U.S. patent application number 14/797779 was filed with the patent office on 2015-11-05 for apparatus and method for downhole steam generation and enhanced oil recovery.
The applicant listed for this patent is R.I.I. North America Inc.. Invention is credited to Fred SCHNEIDER, Lynn P. TESSIER.
Application Number | 20150315889 14/797779 |
Document ID | / |
Family ID | 54354904 |
Filed Date | 2015-11-05 |
United States Patent
Application |
20150315889 |
Kind Code |
A1 |
SCHNEIDER; Fred ; et
al. |
November 5, 2015 |
APPARATUS AND METHOD FOR DOWNHOLE STEAM GENERATION AND ENHANCED OIL
RECOVERY
Abstract
A burner is arranged for access to a cavity in a target zone of
a hydrocarbon reservoir. The burner is operated into the cavity to
create and sustain hot combustion gases at a steady state for
flowing into and permeating through the target zone. Water is
injected into the target zone and permeates laterally therein. The
hot combustion gases and the water in the target zone interact to
form a steam drive front in the hydrocarbon reservoir.
Inventors: |
SCHNEIDER; Fred; (Calgary,
CA) ; TESSIER; Lynn P.; (Eckville, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
R.I.I. North America Inc. |
Calgary |
|
CA |
|
|
Family ID: |
54354904 |
Appl. No.: |
14/797779 |
Filed: |
July 13, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13629114 |
Sep 27, 2012 |
9115579 |
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14797779 |
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12687711 |
Jan 14, 2010 |
8333239 |
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13629114 |
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61145501 |
Jan 16, 2009 |
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Current U.S.
Class: |
166/250.01 ;
166/302; 166/381; 166/59 |
Current CPC
Class: |
E21B 36/02 20130101;
E21B 17/18 20130101; E21B 43/168 20130101; E21B 43/243 20130101;
E21B 47/06 20130101 |
International
Class: |
E21B 43/243 20060101
E21B043/243; E21B 43/16 20060101 E21B043/16; E21B 47/06 20060101
E21B047/06; E21B 17/18 20060101 E21B017/18 |
Claims
1. A system for enhanced oil recovery from a hydrocarbon reservoir
accessed by a cased and completed wellbore having a wellhead, the
system comprising: a downhole burner for creating hot combustion
gases within a target zone in the hydrocarbon reservoir; and at
least two tubing strings positioned within the wellbore for forming
three discrete fluid passageways for conducting at least fuel and
oxidant to the downhole burner, wherein one of the three discrete
fluid passageways is a sealed fluid passageway for isolating the
other two of the three discrete fluid passageways from one
another.
2. The system of claim 1, wherein the sealed fluid passageway is
pressurized to a pressure higher than a pressure in both the fuel
passageway and the oxidant passageway.
3. The system of claim 1, wherein the sealed fluid passageway is
pressurized with an inert gas.
4. The system of claim 3, wherein the inert gas is nitrogen
gas.
5. The system of claim 1, wherein the at least two tubing strings
are concentric tubing strings.
6. The system of claim 5, wherein the three discrete fluid
passageways further comprise an outer fluid passageway, the sealed
fluid passageway and an inner fluid passageway, and wherein the at
least fuel is conducted through the outer passageway, the oxidant
is conducted through the inner fluid passageway and the sealed
fluid passageway is pressurized with nitrogen gas.
7. The system of claim 5, wherein the three discrete fluid
passageways further comprises an outer fluid passageway, the sealed
fluid passageway and an inner fluid passageway, and wherein the
oxidant is conducted through the outer passageway, the at least
fuel is conducted through the inner fluid passageway and the sealed
fluid passageway is pressurized with nitrogen gas.
8. The system of claim 1, further comprising a sensor for
monitoring for changes in pressure in the sealed fluid
passageway.
9. A process of creating a drive front in a hydrocarbon reservoir
for enhanced oil recovery comprising the steps of: positioning a
burner assembly within a target zone in the hydrocarbon reservoir;
providing a fuel passageway for delivering fuel to the burner
assembly; providing an oxidant passageway for delivering oxidant to
the burner assembly; and isolating the fuel passageway from the
oxidant passageway.
10. The process of claim 9, wherein isolating the fuel passageway
from the oxidant passageway further comprises providing a sealed
fluid passageway.
11. The process of claim 10, further comprising pressurizing the
sealed fluid passageway to a pressure higher than the pressure in
both the fuel passageway and the oxidant passageway.
12. The process of claim 11, wherein pressurizing the sealed fluid
passageway further comprises pressurizing the sealed fluid
passageway with an inert gas.
13. The process of claim 12, wherein the inert gas further
comprises nitrogen gas.
14. The process of claim 10, further comprising monitoring the
sealed fluid passageway for changes in pressure.
15. A process of creating a drive front in a hydrocarbon reservoir
for enhanced oil recovery comprising the steps of: conducting at
least fuel and oxidant to a downhole burner assembly positioned
within the hydrocarbon reservoir; isolating the at least fuel from
the oxidant with an inert gas; and combusting the at least fuel and
oxidant to create the drive front.
16. The process of claim 15 wherein isolating the at least fuel
from the oxidant with an inert gas further comprises pressurizing
the inert gas to a pressure greater than a pressure of the at least
fuel and the oxidant.
17. The process of claim 15, wherein the inert gas is nitrogen
gas.
18. The process of claim 15, wherein conducting at least fuel and
oxidant further comprising monitoring for changes in pressure.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This is a continuation-in-part application that claims the
benefits under 35 U.S.C. 120 of the US Published Patent Application
Ser. No. US 2013/0020076, filed on Jan. 14, 2010, which is a
continuation-in-part application and claims the benefit of US
Published Patent Application Ser. No. US 2010/0181069, filed on
Jan. 14, 2010, which is a non-provisional and further claims the
benefits under 35 U.S.C. 119(e) of US provisional Patent
Application Ser. No. 61/145,501, file on Jan. 16, 2009, the
entireties of which are incorporated fully herein by reference.
FIELD OF THE INVENTION
[0002] The present invention relates a method for creating a drive
front in a target zone in a hydrocarbon reservoir for enhanced oil
recovery. More specifically, a downhole burner is arranged to
access a cavity in the target zone for creating hot gases which
enter into the target zone. Water injected into the target zone
forms a steam drive front hydrocarbon reservoir.
BACKGROUND OF THE INVENTION
[0003] It is known to conduct enhanced oil recovery (EOR) of
hydrocarbons from subterranean hydrocarbon formations after primary
recovery processes are no longer feasible. EOR include thermal
methods such as in-situ combustion, steam flood, and miscible
flooding which use various arrangements of stimulation or injection
wells and production wells. In some techniques the stimulation and
production wells may serve both duties. Other techniques include
steam flooding, cyclic steam stimulation (CSS), in-situ combustion
and steam assisted gravity drainage (SAGD). SAGD uses closely
coupled, a horizontally-extending steam injection well forming a
steam chamber for mobilizing heavy oil for recovery at a
substantially parallel and horizontally-extending production
well.
[0004] Thermal methods of EOR can only be implemented in wells that
have been completed for thermal completions. Due to the high
temperatures used in thermal completions, wells employing such EOR
techniques must be completed using materials, such as steel and
cement that can withstand high temperatures. Wells that were not
completed with such high temperature resistant materials cannot
implement thermal completions for EOR. Accordingly, well operators
must decide on whether or not to implement of thermal EOR and based
on this decision complete a well using (or not) high temperature
resistant materials.
