An impact-resistant cement slurry for oil and gas wells, its preparation method and use

Abstract

This invention relates to the field of oil and gas well cementing engineering, and discloses an impact-resistant and toughening cement slurry for oil and gas wells, its preparation method, and its application. The composite toughening agent in the cement slurry is composed of modified ultrafine elastic rubber powder and modified mineral whiskers. This oil well cement slurry system draws on the microstructural characteristics of mineral whiskers and ultrafine rubber particles, and utilizes four key additives—dispersant, stabilizer, fluid loss reducer, and retarder—to effectively regulate the pore structure of the cement stone, forming a reinforcing and toughening structure in the oil well cement stone with the same structural properties as mineral whiskers, making the oil well cement stone more dense. The cement stone formed by this method has the structural characteristic of "intrinsic toughening," and can significantly improve the compressive strength, toughness, and impact resistance of the oil well cement stone under high-frequency impact loads through "crack bridging," "crack deflection," "whisker pull-out," and "particle filling."

Description

Technical Field

[0001] This invention relates to the field of oil and gas well cementing engineering technology, specifically to an impact-resistant and tough cement slurry for oil and gas wells, its preparation method and application, which is suitable for oil and gas well cementing operations with high requirements for the impact resistance of cement sheaths. Background Technology

[0002] In oil and gas well cementing, cement is injected into the annular space between the casing and the wellbore or between the casing. After the cement slurry solidifies, it forms a cement sheath, which supports and protects the casing and seals the underground oil, gas, and water layers. Cement is a brittle material, and under special construction environments, it often exhibits brittleness and cracking under tension and bending. Oil well cement also suffers from these defects. As oilfield development conditions become increasingly complex, the inherent defects of the cement material have a growing impact on cementing quality. Under the complex alternating formation stress and subsequent perforation and fracturing operations, especially narrow-gap, thin cement sheaths, the cement sheath is prone to breakage and has poor impact resistance, leading to interlayer sealing failure and the formation of flow channels. This can cause cross-flow between oil, gas, and water layers, severely affecting cementing quality and normal oil and gas well production. Therefore, adding tough and elastic materials to the cement slurry and scientifically designing the cement slurry system to improve the impact resistance of the cement sheath is crucial for maintaining its integrity in oil and gas wells. With the increasing demand for oil and gas exploration and development to increase reserves and production in my country, the complex downhole conditions have placed higher demands on the mechanical properties of cement sheaths. Improving the toughness of cement stone so that it can maintain good mechanical integrity under alternating stress conditions has become a research hotspot.

[0003] The Drilling Engineering Technology Research Institute of China National Petroleum Corporation (CNPC) has applied for a patent entitled "A Low-Temperature High-Strength and Toughness Cement Slurry and Its Preparation Method and Application" (CN106986584A), which provides a low-temperature high-strength and toughness cement slurry, its preparation method, and its application. The provided low-temperature high-strength and toughness cement slurry possesses early strength, high strength, low elastic modulus, and micro-expansion characteristics. It can effectively improve the inherent defects of cement stone at low temperatures, such as slow strength development, low strength, brittleness, and easy shrinkage. It can be well applied to cementing in tight oil horizontal wells and coalbed methane wells, shortening the development cycle of oil and gas wells, improving cementing quality, and extending the service life of oil and gas wells, providing technical support for the long-term, safe, and effective operation of oil and gas wells.

[0004] Yangtze University and Jingzhou Jiahe Technology Co., Ltd. have applied for a patent entitled "A Pre-cured Resin-Based High-Binder Toughness Cement Slurry for Wellbore Pluging, Its Preparation Method and Application" (CN115504713B). This patent provides a pre-cured resin-based high-binder toughness cement slurry for wellbore plugging, its preparation method, and its application. The pre-cured resin, after emulsification, forms fine particles with deformable capabilities, which can be well dispersed in the cementitious matrix, preventing the resin and cement from clumping together. The resulting cement stone exhibits high bonding strength and micro-expansion, ensuring a high-strength bond with the formation wall or casing wall. It also possesses strong toughness, enabling the cement slurry to meet the compressive strength requirements of general cementing operations. Furthermore, the cement stone is resistant to certain acid and alkali corrosion, ensuring the long-term effectiveness of abandoned cement plugs in wellbore plugging.

