Nano-modified CO2 response foam plugging agent and preparation method thereof

Abstract

The invention belongs to the technical field of oil exploitation foam plugging agents, and particularly relates to nano-modified CO2 multi-chain alkyl amidine, a CO2 response foam plugging agent, a preparation method and application. The CO2-responsive multi-chain alkyl amidine provided by the invention is obtained by electrostatic adsorption of an active adsorption center (tertiary carbon or tertiary nitrogen) of the multi-chain alkyl amidine and part of negatively charged nano silicon dioxide-calcium carbonate, is sensitive in stimulation response to CO2, has good foaming amount, foam stability and temperature and salt resistance, is environment-friendly and easy to degrade, and has a good application prospect. The foam plugging agent can avoid pollution of an oil layer and plugging of a stratum and can be used for preparing a CO2 response foam plugging agent.

Description

Technical Field

[0001] The invention belongs to the technical field of foam plugging agents for petroleum exploitation, and in particular relates to a nano-modified CO2 multi-chain alkyl amidine, a CO2 responsive foam plugging agent, and a preparation method and application thereof. Background Art

[0002] At present, under the background of international energy shortage, the international community advocating energy conservation and emission reduction, and the difficulty of oil extraction in my country, major oil fields in my country are actively upgrading their technology. CO2 flooding technology is mature and has been applied on a large scale abroad. It can increase the recovery rate by more than 10% in the process of exploitation of low-permeability oil reservoirs, which has positive significance for my country's energy development. However, in the process of field application of CO2 flooding technology, due to the existence of reservoir fractures, CO2 will inevitably flow along the fractures, which will not only reduce the recovery efficiency of CO2 for crude oil, resulting in unsatisfactory extraction results, but also cause CO2 discharge to cause environmental pollution.

[0003] In the prior art, the solution based on environmental protection and non-pollution to the formation is usually to seal the cracks with foam plugging agents. However, conventional plugging agents have problems such as low foaming volume, poor foam stability, poor temperature and salt resistance, and the sealing effect is not ideal. Summary of the invention

[0004] In view of the above technical problems, the present invention provides a nano-modified CO2 multi-chain alkyl amidine, a CO2 responsive foam plugging agent, and a preparation method and application. The nano-modified CO2 multi-chain alkyl amidine provided by the present invention is obtained by electrostatic adsorption of the active adsorption center (tertiary carbon or tertiary nitrogen) of the multi-chain alkyl amidine and partially negatively charged nano-silicon dioxide-calcium carbonate, has a specific absorption effect on CO2, a high foaming volume, good foam stability and temperature and salt resistance, and is environmentally friendly and easy to degrade. It can be used to make a foam plugging agent for CO2 measures to prevent gas channeling and improve the recovery rate.

[0005] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solutions: The first aspect of the present invention provides a nano-modified CO2-responsive multi-chain alkyl amidine, the structural formula of which is shown below:

[0006] Where R = C 14 H 28 .

[0007] The nano-modified CO2-responsive multi-chain alkyl amidine is obtained by electrostatic adsorption of the active adsorption center (tertiary carbon or tertiary nitrogen) of the multi-chain alkyl amidine and partially negatively charged nano-silicon dioxide (SiO2)-calcium carbonate (CaCO3). The multi-chain alkyl amidine has a specific absorption effect on CO2 and is a CO2-responsive multi-chain alkyl amidine. Compared with single-chain alkyl ethers, on the one hand, the multi-chain alkyl amidine is more sensitive to the stimulation of CO2, and on the other hand, the protonation of the multi-chain alkyl amidine combines with CO2 to form a multi-chain alkyl amidine bicarbonate, which has more long-chain lipophilic tail groups (R=C 14 H 28 ), thus having lower surface tension, better foaming effect, higher foaming volume and foam stability, and thus being able to improve crude oil recovery. By adsorbing some negatively charged nano-silica on the active adsorption center (tertiary carbon or tertiary nitrogen) of the multi-chain alkyl amidine, combined with the cubic structure of nano-scale calcium carbonate, the dual effects of increasing strength and modification can be achieved, improving its temperature resistance and salt resistance, and further improving its stability. The CO2-responsive foam plugging agent made with the nano-modified CO2-responsive multi-chain alkyl amidine as the main component or the only component can achieve the purpose of high-strength plugging of geological reservoir fractures.

