CA1049926A - Flooding with micellar dispersions having connate water compatibility - Google Patents

Abstract

FLOODING WITH MICELLAR DISPERSIONS HAVING
CONNATE WATER COMPATIBILITY

ABSTRACT OF THE DISCLOSURE

Improved flooding of a subterranean formation con-taining connate water of a particular salinity with a micellar dispersion comprised of surfactant, water, hydro-carbon, cosurfactant and optionally electrolyte is obtained by designing the cosurfactant(s) within the micellar dis-persion to be more hydrophilic with an increase in salinity and also designing the cosurfactant to permit the micellar dispersion to solubilize at most a minimum amount of the connate water. Preferably, the cosurfactant is preselected to impart the desired compatibility of the dispersion with the salinity of the connate water or a cosurfactant can be blended with another cosurfactant to obtain the desired viscosity of the micellar dispersion and desired compati-bility with the connate water. Generally speaking, the cosurfactant should have an increasing hydrophilicy as the salinity of the connate water increases.

Description

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1049926 :
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, ~ sAC~GROUND OF THE INVENTION ¦
; Field of the Invention . _ .
This invention relates to injecting a micellar dis-~; persion into a subterranean formation and displacing it ~ toward a production means in fluid communication therewith :
.: : to recover crude oil therethrough. .
. Description of the Prior Art The prior art recognizes that micellar dispersions are useful to displace crude oil from subterranean formations, , e.g. se .5 Patent Nos. 3,254 714: 3,275,075; 3,506,070 ¦~

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,, 1 3,497,006; 3,613,786; 3,734,185; 3,740,343; 3,827,496; and2 other patents defining surfactant systems and assigned to 3 Marathon Oil Company, Esso Production Research Company, 4 Shell Oil Company, Union Oil Company, Mobil Oil Company, 5 ~exaco Oil Company, etc. The micellar dispersion is 6 usually followed by an aqueous mobility buffer and then a water drive to displace the crude oil from the reservoir.
8 The prior art has taught different methods of enhancing 9 the compatibility of the micellar dispersion with the connate water to obtain improved oil recovery:
11 Davis in U.S. 3,476,184 teaches that the micellar dis-12 persion slug should have a small hydrophilicy in the front 13 portion and a relatively larger hydrophilicy in the back 1~ portion thereof.
Jones, in U.S. 3,482,631 teaches that improved oil 16 recovery is obtained by injecting before the micellar dis-17 persion an aqueous pre-slug containing a viscosity imparting 18 agent and electrolyte and/or cosurfactant.
19 Jones also teaches in U.S. 3,520,366 improved oil recovery can be obtained by injecting previous to the 21 micellar dispersion an aqueous slug containing cosurfactant 22 or electrolyte and cosurfactant.
23 Poettmann in U.S. 3,324,944 teaches improved oil 24 recovery is obtained by injecting previous to the micellar dispersion a hydrocarbon preslug to preferentially build up 26 an oil bank ahead of the micellar dispersion which in turn 27 preferentially pushes oil through the formation and displaces 28 a portion of the connate water.
29 Gogarty in U.S. 3,343,597 teaches improved oil recovery by injecting an aqueous slug of controlled ions to protect 31 a subsequently injected micellar dispersion from the connate water.

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~ 1049926 1 Tosch et al in U.S. 3,561,530 teach improved flooding

