CN107268103B - Water-soluble PVA fiber and preparation method and application thereof - Google Patents

Water-soluble PVA fiber and preparation method and application thereof Download PDF

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CN107268103B
CN107268103B CN201610213437.2A CN201610213437A CN107268103B CN 107268103 B CN107268103 B CN 107268103B CN 201610213437 A CN201610213437 A CN 201610213437A CN 107268103 B CN107268103 B CN 107268103B
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pva
oil
fiber
fracturing fluid
spinning
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CN107268103A (en
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王华全
王建
周霖
李海英
向鹏伟
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China Petrochemical Corp
Sinopec Sichuan Vinylon Works
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Sinopec Sichuan Vinylon Works
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    • D01F6/00—Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof
    • D01F6/44—Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof from mixtures of polymers obtained by reactions only involving carbon-to-carbon unsaturated bonds as major constituent with other polymers or low-molecular-weight compounds
    • D01F6/50—Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof from mixtures of polymers obtained by reactions only involving carbon-to-carbon unsaturated bonds as major constituent with other polymers or low-molecular-weight compounds of polyalcohols, polyacetals or polyketals
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    • C09K8/00—Compositions for drilling of boreholes or wells; Compositions for treating boreholes or wells, e.g. for completion or for remedial operations
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    • C09K8/60—Compositions for stimulating production by acting on the underground formation
    • C09K8/62—Compositions for forming crevices or fractures
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    • C09K8/00—Compositions for drilling of boreholes or wells; Compositions for treating boreholes or wells, e.g. for completion or for remedial operations
    • C09K8/60—Compositions for stimulating production by acting on the underground formation
    • C09K8/62—Compositions for forming crevices or fractures
    • C09K8/66—Compositions based on water or polar solvents
    • C09K8/68—Compositions based on water or polar solvents containing organic compounds
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    • C09K8/00—Compositions for drilling of boreholes or wells; Compositions for treating boreholes or wells, e.g. for completion or for remedial operations
    • C09K8/60—Compositions for stimulating production by acting on the underground formation
    • C09K8/62—Compositions for forming crevices or fractures
    • C09K8/70—Compositions for forming crevices or fractures characterised by their form or by the form of their components, e.g. foams
    • D—TEXTILES; PAPER
    • D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
    • D01D—MECHANICAL METHODS OR APPARATUS IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS
    • D01D1/00—Treatment of filament-forming or like material
    • D01D1/02—Preparation of spinning solutions
    • D—TEXTILES; PAPER
    • D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
    • D01D—MECHANICAL METHODS OR APPARATUS IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS
    • D01D5/00—Formation of filaments, threads, or the like
    • D01D5/06—Wet spinning methods
    • D—TEXTILES; PAPER
    • D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
    • D01F—CHEMICAL FEATURES IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS; APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OF CARBON FILAMENTS
    • D01F1/00—General methods for the manufacture of artificial filaments or the like
    • D01F1/02—Addition of substances to the spinning solution or to the melt
    • D01F1/10—Other agents for modifying properties
    • D—TEXTILES; PAPER
    • D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
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    • D01F11/00—Chemical after-treatment of artificial filaments or the like during manufacture
    • D01F11/04—Chemical after-treatment of artificial filaments or the like during manufacture of synthetic polymers
    • D01F11/06—Chemical after-treatment of artificial filaments or the like during manufacture of synthetic polymers of macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds
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    • C09K2208/08—Fiber-containing well treatment fluids
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Abstract

The PVA fiber consists of polymerization degree of 1500-2500 and alcoholysis degree AdSatisfies the relation of 86 percent to AdSpinning PVA with the mol/mol percent of less than or equal to 95.0 percent. The PVA fiber provided by the invention has special water solubility, is favorable for improving the sand carrying capacity of fracturing fluid when being used for fracturing construction of oil and gas fields, and can be timely drained back to the ground after the fracturing construction is finished due to good water solubility, so that the yield of the oil and gas fields is greatly increased. The preparation method is simple and suitable for industrial production.

Description

Water-soluble PVA fiber and preparation method and application thereof
Technical Field
The invention relates to a PVA fiber, in particular to a PVA fiber and a preparation method and application thereof.
