Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Title of the Invention
Oil Recovery Process Employing Amphoteric Surfactants
10
BACKGROUND OF THE INVENTION
This invention relates generally to the field of Enhanced Oil Recovery (EOR)
and more
specifically to an Oil Recovery Process employing mixtures of amphoteric
surfactants.
The amphoteric surfactants are betaines containing both saturated and
unsaturated
hydrophobic hydrocarbyl groups and are derived from naturally occurring oils
and fatty
acids rendering them green and biodegradable.
This invention also relates to the recovery of oil from subterranean oil
reservoirs and
more particularly to improved chemical flooding operations involving the use
of certain
mixtures of amphoteric surfactants that are suitable for use in brines
containing
relatively high concentrations of divalent metal ions and at high temperature
ranges.
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Crude oil is recovered from oil-bearing reservoirs generally by three
processes
designated primary, secondary and tertiary recovery. In primary recovery the
oil is
produced through a producing well by taking advantage of the pressure exerted
on
underground pools of oil by gas or water present with the oil. Approximately
20% of the
original oil in place (00IP) is recovered by this process. Once this pressure
has been
exhausted other means of recovering the remaining oil must be employed. In
secondary recovery the well may be re-pressurized with gas or water injected
through
one or more injection wells to recover approximately an additional 20% of the
00IP.
to Other secondary recovery methods include acidizing and/or fracturing to
create multiple
channels through which the oil may flow. After secondary recovery means have
been
exhausted and fail to produce any additional oil, tertiary recovery can be
employed to
recover additional oil up to approximately 60% 00IP. Tertiary oil recovery
processes
include, but are not limited to, steam flooding, polymer flooding,
microbiological flooding,
is and chemical flooding.
Chemical flooding includes the use of surfactants for lowering the interfacial
tension
(IFT) between the injection brine and the residual oil usually to an ultra-low
value of
below 1 x 10-2 mN/m. Mobility control agents such as polymers are usually
employed
20 along with surfactants to adjust the mobility ratio between the oil and
the injection brine.
It has also been found that alkali, when included in the injection brine, can
react with the
acidic material present in the trapped oil to form surface-active salts that
enhance the
effectiveness of the injected surfactant. Alkali also is preferentially
adsorbed onto the
reservoir and therefore reduces the loss of surfactant and polymer through
adsorption.
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Alkaline-Surfactant-Polymer Flooding (ASP) has been the subject of numerous
studies,
papers and patents, for example U.S. Patent 4,004,638 issued to Burdyn et al
in 1977
and U.S. Patent 6,043,391 issued to Berger at al. in 2000. Several other
tertiary
chemical processes for enhanced oil recovery include Alkaline Surfactant (AS),
Alkaline
Polymer (AP), and Alkaline flooding. The alkali commonly used in these
applications are
inorganic alkali including, but are not limited to, sodium hydroxide, sodium
carbonate,
the combination of sodium hydroxide and sodium carbonate, and sodium
silicates.
There are many examples of the prior art that discuss the use of different
types of
to surfactants and/or surfactant formulations for EOR including amphoteric
surfactants. As
is known by those who are familiar with the art, amphoteric surfactants have
the
advantages of providing low IFT, tolerance to salt and di-valent cations and
fair to low
adsorption loss to the formation. U.S. Pat. No. 4,216,097 to Stoumas,
discloses a
process for the recovery of oil from subterranean reservoirs employing an
aqueous
solution of an amphoteric surfactant. The amphoteric surfactant is used at a
relatively
low concentration within the range of 0.001 to 0.1 weight percent and is
injected in a
relatively large pore volume amount of at least 0.5 pore volume. U.S. Pat. No
4,554,974 to Kalpakel, et at. discloses a method for recovering petroleum
using a
surfactant slug comprising an aqueous solution containing about 0.001 to about
5% by
weight of an amphoteric surfactant and an effective amount of high molecular
weight
homopolysaccharide gum thickener derived from the fungus strains of genus
Schlerotium.
