Rigid film-forming type nano fluid loss agent as well as preparation method and application thereof

Abstract

The invention provides a rigid film-forming type nano fluid loss agent as well as a preparation method and application thereof, and belongs to the technical field of oil and gas well cementing cement admixtures. The preparation method comprises the following steps: uniformly mixing 2-acrylamido-2-methylpropanesulfonic acid, itaconic acid and allyl polyoxyethylene ether to obtain a solution A; dispersing the modified nano material in absolute ethyl alcohol to obtain a suspension B; and mixing the solution A and the suspension B, uniformly stirring, adding an initiator, carrying out constant-temperature reaction for 5-8 hours, and then washing, drying and crushing a reaction product to obtain the rigid film-forming type nano fluid loss agent. The fluid loss agent has good high-temperature stability, salt tolerance and fluid loss reduction performance, the compressive strength of set cement can be greatly improved, the set cement structure is compact, and the comprehensive performance of the set cement is remarkably improved. And the requirements of oil well cementing operation in different environments and at different temperatures can be met, and the safety of well cementing is remarkably improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of oil and gas well cement additives, and particularly relates to a rigid film-forming nano fluid loss reducer and its preparation method and application. Background Art

[0002] As the "blood of industry" in the world and the main energy and chemical raw material in the world today, petroleum has a history of more than a hundred years of use since the steam engine era, and its status is unshakable. With the depletion of shallow oil and gas resources, the development of petroleum is advancing towards deep and ultra-deep layers. Deep wells or ultra-deep wells have the characteristics of high temperature, high pressure, and high salinity, which bring problems such as high-temperature setting damage, serious instability, out-of-control filtration, and a decrease in cement strength to cement slurry cementing. These situations significantly increase the difficulty of cementing, and in severe cases, it may even lead to cementing failure.

[0003] Adding a fluid loss reducer to the cement slurry is an important measure to reduce out-of-control filtration, improve the space filling of cement voids, increase cement strength, and enhance the safety of cementing.

[0004] In the prior art, 2-acrylamido-2-methylpropanesulfonic acid (also known as AMPS) is a widely used raw material for fluid loss reducers. It has good water solubility and stability and is widely used in high-temperature and high-pressure wells.

[0005] However, the existing AMPS-based fluid loss reducers still have certain defects. For example, the patent with the publication number CN108690582A discloses a solid fluid loss reducer for oil well cement and its preparation method. AMPS, itaconic acid, and allyl polyethylene glycol monomers are dissolved in deionized water, and an initiator is added dropwise for reaction at 50-60°C, and then freeze-dried to obtain a solid fluid loss reducer. This fluid loss reducer has good salt tolerance, temperature resistance, and fluid loss reduction performance, but its application range is narrow, the fluid loss is too large, and the compressive strength is relatively low. Summary of the Invention

[0006] In view of this, the purpose of the embodiments of the present application is to provide a rigid film-forming nano fluid loss reducer and its preparation method and application to solve the problems of insufficient compressive strength, large fluid loss, and thus general fluid loss reduction performance of the fluid loss reducer in high-temperature and high-salt environments in the prior art. Moreover, the preparation method of the rigid film-forming nano fluid loss reducer provided by the embodiments of the present application is simple and easy to implement.

[0007] The embodiments of the present application are implemented as follows: The embodiments of the present application provide a rigid film-forming nano fluid loss reducer, including the structure shown in structural formula (1): Structural formula (1); In formula (1), the spherical nucleus connected to three oxygens is any one of the elements Si, Ti, Fe, and Al.

[0008] This application also provides a preparation method for the above-mentioned rigid film-forming nano-fluid loss reducer, including the following steps: S1. Take appropriate amounts of 2-acrylamido-2-methylpropanesulfonic acid, itaconic acid, and allyl polyoxyethylene ether and dissolve them in deionized water. Adjust the pH value to 5-7. After mixing evenly, obtain solution A; S2. Take appropriate amounts of modified nano-materials and disperse them in absolute ethanol to obtain suspension B; the modified nano-materials are any one of KH570@SiO2, KH570@TiO2, KH570@Fe2O3, and KH570@Al2O3.

[0009] S3. Mix solution A and suspension B, stir evenly, add an initiator, and react at a constant temperature of 65°C for 5-8 hours. Then wash, dry, and pulverize the reaction product to obtain a rigid film-forming nano-fluid loss reducer.

[0010] Furthermore, the preparation method of the modified nano-materials in step S2 includes the following steps: S21. Obtain nano-materials, and the nano-materials are any one of nano-silica, nano-titanium dioxide, nano-ferric oxide, and nano-aluminum oxide; S22. By mass, take 10 parts of nano-materials, fully dry them, place them in 100 parts of toluene solution, and disperse evenly; add 28 parts of γ-methacryloxypropyltrimethoxysilane to it and mix evenly. React at 80°C for 5 hours, and then separate and wash the reactants to obtain a wet product; S23. Dry and pulverize the wet product to obtain modified nano-materials.

[0011] Furthermore, the mass ratio of 2-acrylamido-2-methylpropanesulfonic acid to itaconic acid in step S1 is (5-7):(1-5), and the dosage of allyl polyoxyethylene ether is 8-10% of the total mass of the two monomers 2-acrylamido-2-methylpropanesulfonic acid and itaconic acid.

[0012] Furthermore, the dosage of the modified nano-materials is 1.5-3% of the total mass of the three monomers 2-acrylamido-2-methylpropanesulfonic acid, itaconic acid, and allyl polyoxyethylene ether.

