Construction of geothermal prediction model and well arrangement method of groundwater source heat pump system

Abstract

This invention discloses a method for constructing a geothermal prediction model and a well layout method for a groundwater source heat pump system. A three-dimensional coupled water flow and heat transport model of the operating state of the groundwater source heat pump system is established in a suitable area. By predicting the changes in the water flow field and temperature field under different pumping-injection ratios and well spacing, a reasonable well layout scheme for the groundwater source heat pump system can be determined. This application can improve energy utilization efficiency, avoid thermal pollution, ensure long-term sustainability, and reduce the impact on groundwater resources and the ecological environment.

Description

Technical Field

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

[0002] Groundwater source heat pump systems are a highly efficient and energy-saving technology that utilizes shallow geothermal resources for heating and cooling. This system uses a closed underground piping system to exchange heat with the temperature of groundwater or soil, thereby regulating the internal temperature of a building. Due to its high efficiency, energy saving, and environmental friendliness, groundwater source heat pump systems have been widely used in modern building energy conservation.

[0003] The pump-injection ratio is a key parameter of groundwater source heat pump systems, involving the balance between groundwater extraction and reinjection. Studies have shown that the pump-injection ratio has a significant impact on the energy efficiency and long-term stability of groundwater source heat pump systems. An unreasonable pump-injection ratio may disrupt the underground temperature field, affecting the system's heat exchange efficiency and even leading to system failure. Currently, methods for determining the pump-injection ratio mainly include empirical formulas, heat balance calculations, and field tests. Empirical formulas are simple and easy to use, but they are usually based on data under specific conditions and may not accurately reflect the actual situation under different geological and climatic conditions. Heat balance calculations can provide a theoretical pump-injection ratio, but require accurate input parameters, which may be difficult to obtain precisely in practice. Field tests can provide direct, real-world pump-injection ratio data, but they are costly, time-consuming, and may be limited by experimental conditions, failing to fully represent actual application scenarios. Well spacing is another key parameter of groundwater source heat pump systems, significantly affecting the system's operating efficiency and environmental impact. Insufficient well spacing may lead to changes in the groundwater flow field and geothermal field, directly affecting the efficiency and lifespan of the heat pump system. Furthermore, the well spacing also affects groundwater quality and the surrounding ecological environment. Therefore, rationally determining the pumping-injection ratio and well spacing is crucial for the efficient operation of groundwater source heat pump systems.

[0004] The information disclosed in this background section is intended only to enhance the understanding of the background technology of this disclosure and should not be construed as an admission or in any way implying that the information constitutes 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, this disclosure provides a method for constructing a geothermal prediction model and a well layout method for a groundwater source heat pump system. By combining pump-injection tests and empirical parameters, a three-dimensional water flow and heat coupling transport model of the operating state of the groundwater source heat pump system at the site level is established in a suitable area. By predicting the changes in the water flow field and temperature field under different pump-injection ratios and different well spacings, a reasonable well layout scheme (i.e., well spacing and pump-injection ratio) for the groundwater source heat pump system is determined.

[0006] According to one aspect of this disclosure, a method for constructing a geothermal prediction model is provided, comprising the following steps:

[0007] (1) Determine the scope and depth of the geothermal utilization area and construct a hydrogeological conceptual model of the area;

[0008] (2) Based on the above hydrogeological conceptual model, establish a coupled equation for the groundwater flow model and the heat transport equation;

[0009] (3) The boundary conditions of the proposed geothermal utilization area are generalized (referring to a processing method of geographic data in relevant software, such as ArcGIS, with the aim of simplifying the geometric shape of the data, reducing the complexity of the data, and maintaining the main characteristics and distribution patterns of the data as much as possible), and the strata are vertically generalized.

[0010] (4) The super grid surface of the geothermal proposed utilization area is divided into grids, and the grid of the mining well area is refined;

[0011] (5) Set boundary conditions to construct a steady flow model, set the initial water level depth of the steady flow model, and use it as the initial flow field for the subsequent instantaneous flow model;

[0012] (6) Set the temperature of each stratum in the geothermal utilization area. The surface layer is taken as the annual average temperature of the geothermal utilization area, and the values ​​of each layer below are determined by multiplying the depth from the constant temperature zone by the geothermal warming rate.

[0013] (7) Assign values ​​to the hydrogeological parameters of the proposed geothermal utilization area;

[0014] (8) Set the simulation period, the temperature difference threshold between the inlet and outlet and the temperature fluctuation threshold at the end of each recovery period to construct the geothermal prediction model.

[0015] In some embodiments of this disclosure, in step (2), the groundwater flow model equation is as follows:

[0016] ;

[0017] Where: — Geothermal potential utilization range; H — Aquifer head; Kxx, Kyy, Kzz — Permeability coefficients in the x, y, and z directions, respectively; — Permeability coefficient in the boundary normal direction; — Unit storage coefficient; — Gravitational specific yield; — Source-sink term; — Upper boundary; — Second type boundary; n — Normal direction outside the study area boundary; q(x, y, z, t) — Unit width flow rate of the second type boundary; The heat transport equation is as follows:

[0018] ;

[0019] In the formula: C eq —Equivalent volumetric heat capacity; Ceq= Where θ represents porosity, and ρC represents the total volumetric heat capacity in the porous medium; C L =ρw×Cw, representing the volumetric heat capacity of water, where ρw represents the density of water and Cw represents the specific heat capacity; λ—equivalent thermal conductivity coefficient; Q T —A typical heat source; qT is the heat flux flowing in at the boundary Г2.

[0020] In some embodiments of this disclosure, the hydrogeological parameters in step (6) include permeability coefficient, water supply, water storage rate, geothermal heat flow value, porosity, water volumetric specific heat capacity, soil volumetric specific heat capacity, water thermal conductivity, soil thermal conductivity, longitudinal dispersion, and transverse dispersion.

[0021] In some embodiments of this disclosure, in step (4), the Triangle algorithm is used to mesh the supergrid surface of the geothermal proposed utilization area.

[0022] According to a second aspect of this disclosure, a well layout method for a groundwater source heat pump system is provided, comprising the following steps:

[0023] (1) Design different pumping-irrigation ratio schemes, and obtain the flow field distribution and temperature field simulation results during the simulation period based on the established geothermal prediction model;

[0024] (2) Calculate the area of ​​the temperature plume and the maximum operating power of the geothermal system under the different pumping-irrigation ratio schemes, and calculate the maximum power value per unit area. The scheme with the largest maximum power value per unit area is determined as the optimal pumping-irrigation ratio.

