Acidic cross-linking agent and polymer fracturing fluid

Abstract

The invention provides an acidic cross-linking agent and a polymer fracturing fluid, the acidic cross-linking agent is obtained by reacting the following raw materials at a preset reaction temperature: inorganic zirconium, inorganic aluminum, polyol, organic acid and an aqueous solution, and the polyol is one or two of glycerol and ethylene glycol. The acidic cross-linking agent provided by the invention can stably exist under an acidic condition, can realize acidic cross-linking and has good compatibility with a polymer, and a polymer fracturing fluid prepared by the acidic cross-linking agent provided by the invention is stable in gel at a high temperature, has excellent high-temperature shear resistance and gel breaking performance, is low in residue content and small in damage to a stratum, and can be used as a fracturing fluid fracturing fluid. The method is especially suitable for alkali-sensitive stratums.

Description

Technical Field

[0001] The present invention relates to the field of fracturing fluids for oil and gas fields, and more particularly, to an acidic crosslinking agent and a polymer fracturing fluid. Background Art

[0002] Hydraulic fracturing is an important technical measure for increasing production of oil and gas wells and injection of water wells. The purpose of fracturing is to form fractures with a certain size and conductivity in the formation, and its success is highly related to the performance of the fracturing fluid used. Hydraulic fracturing has certain requirements for the performance of the fracturing fluid. Currently, the most widely used fracturing fluid system is still water-based fracturing fluid (accounting for 65%). Among water-based fracturing fluids, boron-crosslinked fracturing fluid accounts for 40%, titanium- and zirconium-crosslinked fracturing fluid accounts for 10%, and uncrosslinked linear gel accounts for 15%.

[0003] Conventional water-based fracturing fluids require an alkaline crosslinking environment and cause serious damage to low-permeability and alkali-sensitive reservoirs. When the fracturing fluid enters the oil and gas layer, due to the reaction between clay minerals and alkali, a lot of silica sol will be formed, blocking the channels and causing secondary damage to the formation. Therefore, the application of acidic fracturing fluid is imperative. Most of the fracturing fluid systems currently used in oil fields are composed of hydroxypropyl guar gum, boron crosslinking agent and other additives. Hydroxypropyl guar gum has a high water-insoluble content and causes great damage to the formation, and cannot meet the requirements of high-temperature and deep fracturing reconstruction; moreover, in recent years, the price of guar gum has increased, resulting in a relatively high cost of guar gum fracturing fluid. Secondly, the crosslinking agents commonly used in water-based fracturing fluids are inorganic boron or organic boron crosslinking agents. These traditional crosslinking agents need to crosslink under alkaline conditions, and the crosslinking pH is 9-11. The gel-forming effect is not good under acidic conditions, and even cannot form a gel.

[0004] In recent years, polymer fracturing fluids have begun to be widely used. The polymer solution can obtain better viscoelasticity under the action of a crosslinking agent and can better meet the sand-carrying capacity required for fracturing reconstruction. Among them, the performance of the crosslinking agent directly determines the quality of the fracturing effect. Common crosslinking agents such as boron crosslinking agents have an unsatisfactory crosslinking effect with synthetic polymers. Moreover, with the long-term water injection development of oil and gas reservoirs, most formations are now alkali-sensitive formations, and the alkali-sensitivity problems brought by boron crosslinking agents cannot be ignored. And aluminum crosslinking agents are prone to hydrolysis at high temperatures and high salinity, resulting in unstable gels and limited application ranges.

[0005] Therefore, developing an acidic crosslinking agent and a polymer fracturing fluid with less damage to low-permeability and alkali-sensitive reservoirs is a technical problem that needs to be solved urgently at present. Summary of the Invention

[0006] In view of this, the present invention aims to solve the technical problems of poor temperature and shear resistance and gel-breaking performance of traditional polymer fracturing fluids.

[0007] The first aspect of the present invention provides an acidic crosslinking agent.

