Temperature-resistant polycarboxylic acid dispersing agent for oil well cement and preparation method of temperature-resistant polycarboxylic acid dispersing agent

Abstract

The invention belongs to the technical field of dispersants for oil well cement, and particularly relates to a temperature-resistant polycarboxylic acid dispersant for oil well cement and a preparation method thereof. The polycarboxylic acid dispersant has a structure as shown in formula (1). The dispersant provided by the invention has good dispersing performance at high temperature, has good compatibility with other oil well cement admixtures at 150 DEG C, and can effectively reduce the initial consistency of cement paste; other properties of the cement paste and set cement are not influenced, the preparation method is simple, the raw material cost is low, and the production and use processes are environment-friendly.

Description

Technical Field

[0001] This invention belongs to the technical field of dispersants for oil well cement, and specifically relates to a temperature-resistant polycarboxylate dispersant for oil well cement and its preparation method. Background Technology

[0002] In oil and gas well cementing, cement slurry needs to flow through the hollow casing and then return from the bottom of the well in the narrow annular space between the casing and the well wall. This requires the cement slurry to have good properties. Generally, various admixtures are added to the cement to adjust its properties and meet the construction requirements. Dispersants, as one of the three major admixtures in oil well cement, can reduce the flow resistance of the cement slurry, maintain its fluidity, and enable it to achieve turbulent flow at lower pumping speeds, which is beneficial to improving cementing quality and plays a crucial role in cementing operations. In recent years, oil and gas exploration and development have gradually expanded into high-temperature, high-pressure, and complex environments. Deep, high-temperature environments severely affect the rheological properties of cement slurry; therefore, there is an urgent need to develop high-performance dispersants to meet the production requirements of deep, ultra-deep, and complex wells.

[0003] Currently, sulfonated aldehyde-ketone condensate dispersants are widely used in oil well cement dispersants both domestically and internationally. They adsorb onto cement particles via electrostatic attraction, generating electrostatic repulsion to prevent flocculation. They exhibit good performance in high-temperature cement slurries and possess advantages such as low cost, simple preparation, and good compatibility with most admixtures. However, with the continuous emergence of various new materials and increasingly stringent environmental standards, these dispersants also suffer from low dispersion efficiency and environmental pollution. To address these issues, polycarboxylate dispersants have emerged as a promising option due to their highly designable molecular structure, excellent dispersion performance, and environmental friendliness, making them a key development direction and research hotspot in high-performance cement dispersants in recent years.

[0004] Polycarboxylate dispersants, as a new generation of dispersants, are widely used in the construction industry. These dispersants are comb-like polymers, typically composed of a polycarboxylate backbone and polyether side chains. They disperse cement particles through electrostatic repulsion and steric hindrance. However, due to their poor temperature resistance, poor compatibility, and strong retarding properties, they cannot be directly and universally applied in the oil well cement industry. Furthermore, research on the application of polycarboxylate dispersants in high-temperature oil well cement is insufficient, resulting in limited improvement in the temperature resistance of current polycarboxylate dispersants, which still cannot meet the requirements of high-temperature cementing. Therefore, to adapt to the increasing practical production needs of high-temperature deep wells, it is urgent to develop a polycarboxylate dispersant with high temperature resistance, weak retarding properties, and strong compatibility. Summary of the Invention

[0005] The purpose of this invention is to address the problems of insufficient temperature resistance, poor compatibility, and strong retarding properties of traditional polycarboxylate dispersants by providing a temperature-resistant polycarboxylate dispersant for oil well cement and its preparation method. By simultaneously introducing phosphate anchoring groups, rigid groups, and cationic groups, the resulting dispersant exhibits excellent dispersing performance at high temperatures and good compatibility with other oil well cement admixtures at 150°C. It effectively reduces the initial consistency of cement slurry without affecting other properties of the cement slurry and cement paste. Furthermore, the preparation method is simple, the raw material cost is low, and the production and use processes are environmentally friendly, greatly solving the problems of poor temperature resistance, strong retarding properties, and poor compatibility of traditional polycarboxylate dispersants.

[0006] In a first aspect, the present invention provides a temperature-resistant polycarboxylate dispersant for oil well cement, having the structure shown in formula (1):

[0007]

[0008] Wherein, R1 is hydrogen or a carboxyl group, and R2 is a carboxyl group; or, R1 and R2 form a ring to form an acid anhydride;

[0009] R3 is hydrogen, C1-C6 alkyl, or C1-C6 carboxyalkyl;

[0010] R4 is a phosphate group, a phosphate ester group, or a phosphate alkyl ester group;

[0011] R5, R6, and R8 are each independently hydrogen or C1-C6 alkyl;

[0012] R7 is a quaternary ammonium ion; or, R6 and R7 form a ring to form a cyclic quaternary ammonium ion;

[0013] R9 is a C6-C16 aryl, C5-C16 hydrocarbon cycloyl, or C5-C16 heterocyclic group;

[0014] m is an integer from 1 to 6;

[0015] n is an integer between 40 and 60;

[0016] a, b, c, d, e are the number of moles and a:b:c:d:e = 0.04~0.4:0.01~0.15:0.02~0.25:0.04~0.20:0.01~0.15.