[0013] Furthermore, the dosage of the initiator in step S3 is 0.9-1.3% of the total mass of the four monomers 2-acrylamido-2-methylpropanesulfonic acid, itaconic acid, allyl polyoxyethylene ether, and modified nano-materials.

[0014] Further, the initiator described in step S3 is a mixed solution of persulfate and sodium bisulfite, and the persulfate is one or more of potassium persulfate, sodium persulfate, and ammonium persulfate.

[0015] Further, the mass ratio of the persulfate to the sodium bisulfite is 1:1.

[0016] Based on the above steps, a rigid film-forming nano fluid loss reducer is obtained. The fluid loss reducer forms a bridge by attaching to the outer layer of cement particles based on molecular chains, constructs a network structure with a dense filter cake, and restricts the free flow of free fluid, thereby achieving the purpose of reducing fluid loss.

[0017] This application also provides the application of the rigid film-forming nano fluid loss reducer.

[0018] Further, the rigid film-forming nano fluid loss reducer is mixed with cement to prepare cement slurry and / or cement stone. The rigid film-forming nano fluid loss reducer fills into the cement voids, improves the structural strength of the cement, reduces fluid loss, and has good thermal stability and salt resistance. Using it in oil well cementing can effectively improve the safety of cementing.

[0019] Compared with the prior art, the beneficial effects of this application are as follows: 1. The rigid film-forming nano fluid loss reducer provided by this application has a molecular structure with modified inorganic nanoparticles as the core, endows the polymer with the thermal stability of the inorganic nanoparticles, and at the same time inhibits the desorption of the adsorption groups such as sulfonic acid groups and carboxylic acid groups on the surface of cement particles, ensuring the extension of the molecular weight and showing excellent high-temperature stability. At high temperatures, the structure does not deform, and problems such as coagulation failure, instability, and filtration out of control will not occur.

[0020] 2. The rigid film-forming nano fluid loss reducer provided by this application has polymer molecular chains connected around the inorganic nanoparticles to form a stable 3D network structure. The nanoparticles have a high specific surface area, providing a seeding surface for the hydration reaction, effectively promoting the hydration reaction through the seeding effect, generating calcium silicate hydrate (C−S−H), and making the cement stone structure more dense. At the same time, the composite materials in the cement pore solution can be more easily filled between cement particles during the hydration process to form a denser microstructure, significantly improving the compressive strength of the cement stone.

[0021] 3. The rigid film-forming nano-fluid loss reducer provided by this application has a preparation method based on the principle of free radical aqueous solution polymerization. The combined action of the dimethyl group and the sulfomethyl group in the AMPS structure sterically hinders the hydrolysis reaction of the non-ionic amide group, making the amide group less likely to hydrolyze at high temperatures and having strong thermal stability. The modified nano-materials have good dispersibility, which helps the fluid loss reducer to disperse into a rigid film in the cement voids, control the water loss of the cement slurry, and improve the compressive strength of the cement slurry. It makes the structure of the cement stone more dense and the mechanical properties better through an additional plugging / filling effect.

[0022] 4. The rigid film-forming nano-fluid loss reducer provided by this application can be used under the conditions of 90 - 180 °C, which can meet the requirements of well cementing in different regions and at different temperatures. The polymer / nano composite fluid loss reducer has excellent water loss reduction performance, temperature and salt resistance performance. The cement slurry has good fluidity, a smooth consistency curve and a short transition time, and there are no bulges or cores in the cement slurry. Brief Description of the Drawings

[0023] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the following will briefly introduce the drawings required to be used in the embodiments. Obviously, the drawings described below are only some embodiments of this application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0024] Figure 1 It is the synthesis route diagram of the rigid film-forming nano-fluid loss reducer prepared by the present invention; Figure 2 It is the comparative thermogravimetric analysis diagram of the fluid loss reducers prepared in Example 1 and Comparative Example 1 of the present invention, where Figure 2 (a) is the TGA curve diagram, Figure 2 (b) is the DSC curve diagram; Figure 3 It is the comparative thickening curve diagram of the cement slurries using the fluid loss reducers prepared in Example 1 and Comparative Example 1 of the present invention under the conditions of 120 °C and 60 MPa; Figure 4 It is the comparative thickening curve diagram of the cement slurries using the fluid loss reducers prepared in Example 1 and Comparative Example 1 of the present invention under the conditions of 180 °C and 80 MPa; Figure 5 (a) is the SEM characterization diagram of the cement stone using the fluid loss reducer prepared in Comparative Example 1 of the present invention, Figure 5 (b) is the SEM characterization diagram of the cement stone using the fluid loss reducer prepared in Example 1 of the present invention; Figure 6 (a) is the transmission electron microscope image of the commercially available nano-silica; Figure 6(b) Transmission electron micrograph of modified KH570@SiO2 of this application; Figure 7 It is the molecular morphology diagram of the rigid film-forming nano-fluid loss reducer AIAN prepared in Example 1 of this application. Specific implementation manners

[0025] To make the objectives, technical solutions and advantages of this application clearer, the following examples are used to further elaborate on this application in detail. The illustrative implementation manners and descriptions of this application are only for explaining this application and do not serve as a limitation to this application. Any product identical or similar to this application obtained by anyone under the inspiration of this application or by combining the features of this application with those of other existing technologies falls within the protection scope of this application.

