CO2 slow response type gel for ultra-high-temperature oil reservoir and preparation method of CO2 slow response type gel

Abstract

The invention belongs to the technical field of oil-gas field development, and relates to a CO2 slow response type gel for an ultra-high-temperature oil reservoir and a preparation method of the CO2 slow response type gel. The invention relates to a CO2 slow response type gel for an ultra-high temperature oil reservoir. The CO2 slow response type gel comprises an anionic surfactant, a cross-linking agent, a thiourea auxiliary agent and water. The CO2 slow response type gel for the ultra-high-temperature oil reservoir is relatively low in viscosity before being in contact with CO2, and can be well injected into a deep stratum, so that the swept area is enlarged; and after CO2 is introduced, at the temperature of 140 DEG C or above, after 5 hours, cross-linking is performed to form a three-dimensional network structure, the volume expansion viscosity is increased, and good viscoelasticity is achieved, so that the stratum is better blocked.

Description

Technical Field

[0001] The present invention belongs to the technical field of oil and gas field development, and relates to a CO2 slow-response gel for ultra-high temperature oil reservoirs and a preparation method thereof, and in particular to a CO2 slow-response gel for ultra-high temperature oil reservoirs above 140°C and a preparation method thereof. Background Art

[0002] With the continuous application of CO2 flooding technology, some problems have also arisen. Especially when there is heterogeneity in the reservoir, such as fractures, large pores and high permeability zones, viscous fingering will be formed during CO2 flooding. Therefore, in the early stage of CO2 flooding, the phenomenon of "seeing gas" often occurs, resulting in a decrease in CO2 sweep efficiency, affecting the effect of CO2 flooding to improve oil recovery, and the economic benefits are also reduced. Therefore, in the CO2 flooding technology for heterogeneous reservoirs, it is particularly important to prevent CO2 gas channeling and improve CO2 sweep efficiency.

[0003] Scholars at home and abroad have accumulated many methods to prevent gas channeling, and they have been widely applied to low permeability reservoirs at home and abroad. At present, the main methods to prevent CO2 gas channeling include water-gas alternating injection (WAG), polymer gel sealing, chemical precipitation, CO2 foam and CO2 thickening to adjust the reservoir, which has played a positive role in gas channeling prevention and control, but there are also certain limitations. For example: water-gas alternating injection cannot be applied to severe heterogeneous conditions, the instability of fluidity during gas injection leads to injection deficit and equipment corrosion, and water may hinder the miscibility of CO2 and crude oil; polymer plugging agents mainly include polyacrylamide, chrysosporium gum and pre-cross-linked bulk particles (PPG), etc., and their selection is based on the temperature and mineralization of the formation. The polymer gel has high strength, but the retention of high viscosity system will cause serious damage to the formation, the blocking performance of CO2 crossflow is poor and the gel injectivity is limited, which cannot effectively block the deep reservoir; chemical precipitation is not controllable, and the improvement effect is difficult to be effectively controlled, which may cause damage to the reservoir; CO2 foam strength is not high, it is difficult to control foaming under reservoir conditions, and it cannot be applied to severe heterogeneous conditions; CO2 thickening method is costly and difficult to configure. Traditional methods of preventing gas crossflow are listed as follows: The Chinese invention patent with publication number CN117304892A discloses a CO2-responsive ionic liquid gel sealing agent and its preparation method and application. The CO2-responsive ionic liquid gel sealing agent disclosed herein can quickly form a gel in an acidic environment, block high-permeability gas channeling channels, expand the gas sweep volume, and effectively solve the CO2 drive gas channeling problem in low-permeability oil reservoirs. However, the gel responds to CO2 too quickly and cannot penetrate deep into the formation for deep sealing, causing great damage to the reservoir and seriously affecting the subsequent water injection effect. In addition, the applicable reservoir temperature of the gel is 80°C, which cannot achieve high-temperature sealing of the formation. The gel has a low viscosity and is prone to water precipitation in the formation, and its ability to seal formation cracks fails.

