NO20120010A1 - Process for the treatment of hydrocarbons - Google Patents

Description

Process for treating hydrocarbons

Field of the invention

The present invention relates to a method for treating hydrocarbons, particularly aimed at reducing the water content in a stream of hydrocarbons, in addition to an installation that is appropriate for implementing this method.

Technical background

Hydrocarbons extracted from reservoirs (called production crude oil) must generally be treated before being stored and/or transported to refineries where they are upgraded. One of the main treatments consists in removing production water that is mixed with the hydrocarbons. This treatment is generally carried out by separation by gravity, possibly completed by electrostatic coalescence.

When the extracted hydrocarbons are of high density and high viscosity (heavy oils or extra heavy oils) the hydrocarbons must be further processed in an upgrading unit (or "upgrader") upstream of refining, strictly speaking, because standard refineries are essentially designed to process lighter crudes . The upgrade produces a light synthetic oil which can then be transferred for refining.

It is known that by mixing the heavy oils with a hydrocarbon solvent (lighter than heavy oil) it is possible to obtain a diluted heavy crude oil with a high API grade in addition to lower viscosity. In this way, the transfer of the heavy oils from the production site to the upgrading unit is promoted by fluidizing them with the solvent.

As a hydrocarbon solvent, naphtha is generally used, which is a hydrocarbon fraction comprising mainly C6-C20 hydrocarbons. With this solvent it is possible to increase the API grade of the hydrocarbons to be treated, typically to a value of about 20 at most (in the case of heavy oils). The solvent is generally recycled by a distillation process at the upgrader, and then brought back to the production site in a pipe in the opposite direction to the main pipe to transport the produced hydrocarbons.

Naphtha is used because of its good compatibility with heavy oils, with which it is possible to obtain a homogeneous mixture, and to avoid the risk of biphase separation or the formation of deposits during transport to the upgrading unit.

Removal of the water mixed with the hydrocarbons also causes special problems in the case of heavy oils. It is actually crucial to separate the oil and the water because oil/water emulsions (either oil in water or water in oil) tend to be very stable. Oil/water separation is conventionally achieved by gravity separation. According to Stokes' law, the settling rate of a water particle in an oil phase is actually proportional to the specific gravity difference between the oil phase and the water, and is inversely proportional to the viscosity of the oil phase. When the oil phase has a high viscosity and a high density (and therefore a density close to the density of water), setting of the water is therefore very poorly achieved.

In order to improve the separation of water, it is possible to increase the size of the separators or to increase the temperature at which the separation is carried out in order to reduce the viscosity of the oil phase, which means a high cost and which causes serious practical problems. Mixing the production crude oil with the hydrocarbon solvent (naphtha) was also proposed ahead of the gravity separation step. This step nevertheless typically allows an increase in the API grade of the hydrocarbons up to a value of about 20 at most, which is insufficient to facilitate the oil/water separation in a completely satisfactory manner (the size of the separators remains noticeably very large).

Document WO 99/19425 further describes a method for upgrading heavy oils which is more specifically aimed at hydrocarbons which are recovered from mining residues and which contain a lot of solid materials. A hydrocarbon solvent is added to the heavy oils. The separation of water is partly carried out by means of flash decompression of the mixture of heavy oils and of the hydrocarbon solvent (consisting of the evaporating part of the hydrocarbons and the water) and additionally by means of a hydrocyclone. The scheme is based on the precipitation of certain hydrocarbon compounds by means of the solvents used. This is a very complex form.

Therefore, there is a need for a method for the treatment of hydrocarbons which provides the possibility of carrying out an oil/water separation more efficiently, simply, more economically and faster than in the existing methods, especially for heavy oils.

Summary of the invention

The invention relates, firstly, to a method for treating hydrocarbons, where said method comprises: providing an output stream of hydrocarbons comprising water,

adding a liquid solvent to the output stream of hydrocarbons to provide an intermediate stream of hydrocarbons, said liquid solvent comprising a mass ratio of C3-C6 alkanes greater than or equal to 80%,

separating by gravity the intermediate stream of hydrocarbons into an oil phase and an aqueous phase,

decompress the oil phase and separate the oil phase into a gas phase with

hydrocarbons and a liquid hydrocarbon phase,

recycling the hydrocarbon gas phase to at least partially provide

the liquid solvent, and

recover the liquid hydrocarbon phases.

According to one embodiment, the output stream of hydrocarbons has an API degree comprised between 5 and 25 and the intermediate stream of hydrocarbons has an API degree greater than or equal to 30, preferably greater than or equal to 35, most preferably greater than or equal to 40 .

