A method of constructing an artificial hot reservoir of hot dry rock by hydraulic fracturing

Abstract

The present application belongs to the technical field of hot dry rock development, and particularly relates to a method for building hot dry rock artificial heat reservoir by hydraulic fracturing. The method comprises the following steps: S1, a step of injecting low-viscosity slickwater fracturing fluid into a target hot dry rock reservoir by using a step-up injection rate from low injection rate to high injection rate, and then stopping pumping for a period of time; S2, a step of injecting medium-viscosity slickwater fracturing fluid into the target hot dry rock reservoir by using a high injection rate; and S3, a step of injecting low-viscosity slickwater fracturing fluid into the target hot dry rock reservoir by using a step-down injection rate from high injection rate to stopping pumping. The method can effectively improve the complexity and connectivity of reservoir fractures, guarantee the seepage channel of the fractures, and increase the heat exchange area of the hot dry rock, so as to extract the heat energy in the hot dry rock and effectively realize heat energy replacement.

Description

Technical Field

[0001] This invention belongs to the field of hot dry rock development technology, specifically relating to a method for constructing artificial hot dry rock reservoirs using hydraulic fracturing. Background Technology

[0002] Hot dry rock is a globally recognized efficient, low-carbon, clean, and renewable energy source. Compared to other renewable energy sources, it features enormous resource reserves, zero pollution emissions, and high thermal utilization efficiency. my country possesses vast hot dry rock reserves, with reserves at depths of 3–10 km equivalent to 856 trillion tons of standard coal, indicating broad development prospects.

[0003] Developing hot dry rock using Enhanced Geothermal Systems (EGS) typically involves hydraulic fracturing to connect and modify natural microfractures, constructing a network of fractures within the underground reservoir. This creates a highly permeable artificial reservoir within the hot dry rock, forming a fluid flow and heat exchange channel for a "cold injection, hot extraction" cycle. However, due to the complex geological conditions of hot dry rock, characterized by high temperature, high strength, high density, and high stress, fracturing operations present challenges such as difficulty in initiating fractures, connecting fractures, and creating fractures. This makes it difficult to form a complex, three-dimensional fracture network, easily leading to thermal short-circuit effects, resulting in low heat exchange efficiency and impacting subsequent power generation. Therefore, considering the characteristics of hot dry rock reservoirs and the current state of hydraulic fracturing in hot dry rock, there is an urgent need to develop methods for constructing artificial hot dry rock reservoirs using hydraulic fracturing to facilitate the efficient development of hot dry rock thermal energy.

[0004] In view of this, the present invention is hereby proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a method for constructing artificial thermal reservoirs in dry hot rock using hydraulic fracturing. This method can effectively increase the complexity and connectivity of reservoir fractures, ensure fracture seepage channels, increase the heat exchange area of ​​dry hot rock, and extract thermal energy from dry hot rock, thus effectively realizing thermal energy replacement.

[0006] To overcome the shortcomings of the prior art, the present invention provides the following technical solution:

[0007] A method for constructing artificial thermal reservoirs in dry hot rock using hydraulic fracturing includes the following steps:

[0008] S1. Using a step-by-step injection method from low to high displacement, inject low-viscosity slickwater fracturing fluid into the dry hot rock target reservoir, and then stop the pump for a period of time.

[0009] S2. Subsequently, a high-volume injection method was used to inject medium-viscosity slickwater fracturing fluid into the dry hot rock target reservoir.

[0010] S3. Finally, a step-down injection method from high displacement to pump shutdown is adopted to inject low-viscosity slickwater fracturing fluid into the dry hot rock target reservoir.

[0011] Further, in step S1, the low displacement is 0.3m³. 3 / min; the high displacement is 3.0m 3 / min.

[0012] Furthermore, in step S1, the gradient amplitude of each step increase in displacement is 0.3m. 3 / min; in each gradient, the injection rate of low-viscosity slickwater fracturing fluid is 100–300 m³ / min. 3 .

[0013] Furthermore, in step S1, the pump stop time is 100–200 min.