[0008] The second aspect of the present invention provides a preparation method of an acidic crosslinking agent.

[0009] The third aspect of the present invention provides a polymer fracturing fluid.

[0010] Specifically, the present invention is realized through the following technical solutions:

[0011] The technical solution of the first aspect of the present invention provides an acidic crosslinking agent, which is obtained by reacting the following raw materials at a preset reaction temperature: inorganic zirconium, inorganic aluminum, polyol, organic acid and aqueous solution, and the polyol is one or two of glycerol and ethylene glycol.

[0012] In some technical solutions, optionally, the mass ratio of inorganic zirconium, inorganic aluminum, polyol, organic acid and aqueous solution is (5-10):(5-10):(10-20):(20-30):(60-105).

[0013] In some technical solutions, optionally, the mass ratio of inorganic zirconium, inorganic aluminum, polyol, organic acid and aqueous solution is 7:7:15:25:80.

[0014] In some technical solutions, optionally, the inorganic zirconium is one or two of zirconium oxychloride and zirconium trichloride.

[0015] In some technical solutions, optionally, the inorganic aluminum is one or two of aluminum trichloride and aluminum sulfate.

[0016] In some technical solutions, optionally, the organic acid is one or two of lactic acid and acetic acid.

[0017] In some technical solutions, optionally, the preset reaction temperature is greater than or equal to 40°C and less than or equal to 60°C.

[0018] The second aspect of the present invention provides a preparation method of a polymer fracturing fluid, including: taking inorganic zirconium and inorganic aluminum and adding them into an aqueous solution, mixing evenly to obtain a mixture, and heating the mixture to a preset reaction temperature; adding polyol to the mixture, stirring and dissolving, then adding organic acid, and carrying out a reflux reaction under stirring conditions to obtain an acidic crosslinking agent.

[0019] The third aspect of the present invention provides a polymer fracturing fluid, including: the acidic crosslinking agent of any technical solution of the first aspect of the present invention; or the acidic crosslinking agent prepared by the preparation method of the acidic crosslinking agent of the technical solution of the second aspect of the present invention.

[0020] In some technical solutions, optionally, the polymer fracturing fluid further includes an aqueous polymer solution, a flowback aid, and an anti-swelling agent.

[0021] In some technical solutions, optionally, the volume ratio of the aqueous polymer solution, the acidic crosslinking agent, the flowback aid, and the swelling inhibitor is (97.2 - 98.6):(0.3 - 0.5):(0.5 - 1):(0.5 - 1).

[0022] In some technical solutions, optionally, the volume ratio of the aqueous polymer solution, the acidic crosslinking agent, the flowback aid, and the swelling inhibitor is 98:0.4:0.8:0.8.

[0023] In some technical solutions, optionally, in the aqueous polymer solution, the mass percentage of the polymer is 0.5% - 1%.

[0024] In some technical solutions, optionally, in the aqueous polymer solution, the molecular weight of the polymer is 1,000,000 - 2,000,000.

[0025] In some technical solutions, optionally, the flowback aid is a quaternary ammonium salt type flowback aid. Optionally, the flowback aid is a mixed solution of alkyl polyglycoside and fatty amine polyoxyethylene ether.

[0026] In some technical solutions, optionally, the swelling inhibitor is a mixed solution of a cationic quaternary ammonium salt polymer and potassium chloride.

[0027] The present invention provides an acidic crosslinking agent with good crosslinking effect with an aqueous polymer solution, and at the same time provides a polymer fracturing fluid prepared by using the above crosslinking agent. The acidic crosslinking agent is stable under acidic conditions, can achieve acidic crosslinking, has good compatibility with the polymer. The polymer fracturing fluid prepared therefrom has stable gel at high temperature, has excellent temperature and shear resistance performance and gel-breaking performance, has low residue content, and causes little damage to the formation. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The accompanying drawings herein are incorporated into the specification and form a part of the specification, showing embodiments consistent with the present invention, and are used together with the specification to explain the principles of the present invention.

