FIELD OF THE INVENTION
[0001] This invention relates to an modified process for hydrocarbon recovery from an underground reservoir by
in situ combustion and employing a horizontal production well.
BACKGROUND OF THE INVENTION
[0002] Commonly assigned
U.S. Patent 5,626,191 issued May 6, 1997 (hereinafter the '191 patent) discloses an
in situ combustion processes for producing hydrocarbon from an underground hydrocarbon reservoir utilizing (i) at least one injection well placed relatively high in an oil reservoir for injecting an oxidizing gas into the hydrocarbon formation, and (ii) a production well for producing liquefied or gasified hydrocarbon from the hydrocarbon reservoir. The production well has a vertical section which is in communication with a horizontal leg extending substantially perpendicularly outwardly from the vertical section and having a "toe" portion and a "heel" portion. The horizontal leg is completed relatively low in the reservoir, and at a "heel" portion thereof is in communication with the vertical section. Air, or other oxidizing gas, such as oxygen-enriched air, is injected through the injection well into the hydrocarbon reservoir, typically via perforations in the upper part of a vertical injection well, located in the vicinity of the "toe" of the horizontal leg of the production well. The horizontal leg of the production well is oriented generally perpendicularly to a generally quasi-vertical combustion front of combusting hydrocarbon which is produced upon ignition of a portion of the hydrocarbon in the reservoir proximate the injection well. Such combustion front is supplied with oxidizing gas via the injection well. The "toe" of the horizontal leg portion is positioned in the path of the advancing combustion front. The resulting combustion front propagates from the "toe" of the horizontal leg along the horizontal leg in the direction of and towards the "heel" portion. During this process heated hydrocarbon in the reservoir in advance of the moving combustion front becomes liquefied or gasified and flows into the horizontal leg, and from such leg thereafter removed to the surface via the vertical section of the production well. This process of
U.S. Patent 5,626,191 is called "THAI™", an acronym for "toe-to-heel air injection", and a registered trademark of Archon Technologies Ltd., a subsidiary of Petrobank Energy and Resources Ltd., Calgary, Alberta, Canada.
[0003] U.S. Patent 6,412,557 , also commonly assigned, discloses a similar but modified process having the added step of placing a hydrocarbon upgrading catalyst along, within, or around the horizontal leg to substantially decrease the viscosity of the hydrocarbon and upgrade the quality of the hydrocarbon and increasing the flow of hydrocarbon from the reservoir into the horizontal leg of the production well for subsequent removal to surface. Such modified process is known in the industry by the trademark CAPRI™, likewise a registered trademark of Archon Technologies Ltd.
[0004] US 2006/207762 A1, and
US 2007/256833 A1, teach a similar process to that of THAI™, further comprising the additional step of providing injection tubing inside the production well within the vertical section and substantially along the length of the horizontal leg to a position proximate the "toe" thereof, for the purpose of injecting a non-oxidizing medium comprising steam, water, or a non-oxidizing gas via said tubing to the "toe" region of said horizontal leg. The injection of such non-oxidizing medium into the "toe" region of the horizontal leg has the effect of displacing any oxidizing gas in such area and thus preventing combustion of upgraded hydrocarbon which has flowed into the horizontal leg, and further increases the ambient pressure in the horizontal leg so as to prevent or reduce further inflow of oxidizing gas from the injection well which is injecting oxidizing gas into the hydrocarbon reservoir.
[0005] Disadvantageously, in each of the above prior art methods for recovering liquefied and/or gasified hydrocarbons from a hydrocarbon formation oxidizing gas is needed to be injected proximate the toe of the horizontal leg, and remote from the vertical section of the production well. Such site of injection of oxidizing gas is remote from the vertical section of the production well, the surface of the production well being the location where oxidizing gas is typically generated. The injection and vertical section of the production wells can be separated by one (1) kilometer or more. Thus such prior art methods thus typically require transport of the oxidizing gas to the site of the injection well via piping from the production well, or alternatively require installation of equipment at the injection well site to permit generation of oxidizing gases for subsequent injection. Such requires clear access, via clearcutting, and/or increased space at the injection well site to accommodate additional oxidizing gas delivery and/or generation and compression facilities, thereby increasing the environmental "footprint" and impact of drilling operations on the environment, and also typically results in increased cost.
[0006] Thus a need thus exists for a modified process of THAI™ and CAPRI™ wherein such drawbacks are eliminated.
SUMMARY OF THE INVENTION
[0007] The method of the present invention is to a modified
in situ hydrocarbon recovery process that instead of injecting oxidizing gas near the "toe" portion of the horizontal leg injects oxidizing gas in or near the producing vertical section of the production well (ie at the "heel" portion). The modified process obviates the need for a separate drilling/production pad for oxidizing gas injection, thereby reducing cost and decreasing detrimental environmental impact of
in situ recovery methods.
[0008] Advantageously, the process of the present invention in a particular third embodiment described below further eliminates the need for a separate oxidizing gas injection well, in that in such refinement the vertical section of the production well also serves as the injection well, thereby reducing well drilling costs and reducing the capital costs.
[0009] Specifically, rather than being a "toe-to heel" process, the process of the present invention is a "heel-to-toe" process. The oxidizing gas injection point is modified to be at the "heel" as opposed to the "toe" so that the combustion front moves in the opposite direction from that of the THAI™ process, namely from the direction of the "heel" of the horizontal well towards the "toe".
[0010] In the present invention three regions of the reservoir are developed relative to the position of the combustion zone. Near the "heel" and after the passage of the combustion front away from the "heel" lies the burned oil-depleted zone which results after injection of the oxidizing gas and after the combustion front has advanced for a period outwardly and away from the injection well and the "heel" portion of the horizontal leg. Such burned zone is filled substantially with oxidizing gas. Next lies the coke zone, which is essentially the area within the reservoir which the oxidizing gas has been able to then penetrate in the reservoir, and is essentially the area at which the combustion front exists (the combustion which occurs being that of the remaining coke which is the hydrocarbon then remaining after the lighter hydrocarbons within such reservoir and ahead of such combustion front have been liquefied or gasified and have flowed into the horizontal leg and thereafter removed to surface). Lastly, towards the "toe" of the horizontal well lies the region of the reservoir containing hydrocarbons which the combustion front is advancing toward.
[0011] At higher oxidant injection rates, reservoir pressure increases and oxidizing gas in the burned zone, containing residual oxygen, can be forced into the horizontal leg of the production well. This is prevented in the process of the present invention by injecting, either for a limited time, or continuously, a medium such as a non-oxidizing gas, carbon dioxide, and/or steam or water, to increase the pressure within the horizontal leg of the production well.
