Self-optimization fracture network fracturing method of coal-bed gas well based on intelligent response material

Abstract

The invention discloses a self-optimization fracture network fracturing method for a coal-bed gas well based on an intelligent response material. The method comprises the steps that firstly, a shaft is prepared, and intelligent fracturing fluid initial injection and efficient sand-carrying stage triggering are conducted; 2, crack net expansion and temporary plugging steering and deep penetration stage triggering; step 3, intelligent dynamic optimization and sand paving strategy execution; 4, triggering, cementing and curing in a strong supporting stage; step 5, carrying out collaborative development and comprehensive utilization after pressing; the three components of the fracturing fluid are intelligently responded according to stratum environment changes, the monitoring unit collects signals such as underground temperature, strain and sound waves in real time, and the crack propagation form is dynamically tracked in combination with microseismic data. The method improves the fracturing effect, has refinement, controllability, compatibility and reliability, and realizes monitoring-evaluation-execution full-closed-loop control.

Description

Technical Field

[0001] This invention belongs to the field of coalbed methane development engineering technology and relates to a self-optimizing fracture network fracturing method for coalbed methane wells based on intelligent response materials. Through the synergistic effect of temperature-sensitive-pH dual-response fracturing fluid, magnetic navigation temporary plugging and steering, and AI closed-loop control, dynamic optimization and precise shaping of the fracture network are achieved. It is applicable to the stimulation of medium-deep coalbed methane reservoirs with a burial depth >2000m. Background Technology

[0002] Coalbed methane (CBM), as an important unconventional natural gas resource, has dual strategic value for optimizing the energy structure and ensuring coal mine safety through its efficient development. In recent years, with the increasing exploitation of shallow CBM resources in my country, medium-deep CBM reservoirs (burial depths exceeding 2000 meters) have gradually become a key area for continued development. However, medium-deep coal reservoirs generally exhibit geological characteristics such as high ground stress, high temperature and pressure, and strong heterogeneity, posing significant challenges to traditional fracturing technologies. Deep coal reservoirs (burial depths exceeding 3000 meters) exhibit the "four highs"—high filtration loss, high fracturing pressure, high adsorbed gas ratio, and high closure stress—severely restricting the economic development of CBM. Currently, unconventional reservoir fracturing faces three major technical bottlenecks: 1. Insufficient precision in fracture control: Traditional temporary plugging and redirection methods rely on random spherical plugging, with a redirection success rate of only 60-70%, making it difficult to form complex fracture networks. Microseismic monitoring shows that the number of branch fractures in conventional hydraulic fracturing is mostly less than 15.

[0003] 2. Poor adaptability of proppant: Conventional ceramsite is difficult to lay effectively in microcracks, with an annual decay rate of over 40% in conductivity. Although in-situ self-supporting styrene (ISSPFF) technology can improve the permeability of microcracks, its curing speed is significantly affected by temperature fluctuations.

[0004] 3. Static fracturing parameters: Parameters such as fracturing fluid displacement and sand ratio rely on pre-design and cannot respond to dynamic changes in the formation. While online monitoring systems (CN120195343A) can monitor fracturing fluid viscosity and pH in real time, they lack autonomous decision-making capabilities. Existing technologies, such as CN118171452A which proposes a parameter optimization model, rely on static geological data; and ZL202111624256.6 which develops magnetically responsive materials, fail to achieve real-time control of fracture propagation. Particularly lacking are: 1. a formation-environment-adaptive fracturing fluid rheological control mechanism; 2. millimeter-level precise positioning technology for temporary plugging wells; and 3. a multi-functional synergistic solution integrating fracturing, geothermal energy, and CO2 sequestration. This leads to bottlenecks in mid-to-deep coalbed methane fracturing, such as a limited number of branch fractures (<15) and rapid conductivity decay (annual decay >40%). Therefore, a systematic solution integrating smart materials and dynamic optimization is urgently needed. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention aims to provide a self-optimizing fracture network fracturing method for coalbed methane wells based on intelligent response materials, and a method for improving the efficiency of fracture network volume transformation through multi-stage iterative fracturing. This method utilizes distributed acoustic sensing (DAS) and distributed temperature sensing (DTS) fiber optics to collect downhole temperature, strain, and acoustic signals in real time, and dynamically tracks fracture propagation morphology using microseismic data. This design replaces traditional reliance on laboratory simulation devices or offline core testing, enabling in-situ dynamic evaluation of the temporary plugging effect. It innovatively introduces a reinforcement learning algorithm, analyzing monitoring data every 30 minutes to dynamically adjust the displacement (±2 m³ / min), sand ratio (±3%), and temporary plugging ball delivery strategy. For example, when the fracture network complexity index (FCI) < 4.0, it automatically increases the displacement and replenishes temporary plugging balls. Compared to existing technologies that only monitor without regulating, this invention achieves a fully closed-loop control system of "monitoring-evaluation-execution."

