Preparation method of plugging agent for oilfield drilling fluid

Abstract

The present invention belongs to the technical field of plugging agent preparation, and specifically relates to a method for preparing a plugging agent for oilfield drilling fluid. The method for preparing a plugging agent for oilfield drilling fluid of the present invention first uses acrylamide, 3-acrylamide-3-methylbutyric acid and N-allyl-4-methylbenzenesulfonamide as monomers, azobisisobutylamidine hydrochloride as an initiator, and prepares hydrolyzed polyacrylamide through polymerization-hydrolysis reaction, then the hydrolyzed polyacrylamide is compounded with scleroglucan, and p-phenylenediamine and chromium acetate are used as cross-linking agents to prepare a plugging agent for oilfield drilling fluid, and the plugging agent prepared in this way has good injectability, compressive strength and stability.

Description

Technical Field

[0001] The invention belongs to the technical field of plugging agent preparation, and specifically relates to a method for preparing a plugging agent for oilfield drilling fluid. Background Art

[0002] In recent years, with the continuous deepening of oil and gas resource exploration and development, the underground environment has become more complex and the construction difficulty has increased day by day. Well leakage will lose a large amount of working fluid, pollute the reservoir, seriously delay construction, and may even cause other major accidents such as blowouts and well collapses, resulting in huge economic losses. Therefore, it is particularly important to use effective technical means to prevent and control well leakage in drilling operations. Traditional plugging methods include bridging plugging, cement slurry plugging, polymer gel plugging, etc. However, due to the limitations of the shape, density, temperature resistance and pressure resistance of the material itself, traditional bridge plug plugging materials often have problems such as unstable bridging effect, difficulty in forming effective plugging at the leaking layer, and difficulty in improving the pressure bearing capacity of the formation. Even if the plugging material has entered the leaking layer to form a stable plugging plug, under the continuous action of the reverse stress of the formation, the plugging strength of the bridge plug will continue to decrease, and eventually be squeezed out of the leakage channel, causing leakage again. Cement plugging often has a long construction period, lack of bridge materials, sometimes unable to stay in the leaking layer channel and bond well with the formation, and the plugging effect is difficult to ensure.

[0003] Compared with the above plugging materials, polymer gel plugging technology uses polymer materials to cross-link to form a three-dimensional network structure of viscoelastic body, which has the same deformation property as flexible elastic plugging materials, reduces the restriction of the leakage channel to the plugging material, reaches the leakage layer through deformation, and achieves the plugging effect through solidification or expansion. Polymer gel plugging materials are mainly divided into three categories: composite gel plugging materials, natural polymer systems and polyacrylamide cross-linked gels. Polyacrylamide cross-linked gel has attracted widespread attention due to its significant water plugging effect. However, the existing polyacrylamide water plugging materials have poor temperature and salt resistance, poor retention ability of plugging materials in the leakage channel and low plugging strength, resulting in low success rate of leakage plugging and serious losses. Therefore, it is necessary to explore a new plugging agent for oilfield drilling fluid. Summary of the invention

[0004] The purpose of the present invention is to provide a method for preparing a plugging agent for oilfield drilling fluid. The plugging agent for oilfield drilling fluid prepared by the method has good injectability, stability and compressive strength.

[0005] The preparation method of the plugging agent for oilfield drilling fluid of the present invention comprises the following steps:

[0006] (1) adding acrylamide, 3-acrylamide-3-methylbutyric acid and N-allyl-4-methylbenzenesulfonamide into a reaction vessel, then adding deionized water, and finally adding sodium hydroxide powder to adjust the pH value of the reaction system to 7.5;

[0007] (2) nitrogen was passed into the reaction vessel for 1.2-1.5 hours to expel oxygen, and then azobisisobutylamidine hydrochloride was added, and the polymerization was carried out at a constant temperature of 54-56°C for 8.2-8.4 hours. Nitrogen was continuously passed during the reaction. After the reaction was completed, deionized water and sodium hydroxide powder were added, and a hydrolysis reaction was carried out at 80-83°C;

