Note: Descriptions are shown in the official language in which they were submitted.
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RECOVERY OF HYDROCARBONS FROM UNDERGROUND RESERVOIRS
TECHNICAL FIELD
[001] The technical field relates to methods and systems for recovering
hydrocarbons from an
underground reservoir.
BACKGROUND
[002] Current methods for recovering hydrocarbons from underground reservoirs
are not
always efficient. For light oil, only about 50% of the original oil in place
in a reservoir is
recovered by existing technologies. For heavy oil, the recovery in some cases
is less than 10%.
In certain situations, bitumen is so heavy that it does not flow at all and no
oil can be recovered
by conventional drilling and pumping; instead, enhanced oil recovery (EOR)
processes are
required. Exemplary EOR technologies include polymer enhanced waterfloods,
solvent
enhanced gas floods, and the addition of thermal energy (e.g., steam, in-situ
combustion, or
electricity). For heavy oil and bitumen recovery, steam assisted gravity
drainage (SAGD) has
become increasingly popular due to a high recovery factor. Despite enhanced
recovery
processes, though, significant quantities of hydrocarbons are left behind in
the reservoirs after
initial recovery (e.g., cellar oil).
[003] Given today's high demand for oil, there remains a need for further
recovery of residual
hydrocarbons, especially bitumen and other residual heavy oil. Currently,
known heavy oil
reservoirs in North America and vast reservoirs elsewhere in the world contain
significant
amounts of hydrocarbons. A technology for recovering a greater percentage of
the residual or
stranded oil from existing reservoirs could present immense opportunities for
the oil industry.
[004] While various attempts have been made to enhance hydrocarbon recovery or
to recover
stranded hydrocarbons, there still exists a need for improved methods and
solutions (e.g.,
methods and solutions which can be simpler, more efficient in terms of yield,
or more cost
effective).
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SUMMARY
[005] In general, the present specification describes methods and related
systems for recovering
hydrocarbons from a hydrocarbon-bearing formation.
[006] In one implementation, there is provided a method for recovering
hydrocarbons. The
method includes producing the hydrocarbons from a portion of a production well
located in an
adjacent location outside of the hydrocarbon-bearing formation via a plurality
of channels
between the hydrocarbon-bearing formation and the adjacent location, the
plurality of channels
fluidly connecting the hydrocarbon-bearing formation and the portion of the
production well.
[007] In some aspects of the method, at least a portion of a first production
well is positioned in
a formation adjacent to the hydrocarbon-bearing formation, and a plurality of
channels
communicating with the production well are formed. The channels extend from
the portion of
the production well to the hydrocarbon-bearing formation, so as to provide
continuity between
the production well and the hydrocarbon-bearing formation. The hydrocarbons
can be collected
from the hydrocarbon-bearing formation through the production well and can be
produced to
surface.
[008] In another implementation, there is provided a method for recovering
hydrocarbons from
a hydrocarbon-bearing formation. The method includes the steps of providing at
least a portion
of a production well at an adjacent location outside of the hydrocarbon-
bearing formation,
providing an injection well adapted for injecting a heated fluid or viscosity-
reducing agent into
the hydrocarbon-bearing formation, providing a plurality of channels that
provide fluid
communication between the portion of the production well and the hydrocarbon-
bearing
formation, and producing hydrocarbons from the hydrocarbon-bearing formation
through the
portion of the production well. The hydrocarbons are produced via at least
some of the plurality
of channels that provide fluid communication from the hydrocarbon-bearing
formation to the
portion of the production well located outside of the hydrocarbon-bearing
formation.
[009] In some aspects of the methods, the hydrocarbon-bearing formation
contains bitumen. In
some aspects of the method, the adjacent location is in an underlying
formation that is beneath
the hydrocarbon-bearing formation. In some aspects of the methods, the
underlying formation
contains hydrocarbons. In some aspects of the methods, the underlying
formation has a higher
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degree of consolidation than the hydrocarbon-bearing formation.
[010] In some aspects of the methods, the channels further provide fluid
communication
between the portion of the production well and the underlying formation, and
the underlying
formation contains additional hydrocarbons. In some aspects, the methods for
recovering
hydrocarbons include the step of recovering the additional hydrocarbons from
the underlying
formation through the production well. In some aspects of the methods, the
injection well is
arranged substantially parallel to the portion of the production well.
[011] In some aspects of the methods, the portion of the production well is
oriented at an angle
from vertical to horizontal or beyond horizontal, so as to collect the
hydrocarbons from the
hydrocarbon-bearing formation. In some aspects of the methods, the portion of
the production
well is positioned substantially horizontal. In some aspects of the methods,
the heated fluid is
steam.
[012] In some aspects of the methods, the hydrocarbon-bearing formation
includes a formation
production well. In some aspects of the methods, the adjacent location
includes an additional
production well. In some aspects of the methods, the hydrocarbon-bearing
formation includes at
least two formation production wells and an infill region between the at least
two formation
production wells; the portion of the production well is positioned in the
underlying formation
under the infill region.
[013] In some aspects of the methods, the channels are formed by perforating,
hydraulic
fracturing, acid fracturing, acidizing, drilling, or jetting. In some aspects
of the methods, the
channels are formed by acidizing or acid fracturing, and acid is directed by
orifices or jets from
the portion of the production well towards the hydrocarbon-bearing formation.
In some aspects
of the methods, the channels are formed by hydraulic fracturing using a
fracturing fluid, and the
fracturing fluid contains a proppant. In some aspects of the methods, the
channels are formed by
perforation using a stream of hot gas and fine metal particles. In some
aspects of the methods,
the channels are formed by drilling using a rotating drill bit. In some
aspects of the methods, the
channels are formed by jetting using a high-pressure fluid. In some aspects of
the methods, the
high-pressure fluid contains at least one of (a) fine particles to augment the
jetting process,
(b) acid, and (c) an abrasive grit.
