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

Abstract

A method for fracturing dry hot rock and a method for extracting heat from dry hot rock. The method for fracturing dry hot rock comprises the following steps: (1) selecting a cased hole completion section in a heat-extracting well located in dry hot rock, and dividing the cased hole completion section into n sections to be treated; (2) filling an oil pipe of the cased hole completion section with a fracturing fluid in a first displacement, and adding a soluble ball along with the fracturing fluid; (3) selecting a fracture development layer section in the section to be treated to perform sand blasting perforation, so as to obtain a target layer section; (4) subjecting the target layer section to fracturing construction by using supercritical carbon dioxide, so as to obtain a fracturing section; and (5) repeatedly performing steps (2)-(4), until the fracturing of all the sections to be treated is completed, wherein n is selected from 8-12.

Description

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

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of Chinese patent application 202311783515.9, filed on December 22, 2023, the contents of which are incorporated herein by reference. Technical Field

[0003] The present invention relates to the technical field of fracturing hot dry rocks, and in particular to a method for fracturing hot dry rocks and a method for extracting heat from hot dry rocks. Background Art

[0004] Hot dry rock generally refers to a high-temperature rock mass with no or only a small amount of fluid inside. It has the characteristics of large resources, zero emissions, and high utilization rate. It can be widely used in power generation, heating, etc., and is a renewable clean energy that is the focus of research and development in countries around the world.

[0005] Currently, hot dry rock geothermal resources are mostly developed through EGS systems. This involves using fracturing fluid to create a network of interconnected fractures between two or more wells. Fluid is then injected to bring underground heat to the surface, enabling geothermal energy extraction. While this technology is the mainstream development direction for hot dry rock development, it is difficult to achieve precise stimulation due to the fact that hot dry rock wells are typically completed with open holes or screens. Furthermore, there are issues such as limited stimulation section length, difficulty connecting injection and production wells, significant fluid loss, and significant technical risks.

[0006] Therefore, there is an urgent need for better heat extraction methods to extract heat from hot dry rocks. Summary of the Invention

[0007] The purpose of the present invention is to solve the problems of difficult connection of hot dry rock injection and production wells, small transformation volume and low heat extraction efficiency in the prior art, and to provide a method for fracturing hot dry rock and a method for extracting heat from hot dry rock.

[0008] In order to achieve the above object, a first aspect of the present invention provides a method for fracturing hot dry rock, which comprises the following steps:

[0009] (1) selecting a casing completion section in a hot dry rock well, and dividing the casing completion section into n sections to be processed;

[0010] (2) filling the oil tubing of the casing completion section with a first displacement of fracturing fluid, and optionally adding soluble balls along with the fracturing fluid;

[0011] (3) selecting a fracture-developed layer section in the section to be treated and performing sandblasting and perforation to obtain a target layer section;

[0012] (4) fracturing the target layer using supercritical carbon dioxide to obtain a fracturing section;

[0013] (5) Repeat steps (2) to (4) to complete fracturing of all sections to be treated;

[0014] Wherein, said n is selected from 8-12.

[0015] A second aspect of the present invention provides a method for extracting heat from hot dry rocks, wherein the method includes fracturing and heat exchange, wherein the fracturing method is the method described in the first aspect.

[0016] Through the above-mentioned technical solution, the present invention provides a method for fracturing hot dry rock and a method for heat extraction. The method for fracturing hot dry rock according to the present invention does not require the connection of injection and production wells, and improves heat exchange efficiency by forming complex fractures in the near-wellbore area. By segmenting the hot dry rock through the casing completion section, and simultaneously performing sandblasting and perforating and fracturing with supercritical carbon dioxide, the present invention can produce a more complex fracture network in the near-wellbore area at a lower fracture initiation pressure. This method has the advantages of low heat storage engineering difficulty and low technical risk. Unlike traditional EGS single-well heat extraction technology, it can achieve "pumpless" and efficient single-well geothermal extraction technology. DETAILED DESCRIPTION

[0017] The endpoints of the ranges and any values ​​disclosed herein 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 endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0018] A first aspect of the present invention provides a method for fracturing hot dry rock, wherein the method comprises the following steps:

[0019] (1) selecting a casing completion section in a hot dry rock well, and dividing the casing completion section into n sections to be processed;

[0020] (2) filling the oil tubing of the casing completion section with a first displacement of fracturing fluid, and optionally adding soluble balls along with the fracturing fluid;

[0021] (3) selecting a fracture-developed layer section in the section to be treated and performing sandblasting and perforation to obtain a target layer section;

[0022] (4) fracturing the target layer using supercritical carbon dioxide to obtain a fracturing section;

[0023] (5) Repeat steps (2) to (4) to complete fracturing of all sections to be treated;

[0024] Wherein, said n is selected from 8-12.