According to one embodiment, the liquid solvent comprises a mass ratio of C3-C6 alkanes greater than or equal to 80%, preferably greater than or equal to 95%.

According to one embodiment, the recycling of the hydrocarbon gas phase to at least partially provide the liquid solvent comprises the decompression of the hydrocarbon gas phase and optionally an addition of liquid solvent.

According to one embodiment, the step of providing the output stream of hydrocarbons comprises:

extracting hydrocarbons from an underground formation,

optionally degasing the extracted hydrocarbons, and optionally removing the solid materials mixed with the extracted hydrocarbons.

According to one embodiment, the output stream of hydrocarbons comprises less than 20,000 ppm solids, preferably less than 10,000 ppm solids, and most preferably less than 5,000 ppm solids, in a mass ratio.

According to one embodiment:

separation by gravity of the intermediate stream of hydrocarbons produced at a pressure comprised between 3 and 15 bar, preferably between 5 and 10 bar, and/or

separation of the oil phase into the hydrocarbon gas phase and into the hydrocarbon liquid phase carried out at a pressure comprised between 1 and 3 bar, preferably between 1 and 2 bar.

According to one embodiment, the aforementioned method further comprises: transporting the hydrocarbon liquid phase followed by upgrading of

the hydrocarbon liquid phase, or

transporting the oil phase followed by upgrading the oil phase, where said upgrading includes decompression of the oil phase, separation of

the oil phase into the hydrocarbon gas phase and into the hydrocarbon liquid phase and recycling the hydrocarbon gas phase to at least partially provide the liquid solvent.

The invention further relates to an installation for the treatment of hydrocarbons, which includes:

a line delivering a stream of hydrocarbons,

a line that delivers liquid solvent that opens into the line that

delivers a stream of hydrocarbons,

a unit for separation of water/hydrocarbons by gravity, provided

at the line supplying a stream of hydrocarbons,

a line diverting an oil phase and a line diverting a water phase, connected to an outlet of the water/hydrocarbon gravity separation unit,

decompression agents on the line that lead away an oil phase,

a liquid/gas separation unit provided with the line leading away a

oil phase,

a line for diverting a hydrocarbon gas phase and a line for diverting a hydrocarbon liquid phase connected to the outlet of the liquid/gas separation unit,

wherein the line for diverting a hydrocarbon gas phase supplies a liquid solvent recycle line, wherein said liquid solvent recycle line at least partially supplies the liquid solvent supply line.

According to one embodiment, the previously mentioned installation comprises compression means on the line to lead away the hydrocarbon gas phase, and in which the liquid solvent supply line is supplied from the liquid solvent recycling line and by a line providing additional liquid solvent.

According to one embodiment, the aforementioned installation comprises:

means for extracting hydrocarbons in an underground formation, from

which line supplying a stream of hydrocarbons comes from,

possibly means to remove solid materials that are mixed with

the hydrocarbons, and

possibly means for degassing the hydrocarbons, on the line for delivering a stream of hydrocarbons.

According to one embodiment, the aforementioned installation comprises:

a unit for the production of hydrocarbons,

an intermediate unit, which includes the unit for separation of

water/hydrocarbons by gravity,

a hydrocarbon upgrading unit,

a first pipeline for transporting hydrocarbons from the hydrocarbon production unit and supplying the intermediate unit, and

a second pipeline for transporting hydrocarbons from the intermediate unit and supplying the hydrocarbon upgrading unit.

According to one embodiment, the intermediate unit comprises the liquid/gas separation unit, where the installation also optionally comprises a line that supplies ten sets which opens out into the second pipeline for the transport of hydrocarbons, and: the line for recycling the liquid solvent is included in the

intermediate unit, or

the liquid solvent recycling line originates in the intermediate unit and opens into the first pipeline for transporting hydrocarbons.

According to one embodiment, the upgrading unit comprises the liquid/gas separation unit, and

the liquid solvent recycling line originates from

the upgrading unit and supplies the intermediate unit, or

the line for recycling the liquid solvent originates from the upgrading unit and opens into the first pipeline for transporting hydrocarbons.

According to one embodiment, the above-mentioned method is used on an installation as described above.

With the present invention, it is possible to overcome the disadvantages in the state of the art. More specifically, it provides a method for the treatment of hydrocarbons which provides the possibility of performing an oil/water separation more efficiently, simply, more economically and faster than in existing methods, especially for heavy oils.

This is achieved by the use of a light solvent based on C3-C6 alkanes (preferably based on C3 and C4 alkanes), which is mixed with hydrocarbons in order to significantly increase the API grade of the latter. In this way, oil/water separation is promoted. The light solvent can then be easily removed

(separated from the hydrocarbons with which it was mixed) without resorting to distillation, thereby being recycled.

