Closed type single geothermal well heat exchange structure and heat removal method

Abstract

The invention discloses a closed type single geothermal well heat exchange structure and a heat removal method. The closed type single geothermal well heat exchange structure comprises a well lid, a pipe body, a well plugging device, an ascending pipe and a geothermal sleeve. The well lid and the well plugging device are arranged at the two ends of the pipe body to form a cavity, the ascending pipe penetrates through the well lid and extends into the cavity, a first channel is defined by the well lid, the pipe body, the well plugging device and the ascending pipe and communicated with the ascending pipe, and the well lid is provided with a through hole for a circulating working medium to enter. The circulating working medium flows out of the ascending pipe from top to bottom along the first channel; a geothermal sleeve is arranged on the outer wall of the bottom of the pipe body in a surrounding mode, a geothermal channel is defined by the geothermal sleeve, the outer wall of the pipe body and the blowout preventer, the geothermal sleeve is provided with a water inlet hole and a water drainage hole, and the water inlet hole, the geothermal channel and the water drainage hole are sequentially communicated, so that geothermal fluid of a geothermal reservoir flows out from the water drainage hole along the geothermal channel from bottom to top and is discharged to the crack. And heat exchange with the circulating working medium is realized. Forced convection heat exchange of fluid inside and outside the pipe body is achieved, the heat exchange coefficient is increased, and the heat extraction power is increased.

Description

Technical Field

[0001] The present invention relates to the technical field of geothermal well reconstruction, and in particular to a closed single geothermal well heat exchange structure and a heat extraction method. Background Art

[0002] Geothermal energy is a natural, renewable, clean heat energy extracted from the earth's crust. It has the advantages of stable temperature, no seasonal and weather influence, and high utilization coefficient. It is widely used in heating, power generation, agriculture, aquaculture, hot spring bathing and other fields. Traditional hydrothermal geothermal energy development technology is mainly based on direct water extraction. The amount of reinjection depends on the actual conditions of the formation. When the reinjection rate is low, it will damage the groundwater resources, cause the water level to drop, and even cause ground subsidence; unfavorable reinjection of geothermal fluids will cause thermal pollution and affect the thermal recovery of the reservoir; in addition, groundwater contains gases such as hydrogen sulfide, which will cause surface chemical pollution. In addition, geothermal well reinjection is difficult, extraction and injection are unbalanced, the power consumption of the extraction pump is large when the water level is too low, the operation and maintenance costs are high, and low permeability and even dry eye formations have become bottlenecks restricting the development of hydrothermal geothermal resources.

[0003] At present, most of the medium-deep single-well heat exchangers (DHE) are used for heat extraction. They are mainly composed of rocks, wellbore, cement, heat exchange pipelines, well sealers and insulation pipes. The injected fluid exchanges heat with the outer wall of the wellbore and the rock of the geothermal reservoir through heat conduction. Due to the low heat transfer coefficient, the single-well heat extraction power and water supply temperature are low. The heat extraction load of the medium-deep single-well heat exchanger is only equivalent to 20%-40% of the traditional pumping and irrigation mining method. Therefore, the low heat extraction capacity and poor heat exchange characteristics of the single-well heat exchanger have become a technical bottleneck restricting the development of medium- and low-temperature geothermal energy. Summary of the invention

[0004] The technical problem to be solved by the present invention is that the single-well heat exchanger only conducts heat exchange with the rocks of the geothermal reservoir through the outer wall, and has low heat extraction capacity and poor heat exchange characteristics.

[0005] In order to solve the above technical problems, the present invention provides a closed single geothermal well heat exchange structure, which is used to extend into a geothermal reservoir to extract heat. The geothermal reservoir has a plurality of cracks. The closed single geothermal well heat exchange structure includes a well cover, a pipe body, a well sealer, a riser, and a geothermal casing;

[0006] The manhole cover and the well sealer are sealed and installed at both ends of the pipe body to form a cavity, the riser passes through the manhole cover and extends into the cavity, a first channel is formed between the manhole cover, the pipe body, the well sealer and the riser, the first channel is communicated with the lower end of the riser, and the manhole cover has a through hole for circulating working medium to pass through, so that the circulating working medium flows from top to bottom along the first channel and flows out of the riser;

[0007] The outer wall of the bottom of the pipe body is surrounded by a geothermal casing, and a geothermal channel is formed between the geothermal casing, the outer wall of the pipe body and the well capping device. The geothermal casing is provided with a water inlet hole and a drainage hole above the water inlet hole. The water inlet hole, the geothermal channel and the drainage hole are connected in sequence, so that the geothermal fluid of the geothermal reservoir flows from bottom to top along the geothermal channel and flows out from the drainage hole to the fracture to complete heat exchange with the circulating working medium.

