High-strength low-molecular polymer gel system, preparation method therefor and use thereof

Abstract

Provided in the present invention are a high-strength low-molecular polymer gel system, a preparation method therefor and the use thereof. Raw materials of the polymer gel system comprise: 4-6% of a polymer emulsion, 0.4-0.8% of a phenolic cross-linking agent, 0-0.3% of a catalyst, 0.2-0.5% of an oxygen scavenger and 0.2-0.4% of a stabilizer, with the balance being water. The polymer emulsion is formed by copolymerizing an acrylamide monomer and a sodium p-styrenesulfonate monomer. The polymer gel plugging agent system disclosed by the present invention has good injectivity in the medium and deep portions of strata, and the polymer gel has high gel forming strength and large elasticity modulus after gelling and can improve the steam channeling plugging effect for heavy oil reservoirs.

Description

A high-strength low-molecular polymer jelly system and its preparation method and application

[0001] Cross-reference information

[0002] This application claims priority to the Chinese patent application filed with the China Patent Office on February 4, 2024, with application number 202410157119.3 and invention name “A high-strength low-molecular polymer jelly system, its preparation method and application”, the entire contents of which are incorporated into this application by reference. Technical Field

[0003] The invention belongs to the field of oilfield chemistry, and particularly relates to a high-strength low-molecular polymer jelly system and a preparation method and application thereof. Background Art

[0004] The main development methods for heavy oil reservoirs are steam flooding and steam stimulation. However, heavy oil reservoirs are characterized by complex geological structures, loose cementation, and strong formation heterogeneity. After long-term steam injection development, high-temperature steam has a significant impact on the geological structure, exacerbating reservoir heterogeneity and forming high-permeability steam channeling channels. This reduces steam sweep efficiency and steam utilization, severely restricting the benefits of steam stimulation development. Steam channeling is an urgent problem that needs to be addressed in the steam injection development of heavy oil reservoirs. Regarding steam channeling control, in addition to adjusting the gas injection process to improve steam channeling, steam sealing is also a key measure in channeling prevention technology. Chemical sealing technology is one of the most effective methods for blocking steam channeling and improving the steam sweep coefficient. The key to this technology is the development of high-temperature resistant sealing agents.

[0005] Currently, the main plugging agents used to prevent steam channeling in heavy oil reservoirs include high-temperature foams, high-temperature gels, solid particles, and resins. During steam flooding, multiple temperature zones typically develop: an ultra-high temperature zone near the wellbore (350°C-200°C), a high-temperature zone in the middle and deep layers of the formation (200°C-110°C), and a medium-low temperature zone (<100°C). The main plugging agents used to prevent channeling in the ultra-high temperature zone include inorganic particles and high-temperature tannin extract systems, which offer excellent high-temperature resistance. However, inorganic particles have limited migration capacity within the formation and poor curing time adjustability, making them difficult to achieve channeling in deep and medium formations. Tannin extract systems can withstand temperatures up to 250°C, and their low viscosity (<10 mPa·s) makes large injections into formations prone to entering channels of varying sizes, potentially damaging medium- and low-permeability reservoirs. Furthermore, any misplaced blockages are difficult to address, impacting subsequent development efforts. Therefore, high-temperature foams or high-temperature gels are the primary plugging agents used to prevent channeling in the middle and high-temperature zones of the formation. High-temperature foams can be prepared using high-temperature-resistant surfactants, which improve steam sweep efficiency, enhance injectability, and minimize reservoir damage. However, their ability to block large pores is limited, but their effectiveness is short-lived. High-temperature gel systems, primarily composed of high concentrations of heat-resistant polymers and crosslinkers, typically contain polymers greater than 1% and exhibit high viscosity, resulting in limited injectability and difficulty sealing deep steam channeling. Furthermore, gel strength is limited, requiring a higher polymer concentration to achieve high strength.

[0006] For profile control and plugging in deep oil reservoirs, there is a contradiction between formation damage, injectivity and plugging ability, and this phenomenon is particularly prominent for steam plugging. Summary of the Invention

[0007] To solve the above technical problems, the present invention aims to provide a high-strength low-molecular polymer jelly system and a preparation method thereof, wherein the jelly system is resistant to high temperatures, has high gel strength, and has good injectability.

[0008] To achieve the above object, the present invention provides a high-strength low-molecular polymer jelly system, wherein the raw materials thereof include, by mass percentage: 4-6% polymer emulsion, 0.4-0.8% phenolic crosslinking agent, 0-0.3% catalyst, 0.2-0.5% oxygen scavenger, 0.2-0.4% stabilizer, and the balance water;

[0009] The polymer emulsion is formed by copolymerization of acrylamide monomer and sodium p-styrene sulfonate monomer, wherein the molar weight of the sodium p-styrene sulfonate monomer accounts for 8-15% of the total monomer amount.

