Note: Descriptions are shown in the official language in which they were submitted.
~.o~6~9
This invention relates to a method for increasing the production of
fluids from subterranean fluid-bearing formations. More particularly, this
invention relates to a method in which the productivity of a hydrocarbon-
bearing formation containing acid-soluble components, and with or without
water-sensitive clays or shales, is improved upon treatment of the formation
with an aqueous solution of a non-oxidizîng mineral acid (or carbon dioxide)
and an antiscale as hereinafter describecl, said anti-scale compound effecting
:.
the elimination of plugging of capillary openings due to post-precipitation
`~ of dissolved salts subsequent to the acidization, as well as effecting elimi-
nation of mineral scale on production equipment such as pumps, or tubing,
caused by such precipitation.
- The technique of increasing the permeability of a subterranean
hydrocarbon-bearing formation and of removing obstructing acid-soluble mine-
ral scale for the purpose of stimulating the production of fluids therefrom
has long been practiced in the art. One such method, known as acidizing, is
`~ widely utilized in treating sub-surface acid-soluble geological formations,
, e.g., limestone, or dolomite. The technique is not limited to application in
formations of high acid solubility Sandstone and gypsum-containing forma-
tions may require acidization if the produced water is unstable with respect
to CaCO3. In the usual well-acidizing procedure, a non-oxidizing mineral acid
is introduced into the well and under sufficient pressure is forced into the
adjacent subterranean formation, where it reacts with formation components,
and dep~sited mineral scale, particularly the carbonates such as calcium car-
bonate, and magnesium carbonate, to form the respective salt of the acid, car-
bon dioxide and water. The usual mineral acid employed in such acidization
procedures is hydrochloric acid.
. .
~uring the acidizing process, passageways for fluid flow are created
or existing passageways therein are enlarged, thus stimulating the production
` of oil, water, brines and various gases. If desired, the acidization may be
carried out at an injec~ion pressure sufficiently great to create fractures in
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-- 1 --
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l~S~lLB~
- ~he strata or formation which has the desired advantage of opening up passage-
ways into the formation along which the acid can travel to more remote areas
from the well bor~, The salt formed upon neutralization of the acid is exten-
sively water-soluble and is readily removed by reverse flow from the formation
.
via the well bore.
There are9 however, troublesome complications attending ~he use of
hydrochloric acid or other similar non-oxidizing mineral acids. In the acidi-
zing process~ the following primary beneficial reaction occurs:
CaC03 + 2~1Cl ~-~ CaC12 ~ H20 + C02.
Under the higher pressures required ~o conduc~ an acidization, the C02 is
dissolved in the reaction mixture consisting of spent acid and connate water:
C2 ~ H20 ~ H2C3 ~ ~ H -1 HC03 ~ > 2H+ + C03 .
` The equilibria may be summarized and written:
Ca~HC03)2 ~ CaC03 + ~12C3 ~ ~120
. After acidization is completed, the well is often back-flowed in the
: case of a water injection well (in order to clean out formation and tubing)
-~ and put back on production in the case of a producing oil or gas well. In
.
- both cases, pressure diminishes, and C02 breaks out of solution, inducing
CaC03 to precipitate. Such precipitation, when it occurs within the capilla-
; 20 ries of a tight formation or on the tubing orannulus as a mineral scale, can
severely lessen the rate of production or injection by plugging such capilla-
ries or well equipment.
It is known that polyphosphates are effective in retarding CaC03
precipitation. These polyphosphates are unsatisfactory in acidic solutions
because they undergo rapid hydrolysis in the presence of mineral acid, and,
as a result, lose their scale inhibi~ing properties. In addition, one hydro-
lytic reaction product, the phosphate ion (P04 3), can precipitate with cal-
cium or barium ions present in the produced water, causing additional plugging
or scale deposition, further aggrava*ing the problem. Other known scale inhi-
bitors, are the "glassy" phosphates, which are unsatisfactory because of their
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~(~51~49
- slight solubility in acidic media and the tendency to form objectionable hydro- -
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lytic reaction products.
