Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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PROCESS FOR DEASPHALTING BITUMEN
FIELD OF THE INVENTION
The present invention relates to the f1eld of upgrading heavy oil or bitumen and, in
particular, to a process for deasphalting heavy oil or bitumen.
BACKGROUND OF THE INVENTION
There are many subterranean tar sand formations throughout the world which contain
high viscosity heavy oil and bitumen. The vast Athabasca tar sand field and the Cold Lake
deposits in Alberta, Canada represent some of the most notable examples of such formations.
For the purposes of this application, all viscous hydrocarbons, including heavy crude oil and
bitumen, will be referred to herein as bitumen.
A variety of methods have been proposed for recovering bitumen from these
formations by increasing the mobility of the bitumen. Such methods include solvent injection
and thermal steam injection processes. One known method for recovery of bitumen is the so-
called Cyclic Steam Stimulation (CSS) process.
In the CSS process, steam is injected through a well into a bitumen-bearing formation.
Heat transferred to the formation lowers the viscosity of the bitumen, thereby improving the
mobility thereof. Several cycles of steam injection and bitumen production are continued
until bitumen production becomes too low to justify further steam injection.
Bitumen is recovered in the CSS process as a water-in-bitumen emulsion or as a
mixture of a water-in-bitumen emulsion and free water which has a high viscosity due to a
relatively high concentration, for example from about 15 to 40%, of asphaltene in bitumen.
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Unlike conventional crude, viscous bitumen cannot be transported by pipeline. One method
for transporting bitumen in a pipeline includes heating the bitumen prior to and during
transport. However, this method is expensive and very impractical as heating equipment must
be installed and the pipeline must be insulated.
Another method for transporting bitumen involves diluting the bitumen with a C5-Clo
gas plant condensate diluent. For example, bitumen from the Cold Lake field is typically
diluted with 27 to 30% (vol) C5-Clo gas plant condensates to sufficiently reduce the viscosity
of the bitumen for transport to a refinery. However, the disadvantages of this method are the
dependency on the availability of gas plant condensates, loss of the diluent during blending
and recovering the full cost of the diluent from customers, i.e. refineries.
Partial upgrading has therefore been proposed to separate the heavier fraction of
bitumen prior to transport. Known partial upgrading processes include separation of the
heavier fraction by distillation or by using light hydrocarbon solvents. One such process
involves dissolving bitumen in 2 to 10 times (v/v) of a C3-CI0 light hydrocarbon solvent to
lower the viscosity by precipitating the solvent-insoluble asphaltene and subsequently
removing the precipitate by liquid/solid separation.
French Patent Application Number 2,579,218 (Ballmgartner, P., September 26, 1986)
relates to a process for deasphalting heavy hydrocarbon oils. The process consists of forming
an oil-in-water emulsion and adding a sufficient quantity of a deasphalting solvent to separate
the mixture into two phases, the upper phase consisting of a mixture of deasphalted oil and
solvent and the lower phase consisting of a suspension of asphaltene in water. The water:oil
ratio in the emulsion is in the range of from 25:75 to 40:60, preferably in the range of from
30:70 to 50:50. Optionally, the oil-in-water emulsion is prepared by mixing the heavy oil
with water and with a surfactant, the proportion of surfactant sufficient to form an oil-in-water
emulsion.
United States Patent Number 4,634,520 (Angelov, G. et al, January 6, 1987) describes
a process for simultaneous de-emulsification and deasphalting of a heavy oil/water emulsion.
A heavy oil/water emulsion is mixed with from 2 to 5 times by weight of pentane or a
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mixture of pentane, butane and hexane, of which pentane is the major component.
Deasphalted oil, asphaltics and emulsion water are recovered separately in three different
phases. The solvent-insoluble asphaltics coalesce around the dispersed emulsion water such
that particles comprising water droplets stabilized by a sheath of asphaltics settle out of the
emulsion. After some of the oil and solvent mixture is decanted, the particles are coalesced
into large stable agglomerates by feeding the mixture to a hot water bath at a temperature of
from 85 to 95C. The agglomerates are skimmed from the surface of the water.
