Chitosan graft copolymer, method for preparing the same, and drilling fluid

Abstract

The application relates to the field of oilfield chemical drilling fluid treating agents, and discloses a chitosan graft copolymer, a preparation method thereof and a drilling fluid, the chitosan graft copolymer has a structure shown in formula (I), the number average molecular weight is 200000-600000; m is 1200-3500, X and Z are independently H or -R1COOM1 or a polymer chain segment; wherein, R1 is C1-C5 alkylene, M1 is H, Na or K; the polymer chain segment contains structure unit A and structure unit B, the structure unit A contains at least two -COOM2, M2 is H, Na or K, the structure unit B contains a cyclic lactam structure; Y is H or a quaternary ammonium salt structure with an ester group. The chitosan graft copolymer provided by the application has good wall solidifying performance and fluid loss reduction performance, and the well wall stability of a formation with broken mud shale and easy collapse is ensured from the aspects of wall solidifying and reduction of filtrate invasion.

Description

Technical Field

[0001] This invention relates to the field of oilfield chemical drilling fluid treatment agents, specifically to a chitosan graft copolymer, its preparation method, and drilling fluid. Background Technology

[0002] In recent years, with the continuous expansion of oil and gas exploration and development, drilling has encountered more and more easily collapsible formations such as highly reactive mudstone and shale, well-developed bedding fractures, and fractured zones, making wellbore stabilization increasingly difficult. For highly reactive mudstone and shale formations, existing strong inhibitors such as polyetheramine alkyl glycosides, polyetheramines, and polyamines are already quite effective. However, for easily collapsible formations such as well-developed bedding fractures and fractured zones, not only are strong drilling fluid inhibitory properties required, but also higher demands are placed on chemical wall stabilization performance and the ability to reduce filtrate intrusion.

[0003] In recent years, commonly used wall-stabilizing agents mainly include silicate-based, organosilicon-based, and polyaluminum-based agents. These agents utilize the temperature, pH, and salinity conditions after entering the formation to undergo physical or chemical changes, achieving the effect of depositing and blocking bedding fractures or forming a cemented seal, thereby sealing or consolidating the wellbore. However, these wall-stabilizing agents have limited actual wall-stabilizing and anti-collapse effects, significantly impact drilling fluid rheology, are prone to high-temperature failure, and have environmental impacts. Furthermore, their filtration reduction effect is poor, leading to stress changes in the filtrate invading the formation and causing wellbore collapse. To better address the challenges of wellbore instability and filtration reduction in formations prone to collapse, such as those with well-developed bedding fractures and fractured zones, the performance of existing commonly used wall-stabilizing agents urgently needs improvement. Besides enhancing wall-stabilizing performance, it is also necessary to enhance filtration reduction performance to meet the technical requirements for wellbore stability in formations prone to collapse, such as those with well-developed bedding fractures and fractured zones. Therefore, it is necessary to develop high-efficiency wall-stabilizing and filtration-reducing agents that combine wall-stabilizing and filtration-reducing effects to meet the urgent technical needs in the field. Summary of the Invention

[0004] The purpose of this invention is to overcome the problem of existing technologies lacking both good wall-fixing and filtration loss reduction effects, and to provide a chitosan graft copolymer, its preparation method, and drilling fluid. The chitosan graft copolymer provided by this invention has good wall-fixing and filtration loss reduction effects, is non-biotoxic, and is environmentally friendly.

[0005] To achieve the above objectives, the first aspect of the present invention provides a chitosan graft copolymer, wherein the chitosan graft copolymer has the structure shown in formula (I) and a number-average molecular weight of 200,000-600,000.

[0006]

[0007] m is 1200-3500, X and Z are each independently H or -R1COOM1 or polymeric segments, and the content of polymeric segments is 0.15-20wt% based on the total amount of chitosan graft copolymer; wherein, R1 is a C1-C5 alkylene group, M1 is H, Na or K; the polymeric segment contains structural unit A and structural unit B, structural unit A contains at least two -COOM2, M2 is H, Na or K, and structural unit B contains a cyclic lactam structure; Y is H or a quaternary ammonium salt structure with an ester group.

[0008] Preferably, the mass ratio of -R1COOM1 to the polymeric chain segment is 1:1-1.5, and the mass ratio of structural unit A to structural unit B in the polymeric chain segment is 1:0.5-2.

[0009] Preferably, Y is H or

[0010] Wherein, R2-R4 are each independently H or C1-C5 alkyl groups, preferably H; R5 is a C1-C5 alkylene group; R6-R8 are each independently C1-C5 alkyl groups; T - For F - Cl - ,Br - Or I - Cl is preferred - .

[0011] Preferably, structural unit A is a structural unit having the structure shown in formula (1), and structural unit B is a structural unit having the structure shown in formula (2);

[0012]

[0013] Among them, R9-R 13 Each is independently an H or C1-C5 alkyl group, preferably H; M2 and M3 are each independently H, Na or K.

[0014] A second aspect of the present invention provides a method for preparing a chitosan graft copolymer, the method comprising the following steps:

[0015] (1) Chitosan was carboxylated with the halocarboxylic acid shown in formula (II) to obtain the first intermediate product;

[0016] (2) The first intermediate product is reacted with the quaternary ammonium salt shown in formula (III) to obtain the second intermediate product;

[0017] (3) In the presence of an initiator, the second intermediate product and the monomer are subjected to a graft copolymerization reaction in water; wherein the monomer includes: monomer A' and monomer B', wherein monomer A' is a monomer having the structure shown in formula (1') and monomer B' is a monomer having the structure shown in formula (2');

[0018]

[0019]

[0020] Among them, R1-R 13 The definition corresponds to the definition above; T is F, Cl, Br or I, preferably Cl.

[0021] A third aspect of the present invention provides a chitosan graft copolymer obtained by the method described in the second aspect above.

