Note: Descriptions are shown in the official language in which they were submitted.
_IELD OF I~ INVENTION
This invention conc~rns an improved viscous fluid
and an enhanced oil recovery process using the 1uid. More
particularly, this improvement concerns a viscous, aqueous,
hydrophilic polymer-containing fluld, the fluid con~aining an
aromatic additive which protects the pol~mer from bacterial
attack and improves the injectability of the fluid and
reduces plugging sometimes experienced when similar fluids
are injected into subterranean formations.
BACKGROIJND OF THE INVENTION
Persons skilled in the art of recovering oil or
petroleum fxom subterranean formations ordinarily employ so-
called primary recovery techniques first, so long as oil may
be reco~ered under acceptable economic conditions thereby.
Once primary production is no longer economically feasible,
some form of supplemental or enhanced recovery is applied to
the subterranean formation. One of the earliest used and
most popular forms of enhanced recovery is water injection,
in which either fresh water or brine is injected into the
~0 subterranean fonmation to displace or push the residual oil
through the formation toward a spaced-apart production well,
from which it is recovered to the surface of the earth. Since
the viscosity of the oil present in the subterranean
formation is usually higher than the viscosity of water or
other aqueous fluids injected into the formation, there is a
strong tendency for the more mobile (less viscous) aqueous
fluid to bypass a substantial portion of the oil. This is
sometimes raferred to in the literature as viscous fingering.
The result is that only a portion of the residual oil is
displaced by the aqueous fluid.
1--
This problem h~s been recogniæed by persons skilled
in the art of oil recovery, an~ various literature references
describe method~ for increasing the ability of the flooding
medium to displace residual oil. Ik is well known in the art
of oil recovery and described in the literature pertaining
thereto ~hat incorpora~ion of sufficient ~nount of certain
polymeric materials in the aqueous flooding medium to
increase the viscosity thereof to a value more nearly equal
to or greater than the viscosity of the oil, reduces or
eliminates the tendency for the injected aqueous fluid to
bypass or finger through the residual oil in the formation.
Many substances have been disclosed in the literature for
incorporation in the flooding medium for the purpose of
increasing the viscosity of the injected fluid. U.S. Patent
2,827,964 and U.S. Patent 3,039,529 describe the use of high
molecular weight, partially hydrolyzed polyacrylamides as
thickening agents for a~ueous fluids employed in oil recovery
operations. U.S. 3,581,824 describes the use of heteropoly-
saccharid~s produced by fermentation of carbohydrates by
bacteria of the genus Xanthomonas for the same purpo~e.
It is important to recognize the difference between
the effect achieved by injecting a viscous, hydrophilic
polymer-containing fluid in~o a forma~ion as contrasted to
injecting an agueous fluid containing a surface active agent
i.e., a surfactant. The surfactant-containing fluid
decreases the interfacial tension between the residual oil
and the flooding medium in the flow channels through which
the fluid passes, and will therefore reduce the residual oil
in the portion of the formation contacted by the injected
surfactant fluid. A fluid containing any of ~he hydrophilic
4 ~ ~
pol~mers normally used for viscous floodlng oil recovery
methods daes not reduce the interacial tension between
residual oil and the injected a~ueous medium, and SG does not
reduce the oil saturation in ~he flow channels through which
it passes. The purpose for using a hydrophilic polymer-
containing fluid is to increase the number o~ flow channnels
contacted by the injected fluid, or to improve the volumetric
sweep efficiency of the oil recovery method. It is common
practice to employ both a surfactan~ solu~ion and a viscous,
hydrophilic polymer-containing fluid in an optimum state-of-
the-art chemical flooding process, although either may be
used alone without the other.
A~ueous fluids containing sufienct hydrophilic
polymer to increase the viscosity thereof to a value equal to
or greater than the oil viscosity for the purpose of
increasing the volumetric sweep efficiency, are commonly
referred to in the art as mobility control or mobility buffer
fluids. The ability of the variou~ classes of polymers
employed in mobility c~ntrol fluid to produce the desired
increase in the viscosity of the injected fluid depends on
various actors including the salinity of the aqueous fluid
present in the formation, the physical and chemical
characteristics o~ the formation, and the nature of the
residual oil.
It is recognized by persons skilled in the art of
enhanced oil recovery processes employing mobility control
fluids, that numerous problems are encountered in the use of
these fluids. Injectivity problems are sometimes encountered
due to improper hydration of the polymer, bacterial growth
and other contaminants.
