Method for simulating cross-seasonal heat storage of buried pipe well group in geothermal reservoir

Abstract

A method for simulating cross-seasonal heat storage of a buried pipe well group in a geothermal reservoir is characterized in that hot water and cold water are respectively injected in different seasons by arranging different injection ports in a countercurrent cross injection mode, so that a relatively balanced temperature distribution pattern of a'hot area 'and a'cold area' is formed in a stratum, and the volume structure of a buried pipe is simplified into a line unit model; discretizing the pipeline area by adopting a finite element method; on the basis, initial temperature field distribution of soil and initial parameters of fluid in a buried pipeline unit are set, a proper numerical solution method is selected to solve the pipeline unit model, and the stability of the calculation process and the accuracy of the result are ensured through real-time monitoring; in order to further analyze the influence of underground water seepage on the system performance, an underground water seepage module is introduced, and the difference between summer refrigeration and winter heat supply effects under the seepage condition or not is compared and researched; the invention further comprises a system, equipment and a storage medium for implementing the method.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of geothermal energy utilization, and particularly relates to a method for simulating the cross-seasonal heat storage of a group of buried pipe wells in a geothermal reservoir, which is used to reflect various key physical phenomena and complex dynamic changes in the heat storage process of the group of buried pipe wells. BACKGROUND

[0002] As a high-efficiency technical form in the ground source heat pump system, the borehole heat exchanger (BHE) has been widely used in multiple fields and occupies an important position in the renewable energy technology system. The system realizes building heating in winter and cooling in summer by utilizing the heat storage characteristics of underground rock-soil layers, and has the advantages of energy saving, environmental friendliness, and significant reduction of greenhouse gas emissions. With the continuous improvement of technical level and the deepening of the concept of sustainable development, the application scale and technical performance of the BHE system are continuously optimized, and it has become one of the key technologies to promote the transformation of global energy structure.

[0003] The energy storage mechanism of the BHE system is complex, which covers multiple disciplines such as thermodynamics, geology, materials science, and fluid mechanics. Its core process mainly reflects the following key aspects: analyzing the heat transfer and storage mechanism between the buried pipe and the surrounding soil medium according to the principle of thermodynamics; studying the influence of different geological structures and stratum characteristics on heat conduction, diffusion, and stability of the buried pipe based on the theory of geology; exploring the thermal physical properties, durability, and compatibility of the buried pipe material with soil and heat transfer medium from the perspective of materials science; using fluid mechanics theory to describe the flow characteristics, heat transfer law, and pressure distribution of the heat transfer fluid inside the buried pipe. The above basic processes constitute the coupled response in the heat storage of the buried pipe, and each process influences each other, forming a complex buried pipe heat storage process.

[0004] It is essential to build reliable numerical analysis methods and tools for in-depth analysis of the ground heat exchanger (BHE) storage process. Since the ground heat exchanger technology entered the stage of engineering application, relevant numerical simulation research has gradually developed, and has been continuously developed with the increasing demand of technology. With the increasing demand of society for energy storage efficiency and utilization level, the accuracy and applicability of numerical model of ground heat exchanger in engineering project are also put forward higher standard. The early numerical analysis model mostly uses simplified two-dimensional semi-analytical and semi-numerical method, which is only suitable for preliminary estimation of the storage process under idealized and homogeneous conditions. However, with the significant enhancement of computer computing power and the deepening understanding of the mechanism of underground heat transfer, more accurate full three-dimensional fully coupled numerical model has been developed. This progress makes it possible to simulate the key factors such as complex pipe layout and non-uniformity of soil thermal properties in actual engineering, thereby greatly improving the accuracy and engineering practicability of simulation results. Although the current numerical analysis model of BHE system has strong functions and high precision, there are still many aspects to be improved in model adaptability, calculation efficiency and combination with field measured data.

