A self-cleaning active drag reducer and its preparation method

Abstract

The present invention discloses a self-cleaning active drag reducer and its preparation method, belonging to the technical field of oilfield chemistry. The drag reducer is made of the following components by mass concentration: 30-50% of a composite copolymer, 1-15% of a desorption promoter, 0.02-0.4% of a main suspension agent, 0.15-0.6% of a suspension activator, and the rest is a solvent; Preparation of the composite copolymer: First, dissolve polyvinyl alcohol and carboxymethyl hydroxypropyl guanidine gum in water to form an aqueous solution, add acrylamide, sodium acrylate, a benzene ring-containing rigid monomer, a reinforcing agent, and urea to the aqueous solution to obtain a composite reaction solution; Then add an initiator to carry out a polymerization reaction to obtain a polymer colloid; Cut, crush, and dry the polymer colloid to obtain a composite copolymer powder. The drag reducer of the present invention has both a thickening effect. On the basis of having variable viscosity and strong sand-carrying ability, it strengthens the characteristics of low adsorption and low residue of the polymer. At the same time, it also has the function of promoting the dissociation of adsorbed gas into free gas and dredging and cleaning the formation, effectively improving the oil and gas recovery rate and stable production capacity.

Description

Technical Field

[0001] The present invention relates to the technical field of oilfield chemistry, and particularly to a self-cleaning active drag reducer and a preparation method thereof. Background Art

[0002] Hydraulic fracturing is the core technology for increasing the reserves and production of unconventional oil and gas. The slickwater fracturing fluid with water-soluble thickeners as the core is the key material for hydraulic fracturing technology. The variable-viscosity emulsion-type polyacrylamide thickener that matches the volume transformation concept is the main body of application. However, due to the influence of polymerization technology and suspension technology, there are still a series of problems. (1) Adsorption damage: In order to obtain good drag reduction and sand-carrying performance, ultra-high molecular weight polyacrylamide (PAM) is used. Due to the action of hydrogen bonds and the like, the polymer is extremely easy to adsorb with the reservoir, and this adsorption phenomenon will cause the blockage of reservoir pores and channels, thereby affecting the flow of oil and gas and ultimately leading to a decrease in recovery efficiency. (2) Solid residue damage: The solid residues brought by external fluids are easy to block the pore throats, thereby reducing the reservoir permeability. An ideal fracturing fluid system should be able to effectively transport the fracturing proppant while generating less solid residue and maintaining a high reservoir permeability. However, the existing powder emulsion suspension technology uses a large amount of mineral suspension agents, bringing insoluble residues; the inverse emulsion products have problems of oil-water emulsification and forming composite residues with polymers.

[0003] The thickeners reported in the relevant literature in the prior art only solve some problems of salt tolerance, sand-carrying, and adsorption problems of shale reservoirs under low-concentration conditions in the slickwater stage, or unilaterally optimize the polymer molecular structure, and have not yet developed a functional self-cleaning fracturing fluid drag reducer that has low adsorption, low residue, and can promote methane desorption and clean and dredge the formation for different reservoirs at high-concentration solutions. Summary of the Invention

[0004] In view of the functional defects such as adsorption damage and solid residue damage existing in the existing thickeners, the present invention provides a self-cleaning active drag reducer. This drag reducer not only has the function of reducing drag but also has the function of thickening, and can be used as a thickener.

[0005] The self-cleaning active drag reducer provided by the present invention comprises the following components in mass percentage:

[0006] 30-50% of a composite copolymer powder, 1-15% of a desorption promoter, 0.02-0.4% of a main suspension agent, 0.15-0.6% of a suspension activator, and the balance being a water-soluble solvent, with a total of 100%.

[0007] The preparation method of the composite copolymer is as follows:

[0008] (1) Dissolve polyvinyl alcohol and carboxymethyl hydroxypropyl guanidine gum in water to form an initial composite low-molecular-weight polymer aqueous solution, and then add acrylamide, sodium acrylate, a rigid monomer containing a benzene ring, a reinforcing agent, and urea to the aqueous solution to obtain a composite reaction solution.

[0009] The rigid monomer containing a benzene ring is selected from any one of the following six molecular structural formulas:

[0010]

[0011]

[0012] Among them, the R 3 group is -COONa or -SO 3 Na.

[0013] The molar ratio of acrylamide, sodium acrylate, and the rigid monomer containing a benzene ring is 1:(0.05 - 0.4):(0.01 - 0.1). In the composite reaction solution, the total mass fraction of acrylamide, sodium acrylate, and the rigid monomer containing a benzene ring is 15 - 40%.

[0014] In the composite reaction solution, the mass fraction of urea is 1 - 20%; urea has the functions of dissociating the adsorption of polyacrylamide and promoting dissolution.

[0015] The reinforcing agent is N,N-methylenebisacrylamide. In the composite reaction solution, the concentration of the reinforcing agent is 20 - 1000 mg / L, preferably 100 - 500 mg / L, and most preferably 100 - 200 mg / L.

[0016] The initiator is a redox initiator system composed of ammonium cerium nitrate and sodium bisulfite, and the mass ratio of the two is 1:1. Among them, the addition amount of ammonium cerium nitrate in the composite reaction solution is 30 - 200 mg / L, preferably 60 - 150 mg / L, and most preferably 80 - 120 mg / L.

[0017] The molecular weight of the polyvinyl alcohol is 10,000 - 150,000, preferably 20,000 - 120,000, more preferably 30,000 - 100,000, and most preferably 50,000 - 80,000. The degree of alcoholysis is 80 - 85%. In the polymerization system, the mass fraction of polyvinyl alcohol is 0.5 - 6%, preferably 1 - 5%, more preferably 1 - 4%, and most preferably 1.5 - 3%.