[0010] According to a specific embodiment of the present invention, preferably, the relative molecular mass of the polymer in the polymer emulsion is 600,000-800,000.

[0011] According to a specific embodiment of the present invention, preferably, the preparation method of the polymer emulsion is as follows:

[0012] Under nitrogen protection, acrylamide monomer and emulsifier are mixed in water and preheated to the polymerization reaction temperature, a portion of initiator is added, and then sodium p-styrene sulfonate monomer is dropped into the water. After the dropwise addition is completed, N,N,N',N'-tetramethylethylenediamine and the remaining initiator are added to carry out copolymerization reaction to obtain the polymer emulsion.

[0013] According to a specific embodiment of the present invention, preferably, in the method for preparing the polymer emulsion, the amount of the emulsifier used is 0.05-0.1% of the total mass of the monomers; the emulsifier is compounded by anionic surfactant SDS and nonionic surfactant OP-10 in a mass ratio of 1-1.2:1.

[0014] According to a specific embodiment of the present invention, preferably, in the method for preparing the polymer emulsion, preferably, the mass ratio of the total mass of monomers to water is 1:1.5-2.

[0015] According to a specific embodiment of the present invention, preferably, in the method for preparing the polymer emulsion, the amount of the initiator used is 0.5-1% of the total mass of the monomers; and the initiator is ammonium persulfate.

[0016] According to a specific embodiment of the present invention, preferably, in the method for preparing the polymer emulsion, the amount of N,N,N',N'-tetramethylethylenediamine used is 10-20% of the mass of the initiator.

[0017] According to a specific embodiment of the present invention, preferably, in the method for preparing the polymer emulsion, the copolymerization reaction temperature is 60-65° C., and the reaction time is 8-10 h.

[0018] The polymer emulsion prepared by the invention has the appearance of a viscous liquid and contains 32-35% (mass fraction) of a polymer, which is a low-molecular polymer with a relative molecular mass of 600,000-800,000.

[0019] According to a specific embodiment of the present invention, more preferably, the preparation method of the polymer emulsion is as follows:

[0020] S1: Add acrylamide monomer and a certain amount of water into a four-necked flask equipped with a stirrer, introduce nitrogen gas for purging, and heat the reaction solution to 60-65°C;

[0021] S2: After adding a certain amount of emulsifier and stirring for 20-30 minutes, add 2 / 3 of ammonium persulfate initiator, and then slowly drop sodium p-styrene sulfonate. After the dropwise addition is complete, add N,N,N',N'-tetramethylethylenediamine;

[0022] S3: Then, the remaining ammonium persulfate initiator is added dropwise to the four-necked flask and mixed and stirred. After reacting at 60-65°C for 8-10 hours, stirring is stopped, the temperature is lowered, and the material is discharged to obtain a polymer emulsion;

[0023] The emulsifier is prepared by compounding anionic surfactant SDS and nonionic surfactant OP-10 in a mass ratio of 1-1.2:1, and the amount used is 0.05-0.1% of the total mass of the monomers; the amount of ammonium persulfate initiator used is 0.5-1% of the total mass of the monomers; and the amount of N,N,N',N'-tetramethylethylenediamine used is 10-20% of the mass of the ammonium persulfate initiator.

[0024] According to a specific embodiment of the present invention, preferably, the phenolic crosslinking agent is a water-soluble phenolic resin crosslinking agent, or a composite crosslinking agent of a phenolic crosslinking agent and an aldehyde crosslinking agent, more preferably a water-soluble phenolic resin crosslinking agent.

[0025] According to a specific embodiment of the present invention, preferably, the preparation method of the water-soluble phenolic resin cross-linking agent comprises the following steps:

[0026] Under the catalysis of an alkaline catalyst, phenol and formaldehyde in a molar ratio of 1:2-3 are subjected to a condensation reaction to obtain the water-soluble phenolic resin cross-linking agent.

[0027] According to a specific embodiment of the present invention, preferably, in the preparation of the water-soluble phenolic resin cross-linking agent, the condensation reaction temperature is 80-90° C. and the time is 1.5-2 h.

[0028] According to a specific embodiment of the present invention, preferably, in the preparation of the water-soluble phenolic resin cross-linking agent, the alkaline catalyst includes at least one of sodium hydroxide, sodium carbonate, and ammonia water, more preferably sodium hydroxide.

[0029] According to a specific embodiment of the present invention, preferably, in the preparation of the water-soluble phenolic resin cross-linking agent, the amount of the alkaline catalyst used is 4-6% of the total mass of phenol and formaldehyde.

