Mullite whisker modified toughening agent, preparation method thereof and well cementation cement slurry containing mullite whisker modified toughening agent

Abstract

The invention discloses a mullite whisker modified toughening agent, a preparation method thereof and well cementation cement slurry containing the mullite whisker modified toughening agent, and belongs to the technical field of oil-gas field development well cementation materials, the mullite whisker modified toughening agent comprises the following components by weight: 10-20 parts of mullite whisker, 0.05-0.4 part of a surfactant, and 3-18 parts of nano silica. The mullite whisker modified toughening agent provided by the invention has a good application effect in well cementation cement slurry, the particle size of the toughening agent is close to that of oil well cement particles, and when set cement forms micro cracks, the advantages of smaller size, special three-dimensional needle-shaped structure and the like of the toughening agent can be utilized to improve the toughness of the cement slurry. The mechanical property of the set cement is improved through the strengthening effects of crack bridging, deflection, whisker pulling-out and the like.

Description

Technical Field

[0001] This invention belongs to the field of cementing materials technology for oil and gas field development, and specifically relates to a mullite whisker modified toughening agent, its preparation method, and cementing slurry including the same. Background Technology

[0002] Cementing operations in oil and gas wells involve injecting cement slurry into the annulus between the wellbore and the casing. After the slurry hardens, it forms cement stone, which serves to seal, support, and protect the casing. Currently, oil and gas well development is increasingly focused on deeper and ultra-deep formations, inevitably leading to challenges in cementing engineering, such as lower cement stone strength and faster strength decay under high temperature and pressure conditions. During oil and gas well development, downhole loads are applied to the cement sheath through the casing. This is especially true during large-scale hydraulic fracturing in shale gas wells and the periodic high-intensity injection and production in gas storage facilities, which subject the cement sheath to cyclical dynamic loads. This deteriorates the cement sheath's performance, making it prone to brittle fracture and cracking, resulting in the loss of its integrity and the loss of its sealing function against underground oil, gas, and water layers. This can lead to interlayer flow, casing corrosion, and even the abandonment of the oil and gas well.

[0003] Currently, conventional oil well cement toughening agents face numerous problems in ultra-deep well cementing, such as low compressive strength and rapid strength decay of cement stone at high temperatures. Therefore, given the current high-temperature operating conditions with downhole temperatures exceeding 240℃, it is crucial to develop a toughening agent suitable for toughening and resisting high-temperature cement stone. Existing commonly used oil well cement stone toughening admixtures include rubber particles, fibers, graphite, and latex, primarily aimed at improving the mechanical properties and durability of oil well cement stone to extend its service life. However, commonly used toughening agents all have certain limitations. For example, rubber particles have poor compatibility with cement slurry; fiber materials are prone to agglomeration in cement slurry, easily leading to pipe blockage; graphite materials have poor dispersibility in cement slurry; and latex materials have insufficient temperature resistance and require large quantities.

[0004] In the prior art, for example, the invention patent with publication number CN114525119A, entitled "A Preparation Method of Inorganic Fiber Toughening Agent for Cement Slurry in Oil and Gas Wells," discloses a method of pretreating basalt fiber, carbon fiber, brucite fiber, and silicon carbide fiber, then mixing them, and then subjecting them to surface roughening and surface modification processes to obtain an inorganic fiber toughening agent. Another example is the invention patent with publication number CN113402186A, entitled "Preparation Method of Cement Slurry Toughening Agent, Cement Slurry and Preparation Method Thereof," which performs surface modification treatment on carbon fiber and nanoparticles respectively, and then, by controlling temperature and time, causes the surface-modified nanoparticles and surface-modified carbon fiber to react and bond together through chemical bonding to obtain a cement slurry toughening agent.

[0005] While the aforementioned existing technologies can improve the toughness of cement sheaths, they still suffer from problems such as deteriorated rheological properties and strength reduction in cement slurry at high temperatures above 240°C. Therefore, it is particularly important to develop a toughening agent that does not affect the performance of high-temperature cementing slurry applications and can also enhance the cement sheath. Summary of the Invention

[0006] To address the problems of the prior art, the main objective of this invention is to provide a mullite whisker modified toughening agent, its preparation method, and a cementing slurry comprising the same. The mullite whisker modified toughening agent of this invention exhibits good dispersibility in aqueous solution, stable performance, strong toughening properties, and high-temperature resistance. Furthermore, the cementing slurry prepared using the mullite whisker modified toughening agent of this invention demonstrates good stability, no sedimentation, and adjustable thickening time. The resulting cement slurry exhibits excellent performance and mechanical properties at a high temperature of 240°C, meeting not only the requirements of on-site cementing construction but also ensuring the long-term integrity of the cementing seal.

