A method for preparing a dispersant for oil well cement

Abstract

The application discloses a preparation method of a dispersant for oil well cement, and comprises the following steps: adding a first carboxylic acid monomer, a catalyst and a polymerization inhibitor into a monovalent terminal amine polyether to obtain an amide type macromonomer through an amidation reaction; and performing a free radical polymerization reaction on the amide type macromonomer, a second carboxylic acid monomer and a cationic monomer under the action of an initiator and a chain transfer agent to obtain the dispersant for oil well cement. In the application, the preparation of the unsaturated amide type macromonomer can be performed through the amidation reaction without a solvent, the product does not need to be further treated and can be directly used in the subsequent polymerization reaction, the process is safe and environmentally friendly, and the atomic conversion rate is high. Moreover, the anion and cation adsorption anchoring effects in the molecular structure of the dispersant are complementary, the proportion of carboxylic acid in the polycarboxylic acid molecular structure can be reduced, the original adsorption and dispersion effects can be maintained, the block polyether long side chain steric hindrance effect can effectively prevent the cement particles from being aggregated, the rheological property of the cement slurry can be improved, the high dispersion performance and the low retarding effect can be co-existed.

Description

Technical Field

[0001] This invention relates to the field of cementing operations in oilfield development, and in particular to a method for preparing a dispersant for oil well cement. Background Technology

[0002] Cementing is a crucial step in oil well construction and is a one-time project. The quality of cementing directly affects subsequent well completion, oil production, and workover operations. Cementing operations mainly consist of two steps: casing installation and cementing. Cementing involves pumping cement slurry into the annulus between the casing and the wellbore, requiring the pumped slurry to have good flow properties. However, with the increasing complexity of exploration and development environments, various admixtures or additives such as retarders, fluid loss reducers, weighting agents, and latex materials are often added to the cement slurry during actual construction. This often leads to poor slurry flowability and difficulty in pumping. Therefore, dispersants are often added to the cement slurry to improve its flow properties and rheological properties, enabling turbulent displacement of the cement slurry under low pump pressure and improving the quality of cementing in oil and gas wells.

[0003] Currently, the most widely used oil well cement dispersant worldwide is sulfonated acetone-formaldehyde condensate dispersant. The product is typically a reddish-brown powder. Its dispersion mechanism involves adsorption onto the surface of cement particles, increasing the zeta potential of the cement particles, and dispersing them through electrostatic repulsion. It exhibits good temperature and salt resistance. However, as people's awareness of green, safe, and environmentally friendly practices has gradually increased, the production and use of sulfonated acetone-formaldehyde condensate dispersants have been restricted for the following reasons: First, its raw materials, such as acetone and formaldehyde, are toxic and polluting, leading to environmentally unfriendly production and application processes. Second, sulfonated acetone-formaldehyde has a simple structure, and due to its limited dispersion mechanism, it requires large dosages and has low dispersion efficiency. Finally, with the continuous emergence of new oil well cement admixtures, incompatibility issues with new additives have arisen.

[0004] Polycarboxylate (PCE) is a comb-shaped polymer composed of anionic anchoring groups in the main chain and hydrophilic nonionic long branches. It is a new generation of pollution-free, high-performance cement dispersant. The first generation of PCE (JP57118058) was invented in Japan in 1981. Due to its excellent molecular designability, it can meet the needs of different application environments. After more than two decades of development, it has completely dominated the global market for water-reducing agents in building concrete and is known as a high-performance water-reducing agent in China. However, research by Zhai et al. in "Characteristics of polycarboxylate-based dispersant suitable for medium and low temperature oil well cementing" shows that conventional polycarboxylate water-reducing agents, when directly applied to oil well cement, cannot fully meet the cementing requirements. The carboxylic acid groups in the main chain of conventional polycarboxylate molecules can adsorb onto the surface of positively charged aluminate phases or onto the surface of negatively charged silicate phases through calcium ion bridging, achieving a dispersion effect through electrostatic repulsion and steric hindrance. However, its high acid-to-ether ratio, high charge density, and strong adsorption properties in its molecular structure can delay the formation and growth of CSH crystal nuclei, hindering the cement hydration process. This is especially true in low-temperature cementing projects at 40–120℃, where it exhibits problems such as long thickening time and low early strength. Furthermore, when conventional polycarboxylate dispersants are used with commonly used anionic fluid loss reducers and retarders in oil well cement, they compete for adsorption, resulting in poor dispersion and potential compatibility issues. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing a dispersant for oil well cement, in order to solve the above-mentioned problems.

