Note: Descriptions are shown in the official language in which they were submitted.
CA 2961312 2017-03-16
HORIZONTAL FRACTURES IN VARIOUS COMBINATIONS OF INFILL WELLS,
INJECTION WELLS, AND PRODUCTION WELLS
TECHNICAL FIELD
[0001] The technical field relates to recovery of hydrocarbons from
hydrocarbon formations.
BACKGROUND
[0002] Bitumen or heavy oil is abundant in different parts of the world,
including Canada, the
United States, Venezuela, and Brazil. However, the oil is highly viscous at
reservoir
temperatures and does not flow readily. Therefore, bitumen cannot be produced
by conventional
methods. In a number of cases, the heavy oil is thermally treated to reduce
the viscosity and this
makes it flow more easily.
[0003] Currently, the most common thermal-recovery processes are steam-based
technologies,
such as steam-assisted gravity drainage (SAGD) and cyclic-steam stimulation
(CSS). In these
processes, bitumen reservoirs are heated by steam injection; the bitumen is
brought to the
surface and later diluted with condensates for pipeline transportation.
[0004] Solvent injection can be used to enhance the performance of SAGD and
CSS by
introducing hydrocarbon solvent additives to the injected steam. The operating
conditions for
the solvent co-injection process are similar to SAGD.
[0005] During the start-up phase of a typical SAGD operation, the hydrocarbon-
bearing
formation is heated by injecting steam into the injection well and/or the
production well.
Through convection and conductive heating, the steam reduces the viscosity of
the
hydrocarbons in the hydrocarbon-bearing formation to establish fluid
communication between
in the injection well and the production well. The start-up phase of a SAGD
operation would be
maintained until the hydrocarbons in the region of the formation between the
injection well and
the production well become mobile and there is fluid communication between the
two wells.
[0006] In addition, some hydrocarbon-bearing formations, including formations
having inclined
heterolithic stratification (IHS), contain structural baffles which prevent
steam chambers from
1
CA 2961312 2017-03-16
being formed in the desired size and shape.
[0007] While various attempts have been made to enhance hydrocarbon recovery
and to reduce
the length of the SAGD start-up process, there still exists a need for
improved methods and
solutions for recovering hydrocarbons from a hydrocarbon-bearing formation.
SUMMARY
100081 In general, the present specification describes methods and systems to
produce
hydrocarbons from a hydrocarbon-bearing formation.
[0009] In one implementation, there is provided a method for recovering
hydrocarbons from a
hydrocarbon-bearing reservoir. The method includes: achieving fluid
communication between
an injection well and a production well in a well pair formed in the
reservoir, wherein the
injection well injects a mobilizing fluid and the production well produces a
production fluid;
deliberately initiating a fracture in the reservoir, the fracture extending
from a horizontal portion
of the injection well along a generally horizontal plane relative to the
horizontal portion of the
injection well; and producing hydrocarbons included in the production fluid
from the
hydrocarbon-bearing reservoir through a portion of the production well from a
production
chamber induced in the reservoir by the mobilizing fluid, wherein the volume
of the production
chamber is increased by the fracture.
[0010] In some aspects of the method, the production well includes a
multilateral production
well. In some aspects of the method, the method includes the additional steps
of: providing an
infill well in the hydrocarbon-bearing reservoir in proximity to the injection
well and the
production well; deliberately initiating an infill well fracture, the infill
well fracture extending
from a horizontal portion of the infill well along a generally horizontal
plane relative to the
horizontal portion of the infill well; and producing hydrocarbons included in
the production
fluid from the hydrocarbon-bearing reservoir through a portion of the infill
well from the
production chamber.
100111 In some aspects of the methods, the injection well is located at a
position of the reservoir
with a vertical overburden stress greater than a horizontal stress and the
methods include the
2
CA 2961312 2017-03-16
step of increasing the horizontal stress at the position such that it is
greater than the vertical
overburden stress.
[0012] In some aspects of the methods, the step of increasing the horizontal
stress includes
injecting the mobilizing fluid at a pressure at or near the reservoir's
maximum operating
pressure and at a high temperature.
100131 In some aspects of the methods, the position is about 300 meters below
a topmost
surface of the reservoir. In some aspects of the methods, the mobilizing fluid
includes steam. In
some aspects of the methods, the mobilizing fluid is injected at a rate of
about 400 tonnes/day.
[0014] In another implementation, there is provided a method for recovering
hydrocarbons
from a hydrocarbon-bearing reservoir. The method includes: achieving fluid
communication
between a first and a second injection well and a production well in well
pairs formed in the
reservoir, wherein the first and second injection wells inject a mobilizing
fluid and the
production well produces a production fluid; deliberately initiating a first
fracture in the
reservoir, the first fracture extending from a horizontal portion of the first
injection well along a
first generally horizontal plane relative to the horizontal portion of the
first injection well;
deliberately initiating a second fracture in the reservoir, the second
fracture extending from a
horizontal portion of the second injection well along a second generally
horizontal plane
relative to the horizontal portion of the second injection well; and producing
hydrocarbons
included in the production fluid from the hydrocarbon-bearing reservoir
through a portion of the
production well from production chambers induced in the reservoir by the
mobilizing fluid,
wherein the volume of the production chambers are increased by the first and
second fractures.