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: A self-optimizing fracture network fracturing method for coalbed methane wells based on smart response materials includes the following steps: Step 1, Wellbore preparation and initial injection of intelligent fracturing fluid: s1.1, Wellbore and Perforation: Preparation work for well cleaning and flushing of the target coalbed methane horizontal well section; deep penetration ejection holes are used, with a hole density of 16-20 holes / meter and a penetration depth of ≥800mm; s1.2, Inject intelligent fracturing fluid: Pump intelligent fracturing fluid at a flow rate of 18 m³ / min and a sand ratio of 12%; the intelligent fracturing fluid includes: temperature trigger PNIPAM, pH trigger SiO2-COOH, and proppant; s1.3, Initial stage behavior and triggering of efficient proppant carrying stage: In the initial stage, the fracturing fluid is in a low temperature and neutral pH state with low fluid viscosity; when the fracturing fluid enters the wellbore, the temperature rises, triggering the efficient proppant carrying stage. The temperature triggering agent PNIPAM undergoes a rapid phase change and self-assembles into a three-dimensional network gel, which increases the fluid viscosity. Step 2, suture mesh expansion and temporary plugging and reversal: s2.1, Fracture Monitoring and Decision Making: The monitoring unit monitors downhole pressure, temperature, pH value, and fracture morphology depicted by microseismic mapping in real time; when the main fracture length is detected to extend to 120m, it is determined that a deflection is necessary to generate branch fractures. S2.2, Magnetic navigation temporary plugging: Deploy the magnetic response temporary plugging ball and activate the wellhead electromagnetic field device to precisely guide the temporary plugging ball to seal the entrance of the main fracture that has been formed; S2.3, Fracturing and Deep Penetration Stage Triggering: The pump flow rate is increased to 22 m³ / min. The high flow rate generates higher pressure at the entrance of the temporarily plugged main fracture, forcing the fracturing fluid to turn and enter the natural weak surface or stress shadow zone deep in the reservoir, expanding new branch fractures; when the fracturing fluid enters the inherent acidic microfracture environment of the coal matrix, the deep penetration stage is triggered. The pH trigger SiO2-COOH is carboxylated, the original gel structure depolymerizes, and the viscosity drops sharply. Step 3, Intelligent Dynamic Optimization and Sand Laying Strategy Execution: S3.1 Intelligent collaborative control: Dynamically optimizes discharge rate and sand ratio based on real-time data from the monitoring unit; s3.2, Optimization Strategy: Based on the reinforcement learning AI platform, the system determines whether to adjust the flow rate and grit ratio according to the monitored seam complexity index FCI and seam width. If the seam complexity index FCI < 4.0, the flow rate is increased to aggressively create seams; if the monitored seam width > 10mm, the grit ratio is increased to strengthen support. s3.3, Final application: According to the optimized displacement and sand ratio, the proppant is applied into the formed complex crack network; Step 4, Strong Support Stage Triggering, Bonding and Curing: S4.1, Strong Support Stage Trigger: After construction is completed, the crack closes under the closing pressure. When the pressure exceeds 30MPa, the strong support stage is triggered, the proppant is squeezed and ruptured, and epoxy resin is released. s4.2, Bonding and Curing: The released epoxy resin undergoes a curing reaction at the formation temperature, bonding the surrounding ceramic particles into a strong and elastic overall network; Step 5, Post-fracturing collaborative development and comprehensive utilization: After fracturing is completed, multi-functional collaborative development is carried out based on the huge fracture network formed.

[0007] The present invention also includes the following technical features: Specifically, the intelligent fracturing fluid includes: The temperature trigger agent PNIPAM has a viscosity that increases to 200-300 mPa·s at 40-60℃. The pH trigger agent SiO2-COOH has a viscosity that decreases to 5-10 mPa·s when pH < 6.0; The proppant is an epoxy resin microcapsule coated with ceramic particles, which is activated by a closing pressure >30MPa.

