3-Sulfoxy-1,2-propylene glycols-1-esters of tricyclo 4.2.2.0.sup.2,5) dec-9-ene-3,4,7,8-tetracarboxylic acid are prepared. These compounds are useful as surfactants, biocides and as cosurfactants in enhanced oil recovery.

FIELD OF THE INVENTION 
This invention relates to 3-sulfoxy-1,2-propylene glycols-1-esters of 
tricyclo(4.2.2.0.sup.2,5)dec-9-ene-3,4,7,8-tetracarboxylic acid. More 
particularly, this invention relates to 3-sulfoxy-1,2-propylene 
glycols-1-esters of 
tricyclo(4.2.2.0.sup.2,5)dec-9-ene-3,4,7,8-tetracarboxylic acid wherein 
the said compounds are of the structural formula I: 
##STR1## 
wherein R is selected from the group consisting of phenyl naphthalene, 
anthracenyl, biphenyl, and phenanthrenyl; alkyl moieties of 1 to 22 carbon 
atoms, and phenylalkyl, biphenylalkyl, alkylphenyl, alkylbiphenyl and 
cyclohexyl moieties containing 6 to 40 carbon atoms, wherein R can be 
substituted with nitro, halogen, cyano and carboalkoxy moieties of 1 to 12 
carbon atoms. 
For convenience these compounds are referred to as 3-sulfoxy-1,2-propylene 
glycols-1-esters of 
tricyclo(4.2.2.0.sup.2,5)dec-9-ene-3,4,7,8-tetracarboxylic acid. These 
compounds possess biocidal properties. The invented compounds of molecular 
weights within the range of from about 400 to about 1200 act as 
cosurfactants useful in enhanced oil field recovery. These compounds are 
also useful as surfactants and biocides, and can be used as hydraulic 
fluids when of sufficiently low molecular weight, and as chemical 
intermediates. 
Cosurfactants function as coupling agents for surfactants and reservoir 
brines for the purpose of enhancing crude oil production. Surfactant and 
cosurfactant mixtures are dissolved in brines in low concentration to form 
micellar fluids or solutions. These micellar solutions can be described as 
microemulsions containing surfactants which act to reduce the interfacial 
tension between water and oil. A second component, a cosurfactant, usually 
an alcohol, is used to improve the quality of the micellar solution. An 
efficient cosurfactant increases the micelles' capacity to solubilize more 
oil or water and still form stabilized solutions. 
Compounds used as cosurfactants in the prior art have been alcohols such as 
isopropyl alcohol, amyl and hexyl alcohols and their ethoxylated 
derivatives. These cosurfactants have limited capabilities because of the 
variety of reservoir conditions encountered in enhanced oil recovery 
programs. For example, special systems must be designed for reservoirs 
which are essentially fresh water, that is, those which contain 6000 ppm 
or less monovalent ions, and those which are essentially hard water, those 
which contain 50,000 ppm monovalent ions plus 500 ppm or more of the 
divalent ions. Cosurfactants should perform so as to achieve a stable 
fluid when the water-cosurfactant mixture is in contact or mixed with 
crude oil. Molecular weight of the cosurfactant should be sufficiently low 
to permit passage through semipermeable rock formations and achieve 
mobility control. 
This invention accordingly also relates to a new and unique family of low 
molecular weight compounds which are suitable for use as cosurfactants for 
enhanced crude oil recovery. These compounds in use lower the interfacial 
tension between water and oil, are low molecular weight of from about 400 
to about 1200, and are required in only low concentrations to formulate 
micellar fluids. 
BACKGROUND OF THE INVENTION 
Tricyclo(4.2.2.0.sup.2,5)dec-9-ene-3,4,7,8-tetracarboxylic dianhydride, a 
known compound, is the adduct of two moles of maleic anhydride and one 
mole of benzene. It has the structure: 
##STR2## 
It is known to react maleic anhydride with benzophenone in benzene solution 
by exposing the reaction mixture to direct sunlight to prepare 
tricyclo(4.2.2.0.sup.2,5)dec-9-3,4,7,8-tetracarboxylic-3,4,7,8-dianhydride 
(D. Bryce-Smith, et al., Chem & Ind. (London) 1962, 2060). D. Bryce-Smith, 
et al., obtained 93% yield by exposing 14 g of maleic anhydride and 2.8 g 
of benzophenone in 265 ml of benzene in a Pyrex tube to direct sunlight 
for 72 hours. The tetraallyl esters of these compounds are reacted with a 
mercaptan and oxygen in the presence of a dye sensitizer under irradiation 
by visible light. The products, the title compounds, are tetraesters in 
which the ester moieties have been converted from --O--CH.sub.2 
CH.dbd.CH.sub.2 to --O--CH.sub.2 --CH(OH)--CH.sub.2 --SO--R, i.e., 
beta-hydroxysulfoxide derivatives of the original allyl esters of 
tricyclo(4.2.2.0.sup.2,5)dec-9-ene-3,4,7,8-tetracarboxylic acid. 
