Construction method of in-situ grouting water-blocking system of coal underground gasification isolation wall

Abstract

The application discloses a construction method of an in-situ grouting water-blocking system of a coal underground gasification isolation wall, and relates to the technical field of coal underground gasification isolation. The method comprises six steps of monitoring deployment, biological barrier construction, initial physical grouting isolation before gasification, chemical grouting barrier construction before gasification, dynamic physical grouting isolation during gasification, and final physical grouting isolation after gasification, integrates physical, chemical and biological triple isolation means, and forms a three-dimensional three-level three-layer grouting isolation system. Meanwhile, in combination with real-time monitoring and cloud intelligent regulation and control, efficient isolation and plugging of the whole process of coal underground gasification is realized, migration and pollution of pollutants to underground water are effectively prevented, geological stability is ensured, and environmental safety guarantee is provided for industrialization of coal underground gasification.

Description

Technical Field

[0001] This invention relates to the technical field of underground coal gasification isolation, and more particularly to a method for constructing an in-situ grouting water-blocking system for underground coal gasification isolation walls. Background Technology

[0002] Underground coal gasification (UCG), a revolutionary technology for converting deep coal seams into combustible gases in situ, utilizes modern UCG processes based on Controlled Retreat Injection Point (CRIP) technology, combined with directional drilling and remote surface control systems, to achieve efficient conversion of deep coal seams. However, this technology faces severe environmental bottlenecks in its industrialization process. Toxic organic compounds such as phenol and polycyclic aromatic hydrocarbons, as well as gasification byproducts such as tar, heavy metals, H2S, and NH3, generated during the gasification process are prone to migration and diffusion into aquifers, which has become the primary problem restricting its development.

[0003] The high temperature and pressure environment of the gasification zone makes the pollutant diffusion mechanism extremely complex. On the one hand, the expansion of the gasification cavity can trigger overlying rock fissures, forming the main channels for pollutant migration; on the other hand, studies have shown that without effective containment measures, the aforementioned pollutants can diffuse to the surrounding aquifers within 30 days, posing a serious threat to groundwater resources.

[0004] Existing remediation technologies for this problem mainly rely on single-level dispersed barriers, but each has its limitations and is difficult to adapt to complex hydrogeological conditions. Physical grouting technology, using traditional cement-based materials, is prone to shrinkage and cracking under thermal stress, leading to a significant decrease in water-blocking efficiency and an inability to effectively intercept dissolved pollutants. Chemical barrier isolation technologies, using organic compounds such as activated carbon, can adsorb organic matter, but the required thickness and cost increase exponentially, the removal rate of ionic heavy metals is low, and regeneration is difficult after adsorption saturation. Furthermore, barriers exceeding 2 meters are required for effectiveness, resulting in poor economic efficiency and practicality. Bioremediation technologies often employ the injection of phenol-degrading bacteria, but are limited by factors such as underground environmental temperature and pH, and single strains have low colonization efficiency in heterogeneous environments. In addition, the aforementioned existing technologies do not adequately consider the need to replace isolation technologies and materials as gasification progresses, resulting in significant time-limited limitations in isolation effectiveness.

[0005] In summary, existing technologies have shortcomings in terms of physical barrier, chemical adsorption, biological synergy, and dynamic adaptation. There is an urgent need to develop a synergistic system that can integrate physical isolation, chemical isolation, and biological-assisted isolation to achieve real-time three-dimensional all-round isolation and sealing of underground coal gasification processes, and prevent the leakage and spread of toxic substances. Summary of the Invention

[0006] The purpose of this invention is to address the problem in existing underground coal gasification technologies where pollutants easily migrate and diffuse through fissures caused by gasification, polluting groundwater, and the shortcomings of existing isolation technologies such as physical barrier failure, limitations of chemical adsorption, insufficient stability of bioremediation, and difficulty in dynamically adapting to the entire gasification process. By constructing an in-situ grouting and water-blocking system for a gasification isolation wall based on three-stage grouting technology, combining physical, chemical, and biological triple isolation layers and a three-dimensional sealing strategy, this invention achieves multi-dimensional and effective isolation and sealing of the underground gasification area, preventing harmful gases and liquids from leaking into the groundwater system, ensuring underground environmental safety, and providing environmental safety guarantees for the industrialization of underground coal gasification.

[0007] To achieve the above objectives, the present invention provides a method for constructing an in-situ grouting water-blocking system for underground coal gasification isolation walls, comprising the following steps:

[0008] S1: Monitoring Deployment: Based on the underground gasification site selection and engineering design, implement comprehensive monitoring deployment around the underground gasification area:

[0009] S2: Construction of biological barrier: Before the start of the underground coal gasification project, the microbial community sorted by single-cell Raman is mixed with the carrier and injected into the aquifer. Then, nutrient pulses are injected to stimulate the microorganisms to form a biofilm. During the gasification process, the activity of the microbial community is maintained by the nutrient solution.

[0010] S3: Initial physical grouting isolation before gasification: Before gasification, prepare nano-silica sol-based composite grouting material, arrange boreholes along the direction of the fracture, and use directional negative pressure grouting to seal the original fractures at the interface between the coal pillar and the water-proof layer on the side of the gasification chamber.

[0011] S4: Construction of a pre-gasification chemical grouting barrier: For the clay impermeable layer adjacent to the aquifer, grouting holes are arranged in a quincunx grid pattern, and K is injected. + The base composite grout enhances the stability of clay through alternating high and low pressure grouting methods;

[0012] S5: Dynamic physical grouting isolation during gasification: A temperature-pH sensitive self-healing polyurethane composite grout modified with nanoparticles is used to target the detected crack initiation points for grouting. The temperature-responsive self-healing properties of the DA bond and the pH-responsive swelling properties of the PAA segment of the grout are utilized to achieve adaptive sealing.

[0013] S6: Final physical grouting isolation after gasification: After gasification is completed and the temperature of the gasification chamber drops below 80℃, natural mineral slurry material is used to fill the main fracture through three-level pressure gradient grouting. After curing, CO2 is injected to achieve mineralization and preservation.

[0014] Furthermore, the preparation method of the silica sol-based composite grout used in step S3 is as follows:

[0015] Step-a1: Take 5% of the total water volume of deionized water and KH-550, add acetic acid to adjust the pH to 4-5, stir for 15 minutes to hydrolyze and activate, and prepare a pre-hydrolyzed KH-550 solution;

[0016] Step-a2: Slowly add nano-SiO2 powder and water to a high-speed shear press at 3000 rpm, with a water-to-nano-SiO2 powder mass ratio of 8-12:1, and continue shearing for 20 minutes; then add pre-hydrolyzed KH-550 solution and continue shearing for 10 minutes, and add ammonia water with a mass fraction of 25-28% dropwise to adjust the pH to 9.5-10.5, and shear for another 15 minutes to obtain a stable nano-SiO2 sol;

[0017] Step-a3: Transfer the nano-SiO2 sol to low-speed stirring, set the stirring speed to 300-500 rpm, and stir for 8-10 minutes; add 0.1-0.25 parts of medium-viscosity CMC dissolved in water in advance, mix well, and let stand to defoam before use.

[0018] Step-a4: Select 100 parts fly ash cement and 0.3-0.8 parts lithium carbonate accelerator, dry mix for 3 minutes until uniform; then sprinkle in 0.8-1.5 parts polypropylene fiber in three batches, stirring at low speed for 1 minute after each addition to ensure that the fiber monofilaments are fully separated and there is no agglomeration, and finally make fiber dry material.

[0019] Step-a5: Mix the nano-SiO2 sol obtained in Step-a3 with 0.5-1.2 parts of polycarboxylate superplasticizer to obtain a sol-superplasticizer mixture;

[0020] Step-a6: Pour the dry fiber material prepared in Step-a4 into the mixing pot, start low-speed mixing, then pour in the sol-water reducing agent mixture prepared in Step-a5 and stir for 2 minutes; stir at high speed for 3 minutes until the slurry is uniform and glossy, thus producing nano-silica sol-based composite grouting material.

[0021] Furthermore, the preparation method of the temperature-pH sensitive self-healing polyurethane composite slurry used in step S5 is as follows:

[0022] Step-b1: Disperse nano-SiO2 in anhydrous ethanol, add 3-aminopropyltriethoxysilane and reflux for 6 h to obtain aminated SiO2;

[0023] Step-b2: Aminated SiO2 is reacted with furan-2-carboxaldehyde to prepare F-SiO2;

[0024] Step-b3: Under nitrogen protection, polyether polyol and MDI are added to the reactor and reacted at 80°C for 2 hours to obtain terminal-NCO polyurethane prepolymer; after cooling to 60°C, FGE is added and reacted for 1 hour to obtain F-PU;

[0025] Step-b4: Dissolve PAA in the mixed solvent and slowly add it to F-PU, stirring at 40°C for 30 minutes;

[0026] Step-b5: Add F-SiO2 and BMI to the mixed solution prepared in Step-b4, and react at 60°C for 2 hours to trigger the Diels-Alder reaction; then add TEA and DBTDL, and catalyze chain extension at 50°C for 1 hour.

