Note: Descriptions are shown in the official language in which they were submitted.
1~751 3~8
BACKGR~rJND OF THE INVENTION
Field of the Invention
_
; This invention relates to injecting a micellar dispersion
into a subterranean formation and displacing it toward a
- production means in fluid communication with the formation
to recover crude oil therethrough.
Description of the Prior Art
.
~ icellar dispersions are useful for recovering crude
oil from subterranean reservoirs, e.g. U.S. Patent Nos.
3,254,714; 3,275,0/5; 3,506,070i 3,~97,00~; 3,613,786;
3,734,1BS; 3,740,343; 3,827,496; and other patents defining
surfactant systems and assigned to Marathon Oil Company, Esso
Production Research Co., Shell Oil Company, Union Oil Company,
Mobil Oil Company, Texaco Oil Company, etc. The prior art
generally teaches that the micellar dispersion is injected
into the oil-bearing formation followed by a mobility control
buffer and th~n a water drive to displace previously injected
slugs toward a production well to recover crude oil thcrethrough.
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1 The prior art generally teaches that the viscosity of a
2 micellar dispersion can be controlled by the water eoncentra-
3 tion--see U.S. 3,254,71~; that cosurfactant can be added to
4 a soluble oil to achieve proper viscosity--U.S. 3,~77,511;
S and that water-soluble salts can be added to control the
6 viscosity--see U.S. 3,330,3~3. Also, -the prior art has
7 recognized that high molecular weight polymers can be
8 added to the micellar dispçrsion to increase the viscosity
9 and that the hydrocarbon used in making up the dispersion
ean influence the viscosity--see U.S. 3,412,791.
11 Designing the micellar dispersion to have the desired
12 viseosity is important in secondary and tertiary oil
13 reeovery processes. If vlseosity is too low, mobility will
14 be too high and the slug will unstably and ineffieiently
displaee oil and will eause "viseous fingering". If, on
16 the other hand, slug viscosity is too high, either the mobility
17 buffer, i.e. aqueous polymer solution, intended to drive
18 the slug will finger into the slug, or excessive polymer
19 eoncentrations within the buffer will be required. Since
polymer is expensive, the latter alternative is eeonomieally
21 unattractive. By selecting the proper type and eoncentration
22 of eosurfaetant, slug viseosity ean be adjusted so that
the slug will neither finger into the oil that it is intended
24 to displaee, nor will excessive polymer be required.
In summary, the prior art has recognized that the
26 viscosity of the mieellar dispersions ean be affeeted by
27 hydroearbon, eleetrolyte, polymer, water, and aleohols;
28 these aleohols, in most cases, have been water-soluble alcohols.
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S~ RY O F T~IE INVF.NTION
~ pplicants have (llscovered that the vlscoslty of
mlcellar disperslons can be ad~usted by incorporating a
relatively water-insolllble cosurfactant to obtain a high
viscosity or incorporating a water-soluble cosurfactant with
the micellar dispersion to obtain a low viscosity. That is,
by increasing the hydrophilicy of the cosurfactant, the
viscosity of the micellar dispersion is lowered.
In one particular aspect the present invention provides
in a process for recovering hydrocarbon from a subterranean
formation having at least one injection means in fluid
communication with at least one production means and wherein
a micellar dispersion of predetermined viscosity and comprised
of water, hydrocarbon, cosurfactant(s), surfactant, and
optionally electrolyte is injected into the formation and
displaced toward the production means to recover hydrocarbon
therethrough, the improvement comprising admixing with the
micellar dispersion a more hydrophilic cosurfactant than the
cosurfactant within the dispersion to obtain a low viscosity
micellar dispersion or incorporating a less hydrophilic
cosurfactant than the cosurfactant within the micellar
dispersion to obtain a higher viscosity, said more or less
hydrophilic cosurfactant being a Cl to about C2 5 organic
compound or a mixture of Cl to about C25 organic compounds,
and thereafter injecting the dispersion of a desired viscosity
into the formation and displacing it toward the production
means to recover hydrocarbon therethrough.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 shows the influence of p-pentanol and p-hexanol
on the same micellar dispersion composition (defined in
Example I). The p-hexanol has very little water solubility
and obtains high viscosities whereas the p-pentanol is more
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hyclrophi.l:ic nncl obta:ins lowcr vi.scosities.
