Abstract:
A process and system which integrates on-site heavy oil or bitumen upgrading and energy recovery for steam production with steam-assisted gravity drainage (SAGD) production of the heavy oil or bitumen. The heavy oil or bitumen produced by SAGD is flashed to remove the gas oil fraction, and the residue is solvent deasphalted to obtain deasphalted oil, which is mixed with the gas oil fraction to form a pumpable synthetic crude. The synthetic crude has an improvement of 4-5 degrees of API and lower in sulfur, nitrogen and metal compounds. The synthetic crude is not only more valuable than the heavy oil or bitumen, but also has substantial economic advantage of reducing the diluent requirement since it has lower viscosity than the heavy oil or bitumen. The asphaltenes, following an optional pelletizing and/or slurrying step, are used as a fuel for combustion in boilers near the steam injection wells for injection into the heavy oil or bitumen reservoir. This eliminates the need for natural gas or other fuel to produce steam at reservoir location and thus improves the economics of the heavy oil or bitumen production substantially. Alternatively, the asphaltenes are used as a feedstock for gasification to produce injection steam, synthesis gas. The CO 2  could be used as additive with injection steam to enhance the performance of SAGD and the hydrogen could be exported to nearby processing facility. The invention upgrades the heavy oil or bitumen to a synthetic crude of improved value that can be pipelined with reduced amount of diluent, while at the same time using the asphaltene fraction of the residue for combustion to fulfill the energy requirements for generating injection steam for SAGD.