[0005] Current research on improving the impact resistance of cement paste mainly focuses on elastic and toughening materials. Adding elastic particles to cement slurry can effectively improve the elasticity of cement paste and enhance the deformation capacity of the cement ring under alternating stress; adding toughening materials to cement slurry reduces the brittleness of cement paste and improves the integrity of the cement ring under impact stress. However, the following problems exist with the currently widely used elastic particles and toughening materials: (1) Domestic research on elastic materials mainly includes dispersible latex powder, rubber particles and other materials. Their elastic properties are still inferior to those of similar foreign products. Cement stone has a large residual deformation after being compressed, which can easily lead to interface sealing failure. Latex materials need to be emulsified during the preparation process, which will introduce a large amount of air into the cement slurry during the preparation process, resulting in serious foaming. Rubber particles are organic materials and cement is an inorganic mineral material. The difference in interface properties between the two leads to poor bonding and limits their use.

[0006] (2) The current toughening method mainly uses organic fibers to improve the toughness of brittle cement stone. However, the aggregation of fibers results in a thicker cement paste with poor rheological properties. Furthermore, the amount of fiber added is also very limited due to the limitations of the mixing process.

[0007] Therefore, it is necessary to develop high-performance elastic and tough materials suitable for oil well cement to form high-performance cement slurry technology, so as to improve the impact resistance and long-term sealing integrity of cement stone under complex working conditions. Summary of the Invention

[0008] Existing elastic and tough materials and cement slurry systems improve the toughness of cement stone and enhance the deformation capacity of cement rings under alternating loads (low loading rates). However, for perforation operations (high loading rates), existing tough cement slurry systems have failed to effectively improve the cement stone's resistance to breakage under impact loads. Furthermore, in the design of cement slurry systems, the particle size distribution based on the close packing design is the average particle size. The actual particle size distribution approximates a normal distribution, with minimum and maximum particle sizes. Therefore, existing close packing designs do not fully reflect the actual particle size distribution.

[0009] Therefore, by modifying ultrafine elastic materials and combining them with highly dispersed mineral toughening materials, a composite toughening agent is formed, and the cement slurry is meticulously designed. This oil well cement slurry system draws on the microstructural characteristics of mineral whiskers and ultrafine rubber particles, utilizing four key additives—dispersants, stabilizers, fluid loss reducers, and retarders—to effectively regulate the pore structure of the cement stone. This results in a reinforced and toughened structure in the oil well cement stone with properties similar to that of mineral whiskers, making the cement stone more dense. The cement stone formed by this meticulously designed impact-resistant and toughening cement slurry system possesses an "endogenous toughening" structural characteristic. Under impact loads, it can significantly improve the compressive strength, toughness, and impact resistance of the oil well cement stone through actions such as "crack bridging," "crack deflection," "whisker pull-out," and "particle filling," which is crucial for maintaining the integrity of the cement sheath in oil and gas wells.

[0010] The purpose of this invention is to provide an impact-resistant and toughening cement slurry for oil and gas well cementing operations, which can improve the inherent defects of cement stone, such as high brittleness and easy breakage under impact loads. The key component of this impact-resistant and toughening cement slurry is a composite toughening agent; the composite toughening agent is composed of modified ultrafine rubber powder and mineral whiskers, overcoming the shortcomings of poor bonding between rubber particles and cement and the easy agglomeration of organic fibers. It leverages the microstructural characteristics of mineral whiskers and ultrafine rubber particles, enabling them to synergistically exert reinforcement and toughening effects at the nano- to micron scale. Simultaneously, by rationally designing key admixtures and their dosage, the pore structure of the cement stone is effectively controlled, resulting in a reinforcing and toughening structure in the oil well cement stone with the same properties as the mineral whisker structure, making the oil well cement stone more dense and achieving the goal of improving the impact resistance of the oil well cement stone.

[0011] To achieve the above-mentioned technical objectives, the present invention provides the following technical solution: An impact-resistant and toughening cement slurry for oil and gas wells is composed of oil well cement, silica sand, composite toughening agent, dispersant, fluid loss reducing agent, retarder, stabilizer, defoamer and water, wherein the composite toughening agent is composed of modified ultrafine elastic rubber powder and modified mineral whiskers.

[0012] Furthermore, the mass fractions of each component are as follows: based on 100 parts of oil well cement, add 30-40 parts of silica sand, 3-5 parts of composite toughening agent, 1-2 parts of dispersant, 1.5-3 parts of water loss reducer, 0.5-1.5 parts of retarder, 1-2 parts of stabilizer, 0.2-1.0 parts of defoamer, and 44-60 parts of water.

[0013] Furthermore, the mass ratio of the composite toughening agent is: modified ultrafine elastic rubber powder: modified mineral whiskers = (1:2) ~ (2:3).

[0014] Furthermore, the modification method of the modified ultrafine elastic rubber powder is as follows: add hypochlorous acid solution to ultrafine rubber powder, keep it at a constant temperature for reaction, filter the mixture, clean the modified ultrafine rubber powder with deionized water, and then dry it.

