Alcohol-based multi-effect descaling cleaning agent for shale oil wells and preparation method thereof

Abstract

The present application relates to the technical field of oilfield cleaning agent, and particularly relates to an alcohol-based multi-effect scale removal cleaning agent for shale oil wells and a preparation method thereof, the alcohol-based multi-effect scale removal cleaning agent comprises the following raw materials in parts by mass: 100 parts of alcohol-based base fluid, 16-23 parts of side chain modified polyether ester, 7-11 parts of organic acid, 5-8 parts of chelating agent, 3-5 parts of glycoside surfactant, 3-5 parts of polyoxyethylene surfactant, 2-3 parts of polyvinyl alcohol, 25-32 parts of ethylene glycol mono-C2-4 ether, and 2-3 parts of silicate; the side chain modified polyether ester is obtained by side chain containing alkenyl polyether ester after high molecular initiator, propylene oxide and / or ethylene oxide, and allyl glycidyl ether ring-opening polymerization, and then polymerization of the side chain containing alkenyl polyether ester with (meth) acrylic acid, (meth) acrylic C4-6 alkyl ester, and benzyl (meth) acrylic ester; the alcohol-based base fluid comprises 60-80 wt% of C1-3 monohydric alcohol.

Description

Technical Field

[0001] This invention relates to the field of oilfield cleaning agent technology, specifically to an alcohol-based multi-effect descaling and cleaning agent for shale oil wells and its preparation method. Background Technology

[0002] During long-term operation, oil wells accumulate significant amounts of scale, which can spread throughout the oil reservoir, wellbore, tubing, pumps, and production equipment. Excessive scale buildup can negatively impact well production, leading to decreased output; severe scaling can even pose serious safety hazards. Therefore, timely removal of scale from oil wells is crucial. The composition of oil well scale is complex, primarily including water scale, organic scale (wax, asphalt, and other long-chain organic compounds), and inorganic deposits (mainly calcium carbonate, calcium sulfate, and barium sulfate). Regular cleaning of oil well scale is necessary. Conventional oil well cleaning agents typically consist of surfactants and solvents, with auxiliary agents such as filtration reducers added as needed. Existing technologies often employ acidic or alkaline cleaning agents, utilizing their acid / alkalinity to react with inorganic alkaline salts for removal. For example, CN1524923A discloses an acidic organic cleaning and scale inhibitor composed of hydrochloric acid, acetic acid, quaternary ammonium salt, sodium dodecylbenzenesulfonate, alkylphenol polyoxyethylene ether, industrial naphtha, ethylene glycol monobutyl ether or ethanol, organic phosphate ester or salt, and octadecyl alcohol polyoxyethylene ether. Another example is CN108641694A, which discloses an alkaline oil well scale remover made from the following raw materials in parts by weight: 6 parts tetrasodium iminodisuccinate solution, 5-8 parts diethylenetriaminepentaacetic acid solution, 3-4 parts sodium ethylenediaminetetramethylenephosphonate, 10-15 parts aminotrimethylenephosphonic acid, 9-12 parts polymaleic acid, 5-8 parts oxalic acid solution, and 22-26 parts potassium hydroxide solution. However, acidic / alkaline cleaning agents may corrode equipment and cause some damage to the geology. Currently, it is more recommended to develop neutral cleaning agents, which have less corrosion to equipment and less damage to the formation.

[0003] CN110003871A discloses a rapid cleaning, unclogging, and descaling agent for oil wells. The raw materials for its preparation include gasoline, condensate oil, diesel oil, n-heptanol, Span-20, AEO-3, Twee-60, water-soluble ammonium polyphosphate, ammonium citrate, 1,2-cyclohexanediaminetetraacetic acid, water, furfural, ethylenediamine, succinate, copper chloride, and sucrose fatty acid esters. CN115820233A discloses a shale gas horizontal wellbore cleaning agent comprising the following components: 3%–6% alcohol ether glycosides, 6%–12% fatty acid alkanolamide phosphate esters, 9.6%–14.4% sodium secondary alkyl sulfonate, 4.8%–7.2% sodium dodecyl diphenyl ether disulfonate, 8.1%–11.7% dodecylbenzene sulfonic acid, 1.8%–2.6% isopropanolamine, 1%–3% glycerol polyoxypropylene ether, and the remainder being deionized water.

