A triple-responsive rheological modifier to carbon dioxide, temperature and pressure, preparation method and application thereof

Abstract

This invention discloses a triple-responsive rheology modifier for carbon dioxide, temperature, and pressure, its preparation method, and its application, belonging to the field of oil and gas field development technology. The rheology modifier comprises N,N-dimethylacrylamide, 2-acrylamido-2-methylpropanesulfonic acid, a carbon dioxide-responsive monomer, an alkyl methacrylate hydrophobic monomer, oleamide-propyl dimethylamine oxide sulfobetaine, a crosslinking agent, 2,2'-azobisisobutylamidine dihydrochloride, 3-mercaptopropionic acid, and water. The rheology modifier of this invention exhibits triple-responsive characteristics to carbon dioxide, temperature, and pressure, enabling viscosity stability under high temperature, high pressure, and high salinity conditions during fracturing in complex reservoir environments, controllable gel breaking during well shut-in, and intelligent utilization and release of carbon dioxide, achieving intelligent and low-carbon control throughout the entire fracturing, well shut-in, and oil displacement process.

Description

Technical Field

[0001] This invention relates to the field of oil and gas field development technology, especially the field of oilfield chemistry technology, specifically to a triple-responsive rheology modifier for carbon dioxide, temperature and pressure, its preparation method and application. This triple-responsive rheology modifier is suitable for the integrated process of carbon dioxide capture, utilization and storage (CCUS) pressure-driven displacement. Background Technology

[0002] With the rapid development of unconventional oil and gas resources, reservoir conditions are gradually evolving towards deeper, higher-temperature, higher-pressure, and higher-salinity formations. The traditional staged fracturing-shut-in-displacement process is no longer sufficient for efficient development in low-permeability reservoirs such as tight oil and shale gas, mainly due to insufficient sand-carrying capacity of fracturing fluids, difficulties in flowback, severe reservoir damage, and low energy utilization. To improve fracturing efficiency and resource recovery, integrated fracturing-shut-displacement technology has emerged. This technology utilizes fracturing media (such as carbon dioxide or carbon dioxide composite fluids) directly after fracturing for well shut-in and oil displacement, achieving continuous fracturing-shut-in-displacement operations, thereby improving fracture extension, energy utilization, and oil recovery. Existing fracturing fluid systems mainly include water-based fracturing fluids, oil-based fracturing fluids, and carbon dioxide foam fracturing fluids. Among these, water-based systems (such as guar gum, carboxymethyl cellulose, and polyacrylamide) are prone to degradation or rapid viscosity decay under high temperature, high salt, and high shear conditions, leading to reduced sand-carrying capacity and insufficient fracture support. Viscoelastic surfactant (VES) systems have attracted attention due to their lack of polymer backbone and residue pollution, but they still suffer from insufficient temperature resistance, poor salt and shear resistance, limited response regulation, complex synthesis, and high cost. Oil-based systems are costly and cause serious environmental pollution. Although carbon dioxide foam systems have good flowback and low residue characteristics, their foam stability is poor, and it is difficult to meet the viscosity requirements of both fracturing and oil displacement stages. In recent years, carbon dioxide-responsive rheological regulation systems have become a research hotspot. These systems typically introduce basic functional groups such as tertiary amines and guanidine groups, which, under the action of carbon dioxide, form carbonates or bicarbonates, promoting molecular protonation and network structure construction, thereby achieving viscosity enhancement. However, existing carbon dioxide-responsive systems are mostly designed for single fracturing applications and rely solely on carbon dioxide to trigger viscosity changes. Some systems introduce strongly hydrophobic associations or chemical cross-linking networks to ensure temperature and salt resistance, but these often require external oxidants or enzyme treatments to break the gel, leading to dependence on breaker agents, residual risks, and insufficient conductivity recovery. Therefore, it is difficult to achieve dynamic viscosity control during fracturing and well shut-in processes.