International Publication Number WO 90/06350 (Muller, A., June 14, 1990) teaches a
solvent-deasphalting process for a bitumen-in-water emulsion, which is performed in the
presence of a surfactant selected to provide a three-phase mixture. The volume of solvent is
from 2 to 5 times the volume of the bitumen-in-water emulsion. The upper phase contains
the solvent and deasphalted bitumen, while the intermediate phase is aqueous and the lower
phase contains the solvent-insoluble asphaltene. The intermediate phase contains the
surfactant as well as any soluble mineral salts which were present in the bitumen-in-water
emulsion. The asphaltene is in a semi-solid or solid form which is difficult to handle.
Bearing in mind that the partial upgrading is to be performed at the production site to
facilitate transport to a refinery, the disadvantages of the processes for partial upgrading
described above are that they increase production costs by involving a number of steps, costly
equipment for heating or supplying water baths, relatively sophisticated liquid/solids
separation techniques and equipment, and/or the addition of a significant amount, up to 10
times by volume, of a solvent.
Moreover, the asphaltene is in the form of a waste product when it is separated from
bitumen using the above-described processes. As mentioned previously, asphaltene is
typically recovered as a solid or a semi-solid which is difficult to handle. Also, in currently
known processes wherein asphaltene is removed from the bitumen as an asphaltene-in-water
emulsion, the water content is too high for the asphaltene-in-water emulsion to be useful as a
fuel. For example, an asphaltene-in-water emulsion produced from a bitumen-in-water
emulsion having a typical water content of 30% and an asphaltene yield of 20 to 30% (based
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on bitumen) will have a water content of from 59 to 68% water, which is too high for use as
a fuel. Another requirement for a fuel is a stable asphaltene-in-water emulsion.It will be appreciated by those skilled in the art that an integrated process for
deasphalting bitumen and producing a useable asphaltene product would be very desirable.
One particularly advantageous use for asphaltene is as a fuel. CSS is an energy-intensive
process requiring three barrels of steam (water-equivalent) to produce one barrel of oil. The
most preferred fuel for generating steam is natural gas although its availability and cost
continue to be of concern. It would therefore be very advantageous to produce an asphaltene
emulsion from a partial upgrading process for use as a fuel for steam generation.
Another use for an asphaltene product is for plugging the steam-swept zones of areservoir to produce bitumen from unswept zones during CSS, thereby increasing the sweep
efficiency of the process.
Bitumen also contains heavy fractions which are rich in heavy metals, such as nickel
and vanadium, and sulfur. It will be appreciated by those skilled in the art that a relatively
simple partial upgrading process which increases the value of bitumen by removal of the
heavy metals and sulfur would be very advantageous.
SUMMARY OF THE INVENTION
According to one aspect of the present invention, there is provided a process for
upgrading bitumen, comprising the steps of: de-watering a bitumen/water emulsion to reduce
the concentration of water therein to a concentration in the range of from about 0 to about
20% by volume; adding a solvent and an asphaltene-dispersing surfactant to the de-watered
bitumen/water emulsion to form a stable asphaltene-in-water emulsion; settling the mixture
into two phases, the upper phase comprising deasphalted bitumen and the lower phase
comprising an asphaltene-in-water emulsion; and separating the two phases.
