Underground in-situ high-temperature gas fracturing and supporting integrated system and operation method thereof

Abstract

The invention provides an underground in-situ high-temperature gas fracturing and supporting integrated system and an operation method thereof, and relates to the technical field of unconventional natural gas extraction and coal mine gas treatment. The system comprises a ground monitoring supply unit, an integrated downhole operation tool string and a composite pipe cable. The method comprises the following steps: firstly, carrying out thermal shock embrittlement on a coal body by utilizing high-temperature inert gas generated by chemical reaction, then modulating the high-temperature inert gas into pressure pulse waves to carry out brittle dynamic fatigue crack propagation, and simultaneously, synchronously injecting a thermal expansion macromolecular propping agent accurately triggered by temperature, so as to realize time-space synchronization of fracturing and supporting. Through a continuous process of'high-temperature embrittlement-fatigue extension-intelligent support 'and by means of real-time monitoring and closed-loop regulation and control of the distributed optical fiber sensor, the problems that traditional gas fracturing cracks are limited in complexity and a propping agent is difficult to transport are solved, a complex crack network with lasting flow conductivity can be efficiently formed, and the fracturing efficiency is improved. And the low-permeability coal seam gas extraction and coal seam gas recovery efficiency is remarkably improved.

Description

Technical Field

[0001] This invention relates to the fields of unconventional natural gas extraction and coal mine gas control technology, specifically to an integrated system for in-situ high-temperature gas fracturing support in underground mines and its operation method. Background Technology

[0002] The economic development of low-permeability coal seams relies on the formation of complex fracture networks with long-term conductivity. Current waterless fracturing technologies, such as liquid CO2 or nitrogen fracturing, mainly depend on the hydrostatic pressure or phase change pressure of the fluid, and suffer from the following bottlenecks: 1. Simple fracturing mechanism and limited fracture network complexity: Traditional cold gas fracturing is mainly based on tensile failure, which is difficult to efficiently activate a large number of closed natural fractures and bedding in coal and rock, and does not deeply modify the mechanical properties of coal.

[0003] 2. Low propping efficiency and insufficient long-term flow capacity: Conventional proppants (quartz sand, ceramsite) have high density and poor suspension and migration capacity in low viscosity gas. They are very easy to settle and accumulate in the section of the fracture near the wellbore, resulting in a "propping gap" deep in the fracture. Furthermore, rigid proppants are at risk of embedding into the coal wall and breaking under closure stress.

[0004] 3. Dispersed equipment and processes, poor coordination: "Fracturing" and "propping" are usually two independent operation stages, and even use different equipment and fluids, resulting in long construction cycles, high costs, and the inability of proppant distribution to match the fracture morphology in real time.

[0005] In recent years, the concepts of thermally stimulated fracturing and novel proppants have been proposed. For example, reservoirs can be heated by electricity or steam to generate thermal stress, but the heating range is limited and energy consumption is high. Other studies have proposed expandable resin-coated proppants, but their expansion depends on formation temperature, the reaction time is long and uncontrollable, and they cannot achieve synchronous fixed-point propping during the fracturing process.

[0006] Therefore, existing technologies lack a systematic solution that can coordinate the three mechanisms of thermal fracturing (non-combustion), fatigue damage, and intelligent support in the same space and time through integrated equipment, making it difficult to significantly improve the efficiency and long-term effects of low-permeability coal seam modification. Summary of the Invention

[0007] The purpose of this invention is to provide an integrated in-situ high-temperature gas fracturing and propulsion system and its operation method in wells, which can overcome the defects of existing technologies such as the disconnect between fracturing and propulsion, insufficient fracture complexity and long-term conductivity. Through an integrated downhole operation tool string, it can achieve rapid thermal shock and embrittlement of coal body by high-temperature gas (non-combustion), fatigue crack propagation under alternating load, and simultaneous injection of temperature-triggered thermal expansion polymer proppant to achieve adaptive expansion and anchoring in the fracture, ultimately forming a complex and durable high-efficiency seepage channel.

[0008] To achieve the above objectives, in a first aspect, the present invention provides an integrated downhole in-situ high-temperature gas fracturing support system, comprising a surface monitoring and supply unit, an integrated downhole tool string, and a composite cable connecting the surface monitoring and supply unit and the integrated downhole tool string. The ground monitoring and supply unit delivers liquid chemical thermal reactant and thermally expanding polymer proppant to the integrated downhole tool string via a composite cable; the composite cable is equipped with distributed fiber optic sensors for real-time monitoring of temperature field changes and acoustic events. The integrated downhole tool string includes: The high-temperature gas in-situ generation and modulation chamber is used to provide a site for the chemical reaction of liquid chemothermal reactants and to modulate the high-temperature inert gas generated after the chemical reaction into high-temperature pulse gas. And a proppant composite injection module, used to mix thermally expandable polymer proppant with high-temperature pulsed gas to form a mixed fluid, and inject the mixed fluid into the target coal seam; Based on temperature field changes and acoustic events, the ground monitoring and supply unit outputs control commands to the integrated downhole tool string to dynamically adjust the temperature of the high-temperature inert gas, the pulse parameters of the high-temperature pulsed gas, the concentration of the thermally expanding polymer proppant, and the injection temperature of the mixed fluid.

