Modified polymers and their preparation methods, gel particles and applications

Abstract

This invention relates to the field of oilfield chemistry, and discloses a modified polymer, its preparation method, gel particles, and applications. The modified polymer contains structural unit A as shown in formula (I) and structural unit B as shown in formula (II); wherein the weight ratio of structural unit A to structural unit B is 1:(0.1-2); wherein R1 and R2 are each independently -H or C1-C5 alkyl groups; R3 and R4 are each independently -H or C1-C3 alkyl groups; R5 is a C1-C15 alkylene group; Z is H, Na, or K; and Q represents graphene oxide partially modified by an alkanolamine compound. This modified polymer exhibits excellent temperature resistance, salt resistance, and expansion properties, and after expansion, it possesses good elasticity and toughness. The gel particles prepared from this modified polymer, as a profile control and water shut-off agent, demonstrate strong temperature and salt resistance, high sealing strength for large pores, and effectively reduce the permeability of the aqueous phase, thus well meeting the requirements for deep profile control and water shut-off effects in high-salinity oil reservoirs.

Description

Technical Field

[0001] This invention relates to the field of oilfield development and recovery, specifically to a modified polymer, its preparation method, gel particles, and applications. Background Technology

[0002] With the continuous development of old oilfields, high-permeability seepage channels have formed within the reservoirs, resulting in ineffective circulation of injected fluids and significantly reducing the efficiency of oilfield development. To alter the formation water seepage state, seal high-permeability water flow channels in oil wells, and increase oil well production, profile control and water-blocking agents are needed to treat the oil and water wells. For high-temperature, high-salinity reservoirs, taking the Zhongyuan Oilfield as an example, the ground temperature reaches over 90℃, and the salinity reaches 10×10⁻⁶. 4 -30×10 4 mg / L, most conventional plugging agents have poor tolerance to high temperature and high mineralization environments, resulting in unsatisfactory actual plugging effects.

[0003] Currently, profile control and water shut-off agents used in the field can be categorized into gel-based, gel-based, granular, and other types. Granular agents include inorganic granules (such as clay), ultrafine cement, and bulk-expanded granules. To achieve deep profile control and shut-off, the application of bulk-expanded granular agents has increased significantly in recent years. However, the adaptability of existing bulk-expanded granular agents to high temperatures and high mineralization still needs improvement.

[0004] Therefore, improving the temperature resistance and salt resistance of profile control and water plugging agents is of great significance for effectively reducing the seepage capacity of high-permeability channels and achieving effective deep plugging. Summary of the Invention

[0005] The purpose of this invention is to address the problems of insufficient temperature and salt resistance and low sealing strength of existing profile control and water plugging agents, which result in unsatisfactory deep plugging effects. This invention provides a modified polymer, its preparation method, gel particles, and applications.

[0006] To achieve the above objectives, the first aspect of the present invention provides a modified polymer comprising structural unit A as shown in formula (I) and structural unit B as shown in formula (II); wherein the weight ratio of structural unit A to structural unit B is 1:(0.1-2);

[0007]

[0008] Wherein, R1 and R2 are each independently -H or C1-C5 alkyl groups; R3 and R4 are each independently -H or C1-C3 alkyl groups; R5 is a C1-C15 alkylene group; Z is H, Na, or K;

[0009] Q represents graphene oxide partially modified by alkanolamine compounds.

[0010] A second aspect of the present invention provides a method for preparing a modified polymer, comprising: reacting monomer A', monomer B' and modified graphene in the presence of an initiator, a crosslinking agent and water to obtain a modified polymer;

[0011] The weight ratio of monomer A', monomer B' and modified graphene is 100:(1-200):(1-10);

[0012] The modified graphene is graphene oxide partially modified by alkanolamine compounds;

[0013] The monomer A' is a monomer having the structure shown in formula (IV), and the monomer B' is a monomer having the structure shown in formula (V).

[0014]

[0015] Wherein, R1 and R2 are each independently -H or C1-C5 alkyl groups; R3 and R4 are each independently -H or C1-C3 alkyl groups; R5 is a C1-C15 alkylene group; and Z is H, Na, or K.

[0016] A third aspect of the present invention provides a modified polymer prepared by the method described in the second aspect above.

[0017] A fourth aspect of the present invention provides a gel particle, which is obtained by sequentially granulating, drying, pulverizing and sieving a polymer.

[0018] The polymer is the modified polymer described in the first or third aspect above.

[0019] The fifth aspect of this invention provides the application of the gel particles described in the fourth aspect above as profile control and water shut-off agents in oil extraction.

