Salt response type high-temperature-resistant water-based drilling fluid tackifier as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of drilling fluid tackifiers in oil exploration and development, and particularly relates to a salt response type high-temperature-resistant water-based drilling fluid tackifier as well as a preparation method and application thereof. The salt response type high-temperature-resistant water-based drilling fluid tackifier comprises the following components in parts by weight: 2-40 parts of a first amide monomer, 2-30 parts of a betaine monomer, 2-40 parts of a second amide monomer and 0.3-0.5 part of an initiator. The preparation method comprises the following steps: dispersing and dissolving a first amide monomer, a betaine monomer and a second amide monomer in a container containing distilled water under nitrogen protection and stirring conditions; under the protection of nitrogen, dispersing an initiator in the mixed solution prepared in the step 1, continuing for a preset time, and then heating to carry out polymerization reaction; and then purifying with acetone and carrying out vacuum drying to obtain a target product. The tackifier can be applied to the water-based drilling fluid. The salt-resistant water-based drilling fluid has good salt resistance, can keep good rheology and filtration loss of the water-based drilling fluid, stabilizes the well wall, balances the formation pressure, carries rock debris and lubricates a drilling tool.

Description

Technical Field

[0001] The invention belongs to the technical field of drilling fluid viscosity enhancers in petroleum exploration and development, and specifically relates to a salt-responsive high-temperature resistant water-based drilling fluid viscosity enhancer, a preparation method and an application thereof. Background Art

[0002] At present, with the rapid growth of global oil energy demand and the gradual depletion of onshore oil reserves, unconventional reservoirs are gradually being exploited by major oilfield companies, among which salt-gypsum layers have a good reservoir distribution. Bentonite is the main component of water-based drilling fluid. Since the negative charge on its surface is caused by lattice substitution, it is highly sensitive to salt. When the water-based drilling fluid is pumped into the wellbore, on the one hand, due to the electrostatic attraction formed by the bentonite surface and the intruding electrolyte cations, a flocculation or aggregation structure is generated, and the hydration dispersibility of the bentonite particles becomes poor. On the other hand, most water-based drilling fluid treatment agents (such as polymer thickeners) are polyelectrolytes, and their molecular chains are easily curled by electrostatic attraction under the action of salt, thereby reducing solubility or even insolubility, and losing their effectiveness. These two factors lead to the deterioration of the rheological properties and filtration properties of water-based drilling fluids, which further leads to frequent drilling accidents, such as well leakage, increase in well diameter, formation collapse, stuck drill and well wall instability.

[0003] There are reports on water-based drilling fluid thickeners in the prior art. For example, Chinese patent document CN110628395A discloses a method for preparing a drilling fluid thickener, wherein polyisobutylene, hydroxypropyl methylcellulose, dioctyl phthalate, ethyl 2-cyanoacrylate and polyacrylate are stirred and mixed to obtain mixture one; methyl sulfonic acid, polyethylene glycol, polyvinyl acetate and dimethyl diallyl ammonium chloride are added to the mixture, and the mixture is heated and stirred under vacuum conditions to obtain mixture two; lubricants and dicyclohexylamine are added to mixture two, and the mixture is stirred and mixed to obtain a drilling fluid thickener. The invention has good viscosity stability and temperature resistance. However, the thickener synthesis process involved in the invention is complicated, the monomers are various, and the molecular structure is essentially incompatible with salt and does not have salt resistance. It is easy to cause the performance of the drilling fluid to deteriorate (viscosity reduction, drilling fluid flocculation) and increase the filtration loss in the salt-gypsum layer drilling, thereby increasing the drilling risk.

[0004] For another example, Chinese patent document CN109796946A discloses a modified psyllium seed husk thickener for drilling fluid, comprising the following mass percentage components: psyllium seed husk 31-36%, NaOH 34-35%, isopropanol 18-19%, propylene oxide 6-8%, hydrophilic nano-silica 6-8%, and the balance is deionized water. It is mainly synthesized by solution synthesis to form hydroxyethyl psyllium seed husk, and on this basis, it is combined with hydrophilic nano-silica to form a hydroxyethyl psyllium seed husk-nano-silica composite; the viscosity-increasing effect and temperature resistance of the drilling fluid system are increased; compared with the current synthetic polymers, it is more suitable for use in clay-free drilling fluids, solid-free drilling fluids and solid-free completion fluids, which have greater limitations in use and do not have salt resistance.