Figure 2 shows thc effect of four different alcohols
on the composition deEined in Example II. Although the same
viscosity can be obtained using any of the four alcohols
shown in this figure, a broad range of vlscosities is
available as a Eunction oE alcohol concentration. For example,
slug viscosity as low as 20 cp. or as high as 150 cp. can be
obtained with the least water-soluble alcohol nonyl phenol.
The maximum obtainable viscosity with a slightly more
water-soluble p-hexanol is about 100 cp. Although a viscosity
of about 70 cp. can be obtained using either 2-hexanol or
n-pentanol, experience has shown that oil recovery efficiency
drops off at the low end of the alcohol
.
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1 concentration range. ~s a practical matter, -the maximum
2 viscosities obtainable usincJ 2-hexanol and n-pentanol and
3 still obtain eEfective oil-displacing characteristics is
4 about 38 to 30 cp, respectively.
6 PREFERRED EMBODIMENTS OF THE INVENTION
.~
. 7 The term "micellar dispersion" as used herein is meant
to include miceilar solutions, microemulsions, "transparent
9 emulsions", hydrous soluble oils, micellar sys-tems con-
taining lamellar micelles, etc. These systems can be oil-
11 external or water-external, they can act li~e they are
12 either oil-external or water-ex-ternal or both, and they can
13 also be in an "intermediate region" between a "classically"
14 oil-external micellar system and a "classically" water-
external micellar system. However, all of the systems,
16 regardless of the externali-ty properties, are thermodynamically
17 stable and optically clear; however, color bodies within the
18 different components can prevent the transmission of light.
19 The micellar dispersions are composed of hydrocarbon,
water, petroleum sulfonate, cosurfactant, and optionally
21 electrolyte. Additional component(s) can be added if
22 desirable to impart properties to the micellar dispersion.
23 However, these components must be compatible with the other
24 components of the dispersion and not impart adverse properties
to the system.
26 Examples of the components useful with -the micellar
27 dispersion are defined wikhin the patents mentioned in
28 the "Description of the Prior Art".
29 The surfactant can be anionic, nonionic, or cationic,
or mixtures thereof Preferably, it is a monovalent
31 cation containing petroleum sulfonate obtained by sulfonating
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1 a fraction oE crude oil, e.g. gas oil, or whole or topped
2 crude oil and thereafter neutralizing with ammonium hydroxide
3 or sodium hydroxide. Desirably, the petroleum sulfonate has
4 an a~erage equivalent weighl within the range of about 350
to about 525 and more preferably about 390 to about 460 and
most preferably about 400 to about 450. The petroleum
7 sulfonate can contain unreacted hydrocarbon and salts (herein-
after defined as electrolytes).
9 The hydrocarbon is typically crude oil, a fraction
thereof, unreacted vehicle oil within the surfactant,
11 synthesized hydrocarbon, mixtures thereof, or like materials.
12 Water within the micellar dispersion can be distilled
13 water, fresh water, or water containing a moderate amount of
14 salts. Typically, the water contains about 5 to about
50,000 ppm of TDS (total dissolved solids). Preferably, the
16 water does not contain sufficient amounts of multi-valent
17 cations that will displace or exchange a significant amount of
18 the cations on the surfactant.
19 Useful electrolytes include water-soluble inorganic
salts, inorganic bases, inorganic acids, or mixtures thereo~.
21 Typically, the salts are reaction by-products from the
22 preferred petroleum sulfonate, e.g. ammonium sulfate, ammonium
23 sulfite, sodium sulfate, sodium sulfite, etc., but the
24 electrolytes can be added or blended with other electrolytes
in the aqueous phase of the micellar dispersion mixture.