[0003] Furthermore, existing CO2-responsive fluids generally neglect the synergistic effect of temperature and pressure. After fracturing, as pressure decreases and temperature increases during the well-clogging phase, dissolved CO2 gradually escapes from the system. If this process can be effectively utilized, it can not only achieve self-regulating viscosity breaking, but also displace formation crude oil with the escaped CO2, further improving recovery rate. Moreover, carbon utilization can be achieved through CO2 recycling and storage. By introducing response sites and reversible cross-linking networks that can couple with the CO2 dissolution-dissociation equilibrium into the rheology modifier, the system can achieve in-situ rheological enhancement during the fracturing injection phase by introducing CO2. During well-clogging recovery and well-opening flowback depressurization, the system spontaneously reduces viscosity and disintegrates its structure without or with minimal dependence on external breaker, improving flowback efficiency and promoting the recovery of fracture conductivity, thereby achieving a synergistic process of "viscosity enhancement—regulation—self-breaking—displacement / flowback".

[0004] Therefore, existing carbon dioxide-responsive rheology modifiers suffer from problems such as a single response mechanism, reliance on additional breaker agents, and lack of synergistic coupling with the hydraulic fracturing and displacement process, making them unsuitable for the complex working conditions of integrated hydraulic fracturing and displacement operations in deep tight oil formations. Developing an intelligent rheology modifier system that combines triple response characteristics of carbon dioxide, temperature, and pressure, along with controllable viscosity regulation and carbon dioxide utilization capabilities, is of significant scientific and engineering value for achieving integrated fracturing and oil displacement, promoting the integration of oil and gas development with CCUS (Continuous Coal Fuel System), improving tight oil recovery, and realizing green and low-carbon extraction. Summary of the Invention

[0005] To address the aforementioned problems, one objective of this invention is to provide a triple-responsive rheology modifier based on carbon dioxide, temperature, and pressure. This rheology modifier incorporates reversible protonation active sites triggered by carbon dioxide into its polymer chain, which can couple with the dissolution / dissociation equilibrium of injected carbon dioxide. This enables in-situ temporary storage and release of carbon dioxide, along with reversible rheological control, thereby enhancing the synergistic efficiency of the entire carbon dioxide fracturing-steaming-displacement process during construction. This rheology modifier can achieve viscosity stability under high temperature, high pressure, and high salinity conditions during fracturing in complex reservoir environments, controllable gel breaking during well steaming, and intelligent utilization and release of carbon dioxide. It solves the problems of flowback difficulties, uncontrollable viscosity, environmental pollution, and low carbon utilization efficiency inherent in existing fracturing fluid systems in high-temperature, high-pressure tight reservoirs, achieving intelligent and low-carbon control of the entire fracturing, well steaming, and oil displacement process.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A rheology modifier that responds to carbon dioxide, temperature, and pressure, comprising the following substances in parts by weight:

[0008] N,N-Dimethylacrylamide, 4.0~11.0 parts;

[0009] 2-Acrylamido-2-methylpropanesulfonic acid (AMPS), 1.0~3.0 parts;

[0010] Carbon dioxide responsive monomer, 2.0~7.5 parts;

[0011] Alkyl methacrylate hydrophobic monomers, 0.5~1.5 parts;

[0012] Oleamide propyl dimethylamine oxide sulfobetaine, 0.5~4.5 parts;

[0013] Crosslinking agent, 0.05~0.8 parts;

[0014] 2,2'-Azobisisobutylamidine dihydrochloride, 0.02~0.1 parts;

[0015] 3-Mercaptopropionic acid, 0–0.03 parts;

[0016] The remainder is water;

[0017] The total weight of the above components is 100 parts.

[0018] In one specific embodiment of the present invention, the carbon dioxide responsive monomer is 2-(dimethylamino)ethyl methacrylate, 2-(diethylamino)ethyl methacrylate, or N-[3-(dimethylamino)propyl]methacrylamide.

[0019] In one specific embodiment of the present invention, the alkyl methacrylate hydrophobic monomer is lauryl methacrylate or tetradecyl methacrylate.

[0020] In one specific embodiment of the present invention, the crosslinking agent is prepared by a method comprising the following steps: (The crosslinking agent is prepared from nanocellulose (CNF) and nanohydrotalcite (HT)).

[0021] A1. Selectively oxidize the aqueous dispersion of nanocellulose to carboxylated nanocellulose (T-CNF).

[0022] A2. Disperse nano-hydrotalcite in deionized water. Under stirring conditions, slowly add the carboxylated nanocellulose dispersion to the nano-hydrotalcite dispersion and continue stirring for 2 minutes. After 4 hours, the product is obtained; wherein the mass ratio of nano-hydrotalcite dispersion and carboxylated nanocellulose is 1:(4 19).