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[014] In some aspects of the methods, the hydrocarbon-bearing formation is
partially depleted
by a previous recovery operation. In some aspects, the methods include the
step of recovering
the hydrocarbons from the hydrocarbon-bearing formation through the production
well. In some
aspects, the methods include the step of draining the hydrocarbons by gravity
into the production
well. In some aspects of the methods, the production well is drilled from a
mine face at the
adjacent location.
[015] In some aspects of the methods, producing the hydrocarbons includes
operating a steam
assisted in-situ hydrocarbon recovery process. In some aspects of the methods,
the steam
assisted in-situ hydrocarbon recovery process includes a steam assisted
gravity drainage system.
In some aspects of the methods, the steam assisted in-situ hydrocarbon
recovery process includes
a cyclic steam stimulation system. In some aspects of the methods, producing
the hydrocarbons
includes operating a combustion process by injecting a combustible fuel into
the hydrocarbon-
bearing formation using the injection well. In some aspects of the methods,
producing the
hydrocarbons includes using at least one of electrical heating,
electromagnetic heating, radio
frequency heating, solvent injection, carbon dioxide flooding, non-condensable
gas injection,
flue gas flooding, surfactants injection, alkaline chemicals injection, and
microbial enhanced
recovery.
[016] In another implementation, there is provided a method for recovering
bitumen from a
bitumen-bearing formation. The method includes mobilizing the bitumen in the
bitumen-bearing
formation by injecting steam into the bitumen-bearing formation by way of an
injection well
included in the bitumen-bearing formation, draining the mobilized bitumen by
gravity through a
plurality of channels, and producing the bitumen from a portion of a
production well located in
an underlying formation beneath the bitumen-bearing formation, the plurality
of channels fluidly
connecting the bitumen-bearing formation and the portion of the production
well.
[017] In another implementation, there is provided a system for recovering
hydrocarbons from
a hydrocarbon-bearing formation. The recovery system includes a production
well, at least a
portion of which is positioned in a location adjacent to the hydrocarbon-
bearing formation. The
recovery system also includes an injection well adapted for injecting a heated
fluid or viscosity-
reducing agent, at least a portion of which is positioned in the hydrocarbon-
bearing formation,
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and a plurality of channels that communicate with the production well. The
channels extend
from the portion of the production well to the hydrocarbon-bearing formation
to provide
continuity between the production well and the hydrocarbon-bearing formation.
[018] In some aspects of the system, the hydrocarbon-bearing formation
contains bitumen and
the adjacent location is an underlying formation that is beneath the
hydrocarbon-bearing
formation.
[019] In some aspects, the system includes production equipment for producing
the
hydrocarbons from the hydrocarbon-bearing formation through the production
well. In some
aspects of the system, the heated fluid includes steam.
[020] In some aspects of the system, the production equipment includes a steam
assisted gravity
drainage system. In some aspects of the system, the production equipment
includes a cyclic
steam stimulation system. In some aspects of the system, the production
equipment is
configured to operate a combustion process by injecting a combustible fuel
into the hydrocarbon-
bearing formation using the injection well. In some aspects of the system, the
production
equipment is configured to mobilize the hydrocarbons using at least one of
electrical heating,
electromagnetic heating, radio frequency heating, solvent injection, carbon
dioxide flooding,
non-condensable gas injection, flue gas flooding, surfactants injection,
alkaline chemicals
injection, and microbial enhanced recovery.
[021] In some aspects of the system, the production well is drilled from a
drainage pit at the
adjacent location.
[022] In a further implementation, there is provided a system for recovering
bitumen from a
bitumen-bearing formation. The system includes a production well that has a
substantially
horizontal portion positioned in an underlying formation beneath the bitumen-
bearing formation
and adapted to receive mobilized bitumen, an injection well that is adapted to
inject steam into
the bitumen-bearing formation and has at least a portion positioned in a
bitumen-bearing
formation, and a plurality of channels that communicate fluidly with the
production well, the
channels extending from the horizontal portion of the production well to the
bitumen-bearing
formation to provide continuity between the production well and the bitumen-
bearing formation
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to allow mobilized bitumen to drain from the bitumen-bearing formation into
the production
well.
[023] Methods and systems described herein can enhance recovery of
hydrocarbons from
reservoirs in several respects. In some implementations, for example, the
methods and systems
can provide access to hydrocarbons that are generally considered to be
stranded (e.g., cellar
hydrocarbons, bypassed hydrocarbons, etc.). Furthermore, methods and systems
described
herein can provide dual access to hydrocarbons from a target reservoir and to
hydrocarbons from
a formation adjacent to (e.g., beneath, next to, etc.) the target reservoir.
In some
implementations, the methods and systems can facilitate drilling of production
wells where target
reservoirs are relatively unconsolidated. Methods and systems described herein
can also be
implemented where given reservoir conditions (e.g., thickness of a reservoir)
do not favourably
accommodate a production well within the reservoir.
