Carbon dioxide self-thickening gel foam system, preparation method and application thereof

Abstract

The application discloses a CO2 self-thickening gel foam system which is composed of the following components: 3-10wt% of non-ionic responsive surfactant, 1-10wt% of anionic-non-ionic foaming agent, 1-5wt% of rheological modifier, 3-10wt% of salt additive, and the rest of water. The application discloses a preparation method of the CO2 self-thickening gel foam system, which comprises the following steps: (1) adding the formula amount of non-ionic responsive surfactant and the formula amount of rheological modifier into the formula amount of water, stirring at a first stirring speed for a first stirring time, and obtaining a uniformly dispersed mixed solution; (2) adding the formula amount of anionic-non-ionic foaming agent and the formula amount of salt additive into the mixed solution respectively, stirring at a second stirring speed for a second stirring time, and obtaining the CO2 self-thickening gel foam system. The application further discloses an application of the CO2 self-thickening gel foam system as a CO2 channeling blocking agent.

Description

Technical Field

[0001] This invention belongs to the field of petroleum engineering, specifically relating to a CO2 self-thickening gel foam system, its preparation method, and its application. Background Technology

[0002] In his dissertation, "Research and Application of Carbon Dioxide Flooding Technology," Wang Zhe of Northeast Petroleum University points out that "CO2 flooding technology refers to a tertiary oil recovery technology that injects CO2 gas into the oil reservoir to improve reservoir recovery by extracting residual oil and gas from the formation. Among many enhanced oil recovery technologies, CO2 flooding technology has a wider application prospect and more obvious technological advantages. It can not only effectively reduce greenhouse gas emissions but also maximize energy extraction." In other words, CO2 flooding technology is an effective way to achieve a win-win situation of increased oil production and carbon sequestration, realizing the resource utilization of greenhouse gases and improving oil and gas recovery.

[0003] CO2's low density and viscosity facilitate gravity overburden formation, viscous fingering, and reservoir heterogeneity, making it a key factor influencing CO2 flooding sweep volume and gas channeling. In CO2 flooding, gas channeling becomes a major constraint on its effectiveness. For example, the 2017 article by Zhao Xisen et al. in the *Journal of Southwest Petroleum University (Natural Science Edition)*, titled "Study on the Gas Channeling Law of CO2 Flooding in Heterogeneous, Ultra-Low Permeability Reservoirs," points out: "The swept volume of carbon dioxide gas is severely affected by gas channeling. The stronger the core heterogeneity, the more severe the gas channeling phenomenon, and the worse the gas flooding effect. When the permeability difference is small, the recovery rate decreases with increasing permeability difference. When the difference is greater than 100, the recovery rate drops sharply, gas channeling is severe, and low-permeability reservoirs are difficult to flood, resulting in low overall recovery." After fracturing in low-permeability reservoirs, the presence of fractures and high-permeability bands exacerbates reservoir heterogeneity and gas channeling, reducing the CO2 swept volume and significantly impacting development effectiveness.

[0004] To address CO2 channeling, various techniques have been developed, including injection-production control, gas-water alternation, stratified gas injection, well network adjustment, and chemical plugging, to slow down gas channeling and improve CO2 sweep efficiency.

[0005] Chinese invention patent application CN 107435532A discloses a method for controlling CO2 channeling using a CO2-responsive surfactant. The steps are as follows: First, the CO2-responsive surfactant is mixed with water at room temperature and pressure to obtain a CO2-responsive surfactant solution, wherein the mass concentration of the CO2-responsive surfactant is 0.1-10%; then, the CO2-responsive surfactant solution is injected into the reservoir; and then the injected CO2 fluid is restored; the CO2-responsive surfactant is selected from amidine compounds, guanidine compounds, and amidine / guanidine mixtures.

[0006] Chinese invention patent application CN 104975829A discloses a CO2 flooding reservoir development method with graded flow control. For reservoirs composed of homogeneous cores and heterogeneous cores with a permeability difference of no more than 30, a water-gas alternating injection method is used for development. For reservoirs composed of heterogeneous cores with a permeability difference in the range of 30 to 100, a CO2 flooding method is used. During the CO2 flooding process, when gas channeling occurs in the production well, small molecule fatty amines are injected into the formation as the main agent to seal it. For reservoirs composed of heterogeneous cores with a permeability difference of more than 100, a CO2 flooding method is used. During the CO2 flooding process, when gas channeling occurs for the first time in the production well, an elastic strong adhesive is injected into the formation to seal it. When gas channeling occurs again in the production well, small molecule fatty amines are injected into the formation as the main agent to seal it.

