A friction reducer, its preparation method and a low-friction hydrocarbon self-healing ultra-high density cementing slurry

Abstract

This invention provides a friction-reducing agent, its preparation method, and a low-friction, hydrocarbon-reactive, self-healing ultra-high-density cement slurry, comprising: 100 parts by weight of cement, 50-190 parts by weight of weighting material, 30-50 parts by weight of anti-fading material, 2-5 parts by weight of self-healing agent, 2.0-5.0 parts by weight of fluid loss reducing agent, 0.5-2.0 parts by weight of retarder, 0-4.0 parts by weight of drag-reducing agent, 0.5-3.0 parts by weight of suspending agent, 0.5-1.5 parts by weight of friction-reducing agent, and 0.1-0.5 parts by weight of defoamer. This invention utilizes a polymer friction-reducing agent to reduce the friction of high-density cement slurry, increase its flow index, reduce its consistency coefficient, and improve its ability to suspend metal ions at high temperatures. The introduction of a hydrocarbon-reactive self-healing agent, through the adsorption and expansion of natural gas by the self-healing material, repairs micro-cracks, effectively improving the long-term sealing integrity and subsequent anti-channeling capability of the cement sheath.

Description

Technical Field

[0001] This invention relates to the field of cementing slurry technology, and more specifically, to a friction-reducing agent and its preparation method, and a low-friction, self-healing, ultra-high-density cementing slurry that reacts with hydrocarbons. Background Technology

[0002] With the advancement of oil and gas exploration and development technologies, the proportion of deep and ultra-deep wells in natural gas wells is increasing, with some wells reaching depths of 8000m. As well depths continue to increase, limitations imposed by complex geology and wellbore structure result in long open-hole sections (1500–2000m) and narrow safe density windows (0–0.12 g / cm³). 3 The wellbore faces challenges such as active oil and gas formations, high bottom-hole temperatures, high gas reservoir pressure, and high risk of gas channeling. To stabilize the gas reservoir, high-density drilling fluids and cement slurries are often used. However, traditional high-density cement slurry systems suffer from instability, poor fluidity, high consistency, and weak anti-channeling properties, making it difficult to guarantee cementing quality.

[0003] High-density and ultra-high-density cement slurries used in deep and ultra-deep wells need to have high performance, mainly in the following aspects: (1) They need to have ultra-high density to stabilize the formation and excellent rheological properties to ensure displacement efficiency; (2) They need to have good system stability to overcome the problems of cement slurry settling, poor fluidity, excessive consistency and slow strength development caused by the reduction of effective cement material after the addition of weighting materials in traditional high-density cement slurries; (3) The cement ring formed needs to overcome the problem of cement ring integrity failure caused by the brittleness and easy cracking of high-density cement stone, and also needs to have strong long-term sealing integrity and later anti-channeling ability.

[0004] Therefore, it is necessary to develop self-healing cement slurry that exhibits low friction, good system stability, and excellent construction performance under high temperature and high pressure to ensure the safety of cementing operations, reduce the risk of gas channeling in the later stages, and ensure the long-term, efficient, and stable operation of deep and ultra-deep wells. Summary of the Invention

[0005] In view of this, the present invention proposes a friction-reducing agent and its preparation method, as well as an ultra-high density cement slurry, aiming to solve the above-mentioned technical problems existing in the current ultra-high density cement slurry.

[0006] This invention proposes a friction-reducing agent, the raw material composition of which includes: 100.0 parts by weight of 2-acrylamide-2-methylpropanesulfonic acid, 0.5-1.5 parts by weight of carboxylic acid monomers, 3-5 parts by weight of amide monomers, 0.1-0.5 parts by weight of sodium salt, 2-6 parts by weight of alcohol polymers, 1-2 parts by weight of chain transfer agent, 0.4-0.7 parts by weight of initiator, and 350-450 parts by weight of water.

[0007] Furthermore, in the above-mentioned friction-reducing agent, the carboxylic acid monomer includes at least one of acrylic acid and maleic anhydride.

[0008] Furthermore, in the above-mentioned friction-reducing agent, the amide monomer includes at least one of acrylamide and N,N-dimethylacrylamide.

[0009] Furthermore, in the above-mentioned friction-reducing agent, the chain transfer agent includes at least one of 2,4-diphenyl-4-methyl-1-pentene and α-methylstyrene dimer.

[0010] Furthermore, in the above-mentioned friction-reducing agent, the alcohol polymer includes at least one of polyvinyl alcohol and polyethylene glycol.

[0011] This invention also provides a method for preparing a friction-reducing agent, comprising the following steps:

[0012] A mixed solution is obtained by mixing water, 2-acrylamide-2-methylpropanesulfonic acid, carboxylic acid monomers, amide monomers, sodium salts, alcohol polymers, and chain transfer agents;

[0013] Stir the above mixed solution and heat it to 50-70°C. After all the components in the mixed solution have dissolved uniformly, add the initiator to the mixed solution and react at a constant temperature for 2-3 hours.

[0014] Add a pH adjuster to adjust the pH of the mixed solution to 5-6, and allow it to cool naturally to room temperature to obtain a friction-reducing agent.

[0015] The method for preparing the friction-reducing agent in this invention is simple. The resulting friction-reducing agent exhibits good high-temperature resistance, increases the flow index of cement slurry, reduces the consistency coefficient of cement slurry, reduces the friction of cement slurry, improves the suspension capacity of metal ions at high temperatures, and does not negatively affect water loss performance or thickening time. It is suitable for high-density and ultra-high-density cement slurries used in high-temperature and high-pressure environments. The low-friction, self-healing, ultra-high-density cement slurry formulated using the friction-reducing agent of this invention exhibits low friction and good rheological properties (n≥0.98, K≤0.17Pa·s). n The system exhibits good stability (cement slurry settling stability at high temperatures ≤0.02g / cm³). 3 The density difference between the top and bottom of the cement stone at high temperatures is ≤0.02g / cm³. 3 It has low water loss (≤40mL) and other good overall performance. Under the same safety density window, it can be pumped with a larger displacement to improve displacement efficiency and enhance the bonding ability of the two interfaces.

