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

Abstract

A method for simulating heat storage of a buried pipe well group in a geothermal reservoir adopts staggered arrangement to replace traditional sequential arrangement, so that the distance between buried pipes is more reasonable, heat interference is minimized, the volume shape of the buried pipes is simplified into a linear unit structure, pipeline volume units are dispersed by adopting a finite element method based on various theories, and the heat storage efficiency of the buried pipe well group is improved. The calculated amount is reduced; and fluid heat transfer characteristics in the pipeline are accurately captured. Then setting soil initial temperature field distribution and initial parameters of fluid in a buried pipeline unit, solving a pipeline unit model by adopting a proper numerical calculation method, and performing real-time monitoring to ensure that a calculation result is stable and accurate; factor sensitivity analysis is carried out by changing in-well parameters and operation parameters, the influence of rock-soil body thermophysical parameters and buried pipe heat exchange characteristic factors on the geothermal reservoir thermal exploitation efficiency is comprehensively researched, and a scientific basis is provided for optimal design and operation of a buried pipe well group. The invention further comprises a system, equipment and a storage medium for implementing the method.

Description

Technical Field

[0001] The present invention relates to the technical field of geothermal energy utilization, and in particular to a method for simulating heat storage of a buried pipe well group in a geothermal reservoir, which is used to reflect various key physical phenomena and complex dynamic changes in the heat storage process of the buried pipe well group. Background Art

[0002] With the growing global demand for clean energy and the increasing emphasis on energy conservation and emission reduction, geothermal energy, a renewable, widespread, and stable energy resource, is attracting increasing attention for its development and utilization. Well cluster heat storage technology plays a crucial role in improving geothermal energy utilization efficiency and balancing fluctuations in energy supply and demand, making it a key component in achieving sustainable geothermal energy utilization. Storing heat underground through buried pipes and extracting it when needed can effectively address seasonal imbalances in energy supply and demand. For example, by utilizing summer-stored heat during winter heating demand, the overall efficiency of energy utilization can be improved.

[0003] The mechanism of underground heat storage is complex, encompassing multiple disciplines including thermal engineering, geology, materials science, and fluid mechanics. Its core processes are primarily reflected in the following key aspects: Analyzing the heat transfer and storage mechanisms between the underground pipe and the surrounding soil medium based on thermal engineering principles; Studying the influence of different geological structures and formation characteristics on heat conduction, diffusion, and underground pipe stability based on geological theory; Investigating the thermophysical properties, durability, and compatibility of underground pipe materials with soil and heat transfer media from a materials science perspective; Applying fluid mechanics theory to describe the flow characteristics, heat transfer patterns, and pressure distribution of the heat transfer fluid within the underground pipe. These fundamental processes constitute the coupled response of underground pipe heat storage, and the mutual influence of these processes creates a complex underground pipe heat storage process.

[0004] To analyze the underground heat storage process, establishing numerical analysis methods and tools is essential. Since the introduction of underground heat storage technology into engineering practice, related numerical analysis has been gradually developed and continues to advance. With the increasing demand for energy storage and utilization efficiency in society, the standards and expectations for numerical analysis models for underground heat storage in various engineering projects have also risen accordingly. Initially, numerical analysis models were mostly simple two-dimensional semi-analytical and semi-numerical models, capable of only providing preliminary estimates for idealized underground heat storage scenarios. With the rapid advancement of computer technology and a deepening understanding of heat storage mechanisms, full three-dimensional, fully coupled models have now been successfully constructed. This shift has made it possible to simulate factors such as complex underground pipe layouts and heterogeneous soil thermophysical properties found in real-world projects, greatly improving the accuracy and realism of simulations. Although current numerical analysis models for underground heat storage are relatively comprehensive, much work remains to be done to improve and refine them.

[0005] First, the traditional sequential well cluster layout method arranges underground pipes in straight lines or regular rows and columns. This approach can lead to significant thermal interference between adjacent pipes, as their heat exchange areas easily overlap, affecting overall heat transfer efficiency. Second, to accurately simulate the dynamic changes in the well cluster's heat storage process, many current numerical analysis models for underground pipe heat storage are typically discretized into multiple three-dimensional volume elements (such as those used in the finite volume method). These elements encompass not only the pipes themselves but also the surrounding soil medium. For example, Zhou Qiaolan of Chang'an University, in "Analysis of Heat Extraction and Storage Performance of Different Types of Underground Pipe Heat Exchangers," published in the journal Engineering Science and Technology (Issue 6, 2024), introduced a method for simulating underground pipe well cluster heat storage. This method details the layout of U-shaped pipes and how to mesh their different sections. While this method offers significant advantages in accuracy, it requires the discretization of a large number of three-dimensional elements, resulting in a significant computational workload. This enormous computational demand not only consumes significant computing resources, but also significantly reduces computational efficiency and prolongs the simulation analysis time. In addition, the large thermal interference between well groups in the traditional pipe layout method further affects the speed of obtaining results and the overall efficiency improvement. Summary of the Invention

