Mine water recharge and permeation simulation method and test system

Abstract

The present application relates to coal mine water treatment and groundwater recharge technical field, specifically a kind of mine water recharge and increase infiltration simulation method and test system, the method includes: preparation of rock core sample and simulation mine water, set formation temperature and recharge water temperature to simulate initial temperature difference working condition;Calibration initial permeability;Simulate mine water recharge and plug evolution process, record the permeability after plugging;One or more permeability increasing treatments are performed on the plugged rock core: step-by-step pressurized hydraulic permeability increasing, pulse high pressure physical permeability increasing, chemical acid cleaning and scale removal permeability increasing, test the permeability after permeability increasing;Calculate the permeability recovery rate and permeability increasing rate, and quantitatively evaluate the permeability increasing effect;Data analysis and mechanism summary.The present application also discloses a test system for implementing the method.The present application can reproduce the real working conditions of mine water recharge, plugging attenuation and multi-method permeability increasing in laboratory, and provide reliable test basis for field recharge and permeability increasing engineering design.

Description

Technical Field

[0001] This invention relates to the field of coal mine water treatment and groundwater recharge technology, specifically a simulation method and experimental system for mine water recharge and infiltration enhancement. Background Technology

[0002] During coal mining, to ensure mining safety, large amounts of groundwater need to be drained, leading to a drop in the groundwater level in the mining area, forming regional drawdown cones, and causing groundwater resource loss and ecological and environmental problems. Reinjecting treated mine water into underground aquifers is a key technical means to achieve zero mine water discharge, replenish groundwater, and restore the ecology of the mining area.

[0003] However, during mine water reinjection, the presence of suspended solids, calcium and magnesium ions, and bicarbonate ions in the water easily leads to physical, chemical, and biological complex blockages in the pores and fractures of the aquifer. This causes a rapid decline in the permeability of the reinjection well and a continuous decrease in the reinjection flow rate, severely affecting the long-term stability of the reinjection project. On-site methods such as hydraulic pressurization, pulse fracturing, and chemical well washing are commonly used to enhance permeability. However, the design of these methods currently relies heavily on experience, lacks systematic laboratory experimental data support, and has unclear permeability enhancement mechanisms, resulting in problems such as poor permeability enhancement effects or resource waste.

[0004] Existing indoor reinjection simulation test technologies are mostly limited to simulating a single reinjection seepage process, and cannot simultaneously simulate the evolution of blockage and the subsequent composite infiltration process. It is difficult to quantitatively evaluate the effects and recovery patterns of different infiltration methods, resulting in limited guidance of indoor research results for field engineering. Summary of the Invention

[0005] The purpose of this invention is to provide a method and test system for simulating mine water reinjection and infiltration enhancement, so as to solve the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution.

[0007] A method for simulating mine water reinjection and infiltration enhancement includes the following steps: S1, test preparation: collect undisturbed rock cores from the aquifer in the mine area, process them into standard rock core samples, and prepare simulated mine water; load the rock core samples into a triaxial seepage holder, apply in-situ geostress, and set the formation temperature and reinjection water temperature through a temperature control auxiliary unit to simulate the initial temperature difference condition.

[0008] S2. Initial parameter calibration: Simulated mine water was injected into the core sample to replicate the temperature difference conditions. Clean groundwater was used to conduct a steady-state seepage test to determine the initial stable permeability k0 of the core sample.

[0009] S3. Plugging Evolution Simulation: Simulated mine water is continuously injected into the core sample for steady-state reinjection, and the permeability change is monitored in real time until the permeability of the core sample stabilizes and decays, forming a stable clogging state. The permeability k1 after clogging is recorded.

[0010] S4. Staged composite permeation simulation: Maintaining dynamic temperature evolution conditions, for core samples in a stable blockage state, perform one or more of the following permeation enhancement treatments: staged pressurized hydraulic permeation, pulsed high-pressure physical permeation, and chemical acid washing and descaling permeation; after each permeation enhancement treatment is completed, restore steady-state reinjection and test the corresponding stable permeability k2.

[0011] S5. Evaluation of Infiltration Enhancement Effect: Based on k0, k1 and k2, calculate the permeability recovery rate and infiltration ratio of each infiltration enhancement treatment to quantitatively evaluate the infiltration enhancement effect.

[0012] S6. Data Analysis: Organize experimental data, analyze the clogging mechanism and the permeation mechanism of each permeation enhancement treatment, and summarize the permeation enhancement process parameters.

[0013] As a further aspect of the present invention: in step S1, the formation temperature is higher than the reinjection water temperature to simulate the temperature difference condition of cold water being injected into a hot formation.

[0014] As a further aspect of the present invention: in step S3, the real-time monitoring includes monitoring at least one of the following: reinjection pressure, reinjection flow rate, effluent water quality, and temperature dynamic changes.

[0015] As a further aspect of the present invention: in step S3, the criterion for determining the stable decay of the permeability is: the permeability fluctuation does not exceed 3% and lasts for more than 1 hour.

