Note: Descriptions are shown in the official language in which they were submitted.
1
TITLE
[0001] Low-pressure method and apparatus for producing hydrocarbons from
an
underground formation using electric resistive heating and solvent injection
FIELD
[0002] This relates to a method of producing hydrocarbons from an
underground
formation.
BACKGROUND
[0003] Heavy oil is often produced using SAGD (steam assisted gravity
drainage)
processes. In SAGD, there is a preheating phase and a production phase. The
preheating
phase proceeds until the hydrocarbons are sufficiently warm to allow mobility.
The process
then moves to the production phase. Generally speaking, SAGD uses pairs of
horizontal
wells, where the top well is a steam injection well and the bottom well is a
production well.
Heat associated with the steam is applied to the top well to reduce the
viscosity of the heavy
oil, and hydrocarbons are recovered from the bottom well and pumped to
surface.
SUMMARY
[0004] According to an aspect, there is provided a method of producing
hydrocarbons
from an underground formation having an array of horizontal wells, comprising
the steps of
identifying one or more producer well sections and one or more heater well
sections in the
array of horizontal wells; inserting one or more heater strings into at least
one heater well
section, the heater string comprising a heating element and a flow passage for
transporting
fluid from a fluid input to at least one injection port; activating the
heating element of the
heater string to heat the formation sufficient to produce hydrocarbons from
the formation
immediately adjacent to the at least one heater well section; heating and
injecting a solvent
into the at least one heater well in the gaseous phase through the at least
one injection port of
the heater string such that the solvent is injected into the voidage in the at
least one heater
well section created by the produced hydrocarbons; and producing hydrocarbons
from at least
one producer well.
[0005] According to another aspect, the solvent may be injected into the
formation prior
to hydrocarbons being produced from the at least one producer well.
Date Regue/Date Received 2022-09-26
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[0006] According to another aspect, the heater string may comprise a
plurality of injection
ports spaced along a length of the heater string. The plurality of injection
ports may be scaled
to distribute solvent in a desired distribution along a length of the heater
string. A plurality of
injection ports may be connected to separate injection tubes. The injection
through each
injection port may be independently controlled. An injection rate through each
injection port
may be selected to achieve a desired distribution of solvent.
[0007] According to another aspect, the heating element may be a
resistive heater.
[0008] According to another aspect, the solvent may be injected into the
heater string as a
liquid and may be vapourized prior to injection into the voidage.
[0009] According to another aspect, the solvent may be injected into the
heater string in a
gaseous phase.
[0010] According to another aspect, the solvent may comprise a light
hydrocarbon or a
manufactured hydrocarbon compound.
[0011] According to another aspect, the solvent may comprise dimethyl
ether.
[0012] According to another aspect, the method may further comprise the
step of injecting
a carrier gas after injecting the solvent to promote the production of
hydrocarbons, and the
carrier gas may comprise a carbon-containing gas, an inert gas, or a carbon-
containing gas
and an inert gas.
[0013] According to another aspect, the method may further comprise the
steps of
identifying locations within the underground formation that require additional
heating, and
providing one or more heater wells in one or more identified locations,
wherein providing a
heater well comprises the steps of drilling a heater well borehole in the one
or more identified
locations using a drill string, the heater well borehole comprising an entry
portion drilled at an
angle of less than 90 degrees to a ground surface, an exit portion extending
to the ground
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surface, and a horizontal portion connecting the entry portion and the exit
portion, attaching
an elongate supplemental heater to the drill string at the exit portion,
withdrawing the drill
string from the heater well borehole such that the elongate supplemental
heater is disposed
within at least a portion of the heater well borehole, detaching the elongate
supplemental
heater from the drill string, and filling the heater well passage with a
filling material that
surrounds the supplemental heater.
[0014] According to another aspect, the filling material may comprise
cement.
[0015] According to another aspect, the cement may further comprise an
additive that
increases the thermal conductivity of the cement.
