Note: Descriptions are shown in the official language in which they were submitted.
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SOLIDS-STABILIZED WATER-IN-OIL EMULSION
AND METHOD FOR USING SAME
FIELD OF THE INVENTION
The present invention relates to a solids-stabilized water-in-oil emulsion
used
for enhanced crude oil recovery. More specifically, the stability of the
solids-stabilized
water-in-oil emulsion is enhanced by the method of pretreating the oil prior
to
emulsification. The pretreatment step can be accomplished by adding dilute
acid to the
oil, adding a lignosulfonate additive to the oil, sulfonating the oil,
thermally treating the
oil in an inert environment, thermally oxidizing the oil, and combinations
thereof. The
improved emulsion may be used either as a drive fluid to displace hydrocarbons
from a
subterranean formation or as a barrier fluid for diverting the flow of
hydrocarbons in
the formation.
BACKGROUND OF THE INVENTION
It is well known that a significant percentage of oil remains in a
subterranean
formation after the costs of primary production rise to such an extent that
further oil
recovery is cost ineffective. Typically, only one-fifth to one-third of the
original oil in
place is recovered during primary production. At this point, a number of
enhanced oil
recovery (EOR) procedures can be used to further recover the oil in a cost-
effective
manner. These procedures are based on re-pressuring or maintaining oil
pressure
and/or mobility.
For example, waterflooding of a reservoir is a typical method used in the
industry to increase the amount of oil recovered from a subterranean
formation.
Waterflooding involves simply injecting water into a reservoir, typically
through an
injection well. The water serves to displace the oil in the reservoir to a
production
well. However, when waterflooding is applied to displace viscous heavy oil
from a
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formation, the process is inefficient because the oil mobility is much less
than the water
mobility. The water quickly channels through the formation to the producing
well,
bypassing most of the oil and leaving it unrecovered. For example, in
Saskatchewan,
Canada, primary production crude has been reported to be only about 2 to 8% of
the
original oil in place, with waterflooding yielding only another 2 to 5% of
that oil in
place. Consequently, there is a need to either make the water more viscous, or
use
another drive fluid that will not channel through the oil. Because of the
large volumes
of drive fluid needed, it must be inexpensive and stable under formation flow
conditions. Oil displacement is most efficient when the mobility of the drive
fluid is
significantly less than the mobility of the oil, so the greatest need is for a
method of
generating a low-mobility drive fluid in a cost-effective manner.
Oil recovery can also be affected by extreme variations in rock permeability,
such as when high-permeability "thief zones" between injection wells and
production
wells allow most of the injected drive fluid to channel quickly to the
production wells,
leaving oil in other zones relatively unrecovered. A need exists for a low-
cost fluid
that can be injected into such thief zones (from either injection wells or
production
wells) to reduce fluid mobility, thus diverting pressure energy into
displacing oil from
adjacent lower-permeability zones.
In certain formations, oil recovery can be reduced by coning of either gas
downward or water upward to the interval where oil is being produced.
Therefore, a
need exists for a low-cost injectant that can be used to establish a
horizontal "pad" of
low mobility fluid to serve as a vertical barrier between the oil producing
zone and the
zone where coning is originating. Such low mobility fluid would retard
vertical coning
of gas or water, thereby improving oil production.
For moderately viscous oils -- i.e., those having viscosities of approximately
20-100 centipoise (cP) -- water-soluble polymers such as polyacrylamides or
xanthan
gum have been used to increase the viscosity of the water injected to displace
oil from
the formation. For example, polyacrylamide was added to water used to
waterflood a
24 cP oil in the Sleepy Hollow Field, Nebraska. Polyacrylamide was also used
to
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viscosify water used to flood a 40 cP oil in the Chateaurenard Field, France.
With this
process, the polymer is dissolved in the water, increasing its viscosity.
While water-soluble polymers can be used to achieve a favorable mobility
waterflood for low to moderately viscous oils, usually they cannot
economically be
applied to achieving a favorable mobility displacement of more viscous oils --
i.e.,
those having viscosities of approximately 100 cP or higher. These oils are so
viscous
that the amount of polymer needed to achieve a favorable mobility ratio would
usually
be uneconomic. Further, as known to those skilled in the art, polymer
dissolved in
water often is desorbed from the drive water onto surfaces of the formation
rock,
entrapping it and rendering it ineffective for viscosifying the water. This
leads to loss
of mobility control, poor oil recovery, and high polymer costs. For these
reasons, use
of polymer floods to recover oils having viscosities in excess of 100 cP is
not usually
technically or economically feasible. Also, performance of many polymers is
adversely
affected by levels of dissolved ions typically found in formations, placing
limitations on
their use and/or effectiveness.
Water and oil macroemulsions have been proposed as a method for producing
viscous drive fluids that can maintain effective mobility control while
displacing
moderately viscous oils. For example, water-in-oil and oil-in-water
macroemulsions
have been evaluated as drive fluids to improve oil recovery of viscous oils.
Such
emulsions have been created by addition of sodium hydroxide to acidic crude
oils from
Canada and Venezuela. The emulsions were stabilized by soap films created by
saponification of acidic hydrocarbon components in the crude oil by sodium
hydroxide.
These soap films reduced the oil/water interfacial tension, acting as
surfactants to
stabilize the water-in-oil emulsion. It is well known, therefore, that the
stability of
such emulsions substantially depends on the use of sodium hydroxide (i.e.,
caustic) for
producing a soap film to reduce the oil/water interfacial tension.
Various studies on the use of caustic for producing such emulsions have
demonstrated technical feasibility. However, the practical application of this
process
for recovering oil has been limited by the high cost of the caustic, likely
adsorption of
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the soap films onto the formation rock leading to gradual breakdown of the
emulsion,
and the sensitivity of the emulsion viscosity to minor changes in water
salinity and
water content. For example, because most formations contain water with many
dissolved solids, emulsions requiring fresh or distilled water often fail to
achieve design
potential because such low-salinity conditions are difficult to achieve and
maintain
within the actual formation. Ionic species can be dissolved from the rock and
the
injected fresh water can mix with higher-salinity resident water, causing
breakdown of
the low-tension stabilized emulsion.
Various methods have been used to selectively reduce the permeability of high-
permeability "thief' zones in a process generally referred to as "profile
modification."
Typical agents that have been injected into the reservoir to accomplish a
reduction in
permeability of contacted zones include polymer gels or cross-linked
aldehydes.
Polymer gels are formed by crosslinking polymers such as polyacrylamide,
xanthan,
vinyl polymers, or lignosulfonates. Such gels are injected into the formation
where
crosslinking reactions cause the gels to become relatively rigid, thus
reducing
permeability to flow through the treated zones.
In most applications of these processes, the region of the formation that is
affected by the treatment is restricted to near the wellbore because of cost
and the
reaction time of the gelling agents. Once the treatments are in place, the
gels are
relatively immobile. This can be a disadvantage because the drive fluid (for
instance,
water in a waterflood) eventually finds a path around the immobile gel,
reducing its
effectiveness. Better performance should be expected if the profile
modification agent
could slowly move through the formation to plug off newly created thief zones,
penetrating significant distances from injection or production wells.
McKay, in U.S. Pat. No. 5,350,014, discloses a method for producing heavy oil
or bitumen from a formation undergoing thermal recovery. McKay describes a
method
for producing oil or bitumen in the form of oil-in-water emulsions by
carefully
maintaining the temperature profile of the swept zone above a minimum
temperature,
T,. If the temperature of the oil-in-water emulsion is maintained above this
minimum
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temperature, the emulsion will be capable of flowing through the porous
subterranean
formation for collection at the production well. McKay describes another
embodiment
of his invention, in which an oil-in-water emulsion is inserted into a
formation and
maintained at a temperature below the minimum temperature. This relatively
immobile
emulsion is used to form a barrier for plugging water-depleted thief zones in
formations being produced by thermal methods, including control of vertical
coning of
water. However, the method described by McKay requires careful control of
temperature within the formation zone and, therefore, is useful only for
thermal
methods of recovery. Consequently, the method disclosed by McKay could not be
used for non-thermal (referred to as "cold flow") recovery of heavy oil.
A new process has recently been disclosed that uses novel solids-stabilized
emulsions for enhanced oil recovery. U.S. Patent 5,927,404 describes a method
of
using the novel solids-stabilized emulsion as a drive fluid to displace
hydrocarbons for
enhanced oil recovery. U.S. Patent 5,855,243 claims a similar method of using
a
solids-stabilized emulsion, whose viscosity is reduced by the addition of a
gas, as a
drive fluid. U.S. Patent 5,910,467 claims the novel solids-stabilized emulsion
described in U.S. Patent 5,855,243. U.S. Patent 6,068,054 describes a method
for
using the novel solids-stabilized emulsion as a barrier for diverting the flow
of fluids in
the formation.
Preparing a solids-stabilized emulsion with optimum properties is key to
successfully using the emulsion for enhanced oil recovery. Two important
properties
are an emulsion's stability and its rheology. The solids stabilized emulsion
should be
shelf-stable, that is, the emulsion should be able to remain a stable emulsion
without
water or oil breakout when left undisturbed. In addition, the emulsion should
be stable
under flow conditions through porous media, i.e. in a subterranean formation.
The
emulsion's rheological characteristics are also important. For instance, EOR
methods
for which this emulsion may be used include injecting the emulsion as a drive
or barrier
fluid into a subterranean formation. Accordingly, the emulsion should have an
optimum viscosity for injection and to serve as either a drive or barrier
fluid. In
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practicing EOR, and particularly with using the emulsion as a drive fluid, it
is useful to
match the rheology of the emulsion with the rheology of subterranean oil to be
produced. Oil displacement using a drive fluid is typically more efficient
when the
drive fluid has a greater viscosity than that of the oil to be displaced. In
addition to
providing stability to the solids-stabilized emulsion, the invention described
herein will
allow the user to prepare solids-stabilized emulsions with a wide range of
rheology to
match that of the oil to be produced.
Because water and oil are readily available at most production sites, water-in-
oil emulsions are a good choice for making the solids-stabilized emulsions for
EOR.
Some oils possess the chemical composition and physical properties necessary
to make
stable solids-stabilized water-in-oil emulsions with a wide range of solids.
The added
solids interact with components of oil, i.e., polars and asphaltenes,
resulting in an
increase in their effectiveness as surface-active agents. This interaction is
specific to
the type of solids and the composition of the oil to which they are added.
However, if the oil does not contain the right type and sufficient
concentration
of polar and asphaltene compounds, the addition of solids is ineffective
because the
solids are not adequately and suitably modified to function as stabilizers of
the oil-
water interface. Accordingly, some oils do not form stable solids-stabilized
water-in-
oil emulsions with any solids, or, some oils may form stable emulsions with
some types
of solids, e.g. silica, and may not form similar stable emulsions with other
types of
solids, e.g., clays and coal dust. The previously cited art suggests that
asphaltenes or
polar hydrocarbons may be added to these oils to improve their ability to form
stable
emulsions. U.S. Patent 5,855,243, column 7, lines 6-10; U.S. Patent 5,927,404
column 6, lines 44-47; U.S. Patent 5,910,467 column 7, lines 3-6. However,
this
addition is not always successful because incompatibility between some oil
components
and the added asphaltenes and polars can result in phase separation or
rejection of the
added compounds. These cases limit the scope of the inventions disclosed in
the U.S.
Patents cited above.
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To broaden the scope and improve the solids-stabilized emulsions described in
U.S. Patents 5,927,404, 5,855,243, 5,910,467, 6,068,054, an approach is needed
that
suitably modifies the oil composition so that it is responsive to the addition
of solids
for the preparation of stable water-in-oil emulsions. The present invention
satisfies this
need.