[0023] In this step, the carboxyl groups on the surface of carboxylated nanocellulose are... With nano-hydrotalcite layers Electrostatic attraction and ionic bonding occur at the sites, thereby forming a stable nanocomposite structure. The resulting suspension system is a carboxylated nanocellulose / hydrotalcite composite crosslinking agent, which should be stored in the dark and at low temperature for later use.

[0024] Another object of the present invention is to provide a method for preparing the above-mentioned rheology modifier, which is simple to operate, has a stable process, uses readily available raw materials, and is inexpensive. The specific solution is as follows:

[0025] A method for preparing a rheology modifier includes the following steps:

[0026] B1. Dissolve oleamide propyl dimethylamine oxide sulfobetaine in water, add alkyl methacrylate hydrophobic monomers and carbon dioxide responsive monomers, stir under a carbon dioxide atmosphere to form a homogeneous system, and then add N,N-dimethylacrylamide and 2-acrylamido-2-methylpropanesulfonic acid in sequence.

[0027] B2. Add 2,2'-azobisisobutylamidine dihydrochloride and 3-mercaptopropionic acid, and carry out free radical copolymerization reaction in a carbon dioxide atmosphere at 50~60℃ for 6-8 hours, then cool and dry. The crosslinking agent can be added before or after polymerization.

[0028] Another object of the present invention is to provide the application of the above-mentioned rheology modifier in a fracturing-flooding integrated process, wherein, during the fracturing construction stage, fracturing fluid containing the above-mentioned rheology modifier is injected into the formation together with carbon dioxide.

[0029] The rheology modifier of the present invention is a polymer system with triple response characteristics to carbon dioxide, temperature, and pressure. Its polymer backbone is based on N,N-dimethylacrylamide and AMPS as a hydrophilic backbone, and a carbon dioxide-responsive side group containing a tertiary amine group is introduced through a carbon dioxide-responsive monomer. This side group undergoes protonation during high-pressure carbon dioxide dissolution to form a strongly positively charged –NH group. + (CH3)2HCO3 -Ion-pair structure, electrostatic repulsion induces main chain extension and significantly increases system viscosity. When a composite crosslinking agent prepared from nanocellulose and nanohydrotalcite is used, this crosslinking agent plays a core role in nano-reinforcement and reversible network construction in the system: the high aspect ratio fiber skeleton of T-CNF and the two-dimensional charged structure of HT sheets can generate strong electrostatic attraction and ion bridging with polymer chains under the drive of carbon dioxide protonation. This allows the cation centers formed after the protonation of tertiary amine groups to be synergistically anchored to the carboxyl groups of T-CNF and the negatively charged regions on the surface of HT sheets, thereby generating dynamic nano-crosslinking nodes composed of "polymer chain - cellulose chain - double metal hydroxide sheet". With the increase of carbon dioxide concentration and pressure, the degree of protonation of tertiary amine groups increases, the charge density is higher, and the number and strength of nano-crosslinking points increase simultaneously, further enhancing the macroscopic viscosity and achieving a triple-enhanced coupling of carbon dioxide response, pressure response and nanostructure response. Meanwhile, the flexible fiber network of T-CNF and the layered spatial architecture of HT form a stable three-dimensional support framework in solution, which not only improves the stability and shear resistance of the hydrophobic association structure, but also maintains the integrity and toughness of the network under high temperature, high mineralization and dynamic pressure environments, significantly enhancing the system's resistance to thermal degradation and sand-carrying capacity. When carbon dioxide is released from the system, the tertiary amine groups are deprotonated, the electrostatic attraction is weakened, the nano-crosslinking nodes relax, the polymer chains shrink, and the system viscosity is significantly reduced; however, after carbon dioxide is reintroduced, the charge accumulates again, and the cellulose-layered bimetallic hydroxide composite interface induces the rapid reconstruction of nano-crosslinking points, so that the viscosity is completely restored or even slightly enhanced, exhibiting excellent structural memory and reversible cycle stability. In the high temperature and high salinity environment at the bottom of the well, the hydrophobic side chains of alkyl methacrylates activate intermolecular hydrophobic association to form a dynamically recombinant hydrophobic association network. This mechanism can achieve a "temperature / salinity synergistic anti-phase thickening" effect, effectively offsetting the viscosity decay of the hydrophilic skeleton under harsh conditions. This ensures that the viscosity of the rheology modifier does not decay or even increases under high shear, high temperature and high salinity conditions, achieving adaptive stability of thermal response.

