U.S. patent application number 12/240954 was filed with the patent office on 2009-10-01 for system and method for extraction of hydrocarbons by in-situ radio frequency heating of carbon bearing geological formations.
Invention is credited to Hsueh-Yuan Pao.
Application Number | 20090242196 12/240954 |
Document ID | / |
Family ID | 40512133 |
Filed Date | 2009-10-01 |
United States Patent
Application |
20090242196 |
Kind Code |
A1 |
Pao; Hsueh-Yuan |
October 1, 2009 |
SYSTEM AND METHOD FOR EXTRACTION OF HYDROCARBONS BY IN-SITU RADIO
FREQUENCY HEATING OF CARBON BEARING GEOLOGICAL FORMATIONS
Abstract
A method of producing liquid hydrocarbons from a
hydrocarbon-bearing rock in situ in a geological formation begins
with exploring the formation by drilling a plurality of boreholes
into the formation and taking core samples of the
hydrocarbon-bearing rock and at least one overburden layer.
Electrical parameters of the hydrocarbon-bearing rock and the
overburden layer are determined, as well as a roughness of a
boundary between the hydrocarbon-bearing rock and the at least one
overburden layer. These electrical parameters are used to construct
a computer model of a portion of the hydrocarbon-bearing rock and
at least one overburden layer, the computer model based upon
modeling the formation as a rough-walled waveguide. This computer
model is used to simulate propagation of radio frequency energy
within the hydrocarbon-bearing rock, including simulation of radio
frequency wave confinement within the hydrocarbon-bearing rock, at
several frequencies and temperatures. A frequency for retorting is
selected based upon simulation results. Radio frequency couplers
are installed into at least one borehole in the hydrocarbon-bearing
rock and driven with radio frequency energy to heat the
hydrocarbon-bearing rock. As the rock heats, it releases carbon
compounds and these are collected.
Inventors: |
Pao; Hsueh-Yuan; (San Jose,
CA) |
Correspondence
Address: |
LATHROP & GAGE LLP
4845 PEARL EAST CIRCLE, SUITE 201
BOULDER
CO
80301
US
|
Family ID: |
40512133 |
Appl. No.: |
12/240954 |
Filed: |
September 29, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60976314 |
Sep 28, 2007 |
|
|
|
Current U.S.
Class: |
166/248 ;
166/57 |
Current CPC
Class: |
E21B 43/2401
20130101 |
Class at
Publication: |
166/248 ;
166/57 |
International
Class: |
E21B 43/24 20060101
E21B043/24; E21B 36/00 20060101 E21B036/00; E21B 36/04 20060101
E21B036/04 |
Claims
1. A method of producing liquid hydrocarbons from a
hydrocarbon-bearing rock in situ in a geological formation
comprising: drilling a plurality of boreholes into the formation
and taking core samples of the hydrocarbon-bearing rock and at
least one overburden layer therefrom; determining electrical
parameters of the hydrocarbon-bearing rock and the overburden
layer; performing a seismic study to determine a roughness of a
boundary between the hydrocarbon-bearing rock and the at least one
overburden layer; constructing a computer model of electromagnetic
properties of a portion of the hydrocarbon-bearing rock and at
least one overburden layer, the computer model based upon modeling
the formation as a rough-walled waveguide; using the computer model
to simulate propagation of radio frequency energy within the
hydrocarbon-bearing rock, including simulation of radio frequency
wave confinement within the hydrocarbon-bearing rock, at a
plurality of frequencies; selecting a frequency of the plurality of
frequencies; placing a first radio frequency coupling apparatus
into at least one borehole in the hydrocarbon-bearing rock; driving
the first radio frequency coupling apparatus with radio frequency
energy to heat the hydrocarbon-bearing rock; and collecting carbon
compounds released from the rock.
2. The method of claim 1, wherein the hydrocarbon-bearing rock is
oil shale.
3. The method of claim 2, further comprising: electromagnetically
logging the boreholes to determine electrical parameters of the
hydrocarbon-bearing rock and the at least one overburden layer; and
wherein determining electrical parameters of the
hydrocarbon-bearing rock comprises analysis of data from the step
of electromagnetically logging and data from studies of core
samples at a plurality of temperatures to determine temperature
dependence of the electrical parameters.
4. The method of claim 1 further comprising determining electrical
characteristics of at least one underlying layer.
5. The method of claim 1 further comprising observing the formation
for changes in the electrical parameters of the hydrocarbon-bearing
rock, and when changes occur in the electrical parameters adjusting
a parameter selected from the group consisting of a phase shift
between two couplers, a frequency of the radio frequency energy, a
parameter of the impedance matching circuitry, and a dimension of
the radio frequency coupling apparatus in response thereto.
6. The method of claim 5 further comprising adjusting parameters of
the computer model to match the changed electrical parameters and
re-simulating to verify continued confinement of applied radio
frequency energy within the hydrocarbon-bearing rock.
7. The method of claim 1 wherein there is a second radio frequency
coupling apparatus in a second borehole in the hydrocarbon-bearing
rock, and wherein the radio frequency energy applied to the second
radio frequency coupling apparatus is applied at a phase offset
from a phase of the radio frequency energy applied to the first
radio frequency coupling apparatus; the phase offset determined to
direct radio frequency energy towards a production zone of the
hydrocarbon-bearing rock.
8. The method of claim 7, wherein the phase offset is also
determined to direct controlling wave direction to direct the radio
frequency energy away from a freeze wall.
9. The method of claim 1, wherein the first radio frequency
coupling apparatus comprises a first and a second dipole coupling
element, and wherein the first and the second dipole coupling
element are driven to produce a pattern of radiation into the
hydrocarbon-bearing rock that is vertically narrower than a pattern
produced by a dipole such that electromagnetic radiation strikes
the boundary between the hydrocarbon-bearing rock and the layer of
overburden primarily at an angle where it will be reflected back
into the formation.
10. The method of claim 1, wherein the first radio frequency
coupling apparatus comprises a radiator rod coupled to the center
conductor of a coaxial transmission line, and a plurality of radial
groundplane rods coupled to the outer conductor of the coaxial
transmission line.
