Fracturing fluid for reservoir transformation as well as preparation method and application of fracturing fluid

Abstract

The invention relates to a fracturing fluid for reservoir transformation as well as a preparation method and application thereof, and aims to solve the problems of poor high-temperature resistance, poor shearing performance, poor gel breaking performance and residual residues of a fracturing fluid used for a reservoir of which the temperature is greater than or equal to 200 DEG C in the prior art. The fracturing fluid for reservoir transformation comprises a quadripolymer thickening agent, a cross-linking agent, a cross-linking accelerant, a gel breaker and water. According to the fracturing fluid for reservoir transformation, the formula of the fracturing fluid is designed, the quadripolymer thickening agent is introduced to adjust the fracturing fluid system, and the synergistic effect among the components is utilized, so that the obtained fracturing fluid can tolerate the high temperature of 180 DEG C or above, the system is high in gel breaking efficiency and low in residue content, and the reservoir development benefit can be further improved.

Description

Technical Field

[0001] The invention relates to the technical field of oilfield chemistry, and in particular to a fracturing fluid for reservoir reconstruction, a preparation method and application thereof. Background Art

[0002] At present, the conventional fracturing fluid system is only suitable for formations with temperatures below 160°C, and its rheology and sand carrying capacity can no longer meet the needs of ultra-deep well reservoir reconstruction.

[0003] For example, CN113684017A discloses a low-residue water-based fracturing fluid, including a thickener, 200ppm-2000ppm of diisopropylbenzene peroxide, and 100ppm-800ppm of alkylamine oxide, wherein the thickener is a plant gum or a synthetic polymer. The low-residue water-based fracturing fluid has good shear resistance, high viscosity, and different gel breaking speeds at different temperatures. It is intelligently controllable and can be applied to oil reservoirs at 75-140°C. At the same time, the gel breaking speed can be adjusted by controlling the amount of diisopropylbenzene peroxide added, and the application range is wider.

[0004] However, with the rapid development of oil and gas exploration, exploitation is carried out in deep formations, such as deep carbonate oil reservoirs, deep volcanic gas reservoirs, deep carbonate gas reservoirs, tight sandstone gas reservoirs and other reservoirs, where the reservoir temperature is as high as over 180°C. Therefore, there is an urgent need to develop a new low-damage fracturing fluid system that can be applied to high-temperature (above 180°C) reservoirs, has heat and shear resistance, is easy to break, and has no residue. Summary of the invention

[0005] In view of the problems existing in the prior art, the object of the present invention is to provide a fracturing fluid for reservoir transformation and a preparation method and use thereof, so as to solve the problems of high temperature resistance, poor shear performance, poor gel breaking performance and residual residue in the prior art fracturing fluid used for reservoirs ≥200°C.

[0006] To achieve this object, the present invention adopts the following technical solutions:

[0007] In a first aspect, the present invention provides a fracturing fluid for reservoir reconstruction, wherein the fracturing fluid for reservoir reconstruction comprises: a tetrapolymer thickener, a cross-linking agent, a cross-linking accelerator, a breaker and water.

[0008] The fracturing fluid for reservoir transformation provided by the present invention designs the formula of the fracturing fluid, introduces a tetrapolymer thickener to adjust the fracturing fluid system, and utilizes the synergistic effect between the components, so that the obtained fracturing fluid can withstand high temperatures above 180°C, and the system has high gel breaking efficiency and low residue content, which can further improve the benefits of reservoir development.

[0009] As a preferred technical solution of the present invention, the fracturing fluid for reservoir reconstruction comprises, by weight: 1-2 parts of a tetrapolymer thickener, 0.2-0.3 parts of a crosslinking agent, 0.2-0.3 parts of a crosslinking accelerator, 0.1-0.2 parts of a breaker and 95.2-97.5 parts of water.

[0010] As a preferred technical solution of the present invention, the tetrapolymer thickener is obtained by copolymerizing acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, N,N'-dimethylacrylamide and 4-((2-(allylbromoamino)ethyl)amino)-4-oxybutane-1-sulfonic acid by a step-by-step inverse emulsion polymerization method.

[0011] Preferably, the molecular weight of the tetrapolymer thickener is 6 million to 10 million.

[0012] As a preferred technical solution of the present invention, the cross-linking agent includes one or a combination of at least two of boric acid, sodium borate or sodium chromate.

[0013] As a preferred technical solution of the present invention, the cross-linking accelerator includes one or a combination of at least two of aluminum citrate, zirconium oxychloride or sodium bicarbonate.

