U.S. patent application number 13/000449 was filed with the patent office on 2011-05-26 for producing hydrocarbon fluid from a layer of oil sand.
Invention is credited to Bruno Best.
Application Number | 20110120704 13/000449 |
Document ID | / |
Family ID | 39938298 |
Filed Date | 2011-05-26 |
United States Patent
Application |
20110120704 |
Kind Code |
A1 |
Best; Bruno |
May 26, 2011 |
PRODUCING HYDROCARBON FLUID FROM A LAYER OF OIL SAND
Abstract
A method of producing hydrocarbons from a layer of oil sand
located in a formation comprises creating a plurality of boreholes
in the formation, including a first borehole and a second borehole
spaced from the first borehole in a selected direction along which
the layer of oil sand extends, and creating a cavity in the layer,
the cavity being in fluid communication with the first borehole;
extending the cavity in the selected direction by operating fluid
jetting means via the first borehole to jet a stream of fluid
against the cavity wall; when the cavity is in fluid communication
with the second borehole, operating the fluid jetting means via the
second borehole to jet a stream of fluid against the cavity wall so
as to further extend the cavity; and transporting a slurry of fluid
and oil sand from the cavity to a processing facility.
Inventors: |
Best; Bruno; (Rijswijk,
NL) |
Family ID: |
39938298 |
Appl. No.: |
13/000449 |
Filed: |
June 30, 2009 |
PCT Filed: |
June 30, 2009 |
PCT NO: |
PCT/EP2009/058166 |
371 Date: |
February 1, 2011 |
Current U.S.
Class: |
166/269 |
Current CPC
Class: |
E21B 41/0078 20130101;
E21B 43/30 20130101; E21B 43/29 20130101 |
Class at
Publication: |
166/269 |
International
Class: |
E21B 43/16 20060101
E21B043/16 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 2, 2008 |
EP |
08159545.6 |
Claims
1. A method of producing hydrocarbon fluid from a layer of oil sand
located in an earth formation, the method comprising: creating a
plurality of boreholes in the earth formation, including a first
injection borehole and a second injection borehole spaced from the
first injection borehole in a selected direction along which the
layer of oil sand extends, and creating a cavity in the layer of
oil sand, the cavity being in fluid communication with the first
injection borehole; extending the cavity in the selected direction
by operating fluid jetting means via the first injection borehole
to jet a stream of fluid against a wall of the cavity; when the
cavity is in fluid communication with the second injection
borehole, operating the fluid jetting means via the second
injection borehole to jet a stream of fluid against the wall of the
cavity so as to further extend the cavity; and transporting a
slurry of fluid and oil sand, resulting from operation of the fluid
jetting means, from the cavity via a discharge borehole to a
processing facility for processing the slurry, the discharge
borehole having a lower section extending in the selected direction
and being in fluid communication with the cavity at said wall of
the cavity.
2. The method of claim 1, wherein the step of operating the fluid
jetting means via the second injection borehole comprises removing
the fluid jetting means from the first injection borehole and
inserting the fluid jetting means into the second injection
borehole.
3. The method of claim 1, wherein the second injection borehole is
created after creating the first injection borehole, in
correspondence with extension of the cavity in the selected
direction.
4. The method of claim 1 wherein the method further comprises
inserting a stream of refill material into the cavity via the first
injection borehole.
5. The method of claim 4, wherein the stream of refill material
comprises sand.
6. The method of claim 4 wherein the stream of refill material is
transported from the processing facility to the cavity.
7. The method of claim 1 wherein the lower section of the discharge
borehole is provided with a liner adapted to be changed in length,
and wherein the method further comprises changing the length of the
liner in correspondence with extension of the cavity in the
selected direction.
8. The method of claim 7, wherein the liner is adapted to be
shortened, and wherein the step of changing the length of the liner
comprises shortening the liner in correspondence with extension of
the cavity in the selected direction.
9. The method of claim 8, wherein shortening the liner comprises
operating a cutting device to cut the liner, preferably wherein the
liner is made of a non-metal material, more preferably of a
plastics material.
