A nano-modified CO2 responsive foam plugging agent and preparation method thereof

Abstract

The present invention belongs to the technical field of foam plugging agents for oil exploitation, and particularly relates to a nano-modified CO2 multi-chain alkyl amidine, a CO2-responsive foam plugging agent, a preparation method and an application thereof. The CO2-responsive multi-chain alkyl amidine provided by the present invention is obtained by electrostatic adsorption of the active adsorption centers (tertiary carbon or tertiary nitrogen) of the multi-chain alkyl amidine and partially negatively charged nano-silica-calcium carbonate. It is sensitive to the stimulation of CO2, has good foaming capacity, foam stability, temperature and salt resistance, and is environmentally friendly and easily degradable, which can avoid the pollution of the oil layer and the blockage of the formation, and can be used to prepare a CO2-responsive foam plugging agent.

Description

Technical Field

[0001] This invention belongs to the field of oil extraction foam plugging agent technology, and particularly relates to a nano-modified CO2 polyalkylamine, a CO2-responsive foam plugging agent, its preparation method and application. Background Technology

[0002] Currently, against the backdrop of international energy shortages, international advocacy for energy conservation and emission reduction, and the challenges of oil extraction in my country, major oilfields across the country are actively upgrading their technologies. CO2 enhanced oil recovery (EOR) technology is mature and has been applied on a large scale abroad. It can increase oil recovery rates by more than 10% in the extraction of low-permeability reservoirs, which is of positive significance to my country's energy development. However, during the field application of CO2 EOR technology, the presence of reservoir fractures inevitably leads to CO2 gas migration along the fractures. This not only reduces the efficiency of CO2 recovery of crude oil, resulting in unsatisfactory extraction results, but also causes CO2 emissions, leading to environmental pollution.

[0003] In existing technologies, solutions that prioritize environmental protection and avoid polluting the formation typically involve sealing cracks with foam sealants. However, conventional sealants suffer from problems such as low foaming volume, poor foam stability, and poor temperature and salt resistance, resulting in unsatisfactory sealing effects. Summary of the Invention

[0004] To address the above technical problems, this invention provides a nano-modified CO2 polyalkylamidine, a CO2-responsive foam plugging agent, its preparation method, and its applications. The nano-modified CO2 polyalkylamidine provided by this invention is obtained by electrostatic adsorption of the active adsorption center (tertiary carbon or tertiary nitrogen) of polyalkylamidine with a portion of negatively charged nano-silica-calcium carbonate. It exhibits specific CO2 absorption, high foaming capacity, good foam stability, temperature and salt resistance, and is environmentally friendly and easily degradable. It can be used to prepare foam plugging agents for CO2 control operations to prevent gas channeling and improve oil recovery.

[0005] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0006] The first aspect of this invention provides a nano-modified CO2-responsive multi-chain alkylamidinium, the structural formula of which is shown below:

[0007]

[0008] Where R=C 14 H 28 .

[0009] This nano-modified CO2-responsive polyalkylamidine is obtained by electrostatic adsorption of the active adsorption center (tertiary carbon or tertiary nitrogen) of the polyalkylamidine with partially negatively charged nano-silica (SiO2)-calcium carbonate (CaCO3). The polyalkylamidine exhibits specific absorption of CO2, making it a CO2-responsive polyalkylamidine. Compared to single-chain alkyl ethers, this polyalkylamidine is more sensitive to CO2 stimulation. Furthermore, the protonation of this polyalkylamidine and its combination with CO2 form polyalkylamidine bicarbonate, which has more long-chain lipophilic tail groups (R=C). 14 H 28 This results in lower surface tension, better foaming effect, higher foaming volume and foam stability, thereby improving crude oil recovery rate. Adsorbing partially negatively charged nano-silica onto the active adsorption centers (tertiary carbon or tertiary nitrogen) of polyalkylamidine, combined with the cubic structure of nano-sized calcium carbonate, achieves a dual effect of increasing strength and modification, improving its temperature and salt resistance, and further enhancing its stability. CO2-responsive foam plugging agents made with this nano-modified CO2-responsive polyalkylamidine as the main or sole component can achieve high-strength sealing of geological reservoir fractures.

[0010] The second aspect of this invention provides the application of the above-mentioned nano-modified CO2-responsive polyalkylamidine in the preparation of CO2-responsive foam plugging agents.

[0011] A third aspect of the present invention provides a CO2-responsive foam plugging agent made from the above-mentioned nano-modified CO2-responsive polyalkylamidine.

[0012] Preferably, the nano-modified CO2-responsive polyalkylamine is the main component or the only component of the CO2-responsive foam plugging agent.