[0008] Specifically, in s1.3, initially at low temperature, the pH trigger SiO2-COOH is in an inert state, the temperature trigger PNIPAM is soluble in water, the fluid viscosity is low, and it is easy to pump; The high-efficiency proppant carrying stage includes: fracturing fluid entering the high-temperature formation in the wellbore, the temperature rises to 40-60°C, triggering the high-efficiency proppant carrying stage. The temperature triggering agent PNIPAM undergoes a violent phase transition at its lowest critical dissolution temperature (LCST), the polymer chains undergo dehydration and shrinkage, and self-assemble into a three-dimensional network structure. The fluid transforms into a jelly-like gel, with the viscosity increasing to 200-300 mPa·s. The high viscosity can suspend and carry the proppant, preventing it from settling in the wellbore and main fracture, and ensuring that the proppant is effectively laid to the target location.

[0009] Specifically, in s2.2, the temporary plugging ball includes an Fe3O4 core and a biodegradable PLGA shell; wherein, the Fe3O4 core has a diameter of 2-3 mm, and the biodegradable PLGA shell has a degradation temperature of 60℃; the electromagnetic field strength of the wellhead electromagnetic field device is 0.5-1.5T.

[0010] Specifically, in s2.3, the deep penetration stage includes: when the fracturing fluid enters the inherent acidic microfracture environment of the coal matrix, the pH is <6.0, the pH trigger SiO2-COOH is carboxylated, the negative charge and hydrophilicity of the nanoparticle surface are weakened, the repulsive force between particles is reduced, the original gel structure is depolymerized, the viscosity drops sharply to 5-10 mPa·s, and the low viscosity fluid can penetrate the nanoscale or microscale pores and fractures that conventional fracturing fluids cannot enter, thereby maximizing the expansion of the effective modification volume.

[0011] Specifically, the monitoring unit includes a distributed acoustic sensor (DAS) and a distributed temperature sensor (DTS) fiber optic cable; the monitoring unit monitors downhole temperature, strain, acoustic signals, and pH value, and can dynamically track crack propagation morphology by combining microseismic data.

[0012] Specifically, in s4.1, the strong support stage includes: when the fracture closure pressure exceeds 30MPa, the proppant is squeezed and crushed, releasing epoxy resin which undergoes a curing reaction at the formation temperature, automatically cementing the surrounding ceramic particles, enhancing the compressive strength of the proppant agglomerates, resisting the high closure pressure of the formation, reducing the backflow of proppant, and maintaining the fracture's long-term high conductivity.

[0013] Compared with the prior art, the present invention has the following technical effects: This invention features precision in both time and space: intelligent response: the three functional components are activated sequentially at different stages and for different physicochemical environments, achieving one-time intelligent operation without multiple interventions; it solves the core contradiction in the industry: it perfectly balances the contradiction between high viscosity for sand carrying and high viscosity for deep penetration, a contradiction that traditional fracturing fluids cannot reconcile.

[0014] This invention greatly improves fracturing effect: it expands the volume of fracturing by mobilizing more remaining resources through deep penetration; it enhances flow conductivity by creating a long-term stable and efficient flow channel through intelligent bonding, ultimately increasing single-well production and recovery rate.

[0015] This invention aligns with the trend of applying adaptive or self-healing smart materials in coalbed methane engineering.

[0016] This invention offers precision and controllability: It precisely controls the molecular weight and distribution of polymers through living polymerization methods such as atom transfer radical polymerization (ATRP), achieving accurate regulation of the phase transition temperature. This invention also offers functionalization and compatibility: Surface modification of nanoparticles enables them not only to respond to pH but also to exhibit good compatibility with polymer networks, preventing aggregation. Furthermore, this invention demonstrates the reliability of microencapsulation technology: Employing more precise interfacial polymerization or in-situ polymerization processes, it prepares thermally expandable microcapsules with good monodispersity, uniform wall thickness, and matched mechanical strength, ensuring stability during pumping and precise rupture under target pressure. Attached Figure Description

[0017] Figure 1 The logical control flowchart of the AI ​​intelligent dynamic optimization and sand-laying strategy execution process based on reinforcement learning. Detailed Implementation

[0018] The following are specific embodiments of the present invention. It should be noted that the present invention is not limited to the following specific embodiments. All equivalent modifications made based on the technical solutions of this application fall within the protection scope of the present invention.

[0019] Example: This embodiment provides a self-optimizing fracture network fracturing method for coalbed methane wells based on intelligent response materials. It utilizes a multifunctional intelligent fracturing fluid system whose components can automatically perform three key tasks—efficient proppant transport, deep penetration, and strong support—at different stages of fracturing based on changes in the formation environment (temperature, acidity, and pressure). The entire process is optimized through intelligent decision-making. The specific implementation steps are as follows: Step 1, Wellbore preparation and initial injection of intelligent fracturing fluid: (1.1) Wellbore and perforation: Well cleaning and other preparatory work are carried out for the target coalbed methane horizontal well section; deep penetration ejection holes are adopted with a hole density of 16-20 holes / meter and a penetration depth of ≥800mm to ensure that the fracturing fluid can effectively enter the formation and create a good start for the subsequent formation of complex fracture network.

