Guar gum composition for oil field development and method for preparing the same

Abstract

The application discloses a guar gum composition for oil field exploitation and a preparation method thereof, and relates to the technical field of guar gum. The method comprises the following steps: alkalizing, cation etherizing and copolymerizing AM-AMPS with natural guar gum to obtain an organic modified guar gum; introducing active groups through a silane coupling agent KH-560; and finally, carrying out in-situ sol-gel reaction with SiO2-TiO2 composite precursors to form an organic-inorganic interpenetrating network structure. The guar gum composition has good structural stability and viscosity retention capacity at high temperatures, and is suitable for fracturing construction of deep high-temperature oil and gas reservoirs.

Description

Technical Field

[0001] This invention relates to the field of guar gum technology, specifically to a guar gum composition for oilfield development and its preparation method. Background Technology

[0002] Guar gum is a natural high-molecular-weight polysaccharide. Its main chain consists of mannose units linked by β-1,4-glycosidic bonds, and its side chains are linked by galactose units through α-1,6-glycosidic bonds. Due to its excellent water solubility, thickening properties, and cross-linking ability with cross-linking agents, it is widely used in oilfield fracturing fluid systems. Chinese Patent Publication No. CN101495595B discloses oxidized guar gum for oilfield maintenance fluids, which contains aldehyde guar gum produced by enzymatic oxidation of non-derived linear guar gum or guar gum derivatives. The enzyme used to oxidize guar gum to aldehyde guar gum is galactose oxidase, which can be used in combination with catalase or catalase and peroxidase. Aldehyde guar gum can be used as an effective gelling agent for oilfield maintenance fluids such as hydraulic fracturing fluids and injection fluids. However, the heat resistance of guar gum in the above-mentioned existing technologies is not good. When the bottom temperature exceeds 120°C, the glycosidic bonds in the guar gum molecular chain will undergo thermal degradation and breakage, resulting in a sharp drop in the viscosity of the fracturing fluid and a significant reduction in its sand-carrying capacity, which seriously affects the fracturing operation effect and the production capacity of oil and gas wells. Summary of the Invention

[0003] The purpose of this invention is to provide a guar gum composition for oilfield development and its preparation method, so as to solve the technical problem of poor high-temperature resistance of the guar gum composition mentioned in the background art.

[0004] To achieve the above objectives, the present invention provides the following technical solution:

[0005] A method for preparing a guar gum composition for oilfield development includes the following steps:

[0006] S1. Dissolve natural guar gum powder in water, and add sodium hydroxide under nitrogen protection for alkali activation to obtain alkali-activated guar gum solution.

[0007] S2. Under nitrogen protection, 2,3-epoxypropyltrimethylammonium chloride is added to the alkali-activated guar gum solution to carry out an etherification reaction, and a cationic intermediate solution is obtained.

[0008] S3. Under nitrogen protection, ammonium persulfate and sodium bisulfite are added to the cationization intermediate solution for pre-activation;

[0009] S4. Under nitrogen protection, a graft copolymerization reaction was carried out by adding a mixture of monomers consisting of acrylamide and 2-acrylamido-2-methylpropanesulfonic acid to the pre-activated solution. After the reaction was completed, the pH was adjusted to 7.0, deionized water was added for dilution, and dialyzed. After dialysis, the solution was concentrated by rotary evaporation, and anhydrous ethanol was added to the concentrate for alcohol precipitation. The solution was stirred, filtered, and washed with a mixed solvent of ethanol and acetone. The solution was then vacuum dried, ground, and sieved to obtain modified guar gum powder.

[0010] S5. Under nitrogen protection, an ethanol solution of tetraethyl orthosilicate and an acetic acid-ethanol solution of tetrabutyl titanate are mixed to prepare a silicon-titanium composite precursor mixture.

[0011] S6. Under nitrogen protection, the modified guar gum powder is dissolved in water, ethanol and silane coupling agent KH-560 are added, and the mixture is reacted under triethylamine catalysis to obtain a modified guar gum solution modified with coupling agent.

[0012] S7. Under nitrogen protection, a mixture of silicon-titanium composite precursors was added to the modified guar gum solution modified with coupling agent to carry out an in-situ sol-gel hybrid reaction to obtain a hybrid reaction solution. Sodium citrate and aluminum chloride hexahydrate were added to the hybrid reaction solution in sequence, with a mass ratio of sodium citrate to aluminum chloride hexahydrate of 3:(0.3-0.8). The reaction was heated and stirred, and the reaction solution was allowed to stand and age under nitrogen protection. Anhydrous ethanol was added to precipitate the guar gum, and the mixture was stirred. After filtration, the mixture was washed with deionized water until the pH of the washing solution was neutral. The mixture was then washed with a mixed solvent of ethanol and acetone. The mixture was vacuum dried, ground, and sieved to obtain the guar gum composition.

[0013] In the technical solution of this invention, the high-temperature resistance of guar gum is improved in the following ways: (1) The fundamental principle that natural guar gum is not resistant to high temperatures is that the thermal cracking of the glycosidic bonds in the main chain and the irreversible collapse of the molecular chain conformation are the reasons. The first aspect is to improve its high-temperature resistance by stabilizing the conformation and the heat-resistant structural units. Specifically, quaternary ammonium salt cationic functional side groups are covalently grafted onto the main chain through etherification reaction. The electrostatic repulsion between the groups forces the molecular chain to maintain an extended conformation, inhibits entanglement and collapse at high temperatures, and enables the molecular chain to maintain a large hydrodynamic volume even when some glycosidic bonds have been broken, thus delaying the decrease in viscosity. It should be noted that the thermal cracking of glycosidic bonds is a chemical process controlled by temperature and activation energy. Electrostatic repulsion cannot directly reduce its breaking rate. The core contribution is to improve the conformation maintenance ability after chain breakage and to transform the collapse into a gradual decay. Then, poly(AM-co-AMPS) segments are introduced through graft copolymerization: AM amide groups can form an intermolecular hydrogen bond network to enhance structural strength in the medium and low temperature range, and AMPS sulfonic acid groups, after deprotonation, form a highly symmetrical resonance delocalized stable structure with SO bonds. It has a high thermal decomposition temperature and is completely stable under operating temperature. Through the above effects, the high temperature resistance of guar gum is initially improved. (2) Add covalently bonded inorganic reinforcing phases to the organic matrix to compensate for the thermal degradation loss of the organic skeleton at the structural level. Specifically, active silanol groups are first introduced into the modified guar gum molecular chain using KH-560 coupling agent to form an organic-inorganic covalent molecular bridge. Then, an in-situ SiO2-TiO2 hybrid inorganic phase is generated through an acid-catalyzed sol-gel reaction. The thermal stability of the in-situ generated inorganic phase is much higher than that of the organic component. It is covalently anchored to the organic framework by the coupling agent. It should be noted that the inorganic reinforcing phase itself cannot change the thermal decomposition rate of glycosidic bonds. However, when the glycosidic bonds are gradually broken, the intact inorganic network framework acts as a structural support to maintain the connectivity of the system. At the same time, the conformational changes of the organic chain segments are constrained by covalent bonds, so that the system can still maintain effective viscosity during the continuous breaking of glycosidic bonds, further improving the high-temperature resistance of guar gum.

