Note: Descriptions are shown in the official language in which they were submitted.
Background of the Invention
This invention relates to a me-thod for recove~ing high-
viscosity oil from subsurface formations, and in particular,
relates to a method for reducing the viscosity of the oil by the
in-situ heating of an underlying salt water formatlon using heat
produced by heat energy radiating nuclear waste materials.
It is well known in the petroleum industry that there
are vast reservoirs of petroleum materials in the ear-th which have
not been produced because the petroleum exists in a highly viscous
and waxy state such that it cannot be pumped by conventional means.
Such petroleum products include those known as tar ~ands, oil
shale and asphalt rock. ~s a result of this common condition,
many methods have been attempted for recovering the petroleum in
such deposits. Among such methods is included increasing the
temperature of the petroleum in-situ in -the ear-th formation to
lower its viscosity, thereby enabliny conventional production
methods to be used to recover the petroleum.
Prior methods have employed chemical heating means or
electrical heaters suspended within the bore holes adjacent the
petroIeum-bearing strata, and the passage of electric current
t~rough the formation by the use oE electrodes in the plurality
of adjacent wells. Additionally, gases such as CO2 have been
pumped down into a well and into the oil-bearing formation to
chemically combine with the oil and lower its viscosity, and in
other applications the oil itself has even been ignited to produce
heat and gases which would generate pressure to force the oil out
of the formation into adjacent well bores while heating the vis-
cous petroleum in the formation.
The above-mentioned prior art systems have met with
only limited success for two primary reasons. Firs-t, the prior
art arrangements have encountered major difficulties in supplyiny
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an adequate source of heat within the bore hole itself and ulti-
mately to the formation over ex-tended periods of time. Secondly,
the prior art apparatus and methods for removing oil have lacked
an efficient means for effectively transferring the heat from a
heat source within the bore hole or limited area surrounding the
bore hole to the petroleum-bearing strata itself. Such conven-
tional heat sources as heretofore employed for these purposes are,
from a thermo-dynamic standpoint, a point source of heat since
the actual dimension of the heating source itself is practically
negligible as compared to the size and volume of the surrounding
formation.
In recent years, attempts to reduce the viscosity of
the petroleum contained in subsurface strata have been directed
to the use of nuclear reactions in which the greater portion of
the energy released by the reactions is liberated as heat. One
such method, described in UOS. Patent 3,24~,695, utilizes energy-
radiating nuclear waste material placed within a bore hole to a
point within the suhsurface petroleum-bearing strata. As an added
benefit, a use is found for radioactive wastes which in recent
years has presented a serious disposal problem.
~ owever, implacement of nuclear wastes within the petro-
leum-bearing strata must be carefully controlled in order -to avoid
increasing the temperature of the strata arbitrarily, thus charrin~
the crude oil surrounding the implacement point and changing the
permeability and flow characteristics of the formation. If such
charring does occur, the removal of the petroleum may become even
more difficult than prior to the appllcation of the heat.
The disadvantages of the prior art, and especially the
invention claimed in the afore-mentioned U.S. patent are overcome
wit~ the present invention and a method for reducing the viscosity
of subsurface petroleum-bearing deposits is disclosed. More
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particularly, the method of the present invention pe~mits use of
higher concentrations o~ nuclear waste material withou-t overheating
or damaging the subsur~ace petroleum deposit and any problems
related to possible radioactive contamination of the recovered
petroleum is avoided, and a safe and convenient means is provided
for disposing of spent nuclear waste material.
Summary of the Invention
This invention is for an improved method of reducing
the viscosity of petroleum situated in subsurface strata by
utilizing the heat of reaction o~ nuclear waste material to ele~
vate the temperature of an underlying water strata to cause a
corresponding elevation of temperature in the petroleum-bearing
strata overlying the water strata. The invention is particularly
adaptable for use when the strata comprises a salt water formation
underlying the oil-bearing structure.
