Thermal tracing test device and method for determining comprehensive hydrogeological conditions of aquifer

Abstract

The invention discloses a thermal tracing test device and method for determining the comprehensive hydrogeological condition of an aquifer, and the device comprises a water storage system, a medium groove, a heating system, and a distributed optical fiber data collection system. The device is simple in structure and intelligent and convenient to operate, instantaneous / continuous linear heat source excitation can be achieved through the heating system, and the water pressure and temperature change conditions of all positions are monitored in real time through the distributed optical fiber data acquisition system; the comprehensive hydrogeological parameters such as the flow velocity, the flow direction, the permeability coefficient, the thermal diffusion coefficient, the thermal capacity and the heat conductivity coefficient of underground water are studied, the heating system and the distributed optical fiber data acquisition system can be used for indoor tests and field tests, operation is easy and convenient, data precision is high, and practicability is high.

Description

Technical Field

[0001] The invention relates to a thermal tracer test device and method for determining comprehensive hydrogeological conditions of an aquifer, and belongs to the technical field of groundwater thermal tracer tests in the green, low-carbon, clean energy industry. Background Art

[0002] The determination of hydrogeological conditions such as groundwater flow velocity and direction and aquifer hydrogeological parameters plays an important role in the normal development of the project. However, the equipment and methods used in existing survey methods are mostly time-consuming and labor-intensive, and many methods no longer meet the environmental protection requirements of new-era engineering projects.

[0003] At present, the most commonly used methods for measuring groundwater flow velocity and direction are the three-hole method and the isotope tracer method. The three-hole method has requirements for the layout of the boreholes and needs to obtain water level data from three boreholes at the same time. The isotope tracer method is strictly controlled due to the radioactivity of isotopes. There are currently two main types of tests for the determination of permeability and thermal conductivity: indoor tests and field tests. The test methods for permeability are relatively mature, but the determination of thermal conductivity is still in the development stage, which mainly uses thermal response tests for determination. The cycle of thermal response tests is often relatively long, and it is difficult to quickly obtain the thermal conductivity of the aquifer, and it is also impossible to obtain groundwater flow velocity and direction information in a single hole. Summary of the invention

[0004] In order to achieve single-hole determination of comprehensive hydrogeological conditions such as groundwater flow velocity and direction, permeability coefficient and thermal conductivity, the present invention provides a thermal tracer test device and method for determining comprehensive hydrogeological conditions of an aquifer with simple operation and comprehensive functions.

[0005] In order to solve the above technical problems, the technical solutions adopted by the present invention are as follows:

[0006] A thermal tracer test device for determining the comprehensive hydrogeological conditions of an aquifer, comprising a water storage system, a medium tank, a heating system and a distributed optical fiber data acquisition system;

[0007] The water storage system includes a first upper water storage tank, a first lower water storage tank, a second upper water storage tank and a second lower water storage tank;

[0008] The first upper water storage tank and the second upper water storage tank are respectively arranged on both sides of the medium tank; the first upper water storage tank and the medium tank are separated only by the first water permeable plate, and the second upper water storage tank and the medium tank are separated only by the second water permeable plate;

[0009] The first lower water storage tank is arranged at the bottom of the first upper water storage tank, and a first water level regulating plate is arranged on the first upper water storage tank. When the first water level regulating plate is adjusted, the overflowing water falls into the first lower water storage tank; the second lower water storage tank is arranged at the bottom of the second upper water storage tank, and a second water level regulating plate is arranged on the second upper water storage tank. When the second water level regulating plate is adjusted, the overflowing water falls into the second lower water storage tank;

[0010] There are more than one layer of medium in the medium tank, and the medium is provided with a test main hole and observation points that run through the entire height direction of the medium. The number of observation points is more than six. The test main hole is set at the center of the medium, and the observation points are distributed around the test main hole;

[0011] The heating system includes a heating rod, an electric wire and a power supply connected in sequence. The heating rod is arranged in the main test hole. The instantaneous / continuous heat source is excited by adjusting the power supply, thereby changing the temperature field in the aquifer.

[0012] The distributed fiber optic data acquisition system includes distributed optical fiber and optical fiber demodulator. The main test hole and observation points are equipped with distributed optical fibers set along the height direction, that is, the optical fiber demodulator vertically penetrates from the bottom of the medium to the top of the medium; the distributed optical fiber monitors and records the temperature and water pressure at the measured position, and analyzes and outputs the data through the optical fiber demodulator.

[0013] The water level of the first upper water tank is controlled by the height of the first water level regulating plate, and the water level of the second upper water tank is controlled by the height of the second water level regulating plate. Excess water flows into the first lower water tank and the second lower water tank respectively through the first water level regulating plate and the second water level regulating plate.

[0014] In order to achieve omnidirectional measurement, the distributed optical fiber on the test main hole spirals up around the inner or outer wall of the test main hole.

[0015] In order to improve the measurement accuracy, the first water-permeable plate and the second water-permeable plate are both provided with sand-isolating and water-permeable gauze on one side adjacent to the medium to ensure that water can pass normally while isolating the sand.

[0016] As one of the specific preferred implementation schemes, the first water-permeable plate and the second water-permeable plate are both provided with water-permeable holes, and the water-permeable holes are provided with movably connected rubber plugs. The position of the water-passing section can be adjusted by opening or plugging the rubber plugs on the water-permeable holes at different positions on the first water-permeable plate and the second water-permeable plate.

[0017] In order to meet the requirements of routine tests, the medium includes a phreatic aquifer, a weakly permeable layer and a confined aquifer that are connected in sequence from top to bottom. The medium is replaced as needed to simulate the phreatic aquifer, a weakly permeable layer and a confined aquifer. Different aquifer media can choose sandy soil and clay soil with different particle sizes and different compositions.