According to another aspect of the present invention, there is provided a process for
upgrading bitumen, comprising the steps of: adding an inversion surfactant downhole to invert
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a water-in-bitumen emulsion to a bitumen-in-water emulsion; pumping the bitumen-in-water
emulsion to the surface; de-watering the bitumen-in-water emulsion to reduce theconcentration of water therein to a concentration in the range of from about 0 to about 20%
by volume; adding a solvent to the de-watered bitumen-in-water emulsion; adding an
asphaltene-dispersing surfactant to the bitumen-in-water emulsion to form a stable asphaltene-
in-water emulsion; settling the mixture into two phases, the upper phase comprising
deasphalted bitumen and the lower phase comprising an asphaltene-in-water emulsion; and
separating the two phases.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
A process for partially upgrading bitumen according to the present invention includes
treating a bitumen/water emulsion, for example a wellhead emulsion, by at least partially de-
watering the emulsion, adding a solvent and an asphaltene-dispersing surfactant to the de-
watered emulsion, and settling the resultant mixture into a first layer cont~ining deasphalted
bitumen (DAB) and solvent and a second layer cont~ining a stable asphaltene-in-water
emulsion. The asphaltene particles are dispersed in a continuous water phase which is
separated from the DAB and solvent. The bitumen is thus partially upgraded by deasphalting,
de-watering and reducing the concentration of other impurities. Furthermore, the DAB has a
significantly lower viscosity, facilitating transport to a refinery. As used herein, the term
bitumen/water emulsion will be understood to include water-in-bitumen and bitumen-in-water
emulsions and mixtures of water-in-bitumen emulsions and free water.
Thus, in accordance with the present invention, the bitumen is of a higher quality, and
therefore of a higher value. Furthermore, the asphaltene is separated *om the bitumen as a
stable asphaltene-in-water emulsion. The stable asphaltene-in-water emulsion produced by the
present invention has a relatively low viscosity, especially as compared with known processes
wherein the asphaltene is in the form of a solid or a semi-solid and is typically regarded as a
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waste material which is difficult to handle. The asphaltene-in-water emulsion can be used as
an alternate fuel, as a CSS process enhancer and as road pavement and roofing material.
As discussed previously herein, bitumen is typically recovered from a well by a CSS
process in the form of a water-in-bitumen emulsion or as a mixture of a water-in-bitumen
emulsion and free water. In one embodiment of the present invention, the bitumen/water
emulsion is de-watered to a water content in the range of from about 0 to about 20% by
volume, by a process known to those skilled in the art. Such processes include heat
treatment, addition of a solvent, addition of a chemical demulsifier, electrostatic coalescence,
membrane processes and combinations thereof.
By reducing the water content in the bitumen/water emulsion, the asphaltene-in-water
emulsion is produced as a usable product. As mentioned previously herein, an asphaltene-in-
water emulsion produced from a bitumen-in-water emulsion having a typical water content of
30% and an asphaltene yield of 20 to 30% (based on bitumen) will have a water content of
from 59 to 68% water which is too high for use as a fuel. In accordance with the present
invention, the water content of the asphaltene-in-water emulsion is reduced substantially to
provide a product which is useful, for example as a fuel, instead of a waste product. The de-
watering step has the further advantage that some of the impurities, such as sodium, calcium,
magnesium and silica, are removed in the discarded water. The resultant asphaltene-in-water
emulsion is therefore of a higher quality.
The solvent deasphalting step is performed by addition of a solvent and an asphaltene-
dispersing surfactant to the bitumen/water emulsion. Suitable solvents are one or more C3-CI5
hydrocarbons or C5-Clo gas plant condensates. Preferably, the solvent is a C3-C10
hydrocarbon. Examples of suitable solvents are propane, butane, pentane, hexane, heptane
and naphtha. As in conventional deasphalting, the yield of DAB increases while the quality
of the DAB deteriorates with higher molecular weight solvents. A solvent is therefore
selected such that it provides a good yield of DAB with acceptable quality.
Preferably, the bitumen/water emulsion, solvent and surfactant are mixed in a static in-
line mixer. The in-line mixer is a tube or pipe having several alternating right- and left-
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handed helices oriented so that each leading edge is at 90 to the trailing edge of the oneahead. The flow rate of fluids, the internal diameter of the tube or pipe and the number of
elements are some of the parameters that can be varied to obtain good mixing and the
required residence time to separate the asphaltenes.
The solvent is added to the bitumen/water emulsion, for example, in a ratio of from
about l:1 to about 5:1 (v/v). Solvent deasphalting may be conducted at temperatures and
pressures ranging from ambient temperatures and pressures to conditions typical of existing
processing streams, for example to temperatures up to about 150C and pressures up to about
200 psi.