A brief review of the sources o~ radioactive nuclear
waste materials and their characteristics is necessary here. The
use of nuclear energy in this country is progressing at a rapid
pace, leading to the construction of numerous facilities which
produce energy from nuclear fission. In a typical fission reactor,
a neutron is absorbed by a fissionable material, resultlng in
fission of that material with a resulting release of energy and
the production of other neutrons and other elements, both radio-
- active and inert. The elemental by-products are commonly referred
to as fission products and accumulate within the reactor throughout
the power generating lifetime of a particular fuel element. A
wide variety of fission products are produced, the actual distri-
bution of which depends upon the particular fission process utilized,
with both long lived and short-lived products. The short-lived
1g~9~38~8
products generally have h~lf-lives measured in terms of hours
whereas the longer-lived products have half-lives measured in
terms of years. A ~urther distinction between fission products
is the mechanism by which they decay, i.e., the type of radiation
which is immanated.
I'he actual distribution of fisslon products obtained
from a given reactor will depend upon the specific fission process
which occurs within the reactor 7 Hence, no generalization is
attempted with respect to a particular mix of fission isotopes
which might be available to use in the present invention. In all
of the fission processes in use today, the fuel becomes expended
at some time and must be remo~ed from the reactor for processing.
In all of the processes, the radioactive fission isotopes are
separated from the fissionable materials for disposal, while the
fissionable materials are recovered and processed into fuel ele-
ments for other reactors.
The fission products which remain after processing are
generally the long-lived products since there is an appreciable
delay between the time a fuel element is removed from a reactor
and the time it is actually subjected to processing. The ac-tual
residue from the processing operation is voluminous and must be
reduced in volume for efficient handling. This volume reduction
can be accomplished by any number of conventional distillation
techniques whereby the radioactive isotopes are further separated
from non-radioactive material and concentrated into a form for
disposal. Disposal of such material poses difficult environmental
problems to prevent contamination of the atmosphere,or the earth.
The package of these concentrated isotopes requires
careful consideration, balancing between the need to shield the
environment from harmful radioactivity and the need to provide ~or
removal of the heat generated from the decay processes. ~he
radiation emitted hy the fission products may be any o~ the
three prevalent radiations: alpha~ beta or gamma ray. Alpha
radiation requires only minor shielding but the capture of these
rather "large" particles produces considerable heat generation.
Beta radiation (electron emission) requires moderate shielding
and again this capture results in significant heat generation.
Gamma radiation (X-ray radiation) is the most penetratin~ of the
radiations emitted and requires a heavy lead shielding which
typifies most shielding installations. For purposes of the
present invention, it.would be desirable to prepare an isotope
mi~ in which the beta and alpha radiations are predominant.
A table of radio-isotopic materials that possess the
decay characteristics above discussed are provided in the
Standard Handbook for Mechanical Engineers (Seventh Edition, 1967).
Typically strontium and cesium are some of the more common
fission products available in a sufficient quantity.
Accordingly, the invention comprehends a method of
heating high viscosity petroleum products in a selected subsurface
earth formation overlying a salt water formation, comprising
the steps of providing an input bore hole into the salt water
formation, providing a production bore hole into the petroleum
product formation and in spaced relation to the input bore hole,
positionin~ in the input bore hole and within the salt water
formation a selected source of nuclear waste material, the
radiation emissions of which generate sufficient heat for
increasing the temperature of the salt water in the formation
sufficiently to increase the temperature of -the formation con-
taining the petroleum products for reducing the viscosity of the
products, and withdrawing the reduced viscosity petroleum products
through a production bore hole.
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The inventi~on also perta~ins to apparatus ~or heating
high viscosity petroleum products in a se~ected subsurface earth
formation overlying a salt water formation, including generating
means for producing heat from nuclear waste material, and access
means defining a first bore hole extending from the earth's
surface into the salt water formation for positioning the
generating means within the salt water formation. The generating
means is operative to reduce the viscosity of the high viscosity
petroleum products. Production means defining a second bore
hole extends from the earth's surface into the selected subsurface
formation, the second bore hole being in spaced relation to the
first bore hole, for withdrawing the reduced viscosity petroleum
products from the selected subsurface earth formation.
