A crosslinking agent, a micro-crosslinking polycarboxylic acid dispersant and a corresponding preparation method

Abstract

The present application relates to the technical field of oilfield development cementing operation, and particularly relates to a crosslinking agent, a micro-crosslinking polycarboxylic acid dispersant and a corresponding preparation method. A divinyl carboxylic acid-beta-cyclodextrin diester is added during synthesis, and the micro-crosslinking polycarboxylic acid dispersant formed can obtain better dispersing performance. Meanwhile, the crosslinking between polymers can improve the temperature resistance. Through the crosslinking agent, the micro-crosslinking polycarboxylic acid dispersant and the corresponding preparation method, the problems that the conventional polycarboxylic acid water reducing agent applied in oil well cement can inhibit the hydration of cement, is not conducive to the early strength development of cement stone and has poor dispersing performance at high temperature and the like can be solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of oilfield development cementing operation, in particular to a crosslinking agent, a micro-crosslinking polycarboxylic acid dispersant and a corresponding preparation method. BACKGROUND

[0002] Cementing operation mainly has two links of casing and cement injection, cement injection is to pump cement slurry into the annulus between the casing and the wellbore, and the cement slurry to be pumped is required to have good flow performance. However, with the gradual deepening of exploration and development, more and more complex well conditions such as high temperature and high pressure, and accordingly, various retarders, fluid loss reducers, weighting agents, resin emulsions and other additives or admixtures often lead to poor slurry flowability and difficulty in pumping. Therefore, it is necessary to add a dispersant to the cement slurry to improve the flow performance of the cement slurry and improve its rheological properties, so that the cement slurry can realize turbulent displacement under low pump pressure, and improve the quality of cement injection in oil and gas wells.

[0003] The commonly used oil well cement dispersants at present include lignin sulfonate, polynaphthalene sulfonate and sulfonated acetone-formaldehyde condensate. Lignin sulfonate has unstable raw material sources and complex composition, which usually causes unstable product performance, polynaphthalene sulfonate and sulfonated acetone-formaldehyde condensate are usually orange red or red brown powders, formaldehyde, one of the key production raw materials, has toxicity and pollution, and the condensate has a single structure, a large amount of dosage and low dispersion efficiency.

[0004] Polycarboxylic acid (PCE) water reducer is usually a comb-shaped polymer composed of a carboxylic acid anion anchoring group main chain and a hydrophilic non-ionic long chain branch. Since the first generation of PCE was invented in Japan in 1981, it has completely occupied the world building concrete water reducer market after more than twenty years of development, and is called high-performance water reducer in China. The research of Zhai et al. "Characteristics of polycarboxylate-based dispersants suitable for medium and low temperature oil well cementing" shows that the conventional PCE water reducer directly applied to the medium and low temperature cementing slurry has obvious dispersion effect better than that of sulfonated acetone-formaldehyde condensate, but has problems such as long thickening time and low early strength; and in the high temperature and high pressure cement slurry environment, the polyethylene glycol side chain of the conventional PCE is easy to hydrolyze and break, the dispersion effect is poor, and the cement slurry performance is unstable. SUMMARY

[0005] To solve the above technical problems, the application provides a crosslinking agent, a micro-crosslinking polycarboxylic acid dispersant and a corresponding preparation method, which can solve the problems that the conventional polycarboxylic acid water reducing agent applied in oil well cement can inhibit the hydration of the cement, is not conducive to the development of the early strength of the cement stone and has poor dispersion performance at high temperature, can improve the rheological property of the cement slurry, has little influence on the thickening time and the strength of the cement stone and is suitable for the middle and high temperature oil well cement.

[0006] The application is realized by adopting the following technical scheme:

[0007] The crosslinking agent is a divinyl carboxylic acid-beta-cyclodextrin diester, and the preparation raw materials thereof include beta-cyclodextrin, N,N-dimethylformamide solvent, a first carboxylic acid monomer, a catalyst and a polymerization inhibitor; wherein the mass ratio of the beta-cyclodextrin and the N,N-dimethylformamide solvent is 1:(3-4), and the molar ratio of the beta-cyclodextrin and the first carboxylic acid monomer is 1:(2.05-2.10).