[0012] Accordingly, in one broad aspect of the process of the present invention, to realize the advantage of being able to inject the oxidizing gas proximate or in the vertical section of the production well, a modified process for recovering liquefied or gasified hydrocarbon from an underground hydrocarbon reservoir is disclosed, comprising the steps of:
- (a) providing at least one production well having a substantially horizontal leg positioned relatively low in said reservoir, said horizontal leg having at one end thereof a heel portion and at an opposite end thereof a toe portion, said horizontal leg adapted to permit inflow of hydrocarbon into an interior of said horizontal leg, said production well having a substantially vertical section connected to said horizontal leg proximate said heel portion thereof;
- (b) providing production tubing inside said production well extending within said vertical section and within at least a portion of said horizontal leg to collect said hydrocarbon which flows into said horizontal leg;
- (c) injecting periodically or continuously a medium into the production well, e.g. into the horizontal leg proximate the heel portion thereof, wherein said medium is selected from the group of mediums comprising alone or in combination, a non-oxidizing gas, carbon dioxide, steam, or water;
- (d) supplying an oxidizing gas to said underground reservoir, at least initially, at a location of or proximate said vertical section of said production well, wherein said step of supplying said oxidizing gas is accomplished by supplying said oxidizing gas to said hydrocarbon reservoir via perforations in an injection well;
- (e) igniting hydrocarbon within said hydrocarbon reservoir proximate said vertical section of said production well, so as to cause combustion of a portion of said hydrocarbon in said hydrocarbon reservoir proximate said vertical section and thereby create a combustion front which advances outwardly and away from said injection well in at least a direction along said horizontal leg and towards said toe portion thereof;
- (f) causing heated hydrocarbon from said reservoir to flow from upper regions thereof and collect in said horizontal leg; and
- (g) removing from the production well, via said production tubing, said hydrocarbon which has flowed into said horizontal leg.
[0013] Regarding step (g) above, the removal of the hydrocarbon from the production well via the production tubing is typically without pumping, but may require pumping in order to be removed from the horizontal leg if sufficient quantities of gases such as gasified hydrocarbon, carbon dioxide or nitrogen do not flow into the horizontal leg and thus the production tubing under significant ambient pressure of the hydrocarbon formation, as may occur during a start-up period. The normal mechanism of producing oil by reducing the mixed-fluid density with gases is called 'gas lift'.
[0014] In a first refinement/embodiment of the above process of the present invention, the injection of the oxidizing gas proximate the vertical section of the production well is accomplished via the drilling of a separate injection well proximate the vertical section of the production well so as to permit the oxidizing gas to be injected into the formation via such injection well proximate the production well. In this manner, and advantageously, the same drilling pad can then be used for drilling both the production well and the injection well, thus saving on expense and cost of well drilling.
[0015] Additionally, and advantageously, because the injection well is situated proximate the production well which typically has power generation equipment used for production, oxidizing gas can usually and more easily be obtained and immediately injected into the injection well, which would not otherwise be capable of being done were the injection well positioned remote from the vertical section of the production well as in the prior art.
[0016] In a second embodiment of the invention, the injection well is a side entry well within the vertical section of the production well, thus again allowing the injection well to be situated proximate the injection well so as to achieve the above benefits,
as well as the additional benefit in that the upper portion of the vertical section of the production well can be used when drilling the side entry well, thus further reducing drilling costs.
[0017] Specifically, in such second preferred embodiment, the present invention comprises a process for recovering liquefied or gasified hydrocarbon from an underground hydrocarbon formation comprising the steps of:
- (a) providing at least one production well having a substantially horizontal leg positioned relatively low in said formation, said horizontal leg having at one end thereof a heel portion and at an opposite end thereof a toe portion situated in the formation slightly lower in elevation than said heel portion, said horizontal leg adapted to permit inflow of liquefied hydrocarbon into an interior of said horizontal leg, said production well having a substantially vertical section connected to said horizontal leg proximate said heel portion thereof;
- (b) providing production tubing inside said production well extending downwardly within said vertical section and along said horizontal leg to said toe portion, to collect said hydrocarbon which flows into said horizontal leg;
- (c) providing injection tubing in said production well, said injection tubing extending downwardly in said vertical section to said heel portion;
- (d) injecting a medium into said production well via said injection tubing wherein said medium is selected from the group of mediums comprising alone or in combination, a non-oxidizing gas, steam, water, or carbon dioxide;
- (e) providing an injection well as a side track re-entry from said vertical section of said production well, which injection well extends into the hydrocarbon formation;
- (f) supplying an oxidizing gas to a portion of said hydrocarbon formation via said injection well, wherein said step of supplying said oxidizing gas is accomplished by supplying said oxidizing gas to said hydrocarbon reservoir via perforations in said injection well;
- (g) igniting said hydrocarbon in said hydrocarbon formation proximate said vertical section so as to cause combustion of a portion of said hydrocarbon in said hydrocarbon formation and thereby create a combustion front which advances outwardly and away from said vertical section in at least a direction along said horizontal leg and towards said toe portion thereof; and
- (h) removing from the production well, via said production tubing, hydrocarbon which has flowed into said horizontal leg.
[0018] In a third preferred embodiment the present invention comprises a method of producing hydrocarbon from a hydrocarbon reservoir whereby the necessity of an injection well for injecting the oxidizing gas is completely eliminated, thus reducing the cost of implementing the
in situ process of the present invention.
[0019] Specifically, in such third and preferred embodiment of the present invention, the vertical section of the production well is perforated to permit an oxidizing gas (which is provided to such vertical section) to escape into the hydrocarbon formation proximate the vertical section. In such manner, the need to drill a separate injection well is eliminated.
[0020] Again, as part of the method of the present invention, a medium in the form of a non-oxidizing gas, carbon dioxide, steam or water is injected either continuously or intermittently into the production well via injection tubing, which extends to the heel portion of the production well. A series of "packers" located in the production well may be provided to isolate the oxidizing gas supplied to the vertical section of the production well from the heel portion of the horizontal leg of the production well to which the non-oxidizing medium is supplied.
