Salt-resistant cement slurry which does not disperse on contact with water and method for its preparation

Abstract

The application discloses a salt-resistant water-non-dispersible cement slurry and a preparation method thereof. The salt-resistant water-non-dispersible cement slurry comprises the following components in the following proportions by weight: 100 parts by weight of cement, 2-8 parts by weight of salt-resistant water-non-dispersible material, 0.5-2 parts by weight of a drag-reducing agent, 0.2 parts by weight of a defoaming agent and 37-56 parts by weight of slurry water; wherein the salt-resistant water-non-dispersible material comprises the following components in the following proportions by weight: 100 parts by weight of N, N-dimethyl acrylamide, 3-6 parts by weight of acrylic acid, 10-20 parts by weight of 2-acrylamide-2-methylpropanesulfonic acid, 5-15 parts by weight of a cyclic monomer, 0.1-0.4 parts by weight of a branching agent, 5-15 parts by weight of a cationic monomer, 0.3-3 parts by weight of a crosslinking agent and 400-500 parts by weight of water. The salt-resistant water-non-dispersible cement slurry has good salt resistance, can significantly improve the water-non-dispersible performance of the cement slurry regardless of whether the slurry water is fresh water, seawater or salt water with a NaCl content of 0-18 wt%, has good water invasion resistance and simultaneously has excellent rheological properties.

Description

Technical Field

[0001] This invention relates to the field of cementing engineering in oil and gas drilling operations, and more particularly to a salt-resistant, water-resistant, non-dispersible cement slurry and its preparation method. Background Technology

[0002] Currently, many oilfields both domestically and internationally that have entered the late stages of development commonly possess high-pressure brine layers (or brines), such as the Tarim Oilfield in my country. During cementing in high-water-cut formations, traditional cement slurry is highly susceptible to erosion and dilution by formation water during the setting process, leading to cement erosion in the water-bearing zone, reduced interfacial bonding quality, and compromised cement sheath seal integrity.

[0003] In recent years, considerable research has been conducted on problems such as water intrusion and water channeling that are prone to occur during cementing of high water-cut oil and gas wells. However, existing anti-water intrusion cement slurries do not take into account the situation of seawater or brine slurry preparation, and cannot be used in cementing operations of brine layers (brine layers) in water-cut and high water-cut oil and gas wells, as well as in offshore cementing operations, thus limiting their application scope. Summary of the Invention

[0004] This invention provides a salt-resistant, water-resistant, non-dispersible cement slurry and its preparation method, which can solve the water intrusion problem in cementing operations with high salt and high water content.

[0005] This invention provides a salt-resistant, water-resistant, non-dispersible cement slurry, comprising the following components in parts by weight: 100 parts by weight of cement, 2-8 parts by weight of a salt-resistant, water-resistant, non-dispersible material, 0.5-2 parts by weight of a drag-reducing agent, 0.2 parts by weight of a defoamer, and 37-56 parts by weight of slurry preparation water; wherein the salt-resistant, water-resistant, non-dispersible material comprises the following components in parts by weight: 100 parts by weight of N,N-dimethylacrylamide, 3-6 parts by weight of acrylic acid, 10-20 parts by weight of 2-acrylamido-2-methylpropanesulfonic acid, 5-15 parts by weight of a cyclic monomer, 0.1-0.4 parts by weight of a branching agent, 5-15 parts by weight of a cationic monomer, 0.3-3 parts by weight of a crosslinking agent, and 400-500 parts by weight of water.

[0006] Furthermore, drag-reducing agents include sulfonate drag-reducing agents.

[0007] Furthermore, defoamers include ester-based defoamers and / or silicone-based defoamers.

[0008] Furthermore, the slurry preparation water includes at least one of fresh water, seawater, and brine with a NaCl content of 0–18% wt%.

[0009] Furthermore, the cyclic monomer includes at least one of N-vinylpyrrolidone, N-vinylvalerolamide, and N-vinylcaprolactam.

[0010] Furthermore, the branching agents include pentaerythritol and / or dipentaerythritol.

[0011] Furthermore, the cationic monomer includes at least one of acryloyloxyethyltrimethylammonium chloride, dimethyldiallylammonium chloride, and dimethyldiallylammonium bromide.

[0012] Furthermore, the crosslinking agent includes at least one of 3-allyloxy-2-hydroxypropanesulfonic acid, N,N-methylenediacrylamide, hydroxyethyl acrylate, and hydroxyethyl methacrylate.

[0013] This invention provides a method for preparing the above-mentioned salt-resistant, water-resistant, non-dispersible cement slurry, comprising the following steps: N,N-dimethylacrylamide, acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, a cyclic monomer, a branching agent, and water are added sequentially to a reaction vessel according to the weight parts of each component to obtain a reaction solution. The mixture is stirred at 100 rpm until all components are completely dissolved. The pH value of the reaction solution is adjusted to 7-9, and the temperature of the reaction solution is raised to 35-55°C. An initiator is added dropwise to the reaction solution, and after reacting for 0.5-1 hour, a mixed solution of a cationic monomer and a crosslinking agent is added dropwise. The reaction is continued for 3-4 hours, and the temperature of the reaction solution is cooled to room temperature to obtain a salt-resistant, water-resistant, non-dispersible material. The salt-resistant, water-resistant, non-dispersible material, a drag-reducing agent, and slurry preparation water are added to a constant-speed stirrer according to the weight parts of each component. After stirring evenly, an antifoaming agent is added. Set the mixing speed of the constant speed mixer to 4000±200 r / min, pour all the cement into the constant speed mixer within 15 seconds, then increase the mixing speed of the constant speed mixer to 12000±500 r / min and continue mixing for 35 seconds to obtain a salt-resistant cement slurry that does not disperse when exposed to water.

[0014] Furthermore, the initiator includes ceric ammonium sulfate and / or ceric ammonium nitrate. The weight ratio of initiator to branching agent is 3:1 to 4:1.

[0015] Compared with the prior art, the present invention has the following advantages:

[0016] The salt-resistant, water-resistant, non-dispersible cement slurry of this invention exhibits excellent salt resistance. Regardless of whether the slurry is prepared with fresh water, seawater, or brine with a NaCl content of 0–18% wt%, it significantly improves the non-dispersible property of the cement slurry upon contact with water, providing good resistance to water intrusion, while also possessing excellent rheological properties. When used for cementing operations in water-bearing and high-water-cut oil and gas wells in brine formations (brine layers) and for offshore cementing operations, it effectively prevents formation water from eroding the cement slurry, ensuring smooth cementing operations and improving cementing quality, especially in brine (brine layer) sections. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a diagram illustrating the process of pouring cement slurry 3 into water, as described in an embodiment of the present invention.

