Method for fracturing hot dry rock and method for collecting heat from hot dry rock

Abstract

The invention relates to the technical field of fracturing of hot dry rocks, and discloses a method for fracturing the hot dry rocks and a method for collecting heat from the hot dry rocks. The invention provides a method for fracturing hot dry rock, which comprises the following steps of: (1) selecting a cased well completion section in a heating well arranged on the hot dry rock, and dividing the cased well completion section into n sections to be treated; (2) the oil pipe of the cased well completion section is filled with fracturing fluid at the first displacement, and optionally, soluble balls are added along with the fracturing fluid; (3) selecting a crack development layer section in the section to be treated for sand blasting perforation to obtain a target layer section; (4) carrying out fracturing construction on the target interval by using supercritical carbon dioxide to obtain a fractured section; (5) the steps (2)-(4) are repeated, and all the sections to be treated are fractured; wherein n is selected from 8 to 12.

Description

Technical Field

[0001] The present invention relates to a fracturing technology for hot dry rock, and specifically to a method for fracturing hot dry rock and a method for extracting heat from hot dry rock. Background Art

[0002] Hot dry rock generally refers to a high-temperature rock mass with little or no internal fluid, which has the characteristics of large resource volume, zero emissions, high utilization rate, etc., and can be widely used for power generation, heating, etc. It is a renewable clean energy that is the focus of research and development in various countries around the world.

[0003] At present, the development of hot dry rock type geothermal energy is mostly realized through the EGS system, that is, a large-scale fracturing technology using fracturing fluid is used to create an artificial heat storage, and a connected fracture network is formed between two or more wells, and geothermal energy is extracted through the flow of fluid in the injection and production wells. Although this technology is the mainstream development direction of hot dry rock development, due to the fact that hot dry rock is generally open-hole completion or slotted liner completion, it is difficult to achieve fine transformation, and there are problems such as limited length of the transformed section, difficulty in connecting injection and production wells, serious loss of working fluid, and high technical risks.

[0004] Therefore, there is an urgent need for a better method for extracting heat from hot dry rock. Summary of the Invention

[0005] The purpose of the present invention is to overcome the problems existing in the prior art, such as the difficulty in connecting injection and production wells of hot dry rock, small transformation volume and low heat extraction efficiency, and to provide a method for fracturing hot dry rock and a method for extracting heat from hot dry rock.

[0006] To achieve the above purpose, the first aspect of the present invention provides a method for fracturing hot dry rock, which includes the following steps:

[0007] (1) Select the casing completion section in the production well drilled in the hot dry rock, and divide the casing completion section into n sections to be processed;

[0008] (2) Inject fracturing fluid into the tubing of the casing completion section at a first displacement, and optionally, add soluble balls with the fracturing fluid;

[0009] (3) Select the fracture-developed section in the section to be processed for sandblasting perforation to obtain the target section;

[0010] (4) Use supercritical carbon dioxide to perform fracturing construction on the target section to obtain a fractured section;

[0011] (5) Repeat steps (2)-(4) to complete the fracturing of all sections to be processed;

[0012] Wherein, n is selected from 8-12.

[0013] The second aspect of the present invention provides a method for extracting heat from hot dry rock, which includes fracturing and heat exchange, wherein the fracturing method is the method described in the first aspect.

[0014] Through the above technical solutions, the present invention provides a method for fracturing hot dry rock and a method for extracting heat. The method for fracturing hot dry rock according to the present invention does not require connecting injection and production wells. By forming complex fractures in the near-wellbore zone, the heat exchange efficiency can be improved. The present invention performs segmented treatment on the casing completion section of hot dry rock, and at the same time, sandblasting perforation is carried out and the strong solubility and strong penetrability characteristics of supercritical carbon dioxide are utilized. It is easy to enter the microscopic pores of the rock and interact with the rock, and can generate a complex fracture network, which has no damage to the reservoir, can achieve a lower fracture initiation pressure, and generate a more complex fracture network in the near-wellbore zone. It has the advantages of low difficulty in reservoir engineering and small technical risks. Different from the single-well heat extraction technology of traditional enhanced geothermal systems (EGS), it can realize an efficient single-well geothermal extraction technology of "pump-free drive". Detailed Embodiments