[0005] In summary, the existing water-based drilling fluid thickeners have the following disadvantages:

[0006] (1) Traditional viscosifiers have poor salt resistance, making it difficult for water-based drilling fluids to maintain good rheology and filtration, stabilize the wellbore, balance formation pressure, carry cuttings, and lubricate drilling tools.

[0007] (2) Under high temperature conditions, the molecular chains of the thickener undergo thermal degradation and become ineffective.

[0008] In view of the technical difficulty that the current water-based drilling fluid thickener fails in salt-gypsum layers due to a large amount of electrolyte salt ions and high temperature environment, resulting in deterioration of the rheological and filtration properties of the water-based drilling fluid, and further causing drilling accidents, it is necessary to provide a method that fundamentally solves the problem of deterioration of the rheological and filtration properties of water-based drilling fluid in salt-gypsum layers and high temperature environments. Summary of the invention

[0009] In order to solve the above technical problems, the present invention provides a salt-responsive high-temperature resistant water-based drilling fluid viscosity enhancer, a preparation method and an application thereof.

[0010] To achieve the above object, the technical solution adopted by the present invention is:

[0011] A salt-responsive high-temperature resistant water-based drilling fluid thickener comprises the following raw materials in parts by weight: 2-40 parts of a first amide monomer, 2-30 parts of a betaine monomer, 2-40 parts of a second amide monomer, and 0.3-0.5 parts of an initiator.

[0012] The molar ratio of the first amide monomer, the betaine monomer and the second amide monomer is 1-4:8-2:1-4.

[0013] The first amide monomer and the second amide monomer are one or a combination of two or more of acrylamide, N-vinyl-ε-caprolactam, N-(4-bromophenyl)prop-2-eneamide, N-allyl p-toluenesulfonamide, 2,2,2-trichloroacetamide allyl ester, prop-2-ene-1-sulfonamide, N-allyl-2-chloroacetamide, N-(allyloxy)-2-nitrobenzenesulfonamide, diene-3-amino-7-oxabicyclo[2.2.1]hept-5-ene-2-carboxamide, and N-(3-allylpyridin-4-yl)pivalamide.

[0014] The betaine monomer is one or a combination of two or more of 2-methacryloyloxyethyl 2-trimethylaminoethyl phosphate, [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide, 3(-N,N-dipropylene-N-methylamino)propanesulfonate sodium, vinylpyridine derivative sulfobetaine, acrylamide derivative sulfobetaine, and methacrylate derivative sulfobetaine.

[0015] The initiator is one or a combination of two or more of ammonium persulfate, sodium bisulfite, potassium persulfate, ferrous sulfate, hydrogen peroxide, benzoyl peroxide, N,N-diethylaniline, persulfate, and mercaptan.

[0016] A method for preparing a salt-responsive high-temperature resistant water-based drilling fluid thickener comprises the following steps:

[0017] Step 1: dispersing and dissolving the first amide monomer, the betaine monomer and the second amide monomer by weight in a container containing distilled water under nitrogen protection and stirring;

[0018] Step 2: Under nitrogen protection, disperse 100 parts by weight of the initiator in the mixed solution prepared in step 1, heat it for a preset time, and then perform a polymerization reaction;

[0019] Step 3: After the reaction is completed, purify with acetone three times and vacuum dry to obtain the target product.

[0020] In the step 1, the ratio of the total mass of the first amide monomer, the betaine monomer and the second amide monomer to the mass of distilled water is 1:3.

[0021] The preset standing time in the step 2 is 0.5 hours; the mass concentration of the initiator in the aqueous solution of the initiator is 0.1-0.5 g / L; and the stirring speed during the stirring reaction is 300-500 rpm.

[0022] The drying in step 3 is vacuum drying at 45-55° C.; the drying time is 6-8 hours; and the acetone for washing is continuously added and stirred until the precipitate is completely precipitated.

[0023] The invention discloses an application of a salt-responsive high-temperature resistant water-based drilling fluid thickener, wherein the salt-responsive high-temperature resistant water-based drilling fluid thickener is applied as a thickener to water-based drilling fluid.

