A zwitterionic polymer foam stabilizer, its preparation method and its application

Abstract

This invention relates to an amphoteric polymer foam stabilizer, its preparation method, and its application, relating to the technical field of foam drilling fluid systems. The method includes the following steps: dissolving AMPS in a solvent to form an AMPS solution, adjusting the pH to 6-7; adding acrylamide and a temperature-resistant monomer to obtain a monomer mixture solution, followed by deoxygenation treatment; adding a crosslinking agent after deoxygenation, and reacting at a temperature of 60-70°C to obtain the amphoteric polymer foam stabilizer; and then compounding the amphoteric polymer foam stabilizer into a foam drilling fluid system. The foam drilling fluid system formulated using the amphoteric polymer as a foam stabilizer in this invention exhibits good foam stabilization effects and excellent resistance to salt, calcium, and temperature variations.

Description

Technical Field

[0001] This invention relates to the technical field of foam drilling fluid systems, specifically to an amphoteric polymer foam stabilizer, its preparation method, and its application. Background Technology

[0002] Due to the thermodynamic and kinetic instability of foam, it is more prone to breakage under high temperature and high pressure conditions, making foam stabilizers and foaming agents crucial as core treatment agents. In addition, foam drilling fluids face two main challenges in their use: high temperature and high salinity. To date, researchers both domestically and internationally have developed numerous foam stabilizers to improve foam stability.

[0003] Existing foam stabilizers can be broadly categorized into macromolecular foam stabilizers, surfactant foam stabilizers, and solid particulate foam stabilizers. The first category, macromolecular foam stabilizers, includes polymers, xanthan gum, gels, starch, and cellulose. These substances increase foam viscosity and reduce foam flowability, thus providing a certain foam-stabilizing effect. However, their application is complex, their effectiveness is limited, and their foaming volume is low. Polymer foam stabilizers are the most widely used. The second category, surfactant foam stabilizers, utilizes surfactants. Some surfactants can form monolayer structures at the interface, and their interconnections can suppress fluctuations in spatial density at the air-water interface, thus possessing a certain foam-stabilizing effect. Examples include quaternary ammonium salt surfactants. Some anionic surfactants, such as sodium dodecyl sulfate and sodium fatty alcohol ether sulfate, also have some foam-stabilizing properties. However, the synergistic effect between surfactant foam stabilizers and blowing agents is limited; not every blowing agent can find a foam stabilizer with a synergistic effect. The third type, solid particulate foam stabilizers, while exhibiting significant improvements in foam stability due to their large molecular weight, suffer from poor long-term stability at high temperatures. Furthermore, their molecules coil under high salinity conditions, leading to a drastic decrease in viscosity and consequently, a reduction in their foam-stabilizing effect. Solid particulate foam stabilizers, however, possess unique advantages in high-temperature, high-salinity reservoirs.

[0004] Numerous experiments have shown that surfactant-based foam stabilizers are less effective than macromolecular and particulate foam stabilizers. Macromolecular foam stabilizers are primarily high-molecular-weight substances that increase viscosity; however, under high-temperature conditions, their viscosity decreases significantly, leading to a sharp decline in foam stabilization. After long-term aging, the foam stabilization effect disappears entirely. Therefore, for high-temperature oil reservoirs, solid particulate foam stabilizers are selected to improve the long-term stability of the foam. While solid particles are not temperature-sensitive, they can only disperse in solution and cannot be integrated into the foaming system, thus easily agglomerating and settling. They are generally difficult to adsorb at the gas-liquid interface, thus not only failing to stabilize the foam but also reducing its foaming effect. Therefore, it is necessary to modify the solid particulate material. Modified solid particles exhibit good dispersibility in aqueous solution, moderate wettability, and stable adsorption at the gas-liquid interface, thereby improving foam stability. In view of this, this invention provides an amphoteric polymer foam stabilizer, its preparation method, and its applications. Summary of the Invention

[0005] This invention addresses the problems of leakage and unstable foaming effects in conventional drilling fluid systems caused by low reservoir pressure, high formation temperature, and high mineralization due to long-term development. It provides an amphoteric polymer foam stabilizer, its preparation method, and its application.