[0009] According to the present invention, an integrated in-situ high-temperature gas fracturing support system for downhole applications is provided, comprising two types of liquid chemithermal reactants; the high-temperature gas in-situ generation and modulation chamber includes: a high-efficiency cyclone mixer, an adiabatic reaction chamber, and a high-frequency pulse modulation valve; the high-efficiency cyclone mixer is used to mix the two liquid chemithermal reactants uniformly, and after uniform mixing, a chemical reaction occurs in the adiabatic reaction chamber to generate high-temperature inert gas; the high-frequency pulse modulation valve is used to modulate the high-temperature inert gas into a high-temperature pulse gas with a specific frequency and amplitude, forming a pressure pulse wave. According to the present invention, an integrated in-situ high-temperature gas fracturing propulsion system for downhole is provided, wherein the thermally expandable polymer proppant is a core-shell structured microsphere, the outer shell of the core-shell structured microsphere is a thermosetting resin coating, and the core is a thermoplastic polymer material. According to the present invention, an integrated in-situ high-temperature gas fracturing propping system for downhole applications includes a proppant composite injection module comprising: A Venturi gas-solid mixer is used to draw in thermally expandable polymer proppant at a set concentration using the negative pressure generated by a pressure pulse wave, and to uniformly mix the pressure pulse wave with the thermally expandable polymer proppant. And a temperature field control ring, surrounding the outlet of the Venturi gas-solid mixer, is used to adjust the outlet temperature of the uniformly mixed pressure pulse wave and the thermally expanding polymer support to the glass transition temperature of the thermosetting resin coating according to control commands. According to the present invention, an integrated in-situ high-temperature gas fracturing support system for downhole is provided, wherein the frequency range of the pressure pulse wave is 0.5Hz–10Hz and the temperature range is 200℃–500℃. According to the present invention, an integrated downhole in-situ high-temperature gas fracturing propulsion system is provided, wherein the composite cable includes a central tube and an outer tube, and an annular channel is provided between the central tube and the outer tube. The central tube is used to transport liquid chemothermal reactant, and the annular channel is used to transport thermally expanding polymer proppant to the integrated downhole tool string through inert gas. According to the present invention, an integrated in-situ high-temperature gas fracturing support system for downhole is provided, wherein the distributed optical fiber sensor includes a distributed optical fiber temperature sensing unit and a distributed optical fiber acoustic sensing unit, and the distributed optical fiber is disposed on the pipe wall of the annular channel. According to the present invention, an integrated downhole in-situ high-temperature gas fracturing support system is provided, wherein the integrated downhole tool string further includes a downhole integrated control module and a multi-functional nozzle and monitoring module; the downhole integrated control module is used to receive control commands. The multi-functional nozzle and monitoring module includes: Switchable nozzles are used to convert mixed fluids into high-energy jets of specific shapes, which directly act on coal and rock formations to achieve differentiated fracturing objectives. Downhole high-definition cameras are used to provide direct optical images of the wellbore and near-wellbore fracture areas for real-time visual diagnostics. And miniature acoustic wave transmitters and receivers, used to actively transmit acoustic signals into the formation and receive their reflected, refracted and scattered signals, in order to detect invisible information about the formation and fractures around the wellbore. According to the present invention, an integrated downhole in-situ high-temperature gas fracturing support system is provided, wherein the surface monitoring and supply unit is equipped with a thermo-mechanical coupled fracture propagation model and a proppant migration optimization algorithm. Based on temperature field changes and acoustic events, the system outputs control commands to the integrated downhole operation tool string through the thermo-mechanical coupled fracture propagation model and the proppant migration optimization algorithm.

[0010] In a second aspect, the present invention provides a method for continuous in-situ fracturing support operations, employing the integrated downhole in-situ high-temperature gas fracturing support system of the first aspect, the method comprising: The integrated downhole tool string is lowered to the designed fracturing section of the target coal seam and anchored. A high-temperature inert gas is generated in an in-situ high-temperature gas generation modulation chamber to thermally shock embrittle the coal body. A pressure pulse wave is generated by a high-frequency pulse modulation valve, and a thermally expanding polymer proppant is injected into the proppant composite injection module to carry out brittle fatigue crack propagation and propping synergistic operation. Based on temperature field changes and acoustic events, control commands are output to the integrated downhole tool string to dynamically adjust the temperature of the high-temperature inert gas, the pulse parameters of the high-temperature pulsed gas, the concentration of the thermally expanding polymer proppant, and the injection temperature of the mixed fluid. After completing the current fracturing section, a temporary plugging and redirection operation is performed, and the integrated downhole tool string is moved to the next designed fracturing section for continuous operation.

[0011] This invention has at least the following beneficial effects: 1. In-depth innovation in mechanism and equipment: A pioneering approach integrates two mechanisms—thermal shock embrittlement and alternating load fatigue fracturing—downhole through a high-temperature gas in-situ generation modulation chamber and a proppant composite injection module. This rapidly reduces coal strength and increases brittleness, while subsequent alternating pressure pulses, like repeatedly bending a metal wire, promote fatigue propagation of fractures with lower energy consumption, forming a more complex fracture network. This efficiency is far superior to single static pressure fracturing.

