Preparation method of polyacrylamide / acrylic acid copolymer emulsion with high acrylic acid content

Abstract

The invention discloses a preparation method of a high-acrylic-acid-content polyacrylamide / acrylic acid copolymer emulsion for improving the recovery efficiency of a high-temperature and high-salt oil reservoir, and belongs to the technical field of oilfield chemistry and functional polymer materials. According to the method, a reversed-phase microemulsion polymerization system is adopted, a combination of a cationic surfactant hexadecyl trimethyl ammonium bromide and an amphiphilic initiator azodiisobutyronitrile is introduced, an electrostatic enrichment effect is generated at a water core interface, and acrylate anions are selectively adsorbed and locally concentrated, so that the reactivity rate of a monomer is regulated and controlled, and the amphiphilic polymer is prepared. And the grafting proportion of acrylic acid in the copolymer is obviously improved. The method is simple in process and mild in condition, and the obtained emulsion has the advantages of being high in solid content, good in storage stability, fast in dissolution, free of fisheye and the like, is suitable for high-temperature and high-salinity oil reservoir conditions and has good industrial application prospects.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of oilfield chemistry and functional polymer materials, and particularly relates to a preparation method of a novel polymer for oil displacement used in enhanced oil recovery (EOR) of high-temperature and high-salt reservoirs, and especially relates to a microemulsion preparation method for realizing high-acrylic-acid-content polyacrylamide / acrylic acid (PAM / AA) copolymer emulsion by electrostatic enrichment and monomer reactivity control. BACKGROUND

[0002] With the continuous development of global conventional oil and gas resources, oilfields have generally entered the late stage of development with high water cut and high recovery degree, and the recovery rate is facing a bottleneck. At the same time, unconventional resources such as shale oil, tight oil and deep / ultra-deep oil and gas have become the main replacement, but the harsh reservoir conditions (high temperature, high salinity, low permeability) have posed a severe challenge to existing enhanced oil recovery (EOR) technologies. The efficiency of polymer flooding, as the core technology of chemical flooding, depends on the temperature resistance and salt tolerance of the oil-displacing polymer.

[0003] Polyacrylamide (PAM) and its copolymers are the mainstream materials of polymer flooding. Polyacrylamide polymers are widely used in oilfield acidizing and fracturing due to their good water solubility and high drag reduction rate. This high molecular material can greatly increase the viscosity of the displacement fluid after dissolving in water, effectively adjusting the oil-water mobility ratio underground, so that the displacement fluid can enter the low-permeability oil layer more uniformly, expanding the swept volume. In China, polymer flooding technology has been widely used in Daqing, Shengli and other large oilfields, making a historic contribution to improving the recovery rate of old oilfields. Its technical maturity and application scale are at the world leading level.

[0004] However, the traditional free radical copolymerization of polyacrylamide / acrylic acid (PAM / AA) copolymer results in insufficient carboxyl content in the product due to the lower reactivity of acrylic acid (AA) monomer than that of acrylamide (AM), which limits its ion strength resistance and viscosity retention ability in high-temperature and high-salt environments. In addition, the existing product forms have inherent defects: powdered products dissolve slowly and are prone to caking to form "fish eyes"; while conventional emulsion products dissolve quickly, but have poor long-term storage stability and often require the addition of demulsifiers, which introduces additional impurities and affects performance.

[0005] Reverse microemulsion polymerization provides an ideal platform for preparing high-performance polymer emulsions, as it can form uniform and stable nanoscale droplets. However, how to precisely control the reactivity of AA monomer in this system and break through the limitations of traditional reactivity is a key technical issue for obtaining products with excellent solubility, storage stability and outstanding application performance.