[0005] Firstly, during the long-term operation of BHE (borehole heat exchanger) system, especially under high-intensity cycling conditions, heat is likely to accumulate in the underground stratum. Due to the limited heat conduction capacity of the stratum itself, the continuous accumulation of heat may cause the "heat accumulation" phenomenon, thereby reducing the heat exchange efficiency of the system. This problem is usually referred to as "thermal balance problem", that is, the underground heat is difficult to diffuse in time, causing the continuous rise or fall of the temperature field around the heat exchanger, thereby affecting its heat exchange performance, and even threatening the long-term stable operation of the system. For example, Wang L et al. published a paper in Heat Science and Technology in 2016, "Research on the operating characteristics of ground source heat pump system under unbalanced cooling and heating load", in which the operating characteristics of ground source heat pump system under unbalanced cooling and heating load were simulated and calculated. With the increase of system operation time, heat accumulation phenomenon occurs in the rock-soil layer, resulting in the gradual weakening of the heat storage capacity. Secondly, in order to more accurately simulate the dynamic changes in the heat storage process of well group, most of the current numerical models of ground heat exchanger usually use three-dimensional volume elements to discretize the system (such as grid elements in finite volume method), which not only include the pipe structure itself, but also the surrounding soil medium. This high computational demand not only consumes a large amount of computing resources, but also seriously affects the calculation efficiency, prolonging the time cost of simulation analysis. Finally, the existence of seepage layer in the rock-soil layer further affects the energy storage effect of well group. The flow of underground water changes the heat distribution pattern and transfer path in the stratum, thereby affecting the heat storage efficiency and thermal stability of the system to different degrees. SUMMARY

[0006] In order to overcome the defects of the prior art, the purpose of the present application is to provide a method for simulating the cross-seasonal heat storage of a group of buried pipe wells in a geothermal reservoir, which divides the seasonal injection of hot water and cold water by designing different injection ports, so as to make the formation form a "hot zone" and a "cold zone" in a relatively balanced manner. In summer, hot water is injected through one side of the injection port to raise the formation temperature and form a hot zone, while in winter, cold water is injected through the other side of the injection port to form a cold zone. With the extension of the operation cycle, the temperature of the hot zone gradually rises, and the temperature of the cold zone gradually drops, so that the winter heating capacity and the summer cooling capacity continue to increase. This method can effectively avoid the problem of single-direction heat accumulation, and with the passage of time, the hot zone will become hotter and the cold zone will become colder, so as to achieve better heating effect in winter and better cooling effect in summer. The method of using a line unit instead of a pipeline volume unit is used to simulate the heat exchange process of the well group, and by establishing a well group heat storage calculation and analysis model, the heat transfer process in the borehole and the heat transfer process outside the borehole in the heat storage process of the buried pipe well group can be effectively simulated, which has the advantages of comprehensive model function, high calculation efficiency, etc., and solves the problems of high demand for computing resources, complex model establishment, limited scalability and poor flexibility in the traditional modeling process.

[0007] In order to achieve the above-mentioned purpose, the technical scheme of the present application is as follows: A method for simulating the cross-seasonal heat storage of a group of buried pipe wells in a geothermal reservoir, comprising the following steps: Step one, optimizing the water injection mode of the buried pipe well group The boreholes of the buried pipe well group are connected to each other, and the water injection mode of the U-shaped pipe in the buried pipe well group adopts countercurrent heat exchange; Step two, simplifying the pipeline volume unit The pipeline volume unit of the buried U-shaped pipe is discretized by using a parallel finite element method, and the circulating fluid in the U-shaped pipe and the pipe wall are simplified as a one-dimensional heat exchange pipe, i.e. a one-dimensional heat exchange pipe simplified unit; Step three, constructing a pipeline flow model A pipeline flow model is established in the three-dimensional modeling, and the pipeline is regarded as a curve in the three-dimensional model for modeling by using the one-dimensional heat exchange pipe simplified unit; Step four, jointly solving the temperature changes in and outside the pipe In the pipe outside part, the temperature response in the rock-soil medium is calculated by solving the transient three-dimensional heat conduction or heat-seepage coupling equation; in the pipe inside part, the temperature and velocity distribution of the fluid in the U-shaped pipe are calculated by coupling the flow equation and the energy equation of the pipe inside circulating fluid medium; finally, the temperature changes in and outside the pipe are jointly solved by using a parallel finite element calculation method in the pipeline flow model.

[0008] The specific steps of the step one of optimizing the water injection mode of the buried pipe well group are as follows: (1.1) First, each independent borehole is processed to make the U-shaped tubes in each borehole communicate with each other to form a unified circulating channel; (1.2) The U-shaped tube adopts the water injection mode of counter-flow heat exchange, that is, in summer, circulating water is injected from the left side, and in winter, the injection is switched to the right side.