[0006] To achieve the above objectives, the present invention provides a method for preparing a dispersant for oil well cement, the method comprising:

[0007] The first carboxylic acid monomer, catalyst and polymerization inhibitor are added to the mono-terminated amine polyether, and the amide macromonomer is obtained by amidation reaction;

[0008] The amide-type macromonomer, the second carboxylic acid monomer, and the cationic monomer undergo free radical polymerization under the action of an initiator and a chain transfer agent to obtain the dispersant for oil well cement.

[0009] Optionally, the first carboxylic acid monomer, catalyst, and polymerization inhibitor are added to the mono-terminated amine polyether to obtain an amide-type macromonomer via an amidation reaction, including:

[0010] Under nitrogen protection, the mono-terminated amine polyether is heated to 55℃~70℃ and then the first carboxylic acid monomer, catalyst and polymerization inhibitor are added.

[0011] The temperature was further increased to 130–170°C and kept constant for 5–8 hours to carry out the amidation reaction, thereby obtaining the amide macromonomer.

[0012] Optionally, the general formula of the mono-terminated amine polyether is:

[0013]

[0014] Where x and y are the average molar additions of polypropylene glycol (PPO) and polyethylene glycol (PEO), respectively, and x+y is an integer from 20 to 60.

[0015] Optionally, the molar ratio of the monoamine-terminated polyether to the first carboxylic acid monomer is 1:1.05 to 1.10.

[0016] Optionally, the first carboxylic acid monomer includes at least one of the following: maleic anhydride, acrylic acid, maleic acid, and methacrylic acid.

[0017] Optionally, the catalyst comprises at least one of the following: p-toluenesulfonic acid, concentrated sulfuric acid, ethylsulfonic acid, and benzenesulfonic acid; wherein the mass of the catalyst is 0.5% to 5% of the mass of the mono-terminated amine polyether.

[0018] Optionally, the polymerization inhibitor includes at least one of the following: hydroquinone, p-tert-butylcatechol, 2,6-di-tert-butyl-p-methylphenol, and p-benzoquinone; wherein the mass of the polymerization inhibitor is 0.1% to 2% of the mass of the first carboxylic acid monomer.

[0019] Optionally, the amide-type macromonomer, the second carboxylic acid monomer, and the cationic monomer undergo a free radical polymerization reaction under the action of an initiator and a chain transfer agent to obtain the dispersant for oil well cement, comprising:

[0020] A mixed solution of the amide macromonomer and the cationic monomer is added to the reaction vessel as a base liquid;

[0021] The mixed solution of the second carboxylic acid monomer and the chain transfer agent, and the initiator are added dropwise to the reaction vessel to carry out a free radical polymerization reaction;

[0022] After the free radical polymerization reaction, an alkaline substance is added to the product to obtain a dispersant.

[0023] Optionally, the molar ratio of the amide macromonomer to the sum of the molar ratios of the second carboxylic acid monomer and the cationic monomer is 1:2 to 1:5; the molar ratio of the cationic monomer to the sum of the molar ratios of the second carboxylic acid monomer and the cationic monomer is 1:1 to 1:5.

[0024] Optionally, the first carboxylic acid monomer and the second carboxylic acid monomer are the same.

[0025] Optionally, the cationic monomer includes at least one of the following: methacryloyloxyethyltrimethylammonium chloride, dimethyl diallyl ammonium chloride, methacrylamidopropyltrimethylammonium chloride, or allyltrimethylammonium chloride.

[0026] Optionally, the initiator includes at least one of the following: ammonium persulfate, sodium persulfate, and potassium persulfate; wherein the mass of the initiator is 0.5% to 4% of the total mass of the amide macromonomer, the second carboxylic acid monomer, and the cationic monomer.