[024] The details of one or more implementations are set forth in the
description below. Other
features and advantages will be apparent from the specification and the
claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[025] Features and advantages of embodiments of the present application will
become apparent
from the following detailed description and the appended drawings, in which:
[026] FIG. la is a schematic view showing a typical configuration of
injection/production wells
in a hydrocarbon reservoir for SAGD;
[027] FIG. lb is a cross-sectional view taken from A-A in FIG. I a,
additionally showing a
steam chamber created in the reservoir;
[028] FIGs. 2a-2d are schematic views showing cellar oil trapped under SAGD
production
wells at the bases of reservoirs which are in various geological shapes, in
which FIG. 2a shows
an undulating base of a pay zone, FIG. 2b shows a dipping base of a pay zone,
FIG. 2c shows a
faulted base of a pay zone, and FIG. 2d shows a partially collapsed base of a
pay zone;
[029] FIG. 3a shows an exemplary arrangement of a pair of horizontal
injection/production
wells for a SAGD operation in accordance with methods and system described
herein, in which
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the steam injector is in the reservoir (pay) and the production well is in an
adjacent, underlying
formation;
[030] FIG. 3b is a cross-sectional view taken from B-B in FIG. 3a,
additionally showing a
steam chamber created in the reservoir;
[031] FIG. 4a is a schematic view showing perforations that connect a SAGD
production well
to a reservoir formation;
[032] FIG. 4b is a cross-sectional view of FIG. 4a, additionally showing a
steam chamber
created in the reservoir, with perforations connecting the production well to
the steam chamber;
[033] FIG. 4c shows a jet perforator firing streams of hot gas and fine metal
particles at high
speed through the wall of the production casing or liner and into a formation
adjacent to a
production well;
[034] FIG. 5a is a schematic view showing fractures that connect a SAGD
production well to a
reservoir formation;
[035] FIG. 5b is a cross-sectional view of FIG. 5a, additionally showing a
steam chamber
created in the reservoir, with fractures connecting the production well to the
steam chamber;
[036] FIG. 5c is a schematic view showing a formation rock being fractured by
fracturing fluid
at high pressure;
[037] FIG. 5d is a schematic view showing a proppant holding open a fractured
portion of a
formation rock;
[038] FIG. 6a is a schematic view showing acidized fractures that connect a
SAGD production
well to a reservoir formation;
[039] FIG. 6b is a cross-sectional view of FIG. 6a, additionally showing a
steam chamber
created in the reservoir, with acidized channels or fractures connecting the
production well to the
steam chamber;
[040] FIG. 6c shows a sample fracture face before and after acidization;
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[041] FIG. 7a is a schematic view showing drilled boreholes that connect a
SAGD production
well to a reservoir formation;
[042] FIG. 7b is a cross-sectional view of FIG. 7a, additionally showing a
steam chamber
created in the reservoir, with drilled boreholes connecting the production
well to the steam
chamber;
[043] FIG. 8a is a schematic view showing hydraulically jetted perforations
that connect a
SAGD production well to a reservoir formation;
[044] FIG. 8b is a cross-sectional view of FIG. 8a, additionally showing a
steam chamber
created in the reservoir, with hydraulically jetted perforations connecting
the production well to
the steam chamber;
[045] FIG. 8c is a schematic view showing a hydraulic jetting tool boring a
perforation through
a production casing or uncased borehole into a formation;
[046] FIG. 9a is a schematic view showing drilled or jetted boreholes that
connect an offset
production well to a reservoir formation;
[047] FIG. 9b is a cross-sectional view of FIG. 9a, additionally showing a
steam chamber
created in the reservoir, with drilled or jetted boreholes connecting the
production well to the
steam chamber;
[048] FIG. 10 is a schematic view showing both an injection well and a
production well being
initiated from a mine face, in which the production well is located in an
adjacent formation
beneath a hydrocarbon-bearing reservoir; and
[049] FIG. 11 is a schematic view showing a production well located in a
formation beneath a
hydrocarbon-bearing reservoir and, at the same time, positioned under an
infill region formed
between two SAGD steam chambers within the reservoir, where the production
well is connected
to the reservoir through perforations, fractures, acidized channels, drilled
boreholes, or
hydraulically jetted boreholes.
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DETAILED DESCRIPTION
[050] The present description relates to methods and systems for recovering
hydrocarbons from
underground reservoirs. Generally, in these methods and systems, at least a
portion of a first
production well is positioned in a geological formation that is adjacent to
and distinct from a
target hydrocarbon-bearing reservoir, and channels are formed between the
production well and
the reservoir to establish fluid communication therebetween. The channels can
be provided by
various techniques, including, without limitation, perforating, fracturing,
acidizing, drilling,
jetting, and the like. Hydrocarbons can then be collected from the reservoir
through the
production well and recovered to surface.
[051] Conventionally, a production wellbore is provided within, and collects
production fluid
from, a hydrocarbon-bearing or oil-bearing reservoir. Much effort has been
invested in
attempting to access cellar or stranded oil; however, such attempts have
almost always been
made through a production well drilled into the target reservoir formation.
The present methods
and systems take a different approach by intentionally locating a production
well in a formation
adjacent to (e.g., beneath, next to, etc.) the target reservoir formation,
with the aim of improving
overall recovery of hydrocarbons from the reservoir.
[052] Throughout this specification, numerous terms and expressions are used
in accordance
with their ordinary meanings. Provided below is a discussion of some terms and
expressions that
are used herein.
[053] A "formation" or "geological formation" is a fundamental unit of
lithostratigraphic
classification. A formation includes rock strata that have comparable
lithologies, facies, or other
similar properties. Formations can be defined on the basis of the thickness of
the rock strata of
which they consist, and the thickness of different formations can vary widely.
A given
stratigraphic column can include a number of formations. In the oil sands area
of Northeastern
Alberta, for example, the stratigraphic column consists of the following major
formations (from
basement to surface): Pre-Cambrian (basement), Devonian carbonates, McMurray
oil sands,
Wabiskaw sands and mudstones, Clearwater shales, Grand Rapids sandstones, and
Quaternary
sediments.
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[054] The "McMurray formation" or "McMurray sands" is a stratigraphic unit of
Early
Cretaceous age in the Western Canada Sedimentary Basin of Northeastern
Alberta. It lies
unconformably on Pre-Cretaceous erosion surfaces that generally comprise
Devonian limestone,
which is mainly carbonate rock. The McMurray sands are largely unconsolidated
and the sand
grains that form the formation are mostly held together by very viscous crude
oil. The
McMurray formation holds most of the vast hydrocarbon resources of the
Athabasca bituminous
sand deposit.
