Method for parallel computing simulation of buried pipe well group thermal exploitation in geothermal reservoir

Abstract

The invention discloses a parallel computing simulation method for thermal exploitation of a buried pipe well group in a geothermal reservoir, which comprises the following steps of: dispersing a grid volume unit of a buried pipe by adopting a parallel finite element unit method, and simplifying the buried pipe and circulating fluid in the pipe into a one-dimensional linear finite element unit; constructing a plurality of pipeline flow models arranged in an array, and combining the in-pipe one-dimensional linear units and the out-pipe three-dimensional volume units to obtain a well group type pipeline flow geometric model; a parallel finite element unit method is adopted to be combined with a non-isothermal pipeline flow physical field, an underground water seepage physical field and a porous medium heat transfer physical field to conduct multi-physical-field coupling, and a well group type pipeline flow numerical model is obtained; fluid flow and convective heat transfer in the buried pipe and pipe wall heat conduction are solved in a combined mode; and performing factor sensitivity analysis by changing different thermophysical parameters of the rock-soil body and heat exchange characteristic factors of the buried pipe well group. The invention provides a new method for researching fluid flowing and heat transfer behaviors of the buried pipe well group, and provides a new idea for optimal design and efficient simulation of thermal exploitation of the buried pipe well group in a geothermal reservoir.

Description

Technical Field

[0001] The present invention relates to the technical field of thermal exploitation of geothermal reservoirs, and particularly to a method for parallel computing and simulating the thermal exploitation of a buried pipe well group in a geothermal reservoir, which is used to analyze the thermal exploitation conditions of a buried pipe well group composed of multiple buried pipes under different stratifications and seepage conditions of the rock and soil mass. Background Art

[0002] The heat extraction process of buried pipes in a geothermal reservoir is a complex unsteady process with a large spatial area span and a long action time. By establishing theoretical and numerical models for the thermal exploitation of a buried pipe well group under the stratification and seepage conditions of the rock and soil mass in the geothermal reservoir, the heat extraction process of the buried pipe well group under actual complex geological conditions can be more accurately described, and the long-term performance of the ground source heat pump system under complex conditions can be scientifically predicted, providing a theoretical basis and technical support for the optimal design and efficient operation of the ground source heat pump system.

[0003] Actual ground source heat pump projects usually form a buried pipe well group composed of dozens or even hundreds of buried pipes. When the well group exists, heat transfer interference phenomena will occur between adjacent buried pipes, which has an important impact on the efficient operation of the ground source heat pump system. Relevant scholars have conducted relevant research on the heat transfer characteristics of buried pipe well groups under homogeneous conditions. However, due to the differences in the thermal physical properties of each layer in the stratified rock and soil mass, it will inevitably have different effects on the heat transfer law between the buried pipes in the well group. Therefore, it is necessary to study the temperature response law in the stratified rock and soil mass under the action of the pipe group to provide a reference for the design and operation of actual buried pipe well group projects.

[0004] A well group system composed of multiple vertical buried pipe heat exchangers generally consists of single U or double U-shaped high-density polyethylene pipes placed in boreholes with a depth of 20 - 200m and a diameter of 0.15 - 0.75m and the surrounding backfill materials. In numerical calculations, if the conventional grid division method is used to deal with the flow and heat transfer problems in the well group, a large number of grids are inevitably required, resulting in excessive consumption of computing resources and time; and usually, for this slender structure during grid division, it is generally difficult to ensure the grid quality, resulting in difficulties in the convergence of the calculation results.

[0005] In view of this, the present invention is specifically proposed to provide a reference for improving and developing the existing numerical model for heat exchange of buried pipe well groups. Summary of the Invention

[0006] To solve the above problems, the present invention proposes a method for parallel computing and simulating the thermal exploitation of a buried pipe well group in a geothermal reservoir, which provides a new method for the research on the fluid flow and heat transfer behavior of the buried pipe well group, and provides a new idea for the optimal design and efficient simulation of the thermal exploitation of the buried pipe well group in the geothermal reservoir.

[0007] This method is based on the following two understandings: (1) The finite element numerical method adopted is applicable to the coupling of one-dimensional linear elements inside the pipes and three-dimensional volume elements outside the pipes in the buried pipe well group; (2) The parallel finite element method is used to synthesize the fluid flow, aquifer seepage, and porous medium heat transfer modules to jointly solve the fluid flow, convective heat transfer, and heat conduction through the pipe wall problems in the buried pipe well group, improving the solution efficiency of the three-dimensional finite element numerical model.