According to certain specific embodiments, the invention also has one or preferably several of the advantageous features listed below.

The size of the water/oil separators can be reduced compared to the state of the art where naphtha is mixed with production crude oil before water/oil separation.

The heating requirement is reduced at the water/oil separation stage compared to the state of the art where naphtha is mixed with the production crude oil before the water/oil separation.

The API degree of the hydrocarbons is more significantly increased than in the state of the art where naphtha is mixed with the production crude oil before the water/oil separation, which increases the water/oil separation degree. Typically, the time in the separators can thus be reduced to a couple of minutes instead of one or more hours.

The recovery of the solvent can be carried out in a simple way, at a pressure close to atmospheric pressure, and without using any distillation column. The solvent is recycled with minimal loss (losses are particularly reduced compared to the conventional scheme).

According to the embodiments, the solvent can also be used to fluidize hydrocarbons and promote their transport between the production site and the water/oil separation unit and/or between the water/oil separation unit and the upgrading unit.

Compared to document WO 99/19425, the invention provides a much simpler method and installation for the treatment of hydrocarbons, where the water is specifically removed by simple separation by gravity and without resorting to partial evaporation.

Brief description of the figures

Figure 1 schematically illustrates an embodiment of the installation for treating hydrocarbons according to the invention. Figures 2 to 5 schematically illustrate four alternative embodiments of the installation for treating hydrocarbons according to the invention.

Description of embodiments of the invention

The invention will now be described in more detail and in a non-limiting manner in the following description.

Treatment of hydrocarbons containing water

In the following, the terms "upstream" and "downstream" are defined relatively in relation to the direction of transport of the various fluids in the installation.

With reference to Figure 1, an installation for treating hydrocarbons according to the present invention comprises a line for delivering a stream of hydrocarbons 1. The stream of hydrocarbons to be treated arrives through this hydrocarbon stream supply line 1. It may comprise a liquid phase and a gas phase and the contains water.

Degassing means 2 for the hydrocarbons can be provided on the hydrocarbon stream supply line 1. A line for diverting gases 3 is then connected to the outlet of the degassing means 2. A major part of the gas phase from the hydrocarbon stream can thus be removed at this stage, if necessary.

The degassing means 2 may comprise one (or play the role of one) "slug catcher", i.e. provide a function to prevent shutdown or overpressure from passing into the subsequent levels of the method.

Optionally, pumping means 4 may be provided on the hydrocarbon flow feed line 1 downstream from the degassing means 2 to compress the flow of hydrocarbons if necessary.

The installation according to the invention also includes a line for the supply of liquid solvent 5, where this opens out into the hydrocarbon flow supply line 1. In this way, the flow of hydrocarbons and the liquid solvent are mixed to provide an intermediate flow of hydrocarbons. A static or motorized mixer may be provided to ensure mixing of the fluids originating from both these lines, but this is generally not required.

The liquid solvent is itself based on hydrocarbons and comprises a mass ratio of CrCe-alkanes of greater than or equal to 80%, preferably greater than or equal to 85%, most preferably greater than or equal to 90% and ideally greater than or equal to 95%.

According to one embodiment, the liquid solvent comprises a mass ratio of C3-C4 alkanes of greater than or equal to 80%, preferably greater than or equal to 85%, most preferably greater than or equal to 90% and ideally greater than or equal to 95 %. This liquid solvent is generally of the LPG (Liquefied Petroleum Gas) type.

According to another embodiment, the liquid solvent comprises a mass ratio of with C5 and C6 alkanes of greater than or equal to 80%, preferably greater than or equal to 85%, most preferably greater than or equal to 90% and ideally greater than or equal to 95%.

The output stream of hydrocarbons is generally a so-called heavy oil or extra heavy oil. Preferably, this output stream of hydrocarbons has an API grade comprised between 5 and 25.

The API grade can be measured in accordance with the ASTM D287 standard.

By adding a liquid solvent it is possible to significantly increase the API grade, and thus the intermediate stream of hydrocarbons preferably has an API grade greater than or equal to 30, most preferably greater than or equal to 35, ideally greater than or equal to 40.

The choice of the solvent which is essentially based on C3-C6 alkanes is optimal. Hydrocarbons having more than 6 carbon atoms are actually difficult to recycle once they have been mixed with the output stream of hydrocarbons and they do not allow an increase in the API grade in a completely satisfactory manner.

In this respect, the choice of a solvent essentially based on C3-C4 alkanes generally provides a particularly good result.

