Carbon dioxide intelligent response type step-by-step deep anti-channeling gel for oil and gas reservoirs and preparation method

Abstract

The invention discloses carbon dioxide intelligent response type step-by-step deep anti-channeling gel for oil and gas reservoirs and a preparation method, and relates to the field of carbon dioxide flooding recovery efficiency improvement. The carbon dioxide intelligent response type monomer is obtained by reacting chloropropene with N, N, N '-trimethylethylenediamine. The carbon dioxide intelligent response type monomer and the main monomer are prepared into a monomer aqueous solution, and then the chitosan is prepared into an aqueous solution. The preparation method comprises the following steps: uniformly mixing half of a chitosan aqueous solution and half of a monomer solution, heating to 60-80 DEG C, adding half of an initiator, carrying out a polymerization reaction for 2-3 hours, continuously adding the rest of the chitosan aqueous solution, monomer solution and initiator, carrying out a reaction for 4-6 hours, finally respectively adding a gelling agent and a coagulant to obtain a polymer solution, and introducing carbon dioxide to form the deep anti-channeling gel. The gel is low in viscosity and good in injectability before carbon dioxide response, the viscosity of a system is increased after the response, the sweep efficiency can be obviously improved, deep channeling is prevented step by step, a carbon dioxide channel is blocked, a water channel and a natural gas channel are not blocked, and the recovery efficiency is obviously improved.

Description

Technical Field

[0001] The present invention belongs to the field of chemical oil displacement, and relates to a gas drive sweep volume expansion anti-channeling agent and a preparation method thereof, specifically a carbon dioxide drive intelligent response type step-by-step deep profile anti-channeling gel for oil and gas reservoirs and a preparation method thereof. Background Art

[0002] In recent years, the country has put forward the national strategies of carbon peak and carbon neutrality. Geological storage and utilization of carbon dioxide is an effective way to directly achieve carbon peak and carbon neutrality. Using carbon dioxide to drive oil can not only effectively achieve the storage of carbon dioxide, but also further improve the oil recovery rate by using the properties of carbon dioxide. The reason for choosing carbon dioxide flooding in low-permeability oil reservoirs is that compared with high-permeability oil reservoirs, the migration ability of carbon dioxide in low-permeability oil reservoirs is weakened, and the gas channeling time is greatly delayed. Carbon dioxide has been injected into the low-permeability oil reservoirs in the Yanchang Oilfield and certain effects have been achieved.

[0003] In fact, during the process of using carbon dioxide to drive oil, almost all of the carbon dioxide has gas escape, which reduces the degree of carbon dioxide sweep volume expansion. The ordinary anti-channeling technology is to thicken the viscosity of the aqueous phase after adding chemical additives. The injectivity in ultra-low permeability oil reservoirs is poor, and it is more difficult than water flooding displacement, and it is difficult to achieve deep channeling sealing, resulting in poor final carbon dioxide flooding effect.

[0004] There are also many oilfields that add expanders to cement as gas channeling prevention agents. There is chemical expansion, namely lattice expansion and gas generation expansion, and physical expansion, namely aerated cement. However, the method of injecting expanders has the following disadvantages: (1) It will cause uneven stress distribution in the plugging matrix, resulting in cracks and creating new channels for channeling; (2) The infiltration of gas significantly reduces the strength of the plugging matrix. In addition, the cement often produces permanent plugging, and it is also difficult to reach the deep formation for effective plugging of carbon dioxide gas channeling. There are also records of synthesizing a new gas channeling prevention agent using polyethylenepolyamine, epichlorohydrin, trimethylamine, etc., which can increase the resistance coefficient of the high-permeability layer of the core and decrease the flow rate ratio between the high- and low-permeability layers. However, the plugging ability decreases after water immersion and is not suitable for carbon dioxide flooding in ultra-low permeability oil reservoirs. The invention patent ZL 200710172367.4, "Gas Channeling Prevention Agent for Carbon Dioxide Flooding in Ultra-Low Permeability Oil Reservoirs and Its Application", prepared a carbon dioxide flooding gel gas channeling prevention agent, which forms an organic salt precipitate by the reaction of carbon dioxide and ethylenediamine to block the gas channeling path, and adding isolation liquid ethanol can effectively control the time. However, the organic salt precipitate is easily dissolved quickly after the intrusion of formation water, resulting in the failure of the plugging effect. The invention patent ZL 201310523013.2, "A Gas Flooding Gas Channeling Prevention Agent and Its Application Method", uses inorganic aluminum salts, ethylenediamine, urea, etc. to prepare an inorganic gel with a viscosity of 500 mPa·s, and finally forms a salt precipitate, which has poor stability and is easily dissolved quickly when invaded by formation water. Some people also use foam to plug carbon dioxide gas channeling. The main reason for the profile control and oil displacement effects of foam lies in the seepage characteristics of foam in porous media, that is, the function of foam plugging large pores but not small pores and plugging water but not oil, resulting in uniform advancement of foam in high- and low-permeability layers. At the same time, foam also has the ability to plug gas channeling, enabling the subsequent injected water or gas to enter the low-permeability layer to achieve the purpose of profile adjustment. Foam has a certain ability to seal channeling, but due to too strong formation heterogeneity, gas breakthrough is likely to occur. And higher-strength foam requires adding high-molecular-weight polymers to enhance the thickness of the foam interface film, but this is difficult to meet the injectability requirements of ultra-low permeability oil reservoirs. It can be seen that it is impossible to achieve both injectability and high-efficiency gas channeling prevention. Some researchers also use gel foam to plug carbon dioxide gas channeling wells, which has produced a good plugging effect. However, for ultra-low permeability oil reservoirs, there are still problems such as poor injectability, difficulty in passing through ultra-low permeability areas and entering large fractures and large holes, and it is impossible to achieve the plugging of the target position of large fractures and large holes in the deep formation. The invention patent ZL202310047337.7, "A Gel Gas Channeling Prevention Agent for Expanding the Swept Volume in Carbon Dioxide Flooding in Ultra-Low Permeability Oil Reservoirs and Its Application", uses the product of the intelligent response of small molecule tertiary amine and carbon dioxide and the counterion self-assembly to generate worm-like micelles to achieve the expansion of the swept volume. The viscosity of the pre-injected liquid is like water, although the injectability is good, but it is easy to leak, easily miss the target layer, and the deep propulsion rate and effect are limited, and it cannot achieve the ability to improve the formation profile step by step in the deep formation.

