A deep regulation and displacement system suitable for fractured reservoirs, its preparation method and application

Abstract

This invention provides a deep moderating and displacement system suitable for fractured reservoirs, its preparation method, and its application. The moderating and displacement system comprises the following raw materials in parts by weight: 0.2-1 parts of partially hydrolyzed polyacrylamide (HPAM), 0.1-0.6 parts of polyethyleneimine (PEI), 0.2-0.4 parts of silane-modified micron-sized inorganic fibers, 0.1-0.8 parts of encapsulated citric acid, 0.02-0.2 parts of heat stabilizer, 0.02-0.1 parts of metal ion complexing agent, and 196.9-199.36 parts of water. The moderating and displacement system of this invention has low initial viscosity, small injection pressure gradient, strong shear recovery ability, significant deep plugging effect, and excellent long-term thermal stability. Furthermore, it can be adjusted according to the target reservoir temperature and the dominant fracture aperture, achieving effective adaptation to fractured reservoirs with different apertures.

Description

Technical Field

[0001] This invention relates to a deep regulation and drive system suitable for fractured oil reservoirs, its preparation method and application, belonging to the fields of oilfield chemistry and enhanced oil recovery technology. Background Technology

[0002] In the development of fractured reservoirs, the displacing fluid injected into the formation tends to flow along the high-permeability fracture network, while the crude oil in the low-permeability layer is difficult to displace effectively, resulting in low sweep efficiency and unsatisfactory oil recovery. Deep moderating displacement technology aims to control the flow path of the injected fluid, forcing subsequent displacing fluids to change direction by blocking or partially blocking high-permeability fracture channels, thereby improving the sweep efficiency and achieving the goal of improving oil recovery. Currently, there are three main moderating displacement technologies commonly used for fractured reservoirs: polymer gel systems, pre-crosslinked particle systems, and foam systems. The principle of polymer gel systems is that polymers (such as partially hydrolyzed polyacrylamide HPAM) react chemically with crosslinking agents underground to form a three-dimensional network structure gel, thereby blocking high-permeability channels. This technology is highly mature, has high strength after gelation, significant sealing effect, and a wide range of applications. However, there is a contradiction between its injectability and underground gel strength: high-concentration systems are difficult to inject, while low-concentration systems have limited final strength. Furthermore, the system is susceptible to irreversible polymer chain degradation due to shear stress during injection, severely affecting deep gelation performance. Gelation time is also difficult to control precisely, with premature gelation leading to near-wellbore blockage, decreased gelation strength in deep reservoirs, or failure to gel, impacting deep reservoir regulation and displacement effects. Pre-crosslinked particle systems inject pre-crosslinked elastic particles into the formation, using "bridging-blocking" and "deformation-migration" mechanisms to seal fractures or pore throats. This system exhibits good shear resistance, stable injection process, no need to wait for underground gelation time, and selective entry into high-permeability zones. However, its effective depth is limited, and particles tend to accumulate near the wellbore or at fracture entrances, resulting in decreased sealing effectiveness for deep fractures with increasing distance. Foam systems utilize gas, foaming agents, and foam stabilizers to form stable foam, achieving sealing of high-permeability channels through the Jamin effect in gas-liquid two-phase flow. This system possesses excellent flow control capabilities, selectively sealing high-permeability zones with minimal damage to low-permeability matrix, and dynamically adjustable sealing strength. However, the stability of foam is highly dependent on temperature, salinity and crude oil properties, and it is prone to collapse under harsh reservoir conditions; its sealing strength is generally lower than that of solid gel, and it may be breached in high-intensity crossflow channels; in addition, the construction process is relatively complex, involving gas injection and ground foaming, and has high requirements for equipment and operation.

[0003] In summary, while existing polymer gel systems have achieved some success in practice, they all face the common challenge of balancing effective deep migration, high-strength in-situ plugging, and long-term stability when dealing with the specific scenario of deep regulation and displacement in fractured reservoirs. Furthermore, existing technologies have explored adding nanomaterials to enhance the gel or employing delayed crosslinking techniques, but these methods struggle to simultaneously achieve good injectability, high strength recovery after deep migration, and long-term stability. Specifically, existing systems often struggle to resolve the contradiction between "low-viscosity injection" and "high-strength gelation in deep reservoirs," as well as the critical bottleneck of "irreversible shear degradation." To overcome these shortcomings of existing technologies, this invention is proposed. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a deep flood control system suitable for fractured reservoirs, its preparation method, and its application. The technical problem this system aims to solve is overcoming the following contradictions that existing polymer gel flood control systems cannot simultaneously address. One of the three major technical problems is the poor injectability of the flood control system. Specifically, conventional polymer gel systems have high initial viscosity and poor injectability, leading to a sharp increase in injection pressure, huge pumping energy consumption, and even failure to achieve the target injection volume.

[0005] The second of the three major technical issues involves the performance degradation of the modulating and flooding system after formation shearing. Specifically, after undergoing shear dilution in formation pores, the viscosity of the polymer gel modulating and flooding system in the target area of ​​the deep reservoir is not ideal, resulting in relatively low plugging strength and failing to achieve the desired modulating and flooding effect.

[0006] The third of the three major technical issues involves the poor long-term stability of the plugging body in high-temperature and high-mineralization formation conditions. Specifically, the polymer gel plugging system is affected by formation temperature and mineralization, which reduces the system's stability and limits the plugging time, thus failing to achieve the desired long-term plugging and plugging effect.

[0007] The core design of this invention lies in the fact that its key components (microcapsule trigger temperature and silane-modified fiber length) can be adjusted according to the target reservoir temperature and the dominant fracture aperture, achieving effective adaptation to fractured reservoirs with different apertures. This solves the problems existing in the above-mentioned polymer gel-based modulator-deployment systems in deep modulator-deployment of fractured reservoirs.

[0008] The technical solution of the present invention is as follows:

[0009] A deep regulation and drive system suitable for fractured reservoirs comprises the following raw material components in parts by weight: 0.2-1 parts of partially hydrolyzed polyacrylamide (HPAM), 0.1-0.6 parts of polyethyleneimine (PEI), 0.2-0.4 parts of silane-modified micron-sized inorganic fibers, 0.1-0.8 parts of encapsulated citric acid, 0.02-0.2 parts of heat stabilizer, 0.02-0.1 parts of metal ion complexing agent, and 196.9-199.36 parts of water.

[0010] According to a preferred embodiment of the present invention, the deep regulation and drive system suitable for fractured reservoirs comprises the following raw material components in parts by weight: 0.4-0.8 parts of partially hydrolyzed polyacrylamide (HPAM), 0.2-0.4 parts of polyethyleneimine (PEI), 0.2-0.4 parts of silane-modified micron-sized inorganic fiber, 0.3-0.5 parts of encapsulated citric acid, 0.1 parts of heat stabilizer, 0.06 parts of metal ion complexing agent, and 197.74-198.74 parts of water.

[0011] According to a preferred embodiment of the present invention, the deep regulation and drive system suitable for fractured reservoirs comprises the following raw material components in parts by weight: 0.6 parts of partially hydrolyzed polyacrylamide (HPAM), 0.3 parts of polyethyleneimine (PEI), 0.3 parts of silane-modified micron-sized inorganic fiber, 0.4 parts of encapsulated citric acid, 0.1 parts of heat stabilizer, 0.06 parts of metal ion complexing agent, and 198.24 parts of water.

[0012] According to a preferred embodiment of the present invention, the degree of hydrolysis of partially hydrolyzed polyacrylamide (HPAM) is 5% to 15%, preferably 10%.

[0013] According to a preferred embodiment of the present invention, the weight-average molecular weight of the partially hydrolyzed polyacrylamide (HPAM) is 5-10 million, preferably 8 million.

[0014] According to the present invention, the weight-average molecular weight of polyethyleneimine (PEI) is preferably 10,000 to 70,000, and more preferably 25,000.

[0015] According to a preferred embodiment of the present invention, the heat stabilizer is thiourea.

[0016] According to a preferred embodiment of the present invention, the metal ion complexing agent is disodium ethylenediaminetetraacetate (EDTA-2Na).

[0017] According to a preferred embodiment of the present invention, the water is formation water. The salinity is 0-100,000 mg / L, and the divalent cation concentration is 0-2,000 mg / L. A preferred salinity is 3,000 mg / L and the divalent cation concentration is 200 mg / L (corresponding to low-to-medium salinity reservoirs). For high-salinity reservoirs, simulated formation water with higher salinity (e.g., 35,000 mg / L, 65,000 mg / L, or 100,000 mg / L) can be prepared as needed to verify the adaptability of the system of the present invention under various salinity conditions.

[0018] A preferred method for preparing silane-modified micron-sized inorganic fibers according to the present invention includes the following steps:

[0019] Sepiolite fibers were fully dispersed in a mixed solvent of ethanol and water, and silane coupling agent γ-aminopropyltriethoxysilane (APTES) was added. After reaction, centrifugation, washing, and drying, silane-modified micron-sized inorganic fibers were obtained.

[0020] Preferably, the sepiolite fibers are commercially available products with a fiber diameter of 0.5-2 μm and a length of 10-100 μm. To ensure safe injection of the system, the fiber length should be less than the opening of the target crack; at the same time, a sufficient aspect ratio should be maintained to form an effective network. For wider cracks, longer fibers can be used accordingly; for finer cracks, shorter fibers can be selected.

[0021] Preferably, in the mixed solvent of ethanol and water, the volume ratio of ethanol to water is 8:1-10:1, more preferably 9:1. The mass ratio of sepiolite fiber to the volume ratio of the mixed solvent is 0.01-0.1 g / mL.

[0022] Preferably, the mass ratio of sepiolite fiber to silane coupling agent γ-aminopropyltriethoxysilane (APTES) is 100:1-100:5, and more preferably 100:3.

[0023] Preferably, the reaction temperature is 60℃-80℃, the reaction time is 4-8h, and the reaction is carried out under reflux and stirring conditions; more preferably, the reaction temperature is 70℃, and the reaction time is 6h.

[0024] According to the present invention, the preparation steps of silane-modified micron-sized inorganic fibers aim to graft active amino functional groups onto the surface of sepiolite fibers via a silanization reaction. The core chemical reaction comprises two steps (chemical reaction formulas are shown in [reference needed]). Figure 1 ):

[0025] ① Hydrolysis of silane coupling agents: The silane coupling agent γ-aminopropyltriethoxysilane (APTES) first undergoes hydrolysis in an alcohol-water environment, where its ethoxy group is replaced by a hydroxyl group to generate a reactive silanol product.

[0026] ② Condensation reaction with sepiolite fiber surface: The generated silanol undergoes dehydration condensation with the silanol on the sepiolite fiber surface to form siloxane bonds, thereby grafting the propyl chain with terminal amino group onto the sepiolite fiber surface in a covalent manner.

[0027] Through the above reactions, inorganic sepiolite fibers were transformed into an active material with a surface rich in amino groups. These amino groups play a crucial role in the gel system: firstly, under acidic conditions provided by citric acid, the amino groups on the surface of the inorganic sepiolite fibers can be protonated, leading to ionic crosslinking with the carboxyl groups of partially hydrolyzed polyacrylamide, thus fixing the silane-modified fibers onto the gel network via ionic crosslinking; secondly, under long-term exposure to deep high temperatures (e.g., 90°C), the amino groups on the surface of the silane-modified fibers can further undergo amidation reactions with the carboxyl groups in the partially hydrolyzed polyacrylamide, forming covalent bonds and thus constituting a dense gel network; furthermore, it can also generate strong electrostatic, hydrogen bond, and ionic interactions with polyethyleneimine and released citric acid in the system. This synergy between physical entanglement and chemical crosslinking is the basis for constructing the "fiber-reinforced-chemically crosslinked" dual network in this invention.