[0027] Optionally, the chain transfer agent includes at least one of the following: sodium hypophosphite, sodium methylpropenesulfonate, mercaptoacetic acid, 3-mercaptopropionic acid, and mercaptoethanol; wherein the mass of the chain transfer agent is 0.2% to 3% of the total mass of the amide macromonomer, the second carboxylic acid monomer, and the cationic monomer.

[0028] Optionally, the dropping time of the mixed solution of the second carboxylic acid monomer and the chain transfer agent is 2-4 hours, and the dropping time of the initiator is 2.5-4.5 hours; wherein the dropping time of the initiator is longer than the dropping time of the mixed solution of the second carboxylic acid monomer and the chain transfer agent.

[0029] Optionally, the conditions for the free radical polymerization reaction include: a reaction temperature of 60–90°C and a total polymerization reaction time of 4–8 h.

[0030] Optionally, the alkaline substance includes at least one of the following: sodium hydroxide, potassium hydroxide, calcium hydroxide, and sodium carbonate; wherein the alkaline substance adjusts the pH value of the product to 6-8.

[0031] The technical effects and advantages of this invention are as follows:

[0032] This invention provides a method for preparing a dispersant for oil well cement, the method comprising: adding a first carboxylic acid monomer, a catalyst and a polymerization inhibitor to a mono-terminated amine polyether, and obtaining an amide-type macromonomer through an amidation reaction; wherein the amide-type macromonomer, the second carboxylic acid monomer and the cationic monomer undergo a free radical polymerization reaction under the action of an initiator and a chain transfer agent to obtain the dispersant for oil well cement.

[0033] In this invention, the preparation of unsaturated amide macromonomers can be carried out without a solvent environment for amidation reactions. The products require no further processing and can be directly used for subsequent polymerization reactions. The production process is simple, safe, and environmentally friendly, with high atom conversion rate. Moreover, the complementary adsorption and anchoring effects of anions and cations in the dispersant molecular structure can reduce the proportion of carboxylic acid in the polycarboxylic acid molecular structure while maintaining the original adsorption and dispersion effects. The steric hindrance of the long side chains of block polyethers can effectively prevent cement particle agglomeration, improve the rheological properties of cement slurry, and achieve both high dispersibility and low retardation.

[0034] Other features and advantages of the invention will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures pointed out in the description and the drawings. Attached Figure Description

[0035] Figure 1 This is a flowchart of the preparation method for dispersants used in oil well cement.

[0036] Figure 2 Infrared spectrum of amide-type polycarboxylate dispersant for oil well cement;

[0037] Figure 3 Thermogravimetric curves of amide-type polycarboxylate dispersants for oil well cement;

[0038] Figure 4 Thickening curve (85℃ × 46.2MPa) of 0.5% sulfonated aldehyde-ketone condensate (a);

[0039] Figure 5 Thickening curve (85℃ × 46.2MPa) of amide-type polycarboxylic acid dispersant (b) for oil well cement prepared in Example 1 at 0.5%. Detailed Implementation

[0040] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Furthermore, the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0041] It should be noted that the structures, proportions, sizes, etc., illustrated in the accompanying drawings are merely for illustrative purposes to aid those skilled in the art and to facilitate understanding and reading. They are not intended to limit the scope of the invention and therefore have no substantial technical significance. Any modifications to the structure, changes in proportions, or adjustments to size, without affecting the effectiveness and purpose of the invention, should still fall within the scope of the technical content disclosed herein. Furthermore, the terms "upper," "lower," "left," "right," "middle," and "one" used in this specification are merely for clarity and not intended to limit the scope of the invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the invention.

[0042] This invention discloses a method for preparing a dispersant for oil well cement, which is described below in conjunction with... Figure 1 Detailed explanation:

[0043] 1. Preparation of unsaturated amide macromonomers: The first carboxylic acid monomer, catalyst and polymerization inhibitor are added to the mono-terminated amine polyether, and the amide macromonomer is obtained through amidation reaction.

