A heat-resistant oil well cement fluid loss additive and its preparation method

Abstract

The invention relates to the technical field of cementing for oil and gas well development, and discloses a temperature-resistant oil well cement fluid loss additive and a preparation method thereof. The fluid loss additive is prepared by initiating polymerization of 50-65 parts of acrylamide, 10-15 parts of N,N-dimethylacrylamide, 5-8 parts of polyethylene glycol monomethyl ether acrylate, and 2-10 parts of alkenyl naphthalene organosilicon monomers. The alkenyl naphthalene organosilicon monomers contain rigid naphthalene rings and siloxane structures, and are capable of withstanding high temperatures without being easily deformed or decomposed. Multiple carboxyl and sulfonic acid groups can be adsorbed on cement particles through electrostatic action to block pores of the cement particles. The introduced long side chain structure can form effective steric hindrance to prevent flocculation and precipitation between cement particles. The fluid loss additive has good water loss control capabilities and the ability to improve the rheological properties of cement slurry, can significantly reduce the water loss of cement slurry during oil and gas drilling and cementing, and has a wide range of applications.

Description

Technical Field

[0001] The invention relates to the technical field of well cementing for oil and gas well development, in particular to a temperature-resistant oil well cement fluid loss additive and a preparation method thereof. Background Art

[0002] In the exploration and development of energy resources such as oil and natural gas, oil well cementing operations are a critical step in ensuring wellbore stability and improving oil and gas recovery rates. However, during the cementing process, the cement slurry often loses water due to pressure differentials. This means that free water in the cement slurry filters out through the permeable formation and enters the formation. This water loss not only reduces the fluidity and thickening time of the cement slurry, but in severe cases can even cause the cement slurry to lose pumping capacity, resulting in cementing failure. It can also damage the oil and gas formations, hindering the effective development of oil and gas resources. To address these issues, the industry widely uses oil well cement fluid loss additives. The main function of fluid loss additives is to reduce the water loss of cement slurry, thereby protecting water-sensitive formations, improving cementing operations, ensuring construction safety, and preventing oil and gas formation contamination.

[0003] Traditional oil well cement fluid loss additives are mostly copolymers made from monomers such as acrylamide, acrylic acid, and 2-acrylamide-2-methylpropanesulfonic acid. However, during cementing operations in deep wells, ultra-deep wells, and wells with abnormal geothermal gradients, these fluid loss additives can experience hydrolysis or molecular chain scission as bottomhole temperatures rise (150°C and above). This significantly increases the water loss of the cement slurry, making it difficult to meet the demands of high-temperature deep well cementing operations. Furthermore, due to poor dispersibility, the cement slurry tends to thicken during the cement mixing process, exhibiting strong thixotropy and hindering on-site construction. Natural polymer-modified fluid loss additives (such as cellulose, starch, and lignin) experience side chain substituent disconnection and functional group detachment under high temperature conditions, resulting in the fluid loss additive failure.

[0004] Patent No. CN100355854C discloses a dispersed fluid loss additive for oilfield cementing and a preparation method thereof. The dispersed fluid loss additive has a highly efficient fluid loss reduction effect, low free water content, good fluidity, a wide applicable temperature range (20-120°C), and is suitable for different types of oil well cements. However, the main component of the fluid loss additive is a cross-linked polyvinyl alcohol polymer. Due to the use of polyvinyl alcohol, the fluid loss additive has poor high temperature and salt resistance. Patent No. CN102191027B discloses a high-temperature resistant dispersed oil well cement fluid loss additive and a preparation method thereof. The additive comprises monomers such as 2-acrylamido-2-methylpropanesulfonic acid, N,N-dimethylacrylamide, acrylamide, and maleic anhydride. Although the addition of maleic anhydride can further enhance the dispersibility of the fluid loss additive and improve the rheological properties of the cement slurry, it does not solve the problem of easy hydrolysis at high temperatures. Furthermore, the additive has problems such as a complex preparation process, high cost, and a limited scope of application.

[0005] In summary, the present invention aims to synthesize a monomer that is resistant to high temperatures and has good dispersibility, and introduce it into a fluid loss additive to solve the problems of oil well cement fluid loss additives in the prior art, such as performance degradation and poor dispersibility under high temperature conditions. Summary of the Invention

[0006] The present invention aims to overcome the shortcomings of the prior art and provides a temperature-resistant oil well cement fluid loss additive and a preparation method thereof, thereby solving the problems of the prior art oil well cement fluid loss additive in terms of performance degradation and poor dispersion performance under high temperature conditions.