[0022] A fourth aspect of the present invention provides a drilling fluid comprising the chitosan graft copolymer described in the first or third aspect above as a filtration loss reducer.

[0023] Through the above technical solution, the present invention can achieve the following beneficial effects:

[0024] The chitosan graft copolymer provided by this invention exhibits good wall-consolidation and filtration loss reduction properties in drilling fluids, is non-biotoxic, and environmentally friendly. It provides excellent chemical consolidation of the wellbore, effectively consolidating formations prone to collapse such as those with bedding fractures and fractured zones. Simultaneously, it prevents filtrate from infiltrating the formation and causing stress changes, thus effectively reducing filtration loss. This invention effectively solves the problem of wellbore instability in formations prone to collapse, such as those with bedding fractures and fractured zones, meeting the technical requirements for wellbore stability in these formations. Furthermore, the preparation process of the chitosan graft copolymer provided by this invention involves mild reaction conditions, uses water as a solvent, has low energy consumption, and produces no wastewater, waste gas, or waste residue. Attached Figure Description

[0025] Figure 1 The infrared spectrum of the sample obtained in Example 1 of this invention;

[0026] Figure 2 (a)-(d) are photographs of the unsoaked core column, the core column soaked in water, the core column soaked in the sample of Example 1, and the core column soaked in the comparative sample, respectively. Detailed Implementation

[0027] 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.

[0028] In this invention, the C1-C5 alkyl group refers to an alkyl group having 1-5 carbon atoms; the C1-C5 alkylene group refers to an alkylene group having 1-5 carbon atoms.

[0029] The first aspect of the present invention provides a chitosan graft copolymer, wherein the chitosan graft copolymer has the structure shown in formula (I) and a number-average molecular weight of 200,000-600,000;

[0030]

[0031] m is 1200-3500, X and Z are each independently H or -R1COOM1 or polymeric segments, and the content of polymeric segments is 0.15-20wt% based on the total amount of chitosan graft copolymer; wherein, R1 is a C1-C5 alkylene group, M1 is H, Na or K; the polymeric segment contains structural unit A and structural unit B, structural unit A contains at least two -COOM2, M2 is H, Na or K, and structural unit B contains a cyclic lactam structure; Y is H or a quaternary ammonium salt structure with an ester group.

[0032] The inventors of this invention discovered in their research that by simultaneously introducing structural unit A and structural unit B into the chitosan structure and controlling the content of each structural unit within the aforementioned range, the obtained chitosan graft copolymer exhibits a good filtration loss reduction effect.

[0033] In this invention, the C1-C5 alkylene groups can be straight-chain, branched, or cyclic, for example, -CH2-, -CH2CH2-, or -CH2CH2CH2-.

[0034] In a preferred embodiment of the present invention, Y is H or

[0035] Wherein, R2-R4 are each independently H or C1-C5 alkyl groups, preferably H; R5 is a C1-C5 alkylene group; R6-R8 are each independently C1-C5 alkyl groups, preferably methyl; T - For F - Cl - ,Br - Or I - Cl is preferred -.

[0036] In this invention, R6-R8 can be the same or different, but are preferably the same.

[0037] In this invention, the C1-C5 alkyl groups can be straight-chain, branched, or cyclic, for example, -CH3, -CH2CH3, -CH2CH2CH3, -CH(CH3)2, or -C(CH3)3.

[0038] In a preferred embodiment of the present invention, the mass ratio of -R1COOM1 to the polymeric chain segment is 1:1-1.5, and the mass ratio of structural unit A to structural unit B in the polymeric chain segment is 1:0.5-2.

[0039] In a preferred embodiment of the present invention, the structural unit A is a structural unit having the structure shown in formula (1).

[0040] Among them, R9-R 10 Each is independently an H or C1-C5 alkyl group, preferably H; M3 and M4 are each independently H, Na or K.

[0041] In a preferred embodiment of the present invention, the structural unit B is a structural unit having the structure shown in formula (2);

[0042]

[0043] Among them, R 11 -R 13 Each is independently an H or C1-C5 alkyl group.

[0044] In this invention, when R9-R 13 When each is H, structural unit A can be a structural unit provided by maleic anhydride, and structural unit B can be a structural unit provided by N-vinylcaprolactam. That is, in a specific embodiment of the present invention, the polymeric segments in the chitosan graft copolymer structure include structural units provided by maleic anhydride and N-vinylcaprolactam.

[0045] In a preferred embodiment of the present invention, the polymeric segment further comprises at least one of structural unit C, structural unit D, structural unit E and structural unit F; wherein, structural unit C is selected from at least one structural unit having the structure shown in formula (3), structural unit D is a structural unit having the structure shown in formula (4), structural unit E is a structural unit having the structure shown in formula (5), and structural unit F is a structural unit having the structure shown in formula (6).

[0046]

[0047] Among them, R 14 -R 16 R 19 -R 21 R 23 -R 25 R 28 -R 30 Each is independently an H or C1-C5 alkyl group, preferably H;

[0048] R 17 It is -CO-O;

[0049] R 18 R 22 R 26 Each is an independent alkylene group, either a C1-C5 bond or a C1-C5 bond;

[0050] R 27 It is a C1-C5 alkyl group, preferably -CH3, -CH2CH3, -CH(CH3)2, or -C(CH3)3;

[0051] M5 and M6 are each independently H, Na, or K.

[0052] In this invention, when R 14 -R 16 Each is H, R 17 For -CO-O, R 18 When R is a C4 alkylene group, then structural unit C is provided by acryloyloxybutyric acid. 19 -R 21 Each is H, R 22 When R is a bond, then structural unit D is a structural unit provided by acrylonitrile. 23 -R 25 Each is H, R 26 When R is a bond, then structural unit E is a structural unit provided by vinyltrialkoxysilane. 23 -R 30 If each is H, then structural unit E is a structural unit provided by sulfonated styrene. That is, in a specific embodiment of the present invention, the polymeric segments in the chitosan graft copolymer structure also include structural units provided by at least one of acryloyloxybutyric acid, acrylonitrile, sulfonated styrene, and vinyltrialkoxysilane.