[0004] However, the above-mentioned cleaning agents / descaling agents are not suitable for shale oil wells. Shale reservoirs have ultra-low permeability and nanoscale pore structures, and are developed using horizontal drilling and hydraulic fracturing technologies. This extraction method leads to an increased contact area between the wellbore and the formation, significantly increasing the risk of scaling. The chemicals in fracturing fluids are incompatible with formation fluids; in addition, impurities in shale oil wells contain small-diameter sand particles, which provide nuclei for wax deposition, making shale oil wells more prone to wax formation. Shale oil wells are typically in environments with higher temperatures and pressures, and the temperature and pressure variations are greater, resulting in a more complex scaling process and a greater likelihood of forming complex mixed scale. Conventional oil well cleaning agents are designed for single types of scale, such as acidic agents mainly for calcium carbonate scale and solvent-based agents mainly for wax scale, which cannot meet the needs of shale oil wells for multi-effect descaling agents. Moreover, conventional cleaning agents require flowback after use, but shale reservoirs have extremely low permeability, resulting in low flowback efficiency, and residual liquid may cause further damage to the reservoir. Summary of the Invention

[0005] To address the issue that existing descaling agents cannot meet the descaling requirements of shale oil wells, this invention proposes an alcohol-based multi-effect descaling agent for shale oil wells and its preparation method. Using an alcohol-based liquid, corrosion is not a concern, and it provides cleaning and protection against complex scale formations, including both inorganic and organic scales. This effectively protects the oil reservoir and improves well productivity.

[0006] The present invention provides the following technical solutions to solve the above-mentioned technical problems:

[0007] A multi-effect alcohol-based descaling and cleaning agent for shale oil wells comprises the following raw materials in parts by weight: 100 parts alcohol-based base liquid, 16-23 parts side-chain modified polyether ester, 7-11 parts organic acid, 5-8 parts chelating agent, 3-5 parts glycoside surfactant, 3-5 parts polyoxyethylene surfactant, 2-3 parts polyvinyl alcohol, 25-32 parts ethylene glycol mono-C2-4 ether, and 2-3 parts silicate; the side-chain modified polyether ester is obtained by ring-opening polymerization of a polymer initiator, propylene oxide and / or ethylene oxide, and allyl glycidyl ether to obtain an alkenyl polyether ester containing side chains, which is then polymerized with (meth)acrylic acid, (meth)acrylic acid C4-6 alkyl ester, and (meth)acrylic acid benzyl ester; the alcohol-based base liquid comprises 60-80 wt% C1-3 monohydric alcohol.

[0008] Furthermore, in the preparation of side-chain modified polyether esters, the polymeric initiator is selected from polyols with a number average molecular weight of 200-400, such as polyethylene glycol and polypropylene glycol; the mass ratio of the polymeric initiator, propylene oxide and / or ethylene oxide, and allyl glycidyl ether is 1:30-40:3-5. The side-chain modified polyether ester is in polymer form or in solution form; if in solution, it is preferably an alcoholic aqueous solution of the side-chain modified polyether ester with a solid content of 20-30%. During the preparation of the side-chain modified polyether ester, an alcoholic aqueous solution is used as the reaction medium. After the reaction, an alcoholic aqueous solution of the side-chain modified polyether ester is directly obtained without further post-treatment and can be directly used to formulate alcohol-based multi-effect descaling and cleaning agents.

[0009] Furthermore, the C4-6 alkyl methacrylate is selected from at least one of butyl methacrylate, pentyl methacrylate, and hexyl methacrylate; even further, the mass ratio of the side chain containing alkenyl polyether ester, (meth)acrylate, C4-6 alkyl methacrylate, and benzyl methacrylate is 100:30-40:15-20:4-6. The proportion of side chain monomers needs to be reasonably controlled to ensure the synergistic effect of the functional groups in the polymer molecular chain. (Meth)acrylate imparts water solubility to the polymer and can also disperse inorganic scale particles through electrostatic repulsion and chelate calcium and magnesium ions; if the amount of (meth)acrylate is too small, it will not be effective, the polymer's solubility in alcohol-based solutions will decrease, and its ability to remove inorganic scale will decline accordingly; however, the amount of (meth)acrylate should not be too large either, otherwise the molecular weight will be too hydrophilic, failing to wet the hydrophobic wax crystal surface, significantly reducing the wax removal and prevention ability, and failing to achieve the multi-functional effect. (Meth)acrylate C4-6 alkyl esters provide short-chain alkyl groups, which can be effectively adsorbed on the surface of wax crystals, destroying their crystalline network and playing a role in preventing waxing; (Meth)acrylate benzyl ester introduces aryl structures into the side chain, which has a conjugation effect on heavy components such as asphaltenes and gums in organic scale, and can effectively disperse asphaltenes; excessive (Meth)acrylate benzyl ester content will lead to increased polymer rigidity and decreased solubility.