[0027] Step-b6: Cool the mixed solution obtained in Step-b5 to 25°C and adjust the solid content to 30-40% to obtain the target composite slurry;

[0028] Step-b7: Perform vacuum degassing on the composite slurry obtained in Step-b6 to remove solvent and air bubbles, so that the composite slurry reaches the required viscosity.

[0029] Step-b8: Store the composite slurry treated in Step-b7 in a sealed container to avoid moisture and air contamination and prevent the composite material from reacting.

[0030] Furthermore, the method for preparing the natural mineral slurry material used in step S6 is as follows:

[0031] Step-c1: Place fly ash in an industrial microwave device and microwave irradiate for 3-5 minutes to induce microcracks on the glass surface; then add the above materials to a mixer in the following proportions: fly ash 35-40%, steel slag powder 30-35%, slag 25-30%, silica fume 5-8%, 0.5% nano Ca(OH)2 seed crystals, and UEA expansion agent 3-5%, and mix at 200 r / min for 4 minutes.

[0032] Step-c2: Mix formic acid and acetic acid at a mass ratio of 3:1 and dilute to a concentration of 12%. Spray the mixture onto the dry powder prepared in Step-c1. Continue stirring for 5 minutes and let stand for 120-180 minutes to deeply activate the activity.

[0033] Step-c3: Add 70% of the total water volume of the activated dry powder obtained in Step-c2 to clean water at a temperature of 25±2℃ and an accelerator. The accelerator accounts for 4-6% of the total weight of the cementitious material and is a sulfoaluminate type accelerator made of calcium aluminate and gypsum in a mass ratio of 3:1. Stir at 280-300 r / min for 4 minutes. Then add 0.1-0.15% of polycarboxylate superplasticizer and stir at 450-550 r / min for 5 minutes to form a homogeneous slurry.

[0034] Furthermore, the K used in step S4 + The preparation method of the base composite slurry is as follows:

[0035] Step-d1: Add KCl and KNO3 in a mass ratio of 6:4 to 60% of the total water volume in 40°C warm water and stir at 300 rpm for 10 minutes. The K in the slurry... + The total amount is 15–20 wt%, which dissolves in the carrier water to form a saturated solution, ensuring that the driving force of ion diffusion is maximized;

[0036] Step-d2: Add 1–2 wt% Na₂CO₃, 2–4 wt% Na₂SiO₃, and 0.05–0.1 wt% HEDP sequentially, maintaining the pH at 9.5 ± 0.2, stirring at 500 rpm for 5 minutes until transparent, promoting K... + It is fixed between clay mineral layers and generates CaCO3 micro-precipitates to assist in sealing;

[0037] Step-d3: Slowly add 3–5 wt% bentonite, 0.5–1.2 wt% guar gum, and 0.3–0.8 wt% polyacrylamide at 1500 rpm for 15 min. The viscosity should be ≥300 cP. High-speed shear dispersion is used to enhance viscosity stability and prevent the slurry from preferentially flowing out along large pores.

[0038] Step-d4: Finally, add 0.1–0.3 wt% PCE to reduce the surface tension of the slurry, improve its wettability in low-permeability clay, and add water to the target volume. Rotate at 200 rpm for 30 minutes until the viscosity stabilizes at 250 ± 50 cP. Allow to mature at a low speed to produce K. + Base composite slurry.

[0039] Furthermore, the specific method for step S1 is as follows:

[0040] Based on the underground gasification site selection and engineering design, a comprehensive monitoring deployment was implemented around the underground gasification area: microseismic monitoring instruments were pre-embedded for real-time geological surveys and monitoring of fracture propagation; distributed fiber optic sensors and resistivity tomography equipment were deployed to generate real-time slurry diffusion cloud maps based on the dynamic changes in the diffusion temperature mechanical field; downhole explosion-proof sensors were simultaneously installed, and a bundled tube monitoring system was used to detect the components and concentrations of various pollutant gases in real time, while vacuum negative pressure sampling was implemented through a heated pipeline; the above-ground portion used laser photoacoustic spectroscopy rapid detection technology and microfluidic chip integrated electrochemical sensors to invert gas concentration changes by combining downhole pressure and temperature data; high-pressure anti-fouling pressure sensors and multi-parameter ion-selective electrode arrays were installed near the underground aquifer to monitor groundwater pressure and ion migration in real time.

[0041] Furthermore, the specific method for step 2 is as follows:

[0042] Step 2-1: Based on the characteristics of underground gasification pollution and the hypoxic, low-temperature, and high-salt environment of the aquifer, single-cell Raman spectroscopy was used to collect samples from groundwater and polluted sludge in the gasification zone. The scRACS-SIP technology was used to identify strains with high in-situ metabolic activity by stable isotope probe labeling, and microorganisms were selected in a targeted manner. The scRACS-sorted strains were then amplified in an anaerobic tank to simulate the underground environment. Microorganisms that could survive for a long time were injected into the underground aquifer and activated upon encountering pollutants.

[0043] Step 2-2: After mixing the bacterial agent with the carrier, inject the mixture into the aqueous layer and inject nutrient pulses to stimulate microorganisms to secrete EPS and autonomously form a biofilm. Spore-forming bacteria can directly adsorb onto the carrier and are activated upon encountering pollutants; while non-spore-forming bacteria can be loaded in stages, concentrating the bacterial solution to 10. 9 CFU / mL was mixed with PEI-modified support and adsorbed for 2 h. The mixture was dried under anaerobic conditions to a water content of 20% and then injected into the aquifer for nutrient activation.

[0044] Steps 2-3: Using a vaporizing agent delivery pipeline, the bacterial agent-carrier is pumped into the target aquifer in a stepped manner at a solid-liquid ratio of 1:5; and pH and Cl are monitored in real time. - and Ca 2+ Timely replenishment of O2, nitrates, or carbon sources is necessary to maintain activity.

[0045] Steps 2-4: Deploy downhole sensors to monitor permeability coefficient K and redox potential ORP; combine B-GFP fluorescence tracing technology to track active foci migration and dynamically adjust injection parameters.

[0046] Furthermore, the specific method for step S3 is as follows:

[0047] Nano-silica sol-based composite grouting material was prepared and activated. Based on the geological survey results, boreholes were arranged along the direction of fracture development or perpendicular to the main fracture direction. The grouting material was injected under directional negative pressure into the primary fracture at the interface between the coal pillar and the water-resistant layer of the coal pillar on the side of the gasification chamber for grouting isolation and sealing. The depth of the sealing area was greater than 1.2 times the design height of the gasification chamber, and grid-like grouting holes were arranged in the intersection area of ​​faults, etc. The borehole delivery pipeline used a double plug system or sleeve valve pipe technology to isolate the borehole in sections, and grouting was carried out in sections from the bottom to the top of the borehole, giving priority to the treatment of deep areas.

[0048] Furthermore, the specific method for step S4 is as follows:

[0049] Step 4-1: Grouting hole layout: Grouting holes are laid out in a quincunx grid, with the hole spacing set to 1.5–2.5 times the design diffusion radius; casing follow-up drilling rig is used for construction, and PVC perforated pipes with filter screens are lowered in, with the filter screen aperture ≤100μm, to prevent clay particles from clogging the pipeline;

[0050] Step 4-2: Grouting parameter control: The temperature and pressure field changes of grout diffusion are monitored in real time by micro-vibration sensors and distributed optical fiber sensors (DTS); the grouting method is selected according to the permeability coefficient of the clay layer, and high and low pressure injection is carried out alternately at a frequency of 5-10Hz to break the capillary resistance of the clay.

[0051] The grouting process involves phased pressure control: initially maintaining 0.3–0.5 MPa for permeation grouting, then maintaining 0.8–1.5 MPa for compaction grouting, and finally limiting the pressure to no more than 2.0 MPa to prevent hydraulic fracturing. The hydraulic plunger pump operates at a pressure range of 0–20 MPa, with the flow rate precisely controlled between 0.5–50 L / min, where the permeability coefficient k < 10. -7 A low-permeability layer with a flow rate of cm / s, controlled at 2–5 L / min, and a permeability coefficient k > 10. -8 A medium-permeability layer with a flow rate of cm / s, with a flow rate controlled at 10–20 L / min;

[0052] Step 4-3: Special working condition adjustments: For low-permeability or easily clogged working conditions, a 0.5% surfactant solution can be injected before grouting to reduce interfacial tension; to inhibit pipe blockage caused by divalent ion scaling, 0.1% sodium citrate is added to the grout, and a dual-channel flushing system is used for periodic pipeline maintenance to ensure a stable and efficient grouting process.

[0053] Furthermore, the specific method for step S6 is as follows:

[0054] Step 6-1: In the first stage, after the temperature of the gasification chamber drops below 80℃, low-pressure permeation grouting of 0.3-0.8MPa is used to fill micro-cracks with a width of <0.1mm by utilizing the high fluidity of the grout before initial setting, thus encapsulating and adsorbing pollutants.