[0013] A fourth aspect of this invention provides a method for preparing the above-mentioned nano-modified CO2-responsive polyalkylamidinium, comprising the following steps:

[0014] S1. N,N-Dimethylacetamide dimethyl acetal and 1,14-tetradecyl diamine react via an amide acetal reaction under the action of a catalyst to generate polychain alkylamidinium;

[0015] S2. The nano-silica modified with nano-calcium carbonate is mixed with the polyalkylamidine, and after being ultrasonically dispersed evenly, the temperature is raised to 60~70℃, and then the reaction is carried out under stirring for 3~4 h to obtain the nano-modified CO2-responsive polyalkylamidine.

[0016] The preparation method first uses polyamines as raw materials to generate polyalkylamidinium (systematically named 4,19-bis(14-aminotetradecyl)-2,3,20,21-tetramethyl-2,4,19,21-tetraazacotetracosane) via the amide acetal method. The reaction mechanism of this step is as follows:

[0017]

[0018] For this polychain alkylamidine, the preparation method uses nano-silica modified with nano-scale calcium carbonate to modify its surface, so that the polychain alkylamidine can be electrostatically adsorbed with Nano-SiO2-CaCO3 to form nano-modified CO2-responsive polychain alkylamidine.

[0019] Preferably, the method for preparing the polyalkylamidine in S1 is as follows: 1,14-tetradecyldiamine is dissolved in methanol to obtain a 1,14-tetradecyldiamine solution; the N,N-dimethylacetamide dimethyl acetal is mixed with the catalyst, and then added dropwise to the 1,14-tetradecyldiamine solution at a rate of 23.5%~43.5% v / v per minute. After the addition is complete, the mixture is reacted at an inert atmosphere and at 80~90°C for at least 4 hours; after the reaction is completed, the methanol is removed from the reaction mixture, and the resulting liquid product is the polyalkylamidine. The 23.6%~43.5% per minute refers to 23.6%~43.5% of the total volume of the mixture of N,N-dimethylacetamide dimethyl acetal and the catalyst added per minute.

[0020] Preferably, the molar ratio of 1,14-tetradecyldiamine to N,N-dimethylacetamide dimethyl acetal in S1 is 1:(0.46~0.68).

[0021] Preferably, the catalyst in S1 is selected from L-proline, p-toluenesulfonic acid, or trifluoromethanesulfonic acid. Compared with conventional acidic catalysts, such as sulfuric acid, hydrochloric acid, and alumina, it has stronger activity, can significantly improve reaction efficiency, reduce by-product formation, and ensure the yield of polyalkylamidine in the product.

[0022] More preferably, the molar ratio of N,N-dimethylacetamide dimethyl acetal to the catalyst in S1 is (1.5~2.5):1.

[0023] Alternatively, methanol can be removed from the reaction mixture by means of rotary evaporation at 40-60°C.

[0024] Preferably, each mole of the 1,14-tetradecyldiamine is dissolved in 420-546 mL of the methanol.

[0025] Preferably, the preparation method of the nano-calcium carbonate modified nano-silica in S2 is as follows: 1-1.5 parts of calcium carbonate are evenly dispersed in water, 1.5-2 parts of nano-silica are added, ultrasonically dispersed, and then heated to 55-65°C. The reaction is kept at this temperature for at least 20 hours under stirring to obtain the dispersion of the nano-calcium carbonate modified nano-silica.

[0026] More preferably, the stirring speed is 300~400 r / min.

[0027] Preferably, in S2, the mass ratio of the nano-calcium carbonate-modified nano-silica to the mass of the polyalkylamidine in the dispersion of nano-calcium carbonate-modified nano-silica is (1~2):(3~5).

[0028] Optionally, the ultrasonic dispersion time in S2 is 20-30 min.

[0029] Preferably, the stirring speed in the stirring state described in S2 is 400~500 r / min.

[0030] The beneficial effects of this invention are as follows:

[0031] (1) The nano-modified CO2-responsive polyalkylamidine provided by this invention combines with CO2 through the protonation of polyalkylamidine to form polyalkylamidine bicarbonate. Compared with the commonly used single-chain polyalkylamidine, the polyalkylamidine of this invention can adsorb more CO2 and is more sensitive to CO2 stimulation. At the same time, the polyalkylamidine bicarbonate has a long-chain lipophilic tail group (R=C). 14 H 28 It has lower surface tension and higher surface activity, resulting in better foaming volume and foam stability, better foaming effect, and can significantly improve the foam sealing effect.

[0032] (2) The method for preparing CO2-responsive polyalkylamidines modified by the present invention firstly synthesizes polyalkylamidines through an acetal reaction using polyamines under the action of a catalyst. Then, it is modified with nano-calcium carbonate-modified nano-silica (Nano-SiO2-CaCO3). The cubic structure of nano-calcium carbonate further fills the tetrahedral space structure of silica, forming a denser and stronger spatial network structure, thereby significantly improving the stability and temperature and salt resistance of the foam. Therefore, after nano-modification, the resulting product exhibits superior oil resistance, significantly improved foam stability under reservoir conditions, and thus expands the swept volume of CO2 huff and puff, improving oil recovery efficiency.