[0024] Beneficial effects:

[0025] (1) The salt-responsive high-temperature resistant water-based drilling fluid thickener in the present invention has a special anti-polyelectrolyte effect and a positive responsiveness to salt. It essentially realizes the transformation from "resisting salt" to "responding to salt", is essentially compatible with salt, and has good filtration loss reduction performance when applied to deep well salt paste layers. Its mechanism: The positive and negative ion groups with the same charge on the molecular chain of the water-based drilling fluid thickener use electrostatic attraction to form a curled spherical structure with a net charge of 0. As the ion strength of the electrolyte sodium chloride gradually increases, the chloride ions and sodium ions destroy the spatial network structure formed by the positive and negative ion groups on the thickener molecular chain through electrostatic force, so that the molecular chain changes from a curled spherical structure to an extended flexible chain structure. The extension of the molecular chain leads to an increase in the fluid dynamic size and gyration radius of the thickener, enhanced solubility, and increased viscosity, giving it a "salt-responsive" characteristic.

[0026] (2) The thickener in the present invention has excellent thickening, salt resistance and temperature resistance, and can adapt to high-temperature deep well salt-paste formations; experiments have shown that the salt-responsive high-temperature resistant water-based drilling fluid thickener of the present invention can withstand temperatures up to 150°C and salt response to saturation.

[0027] (3) The salt-responsive high-temperature resistant water-based drilling fluid thickener of the present invention can effectively prevent clay particles from agglomerating in a high-temperature, high-salt environment to form a dense mud cake, reduce water penetration, and thus reduce filtration loss.

[0028] (4) The salt-responsive high-temperature resistant water-based drilling fluid thickener of the present invention exhibits low viscosity at high shear rates and high viscosity at low shear rates. It has good viscoelasticity and shear thinning properties, which is beneficial for suspending and carrying cuttings, cleaning the wellbore, and enhancing the stability of the wellbore wall.

[0029] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention and implement it according to the contents of the specification, the following is a detailed description of the preferred embodiments of the present invention in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0031] Figure 1 This is the thermogravimetric diagram of the salt-responsive high-temperature resistant water-based drilling fluid viscosity enhancer prepared in Example 5.

[0032] Figure 2 This is the infrared spectrum of the salt-responsive high-temperature resistant water-based drilling fluid viscosity enhancer prepared in Example 5.

[0033] Figure 3 This is a curve diagram showing the change in viscosity of the salt-responsive high-temperature resistant water-based drilling fluid thickener prepared in Example 5 as a function of shear rate. DETAILED DESCRIPTION

[0034] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0035] Embodiment 1:

[0036] A salt-responsive high-temperature resistant water-based drilling fluid thickener comprises the following raw materials in parts by weight: 2-40 parts of a first amide monomer, 2-30 parts of a betaine monomer, 2-40 parts of a second amide monomer, and 0.3-0.5 parts of an initiator.

[0037] In actual use, the first amide monomer, the betaine monomer and the second amide monomer are dispersed and dissolved in a container containing distilled water under nitrogen protection and stirring conditions, wherein the ratio of the total mass of the first amide monomer, the betaine monomer and the second amide monomer to the mass of the distilled water is 1:3; then, under nitrogen protection, the initiator is dispersed in the mixed solution prepared above, and the mass concentration of the initiator in the aqueous solution of the initiator is 0.1-0.5 g / L; the stirring speed during the stirring reaction is 300-500 rpm; after 0.5 hours, it is heated to carry out a polymerization reaction; after the reaction is completed, it is purified three times with acetone and vacuum dried to obtain the target product, wherein the drying is vacuum drying at 45-55° C.; the drying time is 6-8 hours; the washing acetone is continuously added and stirred until the precipitate is completely precipitated.

[0038] The salt-responsive high-temperature resistant water-based drilling fluid thickener of the present invention has a special anti-polyelectrolyte effect and a positive response to salt. It essentially realizes the transformation from "resistance to salt" to "salt response" and is essentially compatible with salt.

[0039] The thickener in the present invention has excellent thickening, salt resistance and temperature resistance, and can adapt to high-temperature deep well salt-paste formations; experiments have shown that the salt-responsive high-temperature resistant water-based drilling fluid thickener of the present invention can withstand a temperature of up to 150°C and responds to salt to saturation.

[0040] The salt-responsive high-temperature resistant water-based drilling fluid thickener of the present invention can effectively prevent clay particles from agglomerating in a high-temperature, high-salt environment to form a dense mud cake, reduce water penetration, and thus reduce filtration loss. It has good filtration loss reduction performance when applied to deep well salt-gypsum layers.

[0041] The salt-responsive high-temperature resistant water-based drilling fluid thickener of the present invention exhibits low viscosity at high shear rates and high viscosity at low shear rates, has good viscoelasticity and shear thinning properties, is conducive to suspending and carrying cuttings, cleaning the wellbore, and enhancing the stability of the wellbore wall.

