Preparation method of ultra-high-temperature-resistant workover fluid capable of protecting ultra-deep oil and gas reservoir

Abstract

The invention discloses a preparation method of an ultra-high-temperature-resistant workover fluid capable of protecting an ultra-deep oil and gas reservoir, which is characterized by comprising the following steps of: adding 10 parts by weight of nano SiO2 and 50-350 parts by weight of solvent into a three-mouth reaction bottle provided with a reflux condensing tube, stirring at room temperature to disperse the nano SiO2, heating to 70-90 DEG C, adding 0.5-10 parts by weight of anionic modifier, reacting for 8-24 hours under reflux, and cooling to room temperature to obtain the ultra-high-temperature-resistant workover fluid capable of protecting the ultra-deep oil and gas reservoir. Then centrifuging the reaction system to remove the solvent and the modifier which does not participate in the reaction, and carrying out vacuum drying on the product under heating to obtain nano SiO2-SC containing anions; the preparation method comprises the following steps: pouring 1.0-50 parts of nano SiO2-SC into 1000 parts of a solvent at normal temperature, stirring until the nano SiO2-SC is uniformly dispersed, then pouring 1.0-20 parts of a thickening agent into a nano SiO2-SC system, stirring until the thickening agent is completely dissolved, and then sequentially adding 5.0-120 parts of a viscosity stabilizer, 0.1-10 parts of a bactericide and 0.1-10 parts of a heat stabilizer into the thickening agent solution while stirring, so as to obtain the ultra-deep oil and gas reservoir protection agent capable of protecting the ultra-deep oil and gas reservoir. And the workover fluid can resist the ultrahigh temperature of 180-240 DEG C.

Description

Technical Field

[0001] The invention relates to a method for preparing ultra-high temperature resistant well repairing fluid capable of protecting ultra-deep oil and gas reservoirs, and belongs to the fields of petroleum exploitation, oilfield chemistry and oilfield polymers. Background Art

[0002] During the continuous development of oil and gas fields, workovers are often necessary to ensure the normal production of oil and gas wells, such as repairing oil casing, salvaging fallen objects, and sidetracking new oil layers. During workover operations, workover fluid is crucial. Its main functions are to balance formation pressure, prevent blowouts and wellbore collapse, carry back rock, and clean the wellbore. Most of the wells in my country's Shunbei Oil and Gas Field are over 8,000 meters deep, with an average bottomhole temperature exceeding 160°C. Some wells have bottomhole temperatures as high as 210°C or even higher. A large number of ultra-deep wells need to be workovered every year, and the formation pressure coefficients of these ultra-deep wells are almost all below 1.0. In ultra-deep oil and gas well workover operations, the workover fluid used, in addition to formation water or water added to formation water, often includes slurries containing solid materials such as bentonite and sulfonated asphalt. These solids-containing workover fluids can experience significant losses under large positive pressure differentials, clogging reservoir fractures and matrix pores, damaging the formation and causing a decrease in permeability. This severely impacts post-workover oil and gas production recovery, sometimes resulting in a 30% to 50% drop in production capacity. Therefore, to protect the reservoir and mitigate losses, oilfield operators add xanthan gum or water-soluble modified cellulose ethers such as sodium carboxymethyl cellulose, sodium polyanionic cellulose, and hydroxyethyl cellulose to brine workover fluids to significantly increase their viscosity. However, at bottomhole temperatures above 100°C, these water-soluble modified cellulose ethers undergo severe thermal and oxidative degradation, almost completely losing their viscosity. Xanthan gum has a significantly higher heat resistance temperature in brine than modified cellulose ethers. It exhibits significant shear-thinning and thixotropic properties, which facilitate wellbore flow and bottomhole sand and rock removal. However, it also undergoes severe thermal and oxidative degradation at temperatures above 120°C, causing a sharp drop in the viscosity of the brine workover fluid and rendering it inoperable. Adding high concentrations of organic salts such as potassium or sodium formate (over 30% by weight) to the xanthan gum workover fluid can somewhat increase its heat resistance. However, even when the workover fluid reaches saturation with the organic salts, for example, at a potassium formate concentration of 76% by weight, the xanthan gum's heat resistance temperature does not exceed 180°C. Furthermore, the addition of high concentrations of potassium or sodium formate significantly increases the cost of the workover fluid. This suggests that neither xanthan gum nor water-soluble modified cellulose ethers are suitable for use in ultra-high-temperature, ultra-deep oil and gas well workover operations with bottomhole temperatures exceeding 180°C. These issues with workover fluids result in long workover times, high workover costs, and incomplete recovery of production capacity after workover. Therefore, the development of workover fluids that can protect ultra-deep oil and gas reservoirs and withstand ultra-high temperatures has important practical applications for reducing workover fluid losses, ensuring the safety of workover operations, and fully restoring oil and gas well productivity. In 2016, Liu Fupeng et al. disclosed a workover fluid viscosifier and manufacturing method (Chinese Patent CN105820803A). They used xanthan gum as a viscosifier in the workover fluid. To address the high-temperature stability limit of xanthan gum at 120°C, potassium formate was added to the workover fluid to increase its operating temperature, but the maximum temperature was only raised to 140°C.Wu Le et al., Drilling and Completion Fluids, 2011, 28(6), 77−80, reported that xanthan gum had a mass percentage concentration of 76% and a density of 1.59 g / cm. 3 The temperature at which xanthan gum is thermally stable for 16 hours in a saturated potassium formate aqueous solution is 180 °C. However, after the aging temperature is higher than 180 °C, xanthan gum undergoes oxidative degradation and the solution has almost no viscosity-enhancing property. Zhang Zhixuan et al., Contemporary Chemical Industry, 2022, 51(6), 1431−1434. The study found that the workover fluid using xanthan gum as a viscosity enhancer has a strong sand-carrying and rock-carrying capacity and can be naturally degraded. In addition, it has been used in 346 wells in the Sebei gas field where the formation pressure coefficient is between 0.72 and 1.00, but the bottom hole temperature in the Sebei gas field is lower than 110 °C. Summary of the Invention