[0016] As a further aspect of the present invention: in step S4, the stepwise pressurization hydraulic permeation enhancement adopts a graded pressurization and stabilization mode, with each pressure being lower than the rupture pressure of the core sample, and each stabilization time being 90-120 minutes.

[0017] As a further aspect of the present invention: In step S4, the pulsed high-pressure physical permeation enhancement adopts a periodic pulsating pressure with a frequency of 0.5-5Hz, the pulse peak pressure is higher than the steady-state reinjection pressure and lower than the rupture pressure of the core sample, and the pulse disturbance time is 30-180min.

[0018] As a further aspect of the present invention: In step S4, the chemical acid washing for descaling and penetration enhancement uses a corrosion-inhibiting hydrochloric acid descaling agent with a concentration of 5%-10%, and the injection amount is 2-3 times the pore volume of the rock core sample. After the sealed soaking reaction, it is rinsed with clean water.

[0019] As a further aspect of the present invention: in step S5, the calculation formulas for the permeability recovery rate η and the permeability enhancement ratio n are as follows: ; .

[0020] The present invention also proposes a mine water reinjection and infiltration simulation test system for realizing the mine water reinjection and infiltration simulation method as described above, comprising: a core clamping device for clamping the core sample and applying in-situ stress.

[0021] A mine water preparation system, connected to the core clamping device, is used to prepare and store simulated mine water.

[0022] The reinjection power system is connected between the mine water distribution system and the core clamping device to provide steady-state reinjection or pulsed reinjection power.

[0023] A chemical injection system, connected to the core clamping device, is used to inject chemical permeation-enhancing agents.

[0024] The temperature control auxiliary unit is connected to the core clamping device and the mine water dispensing system respectively, and is used to independently control the temperature of the core sample and the simulated mine water temperature.

[0025] The real-time monitoring system includes at least one pressure sensor, at least one flow sensor, at least one temperature sensor, and a data acquisition unit.

[0026] As a further aspect of the present invention: the reinjection power system includes a constant pressure and constant flow reinjection pump and a pulse booster system; the inlet of the constant pressure and constant flow reinjection pump is connected to a mine water distribution tank, and the outlet is connected to the inlet of the core clamping device via the pulse booster system.

[0027] Compared with the prior art, the beneficial effects of the present invention are: 1. Full process simulation: For the first time, the entire process of "mine water reinjection → medium blockage and attenuation → hydraulic / pulse / chemical composite infiltration" is completely simulated, filling the gap that existing indoor tests cannot simultaneously reproduce the entire process of reinjection and infiltration, and truly reproducing the on-site working conditions.

[0028] 2. Quantitative evaluation: By calculating the permeability recovery rate and permeability enhancement ratio, the permeability enhancement effects of different permeability enhancement methods can be quantitatively compared, the optimal permeability enhancement process parameters can be identified, and a scientific basis can be provided for on-site engineering design, avoiding the blind selection of permeability enhancement measures.

[0029] 3. Temperature difference simulation: By simulating the initial temperature difference condition of "cold water injection into hot formation" through the temperature control auxiliary unit, the dynamic evolution of temperature can be monitored in real time, which can reveal the coupling effect mechanism of temperature on blockage formation and permeability enhancement.

[0030] 4. High applicability: The test system is modularly designed, and the parameters can be flexibly adjusted according to the hydrogeological conditions and water quality differences in different mining areas. It is easy to operate, and the test process is standardized and repeatable, which has both engineering application value and academic research value. Attached Figure Description

[0031] Figure 1 This is a flowchart of the mine water reinjection and infiltration simulation method of the present invention.

[0032] Figure 2 This is a schematic diagram of the structure of the mine water reinjection and infiltration simulation test system of the present invention.

[0033] In the diagram: 1. Mine water mixing tank; 2. Agitator; 3. Constant pressure and constant flow reinjection pump; 4. Pulse booster system; 5. Chemical reagent storage tank; 6. Metering pump; 7. Triaxial seepage clamp; 8. Rock core sample; 9. Confining pressure loading device; 10. Axial pressure loading device; 11. Pressure sensor; 12. Flow sensor; 13. Data acquisition instrument; 14. Computer; 15. Drainage tank; 16. Temperature sensor; 17. Temperature control auxiliary unit. Detailed Implementation

[0034] The technical solution of this application will be further described in detail below with reference to specific embodiments.

[0035] The embodiments of this application are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this application, and should not be construed as limiting this application.

[0036] Example

[0037] This embodiment provides a method and test system for simulating mine water reinjection and infiltration enhancement, used to simulate the mine water reinjection and infiltration process at a depth of 300m in a coal mine.

[0038] I. Experimental System Setup.

[0039] As attached Figure 2 As shown, the test system used in this embodiment includes: a core clamping device: a triaxial flow clamp 7 is used to clamp the core sample 8. The triaxial flow clamp 7 is connected to the confining pressure loading device 9 and the axial pressure loading device 10 respectively to simulate in-situ in-situ stress.

[0040] Mine water preparation system: including mine water preparation tank 1 and agitator 2, used for preparing and storing simulated mine water.

