U.S. patent application number 11/533629 was filed with the patent office on 2007-05-10 for recovery of hydrocarbons using electrical stimulation.
Invention is credited to Alphonsus Forgeron.
Application Number | 20070102152 11/533629 |
Document ID | / |
Family ID | 37890057 |
Filed Date | 2007-05-10 |
United States Patent
Application |
20070102152 |
Kind Code |
A1 |
Forgeron; Alphonsus |
May 10, 2007 |
RECOVERY OF HYDROCARBONS USING ELECTRICAL STIMULATION
Abstract
A method of recovering hydrocarbon such as heavy oil or bitumen
from an underground oil-rich reservoir formation such as oil sand
or oil shale is provided. One or more substantially vertical wells
are drilled into the formation so that the bottom portion of each
well extends into the formation and, preferably, below the bottom
of the formation. The bottom portion of each well may be enlarged
relative to the rest of the well. The bottom portion of the well is
substantially filled with conductive liquid, sealed at the surface
and high voltage power of up to 72,000 Volts or more is applied via
an electrical conductor having an electrode submerged in the
conductive liquid. The resulting current flow increases the
formation temperature, causing the heavy oil or bitumen to flow
from the formation into the bottom portion where it can be removed
from the well.
Inventors: |
Forgeron; Alphonsus;
(Calgary, AB) |
Correspondence
Address: |
BENNETT JONES;C/O MS ROSEANN CALDWELL
4500 BANKERS HALL EAST
855 - 2ND STREET, SW
CALGARY
AB
T2P 4K7
CA
|
Family ID: |
37890057 |
Appl. No.: |
11/533629 |
Filed: |
September 20, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60596390 |
Sep 20, 2005 |
|
|
|
Current U.S.
Class: |
166/249 ;
166/272.1; 166/302; 166/306 |
Current CPC
Class: |
E21B 43/2401
20130101 |
Class at
Publication: |
166/249 ;
166/272.1; 166/302; 166/306 |
International
Class: |
E21B 43/24 20060101
E21B043/24; E21B 36/00 20060101 E21B036/00 |
Claims
1. A method for recovering hydrocarbons such as heavy oil or
bitumen from an underground oil-rich reservoir formation,
comprising: (a) providing one or more substantially vertical wells,
each well having a bottom portion extending into the oil-rich
reservoir formation and each well spaced apart from one another;
(b) adding to each well a conductive liquid to substantially fill
the bottom portion of each well; (c) inserting an electrical
conductor comprising an electrode into each well so that the
electrode is at least partially submerged in the conductive liquid;
(d) applying electrical power to the electrical conductor at a
voltage sufficient to heat the conductive liquid and the oil-rich
reservoir formation to a temperature sufficient to heat the heavy
oil or bitumen in the oil-rich reservoir formation; and (e)
substantially sealing the top of each well to maintain a
sufficiently high pressure in each well to prevent evaporation once
saturation temperature is reached and to force the heated heavy oil
or bitumen to flow into the bottom portion of the well and through
the well to the surface of the well.
2. The method as set forth in claim 1, whereby the bottom portion
of each well is enlarged relative to the rest of the well.
3. The method as set forth in claim 1, whereby the voltage ranges
from between about 13,000 Volts to about 72,000 Volts, or
higher.
4. The method as set forth in claim 1, wherein the oil-rich
reservoir formation is heated to a temperature of between about
100.degree. C. to about 300.degree. C., or higher.
5. The method as set forth in claim 1, wherein the pressure in each
well is between about 0.1 MPa to about 6.9 MPa or higher.
6. The method as set forth in claim 1, whereby the saturation
temperature is about 250.degree. C. to about 350.degree. C.
7. The method as set forth in claim 1 further comprising adding a
wetting agent to the conductive liquid.
8. The method as set forth in claim 1, whereby the conductive
liquid comprises an electrolyte selected from the group consisting
of sulfates, nitrates, acetates, oxalates, bitterns, bromides, and
any combination of sulfates, nitrates, acetates, oxalates, bitterns
and bromides.
9. The method as set forth in claim 1, the heated heavy oil or
bitumen further comprising brackish water, silt and sand, whereby
the heated heavy oil or bitumen rises to the top of the conductive
liquid and is separated from the brackish water, silt and sand.
10. A method for recovering hydrocarbons such as heavy oil or
bitumen from an underground oil-rich reservoir formation,
comprising: (a) providing one or more substantially vertical wells,
each well having a bottom portion extending into the oil-rich
reservoir formation and each well being lined with a casing; (b)
inserting a production tubing into each well, said production
tubing extending at least partially into the bottom portion of said
well; (c) adding to each well a conductive liquid to substantially
fill the bottom portion of each well; (d) inserting through the
production tubing an electrical conductor comprising an electrode
so that the electrode is at least partially submerged in the
conductive liquid; (e) applying electrical power to the electrical
conductor at a voltage sufficient to heat the conductive liquid and
the oil-rich reservoir formation to a temperature sufficient to
heat the heavy oil or bitumen in the oil-rich reservoir formation;
and (f) substantially sealing the top of each well to maintain a
sufficiently high pressure in each well to prevent evaporation once
saturation temperature is reached and to force the heated heavy oil
or bitumen to flow into the bottom portion of the well and through
the production tubing to the surface of the well.
11. The method as set forth in claim 10, whereby the production
tubing is moveable so that it can be raised or lowered within the
well.
12. The method as set forth in claim 10, whereby each well is
sealed by means of a surface arrangement comprising a valve, said
valve having an open and a closed position such that when the valve
is in the open position the heavy oil or bitumen can flow through
the production tubing and be removed at surface.