[0014] Furthermore, in step S2, the high displacement is 3.0m³. 3 / min;

[0015] And / or, the injection volume of the medium-viscosity slickwater fracturing fluid is 600–900 m³. 3 .

[0016] Furthermore, in step S3, the high displacement is 3.0m³. 3 / min.

[0017] Furthermore, in step S3, the gradient magnitude of each step reduction in emission rate is 0.3m. 3 / min; in each gradient, the injection rate of low-viscosity slickwater fracturing fluid is 100–200 m³ / min. 3 .

[0018] Furthermore, the viscosity of the low-viscosity slickwater fracturing fluid is <5 mPa·s.

[0019] Furthermore, the viscosity of the medium-viscosity slickwater fracturing fluid is 18–20 mPa·s.

[0020] Furthermore, the drag-reducing agent in the low-viscosity slickwater fracturing fluid and the medium-viscosity slickwater fracturing fluid is a polyacrylamide.

[0021] Compared with the prior art, the technical solution of the present invention has at least the following technical effects:

[0022] The present invention describes a hydraulic fracturing method for constructing artificial thermal reservoirs in dry hot rock. This method involves several hydraulic fracturing steps, including creating complex fractures by varying the discharge rate (liters) of low-viscosity slickwater, stopping the pump and changing direction, using medium-viscosity slickwater at a fixed discharge rate to connect and enlarge fractures, and using low-viscosity slickwater with varying discharge rate (decreases) to create complex fractures. These steps form a complex fracture system in the dry rock, connecting the injection and production wells and providing a flow channel for the subsequent thermal recovery medium. This effectively increases the complexity and connectivity of the reservoir fractures, ensures the seepage channels in the fractures, and increases the heat exchange area of ​​the dry hot rock to extract thermal energy, thus effectively achieving thermal energy replacement. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Those skilled in the art should understand that the embodiments described are merely illustrative of the invention and should not be considered as specific limitations thereof. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention. Process parameters not specifically specified in the following embodiments are generally performed under conventional conditions.

[0024] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0025] This invention provides a method for constructing artificial thermal reservoirs in dry hot rock using hydraulic fracturing, comprising the following steps:

[0026] Step 1: Using a stepped injection method from low to high displacement, perform variable displacement construction by injecting low-viscosity slickwater fracturing fluid into the target dry hot rock reservoir to create a complex fracture network in the reservoir; then stop the pump for a period of time and wait for the fractures to change direction, making the fracturing fractures more complex.

[0027] Step 2: Subsequently, a high-volume injection method is used to inject medium-viscosity slickwater fracturing fluid into the dry hot rock target reservoir, thereby increasing the connectivity of the fractures.

[0028] Step 3: Finally, a stepped reduction injection method from high displacement to pump shutdown is adopted to carry out variable displacement construction, injecting low-viscosity slickwater fracturing fluid into the dry hot rock target reservoir to further increase the complexity of the fracturing fractures.

[0029] The present invention describes a hydraulic fracturing method for constructing artificial thermal reservoirs in dry hot rock. This method involves several hydraulic fracturing steps, including creating complex fractures by varying the discharge rate (liters) of low-viscosity slickwater, stopping the pump and changing direction, using medium-viscosity slickwater at a fixed discharge rate to connect and enlarge fractures, and using low-viscosity slickwater with varying discharge rate (decreases) to create complex fractures. These steps form a complex fracture system in the dry rock, connecting injection and production wells, providing a flow channel for the subsequent thermal recovery medium, effectively increasing the complexity and connectivity of reservoir fractures, ensuring fracture seepage channels, and increasing the heat exchange area of ​​the dry hot rock to extract thermal energy.