[0028] According to a preferred embodiment of the present invention, the preparation method of encapsulated citric acid includes the following steps: dissolving ethyl cellulose as a wall material in dichloromethane as an organic solvent to obtain a wall material solution; adding citric acid powder as a core material to the above wall material solution and mixing thoroughly to obtain a suspension (citric acid is insoluble in dichloromethane and exists in the form of solid particles); and then spray drying to obtain encapsulated citric acid.

[0029] Preferably, the ethoxylated component of the wall material, ethyl cellulose, has an ethoxylated content of 44%-49%. By selecting wall materials with different ethoxylated contents, the thermal response temperature of the microcapsules can be adjusted to suit reservoirs at different temperatures. For example, wall materials with ethoxylated contents of 49% and 44% are suitable for reservoirs at 90°C and 60°C, respectively.

[0030] Preferably, the mass concentration of the wall material solution is 10%-15%, and more preferably 10%.

[0031] Preferably, the particle size of the core material citric acid powder is 10-30 μm, and more preferably 20 μm.

[0032] Preferably, the mass ratio of the wall material ethyl cellulose to the core material citric acid powder is 1:1-1:3, and more preferably 1:2.

[0033] Preferably, after adding the core material citric acid powder to the wall material solution, the solution is sheared at a speed of 8000-12000 rpm for 5-15 minutes to form a uniform and stable suspension; preferably, the speed is 10000 rpm and the shearing time is 10 minutes.

[0034] Preferably, a centrifugal atomizer is used for spray drying; the atomizer speed is set to 20,000-30,000 rpm, the feed rate is 5-15 mL / min, the inlet temperature is controlled at 80-100℃, and the outlet temperature is controlled at 40-60℃.

[0035] The above-mentioned method for preparing a deep regulation and drive system suitable for fractured reservoirs includes the following steps:

[0036] Under stirring conditions, partially hydrolyzed polyacrylamide (HPAM), a heat stabilizer, and a metal ion complexing agent were added to water in sequence and dispersed thoroughly. Silane-modified micron-sized inorganic fibers were added and dispersed thoroughly. Polyethyleneimine (PEI) was added and dispersed thoroughly. Finally, encapsulated citric acid was added and dispersed thoroughly to obtain a deep regulation and drive system suitable for fractured reservoirs.

[0037] The above-mentioned deep regulation and drive system applicable to fractured reservoirs is applied in the regulation and drive of fractured reservoirs.

[0038] According to a preferred embodiment of the present invention, the reservoir temperature is 60℃-90℃.

[0039] The advantages of this invention compared to other modulators are as follows:

[0040] (1) The injection properties of the modified drive system of the present invention are excellent. The system is initially a low-viscosity dispersion. This is due to the use of low-concentration partially hydrolyzed polyacrylamide and microcapsules and modified fibers dispersed in solid form, which can significantly reduce the wellbore injection pressure and make it easier to penetrate into complex fracture network systems.

[0041] (2) The deep gelation effect of the system of this invention is good, and the deep regulation and driving effect is excellent. After experiencing strong shearing action in wellbore boreholes and formation pores, the polymer chains of traditional polymer gel systems undergo irreversible degradation, resulting in a severe decrease in their strength at depth. This invention ensures deep performance through a dual mechanism: First, it uses microcapsules to encapsulate citric acid to achieve a temperature-responsive delayed release effect, providing protection for the crosslinking reinforcement during low-temperature transport, allowing it to reach the deep target area directly; Second, it innovatively introduces silane-modified fibers, which, after shearing, can assist the system in restoring its performance through physical network support and unreacted active sites. When the system reaches the deep high-temperature region, the microcapsules rupture upon heating to release citric acid, triggering rapid secondary crosslinking, which, in synergy with the fiber network, achieves strength growth, thereby forming a high-strength regulation and driving sealing system at depth.

[0042] (3) The plugging system of this invention has high plugging strength and long-term stability. Compared with foam systems with relatively low plugging strength or pre-crosslinked particles that are prone to dehydration and shrinkage, this invention constructs a composite structure of "chemical crosslinking network + physical fiber skeleton". Polyethyleneimine and partially hydrolyzed polyacrylamide are crosslinked by transamidation reaction to form covalent bonds. The protonated amino groups on the surface of silane-modified fibers and in polyethyleneimine can form dense ionic crosslinking points with the carboxyl and citrate anions in partially hydrolyzed polyacrylamide. In addition, under long-term action at deep high temperature (e.g., 90°C), the carboxyl groups in partially hydrolyzed polyacrylamide can further undergo amidation reaction with the amino groups on the surface of silane-modified fibers and in polyethyleneimine to form covalent bonds, thereby constituting a dense gel network. At the same time, the heat stabilizer and metal ion complexing agent in the system can effectively resist the damage of high temperature and high salinity to the gel network. The plugging body formed by this system has high strength and is not easily broken, and has good long-term stability in high temperature and high salinity environments with low dehydration rate, which can meet the requirements of long-term stable production in fractured reservoirs.

[0043] (4) The temperature response of the system of this invention is wide. The change in gel strength of the system is triggered by the temperature of the target reservoir, realizing precise control of "protection during migration and strengthening at the target". By selecting ethyl cellulose with different ethoxy content as microcapsule wall material, its thermal response temperature point can be flexibly adjusted, so that the system of this invention can adapt to fractured reservoirs with different temperatures from 60℃ to 90℃, and has strong universality.

[0044] Key Inventions

[0045] 1. "Low-viscosity injection - deep reinforcement" performance reversal design: By using low-concentration HPAM, solid-phase dispersed encapsulated citric acid and silane-modified micron-sized inorganic fibers to construct the initial low-viscosity working fluid, excellent injectability is ensured; by utilizing the temperature of the deep formation to trigger the microcapsule rupture, the citric acid is released to synergistically enhance the fiber network and enhance the gel strength, realizing the performance transformation from an easily injectable fluid to a high-strength modulated drive system.

[0046] 2. "Temperature-responsive delayed release and triggered enhancement" mechanism: Citric acid is encapsulated in ethyl cellulose microcapsules to achieve delayed and targeted release of the crosslinking enhancer. The thermal softening temperature of the wall material is controlled by adjusting the ethoxy content to match the target reservoir temperature. During the low-temperature injection phase, the microcapsules remain intact; as the system enters the deep high-temperature zone, the wall material softens and fractures, releasing citric acid and transforming the target reservoir into an acidic environment. Under acidic conditions, polyethyleneimine and partially hydrolyzed polyacrylamide can crosslink via transamidation to form covalent bonds. Simultaneously, the amino groups on the fiber surface and in polyethyleneimine can be protonated, generating strong electrostatic attraction with citrate ions and carboxylate anions in partially hydrolyzed polyacrylamide, forming dense ionic crosslinking points. These points, through their fibrous structure, form physical anchors on the fracture surface, significantly enhancing flow resistance and sealing strength. Furthermore, under long-term exposure to deep high temperatures (such as 90°C), the carboxyl groups in partially hydrolyzed polyacrylamide can further undergo amidation reactions with the amino groups on the surface of silane-modified fibers and in polyethyleneimine to form covalent bonds, thereby triggering further reinforcement of the gel network. After undergoing shearing and transport to deeper layers, the system's performance is significantly restored and enhanced.

[0047] 3. Dual Reinforcement Mechanism of "Fiber Reinforcement-Chemical Crosslinking": This innovative approach introduces micron-sized inorganic fibers with silane-modified surfaces into the gel modulated system. The modified fibers not only reinforce the gel through physical entanglement and network support, but also, under acidic conditions, the amino functional groups grafted onto their surface can be protonated, leading to ionic crosslinking with citrate ions and carboxylate ions in partially hydrolyzed polyacrylamide. Furthermore, under long-term exposure to deep high temperatures (e.g., 90°C), the amino groups on the modified fiber surface may further undergo amidation reactions with the carboxyl groups in partially hydrolyzed polyacrylamide, forming covalent bonds. This constructs a robust composite reinforcement framework, enhancing the overall strength, shear recovery, and long-term thermal stability of the system.

[0048] Invention Effects

[0049] 1. The regulating and driving system developed in this invention has low initial viscosity, small injection pressure gradient, and minimal damage to low-permeability matrix, which can effectively improve the industry problem of difficult injection of high-concentration systems.

[0050] 2. The system developed in this invention has strong shear recovery capability. After undergoing high-speed shearing in simulated boreholes, the system can significantly restore its shear sealing strength by relying on the fiber network and citric acid-triggered cross-linking after being left to stand or at a certain reservoir temperature.

[0051] 3. The deep plugging effect of the regulating drive system developed in this invention is significant. After undergoing formation shear and migrating to the deep high-temperature region, the system can form a high-strength plugging system through the temperature-responsive delayed release and triggering enhancement mechanism of microcapsules. Its energy storage modulus is significantly improved compared with the initial state, and it can overcome the high pressure gradient and effectively plug high-permeability fracture channels.

[0052] 4. The regulating drive system developed in this invention has excellent long-term thermal stability, thanks to the stabilizing effect of the fiber skeleton and the effective protection of the heat stabilizer and complexing agent. After long-term aging in a high temperature and high mineralization environment, the system retains high gel strength, has low dehydration shrinkage, and significantly extends the effective period of sealing.

[0053] 5. The modified flow system developed in this invention has a simple preparation process, wide applicability, readily available raw materials, and a simple preparation method, making it easy to scale up production. By selecting ethyl cellulose with different ethoxy content as the wall material, the trigger temperature point of the microcapsules can be flexibly adjusted. By adjusting the length of the silane-modified fiber, it can be adapted to fractured reservoirs with different apertures, thereby meeting the reservoir requirements at different temperatures.

[0054] Application scenarios

[0055] The composite gel system involved in this invention has clear and significant application value in the field of enhanced oil and gas recovery (EOR). Its core application lies in solving key challenges in the development of fractured reservoirs: This system, with its unique properties of "low-viscosity injection, deep triggering, and high-strength plugging," can effectively plug fracture channels by adjusting the ethoxy content of the microcapsule wall material to match the target reservoir temperature, and by adjusting the length of the silane-modified fibers to match the reservoir fracture aperture. This forces subsequent displacement fluids to redirect to the unaffected oil-bearing matrix, significantly increasing the swept volume and oil washing efficiency of water injection or chemical flooding, ultimately improving oil recovery. Specifically, it is suitable for sandstone and carbonate reservoirs with significant fracture channeling, difficult matrix fluid absorption, and where conventional modulated displacement systems struggle to achieve effective deep plugging. Attached Figure Description

[0056] Figure 1 A route diagram for the preparation of silane-modified micron-sized inorganic fibers;

[0057] Figure 2 The cumulative citric acid release rate curves of EC-49% microcapsules at different temperatures in Experiment Example 6 are shown.

[0058] Figure 3 The cumulative release rate curves of citric acid from EC microcapsules with different ethoxy groups at 90°C are shown in Example 6.

[0059] Figure 4 This is the standard curve of citric acid concentration versus peak area in Experiment Example 6. Detailed Implementation

[0060] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with embodiments and comparative examples. The following embodiments are for illustrative purposes only and do not limit the scope of protection of this invention. Unless otherwise specified, the raw materials used in the embodiments are all commercially available products.

[0061] Example 1

[0062] A deep regulation and drive system suitable for fractured reservoirs comprises the following raw material components by mass: 0.6 g of 10% hydrolyzed polyacrylamide (HPAM) (weight-average molecular weight 8 million), 0.1 g of heat stabilizer thiourea, 0.06 g of metal ion complexing agent EDTA-2Na, 0.3 g of polyethyleneimine (PEI) (weight-average molecular weight 25,000), 0.3 g of silane-modified micron-sized inorganic fibers, 0.4 g of encapsulated citric acid, and water (simulated formation water with a total salinity of approximately 3000 mg / L and a divalent cation concentration of 200 mg / L, of CaCl2 type, including: Na...). + 848 mg / L, K + 30 mg / L, Ca 2+ 120 mg / L, Mg 2+ 80 mg / L, Cl - 1625 mg / L, HCO3 - 200 mg / L, SO4 2- 100 mg / L) 198.24 g.

