Delayed expansion plugging material, preparation method thereof and delayed expansion plugging system

Abstract

The invention belongs to the technical field of plugging agents for petroleum drilling, and particularly relates to a delayed expansion plugging material and a preparation method thereof, and a delayed expansion plugging system containing the delayed expansion plugging material. The delayed expansion plugging material provided by the invention is prepared from the following raw materials in parts by weight through reaction: 100 parts of a double-bond-containing carboxylic ester monomer, 10-30 parts of a double-bond-containing carboxylic acid monomer, 5-20 parts of graphite powder, 1-3 parts of a cross-linking agent, 0.3-2 parts of an initiator, 45-130 parts of a solvent and 0-50 parts of solid filler. According to the delayed expansion plugging material provided by the invention, the cost is reduced while the retardancy, the final expansion rate and the strength are ensured.

Description

Technical Field

[0001] The present invention belongs to the technical field of lost circulation materials for oil drilling, and particularly relates to a delayed expansion lost circulation material and a preparation method thereof, as well as a delayed expansion lost circulation system comprising the delayed expansion lost circulation material. Background Art

[0002] The problem of lost circulation severely restricts the drilling speed and is widespread in major oilfields in China. Among numerous lost circulation control methods, bridging plugging is one of the main lost circulation control methods. Among them, water-swellable lost circulation materials are widely used as bridging plugging materials, including natural water-swellable lost circulation materials and chemically synthesized water-swellable lost circulation materials. Chemically synthesized water-swellable materials are widely used due to their characteristics such as large water absorption ratio and high strength. After being used in combination with bridging plugging materials, they can increase the retention ability of the lost circulation material in the lost zone, and at the same time, after swelling, they can increase the plugging ability of the bridging plugging cushion. However, the water absorption speed of this type of swelling lost circulation agent is too fast, and it almost completely swells in half an hour. Often, it has already swollen too much during the on-site preparation process and pumping, resulting in difficulty for the lost circulation agent to enter the lost zone. Some of the lost circulation agent that enters the lost zone has a low strength of the stuffing layer due to premature swelling, and the lost circulation control effect is poor. Therefore, it is necessary for the swelling lost circulation agent to have the characteristic of delayed expansion.

[0003] Currently, the main methods for achieving delayed expansion at home and abroad are the encapsulation method, the method of grafting hydrophobic monomers, and the non-aqueous carrier liquid method. Encapsulation method: A hydrophobic material is coated on the surface of the water-absorbing particles. When it reaches the lost circulation formation, the coating material melts, dissolves under the action of the formation temperature, or cracks to a certain extent under the action of shear force, and the water-absorbing particles are released, absorb a large amount of formation water, and expand in volume to plug the lost circulation cracks or pores. However, the technical disadvantages of the current methods for achieving delayed expansion at home and abroad are also obvious. For example, the main problems existing in achieving delayed expansion by the encapsulation method are: (1) The selection range of the coating material is very limited; (2) The encapsulation difficulty is large; (3) The encapsulation is uneven and needs to be repeated many times to be completely encapsulated; (4) The encapsulation process is complex and it is difficult to achieve industrialization. Method of grafting hydrophobic monomers: Hydrophobic monomers have an inhibitory effect on the entry of water molecules into the interior of the water-absorbing particles. Therefore, a certain amount of hydrophobic monomers can be grafted to slow down the water absorption and expansion. Although certain effects have been achieved in achieving delayed expansion by grafting hydrophobic monomers, when introducing hydrophobic monomers, the water absorption ratio of the water-absorbing material should also be taken into account. Non-aqueous carrier liquid method: On the ground, a hydrophobic liquid with a certain concentration is used as the carrier liquid, and the water-absorbing particles undergo slight swelling. When it reaches the lost circulation formation, under the dilution action of the formation water, the concentration of the carrier liquid decreases, and the water-absorbing particles further absorb water and expand to fill the lost circulation channel. The problem with this method is that after the carrier liquid is diluted by the formation water, the final swelling degree of the water-absorbing particles decreases and cannot reach the swelling degree when directly adding clear water.

