A high-temperature strengthening and toughening oil well cement admixture and its preparation method

Abstract

This invention relates to the field of cement admixture technology, specifically to a high-temperature reinforced and toughened oil well cement admixture and its preparation method. The invention prepares a toughening agent based on surface-grafted tricalcium silicate polyimide fibers, wollastonite fibers, and mullite whiskers; a high-temperature stabilizer based on calcined shale powder and nano-alumina; a dispersant; and modifies carbon nanotubes and halloysite nanotubes, while simultaneously adjusting the modification process in real time to improve the modification effect, thus preparing reinforcing and toughening components. Finally, these components are mixed in a preset ratio to obtain the high-temperature reinforced and toughened oil well cement admixture. The cement admixture of this invention consists of a toughening agent, a high-temperature stabilizer, a dispersant, and reinforcing and toughening components, and can effectively improve the high-temperature reinforcement and toughening effect of oil well cement.

Description

Technical Field

[0001] This invention relates to the field of cement admixture technology, specifically to a high-temperature enhanced and toughened oil well cement admixture and its preparation method. Background Technology

[0002] Cement sheaths are ring-shaped cement stones used in oil well cementing operations to ensure wellbore stability, isolate fluids between different formations, and prevent oil and gas leakage. However, the coupling effect of downhole high temperatures and fracturing cyclic loads can damage the integrity of cement sheaths and induce annular channeling. To improve the mechanical properties of cement sheaths, high-temperature reinforcing and toughening cement admixtures are usually added, and carbon nanotubes and halloysite nanotubes are used as reinforcing and toughening components in the cement admixtures to improve the toughness and strength of the cement.

[0003] However, the hydrophobicity and van der Waals forces of nanomaterials can easily lead to uneven dispersion and agglomeration of reinforcing and toughening components in cement matrix composites, thus affecting the performance of the cement matrix. Therefore, carbon nanotubes and halloysite nanotubes are usually surface modified or dispersed. Currently, low-temperature plasma treatment is commonly used for modification. However, the modification process usually relies on fixed modification power and modification time, which may lead to a mismatch between the modification effect and the actual needs, thus affecting the preparation effect of cement admixtures. Summary of the Invention

[0004] To address the technical problem of unsatisfactory preparation results of cement admixtures, the present invention aims to provide a high-temperature reinforced and toughened oil well cement admixture and its preparation method. The specific technical solution adopted is as follows:

[0005] A method for preparing a high-temperature reinforced and toughened oil well cement admixture, the method comprising:

[0006] Toughening agents were prepared based on surface-grafted tricalcium silicate polyimide fibers, wollastonite fibers and mullite whiskers.

[0007] High-temperature stabilizers prepared based on calcined shale powder and nano-alumina;

[0008] Preparation of dispersants;

[0009] Carbon nanotubes and halloysite nanotubes were modified to prepare reinforcing and toughening components;

[0010] During the modification process, the operating power of the plasma processor and the plasma density parameters at each measuring point within it are obtained at each monitoring time. At each monitoring time, for each measuring point, the ion energy deviation is obtained based on the deviation of the plasma density parameters relative to the preset density parameters, and the modification distribution difference parameters are obtained based on the differences between the ion energy deviations at different measuring points. During the modification process, the operating power of the plasma processor is adjusted based on the modification distribution difference parameters at each monitoring time and the distribution characteristics of the ion energy deviations at the measuring points, and the adjustment is iteratively adjusted until the preset modification termination condition is met.

[0011] The toughening agent, the high-temperature stabilizer, the dispersant, and the reinforcing and toughening components are mixed in a preset ratio to obtain a high-temperature reinforced and toughened oil well cement admixture.

[0012] Furthermore, the method for obtaining the plasma density parameter includes:

[0013] Langmuir probes are installed at each measurement point in the plasma processor, and the product of the probe current and probe voltage at each monitoring moment is used as the plasma density parameter at the corresponding measurement point.

[0014] Furthermore, the methods for obtaining the preset density parameters include:

[0015] During the modification process, any monitoring time is taken as the target time, and the operating power at the target time is taken as the target operating power; during the no-load operation of the plasma processor, the plasma density parameter at any measuring point under the target operating power is taken as the preset density parameter at the target time.

[0016] Furthermore, the dispersant comprises sodium dodecylbenzenesulfonate powder.

[0017] Furthermore, the method for obtaining the modified distribution difference parameter includes:

[0018] At each monitoring time, based on the distribution characteristics of the ion energy deviation at all measuring points, an ion energy reference deviation is obtained. By combining the differences between the ion energy deviation at each measuring point and the ion energy reference deviation, the modification distribution difference parameter at the corresponding monitoring time is obtained.

[0019] Furthermore, adjusting the operating power of the plasma processor includes:

[0020] At each monitoring moment, the modified state parameters are obtained based on the ion energy reference deviation and the modified distribution difference parameter, and the power adjustment direction weight is determined based on the modified state parameters.

[0021] By integrating the power adjustment direction weight and the modified state parameters, a power adjustment weight is obtained. The power adjustment weight is then used to weight a preset power adjustment step size to obtain a power adjustment value.

[0022] The operating power at each monitoring time is added to the power adjustment value to obtain the operating power of the plasma processor at the next monitoring time; wherein, when the operating power of the plasma processor at the next monitoring time is higher than the preset upper limit power, the operating power of the plasma processor is set to the preset upper limit power; when the operating power of the plasma processor at the next monitoring time is lower than the preset lower limit power, the operating power of the plasma processor is set to the preset lower limit power.