[0015] Furthermore, the modification method of the modified mineral whiskers is as follows: First, the mineral whiskers are pretreated by adding them to a hydrogen peroxide solution, and after ultrasonic treatment at room temperature, the mixture is washed, filtered, and dried; then, the pretreated mineral whiskers are mixed with an ethanol aqueous solution, and an ethanol solution of tetraethyl orthosilicate is added dropwise, followed by a reaction at room temperature. The resulting solution is washed, filtered, and dried.

[0016] Furthermore, the dispersant is one of lignin sulfonate dispersants, sulfonated acetone-formaldehyde condensate dispersants, polycarboxylic acid dispersants, and polymer dispersants; the water loss reducing agent is one of 2-acrylamide-2-methylpropanesulfonic acid water loss reducing agents, modified polyvinyl alcohol water loss reducing agents, hydroxyethyl cellulose and carboxymethyl cellulose water loss reducing agents.

[0017] Furthermore, the retarder is one of the following: hydroxycarboxylic acid retarder, cellulose and its derivatives retarder, lignin sulfonate and its derivatives retarder, modified sugar compound retarder, inorganic acid and its salt retarder, organophosphate retarder, and polymer retarder; the stabilizer is one of the following: xanthan gum, cellulose and its derivatives stabilizer.

[0018] Furthermore, the defoamer is one of the following: organic fatty and fatty alcohol defoamers, organic polyether defoamers, organosilicon defoamers, and polyether-modified organosilicon defoamers; the oil well cement is one of the following: oil well grade A cement, oil well grade C cement, and oil well grade G cement; and the water is fresh water or low-mineralized water from the well site.

[0019] The method for preparing an impact-resistant and tough cement slurry for oil and gas wells, as described above, includes the following steps: (1) Take the formula amount of oil well cement, silica sand, composite toughening agent, dispersant and stabilizer and mix them evenly to obtain mixture A; (2) Take the prescribed amounts of water loss reducer, retarder, and defoamer and add them to water to obtain mixture B; (3) Mix the mixture A obtained in step (1) and the mixture B obtained in step (2) to obtain the impact-resistant and tough cement slurry for oil and gas wells.

[0020] The above-described application of an impact-resistant and tough cement slurry for oil and gas wells in cementing operations where the impact resistance of the cement sheath is required is based on the application of such slurry.

[0021] The basic principles of the above technical solution are briefly described below: To improve the impact load resistance of cement paste, this invention uses a composite toughening agent in the preparation of the cement slurry. Through the synergistic reinforcement and toughening effect of modified ultrafine elastic rubber particles and mineral whiskers, the agent mitigates stress concentration caused by internal structural irregularities when the cement paste is subjected to impact loads, increases the tensile strength limit at stress concentration points, and reduces localized plastic deformation of the cement paste, thereby increasing its resistance to uneven failure. Furthermore, the internal inhomogeneity of the cement paste leads to internal cracks, and the crack-inhibiting effect of the mineral whiskers effectively reduces the formation of these micro-cracks.

[0022] The preparation principle of modified ultrafine rubber particles in composite toughening agents is as follows: ultrafine rubber powder is surface modified with sodium hypochlorite solution. The strong oxidizing property of sodium hypochlorite is used to oxidize and corrode the surface of rubber particles, oxidizing the active groups such as double bonds and methylene groups on the surface of rubber powder into hydroxyl, carbonyl, aldehyde and carboxyl groups, thereby enhancing the polarity of the rubber particle surface and improving the interfacial interaction between the rubber particle surface and cement stone.

[0023] Mineral whiskers in composite toughening agents refer to single crystals produced through the orderly growth of crystallizable substances such as inorganic compounds or chemical elements via artificial synthesis. Whiskers are needle-shaped with an aspect ratio typically greater than 10. As single crystals, they have few internal defects, exhibiting high strength and elastic modulus, capable of withstanding external loads while maintaining good mechanical properties. They have low hardness, similar to aluminum; high aspect ratio, with diameters ranging from 0.1 to 0.6 μm and lengths from 3 to 20 μm; good abrasion resistance; good heat resistance, exhibiting good thermal insulation at high temperatures; and good chemical stability. Furthermore, they possess excellent micro-reinforcing and filling capabilities, improving the mechanical properties of cement-based composites and maintaining stable performance under various environments. However, the long aspect ratio and small size of mineral whiskers in composite toughening agents result in a large specific surface area and surface energy. When added to cement slurry, they can cause severe agglomeration, which hinders whisker dispersion and consequently affects the toughening effect. Therefore, surface modification of the mineral whiskers can effectively improve this agglomeration phenomenon, thereby increasing the dispersion of the whiskers in the cementitious material and significantly increasing the contact area between the mineral whiskers and the cement-based material. This allows the single whiskers to be more tightly wrapped by the cement-based material, resulting in more energy being consumed during crack deflection and further improving the mechanical properties of the cementitious material. Based on this, this section introduces a coupling agent, tetraethyl orthosilicate (TEOS), utilizing the hydrolytic properties of TEOS to achieve SiO2 loading on the surface of the mineral whiskers. Mineral whiskers have a large number of hydroxyl (-OH) groups on their surface, giving them strong hydrophilic properties. However, the -OH functional groups on the whisker surface have low activity. In contrast, SiO2 contains a large number of highly active hydroxyl (-OH) groups and is microsphere-shaped. When a large number of nano-SiO2 particles are loaded on the whisker surface, the overall surface area is increased. This is equivalent to introducing a large number of highly active hydroxyl groups onto the whisker surface, thereby increasing the activity of the whisker surface groups and enhancing the bonding force between the whisker and the cement-based material interface. This enhances the toughness and impact resistance of cement stone and ensures the integrity of the cement ring seal.