[0006] To address the aforementioned technical problems, the first objective of this invention is to provide a method for preparing an amphoteric polymer foam stabilizer, comprising the following steps:

[0007] Step 1: Dissolve AMPS (2-acrylamide-2-methylpropanesulfonic acid monomer, anionic monomer) in a solvent to form an AMPS solution, and adjust the pH of the AMPS solution to 6-7;

[0008] Step 2: Add acrylamide and thermo-resistant monomer to the AMPS solution after pH adjustment. The molar ratio of AMPS, acrylamide (neutral monomer), and thermo-resistant monomer (cationic monomer) is (2-4):(8-11):(0.5-2). After the acrylamide and thermo-resistant monomer are completely dissolved to form a monomer mixed solution, deoxygenation treatment is performed.

[0009] Step 3: After deoxygenation treatment, a crosslinking agent is added to the monomer mixture solution. The molar ratio of the crosslinking agent to the AMPS is (0.01-0.2):(2-4). The monomer mixture solution with the added crosslinking agent is reacted at a temperature of 60-70℃ for 4-6 hours. The solvent is then removed by drying to obtain the zwitterionic polymer foam stabilizer.

[0010] This invention addresses the issue that existing macromolecular foam stabilizers, surfactant foam stabilizers, and solid particulate foam stabilizers, due to their varying performance characteristics, can negatively impact their application. For example, existing macromolecular foam stabilizers experience a sharp decline in foam stabilization efficiency when used in high-temperature formations due to the decrease in liquid phase viscosity; while existing solid particulate foam stabilizers are suitable for high-temperature formations, the solid particles tend to agglomerate and settle within the system. This invention provides a method for preparing a zwitterionic polymer foam stabilizer, which improves foam stability.

[0011] The beneficial effects of this invention are as follows: The zwitterionic polymer foam stabilizer prepared by this invention can solve the problems of conventional foam stabilizers having a sharp decline or even disappearance in foam stabilization effect under conditions of low formation pressure, high formation temperature, and high salinity, as well as being complicated to use. It provides a high-performance foam stabilizer for foam drilling fluid systems. Furthermore, experiments have shown that the foam drilling fluid system formulated with the zwitterionic polymer foam stabilizer of this invention has certain resistance to salt and calcium, temperature resistance, and good foam stabilization effect, which provides technical support for gas storage measures in depleted gas reservoirs.

[0012] Based on the above technical solution, the present invention can be further improved as follows.

[0013] Furthermore, in step 1, the solvent is deionized water or distilled water; the pH of the AMPS solution is adjusted to 6-7 using NaOH or ammonia. Preferably, NaOH is used to adjust the pH of the AMPS solution to 6-7.

[0014] Further, in step 2, the thermoresistant monomer is DMDAAC (dimethyl diallyl ammonium chloride); the specific method for the deoxygenation treatment is to introduce nitrogen gas into the monomer mixture solution for at least 20 minutes; in step 3, the crosslinking agent is N,N'-methylenebisacrylamide.

[0015] The second objective is to provide an amphoteric polymer foam stabilizer, which is prepared by the preparation method described in any of the above-mentioned methods.

[0016] The third objective is to provide a foam drilling fluid system comprising the aforementioned zwitterionic polymer foam stabilizer.

[0017] The beneficial effects of adopting the above scheme are: the foam drilling fluid system formulated by the present invention using zwitterionic polymer as foam stabilizer has good foam stabilizing effect and has resistance to salt and calcium and temperature.