[0012] 2. A revolutionary breakthrough in the spatiotemporal synchronization of fracturing and proppant: Through the integrated coaxial design of the proppant composite injection module and the high-temperature gas in-situ generation and modulation chamber, proppant and fracturing fluid are injected, transported, and delivered to the fracture front simultaneously. The temperature-triggered expansion mechanism ensures that the proppant is automatically activated, expanded, and anchored in the high-temperature zone of the distal fracture requiring support, solving the global challenge of proppant migration and distribution in gas fracturing and greatly improving long-term flow conductivity.

[0013] 3. High Integration and Intelligence: The integrated downhole tool string integrates functions such as high-temperature gas generation, pulse modulation, precise composite injection of proppant, and near-field monitoring, realizing in-situ integrated downhole operations of "fracture creation, fracture widening, propping, and monitoring." Combined with fiber optic sensing and intelligent algorithms, a rapid closed loop from sensing to execution is formed, with strong process adaptability.

[0014] 4. Safe, efficient, and durable: In-situ chemical heating avoids the risks associated with transporting high-temperature, high-pressure gases from the surface, and boasts high energy utilization. The fatigue fracturing mechanism allows for the formation of complex fracture networks even at relatively low average downhole pressures, reducing engineering risks. The flexible propping layer formed by the thermally expanding polymer proppant exhibits strong anti-embedding capabilities and slow conductivity decay, ensuring long-term production enhancement. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0016] In the attached diagram: Figure 1 This is a schematic diagram of the integrated system for in-situ high-temperature gas brittle fatigue fracturing and intelligent support in low-permeability coal seams according to the present invention. Figure 2 This is a schematic diagram illustrating the working principle of the high-temperature gas in-situ generation modulation chamber of the present invention. Figure 3 This is a schematic diagram illustrating the working principle of the proppant composite injection module of the present invention. Figure 4 This is a flowchart of the continuous operation method for on-site fracturing support according to the present invention. Detailed Implementation

[0017] 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 with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0018] The following detailed description of some embodiments of the present invention will be provided in conjunction with the accompanying drawings. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0019] Please see Figure 1 This invention provides an integrated system for in-situ high-temperature gas brittle fatigue fracturing and intelligent support in low-permeability coal seams. It is an integrated downhole equipment and continuous field operation process suitable for low-permeability coal seams, combining high-temperature gas initiation, brittle fatigue fracturing, and intelligent fixed-point support with thermal expansion proppant. The system includes a surface intelligent monitoring and supply unit (hereinafter referred to as the surface monitoring and supply unit), an integrated downhole tool string, and a composite cable connecting the surface monitoring and supply unit and the integrated downhole tool string.

[0020] The surface monitoring and supply unit includes an inert gas (e.g., high-purity nitrogen) source, a liquid chemithermal reactant storage tank (for storing liquid chemithermal reactants, including thermal reactant A and thermal reactant B), a thermally expandable polymer proppant storage tank, and a data acquisition and control system. This data acquisition and control system incorporates a thermo-mechanical coupled fracture propagation model and a proppant migration optimization algorithm. The surface monitoring and supply unit delivers liquid chemithermal reactants and thermally expandable polymer proppant to the integrated downhole tool string via a composite cable.

[0021] The composite cable employs a coaxial multi-channel design. The outer tube is a high-temperature and high-pressure resistant alloy tube, while the central tube uses a dual-tube structure for independently transporting thermal reactant A and thermal reactant B. The annular channel is used to transport the thermally expanding polymer proppant to the integrated downhole tool string via inert gas. The outer tube wall is embedded with distributed fiber optic sensors (including distributed fiber optic temperature / acoustic (DTS / DAS) sensing units) and a power cable. The distributed fiber optic sensors are used to monitor temperature field changes and acoustic events in real time. The power cable safely and stably transmits electrical energy from the surface to the well depth of several thousand meters, ensuring the normal operation of the integrated downhole tool string's control, drive (pulse modulation, heating / cooling), monitoring (camera, acoustic waves), and mechanical actions (anchoring / movement).

[0022] The ground monitoring and supply unit outputs control commands to the integrated downhole tool string based on temperature field changes and acoustic events, using a built-in thermo-mechanical coupling fracture propagation model and proppant migration optimization algorithm.

[0023] It should be noted that the thermo-mechanical coupled crack propagation model is a numerical model of rock fracture mechanics that considers the dual coupling effect of temperature and stress fields. Its core purpose is to describe and predict the initiation, propagation, direction, and final fracture network morphology of coal and rock cracks under the combined action of "high-temperature thermal shock" and "alternating fatigue load". This will be discussed in detail below.

[0024] 1. Model input parameters.

[0025] Basic physical properties: elastic modulus, Poisson's ratio, tensile / compressive strength, fracture toughness, coefficient of thermal expansion, specific heat capacity, and thermal conductivity of coal and rock.

[0026] Real-time dynamic data, including: Temperature field: Coal and rock temperature distribution (thermal shock range and gradient) monitored in real time by DTS.