[0008] The structural general formula of the crosslinking agent is shown in formula I.

[0009]

[0010] Wherein, R1 is H or COOH.

[0011] The amount of the catalyst is 0.5-3% of the mass of the beta-cyclodextrin, and the amount of the polymerization inhibitor is 0.5-2% of the mass of the first carboxylic acid monomer.

[0012] The preparation method of the crosslinking agent comprises the following steps: under the protection of nitrogen, the beta-cyclodextrin is completely dissolved in the N,N-dimethylformamide solvent, the temperature is raised to 60-70 DEG C, the first carboxylic acid monomer, the catalyst and the polymerization inhibitor are added, the temperature is raised to 90-130 DEG C, then the temperature is kept constant for 10-15 h for sufficient esterification reaction, the temperature is reduced to 70-80 DEG C, and the solvent is distilled out under reduced pressure to obtain the crosslinking agent, i.e., the divinyl carboxylic acid-beta-cyclodextrin diester.

[0013] The preparation raw materials of the micro-crosslinking polycarboxylic acid dispersant include the crosslinking agent, and further include a polyether macromonomer, a second carboxylic acid monomer, a sulfonic acid monomer, an initiator and a chain transfer agent; the molar ratio of (the polyether macromonomer+the second carboxylic acid monomer+the sulfonic acid monomer) to the crosslinking agent is 100:(0.5-1.0), and the molar ratio of the polyether macromonomer, the second carboxylic acid monomer and the sulfonic acid monomer is 1:(1-2):(3-4).

[0014] The structural general formula of the dispersant is shown in formula II.

[0015]

[0016] Wherein, R1 is H or COOH, R2 is H or CH3, R3 is sulfonic acid group; n represents the degree of polymerization: n = 20~60; a, b, c represent the molar ratio of monomers: a:b:c = 1:(1~2):(3~5).

[0017] The polyether macromonomer is one or more of isobutenol polyethylene glycol ether, isoamylenol polyethylene glycol ether and ethylene glycol monovinyl polyethylene glycol ether, and the molecular weight is 1000~3000 g / mol.

[0018] The sulfonic acid monomer is one or more of 2-acrylamide-2-methylpropane sulfonic acid, sodium p-styrene sulfonate and sodium allyl sulfonate.

[0019] The amount of the initiator is 1~4% of the total mass of the polyether macromonomer, the second carboxylic acid monomer and the sulfonic acid monomer, and the amount of the chain transfer agent is 0.5~3% of the total mass of the polyether macromonomer, the second carboxylic acid monomer and the sulfonic acid monomer.

[0020] A preparation method of a micro-crosslinking polycarboxylic acid dispersant comprises the following steps:

[0021] Step S1. The polyether macromonomer solution is used as a bottom solution; the crosslinking agent, the second carboxylic acid monomer, the sulfonic acid monomer and the chain transfer agent are mixed to form a mixed solution;

[0022] Step S2. The mixed solution and the initiator solution are added into the bottom solution in a dropwise form to perform a polymerization reaction.

[0023] Step S3. After the polymerization reaction is completed, the temperature is cooled to room temperature, and the pH value is adjusted to 6~8.

[0024] In the step S2, during the polymerization reaction, the solid content is controlled to be 30~50 wt%, and the reaction temperature is controlled to be 60~75 DEG C.

[0025] In the step S2, the dropwise adding time of the mixed solution is 3~4 h, the dropwise adding time of the initiator solution is 3.5~4.5 h, and the dropwise adding time of the initiator solution is greater than that of the mixed solution.

[0026] In the step S2, after the dropwise adding of the initiator solution is completed, the aging is continued for 0.5~1 h.

[0027] Compared with the prior art, the beneficial effects of the present application are as follows:

[0028] 1. The crosslinking agent, i.e. divinyl carboxylic acid-beta-cyclodextrin diester, can be used to produce the micro-crosslinking polycarboxylic acid dispersant for oil well cement, so that the dispersant has better dispersing performance, and meanwhile, the temperature resistance of the dispersant can be improved.

