Horizontal well heat extraction method using gravity assisted heat pipe

Abstract

The invention discloses a horizontal well heat extraction method using gravity assisted heat pipes, which belongs to the technical field of geothermal development and is characterized by comprising the following steps: a, fracturing a horizontal section of a horizontal well; b, a plurality of packers are arranged at the front end of an evaporation section of the gravity assisted heat pipe, and then the gravity assisted heat pipe which is filled with a liquid working medium and is in a negative pressure state is put down in the sleeve; c, a soft heat conduction part is arranged on the outer wall of the evaporation section of the gravity heat pipe; d, a porous surface coating is arranged on the inner wall of the evaporation section of the gravity assisted heat pipe; e, a drainage ring is arranged in the vertical section of the gravity assisted heat pipe; f, a converging groove is formed in the inner wall of the bent pipe section of the gravity assisted heat pipe; and g, after the liquid working medium is boiled and gasified, steam sequentially passes through the evaporation section and the bent pipe section to upwards flow to the vertical section under the action of pressure difference, is subjected to heat release condensation in the vertical section and then flows back to the evaporation section under the action of gravity. The device is suitable for horizontal well heat collection, mutual influence of two-phase working media in the transfer process can be avoided, and the heat collection efficiency is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of geothermal development, and in particular to a method for extracting heat from horizontal wells using gravity heat pipes. Background Art

[0002] The equivalent thermal conductivity of a gravity heat pipe can reach a hundred times that of a good metal conductor, and it is one of the most efficient heat transfer devices currently known. After filling the working fluid in the gravity heat pipe, the vacuum inside the pipe is evacuated to keep it in a negative pressure state. When the gravity heat pipe operates, the liquid working fluid at the bottom of the gravity heat pipe is heated by the high-temperature environment outside the pipe. When the temperature inside the pipe reaches the boiling point of the working fluid, the liquid working fluid vaporizes after boiling. The vapor flows upward to the condensation section under the action of the pressure difference, condenses after releasing heat, and then flows back to the evaporation section under the action of gravity, repeating the cycle.

[0003] Currently, the use of gravity heat pipes for heat extraction in horizontal wells mainly involves the structure of the overall device, and there is less research on the heat transfer of gravity heat pipes.

[0004] Chinese patent document with publication number CN112682974A and publication date April 20, 2021 discloses a heat exchange water pipe gravity heat pipe underground heat exchange system for exploiting dry hot rock geothermal energy, which is characterized in that: it includes an artificial heat storage: placed underground for absorbing and storing the heat in underground rocks; A gravity heat extraction device: The gravity heat extraction device includes a gravity heat pipe, and the gravity heat pipe extends from the artificial heat storage placed underground to the ground. A heat exchange fluid medium flows in the gravity heat pipe. The gravity heat pipe includes an evaporation section, an adiabatic section, and a condensation section; the evaporation section of the gravity heat pipe is placed in the artificial heat storage, and the artificial heat storage transfers the absorbed rock heat to the heat exchange fluid medium in the gravity heat pipe. The heat exchange fluid medium in the gravity heat pipe evaporates into a gas after absorbing the heat of the artificial heat storage in the evaporation section, and releases heat and condenses through the adiabatic section to the condensation section. The adiabatic section is placed between the evaporation section and the condensation section, and a heat insulation layer is provided outside the adiabatic section; A heat exchange device: used to transfer the heat in the gravity heat extraction device. The heat exchange device includes a heat exchange water pipe, and the heat exchange water pipe is wound outside the condensation section. The water in the heat exchange water pipe absorbs the heat in the heat exchange fluid medium in the condensation section.

[0005] The heat exchange water pipe gravity heat pipe underground heat exchange system for exploiting dry hot rock geothermal energy disclosed in this patent document uses the self-gravity of the fluid to achieve cyclic heat absorption and heat release, and uploads the heat, so that the heat thousands of meters underground can be transported to the ground for utilization. However, it is not suitable for heat extraction from horizontal wells, and the heat extraction efficiency is low. Summary of the Invention

[0006] In order to overcome the defects of the above-mentioned prior art, the present invention provides a method for extracting heat from a horizontal well using a gravity heat pipe. The present invention is suitable for heat extraction from horizontal wells, can avoid the mutual influence of two-phase working fluids during the transfer process, and improve the heat extraction efficiency.