[0018] The molecular weight of the carboxymethyl hydroxypropyl guanidine gum is 50×10 4 - 200×10 4 and most preferably 100×10 4 - 150×10 4。The mass fraction of carboxymethyl hydroxypropyl guar gum in the polymerization system is 0.5 - 5%, more preferably 1 - 4%, and most preferably 2 - 3%.

[0019] (2) An initiator is added to the composite reaction solution for polymerization. The polymerization reaction temperature is -5 to 40°C. When the temperature rise in the polymerization reaction system does not exceed 1°C within 30 minutes, the polymerization reaction is considered complete, and a polymer colloid is obtained. The polymerization reaction temperature is preferably 10 - 20°C.

[0020] (3) After taking out the polymer colloid, it is cut, crushed, dried, and sieved to obtain a composite copolymer powder. The molecular weight of the powder is 4 million - 12 million.

[0021] The water-soluble solvent is a mixed solvent composed of polyethylene glycol 200, polypropylene glycol 400, and N-methylpyrrolidone. The mass ratio of polyethylene glycol 200: polypropylene glycol 400: N-methylpyrrolidone is (30 - 84):(15 - 60):(1 - 10). Among them, polyethylene glycol 200 and polypropylene glycol 400 provide a certain viscosity for the suspension system and activate the suspension main agent to achieve suspension stability. N-methylpyrrolidone is a small molecule nitrogen-containing compound, which further reduces the static adsorption amount of polyacrylamide in the reservoir by competitive adsorption and occupation. Conventional oil-based suspension drag reducers have slower dispersion speed of polyacrylamide powder in water due to the oil in the external phase, and the hydration of polyacrylamide powder needs to be promoted by the action of penetrants or co-solvent surfactants. However, the water-soluble solvent of the present invention is quickly miscible with water itself, enabling the composite copolymer powder to be quickly dispersed and dissolved in water.

[0022] The suspension main agent is bacterial nanocellulose (BNC), with a diameter of 30 - 50 nm and a crystallinity of 70 - 90%. The addition amount accounts for 0.05 - 1.0% of the composite copolymer powder, more preferably 0.1 - 0.7%, and most preferably 0.3 - 0.5%. Bacterial nanocellulose is dispersed in the water-soluble solvent and forms a three-dimensional network structure through hydrogen bond self-assembly. At the same time, there is a hydrogen bond interaction between bacterial nanocellulose and the composite copolymer powder. Using bacterial nanocellulose as the suspension main agent makes the suspension system have excellent stability. At the same time, bacterial nanocellulose itself has excellent degradability and no residue content after degradation, improving the cleanliness of the product. Traditional suspension systems mainly use organically modified clay as the main suspension main agent, which has good stability but also brings a large amount of solid residues, causing formation plugging.

[0023] The suspension activator is ethylene glycol or hexamethylphosphoric triamide, and the addition amount is 0.2%-3% of the composite copolymer powder, more preferably 0.5-2%, and most preferably 1-1.5%. The composite copolymer powder can form a hydration film under the action of the suspension activator. On the one hand, the formed hydration film makes it difficult for the composite copolymer powder to settle during the collision process in the suspension system, improving the stability of the suspension system. On the other hand, it realizes the rapid dissolution of the powder in water. Among them, hexamethylphosphoric triamide can further reduce the adsorption damage of polyacrylamide in different reservoirs.

[0024] The desorption promoter is a sulfonate surfactant, preferably sodium α-olefin sulfonate with C10-C12, and the addition amount is 1-15% of the composite copolymer powder, more preferably 3-10%, and most preferably 5-8%. This surfactant can change the surface wettability of the coal reservoir, displace methane adsorbed state through water molecules, and then realize the desorption of methane adsorbed gas.

[0025] The present invention also provides a preparation method of a self-cleaning active drag reducer, and the steps are as follows:

[0026] S1. Prepare a mixed solvent of polyethylene glycol 200, polypropylene glycol 400, and N-methylpyrrolidone;

[0027] S2. Divide the mixed solvent into two parts. Add the desorption promoter to one part of the mixed solvent, stir for 15-20 minutes, then slowly add the suspension activator, stir for 30 minutes to fully mix the suspension activator with the solution, and then add the composite copolymer powder uniformly while stirring. After adding, continue to stir for 1.5-2 hours to obtain a pre-hydrated and activated drag reducer solution;

[0028] S3. Add the suspension main agent to the other part of the mixed solvent and stir evenly to obtain a suspension main agent concentrate;

[0029] S4. Add the suspension main agent concentrate to the drag reducer solution in step S2 and stir for 1 hour to obtain a self-cleaning active drag reducer.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0031] (1) In the present invention, a rigid monomer is introduced into the polyacrylamide structure to reduce the static adsorption of the drag reducer in different reservoirs through steric hindrance. Polyvinyl alcohol and carboxymethyl hydroxypropyl guar gum contain a large number of hydroxyl groups, which can form intermolecular hydrogen bonds with the amide groups of polyacrylamide, improving the viscosity-increasing and sand-carrying performance of the product. A small amount of enhancer is added during the preparation of the composite copolymer, which can further strengthen the network structure of polyacrylamide and carboxymethyl hydroxypropyl guar gum. A relatively high content of urea is introduced during the synthesis process. Urea contains N-H bonds and forms competitive adsorption with polyacrylamide on the reservoir, thereby greatly reducing the polymer adsorption amount and forming a low-adsorption and strong sand-carrying composite copolymer powder.

