High-temperature-resistant zwitterionic polymer tackifier for composite calcium salt completion fluid as well as preparation method and application of high-temperature-resistant zwitterionic polymer tackifier

Abstract

The invention provides a high-temperature-resistant zwitterionic polymer tackifier for a composite calcium salt completion fluid as well as a preparation method and application of the high-temperature-resistant zwitterionic polymer tackifier. The preparation method of the polymer tackifier comprises the following steps: adding hydroquinone into an isocyano ethyl methacrylate solution, adding the obtained mixed solution into a dimethylaminoacethydrazide solution, and reacting; centrifuging, washing and drying to obtain an intermediate monomer; adding the intermediate monomer and hydroquinone into tetrahydrofuran, stirring and dissolving, adding beta-propiolactone, and reacting to obtain a zwitterionic monomer A; the preparation method comprises the following steps: adding a temperature-resistant anionic monomer, an acrylamide monomer, a zwitterionic monomer A and a temperature-resistant cationic monomer into deionized water, uniformly stirring, adjusting the pH value of the system to 7-8, introducing nitrogen to remove oxygen, heating to a reaction temperature, adding an initiator, and reacting to obtain the temperature-resistant water-soluble polymer. The tackifier provided by the invention can resist high temperature and composite calcium salt, and can significantly improve the viscosity of the completion fluid under a high temperature condition.

Description

Technical Field

[0001] The invention relates to a high-temperature resistant zwitterionic polymer tackifier for composite calcium salt completion fluid, a preparation method and application thereof, and belongs to the field of oilfield chemistry in the petroleum industry. Background Art

[0002] Completion fluid technology is a major engineering challenge in oil and gas well completion. With increasing drilling depths, especially when encountering complex formations and large sections of shale, inaccurate understanding of formation characteristics and pressure profiles often leads to an inability to respond promptly to changes in reservoir properties, resulting in frequent blowouts and well kicks. Completion fluids must not only balance formation pressure, purify the wellbore, stabilize the wellbore, and control filtration and leakage, but also maintain excellent temperature resistance, salt resistance, and corrosion resistance. Solids-free completion fluids, which contain no solid particles or clay, can significantly reduce reservoir damage and have garnered widespread attention in recent years.

[0003] In solids-free completion fluids, viscosifiers are crucial core additives. Solids-free completion fluids inherently lack viscosity and shear force, making it difficult to suspend cuttings and clean the wellbore. However, solids-free completion fluids with the addition of viscosifiers can effectively suspend rock and reduce downhole fluid loss. When bottomhole temperatures exceed 180°C, synthetic polymer viscosifiers are often used to improve the rheological properties of the completion fluid. However, most existing synthetic polymers easily curl and aggregate in high-concentration solutions of inorganic, high-valent salts (such as CaCl2 and CaBr2), leading to polymer precipitation and impaired completion fluid performance.

[0004] Chinese patent document CN104650827A has developed a temperature-resistant, slightly cross-linked tackifier. Its raw materials are alkenyl sulfonic acid, alkenyl amide, and alkenylbenzene. This tackifier still has a good tackifying effect after 16 hours of hot rolling aging at 165°C, which is better than the similar foreign product HE300, but it cannot meet the higher temperature resistance requirements (≥180°C). Chinese patent document CN118459660A uses an initiator to polymerize 2-acrylamido-2-methylpropanesulfonic acid, dimethylaminopropyl acrylamide, sodium p-styrene sulfonate, a hydrophobic monomer, and a micro-crosslinker into a linear copolymer, and blends it with a micron-sized inert bridging material to develop a high-temperature resistant polymer tackifier for calcium chloride brine completion fluid that is resistant to temperatures of 170°C. However, its performance fails above 180°C. Chinese patent document CN114214049A discloses a method for preparing a solid-free viscosifying workover fluid for ultra-deep and ultra-high temperature oil and gas wells. The method adds an ultra-high temperature polymer cross-linking agent, an ultra-high temperature polymer stabilizer, and an ultra-high temperature thermal stabilizer to a thickener solution, thereby enabling the completion fluid to maintain good performance at temperatures above 180°C, thus meeting the requirement for maintaining stable viscosifying properties in high-temperature solid-free brine. However, the maximum density of the brine used is 1.3 g / cm 3 , and the added salt is a monovalent sodium salt, which does not meet the conditions for the use of high-density completion fluid.

