within the frequency range of 5

- 1000 MHz. The oil shale samples were furnished by LETC and had yields

ranging in value from about 0.025 L/kg (6 gal /ton) to 0.338 L/kg (81 gal /ton).

2
2. SAMPLE HOLDER CHARACTERIZATION

As previously reported in the NBS Final Report SR-723-8-82, the hightemperature sample holder was characterized at room temperature (25°C) by

measuring three known dielectric standards. Inserting these standards in turn

as Yl in the sample holder allowed the elements Y^, Y

2

, and Y

3

of the tt- network representation of the intervening circuit (figure 1 ) to be solved at

each frequency, thereby allowing the dielectric properties of an unknown

sample to be determined. However, once the sample holder is heated, changes occur in its physical properties and dimensions which, in turn, change the

sample holder calibration as a function of temperature making it necessary to measure the three known dielectric samples at every temperature and frequency

before the dielectric properities of the unknown oil shale samples can be

correctly determined at elevated temperatures up to 500°C.

2.1 Dielectric Samples

Four known dielectric samples consisting of quartz, glass, ceramic and

molybdenum were used to characterize the sample holder at room and elevated

temperatures. While only three known dielectric samples are actually required

to characterize the sample holder, the fourth dielectric standard sample is

used as the unknown sample which allows a direct comparison to be made between

known standard values and measured values as a function of frequency and

temperature. These four samples were chosen because of their well-known

dielectric properties that remain fairly constant over the whole temperature

and frequency range. Moreover, their constants of thermal expansion closely

resemble that of the large ceramic bead which holds the sample throughout the

measurement run. This means, that once the sample holder is heated to 500°C,

the standard samples will not expand at a faster rate than that of the

ceramic, preventing the bead from fracturing.

2.1.1 Preparation of Samples and Sample Holder

The four dielectric samples were machined into disks 2.540 cm (1.000

inch) in diameter and 6.477 mm (0.255 inch) thick. The diameter of the sample

cavity in the ceramic bead was made approxmately 0.051 mm (0.002 inch) larger

than the sample disk to allow for thermal expansion. After loading the sample

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disk in the cavity, the endplate was placed in position on the sample holder

and preloaded by tightening the compression springs over the bolts holding the

spider clamp as shown in figure 2. Typically, 454 kg {1,000 lbs) of pressure

is applied to the endplate and to the sample. This helps to insure that

proper electrical contact is maintained between the sample and the conductors

throughout the heated measurement run. Also, this type loading simulates an overburden pressure of approximately 8790 x 10^ Pa (1275 psi). Finally,

insulation is placed around the outside of the sample holder and endplate to

achieve better temperature regulation throughout the heating cycle.

2.2 Measurement Procedure and Results of Standard Samples

The EM properties of permittivity (dielectric and attenuation constants)

of the dielectric samples measured in the sample holder were obtained from the

measured admittance. The admittance, in turn, was obtained by measuring the

input reflection coefficient of the holder with its sample at the plane of

measurement with an Automatic Network Analyzer (ANA). This technique was previously described in detail in NBS Final Report SR-723-8-82. The measurement

uncertainty of reflection coefficient used in these measurements was 0.004 in

magnitude and 0.4 degrees in angle. Just prior to the measurement run, the

sample was evacuated by means of a vacuum pump connected to the sample

holder. Approximately 10 minutes was required to pump the system down to less

than 4.66 Pa (35 microns of mercury), assuming that no leaks were present

around the gold wire seals. The sample was then purged with nitrogen to remove any residual oxygen. The evacuation and purging operation was used on

all the oil shale samples and also on the molybdenum standard sample, which

had the characteristic of oxidizing quite rapidly when heated.

Measurements on the dielectric samples were taken between the frequencies

of 5 and 1,000 MHz in 5 MHz steps and at temperatures of 25°C (room temperature), 50®C, 100°C, 150®C, 200°C, and then in 25° steps up to 500°C. High

quality thermocouples (chromel -constantan) were used to monitor temperatures

throughout the complete test cycle. The time/temperature heating profile that

was finally employed was 1.6°C/min, which gave uniform heating of the sample

holder and sample over the whole temperature range up to 500°C. Figure 3

shows the heating profile that was used for the permittivity measurements

.

