A method for obtaining key parameters of pollutant migration under the influence of site-scale temperature-hydrodynamic coupling.

Abstract

The present invention discloses a method for obtaining key parameters of pollutant migration under the influence of site-scale temperature-hydrodynamic coupling, and a method for obtaining permeability parameters, thermal conductivity and diffusion coefficient of a contaminated site based on numerical simulation of multi-field coupling of hydrodynamic field-temperature field-concentration field. Site pollutant migration parameters are key indicators for site organic pollution investigation and treatment. Currently, the acquisition of aquifer parameters mainly relies on hydrogeological surveys, and the test methods and physical fields are single. Based on this, the present invention proposes the above method. The method shown in the present invention includes establishing a water-heat-salt coupling model for an organic polluted site through site drilling data and field physical test results in the early stage, performing multi-field coupling numerical inversion based on the site model and combining multiple field data, and adjusting the model parameters through manual trial and error to improve the model accuracy and obtain the optimal model.

Description

Technical Field

[0001] The present invention relates to the field of obtaining key parameters of site pollutant migration, and in particular to a method for obtaining key parameters of pollutant migration under the influence of site-scale temperature-hydrodynamic coupling. Background Art

[0002] In the process of pollution site treatment and remediation, the acquisition of various parameters of aquifers depends on hydrogeological surveys. Through various hydrogeological tests, geophysical explorations, and hydrogeological drilling, the geological structure and hydrogeological parameters of aquifers are determined, which is conducive to making qualitative and quantitative judgments on pollutant concentrations, distribution ranges, and migration characteristics.

[0003] The dynamic evolution of the seepage field and temperature field, and the solute migration characteristics of the aquifer are crucial to site management and the evaluation of the management effect. Among them, the permeability coefficient, thermal conductivity coefficient, and diffusion coefficient are important parameters for describing the seepage field, temperature field, and solute migration characteristics of the aquifer. They are also the basic data for groundwater resource calculation and pollution prevention and control. Improving the accuracy of parameter solutions is of great significance for guiding site management and remediation. At present, multiple survey methods are used in combination, and multiple physical fields are coupled to obtain aquifer parameters. This method has the advantages of high accuracy and low multi-solution.

[0004] There are currently few studies on obtaining important parameters of aquifers through multi-field coupling numerical model calculations, and the tests on multi-field coupling of groundwater are mainly based on laboratory scale. Starting from the site scale, there are few field tests in China that simultaneously obtain multiple important parameters of the site through coupled tracer tests. Therefore, by building a site-scale water-heat-salt coupling tracer test platform and conducting field tests, combined with the results of previous pumping tests, micro-water tests, and geotechnical tests, multi-field coupling numerical simulations are implemented to obtain key parameters such as site pollutant permeability, thermal conductivity, and diffusion coefficient. Summary of the invention

[0005] Purpose of the invention: In view of the above-mentioned deficiencies in the prior art, the purpose of the present invention is to provide a coupled simulation method and system for site-scale water-heat-salt multi-physical fields. First, a site-scale water-heat-salt coupled tracer test platform is constructed to perform three-dimensional multi-parameter monitoring (temperature, water pressure, conductivity, etc.) to obtain hydraulic, temperature and concentration response signals of low permeability formations, and accumulate three-dimensional long-term series data of hydrodynamic field, temperature field and concentration field, which are used as the basis for adjusting model parameters.

[0006] Technical solution: To achieve the above purpose, the present invention proposes a method for obtaining key parameters of pollutant migration under the influence of site-scale temperature-hydrodynamic coupling, which includes the following specific steps:

[0007] 1) For the contaminated site, water injection well H1, pumping well H4, observation wells H0, H2, H3 are arranged, and preliminary experiments are carried out on each well, including geotechnical test, pumping test and micro-water test, to obtain the initial value of the permeability coefficient of the site aquifer, which will serve as the standard for subsequent model correction;

[0008] 2) Based on the preliminary experiment, coupled tracer tests were carried out on each well: pumping test - calculating the permeability coefficient by observing the water level change of the aquifer, heat tracer test - calculating the thermal conductivity by observing the relationship between the depth and temperature change in each well, salt tracer test - calculating the diffusion coefficient by converting the conductivity into concentration by observing the relationship between the depth and conductivity change, and setting probes according to the positions of the test wells and observation wells to monitor the temperature, conductivity and permeability coefficient of aquifers at different depths;