[0044] Specifically, under nitrogen protection, the mono-terminated amine polyether is heated to 55℃~70℃, the first carboxylic acid monomer, catalyst and polymerization inhibitor are added, and then the temperature is slowly raised to 130~170℃ and kept at a constant temperature for 5~8h for full amidation. The amide-type macromonomer is then obtained by cooling.

[0045] The molar ratio of the mono-terminated amine polyether to the first carboxylic acid monomer is 1:1.05 to 1.10.

[0046] The general formula (Ⅰ) of the mono-terminated amine polyether is:

[0047]

[0048] In the formula, x and y are the average molar additions of polypropylene glycol (PPO) and polyethylene glycol (PEO), respectively, x+y is an integer from 20 to 60, x is preferably an integer from 0 to 10, and y is preferably an integer from 20 to 50.

[0049] Wherein, the first carboxylic acid monomer is one or more of maleic anhydride, acrylic acid, maleic acid, and methacrylic acid in any proportion.

[0050] The catalyst is one or more of p-toluenesulfonic acid, concentrated sulfuric acid, ethylsulfonic acid, and benzenesulfonic acid in any proportion, and its amount is 0.5% to 5% of the mass of the mono-terminated amine polyether, preferably 2% to 3%.

[0051] The polymerization inhibitor is one or two of hydroquinone, p-tert-butylcatechol, 2,6-di-tert-butyl-p-methylphenol, and p-benzoquinone, in any proportion, and its amount is 0.1% to 2% of the mass of the carboxylic acid monomer, preferably 0.5% to 1%.

[0052] 2. Free radical polymerization reaction: The amide macromonomer, the second carboxylic acid monomer, and the cationic monomer undergo free radical polymerization reaction under the action of an initiator and a chain transfer agent to obtain the dispersant for oil well cement.

[0053] Specifically, a mixed solution of unsaturated amide macromonomer and cationic monomer is added to the reaction vessel as a base liquid before the reaction begins; a mixed solution of second carboxylic acid monomer and chain transfer agent, and an initiator solution are added to the reaction vessel dropwise to carry out the reaction, thereby improving the conversion rate of macromonomer.

[0054] Throughout the reaction, the solid content is controlled at 30–55 wt%, the reaction temperature is controlled at 60–90 °C, the dropwise addition time of the mixed solution of the second carboxylic acid monomer and the chain transfer agent and the initiator solution is 2–4 h and 2.5–4.5 h respectively, and the dropwise addition time of the initiator solution must be longer than the dropwise addition time of the mixed solution of the second carboxylic acid monomer and the chain transfer agent. After the initiator solution is added, the temperature is maintained for aging for 0.5–2 h, and the total polymerization reaction time is controlled at 4 h–8 h.

[0055] After the polymerization reaction is completed and cooled to room temperature, one or more of sodium hydroxide, potassium hydroxide, calcium hydroxide, and sodium carbonate are added to the reaction product to adjust the pH value to 6-8.

[0056] The molar ratios of the various monomers satisfy the following: unsaturated amide macromonomer: (second carboxylic acid monomer + cationic monomer) = 1:2 to 1:5, and cationic monomer: (second carboxylic acid monomer + cationic monomer) = 1:1 to 1:5.

[0057] The second carboxylic acid monomer is the same as the first carboxylic acid monomer mentioned above.

[0058] The cationic monomer is one or more of the following in any proportion: methacryloyloxyethyltrimethylammonium chloride, dimethyldiallylammonium chloride, methacrylamidopropyltrimethylammonium chloride, and allyltrimethylammonium chloride.

[0059] The initiator is one or more of ammonium persulfate, sodium persulfate, and potassium persulfate, and its dosage is 0.5% to 4% of the total mass of the unsaturated amide macromonomer, the second carboxylic acid monomer, and the cationic monomer, preferably 1.5% to 3%.

[0060] The chain transfer agent is one or more of sodium hypophosphite, sodium methyl methacrylate, mercaptoacetic acid, 3-mercaptopropionic acid, and mercaptoethanol, and is used in an amount of 0.2% to 3% of the total mass of the unsaturated amide macromonomer, the second carboxylic acid monomer, and the cationic monomer, preferably 0.5% to 1.5%.

