Advantage flow evaluation method based on tracer migration

Abstract

The invention discloses a dominant flow evaluation method based on tracer migration. According to the method, in the design process, the influence of soil layer permeability difference on the tracer breakthrough curve is fully considered, and a systematic tracer breakthrough curve calculation method and a qualitative judgment process are provided. And predicting the change trend of the breakthrough curve through a numerical simulation test. According to the method, the accuracy of breakthrough curve judgment can be effectively improved, and the method is suitable for tracer migration analysis under different types of soil layers and complex geological conditions. By means of the method, the diffusion and dominant flow migration process of the tracer agent can be better evaluated, and reliable data support is provided for underground fluid migration and pollution monitoring.

Description

Technical Field

[0001] The present invention relates to the field of hydrogeology, and particularly to a method for evaluating preferential flow based on tracer migration. Background Art

[0002] In the field of hydrogeology, the research on seepage and solute transport in soil layers is a key topic for groundwater resource management, prediction of pollutant migration, and evaluation of reservoir characteristics. However, due to the heterogeneity of natural soil media, traditional preferential flow models have insufficient accuracy in describing the processes of groundwater flow and solute transport. Especially under the conditions of significant differences in permeability, porosity distribution, and fracture development, there are large deviations in the prediction of breakthrough curves. In addition, it is difficult to accurately measure seepage parameters and hydrodynamic parameters by conventional means, further increasing the difficulty of model application.

[0003] As an important analytical tool, the tracer technique can directly reflect the groundwater flow path, flow velocity, and solute distribution characteristics by observing the migration law of tracers in soil layers, effectively solving the problem that the migration law of traditional methods is unclear in heterogeneous media. Summary of the Invention

[0004] In view of the above problems, the present invention provides a method for calculating and judging tracer breakthrough curves based on the difference in soil layer permeability. Through analytical solutions, the migration law of tracers in soil layers with different permeabilities is systematically analyzed, and the accuracy and applicability of the method are verified. In sites where the influence of preferential flow is significant, this method can effectively identify characteristics such as early arrival peaks, double peaks, and trailing peaks, such as shortened breakthrough time, increased concentration peak value, and long-tail effect, providing a scientific basis for groundwater resource assessment, pollution site remediation, and related fields, and laying a foundation for tracer migration research and engineering applications.

[0005] To achieve the above object, the present invention provides a method for evaluating preferential flow based on tracer migration, including:

[0006] Constructing a soil body tracer migration model;

[0007] Performing dimensionless treatment on the soil body tracer migration model, and using the Green's function method to analytically solve the dimensionless soil body tracer migration model to obtain an analytical function;

[0008] Substituting different first parameter information into the analytical function for calculation to obtain a plurality of first breakthrough curves, and extracting first key curve feature information from the plurality of first breakthrough curves. The first key curve feature information includes at least one of single-peak feature, double-peak feature, trailing-peak feature, and early arrival peak feature. The first parameter information includes first seepage velocity ratio information and first soil layer thickness ratio information;

[0009] Construct a breakthrough curve feature classification chart based on the first key curve feature information and display it;

[0010] Obtain second parameter information, which is obtained by actual soil measurement;

[0011] Based on the second parameter information and the breakthrough curve feature classification chart, obtain the second breakthrough curve and the second key curve feature information corresponding to the current actual soil;

[0012] Generate the preferential flow evaluation information of tracer migration corresponding to the current actual soil according to the second breakthrough curve and the second key curve feature information.

[0013] In some embodiments, constructing a soil tracer migration model includes:

[0014] Set the geometric parameters of the soil, and the geometric parameters include the length and thickness of the soil;

[0015] In addition, set the initial conditions, boundary conditions, and continuity conditions of the soil tracer migration model.

[0016] In some embodiments, the soil includes a first layer of soil and a second layer of soil arranged in sequence from top to bottom, and the soil tracer migration model is represented by formula (1) and formula (2);

[0017] Formula (1) is as follows:

[0018] ;

[0019] Formula (2) is as follows:

[0020] ;

[0021] In formula (1) and formula (2), is the tracer concentration of the first layer of soil, is the tracer concentration in the second layer of soil, is the longitudinal effective hydrodynamic coefficient of the first layer of soil, is the transverse effective hydrodynamic coefficient of the first layer of soil, is the longitudinal effective hydrodynamic coefficient of the second layer of soil, is the transverse effective hydrodynamic coefficient of the second layer of soil, is the retardation coefficient of the first layer of soil, is the retardation coefficient of the second layer of soil, is the seepage velocity of the first layer of soil, is the seepage velocity of the second layer of soil.

[0022] In some embodiments, the boundary conditions are represented by formula (3), and formula (3) is as follows:

[0023] ;

[0024] The initial conditions are represented by Equation (4), and Equation (4) is as follows:

[0025] ;

[0026] The continuity conditions are represented by Equation (5) and Equation (6), and Equation (5) is as follows:

[0027] ;

[0028] Equation (6) is as follows:

[0029] ;

[0030] In Equations (5) to (6), is the height of the second layer of soil, is the porosity of the first layer of soil, is the porosity of the second layer of soil.