[0004] Patent document CN 108048055 A discloses a novel delay-expandable plugging agent and its preparation method. The novel delay-expandable plugging agent is prepared by copolymerization of acrylate, 2-acrylamido-2-methylpropanesulfonate, acrylic acid and a crosslinking agent. Under formation conditions, the ester groups in this material will gradually hydrolyze into corresponding hydrophilic functional groups such as sulfonic acid or carboxylic acid. This process is a transformation from hydrophobicity to hydrophilicity, with the volume gradually increasing. The hydrolysis process is usually very slow below 50 °C, while it will hydrolyze faster at formation temperature, thus realizing its rapid expansion under formation conditions and finally realizing its performance of delayed expansion. However, this material has disadvantages such as high raw material cost and complex preparation process, and the solvent used in the reaction needs to be removed, which restricts its popularization and application.

[0005] Based on this, the existing technology needs to be improved. Summary of the Invention

[0006] The purpose of the present invention is to provide a delay-expandable plugging material, which reduces the cost while ensuring the delay property, final expansion ratio and strength.

[0007] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0008] According to the first aspect of the present invention, there is provided a delay-expandable plugging material, which is formed by reacting the following raw materials, and the raw material ratio is calculated by weight: 100 parts of double-bond-containing carboxylic acid ester monomer, 10 - 30 parts of double-bond-containing carboxylic acid monomer, 5 - 20 parts of graphite powder, 1 - 3 parts of crosslinking agent, 0.3 - 2 parts of initiator, 45 - 130 parts of solvent and 0 - 50 parts of solid filler.

[0009] According to some embodiments of the present invention, the double-bond-containing carboxylic acid ester monomer is one or a mixture of more than one of propyl acrylate, butyl acrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate.

[0010] According to some embodiments of the present invention, the double-bond-containing carboxylic acid monomer is one or a mixture of two of acrylic acid or methacrylic acid.

[0011] According to some embodiments of the present invention, the crosslinking agent is N,N'-methylenebisacrylamide or N,N'-vinylenebisacrylamide.

[0012] According to some embodiments of the present invention, the particle size of the graphite powder is 100 - 10000 mesh.

[0013] According to some embodiments of the present invention, the initiator is azobisisobutyronitrile.

[0014] According to some embodiments of the present invention, the solvent is one or a mixture of more than one of n-butanol, tert-butanol, sec-butanol, n-pentanol, isopentanol.

[0015] According to some embodiments of the present invention, the solid filler is a mixture of one or more of bentonite, calcium carbonate particles, barite powder, fruit shells, and sand.

[0016] According to a second aspect of the present invention, there is provided a method for preparing the delayed expansion plugging material according to the first aspect of the present invention, which includes:

[0017] Mixing a double bond carboxylic acid ester monomer, a double bond carboxylic acid monomer, graphite powder, a crosslinking agent, an initiator, a solvent, and a solid filler evenly according to a ratio, and then reacting at 60-100 °C for 5-10 hours to obtain a colloid;

[0018] Crushing the colloid into required particle sizes to obtain the delayed expansion plugging material.

[0019] According to some embodiments of the present invention, the required particle sizes are 20 mesh to 40 mesh.

[0020] According to some embodiments of the present invention, after mixing each raw material evenly according to a ratio, it is heated to 60-70 °C to initiate the reaction. When the reaction is initiated, the temperature of the reaction system is controlled between 60-100 °C through a circulating bath for the reaction.

[0021] According to a third aspect of the present invention, there is provided a delayed expansion plugging system, which includes the delayed expansion plugging material according to the first aspect of the present invention.

[0022] By adopting the above technical solutions, the present invention has the following advantages compared with the prior art:

[0023] The delayed expansion plugging material provided by the present invention has the effect of delayed expansion, and hardly undergoes water absorption expansion in clear water or 1% sodium hydroxide solution (when soaked at room temperature in clear water or 1% sodium hydroxide brine for 2 h, the water absorption expansion rate ≤ 30%), and the water absorption expansion reaches more than 4 times under the condition of 1% sodium hydroxide at 80 °C.

[0024] The delayed expansion plugging material provided by the present invention has uniform texture, wide sources of raw materials for preparation, simple preparation process, no need to remove the solvent additionally, low cost, and is suitable for popularization and application in the field of drilling plugging. Specific Embodiments

[0025] It should be understood that the embodiments of the present invention shown in the exemplary embodiments are merely illustrative. Although only a few embodiments of the present invention are described in detail, those skilled in the art can easily appreciate that various modifications are feasible without substantially departing from the teachings of the subject matter of the present invention. Accordingly, all such modifications should be included within the scope of the present invention. Without departing from the gist of the present invention, other substitutions, modifications, variations and deletions can be made to the design, operating conditions and parameters, etc. of the following exemplary embodiments.