[0025] (3) Based on the above-mentioned optimal pumping-irrigation ratio, different well spacings are designed, and two modes of large and small flow rates are set according to the pumping well flow rate and irrigation well flow rate of the optimal pumping-irrigation ratio, respectively, to simulate and predict the water level and temperature plume distribution of the pumping and re-irrigation wells.

[0026] (4) Compare the effects of geothermal system operation on the surrounding flow field, temperature field and heat penetration of pumping wells under different well spacings, and select the well spacing with the least impact on the efficiency of heat pump unit as the optimal well spacing.

[0027] One or more technical solutions provided in the embodiments of this application have at least one of the following technical effects or advantages:

[0028] Using coupled simulations of groundwater flow and heat transport equations to guide well placement in groundwater source heat pump systems can ensure more accurate and efficient system design. By optimizing 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. Attached Figure Description

[0029] Figure 1 This is a bar chart showing the comprehensive results of K9 pumping and reinjection in one embodiment of this application.

[0030] Figure 2 This is a bar chart showing the comprehensive results of K10 pumping and reinjection in one embodiment of this application.

[0031] Figure 3 This is a schematic diagram of the simulated range in one embodiment of this application.

[0032] Figure 4 This is a mesh partitioning diagram in one embodiment of this application.

[0033] Figure 5 This is the water level fitting effect of well K9 in one embodiment of this application.

[0034] Figure 6 This is the water level fitting effect of hole K10 in one embodiment of this application.

[0035] Figure 7 This is a schematic diagram of the pumping ratio setting in one embodiment of this application.

[0036] Figure 8 The figure shows the annual variation of the flow field in the unconfined aquifer during the first year of a pumping and injection cycle in one embodiment of this application; where A: end of the cooling period; B: end of the cooling intermission period; C: end of the heating period; D: end of the heating intermission period.

[0037] Figure 9 The figure shows the annual change of the flow field in the unconfined aquifer during the fifth year of a pumping and injection cycle in one embodiment of this application; where A: end of the cooling period; B: end of the cooling intermission period; C: end of the heating period; D: end of the heating intermission period.

[0038] Figure 10 The figure shows the annual variation of the flow field in the unconfined aquifer during the 10th year of a pumping and injection cycle in one embodiment of this application; where A: end of the cooling period; B: end of the cooling intermission period; C: end of the heating period; D: end of the heating intermission period.

[0039] Figure 11The figure shows the annual temperature field change at the bottom of the unconfined aquifer during the first year of a pumping and injection cycle in one embodiment of this application; where A: end of the cooling period; B: end of the cooling intermission period; C: end of the heating period; D: end of the heating intermission period.

[0040] Figure 12 The figure shows the annual variation of the temperature field at the bottom of the unconfined aquifer during the fifth year of a pumping and injection cycle in one embodiment of this application; where A: end of the cooling period; B: end of the cooling intermission period; C: end of the heating period; D: end of the heating intermission period.

[0041] Figure 13 The figure shows the annual variation of the temperature field at the bottom of the unconfined aquifer during the 10th year of a pumping and injection cycle in one embodiment of this application; where A: end of the cooling period; B: end of the cooling intermission period; C: end of the heating period; D: end of the heating intermission period.

[0042] Figure 14 This is a temperature change curve of the profile at the end of the refrigeration period of a pumping and filling process in one embodiment of this application.

[0043] Figure 15 This is a temperature change curve at the end of a heating season during a pumping and filling process, as shown in one embodiment of this application.

[0044] Figure 16 This is a line graph showing the temperature change at a pumping well in one embodiment of this application.

[0045] Figure 17 The annual variation of the flow field in the unconfined aquifer during the first year of a single pumping and two irrigation cycles in one embodiment of this application; wherein, A: end of the cooling period; B: end of the cooling intermission period; C: end of the heating period; D: end of the heating intermission period.

[0046] Figure 18 The figure shows the annual variation of the flow field in the unconfined aquifer during the fifth year of a pumping and irrigation cycle in one embodiment of this application; where A: end of the cooling period; B: end of the cooling intermission period; C: end of the heating period; D: end of the heating intermission period.

[0047] Figure 19 The figure shows the annual variation of the flow field in the unconfined aquifer during the 10th year of a single pumping and two irrigation cycles in one embodiment of this application; where A: end of the cooling period; B: end of the cooling intermission period; C: end of the heating period; D: end of the heating intermission period.

[0048] Figure 20 The annual variation of the temperature field at the bottom of the unconfined aquifer during the first year of a pumping and two-irrigation cycle in one embodiment of this application; wherein, A: end of the cooling period; B: end of the cooling intermission period; C: end of the heating period; D: end of the heating intermission period.

[0049] Figure 21 The figure shows the annual variation of the temperature field at the bottom of the unconfined aquifer during the fifth year of a pumping and irrigation operation in one embodiment of this application; where A: end of the cooling period; B: end of the cooling intermission period; C: end of the heating period; D: end of the heating intermission period.

[0050] Figure 22 The figure shows the annual variation of the temperature field at the bottom of the unconfined aquifer during the 10th year of a pumping and irrigation cycle in one embodiment of this application; where A: end of the cooling period; B: end of the cooling intermission period; C: end of the heating period; D: end of the heating intermission period.

[0051] Figure 23 This is a temperature change curve of the cross-section at the end of the cooling period of one pump and two tanks in one embodiment of this application.

[0052] Figure 24 This is a temperature change curve at the end of the heating season in one embodiment of this application.

[0053] Figure 25 This is a line graph showing the temperature change at the pumping well with one pump and two injection points in one embodiment of this application.

[0054] Figure 26 The flow field change of the unconfined aquifer in the 5th year of one embodiment of this application (well spacing 70m); wherein, A: end of low-flow cooling period; B: end of high-flow cooling period; C: end of low-flow cooling intermittent period; D: end of high-flow cooling intermittent period; E: end of low-flow heating period; F: end of high-flow heating period; G: end of low-flow heating intermittent period; H: end of high-flow heating intermittent period.

