A cross-linking agent and its preparation method and application

Abstract

The present invention provides a crosslinking agent comprising, by weight, 15 to 35 parts of a metal salt; 20 to 60 parts of an organic ligand; 25 to 65 parts of a solvent; 1 to 5 parts of a surfactant; and 0.5 to 2.0 parts of an initiator. The crosslinking temperature of the crosslinking agent provided by the present invention is controllable between 40 and 100°C. The crosslinking position of the crosslinking acid can be determined based on the target reservoir temperature field, allowing for personalized crosslinking agent selection. This reduces string friction and construction pressure, increases construction displacement, and achieves acid fracturing effects that create long fractures and deep penetration, thus having promising application prospects. The present invention also provides a preparation method and application of the crosslinking agent.

Description

Technical Field

[0001] The invention belongs to the technical field of oilfield chemistry, and in particular relates to a cross-linking agent and a preparation method and application thereof. Background Art

[0002] As exploration and development continue to deepen, reservoir depths and temperatures continue to rise. Existing acid systems struggle to meet the demands of transforming these "three highs and one deep" reservoirs. For example, in Northwest China, carbonate reservoirs have burial depths of 7,300 meters or more and fracture pressures of 150 MPa or more. This results in high wellhead pressures, limited displacement, and difficulty in fracture initiation and extension, impacting the effectiveness of acid fracturing. Currently, the maximum pressure limit for domestic fracturing equipment is 140 MPa, and operating pressures are no more than 112 MPa. Excessively high operating pressures pose significant safety risks, necessitating measures to reduce operating pressures. One key approach is to reduce the friction of the working fluid.

[0003] Acid is a heterogeneous and unstable chemical system formed by mixing a variety of additives in a certain proportion. It can be divided into cross-linked acid, thickened acid, emulsified acid, etc. Since a cross-linking agent is added to the cross-linked acid, a network structure can be better formed between the cross-linking agent and the thickener, which has better advantages in temperature resistance, which can reach 180°C. However, at the same time, the addition of the cross-linking agent also greatly increases the friction of the acid in the wellbore. Although the existing cross-linked acid technology can also delay cross-linking, it cannot achieve the control of multiple cross-linking temperatures. In ultra-deep well construction, it cannot minimize pipeline friction and construction pressure. Therefore, how to control the cross-linking temperature of the cross-linked acid through a cross-linking agent so that cross-linking occurs at a specific position in the wellbore, minimize pipeline friction, and improve the acid fracturing effect is one of the problems that technicians in this field urgently need to solve. Summary of the Invention

[0004] In view of this, the purpose of the embodiments of the present invention is to provide a cross-linking agent and a preparation method and application thereof. The cross-linking temperature of the cross-linking agent provided by the present invention is controllable at 40-100°C.

[0005] The present invention provides a cross-linking agent, which comprises, in parts by weight:

[0006] 15-35 parts of metal salt;

[0007] 20-60 parts of an organic ligand;

[0008] 25-65 parts of solvent;

[0009] 1 to 5 parts of surfactant;

[0010] 0.5 to 2.0 parts of initiator.

[0011] Preferably, the metal salt comprises:

[0012] aluminum and zirconium salts;

[0013] The mass ratio of the zirconium salt to the aluminum salt is (1-3):1.

[0014] Preferably, the aluminum salt is aluminum trichloride; and the zirconium salt is selected from zirconium oxychloride octahydrate or zirconium sulfate.

[0015] Preferably, the organic ligand is selected from three of the group consisting of small molecule alcohols, α-hydroxycarboxylic acids, polyols, polyhydroxycarboxylates, and β-diketones.

[0016] Preferably, the small molecule alcohol is selected from one of methanol, ethanol or isopropanol;

[0017] The α-hydroxycarboxylic acid is selected from one of lactic acid, citric acid or tartaric acid;

[0018] The polyol is selected from one or more of xylitol, sorbitol, pentaerythritol, glycerol or ethylene glycol.

[0019] Preferably, the polyhydroxycarboxylate is selected from sodium gluconate;

[0020] The β-diketone is selected from one or more of benzoyl acetone, acetylacetone, and trifluoroacetylacetone.