[0017] In some implementations, R7 is -COO(CH2). p [N(CH3)3] + -(CH2) p [N(CH3)3] + Or -CON(CH2) p [N(CH3)3] +p is an integer from 1 to 6; or, R6 and R7 form a ring to form -(CH2CH2). q (CH3)N + (CH3)(CH2CH2) q - where q is an integer from 1 to 6.

[0018] In some embodiments, R9 is a phenyl or pyrrolidone group.

[0019] In some implementations, the weight-average molecular weight of the polycarboxylic acid dispersant is 10,000 to 80,000.

[0020] A second aspect of the present invention provides a method for preparing the aforementioned polycarboxylic acid dispersant, comprising:

[0021] Under anaerobic conditions, and in the presence of an initiator and a chain transfer agent, monomer I having the structural unit shown in formula (i), monomer II having the structural unit shown in formula (ii), monomer III having the structural unit shown in formula (iii), monomer IV having the structural unit shown in formula (iv), monomer V having the structural unit shown in formula (v), and water are subjected to a free radical copolymerization reaction.

[0022]

[0023] The definitions of R1, R2, R3, R4, R5, R6, R7, R8, R9, m, and n are the same as before;

[0024] In some implementations, the preparation method includes the following steps:

[0025] S1: Before the reaction, add monomer III, monomer IV, monomer V, chain transfer agent and one part of distilled water to the reaction vessel, and purge with nitrogen for 10 to 30 minutes. At the same time, stir at 30 to 50°C for 10 to 30 minutes and then heat to 50 to 80°C.

[0026] S2: Dissolve monomer I and monomer II in a second part of distilled water, denoted as solution A. Dissolve a certain amount of initiator in a third part of distilled water to prepare solution B. Add solutions A and B to the reaction vessel dropwise, with solution A added for 4 to 6.5 hours and solution B added for 5.5 to 8 hours. After both are added, the entire system is aged at 50 to 80°C for 0.5 to 2 hours. The solid content of the entire reaction system is controlled at 30 to 50%.

[0027] S3: After the reaction is complete, adjust the pH of the reaction product to 6-8 to obtain the temperature-resistant polycarboxylic acid dispersant. The pH-adjusting substance is selected from one or more of sodium hydroxide, potassium hydroxide, and calcium hydroxide.

[0028] In some implementation schemes, the mass ratio of the aforementioned monomers I, II, III, IV, and V is 0.5–3:0.05–1.5:0.5–3.5:10–50:0.05–1.5.

[0029] In some implementations, the mass ratio of monomer III to monomer I is 1:3 to 3:1.

[0030] In some embodiments, monomer II is selected from at least one of vinyl phosphate, 2-(methacryloyloxy)ethyl phosphate, and vinyl phosphate.

[0031] In some embodiments, monomer III is selected from at least one of methacryloyloxyethyltrimethylammonium chloride, dimethyl diallyl ammonium chloride, methacrylamidopropyltrimethylammonium chloride, and allyltrimethylammonium chloride.

[0032] In some embodiments, monomer V is selected from at least one of N-vinyl-2-pyrrolidone (NVP) and styrene.

[0033] In some embodiments, monomer I is selected from at least one of acrylic acid, methacrylic acid, maleic acid, and maleic anhydride; and / or monomer IV is selected from at least one of isopentenyl polyoxyethylene ether (TPEG) and methyl allyl polyoxyethylene ether (HPEG).

[0034] In some embodiments, the initiator is selected from at least one of ammonium persulfate, sodium persulfate, and potassium persulfate.

[0035] In some embodiments, the chain transfer agent is selected from at least one of sodium methacrylate, sodium hypophosphite, mercaptoacetic acid, 3-mercaptopropionic acid, and mercaptoethanol; the amount of initiator is 0.2 to 0.4% wt and the amount of chain transfer agent is 0.3 to 0.4% wt, based on the total weight of the monomers.