[0033] (3) The nano-modified CO2-responsive foam plugging agent of the present invention is an environmentally friendly and easily degradable surfactant that can avoid oil layer pollution; the response to CO2 is reversible, and after absorbing CO2, it can form bicarbonate, which has a high-efficiency plugging effect on cracks in low-permeability and ultra-low-permeability heterogeneous oil reservoirs that are prone to CO2 gas channeling. When N2 or air is introduced, it can decompose into neutral amidine and defoam, and will not block the formation. Attached Figure Description

[0034] Figure 1 The infrared spectrum of CO2-responsive polyalkylamidine powder in Test Example 1 of this invention;

[0035] Figure 2 The image shows the 1H NMR spectrum of the CO2-responsive polyalkylamidine powder in Example 1 of this invention. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. All other embodiments obtained by those skilled in the art based on the implementation methods of this invention without inventive effort fall within the protection scope of this invention.

[0037] To address the issue of unsatisfactory displacement effects caused by gas channeling during CO2 oil displacement, existing technologies often employ easily degradable foam plugging agents to seal gas channeling pathways. However, conventional foam plugging agents suffer from problems such as poor oil resistance, low foaming capacity, poor foam stability, and poor temperature and salt resistance.

[0038] To address the above problems, embodiments of the present invention provide a nano-modified CO2-responsive multi-chain alkyl amidine, the structural formula of which is shown below:

[0039]

[0040] Where R=C 14 H 28 .

[0041] This invention also provides the application of the above-mentioned nano-modified CO2-responsive polyalkylamidine in the preparation of CO2-responsive foam plugging agents.

[0042] This invention also provides a CO2-responsive foam plugging agent.

[0043] This invention also provides a method for preparing the above-mentioned nano-modified CO2-responsive polyalkylamidinium, comprising the following steps:

[0044] S1. N,N-Dimethylacetamide dimethyl acetal and 1,14-tetradecyl diamine react via an amide acetal reaction under the action of a catalyst to generate polychain alkylamidinium;

[0045] S2. The nano-silica modified with nano-calcium carbonate is mixed with the polychain alkylamidine, and after being ultrasonically dispersed evenly, the temperature is raised to 60~70℃, and then the reaction is carried out under stirring for 3~4 h to obtain the nano-modified CO2-responsive foam plugging agent.

[0046] The present invention will be described below through specific embodiments.

[0047] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0048] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0049] Example 1

[0050] This embodiment provides a nano-modified CO2-responsive foam plugging agent, and the specific steps of its preparation method are as follows:

[0051] (1) Preparation method of nano-calcium carbonate modified nano-silica

[0052] Step 1: Disperse 1 part of nano calcium carbonate in 5 parts of distilled water and stir until well mixed;

[0053] Step 2: Add 1.5 parts of nano-silica to the solution from Step 1, and use ultrasonic vibration for 15 min to disperse the two evenly.

[0054] Step 3: Heat the solution from Step 2 to 55°C and keep it at that temperature for 20 h with stirring at 300 r / min to obtain a dispersion of nano-calcium carbonate modified nano-silica.

[0055] (2) Preparation method of CO2-responsive polyalkylamidine

[0056] Step 1: Add 45.7 g (0.2 mol) of 1,14-tetradecyldiamine to a 250 mL four-necked flask equipped with a stirrer, constant pressure funnel, nitrogen purging device, and thermometer, then add 100 mL of methanol and stir until completely dissolved.

[0057] Step 2: Weigh 13.32 g (0.1 mol) of N,N-dimethylacetamide dimethyl acetal into a 50 mL beaker, add 5.76 g (0.05 mol) of catalyst L-proline and stir until homogeneous.

[0058] Step 3: Turn on the condenser and stir at 400-500 r / min. Add the solution from Step 2 slowly dropwise to the four-necked flask from Step 1 through a constant pressure funnel at a rate of 5 mL / min. After the addition is complete, introduce nitrogen gas and heat the mixture at 80°C for 4 h under nitrogen protection.

[0059] Step 4: After the reaction is complete, the reaction mixture is subjected to rotary evaporation (40~60℃) to remove methanol, and a liquid product is obtained with a yield of 92%.

[0060] (3) Preparation method of nano-modified CO2-responsive foam plugging agent

[0061] One part of nano-calcium carbonate modified nano-silica (mass of nano-calcium carbonate modified nano-silica in the dispersion) was mixed with three parts of CO2-responsive polyalkylamidine. After ultrasonic vibration for 20 min, the mixture was heated to 60℃ and stirred at 400 r / min for 3 h to obtain the final product.

