Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THE INVENTION
16 Field of the Invention
17 This invention relates to injecting a micellar dis-
18 persion into a subterranean formation and displacing it
19 toward a production means in fluid communication with the
formation to recover crude oil therethrough.
21 Description of the Prior Art
22 Micellar dispersions are useful for recovering crude
23 oil from subterranean reservoirs, see for example U.S.
24 Patent Nos. 3,254,714; 3,275,075; 3,506,070; 3,497,006;
3,613,786; 3,734,185; 3,740,343; 3,827,A96; and other
26 patents defining surfactant systems and assigned to Marathon
27 Oil Company, Esso Production Research Company; Shell Oil
28 Company; Union Oil Company, Mobil Oil Company, Texaco Oil
29 Company, etc. The micellar dispersion is injected into the
formation followed by a mobility buffer and then a water
31 drive to displace crude oil from the formation.
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1 Patents representative of the prior art include:
2 Gogarty et al in U.S. 3,443,635 teach that the hydro-
3 carbon and water can be simultaneously displaced from the
4 formation by determining the relative permeabilities of the
water and the oil in the reservoir, then calculating the
6 desired mobility of the displacing fluid.
7 Gogarty teaches in U.S, 3,493,051 improved flooding by
8 incorporating alkali metal hydroxide into the micellar
9 dispersion to make the dispersion more hydrophilic.
U.S. 3,507,331 and 3,520,365 to Jones define an im-
11 proved method of designing the flooding system to impart
12 stability to the micellar dispersion.
13 Healy et al in "Physical Chemical Aspects of Micro-
14 emulsion Flooding", Society of Petroleum Engineers ~ournal,
14 (5), Page 491, October, 1974, teaches optimization of a
16 microemulsion for oil recovery is obtained by adjusting the
17 electrolyte concentration to "optimal salinity".
18 Design of micellar systems for improved oil recovery is
19 usually effected with petroleum sulfonates, hydrocarbon,
water, electrolyte, and one or more alcohols as the co-
21 surfactants. Often, the choice of petroleum sulfonate,
22 is limited and may not be the optimum one for the connate
23 water and/or crude oil within the reservoir. As a result,
24 oil recoveries are generally lower than that desired if a
more desirable surfactant could be used.
26 If the micellar dispersion is improperly constituted
27 such that it solubilizes a considerably larger volume of
28 connate water than it solubilizes crude oil, the high amount
29 of water take-up dilutes the surfactant concentration and
reduces the micellar dispersion's ability to solubilize crude
31 oil--in some cases to zero. In such cases, the micellar dis-
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iOIl lo~e. Lts al)iliLy to disl)lncc cru(le oil at residual oil
saturation and the oil recovery eff:icicncy is reduced.
On the otller hand, a micellar dispersion can be
improperly designe~ to solubllize large amounts of crude oil, but
little or no water. Again, oil recovery efficiency suffers
because, although the micellar dispersion can readily displace
crude oil from a reservoir rock, the aqueous mobility buffer and
drive fluids are incapable of "miscibly" displacing the micellar
dispersion; the latter can be left in the rock since its mobility
10 is reduced.
SUMMARY OF THE IN~E~TION
-
Applicant has discovered that optimum oil recovery
is obtained by designing the micellar dispersion to solubilize
about equal volumes of connate water and the crude oil ~hydrocarbon)
within the reservoir. This solubility characteristic is controlled,
to a large degree, by selection of the proper type and concentration
of cosurfactant used to prepare the micellar dispersion. Such a
j selection is obtained from data resulting from solubilizing
different amounts of connate water and crude oil at different
20 cosurfactant concentrations. The cosurfactant concentration at
< which the solubilization or uptake of the hydrocarbon and connate
. water is about equal, is the preferred design of the micellar
dispersion to obtain maximum oil recovery.
In one particular aspect the present invention
~, provides in a process for recovering crude oil from a subterranean
formation wherein a micellar dispersion comprised of water, hydro-
carbon, surfactant, cosurfactant, and inorganic electrolyte is
~r, injected into the formation to displace crude oil therefrom, the
improvement comprising injecting into the formation a micellar
30 dispersion which solubilizes substantially equal volumes of crude
eon~e
' ~ oil and~water.
In another particular aspect the present inventlon
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~ovi(l~ s l-ro(~ ; For ro(~ovorin~ crll(le oi1 From a .~uhterranean
forma~iol1 w~rcin ~1 n~ ellar dispersiol1 con~pris:ing water, hydrocarbvn
surfactant, cosurf~ctant, and inorgan:l.c ~l.ectrolyte is i.njected
into the ~or~ation to displace crude oil Lherefrom, the .improvement
comprlslng designing the miccl.lar dispers:ior1 to soluh.l.lize
~ ~ 0,7~l f ~
substant:i.al.1.y equal volumes o~ crude oil and ~ water and thereafter
injecting the micellar dispers.ion into the formation and displacing
it therethrough to recover crude oil.