[0008] The second aspect of the present invention provides the use of the above-mentioned nano-modified CO2 responsive multi-chain alkyl amidine in the preparation of a CO2 responsive foam plugging agent.

[0009] The third aspect of the present invention provides a CO2 responsive foam plugging agent, which is made of the above-mentioned nano-modified CO2 responsive multi-chain alkyl amidine.

[0010] Preferably, the nano-modified CO2 responsive multi-chain alkyl amidine is the main component or the only component of the CO2 responsive foam plugging agent.

[0011] The fourth aspect of the present invention provides a method for preparing the above-mentioned nano-modified CO2-responsive multi-chain alkyl amidine, comprising the following steps: 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.

[0012] The preparation method first uses polyamine as a raw material to generate a multi-chain alkyl amidine (systematically named 4,19-bis(14-aminotetradecyl)-2,3,20,21-tetramethyl-2,4,19,21-tetraazadocosane) through an amide acetal method. The reaction mechanism of this step is as follows:

[0013] For the multi-chain alkyl amidine, the preparation method uses nano-silicon dioxide modified by nano-scale calcium carbonate to modify it in a surface modification manner, so that the multi-chain alkyl amidine and Nano-SiO2-CaCO3 are electrostatically adsorbed to form nano-modified CO2-responsive multi-chain alkyl amidine.

[0014] Preferably, 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 23.5%~43.5% v / v per minute, and reacting at 80~90°C in an inert atmosphere for at least 4 hours after the dripping is completed; after the reaction is completed, methanol is removed from the reaction mixture, and the obtained liquid product is the multi-chain alkyl amidine. Wherein adding 23.6%~43.5% per minute means adding 23.6%~43.5% of the total volume of the mixture of N,N-dimethylacetamide dimethyl acetal and the catalyst per minute. Preferably, the molar ratio of the 1,14-tetradecyl diamine to the N,N-dimethylacetamide dimethyl acetal in S1 is 1:(0.46-0.68).

[0015] 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, aluminum oxide, etc., it has stronger activity, can greatly improve the reaction efficiency, reduce the generation of by-products, and ensure the yield of multi-chain alkyl amidine in the product.

[0016] Further preferably, the molar ratio of the N,N-dimethylacetamide dimethyl acetal to the catalyst in S1 is (1.5-2.5):1.

[0017] Optionally, the method for removing methanol from the reaction mixture can be to remove it at 40-60° C. by rotary evaporation or the like.

[0018] Preferably, 420-546 mL of the methanol is used to dissolve each mole of the 1,14-tetradecyl diamine.

[0019] Preferably, the preparation method of the nano-silicon dioxide modified by nano-calcium carbonate in S2 is: disperse 1-1.5 parts of calcium carbonate evenly in water, add 1.5-2 parts of nano-silicon dioxide, ultrasonically disperse, and then heat to 55-65°C, and keep the temperature under stirring for at least 20 hours to obtain a dispersion of the nano-silicon dioxide modified by nano-calcium carbonate.

[0020] More preferably, the rotation speed in the stirring state is 300-400 r / min.

[0021] Preferably, the mass ratio of the nano-silicon dioxide modified with nano-calcium carbonate to the polyalkyl amidine in the dispersion of the nano-silicon dioxide modified with nano-calcium carbonate in S2 is (1-2):(3-5).

[0022] Optionally, the ultrasonic dispersion time in S2 is 20 to 30 min.

