A method for mining hot dry rock geothermal three-dimensional well pattern

Abstract

The present invention discloses a method for exploiting hot dry rock geothermal three-dimensional well network, comprising the steps of: drilling vertical wells, horizontal wells, and branch wells in two staggered rows according to a constructed three-dimensional well network model; dividing the two rows of vertical wells, horizontal wells, and branch wells into an injection well group and a production well group; performing synchronous opposite-direction fracturing on the branch wells of the injection well group and the branch wells of the production well group to form a fracture network connection; and pumping water into the injection well group and extracting water from the production well group. The present invention adopts a fishbone well structure fracturing method to form a complex fracture network for heat exchange. By drilling two rows of staggered vertical wells into the hot dry rock formation, horizontal wells are then drilled in opposite directions, and parallel staggered branch wells are drilled in opposite directions between adjacent horizontal wells to form a fishbone well structure. After synchronous opposite-direction fracturing between adjacent opposing branch wells, a complex fracture network connection is formed between the fishbone well structures. The connection construction operation is relatively convenient, and the heat exchange efficiency can be effectively improved through the large-area fracture network.

Description

Technical Field

[0001] The present invention relates to the technical field of geothermal development, and in particular to a method for mining hot dry rock geothermal three-dimensional well patterns. Background Art

[0002] Geothermal energy is gradually becoming a crucial component of my country's future energy mix and is crucial for achieving its "dual carbon" goals. Geothermal resources are generally categorized by their depth: shallow, hydrothermal, and hot dry rock. Shallow and hydrothermal geothermal resources, with relatively low technical requirements for development, have been commercialized and widely used for heating and power generation.

[0003] In contrast, hot dry rock resources are buried below 3,000 meters underground, with temperatures exceeding 150°C. They contain enormous energy, but their development technology is relatively difficult. Considering the difficulty of exploration and development of hot dry rock geothermal energy and the technological development trend, hot dry rock geothermal energy with a burial depth of less than 5,500 meters will become a key area of ​​geothermal energy research in the next few decades. Hot dry rock resources differ significantly from traditional geothermal resources in terms of temperature, lithology, and density. Their development faces multiple challenges such as high technical requirements, high economic costs, and unknown geological risks. Among them, how to achieve efficient connectivity and heat exchange between wells in deep high-temperature areas to improve the efficiency of hot dry rock development has become a core problem.

[0004] Therefore, a method for exploiting hot dry rock geothermal energy is urgently needed to solve the problem that conventional geothermal wells are currently used in hot dry rock geothermal exploitation, where the depth is too deep, resulting in difficulty in connecting wells and low heat exchange efficiency. Summary of the Invention

[0005] The purpose of the present invention is to provide a dry hot rock geothermal three-dimensional well network mining method to solve the technical problems in the prior art such as difficulty in connecting wells and low heat exchange efficiency due to excessive depth.

[0006] In order to solve the above technical problems, the present invention specifically provides the following technical solutions:

[0007] A method for mining hot dry rock geothermal three-dimensional well patterns, comprising the following steps:

[0008] Step 100: Based on the geological data of the underground rock formation, a three-dimensional well pattern model for hot dry rock geothermal extraction is designed. Then, according to the three-dimensional well pattern model, two rows of vertical wells are staggered and drilled into the hot dry rock formation. Multiple horizontal wells are drilled opposite to the bottom of the two rows of vertical wells. Branch wells are drilled laterally to each horizontal well, so that the branches of adjacent horizontal wells are coplanar and parallel to the horizontal well axis, forming a fishbone well structure.

[0009] Step 200: Horizontal wells drilled in the same direction and their connected vertical wells and branch wells are classified as an injection well group, while horizontal wells drilled in opposite directions and their connected vertical wells and branch wells are classified as a production well group;

[0010] Step 300: Fracture the branch wells of the injection well group in order from the bottom of the well to the wellhead. Simultaneously, fracture the branch wells of the production well group in order from the wellhead to the bottom of the well, so as to form a fracture network between adjacent and parallel branch wells.

[0011] Step 400: Pump cold water into the injection well group and extract water from the production well group. The cold water enters the fracture network along the vertical, horizontal, and branch wells of the injection well group, exchanges heat, and forms geothermal water, which is then produced from the branch wells, horizontal, and vertical wells of the production well group.