[0006] Although the reverse microemulsion polymerization system provides a good reaction environment for preparing nanoscale polymer emulsion, it is still limited in regulating the composition of copolymer due to the inherent reactivity ratio of monomers. Studies have shown that in the conventional reverse microemulsion, the difference in the reactivity ratio of AA and AM still makes it difficult to break through 20% of the proportion of AA segment (on the premise of ensuring the molecular weight), which is difficult to meet the higher requirements of polymer salt resistance under extreme reservoir conditions. In addition, the existing technology often uses methods such as adjusting the feeding ratio, adding complexing agents or changing the initiation system to try to increase the AA content, but these methods often lead to a decrease in emulsion stability or difficulty in controlling the polymerization process, and have not fundamentally solved the problem of low AA reactivity ratio.

[0007] Therefore, how to actively regulate the local reaction concentration of AA monomer in the reverse microemulsion system, break through the reactivity ratio limit, and realize the controllable preparation of high carboxyl content copolymer has become a technical problem to be solved in the field. There is no report on the directional improvement of AA participation in copolymerization in reverse microemulsion by interface electrostatic enrichment strategy.

[0008] The application discloses a high-acrylic-acid-content polyacrylamide / acrylic high polymer, namely, a polyacrylamide / acrylic emulsion with high acrylic acid content, high solid content, high molecular weight and stability is obtained by a reverse microemulsion polymerization method, the combination of a cationic surfactant and an amphiphilic initiator, the problems of slow dissolution of traditional powders and poor stability of traditional emulsion products are solved, and the polyacrylamide / acrylic emulsion has a wide application prospect. SUMMARY

[0009] To solve the above technical problems, the application creatively proposes a new reverse microemulsion polymerization method based on the "electrostatic enrichment effect" to regulate the local concentration of monomers. The core lies in that an amphiphilic initiator is introduced into the interface and internal microenvironment of the water core (microreactor) of the reverse microemulsion, and a cationic surfactant with positive charge is introduced at the same time. The amphiphilic initiator is mainly gathered at the oil-water interface, and the surfactant selectively adsorbs and enriches the acrylic acid anion (AA - ) through strong electrostatic interaction, so as to significantly increase the local effective concentration of AA - in the water core relative to that of acrylamide (AM) before the polymerization reaction occurs. Through the interface double "pre-enrichment" strategy of the initiator and the surfactant, the actual feeding ratio of the two monomers is changed on the microscale, the participation and access rate of AA - in the copolymerization reaction are effectively improved, and the carboxyl density in the polymer molecular chain is finally higher than that in the conventional method.

[0010] A method for preparing a high-acrylic acid content polyacrylamide / acrylic acid polymer involves polymerization via a reverse microemulsion process, followed by the addition of cationic surfactants to further increase the proportion of acrylic acid monomers. Compared to other methods for preparing polyacrylamide polymers, this invention offers advantages such as low cost, high solids content, simple operation, and stable, high-performance polymer emulsions.

[0011] A method for preparing a polyacrylamide / acrylic acid polymer with high acrylic acid content is as follows: First, the polymerization inhibitor in the monomer acrylic acid is removed using alumina and neutralized with anhydrous sodium carbonate. An aqueous monomer solution is prepared and an aqueous emulsifier is added, followed by nitrogen deoxygenation. Then, an oil phase and an oil emulsifier are prepared and placed in a five-necked round-bottom flask equipped with a mechanical stir bar, nitrogen purging, a thermometer, and a spherical condenser, and placed in a water bath (60-80℃). The prepared aqueous monomer solution is slowly added dropwise to the round-bottom flask while being stirred at high speed (500-800 rpm) for a period of time to form a stable, slightly transparent reverse microemulsion. An amphiphilic initiator is added to initiate the reaction, which is then allowed to proceed for a period of time. The resulting emulsion is then post-treated by adding a demulsifier to break the emulsion, washing, and drying until constant weight is achieved.

[0012] The monomer aqueous solution is composed of neutralized acrylic acid and acrylamide in a 1:4 ratio, with a concentration of 20-40 wt%. The solvent is deionized water. The aqueous emulsifier is a cationic surfactant, cetyltrimethylammonium bromide (CTAB), with a concentration of 1-5 wt%.

