Carbonate rock thermal reservoir acidification fracturing temperature-sensitive acid liquid thickening agent and its preparation and application

Abstract

The application provides a temperature-sensitive acid thickening agent for carbonate rock thermal reservoir acidification fracturing and preparation and application thereof, and belongs to the technical field of oil and gas and geothermal resource development. The temperature-sensitive acid thickening agent for carbonate rock thermal reservoir acidification fracturing is prepared from the following raw materials in parts by mass: hydrophilic group modified cellulose macromolecule 6-10 parts, amide monomer 2-4 parts, temperature-resistant monomer 1-3 parts, olefin quaternary ammonium salt monomer 3-5 parts, hydrophobic monomer 0.1-1 part, initiator 0.05-0.12 part, cosolvent 1-3 parts and deionized water 120-180 parts. The thickening agent can play the function of 'heat thickening' under the condition of high temperature and strong acid, realizes the performance transformation of good fluidity under low temperature and significant viscosity increase in high temperature environment, and has the comprehensive advantages of low friction, filtration loss reduction, low damage and easy flowback, so that the application bottleneck of the existing thickened acid in deep thermal reservoir modification is effectively broken through.

Description

Technical Field

[0001] This invention relates to a temperature-sensitive acid thickener for acid fracturing of carbonate rock thermal reservoirs, its preparation and application, belonging to the field of oil and gas and geothermal resource development technology. Background Technology

[0002] Carbonate reservoirs contain abundant oil, gas, and geothermal resources. However, as extraction progresses, reservoir temperatures rise significantly. Carbonate geothermal reservoirs generally face challenges such as high rock strength, strong heterogeneity, and low natural yield, necessitating reservoir stimulation to enhance production capacity. Acid fracturing is a commonly used stimulation method. Thickened acid, due to its high viscosity, can effectively reduce the hydrogen ion mass transfer rate, slow down the acid-rock reaction, and prevent rapid acid consumption at high temperatures. This promotes acid migration into deeper fractures, expands the acid etching range, and improves the effectiveness of acid fracturing.

[0003] Existing thickened acid systems still have significant limitations: First, they lack temperature resistance, with viscosity rapidly decreasing at high temperatures, leading to a weakened retardation effect and limited acid application distance. Second, they have high friction, with excessive viscosity at low temperatures significantly increasing pumping friction and increasing the burden on construction pressure. Third, they suffer from severe filtration, with high-temperature viscosity reduction exacerbating acid filtration and limiting the scope of modification. Fourth, they cause significant reservoir damage, as traditional thickeners are difficult to completely degrade, often resulting in residue clogging pore throats and affecting flowback, and exacerbating secondary damage along with byproducts and residual acid.

[0004] Therefore, there is an urgent need to develop novel thickened acid systems that can maintain high viscosity at high temperatures to slow down the reaction and enhance deep well stimulation capabilities, while maintaining low viscosity during low-temperature pumping to reduce friction. These systems should also possess advantages such as low residue, low damage, and thorough backflow, achieving the functional characteristics of "easy flow at low temperatures and increased viscosity at high temperatures." Currently, some progress has been made in research. For example, Chinese patent document CN103820100A discloses a high-temperature fractured carbonate rock thickened acid with a temperature resistance up to 130℃, reducing the acid-rock reaction rate by 52% and, to some extent, reducing tubing corrosion and reservoir damage. Chinese patent document CN112745454A discloses a high-temperature deep well acidizing thickener, whose system viscosity remains above 30 mPa·s at 160℃. However, these thickeners are still constrained by Arrhenius's law, generally subject to the basic principle of "viscosity reduction upon heating," resulting in high friction and insufficient high-temperature viscosity. Furthermore, existing temperature-sensitive thickened acid systems exhibit weak temperature sensitivity, small viscosity-increasing range, and poor temperature resistance. For example, Chinese patent document CN110982507A discloses an acid thickener for acid fracturing, but its operating temperature is only up to 60°C, far below the lower critical threshold of common geothermal reservoir temperatures. Furthermore, it has high initial viscosity and a very small thickening effect, lacking the characteristic of "low-temperature flow, high-temperature thickening," making it unsuitable for current geothermal reservoir acid fracturing engineering scenarios. Existing temperature-sensitive thickening materials in other fields often struggle to withstand the extreme environments of high temperatures and strong acids encountered in deep-earth engineering, or require additional crosslinking agents or external support systems. This undoubtedly increases the risk of reservoir damage, as exemplified by the temperature-controlled viscosity-changing acid gelling agent disclosed in Chinese patent document CN101864031A.

