Method and system for recovering and processing hydrocarbon mixture

Abstract

A steam-based method and system for recovering and processing a hydrocarbon mixture from a subterranean formation. Steam is injected into the subterranean formation to mobilize said hydrocarbon mixture, then the mobilized hydrocarbon mixture is recovered, a self-sufficient diluent is added, and the mixture is separated to produce separated water and separated hydrocarbon. The separated hydrocarbon is deasphalted to produce a deasphalted hydrocarbon and asphaltenes, which is combusted in an oxycombustion process to generate steam and/or energy and CO.sub.2, and said the steam is injected into the formation.

Claims

1. A steam based method of recovering and processing a hydrocarbon mixture from a subterranean formation, comprising: (i) injecting steam into said formation to mobilise said hydrocarbon mixture; (ii) recovering said mobilised hydrocarbon mixture, wherein said mobilised hydrocarbon mixture comprises water and hydrocarbon; (iii) separating said hydrocarbon mixture to produce separated water and separated hydrocarbon, wherein a first diluent is added to said mobilised hydrocarbon mixture prior to said separation; (iv) fractionating said separated hydrocarbon to produce at least one heavier fraction and at least one lighter fraction; (v) deasphalting said heavier fraction to produce a deasphalted hydrocarbon and asphaltenes; (vi) adding a second diluent to said deasphalted hydrocarbon; (vii) combusting said asphaltenes in an oxycombustion process to generate steam and CO.sub.2; and (viii) injecting said steam produced in step (vii) into said formation, wherein said method is at least partially self-sufficient in terms of steam generation, and wherein at least some of said first and second diluent for addition to said mobilised hydrocarbon mixture and to said deasphalted hydrocarbon comprises said lighter fraction obtained directly during fractionation.

2. The method of claim 1, wherein said lighter fraction comprises naphtha, kerosene and light gas oils.

3. The method of claim 1, wherein said deasphalting is solvent deasphalting.

4. The method of claim 3, wherein said method is at least partially self-sufficient in terms of solvent for deasphalting.

5. The method of claim 4, wherein the solvent used in said deasphalting is said lighter fraction obtained directly during fractionating.

6. The method of claim 5, wherein the lighter fraction comprises propane, butane, pentane, hexane, or mixtures thereof.

7. The method of claim 1, wherein the solvent used in said deasphalting is CO.sub.2 generated during the generation of steam or during oxycombustion.

8. The method of claim 1, wherein at least a portion of the CO.sub.2 produced during said oxycombustion is captured and stored.

9. The method of claim 1, wherein at least a portion of the CO.sub.2 generated during steam generation is captured and stored.

10. The method of claim 1, further comprising upgrading said deasphalted hydrocarbon.

11. The method of claim 10, wherein said upgrading comprises thermal visbreaking.

12. The method of claim 10, wherein said upgrading comprises thermal cracking.

13. The method of claim 10, comprising adding a third diluent to said upgraded hydrocarbon.

14. The method of claim 13, wherein said method is at least partially self-sufficient in terms of said third diluent.

15. The method of claim 13, wherein said third diluent comprises a lighter fraction obtained directly during fractionating.

16. The method of claim 15, wherein said lighter fraction comprises naphtha, kerosene, light gas oils, or mixtures thereof.

17. The method of claim 1, comprising: (i) injecting steam into said formation to mobilise said hydrocarbon mixture; (ii) recovering said mobilised hydrocarbon mixture, wherein said mobilised hydrocarbon mixture comprises water and hydrocarbon; (iii) separating said hydrocarbon mixture to produce separated water and separated hydrocarbon, wherein said first diluent is added to said mobilised hydrocarbon mixture prior to said separation; (iv) fractionating said separated hydrocarbon to produce at least one heavier fraction and at least one lighter fraction; (v) deasphalting said heavier fraction to produce a deasphalted hydrocarbon and asphaltenes; (vi) adding said second diluent to said deasphalted hydrocarbon; (vii) combusting said asphaltenes in an oxycombustion process to generate steam and CO.sub.2; (viii) upgrading said deasphalted hydrocarbon to produce upgraded hydrocarbon; (ix) adding a third diluent to said upgraded hydrocarbon; and (x) injecting said steam produced in step (vii) into said formation, wherein said method is at least partially self-sufficient in terms of steam generation, and wherein at least some of said first, second and third diluent for addition to said mobilized hydrocarbon mixture, said deasphalted hydrocarbon and said upgraded hydrocarbon comprises said lighter fraction obtained directly during fractionation.

18. The method of claim 17, wherein said oxycombustion process in step (vii) generates energy, wherein said energy is applied to generate steam, and wherein said steam is injected into said formation.

19. The method of claim 1, wherein said separated water is cleaned and recycled for steam generation.

20. The method of claim 19, wherein said separated water is converted to steam using energy generated in said oxycombustion.

