A low-cost salt-resistant chemical cold-extraction viscosity reducer, its preparation method and application

Abstract

This invention discloses a low-cost, salt-resistant chemical viscosity reducer for cold oil recovery, relating to the field of oilfield production technology. The chemical viscosity reducer comprises a block copolymer and silica. The block copolymer is obtained by integrating monomer A containing sulfobetaine groups and monomer B containing tertiary amine groups onto a polystyrene backbone via a reversible addition-fragmentation chain transfer polymerization reaction. The chemical viscosity reducer prepared by this invention simplifies the composition of multi-component viscosity reducers, reduces costs, and also exhibits excellent salt resistance, meeting the needs of cold viscosity reduction in heavy oil recovery in high-salt reservoirs.

Description

Technical Field

[0001] This invention relates to the field of oilfield production technology, specifically to a low-cost salt-resistant chemical cold recovery viscosity reducer, its preparation method, and its application. Background Technology

[0002] Currently, global energy demand is highly dependent on the development of existing fossil fuels. The effective development of heavy oil has a significant impact on global energy supply. Currently, conventional oil reservoirs account for only 30% of the world's oil reservoirs, with the majority being unconventional petroleum products characterized by high viscosity, high density, and poor fluidity, including heavy oil, oil sands, and bitumen. Furthermore, complex reservoir conditions greatly restrict the exploitation and utilization of unconventional petroleum. The key to heavy oil extraction is reducing viscosity and improving fluidity. To this end, various viscosity reduction methods have been developed, such as physical viscosity reduction, microbial viscosity reduction, and chemical viscosity reduction. Chemical viscosity reducers, as important extraction aids, have been widely used in the thermal recovery of heavy oil. However, with the continuous extraction of heavy oil from deep wells, traditional viscosity reduction methods, primarily based on steam injection, face problems such as high injection cycles, high energy consumption, high cost, low thermal efficiency, and low recovery rates. Therefore, developing chemical cold-process viscosity reducers that can adapt to non-steam injection is of great significance for achieving low-energy and high-efficiency extraction of heavy oil.

[0003] Currently, in the cold production of heavy oil, the relatively high salinity of reservoir water severely limits the emulsification and viscosity-reducing performance of chemical viscosity reducers. Emulsification viscosity reduction technology mainly involves injecting a surfactant solution into the wellbore to transform the high-viscosity crude oil from a water-in-oil emulsion to an oil-in-water emulsion, thereby reducing the viscosity of heavy oil and improving oil production efficiency.

[0004] In the prior art, patent CN102618239A discloses a salt- and temperature-resistant heavy oil emulsifying viscosity reducer, which is composed of 13 chemical agents, including anionic surfactants, nonionic-anionic surfactants, and nonionic surfactants. Although it has good salt resistance and temperature resistance, the formula is too complex, and the coexistence of multiple surfactants leads to a "chromatographic effect." In pilot tests, the actual application effect for chemical cold recovery was not ideal, and the addition of a large number of chemical agents brought great difficulties to the subsequent treatment of oilfield water and the refining and processing of heavy oil. CN114716992B discloses a salt- and temperature-resistant heavy oil emulsifying viscosity reducer and its preparation method. The emulsifying viscosity reducer is composed of polyethylene glycol, sulfopropyl polyoxyethylene dodecyl alcohol ether, and oleic acid amide hydroxysulfonyl betaine. The salt resistance of the system is improved by compounding anionic surfactants with betaine surfactants. CN112442350B discloses a viscosity reducer for heavy oil cold production huff and puff, its preparation method, and its application. The viscosity reducer is obtained by combining a copolymer of acrylamide and silicone-containing acrylate with fatty acid polyethylene ether sulfonate and betaine-based surfactants, achieving a viscosity reduction rate of up to 90.07%. The aforementioned patent only uses sulfobetaine in heavy oil viscosity reduction through mixing, resulting in a viscosity reducer product with poor stability and lacking rheological adjustment capabilities. CN115895634A discloses a heavy oil viscosity reducer composition and its preparation method. The combination of a low molecular weight amphiphilic polymer and a nano-hydrophobic modified material enhances the viscosity reduction effect. The nano-hydrophobic modified material is obtained by modifying nano-silica. However, the aforementioned patent uses hydrophobic silica, which is insoluble in water and can be dispersed into the network structure of the asphaltene in heavy oil, thus dispersing the heavy oil. At the same time, the aforementioned patent does not consider the impact of high formation salinity on the performance of viscosity reducers. High salinity conditions can easily cause polymer viscosity reducers to fail, and the use of hydrophobic materials is difficult to dissolve in water, which brings new challenges to the current chemical waterflooding extraction technology and makes practical application difficult.