[0018] A thermal tracer test method for determining the comprehensive hydrogeological conditions of an aquifer, using the thermal tracer test device for determining the comprehensive hydrogeological conditions of an aquifer, comprises the following steps:

[0019] 1) Adjust the water permeability position on the first water permeable plate and the second water permeable plate;

[0020] 2) Fill the medium slots with medium in layers and install a distributed optical fiber data acquisition system;

[0021] 3) adding water to the first upper water storage tank and the second upper water storage tank to stratify and saturate the medium in the medium tank;

[0022] 4) Start the distributed optical fiber data acquisition system to collect water pressure, temperature and heat flux density data in real time;

[0023] 5) controlling the water levels in the first upper water storage tank and the second upper water storage tank by means of the first water level regulating plate and the second water level regulating plate to form a stable seepage field and an unstable seepage field under different hydraulic gradients;

[0024] 6) Turn on the heating system to excite the instantaneous heat source and the constant heat source. By changing the output power of the heating rod, the excitation intensity of the heat source in the main test hole is changed, thereby changing the temperature field in the aquifer;

[0025] 7) The water pressure, temperature and heat flux density changes of the aquifer are recorded in real time through the distributed optical fiber data acquisition system, and the water pressure, temperature and heat flux density data of the whole test process are derived;

[0026] 8) Turn off the heating system and distributed optical fiber data acquisition system, and end the test;

[0027] 9) The comprehensive hydrogeological conditions such as flow velocity, flow direction and hydrogeological parameters of the aquifer are determined by using the full process data of the main test hole and observation points during the test.

[0028] In the above step 1), the position of the water-passing section is adjusted by opening or plugging the rubber plugs on the water-permeable holes at different positions on the first water-permeable plate and the second water-permeable plate.

[0029] The permeability of the aquifer is calculated using the theory of steady flow and unsteady flow of groundwater between rivers and channels, and the thermal conductivity of the aquifer is calculated using the theory of groundwater heat transfer. The permeability and thermal conductivity of the aquifer can also be calculated simultaneously using microthermal tests under unsteady flow conditions.

[0030] The steady flow formula for single well pumping is used to calculate the permeability coefficient:

[0031]

[0032] The permeability coefficient is calculated using the steady flow formula with an observation well:

[0033]

[0034] The permeability coefficient is calculated using the unsteady flow formula for single well pumping:

[0035]

[0036] In the above formula: Q is the stable pumping flow of the pumping well; K is the permeability coefficient of the aquifer; H0 is the initial phreatic layer thickness; R is the influence radius; s w is the drawdown of the pumping well; r w is the radius of the pumping well. r is the horizontal distance from a certain observation hole to the pumping well; μ * is the water storage coefficient of the aquifer; s is the drawdown of the corresponding observation well.

[0037] Heat transfer mainly describes the problem of thermal field, which can be described and solved by heat conduction equation and convection-diffusion equation.

[0038] When the groundwater velocity is 0, heat transfer occurs mainly by heat conduction:

[0039]

[0040] When the groundwater velocity is not zero, heat transfer mainly occurs by convection diffusion:

[0041]

[0042] In the above formula: T is temperature: α is thermal conductivity: u represents flow velocity vector.

[0043] The above control equations can be solved by constructing a complete mathematical model in combination with the initial conditions and boundary conditions under actual conditions. After the non-stable temperature field is excited, the thermal diffusion coefficient, effective thermal conductivity and heat capacity of the aquifer can be solved simultaneously.

[0044] The one-dimensional heat conduction model with finite boundaries in the experiment can be expressed as the following well-defined problem:

[0045] Let the temperature function be u and the time function be T, then:

[0046]

[0047] Homogenize the variables and set:

[0048]

[0049] Substituting into formula (6), we can get:

[0050]

[0051] Where u is the temperature, K; (ρ c ) fs is the heat capacity of porous media, J / m 3 ·K; λ is the effective thermal conductivity, W / m·K; x is the position of the sand box observation point, m; t is the time, s; L is the length of the sand box, m; x′ is the dimensionless distance; u′ is the dimensionless temperature; t′ is the dimensionless time.

[0052] By homogenizing the boundary of equation (8), we can obtain the homogeneous boundary of the homogeneous equation, and let:

[0053] u′(x′,t′)=V(x′,t′)+W(x′,t′) (9)

[0054] Where W(x′, t′) = -x′ + 1.

[0055] Substituting into the original equation we get:

[0056]

[0057] Separate the variables of V(x′, t′) and set V(x′, t′) = X(x′) · T(t′), then:

[0058]

[0059] Transforming the equation into a system of equations, we get:

[0060]

[0061] From formula (10), we can know that:

[0062] V| x′＝0 =X(x′)·T(t′)=X (0) 'T(t')=0 (13)

[0063] V| x′＝1 =X(x′)·T(t′)=X (1) ·T(t′)=0 (14)

[0064] In order for the equation to make sense, T(t′)≠0, so X (0) =0,X (1) =0.

[0065] but

[0066] analyze:

[0067] ①When λ0<0,

[0068]

[0069]

[0070] A=B=0, X(x′)≡0, discard it.

[0071] ②When λ0=0,

[0072] X(x′)=Ax′+B.

[0073] X (0) =B=0.X (1) =A+B=0.

[0074] A=B=0, X(x′)≡0, discard it.

