CA1057650A - Mechanical wave heating of bituminous sands - Google Patents

Abstract

A B S T R A C T

Underground bituminous sand deposits are heated by mechanical wave energy to fluidize the bituminous sand thereby to facilitate extraction thereof. For uniform, circular, symmetrical dispersion of mechanical wave energy of high-power and low-frequency, a mechanical wave energy radiator is provided comprising a cylindrical elastic tube of springy steel or the like preferably dimpled or corrugated and closed at one end and containing a liquid medium. Mechanical wave energy is applied to the liquid medium by a reciprocating source or the like connected to the radiator by a rigid walled tubular pipe or the like. The axial length of the radiator tube should be an odd multiple of one-quarter wavelength of the mechanical wave energy transmitted. Cavitation within the liquid is avoided by biasing the system with a steady state pressure at least as great as the maximum negative pressure swing of the mechanical waves in the liquid. Trans-formers are disclosed for accommodating changes in pipe dia-meter and changes in liquid medium throughout the system.

Description

i5(J

FIELD TO WHICH THE INVENTION RELATES `~
The present invention relates to a method of heating ln situ an underground deposit of naturally occurring hydrocarbons, such as petroleum entrapped within a deposit of sand or the like, by mechanical wave energy, for the purpose of facilitating extraction of the hydrocarbons.

BACKGROUN~ OF THE INVENTION

: . . .
In northern Alberta are located what are popularly ` known as "tar sands" (and which probably would be more appropri~
; 10 ately referred to as "bituminous sands") occasionally exposed ~ at the surface of the ground but generally overlaid by soil ; to varying depths. The bituminuous sands comprise a heavy percentage of quartz sand (say 80%), small amounts of clay, of the order of 5% water, and of the order of 15% (frequently less) bitumen by weight. The bituminous sand deposits are ;;~
estimated to contain more than one million million barrels ~ -,: , .. .
of oil. -~ For many years efforts have been made to recover ;~ the oil, and several processes have been proposed for the purpose. Many proposals have involved the mining of the sand and the extraction of the petroleum from the sand there--... .
after. The mining techni~ues and associated extraction techniques . .
; have generally involved intolerably high capital investments, energy expenditures, ecological damage, and extraction and refining costs.
Various methods have been proposed to extract the petroleum from the sands in situ without requiring the ., :
mining of the sands. Recognizlng that most recoverable petroleum , ~J deposits have been located at much yreater depths and therefore ~ 30 at higher temperatures and pressures than are to be found - , '.:' :

~5$~5~
in the Alberta bituminous sands, engineers have proposed the artificial creation of similar conditions in the bituminous sands of Alberta. Electric current applied across terminals embedded in a bituminous sand deposit for the purpose of , the heating of a portion of the bituminous sand deposit by electrical conduction has not been successful, usually because of the formation of carbonized paths between the electrodes, limiting current flow to these paths. Since the thermal conductivity of the deposits is relatively low, the heating of paths of relatively small dimensions within a bituminous sand deposit has not been successful in raising the overall temperature of the deposit (or a sufficiently large volume thereof) to the desired value.
It has also been proposed to extract petroleum ~
from underground bituminous sand deposits by forcing steam ~ I
. ,~, into the deposits. The use of steam has required the generation at the surface of large amounts of process heat, and the ~ problem exists that the steam cannot always be sufficiently i~ confined to the particular portion of the deposit from which the petroleum is intended to be extracted but rather tends .. , . ,:
1 to blow out of the deposit being treated. As much as half ; a ton of steam has been required per barrel of oil recovered.
Nuclear explosions have been advocated, but `, have not yet been experimentally tested, to realize much the same objective of increasing the heat and pressure within the underground deposit so as to enable at least a portion to be recovered. It is apparent however that at least some of ~he petroleum would be carbonized by a nuclear explosion, and a significant portion or perhaps all of the petroleum that could be recovered in such a process (if the process ~ -were practicable at all) would be contaminated by radioactivity.
-,.: ' ' ,.

