A method for optimizing design parameters of a carbonate rock geothermal well group

Abstract

The application discloses a kind of carbonate rock geothermal well group design parameter optimization method, it is related to carbonate rock geothermal reservoir development technical field, including based on block geologic model, establish damage mechanics finite element model and geothermal injection-production production multi-field coupling finite element model;Based on damage mechanics finite element model, the distribution characteristics of natural fracture are obtained by trial and error-phenomenon matching;Based on the distribution characteristics of natural fracture, the relationship between damage variable and permeability, the relationship between damage variable and thermal conductivity is introduced into multi-field coupling finite element model, combined with well pattern and construction parameter, displacement field, seepage field and temperature field in the process of geothermal injection-production construction are calculated, and geothermal injection-production design parameter is optimized.Therefore, by using the above-mentioned carbonate rock geothermal well group design parameter optimization method, the influence of natural fractures in geothermal reservoir on geothermal injection-production engineering is considered, and the injection-production water balance can be accurately realized.

Description

Technical Field

[0001] This invention relates to the field of carbonate geothermal reservoir development technology, and in particular to a method for optimizing the design parameters of carbonate geothermal well groups. Background Technology

[0002] Geothermal energy, as a clean energy source, has received widespread attention and research. Geothermal development in the carbonate buried hill reservoirs of the North China Oilfield has a history of nearly 40 years and has achieved considerable progress. Due to the large area, high temperature, well-developed reservoir fractures, high rock strength, and favorable thermal conditions of the deep geothermal reservoirs in the North China Oilfield, it is becoming a hotspot for geothermal development.

[0003] For deep geothermal development, the current challenges include: (1) Non-uniform distribution of natural fractures in the reservoir. Due to the high degree of rock fragmentation at the buried hill surface and strong absorption of seismic waves, it is difficult to accurately determine the distribution of natural fractures in the buried hill internal geothermal reservoir. Furthermore, the accuracy of geothermal injection-production models established using simplified measures such as uniform permeability estimation is low. (2) Due to the lack of information on the non-uniform distribution of natural fractures, it is difficult to arrange injection and production well locations based on the distribution of natural fractures in the reservoir, and it is difficult to ensure the balance of injection and production water volume among the wells.

[0004] Therefore, it is necessary to provide a method for predicting the distribution of natural fractures to optimize the design parameters of carbonate geothermal well groups, and to provide a reference for achieving injection-production balance in engineering applications. Summary of the Invention

[0005] The purpose of this invention is to provide a method for optimizing the design parameters of a carbonate geothermal well group. The well locations are arranged according to the distribution of natural fractures to ensure the efficiency of seepage and convection heat transfer between the wells in the group. At the same time, the layout of injection wells and production wells in the well group and the ratio of injection wells to production wells are optimized according to the conductivity of each well to keep the total amount of water produced and injected in balance.

[0006] To achieve the above objectives, the present invention provides a method for optimizing the design parameters of carbonate geothermal well groups, comprising:

[0007] Based on the characteristics of carbonate geothermal reservoirs, a block geological model is constructed, including the top layer, carbonate buried hill reservoirs, and the bottom layer.

[0008] Based on the block geological model, a damage mechanics finite element model and a multi-field coupled finite element model of geothermal injection and production were established.

[0009] Based on the finite element model of damage mechanics, the main direction angle of orogenic movement is determined by trial-and-error matching, and the numerical solution of natural fracture damage variables in carbonate buried hill reservoirs is calculated to obtain the distribution characteristics of natural fractures.

[0010] Based on the distribution characteristics of natural fractures, the relationship between damage variables and permeability, and the relationship between damage variables and thermal conductivity are introduced into a multi-field coupled finite element model. Combined with well layout and construction parameters, the displacement field, seepage field, and temperature field during geothermal injection and production are calculated, and the geothermal injection and production design parameters are optimized.

[0011] Furthermore, the damage mechanics finite element model and the multi-field coupled finite element model both employ the same block finite element model:

[0012] The boundary conditions for the block finite element model include setting zero-displacement constraint boundaries on the bottom surface and four sides of the model.

[0013] The loads on the block finite element model include self-weight load, top surface force load, initial ground stress, and orogenic load.

[0014] Furthermore, the orogenic load is applied by displacement loading; the top surface force load is balanced with the initial geostress field.

