Note: Descriptions are shown in the official language in which they were submitted.
10~i889Z
This invention relates to the treatment of oil wells
and more particularly to the removal of viscous crude oil,
waxes, asphaltenes and resins of petroleum origin from wells,
flow lines and the pore spaces in oil-bearing formations.
In the production of petroleum oil and/or gas from a
subterranean formation through a well bore leading to the
surface of the earth, difficulty is often encountered due to
the accumulation of heavy hydrocarbon deposits in flow passages
within the well, but more particularly within the pore spaces
of the oil-bearing formation itself. The accumulation of heavy
hydrocarbons such as waxes, asphaltenes and resin precipitates
of petroleum origin ultimately can result in plugging. Theæe
accumulations of heavy hydrocarbons are solid or semi-solid at
the conditions existing within the well and oil-bearing forma-
tion and can reduce the size of the passageways through which
the oil or gas ml~st flow Eventually, with continued produc-
tion, the well flow passages and the pores of the oil-bearing
formation become plugged or restricted. In aggravated cases, ~ -
accumulation of these heavy hydrocarbons can occur to the
extent that the fluid flow to the well, or within the well flow
passages, is completely restricted. -~
A variety of procedures to remove ~hese accumulations ~
of heavy hydrocarbons involving contacting the accumulations -
with solvents for heavy hydrocarbons are known to the art. ~ ~
Generally, expensive aromatic solvents like toluene, benzene, -
xylene and hydrocarbon distillates having high aromatic
contents, or mixtures of these aromatic compounds with diesel
or crude oil are employed. These conventional solvent composi- - -
tions are usually applied with pressure and in some cases ~ -
require preheating prior to injection into the well. One
drawback in prior art solvent treatments is the rapid swelling ~ - -
of the heavy hydrocarbon deposits in the pores of the formation
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when contacted with conventional solvent compositions. It is a
well known phenomenon that solids when contacted with solvent
must swell before they can dissolve. m e resulting swelled
deposits aggravate the plugging condition by more completely
filling the pore spaces. Any further solvent injection is use-
less unless sufficient pressure is available to overcome this
plugging. Even then, the tendency of the injected solvent
composition is to finger through the largest channel network in
the formation which offers the least resistance and to displace
10 these accumulations of viscous crude oil, waxes, asphaltenes `
and resin precipitates further away from the well, where they
may be in time dissolved and/or dispersed. However, such
finger channels may represent only a small fraction of the
total channel network of the formation. In most cases, this
gives satisfactory results for a short duration but upon return
of the well to production these finger channels become rapidly
plugged again.
In addition to the above described plugging problem,
all oil-bearing sand formations contain interstitial water in
the form of a continuous channel network. m is thin film of
water, which is generally immiscible with conventional
solvents, further retards the action of the solvents in dis-
solving the heavy hydrocarbons. m ere exists a need in the oil
recovery art for economical and effective solvent compositions
useful for removing heavy hydrocarbon accumulations which
avoid the disadvantages and drawbacks associated with the prior
known methods and solvent compositions for trea~ing oil wells. -~
Wç have now found an economical and effective method
for removing viscous crude oil, waxes, asphaltenes and resin
precipitates of petroleum origin from pore spaces of oil-
bearing formations through the use of novel solvent composi-
tions. These novel compositions are miscible with the
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interstitial water and penetrate the pore formation by usingthe interstitial water network as flow channels, thus effec-
tively dissolving the heavy hydrocarbon precipitates and
cleansing the pores without substantial fingering. These
solvent compositions comprise about 45 to 85 volume percent
of a normally liquid aliphatic hydrocarbon boiling within the
range of about 120 F. to about 550 F., about 5 to 45 volume
percent of a normally liquid aromatic hydrocarbon, about 0.5
to 6 volume percent of an ether of an aliphatic polyhydric
alcohol, and about 1 to 15 volume percent of a lower alkyl
monohydric alcohol.