[055] As used herein, the term "overburden" refers to the sediments or earth
materials
overlaying a formation containing a hydrocarbon-bearing zone.
[056] The term "reservoir" refers to a subsurface formation containing one or
more natural
accumulations of hydrocarbons, which are generally confined by relatively
impermeable rock or
other geological layers of materials. Typically, a reservoir formation
containing recoverable
hydrocarbons, referred to as the "pay", is formed between a top cap layer and
a bottom base.
[057] As used herein, "oil sands reservoir" refers to a subsurface formation
that is primarily
composed of a matrix of unconsolidated sand, with hydrocarbons, such as
bitumen or extremely
heavy crude oil, occurring in the porous matrix.
[058] The term "hydrocarbons" refers to a combination of different
hydrocarbons or a
combination of various types of molecules that contain carbon atoms and
attached hydrogen
atoms. Hydrocarbons include a large number of different molecules in gaseous,
liquid, or solid
phase having a wide range of molecular weights, and can include bitumen, heavy
oil, lighter
grades of oil, and natural gas. Elements (e.g., sulphur, nitrogen, oxygen),
metals (e.g., iron,
nickel, vanadium), and compounds (e.g., carbon dioxide, hydrogen sulphide) are
sometimes
present in the form of impurities in a desired hydrocarbon mixture.
[059] The term "perforating" or "perforation" refers to eroding a hole (e.g.,
in the casing of a
well and the formation surrounding the well). By way of example, jet
perforators can fire a
stream of hot gas and fine metal particles at a speed of ¨10,000 m/s towards
the wall of a
production casing. The depth of perforation can be augmented by simultaneous
application of
high pressure gas, or by sleeves of propellant external to the perforating
device (also known as a
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perforating gun).
[060] As used herein, "fracturing" includes a process for structurally
degrading a geological
formation around a wellbore by applying thermal and/or mechanical stress. Such
structural
degradation generally enhances the permeability of the formation to fluids.
Examples of
hydraulic fracturing for use in the present methods and systems include,
without limitation,
hydraulic fracturing and acid fracturing.
[061] "Hydraulic fracturing" refers to a method of using pump rate and
hydraulic pressure of a
hydraulic fracturing fluid, which can be a liquid or gas or a combination
thereof, to fracture or
crack a subterranean formation, thereby creating relatively large flow
channels through which
hydrocarbons can move into a well.
[062] "Proppant" or "propping agent" refers to sized particles mixed with
fracturing fluid to
hold fractures open after a hydraulic fracturing treatment. In addition to
naturally occurring sand
grains, man-made or specially engineered proppants, such as resin-coated sand
and ceramic
beads, can also be used. Proppant materials are carefully sorted for size and
sphericity to provide
an efficient conduit for production of fluid from a reservoir to a wellbore.
[063] "Acid fracturing" refers to a fracturing method in which an acid is used
in the fracturing
fluid to increase or restore permeability to a formation.
[064] The term "acidizing" refers to injecting an acid into a formation that
can be dissolved by
acid, such as a formation containing calcium carbonate sediments, thereby
creating flow paths in
the target formation. Exemplary acids for use herein include, without
limitation, hydrochloric
acid (HC1).
[065] The term "drilling" refers to the creation of a borehole in a formation
by rotating a drill
bit and simultaneously applying an axial load to the bit.
[066] As used herein, "directional drilling" refers to steering the drill bit
in a desired direction.
[067] The expression "coiled tubing drilling" refers to use of continuous, non-
segmented pipe
to convey the drilling assembly to the formation. The coiled tubing itself
does not rotate. The
drilling assembly includes a downhole motor that rotates the drill bit and can
also contain a
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directional measurement device and a steering assembly.
[068] The term "jetting" refers to pumping fluids at high pressure through a
nozzle to erode a
hole into a formation. The nozzle can be conveyed to the formation via jointed
or continuous
pipe. The high-pressure fluid can contain fine particles to augment the
jetting process, or acid to
dissolve rock simultaneously.
[069] "Sand control" includes preventing or otherwise alleviating the buildup
of particles in a
production well. Sand can present major obstacles to production through
reduced production
rates, sand bridging, erosion of equipment, and sand disposal and removal.
Sand control can be a
substantial problem when the produced fluids flow from an unconsolidated
formation.
[070] A "production well" or "producer" includes any well or wellbore from
which
hydrocarbons can be produced, regardless of its configuration or arrangement.
The production
well can be configured vertically, horizontally, or at any angle from vertical
to horizontal or
beyond horizontal, in any portion thereof.
[071] As used herein, "vertical" direction is the direction of gravity force
and "horizontal"
direction is perpendicular to the direction of gravity force.
[072] "Stranded hydrocarbons" include hydrocarbons of any viscosity that are
not recoverable
at commercially attractive extraction rates at given reservoir conditions
and/or recovery
operations. Examples of stranded hydrocarbons recovered by the present methods
and systems
include, without limitation, cellar hydrocarbons and hydrocarbons in an infill
or bypassed region.
[073] The expression "cellar hydrocarbons" refers to the stranded hydrocarbons
that are
accumulated or located at the base of a reservoir.
[074] As used herein, "infill region" or "bypassed region" refers to an area
formed between at
least two production wells in a reservoir, in which a significant quantity of
hydrocarbons, in the
form of bitumen, heavy oil, or otherwise, remains unrecovered by normal
recovery operations.
[075] A "chamber" within a reservoir or formation includes a region that is in
fluid
communication with a particular well or wells, such as an injection or
production well. For
example, in a SAGD process, a steam chamber is the region of the reservoir in
fluid
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communication with a steam injection well; this is also the region that is
subject to depletion,
primarily by gravity drainage, into a production well. Thus, a chamber can be
a depleted region.