Another important property of an aqueous mobili~y
control fluid relating to the flow resistance of the pol~ner
fluid through a porous medium such as a pe~neable,
subterranean oil-containing earth formation is recogni~ed and
a "screen factor" has been defined, which relates to the
ability of the fluid to flow under such conditions. The
scrPen factor is a measure of the viscoelastic behavior of
~he polymer fluid.
Another serious problem which has been recognized
as occuring in the use of all of the hydrophilic polymers
descxibed in the literature for use in mobility control
fluids, is bacterial degradation of the polymer contained in
the fluid, which causes loss in fluid viscosity. It is not
unusual for fluids injected into subterranean earth
formations for oil recovery purposes to remain in the
formation for many months or even years, and so the fluid
properties will be adversely affected even though the rate of
bacterial decomposition of the polymer is relatively slow.
Many methods have been described in the literature for
reducing the problem associated with bacterial decomposition
of hydrophilic polymers, but most which have been described
heretofore are either of limited effectiveness or are
prohibitively expensive.
DESCRIPTION OF PRIOR ART
U. S. 3,410,342 describes the use of organic
materials including benzene, toluene, or xylene to stabilize
the miscibility of the components of a surfactant fluid.
U. S. 3,800,877 describes the use of aldehydes such
as formaldehyde as an oxygen scavenger and bactericide for a
polymer fluid.
SUMMARY OF INVENTI~N
The present invention concerns a method of treatiny
an a~ueous, hydrophilic polymer-containing fluid with an
affective amount of an aromatic material.
The aromatic treating materials afford a very high
degree of protection against bacterial decomposition of the
hydrophilic polymer, thereby preventing decrease in fluid
screen factor and viscosity. '~hP affective aromatic
materials include benzene, toluene, ~ylene, and C1 - C5
alkyl-substituted benzene and toluene.
DESCRIPTION OF THE PREFERRED EMBODIMENT5
The present invention cencerns an improved aqueous
fluid containing a viscosifying amount of a hydrophilic
polymer, which fluid exhibits more stable injec~ivity
characteristics, and the screen factor and viscosity remain
constant over longer periods of time since the fluid is more
resistent to attack by bacteria present in oil field brines
or from surface contamination than presently-used fluids.
The fluid is especially suitable for use in an oil recovery
method in which the aqueous mobility control fluid is
injected into the formation for the purpose of increasing the
volumetric efficiency of the displacement process. The fluid
may be used as substantially the only fluid injected in~o the
formation, or it may be used in combination with, preferably
immediately aftex injection of, an aqueous fluid containing a
surface active agent or surfactant, which reduces the
residual oil saturation in the portion of the formation
contacted by the surfactant fluid. The fluid injected into
the formation may contain at least one surfactant and at
least one polymer.
_5_
4 ~ ~
One preerred class of hydrophilic polymers
suitable for use in carrying out the present invention,
include ionic polysaccharides such as those available
co~nercially which are produced by fermentation of
carbohydrates by bacteria of the genus Xanthomonas. Examples
of such heteropolysaccharides are those produced by action of
Xanthomonas Campestris, Xanthomonas Begonia, Xanthomonas
Phaseoli, Xanthomonas Hederae, Xanthomonas Incanae,
Xanthomonas Carotae, and Xanthomonas Translucens. Of these,
the preferred species is ionic polysaccharide B-1459, which
is prepared by culkurring the bacterium Xanthomonas
Campestris in NRRL B~1459, U. S. Department of Agriculture,
on a well aerated medium containing commercial glucose,
organic nitrogen sources, dipotassium hydrogen phosphate and
various trace elements. Fermentation is carried to
completion in four days or less at a pH of about 7 and a
temperature of 28C. Polysaccharide B-1459 is available
under the tradename Xanflood~ 9702 from Kelco Company.
Production of this and related heteropolysaccharides is well
described in Smiley, K.L. "Microbia Polysaccharide--A
Review", Food Technolo~y 20,9:112-116 (1966) and in Moraine,
R.A., Rogovin, S.P., and Smiley, K. L. "Kinetics of
Polysaccharide B-14S9 Synthesis", J. ermentation
Technolo~y, 44, page 311-132 (1966). Other fermented
polymers used for oil recovery such as that produced by the
fungus species sclerotium may be used in this invention.
