A modified polymer, a super-hydrophobic drag reducer and a preparation method and application thereof

Abstract

The application relates to the technical field of unconventional oil and gas downhole operation fracturing fluid, and discloses a modified polymer, a super-hydrophobic drag-reducing agent and a preparation method and application thereof. The polymer contains structural unit A, structural unit B, structural unit C and structural unit D; the structural unit A is a structural unit with a structure shown in formula (1); the structural unit B is a structural unit with a structure shown in formula (2); the structural unit C is a structural unit with a structure shown in formula (3); and the structural unit D is a structural unit with a structure shown in formula (4). The drag-reducing agent has good hydrophobicity; can effectively change the wettability of a rock surface, effectively weaken water invasion into a stratum, has good reservoir protection effect; has good sand-carrying performance and can meet fracturing construction requirements.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of fracturing fluid for unconventional oil and gas downhole operation, in particular, to a modified polymer, a super-hydrophobic drag reducer and a preparation method and application thereof. BACKGROUND

[0002] The slick water fracturing fluid technology is a key technology for realizing three-dimensional reconstruction in large-scale volume fracturing, and through forming larger and more complex fractures, the large-scale, all-round and multi-dimensional reservoir reconstruction effect is achieved. Meanwhile, the slick water fracturing technology also has the advantages of significantly reducing operation cost and reducing reservoir damage.

[0003] At present, the slick water fracturing fluid is mostly suitable for low-permeability, natural fracture development and low closure stress formation. With the attention paid to the exploitation of shale oil and gas layers, the demand for slick water fracturing fluid is increasing, and the drag reducer as the core part of the slick water fracturing fluid system puts forward higher requirements on its performance, characteristics and the like.

[0004] At present, the existing drag reducers for fracturing mainly include the following types:

[0005] The solid powder type polyacrylamide drag reducer needs to be dissolved by using a specific device before being mixed on site, and has the defects of slow dissolution speed, easy fish-eye formation, poor shear resistance and the like;

[0006] The emulsion type polyacrylamide drag reducer has poor temperature resistance, salt resistance and calcium resistance, and the organic solvent contained therein also causes new pollution to the formation and has poor reservoir protection effect;

[0007] The water-in-water type polyacrylamide drag reducer has the defects of low viscosity, poor sand carrying performance, poor inhibition and low utilization rate;

[0008] The suspension type polyacrylamide drag reducer has poor stability, thereby leading to the phenomenon of easy stratification or even precipitation for a long time on site.

[0009] Therefore, it is necessary to develop a new super-hydrophobic multifunctional drag reducer for fracturing fluid, so as to meet the needs of large-scale volume fracturing and downhole fracturing construction of unconventional oil and gas wells, and to realize the quality improvement and efficiency increase of unconventional oil and gas reservoirs. SUMMARY

[0010] The present application relates to the technical field of fracturing fluid for unconventional oil and gas downhole operation, in particular, to a modified polymer, a super-hydrophobic drag reducer and a preparation method and application thereof.

[0011] To achieve the above object, a first aspect of the present application provides a modifying polymer containing structural unit A, structural unit B, structural unit C and structural unit D, wherein the molar ratio of the structural unit A, the structural unit B, the structural unit C and the structural unit D is 1:18-22:0.5-1.5:3.5-8;

[0012] The structural unit A is a structural unit having a structure represented by formula (1); the structural unit B is a structural unit having a structure represented by formula (2); the structural unit C is a structural unit having a structure represented by formula (3); and the structural unit D is a structural unit having a structure represented by formula (4);

[0013]

[0014] wherein,

[0015] In formula (1), R1 is -(CH2) m -CH3, R2 is -CH2-SO3M + wherein M is Na, K or Ca, and m is a positive integer of 11-13;

[0016] In formula (2), R3 is H or -CH3;

[0017] In formula (3), R4 is H or -CH3, R5 is -(CH2) m -, and R6 is -Si(OR 1 )3, wherein R 1 is -CH3 or -CH2CH3, and m is a positive integer of 1-3;

[0018] In formula (4), R7 is H or -CH3, and M is Na, K or Ca.

[0019] A second aspect of the present application provides a super-hydrophobic drag reducer, which is obtained by grafting modification of silica with the modifying polymer of the first aspect, monomer I and monomer II, wherein the monomer I and the monomer II are different and each is independently selected from one of aminopropyltriethoxysilane, n-octyltriethoxysilane, perfluorooctyltriethoxysilane and methoxytrimethylsilane.