[0053] In a preferred embodiment of the present invention, the vinyltrialkoxysilane is selected from at least one of vinyltrimethoxysilane, vinyltriethoxysilane, vinyltriisopropoxysilane, and vinyltritert-butoxysilane.

[0054] In a preferred embodiment of the present invention, the mass ratio of chitosan, structural unit A, structural unit B, structural unit C, structural unit D, structural unit E and structural unit F is 1:(1.6-3):(2-4):(2.5-4):(1-2.5):(3-5.5):(4-5), preferably 1:(2-3):(2.5-4):(3-4):(1-2):(3-5):(4-4.5).

[0055] The inventors of this invention discovered in their research that, based on the presence of unit A and structural unit B in the polymer chain segment of the chitosan graft copolymer, introducing structural unit C and controlling the content of each structural unit within the aforementioned range can further improve the filtration loss reduction effect of the chitosan graft copolymer.

[0056] Furthermore, by introducing structural unit D into the polymer chain segments of the chitosan graft copolymer, which already contain structural units A, B, and C, and controlling the content of each structural unit within the aforementioned range, the filtration loss reduction effect of the chitosan graft copolymer can be further improved.

[0057] Furthermore, based on the presence of structural units A, B, C, and D in the polymer chain segments of the chitosan graft copolymer, structural unit E is introduced, and the content of each structural unit is controlled within the aforementioned range. In addition to having a good filtration loss reduction effect, the chitosan graft copolymer also has good wall-fixing properties.

[0058] Furthermore, by introducing structural unit F into the polymer chain segments of the chitosan graft copolymer, which already contain structural units A, B, C, D, and E, and controlling the content of each structural unit within the aforementioned range, the filtration loss reduction effect and wall-solidification performance of the chitosan graft copolymer can be further improved.

[0059] A second aspect of the present invention provides a method for preparing a chitosan graft copolymer. According to a preferred embodiment, the method includes the following steps:

[0060] (1) The chitosan aqueous solution is alkalized and gelatinized with an alkaline compound and an alcohol compound, and then the product obtained by the alkalization and gelatinization is carboxylated with the halocarboxylic acid shown in formula (II) to obtain the first intermediate product.

[0061] (2) The first intermediate product is reacted with the quaternary ammonium salt shown in formula (III) to obtain the second intermediate product;

[0062] (3) In the presence of an initiator, the second intermediate product and the monomer are subjected to a graft copolymerization reaction in water; wherein the monomer includes: monomer A' and monomer B', wherein monomer A' is a monomer having the structure shown in formula (1') and monomer B' is a monomer having the structure shown in formula (2');

[0063]

[0064]

[0065] Among them, R 1 -R 13 The definition is the same as the definition above; T is F, Cl, Br or I, preferably Cl.

[0066] In this invention, chitosan aqueous solution is first activated using alkaline and alcoholic compounds. The activated chitosan is then modified sequentially using halocarboxylic acids and quaternary ammonium salts. Finally, the modified chitosan is grafted with monomers A' and B' to obtain the chitosan graft copolymer. The chitosan graft copolymer provided by this invention exhibits good wall-stabilizing properties and reduced filtration loss in drilling fluids, is non-toxic, and environmentally friendly. Furthermore, the preparation process of the chitosan graft copolymer provided by this invention utilizes mild reaction conditions, uses water as a solvent, has low energy consumption, and produces no wastewater, waste gas, or waste residue.

[0067] In a preferred embodiment of the present invention, in step (1), chitosan is activated by alkalizing and gelatinizing it with alkaline compounds and alcohols, making it easier for chitosan to undergo subsequent reactions.

[0068] In this invention, in order to promote the full progress of the alkalization and gelatinization process, the conditions for alkalization and gelatinization include: a temperature of 55-70℃, preferably 56-67℃, a time of 0.5-2h, and the alkalization and gelatinization is carried out under stirring conditions.

[0069] In a preferred embodiment of the present invention, the alkaline compound is selected from sodium hydroxide and / or potassium hydroxide.

[0070] In a preferred embodiment of the present invention, the alcohol compound is selected from at least one of ethanol, glycerol and isopropanol.

[0071] In a preferred embodiment of the present invention, the mass ratio of chitosan, water, alkaline compound, and alcohol compound is 1:(10-30):(1-3):(2-5). When the amounts of each raw material are within the above range, the chitosan can be fully activated.

[0072] In a preferred embodiment of the present invention, in order to promote the full progress of the carboxylation reaction, the conditions for the carboxylation reaction include: a temperature of 70-85°C, a time of 3-6 hours, and a pH value of 9-11.

[0073] In this invention, to ensure that the pH value of the solution undergoing the carboxylation reaction meets the above conditions, an alkaline pH adjuster conventionally used in the art can be employed. Preferably, the alkaline pH adjuster is selected from sodium hydroxide or potassium hydroxide.

[0074] In a preferred embodiment of the present invention, in order to ensure that the activated chitosan is fully modified, the mass ratio of chitosan to halocarboxylic acid is 1:(3-5), preferably 1:(4-5).

[0075] In this invention, there is no particular limitation on the type of halocarboxylic acid, as long as it has the structure shown in formula (II). Preferably, the halocarboxylic acid is selected from at least one of chloroacetic acid, 3-chloropropionic acid, and 4-chlorobutyric acid.

[0076] In a preferred embodiment of the present invention, in order to allow the first intermediate product to fully react with the quaternary ammonium salt to generate the second intermediate product, the conditions for the addition reaction include: a temperature of 105-130°C and a time of 2-4 hours.