[0026] For the specific experimental steps or conditions not specified in the examples, the operations or conditions of the conventional experimental steps described in the existing technologies in this field can be followed. The reagents and other instruments not indicating the manufacturer can be conventional reagent products obtained through commercial purchase. In addition, the drawings are only schematic diagrams of the embodiments of this application and are not necessarily drawn to scale. The same reference numerals in the drawings represent the same or similar parts, so the repeated descriptions thereof will be omitted. Some of the block diagrams shown in the drawings are functional entities and do not necessarily correspond to physically or logically independent entities.

[0027] This application provides a preparation method for a rigid film-forming nano-fluid loss reducer, which specifically includes the following steps: S1. Prepare solution A: By mass, take 50-70 parts of 2-acrylamido-2-methylpropanesulfonic acid (abbreviated as AMPS), 10-50 parts of itaconic acid, and an appropriate amount of allyl polyoxyethylene ether (abbreviated as APEG). The mass of APEG is preferably 8-10% of the total mass of the two monomers AMPS and itaconic acid; dissolve the three monomers in an appropriate amount of deionized water; add an alkali solution to adjust the pH value to 5-7, and then stir well to mix evenly to obtain solution A.

[0028] The alkali solution used is preferably a 20% sodium hydroxide solution by mass fraction, and the stirring time is preferably more than 20 minutes.

[0029] S2. Preparation of modified nanomaterials: Nano silicon dioxide, nano titanium dioxide, nano iron trioxide, and nano aluminum trioxide are purchased from the market. Any one of them is selected and fully dried first. The drying condition is preferably dried at 80°C for 24 hours, cooled to room temperature after drying, and sealed to avoid moisture. Then, according to the mass parts, 10 parts of nanomaterials are weighed and placed in 100 parts of toluene solution and fully dispersed, preferably ultrasonically dispersed for more than 30 minutes to obtain a uniform suspension; 28 parts of γ-methacryloxypropyltrimethoxysilane are added to the suspension, and the dispersion is continued to make it fully uniform, preferably ultrasonically mixed for more than 5 minutes. Then react at 80°C, and the reaction process is specifically condensation reflux and magnetic stirring for 5 hours. After the reaction is completed, the reactants are centrifuged and washed clean, preferably with ethanol, to obtain a wet product; the wet product is fully dried, preferably dried at 60°C; ground and crushed to obtain a finished modified nanomaterial. Nano-silicon dioxide, nano-titanium dioxide, nano-ferric oxide and nano-aluminum oxide were all modified, and the products obtained after modification were recorded as KH570@SiO2, KH570@TiO2, KH570@Fe2O3 and KH570@Al2O3, respectively.

[0030] Since nanomaterials such as nano-silicon dioxide have active hydroxyl groups on their surfaces, they have high free energy and are prone to agglomeration. Figure 6 As shown in (a), when the nanomaterial is not modified, it can be seen from the scanning electron microscope that the molecules have aggregated and are distributed in blocks or clusters. The nanomaterial is modified using γ-methacryloxypropyltrimethoxysilane. After hydrolysis, the silane oxygen end group of γ-methacryloxypropyltrimethoxysilane can react with the active silanol group on the surface of the nanomaterial, thereby connecting with the nanomaterial. The organic functional group at the other end is evenly distributed, resulting in a large steric hindrance, thereby preventing and reducing the aggregation of the nanomaterial. The other end can also establish a bridge with the polymer matrix to improve the compatibility of the nanomaterial with the organic medium, thereby effectively and evenly connecting the inorganic powder and the polymer matrix, with stronger dispersibility and better interface bonding. Please refer to Figure 6 As shown in (b), the modified KH570@SiO2 particles are evenly distributed and present a chain or network structure, and no obvious agglomeration phenomenon is found.

[0031] S3. Preparation of suspension B: Select any one of the modified nanomaterials KH570@SiO2, KH570@TiO2, KH570@Fe2O3, KH570@Al2O3, and its dosage is preferably 1.5 - 3% of the total mass of the three monomers AMPS, itaconic acid, and APEG; then disperse the modified nanomaterial thoroughly in anhydrous ethanol to obtain suspension B. The time for dispersing the modified nanomaterial in anhydrous ethanol is preferably more than 30 minutes.

[0032] Verified by the applicant, KH570@SiO2, KH570@TiO2, KH570@Fe2O3, and KH570@Al2O3 can all play a good promoting role in the performance of the fluid loss reducer, making the prepared fluid loss reducer have good thermal stability, fluid loss reduction performance, and promoting the cement to have good structural strength, all of which can achieve the purpose of this application. Among the four modified nanomaterials, KH570@SiO2 is more preferably selected because the main component of cement is silicate, and nano-silica is homogeneous with cement, having a better pozzolanic effect, and can quickly react with C-H to be converted into calcium silicate hydrate C-S-H with a large specific surface area and strong cementing force.

[0033] S4. Under a nitrogen atmosphere, put solution A and suspension B into a reaction vessel and mix them evenly, stir for more than 20 minutes to obtain a reaction system. The reaction system is refluxed in a constant temperature environment of 65°C, and nitrogen is continuously purged for 30 minutes. Then add the initiator and carry out a constant temperature reaction for 5 - 8 hours.

[0034] Introducing nitrogen into the reaction vessel can remove residual gases such as oxygen in the vessel and avoid interference of gases such as oxygen with the monomer polymerization reaction; continuously introduce nitrogen until the reaction vessel is sealed to ensure that no new gases such as oxygen will mix in during the reaction process. Specifically, continuously introduce nitrogen into the reaction vessel until the initiator is added, and after adding the initiator, the reaction vessel is sealed, then the introduction of nitrogen can be stopped. Whether nitrogen remains in the reaction vessel has no impact on the reaction. Helium, argon, or other inert gases can also be introduced to expel oxygen, and this application does not make any restrictions.

