CN116836337A - Environment-friendly strong-blocking high-temperature-resistant blocking agent for water-based drilling fluid and preparation method and application thereof - Google Patents

Abstract

The invention provides an environmentally friendly strong plugging and high-temperature resistant plugging agent for water-based drilling fluid and its preparation method and application. The preparation method of the blocking agent includes the steps of: adding corn starch to an ethanol aqueous solution, and then adding an alkali to perform alkalization treatment; then continuing to add monochloroacetic acid to perform an etherification reaction; after the reaction is completed, adjust the pH of the reaction solution to be 6.5~7.0, after filtering, washing and drying, carboxymethyl starch is obtained; carboxymethyl starch is added to water and pre-gelatinized to obtain starch paste; amide monomer and rigid monomer are added to water to obtain grafting Monomer solution; add the obtained graft monomer solution to the starch paste, adjust the pH value of the system to 6.5-7.5, add an initiator under a nitrogen environment, and carry out the reaction. The blocking agent of the present invention is a degradable blocking agent that is resistant to high temperatures of 180°C, and overcomes the shortcomings of existing environmentally friendly degradable natural polymer blocking agents that have insufficient high-temperature stability.

Description

An environmentally friendly strong sealing and high-temperature resistant sealing agent for water-based drilling fluids and its preparation method and application

Technical field

The invention relates to an environmentally friendly strong plugging and high-temperature resistant plugging agent for water-based drilling fluids and its preparation method and application, and belongs to the field of oilfield chemistry in the petroleum industry.

Background technique

During the drilling process, the liquid and solid particles in the drilling fluid leak into the fractured formation under pressure, which not only causes damage to the reservoir, but also causes complex underground conditions such as well wall instability. In serious cases It may even cause major safety issues such as well leakage and blowout. The use of plugging agents to form a dense plugging layer on the surface of the well wall can effectively prevent the solid particles of drilling fluid from migrating to the formation, reduce the penetration of wellbore working fluid into the formation, and reduce the risks of downhole operations.

However, as the situation of environmental protection becomes increasingly severe, government departments have higher and higher requirements on environmental protection issues and management efforts are becoming stronger and stronger. The environmental performance of drilling fluid treatment agents has received great attention from relevant departments. At the same time, the discharge of drilling waste fluid and waste solids has also been strictly restricted. Petroleum, heavy metals, and refractory polymers contained in drilling waste are harmful to humans, livestock, and the environment. If left untreated or left untreated, they will pollute surface water, damage soil structure, and endanger the health of animals and plants. Growth and human life and health.

Natural materials such as starch, cellulose, and vegetable gums have attracted much attention from oilfield chemists due to their easy biodegradability. Modified products can be obtained through carboxylation, sulfonation, graft copolymerization, etc., which has become an important environmentally friendly oilfield chemical materials. However, there are still certain problems in using modified natural materials in formation plugging applications: Environmentally friendly plugging agents have insufficient temperature resistance and are easily degraded under high temperature conditions in the formation, losing their plugging effect. Their use in high-temperature wells and complex formations is limited. extremely restrictive.

Chinese patent document CN107502316A discloses an environmentally friendly plugging agent for water-based drilling fluid and its preparation method. This method uses glucose to prepare carbon balls and coats them with a layer of polyacrylamide-N-isoacrylamide material. This plugging agent has low biological toxicity and can ensure optimal plugging performance under saturated brine conditions of 120°C. However, this method cannot satisfy formation plugging at high temperatures of 150°C. Chinese patent document CN109735311A discloses an environmentally friendly plugging agent for drilling fluids and a preparation method thereof. The plugging agent is made of modified starch and lignocellulose and has low biofluorescence. However, the plugging agent needs to be used during use. Combined with a certain amount of antioxidants, it prevents microbial bacteria or the environment from damaging the structural properties of the sealing agent.

Therefore, the preparation of an environmentally friendly plugging agent with excellent temperature resistance is of great significance for drilling in deep high-temperature formations with high environmental requirements and harsh formation conditions.

Contents of the invention

In view of the shortcomings of the existing technology, especially the shortcomings of the existing environmentally friendly sealing agents: (1) the toxicity evaluation of most treatment agents is not comprehensive, and the environmental performance cannot fully meet the environmental protection requirements; (2) the high temperature resistance is insufficient. It degrades and fails under high-temperature conditions and cannot meet the drilling needs of deep high-temperature formations. The present invention provides an environmentally friendly strong sealing and high-temperature resistant sealing agent for water-based drilling fluids and its preparation method and application. The blocking agent of the present invention is a degradable blocking agent that is resistant to high temperatures of 180°C, and overcomes the shortcomings of existing environmentally friendly degradable natural polymer blocking agents that have insufficient high-temperature stability.