[0009] 3) Construct a three-dimensional groundwater flow field model, process the contaminated site data of the test area into spatial coordinates, set initial conditions and boundary conditions, and input the permeability, thermal conductivity, and diffusion coefficient obtained from the field test into the simulation software COMSOL Multiphysics 5.6 for three-dimensional modeling. According to the locations of the test wells and observation wells, the model is divided into three layers to obtain a three-dimensional groundwater flow field model of the contaminated site;

[0010] 4) Collect groundwater level data from observation wells H0, H2, and H3 of the contaminated site, and obtain groundwater level data within the same observation period in the constructed three-dimensional groundwater flow field model of the contaminated site, compare the measured water level value with the simulated water level value, and obtain the root mean square error of the groundwater level. Adjust the model parameters according to the initial value of the permeability coefficient of the aquifer obtained in the preliminary test, so that the root mean square error of the groundwater level is within the preset range;

[0011] 5) Use the corrected three-dimensional groundwater flow field model of the contaminated site to perform multi-field coupling simulation of groundwater flow field, temperature field, and solute concentration field. For groundwater flow field simulation, select the Darcy's law module in COMSOL Multiphysics 5.6 software, for temperature field simulation, select the porous medium heat transfer module in the software, and for solute concentration field distribution, select the porous medium dilute species transfer module in the software. Perform multi-physics field simulations of groundwater flow field-temperature field, groundwater flow field-solute concentration field, and groundwater flow field-temperature field-solute concentration field, respectively, to obtain the influence relationship between the fields under full coupling conditions;

[0012] 6) Using the monitoring data at different depths in the tracer test, adjust and calibrate the permeability coefficient, thermal conductivity coefficient and diffusion coefficient in the groundwater flow field model to determine the optimal model for the contaminated site;

[0013] 7) Based on the optimal model of the contaminated site, the pollutant migration parameters are predicted. The water level, temperature, conductivity or concentration of the aquifer are input into the optimal model to obtain the pollutant migration parameters, namely, permeability, thermal conductivity and diffusion coefficient.

[0014] Furthermore, in the step 1), the experimental area of ​​the contaminated site is a 3×3m square, wherein the injection well H1, the pumping well H4 and the observation wells H2 and H3 are located at the four corners of the square experimental area, and the observation well H0 is located at the center of the square experimental area.

[0015] Furthermore, in the step 1), the data of the pumping test and the micro-water test are processed by the Theis matching method, and the geological parameters of the aquifer are determined by comparing the measured curve with the theoretical curve.

[0016] Furthermore, in the step 2), the probes in each well are HR8801 water level temperature monitoring recorder and HR-206A online conductivity sensor, which are a group connected to the underground measurement and control terminal, wherein the observation wells H0, H2, and H3 are respectively provided with water level temperature integrated sensors and conductivity sensors at depths of 8.5m, 9.5m, 10.5m, 11.5m, and 12.5m; the pumping well is provided with a group of water level temperature integrated sensors and conductivity sensors at a depth of 11.5m; and the injection well is provided with a group of water level temperature integrated sensors and conductivity sensors at a depth of 12.5m.

[0017] Furthermore, in the step 3), the plane range of the three-dimensional structural model is a rectangle, the major axis of the rectangle is parallel to the line connecting the pumping and injection wells, the major axis is 18.55m, the minor axis is 10.11m, and the average vertical height is 18.67m; the model is divided into three layers according to the locations of the test wells and the observation wells, specifically: the surface to a burial depth of 4m is generalized as a fill layer, the burial depth of 4m to 13.5m is generalized as a clay layer, and the burial depth of 13.5m to the bottom of the model is generalized as a bedrock layer.

[0018] Furthermore, in step 3), the initial conditions and boundary conditions of the groundwater flow field model of the contaminated site are set as follows:

[0019] The boundaries parallel to the artificial groundwater flow field are set as no-flow boundaries, the top and bottom surfaces of the model are no-flow boundaries, and the two side boundaries perpendicular to the main groundwater flow direction are set at the observation well position and set as constant head boundaries, and their head values ​​are set by the interpolation function; the top and bottom surfaces of the model are set as thermal insulation boundaries, the sides are set as open boundaries, and the injection wells are set as line heat source boundaries; the parameter settings of the porous medium dilute species transfer module are the same as those of the heat conduction module, the initial concentration of the model dilute species NaCl is set to 0, the top and bottom surfaces of the model are set as no flux boundaries, the sides are set as open boundaries, and the injection wells are set as line mass sources, and the mass flow rate of the solute substance is controlled by a piecewise function.

