Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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A SURFACTANT, THE PREPARATION OF THE SAME AND USE THEREOF
FIELD OF THE INVENTION
The present invention relates to a macromolecule surfactant used for
dispersing heavy oil in
water and preventing heavy oil particles from aggregation so as to reduce
viscosity and
improve flowability of the heavy oil, and to the preparation and use thereof.
BACKGROUND OF THE INVENTION
Among oil&gas resources of the world, common crude oil only accounts for about
30%,
while heavy oil and ultra heavy oil resources account for 70% or so. The
onshore heavy oil
and asphalt resources also account for over 20% of the total oil resource in
China. As the
heavy oil and ultra heavy oil have the general properties of high viscosity,
high density and
high contents with resin & asphaltene, there are huge difficulties in
exploitation and
transportation of the ultra heavy oil. Since the exploitation of the heavy oil
from 1960s,
thermal recovery technology (i.e. heating method) and cold recovery technology
of the heavy
oil have been developed, wherein the main exploiting mode of the thermal
recovery
technology includes cyclic steam stimulation, steam flooding etc, and the main
means of the
cold recovery technology include blending light crude oil for viscosity
reduction and chemical
viscosity reduction etc. Most technologies have been widely used in heavy oil
exploitation
and good effects have been achieved. Among them, the research on reducing
viscosity of
heavy oil by emulsification with surfactant is most active, and it always is a
focus of
international research.
The principle of reducing viscosity by using surfactant can be classified as
follows: (1)
reducing viscosity by emulsification, that is, the viscosity is reduced by
converting a W/O
emulsion phase to an O/W emulsion phase with surfactant; (2) reducing
viscosity by
demulsification, that is, in the presence of surfactant, a W/O emulsion is
demulsified to form
free water and the viscosity is reduced by forming "oil-in-water", "suspended
oil" or "floating
oil on water" according to the free water amount and flow rate; and (3)
reducing viscosity by
adsorption, that is, an aqueous solution of surfactant is injected into oil
well so as to destroy
the film of heavy oil on the surface of oil pipe or sucker rod, inverse the
surface wettability
thereof to be hydrophilic and form continuous water film thereby reducing the
resistance of
crude oil flow during the oil pumping. The three principles tend to exist
simultaneously.
However, the dominant principle of reducing viscosity may vary with different
surfactants
and conditions.
The key point of reducing viscosity by emulsification is to form properly
stable O/W
emulsion, which will not undergo demulsification and delamination during the
whole
exploitation process, while can be easily demulsified and dehydrated finally
in the oil
gathering station or oil refinery. Accordingly, the selected emulsifying
viscosity reducer
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should have the following two characteristics: (1) it can emulsify the heavy
oil well and form
relatively stable O/W emulsion, or it can water-wet the oil pipe or sucker rod
well and form
stable water film; and (2) the formed O/W emulsion cannot be too stable,
otherwise it will
affect the next step of dehydration. In addition, the selected surfactant also
should have the
features of high efficiency, low price, sufficient supply and less
consumption.
According to the charge after dissolution, the emulsifying viscosity reducer
can be classified
to four categories: anionic, cationic, ampholytic and non-ionic. According to
the functional
group carried by the surfactant, the emulsifying viscosity reducer can be
classified to fatty
acid salt (anionic), petroleum sulfonate (anionic), polyoxyethylene
alkylphenol ether
(non-ionic) and the like. Among them, carboxylate surfactant has relatively
good
emulsification effect on ultra heavy oil, while OP and Tween non-ionic
surfactant have
relatively good emulsification effect on common heavy oil. The commonly used
emulsifying
viscosity reducer comprises AE1910, J-50, GY-1, BN-99 and HRV and the like.
The
surfactant used for incorporating active water into heavy oil comprises sodium
alkylsulfonate,
sodium alkylbenzenesulfonate and OP-10.
In recent years, the study on the formulation of emulsifying viscosity reducer
is very active.
These emulsifying viscosity reducers mostly have formulation comprising multi-
components,
both non-ionic and ionic surfactants, in synergistic combinations. For a part
of emulsifying
viscosity reducers, their formulations additionally comprise alkali, C1-C4
alcohol, biopolymer
and freezing point reducing agent.
