CA1183909A - Rf applicator for in situ heating - Google Patents
Rf applicator for in situ heatingInfo
- Publication number
- CA1183909A CA1183909A CA000376811A CA376811A CA1183909A CA 1183909 A CA1183909 A CA 1183909A CA 000376811 A CA000376811 A CA 000376811A CA 376811 A CA376811 A CA 376811A CA 1183909 A CA1183909 A CA 1183909A
- Authority
- CA
- Canada
- Prior art keywords
- transmission line
- oil shale
- energy
- impedance
- overburden
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- E—FIXED CONSTRUCTIONS
- E21—EARTH DRILLING; MINING
- E21B—EARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
- E21B43/16—Enhanced recovery methods for obtaining hydrocarbons
- E21B43/24—Enhanced recovery methods for obtaining hydrocarbons using heat, e.g. steam injection
- E21B43/2401—Enhanced recovery methods for obtaining hydrocarbons using heat, e.g. steam injection by means of electricity
-
- E—FIXED CONSTRUCTIONS
- E21—EARTH DRILLING; MINING
- E21B—EARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B36/00—Heating, cooling, insulating arrangements for boreholes or wells, e.g. for use in permafrost zones
- E21B36/04—Heating, cooling, insulating arrangements for boreholes or wells, e.g. for use in permafrost zones using electrical heaters
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B6/00—Heating by electric, magnetic or electromagnetic fields
- H05B6/64—Heating using microwaves
- H05B6/80—Apparatus for specific applications
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B2214/00—Aspects relating to resistive heating, induction heating and heating using microwaves, covered by groups H05B3/00, H05B6/00
- H05B2214/03—Heating of hydrocarbons
Abstract
RF APPLICATOR FOR IN SITU HEATING
Abstract of the Invention A coaxially fed applicator for in situ RF heating of sub-surface bodies with a coaxial choke structure for reducing outer conductor RF currents adjacent the radiator. The outer conductor of the coaxial transmission line supplying RF energy to the radiator terminates in a coaxial structure comprising a section of coaxial line extending toward the RF radiator from the termi-nation for a distance approaching a quarter wavelength at the RF frequency and a coaxial stub extending back along the coaxial line outer conductor from the termination for a distance less than a quarter wavelength at said frequency. The central con-ductor of the coaxial transmission line is connected to an enlarged coaxial structure approximately a quarter of a wave-length long in a region beyond the end of the outer conductor coaxial choking structure.
Abstract of the Invention A coaxially fed applicator for in situ RF heating of sub-surface bodies with a coaxial choke structure for reducing outer conductor RF currents adjacent the radiator. The outer conductor of the coaxial transmission line supplying RF energy to the radiator terminates in a coaxial structure comprising a section of coaxial line extending toward the RF radiator from the termi-nation for a distance approaching a quarter wavelength at the RF frequency and a coaxial stub extending back along the coaxial line outer conductor from the termination for a distance less than a quarter wavelength at said frequency. The central con-ductor of the coaxial transmission line is connected to an enlarged coaxial structure approximately a quarter of a wave-length long in a region beyond the end of the outer conductor coaxial choking structure.
Description
Background of the Invention Structures for supplying RF energy to subsurface formations have been proposed such as those disclosed in Patent No. 4~140,179 wherein a coaxial line extending through an outer casing terminates in a dipole arrangement in a body of oil shale. However, in such structures, portions of the energy were lost due to RF currents flowing back up the bore hole on the outside of the coaxial line.
Thus, the heating of the subsurface body occurred partly above the region where the heating was desired. The dipole arrangement was such that the impedance match to the coaxial line and the radiation pattern were very sensitive to changes in the impedance of the shale due to changes in temperature and content of organic material.
_ mmary of the_Invention In accordance with this invention, there is provided an RF appllcator supplied with energy through a coaxial transmission line whcse outer conductor terminates in a choking structure com-prisin~ an enlarged coaxial stub extending bac~ along said outer conductorO More specifically, the applicator comprises an en-larged cylindrical member connected to the central conductor of the transmission line. Tne outer conductor of the coaxial trans-mission line is connected to a section of coaxially positioned conductive tubing having a substantially larger diameter than said outer conductor of said coaxial transmission line.
More specifically, this invention provides for a conductive sealing casing extending from the surface through loose material to consolidated overburden formations. A coaxial transmission line has a pipe acting as an outer conductor extending from the surface to an RF applicator which may be a radiator or a field defining electrode with said outer conduc-tor being electrically connected to an enlarged conductor structure surrounding the outer conductor adjacent its lower end with the structure forming a reentrant region extending back along the outer conductor to reduce RF currents flowing back up the outer conductor from the RF applicator. An inner conductor of the coaxial transmission line extending from the surface into the subsurface formation to be heated is directly connected to an enlarged conductive electrode structure to form the primary electrode structure for coupling RF energy into the formation either as a radiator or as an electrode of a captive fi.eld structure.
This invention ~urther provides for supp].ying fluid through the transmisciion line erom the surface to the applicator. More specificallyt the fluid may be high pressure liquid for injection into the formation being hea-ted or may be a gaseous medium for im-proving the dielectric strength of -the regions of the RF applica-tor or may be either li~uid or gaseous medium for -the purpose of flushing the products of pyrolysis collected below the RF applica--tor to the surface.
This invention further discloses a transmission line system for supplying power to a subsurfaee RF app]ica-tor -through a variable impedance matching unit from a transmitter so -that variations in the impedance of the oil shale formation due to variations in its temperature or due to variations in the frequen-ey of the RF energy applied may be matched -to the output impedance of the -transmitter.
In aecordance with the present invention, there is pro-vided the method of producing organic products from a body of oil shale beneath an overburden comprising: generating electrical energy in the frequency range be-tween 100 kilohertz and 100 mega-her-tz; transmitting said energy via a Eirst transmission line hav-int a first charaeteristie impedance through a variable impedance matching structure to a seeond transmission line having a seeond eharaeteristic impedanee and ex-tending through said overburden to a radiating strueture positioned in said body of oil shale; and varying the impedanee matehing of said structure -to compensate for ehanges in temperature of said oil shale body.
In aceordance with the present invention, there is fur-ther provid~d a syC;tem Eor produeing organic produets frorn a body oE o.i.l. shaLe beneat:h an ove~rburden eomprising: rneans for genera-t-i.n~ el~etrlea:l on~t^cJy in the Erequeney rancJe between 100 kilohert~
arld l()0 me~gahert~; Ineans l-or transmitting said energy via a first Irnr~ rli..s.qic)rl l.ine havirlg a f:irst eharaeteristie impedanee through 3() a variclb:le impedancc.~ matehing strueture to a seeond transmission L;ine hav:ing a seeorld eharacterist:ie impedance and extending through said overburden to a radiating structure posi-tioned in said body of oil shale; and means for varying the frequency of said energy to vary -the pattern of said energy radiating into said body of oil shale.
Brief Description of the Drawings Other and further objects and a~vantages of this invention will be apparent as the description thereof progresses, reference beiny had to the accompanying drawings wherein:
FIG. 1 illustrates a longitudinal sectional view of a sub-surface RF applicator incorporated in a system embodying the invention;
FIG. 2 is a transverse sectional view of the applicator transmission line of FIG. 1 taken along line 2-2 of FIG. l;
FIG. 3 is a transverse sectional view of the RF applicator choke structure of FIG. 1 taken along line 3-3 of FIG. l;
FIG. 4 is a transverse sectional view of the lower end of the choke structure of FIG. 3 taken along line 4-4 of FIG. 2;
FIG. 5 is a transverse sectional view of the struc.ure of FIG. 1 taken along line 5-5 of FIG. 1 illustrating the lower dipole of the radiating structure of FIG. l; and FIG. 6 is a plan view illustrating a power layout and control system for utilizing a plurality of the systems of FIG. 1.