[0036] The polycarboxylic acid dispersant provided by this invention contains structural units shown in formulas (i) to (v), which respectively provide carboxyl groups, phosphate groups, cationic groups, polyether groups, and rigid cyclic groups. The carboxyl groups and polyether groups provide electrostatic repulsion and steric hindrance effects, respectively, preventing cement particle flocculation and reducing cement paste viscosity. However, in high-temperature and high-salt environments, the carboxyl groups are prone to decarboxylation, leading to a decrease in adsorption capacity. Simultaneously, long side chains are prone to coiling, thus affecting the steric hindrance effect. Therefore, phosphate groups are introduced. Phosphate groups have good temperature resistance and salt resistance, giving polycarboxylic acid molecules good adsorption stability at high temperatures. The rigid cyclic groups increase the rigidity of the molecular chain, improving the temperature resistance of the dispersant and effectively improving the rheological properties of high-temperature cement paste. Furthermore, the introduction of cationic groups provides adsorption sites, reducing the retarding effect of anionic groups, and has no adverse effect on the thickening time of cement paste or the compressive strength of cement stone. Through the synergistic effect of these various groups, the effects of high temperature resistance, strong dispersion, and low retarding are achieved.

[0037] The beneficial effects of this invention are as follows:

[0038] (1) The polycarboxylic acid dispersant provided by this invention introduces phosphate anchoring groups, rigid cyclic groups, and cationic groups simultaneously for the first time. Phosphate groups can enhance the adsorption capacity of dispersant molecules at high temperatures, and rigid cyclic groups can increase the rigidity of molecular chains and improve the thermal stability of the dispersant molecular structure. At the same time, the introduction of cationic groups replaces some carboxyl groups, reducing the retarding effect. Experiments have shown that the polycarboxylic acid dispersant of this invention has good thermal stability at temperatures not exceeding 200℃ and good dispersibility at high temperatures. It can effectively reduce the initial consistency of cement paste and has the characteristics of high temperature resistance, strong dispersibility, and low retarding effect.

[0039] (2) The polycarboxylic acid dispersant provided by the present invention has a simple preparation method, low raw material cost, environmentally friendly production and use process, easy storage, and is conducive to industrial production;

[0040] (3) The polycarboxylic acid dispersant provided by the present invention can be applied to oil and gas cementing engineering. It has good compatibility with most oil well cement admixtures and can better meet the cementing construction requirements of different oil and gas wells. It has broad application prospects.

[0041] The following are the definitions of terms used in this invention:

[0042] C1-C6 alkyl refers to saturated straight-chain or branched alkyl groups having 1 to 6 carbon atoms, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, pentyl, and hexyl.

[0043] C1-C6 carboxyalkyl refers to the group "-alkyl-COOH", and the alkyl group has 1 to 6 carbon atoms;

[0044] The formation of an anhydride by the cyclic interaction of R1 and R2 refers to the connection of R1 and R2 with carbon atoms in the main chain directly connected to R1 and R2 to form a ring containing the -CO-O-CO- structure, such as a ring containing -CO-O-CO-, -CH2-CO-O-CO-CH2-, or -CO-O-CO-CH2-.

[0045] The phosphate group refers to the group -PO(OH)2;

[0046] The phosphate ester group refers to the group -PO(OR)2, where R is an alkyl group;

[0047] The alkyl phosphate group refers to the group -CO-(CH2). t -PO(OH)2, where t is an integer greater than 0;

[0048] Quaternary ammonium ions refer to those with the general formula R a R b R c R d N + The group, R a、 R b、 R c、 R d These can be the same or different carbon-containing groups, such as the same or different alkyl groups.

[0049] The formation of a cyclic quaternary ammonium ion by R6 and R7 refers to the connection between R6 and R7 and the carbon atoms in the main chain directly connected to R6 and R7, forming an ion containing -R. a R b R c R d N + The ring of the structure.

[0050] C6-C16 aryl refers to aromatic cyclic groups having a ring consisting of 6-16 carbon atoms, such as phenyl, naphthyl, biphenyl, anthracene, and pyrene.

[0051] C5-C16 hydrocarbon cycloalkanes refer to saturated hydrocarbon cycloalkanes with 5 to 16 cyclic carbon atoms, such as cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclononyl, and cyclodecyl.

[0052] C5-C16 heterocyclic groups refer to saturated heterocyclic groups with 5 to 16 cyclic carbon atoms and heteroatoms N, O or S, such as pyrrolidone, thiophene, imidazole, pyrazol, and pyrimidinyl. Attached Figure Description

[0053] Figure 1 Thermogravimetric curve of the temperature-resistant polycarboxylate dispersant for oil well cement prepared in Example 1;

[0054] Figure 2Infrared spectrum of the temperature-resistant polycarboxylate dispersant for oil well cement prepared in Example 1;

[0055] Figure 3 Thickening curve (150℃ × 94MPa) of the temperature-resistant polycarboxylate dispersant for oil well cement prepared in Example 1 containing 0.5% bwoc. Detailed Implementation

[0056] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions are followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be obtained commercially.