[0018] Furthermore, the foam drilling fluid system also includes a foaming agent, nano-magnesium aluminum silicate (NMAS), cellulose microfibers, and deionized water; the weight percentages of each component in the foam drilling fluid system are as follows: zwitterionic polymer foam stabilizer 0.25-0.75 parts, foaming agent 0.1-0.3 parts, nano-magnesium aluminum silicate 1-3 parts, cellulose microfibers 0.5-1.5 parts, and deionized water 49.75-149.25 parts.

[0019] The beneficial effects of adopting the above-mentioned further scheme are as follows: the zwitterionic polymer is used as a foam stabilizer in the foam drilling fluid system. The system components mainly include foaming agent, foam stabilizer, nano-magnesium aluminum silicate (NMAS), cellulose micron fibers, and deionized water. The compounded drilling fluid system is suitable for reservoirs with formation temperatures below 140℃ and high salinity. Experimental studies have shown that the compounded system has a good foam stabilizing effect, with a foam half-life of more than 60 hours. It also has the ability to resist 18wt% NaCl and 4wt% CaCl2. After aging at 140℃ for 16 hours, the system still has a foam half-life of more than 60 hours and still has a good foam stabilizing effect.

[0020] Furthermore, the weight proportions of each component in the foam drilling fluid system are as follows: 0.5 parts zwitterionic polymer foam stabilizer, 0.2 parts foaming agent, 2 parts nano magnesium aluminum silicate, 1 part cellulose micron fiber, and 99.5 parts deionized water.

[0021] Furthermore, the foaming agent is AD300 or AD300-1.

[0022] The fourth objective is to provide a method for preparing a foam drilling fluid system, comprising the following steps: dissolving an amphoteric polymer foam stabilizer in deionized water and stirring until homogeneous to form an amphoteric polymer foam stabilizer solution; adding nano-magnesium aluminum silicate and cellulose micron fibers to the amphoteric polymer foam stabilizer solution and stirring again until homogeneous to form a mixed solution; adding a foaming agent to the mixed solution and performing variable frequency high-speed stirring until homogeneous to obtain a foam drilling fluid system.

[0023] The beneficial effects of adopting the above scheme are: the drilling fluid system formulated with the zwitterionic polymer described in this invention as a foam stabilizer has a low initial foaming volume and a drilling fluid system density of 0.8-0.9 g / cm³. 3 .

[0024] Furthermore, the specific conditions for the stirring step in forming the zwitterionic polymer foam stabilizer solution are: a stirring speed of 200-800 r / min and a stirring time of 5-15 min; the specific conditions for the stirring step in forming the mixed solution are: a stirring speed of 200-800 r / min and a stirring time of 5-15 min; the speed of the variable frequency high-speed stirrer is 3000-5000 r / min and the stirring time is 0.5-2 min. Attached Figure Description

[0025] Figure 1 This is a flowchart illustrating the preparation and application of an amphoteric polymer foam stabilizer according to the present invention.

[0026] Figure 2 This is the infrared spectrum analysis diagram of the present invention. Detailed Implementation

[0027] The principles and features of the present invention are described below. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0028] The following embodiments of the present invention provide an explanation of the source of the pharmaceuticals or reagents used:

[0029] NMAS (sodium magnesium aluminum silicate) was purchased from Guangzhou Shengxin Chemical Technology Co., Ltd.

[0030] CMF (cellulose microfibers) was purchased from the Institute of Chemistry, Chinese Academy of Sciences;

[0031] AD300 was purchased from Shandong Dongying Aoda Petrochemical Co., Ltd.

[0032] The AD300-1 is an improved version of the AD300 and was purchased from Shandong Dongying Aoda Petrochemical Co., Ltd.