[0030] According to a specific embodiment of the present invention, preferably, the water-soluble phenolic resin crosslinker is prepared from phenol and formaldehyde in the presence of an alkaline catalyst, and the specific preparation method is as follows:

[0031] S1: Phenol and alkaline catalyst solution were placed in a three-necked flask, stirred and the temperature was raised to 45°C, and the temperature was controlled not to exceed 45°C;

[0032] S2: Add 80% formaldehyde solution dropwise within 30 minutes, raise the temperature to 80°C, and react for 60-80 minutes;

[0033] S3: Add the remaining 20% ​​formaldehyde solution to the above reaction solution, raise the temperature to 90°C, and stir the mixture at constant temperature for 20-30 minutes. After the reaction is completed, a transparent brown-red liquid is obtained, which is a water-soluble phenolic resin crosslinking agent.

[0034] According to a specific embodiment of the present invention, preferably, the catalyst is acetic acid and / or ammonium chloride, more preferably ammonium chloride.

[0035] According to a specific embodiment of the present invention, preferably, the oxygen scavenger is thiourea.

[0036] According to a specific embodiment of the present invention, preferably, the stabilizer is polypropylene fiber and / or nano-silicon, preferably nano-silicon.

[0037] According to a specific embodiment of the present invention, preferably, the median particle size of the nano-silicon is 8-15 nm. More preferably, the nano-silicon dioxide is added in the form of nano-silica sol; the content of nano-silica dioxide in the nano-silica sol is 28-32%.

[0038] According to a specific embodiment of the present invention, preferably, the water is clean water or treated oilfield reinjection wastewater.

[0039] The present invention also provides a method for preparing the above-mentioned high-strength low-molecular polymer jelly system, which comprises the following steps:

[0040] (1) adding a phenolic crosslinking agent, a catalyst, and an oxygen scavenger into water in proportion and stirring uniformly to obtain a solution A;

[0041] (2) adding a stabilizer to the solution A in proportion and stirring uniformly to obtain a solution B;

[0042] (3) Under stirring conditions, the polymer emulsion is added to the solution B and stirred thoroughly to obtain the high-strength low-molecular polymer jelly system.

[0043] In the above-mentioned method for preparing the high-strength low-molecular polymer jelly system, preferably, the stirring speed in step (3) is 150-200 rpm and the stirring time is 20-30 min.

[0044] The present invention also provides an application of the high-strength low-molecular polymer gel system in plugging steam channeling in heavy oil reservoirs.

[0045] In the above application, preferably, when the formation temperature is less than 80°C, the raw materials of the high-strength low-molecular polymer jelly system include: 4-6% polymer emulsion, 0.4-0.8% phenolic crosslinker, 0.2-0.3% catalyst, 0.2-0.3% deoxidizer, 0.2-0.3% stabilizer, and the balance water.

[0046] In the above application, preferably, when the formation temperature is 80-110°C, the raw materials of the high-strength low-molecular polymer jelly system include: 4-6% polymer emulsion, 0.4-0.8% phenolic crosslinker, 0.1-0.2% catalyst, 0.3-0.4% deoxidizer, 0.2-0.3% stabilizer, and the balance water.

[0047] In the above application, preferably, when the formation temperature is greater than 110°C, the raw materials of the high-strength low-molecular polymer jelly system include: 4-6% polymer emulsion, 0.4-0.8% phenolic crosslinker, 0-0.1% catalyst, 0.3-0.5% deoxidizer, 0.3-0.4% stabilizer, and the balance water.

[0048] The technical solution provided by the present invention has the following beneficial effects:

[0049] The polymer emulsion used in the high-strength low-molecular-weight polymer gel system prepared by the present invention is a low-molecular-weight polymer copolymerized by acrylamide and sodium p-styrene sulfonate, and the sodium p-styrene sulfonate comonomer makes the low-molecular-weight polymer have better temperature resistance. The molecular weight of the low-molecular-weight polymer in the synthesized polymer emulsion is 600,000-800,000. When a high polymer dosage is used, the viscosity of the gelled liquid is low, and the viscosity of the gelled liquid is less than 500 mPa·s at the wellbore or formation temperature. The system has good migration performance in the deep formation during injection. In addition, the high dosage of the low-molecular-weight polymer leads to high gelling strength of the polymer gel, a large elastic modulus after gelling, and high plugging strength, which can effectively plug large pores and improve the steam channeling sealing effect in heavy oil reservoirs.

[0050] The high-strength low-molecular polymer gel system prepared by the present invention has an adjustable gelling time at different temperatures. The low viscosity and controllable gelling time of the gelling liquid make it have good injectability. It has good gelling performance under the condition of ensuring injectability, has little damage to medium and low permeability oil layers, and has a good plugging effect on large channels after gelling. The high-strength, high-temperature resistant polymer gel has a controllable gelling time under low-temperature formation conditions without steam injection, has good thermal stability during steam injection, and has a long-term plugging effect on steam channeling channels. It effectively solves the problems of poor gelling performance of conventional high-temperature resistant plugging agent systems under low-temperature conditions and poor injectability of plugging agents under high strength, and can be used for long-term channeling in deep formations during steam injection. DETAILED DESCRIPTION

[0051] In order to have a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention is now described in detail below, but it should not be understood as limiting the scope of implementation of the present invention.

