Cleanable degradable fibers and methods of making and using the same

Abstract

The present application relates to the technical field of fracturing aids, and discloses a clean degradable fiber, a preparation method and application thereof, the clean degradable fiber is obtained by the following method: firstly, polyadipic acid, polylactic acid, bisphenol A type epoxy resin, talcum powder and an antioxidant are stirred uniformly to obtain a mixture; then, the mixture is added to polyvinyl alcohol, heated and stirred until dissolved to obtain a spinning mucilage; finally, the spinning mucilage is sprayed and adhered to be collected, and after drying, scattering and cooling, the clean degradable fiber is obtained. The clean degradable fiber has the characteristics of low damage, degradability and high temperature resistance, and has good sand suspending, sand preventing and viscosity increasing properties. When the clean degradable fiber is applied in oil fracturing, on the one hand, the average sand ratio can be improved, so that the filling degree of proppants in the fracture is improved, and the influence of proppant embedding on the flow conductivity is reduced; on the other hand, the proppant settling speed can be effectively reduced, and the supporting effect of the main producing layer is ensured.

Description

Technical Field

[0001] This invention relates to the field of fracturing additives, specifically a clean, biodegradable fiber, its preparation method, and its application. Background Technology

[0002] In the petroleum industry, fracturing refers to a method of creating fractures in oil and gas reservoirs using hydraulic force during oil or gas production; it is also known as hydraulic fracturing. Fracturing artificially creates fractures in the formation to improve the underground flow environment of oil, increase oil well production, and plays an important role in improving bottomhole flow conditions, mitigating inter-layer flow, and improving reservoir activation.

[0003] With the continuous development of oil extraction, the scale of fracturing is becoming larger and larger, and the sand production rate during gas testing is increasing significantly, which also brings great difficulties to gas testing and subsequent operations. This difficulty is mainly manifested in the stability of sand production during oil well fracturing. Experiments show that fibers have a wrapping and restraining effect on proppant, which can significantly reduce the proppant settling velocity and improve the proppant profile; it can also enhance the stability of the filled sand body and help control sand production. By taking multiple measures such as high sand ratio injection with fibers during fracturing and controlling the blowout regime, the probability of post-fracturing sand production can be reduced.

[0004] However, with increasing environmental protection efforts, the environmental problems of ordinary fibers have become increasingly prominent, leading to a demand for clean solutions. The emergence of clean biodegradable fibers is timely. These fiber materials gradually degrade in the underground environment, avoiding the persistent pollution of the environment caused by traditional sand control materials, while also reducing potential environmental risks, which meets the growing global demand for sustainable development.

[0005] Therefore, in response to the problem of sand production when using existing conventional fracturing fluids during fracturing operations in oil and gas wells, there is an urgent need to provide an ideal sand control material for fracturing stimulation that can both ensure the sand control effect of oil wells and meet environmental protection requirements. Summary of the Invention

[0006] This invention provides a clean, biodegradable fiber, its preparation method, and its application, overcoming the shortcomings of the prior art. It can effectively solve the problem of sand production when using conventional fracturing fluids during oil and gas well fracturing operations.

[0007] One of the technical solutions of the present invention is achieved by the following measures: a clean and biodegradable fiber, wherein the raw materials include, by weight, 65 to 75 parts of polyadipic acid, 20 to 45 parts of polylactic acid, 6 to 8 parts of bisphenol A epoxy resin, 1 to 2 parts of talc, 0.5 to 1 part of antioxidant and 50 to 80 parts of polyvinyl alcohol.

[0008] The following are further optimizations and / or improvements to one of the above-mentioned technical solutions: The above-mentioned clean and biodegradable fibers are obtained by the following method: The first step is to mix the required amounts of polyadipate, polylactic acid, bisphenol A epoxy resin, talc, and antioxidant to obtain a mixture. The second step is to add the mixture to the required amount of polyvinyl alcohol, heat and stir until dissolved to obtain a spinning viscous solution; The third step involves placing the spinning slurry into an electrostatic spinning machine for spraying, adhesion, and collection to obtain fiber felt. The fourth step involves drying, breaking up, and cooling the fiber felt to obtain clean, biodegradable fibers.