11. A system for extracting marketable hydrocarbons from a
carboniferous formation covered by an overburden layer, comprising:
at least one radio frequency source; at least one coupler for
coupling radio frequency energy from the radio frequency source
into a heated zone of the carboniferous formation; wherein the
radio frequency source operates at a frequency chosen to provide
deep penetration of radio frequency energy into the carboniferous
formation and chosen such that a high percentage of radio frequency
energy striking a boundary between the carboniferous formation and
the overburden layer is reflected back into the carboniferous
formation.
12. The system of claim 11 wherein the frequency is further chosen
by: determining electrical properties of the carboniferous
formation at various temperatures; using the electrical properties
of the carboniferous formation in a cole-cole model of absorption
to model penetration of the radio frequency energy into the
carboniferous formation, and choosing the frequency such that
adequate penetration is obtained.
13. The system of claim 12, wherein the frequency is further chosen
by: determining electrical properties of the overburden layer;
using the electrical properties of the overburden layer and the
carboniferous formation in a model of a boundary of the overburden
layer and the carboniferous formation, the model of the boundary
modeling the boundary as a rough-walled waveguide and being used to
choose a frequency where a majority of radio frequency energy from
the carboniferous formation that strikes the boundary is reflected
back into the carboniferous formation.
14. The system of claim 11, wherein the coupler comprises a
plurality of groundplane rods driven radially outwards into a
boundary between the overburden layer and the carboniferous
formation, and a coupling rod.
15. The system of claim 11, wherein the coupler comprises a
colinear plurality of center-fed, half-wave, dipoles.
16. The system of claim 11, further comprising a freeze-wall
surrounding the heated zone of the carboniferous formation.
17. The system of claim 16, wherein there are a plurality of
couplers and wherein a first coupler of the plurality of couplers
is driven with radio frequency energy at a phase offset from a
second coupler of the plurality of couplers to direct radio
frequency energy into a heated zone and away from the freeze
wall.
18. The system of claim 11, further comprising means for
selectively allocating power from the RF source to a plurality of
discrete zones in the carboniferous formation.
Description
RELATED APPLICATIONS
[0001] The present application claims the benefit of priority to
Provisional Application Ser. No. 60/976,314 filed Sep. 28, 2007,
and is incorporated herein by reference.
FIELD
[0002] The present apparatus and method relates to the extraction
of hydrocarbons from hydrocarbon-bearing geological formations. In
particular, the method is applicable to extraction of hydrocarbons
from oil-shale and tar sands, and may also be useful in enhanced
oil recovery from oil fields.
BACKGROUND
Formations Bearing Low Motility Carbon Compounds
[0003] Many carbon and hydrocarbon-bearing geological formations
contain carbon-containing compounds that lack sufficient mobility
for tapping with simple wells. For example, oil-shales, tar sands,
hydrocarbon-bearing shale, and low-grade coal are carbon-bearing
sedimentary rocks containing carbon compounds that do not migrate
efficiently into wells for recovery under ordinary conditions.
[0004] Oil shale is a general term applied to a group of fine black
to dark brown shale rich enough in low motility or non-mobile
organic material (called kerogen) to yield petroleum-like oil upon
retorting. The kerogen in oil shale is converted to oil through
pyrolysis. During pyrolysis the oil shale is heated to temperatures
in the range 250-500.degree. C. in the absence of air. The kerogen
is converted to oil and separated out, a process called
"retorting".
Retorting
[0005] The kerogen in oil shale is converted to oil through
retorting. During retorting the oil shale is heated to temperatures
in the range 250-500.degree. C. in the absence of air. Some
volatile components of the kerogen may evaporate or liquify and can
be recovered. Other components of the kerogen may pyrolize into
shorter chain hydrocarbons that can then also be recovered from the
shale. The net effect is that retorting converts some or all of the
kerogen to oil that is then separated out. Additionally, residual
carbon compounds in hot rock, including oil shale, coal, or coke,
can react with water and/or hydrogen to produce recoverable gasses
and hydrocarbons in reactions akin to those that occur during
liquefaction of coal.
[0006] Extracting kerogen from carbon-bearing sedimentary rock in
such formations has been accomplished by mining the rock. Once the
rock is mined, it may be retorted using temperatures at the higher
end of the range in a retort to extract hydrocarbons; alternatively
the kerogen in some such rocks can be burned directly in a furnace.
Spent rock must then be disposed of. This process of mining and
surface retorting is also known as "ex-situ retorting". Ex-situ
retorting is widely recognized as posing considerable environmental
problems due to the surface disturbance involved with mining and
disposal of spent rock; it also requires much labor and heavy
machinery.
[0007] Some companies have experimented with "in-situ retorting."
This process extracts carbon compounds by heating carbon-containing
rock while it is essentially intact and still in place in a
formation. In-situ retorting offers potential advantages in that
labor and machinery required, as well as environmental damage
associated with mining and spent rock disposal, are all potentially
reduced.
[0008] Other companies have experimented with "modified in-situ
retorting" wherein a portion of rock is mined to create voids in
the formation, the mined rock being subjected to ex-situ retorting.
In modified in-situ retorting, rock remaining in the formation
after mining is rubbleized into the voids, the un-mined rubble is
then heated to extract carbon compounds.
[0009] In-situ and modified in-situ retorting experiments have not
been wholly successful.
Deposits
[0010] Thousands of acres of oil-shale deposits having deposit
thickness from 500 to 2000 feet covered by from 500 to 1000 feet of
overburden, exist in the Green River formation of Colorado, Utah,
and Wyoming. In some places these deposits rise to the surface. The
Green River deposits contain carbon compounds in kerogen form,
yielding from 15 to over 50 gallons of hydrocarbons per ton when
assayed through mining and surface retorting.
[0011] The Green River deposits, together with other sedimentary
rock deposits bearing low-motility carbon compounds worldwide,
including large oil shale deposits in Canada, and some deposits in
other countries, represent a substantial reserve of carbon
compounds. Mining and surface retorting of these deposits has many
potential environmental consequences, risks, and costs. It is
desirable to find a way to efficiently extract carbon compounds
from these carbon-bearing rocks that does not require mining.
