Amphiphilic surfactant containing sulfobetaine group benzoxazine, preparation method of amphiphilic surfactant and efficient oil displacement flushing fluid

Abstract

The invention relates to the technical field of oil field well cementation, in particular to an amphiphilic surfactant containing sulfobetaine group benzoxazine, a preparation method of the amphiphilic surfactant and efficient oil displacement flushing fluid. The amphiphilic surfactant is prepared from the following components in parts by weight: 10 to 20 parts of a p-hydroxybenzene compound, 15 to 25 parts of a diaminobenzene compound, 10 to 15 parts of paraformaldehyde, 5 to 10 parts of toluene and other organic solvents, and 10 to 20 parts of 1, 3-propane sultone. The efficient oil displacement flushing fluid prepared from the amphiphilic surfactant containing sulfobetaine group benzoxazine has the advantages of good temperature resistance and high well wall flushing efficiency at different temperatures, can meet the field well cementation requirements, and has the advantages of simple field construction and remarkable improvement of the well cementation quality.

Description

Technical Field

[0001] The invention relates to the technical field of oilfield cementing, and in particular to an amphiphilic surfactant containing sulfonate betaine group benzoxazine and a preparation method thereof, and a high-efficiency oil displacement flushing fluid. Background Art

[0002] As my country's demand for oil and gas increases, the exploration of oil and gas wells becomes increasingly difficult. With the emergence of some deep wells, ultra-deep wells, and complex oil wells, the requirements for the quality of oil well cementing and the difficulty of improving cementing quality are becoming increasingly high. Among them, the pre-fluid can be divided into isolation fluid and flushing fluid according to its properties. Flushing fluid is usually prepared by adding various surfactants and drilling fluid to water. In on-site construction, flushing fluid can be used alone before isolation fluid or in combination with it. The main function of flushing fluid is to clean the well wall and improve the rheology of drilling fluid, improve the displacement efficiency of drilling fluid and the bonding strength of cement sheath interface, and ensure the sealing quality of cement sheath.

[0003] At present, most oil fields in my country use water-based mud flushing agents that are mainly hydrophilic. They have a good flushing effect on water-based mud, but there are still certain defects for oil-based drilling fluids. During on-site cementing construction, oil-based drilling fluids will form a thin, tough and dense filter cake on the well wall, which will seriously reduce the interface bonding strength, seriously reduce the cementing quality, and even cause oil, gas and water crossflow. Therefore, before cementing operations, a flushing fluid with a wetting reversal and efficient flushing effect should be injected to clean the oil film and filter cake attached to the interface, improve the bonding environment of the cement ring interface, and thus improve the cementing quality.

[0004] There are many types of flushing fluids currently used for oil-based drilling fluids. The Chinese patent with application number CN103965845A discloses a flushing fluid composed of nonionic surfactants, anionic surfactants, organic acids, and viscosity and shearing agents, which has an efficient flushing effect on oil-based drilling fluids. The Chinese patent with application number CN103555304B discloses a high-efficiency flushing and isolation fluid prepared by adding 1 to 1.5 parts of surfactants, 4 to 5 parts of chelating agents, 2 to 4 parts of suspension stabilizers, 0.6 to 0.8 parts of tackifiers, 0.5 to 0.75 parts of viscosity and shearing agents, 25 to 150 parts of weighting agents, 1 to 5 parts of pH regulators, and 0.2 to 0.4 parts of defoamers to 100 parts of clean water. The fluid has the dual functions of flushing and isolation, has high flushing efficiency, a wide range of density adjustment, good suspension stability, and can effectively improve the interface cementation environment and improve cementing quality. However, the existing flushing fluids still have the disadvantages of poor temperature resistance and low flushing efficiency, so that their on-site application effects cannot meet the standard requirements. Therefore, it is particularly important to develop a flushing fluid suitable for different temperatures. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of the prior art and solve the problem that the oil film and oil slurry adhered to the casing wall and the well wall by the drilling fluid, resulting in a decrease in the cement sheath interface bonding strength. An amphiphilic surfactant containing sulfonated betaine group benzoxazine and a preparation method thereof, and a high-efficiency oil displacement flushing fluid are provided. The high-efficiency oil displacement flushing fluid has the advantages of good temperature resistance and high flushing efficiency for the well wall at different temperatures, can meet the requirements of on-site cementing, and has the advantages of simple on-site construction and significantly improved cementing quality.