[0030] In the above-mentioned method for constructing artificial thermal reservoirs from dry hot rock using hydraulic fracturing, as a preferred embodiment, in step S1, the low discharge rate is 0.3 m³ / s. 3 / min; high displacement is 3.0m 3 / min; where the gradient amplitude of each step increase in displacement is 0.3m. 3 / min (from 0.3m) 3 Injection begins at a flow rate of / min; at 0.6m 3 / min injection rate; at 0.9m 3 / min injection rate; at a rate of 1.2m 3 / min injection rate; at a rate of 1.5m 3 / min injection rate; at a rate of 1.8m 3 / min injection rate; at 2.1m 3 / min injection rate; at 2.4m 3 / min injection rate; at 2.7m 3 / min injection rate; at 3.0m 3 / min injection rate). Optionally, in each gradient, the injection rate of low-viscosity slickwater fracturing fluid is 100–300 m³ / min. 3 (e.g., 100m) 3 150m 3 200m 3 250m 3 300m 3 )

[0031] In the above-mentioned method for constructing artificial thermal reservoirs in dry hot rock using hydraulic fracturing, as a preferred embodiment, in step S1, the pump stop time is 100-200 min (e.g., 100 min, 120 min, 140 min, 160 min, 180 min, 200 min).

[0032] In the above-mentioned method for constructing artificial thermal reservoirs from dry hot rock using hydraulic fracturing, as a preferred embodiment, in step S2, the high displacement is 3.0 m³ / s. 3 / min; optionally, the injection rate of medium-viscosity slickwater fracturing fluid is 600–900 m³ / min. 3 (e.g., 600m) 3 650m 3 700m 3 750m 3 800m 3 850m 3 900m 3 ).

[0033] In the above-mentioned method for constructing artificial thermal reservoirs from dry hot rock using hydraulic fracturing, as a preferred embodiment, in step S3, the high displacement is 3.0 m³ / s. 3 / min; where the gradient amplitude of each step reduction in emission rate is 0.3m. 3 / min (at 3.0m)3 / min injection rate; at 2.7m 3 / min injection rate; at 2.4m 3 / min injection rate; at 2.1m 3 / min injection rate; at a rate of 1.8m 3 / min injection rate; at a rate of 1.5m 3 / min injection rate; at a rate of 1.2m 3 / min injection rate; at 0.9m 3 / min injection rate; at 0.6m 3 / min injection rate; at 0.3m 3 Injection rate / min, then pump stop). Optionally, in each gradient, the injection rate of low-viscosity slickwater fracturing fluid is 100–200 m³ / min. 3 (e.g., 100m) 3 120m 3 140m 3 160m 3 180m 3 200m 3 ).

[0034] In the above-mentioned method for constructing artificial thermal reservoirs in dry hot rock using hydraulic fracturing, as a preferred embodiment, the viscosity of the low-viscosity slickwater fracturing fluid is <5 mPa·s; more preferably, the viscosity of the low-viscosity slickwater fracturing fluid is 3 to 4 mPa·s.

[0035] In the above-mentioned method for constructing artificial thermal reservoirs in dry hot rock using hydraulic fracturing, as a preferred embodiment, the viscosity of the medium-viscosity slickwater fracturing fluid is 18-20 mPa·s.

[0036] In the aforementioned method for constructing artificial thermal reservoirs in hot dry rock using hydraulic fracturing, as a preferred embodiment, the drag-reducing agent in the low-viscosity slickwater fracturing fluid and the medium-viscosity slickwater fracturing fluid is a polyacrylamide-based agent. Adding a small amount of drag-reducing agent to the slickwater fracturing fluid can reduce the contamination of the formation by the oil phase dispersion in conventional emulsion drag-reducing agents; this is a conventional technique in the field, and the amount of drag-reducing agent added is also conventional, so it will not be elaborated further. Using polyacrylamide powder as the drag-reducing agent, the drag reduction rate is >75%.

[0037] The present invention will now be described in detail with reference to embodiments thereof. These examples are provided by way of explanation and not by way of limitation. In fact, those skilled in the art will recognize that modifications and variations can be made to the present invention without departing from its scope or spirit. For example, a feature shown or described as part of one embodiment may be used in another embodiment to produce yet another embodiment. Therefore, it is desirable that the present invention encompass such modifications and variations that fall within the scope of the appended claims and their equivalents.

[0038] In the embodiments of the present invention, unless otherwise specified, the experimental methods used are conventional methods, and the materials and reagents used are commercially available unless otherwise specified.