100151 In some aspects of the methods, the production well includes a
multilateral production
well. In some aspects of the methods, the production well is heated with an
electrical heater, by
RF, or other heating methods without steam.
[00161 In some aspects of the methods, the first injection well is laterally
offset from the second
injection well. In some aspects of the methods, the production well is
laterally offset from the
first production well or the second production well. In some aspects of the
methods, the lateral
offset avoids an inclined heterolithic stratification (IHS) baffle in the
hydrocarbon-bearing
3
CA 2961312 2017-03-16
reservoir. In some aspects of the methods, the production well continues to be
heated after fluid
communication is achieved between the injection well and the production well.
[0017] In some aspects of the methods, initiating the fracture includes
injecting a high pressure
fluid. In some aspects of the methods, the fluid is steam. In some aspects of
the methods, the
mobilizing fluid includes solvent without steam. In some aspects of the
methods, the mobilizing
fluid includes solvent co-injected with steam. In some aspects of the methods,
the mobilizing
fluid includes steam. In some aspects of the methods, the methods include
recovering the
hydrocarbons. In some aspects of the methods, producing the hydrocarbons
includes draining
the hydrocarbons by gravity into the production well. 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.
[0018] 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.
100191 In some aspects of the methods, the first or the second injection well
is located at a
position of the reservoir with a vertical overburden stress greater than a
horizontal stress and
includes the step of increasing the horizontal stress at the position such
that it is greater than the
vertical overburden stress.
100201 In some aspects of the methods, the step of increasing the horizontal
stress includes
injecting the mobilizing fluid at a pressure at or near the reservoir's
maximum operating
pressure and at a high temperature.
100211 In another implementation, there is provided a method for recovering
bitumen from a
bitumen-bearing reservoir. The method includes: achieving fluid communication
between an
injection well and a multilateral production well in a well pair formed in the
reservoir, wherein
the injection well injects a mobilizing fluid and the production well produces
a production fluid;
deliberating initiating a fracture in the reservoir, the fracture extending
from a horizontal
4
CA 2961312 2017-03-16
portion of the injection well along a generally horizontal plane relative to
the horizontal portion
of the injection well; and producing the bitumen included in the production
fluid from the
bitumen-bearing reservoir through a portion of the multilateral production
well from a
production chamber induced in the reservoir by the mobilizing fluid, wherein
the volume of the
production chamber is increased by the fracture.
[0022] In another implementation, there is provided a method for recovering
bitumen from a
bitumen-bearing reservoir. The method includes: achieving fluid communication
between an
injection well and a multilateral production well in well pair formed in the
reservoir, wherein
the injection well injects a mobilizing fluid and the multilateral production
well produces a
production fluid; deliberately initiating a fracture extending from a
horizontal portion of the
injection well along a generally horizontal plane relative to the horizontal
portion of the
injection well; producing bitumen included in the production fluid from the
bitumen-bearing
reservoir through a portion of the multilateral production well from a
production chamber
induced in the reservoir by the mobilizing fluid, wherein the volume of the
production chamber
is increased by the fracture; providing the infill well in the hydrocarbon-
bearing reservoir in
proximity to the injection well and the production well; deliberately
initiating an infill well
fracture extending from a horizontal portion of an infill well along a further
generally horizontal
plane from the horizontal portion of the infill well, the infill well in
proximity to the injection
well and the multi-lateral production well; and producing bitumen included in
the production
fluid from the bitumen-bearing reservoir through a portion of the multilateral
production well
from an infill well production chamber induced in the reservoir by the
mobilizing fluid.
[0023] In another implementation, there is provided a method for recovering
bitumen from a
bitumen-bearing reservoir. The method includes achieving fluid communication
between a first
injection well and a production well and a second injection well and the
production well in well
pairs formed in the reservoir, wherein the first injection well is spaced
apart from the second
injection well, the production well is located below the first and second
injection wells, and the
injection wells inject a mobilizing fluid and the production well produces a
production fluid;
deliberately initiating a first fracture in the reservoir, the first fracture
extending from a
horizontal portion of the first injection well along a first generally
horizontal plane relative to
the horizontal portion of the first injection well; deliberately initiating a
second fracture in the
CA 2961312 2017-03-16
reservoir, the second fracture extending from a horizontal portion of the
second injection well
along a second generally horizontal plane relative to the horizontal portion
of the second
injection well; and producing the hydrocarbons included in the production
fluid from the
bitumen-bearing reservoir through a portion of the multilateral production
well from production
chambers induced in the reservoir by the mobilizing fluid, wherein the volume
of each of the
production chambers is increased by the fracture.
[0024] In another implementation, there is provided a method for recovering
bitumen from a
hydrocarbon-bearing reservoir. The method includes: achieving fluid
communication between
the injection well and the production well in a well pair formed in the
reservoir, wherein the
injection well injects steam, the production well produces a production fluid,
and the injection
well is at a position in the reservoir with a vertical overburden stress
greater than a horizontal
stress; injecting steam into the injection well at a pressure close to a
maximum operation
pressure of the reservoir and a high temperature to modify a stress regime at
the position to
increase the horizontal stress until it is greater than the vertical
overburden at the position;
deliberately initiating a fracture in the reservoir, the fracture extending
from a horizontal portion
of the injection well along a generally horizontal plane relative to the
horizontal portion of the
injection well; and producing hydrocarbons included in the production fluid
from the
hydrocarbon-bearing reservoir through a portion of the production well from a
production
chamber induced in the reservoir by the mobilizing fluid, wherein the volume
of the production
chamber is increased by the fracture.