[0014] As a preferred technical solution of the present invention, the breaker includes ammonium persulfate.

[0015] As a preferred technical solution of the present invention, the fracturing fluid for reservoir reconstruction also includes a functional additive.

[0016] As a preferred technical solution of the present invention, the functional additive includes one or a combination of at least two of a clay stabilizer, a high temperature stabilizer, an iron ion stabilizer, a pH adjuster, a proppant, a viscosity promoter, a drainage agent or an anti-swelling agent.

[0017] In a second aspect, the present invention provides a method for preparing a fracturing fluid for reservoir transformation as described in the first aspect, the preparation method comprising: first mixing a tetrapolymer thickener and water according to a formula, then adding a gel breaker for a second mixing, and then adding a cross-linking agent and a cross-linking aid to react to obtain a fracturing fluid for reservoir transformation.

[0018] In a third aspect, the present invention provides a use of the reservoir reconstruction fracturing fluid as described in the first aspect, wherein the use comprises using the reservoir reconstruction fracturing fluid to perform reservoir reconstruction on a high-temperature reservoir.

[0019] Compared with the prior art solutions, the present invention has the following beneficial effects:

[0020] (1) The ultra-high temperature reservoir transformation fracturing fluid system provided by the present invention has the ability of online mixing, and does not require advance mixing at a mixing station, which can greatly reduce the mixing time and improve the efficiency of reservoir transformation construction.

[0021] (2) The ultra-high temperature reservoir transformation fracturing fluid system provided by the present invention has the ability to continuously change viscosity. The viscosity of the fracturing fluid can be changed by adjusting the amount of modified thickener. There is no need to prepare the fluid in advance at the fluid preparation station, which can greatly reduce the preparation time and improve the efficiency of reservoir transformation construction.

[0022] (3) The molecular weight of the thickener in the ultra-high temperature reservoir reconstruction fracturing fluid system provided by the present invention is 6 million to 10 million, which can achieve efficient gel breaking with low residue content under the action of the gel breaker. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a shear test result diagram of the reservoir reconstruction fracturing fluid obtained in Example 1 of the present invention;

[0024] Figure 2 This is a diagram showing the shear test results of the reservoir reconstruction fracturing fluid obtained in Example 2 of the present invention;

[0025] Figure 3 This is a diagram showing the shear test results of the reservoir reconstruction fracturing fluid obtained in Example 3 of the present invention;

[0026] Figure 4 This is a shear test result diagram of the reservoir reconstruction fracturing fluid obtained in Example 4 of the present invention;

[0027] Figure 5 This is a shear test result diagram of the reservoir reconstruction fracturing fluid obtained in Example 5 of the present invention;

[0028] Figure 6 This is a diagram showing the shear test results of the reservoir reconstruction fracturing fluid obtained in Example 6 of the present invention.

[0029] The present invention is further described in detail below. However, the following examples are only simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims. DETAILED DESCRIPTION

[0030] To better illustrate the present invention and facilitate understanding of the technical solution of the present invention, typical but non-limiting embodiments of the present invention are as follows:

[0031] This embodiment provides a fracturing fluid for reservoir reconstruction, which includes: a tetrapolymer thickener, a cross-linking agent, a cross-linking accelerator, a breaker and water.

[0032] Specifically, the fracturing fluid for reservoir reconstruction comprises, by weight: 1-2 parts of a tetrapolymer thickener, 0.2-0.3 parts of a crosslinking agent, 0.2-0.3 parts of a crosslinking accelerator, 0.1-0.2 parts of a breaker, and 95.2-97.5 parts of water.

[0033] The tetrapolymer thickener is obtained by copolymerizing acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, N,N'-dimethylacrylamide and 4-((2-(allylbromoamino)ethyl)amino)-4-oxybutane-1-sulfonic acid by a step-by-step inverse emulsion polymerization method.