2 by enhancing the compatibility of the micellar dispersion

3 with the connate water by first determining the salinity of

4 the connate water, then selecting the desired mole ratio of water to surfactant within the micellar solution based on an 6 equilibrium curve.
7 Burdge in U.S. 3,623,553 teaches that the brine toler-ance of a micellar dispersion can be increased by incorpora-9 ting low average equivalent weight surfactants within the micellar dispersion or increasing the average equivalent 11 weight of the surfactant to obtain lower brine tolerances.
12 Sydans~ et al in U.S. 3,648,770 teach improved flooding 13 of a reservoir by first determining the predominant cation 14 within the connate water, then designing the micellar dispersion to contain a cation which has a greater affinity 16 for the petroleum sulfonate within the micellar dispersion 17 than the predominant cation within the connate water, and 18 then injecting and displacing the micellar dispersion through 19 the formation to recover crude oil therethrough.
Gogarty in U.S. 3,648,773 teaches that improved flooding 21 of a reservoir containing relatively high concentration of 22 divalent cations is obtained by designing the micellar 23 dispersion to contain a relatively low average equivale~_ 24 weight sulfonate.
Knight et al in U.S. 3,844,350 teach improved flooding 26 of reservoirs containing high divalent cation concentrations 27 within the connate water by injecting previous to the 28 micellar dispersion an aqueous preslug containing 50-2,000 29 ppm of a biopolymer--the biopolymer "insulates" the micellar dispersion from the connate water.

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1 SUMMARY OF THE INV~NTION
2 Applicants have discovered that improved flooding with 3 micellar dispersions containing cosurfactant~s) is obtained 4 by increasing the hydrophilicy of the cosurfactant where the salinity of the connate water is high or decreasing 6 the hydrophilicy where the salinity of the connate water is less. The cosurfactant(s) is also designed to impart the 8 desired viscosity to the micellar dispersion and also to 9 permit the dispersion to solubilize at most only a minimum amount of the connate water, i.e. the dispersion can be 11 dehydrated to a limited extent by the connate water but 12 preferably the dispersion is designed to solubilize little 13 or no connate water.

BRIEF DESCRIPTION OF T~IE DRAWINGS
16 Figure l illustrates the relationship between cosur-17 factant concentration and brine concentration on the phase 18 behavior of a micellar dispersion. This micellar dispersion 19 is identified in Example I. Electrolyte concentrations shown on the abscissa of Figure I include only salts added 21 to the water used to make up the micellar dispersion and do 22 not include 3900 ppm of ammonium sulfate concentration 23 contributed by the petroleum sulfonate. The added salts or 24 electrolyte are 0.9% by weight calcium and magnesium, and 99.l~ sodium and chloride. As this graph illustrates, added 26 electrolyte reduces the amount of n-pentanol required to 27 solubilize the hydrocarbon. Also, an increase in electrolyte 28 reduces the alcohol concentration that causes an aqueous 29 phase to be expelled from the micellar dispersion and also results in a narrowing of the "single-phase band" with 31 increasing electrolyte concentration. The negative slope of ., . . ~

1 the single phase region is characteristic of substantially 2 water-insoluble cosurfactants.
3 Figure 2 illustrates the cosurfactant concentration 4 required to achieve "minimum viscosity" of the micellar dispersion as a function of water salinity for dispersions 6 made from a variety of surfactant types. Compositions of these micellar dispersions are defined in Example II. The 8 inverted triangular data points represent a micellar dis-9 persion containing O.l~ of isopropyl alcohol and the upright triangular data points represent a micellar dispersion 11 containing 0.02% isopropyl alcohol. The circular data 12 points represent a micellar dispersion containing ~.41%
13 isopropyl alcohol while the square data points represent a 14 micellar dispersion containing no isopropyl alcohol. The point of "minimum viscosity" corresponds approximately to 16 the center of the "single-phase stability band" as shown in 17 Figure l, e.g. for an electrolyte concentration of 4,000 18 ppm, the cosurfactant concentration to achieve minimum 19 viscosity is about l.35. Also, this point of minimum viscosity corresponds to the point farthest removed from slug instability.
21 The difference in the required n-amyl alcohol concentration 22 between the two upper or the two lower curves is mainly due to 23 different isopropyl alcohol concentrations in the micellar 24 dispersion slugs.