On the other hand, Ci and C2 alkanes are very light and it will be necessary to operate at very cold temperatures or at very high pressures to be able to have them available in liquid form, which is inevitable to be able to to mix them with the output stream of hydrocarbons to increase the API grade.

The molar ratio of the hydrocarbon fractions in the output stream of hydrocarbons and of hydrocarbons in the liquid solvent is selected to achieve the desired API grade in the intermediate stream of hydrocarbons. This molar ratio is also adjusted in accordance with the risk of precipitation when depositing asphaltenes. In general, this molar ratio is comprised between 0.2 and 5, preferably between 0.5 and 2, especially between 0.8 and 1.25, and ideally close to 1. This corresponds to a mass ratio of solvent that is much smaller than that which becomes used in the prior art with solvents of the naphtha type.

The exact composition of the liquid solvent, and for example the relative C3 and C4 ratios (in the case of a liquid solvent based on C3 and C4 alkanes) can be chosen according to the limitations of the process, or can itself be considered a limitation (eg because a particular LPG stream is available within the scope of the overall hydrocarbon producing and processing process). In the second case, other process parameters are adjusted depending on this limitation (ratio of the hydrocarbon molar fractions in the hydrocarbon output stream and of hydrocarbons in the liquid solvent, operating temperature and pressure...).

The intermediate flow of hydrocarbons, via

the hydrocarbon stream supply line 1, enters a water/hydrocarbon gravity separation unit 6. By "water/hydrocarbon gravity separation unit" is meant any set of means which can separate a mixture of water and liquid hydrocarbons into an aqueous phase and an oil phase by the action of gravity, where the aqueous phase is denser than the oil phase.

Therefore, the water/hydrocarbon gravity separation unit 6 is not a unit that can perform water/hydrocarbon separation by evaporation (flash decompression). This is advantageous because sudden changes in pressure are a disadvantage for water/hydrocarbon separation as they induce strong shear, which tends to regenerate emulsions. Within the scope of the method according to the invention, one therefore operates at constant or quasi-constant pressure during the water/hydrocarbon separation.

The water/hydrocarbon gravity separation unit 6 may comprise any separator known to those skilled in the art, with or without means for destabilizing emulsions, such as means for spraying the oil/water interface, and with or without heating means.

The water/hydrocarbon gravity separation unit 6 can, for example, be an apparatus as described in document WO 2005/100512.

If necessary, the water/hydrocarbon gravity separation unit 6 can include desalination agents. The desalination means typically comprise at least two consecutive separators, with a supply line for demineralised water between the separators.

Separation by gravity carried out within the water/hydrocarbon gravity separation unit 6 is generally achieved at a pressure comprised between 3 and 15 bar, preferably between 5 and 10 bar, for example between 7 and 8 bar (all the pressure values mentioned in the present application are absolute values ).

In general, it is not necessary to heat the output stream of hydrocarbons or the intermediate stream of hydrocarbons or provide additional heating during separation by gravity because the mixing of the output stream of hydrocarbons with the liquid solvent allows a sufficient increase in the API grade of the hydrocarbons such that separation by gravity is carried out quickly and efficiently without any heating (this is then carried out at room temperature).

Separation by gravity provides an oil phase and an aqueous phase, which are respectively led away in a line that leads away an oil phase 8 and a line that leads away an aqueous phase 7.

The aqueous phase generally undergoes a subsequent treatment before, for example, being released into the environment or reused within the scope of the overall process for the production of hydrocarbons. The quality of the water is still better than in the methods in the state of the art, the aqueous phase contains a smaller proportion of hydrocarbons and a smaller proportion of solid particles (because the solid particles are decanted and are therefore easier to remove during the hydrocarbon/water separation due to the relatively high fluidity of the hydrocarbons). Therefore, the subsequent treatment of the aqueous phase can be more reduced and simpler than in the known technique.

The oil phase then undergoes a step of separation into a hydrocarbon gas phase and a liquid hydrocarbon phase, inside a liquid/gas separation unit 12, supplied from the line leading away an oil phase 8. The hydrocarbon gas phase is sampled through a line for diverting a hydrocarbon gas phase 14 and the liquid the hydrocarbon phase is sampled through a line for the diversion of a liquid hydrocarbon phase 13.

The oil phase has essentially the same chemical composition as the hydrocarbon intermediate stream (mixture of the hydrocarbon output stream and the liquid solvent), except for the water content. The hydrocarbon gas phase from the separation in the liquid/gas separation unit 12 has essentially the same chemical composition as the liquid solvent. And, the liquid hydrocarbon phase from the liquid/gas separation unit 12 has essentially the same chemical composition as the hydrocarbon output stream (except for the water content).