[0007] While the aforementioned technical solutions can achieve CO2 containment to some extent, there are still no effective technologies for controlling fractures and high-permeability channels in low-permeability reservoirs. This is especially true for low-permeability reservoirs, which are often deeply buried and have temperatures exceeding 120°C. Ordinary foam systems exhibit poor stability under high-temperature conditions and cannot effectively control high-permeability channels and fractures. Furthermore, polymer-based gels can easily contaminate the reservoir, causing reservoir damage. Summary of the Invention

[0008] Purpose of the invention: In order to overcome the technical problems of existing plugging materials having limited ability to control high-permeability channels and fractures in low-permeability reservoirs, and polymer gels easily causing damage to the reservoir matrix, this invention provides a CO2 self-thickening gel foam system, its preparation method and application, which has excellent injection performance, foaming performance, thickening performance and sealing performance, and has low damage to low-permeability reservoir matrix when it breaks down in oil.

[0009] Technical solution: A CO2 self-thickening gel foam system, composed of the following components by mass percentage:

[0010] The content of nonionic responsive surfactant is 3-10 wt%, the content of anionic nonionic foaming agent is 1-10 wt%, the content of rheology modifier is 1-5 wt%, the content of salt auxiliaries is 3-10 wt%, and the balance is water.

[0011] Furthermore, the nonionic responsive surfactant is a C16-C22 nonionic tertiary amine responsive surfactant.

[0012] Furthermore, the nonionic responsive surfactant is one or more of lauric acid diethanolamide, coconut oil diethanolamide, oleic acid diethanolamide, and palm oil diethanolamide.

[0013] Furthermore, the anionic nonionic foaming agent is an anionic nonionic surfactant containing polyoxyethylene alkyl ether functional groups.

[0014] Furthermore, the anionic nonionic foaming agent is one or more of C10-C18 alkyl polyoxyethylene ether carboxylate, C10-C18 alkyl polyoxyethylene ether sulfonate, and C10-C18 alkyl polyoxyethylene ether sulfate.

[0015] Furthermore, the rheology modifier is a nanoscale particulate rheology modifier.

[0016] Furthermore, the rheology modifier is one or more of nano-sized sodium-based bentonite, nano-sized calcium-based bentonite, and nano-sized fly ash.

[0017] Furthermore, the salt auxiliary is one or more of CaCl2, NaCl, and MgCl2.

[0018] The preparation method of the above-mentioned CO2 self-thickening gel foam system includes the following steps:

[0019] (1) Add the formulated amount of nonionic responsive surfactant and the formulated amount of rheology modifier to the formulated amount of water, stir at the first stirring speed for the first stirring time, and obtain a uniformly dispersed mixture.

[0020] (2) Add the formula amount of anionic nonionic foaming agent and the formula amount of salt additive to the mixture respectively, and stir at the second stirring speed for the second stirring time to obtain the CO2 self-thickening gel foam system.

[0021] Furthermore, in step (1), the first stirring speed is at least 10,000 rpm, preferably 10,000 to 20,000 rpm;

[0022] The first stirring time is at least 30 minutes, preferably 30 to 60 minutes.

[0023] Furthermore, in step (2), the second stirring speed is at least 200 rpm, preferably 200 to 1000 rpm;

[0024] The second stirring time is at least 10 minutes, preferably 10 to 30 minutes.

[0025] The CO2 self-thickening gel foam system is prepared by any of the above-mentioned methods for preparing CO2 self-thickening gel foam systems.

[0026] Application of any of the above-mentioned CO2 self-thickening gel foam systems in oil extraction.

[0027] Furthermore, any of the above-mentioned CO2 self-thickening gel foam systems can be used as CO2 blocking agents.

[0028] Furthermore, the specific steps for the above application are as follows:

[0029] Continuously introduce CO2 into the CO2 self-thickening gel foam system, then stir at a speed of 2000-5000 rpm for 2-5 minutes before injecting it into the target formation.