[0007] The present invention is realized through the following technical solutions: A method for extracting heat from a horizontal well using a gravity heat pipe, characterized by comprising the following steps: a. Conduct a fracturing operation on the horizontal section of the horizontal well; b. First, set a plurality of packers at the front end of the evaporation section of the gravity heat pipe, and then lower the gravity heat pipe filled with liquid working fluid and in a negative pressure state into the casing. When the evaporation section of the gravity heat pipe reaches the preset position, the packers expand and contact the inner wall of the casing; c. A soft heat-conducting component is arranged on the outer wall of the evaporation section of the gravity heat pipe, and the soft heat-conducting component contacts the inner wall of the casing; d. A porous surface coating is formed on the inner wall of the evaporation section of the gravity heat pipe by anodic oxidation or micro-arc oxidation; e. A drainage ring is arranged in the vertical section of the gravity heat pipe, and the liquid working fluid flowing down on the inner side of the elbow section of the gravity heat pipe is drained to the outside through the drainage ring; f. A confluence groove is arranged on the inner wall of the elbow section of the gravity heat pipe, and the area of the confluence groove is one-fourth of the area of the elbow section; g. The liquid working fluid located in the evaporation section of the gravity heat pipe reaches the boiling point of the liquid working fluid under the action of the heat of the formation outside the pipe. After the liquid working fluid boils and vaporizes, the vapor flows upward through the evaporation section and the elbow section to the vertical section under the action of the pressure difference, condenses and releases heat in the vertical section, and then flows back to the evaporation section under the action of gravity, and so on in a cycle.

[0008] In the step a, the fracturing operation refers to dry sand fracturing with carbon dioxide, specifically, using liquid carbon dioxide as the fracturing fluid, adding a heat-conducting additive, using artificial ceramsite as the proppant. During the fracturing process, the state of carbon dioxide on the ground and in the wellbore is liquid. The liquid carbon dioxide carries the artificial ceramsite into the formation through a closed sand mixing device. Under the action of the high temperature at the bottom of the well, the liquid carbon dioxide gasifies and is discharged from the formation in a gaseous state, and the artificial ceramsite remains in the formation to form a supporting fracture.

[0009] The heat-conducting additive is graphite powder.

[0010] In the step c, there are eight soft heat-conducting components.

[0011] The soft heat-conducting components are arranged uniformly along the circumference of the gravity heat pipe.

[0012] In the step c, the soft heat-conducting components are connected to the gravity heat pipe by welding, and the soft heat-conducting components are aluminum heat-conducting strips or copper heat-conducting strips.

[0013] In step d, the porous surface coating is a hydrophilic surface, which is used to accelerate the evaporation rate of the liquid working medium in the evaporation section.

[0014] The liquid working medium is water or liquid ammonia.

[0015] The drainage ring is a tapered ring.

[0016] In step e, the drainage ring drains the liquid working medium flowing down the inner side of the elbow section of the gravity heat pipe to the outer side, specifically referring to that the liquid working medium flows downward along the pipe wall under the action of gravity, and is drained to the outer side by the action of the drainage ring in the vertical section of the gravity heat pipe.

[0017] The beneficial effects of the present invention are mainly manifested in the following aspects: 1. In the present invention, a. fracturing operation is carried out on the horizontal section of the horizontal well; b. first, a plurality of packers are arranged at the front end of the evaporation section of the gravity heat pipe, and then the gravity heat pipe filled with liquid working medium and in a negative pressure state is lowered into the casing. When the evaporation section of the gravity heat pipe reaches the preset position, the packers expand and contact the inner wall of the casing; c. a soft heat-conducting component is arranged on the outer wall of the evaporation section of the gravity heat pipe, and the soft heat-conducting component contacts the inner wall of the casing; d. a porous surface coating is formed on the inner wall of the evaporation section of the gravity heat pipe by anodic oxidation or micro-arc oxidation; e. a drainage ring is arranged in the vertical section of the gravity heat pipe, and the liquid working medium flowing down the inner side of the elbow section of the gravity heat pipe is drained to the outer side through the drainage ring; f. a confluence groove is arranged on the inner wall of the elbow section of the gravity heat pipe, and the area of the confluence groove is one-fourth of the area of the elbow section; g. the liquid working medium located in the evaporation section of the gravity heat pipe reaches the boiling point of the liquid working medium under the action of the formation heat outside the pipe. After the liquid working medium is vaporized by boiling, the steam flows upward through the evaporation section and the elbow section in turn under the action of the pressure difference, and is condensed by releasing heat in the vertical section and then flows back to the evaporation section under the action of gravity, so as to circulate. Compared with the prior art, it is suitable for heat extraction in horizontal wells, can avoid the mutual influence of two-phase working media during the transfer process, and improve the heat extraction efficiency.

[0018] 2. In the present invention, the heat-conducting additive is graphite powder, which can effectively improve the heat transfer and conduction ability of the surrounding rock, so as to meet the continuous heat energy supply in the evaporation section of the gravity heat pipe.

[0019] 3. In the present invention, when lowering the gravity heat pipe into the casing, a plurality of packers are arranged at the front end of the evaporation section of the gravity heat pipe. When the evaporation section of the gravity heat pipe reaches the preset position, the packers expand and contact the inner wall of the casing, which can seal the heat energy in the evaporation section space, maintain the heat energy in the evaporation section, ensure the effective utilization of underground heat energy, and effectively avoid the rapid loss of heat energy resulting in no heat energy supply in the evaporation section.