[0075] ③When λ0>0, let λ0=β 2 ,have:

[0076] X(x′)=Acosβx′+Bsinβx′,

[0077] X (0) =A=0,X (1) =Bsinβ=0,

[0078] B is not 0, so sinβ=0, β=nπ. (n=1, 2, 3,...), λ0=n 2 π 2 ,get:

[0079] X n (x′)=B n sinnπx′.(n=1, 2, 3...) (16)

[0080] For T(t′),

[0081] T′(t′)+λ0T(t′)=0, let λ0=n 2 π 2 Substituting in, we have:

[0082] T′(t′)+n 2 π 2 T(t′)=0, that is, T′ n (t′)+n 2 π 2 T n (t′)=0, the solution is:

[0083]

[0084] From the separation of variables, we know that: V(x′, t′) = X(x′) · T(t′), so:

[0085]

[0086] Vn Cumulative summation of (x′, t′) yields:

[0087]

[0088] Substituting t′=0 into equation (18), we can obtain:

[0089] V(x′, 0) = D n sinnπx′=x′-1 (20)

[0090] By Fourier transform, we can get:

[0091]

[0092] Substituting formula (21) into formula (19), we can obtain:

[0093]

[0094] Substituting formula (22) into formula (9), we can obtain:

[0095]

[0096] At this time, the standard curve can be drawn according to formula (23): Figure 5 , and at the same time, substituting the variables in formula (7) into formula (23), we can get:

[0097]

[0098]

[0099]

[0100] Where α is the thermal diffusion coefficient, m 2 / s; the other symbols have the same meanings as above.

[0101] According to the temperature change data during the test, the measured curve under the non-steady heat conduction test can be drawn. The thermal diffusion coefficient of the porous medium can be obtained by fitting the standard curve with the measured curve. The effective thermal conductivity of the aquifer can be obtained through the stable heat conduction test. The heat capacity of the porous medium can be obtained by combining the two. Therefore, the thermal diffusion coefficient, thermal conductivity and heat capacity of the porous medium aquifer can be solved simultaneously through different stages of the heat conduction test.

[0102] Using water level data, the positions with the same water level can be connected to obtain isowater lines. Streamlines are perpendicular to isowater lines and point from high water level to low water level. Isowater lines and streamlines can be used to draw aquifer flow field diagrams. The density of isowater lines represents the magnitude of groundwater flow velocity, and the direction of streamlines represents the flow direction of groundwater. From this, the flow velocity and direction of groundwater can be found out. Or, using the temperature distribution and migration law that can be measured by distributed optical fiber in the main test hole, when there is natural flow of groundwater, the temperature changes in different directions in the main test hole are different. The temperature changes quickly in the main direction of groundwater flow. At the same time, the greater the flow velocity, the faster the temperature changes. According to the temperature change rate in different directions, the flow velocity and direction of groundwater can be found out. Or, using the temperature distribution and migration law that can be measured by distributed optical fiber in the observation point, when there is natural flow of groundwater, the temperature changes at different observation points at the same distance from the main test hole but in different directions are different. The temperature changes quickly in the main direction of groundwater flow. At the same time, the greater the flow velocity, the faster the temperature changes. According to the temperature change rate of observation points at the same distance and in different directions, the flow velocity and direction of groundwater can be found out.

[0103] It is also possible to combine the water pressure, temperature and heat flux density data of the distributed optical fiber data acquisition system to construct a three-dimensional hydrothermal coupling numerical model that is consistent with the size conditions of the indoor model or the field model. The three-dimensional numerical model can be used to reproduce the experimental conditions of the actual model. The water level and temperature conditions of the numerical model can be made consistent with the actual model by adjusting the permeability coefficient and thermal conductivity coefficient of the model. The permeability coefficient and thermal conductivity coefficient of the aquifer can be inverted, and the inverted model can also directly obtain the flow velocity and direction information of groundwater.

[0104] This application has good compatibility and can use a variety of different methods to determine the permeability coefficient, thermal conductivity and flow velocity and direction. In this way, a more convenient test method can be selected according to actual conditions.

[0105] Distributed optical fiber is a new type of material that has developed rapidly in recent years. It can realize continuous observation of water pressure and temperature in the area where the optical fiber is laid. Combining it with the single-hole thermal tracer test can realize the comprehensive measurement of flow velocity, flow direction, permeability coefficient and thermal conductivity, which can greatly improve work efficiency and reduce test costs.

[0106] The technologies not mentioned in the present invention are all referred to the prior art.

[0107] Beneficial effects: Compared with the prior art, the device of the present invention has a simple structure, intelligent and convenient operation, can realize instantaneous / continuous linear heat source excitation through the heating system, monitor the changes of water pressure, temperature and heat flux density in various places in real time through the distributed optical fiber data acquisition system, and study the flow velocity and direction of groundwater, permeability coefficient, thermal diffusion coefficient, heat capacity and thermal conductivity and other comprehensive hydrogeological parameters. The heating system and distributed optical fiber data acquisition system can be used for both indoor and field tests, with simple operation, high data accuracy and strong practicality. BRIEF DESCRIPTION OF THE DRAWINGS

[0108] Figure 1 A schematic diagram of the structure of a heat tracer test device for determining the comprehensive hydrogeological conditions of an aquifer according to the present invention;

[0109] Figure 2 A top view of the thermal tracer test device for determining the comprehensive hydrogeological conditions of an aquifer according to the present invention;

[0110] Figure 3 It is a schematic diagram of the structure of the heating system of the present invention;

[0111] Figure 4 This is a schematic diagram of the structure of the distributed optical fiber data acquisition system of the present invention;

[0112] Figure 5 The standard curve of the calculation process of the present invention;

[0113] Figure 6 This is the curve wiring process of Example 1.