[0008] (3) After the hydrolysis reaction is completed, pour ethanol into the mixture for washing to remove impurities, and then dry it in a vacuum drying oven to obtain a colloid;

[0009] (4) The colloid prepared in step (3) and hard glucan are dissolved in high salt water, and stirred continuously to make them dispersed evenly. Then, p-phenylenediamine and chromium acetate are added and stirred for 2.5-3 hours. Finally, cross-linking is carried out in a constant temperature closed environment at 70-73°C to prepare a plugging agent for oilfield drilling fluid.

[0010] in:

[0011] In step (1), the mass ratio of acrylamide, 3-acrylamide-3-methylbutyric acid and N-allyl-4-methylbenzenesulfonamide is 7.5-7.6: 1.2-1.3: 1.1-1.2.

[0012] In step (1), the total mass of acrylamide, 3-acrylamide-3-methylbutyric acid and N-allyl-4-methylbenzenesulfonamide accounts for 22% of the total mass of acrylamide, 3-acrylamide-3-methylbutyric acid, N-allyl-4-methylbenzenesulfonamide and deionized water.

[0013] The mass of azobisisobutyramidine hydrochloride in step (2) accounts for 1.0% of the total mass of acrylamide, 3-acrylamide-3-methylbutyric acid, N-allyl-4-methylbenzenesulfonamide and deionized water.

[0014] After the reaction in step (2) is completed, first add deionized water accounting for two-thirds of the volume of the reaction container, and then add sodium hydroxide powder to adjust the pH value of the reaction system to 12.

[0015] The hydrolysis reaction time in step (2) is 1.3-1.5h.

[0016] In step (3), the vacuum drying temperature is 103-105° C., and the vacuum drying time is 1-1.2 h.

[0017] The stirring time in step (4) is 13-14 hours.

[0018] The cross-linking time in step (4) is 2.2-2.4 h.

[0019] In step (4), the sum of the masses of the colloid, scleroglucan, brine, p-phenylenediamine and chromium acetate is 100%, wherein the colloid accounts for 0.35-0.37%, scleroglucan accounts for 0.0628-0.0630%, p-phenylenediamine accounts for 0.28-0.30%, chromium acetate accounts for 0.25-0.27%, and the balance is brine.

[0020] The salt mass concentration of the high-salt water in step (4) is 40324 mg / L, and its chemical composition is Na + :12045 mg / L, K + :310mg / L、Ca 2+ :1138mg / L、Mg 2+ :402mg / L、Sr 2+ :415mg / L、SO4 2- :124mg / L、HCO3 - :278mg / L、Cl - : 25252 mg / L; in step (4), high salt water is used to simulate formation water.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] (1) The method for preparing the plugging agent for oilfield drilling fluid of the present invention comprises the following steps: firstly, using acrylamide, 3-acrylamide-3-methylbutyric acid and N-allyl-4-methylbenzenesulfonamide as monomers and azobisisobutylamidine hydrochloride as an initiator, preparing hydrolyzed polyacrylamide through a polymerization-hydrolysis reaction; then, compounding the hydrolyzed polyacrylamide with scleroglucan, and using p-phenylenediamine and chromium acetate as cross-linking agents to prepare the plugging agent for oilfield drilling fluid. The plugging agent prepared in this way has good injectability, compressive strength and stability.

[0023] (2) The preparation method of the plugging agent for oilfield drilling fluid of the present invention is as follows: when preparing hydrolyzed polyacrylamide, carboxyl groups are introduced into the polyacrylamide macromolecular chain by adding 3-acrylamide-3-methylbutyric acid, and the electrostatic repulsion and hydrogen bonding of the carboxyl groups are used to form a complex three-dimensional network structure of polyacrylamide. The rigid side groups it possesses are conducive to increasing steric hindrance and improving thermal stability. N-allyl-4-methylbenzenesulfonamide contains both polymerizable double bonds and hydrophobic groups. Through the van der Waals forces between hydrogen bonds and hydrophobic groups, a more stable cross-linked network structure is formed through polymerization reaction, thereby enhancing the temperature resistance and salt resistance of the prepared polyacrylamide.

