A thermal tracer test device and method for determining the comprehensive hydrogeological conditions of an aquifer

Abstract

The present invention discloses a thermal tracer test device and method for determining the comprehensive hydrogeological conditions of an aquifer. The thermal tracer test device comprises a water storage system, a medium tank, a heating system, and a distributed fiber optic data acquisition system. The device has a simple structure and is intelligent and convenient to operate. The heating system can be used to excite a transient or continuous linear heat source. The distributed fiber optic data acquisition system monitors water pressure and temperature changes at various locations in real time, allowing for the study of comprehensive hydrogeological parameters such as groundwater flow rate and direction, permeability, thermal diffusivity, heat capacity, and thermal conductivity. The heating system and distributed fiber optic data acquisition system can be used for both indoor and field tests, offering simple operation, high data accuracy, and strong practicality.

Description

Technical Field

[0001] The present invention relates to a thermal tracer test device and method for determining comprehensive hydrogeological conditions of an aquifer, belonging to the technical field of groundwater thermal tracer testing 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 means are mostly time-consuming and labor-intensive, and many methods no longer meet the environmental protection requirements of new-era engineering projects.

[0003] Currently, 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 placement of boreholes and requires simultaneous acquisition of water level data from all three boreholes. The isotope tracer method is subject to strict regulations due to the radioactivity of isotopes. The determination of permeability and thermal conductivity currently falls into two main categories: indoor tests and field tests. While the testing methods for permeability are relatively mature, the determination of thermal conductivity is still in its developmental stages, primarily using thermal response tests. These tests often have long cycles, making it difficult to quickly obtain the thermal conductivity of the aquifer, and it is also impossible to specifically obtain groundwater flow velocity and direction information from a single borehole. Summary of the Invention

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

[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 a first permeable plate, and the second upper water storage tank and the medium tank are separated only by a second permeable plate;

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

[0010] The medium tank is equipped with more than one layer of medium, 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 located in the center of the medium, and the observation points are distributed around the test main hole.

[0011] The heating system includes a heating rod, wires, and power supply connected in sequence. The heating rod is placed in the main test hole. By adjusting the power supply, the instantaneous / continuous heat source is excited, 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 location, 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 all-round measurement, the distributed optical fiber on the test main hole spirals around the inner or outer wall of the test main hole.

[0015] In order to improve the measurement accuracy, the first and second water-permeable plates 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.

[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, aquitard and a confined aquifer that are connected in sequence from top to bottom. The medium is replaced as needed to simulate the phreatic aquifer, aquitard and a confined aquifer. Different aquifer media can select 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 media slots with media in layers and install a distributed fiber optic 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 fiber optic 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 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) Using a distributed fiber optic data acquisition system, the water pressure, temperature, and heat flux density changes of the aquifer are recorded in real time, and the water pressure, temperature, and heat flux density data of the entire 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 coefficient 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 coefficient and thermal conductivity of the aquifer can also be calculated simultaneously using micro-thermal 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 rate of the pumping well; K is the permeability coefficient of the aquifer; H0 is the initial thickness of the water layer; 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 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 the flow velocity vector.

[0043] The above-mentioned 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 let:

[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 the porous medium, 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] Converting 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 to make the equation meaningful, T(t′)≠0, so X (0) =0,X (1) =0.

[0065]

[0066] analyze:

[0067] ①When λ0<0,

[0068]

[0069] Since A=B=0, X(x′)≡0, we discard it.

[0070] ②When λ0=0,

[0071] X(x′)=Ax′+B.

[0072] X (0) =B=0.X (1) =A+B=0.

[0073] Since A=B=0, X(x′)≡0, we discard it.

[0074] ③When λ0>0, let λ0=β 2 ,have:

[0075] X(x′)=Acosβx′+Bsinβx′,

[0076] X (0) =A=0,X (1) =Bsinβ=0,

[0077] B is not 0, so sinβ=0, β=nπ.(n=1,2,3,…), λ0=n 2 π 2 ,get:

[0078] X n (x′)=B n sinnπx′.(n=1,2,3…) (16)

[0079] For T(t′),

[0080] T′(t′)+λ0T(t′)=0, set λ0=n 2 π 2 Substituting in, we have:

[0081] 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:

[0082]

[0083] From the separation of variables, we know that V(x′,t′)=X(x′)·T(t′), so we have:

[0084]

[0085]

[0086] V n By summing (x′, t′), we can get:

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

[0099] Based on the temperature change data during the test, the measured curve under the unsteady heat conduction test can be drawn. The thermal diffusivity of the porous medium can be calculated by fitting the standard curve with the measured curve. The effective thermal conductivity of the aquifer can be calculated through the stable heat conduction test. The heat capacity of the porous medium can be calculated by combining the two. In this way, the thermal diffusivity, thermal conductivity and heat capacity of the porous medium aquifer can be simultaneously solved at different stages of the heat conduction test.