:
~OS 7fif~fsfuf 1, SUMMARY OF THE INVENTION
The presient inventors have recognized that some extraction techniques for recovery of oil from bituminous sands and the like would be much more satisfactory if thiere were a satisfactory method of heating a sufficiently large volume of the bituminous sands ln situ, without undue consumption or destruction (as by burning, carbonizingf~ etc.) of the petrolewn entrapped within the sands. The present invention `f accordingly has as its principal object the provision of ;~;
la a method of heating a selected portion of a hydrocarbon deposit in situ without undesired combustion in situ of the constituent hydrocarbons, within the limits imposed by the nature of . . . ~ .
the constituents of the deposit, the surrounding environment, and the equipment used~
The present invention is the mechanical wave heating of a selected portion of an underground deposit of naturally occurring hydrocarbons, especially a petroleum deposit entrapped within a deposit of sand or the like. -~
tIn thls specificatlon, "hydrocarbon" means one or more consti~
tuents of petroleum or other naturally-occurring underground deposits, some of which may be entrapped within deposits of other materials (e.g. sand), and which are composed of the elements hydrogen and carbon, sometimes with the addition of other elements.
At sufficiently elevated temperature (about 200F in the case of bituminous sands) the petroleum either ;~
alone or in combination with other materials in the deposits becomes fluid. It can then be pumped out of the well. The pumping-out may be facilitated by the application by a fluid under pressure, preferably an inert gas, within the deposit :. i ` ~ ~ 3 ~
~-.

.,., :

so as to force the fluidized portion o the deposit to the well shaft and thence to the surface. Other extraction techniques (e.g. application of water or steam under pressure) applicable to petroleum in fluid form available at or in the vicinity of a well may be applied. The present invention is not primarily directed to the extraction process which follows the heating of the underground deposit; the present invention is primarily directed to the meahanical wave heating technique ~er se, which will then be followed or accompanied by a suitable extraction process. (It is contemplated that the heating may continue during at least some portion of the time required for extraction of the petroleum.) However, possible extraction techniques will be described for use in conjunction with the invention and in a secondary aspect the invention embraces . . .
the combination of extraction techniques with the mechanical wave heating techniqueO
The mechanical wave heating may conveniently be implemented by means of a mechanical wave radiator located in a well communicating with the selected portion of the deposit to be heated. The radiator radiates mechanical wave energy directly from its location within the well to the selected portion of the deposit. To this end, the radiator ; may be immersed in the material of which the deposit is made or in suitable oil or other fluid medium. The radiator should preferably be capable of radiating the energy to the ~urrounding medium in a wide radiation pattern. The terms "radiate"
and "radiation" must be understood, in relation to mechanical ~`
wave phenomena, as referring to wave phenomena in a material ~ `
medium. ; .
The required mechanical wave radiator for dis-persing mechanical wave energy in a circular symmetrical .~
~ - ~ 4 76S ~ :~

configuration may conveniently be in the form o a cylindrical tube, preferably a thin metal hollow circular structure which contains a liquid medium. The tube is closed at one end and coupled at the other end to a source of mechanical wave ' energy. The closed end is made preferably of rigid reflecting ~, material such as relatively thick steel. The side walls of the tube, however, are made of elastic material, such as a springy steel, for oscillatory deflection in response ~
to the application of mechanical wave energy from the source ~`
to the working liquid within the tube. The side walls may, if desired, be corrugated parallel to the cylindrical axis ~-~, of the tube to increase the effective radiating surface and `1 improve the capability of the side walls to deflect radially, and in any event must be designed to yield sufficiently to 1 . ' transfer energy into the surrendering medium. The axial , length of the radiator should be an odd multiple of one-quarter i~ wave length of the mechanical waves being radiated so that ~ the radlatox bPhaves as~a resonant element.
~ The source of mechanical waves can conveniently i 20 be a reciprocating piston whose output may be transmitted ~ within a rigid tubular pipe, acting as a transmission line, ;
:1 . : ;
; to the open end of the radiator tube.
If for some reason the working fluid within ~ the tube is to be different from the working 1uid within ;
;, the transmission line. a piston working in a cylinder serially ¦ connected in the transmission line can separate the two fluids from one another and transmit the mechanical wave energy from~one fluid medium to the other. The piston behaves as a transformer for~the mechanical wave energy. Such a trans~
former can be included elsewhere in the system if required.