SUMMARY OF THE INVENTION
According to the invention, there is provided a method for enhancing the
stability of a solids-stabilized water-in-oil emulsion, said method comprising
the step of
pretreating at least a portion of the oil prior to emulsification.
In one embodiment of the invention, the oil pretreatment step comprises the
addition of dilute organic or mineral acid to at least a portion of the oil
prior to
emulsification.
In another embodiment of the invention, the oil pretreatment step comprises
the
addition of a lignosulfonate additive to at least a portion of the oil prior
to
emulsification.
In another embodiment of the invention, the oil pretreatment step comprises
sulfonating at least a portion of the oil prior to emulsification.
In another embodiment of the invention, the oil pretreatment step comprises
thermally treating at least a portion of the oil in an inert environment prior
to
emulsification.
In another embodiment of the invention, the oil pretreatment step comprises
thermally oxidizing at least a portion of the oil prior to emulsification.
Combinations of these embodiments may also be used.Further disclosed is a
method for producing hydrocarbons from a subterranean formation, comprising:
a) making a solids-stabilized water-in-oil emulsion with the pretreated oil;
b) contacting the formation with said solids-stabilized emulsion, and
c) producing hydrocarbons from the formation using said solids-stabilized
emulsion.
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DETAILED DESCRIPTION OF THE INVENTION
Solids-stabilized water-in-oil emulsions have been generally described in US
5,927,404, US 5,855,243 and US 5,910,467. Such emulsions are made by the
process
of combining oil with submicron to micron-sized solid particles and mixing
with water
until the solids-stabilized water-in-oil emulsion is formed.
As disclosed in the above referenced U.S. patents, the solid particles should
have certain physical properties. The individual particle size should be
sufficiently
small to provide adequate surface area coverage of the internal droplet phase.
If the
emulsion is to be used in a porous subterranean formation, the average
particle size
should be smaller than the average diameter of pore throats in the porous
subterranean
formation. Methods for determining average particle size are discussed in the
previously cited U.S. patents. The solid particles may be spherical in shape,
or non-
spherical in shape. If spherical in shape, the solid particles should
preferably have an
average size of about five microns or less in diameter, more preferably about
two
microns or less, even more preferably about one micron or less and most
preferably,
100 nanometers or less. If the solid particles are non-spherical in shape,
they should
preferably have an average size of about 200 square microns total surface
area, more
preferably about twenty square microns or less, even more preferably about ten
square
microns or less and most preferably, one square micron or less. The solid
particles
must also remain undissolved in both the oil and water phase of the emulsion
under the
formation conditions.
The present invention allows the formation of stable solids-stabilized
water-in-oil emulsions from oil that would otherwise lack adequate polar and
asphaltene compounds to form such stable emulsions. The oil needed to make a
stable
emulsion using the method described by U.S. Patents 5,927,404, 5,855,243 and
5,910,467, has to contain a sufficient amount of asphaltenes, polar
hydrocarbons, or
polar resins to stabilize the solid-particle-oil interaction. But, as noted,
some oils do
not have the sufficient type or amounts of these compounds to allow the
formation of
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stable solids-stabilized emulsions. Pursuant to the present invention, the oil
is
pretreated to promote the formation of a stable solids-stabilized water-in-oil
emulsion.
The oil used to make the solids-stabilized emulsion of the current invention
can
be oil of any type or composition, including but not limited to crude oil,
refined oil, oil
blends, chemically treated oils, or mixtures thereof. Crude oil is unrefined
liquid
petroleum. Refined oil is crude oil that has been purified in some manner, for
example,
the removal of sulfur. Crude oil is the preferred oil used to practice this
invention,
more preferably, the crude oil is produced from the formation where the
emulsion is to
be used. The produced crude oil may contain formation gas, or formation water
or
brine mixed with the oil. It is preferred to dehydrate the crude oil prior to
treatment,
however, mixtures of oil, formation gas and/or formation brine may also be
used in this
invention.
Preferably, formation water is used to make the emulsion, however, fresh water
can also be used and the ion concentration adjusted as needed to help
stabilize the
emulsion under formation conditions.
Solids-stabilized water-in-oil emulsions according to the present invention
are
useful in a variety of enhanced oil recovery applications generally known in
the art,
including, without limitation, using such emulsions (a) as drive fluids to
displace
hydrocarbons in a subterranean formation; (b) to fill high permeability
formation zones
for "profile modification" applications to improve subsequent EOR performance;
and
(c) to form effective horizontal barriers, for instance, to form a barrier to
vertical flow
of water or gas to reduce coning of the water or gas to the oil producing zone
of a
well.
Attached in Table 1 are detailed physical and chemical property
characterization data for three different types of crude oils which are
referenced as
Crude Oil #1, Crude Oil #2 and Crude Oil #3. Crude Oil #1 and Crude Oil #3
possess
properties that enable formation of stable water in crude oil emulsions with
the
addition of solids, as described in U.S. Patents 5,927,404, 5,855,243 and
5,910,467.
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However, Crude Oil #2 does not form a stable solids-stabilized water-in-oil
emulsion
when using the same method.
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TABLE 1
PHYSICAL & CHEMICAL PROPERTIES OF CRUDE OII.S
PROPERTY Crude Oil #1 Crude Oil #2 Crude Oil #3
API Gravity 16.8 15.5 8.6
Viscosity (cP) 4800 2400 384,616
(25 C, 1 sec l)
Interfacial Tension (dynes/cm) 2.2 33.7
Sea Water
Asphaltenes (n-heptane insolubles (wt.%)) 0.1 0.02 2.6 13.7
Toluene Equivalence 0.0 14 20
Sulfizr (wt.%) 0.12 0.98 3.89
Nitrogen (wt.%) 0.18 0.07 0.19
Distillation Cuts (Vol. %)
IC5/175 F Lt. Naph -- 0.6 0.2
175/250 F Med. Naph -- 1.3 --
250/375 F Hvy. Naph 1.80 3.22 1.0
375/530 F Kerosene 7.83 12.39 4.8
530/650 F Lt. Gasoil 9.88 14.27 9.5
650/1049 F PGO 38.04 42.41 38.8
1049 F + Resid 42.45 25.80 45.7
HPLC Fractions (wt. %)
Mass Recovery 83.8 56.6 66.99
Saturates 41.7 28.51 17.67
1-Ring 7.5 11.40 10.07
2-Ring 7.0 9.85 12.89
3-Ring 7.6 7.96 10.15
4-Ring 13.0 16.06 20.93
Polars 23.2 26.23 28.29
Aromaticity 17.1 20.27 22.37
latrascan data
Saturates 27.2 19.4 6.4
Aromatics 44.7 44.7 42.5
NSO's 19.0 30.1 29.0
Asphaltenes (npentane insolubles) (wt. %) 8.9 5.8 22.1
Arom./Saturates 1.64 2.3 6.66
NSO's/Asph. (n-pentane insoluble) 2.13 5.19 1.31
TAN 6.2 6.2 3.13
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TABLE 1 (continued)
PHYSICAL & CHEMICAL PROPERTIES OF CRUDE OILS
PROPERTY Crude Oil #1 Crude Oil #2 Crude Oil #3
HPLC Determined
Distribution of Acid Fractions (%)
250 MW 8.5 47.2 22.4
300 MW 23.9 24.5 20.7
425 MW 30.5 15.9 20.4
600 MW 20.4 7.0 14.6
750 MW 16.7 5.4 21.7
Acid Aromaticity 8.6 17.2 19.0
Metals (ppm)
Ca 30-160 4.22 1.83
Na 10.4-15.5 1.51 11.2
V 0.16-0.31 69.6 434
Ni 9.05-13.0 65.6 102
Crude Oil #2 differs from Crude Oils #1 and #3 in the following ways:
1. Crude Oil #2 has a higher resin/asphaltene ratio,
2. Crude Oil #2 has a higher proportion of lower molecular weight naphthenic
acids,
and
3. Crude Oil #2 has lower calcium and sodium as compared to the Crude Oil #1.
These differences suggest:
1. the surface-active species, i.e., asphaltenes and acids/resins, which are
the key components essential for emulsification, are not readily
available to stabilize the water droplets in Crude Oil #2, and
2. pretreatment of the oil to alter its physical properties and chemical
composition is a potential route to enhance the stability of the emulsion.
Accordingly, the present invention describes a method of pretreating oil to
increase the stability of the solids-stabilized emulsion. Several embodiments
of this
invention will now be described. As one of ordinary skill in the art can
appreciate, an
embodiment of this invention may be used in combination with one or more other
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embodiments of this invention, which may provide synergistic effects in
stabilizing the
solids-stabilized emulsion.
Pretreatment of Oil with Dilute Acid
One method of pretreating oil to enhance its ability to form a stable solids-
stabilized water-in-oil emulsion is to pretreat the oil with dilute mineral or
organic acid
prior to emulsification. This acid pretreatment results in modifications to
the oil and
surface of the solids: (1) The basic nitrogen containing components of the oil
are
converted to the corresponding mineral or organic acid salts. These salts are
more
surface-active than the basic nitrogen containing components themselves and
thus
contribute to improving the stability of the solids-stabilized water-in-oil
emulsion; (2)
If the oil contains napthenic acids, the stronger mineral or organic acids
displace the
napthenic acids from the basic nitrogen containing compounds to which they are
complexed thereby providing higher surface activity; (3) The protons from the
acid act
to protonate the anionic charged sites on the surface of the solids and thus
modify the
solids' surface to improve its interaction with the surface-active components
of oil
(either preexisting in the oil or generated by the acid treatment); (4) If the
oil contains
calcium and naphthenic acids, the mineral or organic acids can displace the
calcium and
free the naphthenic acids, which are more surface-active than the calcium
naphthenates.
Making the Solids-stabilized Water-in-Oil Emulsion Usin2 Dilute Acid
Pretreatment
To make this embodiment of the invention, dilute mineral or organic acid is
added to the oil prior to emulsification. Solid particles can be added to the
oil either
before or after the acid pretreatment, but it is preferred to add the solids
to the oil and
then acid pretreat the oil with the solids. After the acid pretreatment and
solids
addition, the solids-stabilized emulsion is formed by adding water in small
aliquots or
continuously and mixing, preferably at a rate of between 1000 to 12000 rpm,
for a time
sufficient to disperse the water as small droplets in the continuous oil
phase. It is
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preferred to have a water concentration in the water-in-oil emulsion of 40 to
80%,
more preferably 50 to 65%, and most preferably 60%.
The acid is added to the oil with mixing, preferably for about 5 to 10 minutes
at
25 to 40 C. The preferred acid treat rate is between 8 and 30,000 ppm. The
dilute
acid may be mineral acid, organic acid, a mixture of mineral acids, a mixture
of organic
acids, or a mixture of mineral and organic acids. The preferred mineral acids
are
hydrochloric and sulfuric acid. However, other mineral acids can be used,
including
but not limited to perchloric acid, phosphoric acid and nitric acid. The
preferred
organic acid is acetic acid. However, other organic acids may also be used
including,
but not limited to para-toluene sulfonic, alkyl toluene sulfonic acids, mono
di and
trialkyl phosphoric acids, organic mono or di carboxylic acids (e.g. formic),
C3 to C16
organic carboxylic acids, succinic acid, and petroleum naphthenic acid.
Petroleum
naphthenic acid can also be added to increase the surface-activity in the oil,
or oils
containing high naphthenic acid can be blended with the oils of interest to
provide the
increased surface-activity.
The solid particles are preferably hydrophobic in nature. A hydrophobic
silica,
sold under the trade name Aerosil R 972 (product of DeGussa Corp.) has been
found
to be an effective solid particulate material for a number of different oils.