Background
The PVA (polyvinyl alcohol) fiber is a fiber with excellent performance, has the characteristics of high strength, high modulus, low elongation and the like, has excellent wear resistance, seawater corrosion resistance, weather resistance and good bonding performance with a base material interface, is widely used as a net for shallow sea laver culture, a high-performance rope, a tire cord, a production cloth, a cement reinforcing material, plastics, a rubber reinforcing material and the like, and has wide market potential.
In recent years, researchers at home and abroad have continuously conducted a great deal of research around PVA fibers. CN200510057435A discloses a method for preparing high-performance polyvinyl alcohol fiber, which adopts a composite modifier composed of a nitrogen-containing compound, a hydrophilic auxiliary additive and water to carry out intermolecular hydrogen bond composite with polyvinyl alcohol to prepare modified polyvinyl alcohol, carries out melt spinning on the modified polyvinyl alcohol in an extrusion-spinning device to prepare nascent fiber, and then carries out multi-stage stretching, drying and heat setting on the nascent fiber to prepare the high-performance polyvinyl alcohol. CN200610021470A discloses a wear-resistant PVA acetal fiber, which is prepared by wet spinning 100 parts of polyvinyl alcohol, 2-6 parts of an additive and 400-900 parts of deionized water. CN201110300982.2A discloses a PVA fiber, which is prepared by adopting equipment with spinning head specification of less than or equal to 5000 holes, aperture of 0.125-0.2 mm and discharge capacity of 1000-1300 ml/min and dry-wet process, and the linear density of the prepared PVA fiber is 6.0-10.0 dtex. CN201110238175.2A discloses a high-strength, high-modulus and high-melting-point PVA fiber, the adopted spinning solution contains 15-17 wt% of PVA, 1.2-1.6 wt% of boric acid and 0.05-0.1 wt% of copper sulfate, the adopted spinning coagulating bath contains 15-50 g/L of sodium hydroxide and 5-50 g/L of boric acid, the strength of the prepared PVA fiber is more than or equal to 13.5cN/dtex, the modulus is more than or equal to 320cN/dtex, and the initial melting point is more than or equal to 108 ℃. CN201310251768A discloses a preparation method of polyvinyl alcohol filament fiber, disclosing production processes of preparing, metering, spinning, solidifying, secondary solidifying, washing, drying, oiling, primary winding, hot plate stretching, twisting, secondary winding and the like of a polyvinyl alcohol spinning solution. Due to the properties of the fibers, the fibers are difficult to be used in the field of oil and gas fields (such as oil and gas field well cementation, oil and gas field fracturing temporary plugging construction, oil and gas field fracturing construction and the like) or difficult to degrade, which causes pollution to the stratum, so that the use of the fibers is greatly limited.
Disclosure of Invention
In order to solve the problems of the prior art, according to a first aspect of the present invention, it is an object of the present invention to provide a PVA fiber which is water-soluble at a relatively low temperature.
The percentages are all mass percentages unless otherwise specified.
The purpose of the invention is realized by the following technical measures:
the PVA fiber is characterized in that the degree of polymerization of the PVA fiber is 1500-2500, and the degree of alcoholysis AdSatisfies the relation of 86 percent to Ad(mol/mol)% less than or equal to 95.0% PVA fiber, and the PVA fiber has dissolving temperature in waterSDegree of alcoholysis A of polyvinyl alcohol (C.)d(mol/mol)% satisfies the following formula (I):
3.3Ad-265≤TS≤3.3Ad-260 (Ⅰ)。
according to one embodiment of the present invention, the PVA fiber has a single fiber linear density of 0.5 to 50 dtex.
According to an embodiment of the present invention, the PVA fibers have an elongation at break of 5 to 30%.
According to one embodiment of the present invention, the PVA fiber has a dry breaking strength of 3 to 15 cN/dtex.
According to a second aspect of the present invention, there is provided a method for producing the above PVA fiber.