[0004] A Chinese invention patent with publication number CN113652214A discloses a supercritical carbon dioxide channel sealing agent. The channel sealing agent disclosed therein is prepared from the following raw materials in parts by weight: 10-30 parts of foaming agent, 20-35 parts of diamine, 45-60 parts of dibasic anhydride, 85-100 parts of solvent, 5-15 parts of cross-linking agent, 2-8 parts of initiator and 1-10 parts of reinforcing agent. Since the channel sealing agent contains multiple raw material components, this complex composition may increase the complexity and cost of the preparation process. The channel sealing agent may contain some chemical substances, such as initiators, which may cause a certain degree of pollution or impact on the environment. The scope of application of the channel sealing agent may be subject to certain restrictions. For example, it may not be suitable for certain special well environments or oil well characteristics.

[0005] Therefore, traditional methods to prevent gas channeling are not applicable to ultra-high temperature formation conditions. Not only are water separation prone to occur, and the ability to seal formation fractures is poor, but gas channeling is also prone to occur during CO2 flooding, and there is no good pressure-bearing and sealing capability. Summary of the invention

[0006] In view of the defects of traditional gas channeling prevention methods, the present invention provides a CO2 slow-response gel for ultra-high temperature oil reservoirs and a preparation method thereof.

[0007] Specifically, the present invention is achieved through the following technical solutions: A CO2 slow-response gel for ultra-high temperature oil reservoirs comprises an anionic surfactant, a cross-linking agent, a thiourea auxiliary agent and water.

[0008] The CO2 slow-response gel for ultra-high temperature oil reservoirs comprises: 0.5-1.0 wt% of anionic surfactant, 0.9-2.0 wt% of cross-linking agent, 2.4-3.5 wt% of thiourea additive and the balance of water.

[0009] The CO2 slow-response gel for ultra-high temperature oil reservoirs comprises: 0.5-0.8 wt% of anionic surfactant, 0.9-1.6 wt% of cross-linking agent, 2.4-3.0 wt% of thiourea additive and the balance of water.

[0010] The above-mentioned CO2 slow-response gel for ultra-high temperature oil reservoirs, the anionic surfactant includes one of AMPS, APAM, FMS, and succinic acid monooctadecylamide sulfonic acid sodium salt.

[0011] The CO2 slow-response gel for ultra-high temperature oil reservoirs, wherein the cross-linking agent comprises one of amino resin, phenolic resin, alkyd resin and acrylic resin.

[0012] The above-mentioned CO2 slow-response gel for ultra-high temperature oil reservoirs, the thiourea auxiliary agent includes one of 1,3-dimethylthiourea, 1,3-diethylthiourea, 1,1,3,3-tetramethylthiourea, and 1,2-diphenylethylenediaminethiourea.

[0013] In the above-mentioned CO2 slow-response gel for ultra-high temperature oil reservoirs, the anionic surfactant is AMPS; the cross-linking agent is phenolic resin; and the thiourea auxiliary agent is 1,2-diphenylethylenediaminethiourea.

[0014] On the other hand, the present invention also provides a method for preparing a CO2 slow-response gel for ultra-high temperature oil reservoirs, comprising: (1) Dissolve the anionic surfactant in water according to the ratio and stir until it becomes transparent and there is no obvious fish-eye obstruction; (2) Add a cross-linking agent and a thiourea additive in order according to the ratio, stir to fully dissolve the raw materials, and obtain a CO2 slow-response gel solution.

[0015] In the above-mentioned method for preparing the CO2 slow-response gel for ultra-high temperature oil reservoirs, in step (1), the stirring time is 30 to 40 minutes.

[0016] In the above-mentioned method for preparing the CO2 slow-response gel for ultra-high temperature oil reservoirs, in step (2), the stirring time is 20 to 60 minutes.

[0017] The technical solution of the present invention has the following beneficial effects: (1) The CO2 slow-response gel for ultra-high temperature oil reservoirs of the present invention has a low viscosity before contacting CO2, and can be well injected into deep formations to expand the affected area; after the CO2 is introduced, at a temperature above 140°C, after 5 hours, it will cross-link to form a three-dimensional network structure, its volume expansion viscosity increases, and it has good viscoelasticity, thereby better sealing the formation; (2) The CO2 slow-response gel for ultra-high temperature oil reservoirs of the present invention has simple preparation conditions and is easy to synthesize under laboratory and field conditions. These characteristics make the CO2 slow-response gel a potential ideal carbon dioxide gas channeling repair material; (3) The CO2 slow-response gel for ultra-high temperature oil reservoirs of the present invention is expected to promote the development and utilization of ultra-high temperature oil reservoirs, improve the recovery rate, make important contributions to the construction of a carbon neutral technology system, and further promote the coordinated development of oil field development and environmental protection; (4) The CO2 slow-response gel for ultra-high temperature oil reservoirs of the present invention increases the contact area and interaction opportunities between CO2 and crude oil in the formation as much as possible, explores the use of CO2 to improve the ultimate recovery rate of low permeability oil reservoirs, and contributes to the construction of a carbon neutral technology system. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the following detailed description of the preferred embodiment.The drawings are only for the purpose of illustrating the preferred embodiments and are not to be construed as limiting the invention.