[0025] In the present invention, the method of fracturing hot dry rock does not require the operation of connecting injection and production wells, and improves the heat exchange efficiency by forming complex fractures in the near-wellbore area. The present invention performs segmented processing on the casing completion section in the hot dry rock production well, and simultaneously performs sandblasting and perforation and uses supercritical carbon dioxide to perform fracturing construction on the target layer section, which can achieve a lower fracturing pressure and produce a more complex fracture network in the near-wellbore area. It has the advantages of large single-well transformation volume, low difficulty of heat storage engineering, and low technical risk. Unlike the traditional EGS single-well heat extraction technology, it can realize "pump-free" efficient single-well geothermal extraction technology. In the present invention, supercritical carbon dioxide has the characteristics of strong solubility and strong penetration, and can easily enter the microscopic pores of the rock to interact with the rock, produce a complex fracture network, and does not harm the reservoir.

[0026] In the present invention, formal fracturing construction is carried out according to the designed fracturing fluid volume and displacement, the lateral fractures in the near-wellbore area are expanded, and the precise segment transformation of the fracture development layer in the vertical direction is achieved at the same time. The entire vertical long screen pipe section is transformed by hydraulic injection of supercritical carbon dioxide, which can achieve a higher single-well transformation volume.

[0027] In some specific embodiments of the present invention, in step (1), the casing completion section in the hot dry rock well is selected as the target layer section for transformation, and the target layer section for transformation is divided into n sections to be treated from bottom to top according to the distribution of the fracture development layer.

[0028] In the present invention, the types of underground rock formations in the target layer segment for transformation include not only fracture-developed layers but also layers with no or few fractures. The fracture-developed layers in the target layer segment for transformation are scattered in the vertical direction. According to the distribution of the fracture-developed layers, the target layer segment for transformation is divided from bottom to top into n sections to be processed, namely the first section to be processed, the second section to be processed, the third section to be processed, and so on until the nth section to be processed. After the division, each section to be processed contains a fracture-developed layer segment. Preferably, the cumulative total length of the fracture-developed layer segments in each section to be processed is equal.

[0029] In some specific embodiments of the present invention, in step (1), the fracture development layer includes a Class I fracture layer and / or a Class II fracture layer; a porosity φ ≥ 10% is a Class I fracture, and a porosity φ 5% ≤ 10% is a Class II fracture; the cumulative total length of the Class I fracture layer and the Class II fracture development section is 400-500m.

[0030] Porosity φ is the ratio of the rock's pore space volume to the rock's volume, reflecting the formation's physical properties. Fractures with a porosity φ below 5% require higher initiation pressures, making fracturing more difficult. Based on the distribution of fracture-developing layers, the present invention divides the target layer into n treatment sections from bottom to top. Sandblasting and perforating the Class I and / or Class II fracture layers within each treatment section facilitates the full transformation of both Class I and Class II fracture layers, resulting in better fracture formation and the formation of complex fractures, which improves heat exchange efficiency.

[0031] In some specific embodiments of the present invention, in step (1), n ​​is an integer between 8 and 12, and can be 8, 9, 10, 11 or 12.

[0032] In some specific embodiments of the present invention, the depth of the well section of the heat production well of the present invention is 2500-3500m, and the length of the target layer section selected for transformation is 800-1000m. The present invention selects the length of the target layer section for transformation to be 800-1000m, which means: a well section with a length of 800-1000m is selected from the heat production well with a well section depth of 2500-3500m as the target layer section for transformation. Among them, the selection of the target layer section for transformation is common knowledge in the field, and the present invention will not elaborate on it. The casing specification of the target layer section for transformation is P110, the casing diameter can be 177.8mm, and the wall thickness is 11.51mm. Casings with sizes within the above range can further achieve a higher single-well transformation volume, thereby contributing to the realization of efficient single-well geothermal extraction.

[0033] In some specific embodiments of the present invention, the tubing used in the target reservoir section for reconstruction is P105, with a diameter of 88.9 mm and a wall thickness of 9.53 mm. Tubing within this range can further increase the volume of a single well reconstruction, contributing to efficient single-well geothermal recovery.