Shell's In-Situ Retorting Process
[0012] U.S. Pat. No. 7,225,866 to Berchenko, et al., hereinafter
Berchenko, assigned to Shell oil, discloses, in 320 pages
incorporated herein by reference, methods of increasing the
motility of carbon compounds in some oil shale formations by
heating the formation in place using electrical resistance-heated
heating wells. As the formation's temperature increases, some
carbon compounds in the formation are retorted, mobilizing through
a effects including the decrease in viscosity of hydrocarbons with
increased temperature, melting of some solids, vaporization of
volatile compounds, as well as decomposition into lighter molecular
weight, more mobile, compounds through anhydrous and hydrous
pyrolysis--this high temperature process in rock still in place in
the formation is known as in-situ retorting. Berchenko then taps
the mobilized compounds as liquid and gas with production wells
separate from those through which heat is applied to the formation.
The method of Berchenko may require that from seven to more than
twenty times as many heating wells as production wells be drilled
into the formation. (Berchenko, claims 1, 8, 14, and 16)
[0013] In a Shell Oil embodiment, a freeze wall is constructed to
seal off groundwater by drilling 2000' wells, eight feet apart,
around the perimeter of a 10 acre working zone, and then
circulating a super-chilled liquid into those holes to freeze the
ground to -60.degree. F. The working zone is then largely dewatered
to control humidity and avoid excess steam production during
retorting. Recovery wells are drilled on 40 foot spacing within the
working zone.
[0014] A large number of helical heating wells, from 7 to 20 or
more times as many heating wells as production wells, are drilled
in a pattern around the production wells. When 7 times as many
heating wells as production wells are used, Berchenko discloses
these heating wells as about eight to fifteen meters from the
production wells. An electrical heating element is lowered into
each heating well and allowed to heat the kerogen to 650 (aprox
340.degree. C.) to 700.degree. F. (aprox 370.degree. C.) over a
period of one to four years, slowly converting it into oils and
gases, which are then pumped to the surface. Once the formation is
well heated, Berchenko also discloses a possibility of injecting
oxidizer into heating wells to further heat the formation by
combustion in place.
[0015] The in-situ method of Berchenko requires close to 100%
surface disturbance, greatly increasing the footprint of extraction
operations in comparison to conventional oil and gas drilling, in
part because of the large number and close spacing of freeze-wall,
heating, and production wells required.
[0016] Berchenko also summarizes other techniques that have been
proposed, and in some cases tried, for in-situ and modified in-situ
retorting of oil shale formations. These methods range from heating
of formations by combustion through injection of oxygen-rich gas
into heating wells to detonating nuclear weapons within the
formation.
Heavy Oil and Tar Sands
[0017] Heavy oil and oil sands occur world-wide, but the two
largest known deposits are the Athabasca Tar Sands in Alberta,
Canada and the Orinoco extra heavy oil deposit in Venezuela. Some
tar sand deposits exist in the United States. Much deep off-shore
oil is heavy oil as well. The bitumenous hydrocarbon content of
these deposits is relatively immobile under ordinary conditions,
such that primary recovery is slow and may yield less than eight
percent of the hydrocarbon content of the rock. Such oil is
sometimes recovered with cyclic steam stimulation or steam assisted
gravity drainage, both techniques involving use of steam to heat a
formation to encourage flow of heavy oil.
Enhanced Oil Recovery (EOR)
[0018] Typically only 20-30 percent of a reservoir's original crude
oil content can be pumped out of the sand through simple drilling,
this is primary recovery. Secondary recovery, typically involving
injecting water under pressure, yields another 10-20 percent;
however, this water can present a significant waste disposal
problem as the water may be pumped out of the well with the oil.
Tertiary recovery may also be used, often involving liquid carbon
dioxide injected under pressure; this acts as a solvent, reducing
the oil's viscosity and allowing a little more recovery.
[0019] EOR is a generic term for techniques, including secondary
and tertiary recovery, for increasing the amount of oil that can be
extracted from an oil field. Using EOR, 30-60%, or more, of the
reservoir's original oil may be recovered.
[0020] Gas injection is a commonly used EOR technique. Here, gas
such as carbon dioxide (CO.sub.2), natural gas, or nitrogen is
injected into the reservoir whereupon it expands and thereby pushes
additional oil to a production well-bore, and moreover the gas
dissolves in the oil to lower its viscosity and improves the flow
rate of the oil. Oil displacement by CO.sub.2 injection relies on
the phase behavior of CO.sub.2 and crude oil mixtures that are
strongly dependent on reservoir temperature, pressure and crude oil
composition. These mechanisms range from oil swelling and viscosity
reduction for injection of immiscible fluids (at low pressures) to
completely miscible displacement in high-pressure applications. In
these applications, more than half and up to two-thirds of the
injected CO.sub.2 returns with the produced oil and may be
re-injected into the reservoir. The remainder is trapped in the oil
reservoir by various means.
[0021] Other techniques for EOR include thermal recovery (where
heat reduces viscosity of hydrocarbons in the formation to improve
flow rates), and chemical injection, where polymers and/or
detergent-like surfactants are injected to help lower the surface
tension that often prevents oil droplets from moving through a
reservoir, thereby increasing effectiveness of water floods.
[0022] EOR techniques, including thermal recovery and gas
injection, can benefit from the controlled application of heat to
the reservoir.
Volumetric Heating of Carbon-Containing Formations by Radio
Waves
[0023] The concept of volumetric heating by radio waves (radio
frequency processing) of oil shale was developed by Illinois
Institute of Technology and Raytheon in the late 1970s. The concept
was to heat modest volumes of shale over a period of time using
vertical electrode arrays driven by high-power radio-frequency AC
sources. The radio-frequency energy is expected to propagate into
and through the formation, where much of it will be absorbed by the
formation--resulting in heating of the formation.
[0024] U.S. Pat. Nos. 4,135,579, 4,140,179, 4,196,329, 4,301,865,
4,320,801, 4,457,365, 4,485,869, 4,487,257, 4,508,168, and
4,583,589, disclose this concept of using a variety of electrode
and radiator assemblies. Of these, U.S. Pat. Nos. 4,508,168,
4,583,589, and 4,457,365, assigned to Raytheon, describe combined
production well and coaxially-fed radiator assemblies, that provide
better vertical control of radiation than experimental predecessors
(background U.S. Pat. Nos. 4,508,168, 4,583,589). U.S. Pat. No.