[0020] This invention uses specific modified graphene oxide and... Structural units, from The structural units together form a graphene-modified polymer, which exhibits excellent temperature resistance, salt resistance, and expansion properties, and displays good elasticity and toughness after expansion. Gel particles prepared from this modified polymer demonstrate high-temperature and high-salinity tolerance. Under conditions of 60-120℃, in brine with a salinity of 30,000-300,000 mg / L, the expansion ratio is 10-50, and the elasticity of the expanded particles is 600-2000 Pa. As a profile control and water shut-off agent, these gel particles exhibit strong temperature and salt resistance, high sealing strength for large channels, and effectively reduce the permeability of the aqueous phase, perfectly meeting the requirements for deep profile control and water shut-off in high-salinity oil reservoirs. When these gel particles are used in combination with a polymer solution for oil displacement, the recovery rate can be increased by more than 10% compared to waterflooding. Detailed Implementation

[0021] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0022] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0023] In a first aspect, the present invention provides a modified polymer comprising structural unit A of formula (I) and structural unit B of formula (II); wherein the weight ratio of structural unit A to structural unit B is 1:(0.1-2).

[0024]

[0025] Wherein, R1 and R2 are each independently -H or C1-C5 alkyl groups; R3 and R4 are each independently -H or C1-C3 alkyl groups; R5 is a C1-C15 alkylene group; Z is H, Na, or K;

[0026] Q represents graphene oxide partially modified by alkanolamine compounds.

[0027] According to the present invention, based on satisfying the above structure and composition, preferably, in the modified polymer, the weight ratio of structural unit A to structural unit B is 1:(0.5-1);

[0028] Preferably, in structural unit A shown in formula (I) and structural unit B shown in formula (II), R1 and R2 are each independently -H or C1-C2 alkyl groups; R3 and R4 are each independently -H or C1-C2 alkyl groups; and R5 is a C1-C10 alkylene group.

[0029] According to the present invention, more preferably, in structural unit A shown in formula (I) and structural unit B shown in formula (II), R1 and R2 are each independently -H or -CH3; R3 and R4 are each independently -H or -CH3; and R5 is a C1-C6 alkylene group.

[0030] According to the present invention, in structural unit A shown in formula (I), Q represents graphene oxide partially modified by alkanolamine compounds. By introducing this specific modified graphene into the polymer structure, the temperature resistance, salt resistance and expansion properties of the polymer can be significantly improved, thereby making the polymer more suitable for deep profile control operations in high-salinity oil reservoirs.

[0031] According to the present invention, the alkanolamine compound has the structure shown in formula (III).

[0032]

[0033] R6 and R7 are each independently selected from at least one of -H and C1-C5 alkyl groups.

[0034] Preferably, in formula (III), R6 and R7 are each independently selected from at least one of -H and C1-C3 alkyl groups.

[0035] More preferably, the alkanolamine compound is selected from at least one of 2-hydroxyethylamine, N,N-diethylethanolamine and N,N-di-n-propylethanolamine.

[0036] According to the present invention, the modified graphene represented by Q is prepared by reacting graphene oxide with an alkanolamine compound as shown in formula (III) above. In the present invention, the graphene oxide is obtained through conventional commercial channels or by preparation methods known in the prior art, and has abundant hydroxyl and carboxyl groups distributed on its surface. The hydroxyl groups in the alkanolamine compound shown in formula (III) above can undergo esterification with some of the surface carboxyl groups in the graphene oxide, thereby partially modifying the graphene oxide. Furthermore, the graphene oxide can undergo dehydration condensation with the amino groups in the amide molecule through its surface hydroxyl groups, thereby connecting with the amide molecule. Specifically, in structural unit A shown in formula (I), the graphene oxide partially modified by the alkanolamine compound represented by Q has the structure shown in formula (VI).

[0037]

[0038] in, Indicates a graphene oxide matrix; This represents the surface hydroxyl groups of graphene oxide; * indicates the surface carboxyl group of graphene oxide; * indicates the connection position of graphene oxide partially modified by alkanolamine compounds with N in formula (I); R6 and R7 are each independently selected from at least one of -H and C1-C5 alkyl groups. The surface of the graphene oxide matrix has multiple surface hydroxyl groups, surface carboxyl groups, and modifying groups from alkanolamine compounds.

[0039] In this invention, the conditions for preparing the modified graphene by reacting the graphene oxide with an alkanolamine compound include: a pH of 1-2 in the reaction system, a reaction temperature of 55-65°C, and a reaction time of 1-2 h.

[0040] In the above preparation process, preferably, the weight ratio of graphene oxide to alkanolamine compound is 1:(0.5-1.5).

[0041] According to the present invention, the modified polymer satisfies the above-mentioned structure and composition, thereby exhibiting strong tolerance to high temperature and high salinity environments. The modified polymer has excellent temperature resistance, salt resistance, and expansion properties. Under conditions of 60-120℃, the expansion ratio of the modified polymer in brine with a salinity of 30,000-300,000 mg / L is 10-50, which can well meet the performance requirements of profile control and water shut-off materials for deep profile control operations in high salinity oil reservoirs.