[0020] (1.2) Injection of intelligent fracturing fluid: Start pumping intelligent fracturing fluid at a flow rate of 18 m³ / min and a sand ratio of 12%. This intelligent fracturing fluid has been premixed and includes: a temperature-triggered thickener (PNIPAM), which is used to achieve the efficient sand carrying stage; a pH-triggered viscosity reducer (carboxylated silica nanoparticles, SiO2-COOH), which is used to achieve the deep penetration stage; and a stress-triggered proppant (ceramsite with thermal expansion microcapsules on the surface), which is used to achieve the strong proppant stage. Specifically, the intelligent fracturing fluid in this embodiment includes: a temperature-sensitive component: PNIPAM polymer (1.0-2.0 wt%), whose viscosity increases to 200-300 mPa·s at 40-60℃; a pH-responsive component: carboxylated SiO2 nanoparticles (0.5-1.2 wt%), whose viscosity decreases to 5-10 mPa·s when pH < 6.0; and a self-healing proppant: epoxy resin microcapsules (50-100 μm thick) coated on the surface of ceramic particles, which are triggered to cure when the closing pressure > 30 MPa.

[0021] Specifically, in temperature-triggered poly(N-isopropylacrylamide) (PNIPAM), atom transfer radical polymerization (ATRP) allows for precise control of molecular weight and structure (e.g., block, star), resulting in an extremely narrow molecular weight distribution (PDI < 1.1), a more concentrated phase transition temperature (LCST), and a more rapid and controllable viscosity increase. The preparation steps for PNIPAM (ATRP method) include: ① Reagent preparation: NIPAM monomer (purified), cuprous bromide (CuBr) / bipyridine (bpy) catalytic system, p-toluenesulfonate initiator (e.g., EBiB), and solvent (water / alcohol mixed solvent). ② Preparation process: The reaction flask was evacuated and filled with an inert gas (such as nitrogen or argon) several times to ensure the system was oxygen-free; under an inert atmosphere, reagents were added in a molar ratio of monomer:initiator:catalyst = 100:1:1; the reaction was stirred at 60-70℃ for 6-12 hours; after the reaction was completed, the reaction was terminated by exposure to air; the copper catalyst was removed by passing the reaction solution through a neutral alumina column, and then the polymer was precipitated in excess cold diethyl ether; after filtration, it was vacuum dried to obtain purified PNIPAM. ③ Experimental results: PNIPAM with a target molecular weight (Mn) of 50,000 g / mol was synthesized. GPC test: Mn = 48,500 g / mol and PDI = 1.08 were measured, proving that the molecular weight was precisely controlled and the distribution was extremely narrow. DSC test: Phase transition temperature (LCST) is 32.5℃ (low-concentration aqueous solution), with a phase transition range of only 2℃ (traditional methods typically use 5-10℃). Rheological test: A 1wt% aqueous solution was prepared and heated from 25℃ to 45℃. The viscosity increased sharply near 35℃, from ~10 mPa·s to 280 mPa·s (shear rate 100 s⁻¹). -¹). Compared with the traditional method (viscosity slowly increases to 200 mPa·s), the results of this embodiment show a more sensitive temperature response and a more prominent synergistic effect.

[0022] Specifically, the pH trigger, namely carboxylated silica nanoparticles (SiO2-COOH), is prepared by a one-pot co-condensation hydrolysis method; the carboxyl source is directly introduced into the synthesis system to achieve uniform and high-density surface carboxyl functionalization. The preparation steps of carboxylated silica nanoparticles (SiO2-COOH) include: ① Reagent preparation: tetraethyl orthosilicate (TEOS), carboxylated silicon source (such as 3-(trihydroxysilyl)propionic acid), THSP, ammonia catalyst, and ethanol / water mixed solvent. ② Preparation process: TEOS and THSP are dissolved in ethanol at a certain molar ratio (e.g., 9:1); under vigorous stirring, an ethanol / water solution containing ammonia is rapidly added; the reaction is carried out at 40℃ for 12 hours, during which TEOS and THSP undergo co-hydrolysis and condensation to form SiO2 nanoparticles with uniformly distributed carboxyl groups; after the reaction, byproducts and unreacted substances are removed by centrifugation or dialysis, and finally, SiO2-COOH nanoparticles are obtained by freeze-drying. ③ Experimental results: SiO2-COOH with a particle size of ~50 nm and a carboxyl density of 1.2 mmol / g was synthesized. TEM test: The particles are monodisperse spherical with an average particle size of 52±5 nm. Titration test: The surface carboxyl density was measured to be 1.25 by conductivity titration. mmol / g. Rheological test: In buffer solution at pH=9, a 2 wt% SiO2-COOH dispersion formed a gel with a viscosity >5000 mPa·s (after standing). In buffer solution at pH=5, it rapidly depolymerized, and the viscosity decreased to 8 mPa·s within 1 minute (shear rate 100 s⁻¹). - ¹), with a rapid and thorough response. Compatibility test: No incompatibility or abnormal aggregation occurred when mixed with PNIPAM solution under acidic conditions.

