Gas reservoir crack mixed temporary plugging agent and preparation method thereof

Abstract

The invention belongs to the technical field of oilfield chemistry, and relates to a gas reservoir crack mixed temporary plugging agent and a preparation method thereof. The temporary plugging agent is prepared from the following components in parts by mass: a water-soluble high-molecular polymer, heat-resistant starch, degradable fibers, a strength improver and water, the strength improver is montmorillonite powder wrapped by polyvinyl alcohol. The water-soluble high-molecular polymer is matched with the degradable fibers and the starch particles to be interwoven and connected to form a net-shaped structure, so that the pressure resistance is improved, and the temporary plugging effect is improved; according to the strength improving agent, montmorillonite powder wrapped by polyvinyl alcohol is added, in the process that the temporary plugging agent still flows downwards, the polyvinyl alcohol on the surface of the montmorillonite powder is melted along with decline and temperature rise, so that the montmorillonite powder leaks out and absorbs water again to swell, and the strength of the temporary plugging agent is improved. And montmorillonite powder wrapped by heat-resistant starch-degradable fiber-polyvinyl alcohol is cross-linked to form a rich three-dimensional system structure as a climbing skeleton, so that the temporary plugging agent can temporarily plug cracks at positions needing temporary plugging.

Description

Technical Field

[0001] This invention belongs to the field of oilfield chemical technology, and more specifically, this invention relates to a gas reservoir fracture mixed temporary plugging agent and its preparation method. Background Technology

[0002] In the development of low-permeability oil and gas reservoirs, fracturing is one of the main production enhancement measures. Its purpose is to create a fracture in the low-permeability reservoir, increase the drainage area, and improve oil and gas production. Temporary plugging and diversion fracturing technology involves adding a temporary plugging agent in real time during the fracturing process. Based on the principle that fluids flow in the direction of least resistance, the temporary plugging agent enters the borehole connected to the original fracture or high-permeability layer along with the fracturing fluid. It accumulates at the borehole and in the original fracture (or high-permeability zone), forming a high-strength filter cake bridge, preventing subsequent fracturing fluid from entering the original fracture and high-permeability zone. This inevitably increases the bottom hole pressure to a certain extent. Under certain horizontal biaxial stress difference conditions, secondary fracturing occurs, which changes the original fracture initiation direction to create a new fracture and establish a new high-conductivity oil and gas flow channel.

[0003] A search revealed that patent document CN107090282B discloses a mixed plugging agent, a mixture of plugging agents, a plugging method, and its application. The mixed plugging agent comprises the following components by weight: 1-9 parts water-soluble polymer, 3-29 parts sand, and 0-19 parts soluble or biodegradable fiber. The mixed plugging agent is prepared into a plugging agent mixture using 10-100 parts by weight of a carrier liquid. In some high-temperature formations, this plugging agent lacks heat-resistant components and cannot maintain stable performance. High temperatures cause physical or chemical changes in the components of the plugging agent, such as degradation of the polymer, softening or decomposition of the fiber, leading to a decrease in the plugging performance and failure to meet the plugging requirements of high-temperature formations. For some high-pressure formations, this plugging agent may not provide sufficient pressure resistance. Although the sand in its composition can provide some support, the overall pressure-resistant structure is not dense and robust enough, making it easily crushed under high pressure, resulting in plugging failure.

[0004] In summary, given the shortcomings of existing temporary plugging agents, a hybrid temporary plugging agent for gas reservoir fractures and its preparation method are proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a mixed temporary plugging agent for gas reservoir fractures and its preparation method, which solves the problems of insufficient stability and insufficient pressure resistance of existing temporary plugging agents.

[0006] This invention is achieved through the following technical solution: This invention discloses a gas reservoir fracture mixed temporary plugging agent, which comprises the following components by mass: 2-10 parts water-soluble polymer, 5-30 parts heat-resistant starch, 5-20 parts biodegradable fiber, 5-10 parts strength improver, and 30-100 parts water; The strength improver is montmorillonite powder coated with polyvinyl alcohol.

[0007] Furthermore, the water-soluble polymer is polyacrylamide and / or 2-acrylamido-2-methylpropanesulfonic acid; Polyacrylamide has a molecular weight of 11 million to 25 million.

[0008] Furthermore, the biodegradable fiber includes one or more of polyvinyl alcohol fiber, modified polyester fiber, and polyurethane fiber.

[0009] Furthermore, the strength improver is a mixture formed by mixing and stirring montmorillonite powder and polyvinyl alcohol, followed by drying and pulverizing.