[0009] In the first step above, the stirring time is 1.0h to 1.5h, and the stirring temperature is 25℃±2℃.

[0010] In the second step above, the heating temperature is 180℃ to 220℃, and the stirring time is 1.0h to 1.5h.

[0011] In the third step above, the drying temperature is 100℃ to 110℃ and the drying time is 3.5h to 4.5h.

[0012] The second technical solution of the present invention is achieved through the following measures: a method for preparing clean and biodegradable fibers, carried out according to the following method: The first step is to mix the required amounts of polyadipate, polylactic acid, bisphenol A epoxy resin, talc, and antioxidant to obtain a mixture. The second step is to add the mixture to the required amount of polyvinyl alcohol, heat and stir until dissolved to obtain a spinning viscous solution; The third step involves placing the spinning slurry into an electrostatic spinning machine for spraying, adhesion, and collection to obtain fiber felt. The fourth step involves drying, breaking up, and cooling the fiber felt to obtain clean, biodegradable fibers.

[0013] The third technical solution of the present invention is achieved through the following measures: the application of a clean and biodegradable fiber in the preparation of fiber-suspended fracturing fluid, wherein the fiber-suspended fracturing fluid comprises, by weight, 500 parts water, 0.20 to 0.35 parts guar gum, 0.06 to 0.09 parts pH adjuster, 20 to 30 parts potassium chloride, 0.5 to 1.5 parts demulsifier, 0.5 to 1.5 parts drainage aid, 0.05 to 0.15 parts bactericide, and 0.3 to 1.2 parts clean and biodegradable fiber.

[0014] The following are further optimizations and / or improvements to the third technical solution of the above invention: The pH adjuster mentioned above includes a pH acidic adjuster and a pH alkaline adjuster in a mass ratio of 1:2. The pH acidic adjuster is citric acid, and the pH alkaline adjuster is sodium hydroxide.

[0015] The clean, biodegradable fiber of this invention features low damage, biodegradability, and high-temperature resistance. It also possesses excellent sand-suspending, sand-controlling, and viscosity-enhancing properties. Applying this clean, biodegradable fiber to oil fracturing improves, on the one hand, the average sand ratio, thereby increasing the proppant filling within the fracture and reducing the impact of proppant embedding on conductivity. On the other hand, it effectively reduces proppant settling velocity, ensuring the support effect on the main producing layer. Furthermore, while maintaining good sand-suspending effects, adding this clean, biodegradable fiber to the fracturing fluid reduces polymer usage, thus lowering apparent viscosity and facilitating fracture height control. This effectively solves the sand production problem encountered when using conventional fracturing fluids during oil and gas well fracturing operations. Attached Figure Description

[0016] Figure 1 This is a curve comparison of the sedimentation rate of the clean biodegradable fiber of the present invention.

[0017] Figure 2 This is a comparison chart showing the effect of the clean biodegradable fiber of the present invention on suspended sand fracturing.

[0018] Figure 3 This diagram shows the distribution of the clean, biodegradable fibers of this invention in the support.

[0019] Figure 4 The graph shows the degradation rate of the fiber-suspended fracturing fluid containing the clean and biodegradable fibers of this invention at a formation temperature of 60°C.

[0020] Figure 5 The graph shows the degradation rate of the fiber-suspended fracturing fluid containing the clean and biodegradable fibers of this invention at a formation temperature of 80°C.

[0021] Figure 6 The graph shows the degradation rate of the fiber-suspended fracturing fluid containing the clean and biodegradable fibers of this invention at a formation temperature of 100°C.

[0022] Figure 7 The graph shows the degradation rate of the fiber-suspended fracturing fluid containing the clean and biodegradable fibers of this invention at a formation temperature of 120°C.

[0023] Figure 8 This is a graph showing the viscosity-temperature curves of conventional fracturing fluid at different times.