Other
hydrophobic (or oleophilic) solids can also be used, for example, divided and
oil-
wetted bentonite clays, kaolinite clays, organophilic clays or carbonaceous
asphaltenic
solids. The preferred treat rate of solids is 0.05 to 0.25 wt% based upon the
weight of
oil.
After the emulsion is prepared, its pH can be adjusted by adding a calculated
amount of weak aqueous base to the emulsion for a time sufficient to raise the
pH to
the desired level. It is desirable to adjust emulsion pH in the 5 to 7 range.
However,
adjusting pH is optional as in some cases it is desirable to inject an acidic
emulsion and
allow the reservoir formation to buffer the emulsion to the reservoir
alkalinity.
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Ammonium hydroxide is the preferred base for pH adjustment. Stronger bases
like sodium hydroxide, potassium hydroxide and calcium oxide have a negative
effect
on emulsion stability. One possible explanation for this effect is that strong
bases tend
to invert the emulsion, i.e. convert the water-in-oil emulsion to an oil-in-
water
emulsion. Such an inversion is undesirable for the purposes of this invention.
In addition to increasing the stability of the solids-stabilized water-in-oil
emulsion, the acid pretreatment method results in an emulsion with lower
viscosity
compared to one produced without acid pretreatment. This reduced viscosity
aids in
enhancing the injectivity of the emulsion. Thus, one may decrease the
viscosity of a
solids-stabilized emulsion by suitably adjusting the amount of acid
pretreatment. This
ability to manipulate the viscosity of the emulsion allows the user to
optimally match
the rheological characteristics of the emulsion to that of the oil to be
recovered
specifically for the particular type EOR method used. As noted in U.S. Patents
5,855,243 and 5,910,467, gas may also be added to further lower the viscosity
of the
emulsion.
Another embodiment of this invention is to pretreat a slipstream or master
batch of oil with dilute acid as described above and subsequently mix the
slipstream
with a main stream of oil prior to water addition and emulsification. This
main stream
of oil is preferably untreated crude oil, however, it may be any oil,
including oil that
has been treated to enhance its ability to form a stable emulsion or treated
to optimize
its rheology. If this slipstream method is used, the amounts of solids and
dilute acid
needed for the slipstream treatment are scaled accordingly to obtain the
desired
amounts in the resulting emulsion.
Examples:
The following laboratory tests were conducted to demonstrate the effectiveness
of acid pretreatment on enhancing an oil's ability to form stable solids-
stabilized water-
in-oil emulsions. These examples focused on Crude Oil #2 and another crude
oil,
Crude Oil #4. Neither of these crude oils form stable solids-stabilized
emulsions by the
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method described in U.S. Patents 5,927,404, 5,855,243 and 5,910,467. Physical
properties for Crude Oil #4 are given in Table 2. The tests demonstrated that
the acid
pretreatment enhanced the oils' abilities to form stable solids-stabilized
emulsions.
Stable emulsions were formed in the pH range of 1.2 to 7.0, and up to 72 wt%
water
was incorporated into these emulsions.
TABLE 2
PHYSICAL & CHEMICAL PROPERTIES OF CRUDE OILS
PROPERTY Crude Oil #4
API Gravity 17.2
Viscosity (cP) 8500
(25 C, 1 sec -')
Asphaltenes (n-heptane insolubles) (wt.%) 0.1
Asphaltene (cyclohexane insolubles) (wt.%) 3.25
Toluene Equivalence 0.0
Sulfur (wt. %) 0.12
Nitrogen (wt. %) 0.26
Distillation Cuts (Vol. %)
IC5/175 F Lt. Naph ---
175/250 F Med. Naph ---
250/375 F Hvy. Naph 0.03
375/530 F Kerosene 6.09
530/650 F Lt. Gasoil 8.67
650/1049 F PGO 36.48
1049 F + Resid 48.73
HPLC Fractions (wt. %)
Mass Recovery 84.4
Saturates 43.3
1-Ring 7.6
2-Ring 6.8
3-Ring 7.5
4-Ring 12.6
Polars 22.2
Aromaticity 15.6
latroscan Data
Saturates 35.4
Aromatics 39.8
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NSO's 15.4
Asphaltene 9.4
Arom./Saturates 1.13
NSO's/Asph. 1.64
TABLE 2 (continued)
PROPERTY Crude Oil #4
TAN 5.4
HPLC Determined
Distribution of Acid Fractions (%) **
250 - 300MW 15.4
300 - 425 MW 14.7
425-600 MW 27.1
600 -750MW 21.5
750 + MW 21.3
Acid Aromaticity 8.6
Metals (ppm)
Ca 400-900
Na 7.7-15.3
V 0.2-0.9
Ni 11.2-17.9
Mn 13.1
K 181-935
Mg 1.1-25.2
In a typical experiment, dilute aqueous mineral or organic acid (0.35 to 35%
concentration) was added to the oil at a treat rate of 8 to 30,000 ppm and
thoroughly
mixed for 10 minutes using a Waring blender or a Silverson homogenizer. Solid
particles were added followed by mixing. After acid pretreatment was
completed,
water was added to the oil in small aliquots with mixing, which resulted in a
solids-
stabilized water-in-oil emulsion.
Emulsions prepared by oil pretreatment with dilute aqueous acid were
subjected to the following tests:
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1. Shelf stability at 25 C for 48 hours
2. Optical microscopy and/or Nuclear Magnetic Resonance (NMR) for
determination of water droplet size / size distribution
3. Microcentrifuge test -- emulsion stability to centrifugation (as
described in Appendix-1)
4. Emulsion stability -- flow through a sand pack (this micropercolation
test is described in Appendix-1)
5. Emulsion rheology using a Brookfield viscometer (cone(#51) and plate
configuration) at 60 C in a shear range of 1.92 to 384 sec"'.
Test results for Crude Oil #2 using hydrochloric acid and sulfuric acid
pretreatment are presented in Tables 3-6. Results for Crude Oil #4 using
sulfuric acid
and acetic acid pretreatment are presented in Table 7.
Example 1: Hydrochloric Acid Pretreatment of Crude Oil #2
Crude Oil #2 was used to prepare a 60/40 water-in-oil emulsion with 0.15 wt%
hydrophobic silica, Aerosil R 972, but without acid pretreatment. As shown in
Table
3, the solids-stabilized emulsion was shelf stable, however, the emulsion was
unstable
in the microcentrifuge and micropercolation tests as evidenced by the high
water
(brine) breakout (%bbo). Dispersed water droplets ranged in the size from 1 to
10
microns in diameter.
The effect of hydrochloric acid pretreatment on the stability of the solids-
stabilized emulsion was then tested. Crude Oil #2 was used to prepare a 60/40
solids-
stabilized water-in-oil emulsion. However, in this example, the oil was
pretreated with
hydrochloric acid at a rate of 38,000 ppm followed by addition of 0.15 wt% of
Aerosil R 972. Dispersed water droplets ranged in size from 1 to 2 microns in
diameter. As shown in Table 3, the hydrochloric acid pretreatment resulted in
enhanced microcentrifuge and micropercolation stability and therefore enhanced
emulsion stability as indicated by the decreased amount of water breakout in
both
tests.
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TABLE 3
Pretreatment of Crude Oil #2 With Hydrochloric Acid
Pretreat Procedure: 38,000 ppm HCl added to crude and mixed using Waring
Blender
for 10 min.
HCl Crude/ Solid particles Shelf Droplet Micro- Micro-
Water (Aerosil Stability diameter centrifuge percolation
R972)
ppm (wt%) (2 days) (microns) (%bbo) (%bbo)
0 40/60 0.15 stable 10 to 1 18 35
38,000 40/60 0.0 stable 10 to 1 0 20
38,000 40/60 0.15 stable 2 to 1 0 5
38,000 33/66 0.15 stable 2 to 1 0 4
bbo :: brine (water) breakout in microcentrifuge test using Ottawa sand
Example-2: Sulfuric Acid Pretreatment of Crude Oil #2
Crude Oil #2 was used to make a 60/40 water-in-oil emulsion containing 0.15
wt% of Aerosil R 972 with no acid pretreatment. As shown in Table 4, this
emulsion, though shelf-stable, was unstable in the microcentrifuge and
micropercolation tests. Dispersed water droplets ranged in size from 1 to 10
microns
in diameter.
A 60/40 water-in-crude oil emulsion was made with sulfuric acid pretreatment
of Crude Oil #2, but without the addition of solids. The sulfuric acid was
added at a
rate of 8750 ppm, based on the weight of the oil. The resulting emulsion was
very
unstable in the microcentrifuge and micropercolation tests.
A 60/40 water-in-crude oil emulsion was prepared with sulfuric acid
pretreatment of Crude Oil #2 at a rate of 8750 ppm, based on the weight of the
oil,
with 0.15 wt% of Aerosil R 972. As shown in Table 4, this procedure resulted
in a
stable emulsion. Dispersed water droplets ranged in size from 1 to 2 microns
in
diameter. The pH of the resultant emulsion was 1.2. The sulfuric acid
pretreatment of
oil resulted in enhanced microcentrifuge and micropercolation stability as
indicated by
the decreased amount of water or brine breakout (%bbo).
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A 60/40 water-in-crude oil emulsion was prepared with sulfuric acid
pretreatment of Crude Oil #2 at a treat rate of 8750 ppm, based on the weight
of the
oil, followed by addition of 0.15 wt% of a hydrophilic silica, Aerosil 300
(product of
DeGussa Corp.). This procedure did not provide a stable water-in-oil emulsion,
as the
emulsion had increased water breakout in the microcentrifuge and
micropercolation
tests. The poor performance of the hydrophilic silica, Aerosil 300, suggests
that
hydrophobic solids, in general, are required for the formation of stable
emulsions using
dilute acid pretreatment.
TABLE 4
Pretreatment of Crude Oil #2 With Sulfuric Acid
Pretreat Proc: 8750ppm HzSO4 added to crude & mixed using Waring Blender for
10
min.
H2SO4 Oil/ Solid particles Shelf Droplet Micro- Micro-
Water (Aerosil Stability diameter centrifuge percolation
R972)
ppm (wt%) (2 days) (microns) (%bbo) (%bbo)
0 40/60 0.15 stable 10 to 1 18 35
8750 40/60 0.0 stable 10 to 1 20 91
8750 40/60 0.15 stable 2 to 1 0 0
8750 33/66 0.15 stable 2 to 1 1 2
8750 40/60 0.10 stable 2 to 1 0 0
8750 40/60 0.075 stable 2 to 1 0 0
bbo :: brine (water) breakout in micropercolation test using Ottawa sand
Example-3: Increasing the Water Content of Sulfuric Acid Pretreated Crude
Oil #2
As shown in Table 5, about 70 wt% water could be incorporated into the
resulting solids-stabilized water-in-oil emulsion made by pretreating Crude
Oil #2 with
dilute sulfuric acid. Above about 72 wt% water, an increase in water droplet
size was
observed. Above about 80 wt% water, the emulsion phase separated as an
emulsion
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and excess water. The rheological measurements show that the viscosity of the
emulsions increased with an increase in the water content of the emulsion.