[0015] Furthermore, the differences between the damage mechanics finite element model and the multi-field coupled finite element model include load conditions and rock properties. The multi-field coupled finite element model also includes pore seepage properties and thermodynamic properties.

[0016] Furthermore, the damage mechanics finite element model includes two scalar variables, tensile damage and compressive damage, to characterize the damage evolution mechanism of the material, and comprehensively measures the degree of damage to the material by tensile damage and compressive damage through damage variables.

[0017] Furthermore, the orogenic movement includes two equivalent orogenic movements: first stretching, then compression.

[0018] Furthermore, the trial-and-error matching method, by giving the direction angle value of the main direction of the orogenic stretching-compression, makes the numerical solution of the natural crack damage variable match the measured phenomenon best, and takes the direction angle value at this time as the main displacement direction angle of the orogenic movement.

[0019] Furthermore, the multi-field coupled finite element model includes setting a gravity load and an overlying stratum pressure of 57 MPa; taking the pore pressure boundaries around the reservoir and on the top and bottom surfaces as hydrostatic pressure boundaries; taking the temperature boundaries on the reservoir sides and top surfaces as adiabatic boundaries, and the temperature boundary on the bottom surface as a given temperature boundary; taking the pore pressure boundaries of the injection wells and production wells according to the actual measured values ​​in the engineering, taking the temperature boundary at the injection wellhead as the observed value, and taking the temperature boundary at the production wellhead as a free boundary.

[0020] Furthermore, in the multi-field coupled finite element model, the initial geostress field is the geostress field calculated by elastic stress equilibrium under natural gravity; the initial pore pressure field is the hydrostatic pressure field when the hydrostatic level is -100m, and the pore pressure boundary is a constant pore pressure boundary, set according to the wellhead pressure or water level curve of actual engineering data; the temperature gradient of the initial temperature field is set according to actual engineering experience, and the temperature boundary conditions are set according to the analysis of single-well geothermal logging curves.

[0021] Furthermore, optimize geothermal injection and production design parameters, including adjusting the ratio of injection wells to production wells based on the flow capacity of each well under given injection and production pressure conditions, and optimizing the setting of injection wells and production wells according to the principle of interval arrangement of injection wells and balance of total injection and production water.

[0022] Therefore, the present invention employs the above-mentioned method for optimizing the design parameters of carbonate geothermal well groups, and has the following technical effects:

[0023] (1) This invention uses the finite element method of damage mechanics to predict and calculate the distribution of natural fractures formed by orogenic movement, and arranges well locations according to the distribution of natural fractures to ensure the efficiency of seepage and convection heat transfer between wells in the well group.

[0024] (2) Based on the thermal-fluid-solid three-field coupled finite element method, this invention performs numerical simulation of the injection and production process of geothermal reservoir in the target block, gives the order of the conductivity of each well, and optimizes the layout of injection wells and production wells in the well group and the ratio of injection and production wells to keep the total amount of water production and injection balanced.

[0025] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0026] Figure 1 This is an example of an optimization method for design parameters of a carbonate geothermal well group, showing the top surface structural model of the geothermal reservoir, where (a) is a plan view of the top surface of the geothermal reservoir and (b) is a side view of the top surface of the geothermal reservoir.

[0027] Figure 2 This is an example of an optimization method for design parameters of a carbonate geothermal well group. The example uses a Petrel geological model of the block, where (a) is a schematic diagram of the model grid division, and (b) is a carbonate buried hill reservoir in the model.

[0028] Figure 3 This is a schematic diagram of the boundary and applied load in an embodiment of a method for optimizing design parameters of carbonate geothermal well groups;

[0029] Figure 4This is an example of an optimization method for design parameters of a carbonate geothermal well group. The example shows the numerical solution cloud map of the damage value and natural fracture distribution on the buried hill surface, as well as the distribution of natural fractures obtained by seismic wave analysis. (a) is the distribution of the natural fracture fracture zone represented by the damage variable, and (b) is the distribution of natural fractures on the buried hill surface obtained by seismic analysis.

[0030] Figure 5 This is an optimization method for design parameters of carbonate geothermal well groups. In the example, a slice display cloud map of damage variables of natural fracture distribution in buried hill reservoirs is shown.

[0031] Figure 6 This is an example of an optimization method for design parameters of carbonate geothermal well groups. The numerical solution of damage values ​​of natural fracture distribution is compared with the observation information of natural fractures at each well location of Well Ma.

