U.S. patent application number 14/778927 was filed with the patent office on 2016-02-18 for increasing hydrocarbon recovery from reservoirs.
This patent application is currently assigned to Statoil Petroleum AS. The applicant listed for this patent is STATOIL PETROLEUM AS. Invention is credited to Jan Havard JORANSON, Halvor KJORHOLT, Fredrik VARPE.
Application Number | 20160047179 14/778927 |
Document ID | / |
Family ID | 48226817 |
Filed Date | 2016-02-18 |
United States Patent
Application |
20160047179 |
Kind Code |
A1 |
KJORHOLT; Halvor ; et
al. |
February 18, 2016 |
INCREASING HYDROCARBON RECOVERY FROM RESERVOIRS
Abstract
A method, system and apparatus for producing hydrocarbons from a
low permeability reservoir formation. A wellbore (3) with a
plurality of fractures (7, 9) designated as one of a first (7) or a
second (9) set of fractures is provided. A first fluid conduit (11)
is formed by an annulus between an outer casing (10) of a tubular
and an inner tubular (16) member, and is arranged to transport
produced hydrocarbons. An interior of the inner tubular member
forms a second fluid conduit (12) which is arranged to transport an
injection fluid. A set of first openings (14) is provided in fluid
connection with the first fluid conduit, each first opening being
located to substantially align with one of a first set of
fractures. A set of second openings (15) is provided in fluid
connection with the second fluid conduit, each second opening being
located to substantially align with one of a second set of
fractures. A high pressure fluid is injected into the second set of
fractures, which pushes hydrocarbons located in the low
permeability reservoir towards the first set of fractures, thereby
increasing the recovery rate of hydrocarbons in the low
permeability reservoir.
Inventors: |
KJORHOLT; Halvor;
(Trondheim, NO) ; JORANSON; Jan Havard;
(Stavanger, NO) ; VARPE; Fredrik; (Stavanger,
NO) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
STATOIL PETROLEUM AS |
Stavanger |
|
NO |
|
|
Assignee: |
Statoil Petroleum AS
Stavanger
NO
|
Family ID: |
48226817 |
Appl. No.: |
14/778927 |
Filed: |
March 21, 2014 |
PCT Filed: |
March 21, 2014 |
PCT NO: |
PCT/EP2014/055716 |
371 Date: |
September 21, 2015 |
Current U.S.
Class: |
166/308.1 ;
166/185; 166/242.1; 166/316; 166/52 |
Current CPC
Class: |
E21B 34/06 20130101;
E21B 43/26 20130101; E21B 43/14 20130101; E21B 33/124 20130101;
E21B 17/18 20130101; E21B 43/255 20130101 |
International
Class: |
E21B 17/18 20060101
E21B017/18; E21B 43/26 20060101 E21B043/26; E21B 34/06 20060101
E21B034/06; E21B 33/124 20060101 E21B033/124; E21B 43/14 20060101
E21B043/14 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 21, 2013 |
GB |
1305208.9 |
Claims
1. A method of completing a well for producing hydrocarbons from a
low permeability reservoir formation, the method comprising:
drilling a wellbore into the low permeability reservoir formation;
performing a hydraulic fracturing operation to induce a plurality
of fractures in the reservoir at known locations; designating a
first set of fractures and a second set of fractures; completing
the well using a tubular, the tubular comprising an outer casing
and a tubular inner member disposed within the outer casing,
wherein the tubular inner member and the outer casing define an
annulus, the annulus forming a first fluid conduit arranged to
transport produced hydrocarbons, and an interior of the inner
tubular member forming a second fluid conduit arranged to transport
an injection fluid, a set of first openings in fluid connection
with the first fluid conduit, each first opening being located to
substantially align with one of the first set of fractures, and a
set of second openings in fluid connection with the second fluid
conduit, each second opening being located to substantially align
with one of the second set of fractures.
2. The method according to claim 1, further comprising providing a
valve to at least some of the first set of openings, the valve
arranged to control a flow of hydrocarbons into the first fluid
conduit.
3. The method according to claim 1, further comprising providing a
valve to at least some of the second set of openings, the valve
arranged to control a flow of injection fluid from the second fluid
conduit.
4. The method according to claim 1, further comprising providing at
least one packer disposed in proximity to an opening of the first
set of openings and a further packer disposed in proximity to an
opening of the second set of openings, wherein the packers are
arranged to ensure no fluid connection between the first set of
openings and the second set of openings.
5. The method according to claim 1, wherein the low porosity
reservoir formation comprises a shale formation.
6. The method according to claim 1, wherein the first set of
fractures and the second set of fractures are disposed along a main
axis of the well such that a fracture of the first set of fractures
alternates with a fracture of the second set of fractures.
7. A method of producing hydrocarbons from a low permeability
reservoir formation, the method comprising, in a well in a low
permeability reservoir formation, the well comprising a plurality
of hydraulic fractures, each fracture being designated as one of a
first set of fractures and a second set of fractures: injecting an
injection fluid from an inner tubular member disposed in an outer
casing of a tubular into at least one of the second set of
fractures to increase a pressure in the low permeability reservoir;
and producing hydrocarbons from at least one of the first set of
fractures such that the hydrocarbons flow into an annular portion
of the tubular defined by the outer casing and the inner tubular
member.
