The Thermal Conductivity and DiffusivityOf Green River Oil ShalesM. Prats, SPE-AIME, SheIIDevelopmentCo,S, M. O’Brien, Shell DevelopmentCo.

IntroductionThermal decomposition of the essentially insolubleorganic matter in oil shales is the easiest way to obtainshale oil. Proper planning of both surface and sub-surface thermal oil-shale recovery operations requiresvalues of the thermal conductivity and diffusivity ofoil shales,

There are few publications reporting thermal con-ductivities of oil shale from the Green River forma-tion. Gavin and Sharpl reported three values for thethermal conductivity of an oil-shale sample assaying42.7 gal/ton, Their reported values were obtainedover the temperature range from 77° to 167°F, butthe direction with respect to the bedding plane inwhich the measurement: were taken was not indi-cated. Thomasz presented thermal conductivity dataof an oil shale assaying 30 gal/ton and at a meantemperature of 104”F, finding values parallel to thebedding plane to be 30 percent higher than thosenormal to it and finding essentially no effect of stresslevels of 1,000 psi and above.

Tihen et al.’ report on the thermal conductivity anddiffusivity at room temperature of unconfined raw,retorted, and burned oil shales assaying from 8,6 to58,6 gal/ton. Correlations for thermal conductivityare given for temperatures as high as 1,100”F whileconsidering the anisotropic character of the oil shales.Though bolted, samples developed cracks during heat-ing, suggesting those results may be more applicable

to rubbled pieces in subsurface cavities or large sur-face retorts than to the calculation of heat losses froma process zone in subsurface thermal operations.

This report presents thermal conductivity data ofconfined Green River oil shales over a wide range oftemperature, fluid pressure, axial stress, and kerogencontent, The bulk of our measurements were carriedout on oil shales as they are found in nature; that is,they were not previously retorted. At the higher tem-peratures, however, our reported values include theeffects of at least some decomposition of the organicmatter. Thermal conductivities of burned (organic-free) oil shales were measured on only two samples.

The effectsof kerogen content, fluid pressure, axialstress, temperature, orientation, heating time, andmineral composition on the thermal conductivities ofoil shales were investigated. These basic rcsu[ts werethen used together with specific gravity and a correla-tion of specificheat with oil yield by Fischer assay andte:ilperature to obtain calculated thermal diffusivitiesfor each sample.

InstrummtationThe transient line heat-source (probe) method, whoseapplication is not particularly complicated by theaddition of means for stressing the sample, was usedin our investigation. The method, which has beendescribed by Woodside and Messmer,J’5 has been

Thermal conductivitiesof Green River oil shales vary fourfold, decreasing with increasingoil yield and temperature. Values also decrease as the kerogen decomposes, but thesechanges are small after about 9 hours. Mineral composition, geographic location, depth.of burial, axial stress, and pressure have no significant eflect. The thermal properties,which are transversely isotropic, are applicable to the calculation of heat losses fromin-situ recovery operations.

JANUARY, 1975 97

successfully applied to porous rock s~mples understress.

This method for measuring thermal conductivityemploys a probe containing a long electric heater anda thermocouple fcw measuring the temperature risenear the center of the sample into which the probe isinserted. A measurement is made by turning on theheater, generating heat at an axially uniform xmstantrate, and recording the temperature rise M a functionof time. After a time, dependent on probe diameterand construction and on thermal contact resistance,the temperature increases linearly with the logarithmof time, measured from the instant the heater is turnedon. Typically, it takes about 10 to 40 seconds in ourequipment for the log-Iinear behavior to start. Thislog-linear response continues for about 1 minute forsamples having a thermal conductivity of about 1.5Btu/ft-hr-°F and longer for lower thermal conductiv-ities. This interval is adequate for the determinationof thermal conductivity of all the oil shale samplesstudied, The line-probe method for measuring thermalconductivity is completely analogous to that of deter-mining the permeability-thickness product from thepressure drop vs log time response resulting fromwell drawdown tests. Accordingly, results of the tran-sient line-probe method are independent of any con-tact resistance between heater and sample (skin). Theinsensitivity of the thermal conductivity measure-ments on the contact resistance was confirmed bymeans of special tests in which gases, liquids, andgreases were used between probe and sample, andwith slightly different hole size, No effect was ob-served under our experimental conditions.

Details of the electrical heater-thermocouple probeare shown in Fig. 1, The probe has a length of 45!Nin, and its nose has an outer diameter of 0.050 in. Apiece of Type 310 stainless steel tubing serves as theoutside pressure sheath. Inside this tubing there is abrittle ceramic insulator 0.035 in, in diameter. Thereare four longitudinal holes inside this ceramic insula-tor. Two of these holes are used to carry the AWGNo. 38 Advance electrical heater wire in and out ofthe probe. Advance wire is used for the heater elementbecause of its low temperature coefficient of electricalresistivity. The other two holes carry the chromel andalumel thermocouple wires; the junction is located inone hole near the effective center of the probe.