[0032] Figure 7 This is an optimization method for design parameters of carbonate geothermal well groups. The damage value distribution curves along the well trajectory of 18 geothermal wells in the example are shown.

[0033] Figure 8 This is a flowchart illustrating the calculation of displacement field, seepage field, and temperature field during the geothermal injection and production process in an example of an optimization method for design parameters of carbonate rock geothermal well groups.

[0034] Figure 9 This is a diagram showing the relationship between conductivity and damage variables in an example of an optimization method for design parameters of carbonate geothermal well groups.

[0035] Figure 10 This is an optimization method for design parameters of carbonate geothermal well groups. In the embodiment, after introducing damage variables, the porosity cloud map of a multi-field coupled finite element model is presented.

[0036] Figure 11 This is an optimized design parameter method for a carbonate geothermal well group. In this example, the measured curves of water production over time are obtained from existing wells in the target block and 12 water production wells in adjacent blocks.

[0037] Figure 12 This is an optimization method for design parameters of a carbonate geothermal well group. In this example, the water injection volume of eight geothermal injection and production wells varies with time.

[0038] Figure 13 This is an optimization method for design parameters of a carbonate geothermal well group. In the example, the dynamic water level of the geothermal well production well and injection well changes over time.

[0039] Figure 14 This is an optimization method for design parameters of carbonate geothermal well groups. In the example, the temperature variation curve with depth obtained from existing well measurements in the target block is shown.

[0040] Figure 15 This is a temperature field distribution cloud map at the top of the target reservoir in an example of an optimization method for design parameters of a carbonate geothermal well group, where (a) is the stable temperature field after 10 hours of injection and production, and (b) is the temperature field after 864,000 hours (100 years) of injection and production.

[0041] Figure 16 This is an example of an optimization method for design parameters of a carbonate geothermal well group. The pore pressure field distribution cloud map at the top of the target reservoir is shown in the example, where (a) is the pore pressure field after 10 hours of injection and production, and (b) is the pore pressure field after 864,000 hours (100 years) of injection and production.

[0042] Figure 17 This is an example of an optimization method for design parameters of a carbonate geothermal well group. The example shows the changes in water injection and production flow rates over time for each of the 18 wells in the JR well group. Detailed Implementation

[0043] The present invention will be explained in more detail through the following embodiments. The purpose of disclosing the present invention is to protect all changes and modifications within the scope of the present invention. The present invention is not limited to the following embodiments.

[0044] like Figure 1 As shown, this invention presents a carbonate buried hill reservoir as a block geological model. The upper part of the reservoir consists of Proterozoic Jixian System Wumishan Formation dolomite strata, and the lower part consists of Changcheng System Gaoyuzhuang Formation dolomite strata. The block geological model is 7000m long from north to south and 6600m wide from east to west. The highest point of the buried hill surface has a depth of approximately 2547m, the top surface depth is 2435m, and the bottom surface depth is 6359m. Figure 2 As shown, the geological model of the block includes three materials: the top layer, the carbonate buried hill reservoir, and the bottom layer. The grid near the buried hill surface of the buried hill reservoir has been refined, and the heat exchange sections and bottom ends of the well trajectories of the geothermal wells are located in the upper region of this geothermal reservoir. Figure 2 As shown in (b), the thickness of the upper region of the geothermal reservoir ranges from a maximum of 580m to a minimum of 60m, with a planar grid of 60*60m. The thickness-direction grid is divided into 20 layers, with a minimum thickness of 3m and a maximum thickness of 29m. The inner region, farther from the buried hill surface, has a thickness of approximately 800m and is considered an additional region. This region has a coarser grid with a thickness of approximately 100–200m. Based on this geological model of the block, this invention provides an optimization method for the design parameters of carbonate geothermal well groups, as detailed below:

[0045] Based on the block geological model, a block finite element model was established, using a total of 528,360 C3D8R elements and 550,980 nodes. For example... Figure 3As shown, the boundary conditions of the model are defined as follows: zero-displacement constraint boundaries are set on the bottom and four sides of the model. The loads on the model are defined as: 1) self-weight load; 2) top surface force load, which is in equilibrium with the initial geostress field; 3) initial geostress; 4) orogenic load, which is applied by displacement loading. When calculating the natural fractures generated by orogenic movement, the top surface force load is taken as 1 MPa, at which point the overlying strata have not yet been deposited. In calculating the multi-field coupled geothermal injection and production process, the top surface force load is taken as 57 MPa, representing the pressure load of the overlying strata.