[0021] Preferably, the solvent is selected from two of cyclohexane, ethylene glycol, glycerol, and water;

[0022] The surfactant is selected from one of sodium dodecylbenzenesulfonate, sodium lauryl sulfate or sodium dodecylsulfonate.

[0023] Preferably, the initiator is selected from one of dicumyl peroxide and methyl ethyl ketone peroxide.

[0024] The present invention provides a method for preparing the cross-linking agent described in the above technical solution, comprising:

[0025] mixing a surfactant, a solvent, and a metal salt to obtain a mixture;

[0026] The organic ligand, the initiator and the mixture are reacted to obtain a crosslinking agent.

[0027] The present invention provides a cross-linking acid, comprising: the cross-linking agent described in the above technical solution, or the cross-linking agent prepared by the method described in the above technical solution.

[0028] The cross-linking temperature of the cross-linking agent provided by the present invention is controllable between 40 and 100°C. The cross-linking position of the cross-linked acid can be determined according to the temperature field of the target reservoir, and the cross-linking agent can be selected in a personalized manner to reduce the friction resistance of the pipe string and the construction pressure, increase the construction displacement, and achieve the acid fracturing effect of creating long fractures and deep penetration, which has good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The cross-linking temperature test result of the cross-linking agent prepared in Example 1 of the present invention;

[0030] Figure 2 The cross-linking temperature test result of the cross-linking agent prepared in Example 2 of the present invention;

[0031] Figure 3 The cross-linking temperature test result of the cross-linking agent prepared in Example 3 of the present invention;

[0032] Figure 4 This is the cross-linking temperature test result of the cross-linking agent prepared in Example 4 of the present invention. DETAILED DESCRIPTION

[0033] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0034] The present invention provides a cross-linking agent, which comprises, in parts by weight:

[0035] 15-35 parts of metal salt;

[0036] 20-60 parts of an organic ligand;

[0037] 25-65 parts of solvent;

[0038] 1 to 5 parts of surfactant;

[0039] 0.5 to 2.0 parts of initiator.

[0040] In the present invention, the weight proportion of the metal salt is preferably 20 to 30 parts, more preferably 25 parts.

[0041] In the present invention, the metal salt preferably includes an aluminum salt and a zirconium salt; the aluminum salt is preferably aluminum trichloride; the zirconium salt is preferably zirconium oxychloride octahydrate or zirconium sulfate; the mass ratio of the zirconium salt to the aluminum salt is preferably (1-3):1, more preferably (1.5-2.5):1, and most preferably 2:1.

[0042] In the present invention, the weight portion of the organic ligand is preferably 30 to 50 parts, more preferably 40 parts.

[0043] In the present invention, the organic ligand is preferably selected from three of the group consisting of small molecule alcohols, α-hydroxycarboxylic acids, polyols, polyhydroxycarboxylates, and β-diketones. In the present invention, the small molecule alcohol is preferably selected from one of methanol, ethanol, or isopropanol. In the present invention, the α-hydroxycarboxylic acid is preferably selected from one of lactic acid, citric acid, or tartaric acid. In the present invention, the polyol is preferably selected from one or more of xylitol, sorbitol, pentaerythritol, glycerol, or ethylene glycol. In the present invention, the polyhydroxycarboxylates are preferably selected from sodium gluconate. In the present invention, the β-diketone is preferably selected from one or more of benzoylacetone, acetylacetone, and trifluoroacetylacetone.

[0044] In the present invention, the weight proportion of the solvent is preferably 30 to 60 parts, more preferably 40 to 50 parts, and most preferably 45 parts.

[0045] In the present invention, the solvent is preferably selected from two of cyclohexane, ethylene glycol, glycerol and water.

[0046] In the present invention, the weight proportion of the surfactant is preferably 2 to 4 parts, more preferably 3 parts.

[0047] In the present invention, the surfactant is preferably selected from one of sodium dodecylbenzenesulfonate, sodium dodecyl sulfate or sodium dodecylsulfonate.

[0048] In the present invention, the weight portion of the initiator is preferably 1 to 1.5 parts, more preferably 1.2 to 1.3 parts.

[0049] In the present invention, the initiator is preferably selected from dicumyl peroxide and methyl ethyl ketone peroxide.

