Construction method of geothermal prediction model and well spacing method of underground water ground source heat pump system

Abstract

The invention discloses a geothermal prediction model construction and underground water ground source heat pump system well spacing method, and the method comprises the steps: building a three-dimensional water flow and heat coupling migration model of the operation state of a site-level underground water ground source heat pump system in a suitable region, and predicting the change of a water flow field and a temperature field with different pumping and filling ratios and different well spacing. According to the underground water ground source heat pump system, the energy utilization efficiency can be improved, thermal pollution is avoided, long-term sustainability is ensured, and the influence on underground water resources and the ecological environment is reduced.

Description

Technical Field

[0001] The present invention relates to the field of geothermal energy technology, and specifically to the construction of a geothermal prediction model and a well layout method for a groundwater source heat pump system. Background Art

[0002] The groundwater source heat pump system is an efficient and energy-saving technology that uses shallow underground geothermal resources for heating and cooling. The system uses the temperature of groundwater or soil to exchange heat by burying a closed pipe system underground to adjust the temperature inside the building. Due to its high efficiency, energy saving and environmental friendliness, the groundwater source heat pump system has been widely used in the field of modern building energy conservation.

[0003] The pumping-injection ratio is a key parameter of the groundwater source heat pump system, which involves the balance between the system's extraction and recharge of groundwater resources. Studies have shown that the pumping-injection ratio has a significant impact on the energy efficiency and long-term stability of the groundwater source heat pump system. An unreasonable pumping-injection ratio may lead to the destruction of the underground temperature field, affect the heat exchange efficiency of the system, and even cause the system to fail. At present, the methods for determining the pumping-injection ratio mainly include empirical formulas, heat balance calculations, and field tests. The empirical formula is simple and easy to use, but it is usually based on data under specific conditions and may not accurately reflect the actual situation under different geological and climatic conditions. The heat balance calculation can provide a theoretical pumping-injection ratio, but it requires accurate input parameters, which may be difficult to obtain accurately in practice. Field tests can provide direct, actual pumping-injection ratio data, but they are costly and time-consuming, and may be limited by test conditions and cannot fully represent the actual application scenario. The well spacing is another key parameter of the groundwater source heat pump system, which has a significant impact on the system's operating efficiency and environmental impact. Too small a well spacing may lead to changes in the groundwater flow field and geothermal field, directly affecting the efficiency and service life of the heat pump system. In addition, the setting of well spacing is also related to the change of groundwater quality and the impact on the surrounding ecological environment. Therefore, it is crucial to reasonably determine the pumping ratio and well spacing for the efficient operation of the groundwater source heat pump system.

[0004] The information disclosed in this background technology section is only used to deepen the understanding of the background technology of the present disclosure, and should not be regarded as acknowledging or suggesting in any form that the information constitutes the prior art known to those skilled in the art. Summary of the invention

[0005] In view of at least one of the above technical problems, the present disclosure provides a method for constructing a geothermal prediction model and a well layout method for a groundwater source heat pump system. By combining pumping and recharging tests with empirical parameters, a three-dimensional water flow and heat coupling migration model of the operating status of a site-level groundwater source heat pump system is established in a more suitable area. By predicting the changes in water flow and temperature fields under different pumping and recharging ratios and different well spacings, a reasonable well layout plan (i.e., well spacing and pumping and recharging ratio) for the groundwater source heat pump system is determined.

[0006] According to one aspect of the present disclosure, a method for constructing a geothermal prediction model is provided, comprising the following steps: (1) Determine the scope and depth of the proposed geothermal utilization area and construct a hydrogeological conceptual model of the area; (2) On the basis of the hydrogeological conceptual model, a coupling equation of groundwater flow model and heat transfer equation is established; (3) Generalize the boundary conditions of the proposed geothermal utilization area (a method of processing geographic data in relevant software, such as ArcGIS, which aims to simplify the geometric shape of the data, reduce the complexity of the data, and maintain the main characteristics and distribution patterns of the data as much as possible), and generalize the strata vertically; (4) Meshing the super grid surface of the proposed geothermal utilization area and refining the grid of the production well area; (5) Setting the solution conditions to construct a steady flow model, setting the initial water level depth of the steady flow model, and using this as the initial flow field of the subsequent transient flow model; (6) Setting the temperature of each layer in the proposed geothermal utilization area. The surface layer takes the annual average temperature of the proposed geothermal utilization area, and the values ​​of the layers below are taken according to the depth from the constant temperature zone multiplied by the ground temperature increase rate; (7) Assigning values ​​to the hydrogeological parameters of the proposed geothermal utilization area; (8) The simulation period, the inlet and outlet temperature difference threshold, and the temperature fluctuation threshold at the end of each recovery period are set to construct a geothermal prediction model.

[0007] In some embodiments of the present disclosure, in step (2), the groundwater flow model equation is as follows: ; In the formula: - the intended scope of geothermal utilization; H - aquifer head; Kxx, Kyy, Kzz - the permeability coefficients in the x, y, and z directions respectively; - the permeability coefficients in the direction of the boundary normal; - unit water storage coefficient; - gravity water supply; - source and sink terms; - upper boundary; - second-class boundary; n - normal direction outside the boundary of the study area; q (x, y, z, t) - single-width flow of the second-class boundary; the heat transfer equation is as follows: ; Where: C eq —Equivalent volume heat capacity; Ceq= , where θ represents the porosity, ρC represents the total volume heat capacity in the porous medium; C L =ρw×Cw, which represents the volume heat capacity of water, ρw represents the density of water, and Cw represents the specific heat capacity; λ—equivalent thermal conductivity; Q T —General heat source; qT is the heat flux flowing into the boundary Г2.

[0008] In some embodiments of the present disclosure, in step (6), the hydrogeological parameters include permeability, water supply, water storage rate, geothermal heat flow value, porosity, water volume specific heat capacity, soil volume specific heat capacity, water thermal conductivity, soil thermal conductivity, longitudinal diffusion, and lateral diffusion.

[0009] In some embodiments of the present disclosure, in step (4), the super grid surface of the proposed geothermal utilization area is meshed using the Triangle algorithm.