[0014] Preferably, in step S1, the amount of sodium hydroxide added is 6-10 wt% of the natural guar gum powder;

[0015] The alkali activation conditions are: stirring at 32°C for 30 minutes.

[0016] Preferably, in step S2, the amount of 2,3-epoxypropyltrimethylammonium chloride added is 25-40 wt% of the natural guar gum powder;

[0017] The etherification reaction temperature is 50℃ and the etherification reaction time is 2.5h.

[0018] Preferably, in step S3, the amount of ammonium persulfate added is 0.2–0.4 wt% of the natural guar gum powder;

[0019] The pre-activation temperature is 32℃ and the pre-activation time is 4 min.

[0020] Preferably, in step S4, the mass ratio of acrylamide to 2-acrylamido-2-methylpropanesulfonic acid is 40:(15-20);

[0021] The graft copolymerization reaction was carried out at a temperature of 50°C for 2.5 hours.

[0022] Preferably, in step S5, the volume ratio of tetraethyl orthosilicate to tetrabutyl titanate is 10:(1-3).

[0023] The reaction temperature was 28°C and the reaction time was 1.5 h.

[0024] Preferably, in step S6, the mass ratio of modified guar gum powder to silane coupling agent KH-560 is 10:(0.5~1.5);

[0025] The reaction temperature was 48°C and the reaction time was 2.5 h.

[0026] Preferably, in step S7, the hybridization reaction temperature is 50°C and the reaction time is 3.5 h.

[0027] Preferably, the mass ratio of the modified guar gum powder to sodium citrate is 80:3.

[0028] This invention discovered in experiments that the synergistic effect between the organic framework and the inorganic reinforcing phase depends entirely on the Si-OC covalent bridge formed by the coupling agent. However, this bond is gradually hydrolyzed and broken by continuous nucleophilic attack from water molecules in a high-temperature, water-containing environment. This causes the inorganic reinforcing phase to detach from the organic framework, and the synergistic system transforms from a chemically bonded hybrid material into a physically blended material, affecting its long-term temperature resistance. To solve this technical problem, this invention introduces sodium citrate and aluminum chloride sequentially into the system after the sol-gel hybrid reaction. When prepared at room temperature, sodium citrate acts as a protective shield, firmly encapsulating (chelating) a very small amount of aluminum ions, ensuring that the material does not cross-link prematurely, thus maintaining excellent water solubility. However, when exposed to a high-temperature environment, and the original Si-OC bonds begin to break due to hot water hydrolysis, sodium citrate gradually becomes ineffective with increasing temperature and eventually thermally decomposes, releasing a large amount of the sealed aluminum ions. These aluminum ions rapidly form self-repairing coordination bonds between organic and inorganic substances; the higher the temperature, the faster the old bonds break, the more aluminum ions are released, and the tighter the newly established compensatory bonds become, perfectly achieving dynamic compensation and thus improving the long-term temperature resistance of guar gum.

[0029] A guar gum composition for oilfield development is prepared by the method described above.

[0030] Compared with the prior art, the beneficial effects of the present invention are:

[0031] 1. By grafting quaternary ammonium salt cations and introducing AM-CO-AMPS polymer segments, the temperature tolerance of guar gum is significantly improved from two aspects: conformational stabilization and the introduction of ultra-heat-resistant monomers.

[0032] 2. An in-situ SiO2-TiO2 inorganic network was generated using a coupling agent and a sol-gel method, and then covalently bonded to the organic framework. This inorganic phase does not directly prevent the main chain from breaking, but rather acts as a framework support system after the main chain breaks, maintaining the macroscopic structure and causing the viscosity to decrease slowly rather than collapse instantly, thus ensuring effective sand-carrying capacity over the fracturing timescale.

[0033] 3. To address the problem of performance degradation caused by the hydrolysis of Si-OC covalent bonds at high temperatures, a citric acid chelating aluminum ion system was introduced. The chelated state ensures water solubility at room temperature, while the chelating agent decomposes at high temperatures, and the released aluminum ions quickly form coordination bonds at the organic-inorganic interface. The higher the temperature, the faster the bond breaking, and the more remedial connections are formed, thus achieving dynamic compensation and significantly improving the long-term temperature resistance of the material. Attached Figure Description

[0034] Figure 1 This is a low-magnification SEM image of the guar gum composition particles prepared in Example 1 of the present invention.

[0035] Figure 2 This is a medium-magnification SEM image of the guar gum composition particles prepared in Example 1 of the present invention.

[0036] Figure 3 This is a high-magnification SEM image of the guar gum composition particles prepared in Example 1 of the present invention.

[0037] Figure 4 The XPS spectrum of the guar gum composition prepared in Example 1 of this invention is shown.

[0038] Figure 5 The image shows the XRD pattern of the guar gum composition prepared in Example 1 of this invention. Detailed Implementation

[0039] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0040] Example 1

[0041] A method for preparing a guar gum composition for oilfield development includes the following steps:

[0042] S1. Weigh 100g of natural guar gum powder and add it to 4900mL of deionized water. Stir and swell for 50min under nitrogen protection at 32℃ to form a guar gum aqueous solution. Add 9g of sodium hydroxide to the solution and stir for 30min under nitrogen protection at 32℃ to obtain an alkali-activated guar gum solution.