[0010] Furthermore, the heat-resistant starch has a particle size of not less than 40 mesh.

[0011] Furthermore, the specific method for preparing the heat-resistant starch is as follows: Starch and water are mixed to obtain a dispersion; Adjust the pH of the dispersion to neutral to obtain the pre-reaction solution; The pre-reaction liquid and crosslinking agent are mixed and reacted for the first time at 40-60℃. Then, the system after the first mixing reaction and the esterifying agent are mixed and reacted for the second time at 40-70℃. Finally, the system after the second mixing reaction is dried and pulverized to obtain heat-resistant starch.

[0012] Furthermore, the mass ratio of starch, crosslinking agent and esterifying agent is (90-100):(1.5-2.0):(4-5).

[0013] Furthermore, the crosslinking agent is trimetaphosphate, phosphorus oxychloride, pyrophosphate, or tripolyphosphate; The esterifying agent is an acid anhydride compound.

[0014] This invention also discloses a method for preparing a gas reservoir fracture mixed temporary plugging agent, comprising the following steps: S1. First, the water-soluble polymer is dissolved in water and then stirred and mixed to form a mixed emulsion. S2. Add heat-resistant starch to the mixed emulsion and stir to mix; during the stirring process, add biodegradable fiber so that the biodegradable fiber is interwoven in the gelatinous starch emulsion to obtain a mixed system; S3. Add strength improver to the mixture and stir to form a viscous emulsion with a network skeleton with nodes; S4. The viscous emulsion is dried to form a blocky solid, thus obtaining a gas reservoir fracture mixed temporary plugging agent.

[0015] Furthermore, the blocky solid is crushed or granulated to form a granular temporary plugging agent.

[0016] Compared with the prior art, the present invention has the following beneficial technical effects: This invention discloses a mixed-type temporary plugging agent for gas reservoir fractures, comprising a water-soluble polymer, heat-resistant starch, biodegradable fiber, and a strength modifier. When the water-soluble polymer comes into contact with water, it absorbs water and swells, thereby sealing the fractures. The heat-resistant starch, upon absorbing water, becomes sticky, allowing the temporary plugging agent to adhere to the inner wall of the fracture. Simultaneously, the starch penetrates the fracture, enhancing the plugging effect. The biodegradable fiber and starch particles interweave to form a network structure, improving compressive strength and thus enhancing the temporary plugging effect. Furthermore, all components are biodegradable, thereby improving the reservoir fracture recovery effect. The strength improver of this invention adds polyvinyl alcohol-encapsulated montmorillonite powder. When the temporary plugging agent fills the crack, it expands once through a water-soluble polymer. As the temporary plugging agent continues to flow downwards, the temperature rises, causing the polyvinyl alcohol on the surface of the montmorillonite powder to melt, allowing the montmorillonite powder to leak out and expand again by absorbing water. This, combined with the heat-resistant starch-biodegradable fiber-polyvinyl alcohol-encapsulated montmorillonite powder crosslinking to form a rich three-dimensional system structure as an adhesion skeleton, allows the temporary plugging agent to temporarily block the crack at the desired location. This increases the volume of the plugging agent in the crack's downward flow, further enhancing its adhesion ability and improving the sealing effect.

[0017] In downhole operations, high-temperature environments are frequently encountered. The presence of heat-resistant starch can significantly improve the stability of temporary plugging agents under high-temperature conditions. It can maintain its physical and chemical properties at high temperatures, reducing the risk of plugging agent failure due to temperature increases. The comparative document does not mention any special components for high-temperature environments. Furthermore, starch itself has certain filling and plugging properties. Working synergistically with other components, it can more effectively fill formation pores or fractures, improving the temporary plugging effect. Biodegradable fibers can degrade over a certain period, facilitating subsequent operations. An appropriate increase in fiber content allows for better interweaving within the plugging agent system, forming a more stable network structure, enhancing the strength and toughness of the plugging agent, and enabling smoother degradation when the plugging needs to be removed.

[0018] Furthermore, this invention also designs a specific preparation process for heat-resistant starch. First, starch is mixed with water to form a dispersion, dispersing the starch in the water to provide a uniform reaction environment for subsequent reactions. This step is crucial to ensure uniform starch dispersion and avoid agglomeration, which could lead to uneven reaction. The pH of the dispersion is then adjusted to neutral to obtain a pre-reaction solution. pH value has a significant impact on subsequent crosslinking and esterification reactions. Many crosslinking and esterifying agents function better under neutral conditions, maintaining stable reactivity. If the pH value is too high or too low, it may cause unnecessary side reactions in the crosslinking or esterifying agents, or affect their reactivity with starch molecules.