' 7 ,,. . ~
$~

Another type oE transformer comprises a tapered tubular section for connecting transmission line sections of different diameters. Still another type of transformer comprises a pair of rigidly interconnected pistons working in cylinders (e.g.
transmission line sections) oE different diameters.
In order to avoid internal energy losses due to cavitation, a bias pressure can be supplied to the working liquid. The bias pressure, for example, could be supplied via an air pressure tank located above and communicatin~
through a small opening with the transmission line, the lower `~ part of the air tank being occupied by some of the working liquid of the transmission line so that air is prevented from entering the transmission line.
In summary, in accordance wi-th the present invention, there is provided a method of mechanical wave heating in situ of a selected portion of an underground deposit of hydrocarbons by means of a meahanical wave - radiator immersed in a fluid medium which is in direct contact with the selected portion and is located in a well 20~ communicating with the selected portion of the deposit.
The radiator transmits mechanical wave energy to the selected ; ~
-~1 portion of the deposit until the selected portion becomes ~ ;
fluid. The radiator comprises a tube for containing a liquid medium for transmitting mechanical waves. The tube is closed at one end and, at the other end, has connecting means for connection to a source of mechanical waves. The tube has side walls made of elastic material suitably formed for oscillatory deflection in response t~ the a?plication of - mechanical waves from the source to the liquid medium.

~; - 6 ~ ~ ;
,,.,.", '~' .~

., ' ~
~

,............................................................... . ; .

~5'76~ial SUMMARY OF TE~F DRAWINGS
.:
Figure 1 is a schematic section view of a reciprocating element suitable for generating low-Erequency ;~
high-power mechanical wave energy.
Figure 2 is a schematic section view of a piston coupling element suitable for use as a transformer of low-frequency high-power mechanical wave energy.
Figure 3 is an alternative fluid coupling device suitable for use as a mechanical wave energy transformer.

Flgure 4 is a further alternative fluid coupling - `~
device suitable for use as a mechanical wave energy transformer.
:~
~ Figure 5 is a schematic section view of a ~ : :
,~, high-power low-frequency mechanical wave energy radiator in accordance with the teachings~of the present invention.

~ Figure 6 is a schematic elevation view of an ;l ~ alternative embodiment of a mechanical wave energy radiator ,',, \ '::
,'; \ ~ ~ : .

. ~ \
:''1 \

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

~ ~ \
\

:''' \ ' ,;-'', \ ;:

-, ~ \ .

:, \
:,',;' :

:1057G5i~

in accordance with the teachings of the present invention.
Figure 7 is a cross-section view along the line VII-VII of Figure 6. -Figure 8 is a pressure-versus-time diagram illus-trating the effect of a constant pressure bias on a mechanical wave generated in a liquid.
Figure 9 is a schematic section view of a bias pressure source for use in accordance with the transmission of mechanical wave energy in accordance with the teachings of the invention.
Figure 10 is a schematic section view of an exemplary generation, transmission and radiation system for heating of underground bituminous sand deposits by high-power low-frequency mechanical wave energy in accordance with the teachings of the present invention.

DETAILED DESCRIPTION WITH REFERENCE TO DRAWINGS
, For the generation of relatively low-frequency - high-power mechanical wave energy~ a reciproca~ing piston driven by a source o~ rotary mechanical energy is suitable.
Figure 1 schematically illustrates such an energy source ;~ comprising a connecting drive rod 11 pivotally connected , .... .
~ by wrist pin 13 to piston 15 slideably and sealingly mounted j :
for reciprocating motion within cylindrical sleeve 17, which is provided with a flange 19 for connection to an adjoining ;~ `~
energy transmission device, which can simply be a length of solid metal pipe. The walls of the sleeve 17 should also be constructed of solid metal or the like to avoid absorption -of mechanical wave energy. A working liquid 18 i5 present ~"
,; in the cyllnder~17 to the right of piston 15. The sleeve ,f~ ~ 30 17 and adjoining pipe segments act as a conduit for mechanical . .
~ 7 ,,.,~, ., : , , , , , ~ ", ., .. ,. ,. ; .... . .
. . -. -,- . . . :, : . . . - ~

