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Description  |
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BACKGROUND OF THE INVENTION
Oil is found in subterranean formations or reservoirs in which it has
accumulated, and recovery is initially accomplished by pumping or
permitting the oil to flow to the surface of the earth through wells
drilled into the oil-bearing stratum. Oil can be recovered from such
producing zones only if certain conditions exist. There must be adequate
permeability or interconnected flow channels through the pore network of
the oil-bearing stratums or "pay zone" to permit the flow of fluids
therethrough and recovery efficiency (RE).
In the primary oil recovery stage, the RE is influenced by the natural
energy or drive mechanisms present, such as water drive, gas cap drive,
gravity, drainage, liquid expansion, relative permeability of reservoir
formation, and combinations thereof within the formation and this natural
energy is utilized to recover petroleum. In this primary phase of oil
recovery, the oil reservoir natural energy drives the oil through the pore
network toward the producing wells. When the natural energy source is
depleted or in the instance of those formations which do not originally
contain sufficient natural energy to permit primary recovery operations,
some form of supplemental or artificial drive energy must be added to the
reservoir to continue RE. Supplemental recovery of enhanced recovery is
frequently referred to as secondary recovery, although in fact it may be
primary, secondary or tertiary in sequence of employment. Enhanced
recovery usually encompasses waterflooding or gas injection with or
without additives, and other processes involving fluid or energy injection
whether for secondary or tertiary oil recovery such as the use of steam or
heated water.
Secondary recovery is a term utilized to mean any enhanced recovery first
undertaken in any particular underground formation. Usually it follows
primary recovery but can be conducted concurrently therewith to expedite
production. Waterflooding is the most common method of secondary recovery.
Tertiary recovery refers to any enhanced recovery undertaken following
secondary recovery. Broadly, tertiary recovery encompasses such procedures
as miscible displacement, thermal recovery, or chemical flooding.
All of these procedures have been and, as noted, are being utilized to try
to recover as much oil as possible from any given formation, but none is
completely satisfactory. Many are expensive procedures not only in terms
of equipment to be able to enhance the recovery, but also in terms of the
chemicals and techniques utilized.
Perhaps most importantly it has been found that in many cases the
particular technique used is extremely limited in terms of type of oil
reservoir in which the recovery technique can be utilized and that a broad
procedure for universal use has not been found.
This is particularly true with respect to waterflooding; probably the most
inexpensive and widely practiced enhanced recovery technique. Water does
not displace oil with high efficiency since water and oil are immiscible
and the interfacial tension between water and oil is quite high.
Accordingly, waterflood has produced incremental oil recovery amounting to
about 10 to 15% of the original oil in place (OOIP) in the reservoir. In
efforts to increase the amount of oil displaced from the formation and
bring it to the surface, efforts have been made to utilize certain
chemicals, mostly surfactants, to decrease the interfacial tension (IFT)
between the injection water and the reservoir oil in order to displace and
trap the oil in the underground formation and bring it to the surface.
Such technique is referred to as surfactant flooding.
However, problems have occurred with such chemicals either because they are
not sufficiently active to adequately displace the oil or are costly. More
importantly, their effectiveness is limited by the reservoir
heterogeneity, various reservoir fluids, high salinity, high bivalent ion
concentration, high temperature, and continuous changes in such conditions
along the pore channels in the reservoir. The chemicals tend to be
unstable in or to be decomposed by such conditions and they suffer
chromatographic changes.
No satisfactory stable displacement material or technique has been found
which is economic, effective in the presence of highly concentrated brine,
high temperatures, and/or hardness of the reservoir water, or other
reservoir conditions.
SUMMARY OF THE INVENTION
The present invention provides a process and composition for the enhanced
recovery of oil from an underground source thereof, which process can be
utilized with highly concentrated brines, high temperatures, high divalent
conditions, and/or hard reservoir water.
Briefly, the present invention comprises a method for recovering petroleum
from an underground source thereof comprising injecting into said
underground source a displacement agent comprising a petroleum-displacing
fluid and a modified liposome.
The present invention also comprises a displacement agent for recovery of
petroleum from an underground source thereof comprising a
petroleum-displacing fluid and a modified liposome.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a chart showing presently available surfactants and their
applicability as versus salinity and temperature as compared to the
modified liposomes of the instant invention;
FIG. 2 is a graph of the coreflood results of Example 3A; and
FIG. 3 is a graph of the coreflood results of Example 3B.