8. The method according to claim 7, further comprising controlling
a flow of hydrocarbons into the production tubular using a
valve
9. The method according to claim 7, further comprising controlling
a flow of injection fluid using a further valve.
10. The method according to claim 7, further comprising providing
at least one packer disposed in proximity to an opening of the
first set of openings and a further packer disposed in proximity to
an opening of the second set of openings, wherein the packers are
arranged to ensure no fluid connection between the first set of
openings and the second set of openings.
11. The method according to claim 7, wherein the injection fluid
comprises a gas.
12. The method according to claim 7, wherein the injection of
injection fluid occurs simultaneously with the production of
hydrocarbons.
13. A tubular for producing hydrocarbons from a low permeability
reservoir formation, the tubular comprising: an outer casing; a
tubular inner member disposed within the outer casing, wherein the
tubular inner member and the outer casing define an annulus;
wherein the annulus forms a first fluid conduit arranged to
transport produced hydrocarbons; an interior of the tubular inner
member forms a second fluid conduit arranged to transport an
injection fluid; a first opening in the outer casing in fluid
connection with the first fluid conduit, the first opening arranged
to substantially align with a first fracture in the formation; and
a second opening in the outer casing in fluid connection with the
second fluid conduit, the second opening arranged to substantially
align with a second fracture in the formation.
14. The tubular according to claim 13, wherein the first opening
further comprises a valve, the valve arranged to control a flow of
hydrocarbons into the first fluid conduit.
15. The tubular according to claim 13, wherein the second opening
further comprises a second valve, the second valve arranged to
control a flow of injection fluid out of the second fluid
conduit.
16. The tubular according to claim 13, further comprising a first
packer disposed in proximity to the first opening and a second
packer disposed in proximity to the second opening, wherein the
packers are arranged to ensure no fluid connection between the
first opening and the second opening.
17. A system for producing hydrocarbons from a low permeability
reservoir formation, the system comprising: a wellbore in the low
permeability reservoir formation, the wellbore having plurality of
fractures in the formation induced by hydraulic fracturing at known
locations; a tubular comprising an outer casing and an inner
tubular member, the outer casing and the inner tubular member
forming an annulus therebetween; the annulus forming a first fluid
conduit located in the wellbore and arranged to transport produced
hydrocarbons; an interior of the inner tubular member forming a
second fluid conduit located in the wellbore and arranged to
transport an injection fluid; a set of first openings in fluid
connection with the first fluid conduit, each first opening being
located to substantially align with one of a first set of
fractures; and a set of second openings in fluid connection with
the second fluid conduit, each second opening being located to
substantially align with one of a second set of fractures.
18. The system according to claim 17, further comprising a valve at
at least some of the first set of openings, the valve arranged to
control a flow of hydrocarbons into the tubular.
19. The system according to claim 17, further comprising a further
valve at at least some of the second set of openings, the valve
arranged to control a flow of injection fluid from the tubular.
20. The system according to claim 17, further comprising at least
one packer disposed in proximity to each opening of the first set
of openings and a further packer disposed in proximity to each
opening of the second set of openings, wherein the packers are
arranged to ensure no fluid connection between the first set of
openings and the second set of openings.
21. The system according to claim 17, further comprising: a second
wellbore in the low porosity reservoir formation, the second
wellbore having plurality of fractures induced by hydraulic
fracturing at known locations, and the second wellbore being
located adjacent to the wellbore.
22. The system according to claim 17, wherein a fracture of the
plurality of fractures of the wellbore substantially aligns with a
fracture of plurality of fractures of the second wellbore.
Description
TECHNICAL FIELD
[0001] The invention relates to the field of increasing hydrocarbon
recovery from reservoirs, and in particular shale reservoirs and
tight oil reservoirs.
BACKGROUND
[0002] Shale reservoirs are hydrocarbon reservoirs formed in a
shale formation. It can be difficult to produce the hydrocarbons
from shale reservoirs because the shale formation is of low
porosity and low permeability. This means that when a well is
drilled into the formation, only those fluid hydrocarbons in
proximity to the well are produced, as the other hydrocarbons
further away from the well have no easy path to the well through
the relatively impermeable rock formation.
[0003] A typical production system is illustrated in FIG. 1, in
which a subterranean shale formation 1 is exploited. A reservoir of
liquid hydrocarbons is at a certain depth 2. These are exploited by
drilling a horizontal well 3 from a production facility 4 located
at the surface. A horizontal well 3 allows a greater length the
well to be in contact with the reservoir 2. Note also that
substantially vertical wells may be used.
[0004] The following discussion refers to shale reservoirs, but the
same techniques apply to hydrocarbon recovery from other low
porosity, low permeability formations. In order to improve
hydrocarbon recovery from shale reservoirs, the shale around the
well 3 is often hydraulically fractured, as illustrated in FIG. 2.