[0007] To achieve the above object, the technical solution adopted by the present invention is:

[0008] A method for preparing a heat-resistant oil well cement fluid loss additive is carried out according to the following steps:

[0009] Step (1): Add vinyl naphthyl organosilicon polyamine monomer and N,N-dimethylformamide to a reaction flask under a nitrogen atmosphere, stir evenly, add 16-bromohexadecanoic acid and triethylamine, stir and react, extract with ethyl acetate and deionized water after the reaction is completed, concentrate the organic phase, and separate by column chromatography (silica gel, 10% methanol in dichloromethane) to obtain vinyl naphthalene organosilicon monomer.

[0010] Step (2), under a nitrogen atmosphere, dissolving 50-65 parts of acrylamide, 10-15 parts of N,N-dimethylacrylamide, 5-8 parts of polyethylene glycol monomethyl ether acrylate and 2-10 parts of alkenylnaphthalene organosilicon monomer by weight in deionized water, adjusting the pH with an aqueous sodium hydroxide solution, introducing nitrogen, heating to 60-80° C., adding dropwise 0.5-0.8 parts of an initiator, continuing the reaction for 2-5 hours, and naturally cooling to room temperature to obtain a temperature-resistant oil well cement fluid loss additive.

[0011] Preferably, in step (1), the molar ratio of the vinyl naphthyl organosilicon polyamine monomer, 16-bromohexadecanoic acid, and triethylamine is 1:4.2-5:4.5-6.

[0012] Preferably, the reaction temperature in step (1) is 60-80°C and the reaction time is 12-24h.

[0013] Preferably, the initiator in step (2) is any one of ammonium persulfate, benzoyl peroxide or azobisisobutyronitrile.

[0014] Preferably, the pH in step (2) is adjusted to 6-8.

[0015] Preferably, the preparation method of the vinyl naphthyl organosilicon polyamine monomer in step (1) is carried out according to the following steps:

[0016] Step S1: Under a nitrogen atmosphere, methylvinyldichlorosilane and toluene were added to a reaction flask, and after stirring, 6-hydroxy-2-naphthaldehyde and sodium hydride were added, and the mixture was stirred for reaction. After the reaction was completed, the mixture was filtered, the organic layer was washed with saturated brine, and the organic layer was separated by column chromatography (silica gel, 20% ethyl acetate in n-heptane), and dried to obtain a vinylnaphthyl organosilicon dialdehyde monomer.

[0017] Step S2: Under a nitrogen atmosphere, add 2-[(2-aminoethyl)amino]ethanesulfonic acid sodium salt and methanol to a reaction flask, stir evenly, add vinyl naphthyl organosilicon dialdehyde monomer, stir at 20-35° C. for 2-5 hours, then add sodium cyanoborohydride, react at room temperature for 12-18 hours, filter, concentrate under reduced pressure, separate by column chromatography (silica gel, 5% methanol in dichloromethane), and dry to obtain vinyl naphthyl organosilicon polyamine monomer.

[0018] Preferably, in step S1, the molar ratio of methylvinyldichlorosilane, 6-hydroxy-2-naphthaldehyde, and sodium hydride is 1:2.05-2.2:2.3-2.5.

[0019] Preferably, the reaction temperature in step S1 is 90-110° C., and the reaction time is 5-10 h.

[0020] Preferably, in step S2, the molar ratio of 2-[(2-aminoethyl)amino]ethanesulfonic acid sodium salt, vinylnaphthyl organosilicon dialdehyde monomer, and sodium cyanoborohydride is 2.1-2.3:1:2.5-3.5.