[0006] In order to overcome the defects of the above-mentioned prior art and break through the limitations of traditional modeling methods, the purpose of the present invention is to provide a method for simulating heat storage in underground pipe well groups in geothermal reservoirs, and adopt an interlaced arrangement in the pipe layout of the well group, so that the spacing between the buried pipes is more reasonable and thermal interference is minimized; this staggered pipe layout method not only increases the contact area between the buried pipes and the soil and improves the heat exchange efficiency, but also can better adapt to different terrains and engineering requirements, providing greater flexibility for actual engineering applications; a method of using line units instead of pipe volume units is used to simulate the heat exchange process of the well group, and by establishing a well group heat storage calculation and analysis model, it can effectively simulate the heat transfer process inside the borehole and the heat transfer process outside the borehole during the heat storage process of the buried pipe well group, with the advantages of comprehensive model functions and high computational efficiency, and solves the problems encountered in the traditional modeling process such as high computing resource requirements, complex model establishment, limited scalability and poor flexibility.

[0007] To achieve the above object, the technical solution of the present invention is as follows:

[0008] A method for simulating heat storage in a buried pipe well group in a geothermal reservoir comprises the following steps:

[0009] Step 1: Optimization of underground pipe well groups

[0010] The buried U-shaped pipes are arranged in a staggered manner;

[0011] Step 2: Simplify the pipe volume unit

[0012] The parallel finite element method is used to discretize the buried U-tube volume unit, and the circulating fluid in the U-tube and the tube wall are simplified into a one-dimensional heat exchange tube, that is, a one-dimensional heat exchange tube simplified unit.

[0013] Step 3: Pipeline flow model construction

[0014] Establish a pipeline flow model in the three-dimensional modeling, and use the one-dimensional heat exchange tube simplified unit to model the pipeline as a curve in the three-dimensional model;

[0015] Step 4: Jointly solve the inside and outside of the tube

[0016] Outside the pipe, the temperature response in the geotechnical 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 are coupled to calculate the temperature and velocity distribution of the fluid inside the U-shaped pipe. Finally, a parallel finite element calculation method is used in the pipeline flow model to jointly solve the inside and outside of the pipe.

[0017] Step 5: Perform sensitivity analysis by changing different operating parameters

[0018] By changing different well parameters and operating parameters, factor sensitivity analysis is performed to obtain the optimal parameter combination.

[0019] The specific steps for optimizing the buried pipe well group in step 1 are as follows:

[0020] (1) First, a thermal interference analysis was conducted on the existing sequential arrangement method to clarify the overlap of heat exchange areas between adjacent buried pipes when interference occurs. The optimal spacing between the buried pipes was then re-determined based on numerical simulation.

[0021] (2) Based on the optimal spacing between buried pipes, the buried U-shaped pipes are arranged in a staggered manner.

[0022] The specific steps of simplifying the pipeline volume unit in step 2 are as follows:

[0023] (1) Using the parallel finite element method, the circulating fluid in the U-shaped tube and the tube wall are discretized to form a one-dimensional linear finite element unit;

[0024] (2) Inserting U-shaped circular arc curve elements between discrete one-dimensional linear finite element grids;

[0025] (3) The one-dimensional linear finite element unit and the U-shaped arc curve unit are renumbered so that the finite element unit number and the node number are continuous, thereby forming a simplified one-dimensional heat exchange tube, namely, a one-dimensional heat exchange tube simplified unit.

[0026] The specific steps of constructing the pipeline flow model in step 3 are:

[0027] (1) Use 3D modeling to build the wellbore and backfill material;

[0028] (2) The outside of the tube is in three-dimensional form, and the inside and wall of the tube are simplified units of one-dimensional heat exchange tubes, that is, the tube is modeled as a curve in the three-dimensional model to obtain a geometric model;

[0029] (3) Input the working condition parameters into the geometric model and give them physical meaning, establish the overall layered rock and soil seepage model, and obtain the pipeline flow model.