[0009] The specific steps of simplifying the pipe volume unit in step two are as follows: (2.1) Discrete circulating fluid in the U-shaped tube and the tube wall are formed by using the parallel finite element method to form one-dimensional linear finite element units; (2.2) U-shaped circular curve units are inserted between the discrete one-dimensional linear finite element units; (2.3) The one-dimensional linear finite element units and the U-shaped circular curve units are renumbered to make the finite element unit number and the node number continuous, forming the simplified one-dimensional heat exchange pipe, that is, the one-dimensional heat exchange pipe simplified unit.

[0010] The specific steps of constructing the pipe flow model in step three are as follows: (3.1) The inner and outer parts of the pipe flow model are established by using three-dimensional modeling; (3.2) the outer part adopts a three-dimensional form, and the inner part and the tube wall adopt the one-dimensional heat exchange pipe simplified unit, the pipe is modeled as a curve in the three-dimensional model, and the geometric model is obtained; (3.3) The boundary conditions are input into the geometric model to establish the overall layered rock seepage model, and the pipe flow model is obtained.

[0011] The specific steps of jointly solving the temperature changes in the inner and outer parts of the pipe in step four are as follows: (4.1) In the outer part, the outer rock soil medium energy equation is established according to the heat transfer theory of porous medium to obtain the temperature field distribution of the outer part, wherein the rock soil medium includes the backfill material in the surrounding hole and the layered and seepage rock soil medium outside the hole; the expression of the outer rock soil medium energy equation is: In the formula, is the density of the reservoir fluid, kg / m 3 ; is the specific heat capacity of the formation fluid at constant pressure, J / (kg·K); is the temperature of the formation fluid, ℃; is the flow rate of the reservoir fluid, m / s; is the thermal conductivity of the fluid outside the heat exchange pipe; is the heat transferred to the heat extraction medium by the geothermal fluid through the heat exchange pipe wall, J; In the formula, is the effective specific heat capacity at constant pressure, J / (℃·m 3 ); is the effective thermal conductivity, W / (m·℃) ; is the formation temperature; (4.2) In the pipe section, the pipe fluid flow equation and energy equation are established according to the non-isothermal pipe flow theory, and the temperature field, fluid flow state and stress distribution in the pipe are obtained; The flow equation is shown in equations (3) and (4): In the formula, is the cross-sectional area of the heat exchange pipe, m 2 ; is the fluid density, kg / m 3 ; is the flow rate of the fluid, m / s; is the pressure in the well, Pa; is the inner diameter of the pipe, m; is the specific heat capacity of the fluid at constant pressure, J / (kg·℃) ; is the temperature of the fluid, ℃; is the thermal conductivity of the fluid in the heat exchange pipe, W / (m·℃) ; is the heat transferred by the geothermal fluid to the heat extraction working medium through the wall of the heat exchange pipe, J; In equation (4), is the Darcy friction factor, which is obtained according to the Churchill model: In the formula, is the Reynolds number; is the roughness of the inner pipe; In equation (5), : In the formula, is the temperature on the outside of the heat exchange pipe wall, ℃; is the total equivalent heat transfer coefficient, including the pipe wall thermal resistance and the convective heat transfer resistance of the inner and outer walls, W / (m·℃) ; is the circumference of the pipe wall, m; is the forced convection heat transfer coefficient, W / (m 2 ·℃), calculated by equation (8): In the formula, is the Nusselt number, is the thermal conductivity of the fluid in the heat exchange pipe. For a circular pipe, can be calculated by equation (9): In the formula, Nu is the heat transfer coefficient of the fluid inside the pipe, W / (m·℃); Nu is the heat transfer coefficient of the fluid outside the pipe, W / (m·℃); D and D are the inner diameter and outer diameter of the pipe, respectively, and the heat transfer coefficients inside and outside the pipe are calculated by the Nusselt number Nu and Nu and : In the formula, is the thermal conductivity of the fluid outside the heat exchange pipe; It can be calculated by the Gnielinski formula: In the formula, is the Prandtl number, and the applicable range of the equation is: Re =3000~6×10 6 , Pr =0.5~2000. For natural convection outside the heat exchange pipe, the model proposed by Churchill and Chu can be used for calculation: In the formula, is the Rayleigh number, ; is the dimensionless Grashof number, which represents the ratio of buoyancy and viscous force, and the applicable range of equation (12) is <10 12 ; (4.3) Parallel finite element calculation method is used, based on the pipe outside the rock temperature field obtained in step (4.1), and the pipe inside temperature field obtained in step (4.2), coupling is solved, so that the fluid transient temperature change and the transient temperature change in the rock mass of the calculation model are obtained.

