CN113896831B - A double-effect inhibitor for natural gas hydrate drilling fluid and its preparation method and application - Google Patents

Abstract

The invention provides a double-effect inhibitor for natural gas hydrate drilling fluid and a preparation method and application thereof. The inhibitor drilling fluid has good compatibility and high hydrate decomposition inhibition efficiency, can obviously reduce the hydrate decomposition rate under the overheating condition, reduce the hydration dispersion degree of clay, and synergistically maintain the stability of the well wall of a hydrate formation in the drilling process.

Description

A double-effect inhibitor for natural gas hydrate drilling fluid and its preparation method and application

technical field

The invention relates to a double-effect inhibitor for natural gas hydrate drilling fluid, a preparation method and application thereof, and belongs to the technical field of natural gas hydrate drilling and production in sea areas.

Background technique

Natural gas hydrate is a clathrate hydrate usually composed of more than 99% methane gas and less than 1% other hydrocarbon gases as guest molecules. Natural gas hydrate is a clean alternative energy source. It is a crystalline substance formed by natural gas and water under high pressure and low temperature conditions. The total amount of global hydrate resources is about twice the total amount of traditional fossil energy. The hydrate resources in my country's sea area are about With an oil equivalent of 80 billion tons, it is an important potential high-efficiency clean oil and gas replacement resource, which is particularly important for ensuring the security of the national energy strategy. In recent years, many developed countries such as the United States, Japan, and Canada have carried out hydrate test production, and my country's deep-water natural gas hydrate test production has also made important breakthroughs, but they are far from commercial production.

Subsea natural gas hydrate is extremely sensitive to temperature and pressure. During the drilling process, the interaction between wellbore working fluid and natural gas hydrate, such as mass transfer and heat transfer, can easily induce the decomposition of natural gas hydrate in the reservoir, causing the formation stress around the wellbore to redistribute, Formation strength decreases, resulting in wellbore instability and reservoir damage. By injecting chemical agents to stabilize formation hydrates or reduce the decomposition rate of hydrates, the formation strength decline caused by hydrate decomposition can be effectively suppressed. However, there are few studies on hydrate decomposition inhibitors at present, for example: Chinese patent document CN109321215A discloses a kind of hydration agent composed of poly-3-methylene 2-pyrrolidone, lecithin and poly-N-vinylpyrrolidone used alone or compounded The prepared hydrate decomposition inhibitor can avoid a series of downhole accidents caused by hydrate decomposition. Among them, lecithin has the highest decomposition inhibition efficiency, but lecithin is easy to cause foaming when added to drilling fluid, which limits its addition in drilling fluid. The amount, its addition usually does not exceed 0.5%, and the preparation steps of poly-3-methylene 2-pyrrolidone are cumbersome. Chinese patent document CN112961255A discloses a kind of hydrate decomposition inhibitor prepared by cellulose and 3-[2-(2-aminoethylamino)ethylamino]propyl-trimethoxysilane, which can improve the drilling fluid system The hydrate decomposition inhibitor has the characteristics of simple preparation method and environmental protection. Generally speaking, there are few studies on new gas hydrate decomposition inhibitors, and the existing gas hydrate inhibitors have weak inhibitory effect on clay hydration, so it is of great significance to develop new gas hydrate decomposition inhibitors.

The natural gas hydrate formation in the sea area is buried shallowly, has poor diagenesis, and has a clay content as high as 30%. When water-sensitive clay minerals interact with drilling fluid, the strength of the formation is reduced due to water absorption, which is one of the key factors affecting the stability of the borehole wall. Chinese patent document CN103509533A provides a hydration inhibitor suitable for shale formations, which is prepared from non-ionic polyether and organic small molecule quaternary ammonium salts, which can effectively reduce the well caused by shale hydration during drilling Wall instability problem. Chinese patent document CN106190064A discloses a polyamine inhibitor, which is synthesized by reacting low-molecular-weight amine compounds and heterocyclic compounds under set conditions. It has strong inhibitory ability to mud shale and is compatible with other conventional drilling fluid treatment agents. Good sex, and non-toxic environmental protection. At present, hydration inhibitors are mainly suitable for shale formations, and no dual-effect inhibitors with both hydration inhibition and hydrate decomposition inhibition have been proposed for natural gas hydrate formations.