[0035] The initiator is persulfate, specifically one or more of potassium persulfate, sodium persulfate, and ammonium persulfate. More preferably, the initiator is a mixed solution of persulfate and sodium bisulfite, and the mass ratio of persulfate to sodium bisulfite is 1:1. The dosage of the initiator is preferably 0.9 - 1.3% of the total mass of the four monomers (AMPS, itaconic acid, APEG, and the modified nanomaterial).

[0036] S5. Wash the reaction product thoroughly, preferably use anhydrous ethanol to wash the reaction product to obtain a white colloidal substance. After drying and grinding the white colloidal substance, the finished rigid film-forming nano-fluid loss reducer can be obtained.

[0037] The rigid film-forming nano-fluid loss reducer obtained through the above steps is obtained by reacting modified nano-materials with other monomers and participating in the monomer polymerization process. Please refer to Figure 1 As shown, the molecular chains in the product are interconnected to form a stable 3D network structure. The morphological structure of the product is as shown in formula (1): Formula (1) is: ; In formula (1), the spherical nucleus connected by three oxygens, that is, the modified nano-material nucleus, in other words, it is the element itself of the modified nano-material. For example, when the used modified nano-materials are KH570@SiO2, KH570@TiO2, KH570@Fe2O3, KH570@Al2O3 respectively, the spherical nuclei are silicon element, titanium element, iron element, and aluminum element respectively.

[0038] Formula (1) only shows the molecular structure of the product. The molecular configuration of the product is embodied as a 3D network structure, as shown in formula (2): Formula (2); In formula (2), is the modified nano-material. The sphere in the formula is the modified nano-material nucleus. The nucleus here is not restricted by elements, and the nuclei of different modified nano-materials are different elements. For example, the nuclei of KH570@SiO2, KH570@TiO2, KH570@Fe2O3, KH570@Al2O3 are silicon, titanium, iron, and aluminum respectively. The six branches connected outside the nucleus are γ-methacryloxypropyltrimethoxysilane.

[0039] In formula (2), the blue broken line represents the polymer molecular chain, and the polymer molecular chain has the following structure: .

[0040] Specifically, please refer to Figure 7 As shown, the product (rigid film-forming nano-fluid loss reducer) uses the modified nano-material as the nucleus, and the polymer molecular chains are evenly connected to the nano-material core, forming a stable 3D network structure; Figure 7 The blue chain-like structure in is γ-methacryloxypropyltrimethoxysilane, and the red chain-like structure connected to its outer end is the polymer molecular chain. Moreover, the inorganic nano-particles themselves have the characteristic of high thermal stability. This application endows the fluid loss reducer with the thermal stability of the inorganic nano-particles. The dual effects of the stable 3D structure and the inorganic particles make the fluid loss reducer show excellent thermal stability. And the nano-material core can inhibit the desorption of sulfonic acid groups and carboxylic acid groups on the surface of cement particles, ensuring the extension of the polymer molecular chain, thereby promoting the excellent high-temperature stability of the cement slurry after using this rigid film-forming nano-fluid loss reducer.

[0041] In addition, the present application uses spherical or ellipsoidal modified inorganic nanomaterials, which have a large specific surface area and provide a large number of seeding surfaces for the cement hydration reaction. Through the seed effect, the hydration reaction can be effectively promoted to proceed rapidly, and the calcium silicate hydrate (C-S-H) generated makes the cement stone structure more dense. At the same time, the spherical or ellipsoidal modified inorganic nanomaterials are small in size and have weak steric hindrance compared with nanomaterials such as carbon nanotubes, which strengthens the entanglement and connection effect of polymer chains, forming a structurally stable and relatively dense 3D network structure, making the fluid loss reducer molecules present in nanosize and being more likely to fill between cement particles during the hydration process, forming a dense microstructure, significantly improving the compressive strength of the cement stone, and the filling of cement voids makes the cement surface smoother and shows the characteristics of film formation macroscopically, also effectively increasing the fluid loss reduction property of the cement.

[0042] The present application also provides the application of the rigid film-forming nano-fluid loss reducer in the field of cement treatment. Specifically, taking the rigid film-forming nano-fluid loss reducer provided by the present application as an additive and adding it during the preparation of cement slurry can effectively improve the fluid loss reduction property, thermal stability, salt resistance, and structural stability of the cement slurry and the solidified solid cement (also known as: cement stone), accelerate the curing process of the cement slurry, improve the compressive strength of the cement, and comprehensively and all-roundly enhance various properties of the cement slurry or cement stone.

[0043] In order to enable those skilled in the art to understand the present invention more clearly, the rigid film-forming nano-fluid loss reducer described in the present application will be described in detail below through examples, comparative examples, and test examples.

[0044] Example 1: Raw materials were taken according to the mass ratio. 70 parts of AMPS, 10 parts of itaconic acid, and 8 parts of APEG were dissolved in an appropriate amount of deionized water, and the pH value was adjusted to 6 by adding 20wt% sodium hydroxide solution. Stir for 20 minutes under the condition of a rotation speed of 300r / min to obtain solution A.

[0045] 1.76 parts of KH570@SiO2 were dispersed in absolute ethanol and ultrasonically dispersed for 30 minutes to obtain suspension B.