[0005] Therefore, the present invention is directed to carbon dioxide, which is often in a supercritical state under the conditions of oil and gas reservoir formation temperature and pressure, and has particularly strong penetrability, is prone to gas channeling, reduces the contact between carbon dioxide and crude oil, has poor miscible effect, and the ability to dissolve oil and gas is weakened, thereby affecting the carbon dioxide flooding effect and on-site production problems, and has developed a deep anti-channeling gel, which has a low initial viscosity, improves the injectability of the gel anti-channeling agent, and can enter the carbon dioxide enrichment area to block the target layer of the advantageous channel. Under the reservoir formation, the responsive group and carbon dioxide act to generate bicarbonate quaternary ammonium salt, which is easily ionized in formation water, so that the polymer solubility increases, the polymer molecular chain becomes more extended, and the polymer fluid mechanics volume increases. Under the action of the coagulant, it forms a gel with the gelling agent, and macroscopically shows as a high-viscoelastic fluid, the system viscosity increases rapidly, the flow direction of the subsequent fluid can be changed, and the swept volume can be expanded, and the deep anti-channeling can be achieved step by step, and there is potential application value in improving the oil and gas recovery rate in the low-permeability oil and gas reservoirs of repeated fracturing. Summary of the invention

[0006] In the carbon dioxide intelligent response type step-by-step deep anti-channeling gel and preparation method used in the present invention for oil and gas reservoirs, the deep anti-channeling polymer solution has low initial viscosity and good dispersibility, which improves the injectability of the anti-channeling liquid and can enter the carbon dioxide enrichment area to block the target layer of the advantageous channel. The deep anti-channeling liquid responds intelligently with carbon dioxide under the formation to form a physical cross-linked network structure, and the viscosity of the system increases rapidly, which can change the flow direction of subsequent fluids and expand the swept volume, so as to achieve step-by-step deep anti-channeling. It has potential application value in improving oil and gas recovery rate in oil and gas reservoirs with repeated fracturing. It can block carbon dioxide gas channeling in oil and gas reservoirs, significantly expand the swept efficiency, and is conducive to improving the recovery effect of carbon dioxide drive.

[0007] A carbon dioxide intelligent response type step-by-step deep anti-channeling gel for oil and gas reservoirs and a preparation method thereof, characterized in that: the gel deep anti-channeling agent is composed of the following by mass percentage: Chitosan 1-2%; Monomer main agent 15-25%; Carbon dioxide intelligent response monomer 2-5%; Initiator 0.2~0.6%; Gelling agent 0.1-0.2%; Coagulant 0.4~0.8%; The balance is deionized water.

[0008] Preferably, for the carbon dioxide intelligent response type step-by-step deep anti-channeling gel for oil and gas reservoirs, it is characterized in that the carbon dioxide intelligent response type monomer is N,N,N'-trimethyl-N'-allylethylenediamine, and its preparation method: Add 8.145 - 9.945 g of allyl chloride and 11.700 g of N,N,N'-trimethylethylenediamine into a 250 mL four-necked flask respectively, keep the molar ratio of allyl chloride to N,N,N'-trimethylethylenediamine between 1.1 - 1.3:1, then successively add 50.0 mL of acetone and 7.5 mL of triethylamine, stir evenly, and react for 40 - 60 min while continuously introducing nitrogen and maintaining a constant temperature between 25 - 35 °C. Take out the reaction solution and rotate and evaporate to remove acetone, triethylamine, unreacted allyl chloride and generated hydrogen chloride at 40 - 45 °C to obtain the carbon dioxide intelligent response monomer N,N,N'-trimethyl-N'-allylethylenediamine.