[0077] In a preferred embodiment of the present invention, the mass ratio of chitosan to quaternary ammonium salt is 1:(3-5), preferably 1:(4-5). This preferred embodiment ensures that the first intermediate product is sufficiently modified by the quaternary ammonium salt.

[0078] In this invention, there is no particular limitation on the type of quaternary ammonium salt, as long as it has the structure shown in formula (III). Preferably, the quaternary ammonium salt is selected from methacryloyloxyethyltrimethylammonium chloride and methacryloyloxyethyltrimethylammonium bromide.

[0079] In a preferred embodiment of the present invention, step (3) includes: mixing the second intermediate product, monomer A' and monomer B' in water to obtain a mixture; then adding an initiator to the mixture to carry out a graft copolymerization reaction to obtain a reaction product; and then drying, granulating and pulverizing the reaction product to obtain the chitosan graft copolymer.

[0080] In this invention, there are no particular limitations on the mixing conditions, as long as the second intermediate product, monomer A', and monomer B' are sufficiently dissolved. Preferably, the mixing is carried out under heating conditions at a temperature of 45-68°C.

[0081] In a preferred embodiment of the present invention, to promote the full reaction between the second intermediate product and the monomer, the graft copolymerization reaction conditions include: a temperature of 75-95°C, preferably 78-94°C, a time of 2-8 hours, and a pH value of 8-10. Preferably, the graft copolymerization reaction is carried out under an inert gas atmosphere, wherein the inert gas is selected from nitrogen or argon.

[0082] In this invention, to ensure that the pH value of the solution undergoing the graft copolymerization reaction meets the above conditions, an alkaline pH adjuster conventionally used in the art can be employed. Preferably, the alkaline pH adjuster is selected from sodium hydroxide or potassium hydroxide.

[0083] In a preferred embodiment of the present invention, the monomer A' is a monomer having the structure shown in formula (1'), and preferably, the monomer A' is selected from maleic anhydride.

[0084] In a preferred embodiment of the present invention, the monomer B' is a monomer having the structure shown in formula (2'), and preferably, the monomer B' is selected from N-vinylcaprolactam.

[0085] In this invention, there are no particular limitations on the type and amount of the initiator, and it can be any initiator conventionally used in the art. Preferably, the initiator is selected from at least one of benzoyl peroxide, ammonium persulfate, cerium ammonium nitrate, and azobisisobutylamidine hydrochloride.

[0086] In a preferred embodiment of the present invention, the mass ratio of chitosan to initiator is 1:(0.05-0.2). Using this preferred scheme, the chitosan graft copolymer has good filtration loss reduction properties.

[0087] In a preferred embodiment of the present invention, in order to improve the filtration loss reduction and wall-fixing properties of the obtained chitosan graft copolymer, in step (3), the monomers for the graft copolymerization reaction further include at least one of monomers C', D', E' and F'; wherein, monomer C' is selected from at least one monomer having the structure shown in formula (3'), monomer D' is a monomer having the structure shown in formula (4'), monomer E' is a monomer having the structure shown in formula (5'), and monomer F' is a monomer having the structure shown in formula (6');

[0088]

[0089] Among them, R 14 -R 30 The definitions are the same as those described above, with M5 and M6 being H, Na, or K.

[0090] In a preferred embodiment of the present invention, the monomer C' is selected from acryloyloxybutyric acid; the monomer D' is selected from acrylonitrile; the monomer E' is selected from vinyltrialkoxysilane; and the monomer F' is selected from sulfonated styrene.

[0091] The three alkoxy groups in monomer E' can be the same or different, preferably the same, and all are alkoxy groups with 1-4 carbon atoms. In a preferred embodiment of the invention, the vinyltrialkoxysilane is selected from vinyltrimethoxysilane, vinyltriethoxysilane, vinyltriisopropoxysilane, or vinyltritert-butoxysilane.

[0092] In a preferred embodiment of the present invention, the mass ratio of chitosan, monomer A', monomer B', monomer C', monomer D', monomer E', and monomer F' is 1:(1.6-3):(2-4):(2-4):(1-2.5):(3-5.5):(4-5), preferably 1:(2-3):(3-4):(2.5-4)(1-2):(3-5):(4-4.5). This preferred embodiment improves the wall-fixing properties and filtration loss reduction properties of the obtained chitosan graft copolymer.

[0093] According to a particularly preferred embodiment of the present invention, the preparation method of the chitosan graft copolymer used as the filtration loss reducer includes the following steps: (1) adding chitosan (degree of polymerization m is 1200-3500) to distilled water, stirring evenly, adding an alkaline compound such as sodium hydroxide and an alcohol compound such as ethanol, stirring evenly and then carrying out an alkaline gelatinization reaction, then adding a halocarboxylic acid such as chloroacetic acid as shown in formula (II), stirring evenly and then adjusting the pH of the reaction solution to 9-11 and carrying out a carboxylation reaction for 3-6 hours to obtain intermediate product A1;

[0094] (2) Add the quaternary ammonium salt of formula (III), such as methacryloyloxyethyltrimethylammonium chloride, to intermediate product A1 to carry out an addition reaction to obtain intermediate product B1;

[0095] (3) Add the monomer required for the reaction to distilled water and stir evenly to obtain a monomer aqueous solution; add the monomer aqueous solution to intermediate product B1, stir evenly and adjust the pH value to 8-10, add an initiator such as benzoyl peroxide initiator under nitrogen protection to carry out graft copolymerization, dry, granulate and crush to obtain chitosan graft copolymer, which can be directly used as a filtration reducer for drilling fluid without further separation and purification.

[0096] A third aspect of this invention provides a chitosan graft copolymer prepared by the method described in the second aspect above. The chitosan graft copolymer provided by this invention exhibits good wall-stabilizing properties and reduced filtration loss in drilling fluids, and is non-toxic and environmentally friendly.

[0097] A fourth aspect of the present invention provides a drilling fluid comprising the chitosan graft copolymer described in the first or third aspect above as a filtration loss reducer.