[0029] 2、The micro-crosslinking polycarboxylic dispersant in the application, due to the steric hindrance of the β-cyclodextrin, the molecule is more easily stretched in the solution than the conventional polycarboxylic dispersant, thus a greater adsorption layer thickness can be generated when adsorbed on the cement particles, and the dispersing performance is better, and the micro-crosslinking polycarboxylic dispersant can be applied to oil well cement.

[0030] 3、The micro-crosslinking polycarboxylic dispersant in the application, due to the micro-crosslinking structure between the molecules, the molecule has good temperature resistance, and is suitable for high-temperature well cementing engineering, meets higher construction requirements, and has a good application prospect.

[0031] 4、In the application, the mixed solution and the initiator solution are added to the bottom solution in a dropwise manner for polymerization reaction, and the conversion rate of all monomers can be improved. BRIEF DESCRIPTION OF DRAWINGS

[0032] The application will be further described in detail below with reference to the drawings and specific embodiments of the application.

[0033] Figure 1 Thermogravimetric curve of the micro-crosslinking polycarboxylic dispersant prepared for Example 2;

[0034] Figure 2 Cement slurry 120℃ thickening curve of the cement slurry doped with the micro-crosslinking polycarboxylic dispersant prepared for Example 2;

[0035] Figure 3 Cement slurry 140℃ thickening curve of the cement slurry doped with the micro-crosslinking polycarboxylic dispersant prepared for Example 2. DETAILED DESCRIPTION

[0036] Example 1

[0037] A crosslinking agent, the crosslinking agent is divinyl carboxylic acid-β-cyclodextrin diester, and the preparation raw materials include: β-cyclodextrin, N,N-dimethylformamide solvent, first carboxylic acid monomer, catalyst and polymerization inhibitor. Wherein, the mass ratio of β-cyclodextrin and N,N-dimethylformamide solvent is 1:(3-4), and the molar ratio of β-cyclodextrin and the first carboxylic acid monomer is 1:(2.05-2.10).

[0038] Wherein, the first carboxylic acid monomer is one or more than two arbitrary ratio combinations of maleic anhydride, fumaric acid and acrylic acid. The catalyst is one or two arbitrary ratio combinations of p-toluenesulfonic acid and benzenesulfonic acid, and the amount is 0.5-3% of the mass of β-cyclodextrin, preferably 2%. The polymerization inhibitor is one or more than two arbitrary ratio combinations of hydroquinone, p-tert-butyl catechol and p-benzoquinone, and the amount is 0.5-2% of the mass of the first carboxylic acid monomer, preferably 1%.

[0039] The preparation method of the crosslinking agent comprises the following steps: under the protection of nitrogen, completely dissolving β-cyclodextrin in N,N-dimethylformamide solvent, heating to 60-70℃, sequentially adding catalyst, polymerization inhibitor and first carboxylic acid monomer, then heating to 90-130℃, keeping constant temperature for 10-15h for sufficient esterification reaction, cooling to 70-80℃, and then distilling the solvent under reduced pressure to obtain the crosslinking agent, i.e. divinyl carboxylic acid-β-cyclodextrin diester. The distilled solvent can be reused.

[0040] The structural general formula of the prepared crosslinking agent is shown in formula I:

[0041]

[0042] In the formula, R1 is H or COOH.

[0043] A micro-crosslinking polycarboxylic acid dispersant is prepared from the following raw materials: polyether macromonomer, second carboxylic acid monomer, sulfonic acid monomer, crosslinking agent, initiator and chain transfer agent. In an aqueous solution environment, the polyether macromonomer, second carboxylic acid monomer, sulfonic acid monomer and crosslinking agent are subjected to free radical polymerization under the action of the initiator and chain transfer agent to obtain the micro-crosslinking polycarboxylic acid dispersant. The molar ratio of various monomers satisfies: (polyether macromonomer + second carboxylic acid monomer + sulfonic acid monomer) : crosslinking agent = 100 : (0.5-1.0), polyether macromonomer : second carboxylic acid monomer = 1 : (1-2), and sulfonic acid monomer = 1 : (3-4).

