High-pressure-bearing fiber composite temporary plugging agent for oil well fracturing and preparation method

Abstract

The invention relates to the technical field of oilfield exploitation, in particular to a high-pressure-bearing fiber composite temporary plugging agent for oil well fracturing and a preparation method. The temporary plugging agent is prepared from the following components in parts by weight: 10 to 15 parts of modified polyvinyl alcohol fiber, 1 to 5 parts of polyacrylamide, 15 to 25 parts of calcium carbonate particles and 60 to 75 parts of carrying liquid. The modified polyvinyl alcohol fiber in the temporary plugging agent has good adsorbability, after being injected into a stratum, the modified polyvinyl alcohol fiber tightly adheres to the interior of a smooth pore channel and then is matched with other components to be bent and wound in the pore channel to form a compact filter cake to plug the pore channel, and the modified polyvinyl alcohol fiber has good strength and toughness; the plugging strength of the temporary plugging agent can be ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of oilfield exploitation, and particularly to a high-pressure-bearing fiber composite temporary plugging agent for oil well fracturing and a preparation method thereof. Background Art

[0002] During the development of low-permeability oil and gas reservoirs, temporary plugging fracturing is a commonly used technique in oil and gas field development. It aims to temporarily block specific formations or fractures, guide the fracturing fluid into the target area, thereby optimizing the fracturing effect and increasing oil and gas production. The main method is to inject a temporary plugging agent to block the sections or fractures that do not need to be fractured, forcing the fracturing fluid to bypass the blocked area and enter the unblocked target section. After the fracturing of the target section is completed, the temporary plugging agent is removed through chemical reactions or physical actions to restore the permeability of the non-target area.

[0003] Currently, the commonly used temporary plugging agents in oilfields are fibers and water-soluble particles of different sizes. Utilizing the principle that the temporary plugging agent preferentially enters in the direction with less resistance and accumulates by friction on the inner wall surface of the fracture, the formation pores are blocked. However, the inner walls of some pores are relatively smooth, and the existing temporary plugging agents cannot effectively adhere in the smooth pores, resulting in insufficient plugging strength and the easy failure of the temporary plugging agent during fracturing. Summary of the Invention

[0004] In order to solve the above problems, the present invention provides a high-pressure-bearing fiber composite temporary plugging agent for oil well fracturing and a preparation method thereof.

[0005] The technical solution of the present invention is: a high-pressure-bearing fiber composite temporary plugging agent for oil well fracturing, by weight, includes the following components: 10 - 15 parts of modified polyvinyl alcohol fiber, 1 - 5 parts of polyacrylamide, 15 - 25 parts of calcium carbonate particles, and 60 - 75 parts of carrier fluid.

[0006] Note: The modified polyvinyl alcohol fiber in the above temporary plugging agent has good adsorption properties. After being injected into the formation, the modified polyvinyl alcohol fiber tightly adheres in the smooth pore channels, and then bends and winds with other components in the pore channels to form a dense filter cake to block the pore channels. Moreover, the modified polyvinyl alcohol fiber has good strength and toughness, which can ensure the plugging strength of the temporary plugging agent.

[0007] Further, the carrier fluid is an aqueous xanthan gum solution with a mass concentration of 0.4 - 0.8%.

[0008] Note: The above carrier fluid has good fluidity and dispersibility. The modified polyvinyl alcohol fiber can be evenly dispersed in the carrier fluid and effectively reach the formation pores under the action of the carrier fluid.