Description:
FIELD OF THE INVENTION 
     This invention relates to recovering a pumpable crude oil from a reservoir of heavy oil or bitumen by the steam-assisted gravity drainage (SAGD) process, and more particularly to solvent deasphalting to remove an asphaltene fraction from the heavy oil or bitumen to yield the pumpable synthetic crude, and to combusting the asphaltene fraction to supply heat for generation of the injection steam. 
     BACKGROUND 
     Heavy oil reservoirs contain crude petroleum having an API gravity less than about 10 which is unable to flow from the reservoir by normal natural drive primary recovery methods. These reservoirs are difficult to produce due to very high petroleum viscosity and little or no gas drive. Bitumen, usually as tar sands, occur in many places around the world. 
     The steam-assisted gravity drainage (SAGD) process is commonly used to produce heavy oil and bitumen reservoirs. This generally involves injection of steam into an upper horizontal well through the reservoir to generate a steam chest that heats the petroleum to reduce the viscosity and make it flowable. Production of the heavy oil or bitumen is from a lower horizontal well through the reservoir disposed below the upper horizontal well. 
     Representative references directed to the production of crude petroleum from tar sands include Canadian Patent Application 2,069,515 by Kovalsky; U.S. Pat. No. 5,046,559 to Glandt; U.S. Pat. No. 5,318,124 to Ong et al; U.S. Pat. No. 5,215,146 to Sanchez; and Good, “Shell/Aostra Peace River Horizontal Well Demonstration Project,” 6 th  UNITAR Conference on Heavy Crude and Tar Sands (1995), all of which are hereby incorporated herein by reference. Most of this technology has been directed to improving reservoir production characteristics. Surprisingly, very little attention has been directed to incorporating on-site downstream processing into the upstream field processing of the heavy oil or bitumen for improving the efficiency of operation and overall field production economy. 
     The heavy oil or bitumen produced by the SAGD and similar methods requires large amounts of steam generated at the surface, typically at a steam-to-oil ratio (SOR) of 2:1, i.e. 2 volumes of water have to be converted to injection steam for each volume of petroleum that is produced. Usually natural gas is used as the fuel source for firing the steam boilers. It is very expensive to supply the natural gas to the boilers located near the injection wells, not to mention the cost of the natural gas itself. 
     Another problem is that when the heavy oil or bitumen is produced at the surface, it has a very high viscosity that makes it difficult to transport and store. It must be kept at an elevated temperature to remain flowable, and/or is sometimes mixed with a lighter hydrocarbon diluent for pipeline transportation. The diluent is expensive and additional cost is incurred to transport it to the geographically remote location of the production. Furthermore, aspahaltenes frequently deposit in the pipelines through which the diluent/petroleum mixture is transported. 
     There is an unmet need in the art for a way to reduce the cost of steam generation and the cost and problems associated with heavy oil and/or bitumen surface processing and transporting. The present invention is directed to these unfulfilled needs in the art of SAGD and similar heavy oil and/or bitumen production. 
     SUMMARY OF THE INVENTION 
     The present invention provides a process and systems for producing heavy oil or bitumen economically by steam-assisted gravity drainage (SAGD), upgrading the heavy oil or bitumen into a synthetic crude, and using the bottom of the barrel to produce steam for injection into the reservoir. 
     Broadly, the present invention provides a process for recovering a pumpable synthetic crude oil from a subterranean reservoir of heavy oil or bitumen, comprising the steps of: (a) injecting steam through at least one injection well completed in communication with the reservoir to mobilize the heavy oil or bitumen; (b) producing the mobilized heavy oil or bitumen from at least one production well completed in the reservoir; (c) fractionating the heavy oil or bitumen produced from step (b) at a location adjacent to the reservoir into a first fraction as a minor amount of the heavy crude comprising a gas oil fraction and second fraction comprising a residue; (d) solvent deasphalting the second fraction from step (c) to form an asphaltene fraction and a deasphalted oil fraction essentially free of asphaltenes; (e) combusting the asphaltene fraction from step (d) to produce the steam for injection step (a); and (e) blending the first fraction from step (c) with the deasphalted oil fraction from step (d) to form a pumpable synthetic crude oil. The fractionation is preferably performed under atmospheric pressure. The asphaltene fraction from step (d) can be supplied as a liquid to the combustion step (e), or alternatively the asphaltene fraction from step (d) can be pelletized to obtain asphaltene pellets for supply to the combustion step (e). 
     The combustion step (e) preferably comprises combustion of the asphaltenes in a boiler to produce the injection steam for step (a). By this process, the solvent deasphalting step (d) can be performed at a first location to which the produced heavy oil or bitumen is transported, and the asphaltene fraction can be transported from the first location to a plurality of boilers spaced away from the first location, preferably adjacent to the injection well or wells. The boiler is preferably a circulating fluid bed boiler. 
     In an alternate embodiment, the combustion step (e) comprises gasification of the asphaltene fraction to produce a synthesis gas and the injection steam for step (a). The process can include recovering CO 2  from the synthesis gas and injecting the CO 2  into the reservoir. A portion of the steam produced from gasification can be expanded in a turbine to generate electricity. 
     Another aspect of the invention is a process for recovering a pumpable crude oil from a subterranean reservoir of heavy oil or bitumen. The process comprises the steps of: (a) injecting steam through one or more injection wells completed in communication with the reservoir to mobilize the heavy oil or bitumen; (b) producing the mobilized heavy oil or bitumen from at least one production well completed in the reservoir; (c) solvent deasphalting at least a portion of the heavy oil or bitumen produced from step (b) to form an asphaltene fraction and a deasphalted oil fraction essentially free of asphaltenes; (d) pelletizing the asphaltene fraction from step (c) to obtain asphaltene pellets; and (e) combusting the asphaltene pellets from step (d) to produce the steam for injection step (a). The combustion step (e) in one embodiment comprises combustion in at least one boiler to produce the injection steam for step (a). In one embodiment, the solvent deasphalting step (d) is preferably performed at a first location and the asphaltene fraction is transported from the first location to a plurality of boilers spaced away from the first location adjacent to the one or more injection wells. The at least one boiler is preferably a circulating fluid bed boiler. In an alternate embodiment, the combustion step (e) comprises gasification of the asphaltene pellets to produce a synthesis gas and the injection steam for step (a). The process can include the steps of recovering CO 2  from the synthesis gas and injecting the CO 2  into the reservoir with the steam. A portion of the steam generated from gasification can be expanded in a turbine to generate electricity. 
     Another aspect of the invention is the provision of a system for producing a pumpable synthetic crude oil. The system includes a subterranean reservoir of heavy oil or bitumen; at least one injection well completed in the reservoir for injecting steam into the reservoir to mobilize the heavy oil or bitumen; at least one production well completed in the reservoir for producing the mobilized heavy oil or bitumen; an atmospheric flash unit for fractionating the heavy oil or bitumen produced from the at least one production well into a minor portion comprising a gas oil fraction and a major portion comprising a residue fraction; a solvent deasphalting unit for separating the residue fraction into a minor portion comprising an asphaltene fraction and a major portion comprising a deasphalted oil fraction essentially free of asphaltenes; mixing apparatus for mixing the gas oil fraction and the deasphalted oil fraction to form a pumpable synthetic crude; a pelletizer for palletizing the asphaltene fraction into solid pellets; at least one boiler for combustion of the asphaltene pellets to generate the injection steam; and at least one line for supplying the steam from the at least one boiler to the at least one injection well. 
     A further aspect of the invention is the provision of a process for recovering a pumpable crude oil from a subterranean reservoir of heavy oil or bitumen. The process comprises the steps of: (a) injecting steam through one or more injection wells completed in communication with the reservoir to mobilize the heavy oil or bitumen; (b) producing the mobilized heavy oil or bitumen from at least one production well completed in the reservoir; (c) solvent deasphalting a first portion of the heavy oil or bitumen at a location adjacent to the reservoir to form an asphaltene fraction and a deasphalted oil fraction essentially free of asphaltenes; (d) combusting the asphaltene fraction from step (c) to produce the steam for injection step (a); (e) blending a second portion of the heavy oil or bitumen with the deasphalted oil fraction from step (c) to form a pumpable synthetic crude oil; and (g) pipelining the synthetic crude oil to a location remote from the reservoir. 
     In another aspect, the present invention provides a system for producing a pumpable synthetic crude oil. The system includes a subterranean reservoir of heavy oil or bitumen, at least one injection well completed in the reservoir for injecting steam into the reservoir to mobilize the heavy oil or bitumen, and at least one production well completed in the reservoir for producing the mobilized heavy oil or bitumen. An atmospheric flash unit is used to fractionate the heavy oil or bitumen produced from the production well into a minor portion comprising a light gas oil fraction and a major portion comprising a residue fraction. A solvent deasphalting unit separates the residue fraction into a minor portion comprising an asphaltene fraction and a major portion comprising a deasphalted oil fraction essentially free of asphaltenes. A mixing apparatus is provided for mixing the light gas oil fraction and the deasphalted oil fraction to form a pumpable synthetic crude. A boiler burns the asphaltene fraction as fuel to generate the injection steam. A line supplies the steam from the boiler to the injection well or wells. 
     The system can include a line for supplying the asphaltene fraction in liquid form to the boiler. Alternatively, a pelletizer unit can be used to form the asphaltene into solid pellets. The pelletizer unit preferably comprises: (1) an upright pelletizing vessel having an upper prilling zone, a sphere-forming zone below the prilling zone, a cooling zone below the sphere-forming zone, and a lower aqueous cooling bath below the cooling zone; (2) a centrally disposed prilling head in the prilling zone rotatable along a vertical axis and having a plurality of discharge orifices for throwing asphaltene radially outwardly, wherein a throw-away diameter of the prilling head is less than an inside diameter of the pelletizing vessel; (3) a line for supplying the asphaltene fraction in liquid form to the prilling head; (4) a vertical height of the sphere-forming zone sufficient to allow asphaltene discharged from the prilling head to form substantially spherical liquid pellets; (5) nozzles for spraying water inwardly into the cooling zone to cool and at least partially solidify the liquid pellets to be collected in the bath; (6) a line for supplying water to the nozzles and the bath to maintain a depth of the bath in the pelletizing vessel; (7) a line for withdrawing a slurry of the pellets in the bath water; and (8) a liquid-solid separator for dewatering the pellets from the slurry. 
     The atmospheric fractionator unit, the solvent deasphalting unit and the pelletizer are preferably centrally located with a plurality of the boilers located away from the central location adjacent to injection wells. 
     In an alternate embodiment of the heavy oil or bitumen production system, a slurrying unit is used for pelletizing the asphaltene fraction and forming an aqueous slurry which is supplied to a gasification unit for partial oxidation of the slurry to form a synthesis gas and generating the steam. A line supplies the steam from the gasification unit to the injection well or wells. The slurrying unit can include: (1) an upright prilling vessel having an upper prilling zone, a hot discharge zone below the prilling zone, a cooling zone below the discharge zone, and a lower cooling bath below the cooling zone; (2) a centrally disposed prilling head in the prilling zone rotatable along a vertical axis and having a plurality of discharge orifices for throwing asphaltene radially outwardly, wherein a throw-away diameter of the prilling head is less than an inside diameter of the prilling vessel; (3) a line for supplying a hot, liquid asphaltene stream comprising the asphaltene fraction to the prilling head; (4) a vertical height of the discharge zone sufficient to allow asphaltene discharged from the prilling head to form into liquid droplets; (5) nozzles for spraying water inwardly into the cooling zone to cool and at least partially solidify the liquid droplets to be collected in the bath and form a slurry of solidified asphaltene particles in the bath; (6) a line for supplying water to the nozzles and the bath to maintain a depth of the bath in the prilling vessel; and (7) a line for withdrawing the slurry of the asphaltene particles in the bath water from the prilling vessel. The slurrying unit can also include a liquid-solid separator such as a vibrating screen for dewatering pellets from the slurry. 
     In the gasification system, the atmospheric fractionator unit, the solvent deasphalting unit, the slurrying unit and the gasification unit are preferably centrally located with a plurality of the steam supply lines carrying steam to a plurality of the injection wells located away from the central location. CO 2  can also be generated by and recovered from the gasification unit, and a line or lines can supply the CO 2  from the gasification unit to at least one of the injection wells. A turbine can also be used for expanding a portion of the steam generated by the gasification unit to generate electricity. 
    