DETAILED DESCRIPTION
The essential and unique aspect of the present invention is the use of a
modified liposome in an amount effective to enable enhanced oil recovery.
As used herein, the term "modified liposome" is intended to include all
phospholipid spheres, or vesicles, in which at least one acyl group has
been replaced by a complex phosphoric acid which have been modified;
replaced by a complex phosphoric acid ester. The most common phospholipids
and most suitable for the present invention are the .alpha. lecithins;
also referred to as phosphatidylcholines (PC), which are mixtures of the
diglycerides of stearic, palmitic, and oleic acids linked to the choline
ester of phosphoric acid. The lecithins are found in all animals and
plants such as eggs, soybeans, and animal tissues (brain, heart, and the
like) and can also be produced synthetically. The source of the
phospholipid or its method of synthesis are not critical, any naturally
occurring or synthetic phosphatide can be used.
Examples of specific phosphatides are L-.alpha.-distearoyl) lecithin,
L-.alpha.-(dipalmitoyl) lecithin, L-.alpha.-phosphatide acid,
L-.alpha.-(dilauroyl)-phosphatidic acid, L-.alpha.(dimyristoyl)
phosphatidic acid, L-.alpha.(dioleoyl)phosphatidic acid,
DL-.alpha.(dipalmitoyl)phosphatidic acid,
L-.alpha.(dipalmitoyl)-phosphatidic acid,
L-.alpha.(distearoyl)phosphatidic acid, and the various types of
L-.alpha.-phosphatidylcholines prepared from brain, liver, egg yolk,
heart, soybean, and the like, or synthetically, and salts thereof. Other
suitable modifications include the controlled peroxidation of the fatty
acyl residue cross-linkers in the phosphatidylchlorines (PC) and the
zwitterionic amphiphates which form micelles by themselves or when mixed
with the PCs such as alkyl analogues of PC.
The phospholipids can vary in purity and can also be hydrogenated, fully or
partially, but it is preferred to use the unhydrogenated phosphatides.
The liposomes can be "tailored" to the requirements of any specific
reservoir, to maintain the stability in water and hydrocarbon, without
aggregation or chromatographic separation, and remain well dispersed and
suspended in the injected fluid and the fluid in situ and changes thereof
in composition, as well as the temperature, salinity, bivalent ions,
relative permeability in the reservoir while simultaneously reducing the
interfacial tension between the oil and the brine to ultra-low values by
increasing the capillary number. The liposome can be used with or without
any other solvent or surfactant, without creating any ion exchange
problems and without plugging the porous media in the producing zone.
Another important consideration in the selection of phospholipid is the
acyl chain composition thereof. Currently, it is preferred that it have an
acyl chain composition which is characteristic; at least with respect to
transition temperature of the acyl chain components in egg or soybean PC;
i.e., one chain saturated and one unsaturated or both being saturated. The
possibility of using two saturated chains is not excluded.
The liposomes may contain other lipid components, as long as these do not
induce instability and/or aggregation and/or chromatographic separation.
This can be determined by routine experimentation.
A variety of methods for producing the modified liposomes which are
unilamellar or multilamellar are known and available:
(i) A thin film of the phospholipid is hydrated with an aqueous medium
followed by mechanical shaking and/or sonic irradiation and/or extrusion
through a suitable filter;
(ii) Dissolution of the phospholipid in a suitable organic solvent, mixing
with an aqueous medium followed by removal of the solvent; or
(iii) Use of gas above its critical point (i.e., freons and other gases
such as CO.sub.2 or mixtures of CO.sub.2 and other gaseous hydrocarbons).
In general, they produce liposomes with heterogeneous sizes from about 0.02
to 10 microns or greater. Since (as will be discussed below) liposomes
which are relatively small and well defined in size are preferred for use
in the present invention, a second processing step defined as "liposome
sizing" is for reducing the size and size heterogeneity of liposome
suspensions.
The liposome suspension may be sized to achieve a selective size
distribution of vesicles in a size range less than about 1 micron and
preferably less than about 0.05-0.1 microns. Liposomes in this size range
can readily be sterilized by filtration through a suitable filter. Smaller
vesicles also show a lesser tendency to aggregate on storage, thus
reducing potentially serious blockage or plugging problems when the
modified liposome is injected to the porous oil-bearing stratum. Finally,
liposomes which have been sized down to the submicron range show more
uniform distribution.