[0061] To better explain this solution, specific embodiments are provided below.

[0062] Example 1

[0063] A method for preparing an amide-type polycarboxylate dispersant for oil well cement includes the following steps:

[0064] (1) By weight, 2000 parts of mono-terminated amine polyether (x=10, y=31) with a weight average molecular weight of 2000 were added to a reaction vessel, nitrogen gas was introduced for protection, the mixture was stirred and heated to 70°C, and then 107.8 parts of maleic anhydride, 100 parts of p-toluenesulfonic acid and 2.2 parts of hydroquinone were added. The temperature was then raised to 170°C and kept constant for 6 hours before being cooled to room temperature to obtain an unsaturated amide macromonomer.

[0065] (2) Weigh 2100 parts by weight of the unsaturated amide macromonomer in (1) and 864 parts by weight of methacryloyloxyethyltrimethylammonium chloride, dissolve them in 3000 parts by weight of water and place them in a reaction vessel to form a base liquid. Weigh 180 parts by weight of acrylic acid and 84 parts by weight of sodium hypophosphite, dissolve them in 1000 parts by weight of water to form solution A, and dissolve 112 parts by weight of ammonium persulfate in 700 parts by weight of water to form solution B for later use. Purge nitrogen gas into the reaction vessel for protection, stir and heat to 70°C. Add solution A and solution B to the reaction vessel in the form of dropwise addition, with dropwise addition times of 3h and 3.5h respectively. After the dropwise addition is completed, continue to keep warm and age for 1h, cool to room temperature, and adjust pH=8 with sodium hydroxide to obtain amide polycarboxylic acid dispersant for oil well cement.

[0066] Example 2

[0067] A method for preparing an amide-type polycarboxylate dispersant for oil well cement includes the following steps:

[0068] (1) By weight, 2000 parts of mono-terminated amine polyether (x=10, y=31) with a weight average molecular weight of 2000 were added into a reaction vessel, nitrogen gas was introduced for protection, the mixture was stirred and heated to 55°C, and then 90 parts of methacrylic acid, 10 parts of p-toluenesulfonic acid and 0.1 parts of hydroquinone were added. The temperature was then raised to 130°C and kept at a constant temperature for 8 hours before being cooled to room temperature to obtain an unsaturated amide macromonomer.

[0069] (2) Weigh 2090 parts by weight of the unsaturated amide macromonomer in (1) and 269 parts by weight of dimethyl diallyl ammonium chloride, dissolve them in 2500 parts by weight of water and place them in a reaction vessel to form a base liquid. Weigh 86 parts by weight of methacrylic acid and 4.7 parts by weight of mercaptoacetic acid, dissolve them in 500 parts by weight of water to form solution A, and dissolve 11.7 parts by weight of potassium persulfate in 500 parts by weight of water to form solution B for later use. Purge nitrogen gas into the reaction vessel for protection, stir and heat to 65°C. Add solution A and solution B to the reaction vessel in the form of dropwise addition, with dropwise addition times of 4h and 4.5h respectively. After the dropwise addition is completed, continue to keep warm and age for 0.5h, cool to room temperature, and adjust pH=6 with sodium hydroxide to obtain amide polycarboxylic acid dispersant for oil well cement.

[0070] Example 3

[0071] A method for preparing an amide-type polycarboxylate dispersant for oil well cement includes the following steps:

[0072] (1) By weight, 1000 parts of mono-terminated amine polyether (x=3, y=19) with a weight average molecular weight of 1000 were added to a reaction vessel, nitrogen gas was introduced for protection, the mixture was stirred and heated to 65°C, and then 108 parts of maleic anhydride, 20 parts of p-toluenesulfonic acid and 1.1 parts of hydroquinone were added. The temperature was then raised to 150°C and kept at a constant temperature for 5 hours before being cooled to room temperature to obtain an unsaturated amide macromonomer.