In other words, the separation of the oil phase into the hydrocarbon gas phase and the liquid hydrocarbon phase essentially again separates the intermediate stream of hydrocarbons (with a high API grade) to, on the one hand, the output stream of hydrocarbons (with a low API grade) without most of its water and, on the other hand, the composition of hydrocarbons comprising mainly C3-C6 alkanes (especially C3 and C4 alkanes according to an embodiment) which constitute the liquid solvent, to ensure recycling of this composition.

With this separation step it is preferably possible to recover in the form of the hydrocarbon gas phase more than 50%, preferably more than 75%, most preferably more than 85%, ideally more than 90% or even more than 95%, in a molar ratio , of the hydrocarbons brought in by the liquid solvent. It is nevertheless not inevitable to recover the totality of these compounds, especially when the liquid hydrocarbon phase undergoes subsequent upgrading and/or refining steps, during which the remaining fraction of the added compounds can be isolated.

Before proceeding with the step of separation into the hydrocarbon gas phase and the liquid hydrocarbon phase, the oil phase originating from the water/hydrocarbon gravity separation is decompressed by decompression means 9 provided on the line for removing an oil phase 8.

Typically, the pressure in the oil phase is reduced to between 1 and 3 bar, preferably between 1 and 2 bar for the needs in the separation of the oil phase into the hydrocarbon gas phase and the liquid hydrocarbon phase. The separation is carried out better since the pressure is low, but it is still generally not recommended to carry out the separation exactly at atmospheric pressure (1 bar) because this complicates subsequent recompression of the hydrocarbon gas phase.

The oil phase can also be heated if this is necessary, before the separation or during the separation, using heating means 10,11. It is for example possible to provide a main heating with external heating means 11, preceded by preliminary heating with a heat exchanger 10, against the cooling of the liquid hydrocarbon phase originating from the separation step.

Nevertheless, the heating requirements at this stage are generally actually less significant than in the state of the art, for the distillation of the heavy oil/naphtha mixture. These heating needs may even be non-existent.

In general, the temperature and pressure conditions are chosen (in addition to the molar ratio of the hydrocarbon fractions in the hydrocarbon output stream and of the hydrocarbons in the liquid solvent) such that: the solvent added to the hydrocarbon output stream is in the the liquid state, and remains in the liquid state during the water/hydrocarbon gravity separation, and

this solvent is in the gas phase during the separation of the oil phase.

The choice of conditions is easily made by examining the phase diagram of the solvent.

The hydrocarbon gas phase is recycled to at least partially provide the above-mentioned liquid solvent, causing compression and liquefaction of this phase.

For this purpose, the line for deriving the hydrocarbon gas phase 14 supplies a line for recycling liquid solvent 23, where said liquid solvent recycling line 23 in turn at least partially supplies the supply line 5 for the liquid solvent. Compression means 16,18 are provided on the line for the discharge of a hydrocarbon gas phase 14, with cooling means 17,19 at the outlet of each compressor or compressor stage. One or more compression stages should be considered, but preferably a single compression stage. A separation element 15 can also be provided on the line for the diversion of a hydrocarbon gas phase 14. This separation element 15, upstream of the compression means 16, 18, protects the latter because these compression means 16, 18 should only compress gases.

Pumping means 22 are also provided on the liquid solvent recycling line 23. A separation element 20 may be provided upstream of the pumping means 22, to protect the latter because the pumping means 22 should only compress liquids.

Additional supply of liquid solvent can generally be carried out. The supply line 5 for liquid solvent can thus be supplied both from the recycling line 23 for liquid solvent and from a line to provide additional supply of liquid solvent 24.

Integration of the invention within the scope of production of hydrocarbons The invention can be used within the scope of the production of hydrocarbons, especially petroleum. In this case, the installation according to the invention comprises means for the extraction of hydrocarbons in an underground formation, and the provision of the output stream of hydrocarbons comprises the extraction of hydrocarbons from the underground formation.

Preferably, the output stream of hydrocarbons is a stream of crude oil.

Preferably, no product or compound is added to the hydrocarbons between the extraction from the subsurface formation and the liquid solvent addition steps.

For example, the means for extracting hydrocarbons may comprise a set of wells (or "clusters").

The output stream of hydrocarbons, which is brought to the water/hydrocarbon gravity separation unit 6 via the line for supplying a stream of hydrocarbons 1, preferably contains less than 20,000 ppm of solid materials (by mass), most preferably less than 10,000 ppm of solid materials, and ideally less than 5,000 ppm of solids.

The water/hydrocarbon gravity separation unit 6 can conventionally comprise means for removing solid materials to further subsequently reduce the content of solid materials in the process.