Several techniques are available for reducing the sizes and size
heterogeneity of liposomes, in a manner suitable for the present
invention. Ultrasonic irradiation of a modified liposome suspension either
by standard bath or probe sonication produces a progressive size reduction
down to small unilamellar vesicles (SUVs) between about 0.02 and 0.08
microns in size. A sonicating procedure used to produce SUVs is described
in Example 1. Homogenization is another method which relies on shearing
energy to fragment large liposomes into smaller ones. In a typical
homogenization procedure the modified liposome suspension is recirculated
through a standard emulsion homogenizer until selected liposome sizes,
typically between about 0.1 and 0.5 microns are observed. In both methods,
the particle size distribution can be monitored by conventional laser-beam
particle size determination.
Extrusion of liposomes through a small-pore polycarbonate filter or
equivalent membrane is also an effective method for reducing liposome
sizes down to a relatively well-defined size distribution whose average is
in the range between about 0.03 and 1 micron, depending on the pore size
of the membrane. Typically, the suspension is cycled through one or two
stacked membranes several times until the desired liposome size
distribution is achieved. The liposome may be extruded through
successively smaller pore membranes, to achieve a gradual reduction in
liposome size.
Centrifugation and molecular sieve chromatography are other methods which
are available for producing a liposome suspension with particle sizes
below a selected threshold less than 1 micron. These two respective
methods involve preferential removal of large liposomes, rather than
conversion of large particles to smaller ones. Liposome yields are
correspondingly reduced.
The size-processed liposome suspension may be readily sterilized by passage
through a sterilizing membrane having a particle discrimination size of
about 0.2 microns, such as a conventional 0.22 micron depth membrane
filter. If desired, the liposome suspension can be lyophilized for storage
and reconstituted shortly before use.
As previously noted, the modified liposomes can be utilized with any of the
enhanced recovery techniques. If utilized in the primary recovery where
waterflooding is also utilized it can be incorporated into the waterflood.
In cases in which brine solutions and even highly concentrated brine
solutions are to be utilized, the modified liposome of the present
invention can be utilized either alone or as part of any conventional
surfactant system, whether it be a carboxylate surfactant system of one
utilizing lyotropic liquid crystals of any type. Such surfactant systems
often contain chlorinated hydrocarbons and/or alcohols, polyethoxylated
alcohols, alkyl phenols or other alkylaryl compounds. A common dual
surfactant system is described in U.S. Pat. No. 3,811,505 in which an
ionic surfactant as an alkyl or an alkylaryl sulphonate is used together
with a nonionic surfactant such as a polyethoxylated alkyl phenol or
polyethoxylated aliphatic alcohol. Another dual system is described in
U.S. Pat. No. 3,811,507 utilizing again an ionic surfactant such as a
sulphonate and a sulphated polyethoxylated aliphatic alcohol. A
three-component surfactant system is described in U.S. Pat. No. 3,811,504
which includes an anionic surfactant and sulphated polyethoxylated
aliphatic alcohol, and a nonionic surfactant. While generally
satisfactory, such are not effective when used for enhanced oil recovery
with a high salinity flood and/or high calcium and magnesium water and in
formations with temperature greater than 70.degree. F.
It has been found that these surfactants can be replaced, in whole or in
part, by modified liposome composition of the present invention, either
alone or in combinations with conventional chlorinated hydrocarbons or
alcohols that have been employed in underground oil-containing formations.
It has been found that the modified phosphatides of the present invention
are stable not only in high concentrations of saline but also are
effective even in hard water; that is, those containing large amounts of a
polyvalent metal such as calcium and magnesium. Further the phosphatides
of the present invention permit flooding in oil-bearing formations whose
temperature ranges from 70.degree. to about 350.degree. F. The amount of
modified liposome in the waterflood can be as low as about 0.5 and up to
100 pore volume percent. While large volumes can be used, such is
uneconomical. For waterflooding the modified liposome can be utilized in
any of the conventional waterflooding procedures. The liposome can be
added directly to the water flood as in low tension flooding or as a slug
as is done with some waterflooding techniques.