[0023] Furthermore, the method for obtaining the modified state parameters includes:

[0024] The ion energy reference deviation is used as the numerator, the sum of the modified distribution difference parameter and the preset minimum positive parameter is used as the denominator, and the fractional ratio is used as the modified state parameter.

[0025] Furthermore, the method for determining the power adjustment direction weight includes:

[0026] When the modified state parameter is greater than or equal to the preset equilibrium state threshold, the power adjustment direction weight is set to 1; when the modified state parameter is less than the preset equilibrium state threshold, the power adjustment direction weight is set to -1.

[0027] Furthermore, at each monitoring time, the ratio of the ion energy deviation of each measuring point to the preset density parameter is used as the modification termination parameter at the corresponding measuring point. The preset modification termination condition is that the modification termination parameter at all measuring points is less than the preset termination threshold at a consecutive preset number of monitoring times.

[0028] This invention also proposes a high-temperature reinforced and toughened oil well cement admixture, comprising the following components in parts by weight:

[0029] Toughening agent 60-70 parts; high temperature stabilizer 20-30 parts; reinforcing and toughening components 7-9 parts; dispersant 1-3 parts;

[0030] The toughening agent includes polyimide fibers, wollastonite fibers, and mullite whiskers with surface-grafted tricalcium silicate; the high-temperature stabilizer includes calcined shale powder and nano-alumina; the reinforcing and toughening components include hydrophilically modified carbon nanotubes and halloysite nanotubes; and the dispersant includes sodium dodecylbenzenesulfonate powder.

[0031] The present invention has the following beneficial effects:

[0032] This invention prepares toughening agents based on surface-grafted tricalcium silicate polyimide fibers, wollastonite fibers, and mullite whiskers; prepares high-temperature stabilizers based on calcined shale powder and nano-alumina; prepares dispersants; and performs hydrophilic modification on carbon nanotubes and halloysite nanotubes to prepare reinforcing and toughening components. During the modification process, the operating power of the plasma processor and the plasma density parameters at each measuring point are obtained at each monitoring time. Then, at each monitoring time, for each measuring point, the ion energy deviation is obtained based on the deviation of the plasma density parameter from the preset density parameter, and the modification distribution difference parameter is obtained based on the difference between the ion energy deviations of different measuring points. During the modification process, based on the modification distribution difference parameter at each monitoring time and the distribution characteristics of the ion energy deviation at the measuring points, the operating power of the plasma processor at the next monitoring time is adjusted to improve the modification effect. Iterative adjustments are made until the preset modification termination condition is met. Finally, the toughening agent, high-temperature stabilizer, dispersant, and reinforcing and toughening components are mixed in a preset ratio to obtain a high-temperature reinforced and toughened oil well cement admixture. The cement admixture of the present invention is composed of a toughening agent, a high-temperature stabilizer, a dispersant, and a reinforcing and toughening component. Modified carbon nanotubes and halloysite nanotubes are selected as the reinforcing and toughening components. The cement admixture can effectively improve the high-temperature toughening and strengthening effect of oil well cement. Attached Figure Description

[0033] To more clearly illustrate the technical solutions and advantages in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1 A flowchart illustrating a method for preparing a high-temperature reinforced and toughened oil well cement admixture according to an embodiment of the present invention;

[0035] Figure 2 This is a flowchart of a method for preparing reinforcing and toughening components according to an embodiment of the present invention;

[0036] Figure 3 This is a uniaxial stress-strain curve of cement stone after 7 days of curing in experimental group 1, provided in an embodiment of the present invention.

[0037] Figure 4 This is a uniaxial stress-strain curve of cement stone after 7 days of curing in experimental group 2, provided in one embodiment of the present invention;

[0038] Figure 5 This is a uniaxial stress-strain curve of cement stone after 7 days of curing in experimental group 3, provided in one embodiment of the present invention;

[0039] Figure 6 This is a uniaxial stress-strain curve of cement stone after 7 days of curing in experimental group 4, provided in one embodiment of the present invention;

[0040] Figure 7 The uniaxial stress-strain curve of cement stone after 7 days of curing in the control group provided in one embodiment of the present invention. Detailed Implementation

[0041] To further illustrate the technical means and effects adopted by the present invention to achieve its intended purpose, the following, in conjunction with the accompanying drawings and preferred embodiments, details the specific implementation, structure, features, and effects of a high-temperature enhanced and toughened oil well cement admixture and its preparation method according to the present invention. In the following description, different "one embodiment" or "another embodiment" do not necessarily refer to the same embodiment. Furthermore, specific features, structures, or characteristics in one or more embodiments can be combined in any suitable form.

[0042] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0043] The following description, in conjunction with the accompanying drawings, details the specific scheme of a high-temperature enhanced and toughened oil well cement admixture and its preparation method provided by the present invention.

[0044] Please see Figure 1 The diagram illustrates a flowchart of a method for preparing a high-temperature reinforced and toughened oil well cement admixture according to an embodiment of the present invention, specifically including:

[0045] Step S1: Prepare a toughening agent based on surface-grafted tricalcium silicate polyimide fibers, wollastonite fibers and mullite whiskers.

[0046] Considering that polyimide fibers have high high temperature resistance, high tensile strength and elastic modulus, they can maintain the structural integrity and mechanical properties in oil well cement applications. Wollastonite fibers and mullite whiskers can also maintain excellent toughness and impact resistance in high temperature environments, prevent microcrack propagation, and thus improve the toughness and impact resistance of cement.

