A high temperature resistant and low damage well killing fluid and preparation method thereof

Abstract

The present invention relates to a high temperature resistant and low damage well killing fluid, comprising the following raw materials in parts by mass: 100-150 parts of water, 20-60 parts of composite salt, 1.6-2.5 parts of modified guar gum, 1-1.7 parts of plant alkyl polysaccharide, 2-3 parts of functional polymer, 0.02-0.04 parts of sodium fluorotitanate; the modified guar gum is obtained by reacting hydroxypropyl guar gum and polyethylene glycol diglycidyl ether; the composite salt is a compound of inorganic salt and organic salt; the inorganic salt does not include halogen salt. The well killing fluid of the present invention has a simple formula, uses a composite system of modified guar gum, plant alkyl polysaccharide and composite salt, is environmentally friendly and non-toxic, has good plugging performance, low filtration loss, avoids leakage damage to the reservoir, has high viscosity, adjustable density, can withstand 180°C high temperature aging, is biodegradable, has little pollution to the core, is a non-destructive or low-loss solid-free well killing fluid, and can be widely used in various oil wells.

Description

Technical Field

[0001] The invention belongs to the field of oil well working fluid, and particularly relates to a high temperature resistant and low damage well killing fluid and a preparation method thereof. Background Art

[0002] Well-killing fluid is an important working fluid in oil well operations. In the process of well repair, the working fluid used to control the oil layer pressure by well killing, well washing, side drilling and perforating is called well-killing fluid. The main purpose is to prevent blowouts and well leakage, and the density is selected according to the reservoir pressure and depth. Especially in the late stage of oil and gas well development, when repairing and replacing wells, it is necessary to fill the wellbore with well-killing fluid to prevent blowouts, well wall collapse and other phenomena, so as to ensure the safety of operation and construction, wellbore cleaning and reservoir protection.

[0003] At present, the main problems of conventional completion fluid in application are as follows: 1. Strong corrosiveness to gas reservoirs with high CO2 and H2S content; poor resistance to high temperature in deep buried reservoirs; 2. Large water loss and serious leakage, which pollutes the reservoir; solid phase pollution introduces secondary damage; 3. Conventional Cl-containing - , Ca 2+ The well-killing fluid has salt corrosion and reservoir pollution; 4. High water loss and low viscosity. The ideal well-killing fluid density is adjustable, which is convenient for balancing the formation pressure; all parameters remain stable under the downhole temperature and pressure conditions, with high viscosity and low filtration loss. In order to increase the viscosity of the well-killing fluid, hydroxyethyl cellulose (HEC) thickeners are generally used, because HEC has basically no damage to the geology of the oil well reservoir, but its anti-filtration and high temperature resistance are not good. The prior art also uses polysaccharides as thickeners, such as xanthan gum, alginate, trehalose, chitosan, galactomannan, etc. However, this type of polysaccharide has poor temperature resistance / salt resistance and cannot maintain good performance under high temperature or high salinity conditions. At present, most density regulators in well-killing fluids use inorganic salts, such as halogen salts (NaCl, KCl, CaCl2, etc.) or formates (sodium formate, potassium formate, cesium formate, etc.). However, the use of halogen salts will significantly aggravate the corrosion of oil pipes and equipment, and formates are expensive. Density regulators.

[0004] CN110846014A discloses a well-killing fluid, in which the carrier fluid contains tallow amine polyoxyethylene ether and tallow diethyl betaine. The cooperation of the two surfactants has good stability and viscosity-increasing effect, and at the same time, it causes little damage to the oil well formation. However, the surfactant is expensive, resulting in a high cost of the patented well-killing fluid; and the well-killing fluid is not resistant to high temperatures.

[0005] CN111621268A discloses a drilling fluid made of a high temperature resistant cross-linked polysaccharide polymer, comprising 50-85 parts of a polysaccharide polymer, 1-10 parts of an isocyanate, 0.01-0.5 parts of a catalyst, and 10-45 parts of an organic solvent. The patent utilizes the reaction of hydroxyl groups on the polysaccharide polymer structure with isocyanate to produce a chemical cross-linked structure to achieve the purpose of high temperature resistance. However, the patent contains a large amount of organic solvents. Moreover, the reaction speed of the hydroxyl group and the isocyanate is relatively fast. If it is not properly controlled, cross-linking will occur too quickly, resulting in insufficient working depth. It is not easy to operate in practical operation.