Although the prior art employ amphoteric surfactants as part of various
formulations for
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the recovery of oil, we have unexpectedly found that the degree of
unsaturation and the
distribution of carbon chain lengths in the lipophilic base is of extreme
importance to
lower IFT for a wide range of different gravity oils and brines. Furthermore,
relatively low
pore volumes of the injection fluid including the mixture of the amphoteric
surfactants is
required for effective oil recovery. This present invention provides improved
performance and economics over the prior art.
ro
BRIEF DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION
The present invention provides a new and improved chemical flooding process
for the
recovery of oil from subterranean reservoirs that comprises injecting into one
or more
injection wells and recovering the oil from one or more production wells a
composition
containing:
a) a mixture of amphoteric surfactants each characterized by the formula:
R2
111 +N ROC
Et3
wherein:
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R1 is a hydrocarbyl group containing from 8 to 26 carbon atoms, the average of
all
hydrocarbyl groups having a ratio of Iodine Value (IV) to the Molecular Weight
(MW) of
the hydrocarbyl chain of at least 0.15 or Ri is an alkyl amido group of the
following
structure
R-O-N-CH2CH2CH2
Where R = R1
R2 and R3 are each independently a hydrocarbyl group containing from 1 to 8
carbon
atoms or an alkoxy group containing from 2 to 10 carbon atoms and having a
ratio of
carbon atoms to oxygen atoms within the range of 2 to 3,
R4 is an aliphatic group containing from 1 to 6 carbon atoms, and
A is a sulfonate group or a carboxylate group; and,
b) optionally one or more alkali,
c) optionally one or more thickening agents,
d) optionally one or more co-solvents
e) an aqueous solvent; and;
recovering the oil from one or more production wells.
The injection and production well may be the same well. The aqueous solution
may
contain other ingredients, known to the art, as needed. These include alkali
to reduce
adsorption, thickening agents to provide an effective mobility ratio, and co-
solvent to
improve in product handling, dissolution and compatibility. Alkali may be used
at levels
of 0 to about 2 wt%. Thickening agents may be used at concentrations from 0 to
about 5
wt% and co-solvents may be used at concentrations of from 0 to about 10 wt% of
the
injection fluid.
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In this disclosure amphoteric surfactants and betaines are used
interchangeably to
identify the structure previously described above.
A preferred application of the amphoteric surfactants of the present invention
is their
use with brines or brines containing relatively high concentrations of salt
and divalent
metal ions. They are effective over a wide range of electrolyte concentrations
and they
can be used over a wide range of concentrations and still give ultra-low IFTs.
Furthermore, the mixture of amphoteric surfactants of the present invention
are derived
to from fatty acids and naturally occurring animal, vegetable or marine
oils that are
biodegradable and green in nature.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Detailed descriptions of the preferred embodiment are provided herein. It is
to be
is understood, however, that the present invention may be embodied in
various forms.
Therefore, specific details disclosed herein are not to be interpreted as
limiting, but
rather as a basis for the claims and as a representative basis for teaching
one skilled in
the art to employ the present invention in virtually any appropriately
detailed system,
structure or manner.
The present invention is an improvement over the prior art where amphoteric
surfactants have been used to enhance the recovery of oil. The present
invention
involves a process for of recovery oil from a subterranean reservoir by
injecting an
aqueous liquid containing:
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a) a mixture of amphoteric surfactants, each characterized by the formula:,
R2
R1+N Ft4A'
R,
wherein:
R1 is a hydrocarbyl group containing from 8 to 26 carbon atoms, the average of
all
to hydrocarbyl groups having a ratio of Iodine Value to the Molecular
Weight of the
hydrocarbyl chain of at least 0.15 or Riis an alkyl amido group of the
following structure
R-O-N-CH2CH2CH2
Where R = R1
R2 and R3 are each independently a hydrocarbyl group containing from 1 to 8
carbon
atoms or an alkoxy group containing from 2 to 10 carbon atoms and having a
ratio of
carbon atoms to oxygen atoms within the range of 2 to 3,
R4 is an aliphatic group containing from 1 to 6 carbon atoms, and
A is a sulfonate group or a carboxylate group;
b) optionally one or more alkali,
zo c) optionally one or more thickening agents,
d) optionally one or more co-solvents
e) an aqueous solvent; and;
recovering the oil from one or more production wells.
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The groups R2 and R3 may be the same or different and are selected from the
group
consisting of C1-C8 hydrocarbyl groups or C2 - C10 alkoxy groups having a
ratio of
carbon atoms to oxygen atoms within the range of 2 to 3. Stated otherwise,
where R2 or
R3 is an alkoxy group, it may be ethylene oxide, polyethylene oxide containing
up to 5
ethylene oxide units, propylene oxide, polypropylene oxide containing up to 3
propylene
oxide units, or oligimers of mixtures of ethylene oxide and propylene oxide
containing
no more than 10 carbon atoms. The nature of the R2 and R3 groups are, as noted
previously, somewhat dependent upon the nature of the R1 group or R group.
Where R
or R1 comprises a relatively long chain aliphatic substitutent, R2 and R3
normally will be
relatively short chain hydrocarbyl groups or ethylene oxide derivatives. For
example,
where R or R1 is a C14-C18 aliphatic radical, R2 and R3 normally will be
methyl or
ethyl groups or groups comprising ethylene oxide, propylene oxide, or
polyethylene
oxides.