- Another preferred class of hydrophilic polymer
which may be employed beneficially in the fluiding process of
this invention includes the commercially available, water
soluble high molecular weight, unhydrolyzed or partially
hydrolyze~ po]yacrylamides having molecular weights in khe
range of above 0.2 x 106, preferrably from 0.5 x 106 to 40 x
106, and more preferrably from 3 x 106 to 10 x 106. Co-
polymers of acrylamide and acrylic acid within the same
molecular weight range, may also be used. If the polymer
employed is a partially hydrolyzed polyacrylamide, up to
about 70% and preferably from 12 to 45% of the carboxylamid
groups are hydrolyzed to carboxyl groups. A number of
partially hydrolyzed polyacrylamides and or co-polymers of
acrylamide and acrylic acid are available commercially and
commonly employed for mobility control buffer fluid
formulation. These include, for example, materials marketed
by the Dow Chemical Company under the trade name "Pusher 700"
and "Cyanatrol" available from American Cyan~mid.
Nakurally occurring pol~n~rs may also be employed
as the hydrophilic polymer in ~his process. Included in this
class of effective materials are Guar gum, Locus Bean Gum,
natrual starches and derivatives thereo~, cellulose and its
derivatives including hydroxy ethyl cellulose.
Any of the above described materials may be
employed as the only hydrophilic polymer present in the
mobility control fluid utilized in the oil recovery process
aspect of this invention. It is well recognized that under
certain conditions, improved results are obtained when a
combination of two or more of the above-described hydrophilic
polymers are utilized in an aqueous fluid for oil recovery
purposes, and it is contemplated that this combination of
polymers is within the scope of the present invention.
I~ preparing the aqueous polymer-containing fluid
according to the process of this invention, one or more of
the above described hydrophilic polymers are dissolved in
water in any suitable fashion in order to provide an aqueous
li~uid having the desired viscosity. In oil recovery
processes, it is sometimes desirable to prepare the aqueous
fluid in a moderate salinity brine whose salinity is about
egual to the salinity of the water remaining in the formatio~
at the time ~he fluid is to be injected thereinto. Since the
salinity of the fluid affects the viscosity obtained from any
particular concentration of hydrophilic polymer, great care
must be taken to ensure that the resulting fluid viscosity is
sufficient to provide the desired bene~icial mobility ratio
between the injected fluid and the residual oil present in
the formation. One ef~ectlve method for preparing fluids for
injection into high salinity forma~ions, including processes
employing use of surfactant fluid injection, is to prepare
the mobility fluid using relatively fresh water, or in water
whose salinity is at least significantly less than the
salinity o the brine present in the formation at the time
the fluids are injected thereinto.
The concentration of polymer mixed with water or
brine to form the viscous a~ueous fluid can vary over a
fairly wide range, from about 50 part~ per million to about 5
weight percent, although the pre~erred range is ordinarily
from about 500 parts per million to about 3000 parts per
million. The controlling parameters are the resultant
viscosity of the solution, rather than any particular con-
centration, since the viscosity produced by addition of the
polymer varies with numerous factors. For oil recovery
purposes, the controlling factor should be, that the mobility
of the mobility buffer fluid is less than the mobility of the
residual oil present in the forma~ion under formation
conditions. Ordinarily this requires that the viscosity of
the polymer fluid be e~ual to or greater than the viscosity
of the residual oil, although other factors are well
recognized in the literature pertaining to polymer flooding
oil recovery mothods, and it is sometimes possible to
formulate an aqueous polymer fluid having the desired
mobility (less than ~he mobility of the oil present in the
formation) even though the viscosity of the polymer fluid i5
somewhat less than the viscosity of the petroleum. The
viscosities of polymer fluids commonly employed for oil
recovery purposes can range anywhere from several centipoise
to several hundred centipoise.
The total volume of polymer solution prepared and
injected into a formation in practicing this invention is in
the range of from about .05 to 1.0 pore volumes and
preferrably from 0.2 to 0.5 pore volumes based on the pore
volumes of the oil containing formation to be swept by the
oil recovery fluid. Of course, injection of larger amounts
of polymer fluid will not decrease the amount of oil
recovered, but the increased cost will make the economics of
the process quite unsatisfactory. It is common practice to
inject one or more slugs of polymer-containing fluid into the
formation and to displace that through the formation by
injecting field brine or other less expensive drive fluid. It
is also recognized that the concentration oE pol~mer may be
decreased in a continuous or step wise fashion from the
initial value to 0, thereby obtaining continuously efficient
displacement of the polymer fluid by the subsequently-
injected drive fluid.