[0073] (2) Weigh 1100 parts by weight of the unsaturated amide macromonomer in (1) and 692 parts by weight of methacryloyloxyethyltrimethylammonium chloride, dissolve them in 1500 parts by weight and place them in a reaction vessel to form a base liquid. Weigh 216 parts by weight of acrylic acid and 17 parts by weight of sodium hypophosphite, dissolve them in 600 parts by weight to form solution A, and dissolve 52 parts by weight of ammonium persulfate in 500 parts by weight to form solution B for later use. Purge nitrogen gas into the reaction vessel for protection, stir and heat to 75°C. Add solution A and solution B to the reaction vessel dropwise for 3 hours and 3.5 hours respectively. After the dropwise addition is completed, continue to keep warm and age for 0.5 hours. Cool to room temperature and adjust pH to 7 with sodium hydroxide to obtain amide polycarboxylic acid dispersant for oil well cement.

[0074] Example 4

[0075] A method for preparing an amide-type polycarboxylate dispersant for oil well cement includes the following steps:

[0076] (1) By weight, 1000 parts of mono-terminated amine polyether (x=3, y=19) with a weight average molecular weight of 1000 were added to a reaction vessel, nitrogen gas was introduced for protection, the mixture was stirred and heated to 60°C, and then 79 parts of acrylic acid, 30 parts of p-toluenesulfonic acid and 0.8 parts of hydroquinone were added. The temperature was then raised to 135°C and kept constant for 7 hours before being cooled to room temperature to obtain an unsaturated amide macromonomer.

[0077] (2) Weigh 1080 parts by weight of the unsaturated amide macromonomer in (1) and 538 parts by weight of dimethyl diallyl ammonium chloride, dissolve them in 1300 parts by weight of water and place them in a reaction vessel to form a base liquid. Weigh 144 parts by weight of acrylic acid and 15 parts by weight of mercaptoethanol, dissolve them in 500 parts by weight of water to form solution A, and dissolve 31 parts by weight of sodium persulfate in 500 parts by weight of water to form solution B for later use. Purge nitrogen gas into the reaction vessel for protection, stir and heat to 70°C. Add solution A and solution B to the reaction vessel dropwise for 2 hours and 2.5 hours respectively. After the dropwise addition is completed, continue to keep warm and age for 1 hour. Cool to room temperature and adjust pH to 7 with sodium hydroxide to obtain amide polycarboxylic acid dispersant for oil well cement.

[0078] The above dispersants were tested and analyzed, and the results are as follows:

[0079] Figure 2 The infrared spectrum of the amide-type polycarboxylate dispersant for oil well cement prepared in Example 1 is shown in the figure. As can be seen from the figure, at 1565 cm⁻¹...-1 and 1110cm -1 The peaks at 1725 cm⁻¹ represent the stretching vibrations of the -CONH- bond on the side chain of the amide macromonomer and the -COC- bond on the block polyether, respectively. -1 The peak at 2872 cm⁻¹ represents the stretching vibration of the carboxyl group -COOH on acrylic acid. -1 1565cm -1 The peaks at points 1 and 2 are the stretching vibration peaks of methyl-CH3 and cationic-CN on methacryloyloxyethyltrimethylammonium chloride, respectively. In summary, this indicates that all monomers participate in the polymerization reaction, and the long side chains of the block polyether are connected to the main chain through amide bonds, thus demonstrating the successful preparation of amide-type polycarboxylic acid dispersant for oil well cement.

[0080] Figure 3 The thermogravimetric analysis (TGA) chart shows the amide-type polycarboxylate dispersant for oil well cement prepared in Example 1. The chart indicates that the polymer begins to decompose at 216°C, and the decomposition mainly occurs in two steps, corresponding to the decomposition of the long side chains of the polyether and the decomposition of the molecular backbone. This means that the polymer is suitable for thermal environments below 216°C and meets the cementing requirements of 40–120°C.