[0043] S2. Dissolve 38g of 2,3-epoxypropyltrimethylammonium chloride in 30mL of deionized water. Under nitrogen protection and stirring at 50℃, slowly add the solution to the alkali-activated guar gum obtained in step S1 at a rate of 1.2mL / min. After the addition is complete, react at 50℃ for 2.5h to obtain a cationic intermediate solution.

[0044] S3. Cool the solution obtained in step S2 to 32°C, slowly add 10% hydrochloric acid solution, and adjust the pH of the system to 6.5 under pH meter monitoring; continuously purge nitrogen for 30 min to remove dissolved oxygen; add 0.35 g ammonium persulfate and 0.135 g sodium bisulfite under nitrogen protection, and stir and pre-activate at 32°C for 4 min.

[0045] S4. Prepare a mixed monomer solution by dissolving 40g of acrylamide (AM) and 18g of 2-acrylamido-2-methylpropanesulfonic acid (AMPS) in 400mL of deionized water and purging with nitrogen for 30min to remove oxygen. Under nitrogen protection and stirring at 37℃, add the mixed monomer solution to the reaction system of step S3 by uniform dropwise addition over a period of 1.8h. After the addition is complete, raise the temperature to 50℃ and react at a constant temperature for 2.5h to obtain the graft copolymerization reaction solution. After the reaction was completed, 10% hydrochloric acid was added dropwise to adjust the pH to 7.0, and deionized water was added to dilute to a solid content of about 1.0%. Dialysis was performed for 24 hours using a dialysis bag with a molecular weight cutoff of 100,000 Da (water was changed every 6 hours). After dialysis, the solid content was concentrated by rotary evaporation at 48°C to about 3.5%. Seven times the volume of anhydrous ethanol was added to the concentrate for alcohol precipitation, and the mixture was stirred for 25 minutes. After filtration, the mixture was washed three times with a mixed solvent of ethanol:acetone = 1:1 (volume ratio). The mixture was then vacuum dried at 52°C for 9 hours and ground through a 100-mesh sieve to obtain modified guar gum powder.

[0046] S5. Under dry nitrogen protection, 10 mL of tetraethyl orthosilicate (TEOS) was added to 50 mL of anhydrous ethanol and stirred until homogeneous to obtain a silicon source ethanol solution; 2.5 mL of tetrabutyl titanate (TBT) was added to 3.5 mL of glacial acetic acid and 12 mL of anhydrous ethanol and stirred until homogeneous to obtain a titanium source solution; the titanium source solution was slowly added dropwise to the silicon source ethanol solution at a rate of 1.5 mL / min and stirred at 28 °C for 1.5 h to obtain a silicon-titanium composite precursor mixture.

[0047] S6. Take 80g of the modified guar gum powder obtained in step S4 and add it to deionized water. Stir and dissolve it at 52℃ under nitrogen protection for 1.2h until completely transparent. Then slowly add anhydrous ethanol to make the final volume ratio of ethanol to water 25:75 to prepare a modified guar gum solution. First, add 0.26g of triethylamine to the solution and stir for 5min. Then take 10g of silane coupling agent KH-560 and pre-dilute it with 28g of anhydrous ethanol (4 times the mass). Slowly add it dropwise to the above solution at a rate of 0.8mL / min. Stir and react at 48℃ under nitrogen protection for 2.5h to obtain the coupling agent-modified guar gum solution.

[0048] S7. Cool the solution obtained in step S6 to 38°C, add 5% (w / w) dilute nitric acid solution dropwise, and adjust the pH of the system to 4.5 under pH meter monitoring. Under continuous stirring at 400 rpm and nitrogen protection, slowly add the silicon-titanium composite precursor mixture obtained in step S5 to the above acidic solution at a rate of 1.0 mL / min using a peristaltic pump. After the addition is complete, correct the pH to 4.8, raise the temperature to 50°C and react at a constant temperature for 3.5 h to obtain an organic-inorganic hybrid reaction solution. Then, under stirring at 38°C, first add 3.0 g of sodium citrate and stir for 12 min until completely dissolved; then slowly add 0.7 g of aluminum chloride hexahydrate and stir at 38°C for 40 min to obtain an interface-enhanced hybrid reaction solution. The reaction solution was aged at 28°C under nitrogen protection for 7 hours; 8 times the volume of anhydrous ethanol was added for alcohol precipitation, and the mixture was stirred for 30 minutes; after filtration, the mixture was washed three times with deionized water at room temperature (each time not exceeding 5 minutes) until the pH of the washing solution was neutral; then it was washed twice with a 1:1 mixture of ethanol and acetone; the mixture was vacuum dried at 52°C for 11 hours, ground and passed through a 120-mesh sieve to obtain the guar gum composition.

[0049] The morphology of the guar gum composition prepared in Example 1 is as follows: Figures 1 to 3 As shown in the figure, its surface exhibits a typical micro-rough structure and an in-situ generated inorganic network; the XPS spectrum of the product of Example 1 is shown in the figure. Figure 4 As shown, the presence of characteristic elements and chemical bonds is confirmed; the XRD pattern of the product in Example 1 is shown below. Figure 5 As shown, this reflects the crystal structure characteristics of the hybrid system.

[0050] Example 2

[0051] A method for preparing a guar gum composition for oilfield development includes the following steps:

[0052] S1. Weigh 100g of natural guar gum powder and add it to 4900mL of deionized water. Stir and swell for 50min under nitrogen protection at 32℃ to form a guar gum aqueous solution. Add 7g of sodium hydroxide to the solution and stir for 30min under nitrogen protection at 32℃ to obtain an alkali-activated guar gum solution.

[0053] S2. Dissolve 28g of 2,3-epoxypropyltrimethylammonium chloride in 30mL of deionized water. Under nitrogen protection and stirring at 50℃, slowly add the solution to the alkali-activated guar gum obtained in step S1 at a rate of 1.2mL / min. After the addition is complete, react at 50℃ for 2.5h to obtain a cationic intermediate solution.