[0005] In summary, developing a temperature-responsive intelligent acid thickener with "heat-induced thickening" as its core feature, and combining advantages such as slow acid control, low friction, reduced filtration loss, and low damage and easy return flow, can effectively overcome existing technological bottlenecks and is of great significance for the efficient development of deep carbonate rock geothermal reservoir resources. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a temperature-sensitive acid thickener for acid fracturing in carbonate rock reservoirs, along with its preparation and application. The thickener of this invention uses a natural macromolecular cellulose derivative as a matrix, and achieves structural functionalization through chemical grafting modification, thereby endowing the system with unique temperature-responsive characteristics. Under high-temperature, strong acid conditions, this thickener can exert its core function of "thermal thickening," achieving a performance transformation from good fluidity at low temperatures to significant viscosity increase in high-temperature environments. It also possesses comprehensive advantages such as low friction, reduced filtration loss, low damage, and easy backflow, thus effectively overcoming the application bottleneck of existing thickened acids in deep geothermal reservoir modification.

[0007] The technical solution of the present invention is as follows:

[0008] A temperature-sensitive acid thickener for acid fracturing of carbonate rock thermal reservoirs is prepared from the following raw materials in parts by weight: 6-10 parts of hydrophilic group-modified cellulose macromolecules, 2-4 parts of amide monomers, 1-3 parts of heat-resistant monomers, 3-5 parts of alkene quaternary ammonium salt monomers, 0.1-1 parts of hydrophobic monomers, 0.05-0.12 parts of initiator, 1-3 parts of cosolvent, and 120-180 parts of deionized water.

[0009] According to a preferred embodiment of the present invention, the hydrophilic group in the hydrophilic group-modified cellulose macromolecule is one or more of carboxyl, hydroxymethyl, hydroxyethyl, hydroxypropyl, carboxymethyl, and carboxyethyl; the mass of the hydrophilic group in the hydrophilic group-modified cellulose macromolecule is 5-15% of the total mass of the hydrophilic group-modified cellulose macromolecule, and should not be too high or too low, otherwise the performance will be reduced; more preferably, the hydrophilic group-modified cellulose macromolecule is one or more of carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, carboxymethyl hydroxyethyl cellulose, carboxymethyl hydroxypropyl cellulose, and hydroxypropyl methyl cellulose.

[0010] According to a preferred embodiment of the present invention, the amide monomer is acrylamide (AM) and / or methacrylamide.

[0011] According to a preferred embodiment of the present invention, the heat-resistant monomer is one or more of N-vinylpyrrolidone (NVP), 2-acrylamide-2-methylpropanesulfonic acid (AMPS), N-vinyloxazolidinone (NVO), and N-vinylimidazolium (NVI).

[0012] According to a preferred embodiment of the present invention, the olefinic quaternary ammonium salt monomer is one or more of methacryloyloxyethyltrimethylammonium chloride (DMC), methacryloylpropyltrimethylammonium chloride, dimethyldiallylammonium chloride, and dodecyldimethylallylammonium chloride.

[0013] According to a preferred embodiment of the present invention, the hydrophobic monomer is one or more of butyl methacrylate, lauryl methacrylate, octadecyl methacrylate, and isobutyl methacrylate.

[0014] According to a preferred embodiment of the present invention, the initiator is a two-component redox initiation system of ammonium persulfate and sodium bisulfite, wherein the mass ratio of ammonium persulfate to sodium bisulfite is 1.5~2:1.

[0015] According to a preferred embodiment of the present invention, the co-solvent is one or more of anhydrous ethanol, acetone, cyclohexanone, and butyl acetate.