[0021] Thus in such third preferred embodiment, the method of the present invention comprises a process for recovering liquefied or gasified hydrocarbon from an underground hydrocarbon reservoir, comprising the steps of:
- (a) providing at least one production well having a substantially horizontal leg positioned relatively low in said reservoir, said horizontal leg having at one end thereof a heel portion and at an opposite end thereof a toe portion, said horizontal leg adapted to permit inflow of liquefied hydrocarbon into an interior of said horizontal leg, said production well having a substantially vertical section connected to said horizontal leg proximate said heel portion thereof;
- (b) providing production tubing in said production well, extending from a surface of said production well to at least said heel portion of said production well to collect said hydrocarbon which flows into said horizontal leg;
- (c) providing injection tubing in said production well, said injection tubing extending downwardly in said vertical section to a position extending into at least said heel portion of said horizontal leg;
- (d) injecting a medium into the production well, wherein said medium is selected from the group of mediums comprising alone or in combination, a non-oxidizing gas, carbon dioxide, steam, or water;
- (e) providing perforations in said vertical section of said production well at a position above said heel portion;
- (f) supplying an oxidizing gas to said vertical section and thus to a portion of said hydrocarbon reservoir via said perforations in said vertical section;
- (g) igniting said hydrocarbon in said hydrocarbon reservoir proximate said vertical section so as to cause combustion of a portion of said hydrocarbon in said hydrocarbon reservoir and thereby create a combustion front which advances outwardly and away from said vertical section in at least a direction along said horizontal leg and towards said toe portion thereof; and
- (h) causing heated hydrocarbon from said reservoir to flow from upper regions thereof and collect in said horizontal leg; and
- (i) removing from the production well, via said production tubing, said hydrocarbon which has flowed into said horizontal leg.
[0022] Advantageously, the third embodiment of the present invention also eliminates the need as in the prior art to "close off' (using a cement plug or the like) the horizontal leg of each production well when a series of production wells are situated end to end and when the vertical section of a first production well is subsequently converted to an injection well (see. US '191,col 6, lines 47-col 7, line 9 and Figs. 14D-F thereof). The
in situ method of the present invention, in particular the third embodiment, is a method of further reducing the cost
of in situ recovery by reducing the number of steps, including not only eliminating the need to drill injection wells but also eliminating the necessity of "closing off' other wells as is necessary in the in situ methods of the prior art, as exemplified in US '191 above.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] In the accompanying drawings, which illustrate a number of exemplary embodiments of the invention:
Figure 1A is a perspective schematic view of a prior-art in situ recovery arrangement in a hydrocarbon reservoir, showing air injection wells situated at the toe of each of corresponding horizontal legs of associated production wells;
Figure 1B is a cross section through one injection well and associated production well shown in Figure 1A;
Figure 2A is a schematic cross-section (not to scale) through one injection well and associated production well of a first embodiment of the present invention, using the method of the present invention of causing a combustion front to propagate in the direction of the "toe" of the horizontal leg of the production well, at a point in time close to the time of ignition of the hydrocarbon and the initial propagation of the combustion front;
Figure 2B is a similar cross-section to that of Figure 2A, likewise not to scale, at a subsequent point in time when the combustion front has propagated for a time and moved closer to the "toe" portion of the horizontal leg of the production well;
Figure 2C is a similar cross-section to that of Figure 2B, likewise not to scale, at a still further point in time when the combustion front has further propagated and moved even closer to the "toe" portion of the horizontal leg of the production well;
Figure 3 is a schematic partial cross-section through a hydrocarbon reservoir containing a hydrocarbon-containing formation, which shows a second embodiment of the method of the present invention, namely a production well and associated side entry injection well (not to scale) and further depicting the method of the present invention of causing a combustion front to propagate in the direction of the "toe" of the horizontal leg of the production well, at a point in time close to the time of ignition of the hydrocarbon and the initial propagation of the combustion front;
Figure 4 is a schematic partial cross-section through a hydrocarbon reservoir containing a hydrocarbon-containing formation, which shows a third preferred embodiment of the present invention, namely a cross-section through a production well (not to scale) employing the method of the present invention of causing a combustion front to propagate in the direction of the "toe" of the horizontal leg of the production well, at a point in time close to the ignition of the hydrocarbon and the initial propagation of the combustion front; and
Figure 5 is a perspective schematic view of an in situ recovery method of Figure 4 , showing the third and preferred embodiment of the method of the present invention for recovering hydrocarbons from a hydrocarbon reservoir.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0024] Figure 1A shows a schematic, semi-transparent view of an arrangement of wells utilized in the prior art for
in situ recovery of hydrocarbon from a subsurface hydrocarbon reservoir or formation
10.
[0025] Specifically, Figure 1A schematically depicts the prior art method
of in situ recovery of hydrocarbon disclosed in
US 5,626,191, comprising locating a series of production wells
12, each comprising a substantially vertical section
16 and a substantially horizontal leg
16, having a "toe" portion
18 and a "heel" portion
20. The horizontal leg
16 of production well
12 is located at a lower region of hydrocarbon formation
10, and is substantially porous to allow ingress of fluids. A series of injection wells
22 are provided, situated at a region proximate the "toe" and extending downwardly into the formation
10, with perforations in the upper reaches of the oil-bearing reservoir.
[0026] Figure 1B shows a schematic cross-section through an injection well
22 and associated production well 12 of Figure 1A.
[0027] In the prior art
in situ recovery process depicted in Figures 1A & B , an oxidizing gas 24, such as air (which contains oxygen), oxygen, or oxygen-enhanced air, is injected into the formation
10 via each of injection wells
22, so as to permit a portion of the hydrocarbon in formation
10 to be combusted. Specifically, a portion of the hydrocarbon in hydrocarbon formation
10 in the region of the injection well
22 when supplied with the oxidizing gas
26 is caused to be ignited and caused to combust, thereby forming and creating within formation
10 a substantially vertical and laterally-extending combustion front
26. Such combustion front
26, by way of heat conduction and creation of heated combusted gases within formation
10, heats hydrocarbons in the formation
10 directly ahead and in advance of combustion front
26, causing the more volatile hydrocarbon compounds in formation
10 to gasify and further cause upgrading of a portion of the hydrocarbon solids or bitumens in the formation simultaneously increasing their viscosity so as to create mobile liquefied hydrocarbons
30. The remaining heavier hydrocarbons, particularly coke, remain, which provide fuel for the advancing combustion front
26 and sustain the advance of the combustion front
26 and the
in situ combustion and hydrocarbon upgrading process. Then-mobile liquefied hydrocarbons
30 and gasified components (some of which may subsequently condense as liquids
30), then flow downwardly by action of gravity through the formation and are collected in a lowermost region of the formation
10 by flowing into horizontally-extending horizontal leg
16 of the production well
12. Horizontal leg
16 of production well
12 generally has, at least for a limited time, a gas pressure therein less than that of the formation
10 (due to removal of collected liquid hydrocarbons
30 as well as gaseous hydrocarbons therefrom), Such reduced gaseous pressure in horizontal leg
16 as opposed to within formation
10 in advance of combustion front
26 assists in liquid and gaseous hydrocarbon inflow from hydrocarbon formation
10 into the horizontal
leg 16. At other times, due to injection of medium
52 via injection tubing 50 (discussed below) into horizontal leg
16, horizontal leg
16 may at times may have a gaseous pressure close to, or even in excess of the gas pressure within formation
10.