21. The method of claim 1, which is at least partially self-sufficient in terms of water for steam generation.

22. The method of claim 1, wherein said oxycombustion process in step (vii) generates energy, wherein said energy is applied to generate steam, and wherein said steam is injected into said formation.

23. A system for recovering and processing a hydrocarbon mixture, comprising: (a) a well arrangement for recovering said hydrocarbon mixture comprising a production well; (b) a separator for separating said recovered hydrocarbon mixture into separated water and separated hydrocarbon, said separator having an inlet fluidly connected to said well arrangement, an outlet for separated hydrocarbon fluidly connected to said fractionator and an outlet for separated water; (c) a fractionator having an inlet for separated hydrocarbon connected to said separator, an outlet for a heavier fraction fluidly connected to said deasphalter unit and an outlet for at least one lighter fraction; (d) a deasphalter unit fluidly connected to said fractionator and having an outlet for deasphalted hydrocarbon and an outlet for asphaltenes; (e) a diluent addition tank having an inlet fluidly connected to said deasphalter unit, an inlet for diluent and an outlet for syncrude; (f) an oxycombustion unit fluidly connected to said outlet for asphaltenes of said deasphalter and having an outlet for steam; (g) a first line for transporting steam generated by said oxycombustion unit to said well arrangement; (h) a second line for transporting said at least one lighter fraction from said fractionator directly to said separator or to the line transporting recovered hydrocarbon mixture to said separator; and (i) a third line for transporting said at least one lighter fraction from said fractionator directly to the inlet of said diluent addition tank.

24. The system of claim 23, wherein said outlet for separated water is fluidly connected to a water treatment unit for cleaning water for steam generation.

25. The system of claim 23, further comprising a fourth line for transporting at least one lighter fraction from said fractionator directly to said deasphalter unit.

26. The system of claim 23, further comprising a CO.sub.2 purifier having an inlet fluidly connected to said oxycombustion unit and an outlet connected to a subterranean formation for CO.sub.2 storage.

27. The system of claim 26, wherein said CO.sub.2 purifier further comprises an inlet fluidly connected to a steam generator.

28. The system of claim 23, further comprising a visbreaker having an inlet fluidly connected to said deasphalter unit or said diluent addition tank.

29. The system of claim 23, further comprising a thermal cracker having an inlet fluidly connected to said deasphalter unit or said diluent addition tank.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic view of a cross section of an oil-bearing formation with SAGD well pairs suitable for carrying out the method of the invention;

(2) FIG. 2 is a flow diagram of a method and system of the invention showing the flow of each of steam, diluent, CO.sub.2 and water; and

(3) FIG. 3 is a flow diagram of preferred downstream processing methods for the deasphalted hydrocarbon obtained during the method of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(4) Referring to FIG. 1 it shows a cross section of a reservoir comprising SAGD well pairs. FIG. 1 shows the reservoir shortly after SAGD is started. A covering of overburden 1 lies above the hydrocarbon-containing portion of the reservoir 2. Each SAGD well pair 3, 4 comprises an injector well 5, 6 and a producer well 7, 8. The vertical separation (arrow A) between each well pair is about 5 m. The horizontal separation (arrow B) between each well pair is about 100 m. The injector wells 5, 6 are at the same depth in the reservoir and are parallel to each other. Similarly the producer wells 7, 8 are at the same depth in the reservoir and are parallel to each other. The producer wells are preferably provided with a liner (not shown) as is conventional in the art.

(5) In FIG. 1 steam has been injected into injector wells 5, 6 thus heated areas 9, 10 around each of the injector wells have been formed. In these areas the latent heat from the steam is transferred to the hydrocarbon and, under gravity, it drains downwards to producer wells 7, 8. From producer wells 7, 8 the mobilised hydrocarbon is pumped to the surface.

(6) Referring to FIG. 2 it shows the flow of each of steam, water, diluent and CO.sub.2 through the method and system of the invention.

(7) Considering first the flow of steam and water, initially steam is generated from natural gas by conventional methods (arrow a). The steam is injected via the injection wells of SAGD well pairs into a subterranean formation (arrow b) as described above in relation to FIG. 1. The steam mobilises heavy hydrocarbon present in the formation and heavy hydrocarbon is recovered at the surface from producer wells (arrow c). The mobilised hydrocarbon comprises a mixture of water and hydrocarbon and is routed to a bulk separator wherein the water and hydrocarbon are separated. Diluent is added to the mixture prior to its entry to the separator (arrow n). The separated water is collected (arrow d) and sent to a treatment facility for cleaning so it can be reused for further steam generation (arrow e). The separated hydrocarbon is transported to a fractionator (arrow f) wherein naphtha, kerosene, light gas oils and heavy gas oils are removed (arrow g). The remaining hydrocarbon mixture (i.e. heavier fraction) is transported to a deasphalting unit (arrow h) wherein solvent deasphalting takes place. The deasphalting process produces deasphalted hydrocarbon that is transported out of the deasphalter (arrow i) and asphaltenes that are transported to an oxycombustion unit (arrow j). Oxycombustion of the asphaltenes generates steam for use in hydrocarbon recovery and/or energy that is used to generate further steam (arrow k). Preferably the energy generated is used to convert the separated water from the separator into steam (arrow o). The method of the invention is advantageous because some of the energy inherently present in the hydrocarbon recovered is used to fuel the generation of steam for further hydrocarbon recovery. In this sense the method is at least partially self-supporting in terms of steam-generation.