10. The method of claim 1, wherein the discharge borehole is
provided with pumping means for pumping the slurry via the
discharge borehole to the processing facility.
11. The method of claim 10, wherein the pumping means includes a
pump sealed relative to an inner surface of the liner.
12. The method of claim 10, wherein the pumping means is axially
movable through the discharge borehole, and wherein the method
further comprises axially moving the pumping means through the
discharge borehole in correspondence with changing the length of
the liner.
13. The method of claim 1 wherein the pumping means is driven by a
stream of fluid pumped through a conduit extending through the
discharge borehole.
14. The method of claim 13, wherein at least a portion of said
stream of fluid is injected into the slurry of fluid and oil sand
present in the cavity.
15. (canceled)
Description
[0001] In the industry of hydrocarbon fluid production from
subterranean reservoirs, it is conventional practice that oil is
produced from wellbores by virtue of the high fluid pressures
existing downhole. In case of high viscosity oil, downhole pumps
can be applied to pump the oil to surface, or other methods can be
applied to increase the oil production rate such as steam injection
or CO.sub.2 injection into the formation. However, the conventional
methods are not adequate for the production of bituminous oil such
as occurring in the oil sand reservoirs in Canada. As some oil sand
layers occur at relatively shallow depths, typically between 0 to
200 meters, it is common practice to produce oil from these layers
by surface mining whereby the overburden layer is removed using
draglines and/or shovels and trucks. The produced oil sand is
transported to one or more processing facilities for separation of
hydrocarbon fluid from the sand slurries. However, for oil sand
layers at greater depths, removal of the overburden is costly and
has a significant impact on the environment. Therefore alternative
methods for producing oil sands have been proposed.
[0002] One such alternative method is disclosed in a technical
paper published in CIM magazine by the Canadian Institute of Mining
& Metallurgy, 2001, Vol. 94, Nr. 1054, pages 63-66, entitled
"Hydraulic underground mining of oil sands--the next big step".
This publication discloses a method of producing hydrocarbon fluid
from an oil sand layer located in an earth formation, wherein a
discharge borehole is drilled into the oil sand layer and a fluid
jetting device is operated to excavate the oil sand layer and
thereby form a cavity in the oil sand layer, wherein a slurry of
fluid and oil sand is formed in the cavity as a result of the fluid
jetting operation. The produced slurry is transported via the
discharge borehole to a processing facility for processing the
slurry.
[0003] A different method is disclosed in WO 2007/050180, wherein a
subsurface formation comprising heavy oil and solids is accessed
via vertical injection and production boreholes, pressurized
sufficiently to relieve overburden pressure, and wherein solids and
heavy oil are mobilized and caused to flow through one of the
vertical boreholes by means of varying differential pressure
between the injection and production boreholes. Optionally water
jetting can be used in a short transitional step and used
intermittently or for short periods of time, to locally improve the
flow of slurry towards the production wellbore.
[0004] However, there is still a need for an improved method of
producing hydrocarbon fluid from an oil sand layer.
[0005] In accordance with the invention there is provided a method
of producing hydrocarbon fluid from a layer of oil sand located in
an earth formation, the method comprising:
[0006] creating a plurality of boreholes in the earth formation,
including a first injection borehole and a second injection
borehole spaced from the first injection borehole in a selected
direction in which the layer of oil sand extends, and creating a
cavity in the layer of oil sand, the cavity being in fluid
communication with the first injection borehole;
[0007] extending the cavity in the selected direction by operating
fluid jetting means via the first injection borehole to jet a
stream of fluid against a wall of the cavity;
[0008] when the cavity is in fluid communication with the second
injection borehole, operating the fluid jetting means via the
second injection borehole to jet a stream of fluid against the wall
of the cavity so as to further extend the cavity; and
[0009] transporting a slurry of fluid and oil sand, resulting from
operation of the fluid jetting means, from the cavity via a
discharge borehole to a processing facility for processing the
slurry, the discharge borehole having a lower section extending in
the selected direction and being in fluid communication with the
cavity at said wall of the cavity.