[0024] The dispersant was optimized as follows: two commonly used dispersants, A and B, were selected for dispersion treatment. The potential value of the mineral whisker suspension was measured using a Zeta potentiometer to study the effect of different amounts of dispersant on the potential value of the whisker suspension, thereby optimizing the dispersant with better dispersion effect. The amount of dispersant added has a significant impact on the electrostatic repulsion of the whisker suspension, i.e., it has a significant impact on the dispersion effect. The electrostatic repulsion in the suspension is highest when the amount of dispersant added is 1–2 parts. Specifically, the whiskers exhibit the highest electrostatic repulsion in the suspension when the amount of dispersant A is 1–1.5 parts and the amount of dispersant B is 1.5–2 parts. When the amount of dispersant A is 1.5 parts, the Zeta potential of the whisker suspension is 36.11 mV; when the amount of dispersant B is 2 parts, the Zeta potential of the whisker suspension is 39.02 mV. This demonstrates that, with different dosages of the two dispersants, when the dosage is 2 parts, the use of dispersant B can improve the electrostatic repulsion of the whisker suspension, indicating that the whiskers achieve a better dispersion effect at this point. Therefore, in subsequent studies, dispersant B will be selected, with a dosage of 1.5 to 2 parts.

[0025] The main technical features of the present invention are: (1) A composite toughening agent is added to the cement slurry. The composite toughening agent is composed of modified ultrafine rubber powder and mineral whiskers. It overcomes the disadvantages of poor bonding between rubber particles and cement interface and easy agglomeration of fibers and whiskers. It gives full play to the microstructure characteristics of mineral whiskers and ultrafine rubber particles and can play a synergistic role in strengthening and toughening at the nano-micron scale. At the same time, the key admixtures and additives are reasonably designed to effectively control the pore structure of cement stone, so that the oil well cement stone forms a reinforced and toughened structure with the same properties as the mineral whisker structure, making the oil well cement stone more compact and achieving the goal of improving the impact resistance of oil well cement stone; (2) Add modified ultrafine rubber to cement slurry: use hypochlorous acid oxidation method to oxidize the double bond, methylene and other active groups on the surface of rubber powder into hydroxyl, carbonyl, aldehyde and carboxyl groups, enhance the polarity of the rubber particle surface, thereby improving the interface between the rubber particle surface and cement stone; (3) Add modified whiskers to cement slurry: introduce coupling agent tetraethyl orthosilicate (TEOS), use the hydrolysis characteristics of tetraethyl orthosilicate (TEOS) to load SiO2 on the surface of mineral whiskers, improve the activity of the whisker surface groups, increase the bonding force between the whisker and the cement-based material interface, so as to enhance the toughness and impact resistance of cement stone and ensure the integrity of cement ring sealing.

[0026] Compared with the prior art, the present invention has the following main advantages: 1. The impact-resistant and tough cement grout of the present invention has the characteristics of high compressive strength, high toughness, and good impact resistance: under constant temperature and pressure curing at 110℃, the compressive strength is 26.4MPa after 48 hours, the flexural strength is 8.3MPa after 48 hours, the elastic modulus is 4.5GPa after 48 hours, and the impact energy is 0.092J / cm². 2 Under constant temperature and pressure curing at 150℃, the compressive strength after 48 hours is 27 MPa, the flexural strength after 48 hours is 8.5 MPa, the elastic modulus after 48 hours is 4.7 GPa, and the impact energy is 0.098 J / cm². 2 Under constant temperature and pressure curing at 150℃, when the amount of composite toughening agent added is 5 parts, compared with cement stone without composite toughening agent, the compressive strength remains basically unchanged, the elastic modulus after 48h decreases by 39.7%, and the impact resistance after 48h increases by 47.2%, thus achieving the goal of ensuring the compressive strength of cement stone while enhancing its elasticity, toughness, and impact resistance.