[0024] Figure 9 This is a graph showing the viscosity-temperature curves of the fiber-suspended sand-weighted fracturing fluid of the present invention at different times. Detailed Implementation

[0025] This invention is not limited to the following embodiments, and specific implementation methods can be determined according to the technical solutions and actual conditions of this invention. Unless otherwise specified, all chemical reagents and chemicals mentioned in this invention are well-known and commonly used chemical reagents and chemicals in the prior art; unless otherwise specified, all percentages in this invention are mass percentages; unless otherwise specified, all solutions in this invention are aqueous solutions with water as the solvent, for example, hydrochloric acid solution is an aqueous solution of hydrochloric acid; room temperature in this invention generally refers to a temperature between 15°C and 25°C, generally defined as 25°C.

[0026] The present invention will be further described below with reference to embodiments: Example 1: The clean biodegradable fiber contains, by weight, 65 to 75 parts of polyadipate, 20 to 45 parts of polylactic acid, 6 to 8 parts of bisphenol A epoxy resin, 1 to 2 parts of talc, 0.5 to 1 part of antioxidant and 50 to 80 parts of polyvinyl alcohol.

[0027] In this invention, the antioxidant is a DLPT type antioxidant.

[0028] Example 2: As an optimization of the above examples, clean biodegradable fibers are obtained by the following method: The first step is to mix the required amounts of polyadipate, polylactic acid, bisphenol A epoxy resin, talc, and antioxidant to obtain a mixture. The second step is to add the mixture to the required amount of polyvinyl alcohol, heat and stir until dissolved to obtain a spinning viscous solution; The third step involves placing the spinning slurry into an electrostatic spinning machine for spraying, adhesion, and collection to obtain fiber felt. The fourth step involves drying, breaking up, and cooling the fiber felt to obtain clean, biodegradable fibers.

[0029] Example 3: As an optimization of the above example, in the first step, the stirring time is 1.0h to 1.5h and the stirring temperature is 25℃±2℃.

[0030] Example 4: As an optimization of the above example, in the second step, the heating temperature is 180°C to 220°C and the stirring time is 1.0h to 1.5h.

[0031] Example 5: As an optimization of the above example, in the third step, the drying temperature is 100°C to 110°C and the drying time is 3.5h to 4.5h.

[0032] Example 6: As an optimization of the above examples, the application of the clean biodegradable fiber prepared in the above examples in the preparation of fiber suspension weighted fracturing fluid.

[0033] Example 7: As an optimization of the above examples, the fiber suspension weighted fracturing fluid comprises, by weight, 500 parts water, 0.20 to 0.35 parts guar gum, 0.06 to 0.09 parts pH adjuster, 20 to 30 parts potassium chloride, 0.5 to 1.5 parts demulsifier, 0.5 to 1.5 parts drainage aid, 0.05 to 0.15 parts bactericide, and 0.3 to 1.2 parts clean biodegradable fiber.

[0034] In this invention, the guar gum is GHPG type guar gum, the demulsifier is HY-D type demulsifier, the drainage aid is XZ-ZPF type drainage aid, and the bactericide is XZ-SJ type bactericide.

[0035] Example 8: As an optimization of the above example, the pH adjuster includes a pH acidic adjuster and a pH alkaline adjuster in a mass ratio of 1:2, wherein the pH acidic adjuster is citric acid and the pH alkaline adjuster is sodium hydroxide.