[0030] The specific mechanism of action of rheology modifiers in the integrated pressure-driven displacement process is as follows:

[0031] During the fracturing operation, after the rheology modifier solution and carbon dioxide are co-injected into the formation, the carbon dioxide dissolves in the aqueous phase under high pressure to form a bicarbonate system. This causes a reversible protonation reaction of the tertiary amine groups in the rheology modifier, resulting in molecular chain extension, increased hydrophilicity, and a pressure-increasing viscosity of the system. This creates a highly viscous, proppant-carrying support fluid, promoting full fracture propagation and support. The carbon dioxide dissolution behavior at this stage not only endows the system with intelligent response characteristics but also enables the initial utilization and storage of carbon dioxide.

[0032] After entering the well-clogging stage, the fracture pressure gradually decreases with filtration loss and pressure diffusion, while the temperature rises back towards the formation. This process causes a shift in the carbon dioxide dissolution / dissociation equilibrium in the system, weakening the viscosity-enhancing effect brought about by the protonation of tertiary amines, and gradually transitioning the system from a high-viscosity, sand-carrying state to a flowable state. During the subsequent well-opening and flowback depressurization process, the rapid pressure drop makes it easier for dissolved carbon dioxide in the liquid phase to reach supersaturation and precipitate and be removed, triggering the deprotonation of tertiary amine groups. The polymer chains transform from an extended state to a coiled state, and the inter-chain bridging and hydrophobic association networks disintegrate, resulting in a rapid decrease in system viscosity and achieving pressure drop-triggered self-breaking of the polymer. Simultaneously, during the well-clogging and flowback stages, carbon dioxide (including dissolved and free phases) in fractures and near-wellbore areas migrates towards matrix pores and low-permeability zones driven by concentration gradients and pressure differentials, forming a pressure-clogging-driven cycle of "injection—well-clogging adsorption / diffusion—well-opening pressure differential recovery." After contact with crude oil / condensate, carbon dioxide can produce certain swelling and viscosity reduction, light component extraction, and interfacial tension reduction effects, and can provide additional driving force through gas expansion and compressibility release. For gas-bearing reservoirs, the migration of carbon dioxide and changes in the adsorption / desorption balance can also promote the release and utilization of hydrocarbons from pores / organic matter. In the later stages of well-clogging and production, as pressure is released and carbon dioxide is gradually removed from the system, the rheology modifier maintains a low-viscosity state or further reduces viscosity. Residual polymers are more easily carried out with the flowback fluid, reducing the risk of near-wellbore residue, which is beneficial for restoring fracture conductivity and subsequent production. Overall, this system achieves a synergistic process of "high pressure thickening and sand carrying - well simmering and temperature recovery pre-control - pressure drop self-breaking gel to promote return flow - carbon dioxide migration and displacement to enhance efficiency", and may improve the residence time and efficiency of carbon dioxide in the formation.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] (1) The rheology modifier of the present invention has triple response characteristics of carbon dioxide, temperature and pressure. Through the synergistic effect of carbon dioxide response segments containing tertiary amine groups, alkyl hydrophobic associative segments and nano-crosslinked networks, it can achieve adaptive rheological switching in the process of fracturing-well shut-opening / displacement. That is, under injection and high pressure conditions, carbon dioxide dissolution and tertiary amine protonation enhance the inter-chain interaction, and the system viscoelasticity is improved to meet the requirements of sand carrying and controlled water loss. In the well shut-opening and depressurization stages, as the pressure decays and the carbon dioxide escape / dissociation balance changes, the inter-chain interaction weakens and promotes network rearrangement or disintegration, which reduces viscosity and flow resistance, thereby facilitating flowback and subsequent displacement processes and reducing dependence on external chemical breaker.