13. The method as set forth in claim 10, whereby the electrical
conductor further comprises an insulation jacket suitable for the
operating voltage and temperature.
14. The method as set forth in claim 10, whereby the bottom portion
of each well is enlarged relative to the rest of the well.
15. The method as set forth in claim 10, whereby the voltage ranges
from between about 13,000 Volts to about 72,000 Volts, or
higher.
16. The method as set forth in claim 10, wherein the oil-rich
reservoir formation is heated to a temperature of between about
100.degree. C. to about 300.degree. C., or higher.
17. The method as set forth in claim 10, wherein the pressure in
each well is between about 0.1 MPa to about 6.9 MPa or higher.
18. The method as set forth in claim 10, whereby the saturation
temperature is about 250.degree. C. to about 350.degree. C.
19. The method as set forth in claim 10 further comprising adding a
wetting agent to the conductive liquid.
20. The method as set forth in claim 10, whereby the conductive
liquid comprises an electrolyte selected from the group consisting
of sulfates, nitrates, acetates, oxalates, bitterns, bromides, and
any combination of sulfates, nitrates, acetates, oxalates, bitterns
and bromides.
21. The method as set forth in claim 10 further comprising: (g)
separately removing any gas from the formation that has accumulated
in the bottom portion of the well.
22. The method as set forth in claim 10, the heated heavy oil or
bitumen further comprising brackish water, silt and sand, whereby
the heated heavy oil or bitumen rises to the top of the conductive
liquid and is separated from the brackish water, silt and sand.
23. The method as set forth in claim 10, whereby the underground
oil-rich reservoir formation is oil sand or oil shale.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority benefit from U.S.
Provisional Patent Application No. 60/596,390 filed Sep. 20,
2005.
FIELD OF THE INVENTION
[0002] This invention relates generally to a method of recovering
hydrocarbons such as bitumen from underground formations. More
particularly, this invention relates to a method of recovering
hydrocarbons by drilling one or more substantially vertical wells
in the formation and applying high voltage electrical power
directly to the formation via said wells to increase the
temperature and/or pressure in the formation. The heated
hydrocarbon such as bitumen readily flows to a production cavity in
the well and is elevated to the surface through the well using the
high pressure created within the formation.
BACKGROUND OF THE INVENTION
[0003] Over the past several years, there has been much advancement
in thermal processes applied for recovering heavy, viscous oil
(e.g., bitumen) from subterranean reservoirs such as oil sand
reservoirs, oil shale reservoirs and the like. The most popular
method used today to extract bitumen from underground formations is
Steam Assisted Gravity Drainage (SAGD) and its variations.
[0004] SAGD extraction involves the injection of steam into the
formation through parallel pairs of wells drilled down to the
formation and then direction drilled horizontally for about 1,000
meters. The horizontally drilled top well is used for steam
injection, and the horizontally drilled lower well, generally 5-8
meters below, is used as the production well. As the formation is
heated by the steam injection, the heated bitumen begins to flow
downward towards the lower well. Once communication is established
between the two wells, the bitumen-steam emulsion flows downward by
gravity, into the lower well, along with silt, condensate, and
brackish water. The pressure created by the steam forces the liquid
slurry through a production pipe upward to the surface.
[0005] However, there are several problems that one encounters when
employing SAGD for bitumen extraction. Some of the drawbacks to
using SAGD are as follows: [0006] 1. Multiple boilers are needed to
produce the steam; [0007] 2. A continual large volume of fresh
water is required for making steam; [0008] 3. Large volumes of
Natural Gas are required to fire the boilers; [0009] 4. Condensate
returning from the underground is heavily contaminated; [0010] 5.
Condensate recovery uses large volumes of chemicals for water
treatment; [0011] 6. Steam injection into the formation produces a
less desirable liquid-oil-clay slurry; [0012] 7. Steam injection
disturbs the formation, causing silt and sand washout; [0013] 8.
Boiler operators are required round-the-clock to operate the steam
boilers; [0014] 9. Boiler maintenance is high from corrosive and
dirty condensate used in the boilers; [0015] 10. Contaminated water
disposal is an environmental issue; [0016] 11. The formation
temperature rise is limited by the operating design temperature of
the boilers and the final temperature of the steam arriving at the
formation; [0017] 12. The formation heat-up time using steam is
considered to be a slow process needing improvement; [0018] 13.
Steam may produce a lower formation temperature, resulting in a
lower bitumen recovery rate than other sources of heat such as
electric power; [0019] 14. The costs associated with using remotely
generated steam may be higher than if heat were supplied by
electrical power directly into the formation; and [0020] 15. SAGD
methods are believed to be limited to about 2000 ft in the depth
from which recovery may most economically be realized. The present
invention may be used in depths to 4,000 ft or more, thereby
opening access to the deep bitumen formations for the first time.
The present invention does not need to generate its heat at the
surface, but generates its heat directly within the deep
formation.