[0036] Compared with the prior art, the beneficial effects of the present invention are: First, the clean biodegradable fiber of this invention features low damage, biodegradability, and high-temperature resistance. Its biodegradability is manifested in the absorption and digestion by microorganisms. For example, bacteria or fungi secrete organic acids, enzymes, and other chemical substances that react with the surface of the clean biodegradable fiber. Organic acids, for instance, can break the chemical bonds on the surface of the fiber, thereby altering its chemical structure and creating favorable conditions for subsequent degradation. Regarding the clean biodegradable fiber prepared by this invention, microorganisms secrete esterases to degrade ester bonds, thus breaking down smaller substances such as low-molecular-weight polyesters, diacids, and glycols. These smaller molecule fragments are more easily absorbed and utilized by microorganisms. When applied to oil fracturing, this helps increase the average proppant ratio, thereby improving the proppant filling within the fracture and reducing the impact of proppant embedding on conductivity. Secondly, the clean and biodegradable fibers of this invention can effectively reduce proppant settling and ensure the support effect of the main producing layer. After adding the clean and biodegradable fibers of this invention to the fiber-suspended sand-weighted fracturing fluid, the settling of particles no longer follows Stokes' law, but follows the Kynch settling law. The interaction between the fibers and particles prevents the particles from settling, greatly reducing the settling rate of the proppant. The settling speed is reduced by about 2.5 times, thereby ensuring the good proppant carrying capacity of the fiber-suspended sand-weighted fracturing fluid. At the same time, adding the clean and biodegradable fibers of this invention to the fiber-suspended sand-weighted fracturing fluid is more conducive to increasing the average sand ratio, thereby increasing the proppant filling degree in the fracture and reducing the impact of proppant embedding on the conductivity. On the other hand, it can effectively reduce proppant settling and ensure the support effect of the main producing layer; it is also beneficial to control the fracture height. Third, the clean biodegradable fiber of this invention, while ensuring good sand-carrying performance, can reduce the amount of polymer used in fracturing fluid, thereby reducing the apparent viscosity. The viscosity of the sand-carrying fluid is reduced from 100 mPa·s to 20 mPa·s, which is beneficial for controlling the fracture height. Under the condition that other parameters remain unchanged, the fracture height can be reduced to 58.48% of the original, which greatly reduces the excessive longitudinal extension of the fracture.

[0037] Example 9: This clean, biodegradable fiber is made from raw materials comprising, by weight, 65 parts polyadipate, 20 parts polylactic acid, 6 parts bisphenol A epoxy resin, 1 part talc, 0.5 parts antioxidant (DLPT type antioxidant), and 50 parts polyvinyl alcohol, obtained by the following method: The first step involves mixing the required amounts of polyadipate, polylactic acid, bisphenol A epoxy resin, talc, and antioxidant (DLPT type antioxidant) at room temperature for 1.0 h to obtain a mixture. The second step is to add the mixture to the required amount of polyvinyl alcohol, heat it to 200°C and stir it for 1.0 h. After it is fully dissolved, a spinning viscous solution is obtained. The third step involves placing the spinning slurry into an electrostatic spinning machine for spraying, adhesion, and collection to obtain fiber felt. The fourth step is to dry the fiber felt at 105℃ for 4 hours, then break it up with a breaker and allow it to cool naturally to obtain clean, biodegradable fibers.

[0038] Example 10: This clean, biodegradable fiber is made from raw materials comprising, by weight, 75 parts polyadipate, 45 parts polylactic acid, 8 parts bisphenol A epoxy resin, 2 parts talc, 1 part antioxidant (DLPT type antioxidant), and 80 parts polyvinyl alcohol, obtained by the following method: The first step involves mixing the required amounts of polyadipate, polylactic acid, bisphenol A epoxy resin, talc, and antioxidant (DLPT type antioxidant) at room temperature for 1.0 h to obtain a mixture. The second step is to add the mixture to the required amount of polyvinyl alcohol, heat it to 200°C and stir it for 1.0 h. After it is fully dissolved, a spinning viscous solution is obtained. The third step involves placing the spinning slurry into an electrostatic spinning machine for spraying, adhesion, and collection to obtain fiber felt. The fourth step is to dry the fiber felt at 105℃ for 4 hours, then break it up with a breaker and allow it to cool naturally to obtain clean, biodegradable fibers.

[0039] Example 11: This clean, biodegradable fiber is made from raw materials comprising, by weight, 70 parts polyadipate, 30 parts polylactic acid, 7 parts bisphenol A epoxy resin, 1.5 parts talc, 0.8 parts antioxidant (DLPT type antioxidant), and 60 parts polyvinyl alcohol, obtained by the following method: The first step involves mixing the required amounts of polyadipate, polylactic acid, bisphenol A epoxy resin, talc, and antioxidant (DLPT type antioxidant) at room temperature for 1.0 h to obtain a mixture. The second step is to add the mixture to the required amount of polyvinyl alcohol, heat it to 200°C and stir it for 1.0 h. After it is fully dissolved, a spinning viscous solution is obtained. The third step involves placing the spinning slurry into an electrostatic spinning machine for spraying, adhesion, and collection to obtain fiber felt. The fourth step is to dry the fiber felt at 105℃ for 4 hours, then break it up with a breaker and allow it to cool naturally to obtain clean, biodegradable fibers.