Chinese Patent CN 1778862 discloses a composite emulsifying viscosity reducer
comprising
petroleum sulfonate formaldehyde condensate (anionic surfactant), alkylphenol
or fatty acid
salt-polyoxyethylene ether (nonionic-anionic surfactant) and demulsifier. US
Patent
5,934,303 discloses a process for emulsifying heavy oil with naphthalene
sulfonate
formaldehyde condensate. Wenhui MA etc. disclose (The Study on Heavy Crude Oil
Sulfonates and Its Viscosity Reducing Property, Chemical Engineering of Oil
and Gas, 2006,
35(1): 57-59) heavy oil sulfonate surfactant for reducing viscosity of heavy
oil by
emulsification, which is produced by using of the heavy oil of DAQING as raw
material.
Qingdong WU etc. disclose (Development and Application of CR-1 Heavy Oil
Viscosity
Reducer in High Temperature Reservoirs) that a composite system comprising
several
non-ionic surfactants, alkali, additives and freezing point reducing agent is
used as heavy oil
viscosity reducer. Although the technologies above have certain effects on
reducing viscosity
of heavy oil by emulsification, it is well known that the technology of
reducing viscosity of
heavy oil by emulsification has not been used widely mainly due to the
following reasons: (1)
large amount of emulsifying viscosity reducers are used and then the cost is
high; (2) reducing
viscosity by emulsification needs vigorous stir to form stable O/W emulsion,
which is
difficult to achieve underground; (3) the system of reducing viscosity by
emulsification is
strong alkaline, which leads to higher requirement for device and pipe; (4) it
is so difficult for
emulsified heavy oil to undergo demulsification and dehydration, and it
becomes more
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difficult to deal with the waste water; (5) emulsifying viscosity reducers
have high selectivity
to heavy oils, which brings about great difference in the application effect;
and (6) there are
not many emulsifying viscosity reducers which can be applied in the high
temperature and
high mineralization reservoir condition and the cost of production is very
high. Accordingly,
solving the above-mentioned issues becomes the key for large-scale application
of the
technology of reducing heavy oil viscosity by emulsification, and also is the
trend of research
and development of the technology for reducing heavy oil viscosity.
SUMMARY OF THE INVENTION
The object of the present invention is to prepare a macromolecular surfactant,
which has the
properties of both oil-soluble viscosity reducer and surfactant as follows:
(1) the function of
strong lipophilic group is to render the macromolecular surfactant similar
compatibility with
heavy oil, and thus the macromolecular surfactant can be well adsorbed on the
surface of
heavy oil particles with certain adhesion; (2) the function of weak
hydrophilic group is to
form hydrophilic interfacial film with certain electronegativity on the
surface of heavy oil
particles adsorbed by macromolecular surfactant, there is certain repulsion
force among the
heavy oil particles, the heavy oil particles do not aggregate easily, such
that they are dispersed
in water, and the viscosity of heavy oil is dramatically reduced; (3) strong
lipophilic and weak
hydrophilic macromolecular surfactant must have proper molecular weight so
that single
macromolecule or several macromolecules of surfactant can form adsorption film
around the
surface of heavy oil particle, which is economic and efficient and also
improves the
adsorption stability; and (4) the penetrability and foamability are poor, and
the capability to
reduce surface tension and interfacial tension is weak, it substantially does
not penetrate into
the interior of the heavy oil particles and substantially does not form
emulsified oil with
heavy oil.
The instant heavy oil in water is broken into little particles, the strong
lipophilic group of the
macromolecular surfactant is adsorbed firmly on the surface of heavy oil
particle, and the
weak hydrophilic group of the macromolecular surfactant form hydrophilic film
and form
visible oil in water "heavy oil particle". The heavy oil particles covered by
hydrophilic film
are electrically repulsive with each other such that the heavy oil particles
do not aggregate
easily. The heavy oil particles are in dispersed state in water, which is
supported only by a
layer of water film. The whole system is in paste state and thus the viscosity
of heavy oil is
decreased dramatically. Consequently the macromolecular surfactant can be used
in the field
of heavy oil exploitation, gathering and transportation to achieve the purpose
of reducing
viscosity and improving flowability of the heavy oil.