[0035] (2) The rheology modifier of the present invention can achieve process coupling of "dissolution and carrying-controlled release utilization" of carbon dioxide during operation. In the injection stage, it promotes the dissolution and uniform distribution of carbon dioxide in the fluid. In the well smothering and displacement stages, it releases carbon dioxide and re-participates in the displacement process with changes in pressure / temperature. At the same time, some carbon dioxide may remain in the formation in the form of dissolved state, residual gas or reaction with the formation, thus providing support for the in-situ utilization and potential storage of carbon dioxide in the integrated pressure smothering and displacement scenario. It has the application potential to reduce carbon emissions and improve recovery rate. At the same time, in the well smothering-well opening and subsequent displacement stages, it can achieve viscosity reduction and flow resistance reduction with changes in carbon dioxide balance and network structure, which helps to improve flowback efficiency, reduce residue and potential damage to reservoir conductivity, thereby improving the effect of unconventional reservoir stimulation and subsequent recovery efficiency.

[0036] (3) The raw materials used in the preparation method of the present invention are widely available, green and renewable, and the synthesis conditions are mild. It has the feasibility of scale-up preparation and on-site preparation, and has good application economy and engineering adaptability. Detailed Implementation

[0037] To more clearly illustrate the present invention, specific embodiments are described below. Those skilled in the art should understand that the following description is illustrative rather than restrictive and should not be construed as limiting the scope of protection of the present invention.

[0038] In the following examples, the crosslinking agent is obtained through the following process:

[0039] A well-dispersed 2.0 wt% CNF aqueous dispersion was stirred evenly in an ice bath (0℃). Then, 0.031 g of TEMPO (2,2,6,6-tetramethylpiperidine-1-oxy radical) and 0.210 g of sodium bromide (NaBr) were added to form a catalytic system. Sodium hypochlorite (NaClO) solution was slowly added dropwise as an oxidant under continuous stirring, and the pH of the system was controlled at 10.0 with dilute NaOH solution. The reaction was maintained for 180 min to allow selective TEMPO oxidation of CNF surface to generate carboxyl groups. When the pH of the system was basically stable and no more NaOH was consumed, ethanol was added to terminate the reaction and decompose the residual NaClO. Unreacted substances and byproducts were removed by dialysis or repeated centrifugation and washing to obtain TEMPO-oxidized T-CNF aqueous dispersion.

[0040] The pre-prepared HT (prepared according to patent CN109467109A) was dispersed in deionized water at a mass ratio of HT:T-CNF = 1:9, and a stable HT dispersion was obtained by ultrasonic treatment for 30 minutes.

[0041] The above T-CNF dispersion was slowly added dropwise to the HT dispersion at 1000 r / min and stirred for 4 h to obtain the nano-crosslinking agent T-CNF / HT.

[0042] Example 1

[0043] Dissolve 3.0 parts of oleamide propyl dimethylamine oxide sulfobetaine in deionized water, add 1.0 part of lauryl methacrylate and 2.5 parts of 2-(dimethylamino)ethyl methacrylate, and stir for 30 min to obtain a homogeneous solution; then add 9.0 parts of N,N-dimethylacrylamide and 2.0 parts of AMPS in sequence; add 0.5 parts of the prepared T-CNF / HT crosslinking agent, 0.05 parts of 2,2'-azobisisobutylamidine dihydrochloride and 0.02 parts of 3-mercaptopropionic acid, and carry out free radical copolymerization reaction at 55℃ under carbon dioxide atmosphere for 6 h. After the reaction is completed, cool and dry to obtain rheology modifier 1.

[0044] Example 2

[0045] Dissolve 4.0 parts of oleamide propyl dimethylamine oxide sulfobetaine in water, add 0.8 parts of tetradecyl methacrylate and 3.0 parts of N-[3-(dimethylamino)propyl]methacrylamide, and stir for 30 min; then add 10.0 parts of N,N-dimethylacrylamide and 2.5 parts of AMPS; add 0.7 parts of T-CNF / HT crosslinking agent, 0.08 parts of 2,2'-azobisisobutylamidine dihydrochloride and 0.03 parts of 3-mercaptopropionic acid, and react at 60℃ under a carbon dioxide atmosphere for 8 h. After the reaction is completed, cool and dry to obtain rheology modifier 2.