[0016] This invention also proposes a low-friction, hydrocarbon-reactive, self-healing, ultra-high-density cement slurry. The raw material composition of this cement slurry includes: 100 parts by weight of cement, 50-190 parts by weight of weighting material, 30-50 parts by weight of anti-fading material, 2-5 parts by weight of self-healing agent, 2.0-5.0 parts by weight of fluid loss reducing agent, 0.5-2.0 parts by weight of retarder, 0-4.0 parts by weight of drag reducing agent, 0.5-3.0 parts by weight of suspending agent, 0.5-1.5 parts by weight of friction reducing agent, and 0.1-0.5 parts by weight of defoamer; wherein the friction reducing agent is any one of the friction reducing agents described above.

[0017] Furthermore, in the aforementioned low-friction, hydrocarbon-resistant, self-healing ultra-high density cement slurry, the self-healing agent is a core-shell polymer microsphere structure. The component ratio of the core structure in the core-shell polymer microsphere structure is 100:20–40:2–6 by mass of styrene-based monomers, vinyl polymer crosslinking agents, and initiators. The component ratio of the shell structure in the core-shell polymer microsphere structure is 100:30–70:5–10:2–8 by mass of styrene-based monomers, acrylates, vinyl polymer crosslinking agents, and initiators.

[0018] Furthermore, in the aforementioned low-friction, hydrocarbon-resistant, self-healing, ultra-high-density cement slurry, the weighting material includes at least one of hematite powder, reduced iron powder, and manganese ore powder.

[0019] Furthermore, in the aforementioned low-friction, hydrocarbon-resistant, self-healing, ultra-high-density cement slurry, the anti-fading material includes silica powder.

[0020] Compared with existing technologies, the beneficial effects of this invention are as follows: This invention improves the bulk density of dry-mixed materials by optimizing the dry-mixing formula of ultra-high density cement paste through close packing and particle size distribution. Simultaneously, it selects minerals with smooth, dense surfaces, good sphericity, high chemical activity, and strong ball-bearing and pozzolanic effects as weighting agents to enhance the various properties of the cement paste. In addition, several admixtures, including water loss reducers, retarders, drag reducers, suspending agents, friction reducers, and defoamers, are selected to improve the stability of the cement slurry system and avoid problems such as excessively high consistency and slow strength development. In particular, the use of polymer friction reducers can reduce the friction of high-density cement slurry, increase its flow index, reduce its consistency coefficient, and improve the suspension capacity of metal ions at high temperatures. This solves the problems of cement slurry settling, poor fluidity, poor rheological properties, excessively high consistency, and slow strength development caused by the reduction of effective cementitious material after the addition of weighting materials. The introduction of hydrocarbon self-healing agents can repair microcracks caused by stress-induced microcracks in cement stone, which can be repaired by the expansion of natural gas absorbed by the self-healing material. This can effectively improve the long-term sealing integrity and anti-channeling ability of the cement ring, solving the problem of cement ring integrity failure caused by the brittleness and easy cracking of high-density cement stone. Attached Figure Description

[0021] Figure 1 This is a static cementitious strength curve of the cement slurry prepared in Example 3 of the present invention;

[0022] Figure 2 The graph shows the permeability variation of cement stone obtained after cement slurry curing in Example 3 and Comparative Example 2 of this invention. Detailed Implementation

[0023] The present invention will be further illustrated below with reference to the embodiments, the purpose of which is to better understand the content of the present invention and to demonstrate the essential features of the present invention. Therefore, the embodiments should not be regarded as a limitation on the scope of protection of the present invention.

[0024] This invention provides an ultra-high density cement slurry, the raw material composition of which includes: 100 parts by weight of cement, 50-190 parts by weight of weighting material, 30-50 parts by weight of anti-fading material, 2-5 parts by weight of self-healing agent, 2.0-5.0 parts by weight of fluid loss reducing agent, 0.5-2.0 parts by weight of retarder, 0-4.0 parts by weight of drag reducing agent, 0.5-3.0 parts by weight of suspending agent, 0.5-1.5 parts by weight of friction reducing agent, and 0.1-0.5 parts by weight of defoamer.

[0025] According to a specific embodiment of the present invention, preferably, the cement is Grade G oil well cement.

[0026] The selection of dry-mix materials (weighting materials and anti-fading materials) should follow the following two principles: First, they should have a reasonable particle size distribution to form a good particle gradation effect with cement; second, they should select minerals with smooth and dense surfaces, good sphericity, high chemical activity, and strong ball bearing effect and pozzolanic effect.

[0027] According to a specific embodiment of the present invention, preferably, the weighting material includes at least one of hematite powder, reduced iron powder, and manganese ore powder. The weighting material can be a combination of the following: using iron ore powder alone, using reduced iron powder alone, using manganese ore powder alone, using a mixture of both hematite powder and reduced iron powder, using a mixture of both hematite powder and manganese ore powder, using a mixture of both reduced iron powder and manganese ore powder, or using a mixture of all three: hematite powder, reduced iron powder, and manganese ore powder. The density of the hematite powder can be 4.8–5.2 g / cm³. 3 The particle size distribution can be D50 = 25.14 μm; the density of the reduced iron powder can be 6.8–7.4 g / cm³. 3 The particle size distribution can be D50 = 90.21 μm; the density of the manganese ore powder can be 4.5–5.5 g / cm³. 3The particle size distribution can be D50 = 1.08 μm. The amount of weighting material can be 50, 100, 150, or 190 parts by weight.

[0028] According to a specific embodiment of the present invention, preferably, the anti-fading material is silica powder. The amount of the anti-fading material can be 30, 35, 40, 45, or 50 parts by weight.