[0020] 4. In the present invention, in step c, there are eight soft heat-conducting components, which can ensure sufficient and good contact between the soft heat-conducting components and the inner wall of the casing. When the gravity heat pipe contacts the casing, the soft heat-conducting components will not cause extrusion damage to the gravity heat pipe and the casing.

[0021] 5. In the present invention, the soft heat-conducting components are uniformly arranged along the circumference of the gravity heat pipe. By adopting this specific arrangement method, a more uniform heat transfer capacity can be ensured.

[0022] 6. In the present invention, a porous surface coating is formed on the inner wall of the evaporation section of the gravity heat pipe by anodic oxidation or micro-arc oxidation. On the one hand, in the initial stage of evaporation of the gravity heat pipe, the gas carried in the porous structure can prevent violent boiling from generating violent vibrations and thus damaging the gravity heat pipe. On the other hand, by setting a porous surface coating on the inner wall of the evaporation section of the gravity heat pipe, the obtained porous structure surface is a hydrophilic surface, which is beneficial to improving the evaporation rate of water in the evaporation section.

[0023] 7. In the present invention, a confluence groove is provided on the inner wall of the elbow section of the gravity heat pipe, and the area of the confluence groove is one-fourth of the area of the elbow section. It can enable the downward flowing liquid working medium to flow down through the confluence groove, avoiding the impact of the upward flowing steam working medium on the downward flowing liquid working medium on the inner wall of the elbow section, resulting in the influence of the liquid-vapor circulation channel, thereby ensuring the heat transfer efficiency.

[0024] 8. In the present invention, in step e, the drainage ring drains the liquid working medium flowing down on the inner side of the elbow section of the gravity heat pipe to the outside, specifically referring to that the liquid working medium flows downward along the pipe wall under the action of gravity, and under the action of the drainage ring in the vertical section of the gravity heat pipe, the liquid working medium flowing down on the inner side of the elbow section is drained to the outside. It can effectively avoid the liquid working medium flowing down on the inner side of the elbow section of the gravity heat pipe from dripping at the elbow section and conflicting with the upward flowing steam, thereby ensuring the heat transfer efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The following will further specifically describe the present invention in conjunction with the specification drawings and specific embodiments, where: Figure 1 is a schematic structural diagram of the downward gravity heat pipe of the present invention; Figure 2 is a top view of the drainage ring of the present invention; Figure 3 is a top view of the confluence groove of the present invention; Figure 4 is an arrangement diagram of the soft heat-conducting components along the gravity heat pipe of the present invention; Figure 5 is a microscopic morphology diagram of the porous structure on the inner wall of the evaporation section of the present invention; Markings in the figure: 1. Gravity heat pipe, 2. Evaporation section, 3. Packer, 4. Casing, 5. Soft heat-conducting component, 6. Vertical section, 7. Drainage ring, 8. Elbow section, 9. Confluence groove. Detailed implementation mode

[0026] Embodiment 1 Refer to Figures 1 - 4 , a horizontal well heat extraction method using a gravity heat pipe, comprising the following steps: a. Conduct a fracturing operation on the horizontal section of the horizontal well; b. First, arrange a plurality of packers 3 at the front end of the evaporation section 2 of the gravity heat pipe 1, and then lower the gravity heat pipe 1 filled with liquid working medium and in a negative pressure state into the casing 4. When the evaporation section 2 of the gravity heat pipe 1 reaches the preset position, the packers 3 expand and contact the inner wall of the casing 4; c. A soft heat-conducting component 5 is arranged on the outer wall of the evaporation section 2 of the gravity heat pipe 1, and the soft heat-conducting component 5 contacts the inner wall of the casing 4; d. A porous surface coating is formed on the inner wall of the evaporation section 2 of the gravity heat pipe 1 by anodic oxidation; e. A drainage ring 7 is arranged in the vertical section 6 of the gravity heat pipe 1, and the liquid working medium flowing down inside the elbow section 8 of the gravity heat pipe 1 is drained to the outside through the drainage ring 7; f. A confluence groove 9 is arranged on the inner wall of the elbow section 8 of the gravity heat pipe 1, and the area of the confluence groove 9 is one-fourth of the area of the elbow section 8; g. The liquid working medium located in the evaporation section 2 of the gravity heat pipe 1 reaches the boiling point of the liquid working medium under the action of the formation heat outside the pipe. After the liquid working medium boils and vaporizes, the steam flows upward through the evaporation section 2 and the elbow section 8 in turn under the action of the pressure difference to the vertical section 6, condenses and releases heat in the vertical section 6, and then flows back to the evaporation section 2 under the action of gravity, and so on in a cycle.

[0027] This embodiment is the most basic implementation mode. Compared with the prior art, it is suitable for heat extraction from horizontal wells, can avoid the mutual influence of two-phase working media during the transfer process, and improve the heat extraction efficiency.