[0003] The purpose of the present invention is to eliminate the damage caused to the reservoir by mud workover fluid leaking into the formation, and to improve the anti-aging performance of the existing solid-phase polymer-free brine workover fluid at ultra-high temperatures of 180°C to 240°C. The present invention provides a method for preparing a workover fluid that can be used in ultra-deep low-pressure wells with a formation pressure coefficient below 1.0, and that still has good thickening, sand washing and rock carrying properties, and fluid loss reduction properties under ultra-high temperature bottomhole environments of 180°C and above. The fluid does not contain large-particle solid materials such as bentonite and sulfonated asphalt that damage the reservoir, and can protect ultra-deep oil and gas reservoirs from ultra-high temperature. The method is characterized by using sodium chloroalkylsulfonate Cl(CH2) x SO3Na, sodium bromoalkylsulfonate Br(CH2) x SO3Na, sodium iodoalkylsulfonate I(CH2) x SO3Na, sodium chloroalkylcarboxylate Cl(CH2) x COONa, sodium bromoalkylcarboxylate Br(CH2) x COONa and sodium iodoalkylcarboxylate I(CH2) x At least one of COONa is a modifier, and x is an integer from 1 to 8. Nano-SiO2 is modified, and the particle size of nano-SiO2 is less than 100 nm. Modified nano-SiO2, namely nano-SiO2-SC (see attached Figure 1), then the nano-SiO2-SC is compounded with at least one of the temperature-resistant polymer diutan, gellan gum, welan gum and scleroglucan in at least one of clean water and oilfield formation water, and at least one of trisodium citrate, sodium diethylenetriamine pentaacetate, tetrasodium ethylenediaminetetraacetate, trisodium nitrilotriacetate, sodium hexametaphosphate, sodium formate, potassium formate, sodium acetate, potassium acetate, sodium propionate, potassium propionate and sodium 2-hydroxypropionate is added as a viscosity stabilizer, and phenol, catechol, hydroquinone, resorcinol, propylene glycol ... At least one of dialdehyde, succinyldialdehyde, glutaraldehyde, adipaldehyde, sodium trichlorophenate, sodium disulfide carbamate, and potassium disulfide carbamate is used as a fungicide, and at least one of sodium sulfate (Na2SO3), potassium sulfite (K2SO3), sodium sulfide (Na2S), potassium sulfide (K2S), sodium disulfite (Na2S2O4), potassium dithionite (K2S2O4), sodium bisulfite (NaHSO3), potassium bisulfite (KHSO3), thiourea, and o-xylene thiourea is added as a thermal stabilizer. This fluid is designed to be ultra-high-temperature resistant and can be used for workover of ultra-deep low-pressure wells and protect ultra-deep oil and gas reservoirs.

[0004] The inventors have discovered that the concentration of the thickener in a workover fluid capable of protecting ultra-deep oil and gas reservoirs from ultra-high temperatures, the mass ratio of the modified nanomaterial to the polymer thickener, and the amount of each additive can significantly affect the viscosity and ultra-high temperature resistance of the workover fluid.

[0005] The purpose of the present invention is achieved by the following technical measures, wherein the parts of the raw materials are all parts by weight unless otherwise specified.