[0052] The medicines used in the present invention are all industrial products, wherein the formaldehyde solution is an industrial product with a mass fraction of 35%.

[0053] The phenolic crosslinking agent used in the embodiment of the present invention is prepared as follows:

[0054] 40 g of phenol and 40 mL of 20% by mass sodium hydroxide solution were added to a three-necked flask, stirred, and the temperature was raised to 45°C, controlling the temperature not to exceed 45°C; 80 g of formaldehyde solution was added dropwise over 30 minutes, and the temperature was raised to 80°C, and the reaction was carried out for 1.5 hours; then 20 g of formaldehyde solution was added to the above reaction solution, and the temperature was raised to 90°C. The reaction was stirred at a constant temperature for 30 minutes to obtain the water-soluble phenolic resin crosslinking agent used in the example.

[0055] The various embodiments and comparative examples of the present invention are all based on the preparation of 200 g of polymer jelly system.

[0056] Example 1

[0057] This embodiment provides a high-strength low-molecular-weight polymer jelly system. The raw materials thereof, calculated by weight percentage, include: 5 wt% polymer emulsion, 0.5 wt% water-soluble phenolic resin crosslinking agent prepared by the present invention, 0.2 wt% ammonium chloride (catalyst), 0.3 wt% thiourea (oxidizer), 0.3 wt% nano-silicon (stabilizer), and the balance water.

[0058] Wherein, the preparation method of polymer emulsion is as follows:

[0059] 90 g of acrylamide monomer and 180 g of water were added to a four-necked flask equipped with a stirrer, nitrogen was introduced for purging, and the reaction solution was heated to 60° C.; 0.05% by mass of an emulsifier was added and stirred for 20-30 minutes, 0.4 g of ammonium persulfate initiator was added, and then a solution containing 10 g of sodium p-styrenesulfonate was slowly added dropwise. After the addition was complete, 0.06 g of N,N,N',N'-tetramethylethylenediamine was added dropwise; then the remaining 0.2 g of ammonium persulfate initiator was added dropwise to the four-necked flask, mixed and stirred, and reacted at 60° C. for 8 hours. Then, stirring was stopped, the temperature was lowered, and the material was discharged to obtain a polymer emulsion.

[0060] The mass fraction of the low-molecular polymer in the prepared polymer emulsion is 32%, and the relative molecular mass of the low-molecular polymer is 600,000-800,000.

[0061] In this embodiment, the polymer emulsion is used to prepare a high-strength low-molecular-weight polymer jelly system. The preparation method includes the following steps:

[0062] 1 g of a water-soluble phenolic resin crosslinker was added to an appropriate amount of water and stirred evenly, 0.4 g of ammonium chloride and 0.6 g of thiourea were added and stirred evenly, and 0.6 g of nano-silica sol was added and stirred evenly to obtain a solution;

[0063] The above solution was transferred to an electric stirrer, and 31.25 g of the polymer emulsion was slowly added to the solution at a rotation speed of 150 rpm. Then water was added to make the solution up to 200 g, and stirred for 30 minutes to obtain a high-strength low-molecular polymer jelly system.

[0064] 20 g of the high-strength low-molecular-weight polymer jelly system prepared in this example was injected into ampoules, and placed in high-pressure tanks at 60°C, 90°C, 110°C, and 130°C, respectively, to observe the gelation time. After gelation, the ampoules were placed in high-temperature ovens at 160°C and 180°C to observe their stability and measure their gel strength.

[0065] The gelling time of the high-strength low-molecular-weight polymer jelly system prepared in Example 1 at 60°C, 90°C, 110°C and 130°C was 26h, 15h, 6.5h and 4h respectively; the polymer jelly system in Example 1 was heated at 30°C and a rotation speed of 7.34s. -1 The viscosity at 500 nm was 563.45 mPa·s. After gelation, the elastic moduli of the polymer jelly system at 160°C and 180°C were 123.5 Pa and 117.6 Pa, respectively. After aging for 120 days, the elastic moduli were 110.24 Pa and 102.8 Pa, respectively, and the polymer jelly showed no signs of dehydration.

[0066] Example 2

[0067] This embodiment provides a high-strength low-molecular-weight polymer jelly system. The raw materials thereof include, by weight percentage, 5 wt% of a polymer emulsion, 0.5 wt% of a water-soluble phenolic resin crosslinking agent prepared in the present invention, 0.3 wt% of ammonium chloride, 0.3 wt% of thiourea, 0.3 wt% of a nano-silica sol, and the balance being water.

