An ultra-high temperature resistant spacer fluid system, a preparation method and application thereof

Abstract

The present application relates to a kind of superhigh temperature resistant spacer fluid system and its preparation method and application, belong to oil and gas well cementing spacer fluid technical field.The spacer fluid system includes by weight parts: modified bentonite 10~20 parts, suspension stabilizer 5~10 parts, composite anti-pollution agent 8~15 parts, surfactant 3~6 parts, dispersing agent 1~3 parts, high temperature antioxidant 3~5 parts, weighting agent 60~300 parts, high temperature resistant base fluid 80~160 parts.Suspension stabilizer is self-made high temperature resistant hydrophobic association polymer, composite anti-pollution agent is chelating compound, high temperature resistant base fluid is organic silicon modified polyether polyol and water mixture.The system is stable rheological and suspension performance by the synergistic effect of each component at 240 DEG C, 2 h up and down density difference is less than 0.05 g / cm3, flushing efficiency after pollution is higher than 84%, and cement slurry, drilling fluid compatibility is excellent, can significantly improve the thickening characteristics of mixed slurry, meet the superhigh temperature high pressure cementing operation requirement.

Description

Technical Field

[0001] This invention relates to an ultra-high temperature resistant isolation fluid system, its preparation method and application, belonging to the field of oil and gas well cementing isolation fluid technology, and is particularly suitable for cementing operations in high temperature and high pressure environments such as deep wells and ultra-deep wells. Background Technology

[0002] To improve drilling fluid performance and enhance drilling fluid technology and application, various treatment agents are added to the drilling fluid. These treatment agents are not only important components of the drilling fluid but also specifically improve its performance. However, some drilling fluids and drilling fluid treatment agents can cause serious pollution and induce safety accidents when in contact with cement slurry. Therefore, before injecting cement slurry, a separatory fluid is injected to replace the drilling fluid and improve the cement slurry replacement efficiency, preventing direct contact between the drilling fluid and cement slurry. The separatory fluid also flushes the filter cake and drilling fluid on the wellbore, improving interfacial wetting and thus enhancing interfacial bonding strength and improving cementing quality.

[0003] In the process of oil and gas extraction, cementing is a crucial step in ensuring wellbore stability and preventing wellbore contamination. Currently, the isolation fluid systems used in China have relatively simple functions and lack a comprehensive system. Especially with the extension of oil and gas exploration and development to deep and ultra-deep wells, traditional isolation fluids are prone to failure in high-temperature environments. On the one hand, they have poor suspension stability, which can lead to the sedimentation of solid particles, affecting the isolation effect and potentially causing poor cementing quality, such as loose cement sheath bonding and oil-gas-water channeling. On the other hand, their ability to remove contaminants from the wellbore is limited, which restricts their application in high-temperature and high-pollution environments. Therefore, developing a high-performance, ultra-high-temperature resistant isolation fluid system is of significant practical importance.

[0004] Existing technologies have disclosed various methods to solve the above problems; CN118027927A discloses an anti-fouling oil displacement and isolation fluid and its preparation method; the isolation fluid includes 100 parts by weight of water, 2-3 parts of suspension stabilizer, 15-30 parts of flushing agent, 1-5 parts of anti-fouling agent, 0.2-0.6 parts of primary defoamer and 60-300 parts of weighting agent; the anti-fouling oil displacement and isolation fluid has good compatibility with oil-based drilling fluid and cement slurry, good suspension stability, and good flushing effect on common wall mud cake, high cementing displacement efficiency, and an application temperature of 150℃.

[0005] CN104449606A discloses a high-temperature resistant cementing separator fluid and its manufacturing method. The separator fluid is composed of 100 parts by weight of fresh water, 2-8 parts by weight of suspending agent, 2-10 parts by weight of diluent, 25-400 parts by weight of weighting agent, and 1-15 parts by weight of flushing agent. The separator fluid system is compatible with traditional cement slurry and drilling fluid systems and has good suspension stability and rheological properties. However, this separator fluid only exhibits stable performance at a temperature of 180°C, but its temperature tolerance is insufficient in ultra-high temperature environments.

[0006] CN119286482A discloses a high-temperature resistant cleaning-type isolation fluid; the isolation fluid comprises the following components by weight: 0.2-3 parts of a mixture of xanthan gum and modified sizing agent, 2-15 parts of high-efficiency cleaning agent, 0.5-5 parts of anti-fouling agent, 0.2-3 parts of dispersant, 0.1-0.5 parts of defoamer, 0.5-5 parts of ultrafine powder, 30-80 parts of weighting agent, and 25-90 parts of water; the isolation fluid of the present invention has good compatibility with cement slurry and drilling fluid and has a good flushing effect, but its temperature resistance can only reach 220℃.