[0019] The pre-reaction solution and cross-linking agent are then subjected to a first mixing reaction at 40-60℃. This cross-linking reaction forms chemical bonds between starch molecules, connecting different starch molecules. This enhances the structural stability of the starch, making it less prone to molecular chain breakage or deformation at high temperatures, thus improving its heat resistance. A temperature of at least 40℃ is maintained to provide sufficient energy for the cross-linking reaction to proceed smoothly. If the temperature is too low, the reaction rate will be too slow, affecting production efficiency.

[0020] Then, the system after the first mixing reaction and the esterifying agent are subjected to a second mixing reaction at 40-70℃. Esterification introduces functional groups such as ester groups onto starch molecules. The introduction of these functional groups can alter the physical and chemical properties of starch, further improving its heat resistance. Simultaneously, esterification may also synergistically enhance the stability of starch molecules in conjunction with cross-linking reactions. Similar to cross-linking reactions, a temperature not lower than 40℃ can accelerate the esterification reaction rate, ensuring sufficient energy for the reaction to proceed.

[0021] The system following the second mixing reaction is dried and pulverized to remove moisture, thus improving the stability and shelf life of the starch product. The presence of moisture can affect the starch's properties during subsequent storage or use, such as causing clumping or mold growth.

[0022] This invention also discloses a method for preparing a mixed temporary plugging agent for gas reservoir fractures. First, a water-soluble polymer is dissolved in water and stirred to form a mixed emulsion. This method ensures the polymer is fully dispersed in water, guaranteeing its uniform distribution in subsequent reactions and laying a good foundation for the homogeneity of the entire temporary plugging agent system. If the polymer is not uniformly dispersed, it may form local agglomerates, affecting the performance stability of the temporary plugging agent, such as leading to uneven plugging strength.

[0023] After heat-resistant starch is added to the mixed emulsion, biodegradable fibers are then added, causing the fibers to intertwine within the gelatinous starch emulsion. The heat-resistant starch itself can maintain a certain level of stability and filling performance under high-temperature conditions, while the intertwining of biodegradable fibers further enhances the structural strength of the system. This intertwined structure can increase the toughness and tensile strength of the temporary plugging agent, making it less susceptible to damage under complex stress environments in gas reservoir fractures, such as formation pressure changes and fluid scouring, thereby improving the plugging effect and durability.

[0024] A strength improver is added to the mixture, and after stirring, a viscous emulsion with a network skeleton with nodes is formed. This network skeleton structure greatly improves the overall strength and stability of the temporary plugging agent, which can better resist the high-pressure environment in the gas reservoir fracture, effectively prevent the temporary plugging agent from deforming or being dispersed under pressure, and ensure the reliability of the plugging.

[0025] The viscous emulsion is dried to form a blocky solid, yielding a gas reservoir fracture-mixed temporary plugging agent. The blocky solid form facilitates storage, transportation, and on-site operation. During use, the blocky temporary plugging agent can be crushed or otherwise treated according to the specific conditions of the gas reservoir fractures, offering good practicality and flexibility. Attached Figure Description

[0026] Figure 1 This is a flowchart illustrating the preparation process of the gas reservoir fracture mixed temporary plugging agent of the present invention. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the present invention clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention; that is, the described embodiments are only a part of the embodiments of the present invention, and not all of them.

[0028] The detailed description of the embodiments of the present invention provided in the following figures is not intended to limit the scope of the claimed invention, but merely to illustrate one selected embodiment of the invention. All other embodiments obtained by those skilled in the art based on the figures and embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0029] It should be noted that the terms “comprising,” “including,” or any other variations are intended to cover non-exclusive inclusion, such that a process, element, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to the process, element, method, article, or apparatus.

[0030] The present invention provides a mixed temporary plugging agent for gas reservoir fractures, comprising the following components in parts by weight: 2-10 parts of water-soluble polymer, 5-30 parts of heat-resistant starch, 5-20 parts of biodegradable fiber, 5-10 parts of strength improver, and 30-100 parts of water.

[0031] This mixed temporary plugging agent is prepared by stirring and mixing water-soluble polymer, heat-resistant starch, biodegradable fiber and strength improver in water, followed by drying and granulation.

[0032] The water-soluble polymer is polyacrylamide and / or 2-acrylamido-2-methylpropanesulfonic acid with a molecular weight of 11 million to 25 million. When the water-soluble polymer comes into contact with water, it can dissolve or swell in water to form an aqueous solution or dispersion system because its molecular structure contains a large number of hydrophilic groups, such as cationic groups (e.g., tertiary amine groups, quaternary amine groups, etc.), anionic groups (e.g., carboxylic acid groups, sulfonic acid groups, etc.) and polar nonionic groups (e.g., hydroxyl groups, ether groups, etc.).