[0006] 1. Preparation of Nano-SiO2-SC

[0007] 10 parts of unmodified nano-SiO2 with an average particle size of less than 100 nm and 50 to 350 parts of solvent are added to a three-necked reaction flask equipped with a reflux condenser, stirred at room temperature for 0.5 hour to disperse the nano-SiO2, then heated to 70°C to 90°C, and 0.5 to 10 parts of anion modifier are slowly added. The reaction is carried out under reflux for 8 to 24 hours, and then the reaction system is centrifuged to remove the solvent and the anion modifier that does not participate in the reaction. Finally, the product is vacuum dried at 50°C to 75°C to obtain modified nano-SiO2 containing anions, i.e., nano-SiO2-SC. The modification degree of the synthesized nano-SiO2-SC is 40% to 85%.

[0008] The solvent is at least one of benzene, toluene, xylene, pyridine, tetrahydrofuran (THF), N,N-dimethylformamide (DMF), triethylamine, cyclohexane and ethyl acetate; the anion modifier is sodium chloroalkylsulfonate Cl(CH2) x SO3Na, sodium bromoalkylsulfonate Br(CH2) xSO3Na, sodium iodoalkylsulfonate I(CH2) x SO3Na, sodium chloroalkylcarboxylate Cl(CH2) x COONa, sodium bromoalkylcarboxylate Br(CH2) x COONa and sodium iodoalkylcarboxylate I(CH2) x At least one of COONa, x is an integer from 1 to 8.

[0009] 2. The formula components of the ultra-high temperature resistant workover fluid that can protect ultra-deep oil and gas reservoirs are as follows:

[0010] 1000 parts solvent

[0011] Thickener 1.0-20 parts

[0012] Nano-SiO2-SC 1.0~50 parts

[0013] 5.0-120 parts viscosity stabilizer

[0014] 0.1-10 parts of fungicide

[0015] 0.1-10 parts of heat stabilizer

[0016] The solvent is at least one of clean water and oilfield formation water, the thickener is at least one of the temperature-resistant polymer diutan, gellan gum, welan gum and sclerotin, the viscosity stabilizer is at least one of trisodium citrate, sodium diethylenetriamine pentaacetate, tetrasodium ethylenediaminetetraacetate, trisodium nitrilotriacetate, sodium hexametaphosphate, sodium formate, potassium formate, sodium acetate, potassium acetate, sodium propionate, potassium propionate and sodium 2-hydroxypropionate, the fungicide is phenol, catechol, hydroquinone, resorcinol, malondialdehyde , succinic dialdehyde, glutaraldehyde, adipaldehyde, sodium trichlorophenate, sodium disulfide carbamate and potassium disulfide carbamate, and the heat stabilizer is at least one of sodium sulfate (Na2SO3), potassium sulfite (K2SO3), sodium sulfide (Na2S), potassium sulfide (K2S), sodium disulfite (Na2S2O4), potassium dithionite (K2S2O4), sodium bisulfite (NaHSO3), potassium bisulfite (KHSO3), thiourea and o-xylene thiourea.

[0017] 3. Preparation of ultra-high temperature resistant workover fluids capable of protecting ultra-deep oil and gas reservoirs

[0018] At room temperature, 1.0 to 50 parts of nano-SiO2-SC are slowly poured into 1000 parts of a stirring solvent, and then stirring is continued until the dispersion is uniform. Then, 1.0 to 20 parts of a thickener are slowly poured into the stirring nano-SiO2-SC suspension system, and stirring is continued until the thickener is completely dissolved to obtain a polymer solution with viscosity increasing properties. Then, during the stirring process, 5.0 to 120 parts of a viscosity stabilizer are added to the prepared thickener solution. Then, 0.1 to 10 parts of a fungicide are added during the stirring process and stirring is continued. Then, 0.1 to 10 parts of a heat stabilizer are added and mixed evenly to obtain a density of 1.005 to 1.150 g / cm 3 , can protect ultra-deep oil and gas reservoirs and withstand ultra-high temperature workover fluids of 180℃~240℃.