[0005] Therefore, it is essential to develop a low-cost viscosity reducer with good salt resistance and viscosity-reducing properties for heavy oil chemical cold recovery. Summary of the Invention

[0006] To address the aforementioned limitations of existing technologies, the present invention aims to provide a low-cost, salt-resistant chemical cold production viscosity reducer, its preparation method, and its applications. The present invention integrates monomers containing sulfobetaine groups and monomers containing tertiary amine groups onto a polystyrene backbone via a reversible addition-fragmentation chain transfer polymerization reaction to obtain a block copolymer. This block copolymer is then compounded with water-soluble nano-silica to obtain the low-cost, salt-resistant chemical cold production viscosity reducer. The chemical cold production viscosity reducer prepared by this invention simplifies the composition of multi-component viscosity reducers, reduces costs, and exhibits excellent salt resistance, thus meeting the needs of cold production viscosity reduction in heavy oil reservoirs with high salinity.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A first aspect of the present invention provides a method for preparing a block copolymer, comprising the following steps:

[0009] (1) Mix 1,3-propanesulfonate lactone, 4-vinylphenyl-N,N-dimethylamine and butylhydroxymethylbenzene, dissolve them in acetonitrile and react them. Filter the reaction product, collect the precipitate and wash it to obtain monomer A containing sulfobetaine group.

[0010] (2) After mixing dimethylamine solution, 4-vinylbenzyl chloride, potassium carbonate and methanol, the reaction was carried out. After the reaction was completed, the mixture was filtered to obtain the filtrate. After purifying the filtrate, monomer B containing tertiary amine group was obtained.

[0011] (3) After mixing monomer A, chain transfer agent and free radical initiator, dissolve them in a mixed solvent and react. Dialyze the reaction product and dry it to obtain a macromolecular chain transfer agent.

[0012] (4) After mixing the macromolecular chain transfer agent, free radical initiator and monomer B, the mixture is dissolved in trifluoroethanol and reacted. The reaction product is dialyzed and dried to obtain the block copolymer.

[0013] Preferably, in step (1), the ratio of the amount of 1,3-propanesulfonate lactone, 4-vinylphenyl-N,N-dimethylamine, butylhydroxymethylbenzene and acetonitrile added is (40-43) mmol: (30-35) mmol: (1.2-1.5) mmol: 200 mL.

[0014] Preferably, in step (1), the reaction temperature is 40-60℃ and the reaction time is 20-30h.

[0015] Preferably, in step (1), the washing operation is: washing the precipitate 2-3 times with tetrahydrofuran.

[0016] Preferably, in step (2), the concentration of the dimethylamine solution is 40 wt%.

[0017] Preferably, in step (2), the ratio of the amount of dimethylamine solution, 4-vinylbenzyl chloride, potassium carbonate and methanol added is (20-25) mL: (95-105) mmol: (40-45) g: 200 mL.

[0018] Preferably, in step (2), the filtrate purification operation is as follows: the filtrate is placed under vacuum to remove methanol to obtain crude product; then the crude product is purified by passing it through a silica gel column using a mobile phase.

[0019] More preferably, the mobile phase is a mixture of n-hexane and dichloromethane in a volume ratio of 3:1.

[0020] Preferably, in step (2), the reaction temperature is 60-70℃ and the reaction time is 20-30h.

[0021] Preferably, the chain transfer agent is 4-cyano-4-[(dodecylthioalkylthiocarbonyl)thioalkyl]valerate, and the free radical initiator is 4,4'-azo(4-cyanopentanoic acid).

[0022] Preferably, in step (3), the mixed solvent is a mixture of trifluoroethanol and methanol in a volume ratio of (9-11):1.

[0023] Preferably, in step (3), the ratio of monomer A, chain transfer agent, free radical initiator and mixed solvent is (10-10.5) mmol: (0.15-0.20) mmol: (0.015-0.020) mmol: (5-6) mL.

[0024] Preferably, in step (3), the reaction conditions are as follows: after degassing the mixed solution, nitrogen gas is bubbled in, ice bath treatment is performed for 20-30 min, the temperature is raised to 65-70℃, the reaction is carried out for 16-24 h, and the reaction is quenched by exposing it to air under liquid nitrogen conditions.

[0025] Preferably, in step (3), the drying is freeze drying, the freeze drying temperature is -30℃, and the freeze drying time is 24h.

[0026] Preferably, in step (4), the mass ratio of the macromolecular chain transfer agent, the free radical initiator, and monomer B is 1:(0.3-0.4):(20-60).

[0027] Preferably, in step (4), the concentration of monomer B in trifluoroethanol is 0.25-0.50 mol / L.