[0031] In some embodiments, the dimensionless treatment of the soil tracer migration model is represented by Equation (7), and Equation (7) is as follows:

[0032] ;

[0033] In Equation (7), is the dimensionless thickness calculation parameter, is the dimensionless void ratio calculation parameter, is the dimensionless retardation coefficient, is the normalized form of the transverse diffusion coefficient, is the normalized form of the longitudinal diffusion coefficient, is the dimensionless time, is the Peclet number of the first layer of soil, is the Peclet number of the second layer of soil, is the relative concentration of the first layer of soil, is the relative concentration of the second layer of soil, is the normalized coordinate in the direction, is the normalized coordinate in the

[0034] In some embodiments, the analytical functions are represented by Equation (8) and Equation (9), and Equation (8) is as follows:

[0035] ;

[0036] Equation (9) is as follows:

[0037] ;

[0038] In Equations (8) and (9), is the initial concentration distribution function of the first layer of soil mass, is the kernel function of the first layer of soil mass, representing the transfer relationship between different positions and times of the first layer of soil mass, is the concentration reaction rate function, is the dimensionless coordinate of the calculation point, is the dimensionless time of the calculation point, is the initial concentration distribution function of the second layer of soil mass, is the kernel function of the second layer of soil mass, representing the transfer relationship between different positions and times of the second layer of soil mass.

[0039] In some embodiments, by substituting different first parameter information into the analytical function for calculation, multiple first breakthrough curves are obtained, including:

[0040] Under the condition of fixing the first seepage velocity and the first soil layer thickness of the first layer of soil mass, by changing the second seepage velocity and the second soil layer thickness of the second layer of soil mass, multiple first breakthrough curves are obtained.

[0041] In some embodiments, a breakthrough curve feature classification chart is constructed and displayed according to the first key curve feature information, including:

[0042] The velocity calculation factor and the thickness calculation factor are calculated, and a breakthrough curve feature classification chart is constructed with the velocity calculation factor as the vertical coordinate and the thickness calculation factor as the horizontal coordinate.

[0043] In some embodiments, the velocity calculation factor is represented by Equation (10), and Equation (10) is as follows:

[0044] ;

[0045] In Equation (10), is the average value of the migration velocities of the first layer and the second layer of soil mass, is the migration velocity of the first layer of soil mass, is the migration velocity of the second layer of soil mass, is represented by Equation (11), and Equation (11) is as follows:

[0046] ;

[0047] The thickness calculation factor is represented by Equation (12), and Equation (12) is as follows:

[0048] ;

[0049] In formula (12), is the average value of the thickness of the first layer of soil and the second layer of soil, is the thickness of the first layer of soil, is the thickness of the second layer of soil, which is represented by formula (13), and formula (13) is as follows:

[0050] ;

[0051] In some embodiments, the preferential flow evaluation method based on tracer migration further includes:

[0052] Obtaining the third parameter information in the sample database, where the third parameter information is obtained by measuring the sample soil;

[0053] Obtaining the third breakthrough curve and the third key curve feature information corresponding to the current sample soil according to the third parameter information and the breakthrough curve feature classification chart;

[0054] Obtaining the sample breakthrough curve and the sample key curve feature information of the sample soil corresponding to the current third parameter information in the sample database;

[0055] Calculating the curve similarity value according to the third breakthrough curve and the sample breakthrough curve, and calculating the accuracy rate of the feature information according to the third key curve feature information and the sample key curve feature information;

[0056] Generating the model evaluation information of the soil tracer migration model according to the curve similarity value and the accuracy rate of the feature information.

[0057] Different from the prior art, the above technical solution constructs a mathematical model for tracer migration and uses the Green's function analytical method to solve the mathematical model for tracer migration, which can intuitively reveal the influence laws of different parameters (such as seepage velocity, soil layer thickness, retardation coefficient, etc.) on the breakthrough curve morphology, such as the generation mechanism of early arrival peaks and trailing peaks, and the formation conditions of double-peak characteristics. By simulating the migration process of tracers under different permeability conditions, the corresponding relationship between the velocity calculation, thickness calculation parameter space and the breakthrough curve is formed, and different types of breakthrough curve characteristics, including early arrival peaks, double peaks and trailing peaks, are located in the parameter space. Through the combination of the mathematical model and the analytical solution, a quantitative judgment factor and a graphical analysis method are proposed, which can more accurately identify the characteristics of early arrival peaks, double peaks and trailing peaks, reveal the main control factors of different migration mechanisms, and break through the limitations of traditional homogeneous assumptions. Compared with traditional methods, the prior art often relies only on numerical simulation for separate analysis, lacks the support of theoretical analysis, and is difficult to accurately judge the breakthrough curve characteristics under complex soil layer conditions. The present invention not only improves the calculation efficiency through the coupling of the analytical method and the numerical method, but also improves the accuracy of the results and the theoretical interpretability, and can more effectively solve the problems of formation property evaluation and preferential flow identification in practical engineering.