[0042] In this invention, the degree of mineralization can be expressed as the total salt content (mg / L) in 1L of water. Specifically, in oil fields, it can usually be expressed as the total amount of NaCl, CaCl2, and MgCl2 contained in 1L of water.

[0043] According to the present invention, the viscosity-average molecular weight of the modified polymer is (1.5-3)×10⁻⁶. 7 g / mol.

[0044] According to a preferred embodiment of the present invention, in structural unit A shown in formula (I), R1 is -H, Q is modified graphene obtained by reacting graphene oxide with N,N-diethylethanolamine (wherein the weight ratio of graphene oxide to N,N-diethylethanolamine is 1:0.8-1.2); in structural unit B shown in formula (II), R2 is -H, R3 is -CH3, R4 is -CH3, R5 is -CH2-, and Z is H, Na, or K; the weight ratio of structural unit A to structural unit B is 1:(0.6-0.8). The modified polymer with this specific structure and composition exhibits superior temperature resistance, salt resistance, and expansion properties.

[0045] A second aspect of the present invention provides a method for preparing a modified polymer, comprising: reacting monomer A', monomer B' and modified graphene in the presence of an initiator, a crosslinking agent and water to obtain a modified polymer;

[0046] The weight ratio of monomer A', monomer B' and modified graphene is 100:(1-200):(1-10);

[0047] The modified graphene is graphene oxide partially modified by alkanolamine compounds;

[0048] The monomer A' is a monomer having the structure shown in formula (IV), and the monomer B' is a monomer having the structure shown in formula (V).

[0049]

[0050] Wherein, R1 and R2 are each independently -H or C1-C5 alkyl groups; R3 and R4 are each independently -H or C1-C3 alkyl groups; R5 is a C1-C15 alkylene group; and Z is H, Na, or K.

[0051] According to the present invention, in the preparation method of the modified polymer, preferably, the weight ratio of monomer A', monomer B' and modified graphene is 100:(10-100):(1-5).

[0052] According to the present invention, in the method for preparing the modified polymer, preferably, in monomer A' having the structure shown in formula (IV) and monomer B' having the structure shown in formula (V), R1 and R2 are each independently -H or C1-C2 alkyl; R3 and R4 are each independently -H or C1-C2 alkyl; and R5 is a C1-C10 alkylene.

[0053] According to the present invention, more preferably, in monomer A' having the structure shown in formula (IV) and monomer B' having the structure shown in formula (V), R1 and R2 are each independently -H or -CH3; R3 and R4 are each independently -H or -CH3; and R5 is a C1-C6 alkylene group.

[0054] According to the present invention, in the preparation method of the modified polymer, the modified graphene is graphene oxide partially modified by an alkanolamine compound, which can be prepared by reacting graphene oxide with an alkanolamine compound. By using this specific modified graphene and introducing it into a polymer containing structural units provided by monomers A' and B', the polymer's temperature resistance, salt resistance, and expansion properties can be significantly improved, thereby making the polymer more suitable for deep profile control operations in high-salinity oil reservoirs.

[0055] According to the present invention, in the method for preparing the modified polymer, the definition of the alkanolamine compound is the same as that of the alkanolamine compound involved in the first aspect above. Specifically, the alkanolamine compound has the structure shown in formula (III).

[0056]

[0057] R6 and R7 are each independently selected from at least one of -H and C1-C5 alkyl groups.

[0058] Preferably, in formula (III), R6 and R7 are each independently selected from at least one of -H and C1-C3 alkyl groups.

[0059] More preferably, the alkanolamine compound is selected from at least one of 2-hydroxyethylamine, N,N-diethylethanolamine and N,N-di-n-propylethanolamine.

[0060] According to the present invention, in the preparation method of the modified polymer, the graphene oxide is graphene oxide that can be obtained through conventional commercial channels or by preparation methods known in the prior art, and has abundant hydroxyl and carboxyl groups distributed on its surface. The hydroxyl groups in the alkanolamine compounds represented by formula (III) above can undergo esterification with some of the surface carboxyl groups in the graphene oxide (the ester groups generated by the esterification reaction can be determined by infrared spectroscopy), thereby achieving partial modification of the graphene oxide. Furthermore, the graphene oxide can achieve linkage with the amide molecule through a dehydration condensation reaction between its surface hydroxyl groups and the amino groups in the amide molecule.

[0061] According to the present invention, in the preparation method of the modified polymer, the conditions for preparing the modified graphene by reacting the graphene oxide with an alkanolamine compound include: the pH of the reaction system is 1-2, the reaction temperature is 55-65℃, and the reaction time is 1-2h.

[0062] In the above preparation process, preferably, the weight ratio of graphene oxide to alkanolamine compound is 1:(0.5-1.5).