[0006] CN115074096A discloses a kind of oil-based drilling fluid system based on hydrophobic silica, including hydrophobically modified nano silica, octadecyl trimethyl ammonium chloride, organic soil, oxidized asphalt, calcium oxide, barite, white oil and water. The drilling fluid material of this patent can only be dispersed in white oil and water, and is not a kind of oil well industrial fluid without solid phase. And hydrophobically modified nano silica is difficult to be dispersed in water, and is also difficult to be dispersed in oil. Must cooperate tackifier to improve aqueous phase viscosity, can play suspension effect to solid phase material, whether the performance of this patent drilling fluid system can meet oil well demand, still need to be investigated. And it adopts quaternary ammonium salt cationic surfactant, when encountering high salt water environment, may lose effect, and promptly salt resistance can not meet the requirements.

[0007] The applicant's previous patent CN202310905631.7 discloses a polysaccharide / complex salt solid-free well-killing fluid, including the following raw materials by mass: 100 parts of water, 20-60 parts of complex salt, 1.4-2.2 parts of modified chitosan, 1-1.7 parts of plant alkyl polysaccharide, 3-5 parts of functional polymer, 0.02-0.04 parts of sodium fluorotitanate. The well-killing fluid has good high temperature resistance. After rolling at 180°C for 16 hours of thermal aging, there is no obvious adverse number in density, apparent viscosity, shear force, and HTHP filtration loss, and it has excellent high temperature resistance. However, after practice, the well-killing fluid has no solid phase, will not block the rock pores, and has less damage to the formation, but it still has some damage to the core.

[0008] Therefore, there is an urgent need to develop a well-killing fluid with excellent comprehensive performance, high temperature resistance and low damage to the formation core. Summary of the invention

[0009] In order to solve the problem that the current well-killing fluid cannot meet the requirements of actual oil well work, especially the high temperature resistance and low damage performance need to be further improved, the present invention proposes a high temperature resistant and low damage well-killing fluid, which can withstand a high temperature of 180°C and maintain stable performance; the permeability of the core in the core simulation experiment is low, indicating that the damage to the formation is low; at the same time, the well-killing fluid of the present invention has good biodegradability, and polysaccharides and polymers will not remain in the formation to cause pollution and damage. The well-killing fluid of the present invention has higher practicality under the current premise of environmental protection, and can meet the current growing requirements for low damage to the formation.

[0010] The present invention achieves the above object through the following technical solutions:

[0011] A high temperature resistant and low damage well killing fluid comprises the following raw materials in parts by weight: 100-150 parts of water, 20-60 parts of composite salt, 1.6-2.5 parts of modified guar gum, 1-1.7 parts of plant alkyl polysaccharide, 2-3 parts of functional polymer, and 0.02-0.04 parts of sodium fluorotitanate;

[0012] The modified guar gum is obtained by reacting hydroxypropyl guar gum and polyethylene glycol diglycidyl ether;

[0013] The composite salt is a compound of an inorganic salt and an organic salt; the inorganic salt does not include halogen salts (chloride salts, bromide salts, iodide salts); the organic salt is selected from at least one of sodium humate and sodium bis(1,6-hexamethylenetriaminepentamethylenephosphonate);

[0014] The functional polymer is obtained by copolymerizing the following monomers in parts by mass: 10-13 parts of unsaturated carboxylic acid, 1-1.5 parts of vinyltrialkoxysilane, 4.2-5.7 parts of 2-acrylamido-2-phenylethanesulfonic acid, 0.2-0.3 parts of di(methacryloyloxyethyl) hydrogen phosphate, and 0.2-0.3 parts of polyethylene glycol diacrylate; the number average molecular weight of the polyethylene glycol diacrylate is 300-500; and the weight average molecular weight of the functional polymer is 20,000 to 30,000.

[0015] Compared with the inventor's previous patent technology, the present invention adds polyethylene glycol diacrylate with certain cross-linking properties to the functional polymer, and replaces chitosan with polyethylene glycol-modified guar gum. The polyethylene glycol segment will give the functional polymer a better viscosity-increasing effect, and will not have an adverse effect on the fluid loss reduction of the well-killing fluid. The amount of the functional polymer can be further reduced, reducing the damage to the formation caused by the failure of the polymer to degrade in time.