[0026] According to a first aspect of the present invention, there is provided a delayed expansion plugging material, which is formed by reacting the following raw materials, and the raw material ratio is calculated according to the following parts by weight: 100 parts of a double bond-containing carboxylic acid ester monomer, 10 - 30 parts of a double bond-containing carboxylic acid monomer, 5 - 20 parts of graphite powder, 1 - 3 parts of a crosslinking agent, 0.3 - 2 parts of an initiator, 45 - 130 parts of a solvent, and 0 - 50 parts of a solid filler.

[0027] Preferably, the double bond-containing carboxylic acid ester monomer is one or a mixture of more than one of propyl acrylate, butyl acrylate, ethyl methacrylate, propyl methacrylate, and butyl methacrylate.

[0028] Preferably, the double bond-containing carboxylic acid monomer is one or a mixture of two of acrylic acid or methacrylic acid.

[0029] Preferably, the crosslinking agent is N,N'-methylenebisacrylamide or N,N'-vinylenebisacrylamide.

[0030] Preferably, the initiator is azobisisobutyronitrile.

[0031] Preferably, the solvent is one or a mixture of more than one of n-butanol, tert-butanol, sec-butanol, n-pentanol, and isopentanol. Such solvents not only have good solubility for the polymerization monomers, but also these monomers have relatively high boiling points and certain hydrophobicity. In the polymerization reaction, although the system exotherms violently, it will not cause the solvent to boil or seriously lose. After the reaction is completed, the formed colloid only needs to be cut into blocks and granulated according to requirements, and the solvent does not need to be removed to be actually applied in plugging applications. During the plugging process, the above solvents have poor solubility in water, so they also play a role in delaying expansion. By using these solvents, the preparation cost of the synthetic-based delayed plugging material is significantly reduced, and the preparation process is simplified.

[0032] Preferably, the solid filler is one or a mixture of more than one of bentonite, calcium carbonate particles, barite powder, fruit shells, and sand.

[0033] Preferably, the particle size of the graphite powder is 100 to 10,000 mesh. The addition of the graphite powder serves three purposes: (1) enhancing the hydrophobicity of the plugging agent, which can enhance the delayed expansion effect; (2) increasing the strength of the plugging agent; (3) playing a heat conduction role. Because the reaction is highly exothermic during the polymerization process and the internal heat cannot be dissipated in time, bubbles will be generated, affecting the strength of the plugging agent. After adding the graphite powder, the heat exchange rate with the reaction bath during the reaction process is significantly increased, eliminating the adverse effects of the reaction heat effect.

[0034] The reaction mechanism of the delayed expansion plugging material provided by the present invention is as follows: The double-bond carboxylic acid ester monomer, the double-bond carboxylic acid monomer, and the cross-linking agent undergo a polymerization reaction under the action of an initiator. The double-bond monomers and the cross-linking agent are polymerized through free radical initiation to form a three-dimensional network structure copolymer. The graphite powder, solvent, and solid filler are filled in this three-dimensional network structure. When under formation conditions, the plugging slurry and the water in the formation come into contact with the polymer three-dimensional network structure, and the ester groups in the polymer chains are gradually hydrolyzed. The ester groups are hydrolyzed into carboxylate ions, enhancing the hydrophilicity. The delay mechanism of the delayed expansion plugging material provided by the present invention is as follows: At room temperature, in a dilute sodium hydroxide alkaline solution, the hydrolysis rate of the ester groups is slow, and with the action of a solvent that is immiscible with water, the plugging material can preferably maintain its hydrophobic characteristics without water absorption and expansion for a long time. Under formation conditions, as the temperature increases, the hydrolysis of the ester groups in the plugging agent is accelerated, and finally hydrolyzed into carboxylate ions, resulting in a gradual increase in the water absorption of the plugging agent and gradual water absorption and expansion, thereby achieving the effect of expansion plugging. By adjusting the dosage of the cross-linking agent in the plugging agent, the expansion ratio can be adjusted. As the cross-linking agent increases, the expansion ratio decreases, but the strength increases. By adjusting the ratio of the hydrophobic ester double-bond monomer to the carboxylic acid or sulfonic acid double-bond monomer, the delayed expansion time can be adjusted. The more the content of the hydrophobic monomer, the longer the delayed expansion time, which can be adjusted according to the actual needs of the on-site plugging process.