[0007] To achieve the above objectives, the present invention provides a mullite whisker modified toughening agent comprising the following components in parts by weight: 10-20 parts mullite whiskers, 0.05-0.4 parts surfactant, and 3-18 parts nano-silica.

[0008] Furthermore, the surfactant is selected from one or more of hexadecyltrimethylammonium bromide, polyacrylamide, triethanolamine, or polymethylpyrrolidone.

[0009] Furthermore, the mullite whiskers are prepared using raw materials comprising the following parts by weight: 20-30 parts amorphous SiO2, 20-30 parts Al2(SO4)3 and 50-100 parts Na2SO4.

[0010] Furthermore, the mullite whiskers have a whisker length of 1–5 μm and an aspect ratio of 12–30.

[0011] In another aspect, the present invention provides a method for preparing the aforementioned mullite whisker modified toughening agent, comprising the following steps:

[0012] S1, disperse mullite whiskers in deionized water to obtain a mullite whisker suspension;

[0013] S2, the mullite whisker suspension is stirred and mixed with a surfactant to obtain a first mixture;

[0014] S3, the first mixture is added to the nano-silica solution, and the reaction system is adjusted to weak alkalinity with an acidic solution. At the same time, the reaction system is heated to react and the reaction product is obtained.

[0015] S4. The reaction products are washed, filtered and dried sequentially to obtain the mullite whisker modified toughening agent.

[0016] Furthermore, the mass fraction of mullite whiskers in the mullite whisker suspension is 10-20%.

[0017] Furthermore, the heating reaction is carried out at a temperature of 50–70°C for 1–3 hours.

[0018] Furthermore, the mullite whiskers are prepared using the following method:

[0019] Amorphous SiO2, Al2(SO4)3 and Na2SO4 are mixed and ground to obtain a grinding mixture;

[0020] The ground mixture is heated to 900-1200°C, held at that temperature for 2-4 hours, and then cooled to room temperature in the furnace to obtain the calcined product.

[0021] The calcined product is then washed, dried, and ground in sequence to obtain the mullite whiskers.

[0022] In another aspect, the present invention provides a cementing slurry comprising oil well cement, silica fume, suspending agent, fluid loss reducing agent, dispersant, retarder and the aforementioned mullite whisker modified toughening agent.

[0023] Furthermore, based on the oil well cement mass percentage of 100%, the mass percentage of the mullite whisker modified toughening agent is 0.5% to 2%.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1. This invention uses amorphous SiO2, Al2(SO4)3, and Na2SO4 as raw materials to prepare mullite whiskers for toughening cement stone in well cementing. The preparation process is simple, easy to operate, and has low preparation cost. The prepared mullite whiskers have good dispersibility, high crystallinity, and stable performance in aqueous solution.

[0026] 2. The mullite whisker modified toughening agent provided by the present invention includes mullite whiskers, surfactants and nano silica. Surfactants and nano silica can effectively improve the hydrophilicity and roughness of mullite whiskers and promote cement hydration reaction. The three work synergistically to effectively improve the toughness, high temperature performance and mechanical properties of cement slurry. Moreover, the thickening time is adjustable and the flowability of cement slurry is better.

[0027] 3. The mullite whisker modified toughening agent provided by this invention has good application effect in cementing slurry. The particle size of the toughening agent is similar to that of the oil well cement particles. When the cement stone forms micro cracks, the toughening agent can take advantage of its small size and special three-dimensional needle-like structure to improve the mechanical properties of the cement stone through crack bridging, deflection and whisker pull-out.

[0028] 4. The cement slurry provided by this invention has good stability, no settlement phenomenon, and the cement stone formed has excellent high-temperature mechanical properties and high elastic deformation capacity. It can not only meet the requirements of on-site cementing construction, but also ensure the long-term integrity of cementing. It is beneficial to reduce the damage of downhole operations to cement sheath, reduce the impact of various subsequent cementing operations on the sealing quality, extend the life of oil and gas wells, and improve the recovery rate. Attached Figure Description

[0029] Figure 1 The microstructure diagram of the mullite whisker modified toughening agent prepared in Example 1 of the present invention is shown.

[0030] Figure 2 The microstructure diagram of the mullite whisker modified toughening agent prepared in Example 2 of the present invention is shown;

[0031] Figure 3 The microstructure diagram of the mullite whisker modified toughening agent prepared in Example 3 of the present invention is shown.

[0032] Figure 4 The microstructure diagram of the mullite whisker modified toughening agent prepared in Example 4 of the present invention is shown.

[0033] Figure 5 The thickening curve of cement slurry #1 prepared in Example 1 of the present invention is shown.