[0008] In some embodiments, the water inlet hole is disposed at one end of the geothermal casing close to the well stopper, and the water inlet hole is communicated with the fracture.

[0009] In some embodiments, the aperture of the water inlet hole gradually decreases along the first direction to increase the flow rate of the geothermal fluid entering the geothermal fluid pipeline.

[0010] In some embodiments, the drainage hole is disposed at an end of the geothermal casing away from the well plug, and the drainage hole is communicated with the fracture.

[0011] In some embodiments, the pipe body includes a first casing, a second casing and a third casing connected in sequence along the first direction, the geothermal casing is arranged on the outer wall of the third casing, the first casing and the riser are combined to form a first flow channel, the second casing and the riser are combined to form a second flow channel, the third casing and the riser are combined to form a third flow channel, and the first flow channel, the second flow channel and the third flow channel are connected in sequence to form the first channel.

[0012] In some embodiments, a diameter of the first flow channel is greater than a diameter of the second flow channel, and a diameter of the second flow channel is greater than a diameter of the third flow channel.

[0013] In some embodiments, it also includes cementing cement, a second wellbore and a third wellbore connected in sequence, the outer wall of the first casing is cemented to the cementing cement, the outer wall of the second casing is cemented to the second wellbore, and the outer wall of the geothermal casing is cemented to the third wellbore.

[0014] In some embodiments, the inner wall surface of the third sleeve is provided with ribs, and the ribs are spirally arranged along the length direction of the third sleeve.

[0015] In some embodiments, the angle between the convex rib and the inner wall surface of the third sleeve is 30°-45°.

[0016] The present invention also provides a heat extraction method, comprising the steps of:

[0017] Forming multiple fractures in geothermal reservoirs by means of fracking;

[0018] A manhole cover, a pipe body and a well sealer are sequentially arranged along the depth direction of the formation to form a cavity, a riser passes through the manhole cover and extends into the cavity, a first channel is enclosed between the manhole cover, the pipe body, the well sealer and the riser, the manhole cover has a through hole for circulating working fluid to pass through, and the first channel is connected to the riser;

[0019] A geothermal casing is arranged on the outer wall of the bottom of the pipe body, a geothermal channel is formed between the geothermal casing, the outer wall of the pipe body and the well capping device, a water inlet hole and a drainage hole are opened on the geothermal casing, and the water inlet hole, the geothermal channel and the drainage hole are connected in sequence;

[0020] The geothermal fluid flows from bottom to top along the geothermal channel, the circulating working medium flows from top to bottom along the first channel, and after countercurrent convection heat exchange with the geothermal fluid through the pipe body, flows to the ground device for heating, and the geothermal fluid is discharged to the fracture after absorbing heat through the circulating working medium.

[0021] Compared with the prior art, the closed single geothermal well heat exchange structure of the embodiment of the present invention has the following beneficial effects:

[0022] The geothermal fluid in the geothermal reservoir of the embodiment of the present invention flows into the geothermal channel from the water inlet hole, and flows out of the drainage hole from bottom to top along the geothermal channel to the fissure, while the circulating medium flows into the first channel from the through hole, and flows out of the riser from top to bottom along the first channel. In the process of the circulation of the circulating medium and the geothermal fluid, the pipe body is used to realize countercurrent convection heat exchange. Compared with the previous single-well heat exchanger that only conducts heat exchange with the rock of the geothermal reservoir through the outer wall, the present invention realizes forced convection heat exchange of the internal and external fluids of the pipe body, improves the heat exchange coefficient, and increases the heat extraction power. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of the application state of the closed single geothermal well heat exchange structure of the embodiment of the present invention;