[0046] Based on the finite element model of damage mechanics, tensile damage d t and compressive damage d c Two scalar variables are used to represent the damage evolution mechanism of the material, and the damage variable d is used to comprehensively express d. t and d c The degree of material damage caused is determined by the parameters (damage evolution rate) of the damage mechanics finite element model through "trial calculation-phenomenon matching".

[0047] Among them, the damage variable d and the tensile damage d t and compressive damage d c The relationship is:

[0048] (1-d)=(1-s t d t (1-s) c d c );

[0049] In the formula, s t For d t The coefficient of is a function of tensile stress; s c It is d c The coefficient is a function of compressive stress.

[0050] After repeated calculations, the damage evolution rate values ​​of buried hill reservoir materials are shown in Tables 1 and 2.

[0051] Table 1. Parameter values ​​for the compression damage model.

[0052] 0 0 0.0034 0.00012 0.05 0.003 0.25 0.01 0.27 0.05 0.45 0.055 0.46 0.1 0.5 0.11 0.75 0.5

[0053] Table 2. Parameter values ​​for the tensile damage model

[0054] 0 0 0.1 5.00E-05 0.15 0.00015 0.7 0.0005 0.75 0.0015 0.9 0.002 0.905 0.5 0.75 0.0015 0.9 0.002 0.905 0.5

[0055] The target block is located in the Jizhong Depression of the Bohai Bay Basin. The geothermal reservoir is the Wumishan Formation carbonate rock, belonging to the middle and lower part of the Mesoproterozoic Jixian System, with a maximum thickness of 3340 meters. During the Jixian Period and subsequent orogenic movements, the Wumishan Formation underwent Paleozoic uplift, Mesozoic compressional uplift, and Mesozoic-Cenozoic folding and faulting, resulting in a complex and uneven distribution of natural fractures. To accurately determine the principal directions of stretching and compression during the orogenic movement, this embodiment employs a trial-and-error method: firstly, the orogenic movement is simplified to two equivalent phases of stretching followed by compression; secondly, a series of directional angles for the principal stretching-compression directions of the orogenic movement are assumed. The numerical solution of natural fractures obtained through trial calculations shows the best agreement with measured phenomena; this directional angle value is then taken as the principal displacement direction angle of the orogenic movement. Through trial calculations, the principal stretching direction of the first phase of the orogenic movement is east-west, and the principal compression direction of the second phase is north-south.

[0056] like Figure 4 As shown, the distribution of natural fracture zones represented by the damage variable is similar to the distribution trend of natural fracture zones on the buried hill surface as determined by seismic wave analysis: there are three major faults within the block, and the rest are secondary fracture zones. This indicates that the values ​​of parameters such as the orogenic angle in the model are appropriate, and the obtained numerical solution for natural fractures is consistent with actual observation information. Figure 5 As shown, along a 7km north-south direction, there are 13 slices to illustrate the distribution of damage values ​​within the buried hill. Figure 5 The colors represent the damage value, i.e., the degree of rock fragmentation, and also indicate the density of natural cracks: the part exceeding 0.3 is shown in gray; in the colored part, red represents the highest degree of fragmentation, with a damage value of 0.3, which means the rock is 30% fragmented; blue represents a degree of fragmentation of 0, which means there are no natural cracks.

[0057] like Figure 6 As shown, among the existing Ma wells in this embodiment, Maj1 has the highest damage value in the upper part, Ma70 has the lowest damage value at all locations, and the damage values ​​of Ma94-2x, Maj7, and Ma42-2 are between the two mentioned above, indicating a relatively good degree of natural fracture development. The distribution information of natural fractures with depth in the figure comes from actual fracture measurement data. The red horizontal line segment represents the depth point of the well section where natural fractures (i.e., type I fractures) are developed, and is assigned a value of 140md; the very short red dot on the horizontal line segment represents the location of type II fractures, and is assigned a value of 14md; other depth positions represent locations where no obvious natural fractures are shown; the horizontal dashed line is an indicator line connecting the measured distribution curve of natural fractures to the corresponding well unit.