[0028] Importantly, in the prior art method
of in situ recovery as shown in Figures 1A & B and described above, injection wells
22 are situated proximate the "toe" of the horizontal leg
16, and oxidizing gas injected into the formation at these locations via the injection wells
22. The combustion front
26 which receives oxidizing gas
24 is thus caused to progress outwardly from the injection well
22, and perpendicular to and along the horizontal wells
16 in a direction from the "toe" portion to the "heel" portion.
[0029] Disadvantageously with this prior art method, not only need a drilling pad 32 be created for the production well
12, but an additional and separate drilling pad need be created for the injection well
22, and such separate injection well
22 need be drilled into such formation. In addition, oxygen creation and injection equipment (not shown) must be hauled to and installed at the surface of such injection well
22, as such injection well is remote from the surface of production well
12. Both of such requirements add significantly to the cost of carrying out the prior art methods
of in situ recovery of hydrocarbons.
[0030] Figures 2A-2C herein show a modified (first)
in situ recovery process, which is expressly adapted to eliminate at least one of the above expenses in the prior art methods of
in situ hydrocarbon recovery, namely the expense of creating a separate drilling pad for the injection well
22.
[0031] Specifically, as seen in Figures 2A-2C, a single drilling pad 32 is created by way of clearing of trees and other obstacles, and a single drill platform erected thereon. A production well
12 is drilled using conventional drilling techniques, comprising a vertical section
14, and a further horizontal leg
22 in communication with vertical section
14. The horizontal leg
16 has a "toe" portion
18 and a "heel" portion
20 where it meets vertical section
14. The production well
12 is completed by the usual process of casing well
12, and further by the insertion within such production well
12 of production tubing
40, which extends downwardly in vertical section
14 to such heel portion
20 and preferably along the horizontal leg
16, preferably to toe portion
18 thereof, such production tubing
40 having an open end
42 within said horizontal leg
16. Production tubing
40 is typically coiled tubing as is conventionally used in drilling operations.
[0032] Additional injection tubing
50, likewise typically coiled tubing as is conventionally used in drilling operations, is further provided for injection of a medium
52 into production well
12, such medium
52 comprising a non-oxidizing gas, preferably carbon dioxide due to its diluent effect on hydrocarbons, or alternatively or in combination steam or water or other non-combustible flowable medium. As seen from Figures 2A-2C, injection tubing
50 extends into the "heel" portion
20 of horizontal leg
16. At least one isolation packer
54 is provided to allow medium
52 to be injected, if desired, in a pressurized state from time to time or continuously injected, so as to pressurize from time to time or continuously if desired, horizontal leg
16 to assist in forcing liquefied hydrocarbon
30 into production tubing 40 and inhibiting entry of oxidizing gas into the horizontal leg
16.
[0033] Using the single drilling pad
32, a further injection well
22 is drilled, extending into at least the upper region of the hydrocarbon formation
10. Injection well
22 typically has perforations
75 in a lower end thereof to permit infusion and injection of an oxidizing gas
24 such as air or oxygen into the hydrocarbon-containing region of hydrocarbon formation
10.
[0034] The method of the present invention, in the first embodiment shown in Figures 2A-2C, thereafter operates as follows:
Oxidizing gas 24 is injected into formation 10 via injection well 22. Advantageously, equipment (not shown) used to create oxidizing gas 24 and inject such oxidizing gas 24 need not be located remote from the production well 12, but instead can, by virtue of the method of the present invention, be located proximate to production well 12, and in particular if desired may be located on drilling pad 32 or closely proximate thereto, thereby eliminating the need for clearing and creating a separate drilling pad at a remote site such as would occur if the injection well 22 were located towards the "toe" of horizontal well 16. Also, operation and maintenance of the oxidizing gas supply equipment can conveniently be conducted at the oil-treating site located near well 12. Hydrocarbons proximate the injection well 22 are ignited, and due to the supply of oxidizing gas 24 ,a combustion front 26 is created, which in the method shown in Figures 2A-2C, advances as a substantially vertical laterally extending front (see also Fig. 5 herein) from the "heel" 20 of horizontal leg 16 towards the "toe" 18. Viscous and high viscosity hydrocarbons, including bitumen, in the hydrocarbon formation 10 in advance of the advancing combustion front 26, due to heat which is generated, are caused to upgrade and become liquid, and in the process become less viscous. Some hydrocarbons in the formation 10 in advance of the front 26 will gasify. Liquefied hydrocarbons 30 and gasified hydrocarbons, now being mobile, flow downwardly and into horizontal leg 16 which is made porous (ie has apertures 60 in an upper portion thereof) to permit infusion of such hydrocarbons 30 and thus collection of such hydrocarbons 30.
[0035] Such process continues as combustion front
26 progresses and thus "sweeps" from the "heel" portion
20 to the "toe"
18 of horizontal leg
16.
[0036] Notably, prior to generation of combustion front
26, hydrocarbon formation
10 is preferably initially preheated by injection of a heated non-oxidizing medium
52 such as steam, which is injected into the horizontal leg
16 of production well
12 via injection tubing
40, and removed via production tubing
50 or alternatively via annulus
80 in vertical section
16 if isolation packers
54 are not present. Pre-injection of a heated medium has the benefit of heating the production well
12 and its production components thereby increasing the flowability of liquefied hydrocarbons
30 which flow into horizontal leg
16 of production well
12. This procedure is useful in bitumen reservoirs because cold oil that may enter the horizontal leg
16 will be very viscous and will flow poorly, possible plugging the horizontal leg 16. For formations
10 with mobile oil, extensive pre-ignition steaming is not required for the purpose of heating the oil so that it will flow, however, it can be useful to reduce oil saturations near the oxidizing gas injection well
22 and to raise the hydrocarbon temperature to achieve ignition thereof. Other ignition methods may be employed such as the injection of easily ignitable fuels such as linseed oil, or by injection of hot combustion gas. For bitumen reservoirs, steam is also injected via injector well
22 and may also be injected into the reservoir
10 in the region between the injector well
22 and the toe
18 of the horizontal well
16 to warm the oil and increase its mobility prior to initiating injection of oxidizing gas
24 into the reservoir formation
10.
