CA1232197B - Apparatus and method for in situ heat processing of hydrocarbonaceous formations - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
The disclosure describes a technique for uniform heating of relatively large blocks of hydrocarbonaceous formations in situ using radio frequency (RF) electrical energy that is substantially confined to the volume to be heated and effects dielectric heating of the formations.
An important aspect of the disclosure relates to the fact that certain hydrocarbonaceous earth formations, for example raw unheated oil shale, exhibit dielectric absorption characteristics in the radio frequency range.
In accordance with the system of the invention, a plurality of conductors are inserted in the formations and bound a particular volume of the formations. The phrase "bounding a particular volume" is intended to mean that the volume is enclosed on at least two sides thereof. Electrical excitation is provided for establishing alternating electric fields in the volume. In this manner, volumetric dielectric heating of the formations will occur to effect approximately uniform controlled heating of the volume.

Description

. I' . '13~C~CG~ OIL IN
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This invention relates to the ex~loitatlon of ~ydrocarbon-bearing earth formations, and more particularly, to a system and method or the in situ heating processing of hydrocarbon earing earth formations such a oil shale, tar sands, coal, heavy oil, and other bituminous or viscous petroliferous deposits, The present subject matter is related to subject matter set forth in the cop ending application Serial No. 3gg33g of Jock Bridges Allen Taflove and Richard Snuck filed August 15, 1978 and assigned to the same assignee, as the present application.

Large scale commercial exploitation of certain ,hydrocaxbon-bearing resources, available in huge deposits on the North American continent, has been impeded by a number of problems, especially cost of extraction and environmental impact.. The United states has tremendous coal resources but deep mining techniques are hazardous and to .
s, . leave a large percentage of the deposits in the earth. Strip . Jo .
I., . mining of coal involves environmental damage or expensive . . .
I , reclamation. Oil shale is also plentiful in the United ";
. . 20 States, but the cost of useful fuel recovery has been ,. generally noncompetitive. The same is true for tar sands , which occur in vast amounts in Western Canada Also, heavy ;,~; or viscous oil is left untapped, due to the extra cost ox .

. . extraction/ when a conventional oil well is produced ' 25 Materials such as oil shale, tar sands, and coal "I' , . are amenable to heat processing Jo produce gases and hydra-;, , , carbons liquids. Generally, thought develops the porosity, permeability Andre mobility necessary for wrecker .,. Oil shale is a sedimentary rock which, upon pyrolyzes or distill . .30 Zion, yields a condensable liquid referred to as a shale oil, and n~n-c~ndensable gaseous hydrocarbons.

The condensable liquid may be refined into products which _/ 3 ~23~37 resemble petrol us products. Oil Rand is an erratic mixture of sand, water and bitumen with the bitumen typically present . . I a film around water-envelopPd Rand particles. Using various types of heat processing the bitumen can, with difficulty, be separated. lo as is well known, coal gas and other useful products Jan be obtained from coal using heat processing.
In the destructive distillation of oil shale or other solid or semisolid hydrocarbonaceous materials, the solid material is heated to an appropriate temperature and the emitted products are recovered. This appears a simple enough goal but, in practice, the limited efficiency of the process has prevented achievement ox large scale commercial application.
Regarding viol shale, for example, there is no presently acceptable economical way to extract the hydrocarbon constitu-lo ens. The desired organic constituent, known as kerogen~c~nstitutes a relatively small percentage of the bulk shale material, so very large volumes of shale need to be heated to elevated temperatures in order Jo yield relatively small amounts of useful end products. The handling of the large amounts of material is, in itself, a problem, as is the disposal of wastes. Also, substantial energy is needed to heat the shale, and the efficiency o thy heating process and the need for relatively uniform and rapid heating have been limiting factors ox success. In the case of tar sands, the I volume of material to be handled, as compared to the amount of. recovered product is again relatively fang , since bitumen typically constitutes only about ten percent of the total, by weight.. Material handling of tar sands is particularly difficult even under the bet of condition and the problems of waste disposal are, of course, present hire too.

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~23~7 There have been a number of privy proposals sex forth for the extraction of useful fuel from oil shales and tar sands in situ but, for various reasons, none has gained commercial acceptance. One category of such techniques utilizes partial combustion of the hydrocar-buoyances deposits, but these techniques have generally suffered one or more of the following disadvantages: lack of precise control of the combustion, environmental pollution resulting from disposing of combustion products, 10 and general inefficiency resulting from undesired combustion of the resource.
Another category of proposed in situ extraction techniques would utilize electrical energy for the heating of the formations. For example, in the U. S. Patent No. 2,634,961 there is described a technique wherein electrical heating elements are embedded in pipes and the pipes are when in-sorted in an array of Berlioz in oil shale. The pipes are heated to a relatively h go temperature and eventually the heat conducts through the oil shale to achieve a pyrolyzes thereof.
Since oil shale is not a good conductor of huts technique _ : is problematic in what the pipe must be heated to a con-sidexably higher temperature than the temperature required for pyrolyzes in order to avoid inordinately long processing times.
However overheating of some of the oil shale is inefficient in that it wastes input electrical energy, and may undesirably carbonize organic matte and decompose the rock matrix, thereby limiting the yield Further electrical in Sue techniques have bee termed as "ohmic ground hutting or ~'electrothermi~" pro-cusses wherein the electric conductivity Jo ~he-~ormat-.ions it relied upon to awry an electric current as between electrodes placed in separated whorls. An example of this type of ~echnique,as applied to tar sands, is described in U. S.
Patent No. 3,848,671. A problem with this technique is that the formations under consideration are generally nut sufficiently conductive to facilitate the establishment of efficient uniform heating orients. Variations of the electr~thermic techniques are known as "electrolinking", "electr~car~onization", and "electrogasification" (see, for example, U. So Patent No. 2,79~,279~. In electrolinking or electrocarbonization,~
electric heating is -gain achieved Vim the inherent con-ductility of the fuel bed. The electric current is applied such that a thin narrow fracture path it formed between the electrodes. Along this fracture path, pyrolyzed carbon forms more highly conducting link between the Berlioz in which the elec'.r~des are implanted Current is then passed through this link to cause electrical heating of the surrounding formations In the electrogasificati~n process I electrical heating through the formations is performed ¦ simultaneously with a blast Go air or steam. Generally, 1 I the just described techniques are limited in that only I relatively narrow filament-like heating paths are formed ¦ between the electrodes. Since the formations are usually ¦ not particularly Good conductors of heat, only non-uniform--heating is generally achieved. The. process wends to be slow and requires temperatures near the heating lynx which ¦ are substantially higher than the desired pyrolyzing temperatures, ¦ with the attendant inefficiencies previously described Another approach to in situ processing has bee termed Nelectro~racturingn~ In one variation D C this technique, described id U. 5. Patent No. conduction -6- ..

, o ) through electrodes implanted in the formations is again utilized, the heating briny intended, for example, Jo increase the size of fractures in a mineral hod. In another version, disclosed in I. S. Patent No. 3,69~,8~6, electricity it used , to fracture a shale formation and a thin viscous molten fluid core is formed in the fracture. This fore is then forced to flow out of the whale by injecting high pressured gas in one of the well bores in which an electrode is imp planted, thereby establishing an pen retorting channel.
'10 In general, the above described techniques are .
limited by the relatively low thermal and electrical con-ductility of the bulk formations of interest. While individual conducive paths through the formations can be es~ablisned, , . heat does not radiate at useful rates from these paths, and efficient heating of the overall bulk is difficult to achieve.
A further proposed electrical in situ approach - would employ a set of arrays of dipole antennas located in a plastic or other dielectric oaring Inca formation, such as a tar, sand formation. A VHF or UHF power source would energize the antennas and cause radlaking field to be emitted therefrom.
However, at these frequencies 7 and considering the-electri~al properties of the formations,"khe field intensity drops rapidly as a function of distance away from the antenna. Therefore t one again, non-uniform heating would result in the need for I inefficient overheating of portions-of the formations in order to obtain a least minimum average heating of the bulk . . _ = . _ .
of the formations.
A till further proposed scheme would utilize -in situ electrical inducki~n heating of,form~tions. Again the inherent (although limitea),conduction ability of to -7- , '. - .
.

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formations is relied upon. In particular, secondary induction . heating currents are induced in the formations by forming an underground towardly induction coil and passing electrical current through the turns of the coil. The underground oared is formed by drilling vertical and horizontal Berlioz and conductors are threaded through the Berlioz to form the turns of the toxoid. It has been noted, however, that as the formation are heated and water vapors are removed rum it, the formations become more resistive, and greater . . to currents are required to provide the disarrayed heating.
The above described t chniques are limited by either or both of the relatively low thermal and elec~xical conductivity of the bulk formations of interest. Electrical technique utilized for injecting heat energy into the .
formations have suffered from limitations given rise to by the relatively low electrical conductivity of the bulk formations. In situ electrical technl~ues appear well capable of injecting heat energy into the formations along individual conductive paths or around individual electrodes but this leads to non-uniform heating of the bulk formations j The relatively low thermal conductivity of the formations:.
¦. then comes into play as a limiting factor in attaining a_ ¦ relatively uniformly heated bulk volume. -- The infusion I . resulting from non-uniform heating have tender to render ¦ 25 existing techniques slow and inefficient _ It it an object of the present invention to . provide in situ heat processing of hydrocarbonaceous earth formations utilizing electrical Pxeitation means, in such manner that substantially uniform heating of a particular , . . _ . . _ . . . .. . . . ..

, ... -I .. ; .

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ilk volume so the formations is efficiently achieved.
. Further object of the present invention are to provide a system and method for e~iciently heat processing r~d.tively large blocks of hydrocarbonaceous earth formations 5 With' a minimum of adverse environmental impact and for yielding a high net energy ratio ox energy recovered o energy expended.

_ _ . _._ .. . . .. .

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' . _ . . _ . . _ . _ . = .
- . _. - - --; - = _. - . _ . _ . _ .

r .~.. -.. -. ... ...

swearer OF TOE INVENTION

Applicant have devised a technique fur uniform heating of relatively large blocks of hydrocarbvnaceous formations using radio frequency (RF) electrical energy that is substantially confined to the volume to be heated and effects dielectric heating of the formations. An important aspect of applicants' invention relates Jo the fact that `. certain hydrocarbonaceous earth formations, for example raw unheated oil shale, exhibit dielectric absorption character-is tics in the radio frequency range. As will be described, 10 various practical constraints limit the range of frequencies which are suitable for the RF processing of commercially useful blocks of material in situ. The use of dielectric heating eliminates the reliance on electrical conductivity properties of the formations Which characterize most prior I art electrical in situ approaches Also, unlike other proposed schemes which attempt to radiate electrical energy from antennas in uncontrolled fashion, applicants provide . field confining structures which maintain most of the input 1., . - .
energy in the volume intended to be heated. Conduction currents, which are difficult to establish on a useful uniform basis, . are kept to a minimum, end displacement currents dimmer and provide the desired substantia71y uniform heating.
Since it is not necessary for the resultant heft to propagate over substantial distances in the formations (a in the above described prior art ohmic heating schemes ? the relatî~ely poor thermal conductivity of the Erosions is t nut a particular disadvantage in applicants' technique.
Indeed, in already-processed formations from which the useful products have been removed the retained heat which is .. ..
.