[0027] Stress field: Magnitude and direction of geostress (obtained from previous geological exploration or DAS inversion).

[0028] Load spectrum: obtained from the frequency (0.5-10 Hz), amplitude and waveform of the pressure pulse wave output by the high-frequency pulse modulation valve.

[0029] 2. The model incorporates the following two key physicochemical coupling mechanisms.

[0030] Thermal damage mechanism: After the high-temperature gas is injected, the coal matrix expands due to heat. Because of the huge difference in the coefficients of thermal expansion between minerals (such as quartz) and organic matter (vitrinite) in the coal, intergranular or transgranular microcracks are generated.

[0031] The model quantitatively describes this damage using thermal stress calculation formulas: rising temperature leads to a significant decrease in the elastic modulus and tensile strength of coal and rock (i.e., the "embrittlement" process), creating the conditions for subsequent fatigue propagation.

[0032] Fatigue damage accumulation mechanism: The model incorporates a nonlinear fatigue damage model. Unlike traditional static high-pressure cracking (one-time burst), this model considers subcritical crack propagation at the crack tip under alternating pressure pulses.

[0033] The Paris formula or its modified form describes the relationship between the crack propagation rate da / dN and the stress intensity factor range ΔK. The model can calculate how far a crack can propagate after how many pulse cycles, under conditions below the static fracturing pressure of coal and rock.

[0034] 3. Model output results.

[0035] Crack geometry: crack length, width, height, and spatial orientation (planar / complex network).

[0036] Temperature field distribution: Predicting the cooling process of high-temperature gas in the crack and the area affected by heat.

[0037] Seam network complexity evaluation: quantitatively evaluate the communication and density between the main crack and the branch cracks.

[0038] The proppant transport optimization algorithm is based on gas-solid two-phase fluid dynamics and smart material phase change control. Its core objective is to precisely control the transport, distribution, triggered expansion, and final anchoring position of thermally expanding polymer proppant in complex cracks, achieving intelligent propping where the proppant is used effectively. Specifically: 1. Algorithm input parameters.

[0039] Fluid parameters: flow rate, viscosity, density and temperature of high-temperature gas (especially the outlet temperature after fine-tuning by the temperature field control loop).

[0040] 2. Propionate parameters.

[0041] Physical properties: particle size, density, sphericity.

[0042] Thermal response characteristics: glass transition temperature (Tg) of the outer shell resin coating, core expansion ratio, expansion rate and curing time.

[0043] Crack constraints: Crack geometry (width, roughness) inverted or predicted by a thermo-mechanical coupled crack propagation model.

[0044] 3. Core algorithm logic.

[0045] Phase 1: Simulation of transport trajectory.

[0046] Computational fluid dynamics-discrete element method (CFD-DEM) was used to simulate the motion trajectory of proppant microspheres carried by high-temperature gas in a narrow and rough crack.

[0047] The algorithm focuses on solving the problem of proppant settling caused by low gas viscosity: by optimizing the pulse frequency (intermittent high-speed gas flow) to maintain the suspension of proppant and prevent it from accumulating in the near-wellbore area.

[0048] Phase Two: Temperature Field Matching and Fixed-Point Triggering.

[0049] The temperature field data monitored by DTS is matched and calculated in real time with the thermal response characteristics of the proppant.

[0050] Logic: The algorithm ensures that when the proppant reaches a specific depth in the crack (usually the crack tip or branch point, i.e., a region with higher temperature), the temperature of the surrounding gas is exactly at or slightly higher than the Tg of its shell by adjusting the heating power of the "temperature field control ring".

[0051] Intelligent decision-making: If the DTS shows that the temperature at the far end of the crack is insufficient (heat loss is too fast), the algorithm will instruct the ground to increase the ratio of A / B thermal reactants (increase the initial temperature of the gas), or instruct the temperature field control ring to perform supplemental heating to ensure that the proppant can expand "on time" at the target location.

[0052] Phase 3: Optimization of expansion anchoring and flow guidance capabilities.

[0053] After the proppant expands, the algorithm simulates how it embeds into the coal and rock wall and calculates the final prop joint width and porosity under closure stress.

[0054] The algorithm will reverse-optimize the injection concentration and expansion ratio of the proppant based on the crack conduction capacity required for the target production capacity, avoiding "over-propping" (wasting materials) or "under-propping" (crack closure).

[0055] 4. Algorithm Output Results Optimal injection scheme: The optimal proppant concentration, injection rate, and mixed flow outlet temperature settings for the current fracturing section.

[0056] Propionate distribution cloud map: predicts the three-dimensional distribution of expanded proppant in the crack and identifies potential "propping blank areas".

[0057] Control commands: Real-time adjustment of pulse frequency, temperature control loop power, and proppant injection rate.

[0058] Specifically, the integrated downhole tool string adopts a modular coaxial design, comprising, from top to bottom: a. Electro-hydraulic anchoring and moving module: Enables the integrated downhole tool string to be precisely positioned and moved within the horizontal well section.