[0005] U.S. Pat. No. 3,196,945 to Forrest et al (assigned to Pan
American Petroleum Company) discloses a downhole process comprising
a first igniting a reservoir and then injecting air or an
equivalent oxygen containing gas in an amount sufficient to create
a definite combustion zone or front, the front being at high
temperature, typically 800-2400.degree. F. Called forward
combustion, Forrest contemplates an oxygen rich front for continued
combustion. Demands for large air flow are reduced by co-injection
of water or other suitable condensable fluid into the heated
formation to create steam front that urges the movement of
hydrocarbons or oil. Forrest can co-discharge water and air to the
heated formation for creating high temperature steam.
[0006] U.S. Pat. No. 4,442,898 to Wyatt (assigned to Trans-Texas
Energy Inc.) discloses a downhole vapor generator or burner. High
pressure water in an annular sleeve around the burner combustion
chamber within which an oxidant and fuel are combusted. The energy
from the combustion vaporizes the water surrounding the combustion
chamber, cooling the burner and also creating high temperature
steam for injection into the formation.
[0007] U.S. Pat. No. 4,377,205 to Retallick discloses a catalytic
low pressure combustor for generating steam downhole. The steam
produced from the metal catalytic supports is conducted to steam
generating tubes, and the steam is injected into the formation. Any
combustion gases produced are vented to the surface.
[0008] U.S. Pat. No. 4,336,839 to Wagner et al (assigned to
Rockwell International corp.) discloses a direct firing downhole
steam generator comprising an injector assembly axially connected
with a combustion chamber. The combustion products, including
CO.sub.2, are passed through a heat exchanger where they mix with
pre-heated water and are ejected out of the generator into the
formation through a nozzle.
[0009] U.S. Pat. No. 4,648,835 to Eisenhawer et al. (assigned to
Enhanced Energy Systems) discloses a direct fire steam generator
comprising a downhole burner employing a unique ignition technique
using the gaseous injection of a pyrophoric compound such as
triethylborane. Natural gas is burned and water is introduced to
control combustion. The combustion products, like in Wagner are
mixed with water and the resulting steam and other remaining
combustion products are injected into the formation.
[0010] US Patent Application Publication 2007/0193748 to Ware et al
(assigned to World Energy Systems, Inc.) discloses a downhole
burner for producing hydrocarbons from a heavy-oil formation.
Hydrogen, oxygen and steam are pumped by separate conduits to the
burner. A portion of the hydrogen is combusted and the burner
forces the combustion products out into the formation. Incomplete
combustion is useful in suppressing the formation of coke. The
injected steam cools the burner, thereby creating a super heated
steam which is also injected into the formation along with the
combustion products. CO.sub.2 from the surface is also pumped
downhole for heating and injection into the formation to solubilise
in oil for reducing its viscosity.
[0011] In-situ processes to date have not successfully provided
economic solutions and have not resolved issues of temperature
management, corrosion, coking and overhead associated with existing
surface equipment.
SUMMARY OF THE INVENTION
[0012] The present invention is an apparatus and method of creating
a drive front in a hydrocarbon reservoir. The apparatus is
positioned in a cased wellbore within a target zone in the
hydrocarbon reservoir. The apparatus comprises a downhole burner
fluidly connected to a tubing string extending downhole. The tubing
string comprises a plurality of passages for at least fuel, and
oxidant and water. The downhole burner creates a combustion cavity
within the target reservoir zone by combusting the fuel and the
oxidant, such as oxygen, at a temperature sufficient to melt the
reservoir at the target zone or otherwise form a cavity below the
downhole burner. Once the combustion cavity is created, the
downhole burner operates at steady state for creating and
sustaining hot combustion gases in the combustion cavity, which
flow or permeate into the hydrocarbon reservoir. The hot combustion
gases permeate away from the combustion cavity forming a gaseous
drive front, transferring some of its heat to the rest of the
reservoir.
[0013] Water is also injected into the target zone above the
combustion cavity, which flow or permeate laterally into the
reservoir adjacent the wellbore. In the reservoir, the water acts
to cool the reservoir adjacent the wellbore, decreasing the amount
of heat lost to the overburden. At an interface, the water and hot
combustion gases combine to create a steam and gaseous drive
front.
[0014] Further, the injection of water adjacent the wellbore also
cools the cased wellbore, protecting the casing against the heat
from the steam and hot combustion gases. Accordingly, the present
invention is not limited to use only in thermally completed wells
and can be implemented at any cased wellbore, whether or not the
wellbore was completed for thermal EOR.
[0015] In a broad aspect, a system for enhanced oil recovery from a
hydrocarbon reservoir accessed by a cased and completed wellbore
having a wellhead, comprises a downhole burner for creating hot
combustion gases within a target zone in the hydrocarbon reservoir,
and at least two tubing strings positioned within the wellbore for
forming three discrete fluid passageways for conducting at least
fuel and oxidant to the downhole burner, wherein one of the three
discrete fluid passageways is a sealed fluid passageway for
isolating the other two of the three discrete fluid passageways
from one another.
[0016] In another broad aspect of the invention, a process of
creating a drive front in a hydrocarbon reservoir for enhanced oil
recovery comprising the steps of positioning a burner assembly
within a target zone in the hydrocarbon reservoir, providing a fuel
passageway for delivering fuel to the burner assembly, providing an
oxidant passageway for delivering oxidant to the burner assembly,
and isolating the fuel passageway from the oxidant passageway.
[0017] In another broad aspect of the invention, a process of
creating a drive front in a hydrocarbon reservoir for enhanced oil
recovery comprising the steps of conducting at least fuel and
oxidant to a downhole burner assembly positioned within the
hydrocarbon reservoir, isolating the at least fuel from the oxidant
with an inert gas, and combusting the at least fuel and oxidant to
create the drive front.