The sample cell is essentially a specialized pressurevessel designed to confine the sampley with probeinserted, under a nominal axial loading modified

4 HOLE CERAMIC

TABLE I—LOCATION AND DEPTH OF OIL-SHALE SAMPLE SETS

Sa8~:le DepthLocation fyt)

A Rifle Mine, Colo. -300 * 100D Greeno 1.4, COIO. 1,091 to 2,350E Dillon outcrop, Colo. SurfaceF Utah State 14.36, Utah 2,1%7 to 2,258

TABLE 2—MAJOR MINERALS IN SOME OF TliEOIL-SHALE SAMPLES OF SET A

VolUnro Percent”——Fiaehw Fclds r

.ilr%;I! Q%%) IMomlts CWte Arrsklt6 $@ Quartz—— .

A-2 10.8 49.3 3.4 3.2 13.1 18.5A-3 15.4 25.9 11.0 12.6 4.2 21.9A-4$* 16.0 27.2 8.8 8.2 10.4 17.8A-5t 35.0 18.4 8.3 10.6 6,0 13.0

●Calculated from elemental compoeltlons before end after ecidtreatment.

● ●set c Consl$ted of ssven samples having prOpE@ki similar tOthose of Sample A.4.

@et B consisted of seven samples having properties elmilar tothose of Sample A.5.

by controlled fluid backpressure. For porous rocksamples this hydrostatic pressure can properly becalled pore pressure. For samples such as oil shale,however, the state of stress is somewhat ambiguous,although no more so than under subsurface condi-tions. This is particularly true as the sample becomesplastic at the higher temperatures. It is felt, however,that the achieved simulation of subsurface conditionsis adequate, since the development of cracks in thesample at the higher temperatures is prevented. (Suchcracks are generally observed in the absence of con-finement.) Also, some control of fluid offtake isensured, A schematic view of the cell and associatedequipment is shown in Fig. 2. The equipment isdesigned for use up to l,OOO°F and 4,300-psi fluidpressures. In addition, the sample may be subjectedto an axial compression of up to 4,300 psi (offset bythe fluid pressure up to the amount of the axialcompression).

Comparisons with the thermal conductivity ofPyrex up to a temperature of 400”F, as reported bythe National Bureau of Standards,e show a maximumdifference of less than 1.5 percent. The equipment isthus considered to be working satisfactorily. The aver-age value of 19 different Pyrex thermal conductivitymeasurements, made with our equipment at roomtemperature over a 6-month period and with differentprobes, is 0.656 Btu/ft-hr-°F, with a standard devia-tion of * 0.015 Btu/ft-hr-°F.

THERMOCOUPLE/JUNCTION SEALE

‘-~.:,::..,e,,:.w . . . . ===y====~==. ,- -.A. .... ..- . ...-

‘SEALINGSURFACE

\W:3:;SEN CEMENT

Fig. l—The probe.

98 JOURNAL OF PETROLEUM TECHNOLOGY

TABLE 3-MAJOR MINERALS IN” SAMPLES ADJACENT TO THOSE IN SET D

Core Fischer Volume Percent*Sam Ie

FJDolomite

Num er ‘:t!;h (gtij~$n)IW@pdr

and Calcite Dawsemite Analcite Giass and QuartzD1 1,091 23.4 27.2D2 1,093 14,6 27.6D3 1,120.5 34.1 27,3 —

D4 1,125 25.2 ‘34.8 —D5 1,141.5 61,4 14.1 —D6 1,151,5 36.3 28.9 —D7 1,751 13.9 16.6 11.2D8 1,847.5 ~,, 4 15.7 9.8D9 1,856 70.7 8.0 3.8D1O 1,857 70,0 7.4 3.1Dll 1,854 51.4 10.4 9.6D12 1,920 27,8 12.4 4.6D13 2,048 37.1 14.9 5.4D14 2,357 28.8 13,1 (- 10$4 Ciay)

‘Calculated from elemental compoalt[ons before and after acid treatment.

5.810.8

0.65.21.51.0——

—

18.0 11.221.3 14.918.1

7.2 1::15.2 5,118.1 11.020.3 19.413.8 17.014.914.3 z

7,8 17.115.7

1:: 14.931.0 1.7

Descriptions of SamplesFour sets of oil-shale samples obtained at differentlocations from the Green River formation have beenused in this investigation. Set A was obtained fromthe USBM mine at Anvil’sPoint, COIO.,near the townof Rifle. Set D was obtained from Shell’s Greeno 1-4well in the Piceance Basin, Colo. Set E was obtainedfrom the Dillon outcrop on the western rim of thePiceance Basin. Set F was obtained from cores fromSheII-Utah State No. 14-36, in Utah. Table 1 sum-marizes the locations of our sample sets, The minerclcomposition of oil-shale samples in Sets A and D isgiven in Tables 2 and 3, respectively. Oil-shale Sam-ple Sets B, C, and G were obtained from Set A andwere used for special studies.