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I

essentially "stored", can be advantageously utilized. In an embodiment of the invention, initial heaving of adjacent blocks of hydrocarbonaceous formations is implemented using this retained heat.
In particular, the present invention is directed to a system and method for in situ heat processing of hydrocarbonaceous earth formations In accordance with the system of the invention, a plurality of conductive means are inserted in the formations and bound a particular volume of the formations. As used herein, the phrase "bounding a particular volume" is intended to mean that the volume is enclosed on at least two sides thereof. As will become understood, in the most practical implementations of the invention the enclosed sides are enclosed in an electrical sense and the conductors forming a particular side can be an array of spaced conductors. Electrical excitation means are provided for establishing alternating electric fields in the volume. In this manner, volumetric dielectric heating of the formations will occur to effect approximately uniform heating of the volume.

t ~L~32~

In the preferred embodiment of the invention, the frequency of the excitation is in the radio frequency range and has a frequency between about 1 MHz and 43 MHz.
In this embodiment, the conductive means comprise opposing spaced rows of conductors disposed in opposite spaced rows ox Berlioz in the formations. One particularly ad van- -tageous structure in accordance with toe invention employs D
three spaced rows of condlJctors which form a *xiplate-type of wave guide structure. The stated excitation may by applied 10 as a voltage, for example across different groups of the con-ductile means or as a dipole source, or may be applied as a current which excites at least one current loop in the volume. When a triplate-type of stroker is employed, the conductors of the central row are preferably substantially shorter than the length of the conductors of the outer rows so as to reduce radiation, and resultant heat loss, at the ends ox the conductors.
In accordance with a further feature of the in-mention, the frequency of the excitation is selected as a function of the electrical lousiness of the formations it the confined volume to be sufficiently low awoke the e attenuation distance of the electric field in any direction in the volume is more than twice the physical dimension of the volume in that direction ID this manner, the diminution of the electric field in any direction due o transfer of energy to the formations (as it 9 of course, desirable Jo effect the needed heating) is not so severe as to cause undue non-uniformity of heating in the volume and wasteful over tying of portions thereof. As will be described, a further .

3~3~
technique is employed for obtaining relatively uniform heating by modifying the electric field pattern during the heating process so as to effectively average the electric field intensity in the volume to enhance the uniformity of heating of the volume.
The electrical heating techniques disclosed herein are applicable to various types of hydrocarbon-containing formations, including oil shale, tar sands, coal, heavy oil, partially depleted petroleum reservoirs, etc. The relatively uniform heating which results from the present techniques, even in formations having relatively low electrical conductivity and relatively low thermal conductivity, provides great flexibility in applying recovery techniques. Accordingly, as will be described, the in Sue electrical heating of the present invention can be utilized either alone or in conjunction with other in situ recovery techniques to maximize efficiency for given applications.
More particularly twerp is provided a system for in situ heat processing of hydrocarbonaceous earth formations, comprising:
a plurality of conductive means inserted in said foxmatiorls and bounding a particular volume of said formations;
electrical excitation means for establishing alternating electric fields in said volume;
whereby volumetric dielectric heating of the formations will occur to effect approximately uniform heating of said volume.

I
There is also provided a method for in situ heating of hydrocarbonaceous earth formations, comprising the steps of:
forming a plurality of Berlioz which bound a particular volume of said formations;
inserting elongated electrical conductors in said Berlioz; and introducing electrical excitation to said formations to establish alternating electric fields in said volume;
whereby volumetric dielectric heating of the formations will occur to effect approximately uniform heating of said volume.
¦ There is further provided a system for in situ heat processing of an oil shale bed, comprising:
a plurality of conductive means bounding a particular volume of said bed;
electrical excitation means for establishing alternating electric fields in said volume;
whereby volumetric dielectric heating of the bed I will occur to effect approximately uniform heating ox said volume.
¦ There is also provided a system for in situ heat ¦ processing of a tar sand deposit, comprising:
a plurality of conductive means inserted in said I deposit and bounding a particular volume of said deposit;
electrical excitation means for establishing alternating electric fields in said volume;

-aye-I

whereby volumetric dielectric heating of the deposit will occur to effect approximately uniform heating of said volume.
Further features and advantages of the invention will become more readily apparent from the following detailed description when taken in conjunction with the accompanying drawings.

-13b o 7 BRIEF DESCRIPTION I THE DUNKS

FIG 1 illustrates an in Sue twin load transmission line in earth formations.

FIG. 2 illustrates an in iota biplane transmission line in earth formations.
. I' . .
FIG. 3 illustrate s an in slot replete transmission line in earth formations. . -. ., JIG. PA is a plan view of an in situ structure in . accordance with an embodiment of the invention.

. FIG 4B is an end view of the structure of FIG. PA
as taken trough a section defined by arrows 4b~4b of FUGUE.
. ', FIG. 4C is a side view of the structure of FIG PA

a taken through a section dew iced by arrows 4c-4c of JIG. PA.
'..................................... .
. FIG. 5 illustrates an alternate configuration of the structure of FIG. 4B wherein the outer rows of conductors taper toward each other. .

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FIG. 6 illustrates implementation of the invention I in a situation of a moderately deep no ounce bed.
. - , ' ', , .

FIG. 7 illustrates implementation Do the invention in a situation where a relatively thick resource bed is located ~elati~e;Ly deep in the earth's surface.

, ' FIG. 8 is a graph of the electric field and heating i pattern resulting from a standing wave pattern in a Tripoli-type live cvnfiguratio~.
' ' ' , .

FIG. 9 illustrates a smoothly varying exponential heating pattern which results from modifying of the electric yield pattern during operation.

. FIX. 10 is a graph of operating frequency versus 5 skin depth for an in situ oil shale heating system.

FIG. 11 is a graph of operating frequency versus processing. time for an in situ oil shale heating system.

.
FIG. 12~ illustrates an embodiment of the invention wherein current loop excitation is employed.

FIG. 12B is an enlargement ox a portion of FIX. AYE.
'' - ; , FIG. 13 is a simplified schematic diagram of a system end facility for xec~very of shale Gil and related products from an oil stale bend FIG. 14 is a simplified schematic diagram of a system and facility for recovery of useful constituents from a tar sand formation.

FIG. 15 is a simplified schematic diagram which.
I illustrates how residual heat in "spent" formations can be ¦ utilized for prying resources to be subsequently processed , Fig 16 illustrates an embodiment of the invention : wherein electric dipole excitation is employed. :

FIG. 17 shows a diagram of a non-resonant processing Tahitian.

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DESCRIPTION OF TAO PREFERRED EMBODIMENT
-- _ _ Before describing the preferred implementations of practical forms of the invention the principles of the invention can be initially understood with the aid of the simplified diagrams of Figs I 2 and 3. FIG. 1 illustrate s a twin-lead transmission line defined my a pair ox elongated conductors 101 and 102 which are inserter into hydra-carbonaceous earth formations 10, for example an oil Shelley or coal deposit A source 110 of radio frequency excitation is coupled to the twin-lead transmission lingo The resultant electric field causes heating, the heating being indicated in the FIGURES by the dots. The intensity of the heating is represented by the density of ho dots In FIG. I the field lines, which are in a general standing wave pattern, extend well outside the region between the transmission line leads and substantial radiation occurs from various points with resultant loss of heating control. . tithe actual field pattern will depend, inter alias upon fre~uencyt as will be discussed below, and the illustrations of Figs I 2 and 3 . are for an appropriately chosen exemplary frequency.) In . FIG. 2, there is illustrated a biplane transmission line consisting of spaced parallel conductive plot s 201 and 202 in the formations When excited by a source 210 of RF .
enrage a standing wave field pattern it again established.
Radiation is particularly prevalent at the edges and corners I of the transmission line plates Radiation outside tube transmission line confined region is lest than in FIX but still substantial as is evident from the heaving pattern. FIG. 3 thus rates a triplane transmission line which includes spaced urea parallel plate conductors 3~1 and 302 and a central parallel plate conductor 303 there between. Excitation by an OF source 310, as between the central plate and the outer plate, establishes a fairly well confined field. The central plate 303 is made shorter than the outer plates 301 and 302, and this contributes to minimizing of fringing effects. Standing waves would also normally be present (as in Figs 1 and

2) but, as will be described further hereinbelow, the periodic heating effects caused by standing wave patterns can be averaged out, such as by varying the effective length of the center plot 303 during different stages ox processing. The resultant substantially uniform average heating is illustrated by the dot density in FIG.
I I
It is seen from the Figs 2 and 3 that alternating electric fields substantially confined within a particular . . volume of hydrocarbonaceous formations can effect dielectric . . heating of the bulk material in the volume. The degree of I 20 heating at each elemental volume unit in he bulk will be a ¦ function of the dielectric lousiness of the material at the I particular frequency utilized as well as a function of the ¦ field strength. Thus, an approximately uniform field in the confined volume will give rise to approximately uniform I heating within the volume the heating not being particularly dependent upon conduction currents which are minimal lay compared to displacement currents) in the present techniques.
t As previously indicated the illustrates owe FUGUE 1, 2 and 3 are intended for the purpose of aiding in an initial understanding of the inven~ionO The structures of , t Figs 2 and 3, while being within the purview of the invention, are not presently considered as preferred practical embodiments since plate conductors of large size could no be readily inserted in the formations.
As will become understood, the confining structures of Fogs 2 or 3 can be approximated rows of conductors which are inserted in Berlioz drilled in the formations.
One preferred form of applicants' invented system and method is illustrated in conjunction with Figs PA, 4B and 4C. FIG. PA shows a plan view of a surface of a hydrocarbonaceous deposit having three rows of brollies with elongated conductors therein. This structure is seen to be analogous to the one in FIG. 3., except that the solid parallel plate cQn~uctors are no-placed by individual elongated tubular conductors placed in Berlioz that are drilled in relatively l~sely spaced relationship to form outer rows designated as row 1 and row 3, and a central row designated as row 2. the rows are spaced relatively far apart as compared to the spacing of adjacent conductors of a row. FIG. 4B shows one . conductor from each row; viz., conductor 415 from row 1 conductor 425 from row 2, and cor.duct~r 435 from row 3.
EGO. 4C illustrates the conductors of the central Dow, row 2.
. In the embodiment shown, the Berlioz of the center row j I are drilled to a depth of Lo meters into the ~ormatior.s _ _ ¦. where I is the approximate depth of the bottom boundary of _ , the hydrocarbonaceous deposit. The Berlioz of the outer j rows axe drilled to a depth of Lo which is greater than Lo and extends down into the barren rode below the useful ED deposit. After inserting the conductors into the Berlioz, '. , , , ', .