[0041] The reinjection power system includes a constant pressure and constant flow reinjection pump 3 and a pulse booster system 4. The inlet of the constant pressure and constant flow reinjection pump 3 is connected to the mine water distribution tank 1, and the outlet is connected to the inlet of the triaxial seepage clamp 7 via the pulse booster system 4.

[0042] Chemical injection system: includes chemical storage tank 5 and metering pump 6. The outlet of metering pump 6 is connected to the inlet pipe of triaxial percolator 7 via a tee connector.

[0043] Temperature control auxiliary unit 17: It is connected to the triaxial seepage clamp 7 and the mine water dispensing tank 1 respectively, and is used to independently control the temperature of the rock core sample and the simulated mine water temperature.

[0044] The real-time monitoring system includes a pressure sensor 11 (installed at the inlet, outlet, and inside the core sample), a flow sensor 12 (installed in the inlet and outlet pipelines), a temperature sensor 16 (embedded inside the core sample 8 and installed in the inlet and outlet pipelines), an effluent water quality detection system, a data acquisition instrument 13, and a computer 14. All sensors are connected to the data acquisition instrument 13, which communicates with the computer 14.

[0045] Drainage system: The outlet of the triaxial seepage clamp 7 is connected to the drainage tank 15.

[0046] Before the test, check the sealing of all component connections; turn on the computer 14 and data acquisition instrument 13, and debug each monitoring module; turn on the temperature control auxiliary unit 17, heat the triaxial seepage clamp 7 to 50°C, and cool the simulated mine water in the mine water mixing tank 1 to 20°C.

[0047] II. Experimental Methods.

[0048] As attached Figure 1 As shown, a mine water reinjection and infiltration simulation method of the present invention includes the following steps: Step S1: Experiment preparation.

[0049] Uncirculated sandstone cores were collected from the target recharge layer and processed into standard cylindrical core samples (8) with a diameter of 50 mm and a length of 100 mm. Core sample 8 was dried at 105℃ and saturated under vacuum for 2-4 hours. Its initial porosity φ = 0.18 and initial permeability k0 = 2.5 × 10⁻⁶ were then measured. -14 m 2 Critical rock fracture pressure P cr =30MPa, effective stress in the rock core σ eff =15MPa, initial stress σ0=15MPa, mineral composition is mainly quartz and feldspar, with a small amount of carbonate cement.

[0050] Mine water was collected from the site, and simulated water samples were prepared according to water quality indicators. Key indicators are as follows: suspended solids (SS) concentration c SS =50g / m 3 Calcium ions [Ca 2+ =0.008 mol / L (320 mg / L), bicarbonate ions [HCO3] -The simulated mine water had a concentration of 0.015 mol / L (915 mg / L), pH 7.2, and mineralization of 1200 mg / L, consistent with the actual mine water quality. After preparation, the simulated mine water was allowed to stand for 24 hours to ensure its quality was identical to that of the actual mine water.

[0051] The saturated core sample 8 was loaded into the triaxial seepage holder 7, and an in-situ stress of 15 MPa was applied by the confining pressure loading device 9 and the axial pressure loading device 10. The prepared simulated mine water was injected into the mine water mixing tank 1, and the agitator 2 was turned on to stir evenly and set aside for later use. The chemical descaling agent of the preset concentration was injected into the chemical agent storage tank 5, the metering pump 6 was adjusted, and the injection volume and injection rate of the agent were set. The triaxial seepage holder 7 was set to the high temperature of the in-situ formation through the temperature control auxiliary unit 17, and the simulated mine water was set to the actual low temperature of the mine water in the field to simulate the initial temperature difference condition of "cold water injected into a hot formation".

[0052] The device is specifically configured as follows: Temperature control auxiliary unit 17: Set the initial high temperature of the formation T=323K (50℃), simulate the low temperature of mine water T=293K (20℃), and monitor the dynamic evolution of temperature throughout the process.

[0053] Reinjection power system: Constant pressure and constant flow reinjection pump 3. The set steady-state reinjection pressure is P0 = 2 MPa, and the reinjection flow velocity is v = 5.0 × 10⁻⁶. -6 m / s (corresponding to 0.3 mL / min); the pulse booster system 4 is set with a pulse frequency f = 2 Hz and a pulse peak pressure P peak =6MPa (lower than 0.8P) cr =24MPa).

[0054] Chemical reagent injection system: 5% corrosion-inhibiting hydrochloric acid descaling agent is selected, the injection volume is 2.5 times the pore volume of the rock core, and the soaking reaction time is 120 minutes.

[0055] Monitoring system: Records data for the clogging stage every 10 minutes and data for the permeation enhancement stage every 5 minutes, focusing on monitoring changes in permeability k(t), pressure, flow rate, temperature, and ion concentration.

[0056] Step S2: Initial parameter calibration.

[0057] Under in-situ stress (15 MPa) and temperature difference conditions, clean groundwater was introduced into core sample 8, and steady-state seepage tests were conducted using the clean groundwater. The initial stable permeability of the core sample was determined to be k0 = 2.5 × 10⁻⁶. -14 m 2 The initial seepage resistance is 0.8 MPa·s / cm, and the initial water absorption capacity is 0.015 cm³. 3 / s, as a benchmark for subsequent comparison of infiltration effects.