[0021] Another method tried in the past, without much commercial
success, uses low voltage power (under 15,000 Volts) applied
through vertical and parallel drilled cased wells, where the casing
extended down into the formation. However, problems were also
encountered with this method, including: [0022] 1. Evaporation of
the conductive water occurred around the drilled hole as the
temperature of the pipe increased above evaporation temperature;
[0023] 2. Excess heat concentrated around the drill hole where the
electrical current was most dense, increased evaporation of the
liquid; [0024] 3. Electric pumps were required to pump the bitumen
from the formation to the surface; [0025] 4. Energy losses through
the pipe casing, which conducted the electrical current from the
surface to the formation, caused much of the energy to be absorbed
by the pipe before it got to the formation. This reduced energy
efficiency. It also limited the quantity of power reaching the
formation; [0026] 5. The electrical voltage was applied at a
predetermined maximum conductivity point within the formation. This
method failed to capture the much larger conductivity that existed
by paralleling all the conductivities throughout the formation;
[0027] 6. There is a misconception within the industry that
electrical energy created from steam could not be as efficient as
using steam directly to heat the formation thereby limited
electrical effort using electrical power as the main heat source;
[0028] 7. Low voltages used to date could not viably transmit the
required large power needs into the formation without using closely
spaced, numerous drill holes, making such installations
uneconomical. Low voltage needs high current to transmit large
power loads into the formation, a limiting factor in earlier
experiments; [0029] 8. There is a problem with sand/silt
accumulations seriously interfering with bitumen extraction through
SAGD pipes; and [0030] 9. The overall electrical efficiency from
the electrical energy methods tried in past proved to be less
efficient than that achieved using steam.
[0031] The present invention provides a method for electrically
heating the hydrocarbon within the formation while overcoming one
or more of the above-mentioned limitations found in the prior
art.
SUMMARY OF THE INVENTION
[0032] In one aspect, the present invention provides a method for
recovering hydrocarbons such as heavy oil or bitumen from an
underground oil-rich reservoir formation, including: [0033]
providing one or more substantially vertical wells, each well
having a bottom portion extending into the oil-rich reservoir
formation and each well spaced apart from one another; [0034]
adding to each well a conductive liquid to substantially fill the
bottom portion of each well; [0035] inserting an electrical
conductor comprising an electrode into each well so that the
electrode is at least partially submerged in the conductive liquid;
[0036] applying electrical power to the electrical conductor at a
voltage sufficient to heat the conductive liquid and the oil-rich
reservoir formation to a temperature sufficient to heat the heavy
oil or bitumen in the oil-rich reservoir formation; and [0037]
substantially sealing the top of each well to maintain a
sufficiently high pressure in each well to prevent evaporation once
saturation temperature is reached and to force the heated heavy oil
or bitumen to flow into the bottom portion of the well and through
the well to the surface of the well.
[0038] In another aspect, the present invention provides a method
for recovering hydrocarbons such as heavy oil or bitumen from an
underground oil-rich reservoir formation, including: [0039]
providing one or more substantially vertical wells, each well
having a bottom portion extending into the oil-rich reservoir
formation and each well being lined with a casing; [0040] inserting
a production tubing into each well, said production tubing
extending at least partially into the bottom portion of said well;
[0041] adding to each well a conductive liquid to substantially
fill the bottom portion of each well; [0042] inserting through the
production tubing an electrical conductor comprising an electrode
so that the electrode is at least partially submerged in the
conductive liquid; [0043] applying electrical power to the
electrical conductor at a voltage sufficient to heat the conductive
liquid and the oil-rich reservoir formation to a temperature
sufficient to heat the heavy oil or bitumen in the oil-rich
reservoir formation; and
[0044] substantially sealing the top of each well to maintain a
sufficiently high pressure in each well to prevent evaporation once
saturation temperature is reached and to force the heated heavy oil
or bitumen to flow into the bottom portion of the well and through
the production tubing to the surface of the well.
[0045] In one embodiment, the conductive liquid comprises an
electrolyte selected from the group consisting of sulfates,
nitrates, acetates, oxalates, bitterns, bromides, and any
combinations thereof. As is commonly practiced in the art, the
conductive liquid is usually first tested in the lab to determine
its potential corrosion on in-situ extraction equipment and
upstream process equipment and less corrosive conductive liquids
are selected.
[0046] In one embodiment, the voltage ranges from between about
13,000 Volts to about 72,000 Volts, or higher. In another
embodiment, the temperature of the oil-rich reservoir formation is
between about 100.degree. C. to about 300.degree. C. or higher. In
yet another embodiment, the pressure in each well is between about
0.1 MPa to about 6.9 MPa or higher.
[0047] In a preferred embodiment, the bottom portion of each well
is enlarged relative to the rest of the well. In a further
preferred embodiment, a wetting agent, such as those used in
photographic film development, is added to the conductive liquid to
allow full and intimate contact between the conductive liquid and
the heavy oil or bitumen, thereby enhancing conductivity in the
formation.
[0048] In a further preferred embodiment, the production tubing is
moveable so that it can be raised or lowered within the well to
suit operating needs.
[0049] In another embodiment, any gas that has accumulated in the
top portion of the production cavity, just under the casing, may be
removed separately from the well, if so desired. This is achieved
by simply opening on of the valves on the surface casing and
allowing the formation pressure to push the gas out to a collection
line. The higher formation operating temperatures opens up a wide
range of gas compositions which will be generated, and it may be
desirable to extract this gas.
[0050] In another embodiment, the electrical conductor further
comprises an insulation jacket suitable for the operating voltage
and temperature.
[0051] In a preferred embodiment, the surface of the operating site
undergoes various preparations known in the art to minimize voltage
gradient, surface runoff water penetration, and conductivity, so
that energy losses and unsafe conditions are minimized.
[0052] In one embodiment, the underground oil-rich reservoir
formation is oil sand or oil shale.
[0053] Without being bound by theory, it is thought that one or
more of the following factors may be important in the operation of
the invention.
[0054] It is believed that an initial power input through the
formation is established by being able to apply high voltage
between the wells, using the thin "hydrophilic film" surrounding
each bitumen-encased grain of sand as the main initial conductive
path. High voltage allows spacing between wells of about 20 to
about 200 meters or more, thereby greatly reducing drilling costs
and surface environmental disturbance. High voltage also allows
large power input at low currents, avoiding the input conductor
heating problems encountered by other systems.