[0098] In a preferred embodiment of the present invention, the content of the chitosan graft copolymer is 0.15-20 wt%, preferably 0.5-10 wt%, further 0.5-5 wt%, and even more preferably 0.5-3 wt%, based on the total amount of drilling fluid.

[0099] In this invention, there are no special restrictions on the other components in the drilling fluid besides the chitosan graft copolymer. Those skilled in the art can select drilling fluid components to formulate the drilling fluid according to actual needs, and this invention does not impose any limitations.

[0100] The present invention will be described in detail below through examples. Unless otherwise stated, all raw materials used in the following examples and comparative examples are commercially available products.

[0101] Example 1

[0102] (1) Add 12g of chitosan (degree of polymerization m is 1500) to 200g of distilled water and stir evenly. Add 20g of sodium hydroxide and 30g of ethanol and stir evenly. Perform alkaline gelatinization reaction at 56℃ for 0.5h. Add 42g of chloroacetic acid and stir evenly. Adjust the pH of the reaction solution to 9 with 20wt% sodium hydroxide aqueous solution. Perform carboxylation reaction at 72℃ for 3h to obtain intermediate product A1.

[0103] (2) Add 44g of methacryloyloxyethyltrimethylammonium chloride to intermediate product A1 and carry out an addition reaction at 108℃ for 2h to obtain intermediate product B1.

[0104] (3) Add 32g acryloyloxybutyric acid, 22g maleic anhydride, 18g acrylonitrile, 24g N-vinylcaprolactam, 43g vinyltrimethoxysilane, and 48g sulfonated styrene to 300g distilled water and stir until homogeneous to obtain a monomer aqueous solution; add the monomer aqueous solution to intermediate product B1, stir until homogeneous, heat to 45°C, adjust the pH to 8 with 20wt% sodium hydroxide aqueous solution, add 0.9g benzoyl peroxide initiator under nitrogen protection, and graft copolymerize at 78°C for 2h. Dry, granulate, and pulverize to obtain chitosan graft copolymer.

[0105] The product prepared in Example 1 of this invention was subjected to infrared testing, and the infrared spectrum is shown below. Figure 1 As shown: at 1596cm -1 The peak at 1216 cm⁻¹ is the characteristic absorption peak of chitosan NH. -1 The characteristic absorption peak of the C=O bond is at 1356 cm⁻¹. -1The characteristic absorption peak of the quaternary ammonium group is at 2213 cm⁻¹. -1 The characteristic absorption peak of the carbon-nitrogen triple bond is at 1045 cm⁻¹. -1 The characteristic absorption peak for sulfonic acid groups is 1403 cm⁻¹. -1 The characteristic absorption peak of lactam is at 1253 cm⁻¹. -1 The peak at this point is a characteristic absorption peak for silanes. This indicates that carbonyl groups, quaternary ammonium groups, cyano groups, sulfonic acid groups, lactam groups, and silane groups have been introduced into the chitosan molecular structure.

[0106] Based on the calculated feed amounts (the same applies below), and using chitosan as the baseline, the mass ratio of structural unit A, structural unit B, structural unit C, structural unit D, structural unit E, and structural unit F in the product prepared in Example 1 of this invention is 22:24:32:18:43:48. The number-average molecular weight of the chitosan graft copolymer, determined by gel permeation chromatography, is 278,000.

[0107] Example 2

[0108] (1) Add 12g of chitosan (degree of polymerization m is 2000) to 240g of distilled water and stir evenly. Add 22g of potassium hydroxide and 35g of glycerol and stir evenly. Alkali gelatinize at 58℃ for 1.0h. Add 44g of 3-chloropropionic acid and stir evenly. Adjust the pH of the reaction solution to 10 with 20% potassium hydroxide aqueous solution. Carboxylate at 75℃ for 4h to obtain intermediate product A2.

[0109] (2) Add 46g of methacryloyloxyethyltrimethylammonium chloride to intermediate product A2 and carry out an addition reaction at 115℃ for 3h to obtain intermediate product B2.

[0110] (3) Add 36g acryloyloxybutyric acid, 24g maleic anhydride, 22g acrylonitrile, 28g N-vinylcaprolactam, 48g vinyltriethoxysilane, and 50g sulfonated styrene to 350g distilled water and stir until homogeneous to obtain a monomer aqueous solution; add the monomer aqueous solution to intermediate product B2, stir until homogeneous, heat to 50℃, adjust the pH value to 9 with 20% potassium hydroxide aqueous solution, add 1.1g ammonium persulfate initiator under helium protection, graft copolymerize at 84℃ for 4h, dry, granulate, and pulverize to obtain chitosan graft copolymer.

[0111] Based on the amount of chitosan used, the mass ratio of structural unit A, structural unit B, structural unit C, structural unit D, structural unit E, and structural unit F in the product prepared in Example 2 of this invention is 12:14:18:11:24:25. The number-average molecular weight of the chitosan graft copolymer was determined to be 371,000 by gel permeation chromatography.

[0112] Example 3

[0113] (1) Add 12g of chitosan (degree of polymerization m is 3000) to 280g of distilled water and stir evenly. Add 24g of sodium hydroxide and 45g of isopropanol and stir evenly. Alkali gelatinize at 60℃ for 1.5h. Add 50g of 4-chlorobutyric acid and stir evenly. Adjust the pH of the reaction solution to 11 with 20% sodium hydroxide aqueous solution. Carboxylate at 78℃ for 5h to obtain intermediate product A3.

[0114] (2) Add 50g of methacryloyloxyethyltrimethylammonium chloride to intermediate product A3 and carry out an addition reaction at 120℃ for 4h to obtain intermediate product B3.