3~
Description of the Preferred Embodiment Referring now to FIGS. l-S there is shown an oil shale formation 10 positioned beneath an overburden 12 and on top of a substrate l4. A bore hole 16 has been drilled from the surface through the overburden 12 and through the oil shale 10 into the substrate 14. Overburden 12 may be sedimentary material forming a substantially gas tight cap over the oil shale region 10.
In accordance with ~ell-known practice a seal to the over-burden 12 is formed by a steel casing 18 extending from abovethe surface down~lardly in bore hole 16 to a point beneath the loose surface material and is sealed to the walls of the bore hole by concrete region 20 surrounding steel casing 18. While any desired bore hole size can be used dependent on the size of the RF applicator to be used, the example illustrated herein may have a steel casing 18 whose inner diameter is a standard 18 inches. A well head assembly comprising a flanged bushing 22 and a cap 24 is attached to the top of the steel casing 18, for example, by welding. Such a structure is preferably used to enable pressure to be maintained in the bore hole 16 and to prevent contamination of the bore hole, for example, by ground water.
A coaxial transmission line 26 extends from the cap 24 through the overburden 12 to an RF applicator 28 positioned in the oil shale region 10. The transmission line 26 is preferably forrned ~ith an outer conductor 30 of steel pipe having, Eor example, an internal cliameter oE approximately 6 inches and a thickness o~ approximately a half inch. Several lengths of pipe 30 are joined together by threaded couplings 32 and the upper end o~ the upper ]ength of pipe 30 is threaded into an aperture in ~3~
cap 24 while the lower length o~ pipe 30 i5 threaded into an adaptor coupling structure 34 which provides an enlarged threaded coupling to a coaxial stub 36 extending back up the bore hole 16 for a distance of around an electrical ei~3hth of a wavelength of the freauency band to be radiated into the formation lO by radia-tor 28. ~ stub 38 of the same diameter as stub 36 also extends downwardly frorn adaptor 34 for a distance equal to approximately an electrical quarter wavelenath of said frequellcy band. If desired, a ceramic sleeve 40 having perforations 41 may be placed in the formation lO to prevent caving of said formation during the heating process.
Coaxial transmission line 2~ has an inner conductor 42 made, for example, of steel pipe lengths. The upper end of the upper pipe lengths is threaded into cap 46. A ceramic plate a~ which is attached to cap 24 spaces the inner conductor electrically from the outer conductor 30. Cap plate 46 is mounted on top of plate 44 and threaded to pipe 42 so that pressure .may be main-tained inside the outer conductor 30 of the coaxial transmission line 26. Several lenyths of pipe 42 connected together by metal couplings 48 and spaced from the inner wall of outer conductor 30 by ceramic spacer 50 extend from cap 46 downwardly through outer conductor 30 to a point beyond the lower end of tubular stub 38. An enlarged ceramic spacer 52 surrounds the pipe 42 adjacent its lower end and the lower end of tubular stub 38 to space pipe 42 centrally within coaxial stub 38. Preferably, ceramic spacers 50 rest on top oE couplings 48 so that they may slide ea.sily on the pipe lengths before being screwed into the couplings. Enlarged spacer 52 is held in axial position by metal collars 54 welded to the bottom length of pipe 42.
~:~B~3~:g An enlarged section of pipe 56 is threadably attached to the lower end of the bottom pipe 42 by an enlarging coupling adaptor 58 and the lower end of enlarged t~bular member 56 has a ceramic spacer 60 attached to the outer s~rface thereof to space member 56 from the bore face 16. In the example disclosed herein using approximately 6-inch size for pipe 30, the diameter of pipe 42 is approximately 2 inches inside and 2 3/8 inches out-side. This produces a characteristic impedance for tihe trans-mission from the surface to the ~ applicator 28 of approximately 50 ohrns. By choosing the interior diameter of the stubs 36 and 38 to be, for example, of 12.715 inches, the characteristic impedance of the coaxial line sections comprising pipe 42 and stub 38, may be approximately 100 ohms. The outer diameter of the tubular radiating mernber 56 may be seleçted to be ~ 5/8 inches to produce a radiating surface which may be easily inserted into the well bore 16 through the previollsly installed steel casing 18~ Preferably the size of tubing 56 should be as large as practicable to reduce the vol.age gradient on the surface of the tubing 56 during the radiation of high RF power into the formation 10.
In accordance with this invention the region from the upper end of tubular member 3~ to the lower end of tubular member 38 is made an odd number of quarter wavelengths effective in shale in the operating frequency band of the device and forms an im-pedance matching section 106. L~ore specifically, the distance from the adaptor 34 to the lower end of tubular member 38 is made approximately a quarter wavelength effective in air at the operating ~requency o~ the system. The section 106 of applicator 28 comprisiny stub 38 toyether with the portions oE member 42 adjacent thereto, act as an impedance matching transformer which 3~3~
improves the impedance match between coaxial line 26 and the radiator section 108 of applicator 28. Section 106 also substan-tially reduces the current from the RF power that would flow back up the outside of pipe 30 from ~he lower end thereof until the power had been lost by radiation into overburden 12 or ab-sorbed by loss in the surface of pipe 30. With the structure or this invention, however, the power loss by current flow along the outer surface of the pipe 30 is reduced very substantially so that it is only a few percent of the power transmitted down the transmission line 26.
In accordance with this invention it is to be noted that the dielectric constartt and loss tangent, and hence impedance, of the formation 10 change with temperature as may be seen from Patent 4,140,179. In accordance with tnis invention, the im-pedance of the radiating section 108 changes very little over a wide range of temperatures of formation 10. To compensate for any such temperature impedance variation, an impedance matching device 62 is provided at the surface which may provide an adjust-able impedance to the transmission line 26. The adjustrnent of the impedance matching circuit may be achieved by measuring the effectiv.e power reflected from the applicator 28 back along the transmission line 26 to determine the standing wave ratio 011 the transmission line 26. Thus it may be seen that the radiating structure 10~ may be excited to produce a radiation pattern ~irected primarily radially outward in the plane of the oil sha~le medium with the bulk of the power being confined to the medium. While the frequency may, Eor example, be varied between 1 and 10 megahertz Eor the dimensions given herein, the tubular member 56 is preferably a quarter wavelength long, effec-tive in shale. The spacing between the upper end of tubing 56 and the ~3~
lower end of tubing 38 is preferably a quarter wavelength long, effective in shale with a s~bstantial air gap.
The lengths of the enlarged section 56 and the portion of the section 42, which together form a substantially half wave monopole radiator 108 depend on the fre~uency of the transmitter 64 and the effective radiation wavelength in the medium 10 as well as the radiation impedance of the medium.
Good results have been achieved, for example, at 10 megahertz, if the total length of the radiator 108 had the enlarged radiating section 56 (represented by the portion thereof below cutting line 5 5 of FIG. 1) approximately a seventh of a wave-length in air, and the section of the monopole radiator 108 represented by the extension of the inner conductor 42 beyond the lower end of the cylinder 38 (the portion between cutting line 4-~ and cutting line 5-5 in FIG. 1) approximately a sixth of a wavelength in air. When the medium 10 has a substantial quantity of water therein, for example, when the medium is first being heated, the effective wavelength 108 will be somewhat greater than a half wavelength. However, as heating progresses and the water is either converted to steam or driven off, the dielectric constant in the medium drops and the effective wave-length increases. Operating the monopole radiator 108 with an effective electrical wavelength greater than one-half wavelength reduces the vertical directionality of the pattern. Therefore, radiator 28 preferal)ly has dimensions which in wet shale, having a dielectric constant of, for example, 16 and in spent shale having a dielectric constant as low as 3, result in the radiating monopole 108 being approximately a half wavelength long. Thus, ~or e~ample, for a transmitter frequency of 10 mega-hert~ in which the free space wavelength is 3 X 103 centimeters or 30 meters which is 100 feet, the length of section 56 ischosen to be approximately 14 feet and the distance from the bottom of cylinder 38 to the top of casin~ ~8 is chosen to be 16 feet.