The preparation method of the PVA fiber comprises the following steps:
(1) preparing a spinning solution: dissolving PVA with the polymerization degree of 1500-2500 and the alcoholysis degree of 86.0-95 (mol%) and boric acid in water to prepare spinning stock solution, wherein the mass concentration of the PVA in the stock solution is 12-18%, the addition amount of the boric acid is 0.4-1.5% of the mass of the PVA, heating the stock solution to 90-105 ℃, keeping the pressure at 0.05-0.15 MPa, dissolving for 5-20 hours, filtering and defoaming, and entering a spinning process;
(2) spinning: and (2) pumping the PVA stock solution to a spinning assembly by using a metering pump, spraying the PVA stock solution into a coagulation bath from a small hole of a spinning nozzle, wherein the components of the coagulation bath comprise dimethyl sulfoxide, methanol and ethanol, and the mass ratio of the dimethyl sulfoxide to the methanol to the ethanol is 5-35: 24-35: 36-55 ℃, wherein the temperature of the coagulating bath is-20-10 ℃, PVA stays in the coagulating bath for 10-25 s after being subjected to spinning by a spinneret plate, and thus nascent fiber is prepared;
(3) and (3) post-treatment: carrying out wet-heat stretching, extraction, oiling, stretching heat setting, mechanical curling and other processes on the nascent fiber to prepare water-soluble PVA fiber, wherein ethanol is used as a solvent for the wet-heat stretching, and the temperature is 40-50 ℃; the extracting agent used for extraction is a composition of methanol and ethanol, and the molar ratio of the methanol to the ethanol is 2.8-4.5: 1.5-2.5, and the temperature of the extracting agent is 5-15 ℃.
According to a third aspect of the present invention, the present invention provides use of the PVA fiber described above.
According to one embodiment of the present invention, the present invention provides the use of the above-described PVA fibers in the field of oil and gas fields.
According to one embodiment of the invention, the invention provides the use of the PVA fibers described above in oil and gas field fracturing fluids. The inventor surprisingly finds that when the PVA fiber is added into the fracturing fluid of the oil and gas field, the PVA fiber and the fracturing fluid of the oil and gas field have full effects, so that the PVA fiber and the propping agent can be kept in a good suspension state, the sand carrying performance is greatly improved, and the flowback time is greatly shortened.
According to one embodiment of the invention, the oil and gas field fracturing fluid is any one of water-based fracturing fluids in the prior art.
According to a fourth aspect of the present invention there is provided a field fracturing fluid comprising PVA fibres as described above.
According to one embodiment of the invention, the PVA fiber is added into the oil and gas field fracturing fluid and is uniformly dispersed, wherein the mass content of the PVA fiber in the oil and gas field fracturing fluid is 0.5-3.0%.
A large number of experiments prove that the PVA fiber and the guanidine gum are used in the water-based oil-gas field fracturing fluid, and the suspending and carrying proppant has better performance.
According to one embodiment of the invention, the water-based field fracturing fluid comprises a viscosifier; may also include a crosslinking agent or breaker; the thickening agent is used for improving the viscosity of the fracturing fluid, reducing the filtration loss of the fracturing fluid, suspending and carrying a propping agent, and the common thickening agent is guanidine gum; after the PVA fiber is added into fracturing fluid of oil and gas fields, no thickening agent or less thickening agent is used. The cross-linking agent is one or a combination of a plurality of boric acid, borax, organic boron, organic zirconium, aluminum sulfate, aluminum nitrate, titanium tetrachloride, titanium sulfate, zinc sulfate and organic titanium; the gel breaker is biological enzyme or organic acid such as potassium persulfate, ammonium persulfate, potassium dichromate, potassium permanganate, capsule containing enzyme or acid, amylase, etc.
According to an embodiment of the invention, the oil-gas field fracturing fluid can also be added with assistants such as clay stabilizer, cleanup additive, bactericide, foaming agent, defoaming agent, demulsifier and the like. The clay stabilizer can prevent the clay mineral in the oil-gas layer from hydration expansion and dispersion migration, and can be potassium chloride or anionic surfactant. The bactericide, such as chlorine and quaternary ammonium salt, is added to maintain the stability of the surface of the glue solution and prevent the growth of bacteria in the stratum. The cleanup additive is used for reducing the surface tension or oil-water interfacial tension of the fracturing fluid, increasing the contact angle with rocks and reducing capillary resistance encountered during flowback of the fracturing fluid, such as sodium dodecyl sulfate. The foaming agent acts to provide some momentum to the formation and to displace drainage-promoting fluids from the formation, such as cationic surfactants.
According to an embodiment of the invention, the PVA fiber can be added into the fracturing fluid of the oil and gas field only in the preparation stage of fracturing, or can be added into the fracturing fluid in steps in the early stage of fracturing, the middle stage of fracturing and the tail stage of fracturing.
According to one embodiment of the invention, the PVA fiber is applied to oil and gas field fracturing temporary plugging construction, such as preparation of an oil and gas field fracturing temporary plugging agent.
According to one embodiment of the invention, the PVA fiber is used in oil and gas field cementing construction, such as preparation of oil and gas field cementing agent.
