NO823414L - PROCEDURE AND MEDICINE FOR SURGERY OF OIL OR GAS BURNS. - Google Patents

Description

The present invention relates to a method for treating an oil-bearing formation and the distinctive feature of the method according to the invention is that the formation is brought into contact with an aqueous acidic solution containing a to C . aliphatic alcohol and an effective amount of a phosphate ester surfactant to render the alcohol soluble in said acidic solution.

The invention also relates to an acidic mixture for carrying out the aforementioned method, and the peculiarity of the mixture according to the invention is that it comprises

a) an aqueous acidic solution

b) a C4 to C, „ aliphatic alcohol, and

c) an effective amount of a phosphate ester surfactant

agent to make the alcohol soluble in the nefte

acidic solution.

These and other features of the invention appear in the patent claims.

In general, acidification of oil and gas wells is practiced for a long time for cleaning to stimulate and promote hydrocarbon production. Thus, injection of an aqueous solution of an acid such as hydrochloric acid,,fluoric acid, . acetic acid or similar a common practice. Mutual solvents such as alcohols and ethylene glycol mono-butyl ether are usually added to well stimulating acids to promote wetting of the solids, lower the interfacial tension between the acid and oil, and break down the emulsion layer. A particularly useful mixture is isopropyl alcohol and isooctyl alcohol as described in US Patent 3,819,520 in which isopropyl alcohol acts as a necessary co-solvent to make the isooctyl alcohol soluble and in which the combination must be used in relatively high concentrations to be effective.

Surfactants such as e.g. oxyalkylated polyols or oxyalkylated alkylphenols with sulfated oxyalkylated alcohols and glycol ethers are known to be used together with acids and likewise oxyalkylated alcohols and alkylsulfonate in butyl alcohol are known for many of the above purposes. Other types of surfactants such as e.g. the ethyl oxide adduct of octyl alcohol or nonylphenol has been used.

However, none of these combinations are as effective as desired. The glycol ethers, mixed alcohols and the like are not as good as the surfactants

to wet oily solids, disperse solids or reduce surface and interfacial tension. Furthermore, surfactants often form (stabilize) harmful emulsions and are not as effective in promoting oil/acid/miscibility as the higher alcohols which have very low solubility in aqueous acidic solutions.

The purpose of the present invention is the provision and use of a new oil well acidifying solution which remedies the disadvantages of a previously known technique and with superior ability for oil dispersion, solubilization, emulsification and wetting of solids used in connection with conventional acidifying solutions. Preferably in accordance with the invention, at least about 75 and preferably at least 90 parts by volume of the aqueous acidic solution containing up to about 20% by weight acid is combined with up to 25 and preferably up to 10 parts by volume of a mixture of - aliphatic alcohol and the phosphate ester surfactant, the mixture preferably containing up to about 8 parts by volume of alcohol to 5 parts by volume of surfactant. A water-soluble alcohol with lower molecular

weight (and/or diol)' and a water mixture can be added to a concentrate of the other ingredients as a diluent to make an acidifying additive mixture more manageable out in the field, especially at low temperatures.

The present invention thus provides an acidifying additive mainly consisting of a phosphate ester surfactant to which is added from about 20 to 160 parts by volume of a - C 1Q mainly water-insoluble aliphatic alcohol per 100 parts by volume of the surfactant and a volume of a mixture of a water-soluble lower molecular weight alcohol or diol and water, approximately equal to the sum of the volumes of the surfactant and insoluble alcohol and in which the water is present in an amount of about 2 to 20 percent by volume of the resulting acidifying additive.

The invention further dictates that the aqueous acidic solution can be made up of any conventional acidifying medium, and furthermore that the alcohol with a higher molecular weight can be a C, - C - alcohol and preferably isooctyl alcohol and that the phosphate ester surfactant is preferably a phosphate ester of an oxyalkylated fatty alcohol.

That is a primary object of the present invention

to provide an acidizing additive and a solution with improved oil-displacing ability during acid treatment of a well. It is a further object that this additive or acidic solution is useful in combination with known acidifying treatments,

including a pre-rinse or activating treatment or as a subsequent rinse after other solvents and the like. It is a further purpose that the concentrate or additive should be compatible with conventional oilfield equipment and methods including on-site mixing with the acidifying solution. The fulfillment of these purposes and the presence and fulfillment of other purposes will be apparent from a detailed review of the following.

In general, the objects of the invention are achieved by incorporating a mixture of a phosphate ester surfactant and an alcohol in the acidic solution used for treating an oil well. This incorporation can be achieved by adding the mixture to the acidic solution before injection, as a separate pre-treatment or previously introduced portion of solvent, or also as a post-treatment associated with an acidic solution and which is allowed to mix in situ with the acidic solution . The alcohol is chosen so that it is mainly water-insoluble and consequently acid-insoluble but miscible with oil. The phosphate ester surfactant appears to be uniquely suited to solubilize the alcohol to produce an acidifying mixture of extraordinary oil-displacing properties.

In US Patent 3,819,520, the advantages of providing an acidifying solution containing octyl alcohols for displacing oil were established by observing the interfacial tension between the acidifying solution and an oil phase. The octyl alcohols were dissolved in the acidic solution due to the presence of a significant (total) percentage of a low molecular weight co-solvent alcohol. A pernated phase diagram is shown in the patent inclusively

15% HC1, isooctyl alcohol and isopropyl alcohol and shows that

22 vol% isopropyl alcohol will solubilize the octyl alcohols to an extent of 2 vol%:. in the acid, while 30 vol% isopropyl alcohol will solubilize 20 vol% octyl alcohol. The aforementioned US patent document 3,819,520 also shows that for all practical purposes there are no alternatives to the octanols nor to the C 3 co-solvent alcohol. Thus, solubilization of a high molecular weight alcohol using a co-solvent alcohol is not only limited to the C 8 alcohols but also involves a minimum of 24% by volume of the resulting acidifying solution being an additive.