[0034] Figure 6 The thickening curve of cement slurry #2 prepared in Example 2 of the present invention is shown.

[0035] Figure 7 The thickening curve of cement slurry #3 prepared in Example 3 of the present invention is shown.

[0036] Figure 8 The thickening curve of cement slurry #4 prepared in Example 4 of this invention is shown.

[0037] Figure 9 The thickening curve of the cementing slurry 1* prepared by Comparative Example 1 of the present invention is shown. Detailed Implementation

[0038] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. Furthermore, regarding the numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included within this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range. The invention will now be described in detail with reference to embodiments.

[0039] To achieve the above-mentioned technical objectives, a first aspect of the present invention provides a mullite whisker modified toughening agent comprising the following components in parts by weight: 10-20 parts mullite whiskers, 0.05-0.4 parts surfactant, and 3-18 parts nano-silica.

[0040] The mullite whisker modified toughening agent provided by this invention includes mullite whiskers, surfactants, and nano-silica. The surfactants and nano-silica can effectively improve the hydrophilicity and roughness of mullite whiskers and promote the cement hydration reaction. The three work synergistically to effectively improve the toughness, high-temperature performance, and mechanical properties of cement slurry. Moreover, the thickening time is adjustable, and the cement slurry has excellent flow properties. This makes the cement slurry using this agent perform well in high-temperature environments above 240°C and has excellent mechanical properties. It can not only meet the requirements of on-site cementing construction, but also ensure the long-term integrity of cementing.

[0041] In this invention, the mechanism of action of mullite whisker modified toughening agent in cementing slurry for toughening and high-temperature resistance is mainly based on the following aspects: 1. Due to the small particle size and high surface free energy of mullite whiskers, they have a certain adsorption effect. On the one hand, after mullite whiskers are added to cement slurry, the Ca in the cement slurry... 2+ and [SiO4] 4-1. CSH will preferentially form on the surface of mullite whiskers. As the cement paste gradually solidifies and hardens, it will produce pores of varying sizes. The mullite whiskers coated with CSH will fill the pores in the cement stone, making the interior of the cement stone more compact. 2. After surface modification with surfactants and nano-silica, the surface of the mullite whiskers has better hydrophilicity, rougher surface, and better dispersibility, which can promote the cement hydration reaction. Moreover, the surface of the mullite whisker modified toughening agent has a large number of active hydroxyl groups, which can bind well with the hydration products to form a stable structure, further enhancing the mechanical properties of the cement stone. 3. In the early stage of cement stone stress, the mullite whisker modified toughening agent, with its high strength, connects the two ends of the crack to form a triangular closed bridge, so that the stress is loaded onto the side surface of the crack, thereby inhibiting the crack propagation. In the later stages of cement stone stress, the cracks in the cement stone gradually expand into fissures under stress, causing the mullite whisker modified toughening agent to be pulled out from the cement stone matrix. During the pulling process, the friction between the mullite whiskers and the cement matrix consumes the energy for crack propagation, thereby delaying crack propagation.

[0042] In order to further improve the hydrophilicity and surface roughness of the mullite whisker modified toughening agent and promote the cement hydration reaction, in some preferred embodiments of the present invention, the surfactant is selected from one or more of hexadecyltrimethylammonium bromide, polyacrylamide, triethanolamine or polymethylpyrrolidone.

[0043] In a preferred embodiment of the present invention, the mullite whiskers are prepared using raw materials comprising the following parts by weight: 20-30 parts amorphous SiO2, 20-30 parts Al2(SO4)3, and 50-100 parts Na2SO4. Further, the amorphous SiO2 is microsilica powder with a SiO2 content ≥95%, and the Na2SO4 is analytically pure with a content of not less than 99%.

[0044] The mullite whiskers prepared from the above raw materials exhibit excellent dispersion properties in aqueous solution, high crystallinity, and stable performance. The whisker lengths range from 1 to 5 μm, and the aspect ratios range from 12 to 30. They have smooth surfaces, uniform distribution, and a needle-like shape. By utilizing the advantages of mullite whiskers, such as their small size and unique three-dimensional needle-like structure, the mechanical properties of cement stone can be improved through reinforcement effects such as crack bridging, deflection, and whisker pull-out.

[0045] A second aspect of the present invention provides a method for preparing the aforementioned mullite whisker modified toughening agent, comprising the following steps:

[0046] S1, disperse mullite whiskers in deionized water to obtain a mullite whisker suspension;

[0047] S2, the mullite whisker suspension is stirred and mixed with a surfactant to obtain a first mixture;

[0048] S3, the first mixture is added to the nano-silica solution, and the reaction system is adjusted to weak alkalinity (7.5-9.0) with an acidic solution. At the same time, the reaction system is heated to obtain the reaction product.