[0037] After initiation of combustion and combustion front
26, a non-oxidizing medium
52 in the form of steam, a non-oxidizing gas, carbon dioxide, or water, is injected, either continuously or sporadically via injection tubing
50 into horizontal leg
16, which due to isolation packers
54, can be pressurized. The purpose of such non-oxidizing medium
52 is for a number of reasons. Firstly, increased pressure within horizontal leg
16 reduces or prevents oxidizing gas
24 infusing into horizontal leg
16 from formation
10 which could otherwise detrimentally, in combination with liquefied and gaseous hydrocarbons therein, form an explosive mixture with potentially explosive consequences, or alternatively react with oxygen directly so as to form coke which could otherwise seal the horizontal leg
16 of production well
12. The consequence of having hydrocarbon (oil) and oxygen together in a wellbore is combustion and potentially an explosion with the attainment of high temperatures, perhaps in excess of 1000 °C. This can cause irreparable damage to the wellbore, including the failure of the sand retention screens (not shown). The presence of oxygen and wellbore temperatures over 425 °C. must be avoided for safe and continuous oil production operations. Secondly, injection of medium
52 can serve to pressurize horizontal leg
16 and assist in driving liquefied and gaseous hydrocarbons
30 collected in horizontal leg
16 into the open end
42 of production tubing
40, thereby assisting in drawdown of such liquids
30 and producing such hydrocarbons
30 from producing well
12. Thirdly, medium
52 when injected via injection tubing
50 can be heated. Advantageously, means for heating such medium
52 are, in this method, conveniently capable of being located at the surface of production well
12 and on or near drilling pad
32. Lastly, where the injected medium
52 is carbon dioxide, injection thereof into horizontal well
16 serves as not only a convenient carbon "sink" to allow disposal of such greenhouse gas, but further due to the diluent properties on carbon dioxide on liquid hydrocarbons
30, reduces the viscosity thereof and thus aids in the drawdown of collected liquid hydrocarbons
30 via production tubing
40.
[0038] As seen from Figures 2A-2C, during the advance of combustion front
26, coke is deposited in the reservoir
10 and serves as fuel for the
in situ combustion process. Hot combustion gases
70 advance into formation
10 heating the hydrocarbon therein and any connate water that is present. A portion of these hydrocarbons liquefies and such liquefied hydrocarbons
30 flow, along with combustion gases, into the horizontal leg
16 through the perforations
60, as shown in Figures 2A-2C. The liquefied hydrocarbons
30 flow along and to the "toe"
18 of horizontal leg
16 and enter the open end
42 of production tubing
40 therein, and flow back and then upward to the surface. The process is stable and continuous, with the combustion front
26 continuously advancing towards the "toe"
18 of the horizontal leg
16.
[0039] The oxidizing gas 24, typically air, oxygen or oxygen-enriched air, is injected into the upper part of the reservoir
10. Coke that was previously laid down consumes the oxygen so that only oxygen-free gases contact the oil ahead of the coke zone at the combustion front
26. Combustion gas temperatures of typically 600 °C. and as high as 1000 °C. are achieved from the high-temperature oxidation of the coke fuel. In the mobile oil zone
80 in advance of the combustion front 26, these hot gases 70 and steam heat the oil to over 400 °C, partially cracking the oil, vaporizing some components and greatly reducing the oil viscosity. The heaviest components of the oil, such as asphaltenes, remain on the rock and will constitute the coke fuel later when the combustion front
26 arrives at that location. In the mobile oil zone
80, gases and oil drain downward into the horizontal leg
16, drawn by gravity and at times by the low- pressure sink of the horizontal leg
16 when unpressurized. The coke zone at the combustion front
26 and the mobile oil zone
80 move laterally from the direction from the heel
20 towards the toe
18 of the horizontal well
16. The burned zone section
100 behind the combustion front is depleted of liquids (oil and water) and is filled with oxidizing gas
24. The section of the horizontal well
16 opposite this burned zone
100 is in jeopardy of receiving oxygen or oxidizing gas
24 which will combust the oil present inside horizontal well
16 creating extremely high wellbore temperatures that would damage the steel casing and especially the sand screens that are used to permit the entry of fluids
30 but exclude sand. If the sand screens fail, unconsolidated reservoir sand will enter the horizontal wellbore
16 and necessitate shutting for cleaning-out and remediation with cement plugs. This operation is very difficult and dangerous since the horizontal wellbore
16 can contain explosive levels of oil and oxygen.
[0040] The method of the present invention contemplates a number of ways to prevent influx of oxidizing gas
24 from the formation
10 into the horizontal leg
16. A first method is to reduce the injection rate of the oxidizing gas
24 in order to reduce the reservoir pressure in formation
10. A second method is to reduce the liquefied hydrocarbon
30 drawdown rate via the production tubing
40 (ie reduce the production rate via production tubing
40) to thereby increase wellbore pressure in horizontal leg
16. Both of these methods result in the reduction of hydrocarbon production rates, which is economically detrimental. An alternative and preferred method is that as described previously herein, namely the injection of non-oxidizing medium
52 into horizontal leg
16 via injection tubing
50, which is believed to have little effect on gravity draining of hydrocarbon liquids into horizontal well
16. In any event, such injection of medium
52 may be done periodically and only for a time sufficient to reduce concentrations of oxygen within horizontal leg
16 to less-than-explosive concentrations. In a typical operation, a thermocouple string can be placed along the horizontal section, or within, and the occurrence of elevated temperatures will signal the intrusion of oxidizing gas so that water of steam may be added via tubing 52 to reduce well-bore temperatures, dilute the oxygen present and increase wellbore pressure to inhibit further oxidizing gas entry.
[0041] Figure 3 schematically illustrates a further more preferable embodiment of the method of the present invention, having similar components to those identified in Figures 2A-2C, and having similar methodology. Again, an oxidizing gas in injected into formation
10 via injection well
22, and a combustion front
26 created which "sweeps" from heel
20 to toe
18 of horizontal leg
16, causing liquefied hydrocarbons
30 as well as gasified hydrocarbons to flow into horizontal leg
16 and be delivered to surface via production tubing 40.
[0042] Notably, however, the important and sole distinction in the method
of in situ recovery shown in Figure 3 over the method previously discussed and as shown in Figures 2A-2C is that injection well
22 in the method depicted in Figure 3 is formed as a side entry well from within vertical section
16 of production well
12.
[0043] Advantageously, using the method depicted in Figure 3, injection well
22 is less expensive to drill as an upper portion of such injection well has already been drilled as it is common with vertical section
16 of production well
12.
[0044] Accordingly, not only are cost savings realized in locating the injection well
22 at the location of and in close proximity to the production well
12 and its associated equipment and no separate drill pad
32 needed to be created, but in addition, well drilling costs are reduced when drilling injection well
22.
[0045] Figure 4 depicts a third and most preferred embodiment of the method of the present invention for carrying out
in situ recovery of hydrocarbon. Such method, like the first embodiment of the method of the present invention depicted in Figures 2A-2C, and like the second embodiment of the invention depicted in Figure 3, includes as an integral component of the method the creation of a combustion front 26 which "sweeps" from "heel"
20 to "toe"
18 of horizontal leg
16, thereby causing liquid hydrocarbons 30 to be collected in horizontal leg
16, and thereafter drawn down by production tubing
40 and produced to surface.