[0019] Figure 2 This is a diagram showing the comparative example of the cement slurry 10 of the present invention being poured into water;

[0020] Figure 3 The graph shows the relationship between the root mean square radius and molar mass of the samples in Example 1 and Comparative Example 7 of this invention. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0022] Traditional cement slurries are easily diluted by formation water during cementing in high water-cut formations, leading to cement erosion in the water-bearing zone, reduced interfacial bonding quality, and compromised cement sheath seal integrity. Existing water-resistant cement slurries do not consider seawater or brine mixing, making them unsuitable for cementing operations in water-bearing and high water-cut oil and gas wells in brine formations (brine layers) and offshore cementing operations. This severely restricts normal oil and gas well production and impacts oil and gas field extraction efficiency. Therefore, embodiments of this invention provide a salt-resistant, water-resistant, non-dispersible cement slurry for cementing operations in water-bearing and high water-cut oil and gas wells in brine formations (brine layers) and offshore cementing operations. The salt-resistant, water-resistant, non-dispersible cement slurry comprises the following components in parts by weight: 100 parts by weight of cement, 2-8 parts by weight of the aforementioned salt-resistant, water-resistant, non-dispersible material, 0.5-2 parts by weight of drag-reducing agent, 0.2 parts by weight of defoamer, and 37-56 parts by weight of mixing water.

[0023] In the preparation of salt-resistant, water-insoluble cement slurry, the amount of salt-resistant, water-insoluble material used can be 2, 5, or 8 parts by weight. The salt-resistant, water-insoluble material comprises the following components in parts by weight: 100 parts by weight of N,N-dimethylacrylamide, 3–6 parts by weight of acrylic acid, 10–20 parts by weight of 2-acrylamido-2-methylpropanesulfonic acid, 5–15 parts by weight of cyclic monomers, 0.1–0.4 parts by weight of branching agent, 5–15 parts by weight of cationic monomers, 0.3–3 parts by weight of crosslinking agent, and 400–500 parts by weight of water.

[0024] In particular, by adding N,N-dimethylacrylamide, a skeleton structure of salt-resistant water-dispersible material is formed, which increases the molecular weight of the polymer and facilitates the occurrence of charge neutralization and "bonding-bridging" effects between individual salt-resistant water-dispersible materials and multiple cement particles.

[0025] In the preparation of salt-resistant, water-resistant, non-dispersible materials, acrylic acid can be used in amounts of 3, 5, or 6 parts by weight. Acrylic acid provides an anchoring group for the salt-resistant, water-resistant, non-dispersible material, with the carboxyl groups binding to the CaO on the cement particles. 2+ Electrostatic attraction and adsorption help to enhance the bonding force between salt-resistant, water-resistant non-dispersible materials and cement particles, thereby enhancing the non-dispersible effect when exposed to water.

[0026] In the preparation of salt-resistant, water-insoluble materials, the amount of 2-acrylamide-2-methylpropanesulfonic acid can be 10, 15, or 20 parts by weight. By adding 2-acrylamide-2-methylpropanesulfonic acid to introduce sulfonic acid groups, the salt resistance of the salt-resistant, water-insoluble material can be improved to a certain extent.

[0027] In the preparation of salt-resistant, water-insoluble materials, the amount of cyclic monomers can be 5, 10, or 15 parts by weight. The cyclic monomers include at least one of N-vinylpyrrolidone, N-vinylvaleronamide, and N-vinylcaprolactam. The cyclic monomers can be N-vinylpyrrolidone, N-vinylvaleronamide, or a mixture of N-vinylvaleronamide and N-vinylcaprolactam. N-vinylpyrrolidone, N-vinylvaleronamide, and N-vinylcaprolactam all possess heterocyclic structures, increasing the rigidity of the polymer molecular chain and improving the salt resistance and temperature resistance of the salt-resistant, water-insoluble material.

[0028] In the preparation of salt-resistant, water-resistant, non-dispersible materials, the amount of branching agent can be 0.1, 0.2, or 0.4 parts by weight. The branching agent includes pentaerythritol and / or dipentaerythritol. The branching agent can be pentaerythritol, dipentaerythritol, or a mixture of pentaerythritol and dipentaerythritol. Pentaerythritol and dipentaerythritol increase the branched structure of the salt-resistant, water-resistant, non-dispersible material. On the one hand, this facilitates the polymerization of spherical hyperbranched polymers, improving the polymer's salt resistance; on the other hand, it reduces the polymer's viscosity, improving the anti-dispersion properties of the water-resistant cement slurry while ensuring excellent rheological properties.

[0029] In the preparation of salt-resistant water-dispersible materials, the amount of cationic monomer used can be 5, 10, or 15 parts by weight. The cationic monomer includes at least one of acryloyloxyethyltrimethylammonium chloride, dimethyl diallyl ammonium chloride, and dimethyl diallyl ammonium bromide. The cationic monomer can be acryloyloxyethyltrimethylammonium chloride, dimethyl diallyl ammonium chloride, or a mixture of dimethyl diallyl ammonium chloride and dimethyl diallyl ammonium bromide, etc. Acryloyloxyethyltrimethylammonium chloride, dimethyl diallyl ammonium chloride, and dimethyl diallyl ammonium bromide, on the one hand, increase the positive charge of the salt-resistant water-dispersible material, neutralize the negative charge on the surface of cement particles, reduce the electrostatic repulsion between particles, induce particle aggregation, improve the cohesion of the cement slurry system, and resist the intrusion of external water; on the other hand, through the mutual attraction of positive and negative charges, the salt-resistant water-dispersible material is adsorbed onto the surface of cement particles. Combined with the structural characteristics of spherical hyperbranched polymers, each polymer segment is adsorbed onto the surface of multiple cement particles, enhancing the cohesion of the cement slurry system.

[0030] In the preparation of salt-resistant, water-insoluble materials, the amount of crosslinking agent can be 0.3, 1, or 3 parts by weight. The crosslinking agent includes at least one of 3-allyloxy-2-hydroxypropanesulfonic acid, N,N-methylenediacrylamide, hydroxyethyl acrylate, and hydroxyethyl methacrylate. The crosslinking agent can be 3-allyloxy-2-hydroxypropanesulfonic acid, N,N-methylenediacrylamide, or a mixture of hydroxyethyl acrylate and hydroxyethyl methacrylate. 3-allyloxy-2-hydroxypropanesulfonic acid, N,N-methylenediacrylamide, hydroxyethyl acrylate, and hydroxyethyl methacrylate crosslink multiple molecular segments to form a three-dimensional network structure. This three-dimensional network structure in aqueous solution enhances the cohesion of cement slurry and improves its resistance to external water intrusion. Furthermore, the three-dimensional network structure increases the connections between the chain segments of the salt-resistant, water-insoluble material and maintains the stability of these connections under certain salinity conditions, thus enhancing the polymer's salt resistance.

[0031] In the preparation of salt-resistant materials that do not disperse in water, the amount of water used can be 400, 450, or 500 parts by weight.

[0032] The salt-resistant, water-resistant, non-dispersible material of this invention can significantly improve the water-resistant properties of cement slurry, has good water erosion resistance, and also has excellent rheological properties.