[0016] The preparation method of the above-mentioned temperature-sensitive acid thickener for acid fracturing of carbonate rock thermal reservoirs includes the following steps:

[0017] (1) Disperse the hydrophilic group-modified cellulose macromolecules in a portion of deionized water A and stir until homogeneous; adjust the pH of the system to 7-8, heat to the reaction temperature, remove oxygen by purging with nitrogen, add 3 / 4-4 / 5 of the initiator, and carry out the reaction to obtain mixed solution I;

[0018] (2) Disperse the amide monomer, the heat-resistant monomer, and the alkene quaternary ammonium salt monomer in a portion of deionized water B, stir until homogeneous, and obtain a monomer solution; add the obtained monomer solution dropwise to the mixed solution I obtained in step (1) to carry out the reaction; then add the remaining initiator and continue the reaction to obtain mixed solution II;

[0019] (3) Add the hydrophobic monomer to the co-solvent and stir until dissolved. The resulting hydrophobic monomer solution is added dropwise to the mixed solution II in three batches for reaction. After the reaction is completed, the solution is filtered, washed, dried and crushed to obtain the temperature-sensitive acid thickener for acid fracturing of carbonate rock thermal storage.

[0020] According to a preferred embodiment of the present invention, the stirring speed in step (1) is 500~800 r / min, and the stirring time is 40~80 min.

[0021] According to a preferred embodiment of the present invention, in step (1), the pH is adjusted using a NaOH aqueous solution with a mass fraction of 30-40%; the time for purging nitrogen gas to remove oxygen is 15-30 min; and the reaction temperature is 50-60℃.

[0022] According to a preferred embodiment of the present invention, the initiator in step (1) is added dropwise to the system in the form of an initiator aqueous solution, wherein the mass concentration of the initiator in the initiator aqueous solution is 0.3~0.5g / mL and the dropping rate is 0.8~1.2mL / s.

[0023] According to a preferred embodiment of the present invention, the reaction time in step (1) is 20 to 30 minutes; the reaction is carried out under a nitrogen atmosphere.

[0024] According to a preferred embodiment of the present invention, the mass ratio of the partial deionized water B to the partial deionized water A in step (2) is 0.3~0.4:1.

[0025] According to a preferred embodiment of the present invention, the dropping rate of the monomer solution in step (2) is 0.04~0.06 mL / s.

[0026] According to a preferred embodiment of the present invention, in step (2), after the monomer solution is added dropwise to the mixed solution I, the reaction time is 15 to 20 minutes, the reaction temperature is 50 to 60°C, and the reaction is carried out under a nitrogen atmosphere.

[0027] According to a preferred embodiment of the present invention, the initiator in step (2) is added dropwise to the system in the form of an initiator aqueous solution, wherein the mass concentration of the initiator in the initiator aqueous solution is 0.3~0.5 g / mL and the dropping rate is 0.8~1.2 mL / s; after the initiator is added, the reaction time is 5~10 minutes and the reaction temperature is 50~60℃, and the reaction is carried out under a nitrogen atmosphere.

[0028] According to a preferred embodiment of the present invention, in step (3), the time interval between each addition of the hydrophobic monomer solution is 1 to 2 minutes, and the dropping rate of the hydrophobic monomer solution is 0.04 to 0.06 mL / s.

[0029] According to a preferred embodiment of the present invention, in step (3), the reaction time after the hydrophobic monomer solution is added is 2 to 4 hours, and the reaction temperature is 50 to 60°C; the reaction is carried out under a nitrogen atmosphere, and the stirring speed during the reaction is 400 to 600 r / min.

[0030] According to a preferred embodiment of the present invention, the washing in step (3) is washing with anhydrous ethanol 3 to 5 times; the drying is vacuum drying at 40 to 50°C for 48 to 72 hours.

[0031] According to the present invention, the application of the above-mentioned temperature-sensitive acid thickener for acid fracturing of carbonate reservoirs is described. Preferably, the specific application method is as follows: the obtained temperature-sensitive acid thickener for acid fracturing of carbonate reservoirs is dissolved in an acid solution to obtain a temperature-responsive thickened acid system, which is used for acid fracturing. The acid solution is a hydrochloric acid solution with a concentration of 12~18wt%, and the concentration of the temperature-responsive thickened acid thickener for acid fracturing of carbonate reservoirs in the temperature-responsive thickened acid system is 1~3wt%.

[0032] The technical features and beneficial effects of this invention are as follows:

[0033] 1. Significant temperature-sensitive thickening performance: The thickener of this invention uses cellulose derivatives modified with hydrophilic groups as the matrix. After chemical grafting modification, it has unique temperature response characteristics. It can maintain a low viscosity under low temperature conditions, which is convenient for well pumping. In high temperature and strong acid environment, it exhibits a significant "heat-induced thickening" effect, which effectively slows down the acid-rock reaction rate and expands the range of acid action.