[0008] The present invention is implemented as follows:

[0009] A method for parallel computing to simulate the thermal exploitation of buried pipe well groups in a geothermal reservoir, comprising: discretizing the volume elements of the buried pipe grid using the parallel finite element method, and simplifying the buried pipes and the circulating fluid inside the pipes into one-dimensional linear finite elements; constructing a plurality of pipe flow models arranged in an array, the array arrangement including a sequentially arranged pipe well group and a cross-arranged pipe well group, using the one-dimensional linear elements to model the pipes as curves in a three-dimensional model, and combining the one-dimensional linear elements inside the pipes and the three-dimensional volume elements outside the pipes to obtain a pipe flow geometric model of the well group; using the parallel finite element method to couple multiple physical fields of the pipe flow geometric model of the well group with the non-isothermal pipe flow physical field, groundwater seepage physical field, and porous medium heat transfer physical field to obtain a numerical model of the pipe flow of the well group; based on the numerical model of the pipe flow of the well group, jointly solving the fluid flow, convective heat transfer, and heat conduction through the pipe wall inside the buried pipes to obtain a numerical model with a real temperature distribution and capable of reflecting the heat exchange process of the buried pipe well group; changing different geotechnical thermal property parameters and heat exchange characteristic factors of the buried pipe well group for factor sensitivity analysis, and analyzing the influence of geotechnical thermal property parameters and heat exchange characteristic factors of the buried pipe well group on the thermal exploitation efficiency of the geothermal reservoir from the solved numerical model of the pipe flow of the well group.

[0010] This method utilizes the porous medium heat transfer theory, non-isothermal pipe flow theory, finite element method, and numerical analysis principle. Among them, the porous medium heat transfer theory and non-isothermal pipe flow theory are used for the coupled calculation of multiple physical fields, mainly calculating the parameters of different physical fields separately and finally integrating them. The finite element method is used to simplify the volume elements in the model into line elements, facilitating the calculation of model problems with a large difference in geometric orders of magnitude. The numerical analysis principle mainly optimizes the errors generated during the element simplification process. This method considers the seepage heat transfer problem between the buried pipe heat exchanger and the surrounding stratified geotechnical medium, couples multiple physical fields such as porous medium heat transfer, groundwater seepage, and fluid flow inside the pipe, providing convenience for the fluid flow and heat transfer analysis of the buried pipe well group system.

[0011] The beneficial effects of the present invention compared with the prior art at least include: A method for parallel computing to simulate the thermal extraction of a buried pipe well group in a geothermal reservoir provided by the present invention takes into account the heat transfer problem of seepage in the buried pipe heat exchanger and the surrounding stratified rock and soil media, couples multiple physical fields such as heat transfer in porous media, groundwater seepage, and fluid flow inside the pipeline, and facilitates the fluid flow and heat transfer analysis of the buried pipe well group system. Compared with the prior art, it has at least the following advantages:

[0012] 1. This method utilizes the heat transfer theory of porous media, non-isothermal pipe flow theory, finite element method, and numerical analysis principle. Among them, the heat transfer theory of porous media and non-isothermal pipe flow theory are used for the coupled calculation of multiple physical fields, mainly calculating the parameters of different physical fields separately and finally integrating them. The finite element method is used to simplify the volume elements in the model into line elements, facilitating the calculation of model problems with a large difference in geometric orders of magnitude. The numerical analysis principle mainly optimizes the errors generated during the unit simplification process reasonably.

[0013] 2. In grid processing, a well group type pipe flow geometric model is constructed. The three-dimensional pipe volume element is explicitly represented by one-dimensional linear elements, and the coupling is carried out through one-dimensional linear elements inside the pipe and three-dimensional volume elements outside the pipe. While ensuring the accuracy of the calculation results, it can change the problem of low grid quality caused by the large length-diameter ratio of the heat exchange pipe, and solve the three-dimensional finite element numerical model in parallel, significantly improving the calculation efficiency.

[0014] 3. Creatively, on the basis of the sequential pipe layout method, a cross pipe layout method is adopted, which can not only improve the quality of grid element division, but also make the spacing between each buried pipe more reasonable, reduce the influence of thermal interference on the entire system, and thus improve the heat exchange efficiency.

