In-situ modified nanoparticle CO2 foam channeling sealing system as well as preparation method and application thereof

Abstract

The invention discloses an in-situ modified nanoparticle CO2 foam channeling sealing system, which is composed of the following materials: 1-5 wt% of a nonionic CO2 responsive surfactant; 5 to 10 weight percent of nano particles; 0.1 to 1 wt% of an anionic foaming agent; 1-5 wt% of a salt ion auxiliary agent; and the balance of water. The invention discloses a preparation method of an in-situ modified nanoparticle CO2 foam channeling sealing system, which comprises the following steps: (1) adding a nonionic CO2 responsive surfactant with a formula amount and an anionic foaming agent with a formula amount into water with a formula amount, and uniformly stirring to obtain a mixed solution a; (2) adding the nano-particles into the mixed solution a according to the formula ratio, stirring and performing ultrasonic treatment until the nano-particles are completely dispersed to obtain a mixed solution b; (3) adding the mixed solution b into a high-temperature and high-pressure foam reaction container, introducing high-pressure CO2, and stirring to obtain an acidic mixed solution c; and (4) standing to obtain the in-situ modified nano-particle CO2 foam channeling sealing system.

Description

Technical Field

[0001] The present invention belongs to the field of oil exploitation engineering, and relates to the field of preventing gas channeling in low-permeability reservoirs, in particular to an in-situ modified nanoparticle CO 2 foam channeling plugging system and its preparation method and application. 2 Background Technique

[0002] CO 2 flooding technology is an effective method to achieve a win-win situation of increasing oil production and carbon sequestration. It can realize the resource utilization of greenhouse gases and improve the oil and gas recovery rate. Chinese Patent Application CN 109973060A discloses a device and method for improving oilfield recovery, applying carbon dioxide flooding technology to tight oil development, which not only improves the flooding effect but also can well sequester carbon dioxide underground, reducing the "greenhouse gas" effect in the atmosphere. Carbon dioxide can reduce the viscosity of crude oil, improve the mobility ratio, expand the swept volume, effectively solve the development contradictions such as difficult injection of water into ultra-low permeability reservoirs, insufficient injection, difficult establishment of an effective displacement system, and channeling of injected water along fractures. Carbon dioxide and underground crude oil are mutually fused (miscible), with characteristics such as low miscibility pressure and low interfacial tension, and on average, it can improve the oilfield recovery rate by 5% - 15% on the basis of water flooding, improving the displacement efficiency.

[0003] However, during the CO 2 gas flooding process, due to the characteristics of small gas density, low viscosity, and formation heterogeneity, problems such as CO 2 gravity override, channeling along high-permeability channels, and viscous fingering often occur, which reduces the swept volume of the gas and the gas flooding efficiency. Therefore, gas channeling greatly affects the CO 2 development effect.

[0004] In order to expand the swept volume of gas flooding and improve the CO 2 flooding effect, CO 2 ​Foam has developed into an important technical means to improve the gas-liquid mobility ratio. For example, Chinese invention patent CN 114196389B provides an ultra-low interfacial tension self-assembled carbon dioxide foam flooding agent suitable for low-permeability oil reservoirs, which is composed of the following components: ethane {bis[N-methyl-N-(3-dodecyloxy-2-hydroxy)propyl-N-(2-hydroxy-3-sulfonate)propyl]ammonium chloride}, coconut amide propyl betaine, dodecyl dimethyl amine oxide, sodium salicylate, chelating agent, inorganic salt, and the balance is water. This invention patent also provides a preparation method and application of the ultra-low interfacial tension self-assembled carbon dioxide foam flooding agent. This self-assembled carbon dioxide foam flooding agent has good salt and acid resistance, high viscosity of the foaming liquid, fine and rich foam, good stability, good injectivity in low-permeability oil reservoirs, can improve the oil-water mobility ratio, significantly expand the sweep efficiency, can reduce the oil-water interfacial tension, and significantly improve the oil washing efficiency; this foaming agent will not cause salting-out phenomenon, nor will it chemically react with calcium and magnesium ions to form precipitation. Another example is that Chinese invention patent application CN 114196389A provides an ultra-low interfacial tension self-assembled carbon dioxide foam flooding agent suitable for low-permeability oil reservoirs, which is composed of the following components in weight percentage: ethane {bis[N-methyl-N-(3-dodecyloxy-2-hydroxy)propyl-N-(2-hydroxy-3-sulfonate)propyl]ammonium chloride}: 0.2-0.3%, coconut amide propyl betaine: 0.2-0.3%, dodecyl dimethyl amine oxide: 0.1-0.35%, sodium salicylate: 0.02-0.07%, chelating agent: 0.04-0.14%, inorganic salt: 5-7%, and the balance is water. This invention patent also provides a preparation method and application of the ultra-low interfacial tension self-assembled carbon dioxide foam flooding agent. This self-assembled carbon dioxide foam flooding agent has good salt and acid resistance, high viscosity of the foaming liquid, makes the oil-water interfacial tension reach the order of magnitude of 10 -3 mN / m or below, the generated foam is fine and rich, has good stability, has good injectivity in low-permeability oil reservoirs, can improve the oil-water mobility ratio, significantly expand the sweep efficiency, can reduce the oil-water interfacial tension, and significantly improve the oil washing efficiency; this foaming agent will not cause salting-out phenomenon, nor will it chemically react with calcium and magnesium ions to form precipitation.