[0010] According to a second aspect of the present disclosure, a method for laying out wells in a groundwater source heat pump system is provided, comprising the following steps: (1) Design different pumping ratio schemes and obtain the flow field distribution results and temperature field simulation results during the simulation period based on the established geothermal prediction model; (2) respectively counting the temperature plume area and the maximum operating power of the geothermal system under the different pumping-injection ratio schemes, and calculating the maximum power per unit area, and determining the scheme with the largest maximum power per unit area as the optimal pumping-injection ratio; (3) Based on the above optimal pumping-recharging ratio, different well spacings are designed, and large and small flow modes are set according to the pumping well flow and recharging well flow of the optimal pumping-recharging ratio, so as to simulate and predict the water level and temperature plume distribution of the pumping and recharging wells; (4) The effects of geothermal system operation on the surrounding flow field, temperature field and heat penetration of the pumping wells under different well spacings were compared, and the well spacing with the least impact on the efficiency of the heat pump unit was selected as the optimal well spacing.

[0011] One or more technical solutions provided in the embodiments of the present application have at least any of the following technical effects or advantages: Using coupled simulation of groundwater flow and heat transfer equations to guide the well layout of groundwater source heat pump systems can ensure that the system design is more accurate and efficient. By optimizing the well spacing and pumping-injection ratio, energy utilization efficiency can be improved, thermal pollution can be avoided, long-term sustainability can be ensured, and the impact on groundwater resources and the ecological environment can be reduced, thereby achieving the dual goals of rational development of geothermal energy and environmental protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 This is a bar chart of the comprehensive results of K9 pumping and recharging in one embodiment of the present application.

[0013] Figure 2 This is a bar chart of the comprehensive results of K10 water pumping and recharging in one embodiment of the present application.

[0014] Figure 3 It is a schematic diagram of the simulation range in one embodiment of the present application.

[0015] Figure 4 This is a grid division diagram in one embodiment of the present application.

[0016] Figure 5 This is the K9 hole water level fitting effect in one embodiment of the present application.

[0017] Figure 6 This is the K10 hole water level fitting effect in one embodiment of the present application.

[0018] Figure 7 This is a schematic diagram of the pumping ratio setting in one embodiment of the present application.

[0019] Figure 8 This is the annual change of the flow field of the submerged aquifer in the first year of the one-pumping-one-filling cycle in one embodiment of the present application; wherein, A: the end of the cooling period; B: the end of the cooling intermittent period; C: the end of the heating period; D: the end of the heating intermittent period.

[0020] Fig. 9 This is the annual change of the flow field of the submerged aquifer in the fifth year of the one-pumping-one-filling cycle in one embodiment of the present application; wherein, A: the end of the cooling period; B: the end of the cooling intermittent period; C: the end of the heating period; D: the end of the heating intermittent period.

[0021] Fig.10 This is the annual change of the flow field of the submerged aquifer in the 10th year of the one-pumping-one-filling cycle in one embodiment of the present application; wherein, A: the end of the cooling period; B: the end of the cooling intermittent period; C: the end of the heating period; D: the end of the heating intermittent period.

[0022] Fig.11 This is the annual variation of the temperature field at the bottom of the submerged aquifer in the first year of one pumping and one filling cycle in one embodiment of the present application; wherein, A: the end of cooling; B: the end of cooling intermittent period; C: the end of heating period; D: the end of heating intermittent period.

[0023] Fig.12 This is the annual change of the temperature field at the bottom of the submerged aquifer in the fifth year of one pumping and one filling cycle in one embodiment of the present application; wherein, A: the end of cooling; B: the end of cooling intermittent period; C: the end of heating period; D: the end of heating intermittent period.

[0024] Fig.13This is the annual change of the temperature field at the bottom of the submerged aquifer in the 10th year of one pumping and one filling cycle in one embodiment of the present application; wherein, A: the end of cooling; B: the end of cooling intermittent period; C: the end of heating period; D: the end of heating intermittent period.

[0025] Fig.14 This is a cross-sectional temperature change curve at the end of the one-pump-one-fill refrigeration period in one embodiment of the present application.

[0026] Fig.15 This is a cross-sectional temperature change curve at the end of the one-pump-one-fill heating period in one embodiment of the present application.

[0027] Fig.16 This is a line graph of temperature changes at a pumping well in one embodiment of the present application.

[0028] Fig.17 This is the annual change of the flow field in the submerged aquifer in the first year of one pumping and two fillings in one embodiment of the present application; wherein, A: the end of cooling; B: the end of cooling intermittent period; C: the end of heating period; D: the end of heating intermittent period.

[0029] Fig.18 This is the annual change of the flow field in the submerged aquifer in the fifth year of one pumping and two fillings in one embodiment of the present application; wherein, A: the end of cooling; B: the end of cooling intermittent period; C: the end of heating period; D: the end of heating intermittent period.

[0030] Fig.19 This is the annual change of the flow field in the submerged aquifer in the 10th year of one pumping and two fillings in one embodiment of the present application; wherein, A: the end of cooling; B: the end of cooling intermittent period; C: the end of heating period; D: the end of heating intermittent period.

[0031] Fig. 20 This is the annual variation of the temperature field at the bottom of the submerged aquifer in the first year of one pumping and two fillings in one embodiment of the present application; wherein, A: the end of cooling; B: the end of cooling intermittent period; C: the end of heating period; D: the end of heating intermittent period.

[0032] Fig.21 This is the annual change of the temperature field at the bottom of the submerged aquifer in the fifth year of one pumping and two fillings in one embodiment of the present application; wherein, A: the end of cooling; B: the end of cooling intermission; C: the end of heating; D: the end of heating intermission.

[0033] Fig. 22 This is the annual variation of the temperature field at the bottom of the submerged aquifer in the 10th year of one pumping and two fillings in one embodiment of the present application; wherein, A: the end of cooling; B: the end of cooling intermission; C: the end of heating; D: the end of heating intermission.

[0034] Fig.23 This is a cross-sectional temperature change curve at the end of the one-draw-two-fill refrigeration period in an embodiment of the present application.

[0035] Fig.24This is a cross-sectional temperature change curve at the end of the one-pump-two-fill heating period in one embodiment of the present application.

[0036] Fig.25 This is a line graph of temperature changes at a one-pump-two-filling pumping well in one embodiment of the present application.

[0037] Fig.26 This is the flow field change of the submerged aquifer in the 5th year in an embodiment of the present application (well spacing is 70m); wherein, A: the end of small-flow cooling; B: the end of large-flow cooling; C: the end of the small-flow cooling intermittent period; D: the end of the large-flow cooling intermittent period; E: the end of the small-flow heating period; F: the end of the large-flow heating period; G: the end of the small-flow heating intermittent period; H: the end of the large-flow heating intermittent period.

