Note: Descriptions are shown in the official language in which they were submitted.
CA 02560223 2006-09-20
RECOVERY OF HYDROCARBONS USING ELECTRICAL STIMULATION
CROSS REFERENCE TO F~ELATED APPLICATIONS
This application claims priority benefit from U.S. Provisional Patent
Application
No. 60/596,390 filed September 20, 2005.
FIELD OF THE. INVENTION
This invention relates generally to a method of recovering hydrocarbons such
as bitumen from underground formations. PJlore 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 andl/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
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.
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
1
CA 02560223 2006-09-20
pressure created by the steam forces the liquid slurry through a production
pipe
upward to the surface.
However, there are several problems that one encounters when employing
SAGD for bitumen extraction. Some of the drawbacks to using SAGD are as
follows:
1. Multiple boilers are needed to produce the steam;
2. A continual large volume of fresh water is required for making steam;
3. Large volumes of Natural Gas are required to fire the boilers;
4. Condensate returning from the underground is heavily contaminated;
5. Condensate recovery uses large volumes of chemicals for water
treatment;
6. Steam injection into the formation produces a less desirable liquid-oil-
clay slurry;
7. Steam injection disturbs the formation, causing silt and sand washout;
8. Boiler operators are required round-the-clock to operate the steam
boilers;
9. Boiler maintenance is high from corrosive and dirty condensate used in
the boilers;
10. Contaminated water disposal is an environmental issue;
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;
12. The formation heat-up time using steam is considered to be a slow
process needing improvement;
13. Steam may produce a lower formation temperature, resulting in a lower
bitumen recovery rate than other sources of heat such as electric power;
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
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
CA 02560223 2006-09-20
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.
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:
1. Evaporation of the conductivE; water occurred around the drilled hole as
the temperature of the pipe increased above evaporation temperature;
2. Excess heat concentrated around the drill hole where the electrical
current was most dense, incrE;ased evaporation of the liquid;
3. Electric pumps were required to pump the bitumen from the formation to
the surface;
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;
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;
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 lirnited electrical effort using electrical power
as the main heat source;
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;
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8. There is a problem with sand/'silt accumulations seriously interfering with
bitumen extraction through SAGD pipes; and
9. The overall electrical efficiency from the electrical energy methods tried
in past proved to be less efficient than that achieved using steam.
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 C)F THE INVENTION
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:
~ 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;
~ adding to each well a conductive liquid to substantially fill the bottom
portion
of each well;
~ inserting an electrical conductor comprising an electrode into each well so
that the electrode is at least partially submerged in the conductive liquid;
~ 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
~ 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.
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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:
~ 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;
~ inserting a production tubing into each well, said production tubing
extending at least partially into the bottom portion of said well;
~ adding to each well a conductive liquid to substantially fill the bottom
portion
of each well;
~ inserting through the production tubing an electrical conductor comprising
an electrode so that the electrode is at least partially submerged in the
conductive liquid;
~ 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 oif-rich
reservoir formation; and
~ 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.
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.
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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°C to about 300°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.
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.
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.
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.
In another embodiment, the electrical conductor further comprises an
insulation
jacket suitable for the operating voltage and temperature.
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.
In one embodiment, the underground oil-rich reservoir formation is oil sand or
oil shale.
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.
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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 andl surface environmental
disturbance. High
voltage also allows large power input at I~ow currents, avoiding the input
conductor
heating problems encountered by other systems.
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.
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 ifrom 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 touvards 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.
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 dE:nsity 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
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CA 02560223 2006-09-20
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.
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.
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.
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°C or more as
desired for maximum production and resource recovery.
8
CA 02560223 2006-09-20
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.
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.
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
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CA 02560223 2006-09-20
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.
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.
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.
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.
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
CA 02560223 2006-09-20
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.
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.
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
Figure 1 is an illustration of one arrangement of a well of the present
invention
prior to electrical power being applied to thE: electrical conductor.
Figures 2a to 2e are sequential illustrations showing the progressive changes
in
the well and surrounding oil-rich reservoir formation of Figure 1 after
electrical power
has been applied to the electrical conductor.
Figure 3 shows one embodiment of the surface arrangement with seals,
packing glands, main shut-off valve, and other valves and operating
indicators.
Figure 4 illustrates two adjacent wE:lls extending down from the surface to an
oil-rich reservoir formation.