[0032] (2) The present invention provides a functional self-cleaning fracturing fluid drag reducer that has low adsorption, low residue, self-cleaning properties for different reservoir layers, and promotes methane desorption. It can also be used as a thickening agent. On the basis of having variable viscosity and strong sand-carrying capacity, it further enhances the characteristics of low polymer adsorption and low residue. At the same time, it also has the function of promoting the dissociation of adsorbed gas into free gas and dredging and cleaning the formation, ultimately effectively improving the oil and gas recovery rate and stable production capacity.

[0033] Other advantages, objectives, and features of the present invention will be partially reflected by the following description and partially understood by those skilled in the art through the research and practice of the present invention. Specific Embodiments

[0034] The following describes the preferred embodiments of the present invention. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention and are not used to limit the present invention.

[0035] In all embodiments, unless otherwise specified, the percentage content of each reagent is the mass percentage content.

[0036] The experimental evaluation methods used in Examples 1-16 and Comparative Example 1 are as follows:

[0037] (1) Viscosity-average molecular weight test: Use an Ubbelohde viscometer (0.55 mm tube diameter) to test and calculate according to GB / T 12005.10-92.

[0038] (2) Static adsorption rate test:

[0039] Standard curve establishment: Prepare a fracturing fluid according to the formula of 0.2% powder + 0.2% of 10% ammonium persulfate aqueous solution. Place the fracturing fluid in an environment at 90 °C to break the gel until the viscosity of the gel-breaking fluid is less than 5 mPa·s to obtain a gel-breaking fluid with a powder concentration of 0.2%. Here, "0.2% of 10% ammonium persulfate aqueous solution" means that ammonium persulfate is first prepared into an aqueous solution with a mass fraction of 10%, and then 0.2% of the aqueous solution is added to prepare the fracturing fluid. Respectively transfer 2.5 mL, 3.0 mL, 4.0 mL, 4.5 mL, and 5.0 mL of 0.2% powder gel-breaking fluid into 100 mL volumetric flasks, make up the volume with the preparation water, and filter with a 0.45 μm microporous filter membrane. Measure the ultraviolet spectra of the 5 diluted concentration gel-breaking fluids at 190-240 nm, and perform linear fitting of the concentration-absorbance standard curve at the maximum absorption wavelength λ and wavelengths with λ red shift and blue shift of 2-8 nm. Take the wavelength at which the determination coefficient R 2 > 0.99 and closest to 1 as λ. In practical applications, the preparation water generally refers to the water used on site, which can be lake water, river water, etc. The preparation water used in all embodiments of this application is deionized water.

[0040] Testing the polymer concentration of the gel-breaking fluid before adsorption: Take 4 mL of the above 0.2% powder gel-breaking fluid into a 100 mL volumetric flask, then make up the volume with the prepared solution water, and filter it with a 0.45-micron microporous filter membrane to obtain the test solution before adsorption. Using the prepared solution water as the reference, measure the ultraviolet spectrum of the test solution before adsorption at 190 nm - 240 nm, and take the wavelength λ at the red shift (right shift) of 6 nm at the maximum absorption peak. 1 The absorbance is A 1 .

[0041] Preparation of the polymer solution after adsorption: Take 10 mL of the above gel-breaking fluid into a centrifuge tube, add 1 g of core powder with a mesh number ≥ 100, stir and mix evenly, place it on a shaker at 40 °C for 3 h for adsorption and oscillation, centrifuge the adsorbed sample in a centrifuge at a speed of 4000 r / min for 20 min, take 4 mL of the middle-layer clear liquid into a 100 mL volumetric flask, then make up the volume with the prepared solution water, and filter it with a 0.45-micron microporous filter membrane.

[0042] Preparation of the polymer blank solution after adsorption: Take 10 mL of the prepared solution water into a centrifuge tube, add 1 g of coal powder with a mesh number ≥ 100, stir and mix evenly, place it on a shaker at 40 °C for 3 h for adsorption and oscillation, centrifuge the adsorbed sample in a centrifuge at a speed of 4000 r / min for 20 min, take 2 mL of the middle-layer clear liquid into a 100 mL volumetric flask, then make up the volume with the prepared solution water, and filter it with a 0.45-micron microporous filter membrane.

[0043] Testing the polymer concentration of the gel-breaking fluid after adsorption: Using the blank sample after adsorption as the reference, measure the ultraviolet spectrum of the polymer to be tested after adsorption at 190 nm - 240 nm, and take the absorbance at the wavelength λ 1 to be A 2 , and the static adsorption capacity is calculated according to formula (1).

[0044] (1)

[0045] In the formula:

[0046] X — Static adsorption rate, %;

[0047] A 2 — Absorbance at the wavelength λ 1 nm of the test solution after adsorption;

[0048] A 1 — Absorbance at the wavelength λ 1 nm of the test solution before adsorption.

[0049] (3) Testing the residue content

[0050] Test the residue content of the 0.2% powder. The test method refers to Method 7.10.3 in SYT 7627-2021 Technical Requirements for Water-based Fracturing Fluids for testing and calculation.

[0051] (4) Viscosity Test of 85,000 Brine

[0052] The water quality composition is 85,000 total salinity, 10,000 mg / L calcium ion, 1,000 mg / L magnesium ion, and the rest are sodium ions and chloride ions.