[0038] Fig. 27 The temperature field changes at the bottom of the submerged aquifer in one embodiment of the present application (well spacing is 70m); wherein, A: temperature field changes at the end of the first year with small flow; B: temperature field changes at the end of the first year with large flow; C: temperature field changes at the end of the fifth year with small flow; D: temperature field changes at the end of the fifth year with large flow; E: temperature field changes at the end of the tenth year with small flow; F: temperature field changes at the end of the tenth year with large flow.

[0039] Fig.28 This is the flow field change of the submerged aquifer in the 5th year in an embodiment of the present application (well spacing is 60m); among them, A: the end of small-flow cooling; B: the end of large-flow cooling; C: the end of the small-flow cooling intermittent period; D: the end of the large-flow cooling intermittent period; E: the end of the small-flow heating period; F: the end of the large-flow heating period; G: the end of the small-flow heating intermittent period; H: the end of the large-flow heating intermittent period.

[0040] Fig.29 The temperature field changes at the bottom of the submerged aquifer in one embodiment of the present application (well spacing is 60m); wherein, A: temperature field changes at the end of the first year with small flow; B: temperature field changes at the end of the first year with large flow; C: temperature field changes at the end of the fifth year with small flow; D: temperature field changes at the end of the fifth year with large flow; E: temperature field changes at the end of the tenth year with small flow; F: temperature field changes at the end of the tenth year with large flow.

[0041] Fig.30 This is the flow field change of the submerged aquifer in the 5th year in an embodiment of the present application (well spacing is 50m); among them, A: the end of small-flow cooling; B: the end of large-flow cooling; C: the end of the small-flow cooling intermittent period; D: the end of the large-flow cooling intermittent period; E: the end of the small-flow heating period; F: the end of the large-flow heating period; G: the end of the small-flow heating intermittent period; H: the end of the large-flow heating intermittent period.

[0042] Fig.31The temperature field changes at the bottom of the submerged aquifer in one embodiment of the present application (well spacing is 50m); wherein, A: temperature field changes at the end of the first year with small flow; B: temperature field changes at the end of the first year with large flow; C: temperature field changes at the end of the fifth year with small flow; D: temperature field changes at the end of the fifth year with large flow; E: temperature field changes at the end of the tenth year with small flow; F: temperature field changes at the end of the tenth year with large flow. DETAILED DESCRIPTION

[0043] In order to better understand the technical solution of the present application, the above technical solution will be described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0044] Example: Taking the construction of groundwater source heat pump system in Hanhe Village, Zheng'an Town as an example 1. Overview: Hanhe Village, Zheng'an Town is located in a relatively suitable area for groundwater source heat pumps. It has great potential for the development and utilization of shallow geothermal energy resources and has good construction conditions. It should have broad prospects. Taking the above factors into consideration, Hanhe Village, Zheng'an Town is selected as the numerical simulation area for groundwater source heat pumps. Using the numerical simulation software Feflow, by simulating the changes in water flow and temperature fields under different pumping ratios and different well spacing conditions, the reasonable well layout plan for the relatively suitable area of ​​the groundwater source heat pump system is determined.

[0045] 2. Model establishment 1. Hydrogeological conceptual model: According to the 200 m coring work of the pumping and recharging test holes numbered K9 and K10 in Hanhe Village, Zheng'an Town, it was found that there was a thick cemented layer at 150-160 m in the site, and there was a risk that the wellbore construction could not be drilled through. Therefore, a large-diameter pump suction reverse circulation clean water drilling process was used for drilling. When the wellbore was drilled to this layer using large-diameter clean water reverse circulation construction, drilling difficulties occurred, which were specifically manifested as: the drill bit could not break through the layer, the footage was slow, and the reverse circulation pump had poor drainage. Finally, the depth of K9 was 168 m, and the depth of K10 was 164 m. The depth of the hole was taken as the depth of the numerical simulation study.

[0046] According to the lithology and thickness of each layer, it is vertically generalized in the model. The stratum structure is as follows: Figure 1~Figure 2The vertical generalization of the strata is shown in Table 1. Among them, the first layer is a phreatic aquifer, with the lithology mainly composed of fine sand and silty sand, and the bottom plate is buried at a depth of 32 to 33.5 m; the second layer is a weakly permeable layer, with the lithology mainly composed of silty clay and clay, and the bottom plate is buried at a depth of 44m to 51.9 m; the third layer is a confined aquifer, with the lithology mainly composed of fine sand and the bottom plate is buried at a depth of 56.3m to 57.1m; the fourth layer is a weakly permeable layer, with the lithology of clay and silty clay, and the bottom plate is buried at a depth of 92.3m to 95m; the fifth layer is a confined aquifer, with the lithology of fine sand and the bottom plate is buried at a depth of 95.65m to 100.2m; the sixth layer is a weakly permeable layer, with the lithology of clay and silty clay, and the bottom plate is buried at a depth of 121.7 to 123 m; the seventh layer is a confined aquifer, with the lithology of medium sand and fine sand, and the bottom plate is buried at a depth of 153.9m to 157 m; the 8th layer is a weakly permeable layer, the rock type is clay and silty clay, and the bottom plate is buried at a depth of 164m to 166m.

[0047] Table 1 Results of vertical generalization of strata .

[0048] Therefore, the strata in the simulation area are generalized into 8 layers vertically. After running the model, the Rate Budget calculation module of Feflow is used to simulate the distribution of water inflow and outflow of the recharge wells and pumping wells in each aquifer with the 1st, 5th and 10th year operation periods as the calculation time points. It is found that the water volume of the recharge wells and pumping wells is mainly distributed in the 1st layer (i.e., the phreatic aquifer), the 3rd layer and the 5th layer. Among them, the first layer is a phreatic aquifer, which receives about 50.50% to 52.96% of the water injected during the operation of the geothermal system, and contributes to about 48.36% to 53.75% of the total flow; the third and fifth layers are deep confined aquifers, which receive about 13.27% to 14.48% and 13.21% to 14.42% of the water injected during the operation of the geothermal system, and contribute to 13.13% to 14.78% and 13.02% to 14.66% of the total flow, respectively. In summary, the first layer (phreatic aquifer) is taken as the target layer for simulation.

[0049] 2. Simulation area and mesh generation (1) Simulation scope: The pumping well is located in the northwest corner of Hanhe Village, Zheng'an Town, with a well spacing of 60m. Under natural conditions, the southern boundary is the recharge boundary, the northern boundary is the discharge boundary, the east-west boundary is the zero flow boundary, and the groundwater velocity under the natural flow field is 0.0032m / d. The upper and lower boundaries are set as constant temperature and water-blocking boundaries. According to the K9 pumping volume of 24.12m 3 / h, the impact radius is 28m; the pumping volume is 83.16m 3 / h, the influence radius is 102m; K10 pumping capacity is 37.26m 3 / h, the impact radius is 60m; the pumping volume is 77.26m3 / h, the impact radius is 130.92m. At the same time, based on the actual geological and hydrogeological conditions, a rectangular block of 300m*300m is selected as the model range ( Figure 3 ).