[0024] (3) The preparation method of the plugging agent for oilfield drilling fluid of the present invention is to compound scleroglucan and hydrolyzed polyacrylamide for use. Scleroglucan can be cross-linked with chromium acetate and has good salt and temperature resistance. The prepared plugging agent can be used for water plugging in high mineralization and high shear environments. The hydrolyzed polyacrylamide can be cross-linked with chromium acetate and p-phenylenediamine, so that the prepared plugging agent can meet the long-term plugging requirements of high-temperature and high-water-content oil reservoirs. DETAILED DESCRIPTION

[0025] The present invention is further described below with reference to the embodiments.

[0026] Example 1

[0027] The preparation method of the plugging agent for oilfield drilling fluid described in this embodiment 1 is composed of the following steps:

[0028] (1) adding acrylamide, 3-acrylamide-3-methylbutyric acid and N-allyl-4-methylbenzenesulfonamide into a reaction vessel, then adding deionized water, and finally adding sodium hydroxide powder to adjust the pH value of the reaction system to 7.5;

[0029] (2) nitrogen was passed through the reaction vessel for 1.35 hours to expel oxygen, and then azobisisobutylamidine hydrochloride was added and the polymerization was carried out at a constant temperature of 55°C for 8.3 hours. Nitrogen was continuously passed through the reaction. After the reaction was completed, deionized water and sodium hydroxide powder were added and hydrolysis reaction was carried out at 81°C;

[0030] (3) After the hydrolysis reaction is completed, pour ethanol into the mixture for washing to remove impurities, and then dry it in a vacuum drying oven to obtain a colloid;

[0031] (4) The colloid and hard glucan prepared in step (3) are dissolved in high salt water, and stirred continuously to make them dispersed evenly. Then, p-phenylenediamine and chromium acetate are added and stirred for 2.7 hours. Finally, cross-linking is carried out in a constant temperature closed environment at 71°C to prepare a plugging agent for oilfield drilling fluid.

[0032] in:

[0033] In step (1), the mass ratio of acrylamide, 3-acrylamide-3-methylbutyric acid and N-allyl-4-methylbenzenesulfonamide is 7.55:1.25:1.15.

[0034] In step (1), the total mass of acrylamide, 3-acrylamide-3-methylbutyric acid and N-allyl-4-methylbenzenesulfonamide accounts for 22% of the total mass of acrylamide, 3-acrylamide-3-methylbutyric acid, N-allyl-4-methylbenzenesulfonamide and deionized water.

[0035] The mass of azobisisobutyramidine hydrochloride in step (2) accounts for 1.0% of the total mass of acrylamide, 3-acrylamide-3-methylbutyric acid, N-allyl-4-methylbenzenesulfonamide and deionized water.

[0036] After the reaction in step (2) is completed, first add deionized water accounting for two-thirds of the volume of the reaction container, and then add sodium hydroxide powder to adjust the pH value of the reaction system to 12.

[0037] The hydrolysis reaction time in step (2) is 1.4 h.

[0038] In step (3), the vacuum drying temperature is 104° C. and the vacuum drying time is 1.1 h.

[0039] The stirring time in step (4) is 13.5 h.

[0040] The cross-linking time in step (4) is 2.3 h.

[0041] In step (4), the sum of the masses of the colloid, scleroglucan, brine, p-phenylenediamine and chromium acetate is 100%, wherein the colloid accounts for 0.36%, scleroglucan accounts for 0.0629%, p-phenylenediamine accounts for 0.29%, chromium acetate accounts for 0.26%, and the balance is brine.