[0058] The above description of the invention content is only an overview of the technical solution of the present invention. In order to enable those of ordinary skill in the art to more clearly understand the technical solution of the present invention, and then can be implemented according to the content recorded in the description and the drawings, and in order to make the above objects, other objects, features and advantages of the present invention more easily understood, the following is described in conjunction with the specific embodiments of the present invention and the drawings. Brief Description of the Drawings

[0059] The drawings are only used to illustrate the principles, implementation methods, applications, features and effects of the specific embodiments of the present invention and other related contents, and should not be regarded as a limitation of the present invention.

[0060] In the drawings of the specification:

[0061] Figure 1 It is a step schematic diagram of steps S101 to S107 of the preferential flow evaluation method based on tracer migration described in the specific embodiment;

[0062] Figure 2 It is a flow chart of the method for calculating and judging the tracer breakthrough curve based on the difference in soil layer permeability described in the specific embodiment;

[0063] Figure 3 It is a comparison of the analytical solution of the tracer concentration and the numerical solution based on the finite element method for the double-layer permeability soil layer described in the specific embodiment;

[0064] Figure 4It is the breakthrough curve feature classification chart described in the specific implementation manner;

[0065] Figure 5 It is the verification and comparison with the actual tracer test described in the specific implementation manner (double peak);

[0066] Figure 6 It is the verification and comparison with the actual tracer test described in the specific implementation manner (single peak). Specific implementation manner

[0067] To illustrate in detail the possible application scenarios, technical principles, specific implementable solutions, achievable purposes and effects of the present invention, the following will be described in detail with reference to the specific examples listed and in conjunction with the accompanying drawings. The embodiments described herein are only used to more clearly illustrate the technical solutions of the present invention, and thus are only examples and cannot be used to limit the protection scope of the present invention.

[0068] Referring to "embodiment" herein means that the specific features, structures or characteristics described in connection with the embodiment can be included in at least one embodiment of the present invention. The term "embodiment" appearing in various positions in the specification does not necessarily refer to the same embodiment, nor does it particularly limit its independence or relevance to other embodiments. In principle, in the present invention, as long as there is no technical contradiction or conflict, the technical features mentioned in each embodiment can be combined in any way to form corresponding implementable technical solutions.

[0069] Unless otherwise defined, the meanings of the technical terms used herein are the same as those commonly understood by those skilled in the technical field to which the present invention belongs; the use of the relevant terms herein is only for describing specific embodiments and is not intended to limit the present invention.

[0070] In the description of the present invention, the term "and / or" is an expression used to describe the logical relationship between objects, indicating that three relationships can exist. For example, A and / or B means: there is A, there is B, and there is both A and B at the same time. In addition, the character " / " in this article generally represents an "or" logical relationship between the associated objects before and after.

[0071] In the present invention, terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual quantity, primary or secondary, or order relationship between these entities or operations.

[0072] Without further limitations, in the present invention, the open-ended expressions such as "including", "comprising", "having" or other similar expressions used in the statements are intended to cover non-exclusive inclusion. These expressions do not exclude the possibility that there may be additional elements in the process, method or product including the said elements, so that in a process, method or product including a series of elements, it may not only include those defined elements, but also include other elements not explicitly listed, or elements inherent to such process, method or product.

[0073] Similar to the understanding in the "Examination Guidelines", in the present invention, expressions such as "greater than", "less than", "exceeding" are understood not to include the base number; expressions such as "above", "below", "within" are understood to include the base number. In addition, in the description of the embodiments of the present invention, the meaning of "a plurality of" is two or more (including two), and similar expressions related to "many" are also understood in this way, such as "multiple groups", "multiple times", etc., unless otherwise specifically defined.

[0074] Please refer to Figures 1 to 4 , this embodiment provides a preferential flow evaluation method based on tracer migration, including:

[0075] S101. Construct a soil tracer migration model;

[0076] S102. Nondimensionalize the soil tracer migration model, and analytically solve the nondimensionalized soil tracer migration model using the Green's function method to obtain an analytical function;

[0077] S103. Substitute different first parameter information into the analytical function for calculation to obtain a plurality of first breakthrough curves, and extract first key curve characteristic information from the plurality of first breakthrough curves. The first key curve characteristic information includes at least one of single-peak characteristic, double-peak characteristic, trailing-peak characteristic, and early-arrival peak characteristic. The first parameter information includes first seepage velocity ratio information and first soil layer thickness ratio information;

[0078] S104. Construct a breakthrough curve characteristic classification chart according to the first key curve characteristic information and display it;

[0079] S105. Obtain second parameter information, which is obtained by measuring the actual soil;

[0080] S106. Obtain a second breakthrough curve and second key curve characteristic information corresponding to the current actual soil according to the second parameter information and the breakthrough curve characteristic classification chart;

[0081] S107. Generate preferential flow evaluation information of tracer migration corresponding to the current actual soil according to the second breakthrough curve and the second key curve characteristic information.