[0029] In order to more clearly illustrate the embodiments of the present invention or the embodiments in the related art, the following will briefly introduce the drawings required for use in the description of the embodiments or the related art. Obviously, for those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0030] Figure 1 is the viscosity-temperature curve of the polymer fracturing fluid of the embodiment of the present invention at 100 °C, 100 s -1 and shearing for 90 min;

[0031] Figure 2 is the viscosity-temperature curve of the polymer fracturing fluid of the embodiment of the present invention at 120 °C, 100 s -1 and shearing for 90 min;

[0032] Figure 3 is the viscosity-temperature curve of the polymer fracturing fluid in the embodiment of the present invention at 120 °C for 100 s -1 and sheared for 120 min. Detailed implementation manners

[0033] To make the objectives, embodiments, and advantages of the embodiments of the present invention clearer, the embodiments in the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present invention without creative efforts shall fall within the protection scope of the present invention.

[0034] Embodiment 1

[0035] The acidic crosslinking agent in this embodiment is prepared by reacting raw materials in the following parts by weight: 5 parts of inorganic zirconium, 5 parts of inorganic aluminum, 10 parts of polyol, 20 parts of organic acid, and 60 parts of water; among them, the inorganic zirconium is zirconium oxychloride, the inorganic aluminum is aluminum trichloride, the polyol is glycerol, and the organic acid is lactic acid.

[0036] The preparation process of the acidic crosslinking agent in this embodiment is as follows: Take 5 g of inorganic zirconium and 5 g of inorganic aluminum and add them to 60 g of water in sequence, mix them evenly and then heat up to 50 °C to obtain a mixture; under stirring conditions, add 10 g of polyol to the mixture, stir and dissolve it, then add 20 g of organic acid, and reflux and react for 4 h under stirring conditions at 50 °C to obtain the acidic crosslinking agent.

[0037] Using the acidic crosslinking agent in this embodiment to prepare a polymer fracturing fluid, the polymer fracturing fluid includes the following components in parts by volume: 98.7 parts of an aqueous polymer solution, 0.3 parts of an acidic crosslinking agent, 0.5 parts of a flowback aid, and 0.5 parts of a swelling inhibitor; among them, the polymer is low-molecular-weight polyacrylamide with a molecular weight of 1.5 million, and its mass percentage content in the aqueous polymer solution is 0.8%, the flowback aid is a mixed solution of alkyl polyglycoside and fatty amine polyoxyethylene ether, and the swelling inhibitor is a mixed solution of a cationic quaternary ammonium salt polymer and potassium chloride.

[0038] The preparation process of the polymer fracturing fluid in this embodiment is as follows: Stir and mix 0.5 g of the flowback aid and 0.5 g of the swelling inhibitor evenly to obtain an additive solution. Under stirring conditions, mix 98.7 g of the aqueous polymer solution with the additive solution evenly, and then add 0.3 g of the acidic crosslinking agent and mix evenly to obtain the polymer fracturing fluid.

[0039] Use an RS6000 rheometer to test the temperature and shear resistance of the polymer fracturing fluid prepared in this embodiment. The results are as Figure 1As shown in the figure, where η is the viscosity of the fracturing fluid, t is the shear time, and T is the shear temperature. Starting from Figure 1 it can be seen that the polymer fracturing fluid prepared in this example has a viscosity of 78 mPa·s (the average value of each viscosity value within 1 minute before the end of the experiment) under the conditions of 100 °C, 100 s -1 and a shear time of 90 min, showing excellent temperature and shear resistance performance.

[0040] The gel-breaking performance of the polymer fracturing fluid prepared in this example was evaluated: at 100 °C, 0.05% of the gel-breaking agent ammonium persulfate was added, the gel-breaking time was 5 h, the viscosity of the gel-breaking fluid was 3.2 mm2 / s, and the residue content was 157 mg / L.