[0050] In the present invention, the cross-linking agent is generally a light yellow transparent liquid with no viscosity, which can form a jelly with the thickener to facilitate sand carrying and has a certain delayed cross-linking property. The cross-linking effect occurs in the wellbore, effectively reducing friction.

[0051] The crosslinking agent provided by the present invention comprises a zirconium and aluminum composite central ion, and the temperature resistance of the system is improved by the complementary performance of the two central ions; the polyol ligand increases the solubility of the ligand and the solution; the alcohol amine ligand emulsifies and thickens the solution; and the carboxylate ligand improves the temperature resistance and stability of the crosslinking agent; acetylacetone removes hydrogen from the α-carbon in an alkaline environment to form a carbon anion, causing intramolecular electron transfer and, at the same time, synergistically acting with the carboxyl group of lactic acid to convert the oxygen of the carboxyl group and the carbonyl group into electron-rich nucleophiles, which complex with the central ion (electrophile) that can provide an empty orbital, thereby making the crosslinking agent product more stable in performance.

[0052] The cross-linking agent provided by the present invention can form a gel with the thickener to facilitate sand carrying and help enhance the temperature resistance of the system. The cross-linking temperature of the cross-linking agent series products is controllable between 40 and 100°C. During construction, the cross-linking position of the cross-linking acid can be controlled to 1000m before the bottom of the well according to the reservoir temperature field, so as to minimize construction friction and reduce construction pressure.

[0053] The present invention provides a method for preparing the cross-linking agent described in the above technical solution, comprising:

[0054] mixing a surfactant, a solvent, and a metal salt to obtain a mixture;

[0055] The organic ligand, the initiator and the mixture are reacted to obtain a crosslinking agent.

[0056] In the present invention, the mixing temperature is preferably 30-50°C, more preferably 35-45°C, and most preferably 40°C; the mixing is preferably carried out under stirring, and the stirring time is preferably 10-20 min, more preferably 12-18 min, and most preferably 14-16 min; the stirring speed is preferably 300-400 rpm, more preferably 320-380 rpm, and most preferably 340-360 rpm; the pH value of the mixing is preferably 9-13, more preferably 10-12, and most preferably 10-11; and sodium hydroxide solution is preferably added during the mixing process to adjust the pH value.

[0057] In the present invention, the mixing method preferably includes:

[0058] The temperature and speed are set, a surfactant is added to the solvent, and the mixture is stirred. Then, a metal salt is added, and the temperature and speed are kept constant, and the mixture is stirred until dissolved. A sodium hydroxide solution is added to adjust the pH to obtain a mixture.

[0059] In the present invention, the temperature is preferably 30-50°C, more preferably 35-45°C, and most preferably 40°C; the rotation speed is preferably 300-400 rpm, more preferably 320-380 rpm, and most preferably 340-360 rpm; the stirring and mixing time is preferably 3-7 min, more preferably 4-6 min, and most preferably 5 min; the continued stirring time is preferably 8-12 min, more preferably 10 min; the adjusted pH value is preferably 9-13, more preferably 10-12, and most preferably 10-11.

[0060] In the present invention, the heating rate of the reaction is preferably 0.7 to 1.3°C / min, more preferably 0.8 to 1.2°C / min, more preferably 0.9 to 1.1°C / min, and most preferably 1°C / min; the reaction temperature is preferably 60 to 100°C, more preferably 70 to 90°C, and most preferably 70 to 85°C; the reaction time is preferably 3 to 10 h, more preferably 4 to 9 h, and most preferably 5 to 9 h; and the reaction is preferably carried out under stirring.

[0061] In the present invention, the reaction method preferably comprises:

[0062] An organic ligand is added to the mixture, stirred evenly, and then an initiator is added and stirred for reaction to obtain a crosslinking agent.

[0063] In the present invention, the preparation method of the cross-linking agent preferably includes:

[0064] The temperature was set at 40°C and the rotation speed was set at 350 r / min. The surfactant was added to the solvent and stirred for 5 minutes. Then, the zirconium salt and the aluminum salt were added. The temperature and the rotation speed were kept constant and the stirring was continued for 10 minutes until they were dissolved. Sodium hydroxide solution was added to adjust the pH value to 10-11 to obtain a mixture.

[0065] Add the organic ligand to the obtained mixture, stir evenly, then add the initiator, raise the temperature to 60-100° C. at a heating rate of 1±0.3° C. / min, stir and react for 3-10 hours to obtain a crosslinking agent.