~7~i50 , wave energy, and if the walls 17 and the walls of the adjoining pipe line are smooth and unyielding, the mechanical wave energy will be substantially conEined to pressure variations in the fluid within the conduit, and will not be appreciably absorbed by the pipe walls. -~-The relevant parameters of the liquid 18 in the mechanical wave energy generator may not be completely satisfactory for the transmission or radiation of that energy. ~ ;
Mechanical wave energy transformers suitable for changing ;~
some of the characteristics of the mechanical wave energy , may be provided as required. Three different types of trans~
former are illustrated in Figures 2, 3 and 4.
In Figure 2, the transformer comprises a piston ~ ,. . .
21 slideably mounted within a solid metal cylinder 23. The ends of the cylinder 23 are provided with flanges 25, 27 ,,.. ,,: . i for connection to adjoining pipe sections or the like. It is contemplated in the use of the transformer of Figure 2 ~ i , that a liquid havlng one set of physical ch;aracteristics 11 occupy the space to the left of~the piston 21 and that a~liquid having a different set of physical characteristics ,.~, l will occupy the space to the right of the piston 21, the ; density, viscosity and other relevant characteristics of ~' the two liquids being selected to couple the mechanical wave : ,,:j :
1 input to the mechanical wave output as required.
~ ~ :
l~ The transformer of Figure 3 is suitable where 1 the working liquid has the desired physical properties but where the diameter of the input element does not accord with the diameter~o~the output element. Tn this case, all that : j :
is required is a tapering pipe section 31 having a wide dia-meter terminating end 33 and a narrow diameter terminating , , , i ~ - 8 -. j .

.:

~o~

end 35. A wide diameter flange 37 is provided adjoining the wide diameter end 33 for coupling to an adjacent wide diameter pipe section or the like, and a narrow diameter flange 39 is provided adjacent the narrow diameter end 35 for connection to adjoining narrow pipe sections or the like.
Figure 4 illustrates a transformer suitable for accommodating the situation in which both the pipe diameter and the working liquid require to be varied. In this case a cylinder 41 is provided having a narrow-diameter cylindrical 1~ portion 42 and a wide-diameter cylindrical portion 43. A
double piston element 44 is provided, having a wide-diameter piston 45 slideably mounted in wide diameter cylindrical portion 43 of cylinder 41, and a narrow-diameter piston 46 slideably and sealingly mounted in narrow-diameter cylindrical ~; portion 42 of the cylinder 41. The two pistons 45, 46 are interconnected by a solid connecting rod 47 which may be ~j integral with the two pistons 45, 46. The space 48 between ~!
the pistons 45, 46 may be evacuated or vented to the outside -~ air, as by vent 38. The physical properties of any fluid ~; 20 48 between the pistons 45, 46 should be taken into account in determining the characteristics of the transformer. The cylinder 41 may be provided with wide-diameter flange 49 and narrow-diameter flange 50 for the purpose of permitting . : j connection to adjoining pipe segments or the like.
A suitable mechanical wave energy radiator for , radiating mechanical wave energy uniformly and with circular symmetry about its axis of revolution is illustrated in Figure ' 5. The radiator comprises a circular cylindrical tube 51 terminated by a rigid end wall 53. The tube 51 is also pro-vided with a flange 55 for connection to an adjoining section ;

_ 9 _ :

.: ~ , . . . .

1~57t;50 of the sonic energy transmission line. The walls of the cylindrical tube 51 are sufficiently thin and may be dimpled or otherwise surface-modified to enable the tube 51 to osci-llate radially in response to the pressure variations within the liquid contained by the tube 51. The pressure variations arise from the transmission of sonic energy from the adjoining transmission line. The tube 51 may be made of strong, relatively thin stainless steel, for example. The length of the tube 51 from the flange 55 to the terminating rigid end wall 53 should be an odd multiple of a quarter wavelength of the mechanical wave energy being radiated. This is a condition for end-to-end resonance in a liquid. The thickness of the side walls and the material out of which they are made, and the density of the liquid within the tube 51 will determine other significant physical characteristics of the radiator, ~ although the nature of the fluid in which the radiator is '~ immersed will also affect the radiation characteristics.
The tube 51 will be expected to be several times longer than its diameter; the preferred ratio in any practical appli-, . .j cation is best determined empirically.
Figure 6 illustrates an alternative form of radiator in accordance with the teachings of the present invention~ This radiator comprises an extended cylindrical tube 61 again terminated by an end wall 63 which departs 1 ! :
from a circular cylinder by virtue of corrugations along the length of the tube 61. These corrugations can be clearly ~' ! perceived in the section view of Figure 7. The corrugations ~`~ facilitate radial deflection of the walls of the tube 61, r ' which walls can be made of thin stainless steel or the like ~ 30 as described previously with reference to Figure 5.