These measurements take a total time of 5 hours per sample to complete, making

5
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it important that each measurement run is carefully prepared. A measurement

run consists of taking measurements between 5 and 1,000 MHz in 5 MHz steps at

each of the temperatures specified above up to 500°C. By the time the sample

holder is loaded with a sample, measured over the full temperature range,

allowed to cool down, unloaded, and a new sample reloaded, there is a total

elapsed time of approximately one day.

Of the four standard dielectric samples that were measured, molybdenum,

quartz, and ceramic samples were used to characterize the sample holder, while

the standard sample of glass was used as the unknown material, to evaluate the

characterization, because of its dielectric constant which approximates that

of oil shale and its value which is well known and documented [1,2]. However,

other combinations of these four standard samples can be used. Figure 4 shows

the relative dielectric constant plotted from the measurement data obtained

using a standard dielectric sample of glass as the unknown material as a function of temperature and compared with known standard dielectric values of

glass obtained from other sources [3] and by extrapolation at these same temperatures. Moreover, these values are independent of frequency. Looking

at the plot, one can see the close agreement between the measured values and

the known standard values, which is an indication of the reasonably accurate

results that can be achieved when using the high-temperature sample holder.

3. OIL SHALE MEASUREMENTS

3.1 Oil Shale Samples

The first series of oil shale measurements were made on a few samples of

oil shale taken from a block of shale identified by the LETC as A-1. The

measurements were investigative in nature to determine the integrity of the

sample holder at room and elevated temperatures and determine the extent of

additional measurements. With the successful conclusion of the first series

of elevated temperature runs, the LETC requested the NBS to make additional

measurements on a number of different oil shale samples varying in yield from

0.025 L/kg (6 gal /ton) to 0.338 L/kg (81 gal /ton). This new work was broad

enough in scope to include the coordinated efforts of the LETC to investigate

the organic and mineral matter of like oil shale samples and the University of

Wyoming Physics Department who, funded by the DOE, proposed to develop a

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9
theoretical model of oil shale based upon its electrical and physical properties. Toward this end, provisions were made by the NBS to provide the

University of Wyoming with dielectric measurement data on the oil shale

samples to develop their model.

In the oil shale sample selection process, like oil shale samples were

cut from the same bedding plane from blocks of shale. Different oil yield

samples were selected from different block types. Several samples from each

block type were sent to the NBS for dielectric property measurements at

elevated temperature, while other like samples were tested at the LETC for

material balance Fischer assay and minerals. Table 1 shows the density and

the estimated oil yield information on the oil shale samples received by the

NBS from the LETC for dielectric property measurements. With the exception of

samples designated D and E, the LETC performed their measurements on like oil

shale samples taken from the same block types.

Table 1

Density and oil yield information on oil shale

samples received by the NBS from the LETC.

Block Type Density Oil Yield

Sample

Designation

Number of

Like Samples g/cu cm L/kg (gal /ton)

C

D

E

FG

I

J

L

P

S

T

U

3

3

4

3

3

4

4

2

2

2

2

2

2.28

2.04

2.09

1.82

1.90

1.70

1.57

2.57

1.63

2.28

2.19

2.05

0.088 21

0.158 38

0.142 34

0.234 56

0.204 49

0.280 67

0.338 81

0.025 6

0.309 74

0.088 21

0.113 27

0.154 37

10
3.1.1 Measurement Results of A-1 Oil Shale Samples

A history, containing information on dielectric properties, was established on oil shale samples taken from a block of shale identified by the LETC

as A-1, which had a yield of about 0.094 L/kg (22.6 gal/ton). The samples were machined into disks 2.520 cm (0.992 inch) in diameter and 6.477 mn (0.255

inch) thick with the bedding planes of the samples kept parallel with the disk

diameter. These samples were then measured at low frequencies in a dielectric

sample holder of the Hartshorn Ward type [4] at frequencies of 0.01, 0.02,

0.04, 0.1, 0.2, 0.4, 1.0, 2.0, 5.0, and 10.0 MHz at room temperature (25°C).

Figure 5 shows a plot of the dielectric constant and the imaginary part of oil

shale sample A2 as a function of frequency. While a detailed error analysis

was not performed, it is estimated that the measurement uncertainty is of the

order of +1 to +2 percent on the dielectric constant and +5 percent on the

imaginary part. This sample is representative of the other samples measured

from this same group. These measurements give accurate results on the

dielectric constant and imaginary part of the oil shale samples which, in

turn, help to indicate small differences in loss and oil yield (as indicated

by the dielectric constant) between samples. They also provide a larger data

base on the dielectric properties of the samples over a wider frequency range.

