Precise recharge method for multilayer aquifer in groundwater overexploitation area

Abstract

The present application relates to the technical field of groundwater ecological restoration, and particularly is a method for precise recharge of multi-layer aquifer in groundwater overexploitation area, which aims at the problems of uneven recharge, well blockage, disconnection of well group regulation and control, and single monitoring in traditional recharge technology. The method first carries out hydrogeological survey to determine the parameters of recharge well, and lays out integrated monitoring array. Independent recharge is realized by layered sealing, and uniform recharge is realized by using degradable biological gel to temporarily block the dominant seepage channel. A digital twin platform is constructed to complete the intelligent regulation and control of well group, and the permeability of aquifer is enhanced by magnetic fluid. The parameters are dynamically adjusted in real time during the recharge process, and pulse gas-liquid-solid three-phase backwashing is used to clear the blockage, and in-situ purification and system self-power supply are realized by combining microbial fuel cell. Finally, the recharge scheme is optimized through comprehensive evaluation. The present application can precisely and efficiently recharge multi-layer aquifer, control land subsidence, reduce operation cost, and is suitable for restoration of various groundwater overexploitation areas.

Description

Technical Field

[0001] This invention relates to the field of groundwater ecological restoration technology, specifically a method for precise recharge of multi-layer aquifers in groundwater over-extraction areas. Background Technology

[0002] Groundwater, a crucial component of my country's water resources system, supports drinking water for nearly 70% of the population and irrigation for 40% of agriculture, playing an irreplaceable role in ensuring national water security and supporting economic and social development. However, with the acceleration of my country's industrialization and urbanization, and continuous population growth, groundwater extraction has increased, leading to widespread over-extraction across the country. To date, my country has designated 233 groundwater over-extraction zones, covering a total area of ​​approximately 300,000 square kilometers, with cumulative over-extraction exceeding 250 billion cubic meters. This over-extraction has triggered a series of serious ecological and geological problems, including land subsidence, ground fissures, karst collapse, seawater intrusion, wetland shrinkage, and vegetation degradation, causing enormous losses to people's lives and property and the ecological environment.

[0003] Groundwater recharge is currently recognized internationally as the most effective technology for controlling groundwater over-extraction and restoring the groundwater ecosystem. By artificially injecting qualified water sources such as surface water, reclaimed water, and rainwater into underground aquifers, groundwater reserves can be rapidly replenished, groundwater levels restored, land subsidence curbed, groundwater quality improved, and the functions of the groundwater ecosystem restored. However, existing groundwater recharge technologies still face many unresolved issues in practical applications: First, traditional recharge techniques struggle to achieve uniform replenishment within aquifers. Due to the inherent heterogeneity of aquifers, recharge water tends to flow rapidly along high-permeability channels, exhibiting a "finger-like" phenomenon. This results in low-permeability areas not receiving effective replenishment, leading to low recharge efficiency. Furthermore, the presence of dominant seepage channels accelerates the migration and diffusion of pollutants, increasing the risk of groundwater contamination.

[0004] Secondly, the problem of recharge well blockage remains a major bottleneck restricting the widespread application of recharge technology. Suspended solids, microorganisms, chemical reaction products, and fine particles from the aquifer itself migrate and deposit in the well wall, filter layer, and aquifer pores, causing a gradual decline in the permeability of the recharge well and a significant reduction in the recharge volume. Traditional single-flow backflushing technology can only remove blockages on the surface of the well wall and filter layer, and cannot effectively remove deep blockages inside the aquifer, resulting in limited backflushing effects.

[0005] Furthermore, most existing reinjection technologies are designed and controlled for individual wells, lacking the ability to coordinate and control well groups at a regional scale. In large-scale reinjection projects, there are complex hydraulic interactions between the reinjection wells. Independent control of a single well often leads to uneven distribution of groundwater levels in the region, and may even cause safety hazards such as local ground heave and aquifer rupture.

[0006] Furthermore, monitoring methods during the reinjection process remain relatively limited, failing to provide a comprehensive understanding of the dynamic changes in the aquifer. Existing monitoring technologies primarily focus on conventional parameters such as water level and pressure, lacking effective monitoring methods for crucial information such as the development of fractures and changes in pore structure within the aquifer, making it difficult to accurately assess the reinjection effect and predict potential risks.

[0007] Finally, the issues of ensuring water quality and operating costs of reinjection water are becoming increasingly prominent. Traditional physicochemical pretreatment technologies are costly and prone to secondary pollution. Meanwhile, the monitoring, control, and backwashing processes of the reinjection system consume significant amounts of electricity, increasing the system's operating costs.

[0008] Therefore, there is an urgent need to develop a new groundwater recharge technology that can achieve uniform recharge within aquifers, effectively remove deep blockages, and has the ability to coordinate and regulate regional well groups, in order to solve the above-mentioned problems of existing technologies and provide strong technical support for the comprehensive management of groundwater over-extraction areas in my country. Summary of the Invention

[0009] To address the problems in existing technologies, this invention provides a method for precise recharge of multi-layer aquifers in groundwater over-extraction areas. This method solves the problems of uneven recharge, difficulty in clearing deep blockages, disconnection of well group control, and limited monitoring methods that exist in traditional recharge technologies, thereby achieving precise, efficient, and coordinated recharge of multi-layer aquifers.