[0062] Example 2

[0063] This embodiment provides a nano-modified CO2-responsive foam plugging agent, and the specific steps of its preparation method are as follows:

[0064] (1) Preparation method of nano-calcium carbonate modified nano-silica

[0065] Step 1: Disperse 1 part of nano calcium carbonate in 5 parts of distilled water and stir well;

[0066] Step 2: Add 2 parts of nano-silica to the solution from Step 1, and use ultrasonic vibration for 20 min to disperse the two evenly.

[0067] Step 3: Heat the solution from Step 2 to 65°C and keep it at that temperature for 24 h with stirring at 400 r / min to obtain a dispersion of nano-calcium carbonate modified nano-silica.

[0068] (2) Preparation method of CO2-responsive polyalkylamidine

[0069] Step 1: Add 57.1 g (0.25 mol) of 1,14-tetradecyldiamine to a 250 mL four-necked flask equipped with a stirrer, constant pressure funnel, nitrogen purging device, and thermometer, then add 115 mL of methanol and stir until completely dissolved.

[0070] Step 2: Weigh 16.65 g (0.125 mol) of N,N-dimethylacetamide dimethyl acetal into a 50 mL beaker, add 13.78 g (0.08 mol) of catalyst p-toluenesulfonic acid and stir until homogeneous.

[0071] Step 3: Turn on the condenser and stir at 400-500 r / min. Add the solution from Step 2 to the four-necked flask from Step 1 slowly at a rate of 7 mL / min through a constant pressure funnel. After the addition is complete, introduce nitrogen gas and heat the mixture at 90℃ for 5 h under nitrogen protection.

[0072] Step 4: After the reaction is complete, the reaction mixture is subjected to rotary evaporation (40~60℃) to remove methanol, and a liquid product is obtained with a yield of 93%.

[0073] (3) Preparation method of nano-modified CO2-responsive foam plugging agent

[0074] One part of nano-calcium carbonate modified nano-silica (mass of nano-calcium carbonate modified nano-silica in the dispersion) was mixed with four parts of CO2-responsive polyalkylamidine. After ultrasonic vibration for 30 min, the mixture was heated to 70℃ and stirred at 500 r / min for 4 h to obtain the final product.

[0075] Example 3

[0076] This embodiment provides a nano-modified CO2-responsive foam plugging agent, and the specific steps of its preparation method are as follows:

[0077] (1) Preparation method of nano-calcium carbonate modified nano-silica

[0078] Step 1: Disperse 1.5 parts of nano calcium carbonate in 7.5 parts of distilled water and stir until homogeneous;

[0079] Step 2: Add 2 parts of nano-silica to the solution from Step 1, and use ultrasonic vibration for 18 minutes to disperse the two evenly.

[0080] Step 3: Heat the solution from Step 2 to 60°C and keep it at that temperature for 22 h with stirring at 350 r / min to obtain a dispersion of nano-calcium carbonate modified nano-silica.

[0081] (2) Preparation method of CO2-responsive polyalkylamidine

[0082] Step 1: Add 50.3 g (0.22 mol) of 1,14-tetradecyldiamine to a 250 mL four-necked flask equipped with a stirrer, constant pressure funnel, nitrogen purging device, and thermometer, then add 120 mL of methanol and stir until completely dissolved.

[0083] Step 2: Weigh 19.98 g (0.15 mol) of N,N-dimethylacetamide dimethyl acetal into a 50 mL beaker, add 9.00 g (0.06 mol) of trifluoromethanesulfonic acid catalyst and stir until homogeneous.

[0084] Step 3: Turn on the condenser and stir at 400-500 r / min. Slowly add the solution from Step 2 to the four-necked flask from Step 1 through a constant pressure funnel at a rate of 8 mL / min. After the addition is complete, introduce nitrogen gas and heat the mixture at 85°C for 4.5 h under nitrogen protection.

[0085] Step 4: After the reaction is complete, the reaction mixture is subjected to rotary evaporation (40~60℃) to remove methanol, and a liquid product is obtained with a yield of 90%.

[0086] (3) Preparation method of nano-modified CO2-responsive foam plugging agent

[0087] One part of nano-calcium carbonate modified nano-silica (mass of nano-calcium carbonate modified nano-silica in the dispersion) was mixed with five parts of CO2-responsive polyalkylamidine. After ultrasonic vibration for 25 min, the mixture was heated to 65℃ and stirred at 450 r / min for 3.5 h to obtain the final product.