[0055] Step 6-2: High-pressure compaction grouting at 1.5-2.2MPa is used to remove interstitial water and compact the structure, thereby enhancing the sealing density, taking into account the thixotropic characteristics of the grout during the initial setting period.

[0056] Step 6-3: In the third stage, medium-pressure sealing grouting of 0.5-1.0MPa is used to inject lightweight foamed grout to form a low-permeability sealing layer on top; for cracks with a width >5mm, 1:1 water glass-MgO quick-setting grout is pre-injected to form a temporary skeleton to prevent the loss of aggregate-free grout.

[0057] Step 6-4: After grouting is completed, the cavity is maintained at 60-80℃ by introducing low-pressure steam for 7 days to promote early carbonization reaction. Then, temperature-triggered CO2 injection is adopted. First, 10℃ low-temperature CO2 is injected. When the temperature of the grout rises to 60℃ due to the heat release of hydration, it is switched to supercritical CO2 to enhance its diffusion and penetration in the grout by using the temperature difference.

[0058] The beneficial effects of this invention are:

[0059] 1. Compared to existing technologies that rely heavily on single methods such as physical grouting, chemical adsorption, or bioremediation, which are insufficient to address the complex multi-field coupling environment of underground gasification, the in-situ grouting and water-blocking system for underground coal gasification isolation walls constructed in this invention innovatively integrates physical, chemical, and biological triple isolation technologies to form a three-dimensional sealing barrier, achieving comprehensive and efficient sealing: physical isolation adapts to the entire gasification process in stages, pre-sealing existing fissures before gasification, dynamically intercepting new fissures during gasification, and permanently sealing after gasification. It utilizes environmentally responsive materials such as nano-silica sol-based grouting materials and temperature-pH sensitive self-healing grouting materials to achieve precise filling of fissures of different widths, with a fissure filling rate > 90%; chemical isolation utilizes K... + The base grout immobilizes clay minerals, reducing the expansion index by 60-80%, inhibiting the development of cracks caused by wet-dry cycles, and enhancing the stability of the impermeable layer. Biological isolation utilizes functional microbial communities to form a biofilm, degrading and adsorbing minute pollutants. Microbial activity is maintained for >180 days, with a permeability reduction of <20%, complementing physical and chemical isolation. These three elements synergistically construct a "three-dimensional, three-level, three-layer" grouting system, achieving comprehensive isolation from shallow to deep layers and from macroscopic cracks to microscopic pores, significantly improving the protective efficiency compared to existing single-level dispersed barriers.

[0060] 2. Compared to existing physical grouting materials such as cement-based materials, which are prone to cracking under thermal stress and cannot adapt to dynamic changes in underground pH and temperature, this solution innovatively develops environmentally responsive smart materials and matches them with dynamic processes. The temperature-pH sensitive self-healing polyurethane grout achieves temperature-responsive self-healing through DA bonds, and can penetrate to micro-cracks as small as 0.05mm to repair stress micro-cracks. At the same time, through the pH response of PAA segments, it adapts to changes in the chemical environment of groundwater, solving the problems of thermal cracking failure and adsorption saturation of traditional materials. The nano-silica sol-based grouting material is dynamically proportioned with lithium carbonate coagulant to adapt to the penetration requirements of cracks of different widths, taking into account both fluidity and strength. The gasified natural mineral slurry is injected using a three-stage pressure gradient grouting method, combined with CO2 temperature-triggered sealing, which uses temperature difference to enhance mineralization efficiency, with a sealing rate of >70% within 50 years, breaking through the limitation of incomplete filling in traditional grouting.

[0061] 3. This solution innovatively constructs a closed-loop system integrating multi-dimensional monitoring, cloud-based intelligent decision-making, and rapid terminal response: The monitoring module integrates microseismic monitoring, distributed optical fiber, bundled tube gas detection, and ion electrode array to achieve multi-parameter collaborative sensing of geological stability, gas concentration, and water quality migration; The cloud analysis platform processes the spatiotemporal matrix using CNN algorithms, outputs the leakage risk index R and diffusion coefficient D, dynamically generates grouting parameters, and achieves a terminal response delay of ≤1 minute. In emergency mode, the injection volume can be increased to 200% of the baseline value, solving the problem of lag in traditional manual control; In biological isolation, B-GFP fluorescence tracing and ORP monitoring are combined to adjust the nutrient supply of the microbial community in real time, ensuring that the activity is maintained for >180 days and avoiding microbial inactivation due to environmental fluctuations.

[0062] 4. Compared to existing bioremediation technologies, which suffer from short-lived effects due to difficulties in microbial colonization and poor carrier compatibility, this solution uses coal-based activated coke and nano-Fe3O4 as carriers. PEI modification increases the microbial loading rate to over 90%, enhancing electron transfer efficiency and methanogenesis efficiency. Nutrient pulse injection stimulates microorganisms to secrete EPS, increasing the biofilm's shear resistance by 3 times. This, combined with physical isolation, forms a dynamic interception and degradation synergy, resulting in a permeability coefficient reduction of less than 20%, solving the problems of easy loss and poor sustainability in traditional bioremediation. Attached Figure Description

[0063] Figure 1 This is a schematic diagram of the in-situ grouting water-blocking system for the underground coal gasification isolation wall of the present invention. Detailed Implementation

[0064] The present invention will now be described in further detail with reference to the accompanying drawings. These drawings are simplified schematic diagrams, illustrating only the basic structure of the invention, and therefore only show the components relevant to the invention.

[0065] A method for constructing an in-situ grouting water-blocking system for underground coal gasification isolation walls is disclosed. This in-situ grouting water-blocking system for gasification isolation walls adopts a three-dimensional, three-level, three-layer grouting isolation system, combined with a three-level self-regulating grouting process, and achieves effective protection by using physical, chemical, and biological triple isolation methods to seal the underground coal gasification area in three dimensions.

[0066] The construction method of the in-situ grouting water-blocking system for the gasification isolation wall includes the following steps:

[0067] S1: Monitoring Deployment: Based on the underground gasification site selection and engineering design, implement comprehensive monitoring deployment around the underground gasification area.

[0068] Pre-embedded microseismic monitoring instruments are used for real-time geological condition surveys and fracture propagation monitoring; distributed fiber optic sensors and resistivity tomography (ERT) equipment are deployed to generate real-time slurry diffusion cloud maps based on the dynamic changes in the diffusion temperature mechanical field; downhole explosion-proof sensors are simultaneously installed, and a bundled tube monitoring system is used to detect the components and concentrations of various contaminant gases in real time, while vacuum negative pressure sampling is implemented through a heated pipeline; the aboveground part uses laser photoacoustic spectroscopy (PAS) rapid detection technology and microfluidic chip integrated electrochemical sensors to invert gas concentration changes by combining downhole pressure and temperature data; high-pressure anti-fouling pressure sensors and multi-parameter ion-selective electrode arrays are installed near the aquifer to monitor groundwater pressure and ion migration in real time.

[0069] S2: Biobarrier Construction: Six months before the commencement of the underground coal gasification project, a microbial community sorted by single-cell Raman spectroscopy is mixed with a carrier and injected into the aquifer. Nutrient pulses are then injected to stimulate the microorganisms to form a biofilm. During the gasification process, pollutants can still migrate through tiny gaps due to thermal and tectonic stresses. Therefore, nutrient solutions such as sodium acetate and phosphate are used to stimulate dormant bacteria, increasing the degradation rate and enabling the adsorption of minute pollutants as well as the remediation of the groundwater environment.

[0070] The specific method is as follows:

[0071] Step 2-1: Based on the characteristics of underground gasification pollution and the anoxic, low-temperature, and high-salt environment of the aquifer, single-cell Raman sorting (scRACS) was used to collect samples from groundwater and contaminated sludge in the gasification zone. Stable isotope probes using scRACS-SIP technology were used to identify strains with high in-situ metabolic activity, allowing for targeted selection of microorganisms. The scRACS-sorted strains were then amplified in an anaerobic tank simulating the underground environment. Microorganisms capable of long-term survival, such as Bacillus megaterium (spore dormancy), Desulfovibrio (anaerobic tolerance), and Anammoxbacteria (biofilm protection), were injected into the underground aquifer and activated upon encountering pollutants.

[0072] Step 2-2: After mixing the bacterial agent with the carrier, inject the mixture into the aquifer and inject nutrient pulses (sodium acetate + trace amounts of Ni and Co) to stimulate microorganisms to secrete EPS and autonomously form a biofilm; the shear resistance of the biofilm increases threefold after maturation. Spore-forming bacteria can be directly adsorbed onto the carrier and activated by pollutants; while non-spore-forming bacteria can be loaded in stages. The bacterial solution is concentrated to 10⁹ CFU / mL, mixed with PEI-modified carrier, and adsorbed for 2 hours. Under anaerobic conditions in a N₂ atmosphere, it is dried to a moisture content of 20% and then injected into the aquifer for nutrient activation.