[0015] 4. By simultaneously solving the control equations for heat transfer in porous media, groundwater seepage, and non-isothermal pipe fluid flow, it can effectively simulate the heat exchange process between the overall buried pipe well group system and the geothermal reservoir, and can jointly solve the problems of fluid flow and convective heat transfer inside the pipe and heat conduction of the pipe wall.

[0016] 5. The overall model adopts the parallel finite element method from numerical discretization, solution to post-processing of the results, improving the solution efficiency of the three-dimensional finite element numerical model.

[0017] 6. The method provided by the present invention provides a new method for the research of the fluid flow and heat transfer behavior of the buried pipe well group, and provides new ideas for the optimized design and efficient simulation of the thermal extraction of the buried pipe well group in the geothermal reservoir.

[0018] It should be understood that the implementation of any embodiment of the present invention does not mean that multiple or all of the above beneficial effects need to be simultaneously possessed or achieved. Description of the Drawings

[0019] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only exemplary. For those of ordinary skill in the art, without creative efforts, other implementation drawings can be obtained by extending according to the provided drawings.

[0020] The structures, ratios, sizes, etc. shown in this specification are only used to cooperate with the content disclosed in the specification for those familiar with this technology to understand and read, and are not used to limit the limiting conditions for the implementation of the present invention. Therefore, they do not have substantial technical significance. Any modification of the structure, change in the proportional relationship, or adjustment of the size, without affecting the effects that the present invention can produce and the purposes that can be achieved, should still fall within the scope covered by the technical content disclosed in the present invention.

[0021] Figure 1 Exemplarily shows the calculation flow chart of the present invention for solving the heat transfer model of the buried pipe well group using the parallel finite element method.

[0022] Figure 2 Exemplarily shows the schematic diagram of the coupling of the one-dimensional linear element inside the pipe and the three-dimensional volume element outside the pipe of the present invention.

[0023] Figure 3A Exemplarily shows the schematic diagram of the geometric modeling of the buried pipe well group system of the present invention (cross-sectional view of the sequentially arranged pipe well group).

[0024] Figure 3B Exemplarily shows the schematic diagram of the geometric modeling of the buried pipe well group system of the present invention (cross-sectional view of the cross-arranged pipe well group).

[0025] Figure 4A Exemplarily shows the overall mesh division diagram of the buried pipe well group system of the present invention (mesh division of the sequentially arranged pipe well group system).

[0026] Figure 4B Exemplarily shows the overall mesh division diagram of the buried pipe well group system of the present invention (mesh division of the cross-arranged pipe well group system).

[0027] Figure 5 Exemplarily shows that the present invention has a seepage velocity of 50 m / a (1.59×10 -6 m / s), and the schematic diagram of the change of the outlet temperature of the buried pipes at different positions in the sequentially arranged and cross-arranged pipe well groups.

[0028] Figure 6 Exemplarily shows that the present invention has a seepage velocity of 50 m / a (1.59×10 -6Schematic diagram of the temperature distribution curve of the internal circulating fluid along the well depth in different positions of the buried pipe in the sequential arrangement and cross arrangement pipe well groups under the condition of

[0029] In each of the accompanying drawings, the same or corresponding reference numerals denote the same or corresponding parts. Detailed implementation manners

[0030] In order to make the objectives, technical solutions and advantages of the embodiments of the present invention clearer and more understandable, the embodiments of the present invention will be further described in detail below with reference to the embodiments and the accompanying drawings. Herein, the illustrative embodiments of the present invention and their descriptions are used to explain the present invention, but not to limit the present invention.

[0031] It should be understood that the terms "include / comprise", "consist of" or any other variant is intended to cover non-exclusive inclusion, so that a product, device, process or method including a series of elements not only includes those elements, but also includes other elements that are not explicitly listed when necessary, or further includes elements inherent to such product, device, process or method. Without further limitation, the elements defined by the statement "include / comprise..." or "consist of..." do not exclude the existence of additional identical elements in the product, device, process or method including the said elements.

[0032] It should also be understood that the terms "upper", "lower", "front", "rear", "left", "right", "top", "bottom", "inner", "outer", etc. indicating the orientation or position relationship are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device, component or structure referred to must have a specific orientation, be constructed or operated in a specific orientation, and cannot be construed as a limitation to the present invention.

[0033] The specific implementation and the preferred preferred solutions of the method will be elaborated in detail below with reference to specific embodiments and the accompanying drawings.