[0082] In this embodiment, for the boundary conditions and continuity conditions of the control equation for determining the migration law of common soil tracers, the boundary conditions include the initial concentration setting at the tracer input position, the concentration constraint at the end of the soil seepage path, and the mass continuity and flux continuity conditions at the soil interface. Based on these restrictive conditions, the Green's function method is used to solve the analytical solution of the soil tracer migration model after dimensionless transformation, and an analytical function is obtained. By solving the breakthrough curves under different seepage velocity ratios and different soil layer thickness ratios through the analytical function, multiple first breakthrough curves are obtained, and the key curve characteristic factors (i.e., the first key curve characteristic information) related to normal single peaks, double peaks, trailing peaks, and early arrival peaks are collected, providing a basis for subsequent classification and analysis.

[0083] Construct a breakthrough curve characteristic classification chart according to the first key curve characteristic information. For details, please refer to Figure 4 In the figure, different curve types may form specific regions or distribution trends. Through such a visual representation, not only can the distribution positions of different types of breakthrough curves in the parameter space be intuitively displayed, but it also helps us more conveniently observe and analyze the relationships and distribution laws among these curves, providing more intuitive data support and analysis basis for subsequent studies on soil layer characteristics, permeability differences, and tracer migration mechanisms.

[0084] According to the breakthrough curve characteristic classification chart, match the velocity calculation factor and soil layer thickness calculation factor obtained from the experiment (i.e., the second parameter information), determine the shape of the second breakthrough curve and the second key curve characteristic information, judge the position of the second breakthrough curve in the summary chart, infer information such as formation permeability differences and tracer flow paths through curve characteristics, compare the prediction results with the actual survey data to verify the reliability of the method, and at the same time optimize the values of the velocity and thickness calculation factors to improve the applicability and accuracy of the method.

[0085] This method is based on tracer concentration data, combines analytical solutions with numerical analysis, and systematically analyzes the migration characteristics of tracers under different permeability conditions. Especially in sites where the influence of preferential flow is significant, it can accurately identify key characteristics in the breakthrough curve, such as shortened breakthrough time, increased concentration peak, and long-tail effect. This not only provides a theoretical basis for the accurate extraction of formation seepage parameters, retardation coefficients, and hydrodynamic parameters, but also provides scientific support for groundwater resource assessment and pollution site remediation under complex geological conditions, breaking through the limitations of traditional homogeneous assumptions and having important engineering application value.

[0086] In some embodiments, constructing a soil tracer migration model includes:

[0087] Set the geometric parameters of the soil, and the geometric parameters include the length and thickness of the soil;

[0088] And set the initial conditions, boundary conditions, and continuity conditions of the soil tracer migration model.

[0089] In some embodiments, the soil includes a first layer of soil and a second layer of soil arranged in sequence from top to bottom, and the soil tracer migration model is represented by Formula (1) and Formula (2);

[0090] Formula (1) is as follows:

[0091] ;

[0092] Formula (2) is as follows:

[0093] ;

[0094] In Formula (1) and Formula (2), is the tracer concentration of the first layer of soil, is the tracer concentration in the second layer of soil, is the longitudinal effective hydrodynamic coefficient of the first layer of soil, is the transverse effective hydrodynamic coefficient of the first layer of soil, is the longitudinal effective hydrodynamic coefficient of the second layer of soil, is the transverse effective hydrodynamic coefficient of the second layer of soil, is the retardation coefficient of the first layer of soil, is the retardation coefficient of the second layer of soil, is the seepage velocity of the first layer of soil, is the seepage velocity of the second layer of soil.

[0095] Among them, regarding the calculation method of the retardation coefficient is expressed as follows:

[0096] ;

[0097] In the formula: is the first layer of soil, is the second layer of soil, is the density, is the permeability coefficient of the soil.

[0098] The calculation method for the diffusion coefficient D is as follows:

[0099] ;

[0100] ;

[0101] In the formula: is the longitudinal dispersivity, is the transverse dispersivity, is the molecular diffusion coefficient.

[0102] In some embodiments, the boundary conditions are represented by Equation (3), and Equation (3) is as follows:

[0103] ;

[0104] The initial conditions are represented by Equation (4), and Equation (4) is as follows:

[0105] ;

[0106] The continuity conditions are represented by Equation (5) and Equation (6). Equation (5) is as follows:

[0107] ;

[0108] Equation (6) is as follows:

[0109] ;

[0110] In Equations (5) to (6), is the height of the second layer of soil mass, is the porosity of the first layer of soil mass, is the porosity of the second layer of soil mass.