With reference to Figures 2-5, the installation according to the invention comprises within the scope of production of hydrocarbons in general:

a unit for the production of hydrocarbons 101,

an intermediate unit 103, and

a unit for upgrading hydrocarbons 105.

The unit for the production of hydrocarbons 101 includes in particular the previously mentioned means for extracting hydrocarbons. It can be located on land or offshore. The intermediate unit 103 comprises a set of treatment means and in particular the water/hydrocarbon gravity separation unit 6. It can be located on land or offshore (under water or on the surface). The hydrocarbon upgrading unit 105 (located onshore) is adapted to upgrade the hydrocarbons (i.e. achieve their upgrading). This hydrocarbon upgrading unit 105 comprises a set of means for converting the hydrocarbons into lighter compounds. It may include refining agents or other conversion agents prior to refining.

Between the unit for the production of hydrocarbons 101 and the intermediate unit 103, the hydrocarbons are passed through a first

hydrocarbon transport pipeline 102. Between the intermediate unit 103 and the hydrocarbon upgrading unit 105, the hydrocarbons are passed through a second hydrocarbon transport pipeline 104.

The distance between the hydrocarbon production unit 101 (or certain locations on the hydrocarbon production unit 101, when the latter is geographically extensive) and the intermediate unit 103 may be more than 1 km, or even more than 10 km and even more than 100 km. The distance between the intermediate unit 103 and the hydrocarbon upgrading unit 105 may also be more than 1 km, or even more than 10 km or even more than 100 km.

According to a first embodiment illustrated in figure 2, the set of means described above which allow separation of the oil and the water in addition to the supply, circulation and recirculation of the liquid solvent are comprised in the intermediate unit 103. In particular, the intermediate unit 103 comprises the liquid/gas separation unit 12 and the liquid solvent recycling line 106.

It is therefore within the intermediate unit 103 that the output stream of hydrocarbons is mixed with the liquid solvent, that the intermediate stream of hydrocarbons is separated into an oil phase and an aqueous phase, that the oil phase is decompressed and separated into a hydrocarbon gas phase and a liquid hydrocarbon phase, and that the hydrocarbon gas phase is recycled to partially provide the liquid solvent.

According to an embodiment illustrated in Figure 3, the set of means described above that allows separation of the oil and water in addition to the supply, circulation and recirculation of the liquid solvent is distributed between the intermediate unit 103 and the hydrocarbon upgrading unit 105. More specifically, the separation by gravity carried out in the intermediate unit 103, but the recovery of the compounds constituting the liquid solvent is carried out only in the hydrocarbon upgrading unit 105, which includes the liquid/gas separation unit 12. The liquid solvent recirculation line 106 then leaves the upgrading unit 105 and supplies the intermediate unit 103 .

It is therefore within the intermediate unit 103 that the output stream of hydrocarbons is mixed with the liquid solvent, that the intermediate stream of hydrocarbons is separated into an oil phase and an aqueous phase. Next, it is within the hydrocarbon upgrading unit 105 that the oil phase is decompressed and separated into a hydrocarbon gas phase and a liquid hydrocarbon phase, and that the hydrocarbon gas phase is recycled to partially provide the liquid solvent. The liquid solvent is then returned towards the intermediate unit 103. In this embodiment, the second hydrocarbon transport pipeline 104 coincides with the line for the diversion of an oil phase 8.

According to a third embodiment illustrated in Figure 4, the set of means described above which allows separation of the oil and water in addition to the supply, circulation and recirculation of the liquid solvent is distributed between the intermediate unit 103 and the hydrocarbon production unit 101. More specifically, separation by gravity carried out in the intermediate unit 103, in addition to recovery of the compounds that make up the liquid solvent (wherein the intermediate unit 103 comprises the liquid/gas separation unit 12). The liquid solvent recirculation line 106 then leaves the intermediate unit 103 and opens into the hydrocarbon production unit 101 (preferably at the top of the well) or into the first hydrocarbon transport pipeline 102 (preferably towards the start of this pipeline, i.e. at the outlet of the hydrocarbon production unit 101).

Therefore, it is preferably at the hydrocarbon production unit 101 that the output stream of hydrocarbons is mixed with the liquid solvent. Next, it is within the intermediate unit 103 that the intermediate stream of hydrocarbons is separated into an oil phase and an aqueous phase, that the oil phase is decompressed and separated into a hydrocarbon gas phase and a liquid hydrocarbon phase, and that the hydrocarbon gas phase is recycled to partially provide the liquid solvent . The liquid solvent is then returned to the hydrocarbon production unit 101. In this embodiment, the first hydrocarbon transport pipeline 102 essentially transports the intermediate stream of hydrocarbons described above.