The technical solution of the present invention is as follows:

A method for preparing an environmentally friendly strong plugging and high-temperature resistant plugging agent for water-based drilling fluids, which includes the following steps:

(1) Add corn starch to the aqueous ethanol solution, and then add alkali to perform alkalization treatment; then continue to add monochloroacetic acid to perform the etherification reaction; after the reaction is completed, adjust the pH of the reaction solution to 6.5 to 7.0, filter and wash , dry to obtain carboxymethyl starch;

(2) Add carboxymethyl starch to water for pre-gelatinization to obtain a starch paste; add amide monomers and rigid monomers to water to obtain a graft monomer solution; add the obtained graft monomer solution to the starch paste In the liquid, after adjusting the pH value of the system to 6.5 to 7.5, add an initiator in a nitrogen environment to carry out the reaction; after the reaction is completed, add a precipitant to the reaction system to precipitate, filter, wash, and dry to obtain water-based drilling. Liquid environmentally friendly strong sealing and high temperature resistance sealing agent.

According to the preferred embodiment of the present invention, the volume fraction of ethanol in the ethanol aqueous solution in step (1) is 80%; the ratio of the volume of the ethanol aqueous solution to the mass of corn starch is 1 mL: 0.1-0.5 g.

According to the preferred embodiment of the present invention, the alkali in step (1) is sodium hydroxide or potassium hydroxide; the mass ratio of the alkali to corn starch is 0.1 to 0.25:1.

According to the preferred embodiment of the present invention, the temperature of the alkalizing treatment in step (1) is 40-50°C, and the time of the alkalizing treatment is 4-6 hours.

According to the preferred method of the present invention, the mass ratio of monochloroacetic acid to corn starch in step (1) is 1:0.5-1.

According to the preferred embodiment of the present invention, the temperature of the etherification reaction in step (1) is 40-50°C, and the time of the etherification reaction is 8-10 h.

According to the preferred embodiment of the present invention, in step (1), glacial acetic acid is used to adjust the pH of the reaction solution.

According to the preferred embodiment of the present invention, the washing in step (1) is carried out with a mixture of ethanol and water, and the volume ratio of ethanol and water in the mixture is 2 to 4:1; the drying is at 40 to 50°C. Dry for 8 to 10 hours.

According to the preferred embodiment of the present invention, the concentration of carboxymethyl starch in the starch paste in step (2) is 0.05-0.1g/mL.

According to the preferred embodiment of the present invention, the pre-gelatinization temperature in step (2) is 50-55°C, and the pre-gelatinization time is 20-40 minutes.

According to the preferred embodiment of the present invention, the amide monomer in step (2) is one or a combination of two or more of acrylamide, methacrylamide, and N,N-dimethylacrylamide; the amide The mass ratio of monomer to carboxymethyl starch is 1 to 2:1.

According to the preferred embodiment of the present invention, the rigid monomer in step (2) is 3-methylstyrene, acetylcyclohexene or 4-ethylcyclohexene; the mass of the rigid monomer and carboxymethyl starch The ratio is 1~3:8.

According to the preferred embodiment of the present invention, the concentration of the amide monomer in the graft monomer solution in step (2) is 0.1 to 0.5 g/mL.

According to the preferred embodiment of the present invention, in step (2), a NaOH aqueous solution with a mass fraction of 10% is used to adjust the pH value of the system to 6.5-7.5.

According to the preferred embodiment of the present invention, the initiator in step (2) is ammonium persulfate, potassium persulfate, or a combination of one of ammonium persulfate, potassium persulfate and sodium bisulfite; the quality of the initiator It is 3~7.5% of the mass of carboxymethyl starch.

According to the preferred embodiment of the present invention, the reaction temperature in step (2) is 60-75°C, and the reaction time is 4-6 hours.

According to the preferred embodiment of the present invention, the precipitant in step (2) is an ethanol aqueous solution with a volume fraction of 95%; the ratio of the added volume of the precipitant to the volume of the starch paste is 0.3 to 0.8:1.

