U.S. patent application number 13/166475 was filed with the patent office on 2011-12-29 for producing hydrocarbon material from a layer of oil sand.
This patent application is currently assigned to SHELL OIL COMPANY. Invention is credited to Bruno BEST.
Application Number | 20110315379 13/166475 |
Document ID | / |
Family ID | 42558492 |
Filed Date | 2011-12-29 |
United States Patent
Application |
20110315379 |
Kind Code |
A1 |
BEST; Bruno |
December 29, 2011 |
PRODUCING HYDROCARBON MATERIAL FROM A LAYER OF OIL SAND
Abstract
A method of producing hydrocarbon material from a layer of oil
sand in an earth formation, the layer having a thickness and
extending in an extension direction for more than its thickness,
the method comprising: an injection borehole having an injection
borehole section extending in an injection borehole direction and a
discharge borehole having a discharge borehole section extending in
a discharge borehole direction below the injection borehole
section, wherein both the injection and the discharge borehole
directions deviate less than 45 degrees from the extension
direction; creating a cavity in the layer, the cavity being in
fluid communication with both the injection and the discharge
borehole sections; extending the cavity by operating fluid jetting
means via the injection borehole against a wall of the cavity to
obtain a slurry; and withdrawing the slurry from the cavity via the
discharge borehole to a processing facility.
Inventors: |
BEST; Bruno; (Rijswijk,
NL) |
Assignee: |
SHELL OIL COMPANY
Houston
TX
|
Family ID: |
42558492 |
Appl. No.: |
13/166475 |
Filed: |
June 22, 2011 |
Current U.S.
Class: |
166/275 |
Current CPC
Class: |
E21F 15/08 20130101;
E21B 43/29 20130101; E21B 43/305 20130101; E21C 41/24 20130101 |
Class at
Publication: |
166/275 |
International
Class: |
E21B 43/16 20060101
E21B043/16 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 24, 2010 |
EP |
10167158.4 |
Claims
1. A method of producing hydrocarbon material from a layer of oil
sand located in an earth formation, the layer of oil sand having a
thickness and extending in an extension direction for more than its
thickness, the method comprising: a) creating a borehole
arrangement in the earth formation, including an injection borehole
having an injection borehole section extending in an injection
borehole direction, and a discharge borehole having a discharge
borehole section extending in a discharge borehole direction below
the injection borehole section, wherein both the injection and the
discharge borehole directions are deviating less than 45 degrees
from the extension direction; b) creating a cavity in the layer of
oil sand, the cavity being in fluid communication with both the
injection and the discharge borehole sections; c) extending the
cavity by operating fluid jetting means via the injection borehole
to jet a stream of fluid against a wall of the cavity, to obtain a
slurry comprising fluid, hydrocarbon material, and sand; and d)
withdrawing the slurry from the cavity via the discharge borehole
to a processing facility for processing the slurry.
2. The method according to claim 1 wherein the pressure in the
cavity, while the fluid jetting means is operated, is lower than
the pressure in the pristine oil sand layer before creating the
cavity therein.
3. The method of claim 1 wherein fluid is also injected into the
cavity via the discharge borehole.
4. The method of claim 1 wherein no injection or discharge borehole
in fluid communication with the cavity is arranged, which borehole
is a vertical or near-vertical borehole.
5. The method of claim 1 wherein both the discharge borehole and
the injection borehole are provided with a tubular of a length
adapted to be changed, and wherein the lengths of both tubulars are
changed in correspondence with the extension of the cavity.
6. The method of claim 5 wherein changing the length of at least
one of the tubulars comprises operating a shortening device, in
particular wherein the tubular is made of a non-metal, such as a
plastics material.
7. The method of claim 1 wherein the discharge borehole is provided
with a pump for pumping the slurry via the discharge borehole to
the processing facility and wherein the pump is sealed relative to
an inner surface of the liner.
8. The method of claim 7 wherein the pump is axially movable
through the discharge borehole, and wherein the method further
comprises axially moving the pump through the discharge borehole in
correspondence with changing the length of the liner.
9. The method of claim 1 wherein the pump is driven by a stream of
fluid pumped through a conduit extending through the discharge
borehole, preferably, wherein at least a portion of said stream of
fluid is injected into the slurry of fluid and oil sand present in
the cavity.