[0007] While existing high-temperature isolation fluid systems possess excellent rheological and stability properties and can improve displacement efficiency, their temperature resistance is limited and cannot meet the requirements of complex deep wells, ultra-deep wells, and ultra-high temperature cementing technologies. Therefore, there is an urgent need to develop a cementing isolation fluid system that can withstand temperatures up to 240℃. Summary of the Invention

[0008] The purpose of this invention is to provide an ultra-high temperature resistant isolation fluid system, its preparation method, and its application. This system, through a specific formulation design, can not only withstand working conditions under high temperatures but also effectively remove contaminants from the wellbore, thereby improving the efficiency and quality of cementing operations. Specifically, the isolation fluid system contains a specific proportion of high-temperature suspension stabilizers, anti-fouling agents, and surfactants. These components work synergistically to ensure that the isolation fluid maintains good performance in high-temperature and high-pressure downhole environments. Through a series of laboratory tests and field applications, it has been demonstrated that this isolation fluid system has significant effects on improving cementing displacement efficiency and cementing quality, providing a new solution for cementing operations in deep and ultra-deep wells.

[0009] To achieve the above objectives, the present invention provides the following technical solutions.

[0010] The present invention provides an ultra-high temperature resistant insulating liquid system, which, by weight, comprises the following components:

[0011] 10-20 parts modified bentonite, 5-10 parts suspension stabilizer, 8-15 parts composite antifouling agent, 3-6 parts surfactant, 1-3 parts dispersant, 3-5 parts high-temperature antioxidant, 60-300 parts weighting agent, and 80-160 parts high-temperature resistant base liquid;

[0012] The modified bentonite is obtained by modifying bentonite with a silane coupling agent. The specific preparation method is as follows: the bentonite is dried at 90°C for 2.5 hours, then mixed with the silane coupling agent at a weight ratio of 12:1, and reacted at high speed with stirring at 900 rpm for 1.5 hours. After the reaction is completed, it is cooled to room temperature for later use. The modified bentonite has better high temperature resistance and colloidal stability, can effectively suspend particles in high temperature environments to prevent sedimentation, and enhances the adsorption with the well wall to improve the isolation effect.

[0013] The suspension stabilizer is a high-temperature resistant hydrophobic associative polymer, and its specific preparation method is as follows:

[0014] S1. Using four monomers—2-acrylamido-dimethylpropanesulfonic acid (AMPS), N,N-dimethylacrylamide (DMAA), N-vinylpyrrolidone (NVP), and a laboratory-prepared hydrophobic functional monomer—as raw materials, a suspension stabilizer is prepared by copolymerization under the action of an initiator; specifically, it includes the following four sub-steps:

[0015] S11. Synthesis of hydrophobic functional monomer: N-(3-dimethylaminopropyl)methacrylamide (10.2 g, 0.06 mol), hexadecane bromide (24.4 g, 0.08 mol), and 80 mL of isopropanol were added to a three-necked flask, and nitrogen gas was added for protection. The mixture was then heated in an oil bath to 50 °C and refluxed for 24 hours. The resulting liquid was then rotary evaporated to obtain a pale yellow liquid. Finally, the liquid was washed three times with anhydrous diethyl ether to obtain a white precipitate. The precipitate was then dried under vacuum at room temperature to obtain the hydrophobic functional monomer.

[0016] S12. Dissolve 2-acrylamido-dimethylpropanesulfonic acid, N,N-dimethylacrylamide, N-vinylpyrrolidone and hydrophobic functional monomers in water in a molar ratio of 1:2:0.5:0.25, and adjust the pH of the solution to 7.

[0017] S13. Add the solution obtained in step S12 dropwise into a three-necked flask, purge with nitrogen to remove oxygen, and raise the temperature to 65°C; add 0.1% of the total molar amount of the monomers of the composite initiator ammonium persulfate and sodium bisulfite (molar ratio of the two is 1:1), stir and continue to react for 4 hours.

[0018] S14. After the reaction is complete, the reaction product is washed several times with anhydrous ethanol and dried in a forced-air drying oven until constant weight is achieved. After pulverization, a white powdery material is obtained, which is the suspension stabilizer. The suspension stabilizer prepared by the above method can increase the viscosity of the isolation fluid, improve its suspension capacity and impurity carrying capacity, and ensure that impurities such as mud cake on the well wall can be effectively carried out of the wellbore during the flushing process.

[0019] The antifouling agent is a chelated composite antifouling agent, and its specific preparation method is as follows:

[0020] S21. Dissolve sodium hexametaphosphate (SHMP) in deionized water (concentration 20%), heat to 60°C and stir for 30 minutes to form a homogeneous solution;

[0021] S22. 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTCA) is reacted with ethanolamine (molar ratio 1:0.5) at 70°C for 1 hour to generate amination PBTCA, which enhances its chelating ability.

[0022] S23. Mix sodium hexametaphosphate solution with amination PBTCA at a mass ratio of 1:2, add 5% modified polyethyleneimine (crosslinked with epichlorohydrin), and react at pH=8-9 and 80℃ for 2 hours.