[0033] In summary, the salt-resistant water-resistant non-dispersible material is a hyperbranched cationic polymer with a spherical structure. The cations neutralize the negative charge on the surface of cement particles, reducing electrostatic repulsion between particles, inducing particle aggregation, and increasing the cohesion of the cement paste system, thus resisting the intrusion of external water. The salt-resistant water-resistant non-dispersible material also exhibits a "bonding-bridging" effect with cement particles, adsorbing individual polymers onto the surface of multiple cement particles, maintaining the cohesion of the cement paste system within a suitable range. This resolves the contradiction between cement paste flocculation and good fluidity, allowing the cement paste to maintain good bulk (paste) integrity even under the scouring of external water and high-mineralized water, achieving a non-dispersible and non-segregating effect, demonstrating significant water-resistant non-dispersible properties. The addition of N,N-dimethylacrylamide forms the framework structure of the salt-resistant water-resistant non-dispersible material, increasing the polymer molecular weight and facilitating charge neutralization and "bonding-bridging" effects between individual salt-resistant water-resistant non-dispersible materials and multiple cement particles. The addition of acrylic acid and carboxyl groups interacts with the Ca on the cement particles... 2+Electrostatic attraction enhances the bonding force between the salt-resistant, water-resistant non-dispersible material and cement particles. Adding 2-acrylamido-2-methylpropanesulfonic acid introduces sulfonic acid groups, improving the salt resistance of the material to some extent. Adding cyclic monomers increases the rigidity of the polymer molecular chain, improving the temperature resistance of the material. Adding branching agents increases the branched structure of the material, which on the one hand facilitates the polymerization of spherical hyperbranched polymers, improving the polymer's salt resistance; on the other hand, it reduces the polymer's viscosity, improving the anti-dispersion properties of the water-resistant cement slurry while maintaining its excellent rheological properties. By adding cationic monomers, on the one hand, the positive charge of the salt-resistant water-dispersible material is increased, neutralizing the negative charge on the surface of cement particles, reducing electrostatic repulsion between particles, inducing particle aggregation, and improving the cohesion of the cement slurry system to resist the intrusion of external water. On the other hand, through the mutual attraction of positive and negative charges, the salt-resistant water-dispersible material is adsorbed onto the surface of cement particles. Combined with the structural characteristics of spherical hyperbranched polymers, each polymer chain segment is adsorbed onto the surface of multiple cement particles, enhancing the cohesion of the cement slurry system. By adding crosslinking agents, multiple molecular chains are bonded and crosslinked to form a three-dimensional network structure. The three-dimensional network structure in aqueous solution is beneficial to enhancing the cohesion of the cement slurry and improving its ability to resist the intrusion of external water. The three-dimensional network structure also increases the connection between the chains of the salt-resistant water-dispersible material and can maintain the stability of this connection under certain mineralization conditions, enhancing the salt resistance of the polymer. By optimizing the free radical polymerization conditions, the molecular weight of the salt-resistant water-dispersible material is controlled within a suitable range. This ensures that the molecular weight is not too small to coat multiple cement particles and thus lacks anti-dispersibility, nor that the molecular weight is too large, which would increase the viscosity of the system and cause the water-dispersible cement slurry to be too thick. Therefore, the salt-resistant, water-resistant, non-dispersible cement slurry prepared in this embodiment of the invention exhibits excellent salt resistance. Regardless of whether the slurry is prepared with fresh water, seawater, or brine with a NaCl content of 0–18% wt%, it significantly improves the water-resistant, non-dispersible properties of the cement slurry, providing good resistance to water intrusion, while also possessing excellent rheological properties. When used for cementing operations in water-bearing and high-water-cut oil and gas wells in brine formations (brine layers) and for offshore cementing operations, it effectively prevents formation water from eroding the cement slurry, ensuring smooth cementing operations and improving cementing quality, especially in brine (brine layer) sections.

[0034] In the preparation of salt-resistant, water-non-dispersible cement paste, the amount of drag-reducing agent can be 0.5, 1, or 2 parts by weight. Drag-reducing agents include sulfonate-based drag-reducing agents. These agents further improve the rheological properties of the cement paste through steric hindrance and charge effects.

[0035] In the preparation of salt-resistant, water-non-dispersible cement slurry, defoamers include ester-based defoamers and / or silicone-based defoamers. The defoamer can be an ester-based defoamer, a silicone-based defoamer, or a mixture of both. The defoamer reduces the surface tension of the liquid, removing excess gas from the cement slurry.

[0036] In the preparation of salt-resistant cement slurry that does not disperse in water, the amount of slurry mixing water can be 37, 46, or 56 parts by weight. The slurry mixing water includes at least one of fresh water, seawater, and brine with a NaCl content of 0–18% wt%. The slurry mixing water can be fresh water, seawater, or a mixture of seawater and brine with a NaCl content of 0–18% wt%, etc.

[0037] The salt-resistant, water-resistant, non-dispersible cement slurry prepared according to the embodiments of the present invention exhibits excellent salt resistance. Regardless of whether the slurry is prepared with fresh water, seawater, or brine with a NaCl content of 0–18% wt%, it significantly improves the non-dispersible property of the cement slurry upon contact with water, demonstrating good resistance to water intrusion, while also possessing excellent rheological properties. When used for cementing operations in water-bearing and high-water-cut oil and gas wells in brine formations (brine layers) and for offshore cementing operations, it effectively prevents formation water from eroding the cement slurry, ensuring the smooth progress of cementing operations and improving cementing quality, especially in brine (brine layer) sections.

[0038] An embodiment of the present invention also provides a method for preparing the above-mentioned salt-resistant, water-resistant, non-dispersible cement slurry, comprising the following steps:

[0039] Step 1: According to the weight proportions of each component, add N,N-dimethylacrylamide, acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, cyclic monomer, branching agent and water to the reaction vessel in sequence to obtain the reaction solution.

[0040] In the above steps, the weight parts of each component are as follows: 100 parts by weight of N,N-dimethylacrylamide, 3-6 parts by weight of acrylic acid, 10-20 parts by weight of 2-acrylamido-2-methylpropanesulfonic acid, 5-15 parts by weight of the cyclic monomer, 0.1-0.4 parts by weight of the branching agent, and 400-500 parts by weight of water. The corresponding weight parts of each component are added sequentially to the reaction vessel.

[0041] The reaction vessel can be a four-necked flask equipped with a thermometer, stirrer, and gas delivery tube.

[0042] Step 2: Stir at 100 rpm until all components are completely dissolved. Adjust the pH value of the reaction solution to 7-9 and raise the temperature of the reaction solution to 35-55℃.

[0043] In the above steps, the pH value of the reaction solution can be adjusted using NaOH solution. The concentration of the NaOH solution can be prepared and changed as needed; in this embodiment of the invention, no specific limitation is made. For example, the concentration of the NaOH solution can be 0.05 mol / L, 0.1 mol / L, 0.15 mol / L, etc. The pH value can be adjusted to 7, 8, 9, etc. The temperature of the reaction solution can be increased to 35, 45, 55°C, etc.