[0010] The side-chain modified polyether is prepared by a method including the following steps:

[0011] (T1) Under an inert atmosphere, a polymeric initiator is added to the reaction vessel, the temperature is raised to 80-90℃, propylene oxide and / or ethylene oxide, allyl glycidyl ether and catalyst are added. After all materials are added, the temperature is raised to 105-110℃ and the reaction is maintained for 2-4 hours. The mixture is washed with dilute ammonia water and vacuum distilled to obtain a pale yellow transparent liquid, which is a polyether ester with alkenyl side chain.

[0012] (T2) Under an inert atmosphere, side-chain alkenyl polyether esters are added to an alcohol-water solution, along with 30-50 wt% of persulfate initiator. The temperature is raised to 60-80°C, and an alcohol solution of a mixture of monomers including (meth)acrylic acid, (meth)acrylic acid C4-6 alkyl ester, and (meth)acrylic acid benzyl ester, as well as the remaining persulfate initiator, is slowly added. The reaction is maintained at this temperature for 3-5 hours, then cooled and distilled under reduced pressure to obtain an alcohol-water solution of side-chain modified polyether.

[0013] Further, the inert atmosphere is nitrogen and / or argon, and the addition is slow, completed within 1-2 hours. The alcohol-water solution is a mixture of ethanol and water at a volume ratio of 3-5:1, and the solid content of the resulting side-chain modified polyether alcohol-water solution is 20-30%. In step (T1), the catalyst is selected from at least one of sodium methoxide, sodium ethoxide, boron trifluoride diethyl ether, and dimetallic cyanide complex (DMC), preferably sodium methoxide and / or sodium ethoxide; the amount of catalyst is 0.05-0.1% of the mass of epoxides (the sum of propylene oxide and ethylene oxide); in step (T2), the persulfate is selected from at least one of sodium persulfate, potassium persulfate, and ammonium persulfate, and the amount of persulfate is 1-2 wt% of the total mass of (meth)acrylic acid, (meth)acrylic acid C4-6 alkyl ester, and (meth)acrylic acid benzyl ester.

[0014] In this invention's alcohol-based cleaning agent, the side-chain modified polyether ester is key to achieving multi-effect descaling. This allows the cleaning agent to effectively remove both inorganic and organic scale, while also preventing wax buildup. This enhances the cleaning agent's protection against complex mixed scale, and is one of the core technological highlights that distinguishes this invention from conventional cleaning agents. The inventors also discovered that adding a certain amount of polyvinyl alcohol with a specific molecular weight can simultaneously improve the removal and prevention of both inorganic and organic scale.

[0015] Further, the alcohol-based liquid comprises the following raw materials in parts by weight: 25-38 parts of C1-3 monohydric alcohol, 3-5 parts of C2-4 polyhydric alcohol, 0.5-1.1 parts of polypolyhydric alcohol, 1.2-1.9 parts of aromatic alcohol, and 2.2-3.5 parts by weight of C8-12 long-chain alkyl alcohol.

[0016] Furthermore, the C1-3 monohydric alcohol is selected from at least one of methanol, ethanol, and isopropanol; the C2-4 polyhydric alcohol is selected from at least one of ethylene glycol, 1,3-propanediol, 1,4-butanediol, and glycerol; the polyhydric alcohol is selected from at least one of polyethylene glycol, polypropylene glycol, and polytetrahydrofuran with a number average molecular weight of 1000-2000; the aromatic alcohol is selected from at least one of 2-phenoxyethanol and 2-phenoxypropanol; and the C8-12 long-chain alkyl alcohol is selected from at least one of n-octanol, n-nonanol, n-decanol, undecylol, and dodecanol.