[0035] The delayed expansion plugging material provided by the present invention has the effect of delayed expansion and hardly undergoes water absorption and expansion in clear water or a 1% sodium hydroxide solution (when soaked at room temperature in clear water or 1% sodium hydroxide brine for 2 h, the water absorption expansion rate ≤ 30%), and the water absorption expansion reaches more than 4 times under the condition of 1% sodium hydroxide at 80 °C.

[0036] Compared with the novel delay-expanding plugging agent provided in the patent document CN 108048055 A, the delay-expanding plugging material provided by the present invention has the advantages of wide sources of preparation raw materials, low cost, and simple preparation process. All monomers in the present invention are common monomers sold in the market. During the polymerization process, a high-boiling-point alcohol is selected as the solvent, and the selected alcohol is miscible with water and has certain hydrophobic properties. Therefore, in the present invention, the ratio of the monomer to the solvent is increased, and the volume of the solvent is significantly reduced. During the polymerization process, although the reaction exotherms violently, due to the high boiling point of the monomer, the solvent does not boil or is not lost in large amounts due to volatilization. After the reaction is completed, there is no need to remove the solvent, and it can be directly used as a delay plugging agent after pelletizing. In the present invention, graphite powder is also added to the plugging system. The addition of graphite powder improves the thermal conductivity of the reaction system, avoids adverse factors such as overheating of the system during the reaction that affect the performance of the plugging agent, and the introduction of graphite also enhances the strength and delay-expanding time of the plugging agent. The plugging multiple of this plugging material is effectively controlled by the addition amount of the cross-linking agent, achieving the application effect.

[0037] According to a second aspect of the present invention, there is provided a method for preparing the delay-expanding plugging material according to the first aspect of the present invention, which includes:

[0038] Mix the double-bond-containing carboxylic acid ester monomer, double-bond-containing carboxylic acid monomer, cross-linking agent, graphite powder, initiator, solvent, and solid filler evenly according to the ratio, and then react at 60-100 °C for 5-10 hours to obtain a colloid;

[0039] Crush the colloid into the required particle size to obtain the delay-expanding plugging material.

[0040] In some embodiments, the double-bond-containing carboxylic acid ester monomer, methacrylic acid, graphite powder, cross-linking agent, initiator, solvent, and solid filler are mixed evenly according to the above ratio, and then heated to initiate the reaction under the condition of 60-70 °C. When the reaction is initiated, the temperature of the reaction system is controlled between 60-100 °C through a circulating bath. After reacting for 5-10 hours, stop heating, and after cooling, crush the obtained colloid into the required particle size, which is the delay-expanding plugging material. The method for preparing the delay-expanding plugging material provided by the present invention has the advantages of wide sources of preparation raw materials, simple preparation process, no need to remove the solvent additionally, and low cost, and is suitable for popularization and application in the field of drilling plugging.

[0041] Preferably, the required particle size is 20 mesh to 40 mesh.

[0042] According to the third aspect of the present invention, a delayed expansion plugging system is provided, which includes the delayed expansion plugging material according to the first aspect of the present invention. In addition to the delayed expansion plugging material, the delayed expansion plugging system may further include, for example, rigid particles, elastic particles, organic fiber materials, ultra-low permeability treatment agents, and the like.

[0043] The delayed expansion plugging system provided by the present invention has the synergistic plugging effect of "five-in-one" multifunctions such as expansion, rigidity, elasticity, tension reinforcement, and ultra-low permeability, and can meet the needs of plugging different aperture fractured leakage formations.

[0044] The above technical solutions of the present invention will be described in detail below through specific examples.

