Coaxial integrated wellhead device for geothermal well in high-altitude permafrost region and installation process thereof

Abstract

The application provides a high-altitude permafrost area geothermal well coaxial integrated wellhead device and an installation process thereof, and belongs to the technical field of geothermal heating. The device comprises a wellhead cavity, which is fixedly connected with an oil casing of a geothermal well; a PERT inner pipe, which is arranged inside the wellhead cavity and extends vertically and is communicated with a downhole heat exchange system; a water inlet pipeline assembly, which comprises a water inlet branch pipe that is communicated with the wellhead cavity and is arranged laterally; a water outlet pipeline assembly, which is arranged in a manhole and comprises a water outlet pipe that is communicated with the PERT inner pipe and is arranged at the upper portion of the wellhead cavity; a water inlet passage and a water outlet passage that are coaxially arranged in the wellhead cavity. The device has the advantages of high integration, reliable sealing, strong anti-freezing and anti-settling capacity, and can effectively adapt to the high-altitude permafrost environment, has good heat preservation and corrosion prevention effects, can well meet the long-term stable operation requirements in high-cold areas, and is convenient to install and has high construction efficiency.

Description

Technical Field

[0001] This invention provides a coaxial integrated wellhead device for geothermal wells in high-altitude permafrost regions and its installation process, belonging to the field of geothermal heating technology. Background Technology

[0002] In high-altitude permafrost regions, the development and utilization of geothermal resources face numerous unique challenges. These areas experience frost heave and thaw settlement, large diurnal temperature variations, and short construction windows, leading to problems such as pipeline displacement, seal failure, and difficulty in controlling installation accuracy during the operation and construction of geothermal wellhead equipment.

[0003] Existing geothermal wellhead devices mostly adopt non-integrated, split structures with dispersed inlet and outlet pipelines, resulting in large volumes, disorganized structures, and significant space occupation by the well chamber. There is a lack of standardized integrated solutions for the conversion connection of deep well coaxial casing (inlaid core tube within oil casing), and the reliability of steel-plastic conversion connections is insufficient. In high-altitude permafrost environments, ordinary split devices are prone to shear failure due to displacement caused by soil frost heave and thawing. Traditional connection methods have poor sealing performance under long-term thermal expansion and contraction, making leakage highly likely. Furthermore, existing technologies are cumbersome to install, resulting in extremely low installation efficiency and long construction periods in high-altitude areas with low oxygen levels and limited manual labor. Moreover, there is a lack of deeply integrated insulation and flexible casing sealing solutions for extreme low-temperature environments, leading to severe heat loss at the wellhead and susceptibility to corrosion of metal components by condensate, making it difficult to meet the long-term stable operation requirements of cold regions. Therefore, this invention provides a coaxial integrated wellhead device for geothermal wells in high-altitude permafrost areas and its installation process. Summary of the Invention

[0004] The technical problem solved by this invention is that the device of this invention has a highly integrated structure, reliable sealing, strong anti-freezing and anti-settling capabilities, and combined with the standardized controlled hot-melt process of steel-plastic conversion flange, it ensures connection strength and sealing performance, can effectively adapt to high-altitude permafrost environment, has good thermal insulation and anti-corrosion effect, can well meet the requirements of long-term stable operation in cold regions, and is easy to install and has high construction efficiency.

[0005] To solve the technical problem, the technical solution provided by this invention is: a coaxial integrated wellhead device for geothermal wells in high-altitude permafrost areas and its installation process, including... The wellbore is located at the wellhead of the geothermal well and is fixedly connected to the oil casing of the geothermal well. The PERT inner tube is installed inside the wellbore and extends vertically to connect with the downhole heat exchange system. The water inlet pipeline assembly, installed inside the inspection well, includes a water inlet branch pipe that is connected to the well cavity and is arranged laterally, for conveying heat exchange medium to the well. The water outlet pipeline assembly is installed inside the inspection well, including a water outlet pipe that is connected to the PERT inner pipe and is located at the upper part of the well mouth body, for leading out the medium after heat exchange in the well. A water inlet channel and a water outlet channel are coaxially arranged inside the well mouth. The water inlet channel is connected to the water inlet pipeline assembly, and the water outlet channel is connected to the water outlet pipeline assembly. The inlet and outlet pipeline assemblies are spaced apart in the vertical direction, so that the inlet and outlet channels form independent fluid channels in the wellhead, thereby avoiding short-circuit flow of the inlet and outlet media at the wellhead.