[0012] As a preferred solution of the present invention, the specific method of constructing the three-dimensional well pattern model is:

[0013] Based on the staggered distribution rules of the injection well group and the production well group, and combined with the location and depth of the hot dry rock, the row spacing, staggered spacing and excavation depth of the injection well group and the production well group are determined;

[0014] Based on the requirement of connecting the injection well group and the production well group in the hot dry rock formation, vertical wells, horizontal wells and branch wells are designed for the injection well group and the production well group;

[0015] Determine the depth and location of vertical wells, horizontal wells, and branch wells based on the drilling depths of the injection well group and production well group;

[0016] Determine the orientation and length of horizontal wells based on the spacing between injection and production well groups;

[0017] The orientation and length of the branch wells are determined based on the spacing between the injection well group and the production well group.

[0018] As a preferred embodiment of the present invention, the horizontal well section of the injection well group is arranged opposite to the horizontal well section of the production well group, and the horizontal well section of the injection well group and the horizontal well section of the production well group are parallel to each other to form a horizontal opposing well structure;

[0019] The branch well sections of the injection well group and the branch well sections of the production well group are arranged opposite to each other, and the branch well sections of the injection well group and the branch well sections of the production well group are staggered at a fixed interval to form a branch opposing well structure;

[0020] The horizontal opposing well structure and the branch opposing well structure form a well pattern structure covering the hot dry rock formation, and the well pattern structure is distributed in the thickness of the hot dry rock formation. Place.

[0021] As a preferred solution of the present invention, the overlapping length of the horizontal radial projections of two adjacent and parallel horizontal wells is greater than or equal to the length of the horizontal well.

[0022] The overlapping length of the horizontal radial projections of two adjacent and parallel branch wells is greater than or equal to the length of the branch well.

[0023] As a preferred embodiment of the present invention, in step 400, a water injection string is provided in a vertical well of the injection well group, and a drainage pipeline is provided in a vertical well of the production well group;

[0024] The lower end of the water injection pipe is placed in the horizontal well of the injection well group and does not exceed the branch well. The lower end of the extraction pipe is placed in the horizontal well of the production well group and does not exceed the branch well.

[0025] As a preferred embodiment of the present invention, the number of injection well groups is one more than the number of production well groups, the multiple branch wells of the production well group are distributed bidirectionally symmetrically on the horizontal well, the multiple branch wells of the injection well group located between the two production well groups are distributed bidirectionally symmetrically on the horizontal well, and the multiple branch wells of the injection well group located on the outside are distributed unidirectionally toward the inside of the horizontal well.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] The present invention adopts a fishbone well structure fracturing method to form a complex fracture network for heat exchange. After drilling two rows of vertical wells with an alternating distribution in the hot dry rock formation, horizontal wells are drilled opposite to each other, and parallel and alternating branch wells are drilled opposite to each other between adjacent horizontal wells to form a fishbone well structure. After synchronous opposite fracturing between adjacent opposite branch wells, a complex fracture network is formed between the fishbone well structures. The connection construction operation is relatively convenient, and the heat exchange efficiency can be effectively improved through the large-area fracture network.

[0028] Moreover, by adopting a relatively staggered arrangement of injection well groups and production well groups, the coverage area of ​​the well network within the hot dry rock is effectively increased, the difficulty of inter-well connectivity in deep high-temperature areas is reduced, and the mining effect is enhanced. By adopting a fishbone well structure and synchronously fracturing adjacent opposing branch wells, a complex fracture network is formed, and the distribution of the fracture network within a controllable area is achieved. The formation of the fracture network enables cold water to more fully contact the hot dry rock during the injection process, thereby more effectively absorbing heat and converting it into geothermal water. This method has low operating costs and is easy to replicate and promote. By forming a complex fracture network, increasing the heat exchange contact area, optimizing the heat transfer mechanism, and optimizing the well network layout, it helps to improve the economic efficiency of hot dry rock geothermal development. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for the embodiments or the description of the prior art. Obviously, the drawings described below are merely exemplary, and those skilled in the art can, without inventive effort, derive other implementation drawings based on the provided drawings.