The PVA fiber also has the common performance of the PVA fiber, and can also be used for papermaking, non-woven fabrics and embroidery base fabrics.
The invention has the following beneficial effects:
1. the PVA fiber provided by the invention has special water solubility, is beneficial to improving the sand carrying capacity of fracturing fluid when being used for fracturing construction of oil and gas fields, and can be timely drained back to the ground after the fracturing construction is finished, thereby greatly promoting the yield increase of the oil and gas fields.
2. The soluble PVA fiber provided by the invention is used in the field of oil and gas fields, can reduce the dosage of conventional thickening agent guanidine gum and reduce the damage to the stratum.
3. The soluble PVA fiber provided by the invention has good degradability, and can not cause new pollution to the environment when being used in the field of oil and gas fields.
4. The soluble PVA fiber provided by the invention is used in oilfield fracturing fluid, can obviously shorten the flowback time after fracturing construction is finished, generally, the flowback is finished within two or three days, and the product can be flowback within 2 hours after being used. In terms of the flow back efficiency, the fiber of the present invention has a higher flow back rate than the conventional fiber.
5. The soluble PVA fiber provided by the invention is used in oil field fracturing fluid, has better effect when being used with a proper amount of guanidine gum, the addition amount of the PVA fiber is 0.6% of the quality of the fracturing fluid, and the flowback rate of the fracturing fluid reaches more than 80%; the addition amount of the PVA fiber is 1.2 percent of the mass of the fracturing fluid, and the flowback rate of the fracturing fluid reaches more than 85 percent.
Drawings
FIG. 1 is a graph showing the relationship between the dissolution temperature (Ts) of the PVA fiber product of the present invention in water and the alcoholysis degree (Ad) of PVA, wherein the line Ts1 represents the line Ts 3.3Ad-265, the line Ts2 represents the line Ts 3.3Ad-260, and the curve between the line Ts2 and the line Ts1 is the measured value of the water dissolution temperature of the PVA fiber of the present invention.
Detailed Description
The present invention is described in detail below by way of examples, it should be noted that the examples are only for illustrative purposes and should not be construed as limiting the scope of the present invention, and that those skilled in the art can make insubstantial modifications and adaptations of the present invention based on the above disclosure. The raw materials used in the invention are all commercial products. The PVA fiber single-fiber linear density, elongation at break and dry breaking strength are performed according to GB/T14462-1993. The degree of alcoholysis Ad was determined according to the specification of appendix D of GB/T12010.2-2010.
Testing the water-soluble temperature of the PVA fiber: putting a certain mass of PVA fiber into water (the mass ratio of the PVA fiber to the water is 1: 100), heating the water at 1 ℃ per minute, stirring while heating, and the temperature when the solution is transparent is the water-soluble temperature of the PVA fiber.
Example 1: the water-soluble PVA fiber is prepared by the following main steps:
(1) preparing a spinning solution: PVA with polymerization degree of 1600 and alcoholysis degree of 86.0 (mol)% and boric acid are dissolved in water to prepare spinning stock solution, the mass concentration of the PVA in the stock solution is 15%, the addition amount of the boric acid is 0.5% of the mass of the PVA, the stock solution is heated to 105 ℃, the pressure is maintained at 0.08MPa, the PVA is dissolved for 12 hours, and then the PVA is filtered and defoamed and enters the spinning process.
(2) Spinning: the PVA dope is delivered to the spinning pack by a metering pump and sprayed into a coagulation bath from the small holes of the spinneret. The components of the coagulating bath are dimethyl sulfoxide, methanol and ethanol, and the mass ratio of the dimethyl sulfoxide to the methanol to the ethanol is 13: 25: 41, the temperature of the coagulating bath is-5 ℃, PVA stays in the coagulating bath for 12s after being spun by a spinneret plate, and the nascent fiber is prepared.
(3) And (3) post-treatment: carrying out wet-heat stretching, extraction, oiling, stretching heat setting, mechanical curling, cutting and other working procedures on the nascent fiber to prepare water-soluble PVA fiber, wherein the solvent used in the wet-heat stretching is ethanol, and the temperature is 45 ℃; the extracting agent used for extraction is a composition of methanol and ethanol, and the molar ratio of the two is 2.9: 2.1, the temperature of the extracting agent is 10 ℃.