More particularly, in a preferred embodiment, a
bore hole is provided from the surface to a location within the
selected salt water formation for accepting the nuclear waste
material container, and, producing bore holes are provided ~ ~
that extend into the petroleum-bearing strata from the surface ~ -
and in a preselected proximity to the heat producing bore hole~
Nuclear waste material, which has been packaged in a
convenient form for shipment to the input bore hole location is
positioned therein at a location below the oil bearing formation.
Preferably the waste material is positioned within an underlying
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salt water layer. Alpha, beta and gamma particles given off by
the nuclear waste material create heat which elevates the tempera-
ture of the salt water, thereby elevating the temperature of the
overlying oil stratum by convection from the heated water.
The shielded package of radioactive isotopes must also
provide for removal of the heat generated. Accordingly, it is
felt that in actual practice, the present invention would pxobably
require that limited quantities of radioactive waste materials be
placed in shipping containers which can be adequately cooled by
ambient conditions and thereafter assembled at the drill site into
a final package for insertion into the selected strata or formation.
Once the nuclear waste material package is implaced in
or adjacent to a salt water stra-ta, heating can occur in a variety
of ways. Direct heating will occur as a result of gamma ray
emission from the relatively unshielded container. Heating of the
container will occur due to the absorption of beta and alpha
radiation. This heat will be transferred to the surrounding stra-
tum by conduction through the rock and convection of the salt
water within the stratum. As the temperature of the salt water
elevates, convection elevates the temperature of the overlying
petroleum-bearing strata, with the attendant reduction in the
viscosity of the petroleum. The petroleum products can then be
withdrawn in a conventional manner. .
In summary therefore, it is a feature of the present
invention to provide a method for thermally reducing the viscosity
of hydrocarbon materials contained in a subsurface strata.
It ls a further feature of the present invention to
reduce the viscosity of hydrocarbon materials by elevating the
temperature of the hydrocarbon-bearing strata through heating
the underlying strata
It is still another feature of the present invention
to elevate the temperature of the strata underlyiny a hydrocarbon
material strata through the use of reaction heat produced by
nuclear waste matexials.
~ till another feature of the present invention i5 to
elevate the temperature of the hydrocarbon-bearing formation
without causing thermal damage to the formation.
These and other features and advantages of the present
invention will become apparent from the following detailed descrip-
tion, wherein reference is made to the figures in the accompanying
drawings.
Brief Description of the Drawin~s
_
In order that the manner in which the above-recited
advantages and features of the invention are attained can be
understood in detail, a more particular description of the
invention may be had by reference to specific embodiments
thereof which are illustrated in the appended clrawings, which
drawings form a part of th1s specification. It is to be noted,
however, that th appended drawings illustrate only typical
~9~8~
embodiments of the invention and therefore are not to be con-
sidered limitins of its scope for the invention may admit to
further equally effective embodiments.
In the drawings:
Fig~re 1 is a cross secti.on of the earth at a poin-t
where a reservoir of entrapped petroleum having an underly.ing
salt water strata lies some distance below the surface and
depicts the method of the present invention.
Figure 2 is a shipment container for radioactive
materials intended for insertion into the selected earth strata.
Figure 3 is a cross-sectional view of the container ~;
depicted in Figure 2.
Figure 4 is an insertion package assembled by inter- -~
connecting a plurality of the shipment containers depicted in
Figure 2.
Figure 5 is a cross~sectional view of an alternative
embodiment of the shipment containers depicted :in Figure 2.
Detailed ~escrip~ion of the Preferred Embodiment
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Referring now to Fisure 1, there is shown a preferred
embodiment for hea-ting a selected petroleum-bearing formation
in-situ. A conventional hore hole 10 is shown extending Erom the
surface of the earth 12 to a location within the selected salt
water strata or formation 14. Bore hole 10 can be completed in
a conventional manner by use of steel casing 11. The casing 11
may extend through bore hole 10, or in some applica-tions, the
casing 11 may terminate either at or just below the interface
between the salt water formation 14 and the petroleum producing
formation of interest 18.