26 The cosurfactant, also known as a semi-polar organic
27 compound, cosolubilizer, stabilizing agent~ is an organic
28 compound(s) containing l to about 25 or more carbon atoms
~9 and more preferably 3 to about l~ carbon atoms. It can be
an alcohol, amide, amino compound, ester, aldehyde, ketone,
31 complexes thereof, or a compound containing one or more of
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amido, hydroxy, bromo, chloro, carbonato, mercapto, oxo,
2 oxy, carbonyl, or like cJroups, or mixtures thereof. Specific
3 examples include isopropanol, butanol, amyl alcohols,
4 hexanols, octanols, decyl alcohols, alkyl aryl alcohols such
as n-nonyl phenol and p-nonyl phenol, 2-butoxyhexanol,
6 alcoholic liquors such as fusel oil, mixed isomer5 of pri~ary
7 amyl or hexyl alcohols such as UCAR-HCO (marketed by Union
8 Carbide Company, N.Y., N.Y.~, blends of C12, C13, C14, C15,
9 etc. linear primary alcohols such as Neodol alcohols (marketed
by Shell Chemical Co.), ethoxylated alcohols such as alcohols
11 containing 4 to about 16 carbon atoms that are ethoxylated
12 and optionally sulfated, hydrogenated hydrocarbons such as
13 hydrogenated croton oil, amidized hydrocarbons, and like
14 materials. The preferred cosurfactant is an alcohol which
can be primary, secondary or tertiary alcohol or mixtures
16 thereof and can optionally be ethoxylated and/or sulfated.
17 Concentration of the components within the micellar
18 dispersion vary depending upon the particular component and
19 the particular properties desired of the micellar dispersion.
Typically, the concentration is about 4 to abou-t 86% and
21 preferably about 5 to about 50% and more preferably about 6
22 to about 20% hydrocarbon, about 10 to about 92% and preferably
23 about 40 to about 91% and more preferably about 60 to about
24 90% water, about 4 to about 20% or more and preferably about
25 6 to about 16% and more preferably about 7 to about 12% o~
26 surfactant; about 0.01 to about 20% and preferably about
27 0.05 to about 10% and more preferably about 0.1 to about 3~
28 of cosurEactant, and about 0.001 to about 10% and preferably
29 about 0.01 to about 7.5% and more preferably about 0.25 to
about 5% of electrolyte.
31 The micellar dispersion is injected into the formation
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1 in volume amounts of 1 to about 50% or more, and preferably
2 abo~lt 4 to about 15% FPV (formation pore volume). This is
3 preferably followed by a mobility buffer, preferably an
4 aqueous solution containin~ a water-soluble polymer which
imparts permeability reduction to the formation and/or
6 viscosity-increasing properties to -the aqueous solution--
si 7 examples of volume amounts include about 10 ~o abou~ 200%
FPV or more and preferably about 50 to about 150% FPV, and
9 more preferably about 60 to about 100% FPV. A water drive
is injected to displace the micellar dispersion and the
11 mobility buffer toward a production well in fluid communi-
12 cation with the formation to recover crude oil through said
13 production well.
14 A micellar dispersion will accept or "take-up" so much
of a particular cosurfactant while remaining phase-stable.
16 This cosurfactant range is obtained by titrating the micellar
17 dispersion with the cosurfactant. The micellar dispersion
18 may go through a viscosity maximum ~generally characteristic
19 of micellar systems containing greater than about 60% water)
and then, upon further titration~ the viscosity will decrease.
21 The micellar dispersions are preferably on the "right side"
22 of the viscosity maximum to obtain optimum oil recoveries.
23 More preferably, after the micellar dispersion goes through
24 the viscosity maximum, cosurfactant titration is continued
until the desired viscosity is obtained for flooding a
26 particular formation. A micellar dispersion containing less
27 than about 60% water may not pass through a viscosity maximum
28 upon cosurfactant titration. Instead, the viscosity may pass
29 through a minimum as illustrated in Figure 2. With Figure 2
type systems, it is preferred that the system be at the
31 minimum viscosity or to its "right side" of the viscosity
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1 curve to obtain optim~l oil recovery.
2 The desired viscosity will depend upon the combined
3 mobility of the crude oil and connate water within the
4 formation to be flooded, the design mobility of the mobility
buffer, the "life" o~ the flooding project, and in general,
. the overall design mobility and desired "pay-out" and economics
i 7 of the flooding project.