[0010] In this manner it is achieved that the fluid jetting means
is close to the cavity wall being excavated throughout the fluid
jetting operation, so that the fluid jet always impacts the cavity
wall with great force.
[0011] Suitably the step of further operating the fluid jetting
means comprises removing the fluid jetting means from the first
injection borehole and inserting the fluid jetting means into the
second injection borehole.
[0012] The injection boreholes can be created simultaneously if
desired, however it may be more economical that the second
injection borehole is created after creating the first injection
borehole, in correspondence with extension of the cavity in the
selected direction.
[0013] In order to reduce or prevent subsidence of the overburden
formation, being the earth formation on top of the oil sand layer,
the method preferably further comprises inserting a stream of
refill material into the cavity via the first injection borehole.
Suitably, the stream of refill material comprises sand, for example
cleaned sand transported from the processing facility to the
cavity.
[0014] To accommodate extension of the cavity in the selected
direction, the lower section of the discharge borehole is suitably
provided with a liner adapted to be changed in length, and wherein
the method further comprises changing the length of the liner in
correspondence with movement of the front surface of the cavity in
the selected direction.
[0015] If the lower section of the discharge borehole shortens as a
result of extending the cavity, the liner is suitably adapted to be
shortened, and wherein the step of changing the length of the liner
comprises shortening the liner in correspondence with movement of
the front surface of the cavity in the selected direction. For
example, the step of shortening the liner can comprise operating a
cutting device to cut the liner. To this end the liner is suitably
made from a material that can be cut. The liner can be made of
metals softer than steel, e.g. aluminium. Preferably the liner is
made of a non-metal material, and in particular the liner can be
made of a plastics material. The liner can also be shortened by the
action of a fluid jet. Shortening can be done by cutting or jetting
away coarse discrete pieces of the liner, such as at suitable time
intervals, or by producing small chips of the liner material.
[0016] Suitably, the discharge borehole is provided with pumping
means for pumping the slurry via the discharge borehole to the
processing facility. Preferably the pumping means includes a pump
sealed to an inner surface of the liner. In order to accommodate
the change of length of the liner, it is preferred that the pump is
axially movable through the discharge borehole, and that the method
further comprises axially moving the pump through the discharge
borehole in correspondence with changing the length of the liner.
Suitably the pump is driven by a stream of fluid pumped through a
conduit extending into the discharge borehole. In such case,
preferably at least a portion of said stream of fluid is injected
into the slurry of fluid and oil sand present in the cavity in
order to stir the slurry in the cavity if desired.
[0017] The invention will be described hereinafter in more detail,
and by way of example, with reference to the accompanying drawings
in which:
[0018] FIG. 1 schematically shows a system for use in an embodiment
of the method of the invention;
[0019] FIG. 2 schematically shows a detail of the system of FIG.
1;
[0020] FIG. 3 schematically shows the system of FIG. 1 during a
further stage of the method of the invention;
[0021] FIG. 4 schematically shows a top view at surface of a layout
using the system of FIG. 1; and
[0022] FIG. 5 schematically shows a top view at surface of another
layout using the system of FIG. 1
[0023] In the Figures, like reference numerals relate to like
components.
[0024] Referring to FIGS. 1 and 2 there is shown an earth formation
containing an oil sands layer 2 located between an overburden layer
4 above the oil sand layer 2 and an underburden layer, shown as a
layer of rock material 6, such as limestone, below the oil sand
layer 2. The oil sand layer 2 has respective upper and lower
boundaries 20, 22 extending horizontally. Thus, the layer of oil
sand extends in an extension direction, in particular a
non-vertical extension direction, in this example horizontally
between an overburden and an underburden. The layer of oil sand has
a thickness defining a thickness direction, which is in this
example vertical. The extension direction is different from, often
perpendicular to, the thickness direction, and is in this example
in the horizontal plane. The layer extends more in the extension
direction that its thickness, typically for more than twice its
thickness, such as for more that
[0025] or 10 times its thickness, or even more. It will typically
extend for less than 10000 times its thickness. It will be
understood that the layer can extend along a plane.