[0005] Therefore, how to enhance the stability of the thickener used in solid-free completion fluid in high temperature and high-valent salt (CaCl2, CaBr2) environment and maintain the thickening performance is of great significance to the basic research on enriching deep and ultra-deep solid-free completion fluid. Summary of the Invention

[0006] Aiming at the deficiencies of the prior art, especially the poor compatibility, high temperature stability and salt resistance of the existing high-density solid-free completion fluid thickener, the present invention provides a high temperature resistant zwitterionic polymer thickener for composite calcium salt completion fluid and its preparation method and application. The thickener of the present invention is resistant to high temperature (≥180℃), resistance to composite calcium salt (CaCl 2 / CaBr2), can significantly increase the viscosity of completion fluid under high temperature conditions.

[0007] The technical solutions of the present invention are as follows:

[0008] A method for preparing a high-temperature resistant zwitterionic polymer tackifier for a composite calcium salt completion fluid comprises the following steps:

[0009] (1) Synthesis of zwitterionic monomer A

[0010] (1.1) Hydroquinone (HQ) is added to an isocyanatoethyl methacrylate (MOI) solution, mixed evenly, and the resulting mixed solution is added to a dimethylaminoacetohydrazide (DMAH) solution to react; the reaction is then centrifuged, washed, and dried to obtain an intermediate monomer;

[0011] (1.2) Add the intermediate monomer and hydroquinone (HQ) to tetrahydrofuran, stir and dissolve, then add β-propiolactone to react; filter, wash, and dry to obtain zwitterionic monomer A;

[0012] (2) Preparation of high temperature resistant zwitterionic polymer thickener

[0013] A temperature-resistant anionic monomer, an acrylamide monomer, a zwitterionic monomer A, and a temperature-resistant cationic monomer are added to deionized water and stirred evenly. After adjusting the pH of the system to 7-8, nitrogen is introduced to deoxygenate the system. The temperature is then raised to the reaction temperature, an initiator is added, and the reaction is carried out to obtain a high-temperature-resistant zwitterionic polymer viscosity enhancer for a composite calcium salt completion fluid.

[0014] According to the present invention, preferably, the isocyanoethyl methacrylate (MOI) solution in step (1.1) is obtained by dissolving isocyanoethyl methacrylate in tetrahydrofuran, and the concentration of the isocyanoethyl methacrylate (MOI) solution is 0.05-0.15 g / mL; the mass ratio of hydroquinone (HQ) to isocyanoethyl methacrylate (MOI) is 1:80-120, more preferably 1:100.

[0015] According to the present invention, preferably, the dimethylaminoacetohydrazide (DMAH) solution in step (1.1) is obtained by dissolving dimethylaminoacetohydrazide (DMAH) in tetrahydrofuran, and the concentration of the dimethylaminoacetohydrazide (DMAH) solution is 0.05-0.1 g / mL; the mass ratio of the dimethylaminoacetohydrazide (DMAH) to isocyanoethyl methacrylate is 1-1.5:2.

[0016] Preferably, according to the present invention, the reaction temperature in step (1.1) is 35-45° C., and the reaction time is 2-4 h.

[0017] According to a preferred embodiment of the present invention, the washing in step (1.1) is ether washing for 3-5 times; and the drying is vacuum drying at 70-90° C. for 8-12 h.

[0018] According to the preferred embodiment of the present invention, the mass ratio of hydroquinone (HQ) to the intermediate monomer in step (1.2) is 1:70-90, more preferably 1:80.

[0019] Preferably, according to the present invention, in step (1.2), the ratio of the mass of the intermediate monomer to the volume of tetrahydrofuran is 0.05-0.1 g:1 mL; and the temperature for stirring and dissolving is 40-60°C.

[0020] According to the preferred embodiment of the present invention, the mass ratio of β-propiolactone to the intermediate monomer in step (1.2) is 1:3-3.5, more preferably 1:3.2; and the temperature for stirring and dissolving is 40-60°C.

[0021] According to the preferred embodiment of the present invention, the reaction temperature in step (1.2) is 40-60° C.; and the reaction time is 8-12 h.