[0028] Preferably, in step (4), the reaction conditions are as follows: after degassing the mixed solution, nitrogen gas is bubbled in, ice bath treatment is performed for 20-30 min, the temperature is raised to 65-70℃, the reaction is carried out for 16-24 h, and the reaction is quenched by exposing it to air under liquid nitrogen conditions.

[0029] Preferably, in step (4), the reaction product is dialyzed in methanol and water.

[0030] Preferably, in step (4), the drying is freeze drying, the freeze drying temperature is -30°C, and the freeze drying time is 24 h.

[0031] In a second aspect, the present invention provides a block copolymer.

[0032] A third aspect of the invention provides the use of block copolymers in the preparation of salt-resistant chemical cold-harvesting viscosity reducers.

[0033] In a fourth aspect, the present invention provides a salt-resistant chemical cold-harvesting viscosity reducer comprising a block copolymer and silica.

[0034] Preferably, in the salt-resistant chemical cold mining viscosity reducer, the mass fraction of the block copolymer is 0.05-0.15%, and the mass fraction of silica is 0.05-2.0%.

[0035] Preferably, the silica is water-soluble nano-silica with a particle size of 160-240 nm.

[0036] A fifth aspect of the present invention provides a method for preparing a low-cost salt-resistant chemical cold-harvesting viscosity reducer, comprising the following steps:

[0037] After the block copolymer is mixed evenly with silica, it is dissolved in water to obtain a low-cost salt-resistant chemical cold mining viscosity reducer.

[0038] A sixth aspect of the present invention provides the application of chemical cold-extraction viscosity reducers in heavy oil viscosity reduction.

[0039] The beneficial effects of this invention are:

[0040] This invention integrates monomers containing sulfobetaine groups and monomers containing tertiary amine groups onto a polystyrene backbone via a reversible addition-fragmentation chain transfer polymerization reaction, yielding a block copolymer. The molecular weight, solubility, and salt resistance of the block copolymer can be controlled by adjusting the monomer ratio. The block copolymer only needs to be compounded with water-soluble nano-silica to achieve emulsification and viscosity reduction of heavy oil, simplifying the composition of traditional multi-component viscosity reducers. The chemical cold-production viscosity reducer of this invention exhibits excellent salt resistance and low application cost, meeting the needs of cold-production viscosity reduction in heavy oil reservoirs with high salinity.

[0041] Block copolymers can effectively emulsify heavy oil under high salinity conditions to form low-viscosity oil-in-water emulsions. Water-soluble silica can form well-compatible and stable Pickerlinger emulsions with block copolymers in aqueous solutions, maintaining excellent salt resistance while reducing the cost of pure polymers.

[0042] In Na + Mg 2+ Ca 2+ Al 3+In the presence of ions, both monomers A and B are charged groups. Their high charge density effectively suppresses the strong electrostatic interaction between the block polymer chains and salt ions, allowing the polymer solution system to maintain its inherent viscoelasticity and spatially extended structure. On the other hand, the rigid benzene ring structure of monomer B increases steric hindrance between emulsions, making aggregation less likely and weakening the electrostatic neutralization effect of salt ions on the surface potential of the heavy oil emulsion. This achieves the dual purpose of enhanced salt resistance and viscosity reduction. Attached Figure Description

[0043] Figure 1 Example 1: GPC molecular weight distribution of the block copolymer;

[0044] Figure 2 Example 1: TGA thermogravimetric curve of the block copolymer. Detailed Implementation

[0045] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0046] As described in the background section, the existing salt-resistant viscosity reducers have complex formulations and contain multiple surfactants, which do not provide ideal results for actual chemical cold extraction applications. Furthermore, the addition of large amounts of chemical agents poses significant challenges to the subsequent treatment of oilfield water and the refining and processing of heavy oil.

[0047] Based on this, this application provides a low-cost, salt-resistant chemical cold production viscosity reducer, its preparation method, and its application. This invention integrates monomers containing sulfobetaine groups and monomers containing tertiary amine groups onto a polystyrene backbone via a reversible addition-fragmentation chain transfer polymerization reaction to obtain a block copolymer. The block copolymer is then compounded with water-soluble nano-silica to obtain a low-cost, salt-resistant chemical cold production viscosity reducer. The chemical cold production viscosity reducer prepared by this invention simplifies the composition of multi-component viscosity reducers, reduces costs, and also exhibits excellent salt resistance, meeting the needs of cold production viscosity reduction in heavy oil reservoirs with high salinity.

[0048] From a cost perspective, CN102618239A uses a compound of 13 surfactants to obtain a viscosity reducer, and its emulsification viscosity reducer has a cost of 20,000-23,000 yuan / ton, while the chemical cold mining viscosity reducer obtained by this invention has a cost of only 9,000-11,000 yuan / ton. Therefore, this invention saves approximately 50% in costs.