The water-soluble PVA fiber prepared has the water-soluble temperature of 20 ℃, the single fiber linear density of 6.5dtex, the elongation at break of 8 percent and the dry breaking strength of 6.8 cN/dtex.
Examples 2-10 were prepared by reference to example 1 and operating according to the parameters set forth in accompanying Table 1 and Table 2 below. In tables 1 and 2, DP represents the degree of polymerization, and Ad represents the degree of alcoholysis of polyvinyl alcohol, in mol/mol%.
Attached table 1:
Figure BDA0000959945420000071
attached table 2:
Figure BDA0000959945420000072
Figure BDA0000959945420000081
example 11
The embodiment provides a fiber-containing guar gum fracturing fluid, which is prepared by the following steps:
the method comprises the following steps: adding 0.2 weight part of thickening agent hydroxypropyl guar gum (Kunshan corporation, China Petroleum substance), 0.12 weight part of sodium carbonate and 0.1 weight part of potassium chloride into 100 weight parts of water under stirring, and stirring for 20min to obtain a guar thickening agent water solution;
step two: adding 0.2 part by weight of cross-linking agent aluminum nitrate into the thickening agent aqueous solution under stirring to obtain guar gum fracturing fluid (without fiber guar gum fracturing fluid);
step three: and (2) adding 0.5 part by weight of PVA fiber prepared in the example 1 into the guar gum fracturing fluid, cutting the fiber to 10mm in length, adding the fiber into the oil-gas field fracturing fluid, and uniformly dispersing to obtain the fiber-containing guar gum fracturing fluid.
Step four: the fiber-containing guanidine gum fracturing fluid is added into an oil-gas well along with a propping agent (argil, quartz sand and the like), and 0.02 part by weight of a gel breaker ammonium persulfate is added at the later stage of fracturing construction.
Example 12
Referring to example 11, the high-strength and high-modulus PVA fibers prepared in example 2 were chopped to 6mm in length, and added to the fracturing fluid in the oil and gas field to be uniformly dispersed, and when the PVA fibers were added, the PVA fibers were added to the fracturing fluid in three steps, namely, the pre-fracturing stage, the middle fracturing stage, and the post-fracturing stage, and guar gum and a crosslinking agent were also added to the fracturing fluid in the oil and gas field, and the mass content of the PVA fibers in the fracturing fluid in the oil and gas field was 1.2%.
Example 13
Referring to example 11, the high-strength and high-modulus PVA fibers prepared in example 3 were cut to 12mm in length, and added to the oil and gas field fracturing fluid to be uniformly dispersed, wherein the oil and gas field fracturing fluid further contains 0.3% by mass of guar gum, and the mass content of the PVA fibers in the oil and gas field fracturing fluid is 0.6%.
Example 14
Referring to example 11, the high-strength and high-modulus PVA fibers prepared in example 4 were chopped to a length of 20mm, and added to the oil and gas field fracturing fluid to be uniformly dispersed, and guanidine gum and a cross-linking agent were also added to the oil and gas field fracturing fluid, wherein the mass content of the PVA fibers in the oil and gas field fracturing fluid was 1.5%.
Example 15:
referring to example 11, the high-strength and high-modulus PVA fiber prepared in example 5 is cut into 12mm in length, and is added into the oil and gas field fracturing fluid to be uniformly dispersed, wherein the oil and gas field fracturing fluid does not contain guanidine gum, and the mass content of the PVA fiber in the oil and gas field fracturing fluid is 1.5%.
Example 16:
referring to example 11, the PVA fibers obtained in example 6 were cut to 6mm in length, and were uniformly dispersed in the same oil and gas field fracturing fluid as in example 1, and were added to the fracturing fluid in three steps, i.e., in the pre-fracturing stage, the mid-fracturing stage, and the end-fracturing stage, respectively, when the PVA fibers were added, the mass content of the PVA fibers in the oil and gas field fracturing fluid was 1.2%.
Test example 17: comparative example 1
The embodiment provides a fiber-containing guar gum fracturing fluid, which is prepared by the following steps:
the method comprises the following steps: adding 0.2 weight part of thickening agent hydroxypropyl guar gum (Kunshan corporation, China Petroleum substance), 0.12 weight part of sodium carbonate and 0.1 weight part of potassium chloride into 100 weight parts of water under stirring, and stirring for 20min to obtain a guar thickening agent water solution;
step two: adding 0.2 weight part of cross-linking agent FAL-120 (Wanke oil and gas technology engineering Co., Ltd., Gallery) into the thickener aqueous solution under stirring to obtain guar gum fracturing fluid (without fiber guar gum fracturing fluid);
step three: adding 0.5 part by weight of polyacrylonitrile fibers (the tensile strength is 100MPa, the real density is 0.98g/cm3, the length is 5mm, and the diameter is 78 μm) into the guar gum fracturing fluid, and uniformly mixing to obtain the fiber-containing guar gum fracturing fluid. The fiber-containing guar gum fracturing fluid is applied to fracturing construction of wells at 80 ℃.