[0041] Example Two

[0042] The acidic crosslinking agent of this example was prepared by reacting raw materials in the following weight parts: 8 parts of inorganic zirconium, 8 parts of inorganic aluminum, 15 parts of polyol, 25 parts of organic acid, and 84 parts of water. Among them, the inorganic zirconium was zirconium trichloride, the inorganic aluminum was aluminum sulfate, the polyol was ethylene glycol, and the organic acid was acetic acid.

[0043] The preparation method of the acidic crosslinking agent of this example was: 8 g of inorganic zirconium and 8 g of inorganic aluminum were successively added to 84 g of water, and after mixing evenly, the temperature was raised to 50 °C to obtain a mixture; under stirring conditions, 15 g of polyol was added to the mixture, and after stirring and dissolving, 25 g of organic acid was added, and the mixture was refluxed and reacted for 4.5 h under stirring conditions at 50 °C to obtain the acidic crosslinking agent.

[0044] The polymer fracturing fluid prepared using the acidic crosslinking agent of this example included the following components in volume parts: 98 parts of polymer aqueous solution, 0.4 part of acidic crosslinking agent, 0.8 part of flowback aid, and 0.8 part of swelling inhibitor; among them, the polymer was low-molecular-weight polyacrylamide with a molecular weight of 1 million, and its mass percentage content in the polymer aqueous solution was 1%. The flowback aid was a mixed solution of alkyl polyglycoside and fatty amine polyoxyethylene ether, and the swelling inhibitor was a mixed solution of cationic quaternary ammonium salt polymer and potassium chloride.

[0045] The preparation process of the polymer fracturing fluid of this example was: 0.8 g of flowback aid and 0.8 g of swelling inhibitor were stirred and mixed evenly to obtain an additive solution; under stirring conditions, 98 g of polymer aqueous solution was mixed evenly with the additive solution, and then 0.4 g of acidic crosslinking agent was added and mixed evenly to obtain the polymer fracturing fluid.

[0046] The temperature and shear resistance of the polymer fracturing fluid prepared in this example was tested using an RS6000 rheometer, and the results are as Figure 2 shown in the figure, where η is the viscosity of the fracturing fluid, t is the shear time, and T is the shear temperature. Starting from Figure 2It can be seen that the polymer fracturing fluid prepared in this example has a viscosity of 75 mPa·s (the average value of each viscosity value within 1 minute before the end of the experiment) under the conditions of 120 °C and 100 s -1 and shearing for 90 min, showing excellent temperature and shear resistance performance.

[0047] The gel-breaking performance of the polymer fracturing fluid prepared in this example was evaluated: at 120 °C, 0.08% gel breaker ammonium persulfate was added, the gel-breaking time was 4 h, and the viscosity of the gel-breaking fluid was 3.8 mm 2 / s, and the residue content was 182 mg / L.

[0048] Example Three

[0049] The acidic crosslinking agent in this example is prepared by reacting raw materials in the following parts by weight: 10 parts of inorganic zirconium, 10 parts of inorganic aluminum, 20 parts of polyol, 30 parts of organic acid, and 105 parts of water. Among them, the inorganic zirconium is zirconium oxychloride, the inorganic aluminum is aluminum trichloride, the polyol is ethylene glycol, and the organic acid is acetic acid.

[0050] The preparation process of the acidic crosslinking agent in this example is as follows: Take 10 g of inorganic zirconium and 10 g of inorganic aluminum and add them to 105 g of water in sequence. After mixing evenly, heat up to 50 °C to obtain a mixture; under stirring conditions, add 20 g of polyol to the mixture, stir and dissolve it, then add 30 g of organic acid, and reflux and react for 5 h under stirring conditions at 50 °C to obtain the acidic crosslinking agent.