[0042] The salt mass concentration of the high-salt water in step (4) is 40324 mg / L, and its chemical composition is Na + :12045 mg / L, K + :310mg / L、Ca 2+ :1138mg / L、Mg 2+ :402mg / L、Sr 2+ :415mg / L、SO4 2- :124mg / L、HCO3 - :278mg / L、Cl - :25252mg / L.

[0043] The plugging agent for oilfield drilling fluid prepared in Example 1 was heated to 70°C and the mineralization degree was 4×10 4 The material was aged under the condition of 3400 mg / L, and the gelation time, plugging agent strength and dehydration rate were tested; the time taken for the plugging agent strength to reach Class F is the gelation time, and the gelation time is 76h. The gelation time determines the injectability of the prepared plugging agent; the plugging agent strength is expressed by the storage modulus after aging for 180 days, and the storage modulus is 16.7Pa; the dehydration rate of the plugging agent for oilfield drilling fluid is 3.5% after 120d, which shows that it has good temperature and salt resistance.

[0044] Example 2

[0045] The preparation method of the plugging agent for oilfield drilling fluid described in this embodiment 2 is composed of the following steps:

[0046] (1) adding acrylamide, 3-acrylamide-3-methylbutyric acid and N-allyl-4-methylbenzenesulfonamide into a reaction vessel, then adding deionized water, and finally adding sodium hydroxide powder to adjust the pH value of the reaction system to 7.5;

[0047] (2) nitrogen was passed through the reaction vessel for 1.2 hours to expel oxygen, and then diisobutylamidine hydrochloride was added and the polymerization was carried out at a constant temperature of 54°C for 8.4 hours. Nitrogen was continuously passed through the reaction. After the reaction was completed, deionized water and sodium hydroxide powder were added and hydrolysis reaction was carried out at 80°C;

[0048] (3) After the hydrolysis reaction is completed, pour ethanol into the mixture for washing to remove impurities, and then dry it in a vacuum drying oven to obtain a colloid;

[0049] (4) The colloid prepared in step (3) and hard glucan are dissolved in high salt water, and stirred continuously to make them dispersed evenly. Then, p-phenylenediamine and chromium acetate are added and stirred for 2.5 hours. Finally, cross-linking is carried out in a constant temperature closed environment at 73°C to prepare a plugging agent for oilfield drilling fluid.

[0050] in:

[0051] In step (1), the mass ratio of acrylamide, 3-acrylamide-3-methylbutyric acid and N-allyl-4-methylbenzenesulfonamide is 7.5:1.3:1.1.

[0052] In step (1), the total mass of acrylamide, 3-acrylamide-3-methylbutyric acid and N-allyl-4-methylbenzenesulfonamide accounts for 22% of the total mass of acrylamide, 3-acrylamide-3-methylbutyric acid, N-allyl-4-methylbenzenesulfonamide and deionized water.

[0053] The mass of azobisisobutyramidine hydrochloride in step (2) accounts for 1.0% of the total mass of acrylamide, 3-acrylamide-3-methylbutyric acid, N-allyl-4-methylbenzenesulfonamide and deionized water.

[0054] After the reaction in step (2) is completed, first add deionized water accounting for two-thirds of the volume of the reaction container, and then add sodium hydroxide powder to adjust the pH value of the reaction system to 12.

[0055] The hydrolysis reaction time in step (2) is 1.5 h.

[0056] In step (3), the vacuum drying temperature is 103° C. and the vacuum drying time is 1.2 h.

[0057] The stirring time in step (4) is 13 h.

[0058] The cross-linking time in step (4) is 2.2 h.

[0059] In step (4), the sum of the masses of the colloid, scleroglucan, brine, p-phenylenediamine and chromium acetate is 100%, wherein the colloid accounts for 0.35%, scleroglucan accounts for 0.0630%, p-phenylenediamine accounts for 0.28%, chromium acetate accounts for 0.25%, and the balance is brine.