[0063] According to the present invention, the modified graphene has a structure as shown in formula (VII).

[0064]

[0065] in, Indicates a graphene oxide matrix; This represents the surface hydroxyl groups of graphene oxide; R6 and R7 represent surface carboxyl groups of graphene oxide; each is independently selected from at least one of -H and C1-C5 alkyl groups. The surface of the graphene oxide matrix has multiple surface hydroxyl groups, surface carboxyl groups, and modifying groups derived from alkanolamine compounds.

[0066] According to the present invention, in the preparation method of the modified polymer, based on 100 parts by weight of the monomer A', the initiator is 1-10 parts by weight, the crosslinking agent is 0.2-5 parts by weight, and the water is 1500-3000 parts by weight.

[0067] According to the present invention, in the preparation method of the modified polymer, the crosslinking agent is selected from N,N-methylenebisacrylamide and / or aluminum citrate.

[0068] According to the present invention, in the preparation method of the modified polymer, the initiator is composed of an oxidant and a reducing agent; wherein the weight ratio of the oxidant to the reducing agent is (0.5-1.5):1.

[0069] In this invention, the oxidant in the initiator may be selected from at least one of ammonium persulfate, potassium persulfate, sodium persulfate, hydrogen peroxide, sodium hypochlorite, potassium permanganate, potassium perborate, and sodium perborate; the reducing agent may be selected from at least one of sodium bisulfite, potassium sulfite, sodium thiosulfate, potassium thiosulfate, sodium sulfide, and hydrogen sulfide.

[0070] According to the present invention, in the preparation method of the modified polymer, preferably, monomer A', monomer B', modified graphene and water are first mixed to obtain a mixture, a protective gas is introduced to remove oxygen, and then a crosslinking agent and an initiator are added to initiate the reaction. After the reaction is completed, a polymer colloid is obtained, which is then dried to obtain the modified polymer. The reaction conditions include: a temperature of 45-80℃, preferably 55-65℃; and a time of 0.5-5 h, preferably 1-2 h.

[0071] According to the present invention, in the preparation method of the modified polymer, the protective gas is preferably nitrogen.

[0072] A third aspect of the present invention provides a modified polymer prepared by the method described in the second aspect above.

[0073] According to the present invention, the modified polymer prepared by the method described in the second aspect above has the same structure, composition and properties as the modified polymer described in the first aspect above, and will not be repeated here.

[0074] A fourth aspect of the present invention provides a gel particle, which is obtained by sequentially granulating, drying, pulverizing and sieving a polymer.

[0075] The polymer is the modified polymer described in the first or third aspect above.

[0076] According to the present invention, the granulation, drying, crushing and sieving can all be carried out using conventional processes and conditions used in the preparation of gel particles used as profile control and water shut-off agents in the oilfield field, and the present invention does not have any particular limitations on them.

[0077] According to the present invention, the average particle size of the gel particles is 0.05-2 mm.

[0078] According to the present invention, the gel particles exhibit excellent temperature resistance, salt resistance, and swelling properties. Under conditions of 60-120°C, the gel particles swell by 10-50 times in brine with a salinity of 30,000-300,000 mg / L.

[0079] According to the present invention, the gel particles also have good elasticity. Under conditions of 60-120°C, the elasticity of the gel particles after swelling in saline solution with a mineralization of 30000-300000 mg / L is 600-2000 Pa.

[0080] The gel particles provided by this invention, as a profile control and water shut-off agent for oilfields, exhibit strong temperature and salt resistance, high sealing strength for large channels, and effectively reduce the permeability of the aqueous phase, thus well meeting the requirements for deep profile control and water shut-off effects in high-salinity oil reservoirs. When these gel particles are used in combination with a polymer solution for oil displacement, the recovery rate can be increased by more than 10% compared to waterflooding.

[0081] The fifth aspect of this invention provides the application of the gel particles described in the fourth aspect above as profile control and water shut-off agents in oil extraction.

[0082] The present invention will be described in detail below through examples. Unless otherwise specified, the following examples and comparative examples are all conventional methods; the reagents and materials mentioned are commercially available unless otherwise specified.

[0083] Graphene oxide: brand name INFAN, purchased from Ningbo Fengcheng Nanotechnology Co., Ltd.

[0084] Q1: Modified graphene-I, the preparation process is as follows: graphene oxide and... The mixture was prepared by mixing at a weight ratio of 1:1 to obtain a mixed system; hydrochloric acid was added to adjust the pH of the mixed system to 1.5; and then the mixture was reacted at 60℃ for 1.5 h to obtain modified graphene-I.

[0085] Q2: Modified graphene-II, the preparation process is as follows: graphene oxide and... The mixture was prepared by mixing at a weight ratio of 1:1.5 to obtain a mixed system; hydrochloric acid was added to adjust the pH of the mixed system to 1.5; and then the mixture was reacted at 65°C for 1.5 h to obtain modified graphene-II.