[0058] By comparing the numerical solutions of natural fracture damage values ​​in buried hill reservoirs with actual observed information on natural fractures, the two solutions show the same distribution trend in planar location; that is, well locations with larger observed fracture values ​​also have larger calculated numerical solutions. In the depth direction, the coordinates of well sections with high fracture density are similar. The comparison results demonstrate that the numerical solutions obtained using the method in this embodiment are accurate and consistent with the observed information. Furthermore, based on the damage value distribution along the well trajectories of 18 geothermal wells in the block (…),… Figure 7 It can be seen that the damage value in the existing target reservoir is generally greater than 5%, the natural fractures are well developed, and there are also many well sections with very well developed natural fractures (i.e., damage value greater than 0.1).

[0059] The multi-field coupled finite element model and the damage mechanics finite element model for geothermal injection and production use the same mesh model. The difference lies in the different load conditions and rock properties, the latter including pore flow properties and thermodynamic properties. Before the formation of natural fractures during orogenic movements, carbonate rocks are crystalline lithologies, not sedimentary lithologies, and the initial strata lack porosity; therefore, the former does not include these properties.

[0060] In a multi-field coupled finite element model, natural fractures and their impact on seepage and heat conduction are introduced. Based on the distribution of natural fractures simulated by the damage mechanics finite element model, and combined with well layout and construction parameters, the displacement field, seepage field, and temperature field during geothermal injection and production are calculated, and the design parameters for geothermal injection and production are optimized. Figure 8 As shown.

[0061] In engineering applications, rocks with cracks have higher permeability than rocks without cracks. This means that the relationship between rock damage and permeability is: the greater the rock damage value, the higher the permeability. Therefore, in the multi-field coupled finite element model, this embodiment uses the conductivity coefficient. Perform calculations. The relationship with the penetration rate K is as follows:

[0062]

[0063] In the formula, g is the acceleration due to gravity, and ρ w Let ρ be the density of liquid water, and μ be the dynamic viscosity coefficient of water. Conductivity. The relationship with the damage variable value d, such as Figure 9 As shown, the coordinate axes are all logarithmic coordinates.

[0064] On the other hand, the rock in the geothermal injection stage is an elastic model. This embodiment does not consider the opening or closing of natural fractures during the geothermal injection process, and uses a porous elastic rock model as the block finite element model for geothermal injection. The relationship between the rock elastic modulus E and the damage variable value d is as follows:

[0065] E = E0 * (1 - d);

[0066] In the formula, E0 is the elastic modulus of the initially undamaged rock, and E is the elastic modulus of the rock after it is damaged.

[0067] In the geothermal injection and production stage, the difference between the multi-field coupled finite element model and the damage mechanics finite element model is as follows: the calculation range of the block is reduced to 5km in length and 4km in width; in addition, a gravity load and an overlying stratum pressure of 57MPa are set, which is obtained from the geomechanical analysis of a single well; the pore pressure boundary around the reservoir and on the top and bottom surfaces is taken as the hydrostatic pressure boundary; the temperature boundary on the side and top surfaces of the reservoir is the adiabatic boundary, and the temperature boundary on the bottom surface is the given temperature boundary; the pore pressure boundary of the injection well and the production well is taken according to the actual measured values ​​in the project, and the wellhead temperature of the injection well is the observed value; the temperature boundary at the wellhead of the production well is the free boundary. The initial design included a total of 18 wells, of which 9 were injection wells: JR1-1, JR1-3, JR1-6, JR1-7, JR1-10, JR1-11, JR1-14, JR2-1, and JR2-2; and 14 were production wells: JR1-2, JR1-5, JR1-8, JR1-9, JR1-12, JR1-13, JR2-3, and JR2-4. The porosity derived from damage values ​​on the buried hill surface and the arrangement of each well location are as follows: Figure 10 As shown.

[0068] (1) Setting of initial geostress field and boundary conditions:

[0069] Since the geothermal reservoir block belongs to a depleted oil field, the initial geostress field is the geostress field that has been disturbed after oil extraction. Based on the actual situation of engineering observation, this embodiment takes the initial geostress field as the geostress field after elastic stress balance calculation under natural gravity, with zero displacement constraint boundaries on the perimeter and bottom surface, and surface force boundary on the top surface.