[0030] Figure 1 A schematic diagram of the distribution of injection well groups and production well groups in the three-dimensional well pattern mining method for hot dry rock geothermal energy provided by an embodiment of the present invention;

[0031] Figure 2 A schematic diagram of the horizontal well distribution of the hot dry rock geothermal three-dimensional well pattern mining method provided by an embodiment of the present invention;

[0032] Figure 3 A schematic diagram of a fracture network for a three-dimensional well pattern mining method for hot dry rock geothermal energy provided by an embodiment of the present invention;

[0033] Figure 4 A schematic diagram of the fracture network distribution of the hot dry rock geothermal three-dimensional well pattern mining method provided by an embodiment of the present invention;

[0034] Figure 5 A schematic diagram of water injection in an injection well group of a three-dimensional well pattern mining method for hot dry rock geothermal energy provided by an embodiment of the present invention;

[0035] Figure 6 A schematic diagram of production well group mining in a hot dry rock geothermal three-dimensional well pattern mining method provided in an embodiment of the present invention.

[0036] The numbers in the figure represent the following:

[0037] 1- rock formation; 2- horizontal well; 3- vertical well; 4- injection well group; 5- production well group; 6- branch well; 7- fishbone well structure; 8- fracture; 9- work vehicle;

[0038] 10-Oil pipe; 11-Fracturing tool; 12-Fracturing network; 13-Cold water; 14-Cold water tank; 15-Geothermal water; 16-Extraction device. DETAILED DESCRIPTION

[0039] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0040] like Figure 1-6As shown, the present invention provides a method for mining hot dry rock geothermal three-dimensional well patterns, comprising the following steps:

[0041] Step 100: Based on the geological data of the underground rock formation, a three-dimensional well pattern model for hot dry rock geothermal extraction is designed. Then, according to the three-dimensional well pattern model, two rows of vertical wells are staggered and drilled into the hot dry rock formation. Multiple horizontal wells are drilled opposite to the bottom of the two rows of vertical wells. Branch wells are drilled laterally to each horizontal well, so that the branches of adjacent horizontal wells are coplanar and parallel to the horizontal well axis, forming a fishbone well structure.

[0042] Step 200: Horizontal wells drilled in the same direction and their connected vertical wells and branch wells are classified as an injection well group, while horizontal wells drilled in opposite directions and their connected vertical wells and branch wells are classified as a production well group;

[0043] Step 300: Fracture the branch wells of the injection well group in order from the bottom of the well to the wellhead. Simultaneously, fracture the branch wells of the production well group in order from the wellhead to the bottom of the well, so as to form a fracture network between adjacent and parallel branch wells.

[0044] Step 400: Pump cold water into the injection well group and extract water from the production well group. The cold water enters the fracture network along the vertical, horizontal, and branch wells of the injection well group, exchanges heat, and forms geothermal water, which is then produced from the branch wells, horizontal, and vertical wells of the production well group.

[0045] The geothermal three-dimensional well network mining method of the present invention mainly determines the position and depth of the hot dry rock after obtaining the geological parameters and exploration data of the underground rock formation, and constructs a three-dimensional well network model based on this. According to this three-dimensional well network model, vertical wells, horizontal wells and branch wells connected in sequence are drilled, and multiple vertical wells are staggered in two rows. The parallel and relatively distributed horizontal wells and the vertical wells and branch wells connected thereto can be divided into injection well groups and production well groups. By performing opposite synchronous fracturing on the branch wells of the injection well group and the branch wells of the production well group, a complex fracture network is formed to connect. After cold water is pumped into the injection well group, the cold water can efficiently exchange heat through the fracture network to form geothermal water, and the output is extracted from the production well group, thereby realizing efficient mining of hot dry rock geothermal energy.

[0046] Among them, cold water is converted into hot water and steam under the high temperature of dry hot rock and then mined. Since the heat exchange process takes place in the well and in the complex fracture network, and the branch wells and horizontal wells form a fishbone well structure, after the branch wells are fractured, a complex fracture structure is formed between the fishbone well structure. This fracture structure is distributed over a large area in the dry hot rock formation, which greatly increases the contact area for heat exchange and can achieve better heat exchange effect.

[0047] At the same time, the branch wells of the injection well group and the branch wells of the production well group are subjected to synchronous fracturing in opposite directions, which can ensure that all adjacent and parallel branch wells drilled in opposite directions are subjected to synchronous fracturing, so that the fracturing cracks between the opposite parallel branch wells are connected to form a complex interconnected fracture network.