The asphaltene in the bitumen/water emulsion is not soluble in the solvent and if the
de-watered bitumen/water emulsion was treated with solvent alone, the asphaltene would
separate from the bitumen and the water as a third phase, as described in International
Publication Number WO 90/06350 discussed previously herein. Moreover, the asphaltene
would be in the undesirable form of a solid or a semi-solid. The addition of a suitable
asphaltene-dispersing surfactant in accordance with the present invention results in a two-
phase separation of bitumen/solvent and a stable asphaltene-in-water emulsion. Furthermore,
the asphaltene-in-water emulsion has a relatively low viscosity.
The asphaltene-dispersing surfactant of the present invention is any non-ionic or ionic
surfactant which is capable of forming a stable asphaltene-in-water emulsion. A stable
asphaltene-in-water emulsion is defined herein as being an emulsion in which the asphaltene
particles dispersed in the continuous water phase are small and do not readily settle out of the
continuous phase over a period of time. Preferably, the asphaltene particles of the asphaltene-
in-water emulsion are of an average particle size of about 10 ~m. A stable emulsion is also
an emulsion which can be pumped without breaking.
As will be discussed in more detail below, if the asphaltene-in-water emulsion is to be
used as an emulsion fuel, the surfactant should preferably not contain any sodium.
Accordingly, a non-ionic surfactant is preferred because it does not introduce any undesirable
alkali metal ions to the emulsion or change the pH. The surfactant is selected to have the
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proper hydrophillic-lipophilic balance to create a stable asphaltene-in-water emulsion.
Suitable asphaltene-dispersing surfactants include ethoxylated alkyl phenols, ethoxylated
dialkyl phenols, ethoxylated alcohols, block polymers of ethylene oxide and propylene oxide,
propoxylated alkyl phenols and propoxylated dialkyl phenols. Preferably, the surfactant is an
ethoxylated nonyl phenol with from about 4 to about 40 ethoxy groups per mole of nonyl
phenol.
The asphaltene-dispersing surfactant is preferably used in a concentration in the range
of from about 100 to about 50,000 ppm, more preferably from about 500 to about 10,000
ppm, based on the weight of bitumen/water emulsion. The asphaltene-dispersing surfactant
may be added at ambient conditions or at elevated process stream temperatures, for example
150C, and pressures, for example 200 psi.
The asphaltene-dispersing surfactant may be introduced in the form of an aqueoussolution of the surfactant. In the case wherein the water is substantially completely removed
from the emulsion, water is introduced by way of an aqueous solution of the asphaltene-
dispersing surfactant and/or free water to achieve the desired water content in the asphaltene-
in-water emulsion.
The mixture is then allowed to settle in a separation vessel. Due to the densitydifference, the DAB-solvent mixture separates at the top of the vessel and the asphaltene-in-
water emulsion at the bottom. The asphaltene-dispersing surfactant creates a stable
asphaltene-in-water emulsion.
In another embodiment of the present invention, the water-in-bitumen emulsion is first
inverted downhole to a bitumen-in-water emulsion by injection of an inversion surfactant
directly into the borehole. The bitumen-in-water emulsion is then de-watered at the surface in
a manner known to those skilled in the art, for example, by fl~hing the water continuous
phase, centrifugation, and membrane processes. In the embodiment wherein the
bitumen/water emulsion is inverted downhole, the recovery of bitumen is increased because
the viscosity is reduced.
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A water-in-bitumen emulsion may be inverted by addition of an inversion surfactant
before or after the de-watering step. It will however be appreciated by those skilled in the art
that, as the water concentration in the de-watered bitumen/water emulsion approaches 0%, the
emulsion may not be easily inverted.
Suitable inversion surfactants are ethoxylated alkyl phenols and ethoxylated dialkyl
phenols. Preferably, the inversion surfactant is ethoxylated nonyl phenol. A particularly
suitable ethoxylated nonyl phenol is an ethoxylated nonyl phenol with 10 to 20 ethoxy groups
per mole of nonyl phenol. It is not necessary for the inversion surfactant to create a stable
bitumen-in-water emulsion as the bitumen-in-water emulsion is merely an intermediate in the
integrated process of the present invention. The inversion surfactant is preferably added in a
concentration of from about 50 to about 50,000 ppm, more preferably in a concentration of
from about 100 to about 10,000 ppm, based on the weight of bitumen/water emulsion.