The macromolecular surfactant of the present invention differs essentially
from emulsifier and
oil-soluble viscosity reducer in that: (1) although it has strong lipophilic
group, the present
macromolecular surfactant and oil-soluble viscosity reducer have different
mechanisms: the
macromolecular surfactant is merely adsorbed on the surface of heavy oil
particle, and
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substantially does not penetrate into the interior of heavy oil particle and
the molecular
numbers of colloid and asphaltene contained in the interior aggregation of
heavy oil particle
are not decreased; the macromolecular surfactant will not change the three-
dimensional net
structure formed by colloid and asphaltene in the interior of heavy oil
particle, and will not
change the structural viscosity in the interior of heavy oil particle; (2)
since the
macromolecular surfactant only contains weak hydrophilic group, thus its
foamability is poor,
it substantially will not emulsify the crude oil and it is easy to be
demulsified, thereby greatly
reducing the difficulty of disposing waste water; and (3) the macromolecular
surfactant with
proper molecular weight substantially will not undergo phase inversion, and
thus there is no
risk of viscosity increasing after phase inversion.
The macromolecular surfactant of the present invention is formed by the
copolymerization of
monomer (A) and monomer (B), said monomer (A) is one or more unsaturated
monomers
with strong lipophilic group, having the following general formula:
CHR1=CR2
R
wherein R, R1 and R2, whether the same or different, represent H or C1-CI2
alkyl. The
selection of R, R1 and R2 mainly affects the lipophilicity of the
macromolecular surfactant.
The lipophilicity of the macromolecular surfactant increases with increasing
number of
carbons. The selection of R and R2, especially the position of R is also
relevant to the
characteristic structure of heavy oil. Monomer (A) is selected from the group
consisting of
styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, a-methylstyrene,
trans-(3-methylstyrene, 2,4-dimethylstyrene, cis-(3-methylstyrene, 2,4,6-
trimethylstyrene and
mixtures thereof.
Said monomer (B) is one or more unsaturated monomers with weak hydrophilic
group,
having the following general formula:
CH 2 = CR3
A
wherein R3 represents H or C1-C4 alkyl. A represents COOM, OM, or SO3M, and M
represents H, Na+, K+, C1-C8 alkyl, C1-C8 alkyl ether or C1-C8 alkyl ester.
The selection of R3
mainly affects the salt resistance of the macromolecular surfactant. The salt
resistance of the
macromolecular surfactant increases with increasing number of carbons. Monomer
(B) is
selected from the group consisting of (meth)acrylic acid (including sodium
salt and potassium
salt thereof), (meth)acrylic acid ester (including methyl, ethyl, propyl,
butyl, amyl, hexyl,
heptyl and octyl ester), vinyl alcohol and mixtures thereof.
Monomer (A) comprises from 10% to 90% by weight, preferably from 50% to 70% by
weight
of the total weight of monomer (A) and monomer (B).
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Monomer (B) comprises from 10% to 90% by weight, preferably from 30% to 50% by
weight
of the total weight of monomer (A) and monomer (B).
The initiator used in the polymerization of the present application is the
commonly used
initiator as disclosed in publication documents.
The polymerization in the present application is bulk polymerization as
disclosed in
publication documents. Monomer (A) and monomer (B) in proportion are added
into a reactor
with a stirrer and heated to 50 C-80 C with stirring. After that, 0.1-5 wt%
azobisisobutyronitrile based on the total weight of monomer (A) and monomer
(B) is added to
initiate polymerization for 2-4 hours so as to obtain the present
macromolecular surfactant.
The application of the present macromolecular surfactant will not be
influenced in the
solution without limitation of inorganic salt content. Also, the stability of
the present
macromolecular surfactant will not be affected at the temperature of not
higher than 200 C.