[0030] The specific steps in step 4 are:

[0031] (1) In the part outside the pipe, the energy equation of the rock and soil medium outside the pipe is established based on the porous media heat transfer theory, where the rock and soil medium includes the backfill material in the surrounding hole and the underground stratification and seepage rock and soil medium outside the hole; the energy equation of the rock and soil medium outside the pipe is expressed as:

[0032]

[0033] Where, ρ g is the reservoir fluid density, kg / m 3 ;c p,g is the constant-pressure specific heat capacity of the formation fluid, J / (kg·K); T w is the formation fluid temperature, °C; u g is the reservoir fluid velocity, m / s; λ g is the thermal conductivity of the fluid outside the heat exchange tube; Q wall is the heat transferred from geothermal fluid to the heat medium through the heat exchange tube wall, J;

[0034]

[0035] Where, (ρc p ) eff is the effective specific heat capacity at constant pressure, J / (℃·m 3 );λ eff is the effective thermal conductivity, W / (m·℃); T r is the formation temperature;

[0036] (2) In the pipe part, the flow equation and energy equation of the fluid in the pipe are established according to the non-isothermal pipe flow theory, and the flow state and stress distribution of the fluid in the U-shaped pipe are obtained;

[0037] The flow equation is shown in equations (3) and (4):

[0038]

[0039] The energy equation is shown in formula (5):

[0040]

[0041] Where A p is the cross-sectional area of the heat exchange tube, m 2 ρ f is the fluid density, kg / m 3 ;u f is the fluid velocity, m / s; p is the well pressure, Pa; d p is the inner diameter of the tube, m; c p,f is the constant pressure specific heat capacity of the fluid, J / (kg·℃); T f is the temperature of the fluid, °C; λ f is the thermal conductivity of the fluid in the heat exchange tube, W / (m·℃); Q wall is the heat transferred from geothermal fluid to the heat medium through the heat exchange tube wall, J;

[0042] In formula (4), f D is the Darcy friction factor, according to the Churchill model:

[0043]

[0044] Where Re is the Reynolds number; e is the roughness of the inner tube;

[0045] In formula (5), Q wall :

[0046] Q wall =(hZ) eff (T ext -T f ) (7)

[0047] Where, T ext is the temperature outside the heat exchange tube wall, °C; (hZ) eff is the total equivalent heat transfer coefficient, including the thermal resistance of the tube wall and the convection thermal resistance of the inner and outer walls, W / (m·℃); Z is the circumference of the tube wall, m; h is the forced convection heat transfer coefficient, W / (m 2 ·℃), calculated by formula (8):

[0048]

[0049] Where Nu is the Nusselt number, λ f is the thermal conductivity of the fluid in the heat exchange tube. For a circular tube, (hZ) eff It can be calculated by formula (9):

[0050]

[0051] Where h int is the convection heat transfer coefficient in the tube, W / (m·℃); h extis the convection heat transfer coefficient outside the tube, W / (m·℃); r i With r o are the inner and outer diameters of the circular tube, respectively. The convection heat transfer coefficient inside and outside the tube is expressed by the Nusselt number Nu int and Nu ext calculate:

[0052]

[0053] Where λ g is the thermal conductivity of the fluid outside the heat exchange tube; Nu int It can be calculated by Gnielinski formula:

[0054]

[0055] Where Pr is the Prandtl number, and the applicable range of the equation is: Re = 3000 ~ 6 × 10 6 , Pr = 0.5 ~ 2000. For the natural convection outside the heat exchange tube, it can be calculated by the model proposed by Churchill and Chu:

[0056]

[0057] Where Ra is the Rayleigh number, Ra = Pr Gr; Gr is the dimensionless Grashof number, which represents the ratio of buoyancy to viscous force. The applicable range of formula (12) is Ra < 10 12 ;

[0058] (3) The parallel finite element calculation method is used to combine the rock and soil medium outside the pipe and the circulating fluid medium inside the pipe to obtain the overall control equation group, which is as follows:

[0059] First, the temperature of the fluid inside the pipe and the temperature of the rock and soil outside the pipe are calculated separately. Then, the parallel finite element method is used to jointly solve the temperatures between different media according to the physical field to obtain the transient temperature changes of the fluid in the calculation model and the transient temperature changes in the rock and soil.

[0060] The specific steps in step five are:

[0061] (1) The outlet temperature and heat transfer capacity under different conditions are obtained by changing different operating parameters. Different operating parameters are factors that affect the heat transfer characteristics of the buried pipe. The operating parameters include well parameters and operating parameters. The well parameters include the thermal conductivity of rock and soil stratification, rock and soil density and specific heat capacity, thermal conductivity of backfill materials, groundwater seepage velocity, aquifer location, and geothermal gradient; the operating parameters include the injection temperature of the circulating fluid, the injection flow rate, and the system operation time.