BRIEF DESCRIPTION OF THE FIGURES
[0018] FIG. 1 is a side cross-sectional view of an embodiment of
the present invention, illustrating a combustion cavity in a
hydrocarbon reservoir, the cavity being created by downhole burner
and formed for disseminating hot combustion gases for forming a
gaseous drive front and interacting with water injected uphole of
the cavity for forming an additional steam drive front;
[0019] FIG. 2A is a side quarter-sectional view of a wellhead for
supporting three tubing strings extending down a cased wellbore
according to one embodiment of the present invention;
[0020] FIG. 2B is a side quarter-sectional elevation of the three
tubing strings of FIG. 2A (casing omitted) and illustrating a main
tubing string supporting the downhole burner at a burner interface
assembly, the main tubing string having an intermediate and an
inner tubing string disposed therein;
[0021] FIG. 3 illustrates a quarter-sectional, perspective view
across the casing and three concentric tubing strings;
[0022] FIG. 4 is a side quarter-sectional view of an embodiment of
a downhole burner sealed at a downhole end to a casing for fluidly
connecting a casing annulus and the reservoir through
perforations;
[0023] FIG. 5 is a side, quarter-sectional view of the burner of
FIG. 3 with the casing omitted, and illustrating the fuel
passageway, the oxygen passageway and the nozzle;
[0024] FIG. 6 is a side, quarter-sectional view of the burner of
FIG. 3 with the casing and oxygen passageway omitted for
illustrating the casing seal and an embodiment of fuel passageway
swirl vanes;
[0025] FIG. 7A is a partial cross-sectional view of the nozzle and
an embodiment of a brush-type casing seal of FIG. 3 with the casing
omitted;
[0026] FIG. 7B illustrates an activated brush seal according to
FIG. 7A and showing the stack of flexible brush rings flexing when
constrained by the casing;
[0027] FIG. 8 is an overhead plan view of one concentric brush ring
of a stack of concentric brush rings of a brush seal and an
arrangement of spiral slits and fingers;
[0028] FIG. 9 is a perspective view of two brush rings of the stack
of concentric brush rings according to FIG. 8 illustrating a
rotational offsetting of the spiral slits for forming a tortuous,
restrictive fluid path therethrough;
[0029] FIG. 10 is a schematic representation a main tubing string,
an intermediate tubing latched within the bore of the main tubing
string, and an inner tubing latched and terminated within the bore
of the intermediate tubing, three fluid passageways created
therein, the inner annulus being terminated at the intermediate
mandrel;
[0030] FIG. 11 is a cross-sectional view of the burner interface
assembly illustrating the outer housing, the intermediate and inner
mandrels, the intermediate and inner latch assemblies, and the
backpressure valve assembly;
[0031] FIG. 12 is a side quarter-sectional view of an uphole end of
the intermediate mandrel for illustrating termination of the inner
and intermediate tubing and the inner mandrel having an inner
tubing latch;
[0032] FIG. 13 is a quarter-sectional and elevation view of a step
of the running in of an embodiment of the apparatus of the
invention, more particularly illustrating the main tubing hanger,
and downhole adjacent the reservoir, a torque anchor, outer
housing, pup joint, burner housing, burner nozzle and casing
seal;
[0033] FIG. 14A is a quarter-sectional and elevation view of a
further step according to FIG. 13, more particularly illustrating
the insertion of the intermediate tubing string, hanging the tubing
from an intermediate tubing hanger, latching of the intermediate
mandrel and positioning of the oxygen passageway within the burner
housing;
[0034] FIG. 14B is a close-up of the burner interface assembly of
FIG. 14A for illustrating the intermediate tubing, the intermediate
mandrel and the oxygen passageway;
[0035] FIG. 15A is a quarter-sectional and elevation view of a
further step according to FIG. 13, more particularly illustrating
the insertion of the inner tubing string, hanging the inner tubing
from an inner tubing hanger, latching of the inner mandrel;
[0036] FIG. 15B is a close-up of the burner interface assembly of
FIG. 15A for illustrating the hanging the inner tubing from the
inner tubing hanger, the inner tubing and the inner mandrel;
[0037] FIG. 16A is a schematic representation of an embodiment of a
burner assembly accessing a cavity created artificially by
reaming;
[0038] FIG. 16B is a schematic representation of an embodiment of a
burner assembly accessing a cavity created artificially by
hydraulic washing;
[0039] FIG. 16C is schematic representation representative drawing
of an embodiment of a burner assembly accessing a pre-existing
cavity; and
[0040] FIG. 17 is a schematic representation of a burner assembly
fit with a shroud disposed at a downhole end thereof and receiving
injected water thereabout.
DETAILED DESCRIPTION OF THE INVENTION
[0041] As shown in FIG. 1, a thermal process utilizes a downhole
production of heat, steam and hot combustion gases (primarily CO,
CO.sub.2, and H.sub.2O) to best effect for the recovery of residual
or otherwise intractable hydrocarbons from a hydrocarbon reservoir
10. A burner assembly 20 initially creates a combustion cavity 30
and then creates and sustains the creation of hot combustion gases,
such as CO, CO.sub.2, and H.sub.2O. Addition of water to the
reservoir 10 above the combustion cavity 30 results in the
production of a steam drive front. The steam and hot combustion
gases combine to create a steam and gaseous drive front.
[0042] With further reference to FIGS. 1, 2B, 3, 4 and 13,
apparatus for implementing such a process comprises a burner
assembly 20 at a downhole end of a main tubing string 40 and one or
more additional tubing strings. The main tubing string 40 and other
tubing strings form a plurality of discrete fluid passageways for
supplying the burner assembly 20. As shown in FIG. 4, the downhole
burner 60 is terminated in existing cased wellbore adjacent casing
perforations accessing the reservoir 10. The burner assembly 20 can
comprise a burner interface assembly 50 for fluidly connecting to
the tubing strings, a downhole burner 60, and a casing seal 70 for
sealing a casing annulus 80 between the downhole burner 60 and a
casing 90 of the cased wellbore. The casing annulus 80 is yet
another passageway used for directing water from the casing annulus
80 to the reservoir 10.
[0043] As shown in FIGS. 2A to 4, one approach is to suspend the
burner assembly 20 from a conventional sectional tubing string
supported by a conventional tubing hanger 100 on a wellhead 110.
The casing annulus 80 is formed between the casing 90 of the
wellbore and the main tubing string 40 and extends to the annular
space between the casing 90 of the wellbore and the burner assembly
20.
[0044] An intermediate tubing string 120 having an intermediate
bore, such as an intermediate coil tubing string, is supported by
an intermediate tubing hanger 130 on the wellhead 110 and disposed
within a bore of the main tubing string 40. An intermediate annulus
140 is formed between the main tubing string 40 and the
intermediate tubing string 120.
[0045] An inner tubing string 150, such as an inner coil tubing
string, is supported by an inner tubing hanger 160 on the wellhead
110 and is further disposed within the intermediate bore of the
intermediate tubing string 120, forming an inner annulus 170
therebetween. The inner tubing string 150 further has an inner bore
180.
[0046] The wellhead 110 and tubing hangers 100, 130, 160 can be any
appropriate wellhead and tubing hangers that are commonly available
in the industry, such as the thermal wellhead and tubing hangers
commercially available from StreamFlo Industries, Ltd., located at
Edmonton, Alberta, Canada. The casing annulus 80, the intermediate
annulus 140, inner annulus 170, and the inner bore 180 all define
discrete passageways for supplying the burner assembly 20.
[0047] The casing 90 of the cased wellbore, main tubing string 40,
the intermediate tubing string 120 and the inner tubing string 150,
creating the four discrete passageways, terminate at the burner
interface assembly 50. The casing annulus 80 terminates at the
downhole burner 60 for communication with the reservoir 10. The
inner annulus 170 terminates at the burner interface assembly 50.
The two remaining discrete passageways, the intermediate annulus
140, and inner bore 180, all connect or terminate at the downhole
burner 60.
[0048] In one embodiment, the downhole burner 60 implements at
least two fluid passageways for conducting fuel and oxidant for
combustion. The oxidant is a source of oxygen, conventionally air,
or more concentrated source such as a purified stream of oxygen. In
a preferred embodiment, purified oxygen is used as the oxidant
instead of conventional air, as conventional air produces
combustion gases having a substantial amount of gaseous nitrogen
products.
[0049] The burner interface assembly 50 fluidly connects two of the
discrete passageways to two fluid passageways of the downhole
burner 60. In one arrangement, a third discrete passageway can be
utilized as an isolating passageway between the fuel and the oxygen
for sensing or detecting leaks in the discrete passageways for the
fuel and oxygen.