The additive incorpora~ed in the pol~mer containingre~istance to bacterial degradation is an aromatic cornpound
having the following formula:
R~ ~ 2
~``J
I
R3
wherein R1, R2, and R3 are each hydrogen or C1 to C5 and
preferably Cl - C3 alkyl with the total number of carbon
atoms in Rl, R2 and R3 being from 0 to 5 and preferably from 0
to 3. Examples of preferred operable species are:
benzene
toluene
xylene
ethyl benzene
propyl benæene
propyl toluene
butyl benzene
butyl toluene
The concentration of any one or more of the above
described additives should be in the range from 0.001 to 0.2
and preferably from 0.005 to 0.15 percent by volume. The
above described additive may be incorporated in the water
prior to adding the polymer thereto, or it may be added
simultaneously with the polymer, or it may b~ added to ~he
fluid ater the polymer has been dissolved and or dispersed
in the water. It is understood that the above-stated
concentration range exceeds the solubility of some of the
aromatic compounds described above, particularly the alkyl-
substituted benzenes or toluene. I have found that the amount
-10-
4 4 ~
of aromatic compound added to the polymex fluid may exceed
the solubility without adverse effects of fluid properties.
The excess aromatic material is dispersed or emulsified in
the a~ueous phase. The presence of excess, undissolved
bactericide is sometimes an advantage, since loss of aromatic
compound ~rom the polymer fluid may occur in the formation,
and in such case, the excess aromatic bactericide then
dissolves in the fluid, thereby maintaining the concentration
of dissolved bactericide sufficiently high ta maintain the
bactericidal action.
As mentioned previously, the polymer fluid prepared
according to this invention may be injected into the
formation via one or more injection wells and displaced away
from the wells by injecting field brine or suitable drive
fluid, without injecting any other fluids. This process will
improve the volume of formation swept by the injected fluid,
but will not ordinarily reduce the oil saturation in the pore
spaces and flow channels of the formation contacted by the
1uid. This process will, however, by virtue of contacting
greater volumes of formation, recover more oil than could be
recovered under ordinary circumstances using water injection
alone. Still greater oil recovery is possible i the viscous
fluid is employed in combination with a fluid which reduces
the oil saturation in the portions of the formakion through
which the 1uid passes, such as an a~ueous fluid containing
one or more effective surfactants, or a miscible fluid such
as a hydrocarbon, or an emulsion or micellar dispersion
comprising both an aqueous surfactant-containing phase and a
hydrocarbon phase, all of which are well described in the
literature pertaining to enhanced oil recovery methods. The
polymer and suractant may also be incorporated in one 1uid.
4 ~ 4
The invention will be further described by the
following examples, which are illustrative o specific modes
of practicing the invention but are not intended to be in any
way limitative of the scope of the invention which is defined
by the appended claims.
FIELD EXAMPLE
For the purpose of illustrating a typical perferred
method of applying the process of th~ invention to a
subterranean oil containing foxmation, the following field
example is described.
A subterranean petroleum-con~aining formation is
located at a depth of 4700 feet, and the average thickness of
the formation is 38 feet. The porosity is 42% and the
permeability is 125 millidarcies. The oil contained in the
formation is 20 API gravity crude. This formation has been
produced ~y primary production processes until the oil
production rate has declined and the water- oil ratio has
increased to a point at which further oil production is
economically unfeasible.
The salinity of the water present in the formation
is approximately 1200 parts per million total dissolved
solids including 120 parts per million divalent ions,
principally calcium. It is determined that a suitable
mobility control fluid for ensuring a favorable mobility
ratio between an injected fluid and the residual oil in the
formation can be prepared using field water whose salinity is
800 parts pex million total dissolved solids, and having
dissolved or dispersed therein approximately 1000 parts per
million of a commercially available partially hydrolyzed
polyacrylamide. To this is added 1000 parts pex million
4 ~
toluene to prevent bacterial decomposition of the fluid, to
ensure a desireable screen factor, and to ensure that no
injectivity problems will be encountered during the time the
fluid is being injected into the formation.