[0044]

[0045] The polyether macromonomer is one or more than two arbitrary proportion combinations of isobutenyl alcohol polyethylene glycol ether, isoamylenyl alcohol polyethylene glycol ether and ethylene glycol monovinyl polyethylene glycol ether, and the molecular weight is preferably 1000-3000 g / mol. The second carboxylic acid monomer is one or an arbitrary proportion combination of acrylic acid and methacrylic acid. The sulfonic acid monomer is one or more than two arbitrary proportion combinations of 2-acrylamide-2-methylpropanesulfonic acid, sodium p-styrenesulfonate and sodium allylsulfonate. The crosslinking agent is the above-prepared divinyl carboxylic acid-β-cyclodextrin diester. The initiator is one or more than one of ammonium persulfate, sodium persulfate and potassium persulfate, and the amount is 1-4%, preferably 3%, of the total mass of the polyether macromonomer, second carboxylic acid monomer and sulfonic acid monomer. The chain transfer agent is one or more than one of sodium hypophosphite, sodium methacrylate sulfonate and mercaptoacetic acid, and the amount is 0.5-3%, preferably 1%, of the total mass of the polyether macromonomer, second carboxylic acid monomer and sulfonic acid monomer.

[0046] Specifically, the preparation method of the micro-crosslinking polycarboxylic acid dispersant comprises the following steps:

[0047] ​Step S1. The polyether macro-monomer solution is added to the reaction vessel as a bottom solution before the reaction starts. The cross-linking agent, the second carboxylic acid monomer, the sulfonic acid monomer and the chain transfer agent are mixed to form a mixed solution.

[0048] Step S2. The mixed solution and the initiator solution are added to the reaction vessel in a dropwise manner for polymerization. In this way, the conversion rate of all monomers is improved, the solid content is controlled at 30-50wt% during the whole reaction process, the reaction temperature is controlled at 60-75℃, the dropwise time of the mixed solution of the second carboxylic acid monomer, the sulfonic acid monomer and the chain transfer agent and the initiator solution is 3-4h and 3.5-4.5h respectively, and the dropwise time of the initiator solution must be greater than that of the mixed solution of the second carboxylic acid monomer, the sulfonic acid monomer and the chain transfer agent, and the aging time after the completion of the dropwise addition of the initiator solution is 0.5-1h, and the total polymerization time is controlled at 4h-8h.

[0049] Step S3. After the polymerization reaction is completed, the reaction product is cooled to room temperature, and one or more of sodium hydroxide, potassium hydroxide and calcium hydroxide is added to adjust the pH value to 6-8.

[0050] The structure of the prepared dispersant is shown in Formula II:

[0051]

[0052] wherein R1 is H or COOH, R2 is H or CH3, R3 is a sulfonic acid group; n represents the polymerization degree: n=20-60; a, b, c represent the molar ratio of monomers: a:b:c=1:(1-2):(3-5).

[0053] Example 2

[0054] A micro-cross-linked polycarboxylic acid dispersant is prepared, including the following steps:

[0055] (1) A cross-linking agent, i.e. divinyl carboxylic acid-β-cyclodextrin diester, is prepared.

[0056] The raw materials for preparing the cross-linking agent include β-cyclodextrin, N,N-dimethylformamide solvent, first carboxylic acid monomer, catalyst and polymerization inhibitor. The first carboxylic acid monomer is maleic anhydride, the catalyst is p-toluenesulfonic acid, and the polymerization inhibitor is hydroquinone.

[0057] In a reaction vessel, 1135 parts of β-cyclodextrin and 4540 parts of N,N-dimethylformamide solvent were weighed in, protected by nitrogen, stirred evenly and heated to 70℃, 206 parts of maleic anhydride, 34 parts of p-toluenesulfonic acid and 4.1 parts of hydroquinone were added in turn, stirred evenly and heated to 130℃, kept constant for 10h, then cooled to 80℃, distilled under reduced pressure until no liquid was distilled out, and then the remaining product was cooled to room temperature to obtain the crosslinking agent divinyl carboxylic acid-β-cyclodextrin diester.