[0046] Solution A and suspension B were placed in a three-necked flask and mixed under a nitrogen atmosphere, and stirred for 20 minutes under the condition of a rotation speed of 300r / min to obtain a reaction system. Under a nitrogen atmosphere, the reaction system was refluxed in a constant temperature water bath at 65°C for 30 minutes, 0.987 parts of an initiator composed of ammonium persulfate and sodium bisulfite were added, and then the reaction was kept at a constant temperature of 65°C for 5 hours. Then, the reaction product was washed, dried, ground and pulverized to obtain a rigid film-forming nano-fluid loss reducer, denoted as AIAN.

[0047] The dosages of the above-mentioned monomers and initiators have a certain proportional relationship. Specifically, the dosage of APEG is 10% of the total mass of AMPS and itaconic acid, the dosage of the nanomaterial is 2% of the total mass of AMPS, itaconic acid and APEG, and the dosage of the initiator is 1.1% of the total mass of AMPS, itaconic acid, APEG and the nanomaterial.

[0048] Example 2: Raw materials were taken according to the mass ratio. 60 parts of AMPS, 30 parts of itaconic acid and 7.2 parts of APEG were dissolved in an appropriate amount of deionized water, and a 20 wt% sodium hydroxide solution was added to adjust the pH value to 7. Stirring was carried out for 20 minutes at a rotation speed of 300 r / min to obtain solution A.

[0049] 1.458 parts of KH570@SiO2 were dispersed in absolute ethanol and ultrasonically dispersed for 30 minutes to obtain suspension B.

[0050] Solution A and suspension B were placed in a three-necked flask and mixed under a nitrogen atmosphere. Stirring was carried out for 20 minutes at a rotation speed of 300 r / min to obtain a reaction system. Under a nitrogen atmosphere, the reaction system was refluxed in a constant temperature water bath at 65 °C for 30 minutes, and 1.283 parts of an initiator composed of sodium persulfate and sodium bisulfite were added. Then, the reaction was kept at a constant temperature of 65 °C for 8 hours. Then, the reaction product was washed, dried, ground and pulverized to obtain a rigid film-forming nano fluid loss reducer, denoted as AIAN-2.

[0051] The dosages of the above-mentioned monomers and initiators have a certain proportional relationship. Specifically, the dosage of APEG is 8% of the total mass of AMPS and itaconic acid, the dosage of the nanomaterial is 1.5% of the total mass of AMPS, itaconic acid and APEG, and the dosage of the initiator is 1.3% of the total mass of AMPS, itaconic acid, APEG and the nanomaterial.

[0052] Example 3: Raw materials were taken according to the mass ratio. 50 parts of AMPS, 50 parts of itaconic acid and 10 parts of APEG were dissolved in an appropriate amount of deionized water, and a 20 wt% sodium hydroxide solution was added to adjust the pH value to 5. Stirring was carried out for 20 minutes at a rotation speed of 300 r / min to obtain solution A.

[0053] 3.3 parts of KH570@SiO2 were dispersed in absolute ethanol and ultrasonically dispersed for 30 minutes to obtain suspension B.

[0054] Solution A and suspension B were placed in a three-necked flask and mixed under a nitrogen atmosphere. The mixture was stirred at 300 r / min for 20 minutes to obtain a reaction system. Under a nitrogen atmosphere, the reaction system was refluxed in a constant-temperature water bath at 65 °C for 30 minutes, and an initiator composed of 1.020 parts of potassium persulfate and sodium bisulfite was added. Then, the reaction was maintained at a constant temperature of 65 °C for 5 hours. Subsequently, the reaction product was washed, dried, ground and pulverized to obtain a rigid film-forming nano-fluid loss reducer, denoted as AIAN-3.

[0055] The dosages of the above monomers and initiator have a certain proportional relationship. Specifically, the dosage of APEG is 10% of the total mass of AMPS and itaconic acid, the dosage of the nano-material is 3% of the total mass of AMPS, itaconic acid and APEG, and the dosage of the initiator is 0.9% of the total mass of AMPS, itaconic acid, APEG and the nano-material.

[0056] Example 4: Except for the different modified nano-materials used, the steps, selected raw materials and their dosages in this example are the same as those in Example 1. That is, the only difference between this example and Example 1 is that the modified nano-material used is modified nano-titanium dioxide, i.e., KH570@TiO2, to obtain a rigid film-forming nano-fluid loss reducer, denoted as AIAN-4.

[0057] Example 5: Except for the different modified nano-materials used, the steps, selected raw materials and their dosages in this example are the same as those in Example 1. That is, the only difference between this example and Example 1 is that the modified nano-material used is modified nano-ferric oxide, i.e., KH570@Fe2O3, to obtain a rigid film-forming nano-fluid loss reducer, denoted as AIAN-5.

[0058] Example 6: Except for the different modified nano-materials and initiators used, the steps, selected raw materials and their dosages in this example are the same as those in Example 1. That is, the two differences between this example and Example 1 are that the modified nano-material used is modified nano-aluminum oxide, i.e., KH570@Al2O3; the initiator used is a mixed solution of sodium persulfate, potassium persulfate and sodium bisulfite, with a total mass fraction of sodium persulfate and potassium persulfate being 0.4935 parts and the mass fraction of sodium bisulfite also being 0.4935 parts, and the mass ratio of persulfate to sodium bisulfite still being 1:1. A rigid film-forming nano-fluid loss reducer, denoted as AIAN-6, was obtained.