[0020] A third aspect of the present application provides a method for preparing a super-hydrophobic drag reducer, which comprises:

[0021] (1) contacting silica, monomer C', monomer I and monomer II in the presence of solvent I to perform a first reaction to obtain mixture I; and

[0022] In the presence of solvent II, emulsifier I, chelating agent and alkaline substance, monomers A', B' and D' are contacted to carry out a second reaction to obtain mixture II;

[0023] (2) In the presence of solvent III and emulsifier II, the mixture I is subjected to a third reaction to obtain mixture III;

[0024] (3) Under low oxygen conditions and in the presence of an initiator, the mixture II and the mixture III are contacted to carry out a fourth reaction;

[0025] The monomer A' is selected from monomers having the structure shown in formula (I); the monomer B' is selected from monomers having the structure shown in formula (II); the monomer C' is selected from monomers having the structure shown in formula (III); the monomer D' is selected from monomers having the structure shown in formula (IV);

[0026] The monomers A', B', C', and D' respectively ensure that the prepared polymer contains structural unit A, structural unit B, structural unit C, and structural unit D, and that the molar ratio of the contents of structural unit A, structural unit B, structural unit C, and structural unit D in the prepared polymer is 1:18-22:0.5-1.5:3.5-8;

[0027] The structural unit A is a structural unit with the structure shown in equation (1); the structural unit B is a structural unit with the structure shown in equation (2); the structural unit C is a structural unit with the structure shown in equation (3); and the structural unit D is a structural unit with the structure shown in equation (4).

[0028]

[0029] The definitions of R1, R2, R3, R4, R5, R6, and R7 are the same as those described in the first aspect above.

[0030] A fourth aspect of the present invention provides a superhydrophobic drag reducer prepared by the method described in the third aspect above.

[0031] The fifth aspect of the present invention provides the application of the superhydrophobic drag-reducing agent described in the second or fourth aspect above in fracturing fluid.

[0032] The present invention has at least the following advantages over the prior art:

[0033] (1) The drag-reducing agent provided by the present invention has good hydrophobicity, can change the wettability of the rock surface, can effectively reduce water intrusion into the formation, inhibit shale expansion, and has a good reservoir protection effect.

[0034] (2) The drag-reducing agent provided by the present invention is environmentally friendly, non-biologically toxic, leaves no residue, and completely breaks down the adhesive.

[0035] (3) The drag-reducing agent provided by the present invention has superhydrophobic and strong oleophilic properties. It can repel water and attract oil, and has self-driving force. When used in fracturing fluid, it can improve the recovery rate.

[0036] (4) The drag-reducing agent provided by the present invention has good sand-carrying performance as well as temperature resistance, salt resistance and drag reduction properties, and its backflow liquid can be reused. Attached Figure Description

[0037] Figure 1 This is an exemplary test diagram of the surface wetting performance of fracturing fluid prepared with drag-reducing agent Z3 on rock cores, provided by the present invention.

[0038] Figure 2 This is a graph showing the drag reduction rate of the drag-reducing agent Z3 provided by the present invention as a function of shear rate under different addition amounts. Detailed Implementation

[0039] 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.

[0040] As previously stated, a first aspect of the present invention provides a polymer for modification, the polymer containing structural unit A, structural unit B, structural unit C and structural unit D, wherein the molar ratio of the contents of structural unit A, structural unit B, structural unit C and structural unit D is 1:18-22:0.5-1.5:3.5-8;

[0041] The structural unit A is a structural unit with the structure shown in equation (1); the structural unit B is a structural unit with the structure shown in equation (2); the structural unit C is a structural unit with the structure shown in equation (3); and the structural unit D is a structural unit with the structure shown in equation (4).

[0042]

[0043] in,

[0044] In equation (1), R1 is -(CH2). m -CH3, R2 is -CH2-SO3M + , where M is Na, K or Ca, and m is a positive integer from 11 to 13;

[0045] In equation (2), R3 is H or -CH3;

[0046] In equation (3), R4 is H or -CH3, and R5 is -(CH2). m -, R6 is -Si(OR) 1 )3, where R 1 It is -CH3 or -CH2CH3, where m is a positive integer from 1 to 3;

[0047] In equation (4), R7 is H or -CH3, and M is Na, K or Ca.