[0033] Specifically, polyacrylamide (PAM), a water-soluble polymer, is readily soluble in water but insoluble in most organic solvents. When PAM is added to water, it forms a transparent liquid. Furthermore, when a large amount of PAM is added, the solution becomes viscous, even forming a transparent gel, reducing its fluidity. Adding heat-resistant starch, under stirring, allows the starch to distribute evenly in the gel-like solution. Combined with one or more biodegradable fibers, such as polyvinyl alcohol fibers, modified polyester fibers, or polyurethane fibers, the biodegradable fibers interweave in the solution to form a network structure, thereby increasing the overall compressive strength of the solution. Simultaneously, the viscosity of the starch solution, combined with the biodegradable fibers, enhances penetration and adhesion to the inner walls of cracks, thus improving the temporary plugging effect. The heat-resistant starch is mainly composed of a dispersion of starch and water, the pH of which is adjusted to neutral to obtain a pre-reaction solution. Then, the pre-reaction solution and the crosslinking agent are mixed and reacted for a first time at 40-60℃ for no less than 4 hours. The system after the first mixing reaction and the esterifying agent are mixed and reacted for a second time at 40-70℃ for no less than 4 hours. Finally, the system after the second mixing reaction is dried and pulverized to obtain heat-resistant starch. The particle size of the obtained heat-resistant starch is made to be no less than 40 mesh, thereby improving the adhesion ability to the inner wall of cracks and the bonding strength between starch particles. Finally, by mixing and stirring montmorillonite powder and polyvinyl alcohol, drying and pulverizing them to form a strength improver, the montmorillonite powder coated with polyvinyl alcohol is uniformly mixed in the solution after the addition of biodegradable fibers. The montmorillonite powder coated with polyvinyl alcohol intertwines with the biodegradable fibers, making the montmorillonite powder coated with polyvinyl alcohol act as a network node, thereby further improving the overall skeleton strength. After drying and granulation, the structure of each temporary plugging agent particle is more compact and the structural connection is stronger. When the granulated temporary plugging agent particles are used, firstly, the water-soluble polymer swells upon contact with water. The montmorillonite powder, encapsulated by heat-resistant starch, biodegradable fiber, and polyvinyl alcohol, crosslinks to form a rich three-dimensional system structure that serves as an adhesion framework. This allows the temporary plugging agent to temporarily plug the fractures at the desired location. As the fractures deepen and the temperature rises, the polyvinyl alcohol on the surface of the montmorillonite powder melts, releasing the montmorillonite powder. The montmorillonite powder absorbs water, causing the temporary plugging agent to expand secondary. This increases the volume of the plugging agent in the fracture-falling state, further enhancing its adhesion to the fracture and improving the plugging effect. Furthermore, since the heat-resistant starch and biodegradable fiber in the temporary plugging agent are both biodegradable, the recovery effect on the reservoir can be improved.

[0034] Before preparing the temporary plugging agent, heat-resistant starch needs to be prepared first, which is obtained by the following method: Starch and water are mixed to obtain a dispersion; Adjust the pH of the dispersion to neutral to obtain the pre-reaction solution; The pre-reaction liquid and crosslinking agent are mixed and reacted for the first time at 40-60℃. Then, the system after the first mixing reaction and the esterifying agent are mixed and reacted for the second time at 40-70℃. Finally, the system after the second mixing reaction is dried and pulverized to obtain heat-resistant starch.

[0035] Crosslinking reactions are typically conducted at 40-60℃, where most crosslinking agents exhibit good reactivity, completing the reaction within a reasonable timeframe without causing excessive side reactions due to high temperatures. This temperature range is relatively mild, placing less emphasis on the high-temperature resistance of equipment, which helps reduce production costs. However, excessively high temperatures may increase the likelihood of side reactions, such as starch degradation. Therefore, when conducting crosslinking reactions at this temperature, more stringent control of reaction conditions is required, including reaction time and the amount of crosslinking agent used.

[0036] Starch esterification is carried out at 40-70℃. Within this temperature range, the activity of the esterifying agent and starch molecules is significantly enhanced, accelerating the reaction. As the temperature increases, molecular motion intensifies, and the collision frequency between the esterifying agent and the hydroxyl groups on the starch molecules increases, which is conducive to the formation of ester bonds. At the same time, most starches maintain good stability at this temperature and will not undergo excessive degradation or other side reactions due to excessively high temperatures.