[0073] Steps 2-3: Using a gasifying agent delivery pipeline, pump the bacterial agent-carrier into the target aquifer in a stepwise manner at a solid-liquid ratio of 1:5; and monitor the pH (7.0-8.5) and Cl- concentration in real time. - (<905mg / L), Ca 2+ (<400mg / L), timely supplementation of O2, nitrate (for aerobic bacteria) or carbon source (for anaerobic bacteria) is necessary to maintain activity.

[0074] Steps 2-4: Deploy downhole sensors to monitor permeability coefficient K and redox potential ORP; combine B-GFP fluorescence tracing technology to track active foci migration and dynamically adjust injection parameters.

[0075] Microbial proliferation may reduce aquifer permeability; therefore, the concentration of microbial agents should be controlled to <10. 8 cells / mL, with regular backwashing. After optimization, the system can achieve: a permeability reduction of <20%, microbial activity maintained for >180 days, and activated carbon recycling rate ≥70%.

[0076] S3: Before gasification, pretreatment is carried out on the original fissures and potential unstable areas in the geological environment of the gasification site. The parameter strategy of "low starting pressure, quantitative method, and low pressure stabilization and permeation" is adopted. Combined with the high permeability and coagulation characteristics of the slurry, the fissures are effectively filled and the slurry is prevented from being lost.

[0077] The specific method is as follows:

[0078] Nano-silica sol-based composite grouting material was prepared and activated. Based on the geological survey results, boreholes were directionally arranged along the direction of fracture development, such as parallel to the coal pillar and the interface of the aquitard or perpendicular to the direction of the main fracture. The grouting material was injected into the original fracture at the interface between the coal pillar and the aquitard on the side of the gasification chamber using a directional negative pressure grouting method to form an isolation and sealing structure.

[0079] The depth of the sealing area should be greater than 1.2 times the design height of the gasification chamber, and grid-like grouting holes should be arranged in the intersection area of ​​faults and other structures, with a hole spacing of ≤2m; the drilling spacing should be determined comprehensively based on the fracture connectivity, width estimation and grout diffusion radius, with a preliminary suggestion of 1.5-3m.

[0080] A dedicated batching box is configured for preparing nano-silica sol-based composite grouting material, and the proportions of each component are optimized in real time according to geological conditions. The borehole delivery pipeline employs a double-plug system (such as a double-plug grouting pipe / Packer System) or tube-à-manchette technology for segmented isolation. Tube-à-manchette technology, which allows for pre-embedded steel pipes with rubber-sleeved valves, is preferred. This technology enables repeated grouting of any borehole segment and adapts to the heterogeneous characteristics of fractures. The grouting pipeline should be as short and straight as possible to reduce grout residence time, and valves should be avoided to prevent fiber adhesion and blockage. A precision-grade screw pump with stepless speed regulation and precise pressure control is selected to ensure stable delivery at low flow rates. A segmented grouting method from the bottom to the top of the borehole is adopted, prioritizing the treatment of deep areas.

[0081] Different grouting parameters are adopted for different types of fractures: For fractures between coal pillars with large width and good connectivity, a relatively large grouting volume and high pressure (the upper limit of pressure is strictly controlled within 2.0 MPa) can be used to form a continuous rock barrier; for fine, tortuous fractures at the interface between the coal pillar and the aquitard that may contain water, a grouting method combining low pressure (0.3-0.8 MPa), slow rate (3-8 L / min) and quantitative-pressure stabilization is adopted to utilize the ultrafine particle characteristics and surface activity of nano-SiO2 sol to penetrate and fill the micro fractures.

[0082] The proportion of lithium carbonate coagulant needs to be dynamically adjusted according to geological conditions. For wide fissures, the proportion should be increased appropriately (0.6-0.8 parts) to shorten the gelation time and prevent slurry loss. For micro-fissures, the proportion should be reduced appropriately (0.3-0.5 parts) to prolong the penetration time and ensure sufficient filling.

[0083] The grout should be used within 30 minutes of preparation. If the fluidity is insufficient, the remaining deionized water must be added very slowly and meticulously to ensure the total water-cement ratio is maintained between 0.28 and 0.33 (this parameter directly affects the grout strength, permeability, and water separation). A fluidity tester (such as a Marsh funnel or flow cone) must be available on-site for real-time monitoring. During grouting, the grouting pressure, flow rate, and cumulative grouting volume must be monitored in real-time through methods such as core drilling, water pressure testing, water injection testing, and geophysical exploration. If an abnormal pressure rise occurs, it indicates pipe blockage or fissure saturation; if a sudden drop occurs, it indicates formation fracturing or the formation of a new channel. The pump must be stopped immediately, and the sealing effect and the quality of the grouting mass must be checked. Pumping must be continuous during grouting. After stopping the pump, the pipeline must be cleaned immediately to ensure unobstructed flow. Underground grouting operations involve a high-pressure environment; operating procedures must be strictly followed, safety valves must be installed, and personnel must be kept away from high-pressure pipeline joint areas.

[0084] S4: Before gasification begins, K is used for the clay impermeable layer adjacent to the aquifer. + The base composite slurry is chemically reinforced by K +Through interlayer exchange and fixation with clay minerals such as illite and montmorillonite in the clay layer, the clay loses its ability to absorb water and swell, reducing the clay swelling index by 60-80%. This effectively inhibits the development of cracks caused by wet-dry cycles and enhances the barrier performance of the clay layer.

[0085] K + The preparation, mixing, and injection of the base composite grout require a systematic design that considers the project scale, geological conditions, and equipment capabilities. The specific implementation plan is as follows:

[0086] Step 4-1: Grouting Hole Layout: Grouting holes are arranged in a quincunx grid pattern, with the hole spacing set to 1.5–2.5 times the design diffusion radius; the design diffusion radius refers to K. + The expected radial distance of diffusion of the composite grout in the target clay layer needs to be determined in advance through testing based on the clay layer permeability coefficient, grout characteristics, and engineering requirements. A casing-following drilling rig (with a borehole diameter maintained at 50–100 mm) is used for construction, and a PVC perforated pipe with a filter screen (pore size ≤ 100 μm) is lowered into the pipe to prevent clay particles from clogging the pipeline.

[0087] Step 4-2: Grouting parameter control: The temperature and pressure field changes of grout diffusion are monitored in real time by micro-vibration sensors and distributed optical fiber sensors (DTS). The grouting method is selected according to the permeability coefficient of the clay layer. Alternating high and low pressure injection at a frequency of 5–10 Hz is used to break the capillary resistance of the clay.

[0088] The grouting process involves phased pressure control: initially maintaining 0.3–0.5 MPa for permeation grouting, then maintaining 0.8–1.5 MPa for compaction grouting, and finally limiting the pressure to no more than 2.0 MPa to prevent hydraulic fracturing. The hydraulic plunger pump operates at a pressure range of 0–20 MPa, with a flow rate precisely controlled between 0.5–50 L / min, where the permeability coefficient k < 10. -7 A low-permeability layer with a flow rate of cm / s, controlled at 2–5 L / min, and a permeability coefficient k > 10. -8 A medium-permeability layer with a flow rate of cm / s, with a flow rate controlled at 10–20 L / min.

[0089] Step 4-3: Special working condition adjustment: For low permeability or easily clogged working conditions, 0.5% surfactant solution can be injected before grouting to reduce interfacial tension; to inhibit pipe blockage caused by divalent ion scaling, 0.1% sodium citrate is added to the grout, and a dual-channel flushing system (clean water + dilute hydrochloric acid on standby) is used for periodic pipeline maintenance to ensure a stable and efficient grouting process.

[0090] S5: During the gasification process, a temperature-pH-sensitive self-healing polyurethane composite grout modified with nanoparticles is used for dynamic sealing. Based on real-time monitoring of geological conditions and fracture initiation points, the grout is preferentially injected into fracture areas where the expected temperature rises above 50-60℃ and there is a risk of gas-water seepage, to fully utilize the material's temperature response mechanism; simultaneously, it covers areas with potential pH changes in groundwater, leveraging the material's pH-sensitive characteristics to enhance the sealing effect. This process adopts a "low-temperature, low-pressure targeted pre-grouting + environmentally triggered adaptive sealing" technical approach: utilizing the grout's characteristic of rapid recombination and gelation of DA bonds at low temperatures (≤40℃), a stable primary sealing network is constructed in the early stages of grouting to prevent excessive grout loss; subsequently, relying on the natural temperature rise generated by coal seam gasification and changes in groundwater pH, the grout's deep penetration, swelling, and self-healing functions are triggered, achieving adaptive and enhanced sealing.