[0030] Beneficial Effects: The CO2 self-thickening gel foam system, its preparation method, and its application provided by this invention have the following beneficial effects:

[0031] (1) The CO2 self-thickening gel foam system provided by the present invention includes a nonionic responsive surfactant and an anionic nonionic foaming agent. Before encountering CO2, the viscosity is very low and it is easy to inject into low-permeability reservoirs, thus having good injection characteristics.

[0032] (2) After the CO2 self-thickening gel foam system is injected into the reservoir, it preferentially enters the reservoir's large pores or fractures. After the injection is complete, CO2 is then injected. On the one hand, under the shearing action of the pore throat, the anionic nonionic foaming agent in the system reacts with CO2 to form CO2 foam. On the other hand, as CO2 dissolves in the system, the nonionic responsive surfactant reacts with CO2 to form a gel with higher viscosity, which improves the stability of the formed foam. Under the foaming, thickening, and synergistic effect of the system, a gel foam with strong sealing function is formed to seal the fractures, forcing CO2 into the low-permeability matrix, thereby expanding the CO2 sweep system and improving the recovery rate. Therefore, the CO2 responsive gel foam system has a better sealing effect.

[0033] (3) The CO2-responsive gel foam system has the responsive characteristics of increasing viscosity and foaming when it encounters CO2 and decreasing viscosity and defoaming when it encounters oil. After the system increases viscosity and foams, it breaks down and the viscosity decreases when it encounters crude oil (the CO2-responsive gel foam system will destroy the network structure of the gel when it encounters crude oil, resulting in a decrease in gel viscosity). Large pores or cracks provide oil flow channels for crude oil. Therefore, the CO2-responsive gel foam sealing system has low damage characteristics to the reservoir.

[0034] (4) Compared with other ordinary CO2 foams, the CO2 self-thickening gel foam system provided by the present invention can enhance the stability of the foam and improve the temperature resistance of the CO2 foam after gelation.

[0035] (5) Compared with ordinary gel foam, nonionic responsive surfactants enter the formation and become protonated upon encountering CO2, resulting in increased viscosity and intelligent thickening effect. Compared with traditional macromolecular polymer crosslinked gels, CO2-responsive gels are more intelligent, more shear-resistant, and more heat-resistant.

[0036] (6) The preparation method of the CO2 self-thickening gel foam system provided by the present invention is simple and easy to operate, and can be dispensed online. Attached Figure Description

[0037] Figure 1 This is a schematic diagram showing the change in apparent viscosity of the CO2 self-thickening gel foam system without anionic nonionic foaming agents as a function of shear rate in Experiment Example 1.

[0038] Figure 2 This is a schematic diagram showing the changes in foam volume and half-life of the CO2 self-thickening gel foam system A1 prepared in Example 1 with stirring rate.

[0039] Figure 3 This is a schematic diagram showing the changes in foaming volume and liquid half-life of the CO2 self-thickening gel foam system A2 prepared in Example 2 with stirring rate.

[0040] Figure 4 A schematic diagram showing the changes in foaming volume and liquid half-life of CO2 foam system D1 prepared for Experimental Example 4 with stirring rate.

[0041] Figure 5 This is a schematic diagram showing the changes in foam volume and liquid half-life of the CO2 gel foam system D2 prepared for Experimental Example 5 as a function of stirring rate.

[0042] Figure 6 This is a schematic diagram showing the changes in injection pressure for CO2 self-thickening gel foam system A1 and CO2 gel foam system D2. Detailed Implementation

[0043] The specific embodiments of the present invention are described in detail below.

[0044] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0045] Detection parameters and detection methods:

[0046] 1. Apparent viscosity of CO2 self-thickening gel foam system: The apparent viscosity of the CO2 self-thickening gel foam system under different shear rates was tested using an Anton Paar rotational rheometer. Wherein:

[0047] The higher the apparent viscosity, the better the crack sealing effect of the CO2 self-thickening gel foam system.

[0048] The shear rate measured by the Anton Paar rotational rheometer is 0.01 s⁻¹. -1 ~100S -1 .

[0049] 2. Foaming performance of the CO2 foam system (the CO2 self-thickening gel foam system of this application is also a type of CO2 foam system): The foaming performance of the CO2 foam system under different stirring speeds was tested using a high-temperature and high-pressure foam reactor. Among them:

[0050] The longer the half-life, the better the stability of the CO2 self-thickening gel foam system.