[0055] Figure 27 The temperature field variation at the bottom of the unconfined aquifer in one embodiment of this application (well spacing 70m); wherein, A: temperature field variation at the end of the first year with low flow rate; B: temperature field variation at the end of the first year with high flow rate; C: temperature field variation at the end of the fifth year with low flow rate; D: temperature field variation at the end of the fifth year with high flow rate; E: temperature field variation at the end of the tenth year with low flow rate; F: temperature field variation at the end of the tenth year with high flow rate.

[0056] Figure 28 The flow field change of the unconfined aquifer in the 5th year of one embodiment of this application (well spacing 60m); wherein, A: end of low-flow cooling period; B: end of high-flow cooling period; C: end of low-flow cooling intermittent period; D: end of high-flow cooling intermittent period; E: end of low-flow heating period; F: end of high-flow heating period; G: end of low-flow heating intermittent period; H: end of high-flow heating intermittent period.

[0057] Figure 29 The temperature field variation at the bottom of the unconfined aquifer in one embodiment of this application (well spacing 60m); wherein, A: temperature field variation at the end of the first year with low flow rate; B: temperature field variation at the end of the first year with high flow rate; C: temperature field variation at the end of the fifth year with low flow rate; D: temperature field variation at the end of the fifth year with high flow rate; E: temperature field variation at the end of the tenth year with low flow rate; F: temperature field variation at the end of the tenth year with high flow rate.

[0058] Figure 30The flow field change of the unconfined aquifer in the 5th year of one embodiment of this application (well spacing 50m); wherein, A: end of low-flow cooling period; B: end of high-flow cooling period; C: end of low-flow cooling intermittent period; D: end of high-flow cooling intermittent period; E: end of low-flow heating period; F: end of high-flow heating period; G: end of low-flow heating intermittent period; H: end of high-flow heating intermittent period.

[0059] Figure 31 The temperature field variation at the bottom of the unconfined aquifer in one embodiment of this application (well spacing 50m); wherein, A: temperature field variation at the end of the first year with low flow rate; B: temperature field variation at the end of the first year with high flow rate; C: temperature field variation at the end of the fifth year with low flow rate; D: temperature field variation at the end of the fifth year with high flow rate; E: temperature field variation at the end of the tenth year with low flow rate; F: temperature field variation at the end of the tenth year with high flow rate. Detailed Implementation

[0060] To better understand the technical solution of this application, the above technical solution will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0061] Example: Construction of a groundwater source heat pump system in Hanhe Village, Zheng'an Town

[0062] I. Overview: Hanhe Village in Zheng'an Town is located in a suitable area for groundwater source heat pumps, with great potential for the development and utilization of shallow geothermal energy resources and favorable construction conditions, indicating a promising future. Considering these factors, Hanhe Village in Zheng'an Town was selected as the numerical simulation area for groundwater source heat pumps. Using the numerical simulation software Feflow, the changes in the water flow field and temperature field under different pumping-injection ratios and well spacing were simulated to determine a reasonable well layout scheme for the suitable area of ​​the groundwater source heat pump system.

[0063] II. Model Establishment

[0064] 1. Hydrogeological Conceptual Model: Based on the 200 m core sampling of wells K9 and K10 in Hanhe Village, Zheng'an Town, a thick cemented layer was found at 150-160 m, posing a risk that the well could not be drilled through. Therefore, a large-diameter pump-suction reverse circulation water drilling process was adopted for drilling. When drilling to this layer using the large-diameter water reverse circulation method, drilling difficulties occurred, specifically: the drill bit could not break through the layer, the advance was slow, and the reverse circulation pump drainage was not smooth. Finally, the hole depth of K9 was 168 m and the hole depth of K10 was 164 m. The hole depths were taken as the depths for numerical simulation research.

[0065] Based on the lithology and thickness of each layer, a vertical generalization is performed in the model, and the stratigraphic structure is as follows: Figures 1-2As shown, the vertical generalization of the strata is shown in Table 1. The aquifer consists of seven layers: Layer 1 is a phreatic aquifer, primarily composed of fine sand and silt, with a base depth of 32–33.5 m; Layer 2 is a weakly permeable aquifer, primarily composed of silty clay and clay, with a base depth of 44–51.9 m; Layer 3 is a confined aquifer, composed of fine sand, with a base depth of 56.3–57.1 m; Layer 4 is a weakly permeable aquifer, composed of clay and silty clay, with a base depth of 92.3–95 m; Layer 5 is a confined aquifer, composed of fine sand, with a base depth of 95.65–100.2 m; Layer 6 is a weakly permeable aquifer, composed of clay and silty clay, with a base depth of 121.7–123 m; and Layer 7 is a confined aquifer, composed of medium and fine sand, with a base depth of 153.9–157 m. m; the 8th layer is a weakly permeable layer, with lithology of clay and silty clay, and the bottom plate is buried at a depth of 164m to 166m.

[0066] Table 1. Stratigraphic Vertical Generalization Results

[0067] .

[0068] Therefore, the strata in the simulation area were generalized to 8 layers vertically. After running the model, Feflow's Rate Budget calculation module was used to simulate the water inflow and outflow distribution of reinjection wells and pumping wells in each aquifer, with the 1st, 5th, and 10th year operation periods as calculation points. It was found that the water volume of reinjection wells and pumping wells was mainly distributed in the 1st layer (i.e., unconfined aquifer), the 3rd layer, and the 5th layer. Among them, the first layer is a phreatic aquifer, which receives approximately 50.50%–52.96% of the reinjected water during geothermal system operation and contributes approximately 48.36%–53.75% of the total pumping volume. The third and fifth layers are deep confined aquifers, which receive approximately 13.27%–14.48% and 13.21%–14.42% of the reinjected water during geothermal system operation, respectively, and contribute 13.13%–14.78% and 13.02%–14.66% of the total pumping volume, respectively. In summary, the first layer (phreatic aquifer) is selected as the target layer for simulation.

[0069] 2. Simulation Region and Mesh Generation

[0070] (1) Simulation Scope: The pumping wells are 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, and the east and west boundaries are zero-flow boundaries. The groundwater velocity under the natural flow field is 0.0032m / d. The upper and lower boundaries are defined as isothermal and impermeable boundaries. Based on the pumping volume of K9 of 24.12m³, 3 At a rate of / h, the radius of influence is 28m; the pumping volume is 83.16m³. 3 At a rate of / h, the radius of influence is 102m; the pumping rate at K10 is 37.26m³. 3At a rate of / h, the radius of influence is 60m; the pumping volume is 77.26m³. 3 At / h, the influence radius is 130.92m. Simultaneously, based on actual geological and hydrogeological conditions, a rectangular block of 300m*300m was selected as the model range. Figure 3 ).