[0048] The geothermal three-dimensional well network mining method of the present invention is simple to operate, low in cost, can effectively improve the drilling connection success rate, well connectivity and heat exchange efficiency, and is easy to replicate and promote. Figure 2 As shown, this method relies on multiple parallel horizontal wells, each with multiple intersecting lateral wells drilled within it, forming a "fishbone well structure." Fracturing operations within the fishbone well structure not only create a complex fracture network within the rock formation 1 but also enhance connectivity within the fishbone well structure, expanding the surface area heated by the cold water and thereby improving heat transfer efficiency. After heat exchange, hot water and steam can flow more smoothly through the fractures.

[0049] Based on this, the present invention adopts the fishbone well structure heat exchange technology combined with the horizontal directional multi-branch drilling technology, effectively solving the limitations of existing development technology and realizing the efficient development of dry hot rock geothermal resources.

[0050] like Figure 1-2 As shown in Figure 2, the specific method of constructing a three-dimensional well pattern model is:

[0051] Based on the staggered distribution rules of the injection well group and the production well group, and combined with the location and depth of the hot dry rock, the row spacing, staggered spacing and excavation depth of the injection well group and the production well group are determined;

[0052] Based on the requirement of connecting the injection well group and the production well group in the hot dry rock formation, vertical wells, horizontal wells and branch wells are designed for the injection well group and the production well group;

[0053] Determine the depth and location of vertical wells, horizontal wells, and branch wells based on the drilling depths of the injection well group and production well group;

[0054] Determine the orientation and length of horizontal wells based on the spacing between injection and production well groups;

[0055] Determine the orientation and length of the branch wells based on the spacing between the injection well group and the production well group;

[0056] The included angle between the drilling direction of the branch well and the drilling direction of the horizontal well to which it is connected is 90°.

[0057] In this step, the three-dimensional well network model consists of vertical wells, horizontal wells and branch wells. The vertical wells are divided into two rows with a fixed row spacing to form multiple injection well groups and multiple production well groups, and the two rows of vertical wells are distributed at a fixed staggered spacing. The horizontal wells are formed based on the horizontal directional drilling at the lower end of the vertical wells, so that the horizontal wells are relatively and parallel staggered, that is, the projections of the horizontal wells in the horizontal radial direction overlap. The branch wells are formed from the lateral directional drilling of the horizontal wells, so that there are multiple branch wells relatively and parallel staggered between two adjacent horizontal wells, that is, the projections of the branch wells in the horizontal radial direction overlap.

[0058] Based on this, after a three-dimensional well network is formed according to this model, high-pressure fracturing is performed to form a fracture network between the branch wells due to their close distance, thereby completing the connection between the injection well group and the production well group.

[0059] Specifically, if Figure 1-3 As shown, the horizontal well section of the injection well group and the horizontal well section of the production well group are arranged opposite to each other, and the horizontal well section of the injection well group and the horizontal well section of the production well group are parallel to each other to form a horizontal opposing well structure;

[0060] The branch well sections of the injection well group and the branch well sections of the production well group are arranged opposite to each other, and the branch well sections of the injection well group and the branch well sections of the production well group are staggered at a fixed interval to form a branch opposing well structure;

[0061] The horizontal opposing well structure and the branch opposing well structure form a well pattern structure covering the hot dry rock formation, and the well pattern structure is distributed in the thickness of the hot dry rock formation. Place.

[0062] The horizontal radial projection overlap length between horizontal opposing well structures is greater than or equal to the horizontal well length.

[0063] The horizontal radial projection overlap length between the branch well structures is greater than or equal to the branch well length.

[0064] Among them, the lower end of the water injection pipe is placed in the horizontal well of the injection well group and does not exceed the branch well, and the lower end of the extraction pipe is placed in the horizontal well of the production well group and does not exceed the branch well.

[0065] The injection well group and the production well group are relatively staggered in the hot dry rock, that is, the horizontal wells and the branch wells are relatively staggered, which can effectively increase the coverage area of ​​the injection well group and the production well group in the hot dry rock, thereby forming a complex fracture network, improving the efficiency of heat exchange, and reducing the difficulty of inter-well connectivity between the injection well group and the production well group.

[0066] The horizontal radial projection overlap length between the horizontal opposing well structures is greater than or equal to the horizontal well length. And the horizontal radial projection overlap length between the branch well structures is greater than or equal to the branch well length The distribution area of ​​the fracture network in the hot dry rock can be further increased, thereby improving the heat exchange efficiency.