[0034] The overall flow steps of the method are referred to Figure 1 , and mainly include:

[0035] Step 1: Simplification of the pipeline volume unit:

[0036] The parallel finite element method is used to discretize the buried pipe grid volume unit, and the buried pipe and the circulating fluid in the pipe are simplified into one-dimensional linear finite elements;

[0037] Specifically, in Step 1, the specific steps of the simplification of the pipeline volume unit are as follows, referring to Figure 2 :

[0038] (1) Use one-dimensional linear finite elements to discretize the vertical pipe medium;

[0039] (2) Insert U-shaped circular arc curve elements between discrete one-dimensional linear finite element meshes;

[0040] (3) Renumber the one-dimensional linear finite element elements and the U-shaped circular arc curve elements so that the numbers of the one-dimensional linear finite element elements and the U-shaped circular arc curve finite element elements are continuous, and allocate each grid volume element to each processor for parallel calculation.

[0041] Step 2: Construction of the geometric model of the well group pipeline flow:

[0042] Construct multiple pipeline flow models arranged in an array. The array arrangement includes a sequentially arranged pipe well group and an intersecting arranged pipe well group. Use one-dimensional linear elements to model the pipeline as a curve in a three-dimensional model, and combine the one-dimensional linear elements inside the pipe and the three-dimensional volume elements outside the pipe to obtain the geometric model of the well group pipeline flow;

[0043] Specifically, in Step 2, the specific steps for constructing the geometric model of the well group pipeline flow are as follows. Refer to Figure 3A 、 3B and Figure 4A 、 4B :

[0044] (1) Use three-dimensional volume elements outside the pipe to establish the wellbore and backfill material parts;

[0045] (2) Divide the overall buried pipe well group into sequential arrangement and intersecting arrangement according to the arrangement method. Among them, the sequential arrangement is a 3×3 array regular arrangement with a pipe layout spacing of 5m, and the intersecting arrangement is a 3×3 adjacent column order alternating cross arrangement with a pipe layout spacing of 5m; the buried pipe numbers are sequentially 1 to 9;

[0046] (3) Describe the seepage heat transfer problem of the buried tube heat exchanger and the surrounding stratified geotechnical medium through the combination of one-dimensional inside the pipe and three-dimensional outside the pipe;

[0047] (4) Establish an overall stratified geotechnical seepage model to obtain the overall model.

[0048] Step 3: Multi-physics field coupling of the geometric model of the well group pipeline flow:

[0049] Adopt the parallel finite element method combined with the non-isothermal pipeline flow physical field, the groundwater seepage physical field, and the porous medium heat transfer physical field to perform multi-physics field coupling on the geometric model of the well group pipeline flow to obtain the numerical model of the well group pipeline flow;

[0050] Specifically, in Step 3, the multi-physics field coupling of the geometric model of the well group pipeline flow is specifically as follows:

[0051] The geometric model of the well group pipeline flow is coupled with the in-pipe part and the out-of-pipe part respectively. The in-pipe part includes the buried pipe and the circulating fluid inside the pipe, and the out-of-pipe part includes the wellbore and the backfill material. The backfill material specifically includes the rock and soil medium (backfill material) inside the wellbore and the rock and soil medium (external soil layer) outside the wellbore.

[0052] Step 4: Solve the numerical model of the well group pipeline flow:

[0053] Based on the numerical model of the well group pipeline flow, the fluid flow, convective heat transfer in the buried pipe, and heat conduction in the pipe wall are jointly solved to obtain a numerical model with a real temperature distribution and capable of reflecting the heat exchange process of the buried pipe well group.

[0054] Specifically, in Step 4, when jointly solving the fluid flow, convective heat transfer in the buried pipe, and heat conduction in the pipe wall, it first includes establishing the overall control equation set, specifically:

[0055] (1) Establish the energy equation of the rock and soil medium outside the pipe according to the heat transfer theory of porous media, and the expression is:

[0056]

[0057] Equation (1) is the heat exchange energy equation of the rock and soil medium (backfill material) inside the hole (inside the wellbore). In the equation, ρ g is the density of the reservoir fluid, kg / m 3 ; c p,g is the specific heat capacity at constant pressure of the reservoir fluid, J / (kg·K); T w is the temperature of the reservoir fluid, °C; u g is the flow velocity of the reservoir fluid, m / s; λ g is the thermal conductivity of the fluid outside the heat exchange pipe, W / (m·°C); Q wall is the heat transferred from the reservoir fluid to the heat extraction working fluid through the heat exchange pipe wall, J. Through Q wall the heat exchange process between the wellbore and the heat exchange pipe can be connected.