[0019] Figure 1 This is a photograph of the gel solution prepared in Example 1 before responding to CO2; Figure 2 This is a gelation diagram of the gel solution prepared in Example 1 in response to CO2; Figure 3A This is a microscopic morphology of the gel after the gel solution prepared in Example 1 responds to CO2; Figure 3B This is a microscopic morphology of the gel after the gel solution prepared in Example 1 responds to CO2; Figure 4 This is the infrared spectrum of the gel after the gel solution prepared in Example 1 responds to CO2; Figure 5 TG-DSC graph of the gel solution prepared in Example 1 after responding to CO2; Figure 6 This is a graph showing the dehydration rate of the gel after the gel solution prepared in Example 1 responds to CO2; Figure 7 This is a test diagram of the pressure bearing performance of the gel solution prepared in Example 1 after responding to CO2. DETAILED DESCRIPTION

[0020] In order to fully understand the purpose, features and effects of the present invention, the present invention is described in detail through the following specific embodiments. Except for the following contents, the process method of the present invention adopts conventional methods or devices in the art. Unless otherwise specified, the following terms have the meanings commonly understood by those skilled in the art.

[0021] When a numerical range is disclosed herein, the above range is considered to be continuous and includes the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum values. Further, when a range refers to an integer, every integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe a feature or characteristic, the ranges can be combined. In other words, unless otherwise indicated, all ranges disclosed herein should be understood to include any and all subranges included therein.

[0022] The present invention intends to develop a CO2 slow-response gel suitable for ultra-high temperature reservoirs above 140°C. When faced with highly heterogeneous low-permeability reservoirs, factors such as gravity differentiation and viscous fingering lead to frequent crossflow phenomena, thereby reducing the efficiency and recovery rate of reservoir development.

[0023] To address this problem, the present invention has developed a new type of CO2 slow-response gel, which has the characteristics of controllable response speed, wide applicable temperature range, stable structure, etc. By selecting a suitable CO2 responsive gel system in a targeted manner, we hope to effectively inhibit gas channeling during CO2 flooding, thereby maximizing the contact area and interaction opportunities between CO2 and crude oil in the formation.

[0024] Specifically, in a first aspect, the present invention provides a CO2 slow-response gel for ultra-high temperature oil reservoirs, comprising: an anionic surfactant, a cross-linking agent, a thiourea additive and water.

[0025] The CO2 slow response gel of the present invention is a polyion complex gel, in which a crosslinking agent and a thiourea auxiliary agent are dissolved in an anionic surfactant solution containing an amide group, and then CO2 is introduced to form a stable colloidal structure under the action of high temperature. For the amide system, the CO2 molecule can react with an amine molecule to generate a carbamate salt with a negative charge of 1 unit, and then connect with the protonated amine group of another molecule through electrostatic interaction to achieve a salt bridge bonding of two amine molecules, thereby achieving the purpose of responding to CO2 gas. In this process, the CO2 molecule can dynamically bond to different amine units of the polymer, which can lead to random or orderly crosslinking of the polymer chain. Therefore, it has great application potential in polymer chemical gel.

[0026] The components of the CO2 slow response gel for ultra-high temperature oil reservoirs of the present invention are introduced in detail below: Anionic surfactants The preparation of gel often involves the mixing of oil phase and water phase components. Anionic surfactants have hydrophilic and hydrophobic groups, which can reduce the surface tension of the oil-water interface, enable the mixed system to form a stable emulsion, and provide a uniform basic framework for the formation of gel; in addition, anionic surfactants can adjust the rheological properties of the gel and stabilize the structure of the gel.

[0027] In some preferred embodiments, the anionic surfactant includes one of AMPS, APAM, FMS, and sodium salt of succinic acid monooctadecylamide sulfonate.