Although the -tokal field comprises a numbex of ~ive
spo~ patterns, only one will be considered for this field
example. The wells are located on the corners of a square,
each side being approximately 120 feet in length, and with an
injection well centered at about the center of each square
grid. It is known tha~ the total volumetric efficiency of an
oil recovery process using a polymer fluid in this type
pattern is about 80%. Accordingly, the pore volume of
formation to be contacted by injected fluid in each grid unit
1 s :
120 ~ 120 x 38 x 0.42 ~ 0.8 = 183,859 square feet
One pore volume is eguivalent to 1,375,000 gallons of fluid.
The slug size of mobility buffer fluid e~ployed in
this test is appro~imately .05 pore volumes or 5 pore volumes
pexcent. Accordingly, the volume of the mobility buffer
~luid is ~8,772 gallons. This quan~ity of relatively fresh
water (salinity equal 800 parts per million total dissolved
solids) is utilized for preparing the fluid. The amoun~ of
polymer required to produce an average concentration of 1000
parts per million in this quantity of fluid is 573 pounds.
The same weight of toluene is added to the fluid at the same
time the polymer is added, and the fluid is mixed
sufficiently to produce a homogeneous fluid.
In this particular application, no surfactant or
other oil recovery agent is employed, and the polymer fluid
is injected into the formation and followed by injecting
-13-
;4~
field hrine of approximately lS00 parts per million total
dissolved solids. Brine injection is continued until the
~luid being recovered from the production well is in excess
of 99% by volume water, indicating that substantially all of
~he oil that can be recovered economically by this proce~s
has been recovered.
EXPE:RIl!~ENTAL SECTION
_
The following laboratory tests were performed to
demonstrate the benefits a~hieved by treatment of a~ aqueous
polymer-containing fluid with khe aromatic treating compounds
according to the process of this invention.
In the first series of experiments, the ability of
xylene to inhibit microbial growth in Xanflood polymer was
studied. A solution comprising 10,000 gm/m3 (1.0% by weight)
15 Xanflood~, a biopolymer, was prepared in deionized water.
Xylene was added to two samples of the concentrat~d polymer
solution, and the concentrate was stored for a pexiod of 5
days at room temperature. The concentrated polymer solution
was then diluted wi~h 800 parts per million total solid brine
to obtain a polymer concentration o l,000 gm/m3 (1,000 parts
per million). The fluid viscosity o~ the diluted ~amples was
measured, for the purpose of determining the rate of
viscosity loss o~ the polymer fluid which indicates the rate
at which the polymer in the concentrate has been decomposed
by bacterial action. Three concentrate sclmples were studied,
all containing lO,000 gm/m3 polymer, with xylene
concentrations of 0, 1,000 and 3,000 parts per million. The
following data were obtained:
-14-
4 A~ ~
TABLE I
INHIBITION OF MICROBIAL GROW'~l
IN A POLYMER WITfl ~fYLENE
Viscosity, cp Visco~i~y, ~p vi5c08ity, ~p
Con~rol 1,000 gm/m 3tO00 gm/0
Days Aged(NO Additive~ Xy1e~e Xylene
O 36.6 37.4 36.2
21.6 36.4 36.8
It can be seen from the foregoing that in only five
days, the pol~mer solution without xylene e~perienced a drop
in viscosity from 36.6 to ~1.6, a loss of 41% of its initial
viscosity. The sample containing 1,000 gm/m3 xylene
experienced only negligible, approximately 3.6% lose in
viscosity in the same five day interval. The sample
containing 3,000 ~m/m3 xylene lost essentially no viscosity,
indicating inhibition of microbial attack was complete. It
is concluded from this series of tests that xylen~ is a very
effective material for inhibiting the degradation of
Xanflood~ polymer by microbial action as is evidenced by
degradation in viscosity.
Another series of tests were conducted to determine
the ef~ectiveness of ~oluene for inhibiting loss of viscosity
due to microbial attack on a con~nercially available,
partially hydrolyzed polyacrylamide. The polymer
investigated was Cyanatrol WF 940S~ a hydrolyzed
polyacrylamide available from American Cyanamid Corporation.
The fluid was prepared by dissolving the partially
hydrolyzed polyacxylamide in a mixture of produced water and
field water, which mixture had a salinity of 3400 parts per
million ~otal dissolved solids. The fluid contained 1,000
gm/m3 Cynatrol~. One sample was prepared without a
stabilizing additive for use as a control, and another sample
contained one cubic cen-timeter toluene per 1,000 cubic
~15-
;4~
centimeters of fluid ( equivalent to 1000 parts per million
toluene). The viscosity and screen ~ac~or of the fluids were
determined ini-tially and again ater the flu:ids had been aged
for three weeks at ambient laboratory temperature. The data
are contained in Table II below.