According to the preferred embodiment of the present invention, the washing in step (2) is using absolute ethanol; the drying is drying to constant weight at 50-60°C.

The invention also provides an environmentally friendly strong plugging and high-temperature resistant plugging agent for water-based drilling fluids, which is prepared by the above preparation method.

According to the present invention, the above-mentioned environmentally friendly strong sealing and high-temperature resistant sealing agent for water-based drilling fluid is used in water-based drilling fluid.

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

1. The present invention uses a specific process to modify corn starch. Compared with original corn starch, the modified carboxymethyl starch has better solubility and stability, and then grafts specific types and proportions of amide monomers, The rigid monomer not only enhances the solubility of starch in aqueous solution through the amide group, but also enhances its temperature resistance through the rigid ring branched structure. The plugging agent of the present invention can withstand high temperatures of 180°C, has molecular invariance under high temperature conditions, has good plugging performance, and can effectively plug formation pores and cracks. The present invention adopts a specific rigid monomer, which, compared with other commonly used rigid monomers, improves its temperature resistance and blocking performance while having excellent environmental performance; and the addition ratio of the rigid monomer and the amide monomer is controlled within the range of the present invention. Only within the range can the excellent effects of the present invention be achieved.

2. The raw material composition of the present invention as a whole, combined with the specific preparation method, can achieve the excellent effects of the present invention by working together. The plugging agent molecule of the present invention has low biological toxicity, is an environmentally friendly plugging agent, and can be used in high temperature and other complex formations; the present invention has a wide application range, a high applicable temperature, low biological toxicity, and can meet the requirements of high temperature The demand for environmentally friendly materials for strong stratigraphic sealing.

Detailed ways

The present invention will be further described below through specific examples, but it is not limited thereto.

The raw materials used in the examples are all conventional raw materials and are commercially available; the methods described are prior art unless otherwise specified.

Example 1

A method for preparing an environmentally friendly strong plugging and high-temperature resistant plugging agent for water-based drilling fluids, which includes the following steps:

(1) Add 200 mL of aqueous ethanol solution with a volume fraction of 80% in the flask, add 70g of corn starch under stirring, stir for 5 minutes, add 10g of sodium hydroxide, and alkalize at 40°C for 4 hours; then add 100g of monochloroacetic acid, Carry out etherification reaction at 40°C for 9 hours; then use glacial acetic acid to adjust the pH of the reaction solution to 7.0, filter, and wash the solid obtained 3 times with a mixture of ethanol and water (the volume ratio of ethanol and water is 3:1). The solid obtained is dried in a 45°C oven for 8 hours, and then carboxymethyl starch is obtained after crushing;

(2) Add 100mL deionized water and 8g carboxymethyl starch to the flask, pre-gelatinize the starch at 50°C for 30 minutes to form a starch paste; add 10g amide monomer, 2g rigid monomer to 50mL deionized water in sequence body, stir evenly to obtain a graft monomer solution; add the graft monomer solution to the starch paste and continue stirring, use a 10% mass fraction of NaOH aqueous solution to adjust the pH value of the system to 7.0, and add it to the starch paste under a nitrogen environment. Add 0.4g of initiator to the starch paste, heat the flask to 60°C, and react at 60°C for 4 hours. The stirring speed during the reaction is 300r/min; after the reaction is completed, add 50mL of 95% volume fraction to the system. The ethanol aqueous solution is precipitated for 5 minutes, filtered, and the resulting solid is washed three times with anhydrous ethanol. The resulting solid is dried at 55°C to a constant weight to obtain an environmentally friendly strong sealing and high-temperature resistant sealing agent for water-based drilling fluids.

The above-mentioned amide monomer is acrylamide, the rigid monomer is 3-methylstyrene, and the initiator is ammonium persulfate.

Example 2

A method for preparing an environmentally friendly strong plugging and high-temperature resistant plugging agent for water-based drilling fluids, which includes the following steps:

(1) Add 200 mL of aqueous ethanol solution with a volume fraction of 80% in the flask, add 70g of corn starch under stirring, stir for 5 minutes, add 10g of sodium hydroxide, and alkalize at 40°C for 6 hours; then add 100g of monochloroacetic acid, Carry out etherification reaction at 40°C for 10 hours; then use glacial acetic acid to adjust the pH of the reaction solution to 7.0, filter, and wash the obtained solid three times with a mixture of ethanol and water (the volume ratio of ethanol and water is 2:1). The solid is dried in a 45°C oven for 8 hours, and then carboxymethyl starch can be obtained after crushing;