    
     BRIEF DESCRIPTION OF THE FIGURES 
     FIG. 1 is a schematic perspective view of an underground heavy oil or bitumen reservoir with two pairs of wells. 
     FIG. 2 is a schematic vertical cross-sectional view of the underground heavy oil or bitumen reservoir of FIG.  1 . 
     FIG. 3 is a schematic flow diagram of a heavy oil or bitumen production and processing scheme with steam generation for reinjection into the underground heavy oil or bitumen reservoir according to one embodiment of the invention. 
     FIG. 4 is a schematic flow diagram of a heavy oil or bitumen production and processing scheme with steam generation for reinjection into the underground heavy oil or bitumen reservoir according to an alternate embodiment of the invention with distributed asphaltene combustion. 
     FIG. 5 is a schematic flow diagram of a heavy oil or bitumen production and processing scheme with steam generation for reinjection into the underground heavy oil or bitumen reservoir according to another alternate embodiment of the invention with a centralized asphaltene gasifier. 
     FIG. 6 is a schematic flow diagram of a typical on-site ROSE solvent deasphalting unit used in the heavy oil or bitumen processing according to the present invention. 
     FIG. 7 is a schematic flow diagram of a typical on-site asphaltene pelletizer used in the heavy oil or bitumen processing/steam generation according to the present invention. 
     FIG. 8 is a perspective view of a rotating prilling head used in the pelletizer of FIG.  7 . 
     FIG. 9 is a perspective view of an alternate embodiment of a rotating prilling head used in the pelletizer of FIG.  7 . 
    