[0023] S24. The reaction solution is spray-dried to obtain a white powdery composite antifouling agent. The mechanism of action of the antifouling agent prepared by the above method is mainly as follows: Sodium hexametaphosphate can form a thin, insoluble film on the surface of cement particles, which acts as a barrier to the hydration of cement particles, thereby playing an antifouling role; Amination PBTCA chelates Ca in the cement slurry and drilling fluid contaminant mixture. 2+ Mg 2+ Fe 3+ Al 3+ High-valence metal ions inhibit calcium invasion and weaken Fe 3+ And Al 3+ The resulting cross-linking effect prevents the slurry consistency from increasing, improves the slurry flowability, and plays an anti-pollution role; modified PEI enhances the adsorption and dispersion ability of oil stains;

[0024] The surfactant is a compound of anionic and nonionic surfactants. Specifically, the anionic surfactant is sodium dodecylbenzene sulfonate (LAS), and the nonionic surfactants are dodecylphenol polyoxyethylene ether (OP-10) and fatty alcohol polyoxyethylene ether (JFC-6), with a weight ratio of 2:1:3. The compounded surfactants exhibit antagonistic and synergistic effects, playing a role in reducing interfacial tension, wetting reversal, emulsification and compatibilization, and penetration in the isolation liquid.

[0025] The dispersant is sodium tripolyphosphate, which can prevent the agglomeration of solid particles, so that various particles in the system are uniformly dispersed in the liquid phase, ensuring the stability and uniformity of the isolation liquid system, and improving its performance consistency and reliability.

[0026] The high-temperature antioxidant is a phosphite compound, specifically pentaerythritol diisodecyl diphosphite. Under high-temperature conditions, this antioxidant can capture free radicals generated in the isolation liquid system, inhibit oxidative degradation reactions, protect the chemical structure and performance stability of the isolation liquid, and prolong its effective action time at high temperatures.

[0027] The weighting agent is a high-density mineral powder, specifically 325-mesh barite powder, which has good chemical stability and particle size distribution, can effectively increase the density of the isolation liquid, and will not have a negative impact on other properties of the system.

[0028] The high-temperature resistant base liquid is a mixture of organosilicon-modified polyether polyol and water. The specific preparation method is as follows: 1000g of polypropylene glycol (hydroxyl value 56 mg KOH / g), 150g of γ-aminopropyltriethoxysilane (molar ratio to polyether polyol approximately 0.3:1), and 3g of potassium hydroxide catalyst are selected. The polypropylene glycol is added to a reaction vessel, heated to 90℃, and dehydrated under a vacuum of -0.09 MPa for 1.5 hours. The temperature is then lowered to 70℃, γ-aminopropyltriethoxysilane is added, and after stirring evenly, potassium hydroxide is added. The reaction is carried out at this temperature for 2 hours to obtain organosilicon-modified polyether polyol product A. Product A is mixed with water at a weight ratio of 1:2 to obtain the high-temperature resistant base liquid. This organosilicon-modified polyether polyol exhibits excellent high-temperature resistance, maintaining good chemical stability and rheological properties at high temperatures, providing a stable foundation for the entire isolation liquid system.

[0029] The preparation method of the high-temperature resistant and anti-fouling flushing and isolation fluid system of the present invention includes the following steps:

[0030] Organosilicon-modified polyether polyol and water are mixed in a predetermined ratio and stirred at a stirring speed of 500-1000 r / min for 20-30 minutes to ensure thorough and uniform mixing, thereby obtaining a high-temperature resistant base liquid.

[0031] Slowly add the modified bentonite to the high-temperature resistant base liquid and stir for 20 to 40 minutes to fully dissolve and disperse it. Then add the suspension stabilizer and continue stirring for 10 to 30 minutes to form a uniform suspension solution.

[0032] Antifouling agent, high-temperature antioxidant and surfactant are added to the suspension solution in sequence. After each additive is added, continue stirring for 15 to 20 minutes to ensure that the additives are fully mixed and have a synergistic effect, thereby adjusting the performance of the isolation liquid.

[0033] Finally, slowly add the weighting agent while increasing the stirring speed to 1000-2000 r / min and stirring for 10-30 minutes to ensure that the weighting agent is evenly dispersed in the system, resulting in a high-temperature resistant and anti-fouling flushing and isolation fluid system with uniform density and stable performance.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] The isolation fluid system of the present invention has excellent high temperature resistance and can maintain stable rheological properties and suspension stability in high temperature environments. It effectively solves the problem of performance degradation of existing isolation fluids under high temperature conditions and ensures reliable application in high temperature oil well exploitation operations such as deep wells and ultra-deep wells.