[0049] This invention utilizes a combination of block copolymers and water-soluble silica to prepare a salt-resistant chemical cold-production viscosity reducer. The block copolymer has a large molecular weight and possesses both surface activity and the structural characteristics of a high-molecular-weight polymer, thus enhancing the stability of the viscosity reducer. Its aqueous solution exhibits certain viscosity and rheological regulation capabilities, which are crucial for reducing the water-oil two-phase mobility ratio and improving the sweep efficiency of the chemical displacement fluid in the formation. Water-soluble silica, compared to hydrophobic silica, has different applicable solvent systems. Hydrophobic silica, being insoluble in water, can disperse in the network structure of the asphaltenes in heavy oil, thus dispersing the heavy oil. Water-soluble silica, being soluble in water, has good compatibility with water-soluble polymers, thus emulsifying the heavy oil.

[0050] Meanwhile, this invention obtains block copolymers with larger molecular weights by integrating monomers A and B onto the polystyrene backbone. The larger the molecular weight of the polymer, the higher the stability of the resulting heavy oil emulsion. The viscosity reduction rate of the viscosity reducer is less affected by the polymer molecular weight, but the salt resistance is significantly enhanced. Furthermore, the polymer molecular chains intertwine in water, forming a random spatial structure with weak intermolecular forces. Intermolecular forces and hydrogen bonding between molecular chains are among the factors contributing to the excellent rheological properties of polymers. Both monomers A and B are charged groups, and their high charge density effectively suppresses the strong electrostatic interaction between the block polymer chains and salt ions. The polymer solution system can maintain its inherent viscoelasticity and spatially extended structure. Monomer B also increases the steric hindrance between emulsions, making aggregation less likely and weakening the electrostatic neutralization effect of salt ions on the surface potential of the heavy oil emulsion.

[0051] To enable those skilled in the art to better understand the technical solution of this application, the technical solution of this application will be described in detail below with reference to specific embodiments.

[0052] The test materials used in the embodiments of this invention are all conventional test materials in the art and can be purchased through commercial channels.

[0053] Example 1: Preparation of Block Copolymers

[0054] (1) Mix 41 mmol of 1,3-propanesulfonate lactone, 34 mmol of 4-vinylphenyl-N,N-dimethylamine and 1.4 mmol of butylhydroxymethylbenzene, dissolve in 200 mL of acetonitrile, react at 50 °C for 24 h, cool to room temperature, filter the reaction product, collect the precipitate, wash the precipitate three times with tetrahydrofuran to obtain monomer A containing sulfobetaine group;

[0055] (2) Mix 22 mL of 40 wt% dimethylamine solution, 100 mmol of 4-vinylbenzyl chloride, 41 g of potassium carbonate and 200 mL of methanol, and react at 65 °C for 24 h. After the reaction is complete, filter to obtain filtrate. Remove methanol from filtrate under vacuum to obtain crude product. Then purify crude product by passing it through a silica gel column using a mobile phase composed of n-hexane and dichloromethane in a volume ratio of 3:1 to obtain monomer B containing tertiary amine group.

[0056] (3) Mix 10.2 mmol monomer A, 0.17 mmol 4-cyano-4-[(dodecylthioalkylthiocarbonyl)thioalkyl]valeric acid and 0.017 mmol 4,4'-azo (4-cyanopentanoic acid) and dissolve them in 5.5 mL of mixed solvent to obtain a mixed solution. The mixed solvent is composed of trifluoroethanol and methanol in a volume ratio of 10:1. After degassing the mixed solution, nitrogen gas is bubbled in, and the mixture is treated in an ice bath for 25 min. The temperature is raised to 70 °C and the reaction is carried out for 20 h. The reaction is quenched by exposing the mixture to air under liquid nitrogen conditions. The reaction product is dialyzed to obtain dialysate. The dialysate is freeze-dried to obtain a macromolecular chain transfer agent.

[0057] (4) The macromolecular chain transfer agent, 4,4'-azo (4-cyanopentanoic acid) and monomer B are mixed in a mass ratio of 1:0.33:20 and dissolved in trifluoroethanol until the concentration of monomer B is 0.4 mol / L to obtain a mixed solution. After degassing the mixed solution, nitrogen gas is bubbled in and the mixture is treated in an ice bath for 25 min. The temperature is raised to 70 °C and the reaction is carried out for 20 h. The reaction is quenched by exposing the mixture to air under liquid nitrogen conditions. The reaction product is dialyzed in methanol and water to obtain dialysate. The dialysate is freeze-dried to obtain a pale yellow block copolymer.