[0047] Furthermore, considering that the surface of polyimide fibers is chemically inactive and lacks active groups that can react chemically with cement hydration products (such as calcium silicate hydrate CSH gel), and that the surface of polyimide fibers is hydrophobic while cement slurry is hydrophilic, polyimide fibers are difficult to wet in cement slurry and are prone to forming gaps and weak interface layers with the cement matrix; if polyimide fibers are directly added to cement, when the cement matrix is ​​subjected to stress, cracks will easily propagate along the weak interface layer, and the polyimide fibers will not be able to effectively transfer stress from the matrix to themselves, thereby reducing the strength and toughness of the cement paste;

[0048] Based on this, in one embodiment of the present invention, polyimide fibers, wollastonite fibers, and mullite whiskers with surface grafted tricalcium silicate are selected as basic components to prepare a toughening agent in oil well cement admixtures; wherein, the length of wollastonite fibers is 5um~180um, the length of mullite whiskers is 10um~200um and the diameter is 0.03mm~1mm, and the length of polyimide fibers is 1mm~3mm, and the three can perform multi-scale synergistic toughening.

[0049] For the polyimide fibers, tricalcium silicate is first chemically bonded to the polyimide fibers using a silane coupling agent, thereby forming polyimide fibers with surface-grafted tricalcium silicate. Since tricalcium silicate is hydrophilic and can form strong chemical bonds with cement hydration products, grafting tricalcium silicate onto the surface of polyimide fibers can improve the defects of polyimide fibers and enhance their performance.

[0050] Specifically, polyimide fibers with a length of 2 mm were selected and placed in anhydrous ethanol for ultrasonic cleaning at room temperature to remove surface grease, dust, and other impurities. The cleaned polyimide fibers were then immersed in a 1 mol / L hydrochloric acid solution and heated at 60°C for 30 minutes to slightly corrode the fiber surface, increasing its roughness and specific surface area, activating surface chemical groups, and enhancing the mechanical interlocking and chemical bonding with the coupling agent. The fibers were then washed with deionized water to remove acid and impurities to avoid interfering with subsequent reactions. After washing, the fibers were vacuum dried for 4 hours to obtain pretreated polyimide fibers.

[0051] A silane coupling agent (2 wt% by mass, γ-aminopropyltriethoxysilane, hereinafter referred to as KH550) was added to an ethanol solution with a volume ratio of ethanol to deionized water of 9:1. The pH of the ethanol solution was adjusted to 5.0 with acetic acid to promote the hydrolysis of KH550. The solution was then stirred for 30 min to obtain a KH550 solution.

[0052] Pretreated polyimide fibers were placed in a KH550 solution and stirred at 60°C for 4 hours. The solution was then removed and the active silanol groups generated by KH550 hydrolysis were combined with the polyimide fibers to coat the fiber surface with a coupling agent molecule. The fibers were then rinsed with anhydrous ethanol and dried to obtain KH550 modified polyimide fibers.

[0053] Next, tricalcium silicate powder (industrial grade with a purity >99%) was ultrasonically dispersed in anhydrous ethanol for 30 minutes to break up agglomerated powder and obtain a tricalcium silicate dispersion. Then, KH550-modified polyimide fibers were placed into the tricalcium silicate dispersion, and ammonia was added dropwise to adjust the pH to 10. The alkaline environment is conducive to the condensation reaction between tricalcium silicate and the unreacted groups at the other end of KH550. Then, the mixture was ultrasonically treated at 60°C for 2 hours. Ultrasound not only promotes mixing but also helps to drive the chemical bonding between tricalcium silicate and KH550 molecules on the fiber surface, thus completing the grafting. Finally, the polyimide fibers were taken out, rinsed with anhydrous ethanol, and vacuum dried at 60°C for 2 hours to obtain polyimide fibers with tricalcium silicate grafted on the surface.

[0054] After obtaining the surface-grafted tricalcium silicate polyimide fiber, the surface-grafted tricalcium silicate polyimide fiber, wollastonite fiber, and mullite whiskers are mixed evenly in a weight ratio of 5:3:2 to obtain the toughening agent in the toughening cement admixture.

[0055] It should be noted that the above preparation process is a well-known operating technique and will not be described in detail here.

[0056] Step S2: Prepare a high-temperature stabilizer based on calcined shale powder and nano-alumina.

[0057] In one embodiment of the present invention, shale is first ground to a particle size of 200 mesh (approximately 75 μm), and then placed in a muffle furnace for calcination. The calcination temperature is set at 800°C, the heating rate is 5°C / min, and the holding time is 2 hours. The calcined shale powder obtained after calcination has a particle size of 45 μm to 75 μm. Calcination removes organic matter and transforms the SiO2 in it into a more active amorphous form, enabling it to react more effectively with cement hydration products at high temperatures. The calcined shale powder is then mixed uniformly with nano-alumina at a weight ratio of 99:1 to obtain a high-temperature stabilizer in cement admixtures. The nano-alumina has a particle size of 1 nm to 100 nm. The nano-alumina provides an aluminum source and can synergistically react with active SiO2 to generate more stable hydration products, further consolidating the cement matrix structure and preventing high-temperature damage.

[0058] Step S3: Prepare the dispersant.

[0059] In a preferred embodiment of the invention, sodium dodecylbenzene sulfonate powder is used as a component of the dispersant. By disrupting the van der Waals forces between molecules, agglomeration is avoided, thereby making the cement mixture more uniform and stable.

[0060] Step S4: Modify carbon nanotubes and halloysite nanotubes to prepare reinforcing and toughening components.