The DAB-solvent mixture may then be subjected to a solvent recovery step whereinthe solvent is recovered by distillation. Preferably, the recovered solvent is recycled to the
deasphalting step with make-up solvent. Optionally, enough solvent is left in the DAB during
distillation to meet the pipeline viscosity specification.
Preferably, the asphaltene-in-water emulsion is further enhanced by sonication and/or
by passing the asphaltene-in-water emulsion through a static in-line mixer to create smaller
particles. This is especially desirable if the asphaltene-in-water emulsion is to be used as a
fuel. The asphaltene particles in the asphaltene-in-water emulsion may be made finer by
sonication, for example at 20 to 40 kHz. The use of sonication creates a more stable
asphaltene-in-water emulsion.
The stable asphaltene-in-water emulsion produced in accordance with the present
invention is in a form that may be used in various applications. For example, the asphaltene-
in-water emulsion can be used to enhance the CSS process, as an alternate fuel or as road
pavement and roofing materials.
One problem with the CSS process is that only the zone proximate the injection well is
swept by the steam injected into the well, while further away from the injection well, bitumen
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is still viscous in cold or unswept zones. The steam distribution problem is a result of steam
leaking through pores in the steam-swept zone. A variety of efforts have been made to find
fluids which can be economically injected to plug the pores in the steam-swept zone of the
formation, where steam has displaced most of the viscous oil, so as to divert steam which is
injected thereafter to the cold zones of the formation.
The asphaltene-in-water emulsion of the present invention may be injected downhole
to block high permeability channels so that subsequent injection of steam forces asphaltene
into the pores, thereby reducing the permeability of the rock formation and enhancing the
distribution of steam into the formation, especially into previously cold zones.Another use for the asphaltene-in-water emulsion is as an alternate fuel. It will be
appreciated by those skilled in the art that the creation of an emulsion fuel is difficult using
solid asphaltene. Solid asphaltene must generally be heated to a high temperature and mixed
at a high shear rate with water cont~ining a suitable surfactant. In accordance with the
present invention, there is a fine dispersion of asphaltene in the water. The dispersion may be
made even finer by sonication. If the asphaltene-in-water emulsion is to be used as an
alternate fuel, the surfactant is preferably a non-ionic surfactant with no sodium ions. It will
be appreciated by those skilled in the art that sodium ions would cause corrosion of the boiler
tubes.
It will be appreciated by those skilled in the art that the present invention provides an
integrated process for recovery and partially upgrading bitumen. In accordance with the
present invention, the viscosity of the bitumen is significantly reduced and the quality of the
bitumen is improved. The asphaltene is recovered in a useable form which can be used as a
source of fuel at the production site and which additionally can be used to enhance the
recovery of the bitumen from the rock formation. Furthermore, it is also possible to recycle
the water recovered from the bitumen-in-water emulsion to the steam generation plant at the
production site.
In accordance with the present invention, the viscosity of the bitumen is significantly
reduced by deasphalting. Furthermore, as compared with conventional solvent deasphalting
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processes, less solvent is required. For example, the requirement for solvent can be reduced
to as low as about 1:1 (v/v) of solvent:emulsion. Accordingly, there is a significant savings in
the cost of the solvent and the cost of recovery of solvent.
Described below are one example of a conventional solvent deasphalting process for
comparative purposes and two examples of the process of the present invention. Examples of
the present invention are for illustrative purposes only and are not intended to limit the scope
of the invention defined by the claims below.
Comparative Example 1
Conventional Solvent Deasphalting Process
A wellhead sample cont~ining a water-in-bitumen (30:70) emulsion was obtained from
a CSS-stimulated well from the Cold Lake field in Alberta, Canada. The emulsion was
deasphalted with pentane as a solvent using a pentane to emulsion ratio of 2:1 (v/v) at
ambient conditions. The solvent was first mixed with 50 ml of emulsion using a glass rod.