[0046] Example 3

[0047] Dissolve 3.5 parts of oleamide propyl dimethylamine oxide sulfobetaine in water, add 1.2 parts of lauryl methacrylate and 2.2 parts of 2-(diethylamino)ethyl methacrylate, and stir for 30 min; then add 8.5 parts of N,N-dimethylacrylamide, 1.8 parts of AMPS, 0.6 parts of T-CNF / HT crosslinking agent, 0.06 parts of 2,2'-azobisisobutylamidine dihydrochloride, and 0.015 parts of 3-mercaptopropionic acid. React at 50 °C under a carbon dioxide atmosphere for 6 h, and after cooling and drying, obtain rheology modifier 3.

[0048] Comparative Example 1

[0049] The T-CNF / HT crosslinking agent in Example 2 was replaced with the conventional small molecule crosslinking agent N,N'-methylenebisacrylamide (MBA), while other components and conditions remained unchanged.

[0050] Comparative Example 2

[0051] In Example 3, 2-(diethylamino)ethyl methacrylate was replaced with N,N-dimethylacrylamide (DMAA), while other components and conditions remained unchanged.

[0052] Test Example 1 (Carbon Dioxide Response Viscosity Performance Test)

[0053] Take Example 1 respectively 3 and Comparative Example 1 The obtained rheology modifier was prepared into a 0.5 wt% aqueous solution and allowed to stand at room temperature for 12 h for hydration. A rotational rheometer was used to measure the hydration at 25℃ and a shear rate of 170 s⁻¹. - ¹Testing the initial apparent viscosity under the condition Subsequently, CO2 was bubbled at a flow rate of 300 mL / min for 5 min (viscosity stabilized), and the apparent viscosity after CO2 treatment was immediately tested. , and The difference is the viscosity change in response to carbon dioxide thickening. .

[0054] A portion of the CO2-treated sample was placed in a vacuum drying oven, and a vacuum was drawn to 0.05 MPa (absolute pressure) at 25°C and maintained for 30 min to promote CO2 escape. The apparent viscosity was then measured. .

[0055] To simulate the effect of downhole temperature recovery, a portion of the CO2-treated samples were heated to 80°C in a sealed environment and held at that temperature for 30 minutes to test their apparent viscosity. Further, the apparent viscosity was tested by evacuating to 0.05 MPa (absolute pressure) at 80°C and maintaining the vacuum for 60 min. , and The difference is the viscosity change due to decompression and heating. .

[0056] Table 1 Viscosity response performance of various rheology-modified systems

[0057]

[0058] Note: Comparative Example 2 has no carbon dioxide responsive groups, and its viscosity does not show a significant response to carbon dioxide, temperature, and pressure, so it is omitted.

[0059] Example 1 The viscosity of system 3 increased by 168.8% after carbon dioxide was introduced. The viscosity was 188.6 mPa·s, and after vacuum drying and heating in a vacuum drying oven, the viscosity decreased significantly by 152.9 mPa·s. At 186.4 mPa·s, it exhibits excellent responsiveness to carbon dioxide, temperature, and pressure. In contrast, Comparative Example 1, while showing some response, exhibits little change in viscosity increase or decrease.

[0060] Test Example 2 (Temperature and Salt Resistance Test)

[0061] Take Example 1 respectively 3 and Comparative Example 1 The obtained rheology modifier was used to prepare a simulated high-mineralization solution with a mass concentration of 0.5 wt%, wherein the sodium ion concentration was 2 × 10⁻⁶. 4 mg / L (prepared with NaCl). The sample was aged at 80℃ for 7 days, then cooled to 25℃ and subjected to a shear rate of 170 s⁻¹. - ¹The apparent viscosity after aging was tested below. Apparent viscosity under the same conditions before aging Based on the standard, calculate the viscosity retention rate. Example 1 The viscosity retention rates of samples 3 were approximately 90%, 88%, and 91%, respectively, compared to Comparative Example 1. The values ​​were approximately 73% and 79%, respectively, and no significant phase separation was observed after aging of the system in the examples.