[0034] 2. Excellent temperature and acid resistance: The molecular structure of this thickener is stable and can maintain high viscosity and structural integrity under high temperature (100℃) and strong acid (pH<0.5) conditions, overcoming the defects of existing thickening acid systems that are easy to degrade and have a sudden drop in viscosity under high temperature and strong acid conditions.

[0035] 3. Excellent self-reinforcing ability, no need for external crosslinking agent: The performance of this thickener comes entirely from the intrinsic structural design of the polymer macromolecule itself, rather than relying on additional crosslinking agents or external support systems. This avoids the risk of residues and by-products caused by crosslinking agents and ensures the low-harm characteristics of the thickener.

[0036] 4. Low friction loss: Due to its low viscosity at room temperature, it has low friction with the tubing during pumping, which can reduce the ground pumping pressure and improve the safety and economy of operation.

[0037] 5. Reduce acid loss: The thickening effect formed at high temperature can effectively inhibit acid loss, prolong the migration distance of acid in cracks, and improve the uniformity and depth of acid etching.

[0038] 6. Minimal reservoir damage and thorough backflow: Compared with traditional polymer thickeners, this thickener is easily degraded after acidification, leaving less residue and not clogging pore throat channels. Residual acid backflow is more thorough, thereby reducing secondary damage to the reservoir.

[0039] 7. Strong comprehensive adaptability: This thickener has multiple functions such as temperature-sensitive response, slow acid control, low friction and low damage backflow, and is particularly suitable for acid fracturing stimulation of deep carbonate reservoirs, which significantly improves stimulation efficiency and resource development sustainability. Attached Figure Description

[0040] Figure 1 The infrared spectrum of the temperature-sensitive acid thickener for acid fracturing of carbonate rock thermal reservoirs prepared in Example 1. Detailed Implementation

[0041] The present invention will be further described below with reference to the embodiments and accompanying drawings, but is not limited thereto.

[0042] Unless otherwise specified, the experimental methods described in the examples are conventional methods; the reagents and materials used are commercially available unless otherwise specified.

[0043] In the examples and comparative examples, the hydroxypropyl group in the hydroxypropyl methylcellulose was 7-12% of the mass of the hydroxypropyl methylcellulose, and the methoxy group was 28-30%; the viscosity of the 2wt% aqueous solution at 25°C was 500 mPa·s.

[0044] The mass of hydroxypropyl groups in hydroxypropyl cellulose is 10-12.9% of the mass of hydroxypropyl cellulose, and the viscosity of a 2wt% aqueous solution at 25°C is 400 mPa·s.

[0045] Example 1

[0046] A temperature-sensitive acid thickener for acid fracturing of carbonate rock thermal reservoirs is prepared from the following raw materials in parts by mass: 8 parts of hydrophilic group-modified cellulose macromolecules, 3 parts of amide monomers, 2 parts of heat-resistant monomers, 4 parts of alkene quaternary ammonium salt monomers, 0.5 parts of hydrophobic monomers, 0.1 parts of initiator, 2 parts of cosolvent, and 160 parts of deionized water.

[0047] The cellulose macromolecule modified with hydrophilic groups is hydroxypropyl methylcellulose; the amide monomer is acrylamide (AM); the heat-resistant monomer is N-vinylpyrrolidone (NVP); the alkene quaternary ammonium salt monomer is methacryloyloxyethyltrimethylammonium chloride (DMC); the hydrophobic monomer is butyl methacrylate (BMA); the initiator is ammonium persulfate and sodium bisulfite redox initiator, with 0.06 parts of ammonium persulfate and 0.04 parts of sodium bisulfite; and the cosolvent is anhydrous ethanol.