[0029] In this embodiment, the anti-fading material is composed of silica powder of different finenesses, such as 200 mesh, 500 mesh, and 1250 mesh, with the specific dosage of each fineness varying according to temperature and density. The function of the silica powder is to adjust the calcium-silicon ratio in the cement paste, causing the cement hydration products to transform into a more stable crystal form with lower permeability at high temperatures. The reaction rates between silica powder of different mesh sizes and cement hydration products are different.

[0030] According to a specific embodiment of the present invention, preferably, the drag-reducing agent comprises at least one of polynaphthalene sulfonate and polycarboxylic acid copolymer. For example, the drag-reducing agent can be polynaphthalene sulfonate, polycarboxylic acid copolymer, or a mixture of both. The polynaphthalene sulfonate and polycarboxylic acid copolymer can be commercially available products, such as polynaphthalene sulfonate of model BCD-200L produced by Tianjin Zhongyou Boxing Engineering Technology Co., Ltd., and polycarboxylic acid copolymers of models BCD-210L and BCD-220L produced by Tianjin Zhongyou Boxing Engineering Technology Co., Ltd.

[0031] In this embodiment, the amount of drag-reducing agent can be 0.5, 1, 1.5, 2, 2.5, 3, 3.5, or 4 parts by weight.

[0032] According to a specific embodiment of the present invention, preferably, the defoamer includes at least one of tributyl phosphate and dimethyl silicone oil. For example, the defoamer may be tributyl phosphate, dimethyl silicone oil, or a mixture of both.

[0033] In this embodiment, the amount of defoamer can be 0.1, 0.2, 0.3, 0.4, or 0.5 parts by weight.

[0034] According to a specific embodiment of the present invention, preferably, the raw material composition of the water loss reducing agent includes: 100 parts by weight of 2-acrylamide-2-methylpropanesulfonic acid, 0.1 to 0.5 parts by weight of crosslinking monomer, 1 to 3 parts by weight of molecular weight regulator, 1 to 3 parts by weight of alcohol monomer, 8 to 10 parts by weight of amide monomer, 0.5 to 1.0 parts by weight of carboxylic acid monomer, and 300 to 400 parts by weight of water.

[0035] For example, the preparation method of the water loss reducing agent can be found in Example 1 of the invention patent application number 202211642130.6, entitled "A Salt-Resistant Low-Temperature Early Strength Water Loss Reducing Agent and Its Preparation Method". The model can be the commercially available product BCF-230L.

[0036] In this embodiment, the amount of the dehydration reducing agent can be 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, or 5.0 parts by weight.

[0037] According to a specific embodiment of the present invention, preferably, the raw material composition of the retarder includes: 7-10 parts by weight of vinylphosphonic acid, 0.2-1 parts by weight of diethyl vinylphosphonate, 4-7 parts by weight of divinylbenzene, 5-8 parts by weight of tristyrene-phenol polyoxyethylene ether, and 5-10 parts by weight of N-vinylpyrrolidone.

[0038] For example, the preparation method of the retarder can be found in Example 1 of the invention patent with application number 202210786182.4, "An ultra-high temperature large temperature difference retarder for oil well cement and its preparation method".

[0039] In this embodiment, the amount of retarder can be 0.5, 0.8, 1.0, 1.5, or 2.0 parts by weight.

[0040] According to a specific embodiment of the present invention, preferably, the self-healing agent is a core-shell polymer microsphere structure, wherein the component ratio of the core structure in the core-shell polymer microsphere structure is: styrene-based monomer, vinyl polymer crosslinking agent, and initiator in a mass ratio of 100:20-40:2-6; and the component ratio of the shell structure in the core-shell polymer microsphere structure is: styrene-based monomer, acrylate, vinyl polymer crosslinking agent, and initiator in a mass ratio of 100:30-70:5-10:2-8.

[0041] The initiator can be benzoyl peroxide, azobisisobutyronitrile, or dodecyl peroxide. The styrene-based monomer can be styrene, 2-methylstyrene, ethylvinylbenzene, vinyltoluene, or vinylnaphthalene. The vinyl polymer crosslinking agent can be divinylbenzene, divinyl ether, or divinylethyl urea. The acrylate can be butyl acrylate, butyl methacrylate, dodecyl acrylate, dodecyl methacrylate, or octadecyl acrylate.

[0042] For example, the preparation method of the self-healing agent can be found in Example 1 of the invention patent application No. 201310426597.1 entitled "A core-shell polymer microsphere and its preparation and application". In this example, the amount of self-healing agent can be 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0 parts by weight.

[0043] According to a specific embodiment of the present invention, preferably, the raw material composition of the suspending agent includes: 100 parts by weight of 2-acrylamide-2-methylpropanesulfonic acid, 3-5 parts by weight of cyclic monomers, 0.1-0.5 parts by weight of allyl ammonium chloride monomers, 0.5-0.8 parts by weight of azobisisobutyramidine hydrochloride, and 300-400 parts by weight of water. For example, the raw material composition of the suspending agent includes: 100 parts by weight of 2-acrylamide-2-methylpropanesulfonic acid, 3 parts by weight of acryloylmorpholine, 0.1 parts by weight of octadecylmethyldiallyl ammonium chloride, 0.3 parts by weight of hexadecylmethyldiallyl ammonium chloride, 0.5 parts by weight of azobisisobutyramidine hydrochloride, and 300 parts by weight of fresh water.

[0044] For example, the preparation method of the suspending agent can be found in Example 1 of the invention patent "A high-temperature resistant suspending agent for cement slurry and its preparation method" with application number 202210762717.4.

[0045] In this embodiment, the amount of suspending agent can be 0.5, 0.8, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, or 5.0 parts by weight.