The modified liposome of the instant invention can also be used with the
LPG or other gas miscible slug process. In the LPG technique a liquefied
petroleum gas (LPG); such as ethane, propane, or butane, immiscible with
the typical reservoir of oil and equal to about 5% of pore volume, is
injected into the well and then this slug is followed by either a natural
gas or gas and water which pushes the slug through the reservoir. Since
LPG products are "first contact" miscible with the oil, meaning that they
are miscible with the oil immediately upon contact, they will pick up the
oil as a bank in front of the slug. The slug is maintained in a liquid
state in order to maintain its miscibility with the oil in the underground
formation by maintaining it under the pressure necessary to keep it
liquid. For propane, for example, this is about 1,000 to 1,300 psi or
higher at typical oil reservoir temperatures.
With the instant invention the efficiency of recovery by these methods is
greatly increased. Heretofore there were unsatisfactory area sweep
efficiencies and a correspondingly low overall efficiency of such process
of enhanced recovery. It is believed that this is due based on the fact
that it is known in oil recovery procedures that an oil displacement
process is most efficient when the viscosity of the displacing fluid is
equal to or greater than the viscosity of the displaced fluid. Since gas,
whether LPG or any of the other gases, is used for recovery such as carbon
dioxide, nitrogen, or light hydrocarbons is less viscous and more mobile
than most of the crude oils in the reservoirs, they are not efficient oil
displacement agents. By adding modified liposomes of the present invention
to the gas-water flood recovery, the process is greatly improved. It has
also been noted that the amount of gas need to obtain high oil recovery is
also decreased inasmuch as the presence of the modified liposome causes
the gas to be confined to the zone of interest and prohibits the gas from
channeling through high permeability strata and thereby becoming lost or
unavailable for oil recovery. The modified liposomes can be introduced
either in the gas slug or directly into the reservoir by means of a water
or oil/water vehicle prior to, during, or even after as alternative slugs
of water and gas injection are made into the well. The amount of liposome
used will vary dependent upon the formation dynamics discussed and the
optimum amount can be determined by routine experimentation.
As noted, in addition to the LPG procedure, the use of carbon dioxide (as
disclosed, for example, in U.S. Pat. No. 2,623,596 or U.S. Pat. No.
3,065,790) can be utilized for this miscible slug process. More properly,
such process, to distinguish it from LPG, is called the "carbon dioxide
miscible process". A modification of it using a lean gas, a process
developed by Atlantic Richfield Company, is referred to as the "high
pressure lean gas miscible process".
Flooding techniques in which micelle solutions are utilized are now
commonly accepted tertiary recovery procedures. Micellar flooding utilizes
micellar solutions in slugs followed by driving water in order to recover
the oil. Such micellar solutions conventionally are a combination of a
surfactant, a hydrocarbon, an electrolyte in order to adjust the viscosity
of the solution, and often a co-surfactant. This process is utilized in a
conventional flooding technique. That is, a slug of the micellar solution
is formed in the reservoir by injecting a volume of such micellar solution
into the formation. The slug moves through the formation displacing all of
the oil and water ahead of it toward the producing well. Conventionally,
the micellar slug is followed by a polymer slug or bank of thickened water
for mobility control and after sufficient polymer is injected, drive water
is used as in any conventional water flooding procedure. With the present
invention it has been found that increased recovery is obtained if, in
place of the conventional surfactants used in such micellar material, a
modified liposome of the present invention is utilized. Again, the optimum
amount used is determined by routine experimentation.
The present invention is also applicable to thermal recovery procedures
employing injection of hot fluids into the reservoir itself. Thermal
recovery by hot fluid injection utilizes either a hot water flood, cyclic
steam injection, or steam drive. Any of these procedures can be utilized
and more efficient recovery obtained if there is included a modified
liposome of the present invention in an amount sufficient to enhance
recovery.
The single figure of the drawing illustrates the zone in which the modified
liposomes can be utilized in surfactant flooding when considering a
combination of salinity and temperature. This operational zone is not
possible with present surfactants. At lower salinities (below 4 percent
Total Dissolved Solids), sulfonates can be used over a wide range of
temperatures. As used here, "sulfonates" refer to petroleum and synthetic
surfactants, both of which are available commercially today. At lower
temperatures and higher salinities, oxyalkylated sulfates and sulfonates
can be used, most often in combination with petroleum sulfonates. However,
sulfonates begin to have stability problems at temperatures above
120.degree. F. While they can be applied in typical field projects up to
150.degree. F., the amount of sulfate used must be increased to compensate
for loss from hydrolysis. Surfactants are not available for use under
high-salinity, high-temperature conditions. Note however that the modified
liposomes can be used in the very areas surfactants are not operative.