[0034] In some specific embodiments of the present invention, in step (2), the first displacement is 0.3-0.5m 3 / min. Among them, 0.3-0.5m 3 Injecting fracturing fluid at a low rate of 1 / min not only prevents formation fractures but also displaces clean water. Furthermore, the spray gun used in the sandblasting perforation described herein is a sliding sleeve-type spray gun. After the soluble balls are added with the fracturing fluid, they are transported by the fracturing fluid to a fixed position, allowing the sliding sleeve to be opened for sandblasting perforation. The low-rate ball seating provides a more pronounced pressure display when opening the sliding sleeve, resulting in better results.

[0035] In some specific embodiments of the present invention, in step (2), soluble balls are optionally added with the fracturing fluid, which means that: the casing completion section is divided into n sections to be treated, and soluble balls do not need to be added to the first section to be treated. Soluble balls are added with the fracturing fluid starting from the second section to be treated, and soluble balls are required to be added to the second to nth sections to be treated. The soluble balls are BH-MSP magnesium-aluminum alloy soluble balls produced by Bohai Drilling Engineering Institute.

[0036] In some specific embodiments of the present invention, in step (2), the first section of the oil pipe to be treated is filled with fracturing fluid at a first displacement; alternatively, the first section of the oil pipe to be treated is filled with fracturing fluid containing soluble balls at a first displacement. In the present invention, the first section of the oil pipe to be treated is subjected to sandblasting and perforation treatment. When the sleeve of the sliding sleeve spray gun is exposed, it is not necessary to add soluble balls to the fracturing fluid.

[0037] 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 at room temperature. The room temperature in the present invention has a well-known meaning and is not particularly limited in the present invention, for example, 10-35°C.

[0038] In some specific embodiments of the present invention, in step (3), the sandblasting and perforating process includes: injecting fracturing fluid at a second displacement and hydraulically spraying quartz sand, and after completion, adding displacement fluid into the oil pipe to discharge the quartz sand in the oil pipe to the ground.

[0039] In some specific embodiments of the present invention, in step (3), the second displacement is 2-4m 3 The second displacement is within this range, ensuring that the sleeve is sprayed open and the spray pressure is within a safe range.

[0040] In some specific embodiments of the present invention, in step (3), the displacement fluid is added at a rate of 2-4 m 3 / min.

[0041] In some specific embodiments of the present invention, in step (3), the volume concentration of quartz sand is 5-6%, that is, the volume of quartz sand accounts for the percentage of the volume of the fracturing fluid, and the amount of quartz sand added is 2-4m 3 .

[0042] In some specific embodiments of the present invention, in step (3), the sandblasting and perforating process includes: injecting a fracturing fluid containing quartz sand into the oil pipe of the first section to be treated at a second displacement, and hydraulically spraying the quartz sand. After the hydraulic spraying of the quartz sand is completed, a displacement fluid is added to the oil pipe of the first section to be treated to discharge the quartz sand in the oil pipe of the first section to be treated to the ground. In the present invention, the volume concentration of quartz sand in the fracturing fluid containing quartz sand is 5-6%. The total amount of quartz sand sprayed into the oil pipe of the first section to be treated is 2-4m 3 .

[0043] In some specific embodiments of the present invention, in step (3), the fracture development layer section is a Class I or Class II fracture layer; wherein, a porosity φ ≥ 10% is a Class I fracture, a porosity φ ≤ 5% < 10% is a Class II fracture, and the cumulative total length of the Class I and Class II fracture development sections is 400-500m.

[0044] In some specific embodiments of the present invention, in step (4), the fracturing process includes: injecting liquid carbon dioxide into the oil pipe for fracturing, and replenishing liquid carbon dioxide through the casing refill channel in the casing. Specifically, after the sandblasting and perforating is completed, the casing spray release gate is closed, liquid carbon dioxide is injected into the oil pipe for fracturing, and the casing refill channel gate is opened to replenish liquid carbon dioxide through the casing refill channel.

[0045] In the present invention, after the injected carbon dioxide reaches the well, under the action of the temperature and pressure at the bottom of the well, the temperature of the liquid carbon dioxide is greater than 31.3° C. and the pressure is greater than 7.38 MPa, thereby converting it into supercritical carbon dioxide.

[0046] In some specific embodiments of the present invention, in step (4), the displacement of liquid carbon dioxide injected into the oil pipe is 2-4m 3 / min.

[0047] In some specific embodiments of the present invention, in step (4), the displacement of the added liquid carbon dioxide is 0.8-1m 3 / min.