[0058]

[0059] Equation (2) is the heat exchange energy equation of the rock and soil medium (external soil layer) outside the hole (outside the wellbore). In the equation, (ρc p ) eff is the effective specific heat capacity at constant pressure, J / (°C·m 3 ); λ eff is the effective thermal conductivity, W / (m·°C); T r is the formation temperature.

[0060] (2) Establish the fluid flow equation and energy equation in the pipe according to the non-isothermal pipeline flow theory, and the expression is:

[0061]

[0062]

[0063] Equations (3) and (4) are flow equations, and Equation (5) is the energy equation. In the equations, 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 flow velocity, m / s; f D is the Darcy friction factor; p is the pressure in the well, Pa; d p is the inner diameter of the tube, m; c p,f is the specific heat capacity of the fluid at constant pressure, J / (kg·°C); T f is the fluid temperature, °C; λ f is the thermal conductivity of the fluid inside the heat exchange tube, W / (m·°C); Q wall is the heat transferred from the reservoir fluid to the heat extraction working fluid through the heat exchange tube wall, J.

[0064] In Equation (4), f D is determined according to the Churchill model:

[0065]

[0066] In the equations, Re is the Reynolds number; e is the inner tube roughness.

[0067] In Equation (5), Q wall is:

[0068] Q wall = (hZ) eff (T ext - T f ) (14)

[0069] In the equations, T ext is the temperature outside the heat exchange tube wall, °C; (hZ) eff is the total equivalent heat transfer coefficient, including the tube wall thermal resistance and the convective heat transfer resistances of the inner and outer walls, W / (m·°C); Z is the perimeter of the tube wall, m; h is the forced convection heat transfer coefficient, W / (m 2 ·°C).

[0070] The above h is calculated by Equation (8):

[0071]

[0072] In the equations, Nu is the Nusselt number, λ f is the thermal conductivity of the fluid inside the heat exchange tube.

[0073] For a circular tube, (hZ) eff can be calculated by Equation (9):

[0074]

[0075] In the formula, h int is the convective heat transfer coefficient inside the tube, W / (m·℃); h ext is the convective heat transfer coefficient outside the tube, W / (m·℃); r i and r o are the inner diameter and outer diameter of the circular tube respectively; λ p is the thermal conductivity of the heat exchange tube, W / (m·℃). h int and h ext These two parameters can be calculated through the Nusselt numbers Nu int and Nu ext :

[0076]

[0077] In the formula, λ g is the thermal conductivity of the fluid outside the heat exchange tube, W / (m·℃); the Nusselt number Nu int can be calculated by the Gnielinski formula:

[0078]

[0079] In the formula, Pr is the Prandtl number, and the applicable range of the equation is: Re = 3000 - 6×10 6 , Pr = 0.5 - 2000.

[0080] For natural convection outside the heat exchange tube, the Nusselt number Nu ext can be calculated by the model proposed by Churchill and Chu:

[0081]

[0082] In the formula, Ra is the Rayleigh number, Ra = Pr·Gr; Gr is the dimensionless Grashof number, representing the ratio of buoyancy to viscous force. The applicable range of Equation (12) is Ra < 10 12 .

[0083] (3) Establish the groundwater seepage control equation inside the reservoir according to Darcy's law, and the expression is:

[0084]

[0085]

[0086] Equation (13) is the mass conservation equation, and Equation (14) is the momentum equation. In the formula, is the reservoir porosity; ρ g is the reservoir fluid density, kg / m 3 ; u g is the reservoir fluid flow velocity, m / s; k is the reservoir permeability, mD; μ is the viscosity of water, Pa·s; g is the acceleration due to gravity, m / s 2 ; is the gravity term. During the heat extraction process of downhole heat exchange, the density of the reservoir fluid in the wellbore will change, thus generating a buoyancy force and triggering the phenomenon of natural convection. Therefore, the gravity term is added to describe the action of the buoyancy force.

[0087] (4) The overall control equations are formed by combining the parallel finite element method.

[0088] The overall control equations are conceptual and can be obtained by coupling with numerical simulation software.