[0023] Preferably, the stirring speed in the stirring state in S2 is 400-500 r / min.

[0024] The beneficial effects of the present invention are: (1) The nano-modified CO2-responsive multi-chain alkyl amidine provided by the present invention combines with CO2 to form multi-chain alkyl amidine bicarbonate through the protonation of the multi-chain alkyl amidine. Compared with the currently commonly used single-chain amidine, the multi-chain alkyl amidine of the present invention can adsorb more CO2 and is more sensitive to the stimulation of CO2. At the same time, the multi-chain alkyl amidine bicarbonate has a long-chain lipophilic tail group (R=C 14 H 28 ), has lower surface tension and higher surface activity, thus has better foaming volume and foam stability, better foaming effect, and can greatly improve the foam blocking effect; (2) The preparation method of the nano-modified CO2-responsive multi-chain alkyl amidine provided by the present invention first uses a polyamine to synthesize a multi-chain alkyl amidine through an acetal reaction under the action of a catalyst, and then modifies it with nano-silicon dioxide (Nano-SiO2-CaCO3) modified by nano-calcium carbonate, and further fills the tetrahedral spatial structure of silica with the cubic structure of nano-calcium carbonate to form a more compact and firm spatial network structure, thereby greatly improving the stability and temperature and salt resistance of the foam. Therefore, after nano-modification, the obtained product has excellent oil resistance, and the foam stability under reservoir conditions is significantly improved, thereby being able to expand the swept volume of CO2 throughput and improve oil recovery efficiency.

[0025] (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. It has a reversible response to CO2 and can form bicarbonate after absorbing CO2. It has a high efficiency in plugging cracks in low-permeability and ultra-low-permeability heterogeneous oil reservoirs that are prone to CO2 gas breakthrough. When N2 or air is introduced, it can be decomposed into neutral amidine to eliminate foaming and will not block the formation. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is the infrared spectrum of the CO2-responsive multi-chain alkyl amidine powder in Test Example 1 of the present invention; Figure 2 This is the H NMR spectrum of the CO2-responsive multi-chain alkyl amidine powder in Test Example 1 of the present invention. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work fall within the scope of protection of the present invention.

[0028] In order to solve the problem of unsatisfactory displacement effect caused by gas channeling during CO2 flooding, the existing technology often uses easily degradable foam plugging agents to block gas channeling channels. However, conventional foam plugging agents have problems such as poor oil resistance, low foaming volume, poor foam stability, and poor temperature and salt resistance.

[0029] In view of the above problems, an embodiment of the present invention provides a nano-modified CO2-responsive multi-chain alkyl amidine, the structural formula of which is shown below:

[0030] Where R = C 14 H 28 .

[0031] The embodiment of the present invention also provides the use of the above-mentioned nano-modified CO2 responsive multi-chain alkyl amidine in the preparation of a CO2 responsive foam plugging agent.

[0032] The embodiment of the present invention also provides a CO2 responsive foam plugging agent.

[0033] The present invention also provides a method for preparing the above-mentioned nano-modified CO2-responsive multi-chain alkyl amidine, comprising the following steps: 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 foam plugging agent.

[0034] The scheme of the present invention is described below through specific embodiments.

[0035] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0036] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0037] Example 1 This embodiment provides a nano-modified CO2-responsive foam plugging agent, and the specific steps of the preparation method thereof are as follows: (1) Preparation method of nano-silicon dioxide modified by nano-calcium carbonate Step 1: Disperse 1 part of nano calcium carbonate in 5 parts of distilled water and stir evenly; Step 2: Add 1.5 parts of nano-silicon dioxide to the solution in step 1, and use ultrasonic vibration for 15 minutes to make the two dispersed evenly; Step 3: Heat the solution of step 2 to 55°C, stir at 300 r / min, and keep the temperature for 20 h to obtain a dispersion of nano-silicon dioxide modified with nano-calcium carbonate.