4,135,579, also assigned to Raytheon, describes heating of
formation rock by conducting radio frequency currents between two
or more electrodes inserted into a formation. U.S. Pat. No.
4,140,179, assigned to Raytheon, describes use of a pattern of
radiator wells and production wells, where substantial heating is
reported at distances of over 25 feet from the radiator wells once
water is driven from the formation.
[0025] The Raytheon and Illinois Institute studies have shown that
the dielectric constant and absorption, hence the impedance, of
formations change as they are heated and substances like water are
expelled from them. This effect also results in changes to the
wavelength of electromagnetic radiation in the formation. Further,
typically a length of radiator that is of length 1/6 to 1/7
wavelength in air is approximately half a wavelength in a
formation.
Rough Wall Waveguides
[0026] A named inventor has published an article on modeling
rough-walled waveguides; although the article assumed perfect
conductors for side plates of the waveguide. This article is
entitled "Probability-density function for total fields in a
straight PEC (perfect electrical conductor) rough-wall tunnel,"
Hsueh-Yuan Pao, Microwave and Optical Letters, vol 46 issue 2, pp
128-132, 26 May 2005; the contents of which are incorporated herein
by reference, and known hereinafter as "The Pao Rough-Wall
article."
[0027] Another article on computer modeling lossy rough-walled
waveguides has been published as "Full Wave Analysis of RF Signal
Attenuation in a Lossy Rough Surface Cave using a High Order Time
Domain Vector Finite Element Method," J. Pingenot, et. al, Progress
in Electromagnetics Research (PIERS) 2006, presented Mar. 26
through Mar. 29, 2005, Lawrence Livermore Laboratory document UCRL
Proc 216990 dated 10 Nov. 2005, the contents of which are
incorporated herein by reference, and hereinafter known as "The
Pingenot Lossy Rough Surface Cave article".
<http://www3.interscience.wiley.com/cgi-bin/abstract/110503149/ABSTRAC-
T?CRETRY=1&SRETRY=0>
Waveguides Applied to In-Situ Retorting
[0028] Burnham, "Slow Radio Frequency Processing of Large Oil-Shale
Volumes to Produce Petroleum-Like Shale-Oil", Lawrence Livermore
Laboratory publication UCRL ID 155045, describes an IIT Research
Institute proposal to place three rows each having numerous
vertical, closely-spaced, conductors into holes drilled into a
formation, this is further described in U.S. Pat. No.
4,485,869.
[0029] The conductors in each row are tied together to form what
becomes effectively three large, parallel, plates, serving as an
artificial "tri-plate waveguide" enclosing a volume of rock. The
enclosed volume of rock is then heated by RF energy coupled into
this artificial waveguide structure. Burnham, in his FIG. 2, also
describes a horizontal variation of this proposal, where artificial
conductors are placed into closely-spaced horizontal holes drilled
into the formation on three levels; the conductors on each of the
three levels being connected together to form a plate of a
horizontal tri-plate waveguide.
SUMMARY
[0030] A method of producing liquid hydrocarbons from a
hydrocarbon-bearing rock in situ in a geological formation begins
with exploring the formation by drilling a plurality of boreholes
into the formation and taking core samples of the
hydrocarbon-bearing rock and at least one overburden layer.
Electrical parameters of the hydrocarbon-bearing rock and the
overburden layer are determined, as well as a roughness of a
boundary between the hydrocarbon-bearing rock and the at least one
overburden layer. These electrical parameters are used to construct
a computer model of a portion of the hydrocarbon-bearing rock and
at least one overburden layer, the computer model based upon
modeling the formation as a rough-walled waveguide. This computer
model is used to simulate propagation of radio frequency energy
within the hydrocarbon-bearing rock, including simulation of radio
frequency wave confinement within the hydrocarbon-bearing rock, at
several frequencies and temperatures. A frequency for retorting is
selected based upon simulation results. Radio frequency couplers
are installed into at least one borehole in the hydrocarbon-bearing
rock and driven with radio frequency energy to heat the
hydrocarbon-bearing rock. As the rock heats, it releases carbon
compounds and these are collected.
BRIEF DESCRIPTION OF THE FIGURES
[0031] FIG. 1, a cross section illustrating a formation with
overburden and underlying formations.
[0032] FIG. 2, an illustration of measured electrical parameters of
rock.
[0033] FIG. 3, a flowchart of a method of producing shale oil by
in-situ retorting.
[0034] FIG. 4, frequency response of imaginary part of permitivity
in Cole-Cole model
[0035] FIG. 5, an example of a Cole-Cole diagram.
[0036] FIG. 6 is a top view of a production field.
[0037] FIG. 7 is a cross section of a production field.
[0038] FIG. 8 is a schematic diagram of an embodiment of a coupler
for applying radio frequency energy to a hydrocarbon-bearing
formation.
[0039] FIG. 9 is a schematic diagram of an alternate embodiment of
a coupler for applying radio frequency energy to a
hydrocarbon-bearing formation.
[0040] FIG. 10 is a schematic diagram of a system that applies
power selectively to subunits of the carboniferous formation, each
acting as a discrete waverguide.
[0041] FIG. 11 is a schematic diagram of an alternate embodiment of
a coupler for applying radio frequency energy to a
hydrocarbon-bearing formation.
[0042] FIG. 12 is a schematic diagram of a system that applies
power selectively to subunits of the carboniferous formation, each
acting as a discrete waverguide, and repeats this for a second
carboniferous formation.
DETAILED DESCRIPTION OF THE EMBODIMENTS
RF Properties of Oil and Rock
Conductive Rock
[0043] Generally, overburden and underlying rock layers tend to
have larger water content than hydrocarbon-bearing formations do.
Since water, especially salty water, tends to have greater
conductivity than dielectric rock, these formations are for
purposes of this document often classifiable as conductive
rock.
