Note: Descriptions are shown in the official language in which they were submitted.
CA 02592491 2007-05-29
MICROWAVE PROCESS FOR INTRINSIC PERMEABILITY ENHANCEMENT AND
HYDROCARBON EXTRACTION FROM SUBSURFACE DEPOSITS
Field of the Invention
The present invention relates to the extraction and recovery of subsurface
hydrocarbon
deposits by a process of microwave radiation and permeability enhancement of
reservoir rocks
due to fracturing by selective and rapid heating.
Backuound of the Invention
Oil shale, tar sands, oil sands and subsurface media in specific areas contain
useful
hydrocarbons. For example, it has been reported that there are vast oil shale
deposits in the
United States, and in particular, in the States of Colorado, Utah and Wyoming;
with over 1.5
trillion barrels of oil in the oil shale in these States. There have been many
attempts to extract
the hydrocarbons from these subsurface deposits.
Some of these applications involve removal of the subsurface media to above
ground and
the use of a retort to remove the oil. To avoid the step of excavating or
mining, a number of in-
situ processes have been proposed.
One such proposal employs relatively low microwave power supplied by a
magnetron.
The down hole microwave generator is disclosed in U.S. Patent 4,193,448 issued
March 18,
1980 to Calhoun G. Jeambey, as inventor, and the use of this generator is
disclosed in detail in
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CA 02592491 2007-05-29
U.S. Patent 4,817,711 issued April 4, 1989 to Calhoun G. Jeambey as inventor.
The microwave
generator is a mixer apparatus similar to those used in microwave ovens and is
relatively
ineffective for controlled heating and removing of hydrocarbons. The apparatus
heats the easily
reached hydrocarbons in the pores of the rock and will leave much of the
hydrocarbon away
from the bore hole untouched.
Although not designed for commercially recovering hydrocarbons from oil shale
or other
subterranean locations, a high power microwave system is disclosed in U.S.
Patent 5,299,887
issued April 5, 1994 to Donald L. Ensley, one of the inventors herein. This
system is disclosed
for the removal of contaminant from a sub-surface soil matrix. It is taught in
this patent that the
application of high power microwave energy to chlorinated hydrocarbons
contaminated (CHC)
soil causes micro-fractionation of various soil aggregates, including clay and
rock formations.
This effect increases the local permeability and resulting diffusion rates for
egress of both liquid
and vapor phase CHC.
The teachings of the Ensley 5,299,887 patent were included in U.S. Patent
6,012,520 by
Andrew Yu and Peter Tsou as an alternative to use of high-pressure water jet
drilling to create a
high-permeability web in a hydrocarbon reservoir.
Summary of the Invention
The present invention provides a new economical way of recovering oil
contained in a
rock formation, such as oil shale, by enhancing the permeability of the
subterranean rock by
selective and rapid heating. The basic concept taught by the co-inventor
Ensley is built upon for
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CA 02592491 2007-05-29
efficient recovery of oil from oil shale and of oil from tar sands.
Additionally, the residual oil
from worked and/or abandoned oil wells may be recovered by the apparatus and
method of this
invention.
The method of extracting oil from oil shale, tar sands and oil sands includes
the steps of
drilling a bore hole into the media, encasing the hole with a casing and a
fused quartz extension
or well screen at the bottom of the casing, inserting a microwave carrier with
a directional
antenna at the bottom end into the uncased well and the fused quartz well
screen, and radiating
electromagnetic energy at microwave frequencies from the antenna into the
media surrounding
the antenna.
The apparatus includes a high power (1/2 megawatt or greater) microwave source
which
operates at 1 Gigahertz or higher frequency coupled through a waveguide or
coaxial cable to a
directional antenna in a well. The typical frequency for the microwave source
is 2.45 Gigahertz.
The apparatus further includes a circulator in the waveguide path near the
output of the source to
protect the source from reflected waves. The circulator directs any reflected
waves to a dummy
load. A casing, inside the drilled hole and containing the waveguide, provides
a path for passage
of vaporized water and vaporized or liquified hydrocarbons from the bottom of
the well to the
top for collection and management and recovery of the hydrocarbons. The fluids
are either
pumped or rise because of sufficient pressure created by the heating and
vaporizing of water and
hydrocarbons.
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CA 02592491 2007-05-29
The apparatus may further include a rotator in the waveguide going into the
well to
permit rotation of the lower waveguide and antenna for selecting the direction
of radiation from
the antenna.