[0028] Embodiment 2 Refer to Figures 1 - 4 , a horizontal well heat extraction method using a gravity heat pipe, comprising the following steps: a. Conduct a fracturing operation on the horizontal section of the horizontal well; b. First, arrange a plurality of packers 3 at the front end of the evaporation section 2 of the gravity heat pipe 1, and then lower the gravity heat pipe 1 filled with liquid working medium and in a negative pressure state into the casing 4. When the evaporation section 2 of the gravity heat pipe 1 reaches the preset position, the packers 3 expand and contact the inner wall of the casing 4; c. A soft heat-conducting component 5 is arranged on the outer wall of the evaporation section 2 of the gravity heat pipe 1, and the soft heat-conducting component 5 contacts the inner wall of the casing 4; d. A porous surface coating is formed on the inner wall of the evaporation section 2 of the gravity heat pipe 1 by anodic oxidation; e. A drainage ring 7 is arranged inside the vertical section 6 of the gravity heat pipe 1, and the liquid working medium flowing downward on the inner side of the elbow section 8 of the gravity heat pipe 1 is drained to the outside through the drainage ring 7; f. A confluence groove 9 is arranged on the inner wall of the elbow section 8 of the gravity heat pipe 1, and the area of the confluence groove 9 is one-fourth of the area of the elbow section 8; g. The liquid working medium located inside the evaporation section 2 of the gravity heat pipe 1 reaches the boiling point of the liquid working medium under the action of the heat of the formation outside the pipe. After the liquid working medium is vaporized by boiling, the steam flows upward through the evaporation section 2 and the elbow section 8 in sequence under the action of the pressure difference to reach the vertical section 6, and after releasing heat and condensing in the vertical section 6, it flows back to the evaporation section 2 under the action of gravity, and circulates in this way.

[0029] Preferably, in the step a, the fracturing operation refers to dry sand fracturing with carbon dioxide, specifically, liquid carbon dioxide is used as the fracturing fluid, a heat conduction additive is added, artificial ceramsite is used as the proppant. During the fracturing process, the state of carbon dioxide on the ground and in the wellbore is liquid. The liquid carbon dioxide carries the artificial ceramsite into the formation through a closed sand mixing device. Under the action of the high temperature at the bottom of the well, the liquid carbon dioxide is vaporized and discharged from the formation in a gaseous state, and the artificial ceramsite remains in the formation to form a supporting fracture.

[0030] The heat conduction additive is graphite powder.

[0031] This embodiment is a preferred embodiment. The heat conduction additive is graphite powder, which can effectively improve the heat transfer and conduction ability of the surrounding rocks, so as to meet the continuous heat energy supply of the evaporation section 2 of the gravity heat pipe 1.

[0032] Embodiment 3 See Figures 1 - 4 , a horizontal well heat extraction method using a gravity heat pipe, comprising the following steps: a. Perform a fracturing operation on the horizontal section of the horizontal well; b. First, arrange a plurality of packers 3 at the front end of the evaporation section 2 of the gravity heat pipe 1, and then lower the gravity heat pipe 1 filled with liquid working medium and in a negative pressure state into the casing 4. When the evaporation section 2 of the gravity heat pipe 1 reaches the preset position, the packers 3 expand and contact the inner wall of the casing 4; c. A soft heat conduction component 5 is arranged on the outer wall of the evaporation section 2 of the gravity heat pipe 1, and the soft heat conduction component 5 contacts the inner wall of the casing 4; d. A porous surface coating is formed on the inner wall of the evaporation section 2 of the gravity heat pipe 1 by anodic oxidation; e. A drainage ring 7 is arranged inside the vertical section 6 of the gravity heat pipe 1, and the liquid working medium flowing downward on the inner side of the elbow section 8 of the gravity heat pipe 1 is drained to the outside through the drainage ring 7; f. A confluence groove 9 is arranged on the inner wall of the elbow section 8 of the gravity heat pipe 1, and the area of the confluence groove 9 is one-fourth of the area of the elbow section 8; g. The liquid working medium located in the evaporation section 2 of the gravity heat pipe 1 reaches the boiling point of the liquid working medium under the action of the heat of the formation outside the pipe. After the liquid working medium boils and vaporizes, the vapor flows upward through the evaporation section 2 and the elbow section 8 to the vertical section 6 under the action of the pressure difference, condenses and releases heat in the vertical section 6, and then flows back to the evaporation section 2 under the action of gravity, and so on in a cycle.

[0033] In step a, the fracturing operation refers to dry sand fracturing with carbon dioxide, specifically using liquid carbon dioxide as the fracturing fluid, adding a heat-conducting additive, and using artificial ceramsite as the proppant. During the fracturing process, the carbon dioxide is in a liquid state on the ground and in the wellbore. The liquid carbon dioxide carries the artificial ceramsite into the formation through a closed sand mixing device. Under the action of the high temperature at the bottom of the well, the liquid carbon dioxide gasifies and returns from the formation in a gaseous state, and the artificial ceramsite remains in the formation to form a supporting fracture.

[0034] The heat-conducting additive is graphite powder.

