Enhanced closed heat removal method based on expansion casing

Abstract

The invention discloses a reinforced closed heat removal method based on an expansion casing, and relates to the technical field of geothermal energy development, and the method comprises the following steps: selecting a target geothermal reservoir, and determining the depth of a heat removal section according to a geothermal gradient; drilling to the upper part of the heat removal section, installing a common sleeve on the upper part of the heat removal section, and injecting slurry for well cementation as a first open section; after well cementation is completed, drilling continues to be conducted to the lower portion of the heat extraction section of the geothermal reservoir, and reaming is conducted on the heat extraction section; after broaching, an expandable sleeve is installed on the heat removal section, and pressurized expansion treatment is conducted on the expandable sleeve; cement is filled between the well wall and the expandable casing for well cementation to serve as a second open section; and a heat exchange working medium is injected from the first open section annulus, exchanges heat with the second open section and then is extracted from the central pipe, so that geothermal energy utilization is realized. According to the system, the defects that a traditional closed heat removal system is low in efficiency and small in heat removal amount are overcome remarkably, the heat removal temperature is increased, the heat removal energy efficiency is optimized, and development and utilization of medium-deep geothermal energy are accelerated.

Description

Technical Field

[0001] The present invention relates to the technical field of geothermal energy development, and more particularly to a closed heat extraction method based on expansion casing reinforcement. Background Art

[0002] Geothermal energy is widely distributed, has abundant reserves, is safe, high-quality and has a stable energy supply. Closed heat extraction technology is an important means of developing and utilizing geothermal energy. The heat extraction cycle working fluid used does not exchange working fluid with the formation during the heat extraction process, thus avoiding environmental pollution, equipment corrosion and scaling problems that may be caused by open systems, that is, "extracting heat without taking water", which is particularly suitable for the development of geothermal reservoirs that are water-free, difficult to recharge or extremely difficult to recharge.

[0003] In geothermal closed development, a coaxial casing system is often used to achieve heat exchange. It consists of a vertical well drilled into the geothermal formation and a central pipe in a coaxial position in the wellbore. The circulating fluid is injected into the annulus from the ground through a high-pressure pump, extracts heat from the well wall through thermal convection and heat conduction, and then returns to the ground through the central pipe and flows through the heat exchanger for utilization. Since the closed system and the outside world (geothermal formation) only rely on heat conduction to achieve heat exchange, the system's heat extraction capacity and efficiency are limited.

[0004] Therefore, how to provide a closed heat extraction method based on expansion casing to expand the heat exchange area between the wellbore and the geothermal reservoir, thereby enhancing heat exchange and improving the heat extraction performance of the closed heat extraction system is an urgent problem to be solved by technical personnel in this field. Summary of the invention

[0005] In view of this, the present invention provides a closed heat extraction method based on expansion casing to expand the heat exchange area between the wellbore and the geothermal reservoir, thereby enhancing heat exchange and improving the heat extraction performance of the closed heat extraction system.

[0006] In order to achieve the above object, the present invention adopts the following technical solution: a closed heat extraction method based on expansion casing reinforcement, comprising:

[0007] Select the target geothermal reservoir and determine the depth of the heat extraction section according to the geothermal gradient;

[0008] Drill to the upper part of the heat extraction section, install a common casing at the upper part of the heat extraction section and inject mud for cementing, which is the first opening section;

[0009] After cementing is completed, continue drilling to the lower part of the heat extraction section of the geothermal reservoir and expand the heat extraction section;

[0010] After the hole is expanded, an expandable casing is installed in the heat extraction section, and the expandable casing is subjected to a pressurized expansion process;

[0011] Filling cement between the well wall and the expandable casing as the second opening section;

[0012] The heat exchange medium is injected from the annular space of the first open section, and is extracted from the central tube after heat exchange with the second open section, thereby realizing the utilization of geothermal energy.

[0013] Preferably, both the first open section and the second open section are installed with insulation pipes.

[0014] Preferably, when installing the insulation pipe, the insulation outer pipe is first lowered, one section at a time, and each section of the insulation outer pipe is connected by a section hoop;

[0015] Then put in the insulation inner pipe. The installation method of the insulation inner pipe is the same as that of the insulation outer pipe.

[0016] Preferably, the thermal insulation inner pipe and the thermal insulation outer pipe are connected at the bottom of the well by a sealing nipple.

[0017] Preferably, applying pressure to the expandable casing using an expander;

[0018] During the expansion process, the material of the expandable casing undergoes plastic deformation, and the stress of the material exceeds its yield strength;

[0019] The expanded casing fits tightly against the wellbore wall after expansion.

[0020] Preferably, the cement is thermally conductive cement.

[0021] Preferably, the bottom hole of the heat extraction section is expanded using a rotary jet hydraulic jet or a mechanical reaming tool.

[0022] Preferably, the heat exchange medium is injected from the first open section via a high-pressure pump, and the heat exchanger is used to realize geothermal energy utilization.