[0114] In the figure, 1 is a water system, 11 is a first upper water storage tank, 12 is a first lower water storage tank, 13 is a second upper water storage tank, 14 is a second lower water storage tank, 15 is a first permeable plate, 16 is a second permeable plate, 17 is a first water level regulating plate, 18 is a second water level regulating plate, and 19 is a valve; 2 is a medium tank, 21 is a test main hole, 22 is an observation point, 23 is a submerged aquifer, 24 is a weakly permeable layer, and 25 is a pressurized aquifer; 3 is a heating system, 31 is a heating rod, 32 is an electric wire, and 33 is a power supply; 4 is a distributed optical fiber data acquisition system; 41 is a distributed optical fiber, and 42 is an optical fiber demodulator. DETAILED DESCRIPTION

[0115] In order to better understand the present invention, the content of the present invention is further explained below in conjunction with the embodiments, but the content of the present invention is not limited to the following embodiments.

[0116] The directional words such as "upper", "lower", "left" and "right" in this application are based on the relative directions or positional relationships shown in the drawings and should not be understood as limitations on this application.

[0117] Example 1

[0118] like Figure 1-4 As shown, a thermal tracer test device for determining the comprehensive hydrogeological conditions of an aquifer includes a water storage system 1, a medium tank 2, a heating system 3 and a distributed optical fiber data acquisition system 4;

[0119] The water storage system 1 comprises a first upper water storage tank 11, a first lower water storage tank 12, a second upper water storage tank 13 and a second lower water storage tank 14;

[0120] The first upper water storage tank 11 and the second upper water storage tank 13 are respectively arranged on both sides of the medium tank 2; the first upper water storage tank 11 and the medium tank 2 are separated only by the first water permeable plate 15, and the second upper water storage tank 13 and the medium tank 2 are separated only by the second water permeable plate 16; the water storage system 1 and the medium tank 2 are an integral rectangle, separated by the water permeable plates on both sides;

[0121] The first lower water tank 12 is arranged at the bottom of the first upper water tank 11, and the first upper water tank 11 is provided with a first water level regulating plate 17. When the first water level regulating plate 17 is adjusted, the overflowing water falls into the first lower water tank 12; the second lower water tank 14 is arranged at the bottom of the second upper water tank 13, and the second upper water tank 13 is provided with a second water level regulating plate 18. When the second water level regulating plate 18 is adjusted, the overflowing water falls into the second lower water tank 14; in this example, the first upper water tank 11 and the second upper water tank 13 are respectively provided with vertical slots matching the first water level regulating plate 17 and the second water level regulating plate 18, and the first upper water tank 11 and the second upper water tank 13 can be realized by moving the first water level regulating plate 17 and the second water level regulating plate 18 up and down along the corresponding vertical slots. The water level in the water storage tank 11 and the second upper water storage tank 13 is adjusted; the excess water flows into the first lower water storage tank 12 and the second lower water storage tank 14 respectively through the first water level regulating plate 17 and the second water level regulating plate 18; the first water-permeable plate 15 and the second water-permeable plate 16 are provided with sand-isolating and water-permeable gauze on one side adjacent to the medium to ensure that water can pass normally while isolating sand; the first water-permeable plate 15 and the second water-permeable plate 16 are provided with water-permeable holes, and the water-permeable holes are provided with movably connected rubber plugs. By opening or plugging the rubber plugs on the water-permeable holes at different positions on the first water-permeable plate 15 and the second water-permeable plate 16, the position of the water-passing section is adjusted; the first upper water storage tank 11, the first lower water storage tank 12, the second upper water storage tank 13 and the second lower water storage tank 14 are provided with standby valves 19

[0122] More than one layer of medium is installed in the medium tank 2, and a test main hole 21 and observation points 22 are provided on the medium, which penetrate the entire height direction of the medium. That is, the depth and height of the main hole 21 penetrate the entire height direction of the medium, and the depth and height of the observation point 22 penetrate the entire height direction of the medium. The number of observation points 22 is 16. The test main hole 21 is set at the center of the medium, and the observation points 22 are distributed around the test main hole 21, divided into two circles, with 8 evenly distributed in the inner circle and 8 evenly distributed in the outer circle;

[0123] The heating system 3 includes a heating rod 31, an electric wire 32 and a power source 33 connected in sequence. The heating rod 31 is arranged in the test main hole 21. The instantaneous / continuous heat source is excited by adjusting the power source 33, thereby changing the temperature field in the aquifer;

[0124] The distributed optical fiber data acquisition system 4 includes a distributed optical fiber 41 and an optical fiber demodulator 42. The test main hole 21 and the observation point 22 are both provided with a distributed optical fiber 41 arranged along the height direction, that is, the optical fiber demodulator 42 vertically penetrates from the bottom of the medium to the top of the medium. The test main hole 21 is cylindrical, and the side wall of the test main hole 21 is a permeable layer (sand isolation, permeable water). The distributed optical fiber 41 on the test main hole 21 spirals up around the inner or outer wall of the test main hole 21, and the distributed optical fiber 41 on the observation point 22 is straight; the distributed optical fiber 41 monitors and records the temperature and water pressure at the measured position, and analyzes and outputs the data through the optical fiber demodulator 26.

[0125] In this example, the medium includes a phreatic aquifer 23, a weakly permeable layer 24 and a confined aquifer 25 which are connected in sequence from top to bottom. The medium is replaced as needed to simulate the phreatic aquifer 19, the weakly permeable layer 20 and the confined aquifer 21. Different aquifer media can select sandy soil and clay soil with different particle sizes and different compositions.