[0058] Specifically, the pipeline valves of the pulse booster system 4 and the chemical agent injection system are closed, the constant pressure and constant flow reinjection pump 3 is turned on, clean groundwater is introduced into the core sample 8, the temperature is maintained and the dynamic evolution of the chemical conditions is carried out, and a steady-state seepage test is conducted; the pressure, flow rate, temperature and permeability data are collected in real time by the data acquisition instrument 13, and after the seepage stabilizes, the initial parameters are recorded and the benchmark calibration is completed.

[0059] Step S3: Mine water reinjection blockage evolution simulation.

[0060] Close the clean groundwater passage and switch to the simulated mine water passage. Start the constant pressure and constant flow reinjection pump 3, using the actual on-site reinjection pressure (0-40MPa, which will be adjusted according to different working conditions; in this embodiment, it is 2MPa) and reinjection flow rate (0.1-0.5mL / min); in this embodiment, it is 0.3mL / min (corresponding to 5.0×10⁻⁶). -6 (m / s), continuously injecting low-temperature simulated mine water into the high-temperature rock core for long-term steady-state reinjection.

[0061] The real-time monitoring system is activated to continuously monitor and record the reinjection inlet pressure, core internal pressure, outlet flow rate, and real-time permeability k. t effluent suspended solids content, effluent Ca 2+ Mg 2+ HCO3 - The plasma concentration was monitored, and the temperature dynamics of the fluid inside the core and at the inlet and outlet were monitored in real time by temperature sensor 16. The temperature evolution process (gradually approaching thermal equilibrium from the initial temperature difference) was recorded, and data was recorded every 10 minutes.

[0062] The experiment continued until the core permeability stabilized and stopped decreasing (permeability fluctuations did not exceed 3%, lasting for more than 1 hour). At this point, a stable plugging layer formed inside the core, completing the indoor simulation of the entire reinjection and plugging process. The stable permeability k1 (k1 < k0) of the core after plugging was recorded. Simultaneously, the plugging material at the outlet end was collected for rock composition analysis, which will be used for subsequent plugging mechanism analysis. After 8 hours of experimentation, the core permeability tended to stabilize, with fluctuations not exceeding 3%, lasting for more than 1 hour, completing the plugging simulation. The stable permeability k1 of the core after plugging was recorded as 8.5 × 10⁻⁶. -15 m 2 .

[0063] Blockage Mechanism Analysis: Based on a triple blockage mechanism of physical, chemical, and biological processes, a dynamic prediction model for blockage severity is established. (Formula 2).

[0064] The calculation formulas for each blockage component are as follows: (Formula 3); (Formula 4); (Formula 5); where D ss(t) represents the component of suspended matter (physical) blockage at time t; D chem (t) represents the chemical scaling and blockage component at time t; D bio (t) represents the biological blockage component at time t; The coupling coefficient for the synergistic effect of physical-chemical fouling is dimensionless and was fitted through indoor experiments and calibrated using data on suspended solids and chemical scaling; λ is the settling coefficient of suspended solids (empirical constant); t is the experimental time (s); φ is the core porosity; K sp θ is the carbonate solubility product constant; θ is the biological growth rate coefficient (empirical constant) (1 / s); μ is the biological decay rate coefficient (1 / s).

[0065] A quantitative model of clogging evolution, and a dynamic model characterizing the coupled clogging of suspended matter and scaling in mine water: (Formula 6); where, Cv is the rate of permeability decay over time; Cv is the concentration of suspended solids in the recharge water (mg / L); C i m represents the ion concentration. i The reaction order is [number]. The coefficient representing the impact of suspended solids clogging; This represents the influence coefficient of chemical scaling.

[0066] In this embodiment, λ = 1.2 (dimensionless), K sp =5.0×10 -7 mol 2 / L 2 θ = 5.0 × 10 -5 1 / s, μ=2.5×10 - 5 1 / s =0.3 (dimensionless), experimental results: stable permeability of the core after plugging k1 = 8.5 × 10⁻⁶ -15 m 2 The degree of blockage was calculated as D(t) = 0.66 (dimensionless), where the suspended solids blockage component D... SS (t)=0.38, chemical scaling and clogging component D chem (t)=0.25, bioblockage component D bio (t)=0.06, which is consistent with the triple blockage characteristics of mine water reinjection.

[0067] Substituting the parameter α=0.005m 3 / (g·s), Cv=50g / m 3 β = 0.02 L / (mol·s), n = 2 (the number of major ion species involved in the scaling reaction, i.e., Ca 2+ HCO3 - C1=[Ca 2+] = 0.008 mol / L, m1 = 1 (Ca 2+ (corresponding reaction order), C2=[HCO3) - =0.015mol / L, m2=1 (HCO3) - (Corresponding reaction order).

[0068] Calculations showed that the porosity of the core after plugging was φ(t) = 0.11, which was 38.9% lower than the initial porosity, consistent with the experimentally measured value.

