Acid-soluble water-swelling gel plugging agent as well as preparation method and application thereof

Abstract

The invention relates to an acid-soluble water-swelling gel plugging agent as well as a preparation method and application thereof. The acid-soluble and water-swelling gel plugging agent disclosed by the invention is prepared by polymerizing the following raw materials in parts by weight: 15 to 25 parts of carboxymethyl cellulose, 20 to 40 parts of N, N-dimethylacrylamide, 15 to 30 parts of dimethyl diallyl ammonium chloride and 10 to 35 parts of sodium p-styrenesulfonate. The plugging agent disclosed by the invention can resist high temperature and high pressure, also has high water absorption and salt resistance, is high in acid solubility, fully ensures smooth proceeding of plugging work, avoids damage to a stratum, and is beneficial to proceeding of plugging removal work in the later period. The invention further provides a preparation method and application of the acid-soluble water-absorbing expansible gel plugging agent, the preparation process is simple, the requirement for professional knowledge of operators is low, no special requirement for use equipment exists, the production stability is good, all the raw materials are commercially available, the source is wide, the price is low, and large-scale industrial production is easy to achieve.

Description

Technical Field

[0001] The present invention relates to an acid-soluble water-swellable gel plugging agent, a preparation method thereof and an application thereof, belonging to the technical field of oil well operation plugging. Background Art

[0002] Well leakage is one of the main problems plaguing the development of oil and gas fields. According to statistics, the worldwide well leakage incidence rate is as high as 20% - 25%. The frequent occurrence of well leakage accidents will affect the normal construction of oil and gas development, cause huge economic losses to the drilling project, waste manpower and material resources; it will also lead to a serious drop in downhole pressure and interfere with the stability of the oil well wall. In severe cases, a blowout accident may occur, seriously threatening the safety of drilling operations and the lives of workers. In recent years, with the continuous in-depth exploration and development of oil and gas resources, the problem of well leakage has also attracted the attention of workers.

[0003] In the prior art, although ordinary gel-type particle plugging agents can fit different formation fractures for plugging, the gel plugging agents have low strength, weak pressure-bearing capacity and poor temperature resistance, and cannot meet the plugging operations of ultra-low pressure formations; while the bridging particle plugging agents have strong temperature and pressure resistance but there is a problem that the particle size is not easy to match the fracture width. Therefore, it is urgent to invent a plugging agent with good high temperature resistance, high pressure resistance, good salt resistance, good water absorption and swelling effect, and little environmental impact. Summary of the Invention

[0004] The first object of the present invention is to provide an acid-soluble water-swellable gel plugging agent to solve the problems of poor temperature resistance, weak pressure-bearing capacity, general water absorption and swelling effect, and low acid dissolution rate of the plugging agent in the prior art.

[0005] The second object of the present invention is to provide a preparation method of an acid-soluble water-swellable gel plugging agent to solve the above problems.

[0006] The third object of the present invention is to provide the application of the acid-soluble water-swellable gel plugging agent in drilling fluid to solve the above problems.

[0007] In order to achieve the above objects, the technical solution of the acid-soluble water-swellable gel plugging agent in the present invention is as follows:

[0008] An acid-soluble water-swellable gel plugging agent is polymerized from the following raw materials in parts by weight: 15 - 25 parts of carboxymethyl cellulose, 20 - 40 parts of N,N-dimethylacrylamide, 15 - 30 parts of dimethyldiallylammonium chloride, and 10 - 35 parts of sodium p-styrenesulfonate.

[0009] The beneficial effects of the above technical solution are as follows: In the present invention, carboxymethyl cellulose, N,N-dimethylacrylamide, dimethyldiallylammonium chloride, and sodium p-styrenesulfonate are selected as raw materials and polymerized in water to form an acid-soluble water-swellable gel plugging agent. The component materials of the acid-soluble water-swellable gel plugging agent have good performance and low price. By adjusting the proportions of the components, while improving the swelling performance of the plugging agent, it can also enable the plugging agent to have good pressure-bearing effect, avoiding the "top-heavy and bottom-light" performance of the plugging agent. The polymerized acid-soluble water-swellable gel plugging agent has good water absorption and swelling properties, salt resistance, temperature resistance, and pressure-bearing properties, forms a gel with a high strength grade, and has good acid-soluble effect, meeting the requirements of oil well plugging work and subsequent unplugging work.