[0089] Specifically, in step four, the fluid flow, convective heat transfer in the buried pipe, and heat conduction in the pipe wall are jointly solved, which further includes: for the inside of the pipe, calculating the temperature and velocity distribution of the fluid in the buried pipe, and for the outside of the pipe, calculating the temperature response in the rock and soil mass. Specifically:

[0090] (1) Using the parallel finite element method, solve the overall control equations of the well group pipeline flow numerical model to obtain the transient temperature change, velocity change of the fluid in the calculation model, and the transient temperature change in the rock and soil mass;

[0091] (2) Transmit the calculated temperature change and velocity change data to each processor 1, 2,..., n in the parallel computing system;

[0092] (3) Perform post-processing on each processor to calculate the temperature distribution of the fluid in the calculation model and the temperature response in the rock and soil mass ( Figure 5 、 Figure 6 ). Figure 5 shows a schematic diagram of the temperature change at the outlet of the buried pipes at different positions in the sequentially arranged and cross-arranged well groups under the condition that the seepage velocity of the present invention is 50 m / a (1.59×10 -6 m / s), Figure 6 shows a schematic diagram of the temperature distribution curve of the internal circulating fluid along the well depth of the buried pipes at different positions in the well group under two arrangement methods. As can be seen from Figure 5 、 Figure 6 , the heat exchange efficiency of the cross-arranged well group is higher than that of the sequentially arranged well group in the position area of some pipes. The specific optimization strategy is: for the heat extraction part concentrated in the corner pipe (No. 1, 3, 7, 9) area, the straight arrangement well position is preferably selected; for the heat extraction part concentrated in the side pipe (No. 2, 4, 6, 8) and the middle pipe (No. 5) area, the cross arrangement well position is preferably selected.

[0093] Step 5. Sensitivity analysis of characteristic factors of well group heat transfer:

[0094] Combined with the numerical model after multi-physical field coupling, factor sensitivity analysis is carried out by changing different geotechnical thermal physical parameters and characteristic factors of the buried pipe well group heat transfer, and the influence of geotechnical thermal physical parameters and characteristic factors of the buried pipe well group heat transfer on the thermal exploitation efficiency of the geothermal reservoir is analyzed.

[0095] Specifically, in Step 5, the specific steps of factor sensitivity analysis by changing different geotechnical thermal physical parameters and characteristic factors of the buried pipe well group heat transfer are as follows:

[0096] (1) Analyze the influence of each factor on the heat transfer characteristics of the buried pipe well group, specifically including the groundwater seepage velocity, injection temperature, injection flow rate, and thermal conductivity of the backfill material;

[0097] (2) Set a reasonable change range for each key parameter, change the value of the key parameter in turn, and keep other parameters unchanged. By changing different parameters, the outlet temperature and heat transfer amount under different conditions are obtained. The expression is:

[0098] Q r = c×m×Δt = 1.163×Q×Δt (22)

[0099] In the formula: Q r is the heat transfer amount, kW; c is the specific heat capacity of the circulating fluid, J / (kg·°C); m is the mass of the circulating fluid, kg; Q is the flow rate, m 3 / h; Δt is the water temperature difference between the inlet and the outlet, °C.

[0100] Finally, determine a reasonable pipe layout method and pipe spacing.

[0101] In addition, the well parameters include the well depth, well diameter, spacing, pipe material, geotechnical thermal physical parameters, etc., and the operation parameters include the operation time, operation mode, fluid injection pressure, etc.

[0102] In summary, a method for parallel computing to simulate the thermal extraction of a buried pipe well group in a geothermal reservoir provided by the present invention mainly includes the following five steps: First, the volume unit of the pipeline is discretized by the parallel finite element method, and the internal circulating fluid and the pipe wall of the buried pipe are simplified into a one-dimensional heat exchange pipe; Second, in grid processing, an array layout of a well group type pipeline flow geometric model is constructed, and the three-dimensional pipeline volume unit is explicitly represented by a one-dimensional linear grid unit, and coupling is carried out through the one-dimensional linear unit inside the pipe and the three-dimensional volume unit outside the pipe; Third, the parallel finite element method is used to combine the non-isothermal pipeline flow physical field, the groundwater seepage physical field, and the porous medium heat transfer physical field to perform multi-physical field coupling on the well group type pipeline flow geometric model to obtain a numerical model of the well group type pipeline flow; Fourth, the fluid flow, convective heat transfer inside the buried pipe, and heat conduction of the pipe wall are jointly solved to obtain a numerical model with a real temperature distribution and capable of reflecting the heat exchange process of the buried pipe well group; Fifth, comprehensively analyze the influence of the thermal physical properties of the rock and soil mass and the heat exchange characteristic factors of the buried pipe well group on the thermal extraction efficiency of the geothermal reservoir. By establishing a method for parallel computing to simulate the thermal extraction of a buried pipe well group in a geothermal reservoir, the model adopted in the present invention considers the seepage heat transfer problem of a well group composed of multiple buried pipes and the surrounding stratified rock and soil mass medium. By coupling multiple physical fields (including heat transfer, seepage, and fluid flow), while ensuring the calculation accuracy, the problem of low grid quality caused by the large length-diameter ratio of the heat exchange pipe is solved. By parallelly solving the three-dimensional finite element numerical model, the calculation efficiency is significantly improved, providing a new method for the research on the fluid flow and heat transfer behavior of the buried pipe well group, and providing a new idea for the optimal design and efficient simulation of the thermal extraction of the buried pipe well group in the geothermal reservoir.