Therefore, it is one of the key research directions in the field of natural gas hydrate drilling and production technology to develop dual-effect inhibitors with natural gas hydrate decomposition inhibitory properties and clay hydration inhibitory properties.

Contents of the invention

Aiming at the deficiencies of the prior art, the present invention provides a double-effect inhibitor for natural gas hydrate drilling fluid and its preparation method and application. After the inhibitor of the present invention is added to the drilling fluid, it can significantly improve the inhibition of natural gas hydrate decomposition of the drilling fluid, reduce the mass transfer efficiency of methane in the aqueous solution; at the same time, it can inhibit the hydration and dispersion of clay, reduce the development of formation fractures, and benefit The stability of the well wall during the drilling process is ensured; the double-effect inhibitor of the present invention has both hydrate decomposition inhibition performance and clay hydration inhibition performance, and the preparation method is simple.

Technical scheme of the present invention is as follows:

A double-effect inhibitor for natural gas hydrate drilling fluid, said double-effect inhibitor for natural gas hydrate drilling fluid is obtained by 2-acrylamido-2-methyl-1-propanesulfonic acid and dimethyl diallyl The double-effect inhibitor for natural gas hydrate drilling fluid has the structure shown in the following formula I:

In Formula I, x/y=3.5-5.

According to the present invention, the preparation method of the above-mentioned double-effect inhibitor for natural gas hydrate drilling fluid comprises the steps as follows:

(1) Mix 2-acrylamido-2-methyl-1-propanesulfonic acid and deionized water, and stir to obtain a monomer solution;

(2) Dimethyl diallyl ammonium chloride is added in the monomer solution, and stirred uniformly to obtain a monomer mixed solution;

(3) Adjust the pH of the monomer mixed solution to 7-7.5, and feed nitrogen; then heat to 50-60°C, add an initiator to react; then dry and pulverize to obtain a double-effect inhibitor for natural gas hydrate drilling fluid .

Preferably according to the present invention, the ratio of the mass of 2-acrylamido-2-methyl-1-propanesulfonic acid in step (1) to the volume of deionized water is 0.1-0.3g:1mL.

Preferably according to the present invention, the stirring temperature in step (1) is 10-25° C., the stirring rate is 200-300 rpm, and the stirring time is 5-10 minutes.

Preferably according to the present invention, the stirring temperature in step (2) is 10-25° C., the stirring rate is 200-300 rpm, and the stirring time is 5-10 minutes.

Preferably according to the present invention, the mol ratio of 2-acrylamido-2-methyl-1-propanesulfonic acid to dimethyl diallyl ammonium chloride in the monomer mixed solution described in step (2) is 3～5:1.

Preferably according to the present invention, in step (3), the pH of the monomer mixed solution is adjusted by using a sodium hydroxide solution with a mass fraction of 20 to 50%; Make up the air in the reaction system.

Preferably according to the present invention, the initiator described in step (3) is ammonium persulfate and sodium bisulfite, and the mass ratio of ammonium persulfate and sodium bisulfite is 2:1; To add to the system in the form of an aqueous solution, first add an aqueous solution of ammonium persulfate with a mass concentration of 3-4 mg/mL, and then add an aqueous solution of sodium bisulfite with a mass concentration of 1-2 mg/mL after 5 to 10 minutes.

Preferably according to the present invention, the quality of the initiator described in step (3) is 0.15% of the total mass of 2-acrylamido-2-methyl-1-propanesulfonic acid and dimethyl diallyl ammonium chloride ~0.50%.

Preferably according to the present invention, the reaction time described in step (3) is 4 to 6 hours; the stirring rate during the reaction is 200 to 400 rpm.

Preferably according to the present invention, the drying temperature in step (3) is 80-90° C., and the drying time is 12-24 hours.

According to the present invention, the application of the above-mentioned double-effect inhibitor for natural gas hydrate drilling fluid in natural gas hydrate drilling fluid is used as an inhibitor to inhibit the decomposition of natural gas hydrate and inhibit clay hydration; preferably, the inhibitor in drilling fluid The mass concentration is 0.5-3wt%.