[0048] Preferably, structural unit A is a structural unit with the structure shown in equation (1-1); structural unit B is a structural unit with the structure shown in equation (2-1); structural unit C is a structural unit with the structure shown in equation (3-1); and structural unit D is a structural unit with the structure shown in equation (4-1).

[0049] Equation (1-1): R1 is -(CH2) 11 -CH3, R2 is -CH2-SO3M + M is Na, K, or Ca;

[0050] Equation (2-1): R3 is H;

[0051] Equation (3-1): R4 is -CH3, R5 is -(CH2)3-, and R6 is -Si(OCH3)3;

[0052] Equation (4-1): R7 is H.

[0053] As previously stated, a second aspect of the present invention provides a drag-reducing agent obtained by grafting silica with the modified polymer, monomer I and monomer II described in the first aspect, wherein monomer I and monomer II are different and are each independently selected from one of aminopropyltriethoxysilane, n-octyltriethoxysilane, perfluorooctyltriethoxysilane and methoxytrimethylsilane.

[0054] Preferably, the average particle size of the silica is 20nm-40nm. The inventors of this invention have discovered that the drag-reducing agent in this preferred configuration has stronger hydrophobic properties, which can reduce water intrusion into the formation and protect the reservoir; at the same time, it can also penetrate smaller pores and have a wider coverage area in the formation.

[0055] In a preferred embodiment, the molar ratio of the silica, the modified polymer (calculated as monomer C'), monomer I, and monomer II is 1:0.25-0.5:0.125-0.35:0.125-0.35.

[0056] As described above, a third aspect of the present invention provides a method for preparing a drag-reducing agent, the method comprising:

[0057] (1) In the presence of solvent I, silica, monomer C', monomer I and monomer II are contacted to carry out a first reaction to obtain mixture I; and

[0058] In the presence of solvent II, emulsifier I, chelating agent and alkaline substance, monomers A', B' and D' are contacted to carry out a second reaction to obtain mixture II;

[0059] (2) In the presence of solvent III and emulsifier II, the mixture I is subjected to a third reaction to obtain mixture III;

[0060] (3) Under low oxygen conditions and in the presence of an initiator, the mixture II and the mixture III are contacted to carry out a fourth reaction;

[0061] The monomer A' is selected from monomers having the structure shown in formula (I); the monomer B' is selected from monomers having the structure shown in formula (II); the monomer C' is selected from monomers having the structure shown in formula (III); the monomer D' is selected from monomers having the structure shown in formula (IV);

[0062] The monomers A', B', C', and D' respectively ensure that the prepared polymer contains structural unit A, structural unit B, structural unit C, and structural unit D, and that the molar ratio of the contents of structural unit A, structural unit B, structural unit C, and structural unit D in the prepared polymer is 1:18-22:0.5-1.5:3.5-8;

[0063] The structural unit A is a structural unit with the structure shown in equation (1); the structural unit B is a structural unit with the structure shown in equation (2); the structural unit C is a structural unit with the structure shown in equation (3); and the structural unit D is a structural unit with the structure shown in equation (4).

[0064]

[0065]

[0066] The definitions of R1, R2, R3, R4, R5, R6, and R7 are the same as those described in the first aspect above.

[0067] It should be noted that the low-oxygen conditions mentioned in this invention refer to oxygen content below 0.5% (v).

[0068] In the method described in the third aspect of the present invention, the relevant definitions and types of substituents in the monomers of the structure shown in formula (I), the monomers of the structure shown in formula (III), the monomers of the structure shown in formula (III), and the monomers of the structure shown in formula (IV) correspond to the relevant definitions and types of substituents of the present invention as described above. The present invention will not repeat them here, and those skilled in the art should not understand them as limitations on the technical solutions of the present invention.

[0069] In this invention, monomers A', B', C', and D' can be commercially available or synthesized using known methods in the field of organic synthesis based on the structural formula provided by this invention.

[0070] In this invention, it should be noted that the monomer is approximately completely converted into the corresponding structural units contained in the copolymer, and the amount of the monomer can be consistent with the content of the corresponding structural units contained in the copolymer.

[0071] Preferably, the average particle size of the silicon dioxide is 20nm-40nm.