[0010] The technical solution adopted by this invention to solve its technical problem is: a method for precise recharge of groundwater in multi-layered aquifers in over-extracted groundwater areas, comprising the following steps: Step S1: Conduct comprehensive hydrogeological surveys in the target over-extraction area to ascertain the spatial distribution, lithological characteristics, permeability coefficient, and fracture development patterns of each aquifer, and determine the well locations, depths, and structural parameters of the recharge well group; Step S2: An integrated monitoring array is installed along the axial direction on the inner wall of the well pipe of each reinjection well. The integrated monitoring array includes a distributed fiber optic grating sensing unit and an acoustic emission sensing unit, which are used to collect water level, water pressure, water temperature, water quality parameters and fracture activity signals of each aquifer, respectively. Step S3: Install a layered isolation system in the recharge well to divide the recharge well into independent recharge sections corresponding to each aquifer. Each recharge section is equipped with an independent flow regulating valve, pressure sensor and magnetohydrodynamic injection interface. Step S4: Inject biodegradable biogel into the target aquifer to temporarily block the dominant seepage channels within the aquifer, forcing the reinjected water to diffuse into low-permeability areas, thereby achieving uniform replenishment within the aquifer. Step S5: Construct a regional multi-layer aquifer digital twin platform, integrating hydrogeological survey data, real-time monitoring data, and meteorological and hydrological data to simulate groundwater migration, solute diffusion, and land subsidence processes under different recharge conditions; Step S6: Based on the simulation results of the digital twin platform, formulate a well group coordinated reinjection scheme, inject pretreated reinjection water into the corresponding aquifer through the flow regulating valve of each reinjection section, and at the same time inject magnetic fluid to enhance the aquifer permeability as needed. Step S7: During the reinjection process, the integrated monitoring array collects the dynamic parameters of each aquifer in real time and transmits them to the digital twin platform. The platform dynamically updates the simulation results based on the real-time data and automatically adjusts the reinjection pressure, flow rate and magnetohydrodynamic injection volume of each reinjection well. Step S8: Periodically perform pulsed gas-liquid-solid three-phase alternating backwashing on each reinjection section to remove blockages in the well wall, filter layer and aquifer pores; at the same time, use the microbial fuel cell unit implanted in the filter layer to perform in-situ purification treatment on the reinjection water.

[0011] Specifically, in step S2, the acoustic emission sensing units are arranged at a spacing of 2-5m, with a sampling frequency of not less than 100kHz, capable of identifying the generation and expansion of micro-cracks within the aquifer, and with a positioning accuracy of not less than 0.5m.

[0012] Specifically, in step S4, the biodegradable biogel is prepared using starch-based modified materials, with a gel strength of 0.1-0.5 MPa, a degradation cycle of 30-90 days, and degradation products of carbon dioxide and water, which will not cause secondary pollution to groundwater.

[0013] Specifically, in step S6, the magnetic fluid is prepared using nano-iron oxide particles with a particle diameter of 10-50 nm and an injection concentration of 0.5-2 g / L. After injection, the magnetic fluid is guided to distribute within the aquifer by an external magnetic field to improve pore connectivity.

[0014] Specifically, in step S5, the digital twin platform uses multi-physics coupling simulation technology to simultaneously simulate groundwater flow, solute transport, soil and rock deformation, and biochemical reaction processes, with a time step of 1-12 hours.

[0015] Specifically, in step S6, the pretreatment of the reinjection water includes bar screen, sedimentation, filtration and ultraviolet disinfection. The quality of the pretreated reinjection water meets the requirements of Class III water in the "Groundwater Quality Standard" (GB / T 14848-2017).

[0016] Specifically, in step S8, the pulsed gas-liquid-solid three-phase alternating backwashing process is as follows: first, high-pressure air is injected at a pressure of 0.4-0.9 MPa for 5-15 minutes; then, a high-speed water flow containing quartz sand particles (0.1-0.3 mm in diameter, 3-6 times the normal reinjection flow rate) is injected for 10-30 minutes; finally, clean water is injected for rinsing for 5-10 minutes; the above process is repeated 2-4 times.

[0017] Specifically, in step S8, the electrical energy generated by the microbial fuel cell unit is used to drive the integrated monitoring array, flow regulating valve and magnetohydrodynamic injection device, and the excess electrical energy is stored in the energy storage device.

[0018] Specifically, in step S8, the backwashing cycle is determined based on the flow attenuation rate of the reinjection section. When the flow attenuation rate reaches 15%-25%, the backwashing procedure is started.

[0019] Specifically, it also includes step S9: establishing a comprehensive evaluation system for the reinjection effect, regularly evaluating the water level recovery, water quality improvement, land subsidence control and ecological restoration effects of each aquifer, and continuously optimizing the reinjection plan based on the evaluation results.

[0020] The beneficial effects of this invention are: This invention employs biodegradable biogel temporary plugging technology, which can effectively block the dominant seepage channels within the aquifer, forcing the recharge water to diffuse into low-permeability areas, achieving uniform replenishment within the aquifer, and significantly improving recharge efficiency.

[0021] This invention employs pulsed gas-liquid-solid three-phase alternating backwashing technology, which utilizes the combined action of high-pressure air, high-speed sand-containing water flow, and clean water to effectively remove deep blockages from the well wall, filter layer, and aquifer, thereby extending the service life of the reinjection well.

[0022] This invention employs magnetohydrodynamic enhanced permeation technology, which can improve the pore connectivity of low-permeability aquifers, enhance the infiltration capacity of recharge water, and solve the problem of difficult recharge of low-permeability aquifers.

[0023] This invention constructs a regional multi-layer aquifer digital twin platform, realizing multi-well collaborative intelligent control, which can effectively avoid uneven regional groundwater level distribution and safety hazards caused by independent control of a single well, and improve the scientific nature and safety of recharge projects.

[0024] This invention integrates distributed fiber optic grating sensing and acoustic emission monitoring technologies, enabling a comprehensive understanding of the dynamic changes in the aquifer during the reinjection process, and providing reliable data support for the optimization of reinjection schemes and risk prevention and control.

[0025] The microbial fuel cell unit implanted in this invention not only achieves in-situ purification of reinjection water, ensuring the safety of reinjection water quality, but also generates electricity to drive the system's monitoring and control equipment, realizing the system's self-powered operation and reducing operating costs. Attached Figure Description

[0026] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0027] Figure 1 The overall process flow diagram for precise recharge and replenishment of multi-layer aquifers in groundwater over-extraction areas provided by this invention; Figure 2 This is a system architecture diagram of the integrated monitoring array provided by the present invention; Figure 3 Flow chart of the pulsed gas-liquid-solid three-phase alternating backwashing process provided by the present invention; Figure 4 The flowchart of the collaborative control process of the regional well cluster digital twin platform provided by the present invention. Detailed Implementation

[0028] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments.