It is also known to employ various organic polymers to prevent the
.
precipitation of mineral salts, but many of these polymeric materials are un-
stable in mineral acids, undergoing spontaneous depolymerization to an ineffec-
tive species. Such a polymeric material which undergoes hydrolysis in the pre-
','
-~ sence of acids is polyacrylamide, which is unstable in aqueous media at tempe-
ratures of about 250F. and upwards. Many wells that may be treated by ~he
, method of the present invention have bottom hole temperatures of 250-300F.
or higher.
. Chemically altered natural polymers, and natural polymers themselves,:
are effective inhibitors to prevent the precipitation of mineral salts. How-
ever, some materials such as sodium carboxymethylcelluslose precipitate or de-
compose in the presence of mineral acids. Other known sequestering agents,
such as citric or tartaric acids, and/or complexing agents such as ethylene-
diaminetetraacetic acid and its water-soluble salts, are known inhibitors to
prevent the deposition of boiler scale in aqueous media. Such materials can-
notJ however, be employed in the treatment of subterranean formations, because
they are not appreciably surface active and do not adsorb on the formation
face.
The present invention provides a method for increasing the produc-
tion of fluids from a subterranean fluid-bearing formation containing acid-
- soluble components which comprises injecting into said formation an aqueous
acid solution comprising
~a) from 0.5 to 28% by weight of a non-oxidizing mineral acid
or from 0.01 to 5% by weigh~ of carbon dioxide, and
~b) from 0.005 to 2% by weight of at least one sulfonated anti-
scale compound of the formula
R-(OCH2CH2)n_S03 A (I)
wherein A is an alkali metal or ammonium ion, and
.'~
~L~5~649
-~ R is an alkaryl group having 6 to 18 carbon atoms in its alkyl moiety, or a
saturated or unsaturated aliphatic hydrocarbon group having 8 to 20 carbon
atoms
_ is a number from 1 to 10.
According to one embodiment of this invention, the production of
fluids from a subterranean fluid-bearing formation containing acid-soluble
components is increased by injecting the aqueous acid solution down the well
bore to said formation, and therefrom into said formation under a pressure
~, greater than the formation pressure, maintaining the solution in contact with
the formation strata for a time sufficient for the acid to react chemically
~ith the acid-soluble components of the fol~nation and/or acid-soluble mineral
scale deposited on production equipment9 to etch or enlarge passageways through
the strata and remove the scale, and thereby to increase subs~antially the
~ flow capacity of ~he subterranean formation.
: In accordance with another embodiment, the formation is penetrated
by at least one production well and one injection well, and said solution is
injected into said formation, and displaced through said formation, and fluids
from said formation are recovered through the production well. The anti-scale
compound prevents precipitation of compounds formed by the reaction of the
acid component, ~hereby permitting a substan~ial increase of production of
hydTocarbons from the formation via the production well.
When carrying ou~ the method of the invention, carbon dioxicle is
- concomitantly released~ whereby a beneficial effect, due to the mutual miscibi-
lity of carbon dioxide in the fluid phases, is realized as a reduction in vis- ;cosity and retentive capillary forces, while another beneficial effect is an
increased formation energy, due to the pressure generated by the released car-
bon dioxide.
Another advantage resulting from the employment of the method of
this invention in acidizing fluid-bearing formations is that the post-precipi-
tation of dissolved carbonates is prevented or materially decreased. Such
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- post-precipitation occurs because of the nature of the dissolution reaction:
Ca(~lC3)2 ; ' CaCO3 + 1~2 2
When pressure is released so that spent reaction products from the acidization
process can be removed, carbon dioxide gas can break out of solution, causing
post-precipitation of calcium carbonate. Such post-precipitation occurring
within the formation matrix near the bore hole can decrease pe~neability by
plugging the formation capillaries, par~icularly those near the well bore, and
result in a lower production rate. Furthermore, such post-precipitation can
occur in the tubing or annulus of the well itself and manifest itself as mine-
~t' 10 ral scale, reducing their diameter~s) and resulting in a lower production rate.
The anti-scale compounds are water-soluble sulfonated, ethoxylated,
alkylphenols or alcohols of the formula (I) defined above. A is preferably
sodium, potassium or ammonium. Mixtures of such compounds having different
values for R, n and A can be exployedif desired.