[0115] (3) Add 42g acryloyloxybutyric acid, 26g maleic anhydride, 24g acrylonitrile, 30g N-vinylcaprolactam, 52g vinyltriisopropoxysilane, and 52g sulfonated styrene to 400g distilled water and stir until homogeneous to obtain a monomer aqueous solution; add the monomer aqueous solution to intermediate product B3, stir until homogeneous, heat to 60℃, adjust the pH value to 10 with 20% sodium hydroxide aqueous solution, add 1.5g cerium ammonium nitrate initiator under nitrogen protection, graft copolymerize at 90℃ for 6h, dry, granulate, and pulverize to obtain chitosan graft copolymer.

[0116] Based on the amount of chitosan used, the mass ratio of structural unit A, structural unit B, structural unit C, structural unit D, structural unit E, and structural unit F in the product prepared in Example 3 of this invention is 13:15:21:12:26:26. The number-average molecular weight of the chitosan graft copolymer was determined to be 556,000 by gel permeation chromatography.

[0117] Example 4

[0118] (1) Add 12g of chitosan (degree of polymerization m is 1800) to 300g of distilled water and stir evenly. Add 26g of sodium hydroxide and 50g of isopropanol and stir evenly. Alkali gelatinize at 67℃ for 2h. Add 54g of chloroacetic acid and stir evenly. Adjust the pH of the reaction solution to 11 with 20% sodium hydroxide aqueous solution. Carboxylate at 81℃ for 6h to obtain intermediate product A4.

[0119] (2) Add 52g of methacryloyloxyethyltrimethylammonium chloride to intermediate product A4 and carry out an addition reaction at 130℃ for 4h to obtain intermediate product B4.

[0120] (3) Add 48g of acryloyloxybutyric acid, 28g of maleic anhydride, 28g of acrylonitrile, 32g of N-vinylcaprolactam, 55g of vinyltrimethoxysilane, and 54g of sulfonated styrene to 450g of distilled water and stir until homogeneous to obtain a monomer aqueous solution; add the monomer aqueous solution to intermediate product B4, stir until homogeneous, heat to 68℃, adjust the pH value to 10 with 20% sodium hydroxide aqueous solution, add 1.8g of azobisisobutylamidine hydrochloride initiator under nitrogen protection, graft copolymerize at 94℃ for 8h, dry, granulate, and pulverize to obtain chitosan graft copolymer.

[0121] Based on the amount of chitosan used, the mass ratio of structural unit A, structural unit B, structural unit C, structural unit D, structural unit E, and structural unit F in the product prepared in Example 4 of this invention is 28:32:48:28:55:54. The number-average molecular weight of the chitosan graft copolymer was determined to be 333,000 by gel permeation chromatography.

[0122] Examples 5-12

[0123] Chitosan graft copolymers were prepared according to the method of Example 4, except that the monomer components and amounts used in the preparation of monomer aqueous solution in step (3) are shown in Table 1.

[0124] Table 1

[0125]

[0126] Comparative Example 1

[0127] Chitosan graft copolymers were prepared according to the method in Example 4, except that 28g of maleic anhydride was not added during the preparation of the monomer aqueous solution in step (3).

[0128] Comparative Example 2

[0129] Chitosan graft copolymers were prepared according to the method in Example 4, except that 32g of N-vinylcaprolactam was not added during the preparation of the monomer aqueous solution in step (3).

[0130] Test Example 1

[0131] The wall-bonding properties of the samples prepared in Examples 1-12 and Comparative Examples 1-2 of this invention were tested. The specific operation process is as follows: the core columns were soaked in a sample with a mass concentration of 3wt% at 240℃ for 16 hours, and the compressive strength of the core columns was tested.

[0132] Figure 2 (a) is a photograph of an unsoaked core column. Figure 2 (b) is a photograph of a core column soaked in water. Figure 2(c) Photograph of a core column soaked with 3wt% of the sample from Example 1. Figure 2 (d) Photograph of a core column soaked with 3wt% of Comparative Example 1 sample. Figure 2 As can be seen, the core column soaked in water was severely hydrated, turning into a muddy paste, and the core column shape was no longer complete; the core column soaked in Example 1 was intact in appearance, without cracks, and had an adsorption film on the surface, showing good wall-fixing performance and filtration loss reduction performance; the core column soaked in Comparative Example 1 had many cracks in appearance, indicating severe cracking, indicating serious filtrate intrusion. Combined with the compressive strength results in Table 2, it can be seen that the wall-fixing effect of Comparative Example 1 was not obvious.

[0133] The method for testing the compressive strength of soaked core columns is as follows: Place the soaked core column on a compressive strength tester, and increase the load at a rate of 0.5-0.8 MPa per second until the pressure at which the column fails is the compressive strength. The test results are shown in Table 2.

[0134] Table 2. Test results of compressive strength of core columns in the examples and comparative examples.

[0135]

[0136]

[0137] As shown in Table 2, the chitosan graft copolymer prepared in the embodiments of the present invention exhibits outstanding wall-binding properties.

[0138] Test Example 2

[0139] The sealing and filtration loss reduction performance of the samples prepared in Examples 1-12 and Comparative Examples 1-2 of this invention was tested. Specifically, the effect of a 3 wt% chitosan graft copolymer sample on the filtration loss of a 4 wt% sodium bentonite-based slurry was tested. The test conditions were: high-temperature aging at 240℃ for 16 h.

[0140] The preparation method of 4wt% sodium bentonite-based slurry is as follows: Add 2g of anhydrous sodium carbonate and 40g of sodium bentonite for drilling fluid test to 1L of water, stir for 20min, and then cure at room temperature for 24h to obtain the slurry.

[0141] According to GB / T 16783.1-2014 "Field Testing of Drilling Fluids for Petroleum and Natural Gas Industry - Part 1: Water-based Drilling Fluids", the filtration loss of 4wt% sodium bentonite-based slurry before and after adding 3wt% of the example and comparative samples was tested. The test results are shown in Table 3.