[0006] The objective of the present invention is achieved through the following technical solutions:

[0007] In one aspect, the present invention provides an amphiphilic surfactant containing a sulfonate betaine group benzoxazine, which is prepared from the following components in parts by weight:

[0008] 10-20 parts of p-hydroxybenzene compounds, 15-25 parts of diaminobenzene compounds, 10-15 parts of paraformaldehyde, 5-10 parts of toluene and other organic solvents, and 10-20 parts of 1,3-propane sultone.

[0009] The p-hydroxybenzene compound has a structural formula of A compound wherein "Y" is an alkane containing an amino group.

[0010] Preferably, the p-hydroxybenzene compound is p-dimethylaminoethyl phenol.

[0011] The structural formula of the diamine benzene compound is A compound wherein "R" is an alkyl group having 0-1 benzene rings.

[0012] Furthermore, in a preferred embodiment of the present scheme, the p-hydroxybenzene compound is p-dimethylaminoethyl phenol.

[0013] In a preferred embodiment of this scheme, the diamine benzene compound is 4,4 ， -Diaminotriphenylmethane, 4,4 ， -Methylenedianiline, 4,4 ， - one or more of di-sec-butylaminodiphenylmethane.

[0014] On the other hand, the present invention also provides a method for preparing the above-mentioned amphiphilic surfactant containing benzoxazine sulfonate betaine group, comprising the following preparation steps:

[0015] S1: In a flask equipped with a condenser, add a p-hydroxybenzene compound, a diaminobenzene compound, polyformaldehyde and toluene in sequence to form a reaction system; heat the reaction system to 90°C under stirring and react for 4 to 6 hours; after the reaction system is cooled to room temperature, add anhydrous magnesium sulfate, stir and filter; then filter, remove toluene under reduced pressure and dry to obtain an intermediate product;

[0016] S2: Add the intermediate product and acetone into a flask, raise the temperature to 50°C, and after complete dissolution, add 1,3-propane sultone / acetone solution dropwise therein. After the addition is complete, continue the reaction for 8 to 11 hours, and then filter, dry, and crush to obtain an amphiphilic surfactant containing benzoxazine sulfonate betaine groups.

[0017] The reaction equation of the amphiphilic surfactant containing benzoxazine sulfonate betaine group is:

[0018]

[0019] The above amphiphilic surfactant containing benzoxazine sulfonate betaine group is used as a cleaning agent for flushing oil film, oil slurry and other substances. It has high cleaning efficiency and good temperature resistance.

[0020] In another aspect, the present invention further provides a high-efficiency oil displacement flushing fluid, which is prepared from the following components in parts by weight:

[0021] 10% to 20% of anionic surfactant, 5% to 15% of nonionic surfactant, 10% to 15% of the above-mentioned amphiphilic surfactant containing benzoxazine of sulfonate betaine group, 5% to 10% of co-surfactant, 1% to 5% of dispersant, and the rest is water;

[0022] The co-surfactant is alcohol ether.

[0023] In a preferred embodiment of the present scheme, the anionic surfactant is composed of a 40% mass concentration aqueous solution of sodium dodecylbenzene sulfonate and sodium fatty alcohol polyoxyethylene ether sulfate.

[0024] In a preferred embodiment of this scheme, the nonionic surfactant is polyoxyethylene ether fatty alcohol;

[0025] The structural formula of polyoxyethylene ether fatty alcohol is R-(OCC) x -OH, wherein R is an alkyl group having 6 to 15 carbon atoms, and x is 8 to 25.

[0026] In a preferred embodiment of the present scheme, the alcohol ether includes but is not limited to one or two of propylene glycol butyl ether and ethylene glycol butyl ether.

[0027] In a preferred embodiment of the present scheme, the dispersed phase is one or more of limonene, n-butanol, ethylene glycol, white oil, and diesel.