[0039] Example 1

[0040] The fracturing technology and methods proposed in the application were used to carry out fracturing operations in Unit X of this well group. The specific steps are as follows:

[0041] S1, with 0.3m 3 The injection displacement is increased by a certain amount per minute, gradually increasing the displacement to 3.0m³. 3 At a flow rate of 0.3 m / min, low-viscosity slickwater fracturing fluid is injected during the variable-displacement fracturing operation. 3 / min displacement injection 100m 3 Liquid volume; in 0.6m 3 / min displacement injection 110m 3 Liquid volume; in 0.9m 3 / min displacement injection 140m 3 Liquid volume; in 1.2m 3 / min displacement injection 150m 3 Liquid volume; in 1.5m 3 / min displacement injection 170m 3 Liquid volume; based on 1.8m 3 / min displacement injection 190m 3 Liquid volume; in 2.1m 3 / min displacement injection 210m 3 Liquid volume; in 2.4m 3 / min injection 240m 3 Liquid volume; at 2.7m 3 / min displacement injection 260m 3 Liquid volume; in 3.0m 3 / min displacement injection 300m 3 Liquid volume. The low-viscosity slickwater fracturing fluid is an aqueous solution prepared with a polyacrylamide-based powdered drag reducer. The viscosity of this low-viscosity slickwater fracturing fluid is maintained at 3-4 mPa·s throughout the entire injection process, and the drag reduction rate is maintained at over 75%.

[0042] S2. Stop the pump for 100 minutes and wait for the crack to turn.

[0043] S3, with a length of 3.0m 3 / min injection rate, injecting medium-viscosity slippery fracturing fluid, injection volume is 700m³. 3 The medium-viscosity slickwater fracturing fluid is an aqueous solution prepared with a polyacrylamide-based powdered drag reducer. The viscosity of this medium-viscosity slickwater fracturing fluid remains at 18-20 mPa·s throughout the entire injection process.

[0044] S4, with 0.3m 3 The injection rate is reduced by a step-by-step decrease until the pump is stopped, allowing for variable-displacement fracturing fluid injection of low-viscosity slickwater. Specifically, a 3.0m³ injection rate is used. 3 / min displacement injection 200m 3 Liquid volume; at 2.7m 3 / min displacement injection 190m 3 Liquid volume; in 2.4m 3 / min displacement injection 180m 3 Liquid volume; in 2.1m 3 / min displacement injection 170m 3 Liquid volume; based on 1.8m 3 / min displacement injection 160m 3 Liquid volume; in 1.5m 3 / min displacement injection 150m 3 Liquid volume; in 1.2m 3 / min injection 140m 3 Liquid volume; in 0.9m 3 / min displacement injection 130m 3 Liquid volume; in 0.6m 3 / min displacement injection 120m 3 Liquid volume; in 0.3m 3 / min displacement injection 100m 3 The pump was stopped after the fluid volume was adjusted. The medium-viscosity slickwater fracturing fluid is an aqueous solution prepared with a polyacrylamide-based powdered drag reducer. The viscosity of this medium-viscosity slickwater fracturing fluid is maintained at 18-20 mPa·s throughout the entire injection process.

[0045] Microseismic fracture monitoring results show that the hydraulic fracturing volume is 62.7 × 10⁻⁶. 4 m 3 .

[0046] Example 2

[0047] The fracturing technology and methods proposed in the application were used to carry out fracturing operations in unit Y of this well group. The specific steps are as follows:

[0048] S1, with 0.3m 3 The injection displacement is increased by a certain amount per minute, gradually increasing the displacement to 3.0m³. 3 At a flow rate of 0.3 m / min, low-viscosity slickwater fracturing fluid is injected during the variable-displacement fracturing operation. 3 / min displacement injection 120m 3 Liquid volume; in 0.6m 3 / min displacement injection 150m 3 Liquid volume; in 0.9m 3 / min injection 140m 3 Liquid volume; in 1.2m 3 / min displacement injection 200m 3 Liquid volume; in 1.5m 3 / min displacement injection 250m 3 Liquid volume; based on 1.8m 3 / min displacement injection 300m 3 Liquid volume; in 2.1m 3 / min injection 240m 3 Liquid volume; in 2.4m 3 / min displacement injection 200m 3 Liquid volume; at 2.7m 3 / min displacement injection 150m 3 Liquid volume; in 3.0m 3 / min displacement injection 100m 3 Liquid volume. The low-viscosity slickwater fracturing fluid is an aqueous solution prepared with a polyacrylamide-based powdered drag reducer. The viscosity of this low-viscosity slickwater fracturing fluid is maintained at 3-4 mPa·s throughout the entire injection process, and the drag reduction rate is maintained at over 75%.