[0009] Further, the preparation method of the modified polyvinyl alcohol fiber includes the following steps:

[0010] S1. Add sodium styrene sulfonate into dichloromethane and stir for 5 - 10 min to obtain mixture A. Among them, the mass ratio of sodium styrene sulfonate to dichloromethane is 1:4 - 5;

[0011] S2. Add triethoxysilane into mixture A at 0 - 10 °C, then heat mixture A until the temperature of mixture A reaches 50 - 60 °C, add a catalyst into mixture A, then stop heating. Wait until the temperature of mixture A drops to 20 - 30 °C to obtain mixture B. Among them, the addition amount of triethoxysilane is 15 - 20% of the initial mass of mixture A, and the addition amount of the catalyst accounts for 1 - 2% of the initial mass of mixture A;

[0012] S3. Immerse polyvinyl alcohol fiber into mixture B, heat mixture B under stirring. During the heating process, every time the temperature of mixture B rises by 20 - 25 °C, add an initiator into mixture B once. After the addition of the initiator is completed, stop heating and let it stand for 10 - 15 min, then resume heating until mixture B reaches 70 - 80 °C and keep it warm for 3 - 5 h. Among them, the addition amount of polyvinyl alcohol fiber accounts for 10 - 15% of the initial mass of mixture B, and the single addition amount of the initiator accounts for 0.3 - 0.5% of the initial mass of mixture B;

[0013] S4. After the heat preservation is completed, filter mixture B to take out the polyvinyl alcohol fiber, then wash and dry it to obtain the modified polyvinyl alcohol fiber.

[0014] Note: Through the reaction of triethoxysilane and sodium styrene sulfonate above, a silyl group is introduced onto the benzene ring of sodium styrene sulfonate, and then sodium polystyrene sulfonate is grafted onto the main chain of polyvinyl alcohol fiber through a free radical polymerization reaction, improving the adsorption property of polyvinyl alcohol fiber, enabling calcium carbonate particles to be well embedded with the modified polyvinyl alcohol fiber, ensuring the plugging effect, and the modified polyvinyl alcohol fiber has better flexibility and can be effectively wound together to improve the plugging strength.

[0015] Further, in step S2, the catalyst is triethylamine.

[0016] Note: The above catalyst can effectively improve the reaction efficiency of triethoxysilane and sodium styrene sulfonate, ensuring that sodium styrene sulfonate can fully react.

[0017] Further, in step S3, before the polyvinyl alcohol fiber is immersed in mixture B, it is subjected to plasma treatment by a plasma treatment device. The power during plasma treatment is 100 - 200 W, the treatment time is 5 - 8 min, and the working gas is oxygen.

[0018] Note: Plasma treatment can improve the reaction activity of polyvinyl alcohol fiber, enabling sodium styrene sulfonate to be fully grafted onto the main chain of polyvinyl alcohol fiber.

[0019] Further, in step S3, the initiator is benzoyl peroxide or ammonium persulfate.

[0020] Explanation: The above initiator can provide free radicals, causing sodium styrene sulfonate to undergo free radical polymerization reaction, ensuring the conversion rate of the modified polyvinyl alcohol fiber.

[0021] Further, in step S4, the washing method is to rinse with absolute ethanol.

[0022] Explanation: Rinsing with absolute ethanol can remove the by-products attached to the surface of the modified polyvinyl alcohol fiber, ensuring the dispersibility of the modified polyvinyl alcohol fiber.

[0023] On the other hand, the preparation method of the high-pressure-bearing fiber composite temporary plugging agent for oil well fracturing includes the following steps:

[0024] 1) According to the said parts by weight, add calcium carbonate particles into the carrier fluid, and then stir the carrier fluid at a rate of 330 - 350 r / min. During the stirring process, gradually add the modified polyvinyl alcohol fiber into the carrier fluid, and the addition amount of the modified polyvinyl alcohol fiber per minute accounts for 2 - 6% of its total mass;

[0025] 2) After all the modified polyvinyl alcohol fibers are added to the carrier fluid, heat the carrier fluid to 40 - 50 °C, and add polyacrylamide to the carrier fluid, and continue to stir at a rate of 200 - 240 r / min for 1 - 2 h to obtain the temporary plugging agent.