[0040] Experimental Example 1: Investigating the sand-suspending performance of the clean biodegradable fiber of the present invention.

[0041] Experimental method: Different fiber-reinforced fracturing fluids were prepared, and the formulations are as follows: Formula 1 (0.24 parts guar gum without added clean biodegradable fibers): This conventional weighted fracturing fluid contains, by weight, 500 parts water, 0.24 parts guar gum (GHPG type guar gum), 0.075 parts pH adjuster (0.025 parts pH acidic adjuster and 0.05 parts pH alkaline adjuster), 25 parts potassium chloride, 1.0 part demulsifier (HY-D type demulsifier), 1.0 part drainage aid (XZ-ZPF type drainage aid), and 0.1 part bactericide (XZ-SJ type bactericide). Formula 2 (0.24 parts guar gum + 0.36 parts clean biodegradable fiber): This fiber is used to suspend sand and increase the weight of fracturing fluid. The raw materials, by weight, include 500 parts water, 0.24 parts guar gum (GHPG type guar gum), 0.075 parts pH adjuster (0.025 parts pH acidic adjuster and 0.05 parts pH alkaline adjuster), 25 parts potassium chloride, 1.0 part demulsifier (HY-D type demulsifier), 1.0 part drainage aid (XZ-ZPF type drainage aid), 0.1 part bactericide (XZ-SJ type bactericide), and 0.36 parts clean biodegradable fiber prepared in Example 9 of this invention. Formula 3 (0.30 parts guar gum + 0.36 parts clean biodegradable fiber): This fiber is used to suspend sand and increase the weight of fracturing fluid. The raw materials, by weight, include 500 parts water, 0.30 parts guar gum (GHPG type guar gum), 0.075 parts pH adjuster (0.025 parts pH acidic adjuster and 0.05 parts pH alkaline adjuster), 25 parts potassium chloride, 1.0 part demulsifier (HY-D type demulsifier), 1.0 part drainage aid (XZ-ZPF type drainage aid), 0.1 part bactericide (XZ-SJ type bactericide), and 0.36 parts clean biodegradable fiber prepared in Example 9 of this invention. Formula 4 (0.30 parts guar gum + 0.48 parts clean biodegradable fiber): This fiber-suspended sand-weighted fracturing fluid contains, by weight, 500 parts water, 0.30 parts guar gum (GHPG type guar gum), 0.075 parts pH adjuster (0.025 parts pH acidic adjuster and 0.05 parts pH alkaline adjuster), 25 parts potassium chloride, 1.0 part demulsifier (HY-D type demulsifier), 1.0 part drainage aid (XZ-ZPF type drainage aid), 0.1 part bactericide (XZ-SJ type bactericide), and 0.48 parts clean biodegradable fiber prepared in Example 9 of this invention.

[0042] Formula 5: (0.35 parts guar gum without added clean biodegradable fiber): This fiber-suspended fracturing fluid contains, by weight, 500 parts water, 0.35 parts guar gum (GHPG type guar gum), 0.075 parts pH adjuster (0.025 parts pH acidic adjuster and 0.05 parts pH alkaline adjuster), 25 parts potassium chloride, 1.0 part demulsifier (HY-D type demulsifier), 1.0 part drainage aid (XZ-ZPF type drainage aid), and 0.1 part bactericide (XZ-SJ type bactericide). Formula 6: (0.35 parts guar gum + 0.36 parts clean biodegradable fiber): This fiber is used to suspend sand and increase the weight of fracturing fluid. The raw materials, by weight, include 500 parts water, 0.35 parts guar gum (GHPG type guar gum), 0.075 parts pH adjuster (0.025 parts pH acidic adjuster and 0.05 parts pH alkaline adjuster), 25 parts potassium chloride, 1.0 part demulsifier (HY-D type demulsifier), 1.0 part drainage aid (XZ-ZPF type drainage aid), 0.1 part bactericide (XZ-SJ type bactericide), and 0.36 parts clean biodegradable fiber prepared in Example 9 of this invention.