[0029] like Figures 1-4 As shown, the method for precise recharge of groundwater in multi-layered aquifers in over-extracted groundwater areas according to the present invention includes the following steps: Step S1: Conduct comprehensive hydrogeological exploration in the target over-extraction area, employing various methods such as drilling, geophysical exploration, pumping tests, and tracer tests to thoroughly investigate the spatial distribution, lithological characteristics, thickness, permeability coefficient, hydraulic conductivity, water storage coefficient, and groundwater dynamic conditions of each aquifer. The focus is on investigating the heterogeneous characteristics of the aquifers, including fracture development patterns, pore distribution characteristics, and the location and orientation of dominant seepage channels. Based on the exploration results, and comprehensively considering factors such as the distribution of groundwater funnel areas, water source conditions, topography, transportation conditions, and environmental protection requirements, scientifically determine the well locations, well spacing, well depths, well diameters, and well casing structural parameters of the recharge well group.

[0030] Step S2: An integrated monitoring array is deployed axially along the inner wall of each reinjection well casing. This integrated monitoring array consists of distributed fiber optic grating sensing units and acoustic emission sensing units, arranged at equal intervals along the well casing axis. The distributed fiber optic grating sensing units integrate sensors for water level, water pressure, water temperature, and conductivity, enabling real-time acquisition of conventional hydrogeological parameters of each aquifer. The acoustic emission sensing units consist of multiple high-sensitivity acoustic emission sensors, capable of capturing elastic wave signals released during the generation and expansion of micro-fractures within the aquifer. Through signal analysis and location algorithms, the location, size, and activity status of the fractures are determined. The integrated monitoring array has advantages such as resistance to electromagnetic interference, corrosion resistance, long lifespan, high measurement accuracy, and the ability to achieve distributed continuous monitoring, enabling a comprehensive understanding of the dynamic changes of the aquifer during reinjection.

[0031] Step S3: Install a layered packer system in the reinjection well. This system includes multiple independently expandable rubber packers, the number of which is determined by the number of aquifers. Adjacent packers form independent reinjection sections, each corresponding to a single aquifer. Each reinjection section is equipped with an independent electromagnetic flow control valve, a high-precision pressure sensor, and a magnetohydrodynamic injection interface. The rubber packers are made of acid- and alkali-resistant, aging-resistant butyl rubber, with a working pressure of 0.5-6 MPa. Their expansion diameter can be automatically adjusted according to the well casing inner diameter, effectively sealing between reinjection sections and preventing cross-contamination.

[0032] Step S4: Inject biodegradable biogel into the target aquifer to temporarily block the dominant seepage channels within the aquifer. The biodegradable biogel is prepared using a starch-based modified material, exhibiting excellent injectability and sealing performance. Before injection, the location and size of the dominant seepage channels are determined based on hydrogeological survey results and tracer test data, and the injection volume and parameters of the biogel are calculated. During injection, pressure changes in the aquifer are monitored in real time using an integrated monitoring array to ensure accurate entry of the biogel into the dominant seepage channels. After injection, the biogel forms a gel body within the dominant seepage channels, temporarily blocking high-permeability areas and forcing subsequently injected recharge water to diffuse towards low-permeability areas, thereby achieving uniform recharge within the aquifer. The biogel gradually degrades in the underground environment, with a degradation cycle of 30-90 days. The degradation products are carbon dioxide and water, which will not cause secondary pollution to groundwater.

[0033] Step S5: Construct a regional multi-layered aquifer digital twin platform. Based on high-precision hydrogeological survey data, a three-dimensional multiphysics coupled numerical model is established using the finite element method. The model has a grid resolution of 1-5m and a time step of 1-12h. This model can simultaneously simulate groundwater flow, solute transport, soil and rock deformation, and biochemical reaction processes, accurately predicting groundwater transport patterns, solute diffusion ranges, and land subsidence trends under different recharge conditions. Real-time monitoring data collected by an integrated monitoring array, meteorological and hydrological data, and recharge system operation data are input into the model to achieve dynamic updates and real-time calibration, improving simulation accuracy and prediction reliability. The digital twin platform also has a visualization function, which can intuitively present the regional groundwater flow field, water quality distribution, and land subsidence.

[0034] Step S6: Based on the simulation results of the digital twin platform, formulate a regional well group coordinated reinjection scheme. Taking into account the over-extraction degree, permeability coefficient, allowable recharge, water quantity and quality conditions of the reinjection water source, and the hydraulic interaction between the reinjection wells, determine the initial reinjection pressure and flow rate for each reinjection section of each well. The reinjection water first undergoes pretreatment processes such as a screen, sedimentation tank, quartz sand filter, and ultraviolet sterilizer to remove suspended solids, bacteria, and other pollutants. The pretreated reinjection water meets the requirements of Class III water in the "Groundwater Quality Standard" (GB / T 14848-2017). Then, the pretreated reinjection water is injected into the corresponding aquifer through electromagnetic flow regulating valves and pressure sensors in each reinjection section. For aquifers with poor permeability, magnetic fluid is injected through a magnetic fluid injection interface as needed to improve the pore connectivity of the aquifer and increase reinjection efficiency.

[0035] Step S7: During the reinjection process, the integrated monitoring array collects real-time data on water level, pressure, temperature, conductivity, and acoustic emission signals of each aquifer, and transmits the data to the regional digital twin platform. The platform dynamically updates the simulation results based on the real-time data, predicts the future trend and potential risks of groundwater changes, and automatically generates an optimized reinjection plan. The reinjection pressure and flow rate of each reinjection section are adjusted in real-time by remotely controlling the electromagnetic flow regulating valves of each reinjection well. Simultaneously, the injection volume and location of the magnetohydrodynamic fluid are dynamically adjusted according to changes in the aquifer's permeability. The reinjection pressure of each aquifer is controlled between 0.8 and 1.2 times the hydrostatic pressure of that aquifer to avoid ground heave, aquifer rupture, or cross-contamination. Through coordinated control of the well group, the uniform rise of the regional groundwater level and effective control of ground subsidence are achieved.