Beta-hydroxyalkylsulfoxides can be prepared by the method of Anderson, U.S. 
Pat. No. 3,247,258 which is incorporated by reference, wherein the 
mercaptan (or thiol), the olefin and oxygen are in contact at temperatures 
above 80.degree. C. Anderson indicates that with certain olefins and 
mercaptans such as indene, styrene and thiophenol, the reaction occurs by 
mixing the olefin and mercaptan first, with the oxygen being bubbled 
through the mixture thereafter. Other patents such as Oswald, et al., U.S. 
Pat. No. 3,043,824 and Goodhue, et al., U.S. Pat. No. 3,210,243, which are 
each incorporated by reference, disclose preparing 
beta-hydroxyalkylsulfoxides through (1) a co-oxidation route using a 
hydroperoxide or through (2) oxidation of the sulfide by means of hydrogen 
peroxide. Oswald indicates that the preparation of hydroperoxide products 
by olefin-mercaptan co-oxidation to the sulfoxide requires chain 
initiators, e.g., ultraviolet light and the addition of peroxide compounds 
(hydroperoxides). In the absence of such catalysts, some co-oxidation 
reactions have extremely long induction periods and are not practical to 
carry out. Goodhue teaches that preparation of the sulfoxide using 
hydrogen peroxide is a three-step synthesis through the sulfide which in 
turn is prepared from the mercaptan with epichlorohydrin. Fields, in 
commonly-assigned U.S. Pat. No. 4,040,921, incorporated herein by 
reference, teaches a one-step process for beta-hydroxyalkylsulfoxides by 
reacting an olefin and a thiol with oxygen in the presence of a dye 
sensitizer using visible light at a temperature from -10.degree. C. to 
70.degree. C. 
The object of this invention accordingly is to produce as new compounds the 
3-sulfoxy-1,2-propylene glycols-1-esters of 
tricyclo(4.2.2.0.sup.2,5)dec-9-ene-3,4,7,8-tetracarboxylic acid. These 
compounds are useful as cosurfactants in enhanced oil recovery, as 
surfactants and biocides, and as hydraulic fluids when of sufficiently low 
molecular weight. 
SUMMARY OF THE INVENTION 
This invention relates to 3-sulfoxy-1,2-propylene glycols-1-esters of 
tricyclo(4.2.2.0.sup.2,5)dec-9-ene-3,4,7,8-tetracarboxylic acid which are 
useful as cosurfactants in enhanced oil recovery, surfactants and 
biocides, and as hydraulic fluid when of sufficiently low molecular 
weight. 
DETAILS OF THE INVENTION 
3-Sulfoxy-1,2-propylene glycols-1-esters of 
tricyclo(4.2.2.0.sup.2,5)dec-9-ene-3,4,7,8-tetracarboxylic acid are 
prepared by reacting the tetraallyl ester of 
tricyclo(4.2.2.0.sup.2,5)dec-9-ene-3,4,7,8-tetracarboxylic acid with a 
mercaptan RSH, oxygen at 2-50 psig, and visible light in the presence of a 
dye sensitizer such as Rose Bengal or methylene blue at 
0.degree.-40.degree. C. for 0.1 to 148 hours. The mole ratio of RSH to the 
tetracarboxylic ester can be 1 to 5, preferably 4. The 
3-sulfoxy-1,2-propylene glycols-1-esters are prepared from an olefinic 
alcohol wherein the olefinic moiety has from 3 to 18 carbon atoms. 
Examples of olefinic alcohols useful in preparation of 
3-sulfoxy-1,2-propylene glycols-1-esters are allyl alcohol and crotyl 
alcohol. 