Step four: the fiber-containing guanidine gum fracturing fluid is added into an oil-gas well along with a propping agent (argil, quartz sand and the like), and 0.02 part by weight of a gel breaker ammonium persulfate is added at the later stage of fracturing construction.
Example 18
The static sand-carrying method is adopted to verify the sand-carrying capacity of the fracturing fluid, and the method is carried out at room temperature in a laboratory, and comprises the following experimental steps:
(1) adding a thickening agent hydroxypropyl guar gum in a certain proportion into clear water to prepare a thickening agent water solution;
(2) adding the fibers and the proppant prepared in the example 1 according to experimental requirements (0.3-0.6 mm of ceramsite is selected and meets the SY/T5108-2006 standard, the breakage rate is 4.0% under 69 MPa), adding a proper amount of cross-linking agent aluminum sulfate, stirring to form fracturing fluid, and pouring a mixture of the fracturing fluid, the fibers and the proppant into a measuring cylinder;
(3) the mixture obtained in (2) was left to stand at room temperature for 120min, the height of the proppant settled in the fracturing fluid was recorded and the settling rate (height of settled divided by settling time) was calculated.
Group 1 2 groups of Group 3
Thickener concentration (wt%) 0.50wt％ 0.50wt％ 0.90wt％
Fiber concentration (wt%) 0 0.4 0
Sedimentation Rate (cm/min) 0.074 0.013 0.015
It is apparent from the table that when the concentrations of the thickening agents are all 0.50 wt%, the settling rate of the proppant in 1 group of fracturing fluid (fracturing fluid without fibers) is much greater than that in 2 groups of fracturing fluid (fracturing fluid with fibers), and thus it can be seen that the sand carrying capacity of the fracturing fluid is greatly improved by the addition of the fibers. The settling rates of the proppant in 2 groups of fracturing fluids (the fiber-containing fracturing fluid with the thickening agent concentration of 0.50 wt%) and 3 groups of fracturing fluids (the fiber-free fracturing fluid with the thickening agent concentration of 0.90 wt%) are equivalent, so that the use of the fiber can ensure the sand carrying capacity of the fracturing fluid while reducing the concentration of the thickening agent in the fracturing fluid.
The fracturing fluids of examples 11-17 were tested for sand-carrying capacity with reference to the test method of example 18.
Figure BDA0000959945420000111
As can be seen from the table, the PVA fiber provided by the invention can be added into the fracturing fluid, so that the sand carrying capacity of the fracturing fluid can be obviously improved. In addition, in terms of flowback time after fracturing construction is finished, flowback is finished in two or three days generally, and the product can be flowback within 2 hours after being used, so that the flowback time is not required to be two hours. In terms of flowback efficiency, the flowback efficiency of the fracturing fluid using the fiber of the invention is greatly improved and is higher than that of the fiber of the example 17 (the fiber of the comparative example 1) by more than 20 percent; taking example 11 as an example, the flowback rate of the oil and gas well fracturing fluid of example 11 after 15 hours was about 20% higher than that of example 17. In terms of the sand content of the flowback fluid, the sand content of the flowback fluid using the fiber of the invention is greatly reduced by 10-30% compared with that of the example 17; taking example 11 as an example, the reduction is about 28% compared with example 17. In terms of oil and gas well yield, the oil and gas well yield using the fracturing fluid is greatly improved, and compared with the embodiment 17, the yield is improved by more than 50%; taking example 11 as an example, the production of the fracturing fluid is improved by about 55 percent compared with the production of the oil and gas well using the fracturing fluid of example 17.