[0023] Specifically, the preparation of the proppant, i.e., the epoxy resin core thermal expansion microcapsules, involves in-situ polymerization to prepare microcapsules with melamine-formaldehyde resin (MF) as the wall material. MF resin wall material has high strength and good density, and its mechanical strength (bursting pressure) can be precisely controlled through the synthesis process. ① The preparation steps include: Oil phase preparation: Epoxy resin (e.g., E-51), low-boiling-point solvent (e.g., isooctane, as a foaming agent), and initiator are mixed to form the oil phase. Aqueous phase preparation: Melamine, formaldehyde prepolymer (to form MF prepolymer), emulsifier (e.g., PVP), and pH buffer are dissolved in water. Emulsification: Under high-speed shear (10,000 rpm), the oil phase is slowly added to the aqueous phase to form a stable oil / water emulsion, with droplet size matching the target microcapsule size (e.g., 50 μm). The temperature is slowly increased to 55-60℃, and the pH is adjusted to acidic (~4.0) to allow the MF prepolymer to undergo a condensation reaction at the oil droplet interface, forming a robust cross-linked polymer wall. After the reaction, the mixture was cooled, the pH was adjusted to neutral, and the product was filtered, washed, and dried to obtain free-flowing powdered microcapsules. ② Experimental Results: Microcapsules with a target rupture pressure of 35 MPa were prepared. Optical Microscopy / SEM: The microcapsules were regularly spherical with smooth surfaces, an average particle size of 45±10 μm, and a wall thickness of approximately 1.5 μm. DSC / TGA: The boiling point of the foaming agent was ~120℃, and the exothermic peak of the core epoxy resin curing was ~180℃ (matching the formation temperature). Pressure Test: Pressure was applied to individual microcapsules using a high-pressure chamber, and the rupture moment was observed under a microscope. Statistical Results: The rupture pressure distribution of the microcapsules was concentrated in the range of 32-38 MPa, with an average value of 35.2 MPa, which highly matches the design target. Flow Conductivity Experiment: In a flow conduction chamber, the performance of traditional ceramic particles and microcapsule-coated ceramic particles (weight ratio 1:9) under a closure pressure of 40 MPa was compared. Traditional ceramsite exhibits a 45% decrease in conductivity, while the ceramsite layer with added microcapsules, due to the bonding effect of epoxy resin, only experiences a 14% decrease in conductivity, resulting in a 68.9% reduction in conductivity, which is highly consistent with the target (70%).

[0024] (1.3) Initial Stage Behavior and Triggering of High-Efficiency Propane Carrying Stage: At this stage, the fracturing fluid is at a low temperature (surface temperature) and neutral pH. The pH trigger (SiO2-COOH) is in an inert state, and the fluid viscosity is low. The temperature trigger (PNIPAM) begins to function: When the fracturing fluid enters the wellbore and the temperature rises to the formation temperature of 40-60°C, PNIPAM rapidly undergoes a phase transition, self-assembling into a three-dimensional network gel, which significantly increases the fluid viscosity from tens of mPa·s to 200-300 mPa·s. Specifically, in the high-efficiency proppane carrying stage (PNIPAM temperature triggering), the component is poly(N-isopropylacrylamide) (PNIPAM), and the triggering mechanism is temperature (40-60°C formation temperature). The process: PNIPAM undergoes a dramatic phase transition near its lowest critical solution temperature (LCST). At low temperatures (such as surface temperature), it dissolves in water, resulting in a low solution viscosity that is easy to pump. Once inside high-temperature formations, the polymer chains dehydrate and shrink, self-assembling into a three-dimensional network structure, transforming the fluid into a jelly-like gel. The effect: the viscosity increases dramatically from tens of mPa·s to 200-300 mPa·s. This high viscosity effectively suspends and carries the proppant (ceramsite), preventing it from settling in the wellbore and main fractures, ensuring the proppant is effectively deployed to the target location.