10. The method of claim 1 wherein at least one of the injection
borehole section and the discharge borehole section extends
substantially horizontal.
11. The method of claim 1 wherein the method further comprises
inserting refill material into the cavity.
12. The method of claim 11 wherein the refill material is
transported from the processing facility to the cavity.
13. The method of claim 11 wherein the borehole arrangement in the
earth formation includes a refill borehole having a refill borehole
section extending in a refill borehole direction deviating less
than 45 degrees from the extension direction.
14. The method of claim 11 wherein the refill borehole section is
arranged below the discharge borehole section.
15. The method of claim 11 wherein inserting refill material into
the cavity comprises providing a refill borehole having a refill
borehole section extending in a refill borehole direction deviating
less than 45 degrees from the extension direction, the refill
borehole section being provided with a casing; after extending the
cavity for a selected length, perforating the casing within that
length, and pumping refill material from the refill well through
the perforations.
Description
[0001] This application claims the benefit of European Application
No. 10167158.4 filed Jun. 24, 2010 which is incorporated herein by
reference.
TECHNICAL FIELD OF THE INVENTION
[0002] The present invention relates to a method of producing
hydrocarbon material from a layer of oil sand located in an earth
formation.
BACKGROUND OF THE INVENTION
[0003] In the industry of hydrocarbon production from subterranean
reservoirs, it is conventional practice that oil or gas 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 CO2
injection into the formation. However, the conventional methods are
not adequate for the production of heavy hydrocarbon material
present in rock formations, when the material is not flowing up a
well. Examples are bituminous oil or tar or kerogen occurring in
sands, standstone, or shale based reservoirs in Canada or
elsewhere, e.g. tar sands or Limestone/Dolomite based and
calcareous shale based reservoirs such as found in the Canadian
Athabasca or Grosmont regions. Such a reservoir will herein be
referred to as oil sand. Hydrocarbons from oil sand layers can in
principle be recovered by mining. As some oil sands 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 sands 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.
[0004] 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", by
D. D. Tannant et al. This publication discloses a method of
producing hydrocarbon fluid from an oil sands layer located in an
earth formation, wherein a first horizontal borehole is drilled
into the oil sands layer and a fluid jetting device is operated
through the borehole to excavate the oil sands layer and thereby
form a cavity in the oil sands layer. A slurry of fluid and oil
sands is formed in the cavity as a result of the fluid jetting
operation. Slurry is withdrawn through the borehole, and a stable
cavern is formed containing caved oil sands, water, and possibly
injected air. The cavern is used as a primary fractionator, in
which bitumen rises to the top and sand sinks to the bottom. A
second horizontal borehole is provided above the first borehole, to
an upper part of the cavity, to withdraw water and oil. Once the
bitumen is removed, thickened tailings recovered from the portion
of the oil sands slurry that was sent to surface for processing are
placed back via the second borehole in the upper part of the
cavern.
[0005] Another method is disclosed in WO 2008/064305, in which
horizontal boreholes extending from a main access tunnel are used
to recover oil sands. FIG. 6 of this publication discloses two
horizontal boreholes, one above the other. The lower borehole is a
production well, through which a hydraulic mining bit is operated
to create a mined volume that enlarges upwardly, until it reaches
the level of an upper sand injection well, at which point mining is
stopped and sand is injected from the upper well. Initially the
sand injection well can also be used to create a small mined volume
at its toe, above and separate from the mined volume at the toe of
the production well. The upper mined volume can then be filled with
sand slurry and pressurized, to assist the hydraulic mining process
being applied from below. In a variant of the known method the
lower production and upper sand slurry injection well can also be
operated simultaneously, wherein the sand slurry injection well
sticks out into the cavity and sprays a stream of tailings slurry
into the cavity.
[0006] International patent publications No. WO 2010/000729 and WO
2010/000736 disclose methods of producing hydrocarbon fluid from a
layer of oil sand, wherein a plurality of vertical injection/refill
boreholes and a discharge borehole having a substantially
horizontal borehole section are operated.
[0007] However, there is still a need for an improved method of
producing hydrocarbon material from an oil sands layer.