In the example of FIG. 2, the well is located in a shale (or other
low porosity/low permeability) formation 2 bearing hydrocarbons,
and surrounded above and below by a cap rock formation 5 and the
base rock formation 6 respectively. Once a fracture has been
hydraulically induced, it is typically held open using a
proppant.
[0005] Hydraulic fracturing involves propagating fractures 7
through the shale formation 2 using a pressurized fluid. These
fractures create conduits in the low permeability shale formation.
Hydrocarbon fluids can then migrate through the conduits towards
the well 3. In this way, recovery of hydrocarbons from the
reservoir is improved because hydrocarbons that would not
previously be able to reach the well now have a path to the well
and can be produced.
[0006] Hydraulic fracturing leads to a high initial production of
hydrocarbons trapped in the shale reservoir. However, this high
initial production quickly tails off to a value of typically
between 10 and 20% of the initial production rate. Over the
lifetime of a shale reservoir well, the well may produce an average
of 400-500 BOE (barrels of oil equivalent) per day, peaking in the
initial stages at around 1,500 BOE per day.
[0007] Furthermore, hydraulic fracturing only leads to a part of
the hydrocarbons trapped in the shale being produced. This is
because the pattern of the fractures created during the hydraulic
fracturing process does not provide access to the entire pore space
of the shale formation. Some regions of the shale reservoir are
therefore out of reach by the production well 3 due to the low
permeability of the shale formation. The production rate also drops
because the main driving force pushing hydrocarbons towards the
well is fluid expansion due to pressure depletion. The pressure
reduces as the hydrocarbons are produced.
SUMMARY
[0008] It is an object to improve the efficiency of production of
oil from reservoirs in low permeability formations such as
shale.
[0009] According to a first aspect, there is provided a method of
completing a well for producing hydrocarbons from a low
permeability reservoir formation. A wellbore is drilled into the
low permeability reservoir formation. A hydraulic fracturing
operation is performed to induce a plurality of fractures in the
reservoir at known locations. Each fracture is designated as either
one of a first set of fractures or one of a second set of
fractures. The well is completed using a tubular, the tubular
comprising an outer casing and a tubular inner member disposed
within the outer casing, wherein the tubular inner member and the
outer casing define an annulus, the annulus forming a first fluid
conduit arranged to transport produced hydrocarbons, and an
interior of the inner tubular member forming a second fluid conduit
arranged to transport an injection fluid, a set of first openings
in fluid connection with the first fluid conduit, each first
opening being located to substantially align with one of the first
set of fractures, and a set of second openings in fluid connection
with the second fluid conduit, each second opening being located to
substantially align with one of the second set of fractures. This
allows, in use, injection fluid to be applied to the second set of
fractures which increase the pressure in the formation and pushes
hydrocarbons towards the first set of fractures, making
hydrocarbons easier to produce.
[0010] As an option, a valve is provided to at least some of the
first set of openings, the valve arranged to control a flow of
hydrocarbons into the first fluid conduit. This allows flow to be
controlled or substantially shut of in the event of an unwanted
water or gas breakthrough.
[0011] Valves may also be provided to at least some of the second
set of openings, the valve arranged to control a flow of injection
fluid from the second fluid conduit. An advantage of this is that,
in use, the valves can maintain a similar pressure and/or flow rate
of injection fluid into the second set of fractures along the
length of the well, to maintain an even pressure of injection fluid
in the low permeability formation.
[0012] As an option, a packer is disposed in proximity to the first
set of openings and a further packer is disposed in proximity to
the second set of openings. The packers are arranged to ensure no
fluid connection between the first set of openings and the second
set of openings. In some circumstances, a gravelpack is optionally
used instead of packers. While the gravelpack may not ensure that
there is no fluid connection between the first and second sets of
openings, it will restrict the flow of fluids between the first and
second sets of openings and this may be within acceptable
levels.
[0013] An example of a low permeability reservoir formation is a
shale formation, but it will be appreciated that the techniques may
be applied to any type of low permeability reservoir formation.
[0014] As an option, the first set of fractures and the second set
of fractures are disposed along a main axis of the well such that a
fracture of the first set of fractures alternates with a fracture
of the second set of fractures. This allows more even distribution
of pressure from the injection fluid within the well and ensures
that as much of the reservoir as possible can be subject to
pressure from the injection fluid to increase hydrocarbon
production.
[0015] An advantage of having the second fluid conduit as the inner
conduit is that it has a smaller diameter and can therefore more
easily maintain the high pressure required for the injection
fluid.
[0016] According to a second aspect, there is provided a method of
producing hydrocarbons from a low permeability reservoir formation.
A well in a low permeability reservoir formation is provided with a
plurality of hydraulic fractures, each fracture being designated as
one of a first set of fractures and a second set of fractures. An
injection fluid is injected from an inner tubular member disposed
in an outer casing of a tubular into at least one of the second set
of fractures to increase a pressure in the low permeability
reservoir. Hydrocarbons are produced from at least one of the first
set of fractures such that the hydrocarbons flow into an annular
portion of the tubular defined by the outer casing and the inner
tubular member.