[0066] The present invention provides a cross-linking acid, comprising: the cross-linking agent described in the above technical solution, or the cross-linking agent prepared by the method described in the above technical solution.

[0067] In the present invention, the cross-linking acid preferably further comprises a base liquid.

[0068] In the present invention, the base liquid preferably includes: HCl solution, corrosion inhibitor, synergist, and thickener.

[0069] In the present invention, the mass concentration of the hydrochloric acid solution is preferably 15-25%, more preferably 18-22%, and most preferably 20%.

[0070] In the present invention, the corrosion inhibitor is preferably a high-temperature corrosion inhibitor, and more preferably a ternary compound of a linear alkane quaternary ammonium salt, an imidazoline quaternary ammonium salt, and a quinoline quaternary ammonium salt.

[0071] In the present invention, the synergist is preferably a corrosion inhibitor, more preferably a metal salt compound.

[0072] In the present invention, the thickener is preferably a polymer thickener, more preferably a tetrapolymer of acrylamide, N-vinyl pyrrolidone, acryloyloxyethyltrimethylammonium chloride, and 2-acrylamide-2-methylpropanesulfonic acid.

[0073] In the present invention, the usage ratio of the hydrochloric acid solution, corrosion inhibitor, synergist and thickener is preferably 1000 mL: (40-60) g: (15-25) g: (6-10) g, more preferably 1000 mL: (45-55) g: (18-22) g: (7-9) g, and most preferably 1000 mL: 50 g: 20 g: 8 g.

[0074] In the present invention, the method for preparing the base liquid preferably comprises:

[0075] The HCl solution, the corrosion inhibitor, the synergist and the thickener are mixed to obtain a base fluid.

[0076] In the present invention, the mixing is preferably carried out under stirring conditions, and the stirring time is preferably 20 to 40 minutes, more preferably 25 to 35 minutes, and most preferably 30 minutes.

[0077] In the present invention, the usage ratio of the base liquid and the cross-linking agent is preferably 50 mL: (0.2-0.6) g, more preferably 50 mL: (0.3-0.5) g, and most preferably 50 mL: 0.4 g.

[0078] In the present invention, the preparation method of the cross-linked acid preferably comprises:

[0079] The base liquid and the cross-linking agent are mixed to obtain a cross-linking acid.

[0080] In the present invention, the mixing is preferably uniform stirring.

[0081] In the present invention, the preparation method of the cross-linked acid preferably comprises:

[0082] Take 1000 mL of 20% HCl solution in a mixer, start stirring, add 50 g of high-temperature corrosion inhibitor, 10 g of corrosion inhibitor synergist and 8.0 g of polymer thickener in sequence, and stir for 30 minutes to obtain a base liquid;

[0083] Take 50 mL of the above base liquid, add 0.4 g of cross-linking agent, and stir evenly to obtain cross-linked acid.

[0084] The cross-linking agent provided by the present invention has a central ion composed of two compounds to achieve functional complementarity and improve the temperature resistance of the system; the ligand is a small molecule ligand with small steric hindrance, good solubility and more stable performance, and by changing the type of ligand as well as the reaction temperature and pH value, a series of cross-linking agent products can be formed, so that the cross-linking temperature with the polymer can be controlled between 40 and 100°C. During the construction process, through personalized selection of the cross-linking agent, the cross-linking of the cross-linked acid system is controlled to occur at a specific position in the wellbore, effectively reducing the friction resistance of the construction pipeline and lowering the construction pressure.

[0085] Example 1

[0086] The components of the cross-linking agent are: in parts by weight, 8 parts of zirconium salt, 5 parts of aluminum salt, 28 parts of organic ligand (10 parts of small molecule alcohol, 5 parts of α-hydroxycarboxylic acid, 16 parts of β-diketone), 2 parts of surfactant, 1 part of initiator, and 56 parts of solvent (28 parts of organic solvent, 28 parts of water); the zirconium salt is zirconium oxychloride octahydrate, the aluminum salt is aluminum trichloride, the small molecule alcohol is methanol, the α-hydroxycarboxylic acid is lactic acid, the β-diketone is acetylacetone, the surfactant is sodium dodecylbenzenesulfonate, the organic solvent is cyclohexane, and the initiator is methyl ethyl ketone peroxide.