Technical characteristics of the present invention and beneficial effect are as follows:

1. The present invention utilizes anionic monomer 2-acrylamido-2-methyl-1-propanesulfonic acid and cationic monomer dimethyl diallyl ammonium chloride to free radical polymerize in a certain proportion to produce a natural gas Double-effect inhibitor for hydrate drilling fluid, the cationic group in the obtained double-effect inhibitor molecule can enhance the adsorption capacity of the polymer on the hydrate surface through Coulomb interaction, and the sulfonate group with strong hydration ability Increase the enrichment degree of water molecules on the surface of hydrates, improve the ability of water molecules to participate in the formation of hydrates, reduce the mobility of liquid phase water molecules on the surface of hydrates, thereby reducing the decomposition rate of hydrates under overheating conditions and inhibiting the decomposition of hydrates. Maintain wellbore stability in hydrate formations during drilling.

2. The dual-effect inhibitor of the present invention is a zwitterionic polymer, which contains a quaternary ammonium salt cationic group and a sulfonic acid anionic group, which can achieve a better decomposition inhibition effect at a high concentration, and overcome the effect of lecithin. bubble problem. The cationic group of the inhibitor also enhances the inhibitory ability to clay, reduces the hydration degree of clay through adsorption, and has stronger inhibitory ability than the same type of inhibitor. The inhibitor of the invention has good compatibility with drilling fluid, high hydrate decomposition inhibition efficiency, can significantly reduce the hydrate decomposition rate under overheating conditions, reduce the hydration dispersion degree of clay, and maintain the wellbore stability of the hydrate formation during drilling.

3. The 2-acrylamido-2-methyl-1-propanesulfonic acid used in the present invention and the dimethyl diallyl ammonium chloride monomer have oppositely charged groups, which are difficult to polymerize under normal conditions. Therefore, the present invention adopts a redox initiating system, which has higher initiating ability of free radical polymerization, and successfully prepares zwitterionic polymers. In the present invention, controlling the ratio of anionic monomers to cationic monomers within the range of 3 to 5:1 is the result of a large number of experimental optimizations. Although the increase in the ratio of cationic monomers can improve the adsorption capacity of polymers on the surface of hydrates, the At the same time, if the proportion of the cationic monomer is too high, the cost of polymer preparation and the difficulty of monomer polymerization will be increased; if the proportion of the cationic monomer is too low, the obtained polymer will have low performance in inhibiting the decomposition of natural gas hydrate and inhibiting the hydration of clay. Therefore, it is necessary to select an appropriate monomer ratio to prepare a double-effect inhibitor of natural gas hydrate with good performance.

4. The double-effect inhibitor for natural gas hydrate drilling fluid of the present invention has both hydrate decomposition inhibitory performance and clay hydration inhibitory performance. Only one additive is added to achieve multiple effects, reducing the types of additives, and the natural gas hydrate The performance of the drilling fluid is less affected.

Description of drawings

Fig. 1 is the infrared spectrogram of the dual-effect inhibitor for natural gas hydrate drilling fluid prepared in Example 1.

Fig. 2 is a graph of the linear expansion rate of the rock core in Test Example 4 in pure water, polyamine inhibitor solution and the double-effect inhibitor solution prepared in Example 1.

Detailed ways

The present invention will be further described below in conjunction with specific examples, but not limited thereto.

At the same time, the experimental methods described in the following examples, unless otherwise specified, are conventional methods; the reagents, materials and equipment, unless otherwise specified, can be obtained from commercial sources.

Example 1

A method for preparing a double-effect inhibitor for natural gas hydrate drilling fluid, comprising the following steps:

(1) Mix 17.45g of 2-acrylamido-2-methyl-1-propanesulfonic acid powder with 75mL of deionized water, and stir for 5 minutes at a stirring rate of 200r/min and a temperature of 25°C, Mix evenly to obtain a monomer solution.

(2) Add 3.40 g of dimethyl diallyl ammonium chloride into the monomer solution, and stir for 5 minutes at a stirring rate of 200 r/min and a temperature of 25° C. to obtain a monomer mixed solution.