[0010] To further improve the temperature resistance, salt resistance, pressure-bearing performance, and water absorption and swelling effect of the gel plugging agent and ensure the utilization rate of raw materials, preferably, the acid-soluble water-swellable gel plugging agent is polymerized from the following raw materials in parts by weight: 20-25 parts of carboxymethyl cellulose, 30-40 parts of N,N-dimethylacrylamide, 20-30 parts of dimethyldiallylammonium chloride, and 15-20 parts of sodium p-styrenesulfonate.

[0011] Specifically, for each raw material of the acid-soluble water-swellable gel plugging agent in the present invention:

[0012] Carboxymethyl cellulose (CMC) is a carboxymethylated derivative of cellulose. CMC has special properties such as thickening and water retention, increasing the water absorption and water retention capacity of the plugging agent and maintaining a good gel state; due to its high temperature resistance and salt pollution resistance, and being non-toxic, odorless, and not easily fermented, it can ensure the stability of the synthesized plugging agent and enhance the high temperature resistance and salt pollution resistance of the plugging agent.

[0013] In N,N-dimethylacrylamide (DAMA), the two active hydrogen atoms of the amide group are replaced by methyl groups, preventing the hydrolysis of the amide group under high temperature and high salt conditions, and ensuring the stability of the structure and performance of the synthesized plugging agent. Moreover, under the experimental conditions of the present invention, DMAM cannot self-polymerize, which is beneficial to the synthesis and structure control of the copolymer.

[0014] Dimethyldiallylammonium chloride (DMDAAC) contains double bonds and cationic quaternary ammonium groups in its molecule and can polymerize with many unsaturated monomers. Due to the presence of cationic quaternary ammonium groups in DMDAAC, it is ionized with a positive charge in water, which can effectively improve the salt resistance and alkali pollution resistance of the plugging agent.

[0015] Sodium p-styrenesulfonate (SSS) has strong stability, polymerization resistance, and consolidation resistance, good heat resistance, and will not decompose below 300°C, enhancing the temperature resistance of the plugging agent. At the same time, due to the inducing effect of the sulfonic acid group bound to the para position, it has high polymerizability and can achieve free radical polymerization using general initiators, effectively simplifying the preparation process of the plugging agent and reducing production costs.

[0016] The acid-soluble water-swellable gel plugging agent of the present invention uses a macromolecular cross-linking agent to introduce temperature-resistant groups and water-absorbing groups, improving the temperature resistance of the water-absorbing groups and avoiding the variation of functional groups. At the same time, it improves the water-absorbing performance of the temperature-resistant groups, and can maintain good water-absorbing performance under high-temperature conditions. By introducing rigid ring structures such as benzene rings, heterocycles, or large side groups, the rigidity of the polymer molecular chain is enhanced, further improving the toughness of the gel and its own pressure-bearing capacity.

[0017] By introducing rigid ring structures such as benzene rings, heterocycles, or large side groups, the rigidity of the polymer molecular chain is enhanced, further improving the toughness of the gel and its own pressure-bearing capacity.

[0018] To achieve the above object, the technical solution of the preparation method of the acid-soluble water-swellable gel plugging agent in the present invention is as follows:

[0019] A preparation method of an acid-soluble water-swellable gel plugging agent, which dissolves carboxymethyl cellulose, N,N-dimethylacrylamide, dimethyldiallylammonium chloride, and sodium p-styrenesulfonate in water, and adds an initiator and a cross-linking agent for polymerization reaction.

[0020] The beneficial effects of the above technical solution are as follows: The preparation method of the acid-soluble water-swellable gel plugging agent of the present invention has a simple preparation process, low requirements for the professional knowledge of operators, no special requirements for the equipment used, good production stability, and all monomers are commercially available, with wide sources and low prices, and it is easy to achieve large-scale industrial production.