[0022] According to a preferred embodiment of the present invention, the washing in step (1.2) is performed by washing with ether for 3-5 times; and the drying is performed at 80-100° C. for 8-10 h.

[0023] According to the present invention, the structural formula of the obtained zwitterionic monomer A is shown in the following formula I:

[0024]

[0025] According to the present invention, preferably, the temperature-resistant anionic monomer in step (2) is 2-acrylamido-2-methylpropanesulfonic acid (AMPS), sodium vinyl sulfonate (VS) or sodium styrene sulfonate (SSS).

[0026] According to the preferred embodiment of the present invention, the acrylamide monomer in step (2) is N,N-dimethylacrylamide (DMAA) or N-isopropylacrylamide (NIPAM).

[0027] According to the present invention, preferably, the temperature-resistant cationic monomer in step (2) is dimethyldiallyl ammonium chloride (DMDAAC) or methacryloyloxyethyltrimethylammonium chloride (DMC).

[0028] According to the preferred embodiment of the present invention, the mass ratio of the acrylamide monomer to deionized water in step (2) is 1:3-10.

[0029] According to the preferred embodiment of the present invention, the mass ratio of the temperature-resistant anionic monomer, acrylamide monomer, zwitterionic monomer A, and temperature-resistant cationic monomer in step (2) is 1-3:7:0.45-0.6:0.4-0.7, and more preferably 2:7:0.5:0.5.

[0030] According to the preferred embodiment of the present invention, the stirring rate in step (2) is 200-500 r / min, and the stirring time is 10-20 min.

[0031] Preferably, according to the present invention, in step (2), a sodium hydroxide aqueous solution with a mass fraction of 20%-40% is used to adjust the pH of the system to 7-8.

[0032] According to the preferred embodiment of the present invention, the nitrogen deoxygenation time in step (2) is 20-40 minutes, more preferably 30 minutes.

[0033] According to the preferred embodiment of the present invention, the initiator in step (2) is azobisisobutylamidine hydrochloride (AIBA), and the mass of the initiator is 0.1-1% of the total mass of the temperature-resistant anionic monomer, acrylamide monomer, zwitterionic monomer A and temperature-resistant cationic monomer.

[0034] According to the preferred embodiment of the present invention, the reaction temperature in step (2) is 50-60° C., and the reaction time is 4-6 h.

[0035] The present invention also provides a high-temperature resistant zwitterionic polymer viscosity enhancer for composite calcium salt completion fluid, which is prepared by the above-mentioned preparation method.

[0036] According to the present invention, the above-mentioned high temperature resistant zwitterionic polymer thickener for composite calcium salt completion fluid is used in composite calcium salt completion fluid; preferably, the concentration of the high temperature resistant zwitterionic polymer thickener for composite calcium salt completion fluid is 15-20 g / L, and the composite calcium salt completion fluid has a density of 1.76 g / cm 3 A composite calcium salt solution, wherein the composite calcium salt includes calcium chloride and calcium bromide.

[0037] The technical features and beneficial effects of the present invention are as follows:

[0038] 1. The acrylamide monomer introduced into the zwitterionic thickener of the present invention can significantly improve the molecular weight and temperature resistance of the generated product; the introduced anionic temperature-resistant monomer contains a sulfonic acid group with extremely strong hydration ability, which enhances the stability of the polymer under high temperature conditions; the introduced temperature-resistant cationic monomer provides a cationic group, which can form a stable five-membered ring structure on the polymer molecular chain, further enhancing the rigidity of the polymer molecule; the introduced zwitterionic monomer A contains both carboxylic acid groups and ammonium ions, which can form a charge balance and give the product an "anti-polyelectrolyte effect". Under high salt conditions, the molecular chain is further stretched, significantly increasing the viscosity of the composite calcium salt completion fluid. In addition, the α-methyl group contained in the zwitterionic monomer A increases the steric hindrance between the polymer chains, allowing the stretched polymer molecular chains to further form a stable network structure, significantly improving the flow resistance of the polymer molecules in the completion fluid, thereby achieving the effect of improving the viscosity of the completion fluid.