(3) The mass fraction is that 20% sodium hydroxide solution is added dropwise in the monomer mixed solution obtained in step (2), the dropping time is 5min, and the pH of the regulating system is 7; the gained mixed solution is added in the three-necked flask afterwards , Nitrogen was introduced for 30 minutes, and the air in the flask was exhausted.

(4) Take by weighing 0.038g ammonium persulfate and 0.019g sodium bisulfite initiator, be dissolved in the deionized water of 10mL respectively, obtain ammonium persulfate solution and sodium bisulfite solution; The mixed solution in the three-necked flask is heated to 60°C, and set the magnetic stirring to 200rpm, add ammonium persulfate solution and sodium bisulfite solution in sequence at intervals of five minutes under stirring conditions; continue to react at a stirring rate of 200r/min and a temperature of 60°C 4 hours; after the reaction is completed, the obtained reaction solution is dried at 90° C. for 24 hours, and crushed to obtain a double-effect inhibitor for natural gas hydrate drilling fluid.

The dual-effect inhibitor synthesized in this example was analyzed by infrared spectrum using Shimadzu IRTracer-100 infrared spectrometer (KBr tablet), and the results are shown in FIG. 1 . It can be seen from Figure 1 that 1040cm ^-1 and 1192cm ^-1 are the characteristic absorption peaks of sulfonate, 1544cm ^-1 is the bending vibration of NH and the stretching vibration of CN bond, and 1662cm ^-1 is the C=O bond in the amide group Absorption peak; 3524cm ^-1 is the stretching vibration of NH in the amide group; 2972cm ^-1 is the asymmetric stretching vibration of -CH ₃ . Therefore, the obtained dual-effect inhibitor polymer contains quaternary ammonium salt cationic groups, amide groups and sulfonate anion groups, indicating that the target product is successfully prepared.

Example 2

A method for preparing a double-effect inhibitor for natural gas hydrate drilling fluid, comprising the following steps:

(1) Mix 15.06g of 2-acrylamido-2-methyl-1-propanesulfonic acid powder and 75mL of deionized water, and stir for 5 minutes at a stirring rate of 200r/min and a temperature of 25°C, Mix evenly to obtain a monomer solution.

(2) Add 2.94 g of dimethyl diallyl ammonium chloride into the monomer solution, and stir for 5 minutes at a stirring rate of 200 r/min and a temperature of 25° C. to obtain a monomer mixed solution.

(3) The mass fraction is that 20% sodium hydroxide solution is added dropwise in the monomer mixed solution obtained in step (2), the dropping time is 5min, and the pH of the regulating system is 7; the gained mixed solution is added in the three-necked flask afterwards , Nitrogen was introduced for 30 minutes, and the air in the flask was exhausted.

(4) Take by weighing 0.038g ammonium persulfate and 0.0190g sodium bisulfite initiator, be dissolved in the deionized water of 10mL respectively, obtain ammonium persulfate solution and sodium bisulfite solution; The mixed solution in the three-necked flask is heated to 60°C, and set the magnetic stirring to 200rpm, add ammonium persulfate solution and sodium bisulfite solution in sequence at intervals of five minutes under stirring conditions; continue to react at a stirring rate of 200r/min and a temperature of 60°C 5 hours; after the reaction is completed, the obtained reaction solution is dried at 90° C. for 24 hours, and crushed to obtain a double-effect inhibitor for natural gas hydrate drilling fluid.

Example 3

A method for preparing a double-effect inhibitor for natural gas hydrate drilling fluid, comprising the following steps:

(1) Mix 11.72g of 2-acrylamido-2-methyl-1-propanesulfonic acid powder and 75mL of deionized water, and stir for 5 minutes at a stirring rate of 200r/min and a temperature of 25°C, Mix evenly to obtain a monomer solution.

(2) Add 2.28 g of dimethyl diallyl ammonium chloride into the monomer solution, and stir for 5 minutes at a stirring rate of 200 r/min and a temperature of 25° C. to obtain a monomer mixed solution.