[0025] In another implementation, there is provided a system for recovering
hydrocarbons from
a hydrocarbon-bearing reservoir. The system includes: at least one injection
well and at least
one multilateral production well, the at least one injection well injects a
mobilizing fluid; at
least one fracture deliberately initiated in the reservoir, the at least one
fracture extending from
a horizontal portion of the at least one injection well along a generally
horizontal plane relative
to the horizontal portion of the at least one injection well and the at least
one fracture initiated
after fluid communication has been established between the at least one
injection well and the at
least one multilateral production well; and a production chamber induced by
the mobilizing
fluid, the production chamber having an increased volume due to the fracture.
6
CA 2961312 2017-03-16
100261 In some aspects of the systems, the system includes at least one infill
well in the
hydrocarbon-bearing reservoir in proximity to the at least one injection well
and the at least one
multilateral production well; and at least one infill well fracture, the at
least one infill well
fracture extending from a horizontal portion of the at least one infill well
along a further
generally horizontal plane relative to the horizontal portion of the at least
one infill well.
100271 In another implementation, there is provided a system for recovering
hydrocarbons from
a hydrocarbon-bearing reservoir. The system includes: a first injection well
and a second
injection well in the hydrocarbon-bearing reservoir, the second injection well
spaced apart from
the first injection well, the first and second injection wells inject a
mobilizing fluid; a
multilateral production well, the multilateral production well having a
horizontal portion located
below the first injection well and the second injection well; at least one
fracture deliberately
initiated in the reservoir, the at least one fracture extending from a
horizontal portion of each of
the first injection well and the second injection well along a generally
horizontal plane relative
to the horizontal portions of the first injection well and the second
injection well and the at least
one fractures initiated after fluid communication has been established between
each of the first
and second injection wells and the multilateral production well; and at least
one production
chamber induced by the mobilizing fluid having an increased volume due to the
at least one
fracture.
100281 In some aspects of the systems, the system includes an electric heater
for heating the
production well. In some aspects of the systems, the first injection well is
laterally offset from
the second injection well. In some aspects of the systems, the production well
is laterally offset
from the first injection well or the second injection well. In some aspects of
the systems, the
lateral offset avoids an inclined heterolithic stratification (IHF) baffle in
the hydrocarbon-
bearing reservoir. In some aspects of the systems, the injection well is
adapted for injecting a
heated fluid or viscosity-reducing agent.
[0029] In some aspects of the systems, the heated fluid includes steam. In
some aspects of the
systems, the fractures are formed by injection of a high pressure fluid. In
some aspects of the
system, the high pressure fluid is steam.
7
CA 2961312 2017-03-16
[0030] In some aspects of the systems, the system includes production
equipment for producing
the hydrocarbons from the hydrocarbon-bearing formation through the production
well. In some
aspects of the systems, the production equipment includes a steam assisted
gravity drainage
system. In some aspects of the systems, the production equipment includes a
cyclic steam
stimulation system. In some aspects of the systems, 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.
[0031] In some aspects of the systems, the multilateral production well
includes a plurality of
lateral production wells. In some aspects of the systems, the multilateral
production well is
forked.
[0032] In some aspects of the systems, the at least one fracture is formed
after the reservoir's
stress regime proximate the injection well has been modified. In some aspects
of the systems,
the stress regime is modified by increasing the horizontal stress such that it
is greater than the
vertical overburden stress. In some aspects of the methods, the stress regime
is modified by
injection of a high pressure fluid into the injection well. In some aspects of
the methods, the
fluid includes steam.
[0033] In another implementation, there is provided a system for recovering
bitumen from a
bitumen-bearing reservoir. The system includes: at least one injection well
and at least one
multilateral production well, the at least one injection well injects a
mobilizing fluid; at least
one fracture deliberately initiated in the reservoir, the at least one
fracture extending from a
horizontal portion of the at least one injection well along a generally
horizontal plane relative to
the horizontal portion of the at least one injection well and the at least one
fracture initiated by
injection of steam into the at least one injection well after fluid
communication has been
established between the at least one injection well and the at least one
multilateral production
well; and a production chamber induced by the mobilizing fluid, the production
chamber having
an increased volume due to the fracture.
8
CA 2961312 2017-03-16
[0034] 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 DRAWING
[0035] Features and advantages of embodiments of the present application will
become
apparent from the following detailed description and the appended drawing, in
which:
[0036] FIGs. IA to 1C are schematic cross-sectional views of a hydrocarbon-
bearing formation
showing a typical configuration of a SAGD well pair in which FIG. 1A
illustrates the SAGD
well pair, FIG. 1B illustrates the heat affected zone around the SAGD well
pair, and FIG. 1C
illustrates an exemplary steam chamber that is formed over time after fluid
communication has
been established between the SAGD well pair.