Dielectric Rock
[0044] Dielectric rock is rock that is a less conductive media than
is conductive rock. This is often because presence of large amounts
of nonpolar organic compounds tends t exclude conductive water from
the formation.
Boundaries
[0045] Reflection and leakage takes place as a RF wave propagates
across at the interface from one medium to another medium if the
media differ in electrical properties. The different electrical
properties of the media are distinguished by the constitutive
parameters permittivity .di-elect cons., permeability .mu., and
conductivity .sigma..
[0046] For the most dielectric media, permittivity is the
significant parameter to describe the energy reflection and
transmission at the interfaces. Therefore we can ignore the
permeability and conductivity for most dielectric media. To confine
radio frequency energy inside of a conductive medium, we want
leakage from the formation minimized, while maximizing energy
reflections from interfaces back into the conductive media.
[0047] Hydrocarbon-bearing earth formations occur because of a
unique set of geologic conditions, therefore underlying and
overlying rock formations surrounding the hydrocarbon-bearing earth
formations were formed under different conditions and have
different characteristics than the hydrocarbon-bearing
formation.
[0048] Reflection and leakage are also be affected by
characteristics of the interfaces themselves, including a degree of
roughness of the interface
[0049] Rock's electrical properties vary with frequency as well as
the constituent properties of the rock. In some rock formations,
there may not be a significant difference in the electrical
properties between the hydrocarbon-bearing earth formations and the
surrounding formations; at other frequencies, the difference can be
much larger. Further, as published in the aforementioned Raytheon
patents, some electrical properties of rock can be expected to
change as the rock is heated, in part because water may be driven
out of the rock.
Analyzing the Formation
[0050] FIG. 1 illustrates a cross section of an oil-shale field.
FIG. 3 is a flow chart of a method for developing an oil-shale
field. FIG. 2 is taken from Sternberg and Levitskaya, 2001,
Electrical parameters of soils in the frequency range from 1 kHz to
1 GHz, Radio Science, Vol. 36, No. 4, Pages 709-719; It presents
the relative permittivity measured from Avra Valley, Ariz., and
represents typical soil and rock electric properties. This Figure
shows the wide range of electrical properties that occur in typical
soils and rocks.
[0051] With reference to FIGS. 1 and 3, The field may be mapped
initially with a seismic study 202 or use of other well known
petrophysical mapping tools (not shown) that are known in the art,
such as the interpretation of logs or gravimetric studies. In
seismic studies, sound wave vibrations are propagated into the
ground, as these strike impedance mismatches associated with
various interfaces between layers, such as interfaces between
overburden layers 102, 104, 106, the oil shale hydrocarbon-bearing
formation 108, and underlying layers 110, some sound is reflected.
Seismic studies can provide information about the depth of various
interfaces, and hence the layers, as well as an indication of
roughness of the interfaces.
[0052] Wells may be drilled 204. Electrical properties, including
permittivity .di-elect cons., permeability .mu., and conductivity
.sigma., of rock surrounding the well may be measured with
electromagnetic well logging 206 as known in the art, and core
samples 208 may be taken from each formation drilled through,
including particularly core samples from the lowest layer of
overburden 106, the hydrocarbon-bearing formation 108, and
uppermost underlying layers 110. From these samples, assays for
potential yield may be performed and the hydrocarbon-bearing
formation positively identified 210.
[0053] Since the electrical properties measured with logging
represent properties as they currently exist in the formation, and
these are known to change with temperature, electrical properties
of core samples are determined 212 both under room conditions and
as these samples are heated.
[0054] Since properties, including permittivity .di-elect cons.,
permeability .mu., and conductivity .sigma., may vary with
frequency as well as temperature, these parameters are measured at
a variety of frequencies.
[0055] Simulations of the field distribution between
hydrocarbon-bearing earth formations and surrounding rock have been
performed for some possible sets of electrical parameters of these
layers. The typical results for the rock surrounding the
hydrocarbon-bearing earth formations is in the 20% of field
strength, while 80% of field strength remains inside of
hydrocarbon-bearing earth formations. It is clear that the field
strength in the surrounding rock is much smaller than inside of the
oil shale. With this electrical difference between the layers, a
quasi guide wave structure is in place.
[0056] The bigger the permittivity contrast between layers, the
stronger the reflection will take place at the interface for the
dielectric rock. However this contrast will vary with frequency and
may be absent at some frequencies and temperatures because the
earth's electrical properties vary with frequency.
Cole-Cole Parameters
[0057] In order to predict how far electro-magnetic radiation will
penetrate into the formation, and predict where heating will take
place, simulations using the Cole-Cole model are used. This
requires that Cole-Cole model parameters be determined from
properties of the hydrocarbon-bearing rock formation.
[0058] The sum of the real and imaginary parts of the dielectric
permittivity represents all of the energy in the system on a per
cycle basis. At low frequencies, all the energy is asymptotically
going into storage. At the frequency of maximum movement, some
energy is going into storage but most is lost to dissipation. At
the highest frequencies, all the energy is asymptotically going
into storage, but the total is smaller as shorter distances of
charge separations occur compared to the low frequency limit.
[0059] The frequency of maximum movement defines the time constant
of the system. These systems are over damped harmonic oscillators,
also known as diffusion-limited relaxation processes. The general
form of the model that describes the frequency dependence of such
systems is the Debye-pellat relaxation equation:
' - '' = .infin. + s - .infin. 1 + .omega. .tau. ##EQU00001##
where .di-elect cons.' is the real part of the dielectric
permittivity, .di-elect cons.'' is the imaginary part of the
dielectric permittivity, .di-elect cons..sub..infin. as is the high
frequency limiting value of the permittivity, .di-elect cons..sub.s
is the low frequency limiting value of the permittivity, .omega. is
radian frequency, and .tau. is the relaxation time constant. The
frequency of maximum movement and loss occurs at f=l/.tau.. The
time constant often describes the size of something such as grain
or pore sizes that is limiting the motion of the charge which is
other than the field disequilibrium.
[0060] In general, single relaxations are rarely observed in
natural systems. Instead, there are distributions of relaxations
corresponding to distributions of size scales that influence
movement of charge. There are several equations describing such
distributed systems, with the most common experimental observations
in agreement with the model from Cole and Cole:
' - '' = .infin. + s - .infin. 1 + ( .omega. .tau. ) .alpha.