[0016] In the raw materials of the functional polymer, di(methacryloyloxyethyl) hydrogen phosphate and polyethylene glycol diacrylate both play a cross-linking role, increasing the salt resistance and high temperature stability of the polymer. However, it should be noted that di(methacryloyloxyethyl) hydrogen phosphate cannot be replaced by 2-hydroxyethyl methacrylate phosphate. 2-Hydroxyethyl methacrylate phosphate has three carbon-carbon unsaturated double bonds. Although the degree of cross-linking will be higher, there is no P-OH group. After the functional polymer is prepared, it needs to react with an alkali, the carboxylic acid is converted into a carboxylate, and P-OH will be converted into P-OM (M is Na or K) to increase the water solubility of the functional polymer. The present invention creatively adds a specific monomer copolymerization in a specific proportion to the well-killing fluid to obtain a functional polymer. The polymer main chain and side chain contain rich functional groups, such as carboxyl, phosphoric acid, sulfonic acid, siloxane, and PEG segments. Although the functional polymer in the present invention is added in a small amount, it plays a variety of roles, and plays a multi-function such as reducing filtration loss, lubrication, inhibition, and rheological adjustment.

[0017] Furthermore, in the monomers used to prepare the functional polymer, the unsaturated carboxylic acid is selected from at least one of acrylic acid, methacrylic acid and maleic acid; the vinyltrialkoxysilane is selected from at least one of vinyltriethoxysilane and vinyltripropoxysilane.

[0018] Furthermore, the preparation method of the functional polymer comprises the following steps: adding monomer unsaturated carboxylic acid, vinyl trialkoxysilane, 2-acrylamido-2-phenylethanesulfonic acid, di(methacryloyloxyethyl) hydrogen phosphate, polyethylene glycol diacrylate, initiator and chain transfer agent to an alcohol-water mixed solution, heating to 60-80°C for reaction for 5-8h, and after the reaction is completed, neutralizing with alkali solution to obtain a functional polymer solution. When preparing the well-killing fluid, the functional polymer solution can be used directly, or the functional polymer solution can be dried to powder for use. If the functional polymer solution is used, dilute or concentrate to a solid content of 30-40%.

[0019] Furthermore, the alcohol volume ratio in the alcohol-water mixed solution is 60-80% (alcohol and water are mixed according to 6:4 to 8:2), and the alcohol is ethanol; the initiator is a water-soluble free radical initiator, such as a compound of persulfate and bisulfite according to a mass ratio of 1-2:1-2, the persulfate is selected from at least one of ammonium persulfate and potassium persulfate, and the bisulfite is selected from at least one of sodium bisulfite and potassium bisulfite. The amount of initiator is 1-2% of the total mass of the monomers; the chain transfer agent is selected from at least one of mercaptopropionic acid and thioglycolic acid, and the amount of chain transfer agent is 0.5-0.8% of the total mass of the monomers; the alkali solution is 5-10wt% of sodium hydroxide and / or potassium hydroxide, and the alkali solution is neutralized to a pH of 7-7.5. The chain transfer agent is added to make the molecular weight dispersion of the functional polymer narrower. If the chain transfer agent is not added, the molecular weight dispersion of the obtained functional polymer is wider, and the polymer chains are long and short, which is not conducive to the function of the functional polymer.

[0020] Furthermore, the inorganic salt does not include halogen salts (NaCl, NaBr, KCl, KBr, CaCl2, CaBr2, etc.), and is specifically selected from at least one of sodium hexametaphosphate, potassium hexametaphosphate, sodium dihydrogen phosphate, potassium dihydrogen phosphate, sodium sulfate, and potassium sulfate; the organic salt is a compound of sodium humate and sodium bis(1,6-hexyltriamine pentamethylenephosphonate) in a mass ratio of 3-5:1. The mass ratio of the inorganic salt to the organic salt is 1-1.5:1. The above-mentioned compounded organic acid salt can have a good anti-corrosion effect without adding a corrosion inhibitor, and has extremely excellent thermal stability.

[0021] Furthermore, the inorganic salt is a mixture of potassium hexametaphosphate, sodium dihydrogen phosphate, and sodium sulfate in a mass ratio of 1-2:1-2:2-4.

[0022] The density of the solid-free well-killing fluid of the present invention is 1.27-1.61 g / cm 3 The density of the well-killing fluid is adjusted by the amount of compound salt used. The more compound salt is used, the greater the density of the well-killing fluid. The density of the well-killing fluid can be adjusted by controlling the amount of compound salt according to the needs of different oil wells.