[0035] In step c, there are eight soft heat-conducting components 5.

[0036] This embodiment is another preferred embodiment. When lowering the gravity heat pipe 1 into the casing 4, a plurality of packers 3 are arranged at the front end of the evaporation section 2 of the gravity heat pipe 1. When the evaporation section 2 of the gravity heat pipe 1 reaches the preset position, the packer 3 expands and contacts the inner wall of the casing 4, which can seal the heat energy in the space of the evaporation section 2, maintain the heat energy in the evaporation section 2, ensure the effective utilization of the underground heat energy, and effectively avoid the rapid loss of heat energy resulting in no heat energy supply for the evaporation section 2.

[0037] In step c, there are eight soft heat-conducting components 5, which can ensure sufficient and good contact between the soft heat-conducting components 5 and the inner wall of the casing 4. When the gravity heat pipe 1 contacts the casing 4, the soft heat-conducting components 5 will not cause extrusion damage to the gravity heat pipe 1 and the casing 4.

[0038] Embodiment 4 See Figures 1 - 4 , a method for extracting heat from a horizontal well using a gravity heat pipe, including the following steps: a. Perform a fracturing operation on the horizontal section of the horizontal well; b. First, arrange a plurality of packers 3 at the front end of the evaporation section 2 of the gravity heat pipe 1, and then lower the gravity heat pipe 1 filled with liquid working medium and in a negative pressure state into the casing 4. When the evaporation section 2 of the gravity heat pipe 1 reaches the preset position, the packer 3 expands and contacts the inner wall of the casing 4; c. The outer wall of the evaporation section 2 of the gravity heat pipe 1 is provided with soft heat-conducting components 5, and the soft heat-conducting components 5 contact the inner wall of the casing 4; d. A porous surface coating is formed on the inner wall of the evaporation section 2 of the gravity heat pipe 1 by anodic oxidation; e. A drainage ring 7 is provided inside the vertical section 6 of the gravity heat pipe 1, and the liquid working medium flowing down the inner side of the elbow section 8 of the gravity heat pipe 1 is drained to the outside through the drainage ring 7; f. A confluence groove 9 is provided on the inner wall of the elbow section 8 of the gravity heat pipe 1, and the area of the confluence groove 9 is one-fourth of the area of the elbow section 8; g. The liquid working medium located inside the evaporation section 2 of the gravity heat pipe 1 reaches the boiling point of the liquid working medium under the action of the formation heat outside the pipe. After the liquid working medium is vaporized by boiling, the steam flows upward through the evaporation section 2 and the elbow section 8 to the vertical section 6 under the action of the pressure difference. After releasing heat and condensing in the vertical section 6, it flows back to the evaporation section 2 under the action of gravity, and so on in a cycle.

[0039] In the step a, the fracturing operation refers to dry sand fracturing with carbon dioxide, specifically, liquid carbon dioxide is used as the fracturing fluid, a heat conduction additive is added, artificial ceramsite is used as the proppant. During the fracturing process, the state of carbon dioxide on the ground and in the wellbore is liquid. Liquid carbon dioxide carries artificial ceramsite into the formation through a closed sand mixing device. Under the action of the high temperature at the bottom of the well, the liquid carbon dioxide gasifies and is discharged from the formation in a gaseous state, and the artificial ceramsite remains in the formation to form a supporting fracture.

[0040] Further preferably, the heat conduction additive is graphite powder.

[0041] In the step c, there are eight soft heat conduction components 5.

[0042] The soft heat conduction components 5 are evenly arranged along the circumference of the gravity heat pipe 1.

[0043] This embodiment is another preferred embodiment. The soft heat conduction components 5 are evenly arranged along the circumference of the gravity heat pipe 1. Adopting this specific arrangement method can ensure more uniform heat transfer ability.

[0044] Embodiment 5 See Figures 1 - 4 , a horizontal well heat extraction method using a gravity heat pipe, including the following steps: a. Perform a fracturing operation on the horizontal section of the horizontal well; b. First, set a plurality of packers 3 at the front end of the evaporation section 2 of the gravity heat pipe 1, and then lower the gravity heat pipe 1 filled with liquid working medium and in a negative pressure state into the casing 4. When the evaporation section 2 of the gravity heat pipe 1 reaches the preset position, the packers 3 expand and contact the inner wall of the casing 4; c. The outer wall of the evaporation section 2 of the gravity heat pipe 1 is provided with soft heat conduction components 5, and the soft heat conduction components 5 contact the inner wall of the casing 4; d. A porous surface coating is formed on the inner wall of the evaporation section 2 of the gravity heat pipe 1 by micro-arc oxidation; e. A drainage ring 7 is arranged inside the vertical section 6 of the gravity heat pipe 1, and the liquid working medium flowing down on the inner side of the elbow section 8 of the gravity heat pipe 1 is drained to the outer side through the drainage ring 7; f. A confluence groove 9 is arranged on the inner wall of the elbow section 8 of the gravity heat pipe 1, and the area of the confluence groove 9 is one-fourth of the area of the elbow section 8; g. The liquid working medium located inside the evaporation section 2 of the gravity heat pipe 1 reaches the boiling point of the liquid working medium under the action of the heat of the formation outside the pipe. After the liquid working medium boils and vaporizes, the vapor flows upward through the evaporation section 2 and the elbow section 8 in sequence under the action of the pressure difference to the vertical section 6, condenses and releases heat in the vertical section 6, and then flows back to the evaporation section 2 under the action of gravity, and so on in a cycle.