[0036] Step S8: Periodically perform pulsed gas-liquid-solid three-phase alternating backflushing on each reinjection section to remove blockages from the well wall, filter layer, and aquifer pores. The backflushing cycle is determined based on the degree of blockage in each reinjection section. The backflushing procedure is initiated when the flow rate attenuation rate of the reinjection section reaches 15%-25%. The specific process of pulsed gas-liquid-solid three-phase alternating backflushing is as follows: First, high-pressure air is injected into the reinjection section to loosen the blockages on the well wall and filter layer surface using the impact force of the high-pressure air; then, a high-speed water flow containing quartz sand particles is rapidly injected to remove deep blockages inside the aquifer using the grinding action of the quartz sand particles and the shearing force of the high-speed water flow; finally, clean water is injected to flush out the dislodged blockages from the reinjection well. Repeat the above process 2-4 times to complete one backflushing. Simultaneously, microbial fuel cell units are implanted in the filter layer of each reinjection section. This unit consists of an anode, a cathode, and a proton exchange membrane. The anode surface is loaded with electrogenic microorganisms that can utilize the organic matter in the recharge water as nutrients to carry out metabolic activities and generate electricity. The generated electricity can not only drive the integrated monitoring array, electromagnetic flow control valve, and magnetohydrodynamic injection equipment to achieve self-powering of the system, but also promote the metabolic activities of microorganisms, degrade organic matter and other pollutants in the recharge water, and achieve in-situ purification of the recharge water.

[0037] Step S9: Establish a comprehensive evaluation system for recharge effectiveness and conduct regular comprehensive assessments of the recharge effect. Evaluation indicators include the rate of groundwater level rise, the rate of reduction in the groundwater funnel area, the groundwater quality compliance rate, the rate of reduction in land subsidence rate, recharge efficiency, and ecosystem restoration status. Based on the evaluation results, continuously optimize the recharge plan and operating parameters to continuously improve the recharge effect and system operating efficiency.

[0038] Example 1: A low-permeability multi-layered aquifer recharge project in the North China Plain. This example is located in a typical groundwater over-extraction area in the North China Plain. Due to long-term over-extraction of deep groundwater, the shallow, intermediate, and deep aquifers have all experienced varying degrees of over-extraction. The shallow aquifer has a depth of 5-25m, with lithology mainly consisting of silt and silty sand, and a permeability coefficient of 1-3m / d. The intermediate aquifer has a depth of 40-80m, with lithology mainly consisting of fine and medium sand, and a permeability coefficient of 5-10m / d. The deep aquifer has a depth of 100-160m, with lithology mainly consisting of medium and coarse sand, and a permeability coefficient of 8-15m / d. Thick clay layers are distributed between each aquifer, resulting in weak hydraulic connection. The groundwater level drop rates are 0.5m / year, 1.0m / year, and 1.5m / year, respectively, forming three independent groundwater funnel zones.

[0039] This embodiment employs the precise recharge method for multi-layer aquifers in groundwater over-extraction areas described in this invention. The specific implementation steps are as follows: Step S1: A detailed comprehensive hydrogeological survey was conducted in the target area, involving 15 boreholes with a total drilling depth of 2500m, 8 pumping tests, and 3 tracer tests. The survey clarified the spatial distribution, lithological characteristics, and groundwater dynamics of the three aquifers, with a focus on investigating the heterogeneity of each aquifer and the distribution of dominant seepage channels. Based on the survey results, three recharge wells were determined to be installed at the center of the groundwater funnel area, with a well spacing of 800m, a well depth of 180m, and a well diameter of 300mm, using steel pipes for the well casing.

[0040] Step S2: An integrated monitoring array is installed axially along the inner wall of the well casing of each reinjection well, with a spacing of 1m. Sensing units are installed in the shallow aquifer (5-25m), intermediate aquifer (40-80m), and deep aquifer (100-160m) layers. Each sensing unit integrates a distributed fiber Bragg grating sensor and an acoustic emission sensor. The distributed fiber Bragg grating sensor has measurement accuracies of ±0.5mm for water level, ±0.005MPa for water pressure, ±0.05℃ for water temperature, and ±0.5μS / cm for conductivity. The acoustic emission sensor has a sampling frequency of 200kHz and a positioning accuracy of 0.3m.

[0041] Step S3: Install a layered packer system in each reinjection well, with a total of four rubber packers. The first packer is located at 25-30m, the second at 35-40m, the third at 80-85m, and the fourth at 160-165m. Three independent reinjection sections are formed between adjacent packers, corresponding to the shallow, intermediate, and deep aquifers, respectively. Each reinjection section is equipped with an independent electromagnetic flow control valve, a high-precision pressure sensor, and a magnetohydrodynamic injection interface. The rubber packers are made of butyl rubber, operate at a pressure of 4MPa, and have an automatically adjustable expansion diameter between 280-320mm, providing excellent sealing performance.

[0042] Step S4: Inject biodegradable biogel into each aquifer to seal the dominant seepage channels. Based on the tracer test results, determine the location and size of the dominant seepage channels in each aquifer, and calculate the injection volume and parameters of the biogel. The biogel is prepared using a starch-based modified material with a gel strength of 0.2 MPa and a degradation period of 60 days. During injection, pressure changes in the aquifer are monitored in real time using an integrated monitoring array to ensure that the biogel accurately enters the dominant seepage channels. After injection, allow it to stand for 24 hours until the biogel has completely solidified before recharge.

[0043] Step S5: Construct a digital twin platform for the multi-layered aquifers in this area. The model has a grid resolution of 2m and a time step of 2h. The model is input with hydrogeological survey data, historical groundwater monitoring data, meteorological data, and recharge system design parameters. It can simultaneously simulate groundwater flow, solute transport, and land subsidence processes in three aquifers. The platform has visualization capabilities, enabling real-time display of the regional groundwater flow field and land subsidence.