[0021] By adopting the above technical solution, the beneficial effects of the present invention are:

[0022] (1) Excellent high temperature resistance: The naphthalene ring in the fluid loss agent prepared by the present invention has a stable aromatic ring structure and is not easy to rotate. Its rigid structure can withstand high temperatures without deformation or decomposition, which helps the fluid loss agent maintain its original performance and form at high temperatures and can significantly improve the thermal stability of the fluid loss agent; Siloxane has high bond energy and excellent heat resistance, and can maintain stable chemical properties at high temperatures. At the same time, siloxane has the characteristic of not being wetted by water, which helps the fluid loss agent reduce the influence of water molecules at high temperatures, so that it can still maintain stable performance in high temperature and high humidity environments. The two synergistically play a high temperature resistance role; the multiple carboxylic acid and sulfonic acid groups introduced in the fluid loss agent, after dissolving in water, ionize to generate anions such as sulfonate and carboxylate, which are adsorbed on cement particles through electrostatic action and promote the extension of the polymer chain of the fluid loss agent. The molecular chain does not break in alkaline cement slurry at high temperatures, and the groups do not fall off, and the fluid loss agent has excellent high temperature resistance.

[0023] (2) Good dispersibility: The fluid loss reducer prepared by the present invention introduces multiple carboxylic acid and sulfonic acid groups. After dissolving in water, it ionizes to generate anions such as sulfonate and carboxylate, which are adsorbed on cement particles through electrostatic action, blocking the pores of cement particles, making the cement filter cake dense and compact, enhancing the binding force between the fluid loss reducer and cement particles, and preventing the agglomeration and sedimentation of cement particles. It helps to form a hydration layer through hydration. When the fluid loss reducer molecules are adsorbed on the surface of cement particles, these hydration layers can reduce the friction between cement particles and further promote the dispersion of cement slurry. At the same time, the introduced polyethylene glycol alkyl and hexadecyl long side chain structures can form an effective steric hindrance in a relatively extended conformation to prevent flocculation and precipitation between cement particles, forming a protective layer of a certain thickness and effective steric hindrance on the surface of cement particles, thereby effectively preventing close contact and agglomeration of cement particles, thereby making the cement highly dispersed.

[0024] (3) Wide range of applications: The fluid loss reducer of the present invention can effectively reduce the water loss of oil well cement slurry while increasing its temperature and salt resistance. It can be used for cementing operations in ordinary formations and salt layers and salt water layers, as well as deep wells, ultra-deep wells, and wells with abnormal geothermal gradients. The synthesis method is simple and easy to operate, and the raw materials are reasonably priced and readily available, making it easy to promote in industry. DETAILED DESCRIPTION

[0025] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0026] Unless otherwise stated, the raw materials and reagents used in this application are commercially available or can be prepared by known methods.

[0027] Methylvinyldichlorosilane, CAS number 124-70-9.

[0028] 6-Hydroxy-2-naphthaldehyde, CAS number is 78119-82-1.

[0029] 2-[(2-Aminoethyl)amino]ethanesulfonic acid sodium salt 34730-59-1.

[0030] 16-Bromohexadecanoic acid, CAS number 2536-35-8.

[0031] Polyethylene glycol monomethyl ether acrylate, CAS number 32171-39-4.

[0032] Example 1

[0033] (1) Under nitrogen atmosphere, add 30 mmol of methylvinyldichlorosilane and 120 mL of toluene to a reaction flask, stir evenly, then add 63.6 mmol of 6-hydroxy-2-naphthaldehyde and 72 mmol of sodium hydride, react at 100°C for 8 h, filter, wash the organic layer with saturated brine, separate by column chromatography (silica gel, 20% ethyl acetate in n-heptane), and dry to obtain vinylnaphthyl organosilicon dialdehyde monomer. The preparation reaction formula is as follows:

[0034] (2) Under nitrogen atmosphere, add 55 mmol of 2-[(2-aminoethyl)amino]ethanesulfonic acid sodium salt and 200 mL of methanol to the reaction flask, stir evenly, then add 25 mmol of vinyl naphthyl organosilicon dialdehyde monomer, stir at 25°C for 3 h, then add 75 mmol of sodium cyanoborohydride, react at room temperature for 15 h, filter, concentrate under reduced pressure, separate by column chromatography (silica gel, 5% methanol in dichloromethane), and dry to obtain vinyl naphthyl organosilicon polyamine monomer. The preparation reaction formula is as follows:

[0035] (3) Under nitrogen atmosphere, add 20 mmol of vinyl naphthyl organosilicon polyamine monomer and 270 mL of N,N-dimethylformamide to the reaction flask, stir evenly, add 90 mmol of 16-bromohexadecanoic acid and 104 mmol of triethylamine, react at 70°C for 15 h, extract with ethyl acetate and deionized water, concentrate the organic phase, and separate by column chromatography (silica gel, 10% methanol in dichloromethane) to obtain vinyl naphthalene organosilicon monomer. The preparation reaction formula is as follows:

[0036] (4) Under nitrogen atmosphere, 65 g acrylamide, 12 g N,N-dimethylacrylamide, 5 g polyethylene glycol monomethyl ether acrylate and 2 g alkenylnaphthalene organosilicon monomer were dissolved in deionized water, the pH was adjusted to 7 with a 30% by mass sodium hydroxide aqueous solution, nitrogen was introduced, the mixture was heated to 70 °C, 0.6 g ammonium persulfate was added dropwise, the reaction was continued for 4 h, and the mixture was naturally cooled to room temperature to obtain a heat-resistant oil well cement fluid loss reducer.

[0037] Example 2

[0038] (1) Under nitrogen atmosphere, 80 mmol of methylvinyldichlorosilane and 240 mL of toluene were added to a reaction flask. After stirring evenly, 164 mmol of 6-hydroxy-2-naphthaldehyde and 184 mmol of sodium hydride were added. The mixture was reacted at 110 °C for 5 h. The mixture was filtered, and the organic layer was washed with saturated brine. The mixture was separated by column chromatography (silica gel, 20% ethyl acetate in n-heptane) and dried to obtain a vinylnaphthyl organosilicon dialdehyde monomer.

[0039] (2) Under nitrogen atmosphere, 147 mmol of 2-[(2-aminoethyl)amino]ethanesulfonic acid sodium salt and 420 mL of methanol were added to the reaction flask. After stirring evenly, 70 mmol of vinyl naphthyl organosilicon dialdehyde monomer was added and stirred at 35 °C for 2 h. Then, 175 mmol of sodium cyanoborohydride was added and reacted at room temperature for 18 h. The mixture was filtered, concentrated under reduced pressure, and separated by column chromatography (silica gel, 5% methanol in dichloromethane). After drying, the vinyl naphthyl organosilicon polyamine monomer was obtained.

[0040] (3) Under nitrogen atmosphere, 60 mmol of vinyl naphthyl organosilicon polyamine monomer and 720 mL of N,N-dimethylformamide were added to the reaction flask. After stirring evenly, 252 mmol of 16-bromohexadecanoic acid and 270 mmol of triethylamine were added. The mixture was reacted at 80 °C for 124 h. The mixture was extracted with ethyl acetate and deionized water. The organic phase was concentrated and separated by column chromatography (silica gel, 10% methanol in dichloromethane) to obtain vinyl naphthalene organosilicon monomer.

[0041] (4) Under nitrogen atmosphere, 60 g acrylamide, 10 g N,N-dimethylacrylamide, 6 g polyethylene glycol monomethyl ether acrylate and 4 g alkenylnaphthalene organosilicon monomer were dissolved in deionized water, the pH was adjusted to 6 with a 30% by mass sodium hydroxide aqueous solution, nitrogen was introduced, the mixture was heated to 80 °C, 0.5 g benzoyl peroxide was added dropwise, the reaction was continued for 2 h, and the mixture was naturally cooled to room temperature to obtain a heat-resistant oil well cement fluid loss reducer.

[0042] Example 3

[0043] (1) Under nitrogen atmosphere, 18 mmol of methylvinyldichlorosilane and 90 mL of toluene were added to a reaction flask. After stirring, 39.6 mmol of 6-hydroxy-2-naphthaldehyde and 45 mmol of sodium hydride were added. The mixture was reacted at 90 °C for 10 h. The mixture was filtered, and the organic layer was washed with saturated brine. The mixture was separated by column chromatography (silica gel, 20% ethyl acetate in n-heptane) and dried to obtain a vinylnaphthyl organosilicon dialdehyde monomer.

[0044] (2) Under nitrogen atmosphere, 34.5 mmol of 2-[(2-aminoethyl)amino]ethanesulfonic acid sodium salt and 150 mL of methanol were added to the reaction flask. After stirring evenly, 15 mmol of vinyl naphthyl organosilicon dialdehyde monomer was added. The mixture was stirred at 20°C for 5 h. Then, 52.5 mmol of sodium cyanoborohydride was added. The mixture was reacted at room temperature for 18 h. The mixture was filtered, concentrated under reduced pressure, and separated by column chromatography (silica gel, 5% methanol in dichloromethane). After drying, the vinyl naphthyl organosilicon polyamine monomer was obtained.