[0061] Because carbon nanotubes and halloysite nanotubes have very high strength and stiffness, their nanoscale size allows them to fill the pores of cement matrix to improve the structure of cement matrix, thereby increasing the strength and toughness of cement matrix. However, due to the small particle size of carbon nanotubes and halloysite nanotubes, the surface of carbon nanotubes and halloysite nanotubes is hydrophobic, making them susceptible to agglomeration due to van der Waals forces, which in turn affects the performance of cement matrix.

[0062] Therefore, in one embodiment of the present invention, a plasma treatment device is used to modify carbon nanotubes and halloysite nanotubes. By introducing hydroxyl (-OH) and carboxyl (-COOH) groups on the surface of carbon nanotubes and halloysite nanotubes, they are made hydrophilic. At the same time, after the functional groups are ionized, electrostatic repulsion occurs between the particles, avoiding agglomeration, thereby obtaining the reinforcing and toughening component in cement admixtures; wherein, the purity of the carbon nanotubes and halloysite nanotubes used is ≥99%.

[0063] Please see Figure 2 The diagram illustrates a flowchart of a method for preparing reinforcing and toughening components according to an embodiment of the present invention, specifically including:

[0064] Step S401: During the modification process, obtain the operating power of the plasma processor and the plasma density parameters at each measuring point within it at each monitoring time.

[0065] Specifically, carbon nanotubes and halloysite nanotubes are first mixed evenly in a 1:1 weight ratio, and then the mixture is spread evenly on the stage of the low-temperature plasma processor; the vacuum pump of the plasma processor is turned on, and the modification treatment is carried out under 60 Pa conditions, with air as the treatment atmosphere.

[0066] The total mass of the modified carbon nanotubes and halloysite nanotubes needs to be determined according to the capacity limit of the plasma processor stage. To avoid damage to the nanotube walls caused by excessive power, the output power of the plasma processor is set in the range of 100W~300W during the modification process (i.e., the preset upper limit of power is 300W and the preset lower limit of power is 100W), and the longest modification processing time is 10min. In this embodiment, at the start of modification (the start of operation of the plasma processor), the operating power of the plasma processor is set to 150W.

[0067] Considering that in the early stage of modification, due to the hydrophobicity and chemical inertness of carbon nanotubes and halloysite nanotubes, carbon nanotubes and halloysite nanotubes will adsorb a large number of active ions such as free radicals and ions from the plasma, resulting in a certain degree of reduction in the local ion density of the plasma; as the modification is nearing its end, the consumption of ions in the plasma by carbon nanotubes and halloysite nanotubes will gradually weaken, and the ion density will recover and gradually stabilize.

[0068] The ion density of plasma can reflect the modification state or progress. Therefore, in one embodiment of the present invention, measuring points are set up in the plasma processor to collect plasma density parameters in the local area where different measuring points are located, so as to prepare for subsequent evaluation of the hydrophilic modification of carbon nanotubes and halloysite nanotubes and adjust the operating power of the plasma processor.

[0069] Furthermore, starting from the modification, the operating power of the plasma processor and the plasma density parameters at each measuring point within the plasma processor are collected in real time at each monitoring moment. Among them, four measuring points are set. Since the stage is usually rectangular, the stage is evenly divided into four areas in a grid pattern, and a measuring point is placed at the center of each area. The monitoring frequency is set to once per second, which is consistent with the modification adjustment frequency. The implementer can also adjust the measuring point layout and monitoring frequency as needed.

[0070] Preferably, in one embodiment of the present invention, considering that when the plasma processor is running, the plasma density in the vacuum cavity is often positively correlated with the operating power of the plasma processor, and the greater the plasma density, the greater the modification intensity; and considering that when a Langmuir probe is installed at each measuring point and a voltage is applied, charged particles (electrons and ions) will be attracted or repelled, thereby forming a current on the probe, and the magnitude of the current can indirectly characterize the ion density; then the method for obtaining the plasma density parameter includes:

[0071] Langmuir probes are installed at each measurement point in the plasma processor, and the product of the probe current and probe voltage at each monitoring moment is used as the plasma density parameter at the corresponding measurement point.

[0072] It should be noted that installing Langmuir probes and collecting probe current and probe voltage at each monitoring moment is a well-known technique, and the specific process will not be described in detail here. The unit of probe voltage is V, the unit of probe current is A, and the unit of plasma density parameter is W, which is the same as that of power.

[0073] It should be noted that the product of probe current and probe voltage is only used to characterize the plasma density parameter and is unrelated to the operating power of the plasma processor.

[0074] In step S402, at each monitoring time, for each measuring point, the ion energy deviation is obtained based on the deviation of the plasma density parameter relative to the preset density parameter, and the modification distribution difference parameter is obtained based on the difference between the ion energy deviations of different measuring points.

[0075] Considering that the plasma density parameter will gradually recover and stabilize after the modification is completed, the plasma density parameter at this time is close to the plasma density parameter generated when the plasma processor is unloaded (no material is processed, i.e. the stage is empty). Therefore, the deviation of the plasma density parameter from the density parameter in the unloaded state can reflect the adsorption of active ions in the plasma by carbon nanotubes and halloysite nanotubes during the modification process, thus indirectly characterizing the modification state.

[0076] Based on this, in each monitoring moment, for each measuring point, the ion energy deviation is obtained according to the deviation of the plasma density parameter relative to the preset density parameter. The ion energy deviation indirectly characterizes the modification state. The smaller the ion energy deviation, the greater the possibility that the modification is about to end.