[0059] It should be noted that the electro-hydraulic anchoring and moving module is not the core improvement of this invention. The core of this invention lies in the integrated design and collaborative process of the high-temperature gas in-situ generation and modulation chamber and the proppant composite injection module. The electro-hydraulic anchoring and moving module is merely a conventional downhole auxiliary tool configured to achieve segmented operations. Furthermore, electro-hydraulic anchoring and moving technology is already very mature in the field of oil and gas well engineering. For example, the structure and working principle of tools such as downhole traction devices and hydraulic anchor packers are well known to those skilled in the art. Based on the functional description of "enabling the integrated downhole tool string to be precisely positioned and moved within a horizontal well section," and considering its connection relationship with other modules (such as the downhole integrated control module), those skilled in the art can fully realize the function of this module. Therefore, this invention will not describe its conventional mechanical structure in detail here.

[0060] b. Downhole Integrated Control and Power Module (hereinafter referred to as Downhole Integrated Control Module): Used to receive control commands to coordinate the work of each module and manage power distribution.

[0061] Specifically, the received control commands include: (1) Ground commands: including start-stop control, parameter setting (temperature / frequency / concentration), mode switching, etc.

[0062] (2) Algorithm instructions: Optimization instructions (such as temperature compensation and pulse adjustment) automatically generated by the ground thermo-mechanical coupling crack propagation model.

[0063] Coordination work: (1) Timing control: The start and stop of each module are coordinated in the order of “anchoring → thermal shock → pulse fracturing → proppant injection → unanchoring”.

[0064] (2) Parameter coupling: dynamic balance of multi-module collaboration (such as simultaneously adjusting the reactant ratio, pulse valve and heating ring to ensure stable outlet temperature).

[0065] (3) Fault protection: Detect abnormalities (over-temperature / over-pressure / communication interruption), automatically execute safety procedures and alarm.

[0066] c. For example Figure 2 As shown, the high-temperature gas in-situ generation and modulation chamber (hereinafter referred to as the high-temperature gas in-situ generation and modulation chamber) includes: High-efficiency cyclone mixer: used to instantly and uniformly mix two liquid chemical thermal reactants (such as formulations based on non-explosive redox principles) delivered separately through independent channels in a central tube.

[0067] Insulated reaction chamber: The mixed liquid undergoes a rapid exothermic chemical reaction here, producing a high-temperature inert gas (mainly nitrogen) with a controllable temperature (200℃–500℃) and no open flame within seconds.

[0068] High-frequency pulse modulation valve: Located at the outlet of the adiabatic reaction chamber, it is controlled by the control command received by the downhole integrated control module. It can modulate the continuous high-temperature inert gas into a high-temperature pulse gas with a specific frequency (0.5Hz–10Hz) and amplitude, forming a pressure pulse wave.

[0069] d. For example Figure 3 As shown, the intelligent proppant composite injection module (hereinafter referred to as the proppant composite injection module) is integrated with the high-temperature gas in-situ generation and modulation chamber. It includes: Venturi-type gas-solid mixer: Located downstream of a high-frequency pulse modulation valve, it utilizes the negative pressure generated by pressure pulse waves to draw in and uniformly mix thermally expanding polymer proppant from an independent delivery line at a set concentration. The proppant consists of core-shell structured microspheres with a thermoplastic polymer core and a thermosetting resin coating on the outer shell, and its glass transition temperature (Tg) is precisely designed (e.g., 150°C).

[0070] Temperature field control ring: A miniature electric heating / cooling ring surrounding the outlet of the mixed fluid, used to adjust the outlet temperature of the uniformly mixed pressure pulse wave and the thermally expanding polymer proppant to the glass transition temperature (±20℃) of the thermosetting resin coating according to control commands, so as to ensure that the proppant is precisely triggered when it enters a specific location in the crack.

[0071] e. Multifunctional nozzle and monitoring module: including switchable nozzle (fan / cone), downhole high-definition camera and miniature acoustic wave transmitter and receiver for generating high-speed jets and near-field fracture imaging.

[0072] Switchable nozzles (fan-shaped / conical): The mixture of upstream pressure pulse waves and thermally expanding polymer proppant is transformed into a high-energy jet of a specific shape, which is directly applied to the coal and rock formation to achieve differentiated fracturing objectives.

[0073] Downhole high-definition camera: used to provide direct optical images of the wellbore and near-wellbore fracture areas for real-time visual diagnosis.

[0074] Miniature acoustic wave transmitter and receiver: Actively transmits acoustic wave signals into the formation and receives the reflected, refracted and scattered signals to detect invisible information about the formation and fractures around the wellbore.

[0075] Another embodiment of the present invention provides a method for continuous in-situ fracturing support operations, employing the integrated downhole in-situ high-temperature gas fracturing support system described in the aforementioned embodiment, such as... Figure 4 As shown, the method includes the following steps: S1: Drilling preparation and tool string insertion: After completing drilling operations in the target coal seam, the integrated downhole tool string is lowered to the first designed fracturing section via a composite cable, and the anchoring module is activated for fixation.