[0060] The salt mass concentration of the high-salt water in step (4) is 40324 mg / L, and its chemical composition is Na + :12045 mg / L, K + :310mg / L、Ca 2+ :1138mg / L、Mg 2+ :402mg / L、Sr 2+ :415mg / L、SO4 2- :124mg / L、HCO3 - :278mg / L、Cl - :25252mg / L.

[0061] The plugging agent for oilfield drilling fluid prepared in Example 2 was heated to 70°C and the mineralization degree was 4×10 4 The material was aged under the condition of 400 mg / L, and the gelling time, plugging agent strength and dehydration rate were tested; the time taken for the plugging agent strength to reach Class F is the gelling time, and the gelling time is 75h. The gelling time determines the injectability of the prepared plugging agent; the plugging agent strength is expressed by the storage modulus after aging for 180 days, and the storage modulus is 16.0Pa; the dehydration rate of the plugging agent for oilfield drilling fluid is 4.2% after 120d, which shows that it has good temperature and salt resistance.

[0062] Example 3

[0063] The preparation method of the plugging agent for oilfield drilling fluid described in this embodiment 3 is composed of the following steps:

[0064] (1) adding acrylamide, 3-acrylamide-3-methylbutyric acid and N-allyl-4-methylbenzenesulfonamide into a reaction vessel, then adding deionized water, and finally adding sodium hydroxide powder to adjust the pH value of the reaction system to 7.5;

[0065] (2) nitrogen was passed through the reaction vessel for 1.5 hours to expel oxygen, and then diisobutylamidine hydrochloride was added and the polymerization was carried out at a constant temperature of 56°C for 8.2 hours. Nitrogen was continuously passed through the reaction. After the reaction was completed, deionized water and sodium hydroxide powder were added and hydrolysis reaction was carried out at 83°C;

[0066] (3) After the hydrolysis reaction is completed, pour ethanol into the mixture for washing to remove impurities, and then dry it in a vacuum drying oven to obtain a colloid;

[0067] (4) The colloid prepared in step (3) and hard glucan are dissolved in high salt water, and stirred continuously to make them dispersed evenly. Then, p-phenylenediamine and chromium acetate are added and stirred for 3 hours. Finally, cross-linking is carried out in a constant temperature closed environment at 70° C. to prepare a plugging agent for oilfield drilling fluid.

[0068] in:

[0069] In step (1), the mass ratio of acrylamide, 3-acrylamide-3-methylbutyric acid and N-allyl-4-methylbenzenesulfonamide is 7.6:1.2:1.2.

[0070] In step (1), the total mass of acrylamide, 3-acrylamide-3-methylbutyric acid and N-allyl-4-methylbenzenesulfonamide accounts for 22% of the total mass of acrylamide, 3-acrylamide-3-methylbutyric acid, N-allyl-4-methylbenzenesulfonamide and deionized water.

[0071] The mass of azobisisobutyramidine hydrochloride in step (2) accounts for 1.0% of the total mass of acrylamide, 3-acrylamide-3-methylbutyric acid, N-allyl-4-methylbenzenesulfonamide and deionized water.

[0072] After the reaction in step (2) is completed, first add deionized water accounting for two-thirds of the volume of the reaction container, and then add sodium hydroxide powder to adjust the pH value of the reaction system to 12.

[0073] The hydrolysis reaction time in step (2) is 1.3 h.

[0074] In step (3), the vacuum drying temperature is 105° C. and the vacuum drying time is 1 h.

[0075] The stirring time in step (4) is 14 h.

[0076] The cross-linking time in step (4) is 2.4 h.

[0077] In step (4), the sum of the masses of the colloid, scleroglucan, brine, p-phenylenediamine and chromium acetate is 100%, wherein the colloid accounts for 0.37%, scleroglucan accounts for 0.0628%, p-phenylenediamine accounts for 0.30%, chromium acetate accounts for 0.27%, and the balance is brine.