[0055] It is expected that, as the formation is heated, the
hydrophilic film around each sand grain will evaporate or
dissipate, thereby increasing the conductivity of the formation
such that the power input will be reduced. The present invention
attempts to minimize the above-mentioned undesirable situation
where conductivity may be reduced or lost if the hydrophilic film
is drained away before another conductive path is established.
[0056] One of the functions of the production cavity is to heat the
conductive liquid surrounding the electrode, which in turn heats
the bitumen within the wall of the cavity. The heated bitumen
slowly begins to flow from the wall of the cavity, rising up to the
top of the hot conductive liquid within the cavity. The displaced
bitumen is then replaced with the conductive liquid from the
production cavity. Thus, as time progresses and the formation
around the cavity continues to heat up and the bitumen continues to
float up to the top of the conductive liquid, the conductive liquid
gradually and very positively moves into the formation. Hence, by
heating the formation from outside first, and then gradually
heating towards the center, the cooler central portion of the
formation will maintain conductivity through the hydrophilic film
until the conductive liquid from the cavity has advanced enough to
maintain the conductivity of the formation, partly through the
hydrophilic film and increasingly more through the conductive
liquid.
[0057] In the present invention, the production cavity maintains
the highest temperature. Within the surrounding formation, the
current density and applied unit power are a very small fraction of
current density existing at the production cavity wall. This is
thought to be important for maintaining communication between the
widely spaced wells. If the temperature were to rise prematurely
within the formation, there is a danger of losing communication
between wells. A high temperature would break down the hydrophilic
film and cause the conductivity between wells to drop to levels
that may not allow enough energy to flow into the formation to meet
minimum economic production. Thus, the production cavity is
maintained at a higher temperature, allowing the gradual
displacement of heated bitumen surrounding the cavity to be
replaced by the conductive liquid. Ultimately, as the formation
heats, the conductivity from the disappearing hydrophilic film will
be replaced by the advancing layer of conductive liquid from the
refilled production cavity.
[0058] It is believed that the production cavity serves as a sump
into which the bitumen flows as it leaves the formation. In one
embodiment of the present invention, the production tubing may be
lowered or raised to selectively extract the bitumen that has
slowly separated from the conductive liquid, brine, and silt within
the production cavity. In another embodiment, the well itself is
used to lift the separated bitumen to the surface, powered by the
created pressure within the formation.
[0059] The production cavity may also serve as a sump to hold sand
and silt which falls from the sidewalls of the cavity as bitumen
flows gently from the formation. Ultimately the sand and silt will
build up to reduce the effective cavity working volume. This
build-up is expected to continue till the slope of the cavity
sidewalls are at a 10-40 degree angle of repose, after which time
the build-up will be minimal. The sand and silt may be removed from
the cavity by lowering the production tubing close to the bottom of
the cavity and forcing the sand and silt through the production
tubing on to the surface. By enlarging the diameter of the
production cavity and extending the bottom of the sump some
distance below the formation, it is expected that the sand and silt
build-up falling from the side walls of the cavity may fill the
sump only to the bottom of the formation. This would thereby avoid
the need to remove the sand/silt accumulation.
[0060] Ideally, the production cavity and formation are held at a
pressure above the boiling point of the liquids within the cavity.
The higher pressure prevents the liquids from boiling, and allows
operating temperatures to be held at up to 300.degree. C. or more
as desired for maximum production and resource recovery.
[0061] The electrode added to the end of the conductor increases
the area through which the electrical current flows from the
conductor by 5-10 times or more, thereby reducing the watt density
at the electrode. The heated electrode surrounded by the conductive
liquid is further cooled from the circulating current of water
rising up along the surface of the hot electrode, eliminating hot
spots on the electrode. The cooler electrode reduces the
undesirable tendency to have the bitumen bake onto the electrode,
thereby avoiding the creation of a baked-on carbon insulated layer.
This layer, if allowed to build up, reduces the conductivity of the
electrical circuit and reduces power input into the formation. The
electrode may be coated or plated with a non-corrosive material
such as platinum to reduce or eliminate electrode corrosion from
passage of electrical current and from exposure to corrosive
liquid.
[0062] By varying the conductive liquid and bitumen level within
the production cavity, the resistance to current flow may be
varied. For example, by raising the conductive fluid level within
the cavity, the number of varying resistance layers remaining in
parallel through the formation increases. This reduces the overall
formation resistance. It is thought that this is achieved by the
law of "parallel resistance", which decreases the total resistance
as more of the varying formation resistance levels are put in
parallel. Conversely, by dropping the conductive liquid level in
the production cavity, less resistance layers remain in parallel,
thereby increasing the resistance of the formation. This is one
method to control the level of power flowing in the formation.
Another method of controlling the power into the formation is by
partially removing the conductive liquid from one or more
production cavities, cleaning it to remove the conductive minerals
and impurities, and then reinserting it back into the cavity. This
makes the cavity and conductive liquid less conductive to match the
power input requirements of the operation. Other power varying
methods are possible using tap changers on Variable Voltage Power
Transformers, Voltage regulators; Variable frequency drives for
higher or lower frequencies; etc.
[0063] When the present invention is coupled with existing SAGD
type installations, one would expect to increase the temperature
within the formation between well pairs, and allow greater
production output and higher resource recovery rates. Thus, the
present invention may be applied directly through the existing SAGD
production/injection pipes, once suitably isolated for safety.
Again, the conductive liquid would need to be injected through the
SAGD pipes directly into the SAGD cavity to provide intimate
contact with the formation. Typically, the SAGD pipe pairs are
separated by about 150 meters or so. When each pipe-pair has been
flooded with conductive liquid, and up to 75,000 volts or more is
applied between the SAGD pipes, a current will be established and
will gradually increase as the conductive liquid displaces the
heated bitumen. The temperature and pressure around the SAGD pipes
will increase as power increases, and now the top injection pipe
becomes the production pipe. Gradually the total formation will be
heated between the SAGD pipe pairs, which are separated by up to
150 meters or more.