[0069] Meanwhile, temperature monitoring showed that the internal temperature of the core gradually decreased from the initial 50℃, and the inlet and outlet fluid temperatures tended to reach equilibrium (32℃) after 6 hours, completely reconstructing the entire temperature evolution process and verifying the rationality of the temperature coupling effect.

[0070] Step S4: Simulation of graded composite permeation enhancement.

[0071] For the stable and blocked core sample 8, the temperature dynamic evolution conditions were maintained, and three types of permeability enhancement treatments were carried out in sequence: Step 1: Pressurized hydraulic permeability enhancement simulation.

[0072] Keeping the in-situ stress and reinjection flow rate constant, a staged pressurization mode is adopted, with pressurization gradients of 0.5MPa, 1.0MPa, 1.5MPa, and 2.0MPa. Each pressure is lower than the rock fracture pressure (to avoid core damage), and each pressure is stabilized for 100 minutes. The outlet flow rate, real-time core permeability, and inlet pressure changes are monitored and recorded in real time.

[0073] Stable permeability k under various pressure levels 21 They are respectively: 1.1 × 10 at 0.5 MPa -14 m 2 1.4 × 10 at 1.0 MPa -14 m 2 At 1.5 MPa, 1.6 × 10 -14 m 2 1.7 × 10 at 2.0 MPa -14 m 2 .

[0074] Considering the combined effects of suspended solids blockage, chemical scaling, geostress compression, and infiltration enhancement and remediation, a dynamic evolution model of permeability over time is established, and the coupled equations for the dynamic evolution of permeability are as follows.

[0075] (Formula 1).

[0076] In the formula: The rate of change of permeability over time (m 2 / s); To simulate the concentration (g / m³) of suspended solids (SS) in mine water 3); The recharge water flow velocity (m / s); The activation energy (J / mol) for the carbonate scaling reaction is given. is the universal gas constant, usually taken as 8.314; T is the absolute temperature (unit: K); [Ca 2+ [HCO3] represents the calcium ion concentration in water (mol / L); - [ represents the concentration of bicarbonate ions in water (mol / L)]. This is the influence coefficient of geostress; , For the effective stress and initial stress of the core (MPa); The infiltration and remediation impact coefficient; The permeation enhancement operation pressure (MPa); The critical fracture pressure of the rock (MPa); It is a frequency-time dependent function of pulse infiltration, dimensionless, and its value ranges from 0.1 to 1.0.

[0077] Where α = 0.005m 3 / (g·s), β=0.02L / (mol·s), E=50000J / mol, γ=0.0005m 2 / (s·MPa), δ=0.001m 2 / (s·MPa) =0.6.

[0078] Through calculation, this stage It is a positive value (2.0 × 10). -18 -3.0×10 -18 m 2 The pressure of 1.5 MPa ( / s) indicates that the permeability continues to increase with increasing pressure, and the rate of increase slows down after the pressure is increased to 1.5 MPa, indicating that this pressure is the optimal pressure for increasing pressure.

[0079] Step 2: Simulation of pulsed high-pressure physical permeation.

[0080] Turn off the constant pressure and constant flow reinjection pump 3 and switch to the pulse booster system 4. Use periodic pulsating pressure (sine pulse), set the pulse frequency to 2Hz, and the pulse peak pressure to 6MPa (higher than the steady-state reinjection pressure of 2MPa, lower than the rock fracture pressure) to continuously disturb the blocked rock core for 60 minutes.

[0081] After the disturbance ends, shut down the pulse booster system 4, switch back to the constant pressure and constant flow reinjection pump 3, restore steady-state reinjection pressure and flow rate, and test the stable permeability k after the seepage stabilizes. 22 =2.1×10 -14 m 2To optimize the design of pulsed permeation parameters, an intelligent control algorithm for pulsed permeation parameter optimization is introduced. With the goal of maximizing permeability recovery rate, a multi-parameter optimization model is established for pulse frequency, peak pressure, and action time. The calculation formula is as follows: (Formula 7); Constraints: P peak ≤0.8P cr , , In the formula, η is the permeability recovery rate, characterizing the degree to which the permeability enhancement measures relieve the blockage damage in the rock formation; f is the pulse frequency, in Hz; P peak The pressure is the peak pressure of the pulse, in MPa. 1. Pulse disturbance time, in min; A and B are empirical coefficients for pulse permeability enhancement (A is the promotion coefficient, B is the inhibition coefficient); k2 is the stable permeability of the core after permeation enhancement; k1 is the stable permeability of the core after plugging; k0 is the initial permeability of the core; P0 is the steady-state reinjection pressure, in MPa.

[0082] By combining intelligent optimization algorithms (genetic algorithms / particle swarm optimization introduced into the design of permeability enhancement parameters) with seepage mechanics, the global optimal solution of permeability enhancement parameters can be achieved.

[0083] In this embodiment, A = 1.0 (dimensionless) and B = 0.2 (dimensionless).