The viscosity of the micellar dispersion will depend
9 upon the components and concentration of the components.
For a given micellar dispersion, the hydrophilicy or lack
11 thereof of the cosurfactant influences the viscosity of the
12 micellar dispersion. That is, a hydrophilic cosurfactant
13 obtains low viscosities whereas a less hydrophilic cosurfactant
14 obtains higher viscosities. Thus, for a given micellar
dispersion, one will add a hydrophilic cosur~actant to
16 obtain a lower viscosity. Examples of preferred cosur-
17 factants which exhibit an increase in hydrophilicy as the
below numbers increase include the following:
19 1) p-octanol
2~ p-heptanol
21 3) p-hexanol
22 4) p-pentanol
23 5) p-bu-tanol
24 6) isopropyl alcohol
7) ethanol
26 8) methanol
27 For a given primary, secondary or tertiary alcohol, or other
28 functional groups on the cosurfactant, the higher the
29 molecular weight, the less hydrophilic the cosurfactant
generally is. However, having two or more functional groups
31 on -the cosurfactant molecule generally increases the hydro-
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philicy of ~he mol~cule alld as .~iuch can hclVe an "overridirlcJ"
influence over the molecular ~eight to cleternlinc the hydro--
philicy thereof.
Generally speakincJ, it is desired that the micellar
dispersion be designed to have a greater reciprocal mobility
at reservoir conditions than the combined reciprocal mobility
of the formation fluids, specifically crude oil and connate
water, and gas if presen-t in the formation~ By following
Applicants' teachings, one can design the micellar dispersion
to initially contain the desired cosurfactant for optimum
viscosity design, or one can add a desired cosurfactant to a
micellar dispersion containing a cosurfactant to adjust the
viscosity thereof to the desired viscosity.
Working Examples
The following examples are presented to teach
specific embodi~ents of the invention Unless otherwise
specified, all percents are based on volume and measurements
of the properties are obtained at ambient temperature, i e
22-23C.
EXAMPLE I
A micellar dispersion composition, before alcohol
addition, is obtained by mixing 11.7% of an ammonium
petroleum sulfonate having an average equivalent weight of
420 and being 62 weight percent active sulfonate and obtained
by sulfonating a gas oil with SO3, 22.8% oE a crude oil having
an API gravity of 37~ and a viscosity of 7-9 cp, and 65.5%
water containing 400 ppm of TDS and 10,000 ppm of (NH4)SO4,
Total water concentration of the dispersion, including water
from the sulfonate, is 70~ by weight To this mixture there
; 30 is added p-pentanol or p~hexanol The alcohol concen-tration
~ and the resulting viscosities of the micellar dispersion are
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1 illustrated in Figurc 1.
2 It is evident from Figure 1 that p-pentanol imparts a lower
3 viscosity than p-hexanol. Thus, for a given micellar dispersion
4 composition, and for similar alcohols, the alcohol having the
greater solubility in water obtains a lower viscosity.
6 EXAMPLE II
7 A micellar dispersion composition before alcohol addikion
8 is obtained by mixing 10% ~f an ammonium petroleum sulfonate
which is 61 weight percent active sulfonate and has an
average equivalent weight of 440, 40% of hydrocarbon which
11 is 60% of the crude oil defined in Example I and 40% of
12 heavy naphtha, 50~ of water which contains 400 ppm of TDS and
13 3900 ppm of ammonium sulfate. The total water concentration
14 of this slug, including water from the sulfonate, is 54.5% by
weight. To separate samples of this c~mposition is added
16 four different cosurfactants, i.e. nonyl phenol! p-hexanol,
17 2-hexanol, and n-pentanol. The titration of these compositions
18 and the viscosities thereof are illustrated in Figure 2.
19 It is not intended that this invention be limited by
the specifics taught within the above examples. Rather, all
21 equivalents obvious to those skilled in -the art are intended
22 to be incorporated within the scope of the invention as
24 defined with the specification and appended claims.
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