[0057] Example 1

[0058] A temperature-resistant polycarboxylate dispersant for oil well cement is prepared as follows:

[0059] Weigh out 100 parts of isopentenyl alcohol polyoxyethylene ether (EO degree of polymerization n=40, purchased from Liaoning Aoke Chemical Co., Ltd.), 2.3 parts of N-vinyl-2-pyrrolidone, 7 parts of dimethyl diallyl ammonium chloride, 0.4 parts of mercaptoacetic acid and 100 parts of deionized water respectively and add them to a round bottom flask. Heat to 30°C and stir to dissolve for 20 min. At the same time, purge the solution with nitrogen gas for 10 min. Then heat to 70°C and use it as the bottom solution.

[0060] Then, 6 parts of acrylic acid and 2.5 parts of vinyl phosphoric acid were dissolved in 36 parts of deionized water, and this solution was labeled as solution A; 3.5 parts of ammonium persulfate were dissolved in 40 parts of deionized water, and this solution was labeled as solution B; solutions A and B were added dropwise to round-bottom flasks, respectively, for 5.5 h and 6.5 h, respectively. After all the materials had been added, the mixture was stirred at a constant temperature of 70°C for 0.5 h.

[0061] Finally, 40% NaOH was added to adjust the pH to 7, resulting in a solution of a temperature-resistant polycarboxylate dispersant for oil well cement, wherein the weight-average molecular weight of the temperature-resistant polycarboxylate dispersant for oil well cement is 50,000 to 60,000.

[0062] Example 2

[0063] A temperature-resistant polycarboxylate dispersant for oil well cement is prepared as follows:

[0064] Weigh out 100 parts of isopentenyl alcohol polyoxyethylene ether (EO degree of polymerization n=50, purchased from Liaoning Aoke Chemical Co., Ltd.), 0.5 parts of styrene, 5 parts of methacryloyloxyethyltrimethylammonium chloride, 0.4 parts of sodium hypophosphite and 100 parts of deionized water respectively and add them to a round bottom flask. Heat to 30°C and stir to dissolve for 20 min. At the same time, purge the solution with nitrogen gas for 10 min. Then heat to 65°C and use it as the bottom solution.

[0065] Then, 5 parts maleic acid and 0.5 parts 2-(methacryloyloxy)ethyl phosphate were dissolved in 37 parts deionized water, and this was labeled as solution A; 5 parts potassium persulfate were dissolved in 30 parts deionized water, and this was labeled as solution B; solutions A and B were added dropwise to round-bottom flasks, respectively, for 4.5 h and 7 h, respectively. After all the materials had been added, the mixture was stirred at a constant temperature of 60 °C for 0.5 h.

[0066] Finally, 20% KOH was added to adjust the pH to 8, resulting in a solution of a temperature-resistant polycarboxylate dispersant for oil well cement, wherein the weight-average molecular weight of the temperature-resistant polycarboxylate dispersant for oil well cement is 40,000 to 50,000.

[0067] Example 3

[0068] A temperature-resistant polycarboxylate dispersant for oil well cement is prepared as follows:

[0069] Weigh out 100 parts of isopentenyl alcohol polyoxyethylene ether (EO degree of polymerization n=60, purchased from Liaoning Aoke Chemical Co., Ltd.), 2 parts of N-vinyl-2-pyrrolidone, 6 parts of methacrylamide propyltrimethylammonium chloride, 0.2 parts of sodium methacrylate sulfonate and 100 parts of deionized water respectively and add them to a round bottom flask. Heat to 50°C and stir to dissolve for 20 min. At the same time, purge the solution with nitrogen gas for 10 min. Then heat to 60°C and use it as the bottom solution.

[0070] Then, 6 parts of methacrylic acid and 2 parts of vinyl phosphate were dissolved in 40 parts of deionized water, and this was labeled as solution A; 2 parts of sodium persulfate were dissolved in 34 parts of deionized water, and this was labeled as solution B; solutions A and B were added dropwise to a round-bottom flask, respectively, for 6 hours and 6.5 hours. After all the materials had been added, the mixture was stirred at a constant temperature of 60°C for 1 hour.

[0071] Finally, a 20% Ca(OH)2 solution was added to adjust the pH to 6, resulting in a solution of a temperature-resistant polycarboxylate dispersant for oil well cement, wherein the weight-average molecular weight of the temperature-resistant polycarboxylate dispersant for oil well cement is 30,000 to 50,000.

[0072] Comparative Example 1

[0073] The commercially available sulfonated aldehyde-ketone condensate dispersant SXY, which is a reddish-brown solid powder, was purchased from Chengdu Chuanfeng Chemical Co., Ltd., and is designated as the dispersant for Comparative Example 1.

[0074] Comparative Example 2

[0075] Weigh out 100 parts of isopentenyl alcohol polyoxyethylene ether, 2.3 parts of N-vinyl-2-pyrrolidone, 0.38 parts of mercaptoacetic acid and 100 parts of deionized water respectively and add them to a round bottom flask. Heat to 30°C and stir to dissolve for 20 minutes. At the same time, purge the solution with nitrogen gas for 10 minutes. Then heat to 70°C and use it as the base solution.