[0087] The preparation method of the cross-linking agent is as follows: adding a surfactant to a solvent, setting the temperature to 40°C and the rotation speed to 350 r / min, stirring and mixing for 5 minutes, then adding zirconium salt and aluminum salt, maintaining the temperature and rotation speed unchanged and continuing to stir for 10 minutes until dissolved, adding sodium hydroxide solution to adjust the pH value to 10, and obtaining a mixture; adding an organic ligand to the obtained mixture, stirring evenly, and then adding an initiator, heating to 70°C at a heating rate of 1±0.3°C / min, stirring and reacting for 5 hours, and obtaining a cross-linking agent.

[0088] Example 2

[0089] The cross-linking agent comprises the following components, in parts by weight: 10 parts of zirconium salt, 6 parts of aluminum salt, 33 parts of organic ligand (8 parts of small molecule alcohol, 2 parts of α-hydroxycarboxylic acid, 1 part of polyhydroxycarboxylate, 22 parts of β-diketone), 2 parts of surfactant, 1 part of initiator, and 40 parts of solvent (20 parts of organic solvent, 20 parts of water); the zirconium salt is zirconium oxychloride octahydrate, the aluminum salt is aluminum trichloride, the small molecule alcohol is ethanol, the α-hydroxycarboxylic acid is lactic acid, the polyhydroxycarboxylate is sodium gluconate, the β-diketone is acetylacetone, the surfactant is sodium dodecylsulfonate, the organic solvent is cyclohexane, and the initiator is methyl ethyl ketone peroxide.

[0090] The preparation method of the cross-linking agent is as follows: adding a surfactant to a solvent, setting the temperature to 40°C and the rotation speed to 350 r / min, stirring and mixing for 5 minutes, then adding zirconium salt and aluminum salt, maintaining the temperature and rotation speed unchanged and continuing to stir for 10 minutes until dissolved, adding sodium hydroxide solution to adjust the pH value to 10, and obtaining a mixture; adding an organic ligand to the obtained mixture, stirring evenly, then adding an initiator, raising the temperature to 80°C at a heating rate of 1±0.3°C / min, stirring and reacting for 7 hours, and obtaining a cross-linking agent.

[0091] Example 3

[0092] The cross-linking agent comprises the following components, in parts by weight: 12 parts of zirconium salt, 7 parts of aluminum salt, 38 parts of organic ligand (10 parts of polyol, 5 parts of α-hydroxycarboxylic acid, 23 parts of β-diketone), 2 parts of surfactant, 1 part of initiator, and 40 parts of solvent (20 parts of organic solvent and 20 parts of water); the zirconium salt is zirconium oxychloride octahydrate, the aluminum salt is aluminum trichloride, the polyol is glycerol, the α-hydroxycarboxylic acid is citric acid, the β-diketone is acetylacetone, the surfactant is sodium dodecylbenzenesulfonate, the organic solvent is cyclohexane, and the initiator is methyl ethyl ketone peroxide.

[0093] The preparation method of the cross-linking agent is as follows: adding a surfactant to a solvent, setting the temperature to 40°C and the rotation speed to 350 r / min, stirring and mixing for 5 minutes, then adding zirconium salt and aluminum salt, maintaining the temperature and rotation speed unchanged and continuing to stir for 10 minutes until dissolved, adding sodium hydroxide solution to adjust the pH value to 11, and obtaining a mixture; adding an organic ligand to the obtained mixture, stirring evenly, then adding an initiator, heating to 80°C at a heating rate of 1±0.3°C / min, stirring and reacting for 8 hours, and obtaining a cross-linking agent.

[0094] Example 4

[0095] The cross-linking agent comprises the following components, in parts by weight: 14 parts of zirconium salt, 8 parts of aluminum salt, 43 parts of organic ligand (8 parts of polyol, 4 parts of α-hydroxycarboxylic acid, 2 parts of polyhydroxycarboxylate, 29 parts of β-diketone), 2 parts of surfactant, 1 part of initiator, and 32 parts of solvent (16 parts of organic solvent and 16 parts of water); the zirconium salt is zirconium oxychloride octahydrate, the aluminum salt is aluminum trichloride, the polyol is sorbitol, the α-hydroxycarboxylic acid is citric acid, the polyhydroxycarboxylate is sodium gluconate, the β-diketone is acetylacetone, the surfactant is sodium lauryl sulfate, the solvent is cyclohexane and water, and the initiator is dicumyl peroxide.