[0076] S2: First round of high-temperature embrittlement and initial cracking: The surface monitoring and supply unit pumps in chemical reactants and inert gas. The underground high-temperature gas in-situ generation and modulation chamber is activated, producing a stable high-temperature inert gas (e.g., 350°C). The high-frequency pulse modulation valve is temporarily closed, and the high-temperature inert gas is injected through nozzles at a relatively stable high pressure (higher than the formation fracturing pressure), rapidly thermally shock embrittlement of the coal seam. Due to the difference in thermal expansion coefficients, microcracks appear in the minerals and organic matter within the coal matrix, significantly increasing the overall brittleness of the coal seam.

[0077] S3: Collaborative operation of brittle fatigue crack propagation and intelligent support: A high-frequency pulse modulation valve is activated, modulating the high-temperature inert gas into a pressure pulse wave with a frequency of 3 Hz. This alternating load acts on the coal body, which has been embrittled by thermal shock. Utilizing the characteristic that its fatigue strength is much lower than its static strength, microcracks propagate under low average stress, efficiently connecting natural fractures and forming a complex fracture network. Simultaneously, the intelligent proppant composite injection module is activated. Thermally expandable polymer proppant microspheres are drawn into a Venturi gas-solid mixer and mixed with the pressure pulse wave. The temperature of the two-phase flow outlet is precisely controlled near the Tg of the proppant shell resin (e.g., 150℃) through a temperature field control ring. The mixed fluid enters the fracture, performing a synergistic operation of brittle fatigue crack propagation and propagation. In the high-temperature zone at the fracture front (>150℃), the outer shell of the proppant microspheres softens, the core expands, and the volume increases rapidly (expansion ratio 3–5 times). Under formation closure stress, it solidifies and sets, anchoring itself to the fracture wall like an "expansion bolt," forming effective support, especially at the fracture distal end and branches. In the near-wellbore region where temperatures are lower, the proppant remains intact, facilitating subsequent flowback.

[0078] S4: Closed-loop adaptive control based on real-time monitoring: Distributed optical fiber sensors (DTS / DAS) in the composite conduit cable monitor temperature field changes and acoustic events in real time. The ground-based monitoring supply unit uses this data to invert crack geometry and proppant distribution. Distributed fiber optic sensors: These act only as "sensors," responsible for collecting raw data (temperature changes and acoustic vibrations) and transmitting it to the ground.

[0079] The data acquisition and control system of the ground monitoring supply unit acts as the "brain". Its built-in thermo-mechanical coupling crack propagation model and proppant migration optimization algorithm interpret, calculate and invert the data uploaded by the distributed optical fiber sensors, and finally output the crack morphology and proppant distribution results, and generate the next round of control commands based on them.

[0080] The ground monitoring and supply unit outputs control commands to the integrated downhole tool string based on the inversion results, so as to dynamically adjust the chemical reactant ratio (adjust the temperature of the high-temperature inert gas), the pulse parameters of the high-temperature pulse gas (including pulse frequency and amplitude, to control the fatigue damage rate), as well as the concentration of proppant and the injection temperature of the mixed fluid, so as to achieve personalized and precise operation of "fracture-propping" in different coal and rock properties.

[0081] Specifically, the dynamic adjustment mechanism of the data acquisition and control system of the ground monitoring supply unit is as follows: (1) Overall logical flow of the adjustment Sensing (distributed fiber optic sensor): Real-time acquisition of temperature field changes and acoustic events.

[0082] Analysis (Model Inversion): Outputs crack geometry, temperature field distribution, and crack network complexity evaluation through the built-in model.

[0083] Decision (Comparison Target): Compare the model output with the preset ideal mesh shape (such as complexity, expansion radius) to find the deviation.

[0084] Execution (Parameter Adjustment): Select the corresponding parameter for adjustment based on the deviation type.

[0085] (2) Dynamic adjustment mechanism of the three major parameters Adjust the "chemical reactant ratio" (control the temperature of the high-temperature inert gas). Controlled object: The pumping ratio of ground thermal reactant A and thermal reactant B.

[0086] Triggering conditions: When the DTS temperature field inversion shows that the temperature at the far end of the fracture is too low to trigger proppant expansion; or when the thermal shock range is insufficient and the coal body embrittlement effect is poor.

[0087] Adjustment logic: 1. If the temperature at the far end of the crack is less than the proppant trigger temperature (Tg), increase the proportion of the more exothermic component in agent A / B to increase the initial gas temperature.

[0088] 2. If the near-well temperature is too high, it may damage the equipment → reduce the reactant concentration or pump speed.

[0089] Objective: To ensure that heat can be delivered deep into the cracks, creating a "breeding ground" for proppant expansion.

[0090] Adjust the pulse frequency and amplitude (to control the fatigue damage rate). Controlled object: The switching frequency and opening degree of the downhole high-frequency pulse modulation valve.

[0091] Triggering conditions: When DAS microseismic event inversion shows that the crack propagation direction is unidirectional, the crack network complexity is insufficient, or the propagation speed is too slow.

[0092] Adjustment logic: 1. If micro-seismic events are sparse (too few cracks) → increase the pulse amplitude (pressure upper and lower limits) to forcibly open more cracks.

[0093] 2. If microseismic events are concentrated in a single direction (with a simple fracture network) → adjust the pulse frequency and utilize the differences in the response of coal and rock at different frequencies to activate natural fractures in different directions.