[0017] The alcohol group of this invention is composed of various alcohols. C1-3 monohydric alcohols (preferably ethanol) serve as the main solvent. They have small molecular weights, low viscosity, and low surface tension, allowing them to quickly penetrate into the micro-cracks inside the scale. C2-4 polyhydric alcohols help retain the cleaning fluid. Low molecular weight polyhydric alcohols increase the viscosity of the base fluid, reducing its filtration rate into the micro-fractures of the shale reservoir and prolonging the effective action time. In addition, the long-chain structure helps stabilize the space and prevents the stripped scale particles from re-aggregating and depositing. Aromatic alcohols, such as 2-phenoxyethanol, have good dissolving ability for complex organic scales such as asphaltenes, gums, and heavy waxes, and can also improve the compatibility between polar alcohols and non-polar long-chain alkanes. The long carbon chains in C8-12 long-chain alkyl alcohols are similar to the structure of paraffin wax, which can be adsorbed onto the surface of wax crystals, changing their lattice and preventing their growth and deposition, thus playing a role in preventing wax deposition. However, the carbon chain length cannot be too long, otherwise it will affect water solubility. Alcohol-based fluids are neutral, fundamentally avoiding the severe corrosion problems of acidic cleaning agents on downhole equipment and tubing, making them particularly suitable for shale oil wells requiring long-term protection. Furthermore, compared to many traditional solvent oils (such as toluene and xylene), alcohols have relatively lower toxicity, better biodegradability, and are more in line with the environmental protection requirements of modern oilfield chemistry. The alcohol-based fluid used in this invention is not a simple solvent mixture, but a precision composite carrier designed specifically for the complex scaling characteristics of shale oil wells, comprehensively considering multiple requirements such as dissolution, penetration, stability, and protection.

[0018] Further, the organic acid is selected from at least one of hydroxyethylidene diphosphate, citric acid, malic acid, oxalic acid and alkyl lactate; the chelating agent is selected from at least one of polyaspartic acid (number average molecular weight 1000-1500), ethylenediaminetetraacetic acid or its salt (sodium salt or potassium salt), and aminotrimethylphosphonic acid.

[0019] Preferably, the organic acid is a mixture of hydroxyethylidene diphosphate and citric acid in a mass ratio of 1-2:1, and the chelating agent is a mixture of polyaspartic acid and disodium ethylenediaminetetraacetate in a mass ratio of 1:2-4. Using the above-mentioned compounded organic acid and chelating agent can improve the ability of the alcohol-based multi-effect descaling and cleaning agent for shale oil wells of the present invention to remove and protect against inorganic scale.

[0020] Further, the polyoxyethylene surfactant is selected from at least one of fatty alcohol polyoxyethylene ether, polyoxyethylene nonylphenol ether, polyoxyethylene nonylphenol resin ether, polyoxyethylene sorbitan monooleate, and polyoxyethylene sorbitan monooleate; the glycoside surfactant is selected from at least one of alkyl glucoside, carboxyl alcohol modified alkyl glycoside, and alkyl polyglucoside, such as APG0810, APG0814, and APG1214; the weight average molecular weight of polyvinyl alcohol is 5000-8000; the ethylene glycol monoC2-4 ether is selected from at least one of ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, and ethylene glycol monobutyl ether; and the silicate is selected from at least one of sodium silicate and potassium silicate.

[0021] Optionally, the alcohol-based multi-effect descaling and cleaning agent for shale oil wells of the present invention may further include the following excipients: bactericides, such as 2-methyl-4-isothiazolin-3-one; filtration loss reducers, such as sodium lignosulfonate; and corrosion inhibitors, such as hexamethylenetetramine.

[0022] This invention also provides a method for preparing the above-mentioned alcohol-based multi-effect descaling and cleaning agent for shale oil wells, comprising the following steps:

[0023] (S1) Under an inert atmosphere, the raw material of the alcohol-based liquid is placed in a reactor equipped with stirring and heating. The mixture is stirred to obtain a homogeneous alcohol-based liquid. The temperature is raised to 40-60℃, and side-chain modified polyether ester is added under stirring conditions. The mixture is stirred evenly and then cooled to obtain liquid A.

[0024] (S2) Organic acid, chelating agent, glycoside surfactant, polyoxyethylene surfactant, and polyvinyl alcohol are added to ethylene glycol mono-C2-4 ether and mixed evenly to obtain solution B;

[0025] (S3) Mix liquid A, liquid B, and silicate evenly, mature, and filter to obtain alcohol-based multi-effect descaling and cleaning agent for shale oil wells.

[0026] Furthermore, uniform mixing is achieved by stirring at a stirring rate of 100-200 rpm. Maturation is carried out under stirring conditions at a constant temperature of 25-30℃ for 1-3 hours. The purpose of maturation is to achieve sufficient interaction between the components and improve product stability. Filtration is carried out by filtering out insoluble matter through a 120-200 mesh filter.

[0027] The alcohol-based multi-effect descaling and cleaning agent provided by this invention solves the pipeline blockage problem caused by organic precipitation such as wax and asphalt in the wellbore, effectively removes wax deposits on the well wall and prevents wax crystals from accumulating and re-depositing, significantly reducing the pour point of high-wax crude oil; it does not require the addition of external wax crystal deforming agents and also has a good anti-waxing effect.