[0077] In a preferred embodiment of the present invention, the method for obtaining the preset density parameter includes: during the modification process, taking any monitoring time as the target time and using the operating power at the target time as the target operating power; during the no-load operation of the plasma processor, taking the plasma density parameter at any measuring point under the target operating power as the preset density parameter at the target time.

[0078] Among them, the no-load operation of the plasma processor can be regarded as a blank control to evaluate the plasma density parameters at each measuring point when carbon-free nanotubes and halloysite nanotubes adsorb active ions.

[0079] Specifically, the same operating conditions and parameters of the plasma processor as in step S401 above are set, the stage is unloaded, the vacuum pump of the plasma processor is turned on, starting from 150W, the operating power is continuously increased in preset steps of 1W, and the plasma concentration parameters at any measuring point under each operating power are collected in real time based on the Langmuir probe. The plasma concentration parameters can provide a reference for the local ion concentration at the measuring point during the unmodified process.

[0080] It should be noted that during the modification process, each measuring point corresponds to a plasma concentration parameter at each monitoring time. For ease of understanding, any monitoring time during the modification process is taken as the target time, and the operating power at the target time is taken as the target operating power. Thus, during the no-load operation of the plasma processor, the plasma concentration parameter at any measuring point under the target operating power is taken as the preset density parameter of each measuring point at the target time. By changing the target time, the preset density parameters of all measuring points at each monitoring time can be obtained.

[0081] It should be noted that when the plasma processor is unloaded, the plasma is assumed to be uniformly distributed. The plasma concentration parameters at different measuring points should be the same or similar under each operating power. Therefore, the plasma concentration parameter obtained at any measuring point is used to characterize the plasma concentration parameters at all measuring points. Alternatively, the implementer can take the mean, mode, or median of the plasma concentration parameters at all measuring points under each operating power to obtain the preset concentration parameter under the corresponding operating power. The unit of measurement for the preset density parameter is W.

[0082] After determining the preset density parameters for each measuring point at each monitoring time, the ion energy deviation of each measuring point at each monitoring time during the modification process can be further obtained.

[0083] In one embodiment of the present invention, the method for obtaining ion energy deviation includes:

[0084] At each monitoring moment, for each measuring point, the difference between the preset density parameter and the plasma density parameter is used as the ion energy deviation for the corresponding measuring point.

[0085] The dimensionless unit of ion energy deviation is W. The larger the ion energy deviation, the less saturated the adsorption of plasma by carbon nanotubes and halloysite nanotubes is. To improve the modification efficiency, the operating power of the plasma processor during the modification process needs to be appropriately increased. Conversely, the smaller the ion energy deviation, the closer the modification may be to the end, and the operating power of the plasma processor can be appropriately reduced.

[0086] Furthermore, considering that under ideal conditions, carbon nanotubes and halloysite nanotubes are uniformly distributed, and the modification performance of each region in the plasma processor is basically consistent, that is, the ion energy deviation at different measurement points should be small; however, during the modification process, the inherent characteristics and distribution differences of carbon nanotubes and halloysite nanotubes will cause certain differences in the modification state at each measurement point, further affecting the modification effect.

[0087] In this embodiment of the invention, after obtaining the ion energy deviation, the modification distribution difference parameter is further obtained based on the difference between the ion energy deviations at different measuring points. The modification distribution difference parameter reflects the difference in modification state between the corresponding local areas at different measuring points. The larger the modification distribution difference parameter, the greater the possibility that the overall modification state of carbon nanotubes and halloysite nanotubes on the stage is synchronized. Conversely, it indicates that there is a large difference in the modification state. In order to avoid the risk of insufficient modification or over-treatment, it is necessary to appropriately reduce the adjustment power.

[0088] Preferably, in one embodiment of the present invention, considering that the distribution characteristics of ion energy deviation at all measuring points at each monitoring moment during the modification process, such as the average level, can characterize the general state of ion energy deviation, and thus provide a certain comparative reference; and when the ion energy deviation at a certain measuring point deviates significantly from the general state, it indicates that the modification state at different measuring points differs greatly; then the method for obtaining the modification distribution difference parameter includes:

[0089] At each monitoring time, based on the distribution characteristics of ion energy deviations at all measuring points, an ion energy reference deviation is obtained. By combining the differences between the ion energy deviations at each measuring point and the ion energy reference deviations, the modification distribution difference parameters at the corresponding monitoring time are obtained.

[0090] Specifically, at each monitoring time, the mean of the ion energy deviations of all measuring points is used as the ion energy reference deviation; the difference is measured by the absolute value of the difference, the absolute value of the difference between the ion energy deviation of each measuring point and the ion energy reference deviation is calculated, and the absolute values ​​of the difference between the ion energy deviations of all measuring points and the ion energy reference deviation are accumulated, and the sum is used as the modification distribution difference parameter; the dimension of the modification distribution difference parameter is W.

[0091] Step S403: During the modification process, the operating power of the plasma processor is adjusted according to the modification distribution difference parameters at each monitoring time and the distribution characteristics of the ion energy deviation at the measuring point. The adjustment is iteratively adjusted until the preset modification termination condition is met.

[0092] At each monitoring moment during the modification process, a larger ion energy deviation indicates that the adsorption state of active ions by carbon nanotubes and halloysite nanotubes is far from saturated, and the operating power of the plasma processor can be appropriately increased. However, a larger modification distribution difference parameter indicates a larger difference in the modification state between different regions, requiring a higher operating power of the plasma processor. Based on this, the operating power of the plasma processor at the next monitoring moment can be adjusted according to the modification distribution difference parameter at each monitoring moment and the distribution characteristics of the ion energy deviation at the measuring point.