[0026] A first injection borehole 8 extends vertically from a
mobile injection rig 10 at the earth surface 11 to a cavity 12
formed in the layer of oil sand 2. The cavity has an upper portion
12a filled with air and a lower portion 12b containing a mixture
(referred to hereinafter as "slurry") 13 of water and oil sand
particles.
[0027] A deviated discharge borehole 14 extends from a production
station 15 at the earth surface to the cavity 12 whereby the
production station 15 is horizontally spaced from the mobile
injection rig 10. The discharge borehole 14 has an upper section 16
extending vertically and a lower section 18 extending substantially
parallel to the upper boundary 20 and/or lower boundary 22 of the
oil sands layer 2. Thus, in the present example the lower section
18 extends horizontally. Furthermore, the lower borehole section 18
extends in a selected direction within the layer 2, in this example
an azimuthal direction from the cavity 12, and debouches into the
lower cavity portion 12b at some distance above the bottom of the
cavity. The intersection between the lower borehole section 18 and
the cavity 12 defines a front surface 23 of the cavity 12.
[0028] The selected direction suitably is a direction within the
layer, in particular a non-vertical direction, at an angle of less
than 45 degrees with an upper and/or lower boundary of the layer,
preferably substantially parallel to the upper boundary and/or
lower boundary of the layer. In particular the selected direction
can be at least 45 degrees away from the thickness direction, in
particular at least 45 degrees away from the vertical. Suitably the
selected direction substantially coincides with the extension
direction, so that the cavity is extended within the layer,
substantially parallel with its upper and/or lower boundary, for
more than the layer thickness, such as for between 2 and 5000 times
the layer thickness. The expression substantially parallel herein
accounts for the precision with which deviated boreholes can be
drilled in an underground layer.
[0029] The upper section 16 is provided with a conventional casing
(or liner) 24, whereas the lower section 18 is provided with a
liner 26 of plastics material, for example glass fibre reinforced
plastic, whereby the liner 26 extends a minimal distance into the
cavity 12. Furthermore, a jet pump 28 is positioned in the liner 26
in a manner that the jet pump 28 is sealed relative to the inner
surface of the liner 26 and is axially movable through liner 26. A
fluid conduit 30 for driving the jet pump 28 extends from the
production station 15 through the casing 24 and the liner 26 to the
jet pump 28. When driven by fluid pumped through the fluid conduit
30, the jet pump 28 is arranged to pump the slurry 13 of fluid and
particles from the lower cavity portion 12b, via the annular space
between the fluid conduit 30 on one hand and the liner 26 and
casing 24 on the other hand, to the production station 15. The jet
pump 28 is thereto provided with one or more flow channels 32 (FIG.
2) allowing the slurry to flow in axial direction through the jet
pump 28. The fluid conduit 30 extends further from the jet pump 28
through liner 26 to the cavity 12. A lower end part 34 of the fluid
conduit 30 is provided with a cutter 36 for cutting the liner 26,
one or more nozzles 38 for initially forming the cavity 12 and for
stirring the slurry present in the cavity 12, and a bit or mill 39
for crushing lumps of rock material that may be present in the
cavity 12.
[0030] An injection string 40 for injecting fluid into the cavity
12 extends from the injection rig 10 via the first injection
borehole 8 into the cavity 12, the injection string 40 having a
lower end provided with jetting nozzles 42 located in the upper
portion 12a of cavity 12. An annular seal 43 (such as a rotating
head) is arranged in an upper part of the first injection borehole
8 to seal the annular space formed between the injection string 40
and the wall or casing of the first injection borehole 8.
[0031] Referring further to FIG. 3 there is shown the earth
formation and several of the components shown in FIGS. 1 and 2
during a further stage of operation. The cavity 12 has been
extended in the azimuthal direction of the lower borehole section
18 whereby the front surface 23 of the cavity has moved in said
azimuthal direction. As a result, the lower borehole section 18 has
become shorter. The liner 26 has been shortened at the side of the
cavity 12 in correspondence with shortening of the lower borehole
section 18. The fluid conduit 30 with the jet pump 28 connected
thereto has been pulled upward through discharge borehole 14 over a
distance about equal to the reduction in length of liner 26.