[0025] Step 2, suture mesh expansion and temporary plugging and reversal: (2.1) Fracture monitoring and decision-making: Real-time monitoring of downhole pressure, temperature, pH value and fracture morphology depicted by microseismic mapping; when the main fracture length is detected to extend to about 120m, it is determined that a change in direction is needed to generate branch fractures.

[0026] (2.2) Magnetic navigation temporary plugging: A magnetically responsive temporary plugging ball is deployed, and the wellhead electromagnetic field device is activated to precisely guide (positioning error <0.5m) the temporary plugging ball to seal the entrance of the formed main fracture. Specifically, the temporary plugging ball consists of an Fe3O4 core (diameter 2-3mm) + a biodegradable PLGA outer shell (degradation temperature 60℃); the electromagnetic positioning system uses a wellhead annular electromagnetic field (intensity 0.5-1.5T) with a positioning accuracy ≤±0.5m.

[0027] (2.3) Triggering of the diversion fracturing and deep penetration stage: Increasing the pump flow rate to 22 m³ / min generates higher pressure at the temporarily plugged main fracture entrance, forcing the fracturing fluid to divert into the natural weak surface or stress shadow zone deep within the reservoir, opening new branch fractures. When the fracturing fluid enters the inherent acidic (pH < 6.0) microfracture environment of the coal matrix, the deep penetration stage is triggered: the carboxyl grouping of the pH trigger (SiO₂-COOH) reduces the repulsive force between nanoparticles, and the original weak gel structure depolymerizes. The system viscosity drops sharply to 5-10 mPa·s, becoming as thin as water. Specifically, in the deep penetration stage (SiO₂-COOH pH triggering), the component is carboxylated silica nanoparticles (SiO₂-COOH), and the triggering mechanism is an acidic environment (coal matrix pH < 6.0). The process: Under neutral or alkaline conditions, these nanoparticles may form a weak gel or thickening network through hydrogen bonding and other interactions. When the fluid enters the acidic microfractures unique to coal reservoirs, the carboxyl groups (-COOH) undergo protonation, reducing the negative charge and hydrophilicity of the nanoparticle surface and decreasing the repulsive forces between particles, leading to the deagglomeration of the original structure. The effect: the system viscosity drops sharply to 5-10 mPa·s, becoming as thin as water. This low-viscosity fluid can easily penetrate nanoscale or microscale pores and fractures that conventional fracturing fluids cannot reach, maximizing the effective modified volume (SRV) and introducing finer proppant into these microfractures.

[0028] Step 3: AI-powered intelligent dynamic optimization and sand-laying strategy execution: The closed-loop control includes: a monitoring unit consisting of distributed acoustic sensing (DAS) and distributed temperature sensing (DTS) optical fibers; and a decision-making unit based on a reinforcement learning-based AI platform, with a stitch-mesh complexity index (FCI) ≥ 4.0 as the optimization objective. Specifically, it includes: (3.1) Intelligent collaborative control: The fracturing process is regarded as a sequential decision problem. The AI ​​agent dynamically optimizes the flow rate and sand ratio based on real-time data (such as fracture complexity index FCI, fracture width, pressure, and cumulative fluid / sand volume). The flow rate determines the fracture scale, and the sand ratio determines the conductivity.

[0029] (3.2) Optimization strategy: The AI ​​platform (such as reinforcement learning agent) acts according to preset rules: if FCI (number of branch seams × average length / main seam length) < 4.0, the displacement is increased to aggressively create seams; if the monitored seam width Width > 10mm, the sand ratio is increased to strengthen support.

[0030] (3.3) Final application: At the end of construction, according to the AI-optimized high sand ratio program, a large amount of stress-triggered proppant is applied to the formed complex crack network.

[0031] Step 4: Crack closure, triggering the strong support stage and in-situ bonding and curing. (4.1) Strong Support Stage Triggering: When the fracture closure pressure compresses the proppant layer and the local pressure exceeds the 30 MPa threshold, the strong support stage is triggered. The thermally expanded microcapsules coated on the proppant surface are crushed, and the epoxy resin core is released. After the fracturing is completed, the fracture begins to close under the closure pressure (usually >30 MPa). Specifically, in the strong support stage (thermally expanded microcapsule stress triggering), the component is ceramic particles coated with thermally expanded microcapsules (with epoxy resin core). Triggering mechanism: Fracture closure pressure (>30 MPa). Process: Pumping stage: The microcapsules remain intact during pumping and fracture extension, and the core resin is not released. Fracture closure stage: When the fracturing operation is completed, the fracture begins to compress the proppant layer under the closure pressure. When the local pressure exceeds the 30 MPa threshold, the microcapsules are crushed. Cementing stage: The released epoxy resin undergoes a curing reaction at the formation temperature, automatically cementing the surrounding ceramic particles into a strong, elastic, and integrated network. Effects: Significantly enhances the compressive strength of proppant aggregates, resisting high formation closure pressure. Significantly reduces proppant backflow, improving production safety. Conductivity attenuation rate reduced by 70%: Traditional proppant layers fracture, embed, and migrate under high pressure, leading to blockage of flow channels. The cemented integral structure effectively avoids these phenomena, maintaining high conductivity in fractures over a long period, ensuring unobstructed oil and gas production channels.