[0016] According to another aspect, the additive may comprise metal
filings.
[0017] According to another aspect, the elongate supplemental heater may
comprise an
electric heating element that may be connected at a first end to a positive
side of a power
supply and at a second end to a negative side of the power supply.
[0018] According to another aspect, providing one or more heater wells
may comprise
providing a plurality of heater wells, the supplemental heaters of each of the
heater wells
being connected to a common power supply.
[0019] According to an aspect, there is provided a method of producing
hydrocarbons
from an underground formation having an array of horizontal wells spaced
vertically and
laterally in the underground formation, the method comprising the steps of:
identifying an
upper group of well sections and a lower group of well sections, the upper
group of well
sections being positioned above the lower group of well sections; inserting
heating elements
into the upper and lower groups of well sections, the heating elements in at
least the upper
groups of well sections comprising a flow passage for communicating fluid from
a fluid input
to at least one injection port; creating voidage in the formation immediately
adjacent to the
upper and lower groups of well sections by applying sufficient heat to
mobilize a portion of
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the hydrocarbons and producing the mobilized hydrocarbons; once voidage is
created,
injecting heated gaseous solvent into the voidage of the upper group of well
sections; and
producing hydrocarbons from the lower group of well sections.
[0020] According to another aspect, the method may further comprise the
steps of:
identifying a third group of well sections above the upper group of well
sections; and once
voidage is created, moving the heating elements from the lower groups of well
sections to the
third group of well sections.
[0021] According to an aspect, the solvent may be injected into the
formation prior to
hydrocarbons being produced from the at least one producer well.
[0022] According to another aspect, the heater string may comprise a
plurality of
injection ports spaced along a length of the heater string.
[0023] According to another aspect, the heating element may be a
resistive heater.
[0024] According to another aspect, the solvent may be injected into the
heater string as a
liquid and is vapourized prior to injection into the voidage, or may be
injected into the heater
string in a gaseous phase.
[0025] According to another aspect, each injection port may be connected
to an injection
tube. The injection through each injection port may be independently
controlled. An injection
rate through each injection port may be selected to achieve a desired
distribution of solvent.
[0026] According to another aspect, the solvent may comprise a light
hydrocarbon or a
manufactured hydrocarbon compound.
[0027] According to another aspect, the solvent may comprise dimethyl
ether.
[0028] According to another aspect, the method may further comprise the
step of injecting
a carrier gas after injecting the solvent to promote the production of
hydrocarbons, and the
carrier gas may comprise a carbon-containing gas, an inert gas, or a
combination of a carbon-
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containing gas and an inert gas.
[0029] According to another aspect, the method may further comprise the
steps of
identifying locations within the underground formation that require additional
heating, and
5 providing one or more heater wells in one or more identified locations,
wherein providing a
heater well comprises the steps of drilling a heater well borehole in the one
or more identified
locations using a drill string, the heater well borehole comprising an entry
portion drilled at an
angle of less than 90 degrees to a ground surface, an exit portion extending
to the ground
surface, and a horizontal portion connecting the entry portion and the exit
portion, attaching
an elongate supplemental heater to the drill string at the exit portion,
withdrawing the drill
string from the heater well borehole such that the elongate supplemental
heater is disposed
within at least a portion of the heater well borehole, detaching the elongate
supplemental
heater from the drill string, and filling the heater well passage with a
filling material that
surrounds the supplemental heater.
[0030] According to another aspect, the filling material may comprise
cement.
[0031] According to another aspect, the cement may further comprise an
additive that
increases the thermal conductivity of the cement.
[0032] According to another aspect, the additive may comprise metal
filings.
[0033] According to another aspect, the elongate supplemental heater may
comprise an
electric heating element that may be connected at a first end to a positive
side of a power
supply and at a second end to a negative side of the power supply.