[0063] Preparation of silane-modified micron-sized inorganic fibers:

[0064] 10 g of micron-sized sepiolite fibers (0.5-2 μm in diameter and 10-100 μm in length) were weighed and dispersed in 200 mL of a mixed solvent of ethanol and water (9:1 volume ratio), stirred, and ultrasonically dispersed for 40 minutes. Then, 0.3 g of silane coupling agent γ-aminopropyltriethoxysilane (APTES) was weighed and added, and the mixture was heated to reflux and stirred at 70 °C for 6 hours. After the reaction was completed, the product was centrifuged and washed five times with ethanol to remove unreacted coupling agent. Finally, the product was dried in a vacuum drying oven at 70 °C for 24 hours to obtain silane-modified micron-sized inorganic fibers with amino-grafted surfaces.

[0065] Preparation of encapsulated citric acid:

[0066] The solution was prepared using a spray drying method. First, 20g of ethyl cellulose (49% ethoxylated by mass) was weighed and placed in a 200mL beaker. Then, 150mL of dichloromethane was added and stirred or shaken until completely dissolved. After complete dissolution, more dichloromethane was added to bring the total volume to 200mL and stirred until homogeneous. Next, 40g of citric acid powder (ground to a target particle size of 20μm) was added to the wall material solution at a solid wall material to solid core material mass ratio of 1:2. The mixture was then homogenized using a homogenizer equipped with a rotor-stator high-shear dispersing homogenizer head at 10000rpm for 10min to form a homogeneous, stable, and non-agglomerated suspension. The suspension was then spray-dried using a centrifugal nebulizer. The feed flow rate was set to 10mL / min, the nebulizer speed to 30000rpm, the inlet temperature to 90℃, and the outlet temperature to 50℃. Finally, the dried powder was collected to obtain encapsulated citric acid.

[0067] The above-mentioned method for preparing a deep regulation and drive system suitable for fractured reservoirs includes the following steps:

[0068] Using a top-mounted mechanical stirrer, HPAM, thiourea, and EDTA-2Na were sequentially added to simulated formation water under stirring conditions. The stirrer speed was set to 500 rpm, and stirring was continued for 2 hours until completely dissolved to form a base solution. Subsequently, silane-modified micron-sized inorganic fibers were added to the base solution and dispersed at high speed (8000 rpm) for 10 minutes. Then, polyethyleneimine (PEI) was added, and the mixture was stirred at low speed (500 rpm) for 30 minutes to ensure homogeneity. Finally, encapsulated citric acid was added under slow stirring at 300 rpm, and the mixture was stirred for 10 minutes to obtain the deep regulation and displacement system suitable for fractured reservoirs.

[0069] Example 2

[0070] A deep regulation and drive system suitable for fractured reservoirs, with the raw material composition as described in Example 1, except that: the mass of 10% hydrolyzed polyacrylamide (HPAM) is 0.4 g, and the mass of water is 198.44 g; the other raw material composition is the same as in Example 1.

[0071] The preparation method of the above-mentioned deep regulation and drive system applicable to fractured reservoirs is the same as in Example 1.

[0072] Example 3

[0073] A deep regulation and drive system suitable for fractured reservoirs, with the raw material composition as described in Example 1, except that: the mass of silane-modified micron-sized inorganic fiber is 0.2 g, and the mass of water is 198.34 g; the other raw material composition is the same as in Example 1.

[0074] The preparation method of the above-mentioned deep regulation and drive system applicable to fractured reservoirs is the same as in Example 1.

[0075] Example 4

[0076] A deep regulation and drive system suitable for fractured reservoirs, with the raw material composition as described in Example 1, except that: the mass of polyethyleneimine (PEI) is 0.2 g and the mass of water is 198.34 g; the other raw material composition is the same as in Example 1.

[0077] The preparation method of the above-mentioned deep regulation and drive system applicable to fractured reservoirs is the same as in Example 1.

[0078] Example 5

[0079] A deep regulation and drive system suitable for fractured reservoirs, with the raw material composition as described in Example 1, except that: the mass of encapsulated citric acid is 0.3g and water is 198.34g; the other raw material composition is the same as in Example 1.

[0080] The preparation method of the above-mentioned deep regulation and drive system applicable to fractured reservoirs is the same as in Example 1.

[0081] Example 6

[0082] A deep regulation and drive system suitable for fractured reservoirs, with the raw material composition as described in Example 1, except that: 0.4 g of 10% hydrolyzable polyacrylamide (HPAM), 0.2 g of polyethyleneimine (PEI), 0.2 g of silane-modified micron-sized inorganic fiber, 0.3 g of encapsulated citric acid, and 198.74 g of water are used. The other raw material composition is the same as in Example 1.

[0083] The preparation method of the above-mentioned deep regulation and drive system applicable to fractured reservoirs is the same as in Example 1.

[0084] Example 7

[0085] A deep regulation and drive system suitable for fractured reservoirs, with the raw material composition as described in Example 1, except that: the mass of 10% hydrolyzed polyacrylamide (HPAM) is 0.8 g, and the mass of water is 198.04 g; the other raw material composition is the same as in Example 1.

[0086] The preparation method of the above-mentioned deep regulation and drive system applicable to fractured reservoirs is the same as in Example 1.

[0087] Example 8

[0088] A deep regulation and drive system suitable for fractured reservoirs, with the raw material composition as described in Example 1, except that: the mass of silane-modified micron-sized inorganic fiber is 0.4 g, and the water is 198.14 g; the other raw material composition is the same as in Example 1.

[0089] The preparation method of the above-mentioned deep regulation and drive system applicable to fractured reservoirs is the same as in Example 1.

[0090] Example 9

[0091] A deep regulation and drive system suitable for fractured reservoirs, with the raw material composition as described in Example 1, except that: the mass of polyethyleneimine (PEI) is 0.4 g and the mass of water is 198.14 g; the other raw material composition is the same as in Example 1.

[0092] The preparation method of the above-mentioned deep regulation and drive system applicable to fractured reservoirs is the same as in Example 1.

[0093] Example 10

[0094] A deep regulation and drive system suitable for fractured reservoirs, with the raw material composition as described in Example 1, except that: the mass fraction of encapsulated citric acid is 0.5 g, and the mass fraction of water is 198.14 g; the other raw material composition is the same as in Example 1.

[0095] The preparation method of the above-mentioned deep regulation and drive system applicable to fractured reservoirs is the same as in Example 1.

[0096] Example 11

[0097] A deep regulation and drive system suitable for fractured reservoirs, with the raw material composition as described in Example 1, except that: 0.8 g of 10% hydrolyzed polyacrylamide (HPAM), 0.4 g of polyethyleneimine (PEI), 0.4 g of silane-modified micron-sized inorganic fiber, 0.5 g of encapsulated citric acid, and 197.74 g of water are used; other raw material compositions are the same as in Example 1.

[0098] The preparation method of the above-mentioned deep regulation and drive system applicable to fractured reservoirs is the same as in Example 1.

[0099] Example 12

[0100] A deep regulation and drive system suitable for fractured reservoirs, with the raw material composition as described in Example 1, except that in the preparation of encapsulated citric acid, the wall material is replaced with ethyl cellulose with an ethoxy content of 44% by mass, and the other steps, conditions and raw material composition are the same as in Example 1.

[0101] The preparation method of the above-mentioned deep regulation and drive system applicable to fractured reservoirs is the same as in Example 1.

[0102] Example 13

[0103] A deep regulation and drive system suitable for fractured reservoirs, with the raw material composition as described in Example 1, except that: in the preparation of silane-modified micron-sized inorganic fibers, the length of sepiolite fibers is 50-100 μm; other steps, conditions and raw material composition are the same as in Example 1.

[0104] The preparation method of the above-mentioned deep regulation and drive system applicable to fractured reservoirs is the same as in Example 1.

[0105] Example 14

[0106] A deep regulation and drive system suitable for fractured reservoirs, with the raw material composition as described in Example 1, except that in the preparation of encapsulated citric acid, the wall material is replaced with ethyl cellulose with an ethoxy content of 46% by mass, and the other steps, conditions and raw material composition are the same as in Example 1.

[0107] The preparation method of the above-mentioned deep regulation and drive system applicable to fractured reservoirs is the same as in Example 1.

[0108] Example 15

[0109] A deep regulation and drive system suitable for fractured reservoirs, with the raw material composition as described in Example 1, except that partially hydrolyzed polyacrylamide (HPAM) is replaced with HPAM of equal mass and same degree of hydrolysis (10%) but with a weight-average molecular weight of approximately 5 million.

[0110] The composition of other raw materials is the same as in Example 1.

[0111] The preparation method of the above-mentioned deep regulation and drive system applicable to fractured reservoirs is the same as in Example 1.

[0112] Example 16

[0113] A deep regulation and drive system suitable for fractured reservoirs, with the raw material composition as described in Example 1, except that partially hydrolyzed polyacrylamide (HPAM) is replaced with HPAM of equal mass and same degree of hydrolysis (10%) but with a weight-average molecular weight of approximately 10 million.

[0114] The composition of other raw materials is the same as in Example 1.

[0115] The preparation method of the above-mentioned deep regulation and drive system applicable to fractured reservoirs is the same as in Example 1.

[0116] Example 17

[0117] A deep regulation and drive system suitable for fractured reservoirs, with the raw material composition as described in Example 1, except that partially hydrolyzed polyacrylamide (HPAM) is replaced with HPAM of equal mass and molecular weight but with a degree of hydrolysis of about 15%.

[0118] The composition of other raw materials is the same as in Example 1.

[0119] The preparation method of the above-mentioned deep regulation and drive system applicable to fractured reservoirs is the same as in Example 1.

[0120] Example 18

[0121] A deep regulation and drive system suitable for fractured reservoirs, with the raw material composition as described in Example 1, except that partially hydrolyzed polyacrylamide (HPAM) is replaced with HPAM of equal mass and molecular weight but with a degree of hydrolysis of about 5%.

[0122] The composition of other raw materials is the same as in Example 1.

[0123] The preparation method of the above-mentioned deep regulation and drive system applicable to fractured reservoirs is the same as in Example 1.

[0124] Example 19

[0125] A deep regulation and drive system suitable for fractured reservoirs, with the feedstock composition as described in Example 1, except that polyethyleneimine (PEI) is replaced with an equal mass of PEI but with a weight-average molecular weight of 70,000.

[0126] The composition of other raw materials is the same as in Example 1.

[0127] The preparation method of the above-mentioned deep regulation and drive system applicable to fractured reservoirs is the same as in Example 1.

[0128] Example 20

[0129] A deep regulation and drive system suitable for fractured reservoirs, with the feedstock composition as described in Example 1, except that polyethyleneimine (PEI) is replaced with an equal mass of PEI but with a weight-average molecular weight of 10,000.

[0130] The composition of other raw materials is the same as in Example 1.

[0131] The preparation method of the above-mentioned deep regulation and drive system applicable to fractured reservoirs is the same as in Example 1.

[0132] Example 21

[0133] A deep regulation and drive system suitable for fractured reservoirs is provided, with the raw material composition as described in Example 1, except that in the preparation method of silane-modified micron-sized inorganic fibers, the mass ratio of sepiolite fibers to the silane coupling agent γ-aminopropyltriethoxysilane (APTES) is 100:4. Other steps, conditions, and raw material composition are the same as in Example 1.

[0134] The preparation method of the above-mentioned deep regulation and drive system applicable to fractured reservoirs is the same as in Example 1.