[0044] Step S6: Based on the simulation results from the digital twin platform, formulate a coordinated reinjection scheme for the well cluster. The initial reinjection pressure for the shallow aquifer is 0.15 MPa, and the initial reinjection flow rate is 30 m³ / h. 3 / d; The initial reinjection pressure of the middle aquifer is 0.4 MPa, and the initial reinjection flow rate is 80 m³ / d. 3 / d; The initial reinjection pressure of the deep aquifer is 0.7 MPa, and the initial reinjection flow rate is 120 m³ / d. 3 / d. Due to the poor permeability of shallow aquifers, magnetic fluid is injected into the recharge section of the shallow aquifer. The magnetic fluid is prepared using nano-iron oxide particles with a particle diameter of 20 nm and an injection concentration of 1 g / L. The recharge water uses local surface water, which is pretreated through a screen, sedimentation tank, quartz sand filter, and ultraviolet sterilizer. The pretreated recharge water meets the requirements of Class III water in the "Groundwater Quality Standard" (GB / T 14848-2017).

[0045] Step S7: During the reinjection process, the integrated monitoring array collects dynamic parameters of each aquifer in real time and transmits the data to the digital twin platform. The platform updates the simulation results every 2 hours and automatically adjusts the reinjection pressure and flow rate of each reinjection section in each reinjection well based on real-time changes in water level, water pressure, and acoustic emission signals. For example, when the water level rise rate of a deep aquifer in a certain reinjection well exceeds 0.12 m / d, the platform automatically reduces the reinjection flow rate of that section to 100 m³ / d. 3 / d; When uneven water level rise in shallow aquifers is detected, the platform automatically adjusts the injection volume of magnetofluid to improve the aquifer's permeability. The reinjection pressure of each aquifer is always controlled between 0.9 and 1.1 times the hydrostatic pressure of that aquifer, effectively avoiding ground heave and cross-contamination.

[0046] Step S8: Periodically perform pulsed gas-liquid-solid three-phase alternating backwashing on each reinjection section. When the flow rate attenuation rate of the reinjection section reaches 20%, the backwashing procedure is initiated. The backwashing process is as follows: First, high-pressure air is injected into the reinjection section at a pressure of 0.5 MPa for 10 minutes; then, a high-speed water flow containing 0.2 mm quartz sand particles is rapidly injected at a flow rate four times the normal reinjection flow rate for 20 minutes; finally, clean water is injected for rinsing for 8 minutes; the above process is repeated three times to complete one backwash. Simultaneously, microbial fuel cell units are implanted in the filter layer of each reinjection section. Each unit consists of 12 sets of anodes and cathodes, with the anode surface loaded with electrogenic microorganisms such as Shewanella and Geobacterium. Operational results show that the microbial fuel cell unit can effectively degrade organic matter in the reinjection water, achieving a COD removal rate of over 65%. Simultaneously, the generated electricity can meet the power requirements of the integrated monitoring array, electromagnetic flow control valve, and magnetohydrodynamic injection equipment, realizing the system's self-powered operation.

[0047] Step S9: Establish a comprehensive evaluation system for the reinjection effect, and evaluate the reinjection effect monthly. The evaluation results show that after 8 months of reinjection, the water level of the shallow aquifer rose by an average of 2.8m, the water level of the middle aquifer rose by an average of 4.5m, and the water level of the deep aquifer rose by an average of 6.2m. The areas of the three groundwater funnel zones shrank by 22%, 28%, and 35%, respectively. The land subsidence rate decreased by 65%, and the groundwater quality remained stable without any deterioration.

[0048] Comparative Example 1: Using a traditional reinjection method, three reinjection wells with identical parameters were deployed in the same area. No biogel temporary plugging, magnetohydrodynamic enhancement, or well group coordinated control system was implemented. Fixed reinjection pressure and flow rate were used. After 8 months of operation, the water level in the shallow aquifer rose by an average of 1.1m, the water level in the middle aquifer rose by an average of 2.2m, and the water level in the deep aquifer rose by an average of 3.1m. The areas of the three groundwater funnel zones shrank by 8%, 12%, and 15%, respectively, and the land subsidence rate decreased by 30%. However, because the reinjection water preferentially flows along the dominant seepage channels, the recharge within the aquifer was severely uneven, with water levels in some low-permeability areas barely rising. Furthermore, the flow rate attenuation rate of the reinjection wells reached 55%, requiring frequent backflushing and resulting in high operating costs.

[0049] The comparison shows that the method described in this invention is significantly superior to traditional reinjection methods in terms of improving reinjection efficiency, achieving uniform replenishment, and extending the service life of reinjection wells.

[0050] Example 2: A multi-layered aquifer recharge project in a karst region of Southwest China. This example is located in a groundwater over-extraction area in a karst region of Southwest China. The aquifers in this area are mainly karst aquifers and fissure aquifers. The upper karst aquifer is buried at a depth of 10-50m, with limestone as the lithology. Karst development is strong, with numerous caves and underground rivers, and a permeability coefficient of 50-200m / d. The lower fissure aquifer is buried at a depth of 70-130m, with sandstone as the lithology. Fissure development is moderate, and a permeability coefficient of 10-30m / d. Due to extensive groundwater extraction for local industrial and agricultural production and residential use, the water levels of both aquifers have dropped significantly, leading to problems such as spring drying up, karst collapse, and degradation of surface vegetation in some areas.

[0051] This embodiment employs the precise recharge method for multi-layer aquifers in groundwater over-extraction areas described in this invention. The specific implementation steps are as follows: Step S1: Conduct comprehensive hydrogeological surveys in the target area, employing various methods such as drilling, geophysical exploration, tracer tests, and underground river detection to thoroughly investigate the spatial distribution of karst aquifers and fissure aquifers, karst development characteristics, fissure distribution patterns, and groundwater flow direction. The distribution and direction of underground rivers, as well as the hydraulic connections between karst conduits and fissures, were investigated in detail. Based on the survey results, four recharge wells were selected for placement in a location with relatively uniform karst development and upstream of the underground river. The well spacing is 600m, the well depth is 150m, and the well diameter is 350mm. The well casings are made of fiberglass to prevent corrosion.