In contrast, the present invention provides for the solubilization of the higher molecular weight alcohols by the addition of a phosphate ester surfactant. The alcohol may be substantially any C - Q substantially water insoluble alcohol. All such alcohols in combination with the phosphate ester surfactant and the acidic solution have been found to be effective in its integration and dispersion of oily deposits, sludges and emulsions. They produce a substantially oil-free aqueous phase and an anhydrous oil phase and ..leave the surfaces of the solids water-wet without any appearance

allowing emulsion formation. The C, - C„ alcohols pre-

J 6 8

is drawn by the fact that the rate of its integration and dispersion of the oily muds is greater within this area.

A mixture of closely related branched chain isomeric primary alcohols of the general formula RCP^OH wherein R is a branched heptyl radical and sold as isooctyl alcohol is particularly preferred.

The surfactants used to leave the high molecular weight alcohol soluble in acidic solution are categorically phosphate ester surfactants. They are anionic surfactants prepared from mixtures of mono- and di-phosphate esters and alkyl alcohols, oxyalkylated alcohols or phenols, or the like, in which one or more of the terminal hydroxyl groups are phosphorylated, producing a compound with the following general formula:

wherein R is an alkyl radical, phenyl or alkylphenyl-

group, hydrogen, or a phosphate group, x and y represent the degree of propoxylation and ethoxylation, respectively.

The phosphate ester surfactant is preferably used in the acidic form. However, the partially neutralized form is equivalent for the purposes of the invention to the extent that it is converted to the acidic form in an acidifying solution. The particularly preferred phosphate ester surfactants applicable to the present invention are the phosphate esters of the oxyalkylated fatty alcohols as described in US patent 3,629,127.

Another preferred series of phosphate ester surfactants applicable to the present invention are the phosphate esters of the so-called "Pluronic" polyols as described in US Patent 2,674,619.

When preparing the acidifying solution, it is preferred that the surface-active agent and the high molecular weight alcohol are pre-mixed so that a concentrated additive is produced which is then mixed with the acidifying solution. However, the mixing of the aqueous acidifying solution with the surfactant and the alcohol in any order is equally effective, but not as advantageous in that the concentrated additive can be transported to the field and then added at the well site as desired.

When a concentrate of the surfactant and the alcohol is used, the presence of a diluent to lower the freezing point and acid viscosity of the mixture is preferred. The diluent is preferably a water-soluble alcohol or diol with a low molecular weight, such as methanol, ethanol, n-propanol-isopropyl alcohol, t-butyl alcohol, ethylene glycol or the like. Advantageously, the diluent should also contain some water to maintain the highly polar surfactant in solution, especially under cold climate conditions.

When preparing either the acidifying solution itself, or the additive-concentrate mixture, the amount of high molecular weight alcohol present in relation to the surfactant is preferably at least 1 part by volume of high molecular weight alcohol to 4 parts by volume of phosphate ester surfactant. At this concentration, the acidifying solution will exhibit superior oil dispersion in relation to each of the components individually used together with the acid. Preferably, the ratio between alcohol and surfactant should not exceed approximately 8 parts by volume of alcohol for 5 parts by volume of surfactant. Although concentrations outside this limit are not considered harmful, the ratio of 8:5 roughly corresponds to the upper limit of the surfactant's ability to solubilize the alcohol in the acidic solution. The ratio of 2 parts by volume alcohol to 3 parts by volume surfactant is felt to be a particularly preferred ratio for most alcohol/surfactant mixtures.

When preparing a concentrate for later addition, to the aqueous acidifying solution the mixture of diluent-alcohol or lower molecular weight diol + water should be present in sufficient quantity to lower the freezing point, reduce the viscosity and keep the highly polar surfactant in solution. In general, improvement in the ability to handle the concentrate is observed by adding any volume of the mixture of alcohol (diol) and water. Preferably, approximately 50 or more volume percent alcohol (diol)/water mixture is used per total volume of the resulting diluted concentrate additive. The corresponding resulting water content should be from about 2 to 20% by volume to prevent separation of surfactant at low temperatures.

When preparing the acidifying solution, the relative amount of concentrate in relation to acid solution can be as low as 0.2% by volume to prevent acid/oil emulsion. The maximum effectiveness of the additive will occur up to about 10 to 20% by volume depending on the relative amount of surfactant and high alcohol. molecular weight, since even higher percentages can work. A 95% by volume acid/5% by volume additive mixture is particularly preferred and suitable for most applications. This concentration is also particularly advantageous in relation to the previously known technique in that the presence of the additive does not represent any significant economic factor and the resulting acidifying solution mainly still has full strength. Higher concentrations of up to 25% are very useful where maximum dissolution of oily deposits is desired.

To more fully describe and explain the present invention, how it works and differs from the prior art, and how it is used,

is a more detailed investigation of the experimental basis and observations necessary.

In order to find the desired surfactant, namely one which is effective in solubilizing high molecular weight alcohols in acids, a number of selection trials were carried out using the various known classes of surfactants. The experimental method involved the addition of approximately 40 ml of a selected concentration of acid solution and approximately 5 ml of surfactant to a 50 ml graduated cylinder with a glass stopper. The combination was thoroughly mixed to check solubility. A 1 mL sample of the high molecular weight alcohol was then added. The graduated cylinder was closed and shaken. Observation of the behavior of the resulting mixture for solubilizing the alcohol was noted. The method of adding a further 1 ml of sample alcohol and shaking was repeated until no particular change could be observed. The results of the selection tests are as follows.