[0088] Example 4

[0089] This embodiment provides a nano-modified CO2-responsive foam plugging agent, and the specific steps of its preparation method are as follows:

[0090] (1) Preparation method of nano-calcium carbonate modified nano-silica

[0091] Step 1: Disperse 1.5 parts of nano calcium carbonate in 7.5 parts of distilled water and stir until homogeneous;

[0092] Step 2: Add 1.5 parts of nano-silica to the solution from Step 1, and use ultrasonic vibration for 20 minutes to disperse the two evenly;

[0093] Step 3: Heat the solution from Step 2 to 62°C and keep it at that temperature for 25 hours while stirring at 400 r / min to obtain a dispersion of nano-calcium carbonate modified nano-silica.

[0094] (2) Preparation method of CO2-responsive polyalkylamidine

[0095] Step 1: Add 64.0 g (0.28 mol) of 1,14-tetradecyldiamine to a 250 mL four-necked flask equipped with a stirrer, constant pressure funnel, nitrogen purging device, and thermometer, then add 130 mL of methanol and stir until completely dissolved.

[0096] Step 2: Weigh 18.65 g (0.14 mol) of N,N-dimethylacetamide dimethyl acetal into a 50 mL beaker, add 8.06 g (0.07 mol) of catalyst L-proline and stir until homogeneous.

[0097] Step 3: Turn on the condenser and stir at 400-500 r / min. Slowly add the solution from Step 2 to the four-necked flask from Step 1 through a constant pressure funnel at a rate of 9 mL / min. After the addition is complete, introduce nitrogen gas and heat the mixture at 87℃ for 4.3 h under nitrogen protection.

[0098] Step 4: After the reaction is complete, the reaction mixture is subjected to rotary evaporation (40~60℃) to remove methanol, and a liquid product is obtained with a yield of 94%.

[0099] (3) Preparation method of nano-modified CO2-responsive foam plugging agent

[0100] Two parts of nano-calcium carbonate-modified nano-silica (mass of nano-calcium carbonate-modified nano-silica in the dispersion) were mixed with three parts of CO2-responsive polyalkylamidine. After ultrasonic vibration for 20 min, the mixture was heated to 60℃ and stirred at 400 r / min for 3 h to obtain the final product.

[0101] Example 5

[0102] This embodiment provides a nano-modified CO2-responsive foam plugging agent, and the specific steps of its preparation method are as follows:

[0103] (1) Preparation method of nano-calcium carbonate modified nano-silica

[0104] Step 1: Disperse 1 part of nano calcium carbonate in 5 parts of distilled water and stir well;

[0105] Step 2: Add 1.5 parts of nano-silica to the solution from Step 1, and use ultrasonic vibration for 20 minutes to disperse the two evenly;

[0106] Step 3: Heat the solution from Step 2 to 58°C and keep it at that temperature for 23 h with stirring at 350 r / min to obtain a dispersion of nano-calcium carbonate modified nano-silica.

[0107] (2) Preparation method of CO2-responsive polyalkylamidine

[0108] Step 1: Add 59.4 g (0.26 mol) of 1,14-tetradecyldiamine to a 250 mL four-necked flask equipped with a stirrer, constant pressure funnel, nitrogen purging device, and thermometer, then add 110 mL of methanol and stir until completely dissolved.

[0109] Step 2: Weigh 15.98 g (0.12 mol) of N,N-dimethylacetamide dimethyl acetal into a 50 mL beaker, add 10.33 g (0.06 mol) of the catalyst p-toluenesulfonic acid and stir until homogeneous.

[0110] Step 3: Turn on the condenser and stir at 400-500 r / min. Add the solution from Step 2 slowly dropwise to the four-necked flask from Step 1 at a rate of 10 mL / min through a constant pressure funnel. After the addition is complete, introduce nitrogen gas and heat the mixture at 90℃ for 4 h under nitrogen protection.

[0111] Step 4: After the reaction is complete, the reaction mixture is subjected to rotary evaporation (40~60℃) to remove methanol, and a liquid product is obtained with a yield of 91%.

[0112] (3) Preparation method of nano-modified CO2-responsive foam plugging agent

[0113] Two parts of nano-calcium carbonate-modified nano-silica (mass of nano-calcium carbonate-modified nano-silica in the dispersion) were mixed with four parts of CO2-responsive polyalkylamidine. After ultrasonic vibration for 25 min, the mixture was heated to 65℃ and stirred at 450 r / min for 3 h to obtain the final product.

[0114] Example 6

[0115] This embodiment provides a nano-modified CO2-responsive foam plugging agent, and the specific steps of its preparation method are as follows:

[0116] (1) Preparation method of nano-calcium carbonate modified nano-silica

[0117] Step 1: Disperse 1 part of nano calcium carbonate in 5 parts of distilled water and stir well;

[0118] Step 2: Add 2 parts of nano-silica to the solution from Step 1, and use ultrasonic vibration for 25 minutes to disperse the two evenly.