[0034] An exemplary process is as follows:

[0035] S1, acrylamide, 2-acrylamido-2-methylpropanesulfonic acid and water are first mixed, then an oil phase and an emulsifier are added and first stirred under a protective atmosphere, then an initiator is added and second stirred, and a first heat preservation reaction is performed to obtain a polymer A;

[0036] In the S1 process, the mass ratio of acrylamide, 2-acrylamido-2-methylpropanesulfonic acid and water is controlled to be (2-3):1:(6-7); the first mixing time is 2-3min; the stirring speed of the first mixing is 300-400r / min; the first stirring time is 30-60min; the first stirring speed is 300-400r / min; the second stirring time is 10-20min; the second stirring speed is 300-400r / min; the temperature of the first insulation reaction is 30-60°C, and the insulation is 4-8h; the mass ratio of 2-acrylamido-2-methylpropanesulfonic acid, oil phase and emulsifier is (2.4-2.6):(14.8-15.2):1;

[0037] S2, acrylamide, N,N'-dimethylacrylamide and water are mixed for a second time, and then an oil phase and an emulsifier sulfonated polyvinyl alcohol are added and stirred for a third time under a protective atmosphere, and then an initiator is added and stirred for a fourth time, and a second heat preservation reaction is carried out to obtain polymer B;

[0038] In the S2 process, the mass ratio of acrylamide, N,N'-dimethylacrylamide and water is controlled to be 1:1:(4-4.5); the second mixing time is 5-10min; the stirring speed of the second mixing is 300-400r / min; the third stirring time is 30-60min; the third stirring speed is 300-400r / min; the fourth stirring time is 10-20min; the fourth stirring speed is 100-150r / min; the temperature of the second heat preservation reaction is 30-60℃, and the heat preservation is 3-6h; the mass ratio of N,N'-dimethylacrylamide, oil phase and emulsifier is (3.7-3.8):(14.9-15.2):1;

[0039] S3, acrylamide, 4-((2-(allyl bromide amino)ethyl)amino)-4-oxybutane-1-sulfonic acid and water are mixed for a third time, and then an oil phase and an emulsifier alkylphenol polyoxyethylene ether are added and stirred for a fifth time under a protective atmosphere, and then an initiator is added and stirred for a sixth time, and a third heat preservation reaction is carried out to obtain a polymer C;

[0040] During S3, the mass ratio of acrylamide, 4-((2-(allyl bromide amino)ethyl)amino)-4-oxobutane-1-sulfonic acid and water is controlled to be 1:1:(6-6.2); the time of the third mixing is 10-20min; the stirring speed of the third mixing is 200-300r / min; the time of the fifth stirring is 30-60min; the speed of the fifth stirring is 200-300r / min; the time of the sixth stirring is 10-20min; the speed of the sixth stirring is 100-200r / min; the temperature of the third insulation reaction is 30-60°C, and the insulation is 3-6h; the mass ratio of 4-((2-(allyl bromide amino)ethyl)amino)-4-oxobutane-1-sulfonic acid, oil phase and emulsifier is (2.4-2.6):(14.8-15.2):1;

[0041] S4, mixing polymer A, polymer B and polymer C for the fourth time and adding an initiator to carry out a fourth heat preservation reaction under a protective atmosphere to obtain polymer D, and mixing the obtained polymer D with a diverting agent to obtain a tetrapolymer thickener;

[0042] During S4, the fourth mixing time is 15-20 min; the fourth mixing speed is 100-200 r / min; the temperature of the fourth insulation reaction is 30-60°C, and the insulation is 4-6 h; the mass ratio of polymer A, polymer B and polymer C is 1:1:1; the initiator added is 0.01-0.02 times the total mass of polymer A, polymer B and polymer C; the amount of the diverter used is 0.1-0.2 times the mass of polymer D.

[0043] Wherein, the protective atmosphere in the preparation process of the tetrapolymer thickener is a gas that does not affect the reaction process, such as nitrogen, helium, neon or argon. The oil phase used can be selected as a commonly used oil phase in the art, such as kerosene or white oil. The emulsifier used includes one or a combination of at least two of Span 80, sulfonated polyvinyl alcohol or alkylphenol polyoxyethylene ether. The initiator used includes an oil-soluble initiator commonly used in the art, such as azo initiators and / or peroxides, and illustratively can be selected as azobisisobutyronitrile, azobisisoheptylnitrile, etc. The diverter used can be selected as a commonly used diverter in the art, and illustratively such as being selected as alkylphenol polyoxyethylene ether.