[0076] Then, 6 parts of acrylic acid were dissolved in 30 parts of deionized water, and this was labeled as solution A; 3.24 parts of ammonium persulfate were dissolved in 32 parts of deionized water, and this was labeled as solution B; solutions A and B were added dropwise to a round-bottom flask, respectively, for 5.5 h and 6.5 h, respectively. After all the materials had been added, the mixture was stirred at a constant temperature of 70°C for 0.5 h.

[0077] Finally, add 40% NaOH to adjust the pH to 7, and record this as the dispersant solution of Comparative Example 2.

[0078] Comparative Example 3

[0079] Weigh out 100 parts of methyl allyl alcohol polyoxyethylene ether, 7 parts of dimethyl diallyl ammonium chloride, 0.39 parts of mercaptoacetic acid and 100 parts of deionized water by mass and add them to a round-bottom flask. Heat to 30°C and stir to dissolve for 20 minutes. At the same time, purge the solution with nitrogen gas for 10 minutes. Then heat to 70°C and use it as the base solution.

[0080] Then, 6 parts of acrylic acid were dissolved in 30 parts of deionized water, and this was labeled as solution A; 3.5 parts of ammonium persulfate were dissolved in 39 parts of deionized water, and this was labeled as solution B; solutions A and B were added dropwise to a round-bottom flask, and the addition of solutions A and B was carried out for 5 hours and 6 hours, respectively. After all the materials were added, the mixture was stirred at a constant temperature of 70°C for 1 hour.

[0081] Finally, add 40% KOH to adjust the pH to 7, and record this as the dispersant solution of Comparative Example 3.

[0082] Comparative Example 4

[0083] Weigh out 100 parts of isopentenyl alcohol polyoxyethylene ether, 0.38 parts of mercaptoacetic acid and 100 parts of deionized water by mass and add them to a round bottom flask. Heat to 30°C and stir to dissolve for 20 minutes. At the same time, purge the solution with nitrogen gas for 10 minutes. Then heat to 70°C and use it as the base solution.

[0084] Then, 6 parts of acrylic acid and 2.5 parts of vinyl phosphoric acid were dissolved in 30 parts of deionized water, and this solution was labeled as solution A; 3.2 parts of ammonium persulfate were dissolved in 32 parts of deionized water, and this solution was labeled as solution B; solutions A and B were added dropwise to round-bottom flasks, respectively, for 4.5 h and 6.5 h, respectively. After all the materials had been added, the mixture was stirred at a constant temperature of 70 °C for 0.5 h.

[0085] Finally, add 40% NaOH to adjust the pH to 7, and record this as the dispersant solution of Comparative Example 4.

[0086] Comparative Example 5

[0087] Weigh out 100 parts of methyl allyl alcohol polyoxyethylene ether, 2.3 parts of N-vinyl-2-pyrrolidone, 7 parts of dimethyl diallyl ammonium chloride, 0.4 parts of mercaptoacetic acid and 100 parts of deionized water respectively and add them to a round bottom flask. Heat to 30°C and stir to dissolve for 20 min. At the same time, purge the solution with nitrogen gas for 10 min. Then heat to 70°C and use it as the bottom solution.

[0088] Then, 6 parts of acrylic acid were dissolved in 30 parts of deionized water, and this was labeled as solution A; 3.5 parts of ammonium persulfate were dissolved in 42 parts of deionized water, and this was labeled as solution B; solutions A and B were added dropwise to a round-bottom flask, and the addition of solutions A and B was carried out for 5 hours and 6 hours, respectively. After all the materials were added, the mixture was stirred at a constant temperature of 70°C for 1 hour.

[0089] Finally, add 40% NaOH to adjust the pH to 7, and record this as the dispersant solution of Comparative Example 5.

[0090] Comparative Example 6

[0091] Weigh out 100 parts of isopentenyl alcohol polyoxyethylene ether, 2.3 parts of N-vinyl-2-pyrrolidone, 0.38 parts of mercaptoacetic acid and 100 parts of deionized water respectively and add them to a round bottom flask. Heat to 30°C and stir to dissolve for 20 minutes. At the same time, purge the solution with nitrogen gas for 10 minutes. Then heat to 70°C and use it as the base solution.

[0092] Then, 6 parts of acrylic acid and 2.5 parts of vinyl phosphoric acid were dissolved in 30 parts of deionized water, and this was labeled as solution A; 3.3 parts of ammonium persulfate were dissolved in 36 parts of deionized water, and this was labeled as solution B; solutions A and B were added dropwise to round-bottom flasks, respectively, for 5.5 h and 7.5 h, respectively. After all the materials had been added, the mixture was stirred at a constant temperature of 70°C for 0.5 h.

[0093] Finally, add 40% NaOH to adjust the pH to 7, and record this as the dispersant solution of Comparative Example 6.