[0053] Viscosity test method: Under the condition of 85,000 brine, add 0.2% powder under the condition of 700 r / min rotation speed, stir at a constant speed for 3 min, stop stirring, and use a six-speed rotary viscometer to measure the apparent viscosity value under the condition of 100 r / min.

[0054] Examples 1 - 16 are examples of the preparation method of the composite polymer powder.

[0055] Example 1

[0056] Dissolve polyvinyl alcohol (molecular weight 60,000, degree of alcoholysis 80%) and carboxymethyl hydroxypropyl guar gum (molecular weight 120×10 4 ) in deionized water at 50°C according to the mass fractions of 2.5% and 2.0% respectively to obtain an initial composite low-molecular-weight polymer aqueous solution. Then, feed according to the molar ratio of acrylamide monomer, sodium acrylate, and rigid monomer containing benzene ring sulfonic acid group of 1:0.2:0.05. The total mass fraction of the three monomers is 28%. Stir until dissolved, and adjust the pH value of the system to 8 with sodium hydroxide solution. Then, add 10% urea and 200 mg / L N,N-methylenebisacrylamide in sequence, and dissolve fully to obtain a composite reaction solution. Place the composite reaction solution in a 15°C constant temperature water bath. When the temperature reaches 15 ± 1°C, add a redox initiation system composed of ammonium cerium nitrate and sodium bisulfite, and the mass ratio of the two is 1:1, where the addition amount of ammonium cerium nitrate is 100 mg / L of the polymerization system. The polymerization reaction proceeds. When the temperature rise in the reaction system does not exceed 1°C within 30 minutes, it is considered that the polymerization reaction is basically completed. One hour after the polymerization reaction is completed, take out the colloid, cut the colloid into particles with a size of 3 - 5 mm, spread the colloid flat on a 500-mesh sieve, place it in an oven and dry it at a constant temperature of 95°C for 1 - 3 h, and take out and grind it through a grinder and sieve to obtain a low-adsorption salt-tolerant composite polymer powder with a mesh number ≥ 120.

[0057] The molecular structural formula of the rigid monomer containing benzene ring sulfonic acid group is as follows:

[0058]

[0059] Among them, R 3 group is -SO 3 Na.

[0060] The viscosity-average molecular weight of the low-adsorption and salt-tolerant composite polymer powder obtained in Example 1 is 10.5 million. The static adsorption rate of the No. 8 coal rock with 0.2% powder is 6.0%. The residue content of the 0.2% powder is 20 mg / L. The viscosity value of the 0.2% powder in 85,000 salt water is 45 mPa·s.

[0061] Example 2:

[0062] Change the polyvinyl alcohol (molecular weight 60,000, degree of alcoholysis 80%) in Example 1 with an addition amount of 2.5% by mass fraction to polyvinyl alcohol (molecular weight 10,000, degree of alcoholysis 80%) with an addition amount of 6%.

[0063] The viscosity-average molecular weight of the low-adsorption and salt-tolerant composite polymer powder obtained in Example 2 is 8.53 million. The static adsorption rate of the No. 8 coal rock with 0.2% powder is 4.5%. The residue content of the 0.2% powder is 25 mg / L. The viscosity value of the 0.2% powder in 85,000 salt water is 32 mPa·s.

[0064] Example 3:

[0065] Change the polyvinyl alcohol (molecular weight 60,000, degree of alcoholysis 80%) in Example 1 with an addition amount of 2.5% by mass fraction to polyvinyl alcohol (molecular weight 150,000, degree of alcoholysis 80%) with an addition amount of 0.5%.

[0066] The viscosity-average molecular weight of the low-adsorption and salt-tolerant composite polymer powder obtained in Example 3 is 9.36 million. The static adsorption rate of the No. 8 coal rock with 0.2% powder is 7.5%. The residue content of the 0.2% powder is 32 mg / L. The viscosity value of the 0.2% powder in 85,000 salt water is 30 mPa·s.

[0067] Example 4:

[0068] Change the carboxymethyl hydroxypropyl guar gum (molecular weight 120×10 4 ), with an addition amount of 2.0% by mass fraction to carboxymethyl hydroxypropyl guar gum (molecular weight 50×10 4 ) with an addition amount of 5.0%.

[0069] The viscosity-average molecular weight of the low-adsorption and salt-tolerant composite polymer powder obtained in Example 4 is 8.2 million. The static adsorption rate of the No. 8 coal rock with 0.2% powder is 8.0%. The residue content of the 0.2% powder is 65 mg / L. The viscosity value of the 0.2% powder in 85,000 salt water is 36 mPa·s.

[0070] Example 5:

[0071] Change the carboxymethyl hydroxypropyl guar gum (molecular weight 120×10 4 ), with an addition amount of 2.0% by mass fraction to carboxymethyl hydroxypropyl guar gum (molecular weight 200×10 4), with an increase of 0.5%.

[0072] The viscosity-average molecular weight of the low-adsorption and salt-tolerant composite polymer powder obtained in Example 5 was 11.2 million, the static adsorption rate of No. 8 coal rock with 0.2% powder was 5%, the residue content of 0.2% powder was 15 mg / L, and the viscosity value of 0.2% powder in 85,000 salt water was 33 mPa·s.

[0073] Example 6:

[0074] Change the molar ratio of acrylamide monomer, sodium acrylate, and rigid monomer containing benzene ring sulfonic acid group in Example 1 from 1:0.2:0.05 to 1:0.05:0.01.