Examples of phenols that can be employed to make one group of anti-
scale compounds are straight and branched chain alkylphenols, such as hexyl-,
isohexyl-, heptyl-, octyl-, isooctyl-, nonyl-, decyl-, dodecyl-, tridecyl-,
tetradecyl-, and hexadecyl- phenol. The anti-scale compounds contain one or
more ethoxy groups attached to the alkylphenols. For example, the anti-scale
compounds may be di-, tri-, tetra-, penta-, hexa-, oc~a , nona-, and decaethoxy
; compounds which have been sulfonated. A pre~erred group of co~pounds include
the sodium and ammonium salts of sulfonated C8-C16 alkylphenols containing
from 3 to 10 ethoxy groups.
Representative examples of aicohol compounds useful in the practice
of the invention include the sulfonated, ethoxylated octyl, decyl, dodecyl,
tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl,
and eicosyl alcohols including the branched chain isomers thereof. The alcohol
can be either a primary or secondary alcohol or a mixture of any of these alco-
hols.
The ethoxy portion of the alcohol can be, for example, di-, tri-,
.,
. : .
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lQ51~4~
.,
tetra-, penta-, h0xa-, octa-, nona-, and deca-ethoxy.
A particularly preferred group are derived from Cl2-~18 primary al-
cohols and have from 3 to 10 ethoxy groups, and are especially the sodium and
ammonium sal~s of these materials.
. :.
~,~ According to one embodiment, the preferred aqueous acid composition
of this invention is one comprising an aqueous solution, which may include
brine, and from about 0.5 to about 28% by weigh~ preferably 3 to 15% by weight
~;i of a non-oxidizing mineral acid, such as hydrochloric acid or from about 0.01%
to about 5% by weight preferably 1 to 3% of carbon dioxide, and which contains
:~ 10 therewith between from about 0.005% to about 2% preferably from about 0.05% to
: about 1% by weight of the aforesaid compound (I).
Generally, the aqueous non-oxidizing mineral acid solution will con-
tain an inhibitor to prevent or greatly reduce the corrosive attack of the
acid on metal. Any of a wide variety of compounds known in the art and emplo-
yed for this purpose can be used, e.g., certain compounds of arsenic, nitrogen
or sulfur as described in U.S. Patent No. 1,877,504. The amount of the inhi-
bitor is not highly critical and it may be varied widely. Usually this amount
is defined as a small but effective amount, e.g., from 0.02% to about 2.0% by
weight.
In carrying out one embodiment of the method of this inven~ion a so-
lution containing the desired amount of the non-oxidizing mineral acid or car-
bon dioxide dissolved in water is first prepared. An inhibitor to prevent
corrosion by the mineral acid of the metal equipment associated with the well
is usually added with mixing in the next step. The anti-scale compound in an `
` amount within the stated concentration range is then admixed with the aqueous
acid solution. The thus-prepared acid solution is forced, usually via a suita-
ble pumping system, down the well bore and into contact with the production
equipment and formation to be treated. As those skilled in the art will rea- -
dily understand, the pressure employed is determined by the nature of the for-
mation, the viscosity of the fluid, and other operating variables. The acidi-
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zation method of ~his invention may be carried out at a pr0ssure sufficient
-:~- merely to pene~rate the formation, or it may be of sufficient magnitude to
. :;
overcome the weight of the overburden and create fractures in the formation.
Propping agents to prop open the fractures, as created, for example 20 to 60
mesh sand, in accordance with known fracturing procedures, may be employed in
admixture with the aqueous acidic solution. Generally, it is advisable to
allow the aqueous acid solution to remain in contact with the formation and
production equipment until the acid therein has been substantially depleted
by reaction with the acid-soluble components of the formation and the deposi-
ted scale. After this, the substantially spent treating solution is reversed
out of the ~ell, i.e., it is allowed to flow back out of9 or to be pumped out
-~ of, the formation. Further, as those skilled in the art will understand, the
concentrations of the compound and acid components should be chosen to provide
an acidizing fluid of the desired rheological properties.