[0015] In the ranges disclosed herein, the endpoints and any values are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0016] The first aspect of the present invention provides a method for fracturing hot dry rock, which includes the following steps:

[0017] (1) Select the casing completion section in the production well drilled in hot dry rock, and divide the casing completion section into n sections to be processed;

[0018] (2) Fill the tubing in the casing completion section with fracturing fluid at a first displacement. Optionally, soluble balls are added with the fracturing fluid;

[0019] (3) Select the fracture-developed section in the section to be processed for sandblasting perforation to obtain the target section;

[0020] (4) Use supercritical carbon dioxide to perform fracturing construction on the target section to obtain a fractured section;

[0021] (5) Repeat steps (2)-(4) to complete the fracturing of all sections to be processed;

[0022] Wherein, n is selected from 8-12.

[0023] In the present invention, the method for fracturing hot dry rock does not require connecting injection and production wells. By forming complex fractures in the near-wellbore zone, the heat exchange efficiency can be improved. In the present invention, the casing completion section of the hot dry rock is segmented, and at the same time, sandblasting perforation is carried out and the strong solubility and strong penetrability characteristics of supercritical carbon dioxide are utilized. It is easy to enter the microscopic pores of the rock and interact with the rock, and can generate a complex fracture network without reservoir damage. It can achieve a lower fracture initiation pressure and generate a more complex fracture network in the near-wellbore zone. It has the advantages of low difficulty in thermal reservoir engineering and small technical risks. Different from the single-well heat extraction technology of traditional enhanced geothermal systems (EGS), it can realize an efficient single-well geothermal extraction technology of "pump-free driving".

[0024] In the present invention, formal fracturing construction is carried out according to the designed fracturing fluid volume and displacement to expand the transverse fractures in the near-wellbore zone, and at the same time, precise transformation of the fracture-developed layers in the vertical direction is realized. Through hydraulic jetting of supercritical carbon dioxide, the entire long screen pipe section in the vertical direction can be transformed, and a higher single-well transformation volume can be achieved.

[0025] In some specific embodiments of the present invention, in step (2), the tubing is filled with fracturing fluid at a first displacement, and the first displacement is 0.3 - 0.5 m 3 / min. Optionally, soluble balls are added with the fracturing fluid, which means that among the n segments to be processed in the casing completion section, the first segment to be processed does not need to add soluble balls, and soluble balls are added with the fracturing fluid starting from the second segment to be processed. Soluble balls need to be added to the second to the nth segments to be processed. Among them, the soluble balls are BH-MSP magnesium-aluminum alloy soluble balls of Bohai Drilling Engineering Institute.

[0026] In some specific embodiments of the present invention, in step (2), the first displacement is 0.3 - 0.5 m 3 / min, and the fracturing fluid is injected at a low displacement to ensure that the formation does not fracture and to displace the clear water.

[0027] In some specific embodiments of the present invention, in step (2), the first displacement is 0.3 - 0.5 m 3 / min. The ball is seated at a low displacement. The sandblasting perforation gun in the present invention is a sliding sleeve type. By adding soluble balls with the fracturing fluid to a fixed position, the sliding sleeve is opened to carry out the sandblasting perforation. The pressure display of seating the ball at a low displacement to open the sliding sleeve is more obvious and has a better effect.

[0028] In some specific embodiments of the present invention, in step (3), the process of sandblasting perforation includes: injecting fracturing fluid at a second displacement and hydraulically jetting quartz sand, and after completion, adding displacement fluid into the tubing to discharge the quartz sand in the tubing to the ground.

[0029] In some specific embodiments of the present invention, in step (3), the second displacement is 2 - 4 m 3 / min. Within this range of the second displacement, it is ensured that the casing is jet - opened while ensuring that the jet pressure is within the safe range.

[0030] In some specific embodiments of the present invention, in step (3), the displacement at which the displacement fluid is added is 2 - 4 m 3 / min.

[0031] In some specific embodiments of the present invention, in step (3), the volume concentration of quartz sand is 5 - 6%, that is, the percentage of the volume of quartz sand in the volume of the fracturing fluid. The amount of quartz sand added is 2 - 4 m 3 .