[0009] Preferably, for the carbon dioxide intelligent response type step-by-step deep anti-channeling gel for oil and gas reservoirs, it is characterized in that the main monomer is sodium acrylate.

[0010] Preferably, for the carbon dioxide intelligent response type step-by-step deep anti-channeling gel for oil and gas reservoirs, it is characterized in that the initiator is one of ceric sulfate and ammonium cerium nitrate.

[0011] Preferably, for the carbon dioxide intelligent response type step-by-step deep anti-channeling gel for oil and gas reservoirs, it is characterized in that the gelling agent is one of sodium dodecylbenzenesulfonate and sodium dodecyl sulfate.

[0012] Preferably, for the carbon dioxide intelligent response type step-by-step deep anti-channeling gel for oil and gas reservoirs, it is characterized in that the coagulant accelerator is one of trimethylamine, triethylamine, tetramethylethylenediamine, N,N-dimethylethylenediamine, N,N,N'-trimethylethylenediamine, N,N-dimethylaniline, N-methyl-N-hydroxyethyl-p-toluidine.

[0013] Preferably, for the carbon dioxide intelligent response type step-by-step deep anti-channeling gel for oil and gas reservoirs, it is characterized in that the preparation method of the carbon dioxide intelligent response type step-by-step deep anti-channeling gel includes the following steps:

[0014] (1) Add chitosan into a 5% acetic acid aqueous solution by mass, and use an ultrasonic cleaner for ultrasonic oscillation until the chitosan is completely dissolved to obtain a light yellow transparent chitosan acetate aqueous solution.

[0015] (2) Dissolve the carbon dioxide intelligent response type monomer N,N,N'-trimethyl-N'-allylethylenediamine and the main monomer sodium acrylate in deionized water to prepare a monomer solution.

[0016] (3) Add half of the chitosan acetic acid aqueous solution and half of the monomer solution into a 250 mL four-necked flask in sequence. Continuously introduce nitrogen, heat up to 60 - 80 °C, and then add half of the initiator. Conduct graft polymerization for 2 - 3 h.

[0017] (4) Then add the other half of the chitosan acetic acid aqueous solution and the other half of the monomer solution. Add the other half of the initiator to the four-necked flask using a constant pressure funnel. Continuously introduce nitrogen and conduct graft polymerization for 4 - 6 h to obtain a slightly milky white chitosan grafted N,N,N'-trimethyl-N'-allylethylenediamine / sodium acrylate copolymer solution.

[0018] (5) Add a gelling agent and a coagulant to the copolymer solution respectively, stir evenly to prepare a carbon dioxide intelligent response type step-by-step deep anti-channeling polymer solution. Introduce carbon dioxide into this polymer solution, and its viscosity gradually increases to generate a step-by-step deep anti-channeling gel.

[0019] The "slug" described in this article is a well-known professional technical term, which refers to the fluid injected into the porous medium of the formation. Before it is completely diffused, its shape is approximately like a slug of fluid migrating in the pores in a plunger-like manner.

[0020] The "PV" described in this article is a well-known professional technical term, which refers to the pore volume of the core. For example, injecting 1 PV of fluid means that the volume of the injected fluid is equal to the pore volume of the core.

[0021] Advantages of the present invention

[0022] The present invention provides a novel carbon dioxide intelligent response type functional monomer N,N,N'-trimethyl-N'-allylethylenediamine and its preparation method. The preparation method of this monomer is simple, the conditions are mild, and the yield is high. Conventional commercial functional monomers have only one tertiary amine, while this monomer contains two tertiary amine groups. Compared with the polymers prepared from conventional commercial single functional monomers, the polymer prepared from this monomer has stronger carbon dioxide intelligent response ability, higher degree of ionization in formation water after response, faster response rate and gelation rate. When reacting with carbon dioxide for the same time, the viscosity of the generated gel is higher than that of the polymer prepared from conventional commercial single functional monomers. This polymer solution has a low initial viscosity. After carbon dioxide intelligent response, it forms a physical cross-linked gel. As the amount of carbon dioxide increases, the degree of intelligent response increases, the viscosity of the system gradually increases, and a step-by-step deep anti-channeling gel is generated, which can significantly expand the sweep efficiency, has the ability to only block the carbon dioxide aggregation channels, does not block the water flow channels and natural gas aggregation channels, and has obvious selective plugging ability.

[0023] In medium-high permeability oil and gas reservoirs and repeatedly fractured low-permeability oil and gas reservoirs (low-permeability oil and gas reservoirs generally require multiple repeated fracturing, and shale oil and gas reservoirs also require multiple repeated volume fracturing), it has good injectivity. At the same time, having a certain viscosity can also prevent liquid leakage, reduce water blockage and water sensitivity, and mitigate formation damage. Deep underground in the formation, the anti-channeling gel reacts with carbon dioxide, and the tertiary amine group generates a quaternary ammonium bicarbonate group, enhancing both the hydrophilicity and viscosity of the gel, just like the amide group of polyacrylamide hydrolyzes to form a carboxyl group, greatly increasing its hydrophilicity and thickening property. This anti-channeling agent has good salt and acid resistance, low initial viscosity, and high viscosity after response gelation, which can reach 2000 - 6000 mPa·s. Its viscosity can be determined by the gel concentration, gelling agent, accelerator, formation temperature, and formation salinity. Therefore, it can plug carbon dioxide gas channeling in various oil and gas reservoirs, significantly expand the sweep efficiency, and is beneficial to improving the recovery effect of carbon dioxide flooding.