As can be noted from these tables, the reported

mineral compositions of the samples vary consider-ably, The combined reported volu-meperc&t of dolo-mite and calcite range from 7,4 to 52.7; for dawson-ite, from O to 11.2; for analcite, from O to 12,6; forglasses, from 4,2 to 31.0; and for feldspars and quartz,from 1,7 to 21.9, The sampIes from other sets WOUICIbe likely to extend the range of these volumetric con-centrations, No occlusions were evident,

From the information from Tables 1 through 3,it would appear that the mineral composition, depth,oil assay, and geographic location of the Green Riveroil-shale samples chosen for the determination ofthermal conductivities are quite varied. Except pos-sibly for the fact that none of our samples containednahcolite, they are thought to be representative ofthose in the Green River formation.

Because of the layered nature of oil shales, the

SOLAc;;:;;:;

TRANSFORMER

~,N2 CORE PRESSURE

--l OVEN ~ N, OVERBURDEN PRESSURE

i.— —— .— —

— —1 11

-—

IETER

Y-%yLy&,T5A ‘ PLE CELL

P

(BOURNS)

?1?S$:TERY

~PRODUCTION LINE.—— —.—= ~ VENT

,,lAGcuMuL~-}//j i

II-J

RECORDERI I—— ——

IFig. 2—The aquipment associated with the thermai conductivity ceil.

t-luRECORDER

JANUARY, 1975 99

thermal conductivity normal to the bedding is some-what lower than that parallel to the bedding. Sincethe heat-generating probe used in our thermal con-ductivity apparatus is located along the axis of thesample, cores cut normal to the bedding give rise tothermal conductivity values parallel to the beddingplane. Because the bedding planes are nearly horizon-tal in the in-situ oil shales, these measurements arealso referred to as horizontal thermal conductivities.When a cylindrical core is cut parallel to the bedding,the heat generated within the probe is transferredboth normal to and parallel to the bedding. It is thegeometric mean of the thermal conductivities paraiielto and normal to the bedding that is measured in thesecases. Selected tests showed that the line-probe

method indeed gives the effectivehorizontal and geo-metric mean thermal conductivities of laminatedmaterials.

No precautions were taken to control the humidityof the sample since results had been found to be insen-sitive to the type of fluid present during the contactresistance study,

The influence of local sample variation on themeasured values of thermal conductivity was foundto be minor. This was investigated by measuring thethermal conductivity of seven adjacent samples fromthe same stratigraphic interval for Sample Sets B am?C. A standard deviation of 4 percent was found forsampling variation for each set, which compares veryweii with a reproducibility on a given sample of 2,6

TABLE 4-THERMAL CONDUCTIVITY AND DIFFUSIVITY RESULTS

GeometricMeenHorlzontel

sample

nA2A3

A4A5D1D2D3D4D5D6D7D8D9D 10D 11D 12D 13D 14ElE2E3F1F2F3AlA2A3A4A5AlA3A4AlA2A3A4

. A5-.— Al

A3A4A5AlA3A4

109110531120.511251141.51151.517511847.5185618571864192020482357

223522152190

oilYield

(gel/ton)

-010.815.416.035.023.414.634.125.261.436.313.929.470.770.051.427.837.128,824.331.954,029.851.919.9

-010.815.416.035,0

-o15.416.0

.--010.815.4 ‘16.035.0

-015.416.035.0

-015.416.0

T~;#.

-z-757575757575757575757575757575757575757575757575

392392392392392482482482572572572572572662662662662752752752

3&c;/m&

2.382.442.302.262.062.172.341.982.171.681.982.242.041.611,561,692.091.952.092.152.071.802,241,872.272,382.442.302.262,062.382.302.262,38

2.302.262.062.382,302.262,06

2.302,26

ThermaiConductivity

km “(8tu/ft-hr.°F)

1,1101.0400.8280.7530.6200,8901.1080.5730,6720.3410.5151.0010.6820,3750.3000.4670.7040.5150.6870.8590.7600.4890.8950.4360.8450,9801.0100.7380.7030,5810.9560.7530.6700.888

0.7050.6410.5060.9070,7210.5910.479

0.6040.530

ThermalDiffusivity(u,,, ff/D)

0.8630.7550.6260.5780.4860.6910.8260.4690.5190.2990.4180.7820.5510.3330.2750.4210.5590,4230.5430.6710.6000.4100.6580.3550.6360.6910.6530,4930.4760.3910.6570.4870.4390.595

0.4420.4070.3150.5930,4380,364

.0.288

0.3560.317

SpacificGravity

2,342.442.292.292.052,162,382.04

—

1.592.00

—2,041.73

—1.792.072.032.142S52.071,802.241.872,272.342.442,292>292.052,342.292,292.342.442.292.29”2.052.342.292.292.052.342.292,29

ho -(Btu/ft.hr-”F)

0.978 -1.0500.8370.7800,5480.5970.9770.552

0.2640.515

0.5390.402

0.3390.6630.5730.5710.7400.6150.3870.8590.3870.8030.9270.9940.752o.7f70.5010.8850.7380.6700.8410.9770.7340.6570.4400.9780.7130.5870.5480,7020.8600.580

ThermalConductivity Thermal

Diffusivity(afJ, ft/o).—

0.7730.7620.6360.5910.4320.4660,7160.438

0.2450.414

0.4360.332

0.2890.5310.4520.4410,5780.4850.3250.6310,3150.6040.6650.6420.5050.4790.3390.6190.4790.4340.5730.5940.4620.4120.2750.6500.4350.3570.3310.4560.3910.342

JOURNAL OF PETROLEUM TECHNOLOGY100

percent. Because of its excellent stratigraphical cor-relation over large distances, similar results would beexpected of other Green River oil shales where Occlu-

sions (such as dawsonite and nahcolite) are absent.