[0012] The groundwater seepage is introduced, and the differences of summer refrigeration and winter heating with and without groundwater seepage are compared. The specific steps are: adding a groundwater seepage module in the pipe flow model in step three, analyzing the influence of groundwater seepage on the temperature change of "hot zone" and "cold zone" and the outlet temperature change of the buried pipe group; Then compare the temperature difference of "hot zone" and "cold zone" and the outlet temperature change of the buried pipe group in summer refrigeration and winter heating without the groundwater seepage module.

[0013] The application also includes: A system comprising a processor capable of running the method of simulating the heat storage of the buried pipe well group in the geothermal reservoir.

[0014] An apparatus comprising: Memory: for storing a computer program of the method for simulating heat storage of a ground heat storage layer by a ground heat pipe well group; Processor: for implementing the method for simulating heat storage of a ground heat storage layer by a ground heat pipe well group when the computer program is executed.

[0015] A computer readable storage medium stores a computer program, and the computer program is executed by a processor to implement the method for simulating heat storage of a ground heat storage layer by a ground heat pipe well group.

[0016] Compared with the prior art, the present application has the following beneficial effects: 1. The water injection mode of the ground heat pipe well group in step one is optimized, different injection ports are designed to seasonally inject hot water and cold water, so that the formation forms a relative balance effect of a hot zone and a cold zone, with the extension of the operation cycle, the temperature of the hot zone gradually rises, and the temperature of the cold zone gradually drops, so that the winter heating capacity and the summer cooling capacity are continuously enhanced.

[0017] 2. The line unit is used instead of the pipeline volume unit in step two, so that the calculation amount is greatly reduced, the calculation is simplified, and the heat transfer characteristics of the fluid in the pipeline can be more accurately captured.

[0018] In summary, the line unit is used instead of the pipeline volume unit to greatly reduce the calculation amount, and the heat transfer characteristics of the fluid in the pipeline can be accurately captured, secondly, the innovative water injection mode of the ground heat pipe well group makes the formation form a relative balance distribution state of a hot zone and a cold zone, with the extension of the operation cycle, the temperature of the hot zone gradually rises, and the temperature of the cold zone gradually drops, so that the winter heating capacity and the summer cooling capacity of the system are continuously enhanced, the energy utilization efficiency is continuously enhanced, finally, the numerical model is solved in combination with the multi-physical field coupling, and the influence of the underground water seepage on the heat storage of the ground heat pipe well group is analyzed. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 It is a numerical calculation flowchart of the heat storage of the ground heat pipe well group.

[0020] Fig. 2 (a) is a schematic view of the cross section of the well group; and Fig. 2 (b) is a schematic view of the longitudinal section of the well group.

[0021] Figure 3 It is a simulation effect diagram of the heat storage of the well group by using the line unit instead of the pipeline volume unit for modeling in the heat storage of the well group.

[0022] Fig. 4 (a) is a temperature change diagram of the outlet of observation point 1; and Fig. 4 (b) is a temperature change diagram of the outlet of observation point 2.

[0023] Figure 5 (a) is a temperature comparison chart of the reverse alternating heat exchange system when the observation point 1 has no groundwater seepage; Figure 5 (b) is a temperature comparison chart of the reverse alternating heat exchange system when the observation point 2 has no groundwater seepage. DETAILED DESCRIPTION

[0024] Embodiments of the present application will be described in detail below with reference to the accompanying drawings.

[0025] Referring to Figure 1 A method for simulating the cross-season heat storage of a group of buried pipe wells in a geothermal reservoir, comprising the following steps: Step one, optimization of the water injection mode of the group of buried pipe wells, mutual communication between each borehole, and the water injection mode of the U-shaped pipe using reverse flow heat exchange, i.e. injecting circulating water from the left side in summer and switching to injecting from the right side in winter; In the step one, the specific steps for optimizing the pipe arrangement mode of the well group are as follows: (1) First, process each independent borehole to make the U-shaped pipes in each borehole communicate with each other to form a unified circulating channel, as shown in Figures 2 (a) and 2 (b); (2) The water injection mode of the U-shaped pipe uses reverse flow heat exchange, i.e. injecting circulating water from the left side in summer and switching to injecting from the right side in winter.