Each oil shale sample was then measured in the high-temperature sample

holder at the same frequencies and temperatures that were used for the

standard dielectric samples. The sample holder was operated in the vented

condition allowing gasses and shale oil to escape through a vent tube that is

attached to the endplate as shown in figure 6. A balloon was placed on the

other end of the vent tube allowing the shale oil given off by the sample to

be collected into the balloon. When the balloon starts to expand, this is a good indication that the sample has reached the temperature where retorting

has commenced. This occurs around 375®C, accompanied by a faint odor of

hydrogen sulfide. At approximately 400®C, the first trace of shale oil can barely be seen at the neck of the balloon. By the time the temperature has

reached 475®C, it appears that all effluents have been driven off the oil

shale sample. The heating of the sample holder and samples continues until

500®C has been reached and the final measurement run taken. At this point,

the heaters are turned off and the sample holder allowed to cool down to room temperature. However, for one measurement run, additional measurements were

taken at 15-minute intervals for a total elapsed time of 45 minutes while the

11
Imaginary

Part

Dielectric

Constant

Figure 5. Plots of dielectric constant and imaginary part of oil shale sample

A2 as a function of frequency at room temperature (25®C).

12
ENDPLATE MOVING PLATE

TRANSDUCER

Figure 6. Drawing of endplate.

temperature was held at a constant 500®C. No changes in the measurement

results were noticed between these new data and the data recorded earlier at

500®C. Also, on two of the measurement runs after the sample holder had

cooled down to room temperature (25®C), the room temperature measurements were repeated again allowing a comparison to be made of the dielectric properties

of the oil shale samples before and after retorting. For these particular

samples, the before-and-after dielectric properties were almost identical.

Figure 7 is a plot of some of the measurement data obtained from four of

the oil shale samples as a function of temperature at 500 MHz. This frequency

was chosen because of the good data representation of the A samples at this

point, plus it is is typical of the other measurement frequencies. No explanation is given at this time for the marked increase in the dielectric values

for the oil shale that occur in the 400 to 500®C range. This increase was also noted at all the other measurement frequencies. It is interesting to

13
Imaginary

Part

Dielectric

Constant

500 MHz A2

A3

Tompenatune (C)

Figure 7. Plots of dielectric constant and imaginary part of four oil shale

samples as a function of temperature at 500 MHz.

14
note that in an oil shale report by DuBow [5], pressure curves show that a drastic change in mechanical strength of oil shale samples occurs at around

380®C. In subsequent measurement runs, several modifications in the measurement procedure were tried that could possibly affect the high value dielectric

properties at 400°C and above. These included:

1. reducing the endplate pressure from 454 kg (1000 lbs) to 181 kg (400

lbs),

2. increasing the endplate pressure to 816 kg (1800 lbs),

3. reducing the diameter of the oil shale sample from 2.520 cm (0.992

inch) to 2.222 cm (0.875 inch),

4. reducing the temperature heating profile from 1.6®C/min to 1.0°C/min,

starting at 350®C.

In the final analysis, these modifications did not alter the measurement

results. After the sample holder cool down, as previously reported, the

values of the dielectric properties of the oil shale samples were almost

identical to the original room temperature values.

3.1.2 Measurement Results of Additional Oil Shale Samples

3. 1.2.1 Measurement Conditions

For the additional oil shale samples, three types of measurement conditions were investigated: 1) Measurement of the electrical permittivity

(dielectric and attenuation constants) as a function of sample temperature

with the sample holder operated in two different modes as a) vented, so as to

relieve any developed pressure and b) unvented, so as to retain any developed

pressure. 2) Measure the pressures developed during the unvented mode of

operation as a function of the sample holder temperature. 3) With the sample

held at a fixed temperature, determine the effect of an externally applied

pressure on the electrical permittivity.