[0058] The structural characterization of the block copolymer in this embodiment is as follows: Figure 1-2 As shown, by Figure 1 It can be seen that the molecular weight of the obtained block copolymer is 33.9 kDa, which is derived from... Figure 2 It can be seen that the decomposition temperature of the block copolymer is above 350℃, which shows that it has good thermal stability.

[0059] Example 2: Preparation of Block Copolymers

[0060] (1) Dissolve 40 mmol of 1,3-propanesulfonate lactone, 30 mmol of 4-vinylphenyl-N,N-dimethylamine and 1.2 mmol of butylhydroxymethylbenzene in 200 mL of acetonitrile and react at 40 °C for 24 h. Filter the reaction product, collect the precipitate, and wash the precipitate twice with tetrahydrofuran to obtain monomer A containing sulfobetaine group;

[0061] (2) Mix 20 mL of 40 wt% dimethylamine solution, 95 mmol of 4-vinylbenzyl chloride, 40 g of potassium carbonate and 200 mL of methanol, and react at 60 °C for 20 h. After the reaction is complete, filter to obtain filtrate. Remove methanol from filtrate under vacuum to obtain crude product. Then purify crude product by passing it through a silica gel column using a mobile phase composed of n-hexane and dichloromethane in a volume ratio of 3:1 to obtain monomer B containing tertiary amine group.

[0062] (3) Mix 10 mmol monomer A, 0.15 mmol 4-cyano-4-[(dodecylthioalkylthiocarbonyl)thioalkyl]valeric acid and 0.015 mmol 4,4'-azo (4-cyanopentanoic acid) and dissolve them in 5 mL of mixed solvent to obtain a mixed solution. The mixed solution is prepared by mixing trifluoroethanol and methanol in a volume ratio of 9:1. After degassing the mixed solution, nitrogen gas is bubbled in, and the mixture is treated in an ice bath for 20 min. The temperature is raised to 65 °C and the reaction is carried out for 16 h. The reaction is quenched by exposing the mixture to air under liquid nitrogen conditions. The reaction product is dialyzed to obtain dialysate. The dialysate is freeze-dried to obtain a macromolecular chain transfer agent.

[0063] (4) The macromolecular chain transfer agent, 4,4'-azo (4-cyanopentanoic acid) and monomer B are mixed in a mass ratio of 1:0.3:40 and dissolved in trifluoroethanol until the concentration of monomer B is 0.4 mol / L to obtain a mixed solution. After degassing the mixed solution, nitrogen gas is bubbled in and the mixture is treated in an ice bath for 20 min. The temperature is raised to 65 °C and the reaction is carried out for 16 h. The reaction is quenched by exposing the mixture to air under liquid nitrogen conditions. The reaction product is dialyzed in methanol and water to obtain dialysate. The dialysate is freeze-dried to obtain the block copolymer.

[0064] Example 3: Preparation of Block Copolymers

[0065] (1) 43 mmol of 1,3-propanesulfonate lactone, 35 mmol of 4-vinylphenyl-N,N-dimethylamine and 1.5 mmol of butylhydroxymethylbenzene were dissolved in 200 mL of acetonitrile and reacted at 60 °C for 30 h. The reaction product was filtered, the precipitate was collected, and the precipitate was washed twice with tetrahydrofuran to obtain monomer A containing sulfobetaine group.

[0066] (2) Mix 25 mL of 40 wt% dimethylamine solution, 105 mmol of 4-vinylbenzyl chloride, 45 g of potassium carbonate and 200 mL of methanol, and react at 70 °C for 30 h. After the reaction is complete, filter to obtain filtrate. Remove methanol from filtrate under vacuum to obtain crude product. Then purify crude product by passing it through a silica gel column using a mobile phase composed of n-hexane and dichloromethane in a volume ratio of 3:1 to obtain monomer B containing tertiary amine group.

[0067] (3) Mix 10.5 mmol monomer A, 0.20 mmol 4-cyano-4-[(dodecylthioalkylthiocarbonyl)thioalkyl]valeric acid and 0.020 mmol 4,4'-azo (4-cyanopentanoic acid) and dissolve them in 6 mL of mixed solvent to obtain a mixed solution. The mixed solvent is composed of trifluoroethanol and methanol in a volume ratio of 11:1. After degassing the mixed solution, nitrogen gas is bubbled in, and the mixture is treated in an ice bath for 30 min. The temperature is raised to 68 °C and the reaction is carried out for 24 h. The reaction is quenched by exposing the mixture to air under liquid nitrogen conditions. The reaction product is dialyzed to obtain dialysate. The dialysate is freeze-dried to obtain a macromolecular chain transfer agent.