[0023] Further, the modified guar gum is obtained by a preparation method comprising the following steps: 100 parts by mass of hydroxypropyl guar gum is dissolved in 400-500 parts by mass of an alcohol aqueous solution (the alcohol volume fraction is 30-50%, and the alcohol is at least one of ethanol and isopropanol), 60-90 parts by mass of polyethylene glycol diglycidyl ether is added, and in the presence of a base, the reaction is carried out at 60-80° C. for 5-10 hours to obtain a solution of modified guar gum, which is concentrated to a solid content of 20-30wt% for standby use; the number average molecular weight of the polyethylene glycol diglycidyl ether is 500-800. Guar gum is a natural polygalactomannan gum, which is widely used in the papermaking industry. At present, it is also used in oil well additives. Guar gum can be dissolved in water, has good thickening properties, and its viscosity is several times that of starch with the same molecular weight. However, the effect of directly using guar gum is not good. The modified guar gum obtained by the present invention is a polyethylene glycol segment linking two guar gum units, which has a higher viscosity and molecular weight. In aqueous solution, the polymer chain segments extend, and have good viscosity enhancement and salt resistance effects. The inventors speculate that the modified guar gum and the plant alkyl polysaccharide have a certain synergistic effect, and the modified guar gum and the plant alkyl polysaccharide have a certain intermolecular force, which can more effectively reduce the filtration loss. Compared with the modified chitosan used by the inventors before, the present invention uses modified guar gum, which has better effects, stronger biodegradability, and is more conducive to improving the comprehensive performance of the well killing fluid.

[0024] Furthermore, the plant alkyl polysaccharide is selected from at least one of hexyl glucoside, heptyl glucoside, octyl glucoside, coconut glucoside and lauryl glucoside; preferably, hexyl glucoside and lauryl glucoside are compounded in a mass ratio of 3-4:1. Alkyl glucoside with long and short chains can further improve the performance of well killing fluid. Alkyl glucoside has been widely used in daily chemical fields such as detergents, cosmetics, and food. It has good emulsification ability and stability.

[0025] The second object of the present invention is to provide a method for preparing the above-mentioned high temperature resistant and low damage well killing fluid, comprising the following steps:

[0026] According to the required density of the well killing fluid, compound salt is added to water, stirred and dissolved into a homogeneous solution, and then modified guar gum, plant alkyl polysaccharide, functional polymer and sodium fluorotitanate are added and stirred evenly to obtain a high temperature resistant and low damage well killing fluid.

[0027] Compared with the well killing fluid in the prior art, the excellent effects of the present invention are:

[0028] 1. The well-killing fluid of the present invention has a simple formula and uses a compound system of modified guar gum, plant alkyl polysaccharide and composite salt. It is environmentally friendly and non-toxic, has good plugging performance, low filtration loss, avoids damage to the reservoir caused by leakage, has high viscosity, and has the characteristics of one dose and multiple functions.

[0029] 2. The composite salt of the present invention is an organic salt with a density of 1.27-1.61 g / cm 3 It can be freely adjusted within a certain range and is basically non-corrosive even at high dosages, thus avoiding the high corrosiveness of inorganic salts. It can be safely and permanently used in oil wells without causing corrosion to equipment and oil pipes.

[0030] 3. The well killing fluid of the present invention can withstand temperatures up to 180°C. After high-temperature aging at 180°C, the density, apparent viscosity and HTHP filtration loss are substantially unchanged. The well killing fluid also has good salt resistance and maintains good rheological properties in saturated calcium solution.

[0031] Fourth, the well-killing fluid of the present invention has a good biodegradability rate; in addition, the well-killing fluid has been tested for core permeability and has little pollution to the core. In summary, the well-killing fluid provided by the present invention has no damage or pollution to the oil layer geology and is a non-destructive or low-destructive solid-free well-killing fluid. It can be widely used in various oil wells. DETAILED DESCRIPTION

[0032] To make the purpose, technical scheme and advantages of the present invention clearer, the technical scheme of the present invention will be described in detail below. The following examples are convenient for better understanding of the present invention, but are not intended to limit the present invention. The experimental methods in the following examples are conventional methods unless otherwise specified.

[0033] Hydroxypropyl guar gum was purchased from Shandong Guangpu Biotechnology Co., Ltd., model GP-200, water-insoluble matter ≤4%, apparent viscosity at 30°C 85mpa·s, and hydroxypropyl substitution degree 0.38.