[0086] Q3: Modified graphene-III, the preparation process is as follows: graphene oxide and... The mixture was prepared by mixing at a weight ratio of 1:1 to obtain a mixed system; sulfuric acid was added to adjust the pH of the mixed system to 1.5; and then the mixture was reacted at 65°C for 2 hours to obtain modified graphene-III.

[0087] In the following examples, the weight ratio of structural units contained in the polymer was calculated using the amount of raw materials fed.

[0088] Example 1

[0089] (1) Monomer A' Monomer B' Modified graphene-I was added to the reaction flask, followed by water, and the mixture was thoroughly mixed to obtain a solution.

[0090] (2) Nitrogen gas was introduced to remove oxygen for 30 min. Then, N,N-methylenebisacrylamide and an initiator (ammonium persulfate: sodium bisulfite weight ratio of 1:1) were added to the above mixture to initiate the reaction. The reaction temperature was 60℃ and the reaction time was 1.5 h. After the reaction was completed, a polymer colloid was obtained. After drying, the modified polymer (denoted as P1) was obtained.

[0091] The weight ratio of monomer A': monomer B': modified graphene-I: N,N-methylenebisacrylamide: initiator: water is 100:80:2:0.3:2:1800.

[0092] The viscosity-average molecular weight of P1 is 2.9 × 10⁻⁶. 7 g / mol; In P1, structural unit A Structural Unit B The weight ratio is 1:0.8.

[0093] P1 was granulated, dried at 105℃ to constant weight, pulverized, and sieved to obtain gel particles with an average particle size of 0.2 mm (denoted as S1).

[0094] Example 2

[0095] (1) Monomer A' Monomer B' Modified graphene-I was added to the reaction flask, followed by water, and the mixture was thoroughly mixed to obtain a solution.

[0096] (2) Nitrogen gas was introduced to remove oxygen for 30 min. Then, N,N-methylenebisacrylamide and an initiator (ammonium persulfate: sodium bisulfite weight ratio of 1.2:1) were added to the above mixture to initiate the reaction. The reaction temperature was 65℃ and the reaction time was 1.5 h. After the reaction was completed, a polymer colloid was obtained. After drying, the modified polymer (denoted as P2) was obtained.

[0097] The weight ratio of monomer A': monomer B': modified graphene-I: N,N-methylenebisacrylamide: initiator: water is 100:51:1.5:0.5:2:1800.

[0098] The viscosity-average molecular weight of P2 is 2.7 × 10⁻⁶. 7 g / mol; in P2, structural unit A Structural Unit B The weight ratio is 1:0.5.

[0099] P2 was granulated, dried at 105℃ to constant weight, pulverized, and sieved to obtain gel particles with an average particle size of 0.2 mm (denoted as S2).

[0100] Example 3

[0101] (1) Monomer A' Monomer B' Modified graphene-I was added to the reaction flask, followed by water, and the mixture was thoroughly mixed to obtain a solution.

[0102] (2) Nitrogen gas was introduced to remove oxygen for 30 min. Then, N,N-methylenebisacrylamide and initiator (ammonium persulfate: sodium bisulfite weight ratio of 1.2:1) were added to the above mixture to initiate the reaction. The reaction temperature was 55℃ and the reaction time was 2 h. After the reaction was completed, polymer colloid was obtained. After drying, modified polymer (denoted as P3) was obtained.

[0103] The weight ratio of monomer A': monomer B': modified graphene-I: N,N-methylenebisacrylamide: initiator: water is 100:102:1.5:0.3:2:2000.

[0104] The viscosity-average molecular weight of P3 is 2.5 × 10⁻⁶. 7 g / mol; in P3, structural unit A Structural Unit B The weight ratio is 1:1.

[0105] P3 was granulated, dried at 105℃ to constant weight, pulverized, and sieved to obtain gel particles with an average particle size of 0.2 mm (denoted as S3).

[0106] Example 4

[0107] (1) Monomer A' Monomer B' Modified graphene-I was added to the reaction flask, followed by water, and the mixture was thoroughly mixed to obtain a solution.

[0108] (2) Nitrogen gas was introduced to remove oxygen for 30 min. Then, N,N-methylenebisacrylamide and initiator (ammonium persulfate: sodium bisulfite weight ratio of 1.5:1) were added to the above mixture to initiate the reaction. The reaction temperature was 70℃ and the reaction time was 1 h. After the reaction was completed, polymer colloid was obtained. After drying, modified polymer (denoted as P4) was obtained.

[0109] The weight ratio of monomer A': monomer B': modified graphene-I: N,N-methylenebisacrylamide: initiator: water is 100:155:3:0.5:2:2000.

[0110] The viscosity-average molecular weight of P4 is 2.3 × 10⁻⁶. 7 g / mol; in P4, structural unit A Structural Unit B The weight ratio is 1:1.5.