[0068] Wherein, the preparation method of polymer emulsion is as follows:

[0069] 90 g of acrylamide monomer and 180 g of water were added to a four-necked flask equipped with a stirrer, nitrogen was introduced for purging, and the reaction solution was heated to 65° C.; 0.05% by mass of an emulsifier was added and stirred for 20-30 minutes, 0.6 g of ammonium persulfate initiator was added, and then a solution containing 10 g of sodium p-styrenesulfonate was slowly added dropwise. After the addition was complete, 0.09 g of N,N,N',N'-tetramethylethylenediamine was added dropwise; then the remaining 0.3 g of ammonium persulfate initiator was added dropwise to the four-necked flask, mixed and stirred, and reacted at 65° C. for 8 hours. Then, stirring was stopped, the temperature was lowered, and the material was discharged to obtain a polymer emulsion.

[0070] The mass fraction of the low-molecular polymer in the prepared polymer emulsion is 35%, and the relative molecular mass of the low-molecular polymer is 600,000-800,000.

[0071] In this embodiment, the polymer emulsion is used to prepare a high-strength low-molecular-weight polymer jelly system. The preparation method includes the following steps:

[0072] 1 g of a water-soluble phenolic resin crosslinker was added to an appropriate amount of water and stirred evenly, 0.6 g of ammonium chloride and 0.6 g of thiourea were added and stirred evenly, and 0.6 g of nano-silica sol was added and stirred evenly to obtain a solution;

[0073] The above solution was transferred to an electric stirrer. 31.25 g of the polymer emulsion was slowly added to the solution at a speed of 150 rad / s. Water was then added to make the solution up to 200 g. The mixture was stirred for 30 min to obtain 200 g of a high-strength low-molecular-weight polymer jelly system.

[0074] 20 g of the high-strength low-molecular-weight polymer jelly system prepared in this example was injected into ampoules, and then placed in high-pressure tanks at 60°C, 90°C, and 110°C to observe the gelation time. After gelation, the ampoules were placed in high-temperature ovens at 160°C and 180°C to observe their stability and measure their gel strength.

[0075] The gelling time of the high-strength low-molecular-weight polymer jelly system prepared in Example 2 at 60°C, 90°C and 110°C was 18h, 8h and 1.5h respectively; the polymer jelly system in Example 2 was heated at 30°C and a rotation speed of 7.34s. -1 The viscosity at 502.23 mPa·s was 502.23 mPa·s. After gelation, the elastic moduli of the polymer jelly system at 160°C and 180°C were 118.5 Pa and 108.4 Pa, respectively. After aging for 120 days, the elastic moduli were 101.24 Pa and 92.7 Pa, respectively, and the polymer jelly showed no dehydration.

[0076] Comparing Example 1 with Example 2, it can be seen that increasing the amount of initiator slightly reduces the viscosity of the prepared polymer jelly system. This is mainly because the increase in the amount of initiator increases the free radicals in the polymer synthesis process, increases the number of reaction activity centers, and reduces the polymer molecular weight, thereby reducing the viscosity of the system.

[0077] In Example 2, the amount of catalyst ammonium chloride used has a greater impact on the gelling time of the polymer gel at low temperature, but has a smaller impact on the gelling strength after gelling.

[0078] Example 3

[0079] This embodiment provides a high-strength, low-molecular-weight polymer jelly system. The raw materials, calculated by weight percentage, include: 5 wt% polymer emulsion, 0.5 wt% of a water-soluble phenolic resin crosslinker prepared according to the present invention, 0.05 wt% ammonium chloride, 0.3 wt% thiourea, 0.3 wt% nano-silica sol, and the balance water. The polymer emulsion is the same as that prepared in Example 1, and the polymer jelly is prepared using the same method as in Example 1.

[0080] 20 g of the high-strength low-molecular-weight polymer jelly system prepared in this example was injected into ampoules, and placed in high-pressure tanks at 110°C and 130°C, respectively, to observe the gelation time. After gelation, the ampoules were placed in high-temperature ovens at 160°C and 180°C to observe their stability and measure their gel strength.

[0081] The high-strength low-molecular-weight polymer gel prepared in Example 3 took 18 hours and 10 hours to gel at 110°C and 130°C, respectively. The polymer gel system in Example 3 was heated at 30°C and a rotation speed of 7.34s. -1 The viscosity at 400 nm was 559.65 mPa·s. After gelation, the elastic moduli of the polymer jelly system were 132.9 Pa and 118.1 Pa at 160°C and 180°C, respectively. After aging for 120 days, the elastic moduli were 101.24 Pa and 96.5 Pa, respectively, and the polymer jelly did not dehydrate.