    
     DETAILED DESCRIPTION 
     The present invention integrates heavy oil or bitumen upgrading to a pumpable crude with the production of asphaltenes for fuel to generate the steam used for injection into the heavy oil or bitumen reservoir. This has the substantial economic advantage of eliminating the need to bring natural gas or other fuel to the location of the reservoir for steam generation. At the same time, the heavy oil or bitumen is upgraded by removing the asphaltene fraction, which also contains a substantial portion of the sulfur, nitrogen and metal compounds, thereby producing a synthetic crude that can have an improvement of 4-5 degrees of API, or more. The synthetic crude is not only more valuable than the heavy oil or bitumen, but also has the further substantial economic advantage of eliminating the need for diluent since it has a lower viscosity than the heavy oil or bitumen and is pumpable through a pipeline. 
     With reference to FIGS. 1 and 2, wherein like numerals are used in reference to like parts, a subterranean heavy oil or bitumen reservoir  10  is located below the surface of an overlying layer (not shown). Wells  12 , 14 , 16 , 18  are conventionally completed horizontally in the reservoir  10  according to techniques well-known in the art. Upper wells  14 , 18  are used as steam injection wells, and wells  12 , 16  are used as production wells. Initially, the heavy oil or bitumen in the reservoir  10  is not flowable. Flowable zones or paths are created between wells  14 , 18  and wells  12 , 16 , respectively, by circulating steam through upper injection wells  14 , 18  and performing alternate steam injection and fluid production in the lower wells  12 , 16 , a well-known procedure known in the art as steam soak, or huff and puff. When a flowable path has been created between the injection wells  14 , 18  and the production wells  12 , 16 , the steam injection into the production wells  12 , 16  is generally stopped, and production thereafter occurs according to steam-assisted gravity drainage (SAGD). Steam chests  20 , 22  (see FIG. 2) are allowed to build up and expand as steam is injected into the reservoir  10  through wells  14 , 18  as the heavy oil or bitumen is displaced from the reservoir  10  by gravity drainage to the production wells  12 , 16 . 
     The production can be enhanced, if desired, by using well-known techniques such as injecting steam into one of the wells  14 , 18  at a higher rate than the other, applying electrical heating of the reservoir  10 , employing solvent CO 2  as an additive to the injection steam mainly to enhance its performance, thus improving the SAGD performance. The particular SAGD production techniques which are employed in the present invention are not particularly critical, and can be selected to meet the production requirements and reservoir characteristics as is known in the art. 
     The heavy oil or bitumen and steam and/or water produced from the formation  10  through production wells  12 , 16  is passed through a conventional water-oil separator (not shown) which separates the produced fluids to produce a heavy oil or bitumen stream  30  (see FIG. 3) essentially free of water, while generally keeping the heavy oil or bitumen at a temperature at which it remains flowable. The heavy oil or bitumen stream  30  is split into two portions, a first portion diverted into stream  32  and a second portion  34  which is supplied to solvent deasphalting unit  36 . The solvent deasphalting unit  36  can be conventional, employing equipment and methodologies for solvent deasphalting which are widely available in the art, for example, under the trade designations ROSE, SOLVAHL, DEMEX, or the like. Preferably, a ROSE unit  58  (see FIG. 6) is employed, as discussed in more detail below. The solvent deasphalting unit  36  separates the heavy oil or bitumen into an asphaltene-rich fraction  40  and a deasphalted oil (DAO) fraction  42 , which is essentially free of asphaltenes. By selecting the appropriate operating conditions of the solvent deasphalting unit  36 , the properties and contents of the asphaltenes fraction  40  and the DAO fraction  42  can be adjusted. 
     The DAO fraction  42  is blended in mixing unit  43  with the heavy oil or bitumen from stream  32  to form a mixture of DAO and heavy oil or bitumen supplied downstream via pipeline  44 . The mixing can occur in line, with or without a conventional in-line mixer, or in a mixing vessel which is agitated or recirculated to achieve blending. The split of heavy oil or bitumen between stream  32  and second portion  34  should be such that the DAO/heavy oil or bitumen blend resulting in line  44  is pumpable, i.e. having a sufficiently low viscosity at the pipeline temperatures so as to not require hydrocarbon diluent, and preferably also does not require heating of the line  44 . The blend preferably has a viscosity at 19° C. less than 350 cSt, more preferably less than 300 cSt. For example, if the heavy oil or bitumen  30  produced at the surface has a relatively high viscosity, the amount of the second portion  34  can be increased so as to produce more of DAO fraction  42  so that the resulting blend has a lower viscosity. Similarly, the distribution of asphaltenes/DAO between asphaltene fraction  40  and DAO fraction  42  can be adjusted by changing the operating parameters of the deasphalting unit  36  to produce more or less of asphaltene fraction  40  and/or DAO fraction  42  and a correspondingly higher or lower quality (lower or higher viscosity) DAO fraction  42 . Typically, the asphaltene fraction  40  is about 10-30 weight percent of the heavy oil or bitumen  34 , but can be more or less than this depending on the characteristics of the heavy oil or bitumen  34  and the operating parameters of the solvent deasphalting unit  36 . 
     The asphaltene fraction  40  is supplied to a boiler  46  either as a neat liquid or as a pelletized solid. Where the asphaltene fraction  40  is a liquid, it may be necessary to use heated transfer lines and tanks to maintain the asphaltene in a liquid state, and/or to use a hydrocarbon diluent. The asphaltene fraction  40  is preferably pelletized in pelletizing unit  48 , which can be any suitable pelletizing equipment known for this purpose in the art. The asphaltene pellets can be transported in a dewatered form by truck, bag, conveyor, hopper car, or the like, to boiler  46 , or can be slurried with water and transferred via a pipeline. The boiler  46  can be any lo conventionally designed boiler according any suitable type known to those skilled in the art, but is preferably a circulating fluid bed (CFB) boiler, which burns the asphaltene fraction  40  to generate steam for reinjection to wells  14 , 18  via line  50 . The quantity of asphaltenes  40  can be large enough to supply all of the steam requirements for the SAGD heavy oil or bitumen production. Thus, the need for importing fuel for steam generation is eliminated, resulting in significant economy in the heavy oil or bitumen production. Alternatively, a plurality of boilers  46  can be advantageously used by locating each boiler in close proximity to one or more injection wells  14 , 18  so as to minimize high pressure steam pipeline distances. Any excess steam generation can be used to generate electricity or drive other equipment using a conventional turbine expander. 