[0062] (2) Using the grey correlation analysis method, the influence degree of each factor on thermal mining efficiency is ranked;

[0063] (3) Orthogonal test method was used for random grouping, and the optimal parameter combination was obtained based on heat transfer capacity and heat transfer efficiency.

[0064] The present invention also includes:

[0065] A system includes a processor capable of running the method of simulating heat storage of a buried pipe well group in a geothermal reservoir.

[0066] A device comprising:

[0067] Memory: used to store a computer program for simulating the method of heat storage in a buried pipe well group in a geothermal reservoir;

[0068] Processor: used to implement the method of simulating heat storage of buried pipe wells in a geothermal reservoir when executing the computer program.

[0069] A computer-readable storage medium stores a computer program, which, when executed by a processor, implements the method for simulating heat storage in a buried pipe well group in a geothermal reservoir.

[0070] Compared with the prior art, the present invention has the following beneficial effects:

[0071] 1. The staggered arrangement of the well group pipes in step 1 of the present invention makes the spacing between the buried pipes more reasonable and minimizes thermal interference. This pipe arrangement increases the contact area between the buried pipes and the soil, improves the heat exchange efficiency, and provides strong support for improving the performance of the buried pipe well group heat storage system;

[0072] 2. In step 2 of the present invention, line units are used instead of pipe volume units, which greatly reduces the amount of calculation. While simplifying the calculation, it can more accurately capture the heat transfer characteristics of the fluid in the pipe.

[0073] 3. Step 5 of the present invention combines the numerical model after multi-physics field coupling to conduct factor sensitivity analysis by varying different well parameters and operating parameters. Using grey correlation analysis to rank key parameters, it is possible to more accurately analyze the impact of different factors on thermal storage efficiency.

[0074] In summary, the present invention uses line units instead of pipe volume units, significantly reducing the amount of calculation while accurately capturing the heat transfer characteristics of the fluid in the pipeline. Secondly, the innovative staggered well group pipe layout method makes the buried pipe spacing more reasonable, minimizes thermal interference, increases the contact area with the soil, and improves heat exchange efficiency. Finally, a multi-physics field coupling numerical model is combined to conduct factor sensitivity analysis, and key parameters are ranked through gray correlation analysis, deeply analyzing the impact of different factors on heat storage efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0075] Figure 1 This is the flow chart of the numerical calculation of heat storage in underground pipe wells.

[0076] Figure 2 This is a schematic diagram of the cross-pipe arrangement of the well group heat storage, where: Figure 2 (a) is a schematic diagram of the cross section of the well group; Figure 2 (b) is a schematic diagram of the grid division of the well group cross section.

[0077] Figure 3 This is the effect diagram of the heat storage simulation of the well group.

[0078] Figure 4 This is a schematic diagram of modeling using line units instead of pipeline volume units in well group heat storage, and a diagram of the simulation effect of well group heat storage.

[0079] Figure 5 This is a comparison chart of the outlet temperatures of each wellhead in sequential and cross-arranged well groups.

[0080] Figure 6 Correlation diagram of heat storage rate of different parameters of well group heat storage. DETAILED DESCRIPTION

[0081] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0082] Reference Figure 1 A method for simulating heat storage in a buried pipe well group in a geothermal reservoir comprises the following steps:

[0083] Step 1: Optimize the layout of the underground pipe wells, using a staggered arrangement instead of the traditional sequential arrangement to make the spacing between the underground pipes more reasonable, thereby minimizing thermal interference;

[0084] In step 1, the specific steps for optimizing the well group pipe layout are:

[0085] (1) First, a thermal interference analysis was conducted on the existing sequential arrangement method to clarify the overlap of heat exchange areas between adjacent buried pipes when interference occurs. The optimal spacing between the buried pipes was then re-determined based on numerical simulation.

[0086] (2) Based on the optimal spacing between buried pipes, the staggered arrangement design scheme is as follows Figure 2 、 Figure 3 shown.

[0087] Step 2: Simplify the pipe volume unit by using the parallel finite element method to discretize the pipe volume unit, and simplify the circulating fluid in the U-shaped tube and the tube wall into a one-dimensional heat exchange tube;

[0088] Reference Figure 4 In the step 2, the specific steps of simplifying the pipeline volume unit are as follows:

[0089] (1) Using the parallel finite element method, the circulating fluid in the U-shaped tube and the tube wall are discretized to form a one-dimensional linear finite element unit;

[0090] (2) Inserting U-shaped circular arc curve elements between discrete one-dimensional linear finite element grids;

[0091] (3) The one-dimensional linear finite element unit and the U-shaped arc curve unit are renumbered so that the finite element unit number and the node number are continuous, thereby forming a simplified one-dimensional heat exchange tube, namely, a one-dimensional heat exchange tube simplified unit.