[0023] It can be known from the above technical scheme that compared with the prior art, the present invention discloses a closed heat extraction method based on expansion casing, including: selecting a target geothermal reservoir, determining the depth of the heat extraction section according to the geothermal gradient; drilling to the upper part of the heat extraction section, installing a common casing at the upper part of the heat extraction section and injecting mud cementing as the first opening section; after the cementing is completed, continue to drill to the lower part of the heat extraction section of the geothermal reservoir, and expand the heat extraction section; after the expansion, install an expandable casing in the heat extraction section, and pressurize and expand the expandable casing; fill cement cementing between the well wall and the expandable casing as the second opening section; the heat exchange medium is injected into the annulus of the first opening section, and is extracted from the central pipe after heat exchange with the second opening section to realize geothermal energy utilization. The present invention helps to significantly improve the shortcomings of low efficiency and small heat extraction of traditional closed heat extraction systems, increase the heat extraction temperature, optimize the heat extraction energy efficiency, and accelerate the development and utilization of medium and deep geothermal energy. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0025] Figure 1 A schematic flow chart of a closed heat extraction method based on expansion sleeve enhancement provided by the present invention.

[0026] Figure 2 This is a schematic diagram of the heat extraction structure provided by the present invention. DETAILED DESCRIPTION

[0027] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] The embodiment of the present invention discloses a closed heat extraction method based on expansion sleeve reinforcement, such as Figure 1 As shown, including:

[0029] Select the target geothermal reservoir and determine the depth of the heat extraction section according to the geothermal gradient;

[0030] Drill to the upper part of the heat extraction section, install a common casing at the upper part of the heat extraction section and inject mud for cementing, which is the first opening section;

[0031] After cementing is completed, continue drilling to the lower part of the heat extraction section of the geothermal reservoir and expand the heat extraction section;

[0032] After the hole is expanded, an expandable casing is installed in the heat extraction section, and the expandable casing is subjected to a pressurized expansion process;

[0033] Filling cement between the well wall and the expandable casing as the second opening section;

[0034] The heat exchange medium is injected from the annular space of the first open section, and is extracted from the central tube after heat exchange with the second open section, thereby realizing the utilization of geothermal energy.

[0035] When the closed heat extraction method is adopted in the embodiment of the present invention, the water in the well cannot contact the formation, so it is necessary to use an expandable casing at the bottom of the well for cementing and completion. However, ordinary casing cannot be expanded, and the expandable casing can expand and expand the diameter, close to the expanded well wall, so that the bottom diameter of the well is actually enlarged. Then, high thermal conductivity cement is filled between the well wall and the casing for cementing and completion.

[0036] In the embodiment of the present invention, an expandable casing is lowered into the heat extraction section, and cement is used to seal the expandable casing and the well wall. The specific operation process is to first expand the well bottom, then lower the expandable casing, and then inject high thermal conductivity cement to cement the well after expansion.

[0037] In an embodiment of the present invention, the initial state of the expandable casing is the diameter of an ordinary casing. After being lowered into the bottom of the well, it is pressurized and expanded, and pressure is applied to the expandable casing using a special expansion tool (such as an expander). This pressure is usually transmitted through a liquid or gas medium, resulting in an increase in the outer diameter of the expandable casing. During the expansion process, the material of the expandable casing undergoes plastic deformation. At this time, the stress of the material exceeds its yield strength, resulting in permanent deformation. The degree and uniformity of expansion depend on the applied pressure, the characteristics of the casing material, and the conditions of the surrounding formations. The expanded casing fits tightly against the wellbore wall after expansion, and the wellbore wall collapse is prevented by cementing means, and necessary support is provided. After the expansion is completed, a pressure test or other inspection is performed to ensure the integrity and sealing of the casing so that it can withstand formation pressure and other external stresses during subsequent drilling and production processes.

[0038] Specifically, the second opening section should be drilled to the bottom of the heat reservoir as far as possible to obtain heat energy to the maximum extent, and insulation pipes should be installed in both the first opening section and the second opening section.

[0039] Specifically, the first opening section and the second opening section are both installed with insulation pipes to prevent the high-temperature fluid from being cooled by the low-temperature fluid in the annulus during the production process and affecting the heat extraction effect.

[0040] Specifically, when installing the insulation pipe, first put the insulation outer pipe in, one section at a time, and each section of the insulation outer pipe is connected by a section hoop;

[0041] Then put in the insulation inner pipe. The installation method of the insulation inner pipe is the same as that of the insulation outer pipe.

[0042] Specifically, the thermal insulation inner pipe and the thermal insulation outer pipe are connected at the bottom of the well by a sealing nipple.

[0043] Specifically, applying pressure to the expandable casing using an expander;

[0044] During the expansion process, the material of the expandable casing undergoes plastic deformation, and the stress of the material exceeds its yield strength;

[0045] The expanded casing fits tightly against the wellbore wall after hole expansion, which enlarges the hole diameter and increases the heat exchange area. After hole expansion at the bottom of the well, high thermal conductivity cement is required for cementing.

[0046] Among them, the expandable casing has the diameter of an ordinary casing in its initial state, and is pressurized and expanded after being lowered into the bottom of the well. Therefore, the expandable casing used in the embodiment of the present invention can expand and fit closely to the expanded well wall, so that the bottom diameter of the well is actually enlarged, which is impossible for ordinary casing to do.