[0051] The polymer fracturing fluid prepared using the acidic crosslinking agent in this example includes the following components in parts by volume: 97.5 parts of aqueous polymer solution, 0.5 part of acidic crosslinking agent, 1.0 part of flowback aid, and 1.0 part of swelling inhibitor. Among them, the polymer is low-molecular-weight polyacrylamide with a molecular weight of 2 million, and its mass percentage content in the aqueous polymer solution is 0.5%. The flowback aid is a mixed solution of alkyl polyglycoside and fatty amine polyoxyethylene ether, and the swelling inhibitor is a mixed solution of cationic quaternary ammonium salt polymer and potassium chloride.

[0052] The preparation process of the polymer fracturing fluid in this example is as follows: Stir and mix 1.0 g of flowback aid and 1.0 g of swelling inhibitor evenly to obtain an additive solution; under stirring conditions, mix 97.5 g of aqueous polymer solution with the additive solution evenly, and then add 0.5 g of acidic crosslinking agent and mix evenly to obtain the polymer fracturing fluid.

[0053] The temperature and shear resistance of the polymer fracturing fluid prepared in this example were tested with an RS6000 rheometer, and the results are as Figure 3 shown in the figure. In the figure, η is the viscosity of the fracturing fluid, t is the shear time, and T is the shear temperature. It can be seen from Figure 3 that the polymer fracturing fluid prepared in this example has a viscosity of 75 mPa·s (the average value of each viscosity value within 1 minute before the end of the experiment) under the conditions of 120 °C and 100 s -1, Under the condition of shearing for 120 min, the viscosity of the fracturing fluid was 89 mPa·s (the average value of each viscosity within 1 minute before the end of the experiment), showing excellent temperature and shear resistance performance.

[0054] The gel-breaking performance of the polymer fracturing fluid prepared in this example was evaluated: at 120 °C, 0.05% gel-breaking agent ammonium persulfate was added, the gel-breaking time was 6 h, and the viscosity of the gel-breaking fluid was 2.8 mm 2 / s, and the residue content was 189 mg / L.

[0055] The experimental results show that the acidic crosslinking agent of the present invention and the polymer fracturing fluid prepared therefrom have excellent temperature and shear resistance performance and gel-breaking performance, cause little damage to the reservoir, and have broad application prospects.

[0056] Example 4

[0057] The acidic crosslinking agent of this example was prepared by reacting the following raw materials in parts by weight: 5-10 parts of inorganic zirconium, 5-10 parts of inorganic aluminum, 10-20 parts of polyol, 20-30 parts of organic acid, and 60-105 parts of water.

[0058] In some embodiments, optionally, the inorganic zirconium is one or two of zirconium oxychloride and zirconium trichloride.

[0059] In some embodiments, optionally, the inorganic aluminum is one or two of aluminum trichloride and aluminum sulfate.

[0060] In some embodiments, optionally, the polyol is one or two of glycerol and ethylene glycol.

[0061] In some embodiments, optionally, the organic acid is one or two of lactic acid and acetic acid.

[0062] In some embodiments, optionally, the reaction is a reflux reaction, the reaction temperature is 50 °C, and the reaction time is 4 h - 5 h.

[0063] The preparation process of the acidic crosslinking agent of this example is as follows: Take the formula dosage of inorganic zirconium and inorganic aluminum and add them to water. After mixing evenly, heat up to 50 °C to obtain a mixture; add the formula dosage of polyol to the mixture, stir and dissolve it, then add organic acid, and carry out a reflux reaction at 50 °C under stirring conditions for 4 h - 5 h to obtain the acidic crosslinking agent.

[0064] The polymer fracturing fluid prepared by the acidic crosslinking agent of this example includes the following components in parts by volume: 97.2 - 98.6 parts of aqueous polymer solution, 0.3 - 0.5 parts of acidic crosslinking agent, 0.5 - 1 part of flowback aid, and 0.5 - 1 part of swelling inhibitor.

[0065] In some embodiments, optionally, in the aqueous polymer solution, the mass percentage of the polymer is 0.5%-1%.