[0042] Embodiment 2:

[0043] A salt-responsive high-temperature resistant water-based drilling fluid viscosity enhancer is different from the first embodiment in that the molar ratio of the first amide monomer, the betaine monomer and the second amide monomer is 1-4:8-2:1-4.

[0044] Further, the first amide monomer and the second amide monomer are one or a combination of two or more of acrylamide, N-vinyl-ε-caprolactam, N-(4-bromophenyl)prop-2-eneamide, N-allyl p-toluenesulfonamide, 2,2,2-trichloroacetamide allyl ester, prop-2-ene-1-sulfonamide, N-allyl-2-chloroacetamide, N-(allyloxy)-2-nitrobenzenesulfonamide, diene-3-amino-7-oxabicyclo[2.2.1]hept-5-ene-2-carboxamide, and N-(3-allylpyridin-4-yl)pivalamide.

[0045] Furthermore, the betaine monomer is one or a combination of two or more of 2-methacryloyloxyethyl 2-trimethylaminoethyl phosphate, [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide, 3(-N,N-dipropylene-N-methylamino)propanesulfonate sodium, vinylpyridine derivative sulfobetaine, acrylamide derivative sulfobetaine, and methacrylate derivative sulfobetaine.

[0046] Furthermore, the initiator is one or a combination of two or more of ammonium persulfate, sodium bisulfite, potassium persulfate, ferrous sulfate, hydrogen peroxide, benzoyl peroxide, N,N-diethylaniline, persulfate, and thiol.

[0047] Embodiment three:

[0048] A method for preparing a salt-responsive high-temperature resistant water-based drilling fluid thickener comprises the following steps:

[0049] Step 1: dispersing and dissolving the first amide monomer, the betaine monomer and the second amide monomer by weight in a container containing distilled water under nitrogen protection and stirring;

[0050] Step 2: Under nitrogen protection, disperse 100 parts by weight of the initiator in the mixed solution prepared in step 1, let it stand for a preset time, and then heat it to carry out a polymerization reaction;

[0051] Step 3: After the reaction is completed, purify with acetone three times and vacuum dry to obtain the target product.

[0052] Furthermore, in the step 1, the ratio of the total mass of the first amide monomer, the betaine monomer and the second amide monomer to the mass of distilled water is 1:3.

[0053] Furthermore, the preset standing time in step 2 is 0.5 hours; the mass concentration of the initiator in the aqueous solution of the initiator is 0.1-0.5 g / L; and the stirring speed during the stirring reaction is 300-500 rpm.

[0054] Furthermore, the drying in step three is vacuum drying at 45-55° C.; the drying time is 6-8 hours; and the washing acetone is continuously added and stirred until the precipitate is completely precipitated.

[0055] Embodiment 4:

[0056] The salt-responsive high-temperature resistant water-based drilling fluid thickener is used as a thickener in water-based drilling fluid.

[0057] Embodiment five:

[0058] A salt-responsive high-temperature resistant water-based drilling fluid thickener is prepared by including the following raw materials in parts by weight: 5.61 g of a first amide monomer (acrylamide), 17.64 g of a betaine monomer and 1.75 g of a second amide monomer (N-vinyl-ε-caprolactam), and 0.1 g of an initiator, wherein the initiator is composed of ammonium persulfate and sodium bisulfite, wherein the mass ratio of the ammonium persulfate to the sodium bisulfite is 1:1.

[0059] The preparation method of the above-mentioned salt-responsive high temperature resistant water-based drilling fluid viscosity enhancer is as follows:

[0060] Step 1: Disperse and dissolve 5.61 g of the first amide monomer (acrylamide), 17.64 g of the betaine monomer and 1.75 g of the second amide monomer (N-vinyl-ε-caprolactam) in a three-necked flask containing 75 g of distilled water under nitrogen protection and stirring at 300 rpm.

[0061] Step 2: Under nitrogen protection, disperse 50 mg of initiator ammonium persulfate and 50 mg of sodium bisulfite in the mixed solution for 0.5 hours, heat to 50°C and react for 10 hours. After the synthesized product is purified by repeated washing with acetone three times, it is vacuum dried at 50°C for 10 hours to obtain a salt-responsive high temperature resistant water-based drilling fluid thickener.