(3) The mass fraction is that 20% sodium hydroxide solution is added dropwise in the monomer mixed solution obtained in step (2), the dropping time is 5min, and the pH of the regulating system is 7; the gained mixed solution is added in the three-necked flask afterwards , Nitrogen was introduced for 30 minutes, and the air in the flask was exhausted.

(4) Take by weighing 0.038g ammonium persulfate and 0.0190g sodium bisulfite initiator, be dissolved in the deionized water of 10mL respectively, obtain ammonium persulfate solution and sodium bisulfite solution; Heat to 60°C, set the magnetic stirring to 200rpm, and add ammonium persulfate solution and sodium bisulfite solution sequentially at intervals of five minutes under stirring conditions; continue to stir at 200r/min and temperature at 60°C React for 6 hours; after the reaction is completed, the obtained reaction solution is dried at 90° C. for 24 hours, and crushed to obtain a double-effect inhibitor for natural gas hydrate drilling fluid.

Comparative example 1

In this comparative example, lecithin was used as the gas hydrate inhibitor, and the lecithin was provided by Shanghai Aladdin Biochemical Technology Co., Ltd. with a purity greater than 90%.

Comparative example 2

The preparation method of a kind of dual-effect inhibitor is as described in embodiment 1, difference is: in step (2), add 13.61g dimethyl diallyl ammonium chloride, 2-acrylamido-2-methyl - The molar ratio of 1-propanesulfonic acid to dimethyldiallylammonium chloride is 1:1.

Comparative example 3

A kind of preparation method of dual-effect inhibitor is as described in embodiment 1, difference is: in step (2), add 1.61g dimethyl diallyl ammonium chloride, 2-acrylamido-2-methyl - The molar ratio of 1-propanesulfonic acid to dimethyldiallylammonium chloride is 10:1.

Test example 1

Drilling fluid foaming will reduce the density of the drilling fluid. When the drilling fluid column pressure in the well is lower than the formation pressure, it will cause a kick or blowout. Therefore, the drilling fluid additive is required to have a low foaming rate. Add the double-effect inhibitor prepared in Example 1 and the inhibitor of Comparative Example 1 into 301 mL of water respectively, configure an aqueous solution with a mass concentration of 0.5 wt %, stir at 5000 rpm at high speed for 5 minutes, and then remove it from the stirrer to start Timing, within 20 seconds the slurry inhibitor solution is all introduced into a clean 500mL measuring cylinder, read its total volume in 30 seconds, and calculate the foaming rate according to the following formula: Calculate the foaming rate according to the following formula:

In the formula, A is the foaming rate, unit %; V is the volume of inhibitor aqueous solution after high-speed stirring, unit mL; _V0 is the volume of water, unit mL.

The above test results are shown in Table 1.

Table 1 The foaming properties of the inhibitors of Example 1 and Comparative Example 1

Inhibitor type Drilling fluid volume Foaming rate Comparative example 1 328 8.9% Example 1 303 0.6%

It can be seen from Table 1 that the foaming rate of the dual-effect inhibitor prepared by the present invention is obviously lower than that of the lecithin of Comparative Example 1. Therefore, the gas hydrate kinetic inhibitor prepared by the invention better satisfies the requirement of foaming performance in deep water drilling.

Test example 2

The dual-effect inhibitor prepared in Example 1 was tested for drilling fluid compatibility.

Use the double-effect inhibitor prepared in Example 1 to prepare marine deepwater drilling fluid base slurry, the formula is: water+4wt% bentonite+0.35wt% _Na2CO3 +1wt% double-effect inhibitor prepared in Example ₁ ; The blank drilling fluid with dual-effect inhibitor was used as a comparison.

Routine performance tests were carried out on the two prepared drilling fluid base slurries, and the compatibility of the double-effect inhibitor prepared by the present invention in water-based drilling fluid was evaluated. Refer to the national standard "GB/T 29170-2012 Oil and Gas Industry Drilling Fluid Laboratory Test" to test the rheological parameters and API filtration of the drilling fluid, and the results are shown in Table 2.