[0066] In some embodiments, optionally, the polymer is low molecular weight polyacrylamide with a molecular weight of 1 million - 2 million.

[0067] In some embodiments, optionally, the flowback aid is a quaternary ammonium salt type flowback aid. Optionally, the flowback aid is a solution obtained by mixing alkyl polyglycoside and fatty amine polyoxyethylene ether in a certain ratio.

[0068] In some embodiments, optionally, the swelling inhibitor is a solution obtained by mixing a cationic quaternary ammonium salt polymer and potassium chloride in a certain ratio.

[0069] The preparation process of the polymer fracturing fluid in this embodiment is as follows: The flowback aid and the swelling inhibitor are stirred and mixed evenly to obtain an additive solution. Under stirring conditions, the aqueous polymer solution and the additive solution are mixed evenly, and then an acidic crosslinking agent is added and mixed evenly to obtain the polymer fracturing fluid.

[0070] The polymer fracturing fluid prepared with the acidic crosslinking agent in this embodiment can form a stable gel, and has excellent temperature and shear resistance and gel-breaking performance. The aqueous polymer solution crosslinks with the acidic crosslinking agent of the present invention, and the formed gel has a viscosity above 50 mPa·s after shearing at 120°C for 120 min, and has excellent temperature and shear resistance; 0.05%-0.1% of the gel-breaking agent ammonium persulfate is added to this polymer fracturing fluid, and it is gel-broken at 120°C for 4 - 6 h. The viscosity of the gel-broken fluid is below 4 mm -1 / s, and the residue content is low, less than 200 mg / L, and the gel-breaking performance is excellent. 2 / s, and the residue content is low, less than 200 mg / L, and the gel-breaking performance is excellent.

[0071] Comparative Example 1:

[0072] The formulation and preparation steps of the acidic crosslinking agent and the polymer fracturing fluid in this comparative example are basically the same as those of the acidic crosslinking agent and the polymer fracturing fluid in Example 1. The only difference is that in the step of preparing the acidic crosslinking agent, polyhydric alcohol is used instead of glycerol as the polyhydric alcohol.

[0073] Comparative Example 2:

[0074] The formulation and preparation steps of the acidic crosslinking agent and the polymer fracturing fluid in this comparative example are basically the same as those of the acidic crosslinking agent and the polymer fracturing fluid in Example 1. The only difference is that in the step of preparing the acidic crosslinking agent, diethylene glycol is used instead of glycerol as the polyhydric alcohol.

[0075] Comparative Example 3:

[0076] The formulation and preparation steps of the acidic crosslinking agent and polymer fracturing fluid in this comparative example are basically the same as those of the acidic crosslinking agent and polymer fracturing fluid in Example 1. The only difference is that in the step of preparing the polymer fracturing fluid, the swelling inhibitor used is potassium chloride solution.

[0077] The polymer fracturing fluids prepared by the methods of Comparative Examples 1 to 3 of the present invention were successively tested for temperature and shear resistance and gel-breaking performance. The experimental results were as follows: The acidic crosslinking agent synthesized using polyhydric alcohol or diethylene glycol has a high dosage and is not suitable for the transformation requirements of special reservoirs in Dagang Oilfield; the types of raw materials used for synthesizing the acidic crosslinking agent are numerous, and the cost increases accordingly; the polymer fracturing fluid prepared can withstand a temperature of 120 °C, but only using potassium chloride solution as the swelling inhibitor, the gel-breaking fluid of the fracturing fluid cannot achieve long-term swelling prevention and excellent water-washing resistance.

[0078] This example provides an acidic crosslinking agent, which is obtained by reacting the following raw materials at a preset reaction temperature: inorganic zirconium, inorganic aluminum, polyhydric alcohol, organic acid, and aqueous solution. The polyhydric alcohol is one or two of glycerol and ethylene glycol.