[0100] Using water level data, positions with the same water level can be connected to obtain isowater levels. Streamlines are perpendicular to the isowater levels and point from high water levels to low water levels. Together, the isowater levels and streamlines can be used to draw a flow field map of the aquifer. The density of the isowater levels represents the magnitude of the groundwater flow velocity, and the direction of the streamlines represents the direction of groundwater flow. This can be used to determine the groundwater flow velocity and direction. Alternatively, the temperature distribution and migration patterns measured by distributed optical fibers in the main test hole can be used. When groundwater flows naturally, the temperature changes differently in different directions within the main test hole. The temperature changes faster in the main direction of groundwater flow, and the greater the flow velocity, the faster the temperature changes. The rate of temperature change in different directions can be used to determine the groundwater flow velocity and direction. Alternatively, the temperature distribution and migration patterns measured by distributed optical fibers at observation points can be used. When groundwater flows naturally, the temperature changes differently at different observation points at the same distance from the main test hole but in different directions. The temperature changes faster in the main direction of groundwater flow, and the greater the flow velocity, the faster the temperature changes. The rate of temperature change at observation points at the same distance but in different directions can be used to determine the groundwater flow velocity and direction.

[0101] It is also possible to combine the water pressure, temperature and heat flux density data of the distributed fiber optic 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. By adjusting the permeability coefficient and thermal conductivity coefficient of the model, the water level and temperature conditions of the numerical model operation are made consistent with the actual model. The permeability coefficient and thermal conductivity coefficient of the aquifer are thus inverted. The inverted model can also directly obtain the flow rate and direction information of the groundwater.

[0102] This application is highly compatible and can be used in a variety of ways to determine permeability, thermal conductivity, and flow velocity and direction. This allows you to choose the most convenient test method based on your actual situation.

[0103] 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 and direction, permeability coefficient and thermal conductivity coefficient, which can greatly improve work efficiency and reduce test costs.

[0104] The technologies not mentioned in this invention are all referred to the prior art.

[0105] Beneficial effects: Compared with the existing technology, 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, and monitor the changes in water pressure, temperature and heat flux density at various locations in real time through the distributed optical fiber data acquisition system, and study comprehensive hydrogeological parameters such as groundwater flow rate and direction, permeability coefficient, thermal diffusion coefficient, heat capacity and thermal conductivity. The heating system and distributed optical fiber data acquisition system can be used for both indoor and field experiments, with simple operation, high data accuracy and strong practicality. BRIEF DESCRIPTION OF THE DRAWINGS

[0106] Figure 1 This is a schematic diagram of the structure of the thermal tracer test device for determining the comprehensive hydrogeological conditions of the aquifer according to the present invention;

[0107] 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;

[0108] Figure 3 This is a schematic structural diagram of the heating system of the present invention;

[0109] Figure 4 This is a structural diagram of a distributed optical fiber data acquisition system according to the present invention;

[0110] Figure 5 The calculation process standard curve of the present invention;

[0111] Figure 6 This is the curve wiring process of Example 1.

[0112] In the figure, 1 is the water system, 11 is the first upper water tank, 12 is the first lower water tank, 13 is the second upper water tank, 14 is the second lower water tank, 15 is the first permeable plate, 16 is the second permeable plate, 17 is the first water level regulating plate, 18 is the second water level regulating plate, and 19 is the valve; 2 is the medium tank, 21 is the main test hole, 22 is the observation point, 23 is the submerged aquifer, 24 is the weak permeable layer, and 25 is the pressurized aquifer; 3 is the heating system, 31 is the heating rod, 32 is the wire, and 33 is the power supply; 4 is the distributed optical fiber data acquisition system; 41 is the distributed optical fiber, and 42 is the optical fiber demodulator. DETAILED DESCRIPTION

[0113] In order to better understand the present invention, the content of the present invention is further illustrated below in conjunction with the examples, but the content of the present invention is not limited to the following examples.