The solvent-emulsion mixture was then shaken in an orbital shaker for 10 minutes at 300 rpm.
After mixin~, the asphaltenes were allowed to precipitate.
After 15 minutes of settling, the DAB and pentane layer was pipetted out from the top
of the bottle. The asphaltene and water settled at the bottom of the bottle. The asphaltene
was in a semi-solid form and entrained some of the water. Such a semi-solid asphaltene
precipitate is difficult to handle and to emulsify.
The concentration of vanadium and nickel in the DAB was 98 and 40 ppm,
respectively, as compared to 177 ppm vanadium and 80 ppm nickel in un-deasphalted
bitumen. The viscosity of the DAB was 4000 cp at 23C compared to a bitumen viscosity of
110,000 cp at 23C.
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Example 1
100 g (98 ml) of de-watered bitumen (0% water), 200 ml of pentane and 15.53 g of an
aqueous surfactant solution cont~ining 3% ethoxylated nonyl phenol (11 ethoxy groups per
mole of nonyl phenol) were mixed in an orbital shaker at 250 rpm for 10 minutes. The
mixture was allowed to settle, forming two layers. The top layer was DAB diluted with
pentane and the bottom layer was an asphaltene-in-water emulsion.
The two layers were separated and the pentane was recovered from the DAB. The
asphaltene-in-water emulsion was sonicated at 20 kHz for 29 minutes to make a finer
dispersion.
The DAB yield was 75% (by weight) based on the bitumen starting material and theasphaltene yield was 25% (by weight). The asphaltene-in-water emulsion contained 37%
water. The particle size of the sonicated emulsion was 10 ,um.
The concentration of vanadium, nickel, sodium and calcium in the DAB was 126, 52,
4 and 11 ppm, respectively, as compared to 190 ppm vanadium, 77 ppm nickel, 928 ppm
sodium and 67 ppm calcium in un-deasphalted bitumen. The viscosity of the DAB was 2240
cp at 40C compared to a bitumen viscosity of 12,000 cp at 40C.
The Example generated two useful products. The viscosity of the partially upgraded
DAB was reduced to approximately one-sixth of that of the bitumen starting material. The
metal content of the DAB was approximately 50% lower than that of the bitumen starting
material. The asphaltene-in-water emulsion had a water content sufficiently low to be used as
a fuel to generate steam for the CSS process for recovery of bitumen. The asphaltene-in-
water emulsion is also suitable for injection into the reservoir to improve the sweep efficiency
of the CSS process.
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Example 2
A water-in-bitumen emulsion (100 g) cont~ining 23.3% water from a steam-stimulated
well at Cold Lake, Alberta was centrifuged to reduce the water content to 13.4%. The
emulsion with reduced water was mixed with an ethoxylated nonyl phenol surfactant and a
C5-C~o solvent at room temperature. The ratio of solvent to emulsion was 2.9:1 (v/v). The
DAB yield of 94.3% was higher than that obtained in Example 1, in which a lighter solvent
was used. However, the quality of the DAB was not as good, with concentrations of nickel
and vanadium of 59 ppm and 148.5 ppm, respectively, as compared to the concentrations of
69 and 167 ppm in the original bitumen.
The viscosity of the DAB was 4257 cp at 25C and 1092 cp at 39.7C compared to abitumen viscosity of 33,530 cp at 25C and 5817 cp at 39.8C. Note that the asphaltene yield
in this Example is only 5.7%. Thus, even though the water-in-bitumen emulsion feed
contained only 13.4% water, the asphaltene-in-water emulsion contains 73% water, which is
more than the desired content of 30% or less. To achieve a 30% water content in the
asphaltene-in-water emulsion, the water content in the original water-in-bitumen emulsion
should have been reduced to about 2.4%.
This Example illustrates the effect of a higher molecular weight solvent on the yield
and quality of DAB. It also demonstrates the requirement for a low water content in the
starting bitumen/water emulsion to achieve an asphaltene-in-water emulsion of the desired
water content.