[0034] According to another aspect, providing one or more heater wells
may comprise
providing a plurality of heater wells, the supplemental heaters of each of the
heater wells
being connected to a common power supply.
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[0035] According to an aspect, there is provided an injector string
installed in a well that
extends down from surface, comprising a coiled tubing string having an inner
bore, a
downhole end and a formation section toward the downhole end. A source of
solvent is
connected to the inner bore of the coiled tubing string, the source of solvent
injecting solvent
along the inner bore toward the downhole end of the coiled tubing string. A
series of injection
ports are spaced longitudinally along the formation section of the coiled
tubing string. A
heating element is installed within the inner bore of the coiled tubing string
extending along at
least a portion of the formation section of the coiled tubing string and
connected to a power
source at surface, the heating element heating the solvent such that the
solvent exits the series
of ports as a heated vapour.
[0036] According to another aspect, the solvent may be a liquid or a gas
when injected
into the coiled tubing string.
[0037] According to another aspect, the series of injection ports may be
scaled to
distribute solvent in a desired distribution along a length of the heater
string.
[0038] According to another aspect, a plurality of injection ports may be
connected to
separate injection tubes. There may be a controller that independently
controls the solvent
injection through each injection tube and injection port. The controller may
comprise
instructions to inject the solvent through each injection tube and injection
port to achieve a
desired distribution of solvent.
[0039] According to another aspect, the heating element may be a
resistive heater.
[0040] According to another aspect, the solvent may be injected into the
heater string as a
liquid and vapourized prior to injection into the voidage.
[0041] According to another aspect, the solvent may be injected into the
heater string in a
gaseous phase.
[0042] According to another aspect, the solvent may comprise a light
hydrocarbon or a
manufactured hydrocarbon compound.
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[0043] According to another aspect, the solvent may comprise dimethyl
ether.
[0044] The above aspects and other aspects that will be apparent from the
specification
and drawings may be combined in any reasonable combination as will be
recognized by those
skilled in the art.
BRIEF DESCRIPTION OF THE DRAWINGS
[0045] These and other features will become more apparent from the
following
description in which reference is made to the appended drawings, the drawings
are for the
purpose of illustration only and are not intended to be in any way limiting,
wherein:
FIG. 1 is a schematic drawing of a well pair being heated by a heater string.
FIG. 2 is a detailed side elevation view in section of a portion of a heater
string.
FIG. 3 is an end elevation view of a horizontal wellbore pattern in a
formation
being preheated.
FIG. 4 is an end elevation view of a horizontal wellbore pattern in a
formation
being produced.
FIG. 5 is a side elevation view in section of an expansion nozzle.
FIG. 6 is a top plan view of a series of supplemental heater wells.
FIG. 7 is a side elevation view of a supplemental heater well borehole with a
drill
string in the borehole.
FIG. 8 is a side elevation view of a supplemental heater well borehole with a
supplemental heater being pulled through the well.
FIG. 9 is an end elevation view of an array of production and heater wells.
FIG. 10 is a side elevation view of a directional drilling rig.
DEI __ AILED DESCRIPTION
[0046] There will now be described a method of producing hydrocarbons
from an
underground formation having an array of horizontal wells. The underground
formation is of
a type that contains hydrocarbons, and is generally indicated by reference
numeral 10 in FIG.
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1. Generally speaking, a significant portion of the hydrocarbons will be heavy