[0054] S3. Cool the solution obtained in step S2 to 32°C, slowly add 10% hydrochloric acid solution, and adjust the pH of the system to 6.5 under pH meter monitoring; continuously purge nitrogen for 30 min to remove dissolved oxygen; add 0.25 g ammonium persulfate and 0.135 g sodium bisulfite under nitrogen protection, and stir and pre-activate at 32°C for 4 min.

[0055] S4. Prepare a mixed monomer solution by dissolving 40g of acrylamide (AM) and 16g of 2-acrylamido-2-methylpropanesulfonic acid (AMPS) in 400mL of deionized water and purging with nitrogen for 30min to remove oxygen. Under nitrogen protection and stirring at 37℃, add the mixed monomer solution to the reaction system of step S3 by uniform dropwise addition over a period of 1.8h. After the addition is complete, raise the temperature to 50℃ and react for 2.5h to obtain the graft copolymerization reaction solution. After the reaction was completed, 10% hydrochloric acid was added dropwise to adjust the pH to 7.0, and deionized water was added to dilute to a solid content of about 1.0%. Dialysis was performed for 24 hours using a dialysis bag with a molecular weight cutoff of 100,000 Da (water was changed every 6 hours). After dialysis, the solid content was concentrated by rotary evaporation at 48°C to about 3.5%. Seven times the volume of anhydrous ethanol was added to the concentrate for alcohol precipitation, and the mixture was stirred for 25 minutes. After filtration, the mixture was washed three times with a mixed solvent of ethanol:acetone = 1:1 (volume ratio). The mixture was then vacuum dried at 52°C for 9 hours and ground through a 100-mesh sieve to obtain modified guar gum powder.

[0056] S5. Under dry nitrogen protection, 10 mL of tetraethyl orthosilicate (TEOS) was added to 50 mL of anhydrous ethanol and stirred until homogeneous to obtain a silicon source ethanol solution; 1.5 mL of tetrabutyl titanate (TBT) was added to 3.5 mL of glacial acetic acid and 12 mL of anhydrous ethanol and stirred until homogeneous to obtain a titanium source solution; the titanium source solution was slowly added dropwise to the silicon source ethanol solution at a rate of 1.5 mL / min and stirred at 28 °C for 1.5 h to obtain a silicon-titanium composite precursor mixture.

[0057] S6. Take 80g of the modified guar gum powder obtained in step S4 and add it to deionized water. Stir and dissolve it at 52℃ under nitrogen protection for 1.2h until it is completely transparent. Then slowly add anhydrous ethanol to make the final volume ratio of ethanol to water 25:75 to prepare a modified guar gum solution. First, add 0.26g of triethylamine to the solution and stir for 5min. Then take 6g of silane coupling agent KH-560 and pre-dilute it with 28g of anhydrous ethanol (4 times the mass). Slowly add it dropwise to the above solution at a rate of 0.8mL / min. Stir and react at 48℃ under nitrogen protection for 2.5h to obtain the coupling agent-modified guar gum solution.

[0058] S7. Cool the solution obtained in step S6 to 38°C, add 5% (w / w) dilute nitric acid solution dropwise, and adjust the pH of the system to 4.5 under pH meter monitoring. Under continuous stirring at 400 rpm and nitrogen protection, slowly add the silicon-titanium composite precursor mixture obtained in step S5 to the above acidic solution at a rate of 1.0 mL / min using a peristaltic pump. After the addition is complete, correct the pH to 4.8, raise the temperature to 50°C and react at a constant temperature for 3.5 h to obtain an organic-inorganic hybrid reaction solution. Then, under stirring at 38°C, first add 3.0 g of sodium citrate and stir for 12 min until completely dissolved; then slowly add 0.4 g of aluminum chloride hexahydrate and stir at 38°C for 40 min to obtain an interface-enhanced hybrid reaction solution. The reaction solution was aged at 28°C under nitrogen protection for 7 hours; 8 times the volume of anhydrous ethanol was added for alcohol precipitation, and the mixture was stirred for 30 minutes; after filtration, the mixture was washed three times with deionized water at room temperature (each time not exceeding 5 minutes) until the pH of the washing solution was neutral; then it was washed twice with a 1:1 mixture of ethanol and acetone; the mixture was vacuum dried at 52°C for 11 hours, ground and passed through a 120-mesh sieve to obtain the guar gum composition.

[0059] Example 3

[0060] A method for preparing a guar gum composition for oilfield development includes the following steps:

[0061] S1. Weigh 100g of natural guar gum powder and add it to 4900mL of deionized water. Stir and swell for 50min at 32℃ under nitrogen protection to form a guar gum aqueous solution. Add 8g of sodium hydroxide to the solution and stir for 30min at 32℃ under nitrogen protection to obtain an alkali-activated guar gum solution.

[0062] S2. Dissolve 30g of 2,3-epoxypropyltrimethylammonium chloride in 30mL of deionized water. Under nitrogen protection and stirring at 50℃, slowly add the solution to the alkali-activated guar gum obtained in step S1 at a rate of 1.2mL / min. After the addition is complete, react at 50℃ for 2.5h to obtain a cationic intermediate solution.

[0063] S3. Cool the solution obtained in step S2 to 32°C, slowly add 10% hydrochloric acid solution, and adjust the pH of the system to 6.5 under pH meter monitoring; continuously purge nitrogen for 30 min to remove dissolved oxygen; add 0.3 g ammonium persulfate and 0.135 g sodium bisulfite under nitrogen protection, and stir at 32°C for 4 min for pre-activation.

[0064] S4. Prepare a mixed monomer solution by dissolving 40g of acrylamide (AM) and 17g of 2-acrylamido-2-methylpropanesulfonic acid (AMPS) in 400mL of deionized water and purging with nitrogen for 30min to remove oxygen. Under nitrogen protection and stirring at 37℃, add the mixed monomer solution to the reaction system of step S3 by uniform dropwise addition over a period of 1.8h. After the addition is complete, raise the temperature to 50℃ and react at a constant temperature for 2.5h to obtain the graft copolymerization reaction solution. After the reaction was completed, 10% hydrochloric acid was added dropwise to adjust the pH to 7.0, and deionized water was added to dilute to a solid content of about 1.0%. Dialysis was performed for 24 hours using a dialysis bag with a molecular weight cutoff of 100,000 Da (water was changed every 6 hours). After dialysis, the solid content was concentrated by rotary evaporation at 48°C to about 3.5%. Seven times the volume of anhydrous ethanol was added to the concentrate for alcohol precipitation, and the mixture was stirred for 25 minutes. After filtration, the mixture was washed three times with a mixed solvent of ethanol:acetone = 1:1 (volume ratio). The mixture was then vacuum dried at 52°C for 9 hours and ground through a 100-mesh sieve to obtain modified guar gum powder.