(2) Add 100mL deionized water and 8g carboxymethyl starch to the flask, pre-gelatinize the starch at 50°C for 30 minutes to form a starch paste; add 10g amide monomer, 1g rigid monomer to 50mL deionized water in sequence body, stir evenly to obtain a graft monomer solution; add the graft monomer solution to the starch paste and continue stirring, use a 10% mass fraction of NaOH aqueous solution to adjust the pH value of the system to 7.0, and add it to the starch paste under a nitrogen environment. Add 0.4g of initiator to the starch paste, heat the flask to 75°C, and react at 75°C for 4 hours. The stirring speed during the reaction is 300r/min; after the reaction is completed, add 40mL of 95% volume fraction to the system. The ethanol aqueous solution is precipitated for 5 minutes, filtered, and the resulting solid is washed three times with anhydrous ethanol. The resulting solid is dried at 55°C to a constant weight to obtain an environmentally friendly strong sealing and high-temperature resistant sealing agent for water-based drilling fluids.

The above-mentioned amide monomer is methacrylamide, the rigid monomer is acetylcyclohexene, and the initiator is ammonium persulfate.

Example 3

A method for preparing an environmentally friendly strong plugging and high-temperature resistant plugging agent for water-based drilling fluids, which includes the following steps:

(1) Add 200 mL of ethanol aqueous solution with a volume fraction of 80% in the flask, add 80g corn starch under stirring, stir for 5 minutes, add 10g sodium hydroxide, and alkalize at 40°C for 6 hours; then add 100g monochloroacetic acid, Carry out etherification reaction at 40°C for 10 hours; then use glacial acetic acid to adjust the pH of the reaction solution to 7.0, filter, and wash the obtained solid three times with a mixture of ethanol and water (the volume ratio of ethanol and water is 3:1). The solid is dried in a 45°C oven for 8 hours, and then carboxymethyl starch can be obtained after crushing;

(2) Add 100mL deionized water and 8g carboxymethyl starch to the flask, pre-gelatinize the starch at 55°C for 30 minutes to form a starch paste; add 10g amide monomer, 2g rigid monomer to 50mL deionized water in sequence body, stir evenly to obtain a graft monomer solution; add the graft monomer solution to the starch paste and continue stirring, use a 10% mass fraction of NaOH aqueous solution to adjust the pH value of the system to 7.0, and add it to the starch paste under a nitrogen environment. Add 0.6g of initiator to the starch paste, heat the flask to 75°C, and react at 75°C for 4 hours. The stirring speed during the reaction is 300r/min; after the reaction is completed, add 40mL of 95% initiator to the system. The ethanol aqueous solution is precipitated for 5 minutes, filtered, and the resulting solid is washed three times with anhydrous ethanol. The resulting solid is dried at 55°C to a constant weight to obtain an environmentally friendly strong sealing and high-temperature resistant sealing agent for water-based drilling fluids.

The above amide monomers are acrylamide and N,N dimethylacrylamide, with a mass ratio of 1:1, the rigid monomers are 4-ethylcyclohexene, and the initiators are ammonium persulfate and ammonium persulfate, with a mass ratio of 1:1. Sodium bisulfite.

Example 4

A method for preparing an environmentally friendly strong plugging and high-temperature resistant plugging agent for water-based drilling fluids, which includes the following steps:

(1) Add 200 mL of aqueous ethanol solution with a volume fraction of 80% in the flask, add 90g of corn starch under stirring, stir for 5 minutes, add 10g of sodium hydroxide, and alkalize at 40°C for 4 hours; then add 100g of monochloroacetic acid, Carry out etherification reaction at 40°C for 9 hours; then use glacial acetic acid to adjust the pH of the reaction solution to 7.0, filter, and wash the solid obtained 3 times with a mixture of ethanol and water (the volume ratio of ethanol and water is 3:1). The solid obtained is dried in a 45°C oven for 8 hours, and then carboxymethyl starch is obtained after crushing;

(2) Add 100mL deionized water and 8g carboxymethyl starch to the flask, pre-gelatinize the starch at 50°C for 30 minutes to form a starch paste; add 15g amide monomer, 1g rigid monomer to 50mL deionized water in sequence body, stir evenly to obtain a graft monomer solution; add the graft monomer solution to the starch paste and continue stirring, use a 10% mass fraction of NaOH aqueous solution to adjust the pH value of the system to 7.0, and add it to the starch paste under a nitrogen environment. Add 0.4g of initiator to the starch paste, heat the flask to 60°C, and react at 60°C for 4 hours. The stirring speed during the reaction is 300r/min; after the reaction is completed, add 40mL of 95% initiator to the system. The ethanol aqueous solution is precipitated, filtered, and the resulting solid is washed three times with absolute ethanol. The resulting solid is dried at 55°C to a constant weight to obtain an environmentally friendly strong sealing and high-temperature resistant sealing agent for water-based drilling fluids.