[0033] Example

[0034] 1. Preparation of zwitterionic polymer foam stabilizers and foam drilling fluid systems

[0035] 1.1 Preparation of zwitterionic polymer foam stabilizer

[0036] This embodiment relates to a method for preparing an amphoteric polymer foam stabilizer (e.g., Figure 1 The process includes the following steps:

[0037] Step 1: Dissolve AMPS (2-acrylamide-2-methylpropanesulfonic acid monomer, anionic monomer) in a solvent to form an AMPS solution, and adjust the pH of the AMPS solution to 6-7;

[0038] Step 2: Add acrylamide and thermo-resistant monomer to the AMPS solution after pH adjustment. The molar ratio of AMPS, acrylamide (neutral monomer), and thermo-resistant monomer (cationic monomer) is 3:9:1. After the acrylamide and thermo-resistant monomer are completely dissolved to form a monomer mixed solution, deoxygenation treatment is performed.

[0039] Step 3: After deoxygenation treatment, a crosslinking agent is added to the monomer mixture solution. The molar ratio of the crosslinking agent to the AMPS is 0.1:3. The monomer mixture solution with the added crosslinking agent is reacted at a temperature of 60-70℃ for 4-6 hours. The solvent is then removed by drying to obtain the zwitterionic polymer foam stabilizer.

[0040] Preferably, in step 1, the solvent is deionized water; the pH of the AMPS solution is adjusted to 6-7 using NaOH. In step 2, the thermoresistant monomer is DMDAAC; the specific method for the deoxygenation treatment is to purge nitrogen gas into the monomer mixture solution for 20 minutes; in step 3, the crosslinking agent is N,N'-methylenebisacrylamide.

[0041] Figure 2 This is the infrared spectrum of the zwitterionic polymer. In the figure, 1260 cm⁻¹ -1 The characteristic absorption peak of the sulfonic acid group indicates the presence of AMPS; 906 cm⁻¹ -1 The peak at 3433 cm⁻¹ is a characteristic absorption peak of the five-membered ring in DMDAAC, thus confirming the presence of DMDAAC; -1 The characteristic absorption peak for amide groups is 1631 cm⁻¹. -1 The characteristic absorption peaks of carbon-carbon double bonds confirm the presence of AMPS. Infrared spectroscopy reveals the characteristic groups of all three monomers in the spectrum, confirming their presence.

[0042] 1.2 Preparation method of foam drilling fluid system

[0043] This embodiment relates to a method for preparing a foam drilling fluid system, which includes the following steps:

[0044] Weigh 0.5g of the prepared zwitterionic polymer, dissolve it in deionized water, and then continue adding deionized water until the solution mass is 100g. Place the mixture in a magnetic stirrer, set the speed to 500r / min, and stir at low speed for 10min. Then add 2wt% NMAS and 1wt% cellulose microfibers, place it in the magnetic stirrer again, set the speed to 500r / min, and stir at low speed for 10min. Subsequently, add 0.2wt% foaming agent AD300-1, transfer it to a high-speed stirring cup, and place it in a variable frequency high-speed mixer, set the speed to 4000r / min, and stir at high speed for 1min to obtain a low-density foam drilling fluid system A1.

[0045] The density of this low-density foam drilling fluid system A1 is 0.8 g / cm³. 3 It has a low density and can be used as a high-performance foam stabilizer.

[0046] 2. Testing and detection of foam drilling fluid system A1

[0047] 2.1 Testing of foaming and foam stabilizing effects of foam drilling fluid system A1

[0048] The prepared foam drilling fluid system A1 was quickly transferred to a graduated cylinder. Timing was immediately started, and the foam was observed. The initial volume V0 (the graduation on the graduated cylinder corresponding to the initial foam time) and the half-life T0.5 (the time corresponding to the foam discharging 50 ml of water) were recorded. The initial volume indicates the foaming performance of the system; a larger initial volume indicates better foaming performance. The half-life indicates the foam stability of the system; a larger half-life indicates better foam stability.

[0049] 2.2 Salt resistance of foam drilling fluid system A1

[0050] This test example is used to test the salt resistance of the foam drilling fluid system A1 at room temperature when the zwitterionic polymer of the present invention is used as a foam stabilizer in the drilling fluid system.