[0037] FIGs. 2A to 2C are schematic cross-sectional views of a hydrocarbon-
bearing formation
showing a SAGD configuration with horizontal fractures extending from the
injection well in
which FIG. 2A shows a SAGD well pair, FIG. 2B shows horizontal fractures in
the
hydrocarbon-bearing formation extending from the injection well, and FIG. 2C
shows the
resulting steam chamber formed over time.
[00381 FIG. 3A is a schematic cross-sectional view of the steam chamber of
FIG. 2C where the
production well has a single wellbore and a top plan view of a portion of the
production well.
[00391 FIG. 3B is a schematic cross-sectional view of the steam chamber of
FIG. 2C where the
production well is a multilateral production well and a top plan view of a
portion of the
multilateral production well.
[00401 FIG. 4A is a schematic cross-sectional view of a hydrocarbon-bearing
formation having
two injection wells, two production wells, two steam chambers, and an infill
well.
[00411 FIG. 4B is a schematic cross-sectional view of the hydrocarbon-bearing
formation of
FIG. 4A showing horizontal fractures extending from the injection wells and
the infill well.
[0042] FIGs. 5A to 5C are schematic cross-sectional views of a hydrocarbon-
bearing formation
having a SAGD well pair and baffles in which FIG. 5A illustrates the SAGD well
pair, FIG. 5B
9
CA 2961312 2017-03-16
illustrates the heat affected zone around the SAGD well pair, and FIG. 5C
illustrates the
resulting steam chamber as constrained by the baffles.
[0043] FIGs. 6A and 6B are cross-sectional views of a hydrocarbon-bearing
formation having
two injection wells laterally offset from each other, a heated production
well, and horizontal
fractures extending from the injection wells and through the clay baffle.
[0044] FIG. 6C is a cross-sectional view of the hydrocarbon-bearing formation
of FIG. 6B
showing production of hydrocarbons through a production well having a single
wellbore.
[0045] FIG. 6D is a cross-sectional view of the hydrocarbon-bearing formation
of FIG. 6B
where the production well is a multilateral production well and a top plan
view of a portion of
the multilateral production well.
DETAILED DESCRIPTION
100461 The present description relates to methods and systems for recovering
hydrocarbons
from hydrocarbon-bearing formations. Generally, in these methods and systems,
the
hydrocarbon-bearing formation contains a SAGD well pair and fractures in the
hydrocarbon-
bearing formation are deliberately initiated from the injection well and the
fractures extend
along a generally horizontal plane from the injection well after fluid
communication has been
established between the injection well and the production well. Hydrocarbons
can then be
collected from the formation through the production well and recovered to
surface.
[0047] Throughout this specification, numerous terms and expressions are used
in accordance
with their ordinary meanings. Provided below are definitions of some
additional terms and
expressions that are used in the description that follows.
[0048] 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
CA 2961312 2017-03-16
basement to surface): Pre-Cambrian (basement), Devonian carbonates, McMurray
oil sands,
Wabiskaw sands and mudstones, Clearwater shales, Grand Rapids sandstones, and
Quaternary
sediments.
[0049] The "McMurray formation" or "McMurray sands" is a stratigaphic 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.
[0050] "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, including subsurface formations that are
primarily
composed of a matrix of unconsolidated sand, with hydrocarbons occurring in
the porous
matrix.
[0051] "Hydrocarbons" refer 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.
[0052] "Fracturing" includes a process for structurally degrading a geological
formation around
a wellbore by applying thermal and/or mechanical stress and includes processes
that result in
fractures being present in the hydrocarbon-bearing formation, especially in
formations having
soft rocks and loose sedimentary material such as the McMurray formation. 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,
11
CA 2961312 2017-03-16
hydraulic fracturing and acid fracturing.
[00531 "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.
[0054] "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.
[0055] 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.
[00561 An "injection well" includes a well into which a fluid is injected into
a formation.
[00571 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
[0058] "Bitumen" and "heavy oil" are normally distinguished from other
petroleums based on
their relative densities and/or viscosities, which often depend on context.
Commonly-accepted
definitions classify "heavy oil" as petroleum (the density of which is between
920 and 1,000
kg/m3) and "bitumen" as oil produced from bituminous sand formations (the
density of which is
greater than 1,000 kg/m3). For purposes of this specification, the terms
"bitumen" and "heavy
oil" are used interchangeably such that each one includes the other. For
example, where the
term "bitumen" is used alone, it includes within its scope "heavy oil".
[0059] The "natural reservoir temperature" or "reservoir temperature" is an
ambient
temperature of a cold or unheated reservoir.
12
CA 2961312 2017-03-16
[0060] The reference to "horizontal" includes substantially horizontal and
generally horizontal.
[0061] "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.
[0062] 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
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.
100631 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.
100641 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 can 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 in the
context of
SAGD are not intended to be limited to SAGD applications.
100651 FIGs. IA to 1C illustrates the basic principles of a SAGD operation in
a hydrocarbon-
bearing formation (10). Referring to FIG. 1A, an injection well (20) is
drilled into the formation
and positioned above a production well (30) in the same geological formation
(10). In one
implementation, the injection well (20) includes a horizontal portion that is
positioned about 5
13
CA 2961312 2017-03-16
metres above a horizontal portion of the production well (30). In the
illustrated implementation,
injection well (20) and production well (30) are drilled vertically into the
hydrocarbon-bearing
formation and they become oriented horizontal.