[0049] S4. The reaction products are washed, filtered and dried sequentially to obtain the mullite whisker modified toughening agent.

[0050] In a preferred embodiment of the present invention, the mass fraction of mullite whiskers in the mullite whisker suspension is 10-20%. Controlling the mullite whisker ratio in the mullite whisker suspension within this range results in better dispersion and is more conducive to the modification reaction. To further optimize the modification reaction, the heating temperature is 50-70°C, and the time is 1-3 hours. The stirring speed is 2000-4000 r / min, and the time is 10-30 minutes. The molar concentration of nano-silica in the nano-silica solution is 0.5-3 mol / L.

[0051] In a preferred embodiment of the present invention, the mullite whiskers are prepared by the following method: Step a1, amorphous SiO2, Al2(SO4)3 and Na2SO4 are mixed and ground to obtain a grinding mixture; Step b1, the grinding mixture is heated to 900-1200°C, kept at that temperature for 2-4 hours and then cooled to room temperature in the furnace to obtain a calcined product; Step c1, the calcined product is washed, dried and ground in sequence to obtain the mullite whiskers.

[0052] Step a1 includes the following steps: Al2(SO4)3·18H2O is placed in a box-type high-temperature furnace and calcined for 100-150 min, maintaining the temperature of the box-type high-temperature furnace at 250-350℃ to obtain anhydrous Al2(SO4)3; amorphous SiO2 and anhydrous Al2(SO4)3 are weighed into an agate mortar and ground evenly to obtain SiO2 / Al2(SO4)3 composite particles; then Na2SO4 is weighed and added to the SiO2 / Al2(SO4)3 composite particles and ground evenly to obtain a grinding mixture; the weight ratio of Na2SO4 to SiO2 / Al2(SO4)3 composite particles is 1-2:1.

[0053] Step c1 includes the following steps: washing the calcined product with deionized water, filtering and drying the washed calcined product using a vacuum filter, repeating the above steps several times; drying the filtered calcined product in an oven at 50-70°C until the particle surface is completely dry, and then grinding it thoroughly to obtain mullite whiskers.

[0054] This invention uses amorphous SiO2, Al2(SO4)3, and Na2SO4 as raw materials to prepare mullite whiskers for toughening cement stone in well cementing. The preparation process is simple, convenient, and low in cost. The prepared mullite whiskers have good dispersibility, high crystallinity, and stable performance in aqueous solution.

[0055] A third aspect of the present invention provides a cementing slurry comprising oil well cement, silica fume, suspending agent, fluid loss reducing agent, dispersant, retarder, and the aforementioned mullite whisker modified toughening agent.

[0056] To further improve the toughening and high-temperature resistance of cementing slurry, the mullite whisker-modified toughening agent is 0.5% to 2% of the oil well cement by weight (100%). This invention controls the amount of mullite whisker-modified toughening agent within the above range to achieve a superior toughening effect in cementing slurry. Experimental studies have shown that excessive addition (greater than 2%) leads to difficulty in whisker dispersion, causing stress concentration and affecting the development of cement stone strength; while insufficient addition (less than 0.5%) prevents the whiskers from fully exerting their toughening effect.

[0057] In a preferred embodiment of the present invention, a cementing slurry, based on 100% of the mass percentage of oil well cement, comprises the following raw materials by mass percentage:

[0058]

[0059]

[0060] A fourth aspect of the present invention provides a method for preparing the aforementioned cementing slurry, comprising the following steps:

[0061] Step 1: Weigh out G-grade oil well cement, silica fume, suspending agent, fluid loss reducer, and dispersant, and mix them evenly to obtain a mixed dry powder;

[0062] Step 2: Weigh the mullite whisker modifier and toughening agent and the retarder according to the specified mass percentage and dissolve them in water to obtain a mixed aqueous solution containing mullite whisker modifier;

[0063] Step 3: Place the mixed aqueous solution in a stirrer and rotate it at a low speed (4000±200r / min). Within 10 to 30 seconds, add the mixed dry powder into the mixed aqueous solution. After the mixed dry powder is completely added, cover the stirrer and continue stirring at a high speed (12000±500r / min) for 20 to 50 seconds to obtain the cementing slurry containing mullite whisker modified toughening agent.