[0024] In the figure, 1, manhole cover; 2, pipe body; 21, first casing; 22, second casing; 23, third casing; 231, rib; 3, well sealer; 4, riser; 5, geothermal casing; 51, water inlet pipe; 52, drainage pipe; 6, first channel; 61, first flow channel; 62, second flow channel; 63, third flow channel; 7, geothermal channel; a, fissure. DETAILED DESCRIPTION

[0025] The specific implementation of the present invention is further described in detail below in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0026] like Figure 1As shown, the present invention provides a closed single geothermal well heat exchange structure, which is used to extend into a geothermal reservoir to extract heat. The geothermal reservoir has a plurality of cracks a. The closed single geothermal well heat exchange structure includes a well cover 1, a pipe body 2, a well cap 3, a riser 4, and a geothermal casing 5;

[0027] The manhole cover 1 and the well seal 3 are sealed and installed at both ends of the pipe body 2 to form a cavity. The riser 4 passes through the manhole cover 1 and extends into the cavity. A first channel 6 is enclosed and formed between the manhole cover 1, the pipe body 2, the well seal 3 and the riser 4. The first channel 6 is connected to the lower end of the riser 4. The manhole cover 1 has a through hole for the circulating working medium to pass through, so that the circulating working medium flows from top to bottom along the first channel 6 and flows out from the riser 4;

[0028] The outer wall at the bottom of the pipe body 2 is surrounded by a geothermal casing 5, and a geothermal channel 7 is formed between the geothermal casing 5, the outer wall of the pipe body 2 and the well sealer 3. The geothermal casing 5 is provided with a water inlet hole and a drainage hole above the water inlet hole. The water inlet hole geothermal channel 7 and the drainage hole are connected in sequence, so that the geothermal fluid of the geothermal reservoir flows from bottom to top along the geothermal channel 7 and flows out from the drainage hole to the fracture a to complete heat exchange with the circulating working medium.

[0029] The geothermal fluid in the geothermal reservoir of the embodiment of the present invention flows into the geothermal channel 7 from the water inlet hole, and flows out from the drainage hole along the geothermal channel 7 from bottom to top to the fissure a, while the circulating medium flows into the first channel 6 from the through hole, and flows out from the riser 4 along the first channel 6 from top to bottom. In the process of the circulation medium and the geothermal fluid flowing, the pipe body 2 is used to realize countercurrent convection heat exchange. Compared with the previous single-well heat exchanger that only conducts heat exchange with the rock of the geothermal reservoir through the outer wall, the present invention realizes forced convection heat exchange of the internal and external fluids of the pipe body 2, improves the heat exchange coefficient, and increases the heat extraction power.

[0030] It can be understood that the water inlet hole in this embodiment is connected to the water inlet pipe 51 so that the geothermal fluid in the geothermal reservoir can flow into the geothermal channel 7. At the same time, the drainage hole is connected to the drainage pipe 52 so that the geothermal fluid in the geothermal channel 7 can be discharged.

[0031] In some embodiments, the water inlet hole is arranged at one end of the geothermal casing 5 close to the well cap 3, so that the water inlet hole can penetrate deeper into the geothermal reservoir, and the geothermal fluid carrying more heat can be passed into the geothermal channel 7; the water inlet hole is connected with the fissure a, so as to better collect the geothermal water in the reservoir fissure a and introduce the geothermal water into the geothermal channel 7.

[0032] In some embodiments, the aperture of the water inlet gradually decreases along the first direction. The water inlet in this embodiment adopts a tapered flow channel to increase the flow rate of the geothermal fluid entering the geothermal fluid pipeline, so that the geothermal fluid flows from bottom to top to flush the pipe body 2, so as to better achieve heat exchange with the circulating working medium in the first channel 6. It should be noted that the first direction is the wall thickness direction of the geothermal casing, and this direction is along the direction close to the geothermal channel 7 (such as Figure 1 Preferably, the aperture of the water inlet pipe 51 also gradually decreases along the first direction.

[0033] In some embodiments, a drainage hole is disposed at one end of the geothermal casing 5 away from the well plug 3, and the drainage hole is connected to the fracture a to discharge the geothermal fluid that has undergone heat exchange back into the fracture a of the geothermal reservoir.