[0094] Comparative Example 7

[0095] Weigh out 100 parts of methyl allyl alcohol polyoxyethylene ether, 7 parts of dimethyl diallyl ammonium chloride, 0.4 parts of mercaptoacetic acid and 100 parts of deionized water respectively and add them to a round bottom flask. Heat to 30°C and stir to dissolve for 20 minutes. At the same time, purge the solution with nitrogen gas for 10 minutes. Then heat to 70°C and use it as the bottom solution.

[0096] Then, 6 parts of acrylic acid and 2.5 parts of vinyl phosphoric acid were dissolved in 36 parts of deionized water, and this was labeled as solution A; 3.5 parts of ammonium persulfate were dissolved in 40 parts of deionized water, and this was labeled as solution B; solutions A and B were added dropwise to a round-bottom flask, respectively, for 5.5 hours and 6 hours, respectively. After all the materials had been added, the mixture was stirred at a constant temperature of 70°C for 1.5 hours.

[0097] Finally, add 40% NaOH to adjust the pH to 7, and record this as the dispersant solution of Comparative Example 7.

[0098] I. Thermogravimetric Analysis

[0099] Figure 1 The thermogravimetric analysis (TGA) chart shows the temperature-resistant polycarboxylate dispersant for oil well cement prepared in Example 1. The chart indicates that the polymer begins to lose weight at 200°C, and exhibits two weight loss ranges between 20°C and 600°C, corresponding to the breakage and decomposition of the long side chains and the main molecular chain of the polyether. This demonstrates that the polymer molecules possess good thermal stability at temperatures not exceeding 200°C.

[0100] II. Polymer Structure Characterization

[0101] Figure 2 The infrared spectrum of the temperature-resistant polycarboxylate dispersant for oil well cement prepared in Example 1 is shown. As can be seen from the figure, at 1727 cm⁻¹... -1 and 1110cm -1 The peaks at 1299 cm⁻¹ represent the stretching vibrations of -COOH on the carboxylic acid monomer and -COC- on the polyether macromonomer, respectively. -1 The peak at 1641 cm⁻¹ represents the stretching vibration of the -P=O group in phosphate. -1 The peak at 1351 cm⁻¹ represents the stretching vibration peak of the -C=O ring on the five-membered ring of N-vinyl-2-pyrrolidone. -1 The peak is the stretching vibration peak of the cation -CN; the infrared spectral results show that the molecular structure of the obtained polycarboxylic acid dispersant meets the design requirements.

[0102] III. Application Case 1

[0103] Figure 3Thickening curve (150℃ × 94MPa) of the oil well cement slurry prepared with 0.5% BWOC and a heat-resistant polycarboxylate dispersant as shown in Example 1. (Note: The experimental formula was 100 parts G-grade cement + 40 parts quartz sand + 4 parts water loss reducer - SD130 + 2.5 parts retarder - SD210 + 0.5 parts dispersant from Example 1 + 55 parts tap water, with a density of 1.89 g / cm³.) 3 As shown in the figure, the cement slurry has a low initial consistency (<30 Bc), and the thickening curve is smooth with stable consistency, exhibiting an almost "right-angle" thickening trend without any abnormal gelling phenomena such as bulging or consistency jumps. This indicates that the dispersant of this invention has good dispersibility at high temperatures and can effectively reduce the viscosity of the cement slurry; furthermore, the dispersant of this invention has good compatibility with other additives in the system and still maintains good pumpability at high temperatures, which can better meet the needs of practical engineering applications.

[0104] IV. Application Case Two

[0105] Cement slurry was prepared according to GB / T 19139-2012 "Test Methods for Cement in Oil Wells". Rheological properties, thickening time, and compressive strength were evaluated according to SY / T5504.3-2018 "Evaluation Methods for Admixtures in Oil Well Cement Part 3: Drag Reducers". The cement used was Jiahua G-grade cement. The fluid loss reducer SD130 and retarder SD210 were from Sichuan Qinghe Company. The fluid loss reducer was an AMPS-type fluid loss reducer, and the retarder was an acid-based retarder. The comparative dispersants were the dispersants prepared in Comparative Examples 2-7 and the commonly used sulfonated aldehyde-ketone condensate dispersant SXY (Comparative Example 1). Tables 1 to 3 evaluate the effects of the dispersant samples and comparative examples from the three embodiments of this invention on the rheological properties, thickening time, and compressive strength of the cement slurry at different temperatures.

[0106] The specific formula for each group of experiments is as follows:

[0107] Cement slurry formula A: 100 parts Grade G cement + 4 parts water loss reducer - SD130 + 0.5 parts retarder - SD210 + 40 parts tap water, density 1.89 g / cm³ 3 .

[0108] Cement slurry formulations B1-B9: 100 parts Grade G cement + 4 parts water loss reducer - SD130 + 0.5 parts retarder - SD210 + 0.5 parts dispersant (one of Examples 1-3, Comparative Examples 2-7) + 39.5 parts tap water, with a density of 1.89 g / cm³. 3 .