[0062] Thermogravimetric analysis:

[0063] In a TA Instruments SDT-Q600 thermogravimetric analyzer, an aluminum crucible was used and the nitrogen purge flow rate was 50 mL min -1 The salt-responsive high temperature resistant water-based drilling fluid thickener obtained in this example was subjected to thermogravimetric (TGA) and derivative thermogravimetric (DTG) analysis. The initial temperature was 40°C and the final temperature was 800°C.

[0064] like Figure 1 As shown in the figure, due to the hydrophilic groups in the molecular chain of the salt-responsive anti-high temperature water-based drilling fluid thickener, some free water in the air is adsorbed, and its TG curve slowly decreases when the heating temperature is 40 to 110°C. The functional groups on the side chains of the thickener molecular chain undergo thermal decomposition, resulting in a mass loss rate of 56.2% in the TG curve within the temperature range of 320°C to 450°C. After heating to 450°C, the TG curve of the thickener decreases more gently because the main chain of the molecular chain is basically thermally degraded. In general, the salt-responsive anti-high temperature water-based drilling fluid thickener has good thermal stability, and its thermal degradation temperature is after 320°C.

[0065] Infrared spectroscopy:

[0066] The salt-responsive high-temperature resistant water-based drilling fluid thickener prepared in this example was mixed with potassium bromide in a certain proportion and then pressed at a pressure of 2 MPa for 5-10 minutes to form a thin sheet. The thin sheet was obtained by using an IRTRacer-100 infrared series spectrophotometer at 400-4000 cm -1 The absorption spectrum in the infrared region is obtained in the wavenumber range.

[0067] like Figure 2 As shown, the NH bond of the amide group on the first amide corresponds to a wavelength of 3437 cm -1 The peak at -CH 2 -Stretching vibration peak corresponds to wavelength 2961cm -1 The peak of the C=O bond stretching vibration corresponds to 1725 cm -1 The stretching vibration of the C=O bond in the first amide molecular chain corresponds to a wavelength of 1665 cm -1 The peak value is at 1474cm -1 The peak at 1195cm is the stretching vibration peak of the CN bond on the betaine molecular chain.-1 The peak at is attributed to the stretching vibration of the CN bond of the second amide molecular chain. The stretching vibration peak of the SO bond in the sulfonic acid group in the betaine molecular chain corresponds to a wavelength of 1040 cm -1 In addition, the FT-IR results also show that there is no unsaturated bond C=C in the molecular chain, which indicates that there is no unreacted monomer in the target product.

[0068] In summary, the target product in this example has been successfully prepared.

[0069] Embodiment six:

[0070] A salt-responsive high-temperature resistant water-based drilling fluid viscosity enhancer is prepared by including the following raw materials in parts by weight:

[0071] 7.85g of the first amide monomer (N,N-dimethylacrylamide), 14g of betaine monomer and 3.15g of the second amide monomer (propylene-2-ene-1-sulfonamide), 0.08g of initiator ammonium persulfate / sodium bisulfite (the mass ratio of ammonium persulfate to sodium bisulfite is 1:1). The preparation method of the above salt-responsive high temperature resistant water-based drilling fluid thickener is as follows:

[0072] (1) 7.85 g of the first amide monomer (N,N-dimethylacrylamide), 14 g of the betaine monomer and 3.15 g of the second amide monomer (prop-2-ene-1-sulfonamide) were dispersed and dissolved in a three-necked flask containing 75 g of distilled water under nitrogen protection and stirring at 300 rpm.

[0073] (2) Under nitrogen protection, 40 mg of ammonium persulfate and 40 mg of sodium bisulfite as initiators were dispersed in the mixed solution for 0.5 hours, and heated to 50°C for reaction for 10 hours. The synthesized product was repeatedly washed with acetone for purification three times, and then vacuum dried at 50°C for 10 hours to obtain a salt-responsive high temperature resistant water-based drilling fluid thickener.

[0074] Embodiment seven:

[0075] A salt-responsive high-temperature resistant water-based drilling fluid viscosity enhancer is prepared by including the following raw materials in parts by weight:

[0076] 8.63g of the first amide monomer (N-allyl-2-chloroacetamide), 12.22g of betaine monomer and 4.15g of the second amide monomer (N-vinyl-ε-caprolactam), 0.06g of initiator ammonium persulfate / sodium bisulfite (the mass ratio of ammonium persulfate to sodium bisulfite is 1:1). The preparation method of the above salt-responsive high temperature resistant water-based drilling fluid thickener is as follows:

[0077] (1) 8.63 g of the first amide monomer (N-allyl-2-chloroacetamide), 12.22 g of the betaine monomer and 4.15 g of the second amide monomer (N-vinyl-ε-caprolactam) were dispersed and dissolved in a three-necked flask containing 75 g of distilled water under nitrogen protection and stirring at 300 rpm.