Table 2 Example 1 and blank drilling fluid rheological fluid loss test

As can be seen from Table 2, under the influence of the zwitterionic polymer double-effect inhibitor of the present invention, the viscosity of the base slurry increases to some extent, and the drilling fluid compatibility is good; after adding, the fluid loss control performance of the drilling fluid is obviously improved, It is conducive to the formation of low-permeability mud cake in the formation, and inhibits the decomposition process of hydrate by blocking the mass transfer between drilling fluid and formation.

Test example 3

The inhibitors prepared in Example 1 and Comparative Example 1 were tested for the inhibition performance of natural gas hydrate decomposition.

The specific steps are as follows: Dissolve the test sample in water to prepare an inhibitor solution with a mass concentration of 1 wt%, and place it in the reactor. After the reactor is evacuated, methane gas is introduced to maintain the pressure at 9MPa. After the hydrate is formed in situ in an environment with an internal pressure of 9 MPa and a temperature of 0.5°C, the temperature is raised to 14°C and the temperature and pressure changes in the hydrate reactor after the temperature rise are recorded every minute. After the temperature and pressure are stable for 30 minutes, the hydrate is considered Decomposed completely. According to the temperature and pressure data recorded per minute, the amount of methane gas released during the hydrate decomposition process was calculated by the Peng-Robinson equation, and the average hydrate decomposition rate (mol /L); at a certain moment, the amount of methane gas released in the reactor is divided by the total amount of methane gas released by the complete decomposition of hydrates, which can represent the relative decomposition rate of hydrates at a certain moment during the decomposition process.

According to the above experimental method, the inhibitors prepared in Example 1 and Comparative Example 1 were subjected to the hydrate decomposition inhibition test, and a blank experiment was set at the same time, that is, the above experimental steps were repeated under pure water conditions (without inhibitor). The test results are shown in Table 3. As can be seen from Table 3, under the action of Comparative Example 1, the decomposition rate of hydrate was reduced by 29.5%, and the complete decomposition time of hydrate was prolonged by 45.7%; under the action of Example 1, the decomposition rate of hydrate was reduced by 37.3% %, the complete decomposition time of the hydrate has been prolonged by 64%, and the effect of Example 1 is obviously due to lecithin.

Table 3 Hydrate decomposition inhibition test of Example 1 and Comparative Example 1

Test example 4

The hydration inhibition performance of the dual-effect inhibitor prepared in Example 1 was tested, and a commonly used hydration inhibitor polyamine product (provided by Shandong Juxin Chemical Co., Ltd.) was used as a comparison.

The specific test steps are as follows:

Measure 130 mL of water, add the polyamine inhibitor and the dual-effect inhibitor prepared in Example 1 to it, and prepare an aqueous solution with a mass concentration of 1 wt%. Take 10.0 g of bentonite dried at 105°C and put it in a measuring barrel, and compact it on a hydraulic press with a pressure of 10 MPa for 5 minutes to obtain an artificial bentonite core. After the core was taken out, the prepared polyamine inhibitor with a mass concentration of 1 wt%, the double-effect inhibitor aqueous solution prepared in Example 1, and pure water were respectively added to a linear dilatometer at normal temperature and pressure, and the linear expansion height was measured. The pure water, the polyamine inhibitor and the double-effect inhibitor prepared in Example 1 were tested for the linear expansion rate, and the results are shown in FIG. 2 . Compared with pure water, under the action of Example 1, the expansion rate of the core in 16 hours is significantly reduced, and the effect is better than that of polyamine, which is a similar product, indicating that the prepared double-effect inhibitor can effectively exert the hydration inhibition effect.

Test example 5

The rolling recovery test is a common method to evaluate the dispersion performance of rocks, and it is a dynamic test that simulates the shear rate of the downhole annular space. Measure 6 parts of 350mL water, add potassium chloride to one part to form a potassium chloride solution with a mass concentration of 3wt%, and the other four parts to form a polyamine solution with a mass concentration of 1wt%. The double-effect inhibitor solution prepared in Example 1, Comparative Example 2 and Comparative Example 3, to obtain the solution to be tested. Weigh 20g of cuttings of 6-10 mesh respectively, put them into the roller aging furnace filled with the above-mentioned solution to be tested, roll them at room temperature for 16 hours, take them out, wash the cuttings with standard brine, sieve and dry them with a 40-mesh standard sieve Dry weighing, and the ratio of the mass of cuttings to the initial cuttings was recorded as the cuttings recovery rate, and the results are shown in Table 4. Under the action of the double-effect inhibitor prepared in Example 1 of the present invention, the recovery rate of the rock sample was increased from 19.5% to 92.5%, reflecting the inhibitory effect of the embodiment on the hydration dispersion of the rock sample. In comparative example 2, due to the high proportion of cationic monomers, the difficulty of monomer polymerization increases, the degree of polymerization of the obtained product is relatively low, and its ability to inhibit rock dispersion is poor; in comparative example 3, due to the low proportion of cationic monomers, the polymerization The adsorption capacity of matter on the clay surface becomes worse, and the rolling recovery rate is obviously lower than that of Example 1.