[0024] When the gel deep anti-channeling polymer solution of this invention patent is applied in the case of carbon dioxide gas channeling, there is no need for an isolation fluid between the injected carbon dioxide slug and the gel deep anti-channeling polymer solution. After determining that carbon dioxide injection causes gas channeling, directly inject a certain amount of the prepared gel anti-channeling polymer solution slug, and then inject a carbon dioxide slug. Record the injection pressure at each stage at the same injection rate. This anti-channeling agent has a simple construction process and is easy to operate on-site. After injecting according to the designed injection volume, there is no need to shut in the well for gel setting. As long as there is carbon dioxide in contact with the gel underground, the viscosity of the liquid continuously and rapidly increases while flowing. It changes the subsequent carbon dioxide water absorption profile, which is beneficial to expanding the carbon dioxide sweep efficiency, thereby improving the recovery rate of the oil and gas reservoir. Detailed implementation mode

[0025] The present invention is not limited by the following embodiments, and the specific implementation mode can be determined according to the technical solution of the present invention and the actual situation. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention. All chemical reagents and chemical supplies mentioned in the present invention are well-known and commonly used chemical reagents and chemical supplies in the prior art unless otherwise specified. The resistance coefficient, enhanced oil recovery, etc. mentioned are all special terms in the industry with fixed calculation methods, which will not be elaborated here.

[0026] Example 1

[0027] (1) Preparation of carbon dioxide intelligent response monomer

[0028] 8.145 g of allyl chloride and 11.700 g of N,N,N'-trimethylethylenediamine were respectively added to a 250 mL four-necked flask, keeping the molar ratio of allyl chloride to N,N,N'-trimethylethylenediamine at 1.1:1. Then, 50.0 mL of acetone and 7.5 mL of triethylamine were successively added. After stirring evenly, the reaction was carried out for 40 min under the condition of continuously introducing nitrogen and maintaining a constant temperature of 30 °C. The reaction solution was taken out and rotary evaporated at 40 °C to remove acetone, triethylamine, unreacted allyl chloride and generated hydrogen chloride, obtaining the carbon dioxide intelligent-responsive monomer N,N,N'-trimethyl-N'-allylethylenediamine.

[0029] (2) Preparation of step-by-step deep anti-channeling gel

[0030] 1) 1.0 g of chitosan was added to 29.0 g of 5% acetic acid aqueous solution by mass, and ultrasonic oscillation was carried out using an ultrasonic cleaner until the chitosan was completely dissolved, obtaining a pale yellow transparent chitosan acetate aqueous solution.

[0031] 2) 5.0 g of the carbon dioxide intelligent-responsive monomer N,N,N'-trimethyl-N'-allylethylenediamine and 13 g of the main monomer sodium acrylate were dissolved in 52.0 g of deionized water to prepare a monomer solution.

[0030] 3) 15 g of the chitosan acetate aqueous solution and 35 g of the monomer solution were successively added to a 250 mL four-necked flask. Nitrogen was continuously introduced, and the temperature was raised to 60 °C. Then, 0.2 g of cerium(IV) sulfate was added as an initiator, and the graft polymerization reaction was carried out for 2.5 h.

[0032] 4) Then, the remaining 15 g of the chitosan acetate aqueous solution and the remaining 35 g of the monomer solution were added. Another 0.2 g of the initiator cerium(IV) sulfate was added to the four-necked flask using a constant pressure funnel, and nitrogen was introduced to continuously carry out the graft polymerization reaction for 4 h, obtaining a slightly milky white chitosan grafted N,N,N'-trimethyl-N'-allylethylenediamine / sodium acrylate copolymer solution.

[0033] 5) 0.1 g of the gelling agent sodium dodecylbenzenesulfonate and 0.4 g of the coagulant trimethylamine were respectively added to the copolymer solution, stirred evenly, and a carbon dioxide intelligent-responsive step-by-step deep anti-channeling polymer solution was prepared. The polymer solution was diluted to a solution with a mass fraction of 0.2%, and carbon dioxide was continuously introduced into a sealed container at a rate of 0.5 cm 3 / s, maintaining a pressure of 5 MPa. The change in the viscosity of the system within 20 min of introducing carbon dioxide was measured in situ and in real time online, and measured once every 2 min until the viscosity no longer changed. The gel viscosities measured at different time intervals are shown in Table 1.