[0135] Example 22

[0136] A deep regulation and drive system suitable for fractured reservoirs is provided, with the raw material composition as described in Example 1, except that in the preparation method of silane-modified micron-sized inorganic fibers, the mass ratio of sepiolite fibers to the silane coupling agent γ-aminopropyltriethoxysilane (APTES) is 100:2. Other steps, conditions, and raw material composition are the same as in Example 1.

[0137] The preparation method of the above-mentioned deep regulation and drive system applicable to fractured reservoirs is the same as in Example 1.

[0138] Example 23

[0139] A deep regulation and displacement system suitable for fractured reservoirs, as described in Example 1, differs only in that: the total salinity of water is 35000 mg / L, and the concentration of divalent cations is 700 mg / L (including: Na+). + 11250 mg / L, K + 410 mg / L, Ca 2+ 420 mg / L, Mg 2+ 280 mg / L, Cl - 22440 mg / L, HCO3 - 100 mg / L, SO4 2- (100 mg / L, aqueous form: CaCl2).

[0140] The composition of other raw materials is the same as in Example 1.

[0141] The preparation method of the above-mentioned deep regulation and drive system applicable to fractured reservoirs is the same as in Example 1.

[0142] Example 24

[0143] A deep regulation and displacement system suitable for fractured reservoirs, as described in Example 1, differs only in that: the total salinity of water is 65,000 mg / L, and the concentration of divalent cations is 1,300 mg / L (including Na+). + 20900 mg / L, K + 760 mg / L, Ca 2+ 780 mg / L, Mg 2+ 520 mg / L, Cl - 41640 mg / L, HCO3 - 200 mg / L, SO4 2- (200 mg / L, aqueous form: CaCl2).

[0144] The composition of other raw materials is the same as in Example 1.

[0145] The preparation method of the above-mentioned deep regulation and drive system applicable to fractured reservoirs is the same as in Example 1.

[0146] Example 25

[0147] A deep regulation and displacement system suitable for fractured reservoirs, as described in Example 1, differs only in that: the total salinity of water is 100,000 mg / L, and the concentration of divalent cations is 2,000 mg / L (including: Na+).+ 32150mg / L, K + 1170 mg / L, Ca 2+ 1200 mg / L, Mg 2+ 800 mg / L, Cl - 64080 mg / L, HCO3 - 300 mg / L, SO4 2- 300 mg / L, aqueous form: CaCl2.

[0148] The composition of other raw materials is the same as in Example 1.

[0149] The preparation method of the above-mentioned deep regulation and drive system applicable to fractured reservoirs is the same as in Example 1.

[0150] Comparative Example 1

[0151] A modulated drive system, with the raw material composition as described in Example 1, except that: the silane-modified micron-sized inorganic fibers are replaced with an equal amount of APTES-modified micron-sized silica particles;

[0152] The preparation method of APTES modified micron-sized silica particles is as follows:

[0153] 10 g of micron-sized silica particles (average particle size approximately 10-20 μm, specific surface area approximately 1-5 m² / g) were weighed and dispersed in 200 mL of a mixed solvent of ethanol and water (volume ratio 9:1), stirred, and ultrasonically dispersed for 40 minutes. Then, 0.3 g of the silane coupling agent γ-aminopropyltriethoxysilane (APTES) was weighed and added, and the mixture was heated to reflux and stirred at 70 °C for 6 hours. After the reaction was completed, the product was centrifuged and washed five times with ethanol to remove unreacted coupling agent. Finally, the product was dried in a vacuum drying oven at 70 °C for 24 hours to obtain APTES-modified micron-sized silica particles.

[0154] The composition of other raw materials is the same as in Example 1.

[0155] The preparation method of the above-mentioned modulated drive system is the same as that in Example 1, except that it is the same as above.

[0156] Comparative Example 2

[0157] A modulated drive system with the same raw material composition as described in Example 1, except that: silane-modified micron-sized inorganic fibers and encapsulated citric acid are not added, and the amount of water used is 198.94g; other raw material compositions are the same as in Example 1.

[0158] The preparation method of the above-mentioned modulated drive system is the same as that in Example 1, except that it is the same as above.

[0159] Comparative Example 3

[0160] A modulated drive system, with the raw material composition as described in Example 1, except that: no heat stabilizer (thiourea) is added, and the amount of water is 199.24g; the other raw material composition is the same as in Example 1.

[0161] The preparation method of the above-mentioned modulated drive system is the same as that in Example 1, except that it is the same as above.

[0162] Comparative Example 4

[0163] A modulating drive system, with the raw material composition as described in Example 1, except that: no metal ion complexing agent EDTA-2Na is added, and the amount of water used is 198.3g; the other raw material composition is the same as in Example 1.

[0164] The preparation method of the above-mentioned modulated drive system is the same as that in Example 1, except that it is the same as above.

[0165] Comparative Example 5

[0166] A regulating drive system, with raw material composition as described in Example 1, except that water is replaced with an equal amount of distilled water; other raw material composition is the same as in Example 1.

[0167] The preparation method of the above-mentioned modulated drive system is the same as that in Example 1, except that it is the same as above.

[0168] Comparative Example 6

[0169] A modulated drive system, with the raw material composition as described in Example 1, except that in the preparation method of silane-modified micron-sized inorganic fibers, only the sepiolite fibers are replaced with attapulgite fibers (0.5-2 μm in diameter and 10-100 μm in length). Other steps, conditions, and raw material composition are the same as in Example 1.

[0170] The preparation method of the above-mentioned modulated drive system is the same as that in Example 1.

[0171] Comparative Example 7

[0172] A modulated drive system, with the raw material composition as described in Example 1, except that polyethyleneimine (PEI) is not added, while the other raw material composition is the same as in Example 1.

[0173] The preparation method of the above-mentioned modulated drive system is the same as that in Example 1, except that it is the same as above.

[0174] Comparative Example 8

[0175] A modulated drive system, with the raw material composition as described in Example 1, except that: silane-modified micron-sized inorganic fibers are not added, and the other raw material composition is the same as in Example 1.

[0176] The preparation method of the above-mentioned modulated drive system is the same as that in Example 1, except that it is the same as above.

[0177] Comparative Example 9

[0178] A modulating system with the raw material composition as described in Example 1, except that encapsulated citric acid is not added, and the other raw material composition is the same as in Example 1.

[0179] The preparation method of the above-mentioned modulated drive system is the same as that in Example 1, except that it is the same as above.

[0180] Experimental Example 1

[0181] The initial viscosity and injectability of the modified drive systems prepared in the test examples and comparative examples were determined. The test methods are as follows:

[0182] The working solutions of the deep subsurface regulation and driving systems prepared in Examples 1-11, 13, 15-25, and Comparative Examples 1-9 were tested at 25°C using a Brookfield DV-III Ultra rheometer at 7.34 s. -1 The initial apparent viscosity was measured at a shear rate of [value missing], and each sample was tested in triplicate with the average value taken. Injectability and plugging behavior were evaluated using fractured core flow experiments: To assess the system's adaptability to fractures of different apertures, artificial fractured cores with fracture widths of approximately 100-200 μm (suitable for Examples 1-11, 15-25, and Comparative Examples 1-9) and 150-300 μm (suitable for Example 13) were selected. The core diameter was 2.5 cm and the length was 10 cm. The cores were placed in a core holder, and annular pressure was applied to simulate formation constraint. The working fluid was injected into the core at a constant flow rate of 3.0 mL / min. Pressure changes at the injection end were recorded in real time using a pressure sensor, and the pressure gradient during the stable injection phase was calculated to evaluate the system's injectability and flow resistance in the fractured medium. The results are shown in Table 1.

[0183] Table 1 Initial viscosity and injection pressure gradient of different systems

[0184]

[0185] As shown in Table 1, the initial viscosity of the systems in each embodiment of the present invention is low (≤25 mPa·s), and the injection pressure gradient is small, indicating that the system of the present invention has good injectability. Specifically, Example 13 used longer fibers (50-100 μm) to accommodate wider fractures (150-300 μm), and its initial viscosity and injection pressure gradient increased only slightly compared to Example 1. This demonstrates that the system can be adapted to different fracture apertures by adjusting the fiber length, thus maintaining good injection performance. Example 15 (5 million molecular weight) had lower initial viscosity and injection pressure gradient than Example 1, indicating that while lower molecular weight HPAM is beneficial for reducing injection resistance, its shorter molecular chains and smaller hydrodynamic volume make it difficult to form a continuous and stable three-dimensional network during subsequent gelation. Example 16 had significantly higher initial viscosity and injection pressure gradient than Example 1, demonstrating that while excessively high molecular weight HPAM can provide stronger thickening capabilities, it leads to a significant increase in injection pressure, which is detrimental to the system's injection into the formation. The initial viscosity of Example 17 was higher than that of Example 1. This is because the increased degree of hydrolysis led to an increase in the number of carboxyl groups on the HPAM molecular chain, enhancing intra- and inter-chain electrostatic repulsion, resulting in a more extended molecular chain and a larger hydrodynamic volume, making the system more difficult to inject compared to Example 1. The initial viscosity of Example 18 was lower than that of Example 1, and the injection gradient was not significantly different from that of Example 1. Therefore, considering Examples 17 and 18, a degree of hydrolysis of 10% was selected as the preferred degree of hydrolysis for this invention. Example 19 used a high molecular weight PEI (70,000), whose initial viscosity (17 mPa·s) and injection pressure gradient (0.14 MPa / m) were both higher than those of Example 1, indicating that excessively high molecular weight PEI would slightly increase the system's flow resistance due to its higher solution viscosity. Example 20 used a low molecular weight PEI (10,000), whose initial viscosity (14 mPa·s) and injection pressure gradient (0.11 MPa / m) were slightly lower than those of Example 1, demonstrating that low molecular weight PEI has no significant negative impact on the injectability of the system within the 10,000-70,000 PEI molecular weight range. (Note: Subsequent experiments 2 and 5 will reveal that excessively low molecular weight PEI can severely impair gel strength and plugging performance; therefore, the quality of PEI molecular weight cannot be fully evaluated solely from the perspective of injectability.) The initial viscosity (16 mPa·s) and injection pressure gradient (0.13 MPa / m) of Example 21 (fiber:APTES = 100:4) were slightly higher than those of Example 1. This is because when the amount of APTES is excessive relative to the amount of fiber, the silane coupling agent may undergo a self-condensation reaction after grafting saturation on the fiber surface, forming polysiloxane oligomers and generating multilayer physical adsorption, and even forming weak bridges between different fibers, resulting in a slight decrease in the uniformity of fiber dispersion in the aqueous phase and a slight increase in flow resistance.The initial viscosity (14 mPa·s) and injection pressure gradient (0.11 MPa / m) of Example 22 (fiber:APTES = 1100:2) were slightly lower than those of Example 1, indicating that insufficient APTES content reduced the amino grafting density on the fiber surface, weakened the physical adsorption between the fiber and polymer chains, and correspondingly reduced the system's flow resistance. However, this slight advantage in injectability came at the cost of sacrificing subsequent chemical crosslinking efficiency. As shown in subsequent test examples 2, 3, and 5, the gel strength (3100 Pa), shear recovery capacity (2300 Pa), and fracture plugging rate (55.2%) of Example 22 were significantly lower than those of Example 1 (4251 Pa, 3100 Pa, 73.6%), failing to meet the requirements for high-strength, erosion-resistant plugging bodies in deep fractured reservoirs. Considering both injectability and final gelation performance, the APTES:fiber ratio of 100:3 in Example 1 was preferred as the optimal ratio for achieving the performance reversal of "low-viscosity injection - deep reinforcement". Examples 23-25 ​​were prepared using simulated formation water with different salinities. The initial viscosity showed a slight decreasing trend with increasing salinity, which is attributed to the charge shielding effect of high-concentration salt ions causing the HPAM molecular chains to coil and reducing the hydrodynamic volume. Nevertheless, the initial viscosity of all systems was ≤15 mPa·s, and the injection pressure gradient was ≤0.12 MPa / m, demonstrating that the system of this invention exhibits good injectability across a wide salinity range of 0-100000 mg / L.