[0065] S5. Under dry nitrogen protection, 10 mL of tetraethyl orthosilicate (TEOS) was added to 50 mL of anhydrous ethanol and stirred until homogeneous to obtain a silicon source ethanol solution; 2 mL of tetrabutyl titanate (TBT) was added to 3.5 mL of glacial acetic acid and 12 mL of anhydrous ethanol and stirred until homogeneous to obtain a titanium source solution; the titanium source solution was slowly added dropwise to the silicon source ethanol solution at a rate of 1.5 mL / min and stirred at 28 °C for 1.5 h to obtain a silicon-titanium composite precursor mixture.

[0066] S6. Take 80g of the modified guar gum powder obtained in step S4 and add it to deionized water. Stir and dissolve it for 1.2h at 52℃ under nitrogen protection until it is completely transparent. Then slowly add anhydrous ethanol to make the final volume ratio of ethanol to water 25:75 to prepare a modified guar gum solution. First, add 0.26g of triethylamine to the solution and stir for 5min. Then take 8g of silane coupling agent KH-560 and pre-dilute it with 28g of anhydrous ethanol (4 times the mass). Slowly add it dropwise to the above solution at a rate of 0.8mL / min. Stir and react for 2.5h at 48℃ under nitrogen protection to obtain the coupling agent-modified guar gum solution.

[0067] S7. Cool the solution obtained in step S6 to 38°C, add 5% (w / w) dilute nitric acid solution dropwise, and adjust the pH of the system to 4.5 under pH meter monitoring. Under continuous stirring at 400 rpm and nitrogen protection, slowly add the silicon-titanium composite precursor mixture obtained in step S5 to the above acidic solution at a rate of 1.0 mL / min using a peristaltic pump. After the addition is complete, correct the pH to 4.8, raise the temperature to 50°C and react at a constant temperature for 3.5 h to obtain an organic-inorganic hybrid reaction solution. Then, under stirring at 38°C, first add 3.0 g of sodium citrate and stir for 12 min until completely dissolved; then slowly add 0.5 g of aluminum chloride hexahydrate and stir at 38°C for 40 min to obtain an interface-enhanced hybrid reaction solution. The reaction solution was aged at 28°C under nitrogen protection for 7 hours; 8 times the volume of anhydrous ethanol was added for alcohol precipitation, and the mixture was stirred for 30 minutes; after filtration, the mixture was washed three times with deionized water at room temperature (each time not exceeding 5 minutes) until the pH of the washing solution was neutral; then it was washed twice with a 1:1 mixture of ethanol and acetone; the mixture was vacuum dried at 52°C for 11 hours, ground and passed through a 120-mesh sieve to obtain the guar gum composition.

[0068] Example 4

[0069] A method for preparing a guar gum composition for oilfield development includes the following steps:

[0070] S1. Weigh 100g of natural guar gum powder and add it to 4900mL of deionized water. Stir and swell for 50min under nitrogen protection at 32℃ to form a guar gum aqueous solution. Add 10g of sodium hydroxide to the solution and stir for 30min under nitrogen protection at 32℃ to obtain an alkali-activated guar gum solution.

[0071] S2. Dissolve 40g of 2,3-epoxypropyltrimethylammonium chloride in 40mL of deionized water. Under nitrogen protection and stirring at 50℃, slowly add the solution to the alkali-activated guar gum obtained in step S1 at a rate of 1.2mL / min. After the addition is complete, react at 50℃ for 2.5h to obtain a cationic intermediate solution.

[0072] S3. Cool the solution obtained in step S2 to 32°C, slowly add 10% hydrochloric acid solution, and adjust the pH of the system to 6.5 under pH meter monitoring; continuously purge nitrogen for 30 min to remove dissolved oxygen; add 0.4 g ammonium persulfate and 0.135 g sodium bisulfite under nitrogen protection, and stir and pre-activate at 32°C for 4 min.

[0073] S4. Prepare a mixed monomer solution by dissolving 40g of acrylamide (AM) and 20g of 2-acrylamido-2-methylpropanesulfonic acid (AMPS) in 400mL of deionized water and purging with nitrogen for 30min to remove oxygen. Under nitrogen protection and stirring at 37℃, add the mixed monomer solution to the reaction system of step S3 by uniform dropwise addition over a period of 1.8h. After the addition is complete, raise the temperature to 50℃ and react at a constant temperature for 2.5h to obtain the graft copolymerization reaction solution. After the reaction was completed, 10% hydrochloric acid was added dropwise to adjust the pH to 7.0, and deionized water was added to dilute to a solid content of about 1.0%. Dialysis was performed for 24 hours using a dialysis bag with a molecular weight cutoff of 100,000 Da (water was changed every 6 hours). After dialysis, the solid content was concentrated by rotary evaporation at 48°C to about 3.5%. Seven times the volume of anhydrous ethanol was added to the concentrate for alcohol precipitation, and the mixture was stirred for 25 minutes. After filtration, the mixture was washed three times with a mixed solvent of ethanol:acetone = 1:1 (volume ratio). The mixture was then vacuum dried at 52°C for 9 hours and ground through a 100-mesh sieve to obtain modified guar gum powder.

[0074] S5. Under dry nitrogen protection, 10 mL of tetraethyl orthosilicate (TEOS) was added to 50 mL of anhydrous ethanol and stirred until homogeneous to obtain a silicon source ethanol solution; 3 mL of tetrabutyl titanate (TBT) was added to 3.5 mL of glacial acetic acid and 12 mL of anhydrous ethanol and stirred until homogeneous to obtain a titanium source solution; the titanium source solution was slowly added dropwise to the silicon source ethanol solution at a rate of 1.5 mL / min and stirred at 28 °C for 1.5 h to obtain a silicon-titanium composite precursor mixture.