oil or other
hydrocarbons that require one or more of heat, steam or solvents to be applied
in order to
enhance production, as will be recognized by those skilled in the art. In
these types of
reservoirs, SAGD and other types of thermal processes would normally be
contemplated in
order to produce the hydrocarbons. However, in some situations, SAGD would not
be
economical, or is rendered inoperable, such as when the maximum operating
pressure is too
low to achieve sufficient temperature with steam. Examples may include
reservoirs that lack
a competent cap rock, reservoirs that are in close proximity to quaternary
channels, close
proximity to outcrops or other geological unconfonnities or other reservoirs
where pressure is
too low to support sufficient steam temperature. The process described herein
may be
particularly useful in these types of situations. For example, SAGD operations
typically
operate at around 200 C (1,550kPa), or more commonly around 220 C (2,3201cPa),
but
generally not less than 180 C (1,000kPa). The presently described process may
operate
below or much closer to static reservoir pressure, which may be between, for
example, 100 ¨
800 1cPa, which would correspond to a saturated steam temperature of between
100 C-170 C.
It will be further recognized that the method described herein is not
specifically limited to
these types of formations, and may be applied to other types of formation
where heat, steam
and/or solvents would normally be required to produce oil from the formation.
As the present
method also involves the injection of fluids in a gaseous state, its
efficiency will also be
reduced by a low maximum operating pressure. With this apparatus, the
injection of the
gaseous fluids may still be effectively and uniformly distributed over the
length of the heater
via the plurality of ports spaced along the length of the heater. Further,
this method and
apparatus may present an alternative to surface mining methods for oil sands
recovery.
[0047] An array of wells 12 is drilled in formation 10. FIG. 1 depicts a
pair of wells 12,
as is commonly used in SAGD operations, and this may be considered an array.
In this type
of arrangement, the lower well 12 is considered the producing well, and the
upper well 12 is
considered the heater well. Referring to FIG. 3, another type of array is
shown, where there
are three rows of wells 12. The rows of wells 12 are shown as being offset, as
it is believed
that this promotes a more uniform distribution of heat to fluids being
produced in the lower
row of wells 12. It will be understood that the array of wells 12 may take
various forms with
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respect to the number of wells, their relative position, etc. Furthermore,
while producer wells
are generally at the bottom of the array to take advantage of gravity as the
hydrocarbons flow
downward, this may not be the case in all circumstances.
[0048] Referring to FIG. 1, once the array of wells 12 is drilled and the
producer and
heater wells 12 are identified, a heater string 14 is inserted into one or
more heater wells 12.
Heater string 14 has a heating element 16 and a flow passage 18 that allows
fluid to be
transported from a fluid input 20 to injection ports 22. Heating element 16 is
preferably a
resistive, or electrical heater that generates heat as electrical current is
passed through it, and
may be a radiative heating element. Heating element 16 may be a typical
heating cable as is
known in the art. This arrangement allows conductive or convective heat, which
may be
considered "dry" heat, to be uniformly applied to formation 10 and also allows
heated fluids
to be injected into heater wells 12. In other words, the heat generated by
heating element 16
is transferred by conduction to the wellbore. Within the wellbore, the heat
may then be
transferred to the formation by conduction or convection through the
substances, such as gas
or fluids, in the wellbore. As will be explained below, these heating
strategies are applied
consecutively in order to produce hydrocarbons from a well. However, not all
wells 12 that
are heated will have similar heater strings 14. While at least one heater
string 14 as described
below will be used in the method, other heaters, such as tubing strings that
are only used to
inject heated fluids, or other heating elements (i.e. tubing, cables,
combustion burners, etc.)
that are only used to apply heat.
[0049] Heating element 16 may take various forms as will be recognized.
In one
example, referring to FIG. 2, heating element 16 is depicted as being part of
a concentric
tubing string, where heating element 16 is disposed within an outer tubing
string 24. Heating
element 16 may be a cable or another coiled tubing string of a smaller
diameter that acts as an
electrical heating element that is heated by passing an electrical current
along its length. In
one aspect, it may be possible for the power supply to be direct current and
the heating
element 16 to be electrically connected to outer tubing string 24 at the end
of the heating
section to allow a return path for the current, and is otherwise electrically
isolated. Another
aspect would have a second electrically insulated conductor connected to the
distal end of the
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heating element or heating cable to provide a return path for the current to
the power supply.