[0049] S2. Stop the pump for 180 minutes and wait for the crack to turn.

[0050] S3, with a length of 3.0m 3 / min injection rate, injecting medium-viscosity slippery fracturing fluid, injection volume is 800m³ / min 3 The medium-viscosity slickwater fracturing fluid is an aqueous solution prepared with a polyacrylamide-based powdered drag reducer. The viscosity of this medium-viscosity slickwater fracturing fluid remains at 18-20 mPa·s throughout the entire injection process.

[0051] S4, with 0.3m 3 The injection rate is reduced by a step-by-step decrease until the pump is stopped, allowing for variable-displacement fracturing fluid injection of low-viscosity slickwater. Specifically, a 3.0m³ injection rate is used. 3 / min displacement injection 100m 3 Liquid volume; at 2.7m 3 / min displacement injection 130m 3 Liquid volume; in 2.4m 3 / min displacement injection 160m 3 Liquid volume; in 2.1m 3 / min displacement injection 200m 3 Liquid volume; based on 1.8m 3 / min displacement injection 190m 3 Liquid volume; in 1.5m 3 / min injection 140m 3 Liquid volume; in 1.2m 3 / min displacement injection 120m 3 Liquid volume; in 0.9m 3 / min displacement injection 100m 3 Liquid volume; in 0.6m 3 / min displacement injection 110m 3 Liquid volume; in 0.3m 3 / min displacement injection 110m 3 The pump was stopped after the fluid volume was adjusted. The medium-viscosity slickwater fracturing fluid is an aqueous solution prepared with a polyacrylamide-based powdered drag reducer. The viscosity of this medium-viscosity slickwater fracturing fluid is maintained at 18-20 mPa·s throughout the entire injection process.

[0052] Microseismic fracture monitoring results show that the hydraulic fracturing volume is 67.1 × 10⁻⁶. 4 m 3 .

[0053] Example 3

[0054] The fracturing technology and methods proposed in the application were used to carry out fracturing operations in the Z unit of this well group. The specific steps are as follows:

[0055] S1, with 0.3m 3 The injection displacement is increased by a certain amount per minute, gradually increasing the displacement to 3.0m³. 3 At a flow rate of 0.3 m / min, low-viscosity slickwater fracturing fluid is injected during the variable-displacement fracturing operation. 3 / min displacement injection 200m 3 Liquid volume; in 0.6m 3 / min displacement injection 250m 3 Liquid volume; in 0.9m 3 / min displacement injection 300m 3 Liquid volume; in 1.2m 3 / min injection 240m 3 Liquid volume; in 1.5m 3 / min displacement injection 220m 3 Liquid volume; based on 1.8m 3 / min displacement injection 200m 3 Liquid volume; in 2.1m 3 / min displacement injection 180m 3 Liquid volume; in 2.4m 3 / min displacement injection 160m 3 Liquid volume; at 2.7m 3 / min displacement injection 150m 3 Liquid volume; in 3.0m 3 / min displacement injection 120m 3Liquid volume. The low-viscosity slickwater fracturing fluid is an aqueous solution prepared with a polyacrylamide-based powdered drag reducer. The viscosity of this low-viscosity slickwater fracturing fluid is maintained at 3-4 mPa·s throughout the entire injection process, and the drag reduction rate is maintained at over 75%.

[0056] S2. Stop the pump for 200 minutes and wait for the crack to turn.

[0057] S3, with a length of 3.0m 3 / min injection rate, injecting medium-viscosity slickwater fracturing fluid, injection volume is 600m³. 3 The medium-viscosity slickwater fracturing fluid is an aqueous solution prepared with a polyacrylamide-based powdered drag reducer. The viscosity of this medium-viscosity slickwater fracturing fluid remains at 18-20 mPa·s throughout the entire injection process.