[0050] The downhole burner 60 comprises a burner housing 190 having
a downhole portion 200 for the mixing of fuel and oxygen. The
burner housing 190 supports a high temperature casing seal 70 for
sealing the casing annulus 80 from the combustion cavity 30. The
sealed casing annulus 80 can be used to fluidly communicate water
down to the target zone, which is then injected into the reservoir
10 for creating steam within the target zone, above the combustion
cavity 30.
[0051] With reference to FIGS. 2A, 2B, and 3, one embodiment of the
present invention comprises the burner assembly 20 fluidly
connected to the main tubing string 40. A downhole burner 60 is
positioned at a downhole portion of a cased portion of an injection
well, the casing 90 being perforated into the reservoir 10. The
main tubing string 40 extends downhole and has conduits or
passageways for conducting or transporting each of fuel, and
oxygen, to the downhole burner 60. For ease of installation,
intermediate and inner tubing strings 120, 150 are releasably
connected to the burner assembly 20.
[0052] The downhole components, or as part of the burner assembly
20, can further comprise a torque anchor 210 to set the main tubing
string 40 in the casing 90.
[0053] In greater detail, and with reference to FIGS. 3 to 6, the
burner housing 190 is adapted at an uphole portion 220 for fluid
communication with the intermediate annulus 140 and inner bore 180.
In one embodiment, the burner housing 190 is fluidly connected to
the intermediate annulus 140 and the inner bore 180 through the
burner interface assembly 50. The burner housing 190 comprises two
fluid passageways for fluidly communicating the fuel and
oxygen.
[0054] As best shown in FIGS. 5 and 6, the burner housing 190
comprises the downhole portion or burner nozzle 200 for combustion
of the fuel and oxygen and an uphole portion 220 defining the two
fluid passageways for fluidly communicating the fuel and oxygen to
the nozzle 200. The uphole portion 220 has a bore 230 and a
concentric conduit or tubing 240 extending therethrough for
creating the two fluid passageways. A fuel passageway 250 is
defined by the annular space formed between the bore 230 and the
concentric conduit 240. The concentric conduit 240 further has a
bore defining an oxygen passageway 260.
[0055] The fuel passageway 250 is adapted to fluidly communicate
with the intermediate annulus 140, communicating fuel from the
surface to the nozzle 200. The bore 230 of the burner housing 190
and the fuel passageway 250 open into the nozzle 200 for injecting
the fuel into the nozzle 200. The fuel passageway 250 can further
have fuel swirl vanes 270 for aiding in the mixing of the fuel and
oxygen.
[0056] The oxygen passageway 260 is in fluid communication with the
inner bore 180, communicating oxygen from the surface to the nozzle
200. The oxygen passageway 260 has an opening 280 at a downhole end
for injecting oxygen into the nozzle 200. The oxygen passageway 260
can further have oxygen swirl vanes (not shown) for aiding in the
mixing of the fuel and oxygen. The oxygen and fuel mix for
combustion at the nozzle 200.
[0057] With reference to FIG. 5, as stated above, the fuel
passageway 250 can further have fuel swirl vanes 270 for imparting
a rotation to the fuel being injected into the nozzle 200. The
oxygen passageway 260 can also have oxygen swirl vanes for
imparting a rotation, counter to the direction of the rotation of
the fuel, for maximizing the mixing of the fuel and oxygen for
increasing the efficiency of the combustion of the fuel and oxygen.
In a preferred embodiment, the ratio of swirl velocity to axial
flow velocity of either the fuel or oxygen is substantially
1:2.
[0058] In an alternate embodiment, the opening 280 of the oxygen
passageway 260 can be fitted with a bluff body (not shown) to
reduce the axial momentum of the oxygen for stabilizing the
combustion flame.
[0059] Further, in another alternate embodiment (not shown), the
burner housing 190 can have two side-by-side bores extending
therethrough for forming the fuel passageway and the oxygen
passageway. Each bore can have an opening at a downhole end for
injecting the fuel and oxygen into the nozzle 200 for
combustion.
[0060] Conventional burner discharge arrangements can be employed
including utilizing a plurality of orifices and concentric
discharges. The nozzle 200 can be any open ended tubular structure
that allows mixing and combustion of the fuel and oxygen. As shown,
the nozzle 200 is a typical inverted truncated frusto-conical
nozzle. The truncated apex is fluidly connected to the burner
housing 190 and the nozzle 200 extends radially outwardly towards a
downhole end.
[0061] As shown in FIGS. 4 and 6, the high temperature casing seal
70 can be located on the downhole burner 60 to isolate the casing
annulus 80 from the combustion cavity 30. Accordingly, the casing
seal 70 is generally located low on the downhole burner 60, such as
between the downhole portion of the burner housing or nozzle 200
and the casing 90. In alternate embodiments (not shown), the casing
seal 70 can located between the uphole portion 220 of the burner
housing 190 and the casing 90.
[0062] Often, cased wellbores have casing distortions or kinks
which introduce challenges to installation and tolerances for
related seals to the casing. The casing distortions are an abrupt
shifting of the casing axis resulting in a casing portion that is
narrower than a nominal inner diameter of a typical casing. The
passage of seals and other downhole tools are difficult at best if
the nature of the seal is to initially comprise an outer diameter
of seal which is larger than the inner diameter of casing and
certainly greater than the distortion. Although downhole tools
generally can be manufactured to have a small outer diameter to
allow them to pass through a majority of distortions, seals
generally can not. Seals having small outer diameter, although
capable of passing through the distortions, are unlikely to fully
seal against the casing downhole of the distortion where the casing
again has a nominal inner diameter. Seals must also be able to
withstand the extreme heat conditions created by a downhole burner
when combusting the fuel and oxygen.
[0063] With reference to FIGS. 6 to 9, an embodiment of the casing
seal 70 is a brush-type seal comprising a plurality of flexible,
concentric, metallic brush rings 300 stacked one on top of another.
As best shown in FIGS. 6, 7A and 7B, the brush rings 300 are
stacked one on top of another upon a circumferential stop shoulder
310 at a downhole end of the nozzle 200. Spacer rings 320 can be
provided to alternate between the brush rings 300. The stack of
brush rings 300 and spacer rings 320 is secured in place by a
compression ring 330 exerting an axial securing force to sandwich
the rings 300, 320 to the stop shoulder 310. A compression nut 340
secures the compression ring 330.
[0064] As shown in FIGS. 8 and 9, each seal ring 300 has a
multiplicity of slits 350 that are formed radially inward from an
outer circumference of the seal ring 300 and which terminate before
an inner diameter of the seal ring 300 for forming a plurality of
flexible fingers 360. The fingers are separated at the outer
circumference and connected at the inner diameter. An inner most
radial extension of each slit 350 defines the inner diameter of the
multiplicity of slits 350 and is substantially the same as the
outer diameter of the spacer rings 320. The plurality of fingers
360, flexing from the inner diameter, provide dimensional
variability through flexibility for each concentric seal ring
300.
[0065] Each slit 350 extends radially outwardly in a generally
clockwise direction as viewed looking downhole. This particular
slit arrangement or design is advantageous when removing and
pulling up the casing seal 70. In the event that the casing seal 70
becomes stuck, the clockwise slit arrangement allows the casing
seal to be rotated in a counter-clockwise direction, thus
decreasing the outer diameter of the casing seal 70, and allowing
it to dislodge from the casing 90.