     During startup, it may be desirable to import asphalt pellets, natural gas or other fuel to fire the boiler  46  until the asphaltene fraction  40  is sufficient to meet the fuel requirements for steam generation. Startup may also entail the generation of steam  50  by boiler  46  in sufficient quantities to supply additional steam requirements for injection into wells  12 , 16  during the huff and puff stage of the reservoir  10  conditioning. 
     Referring to FIG. 4, there is shown an alternate embodiment wherein the produced heavy oil or bitumen  30  is separated in flash unit  52 , which is preferably operated essentially at atmospheric pressure to produce atmospheric gas oil fraction  54  and residue  56 . The gas oil fraction  54  preferably consists of hydrocarbons from the heavy oil or bitumen  30  with a boiling range below about 650° F., and the residue  56  comprises hydrocarbons with a higher boiling range. Typically, the gas oil fraction  54  is about 10-20 weight percent of the heavy oil or bitumen  30 , but can be more or less than this, depending on the characteristics of the heavy oil or bitumen  30  and the temperature and pressure of the flash unit  52 . Atmospheric flash unit  52  is conventionally designed, and can be a simple single-stage unit, or it can have one or more trays or packing in a multi-stage tower, with or without reflux. The gas oil fraction  54  has a relatively lower viscosity than the residue  56 . 
     The ROSE unit  58  separates the residue  56  into DAO stream  60  and asphaltenes stream  62  as described elsewhere herein. The DAO stream  60  is blended in mixing unit  63  with the gas oil fraction  54  to yield a blend in line  64  which is a pumpable synthetic crude with a reduced sulfur and metal content by virtue of the fact that the residue has been separated from the gas oil fraction  54  and the asphaltenes separated from the DAO stream  60 . The blend thus has higher value as an upgraded product. The asphaltene fraction  62  is pelletized in a centralized pelletizing unit  64  as before, but is supplied to a plurality of boilers  66 , 68 , 70  which are each located in close proximity to the injection wells to facilitate steam injection. 
     The configuration in FIG. 5 is similar to that of FIGS. 3-4, except that a conventional pressurized gasification unit  72  is employed in place of the CFB boilers, and the asphaltene fraction  74  is preferably pelletized and slurried in slurrying unit  76  to supply the water for temperature moderation in the gasification reactor (not shown). If desired, any asphaltene pellets  78  not required for gasification can be shipped to a remote location for combustion and/or gasification or other use, either as an aqueous slurry or as dewatered pellets. Steam is generated by heat exchange with the gasification reaction products, and CO 2  can also be recovered in a well-known manner for injection into the reservoir  10  with the steam. Hydrogen recovered in line  80  can be exported, for example, to a nearby refinery or synthesis unit for production of ammonia, alkyl alcohol or the like (not shown). Power can also be generated by expansion of the gasification reaction products and/or steam via turbine  82 . This embodiment is exemplary of the versatility of the present invention for adapting the asphaltene combustion to different applications and situations other than combustion as a fuel. 
     With reference to FIG. 6 there is shown a preferred solvent deasphalting unit  58 . The petroleum residue  56  is supplied to asphaltene separator  112 . Solvent is introduced via lines  122  and  124  into mixer  125  and asphaltene separator  112 , respectively. If desired, all or part of the solvent can be introduced into the feed line via line  122  as mentioned previously. Valves  126  and  128  are provided for controlling the rate of addition of the solvent into asphaltene separator  112  and mixer  125 , respectively. If desired, the conventional mixing element  125  can be employed to mix in the solvent introduced from line  122 . 
     The asphaltene separator  112  contains conventional contacting elements such as bubble trays, packing elements such as rings or saddles, structural packing such as that available under the trade designation ROSEMAX, or the like. In the asphaltene separator  112 , the residue separates into a solvent/deasphalted oil (DAO) phase, and an asphaltene phase. The solvent/DAO phase passes upwardly while the heavier asphaltene phase travels downwardly through separator  112 . As asphaltene solids are formed, they are heavier than the solvent/DAO phase and pass downwardly. The asphaltene phase is collected from the bottom of the asphaltene separator  112  via line  130 , heated in heat exchanger  132  and fed to flash tower  134 . The asphaltene phase is stripped of solvent in flash tower  134 . The asphaltene is recovered as a bottoms product in line  74 , and solvent vapor overhead in line  138 . 
     The asphaltene separator  112  is maintained at an elevated temperature and pressure sufficient to effect a separation of the petroleum lo residuum and solvent mixture into a solvent/DAO phase and an asphaltene phase. Typically, asphaltene separator  112  is maintained at a sub-critical temperature of the solvent and a pressure level at least equal to the critical pressure of the solvent. 
     The solvent/DAO phase is collected overhead from the asphaltene separator  112  via line  140  and conventionally heated via heat exchanger  142 . The heated solvent/DAO phase is next supplied directly to heat exchanger  146  and DAO separator  148 . 
     As is well known, the temperature and pressure of the solvent/DAO phase is manipulated to cause a DAO phase to separate from a solvent phase. The DAO separator  148  is maintained at an elevated temperature and pressure sufficient to effect a separation of the solvent/DAO mixture into solvent and DAO phases. In the DAO separator  148 , the heavier DAO phase passes downwardly while the lighter solvent phase passes upwardly. The DAO phase is collected from the bottom of the DAO separator  148  via line  150 . The DAO phase is fed to flash tower  152  where it is stripped to obtain a DAO product via bottoms line  60  and solvent vapor in overhead line  156 . Solvent is recovered overhead from DAO separator  148  via line  158 , and cooled in heat exchangers  142  and  160  for recirculation via pump  162  and lines  122 ,  124 . Solvent recovered from vapor lines  138  and  156  is condensed in heat exchanger  164 , accumulated in surge drum  166  and recirculated via pump  168  and line  170 . 