[0046] According to a specific embodiment of the present invention, the friction reducer is an AMPS (2-acrylamide-2-methylpropanesulfonic acid) polymer that reduces the friction of cement slurry, increases the flow index of high-density cement slurry, reduces the consistency coefficient of high-density cement slurry, and improves the ability to suspend metal ions at high temperatures.

[0047] Preferably, the friction-reducing agent is obtained by polymerization of the following components: 100.0 parts by weight of 2-acrylamide-2-methylpropanesulfonic acid, 0.5 to 1.5 parts by weight of carboxylic acid monomers, 3 to 5 parts by weight of amide monomers, 0.1 to 0.5 parts by weight of sodium salt, 2 to 6 parts by weight of alcohol polymer, 1 to 2 parts by weight of chain transfer agent, 0.4 to 0.7 parts by weight of initiator, and 350 to 450 parts by weight of water.

[0048] Among them, 2-acrylamide-2-methylpropanesulfonic acid has good water solubility, and its molecule contains polymerizable vinyl groups and hydrophilic sulfonic acid groups. It is easy to polymerize with other monomers and has a high anion loading density, which improves the calcium ion binding ability of the polymer product.

[0049] The carboxylic acid monomer can be at least one of acrylic acid and maleic anhydride. For example, the carboxylic acid monomer can be acrylic acid, maleic anhydride, or a mixture of both. In this embodiment, by adding a carboxylic acid monomer, the friction-reducing agent molecule contains a carboxyl group, significantly improving the anchoring ability of the friction-reducing agent molecule on the cement hydration surface. This reduces interfacial tension, improves the wetting efficiency of solid particles, and increases the thickness of the water film layer during cement slurry preparation, thereby reducing slurry friction.

[0050] When the amount of carboxylic acid monomer exceeds 1.5 parts by weight, the thickening time of the cement slurry with the friction reducer prepared according to this invention is significantly prolonged. Therefore, the amount of carboxylic acid monomer should not exceed 1.5 parts by weight. Preferably, the amount of carboxylic acid monomer is 0.5 to 1.5 parts by weight. For example, the amount of carboxylic acid monomer can be 0.5, 0.8, 1.0, 1.3, 1.5, etc.

[0051] The amide monomer can be at least one of acrylamide and N,N-dimethylacrylamide. For example, the amide monomer can be acrylamide, N,N-dimethylacrylamide, or a mixture of both. The amount of amide monomer used can be 3, 3.5, 4, 4.5, or 5 parts by weight.

[0052] In this embodiment, by adding amide monomers, the degree of polymerization and heat resistance of the friction reducer can be improved, so that the polymer molecules of the friction reducer remain stable at high temperatures and do not decompose, thus ensuring the rheological properties of the cement slurry prepared using the friction reducer at high temperatures.

[0053] The sodium salt monomer can be at least one of sodium styrene sulfonate and sodium methpropylene sulfonate, such as sodium styrene sulfonate, sodium methpropylene sulfonate, or a mixture of both. The amount of sodium salt monomer used can be 0.2, 0.3, 0.4, or 0.5 parts by weight.

[0054] In this embodiment, by adding sodium salt monomers, the friction reducer can improve the stability of metal ions at high temperatures, thereby improving the stability of cement slurry prepared using the friction reducer.

[0055] The alcohol polymer can be at least one of polyvinyl alcohol and polyethylene glycol. For example, the alcohol polymer can be polyvinyl alcohol, the alcohol polymer can be polyethylene glycol, or a mixture of both polyvinyl alcohol and polyethylene glycol can be used. The amount of alcohol polymer used can be 2, 2.5, 3, 3.5, 4.5, 5, or 6 parts by weight.

[0056] In this embodiment, by adding alcohol polymers, the friction-reducing agent molecules can contain hydroxyl groups, forming an adsorption layer on the surface of the cement gel material, generating physical steric hindrance, preventing the aggregation of cement particles, thereby improving the dispersibility and stability of cement slurry.

[0057] The chain transfer agent includes at least one of 2,4-diphenyl-4-methyl-1-pentene and α-methylstyrene dimer. The chain transfer agent can be 2,4-diphenyl-4-methyl-1-pentene, α-methylstyrene dimer, or a mixture of both. The amount of chain transfer agent used can be 1, 1.5, or 2 parts by weight.

[0058] In this embodiment, by adding a chain transfer agent, the degree of polymerization and molecular weight distribution of the polymer can be controlled, thereby improving the friction-reducing ability of the friction-reducing agent in ultra-high density cement slurry. In addition, the rheological properties of cement slurry with added friction-reducing agent can be adjusted, and it can also play a certain role in suspension stabilization in cement slurry.

[0059] When preparing friction-reducing agents, the amount of water used can be 350, 370, 390, 400, 410, 430, or 450 parts by weight. The water can be fresh water or deionized water.

[0060] In this embodiment, the above-mentioned friction-reducing agent was obtained by polymerization under the action of 0.4 to 0.7 parts by weight of initiator.

[0061] An initiator is used to induce organic polymerization of the components of the friction-reducing agent to obtain the friction-reducing agent. The initiator can be at least one of benzoyl peroxide, azobisisobutyramidine hydrochloride, and ammonium persulfate. Specifically, the initiator can be benzoyl peroxide, azobisisobutyramidine hydrochloride, ammonium persulfate, a mixture of benzoyl peroxide and azobisisobutyramidine hydrochloride, a mixture of benzoyl peroxide and ammonium persulfate, a mixture of azobisisobutyramidine hydrochloride and ammonium persulfate, or a mixture of benzoyl peroxide, azobisisobutyramidine hydrochloride, and ammonium persulfate. The amount of initiator used can be 0.4, 0.5, 0.6, or 0.7 parts by weight.