The apparatus and method of the present invention provide extraction of
hydrocarbons
from subsurface deposits, which include, but are not limited to, oil shale,
tar sands, heavy oil,
and residual oil from petroleum reservoirs by microwave (greater than 1 GI-1z
frequency)
radiation that vaporizes hydrocarbons or decreases hydrocarbon viscosity for
removal by
conventional pumping technologies.
Further, the intrinsic permeability of the host rock is increased by
fracturing the rock as a
result of rapid microwave heating of the in-situ fluids. The process of
increasing the intrinsic
permeability of the hydrocarbon reservoir rock enhances hydrocarbon removal
efficiencies
during microwave heating. A pressure bubble in permittivity space may be
created that contains
the migration of hydrocarbons from the source region to the extraction bore
hole.
The apparatus and method of this invention provide an enhanced zone of
intrinsic
permeability surrounding bore holes that increases production rates for new or
existing wells
located in subsurface gas or petroleum reservoirs. A permeable skin region is
created around the
well bore that extends several meters radially from the well bore.
The apparatus and method provides a way to remove the hydrocarbons with
minimal
impact to the environment. A single bore hole is drilled to extract
hydrocarbons leaving no
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CA 02592491 2007-05-29
waste, such as clay waste piles, which require additional disposal methods.
Additionally, water
requirements from limited water resources are minimized by use of this
apparatus and method.
Further efficiencies are realized by capturing and employing some of the
volatile vapor
emissions as fuel to power the field portable microwave system; thus, limiting
fuel supplies from
other sources. Gas turbines may be easily employed in this way. The net result
is an increase in
the energy balance where judicious quantities of energy are used to
economically produce
portable forms of energy that have a minimal impact on the environment.
Further, the impact on groundwater resources is minimized or avoided by
containing the
hydrocarbon removal process to the vertical region of extraction while not
disturbing upper or
lower layers of water.
The system for extracting and recovering hydrocarbons from subsurface target
formations
may be a closed system downhole with pressure control to most effectively
extract hydrocarbons
from rock, such as oil shale. Oil shale typically contains 2% to 4% of water.
If there is
insufficient water in the target formation, water may be added through the
encased bore hole.
The water in the target formation is superheated and causes fracturing of the
rock.
Further, the superheated water, from the target formation or added, causes the
pressure to
increase to push the liquified or volatized hydrocarbon to the surface. These
hydrocarbons are
collected in a tank and recovered.
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The pressure created by the superheated water or steam may be controlled by
controlling
the microwave power applied to the antenna positioned in the target formation.
Further, the
frequency of the output of the microwave source may advantageously be 2.45
Gigahertz, which
is the closest frequency to the resonance of water.
The above and other features, objects and advantages of this invention will
become
apparent from a consideration of the foregoing and the following description,
the appended
claims and the accompanying drawings.
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Brief Description of the Drawings
Fig. 1 is a diagrammatic illustration of a mobile microwave hydrocarbon
recovery system, in
accordance with this invention;
Fig. 2 is an enlarged view of the phase array antenna in the well, in
accordance with this
invention;
Fig. 3 is another view of the major components of the system, in accordance
with this invention;
Fig. 4 is a cross-sectional view of the phase boundary from the energy
radiated by the antenna, in
accordance with this invention; and
Fig. 5 is a diagram illustrating the typical stratification in many target
formations containing
hydrocarbons and a pressure controlled system, in accordance with this
invention.
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Detailed Description of the Preferred Embodiments
The specific embodiments of the hydrocarbon recovery system are illustrated in
the
drawings and will be described in detail herein. Figure 1 illustrates the
major components of a
mobile hydrocarbon recovery system. A 400 cycle turbine generator 1, or some
similar source,
supplies electrical power for the system. The output of the generator 1 is
applied to a
transformer/filter unit 3 under the control of a control unit 2. A crowbar
electrical circuit 4 at the
output of the transformer/filter unit 3 prevents an over voltage condition at
the output of the
transformer/filter unit 3 from damaging circuits coupled to its output. Once
triggered, crowbars
4 depend on overload-limiting circuitry, and if that fails, the system is
protected by a line fuse or
circuit breaker (not shown).
A high power (1/2 megawatt or greater) microwave source 5 (klystron) provides
electrical energy down a waveguide 6. The source 5 may be a typical klystron
with an efficiency
between 40% and 50%. Preferably, the source is a sheet-beam klystron which has
an efficiency
close to 65%. The microwave energy travels through waveguide 6, past an arc
detector 7, and
through a circulator 8, to a mode converter 9. The mode converter 9 allows the
microwave
energy carried by waveguide 6 (which may be square or rectangular) to be
carried by a water-
cooled circular waveguide 10 or a coaxial cable (not shown). The microwave
energy is directed
downward into a specially designed well in a bore hole 14 via the water-cooled
waveguide 10.