[0114] 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.

[0115] Example 1

[0116] 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;

[0117] The water storage system 1 includes 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;

[0118] 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 permeable plate 15, and the second upper water storage tank 13 and the medium tank 2 are separated only by a second permeable plate 16; the water storage system 1 and the medium tank 2 are an integral rectangular shape, separated by the permeable plates on both sides;

[0119] 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 overflow 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 overflow 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. 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 first upper water tank 11 and the second water level regulating plate 18 can be realized. The water level in the water tank 11 and the second upper water tank 13 is adjusted; the excess water flows into the first lower water tank 12 and the second lower water 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 movable 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 tank 11, the first lower water tank 12, the second upper water tank 13 and the second lower water tank 14 are all provided with standby valves 19

[0120] The medium tank 2 is provided with one or more layers of medium. The medium is provided with a test main hole 21 and observation points 22 that extend throughout the entire height of the medium. That is, the depth and height of the main hole 21 extend throughout the entire height of the medium, and the depth and height of the observation points 22 extend throughout the entire height of the medium. There are 16 observation points 22. The test main hole 21 is located at the center of the medium, and the observation points 22 are distributed around the test main hole 21 in two circles, with 8 observation points evenly distributed in the inner circle and 8 observation points evenly distributed in the outer circle.

[0121] The heating system 3 includes a heating rod 31, an electric wire 32, and a power supply 33 connected in sequence. The heating rod 31 is arranged in the main test hole 21. By adjusting the power supply 33, the instantaneous / continuous heat source is excited, thereby changing the temperature field in the aquifer.

[0122] The distributed fiber optic 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 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.

[0123] In this example, the medium includes a phreatic aquifer 23, a weakly permeable layer 24, and a confined aquifer 25, which are connected sequentially 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 be selected from sandy soils and clay soils with different particle sizes and different compositions.

[0124] 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:

[0125] 1. Adjust the position of the water-passing section by opening or closing 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;

[0126] 2. Fill the medium slot 2 with medium in layers and install the distributed optical fiber data acquisition system 4;

[0127] 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;

[0128] 4. Start the distributed optical fiber data acquisition system 4 to collect water pressure, temperature and heat flux density data in real time;

[0129] 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;

[0130] 6. Turn on the heating system 3 to activate the instantaneous heat source and the constant heat source. By changing the output power of the heating rod 31, the excitation intensity of the heat source in the test main hole 21 is changed, thereby changing the temperature field in the aquifer.

[0131] 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;

[0132] 8. Turn off the heating system 3 and the distributed optical fiber data acquisition system 4, and end the test;

[0133] 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.

[0134] The permeability of aquifers is calculated using theories of steady and unsteady groundwater flow between rivers and canals, while the thermal conductivity of aquifers is calculated using theories of groundwater heat transfer. Microthermal tests using unsteady flow conditions can also be used to simultaneously calculate both permeability and thermal conductivity.

[0135] The steady flow formula for single well pumping is used to calculate the permeability coefficient:

[0136]

[0137] The permeability coefficient is calculated using the steady flow formula with an observation well:

[0138]

[0139] The permeability coefficient is calculated using the unsteady flow formula for single well pumping:

[0140]

[0141] In the above formula: Q is the stable pumping flow rate of the pumping well; K is the permeability coefficient of the aquifer; H0 is the initial thickness of the water layer; 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 well.

[0142] Heat transfer mainly describes the problem of thermal field, which can be described and solved by heat conduction equation and convection-diffusion equation.

[0143] When the groundwater velocity is 0, heat transfer occurs mainly by heat conduction:

[0144]

[0145] When the groundwater velocity is not zero, heat transfer mainly occurs by convection diffusion:

[0146]

[0147] In the above formula: T is temperature; α is thermal conductivity; u represents the flow velocity vector.

[0148] The above-mentioned 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 simultaneously.

[0149] The one-dimensional temperature conduction model in the experiment can be expressed as the following well-defined problem:

[0150] Let the temperature function be u and the time function be T, then:

[0151]

[0152] Homogenize the variables and let:

[0153]

[0154] Substituting into formula (6), we can get:

[0155]

[0156] Where u is the temperature, K; (ρ c ) fs is the heat capacity of the porous medium, 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.