[0058] (2) Preparation of dispersant.

[0059] The raw materials for preparing the dispersant include polyether macromonomer, second carboxylic acid monomer, sulfonic acid monomer, crosslinking agent, initiator and chain transfer agent. The polyether macromonomer is isobutenyl alcohol polyethylene glycol ether, the second carboxylic acid monomer is acrylic acid, the sulfonic acid monomer is 2-acrylamide-2-methylpropane sulfonic acid, the crosslinking agent is the divinyl carboxylic acid-β-cyclodextrin diester prepared in step (1) above, the initiator is ammonium persulfate, and the chain transfer agent is mercaptoacetic acid.

[0060] In parts by weight, 3000 parts of isobutenyl alcohol polyethylene glycol ether (M w = 3000 g / mol) was dissolved in 5250 parts of water to form a bottom liquid in a reaction vessel, 144 parts of acrylic acid, 828 parts of 2-acrylamide-2-methylpropane sulfonic acid, 93.5 parts of crosslinking agent and 119 parts of mercaptoacetic acid were dissolved in 2500 parts of water to form A liquid for standby, 159 parts of ammonium persulfate was dissolved in 1500 parts of water to form B liquid for standby, nitrogen was introduced into the reaction vessel for protection, continuous stirring and heating to 75℃, A liquid and B liquid were added to the reaction vessel in the form of drop, the drop time was 4h and 4.5h respectively, after the drop was completed, it was continued to be aged for 1h and then cooled to room temperature, the pH was adjusted to 8 with sodium hydroxide, and a micro-crosslinked polycarboxylic acid dispersant was obtained.

[0061] Example 3

[0062] A micro-crosslinked polycarboxylic acid dispersant was prepared, including the following steps:

[0063] (1) Preparation of crosslinking agent, i.e. divinyl carboxylic acid-β-cyclodextrin diester.

[0064] The raw materials for preparing the crosslinking agent include β-cyclodextrin, N,N-dimethylformamide solvent, first carboxylic acid monomer, catalyst and polymerization inhibitor. Among them, the first carboxylic acid monomer is fumaric acid, the catalyst is benzenesulfonic acid, and the polymerization inhibitor is p-tert-butyl hydroquinone.

[0065] In a reaction vessel, 1135 parts of β-cyclodextrin and 3405 parts of N,N-dimethylformamide solvent were weighed out, nitrogen was introduced for protection, and the mixture was stirred and heated to 60°C. Then 238 parts of fumaric acid, 5.7 parts of benzene sulfonic acid and 1.2 parts of p-tert-butyl o-phenylenediamine were added in sequence, the mixture was stirred and heated to 90°C, and kept at this temperature for 15 hours. Then the temperature was lowered to 70°C, and the solvent was distilled off under reduced pressure until no liquid was left. The remaining product was cooled to room temperature to obtain the crosslinking agent, divinyl carboxylic acid-β-cyclodextrin diester.

[0066] (2) Preparation of the dispersant.

[0067] The raw materials for preparing the dispersant include polyether macromonomer, second carboxylic acid monomer, sulfonic acid monomer, crosslinking agent, initiator and chain transfer agent. The polyether macromonomer is iso-pentenyl alcohol polyethylene glycol ether, the second carboxylic acid monomer is methacrylic acid, the sulfonic acid monomer is sodium p-styrenesulfonate, the crosslinking agent is the divinyl carboxylic acid-β-cyclodextrin diester prepared in step (1) above, the initiator is potassium persulfate, and the chain transfer agent is sodium hypophosphite.