[0045] Example 1

[0046] In a 500 mL large beaker, 100 g of propyl acrylate, 30 g of acrylic acid, 5 g of graphite powder (10,000 mesh), 3 g of N,N'-methylenebisacrylamide, 2 g of azobisisobutyronitrile, 130 g of n-butanol, and 50 g of 80-mesh calcium carbonate particles were mixed evenly, heated to 60 °C to initiate polymerization, and the reaction temperature of the system was controlled between 60 and 90 °C with a water bath. After reacting for 10 hours, the reaction was stopped. It was observed that the obtained plugging material had a uniform texture and no bubbles. After cooling to room temperature, the obtained colloid was crushed into particles with a size of 20 to 40 mesh to obtain the delayed expansion plugging material.

[0047] Detection of delay property:

[0048] Water absorption expansion rate = (volume after water absorption - volume before water absorption) / volume before water absorption * 100%;

[0049] The water absorption expansion rate was measured in clear water. After soaking in clear water for 2 hours, the water absorption expansion rate was 8%; after soaking in 1% sodium hydroxide for 2 hours, the water absorption expansion rate was 27%; when measured in 1% sodium hydroxide at 80 °C for 4 hours, the water absorption expansion rate was 5.5 times the original, and when measured for 12 hours, the water absorption expansion rate was 10 times the original.

[0050] Strength test:

[0051] The plugging agent was cut into cubes with a size of 1 cm * 1 cm * 1 cm, and then after 12 hours at 80 °C in 1% sodium hydroxide, the strength of the expanded plugging agent was tested with a universal tester to be 2.3 MPa.

[0052] Example 2

[0053] In a 500 mL large beaker, 100 g of butyl acrylate, 10 g of methacrylic acid, 10 g of graphite powder (100 mesh), 1 g of N,N'-methylenebisacrylamide, 0.3 g of azobisisobutyronitrile and 45 g of n-butanol were mixed evenly, heated to 60 °C to initiate polymerization, and the reaction temperature of the system was controlled between 60 and 90 °C with a water bath. After reacting for 5 hours, the reaction was stopped. The obtained plugging material was observed to have a uniform texture and no bubbles. After cooling to room temperature, the obtained colloid was crushed into particles sized between 20 and 40 mesh to obtain a delayed expansion plugging material.

[0054] Detection of delay properties:

[0055] Water absorption expansion rate = (volume after water absorption - volume before water absorption) / volume before water absorption * 100%;

[0056] The water absorption expansion rate was measured in clear water. After soaking in clear water for 2 h, the water absorption expansion rate was 3%; after soaking in 1% sodium hydroxide for 2 h, the water absorption expansion rate was 15%; when measured at 80 °C in 1% sodium hydroxide for 4 h, the water absorption expansion rate was 8 times the original, and when measured at 12 h, the water absorption expansion rate was 20 times the original.

[0057] Strength test:

[0058] The plugging agent was cut into cubes with dimensions of 1 cm * 1 cm * 1 cm, and then after 12 h under the condition of 80 °C in 1% sodium hydroxide, the strength of the expanded plugging agent was tested using a universal testing machine to be 2.7 MPa.

[0059] Example 3

[0060] In a 500 mL large beaker, 100 g of butyl acrylate, 20 g of methacrylic acid, 20 g of graphite powder (1000 mesh), 2 g of N,N'-methylenebisacrylamide, 1 g of azobisisobutyronitrile and 80 g of tert-butanol were mixed evenly, heated to 70 °C to initiate polymerization, and the reaction temperature of the system was controlled between 60 and 90 °C with a water bath. After reacting for 5 hours, the reaction was stopped. The obtained plugging material was observed to have a uniform texture and no bubbles. After cooling to room temperature, the obtained colloid was crushed into particles sized between 20 and 40 mesh to obtain a delayed expansion plugging material.

[0061] Detection of delay properties:

[0062] Water absorption expansion rate = (volume after water absorption - volume before water absorption) / volume before water absorption * 100%;

[0063] The water absorption expansion rate was measured in clear water. After soaking in clear water for 2 h, the water absorption expansion rate was 5%; after soaking in 1% sodium hydroxide for 2 h, the water absorption expansion rate was 20%; when measured at 80 °C in 1% sodium hydroxide for 4 h, the water absorption expansion rate was 8 times the original, and when measured at 12 h, the water absorption expansion rate was 15 times the original.

[0064] Strength test:

[0065] Cut the plugging agent into 1 cm×1 cm×1 cm cubes, and then after 12 h under the condition of 80 °C in 1% sodium hydroxide, use a universal testing machine to test the strength of the plugging agent after expansion, which is 2.5 MPa.