[0079] The acidic crosslinking agent provided by the present invention can stably exist under acidic conditions, can achieve acidic crosslinking, and has good compatibility with polymers. The polymer fracturing fluid prepared by the acidic crosslinking agent of the present invention has stable gel at high temperature, excellent high-temperature shear resistance and gel-breaking performance, low residue content, and little damage to the formation, and is especially suitable for alkali-sensitive formations. In addition, the present invention uses one or two of glycerol and ethylene glycol as the polyhydric alcohol, which can effectively improve the temperature resistance of the polymer fracturing fluid, has simple raw materials and low dosage, and overcomes the problems of numerous types of raw materials, high dosage, and complex synthesis process of traditional acidic crosslinking agents.

[0080] In some embodiments, optionally, the mass ratio of inorganic zirconium, inorganic aluminum, polyhydric alcohol, organic acid, and aqueous solution is (5 - 10):(5 - 10):(10 - 20):(20 - 30):(60 - 105).

[0081] In this example, the mass ratio of inorganic zirconium, inorganic aluminum, polyhydric alcohol, organic acid, and aqueous solution is (5 - 10):(5 - 10):(10 - 20):(20 - 30):(60 - 105). This not only ensures the excellent high-temperature shear resistance and gel-breaking performance of the polymer fracturing fluid prepared later, but also greatly reduces the dosages of inorganic zirconium, inorganic aluminum, polyhydric alcohol, and organic acid, saving costs. Optionally, the mass ratio of inorganic zirconium, inorganic aluminum, polyhydric alcohol, organic acid, and aqueous solution is 7:7:15:25:80.

[0082] In some embodiments, optionally, the inorganic zirconium is one or both of zirconium oxychloride and zirconium trichloride. The inorganic aluminum is one or both of aluminum trichloride and aluminum sulfate. The organic acid is one or both of lactic acid and acetic acid. The preset reaction temperature is greater than or equal to 40 °C and less than or equal to 60 °C.

[0083] In this embodiment, by limiting the components of inorganic zirconium, inorganic aluminum and organic acid and the reaction temperature, it is possible to ensure that the polymer fracturing fluid prepared later has excellent high-temperature shear resistance and gel-breaking properties.

[0084] The second aspect of the present invention provides a polymer fracturing fluid, comprising: the acidic crosslinking agent according to any one of the embodiments of the first aspect of the present invention.

[0085] The polymer fracturing fluid provided in this embodiment includes the acidic crosslinking agent according to any one of the embodiments of the first aspect of the present invention, and thus has all the beneficial effects of the acidic crosslinking agent according to any one of the embodiments of the first aspect of the present invention, which will not be elaborated here.

[0086] In some embodiments, optionally, the polymer fracturing fluid further includes an aqueous polymer solution, a flowback aid, and an anti-swelling agent.

[0087] In this embodiment, the polymer fracturing fluid further includes an aqueous polymer solution, a flowback aid, and an anti-swelling agent, so that the fracturing fluid of the present invention has good viscoelasticity and can better meet the sand-carrying capacity required for fracturing treatment.

[0088] In some embodiments, optionally, the volume ratio of the aqueous polymer solution, the acidic crosslinking agent, the flowback aid, and the anti-swelling agent is (97.2 - 98.6):(0.3 - 0.5):(0.5 - 1):(0.5 - 1).

[0089] In this embodiment, by controlling the volume ratio of the aqueous polymer solution, the acidic crosslinking agent, the flowback aid, and the anti-swelling agent, the viscoelasticity of the fracturing fluid of the present invention can be further improved, and it can better meet the sand-carrying capacity required for fracturing treatment. Optionally, the volume ratio of the aqueous polymer solution, the acidic crosslinking agent, the flowback aid, and the anti-swelling agent is 98:0.4:0.8:0.8.

[0090] In some embodiments, optionally, in the aqueous polymer solution, the mass percentage of the polymer is 0.5% - 1%. In the aqueous polymer solution, the molecular weight of the polymer is 1,000,000 - 2,000,000.