[0111] P4 was granulated, dried at 105℃ to constant weight, pulverized, and sieved to obtain gel particles with an average particle size of 0.2 mm (denoted as S4).

[0112] Example 5

[0113] (1) Monomer A' Monomer B' Modified graphene-I was added to the reaction flask, followed by water, and the mixture was thoroughly mixed to obtain a solution.

[0114] (2) Nitrogen gas was introduced to remove oxygen for 30 min. Then, N,N-methylenebisacrylamide and initiator (ammonium persulfate: sodium bisulfite weight ratio of 1.5:1) were added to the above mixture to initiate the reaction. The reaction temperature was 70℃ and the reaction time was 1 h. After the reaction was completed, polymer colloid was obtained. After drying, modified polymer (denoted as P5) was obtained.

[0115] The weight ratio of monomer A': monomer B': modified graphene-I: N,N-methylenebisacrylamide: initiator: water is 100:155:3:0.5:2:2000.

[0116] The viscosity-average molecular weight of P5 is 2.2 × 10⁻⁶. 7 g / mol; in P5, structural unit A Structural Unit B The weight ratio is 1:1.5.

[0117] P5 was granulated, dried at 105℃ to constant weight, pulverized, and sieved to obtain gel particles with an average particle size of 0.2 mm (denoted as S5).

[0118] Example 6

[0119] The method of Example 5 was followed, except that modified graphene-I was replaced with an equal weight of modified graphene-II. All other conditions were the same as in Example 5. The modified polymer (denoted as P6) was obtained.

[0120] The viscosity-average molecular weight of P6 is 2.1 × 10⁻⁶. 7 g / mol; in P6, structural unit A Structural Unit B The weight ratio is 1:1.5.

[0121] P6 was granulated, dried at 105℃ to constant weight, pulverized, and sieved to obtain gel particles with an average particle size of 0.2 mm (denoted as S6).

[0122] Example 7

[0123] The method of Example 5 was followed, except that modified graphene-I was replaced with an equal weight of modified graphene-III. All other conditions were the same as in Example 5. The modified polymer was obtained (denoted as P7).

[0124] The viscosity-average molecular weight of P7 is 1.9 × 10⁻⁶. 7 g / mol; In P7, structural unit A Structural Unit B The weight ratio is 1:1.5.

[0125] P7 was granulated, dried at 105℃ to constant weight, pulverized, and sieved to obtain gel particles with an average particle size of 0.2 mm (denoted as S7).

[0126] Comparative Example 1

[0127] (1) Monomer A' Monomer B' Add it to the reaction flask, then add water and mix thoroughly to obtain a mixture;

[0128] (2) Nitrogen gas was introduced to remove oxygen for 30 min. Then, N,N-methylenebisacrylamide and an initiator (ammonium persulfate: sodium bisulfite weight ratio of 1:1) were added to the above mixture to initiate the reaction. The reaction temperature was 60℃ and the reaction time was 1.5 h. After the reaction was completed, a polymer colloid was obtained. After drying, the modified polymer (denoted as DP1) was obtained.

[0129] The weight ratio of monomer A': monomer B': N,N-methylenebisacrylamide: initiator: water is 100:80:0.3:2:1800.

[0130] DP1 was granulated, dried at 105℃ to constant weight, pulverized, and sieved to obtain gel particles with an average particle size of 0.2 mm (denoted as DS1).

[0131] Comparative Example 2

[0132] (1) Monomer A' Monomer B' Graphene oxide (brand name INFAN, purchased from Ningbo Fengcheng Nanotechnology Co., Ltd.) was added to the reaction flask, followed by water, and mixed thoroughly to obtain a mixture.

[0133] (2) Nitrogen gas was introduced to remove oxygen for 30 min. Then, N,N-methylenebisacrylamide and an initiator (ammonium persulfate: sodium bisulfite weight ratio of 1:1) were added to the above mixture to initiate the reaction. The reaction temperature was 60℃ and the reaction time was 1.5 h. After the reaction was completed, a polymer colloid was obtained. After drying, the modified polymer (denoted as DP2) was obtained.

[0134] The weight ratio of monomer A': monomer B': graphene oxide: N,N-methylenebisacrylamide: initiator: water is 100:80:2:0.3:2:1800.

[0135] DP2 was granulated, dried at 105℃ to constant weight, pulverized, and sieved to obtain gel particles with an average particle size of 0.2 mm (denoted as DS2).

[0136] Test case

[0137] The gel particles S1-S7 and DS1-DS2 prepared in Examples 1-7 and Comparative Examples 1-2 were tested for temperature and salt resistance, large-pore plugging strength, and improved oil recovery rate.