[0075] S6. Take 80g of the modified guar gum powder obtained in step S4 and add it to deionized water. Stir and dissolve it at 52℃ under nitrogen protection for 1.2h until it is completely transparent. Then slowly add anhydrous ethanol to make the final volume ratio of ethanol to water 25:75 to prepare a modified guar gum solution. First, add 0.26g of triethylamine to the solution and stir for 5min. Then take 12g of silane coupling agent KH-560 and pre-dilute it with 28g of anhydrous ethanol (4 times the mass). Slowly add it dropwise to the above solution at a rate of 0.8mL / min. Stir and react at 48℃ under nitrogen protection for 2.5h to obtain the coupling agent-modified guar gum solution.

[0076] S7. Cool the solution obtained in step S6 to 38°C, add 5% (w / w) dilute nitric acid solution dropwise, and adjust the pH of the system to 4.5 under pH meter monitoring. Under continuous stirring at 400 rpm and nitrogen protection, slowly add the silicon-titanium composite precursor mixture obtained in step S5 to the above acidic solution at a rate of 1.0 mL / min using a peristaltic pump. After the addition is complete, correct the pH to 4.8, raise the temperature to 50°C and react at a constant temperature for 3.5 h to obtain an organic-inorganic hybrid reaction solution. Then, under stirring at 38°C, first add 3.0 g of sodium citrate and stir for 12 min until completely dissolved; then slowly add 0.8 g of aluminum chloride hexahydrate and stir at 38°C for 40 min to obtain an interface-enhanced hybrid reaction solution. The reaction solution was aged at 28°C under nitrogen protection for 7 hours; 8 times the volume of anhydrous ethanol was added for alcohol precipitation, and the mixture was stirred for 30 minutes; after filtration, the mixture was washed three times with deionized water at room temperature (each time not exceeding 5 minutes) until the pH of the washing solution was neutral; then it was washed twice with a 1:1 mixture of ethanol and acetone; the mixture was vacuum dried at 52°C for 11 hours, ground and passed through a 120-mesh sieve to obtain the guar gum composition.

[0077] Example 5

[0078] A method for preparing a guar gum composition for oilfield development includes the following steps:

[0079] S1. Weigh 100g of natural guar gum powder and add it to 4900mL of deionized water. Stir and swell for 50min under nitrogen protection at 32℃ to form a guar gum aqueous solution. Add 6g of sodium hydroxide to the solution and stir for 30min under nitrogen protection at 32℃ to obtain an alkali-activated guar gum solution.

[0080] S2. Dissolve 25g of 2,3-epoxypropyltrimethylammonium chloride in 30mL of deionized water. Under nitrogen protection and stirring at 50℃, slowly add the solution to the alkali-activated guar gum obtained in step S1 at a rate of 1.2mL / min. After the addition is complete, react at 50℃ for 2.5h to obtain a cationic intermediate solution.

[0081] S3. Cool the solution obtained in step S2 to 32°C, slowly add 10% hydrochloric acid solution dropwise, and adjust the pH of the system to 6.5 under pH meter monitoring; continuously purge nitrogen for 30 min to remove dissolved oxygen; add 0.2 g ammonium persulfate and 0.135 g sodium bisulfite under nitrogen protection, and stir at 32°C for 4 min for pre-activation.

[0082] S4. Prepare a mixed monomer solution by dissolving 40g of acrylamide (AM) and 15g of 2-acrylamido-2-methylpropanesulfonic acid (AMPS) in 400mL of deionized water and purging with nitrogen for 30min to remove oxygen. Under nitrogen protection and stirring at 37℃, add the mixed monomer solution to the reaction system of step S3 by uniform dropwise addition over a period of 1.8h. After the addition is complete, raise the temperature to 50℃ and react at a constant temperature for 2.5h to obtain the graft copolymerization reaction solution. After the reaction was completed, 10% hydrochloric acid was added dropwise to adjust the pH to 7.0, and deionized water was added to dilute to a solid content of about 1.0%. Dialysis was performed for 24 hours using a dialysis bag with a molecular weight cutoff of 100,000 Da (water was changed every 6 hours). After dialysis, the solid content was concentrated by rotary evaporation at 48°C to about 3.5%. Seven times the volume of anhydrous ethanol was added to the concentrate for alcohol precipitation, and the mixture was stirred for 25 minutes. After filtration, the mixture was washed three times with a mixed solvent of ethanol:acetone = 1:1 (volume ratio). The mixture was then vacuum dried at 52°C for 9 hours and ground through a 100-mesh sieve to obtain modified guar gum powder.

[0083] S5. Under dry nitrogen protection, 10 mL of tetraethyl orthosilicate (TEOS) was added to 50 mL of anhydrous ethanol and stirred until homogeneous to obtain a silicon source ethanol solution; 1 mL of tetrabutyl titanate (TBT) was added to 3.5 mL of glacial acetic acid and 12 mL of anhydrous ethanol and stirred until homogeneous to obtain a titanium source solution; the titanium source solution was slowly added dropwise to the silicon source ethanol solution at a rate of 1.5 mL / min and stirred at 28 °C for 1.5 h to obtain a silicon-titanium composite precursor mixture.

[0084] S6. Take 80g of the modified guar gum powder obtained in step S4 and add it to deionized water. Stir and dissolve it at 52℃ under nitrogen protection for 1.2h until it is completely transparent. Then slowly add anhydrous ethanol to make the final volume ratio of ethanol to water 25:75 to prepare a modified guar gum solution. First, add 0.26g of triethylamine to the solution and stir for 5min. Then take 4g of silane coupling agent KH-560 and pre-dilute it with 28g of anhydrous ethanol (4 times the mass). Slowly add it dropwise to the above solution at a rate of 0.8mL / min. Stir and react at 48℃ under nitrogen protection for 2.5h to obtain the coupling agent-modified guar gum solution.