[0045] (3) Under nitrogen atmosphere, 12 mmol of vinylnaphthyl organosilicon polyamine monomer and 180 mL of N,N-dimethylformamide were added to the reaction flask. After stirring evenly, 60 mmol of 16-bromohexadecanoic acid and 72 mmol of triethylamine were added. The mixture was reacted at 60 °C for 24 h. The mixture was extracted with ethyl acetate and deionized water. The organic phase was concentrated and separated by column chromatography (silica gel, 10% methanol in dichloromethane) to obtain vinylnaphthalene organosilicon monomer.

[0046] (4) Under nitrogen atmosphere, 58 g acrylamide, 12 g N,N-dimethylacrylamide, 7 g polyethylene glycol monomethyl ether acrylate and 6 g alkenylnaphthalene organosilicon monomer were dissolved in deionized water, the pH was adjusted to 8 with a 30% by mass sodium hydroxide aqueous solution, nitrogen was introduced, the mixture was heated to 60 °C, 0.8 g azobisisobutyronitrile was added dropwise, the reaction was continued for 5 h, and the mixture was naturally cooled to room temperature to obtain a temperature-resistant oil well cement fluid loss reducer.

[0047] Example 4

[0048] (1) Under nitrogen atmosphere, 45 mmol of methylvinyldichlorosilane and 172 mL of toluene were added to a reaction flask. After stirring, 95.4 mmol of 6-hydroxy-2-naphthaldehyde and 106.5 mmol of sodium hydride were added. The mixture was reacted at 105 °C for 9 h. The mixture was filtered, and the organic layer was washed with saturated brine. The mixture was separated by column chromatography (silica gel, 20% ethyl acetate in n-heptane) and dried to obtain a vinylnaphthyl organosilicon dialdehyde monomer.

[0049] (2) Under nitrogen atmosphere, 90 mmol of 2-[(2-aminoethyl)amino]ethanesulfonic acid sodium salt and 340 mL of methanol were added to the reaction flask. After stirring evenly, 40 mmol of vinyl naphthyl organosilicon dialdehyde monomer was added and stirred at 30 °C for 5 h. Then, 130 mmol of sodium cyanoborohydride was added and reacted at room temperature for 16 h. The mixture was filtered, concentrated under reduced pressure, and separated by column chromatography (silica gel, 5% methanol in dichloromethane). After drying, the vinyl naphthyl organosilicon polyamine monomer was obtained.

[0050] (3) Under nitrogen atmosphere, 35 mmol of vinylnaphthyl organosilicon polyamine monomer and 450 mL of N,N-dimethylformamide were added to the reaction flask. After stirring evenly, 162 mmol of 16-bromohexadecanoic acid and 196 mmol of triethylamine were added. The mixture was reacted at 75 °C for 15 h. The mixture was extracted with ethyl acetate and deionized water. The organic phase was concentrated and separated by column chromatography (silica gel, 10% methanol in dichloromethane) to obtain vinylnaphthalene organosilicon monomer.

[0051] (4) Under nitrogen atmosphere, 55 g acrylamide, 14 g N,N-dimethylacrylamide, 8 g polyethylene glycol monomethyl ether acrylate and 8 g alkenylnaphthalene organosilicon monomer were dissolved in deionized water, the pH was adjusted to 7 with a 30% by mass sodium hydroxide aqueous solution, nitrogen was introduced, the mixture was heated to 65 °C, 0.7 g ammonium persulfate was added dropwise, the reaction was continued for 4 h, and the mixture was naturally cooled to room temperature to obtain a heat-resistant oil well cement fluid loss reducer.

[0052] Example 5

[0053] (1) Under nitrogen atmosphere, 25 mmol of methylvinyldichlorosilane and 120 mL of toluene were added to a reaction flask. After stirring, 53.5 mol of 6-hydroxy-2-naphthaldehyde and 60.5 mmol of sodium hydride were added. The mixture was reacted at 95 °C for 10 h. The mixture was filtered, and the organic layer was washed with saturated brine. The mixture was separated by column chromatography (silica gel, 20% ethyl acetate in n-heptane) and dried to obtain a vinylnaphthyl organosilicon dialdehyde monomer.