[0019] The solvent is at least one of clean water and oilfield formation water, the thickener is at least one of the temperature-resistant polymer diutan, gellan gum, welan gum and scleroglucan, the viscosity stabilizer is at least one of trisodium citrate, sodium diethylenetriamine pentaacetate, tetrasodium ethylenediaminetetraacetate, trisodium nitrotriacetate, sodium hexametaphosphate, sodium formate, potassium formate, sodium acetate, potassium acetate, sodium propionate, potassium propionate and sodium 2-hydroxypropionate, the fungicide is phenol, catechol, hydroquinone, resorcinol, malondialdehyde, At least one of succinic dialdehyde, glutaraldehyde, adipaldehyde, sodium trichlorophenate, sodium disulfide carbamate and potassium disulfide carbamate; the heat stabilizer is at least one of sodium sulfite (Na2SO3), potassium sulfite (K2SO3), sodium sulfide (Na2S), potassium sulfide (K2S), sodium disulfite (Na2S2O4), potassium dithionite (K2S2O4), sodium bisulfite (NaHSO3), potassium bisulfite (KHSO3), thiourea and o-xylene thiourea.

[0020] 4. Ability to protect ultra-deep oil and gas reservoirs from ultra-high temperature workover fluids

[0021] The following method for preparing a workover fluid sample capable of protecting ultra-deep oil and gas reservoirs from ultra-high temperatures is described in Example 1. It is important to note that the following description of the performance of the workover fluid sample prepared according to Example 1 is intended solely to further illustrate the present invention and is not to be construed as limiting the scope of protection of the present invention. Researchers in this field may make non-essential improvements and adjustments to the present invention based on the disclosure herein.

[0022] (1) The relationship between the apparent viscosity of the ultra-high temperature resistant workover fluid that can protect ultra-deep oil and gas reservoirs and the test temperature is shown in Table 1. When the temperature is below 120°C, the apparent viscosity of the ultra-high temperature resistant workover fluid increases with the increase of the test temperature. When the temperature is above 120°C, the apparent viscosity gradually decreases. Within the entire temperature range, the effect of temperature on the apparent viscosity of the ultra-high temperature resistant workover fluid is small, indicating that the ultra-high temperature resistant workover fluid has good temperature resistance.

[0023] Table 1 Effect of test temperature on apparent viscosity of ultra-high temperature resistant workover fluid containing nano-SiO2-SC before aging

[0024]

[0025] Note: Test shear rate: 170.3 s -1

[0026] (2) The relationship between the apparent viscosity and aging temperature of the ultra-high temperature resistant workover fluid that can protect ultra-deep oil and gas reservoirs is shown in Table 2. The aging time for all samples is 16 h. The viscosity retention rate of the ultra-high temperature resistant workover fluid containing nano-SiO2-SC after aging at 140℃ for 16 h is 99.1%. After aging at ultra-high temperatures of 200℃ and 240℃ for 16 h, it still retains a high viscosity retention rate. This is because nano-SiO2-SC is more dispersed than unmodified nano-SiO2. At ultra-high temperatures, the dispersed nano-SiO2-SC particles undergo chemical and physical compounding with the thickener molecular chains in the workover fluid, which enhances the ultra-high temperature resistance of the thickener molecular chains and forms a better aggregate structure. The results in Table 2 show that at ultra-high temperatures, after the thickener undergoes chemical and physical compounding with nano-SiO2-SC, it has good ultra-high temperature anti-aging performance and viscosity-increasing performance, thereby making the ultra-high temperature resistant workover fluid have good sand and rock carrying performance under ultra-high temperature formations, and can also withstand Fe in formation water. 3+ 、Fe 2+ , Ca 2+ and Mg 2+ and other multivalent metal cations.

[0027] Table 2 Apparent viscosity and viscosity retention rate of ultra-high temperature resistant workover fluid containing nano-SiO2-SC at different aging temperatures

[0028]

[0029] Note: Test temperature: 30°C; shear rate: 170.3 s -1 ; Aging time: 16 h; The nanomaterial content in the two workover fluids in the table is 23 g / L, and the polymer, other additives and their respective addition amounts are the same.

[0030] (3) The ultra-high temperature resistant workover fluid that can protect ultra-deep oil and gas reservoirs is shown in Table 3 before and after aging at different temperatures. Table 3 shows that the nano-SiO2-SC workover fluid still exhibits good fluid loss reduction after aging at ultra-high temperature for 16 hours. Compared with the heat-resistant polymer / unmodified nano-SiO2 composite workover fluid, the workover fluid has lower leakage at the ultra-high temperature bottom hole. This is because compared with the unmodified nano-SiO2, nano-SiO2-SC can be better dispersed in the workover fluid, and chemically and physically composited with the heat-resistant polymer at ultra-high temperature to form a composite material of inorganic nanomaterials and polymers. A good supramolecular aggregation structure is also formed at ultra-high temperature, resulting in good fluid loss reduction and strong shielding and temporary plugging ability at the ultra-high temperature bottom hole, which makes the workover fluid have lower leakage at the bottom hole, plays the role of well pressure, and enables the workover fluid to circulate in the annulus, carrying cuttings to the ground and cleaning the wellbore.