[0044] Further, the 4-((2-(allylbromoamino)ethyl)amino)-4-oxobutane-1-sulfonic acid used is obtained by the following process:

[0045] (1) N-(2-dimethylaminoethyl)acrylamide is mixed with water and heated to 40-50° C., then a Lewis base catalyst is added, and 1-butene is continuously introduced to maintain the reactor pressure at 0.5-0.6 kPa, and the reaction is carried out for 2-2.5 hours;

[0046] The solid-liquid ratio of N-(2-dimethylaminoethyl)acrylamide to water is 1:(3-5) in g / mL; the Lewis base catalyst comprises potassium fluoride; and the addition amount of the Lewis base catalyst is 10-12% of the mass of the N-(2-dimethylaminoethyl)acrylamide;

[0047] (2) subjecting the product obtained in step (1) to solid-liquid separation to obtain a liquid product, which is N-(2-(dimethylamino)ethyl)pent-4-enamide; the solid-liquid separation is performed by suction filtration;

[0048] (3) The liquid product obtained in the previous step is added to anhydrous acetic acid and the temperature is increased, and then malonic acid is added to react. During the reaction, sulfur trioxide is continuously introduced to maintain the reactor pressure at 0.5-0.6 kPa, and the sulfonation reaction is continued for 7-8 hours; the mass ratio of the liquid product to the anhydrous acetic acid is 1:(35-45), and the terminal temperature of the heating is 70-80° C.; the liquid-solid mL / g of the anhydrous acetic acid and the malonic acid is (240-260):1;

[0049] (4) distilling the product obtained in step (3) to obtain the product 4-((2-(dimethylamino)ethyl)amino)-4-oxobutane-1-sulfonic acid; the distillation pressure is 0.01-0.1 MPa; the distillation temperature is 60-80° C.;

[0050] (5) adding the product obtained in step (4) to dichloromethane, heating the mixture, adding a catalyst, adding 3-bromo-1-propylene under stirring, and continuing the reaction for 12-13 hours; the volume ratio of the product to dichloromethane is 1:(15-25); the heating temperature is 60-70° C.; the catalyst comprises boron trifluoride; the stirring speed is 300-400 r / min; the solid-liquid ratio of the catalyst to dichloromethane is g / mL 1:(50-70); the solid-liquid ratio of the catalyst to 3-bromo-1-propylene is g / mL 1:(9-11);

[0051] (6) After the reaction is completed, distillation is performed to obtain the product 4-((2-(allylbromoamino)ethyl)amino)-4-oxobutane-1-sulfonic acid; the distillation pressure is 0.0-0.1 MPa; the distillation temperature is 60-70°C.

[0052] The molecular formula of the reaction process is as follows:

[0053]

[0054] Specifically, the cross-linking agent includes one or a combination of at least two of boric acid, sodium borate or sodium chromate.

[0055] Specifically, the cross-linking accelerator includes one or a combination of at least two of aluminum citrate, zirconium oxychloride or sodium bicarbonate.

[0056] Specifically, the breaker includes ammonium persulfate.

[0057] In the present invention, the reservoir reconstruction fracturing fluid also includes a functional additive, and the amount of the functional additive added can be reasonably designed according to the actual function to be enhanced. For example, the functional additive is added in 0-2 parts by weight, which is the number of parts added for a single functional additive.

[0058] Specifically, the functional additives include commonly used functional additives in the art, such as clay stabilizers, high temperature stabilizers, iron ion stabilizers, pH adjusters, proppants, and other fracturing fluid functional additives commonly added to fracturing fluids in the art, such as viscosity promoters, drainage aids, anti-swelling agents, etc.

[0059] The clay stabilizer may be selected from one or a combination of at least two of sodium chloride, potassium chloride, ammonium chloride, tetramethylammonium chloride (TMAC) or other quaternary ammonium molecules.

[0060] The high temperature stabilizer can be thiourea or other high temperature stabilizers commonly used in the art. The high temperature stability of the fracturing fluid can be further enhanced by introducing the high temperature stabilizer, which is beneficial to the embodiment of the fracturing fluid effect.

[0061] The iron ion stabilizer can be selected from diisopropylamine pentaacetic acid and other commonly used iron ion stabilizers in the art.

[0062] Wherein, the pH adjuster can be selected as acetic acid and / or hydrochloric acid, and the acid is added to the fracturing fluid so that the pH value of the fracturing is controlled to be 2-7.3.

[0063] Among them, the proppant includes sand, gravel, glass beads, ceramic proppant, bauxite, tetrafluoroethylene material, fruit core material, processed wood, composite particle combination prepared by adhesive and fine-grade particles (such as silica, alumina, fumed silica, carbon black, graphite, mica, titanium dioxide, metasilicate, calcium silicate, kaolin, talc, zirconium oxide, boron, fly ash, hollow glass microspheres, solid glass or a combination thereof), etc.

[0064] The viscosity promoter may be sodium acetate or other commonly used viscosity promoters in the art.

[0065] The degassing agent may be selected from commonly used degassing agents in the art such as ethylene oxide.

[0066] The anti-swelling agent can be selected from ethylene oxide alcohol and other commonly used anti-swelling agents in the art.