[0126] A thermal tracer test method for determining the comprehensive hydrogeological conditions of an aquifer, using the thermal tracer test device for determining the comprehensive hydrogeological conditions of an aquifer, comprises the following steps:

[0127] 1. The position of the water-passing section can be adjusted by opening or plugging the rubber plugs on the water-permeable holes at different positions on the first water-permeable plate 15 and the second water-permeable plate 16;

[0128] 2. Fill the medium in layers into the medium slot 2 and install the distributed optical fiber data acquisition system 4;

[0129] 3. Add water to the first upper water storage tank 11 and the second upper water storage tank 13 to stratify and saturate the medium in the medium tank 2;

[0130] 4. Start the distributed optical fiber data acquisition system 4 to collect water pressure, temperature and heat flux density data in real time;

[0131] 5. The water levels in the first upper water storage tank 11 and the second upper water storage tank 13 are controlled by the first water level regulating plate 17 and the second water level regulating plate 18 to form a stable seepage field and an unstable seepage field under different hydraulic gradients;

[0132] 6. Turn on the heating system 3 to excite the instantaneous heat source and the constant heat source, and change the excitation intensity of the heat source in the test main hole 21 by changing the output power of the heating rod 31, thereby changing the temperature field in the aquifer;

[0133] 7. Use the distributed optical fiber data acquisition system 4 to record the changes in water pressure, temperature and heat flux density of the aquifer in real time, and derive the water pressure and temperature data of the entire test process;

[0134] 8. Turn off the heating system 3 and the distributed optical fiber data acquisition system 4, and end the test;

[0135] 9. Use the full process data of the test main hole 21 and the observation point 22 during the test to determine the comprehensive hydrogeological conditions such as the flow velocity, flow direction and hydrogeological parameters of the aquifer.

[0136] The permeability of aquifers is calculated using the theory of steady and unsteady flow of groundwater between rivers and canals, and the thermal conductivity of aquifers is calculated using the theory of groundwater heat transfer. The permeability and thermal conductivity of aquifers can also be calculated simultaneously using microthermal tests under unsteady flow conditions.

[0137] The steady flow formula for single well pumping is used to calculate the permeability coefficient:

[0138]

[0139] The permeability coefficient is calculated using the steady flow formula with an observation well:

[0140]

[0141] The permeability coefficient is calculated using the unsteady flow formula for single well pumping:

[0142]

[0143] In the above formula: Q is the stable pumping flow of the pumping well; K is the permeability coefficient of the aquifer; H0 is the initial phreatic layer thickness; R is the influence radius; s w is the drawdown of the pumping well; r w is the radius of the pumping well. r is the horizontal distance between a certain observation hole and the pumping well; μ* is the water storage coefficient of the aquifer; s is the drawdown of the corresponding observation hole.

[0144] Heat transfer mainly describes the problem of thermal field, which can be described and solved by heat conduction equation and convection-diffusion equation.

[0145] When the groundwater velocity is 0, heat transfer occurs mainly by heat conduction:

[0146]

[0147] When the groundwater velocity is not zero, heat transfer mainly occurs by convection diffusion:

[0148]

[0149] In the above formula: T is temperature: α is thermal conductivity: u represents flow velocity vector.

[0150] The above control equations can be solved by constructing a complete mathematical model in combination with the initial conditions and boundary conditions under actual conditions. After the unsteady flow field is excited, the changes in water level and temperature during the test are observed simultaneously, so that the permeability coefficient of the hydrodynamic field and the thermal conductivity coefficient of the temperature field can be solved at the same time.

[0151] The one-dimensional temperature conduction model in the experiment can be expressed as the following well-defined problem:

[0152] Let the temperature function be u and the time function be T, then:

[0153]

[0154] Homogenize the variables and set:

[0155]

[0156] Substituting into formula (6), we can get:

[0157]

[0158] Where u is the temperature, K; (ρ c ) fs is the heat capacity of porous media, J / m 3 ·K; λ is the effective thermal conductivity, W / m·K; x is the position of the sand box observation point, m; t is the time, s; L is the length of the sand box, m; x′ is the dimensionless distance; u′ is the dimensionless temperature; t′ is the dimensionless time.

[0159] By homogenizing the boundary of equation (8), we can obtain the homogeneous boundary of the homogeneous equation, and let:

[0160] u′(x′,t′)=V(x′,t′)+W(x′,t′) (9)

[0161] Where W(x′, t′) = -x′ + 1.

[0162] Substituting into the original equation we get:

[0163]

[0164] Separate the variables of V(x′, t′) and set V(x′, t′) = X(x′) · T(t′), then:

[0165]

[0166] Transforming the equation into a system of equations, we get:

[0167]

[0168] From formula (10), we can know that:

[0169] V| x′＝0 =X(x′)·T(t′)=X (0) ·T(t′)=0 (13)

[0170] V| x′＝1 =X(x′)·T(t′)=X (1) ·T(t′)=0 (14)

[0171] In order for the equation to make sense, T(t′)≠0, so X (0) =0,X (1) =0.

[0172] but

[0173] analyze:

[0174] ④When λ0<0,

[0175]

[0176]

[0177] A=B=0, X(x′)≡0, discard it.

[0178] ⑤When λ0=0,

[0179] X(x′)=Ax′+B.

[0180] X (0) =B=0.X (1) =A+B=0.

[0181] A=B=0, X(x′)≡0, discard it.