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A nuclear waste container 21 is assembled (as will be
hereinafter described) at the well site and using conventional
oil tool equipment, the container 21 will be lowered into bore
hole 10 and implaced in the bore hole in the salt water formation
14. ~ore hole 10, within formation 14, may be sealed by means o~
a conventional packer or sealing plate 13, and a cement plug 32
can be positioned above the seal 13 to seal the lower portion of
the bore hole, containing nuclear waste container 21, from the
remaining portion of the bore hole and to shield the remaining
portion of the bore hole 10 from radiation.
~ conventional producing bore hole 16 is shown extending
from the earth's surface 12 and terminating within the petroleum-
bearing formation 18. The producing bore hole 16 will also be
conventionally cased or lined by a steel casing 11, and the por-
tion of the bore hole 16 within the formation of interest 18, may
also`be cased by a suitable casing section 15. Casing section 15
may be conventionally perforated to form perforations 17 and to
create cracks or fissures 19 into the formation 18. A tubing
string 3A with a conventional pump 23 will be positioned within
bore hole 16. Oil from formation 18, its viscosity low~red by
the heat generated by nuclear waste container 21, will flow
through the fissures 19 and perforation 17 into the interior of
well bore 16 and accumula-te in the well bore as a standing column
of oil 21. The viscosity lowered oil can then be conventionally
pumped to the surface of the earth by means of pump 23 cooperating
with a conventional tubing string 34 having per~orations 23, or
other suitable openings for intake of the oil 21 for storage in
an appropriate storage facîlity (not shown).
Once in position, nuclear waste package 21 will begin
to heat the salt water foxmation 14 in a variety of ways. Direct
heating of the salt water formation 14 will occur as a result of
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gamma ray emission from the relatlvely unshielded package 21.
Heating of the package 21 will occur due to the absorption of
alpha and beta radiation by the shielding material of package 21,
the construction of which will be hereinafter described and by
the nuclear waste material itself. Hea-t genera-ted by alpha and
beta radiation absorption within the nuclear waste material will
be transferred to the shielding material of package 21 by con- -
duction. The heated pac~age 21 will transfer heat to the sur-
rounding strata 14 by conduction through the rock, sand and clay
constituents of ~ormation 14 and by convection to the salt water
within the formation~ The primary mechanism ~or heating the
salt water strata will be conduction through the surrounding rock
structure. Thereafter, convection and vertical conduction of
heat will transfer heat to the overlying oil strata 18 and serve
to elevate the temperature of the overlying oil strata and thus
reduce the viscosity of the oil in formation 18, which can then
be removed in a conventional manner as hereinahove discussed.
It is anticipated that the nuclear was-te material con-
tainer 21 will be implanted in the bore hole 10 to remain for an
extended period of time before sufficient heat has been supplied
to raise the temperature of the surrounding structure sufficiently
to significantly reduce the viscosity of the oil. It may also be
desirable to include some mechanism for natural convection circu-
lation of salt water from formation 14 through the in-terior of
container 21 to insure proper cooling of the container and also
increase the surface area which contacts the salt water in forma-
tion 14. It will also be apparent, that by drilling a plurality
of bore holes 10 and disposing a plurality of nuclear waste pack-
ages 21 in a predetermined design or pattern throughout an oil-
bearing reservoir, a comprehensive pattern of heating of the saltwater formation 14 will be accomplished for heating a broad area
of the petroleum-bearing formation 18. In addition, such heating
of the petroleum materials in ~ormation 18 may also release
absorbed and trapped gases in the petroleum materials which may
act to elevate the formation pressure and help provide a drive
for the oil or petroleum substances into producing well bore 16~
Further, it is also anticipated that other secondary and tertiary
recovery methods could be used in conjunction with the present
invention to recover the heated oil.