[0034] Example 2

[0035] (1) Preparation of carbon dioxide intelligent-responsive monomer

[0036] 9.945 g of allyl chloride and 11.700 g of N,N,N'-trimethylethylenediamine were added to a 250 mL four-necked flask respectively, keeping the molar ratio of allyl chloride to N,N,N'-trimethylethylenediamine at 1.3:1. Then, 50.0 mL of acetone and 7.5 mL of triethylamine were added successively. After stirring evenly, the reaction was carried out for 60 min under the condition of continuously introducing nitrogen and maintaining a constant temperature of 35 °C. The reaction solution was taken out and rotary evaporated at 45 °C to remove acetone, triethylamine, unreacted allyl chloride and generated hydrogen chloride, obtaining the carbon dioxide intelligent-responsive monomer N,N,N'-trimethyl-N'-allylethylenediamine.

[0037] (2) Preparation of step-by-step deep anti-channeling gel

[0038] 1) 2.0 g of chitosan was added to 28.0 g of 5% acetic acid aqueous solution by mass, and ultrasonic oscillation was carried out using an ultrasonic cleaner until the chitosan was completely dissolved, obtaining a pale yellow transparent chitosan acetate aqueous solution.

[0039] 2) 3.0 g of the carbon dioxide intelligent-responsive monomer N,N,N'-trimethyl-N'-allylethylenediamine and 18 g of the main monomer sodium acrylate were dissolved in 42.0 g of deionized water to prepare a monomer solution.

[0040] 3) 15 g of the chitosan acetate aqueous solution and 35 g of the monomer solution were successively added to a 250 mL four-necked flask. Nitrogen was continuously introduced, and the temperature was raised to 80 °C. Then, 0.3 g of the initiator ammonium cerium nitrate was added, and the graft polymerization reaction was carried out for 3 h.

[0041] 4) Then, the remaining 15 g of the chitosan acetate aqueous solution and the remaining 35 g of the monomer solution were added. Another 0.3 g of ammonium cerium nitrate was added as the initiator using a constant pressure funnel on the four-necked flask. Nitrogen was introduced and the graft polymerization reaction was continuously carried out for 6 h to obtain a slightly milky white chitosan-grafted N,N,N'-trimethyl-N'-allylethylenediamine / sodium acrylate copolymer solution.

[0042] 5) 0.2 g of the gelling agent sodium dodecyl sulfate and 0.6 g of the coagulant N,N,N',N'-tetramethylethylenediamine were added to the copolymer solution respectively, and stirred evenly to prepare a carbon dioxide intelligent-responsive step-by-step deep anti-channeling polymer solution. The polymer solution was diluted to a solution with a mass fraction of 0.2%. Carbon dioxide was continuously introduced into a sealed container at a rate of 0.5 cm 3 / s, keeping the pressure at 5 MPa. The change in the viscosity of the system within 20 min of introducing carbon dioxide was measured in-situ and real-time online, and measured once every 2 min until the viscosity no longer changed. The gel viscosities measured at different time intervals are shown in Table 1.

[0043] Example 3

[0044] (1) Preparation of Carbon Dioxide Intelligent Responsive Monomer

[0045] Add 9.180 g of allyl chloride and 11.700 g of N,N,N'-trimethylethylenediamine into a 250 mL four-necked flask respectively, keeping the molar ratio of allyl chloride to N,N,N'-trimethylethylenediamine at 1.2:1. Then add 50.0 mL of acetone and 7.5 mL of triethylamine in sequence. After stirring evenly, carry out the reaction for 50 min under the condition of continuously introducing nitrogen and maintaining a constant temperature of 25 °C. Take out the reaction solution and rotary evaporate to remove acetone, triethylamine, unreacted allyl chloride and generated hydrogen chloride at 42 °C to obtain the carbon dioxide intelligent responsive monomer N,N,N'-trimethyl-N'-allylethylenediamine.

[0046] (2) Preparation of Step-by-Step Deep Plugging Gel

[0047] 1) Add 1.5 g of chitosan into 28.5 g of 5% acetic acid aqueous solution by mass, and use an ultrasonic cleaner for ultrasonic oscillation until the chitosan is completely dissolved to obtain a light yellow transparent chitosan acetate aqueous solution.

[0048] 2) Dissolve 4.0 g of the carbon dioxide intelligent responsive monomer N,N,N'-trimethyl-N'-allylethylenediamine and 20 g of the main monomer sodium acrylate in 46.0 g of deionized water to prepare a monomer solution.

[0049] 3) Add 15 g of the chitosan acetate aqueous solution and 35 g of the monomer solution into a 250 mL four-necked flask in sequence, continuously introduce nitrogen, heat up to 70 °C, and then add 0.25 g of initiator, and carry out graft polymerization reaction for 2 h.

[0050] 4) Then add the remaining 15 g of the chitosan acetate aqueous solution and the remaining 35 g of the monomer solution, add 0.25 g of ammonium cerium nitrate as the initiator to the four-necked flask using a constant pressure funnel, continuously introduce nitrogen and carry out graft polymerization reaction for 5 h to obtain a slightly milky white chitosan grafted N,N,N'-trimethyl-N'-allylethylenediamine / sodium acrylate copolymer solution.