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TABLE 5
Effect of Increasing the Water Content of
Sulfuric Acid Pretreated Crude Oil #2 Emulsion
% water Shelf Micro- Micro- Droplet diameter Viscosity
stability centrifuge percolation 35C, 9.6 s"'
(%bbo) (%bbo) (microns)
60 yes 0 0 <2 15,400
65.5 yes 0 0 <2 15,888
69.2 yes 0 0 <2 20,152
71.4 yes 0 0 <2 27,852
75 yes 0 5 <2 - 5 26,214
80 yes 0 10 <2 - 10
85 phase separates as emulsion & excess water
Note:
Solids : 0.15 wt% Aerosil R 972 Silica
bbo :: brine (water) breakout in micropercolation test using Ottawa sand
Sulfuric acid treat rate : 8750 ppm
Example-4: Decreasing the Solids Content of a 60/40 Water-in-Crude Oil #2
Emulsion
As shown in Table 6, stable emulsions were prepared with the hydrophobic
silica, Aerosil R 972, ranging in concentration from 0.025 wt% to 0.15 wt%.
The
viscosity of the emulsions decreased with decreasing solids content.
TABLE 6
Effect of Decreasing the Solids Content of
Sulfuric Acid Pretreated Crude Oil #2 Emulsion
% Solid particles Shelf Micro- Micro- Droplet viscosity
(Aerosil R972) stability centrifuge percolation diameter 35C, 9.6 s"'
(%bbo) (%bbo) (microns)
0.15 yes 0 0 <2 15400
0.1 yes 0 0 <2 7864
0.075 yes 0 0 <2 7536
0.05 yes 0 0 <2 8192
0.025 yes 0 0 <2 - 5 6389
Note:
Oil/Water ratio = 40/60
bbo :: brine (water) breakout in micropercolation test using Ottawa sand
Sulfuric acid treat rate : 8750 ppm
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Example-5 : Sulfuric and Acetic Acid Pretreatment of Crude Oil #4
Similar to the results on Crude Oil #2, acid pretreatment of Crude Oil #4
resulted in enhanced stability of the resulting solids-stabilized emulsions.
As the data
in Table 7 indicate, pretreatment of the Crude Oil #4 with sulfuric acid at a
rate of
8750 ppm, based on the weight of oil, followed by addition of 0.15 wt% Aerosil
R
972 resulted in a stable emulsion.
Pretreatment of Crude Oil #4 with acetic acid at a treat rate of 24,500 ppm
followed by addition of 0.15 wt% Aerosil R 972 also resulted in a stable
solids-
stabilized 60/40 water-in-oil emulsion. The viscosity of the acetic acid
treated
emulsion was observed to be lower than the sulfuric acid treated counterpart,
suggesting the nature of the acidifying agent could influence emulsion
viscosity.
TABLE 7
Acid Pretreatment of Crude Oil #4
Acid % Solids Shelf Micro- Micro- Droplet viscosity
(Aerosil stability centrifuge percolation diameter 60C, 9.6 s"'
R972) (%bbo) (% bbo) (microns)
None 0.15 yes 0 9 <2 - 10 5240
Sulfuric 0.15 yes 0 3.5 <2 2948
Acetic 0.15 yes 0 0 <2 4095
Note:
Viscosity of Crude Oil #4= 164cP @ 60C, 9.6 s'
bbo :: brine (water) breakout in micropercolation test using Ottawa sand
Sulfuric acid treat rate : 8750 ppm
Acetic acid treat rate: 24,500 ppm
Example-6: Adjusting the pH of the Acid Treated Emulsion
Two approaches are described to produce water-in-oil emulsions in the
preferred pH range of 5 to 7:
a) Neutralization of the prefornied acid treated oil emulsion with the
appropriate amount of base:
Neutralization of the acid pretreated oil with ammonium hydroxide before or
after addition of water is the preferred method to increase the emulsion pH.
In
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contrast, neutralization of the emulsion with sodium hydroxide or calcium
oxide results
in destabilization of the emulsion. As previously noted, a possible
explanation for this
effect is that ammonium hydroxide is a weaker base than sodium hydroxide or
calcium
oxide. Strong bases tend to invert the emulsion, i.e. convert the water-in-oil
emulsion
to an oil-in-water emulsion. Such an inversion is undesirable for the process
of this
invention.
b) Reducing the Acid Treat Rate to Levels Just Enough to Neutralize the Basic
Components of the Oil:
Another approach to obtaining an emulsion in the pH range of 5-7 is to reduce
the acid treat rate to levels just enough to neutralize the basic components
of the oil.
Acids used in this experiment were hydrochloric, sulfuric and acetic acids.
For Crude
Oil #2 and Crude Oil #4, it was found that an acid treat rate of 8.7 ppm was
adequate
to produce the required emulsions at a pH of 5.5 to 6.5. A summary of emulsion
properties for Crude Oil #4 pretreated with 8.75 ppm sulfuric acid is given in
Table 8.
TABLE 8
Summary of Emulsion Properties of a Water-in-Oil Emulsion
Prepared by Pretreatment of Crude Oil #4 with 8.75 ppm Sulfuric Acid
Emulsion ProRerties:
Crude : 40wt%
Water : 60 wt%
Hydrophobic Silica (R 972) : 0.15wt%
Water Droplet Size (Mean Diameter): 6 microns
Shelf Stability : > 2 weeks
Stability to Centrifugation : 0% water breakout
Stability to Percolation through Berea sand: 16% water breakout
Viscosity : 3700 cP @ 60C, 9.6 sec'
pH: 6.2
Example-8: Gas Addition for Viscosity Reduction of Water-in-Oil
Emulsions
Addition of COz to the acid pretreated oil emulsion is effective in reducing
the
viscosity of the emulsion. Experiments have been conducted on emulsions made
from
Crude Oil #2 pretreated with 8700 ppm sulfuric acid and 0.15 wt% Aerosil R
972
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Results shown in Table-9 reveal that at 500 psi pressure and the corresponding
reservoir temperature, emulsion viscosity reduction is feasible using carbon
dioxide
gas. Other gases like ethane and propane can also lower emulsion viscosity
TABLE 9
Influence of CO2 on an Acid Pretreated
Solids-Stabilized Water-in-Crude Oil Emulsion
Emulsion Temp VISCOSITY (cP) at 10 sec"1
( C)
Viscosity (cP) At 10 sec 1
Without CO2 with 500 psi CO2
Crude Oil #2 35 11213 1671
Pretreatment of Oil by Sulfonation Chemistry
Another method for pretreating oil to enhance its ability to make a solids-
stabilized water-in-oil emulsion is to pretreat the oil with a sulfonating
agent prior to
emulsification. The sulfonation procedure can result in chemical modifications
to the
oil and to the surface of the solids. For example, (1) the sulfonation
procedure herein
described creates sulfur-functionalized components of oil, and these
components are
surface active and aid the formation of the water-in-oil emulsion; (2) If
naphthenic
acids are present in the oil, sulfonation will markedly enhance their acidity
and
interfacial activity through the chemically attached sulfonate groups; (3) The
sulfonate
groups from the sulfonating agent will also functionalize the surface of the
solids and
thus modify the solids' surface to improve its interaction with the surface-
active
components of oil (preexistent in the oil or generated from the sulfonation
reaction);
and (4) The basic nitrogen containing components of oil are converted to the
corresponding sulfonates and/or sulfate salts. These salts are more surface-
active than
the base nitrogen containing components themselves and thus contribute to
improving
the stability of the solids-stabilized water-in-oil emulsion.
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Procedure for Preparation of a Solids-Stabilized Water-in-Oil Emulsion Usin~
Sulfonation Chemistry
The oil is pretreated with a sulfonating agent either before or after the
addition
of solid particles, and followed by the addition of water. The water is added
in small
aliquots or continuously and the mixture subjected to shear mixing, preferably
between
1000 to 12000 rpm, for a time sufficient to disperse the water as small
droplets in the
continuous oil phase, typically between 0.5 to 24 hours. It is preferred to
have a water
concentration in the water-in-oil emulsion of 40 to 80%, more preferably 50 to
65%,
and most preferably 60%.
The preferred sulfonating agent is concentrated sulfuric acid. The preferred
treat rate of sulfuric acid to oil is between 0.5 to 5wt%, more preferably 1
to 3wt%,
based on the weight of oil. Other sulfonating agents can be used alone or in
combination with other agents. Such sulfonating agents are generally described
in E.
E. Gilbert, Sulfonation and Related Reactions, Interscience, New York, (1965).
Other common sulfonating agents that may be useful in the present invention
include
fuming sulfuric acid, sulfur trioxide, alkali disulfates, pyrosulfates,
chlorosulfonic acid
and a mixture of manganese dioxide and sulfurous acid. The process temperature
during sulfonation can be from -20 C to 300 C, preferably from 10 C to 100 C
and
more preferably from 20 C to 60 C. Reaction can be accelerated by various
methods,
including without limitation thermal, mechanical, sonic, electromagnetic,
vibrational,
mixing, and spraying.
As can be appreciated by one of ordinary skill in the art, the amount of
sulfonating agent useful in the present invention can be adjusted according
especially to
the nature of the sulfonating agent, and the asphaltene and resin content of
the oils. An
oil containing a large amount of asphaltene may require less sulfonation than
one
containing a small amount of asphaltene. The amount of asphaltene in oil can
be
determined using standard techniques known in the art. The range of
sulfonation can
be from 0.01 to 40%, preferably from 0.1 to 10% and more preferably from 0.1
to 2%
of the mass of the solid particles.
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One method for practicing this embodiment of the invention is to first
sulfonate
the oil, and then add the solid particles. However, addition of the solid
particles to the
oil and sulfonation of the mixture is preferred. The solids can be silica,
clays,
hydrophobic particulates, and/or unfunctionalized and functional.ized asphalts
and their
corresponding mixtures. The preferred treat rate of the solids to the oil is
0.05 to 2.0
wt% solids based on the weight of oil.
The hydrophobic particulates for this embodiment of the invention are any
particulate wherein the hydrophobicity is greater than 50% and less than 99.9%
and
hydrophilic or polar moieties are less than 40% and greater than 0.1% of the
particulate mass. The hydrophilic or polar moieties can be ;Formed as a result
of
sulfonation of the combination of hydrophobic particulates with oil. Examples
of
hydrophobic partieulates useful for this invention include, without
limitation,
phylosilicates, lignin, lignite, coal, gillsonite, silica, dolamite, metal
oxides, layered
oxides, and quaternary onium exchanged phylosilicates.
1'5 Functionalized and unfunctionalized asphalts are alsa effective solids for
making the sulfonate-pretreated solids-stabilized water-in-oil emulsions. In
particular,
phosphonated asphalt that has been sufficiently immersed in the oil,
preferably for 24
hours at 55 C, is an effective solid. The asphalts can be used in their
natural state or
may be functionalized or functionalized by sulfonation agents of the present
invention.
Nonlimiting examples of functional moieties are sulfonic acid, phosphoric
acid,
carboxylic acid, nitric acid or salts thereof, and hydrophilic groups.
After emulsion preparation, the pH of the emulsion can be adjusted as
previously described in connection with the first embodiment ox the invention
related
to pretreating oil with dilute acid. As previously described, a calculated
amount of
weak base is added to the emulsion and the emulsion is subjectec( to shear
mixing for a
time sufficient to raise its pH to the desired level, preferably in the 5-7
range.
Adjusting pH is optional, as in some cases it is desirable to inject an acidic
emulsion
and allow the reservoir formation to buffer the emulsion to the reservoir
alkalinity.
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The viscosity of the emulsion increases with sulfonation. However, the
emulsion viscosity is not a linear function of sulfonating agent addition. The
viscosity
of the emulsion increases at a reduced rate as a function of sulfonation.
Therefore, the
user may make increasingly stable solids-stabilized emulsions via sulfonation,
while
maintaining desirable rheological properties. Further, the viscosity of the
emulsion
may also be reduced by the addition of gas as discussed in U.S. Patents
5,855,243 and
5,910,467.