[0006] Furthermore, both the inlet pipeline assembly and the outlet pipeline assembly are connected to the wellbore body via steel-plastic conversion flanges, and the wellbore body is connected to the oil casing via casing flanges.

[0007] Furthermore, the wellbore has a large-diameter structure with different diameters on the inlet and outlet sides.

[0008] Furthermore, both the inlet and outlet pipeline assemblies are equipped with anti-buoyancy structural components, butterfly valves, flexible metal connections for absorbing pipeline displacement, and connecting short pipes. The inlet pipeline assembly is also equipped with a pressure gauge and a vent valve, and the outlet pipeline assembly is also equipped with a pressure gauge and an air vent valve.

[0009] Furthermore, the length of the metal flexible connection is 300-500mm.

[0010] Furthermore, the elevation of the inlet branch pipe and the outlet pipe is pre-controlled by setting elevation control lines inside the inspection well.

[0011] Furthermore, the steel-plastic conversion flange is connected to the PERT inner tube by heat fusion, and the axis is kept concentric and rotation is avoided during the heat fusion connection process.

[0012] The installation process of the above-mentioned coaxial integrated wellhead device for geothermal wells in high-altitude permafrost areas includes the following steps: S1. Pre-installation and elevation verification of wellhead equipment: After the inspection well and PERT inner pipe are installed, the wellhead equipment is pre-installed, the relative positions of the inlet branch pipe and outlet pipe in the vertical direction are verified, and the elevation is controlled. S2. Oil casing flange installation: Cut and grind the oil casing, and weld and install the oil casing flange. S3. Wellbore body installation: The wellbore body is fixedly connected to the oil casing via the oil casing flange; S4. Inner pipe and steel-plastic conversion connection: Cut the PERT inner pipe and connect the steel-plastic conversion flange to the PERT inner pipe using a heat fusion method; S5. Installation of pipe fittings in the manhole: Install the inlet pipe assembly and the outlet pipe assembly in sequence in the manhole. Connect the outlet pipe to the PERT inner pipe through a steel-plastic conversion flange. Then, perform anti-corrosion treatment on the metal pipe fittings and welded parts, and install an insulation layer on the pipe fittings and valves in the manhole. S6. Casing sealing: The flexible casing of the side wall and the rigid waterproof casing of the base plate are sealed and sealed, and maintenance treatment is carried out.

[0013] Furthermore, the insulation layer is made of B1 grade closed-cell foamed rubber-plastic composite insulation material.

[0014] Furthermore, the flexible sleeve sealing structure of the side wall adopts flange cover and sealing ring for sealing, and the rigid sleeve sealing structure of the base plate adopts layered filling and sealing with hemp braid and asbestos cement.

[0015] The beneficial effects of this invention are: The device of this invention features a highly integrated structure, reliable sealing, and strong resistance to freezing and settlement. It reduces the space occupied by the well chamber and, combined with the standardized controlled hot-melt process of the steel-plastic conversion flange, ensures connection strength and sealing performance. It effectively solves the problem of easy leakage in traditional connection methods under extreme temperature difference environments. It can effectively adapt to high-altitude permafrost environments, has good thermal insulation and corrosion prevention effects, and can well meet the requirements for long-term stable operation in cold regions. Moreover, it is easy to install and has high construction efficiency. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the overall structure of the present invention.

[0017] Figure 2 This is a schematic diagram of the connection between the wellbore body and the oil casing according to the present invention.

[0018] Figure 3 This is a schematic diagram of the water inlet pipeline assembly structure of the present invention.

[0019] Figure 4 This is a schematic diagram of the water outlet pipeline assembly structure of the present invention.

[0020] Figure 5 This is a partial schematic diagram of the oil casing of the present invention.

[0021] 1. Wellbore; 2. Oil casing; 3. Casing flange; 4. PERT inner tube; 5. Inlet water pipeline assembly; 6. Outlet water pipeline assembly; 7. Inlet water channel; 8. Outlet water channel; 9. Steel-plastic conversion flange; 50. Inlet water branch pipe; 51. Anti-buoyancy structural component; 60. Outlet water pipe. Detailed Implementation

[0022] The invention will be further described below with reference to the accompanying drawings.