[0026] Explanation: By gradually adding the modified polyvinyl alcohol fiber in the above preparation method, the modified polyvinyl alcohol fiber can be fully dispersed in the carrier fluid, ensuring the uniformity of the temporary plugging agent. Then, by adding polyacrylamide to increase the viscosity of the temporary plugging agent, the finally prepared temporary plugging agent has good plugging performance.

[0027] The beneficial effects of the present invention are:

[0028] (1) The modified polyvinyl alcohol fiber in the temporary plugging agent of the present invention has good adsorption property. After being injected into the formation, the modified polyvinyl alcohol fiber adheres tightly to the smooth pore channels, and then bends and winds in the pore channels in cooperation with other components to form a dense filter cake to plug the pore channels. Moreover, the modified polyvinyl alcohol fiber has good strength and toughness, which can ensure the plugging strength of the temporary plugging agent.

[0029] (2) In the present invention, triethoxysilane reacts with sodium styrene sulfonate to introduce a silyl group onto the benzene ring of sodium styrene sulfonate, and then sodium polystyrene sulfonate is grafted onto the main chain of polyvinyl alcohol fiber through a free radical polymerization reaction, improving the adsorption property of the polyvinyl alcohol fiber, enabling calcium carbonate particles to be well embedded with the modified polyvinyl alcohol fiber, ensuring the plugging effect, and the modified polyvinyl alcohol fiber has better flexibility and can be effectively wound together to improve the plugging strength.

[0030] (3) In the preparation method of the present invention, the modified polyvinyl alcohol fiber is gradually added, enabling the modified polyvinyl alcohol fiber to be fully dispersed in the carrier fluid, ensuring the uniformity of the temporary plugging agent, and then polyacrylamide is used to increase the viscosity of the temporary plugging agent, so that the finally prepared temporary plugging agent has good plugging performance. Specific Embodiments

[0031] To further elaborate on the methods adopted and the effects achieved by the present invention, the technical solutions of the present invention will be clearly and completely described below in combination with experiments.

[0032] Example 1: The content recorded in this example is a high-pressure-bearing fiber composite temporary plugging agent for oil well fracturing. By weight, it includes the following components: 12 parts of modified polyvinyl alcohol fiber, 3 parts of polyacrylamide, 20 parts of calcium carbonate particles, and 68 parts of carrier fluid; among them, the carrier fluid is an aqueous xanthan gum solution with a mass concentration of 0.6%, and the particle size of the calcium carbonate particles is 5 - 20 μm;

[0033] The preparation method of the modified polyvinyl alcohol fiber includes the following steps:

[0034] S1. Add sodium styrene sulfonate into dichloromethane and stir for 8 min to obtain a mixed solution A; the mass ratio of sodium styrene sulfonate to dichloromethane is 1:4.5;

[0035] S2. Add triethoxysilane to the mixed solution A at 5°C, then heat the mixed solution A until the temperature of the mixed solution A reaches 55°C, add a catalyst to the mixed solution A, then stop heating, and wait for the temperature of the mixed solution A to drop to 25°C to obtain a mixed solution B; among them, the addition amount of triethoxysilane is 18% of the initial mass of the mixed solution A, the addition amount of the catalyst accounts for 1.5% of the initial mass of the mixed solution A, and the catalyst is triethylamine;

[0036] S3. Immerse the polyvinyl alcohol fibers in the mixed liquid B, heat the mixed liquid B under stirring, and add an initiator to the mixed liquid B once every time the temperature of the mixed liquid B rises by 22 °C during the heating process. After the addition of the initiator is completed, stop heating and let it stand for 12 min, then resume heating until the mixed liquid B reaches 75 °C and keep it warm for 4 h. Among them, the addition amount of the polyvinyl alcohol fibers accounts for 12% of the initial mass of the mixed liquid B, the initiator is benzoyl peroxide, and the single addition amount of the initiator accounts for 0.4% of the initial mass of the mixed liquid B.