[0066] As shown in FIG. 9, each seal ring 300 can be rotationally
indexed relative to each adjacent seal ring 300. While enabling
radial flexibility, the slits 350 provide an avenue for fluids to
leak therethrough. In order to minimize the amount of leaking of
fluids through the slits 350, each seal ring 300 is rotated such
that the slits 350 of axially adjacent brush rings 300 are
rotationally offset or misaligned. To further mitigate leakage
through the slits 350, the plurality of concentric brush rings 300
are stacked. Each finger 360 of one seal ring 300 overlaps each
finger 360 of an adjacent seal ring 300, for forming a tortuous
axial path for restricting flow of casing annulus fluids
therethrough.
[0067] Referring back to FIG. 7A, the brush seal 70 has an outer
diameter greater than a nominal inner diameter of a casing 90 in a
cased wellbore as indicated by the dashed line. The greater outer
diameter defines the effective sealing diameter of a particular
brush seal. Brush-type seals having differing effective sealing
diameters can be readily installed depending on the size of the
casing 90 in the cased wellbore.
[0068] When the brush-type seal is run downhole, each finger 360 of
each seal ring 300 flexes uphole, reducing the overall outer
diameter and conforming to the casing 90, while maintaining the
effective sealing diameter. The reduction of the overall outer
diameter of the brush rings 300 allow the brush seal 70 to pass
through a cased wellbore during installation and pass by most
casing distortions. Upon encountering a casing distortion, the ring
fingers 360 of each concentric seal ring 300 can elastically flex
an additional amount to enable movement past the distortion.
[0069] In an alternate embodiment, other casing seals might be
employed including a metallic inflatable packer, such as those now
introduced by Baker Oil Tools, as presented in a paper entitled
"Recent Metal-to-Metal Sealing Technology for Zonal Isolation
Applications Demonstrates Potential for Use in Hostile HP/HT
Environments", published as SPE 105854 in February 2007. Such
inflatable packers are small enough in diameter to also pass
through casing distortions and may be able to withstand the extreme
heat conditions created by the burner. However, such packers can be
damaged by thermal cycling and may not be reusable.
[0070] For example, in a 7 inch (178 mm) casing having an inner
diameter of about 164 mm, a burner bottom hole assembly (BHA)
fluidly connected to the downhole end of a 3-% inch (89 mm) tubing,
can be placed in a cased wellbore having the typical casing
distortions. The burner BHA, comprising the burner interface
assembly, pup joint, and downhole burner, had a total length of
about 5 feet (1524 mm). A 23/8 inch (60 mm) intermediate coil
tubing was disposed within the 31/2 inch (89 mm) tubing, and a 11/4
inch (32 mm) inner coil tubing was disposed within the intermediate
coil tubing. The burner interface assembly was about 708 mm long
and had an outer diameter of about 114 mm, while the burner housing
was about 304 mm long with an outer diameter of about 93 mm. The
brush seal had an outer diameter of about 164 mm and was installed
on a nozzle having a circumferential shoulder of about 120 mm. Each
brush ring and spacer ring had a thickness of about 0.25 mm. The
pup joint, tailored to this particular example, was about 508 mm
long and had an outer diameter of about 27/8 inches (73 mm).
[0071] With reference to FIGS. 3 and 10, the fluid passageways can
be formed by a series of tubing strings disposed in the bore of a
larger tubing, or sectional tubing. Alternatively, two or more
tubing strings might be arranged side-by-side (not shown). As shown
in FIG. 3, the main tubing 40 is run down the cased wellbore
forming the casing annulus 80 or a first casing annular fluid
passageway therebetween. The intermediate tubing string 120 is
disposed concentrically within the bore of the main tubing string
40, forming the intermediate annulus 140 or a second intermediate
annular fluid passageway therebetween. The inner tubing string 150
is further disposed concentrically within the intermediate bore of
the intermediate tubing string 120 forming the inner annulus 170 or
a third inner annular fluid passageway therebetween. The bore of
the inner tubing string 150 further defines the inner bore 180 or a
fourth, inner bore fluid passageway.
[0072] Those skilled in the art would understand that although the
intermediate tubing string 120 is concentrically disposed with the
bore of the main tubing 40, the intermediate tubing string 120 may
not remain concentrically aligned within the bore of the main
tubing 40 as the intermediate tubing string 120 is run downhole.
Similarly, the inner tubing string 150, although concentrically
disposed in the intermediate bore of the intermediate tubing string
120 may not remain concentrically aligned as the inner tubing
string 150 is run downhole.
[0073] In a basic form, two passageways are used for providing fuel
and oxygen to the burner. A third passageway can be provided for
isolating the fuel and oxygen, and even more favourably for acting
as a sensing passageway for determining development of a leak
therebetween.
[0074] With reference to FIGS. 10 to 12, in one embodiment, a
burner interface assembly 50 fluidly connects three passageways of
the main tubing 40 to the fuel and oxygen passageways 250, 260 of
the downhole burner 60. The burner interface assembly 50 can
comprise an outer housing 400 secured intermediate or at the
downhole end of the main tubing string 40, an intermediate mandrel
410 at a downhole end of the intermediate tubing string 120, and an
inner mandrel 420 at a downhole end of the inner tubing string
150.
[0075] The outer housing 400 has a bore which is adapted to
releaseably connect with the intermediate mandrel 410. The
intermediate mandrel 410 has an uphole portion 430 having a bore
which is adapted to releaseably connect with the inner mandrel
420.
[0076] In greater detail, and with reference to FIG. 11, the outer
housing 400 has a bore, an uphole end 440 and a downhole end 450.
The uphole end 440 is adapted to fluidly connect to the main tubing
string (not shown) and the downhole end 450 is adapted to fluidly
connect to a pup joint which supports the downhole burner (not
shown).
[0077] With reference to FIGS. 10 and 11, the intermediate mandrel
410 is fit within the bore of the outer housing 400 forming the
intermediate annulus 140 therebetween. The intermediate mandrel
410, releaseably connected to the outer housing 400 at an
intermediate latch assembly 470, has an uphole portion 430 which is
adapted to fluidly connect to the intermediate tubing string 120.
The uphole portion 430 further has a bore for releaseably
connecting to the inner mandrel 420. In one embodiment, the uphole
portion 430 is an inner latch housing.
[0078] The bore of the outer housing 400 has an inner surface 480
for forming a first intermediate latch 470A. The first intermediate
latch 470A is formed adjacent a downhole end of the outer housing
400.
[0079] Further, the intermediate mandrel 410 has a second
intermediate latch 470B formed at its downhole end. The second
intermediate latch 470B is adapted to releaseably connect to the
complementary first intermediate latch 470A to form the
intermediate latch assembly 470.
[0080] With reference to FIGS. 10 and 12, the inner mandrel 420 is
fit within the bore of the inner latch housing 430 and releasably
connects with the intermediate mandrel 410 at an inner latch
assembly 490. Similar to the intermediate latch assembly 470, the
inner latch assembly 490 comprises a first inner latch 490A and a
complementary second inner latch 490B.
[0081] As shown, the intermediate mandrel 410 is fit within the
bore of the outer housing 400 for latching at the intermediate
latch assembly 470 and sealing at a first seal 500 therebetween.
The inner mandrel 420 is fit within the bore of the inner latch
housing 430 for latching at the inner latch assembly 490 and
sealing at a second seal 510 therebetween.