[0028] AMPS is 2-acrylamide-2-methylpropanesulfonic acid, and its molecular formula is C7H 13 NO4S.

[0029] Wherein, APAM is polyacrylamide. Optionally, APAM can be purchased from Merrill, product number: M29078.

[0030] Among them, FMS is fatty acid monoethanolamide sodium sulfate, and its molecular structure is C18 H 36 CHSO3Na(COHCH2)7.

[0031] Further preferably, the anionic surfactant is AMPS.

[0032] In some preferred embodiments, the content of anionic surfactant in the CO2 slow-response gel of the present invention is 0.5-1.0 wt %, calculated by weight percentage.

[0033] The amount of anionic surfactant added will greatly affect the rheological properties of the gel, such as the strength, elasticity and thixotropy of the gel. When the content of anionic surfactant is too little, the gel texture will be uneven, and the strength and elasticity of the gel will be difficult to meet the use requirements; when the content of anionic surfactant is too high, the stability of the gel will be destroyed. In addition, too much anionic surfactant will make the gel too viscous, with extremely poor fluidity and unable to be injected.

[0034] Further preferably, in terms of weight percentage, the content of anionic surfactant in the CO2 slow-response gel of the present invention is 0.5-0.8 wt%.

[0035] Crosslinking agent The cross-linking agent mainly undergoes cross-linking reaction with the molecules in the gel system through chemical reaction, prompting the linear molecules to form a three-dimensional network structure. In addition, the presence of the cross-linking agent can improve the stability of the gel and adjust the swelling, mechanical and other properties of the gel.

[0036] In some preferred embodiments, the crosslinking agent includes one of amino resin, phenolic resin, alkyd resin and acrylic resin.

[0037] More preferably, the cross-linking agent is phenolic resin.

[0038] In some preferred embodiments, the content of the crosslinking agent in the CO2 slow-response gel of the present invention is 0.9-2.0 wt %, calculated by weight percentage.

[0039] When the cross-linking agent content is too little, the gel will have insufficient strength and poor stability, and will not be able to achieve the expected function; when the cross-linking agent content is too high, the gel will become more brittle and prone to rupture, and will also reduce the swelling properties of the gel.

[0040] Further preferably, in terms of weight percentage, the content of the crosslinking agent in the CO2 fast-responsive gel of the present invention is 0.9-1.6 wt %.

[0041] Thiourea additives Thiourea additives can help adjust the pH value of the system and provide a suitable acid-base environment for the gel formation process. In addition, they can participate in the cross-linking reaction, help the gel form a stable three-dimensional structure, improve the strength and stability of the gel, and improve the gel performance and increase the flexibility and elasticity of the gel.

[0042] In some preferred embodiments, the thiourea auxiliary agent includes one of 1,3-dimethylthiourea, 1,3-diethylthiourea, 1,1,3,3-tetramethylthiourea, and 1,2-diphenylethylenediaminethiourea.

[0043] More preferably, the thiourea auxiliary agent is 1,2-diphenylethylenediaminethiourea.

[0044] In some preferred embodiments, the content of the thiourea auxiliary agent in the CO2 slow-response gel of the present invention is 2.4-3.5 wt %, calculated by weight percentage.

[0045] When the content of thiourea additives is too low, the pH adjustment ability of the system will be limited, thereby affecting the formation process and final performance of the gel, resulting in low gel strength, uneven gel molecular weight distribution, and gel viscoelasticity that does not meet the use requirements; when the content of thiourea additives is too high, the gel will be over-cross-linked, thereby losing flexibility and elasticity, and will also affect the swelling properties of the gel.

[0046] Further preferably, in terms of weight percentage, the content of the thiourea auxiliary agent in the CO2 slow-response gel of the present invention is 2.4-3.0 wt%.

[0047] It has been tested that the CO2 slow-response gel for ultra-high temperature oil reservoirs of the present invention has a low viscosity before contacting CO2, and can be well injected into deep formations to expand the affected area; after the introduction of CO2, at above 140°C, after 5 hours, it will cross-link to form a three-dimensional network structure, its volume expansion viscosity increases, and it has good viscoelasticity, thereby better sealing the formation.

[0048] In a second aspect, the present invention also provides a method for preparing the above-mentioned CO2 slow-response gel, comprising: (1) Dissolve the anionic surfactant in water according to the ratio and stir until it becomes transparent and there is no obvious fish-eye obstruction; (2) Add a cross-linking agent and a thiourea additive in order according to the ratio, stir to fully dissolve the raw materials, and obtain a CO2 slow-response gel solution.