[0028] The alcohol-based multi-effect descaling agent of this invention exhibits good solubility in both water and oil, has a wide range of applications, dissolves wax quickly, and provides good wax prevention. It also demonstrates excellent cleaning and scale prevention effects on inorganic scale. Currently, many oilfields have entered the mid-to-late stages of production, with produced fluids reaching a high water cut level (above 70%). This alcohol-based multi-effect descaling agent can meet the needs of both medium-water-cut (40-60%) and high-water-cut oilfields. Detailed Implementation

[0029] Preparation Example 1

[0030] (T1) Under a nitrogen atmosphere, 1 part by mass of PPG400 was added to the reaction vessel, the temperature was raised to 90°C, and 30 parts by mass of ethylene oxide, 3 parts by mass of allyl glycidyl ether, and 0.03 parts by mass of sodium methoxide were slowly added over 1 hour as a catalyst. After all the materials were added, the temperature was raised to 105°C and the reaction was maintained for 3 hours. The mixture was washed with dilute ammonia and vacuum distilled to obtain a pale yellow transparent liquid, which is a polyether ester with alkenyl side chain.

[0031] (T2) Under a nitrogen atmosphere, 100 parts by mass of side-chain alkenyl polyether ester were added to an alcohol-water solution with a volume ratio of 4:1 for ethanol and water. 0.27 parts by mass of ammonium persulfate initiator were added, and the temperature was raised to 80°C. Over 1 hour, an ethanol solution of a mixture of monomers including 30 parts by mass of acrylic acid, 20 parts by mass of butyl methacrylate, and 4 parts by mass of benzyl acrylate, and 0.27 parts by mass of ammonium persulfate were slowly added. The reaction was maintained at this temperature for 3 hours, then cooled to room temperature and distilled under reduced pressure to obtain an alcohol-water solution of side-chain modified polyether with a solid content of 20%.

[0032] Preparation Example 2

[0033] (T1) Under a nitrogen atmosphere, 1 part by mass of PEG200 was added to the reaction vessel, the temperature was raised to 90°C, and 40 parts by mass of propylene oxide, 5 parts by mass of allyl glycidyl ether, and 0.04 parts by mass of sodium ethoxide were slowly added over 1 hour as a catalyst. After all the materials were added, the temperature was raised to 105°C and the reaction was maintained for 3 hours. The mixture was washed with dilute ammonia and vacuum distilled to obtain a pale yellow transparent liquid, which is a polyether ester with alkenyl side chain.

[0034] (T2) Under a nitrogen atmosphere, 100 parts by mass of side-chain alkenyl polyether ester were added to an alcohol-water solution with a volume ratio of 4:1 for ethanol and water. 0.186 parts by mass of ammonium persulfate initiator were added, and the temperature was raised to 80°C. Over 1 hour, an ethanol solution of a mixture of monomers including 40 parts by mass of acrylic acid, 15 parts by mass of butyl methacrylate, and 6 parts by mass of benzyl acrylate, and 0.434 parts by mass of ammonium persulfate were slowly added. The reaction was maintained at this temperature for 3 hours, then cooled to room temperature and distilled under reduced pressure to obtain an alcohol-water solution of side-chain modified polyether with a solid content of 25%.

[0035] Comparative preparation example

[0036] Under a nitrogen atmosphere, 1 part by mass of PPG400 was added to the reaction vessel, and the temperature was raised to 90°C. Over 1 hour, 30 parts by mass of ethylene oxide and 0.03 parts by mass of sodium methoxide were slowly added as catalysts. After all materials were added, the temperature was raised to 105°C and the reaction was maintained for 3 hours. The mixture was washed with dilute ammonia and vacuum distilled to obtain a pale yellow transparent liquid, which was polyether ester. An alcohol-water solution with a volume ratio of 4:1 was added to prepare a polyether ester solution with a solid content of 20%. Example 1

[0037] (S1) Under a nitrogen atmosphere, 25 kg of ethanol, 3 kg of ethylene glycol, 0.5 kg of PEG1000, 1.9 kg of 2-phenoxyethanol, and 2.2 kg of dodecanol were placed in a reactor equipped with stirring and heating. The mixture was stirred at 150 rpm until homogeneous to obtain an alcohol-based liquid. The temperature was raised to 40°C, and 10 kg of the alcohol-based liquid was taken. 8 kg of the side-chain modified polyether ester solution (solid content 20%) prepared in Preparation Example 1 was added under stirring. The mixture was stirred at 150 rpm until homogeneous and then cooled to obtain liquid A.