[0051] Specifically, the stirring speed of the high-temperature and high-pressure reactor is 4000 r / min, 6000 r / min, 8000 r / min, and 10000 r / min.

[0052] Specific test method: Inject 100-500 mL of the foam system to be tested into the reaction vessel, inject CO2 gas into the reaction vessel to the required pressure and then close the valve. First, stir at low speed to mix the foam system with CO2 to form an acidic solution, and then stir at high speed.

[0053] 3. Evaluation of injection capacity: The sealing effect was tested using a high-temperature and high-pressure core displacement device. The core length used was 10-20cm and the core permeability was 100-500mD.

[0054] Specific testing method: First, use an ISCO pump to inject clean water into the core and test the initial pressure; then pour the prepared CO2 self-thickening gel foam system and polymer cross-linked gel foam system into the intermediate container, inject them into the core through the ISCO pump, and test the pressure to compare the injection pressure of the two systems.

[0055] The present invention will be described in detail below through embodiments.

[0056] Example 1

[0057] CO2 self-thickening gel foam system A1, by mass percentage, consists of the following components:

[0058] The content of nonionic responsive surfactant is 5 wt%, the content of anionic nonionic foaming agent is 2 wt%, the content of rheology modifier is 2 wt%, the content of salt additive is 5 wt%, and the balance is water.

[0059] Furthermore, the nonionic responsive surfactant is a C16-C22 nonionic tertiary amine responsive surfactant.

[0060] Furthermore, the nonionic responsive surfactant is lauric acid diethanolamide.

[0061] Furthermore, the anionic nonionic foaming agent is an anionic nonionic surfactant containing polyoxyethylene alkyl ether functional groups.

[0062] Furthermore, the anionic nonionic foaming agent is sodium C12 alkyl polyoxyethylene ether carboxylate.

[0063] Furthermore, the rheology modifier is a nanoscale particulate rheology modifier.

[0064] Furthermore, the rheology modifier is nano-sized sodium-based bentonite.

[0065] Furthermore, the salt auxiliary is CaCl2.

[0066] The preparation method of the above-mentioned CO2 self-thickening gel foam system includes the following steps:

[0067] (1) Add the formulated amount of nonionic responsive surfactant and the formulated amount of rheology modifier to the formulated amount of water, stir at the first stirring speed for the first stirring time, and obtain a uniformly dispersed mixture.

[0068] (2) Add the formula amount of anionic nonionic foaming agent and the formula amount of salt additive to the mixture, and stir at the second stirring speed for the second stirring time to obtain CO2 self-thickening gel foam system A1.

[0069] Furthermore, in step (1), the first stirring speed is 15,000 rpm;

[0070] The first stirring time is 45 minutes.

[0071] Further, in step (2), the second stirring speed is increased to 500 rpm;

[0072] The second stirring time is 20 minutes.

[0073] The CO2 self-thickening gel foam system is prepared by any of the above-mentioned methods for preparing CO2 self-thickening gel foam systems.

[0074] Application of any of the above-mentioned CO2 self-thickening gel foam systems in oil extraction.

[0075] Furthermore, any of the above-mentioned CO2 self-thickening gel foam systems can be used as CO2 blocking agents.

[0076] Furthermore, the specific steps for the above application are as follows:

[0077] CO2 was continuously introduced into the CO2 self-thickening gel foam system A1, and then stirred at 3500 rpm for 3 minutes before being injected into the target formation.

[0078] Example 2

[0079] CO2 self-thickening gel foam system A2, by mass percentage, consists of the following components:

[0080] The content of nonionic responsive surfactant is 8 wt%, the content of anionic nonionic foaming agent is 5 wt%, the content of rheology modifier is 5 wt%, the content of salt additive is 8 wt%, and the balance is water.

[0081] Furthermore, the nonionic responsive surfactant is a C16-C22 nonionic tertiary amine responsive surfactant.

[0082] Furthermore, the nonionic responsive surfactant is coconut oil-based diethanolamide.

[0083] Furthermore, the anionic nonionic foaming agent is an anionic nonionic surfactant containing polyoxyethylene alkyl ether functional groups.