EXAMPLE I

As a control test, 45 ml of 15% HCl and 5 isooctyl alcohol were added to a 50 ml measuring cylinder with a glass stopper and shaken vigorously. A cloudy dispersion formed which immediately separated into two distinct immiscible layers. After standing for 5 minutes, a 6 mL slightly cloudy oil layer was present on top of a slightly cloudy lower acid phase. This behavior was considered typical of the mainly insoluble high molecular weight alcohols in an acidic medium.

EXAMPLE II

A 40 mL sample of 15 wt% HCl and 5 mL of a liquid surfactant (oxyalkylated polyols, oxyalkylated

in

alkylphenols with sulfated oxyalkylated alcohols and glycol ethers) sold under the trade name "Trerolite AY 31" were placed in the measuring cylinder and mixed. The resulting clear solution with foam. After adding the first ml of isoxyl alcohol, a cloudy dispersion was observed. The second ml of isoxyl alcohol produced an even more cloudy dispersion with a tendency to separate.

3, 4 and 5 ml of isoxyl alcohol were added with separation of a pale yellow oil emulsion as the top. After adding the 5 ml, the emulsion phase was 7 ml in volume after a 5 minute standstill. From this it was concluded that little or no solubilization of the isooctyl alcohol

takes place when the aforementioned AY 31 is the surfactant.

EXAMPLE III-V

The preceding method from Example II was repeated substituting 5 ml of caprylic alcohol, normal octanol, or decyl alcohol for the isooctyl alcohol. The results were identical to example II with the exception that the separation took place

coiled faster in the case of decyl alcohol.

EXAMPLE VI

The method of Example II was repeated using

40 ml of 15% by weight HCl and 15 ml of 9.5 mol ethylene oxide

adduct of nonylphenol, sold under the trade name "Surfonic N-95" added as surfactant. "Surfonic N-95" clumped and crusted when added to the acid. Heating and vigorous stirring resulted in a clear highly foamed solution. After adding the first ml of isooctyl alcohol and shaking, a clear solution with the exception of air bubbles resulted. The second ml of isooctyl alcohol was essentially identical with respect to the results with some phase separation. The 3 ml produced a cloudy solution which entrained air bubbles and separation of an oil layer. With the 4 ml of isooctyl alcohol, the solution seemed to become somewhat clearer, while a 5 ml resulted in an opaque emulsion without foaming. Solution-r one after adding the second ml was viscous. After standing for 15 minutes (5 ml of isooctyl alcohol), 3 ml of clear oil developed on top of about 36 ml of an intermediate layer of cloudy thin emulsion. Visibly pre-

further separation of more isooctyl alcohol phase took place. After 1 hour, three clear layers were observed, 10 ml at the bottom, 31

ml intermediate layer and 9 ml oil on top. "Surfonic N-95" is concluded to be a weak solubilizing substance for isooctyl alcohol in acid and it stabilizes emulsions.

EXAMPLE VII

The above method was repeated using 40 ml

15 wt% HCl and 5 ml of commercial surfactant which was assumed to be oxyalkylated alcohol and alkyl sulphonate in butyl alcohol sold under the trade name "Moreflo II". A clear yellow solution with slight turbidity resulted. After addition of successive 1 mL samples of isooctyl alcohol, the solution after addition of the first mL became a cloudy dispersion which became even more cloudy after the second addition and into an emulsion with an oil phase separation from the third and subsequent additions. After a total of 5 ml of isooctyl alcohol had been added, 1.5 ml of separation was observed. After 5 minutes of standing time, 12 ml of thick emulsion was present in which the rest was cloudy. It is concluded that "Moreflo II"

is a poor solubilizing agent for isooctyl alcohol in 15 wt% HCl.

EXAMPLE VIII

Using the same selection method, 40 ml

15 wt% HCl mixed with 5 ml of a phosphate ester surfactant sold under the trade name "Klearfac AA-420". A clear solution with some foam resulted. The first three additions:: of 1 ml portions of isooctyl alcohol were solubilized resulting in a clear solution. The fourth ml produced a cloudy stable mixture and the fifth a stable emulsion. After a total of 5 ml of isooctyl alcohol had been added and after a 15 minute stand, 1 ml of a clear oil separated on top. The performance of this phosphate ester surfactant appears to be superior to the previously tested surfactants.

EXAMPLE IX

Another phosphate ester surfactant sold under the trade name "Klearfac AA-040" was tested by preparing a clear solution from a combination of 5 ml of surfactant with 40 ml of 15% by weight HCl.

Here too, addition of the first ml of isooctyl alcohol produced a clear solubilized solution with slight cloudiness produced by the addition of the second ml of alcohol.

The third ml produced a cloudy dispersion or emulsion while the fourth resulted in an emulsion. The fifth ral of isooctyl alcohol produced a white emulsion which, after 15 minutes' standing, resulted in 2 ml of somewhat cloudy oil rising to the top of the emulsion.

EXAMPLE X

A third phosphate ester surfactant marketed as "Klearfac AA-270" was similarly tested. To the clear solution successive 1 mL portions of isooctyl alcohol were added followed by mixing. In this case a total of 9 ml was added before the resulting mixture changed from a clear solution with possibly very little turbidity (8 ml) to a translucent turbidity (9 ml) but still categorically a stable mixture. Even after 2 hours, the new ml mixture was still a cloudy stable dispersion without any obvious separation. Only slight foaming and opalescence from about the fourth to the seventh ml of isooctyl alcohol was observed. This mixture (9 ml of isooctyl alcohol, 5 ml of "Klearfac AA-270" and 40 ml of 15% by weight HCl) was allowed to stand overnight. On observation the next day, 4 ml of clear oil formed an upper layer and the bottom layer 50 ml was a clear, stable solution. Thus can. 5 ml of "Klearfac AA-270" permanently dissolve at least about 5 ml of isooctyl alcohol in 15% by weight HCl. More specifically in an approximately 25% by volume solution of surfactant and 75% by volume 15% by weight HCl. This suggests the presence of a specific stoichiometry which is probably characteristic of the formation of a coordination complex or the like in the solution.