[0043] The specific method for examining the sedimentation rate of the clean biodegradable fiber of the present invention is as follows: 30% of the weight of the fiber-suspended sand-weighted fracturing fluid (20-40 mesh ceramsite) was added to the conventional fracturing fluid prepared by Formula 1 and the fiber-suspended sand-weighted fracturing fluid prepared by Formulas 2 to 4, respectively. The mixture was stirred at room temperature for 10 minutes, poured into a 100ml graduated cylinder with plastic wrap, sealed with plastic wrap, and placed in a super constant temperature water bath. The sedimentation rate of the proppant was observed at 87℃, and observed every 5 minutes.

[0044] The specific method for examining the suspended sand fracturing effect of the clean biodegradable fiber of the present invention is as follows: 20% of the weight of the fiber suspended sand weighted fracturing fluid (20-40 mesh ceramsite) is added to the fiber suspended sand weighted fracturing fluid prepared by formulas 5 to 6 respectively. The suspended sand fracturing effect of the clean biodegradable fiber of the present invention is measured by a flowability tester.

[0045] Experimental Results: A comparison of the settling rate curves of the clean, biodegradable fibers of this invention, as shown in the figure. Figure 1 As shown, by Figure 1 It can be seen that after adding the clean and biodegradable fiber prepared in Example 9 of this invention to the fiber-supported fracturing fluid, the sedimentation of the particles no longer follows Stokes' law, but follows the Kynch sedimentation law. The fiber and the particles interact to prevent the particles from settling, greatly reducing the sedimentation rate of the proppant. The sedimentation rate is reduced by about 2.5 times, thereby ensuring the good proppant carrying capacity of the fiber fracturing fluid. The comparison diagram of the suspended sand fracturing effect of the clean biodegradable fiber of the present invention is shown in the figure. Figure 2 As shown, by Figure 2 It is known that, compared with conventional fracturing fluid obtained without the addition of the clean and biodegradable fibers of this invention, fiber-suspended weighted fracturing fluid obtained by adding the clean and biodegradable fibers of this invention is more conducive to increasing the average sand ratio, thereby increasing the filling degree of proppant in the fracture and reducing the impact of proppant embedding on the conductivity; on the other hand, it can effectively reduce proppant settling and ensure the support effect of the main producing layer; and it is beneficial to control the fracture height.

[0046] Experimental Example 2: Investigating the sand-resistant properties of the clean biodegradable fiber of the present invention.

[0047] Experimental method: Take the fiber-suspended sand-weighted fracturing fluid of Formula 2 in Experimental Example 1, add proppant (20-40 mesh ceramsite) to the fiber-suspended sand-weighted fracturing fluid, stir at 500 r / min for 3 min (simulating sand mixing truck stirring), and observe the distribution of the clean and biodegradable fiber of the present invention in the proppant.

[0048] Experimental results: The distribution of the clean, biodegradable fibers of this invention in the support is shown in the figure. Figure 3 As shown, by Figure 3 It is known that the spheres are proppant and the linear structures are clean biodegradable fibers. The clean biodegradable fibers of this invention help control the proppant backflow. The main reason is that the clean biodegradable fibers and the proppant form a composite medium. When the clean biodegradable fibers come into contact with the proppant, the friction coefficient increases. The clean biodegradable fiber network structure can prevent proppant backflow in the early stage of liquid drainage.

[0049] Example 3: The solubility of the clean biodegradable fiber of the present invention.

[0050] Experimental Method: Clean biodegradable fibers prepared in Examples 9 to 11 of this invention were added to 300 mL of water to obtain clean biodegradable fiber aqueous solutions. The degradation ability of these solutions was then investigated under different temperatures, different acid / alkaline solutions, and different bacterial cultures. The different temperatures were 60℃, 120℃, 180℃, and 240℃; the different acid / alkaline solutions were 10% hydrochloric acid and 10% sodium hydroxide solutions; and the different bacterial cultures were cellulose-degrading bacteria and *Trichoderma*.

