NO753970L - - Google Patents

Description

The present invention relates to a method

to increase the production of fluids from underground fluid-bearing formations. More particularly, the present invention relates to a method in which the productivity of a hydrocarbon-containing formation containing acid-soluble components, with or without water-sensitive clays or shale, is improved by treating the formation with an aqueous solution of a non-oxidizing mineral acid (or carbon dioxide) and an anti-flake compound as will be described below. Said anti-flake compound eliminates the clogging of the capillary openings

which is due to a precipitation of dissolved salts after the acidification, at the same time that mineral flakes in production equipment such as pumps or pipes, caused by such precipitation, are eliminated.

Methods have long been known to increase the permeability of underground hydrocarbon-containing formations and to remove obstructing acid-soluble mineral flakes for the purpose of stimulating the production of fluids from such wells. Such a method, which is usually called acidification, is widely used in the treatment of underground acid-soluble geological formations, e.g. limestone or.dolomite. However, the technique is not limited to formations with high acid solubility. Sandstone and gypsum-containing formations may require acidification if the produced water is unstable with respect to CaCG^. In the usual method for acidizing such wells, a non-oxidizing mineral acid is passed down the well under sufficient pressure to force it into the adjacent underground formation, where the solution reacts with components of the formation and deposited mineral flakes, especially carbonates such as calcium carbonate and magnesium carbonate, whereby the corresponding salts of the acid, carbon dioxide and water are formed. The most common mineral acid used during such acidification is hydrochloric acid.

During the acidification process, passages for the liquid are formed or existing passages are increased so as to stimulate the production of oil, water, brine and various gases. - If desired, the acidification can be carried out under a sufficiently high injection pressure to create cracks in certain layers or in the entire formation which thereby opens passages further into the formation so that the acid can act far away from the borehole itself.. The salt or salts that are formed during the neutralization of the acid are highly water-soluble and are easily removed by a return flow from the formation and into the borehole.

However, certain complications arise when using hydrochloric acid or other similar non-oxidizing mineral acids. During the acidification, the following beneficial reaction occurs:

Under the high pressure necessary to carry out acidification, the carbon dioxide is dissolved in the reaction mixture consisting of used water and formation water:

This equilibrium equation can be summarized and written in the following way:

After acidizing is complete, the well is often reverse flowed if you have a water injection well (to clean the formation and adjacent tubing) or returned to production if it is an oil or gas production well. In both cases, the pressure decreases and COg breaks out of the solution and precipitated calcium carbonate is obtained. If such precipitation occurs inside the capillary passages in a dense formation or in adjacent production equipment in the form of mineral flakes, this can significantly lower the production quantity by either the capillary passages and/or adjacent equipment becoming clogged.

It is well known that polyphosphates are very effective in lowering or holding back a CaCO^ precipitate. However, these polyphosphates are unsatisfactory in acidic solutions because they are rapidly hydrolysed in the presence of mineral acids, and thereby the compounds lose their properties with regard to preventing flake formation. In addition to the fat, one of the hydrolysis products, i.e. the phosphate ion (P0^~^), can be precipitated together with calcium or barium ions present in the produced water, which results in further clogging or the formation of flakes, which only increases the problems and difficulties. Other known flake-inhibiting compounds are the so-called "vitreous" phosphates, which are unsatisfactory due to their poor solubility in acidic media and which also tend to form hydrolytic reaction products.

It is also known that different organic polymers can be used to prevent the precipitation of mineral salts, but many such polymeric compounds are unstable mineral acids, and spontaneous depolymerization into ineffective compounds is often obtained. One such polymeric compound which is easily hydrolysed in the presence of acids is polyacrylamide which is unstable in aqueous media at temperatures from 120°C and upwards. Many wells that have been treated with the present method have bottomhole temperatures of 120-150°C or higher.

Chemically modified natural polymers or natural polymers themselves are effective inhibitors to prevent a precipitation of mineral salts. However, it is the case that certain compounds, e.g. sodium carboxymethyl cellulose precipitates or decomposes in the presence of mineral acids. Other known compounds such as citric acid or tartaric acid and/or complexing agents such as ethylenediaminetetraacetic acid and its water-soluble salts are known inhibitory compounds to prevent the deposition of scale in aqueous media. However, such compounds cannot be used in the treatment of underground formations, because they are not particularly surface-active and are not adsorbed on the surface of the formation.