[0023] As shown in the attached drawings: This invention provides a coaxial integrated wellhead device for geothermal wells in high-altitude permafrost regions, including a wellbore body 1, located at the wellhead of the geothermal well and fixedly connected to the oil casing 2 of the geothermal well. The wellbore body 1 has a large-diameter and small-diameter structure, with different diameters on the inlet and outlet sides; a PERT inner tube 4, located inside the wellbore body 1 and extending vertically, communicating with the downhole heat exchange system; an inlet pipeline assembly 5, located inside the inspection well, including an inlet branch pipe 50 communicating with the wellbore body 1 and arranged laterally, for conveying the heat exchange medium to the downhole; and an outlet pipeline assembly 6. The system is installed inside the inspection well and includes an outlet pipe 60 connected to the PERT inner pipe 4 and located at the upper part of the well cavity 1, used to draw out the medium after heat exchange in the well; an inlet channel 7 and an outlet channel 8 are coaxially arranged inside the well cavity 1, the inlet channel 7 is connected to the inlet pipeline assembly 5, and the outlet channel 8 is connected to the outlet pipeline assembly 6; the inlet pipeline assembly 5 and the outlet pipeline assembly 6 are arranged at intervals in the vertical direction, so that the inlet channel 7 and the outlet channel 8 form independent fluid channels in the well cavity 1, thereby avoiding short-circuit flow of the inlet and outlet media at the wellhead.

[0024] As shown in the attached diagram of the instruction manual: both the inlet pipeline assembly 5 and the outlet pipeline assembly 6 are connected to the wellbore body 1 via a steel-plastic conversion flange 9. The steel-plastic conversion flange 9 is connected to the PERT inner pipe 4 via heat fusion. During the heat fusion connection, the axis is kept concentric and rotation is avoided. The wellbore body 1 is connected to the oil casing 2 via a casing flange 3. A sealing gasket is set between the flanges to form a sealed connection. Both the inlet pipeline assembly 5 and the outlet pipeline assembly 6 are equipped with an anti-buoyancy structure 51, a butterfly valve, a metal flexible connection for absorbing pipeline displacement, and a connecting short pipe. The inlet pipeline assembly 5 is also equipped with a pressure gauge and a vent valve. The outlet pipeline assembly 6 is also equipped with a pressure gauge and a vent valve. The length of the metal flexible connection is 300-500mm to buffer the crustal stress and water hammer impact at high altitudes. The elevation of the inlet branch pipe 50 and the outlet pipe 60 is pre-controlled by setting an elevation control line in the inspection well.

[0025] The installation process of the above-mentioned coaxial integrated wellhead device for geothermal wells in high-altitude permafrost areas includes the following steps: S1. Pre-installation and elevation verification of wellhead equipment: The elevation of the inlet branch pipe 50 and the outlet pipe 60 is pre-controlled by setting an elevation control line in the inspection well. The inlet pipe is set to be 600mm from the ground and the outlet pipe is 700mm from the inlet pipe. A coordinate benchmark is established in the high-altitude environment. After the inspection well and PERT inner pipe 4 are installed, the wellhead equipment is pre-installed to verify the relative position of the inlet branch pipe 50 and the outlet pipe 60 in the vertical direction and to control the elevation. S2. Oil casing flange installation: Cut the excess oil casing 2 according to the actual site conditions, grind the pipe ends, and then weld and install the oil casing flange 3. S3. Wellbore body installation: The wellbore body 1 is fixedly connected to the oil casing 2 via the oil casing flange 3. S4. Inner tube and steel-plastic conversion connection: Cut the PERT inner tube 4 and ensure that the cut is flat and vertical. Use hot melt to connect the steel-plastic conversion flange 9 to the PERT inner tube 4. During the hot melt connection, keep the axis concentric and avoid rotation. Rotation is strictly prohibited during insertion to ensure molecular-level fusion in a low-temperature and oxygen-deficient environment. S5. Installation of In-Well Piping: After the wellhead equipment is installed, the downhole heat exchange system is flushed. The inlet pipeline assembly 5 and the outlet pipeline assembly 6 are installed in sequence in the inspection well. The outlet pipe 60 is connected to the PERT inner pipe 4 through the steel-plastic conversion flange 9. The metal pipes and welded parts are treated with anti-corrosion measures. An insulation layer is installed on the in-well pipes and valves. The insulation layer uses B1 grade closed-cell foamed rubber-plastic composite insulation material, supplemented with a 50mm thick anti-damage surface layer, which effectively curbs the heat loss of the wellhead equipment, reduces heat loss by more than 30%, and solves the risk of corrosion of metal components by condensate caused by temperature difference. S6. Casing Sealing: The flexible casing of the side wall and the rigid waterproof casing of the base plate are sealed. The casing sealing includes the sealing structure of the flexible casing of the side wall and the sealing structure of the rigid casing of the base plate. The sealing structure of the flexible casing of the side wall uses flange glands and sealing rings for sealing. The sealing structure of the rigid casing of the base plate uses hemp braid and asbestos cement to fill and seal in layers. The diameter of the hemp braid is 1.5 times the gap, and the compaction depth does not exceed 1 / 3. The surface is flat and full. It is necessary to carry out wet soil enclosure curing for no less than 24 hours to cope with the deformation pressure of the permafrost layer, enhance the sealing performance, and carry out curing treatment.