[0075] The viscosity-average molecular weight of the low-adsorption and salt-tolerant composite polymer powder obtained in Example 6 was 10.85 million, the static adsorption rate of No. 8 coal rock with 0.2% powder was 8.9%, the residue content of 0.2% powder was 42 mg / L, and the viscosity value of 0.2% powder in 85,000 salt water was 27 mPa·s.

[0076] Example 7:

[0077] Change the molar ratio of acrylamide monomer, sodium acrylate, and rigid monomer containing benzene ring sulfonic acid group in Example 1 from 1:0.2:0.05 to 1:0.4:0.1:

[0078] The viscosity-average molecular weight of the low-adsorption and salt-tolerant composite polymer powder obtained in Example 7 was 7.28 million, the static adsorption rate of No. 8 coal rock with 0.2% powder was 4.2%, the residue content of 0.2% powder was 85 mg / L, and the viscosity value of 0.2% powder in 85,000 salt water was 51 mPa·s.

[0079] Example 8:

[0080] Change the molar ratio of acrylamide monomer, sodium acrylate, and rigid monomer containing benzene ring sulfonic acid group in Example 1 from 1:0.2:0.05 to 1:0.18:0.06.

[0081] The viscosity-average molecular weight of the low-adsorption and salt-tolerant composite polymer powder obtained in Example 8 was 1152, the static adsorption rate of No. 8 coal rock with 0.2% powder was 6.2%, the residue content of 0.2% powder was 18 mg / L, and the viscosity value of 0.2% powder in 85,000 salt water was 54 mPa·s.

[0082] Example 9:

[0083] Change the total mass fraction of the three monomers of acrylamide monomer, sodium acrylate, and rigid monomer containing benzene ring sulfonic acid group in Example 1 from 28% to 15%.

[0084] The viscosity-average molecular weight of the low-adsorption and salt-tolerant composite polymer powder obtained in Example 9 was 12.03 million, the static adsorption rate of the No. 8 coal rock with 0.2% powder was 7.0%, the residue content of the 0.2% powder was 38 mg / L, and the viscosity value of the 0.2% powder in 85,000 salt water was 42 mPa·s.

[0085] Example 10:

[0086] The total mass fraction of the three monomers of acrylamide monomer, sodium acrylate, and rigid monomer containing benzene ring sulfonic acid group in Example 1 was changed from 28% to 40%.

[0087] The viscosity-average molecular weight of the low-adsorption and salt-tolerant composite polymer powder obtained in Example 10 was 6.12 million, the static adsorption rate of the No. 8 coal rock with 0.2% powder was 4.2%, the residue content of the 0.2% powder was 15 mg / L, and the viscosity value of the 0.2% powder in 85,000 salt water was 24 mPa·s.

[0088] Example 11:

[0089] The addition amount of N,N-dimethylbisacrylamide in Example 1 was changed from 200 mg / L to 20 mg / L.

[0090] The viscosity-average molecular weight of the low-adsorption and salt-tolerant composite polymer powder obtained in Example 11 was 9.51 million, the static adsorption rate of the No. 8 coal rock with 0.2% powder was 5.6%, the residue content of the 0.2% powder was 10 mg / L, and the viscosity value of the 0.2% powder in 85,000 salt water was 33 mPa·s.

[0091] Example 12:

[0092] The addition amount of N,N-dimethylbisacrylamide in Example 1 was changed from 200 mg / L to 1000 mg / L.

[0093] The viscosity-average molecular weight of the low-adsorption and salt-tolerant composite polymer powder obtained in Example 12 was 11.25 million, the static adsorption rate of the No. 8 coal rock with 0.2% powder was 7.5%, the residue content of the 0.2% powder was 158 mg / L, and the viscosity value of the 0.2% powder in 85,000 salt water was 18 mPa·s.

[0094] Example 13:

[0095] The 10% urea in Example 1 was changed to 1% urea.

[0096] The viscosity-average molecular weight of the low-adsorption and salt-tolerant composite polymer powder obtained in Example 13 was 12.15 million, the static adsorption rate of the No. 8 coal rock with 0.2% powder was 12.5%, the residue content of the 0.2% powder was 15 mg / L, and the viscosity value of the 0.2% powder in 85,000 salt water was 42 mPa·s.

[0097] Example 14:

[0098] Change the 10% urea in Example 1 to 20% urea.

[0099] The viscosity-average molecular weight of the low-adsorption and salt-tolerant composite polymer powder obtained in Example 14 is 9.38 million, the static adsorption rate of the 8# coal rock with 0.2% powder is 4.0%, the residue content of the 0.2% powder is 12 mg / L, and the viscosity value of the 85,000 brine with 0.2% powder is 30 mPa·s.

[0100] Example 15:

[0101] Change the initiation temperature of 15°C in Example 1 to -5°C.

[0102] Change the amount of ammonium cerium nitrate added in Example 1 from 100 mg / L to 200 mg / L. The viscosity-average molecular weight of the low-adsorption and salt-tolerant composite polymer powder obtained in Example 15 is 9.1 million, the static adsorption rate of the 8# coal rock with 0.2% powder is 5.3%, the residue content of the 0.2% powder is 16 mg / L, and the viscosity value of the 85,000 brine with 0.2% powder is 39 mPa·s.

[0103] Example 16:

[0104] Change the initiation temperature of 15°C in Example 1 to 30°C, and change the amount of ammonium cerium nitrate added in Example 1 from 100 mg / L to 30 mg / L.

[0105] The viscosity-average molecular weight of the low-adsorption and salt-tolerant composite polymer powder obtained in Example 16 is 4.52 million, the static adsorption rate of the 8# coal rock with 0.2% powder is 5.5%, the residue content of the 0.2% powder is 10 mg / L, and the viscosity value of the 85,000 brine with 0.2% powder is 18 mPa·s.