[0186] The initial viscosity and injection pressure gradient of Comparative Example 1 were higher than those of Example 1. This is mainly because spherical micron particles have a higher specific surface area, which generates greater steric hindrance and flow resistance during dispersion. In contrast, micron-sized fibers, due to their larger aspect ratio and lower specific surface area, are more easily oriented along the flow direction at low concentrations, thus achieving excellent injectability while ensuring system reinforcement. Comparative Example 2 had the lowest viscosity due to the lack of modified fibers and citric acid microcapsules as reinforcing components. The injection pressure of Comparative Example 4 increased abnormally in the later stages, possibly due to the lack of EDTA-2Na, which caused polymer chain aggregation in the highly salinized water, resulting in increased flow resistance. Comparative Example 5, prepared with distilled water, had an initial viscosity (17 mPa·s) and injection pressure gradient (0.14 MPa / m) slightly higher than those of Example 1. This is because distilled water does not contain salt ions, allowing the HPAM molecular chains to fully extend and increasing the hydrodynamic volume. Comparative Example 6 used attapulgite fibers, whose initial viscosity (16 mPa·s) and injection pressure gradient (0.14 MPa / m) were slightly higher than those of Example 1. Comparative Example 6 also used attapulgite fibers, whose initial viscosity (16 mPa·s) and injection pressure gradient (0.14 MPa / m) were slightly higher than those of Example 1 (15 mPa·s, 0.12 MPa / m). Although attapulgite fibers and sepiolite fibers used the same geometric dimensions, they differed in crystal structure and surface chemical properties. Sepiolite has a unique zeolite-type pore structure, a higher density of surface silanol groups, stronger hydrophilicity, more uniform dispersion in the aqueous phase, and is more easily oriented along the flow direction during high-speed shearing. Attapulgite fibers had a relatively lower density of surface silanol groups, slightly weaker interaction with water, and slightly inferior dispersion uniformity under the same shear conditions, resulting in a slight increase in flow resistance. Since the viscosity of Comparative Example 6 was not significantly different from that of Experimental Example 1, but Experimental Example 1 showed significantly better injectability, sepiolite fibers were selected. Comparative Examples 7-9, lacking PEI, modified fibers, and encapsulated citric acid respectively, all exhibited initial viscosities (12-14 mPa·s) slightly lower than Example 1 (15 mPa·s). This indicates that while these key functional components do contribute to the initial rheology of the system during the injection stage, their impact is relatively small—the absence of a single component only reduces viscosity by 1-3 mPa·s, a decrease of 7%-20%. This further confirms the core design concept of this invention: PEI, modified fibers, and encapsulated citric acid exist primarily in an inert dispersed state during the injection stage, contributing limitedly to the initial rheology of the system; their irreplaceable core value lies in subsequent in-situ activation and synergistic enhancement under deep high-temperature conditions, jointly constructing a high-strength sealing gel network.

[0187] Experimental Example 2

[0188] The gel strength and deep reinforcement effect of the modified driving systems prepared in the test examples and comparative examples after high-temperature aging were investigated. The test methods are as follows:

[0189] Take 50 mL of each of the working solutions prepared in Examples 1-13, Examples 15-25, and Comparative Examples 1-9, and place them in 100 mL stoppered glass bottles. Static age them in a 90°C oven for 72 hours. Additionally, an extra set of experiments was conducted in Example 12, where the system was statically aged in a 60°C oven for 72 hours to simulate the temperature effects experienced by the system in deep oil reservoirs. After aging, the storage modulus (G') of the samples was tested using a Haake Mars 60 rheometer at 90°C, 1 Hz frequency, and 1% strain (within the linear viscoelastic region) to characterize the gel strength. Each sample was tested three times, and the average value was taken. The results are shown in Table 2.

[0190] Table 2 Energy storage modulus (G') of different systems after high-temperature aging

[0191]

[0192] As shown in Table 2, after high-temperature aging, all embodiments of the present invention can form gels with a certain strength (G'>1000 Pa). Example 13 used longer fibers to adapt to wide fracture conditions, and its gel strength was slightly higher than that of Example 1. This shows that adjusting the fiber length to match different fracture scales does not sacrifice the core ability of the system to form a high-strength plug at deep high temperatures. Example 12 can still form a gel with a strength of 3200 Pa after aging at 60°C, indicating that by adjusting the ethoxy content of the wall material, the system of the present invention can effectively adapt to reservoir conditions at lower temperatures. After aging at 60°C for 72 hours, the storage modulus of Example 12 reaches 3200 Pa, which is higher than its 1535 Pa at 90°C. Combined with the release kinetic data of Experiment 6 ( Figure 3As can be seen, this difference stems from the matching effect between the microcapsule release rate and the cross-linking reaction kinetics: at 60°C, citric acid is released slowly and continuously, allowing the cross-linking reaction of HPAM with PEI and modified fibers to proceed in an orderly manner, forming a uniform and dense gel network; however, at 90°C, the excessively high temperature causes the microcapsule release to be too rapid, and the cross-linking reaction proceeds explosively in the initial stage, resulting in a decrease in the uniformity of the network structure and the formation of localized strong cross-links, which in turn reduces the macroscopic mechanical properties. This result fully demonstrates that by adjusting the ethoxy content of the wall material, the triggering temperature of the microcapsules can be matched with the target reservoir temperature, thereby achieving the formation of a high-strength gel at the corresponding temperature. The excellent gelling performance (3200 Pa) exhibited by Example 12 at 60°C corresponds to the performance (4251 Pa) of Example 1 at 90°C, jointly verifying the broad adaptability of the system of the present invention to reservoirs at different temperatures. The gel strength of Example 15 (5 million molecular weight) is only 1850 Pa, far lower than the 4251 Pa of Example 1. This is because the length of the HPAM molecular chain is the physical basis for forming a three-dimensional cross-linked network. When the molecular weight is too low, even with sufficient cross-linking agents and reinforcing fibers, it is difficult to construct a long-range continuous elastic network structure. The gel strength (4380 Pa) of Example 16 (10 million molecular weight) is slightly higher than that of Example 1, indicating that higher molecular weight HPAM can provide a longer molecular chain skeleton, which is beneficial for forming a higher density of cross-linking points. However, as shown in Table 1, this system can no longer meet the core requirements for deep migration in fractured reservoirs due to significant deterioration in injectability. Considering all factors, the 8 million molecular weight of Example 1 can provide sufficient cross-linking skeleton strength while ensuring excellent injectability, and is the preferred molecular weight for the system of this invention. The gel strength of Example 17 (15% degree of hydrolysis) is 3120 Pa, which is significantly lower than that of Example 1. Literature studies have shown that the cross-linking reaction of the HPAM / PEI system mainly depends on the amidation reaction and electrostatic interaction between the carboxyl groups of the HPAM side chain and the amine groups of PEI. When the degree of hydrolysis is too high, the excessively dense negative charge on the HPAM molecular chain increases the electrostatic attraction sites with PEI, but the excessively strong charge repulsion interferes with the orderly formation of the cross-linking network, leading to a decrease in gel structure uniformity and effective cross-linking density. The gel strength of Example 18 (5% hydrolysis) was only 2680 Pa, a decrease of 37%, because the insufficient number of carboxyl groups resulted in a significant reduction in available reaction sites for cross-linking, making it impossible to form a sufficiently dense cross-linking network. These results indicate that the effect of HPAM hydrolysis degree on gel strength exhibits a typical "bell-shaped curve" characteristic, with approximately 10% being the optimal degree of hydrolysis. Too low a degree results in insufficient cross-linking sites, while too high a degree damages network uniformity. The gel strength of Example 19 (PEI molecular weight 70,000) was 3800 Pa, still significantly lower than that of Example 1 (4251 Pa).This is because high molecular weight PEI has long molecular chains, which easily form excessive entanglement in local areas, resulting in uneven distribution of crosslinking points. The gel microstructure exhibits a two-phase separation characteristic of "crosslink-rich regions" and "crosslink-poor regions," leading to deterioration of macroscopic mechanical properties. The gel strength of Example 20 (PEI molecular weight 10,000) was only 2200 Pa, less than 52% of that of Example 1. This is because the molecular chain length of PEI, as a crosslinking agent, directly determines the "bridging ability" of the crosslinking network. Although PEI with a molecular weight of too low (<10,000) has a high density of reactive sites (amino groups), its chain segments are too short, resulting in insufficient effective length of crosslinking bridges formed between HPAM chains, making it difficult to construct a three-dimensional network with good elasticity and toughness. The gel strength of Example 21 was 4400 Pa, slightly higher than that of Example 1 (4251 Pa). This indicates that appropriately increasing the amount of silane coupling agent can increase the amino grafting density on the fiber surface, thereby enhancing the covalent bonding between the fiber and HPAM, and slightly increasing the gel strength. However, based on the data from Example 1, the initial viscosity and injection pressure gradient of this system are both higher than those of Example 1, meaning that this slight increase in strength comes at the cost of infusibility. From an engineering application perspective, the deterioration of infusibility has a far greater impact on deep migration ability than the small gain in strength. Therefore, the 100:3 ratio of Example 1 remains the optimal choice for balancing infusibility and gel strength. The gel strength (3100 Pa) of Example 22 decreased by 27.1% compared to Example 1, demonstrating that insufficient silane coupling agent results in an excessively low density of active amino groups on the fiber surface, severely weakening the chemical bond between the fiber and the polymer network, leading to a significant deterioration in the reinforcing effect. After aging at 90°C for 72 hours, the gel strength of Examples 23-25 ​​gradually decreased with increasing mineralization, but still maintained a strength above 3000 Pa at a mineralization of 100,000 mg / L. This is attributed to the effective complexation of divalent cations by EDTA-2Na in the system of this invention, and the inhibitory effect of the heat stabilizer thiourea on high-temperature oxidation. This demonstrates the excellent salt resistance of the system of this invention.

[0193] The gel strength of Comparative Example 1 was significantly lower than that of Example 1, indicating that although micron-sized SiO2 has a high specific surface area and reactivity, its spherical, isotropic geometry limits its ability to form a continuous mechanical network in three-dimensional space. In contrast, silane-modified fibers, with their one-dimensional linear structure, can effectively overlap and entangle in the gel, forming a through-type physical reinforcement framework. Comparative Example 2, lacking fiber reinforcement and acid-triggered secondary crosslinking, failed to form a gel effectively, resulting in severely insufficient strength. Comparative Example 3 lacked a heat stabilizer, and Comparative Example 4 lacked a complexing agent; both showed significantly lower gel strengths than Example 1, demonstrating the crucial role of heat stabilizers and complexing agents in the long-term thermal stability and gelation stability of the system. Comparative Example 6, using attapulgite fibers, exhibited a significantly lower gel strength (3550 Pa) than Example 1 (4251 Pa), a decrease of 16.5%. This difference stems from the difference in surface chemical properties between the two types of fibers. Due to its unique crystal structure, sepiolite fibers have a higher density of exposed silanol groups on their surface, enabling the grafting of more active amino functional groups during the silanization reaction with APTES. The modified sepiolite fibers have a higher amino density on their surface, which allows them to form denser covalent bonds with HPAM carboxyl groups and to generate stronger electrostatic anchoring with crack walls through protonated amino groups. These combined factors result in superior reinforcing performance of the sepiolite fibers in the system of this invention. Comparative Example 7 (without PEI) had a gel strength of only 180 Pa, at the same low level as Comparative Example 2 (without fibers and microcapsules). This directly demonstrates that even with modified fibers and microcapsules triggering acid release, without PEI as a crosslinking agent, HPAM cannot form an effective chemical crosslinking network, and the physical reinforcement of the fibers cannot compensate for the lack of chemical crosslinking. Comparative Example 8 (without modified fibers) had a gel strength of 1850 Pa, a decrease of 56.5% compared to Example 1, confirming that the fiber physical network is an indispensable skeletal component for constructing high-strength composite gels. Comparative Example 9 (without encapsulated citric acid) had a gel strength of 950 Pa, only 22.3% of Example 1, fully demonstrating the decisive contribution of acid-triggered secondary crosslinking to the final gel strength. The system relies solely on the thermal crosslinking of HPAM and PEI, resulting in a strength far lower than the multi-crosslinked network activated by citric acid in Example 1.