[0066] Referring to FIG. 1B, during the start-up phase of the SAGD operation,
steam is
injected into the injection well (20) and the production well (30) to heat the
formation
surrounding the injection well (20) to form a heat affected zone (34) and to
establish fluid
communication between the injection well (20) and the production well (30).
The steam reduces
the viscosity of the hydrocarbons in the hydrocarbon-bearing formation (10).
100671 At the end of the start-up phase, fluid communication is achieved
between the injection
well (20) and the production well (30), and a production fluid (50) (e.g.,
including mobilized
hydrocarbons and hot water, such as hot water from condensed steam) is
collected in the
production well (30) with the assistance of gravity and produced to surface.
The steam chamber
(40) develops vertically to reach the cap rock and then expands horizontally.
Over time, a steam
chamber (40) will form above the SAGD well pair. FIG. 1C illustrates one
implementation of
the steam chamber (40) once it has been fully formed. In the illustrated
implementation, the
steam injection well (20) and the production well (30) are both located within
the steam
chamber (40). There is a steam/liquid interface between the steam injection
well (20) and the
production well (30). In some implementations, the production well (30) 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 (20) and the production well (30) is also present in other
implementations that
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.
100681 While the SAGD process allows hydrocarbons to be extracted from
hydrocarbon-
bearing formations, the start-up period of a SAGD operation can be 6 months or
longer because
the formation has to be heated to a sufficient degree before fluid
communication can be
established between the injection well and the production well and the
viscosity of the
hydrocarbons have been sufficiently modified. During the start-up period,
hydrocarbons
generally are not produced from the hydrocarbon-bearing formation and steam is
to be
14
CA 2961312 2017-03-16
circulated to heat the interwell region between the injection well (20) and
the production well
(30) and areas of the formation (10) around the SAGD well pair.
100691 FIGs. 2A-2C illustrates an implementation of the method and system for
recovering
hydrocarbons using SAGD. As with FIG. 1A, an injection well (20) and a
production well (30)
are drilled into the hydrocarbon-bearing formation (10). As with the typical
SAGD operation,
steam is circulated in both the injection well (20) and the production well
(30) to heat the
hydrocarbon-bearing formation (10), and more particularly the interwell region
between the
injection well (20) and the production well (30).
[0070] As illustrated in FIG. 2B, this implementation includes the step of
deliberately initiating
a fracture (22) in the hydrocarbon-bearing formation (10) along a horizontal
plane from the
injection well (20). Methods for initiating fractures in the hydrocarbon-
bearing formation (10)
from the injection well (20) are known in the art. The orientation of the
fracture depends on the
stress characteristics and the composition of the hydrocarbon-bearing
formation (10). A fracture
will occur in a plane perpendicular to the direction of the minimum stress. In
shallow reservoirs,
horizontal fractures can be formed by hydraulic fracturing processes where the
horizontal stress
is greater than the vertical overburden stress.
[0071] Based on the stress characteristics of the formation (10) (which can
change depending
on the temperature of the portion of the formation being heated) and the
composition of the
formation (10), the person skilled in the art can select the appropriate
method for inducing
fractures in the formation (10) from the injection wells (20). The person
skilled in the art will
also consider the depth of the SAGD well pair (since stress orientation is a
function of depth)
when determining the method for inducing the horizontal fractures (22). In one
implementation,
the horizontal portion of the injection well (20) from which fractures (22)
are initiated is located
in reservoirs shallower than 150 metres below the surface of formation (10)
metres.
[0072] In deeper formations for which initial mini-frac results suggested
vertical fractures
would be formed from the injection well (20), the stress regime of formation
(10) can be
modified (called "stress distribution") due to injection pressure and thermal
expansion (i.e.,
heaving) resulting from injection of high temperature steam (i.e., jacking
effect in the context of
CA 2961312 2017-03-16
SAGD operation). Modifying the stress regime of the formation (10) to increase
the horizontal
stress until it is greater than the vertical overburden stress allows
horizontal fractures (22) to be
initiated from the injection well (20) instead of vertical fractures, since
fractures (22) will occur
in the plane perpendicular to the direction of the minimum stress.
[0073] In one implementation, the method used to create horizontal fractures
(22) in the
formation (10) in SAGD operation is to inject steam at a pressure close to the
maximum
operation pressure (MOP). The pressure and temperature of the injected steam
modify the stress
regime of formation (10) and lowers the fracture gradient of formation (10)
around the injection
well (20), allowing horizontal fractures (22) to be formed. The horizontal
fractures (22) will be
created at lower pressures than that of MOP at the level of the injection well
(20). This method
can be used in deeper reservoirs which are at the boundary of changing the
direction of the
fracture from vertical to horizontal. The fractures propagating from the
injection well (20)
horizontally can help the steam chamber (40) propagate horizontally and ramp
up the
completion of the start-up phase. The resulting steam chamber will have a
larger volume as a
result.