[0021] As a further improvement, the initiator is a soluble persulfate initiator. Preferably, the initiator is ammonium persulfate.

[0022] The beneficial effects of the above technical solution are as follows: Soluble persulfate initiators are common inorganic initiators, which have high compatibility with the reaction system, can initiate reactions rapidly, are easy to obtain, and are inexpensive, effectively reducing production costs.

[0023] As a further improvement, the mass concentration of the initiator is 0.2%-1%. Preferably, the mass concentration of the initiator is 0.2%.

[0024] The beneficial effects of the above technical solution are as follows: Adding the initiator at the above concentration can efficiently initiate the polymerization reaction and is easy to control the reaction process.

[0025] As a further improvement, the crosslinking agent is N-N'-methylenebisacrylamide.

[0026] As a further improvement, the mass concentration of the crosslinking agent is 0.3%-0.5%. Preferably, the mass concentration of the crosslinking agent is 0.3%.

[0027] As a further improvement, the polymerization reaction is carried out at a temperature of 50-60°C for 2-2.5 h.

[0028] The beneficial effect of the above technical solution is that by controlling the temperature and reaction time of the polymerization reaction, the molecular weight of the copolymer formed by the polymerization reaction can be effectively controlled.

[0029] In order to achieve the above object, the technical solution of the application of the acid-soluble water-swellable gel plugging agent in the drilling fluid in the present invention is as follows:

[0030] An application of an acid-soluble water-swellable gel plugging agent in a drilling fluid.

[0031] The beneficial effect of the above technical solution is that the acid-soluble water-swellable gel plugging agent of the present invention adopts free radical aqueous solution polymerization. By utilizing the macromolecular structure of the crosslinking agent and the toughening effect of carboxymethyl cellulose, several monomers are synthesized into an acid-soluble water-swellable gel plugging agent through a redox system. The formed microstructure can effectively absorb and retain water, and has strong stability. Thus, the plugging agent swells by absorbing water in the lost fracture, fully plugs the hole, and achieves a good plugging effect. Specific embodiments

[0032] The following combines specific embodiments to further describe the present invention. It should be noted that on the premise of no conflict, the following described embodiments or technical features can be arbitrarily combined to form new embodiments. The equipment and raw materials used can be purchased from the market or are commonly used in the art. The methods in the following embodiments are conventional methods in the art unless otherwise specified.

[0033] I. Embodiments of an acid-soluble water-swellable gel plugging agent and its preparation method

[0034] Embodiment 1

[0035] The acid-soluble water-swellable gel plugging agent of this embodiment is polymerized from the following raw materials in parts by weight: 20 parts of carboxymethyl cellulose, 30 parts of N,N-dimethylacrylamide, 30 parts of dimethyldiallylammonium chloride, and 20 parts of sodium p-styrenesulfonate.

[0036] The specific preparation process is as follows:

[0037] (1) Take 20 parts of carboxymethyl cellulose and place it in a reactor containing 350 parts of water. Place the reactor on a magnetic stirrer, heat and stir to fully blend the carboxymethyl cellulose with water to obtain a slightly viscous aqueous carboxymethyl cellulose solution; then add 30 parts of N,N-dimethylacrylamide, 30 parts of dimethyldiallylammonium chloride, and 20 parts of sodium styrenesulfonate, and stir evenly to obtain a homogeneous and stable monomer solution;

[0038] (2) Add ammonium persulfate as an initiator with a mass concentration of 0.2% and N,N'-methylenebisacrylamide as a crosslinking agent with a mass concentration of 0.3% to the monomer solution obtained in step (1), and carry out a polymerization reaction at 60 °C for 2 h (the reaction process needs to be kept airtight) to obtain a gel product;

[0039] (3) After the gel product cools, place it in an oven to dry, and use a multi-functional pulverizer to pulverize it to obtain plugging agent particles (particle size 0.1 - 2 mm).

[0040] Example 2

[0041] The acid-soluble water-swellable gel plugging agent of this example is polymerized from the following raw materials in parts by weight: 25 parts of carboxymethyl cellulose, 35 parts of N,N-dimethylacrylamide, 20 parts of dimethyldiallylammonium chloride, and 20 parts of sodium styrenesulfonate.