[0044] Step 3: Add an initiator to the reaction solution. After reacting for 0.5 to 1 hour, add a mixed solution of cationic monomer and crosslinking agent. After reacting for 3 to 4 hours, cool the reaction solution to room temperature to obtain a salt-resistant material that does not disperse in water.

[0045] In the above steps, the initiator includes ceric ammonium sulfate and / or ceric ammonium nitrate. The initiator can be ceric ammonium sulfate, ceric ammonium nitrate, or a mixture of ceric ammonium sulfate and ceric ammonium nitrate.

[0046] The weight ratio of initiator to branching agent is 3:1 to 4:1, and can be 3:1, 3.5:1, 4:1, etc. A water-soluble initiator is selected based on the polymerization process principle for free radical polymerization. By optimizing the free radical polymerization conditions, the molecular weight of the salt-resistant, water-resistant, non-dispersible material is controlled within a suitable range. This prevents the material from lacking anti-dispersibility due to an insufficient molecular weight to coat multiple cement particles, and also avoids excessively high viscosity due to an excessively large molecular weight. The reaction time can be 0.5, 0.8, or 1 hour after adding the initiator. The reaction time can be 3, 3.5, or 4 hours after adding a mixed solution of cationic monomer and crosslinking agent.

[0047] The preparation method of the above-mentioned salt-resistant, water-resistant, non-dispersible material is simple and the process is controllable. It is suitable for preparing cement slurries with brine and seawater, providing a new material for brine layers (brine layers) in water-bearing and high-water-content oil and gas wells, as well as for offshore cementing operations. The salt-resistant, water-resistant, non-dispersible material of this invention is a colorless or pale yellow transparent liquid with a slight viscosity.

[0048] Step 4: According to the weight proportions of each component, add the salt-resistant, water-resistant, non-dispersible material, drag-reducing agent, and slurry water to the constant speed mixer, stir evenly, and then add the defoamer.

[0049] Step 5: Set the mixing speed of the constant speed mixer to 4000±200 r / min. Pour all the cement into the constant speed mixer within 15 seconds. Then increase the mixing speed of the constant speed mixer to 12000±500 r / min and continue mixing for 35 seconds to obtain salt-resistant cement slurry that does not disperse when exposed to water.

[0050] In the above steps, the stirring speed of the constant speed stirrer can be set to 3800, 4000, 4200 r / min, etc. The stirring speed of the constant speed stirrer can be increased to 11500, 12000, 12500 r / min, etc.

[0051] The following detailed description is provided with reference to specific embodiments:

[0052] Example 1

[0053] According to the weight proportions of each component, 100 parts by weight of N,N-dimethylacrylamide, 3 parts by weight of acrylic acid, 10 parts by weight of 2-acrylamido-2-methylpropanesulfonic acid, 5 parts by weight of N-vinylpyrrolidone, 0.1 parts by weight of pentaerythritol, and 400 parts by weight of water were added sequentially to the reaction vessel to obtain a reaction solution. The mixture was stirred at 100 rpm until all components were completely dissolved. The pH value of the reaction solution was adjusted to 7, and the temperature of the reaction solution was raised to 35°C. 0.3 parts by weight of cerium ammonium sulfate was added dropwise to the reaction solution. After reacting for 0.5 hours, a mixed solution of 5 parts by weight of dimethyldiallylammonium chloride and 0.3 parts by weight of 3-allyloxy-2-hydroxypropanesulfonic acid was added dropwise. The reaction was continued for 3 hours, and the temperature of the reaction solution was cooled to room temperature to obtain sample 1 of a salt-resistant, water-insoluble material.

[0054] The cement slurry formulation is as follows: 100 parts by weight of Jiahua G-grade cement + 2 parts by weight of salt-resistant water-dispersible material sample 1 + 0.5 parts by weight of BCD-200L drag reducer + 0.2 parts by weight of G603 defoamer + 35 parts by weight of fresh water. According to the weight proportions of each component in the cement slurry formulation, all materials except cement and defoamer—salt-resistant water-dispersible material sample 1, drag reducer, and slurry preparation water—are added to a constant-speed mixer. After mixing evenly, the defoamer is added. The mixing speed of the constant-speed mixer is set to 4000±200 r / min. All the cement is poured into the constant-speed mixer within 15 seconds. Then, the mixing speed of the constant-speed mixer is increased to 12000±500 r / min, and mixing continues for 35 seconds to obtain the cement slurry, which is designated as Example Cement Slurry 1.

[0055] Example 2

[0056] The difference from Example 1 is that the cement slurry obtained by adding 100 parts by weight of Jiahua G-grade cement, 5 parts by weight of salt-resistant water-dispersible material sample 1, 1 part by weight of BCD-200L drag reducer, 0.2 parts by weight of G603 defoamer, and 37.8 parts by weight of Bohai seawater is called Example Cement Slurry 2.

[0057] Example 3

[0058] The difference from Example 1 is that the cement slurry obtained by adding 100 parts by weight of Jiahua G-grade cement, 8 parts by weight of salt-resistant water-dispersible material sample 1, 2 parts by weight of BCD-200L drag reducer, 0.2 parts by weight of G603 defoamer, and 48 parts by weight of 18% wt% brine is called Example Cement Slurry 3.

[0059] Example 4

[0060] According to the weight proportions of each component, 100 parts by weight of N,N-dimethylacrylamide, 6 parts by weight of acrylic acid, 20 parts by weight of 2-acrylamido-2-methylpropanesulfonic acid, 15 parts by weight of N-vinylcaprolactam, 0.4 parts by weight of dipentaerythritol, and 500 parts by weight of water were added sequentially to the reaction vessel to obtain a reaction solution. The mixture was stirred at 100 rpm until all components were completely dissolved. The pH value of the reaction solution was adjusted to 9, and the temperature of the reaction solution was raised to 55°C. 1.2 parts by weight of cerium ammonium nitrate were added dropwise to the reaction solution. After reacting for 1 hour, a mixed solution of 15 parts by weight of acryloyloxyethyltrimethylammonium chloride and 3 parts by weight of N,N-methylenediacrylamide was added dropwise. The reaction was carried out for 4 hours, and the temperature of the reaction solution was cooled to room temperature to obtain sample 2 of salt-resistant, water-insoluble material.

[0061] The cement slurry formulation is as follows: 100 parts by weight of Jiahua G-grade cement + 5 parts by weight of salt-resistant water-dispersible material sample 2 + 1 part by weight of BCD-200L drag reducer + 0.2 parts by weight of G603 defoamer + 37.8 parts by weight of Bohai Sea water. According to the weight proportions of each component in the cement slurry formulation, all materials except cement and defoamer—salt-resistant water-dispersible material sample 2, drag reducer, and slurry mixing water—are added to a constant-speed mixer. After mixing evenly, the defoamer is added. The mixing speed of the constant-speed mixer is set to 4000±200 r / min. All the cement is poured into the constant-speed mixer within 15 seconds. Then, the mixing speed of the constant-speed mixer is increased to 12000±500 r / min, and mixing continues for 35 seconds to obtain the cement slurry, which is designated as Example Cement Slurry 4.