The above amide monomers are methacrylamide and N,N dimethylacrylamide. The mass ratio of methacrylamide and N,N dimethylacrylamide is 1:4. The rigid monomer is acetylcyclohexene. , choose ammonium persulfate as initiator.

Comparative example 1

The preparation method of an environmentally friendly strong plugging and high-temperature resistant plugging agent for water-based drilling fluids is as described in Example 1. The difference is that only carboxymethyl starch is used, and the grafting process of step (2) is not performed. .

Comparative example 2

The preparation method of an environmentally friendly strong plugging and high-temperature resistant plugging agent for water-based drilling fluids is as described in Example 1, except that no amide monomer is added in step (2).

Comparative example 3

The preparation method of an environmentally friendly strong plugging and high-temperature resistant plugging agent for water-based drilling fluid is as described in Example 1, except that no rigid monomer is added in step (2).

Comparative example 4

The preparation method of an environmentally friendly strong plugging and high-temperature resistant plugging agent for water-based drilling fluids is as described in Example 1, except that the mass of the amide monomer in step (2) is 20g.

Comparative example 5

The preparation method of an environmentally friendly strong plugging and high-temperature resistant plugging agent for water-based drilling fluids is as described in Example 1, except that N-vinylpyrrolidone is selected as the rigid monomer.

Test example

Perform the following performance evaluation on the prepared blocking agent:

(1) Environmental protection evaluation

According to the industry standard SY/T 6788-2010, luminescent bacteria were used to test the biological toxicity of the blocking agents prepared in the examples and comparative examples. The classification standards are shown in Table 1. The concentration of the substance to be evaluated when the luminescent ability of the luminescent bacteria is reduced by half is EC ₅₀ . As an evaluation index, the EC ₅₀ value is greater than 25,000, indicating that the tackifier is non-toxic. The blocking agent was prepared into an aqueous solution with a mass fraction of 2% for testing. The experimental results are shown in Table 2.

Table 1 Oilfield chemicals and biological toxicity classification

biological toxicity Luminous bacteria EC ₅₀ /(mg·L ^-1 ) Very poisonous <1 Heavy poison 1～100 Poisoned 101～1000 Slightly toxic 1001～25000 non-toxic ＞25000

Table 2 Biological toxicity test results of each embodiment

sample EC ₅₀ (mg/L) 2% Example 1 3.1×10 ⁴ 2% Example 2 4.4×10 ⁴ 2% Example 3 3.4×10 ⁴ 2% Example 4 3.6×10 ⁴ 2% comparison example 1 7.3×10 ⁵ 2% comparison example 2 6.3×10 ⁴ 2% Comparative Example 3 7.2×10 ⁴ 2% vs. 4 9.4×10 ³ 2% Comparative Example 5 2.6×10 ³

It can be seen from Example 1 and Comparative Example 1 that when only modified starch is used, the blocking agent has lower biological toxicity and is more environmentally friendly. It can be seen from Examples 1-4 that when rigid monomers and amide monomers are grafted into modified starch, molecules with a large degree of unsaturation, high degrees of substitution, or linear hydrocarbons substituted by alkyl/amino groups will reduce blocking. Environmentally friendly agent, the EC ₅₀ is reduced, the biotoxicity of the polymer is increased, the rigid monomer is reduced, and the biotoxicity of the grafted polymer is reduced. Adding amide monomers has less impact on biological toxicity, while adding rigid monomers has a greater impact on reducing environmental protection than amide monomers on the environmental protection of blocking agents. It can be seen from Comparative Example 5 that nitrogen-containing heterocycles increase the biological toxicity of polymer molecules. According to the industry standard SY/T6788-2010, an EC ₅₀ greater than 25,000 mg/L is considered non-toxic. The EC ₅₀ of the blocking agents of the embodiments of the present invention are all greater than 25,000 mg/L, meeting environmental protection requirements.