[0005] CO 2 Foam is a dispersion system with CO 2 as the dispersed phase and the surfactant solution as the dispersion medium. In porous media, CO 2 foam can block the liquid film, reduce the gas mobility, and expand the gas flooding swept volume, thereby effectively improving phenomena such as gas channeling and fingering. However, low-permeability oil reservoirs are buried deep, with relatively high temperature and salinity. The liquid film strength of the conventional CO 2 foam system decreases under high-temperature and high-salt conditions, resulting in a decrease in the foam plugging ability of CO 2 foam. Although ordinary nanoparticles strengthen CO 2The foam system can partially solve the above problems, but for ordinary nanoparticle-enhanced CO 2 In the foam system, the modification cost of nanoparticles is high, and they are easily adsorbed on formation rocks after modification, resulting in weakened foam-enhancing effect of the nanoparticles and ultimately affecting the foam channel plugging effect. Summary of the Invention

[0006] Object of the Invention: To solve the problems that the existing foam channel plugging materials have poor stability under high-temperature conditions and the channel plugging ability is reduced due to easy adsorption after modification of nanoparticles, the present invention provides an in-situ modified nanoparticle CO 2 foam channel plugging system and its preparation method and application. The reinforcing agent nanoparticles in the in-situ modified nanoparticle CO 2 foam channel plugging system of the present invention can be in-situ modified in the formation, and have the characteristics of low adsorption loss, strong interfacial adsorption, and strong foam plugging.

[0007] Technical Solution: The in-situ modified nanoparticle CO 2 foam channel plugging system, based on the total mass of the in-situ modified nanoparticle CO 2 foam channel plugging system, is composed of the following materials:

[0008] Nonionic CO 2 responsive surfactant 1-5 wt%;

[0009] Nanoparticles 5-10 wt%;

[0010] Anionic foaming agent 0.1-1 wt%;

[0011] Salt ion auxiliary agent 1-5 wt%;

[0012] The balance is water.

[0013] Furthermore, the nonionic CO 2 responsive surfactant is at least one of diethanolamide laurate, diethanolamide cocoate, diethanolamide oleate, and diethanolamide palmitate.

[0014] Furthermore, the nanoparticles are nano-SiO 2 particles.

[0015] Furthermore, the anionic foaming agent is at least one of sodium dodecylbenzenesulfonate, sodium dodecylsulfonate, and sodium dodecylsulfate.

[0016] Furthermore, the salt ion auxiliary agent is at least one of sodium chloride, sodium benzoate, and sodium p-aminosalicylate.

[0017] Preparation method of the in-situ modified nanoparticle CO 2 foam channel plugging system, comprising the following steps:

[0018] (1), Add the formula amount of non-ionic CO 2 responsive surfactant and the formula amount of anionic foaming agent to the formula amount of water, and stir evenly at the first stirring speed to obtain the mixed liquid a;

[0019] (2), Add the formula amount of nanoparticles to the mixed liquid a obtained in step (1), stir and ultrasonically disperse at the first stirring speed until completely dispersed to obtain the mixed liquid b;

[0020] (3), Add the mixed liquid b obtained in step (2) to a high-temperature and high-pressure foam reaction vessel, and introduce high-pressure CO 2 , stir at the second stirring speed to make the mixed liquid b and high-pressure CO 2 mix evenly to obtain the acidic mixed liquid c;

[0021] (4) After standing the acidic mixed liquid c obtained in step (3) for a period of time, stir at a high speed at the third stirring speed for a certain time to obtain the in-situ modified nanoparticle CO 2 foam plugging system.