Non-exclusive examples of suitable alkalis are sodium hydroxide, sodium
carbonate,
sodium silicate, potassium hydroxide, potassium carbonate, or potassium
silicate.
Non-exclusive examples of thickening agents Include polymers such as xanthan
gum,
polyacrylamide or viscoelastic surfactants such as betaines and amine oxides.
Non exclusive examples of suitable co-solvents include low molecular weight
alcohols,
glycols, polyglycols, and glycolethers such as propylene glycol, ethylene
glycol,
diethylene glycol, iso-propanol, butanol, iso-butanol, hexanol, 2-ethyl-
hexanol, octanol,
ethylene glycol monobutyl ether. The aqueous solvent may be water, an oilfield
brine or
a synthetic brine.
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The amphoteric surfactant contains an inner quaternary ammonium group that is
linked
to a terminal sulfonate group or carboxylate group. The electrical charge on
the inner
quaternary group is electrically balanced by the terminal anionic group and
such
amphoteric surfactants may thus be characterized as dipolar ions or zwitter
ions.
The present invention has unexpectedly found the amount of unsaturation and
the
distribution of various carbon chain lengths of the lipophilic base within the
amphoteric
Non-exclusive examples of amphoteric surfactants which may be employed in
carrying
out the present invention include those having a lipophilic base derived from
coconut oil,
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been found to perform poorly as components for recovering oil. Synthetic
saturated and
unsaturated derivatives having over 90% by weight of one component have also
been
found to perform less effectively than blends but can be used if two or more
are blended
to give the required MW and IV as will be described.
As is understood by those skilled in the art, surfactant molecules are
characterized by
an oil-soluble portion of the molecule that tends to partition into the oil
phase of an oil-
water interface and a water-soluble portion, that tends to partition into the
water phase.
In the amphoteric surfactants employed in the present invention, the sulfonate
or
to carboxylate group is the water soluble portion. In addition, the
ammonium quaternary
group tends to impart water solubility to the surfactant molecule to a degree
depending
upon the characteristics of the substituents, R2 and R3, defined previously.
The greatest
water solubility is observed when the R2 and R3 are methyl or ethyl radicals
or ethylene
oxide derivatives. Propylene oxide derivatives and mixtures of ethylene oxide
and
propylene oxide derivatives van be used to obtain greater oil solubility or
intermediate
solubility.
The aliphatic group, R,t, defined previously, inking the quaternary ammonium
and the
sulfonate or carboxylate groups contains 1 to 6 carbon atoms and, in the case
of R4
containing 2 or more carbon atoms, may be saturated or unsaturated, and
straight or
branched chained. The R4 radical may also be substituted with a group such as
a
hydroxy group, which tends to increase the water solubility of this portion of
the
surfactant molecule. Usually, however, the R4 group will be unsubstituted
hydrocarbyl
radical. In a preferred embodiment of the invention, R4 is an aliphatic group
containing
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from 1 to 4 carbon atoms.
EXAMPLE 1
Analysis of various fatty acid and oils that we have used to synthesize the
various
betaines are shown in Table 1 in decreasing order of their Acid Value (AV).
The AV is
defined as the milligrams of potassium hydroxide necessary to neutralize the
fatty acids
in a 1 gram sample. The AV is a commonly accepted property used in the Fats,
Oils and
Surfactant Industries and can be determined using AOCS Official Method Te la-
64 from
the American Oil Chemists Society.
to TABLE 1 Composition of various fatty acids and oils
Acid or Oil .;12
C12 C1Ai C'6 C161 C18 C181 C182 C183 C20 C201 C202 C22 C221 >C22
C-12998 279 1 99 0.5
C12168 263 1 61 25 11 0.5 1.5
Coconut Olib 255 13 47 19 9.5 3 7 1.5
Palm Kernel 01Ib 250 47 16 8.5 2 17 3
C-14958 245 2 97 1.5
PalmItic acid 9 219 99%
C12148 209 1 70 27 2
Emersol 6321NFG 201 3 5 6 79 6 1
Palm Oilb 200 1 45 3.8 40 10 0.2
Canola Oild 200 4.2 1.9 58.8 21.2 10.2 0.6 1.7 0.3 1
0.1
Llnolelc acid 9 200 99.2
OL-6008 199 0.3 5 0.3 2 61.3 20.4 6.2 2 2.5
Oleic add 9 197 99+
C18-208 197 2 4.5 2.4 23.4 30 19.5 1.5 13 1.3 2.4
Stearic acld 9 197 98
Tallow,BFT 197 3 24 3.5 21 43 5 0.5
EmersoPED 153NFG 196 4 96
Soybean Olid 192 0.8 0.5 0.5 10 4 22 54 8 0.2
Tall Oil fatty add 180 2 59 37 1 1
HEAR 088 176 1.1 2.1 0.1 1.1 11.4 14.7 8.8 0.9 6.7 0.8 1.4
46.6 4.3
Hystrenee 2290f 165 0.6 1.8 94.1
3.5
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Hxstrene T-2802Df 160 2.2 16 79 1.3
a) P&G Chemicals
b) Huish Corporation
c) Cognis Oleochemicals LLC
d) Archer Daniels Midland
e) VVF Ltd.