[0026] Step two, simplification of the pipe volume unit, using the parallel finite element method to discretize the pipe volume unit, and simplifying the circulating fluid in the U-shaped pipe and the pipe wall into a one-dimensional heat exchange pipe; Referring to Figure 3 In the step two, the specific steps for simplifying the pipe volume unit are as follows: (1) Using the parallel finite element method, discretize the circulating fluid in the U-shaped pipe and the pipe wall to form one-dimensional linear finite element units; (2) Insert U-shaped circular arc curve units between the discretized one-dimensional linear finite element grids; (3) Re-number the one-dimensional linear finite element units and the U-shaped circular arc curve units to make the finite element unit numbers and node numbers continuous, forming the simplified one-dimensional heat exchange pipe, i.e. the one-dimensional heat exchange pipe simplified unit.

[0027] Step three, establishing a pipe flow model in the three-dimensional modeling, using one-dimensional linear units to model the pipe as a curve in the three-dimensional model; coupling the linear unit nodes and the three-dimensional grid units outside the pipe, which is conducive to the grid division of the three-dimensional pipe with a limited diameter, In the step three, the specific steps for constructing the pipe flow model are as follows: (1) using three-dimensional modeling to establish the inside and outside parts of the pipe flow model; (2) the outside still adopts a three-dimensional form, and the inside and the pipe wall adopt the one-dimensional heat exchange pipe simplified unit, i.e. modeling the pipe as a curve in the three-dimensional model to obtain a geometric model; (3.3) Input boundary conditions into the geometric model, and build the whole layered rock-soil seepage model to obtain the pipe flow model.

[0028] Step four, in the pipe outer part, calculate the temperature response in the rock-soil medium by solving the transient three-dimensional heat conduction or heat-seepage coupling equation; in the pipe inner part, couple the flow equation and energy equation of the circulating fluid medium in the pipe to calculate the temperature and velocity distribution of the fluid in the U-shaped pipe; finally, in the pipe flow model, adopt the parallel finite element calculation method to jointly solve the fluid flow and convective heat transfer in the U-shaped pipe and the pipe wall heat conduction problem; In step four, the specific steps of adopting the parallel finite element calculation method to integrate the fluid flow and heat transfer module are as follows: (1) In the pipe outer part, establish the pipe outer rock-soil medium energy equation according to the porous medium heat transfer theory to obtain the pipe outer temperature field distribution, wherein the rock-soil medium includes the surrounding hole backfill material and the hole outer underground layered and seepage rock-soil medium; the pipe outer rock-soil medium energy equation expression is: In the formula, is the reservoir fluid density, kg / m 3 ; is the specific heat capacity of the formation fluid at constant pressure, J / (kg·K); is the formation fluid temperature, ℃; is the reservoir fluid flow rate, m / s; is the thermal conductivity of the fluid outside the heat exchange pipe; is the heat transferred to the heat extraction working medium by the geothermal fluid through the heat exchange pipe wall, J.

[0029] In the formula, is the effective specific heat capacity at constant pressure, J / (℃·m 3 ); is the effective thermal conductivity, W / (m·℃); is the formation temperature.

[0030] (2) In the pipe inner part, establish the pipe inner fluid flow equation and energy equation according to the non-isothermal pipe flow theory to obtain the pipe inner temperature field, fluid flow state and stress distribution; The flow equation is shown in formula (3) (4): In the formula, is the cross-sectional area of the heat exchange pipe, m 2 ; is the fluid density, kg / m 3 ; is the flow rate of the fluid, m / s; Pais the pressure in the well, Pa; Dais the inner diameter of the pipe, m; Cpis the specific heat capacity of the fluid at constant pressure, J / (kg °C); Tpis the temperature of the fluid, °C; kpis the thermal conductivity of the fluid inside the heat exchange pipe, W / (m °C); Qpis the heat transferred by the geothermal fluid to the heat extraction working fluid through the wall of the heat exchange pipe, J.