' '; - 1 0 - .
l; ' ' 1~ ~7 ~ ~ ~

Maximum radiation efficiency of the radiator of either Figure 5 or Figure 6 depends upon the achievement of resonance. The length of the liquid column in the tube 51 or 61, the density of the contained liquid, and the wall stiffness are the principal factors determining the resonant frequency. If the walls are relatively stiff, the length of the tube is expected to be the principal factor determining the resonant frequency, and to this end, the length should be an odd mul~iple of a quarter wavelength at the frequency of mechanical energy supplied. If, however, the walls of the radiator have relatively low stiffness, the density and compressibility of the contained liquid and of the external fluid may be paramount parameters. The correct interrelationship . . .
~' of these parameters for any particular application will probably be determined empirically, since the theoretical predictions are difficult to reach and to translate into practical application.
It is desired of course to have substantially l all of the energy generated by the reciprocating source or l other suitable energy source delivered to the radiator without ;
appreciable loss and then transmitted by the radiator to the surrounding medium. A certain amount of the mechanical wave energy can be dissipated undesirably internally as heat if as a consequence of the pressure variations in the liquid medium within the transmission system, vapor-filled bubbles are permitted to form and collapse. This formation and collapse of vapor filled bubbles, referred to as "cavitation", can dissipate large amounts of energy~ The prohlem exists because at any point in the liquid in the transmission line, pressure ~` variations may, unless precautions are taken, generate an 30 apparent "negative pressure" which can permit-vapor bubbles ;~
'~
, .
. . .
.'~ - 11 -:
' .... :

~1:)5~S~
to form in the fluid. These vapor bubbles are generated during periods of rarefaction and collapse during periods of compression of the liquid at any point in the system.
This phenomenon is graphically illustrated in Figure 8, which shows that at any point in the liquid transmission line the pressure rises and falls (e.g. sinusoidally if a reciprocating energy source is used) cyclically over a period of time, as represented by curve A in Figure 8. During periods of minimum pressure Amin vapor bubbles tend to form~ during periods of maximum pressure AmaX these bubbles tend to collapse.
If the periods of minimum pressure Amin give rise to a pressure -P with reference to the steady sta~e pressure Ao in the system, it follows that if the total system pressure were increased by a bias pressure P, the resulting pressure-versus-time curve at any point in the system would be represented : .
by curve B of Figure 8, and that the lowest pressure Bmin would be equal to the steady state pressure Ao of the system at rest. Since gas or vapor bubbles will not form spontaneously in the liquid present in the system at rest (or in any event the liquid can be chosen so that this is true), it follows .: ~
that increasing the steady state pressure in the transmission ~ ;~
line by a bias pressure P will avoid the problem of cavitation.
Accordingly, means for the application oE a gas under at least a pressure P to the liquid transmission system may take the form illustrated in Figure 9. A pipe coupling element 91 has circular cylindrical end portions `
93 terminating in coupling flanges 95 for connection to adjoin-ing pipe sections and the like. A gas pressure chamber 97 ,~. 1 I communicates with the liquid in the transmission line by ;;
- 30 means of a constricted conduit 99. The gas chamber 97 should -~
''..:.

"''' ' .

.