[0017] The flow of hydrocarbons into the production tubular may be
controlled using a valve to limit gas or water breakthrough.
[0018] A flow of injection fluid may be controlled using a further
valve. This allows a substantially uniform flow rate and/or
pressure to be injected to all of the second set of fractures.
[0019] As an option, at least one packer is provided in proximity
to an opening of the first set of openings, and a further packer is
disposed in proximity to an opening of the second set of openings.
The use of packers ensures that there is no fluid connection
between the first set of openings and the second set of
openings.
[0020] The injection fluid optionally comprises a gas.
[0021] It will be appreciated that the steps of injecting an
injection fluid and producing hydrocarbons may occur simultaneously
or sequentially.
[0022] According to a third aspect, there is provided a tubular for
producing hydrocarbons from a low permeability reservoir formation.
The tubular is provided with an outer casing and a tubular inner
member disposed within the outer casing, wherein the tubular inner
member and the outer casing define an annulus. The annulus forms a
first fluid conduit arranged to transport produced hydrocarbons and
an interior of the tubular inner member forms a second fluid
conduit arranged to transport an injection fluid. A first opening
in the outer casing is in fluid connection with the first fluid
conduit, and a second opening in the outer casing is in fluid
connection with the second fluid conduit.
[0023] As an option, the first fluid opening further comprises a
valve, the valve arranged to control a flow of hydrocarbons into
the first fluid conduit. This reduces the risk of water or gas
being produced in the event of a water or gas breakthrough.
[0024] As a further option, the second fluid opening further
comprises a second valve, the second valve arranged to control a
flow of injection fluid out of the second fluid conduit. This
allows even distribution of injection fluid into the formation at
all points along the length of the well.
[0025] As an option, the tubular is provided with a first packer
disposed in proximity to the first opening and a second packer
disposed in proximity to the second opening, wherein the packers
are arranged to ensure no fluid connection between the first
opening and the second opening, thereby reducing the risk of
injection fluid entering the first fluid conduit.
[0026] According to a fourth aspect, there is provided a system for
producing hydrocarbons from a low permeability reservoir formation.
The system comprises a wellbore in the low permeability reservoir
formation. The wellbore has plurality of fractures in the formation
induced by hydraulic fracturing at known locations. A tubular is
provided that comprises an outer casing and an inner tubular
member, the outer casing and the inner tubular member forming an
annulus therebetween. The annulus forms a first fluid conduit
located in the wellbore and arranged to transport produced
hydrocarbons, and an interior of the inner tubular member forms a
second fluid conduit located in the wellbore and arranged to
transport an injection fluid. A set of first openings is in fluid
connection with the first fluid conduit, each first opening being
located to substantially align with one of a first set of
fractures, and a set of second openings is in fluid connection with
the second fluid conduit, each second opening being located to
substantially align with one of a second set of fractures.
[0027] This system allows high pressure fluid to be injected into
the second set of fractures, which pushes hydrocarbons located in
the low permeability reservoir towards the first set of fractures,
thereby increasing the recovery rate of hydrocarbons in the low
permeability reservoir.
[0028] The system optionally includes valves located at at least
some of the first set of openings. The valves are arranged to
control a flow of hydrocarbons into the tubular and reduce the
effects of a gas or water breakthrough.
[0029] As an option, the system includes valves located at at least
some of the second set of openings, the valve arranged to control a
flow of injection fluid from the tubular. This ensures an even flow
rate/pressure of injection fluids at all points along the length of
the well.
[0030] The system is optionally provided with at least one packer
disposed in proximity to each opening of the first set of openings
and a further packer disposed in proximity to each opening of the
second set of openings, wherein the packers are arranged to ensure
no fluid connection between the first set of openings and the
second set of openings. This ensures that injection fluid does not
enter the first fluid conduit.
[0031] As an option, a second wellbore is provided in the low
permeability reservoir formation. The second wellbore has a
plurality of fractures induced by hydraulic fracturing at known
locations, and the second wellbore is located adjacent to the
wellbore.
[0032] As a further option, a fracture of the plurality of
fractures of the wellbore substantially aligns with a fracture of
plurality of fractures of the second wellbore. This improves the
efficiency of recovery of hydrocarbons, as pressure is uniformly
applied to the low permeability reservoir formation.
BRIEF DESCRIPTION OF DRAWINGS
[0033] FIG. 1 illustrates schematically a cross-section of a shale
reservoir in a shale formation;
[0034] FIG. 2 illustrates schematically a cross section of a shale
reservoir after a hydraulic fracturing operation;
[0035] FIG. 3 illustrates schematically a side view and cross
section views of an exemplary combined injection and production
pipe;
[0036] FIGS. 4A and 4B illustrate schematically cross sections of a
further exemplary combined injection and production pipe at
different points along a well;
[0037] FIG. 5 illustrates schematically a side view of a further
embodiment of an exemplary wellbore provided with two tubulars and
a gravelpack;
[0038] FIG. 6 is a flow diagram showing steps of operating a
combined injection and production pipe;
[0039] FIG. 7 illustrates schematically a view of exemplary
adjacent wells; and
[0040] FIG. 8 is a flow diagram showing steps of an alternative
method of installing and operating combined injection and
production pipe.