[0078] (2) Under nitrogen protection, 30 mg of ammonium persulfate and 30 mg of sodium bisulfite as initiators were dispersed in the mixed solution for 0.5 hours, and heated to 50° C. for reaction for 10 hours.

[0079] (3) After the synthesized product was purified three times by repeated washing with acetone, it was vacuum dried at 50°C for 10 h to obtain a salt-responsive high-temperature resistant water-based drilling fluid thickener.

[0080] Embodiment eight:

[0081] A salt-responsive high-temperature resistant water-based drilling fluid viscosity enhancer is prepared by including the following raw materials in parts by weight:

[0082] 9.67g of the first amide monomer (2,2,2-trichloroacetamide allyl ester), 10.1g of betaine monomer and 5.23g of the second amide monomer (N-(3-allylpyridin-4-yl) neopentylamide), 0.1g of initiator, the initiator is made of ammonium persulfate / sodium bisulfite according to the mass ratio of ammonium persulfate to sodium bisulfite of 1:1.

[0083] The preparation method of the above-mentioned salt-responsive high temperature resistant water-based drilling fluid thickener is as follows:

[0084] (1) 9.67 g of a first amide monomer (allyl 2,2,2-trichloroacetamide), 10.1 g of a betaine monomer and 5.23 g of a second amide monomer (N-(3-allylpyridin-4-yl)pivalamide) were dispersed and dissolved in a three-necked flask containing 75 g of distilled water under nitrogen protection and stirring at 300 rpm.

[0085] (2) Under nitrogen protection, 50 mg of ammonium persulfate and 50 mg of sodium bisulfite as initiators were dispersed in the mixed solution for 0.5 hours, and heated to 50° C. to react for 10 hours.

[0086] (3) After the synthesized product was purified three times by repeated washing with acetone, it was vacuum dried at 50°C for 10 h to obtain a salt-responsive high-temperature resistant water-based drilling fluid thickener.

[0087] Embodiment nine:

[0088] A salt-responsive high-temperature resistant water-based drilling fluid viscosity enhancer is prepared by including the following raw materials in parts by weight:

[0089] 10.86g of the first amide monomer (acrylamide), 7.97g of betaine monomer and 6.17g of the second amide monomer (N,N-dimethylacrylamide), and 0.1g of an initiator composed of ammonium persulfate and sodium bisulfite in a mass ratio of 1:1.

[0090] The preparation method of the above-mentioned salt-responsive high temperature resistant water-based drilling fluid thickener is as follows:

[0091] (1) 10.86 g of the first amide monomer (acrylamide), 7.97 g of the betaine monomer and 6.17 g of the second amide monomer (N,N-dimethylacrylamide) were dispersed and dissolved in a three-necked flask containing 75 g of distilled water under nitrogen protection and stirring at 300 rpm.

[0092] (2) Under nitrogen protection, 50 mg of ammonium persulfate and 50 mg of sodium bisulfite as initiators were dispersed in the mixed solution for 0.5 hours, and heated to 50°C for reaction for 10 hours. The synthesized product was repeatedly washed with acetone for purification three times, and then vacuum dried at 50°C for 10 hours to obtain a salt-responsive high temperature resistant water-based drilling fluid thickener.

[0093] Embodiment ten:

[0094] The performance of the salt-responsive high-temperature resistant water-based drilling fluid thickener prepared in Example 3 was evaluated:

[0095] (1) Rheological properties test

[0096] Preparation of brine drilling fluid: Add different masses of NaCl to 400 mL of drilling fluid base slurry with a bentonite content of 4 wt%, stir evenly to obtain brine drilling fluid. The mass concentrations of NaCl in the brine drilling fluid are 1%, 5%, 10%, 20% and 36%, respectively. The tackifier prepared in Example 5 is added to the above-mentioned brine drilling fluid at a mass concentration of 2% and mixed evenly, and the rheological properties before and after aging are tested according to the GB / T16783-2014 drilling fluid test standard. The tackifier prepared in Example 5 is added to NaCl solutions containing 0%, 1%, 5%, 10%, 20% and 36% at a mass concentration of 1% and dispersed evenly. The change in viscosity of the above-mentioned mixed solution relative to the shear rate is measured by a rotational rheometer (Physica MCR301, Austria), and the shear rate range is 1s -1 Up to 1000s -1 The interval between each shear rate was 10 s.