~576S(31 of course be placed above the liquid transmission line to avoid escape of gas into the confined liquid. The chamber 97 may be provided with a suitable gas supply inlet 98 by means of which the gas pressure within the chamber 97 can be varied. The inlet 98 should be of very small diameter so as to avoid sonic energy losses therethrough. The con-striction 99 should also be small so as to minimize the inter-ruption of continuity o the reflective pipe surface and to minimize radiation into the gas chamber 97.
Cavitation can also be avoided by selecting as the working liquid one having a low vapor pressure and little or no dissolved gas or suspended solid particles.
` Selected ones of the above-described components can be arranged to cooperate for the mechanical wave heating of bituminous sands in situ. An exemplary extraction site and apparatus for the mechanical wave heating of bituminous sands in situ are illustrated schematically in Figure 10.
A source of rotary mechanical energy schematically illustrated by element 101 is connected by crank 103 to a reciprocating piston 105 slideably mounted in cylinder 107.
The cylinder 107 is coupled to a pipe section 109 connected by a conduit 111 to a gas pressure chamber 113 which exerts a bias pressure on the liquid (e.g. water) contained in the . ~ ~
transmission line 115 within the interior of the interconnected pipe sections. The initial transmission line portion is fairly wide (thus permitting the piston 105 to have a relatively ~`
~ short stroke) but for long distance transmission, a narrower '~ pipe section 117 may be preferred. For that purpose a trans-~-~ former coupling element 119 is optionally provided to narrow the transmission line to the diameter convenient for long :. , :
distance transmission, if that is necessary.

: ':

~ 6 5~
At the radiating end oE the system, let us assume that it has been empirically determined that the radiator 121 requires to operate at a diameter wider than the pipe section 117 and with an internal fluid other than water.
Accordingly, a transf3rmer section 123 is provided containing both a diverging tapered section 125 and a sliding piston 127 which permits both a widening of diameter and a change in the transmitting fluid. A separate gas chamber 129 con-nected by a small orifice 131 to pipe section 133 is provided ;~
in order to ensure that there is a bias pressure operating on the working fluid for the radiator 121. It may be observed ;~
that the system of Figure 10 is also prov;ded with an elbow portion 135; the provision of such elbow portion should normally .
~ be possible without substantially interfering with the trans-., .
; mission efficiency of the system. ;~;~
If the reciprocating source produces mechanical wave energy at a ~requency of 60 Hz, and glycerine is the working liquidt the wave velocity will be about 1900 metres ;
- per second, and the wavelength about 32 metres. Thus the ~ -`
. .
1~ 2Q radiator should be vf the order of 8 metres in length, or ;~
: . :J . - . :
some odd multiple of this (the exact length preerably being empirically determined, or the frequency of the source adjusted to produce resonance~.
The mechanical wave radiator 121 is loca~ed -~
. . . ~ . . .
i;i within a well shaft 141 provided with a casing 143 having 1 perforations 145 throughout that portion o~ its ~ength located '~`1 , within a bituminous sand layer 1~7 situated between an over- ~
:, ~
~ bu~den layer 149 and a basement rock layer 151. The well ~
. , ., - .

casing 143 is sealed at the top by a well cap 153 into which `

the mechanical wave nergy transmission ~ine section 157 ~
, . .

. . ~"" ,~,.i ,''~ ' :
- - :

~ V~76S~
and an extraction pipe 155 are fitted. The borehole for the well shaft 141 is drilled from the surface through the overburden and the bituminous sand layer. The mechanical wave radiator 121 should preferably be long enough to span the thickness of the oil-sand deposit, the radiator parameters being adjusted to give resonance for the selected length at the operating frequency. If necessary, oil may be intro-duced via extraction pipe 155 into the well shaft 141 so that the radiator 121 has intimate and uninterrupted coupling through a liquid medium to the surrounding bituminous sand formation. The mechanical wave energy will be directed into the bituminous sand in the three-dimensional pattern character-istic of the radiator configuration, modified by the reflections from the upper and lower boundaries of the deposit, where abrupt discontinuities in wave velocity may be expected.
Virtually all the radiated energy is expected to be dissipated in the tar sand, and it will be heated at a rate proportional to the radiator output. As the cylindrical mass coaxial ~, .
~; with and close to the radiator 121 becomes raised in temperature, ;~
and becomes fluid (which is to be expected at about 200E.), its attenuation of the wave energy will decrease, and the energy penetration will increase. The fluid bituminous sand can then be pumped to the surface.
, One or more injection wells 159 may be provided at a distance from the extraction well 141, and used to inject air, or (to avoid combustion) an inert gas, under pressure, i i into the bituminous sand formation, to facilitate expulsion ;~
of the fluid bituminous sand from the well 141 via extraction pipe 155. It is important to note, however, that the mechanical wave energy can be effectively propagated only through a liquid or solid medium, not through a gas. Therefore, if . ~ .
,, ~
' - 15 -, .,' ~: '~