[0039] 2. The anionic temperature-resistant monomer and cationic temperature-resistant monomer used in the present invention have opposite electrical groups, and polymerization is difficult to occur under normal conditions. Therefore, the present invention uses a water-soluble azo initiator with a higher initiation efficiency, and the synthesized product has a higher relative molecular mass and good water solubility. Although the five-membered ring structure formed by the cationic temperature-resistant monomer can significantly improve the temperature resistance of the product, adding a too high ratio will increase the difficulty of the polymerization reaction and increase the cost; and adding a too low ratio will cause the resulting product to fail to meet the temperature resistance requirements. The control of the anionic and cationic monomer addition ratio within the scope of the present invention is the result obtained through a large number of experimental optimizations.

[0040] 3. The zwitterionic thickener of this invention exhibits a "reverse polyelectrolyte effect" and unique "salt-responsive" properties. Under high-salt conditions, the molecular chains stretch and form a stable network structure, significantly increasing the viscosity of the composite calcium salt completion fluid. Even after rolling aging at 180°C in a composite calcium salt environment, it maintains excellent viscosity-enhancing properties, promising broad application prospects in solid-free completion fluids. DETAILED DESCRIPTION

[0041] The present invention will be further described below with reference to specific embodiments, but is not limited thereto.

[0042] Meanwhile, the experimental methods described in the following examples, unless otherwise specified, are conventional methods; the reagents, materials and equipment, unless otherwise specified, can be obtained from commercial channels.

[0043] Example 1

[0044] A method for preparing a high-temperature resistant zwitterionic polymer tackifier for a composite calcium salt completion fluid comprises the following steps:

[0045] (1) 2 g of isocyanoethyl methacrylate (MOI) and 1.5 g of dimethylaminoacetohydrazide (DMAH) were dissolved in 20 mL of tetrahydrofuran (THF) to obtain an isocyanoethyl methacrylate solution and a dimethylaminoacetohydrazide solution, respectively. 0.02 g of hydroquinone (HQ) was added to the obtained isocyanoethyl methacrylate solution and mixed evenly. The obtained mixed solution was added to the dimethylaminoacetohydrazide (DMAH) solution and reacted at 40°C for 3 h to generate a white precipitate. The obtained reaction solution was centrifuged, and the obtained white precipitate was washed three times with ether. The washed white solid was dried in a vacuum oven at 80°C for 10 h to obtain the intermediate monomer. 1.6 g of the intermediate monomer was weighed and mixed with 0.02 g of hydroquinone (HQ), then added to 20 mL of tetrahydrofuran (THF) and stirred to dissolve in a 50°C water bath. Subsequently, 0.5 g of β-propiolactone was added thereto with stirring at 300 r / min, and the mixture was stirred and reacted at 50°C for 10 hours. After the reaction was completed, the reaction liquid was filtered, and the product was washed three times with ether. The washed solid was placed in a vacuum oven at 90°C and dried for 8 hours to obtain a zwitterionic monomer A.

[0046] (2) 28 g of N,N-dimethylacrylamide (DMAA), 8 g of 2-acrylamido-2-methylpropanesulfonic acid (AMPS), 2 g of dimethyldiallylammonium chloride (DMDAAC), and 2 g of zwitterionic monomer A were added to a beaker containing 160 g of deionized water and stirred at a stirring rate of 300 r / min for 15 min to mix uniformly. The pH of the resulting mixed solution was adjusted to 7 using a 20% by mass aqueous solution of NaOH. The mixed solution was transferred to a three-necked flask, purged with nitrogen for 30 min, heated to 50°C, and then 0.2 g of azobisisobutylamidine hydrochloride (AIBA) was added. The mixture was reacted at 50°C for 4 h. The mixture was naturally cooled to room temperature to obtain a high-temperature resistant zwitterionic polymer viscosifier for a composite calcium salt completion fluid.

[0047] The structure of the high-temperature resistant zwitterionic polymer tackifier for the composite calcium salt completion fluid obtained in this example is shown in Formula II:

[0048]

[0049] Example 2

[0050] The preparation method of a high-temperature resistant zwitterionic polymer viscosity enhancer for a composite calcium salt completion fluid is as described in Example 1, except that the reaction temperature in step (2) is 55°C.