[0093] Preferably, in one embodiment of the present invention, considering that at each monitoring moment, the ion energy reference deviation (the average of the ion energy deviations at all measuring points) can characterize the overall modification state or ion adsorption state, and the modification distribution difference parameter can characterize the uniformity of the modification state; based on both, the modification state parameters can be comprehensively evaluated and the power adjustment direction can be determined so as to adjust the operating power of the plasma processor; based on this, adjusting the operating power of the plasma processor at the next monitoring moment includes:

[0094] At each monitoring moment, the modified state parameters are obtained based on the ion energy reference deviation and the difference parameter of the modified distribution, and the power adjustment direction weight is determined based on the modified state parameters;

[0095] By integrating the power adjustment direction weight and the modified state parameters, the power adjustment weight is obtained. The power adjustment value is obtained by weighting the preset power adjustment step size using the power adjustment weight.

[0096] The operating power at each monitoring time is added to the power adjustment value to obtain the operating power of the plasma processor at the next monitoring time. Specifically, if the operating power of the plasma processor at the next monitoring time is higher than the preset upper limit power, the operating power of the plasma processor is set to the preset upper limit power; if the operating power of the plasma processor at the next monitoring time is lower than the preset lower limit power, the operating power of the plasma processor is set to the preset lower limit power.

[0097] Specifically, at each monitoring time, the modified state parameters are first obtained based on the ion energy reference deviation and the difference parameter of the modified distribution.

[0098] In a preferred embodiment of the present invention, considering that the ratio between the ion energy reference deviation and the modification distribution difference parameter at each monitoring time can be used to measure the relative importance of the overall modification state (ion adsorption state) relative to the modification uniformity during the modification process; when the ion energy reference deviation is larger, it indicates that the ion adsorption state is still relatively strong, the possibility of modification ending is low, and it is necessary to focus on increasing the operating power and improving the modification efficiency; while when the modification distribution difference parameter is larger, it indicates that the modification state at different measuring points is seriously uneven, and it is necessary to focus on reducing the operating power and avoiding local over-processing; the method for obtaining the modification state parameter includes:

[0099] The ion energy reference deviation is used as the numerator, the sum of the modified distribution difference parameter and the preset minimum positive parameter is used as the denominator, and the ratio of the fractions is used as the modified state parameter. The preset minimum positive parameter is set to 0.001, which is a dimensionless parameter. The implementer can also adjust the value to avoid the denominator being zero. The modified state parameter is a dimensionless parameter.

[0100] In a preferred embodiment of the present invention, considering that the modification dominates the adjustment direction of the operating power, the method for determining the power adjustment direction weight includes: when the modification state parameter is greater than or equal to the preset equilibrium state threshold, the power adjustment direction weight is set to 1; when the modification state parameter is less than the preset equilibrium state threshold, the power adjustment direction weight is set to -1.

[0101] The preset equilibrium state threshold is set to 1, and the implementer can adjust it according to the actual situation. When the modification state parameter is greater than or equal to 1, it means that the modification is dominated by increasing the operating power and improving the modification efficiency, so the power adjustment direction weight is positive to increase. When the modification state parameter is less than 1, it means that the modification is dominated by reducing the operating power and avoiding local overprocessing, so the power adjustment direction weight is negative to decrease.

[0102] Then, the power adjustment direction weight is multiplied by the modification state parameter to obtain the power adjustment weight. The power adjustment direction weight provides a reference for the adjustment direction, and the modification state parameter provides a reference for the degree of adjustment. Then, the power adjustment weight is used to weight the preset power adjustment step size to obtain the power adjustment value. The preset power adjustment step size is set to 10W. The power adjustment weight is multiplied by the preset power adjustment step size to obtain the power adjustment value at the corresponding monitoring time during the modification process.

[0103] The operating power at each monitoring time is added to the power adjustment value to obtain the operating power of the plasma processor at the next monitoring time. Specifically, if the operating power of the plasma processor at the next monitoring time is higher than the preset upper limit power of 300W, the operating power of the plasma processor is set to the preset upper limit power of 300W; if the operating power of the plasma processor at the next monitoring time is lower than the preset lower limit power of 100W, the operating power of the plasma processor is set to the preset lower limit power of 100W.

[0104] During the modification process, the operating power of the plasma processor is iteratively adjusted at each monitoring time until the preset modification termination condition is met; when the preset modification termination condition is met, the modification process is stopped, and the modified carbon nanotubes and halloysite nanotubes are obtained.

[0105] When the plasma concentration parameters at all measuring points gradually return to stability, it can be indicated that the modification is nearing completion. In a preferred embodiment of the present invention, at each monitoring time, the ratio of the ion energy deviation of each measuring point to the preset density parameter is used as the modification termination parameter at the corresponding measuring point. The preset modification termination condition is that the modification termination parameters at all measuring points are less than the preset termination threshold at a consecutive preset number of monitoring times.

[0106] Specifically, the preset quantity is ≥10. In this embodiment, the preset quantity is set to 10, but the implementer can also adjust it. The preset termination threshold is ≤0.01. In this embodiment, the preset termination threshold is set to 0.01, but the implementer can also adjust it.

[0107] Step S5: The toughening agent, high-temperature stabilizer, dispersant and reinforcing toughening components are mixed in a preset ratio to obtain a high-temperature reinforced and toughened oil well cement admixture.

[0108] After obtaining the toughening agent, high-temperature stabilizer, dispersant and reinforcing and toughening components mentioned above, they can be further mixed to obtain high-temperature reinforced and toughened oil well cement admixtures.