The present invention provides a method for increasing the production of fluids from underground fluid-containing formations containing acid-soluble components, and which includes injecting into said formation an aqueous acid solution consisting of: (a) from 0.5 to 28 percent by weight of a non-oxidizing mineral acid and from 0.01 to 5 weight percent carbon dioxide, and (b) from 0.005 to 2 weight percent of a sulfonated anti- .

flake connection with the following formula:

where A is an alkali metal or ammonium ion, and X is a group of the following formula:

where

R is an alkaryl group having from 6 to 18 carbon atoms in its alkyl part, or a saturated or unsaturated aliphatic hydrocarbon group having from 8 to 20 carbon atoms

n is a number from 1 to 10, and

R^ and R2 which may be the same or different, each is a saturated or unsaturated aliphatic hydrocarbon group of up to 20 carbon atoms, and wherein the total number of carbon atoms in R^ and Rg ranges from 9 to 30.

According to one embodiment of the present invention, the production of fluids from underground fluid-containing formations containing acid-soluble components is increased by injecting an aqueous acid solution down the borehole of said formation and from there into said formation under a pressure greater than the formation pressure, after which you hold up - the solution in contact with different layers in the formation for a sufficiently long time for the acid to react chemically with the acid-soluble components and/or acid-soluble mineral flakes deposited in the production equipment, to etch or increase passages through said layers or to remove said flakes, thereby significantly increasing the flow capacity in the underground formation.

According to another embodiment, the formation is drilled through with at least one production well and one injection well, after which said solution is injected into said formation and displaced through it, after which the fluids from the formation are recovered through the production well. The anti-flake compound prevents precipitation of the compounds formed by the reaction between the acid component and components in the formation, whereby the production of hydrocarbons from the formation via the production well can be significantly increased.

When carrying out the present method, carbon dioxide is released continuously, whereby an advantageous effect is obtained due to the mutual miscibility of carbon dioxide in the liquid phase, this produces a reduction of the viscosity and capillary forces present, while another advantageous effect is an increased formation energy due to the pressure created by the released carbon dioxide..

Another advantage of the present method is that subsequent precipitation of dissolved carbonates is prevented or significantly reduced. Such post-precipitation occurs due to the following reaction:

- If the pressure is lowered so that the reaction products from the acidification process can be removed, the carbon dioxide gas will break out of the solution and produce a post-precipitation of calcium carbonate. If such post-precipitation occurs inside the formation, it usually occurs close to the borehole and can lower the permeability there by the capillary passages being blocked, this happens particularly close to the borehole itself, and this results in a lower production quantity. Furthermore, such post-precipitation can occur in pipes inside the well itself and will manifest itself as mineral flakes, and this reduces the diameter of the pipe or pipes and also results in a lower production quantity. A group of antifouling compounds consists of water-soluble, sulfonated, ethoxylated alkylphenols or alcohols with the following formula

where R is an alkaryl group with from 6 to 18 carbon atoms in the alkyl part or a saturated or unsaturated aliphatic hydrocarbon group

with from 8 to 20 carbon atoms, n is a number from 1 to 10 and A+ is a monovalent cation such as sodium, potassium or ammonium. One can use mixtures of such compounds with different values for R, n and A, if this is desired.

Another group of antiflaking compounds consists of water-soluble, substituted taurines with the following formula

where R and R^ can be the same or different, and each is an aliphatic hydrocarbon group, either saturated or unsaturated, with up to 20 carbon atoms, and where the total sum of carbon atoms

in R and is between 9 and 3^»and where A is an alkali metal or ammonium ion.

Examples of phenols that can be used for the production of a group of anti-flake compounds are straight or branched alkylphenols, such as hexyl, isohexyl, heptyl, octyl, isooctyl, nonyl, decyl, dodecyl, tridecyl -, tetradecyl- and hexadecyl-phenol. The antiflaking compounds contain one or more ethoxy groups linked to the alkylphenols. Thus, e.g. the compounds be dl-, tri-, tetra-, penta-, hexa-, octa-, nona- and decaethoxy compounds which have been sulphonated. A preferred group of compounds includes the sodium and ammonium salts of sulfonated C 6 -C 8 alkylphenols having from 3 to 10 oxy groups.

Representative examples of alcohol compounds

which can be used in the present invention include sulfonated, ethoxylated octyl, decyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, pctadecyl, nonadecyl and eicosyl alcohols, including the branched isomers. The alcohol can be either primary or secondary or a mixture of such alcohols.

The ethoxy part of the alcohol can e.g. be di-, tri-,

tetra-, penta-, hexa-, octa-, nona- or deca-ethoxy.

A particularly preferred group is derived from<C>12""<C>18Primary alcohols and has from 3 to 10 ethoxy groups,

and particularly preferred are sodium and ammonium salts of these compounds.

Representative substituted taurine compounds include those in which either the R group or the R^ group is methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl or eicosyl, including branched and unsaturated variants of such groups, e.g. oleyl. It is understood that mixtures of such R and R^ groups can be used, e.g.

those derived from coconut oil, tall oil, palm oil and the like.