[0059] After being verified by multiple groups of experiments, the fluid loss reducers obtained in Example 1 and Examples 4 to 6 are not much different in terms of thermal stability, salt resistance performance, etc., and all achieve the purpose of this application; and while keeping other variables different, cement slurries and cement stones are respectively made using AIAN, AIAN-4, AIAN-5, and AIAN-6 to verify the structural strength of the cement stone, and the experimental results are basically the same, proving that the selected modified nanomaterials KH570@SiO2, KH570@TiO2, KH570@Fe2O3, and KH570@Al2O3 in this application can all achieve the preset purpose.

[0060] Comparative Example 1: In order to study the influence of modified nanomaterials on the performance of the fluid loss reducer, the applicant prepared a fluid loss reducer without modified nanomaterials according to the method of Example 1, as follows.

[0061] Take raw materials according to the mass ratio, dissolve 70 parts of AMPS, 10 parts of itaconic acid, and 8 parts of APEG in an appropriate amount of deionized water, add a 20wt% sodium hydroxide solution to adjust the pH value to 6, and stir for 20 minutes under the condition of a rotation speed of 300 r / min to obtain Solution A.

[0062] Place Solution A in a three-necked flask under a nitrogen atmosphere and stir for 20 minutes to obtain a reaction system. Reflux the reaction system in a constant temperature water bath at 65°C for 30 minutes, add 0.88 parts of initiator and keep the constant temperature reaction at 65°C for 5 hours, and then wash, dry, grind and crush the reaction product to obtain a rigid film-forming nanoscale fluid loss reducer, denoted as AIA.

[0063] The dosages of the above monomers and initiators have a certain proportional relationship. Specifically, the dosage of APEG is 10% of the total mass of AMPS and itaconic acid, and the dosage of the initiator is 1.1% of the total mass of AMPS, itaconic acid, and APEG. The difference between this comparative example and Example 1 is only that modified nanomaterials are not used in the synthesis process, and other monomers, synthesis steps, and parameters are the same as those in Example 1.

[0064] Comparative Example 2: Purchase the G33S fluid loss reducer commercially. This fluid loss reducer is a commonly used product in oilfields, the manufacturer is Weihui Chemical Co., Ltd., and the product property is a copolymer.

[0065] Next, performance tests and evaluations will be carried out on the three groups of fluid loss reducers obtained in Example 1, Comparative Example 1, and Comparative Example 2 through test examples. The evaluation methods and standards refer to the evaluation indicators in GB / T 19139-2012 "Test Methods for Oil Well Cement" and SY / T 5504.1-2013 "Evaluation Methods for Oil Well Cement Additives - Part 2: Fluid Loss Reducers" to test the water loss, compressive strength, and thickening curve of the cement slurry.

[0066] Test Example 1: The thermal stability of the fluid loss reducer was studied by thermogravimetric analysis and differential thermogravimetric analysis. Specifically, equal weights of AIAN and AIA were weighed and placed in a crucible respectively. The crucible was placed in a TGA / DSC3+ thermogravimetric analyzer, nitrogen was introduced, the heating rate was set at 20 °C / min, and the temperature range was set at 30 - 600 °C. The test results are as Figure 2 shown.

[0067] Specifically, Figure 2 Figure (a) shows the curve of the mass fraction of the fluid loss reducer varying with temperature (also known as the TGA curve). It can be seen from the figure that at about 350 °C, the mass fractions of both fluid loss reducers show a downward trend. The reason is that as the temperature rises, both samples undergo processes such as dehydration and decomposition, resulting in mass changes. When the temperature reaches 600 °C, the residual mass fraction of the AIA fluid loss reducer is 35%, while that of the AIAN fluid loss reducer is 51.5%. The higher residual mass fraction of AIAN than AIA proves that the AIAN fluid loss reducer has better temperature resistance than the AIA fluid loss reducer. Especially in a high-temperature environment (350 - 600 °C), the difference in their thermal stabilities is more obvious.

[0068] Figure 2 Figure (b) shows the curve of the heat change rate of the fluid loss reducer varying with temperature (also known as the DSC curve). It can be seen from the figure that the maximum thermal decomposition temperature of the AIAN fluid loss reducer is 373 °C, while that of the AIA fluid loss reducer is 335 °C. The AIAN fluid loss reducer has better thermal stability. Moreover, the DSC curve of the AIA sample has two endothermic peaks, which also indicates that the AIA fluid loss reducer has more thermal reactions, is more affected by temperature, and has worse thermal stability than the AIAN fluid loss reducer.

[0069] Test Example 2: The same mass of the three fluid loss reducers obtained in Example 1, Comparative Example 1, and Comparative Example 2 was taken respectively, and equal amounts of the same other components were used to prepare cement slurries to investigate the fluid loss reduction performance of the fluid loss reducers under different temperature and pressure conditions. The specific formula of the cement slurry is as follows: Sichuan Jiahua G-grade cement, 5% microsilica, 30% quartz sand, 3% fluid loss reducer, 2% retarder, 0.3% dispersant, 0.1% defoamer, and 44% water, and the water-cement ratio is 0.44.

[0070] Table 1 below records the API fluid loss of different fluid loss reducer cement slurries at different temperatures and salinities.

[0071] Table 1: Influence table of different temperatures and salinities on the API fluid loss of cement slurries

[0072] As can be seen from the table, the AIAN fluid loss reducer prepared in this application has a lower API fluid loss than the AIA fluid loss reducer without modified nanomaterials or the existing G33S fluid loss reducer under the same conditions of temperature, salinity, etc., and the effect is better than that of AIA and G33S. Moreover, in the environment of 90-180°C, the API fluid loss is below 50 mL, showing excellent fluid loss reduction effect. Even in the high-temperature environment of 180°C, the API fluid loss is only 42.4 mL, significantly better than the existing G33S fluid loss reducer (92.5 mL). And under the conditions of 90°C and semi-saturated brine (NaCl concentration 15%), the API fluid loss of AIAN is also lower than that of AIA and the existing G33S products, which also shows that the AIAN cement slurry has better salt resistance and is suitable for high-salt formations.