[0194] Experimental Example 3

[0195] The shear recovery properties of the modulated drive systems prepared in the test examples and comparative examples were evaluated. The test methods are as follows:

[0196] Fresh working fluids from Examples 1, 15, 19-25, Comparative Examples 1-2, and 5-9 were first sheared at 10,000 rpm for 5 minutes using a high-speed shear apparatus to simulate the strong shearing effect of fluid passing through a borehole. To quantify the degree of structural damage caused by shearing, the fluids were immediately sheared at 25°C and a shear rate of 7.34 s⁻¹.-1 Under the specified conditions, the apparent viscosity of the sheared samples was measured using a rheometer. Next, the sheared samples were placed in a 90℃ constant-temperature oven for 72 hours to simulate the temperature effects and performance recovery process experienced by the system in the deep reservoir. To evaluate the strength of the sealing body formed after aging, after aging, a small-amplitude oscillatory shear test was conducted using a rheometer at 90℃, 1 Hz frequency, and 1% strain (ensuring within the linear viscoelastic region). The storage modulus (G') of the samples was measured to characterize the mechanical properties of the recovered material. The results are shown in Table 3.

[0197] Table 3 Shear recovery performance of the system

[0198] As shown in Table 3, the initial viscosity of the system in Example 1 decreased significantly after strong shearing, but its storage modulus recovered to 3100 Pa after high-temperature static aging, demonstrating excellent shear recovery capability. This is mainly attributed to the physical network formed by the silane-modified fibers and the secondary chemical crosslinking triggered by the release of encapsulated citric acid. In Example 15, the G' after shear recovery was only 120 Pa, proving that molecular weight is the basis of shear recovery—too short polymer chains are difficult to rebuild the network through physical entanglement and chemical crosslinking after shearing. In Example 19 (PEI molecular weight 70,000), the strength after recovery was 2200 Pa, significantly lower than the 3100 Pa of Example 1. This is because high molecular weight PEI diffuses slowly and has fewer actual reaction sites, making it difficult to fully rearrange and rebuild a high-strength network within a limited time after shearing. Example 1 (PEI molecular weight 25,000) was able to recover to a high strength of 3100 Pa after shear failure, fully demonstrating that PEI in this molecular weight range has both good reactivity and chain migration ability, making it a better choice for constructing a "reversible-repairable" crosslinked network. Example 20 (PEI molecular weight 10,000) showed a shear recovery strength of only 350 Pa, indicating that PEI with excessively low molecular weight is almost unable to rebuild an effective crosslinked network after shear failure. Example 21 showed a shear recovery strength of 3200 Pa, slightly higher than the 3100 Pa of Example 1. This is consistent with the slightly higher gel strength trend in Example 2, indicating that a higher density of surface amino groups helps retain more active sites on the fibers after shearing, which is beneficial for network reconstruction. Therefore, considering the overall trade-off between shear recovery capability and infusion properties, Example 1 remains the optimal choice. Example 22 (APTES:fiber = 100:2) showed a recovery strength of 2300 Pa, significantly lower than Example 1, demonstrating that fibers with insufficient surface amino groups are unable to provide enough reactive sites for network repair after shear failure. The shear recovery performance data of Examples 23-25 ​​(different mineralizations) show that as the mineralization increases from 35,000 mg / L to 100,000 mg / L, the post-shear viscosity decreases from 8.5 mPa·s to 7.5 mPa·s, and the recovered storage modulus decreases from 2900 Pa to 2400 Pa. This trend is consistent with that in Examples 1 and 2, and is attributed to polymer chain coiling under high salt conditions and the weak interference of divalent cations on the crosslinking reaction. Nevertheless, Example 25 still achieved a recovered modulus of 2400 Pa at an extreme mineralization of 100,000 mg / L, significantly higher than the particle-reinforced system (Comparative Example 1, 827 Pa) and the fiber-free system (Comparative Example 8, 420 Pa), fully demonstrating that the system of the present invention possesses excellent shear recovery capability over a wide range of mineralizations.

[0199] Comparative Example 1, after aging, only formed a weak gel with a storage modulus of approximately 827 Pa, exhibiting insufficient recovery ability. This indicates that isotropic spherical particles cannot provide continuous physical network support after shearing, and their point-like binding with the polymer network makes it difficult to reconstruct an effective support network. Conversely, even if the fibers in Example 1 undergo orientation or breakage after shearing, their remaining segments can still provide support for the recovering gel network through physical entanglement and surface active sites, synergistically triggering new crosslinking points with encapsulated citric acid, achieving better strength recovery. Comparative Example 2, after aging, showed a G' of only 25 Pa, failing to form a gel with structural strength. Combined with its apparent viscosity after shearing, it can be seen that the polymer network of this system was completely destroyed and could not be recovered after shearing, exhibiting mechanical properties similar to low-viscosity fluids and lacking deep-sealing capability. Comparative Example 5 also showed good recovery ability, indicating that the intrinsic recovery mechanism of the system operates well in the absence of high-valence ion interference. Comparative Example 6, after aging, showed a G' of 2000 Pa, significantly lower than the 3100 Pa of Example 1. This indicates that after shearing, the residual fiber segments of attapulgite fibers are less able to efficiently rebuild the physical-chemical dual crosslinking with the polymer network through surface-active amino sites, unlike sepiolite fibers. Due to its higher surface amino density, sepiolite fibers retain more reactive sites after shearing, enabling them to rapidly re-bond with HPAM segments in the acidic environment created by citric acid released from microcapsules, thus more effectively restoring the gel network strength. Comparative Example 7 (without PEI) showed a recovery G' of only 40 Pa, almost no recovery ability, confirming that PEI is key to crosslinked network reconstruction after shearing. Comparative Example 8 (without fibers) showed a recovery G' of 420 Pa, only 13.5% of Example 1, demonstrating that the fiber physical network is the skeletal basis for shear recovery; without fiber support, efficient network reconstruction cannot be achieved solely through chemical crosslinking. Comparative Example 9 (without microcapsules) showed a recovery G' of 180 Pa, further highlighting the crucial role of encapsulated citric acid in shear recovery—without acid-triggered secondary crosslinking, the system can only partially recover through slow HPAM / PEI thermal crosslinking, far below the strength level required for deep plugging. Experimental Example 3 comprehensively demonstrates that only a complete system containing silane-modified fibers and encapsulated citric acid can achieve excellent performance recovery after undergoing strong shear.

[0200] Test Example 4

[0201] The long-term stability of the controlled-drive systems prepared in the test examples and comparative examples was evaluated. The test methods are as follows:

[0202] The working solutions of Examples 1, 12, 15-25, and Comparative Examples 1-9 were placed in a 90°C constant temperature oven. An additional experimental group was set up where Example 12 was placed in a 60°C oven. Samples were taken on days 7, 30, and 60 of aging to observe their condition and measure their storage modulus (G'). Simultaneously, the dehydration rate of the samples before and after aging was measured (centrifugation method). The results are shown in Tables 4 and 5.

[0203] Table 4. Long-term thermal stability and dehydration rate of the system

[0204]

[0205] Table 5. Long-term thermal stability and dehydration rate of the system

[0206] As shown in Tables 4 and 5, the system in Example 1 exhibited excellent long-term thermal stability after aging at 90℃ for 60 days, maintaining a high gel strength retention rate (>85%) and a low dehydration rate. Example 12 (ethoxy content 44%) was designed for a 60℃ reservoir. While it could gel at 90℃, its long-term stability decreased. After aging at 90℃ for 60 days, its modulus was only 900 Pa, with a dehydration rate of 28%, indicating severe performance degradation. This is because EC-44% releases citric acid rapidly at 90℃, causing a large influx of citric acid into the system in a short time, triggering rapid and strong cross-linking in localized areas. This resulted in an uneven gel network structure (locally too dense while other areas were insufficiently cross-linked), thus affecting the overall gel performance. However, after aging at its target temperature of 60℃ for 60 days, the modulus remained at 2600 Pa, with a dehydration rate of only 10%. This is because the release rate of citric acid at its trigger temperature is relatively slow, ensuring that citric acid can diffuse more evenly throughout the gel system, thereby initiating secondary cross-linking and enhancing the gel performance. Its excellent performance at 60℃ echoes the performance of Example 1 at 90℃, jointly verifying the wide applicability of the system of this invention, which can be flexibly adapted to reservoirs at different temperatures by adjusting the ethoxy content. Example 15 (HPAM 5 million) had a modulus of only 800 Pa after 60 days and a dehydration rate of 35%, indicating that HPAM with too low a molecular weight cannot form a sufficiently long molecular chain backbone, and the cross-linked network is prone to chain segment relaxation and breakage during thermal aging. Example 16 (HPAM 10 million) had a modulus of 3800 Pa after 60 days, with performance similar to Example 1, but combined with Experiment 1, its injectability was significantly deteriorated. The moduli of Examples 17 (15% hydrolysis) and 18 (5% hydrolysis) after 60 days were 1900 Pa and 1400 Pa, respectively, both significantly lower than that of Example 1. This demonstrates that a 10% deviation in the degree of hydrolysis leads to a decrease in the stability of the crosslinked network—excessive hydrolysis makes the network prone to hydrolysis, while excessively low hydrolysis results in insufficient crosslinking density. Example 19 (70,000 PEI) had a modulus of 2600 Pa after 60 days with a dehydration rate of 15%, which, while better than the low molecular weight PEI system, was still significantly lower than that of Example 1. Example 20 (10,000 PEI) had a modulus of only 900 Pa after 60 days with a dehydration rate of 38%, demonstrating that when the PEI molecular weight is too low, the crosslinking bridges formed are too short, making the network prone to stress concentration and structural collapse during thermal aging. The 25,000 PEI used in Example 1 achieved a better balance between chain length and reactivity, exhibiting better long-term stability. Example 21 (fiber:APTES=100:4) has a modulus of 3800 Pa and a dehydration rate of 9% after 60 days, which is comparable to Example 1 and slightly better, but this slight advantage comes at the cost of sacrificing initial injectability.Example 22 (fiber:APTES=100:2) showed a modulus of only 1700 Pa after 60 days and a dehydration rate of 22%, demonstrating that insufficient APTES resulted in a low amino density on the fiber surface, weak fiber-polymer interfacial bonding, and a tendency for debonding and phase separation during thermal aging. Long-term stability data from Examples 23-25 ​​(different mineralization levels) showed that as mineralization increased, gel strength retention gradually decreased, while dehydration rate increased accordingly. At a mineralization of 35000 mg / L, the 60-day strength retention was approximately 80% (3200 / 3980), with a dehydration rate of 15%; at a mineralization of 100000 mg / L, the 60-day strength retention was approximately 66% (2000 / 3020), with a dehydration rate of 25%. Although high mineralization poses a challenge to long-term stability, thanks to the efficient complexation of divalent cations by EDTA-2Na and the thermal stability protection of thiourea in the system of this invention, all systems still maintain a high elastic modulus and a low dehydration rate after 60 days of aging.