[0013] The oil phase is No. 7 white oil, and the oil phase emulsifier is a combination of two or more of Span60, Span80, Tween60, Tween80, and OP-10, with a concentration of 20-30wt%.

[0014] The nitrogen deoxygenation time is 10-30 minutes.

[0015] The initiator is an amphiphilic initiator, azobisisobutyronitrile (AIBN) or azobisisoheptanenitrile (AIVN), the solvent is toluene, the concentration is 2-20 wt%, and the amount added to the system is 0.1-1 wt%.

[0016] The reverse microemulsion polymerization reaction time is 2-3 hours.

[0017] The emulsion post-treatment involves dripping the emulsion into anhydrous ethanol and filtering it. The resulting product is then washed and soaked with organic solvents such as anhydrous ethanol, petroleum ether, and propanol to remove the emulsifier from the product surface. The product is then placed in an oven and dried to constant weight. The oven temperature is 80°C, and the drying time is 3-5 hours.

[0018] The present invention has the following beneficial effects: Compared with the prior art, the present invention has the following outstanding advantages: (1) Mechanism innovation: For the first time, a strategy of using the electrostatic enrichment effect of cationic surfactants in reverse microemulsions to regulate the reactivity ratio of AA monomers was proposed and verified. This method starts from the micro-reaction environment, breaks through the limitation of the inherent reactivity ratio of monomers in traditional copolymerization, and provides a new way to achieve copolymers with high carboxyl content.

[0019] (2) Excellent product performance: The proportion of acrylic acid repeating units in the obtained PAM / AA copolymer is significantly higher than that of conventional copolymer products. The higher carboxyl group density endows the product with better salt resistance, thickening and long-term thermal stability, and it is especially suitable for high-temperature and high-salinity oil reservoirs.

[0020] (3) Advantages of process and product form: The reverse microemulsion method directly obtains emulsion products with high solid content, good stability and narrow particle size distribution. It has a long shelf life, does not require demulsification before use, has a fast dissolution speed, no "fish eye" phenomenon, and is convenient for on-site application.

[0021] (4) The process is controllable and easy to scale up: the method has clear steps, mild reaction conditions, and all raw materials are commonly used in industry, so the cost is controllable and it has good prospects for industrial production. Attached Figure Description

[0022] Figure 1 Schematic diagram of X-ray photoelectron spectroscopy of polymer powder in Example 1 of this invention; Figure 2 Transmission electron microscopy image of the polymer emulsion in Example 1 of this invention; Figure 3 Schematic diagram of X-ray photoelectron spectroscopy of polymer powder in Example 2 of this invention; Figure 4 Schematic diagram of X-ray photoelectron spectroscopy of polymer powder in Example 3 of this invention; Detailed Implementation

[0023] The technical solution of the present invention will be further defined below with reference to specific embodiments, but the scope of protection is not limited to the description. Example 1

[0024] A method for preparing a polyacrylamide / acrylic acid polymer with high acrylic acid content is as follows: (1) Place 10g of acrylic acid aluminum peroxide column; (2) The 8g of acrylic acid obtained in step (1) was neutralized to pH 7.0 by slowly adding 20wt% sodium carbonate solution in an ice-water bath to obtain sodium acrylate solution; (3) Prepare an aqueous monomer solution with a concentration of 40wt% using 3.2g of sodium acrylate monomer obtained in step (2) and 12.8g of acrylamide, with deionized water as the solvent, and then add 2.15g of cetyltrimethylammonium bromide (CTAB). (4) Mix 70g of No. 7 white oil, 22.76g of sorbitan oleate (Span80) and 7.24g of polyoxyethylene dehydrated sorbitan monooleate (Tween80) evenly to prepare an oil phase, and place it in a five-necked round-bottom flask equipped with a mechanical stir bar, nitrogen purging, a spherical condenser and a thermometer. (5) Drop the aqueous monomer solution obtained in step (3) into a five-necked flask, and stir for 30 minutes at a mechanical stirring speed of 550 rpm to form a stable reverse microemulsion. (6) 0.5 g of a 10 wt% azobisisobutyronitrile (AIBN) toluene solution was added dropwise to a five-necked flask to initiate the reaction. After 3 h of reaction, a stable reverse microemulsion was obtained. (7) Add 10g of the microemulsion obtained in step (6) to 50g of anhydrous ethanol, filter the resulting suspension, and obtain the crude polymer product. (8) The crude product obtained in step (7) is repeatedly washed and soaked with organic solvents such as anhydrous ethanol, petroleum ether, and acetone, and placed in an 80°C oven for 3-5 hours until constant weight is achieved; XPS analysis was performed on the obtained polymer powder. The ratio of acrylic acid to acrylamide in the feed was 1:4, the ratio of acrylic acid to acrylamide in the product was 8:25, and the weight-average molecular weight was 832,246. Example 2