SUMMARY OF THE INVENTION
[0008] In accordance with the invention there is provided a method
of producing hydrocarbon material from a layer of oil sands located
in an earth formation, the layer of oil sands having a thickness
and extending in an extension direction for more than its
thickness, the method comprising: [0009] creating a borehole
arrangement in the earth formation, including an injection borehole
having an injection borehole section extending in an injection
borehole direction, and a discharge borehole having a discharge
borehole section extending in a discharge borehole direction below
the injection borehole direction, wherein both the injection and
the discharge borehole directions are deviating less than 45
degrees from the extension direction; [0010] creating a cavity in
the layer of oil sands, the cavity being in fluid communication
with both the injection and the discharge borehole sections; [0011]
extending the cavity in the extension direction by operating fluid
jetting means via the injection borehole to jet a stream of fluid
against a wall of the cavity, to obtain a slurry comprising fluid,
hydrocarbon material, and sands; and [0012] transporting the slurry
from the cavity via the discharge borehole to a processing facility
for processing the slurry.
[0013] In this manner, hydrocarbon-containing slurry that is formed
in a lower part of the cavity by the erosive action of the fluid
jetting means and under the influence of gravity, can be
effectively removed via the discharge borehole arranged below the
fluid injection borehole, i.e. in a lower part of the cavity.
[0014] Preferably pressure in the cavity, while the fluid jetting
means is operated, is lower than the bubble point pressure in the
pristine oil sands layer before the cavity is created therein, in
particular 50% or less of the pristine pressure, more in particular
20% or less. Oil sands layers can have gas present, e.g. methane.
The gas can e.g. be adsorbed or dissolved. Lowering the pressure
below the pressure at which gas can be released from pores in the
sand matrix (which pressure is referred to as bubble point
pressure) can lead to damage to the sand matrix, and to the loss of
strength of the oil sands, at the walls of the cavity. Removal of
material by a hydraulic jet becomes much easier, and the
disintegrated oil sand will sink to the bottom of the cavity.
[0015] In one embodiment, fluid is also injected into the cavity
via the discharge borehole. A particular purpose of this is for
stirring or mobilizing the slurry and breaking of any larger lumps
of material in the area of the cavity from which the slurry is
withdrawn via the discharge borehole.
[0016] In one embodiment, no injection or discharge borehole in
fluid communication with the cavity is operated, which borehole is
a vertical or near-vertical borehole. Near-vertical means that the
average angle between the vertical and the borehole from surface to
cavity is less than 45 degrees. The present invention allows to
excavate a layer of oil sands using deviated boreholes, with
horizontal or near-horizontal borehole sections in the oil sands
layer for extended distances, and thus without the need for a
multitude of vertical or near-vertical wells.
[0017] Suitably the discharge borehole is provided with a liner of
a length adapted to be changed, and the injection borehole is
provided with injection tubular of a length adapted to be changed,
and wherein both the lengths of the liner and of the injection
tubular are changed in correspondence with the extension of the
cavity. The tubular can for example be a fluid injection tubular or
a liner.
[0018] The length of such a tubular can be changed by a shortening
device. For example, the step of shortening the liner can comprise
operating a cutting device to cut the liner. The liner can also be
shortened by the action of a fluid jet, or by any other means, e.g.
by milling, explosives, or a laser. Shortening can be done by
removing coarse discrete pieces of the liner, such as at suitable
time intervals, or by producing small chips of the liner material.
To this end the liner is suitably made from a suitable material for
shortening. 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,
such as a material comprising 50 wt % or more of a polymer.
[0019] In one embodiment the discharge borehole is provided with a
pump for pumping the slurry via the discharge borehole to the
processing facility, preferably the pump is sealed relative to an
inner surface of the liner. The pump can be axially movable through
the discharge borehole, and moved in correspondence with changing
the length of the liner. The pump can e.g. be driven by
electricity, but also by a stream of fluid pumped through a conduit
extending through the discharge borehole. In the latter case, at
least a portion of said stream of fluid is suitably injected into
the slurry of fluid and oil sands present in the cavity, e.g. for
stirring.
[0020] The method can further comprise inserting a stream of refill
material into the cavity. The stream of refill material can
comprise tailings that are separated in and transported from the
processing facility to the cavity.
[0021] In one embodiment a refill borehole having a refill borehole
section extending in a refill borehole direction deviating less
than 45 degrees from the extension direction is provided.
Preferably the refill borehole section is arranged below the
discharge borehole section, in particular near or at the lower end
of the cavity or just below, e.g. 0-10 m below. There it is nearly
unaffected by a (partial) collapse of the cavity. Refill material
can be pumped with excess pressure in to the cavity in a controlled
way from below.