[0032] (4.2) Bonding and curing: The released epoxy resin undergoes a curing reaction at the formation temperature, bonding the surrounding ceramic particles into a strong and elastic whole network.

[0033] High compressive strength: Effectively resists high formation closure pressure, preventing proppant breakage and embedment. Anti-backflow: Significantly reduces proppant backflow issues during production, improving safety.

[0034] Stable conductivity: The cemented overall structure enables the fracture to maintain high conductivity over a long period of time, and the attenuation rate is expected to be reduced by more than 70%, ensuring the long-term smooth flow of oil and gas production channels.

[0035] Step 5, Post-Fracturing Collaborative Development and Comprehensive Utilization: After fracturing, leveraging the resulting massive fracture network, multi-functional collaborative development will be carried out: Geothermal Power Generation: Geothermal exchange pipes will be implanted within horizontal wellbores, utilizing the heat exchange area created by fracturing and the formation temperature gradient (approximately 3.5℃ / 100m) to generate electricity. The expected power output per well is 120-150kW. CO2 Storage and Replacement Gas Production: Supercritical CO2 will be injected. On one hand, its strong adsorption properties will replace methane adsorbed on the coal matrix (replacement ratio up to 1:3.2), enhancing recovery. On the other hand, CO2 will be permanently stored in the coal reservoir, with an expected storage capacity of 8×10⁻⁶ m³ / h. 4 For areas with a volume of m³ or more, green development should be implemented.

[0036] The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the specific details of the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0037] It should also be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0038] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A self-optimizing fracture network fracturing method for coalbed methane wells based on smart response materials, characterized in that, Includes the following steps: Step 1, Wellbore preparation and initial injection of intelligent fracturing fluid: s1.1, Wellbore and Perforation: Preparation work for well cleaning and flushing of the target coalbed methane horizontal well section; deep penetration ejection holes are used, with a hole density of 16-20 holes / meter and a penetration depth of ≥800mm; s1.2, Inject intelligent fracturing fluid: Pump intelligent fracturing fluid at a flow rate of 18 m³ / min and a sand ratio of 12%; the intelligent fracturing fluid includes: temperature trigger PNIPAM, pH trigger SiO2-COOH, and proppant; s1.3, Initial stage behavior and triggering of efficient proppant carrying stage: In the initial stage, the fracturing fluid is in a low temperature and neutral pH state with low fluid viscosity; when the fracturing fluid enters the wellbore, the temperature rises, triggering the efficient proppant carrying stage. The temperature triggering agent PNIPAM undergoes a rapid phase change and self-assembles into a three-dimensional network gel, which increases the fluid viscosity. Step 2, suture mesh expansion and temporary plugging and reversal: s2.1, Fracture Monitoring and Decision Making: The monitoring unit monitors downhole pressure, temperature, pH value, and fracture morphology depicted by microseismic mapping in real time; when the main fracture length is detected to extend to 120m, it is determined that a deflection is necessary to generate branch fractures. S2.2, Magnetic navigation temporary plugging: Deploy the magnetic response temporary plugging ball and activate the wellhead electromagnetic field device to precisely guide the temporary plugging ball to seal the entrance of the main fracture that has been formed; S2.3, Fracturing and Deep Permeation Stage Triggering: The pump flow rate is increased to 22 m³ / min. The high flow rate generates higher pressure at the temporarily plugged main fracture entrance, forcing the fracturing fluid to deflect into the natural weak surface or stress shadow zone deep within the reservoir, expanding new branch fractures. When the fracturing fluid enters the inherent acidic microfracture environment of the coal matrix, the deep permeation stage is triggered. The pH trigger SiO2-COOH undergoes carboxylation, the original gel structure depolymerizes, and the viscosity drops sharply. Step 3, Intelligent Dynamic Optimization and Sand Laying Strategy Execution: S3.1 Intelligent collaborative control: Dynamically optimizes discharge volume and sand ratio based on real-time data from the monitoring unit; s3.2, Optimization Strategy: Based on the reinforcement learning AI platform, the system determines whether to adjust the flow rate and grit ratio according to the monitored seam complexity index FCI and seam width. If the seam complexity index FCI < 4.0, the flow rate is increased to aggressively create seams; if the monitored seam width > 10mm, the grit ratio is increased to strengthen support. s3.3, Final application: According to the optimized displacement and sand ratio, the proppant is applied into the formed complex crack network; Step 4, Strong Support Stage Triggering, Bonding and Curing: S4.1, Strong Support Stage Trigger: After construction is completed, the crack closes under the closing pressure. When the pressure exceeds 30MPa, the strong support stage is triggered, the proppant is squeezed and ruptured, and epoxy resin is released. s4.2, Bonding and Curing: The released epoxy resin undergoes a curing reaction at the formation temperature, bonding the surrounding ceramic particles into a strong and elastic overall network; Step 5, Post-fracturing collaborative development and comprehensive utilization: After fracturing is completed, multi-functional collaborative development is carried out based on the huge fracture network formed.