[0042] The specific preparation process is as follows:

[0043] (1) Take 25 parts of carboxymethyl cellulose and place it in a reactor containing 400 parts of water. Place the reactor on a magnetic stirrer, heat and stir to fully blend the carboxymethyl cellulose with water to obtain a slightly viscous aqueous carboxymethyl cellulose solution; then add 35 parts of N,N-dimethylacrylamide, 20 parts of dimethyldiallylammonium chloride, and 20 parts of sodium styrenesulfonate, and stir evenly to obtain a homogeneous and stable monomer solution;

[0044] (2) Add ammonium persulfate as an initiator with a mass concentration of 0.2% and N,N'-methylenebisacrylamide as a crosslinking agent with a mass concentration of 0.3% to the monomer solution obtained in step (1), and carry out a polymerization reaction at 60 °C for 2 h (the reaction process needs to be kept airtight) to obtain a gel product;

[0045] (3) After the gel product cools, place it in an oven to dry, and use a multi-functional pulverizer to pulverize it to obtain plugging agent particles (particle size 0.1 - 2 mm).

[0046] Example 3

[0047] The acid-soluble water-swellable gel plugging agent of this example is polymerized from the following raw materials in parts by weight: 20 parts of carboxymethyl cellulose, 40 parts of N,N-dimethylacrylamide, 25 parts of dimethyldiallylammonium chloride, and 15 parts of sodium p-styrenesulfonate.

[0048] The specific preparation process is as follows:

[0049] (1) Take 20 parts of carboxymethyl cellulose and place it in a reactor containing 450 parts of water. Place the reactor on a magnetic stirrer, heat and stir to fully blend the carboxymethyl cellulose with water to obtain a slightly viscous carboxymethyl cellulose aqueous solution; then add 40 parts of N,N-dimethylacrylamide, 25 parts of dimethyldiallylammonium chloride, and 15 parts of sodium p-styrenesulfonate, and stir evenly to obtain a homogeneous and stable monomer solution;

[0050] (2) Add ammonium persulfate as an initiator with a mass concentration of 0.2% and N,N'-methylenebisacrylamide as a crosslinking agent with a mass concentration of 0.3% to the monomer solution obtained in step (1), and carry out a polymerization reaction at 60°C for 2 h (the reaction process needs to be kept airtight) to obtain a gel product;

[0051] (3) After the gel product cools, place it in an oven to dry, and use a multi-functional pulverizer to pulverize it to obtain plugging agent particles (particle size 0.1 - 2 mm).

[0052] Example 4

[0053] The acid-soluble water-swellable gel plugging agent of this example is polymerized from the following raw materials in parts by weight: 25 parts of carboxymethyl cellulose, 35 parts of N,N-dimethylacrylamide, 25 parts of dimethyldiallylammonium chloride, and 15 parts of sodium p-styrenesulfonate.

[0054] The specific preparation process is as follows:

[0055] (1) Take 25 parts of carboxymethyl cellulose and place it in a reactor containing 500 parts of water. Place the reactor on a magnetic stirrer, heat and stir to fully blend the carboxymethyl cellulose with water to obtain a slightly viscous carboxymethyl cellulose aqueous solution; then add 35 parts of N,N-dimethylacrylamide, 25 parts of dimethyldiallylammonium chloride, and 15 parts of sodium p-styrenesulfonate, and stir evenly to obtain a homogeneous and stable monomer solution;

[0056] (2) Add ammonium persulfate as an initiator with a mass concentration of 0.2% and N,N'-methylenebisacrylamide as a crosslinking agent with a mass concentration of 0.3% to the monomer solution obtained in step (1), and carry out a polymerization reaction at 60°C for 2 h (the reaction process needs to be kept airtight) to obtain a gel product;

[0057] (3) After the gel product has cooled, place it in an oven to dry, and then use a multi-functional grinder to crush it to obtain the plugging agent particles (particle size 0.1 - 2 mm).