[0022] In a preferred option inserting a stream of refill material
into the cavity comprises providing the refill borehole section
with a casing. The casing protects against collapse of the
borehole. After extending the cavity for a selected length, the
casing is perforated within that length, and refill material is
pumped through the perforations.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] The invention will be described hereinafter in more detail,
and by way of example, with reference to the accompanying drawings
in which:
[0024] FIG. 1 schematically shows an example of a production unit
for use in an embodiment of the method of the invention;
[0025] FIG. 2 schematically shows a detail of the production unit
of FIG. 1;
[0026] FIG. 3 schematically shows another example of a production
unit for use in an embodiment of the method of the invention;
and
[0027] FIG. 4 schematically shows a top view at surface of a
production field using embodiments of the present invention.
[0028] In the Figures, like reference numerals relate to like or
similar components.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0029] Referring to FIGS. 1 and 2 there is shown an earth formation
1 containing an oil sands layer 2 located between an overburden
layer 4 above the oil sands layer 2 and an underburden layer, shown
as a layer of rock material 6, such as limestone, below the oil
sands layer 2. Earth formation below the oil sands layer is
referred to as underburden. The oil sands layer 2 has respective
upper and lower boundaries 20, 22 extending generally horizontally
in this example. An overburden can for example be between 50 and
1000 m thick, in particular between 100 and 800 m. The layer of oil
sands extends in an extension direction 21, in particular a
non-vertical extension direction, in this example horizontally
between an overburden and an underburden. The layer of oil sands
has a thickness defining a thickness direction 21a, which is in
this example vertical. The extension direction 21 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 than its thickness, typically for more than
twice its thickness, such as for more that 5 or 10 times its
thickness, or even more. It will typically extend for less than
10000 times its thickness.
[0030] The thickness can for example be between 1 m and 500 m, in
particular between 5 m and 200 m, such as between 10 and 100 m, and
may vary along the extension direction. It will be understood that
the layer can extend along a flat or curved plane.
[0031] An injection borehole 8 is provided which in this example is
a deviated borehole extending from an injection station 10 at the
earth surface 11 to a cavity 12 formed in the layer of oil sands 2.
The cavity has an upper portion 12a containing gas (e.g. CO2,
methane, air, and/or H2S) and a lower portion 12b containing a
mixture (referred to hereinafter as "slurry") 13 of fluid
(preferably water) and oil sands particles comprising hydrocarbon
material and sand, which may partly or fully separate in the
slurry.
[0032] 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 injection
station 10 and debouches into the lower cavity portion 12b at some
distance above the bottom of the cavity.
[0033] The injection borehole 8 and the discharge borehole 14 each
have an upper section 16, 16a extending downwardly, such as
substantially vertically from surface, and a non-vertical lower
section 18, 18a. The expression lower borehole section is used for
a borehole section that is further away from surface along the
borehole trajectory than an upper borehole section. The lower
borehole section 18 of the discharge borehole extends in a
discharge borehole direction, below the injection borehole section
18a of the injection borehole 8, extending in an injection borehole
direction. Each of the injection and discharge borehole directions
is a selected direction within the layer 2, in this example an
azimuthal direction from the cavity 12. The intersection between
the lower borehole section 18a of the injection borehole 8 and the
cavity 12 defines a front surface 23 of the cavity 12.
[0034] Each of these selected directions suitably is a direction
within the layer. The lower sections of the injection and discharge
boreholes each deviate less than 45 degrees from the extension
direction 21, wherein the angle is preferably counted in a vertical
plane through the extension direction. These borehole sections
preferably extend substantially parallel to the upper boundary 20
and/or lower boundary 22 of the oil sands layer 2. 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. In the present example the lower
sections 18, 18a extend substantially horizontally. The expression
"direction" is used herein to refer to a direction without
specifying the sense of direction, unless otherwise indicated. The
extension direction may deviate somewhat from the horizontal plane
due to geological circumstances, as can the directions of the lower
sections 18, 18a in the practice of directional drilling. It is
desired to arrange the lower sections such that they extend for a
substantial length within the oil sands layer, such as for between
50 and 5000 m, in particular between 100 and 2000 m. The injection
and discharge borehole sections preferably deviate less than 30
degrees from the extension direction, more preferably less than 15
degrees. It can alternatively be said that the injection and
discharge borehole sections preferably are substantially horizontal
borehole sections. A substantially horizontal borehole section
deviates 30 degrees or less from the horizontal plane, more
preferably 15 degrees or less. The selected direction can be at
least 45 degrees away from the thickness direction, in particular
at least 45 degrees away from the vertical. All angles specified
herein are to be understood as absolute (positive) values, unless
otherwise specified. It will be understood that when the cavity is
extended along the injection and/or discharge borehole directions
that deviate by a certain angle from the extension direction, the
cavity is at the same time extended in the extension direction.