[0081] The preparation of oil well cement slurry and the testing methods for dispersant performance were conducted in accordance with GB / T 19139-2012 "Test Methods for Oil Well Cement" and SYT 5504.3-2018 "Evaluation Methods for Oil Well Cement Admixtures Part 3: Drag Reducers". Using sulfonated aldehyde-ketone condensate as Comparative Example 1, the rheological properties, thickening time, and compressive strength of the examples and comparative examples were evaluated. The evaluation results are shown in Table 1.

[0082] Table 1 Performance evaluation results of different dispersants

[0083]

[0084] Note: Oil well cement slurry formula: Jiahua G-grade oil well cement + 0.5% BWOC dispersant, water-to-solid ratio 0.44; where %BWOC represents the mass percentage of cement.

[0085] As shown in Table 1, the ratio of thickening time and the ratio of compressive strength are compared with cement paste. Under the thickening test conditions of a set temperature of 85℃, a set pressure of 46.2MPa, and a heating time of 40min, the thickening time of cement paste is 68min. The addition of dispersants leads to varying degrees of extension of thickening time, with sulfonated aldehyde-ketone condensate showing the shortest extension time at 83min, which is 1.19 times that of cement paste. The amide-type polycarboxylate dispersant for oil well cement of this invention shows a slightly longer thickening time than sulfonated aldehyde-ketone condensate, ranging from 1.41 to 1.73 times, but both meet the technical indicators in the petroleum and natural gas industry standard SY / T 5504.3-2018, not exceeding 2 times. The 24h compressive strength of the amide-type polycarboxylate dispersant for oil well cement of this invention is slightly lower than that of sulfonated aldehyde-ketone condensate, but both meet the requirements of SY / T5504.3-2018, and no strong retarding or low early strength is observed.

[0086] From the rheological properties in Table 1 and Figure 4 and Figure 5 As can be seen from the thickening curve, under the same dosage, the dispersion efficiency of the amide-type polycarboxylic acid dispersant for oil well cement of the present invention is much higher than that of sulfonated aldehyde ketone condensate, with better rheological properties and lower initial consistency. Moreover, the thickening curve is stable, with no bulging or stepping, and the thickening is almost "right-angled".

[0087] After cement hydrates in water, the silicate phase carries a negative charge on its surface, while the aluminate phase carries a positive charge. The interaction between these positive and negative charges leads to flocculation of the cement slurry, increasing viscosity and thus increasing the pumping pressure during construction. Dispersants mainly adsorb onto the positive potential points of cement particles through anionic groups, altering the surface charge of the cement particles and forming a hydration film of a certain thickness, thereby dispersing the cement flocculent particles and reducing viscosity. Sulfonated aldehyde-ketone condensates are linear polymers containing only sulfonic acid adsorption groups, so their mechanism of action is limited to electrostatic repulsion to disperse cement particles, resulting in low dispersion efficiency. The amide-type polycarboxylic acid dispersant for oil well cement of this invention has both carboxyl and cationic adsorption groups in its main chain, and the long side chains of the block polyether are connected by amide bonds. These long side chains have steric hindrance and can form a hydration film, greatly improving dispersion efficiency.

[0088] The present invention also provides an apparatus for preparing a dispersant for oil well cement, the apparatus comprising: a reaction unit for adding a first carboxylic acid monomer, a catalyst and a polymerization inhibitor to a mono-terminated amine polyether to obtain an amide-type macromonomer through an amidation reaction; and a obtaining unit for the amide-type macromonomer, a second carboxylic acid monomer and a cationic monomer to undergo a free radical polymerization reaction under the action of an initiator and a chain transfer agent to obtain the dispersant for oil well cement.

[0089] Since the protection provided by this device is similar to that provided by the method described above, it will not be described in detail here. Please refer to the discussion section of the method described above for more information.