While sulfonation of the entire quantity of oil necessary to make such an
emulsion is feasible, it is also possible to sulfonate a slipstream or master
batch of oil
and subsequently mix the slipstream with a main stream of oil prior to water
addition
and emulsification. This main stream of oil is preferably untreated crude oil,
however,
it may be any oil, including oil that has been treated to enhance its ability
to form a
stable emulsion or treated to optimize its rheology. If this slipstream method
is used,
the amounts of solids and sulfonating agent needed for the slipstream
treatment are
scaled accordingly to obtain the desired amounts in the resulting emulsion.
Examples:
This embodiment of the invention has been demonstrated using Crude Oil #2
and another oil, Crude Oil #5, as these oils do not form stable solids-
stabilized
emulsions using the method described in U.S. 5,927,404, 5,855,243 and
5,910,467.
However, as indicated by the experiments below, pretreating the oil with
sulfonation
chemistry improves the oil's ability to form stable solids-stabilized water-in-
oil
emulsions.
In a typical experiment, the solid particles are added to oil and then
sulfonated.
Concentrated sulfuric acid is used as the sulfonating agent, and is added at a
treat rate
of 3 parts of acid per 100 parts of oil. This mixture is stirred on a hot
plate with a
magnetic stirrer attachment at a temperature of around 50 C. Water is then
added to
the oil in small aliquots with mixing, which results in a solids-stabilized
water-in-oil
emulsion.
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These emulsions were subjected to the following tests:
1. Shelf stability at 25 C for 48 hours
2. Optical microscopy and NMR for determination of water droplet size /
size distribution
3. Centrifuge stability (described in Appendix-1)
4. Emulsion stability: flow through a sand pack (the micropercolation test
procedure is given in Appendix-1)
ExamRle I
Crude Oil #2 and solid particulates were co-sulfonated as follows: 12 grams
(g) of Crude Oil #2 and the solid particles, comprised of 0.06 g of 2-
methylbenzyl
tallow intercalated monomorillonite (Organotrol 1665; product of Cimar Corp.)
and
0.12 g ASP-97-021 untreated Billings asphalt (product of Exxon), were combined
in a
glass jar. The mixture was stirred at 50 C for 72 hours. Sulfuric acid was
added at 3
parts acid per 100 parts oil and the mixture stirred at 50 C for 24 hours.
The sulfonated oil and solids were then combined with 18 g of synthetic brine
solution (comprised of 9.4 g sodium chloride, 3.3 g CaC12 (calcium chloride) -
2H20,
0.48g MgC12(magnesium chloride) - 6H20 and 0.16 g potassium chloride per liter
of
distilled water). The brine was added dropwise over 30 minutes at 5000 rpm.
The
emulsion thus formed was mixed for an additional 15 minutes at 7500 rpm.
The oil external solids-stabilized emulsion thus produced was tested for
stability using the micropercolation test as described in Appendix-1. The sand
used in
this test was Ottawa sand and the oil was centrifuged with the sand for one
minute at
50 C. Duplicate samples showed 0% and 3.2% brine breakout (%bbo) following
injection through the sand pack. Light microscopy showed water droplet
diameter less
than 20 microns and a majority of particles having diameters less than 7
microns.
x le
Crude Oil #5 and oxidized asphalt (OX-97-29-180; product of Imperial Oil)
were co-sulfonated according to the previously described procedure. However,
in this
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example the oil and asphalt were stirred together for 2.5 hours at 50 C prior
to the
addition of the sulfonating agent, sulfuric acid at 3 parts sulfuric acid per
100 parts oil.
The sulfonated product was mixed with the synthetic brine solution as
described. The resultant mixture contained 60% aqueous phase content. This oil
external emulsion exhibited a pH of 1.6 and was then neutralized to a pH of
7.3 with
the addition of ammonium hydroxide and then remixed on an Arrow 850 mixer at
350
rpm for 15 minutes. The emulsion pH approximated the pH of Crude Oil #5. This
emulsion showed no brine breakout in the micropercolation test. Droplet
diameters
were less than 10 microns with the majority of water droplets less than 5
microns.
Rheological testing using a cone and plate viscometer demonstrated high
emulsion
stability, i.e. the viscosity remained essentially constant as a function of
cycle number.
Example 3
The same experiment was performed using Crude Oil #5 and 2-methylbenzyl
tallow intercalated montmorillonite (Organotrol 1665, a product of Cimbar
Performance Minerals, Cartersville GA) as the solid particulate. The crude oil
and
solid particles were combined and stirred for 4 hours at 50 C prior to the
addition of
sulfuric acid. Otherwise, this mixture was sulfonated according to the methods
described above.
The synthetic brine solution described above was added to the oil and solids
and mixed as before. The resulting emulsion's pH level was also adjusted to
7.5 with
the addition of ammonium hydroxide and mixing with an Arrow 850 mixer at 350
rpm for 15 minutes. The oil external emulsion exhibited an aqueous phase
droplet
diameter of less than 10 microns and a majority of brine droplets were less
than 5
microns. No brine breakout was found under the micropercolation test described
in
Appendix-1, using Berea sand.
Example 4
Crude Oil #2 and untreated asphalt (ASP-97-021, a product of Imperial Oil
Corporation, Canada) were co-sulfonated. The oil and asphalt were stirred at
50 C for
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72 hours prior to the addition of the sulfuric acid. Otherwise, sulfonation
was
performed by the steps described above.
The solids-stabilized water-in-oil emulsion was produced with the addition of
the synthetic brine solution described above and mixing according to the
procedures
above. However, in this example, the emulsion pH was not adjusted, but
remained
acidic. Light microscopy showed an aqueous phase droplet diameter less than 10
microns with a majority of droplets less than 5 microns. No brine breakout was
found
by the micropercolation test described in Appendix-1, using Ottawa sand.
Example 5
12 g of Crude Oil #2 and 0.06 g of an hydrophobic particulate, Wolastafil-050-
MH-0010 (methylalkoxysilane coated calcium metasilicate having a 1% coating
by
weight of calcium metasilicate -- product of United Mineral Corp.), were co-
sulfonated
as previously described. In this example, the oil and particulate were stirred
at 50 C
for 2.5 hours prior to the addition of the sulfuric acid.
A solids-stabilized water-in-oil emulsion was produced by the above described
procedures, and the emulsion pH was adjusted to 6.1 using ammonium hydroxide.
Light microscopy revealed an aqueous phase droplet diameter of less than 5
microns.
The result of the micropercolation test demonstrated no brine breakout
following
emulsion injection. Rheological testing showed no significant change in
viscosity with
cycle number indicating high shear stability.
Example 6
A solids-stabilized water-in-oil emulsion was formed using Crude Oil #2 and
phosphonated asphalt (Kew 97-149 , a product of Imperial Oil Corporation,
Canada)
as the solid particles. The oil and solids were added together and the mixture
was
stirred at 50 C for 48 hours prior to the addition of sulfuric acid, as
described above.
The resulting water-in-oil emulsion showed aqueous phase droplet diameter
less than 5 microns using light microscopy. The micropercolation test revealed
no
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brine breakout. Rheological testing indicated high emulsion stability, i.e.
the viscosity
remained essentially constant as a function of the number of cycles.
Pretreatment of Oil with Lignosulfonate Additive
Another method of pretreating oil to enhance its ability to form a stabile
solids-
stabilized water-in-oil emulsion is to add a lignosulfonate additive to the
oil prior to
making the emulsion. The salts of lignosulfonic acid (e.g., sodium, potassium,
ammonium, calcium, etc.) are surface-active in nature, and when added to an
oil/water
mixture they will tend to aggregate at the oil/water interface. This effect
increases the
interfacial activity of the oil and enhances the stability of the emulsion.
Preparation of the Lignosulfonate Treated Solids-Stabilized Emulsion
To practice this embodiment of the invention, a lignosulfonate additive is
added
to oil, before or after the addition of the solid particles, but prior to
emulsification. For
the sake of simplicity and clarity, this specification shall reference adding
one type of
lignosulfonate additive to the oil. However, it should be understood that
combinations
of different lignosulfonate additives may be used to practice this embodiment
of the
invention. The lignosulfonate additive is added at a treat rate of between 200
to
20,000 ppm based on the weight of the oil, more preferably 500 to 5000 ppm,
and
even more preferably 500 to 1000 ppm, for 5 to 10 minutes at 25 to 40 C. The
solid
particles are added either before or after lignosulfonate additive addition,
followed by
the addition of water in small aliquots or continuously. The mixture is then
subjected
to shear mixing at a rate of between 1000 to 12000 rpm for a time sufficient
to
disperse the water as small droplets in the continuous oil phase. It is
preferred to have
a water concentration in the water-in-oil emulsion of 40 to 80%, more
preferably 50 to
65%, and most preferably 60%.
The temperature of the emulsion will rise above ambient temperature (25 C)
during mixing. Controlling the temperature of the emulsion during mixing is
not
critical, however, higher temperatures between 40 C and 75 C are preferred.
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Both oil soluble and water-soluble lignosulfonate additives can be used to
enhance the stability of the solids-stabilized water-in-oil emulsion. Non-
limiting
examples of water-soluble lignosulfonates are sulfonate salts of monovalent
cations
like sodium, potassium, and ammonium. Non-limiting examples of oil soluble
lignosulfonates are sulfonate salts of divalent cations like calcium,
magnesium, and
iron. It is preferred to use water-soluble additives because of the ease of
delivery and
the use of water as the delivery solvent. The preferred water-soluble
lignosulfonate
additive is ammonium lignosulfonate. In addition, mixtures of lignosulfonate
salts may
be used to produce the same or an enhanced effect.
A hydrophobic silica, Aerosil0 R 972, was found to be an effective solid for
several types of oil. The invention has been demonstrated using Aerosil0 R-972
at a
treat rate of 0.15wt%, based on the weight of the oil. Other hydrophobic
solids like
divided and oil wetted bentonite clays, organophilic clays or carbonaceous
asphaltenic
solids may also be used. Hydrophilic solid particles can also be used. The
preferred
treat rate for solids is 0.05 to 0.25wt% based on the weight of the oil.
One may first pretreat the oil with the lignosulfonate additive and then add
the
solid particulates. However, it is preferred to add the solid particulates to
the oil and
then add the lignosulfonate additive to the mixture. Optionally, the solid
particulates
can be first treated with the lignosulfonate additive and the treated solids
can be added
to the oil prior to the addition of water and niixing. As aforementioned,
either water
or oil soluble lignosulfonate additives can be used to pretreat the solids.
The choice of
which type of lignosulfonate additive to use depends upon the type of solid to
be
treated. Generally, a hydrophobic solid is treated with a water soluble
lignosulfonate
additive and a hydrophilic solid with an oil soluble lignosulfonate additive.
Such a
choice would enable suitable modification of the solids' surface to render
optimum
hydrophilic and hydrophobic character.
While lignosulfonate pretreatment of the entire quantity of oil necessary to
make a desired emulsion is feasible by this embodiment of the invention, it is
also
possible to pretreat a slipstream or master batch of oil and subsequently mix
the
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slipstream with a main stream of oil prior to water addition and
emulsification. This
main stream of oil is preferably untreated crude oil, however, it may be any
oil,
including oil that has been treated to enhance its ability to form a stable
emulsion or
treated to optimize its rheology. If this slipstream method is used, the
amounts of
solids and lignosulfonate additives needed for the slipstream treatment are
scaled
accordingly to obtain the desired amounts in the resulting emulsion.