[0082] The intermediate annulus 140 is contiguous with an annular
space between the outer housing 400 and the intermediate mandrel
410 and is in fluid communication with the fuel passageway 250 of
the downhole burner 60. The inner bore 180 is contiguous with a
bore of the inner mandrel 420 and is in fluid communication with
the oxygen passageway 260 of the downhole burner 60. In this
embodiment, the inner annulus 170 happens to terminate sealably at
the second seal 510 for isolating the intermediate annulus 140 from
the inner bore 180.
[0083] The sealed inner annulus 170 isolates the intermediate
annulus 140 from the inner bore 180. This separation of the two
discrete passageways provides a safety measure, ensuring that the
fuel and the oxygen are separated by a buffer. In one embodiment,
the sealed inner annulus 170 is also a sensing annulus for
detecting leakage in the transport of the fuel and the oxygen. The
sealed inner annulus 170 can be maintained in a vacuum or other
pressure and is monitored for determining change in pressure
indicative of a leak in either the intermediate annulus 140 or the
inner bore 180.
[0084] In an embodiment and with reference to FIG. 10, the sealed
inner annulus 170 can be positively pressurized with an inert gas,
such as nitrogen (N.sub.2) gas. Inner annulus 170 is pressurized to
a pressure P higher than a pressure in the fuel passageway 140 and
the oxidant passageway 180 for separating and isolating the fuel
and oxident passageways 140,180 from one another.
[0085] Thus, in the event of any leaks or breaks in the sealing of
either the fuel or oxidant passageways the inert gas, under higher
pressure than both the fuel or oxidant passageways 140,180, will
positively enter into either the leaking fuel or oxidant
passageways 140 or 180, avoiding the potential for mixing of the
fuel and oxidant and thereby mitigating risk associated with
accidental combustion of fuel and oxidant within the conveyance
string.
[0086] Further, the pressure P of the inert gas within the sealed
inner annulus 170 can be monitored by a sensor. An unexpected
decrease in the pressure would be indicative of the inert gas
entering into either the fuel or oxidant passageways, indicating a
leak or broken seal.
[0087] In an embodiment, the inner annulus 170 can be pressurized
with N.sub.2 to isolate fuel in the intermediate annulus 140 from
oxidant conveyed in the inner bore 180. In another embodiment, the
intermediate annulus 140 can be used to convey oxidant, while the
inner bore 180 conveys fuel.
[0088] As shown in FIG. 10, in an embodiment, at least two tubing
strings can be positioned within a wellbore for forming three
discrete fluid passageways for conducting at least fuel and oxidant
to a downhole burner. As shown, fluid passageway 170 can be a
sealed fluid passageway for isolating the passageways 140 and 180
from one another.
[0089] The intermediate latch assembly 470 can be any suitable
releasable latch used in the industry, but in a preferred
embodiment, the intermediate latch assembly is a type of latch
assembly disclosed and claimed in U.S. Pat. No. 6,978,830, issued
on Dec. 27, 2005, to MSI Machineering Solutions, Inc., located in
Providenciales, Turks and Caicos.
[0090] Similar to the intermediate latch assembly 470, the inner
latch assembly 490 can be any suitable latch assembly used in the
industry, including that disclosed and claimed in the
aforementioned U.S. Pat. No. 6,978,830.
[0091] As best shown in FIG. 12, an uphole end of the inner latch
housing 430 is fit with a third seal 520 for sealing and isolating
the intermediate annulus 140 from the inner annulus 170. The inner
latch housing 430 further has a second seal 510 for sealing and
isolating the inner annulus 170 from the inner bore 180.
[0092] For redundancy purposes, and to ensure sealing and isolating
of the three discrete passageways, the first, second, and third
seals 500, 510, 520 can be a plurality of individual seals in a
stacked arrangement.
[0093] For greater safety and control of the fuel and oxygen
passageways, and in a particular embodiment, the intermediate
mandrel 410 can further comprise a backpressure valve assembly 600
for controlling the flow of the fuel and oxygen. Fuel is forced
from the intermediate annulus 140 through the backpressure valve
assembly by the first seal 500.
[0094] The backpressure valve assembly 600 comprises two fluid
bypass passageways, each having a backpressure valve. The fluid
bypass passageways bypass the first seal 500. A first bypass
passageway 610, having a first backpressure valve 620, is in fluid
communication with the intermediate annulus 140 for transporting
the fuel from the main tubing string 40 to the fuel passageway 250
of the downhole burner 60. A second bypass passageway 630, having a
second backpressure valve 640, is in fluid communication with the
inner bore 180 for transporting the oxygen to the oxygen passageway
260 of the downhole burner 60.
[0095] Each of the backpressure valves comprises a ball 620A, 640A
and a spring 620B, 640B, biased to apply a constant closing force
on the ball, ensuring that the ball is sealingly fit within a ball
seat 650A, 650B. The constant closing force is greater than the
force applied by the differential fluid pressure between the static
fluid pressure above the backpressure valves 620, 640 and a
reservoir pressure below the backpressure valves 620, 640. For
either the fuel and/or oxygen to flow pass the backpressure valves
620, 640, the injection pressure of the fuel or oxygen must exert
enough force to overcome the combined forces of the spring 620B,
640B and the reservoir pressure.
[0096] In one embodiment, the closing force biasing the ball of the
backpressure valves 620, 640 is based upon a differential pressure
of 200 psi. In this embodiment, the injection pressure of both the
fuel and oxygen must be sufficient to exert sufficient pressure to
overcome the combined forces of the closing force and the force
exerted by the reservoir pressure.
[0097] The injection pressure of the fuel or oxygen does not exceed
the fracturing pressure of the particular target zone.
[0098] In Operation
[0099] In a broad aspect, hot combustion gases can be introduced
into a target zone of a hydrocarbon reservoir and allowed to
permeate therethrough. In one embodiment, introduction of the hot
combustion gases can be accomplished by arranging a burner
assembly, such as a downhole burner, for access to a cavity in a
target zone of the hydrocarbon reservoir. Hot combustion gases from
the burner assembly are permitted to permeate from the cavity and
through the target zone.
[0100] Subsequently, water is also injected into the target zone
and is also allowed to permeate through the target zone for
interacting with the heated target zone and hot combustion gases
therein. The interaction of the water with the hot combustion gases
creates steam within the target zone for creating a drive front in
the hydrocarbon reservoir. While some steam is likely to form in
the cavity, primarily steam forms in the reservoir, spaced from the
cavity itself, at a hot gas/water interface.
[0101] Applicant notes that the cavity can be any pre-existing
cavity, naturally occurring or otherwise artificially created using
downhole tools. A cavity, whether pre-existing or created can be
worked on by a variety or combination of techniques. Cavity size
and shape can be manipulated to extend or otherwise accommodate a
combustion zone of the particular burner assembly and to form a
cavity-to-hydrocarbon reservoir interface. The cavity reservoir
interface, at a cavity envelope, forms an interface surface area
between the hot combustion gases from the burner assembly and the
target zone, and the larger the interface area, the better the
access of the hot gases to the reservoir, particularly when the
reservoir is characterized by a low permeability.
[0102] Simply, one accesses the cavity with a wellbore, whether the
wellbore is pre-existing yet lacking a cavity, or the cavity is
pre-existing and initially lacking a wellbore. Where wellbore
exists or is formed, one runs the burner assembly down the wellbore
to access the target zone. If the cavity does not exit, one is
created. If the cavity was formed by means other than running in
and operating the burner assembly, the burner assembly run downhole
and arranged to access the cavity.