[0026] In summary, compared with the prior art, the present invention has at least the following beneficial effects: Highly integrated structure: The "coaxial inlet and outlet cavity" design integrates the inlet and outlet conversion of the oil casing and PERT inner tube into a single device, which simplifies the well chamber structure, reduces the space occupied by the well chamber, improves the space utilization of the well chamber, and reduces the risk of leakage. Strong resistance to freezing and settlement: By configuring metal flexible connections of specific lengths and flexible casing plugging and asbestos-oil-hemp composite plugging technology, a "breathing" connection system with displacement compensation capability is constructed. It can effectively absorb the physical displacement and shear stress caused by the freezing and thawing settlement of the permafrost layer, avoid pipeline breakage caused by rigid connections, and protect the wellhead equipment from damage.

[0027] Reliable sealing performance: The inlet and outlet pipeline assemblies are connected to the wellbore body through steel-plastic conversion flanges. A sealing gasket is installed between the flanges. Combined with the standardized and controlled hot-melt process of the steel-plastic conversion flanges, the connection strength and sealing performance are ensured, effectively solving the problem of easy leakage of traditional connection methods under extreme temperature difference environments. Excellent thermal insulation and corrosion resistance: High-performance B1 grade closed-cell foamed rubber-plastic composite insulation material is used in combination with a damage-resistant surface layer, which effectively curbs the heat loss of the wellhead device, so as to avoid the risk of corrosion of metal components by condensation caused by temperature difference and ensure the long-term operational stability of the device. Adaptable to high-altitude environments: For high-altitude, low-pressure, and low-temperature environments, a standardized hot-melt connection process and weld anti-corrosion and heat preservation solution are proposed. Combined with modular prefabrication and installation methods, while ensuring connection strength and installation accuracy, the outdoor operation time under high-altitude conditions is significantly shortened, construction efficiency is improved, and the intensity of manual labor is reduced.

[0028] The present invention and its embodiments have been described above. This description is not restrictive, and the accompanying drawings are only one embodiment of the present invention; the actual structure is not limited thereto. In conclusion, if those skilled in the art are inspired by this description and design similar structures and embodiments without departing from the spirit of the invention, such designs should fall within the protection scope of the present invention.

Claims

1. A coaxial integrated wellhead device for geothermal wells in high-altitude permafrost regions, characterized in that, include The wellbore body (1) is located at the wellhead of the geothermal well and is fixedly connected to the oil casing (2) of the geothermal well; The PERT inner tube (4) is installed inside the wellbore body (1) and extends vertically to connect with the downhole heat exchange system; The water inlet pipeline assembly (5) is installed inside the inspection well and includes a water inlet branch pipe (50) that is connected to the well cavity body (1) and is arranged laterally for conveying heat exchange medium to the well. The water outlet pipeline assembly (6) is installed inside the inspection well and includes a water outlet pipe (60) that is connected to the PERT inner pipe (4) and installed at the upper part of the well mouth body (1) for leading out the medium after heat exchange in the well. A water inlet channel (7) and a water outlet channel (8) are coaxially arranged in the well mouth body (1). The water inlet channel (7) is connected to the water inlet pipeline assembly (5), and the water outlet channel (8) is connected to the water outlet pipeline assembly (6). The inlet pipeline assembly (5) and the outlet pipeline assembly (6) are arranged at intervals in the vertical direction, so that the inlet channel (7) and the outlet channel (8) form independent fluid channels in the well mouth body (1), thereby avoiding short-circuit flow of the inlet and outlet water media at the well mouth.