This embodiment of the invention can be used in conjunction with the method
of pretreating oil with dilute mineral or organic acid to further enhance the
surface-
active properties in the oil. The dilute acid addition can occur before or
after
lignosulfonate addition, as the order of addition of the acid and the
lignosulfonate
additive are not critical. However, the acid addition and the lignosulfonate
addition
should occur prior to emulsification. If the lignosulfonate addition is
combined with
acid addition, the pH of the emulsion can be adjusted by adding a calculated
amount of
a weak base, as previously described, to raise the pH to the desired level,
preferably to
a pH of between 5-7.
Examples:
This invention has been demonstrated on Crude Oil #4 and Crude Oil #6, as
these crude oils do not form stable solids-stabilized emulsions using the
method
described in U.S. 5,927,404, 5,855,243 and 5,910,467. Crude Oil #6 is a low
viscosity
crude oil. In a typical experiment, the lignosulfonate additive was added to
the oil at a
treat rate of 0.05 to 0.5wt% based on the weight of the oil and mixed for 10
minutes
using a Silverson homogenizer at from about 1000 to 12,000 rpm. Ammonium
lignosulfonate and calcium lignosulfonate were used as the lignosulfonate
additives in
these examples. Solid particles, either divided bentonite or hydrophilic
silica, were
added at 0.15wt% based on the weight of the oil, followed by further mixing.
Water
was then added to the mixture in small aliquots with further mixing to provide
a solids-
stabilized water-in-oil emulsion.
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Emulsions prepared by the foregoing methods were subjected to the following
tests:
1. Shelf stability at 25 C for 48 hours
2. Optical microscopy and NMR for determination of water droplet size /
size distribution
3. Centrifuge stability (see Appendix-1)
4. Emulsion stability: flow through a sand pack (details of the
micropercolation test procedure is given in Appendix-1)
5. Emulsion rheology using a Brookfield viscometer (cone (#5 1) and
plate configuration) at 60 C in a shear range of 1.92 to 384 sec"'.
Example-1: Crude Oil #4
Test results for Crude Oil #4 pretreated with ammonium lignosulfonate or
calcium lignosulfonate are presented in Table 10. A solids-stabilized 60/40
water-in-
oil emulsion was formed using lignosulfonate pretreatment at 0.5wt% and a
hydrophobic silica, Aerosil R 972, at 0.15wt%.
As indicated in Table 10, the lignosulfonate pretreatment enhanced the
stability
of the emulsions as evidenced by the decreased brine breakout (%bbo) under the
micropercolation test, as compared to the untreated solids-stabilized water-in-
oil
emulsion.
TABLE 10
Influence of 0.5 wt% ammonium and calcium lignosulfonate on a solids-
stabilized water-in-oil emulsion made from Crude Oil #4
Lignosulfonate Micropercolation Emulsion
Additive Stability (%bbo) Viscosity (cP)
at 60 C
None 38 2743
Ammonium Lignosulfonate 4 2620
Calcium Lignosulfonate 8 2620
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Example-2: Crude Oil #6
A solids-stabilized 60/40 water-in-oil emulsion was made with Crude Oil #6
and 0.15wt% hydrophobic silica, Aerosil R 972. No lignosulfonate pretreatment
was
used. The emulsion was unstable with a 40% water breakout under the
micropercolation test. The viscosity of the emulsion at 60 C and 9.6 sec"' was
983 cP.
However, when the same 60/40 water-in- oil emulsion was prepared using
Crude Oil #6 pretreated with 0.5wt% ammonium lignosulfonate, the stability of
the
emulsion was enhanced, with the water breakout reduced to 17%. The viscosity
of the
emulsion at 60 C and 9.6 sec-' increased slightly to 1064 cP.
Example-3: 50/50 Crude Oil Blend using Crude Oil #4 and Crude Oil #6
An untreated solids-stabilized 60/40 water-in-oil emulsion was prepared using
a
50% Crude Oil #4 and 50% Crude Oil #6 blend. The solid particles were
comprised of
a hydrophobic silica, Aerosil R 972, at 0.15wt% based upon the weight of the
oil
blend. The untreated solids-stabilized emulsion had a water breakout of 32%.
Viscosity for this emulsion at 60 C and 9.6 sec' was 2129 cP.
The same emulsion was prepared with a 50/50 Crude Oil #4 / Crude Oil #6
blend that was pretreated with 0.5wt% of ammonium lignosulfonate. The
lignosulfonate treated solids-stabilized emulsion showed enhanced stability as
evidenced by the decrease in brine breakout to 5%. The viscosity of the
treated
emulsion at 60 C and 9.6 sec' remained at 2129 cP. The data indicate that the
treatment enhanced emulsion stability with no change in the viscosity.
Pretreatment of Oil by Thermal Air Oxidation
Another pretreatment embodiment that can be used to increase the stability of
a
solids-stabilized water-in-oil emulsion is to thermally treat the oil, either
before or after
the addition of solid particles, in the presence of air or oxygen.
Thermally treating oil or a mixture of oil and solid particles in the presence
of
air or oxygen causes various reactions to occur in the oil and on the surface
of the
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solid particles. (1) The aromatic components of the oil that have benzyllic
carbons and
those that have fused rings that are oxidizable including, but not limited to
naphthelene
and anthracene, are oxidized to the corresponding acids, ketones or quinone
products.
Organo sulfur and nitrogen compounds present are oxidized to sulfoxides and
nitrogen
oxides. The oxygenated compounds are more surface-active than the aromatic
components themselves and adsorb strongly on the surface of the solid
particles to
improve the stability of the solids-stabilized water-in-oil emulsion. (2) If
naphthenic
acids are present as salts of divalent cations like calcium, air oxidation can
convert
these salts to naphthenic acids and the corresponding metal oxide, for example
calcium
oxide. The free napthenic acid can adsorb on the surface of the solids and
also
improve the stability of the solids-stabilized water-in-oil emulsion. (3)
Thermal
treatment with an air purge dehydrates the solid particles and thus modifies
the solids'
surface to improve its interaction with the surface-active components of oil
(preexistent in the oil or generated from air oxidation).
Preparation of a Solids-Stabilized Emulsion Using Thermal Air Oxidized Oil
To prepare a solids-stabilized water-in-oil emulsion using this method, the
oil is
thermally treated for sufficient time and temperature in the presence of an
air or
oxygen purge to enable the physical and chemical modifications to the oil and
solid
particles. Preferably, the oil is heated to temperatures of between 110-180 C
for 15
minutes to 6 hours, under an air or oxygen purge at a preferred rate of 20 to
100
standard cubic feet per barrel per hour (scf/bbl/hr).
The solid particles may be added before, during or after the thermal air
oxidation step, but should be added before emulsification. However, it is
preferred to
add the solids to the oil and then thermally air oxidize the mixture. The
solid particles
may be hydrophilic or hydrophobic in nature. Fumed silica, sold under the
trade name
of Aerosil0 R 972 or Aerosil0 130 (Products of DeGussa Corp.) were found to be
effective solids for a number of oils. Other solid particles like bentonite
clays, divided
bentonite clays, kaolinite clays, organophilic clays or carbonaceous
asphaltenic solids
may also be used.
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The amount of solid particle added to the oil can vary in the range of about
1%
to 90% based on the weight of the oil, preferably 0.01 to 20 wt%, and more
preferably
0.05 to 5.0 wt%. At the higher concentrations, the mixture of solids and oil
will be a
high solids content slurry.
Bentonite clays, such as those mined in Wyoming, Ga, or other numerous
locations around the world, are particularly suited as stabilizers for water-
in-oil
emulsions. As mined, these clays naturally consist of aggregates of particles
that can
be dispersed in water and broken up by shearing into units having average
particle sizes
of 2 microns or less. However, each of these particles is a laminated unit
containing
approximately 100 layers of fundamental silicate layers of 1 nm thickness
bonded
together by inclusions of atoms such as calcium in the layers. By exchanging
the atoms
such as calcium by sodium or lithium (which are larger and have strong
attractions for
water molecules in fresh water), and then exposing the bentonite to fresh
water, the
bentonite can be broken into individual 1 nm thick layers, called fundamental
particles.
The chemistry of this delamination process is well known to those skilled in
the art of
clay chemistry. The result of this delamination process is a gel consisting of
divided
bentonite clay.
The preferred solid is divided or delaminated bentonite clay that is obtained
as
a gel from the delamination process described above. The amount of gel added
to the
oil before the thermal air oxidation step can very in the range of 5 to 95% of
gel based
on the weight of the oil, preferably 40 to 60%. The weight of bentonite clay
solids in
the gel can very from 1 to 30% based on the weight of the water. When
bentonite clay
gel is used as the solid particle, and is added to the oil and subjected to
the thermal air
oxidation step, water is expelled from the reaction vessel as steam. The
reaction
should be carried out until at least 80% of the water is expelled, preferably
until 95%
of the water is expelled, and even more preferably until 100% of the water is
expelled.
It is preferred to oxidize a slipstream or master batch of a mixture of oil
and
solids and subsequently mix the slipstream with a main stream of oil prior to
water
addition and mixing, i.e. prior to emulsification. This main stream of oil is
preferably
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untreated crude oil, however, it may be any oil, including oil that has been
treated to
enhance its ability to form a stable emulsion or treated to optimize its
rheology. If
untreated crude oil is the main stream, the preferred blending rate is 0.5 to
5%
oxidized oil in the untreated oil main stream, more preferably 0.1 to 2.5%.
After the air oxidation step and solid particle addition, water is added in
small
aliquots or continuously and the mixture is subjected to shear mixing at 1000
to 12000
rpm for a time sufficient to disperse the water as small droplets in the
continuous oil
phase. The temperature of the emulsion will rise above ambient temperature of
25 C
during mixing. Controlling the temperature of the emulsion during mixing is
not
critical. However, higher temperatures between 40 to 70 C are preferred.
Catalysts may be used to enhance the oxidation reaction. Finely divided
catalysts like iron, manganese or nickel, or their oil soluble metal salts can
be used to
catalyze oxidation rates and effect selectivity in the oxidation products.
Such
oxidation promoting catalysts and the techniques of using such catalysts are
well
known in the art, and therefore will not be discussed herein. Oxidation can be
conducted at elevated pressures to further catalyze the reaction rate and
achieve
product selectivity, however, oxidation at ambient pressures is preferred.
The oxidized oil can be further treated with dilute mineral or organic acid to
provide additional stability to the solids-stabilized water-in-oil emulsion.
The preferred
acid treat rate is between 8 and 30,000 ppm. If this acid pretreatment step is
used, the
pH of the resulting emulsion can be adjusted to a preferred range of 5 to 7 by
adding a
calculated amount of weak base to the emulsion. However, adjusting pH is
optional as
in some cases it is desirable to inject an acidic emulsion and allow the
reservoir
formation to buffer the emulsion to the reservoir alkalinity. Ammonium
hydroxide is
the preferred base for pH adjustment. Stronger bases like sodium hydroxide,
potassium hydroxide and calcium oxide have a negative effect on emulsion
stability.
One possible explanation for this effect is that strong bases tend to invert
the emulsion,
i.e. convert the water-in-oil emulsion to an oil-in-water emulsion. Such an
inversion is
undesirable for the purposes of this invention.
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In addition to increasing the stability of the solids-stabilized water-in-oil
emulsion, dilute acid treatment lowers the viscosity of the emulsion. This
reduced
viscosity aids in enhancing the injectivity of the emulsion, and may also be
beneficial in
other aspects in EOR processes, for example, matching the emulsion's rheology
with
that of the subterranean oil to be recovered when using the emulsion as a
drive fluid.
Gas may also be added to further lower the viscosity of the emulsion.