[0037] Among the polyvinyl alcohol fibers, 60% have a length of 2 - 4 mm, 25% have a length of 4 - 8 mm, and 15% have a length of 8 - 10 mm.

[0038] Before the polyvinyl alcohol fibers are immersed in the mixed liquid B, they are subjected to plasma treatment using a plasma treatment device. The power during plasma treatment is 150 W, the treatment time is 6.5 min, and the working gas is oxygen.

[0039] After the heat preservation is completed, filter the mixed liquid B to remove the polyvinyl alcohol fibers, and then wash and dry them to obtain the modified polyvinyl alcohol fibers. Among them, the washing method is to rinse with absolute ethanol.

[0040] On the other hand, the preparation method of the above-mentioned temporary plugging agent includes the following steps:

[0041] 1) According to the said weight parts, add calcium carbonate particles into the carrier liquid, and then stir the carrier liquid at a rate of 340 r / min. During the stirring process, gradually add the modified polyvinyl alcohol fibers to the carrier liquid. The addition amount of the modified polyvinyl alcohol fibers per minute accounts for 4% of its total mass.

[0042] 2) After all the modified polyvinyl alcohol fibers are added to the carrier liquid, heat the carrier liquid to 45 °C, and add polyacrylamide to the carrier liquid, and continue to stir at a rate of 220 r / min for 1.5 h to obtain the temporary plugging agent.

[0043] Example 2: This example is basically the same as Example 1, except that the temporary plugging agent, by weight parts, includes the following components: 10 parts of modified polyvinyl alcohol fibers, 1 part of polyacrylamide, 15 parts of calcium carbonate particles, and 60 parts of carrier liquid.

[0044] Example 3: This example is basically the same as Example 1, except that the temporary plugging agent, by weight parts, includes the following components: 15 parts of modified polyvinyl alcohol fibers, 5 parts of polyacrylamide, 25 parts of calcium carbonate particles, and 75 parts of carrier liquid.

[0045] Example 4: This example is basically the same as Example 1, except that triethoxysilane is added to the mixed liquid A at 0 °C.

[0046] Example 5: This example is basically the same as Example 1, except that triethoxysilane is added to the mixed solution A at 10°C.

[0047] Example 6: This example is basically the same as Example 1, except that the addition amount of triethoxysilane is 15% of the initial mass of the mixed solution A.

[0048] Example 7: This example is basically the same as Example 1, except that the addition amount of triethoxysilane is 20% of the initial mass of the mixed solution A.

[0049] Example 8: This example is basically the same as Example 1, except that the catalyst is added to the mixed solution A until the temperature of the mixed solution A reaches 50°C.

[0050] Example 9: This example is basically the same as Example 1, except that the catalyst is added to the mixed solution A until the temperature of the mixed solution A reaches 60°C.

[0051] Example 10: This example is basically the same as Example 1, except that the addition amount of the catalyst accounts for 1% of the initial mass of the mixed solution A.

[0052] Example 11: This example is basically the same as Example 1, except that the addition amount of the catalyst accounts for 2% of the initial mass of the mixed solution A.

[0053] Example 12: This example is basically the same as Example 1, except that during the heating process, every time the temperature of the mixed solution B rises by 20°C, an initiator is added to the mixed solution B.

[0054] Example 13: This example is basically the same as Example 1, except that during the heating process, every time the temperature of the mixed solution B rises by 25°C, an initiator is added to the mixed solution B.

[0055] Example 14: This example is basically the same as Example 1, except that the single addition amount of the initiator accounts for 0.3% of the initial mass of the mixed solution B.

[0056] Example 15: This example is basically the same as Example 1, except that the single addition amount of the initiator accounts for 0.5% of the initial mass of the mixed solution B.

[0057] Example 16: This example is basically the same as Example 1, except that the addition amount of polyvinyl alcohol fiber accounts for 10% of the initial mass of the mixed solution B.