15
Under actual measurement conditions, items 2 and 3 were difficult to

attain. The main problem encountered with item 2 resulted from the air-cooled

pressure transducer that was obtained for this project. This transducer was designed for measuring gasses up to 500°C, but not fluids. A fluid has to be

used to eliminate the compressible gas volume contained in the vent tube and

the pressure tranducer tube (see fig. 6) in order to externally monitor the

pressure accurately. The transducer air cooling is insufficient to cool the

fluids at 500®C and prevent damage to the pressure transducer. Ideally, the

pressure transducer should be located next to the oil shale sample. In the case of item 3, this was simply a case of not being able to maintain a tight

pressure seal over the whole temperature cycle. Once the oil shale sample

began to expand with heating, the expansion allowed gasses to escape past the

gold wire pressure seals. This condition occurred at about 225®C and

continued until about 400®C when the system resealed, as the oil shale samples

lost compressive strength and their released effluents. In the actual

pressurized measurement runs, dry nitrogen was used to pressurize the sample

to about 3447 x 10 Pa (500 psi ) and was applied externally through the vent

tube. Only two or three measurement runs were attempted since a problem still

existed in holding a pressure seal over the 225®C to 400®C temperature range.

The remainder of the oil shale samples were investigated by measurement

condition la. where the sample is vented so as to relieve any developed gasliquid pressure. This was the condition used for measuring the A-1 oil shale

samples described in section 3.1.1.

3. 1.2. 2 Preparation of Oil Shale Samples

As in the previous section, 3.1.1, the samples from table 1 were machined

into disks 2.520 cm (0.992 inch) in diameter and 6.477 cm (0.255 inch) thick

with the bedding planes of the samples kept parallel with the disk diameter.

These samples were also measured at low frequencies in the Hartshorn Ward type

dielectric sample holder at frequencies of 0.01, 0.02, 0.04, 0.1, 0.2, 0.4,

1.0, 2.0, 5.0, and 10.0 MHz at room temperature (25°C). To help establish a higher degree of confidence in the results of the dielectric measurements,

more than one like sample was prepared and measured for each designated sample

type (see table 1). As before, evacuation and purging of the samples preceded

the heated measurement runs.

16
3. 1.2. 3 Measurement Results

A total of thirty-four oil shale samples were measured between the frequencies of 5 and 1,000 MHz in 5 MHz steps and at temperatures of 25°C (room

temperature) , 50®C, 100°C, 150®C, 200®C, and then in 25® steps up to 500®C. A

desk-top calculator controlled the measurement process, computed the permittivity, analyzed the data, and produced the graphical results. A smoothing

routine was applied to the data to reduce random variations and systematically

induced spikes.

Figures 8-13 show plots of the dielectric constant and the imaginary part

of the complex dielectric constant of all the designated samples from table 1 as a function of temperature at 500 MHz. Again, this frequency was chosen

because of the good data representation of all the oil shale samples at this

point, plus it was typical of the other measurement frequencies. Frequency

plots are shown later on in the text for several oil shale samples. The

figures are ordered in increasing oil yield richness from the leanest, L = 0.025 L/kg (6 gal/ton), to the richest, J = 0.338 L/kg (81 gal/ton). The

values for the dielectric constant in the figures appear to increase from 25°C

to about 200®C before decreasing in value and then increase rapidly, in most

cases, starting around 400®C, as noted previously in figure 7 with the A

samples. The increase in dielectric values up to 200®C probably results from

the moisture being released from the oil shale samples. In reviewing figures

8-13, probably the most significant discovery is that the dielectric constant

of the oil shale samples decrease as the oil yield increases. This phenomena

is even more apparent in figure 14, which compares temperature plots of the

dielectric constant of the lower yield A sample with those of the highest

yield J sample as a function of frequency. One can see the marked difference

in values for dielectric constant between the A and J samples which vary

between 6.5 and 4.0 respectively at 25®C.

Figures 15-16 show frequency plots of the dielectric constant and the

imaginary part as a function of temperature for oil shale samples C, G, D, I. and J. Figures 15 and 16 are given to show effects of frequency on the mea- surement data. With the exception of increased values of dielectric constant

and imaginary part at 15 MHz, which is typical of dielectric measurements at

lower frequencies, the frequency effects for the most part are minimal with

the dielectric values remaining fairly constant above 100 MHz.

17
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8.

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of

dielectric

constant

and

imaginary

part

of

designated

samples

L

and C

asa

function

of

temperature

at

500

MHz.
19

Figure

9.

Plots

of

dielectric

constant

and

imaginary

part

of

designated

samples S

and T

asa

function

of

temperature

at

500

MHz.
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20

Figure

10.

Plots

of

dielectric

constant

and

imaginary

part

of

designated

samples

E

and U

asa

function

of

temperature

at

500

MHz.
21

Figure

11.