[0045] In the step a, the fracturing operation refers to dry sand fracturing with carbon dioxide, specifically, liquid carbon dioxide is used as the fracturing fluid, a heat conduction additive is added, artificial ceramsite is used as the proppant. During the fracturing process, the state of carbon dioxide on the ground and in the wellbore is liquid. The liquid carbon dioxide carries the artificial ceramsite into the formation through a closed sand mixing device. Under the action of the high temperature at the bottom of the well, the liquid carbon dioxide gasifies and returns from the formation in a gaseous state, and the artificial ceramsite remains in the formation to form a supporting fracture.

[0046] The heat conduction additive is graphite powder.

[0047] In the step c, there are eight soft heat conduction components 5.

[0048] The soft heat conduction components 5 are evenly arranged along the circumference of the gravity heat pipe 1.

[0049] In the step c, the soft heat conduction components 5 are connected to the gravity heat pipe 1 by welding, and the soft heat conduction components 5 are aluminum heat conduction strips.

[0050] This embodiment is another preferred embodiment. A porous surface coating is formed on the inner wall of the evaporation section 2 of the gravity heat pipe 1 by anodic oxidation or micro-arc oxidation. On the one hand, in the initial stage of evaporation of the gravity heat pipe 1, the gas carried in the porous structure can prevent violent boiling from generating violent vibration and thus damaging the gravity heat pipe 1; on the other hand, a porous surface coating is arranged on the inner wall of the evaporation section 2 of the gravity heat pipe 1, and the obtained porous structure surface is a hydrophilic surface, which is beneficial to improving the evaporation rate of water in the evaporation section 2.

[0051] Embodiment 6 See Figures 1 - 4 , A horizontal well heat extraction method using a gravity heat pipe, comprising the following steps: a. Perform a fracturing operation on the horizontal section of the horizontal well; b. First, set multiple packers 3 at the front end of the evaporation section 2 of the gravity heat pipe 1, and then lower the gravity heat pipe 1 filled with liquid working medium and in a negative pressure state into the casing 4. When the evaporation section 2 of the gravity heat pipe 1 reaches the preset position, the packer 3 expands and contacts the inner wall of the casing 4; c. A soft thermal conductive component 5 is arranged on the outer wall of the evaporation section 2 of the gravity heat pipe 1, and the soft thermal conductive component 5 contacts the inner wall of the casing 4; d. A porous surface coating is formed on the inner wall of the evaporation section 2 of the gravity heat pipe 1 by micro-arc oxidation; e. A drainage ring 7 is arranged in the vertical section 6 of the gravity heat pipe 1, and the liquid working medium flowing down on the inner side of the elbow section 8 of the gravity heat pipe 1 is drained to the outside through the drainage ring 7; f. A confluence groove 9 is arranged on the inner wall of the elbow section 8 of the gravity heat pipe 1, and the area of the confluence groove 9 is one-fourth of the area of the elbow section 8; g. The liquid working medium located in the evaporation section 2 of the gravity heat pipe 1 reaches the boiling point of the liquid working medium under the action of the formation heat outside the pipe. After the liquid working medium boils and vaporizes, the steam flows upward through the evaporation section 2 and the elbow section 8 in sequence under the action of the pressure difference to the vertical section 6, condenses and releases heat in the vertical section 6, and then flows back to the evaporation section 2 under the action of gravity, and so on in a cycle.

[0052] In the step a, the fracturing operation refers to dry fracturing with carbon dioxide and adding sand, specifically using liquid carbon dioxide as the fracturing fluid, adding a thermal conductive additive, using artificial ceramsite as the proppant. During the fracturing process, the state of carbon dioxide on the ground and in the wellbore is liquid. The liquid carbon dioxide carries the artificial ceramsite into the formation through a closed sand mixing device. Under the action of high temperature at the bottom of the well, the liquid carbon dioxide gasifies and is discharged from the formation in a gas state, and the artificial ceramsite remains in the formation to form a supporting fracture.

[0053] The thermal conductive additive is graphite powder.

[0054] In the step c, there are eight soft thermal conductive components 5.

[0055] The soft thermal conductive components 5 are evenly arranged along the circumference of the gravity heat pipe 1.

[0056] In the step c, the soft thermal conductive component 5 is connected to the gravity heat pipe 1 by welding, and the soft thermal conductive component 5 is a copper thermal conductive strip.