[0054] (2) Under nitrogen atmosphere, 43 mmol of 2-[(2-aminoethyl)amino]ethanesulfonic acid sodium salt and 170 mL of methanol were added to the reaction flask. After stirring evenly, 20 mmol of vinyl naphthyl organosilicon dialdehyde monomer was added and stirred at 30 °C for 4 h. Then, 64 mmol of sodium cyanoborohydride was added and reacted at room temperature for 18 h. The mixture was filtered, concentrated under reduced pressure, and separated by column chromatography (silica gel, 5% methanol in dichloromethane). After drying, the vinyl naphthyl organosilicon polyamine monomer was obtained.

[0055] (3) Under nitrogen atmosphere, 15 mmol of vinylnaphthyl organosilicon polyamine monomer and 210 mL of N,N-dimethylformamide were added to the reaction flask. After stirring evenly, 69 mmol of 16-bromohexadecanoic acid and 78 mmol of triethylamine were added. The mixture was reacted at 80 °C for 24 h. The mixture was extracted with ethyl acetate and deionized water. The organic phase was concentrated and separated by column chromatography (silica gel, 10% methanol in dichloromethane) to obtain vinylnaphthalene organosilicon monomer.

[0056] (4) Under nitrogen atmosphere, 50 g acrylamide, 15 g N,N-dimethylacrylamide, 8 g polyethylene glycol monomethyl ether acrylate and 10 g alkenylnaphthalene organosilicon monomer were dissolved in deionized water, the pH was adjusted to 7 with a 30% by mass sodium hydroxide aqueous solution, nitrogen was introduced, and the mixture was heated to 70 °C. 0.6 g benzoyl peroxide was added dropwise, and the reaction was continued for 3 h. The mixture was naturally cooled to room temperature to obtain a heat-resistant oil well cement fluid loss reducer.

[0057] Comparative Example 1

[0058] Under a nitrogen atmosphere, 65 g of acrylamide, 12 g of N,N-dimethylacrylamide, 5 g of polyethylene glycol monomethyl ether acrylate, and 2 g of vinyl naphthyl organosilicon dialdehyde monomer (prepared in Example 1) were dissolved in deionized water, the pH was adjusted to 7 with a 30% by mass aqueous sodium hydroxide solution, nitrogen was introduced, the mixture was heated to 70° C., 0.6 g of ammonium persulfate was added dropwise, the reaction was continued for 4 h, and the mixture was naturally cooled to room temperature to obtain an oil well cement fluid loss additive.

[0059] Comparative Example 2

[0060] Under a nitrogen atmosphere, 65 g of acrylamide, 12 g of N,N-dimethylacrylamide, 5 g of polyethylene glycol monomethyl ether acrylate, and 2 g of vinyl naphthyl silicone polyamine monomer (prepared in Example 1) were dissolved in deionized water, the pH was adjusted to 7 with a 30% by mass aqueous sodium hydroxide solution, nitrogen was introduced, the mixture was heated to 70° C., 0.6 g of ammonium persulfate was added dropwise, the reaction was continued for 4 h, and the mixture was naturally cooled to room temperature to obtain an oil well cement fluid loss additive.

[0061] Comparative Example 3

[0062] Under a nitrogen atmosphere, 65 g of acrylamide, 12 g of N,N-dimethylacrylamide, and 5 g of polyethylene glycol monomethyl ether acrylate were dissolved in deionized water, the pH was adjusted to 7 with a 30% by mass aqueous sodium hydroxide solution, nitrogen was introduced, the mixture was heated to 70°C, 0.6 g of ammonium persulfate was added dropwise, the reaction was continued for 4 h, and the mixture was naturally cooled to room temperature to obtain an oil well cement fluid loss additive.

[0063] Preparation of cement slurry: The preparation was carried out in accordance with the provisions of the standard GB / T 19139-2012 "Test Methods for Oil Well Cement". The formula was: Jiahua G-grade oil well cement + 3% by mass fluid loss additive + seawater (water-cement ratio of 0.44).