Plots

of

dielectric

constant

and

imaginary

part

of

designated

samples

D

and G

as

a

function

of

temperature

at

500

MHz.
22

Figure

12.

Plots

of

dielectric

constant

and

imaginary

part

of

designated

samples F

and I

asa

function

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temperature

at

500

MHz.
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13.

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of

dielectric

constant

and

imaginary

part

of

designated

samples

P

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as

a

function

of

temperature

at

500

MHz.
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Figure

14.

Comparison

of

temperature

plots

of

dielectric

constant

and

imaginary

part

of

the

lower

yield

A

sample

with

those

of

the

highest

yield

J

sample

as

a

function

of

frequency.
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15.

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Figure

16.

Frequency

plots

of

dielectric

constant

and

imaginary

part

of

designated

samples

I

and J

as

a

function

of

temperature.
Figure 17 is given to point out some of the measurement problems encoun- tered with some of the oil shale samples in the temperature range between

about 150®C and 325°C as shown by the gaps in the data plots. For some reason, this temperature range appeared to be the most critical and troublesome for the sample holder. In this region, some of the values for the

dielectric constant turned out to be quite low and, in a few cases, some dielectric contant values were less than 1, which is not possible. A thorough

investigation of the sample holder revealed that the threaded portion of the

center conductor (figure 2) had loosened slightly. Once this was tightened,

some of the measurement data improved somewhat. Other measures were taken to

clean all parts of the sample holder more thoroughly and frequently to remove

the residual tar-like substance deposited from the shale oil. Increased

amounts of this residual material from the shale oil was given off by the

higher yield samples which created more of a problem with coking and plugging

of the vent holes in the endplate by this tar-like substance. The cleaning of

the sample holder after each measurement run seemed to improve the measurement

results to a certain degree. In spite of the improved measurement results,

there still existed a few gaps in the data plots.

3.1.3 Gas and Liquid Sample Collection

Chemical changes occurring during the heating of oil shale can be investigated by examining the gas and liquid products formed as a function of

temperature during the heating process. Toward this end, gas and liquid

samples were collected by the LETC at the NBS on designated oil shale samples

E and S while they were being measured in the high-temperature sample

holder. Gasses were sampled at the same time interval as the dielectric

measurements were being taken by the NBS. Gas collection was made difficult

by the loss of the pressure seal in the sample holder due to the shale expansion during heating. However, on a subsequent measurement run, data was

collected using a thinner sample of oil shale and a spring arrangement to

reduce the effect of shale expansion on the pressure seals. On this particular run, a tight pressure seal was maintained over the whole temperature

cycle.

The collection system used for the oil and liquid samples is the apparatus shown in figure 18. The system was operated at or below atmospheric

27
(Ss

in

s

s

s

s

m

s

s

C\]

s

s

s

u

®

L3

+>0

L

ffi Q_E

0

t-

'^UD'^SUO^ OtJ'^30y0TQ •^JDJ XjdutBdiiij

•^uDneuoQ otj^oejeig •^jDj XjduiBduij

28

Figure

17.

Frequency

plots

of

dielectric

constant

and

imaginary

part

of

designated

samples

C

and G

as

a

function

of

temperature.
k

29

Gas

and

liquid

collection

system.
pressure because the volume of gas produced is small and so that use could be

made of existing gas sample collection bottles and a gas analysis spectrometer. The Pyrex gas collection bottles were pre-evacuated to approximately

6.66 Pa (50 microns of mercury) and were connected onto the collection system

with a short length of surgical tubing. The scheme of operation that was used

for collecting the gas and liquid samples and their analysis is described in a report [6] by the LETC. At this reporting, no attempt has been made to intercompare the gas analysis results with the dielectric measurement results.

4 . DATA SUMMARY

Making accurate permittivity measurements on oil shale samples at elevated temperatures is no simple task. While heating can change the physical

properties and dimensions of the sample holder, it can also cause the oil

shale to expand even more, creating problems with pressure seals in maintaining good electrical contact and in making accurate measurements over the

whole temperature range difficult to achieve. Under actual measurement conditions, the unvented and pressurized conditions were difficult to attain with

the present sample holder design. However, for the small amount of data that

was available for analyzing, there doesn't appear to be very much difference

between these data and the data collected for like samples in the vented

condi tion.