[0097] (3) Filtration performance test

[0098] The viscosity enhancers prepared in Example 5 were added to the above-mentioned brine drilling fluid at a mass concentration of 2% and mixed evenly. The API low-temperature and low-pressure filtration test was carried out at a constant pressure of 100 psi at ambient temperature (25° C.) in accordance with the GB / T16783-2014 drilling fluid test standard to test the filtration performance before and after aging.

[0099] The experimental results are as follows Figure 3 As shown in Tables 1 to 5 below:

[0100] Table 1 Effect of Example 5 Viscosifier on Rheological and Filtration Properties of Brine Drilling Fluid

[0101]

[0102] Table 2 Effect of Example 6 Viscosifier on Rheological and Filtration Properties of Brine Drilling Fluid

[0103]

[0104]

[0105] Table 3 Effect of Example 7 Viscosifier on Rheological and Filtration Properties of Brine Drilling Fluid

[0106]

[0107] Table 4 Effect of Example 8 Viscosifier on Rheological and Filtration Properties of Brine Drilling Fluid

[0108]

[0109] Table 5 Effect of Example 9 Viscosifier on Rheological and Filtration Properties of Brine Drilling Fluid

[0110]

[0111]

[0112] The most intuitive feature of salt-responsive water-based drilling fluid thickeners is that as the electrolyte sodium chloride ion strength gradually increases, the molecular chain structure becomes more stretched, and the extension of the molecular chain leads to an increase in the fluid dynamic size, viscosity, and gyration radius of the thickener. Figure 3 The results show that the thickener solution exhibits significant shear thinning behavior, in which the viscosity of the thickener solution decreases with increasing shear rate, and the interaction between molecules is destroyed by shear force. On the other hand, the viscosity of the thickener solution gradually increases with increasing sodium chloride concentration, showing a classic anti-polyelectrolyte phenomenon and positive response to salt. Sodium chloride penetrates into the thickener molecular chain through electrostatic attraction, shielding the charge on the thickener molecular chain and promoting its dissolution, thereby increasing the viscosity.

[0113] The experimental results in Table 1 also show that as the sodium chloride concentration in the brine drilling fluid containing the thickener of the present invention increases, its viscosity before and after high-temperature aging also increases, showing a positive responsiveness to salt, which is essentially different from the "salt viscosity reduction" of conventional thickeners. On the other hand, as the thickener molecular chain gradually stretches with the increase of sodium chloride concentration, the solubility is enhanced, and the viscosity increases, the amide group and sulfonate group on the thickener molecular chain form stable hydrogen bonds and ionic bonds with bentonite respectively, and are effectively adsorbed on the surface of bentonite. At the same time, it can effectively prevent a large number of sodium ions from forming ion exchange adsorption between the bentonite layer, so that the bentonite maintains a certain dispersion and avoids flocculation and aggregation of bentonite particles; thereby, under the action of the pressure difference, the well-dispersed bentonite forms a dense mud cake, reducing water penetration, thereby reducing the filtration loss of the brine drilling fluid. Experiments have shown that the salt-responsive high-temperature resistant water-based drilling fluid thickener of the present invention can withstand temperatures of up to 150°C and responds to salt to saturation.

[0114] The salt-responsive high-temperature resistant water-based drilling fluid thickener of the present invention has a special anti-polyelectrolyte effect and a positive response to salt. It essentially realizes the transformation from "resistance to salt" to "response to salt" and is essentially compatible with salt. This is specifically reflected in Tables 1 and Figure 3 The experimental results show that the mechanism is as follows: the positive and negative ion groups with the same charge on the molecular chain of the water-based drilling fluid thickener form a curled spherical structure through electrostatic attraction, and the net charge is 0. As the ion strength of the electrolyte sodium chloride gradually increases, the chloride ions and sodium ions destroy the spatial network structure formed by the positive and negative ion groups on the molecular chain of the thickener through electrostatic force, causing the molecular chain to change from a curled spherical structure to an extended flexible chain structure. The extension of the molecular chain increases the hydrodynamic size and gyration radius of the thickener, enhances its solubility, and increases its viscosity, giving it a "salt response" characteristic.