[0062] Deep and ultra-deep wells are characterized by active oil and gas formations, high bottom-hole temperatures, high gas layer pressures, and a high risk of gas channeling. To stabilize the gas layer, high-density drilling fluids and cement slurries are often used. However, traditional high-density cement slurry systems suffer from instability, poor fluidity, high consistency, and weak anti-channeling properties, making it difficult to guarantee cementing quality. To ensure cementing quality and construction safety, the high-density cement slurry used must possess extremely high density to stabilize the formation, excellent rheological properties, and good system stability to overcome the problems of sedimentation and excessively high consistency caused by the reduction of effective cementitious material after the addition of weighting materials in traditional high-density cement slurries. The friction-reducing agent synthesized in this invention reduces cement slurry friction, improves the rheological properties and stability of the cement slurry, prevents thickening of the cement slurry, and has almost no effect on the thickening time of the cement slurry.

[0063] In this embodiment of the invention, the preparation method of the friction-reducing agent includes the following steps:

[0064] Step 1: Add water, 2-acrylamide-2-methylpropanesulfonic acid, carboxylic acid monomers, amide monomers, sodium salts, alcohol polymers, and chain transfer agents to the reaction vessel to obtain a mixed solution.

[0065] In this step, water, 2-acrylamide-2-methylpropanesulfonic acid, carboxylic acid monomers, amide monomers, sodium salts, alcohol polymers, and chain transfer agents can be added sequentially to the reaction vessel.

[0066] The reaction vessel can be a three-necked or four-necked flask equipped with a thermometer, a stirring device, and a dropping funnel.

[0067] Step 2: Stir the above mixed solution and use a heating device to raise the temperature of the mixed solution to 50-70°C. After all the components in the mixed solution have dissolved evenly, add the initiator to the mixed solution and react at a constant temperature for 2-3 hours.

[0068] In this step, the mixed solution can be stirred at a stirring speed of 150 r / min.

[0069] Step 3: Add a pH adjuster to the reaction vessel to adjust the hydrogen ion concentration index (pH value) of the mixed solution to 5-6, and allow it to cool naturally to room temperature to obtain a friction-reducing agent. For example, the amount of pH adjuster added can be 8, 10, 12, 14, or 16 parts by weight.

[0070] Specifically, the pH adjuster can be a sodium hydroxide solution, and the concentration of the sodium hydroxide solution can be 10%-30%, for example, 10%, 20%, or 30%, etc. In the embodiments of this application, there is no specific limitation.

[0071] The friction-reducing agent prepared in the embodiments of the present invention can be a colorless liquid with a certain viscosity.

[0072] The method for preparing the friction-reducing agent in this invention embodiment is simple. The obtained friction-reducing agent has good high-temperature resistance, can increase the flow index of cement slurry, reduce the consistency coefficient of cement slurry, reduce the friction of cement slurry, improve the suspension capacity of metal ions at high temperature, and does not have a negative impact on water loss performance and thickening time. It is suitable for high-density and ultra-high-density cement slurries used in high-temperature and high-pressure environments.

[0073] The low-friction, self-healing, ultra-high-density cement slurry formulated using the friction-reducing agent of this invention exhibits low friction and good rheological properties (n≥0.98, K≤0.17Pa·s). n The system exhibits good stability (cement slurry settling stability at high temperatures ≤0.02g / cm³). 3 The density difference between the top and bottom of the cement stone at high temperatures is ≤0.02g / cm³.3 It has low water loss (≤40mL) and other good comprehensive performance. Under the same safety density window, it can be pumped with a larger displacement to improve displacement efficiency and enhance the bonding ability of the two interfaces (the bonding surface between the cement sheath and the formation).

[0074] This invention optimizes the dry-mix formulation of ultra-high density cement paste through close packing and particle size distribution, increasing the bulk density and solid content per unit volume of the dry-mix material to reduce cement stone permeability and improve cement stone strength. Simultaneously, minerals with smooth, dense surfaces, good sphericity, high chemical activity, and strong ball-bearing and pozzolanic effects are selected as weighting agents to improve various properties of the cement paste, especially its rheological properties, and reduce its friction.

[0075] In addition, several admixtures, including water loss reducers, retarders, drag reducers, suspending agents, friction reducers, and defoamers, are selected to improve the stability of the cement slurry system and avoid problems such as excessively high consistency and slow strength development. In particular, the use of polymer friction reducers can reduce the friction of high-density cement slurry, increase its flow index, reduce its consistency coefficient, and improve the suspension capacity of metal ions at high temperatures. This solves the problems of cement slurry settling, poor fluidity, poor rheological properties, excessively high consistency, and slow strength development caused by the reduction of effective cementitious material after the addition of weighting materials. The introduction of hydrocarbon self-healing agents can repair microcracks caused by stress-induced microcracks in cement stone, which can be repaired by the expansion of natural gas absorbed by the self-healing material. This can effectively improve the long-term sealing integrity and anti-channeling ability of the cement ring, solving the problem of cement ring integrity failure caused by the brittleness and easy cracking of high-density cement stone.

[0076] This invention also provides a method for preparing ultra-high density cement slurry, comprising: mixing cement, weighting material, anti-fading material, self-healing agent, fluid loss reducing agent, retarder, drag reducing agent, suspending agent, friction reducing agent, defoamer, and water evenly to obtain a low-friction, hydrocarbon-reactive, self-healing ultra-high density cement slurry.

[0077] According to a specific embodiment of the present invention, preferably, under stirring conditions, cement, weighting material, anti-fading material, self-healing agent, water loss reducer, retarder, drag reducer, suspending agent, friction reducer, and defoamer are added to water, and stirring is continued until homogeneous. Parameters such as stirring speed and time can refer to API 10A specifications.

[0078] Preferably, cement, weighting material, anti-fading material, and self-healing agent are uniformly mixed to form a solid material.

[0079] Preferably, the water loss reducer, retarder, drag reducer, suspending agent, friction reducer, and defoamer are added to the water to form a mixed liquid.

[0080] In this embodiment, before adding the solid material to the mixing liquid, the mixing liquid must be thoroughly mixed under stirring to ensure complete dispersion of the additive in the water. The stirring speed can be 4000 r / min ± 200 r / min, and the stirring time can be 15 s.