[0027] 2. The impact-resistant cement slurry of the present invention has a density of 1.9 g / cm³. 3 ~2.1g / cm 3 It is adjustable, has good rheological properties, the slurry has good stability, and low filtration loss.

[0028] 3. The additives used in the impact-resistant and tough cement slurry formulation of this invention are widely available and low in cost. Among them, mineral whiskers are environmentally friendly materials that are natural and pollution-free, and have good economic benefits.

[0029] 4. The impact-resistant and toughened cement slurry of this invention is applicable to cementing operations in unconventional shale oil and gas long horizontal wells and horizontal wells in medium- and low-permeability oil and gas reservoirs. For operations such as perforation and fracturing, it can effectively improve the cement sheath's resistance to breakage, especially improving the cement stone's resistance to breakage under impact loads, ensuring the integrity of the cement sheath and showing broad application prospects. Attached Figure Description

[0030] Figure 1 This is the thickening curve of the impact-resistant and tough cement slurry at 90°C in Example 5 of the present invention; Figure 2 This is the thickening curve of the impact-resistant and tough cement slurry at 120℃ in Example 5 of the present invention. Detailed Implementation

[0031] The present invention will be further described below through specific embodiments and comparative examples, in conjunction with tables and figures, but is not limited thereto.

[0032] In this invention, impact-resistant and tough cement slurry is prepared and its performance is tested according to the relevant provisions of standards such as GB / T 19139-2012 "Test Methods for Oil Well Cement", API RP 10B "Recommended Practices for Oil Well Cement Testing", and SY / T 5546-92 "Test Methods for Application Performance of Oil Well Cement". The mechanical properties of the cement stone are tested according to the relevant provisions of standards such as SY / T 6544-2017 "Performance Requirements for Oil Well Cement Slurry" and SY / T 6466-2016 "Test Methods for Performance of Oil Well Cement Stone". Example 1 (Cement slurry blank sample)

[0033] The impact-resistant and toughening cement slurry of this embodiment is prepared from the following raw material components in parts by weight: 100 parts of G-grade oil well, 30 parts of silica sand, 1 part of dispersant, 2 parts of water loss reducer, 1 part of retarder, 1 part of stabilizer, 0.5 parts of defoamer, and 46 parts of water. The slurry density is 1.90 g / cm³. 3 .

[0034] The preparation method of impact-resistant and tough cement slurry includes the following steps: (1) Take the formula amount of G-grade oil well cement, silica sand, dispersant and stabilizer and mix them evenly (dry mix for 3-5 minutes at room temperature) to obtain mixture A.

[0035] (2) Take the formula amount of water loss reducer, retarder and defoamer and add them to water. Stir at room temperature for 5 to 15 minutes under the condition of 200 rpm in a mixer to obtain mixture B.

[0036] (3) At a speed of 4000 rpm, the mixture A obtained in step (1) is continuously and evenly poured into the constant speed mixer and mixed with the mixture B obtained in step (2) within 15 seconds. Then, the speed is adjusted to 12000 rpm and stirred for 35 seconds to obtain the impact-resistant and tough cement slurry. Example 2

[0037] The impact-resistant and toughening cement slurry of this embodiment is prepared from the following raw material components in parts by weight: 100 parts of G-grade oil well cement, 30 parts of silica sand, 1 part of composite toughening agent, 1 part of dispersant, 2 parts of water loss reducing agent, 1 part of retarder, 1 part of stabilizer, 0.5 parts of defoamer, and 46 parts of water. The slurry density is 1.90 g / cm³. 3 .

[0038] The preparation method is basically the same as in Example 1, except that a composite toughening agent is added in step (1). The composite toughening agent is composed of modified ultrafine elastic rubber powder and modified mineral whiskers, with a mass ratio of: modified ultrafine elastic rubber powder: modified mineral whiskers = (1:2) to (2:3).

[0039] Modification method for ultrafine rubber powder: Ultrafine rubber powder is added to a temperature-controlled reactor equipped with a stirrer, and a certain amount of hypochlorous acid solution is added. The solution is titrated over 1-2 hours, maintaining a constant temperature during the reaction. After a certain reaction time, the mixture is filtered, the modified ultrafine rubber powder is cleaned with deionized water, and then dried to obtain the modified ultrafine rubber powder. Laboratory studies determined the optimal process conditions for surface modification of ultrafine rubber to be: hypochlorous acid concentration of 40%, reaction temperature of 40℃, reaction time of 3 hours, and drying temperature not exceeding 40℃.