[0119] Step 3: Heat the solution from Step 2 to 65°C and keep it at that temperature for 25 h with stirring at 400 r / min to obtain a dispersion of nano-calcium carbonate modified nano-silica.

[0120] (2) Preparation method of CO2-responsive polyalkylamidine

[0121] Step 1: Add 52.5 g (0.23 mol) of 1,14-tetradecyldiamine to a 250 mL four-necked flask equipped with a stirrer, constant pressure funnel, nitrogen purging device, and thermometer, then add 110 mL of methanol and stir until completely dissolved.

[0122] Step 2: Weigh 17.31 g (0.13 mol) of N,N-dimethylacetamide dimethyl acetal into a 50 mL beaker, add 10.51 g (0.07 mol) of trifluoromethanesulfonic acid catalyst and stir until homogeneous.

[0123] Step 3: Turn on the condenser and stir at 400-500 r / min. Add the solution from Step 2 slowly dropwise to the four-necked flask from Step 1 through a constant pressure funnel at a rate of 6 mL / min. After the addition is complete, introduce nitrogen gas and heat the mixture at 85°C for 5 h under nitrogen protection.

[0124] Step 4: After the reaction is complete, the reaction mixture is subjected to rotary evaporation (40~60℃) to remove methanol, and a liquid product is obtained with a yield of 90%.

[0125] (3) Preparation method of nano-modified CO2-responsive foam plugging agent

[0126] Two parts of nano-calcium carbonate modified nano-silica (mass of nano-calcium carbonate modified nano-silica in the dispersion) were mixed with five parts of CO2-responsive polyalkylamidine. After ultrasonic vibration for 30 min, the mixture was heated to 70 °C and stirred at 500 r / min for 3.5 h to obtain the final product.

[0127] Comparative Example 1

[0128] This comparative example provides a nano-modified CO2-responsive foam plugging agent, which is prepared in a manner similar to that of Example 1, except that the catalyst is replaced with sulfuric acid in the preparation of CO2-responsive polyalkylamidine, and the yield of polyalkylamidine is 60%.

[0129] Comparative Example 2

[0130] This comparative example provides a nano-modified CO2-responsive foam plugging agent, the preparation method of which is as follows:

[0131] (1) Preparation method of nano-calcium carbonate modified nano-silica: same as in Example 1

[0132] (2) Preparation method of nano-modified CO2-responsive foam plugging agent

[0133] One part of nano-calcium carbonate-modified nano-silica (mass of nano-calcium carbonate-modified nano-silica in the dispersion) was mixed with three parts of single-chain alkylamidine. After ultrasonic vibration for 20 min, the mixture was heated to 60℃ and stirred at 400 r / min for 3 h to obtain the final product. The single-chain alkylamidine was N'-hexadecyl-N,N-diethylacetamidine prepared according to the preparation method in Example 1 of CN201710952052.2.

[0134] Comparative Example 3

[0135] This comparative example provides a nano-modified CO2-responsive foam plugging agent, which is prepared in basically the same way as in Example 1, except that 1,14-tetradecyldiamine is replaced with octadecyldiamine in the preparation of CO2-responsive polyalkylamidine.

[0136] Comparative Example 4

[0137] This comparative example provides a nano-modified CO2-responsive foam plugging agent, the preparation method of which is as follows:

[0138] (1) Preparation method of CO2-responsive polyalkylamidine: same as in Example 1.

[0139] (2) Preparation method of nano-modified CO2-responsive foam plugging agent

[0140] One part of unmodified nano-calcium carbonate nano-silica (added as a 20% concentration aqueous dispersion, the mass of which is the mass of nano-silica in the dispersion) was mixed with three parts of CO2-responsive polyalkylamidine. After ultrasonic vibration for 20 min, the mixture was heated to 60℃ and stirred at 400 r / min for 3 h to obtain the final product.

[0141] Comparative Example 5

[0142] The conventional foaming agent was purchased from a chemical company. This conventional foaming agent is an azodicarbonamide environmentally friendly foaming agent.

[0143] Test Example 1

[0144] To verify the molecular structure of the CO2-responsive polyalkylamidinium of this application, infrared spectroscopy and nuclear magnetic resonance (NMR) were performed on the CO2-responsive polyalkylamidinium in this study. The results of the infrared spectroscopy and NMR are as follows: Figure 1 and Figure 2 As shown.