[0051] Weigh 0.5g of the prepared zwitterionic polymer, dissolve it in deionized water, and then continue adding deionized water until the solution mass is 100g. Place the mixture in a magnetic stirrer, set the speed to 500 rpm, and stir at low speed for 10 min. Then add 2wt% NMAS and 1wt% cellulose microfibers, and place it in the magnetic stirrer again, setting the speed to 500 rpm, and stirring at low speed for 10 min. Subsequently, add 0.2wt% foaming agent AD300-1, transfer it to a high-speed stirring cup, and place it in a variable frequency high-speed stirrer, setting the speed to 4000 rpm, and stirring at high speed for 1 min. Quickly add sodium chloride of different concentrations, place it in a variable frequency high-speed stirrer, set the speed to 4000 rpm, and stir at high speed for 1 min to obtain the foam drilling fluid system. Quickly transfer the system to a graduated cylinder, start timing, and observe and record the initial volume V0 and half-life T0.5.

[0052] 2.3 Calcium resistance of foam drilling fluid system A1

[0053] This test example is used to test the calcium resistance of the foam drilling fluid system A1 at room temperature when the zwitterionic polymer of the present invention is used as a foam stabilizer in the drilling fluid system.

[0054] Weigh 0.5g of the prepared zwitterionic polymer, dissolve it in deionized water, and then continue adding deionized water until the solution mass is 100g. Place the mixture in a magnetic stirrer, set the speed to 500r / min, and stir at low speed for 10min. Then add 2wt% NMAS and 1wt% cellulose microfiber, and place it in the magnetic stirrer again, setting the speed to 500r / min, and stirring at low speed for 10min. Subsequently, add 0.2wt% foaming agent AD300-1, transfer it to a high-speed stirring cup, and place it in a variable frequency high-speed mixer, setting the speed to 4000r / min, and stirring at high speed for 1min. Quickly add calcium chloride of different concentrations, place it in a variable frequency high-speed mixer, setting the speed to 4000r / min, and stirring at high speed for 1min to obtain the foam drilling fluid system.

[0055] 2.4 Temperature resistance of foam drilling fluid system A1

[0056] This test example is used to test the temperature resistance of the foam drilling fluid system A1 when the zwitterionic polymer of the present invention is used as a foam stabilizer in the drilling fluid system.

[0057] Weigh 0.5 g of the prepared zwitterionic polymer, dissolve it in deionized water, and then continue adding deionized water until the solution mass is 100 g. Place the mixture in a magnetic stirrer, set the speed to 500 r / min, and stir at low speed for 10 min. Then add 2 wt% NMAS and 1 wt% cellulose microfibers, and place the mixture in a magnetic stirrer again, set the speed to 500 r / min, and stir at low speed for 10 min. Subsequently, add 0.2 wt% foaming agent AD300-1, transfer the foaming base solution to an aging tank, and then place it in a roller furnace, set the temperature to 140℃, and hot-roll for 16 h. Remove the base solution and cool it to room temperature. Place the foaming base solution in a high-speed stirring cup, and then place it in a variable frequency high-speed stirrer, set the speed to 4000 r / min, and stir at high speed for 1 min. Quickly transfer the system to a graduated cylinder, start timing, and observe and record the initial volume V0 and half-life T0.5.

[0058] 2.5 Test Results of Foam Drilling Fluid System A1

[0059] The system obtained in the test example was quickly transferred to a graduated cylinder. Timing was started immediately, and the foam was observed. The initial volume V0 (the graduation on the graduated cylinder corresponding to the initial foam time) and the half-life T0.5 (the time corresponding to when 50 ml of water was expelled from the foam) were recorded. The initial volume indicates the foaming performance of the system; the larger the initial volume, the better the foaming performance. The half-life indicates the foam stability of the system; the larger the half-life, the better the foam stability of the system.