[0071] (2) Mesh Generation: In terms of spatial discretization for 3D model modeling, the Triangle algorithm was used to perform triangular mesh generation on the supermesh surface. Local mesh refinement was applied to the mining wells, which are a key focus in the model. This resulted in 3318 planar mesh nodes and 6423 element meshes. Vertically, 8 layers were divided, resulting in 16590 nodes and 25692 element meshes. Figure 4 As shown.

[0072] 3. Boundary conditions and parameter assignment

[0073] (1) Boundary conditions: The main sources and sinks of aquifers in the simulation area are precipitation infiltration recharge and evaporation discharge, artificial well extraction, lateral recharge and discharge, which are specifically characterized as follows: The artificial well extraction item is characterized by the MultilayerWell module in the FEFLOW model, and the extraction dynamic control is supplemented by time series; In the model, the flux is assigned by the given flow boundary, and then the flow is calculated by the software, so as to characterize the lateral recharge and discharge of aquifers at the southern and northern boundaries; The groundwater level depth in the area is greater than the limit evaporation depth (referring to the experience value of Zhengzhou City, set to 4m), and the evaporation value is 0. The precipitation infiltration recharge and evaporation discharge in the simulation area have little impact on the model and can be ignored. The surface sources and sinks are mainly affected by precipitation infiltration recharge, and the surface is generalized as the flux boundary; According to the drilling results, the underground depth of 166m is a thick cohesive soil layer with weak water conductivity and permeability, which is generalized as the water-impermeable boundary.

[0074] Based on the above boundary conditions, a steady flow model is constructed to simulate the initial flow field distribution under given conditions. Based on the water level depths of the two boreholes in the area, the initial water level depth for the steady flow model is set to 8.7m, i.e., 78.3m, which is used as the initial flow field for the subsequent instantaneous flow model.

[0075] Due to the limited area of ​​the simulation zone (300m × 300m), the geothermal temperature difference on the horizontal plane within the zone is relatively small. Therefore, it is assumed that the groundwater temperature at the same elevation within the simulation zone is the same. The temperature values ​​for each layer are as follows: ① The surface layer is taken as the annual average air temperature of the study area, which is 15.0℃; ② The geothermal isothermal zone is taken as 17.3℃, and the values ​​for each layer below are determined by multiplying the depth from the isothermal zone by the geothermal warming rate. Thus, the initial temperature of the final base plate is taken as 22.18℃.

[0076] (2) Parameter assignment: Hydrogeological parameters are a set of parameter indicators that reflect the properties of groundwater aquifers, such as water conductivity and water storage capacity. In the generalization assignment of stratigraphic zones in the study area, the selected hydrogeological parameters are: permeability coefficient (Kx, Ky, Kz), specific yield (µ), and storage capacity (Ss). Based on the collected borehole pumping test data and relevant empirical values, the model parameter zones are divided into 8 parameter zones from top to bottom according to the vertical variation of lithology (Table 2).

[0077] Table 2 Hydrogeological Parameter Values

[0078] .

[0079] Other parameter values ​​are as follows: the geothermal heat flow value of the study area is 60 mw / m 2 The porosity is 0.35, and the specific heat capacity of water is 4.218 MJ / m³. 3 / ℃, soil volumetric specific heat capacity is 2.52 MJ / m 3 / ℃, thermal conductivity of water 0.62 J / m / s / ℃, thermal conductivity of soil 3 J / m / s / ℃, longitudinal dispersion 1.2 m, transverse dispersion 0.12 m.

[0080] III. Model Calibration

[0081] This example uses the pumping and recharge test dataset as the basis for fitting the dynamic water level of the groundwater model. The dynamic water level of wells K9 and K10 is fitted separately, and the simulation duration is the same as the test time for each well, i.e., 23820 minutes. After a parameter cyclic optimization process of "comparison-parameter adjustment," the final fitting effect of the outlet temperature for each well is as follows: Figures 5-6 As shown in Table 3, the model has good consistency with the observed values ​​of the simulated water levels at K9, K10 and the two wells for pumping and recharge. The average absolute error and average relative error of the temperature fitting at the outlet of each well are shown in Table 3, indicating that the groundwater flow model established in this study is stable and reliable.

[0082] Table 3. Water Level Fitting Error Analysis Table

[0083] .

[0084] IV. Simulation Period and Threshold of the Prediction Model

[0085] 1. Simulation period: Based on the model established above, with June 1, 2022 as the initial time point for simulation prediction, the simulation period is set to 10 years, until May 31, 2032. During this period, the operating conditions of the heat exchange holes during the annual cooling period, cooling intermittent period, heating period, and heating intermittent period are considered to construct a geothermal prediction model.

[0086] 2. Threshold Selection: From the perspective of the efficiency of groundwater source heat pump projects, the temperature difference between the inlet and outlet should not be less than 5℃ during operation. From the perspective of the lifespan of groundwater source heat pump projects, the temperature fluctuation at the end of each recovery period should not exceed 2℃ within a 10-year simulation period.

[0087] V. Simulation Study of Pump-Irrigation Ratio Scheme

[0088] Based on the suitability zoning for shallow geothermal energy, the simulated area is considered a relatively suitable zone for groundwater source heat pumps, with a unit inflow rate of 300 m³. 3 / dm~500m 3 / dm, the ratio of unit reinjection volume to unit inflow volume is 50%–80%. Based on the pumping and reinjection tests at test sites K9 and K10, the static burial depth at K9 is 8.73m, and the unit inflow volume is 482m³ / dm. 3 / dm; K10 static burial depth 8.75m, unit inflow 371m³ 3 / dm, the experimental results are shown in Table 4.

[0089] Table 4 Summary of Pumping and Recharge Test Results at the Hanhe Experimental Site

[0090] .

[0091] Based on field tests at the experimental site, the theoretically optimal pumping-irrigation ratio for this simulated area is 1:1 and 1:2, and the optimal pumping-reinforcement volume is 30 m³. 3 / h~60 m 3 / h. Therefore, two schemes were designed for numerical simulation ( Figure 7 Option 1, "1 pumping, 1 injection", has wells spaced 60m apart and arranged in an east-west straight line perpendicular to the water flow direction. Both the pumping and injection volumes are 30m³. 3 / h, with a single well power of 120kW in summer and 90kW in winter; Option 2, "1 pumping and 2 irrigation", is arranged in an east-west straight line with opposite sides, that is, the irrigation wells are located on both sides of the pumping well, perpendicular to the water flow direction, with a well spacing of 60m and a pumping capacity of 60m³ / h. 3 / h, the reinjection volume of both wells is 30m³ / h. 3 / h, summer single well power 240kW, winter single well power 180kW.