[0091] In this embodiment, by controlling the mass percentage of the polymer and the molecular weight of the polymer in the aqueous polymer solution, a stable gel can be formed after being combined with the acidic crosslinking agent, having excellent temperature and shear resistance and gel-breaking properties.

[0092] In some embodiments, optionally, the flowback aid is a quaternary ammonium salt type flowback aid.

[0093] In this embodiment, a quaternary ammonium salt type flowback aid is used as the flowback aid, so that the effect of the working residual liquid flowing back from the formation can be improved compared with the conventional flowback aid, and it is particularly suitable for oilfield exploitation in alkali-sensitive formations.

[0094] In some embodiments, optionally, the swelling inhibitor is a mixed solution of a cationic quaternary ammonium salt polymer and potassium chloride.

[0095] In this embodiment, a mixed solution of a cationic quaternary ammonium salt polymer and potassium chloride is used as the swelling inhibitor. Using potassium chloride alone only has short-term swelling inhibition and no water washing resistance. Compared with the conventional potassium chloride solution, the mixed solution has long-term swelling inhibition and excellent water washing resistance.

[0096] The above are the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. An acidic crosslinking agent, characterized in that, The acidic crosslinking agent is obtained by reacting the following raw materials at a preset reaction temperature: inorganic zirconium, inorganic aluminum, polyol, organic acid, and aqueous solution, and the polyol is one or two of glycerol and ethylene glycol.

2. The acidic crosslinking agent according to claim 1, characterized in that, The mass ratio of the inorganic zirconium, the inorganic aluminum, the polyol, the organic acid, and the aqueous solution is (5-10):(5-10):(10-20):(20-30):(60-105).

3. The acidic crosslinking agent according to claim 2, characterized in that, The mass ratio of the inorganic zirconium, the inorganic aluminum, the polyol, the organic acid, and the aqueous solution is 7:7:15:25:

80.

4. The acidic crosslinking agent according to claim 1, characterized in that, The inorganic zirconium is one or two of zirconium oxychloride and zirconium trichloride; The inorganic aluminum is one or two of aluminum trichloride and aluminum sulfate; The organic acid is one or two of lactic acid and acetic acid.

5. The acidic crosslinking agent according to claim 1, characterized in that, The preset reaction temperature is greater than or equal to 40°C and less than or equal to 60°C.

6. A preparation method of an acidic crosslinking agent, characterized in that, Comprising: Take inorganic zirconium and inorganic aluminum and add them to the aqueous solution. After mixing evenly, a mixture is obtained, and the mixture is heated to the preset reaction temperature; Add polyol to the mixture. After stirring and dissolving, add organic acid, and carry out a reflux reaction under stirring conditions to obtain the acidic crosslinking agent. The polyol is one or two of glycerol and ethylene glycol.

7. A polymer fracturing fluid, characterized in that, Comprising: The acidic crosslinking agent according to any one of claims 1 to 5; Or the acidic crosslinking agent prepared by the preparation method of the acidic crosslinking agent according to claim 6.

8. The polymer fracturing fluid according to claim 7, characterized in that, It further comprises an aqueous polymer solution, a drainage aid, and an anti-swelling agent.

9. The polymer fracturing fluid according to claim 8, characterized in that, The volume ratio of the aqueous polymer solution, the acidic crosslinking agent, the drainage aid, and the anti-swelling agent is (97.2-98.6):(0.3-0.5):(0.5-1):(0.5-1).

10. The polymer fracturing fluid according to claim 8, characterized in that, In the aqueous polymer solution, the mass percentage of the polymer is 0.5%-1%; or In the aqueous polymer solution, the molecular weight of the polymer is 1 million - 2 million; or The drainage aid is a quaternary ammonium salt type drainage aid; or The anti-swelling agent is a mixed solution of a cationic quaternary ammonium salt polymer and potassium chloride.

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