The microwave energy is applied to a radiating antenna 11 which is located at
a selected depth in
a target formation 18.
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The antenna 11 and water-cooled waveguide 10 or coaxial cable are located in a
specially
designed bore hole 14 drilled to the target formation 18 which contains
hydrocarbons. Standard
drilling techniques are used to drill the bore hole to desired depths and
diameters. The bore hole
14 passes through various stratified layers of soil, rock and water as
schematically represented in
Fig. 5. Selected layers, such as each layer of freely running water, are
sealed off by concrete 31
or some other suitable seal to prevent contamination or other interference
with the water or
aquifers.
A casing 29 is placed inside the bore hole 14 and extends above the ground
level and
down into the hole 14 for nearly the entire depth of the hole.
A fused quartz well screen 12 extends from the bottom end of the casing 29.
This screen
12 is perforated before attachment or may be perforated while in the hole 14.
The well screen 12 is located at the level of the target formation from which
hydrocarbons are to be extracted.
Thus, in the hydrocarbon production zone, the radiating antenna 11 is
contained in the
perforated fused quartz well screen 12 or other low loss material such as
ceramic. Preferably, the
antenna 11 is a phase array antenna for directivity and control of the
radiation pattern.
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CA 02592491 2007-05-29
A circulator 8, having a series of ferrite magnets, is included in the
waveguide 6 path to
shift the phase and to shunt any power reflected from the target formation
into a water-cooled
dummy load 13, thereby protecting the klystron tube 5.
A water-cooling system consisting of a heat exchanger 20 and a coolant storage
container
21 provide cooling water for the dummy load 13, circulator 8, klystron tube 5,
waveguide 10 and
antenna 11. The heat exchange 20 may operate at 2 Megawatts.
Arc detectors 7 are strategically placed in the waveguide to detect potential
arcing
problems and to immediately shut down the system if there is an arcing
problem. The arc
detectors 7 are integrated into a central control system 22 that monitors, but
not limited to,
cooling water temperatures, off-gas temperatures, off-gas concentrations, and
power conditions
for the power supply and the klystron, and provides safety controls for the
operation of the
system.
Electromagnetic energy is radiated either horizontally or angled upward, in a
sector along
the length of the antenna from the radiating antenna 11 and induces a phase
boundary 17 into the
surrounding rock of the target formation as the water and hydrocarbons are
liquified or
vaporized. This heating effect occurs due to microwave energy that is directly
absorbed by the
water and hydrocarbons in the phase boundary area 17. As subsurface water and
hydrocarbon
deposits in the phase boundary area liquify or vaporize, the phase boundary
region expands
resulting in a pressure gradient from the phase boundary to the encased well.
Several
atmospheres of pressure relative to the inside of the casing 29 and the bore
hole 14, where the
CA 02592491 2007-05-29
pressures are closer to atmospheric, may occur as a result of heating. A
pressure gradient
develops and thereby forces hot vapor from the subsurface, through the annular
space of the
casing 29, past an off-gas analyzer 15, and diverted to a thermal condenser
tank 16 or a
distillation unit for capture and hydrocarbon component separation.
The pressure in the area of the phase boundary 17 may be monitored by a gauge
30 near
the top of the casing 29, which is closed at the top. See Fig. 5. The pressure
may be controlled
by varying the rate of flow of the material from the well by employing a valve
31 between the
encased well and the thermal condenser and contaminated tank 16. The pressure
may also be
varied by varying the power level of the microwave source 5.
As an alternative to or in addition to pressure in the well, a sump near the
bottom of the
well with piping to the exterior of the well (not shown) may be used to
recover the hydrocarbons
and other liquids or gases from the bottom of the well.
An important effect of microwave radiation of rocks containing hydrocarbons
and/or
water is macro-fracturing of the rock over the area within the phase boundary
17. This effect
significantly increases the intrinsic permeability of the rock, allowing the
efficient egress of
liquid and vapor from the phase boundary through the fractured rock and into
the bore hole for
collection.
The area within the phase boundary 17 is a preferential pathway for the
migration of
water and hydrocarbons (either in gas or liquid form) from the phase boundary
17 to the bore
11
CA 02592491 2007-05-29
hole 14 and well screen 12. Consequently, vapor loss to the surrounding target
formation is
minimal as are potential environmental effects on any surrounding groundwater.