The present invention will be further described in connection with the
following examples which are set forth for purposes of illustration only.
EXAMPLE 1
Salinity scans, stability, (NaCl and CaCl.sub.2) of a number of modified
liposomes were conducted by mixing small volumes of the liposomes at the
specified concentration of salinity. Observations of any instability,
formation of a precipitate, film, etc., were made at 24 hours. The results
of a scan are shown in Table I.
TABLE I
______________________________________
Maximum salinity Tolerance
Sample Concentration %
NaCl % Ca + 2 (ppm)
______________________________________
G-2 1 15 500
5 15
G-4 1 32
5 32
G-10 1 15 5000
5 15 50000
______________________________________
Preparation of sampler G2, G4, and G10 is described in Examples 4 to 19.
EXAMPLE 2
Interfacial tension measurements (IFT) were conducted on Thermostated
University of Texas Spinning Drop Tensionmeter. The results of a number of
these tests are shown in Table II.
TABLE II
__________________________________________________________________________
Minimum Interfacial Tension Results
Sample
Conc.
Prep.
IFT NaCl
IsopropyI
Temp.
Size
No. % Method
Millidyne/cm
Oil
% Alcohol %
C. Micron
__________________________________________________________________________
G-1 2.5 A 16000 C8 0.5 NONE 22 NM
G-1 2.5 A 8700 C16
0.5 NONE 22 NM
G-1 2.5 A 12000 C8 0.5 IPA (5%)
22 NM
G-1 2.5 A 606 C16
0.5 IPA (5%)
22 NM
G-2 2.5 A 612 C8 0.5 NONE 22 NM
G-2 2.5 A 272 C16
0.5 NONE 22 NM
G-2 2.5 A 614 C8 0.5 IPA (15%)
22 NM
G-2 2.5 A 195 C16
0.5 IPA (5%)
22 NM
G-4 1.0 A >200 C16
22.0
NONE 22 >8
G-4 1.0 A >100 C16
22.0
NONE 60 >8
G-4**
1.0 B <1 C16
15-22
NONE 60 <1.2
G-4 1.0 B 200 C16
15 NONE 60 <1.2
G-10**
0.5 C 3 C16
12.7
IPA (10%)
60 <0.1
G-10 0.5 B 667 C16
15 NONE 22 NM
G-10**
0.5 B 16 C16
15 NONE 60 <0.1
G-10 0.5 C 214 C16
15 NONE 22 <0.1
G-10 0.5 C 214 C16
15 NONE 22 <0.1
G-11 0.05
C 5600 C8 13 NONE 60 <0.1
G-12 0.05
C 524 C8 13 NONE 60 <0.1
G-13A
0.5 C 168 C16
15 NONE 60 <0.1
0.25
C 1390 C16
15 NONE 60 <0.1
G-130**
0.5 C 3 C16
15 NONE 60 <0.1
0.25
C 57 C16
15 NONE 60 <0.1
0.125
C 42 C16
15 NONE 60 <0.1
0.0625
C 1000 C16
15 NONE 60 <0.1
G-14 * D 4500 C16
15 NONE 60 <0.1
G-17 * D 1753 C16
15 NONE 60 <0.1
G-18**
* D 3.2 C16
15 NONE 60 <0.1
G-19 * D 1686 C16
15 NONE 60 <0.1
G-21 * D 1251 C16
15 NONE 60 <0.1
G-22 * D 4200 C16
15 NONE 60 <0.1
__________________________________________________________________________
Method of preparation:
A Shaken or stirred with magnetic stirrer.
B Sonicated in 5% to 15% NaCl.
C Precipitated from an isopropyl alcohol solution in water with
agitation.
D Soybean phosphatide fractions separated by chromatograph on silicic
acid column.
*Mole concentration in a drop of oil.
**Low IFT suitable for oil recovery
The preparation of the samples is described in Examples 4 to 19.
EXAMPLE 3
The following procedure was used in preparing waterwet Barea sandstone
cores used for flooding according to the present invention. Barea cores,
10 inches long and 1.5 inches in diameter were fired at 800.degree. F. for
24 hours. The cores were cooled and weighed to determine the dry weight
before saturation with brine of the desired concentration. The cores were
placed in an evacuation chamber and a vacuum of about 1 mm was pulled on
the core for 2 hours. The core was saturated under partial vacuum with
degassed brine and allowed to remain under vacuum for about one hour. The
core was removed from the evacuation chamber and weighed to determine
saturated core weight. The pore volume of the core was calculated by the
relationship: brine saturated core weight (g) - dry core weight (g),
divided by the density of the brine (g/ml) equals the core volume (ml).