[0109] To verify the effectiveness of the oil well cement additives prepared in this scheme, cement additives were obtained by different proportions.

[0110] In Example 1, the preset ratio was set to 60:30:8:2; for a cement admixture with a mass of 100 parts, 60 parts by weight of toughening agent, 30 parts by weight of high temperature stabilizer, 8 parts by weight of reinforcing and toughening component and 2 parts by weight of dispersant were selected and mixed. The mixture was ball-milled in a planetary ball mill for 4 hours to obtain the cement admixture.

[0111] In Example 2, the preset ratio was set to 65:25:7:3; for a cement admixture with a mass of 100 parts, 65 parts by weight of toughening agent, 25 parts by weight of high temperature stabilizer, 7 parts by weight of reinforcing and toughening component and 3 parts by weight of dispersant were selected and mixed. The mixture was ball-milled in a planetary ball mill for 4 hours to obtain the cement admixture.

[0112] In Example 3, the preset ratio was set to 70:20:9:1; for a cement admixture with a mass of 100 parts, 70 parts by weight of toughening agent, 20 parts by weight of high temperature stabilizer, 9 parts by weight of reinforcing and toughening component and 1 part by weight of dispersant were selected and mixed. The mixture was ball-milled in a planetary ball mill for 4 hours to obtain the cement admixture.

[0113] In Example 4, the preset ratio was set to 70:20:7:3; for a cement admixture with a mass of 100 parts, 70 parts by weight of toughening agent, 20 parts by weight of high temperature stabilizer, 7 parts by weight of reinforcing and toughening component and 3 parts by weight of dispersant were selected and mixed. The mixture was ball-milled in a planetary ball mill for 4 hours to obtain the cement admixture.

[0114] To verify the effectiveness of the prepared cement admixture, experimental and control groups were obtained by preparing slurry with oil well cement, with a water-to-solid ratio of 0.44.

[0115] The composition of the oil well cement slurry in the experimental group was: 100% Grade G oil well cement, 35% quartz sand, 10% cement admixture, 1% high-temperature fluid loss reducing agent and 0.3% high-temperature dispersant.

[0116] The composition of the oil well cement slurry in the control group (without cement admixtures) was: 100% Grade G oil well cement, 35% quartz sand, 1% high-temperature fluid loss reducing agent and 0.3% high-temperature dispersant.

[0117] It should be noted that the high-temperature fluid loss reducing agent is an AMPS-amide-carboxylic acid polymer fluid loss reducing agent for oil well cement, abbreviated as G33S; the high-temperature dispersant is a solid acetone-formaldehyde condensate dispersant for oil well cement, abbreviated as USZ.

[0118] The control group and the experimental groups corresponding to Examples 1-4 were tested for compressive strength and tensile strength of cement slurry prepared according to GB / T19139-2012 standard at a curing temperature of 200℃ for curing periods of 3d, 7d and 14d respectively. Uniaxial stress-strain curve tests were also performed on the cement stone samples cured for 7d.

[0119] Please refer to Table 1, which shows the test results of the mechanical properties of cement paste in an experimental group and a control group provided by an embodiment of the present invention.

[0120] Table 1. Test results of mechanical properties of cement paste in experimental and control groups.

[0121]

[0122] As shown in Table 1, the cement stone samples in the control group showed significant high-temperature strength degradation. In contrast, the experimental groups (Examples 1-4) with different preset proportions of cement admixtures showed improved compressive strength after the same curing period compared to the control group (without cement admixtures), both in terms of tensile and compressive strength. This significantly inhibited the strength degradation of oil well cement stone at high temperatures and demonstrated good high-temperature resistance.

[0123] Please see Figures 3-6 The figures show the uniaxial stress-strain curves of cement stone samples from experimental groups 1-4 after 7 days of curing, provided in one embodiment of the present invention; please refer to [link / reference]. Figure 7 It shows the uniaxial stress-strain curve test curve of a cement stone sample after 7 days of curing in a control group according to an embodiment of the present invention; as shown Figure 3-7 As shown, the peak stress and peak strain of the cement stone with oil well cement admixture in each experimental group were higher than those in the control group.

[0124] This invention also proposes a high-temperature reinforced and toughened oil well cement admixture, comprising the following components in parts by weight:

[0125] Toughening agent 60-70 parts; high temperature stabilizer 20-30 parts; reinforcing and toughening components 7-9 parts; dispersant 1-3 parts;

[0126] The toughening agent includes polyimide fibers, wollastonite fibers, and mullite whiskers with surface-grafted tricalcium silicate; the high-temperature stabilizer includes calcined shale powder and nano-alumina; the reinforcing and toughening components include hydrophilically modified carbon nanotubes and halloysite nanotubes; and the dispersant includes sodium dodecylbenzenesulfonate powder.

[0127] In summary, this invention prepares toughening agents based on surface-grafted tricalcium silicate polyimide fibers, wollastonite fibers, and mullite whiskers; prepares high-temperature stabilizers based on calcined shale powder and nano-alumina; prepares dispersants; modifies carbon nanotubes and halloysite nanotubes, and prepares reinforcing and toughening components. During the modification process, the operating power of the plasma processor is adjusted in real time until a preset modification termination condition is met; finally, the components are mixed in a preset ratio to obtain a high-temperature reinforced and toughened oil well cement admixture. The oil well cement admixture of this invention consists of toughening agents, high-temperature stabilizers, dispersants, and reinforcing and toughening components. The modification process is adjusted in real time to improve the modification effect. Through the synergistic effect of each cement admixture component, the high-temperature reinforcement and toughening effect of the oil well cement is improved.