The thiol (or mercaptan) can be aliphatic, aromatic, alicyclic and 
heterocyclic and can be described as being of the general formulae RSH. R 
preferably is a radical of from 1 to 24 carbon atoms, from methyl to 
tetracosyl radicals, more preferably 1 to 18 carbon atoms. Examples of R 
in RSH that can be used are methyl, ethyl, butyl, hexyl, octyl, hexadecyl, 
cyclopentyl, cyclohexyl, phenyl, naphthyl, p-tolyl, benzyl, 
2-benzothiazyl, and 4-pyridyl. Examples of such thiols are methylthiol, 
ethylthiol, n- and isopropylthiol, n-, sec- and tert-butylthiol, 
n-hexylthiol, n-octylthiol, tert-octylthiol, n-dodecylthiol, n- and 
tert-hexadecylthiol, cyclohexylthiol, tetracosylthiol, thiophenol, 
thiocresol, 4-n-dodecylthiocresol, 4-tert-nonylthiocresol, 
pyridine-2-thiol, pyridine-4-thiol, thiophene-3-thiol, furan-2-thiol, 
quinoline-2-thiol, quinoline-4-thiol, phenanthridine-1-thiol, 
1,3,5-triazine-2-thiol. 
Preferably the thiol comprises a thiol containing 1 to 18 carbon atoms. 
These are preferred because they are cheap, reactive, and extend the range 
of derivatives to cover those soluble in various inorganic and organic 
solvents. One or more hydrogens of the aliphatic, alicyclic and aromatic 
moieties such as methyl, ethyl, isobutyl, tolyl and phenyl moieties of the 
above-described thiol compounds can be replaced with nonreactive radical 
groups such as halogens and nitro radicals and, on the alicyclic and 
aromatic moieties, by alkyl moieties. 
The molar ratios of the reactants to prepare the 3-sulfoxy-1,2-propylene 
glycols-1-esters, i.e., the thiols, olefinic compound, oxygen, that can be 
used, can vary considerably. The thiol-olefin ratio is between 0.001 to 5 
moles of thiol per mole of olefin. Substantially equimolar amounts of 
olefin and thiol are preferred. Use of a solvent such as heptane, hexane, 
benzene, acetone, or dioxane at concentrations of 1 to 85 weight percent 
is convenient. When water-miscible solvents such as acetone or dioxane are 
used, water up to 50% by weight of organic solvent may be incorporated. In 
such cases, or when water is used with immiscible solvents such as heptane 
or benzene up to 50% by weight, phase-transfer agents such as cetyl 
trimethyl ammonium bromide, benzyl triethyl ammonium chloride, benzyl 
triphenyl phosphonium chloride, etc., are incorporated at concentrations 
of 0.001 to 1% by weight of total solvent. 
Heptane is the preferred solvent. 
It is essential that at least one optically sensitizing dye be used in 
conjunction with the application of visible light. The term dye sensitizer 
can be defined as being an organic dye which increases spectral response. 
Typical dye sensitizers are fluorescein derivatives, methylene blue, 
certain porphyrins and polycyclic aromatic hydrocarbons. Suitable dye 
sensitizers include Rose Bengal, methylene blue and Eosin. 
Rose Bengal and methylene blue are the preferred dye sensitizers dissolved 
in acetone at 0.1-5% by weight. Sufficient dye is added to give final 
concentrations of 0.02 to 1% by weight in the total reaction mixture; 0.05 
to 0.25% by weight is preferred. Alternatively the dye may be introduced 
bound to an ion-exchange resin in a relatively insoluble form, e.g., 
anionic Rose Bengal or Eosin attached to the strongly basic anion exchange 
resin Amberlite IRA-400 (Rohm and Haas, Philadelphia) or cationic 
methylene blue attached to the strongly acidic cation exchange resin 
Amberlite IRC-200 (J. R. Williams et al., Tetrahedron Letters, 4603 
(1973)). 
The reaction may be run in any type of open or sealed vessel, suitably 
agitated. A particularly useful apparatus for the reaction is the Parr 
Pressure Reaction Apparatus, Item No. 3911, made by the Parr Instrument 
Company of Moline, Ill. This apparatus consists of a heavy-walled clear 
Pyrex bottle connected with a tank of oxygen under pressure; the bottle is 
shaken vigorously during the reaction. Pressures of oxygen of 1 to 250 
psig may be used; 15 to 50 psig O.sub.2 are convenient pressures in the 
laboratory although, commercially, pressures over 100 psig are preferred. 