[0051] Experimental Results: The degradation capacity of the clean biodegradable fiber aqueous solution of the present invention at different temperatures is shown in Table 1. The degradation capacity of the clean biodegradable fiber aqueous solution of the present invention in different acid and alkaline solutions is shown in Table 2. The degradation capacity of the clean biodegradable fiber aqueous solution of the present invention in different bacterial solutions is shown in Table 3. As can be seen from Tables 1 to 3, the clean biodegradable fiber of the present invention has the characteristics of low damage, biodegradability and high temperature resistance. The complete degradation time is ≥16h under different temperatures and different bacterial environments, and the dissolution rate in different acid and alkaline solutions is about 7s.

[0052] Example 4: Investigating the degradation performance of the clean biodegradable fiber of the present invention.

[0053] Experimental method: The fiber-reinforced fracturing fluid of formulation 2 in Experimental Example 1 was used to simulate formation temperature. Different formation temperatures were 60℃, 80℃, 100℃ and 120℃. The fiber-reinforced fracturing fluid was placed at different formation temperatures for different time periods, then removed, filtered, dried and cooled, and weighed to calculate the degradation rate.

[0054] Experimental results: The degradation rate of fiber-reinforced fracturing fluid containing the clean, biodegradable fibers of this invention at a formation temperature of 60°C is as follows: Figure 4 As shown, the degradation rate of the fiber-suspended fracturing fluid containing the clean, biodegradable fibers of this invention at a formation temperature of 80°C is as follows: Figure 5 As shown, the degradation rate of the fiber-suspended weighted fracturing fluid containing the clean, biodegradable fibers of this invention at a formation temperature of 100°C is as follows: Figure 6 As shown, the degradation rate of the fiber-suspended fracturing fluid containing the clean, biodegradable fibers of this invention at a formation temperature of 120°C is as follows: Figure 7 As shown, by Figures 4 to 7 It is known that the fiber-suspended sand-weighted fracturing fluid containing the clean and biodegradable fiber of the present invention degrades fastest at 80℃ and 100℃, and the degradation time to reach 100% degradation rate at 80℃ and 100℃ is 7h to 8h. The fiber-suspended sand-weighted fracturing fluid containing the clean and biodegradable fiber of the present invention degrades slowest at 120℃, and the degradation time to reach 100% degradation rate at 120℃ is 11h to 12h. This indicates that the clean and biodegradable fiber of the present invention has good degradation performance.

[0055] Example 5: Investigating the thickening properties of the clean biodegradable fiber of the present invention.

[0056] Experimental method: The conventional fracturing fluid prepared by Formula 1 in Experimental Example 1 and the fiber-reinforced fracturing fluid prepared by Formula 2 were run at 120°C for 110 min using a Hacker rheometer to obtain the viscosity-temperature curves of the fiber-reinforced fracturing fluid of the present invention at different times.

[0057] Experimental results: Viscosity-temperature curves of conventional fracturing fluid at different times, as shown in the figure. Figure 8 As shown, the viscosity-temperature curves of the fiber-suspended weighted fracturing fluid of the present invention at different times are illustrated. Figure 8 As shown, by Figures 8 to 9 It can be seen that the fiber-suspended sand-weighted fracturing fluid with the addition of the clean and biodegradable fiber of the present invention has a strong sand-suspending capacity, which indicates that the clean and biodegradable fiber of the present invention has good thickening properties.

[0058] Experimental Example 6: Application of the clean biodegradable fiber of the present invention.

[0059] Following large-scale fracturing operations in the Wushen Banner oil and gas production area of ​​the Sulige Gas Field from 2016 to 2018 and the first half of 2019, severe sand trapping and sand burial occurred. From 2016 to 2018, four wells were sand-burialed, with an average burial depth of 9.7 meters. Fourteen wells encountered sand trapping after tubing replacement, with an average sand-washing thickness of 34.6 meters. In the first half of 2019, twelve wells were sand-burialed, with an average burial depth of 15.7 meters. Twenty wells encountered sand trapping after tubing replacement, with an average sand-washing thickness of 43.51 meters. After improvement, the sand-suspending and weighting fracturing fluid prepared with the clean, biodegradable fibers of this invention was added to enhance its sand-suspending capacity. Since the second half of 2019, this method has been applied selectively to different reservoir wells, totaling 33 well applications. The average sand-washing thickness decreased from 34.6 meters to 17.8 meters, a reduction of 48.5%. The application results are shown in Table 4. As can be seen from Table 4, in 2020, by combining the application of the clean and biodegradable fiber sand prevention technology of the present invention, no problems such as sand jamming or sand burial occurred again.