[0048] In some specific embodiments of the present invention, in step (4), the total amount of liquid carbon dioxide injected into each section to be treated is 500-600m 3 , which includes the amount of liquid carbon dioxide injected into the oil pipe and the amount of additional liquid carbon dioxide.

[0049] In some specific embodiments of the present invention, in step (4), the temperature of the supercritical carbon dioxide is greater than 31.3° C., and the pressure is greater than 7.38 MPa.

[0050] A second aspect of the present invention provides a method for extracting heat from hot dry rocks, which includes fracturing and heat exchange, wherein the fracturing method is the method described in the first aspect.

[0051] The present invention is described in detail below through examples. In the following examples, a polyacrylamide emulsion thickener was uniformly mixed with clean water to produce a water-based fracturing fluid. The polyacrylamide emulsion thickener was prepared by inverse emulsion polymerization of acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, and dimethylhexadecylallylammonium chloride in a monomer weight ratio of 6:3:1. The viscosity of the water-based fracturing fluid at room temperature was adjusted by adjusting the amount of clean water in the water-based fracturing fluid.

[0052] In the following examples and comparative examples, if no specific conditions are specified, the experiments were carried out under conventional conditions or those recommended by the manufacturer. All reagents and instruments used, if no manufacturer is specified, are commercially available conventional products.

[0053] Example 1

[0054] (1) In this example, a hot dry rock well in the Bohai Rim region was selected. The lithology of the fracturing well section was metamorphic granite. The well section depth was 2500-3500 m. The maximum formation temperature was 150°C. The length of the target layer section for reconstruction was 800 m. The cumulative total length of the type I and II fracture development sections in the target layer section for reconstruction was 450 m. The target layer section for reconstruction was divided into 10 sections to be treated from bottom to top. Each section to be treated contained a 45 m fracture development section. The casing specification was P110, with an outer diameter of 177.8 mm and a wall thickness of 11.51 mm.

[0055] (2) Run the oil pipe with a hydraulic jet gun into the first section to be treated. The oil pipe specification is P105, the outer diameter is 88.9 mm, the wall thickness is 9.53 mm, and the fluid medium is a water-based fracturing fluid with a viscosity of 15 mPa·s. Open the casing valve and 3 / min to fill the first section of the oil pipe to be treated with fracturing fluid;

[0056] (3) Increase the fracturing fluid flow rate to 4.0m 3 / min, inject fracturing fluid containing quartz sand into the first section to be treated to hydraulically spray quartz sand, the quartz sand particle size is 70-140 mesh, the volume concentration is 6%, and the dosage is 2m 3 After stopping the sandblasting and perforating, add displacement fluid to the oil pipe of the first section to be treated, and drain the quartz sand in the oil pipe to the ground. The displacement volume of the added displacement fluid is 3m 3 / min, obtain the target layer;

[0057] (4) After adding displacement fluid and draining sand, close the casing spray gate and inject 4m 3 / min to inject liquid carbon dioxide into the first section of the oil pipe to be treated for fracturing, and then inject liquid carbon dioxide into the oil pipe through the casing fluid injection channel at a rate of 1m 3 / min displacement to add liquid carbon dioxide to the first section of the oil pipe to be treated; through the oil pipe and casing fluid replenishment channel, a total of 600m 3 Liquid carbon dioxide;

[0058] (5) Repeat steps (2) to (4) to complete fracturing of all the sections to be treated, wherein, in step (2), soluble balls are added with the fracturing fluid starting from the second section to be treated, and soluble balls are required to be added from the second section to the nth section to be treated.

[0059] Example 2

[0060] (1) In this embodiment, a hot dry rock well in the Bohai Rim region was selected. The lithology of the fracturing well section was metamorphic granite, the well section depth was 2500-3500 m, the maximum formation temperature was 150°C, the length of the target layer section for transformation was 800 m, and it was divided into 10 sections to be treated. The cumulative total length of the sections with type I and II fractures was 450 m. The casing specification was P110, with an outer diameter of 177.8 mm and a wall thickness of 11.51 mm.

[0061] (2) Run the oil pipe with a hydraulic jet gun. The specification of the oil pipe is P105, the outer diameter is 88.9mm, the wall thickness is 9.53mm, and the fluid medium is water-based fracturing fluid with a viscosity of 10mPa·s. Open the casing valve and 3 / min to fill the oil pipe in the heat production well with fracturing fluid.