[0103] As shown in FIG. 16A a cavity 1610 can be artificially
created by reaming or hydraulic washing operations. Reaming of
formations accessed by a wellbore is a known technique and includes
tools and methods of bi-directional underreaming and backreaming.
Hydraulic washing tools, including jetting, are also known for
casing and formations. One accesses the target zone with a wellbore
and runs in a tool downhole of the wellbore. In the case of a
reaming tool, actuating the reaming tool such as by expanding the
tool and reaming the target zone to form the cavity. In the case of
a hydraulic washing tool, one actuates the washing tool for
hydraulic washing of the target zone to form the cavity. The burner
60 is run in to access the cavity 1610.
[0104] Any radial limitations of reaming might be further
supplemented with additional hydraulic washing operations using
appropriate combination reaming and hydraulic tools or staged
independent tools.
[0105] As shown in FIG. 16B, a cavity 1620 can be created
artificially by combustion. One accesses the target zone with the
wellbore. The burner assembly 60 is run in to the target zone. The
burner assembly 60 is operated at a first condition for directing
combustion into wellbore to form the cavity 1620. The first
condition may be at higher overall heat output or at higher
temperatures so as to melt or otherwise degrade the target zone
about the discharge of the burner assembly. Thereafter, the burner
assembly 60 is operated at a second condition for directing
combustion into the created cavity to form the hot combustion
gases.
[0106] FIG. 16C illustrates a pre-existing or naturally occurring
cavity 1630, such as geological cavities and cavities formed as a
result prior operations in the hydrocarbon reservoir. One example
of a cavity created by prior operations includes a sand-depleted
cavity in a Cold Heavy Oil Production with Sand (CHOPS) reservoir.
Applicants understand that in some cases of CHOPS production from
the wellbore, a cavity 1630 can be formed about the producing well.
Thus, before the burner assembly 60 is run downhole, there is a
pre-existing cavity in the target zone about the wellbore.
[0107] Water is injected into the target zone by injecting water
from a wellbore annulus 80. In one embodiment, injection of water W
can be accomplished by injecting water W through an annulus 60
about the burner assembly 60 for entering into the target zone. In
an embodiment illustrated previously in FIG. 4, the burner assembly
60 can have an annular seal 70 for sealing the annulus 80 and
permitting injection of the water W into the target zone uphole of
the annular seal. Accordingly, one seals the wellbore annulus 80
with an annular seal 70 at about the burner assembly 60 and water
is injected into the target zone uphole of the annular seal 70.
[0108] With reference to FIG. 17, in another embodiment, and as
described in Applicant's U.S. 61/560,468 and incorporated fully
herein by reference, a burner assembly 1710 can have a shroud 1715
disposed at a downhole end 1720 surrounding a combustion zone 1730
thereof. As shown, the shroud 1715 can comprise an outer shroud
1740 and an inner shroud 1750 surrounding the combustion zone 1730
of the burner assembly 1710. Water W from an outer annulus 1780 is
injected into the target zone from about the shroud 1715.
[0109] As shown, the burner assembly 1710 is illustrated depending
from fuel and oxygen lines 1760 running downhole in a cased
wellbore 1770. In the context shown, the burner assembly 1710 is
positioned for discharge of hot flue gases uphole of a cavity (not
shown) of a target zone within a hydrocarbon-bearing formation. The
shroud 1715 is fit about the combustion zone 1730 of the burner
assembly 1710.
[0110] The outer shroud 1740 is exposed to the target zone. An
outer annulus 1780 is formed between the target zone and the outer
shroud 1740. Water injected above the burner assembly 1710 or in
the annulus 1780 between the oxy/fuel conduit 1760 can flow into
the target zone, along the outer annulus 1780, and to a base of the
outer shroud 1740.
[0111] Injection of water W through the annulus 1780 comprises
injection of water E into the target zone from about the outer
shroud 1740.
[0112] In greater detail for one embodiment, a combustion chamber
30 is formed by melting a target zone at a temperature sufficient
enough to melt the hydrocarbon reservoir 10 at the target zone.
Thereafter, a steady state combustion is maintained for sustaining
a sub-stoichiometric combustion of the fuel and oxygen for
producing hot combustion gases (primarily CO, CO.sub.2, and
H.sub.2O) which enter and permeate through the reservoir 10. The
hot combustion gases create a gaseous drive front and heat the
reservoir 10 adjacent the combustion cavity 30 and the
wellbore.
[0113] Addition of water to the reservoir 10 along the casing
annulus 80 above the combustion chamber 30 injects water into an
upper portion of the reservoir 10 adjacent the wellbore for lateral
permeation through the reservoir 10. The lateral movement of the
injected water cools the wellbore from the heat of the hot
combustion gases and minimizes heat loss to the formation adjacent
the wellbore. The water further laterally permeates through the
reservoir 10 and converts into steam. The steam and the hot
combustion gases in the reservoir 10 form a steam and gaseous drive
front.
[0114] In more detail and referring again to FIGS. 1, and 13-15B,
an injection well is cased and perforated at a target zone of the
reservoir 10.
[0115] A packer is set and a suitable depth of thermal cement is
placed below the target zone. The thermal cement protects the
packer from the downhole burner 60.
[0116] Referring to FIG. 13, a first main tubing hanger 100 is
affixed to a wellhead 110. A burner bottom hole assembly (burner
BHA) 700 comprising a torque anchor 210, the outer housing 400 of
the burner interface assembly 50, a pup joint 710, and the downhole
burner 60 are fluidly connected to a downhole end of a main tubing
string 40. The burner BHA 700 is run downhole to a depth for
positioning the downhole burner 60 within a target zone. In one
embodiment, the downhole burner 60 is positioned at about the
midpoint of the target zone. Once in position, the main tubing
string 40 is rotated to set the torque anchor 210 and the main
tubing string 40 is hung from the main tubing hanger 100.
[0117] As shown in FIGS. 1 and 3, the main tubing string 40 and the
casing 90 of the wellbore form a casing annulus 80 therebetween.
The casing seal 70 between the burner housing 190 and the casing 90
seals the casing annulus 80.
[0118] Referring to FIG. 14B, an intermediate tubing hanger 130 is
supported on the main tubing hanger 100. With reference to FIGS.
14A and 14B, the intermediate mandrel 410 is fluidly connected to a
downhole end of the intermediate tubing string 120, and the
concentric tubing 240 defining the oxygen passageway 260 extends
downhole from the intermediate mandrel 410. As shown in FIG. 14B,
the intermediate tubing string 120 is run downhole within the bore
of the main tubing string 40. The intermediate mandrel 410 is run
downhole until it is tagged with the outer housing 400 of the
burner interface assembly 50. Tagging the intermediate mandrel 410
to the outer housing 400 involves releaseably connecting the outer
housing 400 to the intermediate mandrel 410 at the intermediate
latch assembly 470, forming the intermediate annulus 140
therebetween. The intermediate tubing string 120 is pulled uphole
to stretch the intermediate tubing 120 and remove any slack. The
intermediate tubing string 120 is hung by the intermediate tubing
hanger 130 and then cut to an appropriate length.
[0119] With reference to FIG. 15A, an inner tubing hanger 160 is
supported on the intermediate tubing hanger 130. The inner mandrel
420 of the burner interface assembly 50 is fluidly connected to a
downhole end of the inner tubing string 150, and run downhole
within the intermediate bore of the intermediate tubing string 120.