[0106] Comparative Example 1:

[0107] Charge acrylamide monomer and sodium acrylate in a molar ratio of 1:0.2, and the total mass fraction of the two monomers is 28%. Stir until dissolved, and adjust the pH value of the system to 8 with sodium hydroxide solution. Then, add 10% urea and 200 mg / L N,N'-methylenebisacrylamide (reinforcing agent) in sequence, and dissolve thoroughly to obtain a polymerization system. Place the liquid in a 15°C constant temperature water bath. When the temperature reaches 15 ± 1°C, add a redox initiation system composed of ammonium cerium nitrate and sodium bisulfite, and the mass ratio of the two is 1:1, where the amount of ammonium cerium nitrate added is 100 mg / L of the polymerization system. The polymerization reaction proceeds. When the temperature rise in the reaction system does not exceed 1°C within 30 minutes, it is considered that the polymerization reaction is basically completed. One hour after the polymerization reaction is completed, take out the colloid, cut the colloid into particles with a size of 3 - 5 mm, spread the colloid flat on a 500-mesh sieve, place it in an oven at a constant temperature of 95°C for 1 - 3 h, take it out and grind it through a grinding machine and sieve to obtain the Comparative Example 1 polymer powder with a mesh number ≥ 120.

[0108] The viscosity-average molecular weight of the low-adsorption and salt-resistant composite polymer powder obtained in Comparative Example 1 was 23.2 million, the static adsorption rate of No. 8 coal rock with 0.2% powder was 14.5%, the residue content of 0.2% powder was 46 mg / L, and the viscosity value of 0.2% powder in 85,000 salt water was 12 mPa·s.

[0109] Example 17:

[0110] According to the formulation ratio shown in Table 1, polyethylene glycol 200, polypropylene glycol 400, and N-methylpyrrolidone were pumped into the reaction kettle 1 with a stirring rod in sequence according to the formulation ratio. After pumping, it was stirred thoroughly for 15 min to obtain a mixed solvent. 70% of the mixed solvent was pumped into the reaction kettle 2, and a desorption promoter was added. The emulsifying pump connected to the reaction kettle 2 was turned on. After 15 min of cyclic stirring, a suspension activator was slowly injected during the cycle, so that the suspension activator was fully mixed with the solvent containing the desorption promoter. After injecting the suspension activator for 30 min of circulation, a composite copolymer powder was added to the reaction kettle 2 at a uniform speed, and it was stirred and dispersed cyclically for 1.5 - 2 h to obtain a pre-hydrated and activated drag reducer solution. A suspension main agent was added to the 30% mass fraction of the mixed solvent in the reaction kettle 1, and the emulsifying pump was turned on, and it was stirred cyclically for 30 min to obtain a concentrated suspension main agent solution. The concentrated suspension main agent solution in the reaction kettle 1 was pumped into the reaction kettle 2, and after pumping was completed, it was stirred cyclically for 1 h to obtain a self-cleaning active drag reducer.

[0111] Table 1 Formulation Composition of Example 17

[0112]

[0113] Example 18:

[0114] According to the formulation ratio shown in Table 2, the method steps were the same as those in Example 17.

[0115] Table 2 Formulation Composition of Example 18

[0116]

[0117] Example 19:

[0118] According to the formulation ratio shown in Table 3, the method steps were the same as those in Example 17.

[0119] Table 3 Formulation Composition of Example 19

[0120]

[0121] Example 20:

[0122] According to the formulation ratio shown in Table 4, the method steps were the same as those in Example 17.

[0123] Table 4 Composition of Formulation in Example 20

[0124]

[0125] Example 21:

[0126] According to the formulation ratio shown in Table 5, the method steps are the same as those in Example 17.

[0127] Table 5 Composition of Formulation in Example 21

[0128]

[0129] Example 22:

[0130] According to the formulation ratio shown in Table 6, the method steps are the same as those in Example 17.

[0131] Table 6 Composition of Formulation in Example 22

[0132]

[0133] Example 23:

[0134] According to the formulation ratio shown in Table 7, the method steps are the same as those in Example 17.

[0135] Table 7 Composition of Formulation in Example 23

[0136]

[0137] Example 24:

[0138] According to the formulation ratio shown in Table 8, the method steps are the same as those in Example 17.

[0139] Table 8 Composition of Formulation in Example 24

[0140]

[0141] Example 25:

[0142] According to the formulation ratio shown in Table 9, the method steps are the same as those in Example 17.

[0143] Table 9 Composition of Formulation in Example 25

[0144]

[0145] Example 26:

[0146] According to the formulation ratio shown in Table 10, the method steps are the same as those in Example 17.

[0147] Table 10 Composition of Formulation in Example 26

[0148]

[0149] Example 27:

[0150] According to the formulation ratio shown in Table 11, the method steps are the same as those in Example 17.

[0151] Table 11 Formulation Composition of Example 27

[0152]

[0153] Comparative Example 2 (conventional oil-based suspension drag reducer):

[0154] Pump No. 10 white oil into the reaction kettle with a stirring rod in sequence according to the formulation ratio. After pumping is completed, add organic bentonite and stir and activate for 30 min. Then pump in the mixed emulsifying and dispersing agent formed by Span 80 and fatty alcohol polyoxyethylene ether, stir for 30 min, and then add polymer powder to the reaction kettle and stir for 1 - 2 h to obtain an oil-based suspension drag reducer.