[0157] By homogenizing the boundary of equation (8), we can obtain the homogeneous boundary of the homogeneous equation, and let:

[0158] u′(x′,t′)=V(x′,t′)+W(x′,t′) (9)

[0159] Where W(x′,t′)=-x′+1.

[0160] Substituting into the original equation we get:

[0161]

[0162] Separate the variables of V(x′,t′) and set V(x′,t′)=X(x′)·T(t′), then:

[0163]

[0164] Converting the equation into a system of equations, we get:

[0165]

[0166] From formula (10), we can know that:

[0167] V| x′＝0 =X(x′)·T(t′)=X (0) T(t′)=0 (13)

[0168] V| x′＝1 =X(x′)·T(t′)=X (1) ′T(t′)=0 (14)

[0169] In order to make the equation meaningful, T(t′)≠0, so X (0) =0,X (1) =0.

[0170]

[0171] analyze:

[0172] ④When λ0<0,

[0173]

[0174] A=B=0, X(x′)≤0, discard it.

[0175] ⑤When λ0=0,

[0176] X(x′)=Ax′+B.

[0177] X(0)=B=0. X(1)=A+B=0.

[0178] A=B=0, X(x′)≤0, discard it.

[0179] ⑥ When λ0>0, let λ0=β 2 ,have:

[0180] X(x′)=Acosβx′+Bsinβx′,

[0181] X(0)=A=0, X(1)=Bsinβ=0,

[0182] B is not 0, so sinβ=0, β=nπ.(n=1,2,3,...), λ0=n 2 π 2 ,get:

[0183] X n (x′)=B n sinnπx′.(n=1,2,3…) (16)

[0184] For T(t′),

[0185] T′(t′)+λ0T(t′)=0, let λ0=n 2 π 2 Substituting in, we have:

[0186] T′(t′)+n 2 π 2 T(t′)=0, that is, T′ n (t′)+n 2 π 2 T n (t′)=0, and the solution is:

[0187]

[0188] From the separation of variables, we know that V(x′, t′) = X(x′)·T(t′), so we have:

[0189]

[0190] V n By summing (x′, t′), we can get:

[0191]

[0192] Substituting t′=0 into equation (18), we can obtain:

[0193] V(x′,0)=D n sinnπx′=x′-1 (20)

[0194] By Fourier transform, we can get:

[0195]

[0196] Substituting formula (21) into formula (19), we can obtain:

[0197]

[0198] Substituting formula (22) into formula (9), we can obtain:

[0199]

[0200] 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:

[0201]

[0202] Where α is the thermal diffusion coefficient, m 2 / s; the other symbols have the same meanings as above.

[0203] Based on the temperature change data during the test, the measured curve under the unsteady heat conduction test can be drawn. The thermal diffusivity of the porous medium can be calculated by fitting the standard curve with the measured curve. The effective thermal conductivity of the porous medium can be calculated through the stable heat conduction test. The heat capacity of the porous medium can be calculated by combining the two. In this way, the thermal diffusivity, thermal conductivity and heat capacity of the porous medium aquifer can be simultaneously solved at different stages of the heat conduction test.

[0204] The calculation results of the embodiment are as follows:

[0205]

[0206] Alternatively, a three-dimensional hydrothermal coupling numerical model consistent with the size conditions of the indoor model or the field model can be 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. By adjusting the permeability coefficient and thermal conductivity coefficient of the model, the water level and temperature conditions of the numerical model operation are made consistent with the actual 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 the groundwater.

[0207] Using water level data, positions with the same water level can be connected to obtain isowater levels. Streamlines are perpendicular to the isowater levels and point from high water levels to low water levels. The isowater levels and streamlines together can be used to draw a flow field diagram of the aquifer. The density of the isowater levels represents the magnitude of the groundwater flow velocity, and the direction of the streamlines represents the flow direction of the groundwater. This can be used to identify the flow velocity and direction of the groundwater. Alternatively, the temperature distribution and migration law can be measured using the distributed optical fiber 25 in the test main hole 21. 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 the 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 ascertained based on the temperature change rate in different directions. Alternatively, the temperature distribution and migration law measurable by the distributed optical fiber 25 in the observation point 22 can be used. 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 quickly in the main direction of groundwater flow, and the greater the flow rate, the faster the temperature changes. The flow rate and direction of groundwater can be ascertained based on the temperature change rate at the observation points 22 at the same distance but in different directions.