[0032] In some specific embodiments of the present invention, in step (4), the process of the fracturing operation includes: injecting supercritical carbon dioxide into the tubing for fracturing and adding supercritical carbon dioxide through the casing fluid - supplementing channel in the casing. Specifically, after the sand - jet perforation is completed, the casing blow - down gate is closed, supercritical carbon dioxide is injected into the tubing for fracturing, and the casing fluid - supplementing channel gate is opened to add supercritical carbon dioxide through the casing fluid - supplementing channel.

[0033] In some specific embodiments of the present invention, in step (4), the displacement of injecting supercritical carbon dioxide into the tubing is 2 - 4 m 3 / min.

[0034] In some specific embodiments of the present invention, in step (4), the displacement of adding supercritical carbon dioxide is 0.8 - 1 m 3 / min.

[0035] In some specific embodiments of the present invention, in step (4), the total amount of supercritical carbon dioxide injected into each section to be treated is 500 - 600 m 3 , which includes the amount of supercritical carbon dioxide injected into the tubing and the amount of supercritical carbon dioxide added.

[0036] In some specific embodiments of the present invention, in step (4), the temperature of the supercritical carbon dioxide ≥ 31.3 °C and the pressure ≥ 7.38 MPa.

[0037] In some specific embodiments of the present invention, the well section depth of the present invention is 2500 - 3500 m, and the length of the selected casing completion section is 800 - 1000 m. The meaning of selecting the length of the casing completion section of the present invention is: select the length of one section of the casing completion section of the well section depth of the present invention to be 800 - 1000 m. The casing specification is P110, the casing diameter size can be 177.8 mm, and the wall thickness is 11.51 mm. The casing completion section size within the above range can achieve a higher single - well transformation volume and can realize the efficient single - well geothermal exploitation technology.

[0038] In some specific embodiments of the present invention, the tubing specification is P105, the tubing diameter can be 88.9 mm, and the wall thickness is 9.53 mm. The tubing specification within the above range can achieve a higher single - well transformation volume and can realize the efficient single - well geothermal exploitation technology.

[0039] In some specific embodiments of the present invention, in step (3), the fracture - developed layer section is type - I and type - II fracture layers. Among them, the porosity φ≥10% is type - I fracture, and 5%≤porosity φ﹤10% is type - II fracture. Among them, the porosity φ is the ratio of the volume of the rock pore space to the volume of the rock, reflecting the physical properties of the formation. Selecting the fracture - developed layer section defined in this application is beneficial for better fracture formation, so as to form complex fractures to improve the heat - exchange efficiency. Fractures with a porosity φ lower than 5% require a larger fracture - initiation pressure and are more difficult to fracture. Among them, in the present invention, the total length of the type - I and type - II fracture - developed sections is 400 - 500 m.

[0040] In some specific embodiments of the present invention, the fracturing fluid is a water - based fracturing fluid with a viscosity of 10 - 20 mPa·s.

[0041] The second aspect of the present invention provides a method for extracting heat from hot dry rock, which includes fracturing and heat - exchange. Among them, the fracturing method is the method described in the first aspect.

[0042] The present invention will be described in detail below through examples. In the following examples, the water - based fracturing fluid is prepared by mixing a polyacrylamide - type emulsion thickener and clear water at a volume ratio of 0.15 - 0.2:100. Among them, the polyacrylamide - type emulsion thickener is formed by inverse emulsion polymerization of acrylamide, 2 - acrylamido - 2 - methylpropanesulfonic acid, and dimethylhexadecylallylammonium chloride according to a monomer mass ratio of 6:3:1.

[0043] For those not specifying specific conditions in the following examples and comparative examples, they are carried out according to conventional conditions or conditions recommended by the manufacturer. For reagents or instruments not indicating the manufacturer, they are all conventional products that can be obtained through commercial channels.

[0044] Example 1

[0045] (1) In this embodiment, a hot dry rock well in the Bohai Rim region is selected. The lithology of the fracturing interval is metamorphic granite, the interval depth is 2500 - 3500 m, the maximum formation temperature is 150 °C, and it is divided into 10 intervals to be treated. Among them, the lengths of the intervals with well-developed fractures of types I and II are 450 m, the casing specification is P110, the outer diameter is 177.8 mm, and the wall thickness is 11.51 mm.