[0138] 1. Temperature and salt resistance test

[0139] Gel particles S1-S7 and DS1-DS2, each with a mineralization of 30000 mg / L (30000 mg NaCl added to 1 L of water), were added respectively. The expansion ratio and elasticity of the gel particles at 60℃ and 120℃ were then tested. The results are shown in Table 1-1.

[0140] Gel particles S1-S7 and DS1-DS2, each with a mineralization of 300,000 mg / L (300,000 mg NaCl added to 1 L of water), were added respectively. The expansion ratio and elasticity of the gel particles at 60℃ and 120℃ were then tested. The results are shown in Table 1-2.

[0141] Swelling factor test of gel particles: Weigh the gel particle sample (denoted as m); pour the weighed gel particles into a filter bag, seal it, and place it completely in the saline solution with the above-mentioned mineralization. Then, place the gel particles and saline solution together in a container, seal the container, pressurize it, and place the sealed high-pressure container in ovens at 60℃ and 120℃ respectively for heating. After 24 hours, remove the filter bag and hang it to drip water for 10 minutes, then weigh the entire sample (denoted as m0); at the same time, determine the weight blank value of the unused empty filter bag (denoted as m1). The swelling factor of the gel particles is calculated using the following formula.

[0142]

[0143] Where c is the expansion factor of the gel particles.

[0144] Elasticity test of gel particles: The expanded gel particles were made into cylindrical models with a diameter of 5 cm and a height of 2.5 cm. The elastic modulus of the cylindrical models was tested using a universal testing machine. The elastic modulus was used to characterize the elasticity of the gel particles.

[0145] Table 1-1

[0146]

[0147]

[0148] Note: Table 1-1 shows the test data of gel particles in saline with a mineralization of 30000 mg / L.

[0149] Table 1-2

[0150]

[0151] Note: Table 1-2 shows the test data of gel particles in saline with a mineralization of 300,000 mg / L.

[0152] As shown in Tables 1-1 and 1-2, the gel particles S1-S7 prepared from the modified polymers P1-P7 provided by this invention exhibit an expansion ratio greater than 19, reaching a maximum of 50, in brine at temperatures of 60℃ and 120℃ with a mineralization of 30000 mg / L. The expanded elasticity is greater than 600 Pa, reaching a maximum of 1760 Pa. In brine at temperatures of 60℃ and 120℃ with a mineralization of 300000 mg / L, the expansion ratio is greater than 10, reaching a maximum of 42. The expanded elasticity is greater than 630 Pa, reaching a maximum of 2000 Pa. These particles demonstrate high expansion ratios and high elasticity in high-temperature and high-mineralization environments, exhibiting excellent temperature and salt resistance. In contrast, the gel particles DS1-DS2 prepared from the polymers DP1-DP2 provided in Comparative Example 1-2 show significantly worse expansion performance and elasticity than S1-S7 under the same conditions.

[0153] 2. Large-diameter channel sealing strength test

[0154] The blocking rate of gel particles S1-S7 and DS1-DS2 was tested according to the method specified in "SY / T 6379-1998 Performance Evaluation Method of Particulate Profile Modifiers". The results are shown in Table 2.

[0155] Table 2

[0156] Test object Blocking rate (%) S1 98.5 S2 97.8 S3 97.3 S4 97.1 S5 96.8 S6 96.6 S7 96.5 DS1 89.1 DS2 89.0

[0157] As shown in Table 2, the gel particles S1-S7 prepared from the modified polymers P1-P7 provided by the present invention exhibit excellent plugging performance. In the above plugging test, the plugging rate is greater than 96%, and the plugging strength for large pores is high, which can effectively reduce the permeability of the aqueous phase. Compared with DS1-DS2, it has a significantly better profile control and water plugging effect.

[0158] 3. Enhanced oil recovery testing

[0159] Oil displacement experiments were conducted using heterogeneous cores from interlayer formations in an 80℃ constant temperature chamber, as follows:

[0160] After vacuuming the core, saturate it with 100,000 mg / L brine; use simulated oil to displace the water in the core until no water flows out of the outlet, and calculate the oil saturation; use injected brine at a constant rate to displace the simulated oil in the core under the condition of bound water until the water cut at the outlet reaches 98%, and calculate the water drive recovery rate.

[0161] Gel particles S1-S7 and DS1-DS2 (each with a concentration of 1000 mg / L in the polyacrylamide aqueous solution) were added to a 2000 mg / L polyacrylamide aqueous solution to obtain a composite flooding system. The composite flooding system was injected at the same rate as the water flooding described above, with a current of 0.5 PV, followed by subsequent water flooding until the outlet water cut reached 98%. The percentage increase in oil recovery of the composite flooding system compared to water flooding was calculated, and the results are shown in Table 3.