[0038] (2) Preparation method of CO2-responsive multi-chain alkyl amidine Step 1: Add 45.7 g (0.2 mol) of 1,14-tetradecyl diamine to a 250 mL four-necked flask equipped with a stirrer, a constant pressure funnel, a nitrogen flow device, and a thermometer, and then add 100 mL of methanol and stir to completely dissolve.

[0039] 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 evenly.

[0040] Step 3: Turn on the condensing device, stir at a speed of 400-500 r / min, and slowly add the solution in step 2 to the four-necked flask in step 1 through a constant pressure funnel at a rate of 5 mL / min. After the addition is completed, nitrogen is introduced and the reaction is heated at 80°C for 4 h under nitrogen protection.

[0041] Step 4: After the reaction is completed, the reaction mixture is subjected to rotary evaporation (40-60°C) to remove methanol to obtain a liquid product with a yield of 92%.

[0042] (3) Preparation method of nano-modified CO2-responsive foam plugging agent Mix 1 part of nano-calcium carbonate-modified nano-silica (the mass of nano-calcium carbonate-modified nano-silica in the dispersion) with 3 parts of CO2-responsive multi-chain alkyl amidine, oscillate with ultrasound for 20 min, heat to 60°C, stir at 400 r / min, and keep warm for 3 h to obtain the final product.

[0043] Example 2 This embodiment provides a nano-modified CO2-responsive foam plugging agent, and the specific steps of the preparation method thereof are as follows: (1) Preparation method of nano-silicon dioxide modified by nano-calcium carbonate Step 1: Disperse 1 part of nano calcium carbonate in 5 parts of distilled water and stir evenly; Step 2: Add 2 parts of nano-silicon dioxide to the solution in step 1, and use ultrasonic vibration for 20 minutes to make the two dispersed evenly; Step 3: Heat the solution of step 2 to 65°C, stir at 400 r / min, and keep the temperature for 24 hours to obtain a dispersion of nano-silicon dioxide modified with nano-calcium carbonate.

[0044] (2) Preparation method of CO2-responsive multi-chain alkyl amidine Step 1: Add 57.1 g (0.25 mol) of 1,14-tetradecyl diamine to a 250 mL four-necked flask equipped with a stirrer, a constant pressure funnel, a nitrogen flow device, and a thermometer, and then add 115 mL of methanol and stir to completely dissolve it.

[0045] 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 evenly.

[0046] Step 3: Turn on the condensing device, stir at 400-500 r / min, and slowly add the solution in step 2 to the four-necked flask in step 1 through a constant pressure funnel at a rate of 7 mL / min. After the addition is completed, nitrogen is introduced and the reaction is heated at 90°C for 5 h under nitrogen protection.

[0047] Step 4: After the reaction is completed, the reaction mixture is subjected to rotary evaporation (40-60°C) to remove methanol to obtain a liquid product with a yield of 93%.

[0048] (3) Preparation method of nano-modified CO2-responsive foam plugging agent Mix 1 part of nano-calcium carbonate-modified nano-silica (the mass of nano-calcium carbonate-modified nano-silica in the dispersion) with 4 parts of CO2-responsive multi-chain alkyl amidine, oscillate with ultrasound for 30 min, heat to 70°C, stir at 500 r / min, and react for 4 h to obtain the final product.

[0049] Example 3 This embodiment provides a nano-modified CO2-responsive foam plugging agent, and the specific steps of the preparation method thereof are as follows: (1) Preparation method of nano-silicon dioxide modified by nano-calcium carbonate Step 1: Disperse 1.5 parts of nano calcium carbonate in 7.5 parts of distilled water and stir evenly; Step 2: Add 2 parts of nano-silicon dioxide to the solution in step 1, and use ultrasonic vibration for 18 minutes to make the two dispersed evenly; Step 3: Heat the solution of step 2 to 60°C, stir at 350 r / min, and keep the temperature for 22 h to obtain a dispersion of nano-silicon dioxide modified with nano-calcium carbonate.