27 The term "micellar dispersion" as used herein is meant 28 to include micellar solutions, microemulsions, "transparent 29 emulsions", hydrous soluble oils, micellar systems con-taining lamellar micelles, etc. These systems can be oil-31 external or water-external, they can act like they are 1 either oil-external or water-external or both, and they can 2 also be in an "intermediate region" between a "classically"
3 oil-external micellar system and a "classically" water-4 external micellar system. However, all of the systems, regardless of the externality properties, are thermodynam-6 ically stable and optically clear; but, color bodies within 7 the different components can prevent the transmission of 8 light.
9 The micellar dispersions are composed of hydrocarbon, water, surfactant, cosurfactant, and optionally electrolyte.
11 Additional component(s) can be added to impart desired 12 properties to the micellar dispersion, e.g. high molecular 13 weight polymers to impart desired mobility characteristics.
14 However, these components must be compatible with the other components of the dispersion and not impart adverse properties 16 to the system.
17 Examples of the components useful with the micellar 18 dispersion are defined within the patents mentioned in the 19 "Description of the Prior Art".
The surfactant can be anionic, nonionic, or cationic, 21 or mixtures thereof. Preferably, it is a monovalent cation-22 containing petroleum sulfonate obtained by sulfonating a 23 fraction of crude oil, e.g. gas oil, or whole or topped 24 crude oil. Desirably, the petroleum sulfonate has an average equivalent weight within the range of about 350 to 26 about 525 and more preferably about 390 to about 470. The 27 petroleum sulfonate can contain unreacted hydrocarbon and 28 salts (hereinafter defined as electrolytes).
The hydrocarbon is typically crude oil, a fraction thereof, unreacted vehicle oil within the surfactant, 31 synthesized hydrocarbon, mixtures thereof, or like materials.
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1 water within the micellar dispersion can be distilled 2 water, fresh water, or water containing a moderate amount of 3 salts. Typically, the water contains about 5 to about 4 50,000 ppm of TDS (total dissolved solids). Preferably, the water does not contain sufficient amounts of multi-valent 6 cations to displace a significant amount of the monovalent 7 cations on the surfactant.
8 Electrolytes useful include water-soluble inorganic 9 salts, inorganic bases, inorganic acids, or mixtures thereof.
Typically, the salts are reaction by-products from the 11 preferred petroleum sulfonate, e.g. ammonium sulfate, ammonium 12 sulfite, sodium sulfate, sodium sulfite, etc., but the 13 electrolytes can be added or blended with electrolytes 14 within the micellar dispersion mixture.
The cosurfactant, also known as a semi-polar organic 16 compound, cosolubilizer, or stabilizing agent, is an organic 17 compound(s) containing about l to about 25 or more carbon 18 atoms and more preferably about 3 to about 16 carbon atoms.
19 It can be an alcohol, amide, amino compound, ester, aldehyde, ketone, complexes thereof, or a compound containing one or 21 more of amido, hydroxy, bromo, chloro, carbonato, mercapto, 22 oxo, oxy, carbonyl, or like groups, or mixtures thereof.
23 Specific examples include isopropanol, butanol, amyl alcohols, 24 hexanols, octanols, decyl alcohols, alkyl aryl alcohols such as n-nonyl phenol and p-nonyl phenol, 2-butoxyhexanol, 26 alcoholic liquors such as fusel oil, mixed isomers of primary 27 amyl or hexyL alcohols such as UCAR-HCO (marketed by Union 28 Carbide Company, N.Y., N.Y.), blends of Cl2, Cl3, Cl4, Cl5, 29 etc. linear primary alcohols such as Neodal alcohols (marketed by Shell Chemical Co.), ethoxylated alcohols such as alcohols 31 containing 4 to about 16 carbon atoms that are ethoxylated ` _7_ .... . ............... . . .