[0058] In other embodiments, after adding ammonium persulfate as the initiator and N,N'-methylenebisacrylamide as the crosslinking agent to the monomer solution, a polymerization reaction can be carried out at 50 °C for 2.5 h (the reaction process needs to be kept airtight) to obtain the gel product.

[0059] II. Comparative Examples

[0060] Comparative Example 1

[0061] The acid-soluble water-swellable gel plugging agent of this comparative example is polymerized from the following raw materials in parts by weight: 25 parts of acrylamide and 30 parts of 2-acrylamido-2-methylpropanesulfonic acid.

[0062] The specific preparation process is as follows:

[0063] (1) Take 25 parts of acrylamide and 30 parts of 2-acrylamido-2-methylpropanesulfonic acid and place them in a reactor containing 400 parts of water, stir evenly to obtain a homogeneous and stable monomer solution;

[0064] (2) Add ammonium persulfate as the initiator with a mass concentration of 0.2% and N,N'-methylenebisacrylamide as the crosslinking agent with a mass concentration of 0.3% to the monomer solution obtained in step (1), and carry out a polymerization reaction at 60 °C for 2 h (the reaction process needs to be kept airtight) to obtain the gel product;

[0065] (3) After the gel product has cooled, place it in an oven to dry, and then use a multi-functional grinder to crush it to obtain the plugging agent particles (particle size 0.1 - 2 mm).

[0066] Comparative Example 2

[0067] The acid-soluble water-swellable gel plugging agent of this comparative example is polymerized from the following raw materials in parts by weight: 30 parts of acrylamide and 35 parts of 2-acrylamido-2-methylpropanesulfonic acid.

[0068] The specific preparation process is as follows:

[0069] (1) Take 30 parts of acrylamide and 35 parts of 2-acrylamido-2-methylpropanesulfonic acid and place them in a reactor containing 450 parts of water, stir evenly to obtain a homogeneous and stable monomer solution;

[0070] (2) Add ammonium persulfate as the initiator with a mass concentration of 0.2% and N,N'-methylenebisacrylamide as the crosslinking agent with a mass concentration of 0.3% to the monomer solution obtained in step (1), and carry out a polymerization reaction at 60 °C for 2 h (the reaction process needs to be kept airtight) to obtain the gel product;

[0071] (3) After the gel product has cooled, it is placed in an oven to dry, and then crushed using a multi-functional crusher to obtain the plugging agent particles (particle size 0.1 - 2 mm).

[0072] Comparative Example 3

[0073] The acid-soluble water-swellable gel plugging agent of this comparative example is polymerized from the following raw materials in parts by weight: 35 parts of acrylamide, 40 parts of 2-acrylamido-2-methylpropanesulfonic acid.

[0074] The specific preparation process is as follows:

[0075] (1) Take 35 parts of acrylamide and 40 parts of 2-acrylamido-2-methylpropanesulfonic acid and place them in a reactor containing 500 parts of water, stir evenly to obtain a homogeneous and stable monomer solution;

[0076] (2) Add ammonium persulfate as an initiator with a mass concentration of 0.2% and N,N'-methylenebisacrylamide as a crosslinking agent with a mass concentration of 0.3% to the monomer solution obtained in step (1), and carry out a polymerization reaction at 60°C for 2 h (the reaction process needs to be kept airtight) to obtain a gel product;

[0077] (3) After the gel product has cooled, it is placed in an oven to dry, and then crushed using a multi-functional crusher to obtain the plugging agent particles (particle size 0.1 - 2 mm).

[0078] Comparative Example 4

[0079] The acid-soluble water-swellable gel plugging agent of this comparative example is polymerized from the following raw materials in parts by weight: 30 parts of N,N-dimethylacrylamide, 30 parts of dimethyldiallylammonium chloride.