The measurement uncertainty for the permittivity measurements on the oil

shale samples varied from about 9 percent at 15 MHz for the values of dielectric constant down to about 2 1/4 percent at 500 MHz, while the uncertainty in

the imaginary part was more than 200 percent at all frequencies.

5. CONCLUSIONS

A description of the high-temperature sample holder characterization is

given along with the measurement procedure and the sample preparation. A mea- surement plot of measured and standard values of glass helps to validate the

accuracy of the sample holder at elevated temperatures up to 500®C.

From the experiments performed on the oil shale samples, density and

water content still appear to be two major factors that influence the permittivity of oil shale. Moreover, the results indicate that the dielectric

30
constant of the shale is not strongly influenced by the release of the shale

oil at elevated temperatures as previously suspected. However, it does appear

that the mechanical strength of oil shale does affect the dielectric values at

about 400®C and above.

6. ACKNOWLEDGMENT

The authors wish to thank Raymond Montoya for his excellent job in

preparing the high-temperature sample holder and making the elevated temperature measurements.

7. REFERENCES

[1] Bussey, H. E.; Gray, J. E.; Bamberger, E. C.; Rushton, E.; Russell, G.;

Petley, B. W. ; Morris, D. International comparison of dielectric

measurements. IEEE Trans. Instrum. Meas., Vol . IM-13: 305-311; 1964

December.

[2] Bussey, Howard E.; Morris, Derek; Zal'tsman, E. B.. International

comparison of complex permittivity measurement at 9 GHz. IEEE Trans.

Instrum. Meas., Vol. IM-23, No. 3: 235-239; 1974 September.

[3] Private communication from Corning Glass Works, Corning, New York 14831.

[4] Hartshorn, L.; Ward, W. H. The measurement of permittivity and power

factor of dielectrics at frequencies from lO'^ to 10° cycles per second.

J. IEEE (London), Vol. 79: 597-609; 1936 November.

[5] DuBow, J.; Rajeswar, K. Thermophysical properties of oil shales. Final

Report, Jan. 1977-1980, Contract No. EF-77-S-03-1584, prepared for LETC.

[6] Heppner, R. A. Gas analysis results from National Bureau of Standards

measurements of dielectric permittivity of oil shale. Internal Report,

Sept. 1982, prepared by LETC.

31
NBS-n4A (REV. 2-8C) U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET (See i nstructions)

1. PUBLICATION OR

REPORT NO.

NBSIR 83-1683

2. Performing Organ. Report No. 3. Publication Date January 1983

4. TITLE AND SUBTITLE

DIELECTRIC MEASUREMENTS OF OIL SHALE AS FUNCTIONS OF TEMPERATURE AND FREQUENCY

5. AUTHOR(S)

Ramon L. Jesch and Robert H. McLaughlin

6. PERFORMING ORGANIZATION (If joint or other than NBS. see in structlon s)

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

7. Contract/Grant No.

8. Type of Report & Period Covered

FINAL REPORT

October 81 - Sept. 82

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street, City. State. ZIP)

U.S. Department of Energy

Laramie Energy Technology Center

Laramie, Wyoming

10. SUPPLEMENTARY NOTES

021 Document describes a computer program; SF-185, FIPS Software Summary, is attached.

11. ABSTRACT (A 200-word or less factual summary of most significant information. If document Includes a significant

bl bliography or literature survey, mention it here)

A high-temperature sample holder designed by the National Bureau of Standards

was used to determine the dielectric properties of approximately 40 oil shale samples

as functions of temperature and frequency. A description of the sample holder characterization is given along with the measurement procedure and the sample preparation.

Experimental results are given for different oil shale samples, varying in yield

from 0.024 L/kg (6 gal/ton) to 0.338 L/kg (81 gal/ton), that were measured at room temperature (25 °C) up to 500 °C and within the frequency range of 5 -1000 MHz.

12. KEY WORDS (Six to twelve entries; alphabetical order; capitall ze only proper names; and separate key words by semicolon s) dielectric properties; dielectric constant; electromagnetic; high-temperature sample

holder; oil shale.

13. AVAILABILITY

[221 Unl imited

|_)^ For Official Distribution. Do Not Release to NTIS

122] Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C.

20402.

(22 Order From National Technical Information Service (NTIS), Springfield, VA. 22161

14. NO. OF

PRINTED PAGES

15. Price

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