[0049] Among them, the ratio and raw material types of anionic surfactants, crosslinking agents, and thiourea additives used in the preparation method are the same as those in the CO2 slow-response gel for ultra-high temperature oil reservoirs provided in the first aspect of the present invention, and the present invention will not repeat them here.

[0050] In some preferred embodiments, the preparation method of the CO2 slow-response gel of the present invention comprises: slowly dissolving an anionic surfactant in water, placing it in a magnetic stirrer to dissolve, stirring until transparent and without obvious fish-eye blocking substances to obtain a uniform solution for use, and the stirring time must be ensured to be at least 30 to 40 minutes; then, adding a cross-linking agent and a thiourea auxiliary agent in sequence, stirring for about 20 to 60 minutes to fully dissolve all the agents, and obtaining a CO2 slow-response gel solution.

[0051] The CO2 slow-response gel for ultra-high temperature oil reservoirs of the present invention has simple preparation conditions and is easy to synthesize under laboratory and field conditions. These characteristics make the CO2 slow-response gel a potential ideal carbon dioxide gas channeling repair material.

[0052] Example The present invention is further described below by way of examples, but the present invention is not limited to the scope of the examples. The experimental methods in the following examples without specifying specific conditions are carried out according to conventional methods and conditions. The raw materials used in the following examples are all conventionally purchased.

[0053] Example 1 Slowly dissolve 1.2g of anionic AMPS surfactant solid particles in 200g of water and place it on a magnetic stirrer to dissolve. Stir the solution until it is transparent and there is no obvious fish-eye blocking material, then a uniform solution can be obtained for use. The stirring time should be at least 30min. Then, 2g of phenolic resin crosslinker and 5g of 1,2-diphenylethylenediaminethiourea auxiliary are added to the AMPS solution in sequence, and stirred for about 20 min to fully dissolve all the pharmaceutical materials to obtain a gel solution (see Figure 1 Finally, the gel solution was placed in a high temperature resistant test tube and CO2 was introduced at 5 ml / min. After 3 min, the bottle mouth was sealed and then placed in a test tube rack in a desktop vacuum drying oven preset at 140 °C. After 5 hours, the gel state of the solution was observed (see Figure 2 ), the gel has a certain viscosity and strength after gelation. After the test tube is inverted, the surface of the gel does not deform and the strength is that of a rigid gel.

[0054] Example 2 Take 1.6g of anionic APAM surfactant solid particles and slowly dissolve them in 200g of water, and place them in a magnetic stirrer to dissolve. Stir the solution until it is transparent and there is no obvious fish-eye blocking material, then a uniform solution can be obtained for use, and the stirring time is at least 40min. Then, 3g of acrylic resin crosslinker and 6g of 1,3-dimethylthiourea auxiliary are added to the APAM solution in sequence, and stirred for about 30 min to fully dissolve all the pharmaceutical materials to obtain a gel solution. Finally, the gel solution is placed in a high-temperature resistant test tube and CO2 is passed through at 5 ml / min. After 3 minutes, the bottle mouth is sealed and then placed in a test tube rack in a desktop vacuum drying oven preset at 140 ℃. After 5 hours, the gel state of the solution is observed. The gel has a certain viscosity and strength. After the test tube is inverted, the surface of the gel is slightly deformed, and the strength is slightly lower than that of the rigid gel.

[0055] Example 3 Take 1.4g of FMS fatty acid monoethanolamide sulfate sodium anionic surfactant and slowly dissolve it in 200g of water, and place it in a magnetic stirrer to dissolve. Stir the solution until it is transparent and there is no obvious fish-eye blocking material, then a uniform solution can be obtained for use, and the stirring time is at least 30 min. Then, 2.4g of amino resin crosslinker and 7g of 1,1,3,3-tetramethylthiourea auxiliary are added to the anionic surfactant solution in sequence, and stirred for about 40 min to fully dissolve all the pharmaceutical materials to obtain a gel solution. Finally, the gel solution is placed in a high-temperature resistant test tube and CO2 is passed through at 5 ml / min. After 3 minutes, the bottle mouth is sealed and then placed in a test tube rack in a desktop vacuum drying oven preset at 140 ℃. After 5 hours, the gel state of the solution is observed. The gel has a certain viscosity and strength. After the test tube is inverted, the surface of the gel is slightly deformed, and the strength is slightly lower than that of the rigid gel.