[0082] Comparing Examples 1 and 3, it can be seen that even at temperatures above 110°C and with the addition of a small amount of catalyst, the polymer jelly still exhibits good gelling properties, with a slight increase in the elastic modulus after gelling. Comparing Examples 1, 2, and 3, it can be seen that within a reasonable range of initiator dosage, the prepared low-molecular-weight polymer has little effect on the gelling properties of the jelly.

[0083] Example 4

[0084] This embodiment provides a high-strength, low-molecular-weight polymer jelly system. The raw materials, calculated by weight percentage, include: 5 wt% polymer emulsion, 0.8 wt% of a water-soluble phenolic resin crosslinker prepared according to the present invention, 0.2 wt% ammonium chloride, 0.3 wt% thiourea, 0.3 wt% nano-silica sol, and the balance water. The polymer emulsion is the same as that prepared in Example 1, and the polymer jelly is prepared using the same method as in Example 1.

[0085] 20 g of the high-strength low-molecular-weight polymer jelly system prepared in this example was injected into ampoules, and then placed in high-pressure tanks at 60°C, 90°C, and 110°C to observe the gelation time. After gelation, the ampoules were placed in high-temperature ovens at 160°C and 180°C to observe their stability and measure their gel strength.

[0086] The high-strength low-molecular-weight polymer gel prepared in Example 4 took 19 hours, 11 hours, and 3 hours to gel at 60°C, 90°C, and 110°C, respectively; the polymer gel system of Example 3 took 19 hours, 11 hours, and 3 hours to gel at 30°C and a rotation speed of 7.34s. -1 The viscosity of the polymer jelly system was 513.8 mPa·s at 160°C and 180°C after gelation, and the elastic moduli of the polymer jelly system were 152.2 Pa and 136.5 Pa, respectively. After aging for 120 days, the elastic moduli were 153.3 Pa and 128.6 Pa, respectively, and the polymer jelly did not dehydrate.

[0087] Comparing Example 1 with Example 4, it can be seen that increasing the amount of the homemade water-soluble phenolic resin crosslinker shortens the gelation time of the system and slightly increases the elastic modulus of the polymer gel after gelation.

[0088] Example 5

[0089] This embodiment provides a high-strength, low-molecular-weight polymer jelly system. The raw materials, calculated by weight percentage, include: 5 wt% polymer emulsion, 0.5 wt% of a water-soluble phenolic resin crosslinker prepared according to the present invention, 0.2 wt% ammonium chloride, 0.5 wt% thiourea, 0.3 wt% nano-silica sol, and the balance water. The polymer emulsion is the same as that prepared in Example 1, and the polymer jelly is prepared using the same method as in Example 1.

[0090] 20 g of the high-strength low-molecular-weight polymer jelly system prepared in this example was injected into ampoules, and then placed in high-pressure tanks at 60°C, 90°C, and 110°C to observe the gelation time. After gelation, the ampoules were placed in high-temperature ovens at 160°C and 180°C to observe their stability and measure their gel strength.

[0091] The high-strength low-molecular-weight polymer jelly system prepared in Example 1 had a gelling time of 26 h, 15 h, and 7 h at 60 ° C, 90 ° C, and 110 ° C, respectively; the polymer jelly system in Example 5 had a gelling time of 26 h, 15 h, and 7 h at 30 ° C and a rotation speed of 7.34 s -1 The viscosity at 500 nm was 556.4 mPa·s. After gelation, the elastic moduli of the polymer jelly system at 160°C and 180°C were 130.8 Pa and 119.4 Pa, respectively. After aging for 120 days, the elastic moduli were 121.3 Pa and 109.8 Pa, respectively, and the polymer jelly showed no signs of dehydration.

[0092] Comparing Example 1 with Example 5, it can be seen that increasing the amount of the oxygen scavenger thiourea can slightly improve the strength and long-term stability of the system.

[0093] Comparative Example 1

[0094] This comparative example provides a polymer jelly system, which is the same as Example 1, except that the 5 wt% polymer emulsion in Example 1 is replaced with 2 wt% of acrylamide and 2-acrylamido-2-methylpropanesulfonic acid binary copolymer AM / AMPS. The 2-acrylamido-2-methylpropanesulfonic acid AM / AMPS monomer content in the binary copolymer accounts for 30% of the total monomer content and has a molecular weight of 6.5 million.

[0095] Testing conducted using the same method as Example 1 revealed that the polymer jelly system of this comparative example had a viscosity of 1873.53 mPa·s at 30°C and a rotational speed of 7.34 s⁻¹. This indicates high viscosity and limited injectability. Furthermore, the polymer jelly of this comparative example exhibited poor gelling properties at temperatures below 100°C. After further gelling at 160°C, the elastic modulus was 18.5 Pa. After aging for 60 days, the elastic modulus decreased to 6.75 Pa.

[0096] Compared with Example 1, it can be seen that although the viscosity of the gelling liquid using the heat-resistant binary copolymer is still very high, the gel strength after gelling is low and the thermal stability is poor, which is not suitable for plugging steam channeling in medium and deep areas.