DETAILED DESCRIPTION
[0041] Existing technology for producing hydrocarbons from
reservoirs in low porosity and/or low permeability formations such
as shale is to induce fractures using a high pressure fluid. The
hydrocarbons are subsequently able to migrate through the fractures
to a production tubular. The following description refers to shale
formations, but it will be appreciated that the same techniques may
be used on other types of formation having low porosity and low
permeability.
[0042] FIG. 3 illustrates a section of a tubular in a horizontal
well 3 that has previously been subjected to a hydraulic fracturing
process. The hydraulic fracturing process has induced fractures 7,
9 in the surrounding formation. The tubular is provided with an
outer casing 10 that encloses a first fluid conduit 11 and a second
fluid conduit 12. Packers 13 are used to isolate different sections
of the tubular within the well, and packers are located either side
of a fracture 7, 9 in order to isolate the fracture 7, 9 from a gap
between the well 3 and the casing 10. Pairs of packers 13 may be
used, but it will be appreciated that only one packer is necessary
to isolate the first fluid conduit 11 from the second fluid conduit
12.
[0043] Some of the fractures 7 (termed herein "production
fractures") are used to allow hydrocarbons to migrate towards the
tubular, and other fractures 9 (termed herein "injection
fractures") are used for injecting high pressure fluid. The casing
10 has a first opening 14 that provides a fluid connection between
the well 3 and the first fluid conduit 11. These openings are
substantially aligned with the production fractures 7. The casing
10 has a second opening 15 that provides a fluid connection between
the well 3 and the second fluid conduit 12. It will be appreciated
that a horizontal section of the well will typically be provided
with many such openings 14, 15.
[0044] In normal production, produced hydrocarbons migrate along
the production fractures 7, through the first opening 14 and into
the first fluid conduit 11 such that the first fluid conduit 11
carries produced hydrocarbons. The first opening 14 may be provided
with known filters and sand screens, such as those used with
existing production tubulars. If required, the second opening 15
may also be provided with filters and sand screens. Furthermore,
the first opening 14 may be provided with a valve (not shown) that
can autonomously shut off gas or water in the event of a
breakthrough. An example of such as valve is described in WO
2008/004875, but it will be appreciated that any other type of
valve may be used to control the flow of fluids into the first
fluid conduit 11. The first opening 14 is disposed in a section of
the casing 10 that is located between two packers 13 in order to
isolate the first opening 14 in the well 3.
[0045] In normal production, the second fluid conduit 12 carries
high pressure injection fluid, typically provided from a production
facility 4. The injection fluid passes through the second fluid
conduit 12 and through the second opening 15. As the second opening
15 is also isolated in the well by a pair of packers 13, and is
disposed adjacent to an injection fracture 9, the high pressure
injection fluid passes into the injection fracture. The second
opening 15 may also be provided with a valve to control the volume
and rate of injection fluid passing through the second opening
15.
[0046] A purpose of having a pair of packers 13 isolating the first
opening 14 and a further pair of packers 13 isolating the second
opening is to ensure that there is no direct fluid connection
between the first conduit 11 and the second conduit 12. This would
otherwise lead to a "short circuit" in which high pressure
injection fluid could travel along the well 3 and enter the first
fluid conduit 11.
[0047] In an embodiment, the openings 14, 15 are aligned such that
each first opening 14 is adjacent along the length of the tubular
to a second opening 15 on either side of the first opening 14. This
has the effect of making every other fracture a production fracture
7, with injection fractures 9 between each production fracture 7.
This leads to improved hydrocarbon recovery because high pressure
injection fluid (typically a gas) passes into the injection
fractures 9 and increases the pressure in the formation. This
causes hydrocarbons in the shale formation located between
fractures to move towards production fractures 7, and therefore
enhances hydrocarbon recovery from the formation. Maintaining the
pressure in the formation using the injection fractures 9 increases
the production rate of hydrocarbons.
[0048] The use of simultaneous injection and production maintains
pressure in the low permeability formation and forces hydrocarbons
towards the production fractures. This technique therefore
increases the hydrocarbon production rate significantly compared to
a scenario in which no injection is applied. This differs from
steam injection in known steam assisted gravity drainage (SAGD)
techniques. For example, the disclosure of WO 2010/092338 describes
techniques to lower the viscosity of heavy oils, but makes no
mention of hydraulic fracturing or using pressure applied to
injection fractures to "push" hydrocarbons towards production
fractures.
[0049] As shown in FIG. 3, in an embodiment of the invention the
outer casing 10 forms an outside wall of the first fluid conduit
11. A tubular member 16 having a smaller diameter than the outer
casing 10 is disposed inside the outer casing 10. The first fluid
conduit is therefore formed by an annulus defined between the outer
casing 10 and the tubular member 16. The first opening 14 between
the first fluid conduit and the well 3 can be formed from an
opening in the outer casing. The interior of the tubular member 16
forms the second fluid conduit 12. In this case, the second opening
15 between the well 3 and the second fluid conduit 12 is a passage
that passes through the annulus defining the first fluid conduit 11
to provide a fluid connection between the well 3 and the second
fluid conduit 12.