[0058] Example 17: This example is basically the same as Example 1, except that the addition amount of polyvinyl alcohol fiber accounts for 15% of the initial mass of the mixed solution B.

[0059] Example 18: This example is basically the same as Example 1, except that the power during plasma treatment is 100 W.

[0060] Example 19: This example is basically the same as Example 1, except that the power during plasma treatment is 200 W.

[0061] Example 20: This example is basically the same as Example 1, except that the addition amount of modified polyvinyl alcohol fiber per minute accounts for 2% of its total mass.

[0062] Example 21: This example is basically the same as Example 1, except that the addition amount of modified polyvinyl alcohol fiber per minute accounts for 6% of its total mass.

[0063] Comparative Example 1: Taking Example 1 as a reference, the modified polyvinyl alcohol fiber is replaced with polyvinyl alcohol fiber.

[0064] Comparative Example 2: Taking Example 1 as a reference, triethoxysilane is not added to the mixed solution A.

[0065] Comparative Example 3: Taking Example 1 as a reference, the initiator is added to the mixed solution B at one time.

[0066] Comparative Example 4: Taking Example 1 as a reference, the polyvinyl alcohol fiber is not subjected to plasma treatment.

[0067] Experimental Example: In order to explore the influence of the parameters of each example on the performance of the temporary plugging agent, the artificial filling core method is adopted. The temporary plugging agent prepared in each example is injected into the artificial core mold for plugging. After the plugging is completed, the breakthrough pressure is tested. The specific exploration is as follows:

[0068] Experimental Example 1. Explore the influence of the composition of the temporary plugging agent on the performance of the temporary plugging agent

[0069] Taking Examples 1 to 3 and Comparative Example 1 as experimental comparisons, the breakthrough pressures of the temporary plugging agent under different compositions are shown in Table 1 below:

[0070] Table 1 Breakthrough pressures of the temporary plugging agent under different compositions

[0071] Group Breakthrough Pressure (MPa) Example 1 22.6 Example 2 21.2 Example 3 20.6 Comparative Example 1 14.7

[0072] It can be seen from the data in Table 1 that compared with Examples 1, 2, and 3: the breakthrough pressure of the temporary plugging agent in Example 1 is the highest, indicating that the performance of the temporary plugging agent in Example 1 is the best. This may be because the internal structure of the temporary plugging agent in Example 1 is more compact after plugging. Therefore, the composition of the temporary plugging agent selected in Example 1 is better;

[0073] Example 1 compared with Comparative Example 1: After replacing the modified polyvinyl alcohol fiber with polyvinyl alcohol fiber, the breakthrough pressure of the temporary plugging agent decreased significantly. This may be because the modified polyvinyl alcohol fiber can be fully wound for plugging. Therefore, the composition of the temporary plugging agent selected in Example 1 is more excellent.

[0074] Experimental Example 2. Explore the influence of the addition parameters of triethoxysilane on the performance of the temporary plugging agent

[0075] Using Example 1, Examples 4-7 and Comparative Example 2 as experimental comparisons, the breakthrough pressures under different addition parameters of triethoxysilane are shown in Table 2 below:

[0076] Table 2 Breakthrough pressures under different addition parameters of triethoxysilane

[0077]

[0078]

[0079] From the data in Table 2, it can be seen that when comparing Example 1, Examples 4 and 5: The breakthrough pressure of the temporary plugging agent in Example 1 is the highest, indicating that the performance of the temporary plugging agent in Example 1 is the best. This may be because triethoxysilane can be fully mixed with the mixed solution A at the initial temperature of the mixed solution A in Example 1. Therefore, the initial temperature of the mixed solution A selected in Example 1 is the best;