Sample Preparation and ExperimentalProcedureWhenever possible, cores were cut (in water) bothparallel and perpendicular to the bedding observed inthe sample specimen. In such cases, the core cut paral-lel to the bedding was from within the stratigraphicinterval cut by the vertical core, and the centers ofthe cores were within 3 in, of each other. Such coreswere given the same sample number. Cores werealways about 1.50 in. in diameter by about 3,2 in. inlength, A 0.055-in, hole was drilled (without coolantbut slowly and with intermittent bit withdrawals)along the axis of the cylindrical samples. These cylin-drical cores constitute our samples.

The study on the effect of fluid pressure, axialstress, and temperature was carried out as follows.The sample is placed in the thermal conductivity celland measurements are carried out at atmosphericpressure and no axial load, at 100 psi (nitrogen) and2,000 psi compressive stress, and at 1,800 psi (nitro-gen) and 2,000 psi compressive stress. The fluid pres-sure was applied to the .~ntire exposed surface of theoil-shale sample, including that associated with anyavailable porosity. Measurements were repeated in

SPECIFIC GRAvITY

Fig. 3—Values of the horizontal and geometric meanthermal conductivity measured at room temperature

as a function of specific graviw.

JANUARY, 1975

some cases, and sometimes one of these sets of pres-sure and stress conditions was omitted. The thermalconductivity cell was then placed in the oven and thetemperature was brought up to 392°F. When the tem-perature of the sample was stabilized, the measuringsequence was repeated. This procedure was then car-ried out at 392°, 482°, 572°, 662°, and 752*F formost of the samples in Set A. Since the effects of pres-sure level and the axial stress were found to be negli-gible for samples from Set A, and differences in min-eral content between sets were small, oil-shale samplesfrom other sets were only measured at atmosphericconditions, not necessarily in the cell. These resultswere then related to the specific gravity and oil yieldof the samples. Specificgravities are only nominal andare based on the weight per unit volume of the sampleat room temperature and an assigned weight of 1gin/cc for water at the same temperature, Oil yieldis that obtained by Fischer assay.

ResultsThermal ConductivityOur measured values of the thermal conductivity ofraw oil shales are listed in Table 4. Since results wereinsensitive to pressure and stress levels (as will be dis-cussed later), the tabulated values are the average ofall measurements at a given temperature. Figs. 3 and4 give the values of the horizontal and geometricmean thermal conductivities measured at room tem-perature. Fig. 3 shows that the thermal conductivityincreases exponentially as the specific gravity of theoil shale increases, while Fig. 4 shows that it decreasesexponentially as the oil yield increases. Figs. 5 and 6

201--—–”-=:’ ‘“”“- ‘“– I—.——.

I —UIVEN BY , I

Lf.f+%jo“_~_,~-~-~-.. ,J._ ,: ......1.....i..- j..2,-., . ; .....

! ,

: 0.4 .x i i i ‘1... .. .. -..:. ...y :.~ozm[-r~j--j-q..-.-d++..-d..... . ...... ..p+.----- .- ..:..

‘~’”Ii, oJofA:””:“~””””‘ ~ ‘ ‘ ‘ 0. ;,,,s AND RQ tkROR PF EqW+ , a+s W/~r W’f , :.

f 1.0

5z 0.8.

0.6

0.4 0

“,*I. I I__&._.. :. : : ! ....O : ..-,l”0 10 20 30 40 50

OIL TIELO. GALI1ON

F@. 4-Values of the horizontal and geometricmean thermal conductivity measured at room

temperature as a function of oil yield.

101

F..,,....,....,......4

::, :., . . .. . .

,. ..,..:: . . . . . . . . . .. . . . . . .,M ..::.....,.

... ::lkj::‘.. . .A2 ,.

‘:.. . . . . . . .

““’ :+—..L:.”..

1-::”’: “.::”... .

J__;;::.t,:._J_l+_i:~:::-p“::

I ,0

—.

——

I::—.. —

.1:.—. —

I-j-- .— ..-,.

–4.+ .—.!..

1.: WItH~ A W(RI.E jFJO_,Ojt@ ; ~_ :: i__ .:___ .._. i. : i ~ ~ “_!>:,—:. .—. .. —.. —

.A .. ..– ... . .. . ... . .. . .

.!.:. ll,l~i

j ! ~ ; _.--_..,,.,-::i.~’-:: J:, !-J -++.’

—. .- -. .

.r_ ; :_i: ~. ~_

, ~--’r::; -–:-”l-- “ .-”i ,,, ::1:ij”:~l;j

1 I I I I , .,.

zoo 400 WC. 8000

TEMPERATURE, “F

Fig. E&Effect of temperature on the measured horizontal tharmal conductivity.