[0094] 3. If the micro-vibration energy is too strong (risk of pressure breakage) → reduce the amplitude and use the "fatigue accumulation" method to slowly widen the crack.

[0095] Objective: To control the direction and density of crack expansion by adjusting the intensity and rhythm of the "strikes".

[0096] Adjust the concentration of the proppant and the injection temperature of the mixed fluid. Controlled objects: proppant injection rate (venturi gas-solid mixer intake) and heating power of temperature field control ring.

[0097] Triggering condition: When the inversion results show that the proppant distribution does not match the expectations.

[0098] Adjustment logic: 1. Adjustment of proppant concentration: If a "propping gap" (propping agent not entering) appears at the far end of the fracture → reduce the concentration, increase the gas flow rate, and improve the propping agent's migration ability; if propping agent accumulates in the near-wellbore area → reduce the injection rate or increase the pulse intensity to push it further away.

[0099] 2. Adjustment of the outlet temperature of the mixed fluid: If the DTS shows that the proppant expands prematurely at the crack opening (blockage), reduce the power of the temperature field control ring to delay expansion; if the proppant has entered too deep into the crack and has not yet expanded (unable to anchor), increase the power of the temperature field control ring to trigger it prematurely deep into the crack.

[0100] Objective: To ensure that the proppant "can enter, block where it should, and expand."

[0101] S5: Temporary blocking, turning, and segmented continuous operation: After completing the fracturing operation of the current design section, biodegradable low-temperature temporary plugging balls are injected into the annulus to seal the fracture opening of the current section and perform temporary plugging diversion.

[0102] The integrated downhole tool string is unanchored and moved to the next designed fracturing section. Steps S2-S4 are repeated for continuous operation. This invention can utilize the mobility of the integrated downhole tool string to achieve continuous operation of "high-temperature embrittlement-fatigue propagation-intelligent support" for multiple rounds throughout the entire well section in a single drilling trip.

[0103] Furthermore, the working method may also include: S6: Well shut-in maintenance and well start-up production: After all operations are completed, the well is shut in for several hours to allow the proppant in the fractures to fully undergo thermal expansion and solidification. Then, the well is opened for flowback: unexpanded proppant microspheres and reaction residues are flowed back with the gas. After separation at the wellhead, the proppant can be recovered and processed. This forms a complex fracture network with high conductivity, enabling efficient extraction of gas or coalbed methane.

[0104] The following is a specific embodiment of the present invention.

[0105] It was applied in a low-permeability coalbed methane horizontal well at a depth of 900 meters in a certain basin.

[0106] 1. Operation Preparation: The horizontal section is 1000 meters long and divided into 5 fracturing sections. An integrated downhole tool string is lowered, with a composite cable outer tube diameter of 73 mm.

[0107] 2. First section (200–220 meters): High-temperature embrittlement: After the integrated downhole tool string is positioned, a chemical reactant is injected to generate a 380°C high-temperature inert gas, which is then sprayed at a constant pressure of 28 MPa for 3 minutes. DTS shows that the temperature of the coal body within 2 meters around the wellbore rises to over 120°C.

[0108] Brittle fatigue and intelligent support: Pulse modulation was initiated (frequency 2 Hz, pressure fluctuation 22–32 MPa), while thermal expansion proppant (Tg=160℃) was injected at an 8% sand ratio. The temperature field control loop set the outlet temperature of the mixed fluid to 165℃. Operation was conducted for 10 minutes. DAS monitoring showed microseismic events distributed in a network pattern from near to far.

[0109] 3. Adaptive Control: Based on the DAS event cloud map, it was determined that the fracture propagation towards the south flank was weak. In subsequent pulses, the flow rate proportion of the nozzles towards the south was briefly increased, and the proppant concentration was fine-tuned.

[0110] 4. Continuous operation: Inject temporary plugging ball, and move the integrated downhole tool string to the next section. Repeat the operation, with a total construction time of 18 hours.

[0111] 5. Results: After well shut-in for 6 hours following hydraulic fracturing, and upon reopening and drainage, compared with a neighboring well that used conventional nitrogen fracturing with trailing ceramic proppant, this well achieved 3.2 times the daily gas production during the stable production period. Furthermore, after one year of production, the gas production decline rate of this well was only 40% of that of the neighboring well, demonstrating significantly superior long-term conductivity of the fractures. A large number of unexpanded proppant microspheres were collected from the flowback fluid, confirming the effectiveness of its selective expansion mechanism.

[0112] Other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the embodiments disclosed herein. This invention is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein. It should be understood that the invention is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of the invention is limited only by the appended claims.

Claims

1. A downhole in-situ high-temperature gas fracturing support integrated system, characterized in that, It includes a surface monitoring and supply unit, an integrated downhole tool string, and a composite cable connecting the surface monitoring and supply unit and the integrated downhole tool string; The ground monitoring and supply unit delivers liquid chemical thermal reactant and thermally expanding polymer proppant to the integrated downhole tool string through the composite cable; the composite cable is equipped with distributed fiber optic sensors for real-time monitoring of temperature field changes and acoustic events; The integrated downhole tool string includes: The high-temperature gas in-situ generation and modulation chamber is used to provide a site for the chemical reaction of the liquid chemothermal reactant, and to modulate the high-temperature inert gas generated after the chemical reaction into a high-temperature pulse gas; And a proppant composite injection module, used to mix the thermally expandable polymer proppant with the high-temperature pulsed gas to form a mixed fluid, and inject the mixed fluid into the target coal seam; Based on the temperature field changes and acoustic events, the ground monitoring and supply unit outputs control commands to the integrated downhole tool string to dynamically adjust the temperature of the high-temperature inert gas, the pulse parameters of the high-temperature pulsed gas, the concentration of the thermally expanding polymer proppant, and the injection temperature of the mixed fluid.