[0050] An advantage of having the second fluid conduit 12 defined
by the smaller diameter tubular member 16 is that the smaller
diameter allows a higher pressure to be maintained in the second
fluid conduit 12. However, it will be appreciated that the annulus
defined by the outer casing 10 and the tubular member 16 could be
used as the second fluid conduit 12 for carrying high pressure
injection fluid, and the interior of the tubular member 16 could be
used as the first fluid conduit for carrying produced
hydrocarbons.
[0051] Other arrangements for providing a first fluid conduit 11
and a second fluid conduit 12 in a single outer casing 10 are
possible. FIGS. 4A and 4B show cross-sections at different points
along the length of a well illustrating one such example. In this
example, an outer casing 10a in the well 3 has a dividing wall 17
dividing the outer casing into two sections 11a, 12a. One section
11a acts as the first fluid conduit, the other section 12a acts as
the second fluid conduit. A first opening 14a provides a fluid
connection between the well 3 and the first fluid conduit 11a, and
a second opening 15a provides a fluid connection between the well 3
and the second fluid conduit. It will be appreciated that the
openings 14a, 15a shown in FIG. 4 will in practice be offset along
the length of the well 3 such that the first opening 14a is
disposed in proximity to a production fracture 7 and the second
opening 15a is disposed in proximity to an injection fracture 9,
and that the openings 14a, 15a will be isolated by a pair of
packers 13.
[0052] As shown in FIG. 5, a further exemplary arrangement is to
provide two tubulars 17, 18, hoses or pipes in the same wellbore
such that a production tubular 17 is used for conveying produced
hydrocarbons, and an injection tubular 18 is used for conveying
injection fluid. The openings 19 in the production tubular 17
substantially line up with production fractures 7 and the openings
20 in the second tubular substantially line up with injection
fractures 9.
[0053] In a further exemplary arrangement, otherwise compatible
with the arrangements described above, at least some of the packers
are replaced with a gravelpack. As shown in FIG. 5, gravelpack 21
performs the function of the packers of FIG. 3, in that the
gravelpack 21 restricts the flow of fluid in the annulus between
the well 3 and the outer casing 10 (or, in the case of two
tubulars, between the production tubular 17 and the injection
tubular 18). The gravelpack 21 is unlikely to completely prevent
injection fluids from entering the first openings 14, 19 but it
reduces the flow of injection fluids into the first openings 14, 19
to an acceptable level. Note that a gravelpack 21 along the entire
length of the tubular could be used to replace packers 13
altogether. The use of a gravelpack 21 may be particularly suitable
for the exemplary embodiment shown in FIG. 5 in which two tubulars
17, 18 are used. The tubulars could otherwise be difficult to
isolate using packers. The use of a gravelpack 21 also reduces the
operational complexities in locating the packers 13, and the
absence of packers 13 also means there is no risk of a packer
failure leading to injection fluids entering the production
tubular.
[0054] FIG. 5 is a flow diagram illustrating exemplary steps of
fitting and operating a production tubular in a shale reservoir.
The following numbering corresponds to that of FIG. 5:
[0055] S1. The well is drilled into the reservoir. It may or may
not have a cemented liner installed.
[0056] S2. Hydraulic fracturing is induced at known locations in
the well. The locations for fractures are selected based on
reservoir modelling and geomechanical considerations to optimize
production from the well. The fractures are shown as being oriented
with a main axis substantially perpendicular to the well, but it
will be appreciated that this is not always necessary and in some
cases may be hindered by geological considerations. This is
achieved by drilling the well in the direction of the least
horizontal stress. An advantage of orienting fractures with a main
axis substantially perpendicular to the well 3 is that it makes it
easier to align the fractures with fractures from adjacent wells,
as described in more detail below.
[0057] S3. The well is completed using a combined injection and
production tubular as described above in FIG. 3. The first openings
14 are located adjacent to production fractures 7 and the second
openings 15 may be located adjacent to injection fractures 9, and
the fractures are isolated by at least one or more packers 13 (FIG.
3 shows a pair of packers 13 around each opening, but it will be
appreciated that any number of packers can be used if it prevents
or restricts a flow of fluid between the first and second
openings). As described above, a typical arrangement is for each
alternate fracture to be a production fracture 7 and the fractures
between the production fractures 7 to be injection fractures 9.
Packers are disposed between the outer casing 10 and the well in
such a way as to isolate the first opening 14 from the second
opening 15.
[0058] S4. High pressure injection fluid is passed through the
second fluid conduit 12 and into the injection fractures 9. This
increases the pressure in the reservoir around each injection
fracture, causing hydrocarbons in the reservoir to be pushed
towards adjacent production fractures 7 on either side of each
injection fracture.