. .. : : . . ..

lo 32197 the conductors of row 2 aloe electrically connecter ~uy~ther all coupled to one terminal of an OF voltage source 45~ (see FIG. byway The conductors of the outer rows are o connected together and coupled the other 'L~minal of the RF voltage source 450. Tile zone heated by applied RF energy is approximately illustrated by the cross-hatching ox FIG. PA. The conductors provide an effective confining structure for the alternating electric fields established by the RF excitation. us will become understood, heating below Lo is minimized by selecting the frequency of operation such what a cutoff condition substantially prevents propagation of wave energy below Lo.
. . The use of an array of elated cylindrical conductors to form a field confining structure is ad van-tageous in that installation of these units in Berlioz is more economical than for example, installation of continuous plane sheets on the boundaries of the volume to ye heated in situ. Also, enhanced electric fields in the vicinities.
of the Barlow conductors, through which recovery of the hydrocarbons fluids ultimately occurs, is actually a benefit (even though it represents a degree of hoe in nonuniformity in a system where even heating is striven for) since the formations near the Barlow conductors will be heated first. This tends to create initial permeability porosity and minor fracturing which facilitates orderly recovery of fluids as the overall . bound volume later rises in temperature. To achieve _ . field confinement, the spacing between adjacent conductors of a row should be less than about a quarter wavelength apart ant preferably, less than abut an eighth of a wave-_ __ length apart.
Very large volumes of hydrocarbonacevus deposits . . can be heat processed using the described technique, for I

example volumes of the order of I cubic meters of oil whale.. Large blocks can, it desired be processed in suckle by extending the lengths of the rows of Berlioz - and ooJiductor~; . Alternative field cc)nf inning structures and modes of excitation are possible and will be described ..
; further hereinbelow. At present, however, two alternatives will be mentioned. First, further field confinement can be provided by adding conductors in whorls at the ends of the rows (as illustrated by the dashed }orioles 49G of FIG AYE to form a shielding structure. Secondly, consider the configuration of FIX. S (annuls to the cross-sectional view of Fit;. 4B) worrier the conductors owe the outer rows are tapered toward the central rows at their " ' deep ends so was to improve field uniformity Rand consequently heating uniformity) urethra from the source.
In Figs 1-5 it was assumed, for aye owe illustration, that the hydrocarbonaceous earth formations had a seam at or .
I. near the surface of the earth, or that any overburden had been .~. . removed however, it will be understocked that the invention is . 20 equally applicable to situations where the resource bed is less Jo . . . .
: accessible an for example, underground mining is required -, . :
on FIG. err i~--shown~a situation wherein a moderately , : deep hydrocarbonaceous bed, such as an oil shale layer ox ,.'., ;. . substantial thickness is located beneath barren rock Norma--, 25 lions; In such- instance, a Wright or alto 640 can be mined I" and Berlioz can by! drilled from the surface, as represented .' by the borehc)les 601, 602 and G3:13 of FIX;.. 6, or from the - art. Again eacfi off these bc)rehoies-repr~sents one of a row Do Berlioz o'er a tr:iplate-type configuration .

.

... . ...... .. .

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as is shown in FIG. 4. After the brollies have been . drilled, tubular conductor 611, 612 and 613 are actively lowered into the lower }Cyril portions in the resource bed. The coaxial lines 660 carrying thief energy from a source 650 to the tubular conductors can now be strung down an upper puerilely of one or more of the oriole and then connected across the different rows of tubular conductors at drift 64D. In this manner; there is no substantial heating of the upper barren rock a might be the case if the. conductors were coupled from the surface of each Barlow .
FIG. 7 illustrates a situation wherein a relatively thin hydrocarbonaceous deposit is located well below the errs surface. In such case, a drift or edit 640 is first provided, and horizontal Berlioz are then drilled for the conductors. The FIX. 7 again illustrates triplet type configuration of three row of Berlioz, with the conductors 701, 702 and 703 being vowel in the FIGURE

. . . , I Roy selection of suitable operating frequencies it the present invention depends upon-YarioU5 factors which _ will now be described. As radio freguenc~ OF electron magnetic wave energy propagates within the hydrocarbon-bearing media of interest, electrical energy is continuously converted to heat energy The two primary energy conversion mechanisms are ohmic heating, which results from thicken ductility of the formations, and Selectric heating, which results from notation of molecular dipoles by the alternating electric field of the wave energy At any elemental volume .

Jo 3 point, It within the formations of interest, the dielectric permittivity at a frequency f canoe expressed as Of C 1 E' ~Xg~) jE~I(X~J~
..
where ~r(x,f) is the relative real part of the complex dielectric permittivity~ Err is the relative imaginary part of the dielectric permittivity and represents both conducive and dielectric losses and En is the permi~tivity of free space. The heating power density, U(x,f) a point.
x can be expressed a u 2 3 U of = foe (x~f~EDE (X) watts/meter I

where f is the electric yield intensity at the point x.
At radio frequencies (0~3 MHz. to 300 MHz~) dielectric heating predominates for the types of formations of interest herein, and the shale, tar sand, and oval deposits to be treated can be considered as glossy dielectric".
As the electromagnetic wave energy is converted to heat, the electric field wave progressively decays in exponential fashion as a function of distance along the path of wave propagation. For each electrical skin depth, I
that the wave traverses, there 15 a reduction in the wave electric field by abut 63%. The skin depth, I, is related to the propagation modems permeative_ and the electron _ __ _ _ magnetic wave wryness by the relationship

(3) 10 or _ meters. I .
of or - E - . ............ -:- --- - _.. _ .
. , . ,;' ' ,, .
' ' ' '' ' , ' , .

-- .

I 'I ' The heating resulting from electromagnetic waves in hydrocarbon-beaxing formations diminishes progressively as the wave energy penetrates further into the formations and away from the source thereof. Thus, the use of RF
energy does not, per so, yield uniform heating of the formations of interest unless particular constraints are applied in the selection of frequency and field confining structure An idealized in iota heating technique would elevate all points within the ~efin2d heating zone to the desired processing temperature and leave volumes outside the heating zone at their original temperature. This cannot be achieved in practice, but a useful goal is to obtain substantially uniform final heating of the zone, go temperatures which are within a ~10% range throughout Since the heating power density, U(x,f3! is a function of the sguar2 of the electric-field intensity, E, it is desirable to have E within the range of about I of a given level in most of the processirlg zones. Consider, for expel, the triplane line structure of FOE as being embedded in an oil shale 0rmatio3l. -An electromagnetic . wave is excited by the OF power-source 4~~0 at-the surface- -I
of the oil shale seam and propagates down the tip late line into the shale The wave-~ecays exponentiaily-with . ... . ..
distance from the surface because of conversion ox electrical energy into heat energy. Upon reaching the end Do the center .
conductor, at a depth of Lo meters, it is desired that the wave undergo substantially total reflection. this it achieved I

.

~3~7 by selecting the excitation frequency such that the elf wavelength Jo along the triplet line is sub-staunchly greater than spacing between the outer rows, ""I
thereby giving rise to a cutoff condition.
5 . The result of the wave attenuation and reflection is the generation ox a standing wave along the length of the triplane line . At a point, x r on the line 9 the magnitude of the total standing wave electric field, ET-x, from the end of the center conductor is .

10 ' ETA 5 ETA inn CASEY

. _ _ _,,,, _,, . _ . _ where is the electrical skin depth for a wave traveling along the triplane line, and A is the wavelength along the triplane line I and I being assumed constant along the length of the Lyon I To illustrate thy nature of the standing wave pattern and heating potential resulting from the triplane type line of structure of FIG. (4), equation I can be used to compute the ratio ET(x)/ET(O~ and U~x)~U(O) =
[ET(x)/ET(O)] for the triplane line. Typical results are shown in the graph of FIG. 8. It is seen that ET and U
decay with depth and exhibit t an oscillatory behavior near I
with interleaved peats and nulls separated by a constant distance, ~Q/4, from each other. The position of the deepest peak coincides with the end of the center conductor at Lo;
the position of the deepest null it at Lo /4 . I

c n in situ ~riplate-~ype of structure having heating potential distribution as chosen in JIG. B will-m~re easily meet heating uniformity goals over its length it the oscillatory pattern could be smoothed out. This can be done by modifying the electric field pattern 50 as to .
effectively average the electric field intensity in the .
volume being heated. This may be achieved by physically decreasing the insertion Dwight of toe center conductor by /4 units midway through the heating time.
Pulling each tube owe the center conductor Jo 4 units cut of its respective Barlow, or employing small explosive charges to sever the deepest 4 units of each tube are two ways this can ye cone. Shifting the one of the venter conductor in this manner would shift the entire ! ." . . . .
standing wave pattern toward the surface ox the Dip shale Jo seam by a axis ante o ~QJ4 units. Thus heating peaks . would be moved to the positions of former heaving nlllls, J
and vice voyeurs Averaged over the entire heating time the spatially oscillatory behavior of would largely disappear This can be demonstrated mathematically using equation sand (3?
I- .
.

overall U(X'f)~e~ore center U(X'f)after go ton I + Casey-- + l Jo K71fE'''~ j AL OX _ I\ or , Sweeney OX

- D f~-(X,f~ . [1 + Saab + Sue ¦ (5) . where K ~-~ a constant out by the pQwe~ lye of the ~ourc20 I

, g I to Equation (5; represents a smoothly varying exp~nPntially decreasing distribution of Us as shown in FIG. I X will be understood that electrical mean could alternatively be ; . utilized to modify the electric field pattern so as to average the electric field intensity in the volume being heated. Modification of the phase or frequency of *he excitation could also be employed The described technique of effectively averaging the electric field substantially eliminates peaking-type heating non-uniformitie~, but it is seen what the exponential decay of top electric field still poses difficulties in attaining substantially uniform heating. In order to minimize the latter type of heating non-uniformity, the frequency of operation is selected such that the e attenuation distance I is greater than the Lyon Lo and preferably, treater than twice the length Lo.

. , '- '' . . ', ' ' . ' . .
I' , .
I: .

.