Furthermore, a second injection borehole 44 extends vertically from
a mobile injection rig 46 to the cavity 12. The second injection
borehole 44 is spaced from the first injection borehole 8 in the
azimuthal direction. As is illustrated in FIG. 3, the lower end of
the second injection borehole 44 is positioned closer to the front
surface 23 of cavity 12 than the lower end of the first injection
borehole 8.
[0032] The injection string 40 has been removed from the first
injection borehole 8 and has been installed in the second injection
borehole 44 so as to extend from the injection rig 46 into the
cavity 12 whereby the jetting nozzles 42 again are positioned in
the upper portion 12a of cavity 12. Alternatively another injection
string, similar to injection string 40, can be applied in the
second injection borehole 44. An annular seal 47 (such as a
rotating head) is arranged in an upper part of the second injection
borehole 44 to seal the annular space formed between the injection
string 40 and the wall or casing of the second injection borehole
44.
[0033] The first injection borehole 8 is now provided with a sand
injection string 48 for inserting clean sand into the cavity 12.
The sand injection string 48 is suspended at surface by the mobile
injection rig 10 or by any other suitable means. A rear portion of
the cavity 12 is filled with a body of sand 49, which preferably
includes a binder material such as cement.
[0034] In this example the first and second injection boreholes and
the discharge borehole form a plurality of boreholes.
[0035] In the context of the present description, the assembly of
cavity, discharge borehole, one or more injection boreholes, and
production station is referred to as a "production unit". In the
example described above, the production unit includes two injection
boreholes. However, depending on the stage of operation, the
production unit can include only one, or more than two, injection
boreholes. Generally, the production unit can include any suitable
number of injection boreholes mutually spaced in the azimuthal
direction.
[0036] Referring further to FIG. 4, there is schematically shown a
top view at surface of a layout of a plurality of production units
50, 52, 54, 56, 58. Each production unit 50, 52, 54, 56, 58 is
substantially similar to the production unit described hereinbefore
with reference to FIGS. 1-3, albeit that the number of injection
boreholes varies per production unit depending on the stage of
operation. For ease of reference, the respective discharge
boreholes and cavities are shown in dotted lines.
[0037] Production unit 50 includes discharge borehole 60, cavity
61, injection boreholes 62, 63 and production station 64.
Production unit 52 includes discharge borehole 65, cavity 66,
injection boreholes 67, 68 and production station 69. Production
unit 54 includes discharge borehole 70, cavity 71, injection
boreholes 72, 73, 74 and production station 75. Production unit 56
includes discharge borehole 76, cavity 77, injection boreholes 78,
79, 80 and production station 81. Production unit 58 includes
discharge borehole 82, cavity 83, injection boreholes 84, 85, 86,
87 and production station 88. The cavities 61, 66, 71, 77, 83 have
respective front surfaces 90, 92, 94, 96, 98. Mobile injection rigs
100, 102, 104, 106, 108, 110 are provided at surface, whereby
injection rigs 100, 102, 104, 106, 108 are in fluid communication
with respective injection boreholes 62, 67, 72, 78, 84, and whereby
injection rig 110 is in fluid communication with each one of
injection boreholes 68, 73, 74, 79. The discharge boreholes 60, 65,
70, 76, 82 extend substantially parallel to each other at selected
mutual horizontal spacings. Similarly, the cavities 61, 66, 71, 77,
83 extend substantially parallel to each other at selected
horizontal spacings. The production stations 64, 69, 75, 81, 88 are
in fluid communication with a separation plant 112 via a common
pipeline 114 so as to allow pumping of the respective slurries of
fluid and oil sand particles from the production units 50, 52, 54,
56, 58 via the common pipeline 114 to the separation plant 112
where hydrocarbon fluid is separated from the produced oil sand
particles.