In yet a Eurther particular aspect the present
l0 invention provides in a process for recovering crude oil from a
subterranean formation wherein a micellar dispersion comp~ising
water, hydrocarbon, surfactant, inorganic electrolyte, and co-
surfactant is injected into the formation followed by an aqueous
mobility buffer to displace crude oil therefrom, the improvement
comprising formulating the micellar dispersion to solubilize
substantially equal volumes of the crude oil within the subterranean
Ca~af e
formation and thc water within the aqueous mobility buffer and
, thereafter injecting the micellar dispersion and the aqueous mobility
buffer into the subterranean formation to displace crude oil
20 therefrom.
BRIEF DESCRIPTION OF THE DRAWINGS
O Figure l represents the amount of connate water and
crude oil that is solubilized by a micellar dispersion at different :
cosurfactant concentrations. The micellar dispersion composition ~ -
is defined in E~ample I. At the junc-
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7 ture of the connate water and crud~ oil uptake is the optimum
2 concentration of the cosurfactant for this particular system.
3 Figure 2 represents the percent oil recovery of a
4 micellar dispersion composition defined in Example II. The
curves illustrate that improved oil recoveries are obtained
6 with increased n-amyl alcohol concentrations. That is, as
.~ ~ 7 the alcohol concentration is increased to a point where the
8 micellar dispersion solubilizes about equal volumes of the
9 crude oil and the connate water, improved oil recoveries are
realized.
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PREFERRED EMBODIMENTS OF THE INVENTION
13 The term "micellar dispersion" as used herein is meant
14 to include micellar solutions, microemulsions, "transparent
emulsion", hydrous soluble oils, micellar systems containing
16 lamellar micelles, etc. These systems can be oil-external or
17 water-external, they can act like they are either oil-external
18 or water-external or both, and they can al50 be in an "inter-
19 mediate region" between a "classically" oil-external micellar
system and a "classically" water-external micellar system.
21 However, all of the systems, regardless of the externality
22 properties, are thermodynamically stable and optically
23 clear; however, color bodies within the different components
24 can prevent the transmission of light.
The micellar dispersions are composed of hydrocarbon,
26 water, petroleum sulfonate, cosurfactant, and optionally
27 electrolyte. Additional component(s) can be added ~o
28 impart desired properties to the micellar dispersion.
29 However, these components must be compatible with the other
components of the dispersion and not impart adverse properties
31 to the system.
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1 Examples of the components us~ful with the micellar
2 dispersion are defined within the patents mentioned in the
3 "Description of the Prior Art".
4 The surfactant can be anionic, nonionic, or cationic,
or mixtures thereof. Preferably, it is a monovalent cation-
6 containing petroleum sulfonate obtained by sulfonating a
fraction of crude oil, e.g. gas oil, or whole or topped `
8 crude oil. Desirably, the petroleum sulfonate has an
9 average equivalent weight within the range of about 350 to
about 525 and more preferably about 390 to about 470 and
11 most preferably about 400 to about 470. The petroleum
12 sulfonate can contain unreacted hydrocarbon and salts (here-
13 inafter defined as electrolytes).
14 The hydrocarbon is typically crude oil, a fraction
thereof, unreacted vehicle oil within the surfactant,
16 synthesized hydrocarbon, mixtures thereof, or like materials.
17 Water within the micellar dispersion can be distilled
18 water, fresh water, or water containing a moderate amount of
19 salts. Typically, the water contains about 5 to about
50,000 ppm of TDS (total dissolved solids). Preferably, the
21 water does not contain sufficient amounts of multi-valent
22 cations to displace or exchange a significant amount of the
23 cations on the surfactant. -
Useful electrolytes include water-soluble inorganic
salts, inorganic bases, inorganic acids, or mixtures thereof.
26 Typically, the salts are reaction by-products from the
27 preferred petroleum sulfonate, e.g. ammonium sulfate, ammonium
28 sulfite, sodium sulfate, sodium sulfite, etc. The electrolytes
29 can be added or blended with other electrolytes within the
aqueous phase of the micellar dispersion mixture.
