WO2004011359A2 - Method for transporting crude oils in the form of dispersion - Google Patents

Abstract

The invention concerns a method for transporting in pipes a viscous oil effluent, which comprises the following steps: separating the effluent into at least one solid phase consisting of particles derived from colloidal elements acting on the viscosity of said effluent and into a fluidized liquid phase, maintaining dispersed an amount of particles in said fluidized liquid phase so as to obtain a suspension (2), causing the suspension to circulate in the pipe.

Description

PROCESS FOR TRANSPORTING CRUDE OIL

HEAVY IN THE FORM OF DISPERSION

The present invention relates to the field of transport of effluents

viscous, in particular the so-called "heavy" crudes, for example because of their

asphaltenes content.

There are known methods of transporting viscous crudes which consist

fluidifying the crude by heating, mixing with a fluidizing product, or

treatment prior to transport, for example aqueous emulsion.

However, these techniques are costly in energy, or use

complex processes requiring significant infrastructure which penalizes

the exploitation of deposits.

In the present description, "slurry" means a suspension, or

a dispersion of solid particles in a liquid which can be

circulation, in particular by pumping. This type of slurry flow is already

commonly used during dredging operations in estuaries, rivers,

as well as in the mining industry. The point is to carry a maximum of

solid cuttings with as little pumping energy as possible. In regards to

the petroleum sector, slurry transport is used to enrich

fuels fuels with particles of coal and increase in this way their calorific value. The solid content can reach 60% by mass while

keeping acceptable flow properties.

Thus, the present invention relates to a method of transport in

conduct of a viscous petroleum effluent. According to the invention, the

following steps:

- the effluent is separated into at least one solid phase consisting of

particles from the colloidal elements acting on the viscosity of said

effluent and in a fluidized liquid phase,

- a quantity of particles is kept dispersed in said phase

liquid fluidized so as to obtain a suspension,

- circulating said suspension in the pipe.

The separation step can be carried out by adding an amount of n-

alkane: such as butane, pentane, heptane.

The particles can be removed from the fluidized liquid phase.

The colloidal elements acting on the viscosity can be

asphaltenes.

The particles can be dispersed by mechanical mixing.

The temperature of said suspension in circulation can be controlled

to slow the dissolution of the particles in the effluent.

The temperature of the suspension can be kept below 40 ° C.

Said particles can be encapsulated after separation.

Said particles can be chemically modified before they are

disperse in the fluidized effluent. A dispersing additive of said particles can be added.

A determined quantity of a diluent from said phase can be added

liquid.

It is possible to choose a diluent which poorly solubilizes said particles.

Precipitated asphaltenes can be added in quantity included

between 1 and 30% by mass.

The present invention will be better understood and its advantages

will appear more clearly on reading the following description

examples, in no way limitative, illustrated by the attached figures below,

among:

- Figure 1 compares colloidal and slurry solutions,

- Figures 2 and 2a show the evolution of a slurry as a function of

time,

_- Figures 3 and 4 show the influence of shearing on a slurry,

- Figures 5 and 5a show the influence of temperature on a slurry,

- Figures 6a and 6b show the effectiveness of the encapsulation of

asphaltenes.

The present invention preferably applies to heavy crudes. She

therefore consists in modifying the structural organization of heavy crude which is

behaves like a viscous colloidal suspension, to obtain a

suspension of non-colloidal particles of lower viscosity. The particles concerned by this transformation are, in the context of a preferred embodiment of the present invention, asphaltenes. Asphaltenes are

higher molecular weight molecules in some crudes

oil. They are characterized by their strong polarity and the presence of

polycondensed aromatic nuclei. The recovery of these particles

deployed in crude is largely responsible for the high viscosity of

heavy crudes. This overlap can be removed by maintaining the

asphaltenes in the form of solid particles precipitated from the crude. This

configuration change can be achieved by de-asphalting the crude, then

by dispersing the asphaltenes precipitated in the base liquid, in particular under strong mechanical stirring. A non-limiting procedure was

developed and it was verified that the change in crude morphology under

resulting form of suspension, gives rise to a decrease in the

viscosity. The preferred mode protocol first requires deasphalting of the

gross. Methods already exist for carrying out this operation.