[0084] The calculated permeability recovery rate η = 76.9%, which is consistent with the prediction result of the parameter optimization model (predicted η = 75.2%), with an error of less than 3%. During the pulse disturbance, the peak pressure can instantly approach the fracture initiation threshold. The high-pressure permeation term in Formula 1 is effectively activated and has a positive value, continuously driving the permeability to recover rapidly. This accurately reflects the permeation mechanism of pulse high pressure stripping away blockages and opening micro-fractures, which is highly consistent with the experimental phenomena and dimensional rules.

[0085] Step 3: Simulation of chemical pickling and penetration enhancement.

[0086] Stop mine water reinjection, close the reinjection pipeline, and start the chemical agent injection system. Inject 5% corrosion-inhibiting hydrochloric acid descaling agent into the core, with the injection volume being 2.5 times the pore volume of the core, ensuring that the agent fully fills the pores and fissures of the core. Close the agent injection pipeline and conduct a closed immersion reaction on the core for 120 minutes.

[0087] After the reaction is complete, shut down the chemical reagent injection system, turn on the clean water flushing pipeline, and introduce clean water into the core. Continue flushing until the pH of the effluent is 7.0 to avoid the reagent residue affecting subsequent experiments.

[0088] After flushing, restore steady-state reinjection pressure and flow rate, and continue to introduce simulated mine water. Once the seepage stabilizes, test and record the steady-state permeability k. 23 =2.3×10-14 m 2 To achieve precise control of chemical permeation, a coupling model of chemical permeation agent concentration and reaction time was established to quantify the chemical permeation effect. The formula for calculating the chemical permeation ratio is as follows: (Formula 8); where, For chemical penetration enhancement ratio (a quantitative indicator of chemical penetration enhancement effect); k 23 The stable permeability of the rock core after chemical permeation enhancement, in meters. 2 ; The stable permeability of the core sample after plugging, in meters. 2 ; This is the chemical penetration enhancement coefficient (empirical constant); This refers to the concentration of the chemical descaling agent (hydrochloric acid). The chemical immersion reaction time is expressed in minutes. This is the chemical permeation inhibition coefficient (empirical constant).

[0089] This model reveals the dual "promotion-inhibition" effect in the chemical permeation process, avoiding the problems of "excessive dissolution" or "insufficient repair" in traditional chemical permeation.

[0090] In this embodiment, =0.9 (dimensionless) =0.6 (dimensionless). Calculate the chemical permeation ratio. =2.71, basically consistent with the model prediction (2.68); effluent water quality testing showed that Ca 2+ The concentration rose to 0.012 mol / L, indicating that the chemical agent effectively dissolved the carbonate scale blockage and cleared the pore channels.

[0091] Step S5: Evaluation of the permeation enhancement effect.

[0092] Calculation of quantitative indicators for infiltration enhancement effect: The permeability recovery rate η and infiltration ratio n of each infiltration enhancement method are calculated as the core indicators for quantitatively evaluating the infiltration enhancement effect. The calculation formula is as follows: (Formula 9); (Formula 10); where η is the permeability recovery rate, which characterizes the degree to which the permeability enhancement measures relieve the blockage damage of the rock formation; n is the permeability enhancement ratio, which characterizes the multiple by which the permeability of the rock formation is enhanced relative to the blockage state; k0 is the initial benchmark stable permeability of the core obtained by calibration; k1 is the core permeability of the rock formation in a stable blockage state after the mine water is continuously reinjected; k2 is the core stable permeability measured after the corresponding permeability enhancement treatment is completed and the steady-state reinjection is restored.

[0093] Wherein, k2 includes the permeability k after pressurized osmosis enhancement. 21 Permeability k after pulsed osmosis enhancement 22 Permeability k after chemical permeation enhancement23 The larger η is, the better the permeability enhancement effect and the closer the core permeability recovery is to the initial state; the larger n is, the more significant the improvement in core permeability after permeation enhancement.

[0094] Multi-dimensional comparative evaluation: Initial permeability k0, permeability k1 after clogging, and permeability k after pressurized osmosis enhancement. 21 Permeability k after pulsed osmosis enhancement 22 Permeability k after chemical permeation enhancement 23 A comparison was made to analyze the differences in the infiltration effects of different infiltration enhancement methods.

[0095] Simultaneously, a comprehensive evaluation model incorporating energy efficiency will be added and constructed: (Formula 11); where, The comprehensive efficiency index for enhanced permeability is used to quantify the "comprehensive benefit of permeability recovery per unit of energy / input". The larger the value, the better the enhanced permeability effect. k(t) is the real-time permeability coefficient of the medium during the enhanced permeability process; P(t) is the real-time reinjection pressure; Q(t) is the reinjection flow rate; the numerator is the cumulative permeability recovery amount; and the denominator is the consumption during the enhanced permeability process.

[0096] Simultaneously, by combining changes in reinjection flow rate, changes in seepage resistance, patterns of blockage precipitation / dissolution, and patterns of water chemical evolution, the applicability and effectiveness of each infiltration enhancement method are comprehensively evaluated.

[0097] The core evaluation indicators for each infiltration enhancement method were calculated using Formulas 9 and 10, and the energy efficiency was comprehensively evaluated using Formula 11. The results are shown in the table below.