[0056] Example 4 Take 1.8g of succinic acid monooctadecyl sulfonic acid sodium salt anionic surfactant and slowly dissolve it in 200g of water, and place it in a magnetic stirrer to dissolve. Stir the solution until it is transparent and there is no obvious fish-eye blocking material, then a uniform solution can be obtained for use, and the stirring time is at least 40min. Then, 3.6g of alkyd resin crosslinker and 6g of 1,3-diethylthiourea auxiliary are added to the anionic surfactant solution in sequence, and stirred for about 60 min to fully dissolve all the pharmaceutical materials to obtain a gel solution. Finally, the gel solution is placed in a high-temperature resistant test tube and CO2 is passed through at 5 ml / min. After 3 minutes, the bottle mouth is sealed and then placed in a test tube rack in a desktop vacuum drying oven preset at 140°C. After 5 hours, the gel state of the solution is observed. The gel has a certain viscosity and strength. After the test tube is inverted, the gel is a gelatinous whole that slowly flows to the half of the test tube, and the strength is a medium-strength gel.

[0057] Characterization Example 1 The product obtained in Example 1 was subjected to characterization and analysis such as scanning electron microscopy, infrared spectroscopy, and thermogravimetric scanning, and was tested for dehydration rate and pressure bearing performance.

[0058] Figure 3A and Figure 3B This is a microscopic morphology of CO2-responsive gel. As shown in the figure, the gel system can form an irregular three-dimensional network structure after static gelation, and the formation of the network structure is mainly based on the cross-linking and entanglement of the amide group (-CONH2) in the AMPS surfactant molecule and the hydroxymethyl group (-CH2OH) in the phenolic crosslinker. By observing the microstructure of the gel system at different magnifications, it was found that there were pores ranging from 2 to 8 μm between the three-dimensional network structures. The gel structure often encapsulates free water and bound water to form a network structure with a more obvious three-dimensional appearance; in addition, the amide group is not easily induced by the high temperature environment to prematurely dissolve the chain. The addition of high-temperature stabilizers makes the gel structure more compact and the entanglement and association between the molecular chains more compact, so that the overall gel structure can still maintain a high stability; even under the action of external forces, the three-dimensional network structure has a certain compression space and will undergo a certain deformation.

[0059] Figure 4 is the infrared spectrum of CO2 responsive gel, such as Figure 4 As shown, the meaning of the following characteristic peaks can be clearly derived: 629 cm -1 The characteristic peak corresponds to the bending vibration of the -SO3H group in AMPS, reflecting its presence in the molecular structure; 1043 cm -1 The characteristic peak represents the stretching vibration of the CN bond in the amine functional group, showing the characteristics of this functional group; 2924cm -1 The characteristic peak indicates the stretching vibration of the CH bond in the alkane chain, indicating the existence of the alkane chain; 1431 cm -1 The characteristic peak is related to the bending vibration of the CH bond in the alkane chain, which further confirms the structural characteristics of the alkane chain; 1560 cm -1 The characteristic peak is the bending vibration of the NH bond in the amino functional group, which emphasizes the characteristics of the amino group. According to the above infrared analysis results, the responsive gel mainly uses the amide (-CONH2) group structure to build the main skeleton of the gel. These amide groups play an important role in the formation of the gel and provide strength and stability. By responding to CO2 to form a more stable three-dimensional network structure, and the AMPS containing amide (-CONH2) groups is used to prepare the gel base liquid, the responsive gel has better high temperature and salt resistance. Under high temperature conditions, the gel can maintain its physical structure and properties, and is not easy to degrade or deform. In a high-salt environment, the gel can also effectively maintain its responsiveness.