[0036] The unique anti-fouling agent compound design can effectively resist the interference of various contaminants such as crude oil, minerals, and rock cuttings, maintain good flushing and isolation effects, and reduce the risk of oil well mining accidents and increased operating costs caused by pollution;

[0037] Based on the relationship between molecular structure and temperature resistance, a novel hydrophobic associative suspension stabilizer was synthesized, which enhanced the temperature resistance of the suspension stabilizer. The synergistic effect with modified bentonite further improved the stability and carrying capacity of the system, enabling it to better suspend and carry solid particles, prevent them from depositing on the well wall and tubing, and ensure the cleanliness and smooth flow of the oil well.

[0038] This invention provides a high-performance, cost-effective isolation fluid system solution for the oilfield development industry. Attached Figure Description

[0039] Figure 1 The thickening curve of the cement slurry in Example 2 of this invention under the conditions of 240℃×120MPa is shown.

[0040] Figure 2 This is a thickening curve of cement slurry and drilling fluid at a volume ratio of 7:3 under conditions of 240℃ × 120MPa in Example 2 of the present invention.

[0041] Figure 3 This is a thickening curve of cement slurry and release liquid at a volume ratio of 7:3 under conditions of 240℃ × 120MPa in Example 2 of the present invention.

[0042] Figure 4 This is a thickening curve of cement slurry, drilling fluid, and isolation fluid in a volume ratio of 7:2:1 under conditions of 240℃ × 120MPa in Example 2 of the present invention. Detailed Implementation

[0043] The following specific embodiments further illustrate the high-temperature resistant and anti-fouling flushing and isolation fluid system and its preparation method of the present invention, but the present invention is not limited to the following embodiments.

[0044] Example 1: Weigh out 15 parts of modified bentonite, 8 parts of suspension stabilizer, 12 parts of antifouling agent, 5 parts of surfactant, 2 parts of dispersant, 3 parts of high-temperature antioxidant, 70 parts of weighting agent, and 90 parts of high-temperature resistant base liquid.

[0045] The preparation of modified bentonite involves drying bentonite at 90°C for 2.5 hours, then mixing it with a silane coupling agent at a weight ratio of 12:1, reacting it under high-speed stirring (900 rpm) for 1.5 hours, and then cooling it to room temperature.

[0046] Preparation of the suspension stabilizer: N-(3-dimethylaminopropyl)methacrylamide (10.2 g, 0.06 mol), hexadecane bromide (24.4 g, 0.08 mol), and 80 mL of isopropanol were added to a three-necked flask, and then nitrogen gas was added for protection. Next, the oil bath was heated to 50 °C and refluxed for 24 hours, followed by rotary evaporation to obtain a pale yellow liquid. Finally, the mixture was washed three times with anhydrous diethyl ether to obtain a white precipitate. Finally, the precipitate was dried under vacuum at room temperature to obtain a hydrophobic functional monomer. 2-Acrylamido-dimethylpropanesulfonic acid, ... N,N-dimethylacrylamide, N-vinylpyrrolidone, and hydrophobic functional monomers were dissolved in water, and the pH of the solution was adjusted to 7 to obtain solution A. Solution A was added dropwise to a three-necked flask, nitrogen gas was introduced to remove oxygen, and the temperature was raised to 65°C. Ammonium persulfate and sodium bisulfite (molar ratio of 1:1) were added as initiators, accounting for 0.1% of the total molar amount of monomers, and the mixture was stirred and reacted for another 4 hours. After the reaction was completed, the mixture was purified several times with anhydrous ethanol, dried to constant weight in a forced-air drying oven, and then pulverized to obtain a suspension stabilizer.

[0047] The preparation method of the above-mentioned high-temperature resistant and anti-fouling flushing and isolation fluid system includes the following steps:

[0048] 30 parts of organosilicon-modified polyether polyol and 60 parts of water were stirred at a stirring speed of 600 r / min for 20 minutes to ensure thorough mixing and obtain a high-temperature resistant base liquid.

[0049] Slowly add 15 parts of modified bentonite to the high-temperature resistant base liquid and stir for 25 minutes to fully dissolve and disperse it. Then add 8 parts of suspension stabilizer and continue stirring for 15 minutes to form a uniform suspension solution.

[0050] Add 12 parts of antifouling agent, 3 parts of high-temperature antioxidant and 5 parts of surfactant to the suspension solution in sequence. After each additive is added, continue stirring for 15 minutes to ensure that the additives are fully mixed and have a synergistic effect, thereby adjusting the performance of the isolation liquid.

[0051] Finally, slowly add 70 parts of weighting agent while increasing the stirring speed to 1000 r / min and stirring for 15 minutes to ensure that the weighting agent is evenly dispersed in the system, resulting in a high-temperature resistant and anti-fouling flushing and isolation fluid system with uniform density and stable performance.

[0052] Example 2: Weigh 18 parts of modified bentonite, 6 parts of suspension stabilizer, 10 parts of antifouling agent, 4 parts of surfactant, 1.5 parts of dispersant, 4 parts of high-temperature antioxidant, 150 parts of weighting agent, and 120 parts of high-temperature resistant base liquid; the preparation methods of modified bentonite and suspension stabilizer are the same as in Example 1.