[0092] Step 3: Establish a pipeline flow model in the 3D modeling. Use one-dimensional linear units to model the pipeline as a curve in the 3D model. Coupling the linear unit nodes with the 3D mesh units outside the pipe is beneficial for meshing the finite diameter 3D pipeline.

[0093] In step 3, the specific steps of constructing the pipeline flow model are:

[0094] (1) Use 3D modeling to build the wellbore and backfill material;

[0095] (2) The outside of the tube is still in three-dimensional form, and the inside and wall of the tube are simplified using one-dimensional heat exchange tube units, that is, the tube is modeled as a curve in the three-dimensional model to obtain a geometric model;

[0096] (3) Input the working condition parameters into the geometric model and give them physical meaning, establish the overall layered rock and soil seepage model, and obtain the pipeline flow model.

[0097] Step 4: Outside the tube, calculate the temperature response in the geotechnical medium by solving the transient three-dimensional heat conduction or heat-permeability coupling equation. Inside the tube, couple the flow equation and energy equation of the circulating fluid medium to calculate the temperature and velocity distribution of the fluid in the U-tube. Finally, use the parallel finite element calculation method in the pipeline flow model to jointly solve the fluid flow and convective heat transfer in the U-tube as well as the heat conduction problem of the tube wall.

[0098] In step 4, the specific steps of using the parallel finite element calculation method to integrate the fluid flow and heat transfer modules are as follows:

[0099] (1) In the part outside the pipe, the energy equation of the rock and soil medium outside the pipe is established based on the porous media heat transfer theory, where the rock and soil medium includes the backfill material in the surrounding hole and the underground stratification and seepage rock and soil medium outside the hole; the energy equation of the rock and soil medium outside the pipe is expressed as:

[0100]

[0101] Where, ρ g is the reservoir fluid density, kg / m 3;c p,g is the constant-pressure specific heat capacity of the formation fluid, J / (kg·K); T w is the formation fluid temperature, °C; u g is the reservoir fluid velocity, m / s; λ g is the thermal conductivity of the fluid outside the heat exchange tube; Q wall The heat transferred from geothermal fluid to the heat medium through the heat exchange tube wall, J.

[0102]

[0103] Where, (ρc p ) eff is the effective specific heat capacity at constant pressure, J / (℃·m 3 );λ eff is the effective thermal conductivity, W / (m·℃); T r is the formation temperature.

[0104] (2) In the pipe part, the flow equation and energy equation of the fluid in the pipe are established according to the non-isothermal pipe flow theory, and the flow state and stress distribution of the fluid in the U-shaped pipe are obtained;

[0105] The flow equation is shown in equations (3) and (4):

[0106]

[0107] The energy equation is shown in formula (5):

[0108]

[0109] Where A p is the cross-sectional area of the heat exchange tube, m 2 ρ f is the fluid density, kg / m 3 ;u f is the fluid velocity, m / s; p is the well pressure, Pa; d p is the inner diameter of the tube, m; c p,f is the constant pressure specific heat capacity of the fluid, J / (kg·℃); T f is the temperature of the fluid, °C; λ f is the thermal conductivity of the fluid in the heat exchange tube, W / (m·℃); Q wall The heat transferred from geothermal fluid to the heat medium through the heat exchange tube wall, J.

[0110] In formula (4), f D is the Darcy friction factor, according to the Churchill model:

[0111]

[0112] Where Re is the Reynolds number; e is the roughness of the inner tube.

[0113] In formula (5), Q wall :

[0114] Q wall =(hZ) eff (T ext -T f ) (7)

[0115] Where, T ext is the temperature outside the heat exchange tube wall, °C; (hZ) eff is the total equivalent heat transfer coefficient, including the thermal resistance of the tube wall and the convection thermal resistance of the inner and outer walls, W / (m·℃); Z is the circumference of the tube wall, m; h is the forced convection heat transfer coefficient, W / (m 2 ·℃), calculated by formula (8):

[0116]

[0117] Where Nu is the Nusselt number, λ f is the thermal conductivity of the fluid in the heat exchange tube. For a circular tube, (hZ) eff It can be calculated by formula (9):

[0118]

[0119] Where h int is the convection heat transfer coefficient in the tube, W / (m·℃); h ext is the convection heat transfer coefficient outside the tube, W / (m·℃); r i With r o are the inner and outer diameters of the circular tube respectively. The convection heat transfer coefficient inside and outside the tube is calculated by the Nusselt number Nu int and Nu ext calculate:

[0120]

[0121] Where λ g is the thermal conductivity of the fluid outside the heat exchange tube; Nu int It can be calculated by Gnielinski formula:

[0122]

[0123] Where Pr is the Prandtl number, and the applicable range of the equation is: Re = 3000 ~ 6 × 10 6 , Pr = 0.5 ~ 2000. For the natural convection outside the heat exchange tube, it can be calculated by the model proposed by Churchill and Chu:

[0124]

[0125] Where Ra is the Rayleigh number, Ra = Pr Gr; Gr is the dimensionless Grashof number, which represents the ratio of buoyancy to viscous force. The applicable range of formula (12) is Ra < 10 12 .

[0126] (3) The parallel finite element calculation method is used to combine the rock and soil medium outside the pipe and the circulating fluid medium inside the pipe to obtain the overall control equation group, which is as follows:

[0127] First, the temperature of the fluid inside the pipe and the temperature of the rock and soil outside the pipe are calculated separately. Then, the parallel finite element method is used to jointly solve the temperatures between different media according to the physical field to obtain the transient temperature changes of the fluid in the calculation model and the transient temperature changes in the rock and soil.

[0128] The specific steps to obtain the overall control equations include:

[0129] ①Evenly distribute the one-dimensional linear finite element units and the three-dimensional tetrahedral finite element units to each processor in the parallel computing system;

[0130] ② Calculate the fluid temperature inside the pipe and the rock and soil temperature outside the pipe on each processor;

[0131] ③ Using the parallel finite element method, the temperatures between different media are jointly solved according to the physical field in the parallel computing system to obtain the overall control equations.

[0132] The specific steps of using the parallel finite element calculation method to solve the temperature and velocity distribution of the fluid in the U-shaped tube and the temperature response in the rock and soil are as follows:

[0133] (1) Using parallel computing methods, solve the overall control equations of the computational model to obtain the transient temperature changes, velocity changes of the fluid in the computational model, and the transient temperature changes in the rock and soil;

[0134] (2) transmitting the calculated temperature and speed change data to each processor in the parallel computing system;

[0135] (3) Post-processing is performed on each processor to calculate the temperature and velocity distribution of the fluid in the model and the temperature response in the rock and soil.

[0136] Step 5. By simulating the traditional well group sequential arrangement and the innovative cross arrangement, the temperature distribution characteristics under the same operating conditions are compared and analyzed. On this basis, by changing different well parameters and operating parameters, the factor sensitivity analysis is carried out to comprehensively study the influence of the thermal physical properties of rock and soil and the heat exchange characteristics of buried pipes on the heat storage efficiency of geothermal reservoirs.

[0137] In step 5, the specific steps for comparing the two schemes of conventional well group sequential arrangement and innovative cross arrangement are as follows:

[0138] (1) The same operating conditions were set for both the conventional well group sequential arrangement and the innovative cross arrangement schemes;

[0139] (2) Simulate the two layout schemes, record their temperature distribution and compare them (e.g. Figure 5 shown).

[0140] In step 5, the specific steps for performing factor sensitivity analysis by changing different well parameters and operating parameters are as follows:

[0141] (1) The outlet temperature and heat transfer capacity under different conditions are obtained by changing different operating parameters. Different operating parameters are factors that affect the heat transfer characteristics of the buried pipe. The operating parameters include well parameters and operating parameters. The well parameters include the thermal conductivity of rock and soil stratification, rock and soil density and specific heat capacity, thermal conductivity of backfill materials, groundwater seepage velocity, aquifer location, and geothermal gradient; the operating parameters include the injection temperature of the circulating fluid, the injection flow rate, and the system operation time.

[0142] By changing different parameters, the outlet temperature and heat transfer under different conditions can be obtained. The expressions are:

[0143] Q r =c×m×Δt=1.163×Q×Δt (13)

[0144] Where: Q r is the heat transfer capacity, kW; c is the specific heat capacity of the circulating fluid, J / (kg·℃); Q is the flow rate, m 3 / h; Δt is the water temperature difference between the inlet and outlet, ℃.

[0145] In step 5, the specific steps of comprehensively studying the influence of geothermal thermal physical parameters and buried pipe heat exchange characteristics on the heat extraction efficiency of geothermal reservoirs are as follows:

[0146] (1) Using the grey correlation analysis method, the influence degree of each factor on thermal mining efficiency is ranked (e.g. Figure 6 shown);

[0147] (2) Orthogonal test method was used for random grouping, and the optimal parameter combination was obtained based on heat transfer capacity and heat transfer efficiency.