In some circumstances, it may be desirable to apply more, less, or no heat at
certain points or
lengths within the heater well 12. The amount and location of heat along
heating element 16
may be controlled by providing different materials along its length or by
adjusting the power
5 supply. As a further alternative, the outer tubing string 24 may act as
heating element 16.
The circuit may be completed using various known designs. Other suitable
variations to the
options described above will be recognized by those skilled in the art. In one
example, the
heating element may be three electrically insulated conductors electrically
connected at the
distal end and supplied with alternating current to form a three-phase heater.
A plurality of
10 .. heaters may be installed inside the outer tubing string 24. In another
example, heating
element 16 may be a gas-powered heater instead of electrical. Heating element
16 may be an
elongated heater, or may radiate heat along a defined length, to apply the
heat more evenly
along the wells 12, or at targeted locations along wells 12.
[0050] In addition to heating element 16, heater string 14 also has
injection ports 22 and a
fluid flow path 18. As depicted, fluid flow path 18 is defined by an inner
surface of outer
tubing string 24. Referring to FIG. 1, fluid flow path 18 conducts fluid from
fluid input 20 to
injection ports 22. Preferably, as shown in FIG. 1, there are multiple
injection ports 22
spaced along the length of heater string 14. This results in a more even
distribution of heat. It
will be understood, of course, that injection ports 22 need not be evenly
spaced, and that
heated fluid may be kept from certain parts of formation 10, depending on the
specific
makeup of formation 10 and the strategy being employed by the well producer.
As depicted,
heated fluids are injected from a heated fluid source 26 into heater string
14, where fluids are
heated prior to being injected. Fluids may be heated by a heater that is part
of fluid source 26,
or separate, such as a line heater. It will be understood that other heating
strategies may also
be used. For example, the fluids may be heated in situ by heating element 16
as they pass
along heater string 14 prior to being injected to heat the fluids to the
desired temperature and
pressure when they encounter the formation. This may or may not involve
vaporizing the
fluids as they pass along heater string 14. The fluids may also be vaporized
as they exit heater
string 14 for example, through an expansion nozzle. As can be seen, there are
a variety of
approaches that may be used to ensure the fluids are injected into the
formation at a desired
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temperature and pressure. The fluids being heated and injected may also be
solvents that are
heated to a gas phase prior to being injected. One example of a suitable
solvent is butane,
which converts to a gas at about 50 C and has an adequate phase envelope of
temperature/pressure for the target temperature envisioned. Other C2 ¨ C7
hydrocarbons or
combination of hydrocarbons or manufactured hydrocarbons or alcohol compounds
may also
be used. In some applications, light hydrocarbons or manufactured hydrocarbon
compounds
such as dimethyl ether that may be a gas at atmospheric conditions may be
used. These
solvents are able to mix with the hydrocarbons being produced to provide a
better heat
transfer and reduce the viscosity of the hydrocarbons to allow them to flow
more freely.
While injecting steam into a reservoir decreases the reservoirs relative
permeability to oil,
injecting solvent does not affect the reservoirs relative permeability to oil.
To monitor the
process and the formation conditions, temperature and pressure monitoring
cables (not
shown), such as thermocouple or fiber optic cables, may be introduced in the
wellbore using
techniques that are known in the art.
[0051] Generally, the amount of fluid flowing through different ports 22
along heater
string 14 will vary depending on their position. Accordingly, the sizes of
ports 22 may be
modified to achieve a desired distribution of solvent injected into formation
10 and preferably
an equal distribution. It will also be understood, however, that solvent
travelling to the end of
.. heater string 14 will have a longer period of time to be heated, and
therefore may have more
heat. The desired distribution may be modified to account for this as well,
depending on the
preferences of the user and the characteristics of formation 10. Referring to
FIG. 2, in order
to achieve a desired distribution and retention time within heater string 14,
individual
injection tubing strings 27 may be connected to each port 22, such that
solvent may be
injected at a desired volume and pressure. For example, the pressure may be
higher in an
injection tubing 27 connected to a port at the toe of heater string 14
compared to tubing
connected to a port closer to the heel, such that the velocity of the solvent
is greater when
travelling to the toe, allowing for a more equal heating of solvent. In
addition, the size of the
injection tubing 27 may also vary, such that, for greater pressures, an
equivalent amount of
solvent is injected. Injection tubing 27 may be capillary tubing, or larger
tubing depending on
the requirements of the system. Using larger injection tubing 27 has the
benefit of slowing the
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injection fluid velocity to increase retention time, while capillary tubing
increases the surface
area to volume ratio and requires less space.