[0035] The expression "extending below" in relation to two borehole
sections is used to refer to the situation that one borehole
section extends at a greater vertical depth than the other.
Preferably the two borehole sections extend substantially along the
same trajectory in a vertical projection onto the earth's surface,
which can for example mean that the horizontal deviation in such
projection is 50 m or less, preferably 10 m or less, more
preferably 5 m or less, such as 2 m or less.
[0036] The vertical distance between the discharge borehole section
and the injection borehole section thereabove is suitably in the
range of 1-100 m, preferably between 2 and 50 m, such as between 5
and 30 m.
[0037] The upper borehole sections 16, 16a are each provided with a
conventional casing (or liner) 24, 24a, whereas the lower borehole
sections 18, 18a are each provided with a liner 26,26a, e.g. of
plastics material, for example glass fibre reinforced plastic. The
liner 26 extends a minimal distance into the cavity 12. Furthermore
in this example, 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, such as water, 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 shortening device, in
this embodiment cutter 36, for shortening the liner 26, one or more
nozzles 38 for initially forming the cavity 12 and/or 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. Conduit 30 can be rotatable.
[0038] Alternatively, the discharge borehole can also be set up for
operation in `reverse circulation`, where driving fluid for the jet
pump is pumped from surface via the annulus, and slurry is pumped
via an inner tubular like reference numeral 30. Liner 26 and
jet-pump 28 are suitably designed to withstand the pressure of
driving fluid, e.g. a plastic liner of sufficient strength can be
used. An advantage of this reverse circulation operation is that
there is no wear of the slurry in the annulus. Also the slurry
travelling inside a slowly rotating production pipe will not be
able to settle down. An injection string 40 for injecting fluid
into the cavity 12 extends from the injection station 10 via the
injection borehole 8 into the cavity 12, the injection string 40
having a lower end provided with fluid jetting means in the form of
fluid jetting head 41 comprising jetting nozzles 42, the fluid
jetting head being located in the upper portion 12a of cavity 12.
An annular seal 43 (e.g. such as used in 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. The injection
string 40 can also be provided with a shortening device (not shown)
for shortening the liner 26a extending into the cavity 12, which
can be similar to the shortening device 36 of the conduit 30.
[0039] Injection string 40 can be rotatable.
[0040] In this embodiment there is further provided a refill
borehole 108 which in this example is also a deviated borehole
extending from a refill station 110 at the earth's surface 11 to
the lower end of the cavity 12. The refill borehole 108 has an
upper section 116 extending downwardly, such as substantially
vertically, and a lower section 118. The lower borehole section 118
extends below lower non-vertical section 116 of the discharge
borehole 14, such as between 1 and 20 m below the lower section in
particular between 2 and 10 m, preferably substantially parallel
therewith. The lower borehole section preferably extends
substantially along the lower boundary 22, such as within 5 meters
from the boundary, preferably within 1 m from the boundary. The
refill borehole 108 on this embodiment is provided with casing 124,
preferably a steel casing, and with an injection string 148 for
refill material, which can be rotatable. The injection string is
optional; the injection borehole could alternatively be arranged
without such string, so that the injection slurry is passed through
the casing. The refill borehole section preferably deviates less
than 30 degrees from the extension direction, more preferably less
than 15 degrees. It can alternatively be said that the refill
borehole section preferably is a substantially horizontal borehole
section.