1.01

-’;:’.”:-”: ‘‘ :“ ; ~

i_.-i .:. .+ ,— ; --- -.-;. .;.. –-., ;-.. :’.-.. -~ ! .. . .,

SAMPLE ~:.. . . ..—

Al !. . . ~2. ;...,

-.

...

.,

.—.. - .!. i.:!,,

-.

— ..

.-

: v:x.A

... L..:- :-: .- .

‘ \...........—t’::’”x’,.

v.. .

. A . :A

, .i

.,.-..’.:. ::. .

+●✚. . . . . . . . -;--’*

.4

. . .,; ~“$ “-..:

. . ... . . ..

. . ... . . .

. . . . . ...

. . .. . .::.

. . . . :!.

. . .. . . :.A ,.

:_. . . :.. ,:,_

..:

.,

.!

. .. . .. . . . .. . .. .,.

,.-. $—

. . ..- .. . . . .

— GIVEN BY. . . . .-

,$#*T). : \:.. V:.. .+...+..

=1 “- 1.1494 ~-75] 104 ~ K6667[T-75]%0-7 ‘ “ : : :

‘hG(, ) ;o 75). . . :-. . . ,. ... . ~. -- .:..--...

,. ,. ,,

,.I :.. .!I ;.. I I

200 400 600 800c

TEMPERATURE, “F

Fig. 6-EffecA of temperature on the measured geometric mean thermal conductivity.

102 “ JOURNAL- OF PETROLEUM TECHNOLOGY

*

show that the thermal conductivity decreases as thetemperature increases. Table 4 shows that our meas-ured values range from 1.110 Btu/ft-hr-°F for a leanoil shale to 0.264 Btu/ft-hr-°F for a rich oil shale, ora variation of a factor of about four.

Single exponential curves were fitted to the meas-ured data presented in Figs. 3 and 4 using weightedleast squares. The ratio of the thermal conductivityat any temperature to that at room temperature, givenin Figs. 5 and 6, was fitted to a second-order poly-nomial in (2’-75) and passed through 1 at T = 75oF.

The resultant regression curves are of the form

Y = al[l - h,(T-75) – b2(T-75)2] exp (U,%),

where a,, a,, b,, and b, are constants and x standseither for the specific gravity or for the Fischer assay.The values of the constants in the regression equa-tions for the horizontal and geometric-mean thermalconductivities are given in ‘Fable 5.

From the regression equations we obtain estimatesof the thermal conductivity normal to the beddingplane by assuming that the thermal conductivity ofoil shale can be considered to be transversely iso-tropic, This hpb the dEttiOn k2hG= khHkrw, frOXII

which vertical thermal conductivities as weIl as thedegree of anisotropy can be calculated. The ratio ofthe horizontal to vertical thermal conductivity is usedhere as a measure of the degree of anisotropy. Equa-tions similar to the regression equation were also ob-tained for the vertical thermal conductivity and forthe anisotropy ratio. The constants for these equa-tions are also given in Table 5.

These predictive equations can be evaluated toobtain results similar to those plotted in Fig. 7. Thus,these equations give our best estimates of the thermalconductivities of oil shales over the temperature rangefrom 75° to 750°F and the practical range of organiccontent.

The standard error of the regression equations forthe horizontal and geometric-mean thermal conduc-tivities, as a fraction of the predicted value, rangesfrom less than 2 percent at room temperature and aspecific gravity of 2.2 to slightly more than 18 per-cent at 750”F and a specific gravity of 1.4. The re-gression analysis techniques used in obtaining theseresults are discussed in Refs. 7 and 8.

Oil shale Set A was used to determine the effectof pressure and axial stress on thermal conductivitiesat various temperatures. Results are shown in Table6. Pressures and stresses were varied from atmo-spheric to 1,800 and 2,000 psi, respectively, and tem-peratures were varied from room to 752°F, Both

TABLE 6-SUMMARY OF THE CONSTANTS APPEARINGIN THE PREDICTIVE EQUATIONS

b, X Itl’ b, X ~~’ALL—— as

khn P 0.03702 1.4105 1.0932 4s949kfiff P 0.02151 1.6036 1,149 3.6667kw P 0.01249 1.7969 101848 3.1271kn2i/khv 2.9842 –0.3863 -0,3026 1.5820knn ;A 1.2299 –0.01840 1.0832 4.1!349kv. FA 1.1275 -0.01843 1.1490 3,6667kw FA 1.0338 –0.01846 1.1948 3S271ktiii/kna FA 1.1s95 0.000063-0,3026 1,5820

sample orientations were studied. At any given tem-perature, the thermal conductivity of a given samplewas measured at different values of pressure andstress. But, the values of stress and pressure are notnecessarily the same for each sample or at each tem-perature level.