[0022] Furthermore, the first stirring speed in steps (1) and (2) is 100 - 1000 revolutions per minute.

[0023] Furthermore, the stirring time in step (1) is at least 30 minutes, preferably 30 - 60 minutes;

[0024] The stirring time in step (2) is at least 1 hour, preferably 1 - 2 hours.

[0025] Preferably, the high-pressure CO 2 in step (3) is CO with a pressure greater than 10 MPa 2 .

[0026] Preferably, the second stirring speed in step (3) is 100 - 500 revolutions per minute;

[0027] Preferably, the third stirring speed in step (4) is 4000 - 10000 revolutions per minute, and the stirring time in step (4) is at least 10 minutes, preferably 10 - 60 minutes.

[0028] Furthermore, the standing time in step (4) is at least 5 minutes, preferably 5 - 20 minutes.

[0029] In-situ modified nanoparticle CO 2 foam plugging system, which is prepared by any of the above preparation methods.

[0030] The above-mentioned in-situ modified nanoparticle CO 2The application of the foam plugging system as a CO 2 plugging agent in oil exploitation.

[0031] The in-situ modified nanoparticle CO 2 foam plugging system provided by the present invention, its preparation method and application have the following beneficial effects:

[0032] (1). In the in-situ modified nanoparticle CO 2 foam plugging system provided by the present invention, the nanoparticles have good hydrophilicity, high Zeta potential before encountering CO 2 , have good dispersion stability in water, and have small adsorption loss in the formation;

[0033] (2). When the in-situ modified nanoparticle CO 2 foam plugging system provided by the present invention encounters CO 2 , the non-ionic CO 2 responsive surfactant is protonated to show the properties of a cationic surfactant, and is adsorbed on the surface of the nanoparticles under the action of electrostatic force, thereby in-situ modifying the surface of the nanoparticles, avoiding cumbersome grafting reactions, being simple and easy to operate, and having low cost;

[0034] (3). The in-situ modified nanoparticles have enhanced adsorption at the gas-liquid interface, can improve the stability of CO 2 foam, and enhance the plugging performance of CO 2 foam;

[0035] (4). Compared with other nanoparticle-enhanced CO 2 foam systems, due to the small adsorption loss of the nanoparticles and the in-situ modification occurring only after encountering CO 2 , they have stronger adsorption ability at the gas-liquid interface, higher strength after foaming, and better plugging effect on high-permeability channels;

[0036] (5). The preparation method is simple and easy to operate, and can achieve on-line mixing and injection. Description of the Drawings

[0037] Figure 1 Schematic diagram of the change in the conductivity of the non-ionic CO 2 responsive surfactant before and after passing CO 2 ;

[0038] Figures 2a - 2b Schematic diagram of the change in the surface wettability of the nanoparticles before and after passing CO 2 ;

[0039] Figure 3 Schematic diagram of the foaming performance of the in-situ modified nanoparticle-enhanced CO 2 foam system A1 prepared in Specific Example 1;

[0040] Figure 4 In-situ modified nanoparticles prepared for Specific Example 2 for strengthening CO 2 Schematic diagram of the foaming performance of foam system A2;

[0041] Figure 5 CO prepared for Test Example 3 2 Schematic diagram of the foaming performance of foam system D1;

[0042] Figure 6 Nanoparticle-reinforced CO prepared for Test Example 4 2 Schematic diagram of the foaming performance of foam system D2;

[0043] Figure 7 In-situ modified nanoparticle CO 2 Schematic diagram of the change in pressure before and after injecting foam plugging system A1. Detailed implementation method:

[0044] In the ranges disclosed herein, the endpoints and any values are not limited to the exact ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0045] The present invention will be described in detail below through examples.

[0046] Characterization method:

[0047] 1. Foaming performance of in-situ modified nanoparticle-reinforced CO 2 foam system: The foaming performance of the in-situ modified nanoparticle-reinforced CO 2 foam system was tested using a high-temperature and high-pressure foam reactor under different stirring speeds. Among them, the longer the half-life, the better the stability of the in-situ modified nanoparticle-reinforced CO 2 foam system. Specifically, the stirring speeds of the high-temperature and high-pressure reactor were 4000 r / min, 6000 r / min, 8000 r / min, and 10000 r / min.