[0051] Example 3

[0052] The preparation method of a high-temperature resistant zwitterionic polymer viscosity enhancer for a composite calcium salt completion fluid is as described in Example 1, except that the reaction temperature in step (2) is 60°C.

[0053] Example 4

[0054] The preparation method of a high-temperature resistant zwitterionic polymer viscosifier for a composite calcium salt completion fluid is as described in Example 1, except that the pH is adjusted to 8 in step (2).

[0055] Comparative Example 1

[0056] A method for preparing a polymer viscosifier for a composite calcium salt completion fluid is as described in Example 2, except that N,N-dimethylacrylamide is not added in step (2).

[0057] Comparative Example 2

[0058] A method for preparing a polymer viscosifier for a composite calcium salt completion fluid is as described in Example 2, except that the temperature-resistant anionic monomer 2-acrylamido-2-methylpropanesulfonic acid (AMPS) is not added in step (2).

[0059] Comparative Example 3

[0060] A method for preparing a polymer viscosifier for a composite calcium salt completion fluid is as described in Example 2, except that the temperature-resistant cationic monomer dimethyldiallyl ammonium chloride (DMDAAC) is not added in step (2).

[0061] Comparative Example 4

[0062] A method for preparing a polymer viscosifier for a composite calcium salt completion fluid is as described in Example 2, except that zwitterionic monomer A is not added in step (2).

[0063] Comparative Example 5

[0064] A method for preparing a polymer viscosifier for a composite calcium salt completion fluid is as described in Example 2, except that 8 g of dimethyldiallyl ammonium chloride (DMDAAC) is added in step (2), and the mass ratio of the temperature-resistant anionic monomer to the temperature-resistant cationic monomer is 1:1.

[0065] Comparative Example 6

[0066] A preparation method of a polymer viscosifier for a composite calcium salt completion fluid is as described in Example 2, except that 1 g of dimethyldiallyl ammonium chloride (DMDAAC) is added in step (2), and the mass ratio of the temperature-resistant anionic monomer to the temperature-resistant cationic monomer is 8:1.

[0067] Comparative Example 7

[0068] A method for preparing a polymer viscosifier for a composite calcium salt completion fluid is as described in Example 2, except that 4 g of zwitterionic monomer A is added in step (2).

[0069] Comparative Example 8

[0070] A method for preparing a polymer viscosifier for a composite calcium salt completion fluid is as described in Example 2, except that 1 g of zwitterionic monomer A is added in step (2).

[0071] Comparative Example 9

[0072] A method for preparing a polymer viscosifier for a composite calcium salt completion fluid is as described in Example 2, except that in step (2), [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfonic acid propyl)ammonium hydroxide (SBMA) replaces the zwitterionic monomer A.

[0073] Comparative Example 10

[0074] A method for preparing a polymer viscosifier for a composite calcium salt completion fluid is as described in Example 1, except that the pH is adjusted to 9 in step (2).

[0075] Comparative Example 11

[0076] The tackifier HE300 was purchased from a commercial source.

[0077] Test example

[0078] The following tests were performed on the polymer tackifiers prepared in the Examples and Comparative Examples.

[0079] 1. Determination of viscosity average molecular weight of tackifier

[0080] With reference to the national standard GBT 12005.10-1992 "Polyacrylamide Molecular Weight Determination Viscosity Method", the flow time of the solvent (1.0 mol / L NaCl solution) and the solution were measured at 30°C using a fully automatic capillary viscometer. The intrinsic viscosity [η] of the tackifier was calculated using the Huggins formula and the Kraemer formula. The viscosity-average molecular weight Mη of the tackifier was calculated using the empirical formula Mη = (10000 [η] / 3.73) 1.515.

[0081] 2. Effect of viscosifier on rheological properties and filtration loss performance of completion fluid before and after aging

[0082] Preparation of base fluid:

[0083] Preparation of composite calcium salt completion fluid sample: 400 mL of deionized water was added with 4 g (1%) of the example and comparative example tackifier samples, respectively, and stirred at 5000 r / min at room temperature for 20 min; then, 236 g of calcium chloride and 550 g of calcium bromide were slowly added, and stirred at 8000 r / min at room temperature for 20 min to obtain a composite calcium salt completion fluid with a density of 1.76 g / cm 3 ;

[0084] Completion fluid sample aging treatment: The completion fluid sample was placed in a roller heating furnace, and the aging temperature was set to 180°C and the aging time was 16 hours.