[0207] Comparative Example 1 exhibited significant performance degradation and a high dehydration rate during long-term aging, indicating that micron-sized particles tend to aggregate and settle under high ionic strength and high temperature conditions, disrupting gel homogeneity and creating channels for water loss. Simultaneously, the point-like interface between particles and the gel network is relatively fragile under long-term thermal stress and prone to failure. Conversely, the fibers in Example 1, through mutual entanglement and chemical bonding with the gel, form a stable spatial support framework, effectively inhibiting dehydration shrinkage and thus exhibiting excellent long-term thermal stability. Comparative Example 6 (attapulgite fiber), although also fibrous, had a lower surface silanol density than sepiolite and insufficient grafted amino groups, resulting in inferior 60-day modulus (2100 Pa) and dehydration rate (18%) compared to Example 1, confirming that sepiolite fiber is a superior reinforcing carrier in this system. Comparative Examples 3 (thiourea-free) and 4 (EDTA-free) essentially failed after 60 days, further verifying the indispensability of heat stabilizers and metal ion complexing agents in maintaining the integrity of the gel network under high temperature and high salt conditions. Comparative Example 5 (distilled water) showed slightly better performance than Example 1, indicating that the small amount of high-valence ions in simulated formation water still poses a challenge to long-term stability, while the system of this invention effectively resolves this problem through a complexing agent. Comparative Example 7 (without PEI): No effective gel was formed; the modulus after 60 days was only 50 Pa, with a dehydration rate of 70%, proving that the chemical cross-linking network is the core of long-term gel stability, and fiber physical reinforcement cannot support it independently. Comparative Example 8 (without fibers): The modulus after 60 days was 900 Pa, with a dehydration rate of 40%, showing a significant difference in strength compared to Example 1, proving the crucial role of the fiber skeleton in inhibiting high-temperature dehydration and maintaining network integrity. Comparative Example 9 (without microcapsules): The modulus after 60 days was only 200 Pa, with a dehydration rate of 60%, confirming that acid-triggered secondary cross-linking is not only key to deep reinforcement but also a guarantee for long-term anti-aging—the network formed solely by HPAM / PEI thermal cross-linking without microcapsules rapidly hydrolyzes and breaks down at high temperatures.

[0208] Experimental Example 5

[0209] The selective blocking capability of the modulated drive systems prepared in the test examples and comparative examples was evaluated. The test methods are as follows:

[0210] Parallel core flow experiments were used for evaluation. Fractured cores with diameters of 2.5 cm and lengths of 10 cm, and artificial fracture widths of approximately 100-200 μm and 150-300 μm, as well as homogeneous cores with diameters of 2.5 cm and lengths of 10 cm without fractures, were selected. Only Example 13 used fractured cores with a diameter of 150-300 μm; the other systems used fractured cores with a diameter of 100-200 μm. Before the experiment, all cores were vacuum-saturated with simulated formation water (mineralization 3000 mg / L, divalent cation concentration 200 mg / L). The fractured and homogeneous cores were connected in parallel to the displacement device. Water was first injected simultaneously at a total flow rate of 2.0 mL / min, and the outlet flow rate of each core under steady-state conditions was recorded to calculate the initial flow fraction percentage. Subsequently, the homogeneous core branch was closed, and only the fractured core was injected with 1.0 PV (pore volume) of the working fluid to be tested (injection rate 1.0 mL / min). After injection, close all valves and place the entire system in a 90℃ constant temperature chamber for 72 hours. Then, perform subsequent water drive at a total flow rate of 2.0 mL / min, and record the flow rate of each core sample after stabilization. The plugging rate (%) is calculated using the formula: Plugging rate (%) = (1 - Q) / (2000) 封堵后裂缝流量 / Q 封堵前裂缝流量 The plugging rate of fractured core samples was calculated by multiplying the value by 100%. The control systems of Examples 1, 13, 15-25, Comparative Examples 1-2, 5, and 6-9 were selected for comparison. The results are shown in Table 6.

[0211] Table 6 Results of parallel pipe flow experiments

[0212]

[0213] As shown in Table 6, after treatment with the system of Example 1, the flow rate of fractured cores decreased significantly from the initial 85.2% to 22.5%, with a plugging rate of 73.6%, while the flow rate of homogeneous cores increased accordingly. This indicates that the system effectively plugged high-permeability fracture channels, forcing subsequent fluids to divert to the low-permeability matrix, demonstrating good selective plugging capability. The plugging rate of the system of Example 13, which used longer silane-modified fibers, reached 72.0%, exhibiting almost the same excellent plugging performance as Example 1. This fully demonstrates that by specifically adjusting the length of the silane-modified fibers, this system can effectively adapt to and plug fracture channels of different openings, thereby significantly improving the displacement profile of heterogeneous reservoirs. The plugging rate of Example 15 (5 million molecular weight) was only 38.5%, less than 53% of Example 1. This result is consistent with the low gel strength (1850 Pa) exhibited in Experiment 2. The gel network formed by low molecular weight HPAM is essentially a "weakly connected" structure, with excessively short molecular chain segments, small distances between crosslinking points, and a lack of extensibility and toughness. Under long-term water-driven scouring, this type of weak gel is prone to local breakthrough or overall migration, making it difficult to maintain stable plugging. Example 16 (10 million molecular weight) achieved a plugging rate of 70.6%, on par with Example 1 (73.6%), which matches its higher gel strength (4380 Pa). However, the injection pressure gradient of Example 16 (0.17 MPa / m) was 42% higher than that of Example 1 (0.12 MPa / m), meaning that under the same injection conditions, this system would struggle to reach the target region at the same depth as Example 1. Therefore, the 8 million molecular weight of Example 1 achieved a superior synergy between injectability and plugging performance, which is one of the key innovations of this invention. Example 17 (15% degree of hydrolysis) achieved a plugging rate of 57.9%, and Example 18 (5% degree of hydrolysis) achieved a plugging rate of only 50.0%, both significantly lower than Example 1 (73.6%). This clear gradient in plugging rate data is consistent with the trend of gel strength change in Experiment 2, strongly demonstrating that the degree of HPAM hydrolysis has a significant impact on the final plugging performance of the system, and that there exists a relatively optimal window. Example 19 (PEI molecular weight 70,000) achieved a plugging rate of 61.4%, which, although better than the low molecular weight system, was still significantly lower than the 73.6% of Example 1. Example 20 (PEI molecular weight 10,000) achieved a plugging rate of only 43.0%, and the weak gel formed therein quickly broke through under subsequent water-driven scouring, failing to establish a stable and effective plugging barrier. Combined with the fact that the injection pressure of Example 19 in Experiment 1 was slightly higher, high molecular weight PEI not only failed to improve plugging performance, but was also inferior to Example 1 in both injectability and plugging strength. Example 21 (fiber:APTES = 100:4) achieved a plugging rate of 74.4%, slightly higher than the 73.6% of Example 1. This slight advantage is matched by its slightly higher gel strength (4400 Pa) and shear recovery capacity (3200 Pa).However, considering its negative impact on injectability (Example 1) and the economic cost of higher silane coupling agent dosage, the 100:3 ratio in Example 1 remains the optimal choice for greater engineering applicability. Example 22 (fiber:APTES = 100:2) showed a plugging rate of only 55.2%, a decrease of 18.4 percentage points compared to Example 1. This significant deterioration directly stemmed from its lower gel strength (3100 Pa) and shear recovery ability (2300 Pa), fully demonstrating that sufficient surface amino modification is a necessary condition for achieving efficient fiber reinforcement. The plugging rate data from Examples 23-25 ​​(different mineralizations) showed that as mineralization increased, the plugging rate gradually decreased from 69.6% at 35000 mg / L to 59.4% at 100000 mg / L. This decreasing trend is consistent with the changes in gel strength and long-term stability observed in Examples 2 and 4. Under a mineralization of 100,000 mg / L, the system of the present invention can still achieve a fracture plugging rate of nearly 60%, which is significantly better than the unreinforced system (Comparative Example 2, 5.5%) and the particle-reinforced system (Comparative Example 1, 46.8%), fully demonstrating that the system of the present invention has adaptability to different mineralization levels.

[0214] Although the plugging effect of Comparative Example 1 was better than that of Comparative Example 2, it was significantly lower than that of the fiber-reinforced system. This proves that the three-dimensional network plugging body formed by the fibrous reinforcing agent has higher strength and stability, and can effectively resist the scouring of subsequent water flooding, while the gel reinforced by spherical particles is easily broken through at high flow rates. Comparative Example 2, lacking fiber reinforcement and acid triggering mechanism, had a poor plugging effect and could hardly achieve deep regulation. Comparative Example 5 still showed a good plugging effect without high-valence ion interference, with a plugging rate of 75.9%, slightly higher than 73.6% in Example 1. This further verified the intrinsic properties of the system. The experimental results show that the system of the present invention not only has deep strengthening ability, but can also effectively plug high-permeability channels in target reservoirs and significantly improve the displacement profile of heterogeneous reservoirs. The plugging rate of Comparative Example 6 was 53.5%, a decrease of 20.1 percentage points compared with Example 1 (73.6%). This significant difference is consistent with its lower gel strength (3550 Pa) and shear recovery ability (2000 Pa). During subsequent water flooding, the attapulgite fiber-reinforced gel plugging body, due to its weak fiber-polymer interface bonding, is more prone to localized peeling and breakthrough under hydraulic scouring, leading to a decrease in plugging efficiency. This result clearly demonstrates that sepiolite fiber has irreplaceable advantages in the system of this invention, and its unique surface chemical properties are the key material basis for achieving the synergistic effect of the "fiber reinforcement-chemical crosslinking" dual network. Comparative Example 7 (without PEI) had a plugging rate of only 22.7%, which, although better than Comparative Example 2 (5.5%), was still far lower than Example 1. This indicates that the localized acidic environment formed by fiber physical adsorption and microcapsule acid release can provide a certain plugging ability, but the lack of a chemical crosslinking network constructed with PEI results in severely insufficient plugging body strength, making it easily breached by subsequent water flooding. Comparative Example 8 (without fiber) had a plugging rate of 46.8%, compared to Comparative Example 1 (46.8%) and Comparative Example 2 (5.5%), proving that acid-triggered chemical crosslinking itself has a certain plugging ability, but the lack of fiber skeleton support significantly reduces plugging efficiency. Comparative Example 9 (without microcapsules) had a blocking rate of only 26.9%, confirming that the gel strength formed by the thermal cross-linking of HPAM / PEI is insufficient when there is no acid trigger, making it difficult to achieve effective blocking.

[0215] Experimental Example 6

[0216] To verify the temperature-responsive release characteristics and controllability of the release behavior of encapsulated citric acid microcapsules, the following test method was used:

[0217] (1) Establishment of the citric acid standard curve

[0218] Citric acid standard solutions with concentration gradients of 0.01, 0.05, 0.1, 0.2, 0.5, and 1.0 mg / mL were prepared using the same simulated formation water as in Example 1. High-performance liquid chromatography (HPLC) was used for analysis, with the following chromatographic conditions: Agilent ZORBAX SB-C18 column (4.6 mm × 250 mm, 5 μm); mobile phase: 0.01 mol / L potassium dihydrogen phosphate aqueous solution (pH adjusted to 2.5 with phosphoric acid); flow rate: 1.0 mL / min; column temperature: 30℃; detection wavelength: 210 nm; injection volume: 20 μL. Under these conditions, the standard solutions were analyzed, and a linear regression of peak area against concentration was performed to obtain the standard curve, which is shown in the attached figure. Figure 4 The regression equation is y = 125125.053 × x - 5181.73 (R² = 0.9807).