There does not appear to be any consistent trendon the effect of pressure on thermal conductivity,except possibly at 392”F. In this case the conductivityeither remains the same or increases as the fluid pres-sure increases above 100 psi. Application of Student’st test to the differences in the values of each of the 10samples measured at 100 and 2,000 psig and 392°Fresults in a probability of less than 1 percent thatthere is no pressure effect. However, the average in-crease in the thermal conductivity is very small, lessthan 2 percent, and the effect is ignored in this report.This apparent behavior at 392°F may be related tophase changes of minerals, organic matter, or ofcapillary water in the oil shales. There also does notappear to be any effect of stress on the thermal con-ductivity, a result that is consistent with that reportedby Thomas,*

On the, two oil-shale samples comprising Set G,thermal conductivities were measured as a functionof temperature, both before and after burning off theorganic matter. The raw oil-shale samples wereplaced in the cell and a few measurements were madeup to 392oF. Then air was passed through the cellfor 2 days with the oven at 7500F. Air flow was keptpurposely low to prevent a large increase in thesample temperature during the burning process. Table7 shows the results obtained, For Sample G-1 (50gal/ton) the thermal conductivity at room tempera-ture after burning is 0.315 times that of the raw oilshale. At the higher temperatures the reduction is lesspronounced. For Sample G-2 (12 gal/ton) the thermalconductivity at room temperature after burning wasreduced to 0.36 of the raw value and the effect of

4"0R-H:+:i;l-;lll:l:l`l`l::!'l`'l}'t''ll`:l:!4:i-:lT4... ., 1 1A

* ...

0.10 10 20 30 40 50 60 70

OIL YIELD. GA1I1ON

Fig. 7—Regression cuwes for the horizontal,thermal conductivity as a function of oil

yield and temperature.

JANUARY, 1975 “ 103

TABLE 6-EFFECT OF PRESSURE AND AXIAL STRESS ON THE THERMAL CONDUCTIVITY

Conditions

Ternnera.Stress Pressure

~ (psi) w—o o

75 2,000 1002,000 1,800

0 0392 2,000 100

2,000 1,800

482 2,000 1002,000 1,800

572 2,000 100~.2,000 1,800

662 2,000 1002,000 1,800

752 2,000 1002,000 1,800

Sampla Designation*

A5H A5vm ~

0.546 0.6260.546 0,613

0.516 N.D.0.490 0.5810.496 0.582

N.D. N.D.N.D. N.D.

0.419 0.5060.461 0.506

0.457 N.D.0.405 0.479

N.D. N.DoN.D. 0.358

A4Him-0.7800.779

N.D.0.7070.727

0,6700.670

0,6640.549

0.5870.587

0.5680.592

ANN.D.0.7400.760

N.D.0.6910.709

0.6540.685

0.6330.649

0.6070.574

0.5350.525

A3H A3V A2H A2Vmm 1.06 m0.824 0.852 1,04 N,D,0.850 0.803 1.06 N.D.

N.D. N.D. N.D. N.D.0.742 0.727 0.988 1.010.762 0.748 0.999 1,01

0.701 0.722 MD. N.D.0.757 0.783 N.D. N.D.

0.724 0.679 0,9S6 N.D.0.743 0,731 0.967 N.D.

0.693 0.739 N,D. N.D.0.732 0.702 N,D, N.D.

0.653 0.604 N.D. N.D.0.666 0.604 N.D. N.D.

AIHm0.9780.978

N.D.0.9270.927

0.8850.885

0.8410.641

N.D.0.795

N.D.0.702

AIVm1.091.12

N.D.0.9391.00

0.9560.956

0.6470.902

0.8750.923

N.D.N.D.

*Samples cut normal to bedding planes carry the letter V in their designation. The thermal conductivity arallel to the lamlna.tions is reportad for these samples. Samples cut parallel to bedding ~lanes Kcarry the latter H In t air designation. Thageometric mean of the tharmal conductivities parallel and normal to t e laminations la raported for these samples.

● ●N, D. stands for Not Determined.

burning is rather insensitive to the temperature level.After removal from the cell it was ascertained that

the lean sample (G-2) had not developed any visiblecracks, The rich sample (G-1) could not be removedfrom the cell without breaking it, so it is not knownif cracks developed. It is known, however, that thesample expanded axially about 1/4 in., which is theamount the piston (used to impose axial loads) waspushed out. These measurements were made at at-mospheric pressure and 2,000 psi axial load.

Thermal conductivities of oil shale are affected bythe degree of conversion of kerogen to fluid products.The fraction of converted kerogen is controlled bythe temperature history of the sample, as shown inFig, 8, which is reproduced from Matzick et al.” Al-though the conditions under which that curve wasobtained may not be quite the same as those actuallyexisting in either a surface or subsurface shale-oilextraction process, it may still be used, at least quali-tatively, to illustrate several points. At 750°F it would

TABLE 7—THERMAL CONDUCTIVITIES OFBURNED OIL SHALES

ThermaiConductivity,Btu/ft.hr’F

Tem~$r#ure SampleG-l SampleG-2(50 gal/ton) (12 gal/ton)

[

J 75 0.336 0.941212 0.336 N.D.

RAw ; 392 0.312 0.830

m 572 N,DC* 0.706a 75 0.106 0.339

BURNED

212 0.106 0,319s 392 0.123 06319e 572 0,160q

0.271

u 662 0.169 N.D.e 752 0.244 N.D.

In 842 0.242 0.261c 662e

0.169 N.D.

J

572 0S67 N.D.75 0.099 N.D.

*N. D. means Not Daterminad.