[0060] Table 1. Statistics on the half-life of foam A1 in foam drilling fluid systems.

[0061]

[0062] The test results of foam drilling fluid system A1 are shown in Table 1. As can be seen from the data in Table 1, when the zwitterionic polymer of this invention is used as a foam stabilizer in the drilling fluid system, the initial foaming volume of the system is 125 ml, the density is relatively low, and the foam half-life reaches over 60 hours. In the salt and calcium resistance test of foam drilling fluid system A1, it was found that foam drilling fluid system A1 has salt resistance of 18 wt% NaCl and calcium resistance of 4 wt% CaCl2. Furthermore, after aging at 140℃ for 16 hours, the initial foaming volume of foam drilling fluid system A1 is 115 ml, and the foam half-life still reaches over 60 hours.

[0063] 3. Test and detection of the control drilling fluid system B1

[0064] 3.1 Testing of the foaming and foam-stabilizing effects of drilling fluid system B1

[0065] Weigh 0.5g of hydroxyethyl cellulose and dissolve it in deionized water. Continue adding deionized water until the solution mass is 100g. Place the mixture in a magnetic stirrer and stir at 500 rpm for 10 minutes. Then add 2wt% NMAS and 1wt% cellulose microfibers, and stir again in the magnetic stirrer at 500 rpm for 10 minutes. Next, add 0.2wt% foaming agent AD300-1, transfer to a high-speed stirring cup, and place in a variable frequency high-speed mixer. Stir at 4000 rpm for 1 minute to obtain a low-density drilling fluid system B1. Quickly transfer the system to a graduated cylinder, start timing, and observe and record the initial volume V0 and half-life T0.5.

[0066] 3.2 Salt resistance of drilling fluid system B1

[0067] This comparative example is used to test the salt resistance of the drilling fluid system at room temperature when the foam stabilizer is replaced with hydroxyethyl cellulose and other conditions remain unchanged.

[0068] Weigh 0.5g of hydroxyethyl cellulose and dissolve it in deionized water. Continue adding deionized water until the solution mass is 100g. Place the mixture in a magnetic stirrer and stir at 500 rpm for 10 minutes. Then add 2wt% NMAS and 1wt% cellulose microfibers, and stir again in the magnetic stirrer at 500 rpm for 10 minutes. Next, add 0.2wt% foaming agent AD300-1, transfer to a high-speed stirring cup, and place in a variable frequency high-speed mixer at 4000 rpm for 1 minute. Then, quickly add different concentrations of sodium chloride and stir again in the variable frequency high-speed mixer at 4000 rpm for 1 minute to obtain the foam drilling fluid system. Quickly transfer the system to a graduated cylinder, start timing, and observe and record the initial volume V0 and half-life T0.5.

[0069] 3.3 Calcium resistance of drilling fluid system B1

[0070] The comparative example was used to test the anti-calcium ability of the drilling fluid system at room temperature when the foam stabilizer was replaced with hydroxyethyl cellulose and other conditions remained unchanged.

[0071] Weigh 0.5g of hydroxyethyl cellulose and dissolve it in deionized water. Continue adding deionized water until the solution mass is 100g. Place the mixture in a magnetic stirrer and stir at 500 rpm for 10 minutes. Then add 2wt% NMAS and 1wt% cellulose microfibers, and stir again in the magnetic stirrer at 500 rpm for 10 minutes. Next, add 0.2wt% foaming agent AD300-1, transfer to a high-speed stirring cup, and place in a variable frequency high-speed mixer at 4000 rpm for 1 minute. Then, quickly add different concentrations of calcium chloride and stir again in the variable frequency high-speed mixer at 4000 rpm for 1 minute to obtain the foam drilling fluid system. Quickly transfer the system to a graduated cylinder, start timing, and observe and record the initial volume V0 and half-life T0.5.