[0052] Step S2: An integrated monitoring array is installed axially along the inner wall of each reinjection well casing at 0.8m intervals. Sensing units are installed in the upper karst aquifer (10-50m) and the lower fractured aquifer (70-130m). Each sensing unit integrates sensors for water level, water pressure, water temperature, and conductivity, as well as a flow sensor to monitor the internal flow velocity of the aquifer. Acoustic emission sensors are used to monitor the activity of the karst roof and fractures, providing timely warnings of karst collapse risks.

[0053] Step S3: Install a layered packer system in each reinjection well, with a total of three rubber packers. The first packer is located at 50-55m, the second at 65-70m, and the third at 130-135m. Two independent reinjection sections are formed between adjacent packers, corresponding to the upper karst aquifer and the lower fractured aquifer, respectively. Each reinjection section is equipped with an independent flow regulating valve, pressure sensor, and magnetohydrodynamic injection interface. Multiple jet nozzles are installed in the reinjection section of the karst aquifer to improve the diffusion effect of the reinjection water within the karst conduit.

[0054] Step S4: Inject biodegradable biogel into the upper karst aquifer to seal large underground river channels. Because numerous underground river channels exist within the karst aquifer, the injected recharge water will rapidly drain away, failing to effectively replenish the aquifer. Based on tracer test results, the location and scale of the main underground river channels are determined, and the injection volume and parameters of the biogel are calculated. The biogel has a gel strength of 0.3 MPa and a degradation period of 90 days. During injection, an integrated monitoring array is used to monitor aquifer pressure changes in real time, ensuring that the biogel accurately seals the entrances of the underground river channels, forcing the recharge water to diffuse into surrounding karst fissures and small caves.

[0055] Step S5: Construct a digital twin platform for the multi-layered aquifers in this region. Considering the characteristics of karst and fractured aquifers, a combination of discrete fracture network models and equivalent continuous medium models is used for numerical simulation. The model has a grid resolution of 3m and a time step of 3h, accurately simulating the migration patterns of reinjection water in karst conduits and fractures, as well as the stability changes of the karst roof.

[0056] Step S6: Based on the simulation results from the digital twin platform, formulate a coordinated reinjection scheme for the well group. The initial reinjection pressure of the upper karst aquifer is 0.25 MPa, and the initial reinjection flow rate is 200 m³ / h. 3 / d; The initial reinjection pressure of the lower fractured aquifer is 0.5 MPa, and the initial reinjection flow rate is 100 m³ / d. 3 / d. Recharge water is sourced from local reservoirs and pretreated before being injected into the ground. For areas with poor permeability in the lower-level fractured aquifers, magnetofluid is injected appropriately to improve fracture connectivity.

[0057] Step S7: During the reinjection process, the integrated monitoring array collects dynamic parameters of the two aquifers in real time, including water level, water pressure, water temperature, conductivity, internal flow velocity, and acoustic emission signals. The digital twin platform dynamically adjusts the reinjection plan based on the real-time data. For example, when the flow velocity in a certain area of ​​the karst aquifer is detected to be too fast, the platform automatically reduces the reinjection pressure of that section to prevent rapid loss of reinjection water; when abnormal acoustic emission signals are detected on the karst roof, the platform immediately issues an early warning and adjusts the reinjection pressure to prevent karst collapse.

[0058] Step S8: Periodically perform pulsed gas-liquid-solid three-phase alternating backwashing on both reinjection sections. Since the blockage of karst aquifers is mainly caused by sediment deposition, the backwashing pressure and flow rate are appropriately increased. The backwashing process is as follows: First, inject high-pressure air into the reinjection section at a pressure of 0.6 MPa for 12 minutes; then, rapidly inject a high-speed water flow containing 0.25 mm quartz sand particles at a flow rate 5 times the normal reinjection flow rate for 25 minutes; finally, inject clean water for 10 minutes; repeat the above process twice to complete one backwash. Simultaneously, implant a microbial fuel cell unit in the filter layer to purify the reinjection water in situ, preventing microbial growth and blockage in the karst pipes.

[0059] Step S9: Establish a comprehensive evaluation system for the recharge effect, and evaluate the recharge effect quarterly. The evaluation results show that after 12 months of recharge, the water level of the upper karst aquifer rose by an average of 5.8m, the water level of the lower fissure aquifer rose by an average of 4.2m, dried-up springs began to flow again, the frequency of karst collapse decreased by 85%, and the surface vegetation coverage increased by 15%, achieving good ecological and economic benefits.

[0060] Comparative Example 2: Using a traditional non-plugging recharge method, four recharge wells with identical parameters were deployed in the same area. No biogel temporary plugging or well group coordinated control system was implemented, and fixed recharge pressure and flow rate were used. After 12 months of operation, the water level in the upper karst aquifer rose by an average of 2.3m, and the water level in the lower fissure aquifer rose by an average of 1.8m. The dried-up springs did not re-emerge, and the frequency of karst collapses decreased by only 25%. Simultaneously, due to the large amount of recharged water flowing into underground river pipes and rapidly flowing away, the recharge efficiency was extremely low, resulting in serious water waste. Furthermore, the recharge wells suffered from severe clogging, with a flow rate attenuation rate reaching 60%, leading to unsatisfactory recharge results.

[0061] The comparison shows that the method described in this invention can effectively solve the problems of rapid water loss and uneven replenishment in karst areas, significantly improve the recharge effect, and effectively prevent the risk of karst collapse.

[0062] Example 3: Recharge Project of a Multi-Layer Confined Aquifer in an Arid Northwest Region. This example is located in an inland basin in the arid Northwest region. The area has an arid climate with scarce rainfall and high evaporation rates, making groundwater the only water source. Due to long-term over-exploitation, severe over-extraction has occurred in multiple confined aquifers. The first confined aquifer has a depth of 30-70m, the second 90-150m, and the third 170-250m. Stable impermeable layers exist between the aquifers, resulting in weak hydraulic connections. The groundwater level has dropped at rates of 1.2m / year, 1.8m / year, and 2.5m / year, respectively, forming large-scale deep groundwater funnel zones and causing severe land subsidence and ground fissures.