[0047] Specifically, in terms of the selection of expandable casing materials, in addition to conventional requirements such as high temperature resistance, it must ensure that the mechanical properties of the corresponding steel grade casing of the API standard are met after expansion. The diameter direction can generally expand to 1.4 times the original.

[0048] Specifically, the cement is thermally conductive cement.

[0049] Specifically, the bottom hole of the heat extraction section is expanded using a rotary jet hydraulic jet or a mechanical hole expansion tool.

[0050] Specifically, the heat exchange medium is injected from the first open section via a high-pressure pump, and the heat exchanger is used to realize geothermal energy utilization.

[0051] In a specific embodiment of the present invention, Figure 2 As shown, first, through geological exploration and temperature measurement and other means, the distribution of underground heat sources is understood and the target geothermal reservoir is selected; then the depth of the heat extraction section is determined mainly based on the geothermal gradient (i.e. the change in temperature per meter of depth). Generally, the higher the geothermal gradient, the shallower the heat extraction section can be set. Because the heat extraction has met the engineering requirements, and too deep a heat extraction section may lead to increased drilling and maintenance costs, it is necessary to find a balance between technical feasibility and economy. Finally, drill to the upper part of the heat extraction section of the geothermal reservoir, lower the ordinary casing and inject mud cementing, which is the first opening section;

[0052] Continue drilling down to the lower part of the heat extraction section of the geothermal reservoir, and use rotary jet hydraulic jet or mechanical reaming tools to expand the hole diameter and increase the heat exchange area;

[0053] The expandable casing with good expansion performance is put into the well, and plastic deformation occurs after the expansion construction. It is the second opening section and also the main heat extraction section. After expansion, high thermal conductivity cement is injected to cement the well.

[0054] The specific operation process of heat exchange is: low-temperature heat exchange medium is injected from the annulus of the vertical well through a high-pressure pump, and is extracted from the central pipe after sufficient closed heat exchange with the heat reservoir, and geothermal energy is utilized by using a heat exchanger.

[0055] The casing expansion technology can be used to expand the wellbore volume, thereby expanding the heat exchange area of ​​the heat extraction section and improving the overall heat extraction efficiency. The well type of the closed heat extraction system is not limited to a vertical well. According to the idea of ​​the embodiment of the present invention, a U-shaped, horizontal well or other well type can also be used to enhance the downhole heat exchange by using the downhole heat extraction section casing expansion and reaming technology.

[0056] Utilizing the method of the embodiment of the present invention helps to significantly improve the shortcomings of low efficiency and small heat extraction of traditional closed heat extraction systems, increase the heat extraction temperature, optimize the heat extraction energy efficiency, and accelerate the development and utilization of medium and deep geothermal energy.

[0057] In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part.

[0058] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A closed heat extraction method based on expansion casing reinforcement, characterized in that: include: Select the target geothermal reservoir and determine the depth of the heat extraction section according to the geothermal gradient; Drill to the upper part of the heat extraction section, install a common casing at the upper part of the heat extraction section and inject mud for cementing, which is the first opening section; After the cementing is completed, continue drilling to the lower part of the heat extraction section of the geothermal reservoir and expand the heat extraction section; After the hole is expanded, an expandable casing is installed in the heat extraction section, and the expandable casing is subjected to a pressurized expansion process; Filling cement between the well wall and the expandable casing as the second opening section; The heat exchange medium is injected from the annular space of the first open section, and is extracted from the central tube after heat exchange with the second open section, thereby realizing geothermal energy utilization.

2. The method for strengthening closed heat extraction based on expansion sleeve according to claim 1 is characterized in that: The first opening section and the second opening section are both installed with thermal insulation pipes.

3. The method for closed heat extraction based on expansion sleeve enhancement according to claim 2 is characterized in that: When installing the insulation pipe, first put the insulation outer pipe in, one section at a time, and connect each section of the insulation outer pipe with a section hoop; Then put in the insulation inner pipe. The installation method of the insulation inner pipe is the same as that of the insulation outer pipe.

4. The closed heat extraction method based on expansion sleeve enhancement according to claim 1 is characterized in that: The insulation inner pipe and the insulation outer pipe are connected at the bottom of the well with a sealing short joint.

5. The method for closed heat extraction based on expansion sleeve enhancement according to claim 1 is characterized in that: applying pressure to the expandable casing using an expander; During the expansion process, the material of the expandable casing undergoes plastic deformation, and the stress of the material exceeds its yield strength; The expanded casing fits tightly against the wellbore wall after expansion.

6. The closed heat extraction method based on expansion casing enhancement according to claim 1 is characterized in that: The cement is heat-conducting cement.

7. The closed heat extraction method based on expansion casing enhancement according to claim 1 is characterized in that: Use rotary jet hydraulic jet or mechanical hole reaming tool to expand the bottom hole of the heat extraction section.

8. The closed heat extraction method based on expansion sleeve enhancement according to claim 1 is characterized in that: The heat exchange medium is injected from the first open section via a high-pressure pump, and the heat exchanger is used to realize the utilization of geothermal energy.

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