- there is a danger that injected gas could permeate the under-ground deposit before it has been sufficiently fluidized, a liquid (e.g. water) rather than a gas should be injected via injection wells 159. During the extraction operation, ~ ,~
heating by mechanical wave energy can be continued or not, as empirically determined~ If water is injected into the formation, it is preferably pre-heated at the surface so that the mechanical wave energy is not wasted by heating water. However, mechanical wave energy attenuation by and 10 consequently the heat absorption of the injected water is -expected to be relatively small.
It is conceivable that in some cases the in situ heating of the oil sand should be continued to temperatures sufficient to cause vaporization or gasification, cracking, , and re-gasification of the bitumen, with the gaseous hydrocarbon i products conducted to surface storage or processing facilities h via extraction pipe 155.
At sufficiently elevated temperatures there may be a tendency for the oil to flow relative to the sand, 20 resulting in underground separation of the bitumen from the sand, so that the liquid bitumen alone might be ejected, ' leaving the sand in the deposit, and this of course would be the optimum alternative to pursue, if the phenomenon should occur.
' :.
:'....................................................................... , ' : .:
i EXAMPLE
A representative oil sand deposit has a thickness ; ;
of the order of 150 ft and an overburden thickness of the :, ~
order of 750 ft. These are typical values for the Athabasca deposits in northern Alberta. The oil sand has a typical composition by weight of 83% quartz sand, 12% bitumen, and .. ., ~:
.. . .
~ - 16 : .. :
"''J

S7b~

5% water, and is at a temperature of about 50F. At this temperature the hitumen has a viscosity ranging from 0.5 to 5.0 X 106 centipoises, and this viscosity is reduced to about 1000 centipoises at a temperature of 200F. The latter viscosity represents an adequate degree of mobility for the oil sand, permitting it to be expelled from the ormation ;~
by fluid or gas pressure, and educted to the surface through ~ a duct of suitable diameter.
: The vertical borehole for shaft 141 may be of say 16-inch diameter, drilled from the surface through the ; overburden and the oil-sand deposit, to the rock beneath.
This borehole may have a conventional steel-pipe lining, and at least the upper section of which, following customary practice, may be cemented in place. The steel lining section in the oil-sand is, as indicated above~ perforated, to permit mechanical wave energy to pass outwards, and fluid oil sand , or oil to pass inwards. The injection well 151 may be of i say 10-inch diameter~ drilled from the surface through the :~ overburden to the oil sand, and in this may be installed .. : 20 a steel casing, the upper part of which again may be cemented in place~
. When mechanical wave energy is transmitted from ~:
:. the generator 101 to the radiator 121, the energy is trans-., mitted into the surrounding fluid, in a pattern determined ^. by the radiation characteristics of the radiator 121, and -the relative velocity of the waves in the oil sand and in `~. the rocks above and below this layerO These velocities will ordinarily differ widely, the velocity in fluid bituminous ~:
:
;~I sand being of the order of one fourth the velocity in typical ~; :J 30 rocks, so that the waves radiated into the bituminous sand ::: J :
7 - ,:
,'.' l~tS7~

layer are reflected from the rock layers above and below, and the energy is largely confined to the bituminous sand.
The waves are propagated with small attenuation, and therefore small energy dissipation, through the oil or other liquid medium surrounding the radiator 121, and wlth much higher energy dissipation in the solid bituminous sand surrounding the borehole. This energy dissipation heats -~
the bituminous sand and converts it to a fluid of relatively low viscosity at temperatures possibly as low as 160F.
When it becomes fluid its attenuation decreases markedly, and the wave energy passes freely through it to the solid ~ material beyond~ In this way the wave energy heats and liquefies ';,t a cylinder of constantly increasing diameter, and when this ,. . .diameter reaches a desired value, gas or water under appro-~`l priate pressure is introduced into the injection well 159, ;, and educts the molten material to the surface. Xf the ex-.... . .
~' traction process leaves a cavity around the borehole and ~, it is desired to continue operations at the same site, the cavity from which the oil sand has been extracted can then be flooded with water, and the heating process re-commenced.
Since the water has a relatively low attenuation factor/
the mechanical wave energy is mostly transmitted to the sur-rounding bituminous sand. As this is heated to fluidity, :. .
the diameter of the molten annulus constantly increases.
, When desired, this mass can be educted to the surface, to ;`` be processed there, the cavity ~illed with water, and the heating cycle again repeated. At the time it is desired to abandon this site, the water introduced into the cavity `
may optionally be expelled, and replaced at least in part . :
by the sand resulting from the surface separation process.