[0050] (2) Meshing: In terms of spatial discretization of 3D modeling, the Triangle algorithm is used to perform triangular meshing on the super mesh surface. The local mesh is encrypted for the key mining wells in the model. The model has 3318 plane mesh nodes and 6423 unit meshes. The vertical division is 8 layers, resulting in 16590 nodes and 25692 unit meshes. Figure 4 shown.

[0051] 3. Solution conditions and parameter assignment (1) Solution conditions: The source and sink items of the aquifer in the simulation area mainly include precipitation infiltration recharge and evaporation discharge, artificial well mining, lateral recharge and discharge, which are specifically characterized as follows: the artificial well mining item uses the MultilayerWell module to characterize the mining well in the FEFLOW model, and is supplemented by time series for dynamic mining control; in the model, the lateral recharge and discharge are assigned flux values ​​using a given flow boundary, and then the flow is calculated using the software to characterize the lateral recharge and discharge of the aquifer at the southern and northern boundaries; the groundwater level in the area is greater than the limit evaporation depth (set to 4m based on the empirical value of Zhengzhou City), and the evaporation value is 0. The precipitation infiltration recharge and evaporation discharge in the simulation area have little effect on the model and can be ignored. The surface source and sink items are mainly affected by precipitation infiltration recharge, and the surface is generalized as a flux boundary; according to the drilling results, the lower part is a thick layer of clay at a depth of 166m, with weak water conductivity and permeability, and is generalized as a water barrier boundary.

[0052] According to the above boundary conditions, a steady flow model is constructed to simulate the initial flow field distribution of the model under given conditions. According to the water level burial depth of the two boreholes in the area, the initial water level burial depth of the steady flow model is set to 8.7m, that is, 78.3m, which is used as the initial flow field of the subsequent transient flow model.

[0053] Due to the limited area of ​​the simulation area (300m×300m), the geothermal temperature difference on the horizontal surface in the area is small, and it is assumed that the groundwater temperature at the same elevation in the simulation area is the same. The temperature values ​​of each layer are: ① The surface layer takes the annual average temperature of the study area as 15.0℃; ② The geothermal constant temperature zone takes 17.3℃, and the values ​​of the layers below are multiplied by the geothermal warming rate according to the depth from the constant temperature zone, so the final initial temperature of the bottom plate is taken as 22.18℃.

[0054] (2) Parameter assignment: Hydrogeological parameters are a set of parameter indicators that reflect the properties of groundwater-bearing media such as water conductivity and water storage. In the generalization and assignment of stratigraphic zoning in the study area, the hydrogeological parameters selected are: permeability coefficient (Kx, Ky, Kz), water supply degree (µ) and water storage rate (Ss). Based on the collection of borehole pumping test data and relevant empirical values, the model parameter zoning is divided into 8 parameter zones from top to bottom according to the vertical change of lithology (Table 2).

[0055] Table 2 Hydrogeological parameter values .

[0056] The values ​​of other parameters are as follows: The terrestrial heat flow value in the study area is 60 mw / m 2 , porosity is 0.35, water volume specific heat capacity is 4.218 MJ / m 3 / ℃, the volume specific heat capacity of soil is 2.52 MJ / m 3 / ℃, water thermal conductivity 0.62 J / m / s / ℃, soil thermal conductivity 3 J / m / s / ℃, longitudinal dispersivity 1.2 m, and lateral dispersivity 0.12 m.

[0057] 3. Model Calibration In this example, the pumping and recharging test data set is used as the basis for the dynamic fitting of the groundwater model water level. The dynamic fitting of the pumping and recharging water levels of K9 and K10 holes is performed respectively. The duration of the fitting simulation is the time period of the test of each hole, that is, 23820 minutes. After the parameter cycle optimization process of "control-adjustment", the fitting effect of the outlet temperature of each hole is finally obtained as follows Figure 5~Figure 6 As shown, it can be seen that the water level simulation values ​​of K9, K10 and the two wells for pumping and recharging have good consistency with the observed values. The average absolute error and average relative error of the outlet temperature fitting of each well are shown in Table 3, indicating that the groundwater flow model constructed this time is stable and reliable.

[0058] Table 3 Water level fitting error analysis table .

[0059] 4. Simulation cycle and threshold of prediction model 1. Simulation period: Based on the above-mentioned model, June 1, 2022 is taken as the initial time point of the simulation prediction, and the simulation period is set to 10 years, until May 31, 2032. During this period, the operating conditions of the heat exchange holes in the cooling period, cooling intermittent period, heating period, and heating intermittent period of the year are considered to construct a geothermal prediction model.

[0060] 2. Selection of discrimination threshold: From the perspective of the efficiency of the groundwater source heat pump project, during the operation period, the temperature difference between the water inlet and the water outlet shall not be less than 5°C. From the perspective of the life of the groundwater source heat pump project, within the 10-year simulation period, the temperature fluctuation at the end of each recovery period shall not exceed 2°C.

[0061] 5. Simulation study on pumping-irrigation ratio scheme According to the suitability zoning of shallow geothermal energy, the simulation area is a relatively suitable area for groundwater source heat pumps, with a unit water inflow of 300 m 3 / dm~500m 3 / dm, the ratio of unit recharge volume to unit water inflow volume is 50% to 80%. According to the pumping and recharge test of test sites K9 and K10, the static burial depth of K9 is 8.73m, and the unit water inflow volume is 482m 3 / dm; K10 static burial depth 8.75m, unit water inflow 371m 3 / dm, the test results are shown in Table 4.

[0062] Table 4 Summary of the results of the pumping and recharging test at the Hanhe test site .

[0063] According to the field test in the test field, the optimal pumping and recharging ratios in the simulation area are theoretically 1:1 and 1:2, and the optimal pumping and recharging volume is 30 m 3 / h~60 m 3 / h. Therefore, two schemes were designed for numerical simulation ( Figure 7 ): Scheme 1: "1 pumping and 1 recharging", the well spacing is 60m, and the wells are arranged in an east-west straight line perpendicular to the water flow direction. The pumping and recharging volumes are both 30m 3 / h, the power of a single well is 120kW in summer and 90kW in winter; Scheme 2 "1 pumping and 2 injections" is arranged in an east-west straight line on the opposite sides, that is, the injection wells are located on both sides of the pumping well and are perpendicular to the water flow direction. The well spacing is 60m and the pumping capacity is 60 m 3 / h, and the recharge volume of the two recharge wells is 30m 3 / h, the single well power is 240kW in summer and 180kW in winter.