[0103] The embodiments of the present invention have been described above. The above description is exemplary and not exhaustive, and is not limited to the disclosed embodiments. Many modifications and variations are obvious to those of ordinary skill in the art in the technical field without departing from the scope and spirit of the described embodiments.

[0104] Although several specific implementation details are included in the above discussion, these should not be construed as limiting the scope of the present invention. Some features described in the context of a single embodiment can also be implemented in combination in a single implementation. On the contrary, various features described in the context of a single implementation can also be implemented separately or in any suitable sub-combination in multiple implementations.

Claims

1. A method for simulating heat extraction from a group of underground pipe wells in a geothermal reservoir by parallel computing, characterized in that: include: The parallel finite element method is used to discretize the underground pipe grid volume unit, and the underground pipe and the circulating fluid in the pipe are simplified into one-dimensional linear finite element units. Constructing multiple pipeline flow models arranged in an array, wherein the array arrangement includes a sequentially arranged pipe well group and a cross-arranged pipe well group, using a one-dimensional linear unit to model the pipeline as a curve in a three-dimensional model, combining the one-dimensional linear unit inside the pipe and the three-dimensional volume unit outside the pipe to obtain a well group type pipeline flow geometric model; The parallel finite element method is used to combine the non-isothermal pipe flow physics field, groundwater seepage physics field, and porous medium heat transfer physics field to couple the well group pipe flow geometric model with multiple physical fields and obtain the well group pipe flow numerical model. Based on the well group pipeline flow numerical model, the fluid flow and convective heat transfer in the buried pipe and the heat conduction of the pipe wall are jointly solved to obtain a numerical model with real temperature distribution and capable of reflecting the heat exchange process of the buried pipe well group. The sensitivity analysis of factors was carried out by changing different thermophysical properties of rock and soil and heat exchange characteristic factors of buried pipe well group. The influence of thermophysical properties of rock and soil and heat exchange characteristic factors of buried pipe well group on the heat extraction efficiency of geothermal reservoir was analyzed by the solved well group pipeline flow numerical model.

2. The method according to claim 1, characterized in that The parallel finite element method is used to discretize the buried pipe grid volume unit, and the buried pipe and the circulating fluid in the pipe are simplified into a one-dimensional linear finite element unit, specifically: (1) Discretize the vertical pipeline using one-dimensional linear finite element units; (2) inserting U-shaped arc curve finite element elements between discrete one-dimensional linear finite element elements; (3) Renumbering the one-dimensional linear finite element units and the U-shaped circular arc finite element units to make them continuous, and allocating each mesh volume unit to each processor for parallel calculation.

3. The method according to claim 1, characterized in that Construct multiple pipeline flow models arranged in an array, wherein the array arrangement includes a sequentially arranged pipe well group and a cross-arranged pipe well group. Use a one-dimensional linear unit to model the pipeline as a curve in a three-dimensional model, combine the one-dimensional linear unit inside the pipe and the three-dimensional volume unit outside the pipe, and obtain a well group pipeline flow geometric model, specifically: (1) Use the three-dimensional volume unit outside the pipe to establish the wellbore and backfill material part; (2) According to the arrangement mode, the underground pipe well group is divided into a sequential arrangement pipe well group and a cross arrangement pipe well group, wherein the sequential arrangement is a 3×3 array regular arrangement, and the cross arrangement is a 3×3 adjacent column cross arrangement; (3) The seepage heat transfer between the buried pipe heat exchanger and the surrounding layered rock and soil medium is described by combining the one-dimensional linear unit inside the pipe and the three-dimensional volume unit outside the pipe; (4) Establish an overall layered rock and soil seepage model and obtain a well cluster pipeline flow geometry model.