[0062] Example 5

[0063] According to the weight proportions of each component, 100 parts by weight of N,N-dimethylacrylamide, 4.5 parts by weight of acrylic acid, 15 parts by weight of 2-acrylamido-2-methylpropanesulfonic acid, 10 parts by weight of N-vinylpyrrolidone, 0.2 parts by weight of pentaerythritol, and 450 parts by weight of water were added sequentially to the reaction vessel to obtain a reaction solution. The mixture was stirred at 100 rpm until all components were completely dissolved. The pH value of the reaction solution was adjusted to 8, and the temperature of the reaction solution was raised to 45°C. 0.8 parts by weight of cerium ammonium sulfate was added dropwise to the reaction solution. After reacting for 0.7 hours, a mixed solution of 10 parts by weight of dimethyldiallylammonium chloride and 1.7 parts by weight of 3-allyloxy-2-hydroxypropanesulfonic acid was added dropwise. The reaction was carried out for 3.5 hours, and the temperature of the reaction solution was cooled to room temperature to obtain sample 3 of a salt-resistant, water-insoluble material.

[0064] The cement slurry formulation is as follows: 100 parts by weight of Jiahua G-grade cement + 8 parts by weight of salt-resistant water-dispersible material sample 3 + 2 parts by weight of BCD-200L drag reducer + 0.2 parts by weight of G603 defoamer + 48 parts by weight of 18% wt% brine. According to the weight proportions of each component in the cement slurry formulation, all materials except cement and defoamer—salt-resistant water-dispersible material sample 3, drag reducer, and slurry preparation water—are added to a constant-speed mixer. After mixing evenly, the defoamer is added. The mixing speed of the constant-speed mixer is set to 4000±200 r / min. All the cement is poured into the constant-speed mixer within 15 seconds. Then, the mixing speed of the constant-speed mixer is increased to 12000±500 r / min, and mixing continues for 35 seconds to obtain the cement slurry, which is designated as Example Cement Slurry 5.

[0065] Compare with Example 1

[0066] The cement slurry formula is: 100 parts by weight of Jiahua G-grade cement + 0.5 parts by weight of BCD-200L drag reducer + 0.2 parts by weight of G603 defoamer + 37 parts by weight of fresh water. According to the weight proportions of each component in the cement slurry formula, all materials except cement and defoamer—the drag reducer and slurry preparation water—are added to a constant-speed mixer. After mixing evenly, the defoamer is added. The mixing speed of the constant-speed mixer is set to 4000±200 r / min. All the cement is poured into the constant-speed mixer within 15 seconds. Then, the mixing speed of the constant-speed mixer is increased to 12000±500 r / min, and mixing continues for 35 seconds to obtain the cement slurry, which is recorded as control group cement slurry 1.

[0067] Compare with Example 2

[0068] The only difference from Control Example 1 is that the cement slurry formula is: 100 parts by weight of Jiahua G-grade cement + 1 part by weight of BCD-200L drag reducer + 0.2 parts by weight of G603 defoamer + 42.8 parts by weight of Bohai seawater. The resulting cement slurry is called Control Cement Slurry 2.

[0069] Compare with Example 3

[0070] The only difference from Control Example 1 is that the cement slurry formula is: 100 parts by weight of Jiahua G-grade cement + 2 parts by weight of BCD-200L drag reducer + 0.2 parts by weight of G603 defoamer + 56 parts by weight of 18% wt% brine. The resulting cement slurry is called Control Cement Slurry 3.

[0071] Comparative Example 1

[0072] 240 ml of water, 15 g of acrylamide, 12 g of 2-acrylamido-2-methylpropanesulfonic acid, 2.2 g of vinyltrimethoxysilane, 5 g of sodium vinylsulfonate, 80 g of N,N-dimethylacrylamide, 15 g of acryloyloxyethyltrimethylammonium chloride, 20 g of dimethyldiallylammonium chloride, 17 g of N-vinylpyrrolidone, and 1 g of disodium ethylenediaminetetraacetate were added sequentially to the reaction vessel. The mixture was stirred at 25°C-35°C until completely dissolved. After dissolution, the reaction vessel was placed in a constant temperature water bath, and the water bath temperature was raised to 70°C. When the solution temperature in the reaction vessel reached 40°C, 1 g of ammonium persulfate solution was added to the above mixture and stirred evenly. Then, 1 g of azobisisobutyramidine hydrochloride solution was added, and the reaction was carried out for 4 hours to obtain control sample 1.

[0073] The cement slurry formulation is as follows: 100 parts by weight of Jiahua G-grade cement + 5 parts by weight of Comparative Sample 1 + 1 part by weight of BCD-200L drag reducer + 0.2 parts by weight of G603 defoamer + 37.8 parts by weight of Bohai Sea water. According to the weight proportions of each component in the cement slurry formulation, all materials except cement and defoamer—Comparative Sample 1, drag reducer, and slurry mixing water—were added to a constant-speed mixer. After thorough mixing, the defoamer was added. The mixing speed of the constant-speed mixer was set to 4000±200 r / min. All the cement was poured into the constant-speed mixer within 15 seconds. Then, the mixing speed was increased to 12000±500 r / min, and mixing continued for 35 seconds to obtain the cement slurry, which was designated as Comparative Cement Slurry 1.

[0074] Comparative Example 2

[0075] The only difference from Comparative Example 1 is that the cement slurry formula is: 100 parts by weight of Jiahua G-grade cement + 8 parts by weight of Comparative Sample 1 + 2 parts by weight of BCD-200L drag reducer + 0.2 parts by weight of G603 defoamer + 48 parts by weight of 18% wt% brine. The resulting cement slurry is called Comparative Example Cement Slurry 2.

[0076] Comparative Example 3

[0077] According to the weight proportions of each component, 100 parts by weight of N,N-dimethylacrylamide, 10 parts by weight of 2-acrylamido-2-methylpropanesulfonic acid, 5 parts by weight of N-vinylpyrrolidone, 0.1 parts by weight of pentaerythritol, and 400 parts by weight of water were added sequentially to the reaction vessel to obtain a reaction solution. The mixture was stirred at 100 rpm until all components were completely dissolved. The pH value of the reaction solution was adjusted to 7, and the temperature of the reaction solution was raised to 35°C. 0.3 parts by weight of cerium ammonium sulfate was added dropwise to the reaction solution. After reacting for 0.5 hours, a mixed solution of 5 parts by weight of dimethyldiallylammonium chloride and 0.3 parts by weight of 3-allyloxy-2-hydroxypropanesulfonic acid was added dropwise. The reaction was continued for 3 hours, and the temperature of the reaction solution was cooled to room temperature to obtain control sample 2.