Examples:
In a typical experiment, 200g of oil was placed in a Parr autoclave or three-
necked glass flasks and oxidized at temperatures of 150 to 160 C for 2 to 6
hours
with a continuous purge of air at 80 to 100 scf/bbl/hour. The oxidized oil was
then
blended to various ratios with untreated oil or other thermally air oxidized
oils, as
detailed in the specific examples below. A hydrophobic silica, Aerosil R 972
was
added to the oxidized oil blend at 0.05 to 0.15 wt%, based on the weight of
the oil.
After the solids addition, the product was mixed using a Silverson
homogenizer.
Water was then added in small aliquots with mixing to produce the solids-
stabilized
water-in-oil emulsion.
For the preferred case of thermal air oxidation of a mixture of oil and
divided
bentonite gel, the oil and gel are first mixed to form a slurry. Air or oxygen
gas is
purged into the reactor and the temperature raised to between 150 C and 170 C.
The
water is expelled as steam and can be condensed outside for recovery and
reuse.
For the optional case of acid addition to the oxidized oil, 10 ppm of sulfuric
acid was added to the oxidized sample and mixed for 10 minutes at 40 C.
Addition of
solids and water with mixing followed as described above.
Emulsions prepared by the foregoing methods were subjected to the following
tests:
1. Shelf stability at 25 C for 48 hours
2. Optical microscopy and NMR for determination of water droplet size /
size distribution
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3. Centrifuge stability (described in Appendix-1)
4. Emulsion stability: flow through a sand pack (details of the
micropercolation test procedure is given in Appendix-1)
5. Emulsion rheology using a Brookfield0 viscometer (cone(#51) and
plate configuration) at 60 C in a shear range of 1.92 to 384 sec'.
Example-1 = Untreated Crude Oil #4 Blended with Air Oxidized Crude Oil #4
Aerosil0 R 972 was added at a treat rate of 0.15wt% to untreated Crude Oil
#4, followed by water and mixing to form a 60/40 solids-stabilized water-in-
crude oil
emulsion. This emulsion, though shelf-stable, was unstable in the centrifuge
and
micropercolation tests. Dispersed water droplets ranged in size from 2 to 40
microns
in diameter, and a 54% water breakout was observed in the micropercolation
test
described in Appendix-1, using Berea sand. The viscosity of the emulsion at 60
C and
9.6 sec'' was 3644 cP.
Another batch of Crude Oil #4 was thermally air oxidized according to the
procedure described above. The thermally air oxidized Crude Oil #4 was blended
with
untreated Crude Oil #4 at 2.5wt% of treated oil in the untreated oil. Delivery
of the
thermally air oxidized Crude Oil #4 was in toluene in a 1:2 ratio. A
hydrophobic silica,
Aerosil0 R 972, was added to the blend at 0.15wt% based on the weight of the
blended oil. Addition of water and mixing followed to make a 60/40 solids-
stabilized
water-in-crude oil solids-stabilized emulsion. NMR determined droplet size
distribution indicates that 90% of the water droplets were less than 2 microns
in
diameter. The emulsion's stability improved over that of the untreated Crude
Oil #4
solids-stabilized emulsion, as evidenced by a reduction to 10% water breakout
in the
Berea micropercolation test. The emulsion's viscosity was 2452 cP at 60 C and
10
sec"'. Additionally, the viscosity profiles repeated over a 1-hour shear
cycle.
Ethane gas was added to reduce the thermally air oxidized solids-stabilized
water-in-oil emulsion's viscosity. The resulting emulsion's viscosity was
lowered from
2452 to 390 cP at 60 C with saturation of ethane at 400 psi. The emulsion was
stable
to ethane addition and shearing at 10 sec' for the duration of the experiment
of 5 days.
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Example-2: Blends of Oxidized Crude Oil #4 and Low Viscosity Crude Oil #6
In this experiment Crude Oil #4 and a low viscosity crude oil, Crude Oil #6,
were blended to various ratios. A hydrophobic solid, Aerosil R 972, was added
at
0.15wt% solids to the blended oil, along with 10 ppm sulfuric acid and mixed
for 30
minutes. Water was then added in small aliquots and mixed to provide a 60/40
water-
in-blended oil emulsion. Results are shown in Table 11. As is observed from
the data,
increasing the proportion of the low viscosity Crude Oil #6 decreases the
viscosity of
the 60/40 water-in-blended oil emulsion from 3644 cP (measured at 60 C and 9.6
sec"
') to 983 cP. However, the stability of the emulsions are poor as evidenced by
the 30
to 40% water breakout in the micropercolation test using Berea sand.
TABLE 11
Crude Oil #4/Crude Oil % bbo Viscosity, cP
#6 60 C, 96s'
Blend Ratio
100/0 38 3 644
75/25 34 2621
50/50 32 2129
25/75 41 1638
0/100 40 983
Table 12 shows the effectiveness of thermal air oxidation of the oil before
emulsification to enhance the stability of the resulting emulsion. Crude Oil
#6 was
thermally air oxidized by the method previously described and then blended
with
untreated Crude Oil #4 to result in a 75% untreated Crude Oil #4 to a 25%
thermally
air oxidized Crude Oil #6 blend. A hydrophobic solid, Aerosil R 972, was
added to
the blend along with 10 ppm sulfuric acid, and mixed for 30 minutes. Water was
then
added in small aliquots and mixed to provide a 60/40 water-in-blended oil
emulsion.
. . i i l.. ..
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Results shown in Table 12 illustrate the effectiveness of this method as
indicated by the
micropercolation test using Berea sand.
TABLE 12
Oils Brine Breakout ( /abbo) Viscosity, cP
60 C, 96s"1
75% Crude Oil #4 34 2621
25% Crude Oil #6
75% Crude Oil #4
25% Thermally Air Oxidized 16 2620
Crude Oil #6
Upon addition of 25% of thermally air oxidized Crude Oil #6 to untreated
Crude Oil #4, the stability of the emulsion doubles as evidenced by the
decrease in
percent brine breakout from 34% to 16%.
Example-3: Solids-Stabilized Emulsion Prepared Using, Crude Oil #4 and Divided
Bentonite Gel
A mixture of 70 grams (g) of Crude Oil #4 and 30 g of divided bentonite gel
(providing an oil to gel ratio of 70:30, and with a bentonite solids
concentration of 3.5
wt% in the gel) was air oxidized at a temperature of 160 C for 4 hours with an
air
purge of 80 scf/bbl/hour. About 25 g of water was expelled from the reactor.
The
product from the reaction was used to prepare a solids-stabilized 60/40 water-
in-oil
emulsion. The air oxidized product was blended with untreated crude oil, with
a
resulting blend consisting of 2.4 wt% of the air oxidized product, to 97.6% of
the
untreated crude oil.
The resulting 60/40 water-in-oil emulsion showed a 12% brine breakout in the
rnicropercolation stability test. The emulsion was stable to ethane gas
addition at 400
psi.
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A mixture of 30 g of Crude Oil #4 and 70 g divided bentonite gel (oil to gel
ratio of 30:70) was subjected to thermal air oxidation using as described
above. Water
was expelled from the reactor and the resulting product was an oily solid.
A solids-stabilized 60/40 water-in-oil emulsion was made using the oily solid
product. The amount of oily solid used was 0.1 % based on the weight of the
untreated
crude oil.
The resulting emulsion showed a 20% brine breakout in the micropercolation
stability test. The dispersed water droplets were less than 4 microns in
diameter.
Pretreatment of Oil by Thermal Treatment in an Inert Environment
Another method of pretreating an oil to enhance its ability to form a stable
solids-stabilized water-in-oil emulsion is to thermally treat the oil in an
inert
environment prior to emulsification. This embodiment has the added benefit of
reducing the viscosity of the solids stabilized water-in-oil emulsion.
The thermal treatment can:
a) generate asphaltenic solids which by themselves and/or in combination with
externally added solids provide improved stability to the solids-stabilized
water-in-oil emulsions,
b) reduce viscosity of the crude oil which translates to lower emulsion
viscosity of the solids-stabilized water-in-oil emulsions, and
c) retain or degrade napthenic acids.
Preparation of Solids-Stabilized Water-in-Oil Emulsions with Thermally Treated
Oil
To enhance an oil's physical and chemical properties for the formation of a
stable solids-stabilized emulsion, the oil may be thermally treated in an
inert
environment for a sufficient time, and at a sufficient temperature and
pressure prior to
emulsification. It is preferred to thermally treat the oil by heating to
temperatures
between 250 C-450 C at 30 to 300 pounds/square inch (psi) for 0.5 to 6 hours.
The
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thermal treatment can occur in an inert atmosphere with no purge gas, or
alternatively
in the continuous presence of an inert purge gas. For the preferred method of
thermally pretreating with no purge gas, the oil is initially purged with an
inert gas like
nitrogen for 30 minutes and the autoclave sealed and heated to the required
temperature. For the alternative embodiment of thermally pretreating with a
continuous purge of inert gas, an inert gas like argon is bubbled into the
reactor at 200
to 450 standard cubic feet/barrel/hour (scf/bbl/hour) during the entire course
of
thermal treatment. This process is preferred if a greater reduction in
viscosity is
desired. The latter process will result in a greater percentage destruction of
the surface
active napthenic acids and is less preferred for the purposes of preparing a
stable
emulsion. The treatment severity is suitably chosen to produce the optimum
viscosity
reduction and napthenic acid retention. This treatment severity can vary from
one oil
to another but is within the ranges disclosed.
After the thermal treatment, solids are added followed by water and mixing to
form the solids-stabilized water-in-oil emulsion. The addition of solids to
the oil prior
to the thermal pretreatment is also within the scope of the present invention.
However, in the latter case, the potential for fouling of the process
equipment needs to
be addressed, and thermal treatment conditions optimized to minimize the
equipment
fouling.
The water addition is made in small aliquots or continuously and the mixture
subjected to shear mixing, preferably at between 1000 to 12000 rpm, for a time
sufficient to disperse the water as small droplets in the continuous oil
phase. It is
preferred to have a water concentration in the water-in-oil emulsion of 40 to
80%,
more preferably 50 to 65%, and most preferably 60%. The temperature of the
emulsion will rise above ambient temperature (25 C) during mixing. Controlling
the
temperature of the emulsion during mixing is not critical. However, higher
temperatures between 40 C to 75 C are preferred.
With regards to solids, the solid particles are preferred to be hydrophobic in
nature. Fumed silica, sold under the trade name Aerosil R 972 (product of
DeGussa
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Corp.) was found to be effective for a number of different oils. Other solids
like
divided and oil wetted bentonite clays, kaolinite clays, organophilic clays or
carbonaceous asphaltenic solids may also be used. The preferred concentration
of
solids to oil is in the range of 0.05 to 0.25 wt%.
It is preferred to thermally treat a slipstream of oil to a high level of
severity
and then mix the slipstream with a main stream of oil prior to addition of
solids, water
and mixing to form the emulsion. This main stream of oil is preferably
untreated crude
oil, however, it may be any oil, including oil that has been treated to
enhance its ability
to form a stable emulsion or treated to optimize its rheology.
To further stabilize the solids-stabilized emulsion made with thermally
treated
oil, it is anticipated to be particularly useful to add 0.1 to 1.0 wt% of a
lignosulfonate
additive to the oil prior to emulsification. This method of enhancing the
stability of a
solids-stabilized emulsion, i.e. addition of a lignosulfonate additive, is
described above.
Dilute acid can also be added to the oil prior to emulsification, which will
further enhance the emulsion's stability and reduce the emulsion's viscosity.
This dilute
acid addition is also described herein.