(8) Considering now the flow of diluent through the method, as described above, the separated hydrocarbon is transported to a fractionator wherein a lighter fraction comprising naphtha, light gas oils and heavy gas oils is removed (arrow g). The naphtha and/or middle distillate obtained is used as the diluent that is added to the mixture of hydrocarbon and water prior to its entry to the separator (arrow n). Optionally the lighter fraction may also be used as the solvent in the deasphalting process (arrow l). Moreover the naphtha, kerosene, light gas oils and heavy gas oils obtained from the fractionator is used as a diluent for the deasphalted hydrocarbon mixture (arrow m). The recycling of the naphtha, kerosene, light gas oil and/or heavy gas oil from the heavy hydrocarbon for these purposes is highly advantageous. It avoids the need to transport and store an external diluent specifically for these purposes. Additionally because the diluent is generated from the hydrocarbon mixture into which it is being reintroduced, it is unlikely to cause any instability problems. A further advantage of the method is the compounds present in the heavy hydrocarbon are used in its processing. As above therefore, the method is at least partially self-supporting in terms of production of solvent for solvent deasphalting and/or diluent for addition to crude hydrocarbon mixture and optionally production of syncrude.

(9) Considering now the flow of CO.sub.2 through the method, CO.sub.2 is generated at several points, namely during conversion of natural gas to steam, during oxycombustion of asphaltenes and, in some cases, during upgrading of the deasphalted hydrocarbon mixture. The CO.sub.2 is captured and transported (arrows y, z) to a purifier where it is cleaned. The CO.sub.2 is then pressurised, condensed and pumped to available CO.sub.2 subterranean formation sites (arrow x). A further advantage of the method of the invention is that less CO.sub.2 is released to the atmosphere than in traditional SAGD based processes.

(10) Referring to FIG. 3, it shows a flow diagram of preferred processing methods for the deasphalted hydrocarbon produced in the method of the invention. In one preferred method the deasphalted hydrocarbon is transported to a diluent addition tank (arrow (i)) wherein the hydrocarbon mixture is blended with diluent to produce syncrude (arrow (ii)). As discussed above, the diluent added to the hydrocarbon is preferably obtained from the fractionation carried out on the crude hydrocarbon mixture. In another preferred method the deasphalted hydrocarbon is upgraded in a thermal visbreaker (arrow (iii)). In a typical process the hydrocarbon mixture is heated to 400-500 C. and then transferred to a soaking vessel to soak for 5 to 30 minutes. The resulting upgraded hydrocarbon may be transportable (arrow (iv)) or may be blended with diluent in the diluent addition tank (arrow (v)) to generate syncrude (arrow (ii)). In a further preferred method the deasphalted hydrocarbon is upgraded in a thermal cracker (arrow (vi)). In a typical process the deasphalted hydrocarbon mixture is heated to a temperature of 300-450 C. in the presence of an elevated partial pressure of hydrogen of 100-200 bar and in the presence of a catalyst. A typical residence time may be 0.5 to 2 hours. The resulting upgraded hydrocarbon may be transportable (arrow (vii)) or may be blended with diluent to the diluent addition tank (arrow (viii)) to generate syncrude (arrow (ii)).

(11) The method of the present invention has several advantages including: Oxycombustion of asphaltenes obtained from the hydrocarbon mixture generates steam and/or energy for generation of steam for use in further hydrocarbon recovery Water for steam generation can be recycled by separating out and cleaning the water produced from the hydrocarbon formation along with the hydrocarbon mixture Fractionation of the hydrocarbon mixture produces a lighter fraction, e.g. naphtha and/or light gas oils, that can be used as solvent in the deasphalting process and/or as diluent for the deasphalted hydrocarbon, e.g. in the generation of syncrude Fractionation of the hydrocarbon mixture produces a lighter fraction, e.g. naphtha and/or light gas oils, that can be used as diluent for the crude heavy hydrocarbon mixture to improve the separation process. Little, if any, CO.sub.2 is released to the atmosphere. Instead the CO.sub.2 is captured and stored in a formation.
The method of the invention is therefore at least partially self-supporting. The hydrocarbon mixture recovered from the subterranean formation provides solvent for deasphalting, diluent for the generation of syncrude as well as at least some of the water and steam and/or energy required for steam generation for the hydrocarbon recovery.