[0080] The specific preparation process is as follows:

[0081] (1) Take 30 parts of N,N-dimethylacrylamide and 30 parts of dimethyldiallylammonium chloride and place them in a reactor containing 350 parts of water, stir evenly to obtain a homogeneous and stable monomer solution;

[0082] (2) Add ammonium persulfate as an initiator with a mass concentration of 0.2% and N,N'-methylenebisacrylamide as a crosslinking agent with a mass concentration of 0.3% to the monomer solution obtained in step (1), and carry out a polymerization reaction at 60°C for 2 h (the reaction process needs to be kept airtight) to obtain a gel product;

[0083] (3) After the gel product has cooled, it is placed in an oven to dry, and then crushed using a multi-functional crusher to obtain the plugging agent particles (particle size 0.1 - 2 mm).

[0084] Comparative Example 5

[0085] The acid-soluble water-swellable gel plugging agent of this comparative example is polymerized from the following raw materials in parts by weight: 30 parts of N,N-dimethylacrylamide and 20 parts of sodium p-styrenesulfonate.

[0086] The specific preparation process is as follows:

[0087] (1) Take 30 parts of N,N-dimethylacrylamide and 20 parts of sodium p-styrenesulfonate and place them in a reactor containing 350 parts of water, stir evenly to obtain a homogeneous and stable monomer solution;

[0088] (2) Add ammonium persulfate as an initiator with a mass concentration of 0.2% and N,N'-methylenebisacrylamide as a crosslinking agent with a mass concentration of 0.3% to the monomer solution obtained in step (1), and carry out a polymerization reaction at 60 °C for 2 h (the reaction process needs to be kept airtight) to obtain a gel product;

[0089] (3) After the gel product is cooled, place it in an oven to dry, and use a multi-functional pulverizer to pulverize it to obtain plugging agent particles (particle size 0.1 - 2 mm).

[0090] Comparative Example 6

[0091] The acid-soluble water-swellable gel plugging agent of this comparative example is polymerized from the following raw materials in parts by weight: 30 parts of N,N-dimethylacrylamide, 30 parts of dimethyldiallylammonium chloride, and 20 parts of sodium p-styrenesulfonate.

[0092] The specific preparation process is as follows:

[0093] (1) Take 30 parts of N,N-dimethylacrylamide, 20 parts of dimethyldiallylammonium chloride, and 20 parts of sodium p-styrenesulfonate and place them in a reactor containing 350 parts of water, stir evenly to obtain a homogeneous and stable monomer solution;

[0094] (2) Add ammonium persulfate as an initiator with a mass concentration of 0.2% and N,N'-methylenebisacrylamide as a crosslinking agent with a mass concentration of 0.3% to the monomer solution obtained in step (1), and carry out a polymerization reaction at 60 °C for 2 h (the reaction process needs to be kept airtight) to obtain a gel product;

[0095] (3) After the gel product is cooled, place it in an oven to dry, and use a multi-functional pulverizer to pulverize it to obtain plugging agent particles (particle size 0.1 - 2 mm).

[0096] III. Experimental Examples

[0097] Performance Detection and Comparison of Experimental Example 1

[0098] In this experimental example, the performances of Examples 1 - 4, Comparative Examples 1 - 6, and the commercially available water-swellable plugging agent HJK-5 (II) are detected. The specific experimental process is as follows:

[0099] 1. Swelling rate detection

[0100] Water absorption performance test method: Weigh several grams of the synthesized and dried product using an electronic balance, and record the mass as M 1 , then place it in a beaker filled with sufficient water. After the water-swellable particles have fully absorbed water, use a sieve to filter out the particles in the beaker after water absorption, and weigh the mass after water absorption and record it as M 2 .

[0101] Water absorption multiple formula: K = (M 2 - M 1 ) / M 1

[0102] where K is the water absorption multiple (g / g), that is, the swelling rate;

[0103] M 1 is the mass of the water-swellable particles before water absorption (g);

[0104] M 2 is the mass of the water-swellable particles after water absorption (g).

[0105] The test results are shown in Table 1.

[0106] 2. Temperature resistance detection

[0107] Using a high-temperature rolling oven, add the test fluid (water + 3% water-swellable particle material (swollen state)) to the aging kettle, seal it and place it in a constant-temperature oven, and heat-roll it at a certain temperature for 16 hours. When the test is over and the temperature in the kettle automatically drops to room temperature, open the aging kettle, separate the plugging material, rinse it clean, and then observe the change of the water-swellable particle material with temperature.