The core was then mounted wet in Hassler sleeve and brine (about 2 pore
volume) was pumped through the core before determining the original
permeability to brine. The Hassler is thermostatically heated to stimulate
reservoir temperature.
The brine-saturated core was oil flooded at about 30 ft/day to remove all
the displaceable brine. The oil-flood was carried out using a recycling
oil system and required about 24 hours. The total brine displaced by the
oil saturation was used to calculate initial oil saturation (Soi).
Optionally, oil permeability was determined in a manner analogous to that
used above for establishing original permeability to brine. Prior to
waterflood, the core effluent line was air blown to remove oil.
The oil-flooded core was waterflooded at 3 to 5 feet per day, until the
effluent brine/oil ratio is greater than 99:1. The total oil displaced is
measured and Sow (oil saturation at the end of the waterflood) is
calculated. The residual oil volume remaining in the core is calculated by
subtracting the volume displaced by the waterflood from the water volume
displaced by the oil flood. If desired, water permeability after
waterflood can be determined in a manner analogous to that used above for
original permeability to brine. Cores were routinely conditioned in this
manner prior to carrying out the flooding tests. At this point, the core
simulated an oil reservoir that had been exhaustively waterflooded.
The slug containing the modified liposome is injected at a slower rate,
corresponding to field flow rate of either 1.5 or 1 foot/day as stated for
the pore volume specified. The slug may optionally contain a mobility
buffer or be followed by a mobility buffer. Oil recovery from the core is
measured to determine Soc (final oil saturation after chemical flooding).
Oil recovery efficiency of the chemical flooding (Re) is calculated as
(Sow-Soc/Soc).times.100.
The following are the examples of displacement experiments which
demonstrate the feasibility of the present method.
A. A coreflood (GH-3) at 60.degree. C., using hexadecane as the oil and 15
wt/vol % NaCl as the brine was prepared as above and waterflooded to
residual oil saturation. A displacement experiment conducted at 1.5 ft/d
used a formulation (2.2 pore volume slug) of 0.5% G-4 in 15% NaCl. G-4 was
sonicated to produce a dispersion that would easily filter through 0.2
micron filter paper. The IFT at ambient was 0.041 dyne/cm and less then
0.001 dyne/cm at 60.degree. C. The injected formulation had a viscosity of
1.1 cp. A mobility buffer (1.47 pore volume) of FLOCON 4800 biopolymer
having a viscosity of 11.2 cp. was injected to displace the liposome. An
additional polymer slug containing 3% IPA and FLOCON 4800 was then
injected for one pore volume in an attempt to displace the liposome. A
summary of the coreflood and oil/water ratio is presented below.
______________________________________
Core Soi Sow Soc Re
______________________________________
GH-3 66.2 27.2 24.4 10.3
______________________________________
FIG. 2 shows the coreflood results.
B. A coreflood (GH-5) at 60.degree. C., using hexadecane as the oil and 15
wt/vol % NaCl as the brine was prepared as above and waterflooded to
residual oil saturation. The displacement experiment conducted at one ft/d
shows the effect of a number of methods of liposome preparation. A
liposome formulation (1.1. pore volume slug) corresponding to 0.5% G-10 in
15% NaCl was prepared so that the dispersion would easily filter through
0.22 micron filter paper. The IFT at ambient was 0.667 dyne/cm and 0.0048
at 60.degree. C. and the formulation had a viscosity of 1.1 cp. A second
liposome slug prepared by sonication of G-10 was injected (0.7 pore
volume, 0.5% G-10 in 15% NaCl). This sonicated material filtered through a
0.22 micron filter but plugged a 0.1 micron filter after ca. 15 ml. A
third slug (one pore volume) of the sonicated G-10 was viscosified with
FLOCON 4800 biopolymer such that the viscosity of the resulting slug is
4.5 cp. at 60.degree. C. The resulting IFT of the viscosified liposome
slug was higher, 0.0184 dyne/cm at 60.degree. C. A fourth slug containing
just FLOCON 4800 was then injected for 0.7 pore volume. A summary of the
coreflood and the oil/water ratio is presented below.