[0074] The size of the fractures (22) can depend on a number of factors,
including the nature of
the fracturing fluid, the amount of fluid returned to surface after injection,
the injection rate of
the fracturing fluid, the pressure at which the fluid is driven into the
formation (10), and the
flow rate of the fracturing fluid.
[0075] In the implementation shown in FIGs. 2A to 2C, steam is used to
initiate the horizontal
fractures (22) in the hydrocarbon-bearing formation (10). In one
implementation, the steam is
injected into the injection well (20) at a pressure close to the MOP of the
reservoir, which is
highly dependent on stress regime and depth of the reservoir. Steam injection
rates highly
depend on injectivity of the reservoir. In one implementation, the steam
injection rate is about
400 tonnes/day. In some implementations, the steam injection rate is less than
400 tonnes/day.
[0076] In one implementation, cold water is used as to initiate the horizontal
fractures (22). In
some implementations, nitrogen fracking can be used to initiate the horizontal
fractures (22). In
some implementations, other fracking fluids known to a person skilled in the
art are used to
16
CA 2961312 2017-03-16
initiate the horizontal fractures (22). In some implementations, proppants can
be included in the
fracturing fluid.
100771 In one implementation, at least one of the horizontal fractures (22),
as measured from
the injection well (10), has a length of about 10 metres. In some
implementations, the length of
the horizontal fractures (22) as measured from the injection well (10) is less
than 10 metres.
100781 In the implementation illustrated in FIGs. 2A to 2C, the heat affected
zone (34) and the
resulting steam chamber (40) are larger when compared to the steam chamber of
SAGD
operations without the horizontal fractures (22) in the hydrocarbon-bearing
formation (10) (as
shown in FIG. IC). The larger steam chambers provide fluid communication
between the
injection well (20) and the production well (30) over a greater lateral
distance, and can increase
the overall width (including the volume of the steam chamber), thereby
increasing the volume
of hydrocarbon recovered from the formation. Accordingly, greater production
of production
fluid (50), including hydrocarbons, can be achieved by mobilizing a larger
amount of
hydrocarbons in the hydrocarbon-bearing formation (10) and providing better an
increased area
of fluid communication between the injection well (20) and the production well
(30).
[0079] After horizontal fractures (22) are introduced into formation (10), as
a result of the
increased area of fluid communication and the larger steam chambers that form,
in some
implementations, after horizontal fractures (22) are formed, bitumen
production rates from the
production well (30) at the ramp-up phase can be as high as the bitumen
production rates from a
formation (10) with a fully formed steam chamber (40) without horizontal
fractures. In some
implementations, after horizontal fractures (22) are formed, bitumen
production rates from the
production well (30) can be commensurate with that of a reservoir that has
been in production
for at least 2 years.
100801 In the implementation illustrated in FIGs. 2A to 2C, the production
well (30) has a
single bore. In another implementation, as illustrated in FIGs. 3A and 3B, the
production well
(30) is a multilateral production well (32).
[0081] FIG. 3A includes a cross-sectional view of the hydrocarbon-bearing
reservoir as
illustrated in FIG. 2C and a top plan view of production well (30). In this
implementation, there
17
CA 2961312 2017-03-16
is a risk of premature breakthrough of steam (38) from the injection well (20)
into production
well (30). Premature breakthrough of steam (38) is undesirable because it can
stop production
of the production fluid (50) from production well (30).
100821 To reduce the risk of premature breakthrough of steam (38), the
implementation
illustrated in FIG. 3B can be used. This implementation is substantially
similar to that illustrated
in FIG. 3A, except that the production well is a multilateral production well
(32). Multilateral
wells, including multilateral production wells, are well known to a person
skilled in the art.
Multilateral production well (32) includes a plurality of multilateral
injunctions (36) which
provides for a plurality of lateral production wells (38). The use of a
multilateral production
well (32) further creates a longer production path and allow increased fluid
communication
between the multilateral production well (32) and the injection well (22).
[0083] In typical SAGD operations, the heels of production well (30) and
injection well (20)
can be quite close together. With steam temperature being higher at the heel,
steam coning can
occur at the heel of the production well (30), leading to premature steam
breakthrough. The
risk of premature breakthrough of steam (14) is limited when a multilateral
production well (32)
is used because the distances between the injection well (20) and the
multilateral production
well (32) and the lateral production wells (38) are varying, which can
decrease the likelihood of
steam coning.
100841 The drilling of multilateral wells, including multilateral production
well, is known to a
person skilled in the art. In the implementation illustrated in FIG. 3B, the
multilateral
production well (32) includes at least two lateral production wells (38) at
each multilateral
junction (36). In other implementations, the multilateral production well (32)
can include more
than two lateral production wells (38) at each multilateral junction (34). In
one implementation,
the lateral production wells (38) are substantially in the same plane as the
multilateral
production well (32). In some implementations, the multilateral production
well (32) includes
forked lateral production wells.
100851 Horizontal fractures in the hydrocarbon-bearing reservoir can also be
used in improving
the production of hydrocarbons from an infill well. In SAGD operations, steam
chambers
18
CA 2961312 2017-03-16
around each SAGD well expands with time and there can be unproduced
hydrocarbons within
the hydrocarbon-bearing formation, including in bypassed regions, that are not
produced
between adjacent SAGD well pairs. Infill wells can be used to access the
unproduced
hydrocarbons. Infill wells are typically a single well having a horizontal
portion drilled at
approximately the center-line between the two target adjacent SAGD well pairs.