[0096] The preparation method of the cross-linking agent is as follows: adding a surfactant to an organic solvent, setting the temperature to 40°C and the rotation speed to 350 r / min, stirring and mixing for 5 minutes, then adding zirconium salt and aluminum salt, maintaining the temperature and rotation speed unchanged and continuing to stir for 10 minutes until dissolved, adding sodium hydroxide solution to adjust the pH value to 12 to obtain a mixture; adding an organic ligand to the obtained mixture, stirring evenly, then adding an initiator, raising the temperature to 85°C at a heating rate of 1±0.3°C / min, stirring and reacting for 9 hours to obtain a cross-linking agent.

[0097] Performance testing

[0098] Preparation of base liquid: Take 1000 mL of 20% HCl solution by mass concentration in a mixer, start stirring, and add 50 g of high-temperature corrosion inhibitor (provided by Tianjin Hengzhixin Technology Co., Ltd., a ternary compound of linear alkane quaternary ammonium salt, imidazoline quaternary ammonium salt and quinoline quaternary ammonium salt), 10 g of corrosion inhibitor synergist (provided by Tianjin Hengzhixin Technology Co., Ltd., a metal salt compound cuprous iodide) and 8.0 g of polymer thickener (provided by Southwest Petroleum University, a tetrapolymer of acrylamide, N-vinylpyrrolidone, acryloyloxyethyltrimethylammonium chloride, and 2-acrylamide-2-methylpropanesulfonic acid) in sequence, stir for 30 minutes, and obtain the base liquid.

[0099] 50 mL of the above base liquid was taken, and 0.4 g of the cross-linking agent prepared in Examples 1 to 4 was added respectively, and the mixture was stirred evenly to obtain cross-linking acids with different cross-linking temperatures.

[0100] The cross-linking temperature of the cross-linked acid prepared above was tested by the following method: after filling the sleeve with fracturing fluid, the sample was heated at a controlled heating rate of 3°C / min±0.2°C / min. The test was started from room temperature and the rotor was heated at a shear rate of 170s. -1 The fracturing fluid is rotated and subjected to continuous shear under heating conditions. The temperature corresponding to the "inflection point" where the apparent viscosity increases is characterized as the cross-linking temperature of the sample; the test results Figures 1 to 4 As shown; it can be seen that the cross-linking temperature of the cross-linking agent prepared in Example 1 is 40°C, the cross-linking temperature of the cross-linking agent prepared in Example 2 is 60°C, the cross-linking temperature of the cross-linking agent prepared in Example 3 is 80°C, and the cross-linking temperature of the cross-linking agent prepared in Example 4 is 100°C; the initial viscosity of the system is about 45mPa.s, and the viscosity of the base liquid is kept uncross-linked. When the temperature reaches 40°C ( Figure 1 )、60℃( Figure 2 )、80℃( Figure 3 )、100℃( Figure 4 ), the curve has an inflection point, that is, cross-linking begins, indicating that different cross-linking agents have different cross-linking temperatures.

[0101] The high temperature and shear resistance of the cross-linked acid were tested using an RS6000 high temperature and high pressure rheometer. During the test, the heating rate was 3°C / min, the experimental temperature was 180°C, and the shear rate was 170s. -1 , shear time is 60min; the test results are, at 180℃, 170s -1 After 60 minutes of shearing, the system rheological viscosities corresponding to the cross-linking agents prepared in Examples 1 to 4 were 98.5 mPa.s, 102 mPa.s, 105 mPa.s, and 122 mPa.s, respectively, meeting the viscosity requirement of ≥40 mPa.s in the industry standard Q / SH CG0148-2021 "Technical Requirements for Cross-linked Acids".