[0046] (2) Lower the tubing with a hydraulic jet gun. The tubing specification is P105, the outer diameter is 88.9 mm, the wall thickness is 9.53 mm, the fluid medium is water-based fracturing fluid, and the viscosity is 15 mPa·s. Open the casing valve and fill the tubing in the production well with fracturing fluid at a rate of 0.4 m 3 / min.

[0047] (3) Increase the fracturing fluid displacement to 4.0 m 3 / min to conduct hydraulic jetting of quartz sand. The blender truck starts adding quartz sand. The particle size of the quartz sand is 70 / 140 mesh, the concentration is 6%, and the addition amount is 2 m 3 . After stopping sandblasting and perforating, after completion, add displacement fluid to the tubing to discharge the quartz sand in the tubing to the ground. The displacement of the added displacement fluid is 3 m 3 / min to obtain the target interval.

[0048] (4) After the hydraulic jetting is completed, close the casing blowout gate valve and inject supercritical carbon dioxide into the tubing for fracturing. The displacement of injecting supercritical carbon dioxide into the tubing is 4 m 3 / min for construction. Adjust the displacement according to the pressure, and supplement supercritical carbon dioxide through the casing fluid supplement channel. In the casing fluid supplement channel, the displacement of supercritical carbon dioxide is 1 m 3 / min. A total of 600 m3 of supercritical carbon dioxide is co-injected into the tubing and the casing.

[0049] (5) Repeat steps (2) - (4) to complete the fracturing of all intervals to be treated. Among them, in step (2), starting from the second interval to be treated, soluble balls are added along with the fracturing fluid. Soluble balls need to be added in the second to the nth intervals to be treated.

[0050] Example 2

[0051] (1) In this embodiment, a hot dry rock well in the Bohai Rim region is selected. The lithology of the fracturing interval is metamorphic granite, the interval depth is 2500 - 3500 m, the maximum formation temperature is 150 °C, and it is divided into 10 intervals to be treated. Among them, the lengths of the intervals with well-developed fractures of types I and II are 450 m, the casing specification is P110, the outer diameter is 177.8 mm, and the wall thickness is 11.51 mm.

[0052] (2) Lower the tubing with a hydraulic jet gun. The tubing specification is P105, the outer diameter is 88.9 mm, the wall thickness is 9.53 mm, the fluid medium is water-based fracturing fluid, and the viscosity is 10 mPa·s. Open the casing valve and fill the tubing in the heat production well with fracturing fluid at a rate of 0.5 m 3 / min.

[0053] (3) Increase the fracturing fluid displacement to 2.0 m 3 / min to conduct hydraulic jetting of quartz sand. The blender truck starts adding quartz sand. The particle size of the quartz sand is 70 / 140 mesh, the concentration is 6%, and the addition amount is 2 m 3 . After stopping sandblasting and perforating, after completion, add displacement fluid to the tubing to discharge the quartz sand in the tubing to the ground. The displacement of the added displacement fluid is 3 m 3 / min to obtain the target interval.

[0054] (4) After the hydraulic jetting is completed, close the casing blowout gate and inject supercritical carbon dioxide into the tubing for fracturing. The displacement of injecting supercritical carbon dioxide into the tubing is 2 m 3 / min for construction. Adjust the displacement according to the pressure and add supercritical carbon dioxide through the casing fluid supplement channel. In the casing fluid supplement channel, the displacement of supercritical carbon dioxide is 0.8 m 3 / min. A total of 500 m 3 of supercritical carbon dioxide is co-pumped in the tubing and the casing.

[0055] (5) Repeat steps (2)-(4) to complete the fracturing of all intervals to be treated. Among them, in step (2), starting from the second interval to be treated, soluble balls are added along with the fracturing fluid. Soluble balls need to be added in the second to the nth intervals to be treated.

[0056] Example 3

[0057] (1) In this example, a hot dry rock well in the Bohai Rim region is selected. The lithology of the fracturing interval is metamorphic granite, the well depth of the interval is 2500 - 3500 m, the highest formation temperature is 150 °C, and it is divided into 10 intervals to be treated. Among them, the lengths of the fracture-developed intervals of types I and II are 450 m, the casing specification is P110, the outer diameter is 177.8 mm, and the wall thickness is 11.51 mm.