[0020] Furthermore, in the step 4), when describing the accuracy of the groundwater flow field model, the root mean square error RMSE of the model is calculated, and the model parameters whose root mean square error RMSE meets the preset conditions are selected. The calculation formula of the root mean square error RMSE is as follows:

[0021]

[0022] In the formula, C i0 is the numerical simulation value of permeability coefficient, thermal conductivity coefficient or diffusion coefficient, C ie The actual measured value of permeability coefficient, thermal conductivity coefficient or diffusion coefficient, where n is the number of sampling points.

[0023] Furthermore, in step 5), the mass conservation equation and Darcy velocity equation are used to simulate the groundwater flow field under the unsteady flow state of the site. The energy conservation equation and Darcy velocity equation are as follows:

[0024]

[0025]

[0026] Where t is time, unit is s; ∈ p is the porosity; ρ is the liquid density, in kg / m 3 ;Q m is the input mass source, in kg / (m 3 *s); κ is the permeability, unit is m 2 ; μ is dynamic viscosity, unit is MPa*s; is the pressure difference, in MPa; g is the acceleration due to gravity, in m / s 2 ; u is the groundwater velocity, in m / s 2 .

[0027] Furthermore, in the step 5), the energy conservation equation, heat conduction equation and effective thermal conductivity calculation formula are used to simulate the heat transfer of the porous media in the site. The energy conservation equation, heat conduction equation and effective thermal conductivity calculation formula are as follows:

[0028]

[0029]

[0030] k eff =θ s k s +∈1k f +k disp (6)

[0031] In the formula, C p,fis the constant pressure heat capacity of the fluid, in J / (kg*K); ρ f is the fluid density, its unit is kg / m 3 ; u is the groundwater velocity, in m / s 2 ; T is Kelvin temperature, unit is K; Q is heat source term, unit is J; q is heat flow, unit is W / m 2 ;k eff is the effective thermal conductivity, in W / (m*K), which is determined by the solid matrix k s , fluid thermal conductivity k f The weighted average of the thermal diffusion coefficient k disp Determine, where θ s and ∈1 are weights.

[0032] Furthermore, in step 5), the following porous medium dilute species transfer module control equation is selected to simulate salt migration:

[0033]

[0034] Where ρ is the liquid density in kg / m 3 ; C is the concentration of the dilute substance, in mol / m 3 ; t is time, unit is s; v is the velocity vector of the fluid, unit is m / s; D is the diffusion coefficient of the dilute substance, unit is m 2 / s; R is the source term, the unit is mol / (s*m 3 ).

[0035] Principle of the invention: The acquisition of aquifer parameters depends on hydrogeological surveys. A single test method or a single physical field cannot explore the relationship between multiple parameters. The combination of multiple survey methods and the coupling of multiple physical fields to obtain relevant aquifer parameters to explore the influence relationship between various physical fields has the advantages of high accuracy and fast prediction. In view of the changes in hydrodynamic conditions and temperature and concentration fields involved in the management and control of contaminated sites, the present invention conducts site-scale coupled tracer tests and multi-field coupled numerical simulations to obtain the permeability, thermal conductivity and diffusion coefficient of the test site.

[0036] Beneficial effects: Compared with the prior art, the technical solution of the present invention has the following beneficial technical effects:

[0037] The present invention provides a novel method for obtaining key parameters of pollutant migration based on water-heat-salt multi-field coupled tracer tests and numerical simulations at a site scale. There are few groundwater multi-field coupled tests in my country that obtain important parameters from a site scale, and related numerical calculations mainly focus on studying the impact of temperature on water distribution, ignoring the transient changes of water field to temperature. The method described in the present invention implements multi-field coupled tracer tests of groundwater hydrodynamic field, temperature field, and concentration field at a site scale to obtain data from each field, and uses trial and error combined with numerical simulation to more accurately solve the permeability coefficient, thermal conductivity, and diffusion coefficient of the aquifer, which has a more efficient and accurate application value. The present invention provides a new technical idea for obtaining key parameters of groundwater pollutant migration during the investigation and remediation of contaminated sites. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required to be used in the description of the embodiments or the prior art are briefly introduced below.