[0031] In equation (4), Dais the inner diameter of the pipe, m; In equation (5), Reis the Reynolds number; eis the roughness of the inner pipe.

[0032] In equation (5), : In equation (6), Tpis the temperature of the fluid outside the wall of the heat exchange pipe, °C; Utotais the total equivalent heat transfer coefficient, including the thermal resistance of the pipe wall and the convective thermal resistance of the inner and outer walls, W / (m °C); Pwis the perimeter of the pipe wall, m; hconvis the forced convective heat transfer coefficient, W / (m 2 °C), calculated from equation (8): In equation (9), Nuis the Nusselt number, kpis the thermal conductivity of the fluid inside the heat exchange pipe. For a circular pipe, It can be calculated from equation (9): In equation (10), hpiis the convective heat transfer coefficient inside the pipe, W / (m °C); hpois the convective heat transfer coefficient outside the pipe, W / (m °C); Dand are the inner and outer diameters of the circular pipe, respectively. The convective heat transfer coefficients inside and outside the pipe are calculated through the Nusselt numbers Nuipand Nuop: In equation (11), kpois the thermal conductivity of the fluid outside the heat exchange pipe; It can be calculated through the Gnielinski formula: In equation (12), Prandtl number, the applicable range of the equation: Re =3000~6×10 6 , Pr =0.5~2000. For natural convection outside the heat exchange tube, the model proposed by Churchill and Chu can be used to calculate: wherein, is the Rayleigh number, ; is the dimensionless Grashof number, which represents the ratio of buoyancy and viscous force, and the applicable range of equation (12) is <10 12 .

[0033] (3) Parallel finite element calculation method is used to solve the fluid transient temperature change and the transient temperature change in the rock mass based on the temperature field of the rock mass outside the tube obtained in step (1) and the temperature field inside the tube obtained in step (2), and the specific steps are as follows: First, the fluid temperature inside the tube and the rock mass temperature outside the tube are calculated, and then the parallel finite element method is used to solve the temperature between different media according to the physical field, and the fluid transient temperature change and the transient temperature change in the rock mass are obtained.

[0034] The specific steps to obtain the overall control equation set include: ① The one-dimensional linear finite element unit and the three-dimensional tetrahedral finite element unit are evenly distributed to each processor in the parallel computing system; ② The fluid temperature inside the tube and the rock mass temperature outside the tube are calculated on each processor; ③ The parallel finite element method is used to solve the temperature between different media according to the physical field in the parallel computing system, and the overall control equation set is obtained.

[0035] The specific steps of solving the temperature and velocity distribution of the fluid inside the U-shaped tube and the temperature response in the rock mass by using the parallel finite element calculation method are as follows: (1) The overall control equation set of the calculation model is solved by using the parallel calculation method, and the fluid transient temperature change, velocity change and transient temperature change in the rock mass are obtained; (2) The calculated temperature and velocity change data are transmitted to each processor in the parallel computing system; (3) Post-processing is performed on each processor to calculate the temperature and velocity distribution of the fluid inside the calculation model and the temperature response in the rock mass.

[0036] The influence of groundwater seepage on the heat storage performance of the ground heat exchanger group is analyzed, and the differences in cooling in summer and heating in winter with and without groundwater seepage are compared and analyzed. The specific steps are as follows: in the pipe flow model of step three, the groundwater seepage module is added, the influence of groundwater seepage on the temperature change of the "hot zone" and the "cold zone" and the outlet temperature change of the ground heat exchanger group is analyzed; and the temperature difference between the "hot zone" and the "cold zone" and the outlet temperature change of the ground heat exchanger group in summer cooling and winter heating are compared without the groundwater seepage module.

[0037] The specific steps of analyzing the influence of groundwater seepage on the heat storage performance of the ground heat exchanger group are as follows: (1) By introducing the groundwater seepage layer, the influence of the groundwater seepage layer on the temperature change of the "hot zone" and the "cold zone" and the outlet temperature change of the ground heat exchanger group is analyzed, as shown in Figs. 4(a) and 4(b); (2) The temperature difference between the "hot zone" and the "cold zone" and the outlet temperature change of the ground heat exchanger group in summer cooling and winter heating are compared without the groundwater seepage layer, as shown in Figs. 5(a) and 5(b).