[0155] The formulation of Comparative Example 2 is shown in Table 12.

[0156] Table 12 Formulation Composition of Comparative Example 2

[0157]

[0158] The performance evaluation of the drag reducers prepared in Examples 17 - 27 and Comparative Example 2 is as follows:

[0159] (1) Bulk viscosity test

[0160] Keep the drag reducers of Examples 17 - 27 and Comparative Example 2 at a constant temperature of 25 °C for 30 min, and use a six-speed rotational viscometer to measure the viscosity value under the condition of 100 r / min. Read the indication after 1 min, and the viscosity value is the indication × 3.

[0161] The bulk viscosity test results of Examples 17 - 27 and Comparative Example 2 are shown in Table 13:

[0162] Table 13 Bulk Viscosity Test of Examples 17 - 27 and Comparative Example 2

[0163]

[0164] (2) Viscosity test of 85,000 salt water

[0165] The test method is the same as above, and the test results are shown in Table 14.

[0166] Table 14 Apparent Viscosity Test of Examples 17 - 27 and Comparative Example 2

[0167]

[0168] (3)Static adsorption rate test:

[0169] Standard curve establishment: Prepare the fracturing fluid according to the formula of 0.4% drag reducer + 0.2% of 10% ammonium persulfate aqueous solution. Place the fracturing fluid in an environment of 90 °C to break the gel until the viscosity of the broken gel solution is less than 5 mPa·s to obtain the broken gel solution of 0.4% drag reducer. Respectively transfer 2.5 mL, 3.0 mL, 4.0 mL, 4.5 mL, and 5.0 mL of the broken gel solution into 100 mL volumetric flasks, make up the volume with the preparation water, and filter with a 0.45-micron microporous filter membrane. Measure the ultraviolet spectra of the broken gel solutions at 5 dilution concentrations from 190 - 240 nm. Take the maximum absorption wavelength λ and the wavelengths with a red shift or blue shift of 2 - 8 nm of λ for linear fitting of the concentration-absorbance standard curve, and take the wavelength at which the determination coefficient R 2 > 0.99 and closest to 1 as λ 1 ;

[0170] Measurement of the polymer concentration in the broken gel solution before adsorption: Take 4 mL of the above-mentioned broken gel solution of 0.4% drag reducer into a 100 mL volumetric flask, then make up the volume with the preparation water, and filter with a 0.45-micron microporous filter membrane to obtain the test solution to be measured before adsorption. Using the preparation water as the reference, measure the ultraviolet spectrum of the test solution to be measured before adsorption from 190 nm to 240 nm, and take the wavelength λ at the red shift (right shift) of 6 nm at the maximum absorption peak 1 of the absorbance as A 1 .

[0171] Preparation of the polymer solution after adsorption: Take 10 mL of the above-mentioned broken gel solution into a centrifuge tube, add 1 g of core powder with a mesh number ≥ 100 mesh, stir and mix evenly, place it on a shaker at 40 °C for adsorption and oscillation for 3 h, centrifuge the adsorbed sample in a centrifuge at a speed of 4000 r / min for 20 min, take 4 mL of the middle-layer clear liquid into a 100 mL volumetric flask, then make up the volume with the preparation water, and filter with a 0.45-micron microporous filter membrane.

[0172] Preparation of the polymer blank solution after adsorption: Take 10 mL of the preparation water into a centrifuge tube, add 1 g of coal powder with a mesh number ≥ 100 mesh, stir and mix evenly, place it on a shaker at 40 °C for adsorption and oscillation for 3 h, centrifuge the adsorbed sample in a centrifuge at a speed of 4000 r / min for 20 min, take 2 mL of the middle-layer clear liquid into a 100 mL volumetric flask, then make up the volume with the preparation water, and filter with a 0.45-micron microporous filter membrane.

[0173] Measurement of the polymer concentration in the broken gel solution after adsorption: Using the blank sample after adsorption as the reference, measure the ultraviolet spectrum of the polymer to be measured after adsorption from 190 nm to 240 nm, and take the absorbance at the wavelength λ 1 as A 2 , and the static adsorption capacity is calculated according to the following formula.

[0174]

[0175] In the formula:

[0176] X — Static adsorption rate, %;

[0177] A 2 — Absorbance at λ of the test solution after adsorption 1 nm;

[0178] A 1 — Absorbance at λ of the test solution before adsorption 1 nm;

[0179] The test results are shown in Table 15.

[0180] Table 15 Static adsorption rate test of Examples 17 - 27 and Comparative Example 2

[0181]

[0182] (4)Residue content test

[0183] Test the residue content of 0.4% drag reducer. The test method refers to Method 7.10.3 in SYT 7627 - 2021 Technical Requirements for Water - based Fracturing Fluids for testing and calculation. The test results are shown in Table 16.

[0184] Table 16 Residue content test of Examples 17 - 27 and Comparative Example 2

[0185]

[0186] (5)Drag reduction rate test

[0187] Test the drag reduction rate of the drag reducer under the conditions of fresh water and 85,000 mg / L brine (calcium ion 10,000 mg / L, magnesium ion 1,000 mg / L, and the rest are sodium ion and chloride ion). Execute according to the regulations for measuring the drag reduction rate in Chapter 7.13.1.1 of SY / T 6376 - 2008, and take the drag reduction rate data at 10 min as the drag reduction rate value. The test results are shown in Table 17.