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1 and optio~ally sulfated, hydrogenated hydrocarbons such as 2 hydrogenated croton oil, amidized hydrocarbons, and like 3 materials. The preferred cosurfactant is an alcohol which 4 can be primary, secondary or tertiary alcohol or mixtures thereof and can optionally be ethoxylated and/or sulfated.
6 Concentration of the components within the micellar 7 dispersion vary depending upon the particular component and 8 the particular properties desired of the micellar dispersion.
9 Typically, the concentration is about 4 to about 56% and preferably about 5 to about 50% and more preferably about 11 6 to about 20% hydrocarbon, about 40 to about 92% and preferably 12 about 60 to about 85% and more preferably about 65 to about 13 80% water, about 4 to about 20% or more and preferably about 14 6 to about 16% and more preferably about 7 to about 12% of 15 surfactant, about 0.01 to about 20% and preferably about 16 0.05 to about 10% and more preferably about 0.1 to about 1~
17 of cosurfactant, and about 0.001 to about 10% and preferably 18 about 0.01 to about 7.5% and more preferably about 0.1 to 19 about 5% of electrolyte.
The micellar dispersion is injected into the formation 21 in volume amounts of 1 to about 50% or more, and preferably 22 about 4 to about 15% FPV (formation pore volume). It is 23 preferably followed by a mobility buffer, e.g. an aqueous 24 solution containing a water~soluble polymer which imparts 2~ permeability reduction to the formation and/or viscosity 26 increasing properties to the aqueous solution--examples of 27 volume amounts include about 10 to about 200% FPV or more 28 and preferably about 50 to about 150% FPV, and more prefer-29 ably about 60 to about 100% FPV. A water drive can be injected to displace the micellar dispersion and the mobility 31 buffer toward a production well in fluid communication with .
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1 the formation to recover crude oil thr~ugh said production well.
3 Wi~h the proper type and concentration of cosurfactant(s), 4 a micellar dispersion can, within limits, be designed to accommodate a particular salinity of a connate water. Also, single-phase micellar dispersion systems can be formulated 7 at a given cosurfactant concentration over a range of 8 electrolyte concentrations in the connate water or through 9 a cosurfactant range at a fixed electrolyte concentration.
Increasing the hydrophilicy of the cosurfactant generally 11 increases the amount of an oleophilic cosurfactant, or less 12 hydrophilic cosurfactant, that is needed with certain micellar 13 flooding systems. The micellar dispersion slug must be 14 designed by properly selecting the desired type and concentration of the cosurfactant(s), preferably alcohols, to obtain 16 optimum oil recovery with the particular salinity of the 17 connate water. Such can ~e accomplished by blendin~ two or 18 more cosurfactants, or by choosing a particular cosurfactant(s) 19 and then making up the dispersion--cosurfactant choice will depend upon the type and concentration of the other components 21 of the micellar dispersion, the properties of the formation 22 fluids ti.e. crude oil and connate water) and gas if present, 23 the desired mobility design for the flooding process, the 24 reservoir conditions, etc.
The micellar dispersion is preferably designed such 26 that the cosurfactant concentration and type within the 27 micellar dispersion will solubilize only a minimum amount 28 and preferably no connate water or only a minimum amount of 29 the water within the micellar dispersion is permitted to be expelled or dehydrated from the micellar dispersion. If the 31 connate water is permitted to be solubilized substantially ,:
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1 ¦ within the micellar dispersion, this can cause instability 2 ¦ to occur within the micellar dispersion, resulting in the 3 ¦ formation of an emulsion, loss of mobility control, etc. and 4 ¦ an overall adverse influence on the flooding proeess.