The preferred substituted taurines are those where the R 1 -substituent is a relatively low molecular weight aliphatic hydrocarbon group, e.g. with 1 to 4 carbon atoms, such as methyl, ethyl, n-propyl, isopropyl, n-butyl or isobutyl and where the other substituent R is a saturated or unsaturated, straight or branched aliphatic hydrocarbon chain with from 8 to 20 carbon atoms, more particularly such hydrocarbons which are derived from coconut oil, palm oil and tall oil acids etc, i.e. which have a high content of oleyl groups.

According to one embodiment, the preferred aqueous acidic composition consists of an aqueous solution which may include salt solution, and which contains from 0.5 to 28 weight percent, preferably 3 to 15 weight percent of a non-oxidizing mineral acid such as hydrochloric acid, and from 0.01 to 5 weight percent, preferably from 1 to 3 weight percent carbon dioxide, and which also contains between 0.005 to 2 #, preferably from 0.05 to approx. 1 percent by weight of the aforementioned compound.

Typically, the aqueous non-oxidizing mineral-acid solution will contain an inhibitor to prevent or substantially reduce corrosive attack by the acid on metals. In this respect, a number of compounds known for this purpose can be used, e.g. compounds of arsenic, nitrogen or sulfur as described in US Patent No. I,877,504. The amount of inhibitor is not critical and can vary within a large range. Usually, the amount will be defined as a small but effective amount, i.e. from 0.02 to approx. 2.0% by weight.

When carrying out a method according to the present invention, one first prepares a solution containing the desired amount of said non-oxidizing mineral acid or carbon dioxide dissolved in water. An inhibitor is then added to prevent corrosion of the mineral acid on metal equipment included in the drilling equipment. The anti-flake compound is then added or mixed with the aqueous acid solution in an amount that lies within the aforementioned concentration range. The acid solution produced in this way is pushed, usually via a suitable pump system, down through the well and into contact with the production equipment or formation to be treated. The pressure to be used will be determined by the type of formation, the viscosity of the liquid present and other variables. The acidizing method according to the present invention can be carried out at a pressure that is only sufficient to penetrate the formation, or it can be sufficiently large to compensate for the weight of the overlying masses and create cracks in the formation. Splitting agents for splitting open cracks, e.g. from 20 to 60 mesh sand in accordance with known methods, can be used in mixture with the aqueous acid solution. Usually, it is advantageous to allow the aqueous acid solution to come into contact with the formation and the production equipment until the acid is substantially consumed by reaction with the acid-soluble components of the formation or the deposited flakes. After this, the essentially used solution is taken out of the well, i.e. it is allowed to flow out or pumped out of the formation. It is further understood that the concentration of the various compounds must be chosen so that the acidifying liquid acquires the desired theological properties.

Another embodiment of the present method

can be carried out using a number of injection and production systems which consist of one or more wells that penetrate the layers or formations you wish to process. Such wells can be placed in a certain pattern which is well known from the oil drilling technique. One can e.g. use a so-called "line filling" window, where the injection and production systems stand in rows at a certain distance from each other. The extraction zone, i.e. the part of the formation from which the hydrocarbons are displaced with the help of the driving fluid to the production system, will in this case be the part of the formation that lies below the area between said rows. Another pattern that is very often used is the so-called "circular filling system", where the injection system consists of a central injection well, while the production system consists of a number of production wells that stand at a certain distance from the injection well itself. In a similar way, injection and production

the systems each only consist of a single well, and here the extraction zone will be the part of the formation that lies under an ellipse that is between the two wells. For a more detailed description, of such extraction patterns, reference is made to Uren, L.C., Petroleum, Production Engineering - Oil Field Exploitation, 2nd edition, McGraw Hill Book Company, Inc., New York, 19.39 and US patent no w 3,472,318 and 3,476,182.

When carrying out this embodiment of the invention, the aqueous acidic solution and the anti-flake compound are usually pushed via a suitable pump system, down the injection well itself and into the formation through which it is displaced together with the hydrocarbons in the formation to the production well. As

in other embodiments, the pressure used will be determined by the type of formation, the viscosity of the fluid and other operating variables, and the acidizing method according to the present invention can be carried out at a pressure that is only sufficient to penetrate the formation, or the pressure can be so great that cracks are created in the formation, and in such cases it is possible to use splitting agents as described earlier.