According to a fourth embodiment illustrated in Figure 5, the set of means described above which allows separation of the oil and water in addition to circulation and recirculation of the liquid solvent is distributed between the hydrocarbon production unit 101, the intermediate unit 103 and the upgrading unit 105. More specifically the liquid solvent is mixed with the output stream of hydrocarbons at the outlet of the hydrocarbon production unit 101, separation by gravity is carried out in the intermediate unit 103 and recovery of the compounds constituting the liquid solvent is carried out in the upgrading unit 105 (comprising the liquid/gas separation unit 12). The liquid solvent recirculation line 106 then leaves the upgrading unit 105 and opens into the hydrocarbon production unit 101 (preferably at the top of the well), or into the first hydrocarbon transport pipeline 102 (preferably towards the start of this pipeline, i.e. at the outlet of the hydrocarbon production unit 101).

Therefore, at the hydrocarbon production unit 101, it is preferred that the output stream of hydrocarbons be mixed with the liquid solvent. Then, it is within the intermediate unit 103 that the intermediate stream of hydrocarbons is separated into an oil phase and an aqueous phase. Finally, it is within the upgrading unit 105 that the oil phase is decompressed and separated into a hydrocarbon gas phase and a liquid hydrocarbon phase, and that the hydrocarbon gas phase is recycled to partially provide the liquid solvent. The liquid solvent is then returned to the hydrocarbon production unit 101. In this embodiment, the first hydrocarbon transport pipeline 102 essentially transports the intermediate stream of hydrocarbons described above. In this embodiment, however, the second hydrocarbon transport pipeline 104 coincides with the line for the diversion of an oil phase 8.

The embodiments according to Figures 3 and 5 have the advantage of promoting transport of the hydrocarbons in the second hydrocarbon transport pipeline 104 up to the upgrading unit 105, because the stream of hydrocarbons is mixed at this stage with the liquid solvent, which significantly reduces its viscosity.

In the embodiments according to Figures 2 and 4, it is generally necessary to provide means to fluidize the hydrocarbons circulating in the second hydrocarbon transport pipeline 104. These can be heating means and/or an additive supply line 107 which opens out into the second hydrocarbon transport pipeline 104 and allows injection into the hydrocarbons of a surfactant-type viscosity reducing additive (or DRA) combined with a composition of hydrocarbons having a low or moderate API grade, or even only with a composition of hydrocarbons having a low or moderate API grade, such such as naphtha.

The embodiments according to Figures 4 and 5 have the advantage of promoting the transport of the hydrocarbons in the first hydrocarbon transport pipeline 102 as far as the intermediate unit 103, because the stream of hydrocarbons at this stage is mixed with the liquid solvent, which significantly reduces its viscosity.

In the embodiments according to Figures 2 and 3, it may be necessary to provide means for fluidizing the hydrocarbons circulating in the first hydrocarbon transport pipeline 102, of the same type as above. Nevertheless, such means for fluidizing the hydrocarbons may be unnecessary when the extracted hydrocarbons are sufficiently hot (this may for example be the case within the scope of an extraction with the SAGD process) and/or when the first hydrocarbon transport pipeline is relatively short, where the intermediate unit 103 is positioned near

the hydrocarbon production unit 101.

Claims (16)