[0073] The above experimental data prove that the rigid film-forming nano fluid loss reducer provided in this application has good high-temperature resistance, and the temperature resistance can reach 180°C, which can meet the cementing technical requirements of high-temperature deep wells, and its salt resistance is also better than existing products, with excellent fluid loss reduction ability. After analysis by the applicant, the reason why the rigid film-forming nano fluid loss reducer provided in this application has good temperature resistance is that: a strong chemical bond is formed between the multi-polymer and the modified nano-silica, forming a composite material of the polymer and nano-silica particles; the micro-crosslinked structure is retained, the molecular form is stable, and there are few significant changes in the molecular structure or form; the 3D network structure and micro-crosslinked structure in the composite material make the influence of temperature on the molecular configuration, liquid viscosity and functional groups relatively small, so it shows excellent temperature resistance. The reason for better salt resistance is that: the 3D network structure in the composite material is stable, with a molecular space of stable form; the steric hindrance effect makes the polymer molecular chain remain in a stretched state in a high-salt environment, and the nano-silica has the advantages of high rigidity and good stability, improving the salt resistance of the AIAN cement slurry system.

[0074] Test Example 3: Take the same mass of the three fluid loss reducers obtained in Example 1, Comparative Example 1 and Comparative Example 2 respectively, and select the same amount of the same other components to make cement slurries. The formula of the cement slurries is the same as that in Test Example 2. The cement slurries are changed into solid cement stones, and in a 90°C environment, the three groups of cement stones are cured under the same conditions and time, and the compressive strength of the cement stones using different fluid loss reducers is investigated at different curing days.

[0075] The following records the compressive strength of different cement slurries. Specifically, the compressive strength of the cement stones measured on the 1st, 3rd and 7th days of curing is recorded respectively.

[0076] The three groups of hardened cement pastes show the same pattern, that is, the compressive strength shows an increasing trend with the curing time. The reason is that after the cement concrete is made, the initial strength is relatively low. As time goes by, the hydration process in the cement concrete gradually proceeds, and the strength gradually increases. In the first few days after pouring, the concrete strength increases rapidly, and then the growth rate gradually slows down until it reaches a relatively stable value.

[0077] The AIAN hardened cement paste has better compressive strength than the other two groups of products under the same curing days. Specifically, the compressive strength of the AIAN hardened cement paste after 1 day, 3 days, and 7 days of curing is increased by 31.2%, 42.8%, and 44.9% respectively compared with the AIA hardened cement paste, and is increased by 80.7%, 104.6%, and 107.3% respectively compared with the G33S hardened cement paste. This data directly proves that the rigid film-forming nano-fluid loss additive provided by this application has good mechanical properties. After research, the applicant believes that the reason is that: after the polymer molecules graft-modify the silica nanoparticles, it can promote the hydration process of cement and densify the microstructure of cement, thereby improving the mechanical properties of cement.

[0078] Test Example 4: In order to study the thickening situation of the cement slurries made of AIAN and AIA, the applicant set up two groups of thickening tests. Each group contains two portions of cement slurries. In the cement slurry formulations, except for the different types of fluid loss additives (AIAN and AIA respectively), other components and the dosages of all raw materials are the same.

[0079] Specifically, the cement slurry formulation of the first group is Jiahua G-class oil well cement, 2% fluid loss additive, 1.5% retarder, 35% silica fume, 5% microsilica, and 0.2% dispersant, with a water-cement ratio of 0.44; the test temperature is 120 °C and the pressure is 60 MPa. The cement slurry formulation of the second group is G-class oil well cement, 4% fluid loss additive, 1.5% retarder, 35% silica fume, 5% microsilica, and 0.3% dispersant, with a water-cement ratio of 0.44; the test temperature is 180 °C and the pressure is 80 MPa.

[0080] Figure 3 is the thickening curve graph of the first group of tests, Figure 4 is the thickening curve graph of the second group of tests. Figure 3 and Figure 4Among them, the black curve is the curve of temperature changing with time. Since the temperature peaks of 120°C / 180°C are set, the temperature uniformly rises from room temperature to 120°C or 180°C and then remains unchanged. In the figure, the black line shows a change of first a stable slope and then a horizontal straight line. The red curve is the curve of pressure changing with time. Similarly, since the pressure peaks of 60 MPa / 80 MPa are set, the pressure curve (red line) also shows a situation of stable increase first and then remaining unchanged. The thickening curves of the two groups of experiments also show the same regularity, that is, the consistency of AIAN is first lower than that of AIA, and then after reaching a certain time node, the consistency of AIAN rises rapidly, while the consistency of AIA rises rapidly after a later period of time.