[0034] In some embodiments, the pipe body 2 includes a first casing 21, a second casing 22 and a third casing 23 which are connected in sequence. The first casing 21, the second casing 22 and the third casing 23 are arranged in sequence along the first direction. The geothermal casing 5 is surrounded by the outer wall of the third casing 23 so as to form a geothermal channel 7 with the third casing 23 and the well cap 3; the riser 4 passes through the well cover 1 and is located in the first casing 21, the second casing 22 and the third casing 23, wherein there is a gap between the end of the riser 4 and the well cap 3 to achieve communication between the riser 4 and the third casing 23.

[0035] In this embodiment, the first casing 21 and the riser 4 enclose a first flow channel 61, the second casing 22 and the riser 4 enclose a second flow channel 62, and the third casing 23 and the riser 4 enclose a third flow channel 63. The first flow channel 61, the second flow channel 62 and the third flow channel 63 are connected in sequence to form a first channel 6. The circulating medium flows through the first flow channel 61, the second flow channel 62 and the third flow channel 63 in sequence, absorbs heat and heats up, and then gathers at the bottom of the third flow channel 63 and enters the riser 4 to supply the ground device. Preferably, the diameter of the first flow channel 61 is larger than the diameter of the second flow channel 62, and the diameter of the second flow channel 62 is larger than the diameter of the third flow channel 63, so as to reduce the difficulty of drilling during construction and improve safety.

[0036] In some embodiments, it also includes cementing cement, a second wellbore and a third wellbore connected in sequence, the outer wall of the first casing 21 is cemented on the cementing cement, the outer wall of the second casing 22 is cemented on the second wellbore, and the outer wall of the geothermal casing 5 is cemented on the third wellbore.

[0037] In this embodiment, the first casing 21, the second casing 22 and the geothermal casing 5 are installed by cementing cement, a second wellbore and a third wellbore, thereby improving the stability of the overall structure.

[0038] It can be understood that the cementing cement, secondary wellbore and tertiary wellbore in this embodiment can be a newly excavated well body or the structure of an abandoned oil and gas well. The transformation of these wells can not only reduce the drilling cost and the cost of sealing the abandoned oil and gas wells, but also develop geothermal heating, power generation and other projects according to local conditions.

[0039] In some embodiments, the inner wall surface of the third casing 23 is provided with a convex rib 231, and the convex rib 231 is spirally arranged along the length direction of the third casing 23, so as to change the flow area of ​​the third flow channel 63 and realize the local acceleration of the circulating medium. In the descending process of the circulating medium, shear flow and annular flow are formed under the action of the convex rib 231, thereby strengthening the circumferential flow in the first channel 6, improving the turbulence intensity of the fluid, and increasing the forced convection heat transfer coefficient. At the same time, the convex rib 231 also increases the heat exchange area of ​​the third flow channel 63 and reduces the heat exchange thermal resistance, thereby maximizing the heat exchange capacity of the closed single geothermal well heat exchange structure and improving the heat extraction power.

[0040] In this embodiment, the angle between the rib 231 and the inner wall of the third casing 23 is 30°-45°, which enhances the convective heat transfer coefficient of the circulating medium in the first channel 6 by 10-20%. The geothermal fluid rises in the geothermal pipeline, and the circulating medium spirally descends in the third flow channel 63. The two conduct countercurrent forced convection heat exchange. Compared with the traditional single-well heat exchanger that only conducts heat conduction heat exchange with the rock of the geothermal reservoir through the outer wall, the total heat transfer coefficient of this embodiment can be increased by 2-3 times, and the heat extraction power can be increased by 1 times. It can be understood that the angle between the rib 231 and the inner wall of the third casing 23 can be 30°, 33°, 37°, 40° or 45°, and the specific value of the angle is not particularly limited here.