[0078] The cement slurry formulation is as follows: 100 parts by weight of Jiahua G-grade cement + 5 parts by weight of Comparative Sample 2 + 1 part by weight of BCD-200L drag reducer + 0.2 parts by weight of G603 defoamer + 37.8 parts by weight of Bohai Sea water. According to the weight proportions of each component in the cement slurry formulation, all materials except cement and defoamer—Comparative Sample 2, drag reducer, and slurry mixing water—were added to a constant-speed mixer. After thorough mixing, the defoamer was added. The mixing speed of the constant-speed mixer was set to 4000±200 r / min. All the cement was poured into the constant-speed mixer within 15 seconds. Then, the mixing speed was increased to 12000±500 r / min, and mixing continued for 35 seconds to obtain the cement slurry, designated as Comparative Cement Slurry 3.

[0079] Comparative Example 4

[0080] The only difference from Comparative Example 3 is that the cement slurry formula is: 100 parts by weight of Jiahua G-grade cement + 8 parts by weight of Comparative Sample 2 + 2 parts by weight of BCD-200L drag reducer + 0.2 parts by weight of G603 defoamer + 48 parts by weight of 18% wt% brine. The resulting cement slurry is called Comparative Example Cement Slurry 4.

[0081] Comparative Example 5

[0082] According to the weight proportions of each component, 100 parts by weight of N,N-dimethylacrylamide, 3 parts by weight of acrylic acid, 10 parts by weight of 2-acrylamido-2-methylpropanesulfonic acid, 0.1 parts by weight of pentaerythritol, and 400 parts by weight of water were added sequentially to the reaction vessel to obtain a reaction solution. The mixture was stirred at 100 rpm until all components were completely dissolved. The pH value of the reaction solution was adjusted to 7, and the temperature of the reaction solution was raised to 35°C. 0.3 parts by weight of cerium ammonium sulfate was added dropwise to the reaction solution. After reacting for 0.5 hours, a mixed solution of 5 parts by weight of dimethyldiallylammonium chloride and 0.3 parts by weight of 3-allyloxy-2-hydroxypropanesulfonic acid was added dropwise. The reaction was continued for 3 hours, and the temperature of the reaction solution was cooled to room temperature to obtain control sample 3.

[0083] The cement slurry formulation is as follows: 100 parts by weight of Jiahua G-grade cement + 5 parts by weight of Comparative Sample 3 + 1 part by weight of BCD-200L drag reducer + 0.2 parts by weight of G603 defoamer + 37.8 parts by weight of Bohai Sea water. According to the weight proportions of each component in the cement slurry formulation, all materials except cement and defoamer—Comparative Sample 3, drag reducer, and slurry mixing water—were added to a constant-speed mixer. After thorough mixing, the defoamer was added. The mixing speed of the constant-speed mixer was set to 4000±200 r / min. All the cement was poured into the constant-speed mixer within 15 seconds. Then, the mixing speed was increased to 12000±500 r / min, and mixing continued for 35 seconds to obtain the cement slurry, which was designated as Comparative Cement Slurry 5.

[0084] Comparative Example 6

[0085] The only difference from Comparative Example 5 is that the cement slurry formula is: 100 parts by weight of Jiahua G-grade cement + 8 parts by weight of comparative sample 3 + 2 parts by weight of BCD-200L drag reducer + 0.2 parts by weight of G603 defoamer + 48 parts by weight of 18% wt% brine. The resulting cement slurry is called Comparative Example Cement Slurry 6.

[0086] Comparative Example 7

[0087] According to the weight proportions of each component, 100 parts by weight of N,N-dimethylacrylamide, 3 parts by weight of acrylic acid, 10 parts by weight of 2-acrylamido-2-methylpropanesulfonic acid, 5 parts by weight of N-vinylpyrrolidone, and 400 parts by weight of water were added sequentially to the reaction vessel to obtain a reaction solution. The mixture was stirred at 100 rpm until all components were completely dissolved. The pH value of the reaction solution was adjusted to 7, and the temperature of the reaction solution was raised to 35°C. 0.3 parts by weight of cerium ammonium sulfate was added dropwise to the reaction solution. After reacting for 0.5 hours, a mixed solution of 5 parts by weight of dimethyldiallylammonium chloride and 0.3 parts by weight of 3-allyloxy-2-hydroxypropanesulfonic acid was added dropwise. The reaction was continued for 3 hours, and the temperature of the reaction solution was cooled to room temperature to obtain control sample 4.

[0088] The cement slurry formulation was as follows: 100 parts by weight of Jiahua G-grade cement + 5 parts by weight of Comparative Sample 4 + 1 part by weight of BCD-200L drag reducer + 0.2 parts by weight of G603 defoamer + 37.8 parts by weight of Bohai Sea water. According to the weight proportions of each component in the cement slurry formulation, all materials except cement and defoamer—Comparative Sample 4, drag reducer, and slurry mixing water—were added to a constant-speed mixer. After thorough mixing, the defoamer was added. The mixing speed of the constant-speed mixer was set to 4000±200 r / min. All the cement was poured into the constant-speed mixer within 15 seconds. Then, the mixing speed was increased to 12000±500 r / min, and mixing continued for 35 seconds to obtain the cement slurry, designated as Comparative Cement Slurry 7.

[0089] Comparative Example 8

[0090] The only difference from Comparative Example 7 is that the cement slurry formula is: 100 parts by weight of Jiahua G-grade cement + 8 parts by weight of comparative sample 4 + 2 parts by weight of BCD-200L drag reducer + 0.2 parts by weight of G603 defoamer + 48 parts by weight of 18% wt% brine, and the resulting cement slurry is called Comparative Example Cement Slurry 8.

[0091] Comparative Example 9

[0092] According to the weight proportions of each component, 100 parts by weight of N,N-dimethylacrylamide, 3 parts by weight of acrylic acid, 10 parts by weight of 2-acrylamido-2-methylpropanesulfonic acid, 5 parts by weight of N-vinylpyrrolidone, 0.1 parts by weight of pentaerythritol, and 400 parts by weight of water were added sequentially to the reaction vessel to obtain a reaction solution. The mixture was stirred at 100 rpm until all components were completely dissolved. The pH value of the reaction solution was adjusted to 7, and the temperature of the reaction solution was raised to 35°C. 0.3 parts by weight of cerium ammonium sulfate was added dropwise to the reaction solution. After reacting for 0.5 hours, 0.3 parts by weight of 3-allyloxy-2-hydroxypropanesulfonic acid was added dropwise. After reacting for 3 hours, the temperature of the reaction solution was cooled to room temperature to obtain control sample 5.

[0093] The cement slurry formulation was as follows: 100 parts by weight of Jiahua G-grade cement + 5 parts by weight of control sample 5 + 1 part by weight of BCD-200L drag reducer + 0.2 parts by weight of G603 defoamer + 37.8 parts by weight of Bohai Sea water. According to the weight proportions of each component in the cement slurry formulation, all materials except cement and defoamer—control sample 5, drag reducer, and slurry mixing water—were added to a constant-speed mixer. After thorough mixing, the defoamer was added. The mixing speed of the constant-speed mixer was set to 4000±200 r / min. All the cement was poured into the constant-speed mixer within 15 seconds. Then, the mixing speed was increased to 12000±500 r / min, and mixing continued for 35 seconds to obtain the cement slurry, designated as control sample cement slurry 9.