Table 4 Test data of standard rock sample rolling recovery rate

Claims (7)

1. The double-effect inhibitor for the natural gas hydrate drilling fluid is characterized by being prepared by the polymerization reaction of 2-acrylamido-2-methyl-1-propanesulfonic acid and dimethyl diallyl ammonium chloride free radical, and having a structure shown as the following formula I:

in the formula I, x/y =3.5-5;

the preparation method comprises the following steps:

(1) Mixing 2-acrylamido-2-methyl-1-propanesulfonic acid with deionized water, and uniformly stirring to obtain a monomer solution;

(2) Adding dimethyl diallyl ammonium chloride into the monomer solution, and uniformly stirring to obtain a monomer mixed solution; the molar ratio of the 2-acrylamido-2-methyl-1-propanesulfonic acid to the dimethyldiallylammonium chloride in the monomer mixed solution is 3 to 5;

(3) Adjusting the pH value of the monomer mixed solution to 7-7.5, and introducing nitrogen; then heating to 50-60 ℃, and adding an initiator for reaction; then drying and crushing to obtain the double-effect inhibitor for the natural gas hydrate drilling fluid; the initiator is ammonium persulfate and sodium bisulfite, and the mass ratio of the ammonium persulfate to the sodium bisulfite is 2; the initiator is added into the system in the form of an initiator aqueous solution, firstly, an ammonium persulfate aqueous solution with the mass concentration of 3-4 mg/mL is added, and after 5-10 minutes, a sodium bisulfite aqueous solution with the mass concentration of 1-2mg/mL is added; the mass of the initiator is 0.15 to 0.50 percent of the total mass of the 2-acrylamido-2-methyl-1-propanesulfonic acid and the dimethyl diallyl ammonium chloride.

2. The dual-effect inhibitor for the natural gas hydrate drilling fluid as claimed in claim 1, wherein the ratio of the mass of the 2-acrylamido-2-methyl-1-propanesulfonic acid in the step (1) to the volume of deionized water is 0.1 to 0.3 g.

3. The double-effect inhibitor for the natural gas hydrate drilling fluid as claimed in claim 1, wherein the stirring temperature in the step (1) is 10-25 ℃, the stirring speed is 200-300rpm, and the stirring time is 5-10 minutes.

4. The double-effect inhibitor for the natural gas hydrate drilling fluid as claimed in claim 1, wherein the stirring temperature in the step (2) is 10-25 ℃, the stirring speed is 200-300rpm, and the stirring time is 5-10 minutes.

5. The double-effect inhibitor for the natural gas hydrate drilling fluid as claimed in claim 1, wherein in the step (3), a sodium hydroxide solution with the mass fraction of 20-50% is used for adjusting the pH value of the monomer mixed solution; the time for introducing the nitrogen is 30 minutes.

6. The double-effect inhibitor for the natural gas hydrate drilling fluid as claimed in claim 1, wherein the reaction time in the step (3) is 4-6 hours; the stirring speed in the reaction process is 200 to 400 rpm; the drying temperature is 80 to 90 ℃, and the drying time is 12 to 24 hours.

7. The application of the double-effect inhibitor for the natural gas hydrate drilling fluid in the natural gas hydrate drilling fluid, which is used as the inhibitor for inhibiting the decomposition of natural gas hydrate and inhibiting the hydration of clay; the mass concentration of the inhibitor in the drilling fluid is 0.5-3wt%.

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