[0058] (2) Lower the tubing with a hydraulic jet gun. The tubing specification is P105, the outer diameter is 88.9 mm, the wall thickness is 9.53 mm, the fluid medium is water-based fracturing fluid, and the viscosity is 10 mPa·s. Open the casing valve and fill the tubing in the heat production well with fracturing fluid at a rate of 0.3 m 3 / min.

[0059] (3) Increase the fracturing fluid displacement to 3.0 m 3Perform hydraulic jetting of quartz sand at / min, and the blender truck starts adding quartz sand. The particle size of the quartz sand is 70 / 140 mesh, the concentration is 6%, and the addition amount is 3 m 3 After stopping sandblasting perforation, after completion, displacement fluid is added into the tubing to discharge the quartz sand in the tubing to the ground. The displacement rate of the added displacement fluid is 3 m 3 / min to obtain the target interval.

[0060] (4) After the hydraulic jetting is completed, close the casing flowback gate, and inject supercritical carbon dioxide into the tubing for fracturing. The displacement rate of injecting supercritical carbon dioxide into the tubing is 3 m 3 / min for construction, adjust the displacement according to the pressure, and add supercritical carbon dioxide through the casing fluid supplement channel. In the casing fluid supplement channel, the displacement rate of supercritical carbon dioxide is 1 m 3 / min, and a total of 500 m of supercritical carbon dioxide is pumped in the tubing and the casing. 3 supercritical carbon dioxide.

[0061] (5) Repeat steps (2)-(4) to complete the fracturing of all intervals to be treated. Among them, in step (2), starting from the second interval to be treated, soluble balls are added along with the fracturing fluid, and soluble balls need to be added from the second interval to the nth interval to be treated.

[0062] Example 4

[0063] According to the method of Example 1, select a hot dry rock well in the Bohai Rim region. The difference is that the casing completion section in the production well drilled in the hot dry rock is divided into 8 intervals to be treated, and other conditions and steps are the same.

[0064] Example 5

[0065] According to the method of Example 1, select a hot dry rock well in the Bohai Rim region. The difference is that in step (3), the displacement rate of the fracturing fluid is increased to 1.0 m 3 / min for hydraulic jetting of quartz sand, and other conditions and steps are the same.

[0066] Example 6

[0067] According to the method of Example 1, select a hot dry rock well in the Bohai Rim region. The difference is that in step (4), the displacement rate of injecting supercritical carbon dioxide into the tubing is 1 m 3 / min for construction, and other conditions and steps are the same.

[0068] Comparative Example 1

[0069] (1) In this embodiment, a hot dry rock well in the Bohai Rim region is selected. The lithology of the fracturing interval is metamorphic granite, the interval depth is 2500 - 3500 m, the maximum formation temperature is 150 °C, and it is fractured in 5 sections. Among them, the lengths of the I and II type fracture-developed sections are 450 m, the casing specification is P110, the outer diameter is 177.8 mm, and the wall thickness is 11.51 mm.

[0070] (2) Lower the tubing with a hydraulic jet gun. The tubing specification is P105, the outer diameter is 88.9 mm, the wall thickness is 9.53 mm, and the fluid medium is water-based fracturing fluid with a viscosity of 15 mPa·s. Open the casing valve and fill the tubing in the production well with fracturing fluid at a rate of 0.5 m 3 / min.

[0071] (3) Increase the fracturing fluid displacement to 4.0 m 3 / min to conduct hydraulic jetting of quartz sand. The blender truck starts adding quartz sand. The particle size of the quartz sand is 70 / 140 mesh, the concentration is 6%, and the addition amount is 2 m 3 . After stopping the sandblasting and perforating, after completion, add displacement fluid to the tubing to discharge the quartz sand in the tubing to the ground. The displacement of the added displacement fluid is 3 m 3 / min to obtain the target interval.

[0072] (4) After the hydraulic jetting is completed, close the casing blowout gate and inject supercritical carbon dioxide into the tubing for fracturing. The displacement of injecting supercritical carbon dioxide into the tubing is 4 m 3 / min for construction. Adjust the displacement according to the pressure, and supplement supercritical carbon dioxide through the casing liquid supplement channel. In the casing liquid supplement channel, the displacement of supercritical carbon dioxide is 1 m 3 / min. A total of 500 m 3 of supercritical carbon dioxide is co-injected into the tubing and the casing.