104

appear that 90 percent of the kerogen would be de-composed before the sample temperature could stabil-ize, which normally takes 3.5 to 4.0 hours. Thus, themeasured thermal conductivities at 750°F essentiallyreflect those of fully retorted oil shales. On the otherhand, Fig, 8 also illustrates that at 650°F it wouldtake about 100 hours for 90 percent of the kerogento decompose. In this case, the thermal conductivity(usually measured between 3.5 and 10 hours aftersetting the thermostat) would not necessarily be thesame as that measured after 100 hours at the sametemperature. Fig. 9 shows the effect of heating timeon the thermal conductivity measured at 662°F, Themeasurement at 9 hours (5.5 hours after the ambienttemperature had stabilized) was 0.476 Btu/ft-hr-°F.The thermal conductivity at 300 hours had stabilizedto a value of about 0.412 Btu/ft-hr-°F. The initial

‘01000~T–—

Fig. S-Reaction time for 90-percent decomposition ofkerogen in Coiorado oil shale?

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value at room temperature (a nominal 75°F) was0.581 Btu/ft-hr-°F. Thus, the 9- and 350-hour valuesat 662°F amounted to 82 and 70 percent, respec-tively, of the value at room temperature. This com-pares well with the ratio of 0.79 read from the re-gression curve in Fig, 5 at a temperature of 662°F.In other words, the thermal conductivity after 9 hoursat 662°F ranges from less than 4 percent higher to 11percent lower than the reported correlation value. At752°F the reported values essentially reflect completekerogen decomposition. At 572°F the rate of kerogendecomposition is very slow. Although kerogen de-composition does affect the thermal conductivity ofoil shale, it is not a critical parameter, at least in thosecases where the rate of temperature increase of thesample is relatively slow (such as would be the caseoutside an in-situ process zone). It is possible, how-ever, that at fast heating rates and rapid removal ofdecomposition products, the amount of coke formedwithin the sample would be significantly reduced, andthat this could result in appreciably lower thermalconductivity values than those given by the correla-tions. In no case, however, can the thermal conduc-tivity values be lower than those for burned samples(free of organic matter),

Thermal DiffusdvftyWe have used the predictive equations for our thermalconductivity values, the correlation of specific gravitywith oil yield obtained from the data given in Table 4,

FA = 21.15p’ – 155.1OP + 262.20,and the correlation of specific heat with oil yield andtemperature given by Shaw,%O

C = 0.172+ (0.067+ 0.00162FA) 10-’(460+ 2’),to calculate approximate values for the thermal dif-fusivities of raw oil shales, The values of specificgravity and oil yield for our samples are plotted inFig. 10. Values for Sample A-1, which was the onlyone having a discernible porosity, are obviously offtrend. Accordingly, Sample A-1 was not consideredin developing the correlation between specific gravityand oil yield given above. This correlation is shownby the solid line in Fig. 10.

Horizontal thermal dtiusivities calculated from theexpression a = kh/pc are plotted in Fig. 11. Thesecalculated thermal dtiusivities range in value from0.75 ft2/D for a lean oil shale at room temperatureto 0.15 ft2/D for a rich one at 750°F. Thermal dif-fusivities have also been calculated for each sampleand are included in Table 4. Note that the specificgravity of the bulk oil shale has not been correctedfor temperature. The correction is not an importantone, but would tend to increase the values of the cal-culated thermal diffusivities.

Comparison of our calculated horizontal diffusivi=ties with the measured and calculated values reportedby Tihen et al.’ (whose orientation is not reported) isshown in Fig. 11. Significant differences (as much as50 percent). exist in the room temperature values forsamples assaying 20 to 50 gal/ton.

DiscussionSpecial tests made to study the significance of our

thermal conductivity measurements have been men-tioned in the Introduction and in the sections on In-strumentation and Description of Samples. These in-elude comparisons with reported values on the thermalconductivity of Pyrex, and studies on the repro-ducibility of data on oil shale at room temperature,on the variation of thermal conductivities along anarrow stratigraphic interval, on the effect of fluidpressure and axial load, on the ability of the experi-mental technique to yield effective values of thethermal conductivities parallel and vertical to the bed-ding, and on contact resistance. These limited studiesshowed that our Pyrex results diflered by less than1,5 percent from published values, the duplicatemeasurements had a standard deviation of 2,6 per-cent of the measured value, the thermal conductivitiesof nearby samples along the same stratigraphic inter-

0 100 200 300 400HEATING lIME, HOURS

Fig. 9-Hfect of heating time.

I-II I I ,--l–! I i ] i 1-”:“1...._. -f-.. ... ,+ -. . . ..

1

.. —,.. L ---—,I 1“

, sI I,, . . .. :..,:. ‘.:

l--+ :.! ‘: I I

2.1 2.2 2.3 2.4 2,S

SPECIFIC GRAVITY

Fig. 10-Specific gravity-oil yield relationship.