[0111] In some embodiments, the dimensionless treatment of the soil tracer migration model is represented by Equation (7), and Equation (7) is as follows:

[0112] ;

[0113] In Equation (7), is the dimensionless thickness calculation parameter, is the dimensionless void ratio calculation parameter, is the dimensionless retardation coefficient, is the normalized form of the transverse diffusion coefficient, is the normalized form of the longitudinal diffusion coefficient, is the dimensionless time, is the Peclet number of the first layer of soil mass, is the Peclet number of the second layer of soil mass, is the relative concentration of the first layer of soil mass, is the relative concentration of the second layer of soil mass, is the normalized coordinate in the direction, is the normalized coordinate in the

[0114] direction. In this embodiment, the dimensionless parameters simplify parameters such as concentration, time, and thickness, improving the solution efficiency.

[0115] After dimensionless transformation, the soil tracer migration model becomes:

[0116] ;

[0117] .

[0118] In some embodiments, the analytical function is represented by formulas (8) and (9). Formula (8) is as follows:

[0119] ;

[0120] Formula (9) is as follows:

[0121] ;

[0122] In formulas (8) and (9), is the initial concentration distribution function of the first layer of soil, is the kernel function of the first layer of soil, representing the transfer relationship between different positions and times of the first layer of soil, is the concentration reaction rate function, is the dimensionless coordinate of the calculation point, is the dimensionless time of the calculation point, is the initial concentration distribution function of the second layer of soil, is the kernel function of the second layer of soil, representing the transfer relationship between different positions and times of the second layer of soil.

[0123] In this embodiment, the Green's function method is used to expand the dimensionless soil tracer migration model in integral form:

[0124] ;

[0125] ;

[0126] Where:

[0127] ;

[0128] ;

[0129]

[0130]

[0131] ;

[0132] ;

[0133] ;

[0134] Regarding the function The solution process is as follows:

[0135] ;

[0136] ;

[0137] .

[0138] In some embodiments, different first parameter information is substituted into the analytical function for calculation, and multiple first breakthrough curves are obtained, including:

[0139] Under the condition of fixing the first seepage velocity and the first soil layer thickness of the first layer of soil, by changing the second seepage velocity and the second soil layer thickness of the second layer of soil, multiple first breakthrough curves are obtained.

[0140] In this embodiment, by solving the breakthrough curves under different seepage velocity ratios and different soil layer thickness ratios, the key curve characteristic factors of normal single peak, double peak, trailing peak, and early arrival peak are collected.

[0141] According to the tracer test in a certain place in Fujian, the specific operation steps of the test are as follows: First, determine the experimental site and conduct hydrogeological borehole exploration to clarify the characteristics of the aquifer in the site. At the same time, reasonably set the well spacing according to the site conditions, determine the injection well and the collection well used in the test, and ensure good hydraulic connectivity between the injection well and the collection well. Subsequently, configure the Br⁻ tracer solution, record its initial concentration, and determine the appropriate injection concentration and injection flow rate.

[0142] At the beginning of the experiment, inject the Br⁻ tracer solution into the injection well at a constant flow rate. After injecting for a certain period of time, stop, and record the injection flow rate, concentration, and time during the whole injection process. When the tracer is injected, start sampling synchronously in the collection well. The sampling frequency is relatively high at the beginning, and then gradually decreases according to the change of the tracer concentration. The collected water samples are detected for the Br⁻ concentration using ion chromatography or spectrophotometry. According to the collected data, draw the breakthrough curve.

[0143] After the experiment, evaluate the site to ensure that the tracer will not cause residual impact on the environment, and sort out and analyze the collected experimental data to provide a reliable basis for the subsequent research on the groundwater migration characteristics.

[0144] According to this experiment, the following parameters were obtained. It should be noted in advance that in order to reduce the difficulty of calculation, the test site and related parameters were scaled down in order of magnitude. The parameters are as follows: The overall length of the test site is 4m, the thickness of both soil layers is 0.3m, the tracer migration speed in the upper layer is 0.1m / h, the tracer concentration in the lower layer is 0.07m / h, and the dispersion degree is 0.01m. At the same time, due to the order of magnitude is very small, generally 10 to the negative tenth power, so simplification was carried out. And considering that Br⁻ is an inert tracer and has no adsorption, the retardation coefficient both take 1.

[0145] In this step, the analytical solution of the test site was first verified, and then batch numerical tests were carried out on combinations of different soil layer thicknesses and tracer migration speeds. According to the test results, the analytical solution concentration was calculated and the breakthrough curve was plotted.