[0050] (2) Preparation method of CO2-responsive multi-chain alkyl amidine Step 1: Add 50.3 g (0.22 mol) of 1,14-tetradecyl diamine to a 250 mL four-necked flask equipped with a stirrer, a constant pressure funnel, a nitrogen flow device, and a thermometer, and then add 120 mL of methanol and stir to completely dissolve it.

[0051] 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 catalyst trifluoromethanesulfonic acid and stir evenly.

[0052] Step 3: Turn on the condensing device, stir at a speed of 400-500 r / min, and slowly add the solution in step 2 to the four-necked flask in step 1 through a constant pressure funnel at a rate of 8 mL / min. After the addition is completed, nitrogen is introduced and the reaction is heated at 85°C for 4.5 h under nitrogen protection.

[0053] Step 4: After the reaction is completed, the reaction mixture is subjected to rotary evaporation (40-60°C) to remove methanol to obtain a liquid product with a yield of 90%.

[0054] (3) Preparation method of nano-modified CO2-responsive foam plugging agent 1 part of nano-calcium carbonate-modified nano-silica (the mass of nano-calcium carbonate-modified nano-silica in the dispersion) was mixed with 5 parts of CO2-responsive multi-chain alkyl amidine, and after ultrasonic vibration for 25 min, the temperature was raised to 65°C, and the mixture was stirred at 450 r / min for 3.5 h to obtain the final product.

[0055] Example 4 This embodiment provides a nano-modified CO2-responsive foam plugging agent, and the specific steps of the preparation method thereof are as follows: (1) Preparation method of nano-silicon dioxide modified by nano-calcium carbonate Step 1: Disperse 1.5 parts of nano calcium carbonate in 7.5 parts of distilled water and stir evenly; Step 2: Add 1.5 parts of nano-silicon dioxide to the solution in step 1, and use ultrasonic vibration for 20 minutes to make the two dispersed evenly; Step 3: Heat the solution of step 2 to 62° C., stir at 400 r / min, and keep the temperature for 25 hours to obtain a dispersion of nano-silicon dioxide modified with nano-calcium carbonate.

[0056] (2) Preparation method of CO2-responsive multi-chain alkyl amidine Step 1: Add 64.0 g (0.28 mol) of 1,14-tetradecyl diamine to a 250 mL four-necked flask equipped with a stirrer, a constant pressure funnel, a nitrogen flow device, and a thermometer, and then add 130 mL of methanol and stir to completely dissolve.

[0057] 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 evenly.

[0058] Step 3: Turn on the condensing device, stir at 400-500 r / min, and slowly add the solution in step 2 to the four-necked flask in step 1 through a constant pressure funnel at a rate of 9 mL / min. After the addition is complete, nitrogen is introduced and the reaction is heated at 87°C for 4.3 h under nitrogen protection.

[0059] Step 4: After the reaction is completed, the reaction mixture is subjected to rotary evaporation (40-60°C) to remove methanol to obtain a liquid product with a yield of 94%.

[0060] (3) Preparation method of nano-modified CO2-responsive foam plugging agent Mix 2 parts of nano-calcium carbonate-modified nano-silica (the mass of nano-calcium carbonate-modified nano-silica in the dispersion) with 3 parts of CO2-responsive multi-chain alkyl amidine, oscillate with ultrasound for 20 min, heat to 60°C, stir at 400 r / min, and react for 3 h to obtain the final product.

[0061] Example 5 This embodiment provides a nano-modified CO2-responsive foam plugging agent, and the specific steps of the preparation method thereof are as follows: (1) Preparation method of nano-silicon dioxide modified by nano-calcium carbonate Step 1: Disperse 1 part of nano calcium carbonate in 5 parts of distilled water and stir evenly; Step 2: Add 1.5 parts of nano-silicon dioxide to the solution in step 1, and use ultrasonic vibration for 20 minutes to make the two dispersed evenly; Step 3: Heat the solution of step 2 to 58°C, stir at 350 r / min, and keep the temperature for 23 h to obtain a dispersion of nano-silicon dioxide modified with nano-calcium carbonate.