[0038] Furthermore, reference numerals 116 relate to locations of
injection boreholes yet to be drilled at a further stage of
operation, reference numerals 118 relate to injection boreholes
already drilled but not yet in fluid communication with the
respective cavities 61, 66, 71, 77, 83, and reference numerals 120
relate to injection boreholes currently being drilled.
[0039] In the context of the present description, the assembly of
production units 50, 52, 54, 56, 58 is referred to as a "field
section". The field section described in the example above includes
five production units, however it is to be understood that a field
section can include any suitable number of production units.
[0040] Referring further to FIG. 5 there is schematically shown a
top view at surface of an exemplary layout of a plurality of field
sections 140, 142, 144, 146 whereby field section 140 represents
the assembly of production units 50, 52, 54, 56, 58 described
above. Field sections 142, 144, 146 are substantially similar to
field section 140 albeit these are mirrored relative to field
section 140. Furthermore, field sections 140, 142 are fluidly
connected to separation plant 112 via common pipeline 114, and
field sections 144, 146 are fluidly connected to separation plant
112 via a common pipeline 148.
[0041] During normal operation of the system of FIGS. 1-3, the
first injection borehole 8 and the discharge borehole 14 are
drilled into the oil sands layer 2 using one or more conventional
drilling rigs, and the casing 24 and liner 26 are arranged in the
discharge borehole 14. The mobile injection rig 10 and the
production station 15 are installed at their respective positions
as indicated in FIG. 1. In a next step, the fluid conduit 30 with
the jet pump 28 connected thereto is lowered through the discharge
borehole 14 until end part 34 of the fluid conduit 30 extends just
beyond the far end of the liner 26. Water at high pressure is then
pumped from the production station 15 into the fluid conduit 30 so
that the pumped water is jetted through the nozzles 38 to impact
the formation at the end of the liner 26 with great force. If
desired, the fluid conduit 30 is simultaneously rotated about its
longitudinal axis to induce the bit or mill 39 to crush the rock
formation. As a result the oil sand layer 2 is gradually excavated
so that the cavity 12 and the slurry 13 of water and oil sand
particles are initially formed. Furthermore, by virtue of pumping
of water through fluid conduit 30, the jet pump 28 is operated to
pump the slurry 13 from the cavity 12 via the flow channels 32 of
the jet pump 28 and via the annular space between the fluid conduit
30 and the liner 26/casing 24, to the production station 15. In an
alternative embodiment, the cavity 12 is initiated by underreaming
a lower portion of the first injection borehole 8 and/or a lower
portion of the discharge borehole 14 until fluid communication
between said boreholes 8, 14 is established, or by enlarging said
lower portion(s) in any other suitable manner.
[0042] Once the cavity 12 is sufficiently large so that fluid
communication between the cavity 12 and the injection borehole 8 is
established, in particular so that both boreholes 8,14 are
intersecting the cavity 12, the injection string 40 is lowered into
the first injection borehole 8, and water is pumped at high
pressure from the injection rig 10 into the injection string 40.
The pumped water is jetted through the jetting nozzles 42 and
impacts the wall of the cavity 12 with great force. As a result,
the oil sand layer 2 is further excavated and the slurry 13 of
water and oil sand particles is continuously formed in the cavity
12. The size of the cavity increases as jetting of water through
the nozzles 42 continues. Water is pumped at a somewhat suitable
lower pressure from production station 15 into the fluid conduit 30
to operate the jet pump 28. Thereby, the jet pump 28 pumps the
slurry of fluid and particles from the lower cavity portion 12a,
via the annular space between the fluid conduit 30 and the liner 26
or casing 24, and the flow channels 32 of the jet pump 28, to the
production station 15. Arrows 115 (FIGS. 1 and 2) indicate the
direction of flow of water pumped through fluid conduit 30, and
arrows 116 indicate the direction of flow of the slurry of water
and oil sand through said annular space and channels 32. If
desired, pumping of the slurry of fluid and particles from the
cavity 12 to the production station 15 can be enhanced by
pressurising the cavity 12 up to a few bars with a gas, such as
compressed air or CO.sub.2. Furthermore, a portion of the water
pumped through fluid conduit 30 is jetted into the lower cavity
portion 12b through nozzles 38 in order to achieve some stirring of
the slurry 13 in the cavity 12.