[0037] When using esterifying agents with low reactivity, or when a high degree of substitution in esterified starch needs to be obtained in a shorter time, the temperature can be appropriately increased to 60-70℃. However, at this temperature, strict control of the reaction conditions is required to prevent adverse effects such as excessive starch decomposition.

[0038] Reaction characteristics: High temperatures provide more energy for the reaction, encouraging less reactive esterifying agents to participate. However, excessively high temperatures also increase the likelihood of side reactions such as starch chain breakage and decomposition. Furthermore, high temperatures may require more precise adjustments to other conditions such as pH and reaction time to ensure successful esterification and stable product quality.

[0039] Specifically, the mass ratio of starch, crosslinking agent, and esterifying agent is (90–100):(1.5–2.0):(4–5). Starch, as the basic component, dominates within this ratio range. This ensures that the final product retains the essential properties of starch, such as processability under appropriate conditions, a certain degree of hydrophilicity, or solubility in specific environments. The higher starch content also provides sufficient material basis for the entire system to construct a stable structure, as there are numerous interaction sites between starch molecules and with other components, which facilitates the formation of an effective crosslinking and esterification network.

[0040] An appropriate amount of crosslinking agent (1.5 ~ 2.0) is needed to form a suitable number of crosslinking bonds between starch molecules within this specific mass ratio range. If the amount of crosslinking agent is too small, insufficient crosslinking points will be formed, and the connections between starch molecules will not be tight enough. Under high temperature or stress conditions, the molecular chains are prone to relative sliding, leading to a decrease in the material's heat resistance, stability, and other properties. On the other hand, excessive crosslinking agent may lead to over-crosslinking, reducing the flexibility of the starch molecular chains and making the material brittle and hard. This may affect its processing performance and effectiveness in some applications. For example, in situations where a certain degree of plasticity is required for the temporary plugging agent, excessive crosslinking will make it difficult for it to adapt to crack shapes.

[0041] A suitable amount of esterifying agent (4-5g) can introduce appropriate ester groups onto starch molecules. Appropriate ester groups can alter the physical and chemical properties of starch, such as improving its hydrophobicity and compatibility with certain organic solvents, further enhancing the material's heat resistance. If the amount of esterifying agent is insufficient, too few ester groups will be introduced, resulting in minimal improvement in starch properties; while excessive esterifying agent may cause over-esterification of starch molecules, leading to unnecessary side reactions such as starch chain breakage or the generation of excessive impurities, affecting product quality and performance.

[0042] Crosslinking and esterification reactions work together in a specific ratio to form a stable chemical structure on starch molecules. The network structure formed by crosslinking, together with the functional groups introduced by esterification, enhances the heat resistance of starch. In high-temperature environments, this synergistic effect prevents the thermal decomposition and structural collapse of starch molecules, allowing the material to maintain good sealing performance or other application properties under high-temperature conditions. Simultaneously, this structure also improves the material's stability in complex environments, such as resistance to chemical corrosion and changes in physical stress.

[0043] Specifically, the crosslinking agent is trimetaphosphate, phosphorus oxychloride, pyrophosphate, or tripolyphosphate; the esterifying agent is an acid anhydride compound.

[0044] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0045] Example 1 This embodiment provides a gas reservoir fracture mixed temporary plugging agent, comprising the following components in parts by weight: Two parts of polyacrylamide; 5 parts heat-resistant starch; 5 parts polyvinyl alcohol fiber; Five parts of polyvinyl alcohol-coated montmorillonite powder; 100 portions of water.

[0046] like Figure 1 As shown in the figure, this embodiment also provides a method for preparing a gas reservoir fracture mixed temporary plugging agent, the steps of which are as follows: S1. Add 100 parts of water to a mixing container, then add 2 parts of polyacrylamide, and stir for 15 minutes at a controlled temperature of 45℃ and a speed of 120-180r / min to form a mixed emulsion. S2. Then add 5 parts of heat-resistant starch, and stir for 20 minutes at a controlled temperature of 45℃ and a speed of 220r / min to obtain a mixed system. S3. After stirring at 45℃ and 220r / min for 10 minutes, add 5 parts of polyvinyl alcohol-coated montmorillonite powder mixture to the mixture. After stirring at 45℃ and 320r / min for 60 minutes, a viscous emulsion with a network skeleton with nodes is formed, which is the temporary plugging agent solution. S4. Dry the temporary plugging agent solution in a vacuum environment at a controlled temperature of 45℃ for 5 hours to form a block temporary plugging agent. Then, cut the block plugging agent into granular temporary plugging agent.