[0080] When comparing Example 1, Examples 6 and 7: As the addition amount of triethoxysilane increases, the breakthrough pressure of the temporary plugging agent gradually increases until the breakthrough pressure of the temporary plugging agent in Example 1 reaches the highest. As the addition amount of triethoxysilane continues to increase, the breakthrough pressure of the temporary plugging agent shows no obvious change. This may be because sodium styrenesulfonate has fully reacted. Therefore, considering from the cost perspective, the addition amount of triethoxysilane selected in Example 1 is the best;

[0081] Example 1 compared with Comparative Example 2: After not adding triethoxysilane to the mixed solution A, the breakthrough pressure of the temporary plugging agent decreased significantly. This may be because sodium styrenesulfonate failed to introduce a silyl group, resulting in that calcium carbonate particles cannot be fully embedded with the modified polyvinyl alcohol fiber. Therefore, the preparation method of the modified polyvinyl alcohol fiber selected in Example 1 is the best.

[0082] Experimental Example 3. Explore the influence of the addition parameters of the catalyst on the performance of the temporary plugging agent

[0083] Using Example 1, Examples 8-11 as experimental comparisons, the breakthrough pressures under different addition parameters of the catalyst are shown in Table 3 below:

[0084] Table 3 Breakthrough pressures under different addition parameters of the catalyst

[0085] Group Breakthrough Pressure (MPa) Example 1 22.6 Example 8 20.3 Example 9 20.1 Example 10 21.0 Example 11 22.9

[0086] As can be seen from the data in Table 3, comparing Examples 1, 8, and 9: The breakthrough pressure of the temporary plugging agent in Example 1 is the highest, indicating that the performance of the temporary plugging agent in Example 1 is the best. This may be because at the temperature of the mixed solution A when adding the catalyst in Example 1, the reaction between triethoxysilane and sodium styrene sulfonate is the most complete. Therefore, the temperature of the mixed solution A selected in Example 1 when adding the catalyst is the optimal one;

[0087] Comparing Examples 1, 10, and 11: As the catalyst addition amount increases, the breakthrough pressure of the temporary plugging agent gradually increases until the breakthrough pressure of the temporary plugging agent in Example 1 reaches the highest. As the catalyst addition amount continues to increase, the breakthrough pressure of the temporary plugging agent shows no obvious change. This may be because sodium styrene sulfonate has reacted sufficiently. Therefore, considering from the cost perspective, the catalyst addition amount selected in Example 1 is the optimal one.

[0088] Experimental Example 4. Explore the influence of the addition parameters of the initiator on the performance of the temporary plugging agent

[0089] Taking Example 1, Examples 12 - 15, and Comparative Example 3 as experimental comparisons, the breakthrough pressures under different addition parameters of the initiator are shown in Table 4 below:

[0090] Table 4 Breakthrough pressures under different addition parameters of the initiator

[0091] Group Breakthrough Pressure (MPa) Example 1 22.6 Example 12 21.5 Example 13 21.1 Example 14 21.6 Example 15 22.1 Comparative Example 3 19.4

[0092] As can be seen from the data in Table 4, comparing Examples 1, 12, and 13: The breakthrough pressure of the temporary plugging agent in Example 1 is the highest, indicating that the performance of the temporary plugging agent in Example 1 is the best. This may be because at the temperature increase range of the mixed solution B selected in Example 1, the initiator can generate sufficient free radicals, enabling sodium styrene sulfonate to fully undergo polymerization reaction. Therefore, the temperature increase range of the mixed solution B selected in Example 1 is the optimal one;

[0093] Comparing Examples 1, 14, and 15: The breakthrough pressure of the temporary plugging agent in Example 1 is the highest, indicating that the performance of the temporary plugging agent in Example 1 is the best. This may be because at the single - time addition amount of the initiator selected in Example 1, sodium styrene sulfonate can fully undergo polymerization reaction and there are fewer by - products. Therefore, the single - time addition amount of the initiator selected in Example 1 is the optimal one;

[0094] Comparing Example 1 with Comparative Example 3: After adding the initiator to the mixed solution B at one time, the breakthrough pressure of the temporary plugging agent decreases. This may be because adding the initiator at one time results in that polystyrene sulfonate fails to be fully grafted onto the modified polyvinyl alcohol fiber. Therefore, the addition method of the initiator selected in Example 1 is the optimal one.