[0043] Jetting of water through nozzles 42 is continued so as to
extend the cavity 12 in the azimuthal direction of the lower
borehole section 18 whereby the front surface 23 of the cavity
moves in said azimuthal direction. As a result, a portion 116 of
the liner 26 (FIG. 2) gradually becomes protruding into the cavity
12. In order to reduce the length of, or completely remove, the
protruding liner portion 116, the cutter 36 is operated to cut the
protruding liner portion 116 at time intervals selected in
accordance with the speed of movement of the front surface 23 in
the azimuthal direction. The fluid conduit
[0044] is moved upwardly in correspondence with shortening of the
liner 26 whereby the jet pump 28 slides along the inner surface of
the liner 26. If desired, the fluid conduit 30 is rotated to induce
bit 39 to crush rock particles that may be present in the cavity
12.
[0045] The second injection borehole 44 is drilled into the oil
sand layer 2 before the front surface 23 of the cavity 12 reaches
the location where the second injection borehole 44 intersects the
cavity 12. Alternatively, the second injection borehole 44 can be
drilled after the front surface 23 of the cavity 12 reaches said
location. Next, the mobile injection rig 46 is installed, and the
injection string 40 is removed from the first injection borehole 8
and lowered into the second injection borehole 44. The cavity 12 is
then further excavated in the azimuthal direction of the lower
borehole section 18 in a manner similar to the manner described
above with reference to the situation whereby the injection
string
[0046] extends through the first injection borehole 8. When the
second injection borehole is drilled before the cavity 12 reaches
the location where the second injection borehole 44 intersects the
cavity, fluid jetting can already be started via the second
injection borehole when there is still a remaining wall with the
cavity, but fluid communication with the cavity is already
established. Powerful jetting action can lead to breaking through
to the front surface 23 of the cavity 12 from the second injection
borehole, removing the remaining wall.
[0047] Simultaneously with, or subsequent to, jetting of water into
the cavity 12 via the second injection borehole 44, sand is pumped
into the rear portion of cavity 12 via the sand injection string 48
(FIG. 3). In this manner, the rear portion of cavity 12 is
gradually filled with the body of sand 49. In the context of the
present description, any reference to "the cavity" is meant to
include the upper cavity portion 12a, the lower cavity portion 12b,
and the rear portion filled with sand.
[0048] In the above example, two injection boreholes 8, 44 have
been described for excavating the cavity 12 in the desired
azimuthal direction. In practice, any suitable number of injection
boreholes can be applied whereby the injection boreholes are
mutually spaced in the desired azimuthal direction and whereby each
pair of adjacent injection boreholes is operated in a manner
similar to operation of the injection boreholes 8, 44 described
above. However, in case more than two injection boreholes are
applied, one or more of the injection boreholes can be positioned
between the injection borehole instantaneously used for further
excavating the cavity, and the injection borehole(s)
instantaneously used for pumping sand into the cavity.
[0049] The slurry 13 of water and oil sand is transported from the
production station 15 to a separation plant (not shown) for
separating hydrocarbon fluid and sand particles from the slurry.
Alternatively the production station 15 and the separation plant
can be integrated in a single unit. Suitably, cleaned sand produced
from the separation plant is used to refill the cavity 12 with the
body of sand 49.
[0050] During normal operation of the system shown in FIG. 4, the
discharge borehole 82 and first injection borehole 87 of cavity 83
are drilled first whereafter production from cavity 83 is started.