JANUARY, 197S 10s

I

val had a standard deviation of about 4.0 percent ofthe measured value, the effectsof axial stress and fluidpressure up to 1,800 psig were small (at least forsamples that do not contain easily decomposablesodium carbonates such as dawsonite and nahcolite),experimental results could be properly interpreted inlaminated media, and results were essentially inde-pendent of contact resistance.

our thermal conductivity values are strictly appli-cable to confined, crack-free oil shale sections in thetemperature range 75° to 752°F. At the higher tem-peratures, the reported values include the effects ofat least some decomposition of organic products. Ina subsurface recovery operation, the reported valueswould be specifically applicable to those sections ofunfractured oil shale surrounding and limiting thevolume under extraction. As such, our thermal con-ductivity values may be used to calculate heat lossesfrom the subsurface operation. They may, of course,also be used in any situation where heat transfer isby conduction in samples that do not have cracks,such as might be the case within some oil-shale piecesin surface retorta and in subsurface extraction proc-esses that make use of fragmented or broken oil shale.The rubble pile resulting from a contained subsurfacenuclear explosion is an example of the possible use ofoil-shale fragments in a subsurface recovery operation.

When heat transfer is by conduction only, cracks

will yield a low apparent value for the thermal con-ductivity of the sample. We think this is the majorreason for the relatively low values (compared withours) of the thermal conductivities of raw oil shalesreported by Tihen et ala Examples of their reported

0 10 20 30 40 50 60 70 80OIL WELD, GAL/TON

Fig.’ n-Calculated horizontalthermal diffusivitiesas afunction of oil yield and temperature, com ared with thoseRreported at room temperature by Ti en et al?

106

I

values are given in Fig. 4. On the other hand, thepresence of cracks will result in a high rate of heattransfer in operations using forced convection ofheated fluids, Rates of heat transfer through oilshales where cracks are present cannot be properlycalculated using our data.

NomenclatureC = mean specific heat of raw shale above the

temperature of 77”F, Btu/lb°FFA = oil yield by Fischer assay, gal/ton

kh = thermal conductivity, Btu/ft-hr-°FT = temperature, ‘Fa = thermal diffusivity, ft2/DP = specific gravity (nominal) numerically

equal to bulk density of oil shale,&n/cc

subscriptsH = horizontalG = geometric mean of horizontal and

vertical valuesV = vertical

AcknowledgmentsThe mineralogical determination and sample selectionwas done by D. C. Conner. The design, construction,and checkout of the equipment was done by C. H.Fay, J. C. Adair, and R. Cronim

References1.Gavin, M. J. and Sharp, L. H,: “Some Physical and

Chemical Data on Colorado Oil Shalej” RI 2152, USBM,Washington (Aug. ‘1920),

2. Thomas,G. W.: “SomeEffectsof OverburdenPressureon Oil ShaleDuringUndergroundRetortingflSot. Pet,Eng, J. (March 1966) 1-8; Trans., AIME, 237.

3. Tihen, S. S., Carpantar, H. C., and Sohns,M Wt: “Ther-mal Conductivity and Thermal Diffuswity of GreenRiver Oil Shales,’ Proc., 7th Conf. Thermal Conductivi-ty. NBS SP. Pub. 302 ( 1968) 529-535.

4. Woodside~ W. and Messmer, J, H.: “Thermal Conduc-tivity of Porous Media. I. Unconsolidated Sands; J.Amd. f%Ys. [ 1961a) 32, No. 9, 1688-1699.

S, W;odside, W. and”Messmer, J. H.: ‘“ThermalConduc-tivity of Porous Media, IL Consolidated Rocks; 1, Appl.t%YS, ( 1961b) 32, No. 9, 1699-1706.

6. Flynn, -D. R. ~ NBS Report 7836 (1963) 1-22 (AD 407802), as reported by Touloukian, Y. S., Powell, R. W.,Ho,*C, Y., and Klemens, P. G., “Thermal Conductivity— Nonmetallic So]ids~ Thermophysical Properties ofMatter, IFI/Plenum, New York (1970) 2, Curve 76,930.

7. Guest, P, G.: Numerical Methods of Curve Fitting,Universum Press, Perth Amboy, N. J. (1961) 7.

8. Alder, H, L. and Roassler, E, B,: Statistical Procedures,~r :d,j U. of California, Berkeley (1961) Ch, 20, 362,

. .

9. Matzick, A., Darmenberg, R. O., Ruark, J. R., Phillips,J, E,, Lankford, J, D., and Gutime, B.: “Develo ment

rof the Bureau of Mines’ Gas-Combustion Oil-Shae Re-torting Process: Bulf. 635 USBM (1966).

10. Shaw,_ R. J.: “Specific Heat of Colorado Oil Shale%”USBM Report of Inv. 41S1 (1947).

11.Smith, J. W.: “Spaci13cGravity-Oil Yield Relationshipsof Two Colorado OL1-Shalecoretb” hd. and Eng. Chem.(1956) 48, No. 3,441-444. XPT

Orlglnal mammcrlpt racelverJ In Society of Petrolaum Englneeraoffice Dec. 21, 1973. Revised manuscript received Oct. 10, 1974.@ Copyrkrht 1975 Amedcen lrwtltute of Mlnlng} MetalWlcaLend Petroleum Engineers, Inc.

This paper wIII be Includad in the 1975 Transsctlotw volume.

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