[0038] The present application also includes: A system comprising a processor capable of running the method of simulating the heat storage of the ground heat exchanger group in the geothermal reservoir.

[0039] An apparatus comprising: A memory for storing the computer program of simulating the heat storage of the ground heat exchanger group in the geothermal reservoir; A processor for executing the computer program to realize the method of simulating the heat storage of the ground heat exchanger group in the geothermal reservoir.

[0040] A computer readable storage medium storing a computer program, wherein the computer program is executed by a processor to realize the method of simulating the heat storage of the ground heat exchanger group in the geothermal reservoir.

Claims

1. A method for simulating cross-seasonal thermal storage of buried well groups in geothermal reservoirs, characterized in that, Includes the following steps: Step 1: Optimize the water injection method for the underground pipe well group The boreholes in the underground pipe well group are interconnected, and the U-shaped pipes in the underground pipe well group are injected with water using a counter-current heat exchange method. Step 2: Simplify the pipe volume unit The pipe volume element of the buried U-shaped pipe is discretized using the parallel finite element method. The circulating fluid inside the U-shaped pipe and the pipe wall are simplified into a one-dimensional heat exchange tube, which is the one-dimensional heat exchange tube simplified element. Step 3: Construct the pipeline flow model In 3D modeling, a pipe flow model is established, and the pipe is modeled as a curve in the 3D model by using a one-dimensional heat exchanger tube simplified unit. Step 4: Jointly solve for the temperature changes inside and outside the tube. Outside the pipe, the temperature response in the soil and rock medium is calculated by solving the transient three-dimensional heat conduction or heat-permeability coupling equations. Inside the pipe, the flow equations and energy equations of the circulating fluid medium are coupled to calculate the temperature and velocity distribution of the fluid inside the U-shaped pipe. Finally, the parallel finite element method is used in the pipe flow model to jointly solve the temperature changes inside and outside the pipe.

2. The method for simulating cross-seasonal thermal storage of buried well groups in geothermal reservoirs according to claim 1, characterized in that, The specific steps for optimizing the water injection method of the buried well group in step one are as follows: (1.1) First, each independent borehole is processed so that the U-shaped tubes in each borehole are interconnected to form a unified circulation channel; (1.2) The U-shaped tube adopts a counter-current heat exchange water injection method, that is, in summer, circulating water is injected from the left side, and in winter, it is switched to the right side.

3. The method for simulating cross-seasonal thermal storage of buried well groups in geothermal reservoirs according to claim 1, characterized in that, The specific steps for simplifying the pipe volume unit in step two are as follows: (2.1) The parallel finite element method is used to discretize the circulating fluid and the pipe wall inside the U-shaped pipe to form a one-dimensional linear finite element unit; (2.2) Insert U-shaped circular arc curve elements between discrete one-dimensional linear finite element elements; (2.3) The one-dimensional linear finite element unit and the U-shaped circular arc curve unit are renumbered to make the finite element unit number and the node number continuous, forming a simplified one-dimensional heat exchange tube, i.e., a simplified one-dimensional heat exchange tube unit.

4. The method for simulating cross-seasonal thermal storage of buried well groups in geothermal reservoirs according to claim 1, characterized in that, The specific steps for constructing the pipeline flow model in step three are as follows: (3.1) Use three-dimensional modeling to establish the inside and outside parts of the pipe flow model; (3.2) The outside of the pipe is in three-dimensional form, while the inside of the pipe and the pipe wall are simplified one-dimensional heat exchange tube units. The pipe is modeled as a curve in the three-dimensional model to obtain the geometric model. (3.3) Input boundary conditions into the geometric model to establish an overall layered rock and soil seepage model and obtain the pipeline flow model.