100861 One implementation of the methods and systems to produce hydrocarbons
using infill
wells is illustrated in FIGs. 4A and 4B. Referring to FIG. 4A, two SAGD well
pairs (injection
well 20a and 20b) and production well (30a and 30b) are present in the
hydrocarbon-bearing
reservoir (10) prior to horizontal fractures being induced from the injection
well. In this
implementation, infill well (70) has a horizontal portion located at or near
the middle of the
bypassed region (16) that is between the two steam chambers (40a and 40b)
formed around the
two SAGD well pairs. In some implementations, infill well (70) is not located
at the middle of
the bypassed region.
100871 As shown in FIG. 4B, fracturing is deliberately initiated from each of
the injection wells
(20a and 20b) using techniques known to a person skilled in the art and as
outlined above. The
resulting fractures (22a and 22b) in the hydrocarbon-bearing formation (10)
extend substantially
in a horizontal plane from the injection wells (20a and 20b). Fracturing is
also deliberately
initiated from the infill well (70) using techniques known to a person skilled
in the art and as
outlined above. The resulting infill well fractures (72) in the hydrocarbon-
bearing formation
(10) extend substantially in a horizontal plane from the infill well (70). In
this implementation,
the horizontal fractures (22b) extend beyond the boundaries of steam chamber
(40b) and into
bypassed region (16) of the hydrocarbon-bearing formation (10) between the two
adjacent
SAGD well pairs. The steam (60) injected into the formation (10) through the
injection wells
(20a and 20b) and/or production wells (30a and 30b) mobilizes the hydrocarbons
in bypassed
region (16) and the mobilized hydrocarbons (in the form of production fluid
(80)) is collected
into the infill well (70) by gravity and is produced to surface. The amount of
production fluid
(80) recovered from the hydrocarbon-bearing formation (10) can, therefore, be
higher when
using the implementation shown in FIG. 4B, as compared to one where fractures
are not
initiated from the injection wells (20a and 20b) and the infill well (70).
19
CA 2961312 2017-03-16
100881 The implementation illustrated in FIG. 4B can also be implemented in
hydrocarbon-
bearing formation (10) having baffles and shale drapes between steam chambers
formed around
SAGD well-pairs. Initiating horizontal fractures in the hydrocarbon-bearing
formation (10) will
increase the amount of hydrocarbons extracted from the formation (10) by
recovering
hydrocarbons from bypassed region (16) that is otherwise not accessible due to
presence of
baffles, such as clay baffles and the like.
[0089] In this implementation, the infill well (70) has a single bore. In some
implementations,
the infill well (70) can be a multilateral infill well. In the implementation
illustrated in FIG. 4B,
one infill well is drilled into the hydrocarbon-bearing formation (10). In
other implementations,
more than one infill well is drilled into the hydrocarbon-bearing formation
(10).
[0090] In one implementation, the infill well (70) is operated as a constant
producer as part of
the SAGD operation. In other implementations, the infill well (70) is operated
in CSS.
[0091] Fractures deliberately initiated from injection wells and extending in
the hydrocarbon-
bearing formation from injection wells in a horizontal plane can also be used
for production of
hydrocarbons in hydrocarbon-bearing formations (10) that contain clay baffles
or other baffles.
In one implementation, the hydrocarbon-bearing formation (10) includes
inclined heterolithic
stratification (IHS).
[0092] FIGs. 5A-5C illustrates a SAGD operation in a hydrocarbon-bearing
formation (10)
having baffles (100). In one implementation, baffles (100) include clay
baffles and the like.
Similar to other SAGD operations (including, for example, as illustrated in
FIG. 1A), referring
to FIG. 5A, the hydrocarbon-bearing formation (10) includes an injection well
(20) and a
production well (30), which are positioned between two baffles (100).
Referring to FIG. 5B, as
steam is circulated through the injection well (20) and the production well
(30), the heat
affected zone (34) is created within the hydrocarbon-bearing formation (10)
around the SAGD
well pair. While the steam chamber is designed to have the shape and size of
steam chamber
(46), the baffles (100) restricts the size and shape of the actual steam
chamber (44) =formed
around the SAGD well pair. Baffles (100) can impede the steam from permeating
into areas of
formation (10) beyond the baffles (100). The smaller steam chamber (44) leads
to less
CA 2961312 2017-03-16
hydrocarbons being produced from hydrocarbon-bearing formation (10) and lower
production
rates from the SAGD operation.
100931 FIGs. 6A-6C illustrate an implementation of the systems and methods of
hydrocarbon
recovery that involves fractures in the formation (10) extending from the
injection wells and the
hydrocarbon-bearing formation (10) having baffles (100). In the illustrated
implementation, two
injection wells (20a and 20b) are drilled into the hydrocarbon-bearing
formation (10). A
mobilizing fluid, such as steam, is circulated in injection wells (20a and
20b) to heat the
hydrocarbon-bearing formation (10) to form heated zones (34a and 34b). In this
implementation, the injection wells (20a and 20b) are laterally offset to
avoid drilling into
baffles (100). In other implementations, the injection wells (20a and 20b) are
positioned in
substantially the same horizontal plane.