[0072] In a preferred embodiment, the molar ratio of the silica, the monomer C', the monomer I, and the monomer II is 1:0.25-0.5:0.125-0.35:0.125-0.35.

[0073] According to a preferred embodiment, the method further includes: reacting the mixture obtained after the fourth reaction with an alkyl salt; wherein the alkyl salt is selected from at least one of sodium dodecylbenzenesulfonate and sodium dodecyl sulfate.

[0074] In a preferred embodiment, the conditions for the fifth reaction include: being carried out under stirring conditions, with a stirring speed of 300-350 rpm, a temperature of 20-40°C, and a time of 5-15 min.

[0075] According to another preferred embodiment, in step (1), the conditions for the first reaction include: a temperature of 60-80°C and a time of 36-40h.

[0076] In a preferred embodiment, in step (1), the conditions for the second reaction include: being carried out under stirring conditions, with a stirring speed of 300-350 rpm, a temperature of 20-40°C, and a time of 40-60 min.

[0077] Preferably, solvent I is selected from at least one of water and C1-C6 monohydric alcohols. More preferably, the C1-C6 monohydric alcohol is a straight-chain monohydric alcohol. For example, it can be methanol, ethanol, n-propanol, etc.

[0078] Preferably, in step (1), the emulsifier I is selected from at least one of nonylphenol polyoxyethylene ether and dodecylphenol polyoxyethylene ether.

[0079] It should be noted that the present invention does not impose any particular limitation on the type of chelating agent, and it can be any chelating agent known in the art. However, in order to facilitate the second reaction, in step (1), the chelating agent is selected from at least one of disodium ethylenediaminetetraacetate, ethylenediaminetetraacetic acid, and tetrasodium ethylenediaminetetraacetate. Particularly preferably, in step (1), the chelating agent is disodium ethylenediaminetetraacetate.

[0080] According to a particularly preferred embodiment, in step (2), the conditions for the third reaction include: a temperature of 20-40°C and a time of 10-30 min.

[0081] In a preferred embodiment, solvent II is selected from at least one of solvent oil and No. 5 white oil.

[0082] Preferably, in step (2), the emulsifier II is selected from at least one of nonylphenol polyoxyethylene ether and sorbitan oleate. More preferably, the emulsifier II is a combination of nonylphenol polyoxyethylene ether and sorbitan oleate in a molar ratio of 0.15-0.75:1.

[0083] In a preferred embodiment, in step (3), the conditions for the fourth reaction include: being carried out under stirring conditions, with a stirring speed of 450-500 rpm, a temperature of 50-60°C, and a time of 3-5 h.

[0084] Preferably, in step (3), the initiator is selected from at least one of persulfate, sodium formaldehyde sulfoxylate, and azobisisobutyramidine hydrochloride.

[0085] More preferably, the persulfate is selected from at least one of ammonium persulfate, potassium persulfate, and sodium persulfate.

[0086] In this invention, according to a particularly preferred embodiment, the method for preparing the drag-reducing agent includes the following steps:

[0087] (1) Solvent I is mixed with silica to obtain mixture I-1; mixture I-1 is contacted with monomer C', monomer I and monomer II to carry out a first reaction to obtain mixture I; and

[0088] In the presence of solvent II and an alkaline substance, monomers A' and D' are contacted and the pH is adjusted to 6-7 to obtain mixture II-1; in the presence of emulsifier I, mixture II-1 is contacted with monomer B' to carry out a second reaction to obtain mixture II;

[0089] (2) In the presence of solvent III and emulsifier II, the mixture I is subjected to a third reaction to obtain mixture III;

[0090] (3) Under low oxygen conditions and in the presence of an initiator, the mixture II and the mixture III are contacted to carry out a fourth reaction;

[0091] (4) The mixture obtained after the fourth reaction is reacted with an alkyl acid salt to obtain the drag-reducing agent.

[0092] More preferably, in step (1), the mixing conditions include: being carried out under stirring conditions, with a stirring speed of 300-350 rpm, a temperature of 20-40℃, and a time of 5-15 min.

[0093] As previously stated, a fourth aspect of the present invention provides a drag-reducing agent prepared by the method described in the third aspect above.

[0094] As previously stated, the fifth aspect of the present invention provides the application of the drag-reducing agent described in the second or fourth aspect above in fracturing fluid.