[0057] Further preferably, in the step d, the porous surface coating is a hydrophilic surface, which is used to accelerate the evaporation rate of the liquid working medium in the evaporation section 2.

[0058] The liquid working medium is water.

[0059] The drainage ring 7 is a gradient ring.

[0060] This embodiment is another preferred embodiment. A flow collecting groove 9 is provided on the inner wall of the elbow section 8 of the gravity heat pipe 1, and the area of the flow collecting groove 9 is one-fourth of the area of the elbow section 8, which can enable the downward flowing liquid working medium to flow down through the flow collecting groove 9, avoiding the impact of the upward flowing steam working medium on the downward flowing liquid working medium on the inner wall of the elbow section 8, resulting in the influence on the liquid and steam flow channels, so as to ensure the heat transfer efficiency.

[0061] Embodiment 7 See Figures 1 - 5 , a method for extracting heat from a horizontal well using a gravity heat pipe, comprising the following steps: a. Conduct a fracturing operation on the horizontal section of the horizontal well; b. First, arrange a plurality of packers 3 at the front end of the evaporation section 2 of the gravity heat pipe 1, and then lower the gravity heat pipe 1 filled with liquid working medium and in a negative pressure state into the casing 4. When the evaporation section 2 of the gravity heat pipe 1 reaches the preset position, the packers 3 expand and contact the inner wall of the casing 4; c. A soft heat conducting component 5 is arranged on the outer wall of the evaporation section 2 of the gravity heat pipe 1, and the soft heat conducting component 5 contacts the inner wall of the casing 4; d. A porous surface coating is formed on the inner wall of the evaporation section 2 of the gravity heat pipe 1 by micro-arc oxidation; e. A drainage ring 7 is arranged in the vertical section 6 of the gravity heat pipe 1, and the liquid working medium flowing down inside the elbow section 8 of the gravity heat pipe 1 is drained to the outside through the drainage ring 7; f. A flow collecting groove 9 is arranged on the inner wall of the elbow section 8 of the gravity heat pipe 1, and the area of the flow collecting groove 9 is one-fourth of the area of the elbow section 8; g. The liquid working medium located in the evaporation section 2 of the gravity heat pipe 1 reaches the boiling point of the liquid working medium under the action of the heat of the formation outside the pipe. After the liquid working medium boils and vaporizes, the steam flows upward through the evaporation section 2 and the elbow section 8 to the vertical section 6 under the action of the pressure difference, condenses and releases heat in the vertical section 6, and then flows back to the evaporation section 2 under the action of gravity, and so on in a cycle.

[0062] In the step a, the fracturing operation refers to dry sand fracturing with carbon dioxide, specifically, using liquid carbon dioxide as the fracturing fluid, adding a heat conducting additive, using artificial ceramsite as the proppant. During the fracturing process, the state of carbon dioxide on the ground and in the wellbore is liquid, and the liquid carbon dioxide carries the artificial ceramsite into the formation through a closed sand mixing device. Under the action of high temperature at the bottom of the well, the liquid carbon dioxide gasifies and is discharged from the formation in a gaseous state, and the artificial ceramsite remains in the formation to form a supporting fracture.

[0063] The heat conducting additive is graphite powder.

[0064] In the step c, there are eight soft heat conducting components 5.

[0065] The soft heat conducting components 5 are evenly arranged along the circumference of the gravity heat pipe 1.

[0066] In step c, the soft heat-conducting component 5 is connected to the gravity heat pipe 1 by welding, and the soft heat-conducting component 5 is an aluminum heat-conducting strip.

[0067] In step d, the porous surface coating is a hydrophilic surface, which is used to accelerate the evaporation rate of the liquid working medium in the evaporation section 2.

[0068] The liquid working medium is liquid ammonia.

[0069] The drainage ring 7 is a tapered ring.

[0070] In step e, the drainage ring 7 drains the liquid ammonia flowing down on the inner side of the elbow section 8 of the gravity heat pipe 1 to the outside, which specifically means that the liquid ammonia flows downward along the pipe wall under the action of gravity, and under the action of the drainage ring 7 in the vertical section 6 of the gravity heat pipe 1, the liquid ammonia flowing down on the inner side of the elbow section 8 is drained to the outside.

[0071] This embodiment is the best implementation mode. In step e, the drainage ring 7 drains the liquid working medium flowing down on the inner side of the elbow section 8 of the gravity heat pipe 1 to the outside, which specifically means that the liquid working medium flows downward along the pipe wall under the action of gravity, and under the action of the drainage ring 7 in the vertical section 6 of the gravity heat pipe 1, the liquid working medium flowing down on the inner side of the elbow section 8 is drained to the outside, which can effectively prevent the liquid working medium flowing down on the inner side of the elbow section 8 of the gravity heat pipe 1 from dripping at the elbow section 8 and conflicting with the ascending steam, thereby ensuring the heat transfer efficiency.