[0070] (2) Initial pore pressure field:

[0071] The initial pore pressure field of geothermal injection and production is the pore pressure field after the oil extraction process, which has been disturbed. Based on existing engineering data, it is taken as the hydrostatic pressure field when the static liquid level is -100m.

[0072] (3) Geothermal injection and extraction construction parameters and model pore pressure boundary settings:

[0073] The values ​​of geothermal injection and production construction parameters affect the accuracy of multi-field coupled numerical results. To accurately calibrate the values ​​of these parameters, this embodiment compiles existing relevant engineering construction data and investigates the measurement parameters of water production changes over time in existing wells in the target block and geothermal wells in adjacent blocks. For example... Figure 11 As shown, the maximum water extraction volume is 200m³. 3 / per hour, minimum value is 35m 3The difference is nearly six times per hour, meaning the water production curve of the same well changes over time and is not constant. Figure 12 As shown, the maximum water injection volume is 317m³. 3 / per hour, minimum value is 40m 3 The difference is nearly eight times per hour, meaning that for the same well, the injection rate changes over time. For example... Figure 13 As shown, the lowest dynamic water level at the intake well location is -370 meters, and the highest is close to 0. Throughout the injection and production process, the wellhead pressure of both the injection and intake wells remains essentially constant. In summary, the pore pressure boundary of the multi-field coupled finite element model should be based on the wellhead pressure, i.e., the water level curve, from actual engineering data, and should be a constant pore pressure boundary. The pore pressure of the injection well is the pressure of the injection pipeline, with a maximum of 0.2 MPa and a minimum of 0 MPa; here, we take 0.1 MPa. The pore pressure of the intake well is the dynamic water level at -300 m, i.e., a negative pressure of -0.3 MPa.

[0074] (4) Setting the initial temperature field and temperature boundary conditions:

[0075] like Figure 14 As shown, at a depth of 3200 meters, the highest temperature is 128℃ and the lowest temperature is 109℃; at a depth of 3400 meters, the highest temperature is 132℃ and the lowest temperature is 118℃. The temperature gradient along the well trajectory at each well location is 2℃ / 100 meters on the curve of the interthermal 2-1 well, which has a higher temperature, and approximately 4.5℃ / 100 meters on the curve of the interthermal 1-2 well, which has a lower temperature. Based on experience, the temperature gradient of the initial temperature field of the entire reservoir is taken as 3℃ / 100 meters.

[0076] The temperature boundary conditions and initial conditions of the model were obtained from the analysis of single-well geothermal logging curves, specifically as follows:

[0077] 1) The boundary condition for the well trajectory node temperature of the reinjection well is 50℃, and the well trajectory node temperature of the water extraction well is a calculated value.

[0078] 2) At a TVD of 2900m, the ground temperature is 95℃, and the temperature rise gradient is approximately 3℃ / 100m.

[0079] 3) The upper boundary points are set as thermally insulating boundaries, with no external heat dissipation.

[0080] 4) All points on the bottom and side boundaries are set as normal temperature boundaries.

[0081] Based on the above settings, the numerical solution of the finite element model of the geothermal injection and extraction block was obtained. For emphasis, Figure 15 The image only shows the portion with temperatures below 120°C. Compared to 10 hours after injection and production, the low-temperature zone near the reinjection wellhead has significantly expanded after 100 years of injection and production. For example... Figure 16 As shown, after 100 years of injection and extraction, compared with 10 hours of injection and extraction, since the injection volume and extraction volume are approximately equal, the pore pressure field, which is dominated by hydrostatic pressure, hardly changes after injection and extraction.

[0082] like Figure 17 As shown, under the condition of a 1:1 ratio of injection to production wells, over a 100-year period of injection and production in the 18 wells of the JR well group, the initial injection and production water flow rates were relatively high due to the pressure difference. As the initial large pressure difference gradually disappeared, the later flow became a stable flow, with the maximum production water flow rate being -81 m³ / h. 3 / h (equivalent to 1944 cubic meters / day), the maximum injection flow rate is 75m³ / h. 3 / h (equivalent to 1800 cubic meters / day). The injection and production flows of each well are ranked according to their absolute values, reflecting the conductivity of each well. The total numerical solutions for each injection and production flow are 479.5449 m³ / h. 3 / h and -496.8149m 3 / h, the output is 17.27 m3 / h more than the injection, which is 3.6%.