[0081] In this embodiment, when adding solid materials to the mixing liquid, the stirring speed can be 4000 r / min ± 200 r / min, and the addition time can be 15 s.

[0082] In this embodiment, after adding the solid material to the mixing liquid, the stirring speed can be 12000r / min±500r / min, and the stirring time can be 35s±1s.

[0083] The low-friction, hydrocarbon-reactive, self-healing, ultra-high-density cementing slurry of this invention can form cement slurry systems with varying densities, with the highest system density reaching 2.80 g / cm³. 3 .

[0084] The low-friction, hydrocarbon-reactive, self-healing, ultra-high-density cement slurry system of this invention features low friction, good rheological properties, good system stability, low water loss, and normal early compressive strength development. It also has good workability and mechanical properties, ensuring construction safety and the integrity of the cement sheath seal.

[0085] The low-friction, hydrocarbon-reactive, self-healing, ultra-high-density cementing slurry system of this invention forms cement stone with hydrocarbon-reactive properties. It can self-heal after the cement sheath is subjected to stress and micro-cracks occur, leading to sealing failure. This provides secondary protection and can effectively improve the later sealing performance of the cement sheath, ensuring the life of oil and gas wells.

[0086] The present invention will be described in detail below with reference to specific embodiments:

[0087] Friction reducer Example 1

[0088] Step 1: Add 350 parts by weight of water, 100 parts by weight of 2-acrylamide-2-methylpropanesulfonic acid, 1.0 part by weight of acrylic acid, 3.5 parts by weight of acrylamide, 0.2 parts by weight of sodium styrene sulfonate, 3 parts by weight of polyvinyl alcohol, and 1 part by weight of 2,4-diphenyl-4-methyl-1-pentene to a three-necked flask equipped with a thermometer, stirring device, and dropping funnel, according to 1 g per part by weight, to obtain a mixed solution.

[0089] Step 2: Stir the mixed solution at a stirring speed of 150 r / min, raise the temperature of the mixed solution to 50℃, and after all components in the mixed solution have dissolved uniformly, add 1 part by weight of azobisisobutyramidine hydrochloride to the mixed solution and react at a constant temperature for 2.5 hours.

[0090] Step 3: Add sodium hydroxide solution to the reaction vessel, adjust the hydrogen ion concentration index (pH value) of the mixed solution to 5, and allow it to cool naturally to room temperature to obtain the friction-reducing agent.

[0091] Friction reducer Example 2

[0092] Step 1: Add 350 parts by weight of water, 100 parts by weight of 2-acrylamide-2-methylpropanesulfonic acid, 0.5 parts by weight of maleic anhydride, 5 parts by weight of N,N-dimethylacrylamide, 0.3 parts by weight of sodium styrene sulfonate, 2 parts by weight of polyethylene glycol, and 1 part by weight of 2,4-diphenyl-4-methyl-1-pentene to a three-necked flask equipped with a thermometer, stirring device, and dropping funnel, according to 1 g per part by weight, to obtain a mixed solution.

[0093] Step 2: Stir the mixed solution at a stirring speed of 150 r / min, raise the temperature of the mixed solution to 50℃, and after all components in the mixed solution have dissolved uniformly, add 1 part by weight of azobisisobutyramidine hydrochloride to the mixed solution and react at a constant temperature for 2.5 hours.

[0094] Step 3: Add sodium hydroxide solution to the reaction vessel, adjust the hydrogen ion concentration index (pH value) of the mixed solution to 6, and allow it to cool naturally to room temperature to obtain the friction-reducing agent.

[0095] Friction reducer Example 3

[0096] Step 1: Add 450 parts by weight of water, 100 parts by weight of 2-acrylamide-2-methylpropanesulfonic acid, 0.5 parts by weight of acrylic acid, 1 part by weight of maleic anhydride, 1.5 parts by weight of acrylamide, 2 parts by weight of N,N-dimethylacrylamide, 0.2 parts by weight of sodium methacrylate, 4 parts by weight of polyvinyl alcohol, and 1 part by weight of α-methylstyrene dimer to a three-necked flask equipped with a thermometer, stirring device, and dropping funnel, in 1g per part by weight, to obtain a mixed solution.

[0097] Step 2: Stir the mixed solution at a stirring speed of 150 r / min, raise the temperature of the mixed solution to 60℃, and after all components in the mixed solution have dissolved uniformly, add 1 part by weight of ammonium persulfate to the mixed solution and react at a constant temperature for 3 hours.

[0098] Step 3: Add sodium hydroxide solution to the reaction vessel, adjust the hydrogen ion concentration index (pH value) of the mixed solution to 6, and allow it to cool naturally to room temperature to obtain the friction-reducing agent.

[0099] Cement grout Example 1

[0100] The composition of cement slurry raw materials is shown in Table 1 below:

[0101] Table 1

[0102]

[0103]

[0104] According to API 10A specifications, under stirring conditions, the weighting material, anti-fading material, and self-healing agent are mixed evenly to form a solid material; the fluid loss reducer, retarder, drag reducer, suspending agent, friction reducer, and defoamer are added to water and stirred evenly to form a mixing liquid; the solid material is added to the mixing liquid and stirred until uniform to obtain a low-friction, hydrocarbon-reactive, self-healing, ultra-high density cementing slurry.

[0105] Cement grout Example 2

[0106] The composition of cement slurry raw materials is shown in Table 2 below:

[0107] Table 2

[0108]

[0109] Preparation:

[0110] According to API 10A specifications, under stirring conditions, the weighting material, anti-fading material, and self-healing agent are mixed evenly to form a solid material; the fluid loss reducer, retarder, drag reducer, suspending agent, friction reducer, and defoamer are added to water and stirred evenly to form a mixing liquid; the solid material is added to the mixing liquid and stirred until uniform to obtain a low-friction, hydrocarbon-reactive, self-healing, ultra-high density cementing slurry.