[0182] ⑥When λ0>0, let λ0=β 2 ,have:

[0183] X(x′)=Acosβx′+Bsinβx′,

[0184] X(0) =A=0,X (1) =Bsinβ=0,

[0185] B is not 0, so sinβ=0, β=nπ. (n=1, 2, 3,...), λ0=n 2 π 2 ,get:

[0186] X n (x′)=B n sinnπx′.(n=1, 2, 3...) (16)

[0187] For T(t′),

[0188] T′(t′)+λ0T(t′)=0, let λ0=n 2 π 2 Substituting in, we have:

[0189] T′(t′)+n 2 π 2 T(t′)=0, that is, T′ n (t′)+n 2 π 2 T n (t′)=0, the solution is:

[0190]

[0191] From the separation of variables, we know that: V(x′, t′) = X(x′) · T(t′), so:

[0192]

[0193] V n Cumulative summation of (x′, t′) yields:

[0194]

[0195] Substituting t′=0 into equation (18), we can obtain:

[0196] V(x′, 0) = D n sinnπx′=x′-1 (20)

[0197] By Fourier transform, we can get:

[0198]

[0199] Substituting formula (21) into formula (19), we can obtain:

[0200]

[0201] Substituting formula (22) into formula (9), we can obtain:

[0202]

[0203] At this time, the standard curve can be drawn by formula (23) Figure 5 , and at the same time, substituting the variables in formula (7) into formula (23), we can get:

[0204]

[0205]

[0206]

[0207] Where α is the thermal diffusion coefficient, m 2 / s; the other symbols have the same meanings as above.

[0208] According to the temperature change data during the test, the measured curve under the non-steady heat conduction test can be drawn. The thermal diffusion coefficient of the porous medium can be obtained by fitting the standard curve with the measured curve. The effective thermal conductivity of the porous medium can be obtained through the stable heat conduction test. The heat capacity of the porous medium can be obtained by combining the two. Therefore, the thermal diffusion coefficient, thermal conductivity and heat capacity of the porous medium aquifer can be solved simultaneously through different stages of the heat conduction test.

[0209] The calculation results of the embodiment are as follows:

[0210]

[0211] Alternatively, a three-dimensional hydrothermal coupling numerical model consistent with the size conditions of the indoor model or the field model is constructed in combination with the water pressure, temperature and heat flux density data of the distributed optical fiber data acquisition system 4, and the three-dimensional numerical model is used to reproduce the test conditions of the actual model. The water level and temperature conditions of the numerical model are made consistent with the actual model by adjusting the permeability coefficient and thermal conductivity coefficient of the model, thereby inverting the permeability coefficient and thermal conductivity coefficient of the aquifer. The inverted model can also directly obtain the flow velocity and direction information of groundwater.

[0212] Using water level data, the positions with the same water level can be connected to obtain isowater lines. Streamlines are perpendicular to isowater lines and point from high water level to low water level. Isowater lines and streamlines can be used together to draw a flow field diagram of the aquifer. The density of isowater lines represents the magnitude of groundwater flow velocity, and the direction of streamlines represents the flow direction of groundwater. Thus, the flow velocity and direction of groundwater can be found out. Alternatively, the temperature distribution and migration law measurable by the distributed optical fiber 25 in the test main hole 21 can be determined. When there is natural flow of groundwater, the temperature changes in different directions in the test main hole 21 are different, and the temperature in the main direction of groundwater flow is different. The temperature changes quickly, and the greater the flow rate, the faster the temperature changes. The flow rate and direction of groundwater can be found out according to the temperature change rate in different directions; or the temperature distribution and migration law that can be measured by the distributed optical fiber 25 in the observation point 22, when there is natural flow of groundwater, the temperature changes differently at different observation points 22 at the same distance from the test main hole 21 but in different directions. The temperature in the main direction of groundwater flow changes quickly, and the greater the flow rate, the faster the temperature changes. The flow rate and direction of groundwater can be found out according to the temperature change rate of the observation point 22 at the same distance and in different directions.

[0213] The above device and method have good compatibility and can be used to determine the permeability coefficient, thermal conductivity coefficient and flow velocity and direction in a variety of different ways. In this way, a more convenient test method can be selected according to actual conditions.

[0214] Example 2

[0215] Figure 1 The water storage system 1 and the medium tank 2 are mainly used to construct the required aquifer system, which is suitable for indoor mesoscale tests. When the test is carried out in the field, the test site itself is a natural aquifer system. Therefore, there is no need to use the water storage system 1 and the medium tank 2 during the field test. Only the heating system 3 and the distributed optical fiber data acquisition system 4 are needed to carry out the field test. The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments:

[0216] A thermal tracer test method for determining the comprehensive hydrogeological conditions of an aquifer comprises the following steps during a field test:

[0217] 1) Select appropriate locations to arrange the test main hole 17 and observation point 18;

[0218] 2) Install a distributed optical fiber data acquisition system 4;

[0219] 3) Wait for the water level to stabilize and form a stable natural seepage field;

[0220] 4) Start the distributed optical fiber data acquisition system 4 to collect water pressure and temperature data in real time;

[0221] 5) Turn on the heating system 3 to excite the instantaneous heat source and the constant heat source, and change the excitation intensity of the heat source in the test main hole 17 by changing the output power of the heating rod 22, thereby changing the temperature field in the aquifer;

[0222] 6) Record the water pressure and temperature changes of the aquifer in real time through the distributed optical fiber data acquisition system 4, and derive the water pressure and temperature data of the whole test process;

[0223] 7) Turn off the heating system 3 and the distributed optical fiber data acquisition system 4, and end the test;

[0224] 8) The full process data of the test main hole 17 and the observation point 18 during the test are used to determine the comprehensive hydrogeological conditions such as the flow velocity, flow direction and hydrogeological parameters of the natural aquifer at the test site.