In operation, the bulk of the power is radiated from the section 108 and the section 106 acts as a resonant impedance transformer. The stubs 36 and 38 act as a non-resonant or induc-tive choking structure whose length may be deter~ined empirically to optimize the directive pattern in the horizontal direction as measured in the vertical plane. By varying the frequency, the pattern radiated can also be varied.
Transmitter 64 supplies variable frequency RF power to the impedance matching structure 62 through a coaxial line 66 and the impedance matching structure 62 supplies the RF power to the coaxial line 26 through a coaxial line 68 whose central conductor is connected to the cap 46 and whose outer conductor is connected to the cap 24.
As shown in FIG. 6, transmitter 64 preferably is located remotely from several sites 16 and transmission lines 66 extend distanaes up to in excess of 1,000 feet. Thus, one large trans-mitter installation can be used to feed sequentially different sites 16. It is, therefore, preferable that the standing wave ratio on the transmission lines 66 be maintained as close to unity as possible so that RF losses in the transmission line are minirnized. In addition, it is also desirable that little or no power be fed back into the transmitter 64 to avoid damage to the transmitter equipment as well as to allow the transmitter equip-ment to be tuned ~or maximLIm RF power generating efficiency.
Thus, the impedance matching circuits 62, which may use conven-tional inductors and capacitors, is adjusted in accordance with -10~
well-known practice to produce such impedance matching of the transmission lines 66.
While the radiator 56 may be sized for optimum radiation characteri.stic and/or power at a particular frequency, for example, by making the length of the element 56 an e~fective electrical quarter wavelength at that frequency in the bore 16, it is desirable that the frequency of transmitter 64 be variable to adjust for the different impedances or different formations and/or the different impedances of the formation encountered during different portions of the heating sequence.
Such impedance matches may also be achieved by variation of the output impedance of impedance matching circuit 62 so that by means of a standing wave the proper impedance is reflected through the relatively short transmission line stub 68 and the transmission line 26 to the radiating structure in the for-mation 10.
The impedance matching structure 62 is preferably adjusted for the desired impedance match into the radiating structure 26 with the transmitter 64 at low power, and the impedance match to produce low standing wave ratio in transmission line 66 i5 then ad3usted. However, it should be clearly understood that such impedance matching functions can be controlled in accordance with a preprogrammed schedule.
It has been found that good impedance match to oil shale formations can be obtained over a thirty percent ~requency band without subst:antial loss in the efficiency of transferring RF
power to the Eormation 10.
The transmiss.ion line 26 is preferably pressurized with an inert gas" such as nitrogen, from a source 70 through a pipe 72 tapped int:o bushing 22, through a pipe 74 tapped into cap 24 ~11-~3~
as well as to the interior of pipe ~2 through a pipe 76 connected by a insulating coupling 78.
The source of nitrogen 70 may be of s~fficent pressure to continuously bleed nitrogen into the pipes 42 and 30 as well as the casing 18 so that nitrogen flushes down the face of the bore 16 and through the region bet~een the pipes 42 and 30. Preferably~
the ceramic spacers have apertures in the peripheries thereof to allow the passage of the nitrogen. The nitrogen then presses against liquids 80 collected in the bottom of the bore 16 and forces them up through a producing tubing 82 which may be steel with a ceramic coupling 84 approximately at the lower end of the radiating cylinder 56. Ceramic coupling 84 isolates the tubing 82 which is essentially at ground potential rrom a tubing 86 extending upwardly through pipes 42 to the s~rface and through a cap 88 attached to the top of cap 46 and thence through an insulating coupling 90 to a collection tank 92 where the nitrogen can be recovered, if desired, and re-injected via the source 70 into the formation.
Such a circulation of nitrogen, in addition to aiding in production of kerogen products from the base of the bore 16, may serve to cool overheated portions of the transmission line and/or radiating structure so that high powers may be trans-mitted from the transmitter 64 into the oil shale body 10 with-out voltage breakdown at high voltage points in the structure.
In order to control the flow of gas from supply 70 to the vi~rious regions o the transmission line and radiator, pipes 72 and 74 contain valves 9~. Pipe 76 contains a valve 96 on the grounded side of bushing 78 and the pipe from bushing 90 ~o the collection tank 92 contains a valve 98 so that by opening and closing the valves, gas from the well bore may be increased, '~8~.3~
held constant or decreased during various cycles of the production p~ocess. By maintaining an appropriate purging flow of nitrogen through the well bore 16 before and during application of RF
power, danger of explosion in the region of the R~ applicator may be minimized. Such an explosion could occur, for example, if oxygen, driven o~E from components of the formation or present after installation of the well transmission line, combined with hydrocarbons in gaseous form driven off from the formation when a corona discharge or arc at the RF applicator caused ignition of an explosive mixture. The length of the transmission line 26 should be sufficient to reach any desired region of the oil shale 10 and for thick beds of oil shale may be gradually changed by raising or lowering the transmission line 26. This, in turn, raises or lowers the radiator 28 to expose a different horizontal layer of the oil shale to the maximum intensity of the radiation.
RF breakdown is minimized by the use of the ceramic spacers 50, 52, ~0 and 60 which maintain the various electrical conductors substantially concentric with each other and with the bore hole 16 so that impedance variations along the transmission line due to eccentricities which could otherwise occur between the inner and outer conductors of the coaxial line 26 are minimi~ed. These eccentricities could cause standing wave ratios in excess oE those contemplated thereby causing higher voltage nodes at points on the transmission line or in the RF radiator, The edges of the insulators are preferably beveled to facili-tate relative motion between the conductors during installation and a large insu].ating spacer 52 is posltioned between the lower end of stub 38 and inner conductor pipe 42 since in this region a volta~e maximum can occur. Such a voltage maximum is likely to increase as the standing wave ratio on the transmission line 26 increases so that at large power levels, corona breakdown might occur. Maximum power handling capability, in addition to being limited by voltage breakdown, is limited by the power dissipation of the transmission line and for the structure shown fabricated of conventional steel with surfaces coated with highly conductive material, such as copper, powers in excess of one megawatt may be transmitted through tne transmission line 26 and the radiator 28 into the formation 10.
In the event that the RF applicator 28 is not sufficiently deep, that is, the overburden 12 is not sufficiently thick, some of the RF energy at high powers radiated into the formation 10 may appear at low intensity on the surface. In accordance with this invention, wires, for example steel cables 100, may be welded to cap 22 and stretched radially for several hundred feet to reflect such radiation back into the overburden thereby preventing radiation interference when frequencies of, for example, 10 megahertz or below are used. Generally, frequencies above 10 megahertz are sufficiently absorbed in most overburden formations and lower frequencies are absorbed in those cases where there is substantial moisture content in the overburden.
The spacing between the radial wires can be any desired amount and branch wires from the radial wires may also be attached, if necessary" In addition, where more than one structure is placed in a qiven region, the wires can extend between adjacent structures.
~ s indicated previously in connection with Patent 4,140,179, the impedance changes due to both the absorption of the microwave energy because of changes in conductivity and because of changes in the dielectric constant due to removal of that porti.on of the ~3~3 water which originally existed in the oil shale body. The tem-perature at which such water changes to steam and is produced out of the formation depends on the pressure maintained in the well bore. For example, if the valve 98 remains closed and the bore face having first been flushed with nitrogen is pressurized to 500 psi, the temperature in the oil shale 10 may be raised at the bore face to several hundred degrees fahrenheit with the water still remaining in liquid form in the pores of the oil shale body. Water on the order of 3 to 30 percent may be en-countered and will absorb substantial amounts of the RF power.