[0092] 1. One pump, one filling

[0093] (1) Flow field: The geothermal prediction model constructed in the fourth operational example shows that the flow field distribution during the simulation period indicates that the groundwater flow field of the aquifer changes regularly with the alternation of the operational and intermittent periods. The flow field distribution of the unconfined aquifer during the 1st, 5th, and 10th years of the geothermal system's operational cycle is shown in the figure below. Figures 8-10As shown in the simulation results, the groundwater flow field of the unconfined aquifer exhibits a regular variation during the predicted period, alternating between the operational and intermittent periods. During the operational period, the flow field near the injection wells is affected by human activities, resulting in small water mounds around the injection wells, with a maximum water level of approximately 79.2 m; and a water level funnel near the extraction wells, with a minimum water level of approximately 74.3 m. During the intermittent period, the groundwater flow field of the unconfined aquifer rapidly recovers to its natural flow field, and the groundwater level essentially returns to its initial state by the end of the intermittent period.

[0094] (2) Temperature field: Run the model to obtain the temperature field simulation results during the simulation period, and draw the temperature field distribution maps for the 1st, 5th and 10th years. Figures 11-13 As can be seen, the operation of the groundwater source heat pump system has a significant impact on the surrounding temperature field, and the temperature influence zone gradually spreads downstream under the drive of seepage. Specifically, the temperature variation zone in the first year is mainly distributed near the reinjection well, with a temperature plume area of ​​4325.50 m². 2 Under the influence of the hydraulic gradient, the temperature plume extends as far as 43.66 m towards the pumping well, while the pumping well itself remains unaffected, extending 36.48 m downstream under the drive of the natural flow field. By the fifth year, the temperature plume from the reinjection well had covered the pumping well, at which point the area of ​​the temperature plume was 16030.85 m². 2 It extends downstream by 84.93 m; the area affected by the temperature plume at the end of the 10th year was 28,657.35 m². 2 It extends downstream for 123.04 m.

[0095] Based on this, temperature profiles along the pumping well-recharge well line were drawn at the end of the cooling and heating seasons in years 1, 3, 5, and 10. Figures 14-15 As can be seen, during the cooling period, a high-temperature peak (24.09 ℃) forms at the center of the reinjection well, the same as the water temperature in the reinjection well. The temperature decreases towards both sides due to heat conduction. During the heating period, a low-temperature peak (20.65 ℃) forms at the center of the reinjection well, with the highest temperature (approximately 24 ℃) existing 6–8 m to both sides. The temperature then decreases towards both sides with increasing distance. The temperature curve at the pumping well is related to the year, showing the lowest temperature in the first year and a significant increase in the third year and thereafter. This is attributed to the formation of a thermal pathway between the pumping and reinjection wells, leading to an imbalance between the temperature of the soil and rock mass.

[0096] Observation points were set at the centers of the reinjection well and the pumping well, respectively, and the temperature change curves at the center points of the two wells during the simulation period were derived as follows: Figure 16As shown in Table 5, the temperature of the pumping wells fluctuates and rises due to the regular water injection from the reinjection wells. Specifically, in the first year, the temperature increase is approximately 0.38 ℃, indicating that the thermal pathway between the pumping and reinjection wells is not yet fully established, and the temperature can effectively decrease during the recovery period. In the second year, the pumping well temperature rises rapidly, with an annual increase of approximately 2.00 ℃. Therefore, it is believed that the thermal pathway between the pumping and reinjection wells is initially established at this time, and the temperature plume from the reinjection wells covers the pumping wells, causing their temperature to rise rapidly. Even if the system stops operating during the recovery period, the temperature decrease in the pumping wells remains limited. Subsequently, the thermal pathway between the pumping and reinjection wells is formed, and the pumping well temperature fluctuates stably within a high value range.

[0097] Table 5. Statistics on the temperature rise of pumping wells in different years

[0098] .

[0099] 2. One pump, two empties

[0100] (1) Flow field: The flow field distribution results obtained from the model constructed in the fourth operational example show that the groundwater flow field of the aquifer changes regularly with the alternation of the operational and intermittent periods. The flow field distribution during the 1st, 5th, and 10th years of the geothermal system's operational cycle is shown in the figure below. Figures 17-19 As shown in the simulation results, the groundwater flow field of the unconfined aquifer exhibits a regular variation during the predicted period, alternating between the operational and intermittent periods. During the operational period, the flow field near the injection wells is affected by human activities, resulting in small water mounds around the injection wells, with a maximum water level of approximately 78.97 m; and a water level funnel near the extraction wells, with a minimum water level of approximately 71.65 m. During the intermittent period, the groundwater flow field of the unconfined aquifer rapidly recovers to its natural flow field, and the groundwater level essentially returns to its initial state by the end of the intermittent period.

[0101] (2) Temperature field: Run the model to obtain the temperature field simulation results during the simulation period. Since the unconfined aquifer is the main water exchange layer of the geothermal system, the temperature field distribution maps for the 1st, 5th and 10th years are plotted here as follows. Figures 20-22 As shown, the operation of the groundwater source heat pump system has a significant impact on the surrounding temperature field, with the temperature influence zone gradually spreading downstream under the drive of seepage. Specifically, the temperature variation zone in the first year is mainly distributed near the reinjection well, with a temperature plume area of ​​8687.99 m². 2 Under the influence of the hydraulic gradient, the temperature plume extends as far as 53.34 m towards the pumping well, while the pumping well itself remains unaffected, extending 38.67 m downstream under the drive of the natural flow field. By the fifth year, the temperature plume from the reinjection well had covered the pumping well, at which point the area of ​​the temperature plume was 26045.95 m². 2 It extends downstream by 77.68 m; the area affected by the temperature plume at the end of the 10th year was 41410.53 m². 2 It extends downstream for 107.82 m.