______________________________________
Core Soi Sow Soc Re
______________________________________
GH-5 66.77 34.45 26.01
24.49
______________________________________
FIG. 3 shows the coreflood results.
EXAMPLE 4
400 g of crude soybean phosphatides were dissolved in 600 ml of chloroform
and 1,200 ml of methanol were added, with stirring. A precipitate formed
and settled to the bottom of the flask. The supernatant was decanted and
the sediment washed with 300 ml of methanol. The combined solvents were
evaporated in vacuo. Yield of purified phosphatides (G-4); about 300 g.
EXAMPLE 5
500 g of crude soybean phosphatides were stirred vigorously with two liters
of acetone. A precipitate formed and settled to the bottom of the flask.
The supernatant was decanted and the sediment further washed with 1/l of
acetone. The precipitate was dissolved in 600 ml of chloroform and 1,200
ml of methanol was added. The precipitate which formed was washed twice
successively with 300 ml each of methanol. The combined solvents were
evaporated in vacuo. Yield of purified phosphatides (G-2); about 200 g.
EXAMPLE 6
500 g of crude phosphatides were stirred vigorously with 2/l of acetone. A
precipitate formed. The supernatant was removed and the precipitate washed
with 1/l of acetone. After decanting, the precipitate was dried in vacuo.
The yield of these deoiled phosphatides (G-5); about 350 g.
EXAMPLE 7
The partially purified phosphatides (as per Example 5) were dissolved in a
suitable solvent (e.g. dichloromethane; chloroform or ethanol) and
filtered through a column of dry alumina (aluminum oxide for column
chromatography) or, alternatively, through a mixture of alumina and
silica. The solvent was evaporated in vacuo, yielding (G-10).
EXAMPLE 8
5 g PC (as per Example 7) were dissolved in 350 ml of diethyl ether. Five
hundred mg of phosphiliphase A2 (of Crotalus admanteus or other similar
snake venom) was added, followed by 90 ml of 5 mM CaCl.sub.2 and 1 ml of
concentrated ammonium hydroxide. After stirring for several hours at room
temperature, the ether was evaporated in a stream of nitrogen or air and
the water in vacuo. The residue was dissolved in a mixture of chloroform
and methanol, 9:1, and applied to a column of alumina. Increasing
concentrations of methanol in chloroform were applied and the fractions
tested for presence of lysophospholipid using thin layer chromatography
plates (eluent chloroform-methanol-H.sub.2 O, 60:35:4, by volume). Most of
the lysolecithin (G-11) was eluted in a mixture of 70-80% of methanol and
20-30% chloroform.
EXAMPLE 9
25 g of crude soybean phosphatides were treated with 200 ml of acetone;
after decanting the supernatant, the sediment was again treated with 50 ml
acetone. The residue was dried in vacuo and dissolved in 45 ml of
chloroform, 30 ml of which were applied to a column of silicic acid (Merck
60) and eluted with 200 ml each of the following mixtures of chloroform
and methanol (by volume). 100:0; 90:10; 90:10; 80:20; 70:30; 60:40; 50:50;
40:60; 30:70: 20:80. This was followed by two fractions of 200 ml each
methanol. Each fraction (G-13 to G-22) was evaporated under nitrogen and a
portion applied to thin layer plates of silica gel.
EXAMPLE 10
3 ml of the chloroform solution of the deoiled crude soybean phosphatides
(as per Example 5) were evaporated under nitrogen, 5 ml of 0.4 N KOH in
90% methanol were added and the solution heated for two hours at
45.degree. C. 5 ml of chloroform and 5 ml of water were added and, after
stirring on a cylcomixer, the phases were separated. The lower
chloroform-rich phase was chromatographed on this layer plates of silica
gel and the respective plates sprayed with ninhydrin and phosphorous
sprays. This provided alkali resistant compounds present in the hydrolyzed
esterified crude soybean phosphatides.
EXAMPLE 11
1.5 g of purified soybean phosphatidylcholine (PC) was dissolved in
chloroform methanol. Glass beads were added, the solvent was removed in
vacuo and the residue dried in high vacuum for about 2 hours. The dried
residue was covered with about 300 ml of 13% NaCl and the mixture shaken
for 1 hour at 37.degree. C. resulting in multicellular liposomes of
soybean PC.