[0028] As a further preferred embodiment, the preparation method of the high-efficiency oil-displacing flushing fluid is as follows: weigh an appropriate amount of water into a beaker, add 10% to 15% of an amphiphilic surfactant containing a sulfonated betaine group benzoxazine to the beaker, fully dissolve it in a 40 to 45°C water bath environment, then add 10% to 20% of an anionic surfactant, 5% to 15% of a non-ionic surfactant in sequence, stir evenly, then add 5% to 10% of a co-surfactant, mix evenly, and finally add 1% to 5% of a dispersant, stir for 30 minutes to fully emulsify the solution, and obtain a high-efficiency oil-displacing flushing fluid.

[0029] The above-mentioned high-efficiency oil displacement flushing fluid is used for flushing the well wall of the oil well to improve the flushing efficiency of the well wall at different temperatures.

[0030] In the present invention, on the one hand, the high-efficiency oil displacement flushing fluid has a good temperature-resistant group, benzoxazine, and its temperature resistance reaches above 90°C.

[0031] On the other hand, the high-efficiency oil displacement flushing fluid has a good hydrophilic group - sulfonated betaine, with a quaternary ammonium salt type cationic group and a carboxylate type anionic group. This structure not only solves the hydrophobicity problem of benzoxazine, but also enhances the synergistic effect with other surfactants, thereby enhancing the flushing efficiency.

[0032] The beneficial effects of the present invention are:

[0033] (1) The present invention synthesizes an amphiphilic surfactant containing benzoxazine sulfonate betaine groups, and by introducing benzoxazine groups, the temperature resistance of the surfactant is improved, and the flushing efficiency at 80° C. can be maintained at more than 99%;

[0034] (2) The present invention synthesizes an amphiphilic surfactant containing benzoxazine with a sulfonate betaine group, and solves the hydrophobicity problem of benzoxazine by introducing a sulfonate betaine group and a quaternary ammonium salt type cationic group and a carboxylate type anionic group contained in its structure, thereby enhancing its solubilizing ability and improving the flushing efficiency;

[0035] (3) The high-efficiency oil displacement flushing fluid prepared by the present invention has good mud flushing efficiency. Under the condition of 30% addition, the cleaning efficiency at room temperature and high temperature reaches more than 95%. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a comparison chart of the flushing efficiency of the high-efficiency oil displacement flushing fluid of the embodiment of the present invention at different temperatures. DETAILED DESCRIPTION

[0037] The technical solutions in the present invention will be described clearly and completely below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0038] The experimental methods in the following examples, unless otherwise specified, are all conventional methods, and are performed according to the techniques or conditions described in the literature in the field or according to the product instructions. The materials, reagents, etc. used in the following examples, unless otherwise specified, can all be obtained from commercial channels.

[0039] The surfactants and dispersed phases used in the following examples are all commercially available in the art.

[0040] Example 1

[0041] A high-efficiency oil displacement flushing fluid and a preparation method thereof, wherein the preparation method specifically comprises the following steps:

[0042] S1: In a 100 mL three-necked flask equipped with a condenser, add 17.8 g of p-dimethylaminoethylphenol, 2.67 g of 4,4 ， -diaminotriphenylmethane, 1.5g of paraformaldehyde and 40mL of toluene. The reaction system was heated to 90°C under magnetic stirring and reacted for 5h. After the reaction system was cooled to room temperature, anhydrous magnesium sulfate was added, stirred and filtered. The intermediate product was obtained by filtration, decompression removal of toluene and drying.

[0043] S2: Add 5.7 g of the intermediate product and 35 mL of acetone to a 100 mL three-necked flask, raise the temperature to 50°C, and after complete dissolution, add 1.6 g of 1,3-propane sultone and 15 mL of acetone solution dropwise therein. After the addition is complete, continue the reaction for 10 hours. After filtering, drying, crushing and other steps, an amphiphilic surfactant containing benzoxazine with sulfonate betaine group is obtained.

[0044] S3: Weigh an appropriate amount of water into a beaker, add 10% of the amphiphilic surfactant containing benzoxazine sulfonate betaine group into the beaker, fully dissolve in a water bath at 40-45°C, then add 15% of the mixed solution of sodium dodecylbenzene sulfonate and sodium polyoxyethylene fatty alcohol ether sulfate, 10% of polyoxyethylene ether fatty alcohol in sequence, stir well, add 5% of the auxiliary surfactant propylene glycol butyl ether, mix well, add 5% of n-butanol, stir for 30 minutes to fully emulsify the solution, and obtain a high-efficiency oil displacement flushing fluid.