[0095] The present invention will be described in detail below through examples.

[0096] In the following examples, unless otherwise specified, all raw materials used were commercially purchased.

[0097] In the following examples, unless otherwise specified, room temperature refers to 25±2℃.

[0098] Example 1

[0099] (1) Mix 5 mol of ethanol aqueous solution with a volume concentration of 2% (solvent I) based on ethanol with 0.3 mol of silica (with an average particle size of 20 nm) to obtain mixture I-1;

[0100] The mixing conditions were as follows: the mixture was carried out under stirring conditions, with a stirring speed of 350 rpm, a temperature of room temperature, and a time of 10 min.

[0101] Mixture I1 was contacted with 0.1 mol of monomer C' (R4 is -CH3, R5 is -(CH2)3-, R6 is -Si(OCH3)3), 0.05 mol of aminopropyltriethoxysilane (monomer I), and 0.05 mol of n-octyltriethoxysilane (monomer II) to carry out a first reaction, yielding mixture I; and

[0102] In the presence of 3 mol distilled water (solvent II) and 0.45 mol sodium carbonate (alkaline substance), 0.1 mol monomer A' (R1 is -(CH2)) is added. 11 Mixture II-1 was obtained by contacting 0.7 mol monomer D' (R7 is H) with 0.15 mol nonylphenol polyoxyethylene ether TX-10 (emulsifier I) and 0.01 mol disodium ethylenediaminetetraacetate (chelating agent) with 2 mol monomer B' (R3 is H) to carry out a second reaction, thereby obtaining mixture II.

[0103] The conditions for the first reaction were: temperature 70℃, time 36h; the conditions for the second reaction were: under stirring conditions, stirring speed 300rpm, temperature room temperature, time 50min.

[0104] (2) In the presence of 4 mol of D100 solvent oil (solvent III) and emulsifier II (0.05 mol of nonylphenol polyoxyethylene ether TX-3 and 0.2 mol of dehydrated sorbitan oleate), mixture I was subjected to a third reaction to obtain mixture III;

[0105] The conditions for the third reaction are: room temperature and 10 min.

[0106] (3) Under conditions where the oxygen content is less than 0.5v% and in the presence of an initiator (0.02 mol ammonium persulfate, 0.01 mol sodium formaldehyde bisulfite and 0.005 mol azobisisobutyramidine hydrochloride), mixture II and mixture III are brought into contact to carry out the fourth reaction;

[0107] The conditions for the fourth reaction were: to be carried out under stirring conditions, with a stirring speed of 500 rpm, a temperature of 55℃, and a time of 4.5 h;

[0108] (4) The mixture obtained after the fourth reaction is reacted with 0.1 mol sodium dodecylbenzenesulfonate (alkyl acid salt) to obtain drag-reducing agent Z1;

[0109] The conditions for the fifth reaction were: to be carried out under stirring at a speed of 300 rpm, at room temperature, and for 10 min.

[0110] Example 2

[0111] This embodiment uses a method similar to that of Embodiment 1, except that:

[0112] In step (1), the amount of monomer C' was adjusted to 0.13 mol, the amount of monomer I was adjusted to 0.08 mol, the amount of monomer II was adjusted to 0.08 mol, and the remaining conditions were the same as in Example 1, and drag reducer Z2 was prepared.

[0113] Example 3

[0114] This embodiment uses a method similar to that of Embodiment 1, except that:

[0115] In step (1), the amount of silica is adjusted to 0.4 mol, the amount of monomer B' is adjusted to 2.1 mol, the amount of monomer C' is adjusted to 0.15 mol, the amount of monomer I is adjusted to 0.1 mol, the amount of monomer II is adjusted to 0.1 mol, and the amount of nonylphenol polyoxyethylene ether TX-10 is adjusted to 0.2 mol.

[0116] In step (2), the amount of nonylphenol polyoxyethylene ether TX-3 was adjusted to 0.1 mol, and the amount of dehydrated sorbitan oleate was adjusted to 0.25 mol; the remaining conditions were the same as in Example 1, and drag reducer Z3 was prepared.

[0117] Example 4

[0118] This embodiment uses a method similar to that of Embodiment 3, except that:

[0119] In step (1), the time of the first reaction was adjusted to 40 h; and the amount of nonylphenol polyoxyethylene ether TX-10 was adjusted to 0.25 mol.