[0031] Table 3 API filtration loss of samples after aging for 16 h at different aging temperatures

[0032]

[0033] Note: Test temperature: 30°C; Test time: 0.5 h; The nanomaterial content in both workover fluids in the table is 23 g / L, and the polymer, other additives, and their respective addition amounts are the same.

[0034] (4) The apparent viscosity of the ultra-high temperature workover fluid that can protect ultra-deep oil and gas reservoirs at different shear rates after aging at 240℃ for 16 hours is shown in Table 4. The fluidity index n value in Table 4 is much lower than 1, and the consistency coefficient K value is relatively high. This indicates that the nano-SiO2-SC in the workover fluid and the thickener undergo chemical and physical compounding at ultra-high temperature, resulting in the workover fluid having good viscosity enhancement and pseudoplasticity. This makes its apparent viscosity decrease at high shear rates in the wellbore and has low friction resistance. However, when the annular shear rate decreases, the apparent viscosity increases significantly due to recovery, which is conducive to sand and rock flushing. The results show that the ultra-high temperature workover fluid containing nano-SiO2-SC still exhibits good viscosity enhancement and pseudoplasticity after aging at ultra-high temperature for 16 hours. The workover fluid has good sand and rock flushing properties at the ultra-high temperature bottom hole.

[0035] Table 4 Apparent viscosity and rheological parameters of samples after aging at 240 ℃ for 16 h

[0036]

[0037] Note: The test temperature is 30℃, the fluidity index n is a dimensionless quantity, and the unit of the consistency coefficient K is Pa·s n .

[0038] 5. Ability to protect ultra-deep oil and gas reservoirs with ultra-high temperature resistant workover fluid

[0039] (1) Nano-SiO2-SC and thickener undergo chemical and physical compounding at ultra-high temperature, which makes it still show good viscosity increasing, sand washing and rock carrying properties and filtration loss reduction when the bottom hole temperature is 180℃~240℃, and it can withstand Fe in formation water at ultra-high temperature. 3+ 、Fe 2+ , Ca 2+ and Mg 2+ The surface of nano-SiO2-SC particles has a modified structure similar to that of surfactants, which makes its surface energy significantly lower than that of unmodified nano-SiO2, and its surface also carries anions - SO3 — , —COO — At least one of these makes it more dispersed and less likely to agglomerate. At ultra-high temperatures, the dispersed nano-SiO2-SC particles, through their surface hydroxyl groups, chemically and physically combine with the hydroxyl groups on the polymer chains in the brine solution, enhancing the ultra-high temperature resistance of the polymer chains and forming a more robust aggregate structure. This gives the composite workover fluid excellent viscosity-building properties, sand-flushing and rock-carrying properties, and a temporary shielding and plugging effect at the bottom of the wellbore in ultra-high-temperature formations. This reduces bottomhole fluid losses and allows the workover fluid to circulate in the wellbore and annulus, carrying cuttings to the surface.

[0040] (2) The heat-resistant polymer in the workover fluid can withstand ultra-high temperatures and protect the formation under the action of nano-SiO2-SC. The thickeners in the workover fluid of the invention are all biopolymers, and their ultra-high temperature aging resistance is significantly stronger than the currently commonly used xanthan gum. However, without the compounding of nano-SiO2-SC, the anti-aging temperature of these biopolymers is still below 180°C. However, under the combined action of other additives, the biopolymers in the workover fluid can be well chemically and physically compounded with nano-SiO2-SC at the ultra-high temperature at the bottom of the well, which significantly improves its anti-aging temperature. Unlike synthetic polymers, these biopolymers will completely degrade naturally under high and ultra-high temperatures after completing their functions in the workover fluid system during the workover. Therefore, a small amount of biopolymers leaking into the formation will not cause damage to the formation, will not block the pores and throats of the matrix, and of course it is impossible to block the micro-cracks in the formation.

[0041] (3) Nano-SiO2-SC can protect the formation and restore the oil and gas production capacity of the reservoir after well repair. Nano-SiO2 particles with a particle size of less than 100 nm are modified by low molecular weight to obtain nano-SiO2-SC. They also have a stable rigid structure at ultra-high temperatures, and due to the introduction of anions - SO3 — , —COO —At least one of the above mentioned nano-SiO2-SCs has strong hydrophilicity. After chemical and physical compounding with the thickener in the workover fluid at ultra-high temperature downhole, the rigidity and hydrophilicity of the polymer molecular chain are significantly enhanced, making its molecular structure stable at ultra-high temperature. This significantly enhances the ultra-high temperature resistance, viscosity increasing and salt resistance of the thickener. However, the particle size of nano-SiO2-SC is much smaller than the pore throat size of the matrix and will not clog the formation. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 Schematic diagram of the molecular structure of nano-SiO2-SC. DETAILED DESCRIPTION

[0043] The present invention is described in detail below through examples. It is necessary to point out that the present examples are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Researchers in this field can make some non-essential improvements and adjustments to the present invention based on the above content of the present invention.