f) Crompton
g) Aldrich Chemical
Table 2 shows the effect of the unsaturation of the fatty acids and fatty oils
on IFT and
oil recovery. The un-saturation of fatty acids and fatty oils is determined by
the IV as
described in AOCS Official Method Tg la-64, and is expressed in terms of the
number
of centigrams (cg) of iodine adsorbed per gram of sample or the % iodine
absorbed..
The ratio of the IV to the MW gives an indication of the amount of
unsaturation in a
particular molecule. The higher the ratio of IV/MW, the more unsaturation in
the
molecule. The linear correlation coefficient for the relationship between IFT
and degree
of unsaturation for 164 tests run using the betaines derived from oils and
acids listed in
Table 1 was found to be 0.896.
The betaines were made using a process that is one of many that are well known
by
those familiar with the art by quaternization of a fatty amine derived from
one of the oils
or acids with sodium chloroacetate. Betaines where the hydrocarbyl group is R-
O-N-
CH2CH2CH2 are synthesized from the corresponding fatty acid or oil by reaction
with an
amine such as dimethylaminopropyi amine (DMAPA) to form an amido amine and
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quaternizing the amido amine with sodium chloroacetate. Preferred betaines
formed
from amido amines are fatty alkylamidopropyldimethyl betaines. Multiple
samples were
made using the same fatty acids and fatty oils. The IFT listed in Table 2 is
the average
of minimum 5 repeating samples.
The IFT in Table 2 was measured using 0.1% betaine in a West Texas brine
solution
containing 4,250 ppm total dissolved solids and 150 ppm of divalent cations
using a
University of Texas Model 500 Spinning Drop Tensiometer after 30 minutes of
contact
between the various betaines solutions and the crude oil. It is known to the
familiar of
to the art that a low IFT is conducive to higher oil recovery and that an
IFT of less than 1 x
10-2 mN/m is preferred to recover any significant oil after primary and
secondary
methods have been exhausted. The data in Table 2 show that the higher the
degree of
unsaturation, the lower the IFT. In studies of over 160 different combinations
of crude
oils having API Gravities of 10 to 40, brines having Total Dissolved Solids
(TDS) of
>200 to over 200,000 mg/l. and the betaines based on the acids and oils listed
in Table
I, We have found that a IV/MW value of 0.15 or more is required to give low to
ultra-low
IFTs.
The percent original oil in place (00IP) recovered was measured by preparing
identical
sand packed columns for each test as is commonly employed in the industry.
Each of
the sand packs were saturated with 32% oil and the brine was pumped through
the
bottom of each of the sand packed columns until all the free oil was removed
from the
sand pack. 0.3-pore volume of each injection fluid composition was then pumped
through the bottom of the separate sand pack columns to determine the residual
oil
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removed by each composition. 0.15% Flopaamm 3630S polymer is used along with
the amphoteric surfactants for the oil recovery experiments.
Table 2 Relationship between IFT and Unsaturation at Constant MW
Crude oil: API gravity = 22
Temperature: 45 C
Fatty Acids or Fatty Oils MW AV IV IV/MW IFT Oil Recovery,
Used For Betaine ___________________________________________ % 00IP
Stearic acid 285 197 0.3 0.00 1.397 5.7
Behenyl 350 160 0.4 0.00 1.23 5.8
Tallow, BFT 285 197 48 0.17 0.0299 6.87
Palm oil 281 200 49 0.17 0.0153 7.01
HEAR acid 319 176 90 0.28 0.0367 10.6
Oleic acid 282 199 90 0.32 0.0056 12.6
OL-600 282 199 115 0.41 0.0046 12.8
Canola oil 281 200 115 0.41 0.0035 14.54
Soybean oil 292 192 130 0.44 0.0018 14.8
Tall Oil 311 180 165 0.53 0.0009 15.43
io EXAMPLE 2
Table 3 shows the IFT values obtained using two betaines made from fatty acids
having
very similar molecular weight (Oleic = 282, Stearic = 285) but where oleic
acid contains
unsaturated hydrocarbyl groups and the stearic acid is completely saturated.