The formation can be treated continuously with the acidic solution or the treatment can be temporary. If desired, however, normal filling can be resumed after a certain time. The aqueous* acidic solution containing the antiflaking compound can also be used in a modified water filling operation where a plug or a portion of the aqueous acidic solution is first injected and pressurized into the underground formation. This first step is then followed by a corresponding injection step where a plug or a portion of an aqueous driving liquid, e.g. water, is injected, after which the two steps are repeated. This order can be repeated so that you get a continuous cyclical process. The size of the plugs or portions can be varied within relatively wide limits and will depend on a number of conditions, such as the thickness of the formation, its characteristics as well as the conditions for the subsequent injection of an aqueous, driving medium.

The anti-flake compound provides means whereby ions produced by the reaction between the acid component of the solution and components of the formation, and which will tend to precipitate salts such as calcium carbonate, hydrous iron oxides and calcium sulfate.2H 2 O, will combine with the anti-flake compound to form highly stable complexes so that solid salts do not precipitate from the used solution. This binding of the aforementioned ions from weakly ionizing compounds means that the formed complex remains dissolved in the treating solution and is thus passed through the pores in the formation. Furthermore, the compound in the present composition will provide devices by which nucleation and growth of solids are restrained, so that the used solid salts do not precipitate from the solution. Furthermore will. the compound make it so that you continuously get protection against post-precipitation of salts for a considerable period of time after the treatment, because you get a continuous slow desorption of the compound from the formation surfaces. If, on the other hand, surfactants with only dispersing and suspending properties are used, and which do not have the ability to molecularly bind said produced ions or stop a nucleation and growth of solid salts, then you will get a post-precipitation of said salts from the dissolution and very often a plugging of passages and pores in the formation during the subsequent recovery of the desired hydrocarbons.

It is understood that concentrations of the aforementioned compound and the acid components are chosen so that a displacing liquid with the desired rheological properties is obtained. Furthermore, of course, the connections must be chosen so that account is taken of the formation to be treated as well as other operating conditions.

If desired, one can also add the aqueous mineral acid solution containing the anti-flake compound, a polymeric compound that restrains the acid's tendency to attack calcareous components in the formation. For this purpose, polyvinylpyrrolidone is particularly well suited, which is described in US patent no. 3"749*169"

Example 1

A production well in East Texas was treated as follows.

A treatment mixture was prepared by mixing 10 barrels of salt water containing 2.6 weight percent sodium chloride<p>g

12 barrels of a 28 percent by weight aqueous hydrochloric acid and 0.1 barrel of the sodium salt of sulfonated pentaethoxydodecylphenol.

The treatment mixture was pressed into the formation in an amount of approx. l/2 barrel per minute at a pressure of 32 kg/cm . The pipe pressure was 32 kg/cm<2> and this decreased to zero within a short time. The well can then be returned to production.

Example 2

A mixture was prepared from 10 barrels of brine ($2.6 sodium chloride) and 10 barrels of a 15 weight percent aqueous hydrochloric acid solution containing 0.2 barrels of the antiflaking compound of Example 1. The aqueous acid solution was injected into the producing formation at the same manner as indicated in Example 1. Then 20 barrels of water were used to flush the treated formation, and the water was injected down through the pipe itself, after which 10 barrels of water were injected down through the well pipe. The well can then be returned to production.

Example 3

The aqueous acid solution from Example 2 was injected into another producing formation. A flush of 10 barrels of water was used to force the aqueous acid solution into the formation by injecting the water down the pipe itself. The well can then be returned to production.

Examples 4 - 12

The procedure from Examples 1 to 3 was used, using: Examples 4 to 6 - Sodium salt of a sulphonated pentaethoxy nonylphenol.

Examples 7 to 9 - Sodium salt of a sulfonated pentaethoxy-m-pentadecylphenol.

Examples 10 to 12 - Sodium salt of a sulfonated heptaethoxy-m-pentadecylphenol.

It is of importance that the alkaryl compound is effective in the presence of high concentrations of calcium ions, i.e. 1 or more, and then especially and relatively uniquely in applications where one has high solution temperatures, e.g. above 100°C.

The mixtures used in the present invention are stable even in the presence of mineral acids. Laboratory heat stability tests showed that the compound used in Example 1 remained active after exposure to a temperature of 177°C for 5 days. The compound retained 79.5% of its activity upon 3 hour exposure to 13% by weight sulfuric acid at 177°C.

The alkaryl compositions described above can

is prepared in the following way: The polyethoxyalkylphenol is treated with thionyl chloride for 18 hours at 100°C, whereby the monochlorinated derivative is formed,

and this is then reacted with sodium sulphite for 18 hours at 155°G in a 1/1 volume mixture of water and ethanol in a Paar bomb. The resulting recovered sulfonated product shows approx. 75 $ sulfonation of the terminal ethoxy group. This method is only intended as an example, but the method was, as said, used to produce the specified compositions. /-You can of course also use other synthesis routes. E.g. a sulfated, ethoxylated alkylphenol can be treated with sodium sulfite at 200°C for from 10 to 12 hours, and a relatively high yield (about $75-80) of the desired sulfonated, ethoxylated alkylphenol is obtained. Direct reaction between the ethoxylated alkylphenol and mixtures thereof with reagents such as sulfuric acid or chlorosulfonic acid, however, results in sulphation.