Another embodiment of the method of this invention can be carried
out with a wide variety of injection and production systems which will comprise
one or more wells penetrating the producing strata or formation, Such wells
may be located and spaced in a variety of patterns which are well-known to
those skilled in ~he art. For example, the so-called "line flood" pattern may
; 20 be used, in which the injection and producing systems are composed of rows of
wells spaced from one another. The recovery zone9 i.e., that portion of the
producing formation from which hydrocarbons are displaced by the drive fluid
-` to the produc~ion system will, ln this instance, be that part of the formation
underlying the area between the spaced rows. Another pattern which is frequ-
r.' ently used is the so-called "circular flood" in which the injection system
.,.
comprises a central injection well while the production system comprises a
plurality of production wells spaced about the injection well. Likewise, the
injection and production systems each may consist of only a single well and
here the recovery ~one will be ~hat part of the producing strata underlying a
roughly elliptical area between the two wells which is subject to the displac-
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ing action of the aqueous drive fluid. Ior a mo~e elaborate description of
such recovery pat~erns, reference is made to Uren, L.C.J Petroleum Production
Engineering-Oil Field Ex~loitation, Second Edition, McGraw ~lill Book Company,
Inc., New York, 1939, and to U.S. Patents Nos. 3,472,318 and 3,476,182.
In carrying out this embodiment of the invention, the aqueous acidic
; solution of the anti-scal compound is forced, usually via a suitable pumping
system, down the well bore of an injection well and into the producing forma-
tion, through which it is then displaced together with hydrocarbons of the
formation in the direction of a production well. As in the other embodiment,
; 10 the pressure employed is determined by the nature of the ormation, viscosity
- of the fluid, and other operating variables, and the acidization method of this
invention may be carried QUt at a pressure sufficient merely to penetrate the
formation or it may be of sufficient magnitude to fracture the formation, in
which case propping agents, as described above, may also be included in the
aqueous acidic solution.
The formation may be treated continuously with the acidic solution,
~- or such treatment may be temporary. If desired, however, after a time, con-
- ventional flooding may be resumed. The aqueous acidic solution of the anti-
scale compound also may be applied in a modified water flood operation in which
there is first injected into ~he well bore a slug of the aqueous acidic solu-
tion which is forced under pressure into the subterranean formation. The first
step is then followed by a similar injection step wherein a slug of an aqueous
drive fluid, such as water, is injected, which is thereafter followed by a re-
petition of the two steps. This sequence may be repeated to give a continuous
cyclic process. The size of the slugs may be varied within rather wide limits
and will depend on a number of conditions, including the thickness of the for-
mation, its characteristics and the conditions for the subsequent injection o
the aqueous drive medium.
The anti-scale compound provides means whereby ions, produced by the
reaction of the acid component of the solution with the formation and having
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~!~)5~
tendencies ~o precipitate as salts such as CaC03, hydrous iron oxides and
CaS04 21120, com~ine with the compound to form a highly stable complex so that
solid salts do not precipitate from the spent treating solu~ion. ~is bind-
ing up of ~he aforementioned ions from weakly ionizable compounds permits the
; formed complex to remain dissolved in the treating solution and pass through
the formation pores. Further, the anti-scale compound dissolved in the com-
position provides means whereby the nucleation and growth of the solid itself
is thwarted, so that solid salts do not precipita~e from the spent treating
solution. Finally, the anti-scale compound in the composition provides means
whereby continuous protection against post-precipitation of salts is obtained
for a considerable time after treatment due to continuous slow desorption of
the compound from the formation faces. In contrast, use of surfactants having
merely dispersant and suspending properties, and not posscssing the capability
of molecularly binding these produced ions or thwarting the nucleation and
growth of solid salts, will permit post-precipitation of said salts from such
treating solution with the likelihood of plugging of the formation passageways
during subsequent recovery of desirable formation hydrocarbons.
It should be understood that the concentrations of the compound and
the acid components are chosen to provide a displacing fluid of the desired
rheological proper~ies. Similarly, the appropriate compound is selected on
the basis of the formation being treated as well as other operatin~ conditions
employed,
If desired one ran also add to the aqueous mineral acid solution
containing the anti-scale compound, a polymeric material to retard the tenden-
cy of the acid to attack the calcareous components of the formation. A poly-
vinylpyrrolidone as more particularly described in U.S. Patent No. 3,749,169,
is particularly suitable for this puspose.