[0145]

[0146] Infrared spectrum of CO2-responsive polyalkylamidinium powder from Figure 1 It can be seen that at 3480cm -1 3400cm -1 2970cm -1 2860cm -1 1660cm -1 1245cm -1 1190 cm -1 A strong absorption peak appears near 3480 cm⁻¹. -1 3400cm -1 Two absorption peaks appear, which are the stretching vibration absorption peaks of the -NH2 group, at 2970 cm⁻¹. -1The nearby peak is a stretching vibration peak of -CH3. 2860 cm⁻¹ -1 1470 cm -1 Nearby are the stretching and bending vibration peaks of -CH-, 1344 cm⁻¹ -1 The nearby peak is the bending vibration absorption peak of -CH2-, at 1660 cm⁻¹. -1 The absorption peak is located near the -NH2 bending vibration at 1245 cm⁻¹. -1 The nearby peak is the -N(CH3)2 stretching vibration peak, at 1190 cm⁻¹. -1 The peaks near the point are those of CN stretching vibration. These results indicate that the CO2-responsive multi-chain alkylamidinium molecule contains groups such as -CH3, -CH2-, -CH, -CN, -NH2, and -N(CH3)2, consistent with the aforementioned molecular structure.

[0147] Figure 2 The 1H NMR spectrum (400 MHz, CD3CN) of the CO2-responsive polyalkylamidine powder in Example 1 of this invention is as follows: δ 2.82 (s, 12H), 2.61 (s, 4H), 1.85 (s, 6H), 1.52 -1.20 (m, 84H). The 1H NMR spectrum is consistent with the above molecular structure.

[0148] Test Example 2

[0149] The performance of the nano-modified CO2-responsive foam plugging agents of Examples 1-6 and the conventional foaming agent of Comparative Example 5 were evaluated.

[0150] Evaluation indicators include: oil resistance (foaming volume and half-life), anti-adsorption (foaming volume and half-life), high-temperature and high-pressure foam plugging performance, and surface tension.

[0151] Oil resistance and anti-adsorption testing methods: Refer to the enterprise standard of Dagang Oilfield Binhai Petroleum Technology Group Co., Ltd.: Q / BGBH 0063-2022 Standard Evaluation of Alkyl Amidine for Foaming Agents.

[0152] Testing method for high-temperature and high-pressure foam plugging performance (temperature and salt resistance): measured by resistance factor. Natural cores and produced water from a low-permeability block in Dagang Oilfield were selected. Under conditions of 10855 mg / L salinity (high salinity), 80℃, and 4 MPa formation pressure, a HAYX multi-functional physical simulation experimental instrument for foam displacement (produced by Haian Petroleum) was used. With a back pressure of 4 MPa, the pressure difference P1 across the core was measured when the water permeability of the natural core was measured. A 0.2% nano-modified CO2-responsive foam plugging agent solution was prepared using formation water. The solution was injected using an alternating water-gas injection method with a gas-liquid ratio of 1:1, an injection rate of 0.1 mL / min, and a slug size of 0.1 PV. The pressure difference P2 across the foam-driven core was measured, and the resistance factor was calculated as P2 / P1. Performance comparison with conventional foaming agents showed advantages such as low surface tension, oil resistance, anti-adsorption, and high-temperature and high-pressure foam plugging performance. The results are shown in Tables 1 and 2 below.

[0153] Surface tension testing method: The surface tension was evaluated according to GB / T 5549-2010 standard. The sample (nano-modified CO2-responsive foam plugging agent) was prepared into solutions with formation water at concentrations of 0.2% and 0.3%, respectively.

[0154] Table 1 Oil resistance, anti-adsorption properties and high-temperature, high-pressure foam plugging performance

[0155]

[0156] Table 2 Surface Tension

[0157]

[0158] As can be seen from the above results, the nano-modified CO2-responsive foam plugging agent prepared in the embodiments of the present invention can play a role in preventing gas channeling and sealing fractures by absorbing CO2. It is a high-efficiency plugging agent that can be used in conjunction with CO2 flooding technology in oil fields and can be applied on a large scale.

[0159] Test Example 3

[0160] The surface tension, foaming properties under oil resistance and anti-adsorption conditions, foam plugging performance under high temperature and high pressure, and degradability of the products obtained in Example 1 and Comparative Examples 1-5 were tested.

[0161] Surface tension was tested according to GB / T 5549-2010;

[0162] Tested according to enterprise standard Q / BGBH 0063-2022: oil resistance, anti-adsorption, and high-temperature and high-pressure foam plugging performance;

[0163] Degradability was tested according to GB / T 19277.1.

[0164] The results are shown in Table 3.

[0165] Table 3 Surface tension, foaming properties, foam plugging performance under high temperature and high pressure, and degradability

[0166]

[0167] As can be seen from the above results, compared with Comparative Examples 1-5, the nano-modified CO2-responsive foam plugging agent prepared in Example 1 of this invention has lower surface tension, superior oil resistance, anti-adsorption foaming properties, better foaming effect, and superior high-temperature and high-pressure foam plugging performance (the higher the resistance factor, the better the high-temperature and high-pressure foam plugging performance), indicating that it has better foam stability and temperature and salt resistance, and a superior plugging effect; in addition, it also has the characteristic of easy degradation, which can avoid oil layer pollution and formation blockage. It is a green and efficient plugging agent with great application value.