[0111] Cement grout Example 3

[0112] The composition of cement slurry raw materials is shown in Table 3 below:

[0113] Table 3

[0114]

[0115] Preparation:

[0116] According to API 10A specifications, under stirring conditions, the weighting material, anti-fading material, and self-healing agent are mixed evenly to form a solid material; the fluid loss reducer, retarder, drag reducer, suspending agent, friction reducer, and defoamer are added to water and stirred evenly to form a mixing liquid; the solid material is added to the mixing liquid and stirred until uniform to obtain a low-friction, hydrocarbon-reactive, self-healing, ultra-high density cementing slurry.

[0117] Cement grout comparative example 1

[0118] The friction reducer was removed from the formulation of cement slurry Example 3, while the rest were added normally, as shown in Table 4 below:

[0119] Table 4

[0120]

[0121] Preparation:

[0122] According to API 10A specifications, under stirring conditions, the weighting material, anti-fading material, and self-healing agent are mixed evenly to form a solid material; the fluid loss reducer, retarder, drag reducer, suspending agent, and defoamer are added to water and stirred evenly to form a mixing liquid; the solid material is added to the mixing liquid and stirred until uniform to obtain ultra-high density cement slurry.

[0123] Cement grout comparative example 2

[0124] The self-healing agent was removed from the formulation of cement grout in Example 3, while the rest were added normally, as shown in Table 5 below:

[0125] Table 5

[0126]

[0127]

[0128] Preparation:

[0129] According to API 10A specifications, under stirring conditions, the weighting material and anti-fading material are mixed evenly to form a solid material; the fluid loss reducer, retarder, drag reducer, suspending agent, friction reducer and defoamer are added to water and stirred evenly to form a mixing liquid; the solid material is added to the mixing liquid and stirred until uniform to obtain ultra-high density cement slurry.

[0130] Cement grout comparison example 3

[0131] The self-healing agent and friction reducer were removed from the formulation of cement grout in Example 3, while the rest were added normally, as shown in Table 6 below:

[0132] Table 6

[0133]

[0134] Preparation:

[0135] According to API 10A specifications, under stirring conditions, the weighting material and anti-fading material are mixed evenly to form a solid material; the fluid loss reducer, retarder, drag reducer, suspending agent and defoamer are added to water and stirred evenly to form a mixing liquid; the solid material is added to the mixing liquid and stirred until uniform to obtain ultra-high density cement slurry.

[0136] Experimental Example 1

[0137] The performance of the cement slurries provided in Examples 1-3 and Comparative Examples 1-3 were tested according to API 10A specifications, and the results are shown in Tables 7-10.

[0138] Table 7. Workability of Cement Grout

[0139]

[0140] As shown in Table 7, the density of the low-friction, hydrocarbon-resistant, self-healing, ultra-high-density cement slurry system can reach up to 2.80 g / cm³. 3 It has good fluidity, no free liquid, and the cement slurry settling stability is no greater than 0.02 g / cm³. 3 The density difference between the top and bottom of the cement stone should not exceed 0.02 g / cm³. 3 The water loss at high temperature is no more than 40 mL, and the thickening time is adjustable. Compared with the cement slurry Comparative Examples 1 and 3 without the addition of friction reducer, the cement slurry Examples 1-3 and Comparative Example 2 prepared with friction reducer have basically the same thickening time, but have better fluidity and settling stability.

[0141] Table 8. Rheological properties of cement paste at 180℃

[0142]

[0143]

[0144] The rheological properties of the cement slurries provided in Examples 1-3 and Comparative Examples 1-3 in Table 8 at 180°C were measured using a high-temperature, high-pressure rheometer. The results show that the cement slurries with added friction-reducing agents (Examples 1-3 and Comparative Example 2) exhibit superior rheological properties at high temperatures, possessing lower friction and enabling larger pumping volumes within the same safety density window, thereby improving displacement efficiency and interfacial bonding ability.

[0145] Table 9 Mechanical properties of cement stone

[0146]

[0147] The mechanical properties of cement paste obtained by curing cement slurry at 180℃ are shown in Table 9. The static cementitious strength test results show that cement slurry examples 1-3 have the characteristics of short transition time, early strength initiation time, rapid strength development, and corresponding cement paste 24h strength greater than 28MPa. Figure 1The static gel strength curve for cement slurry Example 3 is shown. The static gel strength curves for cement slurry Examples 1 and 2 are similar to those for Example 3. A comparison of cement slurry Comparative Examples 1-3 with cement slurry Examples 1-3 shows that the addition of friction reducer and self-healing agent did not negatively affect the strength development time of the cement slurry or the compressive strength of the cement paste.

[0148] The self-healing agent in this invention is a high-temperature resistant hydrocarbon self-healing agent developed for high-pressure natural gas wells. When micro-cracks occur in the cement sheath, leading to sealing failure, it adsorbs and expands hydrocarbon molecules with more than C1 in methane and crude oil, thereby sealing the micro-cracks and micro-gaps, achieving a self-healing effect, providing secondary protection, and effectively improving the sealing performance of the cement sheath in the later stage.

[0149] The self-healing properties of cement stone formed in Examples 1-3 and Comparative Examples 1-3 of cement slurry were demonstrated by testing the changes in permeability of cement stone columns containing microcracks before and after curing in methane. The cement stone columns had dimensions of D25mm × L50mm. After cracks were formed penetrating the cement stone using the Brazilian splitting method, they were encapsulated in thermoplastic tubes and placed in a self-developed self-healing cement evaluation device for testing. The experimental results are shown in Table 10. The gas permeability curves for Example 3 and Comparative Example 2 of cement slurry are shown in Table 10. Figure 2 The gas permeability curves of cement slurry Examples 1 and 2 are similar to those of Example 3.