=
[0052] In addition to the design principles described above, other
modifications will be
apparent to those skilled in the art. For example, individual injection tubing
strings 27 may be
connected to multiple ports 22. Based on this, the desired distribution and
injection
characteristics may be achieved using known fluid dynamic principles. Using
these
approaches, a desired solvent and heat distribution may be achieved.
[0053] The basic procedure is as follows. Referring to FIG. 1, heating
element 16 is
activated to heat formation 10 in heater well 12a immediately adjacent to the
section of
heating element 16 producing heat. This may be referred to as the preheating
stage, and may
involve applying heat to more wells than heater well 12a. For example, while
not shown, a
heating element may also be inserted into production well 12b. This heating
element will
generally not include the injection ports, as it will be removed after the
preheat stage is
complete and before fluid is injected, such that a tubing string with ports is
unnecessary. Once
formation 10 is heated sufficiently that some hydrocarbons have sufficient
viscosity to be
produced. These hydrocarbons will be produced from production well 12b that is
below
heater well 12a using production tubing 25, although in some cases
hydrocarbons may also be
produced from heater well 12a. As a result of this mobility of the
hydrocarbons, some
voidage 23 is created in formation 10. Voidage 23 is created as the
hydrocarbons leave
formation 10. Most formations are porous and the hydrocarbons are held within
the pores of
the formation. As the hydrocarbons are heated and flow out of the formation,
this results in
empty space in the pores of the formation, referred to as voidage. The ability
to produce
fluids indicates that the preheating phase is completed and the second phase
can then be
applied to formation 10, which is to produce sufficient fluids and create
sufficient voidage for
the next step.
[0054] Once voidage 23 is created to the desired degree, the next step is
to inject heated
fluids into well 12. The injected fluids are preferably solvents that are
liquids at surface prior
to heating and injections and are then heated to the gaseous phase, which
exits heater string
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13
14 via ports 22 and is injected into the voidage in the formation created by
the hydrocarbons
produced as a result of heating element 16. Production of hydrocarbons from
production well
12 may then proceed according to known methods, for example by installing an
electric
submersible pump.
[0055]
Referring to FIG. 3 and 4, the method described above may also be applied to
other arrays of wells. In this example, there is an array of wells made up of
three general
rows of wells ¨ a bottom row 12c, a middle row 12d and an upper row 12e. An
example of
how hydrocarbons may be produced from this arrangement will now be described.
[0056]
Referring to FIG. 3, a first step may involve heating rows 12c and 12d with
electric heating elements to produce voidage 23 around the heated wells. As
shown, heating
elements 14 in row 12d are similar to those described with respect to FIG. 1
and 2 and are
capable of conductive heating as well as injecting heated fluids, while
heating elements 15 in
row 12e may be conductive heating elements only. In FIG. 4, once a certain
target
temperature and corresponding oil viscosity in the formation has been
achieved, heating
elements 15 may be moved from row 12c to 12e and production tubing 25 may be
inserted
into row 12c. Alternatively, heating elements 15 may be replaced with
injection-type heaters,
or combination heaters 14.
[0057] An
example of a possible series of steps will now be described. Referring to FIG.