[0038] (S2) 0.7 kg of organic acid (a mixture of hydroxyethylidene diphosphate and citric acid in a mass ratio of 2:1), 0.8 kg of chelating agent (a mixture of polyaspartic acid with a number average molecular weight of 1500 and disodium ethylenediaminetetraacetate in a mass ratio of 1:4), 0.3 kg of glycoside surfactant APG0810, 0.5 kg of polyoxyethylene surfactant Tween 20, and 0.2 kg of polyvinyl alcohol (weight average molecular weight of 5000) are added to 2.5 kg of ethylene glycol monobutyl ether and mixed evenly at a stirring speed of 150 rpm to obtain solution B;

[0039] (S3) Mix liquid A, liquid B and 0.2 kg of sodium silicate evenly, and mature at a constant temperature of 25℃ for 3 hours. Filter through a 120-mesh screen to obtain an alcohol-based multi-effect descaling and cleaning agent for shale oil wells. Example 2

[0040] (S1) Under a nitrogen atmosphere, 38 kg of ethanol, 5 kg of ethylene glycol, 1.1 kg of PEG2000, 1.2 kg of 2-phenoxyethanol, and 3.5 kg of n-octanol were placed in a reactor equipped with stirring and heating. The mixture was stirred and mixed evenly to obtain an alcohol-based liquid. The temperature was raised to 40°C, and 10 kg of the alcohol-based liquid was taken. 9.2 kg of the side-chain modified polyether ester solution (solid content 25%) prepared in Preparation Example 2 was added under stirring. The mixture was stirred evenly at a stirring speed of 150 rpm and then cooled to obtain liquid A.

[0041] (S2) 1.1 kg of organic acid (a mixture of hydroxyethylidene diphosphate and citric acid in a mass ratio of 1:1), 0.5 kg of chelating agent (a mixture of polyaspartic acid with a number average molecular weight of 1000 and disodium ethylenediaminetetraacetate in a mass ratio of 1:2), 0.5 kg of glycoside surfactant APG0814, 0.3 kg of polyoxyethylene surfactant NP-10, and 0.3 kg of polyvinyl alcohol (weight average molecular weight of 8000) are added to 3.2 kg of ethylene glycol monobutyl ether and mixed evenly at a stirring speed of 150 rpm to obtain solution B;

[0042] (S3) Mix liquid A, liquid B and 0.3 kg of sodium silicate evenly, and mature at a constant temperature of 25℃ for 3 hours. Filter through a 120-mesh screen to obtain an alcohol-based multi-effect descaling and cleaning agent for shale oil wells. Example 3

[0043] The other conditions are the same as in Example 1, except that the organic acid is hydroxyethylidene diphosphate and the chelating agent is polyaspartic acid. Example 4

[0044] The other conditions are the same as in Example 1, except that the organic acid is citric acid and the chelating agent is disodium ethylenediaminetetraacetate. Comparative Example 1

[0045] The other conditions were the same as in Example 1, except that the side-chain modified polyether ester solution prepared in Example 1 was replaced with an equal mass of the polyether ester solution (20% solid content) prepared in the comparative preparation example. Comparative Example 2

[0046] The other conditions are the same as in Example 1, except that in step (S2), polyvinyl alcohol is replaced with an equal mass of PEG5000.

[0047] Application examples

[0048] The alcohol-based multi-effect descaling and cleaning agents of the above embodiments and comparative examples were subjected to the following performance tests. The alcohol-based multi-effect descaling and cleaning agents and tap water (oilfield reinjection water can be used on site) were mixed at a volume ratio of 1:3 and the following performance tests were conducted.

[0049] 1. Test for wax resistance to organic scale: Add 60g of No. 45 solid paraffin, 40g of No. 80 microcrystalline wax, 240g of No. 0 diesel oil, and 60g of No. -35 diesel oil (as simulated shale crude oil) to each of two 1000mL beakers. Heat to 50℃ to completely dissolve the paraffin. Add 100g of ethanol and 100g of distilled water to each beaker, and stir with a high-speed stirrer for 10 minutes to emulsify. Pour the mixture into two test solution containers. Add 2.00g of a mixture of alcohol-based multi-effect descaling agent and water from the example or comparative example to one test solution container, and stir until homogeneous to obtain the dosing solution. Do not add descaling agent to the other container, serving as a blank solution.

[0050] The wax-coated tube was cleaned successively with petroleum ether, distilled water, and ethanol, dried in a 100°C oven, cooled to room temperature, and weighed to an accuracy of 0.01g. The wax-coated tube was then installed in the measuring device.