In accordance with this invention the temperature in thebore face may be sensed, for example, by a thermo-couple 102 of a type shown in Patent 4,140,179, and as item 102 in FIG. 1, connected to the surface via a wire 104. When the temperature reaches, for example, 700 F~ opening the valve 98 will cause the pressure in the bore face to produce steam from the water cooling the bore face to a temperature below 700 F and pre-venting undesired hot spots at the surface of the formation lOo While the coaxial line 26 has surfaces providing R~ c~rrent flow which are large and hence low in current density for a given power level the coaxial lines 66 and 68 may be, for example, conventional conductive copper coaxial lines having, Eor example, an outer diameter of 3 1/8 inches. Such lines rnay be run for several hundred yards from a central transmitter and preferably have the impedance rnatching structure 62 positioned close to the surface of the well bore 16. Thus, the impedance of the trans-mitter 6~ may be substantially matched to the input impedance of the matchin~ structure 62 to maintain a standing wave ratio in line 66, for example, below 1.5 whereas the transmission line 26 may have a standing wave ratio thereon oE 1.5 to 5 depending on the matching required to optimize the radiation f~om radiator 28.
Referring now to FIG. 6, there is shown a plan view of a plurality of well bores 16 in a well field spaced apart by dis-tances such as several hundred feet and connected via coax cabling through impedance matching structures 6~ to a central transmitter 64 via coaxial lines 66. The ~F power may be sequen-tially shifted in any desired pattern to different radiators in different well bores 16 from a single transmitter housing which may be in~ for example, a control station. Signals fed from the impedance matching structures 62 to the control station may be used to monitor and/or adjust the frequency and impedance matching of the transmitter output to each of the wells.
This completes the description of the particular embodiment of the invention illustrated herein. ~owever, many modifications thereof will be apparent to persons skilled in the art without departing from the spirit and scope of this invention. For example, parallel wire lines could be used to feed the structures in the wells, other frequencies could be used than those indicated and a wide variety of conductive materials could be used for the transmission lines and radiating structures in the wells. Accor-dinglyt it is intended that this invention be not limited by the particular details of the embodiments illustrated herein accept as defined by the appended claims~
Thus, the heating of the subsurface body occurred partly above the region where the heating was desired. The dipole arrangement was such that the impedance match to the coaxial line and the radiation pattern were very sensitive to changes in the impedance of the shale due to changes in temperature and content of organic material.
_ mmary of the_Invention In accordance with this invention, there is provided an RF appllcator supplied with energy through a coaxial transmission line whcse outer conductor terminates in a choking structure com-prisin~ an enlarged coaxial stub extending bac~ along said outer conductorO More specifically, the applicator comprises an en-larged cylindrical member connected to the central conductor of the transmission line. Tne outer conductor of the coaxial trans-mission line is connected to a section of coaxially positioned conductive tubing having a substantially larger diameter than said outer conductor of said coaxial transmission line.
More specifically, this invention provides for a conductive sealing casing extending from the surface through loose material to consolidated overburden formations. A coaxial transmission line has a pipe acting as an outer conductor extending from the surface to an RF applicator which may be a radiator or a field defining electrode with said outer conduc-tor being electrically connected to an enlarged conductor structure surrounding the outer conductor adjacent its lower end with the structure forming a reentrant region extending back along the outer conductor to reduce RF currents flowing back up the outer conductor from the RF applicator. An inner conductor of the coaxial transmission line extending from the surface into the subsurface formation to be heated is directly connected to an enlarged conductive electrode structure to form the primary electrode structure for coupling RF energy into the formation either as a radiator or as an electrode of a captive fi.eld structure.
This invention ~urther provides for supp].ying fluid through the transmisciion line erom the surface to the applicator. More specificallyt the fluid may be high pressure liquid for injection into the formation being hea-ted or may be a gaseous medium for im-proving the dielectric strength of -the regions of the RF applica-tor or may be either li~uid or gaseous medium for -the purpose of flushing the products of pyrolysis collected below the RF applica--tor to the surface.
This invention further discloses a transmission line system for supplying power to a subsurfaee RF app]ica-tor -through a variable impedance matching unit from a transmitter so -that variations in the impedance of the oil shale formation due to variations in its temperature or due to variations in the frequen-ey of the RF energy applied may be matched -to the output impedance of the -transmitter.
In aecordance with the present invention, there is pro-vided the method of producing organic products from a body of oil shale beneath an overburden comprising: generating electrical energy in the frequency range be-tween 100 kilohertz and 100 mega-her-tz; transmitting said energy via a Eirst transmission line hav-int a first charaeteristie impedance through a variable impedance matching structure to a seeond transmission line having a seeond eharaeteristic impedanee and ex-tending through said overburden to a radiating strueture positioned in said body of oil shale; and varying the impedanee matehing of said structure -to compensate for ehanges in temperature of said oil shale body.
In aceordance with the present invention, there is fur-ther provid~d a syC;tem Eor produeing organic produets frorn a body oE o.i.l. shaLe beneat:h an ove~rburden eomprising: rneans for genera-t-i.n~ el~etrlea:l on~t^cJy in the Erequeney rancJe between 100 kilohert~
arld l()0 me~gahert~; Ineans l-or transmitting said energy via a first Irnr~ rli..s.qic)rl l.ine havirlg a f:irst eharaeteristie impedanee through 3() a variclb:le impedancc.~ matehing strueture to a seeond transmission L;ine hav:ing a seeorld eharacterist:ie impedance and extending through said overburden to a radiating structure posi-tioned in said body of oil shale; and means for varying the frequency of said energy to vary -the pattern of said energy radiating into said body of oil shale.
Brief Description of the Drawings Other and further objects and a~vantages of this invention will be apparent as the description thereof progresses, reference beiny had to the accompanying drawings wherein:
FIG. 1 illustrates a longitudinal sectional view of a sub-surface RF applicator incorporated in a system embodying the invention;
FIG. 2 is a transverse sectional view of the applicator transmission line of FIG. 1 taken along line 2-2 of FIG. l;
FIG. 3 is a transverse sectional view of the RF applicator choke structure of FIG. 1 taken along line 3-3 of FIG. l;
FIG. 4 is a transverse sectional view of the lower end of the choke structure of FIG. 3 taken along line 4-4 of FIG. 2;
FIG. 5 is a transverse sectional view of the struc.ure of FIG. 1 taken along line 5-5 of FIG. 1 illustrating the lower dipole of the radiating structure of FIG. l; and FIG. 6 is a plan view illustrating a power layout and control system for utilizing a plurality of the systems of FIG. 1.
3~
Description of the Preferred Embodiment Referring now to FIGS. l-S there is shown an oil shale formation 10 positioned beneath an overburden 12 and on top of a substrate l4. A bore hole 16 has been drilled from the surface through the overburden 12 and through the oil shale 10 into the substrate 14. Overburden 12 may be sedimentary material forming a substantially gas tight cap over the oil shale region 10.
In accordance with ~ell-known practice a seal to the over-burden 12 is formed by a steel casing 18 extending from abovethe surface down~lardly in bore hole 16 to a point beneath the loose surface material and is sealed to the walls of the bore hole by concrete region 20 surrounding steel casing 18. While any desired bore hole size can be used dependent on the size of the RF applicator to be used, the example illustrated herein may have a steel casing 18 whose inner diameter is a standard 18 inches. A well head assembly comprising a flanged bushing 22 and a cap 24 is attached to the top of the steel casing 18, for example, by welding. Such a structure is preferably used to enable pressure to be maintained in the bore hole 16 and to prevent contamination of the bore hole, for example, by ground water.