[0073] (5) Repeat steps (2) - (4) to complete the fracturing of all the intervals to be processed. Among them, in step (2), starting from the second interval to be processed, soluble balls are added along with the fracturing fluid, and soluble balls need to be added from the second interval to the nth interval to be processed.

[0074] The method for fracturing hot dry rock in the example and the comparative example is simulated by Meyer fracturing software, and the simulation is carried out according to the parameters given in this method. The single-well stimulation volume is obtained by simulation. Among them, the definition of the single-well stimulation volume is: the total volume of fractures formed by fracturing and transforming the selected casing completion interval. The results are shown in Table 1.

[0075] Table 1

[0076] Number <![CDATA[Single well transformation volume / × 10 4 m 3 > Example 1 12.8 Example 2 11.1 Example 3 11.8 Example 4 10.7 Example 5 9.8 Example 6 8.4 Comparative Example 1 6.5

[0077] As can be seen from the results in Table 1, Example 1 of the method for fracturing hot dry rock using the present invention has a significantly better single-well stimulation volume. The larger the single-well stimulation volume, the more it indicates that the fracturing method of the present invention can generate a complex fracture network, thereby enabling efficient single-well geothermal extraction technology.

[0078] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A method for fracturing hot dry rock, characterized in that, It includes the following steps: (1) Select the casing completion section in the production well drilled in the hot dry rock, and divide the casing completion section into n sections to be processed; (2) Fill the tubing in the casing completion section with fracturing fluid at a first displacement rate. Optionally, add soluble balls with the fracturing fluid; (3) Select the fracture-developed section in the section to be processed for sandblasting perforation to obtain the target section; (4) Use supercritical carbon dioxide to perform fracturing construction on the target section to obtain a fractured section; (5) Repeat steps (2)-(4) to complete fracturing of all sections to be processed; wherein, n is selected from 8-12.

2. The method according to claim 1, wherein In step (2), the first displacement is 0.3 - 0.5 m 3 / min; Preferably, in step (3), the process of the sandblasting perforation includes: injecting fracturing fluid at a second displacement rate and hydraulically jetting quartz sand, and after completion, adding displacement fluid into the tubing to discharge the quartz sand in the tubing to the ground.

3. According to the method described in claim 2, in step (3), the second displacement is 2-4 m 3 / min; Preferably, in step (3), the displacement of the displacement fluid added is 2-4 m 3 / min; Preferably, in step (3), the particle size of the quartz sand is 70-140 mesh, the volume concentration of the quartz sand is 5-6%, and the amount of the added quartz sand is 2-4m 3 .

4. The method according to any one of claims 1-3, wherein, In step (4), the process of the fracturing construction includes: injecting supercritical carbon dioxide into the tubing for fracturing, and adding supercritical carbon dioxide through the casing fluid compensation channel in the casing.

5. The method according to claim 4, wherein In step (4), the displacement of injecting supercritical carbon dioxide into the oil pipe is 2-4 m 3 / min; Preferably, in step (4), the displacement of the supplementary supercritical carbon dioxide is 0.8 - 1 m 3 / min; Preferably, in step (4), the total amount of supercritical carbon dioxide injected into each segment to be processed is 500 - 600 m 3 .

6. The method according to any one of claims 1-5, wherein, In step (4), the temperature of the supercritical carbon dioxide ≥ 31.3 °C and the pressure ≥ 7.38 MPa.

7. The method according to any one of claims 1-6, wherein, Select the length of the casing completion section to be 800-1000 m.

8. The method according to any one of claims 1-7, wherein, In step (3), the fracture-developed section is type I and type II fracture layers; wherein, the porosity φ ≥ 10% is type I fracture, and 5% ≤ porosity φ < 10% is type II fracture.

9. The method according to any one of claims 1-8, wherein The fracturing fluid is a water-based fracturing fluid with a viscosity of 10-20 mPa·s.

10. A method for extracting heat from hot dry rock, characterized in that, It includes fracturing and heat exchange, wherein the method of the fracturing is the method described in any one of claims 1-9.