[0084] Furthermore, the anionic nonionic foaming agent is sodium C10 alkyl polyoxyethylene ether sulfonate.

[0085] Furthermore, the rheology modifier is a nanoscale particulate rheology modifier.

[0086] Furthermore, the rheology modifier is nanoscale calcium-based bentonite.

[0087] Furthermore, the salt auxiliary is NaCl.

[0088] The preparation method of the above-mentioned CO2 self-thickening gel foam system includes the following steps:

[0089] (1) Add the formulated amount of nonionic responsive surfactant and the formulated amount of rheology modifier to the formulated amount of water, stir at the first stirring speed for the first stirring time, and obtain a uniformly dispersed mixture.

[0090] (2) Add the formula amount of anionic nonionic foaming agent and the formula amount of salt additive to the mixture, and stir at the second stirring speed for the second stirring time to obtain CO2 self-thickening gel foam system A2.

[0091] Furthermore, in step (1), the first stirring speed is 18,000 rpm;

[0092] The first stirring time is 40 minutes.

[0093] Furthermore, in step (2), the second stirring speed is at least 500 rpm;

[0094] The second stirring time is 20 minutes.

[0095] The CO2 self-thickening gel foam system is prepared by any of the above-mentioned methods for preparing CO2 self-thickening gel foam systems.

[0096] Application of any of the above-mentioned CO2 self-thickening gel foam systems in oil extraction.

[0097] Furthermore, any of the above-mentioned CO2 self-thickening gel foam systems can be used as CO2 blocking agents.

[0098] Furthermore, the specific steps for the above application are as follows:

[0099] CO2 was continuously introduced into the CO2 self-thickening gel foam system A2, and then stirred at 3000 rpm for 4 minutes before being injected into the target formation.

[0100] Example 3

[0101] CO2 self-thickening gel foam system A3, by mass percentage, consists of the following components:

[0102] The content of nonionic responsive surfactant is 3 wt%, the content of anionic nonionic foaming agent is 10 wt%, the content of rheology modifier is 1 wt%, the content of salt additive is 10 wt%, and the balance is water.

[0103] Furthermore, the nonionic responsive surfactant is a C16-C22 nonionic tertiary amine responsive surfactant.

[0104] Furthermore, the nonionic responsive surfactant is a tartrate-based diethanolamide.

[0105] Furthermore, the anionic nonionic foaming agent is an anionic nonionic surfactant containing polyoxyethylene alkyl ether functional groups.

[0106] Furthermore, the anionic nonionic foaming agent is C18 alkyl polyoxyethylene ether sodium sulfate.

[0107] Furthermore, the rheology modifier is a nanoscale particulate rheology modifier.

[0108] Furthermore, the rheology modifier is nano-sized fly ash.

[0109] Furthermore, the salt additive is MgCl2.

[0110] The preparation method of the above-mentioned CO2 self-thickening gel foam system includes the following steps:

[0111] (1) Add the formulated amount of nonionic responsive surfactant and the formulated amount of rheology modifier to the formulated amount of water, stir at the first stirring speed for the first stirring time, and obtain a uniformly dispersed mixture.

[0112] (2) Add the formula amount of anionic nonionic foaming agent and the formula amount of salt additive to the mixture, and stir at the second stirring speed for the second stirring time to obtain CO2 self-thickening gel foam system A3.

[0113] Furthermore, in step (1), the first stirring speed is 10,000 rpm;

[0114] The first stirring time is 60 minutes.

[0115] Furthermore, in step (2), the second stirring speed is 200 rpm;

[0116] The second stirring time is 30 minutes.

[0117] The CO2 self-thickening gel foam system is prepared by any of the above-mentioned methods for preparing CO2 self-thickening gel foam systems.

[0118] Application of any of the above-mentioned CO2 self-thickening gel foam systems in oil extraction.

[0119] Furthermore, any of the above-mentioned CO2 self-thickening gel foam systems can be used as CO2 blocking agents.

[0120] Furthermore, the specific steps for the above application are as follows:

[0121] CO2 was continuously introduced into the CO2 self-thickening gel foam system, and then stirred at 2000 rpm for 5 minutes before being injected into the target formation.