[0067] Furthermore, the present invention provides a method for preparing the aforementioned reservoir reconstruction fracturing fluid, specifically, a tetrapolymer thickener and water are first mixed according to a formula, a breaker is then added for second mixing, and a cross-linking agent and a cross-linking aid are added for reaction to obtain the reservoir reconstruction fracturing fluid. If a functional additive is required to be introduced into the reservoir reconstruction fracturing fluid, it can be added together in the first mixing.

[0068] The first mixing includes two stirring processes, the first stirring is stirring at 2910-3090r / min for 2-3min, and the second stirring is stirring at 970-1030r / min for 3-4min; the stirring speed of the second mixing is 300-400r / min, and the time is 15-30min; the reaction time after adding the crosslinking agent and the crosslinking auxiliary agent is 300-400s. The reaction temperature during the preparation process can be controlled at 25-40°C; all the reagents in the first mixing are added during the first stirring process.

[0069] Furthermore, the present invention provides a use of the aforementioned fracturing fluid for reservoir transformation, specifically, using the fracturing fluid for reservoir transformation to transform a high-temperature storage reservoir.

[0070] In the present invention, a high temperature reservoir refers to a reservoir with a reservoir temperature of ≥200°C.

[0071] In order to further illustrate the effect of the aforementioned reservoir reconstruction fracturing fluid provided by the present invention, the present invention provides the following specific embodiments. Except for the reagents that need to be synthesized in the embodiments, the other reagents used are all commercially available reagents and can be purchased from the market. The water quality of the simulated formation water used is detailed in Table 1.

[0072] Table 1

[0073]

[0074] The preparation process of the tetrapolymer thickener used in the following examples is as follows:

[0075] (1) Add 20 parts of acrylamide and 10 parts of 2-acrylamido-2-methylpropanesulfonic acid into a three-necked flask filled with 60 parts of deionized water to prepare an aqueous phase solution; stir the monomers thoroughly with a stirrer to dissolve the monomers;

[0076] (2) During the stirring process, 60 parts of kerosene and 4 parts of Span80 emulsifier were added, and the mixture was stirred for 45 minutes under a nitrogen atmosphere. Then, 1 part of azobisisobutyronitrile initiator was added, and stirring was continued for 15 minutes.

[0077] (3) The solution obtained in step (2) was transferred into an oil bath preheated to 45° C. and reacted for 6 h; the obtained product was polymer A;

[0078] (4) adding 15 parts of acrylamide and 15 parts of N,N'-dimethylacrylamide into a three-necked flask containing 60 parts of deionized water to prepare an aqueous phase solution; stirring the monomers thoroughly with a stirrer to dissolve the monomers;

[0079] (5) During the stirring process, 60 parts of kerosene and 4 parts of sulfonated polyvinyl alcohol (molecular weight 15,000) were added, and the mixture was stirred for 45 minutes under a nitrogen atmosphere. Then, 1 part of azobisisobutyronitrile initiator was added, and stirring was continued for 20 minutes.

[0080] (6) The solution obtained in step (5) was transferred into an oil bath preheated to 60° C. and reacted for 3 h; the obtained product was polymer B;

[0081] (7) adding 10 parts of acrylamide and 10 parts of 4-((2-(allylbromoamino)ethyl)amino)-4-oxobutane-1-sulfonic acid into a three-necked flask containing 60 parts of deionized water to prepare an aqueous phase solution; stirring the monomers thoroughly with a stirrer to dissolve the monomers;

[0082] (8) During the stirring process, 60 parts of kerosene and 4 parts of alkylphenol polyoxyethylene ether (degree of polymerization: 8) were added, and the mixture was stirred for 30 minutes under a nitrogen atmosphere. Then, 1 part of azobisisobutyronitrile initiator was added, and stirring was continued for 20 minutes.

[0083] (9) The solution obtained in step (8) was transferred into an oil bath preheated to 60° C. and allowed to react for 3 h. The obtained product was polymer C.

[0084] (10) Polymer A, polymer B and polymer C were mixed in a mass ratio of 1:1:1 and added to an oil bath at 55°C. The mixture was stirred thoroughly under a nitrogen atmosphere and 1 part of azobisisobutyronitrile was added. The mixture was reacted for 6 hours to obtain a polymer D.

[0085] (11) Add 1 part of diverting agent alkylphenol polyoxyethylene ether (degree of polymerization: 8) to polymer D in step (10), stir thoroughly for 1.5 hours, and the resulting product is filtered to obtain a tetrapolymer thickener (viscosity average molecular weight: 7 million).