A coaxial transmission line 26 extends from the cap 24 through the overburden 12 to an RF applicator 28 positioned in the oil shale region 10. The transmission line 26 is preferably forrned ~ith an outer conductor 30 of steel pipe having, Eor example, an internal cliameter oE approximately 6 inches and a thickness o~ approximately a half inch. Several lengths of pipe 30 are joined together by threaded couplings 32 and the upper end o~ the upper ]ength of pipe 30 is threaded into an aperture in ~3~
cap 24 while the lower length o~ pipe 30 i5 threaded into an adaptor coupling structure 34 which provides an enlarged threaded coupling to a coaxial stub 36 extending back up the bore hole 16 for a distance of around an electrical ei~3hth of a wavelength of the freauency band to be radiated into the formation lO by radia-tor 28. ~ stub 38 of the same diameter as stub 36 also extends downwardly frorn adaptor 34 for a distance equal to approximately an electrical quarter wavelenath of said frequellcy band. If desired, a ceramic sleeve 40 having perforations 41 may be placed in the formation lO to prevent caving of said formation during the heating process.
Coaxial transmission line 2~ has an inner conductor 42 made, for example, of steel pipe lengths. The upper end of the upper pipe lengths is threaded into cap 46. A ceramic plate a~ which is attached to cap 24 spaces the inner conductor electrically from the outer conductor 30. Cap plate 46 is mounted on top of plate 44 and threaded to pipe 42 so that pressure .may be main-tained inside the outer conductor 30 of the coaxial transmission line 26. Several lenyths of pipe 42 connected together by metal couplings 48 and spaced from the inner wall of outer conductor 30 by ceramic spacer 50 extend from cap 46 downwardly through outer conductor 30 to a point beyond the lower end of tubular stub 38. An enlarged ceramic spacer 52 surrounds the pipe 42 adjacent its lower end and the lower end of tubular stub 38 to space pipe 42 centrally within coaxial stub 38. Preferably, ceramic spacers 50 rest on top oE couplings 48 so that they may slide ea.sily on the pipe lengths before being screwed into the couplings. Enlarged spacer 52 is held in axial position by metal collars 54 welded to the bottom length of pipe 42.
~:~B~3~:g An enlarged section of pipe 56 is threadably attached to the lower end of the bottom pipe 42 by an enlarging coupling adaptor 58 and the lower end of enlarged t~bular member 56 has a ceramic spacer 60 attached to the outer s~rface thereof to space member 56 from the bore face 16. In the example disclosed herein using approximately 6-inch size for pipe 30, the diameter of pipe 42 is approximately 2 inches inside and 2 3/8 inches out-side. This produces a characteristic impedance for tihe trans-mission from the surface to the ~ applicator 28 of approximately 50 ohrns. By choosing the interior diameter of the stubs 36 and 38 to be, for example, of 12.715 inches, the characteristic impedance of the coaxial line sections comprising pipe 42 and stub 38, may be approximately 100 ohms. The outer diameter of the tubular radiating mernber 56 may be seleçted to be ~ 5/8 inches to produce a radiating surface which may be easily inserted into the well bore 16 through the previollsly installed steel casing 18~ Preferably the size of tubing 56 should be as large as practicable to reduce the vol.age gradient on the surface of the tubing 56 during the radiation of high RF power into the formation 10.
In accordance with this invention the region from the upper end of tubular member 3~ to the lower end of tubular member 38 is made an odd number of quarter wavelengths effective in shale in the operating frequency band of the device and forms an im-pedance matching section 106. L~ore specifically, the distance from the adaptor 34 to the lower end of tubular member 38 is made approximately a quarter wavelength effective in air at the operating ~requency o~ the system. The section 106 of applicator 28 comprisiny stub 38 toyether with the portions oE member 42 adjacent thereto, act as an impedance matching transformer which 3~3~
improves the impedance match between coaxial line 26 and the radiator section 108 of applicator 28. Section 106 also substan-tially reduces the current from the RF power that would flow back up the outside of pipe 30 from ~he lower end thereof until the power had been lost by radiation into overburden 12 or ab-sorbed by loss in the surface of pipe 30. With the structure or this invention, however, the power loss by current flow along the outer surface of the pipe 30 is reduced very substantially so that it is only a few percent of the power transmitted down the transmission line 26.
In accordance with this invention it is to be noted that the dielectric constartt and loss tangent, and hence impedance, of the formation 10 change with temperature as may be seen from Patent 4,140,179. In accordance with tnis invention, the im-pedance of the radiating section 108 changes very little over a wide range of temperatures of formation 10. To compensate for any such temperature impedance variation, an impedance matching device 62 is provided at the surface which may provide an adjust-able impedance to the transmission line 26. The adjustrnent of the impedance matching circuit may be achieved by measuring the effectiv.e power reflected from the applicator 28 back along the transmission line 26 to determine the standing wave ratio 011 the transmission line 26. Thus it may be seen that the radiating structure 10~ may be excited to produce a radiation pattern ~irected primarily radially outward in the plane of the oil sha~le medium with the bulk of the power being confined to the medium. While the frequency may, Eor example, be varied between 1 and 10 megahertz Eor the dimensions given herein, the tubular member 56 is preferably a quarter wavelength long, effec-tive in shale. The spacing between the upper end of tubing 56 and the ~3~
lower end of tubing 38 is preferably a quarter wavelength long, effective in shale with a s~bstantial air gap.
The lengths of the enlarged section 56 and the portion of the section 42, which together form a substantially half wave monopole radiator 108 depend on the fre~uency of the transmitter 64 and the effective radiation wavelength in the medium 10 as well as the radiation impedance of the medium.
Good results have been achieved, for example, at 10 megahertz, if the total length of the radiator 108 had the enlarged radiating section 56 (represented by the portion thereof below cutting line 5 5 of FIG. 1) approximately a seventh of a wave-length in air, and the section of the monopole radiator 108 represented by the extension of the inner conductor 42 beyond the lower end of the cylinder 38 (the portion between cutting line 4-~ and cutting line 5-5 in FIG. 1) approximately a sixth of a wavelength in air. When the medium 10 has a substantial quantity of water therein, for example, when the medium is first being heated, the effective wavelength 108 will be somewhat greater than a half wavelength. However, as heating progresses and the water is either converted to steam or driven off, the dielectric constant in the medium drops and the effective wave-length increases. Operating the monopole radiator 108 with an effective electrical wavelength greater than one-half wavelength reduces the vertical directionality of the pattern. Therefore, radiator 28 preferal)ly has dimensions which in wet shale, having a dielectric constant of, for example, 16 and in spent shale having a dielectric constant as low as 3, result in the radiating monopole 108 being approximately a half wavelength long. Thus, ~or e~ample, for a transmitter frequency of 10 mega-hert~ in which the free space wavelength is 3 X 103 centimeters or 30 meters which is 100 feet, the length of section 56 ischosen to be approximately 14 feet and the distance from the bottom of cylinder 38 to the top of casin~ ~8 is chosen to be 16 feet.
In operation, the bulk of the power is radiated from the section 108 and the section 106 acts as a resonant impedance transformer. The stubs 36 and 38 act as a non-resonant or induc-tive choking structure whose length may be deter~ined empirically to optimize the directive pattern in the horizontal direction as measured in the vertical plane. By varying the frequency, the pattern radiated can also be varied.
Transmitter 64 supplies variable frequency RF power to the impedance matching structure 62 through a coaxial line 66 and the impedance matching structure 62 supplies the RF power to the coaxial line 26 through a coaxial line 68 whose central conductor is connected to the cap 46 and whose outer conductor is connected to the cap 24.
As shown in FIG. 6, transmitter 64 preferably is located remotely from several sites 16 and transmission lines 66 extend distanaes up to in excess of 1,000 feet. Thus, one large trans-mitter installation can be used to feed sequentially different sites 16. It is, therefore, preferable that the standing wave ratio on the transmission lines 66 be maintained as close to unity as possible so that RF losses in the transmission line are minirnized. In addition, it is also desirable that little or no power be fed back into the transmitter 64 to avoid damage to the transmitter equipment as well as to allow the transmitter equip-ment to be tuned ~or maximLIm RF power generating efficiency.