[0219] (2) Determination of total citric acid loading in microcapsules

[0220] Accurately weigh 50.0 mg of the citric acid microcapsules prepared in Example 1 (denoted as m0) and place them in a 100 mL stoppered conical flask. Add 50.0 mL of phosphate buffered saline (PBS, pH=7.4). Place the conical flask in a 90°C constant temperature water bath shaker and shake at 150 rpm for 4 hours to ensure complete rupture of the wall material and complete release of citric acid. Then, centrifuge the mixture at 10000 rpm for 10 minutes, collect the supernatant in a test tube, and immediately place the sample tube in an ice-water bath to terminate the release reaction of the citric acid microcapsules. Filter the solution through a 0.22 μm aqueous filter membrane to remove all microcapsule particles and wall material fragments. Then, determine the concentration of citric acid in the filtrate using high-performance liquid chromatography (HPLC) (chromatographic conditions are the same as those used for determining the citric acid standard curve). Calculate the mass of citric acid in the filtrate (m0) according to the citric acid standard curve. t The drug loading is approximately 32.6 mg, and calculated according to the formula: Drug loading (%) = (m t The citric acid loading of the microcapsules was calculated by multiplying ( / m0) by 100%. Three parallel determinations were performed, and the average value was taken. The drug loading of the microcapsules in Example 1 (ethoxy content 49%) was approximately 65.2%.

[0221] (3) Release kinetics determination

[0222] Simulated formation water was prepared, with the same composition as that used in Example 1. Two sets of experiments, A and B, were set up to test the effect of temperature on citric acid release behavior at a fixed ethoxy content and the effect of different ethoxy contents on citric acid release behavior at a fixed temperature, respectively.

[0223] A. Release of the same microcapsule at different temperatures: Four 50.0 mg portions of the microcapsules prepared in Example 1 (ethoxy content 49%) were accurately weighed and placed in four 100 mL stoppered conical flasks, with 50.0 mL of simulated formation water added to each. The conical flasks were placed in constant temperature water bath shakers at 60°C, 70°C, 80°C, and 90°C, respectively, and shaken at 100 rpm.

[0224] B. Release of microcapsules with different ethoxy content at specific temperatures: 50.0 mg of each of the microcapsules prepared in Examples 1, 12, and 14 were accurately weighed and placed in a constant temperature water bath shaker at 90°C for release experiments, using the same method as in A.

[0225] At predetermined time points (0, 2, 4, 8, 12, 24, 48, 72 h), 1.0 mL of release medium was removed from each conical flask, and immediately replenished with 1.0 mL of simulated formation water at the same temperature. The removed samples were immediately filtered through a 0.22 μm aqueous filter membrane. To ensure the representativeness of the filtrate and eliminate the influence of filter dead volume, the first 0.2 mL of filtrate was discarded, and subsequent filtrates were collected. The citric acid concentration (C) was determined using the HPLC method described above. t Three parallel experiments were set up for each condition.

[0226] (4) Calculation of cumulative release rate

[0227] The cumulative release rate is calculated using the following formula:

[0228]

[0229] In the formula:

[0230] C t —The concentration of citric acid after filtration from the release medium at time point t, in mg / mL;

[0231] V0 — Initial volume of the release medium, mL;

[0232] t-1 — All sampling times that have occurred from the start of the experiment to the current time t (excluding time t), in the range h;

[0233] V s —Sampling volume per sample, mL;

[0234] C i —Citrate concentration at hour i, mg / mL

[0235] m t —Total mass of citric acid in the microcapsules, mg;

[0236] (5) Results and Discussion

[0237] A. The effect of temperature on release behavior: Figure 2 The cumulative release curves of microcapsules with 49% ethoxylate content are shown at 60°C, 70°C, 80°C, and 90°C. The data indicate that the release behavior exhibits a strong temperature dependence. At 90°C, the microcapsules release rapidly, with a cumulative release rate of 68% after 12 hours and near-complete release after 48 hours; while at 60°C, release is significantly delayed, with a cumulative release rate of only 40% after 72 hours. This result directly confirms that the microcapsule system of the present invention possesses a clear temperature response characteristic: it can effectively retain the core material during the low-temperature injection stage, while completely releasing citric acid when the system enters the deep high-temperature target region (e.g., 90°C), thereby triggering the expected secondary cross-linking reaction.

[0238] B. Regulation of release behavior by ethoxy group content: Figure 3 The release curves of microcapsules with ethoxylated contents of 49%, 46%, and 44% at 90°C were compared. As shown in the figure, the EC-44% microcapsules exhibited the most rapid release, with a cumulative release rate of 47% after 2 hours and 84% after 4 hours. This rapid release leads to a large influx of citric acid into the system in a short period, causing rapid and excessive cross-linking in localized areas, forming an uneven gel network structure (locally too dense while other areas are insufficiently cross-linked), thus affecting the overall mechanical properties of the gel. This is the main reason for the low gel strength (1535 Pa) of Example 12 at 90°C (non-matched temperature). The EC-46% microcapsules showed a release rate of 36.6% after 2 hours and 71% after 4 hours, still too rapid. In contrast, the EC-49% microcapsules exhibited a relatively slow release behavior at 90°C, with a release rate of only 20% after 2 hours, 35% after 4 hours, 55% after 8 hours, 68% after 12 hours, and reaching 85% after 24 hours. This gradual release pattern allows citric acid to diffuse more evenly throughout the gel system, enabling the cross-linking reaction to proceed fully. This is beneficial for forming a high-strength gel with a uniform structure and dense network, which is the key reason why Example 1 exhibits excellent gelling properties (4251 Pa) at 90°C.

[0239] The above results demonstrate that, within the preferred ethoxy content range (44%-49%) of this invention, by adjusting the ethoxy content of ethyl cellulose, the release rate and trigger temperature of the microcapsules at the target temperature can be effectively controlled, thus achieving performance designability.

[0240] in conclusion

[0241] The above examples and test results demonstrate that the fibrous structure plays a crucial role in constructing a three-dimensional physical reinforcement network and achieving a performance reversal of "low-viscosity injection - deep reinforcement". Furthermore, by adjusting the length of the silane-modified fibers (as in Example 13), this system can be adapted to cracks of different apertures, maintaining good injection performance and deep plugging effect (plugging rate >72.0%) even in wider cracks.

[0242] This invention successfully constructs a composite gel system with low viscosity injection, deep triggering, high strength recovery, and long-term stability by using the physical anchoring entanglement and covalent bonding of "silane-modified fibers", the temperature-responsive delayed release and triggered secondary crosslinking of "encapsulated citric acid", and the auxiliary stabilization of heat stabilizers and complexing agents. The system is suitable for fractured reservoirs with obvious fracture channeling and where conventional modulated flow systems are difficult to achieve effective deep sealing, providing a novel solution for improving the oil recovery rate of such reservoirs.

[0243] The above description is merely a specific 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 deep displacement system suitable for fractured reservoirs, characterized in that, The raw material composition includes the following parts by weight: 0.2-1 parts of partially hydrolyzed polyacrylamide (HPAM), 0.1-0.6 parts of polyethyleneimine (PEI), 0.2-0.4 parts of silane-modified micron-sized inorganic fibers, 0.1-0.8 parts of encapsulated citric acid, 0.02-0.2 parts of heat stabilizer, 0.02-0.1 parts of metal ion complexing agent, and 196.9-199.36 parts of water.

2. The deep displacement system for fractured reservoirs according to claim 1, characterized in that, The raw material composition includes the following parts by weight: partially hydrolyzed polyacrylamide (HPAM) 0.4-0.8 parts, polyethyleneimine (PEI) 0.2-0.4 parts, silane-modified micron-sized inorganic fibers 0.2-0.4 parts, encapsulated citric acid 0.3-0.5 parts, heat stabilizer 0.1 parts, metal ion complexing agent 0.06 parts, and water 197.74-198.74 parts; Preferably, the deep regulation and drive system suitable for fractured reservoirs comprises the following raw material components in parts by weight: 0.6 parts of partially hydrolyzed polyacrylamide (HPAM), 0.3 parts of polyethyleneimine (PEI), 0.3 parts of silane-modified micron-sized inorganic fiber, 0.4 parts of encapsulated citric acid, 0.1 parts of heat stabilizer, 0.06 parts of metal ion complexing agent, and 198.24 parts of water.

3. The deep displacement system for fractured reservoirs according to claim 1, characterized in that, Includes one or more of the following conditions: i. The degree of hydrolysis of partially hydrolyzed polyacrylamide (HPAM) is 5% to 15%, preferably 10%; ii. The weight-average molecular weight of partially hydrolyzed polyacrylamide (HPAM) is 5-10 million, preferably 8 million; iii. The weight-average molecular weight of polyethyleneimine (PEI) is 10,000 to 70,000, preferably 25,000.

4. The deep regulation and displacement system suitable for fractured reservoirs according to claim 1, characterized in that, Includes one or more of the following conditions: i. The heat stabilizer is thiourea; ii. The metal ion complexing agent is disodium ethylenediaminetetraacetate (EDTA-2Na); iii. The water is formation water; the mineralization is 0-100,000 mg / L, and the concentration of divalent cations is 0-2,000 mg / L.

5. The deep displacement system for fractured reservoirs according to claim 1, characterized in that, A method for preparing silane-modified micron-sized inorganic fibers includes the following steps: Sepiolite fibers were fully dispersed in a mixed solvent of ethanol and water, and silane coupling agent γ-aminopropyltriethoxysilane (APTES) was added. After reaction, centrifugation, washing, and drying, silane-modified micron-sized inorganic fibers were obtained.

6. The deep regulation and displacement system suitable for fractured reservoirs according to claim 5, characterized in that, Includes one or more of the following conditions: i. The diameter of sepiolite fibers is 0.5-2 μm and the length is 10-100 μm; ii. In the mixed solvent of ethanol and water, the volume ratio of ethanol to water is 8:1-10:1, preferably 9:1; the mass ratio of sepiolite fiber to the volume ratio of the mixed solvent is 0.01-0.1 g / mL; iii. The mass ratio of sepiolite fiber to silane coupling agent γ-aminopropyltriethoxysilane (APTES) is 100:1-100:5, preferably 100:3; iv. The reaction temperature is 60℃-80℃, the reaction time is 4-8h, and the reaction is carried out under reflux and stirring conditions; more preferably, the reaction temperature is 70℃ and the reaction time is 6h.

7. The deep displacement system for fractured reservoirs according to claim 1, characterized in that, The preparation method of encapsulated citric acid includes the following steps: dissolving ethyl cellulose as a wall material in dichloromethane as an organic solvent to obtain a wall material solution; adding citric acid powder as a core material to the above wall material solution and mixing thoroughly to obtain a suspension; and then spray drying to obtain encapsulated citric acid.

8. The deep regulation and displacement system for fractured reservoirs according to claim 7, characterized in that, Includes one or more of the following conditions: i. The ethoxylated component of the wall material, ethyl cellulose, is 44%-49% by mass. ii. The mass concentration of the wall material solution is 10%-15%, preferably 10%; iii. The particle size of the core material citric acid powder is 10-30 μm, preferably 20 μm; iv. The mass ratio of ethyl cellulose wall material to citric acid powder core material is 1:1-1:3, preferably 1:2; v. After adding the core material citric acid powder to the wall material solution, shear it at a speed of 8000-12000 rpm for 5-15 minutes to form a uniform and stable suspension; preferably, the speed is 10000 rpm and the shearing time is 10 minutes. vi. Use a centrifugal atomizer for spray drying; set the atomizer speed to 20,000-30,000 rpm, the feed rate to 5-15 mL / min, the inlet temperature to 80-100℃, and the outlet temperature to 40-60℃.

9. A method for preparing a deep moderating and displacement system suitable for fractured reservoirs as described in any one of claims 1-8, comprising the steps of: Under stirring conditions, partially hydrolyzed polyacrylamide (HPAM), a heat stabilizer, and a metal ion complexing agent were added to water in sequence and dispersed thoroughly. Silane-modified micron-sized inorganic fibers were added and dispersed thoroughly. Polyethyleneimine (PEI) was added and dispersed thoroughly. Finally, encapsulated citric acid was added and dispersed thoroughly to obtain a deep regulation and drive system suitable for fractured reservoirs.

10. The application of the deep regulation and drive system for fractured reservoirs as described in any one of claims 1-8 in the regulation and drive of fractured reservoirs; preferably, the reservoir temperature is 60℃-90℃.

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