TABLE II
THE EFFECTIVENESS OF TOLUENE
AS A BACTERACIDE FOR PARTIALLY
HYDROLYZED ACRYLAMIDE
10 SAMPLE VISCOSITY SCREEN FACTOR
c~ a~ 6 rDm
Inltial After 3 WksInitial After 3 Wks
CONTROL 3 32 11.5 17.0 8.9
1000 gm/m 33 32 17.0 16.g
Toluene
It can be seen from the above data that toluene was
essentially completely effective during a three week aging
period for stabilizing both viscosity and the screen factor,
whereas without additive, the viscosity of an otherwise
identical fluid dropped from 32 to 11.5 centipoise, a drop of
64% and the screen factor dropped from 17 to 8.9, a drop of
about 48%.
Another series of tests were conducted to verify
the effectiveness of toluene as a bactericide for use in
combination with partially hydrolyzed polyacrylamide polymer
under conditions approximating that which would be
experienced in the field. Solutions conkaining 1000 gm/m3
Cynatrol~ and 1000 gm/m3 toluene were prepared in field water
whose salinity was approximately 3400 parts per million total
dissolved solids. The viscosity and screen factor of the
toluene-protected polymer solution was determined initially,
as well as after aging 14 days and 30 days at 49C (120F).
The data observed in this series of tests are presented
below.
-16-
TABL~ III
Days ~gedViscosity Screen
at 49CmPa s (cP) at 10rpm Factor
o 30.3 14.6
14 30.1 12.8
33.1 1~.9
It can be seen from ~he foregoing data that toluene
was essentially completely efective for preserving viscosity
and screen factor values of the fluid over the 30 day period
at the elevated temperatures, since no loss in viscosity was
experienced and in fact a slight increase was obserYed,
although this difference is within the ~imits of experimental
error in determining viscosity. The screen factor declined
only very little from 0 to 14 days, and experienced no loss
from 14 to 30 days, indicatiny excellent stability of the
screen factox as well as viscosity.
Still another experiment was conducted to evaluate
the effectiveness of toluene as an inhibitor to prevent the
loss of viscosity, screen factor, and possibly other physical
properties as a result of biological degradation of a
partially hydrolyzed polyacrylamide polymer. In these tests,
several samples of solution were prepared containing 1000
parts per million Cyanatrol~, a commercially available
polyacrylamide sold by American Cyanamid. One sample was not
treated with a bactericide, to serve as a control to the
other experiments. The second sample was treated with 150
gm/m3 of Dowicide B~, a commercially available bactericide
sold by Dow Chemical Company for use as a bacterial inhibitor
for polyacrylamide. The third was treated with 1000 gm/m3
toluene. The observed data are shown below.
~ 1~5~
TABLE IV
EFFECTIV~NESS OF TOLU~N~ AS A
BACTERICI~E FOR POLYACRYLAMIDE
TIME CONTROL DOWICIDE B~ TOLU~,Na
Weeks Viscosity Screen Viscosity Screen Vi~c08ity Screen
- Factor Factor Factor
0 30.3 1~.6 37.0 1S.2 2~.5 14.4
1 17.5 ~
4 11.7 3.0 28.1 14.3 30.4 14.0
6 3.3 1.8 2~.7 13.3 27.7 13.4
It can be seen from the above the severe 105s in
both viscosity and screen factor of the control sample
containing no toluene or other ~actericide indicates th~
severity of the problem of microbial degradation. Dowicide B
provided good skability although the viscosi~y of the sample
treated with Dowicide B~ dropped from 37.0 to 28.8, a lose of
22%. A slight drop in screen factor was also observed. The
sample ~reated wi~h toluene experienced a drop in viscosity
from 28.5 to 27.7, less ~han a 3% decrease. The screen factor
similarly declined from 14.4 to 13.4, a decline of less than
7%.
The foregoing indicates that toluene is an
extremely effective inhibitor for preventing loss of
viscosity and screen factor, as well as deteriation of other
physical properties in the polymer solution as result of
bacterial attack. While the concentration level for
treatment of Dowicide B~ was considerably less than the
treatment level of toluene employed, the cost of treating a
solution under field conditions with 150 gm/m3 Dowicide B~
would be approximately $135.00 per 1000 barrels of polymer
fluid, versus only $23.00 for treating the same volume of
polymer fluid with 1000 parts per million toluene.