     The DAO separator  148  typically is maintained at a temperature higher than the temperature in the asphaltene separator  112 . The pressure level in DAO separator  148  is maintained at least equal to the critical pressure of the solvent when maintained at a temperature equal to or above the critical temperature of the solvent. Particularly, the temperature level in DAO separator  148  is maintained above the critical temperature of the solvent and most particularly at least 50° F. above the critical temperature of the solvent. 
     With reference to FIG. 7 there is shown a preferred pelletizing unit  48 . The asphaltenes fraction  74  is fed to surge drum  180 . The purpose of the surge drum  180  is to remove residual solvent contained in the asphaltenes  74  recovered from solvent deasphalting unit  58 , which is vented overhead in line  182 , and also to provide a positive suction head for pump  184 . The pump  184  delivers the asphaltenes to the pelletizer vessel  186  at a desirable flow rate. A spill back arrangement, including pressure control valve  188  and return line  190 , maintains asphaltenes levels in the surge drum  180  and also adjusts for the fluctuations in pellet production. The asphaltenes from the pump  184  flow through asphaltenes trim heater  192  where the asphaltenes are heated to the desired operating temperature for successful pelletization. A typical outlet temperature from the trim heater  192  ranges from about 350° to about 650° F., depending on the viscosity and R&amp;B softening point temperature of the asphaltenes. 
     The hot asphaltenes flow via line  194  to the top of the pelletizer vessel  186  where they pass into the rotating prilling head  196 . The rotating head  196  is mounted directly on the top of the pelletizer vessel  186  and is rotated using an electrical motor  198  or other conventional driver. The rotating head  196  is turned at speeds in the range of from about 100 to about 10,000 RPM. 
     The rotating head  196  can be of varying designs including, but not limited to the tapered basket  196   a  or multiple diameter head  196 b designs shown in FIGS. 8 and 9, respectively. The orifices  200  are evenly spaced on the circumference of the heads  196   a , 196   b  in one or more rows in triangular or square pitch or any other arrangement as discussed in more detail below. The orifice  200  diameter can be varied from about 0.03 to about 0.5 inch (about 0.8 to 12.5 mm) to produce the desired pellet size and distribution. The combination of the rotating head  196  diameter, the RPM, the orifice  200  size and fluid temperature (viscosity) controls the pellet size and size distribution, throughput per orifice and the throw-away diameter of the pellets. As the asphaltenes enter the rotating head  196 , the centrifugal force discharges long, thin cylinders of the asphaltenes into the free space at the top of the pelletizer vessel  186 . As the asphaltenes travel outwardly and/or downwardly through the pelletizer vessel  186 , the asphaltenes break up into spherical pellets as the surface tension force overcomes the combined viscous and inertial forces. The pellets fall spirally into the cooling water bath  202  (see FIG. 7) which is maintained in a preferably conical bottom  204  of the pelletizer vessel  186 . The horizontal distance between the axis of rotation of the rotating head  196  and the point where the pellet stops travelling away from the head  196  and begins to fall downwardly is called the throw-away radius. The throw-away diameter, i.e. twice the throw-away radius, is preferably less than the inside diameter of the pelletizing vessel  186  to keep pellets from hitting the wall of the vessel  186  and accumulating thereon. 
     Steam, electrical heating coils or other heating elements  206  may be provided inside the top section of the pelletizer vessel to keep the area adjacent the head  196  hot while the asphaltenes flow out of the rotating head  196 . Heating of the area within the top section of the pelletizer vessel  186  is used primarily during startup, but can also be used to maintain a constant vapor temperature within the pelletizer vessel  186  during regular operation. If desired, steam can be introduced via line  207  to heat the vessel  186  for startup in lieu of or in addition to the heating elements  206 . The introduction of steam at startup can also help to lo displace air from the pelletizer vessel  196 , which could undesirably oxidize the asphaltene pellets. The maintenance of a constant vapor temperature close to the feed  194  temperature aids in overcoming the viscous forces, and can help reduce the throw-away diameter and stringing of the asphaltenes. The vapors generated by the hot asphaltene and steam from any vaporized cooling water leave the top of the vessel  186  through a vent line  208  and are recovered or combusted as desired. 
     The pellets travel spirally down to the cooling water bath  202  maintained in the bottom section of the pelletizer vessel  186 . A water mist, generated by spray nozzles  210 , preferably provides instant cooling and hardening of the surface of the pellets, which can at this stage still have a molten core. The surface-hardened pellets fall into the water bath  202  where the water enters the bottom section of the pelletizer vessel  186  providing turbulence to aid in removal of the pellets from the pelletizer vessel  186  and also to provide further cooling of the pellets. Low levels (less than 20 ppm) of one or more non-foaming surfactants from various manufacturers, including but not limited to those available under the trade designations TERGITOL and TRITON, may be used in the cooling water to facilitate soft landing for the pellets to help reduce flattening of the spherical pellets. The cooling water flow rate is preferably maintained to provide a temperature increase of from about 10° to about 50° F., more preferably from about 15° to about 25° F., between the inlet water supply via lines  212 , 214  and the outlet line  216 . 
     The pellets and cooling water flow as a slurry out of the pelletizer vessel  186  to a separation device such as vibrating screen  218  where the pellets are dewatered. The pellets can have a water content up to about 10 weight percent, preferably as low as 1 or even 0.1 weight percent or lower. The pellets can be transported to a conventional silo, open pit, bagging unit or truck loading facility (not shown) by conveyer belt  220 . The water from the dewatering screen  218  flows to water sump  222 . The water sump  222  provides sufficient positive suction head to cooling water pump  224 . The water can alternatively be drawn directly to the pump suction from the dewatering screen (not shown). The cooling water is pumped back to the pelletizer through a solids removal element  226  such as, for example, a filter where fines and solids are removed. The cooling water is cooled to ambient temperature, for example, by an air cooler  228 , by heat exchange with a cooling water system (not shown), or by other conventional cooling means, for recirculation to the pelletization vessel  186  via line  230 . 
     Typical operating conditions for the preferred pelletizer  48  of FIG. 7 for producing a transportable, flowable asphaltene pellet product are as shown in Table 1 below: 
     