##EQU00002##
where .alpha. describes the breath of the time constant
distribution. Multiple Cole-Cole equations may be summed to
describe a series of different polarization process. These
processes typically vary considerably with environmental influences
such as temperature, pressure, and chemistry.
[0061] FIG. 4 shows a typical frequency response of imaginary part
of the permittivity .di-elect cons.'' of Cole-Cole model plot,
which represents the dielectric loss of the media. It is clear that
there is a maximum about 120 MHz. The maximum loss, which is
associated with the maximum RF energy absorption, takes place at
that frequency.
[0062] Using the Cole-Cole model facilitates finding the optimal
heating frequency. The Cole-Cole parameters are usually determined
experimentally. One can use standard numerical data fitting
algorithms to find the parameters. When plotted on a real-imaginary
plot, the arc center, radius, and end points can be directly
related to these parameters. Wideband data are needed to uniquely
determine the parameters, i.e. a significant part of the arc must
be displayed on the real/imaginary plot. Sternberg and Levitskaya
described how to use graphical method to determine the Cole-Cole
model from the measured data, and how to obtain these data
experimentally (B. K. Sternberg and T. M. Levitskaya, Electrical
parameters of soils in the frequency range from 1 kHz to 1 GHz,
using lumped-circuit methods, Radio Science, July/August 2001, pp
709-719). FIG. 5 shows a typical Cole-Cole diagram.
[0063] Specific samples of the hydrocarbon-bearing earth formations
that we are interested in must be measured to determine 212 the
Cole-Cole parameters for that rock material at normal and elevated
temperatures.
[0064] Since the relaxation time .tau. of the hydrocarbon earth
formation and the overburden (top) and bottom (underlying) rock
layers are different, the relaxation frequency for maximum thermal
conversion in the hydrocarbon earth formation is different within
each of the carboniferous, top, and bottom layers. It is this
difference that results in the large contrast in the permittivities
between the hydrocarbon earth formation and top and bottom rock
layers. This constructs a natural waveguide structure that can
confine the bulk of electromagnetic energy inside
hydrocarbon-bearing earth formations by reflecting energy back into
the formation when energy strikes a boundary with overburden or
underlying layers.
Non-Linear Operation Means Both Conductive Heating and Dielectric
Heating Exist
[0065] Since the applied RF power is extremely high, the non-linear
phenomenon will take place. In addition to the dielectric heating,
the conducting heating will take place in this scenario. There is
usually little free charge in dielectric media--where most charges
are bound in the molecules or atoms. However, the bound charges
will escape from molecules or atoms, as they absorb enough energy,
if the applied external RF power is extremely high. We attribute
this free charge flow, which ultimately forms the conductive
current, to the non-linear effect. The conductive current will
cause the conductive loss. It is this conductive loss that converts
the addition RF energy into thermal energy.
Modeling the Formation and Determining Frequency
[0066] A model of the formation, including the interfaces with the
lowest layer of overburden and the highest underlying layer is then
constructed 214. The model includes Cole-Cole parameters to
determine absorption, thus indicating a range of RF energy
penetration into the formation. The model further includes a model
of the formation as a natural, in situ, waveguide incorporating
into the model layer constitutive parameters permittivity .di-elect
cons., permeability .mu., and conductivity .sigma. and a model of
surface roughness for each boundary between layers; this model is
used for modeling reflections at the boundaries between the
carboniferous formation 108, the lowest layer of overburden 106,
and the highest layer of underlying rock 110. This lossy waveguide
model is based upon those presented in the "The Pingenot Lossy
Rough Surface Cave article" and "The Pao Rough-Wall article."
[0067] Simulations are performed 216 on this model to determine an
optimum frequency at which most RF energy coupled into the
formation will be confined to the carboniferous formation 108,
while providing desired penetration of RF energy into the
formation.
[0068] An optimum operational frequency is then selected 216. We
expect that the operational frequency will be different for every
field, but within the range of 0.5 MHz to 500 MHz, this range of
frequencies is hereinafter known as radio frequencies.
[0069] It is known that electromagnetic energy may reflect when
striking some boundaries at certain angles of incidence, while it
will penetrate the boundary when striking at different angles of
incidence. These angles are determined from the simulations
216.
Freeze Wall
[0070] Refer now to FIG. 6, which gives a top view of a portion of
production field 600, FIG. 7 which gives a cross section of a
production field, as well as FIG. 2. The water table varies in
depth, sometimes dramatically, throughout the western United
States. Excessive water entering the carboniferous formation is
undesirable since it can require large amounts of energy to boil
this water. While in some areas it may be possible to avoid
excessive water incursion without a freeze-wall 605 of frozen
ground, in other locations a freeze-wall may be needed to limit the
amount of water that enters a production zone during the lengthy
retorting process. Need for a freeze wall is determined 222 based
in part upon hydrology of the location and on depths of the
hydrocarbon-bearing rock; a freeze wall is likely needed if the
hydrocarbon-bearing formation is below the water table.
[0071] If a freeze-wall is needed, rows of wells 602 are drilled
and chilled by a freezer 603 to create 224 a freeze-wall 605 in
manner similar to that described by Berchenko.
Inserting Probes to Excite the Formation
[0072] Coupler probes 620, 622 are inserted 226 through wells 604
into the carboniferous formation 108 in order to couple
electromagnetic energy into the formation. More than one primary
coupler probe 620 in wells 604 may be used, since additional probes
driven with appropriate phase may give good control of a pattern of
heating in the formation 108. Where simulation of boundaries
between carboniferous formation 108, lowest overburden 106, and
underlying formations 110 showed large angle of incidence where
energy is reflected back into the carboniferous formation 108,
these coupler probes may be simple quarter-wave rod or half-wave
dipole couplers placed 226 in vertical well bores.