2. The coaxial integrated wellhead device for geothermal wells in high-altitude permafrost areas according to claim 1, characterized in that: The inlet pipeline assembly (5) and the outlet pipeline assembly (6) are both connected to the wellbore body (1) via a steel-plastic conversion flange (9), and the wellbore body (1) is connected to the oil casing (2) via a casing flange (3).

3. The coaxial integrated wellhead device for geothermal wells in high-altitude permafrost areas according to claim 1, characterized in that: The wellbore body (1) has a large and small head structure, with different diameters on the inlet and outlet sides.

4. The coaxial integrated wellhead device for geothermal wells in high-altitude permafrost areas according to claim 1, characterized in that: Both the inlet pipeline assembly (5) and the outlet pipeline assembly (6) are equipped with anti-buoyancy structural components (51), butterfly valves, metal flexible connections for absorbing pipeline displacement, and connecting short pipes. The inlet pipeline assembly (5) is also equipped with a pressure gauge and a vent valve, and the outlet pipeline assembly (6) is also equipped with a pressure gauge and an air vent valve.

5. The coaxial integrated wellhead device for geothermal wells in high-altitude permafrost areas according to claim 4, characterized in that: The length of the metal flexible connection is 300-500mm.

6. The coaxial integrated wellhead device for geothermal wells in high-altitude permafrost areas according to claim 1, characterized in that: The elevation of the inlet branch pipe (50) and the outlet pipe (60) is pre-controlled by setting elevation control lines inside the inspection well.

7. The coaxial integrated wellhead device for geothermal wells in high-altitude permafrost areas according to claim 2, characterized in that: The steel-plastic conversion flange (9) is connected to the PERT inner tube (4) by heat fusion. During the heat fusion connection, the axis is kept concentric and rotation is avoided.

8. The installation process of a coaxial integrated wellhead device for geothermal wells in high-altitude permafrost areas according to any one of claims 1-7, characterized in that, Includes the following steps: S1. Pre-installation and elevation verification of wellhead equipment: After the inspection well and PERT inner pipe (4) are installed, the wellhead equipment is pre-installed, the relative positions of the inlet branch pipe (50) and outlet pipe (60) in the vertical direction are verified, and the elevation is controlled. S2. Oil casing flange installation: Cut and grind the oil casing (2), and weld and install the oil casing flange (3). S3. Wellbore body installation: The wellbore body (1) is fixedly connected to the oil casing (2) through the oil casing flange (3); S4. Inner pipe and steel-plastic conversion connection: Cut the PERT inner pipe (4) and connect the steel-plastic conversion flange (9) to the PERT inner pipe (4) by heat fusion. S5. Installation of pipe fittings in the well: Install the inlet pipe assembly (5) and the outlet pipe assembly (6) in sequence in the inspection well. Connect the outlet pipe (60) to the PERT inner pipe (4) through the steel-plastic conversion flange (9). Then, perform anti-corrosion treatment on the metal pipe fittings and welded parts, and set the insulation layer on the pipe fittings and valves in the well. S6. Casing sealing: The flexible casing of the side wall and the rigid waterproof casing of the base plate are sealed and sealed, and maintenance treatment is carried out.

9. The installation process of a coaxial integrated wellhead device for geothermal wells in high-altitude permafrost areas according to claim 8, characterized in that: The insulation layer is made of B1 grade closed-cell foamed rubber-plastic composite insulation material.

10. The installation process of a coaxial integrated wellhead device for geothermal wells in high-altitude permafrost areas according to claim 8, characterized in that: The flexible sleeve sealing structure of the side wall is sealed with a flange cover and a sealing ring, and the rigid sleeve sealing structure of the base plate is sealed by layering hemp braid and asbestos cement.

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