[0064] The present application will be further described in detail below with reference to specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in this application. In the following embodiments and comparative examples, except for the mullite whiskers and the mullite whisker modified toughening agent which are self-made, the other raw materials are all commercially available products. Among them, the high-temperature suspending agent SD89 (purchased from Sichuan Chuanqing Well Technology Co., Ltd., is a carboxymethyl cellulose suspending agent); the water loss reducing agent G33S (purchased from Weihui Chemical Co., Ltd., is polymerized and modified from 2-acrylamide-2-methylpropanesulfonic acid, amide, carboxylic acid, etc.); the dispersant USZ (purchased from Weihui Chemical Co., Ltd., is polymerized and modified from formaldehyde, acetone, etc.); and the ultra-high temperature retarder SD210 (purchased from Sichuan Chuanqing Well Technology Co., Ltd., is a polyacrylamide retarder).

[0065] Example 1

[0066] As a preferred embodiment of the present invention, this embodiment discloses a mullite whisker modified toughening agent, which, by weight, comprises 10 parts mullite whiskers, 0.05 parts surfactant (cetyltrimethylammonium bromide), and 3 parts nano-silica. Its preparation method includes the following steps:

[0067] Preparation of mullite whiskers: By weight, 30 parts of amorphous SiO2 (A-SiO2, microsilica powder) and 20 parts of anhydrous Al2(SO4)3 were ground evenly to obtain SiO2 / Al2(SO4)3 composite particles; then 50 parts of Na2SO4 were weighed and ground evenly with the SiO2 / Al2(SO4)3 composite particles to obtain mullite whisker precursor; the mullite whisker precursor was placed in a crucible and heated to 900℃ in a box furnace, held for 2 hours and then cooled to room temperature with the furnace to obtain calcined product; the calcined product was washed, filtered and dried in sequence, and then ground to obtain mullite whiskers.

[0068] Preparation of mullite whisker modified toughening agent: 10g of mullite whiskers were weighed and placed in 90g of deionized water to prepare a 10% (w / w) suspension. 0.05g of surfactant (hexadecyltrimethylammonium bromide) was added to the suspension. The suspension was placed in a magnetic stirrer and stirred at 3000r / min for 15min. Then, 100mL of 0.5mol / L nano-silica solution was added. The pH of the reaction system was adjusted to 7.5 with 6mol / L dilute hydrochloric acid solution. The system was then heated to 60℃ and kept at the same temperature and stirring speed for 1h. After the reaction was complete, the mullite whisker modified toughening agent was washed with anhydrous ethanol until neutral. After centrifugation, the product was dried in a 60℃ oven for 12h to obtain the mullite whisker modified toughening agent. The microstructure of the prepared mullite whisker modified toughening agent was characterized, and its microstructure diagram is shown below. Figure 1 Its structure is needle-like and evenly distributed.

[0069] The mullite whisker modified toughening agent prepared in this embodiment was used to prepare cement slurry and test the cement stone performance according to the national standard GB / T19139-2012 "Test Methods for Oil Well Cement" and the industry standard SY / T 6544 "Performance Requirements for Oil Well Cement Slurry". The basic test formula was: 100% G-grade oil well cement + 50% silica fume + 1.3% high-temperature suspending agent SD89 + 1% fluid loss reducing agent G33S + 0.5% dispersant USZ + 5% ultra-high temperature retarder SD210 + 0.5% mullite whisker modified toughening agent of this embodiment + 44% water. The amount of all admixtures and additives added was a percentage of the cement mass, thus obtaining cement slurry No. 1 containing mullite whisker modified toughening agent.

[0070] Example 2

[0071] In another preferred embodiment of the present invention, a mullite whisker modified toughening agent is disclosed, comprising, by weight, 14 parts mullite whiskers, 0.14 parts surfactant (polyacrylamide), and 6 parts nano-silica. Its preparation method includes the following steps:

[0072] Preparation of mullite whiskers: By weight, 25 parts of amorphous SiO2 (A-SiO2, microsilica powder) and 25 parts of anhydrous Al2(SO4)3 were weighed and ground evenly to obtain SiO2 / Al2(SO4)3 composite particles; then 60 parts of Na2SO4 were weighed and ground evenly with the SiO2 / Al2(SO4)3 composite particles to obtain mullite whisker precursor; the mullite whisker precursor was placed in a crucible and heated to 1000℃ in a box furnace, held for 3 hours and then cooled to room temperature with the furnace to obtain calcined product; the calcined product was washed, filtered and dried in sequence, and then ground to obtain mullite whiskers.

[0073] Preparation of mullite whisker modified toughening agent: 14g of mullite whiskers were weighed and placed in 86g of deionized water to prepare a suspension with a mass fraction of 14%. 0.14g of surfactant (polyacrylamide) was added to the suspension. The suspension was then placed in a magnetic stirrer and stirred at 3000r / min for 15min. 100mL of 1mol / L nano-silica solution was added, and the pH of the reaction system was adjusted to 8.0 with 6mol / L dilute hydrochloric acid solution. The system was then heated to 60℃ and kept at the same temperature and stirring speed for 2h. After the reaction was complete, the mullite whisker modified toughening agent was washed with anhydrous ethanol until neutral. After centrifugation, the product was dried in a 60℃ oven for 12h to obtain the mullite whisker modified toughening agent. The microstructure of the prepared mullite whisker modified toughening agent was characterized, and its microstructure diagram is shown below. Figure 2 Its structure is needle-like and evenly distributed.