[0048] The preparation method of the above-mentioned temperature-sensitive acid thickener for acid fracturing of carbonate rock thermal reservoirs includes the following steps:

[0049] (1) Disperse the hydrophilic group-modified cellulose macromolecules in 120 parts of deionized water and stir for 60 min at a stirring speed of 500 r / min until completely dissolved; adjust the pH to 8 with a 35% NaOH aqueous solution, heat to 50℃, keep stirring, and purge with nitrogen to remove oxygen for 20 min; add dropwise 3 / 4 of the initiator aqueous solution (the concentration of the initiator aqueous solution is 0.5 g / mL) at a dropping rate of 0.8 mL / s; after the addition is complete, continue the reaction at 50℃ for 30 min under nitrogen protection to obtain mixed solution I;

[0050] (2) Disperse the amide monomer, the heat-resistant monomer, and the alkene quaternary ammonium salt monomer into 40 parts of deionized water, stir evenly to obtain a monomer solution; add the monomer solution dropwise to the mixed solution I obtained in step (1) at a dropping rate of 0.05 mL / s; after the monomer mixed solution is added, continue to react at 50°C under nitrogen protection for 15 minutes, then add the remaining initiator aqueous solution (the concentration of the initiator aqueous solution is 0.5 g / mL) at a dropping rate of 0.8 mL / s, and continue to react at 50°C under nitrogen protection for 7 minutes to obtain mixed solution II;

[0051] (3) Add the hydrophobic monomer to the cosolvent and mix and stir until completely dissolved. The resulting hydrophobic monomer solution is added to the mixed solution II in three equal batches at a dropping rate of 0.05 mL / s and an interval of 2 minutes between each drop. After the addition is complete, react at 50°C under nitrogen protection for 4 hours. The stirring speed during the reaction is 400 r / min. After the reaction is complete, filter the solution and wash the precipitate three times with anhydrous ethanol. Then, vacuum dry it at 40°C for 48 hours. After pulverization, the temperature-sensitive acid thickener for acid fracturing of carbonate rock thermal storage is obtained.

[0052] The infrared spectrum of the temperature-sensitive acid thickener used for acid fracturing of carbonate rock thermal reservoirs obtained in this embodiment is as follows: Figure 1 As shown, by Figure 1 It can be known that 3329cm -1 The nearby peak represents the stretching vibration of the NH bond in the amide group, primarily originating from the acrylamide monomer; 1725 cm⁻¹ -1 The nearby peak represents the C=O bond stretching vibration of the amide group, mainly originating from the acrylamide and butyl methacrylate monomers; 1340 cm⁻¹ -1 The absorption peak represents the stretching vibration of the CN bond on the pyrrole ring, originating from the N-vinylpyrrolidone monomer; 950 cm⁻¹ -1 The position is a quaternary ammonium salt -CH2-N + The absorption peak of (CH3)3 originates from the monomer methacryloyloxyethyltrimethylammonium chloride; the stretching vibration peak of the -OH bond essentially disappears, and the peak at 1750 cm⁻¹ is observed. -1 A strong ester bond peak was observed, indicating that a graft polymerization reaction occurred.

[0053] Example 2

[0054] A temperature-sensitive acid thickener for acid fracturing of carbonate rock thermal reservoirs is as described in Example 1, except that: 6 parts of hydrophilic group-modified cellulose macromolecules, 2 parts of amide monomers, 1 part of heat-resistant monomers, 3 parts of alkene quaternary ammonium salt monomers, 0.1 parts of hydrophobic monomers, 0.05 parts of initiator, 1 part of cosolvent, and 120 parts of deionized water are used; other conditions and preparation methods are the same as in Example 1.

[0055] Example 3

[0056] A temperature-sensitive acid thickener for acid fracturing of carbonate rock thermal reservoirs is as described in Example 1, except that: 10 parts of hydrophilic group-modified cellulose macromolecules, 4 parts of amide monomers, 3 parts of heat-resistant monomers, 5 parts of alkene quaternary ammonium salt monomers, 1 part of hydrophobic monomers, 0.12 parts of initiator, 3 parts of cosolvent, and 180 parts of deionized water are used; other conditions and preparation methods are the same as in Example 1.

[0057] Example 4

[0058] A temperature-sensitive acid thickener for acid fracturing of carbonate rock thermal reservoirs is described in Example 1, except that the hydrophilic group-modified cellulose macromolecule is hydroxypropyl cellulose, and the other conditions and preparation methods are the same as in Example 1.

[0059] Example 5

[0060] A temperature-sensitive acid thickener for acid fracturing of carbonate rock thermal reservoirs is described in Example 1, except that the amide monomer is methacrylamide, and the other conditions and preparation methods are the same as in Example 1.

[0061] Example 6

[0062] A temperature-sensitive acid thickener for acid fracturing of carbonate rock thermal reservoirs is described in Example 1, except that the olefin quaternary ammonium salt monomer is methacryloylpropyltrimethylammonium chloride, and the other conditions and preparation methods are the same as in Example 1.