[0063] This embodiment employs the precise recharge method for multi-layer aquifers in groundwater over-extraction areas described in this invention. It replenishes groundwater reserves, restores groundwater levels, and curbs land subsidence by artificially diverting surface water for recharge. The specific implementation steps are as follows: Step S1: A detailed comprehensive hydrogeological survey was conducted in the target area, involving 20 boreholes with a total drilling depth of 5000m and 12 pumping tests. The spatial distribution, lithological characteristics, thickness, permeability coefficient, and distribution of the impermeable layers of the three confined aquifers were thoroughly investigated. Based on the survey results, five recharge wells were selected to be installed at the center of the groundwater funnel area, with a well spacing of 1000m, a well depth of 280m, and a well diameter of 350mm. The well casings were made of high-strength steel.

[0064] Step S2: An integrated monitoring array is installed axially along the inner wall of each reinjection well casing, with a spacing of 1.2m. Sensing units are installed in each of the three confined aquifers to monitor water level and pressure changes, as well as deformation of the impermeable layer. Acoustic emission sensors are used to monitor ground fissure activity and provide timely warnings of geological disaster risks.

[0065] Step S3: Install a layered packer system in each reinjection well, consisting of five rubber packers located at 70-75m, 85-90m, 150-155m, 165-170m, and 250-255m respectively. Three independent reinjection sections are formed between adjacent packers, corresponding to three confined aquifers. Each reinjection section is equipped with an independent flow regulating valve, pressure sensor, and magnetohydrodynamic injection interface. The rubber packers are made of high-pressure resistant butyl rubber, with a working pressure of 6MPa, capable of withstanding the high water pressure of deep aquifers.

[0066] Step S4: Inject biodegradable biogel into each confined aquifer to seal the dominant seepage channels. Due to the strong heterogeneity of confined aquifers, multiple high-permeability zones exist. After recharge water is injected, it preferentially flows along the high-permeability zones, resulting in uneven recharge within the aquifer. Based on the results of pumping tests and tracer tests, the location and scale of the high-permeability zones within each aquifer are determined, and the injection volume and parameters of the biogel are calculated. The gel strength of the biogel is 0.4 MPa, and the degradation period is 60 days.

[0067] Step S5: Construct a digital twin platform for the multi-layer aquifers in this area. The model has a grid resolution of 5m and a time step of 6h. The model focuses on simulating groundwater flow and land subsidence processes, and can accurately predict the changing trends of land subsidence and the activity of ground fissures under different recharge conditions. The platform integrates a GIS system, enabling visualized management and decision support for recharge projects.

[0068] Step S6: Based on the simulation results of the digital twin platform, formulate a coordinated reinjection scheme for the well group. The initial reinjection pressure of the first confined aquifer is 0.3 MPa, and the initial reinjection flow rate is 60 m³ / s. 3 / d; The initial reinjection pressure of the second confined aquifer is 0.6 MPa, and the initial reinjection flow rate is 120 m³ / d. 3 / d; The initial reinjection pressure of the third confined aquifer is 1.0 MPa, and the initial reinjection flow rate is 180 m³ / d. 3 / d. The reinjection water uses diverted water from the Yellow River, which is injected underground after strict pretreatment. For the second and third confined aquifers with poor permeability, magnetofluid is injected appropriately to improve the reinjection efficiency.

[0069] Step S7: During the reinjection process, the integrated monitoring array collects dynamic parameters of each aquifer in real time and transmits the data to the digital twin platform. The platform dynamically adjusts the reinjection pressure and flow rate of each reinjection well based on the real-time data to ensure a uniform rise in the regional groundwater level and prevent ground heave or the expansion of ground fissures due to excessively rapid water level rise. Simultaneously, the platform monitors the activity of ground fissures in real time; if any abnormalities are detected, the reinjection plan is immediately adjusted to ensure project safety.

[0070] Step S8: Regularly perform pulsed gas-liquid-solid three-phase alternating backwashing on each reinjection section. The backwashing cycle is 4 months. The backwashing process is as follows: First, inject high-pressure air into the reinjection section at a pressure of 0.7 MPa for 15 minutes; then, rapidly inject a high-speed water flow containing 0.3 mm quartz sand particles at a flow rate 5 times the normal reinjection flow rate for 30 minutes; finally, inject clean water for 10 minutes. Repeat the above process 3 times to complete one backwashing. Simultaneously, implant a microbial fuel cell unit in the filter layer to purify the reinjection water in situ, preventing pollutants carried by the reinjection water from entering the deep aquifer.

[0071] Step S9: Establish a comprehensive evaluation system for the reinjection effect, and conduct a comprehensive evaluation of the reinjection effect every six months. The evaluation results show that after 18 months of reinjection, the water level of the first confined aquifer rose by an average of 5.2m, the water level of the second confined aquifer rose by an average of 7.8m, and the water level of the third confined aquifer rose by an average of 10.5m. The area of ​​the groundwater funnel zone shrank by 40%, the ground subsidence rate decreased by 75%, and the activity of ground fissures was significantly reduced, achieving remarkable treatment results.

[0072] Comparative Example 3: Using the traditional single-well independent reinjection method, five reinjection wells with identical parameters were deployed in the same area. No biogel temporary plugging, magnetohydrodynamic enhancement, or well group coordinated control system was implemented. Fixed reinjection pressure and flow rate were used. After 18 months of operation, the water level in the first confined aquifer rose by an average of 2.1m, the second confined aquifer by an average of 3.5m, and the third confined aquifer by an average of 4.8m. The area of ​​the groundwater funnel zone only shrank by 15%, and the land subsidence rate decreased by 35%. However, due to the lack of coordinated control among the reinjection wells, the regional groundwater level distribution was severely uneven, with localized ground heave occurring in some areas, and ground fissure activity was not effectively controlled. Furthermore, the flow rate attenuation rate of the reinjection wells reached 50%, resulting in high operating costs.