The present invention further relates to the use of the present macromolecular
surfactant in
exploitation, gathering and transportation of heavy oil having a viscosity of
more than 2000
mPa=s to disperse the heavy oil, reduce viscosity and improve flowability of
the heavy oil.
The macromolecular surfactant of the present invention has higher molecular
weight, good
film forming property, dispersity and stability. Single molecular or
multimolecular adsorption
film can be formed around the surface of the heavy oil particle. Moreover, its
penetrability
and foamability are poor and its capability of reducing surface tension and
interfacial tension
is weak. It substantially does not penetrate into the interior of the oil
particle and substantially
does not form emulsified oil with heavy oil. It can be used for dispersing
heavy oil in water
and preventing the aggregation of the heavy oil particles. Consequently, the
present
macromolecular surfactant can be used in the field of heavy oil exploitation,
gathering and
transportation to achieve the purpose of reducing viscosity and improving
flowability of the
heavy oil. It can be used for wellbore lifting, pipe gathering and
transportation and canned
transportation of heavy oil with viscosity (50 C) more than 2,000 mPa=s. It
can also be
applied to increase cyclic steam stimulation, steam drive and SAGD exploiting
effect of
heavy oil, as well as extend exploiting cycle. The feasibility of the
application of water flood
to improve the recovery ratio of heavy oil, even that of the common crude oil
with viscosity
(50 C) less than 2,000 mPa=s is to be explored.
DETAILED DESCRIPTION OF THE INVENTION
Example I
80wt% of styrene and 20wt% of methacrylic acid monomers were charged into a
reactor with
a stirrer, and then heated to 65 C with stirring. Then 2wt% of
azobisisobutyronitrile based
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on the total weight of monomers was added to initiate polymerization, and the
polymerization
was proceeded for three hours so as to obtain the present macromolecular
surfactant.
Example 2
60wt% of a-methylstyrene and 40wt% of acrylic acid monomers were charged into
a reactor
with a stirrer, and then heated to 70 C with stirring. Then 4wt% of
azobisisobutyronitrile
based on the total weight of monomers was added to initiate polymerization,
and the
polymerization was proceeded for two hours so as to obtain the present
macromolecular
surfactant.
Example 3
40wt% of p-methylstyrene and 60wt% of vinyl alcohol monomers were charged into
a reactor
with a stirrer, and then heated to 60 C with stirring. Then lwt% of
azobisisobutyronitrile
based on the total weight of monomers was added to initiate polymerization,
and the
polymerization was proceeded for four hours so as to obtain the present
macromolecular
surfactant.
Example 4
20wt% of 2,4,6-trimethylstyrene, 30wt% of octyl methacrylate, and 50% of
acrylic acid
monomers were charged into a reactor with a stirrer, and then heated to 65 C
with stirring.
Then 3wt% of azobisisobutyronitrile based on the total weight of monomers was
added to
initiate polymerization, and the polymerization was proceeded for two hours so
as to obtain
the present macromolecular surfactant.
Example 5
The macromolecular surfactant thus obtained in Example 1 has a surface tension
of 32 mN/m
in 1% aqueous solution as measured by surface tension apparatus and a
viscosity of 3.7 mPa-s
in 5% aqueous solution as measured by Brookfield viscometer. It could be seen
from the
measuring results that the present macromolecular surfactant has a certain
molecular weight
and limited surface activity.
Example 6
The macromolecular surfactant thus obtained in Example 1 was added at 0.2%
concentration
into heavy oil having a water content of 23% and stirred with glass rod at 50
C so that the
viscosity of heavy oil was reduced from 30,000 mPa-s to 74.5 mPa.s. After kept
at room
temperature for 113 days, the viscosity becomes 350 mPa=s, which is much less
than the
required viscosity (less than 700 mPa-s) for heavy oil exploitation, gathering
and
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transportation. The result shows that the present macromolecular surfactant
can be used for
dispersing heavy oil in water and preventing the aggregation of heavy oil
particles so that it
can be used in the field of heavy oil exploitation, gathering and
transportation to achieve the
purpose of reducing viscosity and improving flowability of the heavy oil.
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