[0063] Example 7

[0064] A temperature-sensitive acid thickener for acid fracturing of carbonate rock thermal reservoirs is described in Example 1, except that the hydrophobic monomer is lauryl methacrylate, and the other conditions and preparation methods are the same as in Example 1.

[0065] Example 8

[0066] A temperature-sensitive acid thickener for acid fracturing of carbonate rock thermal reservoirs is described in Example 1, except that the temperature-resistant monomer is 2-acrylamide-2-methylpropanesulfonic acid, and the other conditions and preparation methods are the same as in Example 1.

[0067] Comparative Example 1

[0068] A temperature-sensitive acid thickener for acid fracturing of carbonate rock thermal reservoirs is described in Example 1, except that: no hydrophilic group-modified cellulose macromolecules are added; other conditions and preparation methods are the same as in Example 1.

[0069] Comparative Example 2

[0070] A temperature-sensitive acid thickener for acid fracturing of carbonate rock thermal reservoirs is described in Example 1, except that no amide monomers are added; other conditions and preparation methods are the same as in Example 1.

[0071] Comparative Example 3

[0072] A temperature-sensitive acid thickener for acid fracturing of carbonate rock thermal reservoirs is described in Example 1, except that no temperature-resistant monomer is added; other conditions and preparation methods are the same as in Example 1.

[0073] Comparative Example 4

[0074] A temperature-sensitive acid thickener for acid fracturing of carbonate rock thermal reservoirs is described in Example 1, except that: no olefin quaternary ammonium salt monomer is added; other conditions and preparation methods are the same as in Example 1.

[0075] Comparative Example 5

[0076] A temperature-sensitive acid thickener for acid fracturing of carbonate rock thermal reservoirs is described in Example 1, except that no hydrophobic monomer is added; other conditions and preparation methods are the same as in Example 1.

[0077] Comparative Example 6

[0078] A temperature-sensitive acid thickener for acid fracturing of carbonate rock thermal reservoirs is described in Example 1, except that: 8 parts of amide monomers are used; other conditions and preparation methods are the same as in Example 1.

[0079] Comparative Example 7

[0080] A conventional acid thickener, polyacrylamide (PAM), is used.

[0081] Comparative Example 8

[0082] A temperature-sensitive acid thickener for acid fracturing of carbonate rock thermal reservoirs is described in Example 1, except that chitosan (degree of deacetylation ≥90%, M...) is used. w =100000) to replace hydrophilic groups to modify cellulose macromolecules.

[0083] Comparative Example 9

[0084] A temperature-sensitive acid thickener for acid fracturing of carbonate rock thermal reservoirs is described in Example 1, except that sodium lignosulfonate (M) is used. w =52000) to replace hydrophilic groups to modify cellulose macromolecules.

[0085] Comparative Example 10

[0086] A temperature-sensitive acid thickener for acid fracturing of carbonate rock thermal reservoirs is described in Example 1, except that cellulose (average molecular weight of 50,000) is used instead of cellulose macromolecules modified with hydrophilic groups.

[0087] Comparative Example 11

[0088] A temperature-sensitive acid thickener for acid fracturing of carbonate rock thermal reservoirs, using hydroxypropyl methylcellulose as the thickener.

[0089] Experimental Example 1

[0090] The thickeners prepared in the examples and comparative examples were mixed with acid solutions to prepare corresponding thickened acid systems. The concentration of the thickener in the thickened acid system was 2 wt%, and the acid solution was a 12 wt% hydrochloric acid solution.

[0091] The temperature-sensitive rheological properties were tested using a high-temperature and high-pressure rheometer. The temperature scan was set to oscillation mode (Ramp mode), the strain was set to 0.1%, the frequency was 1Hz, the temperature scan range was 25-100℃, and the heating rate was 2℃ / min. The results are shown in Table 1-2 below.

[0092] Table 1. Rheological properties of the thickeners in the examples at different temperatures.

[0093]

[0094] Table 2. Rheological properties of thickeners in comparative examples at different temperatures.