Figure 4 provides a generalization of the phase boundary 17 launched into a
target
formation 18 by the phase array antenna 11. The phase boundary 17 is the
location where
microwave power is coupled with the water and hydrocarbons and are
preferentially heated. As
the water and hydrocarbons are vaporized or mobilized as a liquid resulting
from microwave
heating, the phase boundary advances into target formation 18. Water and
hydrocarbon vapors
migrate to the surface under the pressure gradient induced by microwave
heating. Alternatively,
a supplemental vacuum system is employed, if necessary. Additionally,
extraction by
conventional pumping may be used.
Once the phase boundary 17 has reached the maximum radial extent, the antenna
11 and
water-cooled waveguide 10 are rotated around their vertical axes resulting in
the antenna slots
pointing in a different direction for extraction in a new sector. Another
phase boundary 17 is
created in the area adjacent to the previously microwaved region 19. The
subtended angle of
each sector is selected to most efficiently extract the desired hydrocarbons
from the target
formation. The smaller the angle the greater the energy in the sector. The
angle may be 300 for
most target formation. The process is continued until the majority of the
region at a selected
depth has been radiated in all directions. The antenna 11 is either raised or
lowered in the bore
hole 14 to another region in the target formation 18 and the process of
launching phase
boundaries in sequenced sectors is repeated. This process is continued until
the distance of the
phase boundary 17 from the antenna 11 results in diminishing hydrocarbon
recovery rates which
12
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will dictate cessation of the process in that sector and eventually at the
operating depth of the
antenna and in the particular bore hole 14.
At this point in the process, the antenna 11 and water-cooled waveguides 10
are removed
from the bore hole 14. A conventional oil recovery pump continues recovering
liquid
hydrocarbons until recovery rates cease. This process is repeated in
additional bore holes spaced
at approximately twice the electromagnetic propagation distance of the system.
Microwave heating has significant advantages over low frequency heating
(generally less
than 1.0 gigahertz) for the extraction of subsurface hydrocarbons. The
imaginary part of the
permittivity cr" (the loss tangent) is a measure of how dissipative a medium
is and gives the rate
of attenuation to a propagating wave. In the lower RF frequency ranges, et" is
dominated by ion
conductivity. As rock is heated by a low frequency RF source, ions in
groundwater will act as a
charge carrier until approximately 100 degrees centigrade is achieved,
depending on the system
pressure, at which time the water will vaporize, terminating the charge
carrier pathway. Further
heating of the rock will rely on conduction that requires large energy inputs
over substantial time
periods to achieve desirable results. For example, kerogen locked in oil shale
requires
temperatures in the range of 450 to 500 degrees centigrade in order to liquify
for removal. This
requires an additional 350 to 400 degrees centigrade heating by conduction for
RF frequency
heating applications.
Conversely, microwave heating is caused by orientation polarization In a lossy
material,
the electromagnetic energy is turned into heat by friction due to displacing
internal charges when
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CA 02592491 2007-05-29
the material is polarized in place with the alternating electric field of the
propagating microwave.
Most rocks and soils are composed of aluminum silicates, calcium carbonates,
quartz, or similar
mineral compositions that exhibit low loss tangents for propagating microwave
energy while
water and hydrocarbons exhibit higher loss tangents. As a result, microwave
energy can
effectively penetrate various types of rock and directly couple energy into
water and
hydrocarbons resulting in a hydrocarbon removal process that is both effective
and requires
substantially lower quantities of electric power.
This process can be illustrated by comparing heating rates between conduction
and
microwave heating. A sample of oil shale placed in an 1100 watt microwave oven
and heated
for 3 minutes reaches an interior temperature of 103 degrees centigrade at 4
cm from the surface
of the rock. Repeating the experiment in an 11,000 watt conventional oven at
260 degrees
centigrade requires 22 minutes to reach the same temperature in the interior
of the oil shale
sample. The experimental results show dielectric heating by microwave
frequency heats the oil
shale over seven times faster at one tenth of the power requirement compared
to thermal
conduction heating.
The physical process of efficiently heating subsurface hydrocarbon deposits is
based on
the concept of launching a phase boundary in the subsurface using directed
microwave energy,
thereby heating the hydrocarbon to temperatures where liquification or
vaporization occurs. As
hydrocarbons are removed, the remaining rock absorbs limited amounts of energy
allowing the
phase boundary to continue to migrate radially from the access well.