[0046] Importantly, however, in this third embodiment of the method of the present invention shown in Figure 4, there is no step of drilling an injection well
22. Instead, perforations
110 are made in the vertical section
16 of production well
12, and an oxidizing gas
24 injected into such vertical section
16 and thus into formation
10. Oxidizing gas
24 is prevented from injection into horizontal leg
16 by the presence of isolation packers
54 which effectively separate produced liquefied hydrocarbons in horizontal leg 16 from oxidizing gas
24 such as oxygen, thereby preventing formation of explosive mixtures. Injection tubing
50 still serves, like in earlier embodiments, to permit sporadic or continuous injection of non-oxidizing gas
52 into horizontal leg
16 to prevent oxidizing gas
24 within the burned zone
80 of the formation from permeating into horizontal leg
16.
[0047] Advantageously, using the method depicted in Figure 4, the cost of drilling an injection well
22 is completely eliminated. Accordingly, with the method depicted in Figure 4, not only are cost savings realized and environmental impact reduced in being able to have oxidizing injection apparatus at the production well and only on a single drill pad
32 at the production well which is otherwise the case in prior art methods which require creation of a separate drill pad and additional clearing for oxidizing gas creation and injection equipment (not shown), but in addition substantial cost savings are achieved by elimination the necessity to drill any injection well.
[0048] Figure 5 depicts how the method of Figure 4 (ie the third embodiment of the method of the present invention) may be deployed with a series of production wells
12 in a hydrocarbon formation
10, using a combustion front
26 which advances from "heel"
20 to "toe"
18.
1. A process for recovering liquefied or gasified hydrocarbon from an underground hydrocarbon reservoir (10) comprising the steps of:
(a) providing at least one production well having a substantially horizontal leg (16) positioned relatively low in said reservoir, said horizontal leg having at one end thereof a heel portion (20) and at an opposite end thereof a toe portion (18), said horizontal leg adapted to permit inflow of hydrocarbon into an interior of said horizontal leg, said production well having a substantially vertical section (14) connected to said horizontal leg proximate said heel portion thereof;
(b) providing production tubing (40) inside said production well extending within said vertical section and within at least a portion of said horizontal portion to collect said liquefied hydrocarbon which flows into said horizontal leg;
(c) injecting a medium into the production well, wherein said medium is selected from the group of mediums comprising alone or in combination, a non-oxidizing gas, steam, water, or carbon dioxide;
(d) supplying an oxidizing gas to said underground reservoir, at least initially at a location of, or proximate, said vertical section of said production well, wherein said step of supplying said oxidizing gas is accomplished by supplying said oxidizing gas to said hydrocarbon reservoir via perforations (75) in an injection well (22);
(e) igniting hydrocarbon within said hydrocarbon reservoir proximate said vertical section of said production well, so as to cause combustion of a portion of said hydrocarbon in said hydrocarbon reservoir proximate said vertical section and thereby create a combustion front which advances outwardly and away from said injection well in at least a direction along said horizontal leg and towards said toe portion thereof;
(f) causing heated hydrocarbon from said reservoir to drain from upper regions thereof and collect in said horizontal leg; and
(g) removing from the production well, via said production tubing, said hydrocarbon which has flowed into said horizontal leg.
2. The process of claim 1, wherein said vertical section of said production well and said injection well are one and the same.
3. The process of claim 1 wherein the injection well (22) is a side track re-entry of the vertical section of the production well, and extends into an upper region of the reservoir.
4. The process of claim 1 wherein the supply of oxidizing gas is accomplished by drilling an injection well proximate said vertical section of said production well, and said injection well is vertical, slanted, or horizontal.
5. The process of claim 1 wherein said vertical section of said production well is perforated in an upper part thereof to provide said perforations, and said step of supplying an oxidizing gas is achieved at least in part by supplying said oxidizing gas to said reservoir via said vertical section of said production well.
6. The process of claim 1 further comprising the steps of:
providing injection tubing (50) in said production well, said injection tubing extending downwardly in said vertical section to proximate said heel portion of said horizontal leg, and
said step of injecting said medium into said production well being conducted by injecting said medium via said injection tubing.
7. The process of claim 6 wherein an open end of the production tubing is situated in the vicinity of the toe portion of the horizontal leg.
8. The process of claim 1 wherein such medium further comprises a hydrocarbon condensate diluent.
9. The process of claim 3, 4, 6, 7, or 8 wherein said medium is injected continuously or periodically into said production well so as to maintain a positive pressure within the horizontal leg and thereby assist in preventing ingress of said oxidizing gas from the reservoir into the horizontal leg of the production well.
10. The process of any one of claims 1-8 wherein catalyst is placed in, on or around the horizontal leg of the production well.
11. The process of any one of claims 1-8 wherein the oxidizing gas is a mixture of oxygen and carbon dioxide.
12. The process of claim 6, further comprising the steps of:
providing injection tubing in said production well, said injection tubing extending downwardly in said vertical section to a position extending into at least said heel portion of said horizontal leg; and
supplying an oxidizing gas to said vertical section and thus to a portion of said hydrocarbon reservoir via said perforations in said vertical section.
13. The process of claim 12 wherein an open end of the production tubing is situated in the vicinity of the toe portion of the horizontal leg.
14. The process of claim 12 or 13 wherein steam or water are injected continuously or periodically into said injection tubing so as to maintain a positive pressure within the horizontal leg and thereby assist in preventing ingress of said oxidizing gas from the reservoir into the horizontal leg of the production well.
15. The process of claim 12, further comprising the steps of:
further providing an injection well as a side track re-entry from said vertical section of said production well, which side track injection well extends into the hydrocarbon formation; and
supplying an oxidizing gas to a portion of said hydrocarbon formation via said injection well and said side track re-entry injection well.
16. The process of claim 1 or 15 wherein steam or water is injected continuously or periodically into the horizontal leg of the production well so as to maintain a substantially positive pressure within the horizontal leg and thereby assist in preventing ingress of said oxidizing gas from the formation into the horizontal leg of the production well.