[0085] S7. Cool the solution obtained in step S6 to 38°C, add 5% (w / w) dilute nitric acid solution dropwise, and adjust the pH of the system to 4.5 under pH meter monitoring. Under continuous stirring at 400 rpm and nitrogen protection, slowly add the silicon-titanium composite precursor mixture obtained in step S5 to the above acidic solution at a rate of 1.0 mL / min using a peristaltic pump. After the addition is complete, correct the pH to 4.8, raise the temperature to 50°C and react at a constant temperature for 3.5 h to obtain an organic-inorganic hybrid reaction solution. Then, under stirring at 38°C, first add 3.0 g of sodium citrate and stir for 12 min until completely dissolved; then slowly add 0.3 g of aluminum chloride hexahydrate and stir at 38°C for 40 min to obtain an interface-enhanced hybrid reaction solution. The reaction solution was aged at 28°C under nitrogen protection for 7 hours; 8 times the volume of anhydrous ethanol was added for alcohol precipitation, and the mixture was stirred for 30 minutes; after filtration, the mixture was washed three times with deionized water at room temperature (each time not exceeding 5 minutes) until the pH of the washing solution was neutral; then it was washed twice with a 1:1 mixture of ethanol and acetone; the mixture was vacuum dried at 52°C for 11 hours, ground and passed through a 120-mesh sieve to obtain the guar gum composition.

[0086] Comparative Example 1: Natural guar gum powder (same batch as in Example 1) was used directly without any modification.

[0087] Comparative Example 2: The first modified guar gum powder was prepared according to steps S1 to S4 of Example 1, without performing steps S5 to S7, and the product obtained in step S4 was directly used as the final product.

[0088] Comparative Example 3: Natural guar gum powder was used instead of modified guar gum powder, and sol-gel hybrid modification and interface enhancement treatment were performed directly according to steps S5 to S7 of Example 1 (in step S6, natural guar gum powder was used instead of modified guar gum powder), and the remaining steps and conditions were the same as in Example 1.

[0089] Comparative Example 4: The first modified guar gum powder was prepared according to steps S1 to S4 of Example 1. Then, the powder was directly physically ground and mixed with commercial nano-SiO2 and nano-TiO2 at a mass ratio of 100:18:5 to replace the in-situ hybridization modification in steps S5 to S7.

[0090] Comparative Example 5: Prepared according to steps S1 to S7 of Example 1. In step S7, after the sol-gel hybrid reaction is completed, sodium citrate and aluminum chloride are not added for reaction. Instead, aging and post-treatment are carried out directly. The remaining steps and conditions are the same as in Example 1.

[0091] Performance testing:

[0092] I. Base Fluid Viscosity Test: The products obtained in each example and comparative example were dissolved in deionized water at a dosage of 0.5 wt%. The solutions were stirred at 25°C for 2 hours until completely dissolved to form a homogeneous base fluid. The apparent viscosity of the base fluid was measured using a rotational viscometer at 25°C and 6 rpm. Each sample was tested in triplicate, and the average value was taken. This test was used to evaluate whether the product's basic thickening ability and water solubility met the requirements for fracturing fluid preparation.

[0093] II. Temperature and Shear Resistance Tests: The products obtained in each example and comparative example were dissolved in deionized water at a dosage of 0.5 wt% to prepare the base solution. After crosslinking with 0.3 wt% organoboron-zirconium composite crosslinking agent, a high-temperature and high-pressure rheometer was used to test the products at three temperature conditions: 120℃, 150℃, and 170℃, with a constant shear rate of 170 s. -1 The fluid was subjected to continuous shearing for 120 minutes, and the final viscosity at the end of the shearing was recorded. The viscosity retention rate was calculated based on the initial viscosity (the viscosity value after stabilizing for 1 minute after heating to the target temperature). This test is a core indicator for evaluating the temperature and shear resistance of fracturing fluid, directly reflecting the time window during which the product maintains its sand-carrying capacity under high temperature and high shear conditions at the bottom of the well.

[0094] III. Long-term temperature stability test: The products obtained from each example and comparative example were added at 0.5 wt% to prepare cross-linked fracturing fluid (the cross-linking agent is the same as in Test 2), and placed in a high-temperature and high-pressure reactor. The fluid was subjected to a test at 170°C for 170 seconds. -1 Under continuous shearing conditions for 240 min (4 h), viscosity values ​​were recorded every 60 min, and the viscosity retention rate at each time point was calculated based on the viscosity at 60 min. This test was used to evaluate the performance degradation trend of the product under long-term high-temperature service conditions, especially the contribution of interfacial coordination crosslinking enhancement to long-term stability.

[0095] IV. Salt Tolerance Test: The products obtained in each example and comparative example were dissolved at 0.5 wt% in simulated formation water (NaCl 80000 mg / L + CaCl2 8000 mg / L + MgCl2 3000 mg / L) to prepare the base solution. After crosslinking with 0.3 wt% organoboron-zirconium composite crosslinking agent, the solution was tested using a rheometer at 150℃ for 170 seconds. -1 Under these conditions, continuous shearing was performed for 120 minutes, and the final viscosity was recorded. This test was used to evaluate the product's temperature and shear resistance performance in a high-salinity formation water environment.

[0096] V. Thermogravimetric Analysis (TGA): Approximately 10 mg of the product powder obtained from each example and comparative example was taken and analyzed using a simultaneous thermal analyzer under a nitrogen atmosphere (flow rate 50 mL / min) and a heating rate of 10 °C / min. The temperature at which 5% weight loss occurred (T5%) was recorded as the thermal decomposition initiation temperature. This test was used to evaluate the synergistic effect of each modification scheme from the perspective of the intrinsic thermal stability of the material.

[0097] VI. Debris Content Test: The products obtained from each example and comparative example were added at a dosage of 0.5 wt% to prepare cross-linked fracturing fluid, and 0.05 wt% ammonium persulfate breaker was added. The mixture was debrided at 90°C for 2 hours until the system was completely hydrated and debrided. The debrided solution was filtered through a 400-mesh stainless steel sieve, and the filter residue was collected and dried at 105°C to constant weight. The mass of the residue was measured and expressed as the mass of residue per liter of debrided solution (mg / L). This test is used to evaluate the risk of blockage damage to formation pores after the product debrides; the lower the residue content, the less damage the product causes to the reservoir.