1. Procedure for treating hydrocarbons, characterized in that said method comprises: providing an output stream of hydrocarbons comprising water, comprising the extraction of hydrocarbons from a subsurface formation, adding a liquid solvent to the output stream of hydrocarbons to provide an intermediate stream of hydrocarbons, wherein said liquid solvent comprises a mass ratio of C3-C6 alkanes greater than or equal to 80%, separating by gravity the intermediate stream of hydrocarbons in an oil phase and an aqueous phase, decompressing the oil phase and separating the oil phase into a hydrocarbon gas phase and a liquid hydrocarbon phase, recycle the hydrocarbon gas phase to at least partially provide the liquid solvent, and recover the liquid hydrocarbon phase. 2. Method according to claim 1, characterized in that the output stream of hydrocarbons has an API grade comprised between 5 and 25 and that the intermediate stream of hydrocarbons has an API grade that is higher than or equal to 30, preferably higher than or equal to 35, most preferably higher than or equal to 40. 3. Method according to claim 1 or 2, characterized in that the liquid solvent comprises a mass proportion of C3 and C4 alkanes that is greater than or equal to 80%, preferably greater than or equal to 85%, most preferably greater than or equal to 90%, ideally greater than or equal to 95%. 4. Method according to one of claims 1 to 3, characterized in that the recycling of the hydrocarbon gas phase to at least partially provide the liquid solvent comprises compression of the hydrocarbon gas phase and possibly an addition of liquid solvent. 5. Method according to one of claims 1 to 4, characterized in that the steps for providing the output stream of hydrocarbons comprise: degassing the extracted hydrocarbons, and/or removing solid materials mixed with the extracted the hydrocarbons. 6. Method according to one of claims 1 to 5, characterized in that the output stream of hydrocarbons comprises less than 20,000 ppm of solid materials, preferably less than 10,000 ppm of solid materials, most preferably less than 5,000 ppm of solid materials, in a mass ratio. 7. Method according to one of claims 1 to 6, characterized by: separation by gravity of the intermediate stream of hydrocarbons is carried out at a pressure comprised between 3 and 15 bar, preferably between 5 and 10 bar, and/or separation of the oil phase in the hydrocarbon gas phase and in the liquid the hydrocarbon phase is carried out at a pressure comprised between 1 and 3 bar, preferably between 1 and 2 bar. 8. Method according to one of claims 1 to 7, characterized in that it further comprises: transporting the liquid hydrocarbon phase followed by upgrading of the liquid hydrocarbon phase, or transport of the oil phase followed by upgrading of the oil phase, where mentioned upgrading comprises decompressing the oil phase, separating the oil phase into a hydrocarbon gas phase and into the liquid hydrocarbon phase and recycling the hydrocarbon gas phase to at least partially provide the liquid solvent. 9. Method according to one of claims 1 to 8, characterized in that more than 75%, preferably more than 85%, or more than 90% or more than 95% in a molar ratio of the hydrocarbons provided in the liquid solvent are recovered in the hydrocarbon gas phase. 10. Installation for the treatment of hydrocarbons, characterized in that it comprises: a line delivering a stream of hydrocarbons (1), means for extracting hydrocarbons from a subsurface formation, from which the line supplying a stream of hydrocarbons (1) originates, a line supplying liquid solvent (5) which opens into the line which supplies a stream of hydrocarbons (1), a water/hydrocarbon gravity separation unit (6), supplied at the line which supplies a stream of hydrocarbons (1), a line which leads away an oil phase (8) and a line which leads away a aqueous phase (7), connected to the outlet of the water/hydrocarbon gravity separation unit (6), decompressants (9) on the line leading away an oil phase (8), a liquid/gas separation unit (12) supplied from the line leading away a oil phase (8), a line which leads away a hydrocarbon gas phase (14) and a line to diverting a hydrocarbon liquid phase (13) connected to the outlet of the liquid/gas separation unit (12), wherein the line for diverting a hydrocarbon gas phase (14) supplies a line (23) for recycling liquid solvent, said line (23) for liquid solvent recycling at least partially supplies the line (5) which supplies the liquid solvent. 11. Installation according to claim 10, characterized in that it comprises compression means (16,18) on the line which leads away a hydrocarbon gas phase (14) and where the supply line (5) for the liquid solvent is supplied from the recirculation line (23) for the liquid solvent and by a line for supply of supplements of liquid solvent (24). 12. Installation according to claim 10 or 11, characterized in that it comprises: means for removing solid materials mixed with the hydrocarbons, and/or means (2) for degassing the hydrocarbons, on the hydrocarbon flow supply line (1). 13. Installation according to one of claims 10 to 12, characterized in that it comprises: a unit for the production of hydrocarbons (101), an intermediate unit (103), which comprises water/hydrocarbon- the gravity separation unit (6), a hydrocarbon upgrading unit (105), a first hydrocarbon transport pipeline (102) originating from the hydrocarbon production unit (101) and supplying the intermediate unit (103), a second hydrocarbon transport pipeline (104) originating from the the intermediate unit (103) and which supplies the unit for upgrading hydrocarbons (105). 14. Installation according to claim 13, characterized in that the intermediate unit (103) comprises the liquid/gas separation unit (12), where the installation optionally also comprises an additive supply line (107) which opens into the second hydrocarbon transport pipeline (104), and where: the recirculation line (106) for the liquid solvent is covered in it the intermediate unit (103), or the liquid solvent recirculation line (106) originates from it the intermediate unit (103) and opens out into the first hydrocarbon transport pipeline (102). 15. Installation according to claim 13, characterized in that the upgrade unit (105) comprises liquid/gas the separation unit (12), and where: the liquid solvent recirculation line (106) originates the upgrading unit (105) and supplies the intermediate unit (103), or the liquid solvent recirculation line (106) originates the upgrading unit (105) and opens into the first hydrocarbon transport pipeline (102). 16. Method according to one of claims 1 to 9, characterized in that it is used on an installation according to one of claims 10 to 15.