[0090] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a dispersant for oil well cement, characterized in that, The method includes: The first carboxylic acid monomer, catalyst and polymerization inhibitor are added to the mono-terminated amine polyether, and the amide macromonomer is obtained by amidation reaction; The amide-type macromonomer, the second carboxylic acid monomer, and the cationic monomer undergo free radical polymerization under the action of an initiator and a chain transfer agent to obtain the dispersant for oil well cement. The general formula of the mono-terminated amine polyether is: Where x and y are the average molar additions of polypropylene glycol (PPO) and polyethylene glycol (PEO), respectively, and x+y is an integer from 20 to 60; The first carboxylic acid monomer includes at least one of the following: maleic anhydride, acrylic acid, maleic acid, and methacrylic acid; The first carboxylic acid monomer and the second carboxylic acid monomer are the same; The cationic monomer includes at least one of the following: methacryloyloxyethyltrimethylammonium chloride, dimethyl diallyl ammonium chloride, methacrylamidopropyltrimethylammonium chloride, or allyltrimethylammonium chloride; The molar ratio of the monoamine-terminated polyether to the first carboxylic acid monomer is 1:1.05~1.10; The catalyst comprises at least one of the following: p-toluenesulfonic acid, concentrated sulfuric acid, ethylsulfonic acid, and benzenesulfonic acid; wherein the mass of the catalyst is 0.5% to 5% of the mass of the mono-terminated amine polyether; The polymerization inhibitor comprises at least one of the following: hydroquinone, p-tert-butylcatechol, 2,6-di-tert-butyl-p-methylphenol, and p-benzoquinone; wherein the mass of the polymerization inhibitor is 0.1% to 2% of the mass of the first carboxylic acid monomer; The amide-type macromonomer, the second carboxylic acid monomer, and the cationic monomer undergo a free radical polymerization reaction under the action of an initiator and a chain transfer agent to obtain the dispersant for oil well cement, comprising: A mixed solution of the amide macromonomer and the cationic monomer is added to the reaction vessel as a base liquid; The mixed solution of the second carboxylic acid monomer and the chain transfer agent, and the initiator are added dropwise to the reaction vessel to carry out a free radical polymerization reaction; After free radical polymerization, an alkaline substance is added to the product to obtain a dispersant; The molar ratio of the amide macromonomer to the sum of the molar ratios of the second carboxylic acid monomer and the cationic monomer is 1:2 to 1:5; the molar ratio of the cationic monomer to the sum of the molar ratios of the second carboxylic acid monomer and the cationic monomer is 1:1 to 1:

5.

2. The method according to claim 1, characterized in that, A first carboxylic acid monomer, a catalyst, and a polymerization inhibitor are added to a monoamine-terminated polyether, and an amidation reaction is carried out to obtain an amide-type macromonomer, including: Under nitrogen protection, the mono-terminated amine polyether is heated to 55℃~70℃ and then the first carboxylic acid monomer, catalyst and polymerization inhibitor are added. The temperature was further increased to 130~170℃ and kept constant for 5~8 hours to carry out the amidation reaction, and amide-type macromonomers were obtained.

3. The method according to claim 1, characterized in that, The initiator includes at least one of the following: ammonium persulfate, sodium persulfate, and potassium persulfate; wherein the mass of the initiator is 0.5% to 4% of the total mass of the amide macromonomer, the second carboxylic acid monomer, and the cationic monomer.

4. The method according to claim 1, characterized in that, The chain transfer agent includes at least one of the following: sodium hypophosphite, sodium methacrylate sulfonate, mercaptoacetic acid, 3-mercaptopropionic acid, and mercaptoethanol; wherein the mass of the chain transfer agent is 0.2% to 3% of the total mass of the amide macromonomer, the second carboxylic acid monomer, and the cationic monomer.

5. The method according to claim 3, characterized in that, The dropping time of the mixed solution of the second carboxylic acid monomer and the chain transfer agent is 2-4 hours, and the dropping time of the initiator is 2.5-4.5 hours; wherein the dropping time of the initiator is longer than the dropping time of the mixed solution of the second carboxylic acid monomer and the chain transfer agent.

6. The method according to claim 3, characterized in that, The conditions for the free radical polymerization reaction include: a reaction temperature of 60~90℃ and a total polymerization reaction time of 4h~8h.

7. The method according to claim 3, characterized in that, The alkaline substance includes at least one of the following: sodium hydroxide, potassium hydroxide, calcium hydroxide, and sodium carbonate; wherein the alkaline substance adjusts the pH value of the product to 6-8.

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