[0086] The preparation process of 4-((2-(allyl bromide amino)ethyl)amino)-4-oxobutane-1-sulfonic acid in the tetrapolymer thickener is as follows:

[0087] (1) 50 g of N-(2-dimethylaminoethyl)acrylamide was dissolved in 200 mL of deionized water, and heated to 40° C. in a water bath, 5 g of potassium fluoride was added as a Lewis base catalyst, and 1-butene was continuously introduced to maintain the reactor pressure at 0.5 kPa, and the reaction was continued for 2 h;

[0088] (2) Filter the product obtained in the previous step under a negative pressure of 0.1 MPa to filter out the solid matter, and the obtained liquid product is N-(2-(dimethylamino)ethyl)pent-4-enamide;

[0089] (3) The product obtained in the previous step was added to 500 mL of anhydrous acetic acid (ensuring that the mass ratio of the product to the anhydrous acetic acid was 1:40), and heated to 70° C. in a water bath, 2 g of malonic acid was added to promote the reaction, sulfur trioxide was continuously introduced to maintain the reactor pressure at 0.5 kPa, and the sulfonation reaction was continued for 7 h;

[0090] (4) distilling the product at 60° C. and a negative pressure of 0.1 MPa to obtain 4-((2-(dimethylamino)ethyl)amino)-4-oxobutane-1-sulfonic acid;

[0091] (5) Add 15 mL of the product obtained in step (4) to 300 mL of dichloromethane, heat to 60° C. in a water bath, add 5 g of boron trifluoride catalyst, add 50 mL of 3-bromo-1-propylene at a stirring speed of 300 r / min, and continue the reaction for 12 h;

[0092] (6) After the reaction was completed, distillation was performed at 60°C and a negative pressure of 0.1 MPa to obtain the product 4-((2-(allylbromoamino)ethyl)amino)-4-oxobutane-1-sulfonic acid.

[0093] Example 1

[0094] The present embodiment provides a fracturing fluid for reservoir reconstruction, comprising: 1.3 parts of a tetrapolymer thickener (with a degree of polymerization of 7 million), 0.26 parts of a cross-linking agent (boric acid), 0.23 parts of a cross-linking accelerator (aluminum citrate), 0.14 parts of a breaker (ammonium persulfate), and 96 parts of water.

[0095] The preparation process is as follows:

[0096] According to the formula, the tetrapolymer thickener and water are first mixed, and then the gel breaker is added for second mixing, and then the cross-linking agent and the cross-linking auxiliary agent are added for reaction to obtain the fracturing fluid for reservoir reconstruction; during the first stirring process, all the reagents in the first mixture are added;

[0097] Among them, the first mixing includes two stirring processes, the first stirring is stirring at 3000r / min for 2min, and the second stirring is stirring at 1030r / min for 4min; the stirring speed of the second mixing is 300r / min, and the time is 5min; the reaction time after adding the crosslinking agent and the crosslinking aid is 250s; the reaction temperature during the preparation process is controlled at 25°C.

[0098] Example 2

[0099] The present embodiment provides a fracturing fluid for reservoir reconstruction, comprising: 1.7 parts of a tetrapolymer thickener (viscosity-average molecular weight of 7 million), 0.23 parts of a cross-linking agent (sodium borate), 0.27 parts of a cross-linking accelerator (zirconium oxychloride), 0.18 parts of a breaker (ammonium persulfate), and 97 parts of water.

[0100] The preparation process is as follows:

[0101] According to the formula, the tetrapolymer thickener and water are first mixed, and then the gel breaker is added for second mixing, and then the cross-linking agent and the cross-linking auxiliary agent are added for reaction to obtain the fracturing fluid for reservoir reconstruction; during the first stirring process, all the reagents in the first mixture are added;

[0102] The first mixing includes two stirring processes, the first stirring is stirring at 3090r / min for 2min, and the second stirring is stirring at 1030r / min for 3min; the stirring speed of the second mixing is 300r / min, and the time is 5min; the reaction time for adding the crosslinking agent and the crosslinking aid is 250s; the reaction temperature during the preparation process is controlled at 25-40°C.

[0103] Example 3

[0104] The present embodiment provides a fracturing fluid for reservoir reconstruction, comprising: 2 parts of a tetrapolymer thickener (viscosity-average molecular weight of 7 million), 0.3 parts of a cross-linking agent (sodium chromate), 0.2 parts of a cross-linking accelerator (sodium bicarbonate), 0.1 parts of a breaker (ammonium persulfate), and 97.5 parts of water.