[0034] Preparation Example 1

[0035] 10 parts by mass of acrylic acid, 5.7 parts by mass of 2-acrylamido-2-phenylethanesulfonic acid, 1.5 parts by mass of vinyltrialkoxysilane, 0.2 parts by mass of di(methacryloyloxyethyl) hydrogen phosphate, 0.3 parts by mass of polyethylene glycol diacrylate (number average molecular weight 300), 0.2 parts by mass of initiator (compounded with potassium persulfate and sodium bisulfite in a mass ratio of 2:1), and 0.1 parts by mass of chain transfer agent mercaptopropionic acid were added to an ethanol-water solution with a volume fraction of 60% ethanol, heated to 55°C for 8 hours, and after the reaction, neutralized with 5wt% NaOH solution to a pH of 7.5, concentrated to a solid content of 30wt%, to obtain a functional polymer solution, and freeze-dried to obtain a polymer powder. After testing, the weight average molecular weight of the functional polymer obtained in this preparation example is about 22500, and the molecular weight distribution index (M w / M n )=1.85.

[0036] Preparation Example 2

[0037] 13 parts by mass of methacrylic acid, 4.2 parts by mass of 2-acrylamido-2-phenylethanesulfonic acid, 1 part by mass of vinyltrialkoxysilane, 0.3 parts by mass of di(methacryloyloxyethyl) hydrogen phosphate, 0.3 parts by mass of polyethylene glycol diacrylate (number average molecular weight 500), 0.2 parts by mass of initiator (potassium persulfate and sodium bisulfite are compounded in a mass ratio of 2:1), and 0.1 parts by mass of chain transfer agent mercaptopropionic acid are added to a mixed solution of ethanol and water in a volume ratio of 2:1, and the temperature is raised to 60°C for reaction for 8 hours. After the reaction is completed, it is neutralized with 5wt% NaOH solution to a pH of 7.5, concentrated to a solid content of 30wt%, and a functional polymer solution is obtained, which is freeze-dried to obtain a polymer powder. After testing, the weight average molecular weight of the functional polymer obtained in this preparation example is about 25100, and the molecular weight distribution index (M w / M n )=1.82.

[0038] Preparation Example 3

[0039] 100 parts by mass of hydroxypropyl guar gum were dissolved in 400 parts by mass of an ethanol-water solution having a volume fraction of 40% ethanol, 60 parts by mass of polyethylene glycol diglycidyl ether (number average molecular weight 500) were added, and NaOH was added. The mixture was reacted at 60° C. for 6 h under alkaline conditions and concentrated to a solid content of 25 wt % to obtain a modified guar gum solution.

[0040] Preparation Example 4

[0041] 100 parts by mass of hydroxypropyl guar gum were dissolved in 400 parts by mass of an ethanol-water solution having a volume fraction of 40% ethanol, 90 parts by mass of polyethylene glycol diglycidyl ether (number average molecular weight 500) were added, and NaOH was added. The mixture was reacted at 60° C. for 8 h under alkaline conditions and concentrated to a solid content of 25 wt % to obtain a modified guar gum solution.

[0042] Comparative Preparation Example 1

[0043] The other conditions were the same as those in Preparation Example 1, except that no vinyltrialkoxysilane was added.

[0044] Comparative Preparation Example 2

[0045] The other conditions were the same as those in Preparation Example 1, except that di(methacryloyloxyethyl) hydrogen phosphate was not added and the amount of polyethylene glycol diacrylate was 0.5 parts by mass.

[0046] Comparative Preparation Example 3

[0047] The other conditions were the same as those in Preparation Example 1, except that di(methacryloyloxyethyl) hydrogen phosphate was replaced by an equal mass of N,N'-methylenebisacrylamide.

[0048] Comparative Preparation Example 4

[0049] The other conditions were the same as those in Preparation Example 1, except that polyethylene glycol diacrylate was not added and the amount of di(methacryloyloxyethyl) hydrogen phosphate was 0.5 parts by mass.

[0050] Example 1

[0051] The composite salt is a mixture of an inorganic salt (a mixture of potassium hexametaphosphate, sodium dihydrogen phosphate, and sodium sulfate in a mass ratio of 1:1:3) and an organic salt (a mixture of sodium humate and sodium bis(1,6-hexamethylenetriaminepentamethylenephosphonate) in a mass ratio of 3:1) in a mass ratio of 1.5:1. The composite salt of Example 1 can inhibit the hydration of clay components, is environmentally friendly and non-toxic, does not contain halogen salts, has extremely low corrosiveness, and is compatible with metal materials and rubber seals.