[0122] Example 4

[0123] CO2 self-thickening gel foam system A4, by mass percentage, consists of the following components:

[0124] The content of nonionic responsive surfactant is 10 wt%, the content of anionic nonionic foaming agent is 1 wt%, the content of rheology modifier is 4 wt%, the content of salt additive is 3 wt%, and the balance is water.

[0125] Furthermore, the nonionic responsive surfactant is a C16-C22 nonionic tertiary amine responsive surfactant.

[0126] Furthermore, the nonionic responsive surfactant is palm oil diethanolamide. In another embodiment, the nonionic responsive surfactant is a mixture of lauric acid diethanolamide, cocoa butter diethanolamide, shea butter diethanolamide, and palm oil diethanolamide in equal mass ratios.

[0127] Furthermore, the anionic nonionic foaming agent is an anionic nonionic surfactant containing polyoxyethylene alkyl ether functional groups.

[0128] Furthermore, the anionic nonionic foaming agent is a mixture of equal mass ratios of sodium C12 alkyl polyoxyethylene ether carboxylate, sodium C10 alkyl polyoxyethylene ether sulfonate, and sodium C18 alkyl polyoxyethylene ether sulfate. In another embodiment, the anionic nonionic foaming agent is sodium C10 alkyl polyoxyethylene ether carboxylate. In another embodiment, the anionic nonionic foaming agent is sodium C15 alkyl polyoxyethylene ether carboxylate. In another embodiment, the anionic nonionic foaming agent is sodium C18 alkyl polyoxyethylene ether carboxylate. In another embodiment, the anionic nonionic foaming agent is sodium C10 alkyl polyoxyethylene ether sulfonate. In another embodiment, the anionic nonionic foaming agent is sodium C18 alkyl polyoxyethylene ether sulfonate. In another embodiment, the anionic nonionic foaming agent is sodium C12 alkyl polyoxyethylene ether sulfonate. In another embodiment, the anionic nonionic foaming agent is sodium C10 alkyl polyoxyethylene ether sulfate. In another embodiment, the anionic nonionic foaming agent is C18 alkyl polyoxyethylene ether sodium sulfate. In another embodiment, the anionic nonionic foaming agent is C12 alkyl polyoxyethylene ether sodium sulfate.

[0129] Furthermore, the rheology modifier is a nanoscale particulate rheology modifier.

[0130] Furthermore, the rheology modifier is a mixture of nano-sized sodium-based bentonite, nano-sized calcium-based bentonite, and nano-sized fly ash in equal mass ratios.

[0131] Furthermore, the salt additive is a mixture of CaCl2, NaCl, and MgCl2 in equal mass ratios.

[0132] The preparation method of the above-mentioned CO2 self-thickening gel foam system includes the following steps:

[0133] (1) Add the formulated amount of nonionic responsive surfactant and the formulated amount of rheology modifier to the formulated amount of water, stir at the first stirring speed for the first stirring time, and obtain a uniformly dispersed mixture.

[0134] (2) Add the formula amount of anionic nonionic foaming agent and the formula amount of salt additive to the mixture respectively, and stir at the second stirring speed for the second stirring time to obtain the CO2 self-thickening gel foam system.

[0135] Furthermore, in step (1), the first stirring speed is 20,000 rpm;

[0136] The first stirring time is 30 minutes.

[0137] Furthermore, in step (2), the second stirring speed is 1000 rpm;

[0138] The second stirring time is 10 minutes.

[0139] The CO2 self-thickening gel foam system is prepared by any of the above-mentioned methods for preparing CO2 self-thickening gel foam systems.

[0140] Application of any of the above-mentioned CO2 self-thickening gel foam systems in oil extraction.

[0141] Furthermore, any of the above-mentioned CO2 self-thickening gel foam systems can be used as CO2 blocking agents.

[0142] Furthermore, the specific steps for the above application are as follows:

[0143] Continuously introduce CO2 into the CO2 self-thickening gel foam system, then stir at a speed of 2000-5000 rpm for 2-5 minutes before injecting it into the target formation.

[0144] Performance characterization:

[0145] Experimental Example 1

[0146] The configuration of the CO2 self-thickening gel foam system A1 is largely the same as the CO2 responsive gel foam system A1 prepared in Example 1, except that it does not contain anionic nonionic foaming agents.