I

The value of I which is allowable or a particular heaving uniformity criterion can be determined from equation I by sweating the heating potential at x Lo - ~QJ4 the final position of the end of the center conductor) to be a desired percentage of the heating potential at x = U. For example, a heating goal of 10~ in the volume would indicate that the desired percentage is 30~, so we have:

1 + ~i~h2¦ = 0.8[1 + sink ( + sink ! - I I] 6 assuming that E ill - ~Q~4~ - (O). For the present situation, the following inequalities hold true:

A I I Q/~C~L~

Using essay inequalities, equation I can be Raritan as: .

lo 1 ' 0.8L1-~2 inn )] (8) or equivalently as-Sweeney ~L1f~Q) _. 0.125~ . (93 which has the solution L - L 0.35 . (103 Jo , 1 1 Max ', "
. -27- . .

.,. !
*.

Thus, the length owe the center conductor row of the triplate-type line shackled rho exceed 35Q~ of the line attenuation duster in corder to insure heating uniformity within i 10~
over the length of the line. Audi another way, to meet this heating uniformity requirement the frequency of exaltation should be sufficiently low to insure a skin depth of about three times Lo Fur an in situ triplane line type of structure (e.g. Fig 4) with no artificial loading by either lumped capacitances or inductances, the expression for is given my 53) above, and combining I and ~10~ ivy:
.

Lo (f) r peters, (11~

To determine the variation of Lo with frequency for Max oil shale, laboratory tests were conducted to obtain the electrical permittivity of dry Mahogany-type, Colorado oil shale over the frequency range Jo 1 MHz to 40 MHz~
Using the data in conjunction with equations I and (11) curves for and Lo were plotted versus frequency, Max as shown in FIG. lo It is seen, for example, that to allow the use of a single triplate-t~pe structure to process in iota a complete top to bottom section of an oil shale bed with a thickness of 100 meters, the m ximum operating frequency which meets the stated heating uniformity criterion would be 18 MHz. In a similar manner, -FIG. canoe used to determine the maximum operating frequency or triplate-type structures used to heat process shale beds ranging in thickness from 10 meters (em - 95 MY
-. . .

1, . ' ` ' . " ) to 25~0 meters (f = 1 MH2). It will be understood Max that trade-of s as between line length and frequency can be effected when, for example, it is desirable to select a particular frequency to comply with government radix . frequency interference requiremen~sO
Capacitive loading could also be employed to minimize amplitude reduction effects Fur example, series capacitors Jan be inserted at regular intervals along the tubes of the center conductor of the triplane line. These capacitors would act to partially cancel the effective series inductance of the center conductor. Using the expression for I of an arbitrary lousy transmission line, it can be shown that 1 - . .

for an in situ triplate-ty~e line, where is the nominal e attenuation distance Nat the operating frequency, end r is the percentage reduction of the center conductor inductance caused my the inserted capacitors. For example, if the effective center conductor inductance were reduced by 75%
I would increase by 100% to a value of I
Having sex forth considerations which are used in determining maximum operating frequency attention is now turned to the selection of suitable minimum operating f regency ..

.

, Jo I

the rate Jo resource heating it controlled by - U~x~3, the heating power density generated by the electron genetic field. As seen from relationship (2), there no wow types of factors influencing the Nate of heating:
a freguency-independent amplitude factor, En; and a frequency-dependent factor, if of To achieve rapid heating of the resource Cody t it would be disrobe to generate a large value of E. However, if E is increased beyond some maximum value, designated E 7 the RF electric field could cause arc-over Dry breakdown of the rock matrix and carbonized, conducting paths might form between the inner and outer conductors of the in situ confining structure.
This could lead to undesirable short circuiting of the system. To avoid this possibility t the average RF electric field within the strokers constrained Jo be no more than - SUE , where S is a dimensionless await factor in the ,. . ox range 0.~1~0.1. In this way reliable operation is insured despite electric field enhancement at the surfaces of the conducting tubes of the FIG. 4 structure and possi~lG local . 20 variations of thy breakdown level of the resource. A pilot or demonstration scale RF in iota assault could operate . . with a typical S factor close to 0.1 SD that simulated production runs could be completed rapidly. However, a large _ _ . .. scale, commercial facility would likely be designated more conservatively with an S factor close to 0~01, to assure normal operation by an associated high power RF
generator under worst case" conditions. Using Ego = Sioux in relationship (2) yields . .

Uavex3~ ; Lowry (I En axe my I

. _ ;. Jo . .

The RF heating power density varies us the square of S, - so selection ox S has an important impact oaths processing time and, as will be seen, selection of minimum operating - frequency. It is seen from relationships (2) and ~13~ that increasing the product term, of increases the electromagnetic heating power dens try regardless of the electric field amplitude. This product term is found Jo increase monotonically in the frequency range of 1 I to 40 MHz for oil shale. Thus, for a given OF electric field, increasing the operating frequency causes the shale heating rate to increase. Considerations of maximum operating .

frequency, set forth above must ye borne in mind, however.
The minimum processing time at a particular operating frequency, t iffy, can by derived as a function 15 of the fraction, R, of spent shale sensible heat that can be recycled (this aspect to be treated below, the RF electric field breakdown level, Max, of the shale rock, the safety factor, 5, end the loss component, En I of the shale.
Firs, the total RF healing energy required to process one cubic meter of raw oil shale can be cockled, assuming an. -.-toil shale density of 1.6 g/cm3 ~1~6 10 kg/m3~ and assuming . _____ .. . ..

RF heating So - R Lowe J 1 6 ion k . requirement . g a e , , '. ' ' ._ . = (1.2 - R-0.65);lO9 J/m3.(l4al ; . . _ ._ .. . _ Now, t . (f) can be found by dividing the RF heating require-men .

mint of Equation (lea) by the maximum OF heating power density of Equation tl3)~

.
; -31-.2 - 0.65) ~10 my _ S fry ~f)~oEmax /

(4.3 - R~2.3L~_10_ _ sex. (lob)--Sir of) ox I FIG. 11 uses Equation (14b~ to slot versus frequency the minimum processing time (with S = 0.01 end ; 55 = 0.1) or Pi heating of dry,.Mahogany-type Colorado oil shale. It is assumed that Max = I Vim and is independent ox the operating frequency, and that R - Owe.
;~. From JIG. 11, it is seen that, for 5 - 0.1, Tim ranges Rome 0.6 hours at 40 My to 36 hours at 1 to and to an :10 extrapolated time ox about 300 hours at 5.1 Ho For S =

0.01, t . ranges from 60 hours at 40 Ho to 3600 hours men I: (5 months) at 1 MHz.
During the prowesses cycle of block of shale ;. using the resent technique, heft oonductlon.to adjacent - 15 shale regions can tend Jo degrade She desired heating * uniformity by cozily cooling of the boundary planes. of the., .
Swahili block being processed. Further, such thermal con-

4. diction results in heat energy flowing outside the bloc; of i; interest, complicating the problem of controlling the extort 20. and efficiency of the heating process. Such an outflow of I,. heat further increases the necessary heating time. Actual .' . determinakior~ ox heat wow effects is a complex junction by the size and shape of the shale blocks being heaved; however, on or illustration of such efficacy on the graphs of FIG. 11 is depicted I by the dotted line curve for a hypc~thetir at block of shale Jo In order to limit these undesired consequences owe I: . . resource heat conduction it is desirable to complete the processing cycle ox the block being treated before appreciable heat energy can w out of to block. Based on these con I side rations, applicants have selected a ~aximllm electrical processirlg time of alto two weeks with preferred preseason -3;2 I
times being less than this time. From FIG, 11, this rundown would mean that the operating Frequency could , . be no lower than Owe MHz for the S = Owe case, and could ye no lower than 10 MHz for the 5 = 0.01 case An inter-mediate value of S would accordingly yield an intermediate "order of magnitude" frequency of 1 MHz~ The frequency lower bound (based on considerations of heat conduction away from the electrically heated zone and conservative design relative to stale breakdown) can be combined with the frequency upper bound obtainable.. from FIG lo (based on considerations of heating uniformity within the zone and shale skin depth) to define the preferred frequency ;.
range. For blocks of commercially practical size, a maximum frequency of about 40 My is preferred, so the preferred frequency range is about l Ho to 40 MHz. It . should be noted that other confining structures within the purview of the invention, such a wave guides and cavities, will have somewhat different optimum operating frequency ranges because of differences in the electromagnetic I field patterns and heat conduction time peculiar Jo a given geometry.

"" " : ',', ' ','', , ' ,, - ,' ' ' ' ' Jo .

. .

, r I will lye undel_~c)od that Luke ye her ooze tcchnitlues for exciting the alternating clockwork iced attires to t air dielectric heating of the format no bound by the coniininy conductor structures of the invcn~io~l: i.e. ,,

5 _, alt~rnativcs lo the previously described ~cchnigue of Allah voltages across different grouts of the conductors. In FIG. 1;2 there it again shown a triplate-~ype of configuration having rows of condors designate as owe I row 2 and row 3, the conductors again being inserted in :borehc)les drip led in hydrocarb~naces:~us pharmacies such as an oil shale }: Ed Irk toe embodiment of FIG. 12 " the desired field pattern in the " confined volume of formations is established using a current . lockup excitation.
The conductors of eye central row have loop I exciters 121 and 122 formed integrally therewith, the loop exciters 121 providing- magnetic field excitation to the left f the central row conductors and the loop exciters 1~2 providing magnetic field excitation to thus right of the central row conductors. The established alternating electric i 20 . yield pattern, concomitant wit h the varying magnetic field ¦ 3; provides substantially uniform dielectric heating in the manner previously described. The conductors of the central .... row have an outer tubular metal shell 123 and an inner ... I. conductor 124, shown in dashed line in FIG. AYE. Slots 125 . I and 126 are Wormed in the outer tube anal the loops 121 and 122 ; extend from ye inner conductor through the slots and then . reconnect with the outer conductor a; shown the dashed line.
I! The lower portion 120 of ye central row conductor extends from . the bottom of the lop.
In operatic NO an RF current source 127 is coupled . Betty Thea outer tubular conductor 1~3 end the inure conductor .

. ' .- ' ' - .

I

124 and drives current through the loops 121 and 122, thereby establishing alternating magnetic yields and concomitant electric fields which are confined in the volume bound by the rows of conductors in row 1 and row 3.
A quarter wave stub 128 is provided at about the top of the hydrocarbonaceous deposit and, in effect, creates an open circuit which isolates the conductor passing through the overburden from the lower portion thereof. This technique prevents energy from propagating back toward the source and heating the overburden. Considerations of frequency are similar to those discussed above. An advantage of the approach of FIG. 12 is that the voltage carrying capability of the cables can be reduced since the possibility of a voltage breakdown is diminished when using a current drive scheme.
It will be understood that various alternate techniques for excitation of the electric fields can be implemented to obtain dielectric heating as defined herein.
For example, electric dipole excitation could be employed to generate the electric fields in the confined volume.
FIG. 16 illustrates an arrangement wherein electric dipole excitation is used. Center conductor 166 is coupled to electrodes AYE and 166B which protrude from slots in outer conductor 163, and a voltage source 167 it coupled between the inner and outer conductors.

o I I

I

In the configuration of FIG. 12, wherein a current loop drive is utilized, it it advantageous to use a source position which result in an odd number of quarter wavelengths from the position of the current loop TV each end of the eon fat conductor since the source it at a voltage minimum add it is desirable to have voltage maxima at ye open circus Ed terminations to achieve a resonance condition. Similarly, in FIG 16 the dipole surcease preferably located an even number of quarter wavelengths from the ends of the central conductor.