[0072] 3.4 Temperature resistance of drilling fluid system B1

[0073] This comparative example was used to test the temperature resistance of the drilling fluid system when the foam stabilizer was replaced with hydroxyethyl cellulose and other conditions remained unchanged.

[0074] Weigh 0.5g of hydroxyethyl cellulose and dissolve it in deionized water. Continue adding deionized water until the solution mass is 100g. Place the mixture in a magnetic stirrer and stir at 500 rpm for 10 minutes. Then add 2wt% NMAS and 1wt% cellulose microfibers, and stir again in the magnetic stirrer at 500 rpm for 10 minutes. Next, add 0.2wt% foaming agent AD300-1. Transfer the foaming base solution to an aging tank and place it in a roller furnace at 140℃ for 16 hours. Remove the base solution and cool it to room temperature. Place the foaming base solution in a high-speed stirring cup and place it in a variable frequency high-speed stirrer at 4000 rpm for 1 minute. Quickly transfer the system to a graduated cylinder, start timing, and observe and record the initial volume V0 and half-life T0.5.

[0075] 3.5 Test Results of Drilling Fluid System B1

[0076] Quickly transfer the system obtained in the comparative example into a graduated cylinder, immediately start timing and observe the foam, and record the initial volume V0 (the graduation on the graduated cylinder corresponding to the initial foam time) and the half-life T0.5 (the time corresponding to when 50 ml of water is expelled from the foam). The initial volume indicates the foaming performance of the system; the larger the initial volume, the better the foaming performance. The half-life indicates the foam stability of the system; the larger the half-life, the better the foam stability of the system.

[0077] Table 2B2 system initial volume and half-life record

[0078] system initial volume half life B1 175ml 20h B1 + 10wt% NaCl 200ml 18h <![CDATA[B1+2wt%Cacl2]]> 145ml 4h Aging at 140℃ for 16 hours 215ml 14h

[0079] The results are shown in Table 2. The data in Table 2 show that when the foam stabilizer was replaced with hydroxyethyl cellulose in the drilling fluid system, the initial foaming volume was 175 mL, and the foam half-life was 20 h, indicating that the system had a good foam stabilizing effect. In subsequent salt resistance tests, it was found that when the sodium chloride content in the drilling fluid system exceeded 10 wt% NaCl, the system lost its foam characteristics after a period of time. When the sodium chloride content was 10 wt% NaCl, the foam half-life of the system reached 18 h. After adding 2 wt% CaCl2 to the system, the foam half-life of the system was reduced to only 4 h. This indicates that when hydroxyethyl cellulose was used as the foam stabilizer in this drilling fluid system, while maintaining a certain foam stabilizing effect, the system only had resistance to 10 wt% NaCl and 2 wt% CaCl2. Furthermore, after aging the system at 140℃ for 16 h, it was found that the system could maintain a foam half-life of about 14 h, while the initial volume of the system reached 215 mL.

[0080] In summary, when the zwitterionic polymer of this invention is applied to the drilling fluid system, the system exhibits excellent foam stabilization effect, and also possesses salt resistance of 18wt% NaCl, calcium resistance of 4wt% CaCl2, and resistance to high temperature of 140℃, making it a high-performance foam stabilizer.

[0081] The zwitterionic polymer described in this invention uses a temperature-resistant monomer as its cationic monomer, making it suitable for use as a foam stabilizer in drilling fluids in high-temperature formations. In recent years, with the increasing exploitation of oil and gas resources in low-pressure and ultra-low-pressure oil and gas layers, depleted layers, and more sensitive reservoirs, the formation pressure in these oil and gas wells is generally low. The use of conventional oil-based drilling fluids can lead to severe leakage problems, causing reservoir damage. Foam drilling fluids, with their low density and low damage characteristics, can effectively solve the leakage problem. Foam stabilizers, as one of the core processing agents in drilling fluids, play a significant role, determining the duration of foam persistence. However, the thermodynamic and kinetic instability of foam makes it more prone to breakage under high-temperature and high-salinity conditions. Therefore, the selection of foam stabilizers in foam drilling fluids is particularly important.