[0148] The present invention also includes:

[0149] A system includes a processor capable of running the method of simulating heat storage of a buried pipe well group in a geothermal reservoir.

[0150] A device comprising:

[0151] Memory: used to store a computer program for simulating the method of heat storage in a buried pipe well group in a geothermal reservoir;

[0152] Processor: used to implement the method of simulating heat storage of buried pipe wells in a geothermal reservoir when executing the computer program.

[0153] A computer-readable storage medium stores a computer program, which, when executed by a processor, implements the method for simulating heat storage in a buried pipe well group in a geothermal reservoir.

Claims

1. A method for simulating heat storage in a buried pipe well group in a geothermal reservoir, characterized in that: The following steps are involved: Step 1: Optimization of underground pipe well groups The buried U-shaped pipes are arranged in a staggered manner; Step 2: Simplify the pipe volume unit The parallel finite element method is used to discretize the buried U-tube volume unit, and the circulating fluid in the U-tube and the tube wall are simplified into a one-dimensional heat exchange tube, that is, a one-dimensional heat exchange tube simplified unit. Step 3: Pipeline flow model construction Establish a pipeline flow model in the three-dimensional modeling, and use the one-dimensional heat exchange tube simplified unit to model the pipeline as a curve in the three-dimensional model; Step 4: Jointly solve the inside and outside of the tube Outside the pipe, the temperature response in the geotechnical 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 are coupled to calculate the temperature and velocity distribution of the fluid inside the U-shaped pipe. Finally, a parallel finite element calculation method is used in the pipeline flow model to jointly solve the inside and outside of the pipe. Step 5: Perform sensitivity analysis by changing different operating parameters By changing different well parameters and operating parameters, factor sensitivity analysis is performed to obtain the optimal parameter combination.

2. A method for simulating heat storage in a buried tube well group in a geothermal reservoir according to claim 1, characterized in that: The specific steps for optimizing the buried pipe well group in step 1 are as follows: (1) First, a thermal interference analysis was conducted on the existing sequential arrangement method to clarify the overlap of heat exchange areas between adjacent buried pipes when interference occurs. The optimal spacing between the buried pipes was then re-determined based on numerical simulation. (2) Based on the optimal spacing between buried pipes, the buried U-shaped pipes are arranged in a staggered manner.

3. A method for simulating heat storage in a buried tube well group in a geothermal reservoir according to claim 1, characterized in that: The specific steps of simplifying the pipeline volume unit in step 2 are as follows: (1) Using the parallel finite element method, the circulating fluid in the U-shaped tube and the tube wall are discretized to form a one-dimensional linear finite element unit; (2) Inserting U-shaped circular arc curve elements between discrete one-dimensional linear finite element grids; (3) The one-dimensional linear finite element unit and the U-shaped arc curve unit are renumbered so that the finite element unit number and the node number are continuous, thereby forming a simplified one-dimensional heat exchange tube, namely, a one-dimensional heat exchange tube simplified unit.

4. A method for simulating heat storage in a buried tube well group in a geothermal reservoir according to claim 1, characterized in that: The specific steps of constructing the pipeline flow model in step 3 are: (1) Use 3D modeling to build the wellbore and backfill material; (2) The outside of the tube is still in three-dimensional form, and the inside and wall of the tube are simplified using one-dimensional heat exchange tube units, that is, the tube is modeled as a curve in the three-dimensional model to obtain a geometric model; (3) Input the working condition parameters into the geometric model and give them physical meaning, establish the overall layered rock and soil seepage model, and obtain the pipeline flow model.