[0098] Table 1: Viscosity and Thermogravimetric Analysis Results of Base Liquid

[0099] ;

[0100] Table 2: Test results of temperature and shear resistance (170s) -1 (Cut for 120 minutes)

[0101] ;

[0102] Table 3: Results of Long-Term Temperature Stability Tests (170℃, 170s) -1 (Continuous shearing)

[0103] ;

[0104] Table 4: Salt tolerance test results (simulated formation water, 150℃, 170s) -1 (Cut for 120 minutes)

[0105] ;

[0106] As can be seen from the test results in Tables 1 to 4, the guar gum compositions prepared in Examples 1-5 of this invention show significant improvements in high-temperature resistance and shear resistance compared to the comparative examples. Comparative Example 1 (natural guar gum) exhibited extremely low viscosity retention at 150°C and 170°C, while the example groups maintained a viscosity retention of over 58% after shearing at 170°C for 120 minutes (see Table 2). This is mainly due to the effective suppression of molecular chain collapse at high temperatures by the grafted cationic groups and heat-resistant polymer segments (Comparative Example 2), while the in-situ generated SiO2-TiO2 inorganic network provided skeletal support (Comparative Examples 3 and 4). Furthermore, the long-term temperature stability test (Table 3) fully demonstrates that the dynamic coordination compensation mechanism of sodium citrate and aluminum ions can continuously repair the broken network at prolonged high temperatures (Comparative Example 5), resulting in a significant increase in viscosity retention after 240 minutes. The combination of low guar gum residue content (Table 1) and good salt resistance (Table 4) demonstrates that the guar gum composition provided by this invention can fully meet the stringent requirements of fracturing operations in deep high-temperature oil and gas reservoirs.

[0107] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the essence and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a guar gum composition for oilfield development, characterized in that, Includes the following steps: S1. Dissolve natural guar gum powder in water, and add sodium hydroxide under nitrogen protection for alkali activation to obtain alkali-activated guar gum solution; S2. Under nitrogen protection, 2,3-epoxypropyltrimethylammonium chloride is added to the alkali-activated guar gum solution to carry out an etherification reaction, and a cationic intermediate solution is obtained. S3. Under nitrogen protection, ammonium persulfate and sodium bisulfite are added to the cationization intermediate solution for pre-activation; S4. Under nitrogen protection, a graft copolymerization reaction was carried out by adding a mixture of monomers consisting of acrylamide and 2-acrylamido-2-methylpropanesulfonic acid to the pre-activated solution. After the reaction was completed, the pH was adjusted to 7.0, deionized water was added for dilution, and dialyzed. After dialysis, the solution was concentrated by rotary evaporation, and anhydrous ethanol was added to the concentrate for alcohol precipitation. The solution was stirred, filtered, and washed with a mixed solvent of ethanol and acetone. The solution was then vacuum dried, ground, and sieved to obtain modified guar gum powder. S5. Under nitrogen protection, an ethanol solution of tetraethyl orthosilicate and an acetic acid-ethanol solution of tetrabutyl titanate are mixed to prepare a silicon-titanium composite precursor mixture. S6. Under nitrogen protection, the modified guar gum powder is dissolved in water, ethanol and silane coupling agent KH-560 are added, and the mixture is reacted under triethylamine catalysis to obtain a modified guar gum solution modified with coupling agent. S7. Under nitrogen protection, a mixture of silicon-titanium composite precursors was added to the modified guar gum solution modified with coupling agent to carry out an in-situ sol-gel hybrid reaction to obtain a hybrid reaction solution. Sodium citrate and aluminum chloride hexahydrate were added to the hybrid reaction solution in sequence, with a mass ratio of sodium citrate to aluminum chloride hexahydrate of 3:(0.3-0.8). The reaction was heated and stirred, and the reaction solution was allowed to stand and age under nitrogen protection. Anhydrous ethanol was added to precipitate the guar gum, and the mixture was stirred. After filtration, the mixture was washed with deionized water until the pH of the washing solution was neutral. The mixture was then washed with a mixed solvent of ethanol and acetone. The mixture was vacuum dried, ground, and sieved to obtain the guar gum composition.

2. The method for preparing a guar gum composition for oilfield development according to claim 1, characterized in that, In step S1, the amount of sodium hydroxide added is 6-10 wt% of the natural guar gum powder. The alkali activation conditions are: stirring at 32°C for 30 minutes.

3. The method for preparing a guar gum composition for oilfield development according to claim 1, characterized in that, In step S2, the amount of 2,3-epoxypropyltrimethylammonium chloride added is 25-40 wt% of the natural guar gum powder; The etherification reaction temperature is 50℃ and the etherification reaction time is 2.5h.

4. The method for preparing a guar gum composition for oilfield development according to claim 1, characterized in that, In step S3, the amount of ammonium persulfate added is 0.2–0.4 wt% of the natural guar gum powder; The pre-activation temperature is 32℃ and the pre-activation time is 4 min.

5. The method for preparing a guar gum composition for oilfield development according to claim 1, characterized in that, In step S4, the mass ratio of acrylamide to 2-acrylamido-2-methylpropanesulfonic acid is 40:(15-20); The graft copolymerization reaction was carried out at a temperature of 50°C for 2.5 hours.

6. The method for preparing a guar gum composition for oilfield development according to claim 1, characterized in that, In step S5, the volume ratio of tetraethyl orthosilicate to tetrabutyl titanate is 10:(1-3). The mixing temperature was 28°C, and the time was 1.5 hours.

7. The method for preparing a guar gum composition for oilfield development according to claim 1, characterized in that, In step S6, the mass ratio of modified guar gum powder to silane coupling agent KH-560 is 10:(0.5~1.5); The reaction temperature was 48°C and the reaction time was 2.5 h.

8. The method for preparing a guar gum composition for oilfield development according to claim 1, characterized in that, In step S7, the hybridization reaction temperature is 50°C and the reaction time is 3.5 h.

9. The method for preparing a guar gum composition for oilfield development according to claim 1, characterized in that, The mass ratio of the modified guar gum powder to sodium citrate is 80:

3.

10. A guar gum composition for oilfield development, characterized in that, It is prepared by the method described in any one of claims 1 to 9 above.

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