[0162] Table 3

[0163] Test object Increase the recovery rate (%) S1 13.4 S2 12.9 S3 12.5 S4 12.3 S5 11.5 S6 11.3 S7 10.7 DS1 6.5 DS2 6.3

[0164] As shown in Table 3, in the above-mentioned oil displacement experiments, the composite flooding system composed of gel particles S1-S7 prepared by the modified polymer P1-P7 provided by the present invention and polymer solution exhibited excellent oil displacement effect, which can improve the recovery rate by more than 10% compared with water flooding.

[0165] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A modified polymer, characterized in that, The modified polymer contains structural unit A as shown in formula (I) and structural unit B as shown in formula (II); wherein the weight ratio of structural unit A to structural unit B is 1:(0.1-2). Formula (I); Formula (II); Wherein, R1 and R2 are each independently -H or C1-C5 alkyl groups; R3 and R4 are each independently -H or C1-C3 alkyl groups; R5 is a C1-C15 alkylene group; Z is H, Na, or K; Q represents graphene oxide partially modified by alkanolamine compounds.

2. The modified polymer according to claim 1, wherein, The weight ratio of structural unit A to structural unit B is 1:(0.5-1). And / or, R1 and R2 are each independently -H or C1-C2 alkyl groups; R3 and R4 are each independently -H or C1-C2 alkyl groups; and R5 is a C1-C10 alkylene group.

3. The modified polymer according to claim 1 or 2, wherein, The alkanolamine compounds have the structure shown in formula (III). Formula (III); R6 and R7 are each independently selected from -H or C1-C5 alkyl groups.

4. The modified polymer according to claim 3, wherein, R6 and R7 are each independently selected from -H or C1-C3 alkyl groups.

5. The modified polymer according to any one of claims 1-2 and 4, wherein, Under conditions of 60-120℃, the expansion ratio of the modified polymer in brine with a mineralization of 30000-300000 mg / L is 10-50. The viscosity-average molecular weight of the modified polymer is (1.5-3)×10⁻⁶. 7 g / mol.

6. The modified polymer according to claim 3, wherein, Under conditions of 60-120℃, the expansion ratio of the modified polymer in brine with a mineralization of 30000-300000 mg / L is 10-50. The viscosity-average molecular weight of the modified polymer is (1.5-3)×10⁻⁶. 7 g / mol.

7. A method for preparing a modified polymer, comprising: In the presence of an initiator, a crosslinking agent, and water, monomer A', monomer B', and modified graphene are reacted to obtain a modified polymer. The weight ratio of monomer A', monomer B' and modified graphene is 100:(1-200):(1-10). The modified graphene is graphene oxide partially modified by alkanolamine compounds; The monomer A' is a monomer having the structure shown in formula (IV), and the monomer B' is a monomer having the structure shown in formula (V). Formula (IV) Equation (V) Wherein, R1 and R2 are each independently -H or C1-C5 alkyl groups; R3 and R4 are each independently -H or C1-C3 alkyl groups; R5 is a C1-C15 alkylene group; and Z is H, Na, or K.

8. The method according to claim 7, wherein, The alkanolamine compounds have the structure shown in formula (III). Formula (III); R6 and R7 are each independently selected from -H or C1-C5 alkyl groups.

9. The method according to claim 8, wherein, R6 and R7 are each independently selected from -H or C1-C3 alkyl groups.

10. The method according to any one of claims 7-9, wherein, Based on 100 parts by weight of the monomer A', the initiator is 1-10 parts by weight, the crosslinking agent is 0.2-5 parts by weight, and the water is 1500-3000 parts by weight.

11. The method according to any one of claims 7-9, wherein, The crosslinking agent is selected from N,N-methylenebisacrylamide and / or aluminum citrate; And / or, the initiator is composed of an oxidant and a reducing agent; wherein the weight ratio of the oxidant to the reducing agent is (0.5-1.5):

1.

12. The method according to any one of claims 7-9, wherein, The reaction conditions include: a temperature of 45-80℃ and a time of 0.5-5h.

13. The method according to claim 12, wherein, The reaction conditions include: a temperature of 55-65℃ and a time of 1-2 hours.

14. The modified polymer obtained by the method of any one of claims 7-13.

15. A gel particle, characterized in that, The gel particles are obtained by sequentially granulating, drying, pulverizing and sieving the polymer. The polymer is the modified polymer according to any one of claims 1-6 and 14.

16. The gel particles according to claim 15, wherein, The average particle size of the gel particles is 0.05-2 mm.

17. The gel particles according to claim 15 or 16, wherein, Under conditions of 60-120℃, the expansion ratio of the gel particles in saline with a mineralization of 30000-300000 mg / L is 10-50. And / or, under conditions of 60-120°C, the elasticity of the gel particles after swelling in saline with a mineralization of 30000-300000 mg / L is 600-2000 Pa.

18. The application of the gel particles according to any one of claims 15-17 as a profile control and water shut-off agent in oil extraction.

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