[0102] Based on this, temperature profiles along the pumping well-recharge well line were drawn at the end of the cooling and heating seasons in years 1, 3, 5, and 10. Figures 23-24 As can be seen, during the cooling period, a high-value point of temperature plume forms at the center of the reinjection well, with a temperature of 24.09℃, the same as the temperature of the reinjection well water. Due to heat conduction, the temperature decreases towards both sides. During the heating period, a low-value point of temperature plume forms at the center of the reinjection well, with a temperature of 20.65℃. The highest temperature points (approximately 24.3℃) exist 8–10 m to both sides of the periphery, and then decrease towards both sides with increasing distance. The temperature curve at the pumping well is related to the year, showing the lowest temperature in the first year and a significant increase in the third year and thereafter. This is attributed to the formation of a thermal pathway between the pumping and reinjection wells, leading to an imbalance between the temperature of the soil and rock mass.

[0103] Observation points were set at the centers of the reinjection well and the pumping well, respectively, and the temperature change curves at the center points of the two wells during the simulation period were derived as follows: Figure 25 As shown in Table 6, the temperature of the pumping wells fluctuates and rises due to the regular water injection from the reinjection wells. Specifically, the temperature of the pumping wells rises rapidly in the first two years, with an increase of 1.64℃ in the first year and 1.53℃ in the second year. Based on the above figures, it can be inferred that the thermal pathway between the pumping and reinjection wells is initially established at this time, and the temperature plume from the reinjection wells covers the pumping wells, causing their temperature to rise rapidly. Even when the system stops operating during the recovery period, the temperature decrease in the pumping wells remains limited. From the third year onwards, the thermal pathway between the pumping and reinjection wells is formed, and the temperature of the pumping wells fluctuates stably within a high value range.

[0104] Table 6. Statistics on the temperature rise of pumping wells in different years.

[0105] .

[0106] 3. Determining the appropriate pumping ratio

[0107] (1) Flow field: The groundwater flow field of the unconfined aquifer changes regularly with the cyclical alternation of the geothermal system. During the operation period, the highest value of the water mound generated by the "one pumping and one injection" pumping-injection ratio is about 79.2 m, and the lowest value of the water level funnel is about 74.3 m. Under the "one pumping and two injections" pumping-injection ratio scenario, the values ​​are 78.97 m and 71.65 m, respectively, with little difference. During the intermittent period, the groundwater flow field of the unconfined aquifer in both scenarios rapidly recovers to the natural flow field, and the groundwater level basically returns to its initial state at the end of the intermittent period.

[0108] (2) Temperature field: Both pumping-irrigation ratios have a significant impact on the surrounding temperature field distribution, causing the temperature fluctuation of the pumping wells to rise. During the simulation period, the water temperature range of the pumping wells under the "one pumping and one irrigation" ratio was 15℃~19.64℃, and the maximum temperature increase during the year was about 2.00℃ (Year 2); the water temperature range of the pumping wells under the "one pumping and two irrigation" ratio was 15℃~20.91℃, and the maximum temperature increase during the year was about 1.64℃ (Year 1).

[0109] (3) Maximum power per unit area: The temperature plume area and the maximum operating power of the geothermal system under the two pumping and irrigation ratio scenario were statistically analyzed. The maximum power per unit area was calculated as shown in Table 7 below. It can be seen that the maximum power per unit area of ​​"one pumping and two irrigations" is higher than that of "one pumping and one irrigation", which has a better utilization rate of the site.

[0110] Table 7. Statistics of maximum power per unit area under two scenarios.

[0111] .

[0112] In summary, the reasonable pumping-injection ratio for the groundwater source heat pump system in the simulated area is considered to be "one pump and two injections", and the layout is a straight-line, opposite-side arrangement, that is, the injection wells are located on both sides of the pumping well and perpendicular to the water flow direction.

[0113] VI. Simulation Study of Well Spacing

[0114] Based on the above-mentioned pumping-irrigation scheme simulation study, the optimal pumping-irrigation ratio in the simulation area is 1:2, and the layout is a straight-line, opposite-side arrangement. The simulation period is set to 10 years, with well spacing of 70m, 60m, and 50m, and a low flow rate of 30 m³ / h. 3 / h (pump well flow rate is 60 m³ / h) 3 / h, the flow rate for two irrigation wells is 30 m³ / h. 3 / h) and large flow rate 50 m 3 / h (pumping well flow rate is 100 m³ / h) 3 / h, the flow rate for two irrigation wells is 50 m³ / h. 3 Two modes ( / h) are used to simulate and predict the water level and temperature plume distribution of pumping and reinjection wells, thereby proposing the optimal and minimum well spacing for the 1:2 pumping-injection ratio scheme.

[0115] 1. Well spacing 70 m

[0116] (1) Flow field: The flow field distribution during the simulation period was obtained using the model constructed in Example 3. It was found that the groundwater flow field of the aquifer changed regularly with the alternation of the operation period and the intermittent period. Taking the 5th year as a typical year, the flow field distribution during the operation cycle of the geothermal system was plotted as follows. Figure 26As shown, during operation, the flow field near the injection wells was affected by human activity, resulting in water mounds around the reinjection wells. The highest water level under low flow conditions was approximately 79.23 m, while under high flow conditions it was 80.83 m. A water level funnel appeared near the extraction wells, with the lowest water level under low flow conditions being approximately 71.47 m, and under high flow conditions it was 67.65 m. During the intermittent period, the groundwater flow field in the unconfined aquifer rapidly recovered to the natural flow field, and the groundwater level essentially returned to its initial state at the end of the intermittent period.

[0117] (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 towards the pumping well and downstream. Since the unconfined aquifer is the main water exchange layer of the geothermal system, the temperature field distribution at the end of the 1st, 5th, and 10th years is shown in the figure below. Figure 27 As shown, under the low-flow scenario at the end of the first year, the reinjection well did not affect the temperature of the pumping well. The temperature plume extended 46.05 m into the pumping well and 35.46 m downstream, covering an area of ​​8400.83 m². 2 Under high flow rate conditions, the temperature plume from the reinjection well has already covered the pumping well, with a temperature plume area of ​​14364.95 m². 2 Driven by the natural flow field, the temperature plume extended downstream for 46.56 m; by the end of the 5th year, under the low-flow scenario, the temperature plume had covered the pumping well, extending downstream for 78.14 m, with an area of ​​29773.27 m². 2 Under high flow rate conditions, the temperature plume area is 37046.67 m². 2 Driven by the natural flow field, it extends downstream by 91.66 m; under the low-flow scenario at the end of year 10, the temperature plume area is 47409.03 m². 2 Driven by the natural flow field, it extends downstream for 114.54 m, and the temperature plume area is 57683.86 m² under high flow conditions. 2 Driven by the natural flow field, it extends downstream for 127.23 m.