[0097] Comparative Example 2

[0098] This comparative example provides a polymer jelly system that is identical to Example 1, except that the water-soluble phenolic resin crosslinker in Example 1 is replaced with a combination of hydroquinone and urotropine, with the hydroquinone content at 0.2 wt% and the urotropine content at 0.3 wt%. The remaining preparation and testing procedures were the same as in Example 1.

[0099] The phenolic-formaldehyde combination crosslinker system has little effect on the viscosity and gelation time of the prepared polymer jelly system, but has a greater impact on the long-term stability and strength of the polymer jelly. The elastic modulus of the polymer jelly obtained in this comparative example is 75.5 Pa at 160°C. After aging for 120 days, the elastic modulus of the jelly decreases by 20%; the elastic modulus of the polymer jelly at 180°C is 63.4 Pa. After aging for 120 days, the elastic modulus of the jelly decreases by 36%.

[0100] Comparative Example 3

[0101] This comparative example provides a polymer jelly system, which is the same as Example 1, except that the oxygen scavenger in Example 1 is reduced to 0.1 wt %. Other preparations and tests are the same as those in Example 1.

[0102] The amount of scavenger used has little effect on the viscosity of the gelling liquid, gelling time and initial gelling strength of the prepared polymer jelly system, but has a greater impact on the long-term stability and strength of the polymer jelly. After aging the polymer jelly obtained in this comparative example at 160°C for 30 days, the elastic modulus of the jelly decreased by 35%.

[0103] Comparative Example 4

[0104] This comparative example provides a polymer jelly system, which is the same as Example 1, except that the stabilizer in Example 1 is removed in this comparative example. Other preparations and tests are carried out according to Example 1.

[0105] Compared with the polymer jelly prepared in Example 1, the gelling time of the polymer jelly prepared in Comparative Example 3 was slightly prolonged at different temperatures. -1 The viscosity of the polymer jelly was 581.5 mPa·s, and the initial elastic modulus (aged for 1 day) after gelation at 160°C and 180°C was 92.3 Pa and 86.4 Pa, respectively. After aging for 30 days, the polymer jelly was completely degraded. The stability of the polymer jelly system in this comparative example was poor.

[0106] Experimental Example 1

[0107] This experimental example is used to evaluate the injectability and plugging performance of the polymer jelly system prepared in Example 1 and Comparative Example 1 in a sand-filled pipe physical model displacement experiment.

[0108] Two sand-filled pipes with similar permeabilities were prepared, and their injection pressures were measured using oilfield wastewater. The permeabilities of the sand-filled pipes were calculated to be approximately 1120 mD and 1230 mD, respectively. The polymer gel solutions prepared in Example 1 and Comparative Example 1 were injected into the sand-filled pipes with permeabilities of approximately 1120 mD and 1230 mD, respectively, at a rate of 1 ml / min. The injection pressures were recorded. The sand-filled pipes treated with the polymer gel were then sealed and placed in a high-temperature oven (160°C) for aging for 10 days. Steam was then injected to measure the plugging effect, and the residual resistance coefficient was calculated.

[0109] The experimental results are as follows: the equilibrium pressure of the polymer gel solution injected in Example 1 is 0.23 MPa, and the equilibrium pressure of the polymer gel solution injected in Comparative Example 1 is 0.89 MPa. After aging for 10 days, the residual resistance coefficient of Example 1 is 28.2, and the residual resistance coefficient of Comparative Example 1 is 11.4.

[0110] The sand-filled pipe treated in Example 1 was further placed in a high-temperature oven (160°C) and its residual resistance coefficient was regularly measured. The residual resistance coefficient after 30 days of aging was 24, and the residual resistance coefficient after 45 days of aging was 21.4. This evaluation of the sand-filled pipe plugging performance demonstrates that the high-strength, heat-resistant polymer gel prepared in Example 1 can be used to plug steam channeling at medium to deep depths.

Claims

1. A high-strength low-molecular-weight polymer jelly system, wherein the raw materials thereof comprise, by weight percentage: Polymer emulsion 4-6%, phenolic crosslinker 0.4-0.8%, catalyst 0-0.3%, deoxidizer 0.2-0.5%, stabilizer 0.2-0.4%, and the balance water; The polymer emulsion is formed by copolymerization of acrylamide monomer and sodium p-styrene sulfonate monomer, wherein the molar weight of the sodium p-styrene sulfonate monomer accounts for 8-15% of the total monomer amount.

2. The high-strength low-molecular polymer jelly system according to claim 1, wherein: The relative molecular mass of the polymer in the polymer emulsion is 600,000-800,000.