[0073] Where the layer of lowest overburden 106 is not sufficiently
conductive to serve as a groundplane for a quarter-wave rod
coupler, a coupler as illustrated in FIG. 8 may be used to help
minimize shield currents in the coaxial transmission line and
thereby minimize heating of the overburden. A radio-frequency
source 702 drives a coaxial transmission line 706 through impedance
matching apparatus 704. At the boundary between the lowest layer of
overburden 106 and the carboniferous formation 108, the coaxial
transmission line 706 terminates in a coupler 708 that may
incorporate matching circuitry. At this coupler 708, at least four
ground-plane rods 710 are driven radially into the rock outward
from the borehole, these should be at least electrically one fourth
wavelength long and are electrically coupled to the shield of the
coaxial transmission line 706. At this coupler 708 a coupling rod
712, electrically coupled either directly or through a matching
transformer to the center conductor of the coaxial transmission
line, is driven into the carboniferous formation 108.
[0074] Where simulations show that a shallow angle of incidence is
required for most of the radio frequency energy to be reflected
back into the carboniferous formation 108, couplers each having a
colinear array of two or more dipole elements, such as that of FIG.
9, and capable of improved vertical directivity may be placed 226
in similar vertical wells 604. Each dipole element, such as dipole
element 802 and 804, may be fed through an appropriate
balanced-to-unbalanced (balun) matching transformer 806, as known
in the art of antennas, in turn driven through coaxial transmission
lines 810 from a high-power radio frequency source 812 through a
matching circuit 814 located on the surface. In this embodiment, a
phase of one dipole element, such as dipole element 804, may be
adjusted by a phase shift device 816 to more precisely control and
adjust a pattern of radio frequency energy propagating into the
carboniferous formation. The phase shift device may be as simple as
a short length of transmission line.
[0075] A single vertical coupler will introduce electromagnetic
fields that will radiate in all directions in the horizontal plane
in the formation. Where directivity in the horizontal plane is
desired, as for example to protect a freeze wall 605 from being
melted by applied RF energy, additional protective couplers, or
protective probes 622, may be placed 228 in additional vertical
wells 606 spaced near half a wavelength of the selected frequency
in the carboniferous formation 108, and driven with appropriately
phased signals 230, such that almost of the radio frequency energy
propagates in a preferred direction through the formation 108 into
a heated zone 120 of the carboniferous formation that will become a
production zone when retorting temperatures are reached, and that
little radio frequency energy propagates in other directions in the
formation.
[0076] As each coupler is lowered into position, return losses at
the selected frequency are measured, and adjustments are made to
the couplers, balun transformers, and above-ground
impedance-matching circuitry as necessary.
Retorting the Formation In Situ
[0077] Once the probes and associated protective probes have been
inserted, raising the temperature of the formation may begin. Radio
frequency energy is applied 230 from RF sources 607 to the
formation 108 through the probes in driven 604 and protective wells
606 and appropriate, adjustable, impedance-matching circuitry. This
energy need not be applied continuously, since the formation has
sufficient heat capacity to integrate it; this permits use of
lower-cost nighttime power. Sufficient energy is applied over a
period of time to raise the formation 108 to retorting
temperatures.
[0078] Since electrical characteristics of the formation 108 will
change as water is driven out and temperature rises, impedance
mismatches and standing wave ratios at the radio frequency sources,
and standing wave ratios in the coaxial transmission lines, as well
as heating of the formation 108 and penetration of the radio
frequency power through the formation 108 are monitored 234 every
twelve to forty-eight hours, or another time interval as may be
useful to facilitate the conduct of operation.
[0079] When necessary, radio frequency power frequencies and/or the
probe structure may be adjusted 234. Lengths of coupler elements
changed, turns ratios in balun transformers altered, or adjustments
made to parameters of the impedance-matching circuitry to maintain
good coupling of radio frequency power into the formation.
[0080] Producing the Products
[0081] As the formation heats to, and is maintained at, retorting
temperatures in the 250 to 400.degree. C. range, liquid and gaseous
products will begin to accumulate and can be removed either through
separate production wells 608, or through inserting production
equipment in the driven 604 and protective 606 wells along with the
couplers. The resultant liquids and gasses may be produced 238 by
conventional wells, as are known in the art. Interference of
production wells and production equipment with the radio frequency
fields in the formation 108 may be prevented by using nonconductive
materials or by segmenting metallic materials such as pipe into
non-resonant lengths with insulated bushings between. Since there
will be a tendency for rock near the driven wells 604 to heat
somewhat faster than rock elsewhere in the field 600, an early
production well 610 may be installed near them. Fluids and gasses
from production wells 608, 610, are piped to collection and
condensing equipment for handling the expected liquid, vapor, and
gaseous products.
[0082] It is anticipated that driven 604 wells will occur in
clusters to permit directional control of the radio frequency
fields in the formation 108, and that clusters may be spaced as far
as 100 meters apart.
[0083] Some products removed from the formation 108 as vapor,
including many hydrocarbons in the gasoline range, may be condensed
into liquid form at the surface. Many liquids and condensable
vapors, as well as noncondensible gasses, may be transported to
market for sale, while some may be consumed on-site to provide
power for the radio-frequency sources and to maintain the
freeze-wall, if a freeze-wall is needed.
Heavy Oil Extraction and Upgrade
[0084] The technology presented above is able to heat a formation
to lower the viscosity of hydrocarbons, separate unwanted elements
or compositions within a hydrocarbon bearing deposit, and extract
the desirable hydrocarbons. I this regard, there is no need to
release materials that are trapped or bound in shales. The
instrumentalities described herein may be used in porous reservoirs
of sandstone, heavy oil sands, dolomite, limestone, silt, chalk,
etc. to replace or complement steam flooding in the reduction of
viscosity to accelerate production rates. In some instances, such
as the Athabasca Tar Sands, these materials may now be retorted in
situ, such that the need for mining is lessened or eliminated.
[0085] For heavy oil or tar sand recovery applications, radio
frequency heating to a temperature above 150.degree. C. but not
higher than 200.degree. C., using methodology as described above
but without need of a freeze-wall, is used to reduce the viscosity
of the in-situ tars or heavy oils. The invention presented can
perform some enhanced oil recovery alone; or it can use with other
existing EOR technologies to achieve the more efficient recovery
rates.