[0120] In step (2), the amount of nonylphenol polyoxyethylene ether TX-3 was adjusted to 0.15 mol, and the amount of dehydrated sorbitan oleate was adjusted to 0.3 mol; the remaining conditions were the same as in Example 3, and drag reducer Z4 was prepared.

[0121] Example 5

[0122] This embodiment uses a method similar to that of Embodiment 4, except that:

[0123] In step (3), the amount of azobisisobutyramidine hydrochloride is adjusted to 0.01 mol;

[0124] In step (4), the amount of sodium dodecylbenzenesulfonate was adjusted to 0.15 mol; the other conditions were the same as in Example 1, and drag reducer Z5 was prepared.

[0125] Example 6

[0126] This embodiment uses a method similar to that of Embodiment 1, except that:

[0127] Using silica with an average particle size of 100 nm, and with all other conditions the same as in Example 1, drag reducer Z6 was prepared.

[0128] Comparative Example 1

[0129] This comparative example was conducted using a method similar to that of Example 1, except that:

[0130] In step (1), the structure shown in formula (Ⅰ) is not added, that is, monomer A' is not added, and drag reducer DZ1 is obtained.

[0131] Comparative Example 2

[0132] This comparative example was conducted using a method similar to that of Example 1, except that:

[0133] In step (1), the structure shown in formula (II) is not added, that is, monomer B' is not added, and drag reducer DZ2 is obtained.

[0134] Comparative Example 3

[0135] This comparative example was conducted using a method similar to that of Example 1, except that:

[0136] In step (1), the amount of monomer C' is adjusted to 0.25 mol to obtain drag reducer DZ3.

[0137] Comparative Example 4

[0138] This comparative example was conducted using a method similar to that of Example 1, except that:

[0139] In step (1), monomer I is not used, and the amount of monomer II is adjusted to 0.1 mol to obtain drag reducer DZ4.

[0140] Test Example 1

[0141] The drag-reducing agents prepared in the examples and comparative examples were subjected to hydrophobic performance tests according to the following methods, specifically as follows:

[0142] The drag-reducing agents prepared in the examples and comparative examples were mixed with deionized water to prepare fracturing fluids with drag-reducing agent mass concentrations of 0.1%, 0.3%, 0.5%, 0.8%, and 1.0%, respectively. The surface tension of each fracturing fluid was measured at 25°C using a QBZY-2 fully automatic surface / interfacial tensiometer (Shanghai Fangrui Instrument Co., Ltd.) based on the platinum plate method. The specific results are shown in Table 1.

[0143] Test Example 2

[0144] The drag-reducing agents prepared in the examples and comparative examples were subjected to surface wettability tests according to the following methods, specifically as follows:

[0145] The drag-reducing agents prepared in the examples and comparative examples were mixed with deionized water to prepare fracturing fluids with drag-reducing agent mass concentrations of 0.1%, 0.3%, 0.5%, 0.8%, 1.0%, and 1.3%, respectively. Based on the total mass of the fracturing fluid, 0.005 wt% ammonium persulfate was added to the fracturing fluids with mass concentrations of 0.1% and 0.3% for gel breaking, and 0.015 wt% ammonium persulfate was added to the fracturing fluids with mass concentrations of 0.5% and 0.8%. Ammonium was used to break up the gel. 0.03 wt% ammonium persulfate was added to fracturing fluids with mass concentrations of 1.0% and 1.3% to break up the gel. The core was then immersed in the broken-up fracturing fluid and vacuumed for 2 hours (at room temperature). The core was then removed and dried at 120℃ for 2 hours. The water contact angle of the dried core was tested using a QBZY-2 fully automatic surface / interfacial tensiometer (Shanghai Fangrui Instrument Co., Ltd.) to evaluate the surface wetting performance of the drag-reducing agent. The specific results are shown in Table 2.

[0146] Test Example 3

[0147] The drag-reducing agents prepared in the examples and comparative examples were subjected to oil-water interfacial tension testing according to the following method, specifically as follows:

[0148] The drag-reducing agents prepared in the examples and comparative examples were mixed with deionized water to prepare fracturing fluids with drag-reducing agent mass concentrations of 0%, 0.1%, 0.3%, 0.5%, 0.8%, and 1.0%, respectively. The oil-water interfacial tension of each fracturing fluid was measured using a QBZY-2 fully automatic surface / interfacial tension meter (Shanghai Fangrui Instrument Co., Ltd.). The specific results are shown in Table 3.