(2) Rheology and blocking properties of environmentally friendly grafted starch at room temperature and pressure

Preparation of base slurry: slowly add 16g of bentonite to 400 mL of distilled water while stirring, and then age at room temperature for 24 hours to prepare a bentonite base slurry.

Add blocking agent: Take 400mL of base slurry, add 2% (8g) of the example and comparative example products, and stir for 20 minutes at 3000r/min.

Performance test: According to "GB/T 29170-2012, Laboratory Test of Drilling Fluids in the Petroleum and Natural Gas Industry", test the filtration loss at normal temperature and pressure, high temperature and high pressure filtration loss at 180°C and 3.5MPa, and the base slurry after aging at 180°C for 16 hours. Rheological parameters (apparent viscosity, plastic viscosity, dynamic shear force), experimental results are shown in Table 3.

table 3

It can be seen from Comparative Example 1 and the base slurry data that only using modified starch can improve the rheological properties of the base slurry and reduce the fluid loss. However, the modified starch has poor temperature resistance and cannot withstand high temperatures of 180°C and high temperature and high pressure fluid loss. The dosage is reduced and the effect is not good. It can be seen from Example 1 that the temperature resistance of the graft-modified starch has been improved, the ability to adjust the rheology of the base slurry has been enhanced, and the high-temperature and high-pressure filter loss has been reduced to less than 10 mL, meeting the on-site requirements. The graft-modified starch molecular chain introduces a benzene ring or a carbon six-membered ring, which is not easily deformed under high temperature conditions and can improve the temperature and salt resistance of the polymer. It can be seen from Example 1 and Example 2 that increasing the number of rigid monomers in the polymer can improve the temperature resistance of the polymer molecules. However, due to the influence of steric hindrance, the number of rigid rings increases, the synthesis difficulty becomes greater, and the length of the molecular chain becomes longer. Short, manifested as a decrease in base slurry viscosity. From Comparative Example 2, it can be seen that when the amide monomer is removed from the polymer, the hydrophilic properties of the molecules decrease, the force of adsorbing clay particle molecules decreases, and the solubility in the base slurry becomes worse. At the same time, due to the influence of intermolecular steric hindrance , it is difficult for the polymer to form long chains. The performance result is that compared with carboxymethyl starch, the viscosity of the grafted polymer has increased, but compared with the example, the temperature resistance has declined to a certain extent. Under high-temperature dehydration, the polymer molecules The surface of clay particles is dissociated, the negative electricity between clay particles is weakened, and it is easy to agglomerate, and the filtration loss of the base slurry becomes larger. From Comparative Example 3, it can be seen that when the rigid monomer is removed from the polymer, the ability of the molecular chains to resist high-temperature deformation and decomposition is reduced, and the filter loss reduction effect becomes worse under high-temperature conditions. From Comparative Example 4, it can be seen that increasing the number of amide monomers can enhance the adsorption of molecules to the clay of the base slurry. At the same time, the length of the molecular chain increases, the flexibility and ductility of the molecules in the base slurry are enhanced, and the viscosity of the base slurry becomes larger. The normal pressure filtration loss is reduced, but at the same time the temperature resistance effect of the polymer molecules is reduced.

(3) Environmentally friendly grafted starch sand bed blocking experiment

Evenly disperse and compact 300cm ³ of 80-100 mesh quartz sand on the sand bed filter loss meter. Add the base slurry containing 2% (2g in 100mL base slurry) of the blocking agent of the present invention and age it in an oven at 180°C. 16h, add 250mL of aged drilling fluid to the sand bed filter loss meter, and pressurize it to 0.7MPa. Measure the depth of drilling fluid intrusion into the sand bed within 30 minutes at room temperature. The test results are shown in Table 4.

Table 4

It can be seen from the sand bed plugging experiment that the depth of invasion of the sand bed by the plugging agent of the present invention after aging is less than 3 cm. By comparison with the comparative example, it can be seen that the amide monomer and rigid monomer grafted on the modified starch by the polymer of the present invention are The body can synergistically increase the blocking ability.

To sum up, the environmentally friendly strong blocking agent of the present invention grafts flexible molecular chains and rigid monomers on carboxymethyl starch, can be used at high temperatures of 180°C, and can ensure the use of drilling fluids in most areas. Environmental protection requirements for additives.