[0025] A method for preparing a polyacrylamide / acrylic acid polymer with high acrylic acid content is as follows: (1) Place 10g of acrylic acid aluminum peroxide column; (2) The 8g of acrylic acid obtained in step (1) was neutralized to pH 7.0 by slowly adding 20wt% sodium carbonate solution in an ice-water bath to obtain sodium acrylate solution; (3) Prepare an aqueous monomer solution with a concentration of 35wt% using 2.8g of sodium acrylate monomer obtained in step (2) and 11.2g of acrylamide, with deionized water as the solvent, and then add 1.88g of cetyltrimethylammonium bromide (CTAB). (4) Mix 70g of No. 7 white oil, 23g of sorbitan oleate (Span80) and 5.1g of polyoxyethylene dehydrated sorbitan monooleate (Tween80) evenly to prepare an oil phase, and place it in a five-necked round-bottom flask equipped with a mechanical stir bar, nitrogen purging, a spherical condenser and a thermometer. (5) Drop the aqueous monomer solution obtained in step (3) into a five-necked flask, and stir for 30 minutes at a mechanical stirring speed of 550 rpm to form a stable reverse microemulsion. (6) 0.5 g of a 15 wt% azobisisobutyronitrile (AIBN) toluene solution was added dropwise to a five-necked flask to initiate the reaction. After 3 h of reaction, a stable reverse microemulsion was obtained. (7) Add 10g of the microemulsion obtained in step (6) to 50g of anhydrous ethanol, filter the resulting suspension, and obtain the crude polymer product. (8) The crude product obtained in step (7) is repeatedly washed and soaked with organic solvents such as anhydrous ethanol, petroleum ether, and acetone, and placed in an 80°C oven for 3-5 hours until constant weight is achieved; XPS analysis was performed on the obtained polymer powder. The ratio of acrylic acid to acrylamide in the feed was 1:4, the ratio of acrylic acid to acrylamide in the product was 3:8, and the weight-average molecular weight was 895,962. Example 3

[0026] A method for preparing a polyacrylamide / acrylic acid polymer with high acrylic acid content is as follows: (1) Place 10g of acrylic acid aluminum peroxide column; (2) The 8g of acrylic acid obtained in step (1) was neutralized to pH 7.0 by slowly adding 20wt% sodium carbonate solution in an ice-water bath to obtain sodium acrylate solution; (3) Prepare an aqueous monomer solution with a concentration of 35wt% using 2.8g of sodium acrylate monomer obtained in step (2) and 11.2g of acrylamide, with deionized water as the solvent, and then add 1.88g of cetyltrimethylammonium bromide (CTAB). (4) Mix 70g of No. 7 white oil, 23g of sorbitan oleate (Span80) and 5.1g of polyoxyethylene dehydrated sorbitan monooleate (Tween80) evenly to prepare an oil phase, and place it in a five-necked round-bottom flask equipped with a mechanical stir bar, nitrogen purging, a spherical condenser and a thermometer. (5) Drop the aqueous monomer solution obtained in step (3) into a five-necked flask, and stir for 30 minutes at a mechanical stirring speed of 550 rpm to form a stable reverse microemulsion. (6) 0.5 g of a 15 wt% azobisisobutyronitrile (AIVN) toluene solution was added dropwise to a five-necked flask to initiate the reaction. After 3 h of reaction, a stable reverse microemulsion was obtained. (7) Add 10g of the microemulsion obtained in step (6) to 50g of anhydrous ethanol, filter the resulting suspension, and obtain the crude polymer product. (8) The crude product obtained in step (7) is repeatedly washed and soaked with organic solvents such as anhydrous ethanol, petroleum ether, and acetone, and placed in an 80°C oven for 3-5 hours until constant weight is achieved; XPS analysis was performed on the obtained polymer powder. The ratio of acrylic acid to acrylamide in the feed was 1:4, the ratio of acrylic acid to acrylamide in the product was 5:16, and the weight-average molecular weight was 796713.