31 The cosurfactant, also known as a semi-polar organic
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1 compound, cosolubilizer, stabilizing agent, etc., is an
2 or~anic compound~s) containing 1 to about 25 or more and
3 preferably about 3 to about 16 carbon atoms. It can be an
4 alcohol, amide, amino compound, ester, aldehyde, ketone,
complexes thereof, or a compound containing one or more of
6 amido, hydroxy, bromo, chloro, carbonato, mercapto, oxo,
7 oxy, carbonyl, or like groups, or mixtures thereof. Specific
8 examples incl~de isopropanol, butanol, amyl alcohols,
9 hexanols, octanols, decyl alcohols, alkyl aryl alcohols such
as n-nonyl phenol and p-nonyl phenol, 2-buto~yhexanol,
11 alcoholic liquors such as fusel oil, mixed isomers of primary
12 amyl or hexyl alcohols (Alfol alcohols, marketed by Continental
13 Oil Company, ethoxylated alcohols such as alcohols containing
14 about 4 to about 16 carbon atoms that are ethoxylated and
optionally sulfated, hydrogenated hydrocarbons such as
16 hydrogenated croton oil, amidized hydrocarbons, and like
17 materials. The preferred cosurfactant is an alcohol which
18 can be primary, secondary or tertiary alcohol or mixtures
19 thereof and can optionally be ethoxylated and/or sulfated.
2~ Concentration of the components within the micellar
21 dispersion vary depending upon the particular component and
22 the particular properties desired of the micellar dispersion.
23 Typically, the concentration is about 4 to about 86% and
24 preferably about 5 to about 50% and more preferably about 6
25 to about 20~ hydrocarbon, about 10 to about 92% and preferably
26 about 40 to about 91~ and more preferably about 60 to about'
27 90% water, about 4 to about 20% or more and preferably about
28 6 to about 16 and more preferably about 7 to about 12% of
29 surfactant, about 0.01 to about 20% and preferably about
30 0.05 to about 10% and more preferably about 0.1 to about 1%
31 of cosurfactant, and about 0.001 to about 10% and preferably
.
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1 about 0.01 to about 7.5% and more preferably about 0.1 to
2 about 5~ of electrolyte. ~
3 The micellar dispersion is injected into the formation
4 in volume amounts of 1 to about 50% or more, and preferably
5 about 4 to about 15~ FPV (formation pore volume). This is
6 preferably followed by a mobility buffer, preerably an
~; 7 aqueous solution containing a water-soluble polymer which
8 imparts permeability reduction to the formation and/or
viscosity increasing properties to the aqueous solution--
10 examples of volume amounts include about 10 to about 200%
11 FPV or more and preferably about 50 to about 150~ FPV, and
12 more preferably about 70 to about 100% FPV. A water drive
~; 13 is injected to displace the micellar dispersion and the
1 mobility buffer toward a productlon well in fluid communication
5 with the formation to recover crude oil through said production
16 well.
17 The cosurfactant used to make up the micellar dis-
18 ~ persion must permit the micellar dispersion to solubilize
19 substantially equal volumes of the crude oil and the connate
~ 20 water within the subterranean reservoir. That is, the
,"r 21 properties of the connate water as well as the crude oil
22 must be compatible with the micellar dispersion such that
23 the latter will be permitted to solubilize equal volumes
~ 24 thereof. The cosurfactant must impart a property to the
25 micellar dispersion such that it will not be substantially
26 hydrophilic or substantially oleophilic, if either is the
27 case, then the oil recoveries will be adversely influenced.
.2 ~ 28 Determining the desired cosurfactant needed for the
29 particular micellar dispersion will require routine experi-
~' 30 mentation. Such can be effected by obtaining samples of the
' 31 crude oil and the connate water, mixing them separately with
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1 cosurfactant-free micellar dispersion and thereafter adding
2 different quantities of suspected cosurf~ctants desired for
3 the system and obtaining solubilization data. At the
4 juncture of the crude oil uptake and connate water uptake,
for example see Figure 1, is the desired concentration of
6 the particular cosurfactant for the particular micellar dis-
7 persion/crude oil/connate water system. This method permits
one to design a micellar dispersion particularly suited for
9 a particular reservoir. The type of cosurfactant, e.g. HLB
(hydrophil-lipophil balance) and concentration thereof, will
11 influence the desired viscosity of the micellar dispersion;
12 thus, this also has to be considered with designing the
13 optimum solubility properties of the micellar dispersion.
14 The cosurfactant concentration in the micellar dis-
persion is preferably on the "right side" of the viscosity
16 maximum which results from titrating with a cosurfactant a
17 micellar dispersion-free cosurfactant mixture containin~
18 ¦ greater than about 60% water. That is, upon cosurfactant
19 titration, the dispersion mixture generally goes through a
viscosity maximum and thereafter the viscosity decreases.
21 The "right side" is past this viscosity maximum. A micellar
22 dispersion containing less than about 60~ water may not pass
23 through a viscosity maximum upon cosurfactant titration but
24 instead may pass through a minimum viscosity--if this is the
case it is preferred that the system be at the minimum vis-
26 cosity or to the "right side" of the viscosity curve to obtain
27 optimum oil recovery.