[0040] Modification method for modified whiskers: Pretreatment of whiskers is performed by taking 50 ml of 30% hydrogen peroxide solution. Place the solution in a beaker, dilute with deionized water to 300 ml, add 15 g of calcium carbonate whiskers to the solution, and transfer the beaker to an ultrasonic instrument. Stir while sonicating at room temperature for 15 min. After washing, filtering, and drying the mixture, the pretreated calcium carbonate whiskers are obtained. Mix the pretreated calcium carbonate whiskers with ethanol and deionized water (400 ml of ethanol, 2:1 mass ratio of ethanol to deionized water), place the mixture in a beaker, add an appropriate amount of ammonia to adjust the pH of the solution, and then transfer it to a 1000 ml flask and stir magnetically for 30 min. After that, weigh a certain amount of tetraethyl orthosilicate (TEOS) and mix it with a small amount of ethanol. Add the mixture dropwise over 1 h. Then stir the resulting solution at room temperature for a certain period of time to continue the reaction. Wash and filter the reacted solution with deionized water, and then dry it in an oven for 24 h to obtain the modified whiskers. The optimal process conditions for whisker modification, determined through indoor studies, were a reaction time of 5 hours, a pH of 11 for the reaction solution, and a TEOS mass concentration of 0.4 mol / L. Example 3

[0041] The impact-resistant and toughening cement slurry of this embodiment is prepared from the following raw material components in parts by weight: 100 parts of G-grade oil well cement, 30 parts of silica sand, 3 parts of composite toughening agent, 1 part of dispersant, 2 parts of water loss reducing agent, 1 part of retarder, 1 part of stabilizer, 0.5 parts of defoamer, and 46 parts of water. The slurry density is 1.90 g / cm³. 3 .

[0042] The preparation method is the same as in Example 2. Example 4

[0043] The impact-resistant and toughening cement slurry of this embodiment is prepared from the following raw material components in parts by weight: 100 parts of G-grade oil well cement, 30 parts of silica sand, 5 parts of composite toughening agent, 1 part of dispersant, 2 parts of water loss reducing agent, 1 part of retarder, 1 part of stabilizer, 0.5 parts of defoamer, and 46 parts of water. The slurry density is 1.89 g / cm³. 3 .

[0044] The preparation method is the same as in Example 2. Example 5

[0045] The impact-resistant and toughening cement slurry of this embodiment is prepared from the following raw material components in parts by weight: 100 parts of G-grade oil well, 30 parts of silica sand, 4 parts of composite toughening agent, 1 part of dispersant, 2 parts of water loss reducing agent, 1 part of retarder, 1 part of stabilizer, 0.5 parts of defoamer, and 46 parts of water. The slurry density is 1.89 g / cm³. 3 .

[0046] The preparation method is the same as in Example 2.

[0047] Experimental Example 1 The effect of the amount of composite toughening agent added on the engineering performance of cement grout was tested.

[0048] Using the impact-resistant and tough cement slurries from Examples 1-4 as test subjects, the engineering performance of the cement slurries was tested. The test cycle temperature was 120℃, and the static temperature was 150℃.

[0049] See Table 1. In Experiment 1, as the dosage of the composite toughening agent increased, the density, fluidity, and initial consistency of the cement slurry decreased. When the dosage was 3 parts, the basic properties of the cement slurry were good; when the dosage was 5 parts, the consistency of the cement slurry was 25.6 Bc, and the fluidity was 18 cm. Although the fluidity decreased, the slurry properties still met the construction requirements and the performance was good, indicating good compatibility between the composite toughening agent and the cement slurry. In summary, the composite toughening agent has good compatibility with the cement slurry, has little impact on the performance of the cement slurry, and the cement slurry performance is stable, ensuring the construction performance of the impact-resistant and toughening cement slurry.

[0050] Table 1. Effect of Composite Toughening Agent Dosage on Cement Slurry Engineering Performance .

[0051] Experimental Example 2 The effect of the amount of composite toughening agent added on the mechanical properties of cement paste was tested.

[0052] The impact toughness cement slurries of Examples 1-4 were used as test objects to conduct mechanical property tests on cement stone. The test temperature was 120℃, and the static temperature was 150℃.

[0053] See Table 2. In Experiment 2, the enhancement effect on the mechanical properties of cement stone gradually increased with the increase of the composite toughening agent dosage. When the composite toughening agent dosage was 5 parts, the 48-hour flexural strength of the cement stone was 8.4 MPa, which was 40% higher than that of the blank cement stone; the 48-hour elastic modulus of the cement stone was 4.5 GPa, which was 42.3% lower than that of the blank cement stone, showing a significant effect on improving the elasticity and toughness of the cement stone; the 48-hour compressive strength of the cement stone was 24.5 MPa, with minimal strength loss, thus ensuring compressive strength while enhancing the toughness and impact resistance of the cement stone.