'' I,'-- '' ' ' .
\
.

. ' '' ' ' \'' '' ' .- \ .
' -' \ ' ' . \ ' ' ', \
- I, .
-36- .

. ' ' '' , ' ' , ' .

~3~3~ . ) Roaring to I 13, there is shown a simplified schematic diagram of a system and facility for wrecker of shale oil and related products from an oil shale Deed . tri-plate-type configuration of the nature previously.
decided is used in this system Three rows of Berlioz, designated as row I row 2 and row 3, are drilled through the overburden and into the oil shale bed, the central row of Berlioz preferably being ox a lesser depth Han the outer rows. A dry 131 is mined in the overburden above the oil shale form ion Jo that electrical connections .. . .
can be made in the manner described in conjunction with FIG. or Tubular conductors are inserted into the lower portions of the Berlioz of each Dow. An RF source 132 is provided and vb~ains its power from a suitable pier . I plant which may or may jot be located at the site. For ease of illustration the electrical connections are not shown in FIG 13, but they may be the same as those of JIG. 60 A network of pipes for injection of suitable media are provided, the horizontal feed pipes 133, 134 and 135 being coupled to the Barlow of row 1, row 2 and row 3, respectively and suitable violists and cross-couplings also being provided. The art owe injecting suitable . media and recovering subsurface fluids is well developed and not taken alone, the subject of this invention, so the description thereof is limited to that necessary for . . .
an understanding ox the present system and techniques.

Recovered fluids are coupled to a main discharge pipe 136 ¦ and then to suitable processing plant fPquipment which is also we 1 known in the awry Again these well know techniques will no be described in full detail herein but .

a conduit 137 represents the Recess of separation of shale oil vapor and high and low BTU gas, whereas the conduit 138 represents the processing of shale oil vapor, if known manner Jo obtain synthetic crude. The eerily processing system of FIG. 13 will vary somewhat s structure and use, depending upon which of the to-bP-described versions of the present technique are utilized to recover valuable constituents from the oil shale bed r . It will be recognized aye the heating can be advantageously performed to different degrees in order to implement useful extraction of the organic resources from the formations. These techniques will also vary with the 'cope of resource form which the fuel is being recovered.
I In the case of oil shale, three torsions of exkracticn techniques utilizing the invention are set forth, although it will become clear that variations or carbonations of these techniques could be readily employed by those skilled in the art. The first version aims only for recovery of shale oil and by-product gases that correspond to the recovery aim of previously proposed in situ oil shale:_ processing techniques Electrical radio frequency energy is applied, for example using the system of FIG. 13, to heat a.relati~ely large block of oil shale in situ to above kiwi us the temperature passes the point where inherent shale moisture flashes into team, some fracturing, at_ least along bedding planes, will typically by experienced.
Additional interconnecting voids will also form within unfxactured pieces of oil skate during pyrolyzes in the ~00-500C range. While substantially uniform heating is striven fur, heating is not exactly uniform and the oil -38- ..

J
owe; I I
shale nearest toe electrodes will be heat slightly more rapidly than the shale furrier away. As a result, Perle-ability is progressively established outward from the elect dyes, permitting passage of whale oil vapors up the hollow electrode tubes for collection. Ill the same way, the considerable quantity of hydrocarbon gases liberated at shale temperatures between about 203C to 503C will pass is the surface via the tubes. At the surface of the earth the shale oil vapors' and byproduct gases are collected and . 10 processed urn known techniques, as depicted broadly in FIG. 13. In this first version there is not necessarily any attempt to utilize the carbonaceous residue left in . . the spent shale formations.
Another in iota processing version which utilizes the electrical radio frequency heating techniques of the invention would aim to increase the yield o-E useful products from the oil shale resource and to reduce process energy consumption by making full use of the unique attributes of . the disclosed in situ heating technique. wince heating to relatively precise temperatures is possible with the invented Tahitian this second version would apply heating to about ~25C to recover crocked kerogen in liquid form In this manner, the substantial electric energy needed to apply the additional heat to vital Zen the shale oil product would be saved.
Inquiry version of the recess a relatively high degree of porosity and permeability will be present . after removal of the liquid kerogen. Thus, if desirable, . subsequent recovery of the carbonaceous residue on the spent-shale could be achieved my injection of steam and either air or oxygen to initiate a water gas r action. Upon injection, the team and oxygen react with the carbonaceous . ' . ' ~39-- q I

residue to form a low BTU gas which is recoverer and own be for example, for the hydrogenation of the raw shale ire for owns generation of electric power. The degas reaction would also result in a higher spent shale temperature, for example 600C, Han in the case of the first processing version. This would be advantageous when techniques, such as those described below in on-junction with Figs 15, 16, are employed for using residual heat for preheating the raw shale it other blocks in the shale bed. An overall saving of electrical energy would thereby be achieved The creation of shale permeability and wëtability after removal of the liquid kerogen would also permit extraction, in situ, of various csproducts such as aluminum hydroxide, nucleate, uranium or related minerals present in the shale by leaching methods In a third processing version, the electrical heaving techniques of the invention are employed only to relatively lower temperatures, below about 200C to obtain fast fracturing of the shale my vaporization of moisture content whereupon combustion or thermal in situ extraction tuitions can be used to obtain the useful products.
It will be understood that various "hybrid"
extraction approaches; which include the electrical heating techniques of this invention can be employed 9 depending upon the type of oil shale formations in a particular region, availability of electrical energy and other factors relating Jo costs. For exempt , the disclosed electrical radio frequency heating techniques could be employed in either the middle range temperatures or to atop off temperature disk tributions obtained by other heating methods.

I

.

I

Applicants have observed that raw unheated tarsal, heavy oil matrices, and partially depleted petroleum I its exhibit dielectric absorption characteristics at radio frequencies which render possible the use of the prevent techniques or heating of such deposits (tar sands being generally referred to hereafter, for convenience) 80 that bitumen can be recovered therefrom. Again, the relatively low electrical conductivity and relatively low thermal conductivity of the tar wands is not an impediment (as in prior art techniques since dielectric heating is employed. the selection of a suitable range of frequencies it the radio frequency band is based on considerations that are similar ED those set forth above. If the selected frequencies o-f operation are too high, the penetration of energy into the deposit is too shallow (ire. t a small skin depth, as discussed above and relatively large volumes of in situ material cannot be advantageously processed due to large non-unifolmities of heating On the other hand, if the frequency of operation is selected below a certain range the absorption of energy per unit volume will be relatively low since dielectric absorption is roughly propsr~ional Jo frequency over the range of interest Jo top amplitude ox the electrical excitation must be made relatively large in order to obtain-the-~ecessary--heating to prevent pro US cussing times prom becoming inordinately long over practical considerations limit the degree to which the applied excitation can be intensified without the risk of electrical breakdown Thus once a maximum excitation amplitude is selected, the minimum frequency it a-- -function of desired pxocessin~ time- Applicant .
have discovered that the dielectric absorption kirk-teristics of tar sand art generally in a range similar I ' ' .
.. -to that described above in conjunction with oil shale, but somewhat lower frequencies within the radio frequency range are antiGi paled . However, it will be understood what variations in the optimum frequencies will occur for different I types of mineral deposits, different confining structures, and different heating time objectives.
In FIG. 14 there is shown a simplified schematic diagram ox system and facility for recovery and processing of bi~umen;from a subterranean tar sand formation.
tri~late-ty~e configuration is again utilized will three rows Do Berlioz, designated as Rowley, row 2 and row 3, Bills drilled or driven through the overburden and into the tar sand pheromone, as in FIG. 13. A Wright 141 lo mine in the overburden above the tar sand formation so that electrical connections can be made in the manner described in con Unction with JIG. 6. Again, tubular conductors are inserted into the lower portions of the Berlioz ox etch row. on source 142 is provided and as before, for ease of illustration .
the electrical connections are not shown in FIG. 14, although they may be the same as those of JIG. As in FIG. 13, a .
network of pipes for injection of suitably drywall rneaia is provided, the horizontal feed pipes 143 and 145 elan coupled to the Berlioz of row 1 and Dow 3, respectively, in this _ _ _ _ _ instance Pipe 146 is the main collection pipe and suitable . .
valves and cross-couplings are also provided. In the . _ ... _. ., . . _ _ _ _ present instance, after suitable heating of the resource, steam : or hot chemical solutions can typically be injected into at least some of the Berlioz and the hot mobile tars are forced to . . _ . .
. ._ . 42 _ . , . . , . , _ . .

I
the surface for collection via collection pipes 144 and 146 and collection tank 147. Subsequent processing of ye: recovered tars is well developed art and will nut 3ie~described herein. In the illustration of FIG.. 14, the brollies of rows 1 and 3 are utilized as "injectiorl Willis' and the Berlioz of row 2 are used as producing Willis, although it will be understood that various alternate techniques can be used for bringing the heated tars to the O
surface.
As in the case of oil shalt it will be recognized that electrical heating can be advantageously performed to different degrees in order to implement useful extraction of the organic resources from the tar sand formations. .
In a first version of the tar sand or heavy oil recapper technique, electrical heating it applied Jo reduce the viscosity of the in-place jars or heavy oils to a point . where other known complementary processes can be employed to . recover the in-place fuel. In such case, radio frequency -electrical energy can be applied to relatively uniformly heat a block of tar sands to a temperature of about 150~C.
. This, in effect, produces a volume of low viscosity fluids in -- the tar sand matrix which is effectively sealed around its .
periphery my the lower temperature (impermeable or less permeable) cooler tar sands. Simple gravity Dow into producer holes or a pressurized drive, consistent with FIX. 14, can be used to force the low viscosity fluids to the surface using injection of hot fluids. Jo j . In a second version of the technique; useful fuels axe recovered from tar sand and heavy oil deposits by partially or completely p~rolyziny the tars in situ . flea tribal radio iErequency Energy it applied irk accordance with the I, ...

I .