Thus, the impedance matching circuits 62, which may use conven-tional inductors and capacitors, is adjusted in accordance with -10~
well-known practice to produce such impedance matching of the transmission lines 66.
While the radiator 56 may be sized for optimum radiation characteri.stic and/or power at a particular frequency, for example, by making the length of the element 56 an e~fective electrical quarter wavelength at that frequency in the bore 16, it is desirable that the frequency of transmitter 64 be variable to adjust for the different impedances or different formations and/or the different impedances of the formation encountered during different portions of the heating sequence.
Such impedance matches may also be achieved by variation of the output impedance of impedance matching circuit 62 so that by means of a standing wave the proper impedance is reflected through the relatively short transmission line stub 68 and the transmission line 26 to the radiating structure in the for-mation 10.
The impedance matching structure 62 is preferably adjusted for the desired impedance match into the radiating structure 26 with the transmitter 64 at low power, and the impedance match to produce low standing wave ratio in transmission line 66 i5 then ad3usted. However, it should be clearly understood that such impedance matching functions can be controlled in accordance with a preprogrammed schedule.
It has been found that good impedance match to oil shale formations can be obtained over a thirty percent ~requency band without subst:antial loss in the efficiency of transferring RF
power to the Eormation 10.
The transmiss.ion line 26 is preferably pressurized with an inert gas" such as nitrogen, from a source 70 through a pipe 72 tapped int:o bushing 22, through a pipe 74 tapped into cap 24 ~11-~3~
as well as to the interior of pipe ~2 through a pipe 76 connected by a insulating coupling 78.
The source of nitrogen 70 may be of s~fficent pressure to continuously bleed nitrogen into the pipes 42 and 30 as well as the casing 18 so that nitrogen flushes down the face of the bore 16 and through the region bet~een the pipes 42 and 30. Preferably~
the ceramic spacers have apertures in the peripheries thereof to allow the passage of the nitrogen. The nitrogen then presses against liquids 80 collected in the bottom of the bore 16 and forces them up through a producing tubing 82 which may be steel with a ceramic coupling 84 approximately at the lower end of the radiating cylinder 56. Ceramic coupling 84 isolates the tubing 82 which is essentially at ground potential rrom a tubing 86 extending upwardly through pipes 42 to the s~rface and through a cap 88 attached to the top of cap 46 and thence through an insulating coupling 90 to a collection tank 92 where the nitrogen can be recovered, if desired, and re-injected via the source 70 into the formation.
Such a circulation of nitrogen, in addition to aiding in production of kerogen products from the base of the bore 16, may serve to cool overheated portions of the transmission line and/or radiating structure so that high powers may be trans-mitted from the transmitter 64 into the oil shale body 10 with-out voltage breakdown at high voltage points in the structure.
In order to control the flow of gas from supply 70 to the vi~rious regions o the transmission line and radiator, pipes 72 and 74 contain valves 9~. Pipe 76 contains a valve 96 on the grounded side of bushing 78 and the pipe from bushing 90 ~o the collection tank 92 contains a valve 98 so that by opening and closing the valves, gas from the well bore may be increased, '~8~.3~
held constant or decreased during various cycles of the production p~ocess. By maintaining an appropriate purging flow of nitrogen through the well bore 16 before and during application of RF
power, danger of explosion in the region of the R~ applicator may be minimized. Such an explosion could occur, for example, if oxygen, driven o~E from components of the formation or present after installation of the well transmission line, combined with hydrocarbons in gaseous form driven off from the formation when a corona discharge or arc at the RF applicator caused ignition of an explosive mixture. The length of the transmission line 26 should be sufficient to reach any desired region of the oil shale 10 and for thick beds of oil shale may be gradually changed by raising or lowering the transmission line 26. This, in turn, raises or lowers the radiator 28 to expose a different horizontal layer of the oil shale to the maximum intensity of the radiation.
RF breakdown is minimized by the use of the ceramic spacers 50, 52, ~0 and 60 which maintain the various electrical conductors substantially concentric with each other and with the bore hole 16 so that impedance variations along the transmission line due to eccentricities which could otherwise occur between the inner and outer conductors of the coaxial line 26 are minimi~ed. These eccentricities could cause standing wave ratios in excess oE those contemplated thereby causing higher voltage nodes at points on the transmission line or in the RF radiator, The edges of the insulators are preferably beveled to facili-tate relative motion between the conductors during installation and a large insu].ating spacer 52 is posltioned between the lower end of stub 38 and inner conductor pipe 42 since in this region a volta~e maximum can occur. Such a voltage maximum is likely to increase as the standing wave ratio on the transmission line 26 increases so that at large power levels, corona breakdown might occur. Maximum power handling capability, in addition to being limited by voltage breakdown, is limited by the power dissipation of the transmission line and for the structure shown fabricated of conventional steel with surfaces coated with highly conductive material, such as copper, powers in excess of one megawatt may be transmitted through tne transmission line 26 and the radiator 28 into the formation 10.
In the event that the RF applicator 28 is not sufficiently deep, that is, the overburden 12 is not sufficiently thick, some of the RF energy at high powers radiated into the formation 10 may appear at low intensity on the surface. In accordance with this invention, wires, for example steel cables 100, may be welded to cap 22 and stretched radially for several hundred feet to reflect such radiation back into the overburden thereby preventing radiation interference when frequencies of, for example, 10 megahertz or below are used. Generally, frequencies above 10 megahertz are sufficiently absorbed in most overburden formations and lower frequencies are absorbed in those cases where there is substantial moisture content in the overburden.
The spacing between the radial wires can be any desired amount and branch wires from the radial wires may also be attached, if necessary" In addition, where more than one structure is placed in a qiven region, the wires can extend between adjacent structures.
~ s indicated previously in connection with Patent 4,140,179, the impedance changes due to both the absorption of the microwave energy because of changes in conductivity and because of changes in the dielectric constant due to removal of that porti.on of the ~3~3 water which originally existed in the oil shale body. The tem-perature at which such water changes to steam and is produced out of the formation depends on the pressure maintained in the well bore. For example, if the valve 98 remains closed and the bore face having first been flushed with nitrogen is pressurized to 500 psi, the temperature in the oil shale 10 may be raised at the bore face to several hundred degrees fahrenheit with the water still remaining in liquid form in the pores of the oil shale body. Water on the order of 3 to 30 percent may be en-countered and will absorb substantial amounts of the RF power.
In accordance with this invention the temperature in thebore face may be sensed, for example, by a thermo-couple 102 of a type shown in Patent 4,140,179, and as item 102 in FIG. 1, connected to the surface via a wire 104. When the temperature reaches, for example, 700 F~ opening the valve 98 will cause the pressure in the bore face to produce steam from the water cooling the bore face to a temperature below 700 F and pre-venting undesired hot spots at the surface of the formation lOo While the coaxial line 26 has surfaces providing R~ c~rrent flow which are large and hence low in current density for a given power level the coaxial lines 66 and 68 may be, for example, conventional conductive copper coaxial lines having, Eor example, an outer diameter of 3 1/8 inches. Such lines rnay be run for several hundred yards from a central transmitter and preferably have the impedance rnatching structure 62 positioned close to the surface of the well bore 16. Thus, the impedance of the trans-mitter 6~ may be substantially matched to the input impedance of the matchin~ structure 62 to maintain a standing wave ratio in line 66, for example, below 1.5 whereas the transmission line 26 may have a standing wave ratio thereon oE 1.5 to 5 depending on the matching required to optimize the radiation f~om radiator 28.
Referring now to FIG. 6, there is shown a plan view of a plurality of well bores 16 in a well field spaced apart by dis-tances such as several hundred feet and connected via coax cabling through impedance matching structures 6~ to a central transmitter 64 via coaxial lines 66. The ~F power may be sequen-tially shifted in any desired pattern to different radiators in different well bores 16 from a single transmitter housing which may be in~ for example, a control station. Signals fed from the impedance matching structures 62 to the control station may be used to monitor and/or adjust the frequency and impedance matching of the transmitter output to each of the wells.