[0054] Table 2. Effect of Composite Elastic Toughening Agent Dosage on Mechanical Properties of Cement Stone ; Experimental Example 3 Evaluation of the engineering performance of impact-resistant and tough cement slurry systems.

[0055] Using the impact-resistant and tough cement slurry from Example 5 as the test object, the engineering performance of the cement slurry was tested. Test temperatures: 90℃ and 120℃.

[0056] Table 3 Engineering Properties of Impact-Resistant and Tough Cement Slurry ; See Table 3. In Experiment 3, the impact toughness cement slurry system exhibited good cement slurry performance, and the basic properties of the cement slurry system, such as density, fluidity, and API water loss, all met the expected indicators.

[0057] Test Example 4 Test the thickening time of the impact toughness cement slurry.

[0058] Using the impact-resistant and tough cement slurry from Example 5 as the test object, the thickening time of the cement slurry was tested. Experimental temperatures: 90℃ and 120℃. Figure 1 The 90℃ thickening curve of impact-resistant and tough cement slurry. Figure 2 Thickening curve of impact-resistant and tough cement slurry at 120℃.

[0059] Table 4. Test data on thickening time of impact-resistant cement slurry ; See Figure 1 , Figure 2 And Table 4. In Experiment 4, the thickening time of the impact toughness cement slurry at 90℃ was 154 min, and the thickening time at 120℃ was 138 min. The thickening line shape was good, the curves were all flat, and there were no adverse phenomena such as "bulging" or "stepping". Moreover, the thickening transition time was less than 30 min, and it basically showed "right angle" thickening. The impact toughness cement slurry has good engineering performance, is easy to construct, and ensures construction safety and cementing quality.

[0060] Experimental Example 5 Test the mechanical properties of impact-resistant and tough cement grout.

[0061] Using the impact-resistant and tough cement slurry from Example 5 as the test object, the mechanical properties of the cement slurry were tested, mainly including the 48-hour compressive strength, 48-hour flexural strength, 48-hour elastic modulus, and 48-hour impact resistance of the cement paste. The experimental temperatures were 110℃ and 150℃.

[0062] Table 5 Evaluation Results of Mechanical Properties of Impact-Resistant and Tough Cement Slurry ; See Table 5. In Experiment 5, the impact toughness cement stone exhibited a compressive strength greater than 14 MPa, a flexural strength greater than 7 MPa, an elastic modulus less than 5 GPa, and an impact energy greater than 0.09 J / cm² at both 110℃ and 150℃. 2 This meets the expected targets.

[0063] Experimental Example 6 An evaluation of the integrity of the impact-resistant and tough cement grout sealant was conducted.

[0064] The impact toughness cement slurries of Examples 1 and 5 were used as test objects to evaluate the sealing integrity of the cement slurry. The test temperatures were 110℃ and 150℃, and the curing time was 48h.

[0065] Table 6. Evaluation Results of Cement Ring Seal Integrity at 110℃ ; See Table 6. In Test Example 6, after the cement ring blank sample was cured at 110℃ for 48 hours, the cement ring was tested for crosslinking at a crosslinking pressure of 1.0 MPa. The cement ring did not crosslink and the bonding was intact. After 10 rounds of alternating tests with a pressure difference of 15 MPa, the crosslinking pressure was tested again at 1.0 MPa. The first and second interfaces of the cement ring were connected, and a through crack appeared in the cement ring. For the impact-resistant and tough cement grout, after curing at 110℃ for 48 hours, when a pressure of 15MPa was applied and the pressure was changed 0, 10, and 20 times, the cement ring did not show any signs of cross-linking under a cross-linking pressure of 1.0MPa. The cement ring remained intact and well-bonded, and no cracks or defects were observed at the interface. When a pressure of 30MPa was applied and the pressure was changed 10 times, cross-linking still did not occur under a cross-linking pressure of 1.0MPa. After 20 times of cross-linking at 30MPa, the cement ring showed slight cross-linking under a cross-linking pressure of 1.0MPa. Slight bubbles appeared at the interface between the cement ring and the reactor mouth. At this time, the cement ring was still intact and there were no obvious cracks.