[076] Specific examples of the present methods and systems are described below
with reference
to the drawings. Details are provided for the purpose of illustration, and the
methods and
systems can be practiced without some or all of the features discussed herein.
For clarity,
technical materials that are known in the fields relevant to the present
methods and systems are
not discussed in detail.
[077] Some of the drawings and implementations described herein refer to a
SAGD operation.
However, it should be understood that other configurations can be used that
may or may not
involve the use of steam. For example, an injection well may be used to inject
a solvent or other
chemical that can be used to modify the viscosity of the hydrocarbons in the
formation, so that
the hydrocarbons can be produced by gravity to flow to the production well. In
other
configurations, a source of thermal energy other than steam, such as in-situ
combustion, electric
heat, radio frequency energy, and the like, or a combination of any of the
foregoing, can be used
to heat the formation and again modify the viscosity of the hydrocarbons to
cause production of
hydrocarbons by gravity drainage. The implementations described below are
considered in the
exemplary context of SAGD, but are not intended to be limited to SAGD
applications.
[078] FIG. la illustrates the basic principles of a SAGD operation in a
hydrocarbon-containing
reservoir (10). A horizontal steam injection well (11) is located above a
horizontal production
well (12) in the same geological formation (10). Steam (13) is injected into
the injection well
(11) to form a steam chamber above the well pair, and production fluid (14)
(e.g., including
hydrocarbons and hot water, such as hot water from condensed steam) is
collected in the
production well (12) and produced to surface. In the illustrated
implementation, the steam
injection well (11) and the production well (12) are both located within the
steam chamber or
heat affected zone (20). There is a steam/liquid interface between the steam
injection well (11)
and the production well (12). In some implementations, the production well
(12) is not in direct
contact with gaseous steam; in such implementations, the liquid below the
steam/liquid interface
is a mixture of hydrocarbons and condensed steam (hot water). The gas/liquid
interface between
the injection well (11) and the production well (12) is also present in other
implementations that
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involve the injection of a gaseous solvent, such as butane and the like, a
gaseous chemical, such
as carbon dioxide and the like, or air for combustion.
[079] Referring to FIG. lb, a steam-filled chamber (20) is created by steam
(13'), which is
injected into the reservoir (10) through the injection well (11), moving into
the formation around
the injection well (11). The steam chamber (20) surrounds the injection well
(11) and extends
from the horizontal production well (12) towards the top of the reservoir
(10). Production fluid
(14'), which includes condensed steam and hydrocarbons (e.g., bitumen), flows
down the sides of
the steam chamber (20) towards the production well (12). In some
implementations, the
injection well (11) is at a higher pressure than the production well (12). In
further
implementations, the injection well (11) is at a slightly higher pressure than
the production well
(12). In some implementations, it is desirable to maintain a small temperature
difference or
"subcool" between the injection well (11) and the production well (12), to
ensure that the
production well is immersed in liquid.
[080] Referring to FIGs. 2a-2d, geological formations typically are not
perfectly horizontal.
There can be undulations (16) (FIG. 2a) or an inclination (17) at the top or
bottom of a formation
(FIG. 2b), displacements or faults (18) (FIG. 2c), or large sink holes (19)
caused by dissolution
of rock minerals (FIG. 2d). Even though SAGD operators generally attempt to
drill the SAGD
well pairs (injection well (11) and production well (12)) more or less
horizontally, a significant
volume of cellar hydrocarbons (30) can be below the SAGD well pair, as
illustrated in FIGs. 2a-
2d.
[081] Production wells have historically been positioned in the target
reservoir formations for
collection of hydrocarbons therefrom. Using SAGD as an example, the production
well has been
located in the same reservoir formation as the injection well, as illustrated
in FIGs. la, lb, and
2a-2d.
[082] In the present methods and systems, though, a production well is
positioned in an
adjacent location that borders the target reservoir. In some implementations,
the adjacent
location is a formation but not a reservoir. In some implementations, the
adjacent location is a
formation and also a reservoir.
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[083] In one implementation, there is provided a method for recovering
hydrocarbons from a
hydrocarbon-bearing formation. The method includes producing the hydrocarbons
from a
portion of a production well located in an adjacent location outside of the
hydrocarbon-bearing
formation via a plurality of channels between the hydrocarbon-bearing
formation and the
adjacent location. The plurality of channels fluidly connect the hydrocarbon-
bearing formation
and the portion of the production well.
[084] In another implementation, there is provided a method for recovering
hydrocarbons from
a hydrocarbon-bearing formation. The method includes the steps of providing at
least a portion
of a production well outside of the hydrocarbon-bearing formation, providing a
plurality of
channels that provide fluid communication between the portion of the
production well and the
hydrocarbon-bearing formation, and producing hydrocarbons from the hydrocarbon-
bearing
formation through the portion of the production well. Hydrocarbons are
produced via at least
some of the plurality of channels that provide fluid communication from the
hydrocarbon-
bearing formation to the portion of the production well located outside of the
hydrocarbon-
bearing formation.
[085] FIGs. 3a and 3b exemplify one arrangement of a production well relative
to an injection
well in the context of a SAGD operation. As shown in FIGs. 3a, an injection
well (11) and a
production well (12) are drilled either vertically or at an inclination
through the overburden (50)
that overlays a reservoir (pay) (10). When the injection well (11) reaches a
suitable depth within
the reservoir (10), the injection well (11) is then horizontally extended
between the top (21) and
base (22) of the reservoir (10). In comparison, the production well (12) is
drilled further down
below the base (22) of the reservoir (10) and then horizontally extended
within an underlying
formation (40) that is beneath the reservoir (10). FIG. 3b shows a steam
chamber (20) created by
steam (13') injected through the injection well (11) in the reservoir (10).