Next, the discharge borehole 76 and first injection borehole 80 of
cavity 77 are drilled whereafter production from cavity 77 is
started. Similarly, the discharge boreholes 70, 65, 60 and first
injection boreholes 74, 68, 63 of respective cavities 71, 66, 61
are drilled in subsequent order, and production from these cavities
also is started in subsequent order. As a result, the degree to
which the various cavities instantaneously extend in the azimuthal
direction increases from, in subsequent order, cavity 61, to cavity
66, to cavity 71, to cavity 77, to cavity 83. Alternatively,
production from the various cavities can be started simultaneously
or in any other suitable order, so that the cavities
instantaneously extend in the azimuthal direction to any suitable
degree.
[0051] Each production unit 50, 52, 54, 56, 58 is operated
substantially similar to normal operation of the production unit
described with reference to FIGS. 1-3. Thus, the front surfaces 90,
92, 94, 96, 98 of the respective cavities 61, 66, 71, 77, 83
gradually move in the azimuthal direction of respective discharge
boreholes 60, 65, 70, 76, 82 as excavation of the cavities
proceeds. The rear portions of the cavities are refilled with sand
in correspondence with forward movement of the front surfaces. In
the current situation, shown in FIG. 4, mobile injection rig 110 is
used to inject sand via injection boreholes 68, 73, 74, 79 into the
rear portions of respective cavities 66, 71, 77. For this purpose,
mobile injection rig 110 is fluidly connected to injection
boreholes 68, 73, 79 via respective conduits 130, 132, 134.
Injection boreholes 80, 86 and 87 already have been used for sand
injection, therefore these injection boreholes have been
disconnected from mobile injection rig 110. As illustrated in FIG.
4, the injection boreholes 118 have been drilled before being in
fluid communication with the respective cavities. In this manner,
drilling of the injection boreholes does not delay excavation of
the oil sand layer. Some water is separated from the slurries of
fluid and oil sand particles at the respective production stations
64, 69, 75, 81, 88. The slurries are then comingled in common
pipeline 114 and transported to the separation plant 112 where
hydrocarbon fluid is separated from the comingled stream of water
and oil sand particles.
[0052] Instead of excavating the cavities 61, 66, 71, 77, 83 such
that these are separated from each other by portions of rock
material, as shown in FIG. 4, the cavities can be excavated so that
such portions of rock material vanish. In that case, two or more of
the cavities are integrated with each other so as to form a single
large cavity.
[0053] During normal operation of the system shown in FIG. 5, each
field section 142, 144, 146 is operated in substantially the same
manner as field section 140 described with reference to FIG. 4.
Thus, the slurries of water and oil sand particles produced from
the field sections 140, 142, 144, 146 are transported to common
separation plant 112 for separation of hydrocarbon fluid from sand
particles.
[0054] With the method described above it is achieved that
hydrocarbon fluid is produced from the oil sand layer without
removing the overburden layer. Moreover, by refilling the cavities
with sand it is achieved that any subsidence of the overburden
layer is reduced to a minimum. In a preferred embodiment, the
cavities are refilled with sand from the produced slurries of water
and oil sand after cleaning at the separation plant. Suitably a
binding material like cement is mixed into the sand.
[0055] In the examples described above, the discharge borehole is
provided with a single pump (jet pump 28) for pumping the slurry of
fluid and oil sand particles via the discharge borehole to the
production station at surface. However, depending on the depth of
the cavity and/or other operational parameters, a single pump may
not suffice to pump the slurry to surface at an efficient flow
rate. In that case, one or more additional pumps can be applied in
the discharge borehole. For example, the upper section of the
discharge borehole can be provided with a single-stage or
multi-stage centrifugal pump driven by a hydraulic or electric
motor, to pump the slurry to surface. Such centrifugal pump can be
positioned, for example, in the lower end part of the casing
provided in the discharge borehole, just above the liner.
[0056] In the examples described above, the injection boreholes
extend from surface locations mutually spaced in horizontal
direction. In an alternative arrangement, the injection boreholes
extend as deviated boreholes from a single surface location, or as
branch boreholes of a multilateral borehole. Such arrangement can
be attractive in applications whereby the surface area is difficult
accessible, for example if the oil sand layer is located below a
body of water or a swamp area.
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