[0147] First, the effect of shear rate on apparent viscosity was tested on CO2-free CO2 self-thickening gel foam system A1 before CO2 was introduced. Then, the change in apparent viscosity of the system with shear rate after CO2 introduction was tested. The experimental results are shown in […]. Figure 1 As shown.

[0148] Depend on Figure 1 It can be seen that before CO2 is introduced into the CO2 self-thickening gel foam system A1 which does not contain anionic nonionic foaming agent, the apparent viscosity of the system is very low, only a few mPa·s, and the viscosity of the system remains basically unchanged with the increase of shear rate.

[0149] When CO2 is introduced into the CO2 self-thickening gel foam system A1 (which does not contain anionic nonionic foaming agents), the system viscosity reaches over 800 mPa·s after response when the shear rate is zero (at rest). As the shear rate increases, the apparent viscosity initially remains constant and then gradually decreases, indicating that the system exhibits shear-thinning characteristics. This characteristic can achieve the purpose of deep-seated fracturing using CO2-responsive gel systems. The near-wellbore zone has a relatively high shear rate, which reduces the system viscosity and increases its mobility, allowing the system to migrate deeper into the formation. The far-wellbore zone has a relatively low shear rate, resulting in increased system viscosity, which can meet the needs of deep formation CO2 fracture control.

[0150] Experimental Example 2

[0151] The CO2 self-thickening gel foam system A1 prepared in Example 1 was tested using the CO2 foam stability test method to obtain the half-life at different stirring speeds. The experimental results are as follows: Figure 2 As shown in the results, the liquid half-life of the CO2 foam system gradually increases with the increase of shear rate. When the shear rate increases from 4000 r / min to 10000 r / min, the liquid half-life increases from 103 min to 192 min, which further illustrates that the foam stability of the CO2 self-thickening gel foam system A1 is effectively improved.

[0152] Experimental Example 3

[0153] The CO2 self-thickening gel foam system A2 prepared in Example 2 was tested using the CO2 foam stability test method to obtain the half-life at different stirring speeds. The experimental results are as follows: Figure 3 As shown in the results, the liquid half-life of the CO2 foam system gradually increases with the increase of shear rate. When the shear rate increases from 4000 r / min to 10000 r / min, the liquid half-life increases from 133 min to 317 min. Compared with the CO2 self-thickening gel foam system A1 prepared in Example 1, the liquid half-life (stability) of the CO2 self-thickening gel foam system A2 is also increased with the increase of the concentration of responsive surfactant, anionic nonionic foaming agent and rheology modifier.

[0154] Experiment Example 4

[0155] CO2 foam system D1 was prepared using the same formulation and method as in Example 1, except that D1 does not contain nonionic responsive surfactants.

[0156] The half-life of CO2 foam was tested under different shear rates, and the experimental results are as follows: Figure 4As shown in the results, the liquid half-life of the CO2 foam system gradually increases with the increase of shear rate. When the shear rate increases from 4000 r / min to 10000 r / min, the liquid half-life increases from 36 min to 89 min. Compared with the CO2 self-thickening gel foam system A1 prepared in Example 1, when the shear rate increases from 4000 r / min to 10000 r / min, the liquid half-life increases from 108 min to 192 min. The liquid half-life (stability) of CO2 foam system D1 under different shear rate conditions is 1 / 4 of that of system A1. This is mainly because ordinary nonionic surfactants do not have CO2 responsive characteristics, and therefore cannot self-thicken to form a gel to increase the viscosity of the foam liquid film, and thus cannot improve the foam stability.

[0157] Experimental Example 5

[0158] CO2 gel foam system D2 was prepared using the same method as in Example 1, except that 5 wt% of a common polymer crosslinking gel was used instead of 5 wt% of a nonionic responsive surfactant. The 5 wt% polymer crosslinking gel consisted of polyacrylamide and a crosslinking agent of 5 wt% methylenebisacrylamide.