[0064] The use of electrical energy is as cheap as or cheaper than
the use of steam for in-situ bitumen formation heating for the
reasons now following. First, electrical energy is produced in very
large power boilers using full energy recuperation, full and pure
condensate recovery, with little treatment required. This provides
an advantage when compared to the small industrial boilers now used
for steam injection, with minimal energy recuperation, and with
condensate recovered from a sludge mixture of silt, sand, brackish
water, and bitumen products, all recovered from the formation. This
is not favorable for high efficiency steam generation.
[0065] Second, the large power boilers use multi-pass heat
recovery, thereby achieving the highest possible level of energy
recovery. This provides an advantage when compared with the small
SAGD boilers which only partially recover the injected steam which
must flow several thousand meters through un-insulated lines to and
from the formation, where a single pass heat recovery is only
partially achieved.
[0066] Third, the very large power boiler controls and boiler
cleansing technology are the most efficient known today. This
provides an advantage when compared with the industrial controls
and dirty boiler tubes resulting from using highly treated
production-recovered-water taken from the brackish bitumen
formation.
[0067] Fourth, electrical energy is applied directly within the
formation, with negligible transmission losses. This provides an
advantage when compared with steam transported several thousand
meters mostly through un-insulated pipes to get to the formation,
and then the return of the highly contaminated condensate a similar
distance back to the water treatment and recovery plant then on to
the surface boilers.
[0068] Fifth, electrical power may be transmitted to site at a cost
comparable to the power transmission costs already incurred to
power SAGD needs. This provides an advantage when compared with
Natural Gas and the fresh boiler-feed-water pipelines, which must
be constructed long distances to get to the SAGD site. SAGD also
requires electrical power to be brought to site where a large
quantity of electricity is needed to run the boiler fans, pumps,
and water treatment equipment.
[0069] Sixth, "Off-Peak" power, not mentioned in electrical in-situ
power comparisons, can be used at a price reduction of 20-40% for
much of the energy needs. This is possible because of the large
heat sink created within the formation. Power may be cut off and
easily restored as desired by the power company, thereby allowing
"Peak-Power" periods to be bypassed. This feature alone makes
electrical power cheaper than SAGD steam energy.
BRIEF DESCRIPTION OF THE DRAWINGS
[0070] FIG. 1 is an illustration of one arrangement of a well of
the present invention prior to electrical power being applied to
the electrical conductor.
[0071] FIGS. 2a to 2e are sequential illustrations showing the
progressive changes in the well and surrounding oil-rich reservoir
formation of FIG. 1 after electrical power has been applied to the
electrical conductor.
[0072] FIG. 3 shows one embodiment of the surface arrangement with
seals, packing glands, main shut-off valve, and other valves and
operating indicators.
[0073] FIG. 4 illustrates two adjacent wells extending down from
the surface to an oil-rich reservoir formation.
[0074] FIG. 5a illustrates a three dimensional field arrangement of
a typical multi-well production unit.
[0075] FIG. 5b illustrates in cross-section the field arrangement
of FIG. 5a
[0076] FIG. 6 illustrates the electrical current path of the
three-phase arrangement of wells in FIGS. 5a and 5b.
[0077] FIG. 7 illustrates one embodiment of a surface distribution
layout of a plurality of multi-well production units of the present
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0078] An embodiment of the present invention will be described
with particular reference to tar or oil sand formations.
[0079] FIG. 1 illustrates a typical arrangement of a well before
electrical power is applied to the formation. Wellbore 10 extends
through overburden 14 and into oil (tar) sand formation 12. The
bottom portion of wellbore 10 comprises an enlarged production
cavity 16 and the walls 18 of production cavity 16 are
substantially vertical. In the present embodiment, the well further
comprises casing 30 and production pipe or tubing 28, which tubing
extends partially into production cavity 16 and through which the
conductive liquid 26 is added to the production cavity 16. When
bitumen is ultimately produced, the bitumen flows to the surface
through production tubing 28. The casing 30 may be insulated from
the electrical conductor 32 by suitable insulation as is known in
the art (not shown) in order to operate at the voltage and
temperatures necessary for the present invention.
[0080] Surrounding production cavity 16 is oil sand formation 12
comprised of unheated bitumen 20 holding sand 24 and rock 22 in
place. Production cavity 16 is initially filled with conductive
liquid 26, which is unheated, and as such has not started entering
into the formation 12, other than where indigenous streams of
brackish water may exist. A space 37 is left between the surface 36
of the conductive fluid 26 and the top of the production cavity 16,
which space will accumulate gas and steam as the bitumen extraction
process proceeds as shown in FIGS. 2a to 2e. At this initial stage,
negligible bitumen will have separated from the formation to rise
to the surface of the conductive fluid in the production cavity at
this time.
[0081] Electrical conductor 32 is inserted through production
tubing 28 and extends into conductive liquid 26. Attached to
electrical conductor 32 is electrode 34, which is shown as being
fully submerged in conductive liquid 26. The power source may be
single or three-phase AC, or it may be High Voltage DC. It may also
be of a frequency other than the standard 60 Hertz.
[0082] In the example well shown in FIG. 1 and prior to practicing
the invention, the pressure in productive cavity 16 is about 0.0
MPa, the temperature of conductive liquid 26 is around 25.degree.
C. and the temperature of oil sand formation 12 is around
27.degree. C. In general, the oil sand formation will have a
temperature of approximately 25.degree. C. to about 40.degree. C.,
depending on formation depth.