1, in a first phase, a wellbore 12a is pre-heated using a heater tube 14. In
the next phase, a
limited amount of production occurs from wellbore 12b. This creates voidage 23
that
improves the production index (PI) and helps to repair skin damage that may
have been
caused during drilling. In the third phase, solvent injection through heater
tube 14 begins. As
shown, heater tube 14 preferably has multiple injection port 22 and vapourized
solvent or
solvents, for example, butane, is injected into wellbore 12 through these
ports. Providing
multiple injection ports 22 allows for a more effective gravity drainage
process by providing a
more effective or uniform solvent distribution. As mentioned above the solvent
may be
vapourized by passing through heater tube 14, which is heated by heating
element 16 or it
may be injected into heater tube 14 as a vapour. This may be due to
atmospheric conditions
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14
or heating at surface, in which case heater tube 14 merely maintains the
solvent in the vapour
phase as it is injected and heats the solvent to the desired temperature.
Alternatively, the
solvent may be vapourized as it passes through an expansion nozzle at each
injection port 22.
An example of an expansion nozzle is shown in FIG. 5, and identified by
reference numeral
28. Expansion nozzles 28 are well known, and it will be understood that the
actual profile of
expansion nozzles 28 may vary. If present, these expansion nozzles 28 are
attached at
injection ports 22 along heater tube 14. Once the hydrocarbons in the
formation become
mobile, production may begin as described above.
[0058] In another phase, a carrier gas, such as CO2, may be injected along
with the
selected solvent to reduce the solvent requirements, and associated cost, as
well as for voidage
replacement/maintenance. This may be used to promote a lower solvent to oil
ratio, resulting
in better economics for the well. The carrier gas may be injected from a
separate source of
gas such that the carrier gas and solvent mix in the heater tuber 14, or may
be mixed with the
.. solvent prior to injection. A preferred method may be to use the carrier
gas as a displacement
gas whereby the solvent is injected through the ports in pure form followed by
the
displacement gas separately to avoid gas mixing and to move or displace the
solvent further
into the reservoir. In other embodiments, the carrier gas may be a miscible
gas such as CO,
CO2, or an inert gas such as nitrogen, and may be injected in a separate step
from the injection
of the solvent. After injection of the solvent, the carrier gas may injected
separately for the
purpose of transporting the solvent to greater distances from the injection
well, and to reduce
the volume of solvent required and to increase the region of influence of the
solvent and heat
delivered around the well pair.
[0059] In another phase, maintenance heaters may be used to service and
improve the
production from well 12. Existing heater tubes 14 or heating elements 16 may
be used as
maintenance heaters, or new heaters may be inserted instead. In one example,
referring to
FIG. 4, heaters may be removed from lower heater wells 12c and inserted into a
new set of
wells (not shown) drilled above upper wells 12e.
[0060] The
spacing of the heater wells and production wells may be determined by the
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desired region of influence around the well pair or by the economics of the
well operation. It
may be necessary to provide supplementary heater wells 100 to increase
production. These
wells may be drilled with traditional methods, or may be drilled using a
method of directional
drilling that is typically used for subterranean river or road crossings,
which are generally
5 shallow. For example, drilling rig 102 may deploy a subterranean rotary
positive
displacement motor that rotates a drill bit to create a drill hole in the
earth. One example of
such a directional drilling rig 102 is shown in FIG. 10. When supplementary
heater wells 100
are required, the first step is to identify locations within the underground
formation that
require additional heating, such as areas that are not heated or are
insufficiently heated by the
10 heating element of the heater string 14. These may be additional
locations within the reservoir
that may remain outside the region that is heated by the first or second or
third group of wells.