[0044] Example 1

[0045] 10 grams of nano-SiO2 with an average particle size of 30 nm, 110 grams of toluene, and 50 grams of tetrahydrofuran were added to a three-necked reaction flask equipped with a reflux condenser. The mixture was stirred at room temperature for 0.5 hours to disperse the nano-SiO2. The temperature was then raised to 78°C, and 3.257 grams of anionic modifier sodium 3-iodopropylsulfonate was slowly added. The mixture was reacted under reflux for 24 hours. The reaction system was then centrifuged to remove toluene, tetrahydrofuran, and unreacted anionic modifier. Finally, the product was vacuum-dried at 70°C to obtain modified nano-SiO2 containing anions, i.e., nano-SiO2-SC. The degree of modification of the synthesized nano-SiO2-SC was 75.3%.

[0046] At room temperature, 23 g of nano-SiO2-SC was slowly poured into 1000 g of formation water containing 16 g / L of sodium chloride, 6.0 g / L of calcium chloride, 3.0 g / L of magnesium chloride and 10 mg / L of ferrous chloride. Stirring was continued until the mixture was evenly dispersed. 8 g of dimethicone and 4 g of welan gum were then slowly poured into the stirred nano-SiO2-SC suspension system. Stirring was continued until the thickener was completely dissolved. During the stirring process, 60 g of sodium formate, 5 g of sodium diethylenetriamine pentaacetate, 3 g of tetrasodium ethylenediaminetetraacetate, 20 g of potassium formate and 5 g of sodium acetate were added to the prepared thickener solution. 2 g of resorcinol, 1.0 g of glutaraldehyde and 1 g of sodium disulfide carbamate were added during the stirring process. Stirring was continued until the mixture was evenly dispersed. 1.5 g of sodium bisulfite and 2 g of thiourea were then added and stirred evenly. The resulting mixture had a density of 1.103 g / cm 3, can be used in ultra-high temperature oil and gas well workover fluids with bottom hole temperatures of 180℃~240℃.

[0047] Example 2

[0048] 10 grams of nano-SiO2 with an average particle size of 23 nm, 130 grams of xylene, 50 grams of N,N-dimethylformamide, and 70 grams of cyclohexane were added to a three-necked reaction flask equipped with a reflux condenser and stirred at room temperature for 0.5 hours to disperse the nano-SiO2. The mixture was then heated to 80°C and slowly added with an anion modifier, 4.035 grams of sodium 4-bromobutylsulfonate and 3.612 grams of sodium 2-bromoacetate. The mixture was allowed to react under reflux for 16 hours. The reaction system was then centrifuged to remove xylene, N,N-dimethylformamide, cyclohexane, and any unreacted anion modifier. The product was then vacuum dried at 70°C to obtain modified nano-SiO2 containing anions, i.e., nano-SiO2-SC. The degree of modification of the synthesized nano-SiO2-SC was 64.5%.

[0049] At room temperature, add 500g of clean water to 500g of formation water and stir evenly to prepare brine. The formation water contains 28g / L of sodium chloride, 8.0g / L of calcium chloride, 5.0g / L of magnesium chloride and 8. mg / L ferric chloride, slowly pour 30 grams of nano-SiO2-SC into the stirred 1000 grams of salt water, and then continue to stir until it is evenly dispersed, then slowly pour 5 grams of gellan gum, 7 grams of welan gum, and 3 grams of dimethicone into the stirred nano-SiO2-SC suspension system, and continue to stir until the thickener is completely dissolved. Then, during the stirring process, add 40 grams of potassium formate, 30 grams of sodium formate, 5 grams of trisodium nitrotriacetate, 5 grams of sodium hexametaphosphate and 6 grams of tetrasodium ethylenediaminetetraacetate to the prepared thickener solution, and then add 3 grams of resorcinol, 2 grams of malondialdehyde and 2 grams of potassium disulfide carbamate during the stirring process, and continue to stir evenly, then continue to add 2.0 grams of sodium disulfite and 0.5 grams of thiourea, and stir evenly to obtain a density of 1.120 g / cm 3 , can be used in ultra-high temperature oil and gas well workover fluids with bottom hole temperatures of 180℃~240℃.