[0062] (3) Increase the fracturing fluid flow rate to 2.0m 3 / min to hydraulically spray quartz sand, and the sand mixing truck begins to add quartz sand. The quartz sand particle size is 70 / 140 mesh, the concentration is 6%, and the amount added is 2m 3 After the sandblasting and perforation are stopped, the displacement fluid is added to the oil pipe to discharge the quartz sand in the oil pipe to the ground. The displacement of the displacement fluid is 3m 3 / min, and obtain the target layer.

[0063] (4) After the displacement fluid is added and the sand is discharged, the casing spray gate is closed and supercritical carbon dioxide is injected into the oil pipe for fracturing. The displacement of the liquid carbon dioxide injected into the oil pipe is 2m 3 / min construction, adjust the displacement according to the pressure, and add liquid carbon dioxide through the casing refill channel. The displacement of liquid carbon dioxide in the casing refill channel is 0.8m 3 / min, the tubing and casing are pumped 500m 3 Liquid carbon dioxide.

[0064] (5) Repeat steps (2) to (4) to complete fracturing of all the sections to be treated, wherein, in step (2), soluble balls are added with the fracturing fluid starting from the second section to be treated, and soluble balls are required to be added from the second section to the nth section to be treated.

[0065] Example 3

[0066] (1) In this embodiment, a hot dry rock well in the Bohai Rim region was selected. The lithology of the fracturing well section was metamorphic granite, the well section depth was 2500-3500 m, the maximum formation temperature was 150°C, the length of the target layer section for transformation was 800 m, and it was divided into 10 sections to be treated. The cumulative total length of the sections with type I and II fractures was 450 m. The casing specification was P110, with an outer diameter of 177.8 mm and a wall thickness of 11.51 mm.

[0067] (2) Run the oil pipe with a hydraulic jet gun. The oil pipe specification is P105, with an outer diameter of 88.9 mm and a wall thickness of 9.53 mm. The fluid medium is a water-based fracturing fluid with a viscosity of 10 mPa·s. Open the casing valve and 3 / min to fill the oil pipe in the heat production well with fracturing fluid.

[0068] (3) Increase the fracturing fluid flow rate to 3.0m 3 / min to hydraulically spray quartz sand, and the sand mixing truck begins to add quartz sand. The quartz sand particle size is 70 / 140 mesh, the concentration is 6%, and the amount added is 3m 3 After the sandblasting and perforation are stopped, the displacement fluid is added to the oil pipe to discharge the quartz sand in the oil pipe to the ground. The displacement of the displacement fluid is 3m 3 / min, and obtain the target layer.

[0069] (4) After the displacement fluid is added and the sand is discharged, the casing spray gate is closed and supercritical carbon dioxide is injected into the oil pipe for fracturing. The displacement of the liquid carbon dioxide injected into the oil pipe is 3m 3 / min construction, adjust the displacement according to the pressure, and add supercritical carbon dioxide through the casing refill channel. In the casing refill channel, the displacement of liquid carbon dioxide is 1m 3 / min, the tubing and casing are pumped 500m 3 Liquid carbon dioxide.

[0070] (5) Repeat steps (2) to (4) to complete fracturing of all the sections to be treated, wherein, in step (2), soluble balls are added with the fracturing fluid starting from the second section to be treated, and soluble balls are required to be added from the second section to the nth section to be treated.

[0071] Example 4

[0072] According to the method of Example 1, a hot dry rock well in the Bohai Rim region was selected. The difference was that the casing completion section (i.e., the target layer section for transformation) in the hot dry rock well was divided into 8 sections to be treated, each of which contained a 56.25 m fracture development layer section. Other conditions and steps were the same.

[0073] Example 5

[0074] According to the method of Example 1, a hot dry rock well in the Bohai Rim region was selected, except that in step (3), the fracturing fluid flow rate was increased to 1.0 m 3 / min for hydraulically jetting quartz sand, with other conditions and steps being the same.

[0075] Example 6

[0076] According to the method of Example 1, a hot dry rock well in the Bohai Rim region was selected, except that in step (4), the displacement of the liquid carbon dioxide injected into the oil pipe was 1m 3 / min construction, other conditions and steps are the same.

[0077] Comparative Example 1

[0078] (1) In this example, a hot dry rock well in the Bohai Rim region was selected. The lithology of the fracturing well section was metamorphic granite, the well section depth was 2500-3500 m, the maximum formation temperature was 150°C, the length of the target layer section for transformation was 800 m, and it was divided into 5 sections for fracturing. The cumulative total length of the sections with type I and II fractures was 450 m. The casing specification was P110, with an outer diameter of 177.8 mm and a wall thickness of 11.51 mm.