[0083] FIGS. 2a to 2e sequentially illustrate the progressive
changes in the well and surrounding oil sand formation after
electrical power is applied and the wellbore sealed to withstand
the resulting pressure generated by the temperature rise in the
cavity and formation (see FIG. 3 and discussion below).
[0084] With reference first to FIG. 2a, the enlarged production
cavity 16 is slowly being heated via conductive liquid 26 as a
result of electrical power being applied to the electrode 34, which
flows through the conductive liquid 26 and on through the oil sand
formation 12. As previously mentioned, conductive liquid 26
comprises one or more electrolytes and, optionally, a wetting
agent. The surface valve 52 (shown in FIG. 3) is closed at this
point. The pressure in production cavity is slowly rising to 0.1
MPa and when the temperature of the conductive liquid reaches about
100.degree. C., the temperature of the oil sand reservoir heats up
to about 85.degree. C. to about 90.degree. C.
[0085] FIG. 2b illustrates the conductive liquid 26 reaching about
150.degree. C. and the oil sand formation 12 near the production
cavity 16 also rising in temperature (shown as being between about
130-140.degree. C.). The bitumen 20 is now softening due to the
heat addition in the formation and slowly begins to flow upward
along the production cavity walls 18 to the surface 36 of the
conductive liquid 26. The conductive liquid 26 immediately replaces
the void created in the oil sand formation 12 as a result of the
bitumen 20 flowing up to the top of the production cavity 16. As
the temperature of the conductive liquid 26 exceeds 100.degree. C.,
some of the water therein begins to boil and vaporize into steam.
Slowly, the steam pressure and temperature increases within the
cavity and production pipe until the saturation level is reached.
Further, as heating continues, saturation temperatures and
pressures continue to rise (e.g., at this stage the pressure in the
production cavity 16 would be about 0.38 MPa).
[0086] As electrical power continues to be applied, FIG. 2c
illustrates the temperature of the production cavity 16 increasing
to about 200.degree. C., the pressure rising to 0.85 MPa, and
bitumen 20 flowing from the most conductive layers in the oil sand
formation 12 where the greatest heat is applied into the production
cavity 16. The conductive liquid 26 is now moved further into the
oil sand formation 12 and is replaced by bitumen 20, which rises to
the surface 36 of conductive liquid 26.
[0087] FIG. 2d illustrates the commencement of bitumen 20 recovery.
The valve 52 on the production tubing located at the surface (as
shown in FIG. 3) is opened, thereby relieving the pressure at the
top of the production tubing and causing the bitumen to flow upward
to the surface through production tubing 28. The bitumen flow 21
will continue as long as the surface valve 52 is open and the
production cavity pressure is maintained at a level higher than the
hydrocarbon head in the production tubing 28 (e.g., about 3.9
MPa).
[0088] FIG. 2e illustrates bitumen production when the production
cavity temperature reaches 300.degree. C. temperature. It is
expected that temperatures of 325.degree. C. or more may be
possible, depending on the ability of the formation to withstand
the pressure. Further, the pressure rises and reaches about 6.9 MPa
or more. The electrical power used to create the temperature and
pressure within the formation is not limited by any mechanical
equipment other than the seals at the surface that keep the
pressure from escaping.
[0089] It can be seen in FIG. 2e that the production cavity has
gotten much larger at this point and the space 37 between the
surface of the bitumen 20 accumulating on the surface 36 of the
conductive fluid 26 and the top of the production cavity 16 is
filled with gas and steam. The bitumen 20 accumulating at the
surface 36 of the conductive fluid 26 is continuously removed
through the production tubing 28. It is understood that the
production tubing 28 can be raised or lowered to accommodate the
removal of the bitumen 20. Optionally, the gas/steam that
accumulates in space 37 can also be removed from the wellbore and
separately recovered through production tubing.
[0090] It is possible that at certain temperatures and pressures
there may be a bitumen-conductive water density inversion, thereby
causing the water to float on top of the bitumen. For example,
there may be one or two inversions occurring during the practice of
the present invention as the temperature and pressure increases. It
is understood that if such an inversion occurs, the production
tubing elevation and conductive liquid levels will then need to be
adjusted to allow the desired bitumen recovery.
[0091] FIG. 3 shows one embodiment of the surface arrangement for
sealing the wellbore during operation of the invention in order to
withstand the resulting pressure generated by the temperature rise
in the cavity and formation. The contained high pressure achieved
in the present invention prevents the liquid from evaporating once
saturation temperature is reached. Thus, as power increases into
the formation, the resulting temperature and pressure rise are
limited only by the competence of the formation. Formation
temperatures of about 275-300.degree. C. or more are therefore
achievable.
[0092] Surface wellhead arrangement 50 is comprised of various
seals, packing glands 54 and main shut-off valve 52. Valve 51 is
used for bitumen removal, valve 53 for delivering conductive liquid
to the wellbore and valve 55 is used for clean out, as required.
Pressure gauge 56 monitors the pressure in the well and temperature
gauge 57 monitors the temperature in the well.
[0093] Thus, the liquid evaporation problem of concern in earlier
electrical power recovery methods is overcome by sealing the
wellbore with surface wellhead arrangement 50 to withstand the
resulting pressure generated by the temperature rise in the cavity
and formation. It is understood, however, that other surface well
control devices as known in the art may be used.
[0094] Thus, the surface wellhead arrangement 50 is adapted to
allow the electrical conductor 32 to enter the wellbore and be
positioned in the production cavity. The surface wellhead
arrangement 50 also allows the production tubing to extract the
bitumen without losing formation pressure through valve 51. The
surface wellhead arrangement 50 further allows the conductive
liquid to be added or removed from the formation while retaining
the formation pressure through valve 53.