[0149] Test Example 4

[0150] The drag-reducing agents prepared in the examples and comparative examples were subjected to drag-reduction performance tests according to the following methods, specifically as follows:

[0151] The drag-reducing agents prepared in the examples and comparative examples were mixed with deionized water to prepare fracturing fluids with drag-reducing agent mass concentrations of 0.05%, 0.1%, 0.15%, 0.3%, 0.5%, and 0.6%, respectively. The drag reduction rates of each fracturing fluid at different shear rates were measured using a YMZ-II type fracturing fluid friction tester (Jiangsu Huaan Scientific Instruments Co., Ltd.). Specific results are shown in […]. Figure 2 .

[0152] Test Example 5

[0153] The drag-reducing agents prepared in the examples and comparative examples were tested for sand-carrying performance using the following methods, specifically as follows:

[0154] Fracturing fluids with drag-reducing agent concentrations of 0%, 0.05%, 0.1%, 0.15%, and 0.2% were prepared by mixing the drag-reducing agents obtained in the examples and comparative examples with deionized water. After mixing the 40-mesh ceramsite particles with a diameter of 70-mesh at a ratio of 1:1, the mixture was then mixed with the fracturing fluid at a volume ratio of 25:75 and allowed to stand for static sedimentation tests. The sedimentation time and velocity of the ceramsite in each solution were measured. Additionally, 300 mL fracturing fluids with viscosities of 22 MPa·s, 35 MPa·s, and 44 MPa·s were prepared by mixing the drag-reducing agents obtained in the examples and comparative examples with deionized water. After mixing the 20-mesh ceramsite particles with a diameter of 40-mesh at a ratio of 1:1, the mixture was then mixed with the fracturing fluid at a volume ratio of 25:75 and allowed to stand for static sedimentation tests. The sedimentation time and velocity of the ceramsite in each fracturing fluid were measured. Specific results are shown in Table 4.

[0155] Table 1

[0156]

[0157] Table 2

[0158]

[0159] Table 3

[0160]

[0161]

[0162] Table 4

[0163]

[0164] As can be seen from the results in Table 1, the drag-reducing agent provided by the present invention has a good effect on improving the solution surface, can effectively reduce the surface tension of water, and has good hydrophobicity.

[0165] As can be seen from the results in Table 2, the drag-reducing agent provided by the present invention can effectively change the wettability of the rock surface, effectively reduce water intrusion into the formation, and has a good reservoir protection effect.

[0166] As can be seen from the results in Table 3, the drag-reducing agent provided by this invention can effectively reduce the oil-water interfacial tension. When the concentration reaches 0.5% or higher, the oil-water interfacial tension is reduced to 10. -3 The magnitude of the difference not only meets the standard of "NB / T 14003.3-2017 Evaluation of Performance Indicators of Continuously Mixed Shale Gas Fracturing Fluid", but also further verifies that the drag-reducing agent provided by this invention helps to improve the wettability of rock surfaces.

[0167] As can be seen from the results in Table 4, the drag-reducing agent provided by this invention has good sand-carrying performance and can meet the requirements of fracturing construction.

[0168] Figure 1 This is an exemplary test diagram of the surface wetting performance of fracturing fluid prepared with drag-reducing agent Z3 on rock cores, provided by the present invention. Figure 1 As can be seen, the water droplets on the core surface are basically spherical, which can greatly reduce the contact area between the core and the water droplets, indicating that the wettability of the core surface at this time is superhydrophobic wetting.

[0169] Figure 2 This is a graph showing the drag reduction rate of the drag-reducing agent Z3 provided by the present invention as a function of shear rate at different addition amounts. Figure 2 As can be seen, with the increase of shear rate, the drag reduction rate of fracturing fluid containing drag reducer Z3 of different mass concentrations also gradually increases and eventually reaches a constant value; among them, the final constant value of drag reduction rate is the highest when the mass concentration of drag reducer Z3 is 0.15%, which is 77%.