[0146] The characteristics of the collected breakthrough curves are as follows: The normal single peak shows a shape: the breakthrough curve shape presents an approximately symmetric single-peak distribution, and the peak position mainly reflects the value of the soil layer permeability coefficient; The double-peak shape shows: there are cases where there is a low peak in front and a high peak in front, usually showing the superposition effect of different permeable layers or flow velocity regions, and the difference in peak positions reveals the non-uniformity of the soil layer permeability coefficient; The shape characteristics of the trailing peak are: although the peak appears, the tracer concentration gradually decreases in subsequent time without decreasing to zero, which indicates that the migration of the tracer in the soil layer is affected by diffusion or retardation effects, usually reflecting the difference in soil layer thickness; The shape characteristics of the early arrival peak are: the peak appears in the early stage of the time axis, indicating that there are preferential flow paths in the soil layer, resulting in the tracer penetrating at a faster speed, showing significant differences in the migration channels.

[0147] In some embodiments, a breakthrough curve characteristic classification chart is constructed according to the first key curve characteristic information and displayed, including:

[0148] Calculate the velocity calculation factor and the thickness calculation factor, and construct a breakthrough curve characteristic classification chart with the velocity calculation factor as the vertical coordinate and the thickness calculation factor as the horizontal coordinate.

[0149] In this embodiment, in order to summarize different time-concentration curve types, the velocity calculation factor and the thickness calculation factor are used as new plotting coordinates. Specifically, with the velocity calculation factor as the ordinate and the thickness calculation factor as the abscissa, a characteristic classification chart of the breakthrough curve is constructed. In this way, various forms of breakthrough curves can be clearly represented as coordinate points on the chart in this embodiment. It can not only visually display the distribution positions of different types of breakthrough curves in the parameter space, but also more conveniently observe and analyze the relationships between these curves and their distribution laws. In the figure, different curve types may form specific regions or distribution trends. Through such a visual representation, these laws can be more effectively identified, providing more intuitive data support and analysis basis for subsequent studies on soil layer characteristics, permeability differences, and tracer migration mechanisms.

[0150] In some embodiments, the velocity calculation factor is represented by formula (10), and formula (10) is as follows:

[0151] ;

[0152] In formula (10), is the average of the migration velocities of the first soil layer and the second soil layer, is the migration velocity of the first soil layer, is the migration velocity of the second soil layer, is represented by formula (11), and formula (11) is as follows:

[0153] ;

[0154] The thickness calculation factor is represented by formula (12), and formula (12) is as follows:

[0155] ;

[0156] In formula (12), is the average of the thicknesses of the first soil layer and the second soil layer, is the thickness of the first soil layer, is the thickness of the second soil layer, is represented by formula (13), and formula (13) is as follows:

[0157] ;

[0158] In this embodiment, reflects the relationship between the tracer migration velocity and the fluid movement velocity, and is directly related to the seepage velocity, the dominant flow velocity, and the medium permeability. For example, a high velocity calculation factor corresponds to a rapid breakthrough phenomenon, which often occurs in highly permeable fractured media. The tracer will reach the observation point in a short time, showing an early arrival peak. Describes the influence of soil layer thickness or tracer migration path length on the breakthrough curve shape. For example, a larger usually indicates that the tracer has a longer migration time in the soil layer, and is prone to diffusion, dispersion, and retardation effects, resulting in a trailing concentration peak or a multi-peak curve phenomenon.

[0159] Taking the calculated velocity factor as the ordinate and the thickness factor as the abscissa, a summary diagram of the breakthrough curve form is plotted. Please refer to Figure 4 . The soil layer properties determine the tracer migration behavior. For example, highly permeable soil layers often show a shortened breakthrough time and form an early arrival peak, while low permeable soil layers result in a trailing concentration curve due to diffusion and retardation effects. According to Figure 4 the analysis of the rules in, the following conclusions can be drawn: The appearance of the double-peak region usually indicates a significant difference in the soil layer permeability coefficients, resulting in the superposition of the two-layer seepage velocity changes. The formation of the trailing peak is mainly closely related to the difference in soil layer thickness. The change in thickness will affect the diffusion and migration characteristics of the tracer in the soil layer, resulting in a slow and continuous concentration decay process. As for the early arrival peak phenomenon, its fundamental reason lies in the existence of preferential flow. These flow paths provide a fast penetration channel for the tracer, thus significantly shortening the breakthrough time. These characteristics not only reflect the differences in soil layer physical properties but also provide an important basis for further studying the tracer flow rules.

[0160] Taking the velocity calculation factor as the ordinate and the thickness calculation factor as the abscissa, a summary table of the breakthrough curve is plotted. It is found that above the curve is the early arrival peak, below which are mostly single peaks, including normal single peaks and trailing peaks, and the trailing peaks are generally concentrated below the curve and in the part of, between the two curves is the double-peak curve, and its shape has either a short peak in front or a high peak in front.

[0161] In some embodiments, the preferential flow evaluation method based on tracer migration further includes:

[0162] Obtaining the third parameter information in the sample database, where the third parameter information is obtained by measuring the sample soil body;

[0163] According to the third parameter information and the breakthrough curve feature classification chart, obtaining the corresponding third breakthrough curve and the third key curve feature information of the current sample soil body;

[0164] Obtaining the sample breakthrough curve and the sample key curve feature information of the sample soil body corresponding to the current third parameter information in the sample database;

[0165] Calculate the curve similarity value according to the third breakthrough curve and the sample breakthrough curve, and calculate the accuracy rate of the characteristic information according to the third key curve characteristic information and the sample key curve characteristic information;

[0166] Generate the model evaluation information of the soil tracer migration model according to the curve similarity value and the accuracy rate of the characteristic information.