[0051] 5) Add 0.15 g of the gelling agent sodium dodecylbenzenesulfonate and 0.5 g of the coagulant N,N-dimethylaniline into the copolymer solution respectively, stir evenly to prepare a carbon dioxide intelligent responsive step-by-step deep plugging polymer solution. Dilute this polymer solution to a solution with a mass fraction of 0.2%, and continuously introduce carbon dioxide into a sealed container at a rate of 0.5 cm 3 / s, keep the pressure at 5 MPa, and in-situ real-time online test the change of the viscosity of the system within 20 min of introducing carbon dioxide. Measure it once every 2 min until the viscosity no longer changes. The gel viscosities measured at different time intervals are shown in Table 1.

[0052] Example 4

[0053] (1) Preparation of carbon dioxide intelligent response monomer

[0054] 9.563 g of allyl chloride and 11.700 g of N,N,N'-trimethylethylenediamine were respectively added into a 250 mL four-necked flask, keeping the molar ratio of allyl chloride to N,N,N'-trimethylethylenediamine at 1.25:1. Then, 50.0 mL of acetone and 7.5 mL of triethylamine were successively added. After stirring evenly, the reaction was carried out for 40 min under the condition of continuously introducing nitrogen and maintaining a constant temperature of 25 °C. The reaction solution was taken out and rotary evaporated at 44 °C to remove acetone, triethylamine, unreacted allyl chloride and generated hydrogen chloride, obtaining the carbon dioxide intelligent response monomer N,N,N'-trimethyl-N'-allylethylenediamine.

[0055] (2) Preparation of step-by-step deep anti-channeling gel

[0056] 1) 1.7 g of chitosan was added to 28.3 g of 5% acetic acid aqueous solution by mass, and ultrasonic oscillation was carried out using an ultrasonic cleaner until the chitosan was completely dissolved, obtaining a pale yellow transparent chitosan acetate aqueous solution.

[0057] 2) 4.5 g of the carbon dioxide intelligent response monomer N,N,N'-trimethyl-N'-allylethylenediamine and 12.5 g of the main monomer sodium acrylate were dissolved in 42.5 g of deionized water to prepare a monomer solution.

[0058] 3) 15 g of the chitosan acetate aqueous solution and 35 g of the monomer solution were successively added into a 250 mL four-necked flask. Nitrogen was continuously introduced, and the temperature was raised to 75 °C. Then, 0.15 g of the initiator ceric sulfate was added, and the graft polymerization reaction was carried out for 2.5 h.

[0059] 4) Then, the remaining 15 g of the chitosan acetate aqueous solution and the remaining 35 g of the monomer solution were added. Another 0.15 g of the initiator ceric sulfate was added to the four-necked flask using a constant pressure funnel, and nitrogen was introduced to continuously carry out the graft polymerization reaction for 5.5 h, obtaining a slightly milky white chitosan grafted N,N,N'-trimethyl-N'-allylethylenediamine / sodium acrylate copolymer solution.

[0060] 5) 0.18 g of the gelling agent sodium dodecylbenzenesulfonate and 0.65 g of the coagulant N-methyl-N-hydroxyethyl-p-toluidine were respectively added to the copolymer solution, and stirred evenly to prepare a carbon dioxide intelligent response type step-by-step deep anti-channeling polymer solution. The polymer solution was diluted to a solution with a mass fraction of 0.2%, and in a sealed container at 0.5 cm 3Continuously introduce carbon dioxide at a rate of / s, maintain the pressure at 5 MPa, and in-situ and real-time online test the change in the viscosity of the system within 20 minutes of introducing carbon dioxide. Measure it once every 2 minutes until the viscosity no longer changes. The gel viscosities measured at different time intervals are shown in Table 1.

[0061] Comparative Examples 1-4

[0062] In Comparative Examples 1-4, except for changing the dual-intelligent response monomer N,N,N'-trimethyl-N'-allylethylenediamine in Examples 1-4 to the commercial single-response monomer dimethylaminoethyl methacrylate, the experimental procedures, other drugs used and their dosages, experimental reaction conditions, etc. are all corresponding to those in Examples 1-4 one by one, and will not be elaborated here. The performance indicators such as the subsequent viscosity test and carbon dioxide flooding anti-channeling experiment are all carried out according to the conventional experimental requirements and standards in the industry, and will not be expanded here one by one. Performance Test and Analysis

[0063] Viscosity Test

[0064] Study the influence of the carbon dioxide intelligent response time of different systems on the viscosity of the system. Use a Brookfield VIII viscometer to measure the viscosity values of the step-by-step deep anti-channeling gels obtained in Examples 1-4 and Comparative Examples 1-4 at 0 min, 2 min, 4 min, 6 min, 8 min, 10 min, 12 min, 14 min, 16 min, 18 min, and 20 min when introducing carbon dioxide at 60 °C, as shown in Table 1.

[0065] As can be seen from Table 1, the response equilibrium time of the step-by-step deep anti-channeling polymer (Examples 1-4) prepared by the dual-intelligent response monomer in this invention patent is 8-10 min, while the response equilibrium time of the step-by-step deep anti-channeling polymer (Comparative Examples 1-4) prepared by the single-response monomer is 14-16 min.