.3 1 I

.

pencils of the invention to heat a relatively large , -I
block of tar sand in situ to about 500~ C. As the .r~~~ture of the tar sand increases above about 100~ C, the inherent moisture begins to change into Siam. A

.
further increase in temperature to around 150 C sub-Stanley reduces the viscosity of in-place tars or heavy oils. As the pyrolyzes temp~ratuxe is approached, the higher volatile are emitted until complete pyrolyzes of the in-place fuels is accomplished. The tax sands nearest the electrodes will be heated slightly more rapidly than t-he jar wands farther away, so regions of - relatively low viscosity and high permeability will be progressively established outward from the electrodes.
This permits passage of the high volatile and pyrolytic 1 15 product vapors up the Berlioz for collection with or j without a drive. A variation of this second version . would subsequently employ a water gas process as described above, to produce a low BY gas from the remain-ing.pyrolytic carbon. Assay, simple COJnbUS~iOn Ox carbon residues Jan be utilized in order to recover . . residual''en'erg'y'~in~th~'~form' of sensible heat. It will be understood that various combinations or sequences of the . . _ _ -- . . _ .
¦ described steps can be performed, as desired __ _ . . .

.. . ...

.. :.~... ,. ' .

Referring to FIG. 15, there is shown a schematic do which illustrates how residual heat in the "spent"
~ormatl~ns from which constituents have already been eye racked can be utilized for preheating of the next block ox ho resource to be processes. After the bor~hPles are formed in the new zone to be heat processed a system of pipes can be utilized to carry ste~m-~-ater mixtures which effectively transfers residual heat from the just-procPssed zone to the next zone to be processed In FIG. 15, the relatively cool raw resource bed to be processed is illustrated by the bloc 151, and the spent hot resource is represented by the block 152. The water pumped into the block 1~2 via ---- pump 153 and feed pipe 157 becomes very hot steam which is circulated through the pipes 159 to the lock 1510 The system is closed loop" so that aster heat from the steam is expended in the block 151, it is returned as cooler steam or condensate to the block 152 via return pipe 158.
It will be understood that the sequentially processed zones may be adjacent zones to take advantage ox thermal fly outside a volume being processed In particular heat which . flows outside the volume being processed, which might normally . be wasted, can be utilized in preheating zones to be sub-sequently processed. Thus, fur example, rows defining zones .
in the formations being processed can alternate with-and "sandwich" zones to be subsequently processed so that heat I . which flows out of the zones presently being processed can be . to a substantial extent utilized Lowry This technique, along with the use ox residual heat in the "spent formation as described in conjunction with FIG. 15, can substantially reduce the amount of total input energy needed for heat processing. ..

, The present invention allows maximum extraction of desired organic products while keeping pollution and we cumulation to a minimum and still being economically ages. Very little mining if any, it required and : 5 the pollution and waste aspects of above ground retorting .- are no curse, absent the invented technique compares most favorably with those in situ techniques that require combustion, since those techniques necessarily produce hot flue gases that must be cleaned of particulate sulfur, etc. before release into the environed A further advantage is a result of the relatively close control over the heating zone which is a feature of the present invention and greatly reduces the possibility of uncontrolled in situ combustion which can have adverse safety and/or environmental effects.
The invention has been described with reference to particular embodiments but variations within the spirit and scope of the invention will occur Jo those skilled in the art. For example, the term "Berlioz" as used herein is intended generically to include any type of holy or slot in the formation former by any suitable means such as mechanical.
or water-jet drilling, pile driving, etch as well as forms . of mining or excavation, Also, the field confining conductors of the present invention can be of any desired form, including meshes, straps, or flexibly foils, an will depend, to some degree, upon the location an exposure of the particular surface of the volume they confine Fur~herv it will be understood ha in addition Tut resonant THEM type of lines described herein the confining structure can also take the form of single-mode TO or Men situ wave~uides or multimedia --~60 .. .

enclosed cavities In by h instance, standing wave correction, as previously descried, can be employed sub-staunchly average over time the electric field (and resultant in) throughout the confined volume, both electrical and ankle techniques being available as disclosed herein-above. The excitation frequency can also be varied during operation. In the case of a cavity appropriate drifts or edits can be mined to obtain access to drilling locations . leg. as illustrated in FIG. 7) so that conductors can be Sunday to define surfaces that completely confine a . volume to be heated. The resultant "in situ cavity' would be somewhat similar in operation to a microwave oven (but with radio frequency energy being utilized. Mode mixing can reachieved for ex~nple, by utilizing a multiplicity of electric and/or magnetic dipoles at different locations on the walls or within the cavity and sequentially exciting them to obtain different modes to achy Ye substantially uniform heating of the confined volume. Alternatively, conductors . can be inserted and withdrawn from a series of Berlioz 9 as ED previously described. The cavity approach is advantageous . due to the absence of geometrical constraints pertaining to achieving cutoff of potentially radiating wave energy. This _...
means that large blocks of the resource can be processed at once.
Further, it will be understood that nonresonant con-fixing structures can be utilized if desired. For example, FIG.
. 17 is a simplified diagram illustrating how a nonresonant con-fining structure can be utilized in conjuDctiorl with a. sandwich . type of processing technique that utilizes thermal flow from spent . regions. Three loops designated as lop AYE, 170B, and 170C, are illustrated, each loop including, fur example, a pair of in-pow lines of the type illustrated in FUGUE.- However, in this insane , . I

I. I .. ... . ) I

the central row of each triplet line is not intentionally truncated Instead, connecting lines designated by reference -knurls AYE, 171~ and 171C are employed, this being done insertions appropriate horizontal conductors prom a mined .. 5 tunnel. witches 181-187 are provided and are initially positioned as shown in FIG. 17. In operation, the loops are first connected in series and the switch 181 is coupled to the RF source 179. Wave energy is introduced into the first triplet line of loop 170~ and travels around the loop and is then connected via switch 183 Jo lop 170B, and Jo on. Dielectric heating of the hydrocarbonaceous format lions is achieved, with the electric field being progressively attenuated. Accordingly, the loop OWE is heated more than, - the loop 170B which is heated lore than the loop 170C, eta=
When the hydrocarbonaceous deposit of 1ODP AYE has been heated Jo a desired degree, switches 181 and 183 are switched Jo that loop AYE is no longer energized and loop 17DB is now heated to the greatest extent. This procedure is . continued until the alternate layers of hydrocarbonaceous formations are fully heated to the extent desired. After a suitable period of time, typically weeks or months for the . heat from the spunk regions to transfer into the b~ween-loop formations, the between-loop formations can be processed in ~Lmilar manner.
As previously noted, the invention is applicable Jo various types of hydrocarbonaceous deposits, and vane- --lions in technique consistent with the principles ox the invention, wit be employed appending upon the type of resource being exploited,. For example, it the case of coal, ' ' . .
, I . . .
' If .... . . .

the electrical properties of the material indicates that the lower portion of the radix frequency ~pectr~m, for example of the order of 100 XHz, will be useful. Further, it will b understood that as hock processing of a particular resource progresses, the properties of the resource can change and may render advantageous the modification of operating regains for different pro-cussing stages . - . - -Applicants have observed that the raw materials under consideration can tend to exhibit different dielectric properties at different temperatures. As a consequence, it may be desirable Jo modify electrical parameters Jo match the characteristics of the AC power source to the characteristics of the field exciting structure whose properties are influenced by the different dielectric properties of the raw materials. A variable matching network, such as is represented by block 4~1 tin dashed line? of FIG can be used towards this end.
.

,.

.

.

Claims (97)

1. A system for in situ heat processing of hydrocarbonaceous earth formations, comprising:
a plurality of conductive means inserted in said formations and bounding a particular volume of said formations;
electrical excitation means for establishing alternating electric fields in said volume;
the frequency of said excitation means being selected as a function of the volume dimensions so as to establish substantially non-radiating electric fields which are substantially confined in said volume;
whereby volumetric dielectric heating of the formations will occur to effect approximately uniform.
heating of said volume.

2. A system as defined by claim 1 wherein the frequency of said excitation is in the radio frequency range.

3. A system as defined by claim 1 wherein said conductive means comprise opposing spaced rows of conductors disposed in opposing spaced rows of boreholes in said formations.

4. A system as defined by claim 2 wherein said conductive means comprise opposing spaced rows of conductors disposed in opposing spaced rows of boreholes in said formations.

5. A system as defined by claim 3 wherein said rows of conductors comprise three spaced rows of conductors.

6. A system as defined by claim 4 wherein the conductors of each row comprise spaced elongated conductors.

7. system as defined by claim 5 wherein the conductors of each row comprise spaced elongated conductors

8. A system as defined by claim 1 wherein said excitation is applied as a voltage as between different groups of said conductive means.

9. A system as defined by claim 2 wherein said excitation is applied as a voltage as between different groups of said conductive means.

10. A system as defined by claim 6 wherein said excitation is applied as a voltage as between the conductors of the outer rows and the conductors of the central row.

.

11. A system as defined by claim 7 wherein said excitation is applied as a voltage as between the conductors of the outer rows and the conductors of the central row.

12. A system as defined by claim 1 wherein said electrical excitation is a source of current applied to at least one current loop in said volume.

13. A system as defined by claim 2 wherein said electrical excitation is a source of current applied to at least one current loop in said volume.

14. A system as defined by claim 6 wherein said electrical excitation is a source of current applied to at least one current loop in said volume.

15. A system as defined by claim 7 wherein said electrical excitation is a source of current applied to at least one current loop in said volume.

16. A system as defined by claim 1 wherein said electrical excitation is applied across at least one electrical dipole in said volume.

17. A system as defined by claim 2 wherein said electrical excitation is applied across at least one electrical dipole in said volume.

18. A system as defined by claim 6 wherein said electrical excitation is applied across at least one electrical dipole in said volume.

19. A system as defined by claim 7 wherein said electrical excitation is applied across at least one electrical dipole in said volume.

20. A system as defined by claim 6 wherein the conductors of the central row are of substantially shorter length than the conductors of the outer rows so as to reduce radiation at the ends of said conductors.

21. A system as defined by claim 8 wherein the conductors of the central row are of substantially shorter length than the conductors of the outer rows so as to reduce radiation at the ends of said conductors.

22. A system as defined by claim 11 wherein the conductors of the central row are of substantially shorter length than the conductors of the outer rows so as to reduce radiation at the ends of said conductors.

23. A system as defined by claim 15 wherein the conductors of the central row are of substantially shorter length than the conductors of the outer rows so as to reduce radiation at the ends of said conductors.

24. A system as defined by claim 20 wherein the frequency of said excitation is selected such that a half wavelength of electromagnetic energy in the region beyond the center conductor is substantially greater than the spacing between the outer rows to give rise to a cutoff condition in said region.

25. A system as defined by claim 22 wherein the frequency of said excitation is selected such that a half wavelength of electromagnetic energy in the region beyond the center conductor is substantially greater than the spacing between the outer rows to give rise to a cutoff condition said region.