[0062] (2) Preparation method of CO2-responsive multi-chain alkyl amidine Step 1: Add 59.4 g (0.26 mol) of 1,14-tetradecyl diamine to a 250 mL four-necked flask equipped with a stirrer, a constant pressure funnel, a nitrogen flow device, and a thermometer, and then add 110 mL of methanol and stir to completely dissolve.

[0063] 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 catalyst p-toluenesulfonic acid and stir evenly.

[0064] Step 3: Turn on the condensing device, stir at 400-500 r / min, and slowly add the solution in step 2 to the four-necked flask in step 1 through a constant pressure funnel at a rate of 10 mL / min. After the addition is completed, nitrogen is introduced and the reaction is heated at 90°C for 4 h under nitrogen protection.

[0065] Step 4: After the reaction is completed, the reaction mixture is subjected to rotary evaporation (40-60°C) to remove methanol to obtain a liquid product with a yield of 91%.

[0066] (3) Preparation method of nano-modified CO2-responsive foam plugging agent Mix 2 parts of nano-calcium carbonate-modified nano-silica (the mass of nano-calcium carbonate-modified nano-silica in the dispersion) with 4 parts of CO2-responsive multi-chain alkyl amidine, oscillate with ultrasound for 25 min, heat to 65°C, stir at 450 r / min, and react for 3 h to obtain the final product.

[0067] Example 6 This embodiment provides a nano-modified CO2-responsive foam plugging agent, and the specific steps of the preparation method thereof are as follows: (1) Preparation method of nano-silicon dioxide modified by nano-calcium carbonate Step 1: Disperse 1 part of nano calcium carbonate in 5 parts of distilled water and stir evenly; Step 2: Add 2 parts of nano-silicon dioxide to the solution in step 1, and use ultrasonic vibration for 25 minutes to make the two dispersed evenly; Step 3: Heat the solution of step 2 to 65°C, stir at 400 r / min, and keep the temperature for 25 h to obtain a dispersion of nano-silicon dioxide modified with nano-calcium carbonate.

[0068] (2) Preparation method of CO2-responsive multi-chain alkyl amidine Step 1: Add 52.5 g (0.23 mol) of 1,14-tetradecyl diamine to a 250 mL four-necked flask equipped with a stirrer, a constant pressure funnel, a nitrogen flow device, and a thermometer, and then add 110 mL of methanol and stir to completely dissolve.

[0069] 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 catalyst trifluoromethanesulfonic acid and stir evenly.

[0070] Step 3: Turn on the condensing device, stir at a speed of 400-500 r / min, and slowly add the solution in step 2 to the four-necked flask in step 1 through a constant pressure funnel at a rate of 6 mL / min. After the addition is completed, nitrogen is introduced and the reaction is heated at 85°C for 5 h under nitrogen protection.

[0071] Step 4: After the reaction is completed, the reaction mixture is subjected to rotary evaporation (40-60°C) to remove methanol to obtain a liquid product with a yield of 90%.

[0072] (3) Preparation method of nano-modified CO2-responsive foam plugging agent Mix 2 parts of nano-calcium carbonate-modified nano-silica (the mass of nano-calcium carbonate-modified nano-silica in the dispersion) with 5 parts of CO2-responsive multi-chain alkyl amidine, and after ultrasonic vibration for 30 minutes, heat to 70°C, stir at 500 r / min, and keep warm for 3.5 hours to obtain the final product.