[0050] Example 3

[0051] 10 grams of nano-SiO2 with an average particle size of 18 nm, 90 grams of triethylamine, 80 grams of xylene, 70 grams of toluene, and 65 grams of ethyl acetate were added to a three-necked reaction flask equipped with a reflux condenser and stirred at room temperature for 0.5 hours to disperse the nano-SiO2. The temperature was then raised to 85°C, and 3.016 grams of sodium 8-chlorooctylsulfonate and 6.280 grams of sodium 4-bromobutyrate, an anionic modifier, were slowly added. The reaction was allowed to reflux for 24 hours, and the reaction system was then centrifuged to remove triethylamine, xylene, toluene, ethyl acetate, and any anionic modifier that did not react. The product was finally dried in vacuo at 75°C to obtain modified nano-SiO2 containing anions, i.e., nano-SiO2-SC. The degree of modification of the synthesized nano-SiO2-SC was 59.2%.

[0052] At room temperature, 43 grams of nano-SiO2-SC was slowly poured into 1000 grams of stirring water, and then continued to stir until it was evenly dispersed. Then, 9 grams of welan gum, 3 grams of gellan gum and 4 grams of sclerotin were slowly poured into the stirring nano-SiO2-SC suspension system, and continued to stir until the thickener was completely dissolved. Then, during the stirring process, 8 grams of sodium hexametaphosphate, 20 grams of sodium formate and 8 grams of tetrasodium ethylenediaminetetraacetic acid were added to the prepared thickener solution. Then, 0.3 grams of phenol, 0.4 grams of adipaldehyde and 0.2 grams of sodium trichlorophenate were added during the stirring process, and continued to stir evenly. Then, 0.3 grams of potassium dithionite and 0.4 grams of sodium sulfide were added and stirred evenly to obtain a density of 1.078 g / cm 3 , can be used in ultra-high temperature oil and gas well workover fluids with bottom hole temperatures of 180℃~240℃.

[0053] Example 4

[0054] 10 grams of nano-SiO2 with an average particle size of 82 nm, 50 grams of xylene, and 30 grams of benzene were added to a three-necked reaction flask equipped with a reflux condenser. The mixture was stirred at room temperature for 0.5 hours to disperse the nano-SiO2. The temperature was then raised to 87°C, and 5.260 grams of anionic modifier sodium 2-chloroacetate were slowly added. The mixture was reacted under reflux for 24 hours. The reaction system was then centrifuged to remove xylene, benzene, and unreacted anionic modifier. Finally, the product was vacuum-dried at 65°C to obtain modified nano-SiO2 containing anions, i.e., nano-SiO2-SC. The degree of modification of the synthesized nano-SiO2-SC was 63.7%.

[0055] At room temperature, 10 grams of nano-SiO2-SC was slowly poured into 1000 grams of formation water in the stirring process, and the formation water contained 22 g / L of sodium chloride, 5.0 g / L of calcium chloride, and 4.0 g / L of magnesium chloride. The mixture was then stirred until uniformly dispersed. 5 grams of gellan gum and 3 grams of dimethicone were then slowly poured into the stirring nano-SiO2-SC suspension system. The mixture was stirred until the thickener was completely dissolved. During the stirring process, 55 grams of potassium formate, 8 grams of sodium diethylenetriamine pentaacetate, and 10 grams of sodium butyrate were added to the prepared thickener solution. 0.3 grams of phenol, 0.5 grams of succinaldehyde, and 3 grams of sodium trichlorophenate were added during the stirring process. The mixture was stirred evenly. 0.5 grams of thiourea and 0.3 grams of sodium sulfite were then added and stirred evenly. The density was 1.072 g / cm 3 , can be used in ultra-high temperature oil and gas well workover fluids with bottom hole temperatures of 180℃~240℃.

[0056] Example 5

[0057] 10 grams of nano-SiO2 with an average particle size of 55 nm, 130 grams of toluene, and 60 grams of pyridine were added to a three-necked reaction flask equipped with a reflux condenser and stirred at room temperature for 0.5 hours to disperse the nano-SiO2. The temperature was then raised to 68°C, and 1.538 grams of anionic modifiers, 3-bromopropyl sodium sulfonate, and 2.417 grams of sodium 6-iodohexanoate, were slowly added. The reaction was allowed to reflux for 24 hours, and the reaction system was subsequently centrifuged to remove toluene, pyridine, and any unreacted anionic modifiers. The product was finally dried in a vacuum at 60°C to obtain modified nano-SiO2 containing anions, i.e., nano-SiO2-SC. The degree of modification of the synthesized nano-SiO2-SC was 76.1%.