[0047] The granular temporary plugging agent prepared in this embodiment was tested at an oilfield depth temperature of 150°C. The plugging pressure was 45 MPa / M, the plugging rate was 98.7%, and the recovery rate was 99.8%.

[0048] Example 2 This embodiment two provides a gas reservoir fracture mixed temporary plugging agent, comprising the following components in parts by weight: 4 parts polyacrylamide; 15 parts heat-resistant starch; 10 parts modified polyester fiber; Six parts of polyvinyl alcohol-coated montmorillonite powder; 85 parts water.

[0049] This second embodiment also provides a method for preparing a mixed temporary plugging agent for gas reservoir fractures, the preparation steps of which are as follows: S1. Add 85 parts of water to a mixing container, then add 4 parts of polyacrylamide, and stir for 12-15 minutes at a controlled temperature of 45℃ and a speed of 200r / min to form a mixed emulsion. S2. Then add 15 parts of heat-resistant starch, and stir for 15-20 minutes at a controlled temperature of 45℃ and a speed of 180r / min. Then add 10 parts of modified polyester fiber to obtain a mixed system. S3. After stirring at 45℃ and 240r / min for 5 minutes, add 6 parts of polyvinyl alcohol-coated montmorillonite powder mixture to the mixture. After stirring at 45℃ and 340r / min for 70 minutes, a viscous emulsion with a network skeleton with nodes is formed, which is the temporary plugging agent solution. S4. The temporary plugging agent solution is dried in a vacuum environment at a controlled temperature of 45℃ for 4.5 hours to form a block-shaped temporary plugging agent. The block-shaped plugging agent is then granulated to form a particulate temporary plugging agent.

[0050] The temporary plugging agent prepared in this embodiment was tested at an oilfield depth temperature of 155℃, and the plugging pressure was 46 MPa / M, the plugging rate was 99.0%, and the recovery rate was 99.1%.

[0051] Example 3 This embodiment three provides a mixed-type temporary plugging agent for gas reservoir fractures, wherein the mixed-type temporary plugging agent comprises the following components in parts by weight: 8 parts of polyacrylamide; 22 parts heat-resistant starch; 15 parts polyurethane fiber; Eight parts of a mixture of polyvinyl alcohol-coated montmorillonite powder; 60 parts water.

[0052] This embodiment also provides a method for preparing a mixed temporary plugging agent for gas reservoir fractures, the preparation steps of which are as follows: S1. Add 60 parts of water to a mixing container, then add 8 parts of polyacrylamide, and stir for 18 minutes at a controlled temperature of 45℃ and a speed of 220r / min to form a mixed emulsion. S2. Then add 22 parts of heat-resistant starch, and stir for 25 minutes at a controlled temperature of 45℃ and a speed of 200r / min to obtain a mixed system. S3. After stirring at 45℃ and 180r / min for 8 minutes, add 8 parts of the montmorillonite powder mixture coated with polyvinyl alcohol. After stirring at 45℃ and 340r / min for 80 minutes, a viscous emulsion with a network skeleton with nodes is formed, which is the temporary plugging agent solution. S4. The temporary plugging agent solution is dried in a vacuum environment at a controlled temperature of 45℃ for 4 hours to form a block temporary plugging agent. The block plugging agent is then granulated to form a particulate temporary plugging agent.

[0053] The temporary plugging agent prepared in this embodiment was tested at an oilfield depth temperature of 160℃, and the plugging pressure was 48 MPa / M, the plugging rate was 99.7%, and the recovery rate was 98.7%.

[0054] Example 4 This embodiment four provides a mixed-type temporary plugging agent for gas reservoir fractures, wherein the mixed-type temporary plugging agent comprises the following components in parts by weight: 10 parts of polyacrylamide; 30 parts heat-resistant starch; 10 parts of polyurethane fiber 10 parts of polyvinyl alcohol fiber; 10 parts of a mixture of polyvinyl alcohol-coated montmorillonite powder; 30 parts water.