[0167] In this embodiment, according to the breakthrough curve characteristic classification chart, match the experimentally obtained velocity calculation factor and soil layer thickness calculation factor, determine the shape and characteristics of the breakthrough curve, and judge the position of the curve in the summary chart. Infer information such as the formation permeability difference and the tracer flow path through the curve characteristics, compare the prediction results with the actual survey data to verify the reliability of the method, and at the same time optimize the values of the velocity and thickness calculation factors to improve the applicability and accuracy of the method. For specific verification, please refer to Figure 5 and Figure 6 .

[0168] Please refer to Figure 5 The relevant parameters of the specific verification experiment are: = 38 m / h, = 6 m / h, = 10 m, = 12 m. The velocity factor V = 0.42 and the thickness calculation factor B = 1.10 calculated according to the test parameters are roughly in the range of the double-peak area in the Figure 4 summary table, which proves the accuracy of the calculation factor in breakthrough curve prediction.

[0169] Please refer to Figure 6 The relevant parameters of the specific verification experiment are: = 0.72 m / d, = 0.19 m / d, = 2.7 m, = 1.6 m. The velocity factor V = 0.52 and the thickness calculation factor B = 0.77 calculated according to the test parameters are roughly in the range of the single-peak area in the Figure 4 summary table, which proves the accuracy of the calculation factor in breakthrough curve prediction.

[0170] Through the construction of a mathematical model for tracer migration and the use of the Green's function analytical method to solve the mathematical model of tracer migration, the above technical solution can intuitively reveal the influence laws of different parameters (such as seepage velocity, soil layer thickness, retardation coefficient, etc.) on the breakthrough curve morphology, such as the generation mechanism of early arrival peaks and trailing peaks, and the formation conditions of double-peak characteristics. By simulating the migration process of tracers under different permeability conditions, the corresponding relationships between the velocity calculation, thickness calculation parameter space, and breakthrough curves are formed, and different types of breakthrough curve characteristics, including early arrival peaks, double peaks, and trailing peaks, are located in the parameter space. Through the combination of the mathematical model and the analytical solution, a quantitative judgment factor and a graphical analysis method are proposed, which can more accurately identify the characteristics of early arrival peaks, double peaks, and trailing peaks, reveal the main control factors of different migration mechanisms, and break through the limitations of the traditional homogeneous assumption. Compared with the traditional method, the existing technology often relies only on numerical simulation for separate analysis, lacks the support of theoretical analysis, and is difficult to accurately judge the breakthrough curve characteristics under complex soil layer conditions. Through the coupling of the analytical method and the numerical method, the present invention not only improves the calculation efficiency, but also improves the accuracy and theoretical interpretability of the results, and can more effectively solve the problems of formation property evaluation and preferential flow identification in practical engineering.

[0171] Finally, it should be noted that although the above embodiments have been described in the text and drawings of the specification of the present invention, the patent protection scope of the present invention cannot be limited thereby. Any technical solutions obtained by equivalent structure or equivalent process substitution or modification based on the essential concept of the present invention and using the content recorded in the text and drawings of the specification of the present invention, as well as those directly or indirectly implementing the technical solutions of the above embodiments in other related technical fields, are included in the patent protection scope of the present invention.

Claims

1. A method for evaluating dominant flow based on tracer migration, characterized in that: The method comprises: Construct soil tracer transport model; The soil tracer migration model is dimensionally processed, and the dimensionally processed soil tracer migration model is analytically solved using a Green's function method to obtain an analytical function; Substituting different first parameter information into the analytical function for calculation, a plurality of first breakthrough curves are obtained, and first key curve characteristic information is extracted from the plurality of first breakthrough curves, wherein the first key curve characteristic information includes at least one of a single peak characteristic, a double peak characteristic, a tailing peak characteristic, and an early peak characteristic, and the first parameter information includes first seepage velocity ratio information and first soil layer thickness ratio information; Construct and display a breakthrough curve feature classification chart based on the first key curve feature information; Acquiring second parameter information, where the second parameter information is obtained by actual soil measurement; Obtaining the second breakthrough curve and second key curve characteristic information corresponding to the current actual soil body according to the second parameter information and the breakthrough curve characteristic classification chart; The dominant flow assessment information of the tracer migration corresponding to the current actual soil body is generated according to the characteristic information of the second breakthrough curve and the second key curve.

2. The method for evaluating dominant flow based on tracer migration according to claim 1, characterized in that: The construction of soil tracer transport model includes: Setting geometric parameters of the soil body, wherein the geometric parameters include the length and thickness of the soil body; And, the initial conditions, boundary conditions and continuity conditions of the soil tracer migration model are set.