[0045] Example 2

[0046] A high-efficiency oil displacement flushing fluid and a preparation method thereof, wherein the preparation method specifically comprises the following steps:

[0047] S1: In a 100 mL three-necked flask equipped with a condenser, add 12.5 g of p-dimethylaminoethylphenol, 2.35 g of 4,4 ， -diaminotriphenylmethane, 1.3g of paraformaldehyde and 37mL of toluene. The reaction system was heated to 90°C under magnetic stirring and reacted for 5h. After the reaction system was cooled to room temperature, anhydrous magnesium sulfate was added, stirred and filtered. The intermediate product was obtained by filtration, decompression removal of toluene and drying.

[0048] S2: Add 4.8 g of the intermediate product and 32 mL of acetone to a 100 mL three-necked flask, raise the temperature to 50°C, and after complete dissolution, add 1.48 g of 1,3-propane sultone and 13 mL of acetone solution dropwise therein. After the addition is complete, continue the reaction for 10 hours. After filtering, drying, crushing and other steps, an amphiphilic surfactant containing benzoxazine with sulfonate betaine group is obtained.

[0049] S3: Weigh an appropriate amount of water into a beaker, add 13% of an amphiphilic surfactant containing benzoxazine sulfonate betaine group into the beaker, fully dissolve it in a water bath at 40-45°C, then add 12% of a mixed solution of sodium dodecylbenzene sulfonate and sodium polyoxyethylene fatty alcohol ether sulfate, 15% of polyoxyethylene ether fatty alcohol in sequence, stir well, then add 5% of the co-surfactant ethylene glycol butyl ether, mix well, then add 10% of limonene, stir for 30 minutes to fully emulsify the solution, and obtain a high-efficiency oil displacement flushing fluid.

[0050] Example 3

[0051] A high-efficiency oil displacement flushing fluid and a preparation method thereof, wherein the preparation method specifically comprises the following steps:

[0052] S1: In a 100 mL three-necked flask equipped with a condenser, add 15.5 g of p-dimethylaminoethylphenol, 2.15 g of 4,4 ， -methylenedianiline, 1.2g of paraformaldehyde and 35mL of toluene. The reaction system was heated to 90°C under magnetic stirring and reacted for 5h. After the reaction system was cooled to room temperature, anhydrous magnesium sulfate was added and stirred and filtered. The intermediate product was obtained by filtration, decompression and removal of toluene and drying.

[0053] S2: Add 4.8 g of the intermediate product and 30 mL of acetone to a 100 mL three-necked flask, raise the temperature to 50°C, and after complete dissolution, add 1.6 g of 1,3-propane sultone and 15 mL of acetone solution dropwise therein. After the addition is complete, continue the reaction for 10 hours. After filtering, drying, crushing and other steps, an amphiphilic surfactant containing benzoxazine with sulfonate betaine group is obtained.

[0054] S3: Weigh an appropriate amount of water into a beaker, add 15% of an amphiphilic surfactant containing benzoxazine sulfonate betaine group into the beaker, fully dissolve in a 40-45°C water bath, then add 12% of a mixed solution of sodium dodecylbenzene sulfonate and sodium polyoxyethylene fatty alcohol ether sulfate, 15% of polyoxyethylene ether fatty alcohol in sequence, stir well, then add 6% of the co-surfactant propylene glycol butyl ether, mix well, then add 4% of n-butanol, stir for 30 minutes to fully emulsify the solution, and obtain a high-efficiency oil displacement flushing fluid.

[0055] Example 4

[0056] A high-efficiency oil displacement flushing fluid and a preparation method thereof, wherein the preparation method specifically comprises the following steps:

[0057] S1: In a 100 mL three-necked flask equipped with a condenser, add 19.5 g of p-dimethylaminoethylphenol, 2.85 g of 4,4 ， -methylenedianiline, 1.65g of paraformaldehyde and 50mL of toluene. The reaction system was heated to 90°C under magnetic stirring and reacted for 5h. After the reaction system was cooled to room temperature, anhydrous magnesium sulfate was added and stirred and filtered. The intermediate product was obtained by filtration, decompression and removal of toluene and drying.