[0091] The specific steps are as follows:

[0092] Step 5-1: Precise Target Location: Using borehole television, microseismic monitoring, and hydrological testing techniques, accurately locate the main seepage channels, with fracture width ≥ 0.1 mm and permeability of the pore development zone ≥ 10. -8 cm / s. Drilling parameters are designed according to the target location: the drilling angle and the fracture direction are controlled between 30° and 60°, and the depth exceeds the target fracture zone by 0.5-1m to ensure that the borehole directly communicates with the target fracture network.

[0093] After drilling to the target layer, a conventional grouting pipe is installed. The pipe is made of seamless steel and has a diameter of 50-80mm. There is no need to integrate a temperature control-pH regulation module to reduce costs. A directional perforated pipe with an opening rate of 20%-30% or a recyclable packer with a pressure resistance of ≥5MPa can be installed at the end of the grouting pipe to improve the efficiency of grout entering the target fracture and reduce the amount of ineffective injection.

[0094] Step 5-2: Low-temperature pre-grouting: In the grouting station or storage tank, the grout is pre-cooled to 35-40℃ to ensure that the DA bonds are in a stable reorganized state. The cooled grout is injected into the target fracture at low pressure (0.2-0.5MPa) and slow flow rate (2-8L / min). The grouting volume is estimated based on the fracture volume, with a filling coefficient of 1.2-1.5, forming a sealing barrier with initial strength (≥0.5MPa / 24h), providing a basic framework for subsequent environmental response.

[0095] The temperature response mechanism is as follows: as the gasification process proceeds, the temperature of the surrounding rock layer naturally rises to 50-60°C or even higher, the DA reversible bond breaks, the viscosity of the slurry decreases significantly, the fluidity is enhanced, and the slurry can penetrate to micro-cracks ≤0.05mm; when the temperature naturally drops back to below 40°C due to gasification fluctuations or conduction to the surrounding area, the DA bond recombines, achieving in-situ self-repair, repairing micro-cracks (width ≤0.1mm) caused by stress changes, and strengthening the integrity of the sealing structure.

[0096] The pH response mechanism is as follows: In response to changes in groundwater pH caused by underground gasification, or pH differences existing in the target area itself, the PAA segments in the slurry respond automatically; in an acidic environment with pH ≤ 5.0, the PAA carboxyl groups are protonated, and the molecular chains shrink, making the material denser; in an alkaline environment with pH ≥ 8.0, the PAA carboxyl groups are deprotonated, and the repulsive force between molecular chains increases, causing the material to swell and squeeze the fracture space, significantly enhancing the sealing effect.

[0097] Step 5-3: For large areas or complex fractures, segmented intermittent grouting is used to divide the target area into several segments. Each segment undergoes low-temperature pre-grouting as described in Step 6-2. After grouting a segment, grouting is paused, allowing the grout to undergo vaporization, heating, and cooling cycles, as well as possible pH changes, under natural conditions to trigger its adaptive response. Based on pressure and flow rate changes monitored, a decision is made regarding whether to perform supplementary grouting on the same segment or proceed with grouting the next segment.

[0098] Grouting process monitoring primarily focuses on grouting pressure and flow rate to determine if blockage or excessive loss has occurred. Grout is stored in sealed containers, and grouting pipelines are purged with dry nitrogen to prevent the prepolymer's terminal -NCO groups from reacting with water and becoming ineffective. Strict adherence to the low-pressure, slow-injection principle is maintained; pressure should be controlled below the formation fracturing pressure to avoid inducing new fractures. The sealing effect is assessed by observing grout filling through borehole sampling, monitoring changes in upstream / downstream gas / water pressure differentials and flow rates in the target area, or monitoring microseismic activity. If viscosity adjustment is necessary, the anhydrous organic solvent specified in the formulation must be used, such as the original mixed solvent; dilution with water is strictly prohibited. The furan group loading of F-SiO2 must be maintained within the range of 0.8-1.2 mmol / g to ensure sufficient DA reaction sites for effective self-healing.

[0099] S6: After gasification is completed, once the temperature of the gasification chamber drops below 80℃, a three-stage pressure gradient is used to fill the main fractures after coal gasification with natural mineral slurry materials to fix pollutants, maintain formation pressure, and ultimately achieve geological sequestration of carbon dioxide.

[0100] The specific method is as follows:

[0101] Step 6-1: In the first stage, after the temperature of the gasification chamber drops below 80℃, low-pressure permeation grouting of 0.3-0.8MPa is used to fill micro-cracks with a width of <0.1mm by utilizing the high fluidity of the grout before initial setting, thus encapsulating and adsorbing pollutants.

[0102] Step 6-2: In the second stage, high-pressure compaction grouting of 1.5-2.2MPa is used to remove interstitial water and compact the structure, thereby enhancing the sealing density, taking into account the thixotropic characteristics of the grout in the initial setting stage.

[0103] Step 6-3: In the third stage, medium-pressure sealing grouting with a pressure of 0.5-1.0 MPa is used to inject lightweight foamed grout to form a low-permeability sealing layer on top. For cracks wider than 5 mm, a 1:1 water glass-MgO quick-setting grout is pre-injected to form a temporary skeleton to prevent the loss of aggregate-free grout.

[0104] Step 6-4: After grouting, maintain the cavity temperature at 60-80℃ for 7 days by introducing low-pressure steam to accelerate the early carbonization reaction. Then, use temperature-triggered CO2 injection: first inject low-temperature CO2 at 10℃, and when the grout temperature rises to 60℃ due to hydration heat release, switch to supercritical CO2 to enhance its diffusion and penetration within the grout using the temperature difference. During this period, monitor the exothermic signal of the carbonization reaction (CaCO3 formation heat ≈ 75kJ / mol) using acoustic emission technology to map the mineralization front in real time.

[0105] The expected results are: crack filling rate >90%, slurry compressive strength >25MPa after 28 days; CO2 mineralization sequestration rate >70% within 50 years, and surface subsidence controlled at <5mm / year; pollutant leaching concentrations meet the following requirements: heavy metals <0.1mg / L, and benzene compounds not detected.

[0106] The preparation method of the silica sol-based composite grout used in step S3 includes the following steps:

[0107] Step-a1: Take 5% of the total water volume of deionized water and KH-550 (calculated as 1.5% of the mass of nano SiO2), add acetic acid to adjust the pH to 4-5, stir for 15 minutes to hydrolyze and activate, and prepare a pre-hydrolyzed KH-550 solution.

[0108] Step-a2: Slowly add nano-SiO2 powder and water to a high-speed shearing machine at 3000 rpm, with a water to nano-SiO2 powder mass ratio of 8-12:1, and continue shearing for 20 minutes; then add pre-hydrolyzed KH-550 solution and continue shearing for 10 minutes, and add ammonia water with a mass fraction of 25-28% to adjust the pH to 9.5-10.5, and shear for another 15 minutes to obtain a stable nano-SiO2 sol.

[0109] Step-a3: Transfer the nano-SiO2 sol to low-speed stirring, set the stirring speed to 300-500 rpm, and stir for 8-10 minutes; add 0.1-0.25 parts of medium-viscosity CMC dissolved in water in advance, mix well, and let stand to defoam before use.

[0110] Step-a4: Select 100 parts fly ash cement and 0.3-0.8 parts lithium carbonate accelerator, and dry mix for 3 minutes until uniform; then sprinkle in 0.8-1.5 parts polypropylene fiber in three batches, stirring at low speed after each addition, with the speed controlled at 200-300 rpm, for 1 minute; ensure that the fiber monofilaments are fully separated and there is no agglomeration, and finally make fiber dry material.

[0111] Step-a5: Mix the nano-SiO2 sol obtained in Step-a3 with 0.5-1.2 parts of polycarboxylate superplasticizer to obtain a sol-superplasticizer mixture;

[0112] Step-a6: Pour the dry fiber material prepared in Step-a4 into the mixing pot, start low-speed mixing, set the speed to 200-300 rpm, and slowly pour in the sol-water reducing agent mixture prepared in Step-a5. Stir for 2 minutes to initially mix the dry material and liquid. If the fluidity is insufficient, add the remaining deionized water very slowly to control the total water-cement ratio at 0.28-0.33. Then switch to high-speed mixing, set the speed to 800-1000 rpm, and continue stirring for 3 minutes until the slurry is uniform and glossy, thus producing the nano-silica sol-based composite grouting material.

[0113] This parameter setting ensures that the dry fiber material and the sol-water reducing agent mixture are fully impregnated in the low-speed stage to avoid local clumping; while the high-speed stage further improves the homogeneity of the grout and uses shearing action to disperse potential agglomerates, ensuring the fluidity and stability of the grout.

[0114] The preparation method of the temperature-pH sensitive self-healing polyurethane composite slurry used in step S5 is as follows:

[0115] Step-b1: Disperse nano-SiO2 in anhydrous ethanol, add 3-aminopropyltriethoxysilane (APTES) and reflux for 6 h to obtain aminated SiO2;

[0116] Step-b2: Aminated SiO2 is reacted with furan-2-carboxaldehyde to prepare furan-functionalized silica (F-SiO2).