Advantageously, according to the invention, the particles are transported

of asphaltenes in solid form, by the base liquid of the crude in which these

asphaltenes are dispersed in such a way that the liquid obtained is more fluid

than the original crude. Thus, transport by pumping in the pipes is

facility up to refining units. In these refining units, the "slurry" is either introduced as such into these processing units, or after a phase

separation of suspended solid particles, asphaltenes, which can

simplify downstream processes. Example of operating mode:

Asphaltenes are precipitated using pentane according to the standard

American ASTM 893-69. Once filtered (using a porosity 4 frit) and

dried (at 80 ° C for 2 hours), the particles are ground (grinder

Retsch S 1000 ball centrifuge, 15 minutes at 350 rpm) then

sieved between 100 and 500 μm.

For their "slurry", or dispersion, the asphaltenes are dispersed

in deasphalted crude oil with a mechanical agitator RW20 IKA, at 1200

rpm for 20 minutes. The stirring blade is chosen for its top

shearing power. It is a pale serpentine type "bow tie"

which allows an excellent dispersion by the zone of turbulence existing between its windings. The temperature of the sample is maintained at 40 ° C.

In each case described below, 25 g of product are prepared.

_

Test 1: Comparison of two samples, one in the form of

colloidal suspension and the other in slurry form:

a) Two samples containing 10% by mass of asphaltenes were

prepared. The asphaltenes are introduced into the same deasphalted crude

using two different methods:

- one with the procedure described above which results in

a slurry product, - the other with heating at 80 ° C for 1 hour which results in a

produced as a colloidal solution. In this case, we find

substantially the viscosity of a crude having 10% asphaltenes.

The two samples are then observed under the same conditions

under an optical microscope and their viscosity is measured using a rheometer

(type AR2000, plane-plane geometry, with a 1 mm air gap). The

results represented in FIG. 1 (Viscosity in Pa.s as a function of the gradient

shear G) confirm the difference in the morphology of the samples:

no particles are visible under the light microscope for the colloidal solution

1, while slurry 2 contains a lot. Viscosity differences V (Pa.s)

samples (135 Pa.s for the colloidal solution and 40 Pa.s for the slurry)

demonstrate the value of putting asphaltenes in slurry to reduce the

viscosity of heavy crudes. b) A natural asphaltic crude is compared (to 17% of asphaltenes in

mass) with a "slurry" obtained as above but comprising 17% in

mass of asphatene. To be comparable, the two samples were

heated at 40 ° C for 20 minutes. Colloidal crude has a viscosity of

345 Pa.s, while the "slurry" has a viscosity of 95 Pa.s. Process efficiency

is well demonstrated since the drop in viscosity is significant. It can be noted that the viscosity of the slurry in this case is relatively high for a

efficient transport, so dilution may be necessary. Test 2: Monitoring over time the dissolution of the asphaltenes in

slurry suspension:

In order to observe the behavior over time of the morphology of a slurry,

rheological and microscopic evolution of the sample containing 10%

of asphaltenes in slurry is observed over a period of 146 days. during

this time, the sample is left to stand at room temperature (20 ° C)

and direct debits are made. Figure 2 shows

the evolution of the viscosity of the slurry 3 as a function of time. The different

curves (3 to 8) show a progressive redissolution of the asphaltenes which

results in a rise in viscosity to the value of the viscosity of the

colloidal solution 9. Figure 2a gives the viscosity values as a function of time t in days, and the corresponding light microscope photographs

demonstrate the dissolution of asphaltenes. However, this development at the

room temperature is slow, which keeps the benefit of the

viscosity reduction for a pipeline flow of several hours.