[0078] The salt mass concentration of the high-salt water in step (4) is 40324 mg / L, and its chemical composition is Na + :12045 mg / L, K + :310mg / L、Ca 2+:1138mg / L、Mg 2+ :402mg / L、Sr 2+ :415mg / L、SO4 2- :124mg / L、HCO3 - :278mg / L、Cl - :25252mg / L.

[0079] The plugging agent for oilfield drilling fluid prepared in Example 3 was heated to 70°C and the mineralization degree was 4×10 4 The materials were aged at 3700 μg / L and the gelling time, plugging agent strength and dehydration rate were tested. The time required for the plugging agent strength to reach Grade F was the gelling time, which was 77 h. The gelling time determined the injectability of the prepared plugging agent. The strength of the plugging agent was expressed by the storage modulus after aging for 180 days, which was 17.5 Pa. The dehydration rate of the plugging agent for oilfield drilling fluid was 3.1% after 120 days. It can be seen that the plugging agent has good temperature and salt resistance.

[0080] Comparative Example 1

[0081] The preparation method of the plugging agent for oilfield drilling fluid described in this comparative example 1 is the same as that of Example 1, the only difference being that 3-acrylamide-3-methylbutyric acid is not added in step (1), and the mass ratio of acrylamide to N-allyl-4-methylbenzenesulfonamide in step (1) is 7.55:1.15; and the sum of the mass of acrylamide and N-allyl-4-methylbenzenesulfonamide in step (1) accounts for 22% of the sum of the mass of acrylamide, N-allyl-4-methylbenzenesulfonamide and deionized water.

[0082] The plugging agent for oilfield drilling fluid prepared in Comparative Example 1 was heated to 70°C and the mineralization degree was 4×10 4 The plugging agent was aged under the condition of 200 mg / L, and the gelation time, plugging agent strength and dehydration rate were tested; the time taken for the plugging agent strength to reach Class F is the gelation time, and the gelation time is 72h. The gelation time determines the injectability of the prepared plugging agent; the plugging agent strength is expressed by the storage modulus after aging for 180 days, and the storage modulus is 11.4Pa; the dehydration rate of the plugging agent for oilfield drilling fluid is 19.6% after 120d, which shows that its temperature and salt resistance is poor.

[0083] Comparative Example 2

[0084] The preparation method of the plugging agent for oilfield drilling fluid described in this comparative example 2 is the same as that of Example 1, the only difference being that N-allyl-4-methylbenzenesulfonamide is not added in step (1), and the mass ratio of acrylamide to 3-acrylamide-3-methylbutyric acid in step (1) is 7.55:1.25; and the sum of the mass of acrylamide and 3-acrylamide-3-methylbutyric acid in step (1) accounts for 22% of the sum of the mass of acrylamide, 3-acrylamide-3-methylbutyric acid and deionized water.

[0085] The plugging agent for oilfield drilling fluid prepared in Comparative Example 2 was heated to 70°C and the mineralization degree was 4×10 4 The plugging agent was aged under the condition of 400 mg / L, and the gelation time, plugging agent strength and dehydration rate were tested; the time taken for the plugging agent strength to reach Class F is the gelation time, and the gelation time is 74h. The gelation time determines the injectability of the prepared plugging agent; the plugging agent strength is expressed by the storage modulus after aging for 180 days, and the storage modulus is 10.2Pa; the dehydration rate of the plugging agent for oilfield drilling fluid is 17.1% after 120d, which shows that its temperature and salt resistance is poor.

[0086] Comparative Example 3

[0087] The preparation method of the plugging agent for oilfield drilling fluid described in this comparative example 3 is the same as that of Example 1, except that the raw material scleroglucan is not added in step (4). The mass sum of the colloid, high brine, p-phenylenediamine and chromium acetate in step (4) is 100%, wherein the colloid is 0.36%, p-phenylenediamine is 0.29%, chromium acetate is 0.26%, and the balance is high brine.