4. The method according to claim 1, characterized in that: Multi-physics coupling is performed on the well cluster pipeline flow geometric model, specifically: The geometric model of well group pipeline flow is coupled with the inner part and the outer part respectively. The inner part includes the buried pipe and the circulating fluid in the pipe, and the outer part includes the wellbore and the backfill material inside the wellbore and the soil layer outside the wellbore.

5. The method according to claim 1, characterized in that The joint solution of fluid flow, convective heat transfer and wall heat conduction in the buried pipe first includes: establishing the overall control equations, specifically: (1) Based on the porous media heat transfer theory, the energy equation of the rock and soil medium outside the pipe is established, including the backfill material in the surrounding hole and the underground stratified and seepage rock and soil medium outside the hole; (2) Based on the non-isothermal pipeline flow theory, the flow equation and energy equation of the fluid medium in the pipe are established to obtain the flow state and stress distribution of the fluid in the buried pipe; (3) Establish the governing equation of groundwater seepage inside the reservoir based on Darcy’s law, including the porous media of the aquifer and the porous media of the seepage layer; (4) The parallel finite element method is used to perform parallel calculations on the rock and soil medium outside the pipe, the fluid medium inside the pipe, and the groundwater seepage layer to obtain the overall control equation group.

6. The method according to claim 5, characterized in that According to the porous media heat transfer theory, the energy equation of the rock and soil medium outside the pipe is established, and the expression is: In the formula, ρ g is the reservoir fluid density, kg / m 3 ;c p,g is the constant pressure specific heat capacity of the reservoir fluid, J / (kg·K); T w is the reservoir 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, W / (m·℃); Q wall is the heat transferred from the reservoir fluid to the heat extracting medium through the heat exchange tube wall, J; In the formula, (ρc p ) eff is the effective specific heat capacity at constant pressure, J / (℃·m 3 ); eff is the effective thermal conductivity, W / (m·℃); T r is the ground temperature.

7. The method according to claim 5, characterized in that According to the non-isothermal pipe flow theory, the flow equation and energy equation of the fluid medium in the pipe are established, and the expression is: In the formula, 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 flow rate of the fluid, m / s; f D is the Darcy friction factor; 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 the reservoir fluid to the heat extracting medium through the heat exchange tube wall, J.

8. The method according to claim 5, characterized in that According to Darcy's law, the control equation of groundwater seepage inside the reservoir is established, and the expression is: In the formula, is the reservoir porosity; ρ g is the reservoir fluid density, kg / m 3 ;u g is the reservoir fluid velocity, m / s; k is the reservoir permeability, mD; μ is the viscosity of water, Pa·s; g is the gravitational acceleration, m / s 2 ; is the gravity term.

9. The method according to claim 5, characterized in that The joint solution of the fluid flow and convective heat transfer in the buried pipe and the heat conduction of the pipe wall further includes: for the inner part of the pipe, calculating the temperature and velocity distribution of the fluid in the buried pipe, and for the outer part of the pipe, calculating the temperature response in the rock mass, specifically: (1) Using the parallel finite element method, the overall control equations of the well cluster pipeline flow numerical model are solved to obtain the transient temperature change, velocity change of the fluid in the calculation model, and the transient temperature change in the rock and soil; (2) transmitting the calculated temperature change and speed change data to each processor 1, 2, ..., n in the parallel computing system; (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.

10. The method according to claim 1, characterized in that The sensitivity analysis of factors was carried out by changing different geothermal parameters and heat transfer characteristic factors of buried pipe well groups, specifically: (1) Analyze the influence of thermal physical parameters of rock and soil and heat transfer characteristic factors of buried pipe well group on the heat transfer characteristics of buried pipe well group, wherein the thermal physical parameters of rock and soil and heat transfer characteristic factors of buried pipe well group specifically include groundwater seepage velocity, injection temperature, injection flow rate and thermal conductivity of backfill material; (2) Set a reasonable range of variation for each key parameter, change the value of the key parameter in turn, and keep other parameters unchanged. By changing different parameters, the outlet temperature and heat transfer capacity under different conditions are obtained to determine the reasonable pipe layout method and pipe spacing.

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