[0105] The preparation process is as follows:

[0106] According to the formula, the tetrapolymer thickener and water are mixed for the first time, and then the gel breaker is added for the second mixing, and then the cross-linking agent and the cross-linking auxiliary agent are added to react to obtain the fracturing fluid for reservoir reconstruction; 0.3 parts of high temperature stabilizer thiourea, 0.18 parts of viscosity stabilizer (sodium acetate), 0.5 parts of drainage aid (ethylene oxide alcohol), and 0.3 parts of anti-swelling agent (potassium chloride) are also added to the first mixture; all the reagents in the first mixture are added during the first stirring process;

[0107] Among them, the first mixing includes two stirring processes, the first stirring is stirring at 2910 rr / min for 2 minutes, and the second stirring is stirring at 970 r / min for 4 minutes; the stirring speed of the second mixing is 300 r / min, and the time is 30 minutes; the reaction time for adding the crosslinking agent and the crosslinking aid is 250 seconds; the reaction temperature during the preparation process is controlled at 40°C.

[0108] Example 4

[0109] The present embodiment provides a fracturing fluid for reservoir reconstruction, comprising: 1 part of a tetrapolymer thickener (viscosity-average molecular weight of 7 million), 0.2 parts of a cross-linking agent (boric acid), 0.3 parts of a cross-linking accelerator (sodium bicarbonate), 0.2 parts of a breaker (ammonium persulfate), and 95.2 parts of water.

[0110] The preparation process is as follows:

[0111] According to the formula, the tetrapolymer thickener and water are first mixed, and then a breaker is added for second mixing, and then a cross-linking agent and a cross-linking auxiliary agent are added for reaction to obtain a fracturing fluid for reservoir reconstruction; functional auxiliary agents are also added to the first mixture, including 0.3 parts of a viscosity-enhancing promoter and 0.12 parts of a high-temperature stabilizer; all the reagents in the first mixture are added during the first stirring process;

[0112] Among them, the first mixing includes two stirring processes, the first stirring is stirring at 2950r / min for 3 minutes, and the second stirring is stirring at 1030r / min for 3 minutes; the stirring speed of the second mixing is 300r / min, and the time is 40min; the reaction time for adding the crosslinking agent and the crosslinking aid is 150s; the reaction temperature during the preparation process is controlled at 30°C.

[0113] Example 5

[0114] The only difference from Example 1 is that the amount of the tetrapolymer thickener added is 0.1 part.

[0115] Example 6

[0116] The only difference from Example 1 is that the amount of the tetrapolymer thickener added is 3 parts.

[0117] Evaluation Test

[0118] I. Compatibility Evaluation

[0119] The fracturing fluid obtained in Examples 1-6 and simulated formation water were added to a blue threaded bottle at a mass ratio of 1:2, 1:1, and 2:1, respectively, and placed for 48 hours to observe the compatibility; if no precipitation, stratification, or degradation occurs, the compatibility is good, otherwise it is unqualified; the compatibility evaluation results are detailed in Table 2.

[0120] Table 2

[0121] precipitation Layering degradation Compatibility Example 1 none none none qualified Example 2 none none none qualified Example 3 none none none qualified Example 4 none none none qualified Example 5 none none have Failure Example 6 none have none Failure

[0122] II. Gel breaking performance

[0123] The fracturing fluid obtained in Examples 1-6 was mixed with simulated formation water at a mass ratio of 1:2, 1:1, and 2:1, respectively, and then allowed to stand at 200° C. for 16 h. The viscosity was measured using a Haake rheometer. The results are shown in Table 3.

[0124] Table 3

[0125]

[0126] III. Evaluation of residue content

[0127] The fracturing fluid obtained in Example 1-6 was allowed to stand at 200° C. for 16 h, and then the residue content was determined according to step 7.10 of the performance evaluation method for water-based fracturing fluid in SY / T 5107-2016. The results are shown in Table 4.

[0128] Table 4

[0129] Residue content / mg / L Example 1 41 Example 2 52 Example 3 62 Example 4 71 Example 5 5 Example 6 450

[0130] IV. Temperature and shear resistance

[0131] The fracturing fluid obtained in Example 1-6 was subjected to a Haake rheometer at 230°C and 170 s -1 The shear performance of the fracturing fluid was tested for 120 min. The shear performance results of the fracturing fluid obtained in Example 1 are shown in Figure 1 The shear performance results of the fracturing fluid obtained in Example 2 are detailed in Figure 2 The shear performance results of the fracturing fluid obtained in Example 3 are detailed in Figure 3 The shear performance results of the fracturing fluid obtained in Example 4 are detailed in Figure 4 The shear performance results of the fracturing fluid obtained in Example 5 are detailed in Figure 5 The shear performance results of the fracturing fluid obtained in Example 6 are detailed in Figure 6 .