-~ ~ 18 -:. ~
.. ~

~57~5~

The desirability of continuing extraction from the same extraction well or drilling a fresh extraction well remote from the cavity surrounding the first well will be empirically determined. It may be desirable to carry out only one heating cycle at each site. In this case the expulsion of the fluid ; bituminous sand is preferably effected by injecting gas under pressure - e.g. air, nitrogen, or carbon-dioxide~ At the conclusion of the heating cycle, any cavity created may option-- ally be filled with the sand tailings from the surface separ-ation process.
It will be apparent from the above discussion that the present invention may be useful in other situations in which the viscosity of underground hydrocarbon deposits is required to be lowered by heating, as in the case of naturally occurring deposits of heavy oil or bitumen uncombined with sand, or the viscous residues remaining in conventional oil ;1 wells.
Modifications and variations of the foregoing proposals will occur to those skilled in the art. The scope of the invention is to be ascertained by the appended claims.

.

. ,i . ~

:', -' ~
:, ;

19 ::

Claims (13)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. The mechanical wave heating in situ of a selected portion of an underground deposit of hydrocarbons by means of a mechanical wave radiator immersed in a fluid medium which is in direct contact with the said selected portion and located in a well communicating with said selected portion of the deposit, the radiator transmitting mechanical wave energy to the selected portion of the deposit until the selected portion becomes fluid, the said radiator comprising a tube for containing a liquid medium for trans-mitting mechanical waves, said tube being closed at one end and having connecting means at the other end for connection to a source of mechanical waves, said tube having side walls made of elastic material suitably formed for oscillatory deflection in response to the application of mechanical waves from said source to said liquid medium.

2. The method of claim 1, additionally comprising drawing off fluid hydrocarbons from the well.

3. The method of claim 2, wherein the deposit comprises the viscous residue adjacent or at least partially within a conventional oil well which has been at least partially exhausted.

4. The method of claim 2, additionally comprising injecting a fluid under pressure into the hydrocarbon deposit to promote the drawing-off of fluid hydrocarbons from the well.

5. The method of claim 2, wherein the mechanical wave energy is supplied by a mechanical wave transmission system comprising (a) a source of mechanical wave energy, and (b) a transmission line for transmission of mechanical wave energy comprising an enclosed liquid medium coupled at one end to said source of mechanical wave energy and at the other end to the radiator.

6. A method as defined in claim 5, wherein the source of mechanical wave energy is a reciprocating piston working in a cylinder coupled on the output side of the piston to said liquid medium.

7. A method as defined in claim 6, additionally comprising a source of pressure coupled to said liquid medium for application of a bias pressure thereto.

8. The method of claim 1, wherein the side walls of the tube are generally of circular cylindrical form.

9. The method of claim 8, wherein the closed end of the shell comprises a rigid plane wall generally perpen-dicular to the cylindrical axis of the tubular shell.

10. The method of claim 9, wherein the side walls of the tube are of overall circular cylindrical form but are provided with corrugations extending parallel to the cylindrical axis of the tube.

11. The method of claim 9, wherein the side walls and closed end of the tube are made of metal, the closed end being of relatively thick unyielding metal for reflecting mechanical wave energy and the side walls being of relatively thin metal for transmission of mechanical energy to the ex-ternal medium surrounding the radiator.

12. The method of claim 11, wherein the axial length of the tube is substantially greater than its diameter, and wherein the axial length is selected to be an odd multiple of one-quarter wavelength of the mechanical waves supplied by the source,

13. The method of claim 12, wherein the connecting means comprises an opening for connection of the tube to an enclosed liquid medium for transmission of mechanical wave energy.