[0048] Specific test method: Inject 100 - 500 mL of mixed solution c into the reactor, inject CO 2 gas to the required pressure and then close the valve. First, stir at a low speed to mix the mixed solution c with CO 2 to form an acidic solution, and then stir at a high speed to obtain in-situ modified nanoparticle-reinforced CO 2 foam.

[0049] 2. In-situ modified nanoparticle enhanced CO 2 Sealing effect of the foam plugging system: The sealing effect of the in-situ modified nanoparticle enhanced CO 2 foam plugging system was tested using a high-temperature and high-pressure core displacement device. The core used had a length of 10 cm and a permeability of 1000 mD.

[0050] Specific test method: First, use an ISCO pump to inject CO 2 into the fractured core to test the pressure; then pour the prepared 500 mL of the in-situ modified nanoparticle enhanced CO 2 foam system into an intermediate container, inject a certain amount into the core through an ISCO pump, and then use the ISCO pump to inject a certain amount of CO 2 into the core and test the pressure, and compare the injection pressures of CO 2 before and after. Specific Example 1

[0052] In-situ modified nanoparticle CO 2 foam plugging system A1. Based on the total mass of the in-situ modified nanoparticle CO 2 foam plugging system A1, it consists of the following materials:

[0053] Non-ionic CO 2 responsive surfactant 3 wt%;

[0054] Nanoparticles 6 wt%;

[0055] Anionic foaming agent 0.3 wt%;

[0056] Salt ion assistant 3 wt%;

[0057] The balance is water.

[0058] Furthermore, the non-ionic CO 2 responsive surfactant is lauric acid diethanolamide.

[0059] Furthermore, the nanoparticles are nano-SiO 2 particles.

[0060] Furthermore, the anionic foaming agent is sodium dodecylbenzenesulfonate.

[0061] Furthermore, the salt ion assistant is sodium chloride.

[0062] Preparation method of the in-situ modified nanoparticle CO 2 foam plugging system, including the following steps:

[0063] (1). Add the formulated amount of non-ionic CO 2A responsive surfactant and a formulated amount of an anionic foaming agent are added to a formulated amount of water, and after stirring evenly at a first stirring speed, a mixed solution a is obtained;

[0064] (2) Add a formulated amount of nanoparticles to the mixed solution a obtained in step (1), stir at the first stirring speed and ultrasonicate until completely dispersed to obtain the mixed solution b;

[0065] (3) Add the mixed solution b obtained in step (2) to a high-temperature and high-pressure foam reaction vessel, and introduce high-pressure CO 2 , stir at a second stirring speed to make the mixed solution b and high-pressure CO 2 mix evenly to obtain an acidic mixed solution c;

[0066] (4) After allowing the acidic mixed solution c obtained in step (3) to stand for a period of time, stir at a third stirring speed at high speed for a certain time to obtain an in-situ modified nanoparticle CO 2 foam plugging system A1.

[0067] Furthermore, the first stirring speed in steps (1) and (2) is 500 revolutions per minute.

[0068] Furthermore, the stirring time in step (1) is 45 minutes;

[0069] The stirring time in step (2) is 1.5 hours.

[0070] Preferably, the high-pressure CO 2 in step (3) is CO with a pressure of 12 MPa 2 .

[0071] Preferably, the second stirring speed in step (3) is 300 revolutions per minute;

[0072] Preferably, the third stirring speed in step (4) is 6000 revolutions per minute, and the stirring time in step (4) is 30 minutes.

[0073] Furthermore, the standing time in step (4) is 10 minutes.

[0074] The in-situ modified nanoparticle CO 2 foam plugging system A1 is prepared by any of the above preparation methods.

[0075] The above-mentioned in-situ modified nanoparticle CO 2 foam plugging system A1 is used as a CO 2 plugging agent in oil exploitation.

[0076] Using the CO 2Test method for foam stability, obtaining the half-life at different stirring speeds, and the experimental results are as Figure 3 shown. It can be seen from the results that as the shear rate increases, the drainage half-life of the in-situ modified nanoparticle CO 2 foam plugging system A1 also gradually increases. When the shear rate increases from 4000 r / min to 10000 r / min, the drainage half-life increases from 65 min to 134 min, indicating that the CO 2 foam stability is greatly improved. Specific Example 2

[0078] In-situ modified nanoparticle CO 2 foam plugging system A2, based on the total mass of the in-situ modified nanoparticle CO 2 foam plugging system A2, consists of the following materials:

[0079] Non-ionic CO 2 responsive surfactant 5 wt%;

[0080] Nanoparticles 10 wt%;

[0081] Anionic foaming agent 0.3 wt%;

[0082] Salt ion assistant 3 wt%;

[0083] The balance is water.