EXAMP~E 1
A producing well in East Texas can be treated in the ~ollowing man-
ner.
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A treating mixture is prepared by mixing 10 barrels of salt water
`- containing about 2.6% by weight of sodium chloride and 12 barrels of 28% by
weight aqueous hydrochloric acid, and 0.1 barrel of the sodium salt of sulfo-
nated pentaethoxy dodecylphenol is added thereto.
The treating mixtu~e is squ0ezed into the formation at a rate of
about l/2 BPM at 450 psig. The shut-in tubing pressure is 450 psig which is
bled down to zero in a short time. The well can then be returned to produc-
tion.
EXAMPLE 2
- 10 A treating mixture is prepared from 10 barrels of salt water (2.6%
sodium chloride) and lO barrels of 15% by weight aqueous hydrochloric acid so-
- lution containing 0.2 barrel of the anti-scale compound used in Example 1.
The aqueous acidic solution is injected into the producing formation in the
manner approximating that used in Fxample l. Thereafter 20 barrels of water
are used to overflush the treated formation by injection down the tubing, fol-
lowed by injection of lO barrels of ~ater down the casing. The well can then
; be returned to production.
EXAMPLE 3
The aqueous acidic solution of Example 2 is injected into another
producing formation. An overflush of 10 barrels of water is used to force the
aqueous asidic solution into the formation by injection do~n the tubing. The
~` well can then be returned to production.
~i E.XAMPLES 4 T0 12
- The procedure set forth in Examples 1 to 3 above is repeated using:
Examples 4 to 6 - Sodium salt of sulfonated pentaethoxy nonylphenol.
Examples 7 to 9 - Sodium salt of sulfonated p~ntaethoxy m-pentadecylphenol.
- Examples 10 to 12 ~ Sodium salt of sulfonated heptaethoxy m-pentadecylphenol.
It is significant that the alkaryl compound is effective in the pre-
sence of high calcium ion concentrations to 1% by weight or more, and particu-
larly and somewhat uniquely in applications where high aqueous solution tempe-
~.;
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~i3S~L6~
ratures are encourltered such as above 100C.
The composi~ions used i~ the present i~vention are stable even in
- the presence of mineral acids. Laboratory ~hermal stability tests reveal the
compound used in Example 1 above remains 97% active after exposure of its aqu-
eous solution to a ~emperature of 177C. or 5 days. Furthermore, after 3
hours e~posure to 13% by weight sulfuric acid at 177C., the compound retained
79 5% of its activity.
The disclosed alkaryl compositions may be prepared in the following
manner:
The polyethoxy alkylphenol is treated with thionyl chloride for 18
hours at 100C., to form the monochloro derivative, which is then reacted with
sodium sulfite for 18 hours at 155C., in a 1/1 by volume mixture of wa~er and
; ethanol in a Paar Bomb. The resulting recovered sulfonated product, on analy-
sis, showed about 75% sulfonation of the terminal ethoxy group. This method
of preparation is exempla~y only, but was the method employed to prepare the
- ~ested compositions. Those skilled in the art may perceive other synthetic
schemes, For example, a sulfated ethoxylated alkylphenol may be treated with
sodium sulfite at 200C. for 10 to 12 hours, resulting in relatlvely high
yeilds ~75-80%) of the desired sulfonated ethoxylated alkylpenol. Direct re-
action of the ethoxylated al~ylphenol and mixtures thereof with such reagen~s
as sulfuric acid or chlorosulfonic acid results in sulfation.
XAMPLE 13
; Through a water injection well drilled into a limestone formation
there is displaced under pressure down the tubing and into ~he formation an
aqueous 15% by weight hydrochloric acid solu~ion containing 0.5% by weight5
based on the total weight of the solution, of the sodium salt of sulfonated
pentaethoxy nonylphenol. The pressure required to inject the required volume
of water declines considerably, and no increase in said pressure is noted sub-
sequent to treatment, indicating the post-precipitation of CaC03 within ~he
formation leading to permeability reduction is prevented or materially les-
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sened. m e well is then returned to conventional water injection. After
about 6 months the production of hydrocarbons from an adjacent producing well
is substantially increased.