[0095] The arrangement 50 allows the electrical conductor 32 to be
raised or lowered as required. For example, the main shut-off valve
52 can be used to close off the well when the electrical conductor
32 is removed for maintenance or replacement, to maintain the well
pressure. The surface wellhead arrangement 50 also allows the
production tubing to be raised or lowered as required.
[0096] FIG. 4 illustrates two adjacent wells, 62 and 64,
respectively, extending down from the surface 60 to the oil sands
formation 12 to illustrate the establishment of communication
between adjacent wells. Both wells 62 and 64 are enlarged at the
bottom to form respective production cavities 16, which cavities
extend through the oil sand formation 12 and for several meters
below formation 12. Each well comprises production tubing 28
through which electrical conductor 32 passes from the surface to
the formation into the respective production cavities 16, which are
filled with conductive liquid 26. Electrode 34 is attached to each
conductor 32 and is suspended at any desired level within the
formation production cavity. The wellhead arrangement 150 is shown
in one of the many configurations and is used to seal the wells 62
and 64 during operation of the present invention. Each well is
sealed to withstand the highest operating pressures that may be
used.
[0097] It can be seen in FIG. 4 that electrical communication
between adjacent wells is established. Electrical current 66 flows
between the two electrodes 34 of wells 62 and 64, thereby
accelerating the heating of the oil sand formation 12 therebetween.
This allows for more efficient heating of the bitumen in the
formation.
[0098] FIG. 5(a) shows a three-dimensional field arrangement of a
typical production unit comprising a plurality of wells 70, 72, 74
and 76 and FIG. 5b shows such a unit in cross-section. The
three-phase, four-wire power payout is shown consisting of Phase A
(well 70), Phase B (well 76), Phase C (well 72) and the fourth wire
which is the Neutral (well 74). This arrangement is a very familiar
power system which the present invention uses to feed the large
quantity of power required within the formation to make the
operation viable. The Neutral in one layout is solidly grounded,
allowing it to serve as the first production outlet around and upon
which workers may be able to work safely while the power is
flowing.
[0099] FIG. 6 illustrates the electrical current path of the
three-phase arrangement of wells as shown in FIGS. 5a and 5b. The
typical Phase A, B, C with Neutral are shown for each well in the
production unit. Depending on conductivity of the formation and its
depth, the spacing between wells may vary quite widely, for
example, anywhere between about 20 to about 200 meter spacing. The
broken lines 80 represent the current flow between Phase A and B;
however, the current flow is similar between each of the other
phases and the Neutral. The current flow 80 represents the
electrical heating within the formation. As the formation heats
where the current flows, gradually this heat will spread out
towards its surroundings such that all of the formation is
thoroughly heated.
[0100] FIG. 7 illustrates one embodiment of a surface distribution
layout of a plurality of multi-well production units of the present
invention. This configuration allows the minimum number of wells to
be used to totally cover the power into the formation. The present
invention allows a typical production unit to be spaced as shown on
the "top group" to totally heat the formation within the triangles
and on outside a small distance. Note the complete electrical
separation between the top group and bottom groups. Also note that
each separate group has a well in the triangle which matches up
with the adjoining triangle production unit such that the area
between triangles are all capable of being heated from the same A,
B, C phases. Power may be applied between each production triangle
unit and may also be connected between the top and bottom groups as
well.
[0101] The practice of the method of the present invention will be
described using the following two-well example. Two substantially
vertical wells are first drilled with one drill bit from the
surface until reaching the oil sand formation. Drilling is then
continued through the oil sand formation with a larger drill bit to
form an enlarged cavity down to and several meters or so beyond the
bottom of the oil sand formation. This enlarged cavity is the
production cavity into which conductive liquid is added to make
intimate contact with the oil sand formation. The production cavity
also serves as the collection and separation reservoir into which
the bitumen flows and later pressure extracted to the surface.
Preferably, a plurality of wells are drilled in an arrangement such
as shown in FIGS. 5a and 5b, whereby each of the wells is spaced
about 20 to about 200 meters apart depending on formation
conductivity.
[0102] Each well is encased with casing as is known in the art. The
casing is sealed between the casing and the well bore or drill hole
overburden so that the operating pressures that the wells will be
exposed to will be contained. Production tubing is then inserted in
each well through the well casing. The production tubing is sealed
at the surface to seal the production tubing tightly against the
formation operating pressure. The production tubing has its own
bitumen recovery valve and clean-out valve as shown in the surface
wellbore arrangement in FIG. 3.
[0103] The electrical conductor with the electrode attached thereto
is lowered down through the production tubing of each well and
suspended within the production cavity containing the conductive
liquid. It should be noted that minimal power is conducted through
the wall of the production tubing; hence the power loss is
negligible in getting from the surface to the formation. Each well
comprises a surface arrangement for sealing off the well during the
practice of the present invention.
[0104] Initially, each well is sealed off using the surface sealing
arrangement. Electrical power at voltages up to 72,000 Volts or
more is applied to the electrical conductor in each well such that
current is made to flow through the formation from one well to the
next. The use of high voltage not only assists in establishing the
initial communication through the formation, but it also allows
large power input using low amperage. Further, it allows a greater
separation distance between wells, making the technology
potentially more affordable than those using closely spaced
holes.
[0105] Without being bound to theory, it is believed that initial
conduction is established mainly through the thin film of brackish
water encapsulated between each individual sand particle and the
outer bitumen layer also surrounding each sand particle (referred
to previously as the hydrophilic film). Later, communication is
maintained in part through the conductive liquid, which gradually
replaces the displaced heated bitumen. The heated bitumen slowly
rises upward through the conductive liquid towards the surface of
the liquid in a collection cavity.