1. Ein Verfahren zur Gewinnung von verflüssigten oder gasförmigen Kohlenwasserstoffen aus einem unterirdischen Kohlenwasserstoff-Reservoir (10), umfassend die Schritte:
(a) Bereitstellung von wenigstens einer Förderbohrung mit einem im Wesentlichen horizontalen Schaft (16), der relativ weit unten in diesem Reservoir positioniert ist, wobei dieser horizontale Schaft an seinem einen Ende einen Fersenabschnitt (20) und an einem gegenüberliegenden Ende einen Zehenabschnitt (18) hat, wobei dieser horizontale Schaft das Einströmen von Kohlenwasserstoffen in das Innere des horizontalen Schafts erlaubt, wobei die Förderbohrung eine im Wesentlichen vertikale Sektion (14) hat, die mit dem horizontalen Schaft nahe bei dessen Fersenabschnitt verbunden ist;
(b) Bereitstellung von Bohrlochauskleidung (40) innerhalb der Förderbohrung, welche sich über die vertikale Sektion und über wenigstens einen Teil des horizontalen Abschnitts erstreckt, um die verflüssigten Kohlenwasserstoffe zu sammeln, die in den horizontalen Schaft einströmen;
(c) Injizieren eines Mediums in die Förderbohrung, wobei das Medium ausgewählt ist aus der Gruppe von Medien, die einzeln oder in Kombination ein nicht-oxidierendes Gas, Dampf, Wasser, oder Kohlendioxid enthalten;
(d) Einleiten eines oxidierenden Gases in das unterirdische Reservoir, zumindest zu Beginn am Ort oder in der Nähe der vertikalen Sektion der Förderbohrung, wobei dieser Schritt des Einleitens des oxidierenden Gases bewirkt wird durch das Einleiten des oxidierenden Gases in das Kohlenwasserstoff-Reservoir durch Perforationen (75) in einer Injektionsbohrung (22);
(e) Entzünden von Kohlenwasserstoffen innerhalb des KohlenwasserstoffReservoirs nahe bei der vertikalen Sektion der Förderbohrung, so dass ein Teil der Kohlenwasserstoffe in dem Kohlenwasserstoff-Reservoir nahe bei der vertikalen Sektion verbrennt und dadurch eine Verbrennungsfront erzeugt, die sich nach außen und weg von der Injektionsbohrung bewegt, in wenigstens einer Richtung entlang des horizontalen Schafts und in Richtung von dessen Zehenabschnitt;
(f) Bewirken eines Entweichens von erhitzten Kohlenwasserstoffen aus oberen Regionen des Reservoirs, die sich in dem horizontalen Schaft sammeln; und
(g) Entnahme der Kohlenwasserstoffe, die in den horizontalen Schaft eingeströmt sind, aus der Förderbohrung über die Bohrlochauskleidung.
2. Das Verfahren gemäß Anspruch 1, wobei die vertikale Sektion der Förderbohrung und die Injektionsbohrung ein und dasselbe sind.
3. Das Verfahren gemäß Anspruch 1, wobei die Injektionsbohrung (22) ein Nebenzugang der vertikalen Sektion der Förderbohrung ist, der sich in eine obere Region des Reservoirs erstreckt.
4. Das Verfahren gemäß Anspruch 1, wobei das Einleiten des oxidierenden Gases dadurch bewirkt wird, dass eine Injektionsbohrung nahe bei der vertikalen Sektion der Förderbohrung gebohrt wird, und dass diese Injektionsbohrung vertikal, schräg, oder horizontal verläuft.
5. Das Verfahren gemäß Anspruch 1, wobei die vertikale Sektion der Förderbohrung in ihrem oberen Teil perforiert ist um die Perforationen bereitzustellen, und der Schritt, bei dem ein oxidierendes Gas eingeleitet wird, zumindest teilweise dadurch erzielt wird, dass das oxidierende Gas durch diese vertikale Sektion der Förderbohrung hindurch in das Reservoir eingeleitet wird.
6. Das Verfahren gemäß Anspruch 1, des Weiteren umfassend die Schritte:
Bereitstellung eines Injektionsrohrs (50) in der Förderbohrung, wobei dieses Injektionsrohr sich in der vertikalen Sektion nach unten in die Nähe des Fersenabschnitts des horizontalen Schafts erstreckt, und
Durchführung des Schritts, bei dem das Medium in die Förderbohrung injiziert wird, durch Injektion des Mediums durch diese Injektionsrohr hindurch.
7. Das Verfahren gemäß Anspruch 6, wobei ein offenes Ende der Förderbohrung sich in der Nähe des Zehenabschnitts des horizontalen Schafts befindet.
8. Das Verfahren gemäß Anspruch 1, wobei das Medium des Weiteren einen Kohlenwasserstoffkondensat-Verdünner enthält.
9. Das Verfahren gemäß Anspruch 3, 4, 6, 7, oder 8, wobei das Medium kontinuierlich oder in Intervallen in die Förderbohrung injiziert wird, so dass ein positiver Druck innerhalb des horizontalen Schafts aufrechterhalten wird, um besser zu verhindern, dass das oxidierende Gas aus dem Reservoir in den horizontalen Schaft der Förderbohrung gelangt.
10. Das Verfahren gemäß irgendeinem der Ansprüche 1 bis 8, wobei ein Katalysator in, auf, oder um den horizontalen Schaft der Förderbohrung platziert wird.
11. Das Verfahren gemäß irgendeinem der Ansprüche 1 bis 8, wobei das oxidierende Gas eine Mischung aus Sauerstoff und Kohlendioxid ist.
12. Das Verfahren gemäß Anspruch 6, des Weiteren umfassend die Schritte:
Bereitstellung eines Injektionsrohrs in der Förderbohrung, wobei dieses Injektionsrohr sich in der vertikalen Sektion nach unten bis mindestens zu einer Stelle erstreckt, die sich innerhalb des Fersenabschnitts des horizontalen Schafts befindet; und
Einleiten eines oxidierenden Gases in diese vertikale Sektion und somit in einen Teil des Kohlenwasserstoffreservoirs durch die Perforationen in der vertikalen Sektion hindurch.
13. Das Verfahren gemäß Anspruch 12, wobei ein offenes Ende der Förderbohrungsauskleidung sich in der Nähe des Zehenabschnitts des horizontalen Schafts befindet.
14. Das Verfahren gemäß Anspruch 12 oder 13, wobei Dampf oder Wasser kontinuierlich oder in Intervallen in das Injektionsrohr injiziert werden, so dass ein positiver Druck innerhalb des horizontalen Schafts aufrechterhalten wird, um besser zu verhindern, dass das oxidierende Gas aus dem Reservoir in den horizontalen Schaft der Förderbohrung gelangt.
15. Das Verfahren gemäß Anspruch 12, des Weiteren umfassend die Schritte:
Bereitstellung einer zusätzlichen Injektionsbohrung als Nebenzugang ausgehend von der vertikalen Sektion der Förderbohrung, wobei sich diese Nebenzugangs-Injektionsbohrung in die Kohlenwasserstoffansammlung erstreckt; und
Einleiten eines oxidierenden Gases in einen Teil der Kohlenwasserstoffansammlung durch die Injektionsbohrung und durch die Nebenzugangs-Inj ektionsbohrung.