[0055] This embodiment four also provides a method for preparing a mixed temporary plugging agent for gas reservoir fractures, wherein the preparation steps are as follows: S1. Add 30 parts of water to a mixing container, then add 10 parts of polyacrylamide, and stir for 20 minutes at a controlled temperature of 45℃ and a speed of 240r / min to form a mixed emulsion. S2. Then add 30 parts of heat-resistant starch, and stir for 30 minutes at a controlled temperature of 45℃ and a speed of 260r / min. Then add 10 parts of polyurethane fiber and 10 parts of polyvinyl alcohol fiber to obtain a mixed system. S3. After stirring at a controlled temperature of 45℃ and a rotation speed of 260r / min for 15 minutes, add 10 parts of the polyvinyl alcohol-coated montmorillonite powder mixture to the mixture. After stirring at a controlled temperature of 45℃ and a rotation speed of 350r / min for 100 minutes, a viscous emulsion with a network skeleton with nodes is formed, which is the temporary plugging agent solution. S4. The temporary plugging agent solution is dried in a vacuum environment at a controlled temperature of 45℃ for 3.5h to form a block temporary plugging agent. The block plugging agent is then granulated to form a particulate temporary plugging agent.

[0056] The temporary plugging agent prepared in this embodiment was tested at a depth temperature of 160°C in an oilfield. The plugging pressure was 52 MPa / M, the plugging rate was 100%, and the recovery rate was 98.2%.

[0057] Example 5 This embodiment five provides a mixed-type temporary plugging agent for gas reservoir fractures, wherein the mixed-type temporary plugging agent comprises the following components in parts by weight: 5 parts polyacrylamide; 20 parts heat-resistant starch; 5 parts polyurethane fiber 3 parts polyvinyl alcohol fiber; Seven parts of a mixture of polyvinyl alcohol-coated montmorillonite powder; 50 parts water.

[0058] This fifth embodiment also provides a method for preparing a mixed temporary plugging agent for gas reservoir fractures, wherein the preparation steps are as follows: S1. Add 50 parts of water to a mixing container, then add 5 parts of polyacrylamide, and stir for 20 minutes at a controlled temperature of 45℃ and a speed of 180r / min to form a mixed emulsion. S2. Then add 20 parts of heat-resistant starch, and stir for 30 minutes at a controlled temperature of 45℃ and a speed of 260r / min. Then add 5 parts of polyurethane fiber and 3 parts of polyvinyl alcohol fiber to obtain a mixed system. S3. After stirring at a controlled temperature of 45℃ and a rotation speed of 260r / min for 15 minutes, add 7 parts of polyvinyl alcohol-coated montmorillonite powder mixture to the mixture. After stirring at a controlled temperature of 45℃ and a rotation speed of 350r / min for 100 minutes, a viscous emulsion with a network skeleton with nodes is formed, which is the temporary plugging agent solution. S4. The temporary plugging agent solution is dried in a vacuum environment at a controlled temperature of 45℃ for 3.5h to form a block temporary plugging agent. The block plugging agent is then granulated to form a particulate temporary plugging agent.

[0059] The temporary plugging agent prepared in this embodiment was tested at a depth temperature of 160℃ in an oilfield. The plugging pressure was 50 MPa / M, the plugging rate was 100%, and the recovery rate was 97%.

[0060] Example 6 This embodiment six provides a mixed-type temporary plugging agent for gas reservoir fractures, wherein the mixed-type temporary plugging agent comprises the following components in parts by weight: 6 parts polyacrylamide; 25 parts heat-resistant starch; 18 parts polyurethane fiber; Nine parts of a mixture of polyvinyl alcohol-coated montmorillonite powder; 70 parts water.

[0061] This embodiment six also provides a method for preparing a mixed temporary plugging agent for gas reservoir fractures, wherein the preparation steps are as follows: S1. Add 70 parts of water to a mixing container, then add 6 parts of polyacrylamide, and stir for 20 minutes at a controlled temperature of 45℃ and a speed of 180-240r / min to form a mixed emulsion. S2. Then add 25 parts of heat-resistant starch, and stir for 25 minutes at a controlled temperature of 45℃ and a speed of 260r / min. Then add 18 parts of polyurethane fiber to obtain a mixed system. S3. After stirring at a controlled temperature of 45℃ and a rotation speed of 260r / min for 15 minutes, add 9 parts of the polyvinyl alcohol-coated montmorillonite powder mixture to the mixture. After stirring at a controlled temperature of 45℃ and a rotation speed of 350r / min for 100 minutes, a viscous emulsion with a network skeleton with nodes is formed, which is the temporary plugging agent solution. S4. The temporary plugging agent solution is dried in a vacuum environment at a controlled temperature of 45℃ for 3.5h to form a block temporary plugging agent. The block plugging agent is then granulated to form a particulate temporary plugging agent.

[0062] The temporary plugging agent prepared in this embodiment was tested at a depth temperature of 160℃ in the oilfield. The plugging pressure was 55 MPa / M, the plugging rate was 100%, and the recovery rate was 98.5%.