       
         
               
             
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Typical Pelletizer Operating Conditions 
               
             
          
           
               
                 Condition 
                 Range 
                 Preferred Range 
               
               
                   
               
               
                 Asphaltene feed 
                 350° to 700° F. 
                 400 to 600° F. 
               
               
                 temperature 
               
               
                 Pressure 
                 1 atmosphere to 200 psig 
                 Less than 50 psig 
               
               
                 Head Diameter, in. 
                 2 to 60 
                 2 to 60 
               
               
                 Head RPM 
                 100 to 10,000 
                 200 to 5000 
               
               
                 Orifice Size, in. 
                 0.03 to 0.5 
                 Less than 0.5 
               
               
                 Orifice Pitch 
                 Triangular or square 
               
               
                 Orifice capacity 
                 1 to 1000 lbs/hr per orifice 
                 Up to 400 lbs/hr per 
               
               
                   
                   
                 orifice 
               
               
                 Throw-away 
                 1 to 15 feet 
                 2 to 10 feet 
               
               
                 diameter 
               
               
                 Cooling water in, 
                 40 to 165 
                 60 to 140 
               
               
                 ° F. 
               
               
                 Cooling water out, 
                 70 to 190 
                 75 to 165 
               
               
                 ° F. 
               
               
                 Cooling water ΔT, 
                 10 to 50 
                 15 to 25 
               
               
                 ° F. 
               