[0074] The mullite whisker modified toughening agent prepared in this embodiment was used to prepare cement slurry and test the cement stone performance according to the national standard GB / T19139-2012 "Test Methods for Oil Well Cement" and the industry standard SY / T 6544 "Performance Requirements for Oil Well Cement Slurry". The basic test formula was: 100% G-grade oil well cement + 50% silica fume + 1.3% high-temperature suspending agent SD89 + 1% fluid loss reducing agent G33S + 0.5% dispersant USZ + 5% ultra-high temperature retarder SD210 + 1% mullite whisker modified toughening agent of this embodiment + 44% water. The amount of all admixtures and additives added was a percentage of the cement mass, thus obtaining cement slurry No. 2 containing mullite whisker modified toughening agent.

[0075] Example 3

[0076] In another preferred embodiment of the present invention, a mullite whisker modified toughening agent is disclosed, comprising, by weight, 18 parts mullite whiskers, 0.27 parts surfactant (triethanolamine), and 12 parts nano-silica. Its preparation method includes the following steps:

[0077] Preparation of mullite whiskers: By weight, 22 parts of amorphous SiO2 (A-SiO2, microsilica powder) and 28 parts of anhydrous Al2(SO4)3 were weighed and ground evenly to obtain SiO2 / Al2(SO4)3 composite particles; then 80 parts of Na2SO4 were weighed and ground evenly with the SiO2 / Al2(SO4)3 composite particles to obtain mullite whisker precursor; the mullite whisker precursor was placed in a crucible and heated to 1100℃ in a box furnace, held for 3 hours and then cooled to room temperature with the furnace to obtain calcined product; the calcined product was washed, filtered and dried in sequence, and then ground to obtain mullite whiskers.

[0078] Preparation of mullite whisker modified toughening agent: 18g of mullite whisker toughening agent was weighed and placed in 82g of deionized water to prepare a suspension with a mass fraction of 18%. 0.27g of surfactant (triethanolamine) was added to the suspension. The suspension was placed in a magnetic stirrer and stirred at 3000r / min for 15min. Then, 100mL of 2mol / L nano-silica solution was added, and the pH of the reaction system was adjusted to 8.5 with 6mol / L dilute hydrochloric acid solution. The system was then heated to 60℃ and kept at the same temperature and stirring speed for 3h. After the reaction was completed, the mullite whisker modified toughening agent was washed with anhydrous ethanol until neutral. After centrifugation, the product was dried in a 60℃ oven for 12h to obtain the mullite whisker modified toughening agent. The microstructure of the prepared mullite whisker modified toughening agent was characterized, and its microstructure diagram is shown below. Figure 1 Its structure is needle-like and evenly distributed.

[0079] The mullite whisker modified toughening agent prepared in this embodiment was used to prepare cement slurry and test the cement stone performance according to the national standard GB / T19139-2012 "Test Methods for Oil Well Cement" and the industry standard SY / T 6544 "Performance Requirements for Oil Well Cement Slurry". The basic test formula was: 100% G-grade oil well cement + 50% silica fume + 1.3% high-temperature suspending agent SD89 + 1% fluid loss reducing agent G33S + 0.5% dispersant USZ + 5% ultra-high temperature retarder SD210 + 1.5% mullite whisker modified toughening agent of this invention + 44% water. The amount of all admixtures and additives added was a percentage of the cement mass, thus obtaining cement slurry No. 3 containing mullite whisker modified toughening agent.

[0080] Example 4

[0081] As another preferred embodiment of the present invention, this embodiment discloses a mullite whisker modified toughening agent, which, by weight, comprises 20 parts mullite whiskers, 0.40 parts surfactant (polymethylpyrrolidone), and 18 parts nano-silica. Its preparation method includes the following steps:

[0082] Preparation of mullite whiskers: By weight, 20 parts of amorphous SiO2 (A-SiO2) and 30 parts of anhydrous Al2(SO4)3 were weighed and ground evenly to obtain SiO2 / Al2(SO4)3 composite particles; then 100 parts of Na2SO4 were weighed and ground evenly with the SiO2 / Al2(SO4)3 composite particles to obtain mullite whisker precursor; the mullite whisker precursor was placed in a crucible and heated to 1200℃ in a box furnace, held for 4 hours and then cooled to room temperature with the furnace to obtain calcined product; the calcined product was washed, filtered and dried in sequence, and then ground to obtain mullite whisker toughening agent.