100941 In this implementation, steam is not circulated within production well
(30). Rather, the
production well (30) is heated using other methods not using steam. In some
implementations,
the production well (30) is heated using an electrical heater, geothermal
energy, electromagnetic
energy, radio frequency based heating, or a combination of any of the
foregoing. Heat affected
zone (34c) is established around production well (30).
100951 After the heat affected zones (34a, 34b, and 34c) are established and
fluid
communication is established between the injection wells (20a and 20b) and
production well
(30), fractures (22a and 22b) are deliberately initiated from the injection
wells (20a and 20b)
and fractures (22a and 22b) extend along a generally horizontal plane from the
injection wells
(20a and 20b) in the formation (10). The horizontal fractures (22a and 22b)
are initiated using
the methods known to a person skilled in the art and as outlined above.
100961 The fractures (22a and 22b) extend across baffles (100) and allows
steam to reach
portions of the hydrocarbon-bearing formation (10) between baffles (100) that
is otherwise
stranded and not recoverable. Heating of these portions of the hydrocarbon-
bearing formation
(10) mobilizes the hydrocarbons and production fluid (80) between baffles
(100) is collected in
the production well (30) by gravity and produced to surface.
100971 In the implementation illustrated in FIG. 6C, the production well (30)
has a single bore.
CA 2961312 2017-03-16
Production of hydrocarbons in the form of production fluid (80) can be
increased by using a
multilateral production well (32).
100981 FIG. 6D illustrates an alternative implementation of the methods and
systems for
recovering hydrocarbons from the hydrocarbon-bearing formation (10) of FIG. 6c
in which the
hydrocarbon-bearing formation (10) has a multilateral production well (32)
having lateral
production wells (38). In this implementation, multilateral production well
(32) includes two
lateral production well (38) at each multilateral junction (36). In other
implementations, the
multilateral production well (32) can include more than 2 lateral production
wells (38) at each
multilateral junction (34). In one implementation, the lateral production
wells (38) are
substantially in the same plane as the multilateral production well (32).
[0099] In the implementation illustrated in FIG. 6D, the horizontal fractures
(22) can allow
increased fluid communication between the injection wells (20a and 20b) and
multilateral
production well (32). Increased circulation of steam in hydrocarbon-bearing
formation (10)
through horizontal fractures (22) can also allow increased rate of growth of
steam chambers
(40a, 40b, and 40c). In addition, the boundaries of the steam chambers (40a,
40b, and 40c) can
expand beyond the restrictions or baffles created by the baffles (100). The
multilateral
production well (32) and its lateral production wells (38) can collect
additional production fluid
from both of the steam chambers (40a, 40b, and 40c).
[00100] While baffles (100) are illustrated as being parallel to the injection
and production wells
in FIGs. 5A-6D, in some implementations, the injection and production wells
are drilled
perpendicular to the clay baffles and not parallel to the baffles.
1001011The configuration of injection wells and production wells can vary
based on the
characteristics of a given reservoir and a given adjacent location and the
recovery process
chosen. Each of the injection well and 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.
22
CA 2961312 2017-03-16
1001021In 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.
[001031 In the implementations discussed in FIGs. 2A-6C, fracturing is
initiated from the
injection well and/or infill well to develop fractures along a generally
horizontal plane in the
hydrocarbon-bearing formation after completion of the start-up phase. In some
implementations, the horizontal fractures can be initiated from the injection
wells after
production has commenced from the SAGD well pair. In some implementations,
fracturing is
initiated from the injection well and/or infill well when the ramp-up phase
begins.
1001041ln the implementations discussed in FIGs. 2A-6C, fracturing is
initiated after fluid
communication has been established between the SAGD well pair. This permits
the steam
chamber to grow across the length of the horizontal fractures, as well as
above the SAGD well
pair and can increase the size of the resulting steam chamber and increase the
production rate of
bitumen from the formation (10). If fracturing is initiated too early during
the start-up phase,
additional steam may be needed to heat the interwell region sufficiently to
achieve fluid
communication between the SAGD well pair, as the steam would be distributed
across the
horizontal fractures as well.
[00105] Many techniques for mobilizing hydrocarbons are known to the skilled
person,
including 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. These
methods can be used with the methods and systems discussed herein to increase
mobilization of
the hydrocarbons.
[00106J While the implementations illustrated in FIGs. 2A-6D use one to two
production wells
23
CA 2961312 2017-03-16
and one to two injection wells, any number of production wells and injection
wells can be used.
1001071 Although the implementations illustrated in FIGs. 2A-6D include
fractures extending
from injection wells and/or infill wells, fractures can also be initiated from
one or more of the
production wells located in the hydrocarbon bearing formation. Techniques used
for initiating
fractures from the injection wells and/or infill wells as described herein can
be used for
initiating fractures from the one or more production wells.
[00108] While a number of exemplary aspects and implementations have been
discussed above,
those skilled in the art will recognize certain modifications, permutations,
additions, sub-
combinations thereof.
[00109] Although the present specification has described particular
embodiments and examples
of the methods and treatments 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.
24