[0086] Partially or completely pyrolyzing the tars or heavy oil
in-situ, by maintaining the formation at elevated temperatures for
extended times, could upgrade the hydrocarbon products cost
effectively and environment friendly. RF energy is applied as above
described to heat a relatively large block of tar sands or heavy
oil in-situ. As the temperature of the tar sands or heavy oil
increases above 100.degree. C., the inherent moisture begins to
change into steam. A further increase in temperature to around
150.degree. C. substantially reduces the viscosity of in-situ tar
sands or heavy oils. As the pyrolysis temperature in the 200 to
300.degree. C. range is approached, the higher volatiles are
emitted until complete pyrolysis of the in-situ fuels is
accomplished.
Extract the Crude from Deep Offshore
[0087] The invention presented in previous sections also applies to
the extraction of heavy crude oils from deep offshore.
Enhance the Recovery Oil from Stripper Wells
[0088] The technologies presented in previous sections apply to
enhance recovery oil from partially depleted petroleum reservoirs.
Usually there is still 80% remaining organic products in the
partially depleted petroleum reservoirs. High viscosity and low
permeability of rock lower recovery rate below the economic
threshold set by the petroleum industry. Employing our technology
to heat the formation, used along with other enhanced recovery
technology, allows recovering remaining organic products from these
partially depleted petroleum reservoirs.
Selective Emitter Design
[0089] FIG. 10 an emitter array 1100 positioned a borehole 1102
through carboniferous formation 108. The array 1100 is formed using
individual emitter elements 1104, 1106, 1108, 1110 that are
separated by isolation elements 1112, 1114, 1116, 1118. By way of
example, the emitter elements 1104, 1106, 1108, 1110 may be made of
metal, and the isolation elements of a high strength ceramic
material having a high dielectric constant. The respective emitter
elements and isolation elements may use threaded pin and box
couplings as are used on drill pipe, except the isolation elements
form a nonconductive barrier between the emitter elements. An
external dielectric coating 1119 may isolate the emitter elements
1104, 1106, 1108, 1110 from one another and from conductive fluids
in borehole 1102 along the entire length of the emitter array 1100
or selected portions thereof.
[0090] Cable bundle 1120 contains a plurality of transmission lines
810, such that the respective dipole elements of FIG. 9 are coupled
to drive a corresponding conductor rods coupler similar to that of
FIG. 9, but set up in a series configuration. Each dipole element
802, 804, etc. . . . are coupled to drive a corresponding one of
the emitter elements 1104, 1106, 1108, 1110. By way of example,
dipole element 802 by be configured to drive emitter element 1104.
Dipole element 804 may be coupled to drive emitter element 1106.
Additional dipole elements (not shown) may be provided to drive the
remaining emitter elements. Balun 806 may be located within emitter
element 1106. The multi-emitter design is useful because producing
formations are most often not homogenous. Thus, carboniferous
formation 108 may be formed of discrete subunits 108A, 108B, 108C,
108D. Each subunit may be separated from other subunits by
waveguide boundaries, such as boundaries 1122, 1124, These
boundaries may be detected by using conventional petrophysical
tools to log the formation. Such tools include, without limitation,
induction logging tools, gamma ray and neutron logging tools,
microwave logging tools, acoustic logging tools, well logs that
represent cuttings obtained while drilling, and combinations of the
foregoing tools. Techniques for the analysis and interpretation of
data obtained from use of these tools is well known and
conventional in the art. Thus, power can be more selectively
applied to discrete intervals of carboniferous formation 108, such
as where emitter 1106 provides emanation 1126 to subunit 108B and
emitter 1108 provides emanation 129 to subunit 108C. IN this
manner, power may be selectively applied to protect groundwater,
for example, where subunits 108A, 108D border aquifers. It is also
possible to apply power to subunits 108B and 108D while not
applying power to subunit 108C. In this manner, energy costs may be
saved if it would be unproductive to heat subunit C, or if for
environmental or other reasons it is not desirable to heat subunit
C except by conductive heating from subunits 108B and 108D. The
subunits 108A through 108D may each be of any thickness, such as
several meters thick, tens of meters thick, or hundreds of meters
thick.
[0091] It is also possible to configure the circuitry of FIG. 9 in
parallel, as shown in FIG. 11. The RF source 1108 proceeds to
matching circuitry 1102, but this time drives a common transmission
line 1104 that serves as a rail for a plurality of phase shift and
balun circuitry components 1106, 1108, 1110, etc. . . . that
unbalance the matching transmission to make power available from
the respective emitter elements 1104, 1106, 1108, 1110 each
associated with their own respective phases. Here the phase
shifting prevents the respective emitters of the array 1100 from
acting in combination as a single antenna.
[0092] In the embodiments of FIG. 11 it is desirable to place each
of circuitry components 1106, 1108, 1110, etc., and its associated
emitter elements 1104, 1106, 1108, 1110, etc. into a separate
formation subunit. such as subunits 108A through 108D.
Alternatively, a radiative pattern concentrating more of the
effective radiated power into each formation may be obtained by
placing two or more baluns 1106, 1108, 1110, etc., and their
associated emitter elements 1104, 1106, 1108, 1110, etc. in each of
several formations for which heating is desired if an appropriate
phase shifting network is provided at all but one balun of each
formation.
[0093] As shown in FIG. 12, the foregoing concepts may be combined
where power from the RF source 1200 proceeds through matching
circuitry 1202 onto transmission line 1204. In a first
carboniferous formation 108', a first balun 1206 drives a first
emitter element (not shown) that is separated in space and phase
domains from a first phase and balun component 1208. Here the
transmission line 1204 extends through intervening rock 1210 to a
second carboniferous formation 108'' to drive also a second balun
and a second phase and balun circuitry component 1214. In this
instance, the intervening rock 1210 is sufficiently thick to
prevent the electrical components within formations 108' and 108''
from acting as a single antenna.
[0094] While the forgoing has been particularly shown and described
with reference to particular embodiments thereof, it will be
understood by those skilled in the art that various other changes
in the form and details may be made without departing from the
spirit and hereof. It is to be understood that various changes may
be made in adapting the description to different embodiments
without departing from the broader concepts disclosed herein and
comprehended by the claims that follow.
* * * * *
References