The inner tubing string 150 is run downhole until the inner mandrel
420 tags the intermediate mandrel 410 forming the inner annulus
170. Tagging the inner mandrel 420 to the intermediate mandrel 410
involves releaseably connecting the inner mandrel 420 to the
intermediate mandrel 410 at the inner latch assembly 490. The inner
tubing 150 is pulled uphole to stretch the inner tubing 150, hung
by the inner tubing hanger 160 and then cut to an appropriate
length. The bore of the inner tubing string 150 defines the inner
bore 180.
[0120] The intermediate annulus 140 can be fluidly connected to a
source of fuel, and the inner bore 180 can be fluidly connected to
a source of oxidant, such as oxygen. The inner annulus 170 is
sealed and is monitored. Any changes with the pressure within the
sealed inner annulus 170 are indicative of a leak in either the
intermediate annulus 140 or the inner bore 180.
[0121] A further utility of the backpressure valve assembly is to
assure successful latching and continuity of the intermediate and
inner tubing string at the burner interface assembly, an inability
of the either passageway to retain pressure up to the opening
pressure of the valves being indicative of a problem in the
connections of one form or another.
[0122] The fuel can be delivered down the intermediate annulus 140
passing through the first bypass passageway 610 and first
backpressure valve 620 and to the fuel passageway 250. Similarly,
oxygen can be injected down the inner bore 180, through the second
bypass passageway 630 and the second backpressure valve 640 to the
oxygen passageway 260. Both the fuel and oxygen enter the nozzle
200 for combustion. The first and second backpressure valves 620,
640 creates a backpressure greater than that static head to surface
pressure, ensuring that the flow of the fuel and oxygen can be
controlled from the surface by controlling the flow rate of the
fuel and oxygen. If the flow rate of the fuel or oxygen does not
create enough pressure to overcome the pressure exerted by the
closing force of the backpressure valve spring 620B, 640B and the
reservoir pressure, fuel and oxygen cannot pass the first and
second backpressure valves 620, 640.
[0123] After the burner assembly 20 is positioned within the target
zone, the reservoir 10 can be initially flooded with water. Water
is injected down the casing annulus 80 to enter the reservoir 10
through the perforations for increasing the reservoir pressure
adjacent the wellbore. The fuel is then injected downhole. After a
sufficient amount of time to ensure that the fuel has entered the
target zone downhole, the fuel is doped with an accelerant, a
pyrophoric compound such as triethylborane or silane, sufficient
for igniting the fuel. Oxygen is injected to light off the downhole
burner 60. The accelerant is discontinued to create a stable flame
for combustion. A stable flame can be maintained by controlling the
rate of the fuel and oxygen. The fuel and oxygen are controlled to
combust at a temperature to create a combustion cavity 30
sufficient to melt or otherwise form a cavity 30.
[0124] In one embodiment, the downhole burner 60 can be lit off and
operated at a first condition to form a minimum stable flame
temperature of about 2800.degree. C. At such a temperature, it is
believed that the casing 90 and the surrounding reservoir 10
downhole of the burner 60 would melt, forming the combustion cavity
30. The burner 60 is then located or arranged generally uphole of
the cavity. As the combustion cavity 30 expands, molten material
will flow and pool at a bottom of the combustion cavity 30 above
the thermal cement for forming an impermeable glassy bottom.
Further, the heat from the flame continues to be transferred to the
lateral walls by a combination of radiant heat transfer and hot
combustion gases permeating into the reservoir 10. Melting and
enlargement of the combustion cavity 30 ceases when the combustion
cavity 30 is sufficiently large enough that the heat transfer from
the combustion is below the melting point of the reservoir 10. The
lateral walls of the combustion cavity 30 remain porous and
permeable, perhaps in a sintered state.
[0125] Once the combustion cavity 30 has been formed, the fuel and
oxygen are controlled to continue steady state combustion for
creating and sustaining hot combustion gases for flowing and
permeating into the target zone.
[0126] Further, the steady state combustion of the fuel and oxygen
is also under sub-stoichiometric conditions, limiting the amount of
oxygen available for combusting with the fuel. The limited amount
of available oxygen ensures that there is no excess oxygen
available for flowing into the reservoir 10. Excess oxygen flowing
into the reservoir 10 may result in additional combustion within
the reservoir 10 and result in some coking therein.
[0127] Water is delivered down the casing annulus 80. The casing
seal 70 directs the water out the perforations and into the target
zone concurrently as hot combustion gases are created and sustained
at steady state. The injected water and hot combustion gases in the
target zone interact to form a drive front comprising steam and hot
combustion gases.
[0128] The present process further protects the reservoir 10 from
permeability degradation due to chloride scaling by keeping the
chlorides in solution. Most chloride scaling is caused by
introducing water with a dissimilar ion charge during water
flooding. Increasing temperature and/or pressure typically improves
solubility of chlorides. The risks of chlorides deposition are
reduced as both temperature and pressure increase with the
introduction of heat and CO.sub.2 (from the hot combustion gases).
Higher CO.sub.2 concentrations in formed emulsion increases
carbonate solubility. The process can be operated to continually
produce incremental CO.sub.2, gradually increasing concentrations
as the flood progresses.
[0129] Risk of chloride scaling is further mitigated by maintaining
an 80% steam quality downhole which keeps chlorides in solution.
Untreated produced water typically contains upwards of 50,000 ppm
of total dissolved solids, which is typically treated prior to
being passed through boilers for conventional stem flood processes.
Control of the mass and heat balance of the combustion process
permits management of the steam generation in the target zone to be
at about 80% steam quality. The lower steam quality ensures that
there is a sufficient water phase to keep all dissolved solids in
solution and treatment of the produced water is not required.
[0130] In an alternate embodiment, fuel can be injected downhole
through the inner bore 180, while the oxygen can be injected down
through the intermediate annulus 140.
[0131] Further, in an alternate embodiment, where regulation may
prohibit injection of fluid down the casing annulus 80, water can
be injected down one o the other passageways. For example, water
could be injected down the intermediate annulus 140 for injection
at the burner assembly for communication with the hydrocarbon
reservoir. In such an embodiment, the inner annulus 170 can be used
to inject fuel or oxygen, instead of being used as a sensing
annulus for detecting leaks, oxygen or fuel could continue to be
injected down in the inner bore 180. Further, as those skilled in
the art would understand, the intermediate annulus 140 would have a
water injection port in the burner assembly and placed in fluid
communication with the reservoir to allow the injected water to
flow into and permeate through the reservoir and a flow through
packer can be used to isolate the burner assembly 20. One approach
is to locate a flow-through packer at about the burner assembly for
sealing the casing annulus above the water injection port. Water
injected from the intermediate annulus would exit from the water
injection port and into an injection annulus formed in the casing
annulus between the packer and the casing seal.
[0132] Further still, yet, in a further alternate embodiment, the
inner tubing string 150 can be eliminated such as to reduce costs.
In such an embodiment, the main tubing string 40 can be disposed
within the casing 90 forming the casing annulus 80, and the
intermediate tubing string 120 can be disposed in the main tubing
string 40 forming the intermediate annulus 140. The intermediate
tubing string 120 would have a bore forming the inner bore 180.
This embodiment would not have the inner annulus 170 to serve as a
sensing annulus for detecting leaks in the intermediate annulus 140
and/or the inner bore 180.
* * * * *