[0052] Different weight parts of composite salt were added to 100 weight parts of water, and the density was tested. The results are shown in Table 1. Since other components have little effect on the density of the well-killing fluid, the system composed of water and composite salt in Example 1 is approximately regarded as the density of the well-killing fluid.

[0053] Table 1 Density of well killing fluid

[0054]

[0055]

[0056] Example 2

[0057] 50 parts by mass of composite salt were added to 100 parts by mass of water. The composite salt was the same as that in Example 1, which was a mixture of inorganic salt (a mixture of potassium hexametaphosphate, sodium dihydrogen phosphate, and sodium sulfate in a mass ratio of 1:1:3) and organic salt (a mixture of sodium humate and sodium bis(1,6-hexamethylenetriaminepentamethylenephosphonate) in a mass ratio of 3:1) in a mass ratio of 1.5:1. After stirring and dissolving into a homogeneous solution, 8 parts by mass of the modified guar gum solution prepared in Preparation Example 3, 1.4 parts by mass of alkyl glucoside (a compound of hexyl glucoside and lauryl glucoside in a mass ratio of 3:1), 3 parts by mass of the functional polymer dry powder prepared in Preparation Example 1 and 0.03 parts by mass of sodium fluorotitanate were added, and stirred evenly to obtain a polysaccharide / composite salt solid-free well-killing fluid.

[0058] Example 3

[0059] 50 parts by mass of composite salt were added to 100 parts by mass of water. The composite salt was the same as that in Example 1, which was a mixture of inorganic salt (a mixture of potassium hexametaphosphate, sodium dihydrogen phosphate, and sodium sulfate in a mass ratio of 1:1:3) and organic salt (a mixture of sodium humate and sodium bis(1,6-hexamethylenetriaminepentamethylenephosphonate) in a mass ratio of 3:1) in a mass ratio of 1.5:1. After stirring and dissolving into a homogeneous solution, 10 parts by mass of the modified guar gum solution prepared in Preparation Example 4, 1 part by mass of alkyl glucoside (a compound of hexyl glucoside and lauryl glucoside in a mass ratio of 4:1), 2 parts by mass of the functional polymer dry powder prepared in Preparation Example 1 and 0.04 parts by mass of sodium fluorotitanate were added, and stirred evenly to obtain a polysaccharide / composite salt solid-free well-killing fluid.

[0060] Example 4

[0061] 50 parts by mass of composite salt were added to 100 parts by mass of water. The composite salt was the same as that in Example 1, which was a mixture of inorganic salt (a mixture of potassium hexametaphosphate, sodium dihydrogen phosphate, and sodium sulfate in a mass ratio of 1:1:3) and organic salt (a mixture of sodium humate and sodium bis(1,6-hexamethylenetriaminepentamethylenephosphonate) in a mass ratio of 3:1) in a mass ratio of 1.5:1. After stirring and dissolving into a homogeneous solution, 6.4 parts by mass of the modified guar gum solution prepared in Preparation Example 3, 1.7 parts by mass of alkyl glucoside (a compound of hexyl glucoside and lauryl glucoside in a mass ratio of 4:1), 4 parts by mass of the functional polymer dry powder prepared in Preparation Example 1 and 0.04 parts by mass of sodium fluorotitanate were added, and stirred evenly to obtain a polysaccharide / composite salt solid-free well-killing fluid.

[0062] Example 5

[0063] The other conditions are the same as those in Example 2, except that the alkyl glucoside is a single hexyl glucoside.

[0064] Example 6

[0065] The other conditions are the same as those in Example 2, except that the alkyl glucoside is a single lauryl glucoside.

[0066] Comparative Example 1

[0067] Other conditions were the same as those in Example 2, except that the modified guar gum was directly replaced by hydroxypropyl guar gum of equal mass.

[0068] Comparative Example 2

[0069] Other conditions are the same as those in Example 2, except that the functional polymer is prepared in Comparative Preparation Example 1.

[0070] Comparative Example 3

[0071] Other conditions are the same as those in Example 2, except that the functional polymer is prepared in Comparative Preparation Example 2.

[0072] Comparative Example 4

[0073] The other conditions are the same as those in Example 2, except that the functional polymer is prepared in Comparative Preparation Example 3.

[0074] Comparative Example 5

[0075] The other conditions are the same as those in Example 2, except that the functional polymer is prepared in Comparative Preparation Example 4.

[0076] Comparative Example 6

[0077] The other conditions were the same as those in Example 2, except that sodium fluorotitanate was not added.