[0082] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0083] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for preparing an amphoteric polymer foam stabilizer, characterized in that, Includes the following steps: Step 1: Dissolve AMPS in a solvent to form an AMPS solution, and adjust the pH of the AMPS solution to 6-7; Step 2: Add acrylamide and thermo-resistant monomer to the AMPS solution after pH adjustment. The molar ratio of AMPS, acrylamide and thermo-resistant monomer is 3:9:

1. After the acrylamide and thermo-resistant monomer are completely dissolved to form a monomer mixed solution, deoxygenation treatment is performed. Step 3: After deoxygenation treatment, a crosslinking agent is added to the monomer mixture solution. The molar ratio of the crosslinking agent to the AMPS is 0.1:

3. The monomer mixture solution with the added crosslinking agent is reacted at a temperature of 60-70℃ for 4-6 hours. The solvent is then removed by drying to obtain the zwitterionic polymer foam stabilizer. In step 2, the thermoresistant monomer is DMDAAC; the specific method for the deoxygenation treatment is to introduce nitrogen gas into the monomer mixture solution for at least 20 minutes; in step 3, the crosslinking agent is N,N'-methylenebisacrylamide.

2. The method for preparing an amphoteric polymer foam stabilizer according to claim 1, characterized in that, In step 1, the solvent is deionized water or distilled water; the pH of the AMPS solution is adjusted to 6-7 using NaOH or ammonia.

3. A zwitterionic polymer foam stabilizer, characterized in that, The zwitterionic polymer foam stabilizer is prepared by the preparation method according to any one of claims 1 to 2.

4. A foam drilling fluid system, characterized in that, The foam drilling fluid system comprises the zwitterionic polymer foam stabilizer as described in claim 3.

5. The foam drilling fluid system according to claim 4, characterized in that, The foam drilling fluid system also includes a foaming agent, nano-magnesium aluminum silicate, cellulose microfibers, and deionized water; the weight percentages of each component in the foam drilling fluid system are as follows: 0.25-0.75 parts of zwitterionic polymer foam stabilizer, 0.1-0.3 parts of foaming agent, 1-3 parts of nano-magnesium aluminum silicate, 0.5-1.5 parts of cellulose microfibers, and 49.75-149.25 parts of deionized water.

6. The foam drilling fluid system according to claim 5, characterized in that, The weight proportions of each component in the foam drilling fluid system are as follows: 0.5 parts zwitterionic polymer foam stabilizer, 0.2 parts foaming agent, 2 parts nano magnesium aluminum silicate, 1 part cellulose micron fiber, and 99.5 parts deionized water.

7. A foam drilling fluid system according to claim 5 or 6, characterized in that, The foaming agent is AD300 or AD300-1.

8. A method for preparing a foam drilling fluid system according to any one of claims 4 to 7, characterized in that, The process includes the following steps: dissolving the zwitterionic polymer foam stabilizer in deionized water and stirring until homogeneous to form a zwitterionic polymer foam stabilizer solution; adding nano-magnesium aluminum silicate and cellulose micron fibers to the zwitterionic polymer foam stabilizer solution and stirring again until homogeneous to form a mixed solution; adding a foaming agent to the mixed solution and performing high-speed variable frequency stirring until homogeneous to obtain a foam drilling fluid system.

9. The method for preparing a foam drilling fluid system according to claim 8, characterized in that, The specific conditions for the stirring steps to form the zwitterionic polymer foam stabilizer solution are: a stirring speed of 200-800 r / min and a stirring time of 5-15 min; the specific conditions for the stirring steps to form the mixed solution are: a stirring speed of 200-800 r / min and a stirring time of 5-15 min; the speed of the variable frequency high-speed stirrer is 3000-5000 r / min and the stirring time is 0.5-2 min.

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