[0068] (4) The macromolecular chain transfer agent, 4,4'-azo (4-cyanopentanoic acid) and monomer B are mixed in a mass ratio of 1:0.4:25 and dissolved in trifluoroethanol until the concentration of monomer B is 0.4 mol / L to obtain a mixed solution. After degassing the mixed solution, nitrogen gas is bubbled in and the mixture is treated in an ice bath for 30 min. The temperature is raised to 68°C and the reaction is carried out for 24 h. The reaction is quenched by exposing the mixture to air under liquid nitrogen conditions. The reaction product is dialyzed in methanol and water to obtain dialysate. The dialysate is freeze-dried to obtain the block copolymer.

[0069] Example 4: Preparation of Salt-Resistant Chemical Cold Harvesting Viscosity Reducer

[0070] The block copolymer obtained in Example 1 was mixed evenly with water-soluble nano silica particles with an average particle size of 220 nm and then dissolved in water to obtain a chemical cold mining viscosity reducer. In the chemical cold mining viscosity reducer, the mass fraction of the block copolymer was 0.05% and the mass fraction of the water-soluble nano silica particles was 0.10%.

[0071] Example 5: Preparation of Salt-Resistant Chemical Cold Harvesting Viscosity Reducer

[0072] The difference between this embodiment and Embodiment 4 is that the mass fraction of the block copolymer and the mass fraction of the water-soluble nano silica particles in the chemical cold-extraction viscosity reducer are 0.05%.

[0073] Example 6: Preparation of Salt-Resistant Chemical Cold Harvesting Viscosity Reducer

[0074] The difference between this embodiment and Embodiment 4 is that the block copolymer has a mass fraction of 0.1% and the water-soluble nano silica particles have a mass fraction of 0.15% in the chemical cold-extraction viscosity reducer.

[0075] Example 7: Preparation of Salt-Resistant Chemical Cold Harvesting Viscosity Reducer

[0076] The difference between this embodiment and Embodiment 4 is that the mass fraction of the block copolymer and the mass fraction of the water-soluble nano silica particles in the chemical cold-extraction viscosity reducer are 0.15%.

[0077] Example 8: Preparation of Salt-Resistant Chemical Cold Harvesting Viscosity Reducer

[0078] 2. Preparation method:

[0079] The block copolymer obtained in Example 2 was mixed evenly with water-soluble nano silica particles with an average particle size of 160 nm and then dissolved in water to obtain a chemical cold mining viscosity reducer. In the chemical cold mining viscosity reducer, the mass fraction of the block copolymer was 0.10% and the mass fraction of the water-soluble nano silica particles was 0.05%.

[0080] Example 9: Preparation of Salt-Resistant Chemical Cold Harvesting Viscosity Reducer

[0081] The block copolymer obtained in Example 3 was mixed evenly with water-soluble nano silica particles with an average particle size of 240 nm and then dissolved in water to obtain a chemical cold mining viscosity reducer. In the chemical cold mining viscosity reducer, the mass fraction of the block copolymer was 0.15% and the mass fraction of the water-soluble nano silica particles was 2.0%.

[0082] Comparative Example 1:

[0083] The difference between this comparative example and Example 4 is that the block copolymer is prepared by the following steps:

[0084] Monomer A, 4-cyano-4-[(dodecylthioalkylthiocarbonyl)thioalkyl]valeric acid, and 4,4'-azo (4-cyanopentanoic acid) were mixed and dissolved in a mixed solvent of trifluoroethanol and methanol at a volume ratio of 10:1 to obtain a mixed solution. The preparation method of monomer A was the same as in Example 1. The ratio of monomer A, 4-cyano-4-[(dodecylthioalkylthiocarbonyl)thioalkyl]valeric acid, and 4,4'-azo (4-cyanopentanoic acid) to the mixed solvent was 10.2 mmol: 0.17 mmol: 0.017 mmol: 5.5 mL. After degassing the mixed solution, nitrogen gas was bubbled in, and the mixture was treated in an ice bath for 25 min. The temperature was raised to 70 °C and the reaction was carried out for 20 h. The reaction was quenched by exposure to air under liquid nitrogen conditions. The reaction product was dialyzed to obtain a dialysate. The dialysate was freeze-dried to obtain a block copolymer.

[0085] Comparative Example 2:

[0086] The difference between this comparative example and Example 4 is that the block copolymer is prepared by the following steps:

[0087] (1) 4-cyano-4-[(dodecylthioalkylthiocarbonyl)thioalkyl]valeric acid, 4,4'-azo (4-cyanovaleric acid) and monomer B were mixed in a mass ratio of 1:0.33:20 and dissolved in trifluoroethanol until the concentration of monomer B was 0.4 mol / L to obtain a mixed solution. The mixed solution was degassed and then purged with nitrogen gas. The mixture was treated in an ice bath for 25 min, heated to 70 °C, and reacted for 20 h. The reaction was quenched by exposing the mixture to air under liquid nitrogen conditions. The reaction product was dialyzed in methanol and water to obtain a dialysate. The dialysate was freeze-dried to obtain a pale yellow block copolymer.