[0041] FIG. 1 shows the invention with several of the components at
a stage of normal operation after some time of operation. The
cavity 12 is being extended by operating the fluid jetting means
using nozzles 42 via the injection borehole to jet a stream of
fluid against a wall of the cavity, in particular the front surface
23, starting from an initial cavity 12' in an azimuthal direction,
along the parallel lower borehole sections 18 and 18a. The initial
cavity 12' that was created in the layer of oil sands 2 is
indicated with a dashed line. Suitably the jetting fluid is a low
solids fluid, i.e. it contains substantially no solids, such as
less than 10 wt % or less than 1 wt % of solids. Water is a
suitable jetting fluid. The water can contain one or more additives
such as a surfactant, but this is not required. Reference to water
herein is to a fluid that contains at least 80 wt %, preferably at
least 90 wt % of pure water. The temperature of the jetting fluid
(water) can be selected or modified such as by heating. For
example, water at a temperature of 25.degree. C. or above, or
40.degree. C. or above, can be used.
[0042] Thus the front surface 23 of the cavity has been moving in
the extension direction, with the sense of direction generally
uphole, defined by the injection borehole's sense of direction
towards surface. As a result, the lower borehole sections 18, 18a
have become shorter compared to an initial length indicated at 18'
and 18a'. The liners 26 and 26a have been shortened at the side of
the cavity 12 in correspondence with shortening of the lower
borehole sections 18,18a. 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, and likewise the injection string 40 has been retracted, so
that the nozzles stay in sufficient proximity to the front wall 23
so that the fluid jetting is effective to extend the cavity.
Suitably, the nozzles are at a distance of between 0.5 m and 15 m
from the wall against which the fluid jet is exerted.
[0043] During normal operation of the system of FIGS. 1-2, the
injection borehole 8 and the discharge borehole 14, and preferably
the refill borehole that will be discussed later, are drilled into
the oil sands layer 2 using one or more conventional drilling rigs,
and completed as needed, such as with the casings 24, 24a and
liners 26,26a. The injection station 10 and the production station
15 are installed at their respective positions as indicated in FIG.
1. In a next step, the initial cavity is created. 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. Alternatively, the discharge borehole is operated in
reverse circulation as discussed above. 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 sands 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 27 between the fluid conduit 30 and the liner
26/casing 24, to the production station 15.
[0044] Alternatively or in addition, the initial cavity 12' is
created by fluid jetting via the injection borehole, optionally
using equipment and operation similar to what was described above
for the discharge borehole.
[0045] In an alternative embodiment, the cavity 12' is initiated by
underreaming, via injection borehole 8 or discharge borehole 14, or
even from a separate borehole (not shown) such as from a vertical
borehole above the cavity.
[0046] 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 operated via
the first injection borehole 8. Fluid, preferably water, is pumped
at high pressure, such as between 10 and 500 bar, in particular
between 100 and 200 bar from the injection station 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 sands 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 suitable
pressure from production station 15 into the fluid conduit 30 to
operate the jet pump 28. Thereby, the jet pump 28 withdraws the
slurry of fluid and particles from the lower cavity portion 12b,
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 (FIG. 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. Note that in case of
reverse circulation, below the pump arrows 115 and 116 have the
same direction as circulating conventional. Above the pump the
direction of the arrows reverses. Injection of fluid via the
injection well and withdrawal of slurry via the discharge well
occurs simultaneously.
[0047] If desired, pumping of the slurry of fluid and particles
from the cavity 12 to the production station 15 can be enhanced by
maintaining a suitable elevated pressure in the cavity 12. The
pressure can be adjusted by influx and/or outflux of gas, taking
into account gas that is released from the matrix below the bubble
point. Preferably however the pressure in cavity 12 is kept lower
than the pressure in the pristine oil sands layer 2 before the
cavity 12, 12' is created therein, such as at or below 90%, or at
or below 80%, of the hydrostatic pressure in the pristine oil sand
layer. The pressure can be 5 bar below the bubble point pressure,
or lower. At lower pressure, the gas contained in the oil sands
layer can be released, and the sands matrix loses strength and is
jetted away into a slurry relatively easily.
[0048] Furthermore, a portion of the water pumped through fluid
conduit 30 is injected/jetted into the lower cavity portion 12b
through nozzles 38 in order to achieve some stirring of the slurry
13 in the cavity 12, simultaneously with fluid jetting via the
injection borehole.
[0049] 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 117 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 117, the cutter 36 is operated to cut the
protruding liner portion 117 at time intervals selected in
accordance with the speed of movement of the front surface 23 in
the azimuthal direction. The fluid conduit 30 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. Likewise, the
portion of the liner 26a of the injection borehole section 18a
protruding into the cavity is can be shortened using a cutter (not
shown). Alternatively, the liner 26 and/or 26a can be shortened in
another way, such as by using a fluid jet.