[0081] Figure 3 Among them, the thickening time of AIAN is 263 minutes; Figure 4 Among them, the thickening time of AIAN is 178 minutes. The consistency curves of the AIAN products in both groups of times are relatively stable, and there are no abnormal gelling phenomena such as "core wrapping" and "bulging" at high temperatures. Moreover, the thickening transition time is relatively short, and the curve basically shows the characteristics of "right-angle" thickening. These information indicate that the cement slurry system added with AIAN fluid loss reducer has good high-temperature thickening ability. The thickening time of the cement slurry system added with AIA fluid loss reducer is relatively extended because the carboxyl groups in the polymer molecule combine with calcium aluminate in the cement slurry, delaying the cement hydration induction period, and the carboxyl groups combine with calcium ions, inhibiting the formation of CH crystals, resulting in a delay in the thickening time of the cement slurry. Due to the presence of nano-silica particles, the AIAN fluid loss reducer forms a stable 3D space, and the steric hindrance effect ensures the smooth progress of cement hydration.

[0082] Test Example 5: To further verify the fluid loss reduction effect of the fluid loss reducer, the AIAN cement stone and AIA cement stone cured for 7 days in Test Example 3 were respectively selected, and anhydrous ethanol was used for treatment and hydration termination according to the same steps and parameters; and after drying and gold spraying treatment according to the same steps and parameters, SEM was used to characterize the cement stone.

[0083] Figure 5These are SEM images of two hydrated cements. Among them, 5(a) is the SEM image of the hydrated cement prepared with the AIA fluid loss reducer, and 5(b) is the SEM image of the hydrated cement prepared with the AIAN fluid loss reducer. It can be directly seen from the figures that the structure of the AIAN hydrated cement is more compact, with fewer surface voids and a smoother surface; while the AIA hydrated cement has more surface voids and a relatively loose structure. It can be proved that AIA has a certain blocking effect on the voids of the cement, can increase the density of the hydrated cement to a certain extent, but the plugging effect is average, and the free water in the cement slurry can seep out from the cracks or void channels. The plugging effect of AIAN is better. After using the AIAN fluid loss reducer, the cracks or voids of the hydrated cement are covered by the copolymer and nano-silica composite material, resulting in very few pores and a compact structure, which proves that AIAN can effectively optimize the microstructure of the cement.

[0084] The above are only the preferred embodiments of the present application and are not intended to limit the present application. For those skilled in the art, various changes and modifications can be made to the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A rigid film-forming nano-fluid loss additive, characterized in that, It includes the structure shown in Structural Formula (1): Structural formula (1); In Structural Formula (1), the spherical nucleus connected to three oxygens is any one of the elements Si, Ti, Fe, and Al.

2. The preparation method of the rigid film-forming nano fluid loss reducer according to claim 1, characterized in that, It includes the following steps: S1. Take appropriate amounts of 2-acrylamido-2-methylpropanesulfonic acid, itaconic acid, and allyl polyoxyethylene ether and dissolve them in deionized water. Adjust the pH value to 5-7. After mixing evenly, obtain Solution A; S2. Take an appropriate amount of modified nanomaterial and disperse it in absolute ethanol to obtain Suspension B; the modified nanomaterial is any one of KH570@SiO2, KH570@TiO2, KH570@Fe2O3, and KH570@Al2O3; S3. Mix Solution A and Suspension B, stir evenly, add an initiator, and react at a constant temperature of 65 °C for 5-8 hours. Then wash, dry, and pulverize the reaction product to obtain a rigid film-forming type nano-fluid loss reducer.

3. The preparation method of the rigid film-forming nano-fluid loss reducer according to claim 2, characterized in that, The preparation method of the modified nanomaterial described in Step S2 includes the following steps: S21. Obtain a nanomaterial, and the nanomaterial is any one of nano-silica, nano-titanium dioxide, nano-ferric oxide, and nano-aluminum oxide; S22. By mass, take 10 parts of the nanomaterial, place it in 100 parts of toluene solution after sufficient drying, and disperse evenly; add 28 parts of γ-methacryloxypropyltrimethoxysilane thereto and mix evenly. React at 80 °C for 5 hours, and then separate and wash the reactants to obtain a wet product; S23. Dry and pulverize the wet product to obtain a modified nanomaterial.

4. The preparation method of the rigid film-forming nano-fluid loss additive according to claim 2, characterized in that, In Step S1, the mass ratio of 2-acrylamido-2-methylpropanesulfonic acid to itaconic acid is (5-7):(1-5), and the dosage of allyl polyoxyethylene ether is 8-10% of the total mass of the two monomers 2-acrylamido-2-methylpropanesulfonic acid and itaconic acid.

5. The preparation method of the rigid film-forming nano fluid loss reducer according to claim 2, characterized in that, The dosage of the modified nanomaterial is 1.5-3% of the total mass of the three monomers 2-acrylamido-2-methylpropanesulfonic acid, itaconic acid, and allyl polyoxyethylene ether.

6. The preparation method of the rigid film-forming nano-fluid loss additive according to claim 2, characterized in that, In Step S3, the dosage of the initiator is 0.9-1.3% of the total mass of the four monomers 2-acrylamido-2-methylpropanesulfonic acid, itaconic acid, allyl polyoxyethylene ether, and modified nanomaterial.

7. The preparation method of the rigid film-forming nano-fluid loss additive according to claim 2, wherein, In Step S3, the initiator is a mixed solution of persulfate and sodium bisulfite, and the persulfate is one or more of potassium persulfate, sodium persulfate, and ammonium persulfate.

8. The preparation method of the rigid film-forming nano fluid loss reducer according to claim 7, characterized in that, The mass ratio of the persulfate to the sodium bisulfite is 1:

1.

9. Application of the rigid film-forming type nano-fluid loss reducer according to Claim 8.

10. Use of the rigid film-forming nano-fluid loss reducer according to claim 9, characterized in that, Mix the rigid film-forming type nano-fluid loss reducer with cement to make cement slurry and / or cement stone.

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