[0072] The working principle of the present invention is as follows: After the gravity heat pipe 1 is filled with water or liquid ammonia, the vacuum in the gravity heat pipe 1 is evacuated to keep it in a negative pressure state. When the gravity heat pipe 1 operates, the water or liquid ammonia located in the evaporation section 2 of the gravity heat pipe 1 is heated by the high-temperature environment outside the pipe. When the temperature inside the pipe reaches the boiling point of water or liquid ammonia, the water or liquid ammonia is vaporized by boiling, and the steam flows upward through the evaporation section 2 and the elbow section 8 in turn under the action of the pressure difference, condenses and releases heat in the vertical section 6, and then flows back to the evaporation section 2 under the action of gravity, and so on. The water or liquid ammonia in the gravity heat pipe 1 is in a closed cycle, which can avoid polluting the underground water resources and has good environmental protection effects.

Claims

1. A method for heat extraction from horizontal wells using gravity heat pipes, characterized in that, It includes the following steps: a. Conduct a fracturing operation on the horizontal section of the horizontal well; b. First, set multiple packers (3) at the front end of the evaporation section (2) of the gravity heat pipe (1), and then lower the gravity heat pipe (1) filled with liquid working medium and in a negative pressure state into the casing (4). When the evaporation section (2) of the gravity heat pipe (1) reaches the preset position, the packer (3) expands and contacts the inner wall of the casing (4); c. A soft heat-conducting component (5) is arranged on the outer wall of the evaporation section (2) of the gravity heat pipe (1), and the soft heat-conducting component (5) contacts the inner wall of the casing (4); d. A porous surface coating is formed on the inner wall of the evaporation section (2) of the gravity heat pipe (1) by anodic oxidation or micro-arc oxidation; e. A drainage ring (7) is arranged in the vertical section (6) of the gravity heat pipe (1), and the liquid working medium flowing down on the inner side of the elbow section (8) of the gravity heat pipe (1) is drained to the outer side through the drainage ring (7); f. A confluence groove (9) is arranged on the inner wall of the elbow section (8) of the gravity heat pipe (1), and the area of the confluence groove (9) is one-fourth of the area of the elbow section (8); g. The liquid working medium located in the evaporation section (2) of the gravity heat pipe (1) reaches the boiling point of the liquid working medium under the action of the formation heat outside the pipe. After the liquid working medium boils and vaporizes, the vapor flows upward through the evaporation section (2) and the elbow section (8) in turn under the action of the pressure difference to the vertical section (6), condenses and releases heat in the vertical section (6), and then flows back to the evaporation section (2) under the action of gravity, and circulates in this way.

2. The horizontal well heat extraction method using a gravity heat pipe according to claim 1, characterized in that: In the step a, the fracturing operation refers to dry sand fracturing with carbon dioxide, specifically, liquid carbon dioxide is used as the fracturing fluid, a heat-conducting additive is added, artificial ceramsite is used as the proppant. During the fracturing process, the state of carbon dioxide on the ground and in the wellbore is liquid. Liquid carbon dioxide carries artificial ceramsite into the formation through a closed sand mixing device. Under the action of the high temperature at the bottom of the well, liquid carbon dioxide gasifies and is discharged from the formation in a gaseous state, and the artificial ceramsite remains in the formation to form a supporting fracture.

3. A horizontal well heat extraction method using a gravity heat pipe according to claim 2, characterized in that: The heat-conducting additive is graphite powder.

4. A horizontal well heat extraction method using a gravity heat pipe according to claim 1, characterized in that: In the step c, there are eight soft heat-conducting components (5).

5. A horizontal well heat extraction method using a gravity heat pipe according to claim 4, characterized in that: The soft heat-conducting components (5) are evenly arranged along the circumference of the gravity heat pipe (1).

6. A horizontal well heat extraction method using a gravity heat pipe according to claim 1, characterized in that: In the step c, the soft heat-conducting component (5) is connected to the gravity heat pipe (1) by welding, and the soft heat-conducting component (5) is an aluminum heat-conducting strip or a copper heat-conducting strip.

7. A horizontal well heat extraction method using a gravity heat pipe according to claim 1, characterized in that: In the step d, the porous surface coating is a hydrophilic surface, which is used to accelerate the evaporation rate of the liquid working medium in the evaporation section (2).

8. A horizontal well heat extraction method using a gravity heat pipe according to claim 1, characterized in that: The liquid working medium is water or liquid ammonia.

9. A horizontal well heat extraction method using a gravity heat pipe according to claim 1, characterized in that: The drainage ring (7) is a gradient ring.

10. A horizontal well heat extraction method using a gravity heat pipe according to claim 1, characterized in that: In the step e, the drainage ring (7) drains the liquid working medium flowing down on the inner side of the elbow section (8) of the gravity heat pipe (1) to the outer side, specifically, the liquid working medium flows downward along the pipe wall under the action of gravity, and is drained to the outer side by the drainage ring (7) in the vertical section (6) of the gravity heat pipe (1).

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