[0050] The amount of fluid flowing through the injection nozzles 42
can typically be in the range of 50-5000 l/min, in particular
between 100 and 1000 l/min, such as between 200 and 800 l/min. The
amount of fluid flowing through the nozzles 38 can be in the same
range as the amount of water injection through the injection
borehole. An aqueous slurry that is formed and produced during
operation can have a density of between 1100 and 1600 kg/m3. The
pristine oil sand may for example contain between 1 and 50 wt % of
hydrocarbons, based on total oil sand including hydrocarbons, in
particular between 2 and 30 wt %, such as between 5 and 20 wt %.
The width of the cavity in the horizontal plane perpendicular to
the direction of the injection borehole 8 depends on the precise
orientation and operation of the nozzles, and is typically in the
range of 1-50 m, such as between 10 and 40 m. The jetting nozzles
can be arranged to jet in a fixed direction against a front, side,
rear, upper, and/or lower wall of the cavity, or can be movable
such as rotatable. The growth of the cavity in the extension
direction can for example be in the range of between 10 cm/day to
10 m/day, so for example the liners need to be shortened by
approximately 1 m/day.
[0051] In this way, the hydrocarbon material from the oil sand
layer can be produced in a continuous process, by simultaneous
operation of the injection and discharge borehole sections, and
over an extended length, such as for 20 m or more, 50 m or more,
100 m or more, even 500 m or more, and for extended periods of
time, such as for a day or more, a week or more, a month or more,
even a year or more.
[0052] It will be understood that for very thick layers of oil
sands, more than one injection borehole can be arranged at various
heights. Each additional injection borehole can be substantially
similar to injection borehole 8 as described above, with a
non-vertical lower section extending substantially above the
non-vertical lower section 18a, the injection borehole 8 thus
extending below additional injection boreholes. This may be useful
when the vertical thickness of the oil sands layer 2 is 30 m or
more, or 50 m or more.
[0053] If the operation is conducted as described hereinbefore, the
earth's surface may subside above the cavity as a result. On the
other hand, tailings are produced to surface, which are separated
from hydrocarbon material and water, and it is typically desired to
reinject tailings for disposal, and to avoid or reduce
subsidence.
[0054] To this end the refill borehole is provided. In a preferred
operation, the slurry 13 of water and oil sand is transported from
the production station 15 to a separation plant (not shown) for
separating hydrocarbon material and tailings from the slurry. The
hydrocarbon material is recovered as product and optionally subject
to further transport, purification, separation, treatment and/or
processing to further products. Alternatively the production
station 15 and the separation plant can be integrated in a single
unit. The production station and optionally the separation plant
form part of a production facility. Suitably, at least part of the
tailings is used to refill the cavity 12. The tailings can comprise
solids like sand and/or clay. It can be desired to re-use part or
all of the sand produced to surface for other purposes than
reinjection, and to reinject only or predominantly other tailings
like for example clay. For refilling, tailings are pumped into the
rear portion of cavity 12 (such as beginning at the initial cavity
12') via the injection string 148. Suitably, first a cement plug
150 is provided, and then perforations 154 are created in the
casing at the desired locations, through which tailings are pumped
into the cavity. In this manner, the rear portion of cavity 12 is
gradually filled with the body of tailings 149. 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,
the initial cavity 12', and the rear portion filled with refill
material such as tailings or tailings.
[0055] Refilling from below is advantageous for a controlled refill
operation. It will be preferred to maintain a certain distance
between the front surface 23, where the fluid jet impacts and
slurry is discharged, and the area of refill. E.g., the distance
along the extension direction can be 20 m or more, preferably 50 m
or more, such as 100 m or more. Refilling from above would require
a casing/lining to extend without proper support in the cavity for
such a distance, whereas it is likely for the cavity to at least
partially collapse. Reference is made in this regard to FIG. 8 of
WO 2008/064305, showing such an undesirable operation.