[0142] Table 3

[0143] Test slurry Filtration loss FL / mL Sodium bentonite-based slurry 53 Sodium bentonite-based slurry + Sample from Example 1 8.0 Sodium bentonite-based slurry + Sample from Example 2 6.0 Sodium bentonite-based slurry + 3 Samples from Example 3 5.0 Sodium bentonite-based slurry + 3 Samples from Example 4 4.0 Sodium bentonite-based slurry + 3 Samples from Example 5 18.4 Sodium bentonite-based slurry + 3 Samples from Example 6 18.2 Sodium bentonite-based slurry + 3 Samples from Example 7 19.6 Sodium bentonite-based slurry + 3 Samples from Example 8 18.0 Sodium bentonite-based slurry + 3 Samples from Example 9 18.6 Sodium bentonite-based slurry + Sample from Example 10 18.4 Sodium bentonite-based slurry + Sample from Example 11 19.8 Sodium bentonite-based slurry + Sample from Example 12 19.3 Sodium bentonite-based slurry + Comparative Example 1 sample 30.2 Sodium bentonite-based slurry + Comparative Example 2 sample 30.8

[0144] As shown in Table 3, the chitosan graft copolymer samples prepared in the embodiments of the present invention exhibit outstanding blocking and filtration loss reduction performance.

[0145] Test Example 3

[0146] The biotoxicity of the chitosan graft copolymer samples prepared in Examples 1-12 of this invention and the samples prepared in Comparative Examples 1-2 was tested.

[0147] Biotoxic EC 50 The test method for the value is as follows: The samples from the embodiments and comparative examples provided by this invention are added to a 3% sodium chloride solution to prepare 0 mg / dm³ solutions. -3 5000mg.dm -3 10000mg.dm -3 25000mg.dm -3 50000mg.dm -3 100000mg.dm -3 10 mL of each of the test sample solutions was added and allowed to stand for 60 min. Then, 10 mg of luminescent bacteria T3 powder was added sequentially to each of the test sample solutions and thoroughly mixed. Using a 3 wt% sodium chloride solution as a control, the EC50 biotoxicity of the luminescent bacteria and the test sample solutions was determined after 15 min of contact. 50 Value. EC 50 A concentration ≥30000 mg / L is considered non-biotoxic and meets the permitted emission standard. Test results are shown in Table 4.

[0148] Table 4

[0149] Test sample <![CDATA[Biotoxicity EC 50 value / ×10 5 mg / L]]> toxicity Example 1 5.43 Non-biological toxicity Example 2 5.49 Non-biological toxicity Example 3 5.88 Non-biological toxicity Example 4 5.74 Non-biological toxicity Example 5 5.23 Non-biological toxicity Example 6 5.12 Non-biological toxicity Example 7 5.25 Non-biological toxicity Example 8 5.35 Non-biological toxicity Example 9 5.20 Non-biological toxicity Example 10 5.04 Non-biological toxicity Example 11 5.09 Non-biological toxicity Example 12 5.06 Non-biological toxicity Comparative Example 1 4.99 Non-biological toxicity Comparative Example 2 4.78 Non-biological toxicity

[0150] As can be seen from the experimental results in Table 4, the EC of the samples in the embodiments of the present invention is... 50 Value ≥ 5.04 × 10 5 The concentration of mg / L is far greater than the emission standard of 30,000 mg / L, and it has no biological toxicity, making it green and environmentally friendly.

[0151] As can be seen from the above embodiments, the chitosan graft copolymer provided by the present invention has good wall-fixing properties and filtrate loss reduction properties, which ensures the wellbore stability of easily collapsible strata in shale fracture zones from the aspects of wall-fixing and reducing filtrate intrusion.

[0152] 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 chitosan graft copolymer, characterized in that, The chitosan graft copolymer has the structure shown in Formula (I), which contains -R1COOM1 and a quaternary ammonium salt structure, and has a number average molecular weight of 200,000-600,000. Equation (I); m is 1200-3500, X and Z are each -R1COOM1 or polymeric segments, and the content of polymeric segments is 0.15-20wt% based on the total amount of chitosan graft copolymer; wherein R1 is a C1-C5 alkylene group, and M1 is H, Na or K; the polymeric segment contains structural unit A and structural unit B, structural unit A contains at least two -COOM2, M2 is H, Na or K, and structural unit B contains a cyclic lactam structure; Y is a quaternary ammonium salt structure with an ester group.

2. The chitosan graft copolymer according to claim 1, wherein, Y is H or ; wherein, R2-R4 are each independently H or C1-C5 alkyl groups; R5 is a C1-C5 alkylene group; R6-R8 are each independently C1-C5 alkyl groups; T For F Cl ,Br Or I .

3. The chitosan graft copolymer according to claim 2, wherein, R2-R4 are each independently H.

4. The chitosan graft copolymer according to claim 2, wherein, T For Cl .

5. The chitosan graft copolymer according to claim 1 or 2, wherein, The mass ratio of -R1COOM1 to the polymeric chain segment is 1:1-1.5, and the mass ratio of structural unit A to structural unit B in the polymeric chain segment is 1:0.5-2.

6. The chitosan graft copolymer according to claim 1 or 2, wherein, The structural unit A has the structure shown in equation (1), and the structural unit B has the structure shown in equation (2); Equation (1); Equation (2); Among them, R9-R 13 Each is independently an H or C1-C5 alkyl group; M3 and M4 are both H, Na or K.

7. The chitosan graft copolymer according to claim 6, wherein, R9-R 13 Each is independently represented by H.

8. The chitosan graft copolymer according to claim 1 or 2, wherein, The polymer chain segment also contains at least one of structural unit C, structural unit D, structural unit E and structural unit F.