In view of the preceding examples, the phosphate esters appear as a class far superior to other types of surfactants for solubilizing isooctyl alcohol in hydrochloric acid.

EXAMPLES XI-XIV

To test the solubility (more specifically the solubilization, i.e. not necessarily a thermodynamic equilibrium) of other alcohols using the phosphate ester surfactant in acidic solution with 5 ml samples of hexanol, caprylic alcohol, n-octanol and decyl alcohol added to separate measuring cylinders containing mixtures of 40 ml of 15% by weight HCl and 5 ml of "Klearfac AA-270". All except the decyl alcohol resulted in a clear solution indicating excellent solubilization of the alcohol. The decyl alcohol resulted in a cloudy, stable dispersion which is characteristic of good solubilization.

EXAMPLES XV- XVIII

In order to determine alternative commercially acceptable compositions, a series of experiments were conducted to test the idea of preparing a concentrate of a high molecular weight alcohol mixed with a phosphate ester surfactant which could be dissolved at any concentration in well treatment acids, such as .ex. 5%'- 20% HCl and mixtures HC1/HF (ie mud acids). The experiments were planned for

to develop a concentrate that could be easily marketed as a well acidizing additive that could be delivered directly to the field and then added to the acidizing medium. As such, the concentrates must be stable, have a low viscosity to facilitate handling and have a low freezing point. To achieve these practical considerations, the presence of different carriers was investigated.

In EXAMPLE XV, 25 ml of phosphate ester surfactant ("Klearfac AA-270") was added to 25 ml of isooctyl alcohol and

50 ml of isoporpyl alcohol as a carrier (viscosity reducer and freezing point depressant). After stirring, a clear solution resulted. A 5 ml sample of the above mixture was added to 95 ml of a 15% by weight HCl solution. After shaking, a cloudy dispersion resulted

tion. An additional 5 mL sample of the original alcohol/surfactant mixture was added to the acid dispersion with stirring. A clear resolution resulted. From this it was concluded that an increase in the ratio between surfactant and high molecular weight alcohol is necessary for soluble

hot at low total concentrations.

In EXAMPLE XVI, a concentrate was prepared by mixing

35 ml "Klearfac AA-270", 15 ml isooctyl alcohol and 50 ml isopropyl alcohol. Here, too, a clear resolution resulted. Using this concentrate, clear solutions were prepared at 0.5, 1.0, 5.0, and 10.0 vol% concentrate in 5 wt% HCl, 10 wt% HCl, 15 wt% HCl, and 20 wt% HCl and this indicated solubility at all concentrations. Solubility was also observed in the mixture HC1/HF.

In EXAMPLE XVII, to determine other possible viscosity depressants and freezing point depressants, 30 ml of "Klearfac AA-270" and 20 ml of isooctyl alcohol were combined to form a clear solution. This mixture was tested and found to be soluble at all concentrations in methanol, isopropyl alcohol, butyl alcohol and ethylene glycol.

In EXAMPLE XVIII, a mixture of 300 ml of "Klearfac AA-270", 200 ml of isooctyl alcohol, 400 ml of isopropyl alcohol and 100 ml of water was prepared. The clear solution was set aside for testing of pour point and physical properties. The water was added to ensure that the highly polar phosphate ester surfactant would dissolve when the mixture was cooled.

From the above data it appeared that the concentrate mixtures of EXAMPLES XI-XIV were useful for use as acid additives for emulsion prevention, well cleaning and stimulation in general and as sludge remover, wetting agent, dispersing agent, mutual solvent and solubilizing agent. It was further felt that the amount of concentrate necessary in the final acid was as little as 0.2% for prevention of acid/oil emulsions and up to 10-20% by volume for maximum efficiency.

About 5% by volume of the concentrate in acid should be suitable

for most applications.

EXAMPLE XIX

Another commercially available phosphate ester surfactant marketed under the trade name "Pluraflo OF-90" was tested. a manner similar to EXAMPLE XI by placing 40 ml of 15% by weight HCl and 5 ml of "Ploraflo OF-90" in a glass stoppered measuring cylinder. After mixing, a clear solution was produced to which successive 1 ml portions of isooctyl alcohol were added while stirring. After the third 1 ml addition, a slight opalescence was observed in the otherwise clear single-phase solution. By the end of the fifth or sixth 1 ml portion, the opalescence developed to a faint hazy appearance. The seventh ml of isooctyl alcohol showed a stable dispersion and the eighth addition resulted in a more cloudy emulsion. The overall performance of "Pluroflo OF-90" was consistent with EXAMPLE II with the exception that the surfactant

agent is probably not as concentrated as indicated by the somewhat lower ability to solubilize the higher alcohol, but overall it is a very useful alternative to "Klearfac AA-270".

EXAMPLE XX

To test the impact of mixing types or classes

of surfactants was 20 ml sample of "Klearfac AA-270"

added to a 10 ml sample of "Sulfonic N-95" (phosphate ester non-ionic surfactant mixture) to 40 ml of 15% by weight HCl was added 5 ml of the surfactant mixture and this gave a clear solution.

Again, after addition of 1 mL portions of isooctyl alcohol, a slight haze developed to a cloudy dispersion after the third successive mL. The fourth ml cleared to a slight haze and the fifth produced a cloudy emulsion which appeared unstable. From this it was concluded that there is no advantage associated with the use of mixed types or classes of surfactants.