EXAMPLE 12
1.5 g of purified soybean PC was dispersed in 25 ml diethylether and 25 ml
of 13% NaCl. After subjecting to sonic vibrations (in a sonic bath) for 20
minutes, the mixture was shaken for 30-60 minutes at 4.degree. C. and the
ether evaporated under a steam of N.sub.2 and then in vacuo. The final
dispersion of stable plurolamellar vesicles (SPLV) was diluted with water
or 13% NaCl to a final volume of 300 ml.
EXAMPLE 13
The stable plurolamellar vesicles of soybean PC (SPLV) were extruded
through a 0.1 M polycarbonate filter using a pressure of 50-100 psi,
thereby reducing the size of the SPLV.
EXAMPLE 14
1.5 g of purified soybean PC was dispersed in 300 ml of 50 mM Tris-HCl pH
7.5 containing 15 mg FeSO.sub.4 and 200 mg ascorbic acid. After incubating
for 90 minutes the reaction was stopped by adding EDTA to a final
concentration of 2 mM. The peroxidation of the polyunsaturated fatty acyl
residues of soybean PC was followed in a spectrophotometer at 232 nm.
EXAMPLE 15
Small unilamellar vesciles (SUV) of purified soybean phosphatidylcholine
were prepared in 13% NaCl. The diameter of the vesicles was determined by
turbidity measured as absorption at 330 n. After 6 months at 4C it was
again checked and found to have increased in size by less than 20%.
EXAMPLE 16
SUV of purified phosphatidylcholine were prepared in 13% NaCl an stored at
4.degree. C. When CaCl.sub.2 (0.5-5%) was added to the vesicular
dispersion, no visible changes in the apparent size of the dispersion were
observed.
EXAMPLE 17
One g of ground Brea stone was wetted with 2 ml of 13% NaCl and stirred
with 8 ml of 0.5% purified soybean PC in 13% NaCl. After 15 minutes, the
stirring was stopped and; once the powdered stone settled down, a sample
was removed for phosphorus determination. The residual dispersion then
remained in contact with the powder for seven more days at room
temperature. At the following intervals: 3.5h; 24h; 2d; 3d; 4d; 5d; 6d;
and 7d. The mixture was stirred for several minutes and once the mixture
settled down samples were taken for phospholipid phosphorus determination.
About 30-35% of the PC was adsorbed onto the powdered stone in the initial
15 minutes and but little more adsorption occurred in the following seven
days.
EXAMPLE 18
10 g of purified soybean phosphatidylcholine (PC) was dissolved in 200 ml
of isopropyalcohol (IPA) and 400 ml water were added. The mixture was
heated until fully clear. Should some opacity occur, a few drops of
isopropyl alcohol (IPA) were added until the solution became fully clear.
This PC solution was then added, dropwise to 1,400 ml H.sub.2 O or salt
solution (e.g., 18% NaCl) with rapid stirring. Small unilamellar vesicles
formed immediately. The dispersion was extremely stable and could be
stored at room temperature or 4.degree. C. for a year without apparent
change in the size of the vesicles. The residual IPA (10%) could be
removed by dialyzing against water or salt solution. To prevent growth of
microorganism, sodium azide (0.1% w/v) was added as a preservative. The
dispersion whose vesicles have a diameter of about 0.5 m could be filtered
through polycarbonate filter with a pore size of 0.2 mM and was stable to
storage for at least 12 months in room temperature. It was not
precipitated by 0/5-5% NaCl.
EXAMPLE 19
SUV of soybean PC were prepared as per Example 18. The IPA were removed by
dyalysis against 13% NaCl and the vesicular dispersion was stored at
4.degree. C. When heated at about 50.degree. C., or more, the dispersion
became strongly opaque but when cooled to room temperature or when placed
in ice water, the opacity disappeared and there was a full reversal to the
slightly opalescent state of the small vesicles.
From the foregoing examples it is seen that the modified liposomes of the
present invention give the low interfacial tension necessary for good
enhanced oil recovery, require no co-solvents, and suffer no
chromatographic separation even under conditions of high salinity, high
temperatures, and/or hard water.
Also, the present invention is not limited to recovery of oils such as
light or heavy oils, but also to tars and as such the term "petroleum" is
used herein as a generic term to denote such oils and tars.
While the invention has been described in connection with a preferred
embodiment, it is not intended to limit the scope of the invention to the
particular form set forth, but on the contrary, it is intended to cover
such alternatives, modifications, and equivalents as may be included
within the spirit and scope of the invention as defined by the appended
claims.
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