In accordance with the invention, a subterranean
oil-bearing formation is treated by a procedure involving the
steps of contacting the oil-bearing formation with the solvent
composition of this invention. According to the present
invention, oil and gas wells can be treated without resorting
to the necessity of preheating the solvent prior to injection
into the well. Moreover, because of the particular effective-
ness of the present composition and its dissolving activity,
a substantial reduction in the required quantity of solvent
is realized, while still providing an excellent increase in
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productivity along with effective removal and elimination of
all objectionable deposits. The same general mode of opera-
tion can be employed in cleaning out tanks, pumps, refinery
equipment and like in which the heavy hydrocarbon accumulations
are present.
In treating wells to increase the production thereof,
various techniques may be employed ranging from simple appli-
cation of cold solvent to the tubing, pump and other pieces
of oil equipment to more complicated procedures directed to
treating the oil producing formation with the solvent at points
considerably removed from the well. It is generally preferred
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that the injection pressure be maintained below that necessaryto fracture the formation so that reasonably uniform penetra-
tion of the solvent composition into the formation matrix
occurs. After a time the rate can generally be increased as -
the matrix permeability increases due to the solvent action.
In some cases, where deeper penetration is required, standard
displacing fluids may be used to displace the solvent into
the formation. Fluids generally used for this purpose include
nitrogen, natural gas, filtered crude oil, ~erosene, water,
10 polymer solutions and the like.
The normally liquid aliphatic hydrocarbon component
of the present solvent system may be any normally liquid
aliphatic hydrocarbon boiling in the range of about 120 F.
to about 550 F. For example, kerosene or other aliphatic
hydrocarbon distillates derived from petroleum may be used,
but most preferable are aviation turbine fuels, and most pre-
ferred is Jet A, an aviation turbine fuel meeting ASTM standard
specification D-1655 entitled "Standard Specification for
Aviation Turbine Fuels", ASTM Standards, American Society for
Testing Materials, Part 17, November 1971, pages 554-556.
The aromatic hydrocarbon component of the present
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solvent system may be any normally liquid aromatic hydrocarbon
which has a boiling point above about 175 F., e.g., benzene, `
benzol, toluene, xylene, ethylbenzene, cumene, mesitylene,
propylbenzene, etc. Toluene is usually preferred.
The ether component may be any normally liquid
aliphatic ether of an aliphatic polyhydric alcohol which -`
contains at least one free hydroxyl group and has a boiling
point above 212 F. Ether-alcohols of this type containing ~`
30 less than about 20 carbons are useful and those containing
less than 12 carbons are preferred. Suitable ethers of this
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type include the mono-methyl, -ethyl, -propyl, and -butyl
ethers of ethylene glycol and diethylene glycol, and mono-
methyl and di-methyl, -ethyl, -propyl, -butyl ethers of
glycerol, th~ mono-methyl and -ethyl ethers of butanediol,
etc. Most preferred is ethylene glycol monobutyl ether.
The lower alkyl monohydric alcohol component may
contain from 1 to 6 carbon atoms. Preferred alcohols are,
for example, methanol, ethanol, propanol, butanol, etc.,
most preferred, however, is isopropanol.
The proportions in which the foregoing components
are mixed to prepare the new solvent sy~tems are approxi-
mately as follows:
Percent by Volume
Aliphatic hydrocarbon 45-85
Aromatic hydrocarbon 5-45
Ether of an aliphatic 0.5-6
polyhydric alcohol -~
Alkyl monohydric alcohol 1-15
The solvent composition of this invention can be
prepared by simply admixing the ingredients in the desired
proportions.
A preferred solvent composition comprises from
about 50 to about 80 volume percent of normally li~uid ;
aliphatic hydrocarbon, from about 10 to about 30 volume per-
cent of normally liquid aromatic hydrocarbon, from abou~ 1
to about S volume percent of an ether of an aliphatic poly-
hydric alcohol, and from about 1 to about 10 volume percent
of an aIkyl monohydric alcohol.
A particularly preferred solvent of the present
invention contains 77 volume percent aviation turbine fuel
30 Jet A, 20 volume percent toluene, 1 volume percent ethylene ;~
glycol monobutyl ether and 2 volume percent isopropanol.
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The inventions are further described by the following
examples which are illustrative of specific modes of practicing
the invention and are not intended as limiting the scope of the
invention defined by the appended claims.