[0064] 1. One draw and one fill (1) Flow field: The geothermal prediction model constructed in Example 4 is run, and the flow field distribution results obtained during the simulation period show that the groundwater flow field in the aquifer changes regularly with the alternation of the operation period and the intermission period. The flow field distribution of the geothermal system in the operation cycle of the phreatic aquifer in the 1st, 5th, and 10th years is plotted as follows: Figure 8~Figure 10As shown in the figure, according to the simulation results, it can be seen that the groundwater flow field of the phreatic aquifer during the forecast period changes regularly with the alternation of the operation period and the intermittent period. Among them, during the operation period, the flow field near the pumping well was affected by human activities, and a small-scale water hill appeared around the recharge well, with the highest water level of about 79.2 m; a water level funnel appeared near the extraction well, with the lowest water level of about 74.3 m. During the intermittent period, the groundwater flow field of the phreatic aquifer quickly recovered to the natural flow field, and the groundwater level basically recovered to the initial state at the end of the intermittent period.

[0065] (2) Temperature field: Run the model to obtain the temperature field simulation results during the simulation period, and draw the temperature field distribution diagrams for the 1st, 5th, and 10th years ( Figure 11~Figure 13 ), it can be seen that the operation of the groundwater source heat pump system will have a significant impact on the surrounding temperature field. Driven by seepage, the temperature influence zone gradually spreads downstream. Among them, the temperature change zone in the first year is mainly distributed near the recharge well, with a temperature plume area of ​​4325.50 m 2 , the farthest extension to the pumping well is 43.66 m under the action of the hydraulic gradient of pumping and injection, while the pumping well itself is not affected and extends 36.48 m downstream driven by the natural flow field; in the fifth year, the temperature plume of the recharging well has covered the pumping well, and the area of ​​the temperature plume is 16030.85m 2 , extending 84.93 m downstream; at the end of the 10th year, the temperature plume affected an area of ​​28657.35 m 2 , extending 123.04 m downstream.

[0066] On this basis, the temperature profiles along the pumping well-recharge well at the end of the cooling period and heating period in the first, third, fifth and tenth years were drawn ( Figure 14~Figure 15 ), it can be seen that during the cooling period, a high point of the temperature plume is formed at the recharge well point, with a temperature of 24.09 ℃, which is the same as the water temperature of the recharge well. Under the action of heat conduction, the temperature value decreases to both sides; during the heating period, a low point of the temperature plume is formed at the recharge well point, with a temperature of 20.65 ℃. There are high temperature points (about 24 ℃) at 6 to 8 m on both sides of the periphery, and then decrease to both sides with the increase of distance. The temperature curve at the pumping well point is related to the year, showing that the temperature value is the lowest in the first year and increases significantly in the third year and thereafter. The reason for this is that a heat path is formed between the pumping and recharge wells, which causes the heat and cold imbalance of the rock and soil.

[0067] Observation points were set at the center of the recharging well and the pumping well, and the temperature change curves of the two well center points during the simulation period were derived as follows: Fig.16As shown in Table 5, it can be seen that the temperature of the pumping well is affected by the regular water injection of the recharge well, and the temperature value fluctuates and rises. Among them, in the first year, the temperature rise of the pumping well is about 0.38 ℃. It is believed that the heat path between the pumping and recharge wells has not been opened at this time, and the temperature value can be effectively reduced during the recovery period; in the second year, the temperature of the pumping well rises rapidly, and the annual value-added is about 2.00 ℃. Therefore, it is believed that the heat path between the pumping and recharge wells is initially opened at this time, and the temperature feather of the recharge well covers the pumping well, causing its temperature value to rise rapidly. Even if the system stops running during the recovery period, the temperature drop of the pumping well is still limited; then, the heat path between the pumping and recharge wells is formed, and the temperature value of the pumping well fluctuates stably in the high value range.

[0068] Table 5 Statistics of temperature rise of pumping wells in different years .

[0069] 2. One draw, two fills (1) Flow field: The model constructed in Example 4 is run, and the flow field distribution results obtained during the simulation period show that the groundwater flow field in the aquifer changes regularly with the alternation of the operation period and the intermission period. The flow field distribution during the operation cycle of the geothermal system in the 1st, 5th, and 10th years is plotted as follows: Figure 17~Figure 19 As shown in the figure, according to the simulation results, it can be seen that the groundwater flow field of the phreatic aquifer during the forecast period changes regularly with the alternation of the operation period and the intermittent period. Among them, during the operation period, the flow field near the pumping well was affected by human factors, and a small-scale water hill appeared around the recharge well, with the highest water level of about 78.97m; a water level funnel appeared near the extraction well, with the lowest water level of about 71.65m. During the intermittent period, the groundwater flow field of the phreatic aquifer quickly recovered to the natural flow field, and the groundwater level basically recovered to the initial state at the end of the intermittent period.

[0070] (2) Temperature field: Run the model to obtain the temperature field simulation results during the simulation period. Since the phreatic aquifer is the main water exchange layer of the geothermal system, the temperature field distribution diagrams for the 1st, 5th and 10th years are plotted here. Figure 20~Figure 22 As shown in the figure, it can be seen that the operation of the groundwater source heat pump system will have a significant impact on the surrounding temperature field. Driven by seepage, the temperature influence zone gradually spreads downstream. Among them, the temperature change zone in the first year is mainly distributed near the recharge well, with a temperature plume area of ​​8687.99 m 2 , the farthest extension to the pumping well is 53.34 m under the action of the hydraulic gradient of pumping and injection, while the pumping well itself is not affected and extends 38.67 m downstream driven by the natural flow field; in the fifth year, the temperature plume of the recharging well has covered the pumping well, and the area of ​​the temperature plume is 26045.95m 2 , extending 77.68 m downstream; at the end of the 10th year, the temperature plume affected an area of ​​41410.53 m 2 , extending 107.82 m downstream.