[0188] Table 17 Drag reduction rate test of Examples 17 - 27 and Comparative Example 2

[0189]

[0190] (6)Methane desorption test, the test method is as follows:

[0191] a. Weigh 50 g of pulverized coal with a mesh size of 40 - 60 respectively, and dry it to constant weight;

[0192] b. Put the dried coal sample into the coal sample tank, and degas the coal sample in the tank;

[0193] c. After the degassing is completed, fill the coal sample tank with high-purity methane gas. By adjusting the gas inlet and outlet valves, make the pressure gauge reading of the coal sample tank reach the target value. When the pressure gauge reading remains stable within 2 hours, it can be considered that the methane in the tank has reached the adsorption equilibrium state.

[0194] d. Inject 10 mL of the prepared 0.4% drag reducer gel-breaking solution into the coal sample tank and start the stirring device. The stirring time is 30 minutes.

[0195] e. After the coal sample tank reaches the adsorption equilibrium again, connect the gas outlet to the gas collection bag, open the gas outlet valve until the pressure gauge reading of the coal sample tank is 0, and then close the gas outlet valve. Open the valve between the methane metering device and the gas outlet of the coal sample tank, and at the same time start the timing device to record the cumulative desorption amount of the coal sample at each moment during the 120-minute desorption process, with the unit of mL / g.

[0196] The test results are shown in Table 18.

[0197] Table 18 Methane desorption test of Examples 17 - 27 and Comparative Example 2

[0198]

[0199] In summary, the drag reducer prepared by the present invention has functions such as low adsorption, low residue, self-cleaning, and thickening, and has the function of promoting methane desorption. It can be used as a thickening agent, and when applied to hydraulic fracturing, it can effectively improve the oil and gas recovery rate and stable production capacity.

[0200] The above is only a preferred embodiment of the present invention, and does not impose any form of limitation on the present invention. Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some changes or modifications to the above-disclosed technical content to obtain equivalent embodiments with equivalent changes. However, as long as it does not depart from the technical solution of the present invention, any simple modification, equivalent change, and modification made to the above embodiments based on the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A self-cleaning active drag reducing agent, characterized in that: The components include the following mass percentages: Composite copolymer powder 30-50%, desorption promoter 1-15%, suspension main agent 0.02-0.4%, suspension activator 0.15-0.6%, and the rest is water-soluble solvent, totaling 100%; The preparation method of the composite copolymer is as follows: (1) dissolving polyvinyl alcohol and carboxymethyl hydroxypropyl guar gum in water to form an initial composite low molecular weight polymer aqueous solution, and then adding acrylamide, sodium acrylate, a benzene ring-containing rigid monomer, a reinforcing agent and urea to the aqueous solution to obtain a composite reaction solution; The molar ratio of acrylamide, sodium acrylate and benzene ring-containing rigid monomer is 1: (0.05-0.4): (0.01-0.1); the benzene ring-containing rigid monomer is selected from any one of the following six molecular structural formulas: Wherein, the R3 group is -COONa or -SO3Na; (2) adding an initiator to the composite reaction solution to carry out a polymerization reaction at a temperature of -5 to 40° C. to obtain a polymer colloid; (3) taking out the polymer colloid, cutting, crushing, drying and sieving to obtain a composite copolymer powder; The desorption promoting agent is a sulfonate surfactant; The main suspension agent is bacterial nanocellulose, with a diameter of 30 to 50 nm and a crystallinity of 70 to 90%; The suspension activator is ethylene glycol or hexamethylphosphoric triamide; The water-soluble solvent is a mixed solvent consisting of polyethylene glycol 200, polypropylene glycol 400 and N-methylpyrrolidone.

2. The self-cleaning active drag reducing agent according to claim 1, characterized in that: In the composite reaction solution, the mass fraction of polyvinyl alcohol is 0.5-6%, the mass fraction of carboxymethyl hydroxypropyl guar gum is 0.5-5%, the total mass fraction of acrylamide, sodium acrylate and benzene ring-containing rigid monomer is 15-40%, and the mass fraction of urea is 1-20%; the concentration of the enhancer is 20-1000 mg / L.

3. The self-cleaning active drag reducing agent according to claim 1, characterized in that: The enhancer is N,N-methylenebisacrylamide.

4. The self-cleaning active drag reducing agent according to claim 1, characterized in that: The initiator is a redox initiation system composed of ammonium cerium nitrate and sodium bisulfite.

5. The self-cleaning active drag reducing agent according to claim 1, characterized in that: In step (2), the polymerization reaction temperature is 10 to 20°C.

6. The self-cleaning active drag reducing agent according to claim 1, characterized in that: In step (2), the polymerization reaction is considered to be complete when the temperature of the polymerization reaction system does not rise by more than 1° C. within 30 minutes.

7. A method for preparing the self-cleaning active drag reducing agent according to any one of claims 1 to 6, characterized in that: Here are the steps: S1, preparing a mixed solvent of polyethylene glycol 200, polypropylene glycol 400, and N-methylpyrrolidone; S2, the mixed solvent is divided into two parts, the desorption promoter is added to one part of the mixed solvent, and after stirring for 15 to 20 minutes, the suspension activator is slowly added, and the suspension activator is stirred for 30 minutes to fully mix the suspension activator with the solution, and then the composite copolymer powder is added at a uniform speed while stirring, and the stirring is continued for 1.5 to 2 hours after the addition is completed to obtain a pre-hydrated activated drag reducing agent solution; S3, adding the suspension main agent to another mixed solvent, stirring evenly, to obtain a suspension main agent concentrate; S4, adding the concentrated suspension main agent solution to the drag reducing agent solution of step S2, stirring for 1 hour, and obtaining a self-cleaning active drag reducing agent.

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