[0051] Adjust the sample chamber temperature to maintain the test solution temperature at 50℃; adjust the wax deposition chamber temperature to maintain the wax deposition tube temperature at 50℃. Start the circulation pump and start timing; turn off the circulation pump after 30 minutes. During operation, continuously stir the test solution with a stirrer to ensure homogeneity. Five minutes after turning off the circulation pump, remove the wax deposition tube, allow it to cool to room temperature, and weigh it to an accuracy of 0.01g. Calculate the anti-wax rate F using the following formula:

[0052]

[0053] Where m0 is the amount of wax deposited in the blank sample, in g; and m1 is the amount of wax deposited after adding the descaling agent, in g.

[0054] 2. Test for the wax removal rate of paraffin wax:

[0055] Using a polished N80 steel sheet (mass m0), immerse it in molten liquid wax (a mixture of No. 45 solid paraffin and No. 80 microcrystalline wax in a mass ratio of 6:4). After immersion for 1 second, remove it and dry the wax sample. The mass of the steel sheet with the wax sample attached is recorded as m1. Immerse the steel sheet with paraffin attached in a mixture of alcohol-based multi-effect descaling agent and tap water in a volume ratio of 1:3. Seal and immerse at a constant temperature of 50°C for 1 hour. Remove it, dry it, and test the mass of the steel sheet, recording it as m2. Calculate the wax removal rate T according to the following formula:

[0056]

[0057] 3. Test the descaling rate of inorganic scale.

[0058] Composition analysis was performed on inorganic scale from shale oil wells in the target region. The scale contained 55.15 wt% carbonate, 22.63 wt% aluminosilicate, 11.37% sulfate, and 10.85% other components. Based on this, 55 g of calcium carbonate, 30 g of calcium aluminosilicate, and 15 g of calcium sulfate were mixed to create a simulated inorganic scale. A sample of this simulated inorganic scale (mass m0) was placed in a test tube, and a mixture of 50 times the mass of an alcohol-based multi-effect descaling agent and tap water at a volume ratio of 1:3 was added. The mixture was incubated at 50°C with shaking for 12 hours. After filtration, the solid was washed with anhydrous ethanol, dried, and weighed (mass m1). The descaling rate B was calculated using the following formula:

[0059]

[0060] The test results are shown in Table 1 below.

[0061] Table 1 Performance Tests of Alcohol-Based Multi-Effect Descaling and Cleaning Agents

[0062] project Wax resistance (%) Wax removal rate (%) Descaling rate (%) Example 1 83.4 92.7 86.6 Example 2 81.7 90.5 87.0 Example 3 83.2 92.8 82.6 Example 4 83.4 92.8 83.3 Comparative Example 1 73.4 84.2 80.4 Comparative Example 2 77.1 87.5 84.8

Claims

1. An alcohol-based multi-effect descaling and cleaning agent for shale oil wells, characterized in that, The raw materials comprise the following parts by weight: 100 parts alcohol-based liquid, 16-23 parts side-chain modified polyether ester, 7-11 parts organic acid, 5-8 parts chelating agent, 3-5 parts glycoside surfactant, 3-5 parts polyoxyethylene surfactant, 2-3 parts polyvinyl alcohol, 25-32 parts ethylene glycol mono-C2-4 ether, and 2-3 parts silicate; the side-chain modified polyether ester is obtained by ring-opening polymerization of a polymer initiator, propylene oxide and / or ethylene oxide, and allyl glycidyl ether to obtain an alkenyl-containing polyether ester with a side chain, followed by polymerization of the alkenyl-containing polyether ester with (meth)acrylic acid, (meth)acrylic acid C4-6 alkyl ester, and (meth)acrylic acid benzyl ester; the alcohol-based liquid comprises 60-80 wt% C1-3 monohydric alcohol. In the preparation of side-chain modified polyether esters, the polymeric initiator is selected from polyols with a number average molecular weight of 200-400; the mass ratio of polymeric initiator, propylene oxide and / or ethylene oxide, and allyl glycidyl ether is 1:30-40:3-5; the mass ratio of side-chain alkenyl polyether ester, (meth)acrylic acid, (meth)acrylic acid C4-6 alkyl ester, and (meth)acrylic acid benzyl ester is 100:30-40:15-20:4-6; the alcohol-based liquid comprises the following raw materials in parts by mass: 25-38 parts of C1-3 monohydric alcohol, 3-5 parts of C2-4 polyol, 0.5-1.1 parts of polyol, 1.2-1.9 parts of aromatic alcohol, and 2.2-3.5 parts by mass of C8-12 long-chain alkyl alcohol.