[0063] As can be seen from Examples 1 to 6 above, the temporary plugging agent of the present invention has a temperature resistance ≥150℃ and a pressure resistance ≥45MPA.

[0064] In summary, comparing the temporary plugging agents prepared in the various embodiments, it is evident that as the amount of water-soluble polymer, heat-resistant starch, biodegradable fiber, and strength improver added increases, while the amount of water decreases, the required stirring speed increases due to the increased solution viscosity, thus increasing the requirements for production equipment. Correspondingly, the required drying time decreases, reducing the preparation time. At the same time, the corresponding plugging pressure and plugging rate increase, while the degradation rate increases with the increase of montmorillonite powder, and the degradation performance decreases.

[0065] The entire preparation process takes into account the synergistic effects of multiple components, enabling the prepared temporary plugging agent to adapt to the complex environment of gas reservoir fractures. Heat-resistant starch can withstand high-temperature conditions, while strength improvers and fiber-reinforced structures can adapt to complex conditions such as high pressure and high flow rates in fractures, thus improving the applicability of the temporary plugging agent under different gas reservoir conditions.

[0066] The use of biodegradable fibers allows the temporary plugging agent to degrade naturally under certain conditions after the plugging task is completed. This reduces the long-term impact on the gas reservoir environment, meets environmental protection requirements, and is beneficial to subsequent gas reservoir exploitation and production activities, avoiding long-term adverse effects on formation permeability and other aspects caused by residual temporary plugging agents.

[0067] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A mixed-type temporary plugging agent for gas reservoir fractures, characterized in that, Based on parts by mass, it includes the following components: 2-10 parts water-soluble polymer, 5-30 parts heat-resistant starch, 5-20 parts biodegradable fiber, 5-10 parts strength improver, and 30-100 parts water; The strength improver is montmorillonite powder coated with polyvinyl alcohol.

2. The gas reservoir fracture mixed temporary plugging agent according to claim 1, characterized in that, The water-soluble polymer is polyacrylamide and / or 2-acrylamido-2-methylpropanesulfonic acid; Polyacrylamide has a molecular weight of 11 million to 25 million.

3. The gas reservoir fracture mixed temporary plugging agent according to claim 1, characterized in that, The biodegradable fibers include one or more of polyvinyl alcohol fibers, modified polyester fibers, and polyurethane fibers.

4. The gas reservoir fracture mixed temporary plugging agent according to claim 1, characterized in that, The strength improver is a mixture formed by mixing and stirring montmorillonite powder and polyvinyl alcohol, followed by drying and pulverizing.

5. The gas reservoir fracture mixed temporary plugging agent according to claim 1, characterized in that, The heat-resistant starch has a particle size of not less than 40 mesh.

6. The gas reservoir fracture mixed temporary plugging agent according to claim 1, characterized in that, The specific method for preparing the heat-resistant starch is as follows: Starch and water are mixed to obtain a dispersion; Adjust the pH of the dispersion to neutral to obtain the pre-reaction solution; The pre-reaction liquid and crosslinking agent are mixed and reacted for the first time at 40-60℃. Then, the system after the first mixing reaction and the esterifying agent are mixed and reacted for the second time at 40-70℃. Finally, the system after the second mixing reaction is dried and pulverized to obtain heat-resistant starch.

7. A gas reservoir fracture mixed temporary plugging agent according to claim 6, characterized in that, The mass ratio of starch, crosslinking agent and esterifying agent is (90-100):(1.5-2.0):(4-5).

8. A gas reservoir fracture mixed temporary plugging agent according to claim 6, characterized in that, The crosslinking agent is trimetaphosphate, phosphorus oxychloride, pyrophosphate, or tripolyphosphate; The esterifying agent is an acid anhydride compound.

9. A method for preparing a gas reservoir fracture mixed temporary plugging agent according to any one of claims 1-8, characterized in that, Includes the following steps: S1. First, the water-soluble polymer is dissolved in water and then stirred and mixed to form a mixed emulsion. S2. Add heat-resistant starch to the mixed emulsion and stir to mix; during the stirring process, add biodegradable fiber so that the biodegradable fiber is interwoven in the gelatinous starch emulsion to obtain a mixed system; S3. Add strength improver to the mixture and stir to form a viscous emulsion with a network skeleton with nodes; S4. Vacuum dry the viscous emulsion to form a blocky solid, and obtain a gas reservoir fracture mixed temporary plugging agent.

10. The method for preparing the gas reservoir fracture mixed temporary plugging agent according to claim 9, characterized in that, Pulverized or granulated solids are crushed to form granular temporary plugging agents.

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