EXAMPLE XXI

In order to illustrate the beneficial effects of the present invention, a comparative visual test of the dissolution properties of a series of 6 acidifying mixtures was carried out. The first acidifying mixture was a 5% by volume solution of the composition of EXAMPLE XV using a high molecular weight phosphate ester/alcohol in 95% by volume of 15% by weight HCl. The other 5 similar mixtures were known commercially available alternatives including: a 10 vol% ethyl glycol mono-butyl ether in 15 wt% HCl, further a 35 vol% mixture of isopropyl and isooctyl alcohol in 15 wt% HCl sold under the trade name "A -S61" and prepared according to US patent 3,819,520, further a 5% by volume surfactant "Morflo II" in 15% by weight HCl (EXAMPLE VII)

and 5% by volume surfactant "Surfonic N-95" in 15% by weight HCl (EXAMPLE VI). Each mixture was used to dissolve an oily shale mud kept from a water injection well. The sludge contained approximately 20% by weight of heavier hydrocarbons, 70% by weight of acid-soluble minerals (primarily calcium carbonate) and 10% by weight of clay and silica grains (acid-insoluble particles). Substantially identical samples of the sludge were immersed in an excess

of each of the respective acidifying solutions. The acidifying mixture of phosphate ester and high molecular weight alcohol broke down, dissolved and dispersed the semi-solid sludge much faster than any of the other solutions. The oil flowed freely to the top and the particles dispersed

in the aqueous acidic phase.

EXAMPLE XXII

For further testing, a synthetic well mud was prepared by mixing 90 parts by weight of calcium carbonate (CaCO^

and 10 parts by weight of kaolinite clay. To this mixture was added a heavy, waxy crude oil until a stiff paste was formed.

EXAMPLE XXIII

5 grams of the paste was added to 100 ml of 15% by weight HCl in a beaker. Only slow impact was observed as evidenced by bubbling (C02~ release) and release of oil. The small amount of released was sticky and emulsified and the clay remained in an oily lump. The lump of pasta was not disintegrated .. after. 1 hour at room temperature.

EXAMPLE XXIV-XXVI

A concentrate of high molecular weight phosphate ester/alcohol

in accordance with the invention was prepared containing 30% by volume "Klearfac AA-270", 20% by volume isooctyl alcohol, 40% by volume isopropyl alcohol and 10% by volume water. Therefore, a 100 ml test sample of a 5 vol% mixture of the concentrate in 15 wt% HCl will contain the equivalent of 1.5 ml "Klearfac", 1.0 ml isooctyl alcohol and 2.0 ml isopropyl alcohol.

A similar 100 ml acidifying solution without the high molecular weight alcohol was prepared, containing 1.5 ml "Klearfac AA-270", 2.0 ml isopropyl alcohol and 96.5 ml 15% by weight HCl. A 100 ml acidifying mixture was also prepared by combining 1.0 ml of isooctyl alcohol, 2.0 ml of isoporpyl alcohol and 97.0 ml of 15% by weight HCl, without the phosphate ester surfactant being present. This mixture was cloudy and separation would occur unless stirred frequently.

A 5 gram sample of the synthetic oil well mud of EXAMPLE XXII was placed in each of the 100 ml acidifying solutions. The solution containing no isooctyl alcohol disintegrated the sludge faster than the simple 15% by weight HCl solution in EXAMPLE XXIII. It took about 30 minutes for the lump to disappear. The oil on top was emulsified (gummy) with no sign of being dispersed. The solids appeared to be wet with water. The results were better than nothing but not attractive.

The solution containing no surfactant was only slightly better than simple HCl. Most of the isooctyl alcohol was found to float to the top. No foam formation was observed. Released oil was present in the isooctyl alcohol phase. No emulsion was observed. After one hour, the 5 gram sample of oily paste had not disintegrated completely.

In the case of the acidifying solution containing both the isooctyl alcohol and "Klearfac" surfactant, its integration into the oily paste was very rapid with the development of copious amounts of foam. No emulsion was observed. The solution turned dark from solubilized oil (some free oil in the foam). All the sludge was gone within 10 minutes. The solids suspended in the lower aqueous phase were wetted with water.

From the foregoing, it was concluded that the mixture of phosphate ester/high molecular weight alcohol, in the proper ratio, combines to form a mixture which is soluble in acid (15% by weight HCl) and the resulting solution is far superior to each component alone in its integration, dissolution and dispersion of oil sludge that clogs oil wells and injection wells. The new mixture prevents emulsification and foams better than the surfactant alone and suggests that it has a more pronounced surfactant or surfactant character.

EXAMPLES XXVII- XXVIII

In order to determine the effects of varying the relative amount of the surfactant in relation to the high molecular weight alcohol, the following two concentrate mixtures were prepared:

A 5 ml portion of concentrate 1 was added to 95 ml of 15% by weight HCl and produced a cloudy dispersion (emulsion). After adding 5 grams of the oily well mud from EXAMPLE XXII, a slow reaction occurred with much less foaming than EXAMPLE XXVI. It took 20 to 30 minutes to break down the oily lump. Excess isooctyl alcohol may have been responsible for the slow reaction due to the "oil-wetting" of the solids in the sludge.

5 ml of concentrate 2 added to 95 ml of 15% by weight HCl gave a clear acidifying solution. Addition of 5 grams of the oily sludge to 100 ml of the acidifying medium containing concentrate 2 resulted in a faster reaction but not as rapid as EXAMPLE XXVI. It took

approximately 20 minutes to disperse the sludge.