[0095] Experimental Example 5. Explore the influence of the addition amount of polyvinyl alcohol fiber on the performance of the temporary plugging agent

[0096] Taking Example 1, Examples 16 - 17 as experimental comparisons, the breakthrough pressures at different addition amounts of polyvinyl alcohol fibers are shown in Table 5 below:

[0097] Table 5 Breakthrough Pressures at Different Addition Amounts of Polyvinyl Alcohol Fibers

[0098] Group Breakthrough Pressure (MPa) Example 1 22.6 Example 16 20.9 Example 17 21.3

[0099] From the data in Table 5, it can be seen that comparing Example 1, Examples 16, 17: The breakthrough pressure of the temporary plugging agent in Example 1 is the highest, indicating that the performance of the temporary plugging agent in Example 1 is the best. This may be because at the addition amount of polyvinyl alcohol fibers selected in Example 1, polystyrene sulfonate can be fully grafted onto the polyvinyl alcohol fibers. Therefore, the addition amount of polyvinyl alcohol fibers selected in Example 1 is the optimal one.

[0100] Experimental Example 6. Exploring the Influence of Plasma Treatment Parameters on the Performance of the Temporary Plugging Agent

[0101] Taking Example 1, Examples 18 - 21 and Comparative Example 4 as experimental comparisons, the breakthrough pressures under different plasma treatment parameters are shown in Table 6 below:

[0102] Table 6 Breakthrough Pressures under Different Plasma Treatment Parameters

[0103] Group Breakthrough Pressure (MPa) Example 1 22.6 Example 18 21.7 Example 19 21.9 Comparative Example 4 19.7

[0104] From the data in Table 6, it can be seen that comparing Example 1, Examples 18, 19: The breakthrough pressure of the temporary plugging agent in Example 1 is the highest, indicating that the performance of the temporary plugging agent in Example 1 is the best. This may be because at the plasma treatment power of Example 1, the surface activity of the polyvinyl alcohol fibers is the best and the damage to the polyvinyl alcohol fibers is relatively small. Therefore, the plasma treatment power selected in Example 1 is the optimal one;

[0105] Comparing Example 1 with Comparative Example 4: After not performing plasma treatment on the polyvinyl alcohol fibers, the breakthrough pressure of the temporary plugging agent decreases. This may be because plasma treatment can effectively improve the surface activity of the polyvinyl alcohol fibers, enabling polystyrene sulfonate to be fully grafted onto the polyvinyl alcohol fibers.

[0106] Experimental Example 7. Exploring the Influence of the Addition Rate of Modified Polyvinyl Alcohol Fibers on the Performance of the Temporary Plugging Agent

[0107] Taking Example 1, Examples 20 - 21 as experimental comparisons, the breakthrough pressures at different addition rates of modified polyvinyl alcohol fibers are shown in Table 7 below:

[0108] Table 7 Breakthrough Pressures at Different Addition Rates of Modified Polyvinyl Alcohol Fibers

[0109]

[0110]

[0111] As can be seen from the data in Table 7, comparing Examples 1, 20, and 21: The breakthrough pressure of the temporary plugging agent in Example 1 is the highest, indicating that the performance of the temporary plugging agent in Example 1 is the best. This may be because the composition of the temporary plugging agent is more uniform at the addition rate of the modified polyvinyl alcohol fiber in Example 1. Therefore, the addition rate of the modified polyvinyl alcohol fiber selected in Example 1 is the optimal one.