[0059] S5. Hydrocarbons that are pushed towards the production
fractures 7 pass along the production fractures 7 and through the
first openings 14 into the first fluid conduit 11, allowing the
hydrocarbons to be produced from the well 3. Steps S4 and S5 run
simultaneously. The fluid isolation of the first fluid conduit from
the second fluid conduit means that injection and production are
performed simultaneously, and the injection operation enhances the
production.
[0060] It will not always be possible to line up the production
fractures 7 and the injection fractures 9 from each well 3, 18 as
shown. However, even if this alignment cannot be achieved,
production of hydrocarbons is still enhanced. The first 3 and
second 8 wells may be disposed substantially side by side or above
and below one another.
[0061] Turning now to FIG. 8, there is illustrated a further method
that addresses the above problem. The following numbering
corresponds to that of FIG. 8:
[0062] S6. The well is drilled into the reservoir. It may or may
not have a cemented liner installed.
[0063] S7. The well is completed using a combined injection and
production tubular as described above. The first openings 14 are
located adjacent to production fractures 7 and the second openings
15 may be located adjacent to injection fractures 9, and the
fractures are isolated by at least one or more packers 13 (FIG. 3
shows a pair of packers 13 around each opening, but it will be
appreciated that any number of packers can be used if it prevents
or restricts a flow of fluid between the first and second
openings). As described above, a typical arrangement is for each
alternate fracture to be a production fracture 7 and the fractures
between the production fractures 7 to be injection fractures 9.
[0064] S8. Hydraulic fracturing is induced at known locations in
the well. The locations for fractures are selected based on
reservoir modelling and geomechanical considerations to optimize
production from the well. Hydraulic fracturing may be performed
using both the first openings 14 and the second openings 15. This
ensures that during subsequent simultaneous injection and
production, the induced fractures are substantially aligned with
the first openings 14 and second openings 15, and eliminates the
need to align the openings with the fractures during a subsequent
completion operation.
[0065] S9. High pressure injection fluid is passed through the
second fluid conduit 12 and into the injection fractures 9. This
increases the pressure in the reservoir around each injection
fracture, causing hydrocarbons in the reservoir to be pushed
towards adjacent production fractures 7 on either side of each
injection fracture.
[0066] S10. Hydrocarbons that are pushed towards the production
fractures 7 pass along the production fractures 7 and through the
first openings 14 into the first fluid conduit 11, allowing the
hydrocarbons to be produced from the well 3. Steps S9 and S10 occur
simultaneously. The fluid isolation of the first fluid conduit from
the second fluid conduit means that injection and production are
performed simultaneously, and the injection operation enhances the
production.
[0067] The use of a combined injection/production tubular to allow
continuous injection of high pressure fluids into a reservoir at
the same time as producing hydrocarbons that are moved by the
increased pressure can significantly increase the hydrocarbon
recovery and production rate in certain reservoirs. This type of
system is particularly suitable to reservoirs in low porosity, low
permeability formations that use hydraulic fracturing. It may be
used in other types of reservoirs provided there is sufficient
porosity to allow efficient high pressure fluid injection.
[0068] It will be appreciated by a person of skill in the art that
various modifications may be made to the embodiments described
above without departing from the scope of the present
disclosure.
[0069] In an alternative embodiment, there is provided a method of
completing a well for producing hydrocarbons from a low
permeability reservoir formation. A wellbore is drilled into the
low permeability reservoir formation. A hydraulic fracturing
operation is performed to induce a plurality of fractures in the
reservoir at known locations. Each fracture is designated as either
one of a first set of fractures or one of a second set of
fractures. The well is completed using a first fluid conduit
arranged to transport produced hydrocarbons and a second fluid
conduit arranged to transport an injection fluid. A set of first
openings is provided in fluid connection with the first fluid
conduit, each first opening being located to substantially align
with one of the first set of fractures. A set of second openings is
provided in fluid connection with the second fluid conduit, each
second opening being located to substantially align with one of the
second set of fractures. This allows, in use, injection fluid to be
applied to the second set of fractures which increase the pressure
in the formation and pushes hydrocarbons towards the first set of
fractures, making hydrocarbons easier to produce.
[0070] A valve may be provided to at least some of the first set of
openings, the valve arranged to control a flow of hydrocarbons into
the first fluid conduit. This allows flow to be controlled or
substantially shut of in the event of an unwanted water or gas
breakthrough. Valves may also be provided to at least some of the
second set of openings, the valve arranged to control a flow of
injection fluid from the second fluid conduit. An advantage of this
is that, in use, the valves can maintain a similar pressure and/or
flow rate of injection fluid into the second set of fractures along
the length of the well, to maintain an even pressure of injection
fluid in the low permeability formation.
[0071] A packer may be disposed in proximity to the first set of
openings and a further packer is disposed in proximity to the
second set of openings. The packers are arranged to ensure no fluid
connection between the first set of openings and the second set of
openings. In some circumstances, a gravelpack is optionally used
instead of packers.
[0072] While the gravelpack may not ensure that there is no fluid
connection between the first and second sets of openings, it will
restrict the flow of fluids between the first and second sets of
openings and this may be within acceptable levels.