[0039] Figure 1 A flow chart of a method for obtaining key parameters of pollutant migration under the influence of site-scale temperature-hydrodynamic coupling designed for the present invention;

[0040] Figure 2 It is a stereoscopic schematic diagram of a three-dimensional conceptual model of a field-scale pumping and injection well involved in Example 1 of the present invention;

[0041] Figure 3 This is a boundary setting diagram of the three-dimensional conceptual model of the field-scale injection well involved in Example 1 of the present invention. DETAILED DESCRIPTION

[0042] The present invention will be further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and cannot be used to limit the protection scope of the present invention.

[0043] like Figure 1 As shown, the present invention proposes a method for obtaining key parameters of pollutant migration under the influence of site-scale temperature-hydrodynamic coupling, and the method includes the following specific steps:

[0044] 1) For the contaminated site, water injection well H1, pumping well H4, observation wells H0, H2, H3 are arranged, and preliminary experiments are carried out on each well, including geotechnical test, pumping test and micro-water test, to obtain the initial value of the permeability coefficient of the site aquifer, which will serve as the standard for subsequent model correction;

[0045] 2) Based on the preliminary experiment, coupled tracer tests were carried out on each well: pumping test - calculating the permeability coefficient by observing the water level change of the aquifer, heat tracer test - calculating the thermal conductivity by observing the relationship between the depth and temperature change in each well, salt tracer test - calculating the diffusion coefficient by converting the conductivity into concentration by observing the relationship between the depth and conductivity change, and setting probes according to the positions of the test wells and observation wells to monitor the temperature, conductivity and permeability coefficient of aquifers at different depths;

[0046] 3) Construct a three-dimensional groundwater flow field model, process the contaminated site data of the test area into spatial coordinates, set initial conditions and boundary conditions, and input the permeability, thermal conductivity, and diffusion coefficient obtained from the field test into the simulation software COMSOL Multiphysics 5.6 for three-dimensional modeling. According to the locations of the test wells and observation wells, the model is divided into three layers to obtain a three-dimensional groundwater flow field model of the contaminated site;

[0047] 4) Collect groundwater level data from observation wells H0, H2, and H3 of the contaminated site, and obtain groundwater level data within the same observation period in the constructed three-dimensional groundwater flow field model of the contaminated site, compare the measured water level value with the simulated water level value, and obtain the root mean square error of the groundwater level. Adjust the model parameters according to the initial value of the permeability coefficient of the aquifer obtained in the preliminary test, so that the root mean square error of the groundwater level is within the preset range;

[0048] 5) Use the corrected three-dimensional groundwater flow field model of the contaminated site to perform multi-field coupling simulation of groundwater flow field, temperature field, and solute concentration field. For groundwater flow field simulation, select the Darcy's law module in COMSOL Multiphysics 5.6 software, for temperature field simulation, select the porous medium heat transfer module in the software, and for solute concentration field distribution, select the porous medium dilute species transfer module in the software. Perform multi-physics field simulations of groundwater flow field-temperature field, groundwater flow field-solute concentration field, and groundwater flow field-temperature field-solute concentration field, respectively, to obtain the influence relationship between the fields under full coupling conditions;

[0049] 6) Using the monitoring data at different depths in the tracer test, adjust and calibrate the permeability coefficient, thermal conductivity coefficient and diffusion coefficient in the groundwater flow field model to determine the optimal model for the contaminated site;

[0050] 7) Based on the optimal model of the contaminated site, the pollutant migration parameters are predicted. The water level, temperature, conductivity or concentration of the aquifer are input into the optimal model to obtain the pollutant migration parameters, namely, permeability, thermal conductivity and diffusion coefficient.

[0051] Furthermore, in the step 1), the experimental area of ​​the contaminated site is a 3×3m square, wherein the injection well H1, the pumping well H4 and the observation wells H2 and H3 are located at the four corners of the square experimental area, and the observation well H0 is located at the center of the square experimental area.

[0052] Furthermore, in the step 1), the data of the pumping test and the micro-water test are processed by the Theis matching method, and the geological parameters of the aquifer are determined by comparing the measured curve with the theoretical curve.