[0060] In summary, the clean biodegradable fiber of this invention possesses low-damage, biodegradable, and high-temperature resistance characteristics. Simultaneously, it exhibits excellent sand-suspending, sand-controlling, and viscosity-enhancing properties. Applying this clean biodegradable fiber to oil fracturing can, on the one hand, improve the average sand ratio, thereby increasing the proppant filling rate within the fracture and reducing the impact of proppant embedding on conductivity; on the other hand, it can effectively reduce the proppant settling velocity, ensuring the support effect on the main producing layer. Furthermore, while ensuring good sand-suspending effects, the addition of this clean biodegradable fiber to the fracturing fluid can reduce polymer usage, thereby lowering apparent viscosity and facilitating fracture height control. It effectively solves the sand production problem that occurs when using conventional fracturing fluids during oil and gas well fracturing operations.

[0061] The above technical features constitute the embodiments of the present invention, which have strong adaptability and implementation effect. Unnecessary technical features can be added or removed according to actual needs to meet the needs of different situations.

Claims

1. A clean, biodegradable fiber, characterized in that... The raw materials, by weight, include 65 to 75 parts of polyadipic acid, 20 to 45 parts of polylactic acid, 6 to 8 parts of bisphenol A epoxy resin, 1 to 2 parts of talc, 0.5 to 1 part of antioxidant, and 50 to 80 parts of polyvinyl alcohol.

2. The clean biodegradable fiber according to claim 1, characterized in that... Obtained using the following method: The first step is to mix the required amounts of polyadipate, polylactic acid, bisphenol A epoxy resin, talc, and antioxidant to obtain a mixture. The second step is to add the mixture to the required amount of polyvinyl alcohol, heat and stir until dissolved to obtain a spinning viscous solution; The third step involves placing the spinning slurry into an electrostatic spinning machine for spraying, adhesion, and collection to obtain fiber felt. The fourth step involves drying, breaking up, and cooling the fiber felt to obtain clean, biodegradable fibers.

3. The clean biodegradable fiber according to claim 2, characterized in that... In the first step, the stirring time is 1.0h to 1.5h, and the stirring temperature is 25℃±2℃.

4. The clean biodegradable fiber according to claim 2 or 3, characterized in that... In the second step, the heating temperature is 180℃ to 220℃, and the stirring time is 1.0h to 1.5h.

5. The clean biodegradable fiber according to any one of claims 2 to 4, characterized in that... In the third step, the drying temperature is 100℃ to 110℃, and the drying time is 3.5h to 4.5h.

6. A method for preparing clean, biodegradable fibers according to any one of claims 1, 3 to 5, characterized in that... Perform the following steps: The first step is to mix the required amounts of polyadipate, polylactic acid, bisphenol A epoxy resin, talc, and antioxidant to obtain a mixture. The second step is to add the mixture to the required amount of polyvinyl alcohol, heat and stir until dissolved to obtain a spinning viscous solution; The third step involves placing the spinning slurry into an electrostatic spinning machine for spraying, adhesion, and collection to obtain fiber felt. The fourth step involves drying, breaking up, and cooling the fiber felt to obtain clean, biodegradable fibers.

7. The application of a clean, biodegradable fiber according to any one of claims 1 to 5 in the preparation of fiber-reinforced fracturing fluid, characterized in that... The fiber-suspended fracturing fluid comprises, by weight, 500 parts water, 0.20 to 0.35 parts guar gum, 0.06 to 0.09 parts pH adjuster, 20 to 30 parts potassium chloride, 0.5 to 1.5 parts demulsifier, 0.5 to 1.5 parts drainage aid, 0.05 to 0.15 parts bactericide, and 0.3 to 1.2 parts clean biodegradable fiber.

8. The clean biodegradable fiber according to claim 7, characterized in that... pH adjusters include an acidic pH adjuster and an alkaline pH adjuster in a mass ratio of 1:

2. The acidic pH adjuster is citric acid, and the alkaline pH adjuster is sodium hydroxide.

Images