Once the hydrocarbons
within the chamber (20), including any cellar hydrocarbons (30), are
sufficiently mobilized,
production fluid (14'), which includes mobilized hydrocarbons and condensed
steam, are drained
into the lower portion of the chamber (20) and into the production well (12).
As the person
skilled in the art will appreciate, various well-drilling and completion
technologies are currently
available to drill the wells and connect the production well in the underlying
formation to the
hydrocarbon-bearing reservoir. Production wells can be placed at underground
locations with
CA 02913609 2015-11-27
desired configurations using technologies known to the skilled person. While
the
implementation shown in FIGs. 3a and 3b represents one production well (12),
more than one
production well (12) can be used in other implementations.
[086] Once the production well is positioned in a formation adjacent to the
target reservoir,
means for fluid communication ¨ such as channels (100) between the hydrocarbon-
bearing
reservoir and the underlying formation, as shown in FIGs. 3a and 3b ¨ are
established between
the production well and the target reservoir or a specific pay zone in the
reservoir. Numerous
techniques are available to accomplish this step, including, without
limitation, perforating,
hydraulic fracturing, acid fracturing, acidizing, drilling, jetting, etc.
Using one or more of these
techniques, multiple pathways or channels can be created between the
production well and the
reservoir, to allow mobilization of cellar oil and other hydrocarbons and the
collection of such
hydrocarbons into the production well.
[087] Having regard to the geological and operational factors at play, the
skilled person would
be able to choose a suitable method for establishing fluid communication in a
given set of
conditions. For example, where the adjacent formation surrounding a production
well is
sandstone, hydraulic fracturing can be used. In contrast to sandstone,
carbonate rock or
limestone is relatively soft and can be dissolved by acid; therefore,
acidizing or acid fracturing is
considered to be more effective than fracturing in a carbonate formation. The
acid can dissolve a
portion of the carbonate rock to increase permeability and conductivity within
the stimulated
formation.
[088] FIGs. 4a-8c illustrate various processes of forming a plurality of
channels extending from
a production well toward a target reservoir in the context of an exemplary
recovery method ¨
namely, a SAGD extraction process. As shown in these drawings, the channels
provide fluid
communication between the production well and the reservoir, particularly the
lower portion of a
steam chamber created in the reservoir.
[089] Referring to FIGs. 4a-4c, perforations (23) can be formed upwards from a
production
well (12) using a jet perforator (41). In the implementation illustrated by
FIGs. 4a and 4b,
perforations (23) are located at or near the base (22) of the reservoir (10).
Perforations (23)
allow production fluid (14') to flow into the production well (12) from the
reservoir (10) when
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the production well (12) is located in an adjacent formation (40). FIG. 4c
illustrates the jet
perforator (41) firing a stream of hot gas and fine metal particles (42)
towards the wall of the
production casing or cemented liner (44) inside the production well (12) at
different stages.
From left to right, FIG. 4c shows an unfired charge (79), a charge being fired
(80) to create
perforation (23), and two perforations (23) through which production fluid
(14') enters the
production well (12). In one implementation, the jet perforator (41) fires the
stream (42) at a
speed of up to 10,000 m/s. Jet perforations (23) can range from 6 mm to over
30 mm in
diameter. Deep penetrating perforations tend to have a smaller entrance hole
and are used in
harder formations, while big hole charges are used in softer formations. In
one implementation,
the jet perforator (41) erodes one or more holes in the production casing or
cemented liner (44).
Depth of perforations (23) can range from about 200 mm to about 2,000 mm,
depending on the
strength of the formation, the strength of the casing (including steel casing,
cemented liner, and
the like), and the size of the charge. In some implementations, the depth of
at least one of the
perforations (23) is greater than 100 mm into the formation.
[090] Referring to FIGs. 5a-5d, fractures (24) can be formed upwards from a
production well
(12) by hydraulic fracturing. In the implementation illustrated by FIGs. 5a
and 5b, fractures (24)
are located at or near the base (22) of the reservoir (10). Fractures (24)
allow production fluid
(14') to flow into the production well (12) from the steam chamber (20) when
the production
well (12) is located in an adjacent formation (40). FIG. 5c illustrates the
creation of fractures
(24) by hydraulic fracturing, where fracturing fluid (51) is injected at high
pressure to fracture or
force apart the rocks in the adjacent formation (40) and reservoir (10). In
the implementation
shown in FIG. 5d, a proppant (52), such as sand grains, ceramic beads, and/or
the like (including
a combination of any of the foregoing), is added to the fracturing fluid and
pumped into the
fractures (24). The proppant (52) maintains conductivity in the fracture (24)
and ensures that
fluids can flow through the fracture (24) towards the production well (12). In
some
circumstances, the fracturing fluid can leak off into the formation and the
fractures (24) can
close. The proppant (52) can hold the surfaces at fractures (24) apart,
leaving a highly
conductive conduit from the reservoir (10) into the wellbore of the production
well (12). The
proppant (52) can also function as a medium for sand control.
[091] Referring to FIGs. 6a-6c, acidized fractures or channels (25) can be
formed upwards from
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CA 02913609 2015-11-27
a production well (12) by acid fracturing or acidizing. Acidization is usually
applied to a
carbonate formation, extending some distance from the wellbore. For example,
hydrochloric
acid (HCl) dissolves some of the calcium carbonate rock in a formation,
resulting in improved
flow paths through the rock. In some implementations, acids, including
hydrochloric acid and
the like, can be used to dissolve rock to create acidized fissures or
fractures. In some
implementations, acid is forced into the formation by fracturing or cracking
the rock with
hydraulic pressure. Pressure can vary greatly depending on formation depth and
composition. In
the implementation illustrated in FIGs. 6a and 6b, acidized fractures (25) are
located at or near
the base (22) of the reservoir (10). Similar to the fractures (24) shown in
FIGs. 5a-5d, acidized
fractures (25) allow production fluid (14') to flow into the production well
(12) from the steam
chamber (20) when the production well (12) is located in an adjacent formation
(40). FIG. 6c
illustrates the effect of acidization on limestone. With acidizing or acidized
fracturing, the
limestone has improved flow paths or conductivity. In some implementations, to
ensure that the
acid goes towards the target reservoir (10), the fluid containing the acid can
be directed by
appropriately oriented orifices or jets.