Claims

1. A thermal tracer test device for determining the comprehensive hydrogeological conditions of an aquifer, characterized in that: It comprises a water storage system (1), a medium tank (2), a heating system (3) and a distributed optical fiber data acquisition system (4); The water storage system (1) comprises a first upper water storage tank (11), a first lower water storage tank (12), a second upper water storage tank (13) and a second lower water storage tank (14); The first upper water storage tank (11) and the second upper water storage tank (13) are respectively arranged on both sides of the medium tank (2); the first upper water storage tank (11) and the medium tank (2) are separated only by a first water permeable plate (15), and the second upper water storage tank (13) and the medium tank (2) are separated only by a second water permeable plate (16); The first lower water storage tank (12) is arranged at the bottom of the first upper water storage tank (11), and the first upper water storage tank (11) is provided with a first water level regulating plate (17), and when the first water level regulating plate (17) is adjusted, overflowing water falls into the first lower water storage tank (12); the second lower water storage tank (14) is arranged at the bottom of the second upper water storage tank (13), and the second upper water storage tank (13) is provided with a second water level regulating plate (18), and when the second water level regulating plate (18) is adjusted, overflowing water falls into the second lower water storage tank (14); More than one layer of medium is installed in the medium tank (2), and the medium is provided with a test main hole (21) and observation points (22) that penetrate the entire height direction of the medium, and the number of the observation points (22) is more than six, the test main hole (21) is arranged at the center of the medium, and the observation points (22) are distributed around the test main hole (21); The heating system (3) comprises a heating rod (31), an electric wire (32) and a power source (33) connected in sequence. The heating rod (31) is arranged in the test main hole (21). The power source (33) is adjusted to excite the instantaneous / continuous heat source, thereby changing the temperature field in the aquifer. The distributed optical fiber data acquisition system (4) comprises a distributed optical fiber (41) and an optical fiber demodulator (42). The test main hole (21) and the observation point (22) are both provided with a distributed optical fiber (41) arranged along the height direction. The distributed optical fiber (41) monitors and records the temperature and water pressure at the measured position, and analyzes and outputs the data through the optical fiber demodulator (42).

2. The thermal tracer test device for determining the comprehensive hydrogeological conditions of an aquifer according to claim 1, characterized in that: The distributed optical fiber (41) in the test main hole (21) spirally rises around the inner or outer wall of the test main hole (21); and the first water-permeable plate (15) and the second water-permeable plate (16) are both provided with sand-isolating and water-permeable gauze on one side adjacent to the medium.

3. The thermal tracer test device for determining the comprehensive hydrogeological conditions of an aquifer according to claim 1 or 2, characterized in that: The first water-permeable plate (15) and the second water-permeable plate (16) are both provided with water-permeable holes, and the water-permeable holes are provided with movably connected rubber plugs. By opening or plugging the rubber plugs on the water-permeable holes at different positions on the first water-permeable plate (15) and the second water-permeable plate (16), the position of the water-passing section can be adjusted.

4. The thermal tracer test device for determining the comprehensive hydrogeological conditions of an aquifer according to claim 1 or 2, characterized in that: The medium includes a phreatic aquifer (23), a weakly permeable layer (24) and a confined aquifer (25) which are connected in sequence from top to bottom. The medium is replaced as needed to simulate the phreatic aquifer (19), the weakly permeable layer (20) and the confined aquifer (21).

5. A thermal tracer test method for determining the comprehensive hydrogeological conditions of an aquifer, characterized in that: The thermal tracer test device for determining the comprehensive hydrogeological conditions of an aquifer according to any one of claims 1 to 4 comprises the following steps: 1) adjusting the water permeability positions on the first water permeable plate (15) and the second water permeable plate (16); 2) filling the medium slot (2) with medium in layers and installing a distributed optical fiber data acquisition system (4); 3) adding water to the first upper water storage tank (11) and the second upper water storage tank (13) to stratify and saturate the medium in the medium tank (2); 4) starting the distributed optical fiber data acquisition system (4) to collect water pressure and temperature data in real time; 5) controlling the water levels in the first upper water storage tank (11) and the second upper water storage tank (13) by means of a first water level regulating plate (17) and a second water level regulating plate (18) to form a stable seepage field and an unstable seepage field under different hydraulic gradients; 6) Turning on the heating system (3) to excite the instantaneous heat source and the constant heat source, and changing the excitation intensity of the heat source in the test main hole (21) by changing the output power of the heating rod (31), thereby changing the temperature field in the aquifer; 7) Record the water pressure and temperature changes of the aquifer in real time through the distributed optical fiber data acquisition system (4), and derive the water pressure and temperature data of the entire test process; 8) Turn off the heating system (3) and the distributed optical fiber data acquisition system (4), and end the test; 9) The flow velocity, flow direction and hydrogeological parameters of the aquifer are determined by using the full process data of the test main hole (21) and the observation point (22) during the test.

6. The thermal tracer test method for determining the comprehensive hydrogeological conditions of an aquifer according to claim 5, characterized in that: In step 1), the position of the water-passing section is adjusted by opening or plugging the rubber plugs on the water-permeable holes at different positions on the first water-permeable plate (15) and the second water-permeable plate (16).

7. The thermal tracer test method for determining the comprehensive hydrogeological conditions of an aquifer according to claim 5 or 6, characterized in that: The permeability of the aquifer is calculated using the theory of steady flow and unsteady flow of groundwater between rivers and channels, the thermal conductivity of the aquifer is calculated using the theory of groundwater heat transfer, or the permeability and thermal conductivity of the aquifer are calculated simultaneously using microthermal tests under unsteady flow conditions.

8. The thermal tracer test method for determining the comprehensive hydrogeological conditions of an aquifer according to claim 5 or 6, characterized in that: A three-dimensional water-heat coupling numerical model consistent with the size conditions of the indoor model or the field model is constructed by combining the water pressure, temperature and heat flux density data of the distributed optical fiber data acquisition system (4). The three-dimensional numerical model is used to reproduce the test conditions of the actual model. The water level and temperature conditions of the numerical model are made consistent with the actual model by adjusting the permeability coefficient and thermal conductivity coefficient of the model. The permeability coefficient and thermal conductivity coefficient of the aquifer are thus inverted. The inverted model can also directly obtain the flow velocity and direction information of groundwater.