Re~erring now to Figure 2/ 3 and 4, there is shown a
suggested cylindrical container 20 designed to be filled wi-th
radioactive isotope waste material in any form, either a liquid
solid or gas. Container 20 may conveniently be made from a
selected material,such as steel,having sufficient structural
integrity to permit insertion of container 20 into the bore hole
10, without damage to the container which may result in release
o~ the nuclear waste material into the bore hole 10. Further,
as various nuclear waste materials have different radiation char~
acteristics the density of the material used in forming container
20 and the wall thickness of the formed container 20 may be pre-
selected to provide for the desired absorption of alpha and betaradiation. Container 20 has an interior chamber 22 sized to hold
a predetermined amount of nuclear waste material. The amount of
waste material carried within each cylinder will be determined by
the maximum heat generated by the decay process of the radioactive
isotopes, for insuring that each filled container 20 may be trans-
ported under ambient conditions without special need for means of
cooling the container 20. One way in which to insure such removal
of the heat generated by the waste nuclear material within container
20 is to provide sufficient surface area on container 20 that allows
the heat to be conducted away by conduction through the container
walls and thereafter transferred to the atmosphere by convection.
~6:391~
One effective mea~s o providing such increased surface area is
by providing ribs or fins 25. If necessary, provisions for cir-
culating a coolant through and around container 20 could be
provided during transport, but this would greatly reduce the
ability to transport the containers along commercial routes.
Accordingly, in the actual practice of the present invention, it
would probably require that limited quantities of radioactive
isotopes be placed in containers 20 in order that the containers
can be adequately cooled by ambient conditi~ns and thereafter
assembled and filled with additional isotope material at the bore
hole site into a final package 21 for insertion in formation 14
One e~tremity of container 20 is formed with a reduced
diameter end portion 24 having external threads 26 for mating
with the opposite end of another cylinder 20 having a recess 28
and threads 30. After transportation of the desired number of
containers 20 to the bore hole site, a nuclear waste packaye 21
may now be prepared, if such a package was not suitable for
shipment assembled as such. A suitable package ~1 may be formed
by connecting several containers 20 together into a string or
column by means of the threaded portions 26 and 30 of each con-
tainer 20. In this manner, an elongated nuclear waste package
21 may be assembled as shown in Figure 4. The insertion package
must include sufficient shielding (not shown) to protect the
workmen at the earth's surface during the insertion of packaye 21
into bore hole 10, although this shielding probably need not
necessarily accompany package 21 into wellbore 10. Subsequent
recovery of package 21, if necessary, would be accomplished by
withdrawing package 21 back into a suitable shielded structure at
the earth's surface. Again, depending upon the final concentra-
tion of radioactive isotopes within package 21, an external cool-
iny source may have to be provided for temperature maintenance of
package 21 during insertion of the package in-to wellbore 10 and
- 13 -
into the salt water formation 14. If a cement plug 32 is positioned
above package 21 to seal the bore hole, as shown in Flgure 1, the
package 21 could be recovered at a future time by drilling through
plug 32 and grasping the package 21 with conventional downhole
recovery tools.
Referring'now to Figure 5, an'alternative shape 20'is
suggested for the nuclear waste con-tainer. As depicted, the
container 20'is formed to provide integral ribs or ins 25'and
an interior cavity 22'shaped to correspond to the exterior surface
of the container 20' Again, interior chamber 22'is designed to
hold a predetermined amount of nuclear was-te material with the
shape of interior chamber 22'permitting the nuclear waste material
to be positioned within the fins 25'. This spreading of the
nuclear waste ma-terial into t'he fins 25' reduces its concentrated
mass, thereby reducing the absorption heat buildup within the
materiaL itself.
Further, container 20' may be formed with mating threads
(notshown) at opposing extremities to permit the assembly of a
nuclear waste package (not shown) as above-described for container
20. Use of this package will be as above-described for package 21.
It will be apparent from the foregoing description,
that many other variations and modifica-tions may be made in the
method and apparatus described'herein without substantially
departing from the essential concept of the present invention.
Accordingly, it should be clearly understood that the forms of
the invention described herein and depicted in the accompanying ~'
drawings are exemplary only, and are not intended as limitations
to the scope of the present invention.
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