[0108] The test results are shown in Table 1.

[0109] 3. Salt resistance detection

[0110] The salt resistance of water-swellable particles affects whether their performance can be exerted after entering the formation. It is measured by the swelling rate of water-swellable particles after fully absorbing liquid in solutions with different salt concentrations. Considering that the content of sodium salts in the formation is higher than that of calcium salts, in order to fully simulate the salt erosion effect that the plugging agent may be subjected to when entering the application formation. Prepare a composite salt solution of 3% NaCl + 0.6% CaCl 2 + 1% MgCl 2 , and accurately weigh 30 g of the plugging agent sample using an electronic balance and place it in 300 mL of the prepared salt solution for salt resistance performance testing.

[0111] The test results are shown in Table 1.

[0112] 4. Pressure bearing capacity detection

[0113] Conduct pressure-bearing performance testing using a high-temperature and high-pressure dynamic plugging instrument:

[0114] (1) Add the required plugging agent to be tested at a dosage of 10% to 500 mL of drilling fluid base slurry (the base slurry formula by mass percentage: 10% NV-1 (bentonite) + 0.5% PAM (hydrolyzed polyacrylamide) + 3% ordinary lignite + 2 - 3% asphalt + 3% high-temperature and high-salt loss-control agent + 1 - 2% wellbore stabilizer + 1 - 2% polyaluminum + 3 - 5% QS-1 (ultrafine calcium carbonate) + 3 - 5% lubricant + the balance water). Stir with a blender for 1 h to fully and evenly disperse the self-degradable acidifiable plugging agent in the drilling fluid base slurry. After stirring evenly, pour the test sample into the wellbore;

[0115] (2) Close the air switch on the side of the equipment, and press the power switch buttons for kettle temperature, kettle pressure, back pressure, and rotation speed on the front panel; turn on the computer and enter the corresponding experimental information on the software platform;

[0116] (3) Close all valves, set the slit width through the software and start. After reaching the target slit width, screw the nut of the limit rod at both ends of the gripper to the lowest position and fix it. It can be unscrewed by hand, and do not use a wrench to force it;

[0117] (4) Set the target temperature and stirring speed, and click Start Experiment;

[0118] (5) After the temperature rises to the target temperature, open the gas cylinder to provide about 0.5 MPa of pressure to the air pump;

[0119] (6) Set the experimental displacement pressure and the allowable back-off pressure on the software. The back-off is the range of allowable fluctuations of the target displacement pressure up and down, so as to control the start and stop of the gas-driven liquid pump;

[0120] (7) Select the tracking differential pressure mode in the overburden pressure system on the software, set the differential pressure to 2 - 3 MPa and start. The overburden pressure will automatically track the kettle pressure and always be 2 - 3 MPa higher than the kettle pressure;

[0121] (8) Start the displacement pressure, and the displacement pressure is Pt01 in the following table. Open the high-pressure valve at the outlet end of the gripper. Observe the change of the pressure gauge reading during the test. When the pressure gauge shows a reading, leakage also occurs.

[0122] The test results are shown in Table 1.

[0123] 5. Acid solubility detection

[0124] (1) Weigh 400.0 grams of the sample separately with a balance and place it in 1000 mL of 5% HCl;

[0125] (2) After dissolving at 25°C indoors for 24 hours, filter, wash with filter paper respectively, dry in an oven at a constant temperature of 105 ± 2°C for 12 hours, weigh at room temperature of 25°C, and record the data;

[0126] (3) Calculate the acid dissolution rate of the water-swellable gel plugging agent in 5% HCl.

[0127] Acid dissolution rate formula: S = (W 1 -W 2 ) / W 1

[0128] where S is the acid dissolution rate, %;

[0129] W 1 is the mass before acid dissolution, g;

[0130] W 2 is the mass after acid dissolution, g.

[0131] The test results are shown in Table 1.