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EXAMPLE t4
A flooding operation is carrie~d ou~ in an oil-containing rese~voir
in accordance ~ith the process of this invention. Four injection wells are
arranged in a rectangular pattern around a single, centrally located, produc-
tion well in this system. A slug consisting of 75 barrels of an aqueous aci-
dic solution containing 1% by weight, based on the total weight of the solu-
~ion, of the compound used in Example 13, in a 3% by weight hydrochloric a id,
is displaced via each of the four injection wells into the formation at a rate
of about 50 bbl/day. In the next step, 100 barrels of water are injected un-
der pressure into the producing formation through each injection well at a
rate of about 55 bbl/day. This sequence of operations is repeated numerous
times and the result is an increased injection rate of the drive streams into
~ . .
the injection wells and a subsequent increase in the rate of production of
hydrocarbons via the production well.
EXAMPLE 15
An injection well in a formation containing about 20% by weight of
20 HCl-soluble material is treated with 500 gallons of conventional 15% by weight
HCl followed by 1500 gallons of 3% HCl containing 0.5% by weight of the same
compound as used in Example 13. The aqueous acidic mix~ure is displaced from
~: the tubing into the formation with lease water, and the well is shut-in for
24 hours. Thereafter the well is returned to water injection, The injecti
vity of the well is materially increased for a sustained period of time re-
sulting in enhanced hydrocarbon recovery.
EXAMPLES 16 T0 24
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The procedure of Examples 13 to 15 is repeated using sodium salts
o~:
Examples 16 to 18 - Sulfonated pentaethoxy dodecylphenol,
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Examples 19 to 21 - Sulfonated pentaethoxy pentadecylphenol.
Examples 22 to 24 - Sulfonated heptaethoxy pentadecylphenol.
Equivalent results are obtained.
The method can be varied ~o employ injection of a large slug of the
aqueous carbon dioxide solution of the compound followed by the aqueous solu-
. tion of the plymeric mobility control agent, then followed by water injection.
Repetitive treatments of one or all of these s~eps are within the purview of
- the invention. Additionally and/or optionally one may inject gaseous carbon
; dioxide after any or all of these slug treatments, to impart enhanc~d mobility
to the oil by decreasing its ViscosityJ through the injec~ion well.
EXAMPLE 25
Through a water injection well drilled into a limestone formation
there is displaced under pressure down the ~ubing and into ~he formation an
aqueous acidic solution containing 1% by weight of carbon dioxide and 1% by
weight of the sodium salt of sulfonated pentaethoxy nonylphenol. The pressure
required to inject the required volume of water declines considerably and no
increase in said pressure is noted subsequent to treatment, indicating that
post precipitation of CaCO3 within the formation leading to permeability re-
duction is prevented or materially lessened. The well is then returned to
20 conventional water injection. After 8 months, the production of hydrocarbons
from an adjacent producing well is substantilly increased.
EXAMPLE 26
A flooding operation is carried out in a oil-containing reservoir in
accordance with the process of this invention. Four injection wells are arran-
ged in a rectangular pattern around a single centrally located production well
- in this system. A slug consis~ing of 75 barrels of an aqueous acidic solu~ion
containing 2% by weight of carbon dioxide and 0.5% by weight of the same com-
; pound as used in Example 25 is displaced via each of the four injection wells
into the formation at a rate of about 50 bbl/day. In the next step, 100 bar-
rels of wa~er are injected under pressure into the producing formation through
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~L~S~69L~
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j each injection well at a rate of abou~ 55 bbl/day. This sequence of opera-
tions is repeated numerous times and the result is an increased injection
rate of the drive streams into the injection wells and a subsequent increase
in the rate of production of hydrocarbons via the production well.