[0053] Furthermore, in the step 2), the probes in each well are HR8801 water level temperature monitoring recorder and HR-206A online conductivity sensor, which are a group connected to the underground measurement and control terminal, wherein the observation wells H0, H2, and H3 are respectively provided with water level temperature integrated sensors and conductivity sensors at depths of 8.5m, 9.5m, 10.5m, 11.5m, and 12.5m; the pumping well is provided with a group of water level temperature integrated sensors and conductivity sensors at a depth of 11.5m; and the injection well is provided with a group of water level temperature integrated sensors and conductivity sensors at a depth of 12.5m.

[0054] Furthermore, in the step 3), the plane range of the three-dimensional structural model is a rectangle, the major axis of the rectangle is parallel to the line connecting the pumping and injection wells, the major axis is 18.55m, the minor axis is 10.11m, and the average vertical height is 18.67m; the model is divided into three layers according to the locations of the test wells and the observation wells, specifically: the surface to a burial depth of 4m is generalized as a fill layer, the burial depth of 4m to 13.5m is generalized as a clay layer, and the burial depth of 13.5m to the bottom of the model is generalized as a bedrock layer.

[0055] Furthermore, in step 3), the initial conditions and boundary conditions of the groundwater flow field model of the contaminated site are set as follows:

[0056] The boundaries parallel to the artificial groundwater flow field are set as no-flow boundaries, the top and bottom surfaces of the model are no-flow boundaries, and the two side boundaries perpendicular to the main groundwater flow direction are set at the observation well position and set as constant head boundaries, and their head values ​​are set by the interpolation function; the top and bottom surfaces of the model are set as thermal insulation boundaries, the sides are set as open boundaries, and the injection wells are set as line heat source boundaries; the parameter settings of the porous medium dilute species transfer module are the same as those of the heat conduction module, the initial concentration of the model dilute species NaCl is set to 0, the top and bottom surfaces of the model are set as no flux boundaries, the sides are set as open boundaries, and the injection wells are set as line mass sources, and the mass flow rate of the solute substance is controlled by a piecewise function.

[0057] Furthermore, in the step 4), when describing the accuracy of the groundwater flow field model, the root mean square error RMSE of the model is calculated, and the model parameters whose root mean square error RMSE meets the preset conditions are selected. The calculation formula of the root mean square error RMSE is as follows:

[0058]

[0059] In the formula, C i0 is the numerical simulation value of permeability coefficient, thermal conductivity coefficient or diffusion coefficient, Cie The actual measured value of permeability coefficient, thermal conductivity coefficient or diffusion coefficient, where n is the number of sampling points.

[0060] Furthermore, in step 5), the mass conservation equation and Darcy velocity equation are used to simulate the groundwater flow field under the unsteady flow state of the site. The energy conservation equation and Darcy velocity equation are as follows:

[0061]

[0062]

[0063] Where t is time, unit is s; ∈ p is the porosity; ρ is the liquid density, in kg / m 3 ;Q m is the input mass source, in kg / (m 3 *s); κ is the permeability, unit is m 2 ; μ is dynamic viscosity, unit is MPa*s; is the pressure difference, in MPa; g is the acceleration due to gravity, in m / s 2 ; u is the groundwater velocity, in m / s 2 .

[0064] Furthermore, in the step 5), the energy conservation equation, heat conduction equation and effective thermal conductivity calculation formula are used to simulate the heat transfer of the porous media in the site. The energy conservation equation, heat conduction equation and effective thermal conductivity calculation formula are as follows:

[0065]

[0066]

[0067] k eff =θ s k s +∈1k f +k disp (6)

[0068] In the formula, C p,f is the constant pressure heat capacity of the fluid, in J / (kg*K); ρ f is the fluid density, its unit is kg / m 3 ; u is the groundwater velocity, in m / s 2 ; T is Kelvin temperature, unit is K; Q is heat source term, unit is J; q is heat flow, unit is W / m 2 ;k eff is the effective thermal conductivity, in W / (m*K), which is determined by the solid matrix k s , fluid thermal conductivity k fThe weighted average of the thermal diffusion coefficient k disp Determine, where θ s and ∈1 are weights.

[0069] Furthermore, in step 5), the following porous medium dilute species transfer module control equation is selected to simulate salt migration:

[0070]

[0071] Where ρ is the liquid density in kg / m 3 ; C is the concentration of the dilute substance, in mol / m 3 ; t is time, unit is s; v is the velocity vector of the fluid, unit is m / s; D is the diffusion coefficient of the dilute substance, unit is m 2 / s; R is the source term, the unit is mol / (s*m 3 ).