[0088] The plugging agent for oilfield drilling fluid prepared in Comparative Example 3 was heated to 70°C and the mineralization degree was 4×10 4 The plugging agent was aged under the condition of 300 mg / L, and the gelling time, plugging agent strength and dehydration rate were tested; the time taken for the plugging agent strength to reach Class F is the gelling time, and the gelling time is 75h. The gelling time determines the injectability of the prepared plugging agent; the plugging agent strength is expressed by the storage modulus after aging for 180 days, and its storage modulus is 12.9Pa; the dehydration rate of the plugging agent for oilfield drilling fluid is 13.4% after 120d, which shows that its temperature and salt resistance is poor.

Claims

1. A method for preparing a plugging agent for oilfield drilling fluid, characterized in that: It consists of the following steps: (1) adding acrylamide, 3-acrylamide-3-methylbutyric acid and N-allyl-4-methylbenzenesulfonamide into a reaction vessel, then adding deionized water, and finally adding sodium hydroxide powder to adjust the pH value of the reaction system to 7.5; (2) nitrogen was passed into the reaction vessel for 1.2-1.5 hours to expel oxygen, and then azobisisobutylamidine hydrochloride was added, and the polymerization was carried out at a constant temperature of 54-56°C for 8.2-8.4 hours. Nitrogen was continuously passed during the reaction. After the reaction was completed, deionized water and sodium hydroxide powder were added, and a hydrolysis reaction was carried out at 80-83°C; (3) After the hydrolysis reaction is completed, pour ethanol into the mixture for washing to remove impurities, and then dry it in a vacuum drying oven to obtain a colloid; (4) dissolving the colloid and scleroglucan prepared in step (3) in high salt water, stirring continuously to make them dispersed evenly, then adding p-phenylenediamine and chromium acetate and stirring for 2.5-3h, and finally cross-linking in a constant temperature closed environment at 70-73°C to prepare a plugging agent for oilfield drilling fluid; in: In step (1), the mass ratio of acrylamide, 3-acrylamide-3-methylbutyric acid and N-allyl-4-methylbenzenesulfonamide is 7.5-7.6: 1.2-1.3: 1.1-1.2; In step (4), the sum of the masses of the colloid, scleroglucan, brine, p-phenylenediamine and chromium acetate is 100%, wherein the colloid accounts for 0.35-0.37%, scleroglucan accounts for 0.0628-0.0630%, p-phenylenediamine accounts for 0.28-0.30%, chromium acetate accounts for 0.25-0.27%, and the balance is brine.

2. The method for preparing a plugging agent for oilfield drilling fluid according to claim 1, wherein: In step (1), the total mass of acrylamide, 3-acrylamide-3-methylbutyric acid and N-allyl-4-methylbenzenesulfonamide accounts for 22% of the total mass of acrylamide, 3-acrylamide-3-methylbutyric acid, N-allyl-4-methylbenzenesulfonamide and deionized water.

3. The method for preparing a plugging agent for oilfield drilling fluid according to claim 1, characterized in that: The mass of azobisisobutyramidine hydrochloride in step (2) accounts for 1.0% of the total mass of acrylamide, 3-acrylamide-3-methylbutyric acid, N-allyl-4-methylbenzenesulfonamide and deionized water.

4. The method for preparing a plugging agent for oilfield drilling fluid according to claim 1, characterized in that: After the reaction in step (2) is completed, firstly, deionized water accounting for two-thirds of the volume of the reaction container is added, and then sodium hydroxide powder is added to adjust the pH value of the reaction system to 12.

5. The method for preparing a plugging agent for oilfield drilling fluid according to claim 1, characterized in that: The hydrolysis reaction time in step (2) is 1.3-1.5h.

6. The method for preparing a plugging agent for oilfield drilling fluid according to claim 1, characterized in that: In step (3), the vacuum drying temperature is 103-105° C., and the vacuum drying time is 1-1.2 h.

7. The method for preparing a plugging agent for oilfield drilling fluid according to claim 1, characterized in that: The stirring time in step (4) is 13-14 hours; The cross-linking time in step (4) is 2.2-2.4 h.