5. A method for simulating heat storage in a buried tube well group in a geothermal reservoir according to claim 1, characterized in that: The specific steps in step 4 are: (1) In the part outside the pipe, the energy equation of the rock and soil medium outside the pipe is established based on the porous media heat transfer theory, where the rock and soil medium includes the backfill material in the surrounding hole and the underground stratification and seepage rock and soil medium outside the hole; the energy equation of the rock and soil medium outside the pipe is expressed as: Where, ρ g is the reservoir fluid density, kg / m 3 ;c p,g is the constant-pressure specific heat capacity of the formation fluid, J / (kg·K); T w is the formation fluid temperature, °C; u g is the reservoir fluid velocity, m / s; λ g is the thermal conductivity of the fluid outside the heat exchange tube; Q wall is the heat transferred from geothermal fluid to the heat medium through the heat exchange tube wall, J; Where, (ρc p ) eff is the effective specific heat capacity at constant pressure, J / (℃·m 3 );λ eff is the effective thermal conductivity, W / (m·℃); T r is the formation temperature; (2) In the pipe part, the flow equation and energy equation of the fluid in the pipe are established according to the non-isothermal pipe flow theory, and the flow state and stress distribution of the fluid in the U-shaped pipe are obtained; The flow equation is shown in equations (3) and (4): The energy equation is shown in formula (5): (5) Where A p is the cross-sectional area of the heat exchange tube, m 2 ; ρ f is the fluid density, kg / m 3 ;u f is the fluid velocity, m / s; p is the well pressure, Pa; d p is the inner diameter of the tube, m; c p,f is the constant pressure specific heat capacity of the fluid, J / (kg·℃); T f is the temperature of the fluid, °C; λ f is the thermal conductivity of the fluid in the heat exchange tube, W / (m·℃); Q wall is the heat transferred from geothermal fluid to the heat medium through the heat exchange tube wall, J; In formula (4), f D is the Darcy friction factor, according to the Churchill model: Where Re is the Reynolds number; e is the roughness of the inner tube; In formula (5), Q wall : Q wall =(hZ) eff (T ext -T f ) (7) Where, T ext is the temperature outside the heat exchange tube wall, °C; (hZ) eff is the total equivalent heat transfer coefficient, including the thermal resistance of the tube wall and the convection thermal resistance of the inner and outer walls, W / (m·℃); Z is the circumference of the tube wall, m; h is the forced convection heat transfer coefficient, W / (m 2 ·℃), calculated by formula (8): Where Nu is the Nusselt number, λ f is the thermal conductivity of the fluid in the heat exchange tube; for circular tubes, (hZ) eff It can be calculated by formula (9): Where h int is the convection heat transfer coefficient in the tube, W / (m·℃); h ext is the convection heat transfer coefficient outside the tube, W / (m·℃); r i With r o are the inner and outer diameters of the circular tube, respectively. The convection heat transfer coefficient inside and outside the tube is expressed by the Nusselt number Nu int and Nu ext calculate: Where λ g is the thermal conductivity of the fluid outside the heat exchange tube; Nu int It can be calculated by Gnielinski formula: Where Pr is the Prandtl number, and the applicable range of the equation is: Re = 3000 ~ 6 × 10 6 , Pr = 0.5 ~ 2000; For the natural convection outside the heat exchange tube, it can be calculated by the model proposed by Churchill and Chu: Where Ra is the Rayleigh number, Ra = Pr Gr; Gr is the dimensionless Grashof number, which represents the ratio of buoyancy to viscous force. The applicable range of formula (12) is Ra < 10 12 ; (3) The parallel finite element calculation method is used to combine the rock and soil medium outside the pipe and the circulating fluid medium inside the pipe to obtain the overall control equation group, which is as follows: First, the temperature of the fluid inside the pipe and the temperature of the rock and soil outside the pipe are calculated separately. Then, the parallel finite element method is used to jointly solve the temperatures between different media according to the physical field to obtain the transient temperature changes of the fluid in the calculation model and the transient temperature changes in the rock and soil.

6. A method for simulating heat storage in a buried tube well group in a geothermal reservoir according to claim 1, characterized in that: The specific steps in step five are: (1) The outlet temperature and heat transfer capacity under different conditions are obtained by changing different operating parameters. Different operating parameters are factors that affect the heat transfer characteristics of the buried pipe. The operating parameters include well parameters and operating parameters. The well parameters include the thermal conductivity of rock and soil stratification, rock and soil density and specific heat capacity, thermal conductivity of backfill materials, groundwater seepage velocity, aquifer location, and geothermal gradient; the operating parameters include the injection temperature of the circulating fluid, the injection flow rate, and the system operation time. (2) Using the grey correlation analysis method, the influence degree of each factor on thermal mining efficiency is ranked; (3) Orthogonal test method was used for random grouping, and the optimal parameter combination was obtained based on heat transfer capacity and heat transfer efficiency.

7. A system, characterized in that: The invention comprises a processor capable of executing the method for simulating heat storage of a buried pipe well group in a geothermal reservoir as described in any one of claims 1 to 5.

8. A device, characterized in that include: Memory: a computer program for storing the method for simulating heat storage in a buried tube well group in a geothermal reservoir as described in any one of claims 1 to 5; Processor: used to implement the method of simulating heat storage in a group of buried pipe wells in a geothermal reservoir when executing the computer program described in any one of claims 1-5.

9. A computer-readable storage medium, characterized in that The computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the method for simulating heat storage in a buried pipe well group in a geothermal reservoir as described in any one of claims 1 to 5 is implemented.

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