[0208] The above-mentioned apparatus and method are highly compatible and can be used to determine the permeability coefficient, thermal conductivity, and flow velocity and direction in a variety of different ways. This allows the user to select a more convenient testing method based on the actual situation.

[0209] Example 2

[0210] Figure 1 The water storage system 1 and the medium tank 2 are primarily used to construct the desired aquifer system, suitable for indoor mesoscale experiments. When conducting field experiments, the test site itself is a natural aquifer system. Therefore, field experiments do not require the water storage system 1 and the medium tank 2. Only the heating system 3 and the distributed fiber optic data acquisition system 4 are required to conduct field experiments. The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments:

[0211] A thermal tracer test method for determining the comprehensive hydrogeological conditions of an aquifer comprises the following steps during a field test:

[0212] 1) Select appropriate locations to arrange the test main hole 17 and observation point 18;

[0213] 2) Installing a distributed fiber optic data acquisition system 4;

[0214] 3) Wait for the water level to stabilize and form a stable natural seepage field;

[0215] 4) Start the distributed optical fiber data acquisition system 4 to collect water pressure and temperature data in real time;

[0216] 5) Turn on the heating system 3 to excite the instantaneous heat source and the constant heat source. By changing the output power of the heating rod 22, the excitation intensity of the heat source in the test main hole 17 is changed, thereby changing the temperature field in the aquifer;

[0217] 6) Using the distributed optical fiber data acquisition system 4, the water pressure and temperature changes of the aquifer are recorded in real time, and the water pressure and temperature data of the entire test process are derived;

[0218] 7) Turn off the heating system 3 and the distributed optical fiber data acquisition system 4, and end the test;

[0219] 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 method for determining the comprehensive hydrogeological conditions of an aquifer, characterized by: Use of a thermal tracer test device for determining the comprehensive hydrogeological conditions of an aquifer. The thermal tracer test device for determining the comprehensive hydrogeological conditions of an aquifer includes a water storage system, a medium tank, a heating system, and a distributed optical fiber data acquisition system. 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; 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 a first permeable plate, and the second upper water storage tank and the medium tank are separated only by a second permeable plate; The first lower water tank is arranged at the bottom of the first upper water tank, and a first water level regulating plate is provided on the first upper water tank. When the first water level regulating plate is adjusted, the overflowing water falls into the first lower water tank; the second lower water tank is arranged at the bottom of the second upper water tank, and a second water level regulating plate is provided on the second upper water tank. When the second water level regulating plate is adjusted, the overflowing water falls into the second lower water tank; The medium tank is equipped with more than one layer of medium, 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 located in the center of the medium, and the observation points are distributed around the test main hole. The heating system includes a heating rod, wires, and power supply connected in sequence. The heating rod is placed in the main test hole. By adjusting the power supply, the instantaneous / continuous heat source is excited, thereby changing the temperature field in the aquifer. The distributed fiber optic data acquisition system includes distributed optical fibers and a fiber optic demodulator. Distributed optical fibers are installed along the height direction at the main test hole and observation points. The distributed optical fibers monitor and record the temperature and water pressure at the measured locations, and the fiber optic demodulator analyzes and outputs the data. The thermal tracer test method for determining the comprehensive hydrogeological conditions of an aquifer comprises the following steps: 1) Adjust the water permeability position on the first water permeable plate and the second water permeable plate; 2) Fill the media slots with media in layers and install a distributed fiber optic data acquisition system; 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; 4) Start the distributed fiber optic data acquisition system to collect water pressure and temperature data in real time; 5) controlling the water levels in the first upper water storage tank and the second upper water storage tank by 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; 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; 7) Use a distributed fiber optic data acquisition system to record the water pressure and temperature changes of the aquifer in real time and derive the water pressure and temperature data of the entire test process; 8) Turn off the heating system and distributed optical fiber data acquisition system, and end the test; 9) Determine the flow velocity and direction of the aquifer and the comprehensive hydrogeological conditions of the hydrogeological parameters using the full process data of the main test hole and observation points during the test; The thermal conductivity of the aquifer is calculated using the groundwater heat transfer theory. The standard curve is matched with the measured data curve of the heat conduction test using the matching method, and the corresponding coordinate values are recorded. The thermal diffusivity, effective thermal conductivity and heat capacity of the aquifer are obtained through 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 let: Substituting into formula (6), we can get: Where u is the temperature, K; (ρ c ) fs is the heat capacity of the porous medium, 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) Where W(x′,t′)=-x′+1, and W(x′,t′) is a properly chosen function that 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; Assuming V(x′,t′)=X(x′)·T(t′), we have: Where: X(x′) is a one-variable displacement function about x′ only, T(t′) is a one-variable time function about t′ only, 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 about x′ only, and the right side is a function about t′ only. If they are equal, they must be constants, that is, -λ0 is the separation constant; converting the equation into a system of equations, we get: Converting 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 to make the equation meaningful, 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 we have: Among them 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 By summing (x′, t′), we can get: 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 meanings as above; Based on the temperature change data during the test, the measured curve under the unsteady heat conduction test was drawn. The thermal diffusivity of the porous medium was calculated by fitting the standard curve with the measured curve. The effective thermal conductivity of the porous medium was calculated through the stable heat conduction test. The heat capacity of the porous medium was calculated by combining the two.