[0066] Example 4

[0067] In a 500 mL large beaker, mix 100 g of ethyl methacrylate, 30 g of methacrylic acid, 10 g of graphite powder (10,000 mesh), 3 g of N,N'-methylenebisacrylamide, 1 g of azobisisobutyronitrile, and 40 g of n-pentanol evenly, heat to 70 °C to initiate polymerization, use a water bath to control the reaction temperature of the system between 60 and 90 °C, stop the reaction after 5 h, observe that the obtained plugging material is uniform in texture and has no bubbles, and after cooling to room temperature, crush the obtained colloid into 20 - 40 mesh size to obtain a delayed expansion plugging material.

[0068] Detection of delay property:

[0069] Water absorption expansion rate = (volume after water absorption - volume before water absorption) / volume before water absorption×100%;

[0070] Measure the water absorption expansion rate in clean water. After soaking in clean water for 2 h, the water absorption expansion rate is 7%; after soaking in 1% sodium hydroxide for 2 h, the water absorption expansion rate is 28%; at 80 °C in 1% sodium hydroxide for 4 h, the measured water absorption expansion rate is 8 times the original, and at 12 h, the measured water absorption expansion rate is 18 times the original.

[0071] Strength test:

[0072] Cut the plugging agent into 1 cm×1 cm×1 cm cubes, and then after 12 h under the condition of 80 °C in 1% sodium hydroxide, use a universal testing machine to test the strength of the plugging agent after expansion, which is 1.9 MPa.

[0073] Comparative example 1

[0074] In a 500 mL large beaker, mix 100 g of propyl acrylate, 30 g of acrylic acid, 3 g of N,N'-methylenebisacrylamide, 2 g of azobisisobutyronitrile, 130 g of n-butanol, and 50 g of 80 - mesh calcium carbonate particles evenly, heat to 60 °C to initiate polymerization, use a water bath to control the reaction temperature of the system between 60 and 100 °C, stop the reaction after 10 h, observe that there are a large number of bubbles in the obtained plugging material, and after cooling to room temperature, crush the obtained colloid into 20 - 40 mesh size to obtain a delayed expansion plugging material.

[0075] Detection of delay property:

[0076] Water absorption expansion rate = (volume after water absorption - volume before water absorption) / volume before water absorption×100%;

[0077] The water absorption expansion rate was measured in clear water. After soaking in clear water for 2 hours, the water absorption expansion rate was 10%; after soaking in 1% sodium hydroxide for 2 hours, the water absorption expansion rate was 45%; when measured at 80 °C for 4 hours in 1% sodium hydroxide, the water absorption expansion rate was 10 times the original, and when measured at 12 hours, the water absorption expansion rate was 12 times the original.

[0078] Strength test:

[0079] The plugging agent was cut into cubes of 1 cm * 1 cm * 1 cm, and then after 12 hours under the condition of 1% sodium hydroxide at 80 °C, the strength of the expanded plugging agent was tested by a universal testing machine to be 1.3 MPa.

[0080] Comparative Example 2

[0081] In a 500 mL large beaker, 100 g of propyl acrylate, 30 g of acrylic acid, 5 g of graphite powder (10,000 mesh), 3 g of N,N'-methylenebisacrylamide, 2 g of azobisisobutyronitrile, 130 g of isopropanol and 50 g of 80-mesh calcium carbonate particles were mixed evenly, heated to 60 °C to initiate polymerization, and the reaction temperature of the system was controlled between 60 and 90 °C by a water bath. A large number of bubbles were generated during the reaction, and isopropanol boiled. After reacting for 10 hours, the reaction was stopped. It was observed that the obtained plugging material contained a large number of bubbles. After cooling to room temperature, the obtained colloid was crushed into a size of 20 to 40 mesh to obtain a delayed expansion plugging material.

[0082] Detection of delay properties:

[0083] Water absorption expansion rate = (volume after water absorption - volume before water absorption) / volume before water absorption * 100%;

[0084] The water absorption expansion rate was measured in clear water. After soaking in clear water for 2 hours, the water absorption expansion rate was 14%; after soaking in 1% sodium hydroxide for 2 hours, the water absorption expansion rate was 47%; when measured at 80 °C for 4 hours in 1% sodium hydroxide, the water absorption expansion rate was 7.5 times the original, and when measured at 12 hours, the water absorption expansion rate was 10 times the original.