[0085] With reference to GB16783.1-2014 "Field Testing of Drilling Fluids in the Petroleum and Natural Gas Industry Part 1: Water-Based Drilling Fluids", the rheological and filtration properties of the above-described solutions were evaluated.

[0086] 3. Performance test results

[0087] Table 1 Viscosity average molecular weight of tackifiers

[0088]

[0089]

[0090] Table 1 records the viscosity-average molecular weights of the samples in Examples 1-4 and Comparative Examples 1-11. It can be seen that among Examples 1-4, the sample prepared in Example 2 has a higher viscosity-average molecular weight. Comparative Example 1 lacks the acrylamide monomer N,N-dimethylacrylamide (DMAA), resulting in a lower molecular weight product. Comparative Examples 2, 3, and 4, respectively, lack AMPS, DMDAAC, and SBMA monomers. This lack of monomers reduces the molecular weight of the tackifier. Comparative Examples 5, 6, 7, and 8, respectively, increase and decrease the proportions of the temperature-resistant cationic monomer and zwitterionic monomer, resulting in unsatisfactory polymerization and failure to achieve a higher molecular weight. Comparative Example 9 uses [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfonic acid propyl)ammonium hydroxide (SBMA). While the molecular weight increases compared to the previous comparative examples, it is still lower than the zwitterionic monomer A used in the examples of the present invention. Comparative Example 10 modifies the pH, resulting in a lower molecular weight. Comparative Example 11 uses the commercially available tackifier HE300.

[0091] Table 2 Density 1.76g / cm 3 Viscosity increase of calcium chloride / calcium bromide brine after aging at 180℃

[0092]

[0093]

[0094] The test results in Table 2 show that, compared to composite calcium salt completion fluids without a viscosifier, the addition of the viscosifiers prepared in Examples 1-5 significantly increased the apparent viscosity (AV), plastic viscosity (PV), and dynamic shear force (YP) of the completion fluids. Even after rolling aging at 180°C, the viscosifying properties of the examples were maintained, demonstrating that the viscosifiers prepared in the examples possess excellent high-temperature resistance. Among them, the addition of the viscosifier in Example 2 resulted in the highest viscosity and the most excellent performance.

[0095] In summary, the tackifier prepared by the present invention still has excellent tackifying performance after aging in a high-temperature (180°C) composite calcium salt (calcium chloride / calcium bromide) environment, which can enrich the development of high-temperature resistant, high-density, solid-free completion fluid technology.

Claims

1. A method for preparing a high-temperature resistant zwitterionic polymer viscosifier for a composite calcium salt completion fluid, comprising the following steps: (1) Synthesis of zwitterionic monomer A (1.1) Adding hydroquinone (HQ) to an isocyanatoethyl methacrylate solution and mixing uniformly, the resulting mixed solution is added to a dimethylaminoacetohydrazide solution to react; the reaction is then centrifuged, washed, and dried to obtain an intermediate monomer; (1.2) Add the intermediate monomer and hydroquinone to tetrahydrofuran, stir and dissolve, then add β-propiolactone to react; filter, wash, and dry to obtain zwitterionic monomer A; (2) Preparation of high temperature resistant zwitterionic polymer thickener A temperature-resistant anionic monomer, an acrylamide monomer, a zwitterionic monomer A, and a temperature-resistant cationic monomer are added to deionized water and stirred evenly. After adjusting the pH of the system to 7-8, nitrogen is introduced to deoxygenate the system. The temperature is then raised to the reaction temperature, an initiator is added, and the reaction is carried out to obtain a high-temperature-resistant zwitterionic polymer viscosity enhancer for a composite calcium salt completion fluid.