[0068] In a reaction vessel, 1000 parts of iso-pentenyl alcohol polyethylene glycol ether (M w = 1000 g / mol) was dissolved in 9000 parts of water to form a bottom liquid. 86 parts of methacrylic acid, 618 parts of sodium p-styrenesulfonate, 34 parts of the crosslinking agent prepared in (1) and 8.5 parts of sodium hypophosphite were dissolved in 700 parts of water to form A liquid. 17 parts of potassium persulfate was dissolved in 100 parts of water to form B liquid. Nitrogen was introduced into the reaction vessel for protection, and the mixture was continuously stirred and heated to 60°C. A and B liquids were added dropwise into the reaction vessel, and the dropwise time was 3 hours and 3.5 hours, respectively. After the addition was completed, the mixture was kept at the same temperature for 0.5 hours, and then cooled to room temperature. The pH was adjusted to 6 with potassium hydroxide to obtain a micro-crosslinked polycarboxylic acid dispersant.

[0069] Example 4

[0070] A micro-crosslinked polycarboxylic acid dispersant was prepared by the following steps.

[0071] (1) Preparation of the crosslinking agent, divinyl carboxylic acid-β-cyclodextrin diester.

[0072] The raw materials for preparing the crosslinking agent include β-cyclodextrin, N,N-dimethylformamide solvent, first carboxylic acid monomer, catalyst and polymerization inhibitor. The first carboxylic acid monomer is acrylic acid, the catalyst is p-toluenesulfonic acid, and the polymerization inhibitor is p-benzoquinone.

[0073] Into a reaction vessel, 1135 parts of β-cyclodextrin and 3973 parts of N,N-dimethylformamide solvent were weighed out, and nitrogen was introduced for protection. After being uniformly stirred, the mixture was heated to 70°C. Then, 151 parts of acrylic acid, 22.7 parts of p-toluenesulfonic acid and 1.5 parts of p-benzoquinone were sequentially added. After being uniformly stirred and heated to 100°C, the temperature was kept constant for 12 hours. Then, the temperature was reduced to 70°C. The solvent was distilled off under reduced pressure until no liquid was distilled off. After being cooled to room temperature, the remaining product was the crosslinking agent divinyl carboxylic acid-β-cyclodextrin diester.

[0074] (2) Preparation of the dispersant.

[0075] The raw materials for preparing the dispersant include a polyether macro-monomer, a second carboxylic acid monomer, a sulfonic acid monomer, a crosslinking agent, an initiator and a chain transfer agent. The polyether macro-monomer is ethylene glycol mono-vinyl polyethylene glycol ether, the second carboxylic acid monomer is methacrylic acid, the sulfonic acid monomer is sodium allyl sulfonate, the crosslinking agent is the divinyl carboxylic acid-β-cyclodextrin diester prepared in step (1) above, the initiator is sodium persulfate, and the chain transfer agent is sodium methacryl sulfonate.

[0076] Into a reaction vessel, 2000 parts of isopentenyl alcohol polyethylene glycol ether (M w = 2000 g / mol) was dissolved in 2100 parts of water to form a bottom liquid. 172 parts of methacrylic acid, 432 parts of sodium allyl sulfonate, 38.6 parts of the crosslinking agent divinyl carboxylic acid-β-cyclodextrin diester prepared in step (1) and 28 parts of sodium methacryl sulfonate were dissolved in 1000 parts of water to form A liquid. 84 parts of sodium persulfate was dissolved in 800 parts of water to form B liquid. Nitrogen was introduced into the reaction vessel for protection. After being continuously stirred and heated to 70°C, A liquid and B liquid were added dropwise to the reaction vessel. The dropwise time was 4 hours and 4.5 hours, respectively. After the addition was completed, the mixture was aged for 0.5 hours at constant temperature, and then cooled to room temperature. The pH was adjusted to 7 with calcium hydroxide to obtain a micro-crosslinked polycarboxylic acid dispersant.

[0077] Comparative Example 1

[0078] A sulfonated acetone-formaldehyde polycondensate dispersant commonly used in oil well cement, which is a red-brown solid powder, was provided by Sichuanqing Drilling Engineering Co., Ltd.