[0066] Table 1 Viscosity values of the step-by-step deep anti-channeling polymer solution at different times when introducing carbon dioxide (60 °C)

[0067] Table 2 Comparison of response equilibrium time and viscosity change between examples and comparative examples

[0068] Table 2 shows the comparison of the response equilibrium time and viscosity change between the examples and the comparative examples. It can be seen from Table 2 that the response equilibrium time of the examples is shortened by 6 - 8 min compared with the corresponding comparative examples, indicating that the response rate is greatly improved. At the same time interval, the corresponding gel viscosity value obtained by the stepwise deep thief zone prevention polymer prepared with the dual intelligent response monomer is also increased by 38 - 47% compared with that obtained by the stepwise deep thief zone prevention polymer prepared with the single response monomer. It can be seen that the corresponding gel thief zone prevention ability obtained by the stepwise deep thief zone prevention polymer prepared with the dual intelligent response monomer after formation response is significantly increased, and the effect of stepwise profile control and displacement in the deep layer can be achieved.

[0069] Carbon dioxide flooding thief zone prevention experiment

[0070] The carbon dioxide flooding thief zone prevention experiment used Example 2 and Comparative Example 2 for comparative study, and their high-permeability core parameters and low-permeability core parameters are shown in Table 3.

[0071] The simulated formation water was prepared in the laboratory, and its salinity was 11.2×10 4 mg / L. The simulated formation oil was prepared by mixing the degassed and dehydrated crude oil from the oilfield with kerosene, and the viscosity of the formation oil was about 4.8 mPa·s.

[0072] Table 3 High-permeability and low-permeability core parameters of Example 2 and Comparative Example 2 in the core displacement experiment

[0073] The carbon dioxide gas channeling performance evaluation experiment was carried out in the form of a parallel connection of a low-permeability core and a high-permeability core. The experimental steps are as follows:

[0074] (1) Use a vernier caliper to accurately measure and record the length, width, and height of the artificial core.

[0075] (2) Put the low-permeability and high-permeability cores into a vacuum oven and vacuum dry them at 80 °C for 12 h. After 12 h, take out the two dried cores, use a core vacuum pumping and pressurizing saturation device, set the confining pressure and back pressure, and saturate the two cores with formation water for 12 h. Wipe the residual liquid on the surface of the cores after saturating with formation water with filter paper and blotting paper, and use a precision electronic balance to weigh the wet weights of the two cores at this time, and calculate the pore volume of the two cores.

[0076] (3) Use the simulated formation water to flood the two cores at a rate of 0.5 mL / min until the core data is stable, record the pressure at this time, and calculate the permeability of the cores.

[0077] (4) Inject formation oil into the two cores at a rate of 0.5 mL / min until the cores are completely saturated with formation oil, record the volume of saturated oil at this time, and calculate the oil saturation.

[0078] (5) Using a multifunctional core displacement device, with the back pressure kept constant at 5 Mpa, under the environmental condition of 60 °C, a double-tube parallel low-permeability core and a high-permeability core are used, and carbon dioxide gas is injected at a rate of 0.5 mL / min for an oil displacement experiment. Record the initial carbon dioxide displacement pressure at stability until carbon dioxide is detected at the outlet end of one of the cores, then it is judged that gas channeling occurs at this time.

[0079] (6) Inject a deep anti-channeling polymer solution with a mass fraction of 0.2% and a volume of 0.5 PV into the core at a rate of 0.5 mL / min. Record the injection pressure of the anti-channeling solution, then stop injecting, seal and let it stand for 24 h to allow carbon dioxide to fully react with the polymer to undergo a chemical reaction. After standing for 24 h, conduct subsequent carbon dioxide displacement at a rate of 0.5 mL / min, and record the carbon dioxide displacement pressure after anti-channeling.

[0080] Table 4 Double-core displacement experiment results of Example 2 and Comparative Example 2 (back pressure is 5 Mpa)

[0081] (7) Record the oil production at different stages during the entire displacement process, and calculate the injection pressure, initial carbon dioxide displacement recovery rate, and carbon dioxide displacement recovery rate after anti-channeling for the high-permeability and low-permeability cores respectively.

[0082] The double-core displacement experiment results of Example 2 and Comparative Example 2 are shown in Table 4. The injection pressures before anti-channeling in Example 2 and Comparative Example 2 are comparable, and there are obvious changes in the injection pressure after anti-channeling. The injection pressure of the core increases, and the water absorption profile is effectively improved. The recovery rate of the low-permeability core is low during the initial carbon dioxide displacement, while the recovery rate of the high-permeability core is high. Then, after using the anti-channeling gel for anti-channeling and conducting carbon dioxide displacement, the recovery rates of the high- and low-permeability cores are reversed, with the recovery rate of the low-permeability core being high and the recovery rate of the high-permeability core being low, indicating that the high- and low-permeability water absorption profiles are improved. The carbon dioxide displacement pressure after anti-channeling with the anti-channeling gel in Example 2 is 5.77 Mpa higher than the initial carbon dioxide displacement pressure, while the carbon dioxide displacement pressure after anti-channeling with the anti-channeling gel in Comparative Example 2 is 2.91 Mpa higher than the initial carbon dioxide displacement pressure.