Example 13

Through a water injection well drilled into a limestone formation, an aqueous 15 weight percent hydrochloric acid solution containing 0.5 weight percent, based on the total weight of the solution, of the sodium salt of a sulfonated pentaethoxynonylphenol was forced into the formation under pressure. The pressure which was necessary to inject the desired volume of water decreases significantly, and no increase in said pressure could be noticed after the treatment, which clearly indicates that a post-precipitation of calcium chloride inside the formation was prevented. The well was then returned to regular water injection. After 6 months, the production of hydrocarbons from an adjacent production well had increased significantly.

Example 14

A filling was carried out in an oil-containing reservoir by means of the present method. Four injection wells were placed in a rectangular pattern around a single centrally located production well in the aforementioned system. A plug consisting of 75 barrels of an aqueous acid solution containing 1 percent by weight, based on the total weight of the solution, of the compound used in Example 13 in a 3 percent by weight hydrochloric acid solution was displaced via each of the four injection wells into the formation in an amount of approx. 5° barrel per day and night. In the next step, 100 barrels of water were injected under pressure into the production formation through each of the aforementioned injection wells in a quantity of approx. 55 barrels per day and night. This sequence of fillings was repeated several times, and the result was an increasing injection rate of the driving currents into the injection wells and a subsequent increase in the production amount of hydrocarbons via the production well.

Example 15

An injection well in a formation containing approx.

20% by weight HCl-soluble material was treated with 2000 1 normal 15% by weight HC1 followed by 6000 13% HC1 containing 0.5% by weight of the same compound used in Example 13»

The aqueous acid mixture was displaced into the formation at

using water, and the well was then closed for 24 hours. The well was then returned to water injection. Injectability in the well was significantly increased for a significant period of time, which increased hydrocarbon recovery.

Examples 16 - 24

The procedure of Examples 13 to 15 was repeated using the sodium salts of: Examples 16 to 18 - Sulphonated pentaethoxydodecylphenol. Examples 19 to 21 - Sulfonated pentaethoxypentadecylphenol. Examples 22 to 24 - Sulfonated heptaethoxypentadecylphenol.

Corresponding results were obtained as in the aforementioned

examples 13 to 15.

The method can be varied by injecting a larger plug of an aqueous carbon dioxide solution of the aforementioned compound, after which one injects an aqueous solution of a polymeric mobility agent, after which one carries out a normal water filling. Repeated treatments with one or more of these steps fall within the scope of the present invention. In addition to or optionally, gaseous carbon dioxide can be injected after any of these different types of treatment, which improves the oil's mobility by lowering its viscosity.

Example 25

Through a water injection well that had been drilled in a limestone formation, an aqueous acid solution containing 1% by weight of carbon dioxide and 1% by weight of the sodium salt of sulfonated pentaethoxynonylphenol was pressed into the formation under pressure. The pressure required to inject the desired volume of water decreases significantly, and no increase in pressure could be noted after the treatment, indicating that the post-precipitation of calcium carbonate inside the formation was largely prevented, which would have led to a reduced permeability. The well was then returned to regular water injection. After 8 months, the production of the hydrocarbons from an adjacent production well increased significantly.

Example 26

A filling was carried out in an oil-containing reservoir

using the present method. Four injection wells were placed in a rectangular pattern around a single centrally located production well. A plug or portion consisting of 75 barrels of an aqueous acid solution containing 2 weight percent carbon dioxide and 0.5 weight percent of the same compound used in Example 25 was injected and this amount was injected into each of the four injection wells into the formation with a speed

of approx. 50 barrels/day. In the next step, 100 barrels of water were injected under;

pressure into the production formation through each of the injection wells in an amount of approx. 55 barrels/day. This order of filling was repeated several times, and the result was an increased injection rate of the driving currents into the injection wells and a subsequent increase in the production quantity of hydrocarbons via the production well.

Example 27

An injection well in a formation containing approx.

30% by weight of HCl-soluble material was treated with 6000 1

of a 1.5% by weight aqueous carbon dioxide solution containing 0.4% by weight of the compound used in Example 25• The aqueous acid solution was forced into the formation with water, and the well was shut in for 24 hours. The well was then returned to water injection. The injectability in the well was

significantly increased over a longer period of time, which resulted in improved hydrocarbon recovery.