[0058] S4, with 0.3m 3 The injection rate is reduced by a step-by-step decrease until the pump is stopped, allowing for variable-displacement fracturing fluid injection of low-viscosity slickwater. Specifically, a 3.0m³ injection rate is used. 3 / min displacement injection 120m 3 Liquid volume; at 2.7m 3 / min displacement injection 130m 3 Liquid volume; in 2.4m 3 / min displacement injection 150m 3 Liquid volume; in 2.1m 3 / min displacement injection 160m 3 Liquid volume; based on 1.8m 3 / min displacement injection 100m 3 Liquid volume; in 1.5m 3 / min displacement injection 150m 3 Liquid volume; in 1.2m 3 / min displacement injection 160m 3 Liquid volume; in 0.9m 3 / min displacement injection 200m 3 Liquid volume; in 0.6m 3 / min displacement injection 160m 3 Liquid volume; in 0.3m 3 / min displacement injection 120m 3 The pump was stopped after the fluid volume was adjusted. The medium-viscosity slickwater fracturing fluid is an aqueous solution prepared with a polyacrylamide-based powdered drag reducer. The viscosity of this medium-viscosity slickwater fracturing fluid is maintained at 18-20 mPa·s throughout the entire injection process.

[0059] Microseismic fracture monitoring results show that the hydraulic fracturing volume is 56.1 × 10⁻⁶. 4 m 3 .

[0060] Example 4

[0061] The fracturing technology and methods proposed in the application were used to carry out fracturing operations in unit F of this well group. The specific steps are as follows:

[0062] S1, with 0.3m 3 The injection displacement is increased by a certain amount per minute, gradually increasing the displacement to 3.0m³. 3 At a flow rate of 0.3 m / min, low-viscosity slickwater fracturing fluid is injected during the variable-displacement fracturing operation. 3 / min displacement injection 300m 3 Liquid volume; in 0.6m 3 / min injection 240m 3 Liquid volume; in 0.9m 3 / min displacement injection 220m 3 Liquid volume; in 1.2m 3 / min displacement injection 180m 3 Liquid volume; in 1.5m 3 / min displacement injection 160m 3 Liquid volume; based on 1.8m 3 / min displacement injection 120m 3 Liquid volume; in 2.1m 3 / min displacement injection 100m 3 Liquid volume; in 2.4m 3 / min displacement injection 120m 3 Liquid volume; at 2.7m 3 / min displacement injection 150m 3 Liquid volume; in 3.0m 3 / min displacement injection 200m 3 Liquid volume. The low-viscosity slickwater fracturing fluid is an aqueous solution prepared with a polyacrylamide-based powdered drag reducer. The viscosity of this low-viscosity slickwater fracturing fluid is maintained at 3-4 mPa·s throughout the entire injection process, and the drag reduction rate is maintained at over 75%.

[0063] S2. Stop the pump for 140 minutes and wait for the crack to turn.

[0064] S3, with a length of 3.0m 3 / min injection rate, injecting medium-viscosity slippery fracturing fluid, injection volume is 900m³ / min 3 The medium-viscosity slickwater fracturing fluid is an aqueous solution prepared with a polyacrylamide-based powdered drag reducer. The viscosity of this medium-viscosity slickwater fracturing fluid remains at 18-20 mPa·s throughout the entire injection process.

[0065] S4, with 0.3m 3 The injection rate is reduced by a step-by-step decrease until the pump is stopped, allowing for variable-displacement fracturing fluid injection of low-viscosity slickwater. Specifically, a 3.0m³ injection rate is used. 3 / min displacement injection 140m 3 Liquid volume; at 2.7m 3 / min displacement injection 130m 3 Liquid volume; in 2.4m 3 / min displacement injection 110m 3 Liquid volume; in 2.1m 3 / min displacement injection 140m 3 Liquid volume; based on 1.8m 3 / min displacement injection 130m 3 Liquid volume; in 1.5m 3 / min displacement injection 120m 3 Liquid volume; in 1.2m 3 / min displacement injection 100m 3 Liquid volume; in 0.9m 3 / min displacement injection 180m 3 Liquid volume; in 0.6m 3 / min displacement injection 190m 3 Liquid volume; in 0.3m 3 / min displacement injection 200m 3 The pump was stopped after the fluid volume was adjusted. The medium-viscosity slickwater fracturing fluid is an aqueous solution prepared with a polyacrylamide-based powdered drag reducer. The viscosity of this medium-viscosity slickwater fracturing fluid is maintained at 18-20 mPa·s throughout the entire injection process.