Example 1
A Dundee No. 2 sandstone core approximately 1 inch in
diameter and 1 inch long is mounted in a brass tubing with a
curable epoxy composition and cured for approximately 16 hours.
The core is saturated under vacuum with field brine, then im-
mersed in brine, heated to approximately 180 F. and restoredwith hot field crude oil. The field crude contains 7.3 weight
percent asphaltenes and 3.7 weight percent 132 F. melting
point paraffin wax. To this field crude is added 8 weight per-
cent of a 135 F. melting point fully refined paraffin wax.
The restored core is placed in a testing apparatus maintained
at 180 F. This testing apparatus comprises a hollow stainless
steel cylinder having a test core holding means; a test core
mounted in a brass tubing with thermoset resin; a solvent hold-
ing chamber above and in direct communication with the test
core; a top stainless steel closure with gas inlet means; and
a bottom stainless steel closure with outlet means. The system
is cooled to room temperature. Excess crude is removed from
the solvent chamber leaving approximately 1/8 inch layer of
gelled crude oil on the top of the core. Then the chamber is
filled with 85 milliliters of toluene. Nitrogen gas is injected
into the solvent chamber to maintain a pressure of S psi over -~
the solvent. All of the toluene passes through the core in
494 seconds. Distinct flow channels in the gelled crude oil
are noticed on the top face of the core. The bottom face of
the core sample is black show;ng only 4 light spots of approxi-
mately less than 1 square millimeter each.
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Example 2
The above test is repeated except that the toluene
is replaced by the solvent composition of this invention com-
prising an admixture of 77 volume percent of turbine fuel Jet A,
20 volume percent of toluene, 1 volume percent of ethylene
glycol monobutyl ether and 2 volume percent of isopropanol.
All of the solvent composition passes through the core in 313
seconds. Upon inspection the sand is fully exposed on the top
face of the core and there is essentially no gelled crude oil
remaining. On the bottom face the sand is clean and only
slightly brown colored. These comparative tests clearly indi-
cate the superiority of the present solvent composition in
removing crude oil, waxes, asphaltenes and resin precipitates
of petroleum origin from pore spaces of oil-bearing formations
as compared with a conventional solvent.
Example 3
A well was producing 17 API gravity crude at an
average rate of 90 barrels per day. The production had declined
rapidly. An attempt to stimulate production with both hot oil
and acid dispersion treatment was unsuccessful, and the produc-
tion dropped to 20 barrels per day when the well was completely
pumped off. The problem was diagnosed as plugging from waxes,
asphaltenes, and resin precipitates which had accumulated in
the formation around the well bore and blocked flow from the
formation. mis well is taken out of production and 5000 :
gallons of a solvent composition containing 77 volume percent
of aviation turbine fuel Jet A, 20 volume percent of toluene, -
1 volume percent of ethylene glycol monobutyl ether and 2
volume percent of isopropanol is injected into the well. The ~;
~0 well is shut in for about 6 hours, after which the well is - :
placed in production at around 80 barrels per day. After about
three months of production, the production is stabilized to
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10~892
about 45 barrels per day with fluid level 800 feet over pump.
This increase is not observed in the adjacent wells which are
not treated with the solvent.
As will be apparent to those skilled in the art, the
principle of the invention may be applied in various ways in
com~ination with various techniques to effect the removal of
crude oil, wax, asphaltene and resin precipitates of petroleum
origin, and the like, deposited from crude oil or petroleum
distillates and residua in a wide variety of inaccessible
places. In its broadest aspects, the invention consists of
the herein defined solvent mixtures comprising normally liquid
aliphatic hydrocarbons, normally liquid aromatic hydrocarbons,
ethers of aliphatic polyhydric alcohols, and alkyl monohydric
alcohols, and the method of removing waxes, asphaltenes and
resin precipitates of petroleum origin with said solvent compo-
sitions to effect their solution and/or dispersion therein.
Other modes of applying the principle of our invention may be
employed instead of those explained, change being made as
regards the materials or methods disclosed herein, provided
the steps or compositions set forth in any of the following
claims, or the equivalent of such steps or compositions, be
employed or obtained.
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