Examples 28 - 36

The procedure from Examples 25 to 27 was repeated using: Examples 28 to JO - Sulphonated pentaethoxydodecylphenol,

sodium salt.

Examples Jl to 33~Sulfonated pentaethoxypentadecylphenol,

sodium salt.

Examples 34 to 36 Sulfonated heptaethoxypentadecylphenol,

sodium salt.

Corresponding results were obtained.

The examples 37

A production well in eastern Texas was treated as follows: A mixture was prepared by mixing 10 barrels of brine containing 2.6 weight percent sodium chloride and 13 barrels of a 28 weight percent aqueous hydrochloric acid solution and 0.1 barrel of the sodium salt of sulfonated, pentaethoxylated mixed ^j. 2~^ lQ~ alcohols.

The mixture was pressed into the formation in an amount of approx. 1/2 barrel per minute at a pressure of 32 kg/m<2>. The pressure in the pipe itself was 32 kg/cm<2>at the termination, but dropped to zero within a short period of time. The well can then be returned to production.

Example 38

A mixture of 10 barrels of salt water (2.6% by weight sodium chloride) and 9 barrels of 15% by weight aqueous hydrochloric acid solution containing 0.2 barrels of anti-flaking compound from Example 37 was prepared. The aqueous acid solution was injected into the production formation as indicated in Example 37* Then 20 barrels of water were used to flush the treated formation by injecting the water into the pipe itself, after which 10 barrels of water were injected down through the well pipe. The well can then be returned to production.

Example 39

The aqueous acid solution from Example 3°* was injected into another producing formation. A flush of 10 barrels of water was used to force the aqueous acid solution into the formation. The well can then be returned to production.

Examples 40 - 48

The procedure from Examples 37 to 39 was used by using: Examples 40 to 42 - Sulphonated, triethoxylated mixed ('12'"Cl8,"a^kono3's containing 40 $ dodecyl, 30 f> tetradecyl, 20% hexadecyl and about 10 $ octadecyl groups, sodium salt.

Examples 43 to 45 - Sulphonated, triethoxylated mixed C₂Q-C₂ alcohols containing 80% decyl, 10% dodecyl and 10% tetradecyl groups, sodium salt.

Examples 46 to 48 - Sulfonated, pentaethoxylated mixed C₂Q-C₂₂ alcohols containing 85 decyl, 9% dodecyl and 6% tetradecyl groups, sodium salt.

Equivalent compounds were obtained.

It has been found that compounds used in acid solutions according to the present invention are particularly effective in the presence of calcium ion concentrations of 1% by weight or more, then especially and somewhat uniquely in applications where the temperatures are high, e.g. above 100°C. The aliphatic anti-flaking compounds used in accordance with the present invention are temperature stable and effective as anti-flaking compounds even at temperatures up to 150°C, e.g. from 100 to 150°C.

The unusual heat stability of one of the present compounds is graphically shown in the accompanying drawing, which is a diagram produced on a single-cycle semi-logarithmic paper with 70 linear divisions along the abscissa.

The reported data were obtained using the compounds of Examples 46 to 48"

At normal operating pH values of 7.5 and 6.3 in deionized water and representative field water (from the Cote Blanche field) respectively, the half-lives at 116°C were 57.4 (curve 1)

and 33 years (curve 2). The actual experiments were performed at 205°C, and the half-lives were extrapolated to 116°C. It appears that pH 6.3 in the field water at a temperature as high as 204.5°C gives a half-life of 25 days. At a pH of 1, 23% of the activity remained after 15 days at 205°C (curve 3).

In another experiment, the unusual stability of the compound was shown by the fact that after exposure to an aqueous solution of the compound from examples 37 to 39 at 177°C, 93.5% activity was retained after 5 days. After 3 hours of exposure and for a 13% by weight sulfuric acid solution at 177°C, the compound retained 66% of its activity.

The sulfonated ethoxylated aliphatic antiflake compounds can be prepared in the same way as the corresponding alkylphenol derivatives as described in connection with examples 1 to 12.

The compounds used in Examples 37 to 42 above were prepared by reacting commercially available mixed C 1 -C 2 -alcohols (Conoco-Alfol 1218) with ethylene oxide to produce adducts with 5°S 3 ethoxy groups respectively. The resulting respective ethoxylated alcohols were then sulfonated as described above. In a similar manner, the compounds of Examples 43 to 4.8 were prepared using commercially available mixed C 2 -C 2 -C 2 alcohols (Conoco Alfoler 1014 and 1012).

Example 49

A production well in East Texas can be treated in the following way.

A treatment mixture was prepared by mixing .