28 For this invention, the cosurfactant concentration is
29 increased or the titration continued until the concentration
is sufficient to permit the micellar dispersion to solubilize
31 about equal amounts of the connate water and the crude oil.
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1 of course, the desired viscosity of the micellar dispersion
2 will depend upon the combined mobi-lity of the crude oil and
3 the connate water within the formation, the design mobility
4 of the mobility buffer which is injected after the micellar
dispersion, the "life" of the flooding project, and in
6 general, the overall design mobility and desired "payout"
7 and economics of the flooding project.
8 The following examples are presented to teach specific
9 embodiments of the invention~ Unless otherwise specified,
all percents are based on volume and all measurements are
11 made at ambient temperature, i.e. 22-23C.
12 EXAMPLE I
13 A micellar dispersion mixture is obtained by mixing
14 ll.7% of an ammonium petroleum sulfonate having an average
equivalent weight of 420 and being 62 weight percent active
16 and obtained by sulfonating a heavy vacuum gas oil with SO3,
17 22.8% of a crude oil having viscosity of 7-9 cp. and 37 API
18 gravity and identified as "Illinois Crude"; 65.5% water
19 containing 400 ppm of TDS and lO, oon ppm of ammonium sulfate
(does not include water within the petroleum sulfonate--when
21 the latter water is included, the miceliar dispersion contains
22 70.0% water by weight).
23 Figure l illustrates the solubilization behavior of the
24 resulting micellar dispersion upon the addition of n-hexanol,
a relatively water-insoluble alcohol. The crude oil is
26 "Illinois Crude" and the brine or connate water contains
27 lO,000 ppm of ammonium sulfate. Below an n-hexanol concen-
28 tration of 0.43 ml/lO0 ml alcohol-free micellar dispersion,
29 the system rejects the crude oil. For example, at a concentratio
of 0.4 ml of n-hexanol/lO0 ml of alcohol-free micellar
31 dispersion, the dispersion is in equilibrium with a layer of
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1 ¦ crude oil. As the n-hexanol concentration is increased, the
2 1 micellar dispersion solubilizes the crude oil and the crude
3 ¦ oil layer disappears, i.e. the system becomes a single phase
4 ¦ at an n-hexanol concentration of 0.44. The single phase
5 1 region is present over an n-hexanol concentration of 0.44 to .
¦ 0.93 ml but after the 0.93 concentration, the system expels
7 an aqueous phase. Thus, within the single phase region,
this composition has the capacity to solubilize increasing
9 amounts of crude oil with increasing n-hexanol concentra-
tion, but its capacity to solubilize the brine decreases,
11 from an initially high value at the lower limit of the
12 cosurfactant concentration down to zero at the 0.93 ml of n-
13 hexanol. It is.apparent from this graph that the micellar
14 dispersion slug's capacity for solubilizing brine and crude .
15 oil is controlled by the cosurfactant concentration. .
16 At the ~uncture of the brine and crude oil uptake is
17 the optimum concentration of the n-hexanol for this dispersion
18 to obtain maximum oil recovery. :
19 . . EXAMPLE II .
A micellar dispersion mixture is obtained by mixing 10%
21 of an.ammonium petroleum sulfonate having an average equiva-
22 lent weight of 440 and being 61 weight percent active
23 sulfonate and obtained by sulfonating a vacuum gas.oil with `
24 sulfuric acid. 40% of the crude oil defined in Example I,
and 50% of water containing 400 ppm of TDS. The total water
26 concentration of the mixture including water from the
27 petroleum sulfonate is 54.5%. This total water contains
28 3900 ppm of ammonium sulfate, initially contained within the .
29 petroleum sulfonate. To this mixtuxe there iæ added different
amounts of n-amyl alcohol, 1% FPV and 5%.FPV micellar dispersions
31 containing different concentrations of the n-amyl alcohol
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1 followed by a mobility buffer are flooded in 3 inch diameter
2 48 inch long cores. The cores, before flooding, are placed
3 in a tertiary condition by first flooding with water containing
4 6000 ppm of TDS, thereafter they are flooded with the crude
oil identified in Example I until irreducible water saturation
6 and thereafter the cores are flooded with water containing
7 6000 ppm of TDS to irreducible oil saturation. The percent
oil recovery of each of the floods is iLlustrated in Figure
9 2. AS is evident from this figure, increased concentrations ,
of the alcohol permit higher oil recoveries of the micellar
11 dispersion. With this particular system, at the high con-
12 centrations of alcohol, the micellar dispersion solubilizes
13 about equal volumes of the crude oil and the connate water
14 within the cores~
It is not intended that the above examples limit the
16 invention. Rather, it is intended that all equivalents
17 obvious to those skilled in the art be incorporated within '
18 the scope of the invention as defined within the speci-
2D ~ Ati~ and appended clai~s,
22246
28
29
31
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