[0083] Preparation of mullite whisker modified toughening agent: 20g of mullite whisker toughening agent was weighed and placed in 80g of deionized water to prepare a suspension with a mass fraction of 20%. 0.40g of surfactant (polymethylpyrrolidone) was added to the suspension. The suspension was placed in a magnetic stirrer and stirred at 3000r / min for 15min. Then, 100mL of 3mol / L nano-silica solution was added, and the pH of the reaction system was adjusted to 9.0 with 6mol / L dilute hydrochloric acid solution. The system was then heated to 60℃ and kept at the same temperature and stirring speed for 3h. After the reaction was completed, the mullite whisker modified toughening agent was washed with anhydrous ethanol until neutral. After centrifugation, the product was dried in a 60℃ oven for 12h to obtain the mullite whisker modified toughening agent. The microstructure of the prepared mullite whisker modified toughening agent was characterized, and its microstructure diagram is shown below. Figure 1 Its structure is needle-like and evenly distributed.

[0084] The mullite whisker modified toughening agent prepared in this embodiment was used to prepare cement slurry and test the cement stone performance according to the national standard GB / T19139-2012 "Test Methods for Oil Well Cement" and the industry standard SY / T 6544 "Performance Requirements for Oil Well Cement Slurry". The basic test formula was: 100% G-grade oil well cement + 50% silica fume + 1.3% high-temperature suspending agent SD89 + 1% fluid loss reducing agent G33S + 0.5% dispersant USZ + 5% ultra-high temperature retarder SD210 + 2% mullite whisker modified toughening agent of this embodiment + 44% water. The amount of all admixtures and additives added was a percentage of the cement mass, thus obtaining cement slurry No. 4 containing mullite whisker modified toughening agent.

[0085] Comparative Example 1

[0086] Cement slurry was prepared and its cement stone properties were tested according to the national standard GB / T19139-2012 "Test Methods for Oil Well Cement" and the industry standard SY / T 6544 "Performance Requirements for Oil Well Cement Slurry". The basic formula for testing was: 100% Grade G oil well cement + 50% silica fume + 1.3% high-temperature suspending agent SD89 + 1% fluid loss reducing agent G33S + 0.5% dispersant USZ + 5% ultra-high temperature retarder SD210 + 44% water. The dosage of all admixtures and additives was a percentage of the cement mass. The cement slurry density was 1.90 g / cm³. 3 The resulting cement slurry 1* differs from the example 1 in that it does not contain the mullite whisker modifier of the present invention.

[0087] Referring to SY / T 6544 "Performance Requirements for Cement Slurry in Oil Wells", the engineering properties of each cement slurry prepared in Examples 1 to 4 and Comparative Example 1, such as density, fluidity, free fluid, water loss, and thickening time under 240℃×110MPa conditions, were tested. The test results are shown in Table 1.

[0088] Table 1. Test results for density, fluidity, free fluid, water loss, and thickening time of various cementing slurries.

[0089]

[0090] According to the data in Table 1, the cement slurries prepared in Examples 1-4 have low free fluid and water loss, good fluidity, and meet the construction requirements. The thickening curves of the cement slurries prepared in Examples 1-4 and Comparative Example 1 are shown in the figure. Figures 5-9 As shown in the figure, the thickening curves of Examples 1-4 with the addition of the mullite whisker modified toughening agent of the present invention are similar to those of Comparative Example 1 without the addition of the mullite whisker modified toughening agent. This indicates that the mullite whisker modified toughening agent of the present invention has good compatibility with components such as the water loss reducing agent, good stability, no decay of rheological properties, and controllable thickening time at high temperature.

[0091] The cement slurries prepared in Examples 1-4 and Comparative Example 1 were poured into curing molds and then placed in a high-temperature and high-pressure curing autoclave at 260℃ for curing. The evolution of compressive strength, tensile strength, flexural strength, elastic modulus and permeability of cement slurries with different mullite whisker modified toughening agent dosages under curing conditions at 260℃ was tested with reference to SY / T 6466-2000 "Evaluation Method for High Temperature Resistance of Oil Well Cement Stone". The test results are shown in Tables 2, 3 and 4.