[0072] Example 1

[0073] The present invention proposes a method for obtaining key parameters of pollutant migration under the influence of site-scale temperature-hydrodynamic coupling. The embodiment of the present invention takes the constructed site pumping and injection well model as an example.

[0074] (1) Based on the borehole catalog data of the test site, a borehole information text is established, and combined with pumping tests, micro-water tests and geotechnical tests, a conceptual model of the pumping and injection well with the same physical parameters as in the actual scenario is established. Figure 2 As shown in the figure, the plane range of this three-dimensional structural model is a rectangle, and the long axis of the rectangle is parallel to the line connecting the pumping and injection wells, that is, the direction of the groundwater flow in the artificial flow field. The long axis of the rectangle is 18.55m, the short axis is 10.11m, and the average vertical height is 18.67m. The model range is selected according to the location of the test well and the observation well. The aquifer is mainly generalized into three layers, from the surface to the 4m burial depth is generalized as the fill layer, and the burial depth of 4m to 13.5m is generalized as the clay layer. Among them, the 8-13m depth layer is subdivided into 5 fine layers for the subsequent test layer heterogeneity characterization. The burial depth of 13.5m to the bottom of the model is generalized as the bedrock layer. Among them, 8.5m to 13.5m is the main test hole section, and each interval of 1m is subdivided into a small layer. Considering that the overall groundwater gradient of the site is small, the boundaries parallel to the artificial groundwater flow field are set as no-flow boundaries, and the top and bottom surfaces of the model are also no-flow boundaries; at the same time, considering the distribution of the on-site observation well locations and the long test period, the water level in the test area continues to drop with the progress of pumping, so the boundaries on both sides perpendicular to the main flow direction of groundwater are set as constant head boundaries, and their head values ​​are interpolation functions, see Figure 3 The groundwater seepage related parameters in the model are shown in Table 1.

[0075] Table 1. Parameters related to groundwater seepage calculation

[0076]

[0077] (2) Simulation of groundwater flow field: The reliability of the model is determined by comparing the simulated and measured water level values ​​of the H0, H2, and H3 observation wells. In this stage, only the groundwater flow field is simulated, and no multi-field coupling calculation is performed. The simulation is divided into three groups according to different time steps and simulation times. First, the groundwater flow field simulation calculation is performed with a time step of 1 min and a simulation time of 2400 min to calibrate parameters such as the permeability coefficient. Then, the simulation time is extended to observe the stability of the model. See Table 2 for details.

[0078] (3) Based on the groundwater flow field, a combination simulation of different physical fields was performed to compare the influence of different physical fields under full coupling conditions. The specific working condition settings are shown in Table 3. The root mean square error of the simulation results is generally kept in a small range, indicating that the reliability of the model calculation value is high, which provides a good foundation for the groundwater flow model for the subsequent addition of temperature field and solute concentration field simulation calculation.

[0079] (4) According to the data of sensor probes at different depths, the parameters of different strata in the test section are adjusted by artificial trial and error to improve the overall accuracy of the model. The selection of simulation time and step size is mainly based on the specific test process. The parameters of fluid properties and solid matrix properties for the heat transfer module are shown in Table 4.

[0080] Table 2 Groundwater flow field simulation grouping table

[0081]

[0082] Table 3 Grouping table of multi-field coupling simulation

[0083]

[0084] Table 4 Parameters of porous media heat transfer module

[0085]

[0086] Through the artificial trial and error method, the permeability coefficient of the aquifer fine layer in the test section was adjusted according to the changes in the temperature signal at different depths of each well. It was found that within the simulation time of 2400 minutes, the simulated calculated values ​​of the water levels of each test well were closer to the measured values, and the root mean square error decreased. The root mean square error of the H1 injection well decreased the most, by 0.0383, followed by H4 and H0, which decreased by 0.0169 and 0.016 respectively. This shows that the model is finely characterized, making the simulation results closer to the true value, and can well predict the key parameters of aquifer contaminant migration.