The IV,
IV/MW and the IFT data of the mixture of the two samples at various ratios are
shown In
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Table 3. These results again demonstrate that the mixture of amphoteric
surfactants
containing un-saturation is an important property for lowering IFT. The
optimum un-
saturation is also dependent on the brine and crude oil composition, the
temperature
and the formation properties. Note also that the highest IV/MW values do not
necessarily give the lowest IFT.
Table 3 Effect Mixtures of Saturated and Unsaturated Betaines of Similar MW on
IFT
Oleyl Dimethyl Stearyl Dimethyl IV IV/MW IFT, mN/m
betaine, wt% Betaine, wt%
100 0 90 0.317 0.0056
90 10 81 0.286 0.0042
80 20 72 0.254 0.0019
70 30 63 0.222 0.0034
60 40 54 0.19 0.0017
50 50 45 0.159 0.0083
40 60 36 0.127 0.023
30 70 27 0.095 0.087
20 80 18 0.063 0.019
90 9 0.032 0.201
0 100 0.3 0.001 1.397
10 EXAMPLE 3
Table 4 show the effect of various concentrations of mixture of amphoteric
surfactants
made from fatty oils and fatty acids containing un-saturation on the IFT.
The tests were run using brine containing 5 wt% sodium chloride as the aqueous
solvent for the various concentrations of amphoteric surfactant. The data from
Table 4
is shows that the betaine mixtures made with unsaturated oleic acid and
tallow BFT fatty
acid provided low IFT over wide ranges of surfactant concentrations. This is
important
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for oil recovery since the surfactant concentrations is continuously changing
as the
injection fluid propagates through the reservoir due to the adsorption and
dilution. This
is an improvement over the prior art such as Example S-2 from Table I of U.S.
Pat.
4,216,097 that shows ultra-low IFTs below 1 x 10-2 can only be obtained using
concentrations of 0.00075 wt% or less. This may be a disadvantage since the
adsorption may easily exhaust the low concentration of surfactants. U.S.Pat.
4,216,097
shows that extremely low concentrations of surfactant can give extremely low
IFT
values. A surfactant with a much wider range of useful concentrations giving
ultra-low
IFT is required to insure enough surfactant will reach the oil. Generally 0.02
to 5.0 wt %
to is used depending on the amount required to obtained the
desired results.
Table 5 Effect Of Surfactant Concentration On IFT
Surfactant Oleic Dimethyl Betaine Tallow BFT
Dimethyl Betaine
Conc. wt% ------------IFT, mN/m ------------
0.5 0.0178 0.0589
0.3 0.0067 0.0236
0.2 0.0031 0.0193
0.1 0.0012 0.0299
= 0.05 0.0011
0.0076
0.01 0.0007 0.0034
0.005 0.00028 0.0021
EXAMPLE 4
Table 5 shows the data obtained by measuring IFTs for various dimethylbetaines
at 0.1
wt% in various salt solutions against the same crude oil. The data from Table
5 shows
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that the un-saturated betaines derived from oleyl and erucic acids are more
effective in
lowering IFT over a wider range of salt concentrations than their less
unsaturated
counterparts derived from tall oil fatty acid and behenic acid. Note that at
higher salt
concentrations the behenyl betaines becomes insoluble. This is another
advantage of
betaines having some degree of unsaturation in that they are soluble over a
wider range
of salt concentrations than their unsaturated counterparts.
While particular embodiments of the present invention have been illustrated
and
described, the scope of the claims should not be limited by the embodiments
set forth in
io the examples, but should be given the broadest interpretation consistent
with the
description as a whole.
OleylDimethyl Stearic Dimethyl Erucyl Dimethyt Behenyt Dimethyi
NaC1, wt% Betaine BetaIna Betaine _ Betaine
------ IFT, mN/m 65 C, 30 Minutes Readino --
0.5 0.0252 0.0678 0.0032 0.8320
1.0 0.0199 0.0356 0.0046 0.8550
2.0 0.0122 0.0199 0.0060 0.8870
3.0 0.0099 0.0105 0.0090 0.9340
5.0 0.0012 0.076 0.0378 Insoluble
10.0 0.0037 0.0548 0.0567 Insoluble
15.0 0.0079 0.0234 0.0866 Insoluble
20.0 0.0095 0.0789 0.0999 Insoluble
Table 5 Effect Of Salt Concentration On IFT
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