Referring to FIG. 7, one or more heater wells 100 is then provided in one or
more identified
locations by drilling a heater well borehole 104 in the one or more identified
locations using a
drilling rig that has a drill string 114, the heater well borehole 104 having
an entry portion 106
15 drilled at an angle of less than 90 degrees to a ground surface 112, an
exit portion 108
extending to the ground surface 112, and a horizontal portion 110 connecting
entry portion
106 and exit portion 108. Horizontal portion 110 preferably extends through
the oil bearing
formation for a predetermined distance before being directed back to the
surface through exit
portion 108 at a planned location. When the drill string emerges at the far
end of heater well
borehole 104, at ground surface 112, an elongate supplemental heater 116 is
attached to the
end of the drill string at exit portion 108. Supplemental heater 116 may be a
heating cable or a
heating element. Referring to FIG. 8, once supplemental heater 116 is attached
to drill string
114, the drill string 114 is withdrawn from heater well borehole 104 by
drilling rig 102,
pulling supplemental heater 116 through heater well borehole 104 such that
elongate
supplemental heater 116 is disposed within at least a portion of heater well
borehole 104.
Elongate supplemental heater 116 can then be detached from drill string 114,
and remains in
heater well borehole 104, extending along the length of heater well borehole
104. Heater well
borehole 104 is then filled with a filling material such as cement to surround
the supplemental
heater 116. The filling material may displace the drilling mud from the drill
hole and
completely fill the drill hole. In order to increase the thermal conductivity
of the cement,
additive materials such as metal filings may be added to the cement. The
elongate
CA 02924899 2016-03-23
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supplemental heater 116 may be an electric heating element that is connected
at a first end to
a positive side of a power supply and a second end to a negative side of the
power supply, and
where multiple heater wells are provided, the supplemental heaters of each of
the heater wells
may be connected to a common power supply.
[0061]
Referring to FIG. 9, an example of a well configuration having production
wells
12f, heater wells 12g, and supplemental heater wells 100 is shown. In this
example,
production wells 121 are drilled at the lowest point in a production region
130. Heater wells
12g are spaced vertically above the production wells 12f. Supplemental heater
wells 100 are
then spaced vertically above the heater wells 12g and offset in order to
increase the
production from the production region 130. It will be understood that the
heater wells 12g and
supplemental heater wells 100 are spaced such that the region of influence 132
of each of the
wells intersects the region of influence of the adjacent wells. This
connection between the
regions of influence 132 allows the amount of production fluids mobilized to
be increased,
and for the production fluids to flow downward into production wells 121. It
will be
understood that the number, spacing, and arrangement of the wells need not be
similar to what
is shown, and may vary depending on the environment and economics of any given
production site, as will be understood by those skilled in the art.
[0062] As shown in
FIG. 6, the supplemental heater wells 100 may be grouped in a heater
array having multiple resistive heater elements 116 connected to an AC or DC
power supply
118 by two electrical buses 120, each electrical bus 120 including one or a
multiple of
conductors. As will be understood by those skilled in the art, the arrangement
and elements of
this heater array may take various forms. In one example of the heater array,
the heater
elements may include load balancing circuitry at one end of the heater
elements. In another
example of the heater array, the heater elements may include load balancing
circuitry at the
power supply. In another example, the heater elements may include load
balancing circuitry at
one end of the element and at the power supply. These variations of the heater
array may be
combinable such that the heater array includes heater elements with load
balancing circuitry
at one end of the heater elements and at the power supply. In addition, the
array assembly
power supply may contain load shedding circuitry and logic to limit input
power grid peak
CA 02924899 2016-03-23
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demands.
[0063] In this
patent document, the word "comprising" is used in its non-limiting sense to
mean that items following the word are included, but items not specifically
mentioned are not
excluded. A reference to an element by the indefinite article "a" does not
exclude the
possibility that more than one of the element is present, unless the context
clearly requires that
there be one and only one of the elements.
[0064] The
following claims are to be understood to include what is specifically
illustrated
and described above, what is conceptually equivalent, and what can be
obviously substituted.
The scope of the claims should not be limited by the preferred embodiments set
forth in the
examples, but should be given the broadest interpretation consistent with the
description as a
whole.