[0117] The furan group loading in F-SiO2 is 0.8-1.2 mmol / g; the pH response is achieved by swelling switching through PAA carboxyl protonation / deprotonation; the temperature response is achieved by self-repair through DA bond (break at 60℃ / recombination at 40℃).

[0118] Step-b3: Under nitrogen protection, polyether polyol and diphenylmethane diisocyanate (MDI) are added to the reactor and reacted at 80°C for 2 hours to obtain NCO-terminated polyurethane prepolymer; after cooling to 60°C, formylglycine synthase (FGE) is added and reacted for 1 hour to obtain furan-terminated prepolymer (F-PU).

[0119] Step-b4: Dissolve polyacrylic acid (PAA) in a mixed solvent and slowly add it to F-PU, stirring at 40°C for 30 minutes. The mixed solvent is a mixture of anhydrous N,N-dimethylformamide (DMF) and tetrahydrofuran (THF) in a volume ratio of 3:1. It has good polarity and solubility, which can ensure that PAA is completely dissolved and forms a homogeneous system with F-PU, while avoiding side reactions between the solvent and the active groups in the system, thus providing a stable reaction environment for the subsequent Diels-Alder reaction and chain extension reaction.

[0120] Step-b5: F-SiO2 and bismaleimide (BMI) are added to the mixed solution prepared in Step-b4, and the reaction is carried out at 60°C for 2 hours to trigger the Diels-Alder reaction; then triethylamine (TEA) and dibutyltin dilaurate complex (DBTDL) are added, and the chain extension is catalyzed at 50°C for 1 hour.

[0121] Step-b6: Cool the mixed solution obtained in Step-b5 to 25°C and adjust the solid content to 30-40% to obtain the target composite slurry;

[0122] Step-b7: Perform vacuum degassing on the composite slurry obtained in Step-b6 to remove solvent and air bubbles, so that the composite slurry reaches the required viscosity. If it is too thick, an appropriate amount of solvent can be added to adjust it.

[0123] Step-b8: Store the composite slurry treated in Step-b7 in a sealed container to avoid moisture and air contamination and prevent the composite material from reacting.

[0124] The method for preparing the natural mineral slurry material used in step S6 is as follows:

[0125] Step-c1: Place fly ash in an industrial microwave device and microwave irradiate for 3-5 minutes to induce microcracks on the glass surface; then add the above materials to a mixer in the following proportions: fly ash 35-40%, steel slag powder 30-35%, slag 25-30%, silica fume 5-8%, 0.5% nano Ca(OH)2 seed crystals, and UEA expansion agent 3-5%, and mix at 200 r / min for 4 minutes.

[0126] Step-c2: Mix formic acid and acetic acid at a mass ratio of 3:1 and dilute to a concentration of 12%. Spray the mixture onto the dry powder prepared in Step-c1. Continue stirring for 5 minutes and let stand for 120-180 minutes to deeply activate the activity.

[0127] Step-c3: Add 70% of the total water volume of the activated dry powder obtained in Step-c2 to clean water at a temperature of 25±2℃ and an accelerator. The accelerator accounts for 4-6% of the total weight of the cementitious material and is a sulfoaluminate type accelerator made of calcium aluminate and gypsum in a mass ratio of 3:1. Stir at 280-300 r / min for 4 minutes. Then add 0.1-0.15% of polycarboxylate superplasticizer and stir at 450-550 r / min for 5 minutes to form a homogeneous slurry.

[0128] To prepare a lightweight slurry, AES and CAB can be dissolved in 40°C warm water at a mass ratio of 3:2, and 0.38-0.4% polyacrylamide can be added to achieve a density of 0.8-1.0 g / cm³. 3 The foaming liquid is used to generate high water-retaining foam using a physical foaming machine. The foam and slurry are mixed at a volume ratio of 1.8-2.2:1 and slowly stirred at 140-160 r / min for 3 minutes to prepare the sealing foam.

[0129] The K used in step S4 + The preparation method of the base composite slurry is as follows:

[0130] Step-d1: Add KCl and KNO3 in a mass ratio of 6:4 to 60% of the total water volume in 40°C warm water and stir at 300 rpm for 10 minutes. The K in the slurry... + The total amount is 15–20 wt%, which dissolves in the carrier water to form a saturated solution, ensuring that the driving force of ion diffusion is maximized;

[0131] Step-d2: Add 1–2 wt% Na₂CO₃, 2–4 wt% Na₂SiO₃, and 0.05–0.1 wt% HEDP sequentially, maintaining the pH at 9.5 ± 0.2, stirring at 500 rpm for 5 minutes until transparent, promoting K... + It is fixed between the clay mineral layers and generates CaCO3 micro-precipitates to assist in sealing.

[0132] Step-d3: Slowly add 3–5 wt% bentonite, 0.5–1.2 wt% guar gum, and 0.3–0.8 wt% polyacrylamide at 1500 rpm for 15 min until the viscosity is ≥300 cP. High-speed shear dispersion enhances viscosity stability and prevents the slurry from preferentially flowing out along large pores.

[0133] Step-d4: Finally, add 0.1–0.3 wt% PCE to reduce the surface tension of the slurry, improve its wettability in low-permeability clay, and add water to the target volume. Rotate at 200 rpm for 30 minutes until the viscosity stabilizes at 250 ± 50 cP. Allow to mature at a low speed to produce K. + Base composite slurry.

[0134] The microbial community includes native aquifer microorganisms from the original underground gasification practice site or microorganisms adapted to the underground environment and capable of degrading inorganic and organic pollutants in the underground coal gasification process. Given the low permeability and anoxic / anaerobic environment of the aquifer and clay layers, in-situ aquifer microorganisms are prioritized for screening to ensure their colonization capacity and ecological safety.

[0135] Single-cell Raman sorting (scRACS) was used to identify functional bacteria with high in situ metabolic activity in polluted water bodies at sites affected by underground coal gasification. These bacteria included, but were not limited to, Gram-negative bacteria such as *Pseudomonas aeruginosa*, *Extroquens*, *Desulfuricans*, *Nitrosomonaseuropaea*, and anaerobic ammonia-oxidizing bacteria.

[0136] Activated coke is prepared by fluidized bed reaction using high fixed carbon coal (fixed carbon content >75%), and the specific surface area of ​​the prepared activated coke is ≥350 m². 2 / g, and by controlling its ash content to <12% to reduce heavy metal content; and by using acid washing pretreatment to remove soluble metals, the As / Cd leaching amount is reduced by 80%. A 1-3mm coarse particle layer from coal-based activated coke is placed near the injection well to prevent clogging, and 0.5-1mm fine particles are placed at the far end of the pollution plume to enhance the adsorption and interception effect of pollutants; 0.2-0.5mm micro particles are suitable for fine fracture repair, but also have a higher risk of clogging.

[0137] Microorganisms are immobilized on a carrier using a physical adsorption and charge immobilization technique, as detailed below:

[0138] Adding 10% nano-Fe3O4 to coal-based activated coke enhances electron transport capacity, increasing methanogenesis efficiency by 10.8%. Modifying the carrier surface with a 0.5% w / v polyethyleneimine (PEI) coating allows for the adsorption of negatively charged bacteria via positive charge, achieving a loading rate exceeding 90%. A biochar-humic acid composite provides negatively charged sites for metal ion adsorption and simultaneously acts as an electron shuttle to promote anaerobic respiration. The bacterial agent is mixed with the aforementioned carrier and injected into the aquifer, along with a simultaneous nutrient pulse (containing sodium acetate and trace amounts of Ni and Co), stimulating microorganisms to secrete extracellular polymeric substances (EPS) and autonomously form a biofilm.

[0139] Based on the above microbial immobilization technology, the following combined strategy can be adopted: for spore-forming bacteria, direct adsorption can be performed; for non-spore-forming anaerobic bacteria, PEI-modified conductive activated carbon is used, combined with adaptive biofilm induction; at the same time, the carrier is acid-washed and pre-reduced, loaded with microorganisms and then anaerobic dried, and the redox potential (ORP) is monitored in real time after injection.

[0140] The preparation and production of the compound microbial agent first involves laboratory-scale tests, field tracer pilot tests, and injection tests to determine key parameters such as the bacterial proliferation rate, the range of pollutant concentration tolerance, the dosage of the agent, the layout of injection wells, and the area of ​​influence of the agent. Based on the bacterial proliferation patterns, a reasonable sampling and monitoring schedule is determined. After optimization of the compound microbial community, the prepared agent is used for field injection. After determining the injection well locations and completing relevant preparations, the agent is injected into the aquifer via injection wells or in-situ push methods. After a period of static reaction, it is confirmed that the bacterial strain has colonized and multiplied in the underground environment, and that its activity and quantity meet the requirements. Regular sampling through monitoring wells is used to check whether the groundwater pollutant concentration and the survival rate of indigenous microorganisms meet the expected standards.

[0141] The in-situ grouting water-blocking system for the gasification isolation wall also includes a real-time monitoring system and a cloud-based analysis platform.