This completes the description of the particular embodiment of the invention illustrated herein. ~owever, many modifications thereof will be apparent to persons skilled in the art without departing from the spirit and scope of this invention. For example, parallel wire lines could be used to feed the structures in the wells, other frequencies could be used than those indicated and a wide variety of conductive materials could be used for the transmission lines and radiating structures in the wells. Accor-dinglyt it is intended that this invention be not limited by the particular details of the embodiments illustrated herein accept as defined by the appended claims~
Claims (15)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. The method of producing organic products from a body of oil shale beneath an overburden comprising:
generating electrical energy in the frequency range be-tween 100 kilohertz and 100 megahertz;
transmitting said energy via a first transmission line having a first characteristic impedance through a variable imped-ance matching structure to a second transmission line having a second characteristic impedance and extending through said over-burden to a radiating structure positioned in said body of oil shale; and varying the impedance matching of said structure to com-pensate for changes in temperature of said oil shale body.
generating electrical energy in the frequency range be-tween 100 kilohertz and 100 megahertz;
transmitting said energy via a first transmission line having a first characteristic impedance through a variable imped-ance matching structure to a second transmission line having a second characteristic impedance and extending through said over-burden to a radiating structure positioned in said body of oil shale; and varying the impedance matching of said structure to com-pensate for changes in temperature of said oil shale body.
2. The method of producing organic products from a body of oil shale beneath an overburden comprising:
generating electrical energy in the frequency range be-tween 100 kilohertz and 100 megahertz;
transmitting said energy via a first transmission line having a first characteristic impedance through a variable imped-ance matching structure to a second transmission line having a second characteristic impedance and extending through said over-burden to a radiating structure positioned in said body of oil shale; and varying the frequency of said energy to vary the pattern of said energy radiated into said body of oil shale.
generating electrical energy in the frequency range be-tween 100 kilohertz and 100 megahertz;
transmitting said energy via a first transmission line having a first characteristic impedance through a variable imped-ance matching structure to a second transmission line having a second characteristic impedance and extending through said over-burden to a radiating structure positioned in said body of oil shale; and varying the frequency of said energy to vary the pattern of said energy radiated into said body of oil shale.
3. The method of producing organic products from a body of oil shale beneath an overburden comprising:
generating electrical energy in the frequency range be-tween 100 kilohertz and 100 megahertz;
transmitting said energy via a first transmission line having a first characteristic impedance through a variable imped-ance matching structure to a second transmission line having a second characteristic impedance and extending through said over-burden to a radiating structure positioned in said body of oil shale; and varying the frequency of said energy to compensate for changes in the impedance of said oil shale body to said energy.
generating electrical energy in the frequency range be-tween 100 kilohertz and 100 megahertz;
transmitting said energy via a first transmission line having a first characteristic impedance through a variable imped-ance matching structure to a second transmission line having a second characteristic impedance and extending through said over-burden to a radiating structure positioned in said body of oil shale; and varying the frequency of said energy to compensate for changes in the impedance of said oil shale body to said energy.
4. The method of producing organic products from a body of oil shale beneath an overburden comprising:
generating electrical energy in the frequency range be-tween 100 kilohertz and 100 megahertz;
transmitting said energy via a first transmission line having a first characteristic impedance through a variable imped-ance matching structure to a second transmission line having a second characteristic impedance and extending through said over-burden to a radiating structure positioned in said body of oil shale;
varying the frequency of said energy to vary the pattern of said energy radiated into said body of oil shale; and adjusting said impedance matching structure to reduce the power on said first transmission line reflected from said second transmission line and/or said radiating structure.
generating electrical energy in the frequency range be-tween 100 kilohertz and 100 megahertz;
transmitting said energy via a first transmission line having a first characteristic impedance through a variable imped-ance matching structure to a second transmission line having a second characteristic impedance and extending through said over-burden to a radiating structure positioned in said body of oil shale;
varying the frequency of said energy to vary the pattern of said energy radiated into said body of oil shale; and adjusting said impedance matching structure to reduce the power on said first transmission line reflected from said second transmission line and/or said radiating structure.
5. The method of producing organic products from a body of oil shale beneath an overburden comprising:
generating electrical energy in the frequency range be-tween 100 kilohertz and 100 megahertz;
transmitting said energy via a first transmission line having a first characteristic impedance through a variable imped-ance matching structure to a second transmission line having a second characteristic impedance and extending through said over-burden to a radiating structure positioned in said body of oil shale while sensing the reflected power on said second transmission line;
and varying the impedance matching of said structure as a function of said reflected power.
generating electrical energy in the frequency range be-tween 100 kilohertz and 100 megahertz;
transmitting said energy via a first transmission line having a first characteristic impedance through a variable imped-ance matching structure to a second transmission line having a second characteristic impedance and extending through said over-burden to a radiating structure positioned in said body of oil shale while sensing the reflected power on said second transmission line;
and varying the impedance matching of said structure as a function of said reflected power.
6. A system for producing organic products from a body of oil shale beneath an overburden comprising:
means for generating electrical energy in the frequency range between 100 kilohertz and 100 megahertz;
means for transmitting said energy via a first transmission line having a first characteristic impedance through a variable impedance matching structure to a second transmission line having a second character-istic impedance and extending through said overburden to a radiating structure positioned in said body of oil shale; and means for varying the frequency of said energy to vary the pattern of said energy radiating into said body of oil shale.
means for generating electrical energy in the frequency range between 100 kilohertz and 100 megahertz;
means for transmitting said energy via a first transmission line having a first characteristic impedance through a variable impedance matching structure to a second transmission line having a second character-istic impedance and extending through said overburden to a radiating structure positioned in said body of oil shale; and means for varying the frequency of said energy to vary the pattern of said energy radiating into said body of oil shale.
7. The system in accordance with claim 6 wherein said second trans-mission line is a coaxial transmission line having an inner and outer conductor, said radiating structure comprises a radiating element connected to the inner conductor of said second transmission line; and the diameter of said radiating structure is greater than the diameter of the outer conductor of said second transmission line.
8. The system in accordance with claim 7 wherein the diameter of said radiating element is substantially greater than the diameter of the inner conductor of said second transmission line.
9. The method of producing organic products from a body of oil shale beneath an overburden comprising:
generating electrical energy in the frequency range between 100 kilohertz and 100 megahertz;
transmitting said energy via a first transmission line having a first characteristic impedance through a first impedance transformation structure to a second transmission line which has a second characteristic impedance and which extends through said overburden and which is coupled to a radiating structure through a second impedance transformation structure positioned in said body of oil shale and substantially impedance matched to said transmission line; and varying the impedance matching of said first impedance trans-formation structure to compensate for changes in temperature of said oil shale body.
generating electrical energy in the frequency range between 100 kilohertz and 100 megahertz;
transmitting said energy via a first transmission line having a first characteristic impedance through a first impedance transformation structure to a second transmission line which has a second characteristic impedance and which extends through said overburden and which is coupled to a radiating structure through a second impedance transformation structure positioned in said body of oil shale and substantially impedance matched to said transmission line; and varying the impedance matching of said first impedance trans-formation structure to compensate for changes in temperature of said oil shale body.
10. The method of producing organic products from a body of oil shale beneath an overburden comprising:
generating electrical energy in the frequency range between 100 kilohertz and 100 megahertz;
transmitting said energy via a first transmission line having a first characteristic impedance through a variable impedance matching structure to a second transmission line having a second characteristic impedance and extending through said overburden to couple said energy through an impedance matching structure to a radiating structure positioned in said body of oil shale; and varying the frequency of said energy to vary the pattern of said energy radiated into said body of oil shale.
generating electrical energy in the frequency range between 100 kilohertz and 100 megahertz;
transmitting said energy via a first transmission line having a first characteristic impedance through a variable impedance matching structure to a second transmission line having a second characteristic impedance and extending through said overburden to couple said energy through an impedance matching structure to a radiating structure positioned in said body of oil shale; and varying the frequency of said energy to vary the pattern of said energy radiated into said body of oil shale.