The bottle is illuminated with visible light such as ordinary incandescent 
or photoflood bulbs of 50-500 watts, preferably mounted in reflector with 
the light source 11/2 to 3 inches from the vessel. 
The lamps used were General Electric 500 watt photoflood or incandescent 
bulbs and a General Electric 275 watt sunlamp. Specifications of the G.E. 
500 watt photoflood lamp require 1.61 radiated watts from 280 to 400 
nanometers, and 6.9 radiated watts from 400 to 700 nanometers, the range 
of visible light. The G.E. sunlamp has 4.47 radiated watts in the 
ultraviolet range from 280 to 400 nanometers, and 7.03 radiated watts in 
the visible light range of 400 to 700 nanometers. 
Reaction is continued until the calculated amount of oxygen has been 
absorbed as shown by pressure drop; times of 1 to 100 hours may be used, 
depending on the nature of the olefin, the thiol, and the pressure of 
oxygen. Workup generally consists of evaporating the reaction mixture at 
30.degree.-60.degree. C. and 0.1-1 torr, conveniently in a rotating RINCO 
evaporator (BUCHI Vacuum Rotary Evaporator ROTAVAPOR EL, Rinco Instrument 
Company, Inc., Greenville, Ill.). 
The present invention also comprises a method of injecting a micellar slug 
into a subterranean formation comprising the steps of (1) contacting said 
subterranean formation with an aqueous fluid composition comprising water, 
a surfactant, a hydrocarbon, an electrolyte, and a low molecular weight 
cosurfactant within the range of from about 400 to about 1200 of a sulfoxy 
propylene glycol ester; (2) applying sufficient pressure to said 
composition to cause said micellar slug to move through said formation; 
(3) maintaining sufficient pressure while injecting said composition into 
said formation. The said low molecular weight sulfoxy propylene glycol 
esters can be selected from the group consisting of compounds prepared 
from thiophenol, methyl mercaptan, ethyl mercaptan, and n-octyl mercaptan. 
In order to facilitate a clear understanding of the invention, the process 
of preparing 3-sulfoxy-1,2-propylene glycols-1-esters of 
tricyclo(4.2.2.0.sup.2,5)dec-9-ene-3,4,7,8-tetracarboxylic acid and the 
use thereof, the following specific embodiments are described in detail. 
It should be understood, however, that the detailed expositions of the 
instant invention, while indicating preferred embodiments, are given by 
way of illustration only since various changes and modifications within 
the spirit and scope of the invention will become apparent to those 
skilled in the art from this detailed description.

PRELIMINARY EXAMPLE 
Screening tests for suitable cosurfactants to be used as additives for 
enhanced oil recovery have been developed which indicate a relationship 
exists between interfacial tension of the cosurfactant and petroleum 
removal from core samples using a micellar solution. Surfactant-stabilized 
dispersions of water in hydrocarbon are micellar solutions. In addition to 
the required surfactant, water and hydrocarbon micellar solutions can 
contain cosurfactants and electrolytes to improve stability. Alcohols such 
as isopropanol and amyl alcohols typically have served as cosurfactants. 
Sodium chloride and sodium sulfate are examples of electrolytes that are 
used. 
Important aspects of a micellar solution include an ability to solubilize 
water, compatibility with hydrocarbon and crude oil, an increasing 
viscosity with increased water concentration and inversion to an 
oil-in-water solution. In a micelle, surfactant and cosurfactant surround 
dispersed water which exists in the hydrocarbon phase as spherical 
droplets. With additional water, the water droplets increase in size. When 
water is the dispersed phase, the micellar solutions exhibit 
hydrocarbon-like properties of the external phase. As more and more water 
is solubilized in a micellar system, spheres enlarge until inversion takes 
place to form an oil-in-water emulsion. Cosurfactants in a micellar 
solution stabilize the solution to reduce incidence of inversion and phase 
separation. 
The following bench test has been devised as a preliminary vial screening 
test to eliminate need for expensive core tests of cosurfactants. The test 
has been found to have reliability in predicting suitable properties of 
cosurfactants when used in micellar solutions. The principal important 
aspect has been found to be the interfacial tension of the cosurfactant in 
an oil-water mixture. The formulation is required to yield stable fluids 
in brine and to show low interfacial tension (IFT) as well as very good 
miscibility with crude petroleum. 