3. The method for evaluating the dominant flow based on tracer migration according to claim 2, characterized in that: The soil body includes a first soil layer and a second soil layer arranged in sequence from top to bottom, and the soil tracer migration model is expressed by formula (1) and formula (2); The formula (1) is as follows: ； The formula (2) is as follows: ； In formula (1) and formula (2), is the tracer concentration of the first soil layer, is the tracer concentration in the second soil layer, is the longitudinal effective hydrodynamic coefficient of the first layer of soil, is the lateral effective hydrodynamic coefficient of the first layer of soil, is the longitudinal effective hydrodynamic coefficient of the second soil layer, is the lateral effective hydrodynamic coefficient of the second soil layer, is the resistance coefficient of the first soil layer, is the resistance coefficient of the second soil layer, is the seepage velocity of the first soil layer, is the seepage velocity of the second soil layer.

4. The method for evaluating dominant flow based on tracer migration according to claim 2 or 3, characterized in that: The boundary condition is expressed by formula (3), which is as follows: ； The initial condition is expressed by formula (4), which is as follows: ； The continuity condition is expressed by formula (5) and formula (6), and the formula (5) is as follows: ； The formula (6) is as follows: ； In formula (5) to formula (6), is the height of the second soil layer, is the porosity of the first soil layer, is the porosity of the second soil layer.

5. The method for evaluating dominant flow based on tracer migration according to claim 3, characterized in that: The soil tracer migration model is dimensionlessly processed and expressed by formula (7), which is as follows: ； In formula (7), is the dimensionless thickness calculation parameter, is the dimensionless void ratio calculation parameter, is the dimensionless retardation coefficient, is the normalized form of the lateral diffusion coefficient, is the normalized form of the longitudinal diffusion coefficient, is the dimensionless time, is the Peclet number of the first soil layer, is the Peclet number of the second soil layer, is the relative concentration of the first soil layer, is the relative concentration of the second layer, for The normalized coordinates in the direction, for Normalized coordinates in direction.

6. The method for evaluating dominant flow based on tracer migration according to claim 5, characterized in that: The analytical function is expressed by formula (8) and formula (9), and the formula (8) is as follows: ； The formula (9) is as follows: ； In formula (8) and formula (9), is the initial concentration distribution function of the first layer of soil, is the kernel function of the first layer of soil, which characterizes the transfer relationship between different positions and times of the first layer of soil. is the concentration reaction rate function, To calculate the dimensionless coordinates of the point, is the dimensionless time of the calculation point, is the initial concentration distribution function of the second soil layer, is the kernel function of the second soil layer, which characterizes the transfer relationship between different positions and times of the second soil layer.

7. The method for evaluating dominant flow based on tracer migration according to claim 1, characterized in that: Substituting different first parameter information into the analytical function for calculation, a plurality of first breakthrough curves are obtained, including: Under the condition of fixing the first seepage velocity of the first soil layer and the first soil layer thickness, changing the second seepage velocity of the second soil layer and the second soil layer thickness, a plurality of the first breakthrough curves are obtained.

8. The method for evaluating dominant flow based on tracer migration according to claim 1, characterized in that: According to the first key curve characteristic information, a breakthrough curve characteristic classification chart is constructed and displayed, including: The speed calculation factor and the thickness calculation factor are calculated, and the breakthrough curve characteristic classification chart is constructed with the speed calculation factor as the ordinate and the thickness calculation factor as the abscissa.

9. The method for evaluating dominant flow based on tracer migration according to claim 8, characterized in that: The speed calculation factor is expressed by formula (10), which is as follows: ； In formula (10), is the speed calculation factor, is the average of the movement velocities of the first and second soil layers. is the movement velocity of the first layer of soil, is the movement velocity of the second layer of soil, It is expressed by formula (11), which is as follows: ； The thickness calculation factor is expressed by formula (12), and the formula (12) is as follows: ； In formula (12), is the thickness calculation factor, is the average thickness of the first and second soil layers, is the thickness of the first soil layer, is the thickness of the second soil layer, It is expressed by formula (13), which is as follows: 。 10. The method for evaluating dominant flow based on tracer migration according to claim 1, characterized in that: The method further comprises: Acquire third parameter information in the sample database, where the third parameter information is obtained by measuring the sample soil body; Obtaining the third breakthrough curve and the third key curve characteristic information corresponding to the current sample soil body according to the third parameter information and the breakthrough curve characteristic classification chart; Acquire, in the sample database, a sample breakthrough curve and sample key curve characteristic information of the sample soil corresponding to the current third parameter information; Calculating a curve similarity value according to the third breakthrough curve and the sample breakthrough curve, and calculating the accuracy of feature information according to the third key curve feature information and the sample key curve feature information; Model evaluation information of the soil tracer migration model is generated according to the curve similarity value and the accuracy of the characteristic information.

Images