[0079] Comparative Example 2

[0080] A conventional polycarboxylic acid water reducing agent for concrete, which is a gray-white solid powder, was purchased from Shandong Yousuo Chemical Technology Co., Ltd.

[0081] The drawings enclosed with the specification Figure 1The thermogravimetric curve of the micro-crosslinking polycarboxylic acid dispersant prepared in Example 2 is shown in the figure. As can be seen from the figure, the micro-crosslinking polycarboxylic acid has a high thermal decomposition temperature, and the polymer mass remains stable below 300°C. The critical temperature of thermal decomposition is about 312°C, and the polymer rapidly dissociates above 404°C. Therefore, the micro-crosslinking polycarboxylic acid dispersant has strong temperature resistance.

[0082] The preparation of the oil well cement slurry and the performance test method of the dispersant were tested according to GB / T 19139-2012 “Oil Well Cement Test Method” and SYT 5504.3-2018 “Oil Well Cement Admixture Evaluation Method Part 3: Drag Reducing Agent”, respectively. The test results of the rheological properties, thickening time and compressive strength of the examples and comparative examples are shown in Table 1.

[0083] Table 1 Performance test results of different dispersants

[0084]

[0085] Note: The oil well cement slurry formula: Ji Hua G-grade oil well cement + 0.5% bwoc dispersant, water-cement ratio 0.44, %bwoc represents the mass percentage of cement.

[0086] In Table 1, the ratio of thickening time and the ratio of compressive strength are compared with the cement neat slurry. The addition of the dispersant will cause the cement slurry to extend the thickening time to different degrees. The conventional polycarboxylic acid water reducing agent shows a great extension of the thickening time, thereby causing a large decrease in early strength. The micro-crosslinking polycarboxylic acid dispersant of the present application shows a slightly longer thickening time than the sulfonated aldehyde ketone polycondensate, between 1.67 and 1.82 times, but all meet the technical index in the oil and gas industry standard SY / T5504.3-2018, not more than 2 times. The 24h compressive strength of the micro-crosslinking polycarboxylic acid dispersant of the present application is equivalent to that of the sulfonated aldehyde ketone polycondensate, without strong retardation and low early strength. The micro-crosslinking polycarboxylic acid dispersant of the present application shows lower initial consistency and better rheological properties. This is because the steric hindrance of β-cyclodextrin makes the polymer molecules in the solution more easily stretched than the conventional polycarboxylic acid dispersant, adsorbed on the cement particles to produce a larger adsorption layer thickness, thereby having better dispersing performance.

[0087] High temperature and high pressure thickening tests were carried out on Example 2 at 120°C and 140°C. The cement slurry formula was: 70% Ji Hua G-grade cement + 30% silica sand + 5% fluid loss reducer SD130 + 2% retarder SD210 + 0.5% Example 2, water-cement ratio 0.44. The thickening curves of the cement slurry doped with Example 2 at 120°C and 140°C are shown in Figures 1 and 2 of the specification, respectively. Figure 2 and Figure 2 of the specification Figure 3As shown, the initial consistency of both is low, and the thickening linear is stable, no "bulge" occurs, almost "right angle" thickening, no thickening time reversal occurs, therefore, the micro-crosslinking polycarboxylic dispersant is suitable for the medium-high temperature cement slurry system.

[0088] In summary, the person skilled in the art reads the present application file, and according to the technical scheme and technical concept of the present application, various corresponding transformation schemes without creative mental labor are made, which belong to the protection range of the present application.