[0056] Reference is now made to FIG. 3, showing schematically an
alternative example of operating the present invention. In this
example, the operation is started as described above with reference
to FIGS. 1 and 2. The extension of a cavity in the extension
direction 21 is stopped at a certain moment, such as when a certain
horizontal length of the cavity is reached, or when the
constitution of the oil sands layer changes. The tubulars 30,40 are
retracted a certain distance in the injection and discharge
boreholes, such as by 1 to 100 m, preferably 5-50 m, e.g. 20 m,
before a further cavity is created. The liners 26,26a can e.g. be
retracted as well or can be cut off and abandoned. Cement plugs are
suitably set in between cavities along the pathway of the injection
and discharge boreholes. In this way pillars 170 are created
between cavities to prevent or minimize subsidence, and/or to avoid
producing areas that do not contain sufficient hydrocarbons or are
otherwise not interesting to produce. FIG. 3 shows a first cavity
12a that is fully produced and refilled with tailings 149; a second
cavity 12b created and produced after the first cavity 12a, and
being refilled with tailings 149; and a third cavity 12c in
production, substantially as described with reference to FIGS. 1
and 2.
[0057] In the context of the present description, an assembly
comprising a cooperating injection borehole and discharge borehole,
injection, production, refill station and one or more cavities
created along these boreholes is referred to as a production unit.
A production field comprises one or more production units. An
injection, production and/or refill station can include a drilling
rig.
[0058] Referring to FIG. 4, there is schematically shown a top view
at surface of a layout of a production field 201 for recovering
hydrocarbons from an underground oil sands layer. The Figure shows
a plurality of production units 210, 212, 214, 216, 218, 220, 222,
224, 226, 228, 230, 232, 234, 236, 238, 240, 242, 244, 246, 248 in
four field sections 251,252,253,254 on either side of a backbone
260. Each production unit can be substantially similar to and
operated as described hereinbefore with reference to FIGS. 1-3, and
has an injection borehole above a discharge borehole above a refill
borehole, overlapping in the top view.
[0059] The production units are in different stages of operation.
The solid lines, e.g. 270, indicate a section of a production unit
that is producing hydrocarbons (slurry) to a separation plant 275,
whereas the dashed lines, e.g. 280, indicate an area that has
already been produced and is abandoned, or refilled. Units 218,
228, 230 and 240 were the first units to produce and have already
stopped production. Units 210,220,238 and 246 just started
production. Remaining units are in an intermediate stage. At 282,
boreholes for a future production unit are being drilled. The area
285 that is generally defined by the dashed lines can be referred
to as reclaimed area of the production field, and the area 288
generally defined by solid lines can be referred to as producing
area of the production field 201. It shall be clear that only one,
two or three of the field sections 251-254 may be arranged, or may
be developed at different periods in time, and that more or less
production units than shown can be provided in a field section.
[0060] The backbone provides for transport of fluids (slurry,
tailings) between the production units and the separation plant 275
via suitable pipelines/conduits. It concentrates the surface
equipment in a relatively narrow surface area or streak, for easy
accessibility and minimum surface impact. This area is moreover
typically not or only modestly affected by subsidence.
[0061] The backbone can be between 0.1 and 50 km long, preferably
between 0.5 and 20 km, and may grow in the lifetime of a field,
which is suitably developed starting with production units close to
the separation plant 275. The lateral spacing between production
units can be between 10 m and 500 m, preferably between 20 m and
100 m. They can in particular be arranged such that the cavities
along adjacent production units join or overlap, or remain
separate. Each production unit may have a length of between 50 and
5000 m, in particular between 100 and 2000 m. Areas where it is not
desired or possible to produce oil sand can be avoided in the
layout.
[0062] With the method described above it is achieved that
hydrocarbon fluid is produced from the oil sands layer without
removing the overburden layer. Moreover, by refilling the cavities
with tailings it is achieved that any subsidence of the overburden
layer is reduced to a minimum. In a preferred embodiment, the
cavities are refilled with tailings from the produced slurries of
water and oil tailings after cleaning at the separation plant.
Suitably a binding material like cement is mixed into the
tailings.
[0063] 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 additional pump can be
positioned, for example, in the lower end part of the casing
provided in the discharge borehole, just above the liner.
Alternatively or in addition, an additional jet pump or gas lift
can be applied.
[0064] In the examples described above, various boreholes extend
from surface locations mutually spaced in horizontal direction. In
an alternative arrangement, the boreholes can extend as deviated
boreholes from a fewer or 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 sands layer is located below a
body of water or a swamp area.
* * * * *