[0170] 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 method for preparing a superhydrophobic drag-reducing agent, characterized in that, The method includes: (1) In the presence of solvent I, silica, monomer C', monomer I, and monomer II are contacted to carry out a first reaction to obtain mixture I; wherein monomer I and monomer II are different and are each independently selected from one of aminopropyltriethoxysilane and n-octyltriethoxysilane; wherein solvent I is selected from at least one of water and C1-C6 monohydric alcohols; and In the presence of solvent II, emulsifier I, chelating agent and alkaline substance, monomers A', B' and D' are contacted to carry out a second reaction to obtain mixture II; the solvent II is water; (2) In the presence of solvent III and emulsifier II, the mixture I is subjected to a third reaction to obtain mixture III; the solvent III is D100 solvent oil; (3) Under hypoxic conditions and in the presence of an initiator, the mixture II and the mixture III are contacted to carry out a fourth reaction; The monomer A' is selected from monomers having the structure shown in formula (I); the monomer B' is selected from monomers having the structure shown in formula (II); the monomer C' is selected from monomers having the structure shown in formula (III); the monomer D' is selected from monomers having the structure shown in formula (IV). The monomers A', B', C', and D' respectively ensure that the prepared polymer contains structural unit A, structural unit B, structural unit C, and structural unit D, and that the molar ratio of the contents of structural unit A, structural unit B, structural unit C, and structural unit D in the prepared polymer is 1:18-22:0.5-1.5:3.5-8; The structural unit A is a structural unit with the structure shown in equation (1); the structural unit B is a structural unit with the structure shown in equation (2); the structural unit C is a structural unit with the structure shown in equation (3); and the structural unit D is a structural unit with the structure shown in equation (4). Formula (I), Equation (II), Formula (III) Formula (IV), Equation (1), Equation (2), Equation (3), Equation (4), in, In equation (1), R1 is -(CH2). m -CH3, R2 is -CH2-SO3M, where M is Na or K, and m is a positive integer from 11 to 13; In equation (2), R3 is H or -CH3; In equation (3), R4 is H or -CH3, and R5 is -(CH2). m -, R6 is -Si(OR) 1 )3, where R 1 It is -CH3 or -CH2CH3, where m is a positive integer from 1 to 3; In equation (4), R7 is H or -CH3, and M is Na or K; The average particle size of the silica is 20nm-40nm.

2. The method according to claim 1, wherein, The structural unit A is the structural unit of the structure shown in equation (1-1); The structural unit B is the structural unit of the structure shown in equation (2-1); The structural unit C is the structural unit of the structure shown in equation (3-1); The structural unit D is the structural unit of the structure shown in equation (4-1); Equation (1-1): R1 is -(CH2) 11 -CH3, R2 is -CH2-SO3M, M is Na or K; Equation (2-1): R3 is H; Equation (3-1): R4 is -CH3, R5 is -(CH2)3-, and R6 is -Si(OCH3)3; Equation (4-1): R7 is H.

3. The method according to claim 1, wherein, The method further includes: reacting the mixture obtained after the fourth reaction with an alkyl salt; wherein the alkyl salt is selected from at least one of sodium dodecylbenzenesulfonate and sodium dodecyl sulfate.

4. The method according to any one of claims 1-3, wherein, In step (1), the conditions for the first reaction include: a temperature of 60-80°C and a time of 36-40 h; and / or, In step (1), the conditions for the second reaction include: being carried out under stirring conditions, with a stirring speed of 300-350 rpm, a temperature of 20-40°C, and a time of 40-60 min; and / or, In step (1), the emulsifier I is selected from at least one of nonylphenol polyoxyethylene ether and dodecylphenol polyoxyethylene ether.

5. The method according to any one of claims 1-3, wherein, In step (2), the conditions for the third reaction include: a temperature of 20-40°C and a time of 10-30 min; and / or, In step (2), the emulsifier II is selected from at least one of nonylphenol polyoxyethylene ether and sorbitan oleate.

6. The method according to any one of claims 1-3, wherein, In step (3), the conditions for the fourth reaction include: being carried out under stirring conditions, with a stirring speed of 450-500 rpm, a temperature of 50-60℃, and a time of 3-5 h; and / or, In step (3), the initiator is a combination of persulfate, sodium formaldehyde sulfoxylate and azobisisobutyramidine hydrochloride.

7. A superhydrophobic drag reducer prepared by the method according to any one of claims 1-6.

8. The application of the superhydrophobic drag reducer according to claim 7 in fracturing fluid.

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