[0085] Strength test:

[0086] The plugging agent was cut into cubes of 1 cm * 1 cm * 1 cm, and then after 12 hours under the condition of 1% sodium hydroxide at 80 °C, the strength of the expanded plugging agent was tested by a universal testing machine to be 0.8 MPa.

[0087] The experimental results of the above Comparative Example 1 and Example 1 show that compared with the plugging agent without graphite powder, the plugging agent containing graphite powder has higher strength and enhanced delayed expansion performance. And the colloid containing graphite powder has a uniform texture and no bubbles, while the colloid without graphite powder contains a large number of bubbles inside.

[0088] The experimental results of Comparative Example 2 and Example 1 above show that when isopropanol is used as the solvent, due to its low boiling point, the heat in the reaction system causes it to boil, which is not suitable for the polymerization reaction under high-concentration monomers, and the delayed expansion plugging performance and compressive strength of the obtained plugging material are significantly reduced.

[0089] The experiments of Examples 1 to 4 show that the preparation reaction conditions are mild, and granulation can be directly carried out without solvent removal treatment and then applied, and the obtained plugging materials all show good delayed expansion performance.

[0090] The above are only the preferred embodiments of the present invention and are not used to limit the scope of implementation of the present invention; any modification or equivalent replacement of the present invention without departing from the spirit and scope of the present invention shall be covered by the protection scope of the claims of the present invention.

Claims

1. A delayed expansion plugging material, characterized in that, it is formed by the reaction of the following raw materials, and the raw material ratio is calculated according to the following parts by weight: 100 parts of double-bonded carboxylic acid ester monomer, 10 - 30 parts of double-bonded carboxylic acid monomer, 5 - 20 parts of graphite powder, 1 - 3 parts of cross-linking agent, 0.3 - 2 parts of initiator, 45 - 130 parts of solvent, and 0 - 50 parts of solid filler.

2. The delayed expansion plugging material according to claim 1, characterized in that, the double-bonded carboxylic acid ester monomer is one or a mixture of more than one of propyl acrylate, butyl acrylate, ethyl methacrylate, propyl methacrylate, and butyl methacrylate.

3. The delayed expansion plugging material according to claim 1, characterized in that, the double-bonded carboxylic acid monomer is one or a mixture of two of acrylic acid or methacrylic acid.

4. The delayed expansion plugging material according to claim 1, characterized in that, the cross-linking agent is N,N'-methylenebisacrylamide or N,N'-vinylbisacrylamide.

5. The delayed expansion plugging material according to claim 1, characterized in that, the initiator is azobisisobutyronitrile.

6. The delayed expansion plugging material according to claim 1, characterized in that, the solvent is one or a mixture of more than one of n-butanol, tert-butanol, sec-butanol, n-pentanol, and isopentanol.

7. The delayed expansion plugging material according to claim 1, characterized in that, the solid filler is one or a mixture of more than one of bentonite, calcium carbonate particles, barite powder, fruit shell, and sand.

8. The delayed expansion plugging material according to claim 1, characterized in that, the particle size of the graphite powder is 100 - 10000 mesh.

9. A preparation method of the delayed expansion plugging material according to any one of the preceding claims 1 - 8, characterized in that, it includes: mixing the double-bonded carboxylic acid ester monomer, double-bonded carboxylic acid monomer, graphite powder, cross-linking agent, initiator, solvent, and solid filler evenly according to the ratio, and then reacting at 60 - 100 °C for 5 - 10 hours to obtain a colloid; crushing the colloid into the required particle size to obtain the delayed expansion plugging material.

10. The preparation method according to claim 9, characterized in that, the required particle size is 20 mesh - 40 mesh.

11. The preparation method according to claim 9, characterized in that, after mixing each raw material evenly according to the ratio, heating to 60 - 70 °C to initiate the reaction, and when the reaction is initiated, controlling the reaction system temperature between 60 - 100 °C for the reaction through a circulating bath.

12. A delayed expansion plugging system, characterized in that, it includes the delayed expansion plugging material according to any one of the preceding claims 1 - 8.