[0150] Table 10 Self-healing ability of cement stone

[0151]

[0152] From the data in Table 10 and Figure 2 The changes in the permeability curves show that the cement stone with added self-healing agent (Examples 1-3, Comparative Example 1) has a significant reduction in permeability, indicating that the self-healing agent reacts in the methane environment and fills the micro-cracks; the cement stone without added self-healing agent (Comparative Example 2, Comparative Example 3) has almost no change in permeability, indicating that the cracks still exist.

[0153] In summary, the present invention has the following beneficial effects:

[0154] (1) The low-friction, hydrocarbon-resistant, self-healing, ultra-high-density cementing slurry system provided by this invention has a density of up to 2.80 g / cm³. 3 This ensures the stability of the gas layer.

[0155] (2) The low friction self-healing ultra-high density cement slurry system with hydrocarbons provided by the present invention can be used at a maximum temperature of 180°C, which can meet the target layer temperature requirements of deep wells and ultra-deep wells.

[0156] (3) The low-friction, hydrocarbon-resistant, self-healing, ultra-high-density cement slurry system provided by this invention has good system stability (density difference between the upper and lower layers of cement stone at high temperature ≤ 0.02 g / cm³). 3 It has good water loss performance (API water loss ≤40mL) and no free fluid, which can avoid cross-flow channels or downhole accidents caused by cement slurry sedimentation and stratification.

[0157] (4) The low-friction, self-healing, ultra-high-density cement slurry system for hydrocarbon-reactive environments provided by this invention has low friction and good rheological properties (n≥0.98, K≤0.18Pa·s). n With the characteristics of ), under the same safety density window, a larger displacement pump can be used to improve displacement efficiency and enhance the bonding ability of the two interfaces.

[0158] (5) The low friction self-healing ultra-high density cement slurry system with hydrocarbon encounter provided by the present invention has the characteristic of normal early strength development, which can ensure the long-term sealing integrity of the wellbore.

[0159] (6) The low-friction, hydrocarbon-reactive, self-healing, ultra-high-density cement slurry system provided by this invention has hydrocarbon-reactive self-healing properties. When the cement sheath in the well experiences micro-cracks under stress, leading to sealing failure, the self-healing material can absorb natural gas and expand to repair the micro-cracks, achieving a self-healing effect and providing secondary protection. This effectively improves the sealing performance of the cement sheath in the later stages. The comprehensive performance of the cement slurry meets the long-term sealing integrity requirements of high-pressure natural gas wells, ensuring construction safety and the lifespan of oil and gas wells.

[0160] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A friction-reducing agent, characterized in that, The raw material composition of the friction-reducing agent includes: 100.0 parts by weight of 2-acrylamide-2-methylpropanesulfonic acid, 0.5-1.5 parts by weight of carboxylic acid monomers, 3-5 parts by weight of amide monomers, 0.1-0.5 parts by weight of sodium salt, 2-6 parts by weight of alcohol polymers, 1-2 parts by weight of chain transfer agent, 0.4-0.7 parts by weight of initiator, and 350-450 parts by weight of water.

2. The friction-reducing agent according to claim 1, characterized in that, The carboxylic acid monomers include at least one of acrylic acid and maleic anhydride.

3. The friction-reducing agent according to claim 1, characterized in that, The amide monomers include at least one of acrylamide and N,N-dimethylacrylamide.

4. The friction-reducing agent according to claim 1, characterized in that, The chain transfer agent includes at least one of 2,4-diphenyl-4-methyl-1-pentene and α-methylstyrene dimer.

5. The friction-reducing agent according to claim 1, characterized in that, The alcohol polymers include at least one of polyvinyl alcohol and polyethylene glycol.

6. A method for preparing a friction-reducing agent, characterized in that, Includes the following steps: A mixed solution is obtained by mixing water, 2-acrylamide-2-methylpropanesulfonic acid, carboxylic acid monomers, amide monomers, sodium salts, alcohol polymers, and chain transfer agents; Stir the above mixed solution and heat it to 50-70°C. After all the components in the mixed solution have dissolved uniformly, add the initiator to the mixed solution and react at a constant temperature for 2-3 hours. Add a pH adjuster to adjust the pH of the mixed solution to 5-6, and allow it to cool naturally to room temperature to obtain a friction-reducing agent.

7. A low-friction, hydrocarbon-resistant, self-healing, ultra-high-density cementing slurry, wherein, The raw material composition of the cement slurry includes: 100 parts by weight of cement, 50-190 parts by weight of weighting material, 30-50 parts by weight of anti-fading material, 2-5 parts by weight of self-healing agent, 2.0-5.0 parts by weight of water loss reducing agent, 0.5-2.0 parts by weight of retarder, 0-4.0 parts by weight of drag reducing agent, 0.5-3.0 parts by weight of suspending agent, 0.5-1.5 parts by weight of friction reducing agent, and 0.1-0.5 parts by weight of defoamer; wherein the friction reducing agent is the friction reducing agent according to any one of claims 1 to 6.

8. The low-friction, hydrocarbon-resistant, self-healing, ultra-high-density cementing slurry according to claim 7, characterized in that, The self-healing agent has a core-shell polymer microsphere structure. The core structure of the core-shell polymer microsphere structure has a component ratio of styrene-based monomer, vinyl polymer crosslinking agent, and initiator of 100:20-40:2-6 by mass. The shell structure of the core-shell polymer microsphere structure has a component ratio of styrene-based monomer, acrylate, vinyl polymer crosslinking agent, and initiator of 100:30-70:5-10:2-8 by mass.

9. The low-friction, hydrocarbon-resistant, self-healing, ultra-high-density cementing slurry according to claim 7, characterized in that, The weighting material includes at least one of hematite powder, reduced iron powder, and manganese ore powder.

10. The low-friction, hydrocarbon-resistant, self-healing, ultra-high-density cementing slurry according to claim 7, characterized in that, The anti-fading material includes: silica powder.

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