[0094] Comparative Example 10

[0095] The only difference from Comparative Example 9 is that the cement slurry formula is: 100 parts by weight of Jiahua G-grade cement + 8 parts by weight of comparative sample 5 + 2 parts by weight of BCD-200L drag reducer + 0.2 parts by weight of G603 defoamer + 48 parts by weight of 18% wt% brine, and the resulting cement slurry is called Comparative Example Cement Slurry 10.

[0096] Comparative Example 11

[0097] According to the weight proportions of each component, 100 parts by weight of N,N-dimethylacrylamide, 3 parts by weight of acrylic acid, 10 parts by weight of 2-acrylamido-2-methylpropanesulfonic acid, 5 parts by weight of N-vinylpyrrolidone, 0.1 parts by weight of pentaerythritol, and 400 parts by weight of water were added sequentially to the reaction vessel to obtain a reaction solution. The mixture was stirred at 100 rpm until all components were completely dissolved. The pH value of the reaction solution was adjusted to 7, and the temperature of the reaction solution was raised to 35°C. 0.3 parts by weight of cerium ammonium sulfate was added dropwise to the reaction solution. After reacting for 0.5 hours, 5 parts by weight of dimethyl diallyl ammonium chloride was added dropwise. After reacting for 3 hours, the temperature of the reaction solution was cooled to room temperature to obtain control sample 6.

[0098] The cement slurry formulation was as follows: 100 parts by weight of Jiahua G-grade cement + 5 parts by weight of control sample 6 + 1 part by weight of BCD-200L drag reducer + 0.2 parts by weight of G603 defoamer + 37.8 parts by weight of Bohai Sea water. According to the weight proportions of each component in the cement slurry formulation, all materials except cement and defoamer—control sample 6, drag reducer, and slurry mixing water—were added to a constant-speed mixer. After thorough mixing, the defoamer was added. The mixing speed of the constant-speed mixer was set to 4000±200 r / min. All the cement was poured into the constant-speed mixer within 15 seconds. Then, the mixing speed was increased to 12000±500 r / min, and mixing continued for 35 seconds to obtain the cement slurry, designated as control sample cement slurry 11.

[0099] Comparative Example 12

[0100] The only difference from Comparative Example 11 is that the cement slurry formula is: 100 parts by weight of Jiahua G-grade cement + 8 parts by weight of comparative sample 6 + 2 parts by weight of BCD-200L drag reducer + 0.2 parts by weight of G603 defoamer + 48 parts by weight of 18% wt% brine, and the resulting cement slurry is called Comparative Example Cement Slurry 12.

[0101] Experimental Example 1

[0102] Comprehensive performance tests were conducted on cement slurries 1-5 of Examples and cement slurries 1-3 of Comparative Examples. Cement loss and fluidity tests were conducted on cement slurries 1-12 of Comparative Examples.

[0103] The density, free liquid content, thickening time at 70℃×35min×35MPa, and compressive strength at 70℃ for 24h were all determined in accordance with GB / T 19139-2012 "Test Methods for Cement in Oil Wells".

[0104] The flowability test method is as follows: Place a 400mm×400mm×5mm glass plate horizontally and wipe it with a damp cloth to moisten it, but without leaving any water stains. Place a truncated cone mold (a smooth, seamless metal product with an upper diameter of 36mm, a lower diameter of 60mm, and a height of 60mm) in the center of the glass plate, and quickly pour the prepared cement into the truncated cone mold until it is full. Vertically lift the truncated cone mold and simultaneously start a stopwatch, allowing the cement slurry to flow on the glass plate for 30 seconds. Use a ruler to measure the maximum diameter of the cement slurry in two mutually perpendicular directions; this is the flowability.

[0105] The method for testing cement loss is as follows: First, the prepared cement slurry is stirred in a thickener at 70±2℃ under normal pressure for 20 minutes, then removed and allowed to stand for 3 minutes. Next, the cement slurry is poured into a beaker containing 300mL of distilled water (beaker specification: 500mL). The cement slurry is slowly poured in from the mouth of the beaker over a time of 2-3 minutes, with a total volume of 350g. After pouring, the beaker is allowed to stand for 1 minute. The top 245mL of solution is then drawn off using a pipette. The drawn-off solution is stirred thoroughly and its density ρ is measured using a digital liquid density meter. The cement loss is then calculated as M = (ρ-1)×245. A smaller cement loss indicates better preservation of the cement slurry's integrity in an external water environment, signifying stronger non-dispersibility of the material in water.

[0106] The comprehensive performance test results of the control examples cement slurry 1-3 are shown in Table 1.

[0107] Table 1. Comprehensive Performance of Cement Slurry (Comparative Examples 1-3)

[0108]

[0109] During the cement loss test of the control group cement slurry 1-3, the cement slurry dispersed immediately after being poured into the aqueous solution. The water in the beaker became cloudy and opaque, indicating a large cement loss, all exceeding 70g.

[0110] The comprehensive performance test results of cement slurry 1-5 in Examples are shown in Table 2.

[0111] Table 2 Comprehensive Performance Table of Cement Slurry 1-5 in Examples 2

[0112]

[0113] Comparing cement slurry 1 from Example 1 with control group cement slurry 1, cement slurries 2 and 4 from Example 1 with control group cement slurry 2, and cement slurries 3 and 5 from control group cement slurry 3, it is evident that the cement slurry with the added salt-resistant, water-resistant, non-dispersible material from the examples has zero free liquid content, indicating good stability. During the cement loss test, the cement slurry prepared in the examples exhibits strong cohesion, does not diffuse when exposed to external aqueous solutions, and the water in the upper layer of the beaker remains clear and transparent. The cement slurry maintains good slurry integrity. Figure 1 The image shows the cement slurry 3 in Example 3 being poured into water. Furthermore, the addition of the salt-resistant, water-resistant, non-dispersible material prepared in the example had little effect on the thickening time and 24-hour compressive strength of the cement slurry. The fluidity decreased slightly, but remained above 22 cm, maintaining good rheological properties and meeting the requirements of on-site oilfield construction.

[0114] The test results of cement loss and fluidity of the comparative cement slurry 1-12 are shown in Table 3.

[0115] Table 3 Comparative Cement Slurry 1-12: Cement Loss and Flowability Properties

[0116]

[0117]

[0118] Comparing the data in Table 3 with those in Table 2, specifically comparing comparative examples cement slurries 1, 3, 5, 7, 9, and 11 with example cement slurry 2, and comparing comparative examples cement slurries 2, 4, 6, 8, 10, and 12 with example cement slurry 3, we can see that:

[0119] In comparative examples of cement slurry 1 and 2, the existing technical solutions are not resistant to salt / seawater, have poor rheological properties, and cannot be poured out.

[0120] In comparative cement slurries 3 and 4, without the addition of acrylic acid, the polymer reacts with the Ca on the cement particles. 2+ The weak electrostatic attraction leads to partial aggregation between polymer molecules, increasing the consistency of the cement paste, resulting in poor rheological properties and a large amount of cement loss.