[0053] The preparation method of the above-mentioned high-temperature resistant and anti-fouling flushing and isolation fluid system includes the following steps:

[0054] 40 parts of organosilicon-modified polyether polyol and 80 parts of water were stirred at a stirring speed of 800 r / min for 25 minutes to ensure thorough mixing and obtain a high-temperature resistant base liquid.

[0055] 18 parts of modified bentonite were slowly added to the high-temperature resistant base liquid and stirred for 30 minutes to fully dissolve and disperse it. Then, 6 parts of suspension stabilizer were added and stirred for another 20 minutes to form a uniform suspension solution.

[0056] Add 10 parts of antifouling agent, 4 parts of high-temperature antioxidant and 4 parts of surfactant to the suspension solution in sequence. After each additive is added, continue stirring for 20 minutes to ensure that the additives are fully mixed and have a synergistic effect, thereby adjusting the performance of the isolation liquid.

[0057] Finally, slowly add 150 parts of weighting agent while increasing the stirring speed to 1500 r / min and stirring for 20 minutes to ensure that the weighting agent is evenly dispersed in the system, resulting in a high-temperature resistant and anti-fouling flushing and isolation fluid system with uniform density and stable performance.

[0058] Example 3: Weigh 12 parts of modified bentonite, 9 parts of suspension stabilizer, 14 parts of antifouling agent, 3.5 parts of surfactant, 2.5 parts of dispersant, 5 parts of high-temperature antioxidant, 250 parts of weighting agent, and 150 parts of high-temperature resistant base liquid; the preparation methods of modified bentonite and suspension stabilizer are the same as in Example 1.

[0059] The preparation method of the above-mentioned high-temperature resistant and anti-fouling flushing and isolation fluid system includes the following steps:

[0060] 50 parts of organosilicon-modified polyether polyol and 100 parts of water were stirred at a stirring speed of 1000 r / min for 25 minutes to ensure thorough mixing and obtain a high-temperature resistant base liquid.

[0061] Slowly add 12 parts of modified bentonite to the high-temperature resistant base liquid and stir for 20 minutes to fully dissolve and disperse it. Then add 9 parts of suspension stabilizer and continue stirring for 25 minutes to form a uniform suspension solution.

[0062] 14 parts of antifouling agent, 5 parts of high-temperature antioxidant and 3.5 parts of surfactant were added to the suspension solution in sequence. After each additive was added, the mixture was stirred for 20 minutes to ensure that the additives were fully mixed and homogeneous, so as to exert a synergistic effect and adjust the performance of the isolation liquid.

[0063] Finally, slowly add 250 parts of weighting agent while increasing the stirring speed to 2000 r / min and stirring for 25 minutes to ensure that the weighting agent is evenly dispersed in the system, resulting in a high-temperature resistant and anti-fouling flushing and isolation fluid system with uniform density and stable performance.

[0064] Comparative Example 1: Weigh 18 parts of modified bentonite, 6 parts of suspension stabilizer, 10 parts of antifouling agent, 4 parts of surfactant, 1.5 parts of dispersant, 4 parts of high-temperature antioxidant, 150 parts of weighting agent, and 120 parts of high-temperature resistant base liquid; the modified bentonite is the same as in Example 1.

[0065] The suspension stabilizer is a carbon chain polymer. The specific preparation method is as follows: 2-Acrylamido-dimethylpropanesulfonic acid, N,N-dimethylacrylamide, and N-vinylpyrrolidone in a molar ratio of 1:2:0.5 are dissolved in water, and the pH of the solution is adjusted to 7 to obtain solution A. Solution A is added to a three-necked flask equipped with a stirrer, thermometer, and reflux condenser. Nitrogen gas is introduced to remove oxygen, and the temperature is raised to 65°C. Ammonium persulfate and sodium bisulfite (molar ratio 1:1), accounting for 0.1% of the total molar amount of the monomers, are added as initiators. The mixture is stirred and the reaction continues for 4 hours. After the reaction is complete, the mixture is purified several times with anhydrous ethanol, dried in a forced-air drying oven to constant weight, and then pulverized to obtain the suspension stabilizer.

[0066] The preparation method of the above-mentioned high-temperature resistant and anti-fouling flushing and isolation fluid system includes the following steps:

[0067] 40 parts of organosilicon-modified polyether polyol and 80 parts of water were stirred at a stirring speed of 800 r / min for 25 minutes to ensure thorough mixing and obtain a high-temperature resistant base liquid.

[0068] 18 parts of modified bentonite were slowly added to the high-temperature resistant base liquid and stirred for 30 minutes to fully dissolve and disperse it. Then, 6 parts of suspension stabilizer were added and stirred for another 20 minutes to form a uniform suspension solution.

[0069] Add 10 parts of antifouling agent, 4 parts of high-temperature antioxidant and 4 parts of surfactant to the suspension solution in sequence. After each additive is added, continue stirring for 20 minutes to ensure that the additives are fully mixed and have a synergistic effect, thereby adjusting the performance of the isolation liquid.