[092] Referring to FIGs. 7a-7b, small diameter drilled boreholes (26) can be
formed to connect
the production well (12) to the reservoir (10). A conventional drilling rig,
service rig, or coiled
tubing drilling unit can be used to drill such boreholes. The diameters of
drilled boreholes can
vary greatly, depending on the equipment used. In some implementations, the
drilled boreholes
have a diameter in the range of about 30 mm to over 200 mm. In the
implementation illustrated
by FIGs. 7a and 7b, drilled boreholes (26) are located at or near the base
(22) of the reservoir
(10). Boreholes (26) allow production fluid (14') to flow into the production
well (12) from the
steam chamber (20) when the production well (12) is located in an adjacent
formation (40).
[093] In some implementations, a mobile coiled tubing drilling unit can be
used to drill
boreholes (26). In one implementation, the mobile coiled tubing drilling unit
includes a control
unit, a power source, and a reel of coiled tubing, and is mounted on a truck.
The coiled tubing is
spooled onto the reel for storage and transport. When the drilling unit is in
operation, the
continuous tubing passes over a guide or goose neck and feeds into an injector
(tractor
mechanism), which deploys and retrieves the coiled tubing string. The tubing
is then inserted
into a wellbore through pressure containment devices or blowout preventer
(BOP) stacks on top
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of the wellhead. This process is reversed to retrieve and spool coiled tubing
back onto the reel.
For drilling the boreholes (26), a drilling assembly is located at the end of
the coiled tubing. The
assembly can include data sensors, an orienting device, a bent housing motor,
and a drill bit. The
data sensors and orienting device steer the drilling assembly for directional
drilling, and the drill
bit driven by the motor can bore a hole through the wall of the wellbore at a
desired angle. Data
transmitted by the data sensors are received and processed by the control unit
at the surface. In
some implementations, the bent housing in the motor can be replaced by a
steerable device that
is oriented by the driller in the surface control unit. In some
implementations, a small diameter
and flexible drilling assembly, similar to a speedometer cable with a mill
(bit) on the end, is
directed towards the side of the well. A motor in the drilling assembly turns
the inner shaft, and
the inner shaft in turn rotates the mill so that it can drill a borehole into
the formation.
[094] Referring to FIGs. 8a-8c, jetted perforations (27) can be formed using a
hydraulic jetting
tool (81) that runs on jointed tubing or coiled tubing. In the illustrated
implementation,
pressurized jetting fluid is directed through an orifice or nozzle towards the
casing, liner, or inner
wall of an uncased borehole, and the jetting fluid erodes a hole into the rock
surrounding the
wellbore. This is commonly known as "hydro-jetting" or "hydro-slotting". In
the
implementation illustrated by FIGs. 8a-8b, jetted perforations (27) are
located at or near the base
(22) of the reservoir (10). Similar to the fractures (24) shown in FIGs. 5a-
5d, jetted perforations
(27) allow production fluid (14') to flow into the production well (12) from
the steam chamber
(20) when the production well (12) is located in an adjacent formation (40).
The hydraulic
jetting tool (81), which creates deep perforations, can be oriented to avoid
boring towards the
injection well (11) or to achieve lateral access. In some implementations, the
hydraulic jetting
tool can also inject fluids, such as acid, to dissolve rock, including
limestone and the like. In
some implementations, the jetting fluid contains fine particles to augment the
jetting process,
acid, an abrasive grit, or a combination of any of the foregoing. FIG. 8c
shows a hydraulic
jetting tool (81) boring a jetted perforation (27) through the production
casing or liner in the
production well (12) into the formation (40) and reservoir (10). The diameters
of jetted
perforations can vary greatly. In some implementations, at least one of the
jetted perforations
(27) has a diameter in the range of 20 mm to 200 mm. In some implementations,
a small
diameter and flexible pipe (e.g., coiled tubing) with a jetting nozzle at the
end is directed towards
the side of the borehole. Fluid is pumped through the nozzle, jetting a hole
into the formation.
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[095] In the present methods and systems, the configuration of production
wells can vary based
on the characteristics of a given reservoir and a given adjacent location and
the recovery process
chosen. A production well can be vertical, inclined, curved, horizontal, past
horizontal, or at any
angle between vertical and horizontal, partially or in its entirety, and can
be positioned in various
arrangements with respect to other wells, if any. For a given set of
geological and operational
parameters, the skilled person is able to devise suitable configurations,
shapes, and arrangements
of production wells in order to maximize recovery.
[096] In some implementations, the production well can be configured with an
incline or can be
curved. For example, a production well can have vertical, curved, and
horizontal sections, as in
typical SAGD well pairs, or can be arranged vertically or at an incline, as in
a typical cyclic
steam stimulation (CSS) process. In some implementations, at least a portion
of the production
well is oriented at an angle from vertical to horizontal or beyond horizontal,
so as to collect the
hydrocarbons from the hydrocarbon-bearing formation. In some implementations,
at least a
portion of the production well is positioned substantially horizontal.
[097] Where SAGD is used as the recovery method, for example, a production
well does not
necessarily have to be positioned vertically below the injection well. In
certain geological or
operational conditions, it can be beneficial to have a sidetracked or offset
production well. In the
implementation shown in FIGs. 9a and 9b, a production well (12) is located in
an offset position
relative to an injection well (11), with drilled or jetted boreholes (28)
formed accordingly to
connect the production well (12) in the adjacent formation (40) to the
reservoir (10) or the
bottom of the steam chamber (20).