[0064] Temperature resistance test: Add the prepared cement slurry to the 500mL filter loss tube of the high temperature and high pressure water loss instrument, and fill it with 22.6cm 2 In the filter, set the temperature to 100℃, 150℃ and 250℃ respectively, open the pressure reducing valve of the nitrogen bottle, apply 6.9Mpa pressure, slowly unscrew the top valve and bottom valve of the filter cylinder, and use a measuring cylinder to collect the filtrate within 30 minutes to obtain the API water loss within 30 minutes.

[0065] Table 1 High temperature resistance test

[0066]

[0067] From the test results in the above table, it can be seen that with the increase of temperature, the API water loss gradually increases, but the growth rate is not large; at the same temperature, with the increase of the content of alkenyl naphthalene organosilicon monomer, the water loss gradually decreases. When the addition amount of the fluid loss additive is only 3%, the API water loss of the cement slurry at 250°C in Example 4 is only 52 mL, indicating that the prepared fluid loss additive has a good air filtration loss effect at a high temperature of 250°C. This is because, on the one hand, the naphthalene ring has a stable aromatic ring structure that is not easy to rotate, and its rigid structure can withstand high temperatures without deformation or decomposition, which helps the fluid loss additive maintain its original performance and form at high temperatures and can significantly improve the thermal stability of the fluid loss additive. Siloxane has high bond energy and excellent heat resistance, and can maintain stable chemical properties at high temperatures. At the same time, siloxane is not wetted by water, which helps the fluid loss additive reduce the influence of water molecules at high temperatures, allowing it to maintain stable performance in high temperature and high humidity environments. The two work synergistically to exert a high-temperature resistance effect. On the other hand, the multiple carboxylic acid and sulfonic acid groups introduced into the fluid loss additive, after dissolving in water, ionize to form anions such as sulfonate and carboxylate. These are adsorbed on cement particles through electrostatic action and promote the extension of the polymer chain of the fluid loss additive. At high temperatures, the molecular chain does not break and the groups do not fall off in alkaline cement slurry, resulting in excellent high-temperature resistance.

[0068] Furthermore, because seawater contains various salt ions, it maintains good fluid loss control even at high temperatures, demonstrating its excellent salt tolerance. The Comparative Example and Comparative Example 2 contain naphthalene rings and siloxanes, both of which have good heat resistance, and exhibit good high-temperature resistance. Comparative Example 3, which does not contain any heat-resistant groups, exhibits poor high-temperature resistance.

[0069] Cement slurry fluidity retention test: According to the relevant provisions of the national standard SY / T 5504.2-2013, the fluidity of the cement slurry and the fluidity retention at 30 minutes and 60 minutes are tested.

[0070] Cement slurry sedimentation stability test: The prepared cement slurry is cured at 60℃ for 20min, and the free carbon content of the cement slurry and the density difference between the upper and lower parts are measured to characterize the sedimentation stability of the cement slurry.

[0071] Table 2 Dispersion performance test

[0072]

[0073] The test results in the above table show that the fluid loss additive prepared by the present invention can maintain the fluidity stability of cement slurry over a long period of time, indicating that the fluid loss additive can not only be rapidly adsorbed on cement particles in the early stage of hydration, but also continue to play a role during the hydration process, preventing excessive aggregation of cement particles due to the hydration reaction. Generally speaking, the smaller the density difference between the upper and lower parts of the cement slurry and the lower the free liquid content, the better the sedimentation stability of the cement slurry, that is, the more uniform the dispersion of cement particles in the cement slurry.

[0074] As can be seen from the test results in the above table, the fluid loss additive prepared by the present invention has good dispersibility. This is because, on the one hand, the multiple carboxylic acid and sulfonic acid groups introduced into the fluid loss additive, after dissolving in water, ionize to form anions such as sulfonate and carboxylate, which are adsorbed on cement particles through electrostatic action, blocking the pores of cement particles, making the cement filter cake dense and compact, and enhancing the binding force between the fluid loss additive and cement particles. It can also prevent the agglomeration and sedimentation of cement particles and help form a hydration layer through hydration. When the fluid loss additive molecules are adsorbed on the surface of cement particles, these hydration layers can reduce the friction between cement particles and further promote the dispersion of cement slurry. On the other hand, the introduced polyethylene glycol alkyl and hexadecyl long side chain structures can form an effective steric hindrance in a relatively extended conformation to prevent flocculation and precipitation between cement particles, forming a protective layer of a certain thickness and effective steric hindrance on the surface of cement particles, thereby effectively preventing close contact and agglomeration of cement particles, thereby achieving high dispersion of cement.