5 ¦ Tne solubilization properties of the micellar dis-

6 ¦ persion are controlled by the cosurfactant within the

7 ¦ micellar dispersion. The coneentration of hydrophilie eo-

8 ¦ surfactants inereases as the salinity of the eonnate water

9 ¦ inereases and/or the concentration of oleophilie eosurfac-

10 ¦ tants deereases as the salinity of the eonnate water inereases.

11 ¦ It may be desirable to eombine a hydrophilie and an oleophilic

12 ¦ cosurfactant within the micellar dispersion in order to

13 ¦ obtain desired viseosity eharaeteristics of the mieellar

14 dispersion. If the latter is desirable, the hydrophilie and oleophilie eosurfaetants must be blended in the right ratio 16 and present in the optimum coneentration to obtain the 17 desired solubilization properties to the mieellar dispersion.
18 The following examples are presented to teaeh speeific 19 embodiments of the invention. Unless otherwise speeified, all pereents are based on volume and measurements are made 21 at 22-23C.

23 A micellar dispersion composition is obtained by 24 mixing lO% of an ammonium petroleum sulfonate having an average equivalent weight of about 440 and 61 weight pereent 26 active sulfonate, 40% of a crude oil having a viseosity of 27 7-9 ep. and 37 API gravity, 50% of water whieh contains 28 3900 ppm of ammonium sulfate and 400 ppm of other dissolved Z9 solids. The total water concentration in the micellar dispersion mixture is 54.5%, this ineludes water from the 31 petroleum sulfonate. Figure l shows the interaction between , -10-~,,, . .. ... . , ,~ , ~049926 1 the cosurfactant and electrolyte concentrations on the phase 2 behavior of this composition. The electrolyte concentra-3 tions shown on the abscissa of Figure l includes only salts added to the water used to make up the micellar dispersion S composition but do not include the 3900 ppm of ammonium 6 sulfate concentration. This graph shows that an increase in 7 electrolyte concentration of the connate water causes a 8 decrease in the n-pentanol.concentration, i.e. as the salinity 9 of the connate water increases, the concentration of an oleophilic cosurfactant decreases in order to achieve a single 11 phase system.

13 Micellar dispersion compositions containing 10% of an 14 ammonium petroleum sulfonate and 40% of a crude oil having a lS viscosity of 7 cp. and 50~ water containing electrolyte 16 concentrations defined'in the abscissa in Figure 2, are 17 titrated with n-amyl alcohol at different electrolyte concen-18 trations--the minimum viscosity of each micellar dispersion 19 ,as a function of cosurfactant concentration is determined.
The cosurfactant concentration at the minimum viscosity is 21 plotted in Figure 2. The petroleum sulfonate in the dispersions represented by the inverted and upright triangles have an average equivalent weight of about 410-420 and the sulfonates 24 ~represented by the circular and square data points have an average equivalent weight of about 430-440. This figure 26 illustrates that as the salinity of the water increases, the 27 micellar dispersion requires less of the oleophilic cosurfactant.
28 It is not intended that the above examples limit the 29 invention. Rather, it is intended that all equivalents obvious to those skilled in the art be incorporated within the scope of the invention as defined within the speci-fication and appended claims.

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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

In a process for recovering hydrocarbon from a subterranean formation having at least one injection means in fluid communica-tion with at least one production means and wherein a micellar dispersion of predetermined viscosity and comprised of water, hydrocarbon, cosurfactant, and surfactant is injected into the formation and displaced toward the production means to recover hydrocarbon therethrough, the improvement comprising utilizing as the cosurfactant(s) in the micellar dispersion a cosurfactant(s) of sufficient hydrophilicy characteristics and of sufficient concentration to cause the micellar dispersion to remain as a single phase and to solubilize none or a minimum of the connate water within the micellar dispersion or to permit a minimum dehydration of water from the micellar dispersion by the connate water upon initial contact with the connate water, and thereafter injecting the micellar dispersion into the formation and displacing it toward the production means to recover hydrocarbon.

The process of Claim 1 wherein the micellar dispersion contains 4 to about 20% surfactant, about 4 to about 56% of hydrocarbon, about 40 to about 92% water, and about 0.01 to about 20% cosurfactant.

The process of Claim 1 wherein the dispersion contains about 0.001 to about 10% of water-soluble inorganic salt, inorganic base, inorganic acid or mixtures thereof.

The process of Claim 1 wherein the surfactant is a monovalent cation-containing petroleum sulfonate.

The process of Claim 1 wherein the micellar dispersion contains about 65 to about 80% water.

The process of Claim 1 wherein the micellar dispersion contains oleophilic and hydrophilic cosurfactants.

The process of Claim 1 wherein the micellar dispersion contains a hydrophilic cosurfactant.

The process of Claim 1 wherein the micellar dispersion is designed to permit a minimum amount of water to be dehydrated out of the micellar dispersion by the connate water.

The process of Claim 1 wherein the micellar dispersion is designed to not permit the dispersion to solubilize any of the connate water upon initial contact with the connate water.

The process of Claim 1 wherein the micellar dispersion is designed to permit only a minimum amount of the connate water to be solubilized by the micellar dispersion upon the initial contact with the micellar dispersion.

The process of Claim 1 wherein the hydrophilicy of the cosurfactant increases upon an increase in salinity of the connate water.

The process of Claim 1 wherein the cosurfactant(s) is an alcohol(s).