[098] In some implementations, the injection well (11) is not initiated from a
vertical or
inclined orientation, or the production well (12) is not initiated from a
vertical or inclined
orientation; in other implementations, neither the injection well (11) nor the
production well (12)
is initiated from a vertical or inclined orientation. In some implementations,
one or more of the
injection wells (11) is initiated from an access location near a hydrocarbon-
bearing formation. In
some implementations, one or more of the production wells (12) is initiated
from an access
location adjacent to a formation. In some implementations, both injection well
(11) and
production well (12) are initiated from a mine face located in an underlying
formation, as further
CA 02913609 2015-11-27
described in Canadian Patent No. 2,863,396, entitled In Situ Gravity Drainage
System and
Method For Extracting Bitumen From Alternative Pay Regions.
[099] In the implementation illustrated in FIG. 10, an injection well (11) and
a production well
(12) are initiated from a mine face of an adjacent formation (40) below the
reservoir (10), which
itself is under overburden (50). A drainage pit (88) is excavated at a site
(82) using excavation
equipment (84) to create an exposed region (90). The mine face can then be
accessed within the
exposed region (90). The injection well (11) is drilled into the reservoir
(10). The production
well (12) is drilled into the underlying adjacent formation (40) and below the
injection well (11).
Fluid communication between the reservoir (10) and the production well (12) is
established by
channels (100), which can be created using the methods described in the
present description,
such as perforating, jetting, fracturing, acidizing, drilling, and the like or
a combination of any of
the foregoing.
[0100] In some implementations, an infill well can be drilled between
production wells for more
efficient recovery of hydrocarbons from a reservoir. The infill well can be
added at the time of
primary or initial recovery, or at a later time for further recovery. In the
present methods and
systems, such an infill well can be located in a formation that is adjacent to
the oil-bearing
reservoir. Referring to FIG. 11, an infill or bypassed region (70) containing
unswept
hydrocarbons is formed between two mature steam chambers (60a, 60b), each
containing a pair
of wells (injection well (61a, 61b) and formation production well (62a, 62b))
for primary
recovery of hydrocarbons. An additional production well (64) (i.e., an infill
well) can then be
drilled into a cooler, more consolidated underlying formation (40), instead of
being drilled into
the reservoir formation that was disturbed and unconsolidated by prior SAGD
operations. In
some implementations, for example, the hydrocarbon-bearing formation contains
at least two
formation production wells with an infill region therebetween, where at least
a portion of the
production well is positioned in the underlying formation, under the infill
region.
[0101] Drilling into an unconsolidated formation is significantly more
difficult than drilling
through a competent formation. When a reservoir, particularly an oil sands
reservoir, is
disturbed by heat during a SAGD or other EOR process (e.g., in-situ
combustion, electric heating
(including electromagnetic heating and electrical resistive heating), radio
frequency heating,
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solvent injection, carbon dioxide flooding, non-condensable gas injection,
flue gas flooding,
surfactants injection, alkaline chemicals injection, microbial enhanced
recovery, and the like, or
a combination of any of the foregoing), the formation can become
unconsolidated, such that it
has little or no residual strength. In such circumstances, drilling new
production wells into the
unconsolidated formation can be undesirable. The present methods and systems
facilitate
drilling of a production well by positioning the well in an adjacent formation
that is more
consolidated and competent than the target reservoir. Where the adjacent
formation is
sufficiently competent, it is often unnecessary to install a slotted liner or
a cemented liner that
will have to be perforated at a later time.
[0102] Formations adjacent to target reservoirs can also have certain amounts
of hydrocarbons.
In addition to providing access to hydrocarbons in the target reservoir, the
methods and systems
described herein can also provide access to hydrocarbons in adjacent
formations. For example,
where a production well positioned in the adjacent formation is fractured to
provide continuity to
or communication with the target reservoir, the formed fractures or cracks can
also connect the
production well to the adjacent formation and thereby permit access to
hydrocarbons in the
adjacent formation. In some implementations, channels provide fluid
communication between at
least a portion of a first production well and the adjacent formation
containing additional
hydrocarbons. The additional hydrocarbons from the adjacent formation can then
be recovered,
along with hydrocarbons from the target reservoir, through the production
well.
[0103] In the Athabasca oil sands region, the McMurray formation is the target
oil reservoir.
The McMurray sands are underlain by the Devonian carbonates, in which pockets
of oil are often
contained. The McMurray sands are sometimes separated from the Devonian
carbonates by the
Continental formation, which can be permeable and porous and can contain
bitumen. In other
parts of the world, the oil-bearing formations can be underlain by formations
that may or may
not be hydrocarbon-bearing.
[0104] The present methods and systems can be implemented during initial
recovery of
hydrocarbons; they can also be used in a partially depleted reservoir
following a prior recovery
operation. If a target reservoir contains bitumen or heavy oil, it is usually
necessary to mobilize
hydrocarbons prior to production. Many techniques for mobilization are known
to the skilled
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CA 02913609 2015-11-27
person, including, without limitation, injection of hot fluids (e.g., steam),
injection of air for in-
situ combustion, electrical-resistive heating, electromagnetic heating,
injection of polymers for
mobility control, injection of viscosity-reducing agents or solvents,
microbial treatment, and
other similar methods. In some implementations, then, the hydrocarbon-bearing
formation
contains an injection well that is adapted for injecting a heated fluid or
viscosity-reducing agent.
While the implementations shown in FIGs. 3a-9b use one production well and one
injection well,
any number of production wells and injection wells can be used.
[0105] Although the present specification has described particular embodiments
and examples of
the methods and systems discussed herein, it will be apparent to persons
skilled in the art that
modifications can be made to the embodiments without departing from the scope
of the
appended claims.
23