[0102] Compared with CN 108179008 A "A cross-linking agent system, low-concentration polymer cross-linked fracturing fluid and preparation method thereof" and CN 102634329 A "Low-molecular polymer fracturing fluid", the cross-linking agent prepared in the embodiment of the present invention adopts a one-step synthesis method, which is simpler in process and more convenient for on-site use; since acetylacetone is added to the ligand, it has multiple strongly coordinated oxygen atoms and can form a stable coordination compound with the central ion, which greatly improves the temperature resistance of the system (180°C, after 60 minutes of continuous shearing, the viscosity is greater than 80mPa.s), can effectively reduce the acid-rock reaction rate of the acid fluid and its filtration loss in the formation, and is more conducive to the creation of long fractures.

[0103] Compared with CN 103265942 A "Hydroxypropyl guar gum acidic crosslinker and preparation process of crosslinker", in the synthesis of the crosslinker in the embodiment of the present invention, the release temperature of the central ion of the crosslinker is different by changing parameters such as the central ion concentration, reaction temperature and reaction pH value, thereby controlling the crosslinking temperature of the crosslinked acid system. In high-temperature deep well construction, a suitable crosslinker can be selected according to the wellbore temperature field so that crosslinking occurs 1000m from the bottom of the well, thereby minimizing construction friction, increasing construction displacement, and achieving the purpose of deep penetration acid fracturing.

[0104] The cross-linking agent provided by the present invention has a central ion composed of two compounds to achieve functional complementarity and improve the temperature resistance of the system; the ligand is a small molecule ligand with small steric hindrance, good solubility and more stable performance, and by changing the type of ligand as well as the reaction temperature and pH value, a series of cross-linking agent products can be formed, so that the cross-linking temperature with the polymer can be controlled between 40 and 100°C. During the construction process, through personalized selection of the cross-linking agent, the cross-linking of the cross-linked acid system is controlled to occur at a specific position in the wellbore, effectively reducing the friction resistance of the construction pipeline and lowering the construction pressure.

[0105] Although the present invention has been described and illustrated with reference to specific embodiments of the present invention, these descriptions and illustrations do not limit the present invention. It will be clearly understood by those skilled in the art that, without departing from the true spirit and scope of the present invention as defined by the appended claims, various changes may be made to make specific circumstances, materials, compositions of matter, substances, methods or processes suitable for the object, spirit and scope of the present application. All such modifications are intended to be within the scope of the appended claims. Although the methods disclosed herein have been described with reference to specific operations performed in a specific order, it will be understood that these operations may be combined, subdivided or reordered to form equivalent methods without departing from the teachings of the present invention. Therefore, unless otherwise indicated herein, the order and grouping of operations are not limitations of the present application.

Claims

1. A cross-linking agent, comprising, by weight: 15-35 parts of metal salt; 20-60 parts of organic ligand; 25-65 parts of solvent; 1-5 parts of surfactant; 0.5~2.0 parts of initiator; The metal salts include: aluminum and zirconium salts; The mass ratio of the zirconium salt to the aluminum salt is (1-3):1, the aluminum salt is aluminum trichloride; the zirconium salt is selected from zirconium oxychloride octahydrate or zirconium sulfate; The organic ligand is selected from three of the group consisting of small molecule alcohols, α-hydroxycarboxylic acids, polyols, polyhydroxycarboxylates, and β-diketones; the small molecule alcohol is selected from one of methanol, ethanol, or isopropanol; the α-hydroxycarboxylic acid is selected from one of lactic acid, citric acid, or tartaric acid; the polyol is selected from one or more of xylitol, sorbitol, pentaerythritol, glycerol, or ethylene glycol; the polyhydroxycarboxylates are selected from sodium gluconate; and the β-diketone is selected from one or more of benzoylacetone, acetylacetone, and trifluoroacetylacetone. The initiator is selected from one of dicumyl peroxide and methyl ethyl ketone peroxide.

2. The cross-linking agent according to claim 1, characterized in that The solvent is selected from two of cyclohexane, ethylene glycol, glycerol, and water; The surfactant is selected from one of sodium dodecylbenzenesulfonate, sodium lauryl sulfate or sodium dodecylsulfonate.

3. A method for preparing the cross-linking agent according to claim 1, comprising: mixing a surfactant, a solvent, and a metal salt to obtain a mixture; The organic ligand, the initiator and the mixture are reacted to obtain a crosslinking agent.

4. A cross-linked acid comprising: The cross-linking agent according to claim 1, or the cross-linking agent prepared by the method according to claim 3.

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