[0088] Comparative Example 3:

[0089] The difference between this comparative example and Example 4 is that the chemical cold-drilling viscosity reducer only includes the block copolymer prepared in Example 1, and the mass fraction of the block copolymer in the chemical cold-drilling viscosity reducer is 0.05%.

[0090] Comparative Example 4:

[0091] The difference between this comparative example and Example 4 is that the chemical cold mining viscosity reducer only includes water-soluble nano silica particles with an average particle size of 220 nm, and the mass fraction of water-soluble nano silica particles in the chemical cold mining viscosity reducer is 0.10%.

[0092] Test Example 1: Salt Resistance Viscosity Reduction Test

[0093] The viscosity reducers prepared in Examples 4-8 and Comparative Examples 1-4 were subjected to salt resistance viscosity reduction tests, and the specific steps are as follows:

[0094] (1) Prepare a salt concentration of 5.0 × 10⁻⁶. 4 A simulated salt solution with a concentration of mg / L was prepared, and the composition of the simulated salt solution is shown in Table 1.

[0095] Table 1 Composition of simulated salt solutions

[0096]

[0097] (2) Add dehydrated and degassed heavy oil with an initial viscosity of 4850 mPa·s to the prepared simulated salt solution, wherein the oil-water volume ratio of the dehydrated and degassed heavy oil is controlled at 3:7.

[0098] Then, equal amounts of the viscosity reducers prepared in Examples 4-8 and Comparative Examples 1-4 were added, and the mixture was placed in a homogenizer and stirred at 2000 rpm for 1 minute. After standing in a 50℃ water bath for 2 hours, the emulsion viscosity of the heavy oil was measured. The average value of the three measurements was taken, and the viscosity reduction rate R (%) was calculated. The results are shown in Table 2.

[0099] Where R = [(μ0 - μ) / μ0] × 100%

[0100] μ 0 (mPa·s) Initial viscosity of heavy oil;

[0101] μ (mPa·s) Apparent viscosity after standing for 2 hours.

[0102] Table 2. Viscosity Reduction Rate of Viscosity Reducers in Heavy Oil Emulsification

[0103]

[0104] As shown in Table 2, the viscosity reducer obtained by combining the block copolymer obtained by integrating monomers A and B into the polystyrene backbone with water-soluble silica, as described in this invention, achieves a viscosity reduction rate of up to 96.8%. Furthermore, the viscosity reduction rate gradually increases with the increasing mass fractions of the block copolymer and water-soluble silica in the viscosity reducer. In contrast, the viscosity reducers prepared in Comparative Examples 1-4 only achieved a maximum viscosity reduction rate of 84.4%. Therefore, this invention, by combining the block copolymer obtained by integrating monomers A and B into the polystyrene backbone with water-soluble silica, significantly improves the emulsification viscosity reduction effect and salt resistance of the viscosity reducer.

[0105] Test Example 2: Salt Resistance Oil Displacement Test

[0106] The viscosity reducers prepared in Examples 4-8 and Comparative Examples 1-4 were subjected to salt-resistance oil displacement tests. The specific steps are as follows:

[0107] (1) Using the sand-filled pipe flooding model to simulate the formation environment, firstly, mineralized water is used to drive the oil until the produced fluid does not contain crude oil, and the recovery rate η0 of the initial water flooding stage is calculated.

[0108] Where η0 = V1 / V0 × 100%.

[0109] V1 - Volume of extracted oil, in mL;

[0110] V0 - The initial volume of saturated oil, in mL;

[0111] (2) Add equal amounts of the viscosity reducers prepared in Examples 4-8 and Comparative Examples 1-4 respectively, and age them at 50°C in a simulated salt solution for 3 days. The simulated salt solution is the same as in Experiment 1. Water flooding is performed again until the produced fluid does not contain crude oil. The average value is taken after three measurements to calculate the recovery rate of the chemical flooding stage. η (%), and then the total recovery rate was calculated, and the results are shown in Table 3.

[0112] Where η = V1 / V0 × 100%.

[0113] V1 - Volume of extracted oil, in mL;

[0114] V0 - The initial volume of saturated oil, in mL;

[0115] Total recovery rate = η0 + η.

[0116] Table 3. Chemical flooding to enhance oil recovery using viscosity reducers.