[0087] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for obtaining key parameters of pollutant migration under the influence of site-scale temperature-hydrodynamic coupling, characterized in that: The method comprises the following specific steps: 1) For the contaminated site, water injection well H1, pumping well H4, observation wells H0, H2, H3 are arranged, and preliminary experiments are carried out on each well, including geotechnical test, pumping test and micro-water test, to obtain the initial value of the permeability coefficient of the site aquifer, which will serve as the standard for subsequent model correction; 2) Based on the preliminary experiment, coupled tracer tests were carried out on each well: pumping test - calculating the permeability coefficient by observing the water level change of the aquifer, heat tracer test - calculating the thermal conductivity by observing the relationship between the depth and temperature change in each well, salt tracer test - calculating the diffusion coefficient by converting the conductivity into concentration by observing the relationship between the depth and conductivity change, and setting probes according to the positions of the test wells and observation wells to monitor the temperature, conductivity and permeability coefficient of aquifers at different depths; 3) Construct a three-dimensional groundwater flow field model, process the contaminated site data of the test area into spatial coordinates, set initial conditions and boundary conditions, and input the permeability, thermal conductivity, and diffusion coefficient obtained from the field test into the simulation software COMSOL Multiphysics 5.6 for three-dimensional modeling. According to the locations of the test wells and observation wells, the model is divided into three layers to obtain a three-dimensional groundwater flow field model of the contaminated site; 4) Collect groundwater level data from observation wells H0, H2, and H3 of the contaminated site, and obtain groundwater level data within the same observation period in the constructed three-dimensional groundwater flow field model of the contaminated site, compare the measured water level value with the simulated water level value, and obtain the root mean square error of the groundwater level. Adjust the model parameters according to the initial value of the permeability coefficient of the aquifer obtained in the preliminary test, so that the root mean square error of the groundwater level is within the preset range; 5) Use the corrected three-dimensional groundwater flow field model of the contaminated site to perform multi-field coupling simulation of groundwater flow field, temperature field, and solute concentration field. For groundwater flow field simulation, select the Darcy's law module in COMSOL Multiphysics 5.6 software, for temperature field simulation, select the porous medium heat transfer module in the software, and for solute concentration field distribution, select the porous medium dilute species transfer module in the software. Perform multi-physics field simulations of groundwater flow field-temperature field, groundwater flow field-solute concentration field, and groundwater flow field-temperature field-solute concentration field, respectively, to obtain the influence relationship between the fields under full coupling conditions; 6) Using the monitoring data at different depths in the tracer test, adjust and calibrate the permeability coefficient, thermal conductivity coefficient and diffusion coefficient in the groundwater flow field model to determine the optimal model for the contaminated site; 7) Based on the optimal model of the contaminated site, the pollutant migration parameters are predicted. The water level, temperature, conductivity or concentration of the aquifer are input into the optimal model to obtain the pollutant migration parameters, namely, permeability, thermal conductivity and diffusion coefficient.

2. According to claim 1, a method for obtaining key parameters of pollutant migration under the influence of site-scale temperature-hydrodynamic coupling is characterized in that: In the step 1), the experimental area of ​​the contaminated site is a 3×3m square, wherein the injection well H1, the pumping well H4 and the observation wells H2 and H3 are located at the four corners of the square experimental area, and the observation well H0 is located in the center of the square experimental area.

3. The method for obtaining key parameters of pollutant migration under the influence of site-scale temperature-hydrodynamic coupling according to claim 1 is characterized in that: In the step 1), the data of the pumping test and the micro-water test are processed by the Theis matching method, and the geological parameters of the aquifer are determined by comparing the measured curve with the theoretical curve.

4. The method for obtaining key parameters of pollutant migration under the influence of site-scale temperature-hydrodynamic coupling according to claim 1 is characterized in that: In the step 2), the probes in each well are HR8801 water level temperature monitoring recorder and HR-206A online conductivity sensor, which are a group connected to the underground measurement and control terminal, wherein the observation wells H0, H2, and H3 are respectively provided with water level temperature integrated sensors and conductivity sensors at depths of 8.5m, 9.5m, 10.5m, 11.5m, and 12.5m; the pumping well is provided with a group of water level temperature integrated sensors and conductivity sensors at a depth of 11.5m; and the injection well is provided with a group of water level temperature integrated sensors and conductivity sensors at a depth of 12.5m.