5. The method for simulating cross-seasonal thermal storage of buried well groups in geothermal reservoirs according to claim 1, characterized in that, The specific steps for jointly solving the temperature changes inside and outside the tube in step four are as follows: (4.1) In the external part of the pipe, the energy equation of the external soil and rock medium is established based on the porous medium heat transfer theory to obtain the temperature field distribution outside the pipe. The soil and rock medium includes the backfill material inside the surrounding hole and the underground layered and seeping soil and rock medium outside the hole. The expression of the energy equation of the external soil and rock medium is: In the formula, The reservoir fluid density is kg / m³. 3 ; is the isobaric specific heat capacity of the formation fluid, J / (kg·K); The temperature of the formation fluid is ℃; The reservoir fluid velocity is given in m / s. The thermal conductivity of the fluid outside the heat exchanger tube; J represents the heat transferred from the geothermal fluid to the heat extraction medium through the heat exchanger tube wall. In the formula, For effective isobaric specific heat capacity, J / (℃·m 3 ); The effective thermal conductivity is W / (m·℃). Formation temperature; (4.2) In the pipe section, the fluid flow equation and energy equation are established according to the non-isothermal pipe flow theory to obtain the temperature field, fluid flow state and stress distribution in the pipe. The flow equations are shown in equations (3) and (4): In the formula, Let m be the cross-sectional area of ​​the heat exchange tube. 2 ; Fluid density, kg / m³ 3 ; The velocity of the fluid is expressed in m / s. The pressure inside the well is in Pa. Let be the inner diameter of the pipe, in meters (m). is the specific heat capacity at constant pressure of the fluid, J / (kg·℃); The fluid temperature is expressed in °C. The thermal conductivity of the fluid inside the heat exchanger tube is W / (m·℃). J represents the heat transferred from the geothermal fluid to the heat extraction medium through the heat exchanger tube wall. In equation (4), The Darcy friction factor is obtained according to the Churchill model: In the formula, It is the Reynolds number; For the roughness of the inner tube; In equation (5) : In the formula, The temperature on the outer side of the heat exchange duct wall is ℃; The total equivalent heat transfer coefficient, including the wall thermal resistance and the convective thermal resistance of the inner and outer walls, is expressed in W / (m·℃). Let be the circumference of the pipe wall, in meters (m). For forced convection heat transfer coefficient, W / (m 2 ·℃), calculated by equation (8): In the formula, For Nusset numbers, This is the thermal conductivity of the fluid inside the heat exchanger tube; for a circular tube, It can be calculated using equation (9): In the formula, The convective heat transfer coefficient inside the pipe is expressed in W / (m·℃). The external convective heat transfer coefficient is expressed in W / (m·℃). and These represent the inner and outer diameters of the circular tube, respectively. The convective heat transfer coefficients inside and outside the tube are obtained through the Nusselt number. and calculate: In the formula, The thermal conductivity of the fluid outside the heat exchanger tube; It can be calculated using the Gnielinski formula: In the formula, Given the Prandtl number, the equation's applicability is as follows: Re =3000~6×10 6 , Pr =0.5~2000; For natural convection outside the heat exchange tubes, it can be calculated using the model proposed by Churchill and Chu: In the formula, Rayleigh number, ; Let be the dimensionless Grashof number, representing the ratio of buoyancy to viscous force. Equation (12) is applicable to the following range: <10 12 ; (4.3) Using the parallel finite element method, based on the temperature field of the soil outside the pipe obtained in step (4.1) and the temperature field inside the pipe obtained in step (4.2), the coupled solution is performed to obtain the transient temperature change of the fluid and the transient temperature change in the soil and rock mass of the calculation model.

6. The method for simulating cross-seasonal thermal storage of buried well groups in geothermal reservoirs according to claim 1, characterized in that, The study introduces groundwater seepage to compare the effects of summer cooling and winter heating with and without groundwater seepage. The specific steps are as follows: Add a groundwater seepage module to the pipeline flow model in step three to analyze the impact of groundwater seepage on the temperature changes of the "hot zone" and "cold zone" as well as the temperature changes of the buried pipe group outlet. Then, compare the temperature difference between the "hot zone" and "cold zone" without the groundwater seepage module, as well as the temperature changes of the buried pipe group during summer cooling and winter heating.

7. A system comprising a processor, characterized in that, The method for simulating geothermal reservoir storage using buried well groups as described in any of claims 1-6 is capable of being implemented.

8. An apparatus, characterized in that it comprises: Memory: A computer program for storing the method of simulating geothermal reservoir thermal storage using buried pipe well groups as described in any of claims 1-6; Processor: Used to implement the method of thermal storage of buried well groups in simulated geothermal reservoirs when executing any of the computer programs described in claims 1-6.

9. A computer-readable storage medium storing a computer program, characterized in that, When the computer program is executed by the processor, it implements the method for thermal storage of buried well groups in simulated geothermal reservoirs as described in any of claims 1-6.

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