[0078] Effect Example 1 High temperature resistance test

[0079] The experiment was to test the changes in density and apparent viscosity after rolling for 16 hours after the temperature reached 180°C and thermal aging. The results are shown in Table 2 below.

[0080] Table 2 High temperature resistance test

[0081]

[0082] After aging at 180° C., the density, apparent viscosity, plastic viscosity and shear force of the well killing fluid of Example 2 remain stable, indicating that the well killing fluid system of the present invention has good high temperature resistance. The bottom hole temperature of the gas storage reservoir is about 150° C., which can meet the operation requirements of the gas storage reservoir.

[0083] In the high temperature resistance test, Examples 3-6 and Comparative Examples 2-4 showed excellent high temperature resistance performance, which was close to that of Example 1. However, Comparative Example 1 did not use modified guar gum, and its apparent viscosity decreased significantly after high temperature aging.

[0084] Effect Example 2 Well Killing Fluid Performance Test

[0085] The performance of the well killing fluids of the embodiment and the comparative example was tested, and the results are shown in Table 3 below.

[0086] The corrosion rate test is carried out according to the SY / T 0026-1999 method.

[0087] The clay expansion rate test is carried out according to the SY / T 5971-1994 method.

[0088] HTHP fluid loss is the filtrate volume measured at 180°C, 600 psi top pressure, and 100 psi back pressure for 30 minutes.

[0089] Biodegradability is based on BOD5 / COD Cr According to the test, the ratio is above 0.3, which means it is biodegradable. All the well killing fluids of the present invention meet the requirement of biodegradability.

[0090] Table 3 Well Killing Fluid Performance Test

[0091]

[0092] From the data in Table 3, it can be seen that the well killing fluid provided by the present invention has excellent comprehensive performance, extremely low metal corrosion rate, and is compatible with rubber seals; it has low filtration loss, good sealing performance, low water lock effect, low filtration loss at high temperature and high pressure, and good high temperature resistance and stability. After aging at 180°C, the density, viscosity, shear force, and anti-filtration performance are basically unchanged, and can meet the operating requirements of Shengping Gas Storage.

[0093] Effect Example 3 Core damage test

[0094] A core flow test was performed, and several cores that had been washed with oil and salt were taken for parallel tests. The original permeability of the cores was tested with kerosene, and the cores were contaminated with the well-killing fluid prepared in the embodiments of the present invention and the comparative example. The permeability of the contaminated cores was then tested, and the degree of core damage was calculated according to the following formula: D = (1-K2 / K1) × 100%, where K1 is the average value of the original permeability of the cores, and K2 is the permeability of the cores after damage by the well-killing fluid. After damage by the well-killing fluid, the less the permeability decreases, the less damage to the formation. Two groups of cores with different original permeabilities were tested respectively. The initial permeability of the cores in the low permeability group (permeability before contamination) was 30×10 -3 μm 2 Up to 50×10 -3 μm 2 The initial permeability of the high permeability group core (permeability before contamination) is 150×10 -3 μm 2 Up to 200×10 -3 μm 2 , three cores with initial permeability within the above range were selected for damage rate test in each group, and the average value was taken for the final structure. The results are shown in Table 4 below.

[0095] Table 4 Core damage test

[0096]

Claims

1. A high temperature resistant and low damage well killing fluid, characterized in that: The invention comprises the following raw materials in parts by weight: 100-150 parts of water, 20-60 parts of composite salt, 1.6-2.5 parts of modified guar gum, 1-1.7 parts of plant alkyl polysaccharide, 2-3 parts of functional polymer, and 0.02-0.04 parts of sodium fluorotitanate; The modified guar gum is obtained by reacting hydroxypropyl guar gum and polyethylene glycol diglycidyl ether; the modified guar gum is obtained by a preparation method comprising the following steps: 100 parts by mass of hydroxypropyl guar gum is dissolved in 400-500 parts by mass of an alcohol aqueous solution, 60-90 parts by mass of polyethylene glycol diglycidyl ether is added, and the mixture is reacted at 60-80° C. for 5-10 hours in the presence of a base to obtain a modified guar gum solution, which is concentrated to a solid content of 20-30 wt% for standby use; the number average molecular weight of the polyethylene glycol diglycidyl ether is 500-800; The composite salt is a compound of an inorganic salt and an organic salt; the inorganic salt does not include a halogen salt; the organic salt is selected from at least one of sodium humate and sodium bis(1,6-hexamethylenetriaminepentamethylenephosphonate); The functional polymer is obtained by copolymerizing the following monomers in parts by mass: 10-13 parts of unsaturated carboxylic acid, 1-1.5 parts of vinyltrialkoxysilane, 4.2-5.7 parts of 2-acrylamido-2-phenylethanesulfonic acid, 0.2-0.3 parts of di(methacryloyloxyethyl) hydrogen phosphate, and 0.2-0.3 parts of polyethylene glycol diacrylate; the number average molecular weight of the polyethylene glycol diacrylate is 300-500; and the weight average molecular weight of the functional polymer is 20,000 to 30,000.