[0106] Maximum flow of power may be achieved by providing a path of
least resistance through which the power can flow. The resistance
between electrodes is reduced by placing all resistance values,
within the formation, in parallel. The resulting resistance is the
lowest possible level achievable in the formation. This lowest
level resistance is achieved by having a wetting agent added to the
conductive liquid in each production cavity, thereby helping the
conductive liquid make intimate contact with the oil sand
formation. The conductive liquid thereby joins in parallel all of
the high and low conductivity levels existing, from the top to the
bottom of the formation. With all of these high and low resistance
paths in parallel, the final resistance will be a small fraction of
what the lowest individual resistance will be. This allows the
maximum possible flow of power through the formation at any applied
voltage.
[0107] The enlarged cavity (i.e., production cavity) is used as a
production reservoir into which the heated bitumen flows and from
which the bitumen is extracted. The enlarged cavity also serves as
the sand/silt reservoir into which the cleansed sand can fall.
Finally, it serves as the reservoir into which the bitumen may
quietly settle out from the brackish water, sand and silt, allowing
more pure bitumen to be extracted. While the current density at the
electrode will be highest, the large surface area of the electrode
will result in a relatively low watt density to eliminate baking of
bitumen that comes in contact with the electrode.
[0108] The large reservoir of conductive liquid serves not only to
make intimate contact with the formation, but also acts as a heat
equalizing coolant between electrode, conductive liquid, and
formation. The watt density at the interface of the formation and
the liquid is higher than at all points within the formation, as
was found from earlier work. This means that the heat generated
within the formation will be highest at this liquid-formation
interface, and will decrease as the distance into the formation
increases. The interface therefore heats up faster than the
interior of the formation. This allows the bitumen to become hot at
the wall of the cavity first, and slowly rise up through the liquid
to float on the liquid surface.
[0109] Once the bitumen leaves the formation, it is replaced with
conductive liquid. The conductive liquid slowly migrates into the
formation, from which the bitumen has flowed, further improving the
conductivity and the ability to increase power into the formation.
Ultimately, the conductivity between electrodes will mainly be via
the conductive liquid. The heat generated from electrical power
flowing through the conductive liquid will end up being the main
source of heat within the formation.
[0110] It is hypothesized that once the bitumen formation is heated
above a given temperature the conductive film of brackish water
surrounding each sand grain will partly or totally dissipate,
thereby interfering with the formation conductivity. To avoid
possible loss of conductivity, two precautions may be implemented
as follows. First, the conductive liquid can be encouraged to
migrate into the formation as quickly as possible, as described
above, thereby displacing the bitumen with conductive liquid.
Second, the center of the formation may be allowed to heat up more
slowly than that which is located nearest the electrode cavity.
This makes the low current density within the formation and the
high density at the liquid-formation interface automatically
achieve these desired results. Achieving a high current density at
the cavity-to-formation interface is desirable.
[0111] The liquid evaporation problem of concern in earlier
electrical power recovery methods is overcome by sealing the well
to withstand the resulting pressure generated by the temperature
rise in the cavity and formation. The contained high pressure
prevents the liquid from evaporating once saturation temperature is
reached. As power increases into the formation, the resulting
temperature and pressure rise are limited only by the competence of
the formation. As previously mentioned, formation temperatures of
about 275-300.degree. C. or more are achievable.
[0112] As discussed above, FIGS. 2a to 2e are a series of
schematics illustrating the effect on flow of bitumen as both
temperature and pressure increases, thereby leading to the heating
of the bitumen in the formation and flow of the heated bitumen into
the enlarge portion of the well, i.e., the production cavity. FIG.
2e illustrates that the conductive liquid can reach a temperature
of approximately 300.degree. C. and the pressure in the production
cavity reaching 6.9 MPa. Heated bitumen flows from the oil sand
formation into the production cavity and the pressure allows the
bitumen to flow up through the production tubing to the surface of
the well. Thus, the invention does not require the use of
electrical pumps to remove the bitumen as the pressure produced by
the heat from the electrical power flowing through the formation
will allow the bitumen to be extracted using this formation
pressure, at any desired well.
[0113] Further, the present invention allows the bitumen to be
separated from the brackish and conductive liquids within the
production cavity at the formation. Sufficient settling time will
allow the bitumen to float on top of the liquid in the cavity, from
where it may be selectively brought to the surface.
[0114] It is understood that high voltage use at an operating site
is extremely dangerous without applying all possible safety
precautions. Thus, in the present invention, power is applied only
when workers are not within the fenced area. The neutral electrode,
at each four-hole production grouping, may also be used for
production while power is applied to the site, as the neutral is
intended to be solidly grounded thereby allowing continual
production as needed while power is "ON".
[0115] During start-up, there is a possibility the voltage applied
between Phase A and Phase B, as illustrated in FIGS. 6 and 7, may
not be sufficient to allow the high level of power to pass between
wells, since the initial conductivity may be lower than desired.
The present invention allows the voltage across A and B phases to
be switched so that phase A will stay on its original well, but
Phase B will now be connected to the Neutral which is about 58% of
the distance compared to that between Phase A and B. This allows
the power to increase more rapidly until the formation has heated
and conductivity is established.
[0116] While the invention has been described in conjunction with
the disclosed embodiments, it will be understood that the invention
is not intended to be limited to these embodiments. On the
contrary, the current protection is intended to cover alternatives,
modifications and equivalents, which may be included within the
spirit and scope of the invention. Various modifications will
remain readily apparent to those skilled in the art.
* * * * *