[0132] As can be seen from the figure, the final viscosity of the fracturing fluid system for ultra-high temperature reservoir reconstruction is greater than 100 mPa·s, indicating strong temperature and shear resistance. However, the viscosity of Example 5 is only 10 mPa·s at 200°C, which cannot meet the use requirements. Although the shear resistance in Example 6 can meet the requirements, the base fluid viscosity exceeds 600 mPa·s, which cannot be applied on site and cannot meet the needs.

[0133] The results of the above examples show that the fracturing fluid provided by the present invention can be mixed online, can be changed in viscosity and has low damage. The base fluid viscosity can be adjusted by adjusting the amount of thickener added to achieve continuous viscosity change within 5-100mPa·s, and there is no need to prepare the fluid in advance at the fluid preparation station, thus shortening the construction period of reservoir transformation operations. The system has a low molecular weight, and can achieve efficient gel breaking under the action of the gel breaker, reducing the damage caused by the fracturing fluid to the reservoir

[0134] It is stated that the present invention illustrates the detailed structural features of the present invention through the above embodiments, but the present invention is not limited to the above detailed structural features, that is, it does not mean that the present invention must rely on the above detailed structural features to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of the components selected by the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

[0135] The preferred embodiments of the present invention are described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, a variety of simple modifications can be made to the technical solution of the present invention, and these simple modifications all belong to the protection scope of the present invention.

[0136] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0137] In addition, various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A fracturing fluid for reservoir reconstruction, characterized in that: The fracturing fluid for reservoir reconstruction comprises: a tetrapolymer thickener, a cross-linking agent, a cross-linking accelerator, a gel breaker and water.

2. The fracturing fluid for reservoir reconstruction according to claim 1, characterized in that: The fracturing fluid for reservoir reconstruction comprises, by weight: 1-2 parts of a tetrapolymer thickener, 0.2-0.3 parts of a crosslinking agent, 0.2-0.3 parts of a crosslinking accelerator, 0.1-0.2 parts of a breaker and 95.2-97.5 parts of water.

3. The fracturing fluid for reservoir reconstruction according to claim 1 or 2, characterized in that: The tetrapolymer thickener is obtained by copolymerizing acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, N,N'-dimethylacrylamide and 4-((2-(allylbromoamino)ethyl)amino)-4-oxybutane-1-sulfonic acid by a step-by-step inverse emulsion polymerization method; Preferably, the molecular weight of the tetrapolymer thickener is 6 million to 10 million.

4. The fracturing fluid for reservoir reconstruction according to any one of claims 1 to 3, characterized in that: The cross-linking agent includes one or a combination of at least two of boric acid, sodium borate or sodium chromate.

5. The fracturing fluid for reservoir reconstruction according to any one of claims 1 to 4, characterized in that: The cross-linking accelerator includes one or a combination of at least two of aluminum citrate, zirconium oxychloride or sodium bicarbonate.

6. The fracturing fluid for reservoir reconstruction according to any one of claims 1 to 5, characterized in that: The breaker includes ammonium persulfate.

7. The fracturing fluid for reservoir reconstruction according to any one of claims 1 to 6, characterized in that: The fracturing fluid for reservoir reconstruction also includes functional additives.

8. The fracturing fluid for reservoir reconstruction according to any one of claims 1 to 7, characterized in that: The functional additives include one or a combination of at least two of a clay stabilizer, a high temperature stabilizer, an iron ion stabilizer, a pH adjuster, a proppant, a viscosity promoter, a drainage aid or an anti-swelling agent.

9. A method for preparing a fracturing fluid for reservoir reconstruction according to any one of claims 1 to 8, characterized in that: The preparation method comprises: first mixing a tetrapolymer thickener and water according to a formula, then adding a gel breaker for second mixing, and then adding a crosslinking agent and a crosslinking aid for reaction to obtain a fracturing fluid for reservoir reconstruction. If a functional additive is introduced into the fracturing fluid for reservoir reconstruction, it can be added together in the first mixing.

10. A use of the fracturing fluid for reservoir reconstruction according to any one of claims 1 to 9, characterized in that: The use includes using the fracturing fluid for reservoir transformation to transform the high-temperature reservoir.

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