[0095]

[0096] As shown in Tables 1-2, the thickened acid systems in the examples all exhibited significant thermosensitive phase transition characteristics: with increasing temperature, the system gradually transformed from an initial solution state to a network or gel structure, characterized by a significant increase in storage modulus (G′) exceeding the loss modulus (G″). Simultaneously, the loss modulus also increased with increasing temperature, indicating a synchronous increase in system viscosity. In contrast, the comparative system did not exhibit the same pattern. Specifically, Comparative Example 1, lacking hydroxypropyl methylcellulose, did not possess a thermosensitive response; Comparative Example 2, lacking acrylamide, although exhibiting some... Thermosensitive thickening effect was observed, but the viscosity level was significantly low, indicating insufficient thickening ability. Comparative Example 3, lacking N-vinylpyrrolidone, exhibited thickening upon heating, but its structure remained unstable at high temperatures. Comparative Example 4, lacking methacryloyloxyethyltrimethylammonium chloride, showed insufficient acid resistance, leading to acid degradation during heating and the loss of thermosensitive thickening ability. Comparative Example 5, without butyl methacrylate, lost some hydrophobic association sites at high temperatures, resulting in decreased structural stability. Comparative Example 6, with the addition of excessive amide monomers, was affected by interference from long linear polymer chains. The hydrophobic association resulted in the loss of thermal thickening ability; however, Comparative Example 7, using a conventional thickener, did not exhibit temperature-sensitive thickening, and its rheological characteristics were consistent with the traditional system; Comparative Examples 8 and 9 used other common bio-based macromolecules, chitosan and lignin sulfonate, which, due to their strong hydrophilicity, lacked temperature sensitivity, and the resulting products showed no temperature-responsive behavior; if temperature sensitivity were to be achieved through modification with other bio-based materials, "carefully designed" hydrophobic modification would be required, the difficulty and cost of which would far exceed that of this invention patent, making such a roundabout approach impractical; Comparative Example 10 used pure cellulose. Grafting modification resulted in a low grafting rate, leading to a product that was more of a "blend." The large amount of unmodified cellulose resulted in poor solubility in the blend. Comparative Example 11, lacking grafting modification, exhibited poor temperature and salt resistance, rapidly degrading under high-temperature, strong acid conditions and failing to demonstrate thermosensitivity. In summary, the results indicate that the synergistic effect of multiple components is crucial for achieving the thermosensitive thickening effect and high-temperature structural stability of the system. The absence of any functional monomer leads to a decline in system performance or even the loss of thermosensitive characteristics. Therefore, the system of this invention demonstrates greater advantages in application under high-temperature, strong acid conditions.

Claims

1. A temperature-sensitive acid thickener for acid fracturing of carbonate rock thermal reservoirs, characterized in that, The raw materials included in this preparation are: 6-10 parts of hydrophilic group modified cellulose macromolecules, 2-4 parts of amide monomers, 1-3 parts of heat-resistant monomers, 3-5 parts of alkene quaternary ammonium salt monomers, 0.1-1 parts of hydrophobic monomers, 0.05-0.12 parts of initiator, 1-3 parts of cosolvent, and 120-180 parts of deionized water. The hydrophilic group-modified cellulose macromolecule is hydroxypropyl methylcellulose or hydroxypropyl cellulose; the mass of the hydroxypropyl group in the hydrophilic group-modified cellulose macromolecule is 5-15% of the total mass of the hydrophilic group-modified cellulose macromolecule; The amide monomer is acrylamide and / or methacrylamide; The heat-resistant monomer is one or more of N-vinylpyrrolidone, 2-acrylamide-2-methylpropanesulfonic acid, N-vinyloxazolidinone, and N-vinylimidazolium; The olefinic quaternary ammonium salt monomer is one or more of methacryloyloxyethyltrimethylammonium chloride, methacryloylpropyltrimethylammonium chloride, dimethyldiallylammonium chloride, and dodecyldimethylallylammonium chloride; The hydrophobic monomer is one or more of butyl methacrylate, lauryl methacrylate, octadecyl methacrylate, and isobutyl methacrylate. The initiator is a two-component redox initiation system consisting of ammonium persulfate and sodium bisulfite; The co-solvent is one or more of anhydrous ethanol, acetone, cyclohexanone, and butyl acetate.

2. The temperature-sensitive acid thickener for acid fracturing of carbonate rock thermal reservoirs according to claim 1, characterized in that, The mass ratio of ammonium persulfate to sodium bisulfite is 1.5~2:

1.