[0071] On this basis, the temperature profiles along the pumping well-recharge well at the end of the cooling period and heating period in the first, third, fifth and tenth years were drawn ( Figure 23~Figure 24 ), it can be seen that during the cooling period, a high point of the temperature plume is formed at the recharge well point, with a temperature of 24.09℃, which is the same as the water temperature of the recharge well. Under the action of heat conduction, the temperature value decreases to both sides; during the heating period, a low point of the temperature plume is formed at the recharge well point, with a temperature of 20.65℃. There are high temperature points (about 24.3℃) at 8-10 m on both sides of the periphery, and then decrease to both sides with the increase of distance. The temperature curve at the pumping well point is related to the year, showing that the temperature value is the lowest in the first year and increases significantly in the third year and thereafter. The reason for this is that a heat path is formed between the pumping and recharge wells, which causes the hot and cold imbalance of the rock and soil.

[0072] Observation points were set at the center of the recharging well and the pumping well, and the temperature change curves of the two well center points during the simulation period were derived as follows: Fig.25 As shown in Table 6, it can be seen that the temperature of the pumping well is affected by the regular water injection of the recharge well, and the temperature value fluctuates and rises. Among them, the temperature of the pumping well rose rapidly in the first two years, with an increase of 1.64℃ in the first year and 1.53℃ in the second year. Combined with the above figures, it is believed that the heat path between the pumping and recharge wells was initially opened at this time, and the temperature feather of the recharge well covered the pumping well, causing its temperature value to rise rapidly. Even if the system stopped operating during the recovery period, the temperature drop of the pumping well was still limited; in the third year and thereafter, the heat path between the pumping and recharge wells was formed, and the temperature value of the pumping well fluctuated stably in the high value range.

[0073] Table 6 Statistics of temperature rise of pumping wells in different years .

[0074] 3. Determination of reasonable pumping and filling ratio (1) Flow field: The groundwater flow field of the unconfined aquifer changes regularly with the alternation of the geothermal system cycles. During the operation period, the highest water mound produced by the "one pumping and one filling" pumping ratio was about 79.2 m, and the lowest water level funnel was about 74.3 m, while the "one pumping and two filling" pumping ratio was 78.97 m and 71.65 m, respectively, with small differences. During the intermission period, the groundwater flow field of the unconfined aquifer in both scenarios quickly recovered to the natural flow field, and the groundwater level basically returned to the initial state at the end of the intermission period.

[0075] (2) Temperature field: The operation of the two pumping-injection ratios will have a significant impact on the distribution of the surrounding temperature field, causing the temperature fluctuation of the pumping well to increase. During the simulation period, the outlet water temperature of the pumping well under the "one pumping and one injection" ratio ranged from 15°C to 19.64°C, and the maximum temperature increase during the annual operation period was about 2.00°C (in the second year); the outlet water temperature of the pumping well under the "one pumping and two injection" ratio ranged from 15°C to 20.91°C, and the maximum temperature increase during the annual operation period was about 1.64°C (in the first year).

[0076] (3) Maximum power per unit area: The temperature plume area and the maximum operating power of the geothermal system under the two-pumping-and-filling ratio scenario were statistically analyzed, and the maximum power per unit area was calculated as shown in Table 7. It can be seen that the maximum power per unit area of ​​"one pumping and two fillings" is higher than that of "one pumping and one filling", which has a better utilization rate of the site.

[0077] Table 7 Statistics of maximum power per unit area in two scenarios .

[0078] In summary, it is believed that the reasonable pumping and injection ratio of the groundwater source heat pump system in the simulation area is "one pumping and two injections", and the layout method is linear and lateral layout, that is, the reinjection wells are located on both sides of the pumping well and are perpendicular to the water flow direction.

[0079] VI. Well Spacing Simulation Study In the above simulation study of pumping scheme, the optimal pumping ratio of the simulation area is 1:2, and the layout method is linear layout on the opposite side. The simulation period is set to 10 years, and the well spacing is 70m, 60m, and 50m respectively. The small flow rate is set to 30 m 3 / h (the pumping well flow is 60 m 3 / h, the flow rate of the two reinjection wells is 30 m 3 / h) and maximum flow rate 50 m 3 / h (the pumping well flow is 100 m 3 / h, the flow rate of the two reinjection wells is 50 m 3 / h) modes are used to simulate and predict the water level and temperature plume distribution of the pumping and reinjection wells, so as to propose the optimal and minimum well spacing for the pumping and reinjection ratio of 1:2.

[0080] 1. Well spacing 70 m (1) Flow field: The model constructed in Example 3 was run to obtain the flow field distribution results during the simulation period. It was found that the groundwater flow field of the aquifer changes regularly with the alternation of the operation period and the intermission period. Taking the fifth year as a typical year, the flow field distribution during the operation period of the geothermal system is plotted as follows: Fig.26 As shown in the figure, it can be seen that the flow field near the pumping well was affected by human activities during the operation period, and water hills appeared around the recharging well. The highest water level was about 79.23 m in the small flow scenario and 80.83 m in the large flow scenario. A water level funnel appeared near the extraction well, and the lowest water level was about 71.47 m in the small flow scenario and 67.65 m in the large flow scenario. During the intermittent period, the groundwater flow field of the phreatic aquifer quickly recovered to the natural flow field, and the groundwater level basically recovered to the initial state at the end of the intermittent period.

[0081] (2) Temperature field: During the simulation period, the operation of the groundwater source heat pump system will have a significant impact on the surrounding temperature field distribution. Driven by seepage, the temperature influence zone gradually expands and spreads to the pumping well and downstream. Since the phreatic aquifer is the main water exchange layer of the geothermal system, the temperature field distribution diagram at the end of the 1st, 5th and 10th year is drawn here. Fig. 27 As shown in the figure, it can be seen that the recharge well has not yet affected the temperature of the pumping well under the low flow scenario at the end of the first year. Its temperature plume extends 46.05 m toward the pumping well and 35.46 m downstream, with an area of ​​8400.83 m 2 In the large flow scenario, the temperature plume of the recharge well has covered the pumping well. The area of ​​the temperature plume in the large flow scenario is 14364.95 m 2 , driven by the natural flow field, extended 46.56 m downstream; at the end of the fifth year, under the low-flow scenario, the temperature plume had covered the pumping well and extended 78.14 m downstream under the natural flow field, covering an area of ​​29773.27 m 2 , the temperature plume area under the large flow scenario is 37046.67 m 2 , driven by the natural flow field, extended 91.66 m downstream; the temperature plume area under the low flow scenario at the end of the 10th year was 47409.03 m 2 , driven by the natural flow field, it extends 114.54 m downstream, and the temperature plume area is 57683.86 m under the large flow scenario. 2 , driven by the natural flow field, extending 127.23 m downstream.