. . .
Accordingly, it can be seen that the process of this
inven~ion provides substantially improved cost effectiveness
-18-
for treating polymer solutions to prevent loss of physical
properties due to bacterial att~ck.
Another ~eries o~ tests were performed to determine
the effect of variations in concentration o~ toluene on its
effectiveness for stabilizing Xanflood~ polymer against loss
of filterability and viscosity as a result of microbial
attack. All of the solutions contained 1000 parts per
million polymer prepared in dionized water, plus the
indicated amount of toluene. The samples were aged at room
temperature for the periods indicated a~d the presence of
microbial growth was detected gualitatively based on visual
observation, odor, etc. The data are contained in Table V
below.
TABLE V
TOLUENE CONCENTRATION EFFECT
Concentration of Toluene Days Aged
gm/m3 3 10 24
0 (control) + ~ +
+ + +
+ + +
100 + ~ +
500 ~/_ +
1000 - - -
2000 _ _ _
3000 _ _ _
6000 - - -
= microbial growth observed
- = no visible sign of microbial growth
It can be seen from the data contained in Table V
above that toluene is inefective under these conditions o~
polymer concentration and salinity below about 500 parts per
million. Above 500 parts per million, toluene was ~uite
effective for preventing microbial growth over the time
period of these tests. The minimum concentration of toluene
needed for bactericidal action depends on the particular
-19-
polymer and brine, and protection is observed under other
conditions at concentrations far below 500 partg per million~
It is encouraging that over treatment causes no adverse
effects, although ordinarily the pre~erxed method of applying
the invention is to use only as much toluene as is necessary
to achieve the desired protection against microbial
decomposition under the conditions and or the time ~or which
the polymer containing fluid will be present in the
orma~ion.
Another series of test~ were performed to compare
performace of various level6 of toluene treatment in fresh
water and brine (111,000 ppm total dissolved solids.) In
these tests, the toluene was added to a 1% polymer
concentrate, and aged 24 days. Diluted samples were then
prepared and the physical properties measured. The data are
given in Table VI below.
-20-
TABLE VI
COMPARISON OF EFFECTIV~NESS
OF TOLVENE AS BACT~RIClDe IN
~R~SH WAT~R AND BRIN~ POI,~MRR SOLUTION
-
Fresh Wat~r Brine
__,
Toluene Days Filt.1 Visc.2 Apr.3 Filt.1 Visc.2 Apr. 3
- ~ Content Aged
0 0 8631.3 b 69 35 b
0 24 -- 1.4 a -- 1.6 a
101000 24 13330.9 c 124 36 c
2000 2~ -- -- 116 35.6 c
3000 24 -- -- -- 90 36.9 d
6000 24 -- - - 64 35 e
1 Filt. - volume (cc) filtered in 300 sec through 0.8
micron filter wi~h 20 psi pressure
2 Visc. - viscosity measured at 7.3 sec 1 (6 rpm) at am~ient
temperature
3 Apr. - appearance-
a = precipltate
b = slightly cloudy
c = very clear
d = clear
e = ~loudy
It can be seen from the foregoing that viscosity
and filterability, 1000 parts per million toluene is adequate
concentration to prevent loss of physical properties due to
microbial a~tack in fresh water. In the pol~mer fluid
prepared in brine, excellent st~bilization of viscosity
characteristics occurred in all four treating levels. The
cloudy appearance of the brine 1uids treated with 6000 parts
per million toluene suggests that this treatment level is
excessive for these conditions.
.
CONCLUSION
The use of from 10 to 2000 and preferably from
50 to 1500 parts per million of an aromatic treating agent,
preferably benzene, toluene, xylene, or short alkyl chain
substituted benzene or toluene efectively reduces lose of
4 ~. 4
viscosity and screen fac-tor of a hydrophilic pol~mer
containing solution due to microbial action under relatively
long term aging conditions.
While this invention has been described in terms of
S a number of illustrative embodiments, this is done for the
purpose of complete disclosure and is not intended to be in
any way limitative or restrictive of the scope of the
inven~ion. Many variations will become apparent to persons
skilled in the art of oil recovery, without departing form
the true spirit and scope of this invention. It is m~
intention that my invention be limited and restric~ed only by
those limitations and restrictions appearing in the claims
appended immediately hereinafter below.
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