[0062] Test Example 3 (Decompression, Heating, Viscosity Reduction, and Rheology Modifier System: Immersion Recovery Test)

[0063] A static core model-based infiltration method was employed: Shale cores from the same batch were selected, saturated with simulated crude oil after vacuuming, and weighed. The cores were then placed in a 0.5 wt% rheology modifier system and subjected to a "CO2 thickening—depressurization and heating viscosity reduction" process under a set temperature and pressure path before infiltration was carried out (specific temperature and pressure parameters were set as in Test Example 1). The amount of oil extracted was collected periodically, and the infiltration recovery rate was calculated until the recovery rate stabilized, yielding the maximum infiltration recovery rate (see Table 3). The results showed that the maximum infiltration recovery rate of the system in this example could reach approximately 21%. The percentage was 28%, significantly higher than the comparative system, indicating its potential application in the synergistic effect of backflow-absorption displacement.

[0064] Table 3. Oil recovery rate tests for different systems

[0065]

[0066] As demonstrated by the above tests, the three-response rheology modifier of this invention, through the synergistic effect of carbon dioxide response units containing tertiary amine groups and hydrophobic side chains, combined with a nano-reinforced nano-crosslinked network, forms a multi-response structure possessing reversibility, temperature resistance, and salt resistance. This system exhibits low initial viscosity, sensitive response, high shear stability, and recyclability, making it suitable for fracturing and drainage processes in deep, highly mineralized shale gas reservoirs. Furthermore, in practical applications, the monomer ratio and crosslinking agent content can be adjusted according to reservoir temperature, mineralization, and construction requirements to obtain optimal rheology modulation performance and response rate.

[0067] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A triple-responsive rheology modifier based on carbon dioxide, temperature, and pressure, characterized in that, Composed of the following substances in parts by weight: N,N-Dimethylacrylamide, 4.0~11.0 parts; 2-Acrylamido-2-methylpropanesulfonic acid, 1.0~3.0 parts; Carbon dioxide responsive monomer, 2.0~7.5 parts; Alkyl methacrylate hydrophobic monomers, 0.5~1.5 parts; Oleamide propyl dimethylamine oxide sulfobetaine, 0.5~4.5 parts; Crosslinking agent, 0.05~0.8 parts; 2,2'-Azobisisobutylamidine dihydrochloride, 0.02~0.1 parts; 3-Mercaptopropionic acid, 0–0.03 parts; The remainder is water; The sum of the weight parts of the above components is 100 parts; The carbon dioxide responsive monomer is 2-(dimethylamino)ethyl methacrylate, 2-(diethylamino)ethyl methacrylate, or N-[3-(dimethylamino)propyl]methacrylamide; The crosslinking agent is prepared by a method comprising the following steps: A1. Selectively oxidize the aqueous dispersion of nanocellulose to carboxylated nanocellulose; A2. Disperse nano-hydrotalcite in deionized water. Under stirring conditions, slowly add the carboxylated nanocellulose dispersion to the nano-hydrotalcite dispersion and continue stirring for 2 minutes. After 4 hours, the product is obtained; wherein the mass ratio of nano-hydrotalcite to carboxylated nanocellulose is 1:(4 19).

2. The triple-responsive rheology modifier based on carbon dioxide, temperature, and pressure according to claim 1, characterized in that, The alkyl methacrylate hydrophobic monomer is lauryl methacrylate or tetradecyl methacrylate.

3. A method for preparing a carbon dioxide, temperature, and pressure triple-responsive rheology modifier, used to prepare the rheology modifier according to claim 1 or 2, characterized in that, Includes the following steps: B1. Dissolve oleamide propyl dimethylamine oxide sulfobetaine in water, add alkyl methacrylate hydrophobic monomers and carbon dioxide responsive monomers, stir under a carbon dioxide atmosphere to form a homogeneous system, and then add N,N-dimethylacrylamide and 2-acrylamido-2-methylpropanesulfonic acid in sequence. B2. Add 2,2'-azobisisobutylamidine dihydrochloride and 3-mercaptopropionic acid, and carry out a free radical copolymerization reaction in a carbon dioxide atmosphere at 50~60℃. The mixture is left to stand for 8 hours, then cooled and dried, wherein the crosslinking agent is added before or after polymerization.

4. The application of a triple-responsive rheology modifier based on carbon dioxide, temperature, and pressure, characterized in that, The rheology modifier described in claim 1 or 2 is used in the integrated fracturing and fracturing process, wherein, during the fracturing construction stage, fracturing fluid containing the rheology modifier is injected into the formation together with carbon dioxide.

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