[0098]

[0099] All three permeability enhancement methods can effectively restore the permeability of rock cores. Among them, chemical acid washing has the best permeability enhancement effect, pulsed physical permeability enhancement has the highest energy efficiency, and pressurized hydraulic permeability enhancement is simple to operate and has a low cost. On-site, a single permeability enhancement method or a combination of permeability enhancement methods can be selected according to the project requirements.

[0100] During the infiltration process, an adaptive infiltration intelligent control algorithm is introduced to automatically adjust infiltration parameters based on real-time monitoring data. (Formula 12); where P0 is the base pressure; η d η(t) represents the target state value (setpoint); η(t) represents the real-time state value (process variable); K p K i K d These are the parameters of the system's PID controller; This is the cumulative deviation between the target state value and the actual state value over time. The target penetration recovery rate.

[0101] In this embodiment, Kp =2.5, K i =0.8, K d =0.3. This formula can automatically adjust the permeation pressure, pulse parameters, and reagent injection rate to ensure a stable and efficient permeation process, further improving the accuracy of the permeation effect.

[0102] Step S6: Data analysis and mechanism summary.

[0103] Data processing: The data collected throughout the experiment, including pressure, flow rate, permeability, water quality, and temperature dynamic evolution, are processed, filtered, and abnormal data are removed. Permeability changes over time and temperature, reinjection flow rate changes over pressure and temperature, and infiltration enhancement effect comparison bar charts are plotted to present the experimental results intuitively.

[0104] The coupled effect mechanism of temperature dynamic evolution on blockage: Based on the analysis of experimental data, the main effects of temperature evolution on blockage of mine water reinjection include: increased temperature accelerates carbonate scaling, temperature difference causes suspended particles to flocculate and settle, thermal expansion and contraction of rocks narrows cracks, temperature affects microbial activity and induces biomass blockage, and the greater the initial temperature difference, the faster the blockage decays.

[0105] Mechanism Analysis: Combining the initial mineral composition of the core, fracture development characteristics, and blockage composition, the formation mechanism of silt blockage and scaling blockage during mine water reinjection was analyzed. Blockage composition analysis showed that it mainly consisted of suspended solids deposition (58%) and carbonate scaling (37%), with a small amount of biofilm (5%).

[0106] Analysis of the permeation enhancement mechanism shows that: pressurized permeation enhancement mainly relies on hydraulic force to open micro-fractures and unclog pore channels; pulsed permeation enhancement relies on oscillation force to peel away blockages on the surface of pores and fractures, forming new micro-permeation channels; chemical permeation enhancement relies on agents to dissolve carbonate scale and cemented blockages. The synergistic effect of the three can achieve the optimal permeation enhancement effect.

[0107] Parameter optimization: The effects of different reinjection pressures, pulse parameters (frequency, peak pressure, disturbance time), chemical agent concentrations, and soaking times on the permeability enhancement effect were summarized. Based on experimental data, the optimal parameter combination for mine water reinjection permeability enhancement in this mining area was determined to be: pressurized permeability enhancement pressure of 1.5 MPa, pulse permeability enhancement parameters (frequency 2 Hz, peak pressure 6 MPa, disturbance time 60 min), chemical descaling agent concentration of 5%, and soaking time of 120 min. This combination can be directly used in on-site engineering design.

[0108] This mine water reinjection and permeation enhancement simulation method and test system fully simulates the entire process of mine water reinjection → blockage attenuation → hydraulic / pulse / chemical composite permeation enhancement, filling the gap in existing technologies that only simulate reinjection without simulating the dynamic evolution of permeation enhancement. It can comprehensively reproduce the real working conditions of deep well reinjection and permeation enhancement in mines, and the test results closely approximate existing field engineering practices. Using undisturbed rock cores from the mining area, simulating real mine water (low temperature), applying in-situ in-situ stress, simulating high-temperature formations and dynamic temperature evolution, it maximizes the reproduction of on-site formation conditions. Simultaneously, a real-time monitoring system continuously collects parameters such as pressure, flow rate, permeability, water quality, and temperature, ensuring the accuracy, reliability, and continuity of the test data, providing sufficient data support for the analysis of permeation enhancement mechanisms. A graded composite permeation enhancement simulation is employed to compare different permeation enhancement methods. The method effectively calculates the permeability recovery rate and permeability enhancement ratio, clarifying the optimal permeability enhancement process parameters, guiding on-site mine water reinjection and permeability enhancement construction, avoiding blind design of permeability enhancement measures, improving permeability enhancement effect, and reducing project costs. The test process is standardized, repeatable, and highly controllable. It can not only be used for on-site engineering parameter optimization, but also simulate and reveal the physical-chemical-biological mechanisms of mine water reinjection blockage and permeability enhancement. It has both engineering application value and academic research value, and can be widely used in indoor experimental research on mine water reinjection and permeability enhancement in various coal mines. The test system is divided into different modules that can be freely combined and built. The operation is relatively convenient, and the test parameters can be flexibly adjusted according to the differences in hydrogeological conditions and mine water quality of different typical reinjection projects in my country. It has strong applicability and broad prospects for promotion and application.