               
                 Pellet size, mm 
                 0.1 to 5 
                 0.5 to 3 
               
               
                   
               
             
          
         
       
     
     The centrifugal extrusion device  196  results in a low-cost, high-throughput, flexible and self-cleaning device to pelletize the asphaltenes. The orifices  200  are located on the circumference of the rotating head  196 . The number of orifices  200  required to achieve the desired production is increased by increasing the head  196  diameter and/or by decreasing the distance between the orifices  200  in a row and axially spacing the orifices  200  at multiple levels. The orifices  200  can be spaced axially in triangular or square pitch or another configuration. 
     The rotating head  196  can be of varying designs including, but not limited to the tapered basket  196   a  or multiple diameter head design  196   b  shown in FIGS. 8 and 9, respectively. The combination of the head  196  diameter and the speed of rotation determine the centrifugal force at which the asphaltenes extrudes from the centrifugal head  196 . By providing orifices  200  at different circumferences of the head  196   b , for example, it is believed that any tendency for collision of molten/sticky particles is minimized since there will be different throw-away diameters, thus inhibiting agglomeration of asphaltenes particles before they can be cooled and solidified. If desired, different rings  197   a-c  in the head  196   b  can be rotated at different speeds, e.g. to obtain about the same centrifugal force at the respective circumferences. 
     Besides speed of rotation and diameter of the head  196 , the other operating parameters are the orifice  200  size, asphaltenes temperature, surrounding temperature, size of the asphaltenes flow channels inside the head  200  (not shown), viscosity and surface tension of the asphaltenes. These variables and their relation to the pellet size, production rate per orifice, throw-away diameter and the jet breaking length are explained below. 
     The orifice  200  size affects the pellet size. A smaller orifice  200  size produces smaller pellets while a larger size produces larger pellets for a given viscosity (temperature), speed of rotation, diameter of the head  196  and throughput. The throw-away diameter increases with a decrease in orifice  200  size for the same operating conditions. Adjusting the speed of rotation, diameter of the head  196  and throughput, the pellets can be produced with a varied range of sizes. Depending on the throughput, the number of orifices  200  can be from 10 or less to 700 or more. 
     The speed of rotation and diameter of the centrifugal head  196  affect the centrifugal force at which the extrusion of the asphaltenes takes place. Increasing the RPM decreases the pellet size and increases the throw-away diameter, assuming other conditions remain constant. Increase in head  196  diameter increases the centrifugal force, and to maintain constant centrifugal force, the RPM can be decreased proportionally to the square root of the ratio of the head  196  diameters. For a higher production rate per orifice  200 , greater speed of rotation is generally required. The typical RPM range is 100 to 10,000. The centrifugal head  196  diameter can vary from 2 inch to 5 feet in diameter. 
     The viscosity of the asphaltenes generally increases exponentially with a decrease in temperature. The asphaltenes viscosities at various temperatures can be estimated by interpolation using the ASTM technique known to those skilled in the art, provided viscosities are known at two temperatures. The viscosity affects the size of the pellets produced, the higher viscosity of the asphaltenes producing larger pellets given other conditions remain constant. 
     When a slurry of the asphaltenes is desired, e.g. for gasification, the pelletizer  48  is operated as a slurrying unit. The operating conditions are adjusted to produce finer particles, e.g. by rotating the prilling head  196  at a higher RPM. Also, the slurry recovered via line  216  can be recovered directly, without pellet dewatering or water recycle. Preferably, the slurrying unit is operated with water supplied once-through so that the slurry has the desired solids content, typically 50-80 weight percent solids, particularly 60-70 weight percent solids. If desired, the water content in the slurry  216  can be adjusted by adding or removing water as desired. A dispersant can also be added to the slurry. Typical operating conditions for the pelletizer  48  to produce a slurry are given below in Table 2. 
     
       
         
               
             
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Typical Slurrying Unit Operating Conditions 
               
             
          
           
               
                 Condition 
                 Range 
                 Preferred Range 
               
               
                   
               
               
                 Resid feed 
                 350° to 700° F. 
                 400 to 600° F. 
               
               
                 temperature 
               
               
                 Pressure 
                 1 atmosphere to 200 psig 
                 Less than 50 psig 
               
               
                 Head Diameter, in. 
                 2 to 60 
                 6 to 36 
               
               
                 Head RPM 
                 10 to 10,000 
                 500 to 10,000 
               
               
                 Orifice Size, in. 
                 0.03 to 1 
                 Less than 0.5 
               
               
                 Orifice Pitch 
                 Triangular or square 
               
               
                 Orifice capacity 
                 1 to 1000 lbs/hr per orifice 
                 Up to 400 lbs/hr per 
               
               
                   
                   
                 orifice 
               
               
                 Throw-away diameter 
                 2 to 15 feet 
                 4 to 15 feet 
               
               
                 Cooling water in, ° F. 
                 40 to 165 
                 60 to 140 
               
               
                 Cooling water out, ° F. 
                 70 to 190 
                 75 to 165 
               
               
                 Cooling water ΔT, ° F. 
                 10 to 150 
                 15 to 100 
               
               
                 Particle size, mm 
                 0.01 to 1 
                 0.015 to 0.05 
               
               
                   
               
             
          
         
       
     
     It is seen that the above-described invention achieves substantial economic and operational advantages over the prior art. The synthetic crude has a higher value than the heavy oil or bitumen. The synthetic crude can also be transported by pipeline because it has a lower viscosity (4-5° API improvement), thereby eliminating the expense and complication of supplying diluent to the production area. The low-value asphaltene fraction which contains most of the sulfur and nitrogen compounds as well as the metals is burned to supply the heat for raising the injection steam. The invention thus achieves a synergistic integration of upstream and downstream processes at the production field.