[0084] Furthermore, the non-ionic CO 2 responsive surfactant is coconut diethanolamide.

[0085] Furthermore, the nanoparticles are nano-SiO 2 particles.

[0086] Furthermore, the anionic foaming agent is sodium dodecyl sulfate.

[0087] Furthermore, the salt ion assistant is sodium benzoate.

[0088] Preparation method of in-situ modified nanoparticle CO 2 foam plugging system, including the following steps:

[0089] (1), Add the formulated amount of non-ionic CO 2 responsive surfactant and the formulated amount of anionic foaming agent to the formulated amount of water, and stir evenly at the first stirring speed to obtain the mixed solution a;

[0090] (2), Add the formulated amount of nanoparticles to the mixed solution a obtained in step (1), and stir and ultrasonicate at the first stirring speed until completely dispersed to obtain the mixed solution b;

[0091] (3) Add the mixed solution b obtained in step (2) into a high-temperature and high-pressure foam reaction vessel, and introduce high-pressure CO 2 , and stir at a second stirring speed to make the mixed solution b and high-pressure CO 2 uniformly mixed to obtain an acidic mixed solution c;

[0092] (4) After standing the acidic mixed solution c obtained in step (3) for a period of time, stir at a third stirring speed at a high speed for a certain time to obtain an in-situ modified nanoparticle CO 2 foam plugging system A2.

[0093] Furthermore, the first stirring speed in steps (1) and (2) is 300 revolutions per minute.

[0094] Furthermore, the stirring time in step (1) is 50 minutes;

[0095] The stirring time in step (2) is 1.5 hours.

[0096] Preferably, the high-pressure CO 2 in step (3) is CO with a pressure of 13 MPa 2 .

[0097] Preferably, the second stirring speed in step (3) is 200 revolutions per minute;

[0098] Preferably, the third stirring speed in step (4) is 6000 revolutions per minute, and the stirring time in step (4) is 40 minutes.

[0099] Furthermore, the standing time in step (4) is 15 minutes.

[0100] The in-situ modified nanoparticle CO 2 foam plugging system A2 is prepared by any of the above preparation methods.

[0101] The above-mentioned in-situ modified nanoparticle CO 2 foam plugging system A2 is used as a CO 2 plugging agent in oil exploitation.

[0102] Using the test method for the stability of the CO 2 foam, the half-life at different stirring speeds is obtained. The experimental results are as Figure 4 shown. It can be seen from the results that as the shear rate increases, the in-situ modified nanoparticle CO 2The drainage half-life of the foam plugging system A2 also gradually increases. When the shear rate increases from 4000 r / min to 10000 r / min, the drainage half-life increases from 78 min to 146 min. Compared with the in-situ modified nanoparticle CO in the specific embodiment 1 2 For the foam plugging system A1, as the concentrations of the non-ionic surfactant and the nanoparticles increase, the drainage half-life (stability) of the system also increases accordingly. Specific embodiment 3

[0104] In-situ modified nanoparticle CO 2 For the foam plugging system A3, based on the total mass of the foam plugging system, it is composed of the following materials: 2 Based on the total mass of the foam plugging system, it is composed of the following materials:

[0105] Non-ionic CO 2 Responsive surfactant 1 wt%;

[0106] Nanoparticles 5 wt%;

[0107] Anionic foaming agent 0.1 wt%;

[0108] Salt ion auxiliary agent 1 wt%;

[0109] The balance is water.

[0110] Furthermore, the non-ionic CO 2 The responsive surfactant is diethanolamide oleate.

[0111] Furthermore, the nanoparticles are nano-SiO 2 particles.

[0112] Furthermore, the anionic foaming agent is sodium dodecyl sulfate.

[0113] Furthermore, the salt ion auxiliary agent is sodium para-aminosalicylate.