[0075] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the invention can be embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the invention is defined by the appended claims, not the foregoing description, and all variations within the meaning and range of equivalents of the claims are intended to be encompassed therein. Any reference in a claim should not be construed as limiting the claim to which it relates.

Claims

1. A method for preparing a heat-resistant oil well cement fluid loss additive, characterized in that: The preparation method is carried out according to the following steps: Step (1), under a nitrogen atmosphere, adding vinyl naphthyl organosilicon polyamine monomer and N,N-dimethylformamide to a reaction flask, stirring evenly, adding 16-bromohexadecanoic acid and triethylamine, stirring for reaction, after the reaction is completed, extracting with ethyl acetate and deionized water, concentrating the organic phase, and separating by column chromatography to obtain an vinyl naphthalene organosilicon monomer; Step (2), under a nitrogen atmosphere, dissolving 50-65 parts by weight of acrylamide, 10-15 parts of N,N-dimethylacrylamide, 5-8 parts of polyethylene glycol monomethyl ether acrylate and 2-10 parts of alkenylnaphthalene organosilicon monomer in deionized water, adjusting the pH with an aqueous sodium hydroxide solution, introducing nitrogen, heating to 60-80° C., adding dropwise 0.5-0.8 parts of an initiator, continuing the reaction for 2-5 hours, and naturally cooling to room temperature to obtain a heat-resistant oil well cement fluid loss additive; The preparation method of the vinyl naphthyl organosilicon polyamine monomer in step (1) is carried out according to the following steps: Step S1, under a nitrogen atmosphere, adding methylvinyldichlorosilane and toluene to a reaction flask, stirring evenly, adding 6-hydroxy-2-naphthaldehyde and sodium hydride, stirring to react, filtering after the reaction, washing the organic layer with saturated brine, separating by column chromatography, and drying to obtain a vinylnaphthyl organosilicon dialdehyde monomer; Step S2: Under a nitrogen atmosphere, add 2-[(2-aminoethyl)amino]ethanesulfonic acid sodium salt and methanol to a reaction flask, stir evenly, add vinyl naphthyl organosilicon dialdehyde monomer, stir at 20-35°C for 2-5 hours, then add sodium cyanoborohydride, react at room temperature for 12-18 hours, filter, concentrate under reduced pressure, separate by column chromatography, and dry to obtain a vinyl naphthyl organosilicon polyamine monomer.

2. The method for preparing the heat-resistant oil well cement fluid loss additive according to claim 1, wherein: In the step (1), the molar ratio of the vinyl naphthyl organosilicon polyamine monomer, 16-bromohexadecanoic acid, and triethylamine is 1:4.2-5:4.5-6.

3. The method for preparing the heat-resistant oil well cement fluid loss additive according to claim 1, wherein: In step (1), the reaction temperature is 60-80° C. and the reaction time is 12-24 h.

4. The method for preparing the heat-resistant oil well cement fluid loss additive according to claim 1, wherein: The initiator in step (2) is any one of ammonium persulfate, benzoyl peroxide or azobisisobutyronitrile.

5. The method for preparing the heat-resistant oil well cement fluid loss additive according to claim 1, wherein: In the step (2), the pH is adjusted to 6-8.

6. The method for preparing the heat-resistant oil well cement fluid loss additive according to claim 1, wherein: In step S1, the molar ratio of methylvinyldichlorosilane, 6-hydroxy-2-naphthaldehyde, and sodium hydride is 1:2.05-2.2:2.3-2.

5.

7. The method for preparing the heat-resistant oil well cement fluid loss additive according to claim 1, wherein: In step S1, the reaction temperature is 90-110° C., and the reaction time is 5-10 h.

8. The method for preparing the heat-resistant oil well cement fluid loss additive according to claim 1, wherein: In step S2, the molar ratio of 2-[(2-aminoethyl)amino]ethanesulfonic acid sodium salt, vinyl naphthyl organosilicon dialdehyde monomer, and sodium cyanoborohydride is 2.1-2.3:1:2.5-3.

5.

9. A heat-resistant oil well cement fluid loss additive, characterized in that: The method is obtained by the preparation method according to any one of claims 1 to 8.

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