[0128] It should be noted that the order of the above embodiments of the present invention is merely for descriptive purposes and does not represent the superiority or inferiority of the embodiments. The processes depicted in the accompanying drawings do not necessarily require a specific or sequential order to achieve the desired result. In some embodiments, multitasking and parallel processing are also possible or may be advantageous.

[0129] The various embodiments in this specification are described in a progressive manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

Claims

1. A method for preparing a high-temperature reinforced and toughened oil well cement admixture, characterized in that, The method includes: Toughening agents were prepared based on surface-grafted tricalcium silicate polyimide fibers, wollastonite fibers and mullite whiskers. High-temperature stabilizers prepared based on calcined shale powder and nano-alumina; Preparation of dispersants; Carbon nanotubes and halloysite nanotubes were modified to prepare reinforcing and toughening components; During the modification process, the operating power of the plasma processor and the plasma density parameters at each measuring point within it are obtained at each monitoring time. At each monitoring time, for each measuring point, the ion energy deviation is obtained based on the deviation of the plasma density parameters relative to the preset density parameters, and the modification distribution difference parameters are obtained based on the differences between the ion energy deviations at different measuring points. During the modification process, the operating power of the plasma processor is adjusted based on the modification distribution difference parameters at each monitoring time and the distribution characteristics of the ion energy deviations at the measuring points, and the adjustment is iteratively adjusted until the preset modification termination condition is met. The toughening agent, the high-temperature stabilizer, the dispersant, and the reinforcing and toughening components are mixed in a preset ratio to obtain a high-temperature reinforced and toughened oil well cement admixture.

2. The method for preparing a high-temperature reinforced and toughened oil well cement admixture according to claim 1, characterized in that, The method for obtaining the plasma density parameter includes: Langmuir probes are installed at each measurement point in the plasma processor, and the product of the probe current and probe voltage at each monitoring moment is used as the plasma density parameter at the corresponding measurement point.

3. The method for preparing a high-temperature reinforced and toughened oil well cement admixture according to claim 1, characterized in that, Methods for obtaining preset density parameters include: During the modification process, any monitoring time is taken as the target time, and the operating power at the target time is taken as the target operating power; during the no-load operation of the plasma processor, the plasma density parameter at any measuring point under the target operating power is taken as the preset density parameter at the target time.

4. The method for preparing a high-temperature reinforced and toughened oil well cement admixture according to claim 1, characterized in that, The dispersant comprises sodium dodecylbenzenesulfonate powder.

5. The method for preparing a high-temperature reinforced and toughened oil well cement admixture according to claim 1, characterized in that, The method for obtaining the modified distribution difference parameter includes: At each monitoring time, based on the distribution characteristics of the ion energy deviation at all measuring points, an ion energy reference deviation is obtained. By combining the differences between the ion energy deviation at each measuring point and the ion energy reference deviation, the modification distribution difference parameter at the corresponding monitoring time is obtained.

6. The method for preparing a high-temperature reinforced and toughened oil well cement admixture according to claim 5, characterized in that, Adjusting the operating power of the plasma processor includes: At each monitoring moment, the modified state parameters are obtained based on the ion energy reference deviation and the modified distribution difference parameter, and the power adjustment direction weight is determined based on the modified state parameters. By integrating the power adjustment direction weight and the modified state parameters, a power adjustment weight is obtained. The power adjustment weight is then used to weight a preset power adjustment step size to obtain a power adjustment value. The operating power at each monitoring time is added to the power adjustment value to obtain the operating power of the plasma processor at the next monitoring time; wherein, when the operating power of the plasma processor at the next monitoring time is higher than the preset upper limit power, the operating power of the plasma processor is set to the preset upper limit power; when the operating power of the plasma processor at the next monitoring time is lower than the preset lower limit power, the operating power of the plasma processor is set to the preset lower limit power.

7. The method for preparing a high-temperature reinforced and toughened oil well cement admixture according to claim 6, characterized in that, The method for obtaining the modified state parameters includes: The ion energy reference deviation is used as the numerator, the sum of the modified distribution difference parameter and the preset minimum positive parameter is used as the denominator, and the fractional ratio is used as the modified state parameter.

8. The method for preparing a high-temperature reinforced and toughened oil well cement admixture according to claim 6, characterized in that, The method for determining the power adjustment direction weight includes: When the modified state parameter is greater than or equal to the preset equilibrium state threshold, the power adjustment direction weight is set to 1; when the modified state parameter is less than the preset equilibrium state threshold, the power adjustment direction weight is set to -1.

9. The method for preparing a high-temperature reinforced and toughened oil well cement admixture according to claim 1, characterized in that, At each monitoring time, the ratio of the ion energy deviation of each measuring point to the preset density parameter is used as the modification termination parameter at the corresponding measuring point. The preset modification termination condition is that the modification termination parameter at all measuring points is less than the preset termination threshold at a consecutive preset number of monitoring times.

10. A high-temperature reinforced and toughened oil well cement admixture prepared according to any one of claims 1-9, characterized in that, The components include the following parts by weight: Toughening agent 60-70 parts; high temperature stabilizer 20-30 parts; reinforcing and toughening components 7-9 parts; dispersant 1-3 parts; The toughening agent includes polyimide fibers, wollastonite fibers, and mullite whiskers with surface-grafted tricalcium silicate; the high-temperature stabilizer includes calcined shale powder and nano-alumina; the reinforcing and toughening components include hydrophilically modified carbon nanotubes and halloysite nanotubes; and the dispersant includes sodium dodecylbenzenesulfonate powder.

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