[0142] The real-time monitoring system is used to comprehensively monitor the gas concentration, water quality, and integrity of the isolation wall in the underground gasification area. Its core components include a gas monitoring module, a water quality monitoring module, a geological stability monitoring module, and a central control unit. It achieves intelligent linkage with the grouting control terminal through a cloud analysis platform.

[0143] The gas monitoring module adopts a graded monitoring mode of coarse screening downhole and fine measurement on the surface. The downhole tube monitoring system is deployed to detect the composition and concentration of each pollutant gas in real time, completing the preliminary screening and monitoring; the surface part performs high-precision detection to achieve accurate analysis of pollutant gases.

[0144] The water quality monitoring module integrates pressure-chemical coupling monitoring technology and anti-interference electrode technology. By conducting in-situ morphology analysis, it monitors water pressure changes and pollutant transport paths in real time, and completes in-situ morphology analysis of pollutants, providing water quality data support for pollution prevention and control.

[0145] The geological stability monitoring module adopts a three-dimensional coupled early warning model of "microseismic b-value-ERT resistivity-DAS strain". Through multi-parameter collaborative monitoring, it can capture subtle changes in the geological structure of the gasification area in real time and assess the stability of the isolation wall and overlying rock.

[0146] The central control unit, as the core of the system, is responsible for real-time fusion of multi-source information such as gas concentration gradient data, temperature field distribution, water level fluctuations, and microseismic energy maps to generate a three-dimensional model of the leakage path and a risk thermal map, providing a basis for decision-making in subsequent regulation and control.

[0147] This real-time monitoring system has the ability to link real-time detection and dynamic control: after real-time detection of gas composition, concentration and water pollution status in the gasification area, it can automatically trigger the grouting process adjustment mechanism, and minimize the risk of gas leakage and water pollution by adjusting the reagent ratio and injection volume.

[0148] The cloud-based analytics platform receives and shares monitoring data in real time via an IoT gateway. Internally, it integrates a data fusion unit, a neural network decision-making module, and a grouting parameter generator. First, it integrates the gas concentration gradient, aquifer pollutant concentration, and microseismic energy spectrum into a spatiotemporal matrix. Then, it uses a convolutional neural network (CNN) to process the spatiotemporal matrix, outputting a leakage risk index R (0≤R≤1) and a pollution diffusion coefficient D. Finally, it calculates the grouting agent ratio and the injection volume Q (m³) per unit time based on R and D. 3 / h).

[0149] The grouting control terminal automatically adjusts the reagent components based on the mixing parameters sent from the cloud, with an accuracy error of ≤±2%; simultaneously, it adjusts the plunger pump flow rate according to the injection volume Q, with a response delay of ≤1 minute, ensuring timely control; when a sudden change in shallow gas concentration (increase >20% / hour) or aquifer Cr is detected... 6+ When the concentration exceeds the standard (>0.1 mg / L), the grouting control terminal will immediately activate the emergency grouting mode, increasing the injection volume Q to 200% of the benchmark value, thereby achieving rapid risk response and control.

[0150] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A method for constructing an in-situ grouting water-blocking system of a coal underground gasification isolation wall, characterized in that: The method comprises the following steps: S1: monitoring deployment: according to the underground gasification site selection and engineering design, the surrounding area of the underground gasification region is implemented with all-round monitoring deployment; S2: biological barrier construction: before the start of the underground coal gasification project, the single-cell Raman sorted microbial flora is mixed with the carrier and injected into the aquifer, and then a nutrition pulse is injected to stimulate the formation of a biological membrane by the microorganisms, and the activity of the microbial flora is maintained by the nutrition liquid during the gasification process; S3: initial physical grouting isolation before gasification: before gasification, a nano-silica sol-based composite grouting material is prepared, boreholes are arranged along the fracture trend, and a directional negative pressure grouting method is used to seal the original fractures at the interface between the gasification cavity side coal pillar and the aquifuge; S4: Chemical grouting barrier construction before gasification: According to the quincunx grid layout of grouting hole in the clay aquiclude adjacent to the aquifer, inject K + Based on the composite slurry, the stability of clay is enhanced by alternating high and low pressure grouting method; S5: dynamic physical grouting isolation during gasification: a nano-particle modified temperature-pH sensitive self-healing polyurethane composite grouting material is used to target grouting at the detected fracture generation points, and the self-adaptive sealing is realized by using the temperature response self-healing characteristics of the DA bond and the pH response swelling characteristics of the PAA segment of the grouting material; S6: final physical grouting isolation after gasification: after the gasification is completed and the temperature of the gasification cavity drops below 80℃, a natural mineral grout material is used to fill the main fractures through a three-stage pressure gradient grouting, and CO2 is injected after curing to realize mineralization storage; The preparation method of the silica sol-based composite grouting material used in step S3 is as follows: Step-a1: take 5% of the total water amount of deionized water and KH-550, add acetic acid to adjust the pH to 4-5, stir for 15 minutes for hydrolysis and activation, and prepare a pre-hydrolyzed KH-550 solution; Step-a2: slowly add nano-SiO2 powder and water in a 3000 rpm high-speed shearing machine, the mass ratio of water to nano-SiO2 powder is 8-12:1, continue shearing for 20 minutes; then continue shearing for 10 minutes after adding the pre-hydrolyzed KH-550 solution, and add 25-28% ammonia water by mass fraction, adjust the pH to 9.5-10.5, and continue shearing for 15 minutes to obtain a stable nano-SiO2 sol; Step-a3: transfer the nano-SiO2 sol to low-speed stirring, the stirring speed is set to 300-500 rpm, and the stirring time is 8-10 minutes; Add previously dissolved water-soluble medium viscosity CMC, 0.1-0.25 parts, mix well and stand for defoaming before use; Step-a4: select 100 parts of fly ash cement and 0.3-0.8 parts of lithium carbonate accelerator, dry mix for 3 minutes until uniform; then scatter 0.8-1.5 parts of polypropylene fiber in three times, and low-speed stir for 1 minute after each scattering to ensure that the fiber filaments are fully separated and there is no agglomeration phenomenon, finally prepare the fiber dry material; Step-a5: stir the nano-SiO2 sol obtained in Step-a3 and 0.5-1.2 parts of polycarboxylic acid water reducing agent uniformly to obtain a sol-water reducing agent mixture; Step-a6: pour the fiber dry material prepared in Step-a4 into the stirring pot, start low-speed stirring, then pour the sol-water reducing agent mixture prepared in Step-a5 into the stirring pot, stir for 2 minutes; high-speed stirring for 3 minutes until the slurry is uniform and glossy, and a nano-silica sol-based composite grouting material is prepared.

2. The construction method of the in-situ grouting water blocking system of the coal underground gasification isolation wall according to claim 1, characterized in that: The temperature-pH sensitive self-repairing polyurethane composite slurry preparation method used in the step S5 is as follows: Step-b1: disperse nano-SiO2 in anhydrous ethanol, and add 3-aminopropyl triethoxysilane to reflux for 6 hours to obtain aminated SiO2; Step-b2: react the aminated SiO2 with furan-2-formaldehyde to obtain F-SiO2; Step-b3: under nitrogen protection, add polyether polyol and MDI into a reaction kettle, and react at 80°C for 2 hours to obtain a terminal-NCO polyurethane prepolymer; after cooling to 60°C, add FGE and react for 1 hour to obtain F-PU; Step-b4: dissolve PAA in a mixed solvent, and slowly add into F-PU and stir at 40°C for 30 minutes; Step-b5: add F-SiO2 and BMI into the mixed solution prepared in Step-b4, and react at 60°C for 2 hours to trigger Diels-Alder reaction; then add TEA and DBTDL, and catalyze chain extension at 50°C for 1 hour; Step-b6: cool the mixed solution obtained in Step-b5 to 25°C, and adjust the solid content to 30-40% to obtain the target composite slurry; Step-b7: perform vacuum degassing treatment on the composite slurry obtained in Step-b6 to remove solvent and bubbles, so that the composite slurry reaches the required viscosity; Step-b8: store the composite slurry treated in Step-b7 in a sealed container to avoid moisture and air pollution and prevent the composite slurry from reacting.