[0118] In the first and second years, the temperature of the pumping wells rose rapidly under both flow scenarios (Table 8). Under the low flow scenario, the maximum annual temperature increase was 1.87℃ in the first year and 0.62℃ in the second year, and then it fluctuated slightly and remained basically stable. Under the high flow scenario, the increase was 1.91℃ in the first year and 0.92℃ in the second year, and then it fluctuated slightly and remained basically stable.

[0119] Table 8. Statistical Table of Temperature Increase in Pumping Wells in Different Years

[0120] .

[0121] In summary, during the year's operation, the temperature variation of the pumping wells under both flow scenarios was less than 2℃, and its thermal conductivity was acceptable.

[0122] 2. Well spacing: 60m

[0123] (1) Flow field: The running model was used to obtain the flow field distribution results during the simulation period. It was found that the groundwater flow field of the aquifer changed regularly with the alternation of the running period and the intermittent period. Taking the 5th year as a typical year, the flow field distribution during the geothermal system's operating cycle was plotted as follows: Figure 28 As shown, during operation, the flow field near the injection wells was affected by human activity, resulting in water mounds around the reinjection wells. The highest water level under low flow conditions was approximately 78.97 m, and under high flow conditions it was 80.40 m. A water level funnel appeared near the extraction wells, with the lowest water level under low flow conditions being approximately 71.65 m, and under high flow conditions it was 68.00 m. During the intermittent period, the groundwater flow field in the unconfined aquifer rapidly recovered to the natural flow field, and the groundwater level essentially returned to its initial state at the end of the intermittent period.

[0124] (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 towards the pumping well and downstream. Since the unconfined aquifer is the main water exchange layer of the geothermal system, the temperature field distribution at the end of the 1st, 5th, and 10th years is shown in the figure below. Figure 29 As shown, under the low-flow scenario at the end of year 1, the reinjection well did not affect the temperature of the pumping well, and its temperature plume area was 8687.99 m². 2 Driven by the natural flow field, the temperature plume extends downstream for 38.67 m, while under high flow conditions, the temperature plume from the reinjection well has already covered the pumping well, with an area of ​​12544.88 m². 2 Driven by the natural flow field, it extends downstream for 42.75 m; at the end of year 5, under the low-flow scenario, the temperature plume area is 26045.95 m². 2 Driven by the natural flow field, it extends downstream for 77.68 m, and the temperature plume area is 32764.94 m² under high flow conditions. 2 Driven by the natural flow field, it extends downstream for 81.49 m; under the low-flow scenario at the end of year 10, the temperature plume area is 41410.53 m². 2 Driven by the natural flow field, it extends downstream for 107.82 m, and under high flow conditions, the temperature plume area is 50975.26 m². 2 Driven by the natural flow field, it extends downstream for 118.21 m.

[0125] In the first and second years, the temperature of the pumping wells rose rapidly under both flow scenarios (Table 9). Under the low flow scenario, the temperature increased by 1.94℃ and 0.53℃ in the first two years, respectively, and then fluctuated slightly. Under the high flow scenario, the temperature increased by 2.62℃ and 0.85℃ in the first two years, respectively, and then fluctuated slightly before remaining basically stable.

[0126] Table 9. Statistics on the temperature rise of pumping wells in different years

[0127] .

[0128] In summary, under low-flow-rate conditions during the year's operation, the temperature variation of the pumping well is less than 2℃, and its heat penetration is acceptable; however, under high-flow-rate conditions, the maximum temperature variation of the pumping well is greater than 2℃, which will affect the efficiency of the heat pump unit to some extent.

[0129] 3. Well spacing: 50m

[0130] (1) Flow field: The running model was used to obtain the flow field distribution results during the simulation period. It was found that the groundwater flow field of the aquifer changed regularly with the alternation of the running period and the intermittent period. Taking the 5th year as a typical year, the flow field distribution during the geothermal system's operating cycle was plotted as follows: Figure 30 As shown, during operation, the flow field near the injection wells was affected by human activity, resulting in water mounds around the reinjection wells. The highest water level was approximately 78.88 m under low-flow conditions and 80.08 m under high-flow conditions. A water level funnel appeared near the extraction wells, with the lowest water level being approximately 71.09 m under low-flow conditions and 68.37 m under high-flow conditions. During the intermittent period, the groundwater flow field in the unconfined aquifer rapidly recovered to the natural flow field, and the groundwater level essentially returned to its initial state at the end of the intermittent period.

[0131] (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 towards the pumping well and downstream. Since the unconfined aquifer is the main water exchange layer of the geothermal system, the temperature field distribution at the end of the 1st, 5th, and 10th years is shown in the figure below. Figure 31 As shown, it can be seen that the reinjection well at the end of the first year has already affected the temperature of the pumping well. Under the low flow rate scenario, the temperature plume area is 8243.62 m². 2 Driven by the natural flow field, it extends downstream for 36.59 m, and the temperature plume area is 10794.98 m² under high flow conditions. 2 Driven by the natural flow field, it extends downstream for 41.73 m; the temperature plume area at the end of year 5 under the low flow scenario is 22881.90 m². 2 Driven by the natural flow field, it extends downstream for 74.67 m, and the temperature plume area is 27994.99 m² under high flow conditions. 2Driven by the natural flow field, it extends downstream by 80.11 m; under the low-flow scenario at the end of year 10, the temperature plume area is 36572.52 m². 2 Driven by the natural flow field, it extends downstream for 104.78 m, and under high flow conditions, the temperature plume area is 43502.68 m². 2 Driven by the natural flow field, it extends downstream for 113.11m.

[0132] In the first and second years, the temperature of the pumping wells rose rapidly under both flow scenarios (Table 10). Under the low flow scenario, the temperature increase was 2.99℃ in the first year and 0.55℃ in the second year, and then it fluctuated slightly and remained basically stable. Under the high flow scenario, the temperature increase was 3.07℃ in the first year and 0.65℃ in the second year, and then it fluctuated slightly and remained basically stable.

[0133] Table 10: Statistics on Temperature Increase in Pumping Wells in Different Years

[0134] .