[0079] (2) Run the oil pipe with a hydraulic jet gun. The specification of the oil pipe is P105, the outer diameter is 88.9mm, the wall thickness is 9.53mm, and the fluid medium is water-based fracturing fluid with a viscosity of 15mPa·s. Open the casing valve and 3 / min to fill the oil pipe in the heat production well with fracturing fluid.

[0080] (3) Increase the fracturing fluid flow rate to 4.0m 3 / min to hydraulically spray quartz sand, and the sand mixing truck begins to add quartz sand. The quartz sand particle size is 70 / 140 mesh, the concentration is 6%, and the amount added is 2m 3 After the sandblasting and perforation are stopped, the displacement fluid is added to the oil pipe to discharge the quartz sand in the oil pipe to the ground. The displacement of the displacement fluid is 3m 3 / min, and obtain the target layer.

[0081] (4) After the displacement fluid is added and the sand is discharged, the casing spray gate is closed and liquid carbon dioxide is injected into the oil pipe for fracturing. The displacement of the liquid carbon dioxide injected into the oil pipe is 4m 3 / min construction, adjust the displacement according to the pressure, and add supercritical carbon dioxide through the casing refill channel. In the casing refill channel, the displacement of liquid carbon dioxide is 1m 3 / min, the tubing and casing are pumped 500m 3 Liquid carbon dioxide.

[0082] (5) Repeat steps (2) to (4) to complete fracturing of all the sections to be treated, wherein, in step (2), soluble balls are added with the fracturing fluid starting from the second section to be treated, and soluble balls are required to be added from the second section to the nth section to be treated.

[0083] The fracturing methods for hot dry rock in the examples and comparative examples were simulated using Meyer fracturing software, using the parameters provided in this method, to obtain the single-well stimulation volume. The single-well stimulation volume is defined as the total volume of fractures formed by fracturing the selected casing completion section (i.e., the target formation section). The results are shown in Table 1.

[0084] Table 1

[0085] The results in Table 1 show that Example 1, which employs the method of the present invention for fracturing hot dry rock, has a significantly better single-well stimulation volume. The larger the single-well stimulation volume, the more complex the fracture network generated by the fracturing method of the present invention, thereby enabling efficient single-well geothermal extraction technology.

[0086] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A method for fracturing hot dry rock, characterized in that: The steps include: (1) selecting a casing completion section in a hot well drilled on dry hot rock, and dividing the casing completion section into n sections to be processed; (2) filling the oil pipe of the casing completion section with a first displacement of fracturing fluid, and optionally adding soluble balls with the fracturing fluid; (3) selecting a fracture-developed layer section in the section to be treated and performing sandblasting and perforation to obtain a target layer section; (4) performing fracturing operation on the target layer segment using supercritical carbon dioxide to obtain a fracturing segment; (5) Repeat steps (2) to (4) to complete fracturing of all the sections to be treated; Wherein, said n is selected from 8-12.

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

3. The method according to claim 2, in step (3), the second displacement is 2-4m 3 / min; And / or, in step (3), the displacement fluid is added at a rate of 2-4 m 3 / min; And / or, 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 2-4 m 3 .

4. The method according to any one of claims 1 to 4, wherein: In step (4), the fracturing construction process includes: injecting liquid carbon dioxide into the oil pipe for fracturing, and replenishing liquid carbon dioxide through the casing refilling channel in the casing.

5. The method according to claim 4, wherein: In step (4), the displacement of liquid carbon dioxide injected into the oil pipe is 2-4m 3 / min; And / or, in step (4), the displacement of the added liquid carbon dioxide is 0.8-1m 3 / min; And / or, in step (4), the total amount of liquid carbon dioxide injected into each section to be treated is 500-600m 3 .

6. The method according to claim 1, wherein: In step (4), the temperature of the supercritical carbon dioxide is greater than 31.3° C. and the pressure is greater than 7.38 MPa.

7. The method according to claim 1, wherein: The length of the casing completion section is selected to be 800-1000m.

8. The method according to claim 1, wherein: In step (3), the fracture development layer section is a type I and type II fracture layer; wherein, a porosity φ ≥ 10% is a type I fracture, and a porosity φ ≤ 5% < 10% is a type II fracture.

9. The method according to claim 1, 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 rocks, characterized in that: It comprises fracturing and heat exchange, wherein the fracturing method is the method described in any one of claims 1-9.

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