[0109] Cement slurry formula C: 100 parts Grade G cement + 4 parts water loss reducer - SD130 + 0.5 parts retarder - SD210 + 0.5 parts dispersant (comparative example 1) + 40 parts tap water, density 1.89 g / cm³3 .

[0110] Cement slurry formula D: 100 parts G-grade cement + 40 parts quartz sand + 4 parts water loss reducer - SD130 + 2.5 parts retarder - SD210 + 55 parts tap water, density 1.89 g / cm³ 3 .

[0111] Cement slurry formulations E1-E9: 100 parts Grade G cement + 40 parts quartz sand + 4 parts water loss reducer - SD130 + 2.5 parts retarder - SD210 + 0.5 parts dispersant (one of Examples 1-3, Comparative Examples 2-7) + 55 parts tap water, with a density of 1.89 g / cm³. 3 .

[0112] Cement slurry formula F: 100 parts Grade G cement + 40 parts quartz sand + 4 parts water loss reducer - SD130 + 2.5 parts retarder - SD210 + 0.5 parts dispersant (comparative example 1) + 55 parts tap water, density 1.89 g / cm³ 3 .

[0113] Note: In the cement slurry formulation, the amount added to the Comparative Example 1 sample was calculated using the external admixture method, while the other examples and comparative examples were calculated using the internal admixture method, i.e., adding the same mass of mixing water; formulations A to C are suitable for cement slurry systems with temperatures below 100°C; formulations D to F are suitable for cement slurry systems with temperatures above 100°C.

[0114] Table 1. Overall performance of Example 1 and comparative samples under different formulations and temperatures.

[0115]

[0116] Table 2. Overall performance of Example 2 and comparative samples under different formulations and temperatures.

[0117]

[0118]

[0119] Table 3. Overall performance of Example 3 and comparative samples under different formulations and temperatures.

[0120]

[0121] Generally, the flow index (n) and consistency coefficient (K) in rheological properties show opposite trends. The coexistence of a high flow index and a low consistency coefficient indicates high dispersion of the flocculated structure and low content of the cement slurry, reflecting the good dispersing ability of the dispersant. As can be seen from Tables 1-3, compared with the cement slurry prepared using the comparative dispersant, the addition of the dispersant in the embodiments of the present invention significantly increases the flow index and decreases the consistency coefficient, indicating that the dispersant has better dispersing ability and exhibits significantly better dispersing ability at different temperatures.

[0122] Thickening time refers to the time elapsed from the start of heating and pressurization until the cement slurry reaches a specified consistency (usually 100 Bc). It can be used to determine the cementing time at the cementing site. If the thickening time is too short, it may cause a "sausage-filling" accident during cementing operations. If the thickening time is too long, the cement slurry may not solidify for a long time, affecting the working time for continued drilling. A reasonable thickening time should both ensure safe completion of cementing operations and promote the formation of early strength of the cement stone. Cement stone with higher compressive strength generally results in better cementing quality; the compressive strength of the cement stone in the producing formation should not be less than 14.0 MPa after 24–48 hours. The dispersants prepared in Comparative Examples 1–7 have a greater impact on the thickening time and cement stone strength compared to Examples 1–3, resulting in longer thickening times and lower compressive strength. Considering the thickening time and compressive strength results of Examples 1–3, the dispersant of this invention does not cause temperature inversion; although it slightly prolongs the thickening time of the cement slurry, it has no adverse effect on the early strength of the cement stone.

[0123] In summary, the dispersant in Comparative Example 1 is a commonly used sulfonated aldehyde-ketone condensate dispersant in oil fields. The difference between the dispersants in Comparative Examples 2-7 and the dispersant of this invention lies only in that the functional groups contain only one or two of the three groups: phosphate groups, rigid groups, and cationic groups. The dispersant of this invention, however, contains all three groups simultaneously. These results confirm that the dispersant of this invention, by simultaneously introducing these three groups, significantly improves the dispersing ability, has little impact on thickening time and early strength of cement paste, and is significantly superior to commercially available classic products.

[0124] After hydration, cement easily forms a flocculated structure, resulting in high viscosity and difficulty in pumping the cement slurry. This is especially true in the harsh, high-temperature environment of downhole drilling, where the hydration rate accelerates, further worsening the slurry's flow properties. Dispersants can improve these properties. Currently, commonly used sulfonated aldehyde-ketone condensate dispersants in oilfields disperse cement particles solely through electrostatic repulsion, resulting in a simple mechanism and low dispersion efficiency. In contrast, the dispersant of this invention uses carboxylic acid and phosphate anchoring groups to adsorb onto positively charged cement particles in the early stages of hydration. The phosphate groups enhance the adsorption capacity of the dispersant molecules at high temperatures, while the cationic groups do not readily bind with Ca2+. 2+The complexation effect can supplement the adsorption capacity. The rigid ring structure can form planar adsorption, which effectively increases the thickness of the adsorption layer of dispersant molecules on cement particles. The electrostatic repulsion generated can disperse cement particles. At the same time, the long side chains of the molecules adsorbed on the surface of cement particles extend under the action of high temperature and high speed shear, preventing the aggregation between cement particles. Through the joint action of various functional groups, the dispersion efficiency of the dispersant is greatly improved.