[0083] In summary, the gel system constructed by the polymer prepared with the synthesized dual-intelligent response functional monomer (N,N,N'-trimethyl-N'-allylethylenediamine) has a higher injection pressure, a higher recovery rate, and a stronger carbon dioxide gas channeling prevention ability than the gel system constructed by the polymer prepared with a single intelligent response functional monomer (dimethylaminoethyl methacrylate).

Claims

1. A carbon dioxide intelligent response type step-by-step deep anti-channeling gel for oil and gas reservoirs, characterized in that: The deep anti-channeling gel composition (by mass percentage): Chitosan: 1-2%; Main monomer: 15-25%; Carbon dioxide intelligent responsive monomer: 2-5%; Initiator: 0.2-0.6%; Gelling agent: 0.1-0.2%; Coagulant: 0.4-0.8%; The balance is ionized water; (1) The carbon dioxide intelligent response type step-by-step deep anti-channeling gel for oil and gas reservoirs is characterized in that the carbon dioxide intelligent response type monomer is N,N,N'-trimethyl-N'-propyleneethylenediamine, and its preparation method comprises the following steps: 8.145-9.945g of allyl chloride and 11.700g of N,N,N'-trimethylethylenediamine are added to a 250mL four-necked bottle respectively, and the molar ratio of allyl chloride to N,N,N'-trimethylethylenediamine is maintained between 1.1 and 1.3:1, and then 50.0mL of acetone and 7.5mL of triethylamine are added in sequence, and after stirring evenly, the reaction is carried out for 40-60min under the condition of continuous nitrogen introduction and constant temperature of 2-35°C, and the reaction liquid is taken out and rotary evaporated at 40-45°C to remove acetone, triethylamine, unreacted allyl chloride and generated hydrogen chloride to obtain the CO2 responsive monomer N,N,N'-trimethyl-N'-propyleneethylenediamine; (2) The carbon dioxide intelligent response type step-by-step deep anti-channeling gel for oil and gas reservoirs is characterized in that the main monomer is sodium acrylate; (3) The carbon dioxide intelligent response type step-by-step deep anti-channeling gel for oil and gas reservoirs is characterized in that the initiator is one of cerium sulfate and ammonium cerium nitrate; (4) The carbon dioxide intelligent response type step-by-step deep anti-channeling gel for oil and gas reservoirs is characterized in that the gelling agent is one of sodium dodecylbenzene sulfonate and sodium dodecyl sulfate; (5) The carbon dioxide intelligent response type step-by-step deep anti-channeling gel for oil and gas reservoirs is characterized in that the coagulant is one of trimethylamine, triethylamine, tetramethylethylenediamine, N,N-dimethylethylenediamine, N,N,N'-trimethylethylenediamine, N,N-dimethylaniline, and N-methyl-N-hydroxyethyl-p-toluidine.

2. The carbon dioxide intelligent response type step-by-step deep anti-channeling gel for oil and gas reservoirs according to claim 1, characterized in that: The method for preparing the carbon dioxide intelligent response type step-by-step deep anti-channeling gel comprises the following steps: (1) adding chitosan to a 5% by mass acetic acid aqueous solution, and using an ultrasonic cleaning machine for ultrasonic oscillation until the chitosan is completely dissolved to obtain a light yellow transparent chitosan acetic acid aqueous solution; (2) dissolving the carbon dioxide intelligent response type monomer N,N,N'-trimethyl-N'-propyleneethylenediamine and the main monomer sodium acrylate in deionized water to prepare a monomer solution; (3) Add half of the chitosan acetic acid aqueous solution and half of the monomer solution in a 250 mL four-necked flask, continue to introduce nitrogen, raise the temperature to 60-80° C., add half of the initiator, and carry out graft polymerization for 2-3 hours; (4) Then, the other half of the chitosan acetic acid aqueous solution and the other half of the monomer solution are added, and the other half of the initiator is added using a constant pressure funnel, and nitrogen is introduced to continue the graft polymerization reaction for 4 to 6 hours to obtain a slightly milky white chitosan grafted N,N,N'-trimethyl-N'-propyleneethylenediamine / sodium acrylate copolymer solution; (5) A gelling agent and a coagulant are added to the copolymer solution respectively, and the mixture is stirred evenly to obtain a carbon dioxide intelligent response type step-by-step deep anti-channeling polymer solution. Carbon dioxide is introduced into the polymer solution. As the amount of carbon dioxide increases, the degree of intelligent response increases, and the viscosity of the system gradually increases, thereby generating a step-by-step deep anti-channeling gel, which only blocks the carbon dioxide accumulation channel, but does not block the water flow channel and the natural gas accumulation channel, and has obvious selective blocking ability.

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