[0159] The half-life of CO2 foam was tested under different shear rates, and the experimental results are as follows: Figure 5 As shown in the results, the liquid separation half-life of the CO2 foam system gradually increases with the increase of shear rate. When the shear rate increases from 4000 r / min to 10000 r / min, the liquid separation half-life increases from 62 min to 112 min. Compared with the CO2 self-thickening gel foam system A1 prepared in Example 1, when the shear rate increases from 4000 r / min to 10000 r / min, the liquid separation half-life increases from 108 min to 192 min. The liquid separation half-life (stability) of CO2 gel foam system D2 under different shear rate conditions is 1 / 4 of that of system A1. This is because the polymer cross-linked gel in CO2 gel foam system D2 is composed of high molecular cross-links. Under high-speed shear conditions, the polymer chains break, the viscosity decreases, and thus the foam stability deteriorates.

[0160] Experimental Example 6

[0161] The injection capacity results of CO2 self-thickening gel foam system A1 and CO2 gel foam system D2 in the core are as follows: Figure 6As shown, the results indicate that the injection capability of CO2 gel foam system D2 is significantly lower than that of CO2 self-thickening gel foam system A1, further demonstrating that the injection performance of CO2 self-thickening gel foam system A1 is greatly improved. This is mainly because the polymer is a macromolecule with high viscosity between crosslinking. The CO2 self-thickening gel foam system is composed of small molecule responsive nonionic surfactants with a viscosity comparable to water. Therefore, CO2 self-thickening gel foam system A1 has a better injection capability.

[0162] The embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments, and various changes can be made within the scope of knowledge possessed by those skilled in the art without departing from the spirit of the present invention.

Claims

1. A CO2 self-thickening gel foam system characterized by, consists of the following components by mass percentage: The content of the non-ionic responsive surfactant is 3-10wt%, the content of the anionic-nonionic foaming agent is 1-10wt%, the content of the rheological modifier is 1-5wt%, the content of the salt additive is 3-10wt%, and the balance is water, wherein: The non-ionic responsive surfactant is one or more of lauric acid diethanolamide, coconut diethanolamide, tallow diethanolamide and palm diethanolamide; The anionic-nonionic foaming agent is an anionic-nonionic surfactant containing polyoxyethylene alkyl ether functional groups; The rheological modifier is one or more of nano-sodium bentonite, nano-calcium bentonite and nano-fly ash; The salt additive is one or more of CaCl2, NaCl and MgCl2.

2. The CO2 self-thickening gel foam system of claim 1, wherein, The anionic-nonionic foaming agent is one or more of C10-C18 alkyl polyoxyethylene ether sodium carboxylate, C10-C18 alkyl polyoxyethylene ether sodium sulfonate and C10-C18 alkyl polyoxyethylene ether sodium sulfate.

3. A method of preparing a CO2 self-thickening gel foam system according to any one of claims 1-2, characterized in that, The method comprises the following steps: (1) adding the formula amount of non-ionic responsive surfactant and the formula amount of rheological modifier to the formula amount of water, stirring at a first stirring speed for a first stirring time to obtain a uniformly dispersed mixture; (2) adding the formula amount of anionic-nonionic foaming agent and the formula amount of salt additive to the mixture, respectively, and stirring at a second stirring speed for a second stirring time to obtain the CO2 self-thickening gel foam system.

4. The method of making a CO2 self-thickening gel foam system of claim 3, wherein, The first stirring speed in step (1) is at least 10,000 rpm; The first stirring time is at least 30 minutes.

5. The method of claim 4, wherein the CO2 self-thickening gel foam system is prepared by the steps of: The first stirring speed in step (1) is 10,000-20,000 rpm; The first stirring time is 30-60 minutes.

6. The method of claim 3, wherein the CO2 self-thickening gel foam system is prepared by the steps of: The second stirring speed in step (2) is at least 200 rpm; The second stirring time is at least 10 minutes.

7. The method of making a CO2 self-thickening gel foam system of claim 6, wherein, The second stirring speed in step (2) is 200-1,000 rpm; The second stirring time is 10-30 minutes.

8. The CO2 self-thickening gel foam system prepared by the method of any one of claims 3-7.

9. The use of the CO2 self-thickening gel foam system of any one of claims 1, 2 and 8 in oil exploitation.

10. The use of the CO2 self-thickening gel foam system of any one of claims 1, 2 and 8 as a CO2 channeling agent.

11. Use according to claim 10, wherein the compound is ###0002### The specific steps of the above uses are as follows: CO2 is continuously introduced into the CO2 self-thickening gel foam system, and then stirred at a speed of 2,000-5,000 rpm for 2-5 minutes before being injected into the target formation.

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