3. The method for preparing the temperature-sensitive acid thickener for acid fracturing of carbonate rock thermal reservoirs according to any one of claims 1-2, characterized in that, The steps include the following: (1) Disperse the hydrophilic group-modified cellulose macromolecules in a portion of deionized water A and stir until homogeneous; adjust the pH of the system to 7-8, heat to the reaction temperature, remove oxygen by purging with nitrogen, add 3 / 4-4 / 5 of the initiator, and carry out the reaction to obtain mixed solution I; (2) Disperse the amide monomer, the heat-resistant monomer, and the alkene quaternary ammonium salt monomer in a portion of deionized water B, stir until homogeneous, and obtain a monomer solution; add the obtained monomer solution dropwise to the mixed solution I obtained in step (1) to carry out the reaction; then add the remaining initiator and continue the reaction to obtain mixed solution II; (3) Add the hydrophobic monomer to the co-solvent and stir until dissolved. The resulting hydrophobic monomer solution is added dropwise to the mixed solution II in three batches for reaction. After the reaction is completed, the solution is filtered, washed, dried and crushed to obtain the temperature-sensitive acid thickener for acid fracturing of carbonate rock thermal storage.

4. The method for preparing the temperature-sensitive acid thickener for acid fracturing of carbonate rock thermal reservoirs according to claim 3, characterized in that, The stirring speed in step (1) is 500~800 r / min, and the stirring time is 40~80 min; In step (1), the pH is adjusted using a NaOH aqueous solution with a mass fraction of 30-40%; The time for nitrogen gas to be introduced for deoxygenation is 15-30 minutes, and the reaction temperature is 50-60℃.

5. The method for preparing the temperature-sensitive acid thickener for acid fracturing of carbonate rock thermal reservoirs according to claim 4, characterized in that, In step (1), the initiator is added dropwise to the system in the form of an aqueous initiator solution, the mass concentration of the initiator in the aqueous initiator solution is 0.3~0.5 g / mL, and the dropping rate is 0.8~1.2 mL / s; the reaction time is 20~30 minutes; the reaction is carried out under a nitrogen atmosphere.

6. The method for preparing the temperature-sensitive acid thickener for acid fracturing of carbonate rock thermal reservoirs according to claim 3, characterized in that, In step (2), the mass ratio of partially deionized water B to partially deionized water A is 0.3~0.4:1; the dropping rate of the monomer solution is 0.04~0.06 mL / s; after the monomer solution is added to the mixed solution I, the reaction time is 15~20 minutes, the reaction temperature is 50~60℃, and the reaction is carried out under a nitrogen atmosphere. The initiator is added dropwise to the system in the form of an aqueous initiator solution, wherein the mass concentration of the initiator in the aqueous initiator solution is 0.3~0.5 g / mL and the dropping rate is 0.8~1.2 mL / s; after the initiator is added, the reaction time is 5~10 minutes and the reaction temperature is 50~60℃, and the reaction is carried out under a nitrogen atmosphere.

7. The method for preparing the temperature-sensitive acid thickener for acid fracturing of carbonate rock thermal reservoirs according to claim 3, characterized in that, In step (3), the time interval between each addition of the hydrophobic monomer solution is 1 to 2 minutes, and the dropping rate of the hydrophobic monomer solution is 0.04 to 0.06 mL / s; the reaction time after the addition of the hydrophobic monomer solution is completed is 2 to 4 hours, and the reaction temperature is 50 to 60°C; the reaction is carried out under a nitrogen atmosphere, and the stirring speed during the reaction is 400 to 600 r / min; the washing is performed by washing with anhydrous ethanol 3 to 5 times; the drying is performed by vacuum drying at 40 to 50°C for 48 to 72 hours.

8. The application of the temperature-sensitive acid thickener for acid fracturing of carbonate rock thermal reservoirs as described in any one of claims 1-2 in acid fracturing.

9. The application according to claim 8, characterized in that, The specific application method is as follows: dissolve the obtained temperature-sensitive acid thickener for acid fracturing of carbonate rock thermal reservoirs in an acid solution to obtain a temperature-responsive thickened acid system, which is used for acid fracturing. The acid solution is a hydrochloric acid solution with a concentration of 12~18wt%, and the concentration of the temperature-responsive thickened acid thickener for acid fracturing of carbonate rock thermal reservoirs in the temperature-responsive thickened acid system is 1~3wt%.

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