The method of thermally treating oil before emulsification has the added
benefit
of decreasing the solids-stabilized emulsion's viscosity, as compared to a
solids-
stabilized emulsion made with untreated oil. This ability to manipulate the
viscosity of
the emulsion allows the user to optimally match the rheological
characteristics of the
emulsion to that of the oil to be recovered specifically for the particular
type EOR
method used. Gas may also be added to further lower the viscosity of the
emulsion.
Yet another method to reduce the viscosity of a thermally treated solids-
stabilized emulsion is to age the emulsion. The thermally treated solids-
stabilized
emulsion can be aged by simply allowing the emulsion to rest at room
temperature or
at an elevated temperature for a sufficient period of time. The viscosity of
the
emulsion can be reduced by more than 50% by using this method. The aging
process
can be accelerated by centrifugation, preferably repeated centrifugation,
which will
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produce a similar reduction in viscosity of the thermally treated solids
stabilized
emulsion. Centrifugation is conducted preferably at temperatures between 35 C
and
80 C for 15 minutes to 2 hours at 500 to 10,000 rpm.
Examples:
In a typical experiment, 200 g of oil was placed in a PARR autoclave and
heated to temperatures of 150 to 450 C for 0.5 to 6 hours at pressures ranging
from
30 to 280 psi. The thermal pretreatment occurred either an inert atmosphere
with no
purge gas, or alternatively in the continuous presence of a purge gas. For
thermal
pretreatment with no purge gas, the oil was initially purged with an inert gas
like
nitrogen for 30 minutes and the autoclave sealed and heated to the required
temperature. For thermal pretreatment with a continuous purge of inert gas, an
inert
gas like argon was bubbled into the reactor at 200 to 450 scf/bbl/hour during
the entire
course of thermal treatment. A hydrophobic silica, Aerosil R 972, was then
added to
the heat treated oil. Mixing using a Silverson homogenizer followed solids
addition.
Finally, water was added to the oil and solid particles in small aliquots and
mixed to
provide a solids-stabilized water-in-oil emulsion.
The thermal pretreatment method was demonstrated at three levels of severity,
which impacted the following oil properties: (1) total acid number (TAN), (2)
amount
of n-heptane insolubles, (3) toluene equivalence (measure of solubility of the
thermally
generated asphaltenes), and (4) viscosity.
The emulsions prepared by thermally treated oil were subjected to the
following tests:
1. Shelf stability at 25 C for 48 hours
2. Optical microscopy and NiVIR for determination of water droplet size /
size distribution
3. Centrifuge stability (as described in Appendix-1)
4. Emulsion stability: flow through a sand pack (details of the
micropercolation test procedure is given in Appendix-1)
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5. Emulsion rheology using a Brookfield viscometer (cone(#51) and
plate configuration) at 35 or 60 C in a shear range of 1.92 to 384 sec-'.
Example-1
A 60/40 water-in-oil emulsion was prepared using Crude Oil #2 without any
thermal treatment, but with addition of 0.15wt% hydrophobic silica (Aerosil R
972).
This emulsion, though shelf-stable, was unstable in the centrifuge and
micropercolation
tests. Dispersed water droplets ranged in size from 0.4 to 80 microns in
diameter.
Example-2
Crude Oil #2 was thermally treated at 360 C for 6 hours at 280 psi in an inert
environment, using a nitrogen preflush. The resulting oil's viscosity at 35 C
and 9.6
sec"1 was lowered from 643 centipoise (cP) to 328 cP. The TAN was reduced from
6.6 to 3.9. The toluene equivalence increased from 14 to 31 while the n-
heptane
insolubles remained unchanged at 2.7%.
Solid particles, 0.15wt% Aerosil R 972, were added to the thermally treated
Crude Oil #2 followed by water and mixing to form a 60/40 water-in-oil solids-
stabilized emulsion, as previously described. The resulting solids-stabilized
emulsion
had a viscosity of 5734 cP at 35 C and 9.6 sec"', which represented a 63%
reduction in
emulsion viscosity as compared to an untreated solids-stabilized emulsion made
with
untreated Crude Oil #2 and 0.15wt% Aerosil R 972. The NMR determined water
droplet size distribution of the heat treated solids-stabilized emulsion
indicates a
narrow distribution of water droplets in the size range of 2 to 10 microns in
diameter.
The emulsion was stable to flow as no water breakout was observed in the
micropercolation tests described in Appendix - 1. The pH of the emulsion was
about
6.2.
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Example-3
Thermal treatment of Crude Oil #2 at 350 C for 2 hours at 90 psi in an inert
environment resulted in a treated oil whose viscosity at 35 C and 9.6 sec-'
was lowered
from 643 cP to 328 cP. The TAN was reduced from 6.6 to 5.1. The toluene
equivalence increased from 14 to 25 while the n-heptane insolubles remained
unchanged at 2.7%.
Addition of 0.15wt% Aerosil R 972 to the thermally treated oil followed by
water and mixing, as previously described, provided a stable solids-stabilized
60/40
water-in-oil emulsion. NMR revealed a distribution of water droplets in the
size range
of 2 to 14 microns in diameter. A 14% water breakout in the micropercolation
sandpack test and no water breakout in the microcentrifuge test were observed.
The
pH of the emulsion was 6.2. The viscosity of the emulsion at 35 C and 9.6
sec"' was
7373 cP, which represents a viscosity reduction of greater than one-half when
compared to a similar solids-stabilized emulsion prepared from Crude Oil #2,
that had
been pretreated with dilute acid using the method described above.
Example-4
A 60/40 water-in- oil emulsion was prepared with another crude oil, Crude Oil
#4, without any thermal pretreatment, but with the addition of 0.15% of
Aerosil R
972. Crude Oil #4 does not form stable solids-stabilized emulsions by the
method
described in U.S. Patents 5,927,404, 5,855,243 and 5,910,467. Physical
properties for
Crude Oil #4 are contained in Table 2. This emulsion, although shelf-stable,
was
unstable in the centrifuge and micropercolation tests. Dispersed water
droplets ranged
in size from 2 to 40 microns in diameter, and a 54% water breakout was
observed in
the micropercolation test, described in Appendix-1, using Berea sand. The
viscosity of
the emulsion at 60 C and 9.6 sec"' was 3644 cP.
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General Test for Increase in Surface-Activity of Oil
Increases in the surface-activity of oil due to pretreatment can be measured
by
determining the decrease in interfacial tension between the oil and water.
Interfacial
tensions were determined by the standard pendant drop technique at 25 C.
Results for
untreated Crude Oil #4 and pretreated Crude Oil #4 are given below. Note that
interfacial tension results for Crude Oil #4 treated with solid particles and
sulfonation
could not be measured using the standard pendant drop technique.
TABLE 13
Measurement of Interfacial Tension
Oil Interfacial Tension
dynes/cm
Untreated Crude Oil #4 32.3
Crude Oil #4+solid particles (solids) 32.6
Crude Oil #4 + acid pretreatment + solids 15.8
Crude Oil #4 + lignosulfonate + solids 12.5
Solids = 0.15wt% Aerosil R 972
Lignosulfonate = 0. lwt% ammonium lignosulfonate
Acid pretreatment = 8000 ppm sulfuric acid
The present invention has been described in connection with its preferred
embodiments. However persons skilled in the art will recognize that many
modifications, alterations, and variations to the invention are possible
without
departing from the true scope of the invention. Accordingly, all such
modifications,
alterations, and variations shall be deemed to be included in this invention,
as defined
by the appended claims.
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Appendix-1: Micro-Percolation Test for Emulsion Stability
in Flow Through Porous Media
The observation that emulsions that are unstable will form two separate
macroscopic phases, an oil/emulsion phase and a water phase, is relied upon in
order to ascertain the stability of an emulsion on flow through porous media
in a
rapid, convenient assay. A volume of emulsion that passes completely through
the porous media can therefore be centrifuged to form two distinct phases,
whose volumes can be used as a measure of the emulsion stability-the greater
the proportion of water or water originally in the emulsion, that forms a
clear,
distinct phase after passage and centrifugation, the more unstable the
emulsion.
A convenient parameter to measure stability is therefore the "brine-breakout"
or
"bbo", defined as the fraction of the water or brine that is in the emulsion
that
forms the distinct separate aqueous phase. Since it is a proportion, the bbo
is
dimensionless and ranges between one (maximally unstable) and zero
(maximally stable). The brine breakout is measured under a well-defined set of
conditions.
A commercially available special fritted micro-centrifuge tube that is
comprised of two parts is used as the container for the experiment. The bottom
part is a tube that catches any fluid flowing from the top tube. The top part
is
similar to the usual polypropylene microcentrifuge tube, except that the
bottom
is a frit that is small enough to hold sand grains back, but allows the easy
flow of
fluid. In addition, the tubes come supplied with lids to each part, one of
which
serves also as a support that allows the top to be easily weighed and
manipulated while upright. They are available from Princeton Separations,
Inc.,
Adelphia NJ and are sold under the name "CENTRI-SEP COLUMNS."
A heated centrifuge is used to supply the pressure to flow the emulsion
fluid through a bit of sand placed in the upper tube. It was supplied by
Robinson, Inc., (Tulsa, OK) Model 620. The temperature is not adjustable, but
stabilizes at 72 C under our conditions. The top speed is about 2400
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revolutions per minute (RPM) and the radius to the sandpack is 8 centimeters
(cm), which gives a centrifugal force of 520 g. All weights are measured to
the
nearest milligram.
The columns come supplied with a small supply of silica gel already
weighed into the tube. This is discarded, and the weights of both sections
noted. About 0.2 grams (g) of sand is weighed into the top and 0.2 0.01 g of
oil added to the top. Typical sands used for this experiment are Berea or
Ottowa sands. The sand that is used in this test can be varied according to
one's
purpose. For simplicity, one may use unsieved, untreated Ottawa sand, supplied
by VWR Scientific Products. This gives a convenient, "forgiving" system
because the sand particles are rather large and free of clay. Alternatively,
one
may use one fraction that passes through 100 Tyler mesh, but is retained by a
150 mesh, and another fraction that passes through the 150 Tyler mesh, blended
in a ten to one ratio respectively. The tube is weighed again, then
centrifuged
for one minute at full speed on the heated centrifuge. The bottom tube is
discarded and the top is weighed again, which gives the amount of sand and oil
remaining in the top. The sand is now in an oil wetted state, with air and oil
in
the pore space.
Now, 0.18 0.02 g of emulsion is placed on top of the wetted sand, and
the top is weighed again. A bottom tube is weighed and placed below this tube
to catch the effluent during centrifugation.
A separate bottom tube is filled with 0.2 to 0.5 g of emulsion only. This
serves as a control to determine if the centrifuging of the emulsion, without
it
being passed through the oil-wetted sand, causes brine to break from the
emulsion. This step is known as the microcentrifuge test, and is also an
indicator of emulsion stability.
Both tubes are then centrifuged for a noted time (15 to 45 minutes)
depending on the oil viscosity and centrifuge speed. The object in adjusting
the
length of time is to get to a point where at least 75% of the emulsion arrives
in
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the bottom tube after passing through the sand. If less than that appears,
the assembly is centrifuged for an additional time(s).
After spinning, the weight of the top and bottom pieces are again
recorded. If the emulsion is unstable, a clear water phase will be visible in
the
bottom of the tube, below an opaque, black emulsion/oil phase. The volume of
water in the bottom receptacle is then measured by pulling it up into a
precision
capillary disposable pipette (100-200 microliters) fitted with a plunger.
These
are supplied by Drummond Scientific Co. (under the name "Wiretroll II"). The
length of the water column is measured and converted to mass of water through
a suitable calibration curve for the capillary. The water breakout can be then
calculated from these measurements and the knowledge of the weight fraction of
water in the emulsion originally.