Figure 5a illustrates a three dimensional field arrangement of a typical multi-
well production unit.
Figure 5b illustrates in cross-section the field arrangement of Figure 5a
11
CA 02560223 2006-09-20
Figure 6 illustrates the electrical current path of the three-phase
arrangement of
wells in Figures 5a and 5b.
Figure 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
An embodiment of the present invention will be described with particular
reference to tar or oil sand formations.
Figure 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.
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 Figures 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.
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
12
CA 02560223 2006-09-20
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.
In the example well shown in Figure 1 and prior to practicing the invention,
the
pressure in productive cavity 16 is about O.C) MPa, the temperature of
conductive liquid
26 is around 25 °C and the temperature of oil sand formation 12 is
around 27 °C. In
general, the oil sand formation will have a tE:mperature of approximately
25°C to about
40°C, depending on formation depth.
Figures 2a to 2e sequentially illustrai:e 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 Figure 3 and discussion below).
With reference first to Figure 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
Figure 3) is closed at this point. The press>ure in production cavity is
slowly rising to
0.1 MPa and when the temperature of the conductive liquid reaches about
100°-C, the
temperature of the oil sand reservoir heats up to about 85°-C to about
90°C.
Figure 2b illustrates the conductive liquid 26 reaching about 150°-C
and the oil
sand formation 12 near the production caviiry 16 also rising in temperature
(shown as
being between about 130-140°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°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
13
CA 02560223 2006-09-20
continues, saturation temperatures and prE~ssures continue to rise (e.g., at
this stage
the pressure in the production cavity 16 would be about 0.38 MPa).
As electrical power continues to be applied, Figure 2c illustrates the
temperature of the production cavity 16 increasing to about 200°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 aurface 36 of conductive liquid 26.
Figure 2d illustrates the commencernent of bitumen 20 recovery. The valve 52
on the production tubing located at the surface (as shown in Figure 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).
Figure 2e illustrates bitumen production when the production cavity
temperature reaches 300°C temperature. It is expected that temperatures
of 325°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.
It can be seen in Figure 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.
14
CA 02560223 2006-09-20
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.
Figure 3 shows one embodiment off 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°C or more are
therefore
achievable.
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.
Thus, the liquid evaporation problE~m 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.
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 alllows the production tubing to extract
the
bitumen without losing formation pressure through valve 51. The surface
wellhead
l .'p
CA 02560223 2006-09-20
arrangement 50 further allows the conductiive liquid to be added or removed
from the
formation while retaining the formation pressure through valve 53.
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.
Figure 4 illustrates two adjacent wellls, 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.
It can be seen in Figure 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.
Figure 5(a) shows a three-dimensional field arrangement of a typical
production
unit comprising a plurality of wells 70, 72, ,74 and 76 and Figure 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,
16
CA 02560223 2006-09-20
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.
Figure 6 illustrates the electrical currE:nt path of the three-phase
arrangement of
wells as shown in Figures 5a and 5b. Tree 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 wellls 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 IVeutral. 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.
Figure 7 illustrates one embodirnent 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 compllete 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.
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 bituimen flows and later pressure
extracted to
17
CA 02560223 2006-09-20
the surface. Preferably, a plurality of wells are drilled in an arrangement
such as
shown in Figures 5a and 5b, whereby each of the wells is spaced about 20 to
about
200 meters apart depending on formation conductivity.
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 Figure 3.
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.
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.
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 them liquid in a collection cavity.
18
CA 02560223 2006-09-20
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.
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.
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 2~I1 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.
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
x9
CA 02560223 2006-09-20
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.
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 b~e 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.
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 °C or more are achievable.
As discussed above, Figures 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. Figure 2e
illustrates that the
conductive liquid can reach a temperature of approximately 300 °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
20~
CA 02560223 2006-09-20
by the heat from the electrical power flc>wing through the formation will
allow the
bitumen to be extracted using this formation pressure, at any desired well.
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.
It is understood that high voltagc: 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".
During start-up, there is a possibility the voltage applied between Phase A
and
Phase B, as illustrated in Figures 6 and 7, may not be sufficient to allow the
high level
of power to pass between wells, since i:he 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 thc: power to increase more rapidly until
the
formation has heated and conductivity is established.
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, tree 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.
21