[0058] S2: Add 8.5 g of the intermediate product and 40 mL of acetone to a 100 mL three-necked flask, raise the temperature to 50°C, and after complete dissolution, add 2.1 g of 1,3-propane sultone and 24 mL of acetone solution dropwise therein. After the addition is complete, continue the reaction for 10 hours. After filtering, drying, crushing and other steps, an amphiphilic surfactant containing benzoxazine with sulfonate betaine group is obtained.

[0059] S3: Weigh an appropriate amount of water into a beaker, add 12% of an amphiphilic surfactant containing benzoxazine sulfonate betaine group into the beaker, fully dissolve in a water bath at 40-45°C, then add 15% of a mixed solution of sodium dodecylbenzene sulfonate and sodium polyoxyethylene fatty alcohol ether sulfate, 12% of polyoxyethylene ether fatty alcohol in sequence, stir well, add 5% of an auxiliary surfactant ethylene glycol butyl ether, mix well, add 5% of white oil, stir for 30 minutes to fully emulsify the solution, and obtain a high-efficiency oil displacement flushing fluid.

[0060] Comparative Example 1

[0061] The difference from Example 1 is that no amphiphilic surfactant containing benzoxazine with sulfonate betaine group is added, an appropriate amount of water is weighed into a beaker, and 15% of a mixed solution of sodium dodecylbenzene sulfonate and sodium polyoxyethylene fatty alcohol ether sulfate, and 12% of polyoxyethylene ether fatty alcohol are added to the beaker in sequence, and after fully dissolving in a water bath environment at 40-45°C, 5% of the co-surfactant ethylene glycol butyl ether is added, and after mixing evenly, 5% of white oil is added, and the solution is stirred for 30 minutes to fully emulsify and evenly emulsify, thereby obtaining a flushing agent.

[0062] Comparative Example 2

[0063] The difference from Example 1 is that no auxiliary surfactant is added, an appropriate amount of water is weighed into a beaker, 10% of an amphiphilic surfactant containing a sulfonated betaine group benzoxazine is added to the beaker, and it is fully dissolved in a water bath environment at 40-45° C., and then 15% of a mixed solution of sodium dodecylbenzene sulfonate and sodium polyoxyethylene fatty alcohol ether sulfate, and 10% of polyoxyethylene ether fatty alcohol are added in sequence, and after stirring evenly, 5% of n-butanol is added, and the solution is stirred for 30 minutes to fully emulsify and evenly emulsify, thereby obtaining a high-efficiency oil displacement flushing fluid.

[0064] Performance test experiment

[0065] (1) Flushing efficiency

[0066] First, weigh 360 mL of water into a beaker, and add the flushing agent (40 g) synthesized in Example 1, Example 2, Example 3, Example 4, Comparative Example 1 and Comparative Example 2 to the beaker in turn to prepare a 10% aqueous solution, and then place it in a water bath at room temperature and 80°C and heat it to a constant temperature. Remove the outer drum of the rotational viscometer, and weigh the mass of the outer drum after drying as m0; then use a brush to evenly apply the mud base slurry below the scale line of the outer drum so that the surface of the drum is evenly covered with a layer of mud; keep the outer drum of the rotational viscometer coated with mud at room temperature for 5 minutes to 8 minutes until the mud no longer drips from the surface of the drum; weigh the mass m1 of the outer drum of the rotational viscometer with mud, and the applied mass must be greater than 2.00 g. If it does not reach 2.00 g, continue to apply until the mud application quality meets the requirements; while rotating Pour the preheated flushing liquid into the viscometer sample cup until the liquid level reaches the scale line of the sample cup. Place the sample cup in the heating jacket, connect the heating jacket power supply and thermometer, heat the heating jacket, and control the flushing liquid temperature at 80°C; place the test outer drum into the rotary viscometer sample cup filled with flushing liquid, so that the scale line of the test outer drum is flush with the cleaning liquid surface in the rotary viscometer sample cup, start the rotary viscometer, rotate at 200r / min for 5 minutes, take out the outer drum, let it stand at room temperature for 10 minutes, and weigh its mass as m2. Calculate the flushing efficiency according to the following formula:

[0067]

[0068] The experimental results are as follows Figure 1 As shown by Figure 1 As can be seen from Comparative Example 1, the rinsing efficiency is significantly improved by adding the amphiphilic surfactant containing benzoxazine sulfonate betaine group, and the rinsing efficiency is above 95%.