[0073] An example of a low permeability reservoir formation is a
shale formation.
[0074] The first set of fractures and the second set of fractures
may be disposed along a main axis of the well such that a fracture
of the first set of fractures alternates with a fracture of the
second set of fractures. This allows more even distribution of
pressure from the injection fluid within the well and ensures that
as much of the reservoir as possible can be subject to pressure
from the injection fluid to increase hydrocarbon production.
[0075] The first fluid conduit and the second fluid conduit may be
disposed in a tubular comprising an outer casing, and the first set
of openings and the second set of openings are located in the outer
casing. In this case, the second fluid conduit may form an inner
conduit, and the first fluid conduit may be formed in the annulus
between the second fluid conduit and the outer casing. An advantage
of having the second fluid conduit as the inner conduit is that it
has a smaller diameter and can therefore more easily maintain the
high pressure required for the injection fluid.
[0076] In this embodiment, a well in a low permeability reservoir
formation is provided with a plurality of hydraulic fractures, each
fracture being designated as one of a first set of fractures and a
second set of fractures. An injection fluid is injected into at
least one of the second set of fractures to increase a pressure in
the low permeability reservoir. Hydrocarbons are simultaneously
produced from at least one of the first set of fractures such that
the hydrocarbons flow into a production tubular. The flow of
hydrocarbons into the production tubular may be controlled using a
valve to limit gas or water breakthrough. A flow of injection fluid
may be controlled using a further valve. This allows a
substantially uniform flow rate and/or pressure to be injected to
all of the second set of fractures. At least one packer may be
provided in proximity to an opening of the first set of openings,
and a further packer is disposed in proximity to an opening of the
second set of openings. The use of packers ensures that there is no
fluid connection between the first set of openings and the second
set of openings. It will be appreciated that the steps of injecting
an injection fluid and producing hydrocarbons may occur
simultaneously or sequentially.
[0077] In this embodiment, a tubular for producing hydrocarbons
from a low permeability reservoir formation is provided with an
outer casing, a first fluid conduit arranged to transport produced
hydrocarbons, a second fluid conduit arranged to transport an
injection fluid, a first opening in the outer casing in fluid
connection with the first fluid conduit, and a second opening in
the outer casing in fluid connection with the second fluid conduit.
The first fluid opening may further comprise a valve, the valve
arranged to control a flow of hydrocarbons into the first fluid
conduit. This reduces the risk of water or gas being produced in
the event of a water or gas breakthrough. The second fluid opening
may comprises a second valve, the second valve arranged to control
a flow of injection fluid out of the second fluid conduit. This
allows even distribution of injection fluid into the formation at
all points along the length of the well. The tubular may be
provided with a first packer disposed in proximity to the first
opening and a second packer disposed in proximity to the second
opening, wherein the packers are arranged to ensure no fluid
connection between the first opening and the second opening,
thereby reducing the risk of injection fluid entering the first
fluid conduit.
[0078] In this embodiment, a system comprises a wellbore in the low
permeability reservoir formation. The wellbore has plurality of
fractures in the formation induced by hydraulic fracturing at known
locations. A first fluid conduit is located in the wellbore and
arranged to transport produced hydrocarbons. A second fluid conduit
is located in the wellbore and arranged to transport an injection
fluid. A set of first openings is provided in fluid connection with
the first fluid conduit, each first opening being located to
substantially align with one of a first set of fractures. A set of
second openings is provided in fluid connection with the second
fluid conduit, each second opening being located to substantially
align with one of a second set of fractures. This system allows
high pressure fluid to be injected into the second set of
fractures, which pushes hydrocarbons located in the low
permeability reservoir towards the first set of fractures, thereby
increasing the recovery rate of hydrocarbons in the low
permeability reservoir. The first fluid conduit and the second
fluid conduit may be disposed in a tubular comprising an outer
casing, and the first set of openings and the second set of
openings are located in the outer casing. The system may include
valves located at at least some of the first set of openings. The
valves are arranged to control a flow of hydrocarbons into the
tubular and reduce the effects of a gas or water breakthrough.
Similarly, the system may include valves located at at least some
of the second set of openings, the valve arranged to control a flow
of injection fluid from the tubular. This ensures an even flow
rate/pressure of injection fluids at all points along the length of
the well. The system may be provided with at least one packer
disposed in proximity to each opening of the first set of openings
and a further packer disposed in proximity to each opening of the
second set of openings, wherein the packers are arranged to ensure
no fluid connection between the first set of openings and the
second set of openings. This ensures that injection fluid does not
enter the first fluid conduit.
[0079] It is also possible to provide a second wellbore in the low
permeability reservoir formation. The second wellbore has a
plurality of fractures induced by hydraulic fracturing at known
locations, and the second wellbore is located adjacent to the
wellbore. A fracture of the plurality of fractures of the wellbore
may substantially align with a fracture of plurality of fractures
of the second wellbore. This improves the efficiency of recovery of
hydrocarbons, as pressure is uniformly applied to the low
permeability reservoir formation.
* * * * *