[0067] Based on the above-mentioned three-dimensional well pattern model, an embodiment of a three-dimensional well pattern structure formed by excavation is provided below.

[0068] like Figure 1-3 As shown in the figure, the specific structure of the three-dimensional well network formed based on the three-dimensional well network model is as follows:

[0069] The three-dimensional well pattern includes a plurality of injection well groups 4 and a plurality of production well groups 5, and the plurality of injection well groups 4 and the plurality of production well groups 5 are arranged in a double-row staggered manner.

[0070] The use of multiple injection well groups 4 and multiple production well groups 5 arranged in a double row staggered manner can cover more hot dry rocks and reduce the spacing between the wells, making it easier to form a fracture network 12 in a controllable area through fracturing.

[0071] Of course, in order to form a crack network with a controllable range, the following preferred embodiments are provided.

[0072] like Figure 1-3 As shown, both the injection well group and the production well group include a vertical well 3, a horizontal well 2 and a branch well 6. The vertical well 3 is vertically connected to the horizontal well 2, and the horizontal well 2 is located in the dry hot rock formation 1;

[0073] Branch wells 6 are distributed laterally of the horizontal well 2 and connected to the horizontal well 2, and fracture networks 12 are formed between adjacent branch wells;

[0074] Among them, vertical well 3 is drilled vertically downward from the ground to the location of hot dry rock. At , horizontal well 2 is drilled in a direction perpendicular to the vertical well;

[0075] The vertical wells 3 are parallel to each other, the horizontal wells 2 are parallel to each other, and the branch wells 6 are parallel to each other.

[0076] Specifically, the injection well group 4 and the production well group 5 are divided into vertical wells 3, horizontal wells 2 and branch wells 6 for drilling. The horizontal well 2 is vertically connected to the vertical well 3, and the branch wells 6 are distributed laterally of the horizontal well 2 and connected to the horizontal well 2 to form a fishbone well structure 7. The generation area of ​​the fracture network 12 is limited by the branch wells 6 and the horizontal well 2, and the spacing between the branch wells 6 is small, so the fractures are more likely to extend to the branch wells 6, thereby forming a fracture network 12 located in each branch well 6, realizing regional controllable construction of the fracture network 12, and avoiding uncontrollable fracture distribution and waste of water resources.

[0077] Of course, if Figure 1-3As shown, the number of injection well groups 4 is one more than the number of production well groups 5, and the multiple branch wells 6 of the production well group 5 are distributed bidirectionally symmetrically on the horizontal well 2. The multiple branch wells 6 of the injection well group 4 located between the two production well groups 5 are distributed bidirectionally symmetrically on the horizontal well 2, and the multiple branch wells 6 of the injection well group 4 located on the outside are distributed unidirectionally toward the inside of the horizontal well 2.

[0078] Specifically, the number of injection well groups 4 is one more than the number of production well groups 5, so that the production well group 5 can be located between the injection well groups 4. However, there is a certain loss of cold water in the fracture network 12, and reducing the production well group 5 can effectively reduce the empty production rate.

[0079] Of course, in this process, in order to enable the branch well 6 to complete fracturing to form a fracture network 12 as required, an oil pipe 8 and a fracturing tool 11 are placed in the branch well 6. The fracturing tool 11 is a commonly used hydraulic directional extrusion device. After the work vehicle 9 is connected to the oil pipe 8 and pressurized, the fracturing tool 11 can generate pressure on one side or both sides of the branch well 6 to break the hot dry rock formation, thereby forming cracks 8. Various cracks 8 are connected to each other to form a fracture network 12.

[0080] And as Figure 5 and Figure 6 As shown, before mining, the water injection pipe string is extended from the vertical well 3 of the injection well group 4 into the horizontal well 2, and the extraction pipe is extended from the vertical well 3 of the production well group 5 into the horizontal well 2, and then the water injection pipe string is uniformly connected to the cold water tank 14, and the extraction pipe is uniformly connected to the extraction device 16, and injection and production begin.

[0081] During the injection and production process, the cold water 13 in the cold water tank 14 enters the horizontal well 2 and the branch well 6 from the injection pipe of the injection well group 4, and flows into the fracture network 12. The cold water is heated by the rock formation 1 to produce geothermal water 15 mixed with steam, which enters the branch well 6 and the horizontal well 2 of the production well group 5. The extraction device 16 then extracts the geothermal water for use through the extraction pipeline.