[0066] Table 7. Evaluation Results of Cement Ring Seal Integrity at 150℃ ; See Table 7. In Experiment 6, after curing the cement ring blank sample at 150℃ for 48 hours, a cross-linking test was conducted at a cross-linking pressure of 1.0 MPa. No cross-linking was observed in the cement ring, indicating good bonding. After 10 cycles of alternating tests at a pressure difference of 15 MPa, a cross-linking test was conducted again at a cross-linking pressure of 1.0 MPa, and slight cross-linking was observed. After 20 cycles of alternating tests, at a cross-linking pressure of 1.0 MPa, severe gas cross-linking occurred, and a through crack appeared in the cement ring. For the impact-resistant and tough cement grout, after curing at 150℃ for 48 hours, when a pressure of 15MPa was applied and the pressure was changed 0, 10, and 20 times, the cement ring did not show any cross-linking under a cross-linking pressure of 1.0MPa, and the cement ring remained intact and well-bonded. When a pressure of 30MPa was applied and the pressure was changed 10 times, no cross-linking occurred under a cross-linking pressure of 1.0MPa. After 20 times of cross-linking at 30MPa, the cement ring showed slight cross-linking under a cross-linking pressure of 1.0MPa, and slight bubbles appeared at the interface between the cement ring and the reactor mouth. At this time, the cement ring was still intact and there were no obvious cracks.

Claims

1. A cement slurry for oil and gas wells with impact resistance and toughness, characterized in that, The cement slurry is composed of oil well cement, silica sand, composite toughening agent, dispersant, water loss reducing agent, retarder, stabilizer, defoamer and water. The composite toughening agent is composed of modified ultrafine elastic rubber powder and modified mineral whiskers.

2. The impact-resistant and toughening cement slurry for oil and gas wells according to claim 1, characterized in that, The mass fractions of each component are as follows: based on 100 parts of oil well cement, add 30-40 parts of silica sand, 3-5 parts of composite toughening agent, 1-2 parts of dispersant, 1.5-3 parts of water loss reducer, 0.5-1.5 parts of retarder, 1-2 parts of stabilizer, 0.2-1.0 parts of defoamer, and 44-60 parts of water.

3. The impact-resistant and toughening cement slurry for oil and gas wells according to claim 1, characterized in that, The mass ratio of the composite toughening agent is: modified ultrafine elastic rubber powder: modified mineral whiskers = (1:2) ~ (2:3).

4. The impact-resistant and toughening cement slurry for oil and gas wells according to claim 1, characterized in that, The modification method of the modified ultrafine elastic rubber powder is as follows: add hypochlorous acid solution to ultrafine rubber powder, keep it at a warm temperature for reaction, filter the mixture, clean the modified ultrafine rubber powder with deionized water, and then dry it.

5. The impact-resistant and toughening cement slurry for oil and gas wells according to claim 1, characterized in that, The modification method of the modified mineral whiskers is as follows: First, the mineral whiskers are pretreated by adding them to a hydrogen peroxide solution, and after ultrasonic treatment at room temperature, the mixture is washed, filtered and dried; then, the pretreated mineral whiskers are mixed with an ethanol aqueous solution, and an ethanol solution of tetraethyl orthosilicate is added dropwise and reacted at room temperature. The reacted solution is washed, filtered and dried.

6. The impact-resistant and toughening cement slurry for oil and gas wells according to claim 1, characterized in that, The dispersant is one of lignin sulfonate dispersants, sulfonated acetone-formaldehyde condensate dispersants, polycarboxylic acid dispersants, and polymer dispersants; the water loss reducing agent is one of 2-acrylamide-2-methylpropanesulfonic acid water loss reducing agents, modified polyvinyl alcohol water loss reducing agents, hydroxyethyl cellulose and carboxymethyl cellulose water loss reducing agents.

7. The impact-resistant and toughening cement slurry for oil and gas wells according to claim 1, characterized in that, The retarder is one of the following: hydroxycarboxylic acid retarder, cellulose and its derivatives retarder, lignin sulfonate and its derivatives retarder, modified sugar compound retarder, inorganic acid and its salt retarder, organophosphate retarder, and polymer retarder; the stabilizer is one of the following: xanthan gum, cellulose and its derivatives stabilizer.

8. The impact-resistant and toughening cement slurry for oil and gas wells according to claim 1, characterized in that, The defoamer is one of the following: organic fatty and fatty alcohol defoamers, organic polyether defoamers, organosilicon defoamers, and polyether-modified organosilicon defoamers; the oil well cement is one of the following: oil well grade A cement, oil well grade C cement, and oil well grade G cement; the water is fresh water or low-mineralized water from the well site.

9. A method for preparing an impact-resistant and tough cement slurry for oil and gas wells according to any one of claims 1-8, characterized in that, Includes the following steps: (1) Take the formula amount of oil well cement, silica sand, composite toughening agent, dispersant and stabilizer and mix them evenly to obtain mixture A; (2) Take the prescribed amounts of water loss reducer, retarder, and defoamer and add them to water to obtain mixture B; (3) Mix the mixture A obtained in step (1) and the mixture B obtained in step (2) to obtain the impact-resistant and tough cement slurry for oil and gas wells.

10. The application of an impact-resistant and tough cement slurry for oil and gas wells according to any one of claims 1-8 in cementing operations for oil and gas wells where the impact resistance of the cement sheath is required to be high.

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