[0058] At room temperature, 15 grams of nano-SiO2-SC was slowly poured into 1000 grams of stirring water, and then continued to stir until it was evenly dispersed. Then, 3 grams of sclerotin and 9 grams of diugu gum were slowly poured into the stirring nano-SiO2-SC suspension system, and continued to stir until the thickener was completely dissolved. Then, during the stirring process, 70 grams of sodium formate, 5 grams of trisodium citrate and 20 grams of sodium 2-hydroxypropionate were added to the prepared thickener solution. Then, 0.4 grams of catechol and 5 grams of potassium disulfide were added during the stirring process, and continued to stir evenly. Then, 1.0 grams of thiourea and 1.0 grams of sodium bisulfite were added and stirred evenly to obtain a density of 1.080 g / cm 3 , can be used in ultra-high temperature oil and gas well workover fluids with bottom hole temperatures of 180℃~240℃.

Claims

1. A method for preparing a workover fluid capable of protecting ultra-deep oil and gas reservoirs from ultra-high temperatures, comprising: (1) Preparation of nano-SiO2-SC 10 parts of unmodified nano-SiO2 with an average particle size of less than 100 nm and 50 to 350 parts of solvent are added to a three-necked reaction flask equipped with a reflux condenser and stirred at room temperature for 0.5 hours to disperse the nano-SiO2. The temperature is then raised to 70°C to 90°C, and 0.5 to 10 parts of an anion modifier are slowly added. The reaction is carried out under reflux for 8 to 24 hours. The reaction system is then centrifuged to remove the solvent and the anion modifier that does not participate in the reaction. Finally, the product is vacuum-dried at 50°C to 75°C to obtain modified nano-SiO2 containing anions, i.e., nano-SiO2-SC. The degree of modification of the synthesized nano-SiO2-SC is 40% to 85%. The solvent is at least one of benzene, toluene, xylene, pyridine, tetrahydrofuran (THF), N,N-dimethylformamide (DMF), triethylamine, cyclohexane and ethyl acetate; the anion modifier is sodium chloroalkylsulfonate Cl(CH2) x SO3Na, sodium bromoalkylsulfonate Br(CH2) x SO3Na, sodium iodoalkylsulfonate I(CH2) x SO3Na, sodium chloroalkylcarboxylate Cl(CH2) x COONa, sodium bromoalkylcarboxylate Br(CH2) x COONa and sodium iodoalkylcarboxylate I(CH2) x At least one COONa, x is an integer from 1 to 8; (2) Preparation of ultra-high temperature resistant workover fluid capable of protecting ultra-deep oil and gas reservoirs At room temperature, 1.0 to 50 parts of nano-SiO2-SC are slowly poured into 1000 parts of a stirring solvent, and then stirring is continued until the dispersion is uniform. Then, 1.0 to 20 parts of a thickener are slowly poured into the stirring nano-SiO2-SC suspension system, and stirring is continued until the thickener is completely dissolved to obtain a polymer solution with viscosity increasing properties. Then, during the stirring process, 5.0 to 120 parts of a viscosity stabilizer are added to the prepared thickener solution. Then, 0.1 to 10 parts of a fungicide are added during the stirring process and stirring is continued. Then, 0.1 to 10 parts of a heat stabilizer are added and mixed evenly to obtain a density of 1.005 to 1.150 g / cm 3 , can protect ultra-deep oil and gas reservoirs, and can withstand ultra-high temperature workover fluids of 180°C to 240°C; The solvent is at least one of clean water and oilfield formation water, the thickener is at least one of the temperature-resistant polymer diutan, gellan gum, welan gum and scleroglucan, the viscosity stabilizer is at least one of trisodium citrate, sodium diethylenetriamine pentaacetate, tetrasodium ethylenediaminetetraacetate, trisodium nitrotriacetate, sodium hexametaphosphate, sodium formate, potassium formate, sodium acetate, potassium acetate, sodium propionate, potassium propionate and sodium 2-hydroxypropionate, the fungicide is phenol, catechol, hydroquinone, resorcinol, malondialdehyde, At least one of succinic dialdehyde, glutaraldehyde, adipaldehyde, sodium trichlorophenate, sodium disulfide carbamate and potassium disulfide carbamate; the heat stabilizer is at least one of sodium sulfite (Na2SO3), potassium sulfite (K2SO3), sodium sulfide (Na2S), potassium sulfide (K2S), sodium disulfite (Na2S2O4), potassium dithionite (K2S2O4), sodium bisulfite (NaHSO3), potassium bisulfite (KHSO3), thiourea and o-xylene thiourea.

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