3. The construction method of the in-situ grouting water blocking system of the coal underground gasification isolation wall according to claim 1, characterized in that: The natural mineral slurry material preparation method used in the step S6 is as follows: Step-c1: microwave irradiate fly ash in an industrial microwave device for 3-5 minutes to produce microcracks on the surface of the glass body; then, according to the proportions of fly ash 35-40%, steel slag powder 30-35%, slag 25-30%, silica ash 5-8%, 0.5% nano-Ca(OH)2 crystal seeds, and UEA expanding agent 3-5%, add into a blender, and mix at a speed of 200 r / min for 4 minutes; Step-c2: mix formic acid and acetic acid according to a mass ratio of 3:1, dilute to a concentration of 12%, and spray on the mixed dry powder prepared in Step-c1; continue to stir for 5 minutes, and then stand for 120-180 minutes to deeply excite activity; 4. The construction method of the in-situ grouting water blocking system of the coal underground gasification isolation wall according to claim 1, characterized in that: The K used in the step S4 + The preparation method of the base composite slurry is as follows: Step-d1 : KCI and KNO3 were mixed in a mass ratio of 6:4 and added to 60% of the total water at 40°C, stirring at a speed of 300 rpm for 10 min. K + The total amount was 15-20wt%, dissolved in carrier water to form a saturated solution, to ensure the maximum driving force for ion diffusion; Step-d2: 1-2wt% Na2CO3, 2-4wt% Na2SiO3 and 0.05-0.1wt% HEDP were added in turn, pH was maintained at 9.5±0.2, rotation speed was 500rpm, and the solution was stirred for 5min until it became transparent, promoting K + intercalated with clay minerals and generated CaCO3 micro-deposits to assist sealing; Step-c3: add water with a total amount of 70% of the clear water, water temperature 25±2°C, and a speed coagulant accounting for 4-6% of the total weight of the cementing material into the activated dry powder prepared in Step-c2, and the speed coagulant is a sulphoaluminate type coagulant made of calcium aluminate: gypsum according to a mass ratio of 3:1; stir at a speed of 280-300 r / min for 4 minutes; then add 0.1-0.15% of a polycarboxylic acid water reducer, and stir at a high speed of 450-550 r / min for 5 minutes to form a homogeneous slurry. Step-d3: slowly add 3-5wt% of bentonite, 0.5-1.2wt% of guar gum, and 0.3-0.8wt% of polyacrylamide, and disperse at a high speed of 1500 rpm for 15 minutes, so that the viscosity is ≥300 cP, the high-speed shearing dispersion enhances the viscosity stability, and prevents the slurry from preferentially flowing along large pores; Step-d4: Finally add 0.1 - 0.3 wt% PCE to reduce the surface tension of the slurry, improve the wettability in low permeability clay, and make up to target volume, 200 rpm for 30 min, viscosity stabilized at 250 ± 50 cP, low speed maturation, and K is made + Base composite slurry.

5. The construction method of a coal underground gasification isolation wall in-situ grouting water blocking system according to any one of claims 1-4, characterized in that: The step S1 is specifically as follows: According to the underground gasification site selection and engineering design, the surrounding area of the underground gasification area is implemented with all-round monitoring arrangement: the microseismic monitoring instrument is embedded, which is used for real-time geological condition survey and crack expansion monitoring; The distributed optical fiber sensor and resistivity tomography equipment are arranged, the dynamic change of the diffusion temperature mechanics field is real-time drawn, the slurry diffusion cloud picture is drawn, the downhole anti-explosion sensor is embedded, the beam tube monitoring system is used for real-time detection of each pollutant gas component and concentration, the vacuum negative pressure sampling is implemented through the heat tracing pipeline, the ground part is implemented with the laser photoacoustic spectrum rapid detection technology and the microfluidic chip integrated electrochemical sensor, the gas concentration change is inversed combined with the downhole pressure and temperature data, the high-pressure anti-pollution pressure sensor and the multi-parameter ion selective electrode array are installed near the underground aquifer, and the underground water pressure and ion migration are real-time monitored.

6. The construction method of the in-situ grouting water blocking system of the coal underground gasification isolation wall according to claim 5, characterized in that: The step S2 is specifically as follows: Step2-1: based on the underground gasification pollution characteristics and the anoxic, low-temperature and high-salt environment of the aquifer, the single-cell Raman sorting is used to collect samples from the underground water and pollution sludge in the gasification area, the scRACS-SIP technology is used to label and identify the in-situ metabolic active strains, and the microorganisms are selected; the scRACS selected strains are subjected to anaerobic tank simulation underground environment directional amplification, and the long-term survival microorganisms are injected into the underground aquifer and activated by pollutants; Step2-2: After mixing the microbial agent with the carrier, inject it into the aquifer, inject a nutrition pulse to stimulate the secretion of EPS by microorganisms to form biofilm autonomously; spore bacteria can directly adsorb to the carrier and activate when encountering pollutants; non-spore bacteria use phased loading, concentrate the microbial solution to 10 9 CFU / mL, mix with PEI modified carrier for 2h, dry under anaerobic conditions to a moisture content of 20%, and then inject into the aquifer after nutrition activation; Step2-3: The bacteria-carrier is pumped into the target aquifer by using the gasification agent pipeline with a solid-liquid ratio of 1:5 in a ladder form; and the pH, Cl - and Ca 2+ are monitored in real time, and O2, nitrate or carbon source is supplemented in time to maintain activity; Step2-4: the downhole sensor is arranged to monitor the permeability coefficient K and the oxidation-reduction potential ORP; the B-GFP fluorescence tracing technology is combined to track the active focus migration, and the injection parameters are dynamically adjusted.

7. The construction method of the in-situ grouting water blocking system of the coal underground gasification isolation wall according to claim 6, characterized in that: The step S3 is specifically as follows: The nano-silica sol-based composite grouting material is prepared and activated, according to the geological survey result, the drill hole is arranged along the crack development direction or perpendicular to the main crack strike, the slurry is injected into the original crack at the interface between the gasification cavity side coal pillar and the coal pillar aquifer, and the grouting isolation and plugging are carried out; the depth of the plugging area is greater than 1.2 times of the design height of the gasification cavity, and the grid-shaped grouting hole is arranged at the intersection area such as the fault; the double plug system or the sleeve valve pipe technology is used for the drill hole delivery pipeline, the drill hole is segmented and isolated, the slurry is injected from the bottom to the top of the drill hole in sections, and the deep area is preferentially processed.

8. The construction method of the in-situ grouting water blocking system of the coal underground gasification isolation wall according to claim 7, characterized in that: The step S4 is specifically as follows: Step4-1: grouting hole arrangement: the grouting hole is arranged according to the plum blossom-shaped grid, the hole spacing is set to 1.5-2.5 times of the design diffusion radius; the sleeve pipe is used to follow the drilling machine construction, the PVC flower pipe with filter screen is lowered, and the filter screen aperture is ≤100 μm, so as to prevent the clay particles from blocking the pipeline; Step4-2: grouting parameter control: the temperature field and pressure field changes of the slurry diffusion are real-time monitored through the microseismic sensor and the distributed optical fiber sensor (DTS); the grouting mode is selected according to the clay layer permeability coefficient, and the 5-10 Hz frequency alternating high and low pressure injection is used to break the clay capillary resistance; The pressure is controlled in stages in the grouting process: 0.3-0.5 MPa in the early stage for permeation grouting, 0.8-1.5 MPa in the middle stage for compaction grouting, and the pressure in the later stage does not exceed 2.0 MPa to avoid hydraulic fracturing; the working pressure range of the hydraulic piston pump is 0-20 MPa, and the flow rate is accurately controlled at 0.5-50 L / min, wherein the flow rate is controlled at 2-5 L / min for low-permeability layers with a permeability coefficient k<10 cm / s, the flow rate is controlled at 10-20 L / min for medium-permeability layers with a permeability coefficient k>10 cm / s -7 -6 cm / s.​ Step4-3: Special working condition adjustment: For low permeability or easy plugging working condition, 0.5% surfactant solution is injected before grouting to reduce interfacial tension; In order to inhibit the pipe blockage caused by divalent ion scaling, 0.1% sodium citrate is added to the slurry, and a double-channel flushing system is used for periodic pipeline maintenance to ensure stable and efficient grouting process.

9. The construction method of the in-situ grouting water blocking system of the coal underground gasification isolation wall according to claim 8, characterized in that: The specific method of step S6 is as follows: Step6-1: First stage, after the temperature of the gasification cavity is reduced to below 80℃, low pressure penetration grouting of 0.3-0.8MPa is used, the high flowability of the slurry before initial setting is utilized to fill microcracks with a width of <0.1mm and wrap and adsorb pollutants; Step6-2: Second stage, high pressure extrusion grouting of 1.5-2.2MPa is used, according to the thixotropy characteristics of the slurry during initial setting, the interstitial water is discharged and the structure is compacted to enhance the sealing and compactness; Step6-3: Third stage, medium pressure sealing grouting of 0.5-1.0MPa is used, light foaming slurry is injected to form a low permeability sealing layer at the top; For cracks with a width of >5mm, water glass-MgO quick-setting slurry with a volume ratio of 1:1 is pre-injected to form a temporary skeleton to prevent loss of non-aggregate slurry; Step6-4: After grouting is completed, the cavity is maintained at 60-80℃ by passing low pressure steam for 7 days to promote early carbonation reaction; Subsequently, temperature triggered CO2 injection is used, 10℃ low temperature CO2 is injected first, when the temperature of the slurry rises to 60℃ due to hydration heat, supercritical CO2 is switched, and the diffusion and penetration of CO2 in the slurry are strengthened by using temperature difference.

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