[0083] To achieve a strictly balanced injection and production water volume, the injection-production well ratio was changed from 1:1 to 3:2 based on the flow capacity of each well. In this case, 60% (11 wells) of the 18 wells were designated as injection wells, and 7 as production wells. Following the principle of alternating injection and production well arrangements, and taking into account the injection and production flow capacity of each well, two production wells, JR1-13 and JR2-3, were converted to injection wells. Furthermore, injection well JR1-7 was converted to a production well, and production well JR1-8 was converted to an injection well. After optimization, the total injection and production water flow rates are 531.79 m³ / s. 3 / h and 530.35m 3 / h, the relative difference is only 0.27%, reaching the injection-production balance.

[0084] Therefore, this invention adopts the above-mentioned optimization method for design parameters of carbonate geothermal well groups, which takes into account the influence of natural fractures in geothermal reservoirs on geothermal injection and production projects. Combined with a finite element model of force-heat-seepage three-field coupling, the conductivity of each well under a given injection and production pressure is calculated. By optimizing the parameters of injection wells and production wells, the balance of injection and production water volume is accurately achieved.

[0085] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for optimizing design parameters of carbonate geothermal well groups, characterized in that, include: Based on the characteristics of carbonate geothermal reservoirs, a block geological model is constructed, including the top layer, carbonate buried hill reservoirs, and the bottom layer. Based on the block geological model, a damage mechanics finite element model and a multi-field coupled finite element model of geothermal injection and production were established. Based on the finite element model of damage mechanics, the main direction angle of orogenic movement is determined by trial-and-error matching, and the numerical solution of natural fracture damage variables in carbonate buried hill reservoirs is calculated to obtain the distribution characteristics of natural fractures. Based on the distribution characteristics of natural fractures, the relationship between damage variables and permeability, and the relationship between damage variables and thermal conductivity are introduced into a multi-field coupled finite element model. Combined with well layout and construction parameters, the displacement field, seepage field and temperature field during geothermal injection and production are calculated, and the geothermal injection and production design parameters are optimized. The damage mechanics finite element model and the multi-field coupled finite element model both use the same block finite element model: The boundary conditions for the block finite element model include setting zero-displacement constraint boundaries on the bottom surface and four sides of the model. The loads on the block finite element model include self-weight load, top surface force load, initial ground stress, and orogenic load; The orogenic load is applied by displacement loading; the top surface force load is balanced with the initial geostress field. The differences between the damage mechanics finite element model and the multi-field coupled finite element model include load conditions and rock properties. The multi-field coupled finite element model also includes pore seepage properties and thermodynamic properties. The damage mechanics finite element model includes two scalar variables, tensile damage and compressive damage, to characterize the damage evolution mechanism of the material, and comprehensively measures the degree of damage to the material by tensile damage and compressive damage through damage variables; The orogenic movement includes two equivalent orogenic movements: first stretching and then compression. Among them, the trial-and-error matching method is to make the numerical solution of the natural crack damage variable match the measured phenomenon best by giving the direction angle value of the main direction of the orogenic stretching-compression. The direction angle value at this time is taken as the main displacement direction angle of the orogenic movement. The multi-field coupled finite element model includes setting gravity load and overlying strata pressure of 57 MPa; taking the pore pressure boundary around the reservoir and the top and bottom surfaces as hydrostatic pressure boundary; taking the temperature boundary of the reservoir side and top surface as adiabatic boundary, and the temperature boundary of the bottom surface as a given temperature boundary; taking the pore pressure boundary of the injection well and the production well as the actual measured value of the engineering, taking the temperature boundary of the injection wellhead as the observed value, and taking the temperature boundary of the production wellhead as a free boundary; The initial geostress field of the multi-field coupled finite element model is the geostress field calculated by elastic stress equilibrium under natural gravity; the initial pore pressure field is the hydrostatic pressure field when the hydrostatic level is -100m, and the pore pressure boundary is a constant pore pressure boundary, set according to the wellhead pressure or water level curve of actual engineering data; the temperature gradient of the initial temperature field is set according to actual engineering experience, and the temperature boundary conditions are set according to the analysis of single-well geothermal logging curves. Optimizing geothermal injection and production design parameters includes adjusting the ratio of injection wells to production wells based on the flow capacity of each well under given injection and production pressure conditions, and optimizing the setting of injection wells and production wells according to the principle of interval arrangement of injection wells and balance of total injection and production water.

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