[0114] In-situ modified nanoparticle CO 2 Preparation method of the foam plugging system, comprising the following steps:

[0115] (1), Add the formulated amount of non-ionic CO 2 responsive surfactant and the formulated amount of anionic foaming agent to the formulated amount of water, and stir evenly at the first stirring speed to obtain the mixed solution a;

[0116] (2), Add the formulated amount of nanoparticles to the mixed solution a obtained in step (1), stir at the first stirring speed and ultrasonically disperse until completely dispersed to obtain the mixed solution b;

[0117] (3) Add the mixed solution b obtained in step (2) into a high-temperature and high-pressure foam reaction vessel, and introduce high-pressure CO 2 , and stir at the second stirring speed to make the mixed solution b and high-pressure CO 2 uniformly mixed to obtain an acidic mixed solution c;

[0118] (4) After allowing the acidic mixed solution c obtained in step (3) to stand for a period of time, stir at a high speed at the third stirring speed for a certain period of time to obtain an in-situ modified nanoparticle CO 2 foam plugging system A3.

[0119] Further, the first stirring speed in steps (1) and (2) is 100 revolutions per minute.

[0120] Further, the stirring time in step (1) is 60 minutes;

[0121] The stirring time in step (2) is 2 hours.

[0122] Preferably, the high-pressure CO 2 in step (3) is CO with a pressure of 15 MPa 2 .

[0123] Preferably, the second stirring speed in step (3) is 100 revolutions per minute;

[0124] Preferably, the third stirring speed in step (4) is 4000 revolutions per minute, and the stirring time in step (4) is 60 minutes.

[0125] Further, the standing time in step (4) is 20 minutes.

[0126] The in-situ modified nanoparticle CO 2 foam plugging system A3 is prepared by any of the above preparation methods.

[0127] The above-mentioned in-situ modified nanoparticle CO 2 foam plugging system A3 is used as a CO 2 plugging agent in oil exploitation. Specific Example 4

[0129] The in-situ modified nanoparticle CO 2 foam plugging system A4, based on the total mass of the in-situ modified nanoparticle CO 2 foam plugging system, consists of the following materials:

[0130] Nonionic CO 2 responsive surfactant 4 wt%;

[0131] Nanoparticles 8 wt%;

[0132] Anionic foaming agent 1 wt%;

[0133] Salt ion assistant 5 wt%;

[0134] The balance is water.

[0135] Furthermore, the non-ionic CO 2 responsive surfactant is diethanolamide palmitate. In another embodiment, the non-ionic CO 2 responsive surfactant is a mixture of diethanolamide laurate and diethanolamide cocoate in an equal mass ratio. In another embodiment, the non-ionic CO 2 responsive surfactant is a mixture of diethanolamide laurate, diethanolamide cocoate, diethanolamide oleate, and diethanolamide palmitate in an equal mass ratio.

[0136] Furthermore, the nanoparticles are nano-SiO 2 particles.

[0137] Furthermore, the anionic foaming agent is a mixture of sodium dodecylbenzenesulfonate, sodium dodecylsulfonate, and sodium dodecyl sulfate in an equal mass ratio. In another embodiment, the anionic foaming agent is a mixture of sodium dodecylbenzenesulfonate and sodium dodecylsulfonate in an equal mass ratio.

[0138] Furthermore, the salt ion assistant is a mixture of sodium chloride and sodium benzoate in an equal mass ratio. In another embodiment, the salt ion assistant is a mixture of sodium chloride, sodium benzoate, and sodium para-aminosalicylate in an equal mass ratio.

[0139] In-situ modified nanoparticle CO 2 The preparation method of the foam plugging system includes the following steps:

[0140] (1), Add the formulated amount of non-ionic CO 2 responsive surfactant and the formulated amount of anionic foaming agent to the formulated amount of water, and stir evenly at the first stirring speed to obtain the mixed solution a;

[0141] (2), Add the formulated amount of nanoparticles to the mixed solution a obtained in step (1), stir at the first stirring speed and ultrasonicate until completely dispersed to obtain the mixed solution b;

[0142] (3), Add the mixed solution b obtained in step (2) to a high-temperature and high-pressure foam reaction vessel, introduce high-pressure CO 2 , and stir at the second stirring speed to make the mixed solution b and high-pressure CO 2 mix evenly to obtain the acidic mixed solution c;

[0143] (4) After allowing the acidic mixed solution c obtained in step (3) to stand for a period of time, it is vigorously stirred at a third stirring speed for a certain period of time to obtain in-situ modified nanoparticle CO 2 Foam plugging system A4.

[0144] Furthermore, the first stirring speed in steps (1) and (2) is 1000 revolutions per minute.

[0145] Furthermore, the stirring time in step (1) is 30 minutes;

[0146] The stirring time in step (2) is 1 hour.

[0147] Preferably, the high-pressure CO in step (3) 2 is CO with a pressure of 10 MPa 2 .