16. Das Verfahren gemäß Anspruch 1 oder 15, wobei Dampf oder Wasser kontinuierlich oder in Intervallen in das Injektionsrohr injiziert werden, so dass ein im Wesentlichen positiver Druck innerhalb des horizontalen Schafts aufrechterhalten wird, um besser zu verhindern, dass das oxidierende Gas aus der Ansammlung in den horizontalen Schaft der Förderbohrung gelangt.
1. Procédé pour récupérer un hydrocarbure liquéfié ou gazéifié à partir d'un réservoir d'hydrocarbure souterrain (10), comportant les étapes consistant à :
(a) fournir au moins un puits de production ayant une branche sensiblement horizontale (16) positionnée relativement bas dans ledit réservoir, ladite branche horizontale ayant, à l'une de ses extrémités, une partie de talon (20) et, à une extrémité opposée de celle-ci, une partie de pointe (18), ladite branche horizontale étant adaptée pour permettre un écoulement d'entrée d'hydrocarbure à l'intérieur de ladite branche horizontale, ledit puits de production ayant un tronçon sensiblement vertical (14) relié à ladite branche horizontale à proximité de ladite partie de talon de celui-ci,
(b) fournir un tube de production (40) à l'intérieur dudit puits de production s'étendant à l'intérieur dudit tronçon vertical et à l'intérieur d'au moins une partie de ladite partie horizontale pour recueillir ledit hydrocarbure liquéfié qui s'écoule dans ladite branche horizontale,
(c) injecter un fluide dans le puits de production, ledit fluide étant choisi parmi le groupe constitué de fluides comportant, seul ou en combinaison, un gaz non-oxydant, de la vapeur, de l'eau ou du dioxyde de carbone,
(d) fournir un gaz oxydant audit réservoir souterrain, au moins initialement à un emplacement ou à proximité dudit tronçon vertical dudit puits de production, dans lequel ladite étape de fourniture dudit gaz oxydant est réalisée en fournissant ledit gaz oxydant audit réservoir d'hydrocarbure via des perforations (75) dans un puits d'injection (22),
(e) enflammer l'hydrocarbure à l'intérieur dudit réservoir d'hydrocarbure à proximité dudit tronçon vertical dudit puits de production, de manière à entraîner une combustion d'une partie dudit hydrocarbure dans ledit réservoir d'hydrocarbure à proximité dudit tronçon vertical et créer ainsi un front de combustion qui progresse vers l'extérieur et en s'éloignant dudit puits d'injection dans au moins une direction le long de ladite branche horizontale et vers ladite partie de pointe de celui-ci,
(f) amener l'hydrocarbure chauffé provenant dudit réservoir à s'évacuer de régions supérieures de celui-ci et le recueillir dans ladite branche horizontale, et
(g) retirer du puits de production, via ledit tube de production, ledit hydrocarbure qui s'est écoulé dans ladite branche horizontale.
2. Procédé selon la revendication 1, dans lequel ledit tronçon vertical dudit puits de production et ledit puits d'injection sont un seul et même puits.
3. Procédé selon la revendication 1, dans lequel le puits l'injection (22) est une déviation du tronçon vertical du puits de production, et s'étend dans une région supérieure du réservoir.
4. Procédé selon la revendication 1, dans lequel la fourniture du gaz oxydant est réalisée en forant un puits d'injection à proximité dudit tronçon vertical dudit puits de production, et ledit puits d'injection est vertical, oblique ou horizontal.
5. Procédé selon la revendication 1, dans lequel ledit tronçon vertical dudit puits de production est perforé dans une partie supérieure de celui-ci pour fournir lesdites perforations, et ladite étape de fourniture d'un gaz oxydant est réalisée au moins en partie en fournissant ledit gaz oxydant audit réservoir via ledit tronçon vertical dudit puits de production.
6. Procédé selon la revendication 1, comportant en outre l'étape consistant à :
fournir un tube d'injection (50) dans ledit puits de production, ledit tube d'injection s'étendant vers le bas dans ledit tronçon vertical jusqu'à proximité de ladite partie de talon de ladite branche horizontale, et
ladite étape d'injection dudit fluide dans ledit puits de production étant réalisée en injectant ledit fluide via ledit tube d'injection.
7. Procédé selon la revendication 6, dans lequel une extrémité ouverte du tube de production est située au voisinage de la partie de pointe de la branche horizontale.
8. Procédé selon la revendication 1, dans lequel ce fluide comporte en outre un diluant de condensat d'hydrocarbure.
9. Procédé selon la revendication 3, 4, 6, 7 ou 8, dans lequel ledit fluide est injecté de manière continue ou périodique dans ledit puits de production de manière à maintenir une pression positive à l'intérieur de la branche horizontale et contribuer ainsi à empêcher l'entrée dudit gaz oxydant provenant du réservoir dans la branche horizontale du puits de production.
10. Procédé selon l'une quelconque des revendications 1 à 8, dans lequel un catalyseur est placé dans, sur ou autour de la branche horizontale du puits de production.
11. Procédé selon l'une quelconque des revendications 1 à 8, dans lequel le gaz oxydant est un mélange d'oxygène et de dioxyde de carbone.
12. Procédé selon la revendication 6, comportant en outre les étapes consistant à :
fournir un tube d'injection dans ledit puits de production, ledit tube d'injection s'étendant vers le bas dans ledit tronçon vertical jusqu'à une position s'étendant dans au moins ladite partie de talon de ladite branche horizontale, et
fournir un gaz oxydant audit tronçon vertical et ainsi à une partie dudit réservoir d'hydrocarbure via lesdites perforations dans ledit tronçon vertical.
13. Procédé selon la revendication 12, dans lequel une extrémité ouverte du tube de production est située au voisinage de la partie de pointe de la branche horizontale.
14. Procédé selon la revendication 12 ou 13, dans lequel de la vapeur ou de l'eau est injectée de manière continue ou périodique dans ledit tube d'injection de manière à maintenir une pression positive à l'intérieur de la branche horizontale et contribuer ainsi à empêcher l'entrée dudit gaz oxydant provenant du réservoir dans la branche horizontale du puits de production.
15. Procédé selon la revendication 12, comportant en outre les étapes consistant à:
fournir également un puits d'injection sous la forme d'une déviation dudit tronçon vertical dudit puits de production, lequel puits d'injection dévié s'étend dans la formation d'hydrocarbure, et
fournir un gaz oxydant à une partie de ladite formation d'hydrocarbure via ledit puits d'injection et ledit puits d'injection dévié.
16. Procédé selon la revendication 1 ou 15, dans lequel de la vapeur ou de l'eau est injectée de manière continue ou périodique dans la branche horizontale du puits de production de manière à maintenir une pression sensiblement positive à l'intérieur de la branche horizontale et contribuer ainsi à empêcher l'entrée dudit gaz oxydant provenant de la formation dans la branche horizontale du puits de production.