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CA 02592491 2007-05-29
The key to the migration of a microwave induced phase boundary to significant
radial
distances is the permittivity of dry rock and soil no longer containing water
or hydrocarbon.
Power attenuation in the dry rock or soil between the phase boundary and the
well, the region
where all of the hydrocarbons and water have been removed by heating, controls
the radial
distance that the phase boundary can migrate. In order to test the
permittivity of dry rock and
soils, a specially designed resonant cavity with a vector network analyzer and
newly developed
software capable of making accurate measurements down to er"/ er' < 10-5 were
used to measure
the permittivity on a variety of dry soil samples. Values of Cr, the real part
of the permittivity,
fall in the range of 2.6 + 0.1 and using very careful sample preparation,
including temperature
control, values for sr", the imaginary part of the permittivity, showed
repeatable minimum values
as low as 0.006 + 0.001. It is believed the best asymptotic values produced to
date lie near this
limit.
Using these permittivity values with the microwave frequency (f) and the speed
of light
(c ), it is possible to calculate the attenuation loss in the region of dry
soil or rock in the
microwave subsurface region using the following equation.
e " = 0.006
e = 2.6
f = 2.45 x10 911s
c = 2.997 x10 8m / s
\
2
a 2fe (e ¨1
2
_
a = 0.0955 1/m
CA 02592491 2007-05-29
Attenuation loss = 8.6855 d a
Attenuation loss (aDB) = 0.829 db/m
The power per unit area (Ps) flowing past the point z in the forward z-
direction can be estimated
using the following relationship:
Pz = Po 12"
where (Po) is the power per unit area flowing past the point z = 0, (a) is the
attenuation
coefficient, and (z) is the radial distance from the antenna. It is possible
to estimate the skin
depth, the distance at which the amplitude decreases to lie (37%) of its
initial strength.
It is assumed that electromagnetic waves are incident on the soil sample that
consists of
cm of dry soil and then wet soil. As shown in the following figure, microwave
power
penetrates the dry soil with negligible losses until it reaches the wet soil
where nearly all of the
power is absorbed in the first 10 cm of the wet soil which is the active
heating zone. The ability
15 to couple energy into a narrow area has several advantages including the
enhancement of the
rock's intrinsic permeability and the generation of steam.
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CA 02592491 2007-05-29
Power Attenuation with 20 cm of Dry Soil Followed by
Saturated Soil
1 - __________________________________________________________
sit 0.8 ___________________________________________
I 0.6 _____________________________________________
0.4 _______________________________________________
0.2 _______________________________________________
0 ______________
0 0.1 0.2 0.3 0.4 0.5 0.6
Radial Distance in meters
Once all of the water and hydrocarbons have been removed by microwave heating
in the
region between the antenna and the phase boundary, the power intensity can be
calculated as a
function of distance in the dry soil as illustrated in the following figure.
Power Attenuation in Dry Soil
1 _______________________________________________________
It 0.8 __
I 0.6 _________
0.4 ________________________
g 0.2 _____________________________________
0 _______________________________________________________
0 2 4 6 8 10
Radial Distance in meters
Nearly 15 percent of the power being radiated by the antenna is still
available to heat the
water and oil at 10 meters. With 2 megawatts of power radiating from the
subsurface antenna,
approximately 30 kilowatts of power is available for heating at this distance.
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CA 02592491 2007-05-29
Only the permittivity of dry soils comprised of aluminum silicates and quartz
were
measured in the laboratory, however, microwave heating of selected natural
minerals were
performed by McGill and Walkiewicz (1987) and are presented in the following
table.
Chemical Temp, Time,
Mineral composition oc min
Albite fgaAlSiOs 82 7.
Arizonite ' Fe203-3T102 290 10_
Chalcocite Cu2S 746 7_
Chalcopyrite CtsFes2 920 1_
Chromite FeCr20, 156 7.
Cinnabar HS 144 8.
Galena PbS 956 7.
Hematite Fe203 182 7.
Magnetite Fe30. 1,258 2.75
Marble CaCO3 74 4.25
IVIolybdenite MoS2 192 7_
Orpiment As2S3 92 4.6
Orthoclase KAISI308 67 7.
Pyrite FeS2 1,019 6.76
Pyrrhotite Fel ,S- 886 1.76
Quartz SiO2 79 7.
Sphalerite ZriS 87 7_
Tetrahedrite Cu 2StamS,3 151 7_
Zircon ZrSii0. 62 7.