[0109] The above are merely preferred embodiments of the present invention. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention, and these should also be considered within the scope of protection of the present invention. These will not affect the effectiveness of the implementation of the present invention or the practicality of the patent.

Claims

1. A method for simulating mine water reinjection and infiltration enhancement, characterized in that, Includes the following steps: S1. Test preparation: Collect undisturbed rock cores from the aquifer in the mining area, process them into standard rock core samples, and prepare simulated mine water; load the rock core samples into a triaxial seepage holder, apply in-situ geostress, and set the formation temperature and recharge water temperature through a temperature control auxiliary unit to simulate the initial temperature difference condition. S2. Initial parameter calibration: Simulated mine water was injected into the core sample to replicate the temperature difference conditions. Clean groundwater was used to conduct a steady-state seepage test to determine the initial stable permeability k0 of the core sample. S3. Plugging Evolution Simulation: Simulated mine water is continuously injected into the core sample for steady-state reinjection, and the permeability change is monitored in real time until the permeability of the core sample stabilizes and decays, forming a stable clogging state. The permeability k1 after clogging is recorded. S4. Staged composite permeability enhancement simulation: Maintaining dynamic temperature evolution conditions, for core samples in a stable blockage state, perform one or more of the following permeability enhancement treatments: staged pressurized hydraulic permeability enhancement, pulsed high-pressure physical permeability enhancement, and chemical acid washing and descaling permeability enhancement; after each permeability enhancement treatment is completed, restore steady-state reinjection and test the corresponding stable permeability k2; S5. Evaluation of Infiltration Enhancement Effect: Based on k0, k1, and k2, calculate the permeability recovery rate and infiltration ratio of each infiltration enhancement treatment to quantitatively evaluate the infiltration enhancement effect; S6. Data Analysis: Organize experimental data, analyze the clogging mechanism and the permeation mechanism of each permeation enhancement treatment, and summarize the permeation enhancement process parameters.

2. The mine water reinjection and infiltration simulation method according to claim 1, characterized in that, In step S1, the formation temperature is higher than the reinjection water temperature to simulate the temperature difference condition of cold water being injected into a hot formation.

3. The mine water reinjection and infiltration simulation method according to claim 2, characterized in that, In step S3, the real-time monitoring includes monitoring at least one of the following: reinjection pressure, reinjection flow rate, effluent water quality, and temperature dynamic changes.

4. The mine water reinjection and infiltration simulation method according to claim 3, characterized in that, In step S3, the criterion for determining the stable decline of permeability is: the permeability fluctuation does not exceed 3% and lasts for more than 1 hour.

5. The mine water reinjection and infiltration simulation method according to claim 4, characterized in that, In step S4, the stepwise pressurization hydraulic permeation enhancement adopts a graded pressurization and stabilization mode, with each pressure being lower than the rupture pressure of the core sample, and each stabilization time being 90-120 minutes.

6. The mine water reinjection and infiltration simulation method according to claim 1, characterized in that, In step S4, the pulsed high-pressure physical permeation enhancement uses periodic pulsating pressure with a frequency of 0.5-5Hz. The peak pulse pressure is higher than the steady-state reinjection pressure and lower than the rupture pressure of the core sample. The pulse disturbance time is 30-180min.

7. The mine water reinjection and infiltration simulation method according to claim 2, characterized in that, In step S4, the chemical acid washing for descaling and penetration enhancement uses a 5%-10% concentration of corrosion-inhibiting hydrochloric acid descaling agent, with an injection volume of 2-3 times the pore volume of the core sample. After the reaction is carried out in a sealed environment, it is rinsed with clean water.

8. The mine water reinjection and infiltration simulation method according to claim 3, characterized in that, In step S5, the calculation formulas for the permeability recovery rate η and the permeability enhancement ratio n are as follows: ； 。 9. A mine water reinjection and infiltration simulation test system for implementing the mine water reinjection and infiltration simulation method according to any one of claims 1-8, characterized in that, include: Core clamping device, used to clamp core samples and apply in-situ stress; A mine water preparation system, connected to the core clamping device, is used to prepare and store simulated mine water; The reinjection power system is connected between the mine water distribution system and the core clamping device to provide steady-state reinjection or pulse reinjection power. A chemical agent injection system, connected to the core clamping device, is used to inject chemical permeation-enhancing agents; A temperature control auxiliary unit is connected to the core clamping device and the mine water dispensing system respectively, and is used to independently control the temperature of the core sample and the simulated mine water temperature. The real-time monitoring system includes at least one pressure sensor, at least one flow sensor, at least one temperature sensor, and a data acquisition unit.

10. The mine water reinjection and infiltration enhancement simulation test system according to claim 9, characterized in that, The reinjection power system includes a constant pressure and constant flow reinjection pump and a pulse booster system; the inlet of the constant pressure and constant flow reinjection pump is connected to the mine water distribution tank, and the outlet is connected to the inlet of the core clamping device via the pulse booster system.

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