[0092] Table 2. Test results of permeability, flexural strength and elastic modulus of various cementing slurries

[0093]

[0094] Table 3. Test results of compressive strength of various cement slurries

[0095]

[0096] Table 4. Tensile Strength Test Results of Various Cementing Slurries

[0097]

[0098] As shown in Table 2, with the incorporation of the mullite whisker modified toughening agent of the present invention, the permeability and flexural strength of the cement stone are significantly improved. The elastic modulus is reduced by about 30% compared with conventional silica fume cement stone (mullite whisker modified toughening agent content is 0). This indicates that the mullite whisker modified toughening agent of the present invention can effectively improve the elasticity and plasticity of the cement stone, which has a significant impact on the development of oil and gas wells and can greatly reduce the probability of cement sheath cracking and rupture during hydraulic fracturing, periodic strong injection and production, and other operations.

[0099] As shown in Tables 3 and 4, under ultra-high temperature curing conditions of 260℃, the compressive and tensile strengths of cement stone at different curing ages are significantly improved compared to conventional silica fume cement stone. The toughening agent contained in this invention not only enhances the early mechanical properties of the cement stone, but also exhibits relatively small decreases in compressive and tensile strength after 14 and 28 days of curing. In Examples 1-4, the compressive strength of the cement stone cured at 260℃ for 2 days is approximately twice that of conventional silica fume cement stone, and after 28 days of curing, the compressive strength of the cement stone still shows a 40-50% increase compared to conventional silica fume cement stone. This indicates that the toughening agent in this invention improves the high-temperature toughness of the cement stone while ensuring good compressive strength at high temperatures.

[0100] By adopting the technical solution of this invention, after adding the mullite whisker modified toughening agent to the cement slurry, the compressive strength and tensile strength of the cement stone can be effectively enhanced, the toughness of the cement stone can be improved, and the compatibility with the admixture is good, which can meet the cementing construction requirements and improve the cementing quality.

[0101] The embodiments described above are merely illustrative of implementation methods 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. The present invention can also be implemented in other specific ways or forms without departing from its spirit or essential characteristics. Therefore, the described embodiments should be considered illustrative rather than limiting in any respect. The scope of the present invention should be defined by the appended claims, and any variations equivalent to the intent and scope of the claims should also be included within the scope of the present invention.

Claims

1. A mullite whisker modified toughening agent, characterized in that, It includes the following components in parts by weight: 10-20 parts mullite whiskers, 0.05-0.4 parts surfactant, and 3-18 parts nano silica.

2. The mullite whisker modified toughening agent according to claim 1, characterized in that, The surfactant is selected from one or more of hexadecyltrimethylammonium bromide, polyacrylamide, triethanolamine, or polymethylpyrrolidone.

3. The mullite whisker modified toughening agent according to claim 2, characterized in that, The mullite whiskers are prepared using the following raw materials in parts by weight: 20-30 parts amorphous SiO2, 20-30 parts Al2(SO4)3 and 50-100 parts Na2SO4.

4. The mullite whisker modified toughening agent according to claim 3, characterized in that, The mullite whiskers have a whisker length of 1–5 μm and an aspect ratio of 12–30.

5. A method for preparing a mullite whisker modified toughening agent as described in any one of claims 1 to 4, characterized in that, Includes the following steps: S1, disperse mullite whiskers in deionized water to obtain a mullite whisker suspension; S2, the mullite whisker suspension is stirred and mixed with a surfactant to obtain a first mixture; S3, the first mixture is added to the nano-silica solution, and the reaction system is adjusted to weak alkalinity with an acidic solution. At the same time, the reaction system is heated to react and the reaction product is obtained. S4. The reaction products are washed, filtered and dried sequentially to obtain the mullite whisker modified toughening agent.

6. The method for preparing the mullite whisker modified toughening agent according to claim 5, characterized in that, In step S1, the mass fraction of mullite whiskers in the mullite whisker suspension is 10-20%.

7. The method for preparing the mullite whisker modified toughening agent according to claim 5, characterized in that, In step S3, the heating reaction is carried out at a temperature of 50–70°C for 1–3 hours.

8. The method for preparing the mullite whisker modified toughening agent according to any one of claims 5 to 7, characterized in that, The mullite whiskers were prepared using the following method: Amorphous SiO2, Al2(SO4)3 and Na2SO4 are mixed and ground to obtain a grinding mixture; The ground mixture is heated to 900-1200°C, held at that temperature for 2-4 hours, and then cooled to room temperature in the furnace to obtain the calcined product. The calcined product is then washed, dried, and ground in sequence to obtain the mullite whiskers.

9. A cementing slurry, characterized in that, It includes oil well cement, silica fume, suspending agent, fluid loss reducing agent, dispersant, retarder and mullite whisker modified toughening agent as described in any one of claims 1 to 4.

10. The cementing slurry according to claim 9, characterized in that, Based on the oil well cement mass percentage of 100%, the mass percentage of the mullite whisker modified toughening agent is 0.5% to 2%.

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