2. The self-optimizing fracture network fracturing method for coalbed methane wells based on smart response materials as described in claim 1, characterized in that, The intelligent fracturing fluid includes: The temperature trigger agent PNIPAM has a viscosity that increases to 200-300 mPa·s at 40-60℃. The pH trigger agent SiO2-COOH has a viscosity that decreases to 5-10 mPa·s when pH < 6.0; The proppant is an epoxy resin microcapsule coated with ceramic particles, which is activated by a closing pressure >30MPa.

3. The self-optimizing fracture network fracturing method for coalbed methane wells based on smart response materials as described in claim 1, characterized in that, In s1.3, initially at low temperature, the pH trigger SiO2-COOH is in an inert state, the temperature trigger PNIPAM is soluble in water, the fluid viscosity is low, and it is easy to pump; The high-efficiency proppant carrying stage includes: fracturing fluid entering the high-temperature formation in the wellbore, the temperature rises to 40-60°C, triggering the high-efficiency proppant carrying stage. The temperature triggering agent PNIPAM undergoes a violent phase transition at its lowest critical dissolution temperature (LCST), the polymer chains undergo dehydration and shrinkage, and self-assemble into a three-dimensional network structure. The fluid transforms into a jelly-like gel, with the viscosity increasing to 200-300 mPa·s. The high viscosity can suspend and carry the proppant, preventing it from settling in the wellbore and main fracture, and ensuring that the proppant is effectively laid to the target location.

4. The self-optimizing fracture network fracturing method for coalbed methane wells based on smart response materials as described in claim 1, characterized in that, In s2.2, the temporary plugging ball includes an Fe3O4 core and a biodegradable PLGA shell; wherein, the Fe3O4 core has a diameter of 2-3 mm, and the biodegradable PLGA shell has a degradation temperature of 60℃; the electromagnetic field strength of the wellhead electromagnetic field device is 0.5-1.5T.

5. The self-optimizing fracture network fracturing method for coalbed methane wells based on smart response materials as described in claim 1, characterized in that, In s2.3, the deep penetration stage includes: when the fracturing fluid enters the inherent acidic microfracture environment of the coal matrix, the pH < 6.0, the pH trigger SiO2-COOH is carboxylated, the negative charge and hydrophilicity of the nanoparticle surface are weakened, the repulsive force between particles is reduced, the original gel structure is depolymerized, the viscosity drops sharply to 5-10 mPa·s, and the low viscosity fluid can penetrate the nanoscale or microscale pores and fractures that conventional fracturing fluids cannot enter, thereby maximizing the expansion of the effective modification volume.

6. The self-optimizing fracture network fracturing method for coalbed methane wells based on smart response materials as described in claim 1, characterized in that, The monitoring unit includes a distributed acoustic sensor (DAS) and a distributed temperature sensor (DTS) fiber optic cable. The monitoring unit monitors downhole temperature, strain, acoustic signals, and pH value, and can dynamically track fracture propagation morphology by combining microseismic data.

7. The self-optimizing fracture network fracturing method for coalbed methane wells based on smart response materials as described in claim 1, characterized in that, In s4.1, the strong support stage includes: when the fracture closure pressure exceeds 30MPa, the proppant is squeezed and crushed, releasing epoxy resin which undergoes a curing reaction at the formation temperature, automatically cementing the surrounding ceramic particles, enhancing the compressive strength of the proppant agglomerates, resisting the high closure pressure of the formation, reducing the backflow of proppant, and maintaining the fracture's long-term high conductivity.

Images