2. The method for preparing the high temperature resistant zwitterionic polymer viscosity enhancer for composite calcium salt completion fluid according to claim 1, characterized in that: The isocyanoethyl methacrylate solution in step (1.1) is obtained by dissolving isocyanoethyl methacrylate in tetrahydrofuran, and the concentration of the isocyanoethyl methacrylate solution is 0.05-0.15 g / mL; the mass ratio of hydroquinone to isocyanoethyl methacrylate is 1:80-120, preferably 1:100; The dimethylaminoacetohydrazide solution is obtained by dissolving dimethylaminoacetohydrazide in tetrahydrofuran, wherein the concentration of the dimethylaminoacetohydrazide (DMAH) solution is 0.05-0.1 g / mL; and the mass ratio of the dimethylaminoacetohydrazide (DMAH) to isocyanoethyl methacrylate is 1-1.5:

2.

3. The method for preparing the high temperature resistant zwitterionic polymer viscosity enhancer for composite calcium salt completion fluid according to claim 1, characterized in that: In step (1.1), the reaction temperature is 35-45° C., and the reaction time is 2-4 h. The washing is 3-5 times of ether washing. The drying is vacuum drying at 70-90° C. for 8-12 h.

4. The method for preparing the high temperature resistant zwitterionic polymer viscosity enhancer for composite calcium salt completion fluid according to claim 1, characterized in that: In step (1.2), the mass ratio of hydroquinone (HQ) to the intermediate monomer is 1:70-90, preferably 1:80; the mass ratio of the intermediate monomer to the volume of tetrahydrofuran is 0.05-0.1 g:1 mL; and the stirring and dissolving temperature is 40-60° C.; The mass ratio of β-propiolactone to the intermediate monomer is 1:3-3.5, preferably 1:3.2; the temperature for stirring and dissolving is 40-60°C; the temperature for the reaction is 40-60°C; the reaction time is 8-12 hours; the washing is performed by washing with diethyl ether 3-5 times; and the drying is performed at 80-100°C for 8-10 hours.

5. The method for preparing the high temperature resistant zwitterionic polymer viscosity enhancer for composite calcium salt completion fluid according to claim 1, characterized in that: The temperature-resistant anionic monomer in step (2) is 2-acrylamido-2-methylpropanesulfonic acid, sodium vinyl sulfonate or sodium styrene sulfonate; The acrylamide monomer is N,N-dimethylacrylamide or N-isopropylacrylamide; The temperature-resistant cationic monomer is dimethyldiallylammonium chloride or methacryloyloxyethyltrimethylammonium chloride.

6. The method for preparing the high temperature resistant zwitterionic polymer viscosity enhancer for composite calcium salt completion fluid according to claim 1, characterized in that: The mass ratio of the acrylamide monomer to deionized water in step (2) is 1:3-10; The mass ratio of the temperature-resistant anionic monomer, acrylamide monomer, zwitterionic monomer A, and temperature-resistant cationic monomer is 1-3:7:0.45-0.6:0.4-0.7, preferably 2:7:0.5:0.

5.

7. The method for preparing the high temperature resistant zwitterionic polymer viscosity enhancer for composite calcium salt completion fluid according to claim 1, characterized in that: The stirring rate in step (2) is 200-500 r / min, and the stirring time is 10-20 min; In step (2), a sodium hydroxide aqueous solution with a mass fraction of 20%-40% is used to adjust the pH of the system to 7-8; the nitrogen deoxygenation time is 20-40 minutes, preferably 30 minutes.

8. The method for preparing the high temperature resistant zwitterionic polymer viscosity enhancer for composite calcium salt completion fluid according to claim 1, characterized in that: The initiator in step (2) is azobisisobutylamidine hydrochloride, and the mass of the initiator is 0.1-1% of the total mass of the temperature-resistant anionic monomer, acrylamide monomer, zwitterionic monomer A and temperature-resistant cationic monomer; The reaction temperature is 50-60° C., and the reaction time is 4-6 hours.

9. A high temperature resistant zwitterionic polymer viscosifier for composite calcium salt completion fluid, characterized in that: The preparation method according to claim 1 is used for preparation.

10. Use of the high temperature resistant zwitterionic polymer viscosity enhancer for composite calcium salt completion fluid according to claim 9 in composite calcium salt completion fluid, characterized in that: The concentration of the high-temperature resistant zwitterionic polymer viscosity enhancer for the composite calcium salt completion fluid is 15-20 g / L, and the composite calcium salt includes calcium chloride and calcium bromide.

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