From the pattern of the preceding examples it can be seen that phosphate ester surfactants such as "Klearfac AA-270"

can solubilize (presumably with micellar dissolution) high molecular weight alcohols, such as octyl alcohols, in acidic solution in an amount up to about 8 parts alcohol to 5 parts surfactant. The most stable solution was obtained with equal parts surfactant and high molecular weight alcohol, where the total concentration of the mixture (surfactant/alcohol complex) is approximately 25% by volume in the acid. When the total concentration is only 5% by volume in the acid (desirable for economic reasons), the best ratio is about 3 parts surfactant to 2 parts high molecular weight alcohol. Just as one part high molecular weight alcohol to 4 parts surfactant is superior to surfactant alone. For most purposes alcohol alone is not usable due to low solubility.

EXAMPLES XXLX- XXX

To test different high molecular weight alcohols were

a series of 3 concentrates prepared using n-butyl alcohol, normal-hexanol and normal-decanol. Each concentrate was prepared from 30% by volume of "Klearfac", 20% by volume of high molecular weight alcohol, 40% by volume of isoporpyl alcohol and 10% by volume of water. 3 corresponding acidifying solutions were prepared by adding 5% by volume of the concentrate to 95% by volume - 15% by weight of HCl. Each resulting acidifying solution was tested for its ability to decompose the synthetic oil well mud in a manner identical to the previous examples. Everything worked quite simply to disintegrate and disperse the sludge, but the solutions with butyl alcohol and decanol were not much faster than the surfactant alone, and this was confirmed by

C -CD alcohols are preferred more than C - C,Avil could

6 oAlu

are used. All the higher alcohols (C^-^q) cause the oil phase in the sludge to come out clean without any obvious emulsion formation. This is an improvement, even for the slow-acting alcohols (C.-Cn„) over the use of

4 10

surfactant (phosphate ester) alone for well treatment. This property is probably related to the preferred solubility of the higher alcohols into the oil phase of the sludge. E.g. isopropyl alcohol, which is much more water-soluble than butyl alcohol, did not produce the anti-emulsion effect as when using "Klearfac". It is therefore clear that compositions in accordance with the present invention require an alcohol with low water solubility in order to achieve improved penetration of the oily sludges and reduce the formation of emulsions to a minimum.

EXAMPLES XXXI- XXXVII

In order to establish recommended levels for the amount of water in the concentrate, a series of 7 concentrate solutions was prepared as follows:

A pour point test according to ASTM method D-97 was carried out with each of the above solutions. The following table I summarizes the results.

From the foregoing, it was concluded that at least 2% water and no more than about 18% water is preferred when producing a concentrate that will flow under wide temperature limits. The specific densities of concentrate 4 (5% water) and concentrate 6 (15% water) were determined to be 0.925 and 0.950, respectively. A flash point of 78°C, but point of 88°C

and a viscosity (at 10°C) of 38 cp was determined for Concentrate 6 (ASTM D-93).

EXAMPLE. XXXVIII

To further demonstrate;-sat phosphate esters and the high molecular weight alcohol are soluble in acid without the presence of a diluent and that the resulting acidifying solution is highly effective, a 60 ml portion of "Klearfac AA-270" was mixed with 40 ml of isooctyl alcohol under formation of a clear viscous solution. After mixing this with hydrochloric acid at both 5 and 15% strength by weight, it was determined that the mixture of surfactant/alcohol with a high molecular weight is soluble in all proportions. Alcohol included. the lower alcohol weight is thus not necessary for the solubilization of the alcohol with the high molecular weight in the acid.

A 5 ml portion of the above surfactant/alcohol mixture was mixed with 95 ml of 5% by weight HCl and added to 5 grams of the synthetic oil sludge. The sludge disintegrated and dissolved rapidly.

A 1 ml sample of the surfactant/alcohol mixture was then added to 99 ml of 5% by weight HCl and to this was added a further 15 gram sample of synthetic oil sludge. Here, too, the sludge disintegrated and dissolved quickly.

The process was repeated using 3 mL of the surfactant/alcohol mixture and 97 mL of acid slurry (12 wt% HCl/3 wt% HF). The oily sludge disintegrated and dissolved quickly here as well.

From this it was concluded that the complex of phosphate esters/alcohol with a high molecular weight works well alone in acid without a diluent, e.g. with the alcohol of lower alcohol content or with water.

EXAMPLES XXXVIX- XLV

To test the miscibility of the acidifying mixtures

in accordance with the invention with other types of acids, a series of 8 acidifying solutions was prepared using the mixture of 30% surfactant, 20% isooctyl alcohol, 40% isopropyl alcohol and 10% water (EXAMPLE XXIV) as a concentrated phosphate ester/alcohol which indicated in the following table II.

As previously indicated, the acidic solutions to which the surfactant/alcohol mixtures are added may be any of the aqueous solutions of water-soluble acids commonly used for acidizing formations. The aqueous acidic solutions may contain from less than about 5% to about 30% by weight of the acid and yet the phosphate ester surfactant/high molecular weight alcohol mixture becomes soluble and the acidic solution remains stable. Approximately 7 to 15% by weight HCl solution is preferably used when acidizing wells.

The present acidifying additive is considered essentially usable with any of the well known acidifying processes. The additive can be used to treat oil-producing wells, e.g.

in a water supply process for an oil-bearing formation,

and in other secondary and tertiary extraction methods.

In the case of a producing well, the aqueous acidic solution and the surfactant/alcohol additive are injected into the oil-bearing formation, after which the well is returned to oil production. In a water injection well, the acid and surfactant/alcohol additive are injected into the oil-bearing formation, after which the well is returned to oil production. A water injection well injects the acid and surfactant/alcohol additive into the oil-bearing formation followed by further fluid injection.