[0082] In the first and second years, the temperature of the pumping wells rose rapidly under both flow rate scenarios (Table 8). Under low flow rate, the maximum annual temperature rise was 1.87°C and 0.62°C in the second year, and then it fluctuated slightly and remained basically stable. Under high flow rate, the rise was 1.91°C in the first year and 0.92°C in the second year, and then it fluctuated slightly and remained basically stable.

[0083] Table 8 Statistics of temperature rise of pumping wells in different years .

[0084] In summary, the temperature fluctuation of the pumping wells under the two flow scenarios during the operation period of the year was less than 2°C, and the heat penetration was acceptable.

[0085] 2. Well spacing 60m (1) Flow field: Run the model to obtain the flow field distribution results during the simulation period. It is found that the groundwater flow field in the aquifer changes regularly with the alternation of the operation period and the intermission period. Taking the fifth year as a typical year, the flow field distribution during the operation cycle of the geothermal system is plotted as follows: Fig.28As shown in the figure, during the operation period, the flow field near the pumping well was affected by human activities, and water hills appeared around the recharging well. The highest water level was about 78.97 m in the small flow scenario and 80.40 m in the large flow scenario. A water level funnel appeared near the extraction well, and the lowest water level was about 71.65 m in the small flow scenario and 68.00 m in the large flow scenario. During the intermittent period, the groundwater flow field of the phreatic aquifer quickly recovered to the natural flow field, and the groundwater level basically recovered to the initial state at the end of the intermittent period.

[0086] (2) Temperature field: During the simulation period, the operation of the groundwater source heat pump system will have a significant impact on the surrounding temperature field distribution. Driven by seepage, the temperature influence zone gradually expands and spreads to the pumping well and downstream. Since the phreatic aquifer is the main water exchange layer of the geothermal system, the temperature field distribution diagram at the end of the 1st, 5th and 10th year is drawn here. Fig.29 As shown in the figure, at the end of the first year, the recharge well had not yet affected the temperature of the pumping well under the low flow scenario, and its temperature plume area was 8687.99 m 2 , driven by the natural flow field, extends 38.67 m downstream. In the large flow scenario, the temperature plume of the recharge well has covered the pumping well. The temperature plume area in the large flow scenario is 12544.88 m 2 , driven by the natural flow field, extended 42.75 m downstream; at the end of the fifth year, the temperature plume area under the low flow scenario was 26045.95 m 2 , driven by the natural flow field, extends 77.68 m downstream, and the temperature plume area is 32764.94 m under the large flow scenario. 2 , driven by the natural flow field, extended 81.49 m downstream; at the end of the 10th year, the temperature plume area was 41410.53 m 2 , driven by the natural flow field, it extends 107.82 m downstream, and the temperature plume area is 50975.26 m under the large flow scenario. 2 , driven by the natural flow field, extending 118.21 m downstream.

[0087] In the first and second years, the temperature of the pumping wells increased rapidly under both flow rate scenarios (Table 9). Under low flow rate, the temperature increased by 1.94°C and 0.53°C in the first two years, and then fluctuated slightly. Under high flow rate, the temperature increased by 2.62°C and 0.85°C in the first two years, and then fluctuated slightly, remaining basically stable.

[0088] Table 9 Statistics of temperature rise of pumping wells in different years .

[0089] In summary, the temperature fluctuation of the pumping well under the small and medium flow scenarios during the annual operation period is less than 2°C, and the heat penetration is acceptable; while the maximum temperature fluctuation of the pumping well under the large flow scenario is higher than 2°C, and the efficiency of the heat pump unit will be affected to a certain extent.

[0090] 3. Well spacing 50m (1) Flow field: Run the model to obtain the flow field distribution results during the simulation period. It is found that the groundwater flow field in the aquifer changes regularly with the alternation of the operation period and the intermission period. Taking the fifth year as a typical year, the flow field distribution during the operation cycle of the geothermal system is plotted as follows: Fig.30 As shown in the figure, the flow field near the pumping well was affected by human activities during the operation period, and water hills appeared around the recharging wells, with the highest water level of about 78.88 m in the small flow scenario and 80.08 m in the large flow scenario; a water level funnel appeared near the extraction well, with the lowest water level of about 71.09 m in the small flow scenario and 68.37 m in the large flow scenario. During the intermittent period, the groundwater flow field of the phreatic aquifer quickly recovered to the natural flow field, and the groundwater level basically recovered to the initial state at the end of the intermittent period.

[0091] (2) Temperature field: During the simulation period, the operation of the groundwater source heat pump system will have a significant impact on the surrounding temperature field distribution. Driven by seepage, the temperature influence zone gradually expands and spreads to the pumping well and downstream. Since the phreatic aquifer is the main water exchange layer of the geothermal system, the temperature field distribution diagram at the end of the 1st, 5th and 10th year is drawn here. Fig.31 As shown in the figure, it can be seen that at the end of the first year, the recharge well has already affected the temperature of the pumping well. Under the low flow scenario, the temperature plume area is 8243.62 m 2 , driven by the natural flow field, extends 36.59 m downstream, and the temperature plume area is 10794.98 m under the large flow scenario. 2 , driven by the natural flow field, extended 41.73 m downstream; at the end of the fifth year, the temperature plume area under the low flow scenario was 22881.90 m 2 , driven by the natural flow field, extends 74.67 m downstream, and the temperature plume area is 27994.99 m under the large flow scenario. 2 , driven by the natural flow field, extended 80.11 m downstream; at the end of the 10th year, the temperature plume area under the low flow scenario was 36572.52 m 2 , driven by the natural flow field, it extends 104.78 m downstream, and the temperature plume area is 43502.68 m under the large flow scenario. 2 , driven by the natural flow field, extends 113.11m downstream.

[0092] In the first and second years, the temperature of the pumping wells rose rapidly under both flow rate scenarios (Table 10). Under low flow rate, the temperature rose by 2.99°C in the first year and by 0.55°C in the second year, and then fluctuated slightly and remained basically stable. Under high flow rate, the temperature rose by 3.07°C in the first year and by 0.65°C in the second year, and then fluctuated slightly and remained basically stable.

[0093] Table 10 Statistics of temperature rise of pumping wells in different years .

[0094] In summary, the maximum temperature fluctuation of the pumping wells in both scenarios during the annual operation period is higher than 2°C, and the efficiency of the heat pump unit will be affected to a certain extent.