Claims (10)

1. The preparation method of the environment-friendly strong-plugging high-temperature-resistant plugging agent for the water-based drilling fluid comprises the following steps:

(1) Adding corn starch into ethanol water solution, adding alkali, and performing alkalization treatment; then continuously adding monochloroacetic acid to carry out etherification reaction; after the reaction is finished, regulating the pH value of the obtained reaction solution to 6.5-7.0, and obtaining carboxymethyl starch through filtration, washing and drying;

(2) Adding carboxymethyl starch into water, and pre-gelatinizing to obtain starch paste; adding an amide monomer and a rigid monomer into water to obtain a grafting monomer solution; adding the obtained grafting monomer solution into starch paste, adjusting the pH value of the system to 6.5-7.5, and then adding an initiator under the nitrogen environment for reaction; after the reaction is finished, adding a precipitant into the reaction system for precipitation, and filtering, washing and drying to obtain the environment-friendly high-temperature blocking agent for the water-based drilling fluid.

2. The method for preparing the environment-friendly high-temperature blocking agent for water-based drilling fluid according to claim 1, wherein the volume fraction of ethanol in the ethanol aqueous solution in the step (1) is 80%; the ratio of the volume of the ethanol aqueous solution to the mass of the corn starch is 1mL to 0.1-0.5 g;

the alkali is sodium hydroxide or potassium hydroxide; the mass ratio of the alkali to the corn starch is 0.1-0.25:1;

the temperature of the alkalization treatment is 40-50 ℃, and the time of the alkalization treatment is 4-6 h.

3. The method for preparing the environment-friendly high-temperature blocking agent for water-based drilling fluid, which is characterized in that the mass ratio of monochloroacetic acid to corn starch in the step (1) is 1:0.5-1;

the temperature of the etherification reaction is 40-50 ℃, and the time of the etherification reaction is 8-10 h;

adjusting the pH of the reaction solution by using glacial acetic acid; the washing is carried out by using a mixed solution of ethanol and water, wherein the volume ratio of the ethanol to the water in the mixed solution is 2-4:1; the drying is carried out for 8-10 h at 40-50 ℃.

4. The method for preparing the environment-friendly strong plugging high temperature resistant plugging agent for water-based drilling fluid according to claim 1, wherein the concentration of carboxymethyl starch in the starch paste in the step (2) is 0.05-0.1 g/mL;

the temperature of the pregelatinization is 50-55 ℃, and the pregelatinization time is 20-40 min.

5. The method for preparing the environment-friendly strong plugging high temperature resistant plugging agent for the water-based drilling fluid, which is characterized in that the amide monomer in the step (2) is one or more than two of acrylamide, methacrylamide and N, N-dimethylacrylamide; the mass ratio of the amide monomer to the carboxymethyl starch is 1-2:1.

6. The method for preparing the environment-friendly high-temperature blocking agent for water-based drilling fluid, according to claim 1, wherein the rigid monomer in the step (2) is 3-methyl styrene, acetyl cyclohexene or 4-ethyl cyclohexene; the mass ratio of the rigid monomer to the carboxymethyl starch is 1-3:8; the concentration of the amide monomer in the grafting monomer solution is 0.1-0.5 g/mL.

7. The method for preparing the environment-friendly high-temperature blocking agent for water-based drilling fluid, which is characterized in that in the step (2), 10 mass percent NaOH aqueous solution is used for adjusting the pH value of a system to be 6.5-7.5;

the initiator is ammonium persulfate, potassium persulfate or the combination of one of ammonium persulfate and potassium persulfate and sodium bisulphite; the mass of the initiator is 3-7.5% of the mass of carboxymethyl starch.

8. The method for preparing the environment-friendly high-temperature blocking agent for water-based drilling fluid, which is characterized in that the temperature of the reaction in the step (2) is 60-75 ℃, and the reaction time is 4-6 hours;

the precipitant is an ethanol water solution with the volume fraction of 95%; the ratio of the added volume of the precipitant to the volume of the starch paste is 0.3-0.8:1; the washing is carried out by using absolute ethyl alcohol; the drying is to dry to constant weight at 50-60 ℃.

9. An environment-friendly strong-plugging high-temperature-resistant plugging agent for water-based drilling fluid, which is characterized by being prepared by the preparation method of claim 1.

10. The use of the environment-friendly strong plugging high temperature resistant plugging agent for water-based drilling fluid as claimed in claim 9 in water-based drilling fluid.