Test 3: Influence of shear on the dissolution of

asphaltenes:

The shear undergone by the slurry during its flow in pipeline

may disturb its morphology and annihilate too quickly the

decrease in viscosity caused. In order to assess the impact of shear,

various tests have been carried out. Two slurry suspension samples containing 10% by mass

asphaltenes were prepared according to the protocol described above. One is

left to stand, while the other is stirred using a magnetic stirrer

and a magnetic bar. The rheological evolution (viscosity in Pa.s) and

morphological was followed in both cases. The results shown on the

Figure 3 (viscosity as a function of t in days) via curve 10

which corresponds to a sample with stirring and curve 11 which corresponds to

a sample at rest, show no significant difference between the

two samples. Another test consisted in leaving a suspension sample in

slurry in the rheometer, under controlled shear (50 s ^"1 ) and to record its

viscosity throughout the duration of the test, that is to say ten hours h.

Figure 4 shows that under these test conditions, no

viscosity increase V during shearing lasting approximately 8

hours.

These two tests prove the absence of a strong influence of the flow

on the transformation of crude oil in the form of a slurry suspension into a colloidal suspension. It can also be noted that if the slurry configuration had been

highly sensitive to shear, it could not have been carried out because the

sample preparation procedure requires very high

shear. Test 4: Influence of temperature on the dissolution of

asphaltenes:

After showing that the slurry morphology of the crude is stable at

ambient temperature (T = 20 ° C), the influence of temperature is determined.

To test its resistance to temperature, two samples containing 10%

asphaltenes were prepared according to the procedure described and placed in

oven at 40 ° C and 60 ° C. Their rheological and microscopic evolution was

observed. The results of FIG. 5 (ratio of the viscosity at time t over the

viscosity at time 0: Vt / VO, as a function of time h in hours) show that

temperature rise strongly promotes the kinetics of dissolution of

asphaltenes, the kinetics being represented by the slope of the lines 12 (at 40 ° C) and 13 (at 60 ° C). Figure 5a shows the effect of temperature on a sample

after 24 hours. Slurrying heavy crude oil may require

additional precautions, or specific treatments, to block, or

slow down, the - dissolution of the asphaltenes in the crude oil if it has to be

transported at a temperature above 40 ° C.

Test 5: Preliminary encapsulation of asphaltenes:

In order to block the dissolution of asphaltenes to guarantee stability

slurry at temperature and then be able to increase the amount

in asphaltenes introduced in suspension, the asphaltenes can be

advantageously encapsulated before being mixed with the crude. The method of

complex coacervation has been employed, for example described by J. Richard and J- P Benoît in "Microencapsulation" - Engineering Techniques: Engineering

processes; J 2 210, 1-20. The experimental protocol used is as follows: two

100 ml solutions, one containing 1% gelatin, the other 1% gum

arabic are prepared in milli-Q water and maintained at 40 ° C. The pH of

two solutions is adjusted to 6.5. The asphaltenes are then dispersed in the

gelatin solution using a Heidolph shaker for 30 minutes,

always at 40 ° C. Stirring on the order of 700 min ^{-1 is used} . This is

then followed by dropwise addition of the gum arabic solution

(about 3 ml per minute). Then the pH of the mixture is adjusted to 4.5 using a

10% acetic acid solution (predetermined volume). In order that the

coacervate droplets can settle around the oil drops,

agitation is kept constant for one hour. Finally, the system temperature is lowered to 8 ° C to allow the coacervate to gel. We

add 2 ml of glutaraldehyde and the pH is finally adjusted to 9 using a

10% sodium hydroxide solution (predetermined volume) and everything is left

with stirring at 4500 rpm for 12 hours. The capsules obtained are

then filtered, washed with water and toluene and finally dried.

A slurry sample containing 10% encapsulated asphaltenes was

prepared and left in an oven at 40 ° C. Its temperature resistance has been verified by

rheological and microscopic monitoring. Figure 6a shows the structure of the

suspension of encapsulated asphaltenes after 1 day and after 36 days. The

results show that encapsulation was effective in blocking the

dissolution of asphaltenes, the slurry configuration remaining intact after over 30 days at a temperature of 40 ° C. A slight increase in viscosity (from 50 Pa.s to 60 Pa.s) is observed. Figure 6b shows the structure of the

suspension of unencapsulated asphaltenes at the same time: the structure

is no longer of the suspension type, and the viscosity becomes very important again.