191,4aximurri temperature obtained in the indicated time interval
It is possible to estimate the adsorption of microwave energy by comparing the
permittivity measurement with the results presented by McGill and Walkiewicz
(1987).
Aluminum silicates such as albite and orthoclase show only minor heating in a
microwave field
consistent with the low permittivity values measured by the resonant cavity
with the vector
network analyzer. Quartz also showed results that are consistent with the
published data and the
laboratory measurements. For oil reservoirs in limestone or marlstone, typical
of oil shale
deposits, marble while metamorphosed is a similar composition. Marble exhibits
limited
heating in a microwave field which is consistent with other geologic material.
The directionality of the microwave beam produced by the phase array antenna
and the
enhanced intrinsic permeability of the region between the phase boundary and
the well allow for
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CA 02592491 2007-05-29
specific targeting of hydrocarbon rich zones. The ability to target these
zones allows for the
efficient heating of subsurface hydrocarbon deposits while minimizing heat
loss to less desirable
subsurface units. Subsurface zones containing groundwater can be avoided
thereby minimizing
environmental impacts.
Stripper wells, defined as oil wells producing less than 10 barrels of oil per
day, are
limited in production due to low permeable formations surrounding the well.
Commonly, the
effective radius of the stripper well is limited to the radius of the well
itself (e.g. commonly a 6
inch diameter well). Hydrofracturing is commonly used in the gas and petroleum
industry to
increase the permeability of the formation surrounding the well. Fluid is
injected under high
pressure into the well to induce fracturing along existing weakness in the
rock such as bedding
planes or small fractures. Small ceramic balls or similar materials are also
injected to keep the
fracture open during the production phase of the well.
The microwave system has the advantage of fracturing the entire rock formation
surrounding a stripper well up to a radial distance of 10 meters. This "skin"
zone surrounding
the stripper well will exhibit an intrinsic permeability at least four orders
of magnitude greater
than the surrounding formation. Because of the rapid heating by the high power
microwave
system, extensive fracturing of lithofied rock can be expected to further
increase the intrinsic
permeability. Instead of oil flowing to an effective well radius of 6 inches,
microwaved wells
have an effective radius of up to ten meters. Modeling studies suggest that
oil production rates
from microwaved enhanced wells increase by over an order of magnitude.
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CA 02592491 2007-05-29
Vast oil shale and tar sand deposits located around the world contain more oil
than
proven reserves in conventional oil fields. Present technologies to extract
oil from these
resources involve surface retorts or innovative subsurface heaters presently
being tested by Shell
Oil in Colorado. Microwave heating provides an efficient and environmentally
sound method
for the extraction of oil from these deposits and has several significant
advantages both in costs,
timing, and environment impacts.
The follow figure assumes a power generation capacity of 4 MW using power
efficiency
rates ranging from 20 to 50 percent. Small losses will occur in the power
supply and the
waveguide, depending on depth. Klystron tubes proposed for the system are
rated at a 65 percent
efficiency. Therefore, for shallow extraction, less than 500 ft, the
efficiency of the total system
may be around 50 percent. Using the median value for specific heat of 1.3, the
result is the
production of approximately 300 barrels of kerogen per day from a single
production well in the
oil shale deposits. Similar production rates may be applicable to tar sand
deposits.
400 _____________________________________
1
350 __________________ ¨Specific Heat 1.1
¨ = Specific Heat 1.3
300 _________________ ¨ = Specific Heat 1.5
11 250 ________________________ ..===
===== ..=== =
200 -
150 _____________________________________
100 ______________________________________
50 _____________________________________
0 ______________________________________ -1
10 20 30 40 50 60
Percent Efficiency
CA 02592491 2007-05-29
Using the price of $60.00 per barrel of oil, with a 50 percent efficiency, and
the most cost
effective source of available power, the net result is that for every dollar
spent on energy to
power the microwave system an equivalent of approximately $6 of oil is
extracted from the
subsurface. This 6 to 1 ratio is double the ratio for current in-situ
processes presently being
tested in oil shale deposits. Further, the increased efficiency resulting from
using some of the
natural gas from a well to power the system is not included. In addition, oil
will be produced
almost immediately upon the application of microwave power to the subsurface
instead of the
three to four years required by other subsurface heating methods.
While the description above contains specificity, this should not be construed
as limiting
the scope of the invention; but merely as providing illustrations of the
presently preferred
embodiment of the invention. Although preferred embodiments and method for
extracting
subsurface hydrocarbons have been described above, the inventions are not
limited to the
specific embodiments, but rather the scope of the inventions are to be
determined as claimed.
21