EXAMPLE 27
An injection well in a formation containing about 30% by weight of
HCl-soluble material is treated with 1500 gallons of 1.5% by weight aqueous
carbon dioxide solution containing 0.4% by weight of ~he compound used in Ex-
ample 25~ The aqueous acidic solution is displaced from the tubing into the
formation with water and the well is shut in for 24 hours. Thereafter the
well is returned to water injection. The injectivity of the well is material-
ly increased for a sustained period of time resulting in enhanced hydrocarbon
,i recovery,
EXAMPLES 28 T0 36
The procedure of Examples 25 to 27 is repeated using: -
Examples 28 to 30 - Sulfonated pentaethoxy dodecylphenol, sodium salt.
~xamples 31 to 33 - Sulfonated pentaethoxy pentadecylphenol, sodium salt.
Examples 34 to 36 - Sulfonated heptaethoxy pentadecylphenol, sodium salt.
Equivalent results are achieved.
EXAMPLE 37
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A producing well in East Texas can be treated in the following man-
ner.
A treating mixture is prepared by mixing 10 barrels of salt watPr
containing about 2,6~ by weight of sodium chloride and 13 barrels of 28% by
weight aqueous hydrochloric acid, and 0.1 barrel of the sodium salt of sulfo-
~ nated, pentaethoxylated mixed C12-C18 alcohols is added.
-~ The treating mixture is squeezed into the formation at a rate of
about 1/2 BPM at 450 psig. The shut-in tubing pressure is 450 psig, which is
bled do~n to zero in a short time. The well can then be returned to produc-
tion.
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EXAMPLE 38
~ A treating mixture is prepared from 10 barrels of salt water (2.6%
; by weight of sodium chloride) and 9 barrels of 15% by weight aqueous hydrochlo-
ric acid solution containing 0.2 barrel of the anti-scale compound used in Ex-
ample 37. The aqueous acidic solution is injected into the producing formation
:.
in a manner approximating that used in Example 37. Thereafter 20 barrels of
water are used t60verflush ~he treated formation by injection down the tubing,
followed by injection of 10 barrels of water down the casing. The well can
- then be returned to production.
' 10 EXAMPLE 39
The aqueous acidic solution of Example 38 is injected into another
producing formation. An overflush of 10 barrels of water is used ~o force the
,~ aqueous acidic solution into the formation by injection down the tubing. The ~ -
well can then be returned to production.
EXAMPLES 40 T0 48
~ The procedure set fcrth in Examples 37 to 39 above is repeated using
`~ Examples 40 to 42 - SulfonatedJ triethoxylated mixed C12-C18 alcohols
containing 40% dodecyl> 30% tetradecyl, 20% hexadecyl,
and about 10% octadecyl groups, sodium salt.
Examples 43 to 45 - Sulfonated, triethoxylated mixed C10-Cl4 alcohols
containing 80% decy1J 10% dodecyl and 10% tetradecyl
groups, sodium salt.
Examples 46 to 48 - Sulfonated, pentaethoxylated mixed C10-Cl4 alcohols
containing 85% decyl, 9% dodecyl, and 6% tetradecyl
groups, sodium salt. ;~
Equivalent results are achieved.
It has been found that the compounds used in the acid solutions of ;j-
the present invention are especially effective in the presence of calcium ion
concentrations of 1% by weight or more, and particularly and somewhat uniquely
in application where temperature that are high for aqueous solutions are en-
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~5~649
countered, such as above 100C. Thc aliphatic anti-scale compounds used accor-
ding to the present invention are temperature stable and effective as scale in-
hibitors at temperatures up to 150C., e.g. at 100 to 150C.
The unusual thermal stability of one of the species of the compounds
is graphically shown by the accompanying Drawing, which is a graph construcked
on one-cycle semi-logarithmic paper having 70 linear divisions along the ab-
scissa.
. . .
The data were obtained using the compound employed in Examples 46 to
48.
At normal operating p~l values of 7.5 and 6.3 in deionized water and
~` a representative field water (from the Cote Blanche field), respectively, half
lives at 116C. (240~F.) are 57.4 (curve 1) and 33 years (curve 2). The actual
experiments ~ere conducted at 400F., and the half lives were extrapolated to
; 240F. It is seen that at pH 6.3 in field water at as high a temperature as
204.5C. (400F.), a half life of 25 days is attained. At a pH of 1, 23% ac-
'`` tivity remained after lS days at 400~F. (curve 3).