[0125] The dispersant of this invention has significantly improved temperature resistance, effectively reducing the flow resistance of cement slurry at high temperatures, reducing cementing construction pressure, and meeting the requirements for safe and efficient cementing in high-temperature deep wells, thus showing good application prospects.

[0126] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

Claims

1. A temperature-resistant polycarboxylate dispersant for oil well cement, characterized in that: It has the structure shown in equation (1): Wherein, R1 is hydrogen or a carboxyl group, and R2 is a carboxyl group; or, R1 and R2 form a ring to form an acid anhydride; R3 is hydrogen, C1-C6 alkyl, or C1-C6 carboxyalkyl; R4 is a phosphate group, a phosphate ester group, or a phosphate alkyl ester group; R5, R6, and R8 are each independently hydrogen or C1-C6 alkyl; R7 is a quaternary ammonium ion; or, R6 and R7 form a ring to form a cyclic quaternary ammonium ion; R9 is a C6-C16 aryl, C5-C16 hydrocarbon cycloyl, or C5-C16 heterocyclic group; m is an integer from 1 to 6; n is an integer between 40 and 60; a, b, c, d, e are the number of moles and a:b:c:d:e = 0.04~0.4:0.01~0.15:0.02~0.25:0.04~0.20:0.01~0.

15.

2. The polycarboxylic acid dispersant according to claim 1, characterized in that: R7 is -COO(CH2). p [N(CH3)3] + -(CH2) p [N(CH3)3] + Or -CON(CH2) p [N(CH3)3] + p is an integer from 1 to 6; or, R6 and R7 form a ring to form -(CH2CH2). q (CH3)N + (CH3)(CH2CH2) q - where q is an integer from 1 to 6.

3. The polycarboxylic acid dispersant according to claim 1, characterized in that: R9 is a phenyl or pyrrolidone group.

4. The polycarboxylic acid dispersant according to claim 1, characterized in that: The weight-average molecular weight of the polycarboxylic acid dispersant is 10,000 to 80,000.

5. A method for preparing the polycarboxylic acid dispersant according to any one of claims 1 to 4, characterized in that: The preparation method includes: Under anaerobic conditions, and in the presence of an initiator and a chain transfer agent, monomer I having the structural unit shown in formula (i), monomer II having the structural unit shown in formula (ii), monomer III having the structural unit shown in formula (iii), monomer IV having the structural unit shown in formula (iv), monomer V having the structural unit shown in formula (v), and water are subjected to a free radical copolymerization reaction. The definitions of R1, R2, R3, R4, R5, R6, R7, R8, R9, m, and n are the same as in claim 1; The mass ratio of monomer I, monomer II, monomer III, monomer IV, and monomer V is 0.5–3:0.05–1.5:0.5–3.5:10–50:0.05–1.

5.

6. The preparation method according to claim 5, characterized in that, The mass ratio of monomer III to monomer I is 1:3 to 3:

1.

7. The preparation method according to claim 5, characterized in that, The monomer II is selected from at least one of vinyl phosphate, 2-(methacryloyloxy)ethyl phosphate, and vinyl phosphate.

8. The preparation method according to claim 5, characterized in that, The monomer III is selected from at least one of methacryloyloxyethyltrimethylammonium chloride, dimethyldiallylammonium chloride, methacrylamidopropyltrimethylammonium chloride, and allyltrimethylammonium chloride.

9. The preparation method according to claim 5, characterized in that, The monomer V is selected from at least one of N-vinyl-2-pyrrolidone and styrene.

10. The preparation method according to claim 5, characterized in that, The monomer I is selected from at least one of acrylic acid, methacrylic acid, maleic acid, and maleic anhydride; and / or, the monomer IV is selected from at least one of isopentenyl polyoxyethylene ether and methyl allyl polyoxyethylene ether.

11. The preparation method according to claim 5, characterized in that, The initiator is selected from at least one of ammonium persulfate, sodium persulfate, and potassium persulfate; and / or the chain transfer agent is selected from at least one of sodium methylpropenesulfonate, sodium hypophosphite, mercaptoacetic acid, 3-mercaptopropionic acid, and mercaptoethanol.

12. The preparation method according to claim 5, characterized in that, The reaction temperature is 50–80°C, and the reaction time is 0.5–2 hours.

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