[0115] In the absence of conflicts, technicians in this field can combine the relevant technical features in the above examples according to actual conditions to achieve corresponding technical effects. The specific combinations are not described here one by one.

[0116] It should be noted that all directional indications in the embodiments of the present invention (such as up, down, left, right, front, back, etc.) are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0117] In addition, the descriptions of "first", "second", etc. in the present invention are only for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" or "second" may explicitly or implicitly include at least one of the features.

[0118] The above are only preferred embodiments of the present invention. The present invention will not be limited to the embodiments shown herein, but should conform to the widest scope consistent with the principles and novel features disclosed herein. Any simple modification, equivalent changes and modifications made to the above embodiments according to the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A salt-responsive high-temperature resistant water-based drilling fluid thickener, Features: The invention comprises the following raw materials in parts by weight: 2-40 parts of a first amide monomer, 2-30 parts of a betaine monomer, 2-40 parts of a second amide monomer, and 0.3-0.5 parts of an initiator.

2. A salt-responsive high-temperature resistant water-based drilling fluid thickener according to claim 1, Features: The molar ratio of the first amide monomer, the betaine monomer and the second amide monomer is 1-4:8-2:1-4.

3. A salt-responsive high-temperature resistant water-based drilling fluid viscosity enhancer according to claim 1 or 2, Features: The first amide monomer and the second amide monomer are one or a combination of two or more of acrylamide, N-vinyl-ε-caprolactam, N-(4-bromophenyl)prop-2-eneamide, N-allyl p-toluenesulfonamide, 2,2,2-trichloroacetamide allyl ester, prop-2-ene-1-sulfonamide, N-allyl-2-chloroacetamide, N-(allyloxy)-2-nitrobenzenesulfonamide, diene-3-amino-7-oxabicyclo[2.2.1]hept-5-ene-2-carboxamide, and N-(3-allylpyridin-4-yl)pivalamide.

4. A salt-responsive high-temperature resistant water-based drilling fluid viscosity enhancer according to claim 1 or 2, Features: The betaine monomer is one or a combination of two or more of 2-methacryloyloxyethyl 2-trimethylaminoethyl phosphate, [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide, 3(-N,N-dipropylene-N-methylamino)propanesulfonate sodium, vinylpyridine derivative sulfobetaine, acrylamide derivative sulfobetaine, and methacrylate derivative sulfobetaine.

5. The salt-responsive high-temperature resistant water-based drilling fluid viscosity enhancer according to claim 1, Features: The initiator is one or a combination of two or more of ammonium persulfate, sodium bisulfite, potassium persulfate, ferrous sulfate, hydrogen peroxide, benzoyl peroxide, N,N-diethylaniline, persulfate, and mercaptan.

6. A method for preparing a salt-responsive high-temperature resistant water-based drilling fluid viscosity enhancer according to any one of claims 1 to 5, Features: The following steps are included: Step 1: dispersing and dissolving the first amide monomer, the betaine monomer and the second amide monomer by weight in a container containing distilled water under nitrogen protection and stirring; Step 2: Under nitrogen protection, disperse 100 parts by weight of the initiator in the mixed solution prepared in step 1, heat it for a preset time, and then perform a polymerization reaction; Step 3: After the reaction is completed, purify with acetone three times and vacuum dry to obtain the target product.

7. A method for preparing a salt-responsive high-temperature resistant water-based drilling fluid viscosity enhancer as claimed in claim 6, Features: In the step 1, the ratio of the total mass of the first amide monomer, the betaine monomer and the second amide monomer to the mass of distilled water is 1:

3.

8. A method for preparing a salt-responsive high-temperature resistant water-based drilling fluid viscosity enhancer as claimed in claim 6, Features: The preset standing time in the step 2 is 0.5 hours; the mass concentration of the initiator in the aqueous solution of the initiator is 0.1-0.5 g / L; and the stirring speed during the stirring reaction is 300-500 rpm.

9. A method for preparing a salt-responsive high-temperature resistant water-based drilling fluid viscosity enhancer as claimed in claim 6, Features: The drying in step 3 is vacuum drying at 45-55° C.; the drying time is 6-8 hours; and the acetone for washing is continuously added and stirred until the precipitate is completely precipitated.

10. Application of a salt-responsive high-temperature resistant water-based drilling fluid thickener, Features: The salt-responsive high-temperature resistant water-based drilling fluid thickener as described in any one of claims 1 to 6 is applied as a thickener to water-based drilling fluid.

Images