[0082] The above embodiments are merely exemplary embodiments of the present application and are not intended to limit the scope of the present application. The scope of protection of the present application is defined by the claims. Those skilled in the art may make various modifications or equivalent substitutions to the present application within the essence and scope of protection of the present application, and such modifications or equivalent substitutions shall also be deemed to fall within the scope of protection of the present application.

Claims

1. A method for mining hot dry rock geothermal three-dimensional well pattern, characterized in that: The steps include: Step 100: Based on the geological data of the underground rock formation, a three-dimensional well pattern model for hot dry rock geothermal extraction is designed. Then, according to the three-dimensional well pattern model, two rows of vertical wells are staggered and drilled into the hot dry rock formation. Multiple horizontal wells are drilled opposite to the bottom of the two rows of vertical wells. Branch wells are drilled laterally to each horizontal well, so that the branches of adjacent horizontal wells are coplanar with the horizontal well axis and parallel to each other, forming a fishbone well structure. Step 200: Horizontal wells drilled in the same direction and their connected vertical wells and branch wells are classified as an injection well group, while horizontal wells drilled in opposite directions and their connected vertical wells and branch wells are classified as a production well group; Step 300: Fracture the branch wells of the injection well group in order from the bottom of the well to the wellhead. Simultaneously, fracture the branch wells of the production well group in order from the wellhead to the bottom of the well, so as to form a fracture network between adjacent and parallel branch wells. Step 400: Pump cold water into the injection well group and extract water from the production well group. The cold water enters the fracture network along the vertical wells, horizontal wells, and branch wells of the injection well group for heat exchange, forming geothermal water, which is then produced from the branch wells, horizontal wells, and vertical wells of the production well group. Among them, the branch wells of the injection well group and the branch wells of the production well group are subjected to opposite synchronous fracturing; The horizontal well section of the injection well group and the horizontal well section of the production well group are arranged opposite to each other, and the horizontal well section of the injection well group and the horizontal well section of the production well group are parallel to each other to form a horizontal opposing well structure; The branch well sections of the injection well group and the branch well sections of the production well group are arranged opposite to each other, and the branch well sections of the injection well group and the branch well sections of the production well group are staggered at a fixed interval to form a branch opposing well structure; The horizontal opposing well structure and the branch opposing well structure form a well pattern structure covering the hot dry rock formation, and the well pattern structure is distributed in the thickness of the hot dry rock formation. Department; The overlapping length of the horizontal radial projections of two adjacent and parallel horizontal wells is greater than or equal to the length of the horizontal well. ; The overlapping length of the horizontal radial projections of two adjacent and parallel branch wells is greater than or equal to the length of the branch well. .

2. The method for mining hot dry rock geothermal three-dimensional well pattern according to claim 1, characterized in that: The specific method of constructing a three-dimensional well pattern model is as follows: Based on the staggered distribution rules of the injection well group and the production well group, and combined with the location and depth of the hot dry rock, the row spacing, staggered spacing and excavation depth of the injection well group and the production well group are determined; Based on the requirement of connecting the injection well group and the production well group in the hot dry rock formation, vertical wells, horizontal wells and branch wells are designed for the injection well group and the production well group; Determine the depth and location of vertical wells, horizontal wells, and branch wells based on the drilling depths of the injection well group and production well group; Determine the orientation and length of horizontal wells based on the spacing between injection and production well groups; The orientation and length of the branch wells are determined based on the spacing between the injection well group and the production well group.

3. The method for mining hot dry rock geothermal three-dimensional well pattern according to claim 1, characterized in that: In step 400, a water injection string is installed in a vertical well of the injection well group, and a drainage pipeline is installed in a vertical well of the production well group; The lower end of the water injection pipe is placed in the horizontal well of the injection well group and does not exceed the branch well. The lower end of the extraction pipe is placed in the horizontal well of the production well group and does not exceed the branch well.

4. A hot dry rock geothermal three-dimensional well pattern mining method according to any one of claims 1 to 3, characterized in that: The number of injection well groups is one more than the number of production well groups. The multiple branch wells of the production well group are distributed bidirectionally symmetrically on the horizontal well. The multiple branch wells of the injection well group located between the two production well groups are distributed bidirectionally symmetrically on the horizontal well. The multiple branch wells of the injection well group located on the outside are distributed unidirectionally toward the inside of the horizontal well.

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