Claims

1. A high pressure fiber composite temporary plugging agent for oil well fracturing, characterized in that: The invention comprises the following components by weight: 10 to 15 parts of modified polyvinyl alcohol fiber, 1 to 5 parts of polyacrylamide, 15 to 25 parts of calcium carbonate particles and 60 to 75 parts of carrying liquid.

2. The high pressure-bearing fiber composite temporary plugging agent for oil well fracturing according to claim 1, characterized in that: The carrying liquid is a xanthan gum aqueous solution with a mass concentration of 0.4-0.8%.

3. The high pressure-bearing fiber composite temporary plugging agent for oil well fracturing according to claim 1, characterized in that: The preparation method of the modified polyvinyl alcohol fiber comprises the following steps: S1. Add sodium styrene sulfonate into dichloromethane and stir for 5 to 10 minutes to obtain a mixed solution A; wherein the mass ratio of sodium styrene sulfonate to dichloromethane is 1:4 to 5; S2, adding triethoxysilane to the mixed solution A at 0-10°C, then heating the mixed solution A until the temperature of the mixed solution A reaches 50-60°C, then adding a catalyst to the mixed solution A, then stopping the heating, and waiting for the temperature of the mixed solution A to drop to 20-30°C to obtain a mixed solution B; wherein the amount of triethoxysilane added is 15-20% of the initial mass of the mixed solution A, and the amount of the catalyst added is 1-2% of the initial mass of the mixed solution A; S3, immersing the polyvinyl alcohol fiber in the mixed solution B, heating the mixed solution B under stirring, adding an initiator to the mixed solution B once every time the temperature of the mixed solution B rises by 20-25°C during the heating process, stopping heating after the initiator is added, standing for 10-15 minutes, and then resuming heating until the mixed solution B reaches 70-80°C and keeping it warm for 3-5 hours; wherein, the amount of polyvinyl alcohol fiber added accounts for 10-15% of the initial mass of the mixed solution B, and the single amount of initiator added accounts for 0.3-0.5% of the initial mass of the mixed solution B; S4. After the heat preservation is completed, the mixed solution B is filtered to take out the polyvinyl alcohol fiber, and then washed and dried to obtain the modified polyvinyl alcohol fiber.

4. The high pressure-bearing fiber composite temporary plugging agent for oil well fracturing according to claim 1, characterized in that: In step S2, the catalyst is triethylamine.

5. The high pressure-bearing fiber composite temporary plugging agent for oil well fracturing according to claim 1, characterized in that: In step S3, the polyvinyl alcohol fiber is subjected to plasma treatment by a plasma treatment device before being immersed in the mixed solution B. The power of the plasma treatment is 100 to 200 W, the treatment time is 5 to 8 minutes, and the working gas is oxygen.

6. The high pressure-bearing fiber composite temporary plugging agent for oil well fracturing according to claim 1, characterized in that: In step S3, the initiator is benzoyl peroxide or ammonium persulfate.

7. The high pressure-bearing fiber composite temporary plugging agent for oil well fracturing according to claim 1, characterized in that: In step S4, the washing method is to rinse with anhydrous ethanol.

8. A method for preparing a high-pressure fiber composite temporary plugging agent for oil well fracturing, used for preparing the high-pressure fiber composite temporary plugging agent for oil well fracturing as claimed in any one of claims 1 to 7, characterized in that: The following steps are involved: 1) adding calcium carbonate particles into a carrier liquid according to the weight portion, then stirring the carrier liquid at a rate of 330-350 r / min, and gradually adding modified polyvinyl alcohol fiber into the carrier liquid during the stirring process, wherein the amount of modified polyvinyl alcohol fiber added per minute accounts for 2-6% of the total mass of the carrier liquid; 2) After all the modified polyvinyl alcohol fibers are added to the carrying liquid, the carrying liquid is heated to 40-50° C., polyacrylamide is added to the carrying liquid, and stirring is continued at a rate of 200-240 r / min for 1-2 hours to obtain a temporary plugging agent.

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