[0132] Table 1 Performance test comparison of Examples 1 - 4, Comparative Examples 1 - 6 and commercially available plugging agent HJK - 5 (Ⅱ)

[0133]

[0134] As can be seen from Table 1, the acid-soluble water-swellable gel plugging agent of the present invention has good swelling property, acid solubility, pressure-bearing property and salt resistance, and the high-temperature resistance can reach 150°C.

[0135] Experimental Example 2 Application of acid-soluble water-swellable gel plugging agent in drilling fluid

[0136] Prepare a polysulfonate drilling fluid system indoors. The specific formula of the polysulfonate drilling fluid in terms of mass percentage is: 10% NV - 1 (bentonite) + 0.5% PAM (hydrolyzed polyacrylamide) + 3% ordinary lignite + 2 - 3% asphalt + 3% high-temperature and salt-resistant fluid loss reducer + 1 - 2% wellbore stabilizer + 1 - 2% polyaluminum + 3 - 5% QS - 1 (ultrafine calcium carbonate) + 3 - 5% lubricant + the balance of water; after adding 10% of the acid-soluble water-swellable plugging agent of Example 1 to the above drilling fluid system, conduct plugging agent performance tests and find that: in a high-temperature rolling oven, the aging temperature is 150°C, cure for 16 hours, and test its compressive strength ≥ 15 MPa within 48 hours in a high-temperature and high-pressure dynamic plugging instrument (the crack width is 2 mm); in a constant-temperature water bath at 60°C, evaluate the swelling effect in water to reach 153 g / g; the water-swellable property under the addition of 4% calcium salt solution is 104 g / g, and it has strong high-temperature and salt resistance; the acid-soluble water-swellable plugging agent itself can quickly absorb water and swell within 30 minutes and reach the maximum swelling degree within 4 hours; the acid dissolution rate in 5% dilute hydrochloric acid is as high as over 95%, without affecting the plug removal.

[0137] In summary, the main materials of the acid-soluble water-swellable plugging agent in the present invention are widely sourced and have a low price. The synthesis conditions are simple, and it can achieve good economic benefits while consuming low costs. It can be adapted to the plugging operation during the oil drilling process in medium- to high-temperature complex formations. At the same time, the acid dissolution rate is over 95%, which is convenient for the subsequent plug removal work. Therefore, it has good application prospects.

[0138] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. The patent protection scope of the present invention is subject to the claims. All equivalent structural changes made by using the content of the specification of the present invention should, by the same token, be included in the protection scope of the present invention.

Claims

1. An acid-soluble water-swellable gel plugging agent, characterized in that: The invention is prepared by polymerizing the following raw materials in parts by weight: 15-25 parts of carboxymethyl cellulose, 20-40 parts of N,N-dimethylacrylamide, 15-30 parts of dimethyldiallylammonium chloride and 10-35 parts of sodium p-styrene sulfonate.

2. A method for preparing the acid-soluble water-swellable gel plugging agent as claimed in claim 1, characterized in that: Carboxymethyl cellulose, N,N-dimethylacrylamide, dimethyldiallylammonium chloride and sodium p-styrenesulfonate are dissolved in water, and an initiator and a crosslinking agent are added to carry out polymerization reaction.

3. The method for preparing the acid-soluble water-swellable gel plugging agent according to claim 2, characterized in that: The initiator is a soluble persulfate initiator.

4. The method for preparing the acid-soluble water-swellable gel plugging agent according to claim 3, characterized in that: The mass concentration of the initiator is 0.2%-1%.

5. The method for preparing the acid-soluble water-swellable gel plugging agent according to claim 2, characterized in that: The cross-linking agent is N-N'methylenebisacrylamide.

6. The method for preparing the acid-soluble water-swellable gel plugging agent according to claim 5, characterized in that: The mass concentration of the cross-linking agent is 0.3%-0.5%.

7. The method for preparing the acid-soluble water-swellable gel plugging agent according to any one of claims 2 to 6, characterized in that: The polymerization reaction is carried out at a temperature of 50-60° C. for 2-2.5 hours.

8. Use of the acid-soluble water-swellable gel plugging agent as claimed in claim 1 in drilling fluid.

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