[0168] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A nano-modified CO2-responsive multi-chain alkyl amidine, characterized in that: Its structural formula is as follows: Where R = C 14 H 28 ; The preparation method comprises the following steps: S1, reacting N,N-dimethylacetamide dimethyl acetal with 1,14-tetradecyl diamine in the presence of a catalyst through an amide acetal method to generate a multi-chain alkyl amidine; S2. Mix the nano-silicon dioxide modified by nano-calcium carbonate with the multi-chain alkyl amidine, disperse them evenly by ultrasonication, heat them to 60-70°C, and then keep them warm for reaction for 3-4 hours under stirring to obtain the nano-modified CO2-responsive multi-chain alkyl amidine; the preparation method of the nano-silicon dioxide modified by nano-calcium carbonate is as follows: disperse 1-1.5 parts of calcium carbonate evenly in water, add 1.5-2 parts of nano-silicon dioxide, disperse them by ultrasonication, and then heat them to 55-65°C, and keep them warm for reaction for at least 20 hours under stirring to obtain a dispersion of the nano-silicon dioxide modified by nano-calcium carbonate.

2. Use of the nano-modified CO2-responsive multi-chain alkyl amidine according to claim 1 in the preparation of a CO2-responsive foam plugging agent.

3. A CO2 responsive foam plugging agent, characterized in that: It is made from the nano-modified CO2-responsive multi-chain alkyl amidine described in claim 1.

4. The CO2 responsive foam plugging agent according to claim 3, characterized in that: The nano-modified CO2 responsive multi-chain alkyl amidine is the main component or the only component of the CO2 responsive foam plugging agent.

5. The method for preparing the nano-modified CO2-responsive multi-chain alkyl amidine according to claim 1, characterized in that: The following steps are involved: S1, N, N-dimethylacetamide dimethyl acetal and 1, 14-tetradecyl diamine are reacted in the presence of a catalyst to generate a multi-chain alkyl amidine through an amide acetal method; S2. Mix the nano-silica modified with nano-calcium carbonate with the multi-chain alkyl amidine, disperse them uniformly by ultrasonication, heat them to 60-70°C, and then keep them warm for 3-4 hours under stirring to obtain the nano-modified CO2-responsive multi-chain alkyl amidine.

6. The preparation method according to claim 5, characterized in that: The preparation method of the multi-chain alkyl amidine in S1 is: dissolving 1,14-tetradecyl diamine in methanol to obtain a 1,14-tetradecyl diamine solution; mixing the N,N-dimethylacetamide dimethyl acetal with the catalyst, and then dripping it into the 1,14-tetradecyl diamine solution at a rate of 23.6% to 43.5% v / v per minute, and reacting at 80 to 90° C. in an inert atmosphere for at least 4 hours after the dripping is completed; after the reaction is completed, removing methanol from the reaction mixture, and the obtained liquid product is the multi-chain alkyl amidine; and / or The molar ratio of the 1,14-tetradecyl diamine to the N,N-dimethylacetamide dimethyl acetal in S1 is 1:(0.46-0.68); and / or The catalyst in S1 is selected from L-proline, p-toluenesulfonic acid or trifluoromethanesulfonic acid.

7. The preparation method according to claim 6, characterized in that: The molar ratio of the N,N-dimethylacetamide dimethyl acetal to the catalyst in S1 is (1.5-2.5):1; and / or Each mole of the 1,14-tetradecyl diamine is dissolved in 420-546 mL of the methanol.

8. The preparation method according to claim 5, characterized in that: The preparation method of the nano-silicon dioxide modified by nano-calcium carbonate described in S2 is: disperse 1-1.5 parts of calcium carbonate evenly in water, add 1.5-2 parts of nano-silicon dioxide, disperse by ultrasonic, then heat to 55-65°C, and keep the temperature under stirring for at least 20 hours to obtain the dispersion of the nano-silicon dioxide modified by nano-calcium carbonate.

9. The preparation method according to claim 8, characterized in that: The rotation speed of the stirring state is 300-400 r / min.

10. The preparation method according to any one of claims 5 to 9, characterized in that: The mass ratio of the nano-silicon dioxide modified by nano-calcium carbonate in the dispersion of the nano-silicon dioxide modified by nano-calcium carbonate in S2 to the mass ratio of the polyalkyl amidine is (1-2):(3-5); and / or The ultrasonic dispersion time in S2 is 20 to 30 min; and / or The stirring speed in the stirring state described in S2 is 400~500 r / min.

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