CA1051649A - Method for stimulating well production - Google Patents

Abstract

Abstract of the Disclosure A method for increasing the production of fluids from a subterrane-an 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 weight of carbon dioxide, and (b) from 0,005 to 2 % by weight of at least one sulfonated anti-scale compound of the formula

Description

~.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 ' ~' ~

:' ,- ~

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 ,, ~ -- 2 --.

' .

~(~51~49 - slight solubility in acidic media and the tendency to form objectionable hydro- -. .
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 .
'~ ' ' ' ' ~' ' " .

i ~05~L6~
.:.
- 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-, ., . : .
, 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-' ~ .~, . . .

;~

`~ 11;~5~6gL~
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-_ 7 _ : .

.

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 .

:

~!~)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.
. .

_ g _ , , . :
: .: . . . :

~5~9 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.

- 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.

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-~.;
' - 10 -' ,~ ' . ' ~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.

; 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-.. :

, ~5~
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.

.: .
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.

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.

: . .
.

The procedure of Examples 13 to 15 is repeated using sodium salts o~:
Examples 16 to 18 - Sulfonated pentaethoxy dodecylphenol, ; .

`' ' .
, ,: . .

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.

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.

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 .

~L~S~69L~
;` .
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.

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, 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.

`! _ 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.

., ~ - 14 -.

5164~
~ ..

~ 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.

~ 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-<

. .

. -~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~

. ' '' ' : :

64g ; 1014 and 1012).

- 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.

: ,-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.
-:

:
'' . ;' ' ' ' ' .

~ 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.

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.

:

. ~
, .
. , , , ' ~ ' . ' '.: ' ,~ ~ .. . . .. .. .

Claims (18)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method for increasing the production of fluids from a subterranean fluid-bearing formation containing acid-soluble components which comprises in-jecting 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 weight of carbon dioxide, and (b) from 0.005 to 2 % by weight of at least one sulfonated anti-scale compound of the formula (I) wherein A+ is an alkali metal or ammonium ion, and R is an alkaryl group hav-ing 6 to 18 carbon atoms in its alkyl moiety, or a saturated or unsaturated aliphatic hydrocarbon group having 8 to 20 carbon atoms and n is a number from 1 to 10.

2. A method as claimed in claim 1 wherein component (a) of the solution is a mineral acid, and R is an alkaryl group having 6 to 18 carbon atoms in its alkyl moiety.

3. A method as claimed in claim 1 wherein component (a) of the solution is carbon dioxide, and R is an alkaryl group having 6 to 18 carbon atoms in its alkyl moiety.

4. A method as claimed in claim 2 or 3 wherein the anti-scale compound is the sodium salt of sulfonated pentaethoxy nonylphenol, sulfonated penta-ethoxy dodecylphenol, sulfonated pentaethoxy pentadecyl phenol or of sulfona-ted heptaethoxy pentadecylphenol, or of a mixture of such sulfonated polyethoxy-lated alkylphenols.

5. A method as claimed in claim 1 wherein the solution comprises a mineral acid, and R is a saturated or unsaturated aliphatic hydrocarbon group having 8 to 20 carbon atoms.

6. A method as claimed in claim 1 wherein component (a) of the solu-tion is carbon dioxide, and R is a saturated or unsaturated aliphatic hydro-carbon group having 8 to 20 carbon atoms.

7. A method as claimed in claim 5 or 6 wherein the anti-scale compound is the sodium salt of a sulfonated pentethoxylated dodecyl alcohol, a sulfona-ted hexaethoxylated hexadecyl alcohol, a sulfonated heptaethoxylated pentadecyl alcohol, or of a sulfonated pentaethoxylated C12-C18 aliphatic alcohol, or of a mixture of such polyethoxylated aliphatic alcohols.

8. A method as claimed in any of claims 1, 2 or 5 wherein the solution comprises 3 to 15 % by weight of the mineral acid.

9. A method as claimed in any of claims 1, 3 or 6 wherein the solution comprises 1 to 3 % by weight of carbon dioxide.

10. A method as claimed in claim 1, 2 or 3 wherein the solution comprises from 0.05 to 1 % by weight of the anti-scale compound.

11, A method as claimed in calim 5 or 6 wherein the solution comprises from 0.05 to 1 % by weight of the anti-scale compound.

12. A method as claimed in claim 1 wherein the solution is injected into the formation under a pressure greater than formation pressure and maintained in contact with the formation for a period suficient for chemical reaction between the solution and acid-soluble components of the formation to etch pas-sageways through the formation.

13. A method as claimed in claim 1 or 12 wherein the solution is injected into the formation under a pressure sufficient to fracture the formation.

14. A method as claimed in claim 1 or 12 wherein the solution is injected into the formation at a pressure above the formation pressure but insufficiant to create fractures in the formation.

15. A method as claimed in any of claims 1, 2 or 3 wherein 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.

16. A method as claimed in claim l or 12 wherein the solution is injected into the formation under a pressure sufficient to fracture the formation, and said solution contains a propping agent.

17. A method as claimed in claim 1 or 12 wherein the solution is injected into the formation at a pressure above the formation pressure but insufficient to create fractures in the formation, and said solution contains a propping agent.

18. A method as claimed in any of claims 1, 2 or 3 wherein 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, and said solution contains a propping agent.