[0073] Comparative Example 1 This comparative example provides a nano-modified CO2 responsive foam plugging agent, and its preparation method is basically the same as that of Example 1, except that in the preparation of CO2 responsive multi-chain alkyl amidine, the catalyst is replaced by sulfuric acid, and the yield of multi-chain alkyl amidine is 60%.

[0074] Comparative Example 2 This comparative example provides a nano-modified CO2-responsive foam plugging agent, the preparation method of which is as follows: (1) Preparation method of nano-silicon dioxide modified by nano-calcium carbonate: same as Example 1 (2) Preparation method of nano-modified CO2-responsive foam plugging agent 1 part of nano-calcium carbonate-modified nano-silicon dioxide (the mass of nano-calcium carbonate-modified nano-silicon dioxide in the dispersion) was mixed with 3 parts of single-chain alkyl amidine, and after ultrasonic vibration for 20 minutes, the temperature was raised to 60°C, and the mixture was stirred at 400 r / min for 3 hours to obtain the final product. The single-chain alkyl amidine was N'-hexadecyl-N,N-diethylacetamidine prepared according to the preparation method of Example 1 in CN201710952052.2.

[0075] Comparative Example 3 This comparative example provides a nano-modified CO2 responsive foam plugging agent, and its preparation method is basically the same as that of Example 1, except that 1,14-tetradecyl diamine is replaced by octadecyl diamine in the preparation of CO2 responsive multi-chain alkyl amidine.

[0076] Comparative Example 4 This comparative example provides a nano-modified CO2-responsive foam plugging agent, the preparation method of which is as follows: (1) Preparation method of CO2 responsive multi-chain alkyl amidine: same as Example 1.

[0077] (2) Preparation method of nano-modified CO2-responsive foam plugging agent One part of nano-silica that has not been modified with nano-calcium carbonate (added in the form of a 20% aqueous dispersion, the mass being the mass of the nano-silica in the dispersion) was mixed with 3 parts of CO2-responsive multi-chain alkyl amidine, and after ultrasonic vibration for 20 min, the temperature was raised to 60°C, and the mixture was stirred at 400 r / min for 3 h to obtain the final product.

[0078] Comparative Example 5 The conventional foaming agent was purchased from a chemical company. The conventional foaming agent is an azodicarbonamide environmentally friendly foaming agent.

[0079] Test Example 1 In order to verify the molecular structure of the CO2-responsive multi-chain alkyl amidine of the present invention, the present invention conducted infrared spectroscopy, nuclear magnetic resonance and other tests on the CO2-responsive multi-chain alkyl amidine in the study. The infrared spectroscopy and nuclear magnetic resonance test results are as follows: Figure 1 and Figure 2 shown.

[0080]

[0081] CO2 responsive multi-chain alkyl amidine powder infrared spectrum Figure 1 It can be seen that at 3480cm -1 , 3400cm -1 , 2970cm -1 , 2860cm -1 , 1660cm -1, 1245cm -1 , 1190 cm -1 There are strong absorption peaks near 3480 cm -1 、3400cm -1 , there are two absorption peaks, which are the stretching vibration absorption peaks of -NH2 group, 2970cm -1 Nearby is the stretching vibration peak of -CH3. 2860 cm -1 , 1470 cm -1 Nearby are the stretching vibration peak and bending vibration peak of -CH-, 1344 cm -1 Nearby is the bending vibration absorption peak of -CH2-, 1660 cm -1 Nearby is the -NH2 bending vibration absorption peak, 1245cm -1 Nearby is the -N(CH3)2 stretching vibration peak, 1190cm -1 Nearby is the stretching vibration peak of CN. The above results show that the CO2-responsive multi-chain alkyl amidine molecular structure contains group structures such as -CH3, -CH2-, -CH, -CN, -NH2, and -N(CH3)2, which is consistent with the above molecular structure.