Regardless of whether it is a production or injection well, the surfactant/alcohol additive may be mixed with the acidic solution or may precede and/or follow the acidic solution, or any combination thereof. These processes can also be used in connection with pre-treatments and post-treatments with other well-known solvents for a number of purposes such as e.g. and not limited to various aromatic solvents to remove asphaltenes and other heavy deposits, various sulfur-containing solvents and the like.

The principle value of the surfactant/alcohol additive preceding the acidic solution is the displacement of the oil before the acid so that mixing and possible emulsification is reduced. Such a torsion or clumping process also works to dissolve or solubilize organic deposits that could otherwise block the flow of acids into the oil-bearing layers. This batch process of injecting a surfactant/alcohol additive also works to break down emulsions that tend to form due to naturally occurring emulsifiers. It is envisaged that by controlling the concentration of the additive present in sequential lump or portion injection, the specific functions of emulsion breakdown, removal of organic deposits and acidification can be selectively controlled as required.. < .-.

The advantages of the surfactant/alcohol additive being mixed with the acid are the solubilization of the oil in contact with the acid and the improved displacement of the oil with the acid leaving solid surfaces, especially finely divided solids, in a water-moistened state. The surfactant/alcohol additive following the acid is of value in displacing and dissolving oil and organic solids not displaced or dissolved by the previous steps. This is especially the case if the additive has not been used in the previous steps. A portion of additive following the acid solution is particularly valuable in a water-injection well to ensure displacement of any remaining oil so that more pore volume is available for flow

of injected water into the formation.

The amount of acid can be any within the range from e.g. 1000 liters to several thousand liters commonly used in well acidification. However, treatment is generally intended primarily for the zone immediately surrounding a wellbore so that the volumes are usually somewhat smaller than average. Preferred are those from about 1,000

to approximately 20,000 litres. Put another way, the use of from about 100 to about 5,000 liters of acid per meter formation thickness satisfactory, as recommended in US patent 3.548.-945.

If a pretreatment or preflushing portion of surfactant/alcohol additive precedes the acidic solution, the volume of this pretreatment portion should vary from about 1% of the volume of acidic solution for large acid treatment to about 100% of the volume of acidic solution for minor acid treatments. In such cases, the ratio of surfactant to high molecular weight alcohol can also be revised to take into account their individual mutual impact on the oil deposits. Approximately the same volumes should be used for portions of surfactant/alcohol additive used as a backwash to displace the acidic solution into the formation.

Véd cleaning of injection wells, namely by removal

of clogging sludge, emulsions or gravel, where acidification of the formation is not the primary purpose, it is often advantageous to reduce the total volume of acid solution and increase the concentration of additive. This is economically beneficial to keep costs low. Furthermore, the ratio of higher alcohol/phosphate ester surfactant can be increased as in example V to reduce costs (the surfactant being the most expensive).

As indicated above, the essential application of the invention is for oil-producing wells and injection wells in water introduction operations or the like. The process is also sometimes useful for treatment

of gas wells and gas condensate wells. Many gas wells condense some oil and many oil wells condense some gas. Therefore, organic deposits can form in and around the gas wells. Many gas wells produce water. Therefore, mineral deposits can also form in and around gas wells. When the gas wells are acidified to remove such mineral deposits and otherwise increase the flow of gas to the wells, oil present in the formation can emulsify with the acid in a similar way as in oil wells. In such applications, the ability to foam in accordance with the present invention is considered an advantage when extracting acid from the formation and when nitrogen is used for the same purpose. It will thus be clear that many of the same problems that make the use of a surfactant/alcohol additive advisable when acidizing oil wells often also occur in gas and gas condensate wells.

The method of obtaining the advantages of using the present surfactant/alcohol additive during acidification will be better understood from the following examples.

EXAMPLE XLVI

To demonstrate the idea of using a substituted alcohol as a high molecular weight alcohol in the surfactant/alcohol additive, an ethoxylated nonylphenol (4 mol ethyl octyl adduct) with a terminal hydroxyl group and sold under the trade name "Surfonic N401' is used." Surfonic N40" has practically no solubility in 15% by weight HCl, (same as isooctyl) but is dispersed (emulsified) into it. An additive mixture containing 25 ml "Surfonic N40", 25 ml "Pluraflo OFT90"

and 50 ml of isopropyl alcohol was prepared. Additive i '. the agent constituted a clear solution with from 2-10% by volume

in 15 wt% HCl. 100 ml of 5% by volume additive in 15% by weight HCl was added to 5 grams of oil sludge. The observed rate of dissolution/dispersion was not as high or complete as previous isooctyl additives but the results were usable in that the solids were wetted with water and no thick (emulsion) oil layer appeared on top. The experiment was repeated without the ethoxylated nonylphenol and resulted in an unacceptably thick viscous oil layer on top. It was concluded that "Surfonic N40" was usable but not as good as the high molecular weight linear alcohols.

With the oil-soluble, mainly water-insoluble monohydric alcohols being preferred, other alcohols with similar solubility and hydrophilic-lipophilic balance can be used

(HLB) as CD ,-CO0 linear alcohols are used. E.g.

the solubility and HLB of ci2~C22 fatty alcohols with a very high molecular weight, polypropylene-polybutylene glycols, alkyl-substituted phenols and C^2-C22f^acids can be changed to a usable range by reaction with a few moles of ethyl oxide. The resulting substances with the necessary oil solubility and at least one terminal hydroxyl group to

give an alcoholic character, can be represented using the general formula:

R,-Ro-O—FCH„CH_-C4 CH„CH„OH

12 u 2 2 Jx:-: 2 2

wherein R1 is CO^ or CO^C^OH, R2 is a C11 to C hydrocarbon chain, polypropylene oxide, polybutylene oxide, or -(CH2-4~10or2oCO~fatty acid residue/alkyl (Cg-Cl0) substituted phenyl unit, and X is an integer from 3- 15 representing the number of moles of ethylene oxide added to •

EXAMPLES XLVII- LIII

A number of field tests of the present invention were conducted in water injection wells, oil producing wells and* gas producing wells. Field testing involved the use of an additive containing 30% by volume "Klearfac AA-270" as a phosphate ester surfactant, 20% by volume isooctyl alcohol, 40% by volume isopropyl alcohol and 10% by volume water. The results of these tests are presented in table III.