[0060] Figure 5The thermogravimetric analysis diagram of CO2 responsive gel is shown in Figure 2. Figure 5 As shown in the figure, when the test temperature reaches 140 ℃, the mass retention rate of the gel system is 92.85% after thermogravimetric scanning analysis, which shows that the gel system has good temperature resistance within this temperature range. The main reason for the weight loss rate is that the hydrophilic groups such as amide groups are heated and some of them begin to evaporate slowly. There will be no significant degradation of the main chain of the molecule within the range of 140 ℃, which meets the temperature application conditions of the target oil reservoir. Subsequently, when the temperature is continuously heated to about 355 ℃, the hydrophilic amide groups in the gel system begin to decompose on a large scale due to thermal decomposition. At this time, the thermal depolymerization reaction is accelerated until 800 ℃, and the C=O double bonds of the hydrophilic groups such as amide groups in the gel structure are almost completely broken and eliminated due to the increase in ambient temperature, resulting in continuous cracking of the main chain of the molecule and generating a large amount of heat loss. The data show that the mass loss within the test temperature range eventually reaches 67.33%.

[0061] Figure 6 This is the dehydration rate test diagram of CO2 responsive gel, such as Figure 6 As shown in the figure, after the CO2 slow response gel system forms a gel at a temperature of 140 °C, a gradual increase in dehydration rate is observed, but the rate of increase is relatively slow. This phenomenon shows that the gel has high stability in a high temperature environment and can continuously maintain its structure and performance. Under the condition of water preparation, the dehydration rate of the CO2 slow response gel is 4.6%, which further highlights its stability and reliability, and provides a feasible solution for plugging fractures. The development of this CO2 slow response gel system with high temperature stability provides important technical support and guarantee for the development and utilization of ultra-high temperature reservoirs, and is expected to play a positive role in improving oilfield production efficiency, reducing costs and reducing environmental pollution.

[0062] Under laboratory conditions, a pressure test was conducted using a tube with a diameter of 5 mm and a length of 50 cm. When the tube was filled with base liquid, CO2 was introduced at a rate of 5 ml / min for 3 min, and then placed in an oven at 140 °C to wait for gelation. Figure 7 It can be seen that when CO2 is injected, the pressure gradually increases with the increase of injection time. When the injection time is 35 min, the pipeline begins to break through. The final pressure bearing strength of the responsive gel is 1.75 MPa, and the pressure bearing gradient is 3.2 MPa / m. It can be seen that the gel has a strong plugging ability under this experimental condition.

[0063] The present invention has been disclosed above with preferred embodiments, but those skilled in the art should understand that these embodiments are only used to describe the present invention and should not be understood as limiting the scope of the present invention. It should be noted that all changes and substitutions equivalent to these embodiments should be deemed to be included in the scope of the claims of the present invention. Therefore, the scope of protection of the present invention should be based on the scope defined in the claims.

Claims

1. A CO2 slow response gel for ultra-high temperature oil reservoirs, characterized in that: include: Anionic surfactant, crosslinking agent, thiourea additive and water; Among them, the anionic surfactant includes one of AMPS, APAM, FMS, and succinic acid monooctadecylamide sulfonic acid sodium salt; the cross-linking agent includes one of amino resin, phenolic resin, alkyd resin, and acrylic resin; the thiourea auxiliary agent includes one of 1,3-dimethylthiourea, 1,3-diethylthiourea, 1,1,3,3-tetramethylthiourea, and 1,2-diphenylethylenediaminethiourea.

2. The CO2 slow-response gel according to claim 1, characterized in that: include: 0.5~1.0 wt% anionic surfactant, 0.9~2.0 wt% cross-linking agent, 2.4~3.5 wt% thiourea additive and the balance water.

3. The CO2 slow-response gel according to claim 1, characterized in that: include: 0.5~0.8 wt% of anionic surfactant, 0.9~1.6 wt% of cross-linking agent, 2.4~3.0 wt% of thiourea additive and the balance of water.

4. The CO2 slow-response gel according to any one of claims 1 to 3, characterized in that: The anionic surfactant is AMPS; the cross-linking agent is phenolic resin; and the thiourea auxiliary agent is 1,2-diphenylethylenediaminethiourea.

5. The method for preparing the CO2 slow-response gel according to any one of claims 1 to 4, characterized in that: include: (1) Dissolve the anionic surfactant in water according to the ratio and stir until it becomes transparent and there is no obvious fish-eye obstruction; (2) Add a cross-linking agent and a thiourea additive in order according to the ratio, stir to fully dissolve the raw materials, and obtain a CO2 slow-response gel solution.

6. The preparation method according to claim 5, characterized in that In step (1), the stirring time is 30 to 40 minutes.

7. The preparation method according to claim 5, characterized in that: In step (2), the stirring time is 20 to 60 minutes.

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