2. The alcohol-based multi-effect descaling and cleaning agent according to claim 1, characterized in that, The (meth)acrylate C4-6 alkyl ester is selected from at least one of (meth)acrylate, (meth)acrylate pentyl ester, and (meth)acrylate hexyl ester.

3. The alcohol-based multi-effect descaling and cleaning agent according to claim 1, characterized in that, The side-chain modified polyether is prepared by a method including the following steps: (T1) Under an inert atmosphere, a polymeric initiator is added to the reaction vessel, the temperature is raised to 80-90℃, propylene oxide and / or ethylene oxide, allyl glycidyl ether and catalyst are added. After all materials are added, the temperature is raised to 105-110℃ and the reaction is maintained for 2-4 hours. The mixture is washed with dilute ammonia water and vacuum distilled to obtain a pale yellow transparent liquid, which is a polyether ester with alkenyl side chain. (T2) Under an inert atmosphere, side-chain alkenyl polyether esters are added to an alcohol-water solution, along with 30-50 wt% of persulfate initiator. The temperature is raised to 60-80°C, and an alcohol solution of a mixture of monomers including (meth)acrylic acid, 4-6 alkyl (meth)acrylic acid, and benzyl (meth)acrylic acid, as well as the remaining persulfate initiator, is slowly added. The reaction is maintained at this temperature for 3-5 hours, then cooled and distilled under reduced pressure to obtain an alcohol-water solution of side-chain modified polyether.

4. The alcohol-based multi-effect descaling and cleaning agent according to claim 1, characterized in that, C1-3 monohydric alcohols are selected from at least one of methanol, ethanol, and isopropanol; C2-4 polyhydric alcohols are selected from at least one of ethylene glycol, 1,3-propanediol, 1,4-butanediol, and glycerol; the polyhydric alcohols are selected from at least one of polyethylene glycol, polypropylene glycol, and polytetrahydrofuran with a number average molecular weight of 1000-2000; the aromatic alcohols are selected from at least one of 2-phenoxyethanol and 2-phenoxypropanol; and C8-12 long-chain alkyl alcohols are selected from at least one of n-octanol, n-nonanol, n-decanol, undecylol, and dodecanol.

5. The alcohol-based multi-effect descaling and cleaning agent according to claim 1, characterized in that, The organic acid is selected from at least one of hydroxyethylidene diphosphate, citric acid, malic acid, oxalic acid, and alkyl lactate; and / or, The chelating agent is selected from at least one of polyaspartic acid, ethylenediaminetetraacetic acid or its salts, and aminotrimethylphosphonic acid; and / or The polyoxyethylene surfactant is selected from at least one of fatty alcohol polyoxyethylene ether, polyoxyethylene nonylphenol ether, polyoxyethylene nonylphenol resin ether, polyoxyethylene sorbitan monooleate, and polyoxyethylene sorbitan monooleate; and / or The glycoside surfactant is selected from at least one of alkyl glucosides, carboxylic acid-modified alkyl glycosides, and alkyl polyglucosides; and / or, The weight-average molecular weight of polyvinyl alcohol is 5000-8000; and / or the ethylene glycol mono-C2-4 ether is selected from at least one of ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, and ethylene glycol monobutyl ether; and / or, The silicate is selected from at least one of sodium silicate and potassium silicate.

6. The alcohol-based multi-effect descaling and cleaning agent according to claim 1, characterized in that, The organic acid is a mixture of hydroxyethylidene diphosphate and citric acid in a mass ratio of 1-2:1, and the chelating agent is a mixture of polyaspartic acid and disodium ethylenediaminetetraacetate in a mass ratio of 1:2-4.

7. The preparation method of the alcohol-based multi-effect descaling and cleaning agent for shale oil wells according to any one of claims 1-6, characterized in that, Includes the following steps: (S1) Under an inert atmosphere, the raw material of the alcohol-based liquid is placed in a reactor equipped with stirring and heating. The mixture is stirred to obtain a homogeneous alcohol-based liquid. The temperature is raised to 40-60℃, and side-chain modified polyether ester is added under stirring conditions. The mixture is stirred evenly and then cooled to obtain liquid A. (S2) Organic acid, chelating agent, glycoside surfactant, polyoxyethylene surfactant, and polyvinyl alcohol are added to ethylene glycol mono-C2-4 ether and mixed evenly to obtain solution B; (S3) Mix liquid A, liquid B, and silicate evenly, mature, and filter to obtain alcohol-based multi-effect descaling and cleaning agent for shale oil wells.