10 barrels of salt water containing 2.6 weight percent sodium chloride and

12 barrels of 20% by weight aqueous hydrochloric acid and 0.15 barrels of sodium N-methyl-N-oleoyl taurate.

The mixture was pressed into the formation in a quantity of 1/2 barrel per minute at a pressure of 32 kg/cm<2>. The same pressure was present when the tube was closed, but quickly dropped to zero within a short time. The well can then be returned to production.

Example *) 0

A mixture of 10 barrels of salt water (2.6 percent by weight sodium chloride) and 10 barrels of 12 percent by weight aqueous hydrochloric acid solution containing 0.2 barrels of sodium JJ-methyl-H-oleoyltaurate was prepared. The aqueous acid solution was produced into the producing formation in the same way as stated in example 49" Then 20 barrels of water were used to flush the formation by an injection down through the pipe itself, after which 5 barrels of water were injected down through the well pipe itself. The well can then be returned to production.

Example 51

The aqueous acid solution from Example 50 was injected into another producing formation. A flush of 10 barrels was used to force the aqueous acid solution into the formation. The well can then be returned to production.

It is important that the added substance is effective in the presence of high calcium ion concentrations of 10,000 ppm or more.

Examples 52 - 57

The procedure from Examples 49 to 51 was used by using: Examples 52 to 54 - Sodium K-methyl-N-palmitoyl taurate Examples 55 to 57 - Sodium N-methyl-H-talloleic acid taurate

The compounds used in the present invention are temperature stable and effective as flake inhibitors at temperatures of up to 150°C, e.g. from 100 to 150°C.

The compound from examples 49 to 51 can be prepared in the following way: The sodium salt of taurine, KHgCHgCHgSO^Wa was reacted with methylamine, whereby the intermediate sodium N-methyl-taurate was obtained. This intermediate product was reacted with the acid chloride of oleic acid, whereby sodium N-methyl-N-oleoyltaurate was produced.

The reaction conditions to be used during this synthesis are well known.

Example 58

Through a water injection well that had been drilled into a limestone formation, an aqueous acid solution containing 1% by weight of carbon dioxide and 1% by weight of sodium-N-methyl-N-oleoyltaurate was pressed into the formation under pressure. The pressure required to inject the desired volume of water decreases significantly, and no increase in pressure could be noted after the treatment, indicating that post-precipitation of calcium carbonate inside the formation, which would lead to reduced permeability, was largely prevented . The well was then returned to regular water injection. After approx. JO day, the production of hydrocarbons from an adjacent production well increased significantly.

Example 59

A filling of an oil-containing reservoir was carried out using the present method. Four injection wells were placed in a rectangular pattern around a single centrally located production well. A plug consisting of 75 barrels of an aqueous acid solution containing 2% by weight of carbon dioxide and 0.5% by weight of sodium H-methyl-N-oleoyltaurate was pushed into the formation via each of the four injection wells in an amount of approx.

50 barrels/day. In the next step, 100 barrels of water were injected under pressure

into the formation through each of the injection wells in a quantity of approx. 55 barrels/day. This filling was repeated several times, and the result was an increased injection rate of the driving currents into the injection wells and a subsequent increase in the production of hydrocarbons via the production well.

Example 60

An injection well in a formation containing approx.

30% by weight HCl soluble material was treated with 6000 1

of a 1.5% by weight aqueous carbon dioxide solution containing 0.7% by weight sodium N-methyl-N-oleoyltaurate. The aqueous acid solution was pushed into the formation using water, and the well was shut in for 24 hours. Then it was returned to water injection. Injectability in the well increased significantly over a longer period of time and this resulted in improved hydrocarbon recovery.

Examples 6l - 66

The procedure from Examples 5°* to 60 was repeated using

Examples 61 to 63 - Sodium N-methyl-W-palmitoyl taurate Examples 64 to 66 - Sodium K-methyl-N-talloleic acid taurate,

It has been found that compositions according to the present invention are particularly effective in the presence of high calcium ion concentrations, i.e. above approx. 0.5% by weight, and then especially and somewhat unexpectedly in applications where the aqueous solutions have temperatures of over 100°C. Compositions according to the present invention are temperature stable and effective as flake-inhibiting compounds at temperatures up to 150°C, e.g. from 100 to 150°G.

Example 67

Through a water injection well drilled into a limestone formation, an aqueous acid solution containing 1% by weight carbon dioxide and 1% by weight of the sodium salt of sulfonated, pentaethoxylated mixed C-^-C^g alcohols containing 40 $ dodecyl, 30 $ tetradecyl was forced into the formation under pressure , 20 fe hexadecyl and 10 $ octadecyl groups. The pressure required to inject the desired volume of water decreases significantly, and no increase in said pressure could be found after the treatment, which clearly indicates that a post-precipitation of calcium carbonate inside the formation has been prevented to a significant extent, which would lead to reduced permeability. The well was then returned to regular water injection. After approx. 6 months, the production of hydrocarbons from an adjacent production well had increased significantly.