EXAMPLE LIFE

A water injection well, in Smith County, Texas, and used to inject water into the Paluxy formation at a depth of 198 m at a rate of 2,000 barrels per day. day at 140 kg/cm<2>, was treated with a mixture of 1893 liters of 15% by weight HCl containing 5% by volume of the additive in EXAMPLES XLVII-LIII and

757 liters of xylene. The xylene and the acidizing solution were mixed and then injected into the formation and allowed to act for 1 hour. The brine + diverter mixture is then used to flush the formation and an additional 13247 liters of the acidizing solution (with 5% by volume additive) is injected. Water injection was then resumed. Before the treatment, the well received

2000 barrels of water per day at 140 kg/cm 2, while after the treatment the water injection was 4,500 barrels at only 35 kg/cm 2.

It will be easily understood from the foregoing that in addition to the advantages of economy for the additive used in relation to previously known mixtures, the invention leads to savings associated with the operation of injection wells and increased production associated with gas and oil producing wells.

Having described the preferred embodiments of the invention in some detail, it is to be recognized that many changes may be made in the details of the preparation or use of the additive of surfactant/alcohol and acidifying solution without outside the scope and idea of the invention. It is thus envisaged that other acid-stable additives for different specific purposes can be incorporated, including e.g. such additives as corrosion inhibitors, formation stabilizing additives, trace compounds, emulsion breakers, asphaltene solvents and the like. It is therefore to be understood that the invention is not limited to the embodiments indicated herein for exemplifying purposes, but shall only be limited by the scope of the appended patent claims including a followed range of equivalents to which each element therein is entitled.

Claims (10)

1. Procedure for treating an oil-bearing formation, characterized by bringing the formation into contact with an aqueous acidic solution containing a C 1 -C 10 aliphatic alcohol or an alcohol of formula: in which a group is CH^ or - CU^ CH^ OU, is a cn _C2l hydrocarbon chain, polypropylene oxide, polybutylene oxide of -(CH2—)—til2o CO fatty acid residue, alkyl substituted phenyl group and X is an integer from about 3 - 15, pg an effective amount of a phosphate ester surfactant to render the alcohol soluble in said acidic solution. 2. Method as stated in claim 1, characterized in that the phosphate ester-over-flotation active agent is a phosphate ester of an oxyalkylated fatty alcohol, and the aliphatic alcohol is a CD ^- CO 0 such as e.g. isooctyl alcohol. 3. Procedure as specified in claim 1 or 2, k a ri'a' k t. e r i s e r t in that the aforementioned aqueous acidic solution also contains an alcohol or diol with a low molecular weight. 4. An acidifying mixture for carrying out the method as stated in claim 1, characterized in that it comprises: a) an aqueous acidic solution b) a C,-C. _ aliphatic alcohol or an alcohol with 4 10 formula: in which R is a group CH^ - or^ Cf^Cr^OH, R2 is a C-q hydrocarbon chain, polypropylene oxide, polybutylene oxide of~ (CH2~ ^~10 t'""120 CO-^etAcid residue' alkyl substituted phenyl group, and x is an integer from approximately 3-15, and c) an effective amount of a phosphate ester surfactant to render the alcohol soluble in the acidic solution. 5. Acidifying mixture as stated in claim 4, characterized in that. at least 75 and preferably at least 90 parts by volume of said aqueous acidic solution containing up to 20% by weight of acid' is combined with up to 25 and preferably up to 10 parts by volume of a mixture of said aliphatic alcohol and the phosphate ester surfactant wherein mixtures comprise up to about 8 parts by volume alcohol to 5 parts by volume surfactant. 6. Acidifying mixture as stated in claim 4 or 5, characterized in that the acid is selected from the group consisting of HCl, HF, acetic acid, sulfamic acid, citral acid, glycolic acid, NH^HF2 and mixtures thereof and that the aliphatic alcohol is a CD,- C0 O alcohol and that the phosphate ester surfactant is a phosphate ester of an oxyalkylated fatty alcohol. 7. Acidifying mixture as stated in claims 4-6, characterized in that the acid is HCl, HF or mixtures thereof in which the aliphatic alcohol is octyl alcohol and the phosphate ester surfactant is a phosphate ester of oxyalkylated fatty alcohol. 8. Acidifying mixture as stated in claims 4-7, characterized in that it comprises an effective amount of a water-soluble alcohol or diol with a low molecular weight. 9. Acidifying additive, characterized in that it comprises) a C4 _c^o water-soluble aliphatic alcohol or an alcohol of formula: wherein eb group is CH^- or -Cr^Cr^OH, R2 is a cn~ C21 hydrocarbon chain' polypropylene oxide, polybutylene oxide of -(C2"~ ^~io to 20 CO_^ett? uric residue' alkylsu,st;i-tuated phenyl group and x is an integer from approximately 3 to 15, b) a phosphate ester surfactant and, if desired, also a water-soluble low molecular weight alcohol or diol and water. 10. Acidifying additive as stated in claim 9, characterized in that the water-soluble alcohol or diol with a low molecular weight is selected from the group consisting of methanol, ethanol, n-propanol, isopropyl alcohol, ..t-butyl alcohol, and ethylene glycol, the alcohol is a CD ,-CQ o alcohol and the surfactant^ is a phosphate ester of an oxyalkylated fatty alcohol. )