[0095] 4. Determination of reasonable well spacing: By comparing the impact of geothermal system operation on the surrounding flow field, temperature field and thermal penetration of pumping wells under three well spacings, it is found that: (1) Flow field: The groundwater flow field of the phreatic aquifer changes regularly with the alternation of the geothermal system cycles. During the operation period, a water mound of a certain scale is formed near the recharge well, and a water level funnel is formed near the pumping well. The scale of both increases with the increase of pumping and injection flow and the decrease of well spacing, and decreases conversely. Among them, when the well spacing is 50m to 70m in the large flow scenario, the water mound elevation is 80.08m to 80.83m, and the water level funnel elevation is 68.37m to 67.65m; when the well spacing is 50m to 70m in the small flow scenario, the water mound elevation is 78.88m to 79.23m, and the water level funnel elevation is 71.09m to 71.47m. During the intermittent period, the groundwater flow field of the phreatic aquifer quickly recovers to the natural flow field, and the groundwater level basically recovers to the initial state at the end of the intermittent period.

[0096] (2) Temperature field and its influence: The operation of the geothermal system under the three well spacings will have a significant impact on the distribution of the temperature field around it. Under long-term operation, the temperature plume area increases with the increase of pumping and injection flow rate and the decrease of well spacing, and vice versa; the temperature value of the temperature plume center decreases with the increase of pumping and injection flow rate, and vice versa. At the end of the 10th year after the simulation, the temperature plume areas of the wells at different spacings under large flow rate were 57683.86 m 2 (well spacing 70 m), 50975.26 m 2 (well spacing 60 m), 43502.68 m 2 (well spacing is 50 m); the temperature plume areas of wells at different spacings under low flow rates are 47409.03 m 2 (well spacing 70 m), 41410.53 m 2 (well spacing 60 m), 36572.52 m 2(Well spacing 50 m).

[0097] (3) Thermal penetration of pumping wells: The temperature rise of pumping wells increases with the increase of pumping and injection flow and the decrease of well spacing, and decreases conversely. Under the two pumping scenarios, the temperature of the pumping wells generally increases rapidly in the first two years, and then the increase gradually decreases. Among them, the maximum annual temperature rise of wells with different spacings when pumping at a large flow rate is 1.91℃ (well spacing 70m), 2.62℃ (well spacing 60m), and 3.07℃ (well spacing 50m), respectively; the maximum annual temperature rise of wells with different spacings when pumping at a small flow rate is 1.87℃ (well spacing 70m), 1.94℃ (well spacing 60m), and 2.99℃ (well spacing 50m), respectively.

[0098] Therefore, when the threshold of heat penetration temperature fluctuation is 2℃, the efficiency of the heat pump unit will not be affected when the well spacing is 70 m; when the well spacing is 60 m, the efficiency of the heat pump unit will be affected to a certain extent in the large flow scenario; when the well spacing is 50 m, the efficiency of the heat pump unit will be affected to a certain extent in both large and small flow scenarios. It is determined that the well spacing of 70 m is the reasonable well spacing.

[0099] Although some preferred embodiments of the present application have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present application.

[0100] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the inventive concept. Thus, if these modifications and variations of the present application fall within the scope of the claims of the present application and their equivalents, the present application is also intended to include these modifications and variations.

Claims

1. A method for constructing a geothermal prediction model, comprising the following steps: (1) Determine the scope and depth of the proposed geothermal utilization area and construct a hydrogeological conceptual model of the area; (2) On the basis of the hydrogeological conceptual model, a coupling equation of groundwater flow model and heat transfer equation is established; (3) Generalize the boundary conditions of the proposed geothermal utilization area and generalize its strata vertically; (4) meshing the super grid surface of the proposed geothermal utilization area, and further refining the grid of the production well area; (5) Setting the solution conditions to construct a steady flow model, setting the initial water level depth of the steady flow model, and using this as the initial flow field of the subsequent transient flow model; (6) Setting the temperature of each layer in the proposed geothermal utilization area. The surface layer takes the annual average temperature of the proposed geothermal utilization area, and the values ​​of the layers below are taken according to the depth from the constant temperature zone multiplied by the ground temperature increase rate; (7) Assigning values ​​to the hydrogeological parameters of the proposed geothermal utilization area; (8) The simulation period, the inlet and outlet temperature difference threshold, and the temperature fluctuation threshold at the end of each recovery period are set to construct a geothermal prediction model.

2. The construction method according to claim 1, characterized in that: In step (2), the groundwater flow model equation is as follows: ； In the formula: — planned geothermal utilization range; H — water head of aquifer; Kxx, Kyy, Kzz — permeability coefficients in the x, y, z directions respectively; — permeability coefficient in the direction of boundary normal; — unit water storage coefficient; — Gravity water supply; — Source and sink items; —upper boundary; —second-type boundary; n—normal direction outside the boundary of the study area; q(x, y, z, t)—single-width flow of the second-type boundary; The heat transfer equation is as follows: ； Where: C eq —Equivalent volume heat capacity; Ceq= , where θ represents the porosity, ρC represents the total volume heat capacity in the porous medium; C L =ρw×Cw, which represents the volume heat capacity of water, ρw represents the density of water, and Cw represents the specific heat capacity; λ—equivalent thermal conductivity; Q T —General heat source; qT is the heat flux flowing into the boundary Г2.

3. The construction method according to claim 1, characterized in that: In step (6), the hydrogeological parameters include permeability, water supply, water storage rate, geothermal heat flow value, porosity, water volume specific heat capacity, soil volume specific heat capacity, water thermal conductivity, soil thermal conductivity, longitudinal diffusion, and lateral diffusion.

4. The construction method according to claim 1, characterized in that: In the step (4), the super grid surface of the proposed geothermal utilization area is meshed using the Triangle algorithm.

5. A method for laying out wells for a groundwater source heat pump system, comprising the following steps: (1) Design different pumping ratio schemes, and obtain the flow field distribution results and temperature field simulation results during the simulation period based on the geothermal prediction model established in claim 1; (2) respectively counting the temperature plume area and the maximum operating power of the geothermal system under the different pumping-injection ratio schemes, and calculating the maximum power per unit area, and determining the scheme with the largest maximum power per unit area as the optimal pumping-injection ratio; (3) Based on the above optimal pumping-recharging ratio, different well spacings are designed, and large and small flow modes are set according to the pumping well flow and recharging well flow of the optimal pumping-recharging ratio, so as to simulate and predict the water level and temperature plume distribution of the pumping and recharging wells; (4) The effects of geothermal system operation on the surrounding flow field, temperature field and heat penetration of the pumping wells under different well spacings were compared, and the well spacing with the least impact on the efficiency of the heat pump unit was selected as the optimal well spacing.

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