26. system as defined by claim 23 wherein the frequency of said excitation is selected such that a half wavelength of electromagnetic energy in the region beyond the center conductor is substantially greater than the spacing between the outer rows to give rise to a cutoff condition in said region.

27. A system as defined by claim 1 wherein the frequency of said excitation is selected as a function of the electrical lossiness of the formations in said volume to be sufficiently low such that the ? attenuation distance of the electric field in any direction in said volume is more than twice the physical dimension of said volume in that direction.

28. A system as defined by claim 2 wherein the frequency of said excitation is selected as a function of the electrical lossiness of the formations in said volume to be sufficiently low such that the ? attenuation distance of the electric field in any direction in said volume is more than twice the physical dimension of said volume in that direction.

29. A system as defined by claim 3 wherein the frequency of said excitation is selected as a function of the electrical lossiness of the formations in said volume to be sufficiently low such that the ? attenuation distance of the electric field in any direction in said volume is more than twice the physical dimension of said volume in that direction.

30. A system as defined by claim 5 wherein the frequency of said excitation is selected as a function of the electrical lossiness of the formations in said volume to be sufficiently low such that the ? attenuation distance of the electric field in any direction in said volume is more than twice the physical dimension of said volume in that direction.

31. A system as defined by claim 20 wherein the frequency of said excitation is selected as a function of the electrical lossiness of the formations in said volume to be sufficiently low such that the ? attenuation distance of the electric field in any direction in said volume is more than twice the physical dimension of said volume in that direction.

32. A system as defined by claim 24 wherein the frequency of said excitation is selected as a function of the electrical lossiness of the formations in said volume to be sufficiently low such that the ? attenuation distance of the electric field in any direction in said volume is more than twice the physical dimension of said volume in that direction.

33. A system as defined by claim 1 further com-prising means for modifying the electric field pattern so as to average the electric field intensity in said volume to enhance the uniformity of heating of said volume.

34. A system as defined by claim 2 further com-prising means for modifying the electric field pattern so as to average the electric field intensity in said volume to enhance the uniformity of heating of said volume.

35. A system as defined by claim 3 further com-prising means for modifying the electric field pattern so as to average the electric field intensity in said volume to enhance the uniformity on heating of said volume.

36 . A system as defined by claim 5 further com-prising means for modifying the electric field pattern so as to average the electric field intensity in said volume to enhance the uniformity of heating of said volume.

37 . A system as defined by claim 20 further com-prising means for modifying the electric field pattern so as to average the electric field intensity in said volume to enhance the uniformity of heating of said volume.

38. A system as defined by claim 24 further com-prising means for modifying the electric field pattern so as to average the electric field intensity in said volume to enhance the uniformity of heating of said volume.

39. A system as defined by claim 27 further com-prising means for modifying the electric field pattern so as to average the electric field intensity in said volume to enhance the uniformity of heating of said volume.

40. A system as defined by claim 36 wherein said means for modifying the electric field pattern comprises means for modifying the effective length of the conductors of the central row.

41. A system as defined by claim 36 wherein said means for modifying the electric length of the conductors of the central row comprises means for physically shortening the length of said conductors.

42. A system as defined by claim 40 wherein said means for modifying the effective length of said conductors comprises means for electrically modifying the effective length thereof.

43. A system as defined by claim 3 wherein said rows of conductors are inserted in said formations at angles such that said rows are closer together at far ends thereof to compensate for attenuation of the electrical field at said far end.

44. A system as defined by claim 5 wherein said rows of conductors are inserted in said formations at angles such that said rows are closer together at far ends thereof to compensate for attenuation of the electrical field at said far end.

45. A system as defined by claim 30 wherein said rows of conductors are inserted in said formations at angles such that said rows are closer together at far ends thereof to compensate for attenuation of the electrical field at said far end.

46. A method for in situ heating of hydro-carbonaceous earth formations, comprising the steps of:
forming a plurality of boreholes which bound a particular volume of said formations;
inserting elongated electrical conductors in said boreholes; and introducing electrical excitation to said formations to establish alternating electric fields in said volume;
the frequency of said excitation being selected as a function of the volume dimensions so as to establish substantially non-radiating electric fields which are sub-stantially confined in said volume;
whereby volumetric dielectric heating of the formations will occur to effect approximately uniform heating of said volume.

47. A method as defined by claim 46 wherein the frequency of said excitation is in the radio frequency range.

48. A method as defined by claim 46 wherein said boreholes are formed in opposing spaced rows in said formations.

49. A method as defined by claim 48 wherein said rows comprise three spaced rows.

50. A method as defined by claim 47 wherein the step of introducing electrical excitation comprises applying a voltage as between different groups of said conductors.

51. A method as defined by claim 47 wherein the step of introducing electrical excitation comprises applying electrical current to at least one current loop in said volume.

52. A method as defined by claim 47 wherein the frequency of said excitation is selected as a function of the electrical lossiness of the formations in said volume to be sufficiently low such that the ? attenuation distance of the electric field in any direction in said volume is more than twice the physical dimension of said volume in that direction.

53. A method as defined by claim 47 fur her comprising the step of modifying the electric field pattern so as to average the electric field intensity in said volume to enhance the uniformity of heating of said volume.

54. A method as defined by claim 53 wherein the step of modifying the electric field pattern comprises the step of modifying the effective length of some of said conductors.

55. A method defined by claim 47 further comprising the step of withdrawing through said boreholes the valuable constituents resulting from said heating.

56. A method as defined by claim 47 wherein said dielectric heating is continued to heat said volume to a temperature below the temperature required for extraction of valuable constituents from said volume, and further comprising the steps of applying further non-electrical heating means to said volume and withdrawing through said boreholes valuable constituents from said volume.

57. A system for in situ heat processing of an oil shale bed, comprising:
a plurality of conductive means bounding a particular volume of said bed;
electrical excitation means for establishing alternating electric fields in said volume;
the frequency of said excitation means being selected as a function of the volume dimensions so as to establish substantially non-radiating electric fields which are substantially confined in said volume;
whereby volumetric dielectric heating of the bed will occur to effect approximately uniform heating of said volume.

58. A system as defined by claim 57 wherein the frequency of said excitation is in the radio frequency range.

59. A system as defined by claim 57 wherein the frequency of said excitation is in the range between about 1 MHz and 40 MHz.

60. A system as defined by claim 57 wherein said conductive means comprise opposing spaced rows of conductors disposed in opposing spaced rows of boreholes in said bed.

61. A system as defined by claim 59 wherein said conductive means comprise opposing spaced rows of conductors disposed in opposing spaced rows of boreholes in said bed.

62. A system as defined by claim 61 wherein said rows of conductors comprise three spaced rows of conductors.

63. A system as defined by claim 62 wherein the conductors of the central row are of substantially shorter length than the conductors of the outer rows so as to reduce radiation at the ends of said conductors.

64. A system as defined by claim 63 wherein the frequency of said excitation is selected such that a half wavelength of electromagnetic energy in the region beyond the center conductor is substantially greater than the spacing between the outer rows to give rise to a cutoff condition in said region.

65. A system as defined by claim 57 wherein the frequency of said excitation is selected as a function of the electrical lossiness of the formations in said volume to be sufficiently low such that the ? attenuation distance of the electric field in any direction in said volume is more than twice the physical dimension of said volume in that direction.

66. A system as defined by claim 59 wherein the frequency of said excitation is selected as a function of the electrical lossiness of the formations in said volume to be sufficiently low such that the ? attenuation distance of the electric field in any direction in said volume is more than twice the physical dimension of said volume in that direction.

67. A system for in situ heat processing of a tar sand deposit, comprising:
a plurality of conductive means inserted in said deposit and bounding a particular volume of said deposit;
electrical excitation means for establishing alternat-ing electric fields in said volume;
the frequency of said excitation means being selected as a function of the volume dimensions so as to establish substantially non-radiating electric fields which are sub-stantially confined in said volume;
whereby volumetric dielectric heating of the deposit will occur to effect approximately uniform heating of said volume.

68. A system as defined by claim 67 wherein the frequency of said excitation is in the radio frequency range.

69. A system as defined by claim 67 wherein the frequency of said excitation is selected as a function of the electrical lossiness of the formations in said volume to be sufficiently low such that the skin depth of the electric field in any direction in said volume is more than twice the physical dimension of said volume in that direction.

70. system as defined by claim 68 wherein the frequency of said excitation is selected as a function of the electrical lossiness of the formations in said volume to be sufficiently low such that the skin depth of the electric field in any direction in said volume is more than twice the physical dimension of said volume in that direction.

71. A system for in situ heat processing of hydrocarbona-ceous earth formations, comprising:
a waveguide structure comprising a plurality of elongate electrodes and configured such that the direction of propagation of aggregate modes of wave propagation therein is approximately parallel to an elongate axis of said electrodes and bounding a particular volume of earth formations as a dielectric medium bounded therein; and means for supplying electromagnetic energy to said wave-guide structure at a frequency elected to confine said electromagnetic energy in said structure and to dissipate said electromagnetic energy to the earth formations, thereby to substantially uniformly heat the bounded volume.

72. A system for in situ heat processing of hydrocarbona-ceous earth materials, comprising:
a waveguide structure having an elongate shape which pene-trates and bounds a particular volume of earth forma-tions therein and wherein the aggregate direction of propagation of electromagnetic wave modes in said structure is in a direction approximately parallel to an elongate axis of said structure; and means for supplying electromagnetic energy to said wave-guide structure at a frequency selected to confine said energy and to dissipate said electromagnetic energy to said bounded volume thereby to substantially uniformly heat said bounded volume.

73. A system for in situ heat processing of hydrocarbona-ceous earth formations, comprising:
field confining means bounding a particular volume of earth formations and forming an elongate waveguide structure having a direction of aggregate electromag-netic wave propagation mode direction in a direction approximately parallel to an elongate axis of said structure; and means for supplying electromagnetic energy to said wave-guide structure at a frequency to confine said electromagnetic energy in said structure and to cause dielectric heating of said bounded volume to a substantially uniform degree.

74. A system for in situ heat processing of hydrocarbona-ceous earth formations comprising:
a plurality of electrodes placed in a pattern bounding a particular volume of hydrocarbonaceous earth formation, said pattern defining a waveguide structure having said volume bounded therein as a dielectric medium; and means for applying an alternating current to said electrodes, the frequency of said current being selected as a function of a volume dimension so as to establish substantially non-radiating and uniform electro-magnetic fields in said volume, thereby obtaining volumetric dielectric heating of said volume to a temperature sufficient to permit production of hydro-carbonaceous components thereof.

75. A system for in situ heat processing of hydrocarbona-ceous earth formations comprising:
a pattern of conductors bounding a particular volume of hydrocarbonaceous earth formation, said pattern defining an unbalanced transmission line structure having said bounded volume integral therewith as a dielectric medium; and means for supplying alternating current to said con-ductors, the frequency of said current being selected as a function of at least one volume dimension so as to establish substantially non-radiating electro-magnetic fields in said volume.