Test 7: Inerting the asphaltenes by surface polymerization:

Always with the aim of blocking the solvation of asphaltenes when

these are in suspension, we modify the asphaltenes precipitated by acid

acrylic. The acid adsorbed on the asphaltenes is then polymerized. For this

make, to 4 grams of asphaltenes obtained by precipitation with heptane and

dried for two hours under vacuum, 4 grams of acrylic acid are added

and 4 grams of heptane. The suspension is stirred for two hours at

room temperature under an inert atmosphere (argon). Acrylic acid in

excess is removed by filtration and the solid fraction is resuspended

in 8 grams of heptane. After adding 0.04 g of azo-bis-isobutyronitrile, the

suspension is maintained for 4 hours at 60 ° C. with stirring, always under

inert atmosphere. After filtration and washing with heptane, the asphaltenes

modified are dried for 2 hours at 80 ° C. A slurry (sample N ° l)

composed of 2 grams of modified asphaltenes and 18 grams of deasphalted crude oil is prepared according to the procedure already described. We prepare in

parallel another slurry (sample N ° 2) containing 2 grams of asphaltenes

unmodified and 18 grams of deasphalted crude. These two samples of slurry are stored at 80 ° C and the evolution of their viscosity is followed during

time.

After a slight increase during the first hours of

storage of sample No. 1, the viscosity stabilizes at a value which remains

about three times lower than that of sample No. 2 after one week

storage at 80 ° C.

Modification of asphaltenes allows better control of their capacity

to be dissolved in the deasphalted crude.

Test 8: Inerting the asphaltenes by surface modification:

The modification of the surface of asphaltene particles by

oleophobic compounds can inhibit the solvation of asphaltenes. AT

25 cm3 of perfluoroheptanoic acid, 4 g of precipitated asphaltenes are added. The

suspension is stirred at room temperature for 2 hours. After

filtration and washing with heptane, the asphaltenes are dried at 80 ° C. for 2 hours.

A slurry (sample N ° 3) composed of 2 grams of asphaltenes

modified and 18 grams of deasphalted crude oil is prepared according to the

already described. We prepare in parallel a slurry (sample N ° 4) containing 2 grams of unmodified asphaltenes and 18 grams of crude

deasphalted. These two samples are stored at 80 ° C and the evolution of their

viscosity is monitored over time.

The viscosity of sample N ° 3 remains approximately two times lower than that

of sample N ° 4 after one week of heating at 80 ° C

We can therefore clearly improve the process according to the invention by

treating asphaltenes after their precipitation from crudes.

Claims

1) Method for transporting a viscous petroleum effluent by pipeline, characterized in that the following steps are carried out: - the effluent is separated into at least one solid phase consisting of particles from the colloidal elements acting on the viscosity of said effluent and in a fluidized liquid phase, - a quantity of particles is kept dispersed in said liquid phase fluidized so as to obtain a suspension, - circulating said suspension in the pipe. 2) Method according to claim 1, wherein the separation is carried out by adding a quantity of n-alkane: such as butane, pentane, heptane. 3) Method according to one of claims 1 or 2, in which the particles of the fluidized liquid phase. 4) Method according to one of the preceding claims, wherein said elements are asphaltenes. 5) Method according to one of the preceding claims, wherein said particles are dispersed by mechanical mixing. 6) Method according to one of the preceding claims, wherein the temperature of said circulating suspension is controlled to slow down the dissolution of the particles in the effluent. 7) Method according to claim 6, wherein the suspension temperature below 40 ° C. 8) Method according to one of claims 1 to 5, wherein one encapsulates said particles after separation. 9) Method according to one of claims 1 to 5, wherein one modifies chemically said particles before dispersing them in the effluent cutback. 10) Method according to one of the preceding claims, wherein adds a dispersing additive to said particles. 11) Method according to one of the preceding claims, wherein add a determined quantity of a diluent of said liquid phase. 12) Process according to claim 11, in which a diluent is chosen poor solubilization of said particles. 13) Method according to one of claims 2 to 12, wherein the precipitated asphaltenes are added in an amount between 1 and 30% by mass.