3. The high-strength low-molecular polymer jelly system according to claim 1, wherein: The preparation method of the polymer emulsion is as follows: Under nitrogen protection, acrylamide monomer and emulsifier are mixed in water and preheated to the polymerization reaction temperature, a portion of initiator is added, and then sodium p-styrene sulfonate monomer is dropped into the water. After the dropwise addition is completed, N,N,N',N'-tetramethylethylenediamine and the remaining initiator are added to carry out copolymerization reaction to obtain the polymer emulsion.

4. The high-strength low-molecular polymer jelly system according to claim 3, wherein: The amount of the emulsifier is 0.05-0.1% of the total weight of the monomers; the emulsifier is prepared by compounding anionic surfactant SDS and nonionic surfactant OP-10 in a mass ratio of 1-1.2:

1.

5. The high-strength low-molecular polymer jelly system according to claim 3, wherein: The mass ratio of the total mass of monomers to water is 1:1.5-2.

6. The high-strength low-molecular polymer jelly system according to claim 3, wherein: The dosage of the initiator is 0.5-1% of the total weight of the monomers; the initiator is ammonium persulfate.

7. The high-strength low-molecular polymer jelly system according to claim 3, wherein: The amount of N,N,N',N'-tetramethylethylenediamine used is 10-20% of the mass of the initiator.

8. The high-strength low-molecular polymer jelly system according to claim 3, wherein: The copolymerization temperature is 60-65°C, and the reaction time is 8-10h.

9. The high-strength low-molecular polymer jelly system according to claim 1, wherein: The phenolic crosslinking agent is a water-soluble phenolic resin crosslinking agent, or a composite crosslinking agent of a phenolic crosslinking agent and an aldehyde crosslinking agent.

10. The high-strength low-molecular polymer jelly system according to claim 9, wherein: The preparation method of the water-soluble phenolic resin cross-linking agent comprises the following steps: Under the catalysis of an alkaline catalyst, phenol and formaldehyde in a molar ratio of 1:2-3 are subjected to a condensation reaction to obtain the water-soluble phenolic resin cross-linking agent.

11. The high-strength low-molecular polymer jelly system according to claim 10, wherein: The condensation reaction temperature is 80-90°C and the time is 1.5-2h.

12. The high-strength low-molecular polymer jelly system according to claim 10, wherein: The alkaline catalyst includes at least one of sodium hydroxide, sodium carbonate, and ammonia water.

13. The high-strength low-molecular polymer jelly system according to claim 10, wherein: The amount of the alkaline catalyst used is 4-6% of the total mass of phenol and formaldehyde.

14. The high-strength low-molecular polymer jelly system according to claim 1, wherein: The catalyst is acetic acid and / or ammonium chloride.

15. The high-strength low-molecular polymer jelly system according to claim 1, wherein: The oxygen scavenger is thiourea.

16. The high-strength low-molecular polymer jelly system according to claim 1, wherein: The stabilizer is polypropylene fiber and / or nano silicon dioxide.

17. The high-strength low-molecular polymer jelly system according to claim 16, wherein: The median particle size of nano-silica is 8-15nm.

18. The high-strength low-molecular polymer jelly system according to claim 16, wherein: The nano silicon dioxide is added in the form of nano silica sol.

19. A method for preparing the high-strength low-molecular polymer jelly system according to any one of claims 1 to 18, comprising the following steps: (1) adding a phenolic crosslinking agent, a catalyst, and an oxygen scavenger into water in proportion and stirring uniformly to obtain a solution A; (2) adding a stabilizer to the solution A in proportion and stirring uniformly to obtain a solution B; (3) Under stirring conditions, the polymer emulsion is added to the solution B and stirred thoroughly to obtain the high-strength low-molecular polymer jelly system.

20. Use of the high-strength low-molecular polymer jelly system according to any one of claims 1 to 18 in plugging steam channeling in heavy oil reservoirs.

21. The use according to claim 20, wherein: When the formation temperature is less than 80°C, the raw materials of the high-strength low-molecular polymer gel system include: 4-6% polymer emulsion, 0.4-0.8% phenolic crosslinking agent, 0.2-0.3% catalyst, 0.2-0.3% deoxidizer, 0.2-0.3% stabilizer, and the balance water.

22. The use according to claim 20, wherein: When the formation temperature is 80-110° C., the raw materials of the high-strength low-molecular polymer gel system include: 4-6% polymer emulsion, 0.4-0.8% phenolic crosslinking agent, 0.1-0.2% catalyst, 0.3-0.4% deoxidizer, 0.2-0.3% stabilizer, and the balance water.

23. The use according to claim 20, wherein: When the formation temperature is greater than 110° C., the raw materials of the high-strength low-molecular polymer gel system include: 4-6% polymer emulsion, 0.4-0.8% phenolic crosslinking agent, 0-0.1% catalyst, 0.3-0.5% deoxidizer, 0.3-0.4% stabilizer, and the balance water.