[0070] Finally, slowly add 150 parts of weighting agent while increasing the stirring speed to 1500 r / min and stirring for 20 minutes to ensure that the weighting agent is evenly dispersed in the system, resulting in a high-temperature resistant and anti-fouling flushing and isolation fluid system with uniform density and stable performance.

[0071] Comparative Example 2: Weigh 18 parts of modified bentonite, 6 parts of suspension stabilizer, 10 parts of antifouling agent, 4 parts of surfactant, 1.5 parts of dispersant, 4 parts of high-temperature antioxidant, 150 parts of weighting agent, and 120 parts of high-temperature resistant base liquid; the preparation methods of modified bentonite and suspension stabilizer are the same as in Example 1.

[0072] The antifouling agent is a single type of antifouling agent, specifically 2-phosphonobutane-1,2,4-tricarboxylic acid.

[0073] The preparation method of the above-mentioned high-temperature resistant and anti-fouling flushing and isolation fluid system includes the following steps:

[0074] 40 parts of organosilicon-modified polyether polyol and 80 parts of water were stirred at a stirring speed of 800 r / min for 25 minutes to ensure thorough mixing and obtain a high-temperature resistant base liquid.

[0075] 18 parts of modified bentonite were slowly added to the high-temperature resistant base liquid and stirred for 30 minutes to fully dissolve and disperse it. Then, 6 parts of suspension stabilizer were added and stirred for another 20 minutes to form a uniform suspension solution.

[0076] Add 10 parts of antifouling agent, 4 parts of high-temperature antioxidant and 4 parts of surfactant to the suspension solution in sequence. After each additive is added, continue stirring for 20 minutes to ensure that the additives are fully mixed and have a synergistic effect, thereby adjusting the performance of the isolation liquid.

[0077] Finally, slowly add 150 parts of weighting agent while increasing the stirring speed to 1500 r / min and stirring for 20 minutes to ensure that the weighting agent is evenly dispersed in the system, resulting in a high-temperature resistant and anti-fouling flushing and isolation fluid system with uniform density and stable performance.

[0078] The performance of the isolation fluid systems obtained in Examples 1-3 and Comparative Examples 1-2 was tested:

[0079] (1) Rheological properties test of the isolation fluid

[0080] The rheological properties of the isolation fluids prepared in Examples 1-3 and Comparative Examples 1-2 were tested at 30-240°C.

[0081] Table 1. Rheological properties of the isolation fluid at temperatures ranging from 30℃ to 240℃

[0082] ;

[0083] As can be seen from the data in Table 1, the apparent viscosity of the isolation fluid decreased to varying degrees with the increase of temperature. However, even at 240℃, its apparent viscosity was greater than 30 mPa·s, indicating that it still had a certain suspension performance.

[0084] (2) Settling stability test of the isolation fluid

[0085] The isolation liquid was cured in a pressure thickener at the experimental temperature for 20 minutes, then the motor of the pressure thickener was turned off. The cement slurry was kept constant at the target temperature and pressure for 30 minutes. Then, the motor of the pressure thickener was turned on and the slurry was cooled down. The cured cement slurry was poured into the slurry cup of a constant-speed mixer and stirred for 35 seconds at 4000 r / min ± 200 r / min. The mixture was then poured into a 500 mL graduated cylinder, the top of which was sealed with plastic wrap. After standing at room temperature for 2 hours, the density difference and free liquid content were measured. The experimental results are shown in Table 2. The isolation liquid systems of Examples 1-3 and Comparative Example 2 showed good settling stability, with a density difference of less than 0.05 g / cm³ after 2 hours. 3 The free liquid meets the requirements. In contrast, the isolation liquid system of Comparative Example 1 exhibits a sedimentation stability greater than 0.1 g / cm³ at 240°C. 3 ,

[0086] Table 2 Settling stability of the isolation fluid

[0087] ;

[0088] (3) Cleaning efficiency test of the isolation fluid

[0089] Different concentrations of high-mineralization brine (total mineralization of 200,000 mg / L) and acidic gas (carbon dioxide content of 20%) were added to the isolation fluid system. After being placed in a simulated formation environment for 24 hours, the cleaning efficiency before and after contamination was tested. The effect evaluation method used was the rotational viscometer method, and the specific steps are as follows:

[0090] 1) Wash and dry the outer cylinder of the rotational viscometer, weigh it, and record it as W1;

[0091] 2) Immerse the outer cylinder in drilling fluid (the drilling fluid is polysulfonated drilling mud with a density of 1.56 g / cm³). 3 ), so that the mud reaches 30-40mm to the outer cylinder, soak for 15 minutes, then take it out and hang it until there is no mud dripping, weigh it and record it as W2;

[0092] 3) Pour the isolation solution into the sample cup, ensuring that the isolation solution can completely submerge the mud, and wash at a speed of 200 r / min for 15 minutes;

[0093] 4) Remove the outer cylinder, rinse off any residual insulating liquid on the surface with clean water, let it dry, weigh it, and record it as W3;

[0094] 5) Using the formula ; Calculate flushing efficiency .