[0148] Preferably, the second stirring speed in step (3) is 500 revolutions per minute;

[0149] Preferably, the third stirring speed in step (4) is 10000 revolutions per minute, and the stirring time in step (4) is 10 minutes.

[0150] Furthermore, the standing time in step (4) is 5 minutes.

[0151] In-situ modified nanoparticle CO 2 Foam plugging system A4 is prepared by any of the above preparation methods.

[0152] The above in-situ modified nanoparticle CO 2 Foam plugging system A4 is used as a CO 2 plugging agent in oil exploitation.

[0153] Performance and characterization

[0154] Test example 1

[0155] Prepare an aqueous solution of a non-ionic CO 2 responsive surfactant with a mass concentration of 1% (in this test example, the non-ionic CO 2 responsive surfactant used is coconut fatty acid diethanolamide,), and after the non-ionic CO 2 responsive surfactant is completely dissolved, use a conductivity meter to measure the conductivity of the solution, and then alternately introduce CO 2 and N 2 , measure the conductivity of the surfactant solution, and the experimental results are as Figure 1 shown, Figure 1 in which, the squares represent the introduction of carbon dioxide, and the circles represent the introduction of nitrogen. It can be seen from the results that as CO 2With the increase of time, the conductivity gradually increases; with the increase of the time of introducing N 2 (CO 2 escaping), the conductivity gradually decreases again, indicating that the non-ionic surfactant has CO 2 response characteristics. Introducing CO 2 can turn the non-ionic surfactant into a charged ionic surfactant, and after CO 2 escapes, the charged ionic surfactant turns back into an uncharged non-ionic surfactant.

[0156] Test Example 2

[0157] Prepare a mixed solution of a 3% non-ionic CO 2 responsive surfactant (coco diethanolamide) and 6% nano-SiO 2 particles. Take a small amount of the solution and centrifuge it at high speed to obtain nano-SiO 2 particles, then measure the contact angle. Introduce CO 2 and stir to form an acidic mixture. Again, take a small amount of the solution and centrifuge it at high speed to obtain nano-SiO 2 particles, and measure the contact angle. The experimental results are as Figure 2a and Figure 2b shown. It can be seen from the experimental results that before and after introducing CO 2 , the surface of the nano-SiO 2 particles changes from hydrophilic to hydrophobic. This is mainly because the negatively charged nano-SiO 2 particles have an electrostatic interaction with the positively charged ionic surfactant after CO 2 response, and the ionic surfactant is adsorbed onto the surface of the nano-SiO 2 particles, in-situ hydrophobically modifying the surface of the nano-SiO 2 particles.

[0158] Test Example 3

[0159] Prepare the CO 2 foam system D1 using the same method as in Specific Example 1, except that: it does not contain nano-SiO 2 particles.

[0160] Test the half-life of the CO 2 foam under different shear rate conditions. The experimental results are as Figure 5 shown. It can be seen from the results that with the increase of the shear rate, the drainage half-life of the CO 2 foam system D1 also gradually increases. When the shear rate increases from 4000 r / min to 10000 r / min, the drainage half-life increases from 35 min to 67 min. Compared with Specific Example 1, CO 2The foam system D1 only contains surfactants, and the drainage half-life (stability) of the system is reduced by more than half. Therefore, the nano-SiO 2 particles have a greater weight in increasing the stability of the system.

[0161] Test Example 4

[0162] The nano-particle enhanced CO 2 foam system D2 was prepared by the same method as in Example 1, except that: an ordinary non-ionic surfactant was used to replace the non-ionic CO 2 responsive surfactant.

[0163] The half-life of CO 2 foam was tested under different shear rate conditions, and the experimental results are as Figure 6 shown. It can be seen from the results that as the shear rate increases, the drainage half-life of the nano-particle enhanced CO 2 foam system D2 also gradually increases. When the shear rate increases from 4000 r / min to 10000 r / min, the drainage half-life increases from 40 min to 81 min. Compared with Example 1, the ordinary non-ionic surfactant in the system does not have the CO 2 responsive property, so it cannot change from a non-ionic surfactant to an ionic surfactant and adsorb on the surface of the nano-particles for modification. Because the nano-particles cannot adsorb to the gas-liquid interface to improve the foam stability, the drainage half-life (stability) of the nano-particle enhanced CO 2 foam system D2 is much lower than that of the in-situ modified nano-particle CO 2 foam plugging system A1 in Example 1.