[0066] Microseismic fracture monitoring results show that the hydraulic fracturing volume is 52.8 × 10⁻⁶. 4 m 3 .

[0067] In addition, after fracturing, the hot dry rock wells were connected to each other. The water temperature of the hot dry rock injection well was 40℃, and the water temperature of the production well was 130℃, which effectively achieved heat energy exchange.

[0068] The foregoing has described and evaluated some embodiments of the present invention. It should be understood that the present invention is not limited to the specific embodiments described above. Any person skilled in the art can make many possible variations and modifications to the technical solutions of the present invention, or modify them into equivalent embodiments, without departing from the scope of the present invention. This does not affect the essential content of the present invention. Therefore, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention, without departing from the content of the present invention, still fall within the protection scope of the present invention.

Claims

1. A method for constructing artificial thermal reservoirs in dry hot rock using hydraulic fracturing, characterized in that, Includes the following steps: S1. Using a step-by-step injection method from low to high displacement, inject low-viscosity slickwater fracturing fluid into the dry hot rock target reservoir, and then stop the pump for a period of time. S2. Subsequently, a high-volume injection method was used to inject medium-viscosity slickwater fracturing fluid into the dry hot rock target reservoir. S3. Finally, a step-down injection method from high displacement to pump shutdown is adopted to inject low-viscosity slickwater fracturing fluid into the dry hot rock target reservoir.

2. The method for constructing artificial thermal reservoirs in dry hot rock using hydraulic fracturing according to claim 1, characterized in that, In step S1, the low flow rate is 0.3 m 3 / min; the high flow rate is 3.0 m 3 / min.

3. The method for constructing artificial thermal reservoirs in dry hot rock using hydraulic fracturing according to claim 1, characterized in that, In step S1, each gradient amplitude of the stepped displacement is 0.3m 3 / min; in each gradient, the injection amount of the low-viscosity slickwater fracturing fluid is 100-300m 3 .

4. The method for constructing artificial thermal reservoirs in dry hot rock using hydraulic fracturing according to claim 1, characterized in that, In step S1, the pump stop time is 100-200 minutes.

5. The method for constructing artificial thermal reservoirs in dry hot rock using hydraulic fracturing according to claim 1, characterized in that, In step S2, the high displacement is 3.0m³. 3 / min; And / or, the injection volume of the medium-viscosity slickwater fracturing fluid is 600–900 m³. 3 .

6. The method for constructing artificial thermal reservoirs in dry hot rock using hydraulic fracturing according to claim 1, characterized in that, In step S3, the high displacement is 3.0m³. 3 / min.

7. The method for constructing artificial thermal reservoirs in dry hot rock using hydraulic fracturing according to claim 1, characterized in that, In step S3, the gradient magnitude of each step reduction in emission rate is 0.3m. 3 / min; in each gradient, the injection rate of low-viscosity slickwater fracturing fluid is 100–200 m³ / min. 3 .

8. The method for constructing artificial thermal reservoirs in dry hot rock using hydraulic fracturing according to any one of claims 1-7, characterized in that, The viscosity of the low-viscosity slickwater fracturing fluid is <5 mPa·s.

9. The method for constructing artificial thermal reservoirs in dry hot rock using hydraulic fracturing according to any one of claims 1-7, characterized in that, The viscosity of the medium-viscosity slickwater fracturing fluid is 18–20 mPa·s.

10. The method for constructing artificial thermal reservoirs in dry hot rock using hydraulic fracturing according to any one of claims 1-7, characterized in that, The drag-reducing agents in the low-viscosity slickwater fracturing fluid and the medium-viscosity slickwater fracturing fluid are polyacrylamide-based.