[0027] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing a polyacrylamide / acrylic acid polymer with high acrylic acid content, characterized in that: First, alumina is used to remove the polymerization inhibitor from the monomer acrylic acid, and then anhydrous sodium carbonate is used to neutralize it. An aqueous monomer solution is prepared and an aqueous emulsifier is added, followed by nitrogen deoxygenation. Then, an oil phase and an oil emulsifier are prepared and placed in a five-necked round-bottom flask equipped with a mechanical stir bar, nitrogen purging, a thermometer, and a spherical condenser, which is then placed in a water bath. The prepared aqueous monomer solution is slowly added dropwise to the round-bottom flask while being stirred at high speed for a period of time to form a stable reverse microemulsion. An initiator is added to initiate the reaction, which is then allowed to proceed for a period of time. The resulting emulsion is then post-treated by adding a demulsifier to break the emulsion, washing, and drying for a period of time until constant weight is achieved.

2. The method for preparing a high acrylic acid content polyacrylamide / acrylic acid polymer as described in claim 1, wherein the monomer aqueous solution is a neutralized acrylic acid to acrylamide solution with a ratio of 1:4 and a concentration of 30-40 wt%. The solvent is deionized water. The aqueous emulsifier is a cationic surfactant, cetyltrimethylammonium bromide (CTAB), with a concentration of 1-5 wt%.

3. The method for preparing a high acrylic acid content polyacrylamide / acrylic acid polymer as described in claim 1, wherein the oil phase is No. 7 white oil, and the oil phase emulsifier is a combination of two or more of Span60, Span80, Tween60, Tween80, and OP-10, with a concentration of 20-30 wt%.

4. The method for preparing a high acrylic acid content polyacrylamide / acrylic acid polymer as described in claim 1, wherein the nitrogen deoxygenation time is 10-30 min.

5. The method for preparing a high acrylic acid content polyacrylamide / acrylic acid polymer as described in claim 1, wherein the initiator is an amphiphilic initiator azobisisobutyronitrile (AIBN) or azobisisoheptanenitrile (AIVN), the solvent is toluene with a concentration of 2-20 wt%, and the amount added to the system is 0.1-1 wt%.

6. The method for preparing a high acrylic acid content polyacrylamide / acrylic acid polymer as described in claim 1, wherein the polymerization reaction time is 2-3 hours.

7. The method for preparing a high acrylic acid content polyacrylamide / acrylic acid polymer as described in claim 1, wherein the emulsion post-treatment involves dripping the emulsion into anhydrous ethanol and filtering it, washing and soaking the resulting product with organic solvents such as anhydrous ethanol, petroleum ether, and propanol to remove the emulsifier from the product surface, and then drying the product in an oven to constant weight. The oven temperature is 80°C and the drying time is 3-5 hours.

8. A high acrylic acid content polyacrylamide / acrylic acid composite emulsion prepared by the method according to any one of claims 1-6.

9. The application of the composite emulsion according to claim 7 as an oil displacement agent for enhancing oil recovery in high-temperature and high-salinity oil and gas reservoirs.

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