[0041] The present invention also provides a heat extraction method, comprising the steps of:

[0042] S110, forming a plurality of fractures a in the geothermal reservoir by means of fracturing;

[0043] In this step, artificial fractures a are created by fracturing to increase the porosity of the geothermal reservoir, enhance the heat and mass transfer capacity of the geothermal fluid in the fractures a, promote the thermal recovery of the geothermal reservoir, and create external conditions for increasing the heat extraction power. The circulation of the geothermal fluid in the fractures of the geothermal reservoir is as follows: Figure 1 As shown by the arrow located outside the closed single geothermal well heat exchange structure.

[0044] S120, a manhole cover 1, a pipe body 2 and a well plug 3 are sequentially arranged along the depth direction of the formation to form a cavity, a riser 4 passes through the manhole cover 1 and extends into the cavity, a first channel 6 is enclosed between the manhole cover 1, the pipe body 2, the well plug 3 and the riser 4, the manhole cover 1 has a through hole for circulating working fluid to pass through, and the first channel 6 is connected to the lower end of the riser 4;

[0045] In this step, the manhole cover 1 and the well sealer 3 are sealed and installed at both ends of the pipe body 2 to form a cavity, and the pipe body 2 is used to penetrate into the geothermal reservoir so that the circulating working fluid can absorb heat during the flow along the first pass, and then only the riser 4 flows out to the ground device for heating.

[0046] S130, a geothermal casing 5 is arranged around the outer wall of the pipe body 2 located at the geothermal reservoir, a geothermal channel 7 is formed between the geothermal casing 5, the outer wall of the pipe body 2 and the well capping device 3, a water inlet hole and a drainage hole are opened in the geothermal casing 5, and the water inlet hole, the geothermal channel 7 and the drainage hole are connected in sequence;

[0047] In this step, the drainage hole is arranged above the water inlet hole, and a double-tube structure is arranged in the high-temperature section of the geothermal reservoir to form a channel for geothermal fluid heat exchange, which is used to collect the geothermal fluid in the geothermal reservoir fracture a. The geothermal fluid flows through the geothermal channel 7 to exchange heat with the circulating working medium in the first channel 6.

[0048] S140, the geothermal fluid flows from bottom to top along the geothermal channel 7, the circulating medium flows from top to bottom along the first channel 6, and after countercurrent convection heat exchange with the geothermal fluid through the pipe body 2, it flows to the ground device for heating, and the geothermal fluid is discharged to the fracture a after absorbing heat through the circulating medium.

[0049] In this step, the circulating working fluid is Figure 1 The fluid flows in the direction of the arrow in the first channel. This step utilizes countercurrent convection heat exchange. Compared with the previous single-well heat exchanger that only conducts heat through the outer wall and the rock of the geothermal reservoir, the present invention realizes forced convection heat exchange of the internal and external fluids of the pipe body 2, thereby improving the heat transfer coefficient and increasing the heat extraction power.

[0050] In summary, the closed single geothermal well heat exchange structure and heat extraction method provided by the present invention, compared with the traditional coaxial casing single well heat exchange system, is expected to save about 443kg of standard coal per heating season, reduce CO2 emissions by about 1093kg, and reduce NOx emissions by about 16.44kg, compared with coal-fired boilers, under the heat load demand of a 30,000 square meter heating building. The heating season is 180 days, calculated based on conventional coaxial casing single well heating, with a well depth of 3,000 meters, a water supply temperature of 30°C, a return water temperature of 12°C, and a water flow rate of 23m 3 / h, the present invention doubles the original single well heat exchange capacity. Compared with the traditional coaxial casing single well heat exchange system, the cost is lower under the heat load demand of 30,000 square meters of heating buildings.

[0051] In the description of the present invention, it should be noted that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside" and "outside" etc., indicating directions or positional relationships, are based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore should not be understood as a limitation on the present invention.

[0052] In addition, the present invention uses the terms "first", "second", etc. to describe various information, but these information should not be limited to these terms, and these terms are only used to distinguish the same type of information from each other. For example, without departing from the scope of the present invention, "first" information may also be referred to as "second" information, and similarly, "second" information may also be referred to as "first" information.

[0053] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and substitutions can be made without departing from the technical principles of the present invention. These improvements and substitutions should also be regarded as the scope of protection of the present invention.