The water-soluble fibers prepared in examples 7 to 10 are prepared into the oil-gas field fracturing fluid according to example 11, and the oil-gas field fracturing fluid is strong in sand carrying capacity, good in water solubility and free of secondary pollution. Meanwhile, the addition of the PVA fiber can enhance the flowback efficiency of the fracturing fluid, and by taking the example 11 as an example, the addition amount of the PVA fiber is 0.6 percent of the mass of the fracturing fluid, the guanidine gum is also added into the fracturing fluid, the prepared fracturing fluid is used for fracturing construction, and the flowback rate of the fracturing fluid reaches more than 80 percent; the addition amount of the PVA fiber is 1.2 percent of the mass of the fracturing fluid, the prepared fracturing fluid is used for fracturing construction, and the flowback rate of the fracturing fluid reaches more than 85 percent.
When the PVA fiber provided by the invention is used in the field of oil field well cementation and temporary plugging, the PVA fiber can be better combined with a support system, so that the functions of well cementation, temporary plugging and the like can be better played.

Claims (10)

1. A preparation method of PVA fiber is characterized in that the PVA fiber is prepared by spinning PVA with the polymerization degree of 1500-2500 and the alcoholysis degree Ad of 86% to 95.0%, wherein the dissolving temperature TS (DEG C) of the PVA fiber in water and the alcoholysis degree Ad (mol/mol)% of polyvinyl alcohol satisfy the following formula (I):
3.3Ad-265≤TS≤3.3Ad-260(Ⅰ)；
the elongation at break of the PVA fiber is 5-30%;
the preparation method of the PVA fiber comprises the following steps:
(1) preparing a spinning solution: dissolving PVA with the polymerization degree of 1500-2500 and the alcoholysis degree of 86.0-95 (mol%) and boric acid in water to prepare spinning stock solution, wherein the mass concentration of the PVA in the stock solution is 12-18%, the addition amount of the boric acid is 0.4-1.5% of the mass of the PVA, heating the stock solution to 90-105 ℃, keeping the pressure at 0.05-0.15 MPa, dissolving for 5-20 hours, filtering and defoaming, and entering a spinning process;
(2) spinning: and (2) pumping the PVA stock solution to a spinning assembly by using a metering pump, spraying the PVA stock solution into a coagulation bath from a small hole of a spinning nozzle, wherein the components of the coagulation bath comprise dimethyl sulfoxide, methanol and ethanol, and the mass ratio of the dimethyl sulfoxide to the methanol to the ethanol is 5-35: 24-35: 36-55 ℃, wherein the temperature of the coagulating bath is-20-10 ℃, PVA stays in the coagulating bath for 10-25 s after being subjected to spinning by a spinneret plate, and thus nascent fiber is prepared;
(3) and (3) post-treatment: carrying out wet-heat stretching, extraction, oiling, stretching heat setting and mechanical curling on the nascent fiber to prepare water-soluble PVA fiber, wherein ethanol is used as a solvent for the wet-heat stretching, and the temperature is 40-50 ℃; the extracting agent used for extraction is a composition of methanol and ethanol, and the molar ratio of the methanol to the ethanol is 2.8-4.5: 1.5-2.5, and the temperature of the extracting agent is 5-15 ℃.
2. The method of claim 1, wherein: the single fiber density of the PVA fiber is 0.5-50 dtex.
3. The method of claim 1, wherein: the dry breaking strength of the PVA fiber is 3-15 cN/dtex.
4. Use of PVA fibers prepared according to the process of any one of claims 1 to 3 in the field of oil and gas.
5. The use of claim 4, wherein: the application in the field of oil and gas fields is application in fracturing fluid of oil and gas fields.
6. An oil and gas field fracturing fluid comprising PVA fibers prepared by the method of any one of claims 1 to 3, characterized in that: the PVA fiber accounts for 0.5-3.0% of the fracturing fluid of the oil and gas field.
7. The field fracturing fluid of claim 6, wherein: the fracturing fluid of the oil and gas field contains guanidine gum.
8. The field fracturing fluid of claim 7, wherein: a cross-linking agent and a gel breaker are also added into the oil-gas field fracturing fluid; the cross-linking agent is one or a combination of more of aluminum sulfate, aluminum nitrate, titanium tetrachloride, titanium sulfate, organic titanium, zinc sulfate, boric acid and borax; the gel breaker is potassium persulfate, ammonium persulfate, potassium dichromate, potassium permanganate, amylase or organic acid.
9. The use of claim 4, wherein: the application in the field of oil and gas fields is the application in the fracturing temporary plugging construction of the oil and gas fields.
10. The use of claim 4, wherein: the application in the field of oil and gas fields is the application in oil and gas field well cementation construction.
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