[0082] Figure 2 The CO2 response multi-chain alkyl amidine powder hydrogen spectrum (400 MHz, CD3CN) in the test example 1 of the present invention is: δ 2.82 (s, 12H), 2.61 (s, 4H), 1.85 (s, 6H), 1.52 -1.20 (m, 84H). The nuclear magnetic resonance hydrogen spectrum is consistent with the above molecular structure.

[0083] Test Example 2 The performance of the nano-modified CO2 responsive foam plugging agents of Examples 1 to 6 and the conventional foaming agent of Comparative Example 5 were evaluated respectively.

[0084] Evaluation indicators include: oil resistance (foaming volume and half-life), adsorption resistance (foaming volume and half-life), high temperature and high pressure foam sealing performance and surface tension.

[0085] Oil resistance and anti-adsorption test method: refer to the corporate standard of Dagang Oilfield Bingang Petroleum Technology Group Co., Ltd.: Q / BGBH 0063-2022 Foaming agent alkyl amidine standard evaluation.

[0086] High-temperature and high-pressure foam plugging performance (temperature resistance and salt resistance) detection method: measured by resistance factor. The natural core and formation produced water of a low-permeability block in Dagang Oilfield were selected. At a mineralization (high salinity) of 10855 mg / L, a temperature of 80°C, and a formation pressure of 4 MPa, the multifunctional physical simulation experiment instrument HAYX produced by Haian Petroleum was used to set the back pressure to 4 MPa. The pressure difference P1 at both ends of the core was measured when the water permeability of the natural core was measured; 0.2% nano-modified CO2-responsive foam plugging agent solution was prepared with formation water, and the pressure difference P2 at both ends of the foam drive core was measured by alternating water and gas injection, with a gas-liquid ratio of 1:1, an injection rate of 0.1 mL / min, and a segment plug size of 0.1 PV. The resistance factor calculation formula is P2 / P1. Compared with conventional foaming agents, it has the advantages of low surface tension, oil resistance, adsorption resistance, and high-temperature and high-pressure foam plugging. The results are shown in Tables 1 and 2 below.

[0087] Surface tension detection method: refer to GB / T 5549-2010 standard for evaluation, and use formation water to prepare the sample|(nano-modified CO2 responsive foam plugging agent) into solution concentrations of 0.2% and 0.3%, respectively.

[0088] Table 1 Oil resistance, adsorption resistance and high temperature and high pressure foam plugging performance

[0089] Table 2 Surface tension

[0090] It can be seen from the above results that the nano-modified CO2 responsive foam plugging agent prepared in the embodiment of the present invention can prevent gas channeling and plug cracks by absorbing CO2. It is an efficient plugging agent that can be used in conjunction with oil field CO2 flooding technology and can be applied on a large scale.

[0091] Test Example 3 The products obtained in Example 1 and Comparative Examples 1-5 were tested for surface tension, foaming properties under oil resistance and anti-adsorption conditions, foam plugging properties under high temperature and high pressure, and degradability.

[0092] Test surface tension according to GB / T 5549-2010; According to the enterprise standard Q / BGBH 0063-2022 test: oil resistance, adsorption resistance, high temperature and high pressure foam plugging performance; Degradability was tested according to GB / T 19277.1.

[0093] The results are shown in Table 3.

[0094] Table 3 Surface tension, foaming properties, foam plugging properties under high temperature and high pressure, and degradability

[0095] It can be seen from the above results that, compared with comparative examples 1-5, the nano-modified CO2 responsive foam plugging agent prepared in Example 1 of the present invention has lower surface tension, excellent oil resistance and anti-adsorption foaming property, better foaming effect, and excellent high-temperature and high-pressure foam plugging property (the higher the resistance factor, the better the high-temperature and high-pressure foam plugging property), indicating that it has better foam stability and temperature and salt resistance, and has a better plugging effect; and it also has the characteristic of being easily degradable, which can avoid pollution of the oil layer and blockage of the formation. It is a green and efficient plugging agent with great application value.

[0096] 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 in 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 .

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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