5. The method for obtaining key parameters of pollutant migration under the influence of site-scale temperature-hydrodynamic coupling according to claim 1 is characterized in that: In the step 3), the plane range of the three-dimensional structural model is a rectangle, the major axis of the rectangle is parallel to the line connecting the pumping and injection wells, the major axis is 18.55m, the minor axis is 10.11m, and the average vertical height is 18.67m; the model is divided into three layers according to the locations of the test wells and the observation wells, specifically: the surface to a burial depth of 4m is generalized as a fill layer, the burial depth of 4m to 13.5m is generalized as a clay layer, and the burial depth of 13.5m to the bottom of the model is generalized as a bedrock layer.

6. The method for obtaining key parameters of pollutant migration under the influence of site-scale temperature-hydrodynamic coupling according to claim 1 is characterized in that: In the step 3), the initial conditions and boundary conditions of the groundwater flow field model of the contaminated site are set as follows: The boundaries parallel to the artificial groundwater flow field are set as no-flow boundaries, the top and bottom surfaces of the model are no-flow boundaries, and the two side boundaries perpendicular to the main groundwater flow direction are set at the observation well position and set as constant head boundaries, and their head values ​​are set by the interpolation function; the top and bottom surfaces of the model are set as thermal insulation boundaries, the sides are set as open boundaries, and the injection wells are set as line heat source boundaries; the parameter settings of the porous medium dilute species transfer module are the same as those of the heat conduction module, the initial concentration of the model dilute species NaCl is set to 0, the top and bottom surfaces of the model are set as no flux boundaries, the sides are set as open boundaries, and the injection wells are set as line mass sources, and the mass flow rate of the solute substance is controlled by a piecewise function.

7. The method for obtaining key parameters of pollutant migration under the influence of site-scale temperature-hydrodynamic coupling according to claim 6 is characterized in that: In the step 4), when describing the accuracy of the groundwater flow field model, the root mean square error RMSE of the model is calculated, and the model parameters whose root mean square error RMSE meets the preset conditions are selected. The calculation formula of the root mean square error RMSE is as follows: In the formula, C i0 is the numerical simulation value of permeability coefficient, thermal conductivity coefficient or diffusion coefficient, C ie The actual measured value of permeability coefficient, thermal conductivity coefficient or diffusion coefficient, where n is the number of sampling points.

8. The method for obtaining key parameters of pollutant migration under the influence of site-scale temperature-hydrodynamic coupling according to claim 7 is characterized in that: In the step 5), the mass conservation equation and Darcy velocity equation are used to simulate the groundwater flow field under the unsteady flow state of the site. The energy conservation equation and Darcy velocity equation are as follows: Where t is time, unit is s; ∈ p is the porosity; ρ is the liquid density, in kg / m 3 ;Q m is the input mass source, in kg / (m 3 *s); κ is the permeability, unit is m 2 ; μ is dynamic viscosity, unit is MPa*s; is the pressure difference, in MPa; g is the acceleration due to gravity, in m / s 2 ; u is the groundwater velocity, in m / s 2 .

9. The method for obtaining key parameters of pollutant migration under the influence of site-scale temperature-hydrodynamic coupling according to claim 8, characterized in that: In the step 5), the energy conservation equation, heat conduction equation and effective thermal conductivity calculation formula are used to simulate the heat transfer of the porous medium in the site. The energy conservation equation, heat conduction equation and effective thermal conductivity calculation formula are as follows: k eff =θ s k s +∈1k f +k disp (6) In the formula, C p,f is the constant pressure heat capacity of the fluid, in J / (kg*K); ρ f is the fluid density, its unit is kg / m 3 ; u is the groundwater velocity, in m / s 2 ; T is Kelvin temperature, unit is K; Q is heat source term, unit is J; q is heat flow, unit is W / m 2 ;k eff is the effective thermal conductivity, in W / (m*K), which is determined by the solid matrix k s , fluid thermal conductivity k f The weighted average of the thermal diffusion coefficient k disp Determine, where θ s and ∈1 are weights.

10. The method for obtaining key parameters of pollutant migration under the influence of site-scale temperature-hydrodynamic coupling according to claim 1, characterized in that: In the step 5), the following porous medium dilute species transfer module control equation is selected to simulate salt migration: Where ρ is the liquid density in kg / m 3 ; C is the concentration of the dilute substance, in mol / m 3 ; t is time, in seconds; v is the velocity vector of the fluid, in meters per second; D is the diffusion coefficient of the dilute substance, in meters 2 / s; R is the source term, the unit is mol / (s*m 3 ).

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