Claims

1. A closed single geothermal well heat exchange structure, used to extend into a geothermal reservoir for heat extraction, wherein the geothermal reservoir has a plurality of fissures, characterized in that: The closed single geothermal well heat exchange structure includes a well cover, a pipe body, a well sealer, a riser, and a geothermal casing; The manhole cover and the well sealer are sealed and installed at both ends of the pipe body to form a cavity, the riser passes through the manhole cover and extends into the cavity, a first channel is formed between the manhole cover, the pipe body, the well sealer and the riser, the first channel is communicated with the lower end of the riser, and the manhole cover has a through hole for circulating working medium to pass through, so that the circulating working medium flows from top to bottom along the first channel and flows out of the riser; The outer wall of the bottom of the pipe body is surrounded by a geothermal casing, and a geothermal channel is formed between the geothermal casing, the outer wall of the pipe body and the well capping device. The geothermal casing is provided with a water inlet hole and a drainage hole above the water inlet hole. The water inlet hole, the geothermal channel and the drainage hole are connected in sequence, so that the geothermal fluid of the geothermal reservoir flows from bottom to top along the geothermal channel and flows out from the drainage hole to the fracture to complete heat exchange with the circulating working medium.

2. The closed single geothermal well heat exchange structure according to claim 1, characterized in that: The water inlet hole is arranged at one end of the geothermal casing close to the well stopper, and the water inlet hole is communicated with the fissure.

3. The closed single geothermal well heat exchange structure according to claim 1, characterized in that: The aperture of the water inlet hole gradually decreases along the first direction to increase the flow rate of the geothermal fluid entering the geothermal fluid pipeline.

4. The closed single geothermal well heat exchange structure according to claim 1, characterized in that: The drainage hole is arranged at one end of the geothermal casing away from the well plugger, and the drainage hole is communicated with the fissure.

5. The closed single geothermal well heat exchange structure according to claim 1, characterized in that: The pipe body includes a first casing, a second casing and a third casing which are connected in sequence along the first direction. The geothermal casing is arranged on the outer wall of the third casing. The first casing and the riser are combined to form a first flow channel. The second casing and the riser are combined to form a second flow channel. The third casing and the riser are combined to form a third flow channel. The first flow channel, the second flow channel and the third flow channel are connected in sequence to form the first channel.

6. The closed single geothermal well heat exchange structure according to claim 5, characterized in that: The diameter of the first flow channel is greater than the diameter of the second flow channel, and the diameter of the second flow channel is greater than the diameter of the third flow channel.

7. The closed single geothermal well heat exchange structure according to claim 5, characterized in that: It also includes cementing cement, a second wellbore and a third wellbore connected in sequence, the outer wall of the first casing is cemented on the cementing cement, the outer wall of the second casing is cemented on the second wellbore, and the outer wall of the geothermal casing is cemented on the third wellbore.

8. The closed single geothermal well heat exchange structure according to claim 5, characterized in that: The inner wall surface of the third sleeve is provided with convex ribs, and the convex ribs are spirally arranged along the length direction of the third sleeve.

9. The closed single geothermal well heat exchange structure according to claim 8, characterized in that: The included angle between the convex rib and the inner wall surface of the third sleeve is 30°-45°.

10. A heat extraction method, characterized in that the steps include: Forming multiple fractures in geothermal reservoirs by means of fracking; A manhole cover, a pipe body and a well sealer are sequentially arranged along the depth direction of the formation to form a cavity, a riser passes through the manhole cover and extends into the cavity, a first channel is enclosed between the manhole cover, the pipe body, the well sealer and the riser, the manhole cover has a through hole for circulating working fluid to pass through, and the first channel is connected to the riser; A geothermal casing is arranged on the outer wall of the bottom of the pipe body, a geothermal channel is formed between the geothermal casing, the outer wall of the pipe body and the well capping device, a water inlet hole and a drainage hole are opened on the geothermal casing, and the water inlet hole, the geothermal channel and the drainage hole are connected in sequence; The geothermal fluid flows from bottom to top along the geothermal channel, the circulating working medium flows from top to bottom along the first channel, and after countercurrent convection heat exchange with the geothermal fluid through the pipe body, flows to the ground device for heating, and the geothermal fluid is discharged to the fracture after absorbing heat through the circulating working medium.

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