[0117]

[0118] The initial waterflooding stage recovery rate represents the ease with which pure water can be used to displace heavy oil in the test unit. A higher value indicates that the heavy oil is easier to extract, and this does not involve the properties of the viscosity reducer. The chemical flooding stage recovery rate represents the ability of the viscosity reducer to improve the recovery rate; a higher value indicates a better extraction effect of the viscosity reducer. As shown in Table 3, the chemical cold-flooding viscosity reducer prepared in this invention achieves a maximum chemical flooding stage recovery rate of 40.6%, while the viscosity reducers prepared in Comparative Examples 1-4 only achieve a maximum chemical flooding stage recovery rate of 12.4%. This demonstrates that the chemical cold-flooding viscosity reducer prepared in this invention possesses excellent salt resistance and oil displacement performance.

[0119] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for preparing a block copolymer, characterized in that, Includes the following steps: (1) Mix 1,3-propanesulfonate lactone, 4-vinylphenyl-N,N-dimethylamine and butylhydroxymethylbenzene, dissolve them in acetonitrile and react them. Filter the reaction product, collect the precipitate and wash it to obtain monomer A containing sulfobetaine group. (2) After mixing dimethylamine solution, 4-vinylbenzyl chloride, potassium carbonate and methanol, the reaction was carried out. After the reaction was completed, the mixture was filtered to obtain the filtrate. After purifying the filtrate, monomer B containing tertiary amine group was obtained. (3) After mixing monomer A, chain transfer agent and free radical initiator, dissolve them in a mixed solvent and react. Dialyze the reaction product and dry it to obtain a macromolecular chain transfer agent; wherein, the ratio of monomer A, chain transfer agent, free radical initiator and mixed solvent is (10-10.5) mmol: (0.15-0.20) mmol: (0.015-0.020) mmol: (5-6) mL; (4) After mixing the macromolecular chain transfer agent, free radical initiator and monomer B, the mixture is dissolved in trifluoroethanol and reacted. The reaction product is dialyzed and dried to obtain a block copolymer. The mass ratio of the macromolecular chain transfer agent, free radical initiator and monomer B is 1:(0.3-0.4):(20-60).

2. The method for preparing the block copolymer according to claim 1, characterized in that, In step (1), the ratio of the amount of 1,3-propanesulfonate lactone, 4-vinylphenyl-N,N-dimethylamine, butylhydroxymethylbenzene and acetonitrile added is (40-43) mmol: (30-35) mmol: (1.2-1.5) mmol: 200 mL; the reaction temperature is 40-60℃ and the reaction time is 20-30 h.

3. The method for preparing the block copolymer as described in claim 1, characterized in that, In step (2), the ratio of the amount of dimethylamine solution, 4-vinylbenzyl chloride, potassium carbonate and methanol added is (20-25) mL: (95-105) mmol: (40-45) g: 200 mL; the concentration of the dimethylamine solution is 40 wt%; the reaction temperature is 60-70℃ and the reaction time is 20-30 h.

4. The method for preparing the block copolymer according to claim 1, characterized in that, In step (3), the chain transfer agent is 4-cyano-4-[(dodecylthioalkylthiocarbonyl)thioalkyl]valerate, and the free radical initiator is 4,4'-azo(4-cyanovaleric acid); the mixed solvent is a mixture of trifluoroethanol and methanol in a volume ratio of (9-11):

1.

5. The method for preparing the block copolymer according to claim 1, characterized in that, In step (4), the concentration of monomer B in trifluoroethanol is 0.25-0.50 mol / L; the reaction conditions are: after degassing the mixed solution, nitrogen gas is bubbled in, ice bath treatment is performed for 20-30 min, the temperature is raised to 65-70℃, the reaction is carried out for 16-24 h, and the reaction is quenched by exposing it to air under liquid nitrogen conditions.

6. The block copolymer prepared by the preparation method according to any one of claims 1-5.

7. The use of the block copolymer of claim 6 in the preparation of a salt-resistant chemical cold mining viscosity reducer.

8. A salt-resistant chemical cold-harvesting viscosity reducer, characterized in that, The chemical cold-extraction viscosity reducer comprises the block copolymer as described in claim 6 and silica, wherein the mass fraction of the block copolymer in the chemical cold-extraction viscosity reducer is 0.05-0.15%, the mass fraction of silica is 0.05-2.0%, and the silica is water-soluble nano silica with a particle size of 160-240 nm.

9. The preparation method of the salt-resistant chemical cold-harvesting viscosity reducer according to claim 8, characterized in that, Includes the following steps: After the block copolymer is mixed evenly with silica, it is dissolved in water to obtain a salt-resistant chemical cold mining viscosity reducer.

10. The application of the salt-resistant chemical cold-extraction viscosity reducer according to claim 8 in heavy oil viscosity reduction.

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