2. The thermal tracer test method for determining the comprehensive hydrogeological conditions of an aquifer according to claim 1, characterized in that: The distributed optical fiber in the test main hole spirally rises around the inner or outer wall of the test main hole; 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.

3. The thermal tracer test method for determining the comprehensive hydrogeological conditions of an aquifer according to claim 1 or 2, characterized in that: 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 movable rubber plugs. 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, the position of the water-passing section can be adjusted.

4. The thermal tracer test method for determining the comprehensive hydrogeological conditions of an aquifer according to claim 1 or 2, characterized in that: The medium includes a phreatic aquifer, aquitard and a confined aquifer that are sequentially connected from top to bottom. The medium is replaced as needed to simulate the phreatic aquifer, aquitard and confined aquifer.

5. The thermal tracer test method for determining the comprehensive hydrogeological conditions of an aquifer according to claim 1 or 2, characterized in that: In step 1), the position of the water-passing section is adjusted by opening or closing the rubber plugs on the water-permeable holes at different positions on the first water-permeable plate and the second water-permeable plate.

6. The thermal tracer test method for determining the comprehensive hydrogeological conditions of an aquifer according to claim 1 or 2, characterized in that: The permeability coefficient of the aquifer is calculated using the steady flow and unsteady flow theory of groundwater between rivers and channels; or the permeability coefficient and thermal conductivity coefficient of the aquifer are calculated simultaneously using micro-thermal tests under unsteady flow conditions.

7. The thermal tracer test method for determining the comprehensive hydrogeological conditions of an aquifer according to claim 1 or 2, characterized in that: Combined with the water pressure, temperature and heat flux density data of the distributed fiber optic data acquisition system, a three-dimensional hydrothermal coupling numerical model is constructed that is consistent with the size conditions of the indoor model or the field model. The three-dimensional numerical model is used to reproduce the experimental conditions of the actual model. By adjusting the permeability coefficient and thermal conductivity coefficient of the model, the water level and temperature conditions of the numerical model operation are made consistent with the actual 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 the groundwater.

8. The thermal tracer test method for determining the comprehensive hydrogeological conditions of an aquifer according to claim 1 or 2, characterized in that: Using water level data, positions with the same water level can be connected to obtain isowater levels. Streamlines are perpendicular to the isowater levels and point from high water levels to low water levels. Together, the isowater levels and streamlines can be used to draw a flow field map of the aquifer. The density of the isowater levels represents the magnitude of the groundwater flow velocity, and the direction of the streamlines represents the direction of groundwater flow. This can be used to determine the groundwater flow velocity and direction. Alternatively, the temperature distribution and migration patterns measured by distributed optical fibers in the main test hole can be used. When groundwater flows naturally, the temperature changes differently in different directions within the main test hole. The temperature changes faster in the main direction of groundwater flow, and the greater the flow velocity, the faster the temperature changes. The rate of temperature change in different directions can be used to determine the groundwater flow velocity and direction. Alternatively, the temperature distribution and migration patterns measured by distributed optical fibers at observation points can be used. When groundwater flows naturally, the temperature changes differently at different observation points at the same distance from the main test hole but in different directions. The temperature changes faster in the main direction of groundwater flow, and the greater the flow velocity, the faster the temperature changes. The rate of temperature change at observation points at the same distance but in different directions can be used to determine the groundwater flow velocity and direction.

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