Micellar fluids formulated from concentrates containing 40:1 to 5:1 
surfactant-cosurfactants ratios have been tested over a wide range of 
salinities (sodium chloride in water) and hard waters, being examined for 
phase stability, fluid clarity, interphase behavior and miscibility of 
aqueous fluids with crude petroleum. 
The vial screening bench test is an empirical test which comprises mixing 
the micellar fluid and crude petroleum by swirling the fluids together in 
a test tube while observing the interface. A light source is used to 
observe the fluid-oil behavior. The interfacial mixing (and hence 
interfacial tension) is judged upon a scale of very low, moderately low, 
low, medium and high by a comparison with standards previously developed. 
For example, brine solutions of a hardness range from under 6,000 ppm of 
monovalent ions (sodium chloride) to about 50,000 ppm of monovalent ions 
(sodium chloride) are mixed with a 40:1 ratio of surfactant-cosurfactant 
mixture with Second Wall Creek crude. The surfactant is a petroleum 
sulfonate. Surfactant-cosurfactant-brine mixtures are prepared at ambient 
temperature and pressure. 
Stability of the brine solution with surfactant-cosurfactant mixture is 
tested by pouring the mixture into a 50 ml graduated cylinder and allowing 
the solution to stand for one hour undisturbed. Fluids which remained 
single phase and free of sediment are further tested. 20 ml of solution 
are poured into a vial. 4 ml of crude petroleum are added to the vial. The 
vial is turned gently, observing mixing behavior of crude and micellar 
fluid. The vial is then shaken vigorously for one minute, after which the 
vial is allowed to stand undisturbed for one hour. After this period, the 
fluid is evaluated for oil drop-out, number of liquid phases, thickness of 
emulsion and miscibility. Results are correlated with interfacial tension 
of solution and crude by visual observation and spinning drop method of J. 
L. Caylas, et al., "Low Interfacial Tension," American Chemical Society 
Series No. 8 Adsorption At Interfaces, 1975. Formation of round oil 
droplets which separate quickly and failure to form an emulsion indicate a 
high, ineffective interfacial tension characteristic which can render the 
cosurfactant unsuitable as an additive for enhanced oil recovery 
applications. 
EXAMPLE I 
Tricyclo(4.2.2.0.sup.2,5)dec-9-ene-3,4,7,8-tetracarboxylic-3,4,7,8-dianhydr 
ide was prepared by a modification of the method of D. Bryce-Smith, A. 
Gilbert, and B. Vickery, Chemistry and Industry (London) 1962, 2060. They 
obtained a 93% yield by exposing a solution of 14 g of maleic anhydride 
and 2.8 g of benzophenone in 265 ml of benzene in a stoppered Pyrex tube 
to direct sunlight for 78 hours. I refluxed a solution of 29.4 g (0.3 
mole) of maleic anhydride and 3.56 g (0.02 mole) of benzophenone in 800 ml 
of benzene in a Pyrex 2 liter Erlenmeyer flask by irradiating at the 
bottom of the flask with a G.E. sunlamp for 16 hours. The dianhydride was 
filtered; 39 g, 95 mole %. 
EXAMPLE II 
A mixture of 18.7 g (0.068 mole) of the dianhydride of Example I, 40 ml of 
allyl alcohol, 30 ml of toluene, and 1 g of p-toluenesulfonic acid was 
refluxed for 18 hours with a Stark-Dean water trap. Water, 3 ml, was 
collected in a trap. The cooled mixture was washed with 2N NaOH, twice 
with water, dried over anhydrous sodium sulfate, filtered, and distilled 
to a pot temperature of 125.degree. C. at 200 torr. The residue 
crystallized slowly. It was slurried with ether:hexane 1:1, chilled at 
-60.degree. C., and filtered, giving 22.7 g white crystals of tetraallyl 
tricyclo(4.2.2.0.sup.2,5)dec-9-ene-3,4,7,8 tetracarboxylate mp. 
68.degree.-69.degree. C. Analysis: Calcd. for C.sub.26 H.sub.30 O.sub.8 : 
C,66.4; H,6.4. Found: C,66.4; H,6.7. 
EXAMPLE III 
A mixture of 19.9 g (42.68 mmoles) of the tetraallyl ester of Example II, 
24.67 g (169 mmoles) of n-octyl mercaptan, 100 ml of benzene, and 10 ml of 
0.25% Rose Bengal in acetone was shaken in a Parr Instrument shaker at 
25.degree. C. under 25 psig O.sub.2 and irradiation with a G.E. sunlamp. 