2. The integrated downhole in-situ high-temperature gas fracturing support system according to claim 1, characterized in that, The liquid chemical thermal reactant is of two types; the high-temperature gas in-situ generation and modulation chamber includes: a high-efficiency cyclone mixer, an adiabatic reaction chamber, and a high-frequency pulse modulation valve; the high-efficiency cyclone mixer is used to mix the two liquid chemical thermal reactants evenly, and after being mixed evenly, a chemical reaction occurs in the adiabatic reaction chamber to generate a high-temperature inert gas; the high-frequency pulse modulation valve is used to modulate the high-temperature inert gas into a high-temperature pulse gas with a specific frequency and amplitude, forming a pressure pulse wave.

3. The integrated downhole in-situ high-temperature gas fracturing support system according to claim 2, characterized in that, The thermally expandable polymeric support is a core-shell structured microsphere, wherein the outer shell of the core-shell structured microsphere is a thermosetting resin coating, and the core is a thermoplastic polymer material.

4. The integrated downhole in-situ high-temperature gas fracturing support system according to claim 3, characterized in that, The proppant composite injection module includes: A Venturi gas-solid mixer is used to draw in thermally expandable polymer proppant at a set concentration using the negative pressure generated by a pressure pulse wave, and to uniformly mix the pressure pulse wave with the thermally expandable polymer proppant. And a temperature field control ring, surrounding the outlet of the Venturi gas-solid mixer, is used to adjust the outlet temperature of the uniformly mixed pressure pulse wave and the thermally expanding polymer support to the glass transition temperature of the thermosetting resin coating according to the control command.

5. The integrated downhole in-situ high-temperature gas fracturing support system according to claim 2, characterized in that, The frequency range of the pressure pulse wave is 0.5Hz–10Hz, and the temperature range is 200℃–500℃.

6. The integrated downhole in-situ high-temperature gas fracturing support system according to claim 4, characterized in that, The composite cable includes a central tube and an outer tube, with an annular channel between the central tube and the outer tube. The central tube is used to transport liquid chemothermal reactants, and the annular channel is used to transport thermally expanding polymer proppant to the integrated downhole tool string via inert gas.

7. The integrated downhole in-situ high-temperature gas fracturing support system according to claim 6, characterized in that, The distributed optical fiber sensor includes a distributed optical fiber temperature sensing unit and a distributed optical fiber acoustic sensing unit, with the distributed optical fiber disposed on the pipe wall of the annular channel.

8. The integrated downhole in-situ high-temperature gas fracturing support system according to claim 1, characterized in that, The integrated downhole tool string also includes an integrated downhole control module and a multi-functional nozzle and monitoring module; The downhole integrated control module is used to receive the control commands; The multifunctional nozzle and monitoring module includes: A switchable nozzle is used to convert the mixed fluid into a high-energy jet of a specific shape, which directly acts on the coal and rock strata to achieve differentiated fracturing objectives. Downhole high-definition cameras are used to provide direct optical images of the wellbore and near-wellbore fracture areas for real-time visual diagnostics. And miniature acoustic wave transmitters and receivers, used to actively transmit acoustic signals into the formation and receive their reflected, refracted and scattered signals, in order to detect invisible information about the formation and fractures around the wellbore.

9. The integrated downhole in-situ high-temperature gas fracturing support system according to claim 1, characterized in that, The ground monitoring and supply unit has a built-in thermo-mechanical coupled fracture propagation model and proppant migration optimization algorithm. Based on the temperature field changes and acoustic events, it outputs control commands to the integrated downhole tool string.

10. A method for continuous on-site fracturing propping operations, characterized in that, The method employs the integrated downhole in-situ high-temperature gas fracturing support system as described in any one of claims 1-9, the method comprising: The integrated downhole tool string is lowered to the designed fracturing section of the target coal seam and anchored. The high-temperature gas in-situ generation modulation chamber generates high-temperature inert gas to thermally shock embrittle the coal body. A pressure pulse wave is generated by a high-frequency pulse modulation valve, and a thermally expanding polymer proppant is injected into the proppant composite injection module to perform a synergistic operation of brittle fatigue crack propagation and support. Based on temperature field changes and acoustic events, control commands are output to the integrated downhole tool string to dynamically adjust the temperature of the high-temperature inert gas, the pulse parameters of the high-temperature pulsed gas, the concentration of the thermally expanding polymer proppant, and the injection temperature of the mixed fluid. After completing the current fracturing section, a temporary plugging and redirection operation is performed, and the integrated downhole tool string is moved to the next designed fracturing section for continuous operation.

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