[0069] In addition, by Figure 1 It can be seen from the experimental data of Comparative Example 2 that the amphiphilic surfactant containing benzoxazine sulfonate betaine group and the co-surfactant produce a synergistic effect, and the flushing efficiency is significantly improved.

[0070] The above is only a preferred embodiment of the present invention. It should be understood that the present invention is not limited to the form disclosed herein, and should not be regarded as excluding other embodiments, but can be used in various other combinations, modifications and environments, and can be modified within the scope of the concept described herein through the above teachings or the technology or knowledge of the relevant field. The changes and modifications made by those skilled in the art shall not deviate from the spirit and scope of the present invention, and shall be within the scope of protection of the claims attached to the present invention.

Claims

1. An amphiphilic surfactant containing a benzoxazine sulfonate betaine group, characterized in that: The composition is prepared from the following components in parts by weight: 10-20 parts of p-hydroxybenzene compounds, 15-25 parts of diaminobenzene compounds, 10-15 parts of paraformaldehyde, 5-10 parts of toluene and other organic solvents, and 10-20 parts of 1,3-propane sultone.

2. The amphiphilic surfactant according to claim 1, characterized in that: The p-hydroxybenzene compound is p-dimethylaminoethyl phenol.

3. The amphiphilic surfactant according to claim 1, characterized in that The diamine benzene compound is one or more of 4,4'-diaminotriphenylmethane, 4,4'-methylenedianiline, and 4,4'-di-sec-butylaminodiphenylmethane.

4. A method for preparing the amphiphilic surfactant containing benzoxazine with sulfobetaine group according to any one of claims 1 to 3, characterized in that: The method comprises the following preparation steps: S1: In a flask equipped with a condenser, add a p-hydroxybenzene compound, a diaminobenzene compound, polyformaldehyde and toluene in sequence to form a reaction system; heat the reaction system to 90°C under stirring and react for 4 to 6 hours; after the reaction system is cooled to room temperature, add anhydrous magnesium sulfate, stir and filter; then filter, remove toluene under reduced pressure and dry to obtain an intermediate product; S2: Add the intermediate product and acetone into a flask, raise the temperature to 50°C, and after complete dissolution, add 1,3-propane sultone / acetone solution dropwise therein. After the addition is complete, continue the reaction for 8 to 11 hours, and then filter, dry, and crush to obtain an amphiphilic surfactant containing benzoxazine sulfonate betaine groups.

5. High-efficiency oil displacement flushing fluid, characterized in that: The composition is prepared from the following components in parts by weight: 10% to 20% anionic surfactant, 5% to 15% nonionic surfactant, 10% to 15% amphiphilic surfactant containing benzoxazine sulfonate betaine group according to any one of claims 1 to 5, 5% to 10% co-surfactant, 1% to 5% dispersant, and the rest is water; The co-surfactant is alcohol ether.

6. The high-efficiency oil displacement flushing fluid according to claim 5, characterized in that: The anionic surfactant is composed of a sodium dodecylbenzene sulfonate aqueous solution with a mass concentration of 40% and sodium fatty alcohol polyoxyethylene ether sulfate.

7. The high-efficiency oil displacement flushing fluid according to claim 5, characterized in that: The nonionic surfactant is polyoxyethylene ether fatty alcohol; The structural formula of polyoxyethylene ether fatty alcohol is R-(OCC) x -OH, wherein R is an alkyl group having 6 to 15 carbon atoms, and x is 8 to 25.

8. The high-efficiency oil displacement flushing fluid according to claim 5, characterized in that: The alcohol ether includes but is not limited to one or both of propylene glycol butyl ether and ethylene glycol butyl ether.

9. The high-efficiency oil displacement flushing fluid according to claim 5, characterized in that: The dispersed phase is one or more of limonene, n-butanol, ethylene glycol, white oil and diesel.

10. The high-efficiency oil displacement flushing fluid according to any one of claims 5 to 9, characterized in that: It is used to improve the flushing efficiency of the well wall at different temperatures.

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