76. A system for in situ heat processing of hydrocarbona-ceous earth formations comprising:
a substantially tri-plate pattern of electrodes placed in a particular volume of hydrocarbonaceous earth forma-tion and forming a waveguide structure having said volume bounded therein as a dielectric medium wherein adjacent portions of electrodes within a plate are at approximately the same potential; and means for supplying a time varying electric field to said electrodes so as to establish substantially non-radiating electric fields in said volume.

77. A system for in situ heat processing of hydrocarbona-ceous earth formations comprising:
a waveguide structure formed by a pattern of electrodes placed in a particular volume of hydrocarbonaceous earth formation to bound said volume therein as a dielectric medium; and means for supplying alternating current to said waveguide structure at a frequency to effectively confine electromagnetic fields in said structure and to effect substantially uniform dielectric heating of said volume.

78. A system for in situ heat processing of hydrocarbona-ceous earth formations comprising:
an unbalanced transmission line structure deployed in a particular volume of hydrocarbonaceous earth forma-tion, said structure bounding said volume and em-ploying said formation material as a dielectric medium therein; and means for supplying electrical energy to said transmission line structure at a frequency confining said energy in said structure and providing dielectric heating to a controllable degree in said volume.

79. A system for in situ heat processing of hydrocarbona-ceous earth formations comprising:
a waveguide structure formed by bounding a particular volume of earth formations with a pattern of elec-trodes bounding said volume and including said volume as a dielectric medium therein; and means for establishing alternating electromagnetic fields in said bounded volume, the frequency of said alternating fields being selected as a function of a volume dimension, thereby causing volumetric dielectric heating of said volume to an approximately uniform degree.

80. A system for in situ heat processing of hydrocarbona-ceous earth formations comprising:
electrode means bounding a particular volume of earth formations in such a manner as to comprise a wave-guide structure having said volume bounded therein as a dielectric medium; and means for supplying electromagnetic energy to said wave-guide structure at a frequency selected to confine said energy substantially in said volume and to cause heating of said volume by displacement currents to a substantially uniform degree in said volume.

81. A system for in situ heat processing of hydrocarbona-ceous earth formations, comprising:
electrode means bounding a particular volume of earth formations in such a manner as to comprise an unbal-anced transmission line structure having said volume bounded therein as a dielectric medium; and means for supplying electromagnetic energy to said un-balanced transmission line at a frequency selected to cause heating of said volume by displacement currents to a substantially uniform degree in said volume.

82. A system for in situ heat processing of hydrocarbona-ceous earth formations comprising:
electrode means bounding a particular volume of earth formations in such a manner as to comprise an ap-proximately tri-plate transmission line structure having said volume bounded therein as a dielectric medium; and means for supplying electromagnetic energy to said tri-plate transmission line structure at a frequency and field intensity selected to cause heating of said volume to a substantially uniform degree in said volume without significant heat loss to the adjacent unbounded regions and without electrical breakdown of said bounded volume.

83. A system for in situ heat processing of hydrocarbona-ceous earth formations, comprising:
waveguide structure comprising a plurality of electrodes bounding a particular volume of earth formations as a dielectric medium bounded therein; and means for supplying electromagnetic energy to said wave-guide structure at a frequency selected to dissipate said electromagnetic energy substantially only to said bounded medium thereby to substantially uni-formly heat said bounded volume.

84. A. system for in situ heat processing of hydrocarbona-ceous earth formations, comprising:
an unbalanced transmission line structure comprising a plurality of electrodes bounding a particular volume of earth formations as a dielectric medium bounded therein; and means for supplying electromagnetic energy to said un-balanced transmission line structure at a frequency selected to substantially confine said energy to said structure and to dissipate said electromagnetic energy to said dielectric medium by displacement current heating thereof, thereby to substantially uniformly heat said bounded volume without significant heat loss to the adjacent unbounded regions and without electrical breakdown of said bounded volume.

85. A system for in situ heat processing of hydrocarbona-ceous earth formations, comprising:
an approximately tri-plate transmission line structure comprising a plurality of electrodes bounding a particular volume of earth formations as a dielectric medium bounded therein; and means for supplying electromagnetic energy to said ap-proximately tri-plate transmission line structure at a frequency and field intensity selected to dissi-pate said electromagnetic energy to said dielectric medium, thereby to substantially uniformly heat said bounded volume without significant heat loss to the adjacent unbounded regions and without electrical breakdown of said bounded volume.

86. A system for in situ heating of a volume of hydrocar-bonaceous earth formation to an elevated temperature comprising:
electrical excitation means for providing an electrical waveform;

a conductor array located approximately centrally in said volume to which the electrical waveform is applied, said central conductor array comprising a line of conductors inserted in boreholes in the formation, wherein adjacent conductors in the line are separated by a distance of about 1/8 of a wave-length or less of the electrical waveform; and a bounding conductor array comprising at least one line of electrical conductors inserted in boreholes in the formation, adjacent of said conductors in a line being separated by about 1/8 of a wavelength or less of the electrical waveform wherein bounding conductors are at approximately the same potential as the adja-cent unbounded earth formations whereby radiation of electrical energy outside the volume of the hydrocar-bonaceous earth formation is minimized.

87. A method of heating a volume of hydrocarbonaceous earth formations to an elevated temperature comprising:
applying an electrical waveform to a first row of elon-gated conductors penetrating a volume of the forma-tion, adjacent conductors being separated by a distance less than 1/8 of the wavelength of the electrical waveform;
confining the electromagnetic field in the volume by bounding said volume with at least two rows of elon-gated conductors, adjacent conductors in a row being separated by a distance less than 1/8 of the wave-length of the electrical waveform; and varying at least one of (a) the frequency of the electri-cal waveform; (b) the physical length of individual conductors in a row of conductors; (c) the series capacitance of conductors in a row; (d) the effective electrical length of conductors in a row; to facilitate uniform heating of the formation in the direction of the principal axis of the elongated conductors.

88. A method for in situ heat processing of hydrocarbona-ceous earth formations comprising the steps of:
placing a plurality of electrodes into a particular volume of hydrocarbonaceous material in a pattern which bounds said volume and defines an unbalanced trans-mission line structure having said bounded volume present as a dielectric medium bounded therein;
applying alternating current at a radio frequency to said electrodes, said radio frequency being chosen as a function of a volume dimension so as to establish substantially non-radiating electro-magnetic fields which are substantially confined in said volume, thereby effecting approximately uniform heating of said volume to a temperature sufficient to permit production of hydrocarbonaceous components thereof.

89. A method for in situ heating processing of hydrocar-bonaceous earth formations comprising the steps of:
placing a plurality of electrodes into a particular volume of hydrocarbonaceous material in a pattern which bounds said volume and defines a waveguide structure having said bounded volume present as a dielectric medium bounded therein;
applying alternating current at a radio frequency to said electrodes, said radio frequency being chosen as a function of at least one volume dimension so as to establish substantially nonradiating electro-magnetic fields which are substantially confined in said volume, thereby effecting approximately uniform heating;
modifying the electromagnetic field pattern so as to time average the electromagnetic field in said volume to enhance the uniformity of heating of said volume.

90. A method for in situ heat processing of hydrocarbo-naceous earth formations, comprising the steps of;
forming a plurality of holes which bound a particular volume of hydrocarbonaceous material and spaced from each other so as to define an approximately tri-plate structure having said bounded volume of hydrocarbonaceous material present as a dielectric medium bounded therein;
inserting electrical conductors into said holes; and applying alternating current at a radio frequency to said conductors, said radio frequency being chosen as a function of at least one volume dimension so as to establish substantially nonradiating electromagnetic fields which are substantially confined in said volume, thereby effecting approximately uniform heating of said volume.

91 A method for in situ heat processing of hydrocarbona-ceous earth formations, comprising the steps of:
enclosing a particular volume of earth formations on at least two sides thereof with a plurality of spaced electrodes to define a waveguide structure having said enclosed volume present therein as a dielectric medium; and establishing alternating electromagnetic fields in said enclosed volume, the frequency of said alternating fields being selected as a function of a volume dimension, so as to establish substantially non-radiating, confined, electromagnetic fields in said volume, thereby causing volumetric dielectric heating of said volume to effect approximately uniform heating of said volume.

92. A method for in situ heat processing of hydrocarbona-ceous earth formations comprising the steps of:
bounding a particular volume of earth formations with a waveguide structure comprising elongate electrodes having outer electrodes which are at approximately the same potential as the adjacent unbounded earth formations; and propagating electromagnetic energy through the waveguide structure in an aggregate mode of propagation generally parallel to the direction of an elongate axis of said electrodes, thereby substantially con-fining the electromagnetic energy in the waveguide structure and uniformly heating the bounded volume of earth formations.

93. A method for in situ heat processing of hydrocarbona-ceous earth formations, comprising the steps of:
bounding a particular volume of earth formations with a transmission line structure having an inner elongate shaped propagating electrode structure and an outer elongate shaped electrode structure which is at ap-proximately the same potential as the adjacent un-bounded earth formations; and propagating modes of electromagnetic energy in said structure in an aggregate direction generally parallel to an elongate axis of said propagating electrodes, thereby confining said electromagnetic energy in said bounded volume and uniformly heating said bounded volume.

94. A system for in situ heat processing of hydrocarbona-ceous earth formations, comprising:
a multi mode cavity structure comprising a plurality of elongate electrodes and configured such that the direction of wave propagation of a particular mode is parallel to an elongate axis of at least one set of said electrodes, said multi mode cavity structure bounding a particular volume of earth formations as a dielectric medium bounded therein wherein the outer-most electrodes, are at approximately the same potential as the adjacent unbounded earth formations;
and means for supplying electromagnetic energy to said multi mode cavity structure at a frequency selected to confine said electromagnetic energy in said structure and to dissipate said electromagnetic energy to the earth formations; thereby to sub-stantially uniformly heat the bounded volume.

95. The system of claim 94 and further including means for time averaging said electromagnetic energy along the direction of propagation, thereby to enhance the uniformity of heating of the bounded volume of earth formations.

96. A system for in situ heat processing of hydrocarbona-ceous earth formations, comprising:
a waveguide structure having a plurality of rows of con-ductors, the spacing of conductors in a row being less than the spacing of said rows of conductors and bounding a particular volume of earth formations as a dielectric medium bounded therein; and means for supplying electromagnetic energy to said wave-guide structure at a frequency selected to dissi-pate said electromagnetic energy substantially only to said bounded medium, thereby to substantially uniformly heat said bounded volume.

97. The system of claim 96 and further including means for time averaging said electromagnetic energy along a direction of its propagation in said waveguide structure.