11. The method of producing organic products from a body of oil shale beneath an overburden comprising:
generating electrical energy in the frequency range between 100 kilohertz and 100 megahertz;
transmitting said energy via a first transmission line having a first characteristic impedance through a variable impedance matching structure to a second transmission line having a second characteristic impedance and extending through said overburden to couple said energy through all impedance matching structure to a radiating structure which is positioned in said body of oil shale while sensing the reflected power on said second transmission line; and varying the frequency of said energy to compensate for changes in the impedance of said oil shale body to said energy.
generating electrical energy in the frequency range between 100 kilohertz and 100 megahertz;
transmitting said energy via a first transmission line having a first characteristic impedance through a variable impedance matching structure to a second transmission line having a second characteristic impedance and extending through said overburden to couple said energy through all impedance matching structure to a radiating structure which is positioned in said body of oil shale while sensing the reflected power on said second transmission line; and varying the frequency of said energy to compensate for changes in the impedance of said oil shale body to said energy.
12. The method of producing organic products from a body of oil shale beneath an overburden comprising:
generating electrical energy in the frequency range between 100 kilohertz and 100 megahertz;
transmitting said energy via a first transmission line having a first characteristic impedance through a variable impedance matching structure to a second transmission line having a substantially different characteristic impedance from that of said first transmission line and extending through said overburden to couple said energy through an impedance matching structure to a radiating structure positioned in said body of oil shale;
varying the frequency of said energy to vary the pattern of said energy radiated into said body of oil shale; and adjusting said variable impedance matching structure to reduce the power on said first transmission line reflected from said second transmission line and/or said radiating structure.
generating electrical energy in the frequency range between 100 kilohertz and 100 megahertz;
transmitting said energy via a first transmission line having a first characteristic impedance through a variable impedance matching structure to a second transmission line having a substantially different characteristic impedance from that of said first transmission line and extending through said overburden to couple said energy through an impedance matching structure to a radiating structure positioned in said body of oil shale;
varying the frequency of said energy to vary the pattern of said energy radiated into said body of oil shale; and adjusting said variable impedance matching structure to reduce the power on said first transmission line reflected from said second transmission line and/or said radiating structure.
13. The method of producing organic products from a body of oil shale beneath an overburden comprising:
generating electrical energy in the frequency range between 100 kilohertz and 100 megahertz;
transmitting said energy via a first transmission line having a first characteristic impedance through a variable impedance matching structure to a second transmission line having a second characteristic impedance and extending through said overburden to couple said energy through an impedance matching structure to a radiating structure positioned in said body of oil shale while sensing the reflected power on said second transmission line; and varying the impedance matching or said structure as a function of said reflected power.
generating electrical energy in the frequency range between 100 kilohertz and 100 megahertz;
transmitting said energy via a first transmission line having a first characteristic impedance through a variable impedance matching structure to a second transmission line having a second characteristic impedance and extending through said overburden to couple said energy through an impedance matching structure to a radiating structure positioned in said body of oil shale while sensing the reflected power on said second transmission line; and varying the impedance matching or said structure as a function of said reflected power.
14. The system in accordance with claim 6 wherein said second transmission line is a coaxial transmission line having an inner and outer conductor, said second transmission line extends through said over-burden to supply said energy through an impedance matching structure to a radiating structure positioned in said body of oil shale;
said radiating structure comprising a radiating element connected to the inner conductor of said second transmission line;
said impedance matching structure comprising a first tubular member coupled to the lower end of an outer conductor of said second transmission line extending upwardly parallel to said outer conductor and a second tubular member coupled to the lower end of said outer conductor extending downwardly parallel to said inner conductor; and the diameter of said impedance matching structure being substantially greater than the average diameter of the outer conductor of said second transmission line.
said radiating structure comprising a radiating element connected to the inner conductor of said second transmission line;
said impedance matching structure comprising a first tubular member coupled to the lower end of an outer conductor of said second transmission line extending upwardly parallel to said outer conductor and a second tubular member coupled to the lower end of said outer conductor extending downwardly parallel to said inner conductor; and the diameter of said impedance matching structure being substantially greater than the average diameter of the outer conductor of said second transmission line.
15. The system in accordance with claim 14 wherein the diameter of said radiating element is substantially greater than the diameter of said inner conductor of said second transmission line and the distance between the upper end of said radiating element and the lower end of said second tubular member is a quarter wavelength of the operating wavelength of said system.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000451399A CA1179020A (en) | 1980-06-30 | 1984-04-05 | Rf applicator for in situ heating |
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US16472380A | 1980-06-30 | 1980-06-30 | |
| US164,723 | 1980-06-30 |
Related Child Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000451399A Division CA1179020A (en) | 1980-06-30 | 1984-04-05 | Rf applicator for in situ heating |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1183909A true CA1183909A (en) | 1985-03-12 |
Family
ID=22595812
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000376811A Expired CA1183909A (en) | 1980-06-30 | 1981-05-04 | Rf applicator for in situ heating |
Country Status (5)
| Country | Link |
|---|---|
| JP (1) | JPS5729789A (en) |
| AU (1) | AU546295B2 (en) |
| CA (1) | CA1183909A (en) |
| DE (1) | DE3125719A1 (en) |
| FI (1) | FI72630C (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2013158548A1 (en) * | 2012-04-19 | 2013-10-24 | Harris Corporation | Method of heating a hydrocarbon resource including lowering a settable frequency based upon impedance |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP1941001A2 (en) * | 2005-10-24 | 2008-07-09 | Shell Internationale Research Maatschappij B.V. | Methods of producing alkylated hydrocarbons from a liquid produced from an in situ heat treatment |
| US8146669B2 (en) * | 2007-10-19 | 2012-04-03 | Shell Oil Company | Multi-step heater deployment in a subsurface formation |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2757738A (en) * | 1948-09-20 | 1956-08-07 | Union Oil Co | Radiation heating |
| CA1095400A (en) * | 1976-05-03 | 1981-02-10 | Howard J. Rowland | In situ processing of organic ore bodies |
| US4140179A (en) * | 1977-01-03 | 1979-02-20 | Raytheon Company | In situ radio frequency selective heating process |
-
1981
- 1981-05-04 CA CA000376811A patent/CA1183909A/en not_active Expired
- 1981-05-07 AU AU70230/81A patent/AU546295B2/en not_active Ceased
- 1981-05-26 JP JP7995681A patent/JPS5729789A/en active Granted
- 1981-06-25 FI FI811989A patent/FI72630C/en not_active IP Right Cessation
- 1981-06-30 DE DE19813125719 patent/DE3125719A1/en active Granted
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2013158548A1 (en) * | 2012-04-19 | 2013-10-24 | Harris Corporation | Method of heating a hydrocarbon resource including lowering a settable frequency based upon impedance |
| US8726986B2 (en) | 2012-04-19 | 2014-05-20 | Harris Corporation | Method of heating a hydrocarbon resource including lowering a settable frequency based upon impedance |
Also Published As
| Publication number | Publication date |
|---|---|
| DE3125719C2 (en) | 1987-04-02 |
| JPS5729789A (en) | 1982-02-17 |
| AU546295B2 (en) | 1985-08-29 |
| FI72630B (en) | 1987-02-27 |
| AU7023081A (en) | 1982-01-07 |
| DE3125719A1 (en) | 1982-03-18 |
| FI811989L (en) | 1981-12-31 |
| JPS6233397B2 (en) | 1987-07-21 |
| FI72630C (en) | 1987-06-08 |
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