[0135] In summary, during the year's operation, the maximum temperature fluctuation of the pumping wells in both scenarios was higher than 2℃, which would affect the efficiency of the heat pump unit to some extent.

[0136] 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 different well spacings, it was found that:

[0137] (1) Flow field: The groundwater flow field of the unconfined aquifer changes regularly with the cyclical alternation of the geothermal system. During operation, a water mound of a certain size is formed near the reinjection well, and a water level funnel is formed near the pumping well. The size of both increases with the increase of the pumping flow rate and the decrease of the well spacing, and vice versa. Specifically, under the high flow rate scenario with a well spacing of 50m to 70m, the elevation of the water mound is 80.08m to 80.83m, and the elevation of the water level funnel is 68.37m to 67.65m; under the low flow rate scenario with a well spacing of 50m to 70m, the elevation of the water mound is 78.88m to 79.23m, and the elevation of the water level funnel is 71.09m to 71.47m. During the intermittent period, the groundwater flow field of the unconfined 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.

[0138] (2) Temperature field and its impact: The operation of the geothermal system under all three well spacings significantly affects the surrounding temperature field distribution. Under long-term operation, the area of ​​the temperature plume increases with the increase of the pumping water flow rate and the decrease of the well spacing, and vice versa; the temperature value at the center of the temperature plume decreases with the increase of the pumping water flow rate and vice versa. At the end of the 10th year after the simulation, the area of ​​the temperature plume of each well spacing under high flow rate was 57683.86 m².2 (Well spacing 70 m), 50975.26 m 2 (Well spacing 60 m), 43502.68 m 2 (Well spacing 50 m); the temperature plume area of ​​each well spacing under low flow rate conditions is 47409.03 m². 2 (Well spacing 70 m), 41410.53 m 2 (Well spacing 60 m), 36572.52 m 2 (Well spacing 50 m).

[0139] (3) Regarding the thermal conductivity of pumping wells: The temperature rise of pumping wells increases with the increase of pumping flow rate and the decrease of well spacing, and vice versa. Under both pumping scenarios, the temperature of pumping wells generally rises rapidly in the first two years, and then the rate of increase gradually decreases. Specifically, under high flow rate pumping, the maximum annual temperature rise of wells at different spacings is 1.91℃ (well spacing 70m), 2.62℃ (well spacing 60m), and 3.07℃ (well spacing 50m), respectively; under low flow rate pumping, the maximum annual temperature rise of wells at different spacings is 1.87℃ (well spacing 70m), 1.94℃ (well spacing 60m), and 2.99℃ (well spacing 50m), respectively.

[0140] Therefore, when the heat penetration temperature variation threshold is 2℃, the heat pump unit efficiency will not be affected when the well spacing is 70 m; when the well spacing is 60 m, the heat pump unit efficiency will be affected to some extent under high flow rate scenarios; when the well spacing is 50 m, the heat pump unit efficiency will be affected to some extent under both high and low flow rate scenarios. A well spacing of 70 m is determined to be a reasonable well spacing.

[0141] Although some preferred embodiments of this application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this application.

[0142] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from the spirit and scope of its inventive concept. Therefore, if these modifications and variations fall within the scope of the claims of this application and their equivalents, this application also intends 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 geothermal utilization area and construct a hydrogeological conceptual model of the area; (2) Based on the aforementioned hydrogeological conceptual model, a coupled equation for the groundwater flow model and the heat transport equation is established; the groundwater flow model equation is as follows: Where: Ω—proposed geothermal utilization range; H—aquifer head; K xx K yy K zz — These are the permeability coefficients in the x, y, and z directions, respectively; K n —Permeability coefficient along the boundary normal; μ s —Unit water storage coefficient; μ d —Gravity water supply; ε —Source and sink terms; Γ0—Upper boundary; Γ1—Second type boundary; n—Outer normal direction of the study area boundary; q(x, y, z, t)—Unit width flow of the second type boundary; The heat transport equation is as follows: In the formula: C eq —Equivalent volumetric heat capacity; Where θ represents porosity, and ρC represents the total volumetric heat capacity in the porous medium; C L = ρ w×C W ρw represents the volumetric heat capacity of water, and C represents the density of water. W λ represents specific heat capacity; Q represents the equivalent thermal conductivity. T —General heat source; q T It is the heat flux flowing in at the boundary Г2; (3) The boundary conditions of the proposed geothermal utilization area are generalized, and the strata are vertically generalized at the same time; (4) The super grid surface of the geothermal proposed utilization area is divided into grids, and the grid of the mining well area is further refined; (5) Set boundary conditions to construct a steady flow model, set the initial water level depth of the steady flow model, and use it as the initial flow field for the subsequent instantaneous flow model; (6) Set the temperature of each stratum in the geothermal utilization area. The surface layer is taken as the annual average temperature of the geothermal utilization area, and the values ​​of each layer below are determined by multiplying the depth from the constant temperature zone by the geothermal warming rate. (7) Assign values ​​to the hydrogeological parameters of the proposed geothermal utilization area; (8) Set the simulation period, the temperature difference threshold between the inlet and outlet and the temperature fluctuation threshold at the end of each recovery period to construct the geothermal prediction model.

2. The construction method according to claim 1, characterized in that, In step (6), the hydrogeological parameters include permeability coefficient, water supply, water storage rate, geothermal heat flow value, porosity, water volumetric specific heat capacity, soil volumetric specific heat capacity, water thermal conductivity, soil thermal conductivity, longitudinal dispersion, and transverse dispersion.

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

4. A well layout method for a groundwater source heat pump system, comprising the following steps: (1) Design different pumping-irrigation 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) Calculate the area of ​​the temperature plume and the maximum operating power of the geothermal system under the different pumping-irrigation ratio schemes, and calculate the maximum power value per unit area. The scheme with the largest maximum power value per unit area is determined as the optimal pumping-irrigation ratio. (3) Based on the above-mentioned optimal pumping-irrigation ratio, different well spacings are designed, and two modes of large and small flow rates are set according to the pumping well flow rate and irrigation well flow rate of the optimal pumping-irrigation ratio, respectively, to simulate and predict the water level and temperature plume distribution of the pumping and re-irrigation wells. (4) Compare the effects of geothermal system operation on the surrounding flow field, temperature field and heat penetration of pumping wells under different well spacings, and select the well spacing with the least impact on the efficiency of heat pump unit as the optimal well spacing.

Images