[0073] The comparison shows that the method described in this invention can achieve coordinated and precise recharge of multiple confined aquifers in a region, effectively control ground subsidence and ground fissure activity, and is an effective means to address the problem of over-extraction of deep groundwater in the arid Northwest region.

[0074] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of protection claimed by the present invention. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for precise recharge of groundwater from multiple aquifers in over-extracted groundwater areas, characterized in that, Includes the following steps: Step S1: Conduct comprehensive hydrogeological surveys in the target over-extraction area to ascertain the spatial distribution, lithological characteristics, permeability coefficient, and fracture development patterns of each aquifer, and determine the well locations, depths, and structural parameters of the recharge well group; Step S2: An integrated monitoring array is installed along the axial direction on the inner wall of the well pipe of each reinjection well. The integrated monitoring array includes a distributed fiber optic grating sensing unit and an acoustic emission sensing unit, which are used to collect water level, water pressure, water temperature, water quality parameters and fracture activity signals of each aquifer, respectively. Step S3: Install a layered isolation system in the recharge well to divide the recharge well into independent recharge sections corresponding to each aquifer. Each recharge section is equipped with an independent flow regulating valve, pressure sensor and magnetohydrodynamic injection interface. Step S4: Inject biodegradable biogel into the target aquifer to temporarily block the dominant seepage channels within the aquifer, forcing the reinjected water to diffuse into low-permeability areas, thereby achieving uniform replenishment within the aquifer. Step S5: Construct a regional multi-layer aquifer digital twin platform, integrating hydrogeological survey data, real-time monitoring data, and meteorological and hydrological data to simulate groundwater migration, solute diffusion, and land subsidence processes under different recharge conditions; Step S6: Based on the simulation results of the digital twin platform, formulate a well group coordinated reinjection scheme, inject pretreated reinjection water into the corresponding aquifer through the flow regulating valve of each reinjection section, and at the same time inject magnetic fluid to enhance the aquifer permeability as needed. Step S7: During the reinjection process, the integrated monitoring array collects the dynamic parameters of each aquifer in real time and transmits them to the digital twin platform. The platform dynamically updates the simulation results based on the real-time data and automatically adjusts the reinjection pressure, flow rate and magnetohydrodynamic injection volume of each reinjection well. Step S8: Periodically perform pulsed gas-liquid-solid three-phase alternating backwashing on each reinjection section to remove blockages in the well wall, filter layer and aquifer pores; at the same time, use the microbial fuel cell unit implanted in the filter layer to perform in-situ purification treatment on the reinjection water.

2. The method for precise recharge of multi-layer aquifers in groundwater over-extraction areas according to claim 1, characterized in that: In step S2, the acoustic emission sensing units are arranged at a spacing of 2-5m, with a sampling frequency of not less than 100kHz, and are able to identify the generation and expansion of micro-cracks in the aquifer, with a positioning accuracy of not less than 0.5m.

3. The method for precise recharge of multiple aquifers in groundwater over-extraction areas according to claim 1, characterized in that: In step S4, the biodegradable biogel is prepared using starch-based modified materials, with a gel strength of 0.1-0.5 MPa, a degradation cycle of 30-90 days, and degradation products of carbon dioxide and water, which will not cause secondary pollution to groundwater.

4. The method for precise recharge of multi-layer aquifers in groundwater over-extraction areas according to claim 1, characterized in that: In step S6, the magnetic fluid is prepared using nano-iron oxide particles with a diameter of 10-50 nm and an injection concentration of 0.5-2 g / L. After injection, the magnetic fluid is guided to distribute within the aquifer by an external magnetic field to improve pore connectivity.

5. The method for precise recharge of multi-layer aquifers in groundwater over-extraction areas according to claim 1, characterized in that: In step S5, the digital twin platform uses multi-physics coupling simulation technology to simultaneously simulate groundwater flow, solute transport, soil and rock deformation, and biochemical reaction processes, with a time step of 1-12 hours.

6. The method for precise recharge of multi-layer aquifers in groundwater over-extraction areas according to claim 1, characterized in that: In step S6, the pretreatment of the reinjection water includes screen, sedimentation, filtration and ultraviolet disinfection. The quality of the pretreated reinjection water meets the requirements of Class III water in the "Groundwater Quality Standard".

7. The method for precise recharge of groundwater in multi-layered aquifers in over-extracted groundwater areas according to claim 1, characterized in that: In step S8, the specific process of pulsed gas-liquid-solid three-phase alternating backwashing is as follows: First, inject high-pressure air at a pressure of 0.4-0.9 MPa for 5-15 minutes. Then inject a high-speed water flow containing quartz sand particles with a particle size of 0.1-0.3mm, at a flow rate of 3-6 times the normal reinjection flow rate, for 10-30 minutes. Finally, rinse with clean water for 5-10 minutes; repeat the above process 2-4 times.

8. The method for precise recharge of multiple aquifers in groundwater over-extraction areas according to claim 1, characterized in that: In step S8, the electrical energy generated by the microbial fuel cell unit is used to drive the integrated monitoring array, flow regulating valve and magnetohydrodynamic injection device, and excess electrical energy is stored in the energy storage device.

9. The method for precise recharge of multiple aquifers in groundwater over-extraction areas according to claim 1, characterized in that: In step S8, the backwashing cycle is determined based on the flow rate attenuation rate of the reinjection section. When the flow rate attenuation rate reaches 15%-25%, the backwashing procedure is started.

10. The method for precise recharge of multi-layer aquifers in groundwater over-extraction areas according to claim 1, characterized in that: It also includes step S9: establishing a comprehensive evaluation system for the reinjection effect, regularly evaluating the water level recovery, water quality improvement, land subsidence control and ecological restoration effects of each aquifer, and continuously optimizing the reinjection plan based on the evaluation results.

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