In a separate experiment, the unusual stability of the compound is
exhibited by the fact that after exposure of an aqueous solution of the com-
pound of Examples 37 to 39 at 177C., for 5 days, 93.5% of the activity re-
mained Furthermore, after 3 hours exposure to 13% by weight sulfuric acidat 177C., 66% of its activity remained.
The sulfonated ethoxylated aliphatic anti-scale compounds may be
.~
prepared in the same ways as the corresponding alkylphenol derivatiYes as des-
cribed in connection with Examples 1 to 12.
The compounds used in Examples 37 to 42 in the above were prepared
by reacting commercially available mixed C12-C18 alcohols (Conoco-Alfol 1218)
with ethylene oxide to produce adducts having 5 and 3 ethoxy groups respective-
ly The resulting respective ethoxylated alcohols were then sulfonated as des-
cribed abov~ In asimilar manner, the compounds of Examples 43 to 48 were pre-
; 30 pared using commercially available mixed C10-Cl4 alcohols, (Conoco Alfols
7r~Je ~ar~
6 -
. ' '' ' : :
64g
; 1014 and 1012).
EXAMPLE 49
- Through a water injection wel] drilled into a limestone formation
; there is displaced under pressure down the tubing and into the formation an
aqueous acidic solution containing 1% by weight of carbon dioxide and 1% by
;~ weight of the sodium salt of sulfonated, pentae~hoxylated mixed C12-C18 alco-
hols containing 40% dodecyl, 30% te~radecyl, 20% hexadecyl and 10% octadecyl
groups. The pressure required to inject the required volume of water declines
considerably and no increase in said pressure is noted subsequent to ~reatment,
-; 10 indicating that post-precipitation of CaC03 within the formation, leading to
:
permeability reduction is prevented or materially lessened. The well is then
returned ~o conventional water injection. After about 6 nths the production
~`- of hydrocarbons from an adjacent producing well is substantially increased.
~- EXAMPLE 50
,, ' :'
A flooding operation is carried out in an oil-containing reser~oir
ai in accordance with the process of this invention. Four injection wells are
arranged in a rectangular pattern around a single centrally located production
well in this system. A slug consisting of 75 barrels of an aqueous acidic
.: .
solution containing 2% by weight of carbon dioxide and 0.6% by weight of the
compound used in Example 49 is displaced ~ia each of the four injection wells
into the ~rma~ion at a rate of about 50 bbl/day. In the next step, 100 bar-
rels of water are injected under pressure into the producing formation through
each injection well at a rate of about 55 bbl/day. This sequence of operations
.- is repeated numerous times and the result is an increased injection rate of the
drive streams into the injection wells and a subsequent increase in ~he rate
of production of hydrocarbons via the production well.
EXAMPLF 51
: ,-
An injection well in a formation containing about 30% by weight of
HCl-soluble material is treated with 1500 gallons of 1.5% by weight aqueous
carbon dioxide containing 0.5% by weight of the compound used in Example 49.
-:
- 17 -
:
''
. ;' ' ' ' ' .
~ S~ 4~
';
The aqueous acidic solution is displaced from~the tubing into the formation
with lease ~ater and the well shut in for 24 hours. Thereafter the well is
, ~
returned to water injection. The injectivity of the well is materially in-
creased for a sustained period of time resulting in enhanced hydrocarbon re-
cover.
EXAMPLES 52 10 60
The procedure of Examples 49 to 51 is repeated using:
Examples 52 to 54 - Sodium salt of sulfonated, triethoxylated mixed
C12-C18 alcohols containing 40% dodecyl, 30% tetra-
decyl, 20% hexadecyl9 and 10% octadecyl groups,
sodium salt.
Examples 55 to 57 - Sodium salt of sulfonated, triethoxylated mixed
- C10-Cl4 alcohols containing 80% decyl, 10% dedocyl
; and 10% tetradecyl groups, sodium salt.
Examples 58 to 60 - Sodium salt of sulfonated, pentaethoxylated mixed
C10-Cl4 alcohols containing 85% decyl, 9% dodecyl, -
and 6~ tetradecyl groups, sodiu= salt.
:
. ~
,
- 18 -
.
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