9. The thermal tracer test method for determining the comprehensive hydrogeological conditions of an aquifer according to claim 5 or 6, characterized in that: Using water level data, positions with the same water level can be connected to obtain isowater lines. Streamlines are perpendicular to isowater lines and point from high water level to low water level. Isowater lines and streamlines can be used together to draw a flow field diagram of the aquifer. The density of isowater lines represents the magnitude of groundwater flow velocity, and the direction of streamlines represents the flow direction of groundwater. Thus, the flow velocity and direction of groundwater can be found. Alternatively, the temperature distribution and migration law measured by the distributed optical fiber (25) in the test main hole (21) can be used. When there is natural flow of groundwater, the temperature changes in different directions in the test main hole (21) are different, and the temperature changes in the main direction of groundwater flow are different. The faster the flow rate, the faster the temperature changes. The flow rate and direction of groundwater can be determined based on the temperature change rates in different directions. Alternatively, the temperature distribution and migration law can be measured using the distributed optical fiber (25) in the observation point (22). When groundwater flows naturally, the temperature changes differently at different observation points (22) at the same distance from the test main hole (21) but in different directions. The temperature changes faster in the main direction of groundwater flow. At the same time, the faster the flow rate, the faster the temperature changes. The flow rate and direction of groundwater can be determined based on the temperature change rates at the observation points (22) at the same distance but in different directions.

10. The method of calculating the thermal conductivity of an aquifer using the groundwater heat transfer theory according to claim 5 or 6, wherein the standard curve is matched with the measured data curve of the heat conduction test by the wiring method, the corresponding coordinate values ​​are recorded, and the thermal diffusion coefficient, effective thermal conductivity and heat capacity of the aquifer are obtained by calculation; The one-dimensional heat conduction model with finite boundaries in the experiment can be expressed as the following well-defined problem: Let the temperature function be u and the time function be T, then: Homogenize the variables and set: Substituting into formula (6), we can get: in, u is temperature, K; (ρ c ) fs is the heat capacity of porous media, J / m 3 ·K; λ is the effective thermal conductivity, W / m·K; x is the position of the sand box observation point, m; t is the time, s; L is the length of the sand box, m; x′ is the dimensionless distance; u′ is the dimensionless temperature; t′ is the dimensionless time; By homogenizing the boundary of equation (8), we can obtain the homogeneous boundary of the homogeneous equation, and let: u′(x′,t′)=V(x′,t′)+W(x′,t′) (9) Among them, W(x′,t′)=-x′+1, and W(x′,t′) is a properly selected function, which makes the boundary conditions of the new unknown function V(x′,t′) homogeneous. V(x′,t′) and W(x′,t′) themselves have no physical meaning; Substituting into the original equation we get: Assuming that equation (10) has a solution in the form of variable separation, perform variable separation on the solution of the system of equations; When V(x′,t′)=X(x′)·T(t′), we have: Among them: X(x′) is a one-variable displacement function only about x′, T(t′) is a one-variable time function only about t′, both functions are twice differentiable, X″(x′) is the second-order derivative of X(x′), T′(t′) is the first-order derivative of T(t′), the left side of the equation is a function only about x′, and the right side of the equation is a function only about t′. If they are equal, they must be constants, that is, -λ0 is the separation constant; transform the equation into a system of equations, and we get: Transforming the equation into a system of equations, we get: From formula (10), we can know that: V| x′＝0 =X(x′)·T(t′)=X (0) ·T(t′)=0 (13) V| x′＝1 =X(x′)·T(t′)=X (1) ·T(t′)=0 (14) In order for the equation to make sense, T(t′)≠0, so X (0) =0,X (1) =0; but When λ0<0 and λ0=0, equation (15) has only zero solution and is discarded; When λ0>0, let λ0=β 2 ,have: X(x′)=Acosβx′+Bsinβx′, X (0) =A=0,X (1) =Bsinβ=0, B is not 0, so sinβ=0, β=nπ.(n=1,2,3,…), eigenvalue λ0=n 2 π 2 , and obtain the characteristic function: X n (x′)=B n sinnπx′.(n=1,2,3…) (16) Among them, B n is an arbitrary constant. (n=1,2,3…) For T(t′), T′(t′)+λ0T(t′)=0, and the eigenvalue λ0=n 2 π 2 Substituting in, we have: T′(t′)+n 2 π 2 T(t′)=0, that is, T n ′(t′)+n 2 π 2 T n (t′)=0, solve the characteristic function to get: Among them, C n is an arbitrary constant. (n=1,2,3…) From the separation of variables, we know that: V(x′,t′)=X(x′)·T(t′), so: Where D n is an arbitrary constant and D n =B n ·C n .(n=1,2,3…), since the equations and boundary conditions are homogeneous, using the superposition principle, V n Cumulative summation of (x′, t′) yields: Substituting t′=0 into equation (18), we can obtain: V(x′,0)=D n sinnπx′=x′-1.(n=1,2,3…) (20) By Fourier transform, we can get: Substituting formula (21) into formula (19), we can obtain: Substituting formula (22) into formula (9), we can obtain: At this time, the standard curve can be drawn according to formula (23). At the same time, substituting the variables in formula (7) into formula (23), we can get: Where α is the thermal diffusion coefficient, m 2 / s; the other symbols have the same meaning as above; The measured curve under the non-steady heat conduction test was drawn according to the temperature change data during the test. The thermal diffusion coefficient of the porous medium was obtained by fitting the standard curve with the measured curve. The effective thermal conductivity of the porous medium was obtained through the stable heat conduction test. The heat capacity of the porous medium was obtained by combining the two.

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