[0121] In comparative cement slurries 5 and 6, without the addition of cyclic monomers, the cement slurry is not heat-resistant, and its anti-dispersion properties deteriorate after curing.

[0122] In comparative cement slurries 7 and 8, the absence of a branching agent hinders the polymerization of spherical hyperbranched polymers, makes them intolerant to salt / seawater, results in poor rheological properties, and prevents them from being poured out.

[0123] In comparative cement slurries 9 and 10, without the addition of cationic monomers, the bonding force between the polymer and cement particles is weak, resulting in poor anti-dispersion properties. Figure 2 The image shows the situation where cement slurry 10 (the comparative example) is poured into water.

[0124] In comparative cement slurries 11 and 12, without the addition of a crosslinking agent, the polymer's three-dimensional network structure is weak, resulting in poor anti-dispersion performance.

[0125] The cement slurries 1-5 provided by this invention exhibit low cement loss, good anti-dispersion effect, and good rheological properties, indicating that the addition of each component of the salt-resistant, water-resistant, non-dispersible material and the reasonable proportion between the components have a significant impact on the anti-dispersion effect and rheological properties of the cement slurry. Figure 3The molecular conformation diagrams of the samples prepared in Example 1 and Comparative Example 7 show that the slope of the conformation diagram of the salt-resistant water-resistant non-dispersible material sample 1 prepared in Example 1 as a function of molar mass is 0.34 ± 0.00, indicating that the salt-resistant water-resistant non-dispersible material sample 1 prepared in Example 1 is a hyperbranched polymer with a compact structure; the slope of the conformation diagram of the comparative sample 4 prepared in Comparative Example 7 as a function of molar mass is 0.54 ± 0.00, indicating that the comparative sample 4 prepared in Comparative Example 7 is a linear polymer with a random coil conformation. Hyperbranched polymers can adsorb individual polymers onto the surface of multiple cement particles. Through the "bonding-bridging" effect between the polymer and cement particles, the cohesion of the cement slurry system is kept within a suitable range, resolving the contradiction between cement slurry flocculation and good fluidity. This allows the cement slurry to maintain good bulk (slurry) integrity even under the scouring of external water and high-mineralized water, achieving the effect of non-dispersion and non-segregation, and exhibiting significant water-resistant non-dispersible properties.

[0126] On the other hand, it can also be seen from the results of pouring cement slurries 1-5 in Examples and 1-12 in Comparative Examples into water that cement slurries 1-5 in Examples have greater cohesion and do not diffuse when exposed to external aqueous solutions, and the water in the upper layer of the beaker remains clear and transparent, and the cement slurry maintains good slurry integrity; cement slurries 1-4 and 7-8 in Comparative Examples have poor rheological properties and are difficult to pour out smoothly, while cement slurries 5-6 and 9-12 in Comparative Examples disperse immediately after being poured into the aqueous solution, and the cement slurry disperses in the water, making the water in the beaker turbid and opaque.

[0127] Therefore, the salt-resistant, water-resistant, non-dispersible cement slurry prepared in this embodiment of the invention exhibits excellent salt resistance. Regardless of whether the slurry is prepared with fresh water, seawater, or brine with a NaCl content of 0–18% wt%, it significantly improves the water-resistant, non-dispersible properties of the cement slurry, providing good resistance to water intrusion, while also possessing excellent rheological properties. When used for cementing operations in water-bearing and high-water-cut oil and gas wells in brine formations (brine layers) and for offshore cementing operations, it effectively prevents formation water from eroding the cement slurry, ensuring smooth cementing operations and improving cementing quality, especially in brine (brine layer) sections.

[0128] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A salt-resistant cement slurry that does not disperse in water, characterized in that, The components include the following parts by weight: 100 parts by weight of cement, 2 to 8 parts by weight of salt-resistant water-resistant non-dispersible material, 0.5 to 2 parts by weight of drag-reducing agent, 0.2 parts by weight of defoamer, and 37 to 56 parts by weight of grouting water; The salt-resistant, water-resistant, non-dispersible material comprises the following components in parts by weight: 100 parts by weight of N,N-dimethylacrylamide, 3-6 parts by weight of acrylic acid, 10-20 parts by weight of 2-acrylamido-2-methylpropanesulfonic acid, 5-15 parts by weight of cyclic monomer, 0.1-0.4 parts by weight of branching agent, 5-15 parts by weight of cationic monomer, 0.3-3 parts by weight of crosslinking agent, and 400-500 parts by weight of water; The cyclic monomer includes at least one of N-vinylpyrrolidone, N-vinylvalerolamide, and N-vinylcaprolactam; The branching agent includes pentaerythritol and / or dipentaerythritol; The cationic monomer includes at least one of acryloyloxyethyltrimethylammonium chloride, dimethyl diallylammonium chloride, and dimethyl diallylammonium bromide; The crosslinking agent includes at least one of 3-allyloxy-2-hydroxypropanesulfonic acid, N,N-methylenediacrylamide, hydroxyethyl acrylate, and hydroxyethyl methacrylate.

2. The salt-resistant, water-resistant, non-dispersible cement slurry as described in claim 1, characterized in that, The drag-reducing agent includes sulfonate drag-reducing agents.

3. The salt-resistant, water-resistant, non-dispersible cement slurry as described in claim 1, characterized in that, The defoamer includes ester-based defoamers and / or silicone-based defoamers.

4. The salt-resistant, water-resistant, non-dispersible cement slurry as described in claim 1, characterized in that, The slurry preparation water includes at least one of fresh water and brine with a NaCl content of 0-18% wt%.

5. A method for preparing a salt-resistant, water-resistant, non-dispersible cement slurry according to any one of claims 1-4, characterized in that, Includes the following steps: According to the weight proportions of each component, N,N-dimethylacrylamide, acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, cyclic monomer, branching agent and water are added sequentially to the reaction vessel to obtain the reaction solution; Stir at 100 rpm until all components are completely dissolved, adjust the pH value of the reaction solution to 7-9, and raise the temperature of the reaction solution to 35-55°C. An initiator is added dropwise to the reaction solution, and after reacting for 0.5 to 1 hour, a mixed solution of cationic monomer and crosslinking agent is added dropwise. After reacting for 3 to 4 hours, the temperature of the reaction solution is cooled to room temperature to obtain the salt-resistant, water-insoluble material. According to the weight proportions of each component, add the salt-resistant, water-resistant, non-dispersible material, drag-reducing agent, and slurry preparation water to the constant speed mixer, stir evenly, and then add the defoamer. The mixing speed of the constant speed mixer is set to 4000±200 r / min. All the cement is poured into the constant speed mixer within 15 seconds. Then the mixing speed of the constant speed mixer is increased to 12000±500 r / min and mixing is continued for 35 seconds to obtain the salt-resistant cement slurry that does not disperse when exposed to water.

6. The preparation method according to claim 5, characterized in that, The initiator includes cerium ammonium sulfate and / or cerium ammonium nitrate; The weight ratio of the initiator to the branching agent is 3:1 to 4:1.

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