Over 96 hours 7 lb. O.sub.2 were absorbed. The solution was filtered and 
evaporated in a Rinco evaporator at 40.degree. C. and 0.2 torr to give the 
product I where R=n-C.sub.8 H.sub.17, 43.86 g, 95 mole %, as a 
light-brown, viscous oil. Analysis: Calcd. for C.sub.58 H.sub.102 S.sub.4 
O.sub.16 : C,58.9; H,8.6; S, 10.8. Found: C,59.7; H,8.9; S, 11.2. 
EXAMPLE IV 
Interfacial tension of the compound of Example III was determined at 1 
(wt)% concentration between solvent-extracted 5W oil and double-distilled 
water. The control contained no compound of Example III. A Cenco-Du Nouy 
Interfacial Tensiometer No. 70545 with a 6 cm platinum-iridium ring at 
25.degree. C. was used with these results: 
______________________________________ 
Interfacial Tension, 
Product of Example No. 
dynes/cm 
______________________________________ 
Control 41.73 
III 3.87 
______________________________________ 
EXAMPLE V 
The compound of Example III was tested in the vial test as cosurfactant for 
enhanced oil recovery, using 5% petroleum sulfonate as surfactant in 0.8N 
brine (NaCl), adding the cosurfactant to surfactant at a ratio of 1:20, 
and noting the stability of the mixture, as brine tends to cause the 
surfactant to separate (salt) out. The brine-surfactant-cosurfactant 
mixture, 20 ml, was then mixed by shaking with 2.5 ml of crude petroleum 
and the interfacial tension (IFT) observed. Low IFT was indicated by easy 
mixing of the two phases with no separation. Formation of round oil 
droplets that separate quickly indicates a high, ineffective IFT. 
Product of Example III proved effective in lowering the IFT in the vial 
test, giving mixtures of brine-surfactant-cosurfactant fluids which were 
stable, did not separate, and easily formed mixtures of the fluid with 
crude petroleum. 
EXAMPLE VI 
Control of microorganisms in inhibiting or preventing growth of fungi in 
enhanced oil recovery operations is a desirable characteristic of useful 
additives. 
The product of this invention was tested as a biocide and inhibitor for the 
growth of microorganisms by this test: 25 g of agar preparation were 
placed in standard petri dishes. The agar preparation consisted of 23.5 g 
of Bacto Plate Count Agar, Difco Laboratories, Detroit, Mich., dissolved 
in 1 liter of water. Plate Count Agar contains a standard USP formula for 
nutrient agar, consisting of: 
5 g--Pancreatic digest of casein 
2.5 g--Yeast extract 
1 g--Glucose 
15 g--Agar 
Four petri dishes were untreated and used as blanks. To the others, in 
duplicate, were added 2.5 ml of 1% acetone solutions of the product of 
Example III. All plates were uncovered for 4 hours to expose them to the 
spores of adventitious fungi and bacteria, then covered and stored at 
30.degree. C. for 6 days. Ratings were given at this point; 0 represents 
no growth, 5 shows luxuriant colonies of fungi and bacteria. Results were 
as follows: 
______________________________________ 
Product of Example No. 
Growth 
______________________________________ 
Control 5,5 
III 0,0 
______________________________________ 
EXAMPLE VII 
A micellar slug for micellar flooding consisting of 3 (vol)% petroleum 
sulfonate as surfactant, 2 (vol)% petroleum hydrocarbon, 1 (vol)% 
cosurfactant comprising a 3-sulfoxy-1,2-propylene glycol-1-ester, prepared 
from the allyl esters of 
tricyclo(4.2.2.0.sup.2,5)dec-9-ene-3,4,7,8-tetracarboxylic acid and 
n-octyl mercaptan, in a 1.0N NaCl brine solution is prepared. The micellar 
slug fluid is fed into the high pressure injection pump and is injected 
into a 25 foot section sandstone formation in Crawford County, Ill., USA, 
through an injection well at 900 psig. The amount of slug injected is 
about 7% of reservoir pore volume, and the petroleum hydrocarbon is lease 
crude oil. Pattern of injection is two rows of injection wells and three 
rows of producer wells. There are nine wells in each row and total area 
enclosed is 40 acres. Injection and production wells are 460 feet apart 
and adjacent wells are 115 feet apart. Crude oil production increases to 
recover about 30% of the oil in place at start of the injection.