Example 68

A filling was carried out in an oil-containing reservoir using the present method. Four injection wells were placed in a rectangular pattern around a single, centrally located production well. A plug or a portion consisting of 75 barrels of an aqueous acid solution containing 2% by weight of carbon dioxide and 0.6% by weight of the compound from example 67 was injected, and said amount was injected via the four injection wells in an amount of approx. 50 barrels/day. In the next step, 100 barrels of water were injected through each of the injection wells into the formation in a quantity of approx. 55 barrels/day. This sequence of fillings was repeated several times, and the result was an increasing injection rate of the driving currents into the injection wells and a subsequent increase in the production amount of hydrocarbons via the production well.

Example 69

An injection well in a formation containing approx. 30% by weight HCl soluble material was treated with 6000 1 1.5% by weight aqueous carbon dioxide solution containing 0.5% by weight of the compound used in Example 67. The the aqueous acid solution was displaced into the formation using water, and the well was shut in for 24 hours. It was then returned to water injection. The injection capacity in the well increased significantly over a longer period of time and this resulted in improved hydrocarbon recovery.

Examples 70 - 78

The procedure from examples 67 to 69 was used: Examples 70 to 73 - Sodium salt of sulphonated, triethoxy- clay mixed C-^-C^g alcohols containing 40 f> dodecyl, 30 $ tetradecyl, 20% hexadecyl and 10 jb octadecyl groups, sodium salt.

Examples 73 to 75 - Sodium salt of sulfonated, triethoxylated mixed C 12 -C 12 alcohols containing 80% 0decyl, 10% dodecyl and 10% tetradecyl groups, sodium salt.

Examples "j6 to 78 - Sodium salt of sulfonated, pentaethoxylated mixed C-j^-C-^-alcohols containing 85% decyl, 9% dodecyl and 6% tetradecyl groups, sodium salt.

It has been found that compounds according to the present invention are particularly effective in the presence of calcium ion concentrations of 1% by weight or more, and then particularly and somewhat unexpectedly in applications where the aqueous solution can have temperatures of over 100°C.

Claims (8)

1. Method for increasing the production of fluids from an underground fluid-bearing formation containing acid-soluble components where an aqueous acid solution is injected into said formation, characterized in that the aqueous acid solution contains (a) from 0.5 to 28% by weight of a non-oxidizing agent mineral acid or from 0.01 to 5 percent by weight carbon dioxide and (b) from 0.005 to 2% by weight of a sulfonated anti flak connection with the formula where A <+> is an alkali metal or ammonium ion, and X is a group with the formula where R is an alkaryl group having from :6 to 18 carbon atoms in its alkyl group, or a saturated or unsaturated aliphatic hydrocarbon group having from 8 to 20 carbon atoms n is a number from 1 to 10 and R^ and Rg which may be the same or different, each is a saturated or unsaturated aliphatic hydrocarbon group of up to 20 carbon atoms, and wherein the total number of carbon atoms in R^ and Rg is from 9 to 30. 2. Method according to claim 1, characterized in that the anti-flake compound is the sodium salt of a sulfonated pentaethoxynonylphenol, sulfonated penethoxydodecyl - phenol, sulphonated pentaethoxypentadecylphenol or sulphonated heptaethoxypentadecylphenol. 3. Method according to claim 1, characterized in that the anti-flake compound is the sodium salt of a sulfonated pentaethoxylated dodecyl alcohol, an isulfonated hexaethoxylated hexadecyl alcohol, a sulfonated heptaethoxylated pentadecyl alcohol or a sulfonated pentaethoxylated ^ 2. 2' C1& ali*" atic alcohol. 4. Method according to claim 1, characterized in that the anti-flake compound has the following formula where A is an alkali metal or ammonium ion, R^ represents an alkyl group with from 1 to 4 carbon atoms and Rg - CO - represents an acyl group derived from coconut oil, palm oil, tall oil or tallow fatty acids. 5" Method according to claims 1 to 4". characterized in that the solution contains from 3 to 15 percent by weight of the mineral acid. 6. Method according to claims 1 to 4, characterized in that the solution contains from 1 to 3 weight percent carbon dioxide. 7- Method according to claims 1 to 6, characterized in that the solution contains from 0.05 to 1 weight percent of the antiflake compound. 8. Method according to claims 1 to 5, characterized in that the solution contains a splitting agent.