9. The chitosan graft copolymer according to claim 8, wherein, The polymer chain segment also contains structural unit C, structural unit D, structural unit E and structural unit F; wherein, structural unit C has the structure shown in formula (3), structural unit D has the structure shown in formula (4), structural unit E has the structure shown in formula (5), and structural unit F has the structure shown in formula (6). Equation (3); Equation (4); Equation (5); Equation (6); Among them, R 14 -R 16 R 19 -R 21 R 23 -R 25 R 28 -R 30 Each is independently an H or C1-C5 alkyl group; R 17 is -CO-O; R 18 R 22 R 26 Each is an independent alkylene group, either a C1-C5 bond or a C1-C5 bond; R 27 It is an alkyl group of C1-C5; M5 and M6 are each independently H, Na, or K.

10. The chitosan graft copolymer according to claim 9, wherein, R 14 -R 16 R 19 -R 21 R 23 -R 25 R 28 -R 30 Each is independently represented by H.

11. The chitosan graft copolymer according to claim 9, wherein, R 27 -CH3, -CH2CH3, -CH(CH3)2, -C(CH3)3.

12. The chitosan graft copolymer according to claim 9, wherein, The mass ratio of chitosan, structural unit A, structural unit B, structural unit C, structural unit D, structural unit E and structural unit F is 1: (1.6-3): (2-4): (2.5-4): (1-2.5): (3-5.5): (4-5).

13. The chitosan graft copolymer according to claim 12, wherein, The mass ratio of chitosan, structural unit A, structural unit B, structural unit C, structural unit D, structural unit E and structural unit F is 1:(2-3):(2.5-4):(3-4):(1-2):(3-5):(4-4.5).

14. A method for preparing a chitosan graft copolymer, characterized in that, The method includes the following steps: (1) Carboxylating chitosan with the halocarboxylic acid shown in formula (II) yields the first intermediate product; (2) The first intermediate product is subjected to an addition reaction with the quaternary ammonium salt shown in formula (III) to obtain the second intermediate product; (3) In the presence of an initiator, the second intermediate product is grafted copolymerized with a monomer; wherein the monomer comprises: monomer A' and monomer B', wherein monomer A' has the structure shown in formula (1') and monomer B' has the structure shown in formula (2'); Formula (II); Formula (III); Equation (1'); Equation (2'); Among them, R1-R 13 The definition corresponds to the definition in claim 1, 2 or 6; T is F, Cl, Br or I.

15. The method according to claim 14, wherein, T is Cl.

16. The method according to claim 14 or 15, wherein, The monomer further includes at least one of monomer C', monomer D', monomer E' and monomer F'; wherein, monomer C' has the structure shown in formula (3'), monomer D' has the structure shown in formula (4'), monomer E' has the structure shown in formula (5'), and monomer F' has the structure shown in formula (6'); Equation (3'); Equation (4'); Equation (5'); Equation (6'); Among them, R 14 -R 30 The definition corresponds to the definition in claim 9, where M5 and M6 are H, Na, or K.

17. The method according to claim 16, wherein, The mass ratio of chitosan, monomer C', monomer D', monomer E' and monomer F' is 1:(2-4):(1-2.5):(3-5.5):(4-5).

18. The method according to claim 17, wherein, The mass ratio of chitosan, monomer C', monomer D', monomer E' and monomer F' is 1:(2.5-4):(1-2):(3-5):(4-4.5).

19. The method according to claim 14 or 15, wherein, The mass ratio of chitosan, halocarboxylic acid and quaternary ammonium salt is 1:(3-5):(3-5).

20. The method according to claim 14 or 15, wherein, The mass ratio of chitosan, monomer A', and monomer B' is 1:(1.6-3):(2-4).

21. The method according to claim 20, wherein, The mass ratio of chitosan, monomer A', and monomer B' is 1:(2-3):(3-4).

22. The method according to claim 14 or 15, wherein, The degree of polymerization of the chitosan is 1200-3500.

23. The method according to claim 14 or 15, wherein, The halocarboxylic acid is selected from at least one of chloroacetic acid, 3-chloropropionic acid, and 4-chlorobutyric acid.

24. The method according to claim 14 or 15, wherein, The quaternary ammonium salt is selected from methacryloyloxyethyltrimethylammonium chloride.

25. The method according to claim 14 or 15, wherein, The initiator is selected from at least one of benzoyl peroxide, ammonium persulfate, cerium ammonium nitrate, and azobisisobutylammonium hydrochloride.

26. The method according to claim 14 or 15, wherein, The conditions for the carboxylation reaction include: a temperature of 70-85℃, a time of 3-6 hours, and a pH of 9-11.

27. The method according to claim 14 or 15, wherein, The conditions for the addition reaction include: a temperature of 105-130℃ and a time of 2-4 hours.

28. The method according to claim 14 or 15, wherein, The graft copolymerization reaction conditions include: a temperature of 75-95℃, a time of 2-8h, and a pH of 8-10. The graft copolymerization reaction is carried out under inert gas protection.

29. The method according to claim 14 or 15, wherein, The method further includes alkalizing and gelatinizing the chitosan in the presence of an alkaline compound and an alcohol compound before the carboxylation reaction, wherein the conditions for the alkalization and gelatinization reaction are: a temperature of 55-70°C and a time of 0.5-2 h.

30. The method according to claim 29, wherein, The alkaline compound is selected from sodium hydroxide and / or potassium hydroxide.

31. The method according to claim 29, wherein, The alcohol compound is selected from at least one of ethanol, glycerol and isopropanol.

32. The chitosan graft copolymer obtained by the method of any one of claims 14-31.

33. A drilling fluid, characterized in that, The chitosan graft copolymer described in any one of claims 1-13 and 32 is used as a filtration loss reducer.

34. The drilling fluid according to claim 33, wherein, Based on the total amount of drilling fluid, the content of the chitosan graft copolymer is 0.15-20 wt%.

35. The drilling fluid according to claim 34, wherein, Based on the total amount of drilling fluid, the content of the chitosan graft copolymer is 0.5-10 wt%.

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