[0164] Test Example 5

[0165] First, water was injected into the water-saturated core alone to test the basic pressure difference, and then the in-situ modified nano-particle CO 2 foam plugging system A1 and CO 2 were injected to test the injection pressure difference, and the experimental results are as Figure 7 shown. It can be seen from the experimental results that the pressure difference was very low at the beginning of water injection, only a few KPa. When the in-situ modified nano-particle CO 2 foam plugging system A1 and CO 2 were injected, the injection pressure difference reached up to 80 KPa at most. This shows that CO 2 and the in-situ modified nano-particles formed a foam system in the core porous medium, increasing the flow resistance.

[0166] The above describes the embodiments of the present invention in detail. However, the present invention is not limited to the above embodiments, and various changes can be made without departing from the spirit of the present invention within the scope of knowledge possessed by those of ordinary skill in the relevant art.

Claims

1. In-situ modified nanoparticle CO2 foam sealing system, characterized in that: Based on the total mass of the in-situ modified nanoparticle CO2 foam sealing system, it is composed of the following materials: Nonionic CO2 responsive surfactant 1-5wt%; Nanoparticles 5-10wt%; Anionic foaming agent 0.1-1wt%; Salt ion additive 1-5wt%; The balance is water.

2. The in-situ modified nanoparticle CO2 foam sealing system according to claim 1, characterized in that: The nonionic CO2 responsive surfactant is at least one of lauric acid diethanolamide, coconut acid diethanolamide, oleic acid diethanolamide, and palmitic acid diethanolamide.

3. The in-situ modified nanoparticle CO2 foam sealing system according to claim 1, characterized in that: The nanoparticles are nano-SiO2 particles.

4. The in-situ modified nanoparticle CO2 foam sealing system according to claim 1, characterized in that: The anionic foaming agent is at least one of sodium dodecylbenzene sulfonate, sodium dodecyl sulfonate and sodium dodecyl sulfate.

5. The in-situ modified nanoparticle CO2 foam sealing system according to claim 1, characterized in that: The salt ion auxiliary agent is at least one of sodium chloride, sodium benzoate and sodium p-aminosalicylate.

6. The method for preparing the in-situ modified nanoparticle CO2 foam sealing system according to any one of claims 1 to 5, characterized in that: The following steps are involved: (1) adding a formulated amount of a nonionic CO2 responsive surfactant and a formulated amount of an anionic foaming agent to a formulated amount of water, and stirring at a first stirring speed to obtain a mixed solution a; (2) adding the formulated amount of nanoparticles to the mixed solution a obtained in step (1), stirring at a first stirring speed and ultrasonicating until completely dispersed to obtain the mixed solution b; (3) adding the mixed solution b obtained in step (2) into a high-temperature and high-pressure foam reaction vessel, introducing high-pressure CO2, and stirring at a second stirring speed to uniformly mix the mixed solution b and the high-pressure CO2 to obtain an acidic mixed solution c; (4) After the acidic mixed solution c obtained in step (3) is allowed to stand for a period of time, it is stirred at a third stirring speed for a certain period of time to obtain an in-situ modified nanoparticle CO2 foam sealing system.

7. The method for preparing the in-situ modified nanoparticle CO2 foam sealing system according to claim 6, characterized in that: In step (1) and step (2), the first stirring speed is 100-1000 rpm.

8. The method for preparing the in-situ modified nanoparticle CO2 foam sealing system according to claim 6, characterized in that: The stirring time in step (1) is at least 30 minutes, preferably 30-60 minutes; The stirring time in step (2) is at least 1 hour, preferably 1-2 hours.

9. The method for preparing the in-situ modified nanoparticle CO2 foam sealing system according to claim 6, characterized in that: The high-pressure CO2 described in step (3) is CO2 with a pressure greater than 10 MPa; In step (3), the second stirring speed is 100-500 rpm.

10. The method for preparing the in-situ modified nanoparticle CO2 foam sealing system according to claim 6, characterized in that: The third stirring speed in step (4) is 4000-10000 rpm, and the stirring time in step (4) is at least 10 minutes, preferably 10-60 minutes; The standing time in step (4) is at least 5 minutes, preferably 5-20 minutes.

11. In-situ modified nanoparticle CO2 foam sealing system, characterized in that: It is prepared by any one of the preparation methods of claims 6-10.

12. Use of the in-situ modified nanoparticle CO2 foam blocking system as claimed in any one of claims 1 to 5 and 11 as a CO2 blocking agent in oil production.

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