[0095] Table 3. Flushing efficiency before and after contamination of the isolation fluid

[0096] ;

[0097] The results showed that the isolation fluid systems of Examples 1-3 and Comparative Example 1 did not exhibit significant precipitation or stratification after contamination. Their flushing performance decreased by less than 10% compared to before contamination, indicating strong anti-contamination capabilities and effective resistance to complex pollutants in the formation. In contrast, the isolation fluid system of Comparative Example 2 showed better flushing efficiency before contamination, but after contamination, a small amount of precipitation occurred, and the flushing efficiency decreased significantly.

[0098] (4) Compatibility test between the isolation fluid and the drilling fluid cement slurry

[0099] The cement slurry, release fluid, and drilling fluid were mixed evenly in pairs or in all three proportions provided in Table 4, and then tested in a high-temperature, high-pressure thickening apparatus. The compatibility was determined based on the initial consistency and thickening time. The release fluid prepared in Example 2 of this invention had a density of 1.81 g / cm³. 3 The density of the cement slurry used was 1.89 g / cm³. 3 The drilling fluid is a polysulfonated drilling mud with a density of 1.56 g / cm³. 3 .

[0100] Table 4 Thickening Compatibility Experiment

[0101] ;

[0102] According to the proportions in Table 4 above, high-temperature and high-pressure thickening tests were conducted at 240℃ and 120MPa. The results are shown in Table 5. Figure 1 , Figure 2 , Figure 3 and Figure 4 As shown.

[0103] Table 5 Thickening Test Performance of Cement Grout, Release Liquid and Cement Grout Mixture

[0104] ;

[0105] Figure 1 and Figure 2 In contrast, when cement slurry is mixed with drilling fluid, its initial consistency is higher. As the temperature and pressure increase, the thickening curve begins to fluctuate and phenomena such as core inclusion appear. When the thickening time is 129 min, the consistency has reached 78 Bc, which indicates that the compatibility between cement slurry and drilling fluid is poor. Figure 1 and Figure 3 In comparison, mixing the release agent with cement slurry can appropriately increase the thickening time of the cement slurry, which can reduce the initial consistency of the cement slurry and improve its rheological properties. The curve is stable and does not have bulges, indicating that the release agent and cement slurry have good compatibility in thickening. Figure 1 and Figure 4 Compared to blank cement slurry, the thickening time of the mixture of cement slurry, drilling fluid, and separator fluid is extended, which proves that the separator fluid system can effectively decontaminate and prevent the performance of cement slurry. It has good compatibility with both cement slurry and drilling fluid, which can ensure the construction safety of cementing operations. The thickening time of the mixed slurry is greater than 300 minutes, indicating that the separator fluid containing high-temperature resistant suspension stabilizer has good chemical compatibility with drilling fluid and cement slurry, and has strong anti-contamination ability, which can ensure the safety of cement slurry replacement and cementing construction, and meet the cementing needs of high-temperature and ultra-high-temperature deep wells.

[0106] As can be seen from the above embodiments, the ultra-high temperature resistant isolation fluid system of the present invention can effectively solve the problems of existing isolation fluids under high temperature and pollution conditions, has broad application prospects, can significantly improve the cementing quality in oil drilling engineering, and provide strong support for the efficient development of oil and gas resources.

Claims

1. A high-temperature resistant insulating fluid system, characterized in that, By weight, it includes the following components: 10-20 parts modified bentonite, 5-10 parts suspension stabilizer, 8-15 parts composite antifouling agent, 3-6 parts surfactant, 1-3 parts dispersant, 3-5 parts high-temperature antioxidant, 60-300 parts weighting agent, and 80-160 parts high-temperature resistant base liquid; The modified bentonite was obtained by modifying bentonite with a silane coupling agent at a weight ratio of 12:

1. The suspension stabilizer is a high-temperature resistant hydrophobic associative polymer obtained by copolymerizing 2-acrylamido-dimethylpropanesulfonic acid, N,N-dimethylacrylamide, N-vinylpyrrolidone and hydrophobic functional monomers; the hydrophobic functional monomers are prepared by quaternization reaction of N-(3-dimethylaminopropyl)methacrylamide and hexadecane bromide. The preparation method of the hydrophobic monomer is as follows: 0.06 mol N-(3-dimethylaminopropyl)methacrylamide, 0.08 mol hexadecane bromide and 80 mL isopropanol are added to a three-necked flask. Under nitrogen protection, the mixture is refluxed in an oil bath at 50 °C for 24 hours. After rotary evaporation, the mixture is washed three times with anhydrous diethyl ether and dried under vacuum at room temperature to obtain the hydrophobic functional monomer. The preparation method of the suspension stabilizer includes the following steps: S12. Dissolve 2-acrylamido-dimethylpropanesulfonic acid, N,N-dimethylacrylamide, N-vinylpyrrolidone and hydrophobic functional monomers in water in a molar ratio of 1:2:0.5:0.25, and adjust the pH of the solution to 7. S13. The solution from step S12 is added dropwise to a three-necked flask, and after deoxygenation with nitrogen, the temperature is raised to 65°C. A composite initiator accounting for 0.1% of the total molar amount of the monomer is added. The composite initiator is a mixture of ammonium persulfate and sodium bisulfite in a molar ratio of 1:

1. The mixture is stirred and reacted for 4 hours. S14. The reaction product was washed several times with anhydrous ethanol, dried by forced air to constant weight, and then pulverized to obtain a white powdery suspension stabilizer. The composite antifouling agent is a chelate type, prepared by reacting sodium hexametaphosphate solution, amination of 2-phosphonobutane-1,2,4-tricarboxylic acid, and epichlorohydrin crosslinked modified polyethyleneimine. The preparation method of the composite anti-pollution agent includes the following steps: S21. Prepare a 20% aqueous solution of sodium hexametaphosphate and stir at 60°C for 30 minutes to form a homogeneous solution. S22. Mix 2-phosphonobutane-1,2,4-tricarboxylic acid with ethanolamine at a molar ratio of 1:0.5 and react at 70°C for 1 hour to generate amination of 2-phosphonobutane-1,2,4-tricarboxylic acid. S23. Sodium hexametaphosphate solution and amination of 2-phosphonobutane-1,2,4-tricarboxylic acid are mixed at a mass ratio of 1:

2. 5% of modified polyethyleneimine crosslinked with epichlorohydrin is added, and the mixture is reacted for 2 hours at pH 8-9 and 80°C. S24. The reaction solution is spray-dried to obtain a white powdery composite anti-pollution agent; The surfactant is an anionic and nonionic compound of sodium dodecylbenzenesulfonate, dodecylphenol polyoxyethylene ether OP-10 and fatty alcohol polyoxyethylene ether JFC-6 in a weight ratio of 2:1:

3. The high-temperature antioxidant is pentaerythritol diisodecyl diphosphite; The weighting agent is 325 mesh barite powder; The high-temperature resistant base liquid is a mixture of organosilicon-modified polyether polyol and water at a weight ratio of 1:

2.

2. The ultra-high temperature resistant isolation fluid system according to claim 1, characterized in that, The modified bentonite is prepared by drying bentonite at 90°C for 2.5 hours, mixing it with a silane coupling agent at a weight ratio of 12:1, reacting it at a high speed of 900 rpm for 1.5 hours, and then cooling it to room temperature.

3. The ultra-high temperature resistant insulating fluid system according to claim 1, characterized in that, The method for preparing the organosilicon-modified polyether polyol in the high-temperature resistant base liquid is as follows: 1000g of polypropylene glycol with a hydroxyl value of 56mgKOH / g is added to a reaction vessel, heated to 90℃, and dehydrated for 1.5 hours under a vacuum of -0.09MPa; the temperature is then lowered to 70℃, 150g of γ-aminopropyltriethoxysilane is added, and after stirring evenly, 3g of potassium hydroxide is added. The mixture is then reacted at 70℃ for 2 hours to obtain the organosilicon-modified polyether polyol.

4. The ultra-high temperature resistant isolation fluid system according to claim 1, characterized in that, The dispersant is sodium tripolyphosphate.

5. A method for preparing an ultra-high temperature resistant insulating liquid system as described in any one of claims 1-4, characterized in that, Includes the following steps: 1) Mix organosilicon-modified polyether polyol and water at a weight ratio of 1:2, and stir at a stirring speed of 500-1000 r / min for 20-30 minutes to obtain a high-temperature resistant base liquid; 2) Slowly add the modified bentonite to the high-temperature resistant base liquid, stir for 20-40 minutes, then add the suspension stabilizer and continue stirring for 10-30 minutes to form a uniform suspension solution; 3) Add the composite anti-pollution agent, high-temperature antioxidant and surfactant to the suspension solution in sequence. Stir for 15 to 20 minutes after each additive is added to ensure that the additives are mixed evenly. 4) Slowly add the weighting agent while increasing the stirring speed to 1000-2000 r / min and stirring for 10-30 minutes to ensure uniform dispersion of the weighting agent and obtain an ultra-high temperature resistant isolation liquid system.

6. An application of the ultra-high temperature resistant isolation fluid system as described in any one of claims 1-4, characterized in that, The isolation fluid system is used in cementing operations of deep and ultra-deep oil and gas wells with temperatures ≤240℃ and pressures ≤120MPa. It is used to isolate drilling fluid from cementing slurry, flush away loose filter cake on the well wall, and improve cementing displacement efficiency.

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