2. The high temperature resistant and low damage well killing fluid according to claim 1, characterized in that: In the monomers used to prepare the functional polymer, the unsaturated carboxylic acid is selected from at least one of acrylic acid, methacrylic acid and maleic acid; the vinyltrialkoxysilane is selected from at least one of vinyltriethoxysilane and vinyltripropoxysilane.

3. The high temperature resistant and low damage well killing fluid according to claim 1, characterized in that: The preparation method of the functional polymer comprises the following steps: adding monomer unsaturated carboxylic acid, vinyltrialkoxysilane, 2-acrylamido-2-phenylethanesulfonic acid, di(methacryloyloxyethyl) hydrogen phosphate, polyethylene glycol diacrylate, an initiator and a chain transfer agent into an alcohol-water mixed solution, heating to 60-80°C for reaction for 5-8h, and after the reaction is completed, neutralizing with an alkali solution to obtain a functional polymer.

4. The high temperature resistant and low damage well killing fluid according to claim 3, characterized in that: The volume proportion of alcohol in the alcohol-water mixed solution is 60-80%, and the alcohol is ethanol; and the initiator is a water-soluble free radical initiator.

5. The high temperature resistant and low damage well killing fluid according to claim 4, characterized in that: The initiator is a compound of persulfate and bisulfite in a mass ratio of 1-2:1-2, the persulfate is selected from at least one of ammonium persulfate and potassium persulfate, and the bisulfite is selected from at least one of sodium bisulfite and potassium bisulfite.

6. The high temperature resistant and low damage well killing fluid according to claim 3, characterized in that: The amount of initiator used is 1-2% of the total mass of the monomers; the chain transfer agent is selected from at least one of mercaptopropionic acid and thioglycolic acid, and the amount of the chain transfer agent used is 0.5-0.8% of the total mass of the monomers; the alkali solution is 5-10wt% of sodium hydroxide and / or potassium hydroxide, and the alkali solution is neutralized to a pH of 7-7.

5.

7. The high temperature resistant and low damage well killing fluid according to claim 1, characterized in that: The inorganic salt is selected from at least one of sodium hexametaphosphate, potassium hexametaphosphate, sodium dihydrogen phosphate, potassium dihydrogen phosphate, sodium sulfate, and potassium sulfate; the organic salt is a compound of sodium humate and sodium bis(1,6-hexamethylenetriaminepentamethylenephosphonate) in a mass ratio of 3-5:1; the mass ratio of the inorganic salt to the organic salt is 1-1.5:

1.

8. The high temperature resistant and low damage well killing fluid according to claim 7, characterized in that: The inorganic salt is a mixture of potassium hexametaphosphate, sodium dihydrogen phosphate and sodium sulfate in a mass ratio of 1-2:1-2:2-4.

9. The high temperature resistant and low damage well killing fluid according to claim 1, characterized in that: The alcohol volume fraction in the alcohol aqueous solution is 30-50%.

10. The high temperature resistant and low damage well killing fluid according to claim 1, characterized in that: The plant-based alkyl polysaccharide is at least one selected from hexyl glucoside, heptyl glucoside, octyl glucoside, coconut oil glucoside and lauryl glucoside.

11. The high temperature resistant and low damage well killing fluid according to claim 10, characterized in that: The plant alkyl polysaccharide is a compound of hexyl glucoside and lauryl glucoside in a mass ratio of 3-4:

1.

12. The method for preparing the high temperature resistant and low damage well killing fluid according to any one of claims 1 to 11, characterized in that: The following steps are involved: According to the required density of the well killing fluid, compound salt is added to water, stirred and dissolved into a homogeneous solution, and then modified guar gum, plant alkyl polysaccharide, functional polymer and sodium fluorotitanate are added and stirred evenly to obtain a high temperature resistant and low damage well killing fluid.

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