Claims

1. A micro-crosslinking polycarboxylic dispersant, characterized by: The preparation raw materials of the crosslinking agent include a polyether macro-monomer, a second carboxylic acid monomer, a sulfonic acid monomer, an initiator and a chain transfer agent; the molar ratio of (the polyether macro-monomer + the second carboxylic acid monomer + the sulfonic acid monomer) to the crosslinking agent is 100: (0.5-1.0), and the molar ratio of the polyether macro-monomer, the second carboxylic acid monomer and the sulfonic acid monomer is 1: (1-2): (3-4); The crosslinking agent is a divinyl carboxylic acid-beta-cyclodextrin diester, and the preparation raw materials of the crosslinking agent include beta-cyclodextrin, N,N-dimethylformamide solvent, a first carboxylic acid monomer, a catalyst and a polymerization inhibitor; the mass ratio of the beta-cyclodextrin to the N,N-dimethylformamide solvent is 1: (3-4), and the molar ratio of the beta-cyclodextrin to the first carboxylic acid monomer is 1: (2.05-2.10); the structural general formula of the crosslinking agent is shown as formula I: In the formula, R1 is H or COOH. The structural general formula of the dispersant is shown as formula II: In the formula, R1 is H or COOH, R2 is H or CH3, R3 is a sulfonic acid group, n represents a polymerization degree: n = 20-60, and a, b and c represent molar proportions of monomers: a:b:c = 1: (1-2): (3-5).

2. The micro-crosslinking polycarboxylic dispersant according to claim 1, characterized in that: The amount of the catalyst is 0.5-3% of the mass of the beta-cyclodextrin, and the amount of the polymerization inhibitor is 0.5-2% of the mass of the first carboxylic acid monomer.

3. The micro-crosslinking polycarboxylic dispersant according to claim 1 or 2, characterized in that: The method comprises the following steps: Under the protection of nitrogen, the beta-cyclodextrin is completely dissolved in the N,N-dimethylformamide solvent, the temperature is raised to 60-70 DEG C, the first carboxylic acid monomer, the catalyst and the polymerization inhibitor are added, the temperature is then raised to 90-130 DEG C, and then the temperature is kept constant for 10-15 h for sufficient esterification reaction, and then the temperature is reduced to 70-80 DEG C, and the solvent is distilled out under reduced pressure to obtain the crosslinking agent, i.e., the divinyl carboxylic acid-beta-cyclodextrin diester.

4. The micro-crosslinking polycarboxylic dispersant according to claim 1, characterized in that: The polyether macro-monomer is one or more of isobutenol polyethylene glycol ether, isoamylenol polyethylene glycol ether and ethylene glycol monovinyl polyethylene glycol ether, and the molecular weight is 1000-3000 g / mol.

5. The micro-crosslinking polycarboxylic dispersant according to claim 1, characterized in that: The sulfonic acid monomer is one or more of 2-acrylamide-2-methylpropane sulfonic acid, p-styrene sulfonic acid sodium and allyl sulfonic acid sodium.

6. The micro-crosslinking polycarboxylic dispersant according to claim 1, characterized in that: The amount of the initiator is 1-4% of the total mass of the polyether macro-monomer, the second carboxylic acid monomer and the sulfonic acid monomer, and the amount of the chain transfer agent is 0.5-3% of the total mass of the polyether macro-monomer, the second carboxylic acid monomer and the sulfonic acid monomer.

7. The method according to claim 1, characterized in that: The method comprises the following steps: Step S1. The polyether macro-monomer solution is used as a bottom liquid; the crosslinking agent, the second carboxylic acid monomer, the sulfonic acid monomer and the chain transfer agent are mixed to form a mixed solution; Step S2. The mixed solution and the initiator solution are added into the bottom liquid in a dropwise form for polymerization reaction; Step S3. After the polymerization reaction is completed, the temperature is cooled to room temperature, and the pH value is adjusted to 6-8.

8. The method according to claim 7, characterized in that: In the step S2, during the polymerization reaction, the solid content is controlled to be 30-50 wt%, and the reaction temperature is controlled to be 60-75 DEG C.

9. The method according to claim 7, characterized in that: In the step S2, the dropwise adding time of the mixed solution is 3-4 h, the dropwise adding time of the initiator solution is 3.5-4.5 h, and the dropwise adding time of the initiator solution is longer than that of the mixed solution.

10. The method according to claim 9, characterized in that: In the step S2, after the dropwise adding of the initiator solution is completed, the temperature is kept constant for 0.5-1 h for aging. In the step S2, after the dropwise adding of the initiator solution is completed, the temperature is kept constant for 0.5-1 h for aging.

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