A multi-lateral horizontal docking well group wellbore structure for improving heat exchange efficiency of a middle-deep well heat exchange system

Abstract

This application relates to the field of downhole heat exchange system technology, and in particular to a multi-branch horizontal docking wellbore structure for improving the heat exchange efficiency of medium-deep downhole heat exchange systems. The water inlet well includes a water inlet vertical well section, a water inlet displacement section, and a water inlet high-efficiency heat exchange section connected in sequence. There are at least two sets of water inlet high-efficiency heat exchange sections, and the front end of each set of water inlet high-efficiency heat exchange sections is connected to the end region of the water inlet displacement section along the fluid flow path. The return water well includes a return water vertical well section, a return water displacement section, and a return water high-efficiency heat exchange section connected in sequence, and the end region of each set of water inlet high-efficiency heat exchange sections is connected to the front end region of the return water high-efficiency heat exchange section along the fluid flow path. The orientations of the water inlet displacement section and the return water displacement section are opposite to each other. This application can balance heat exchange effect and floor space, and also improve the reliability of the entire heat exchange system.

Description

Technical Field

[0001] This application relates to the field of downhole heat exchange system technology, and in particular to a wellbore structure for a multi-branch horizontal docking well group that improves the heat exchange efficiency of a medium-deep downhole heat exchange system. Background Technology

[0002] The core of a medium-deep downhole heat exchange system lies in the design of the well structure, which directly determines the path length of fluid travel in the high-temperature underground strata and the heat exchange contact area, thereby determining the system's heat exchange efficiency and single-well heating capacity.

[0003] Currently, there are two main well structure schemes for the development of geothermal resources with medium-deep heat exchange at depths of 2000m-3000m: The first is a single-well concentric tube heat exchange scheme, in which the inner and outer channels of the concentric tube serve as cold water injection channels and hot water return channels, respectively, and the fluid returns at the bottom of the well to complete the heat exchange; the second is a horizontal well and vertical well docking heat exchange scheme, in which the horizontal section of the horizontal well is connected to the vertical well, and the fluid penetrates into the high-temperature formation along the horizontal section of the horizontal well to absorb heat, and then returns to the surface through the vertical well to complete the heat exchange.

[0004] However, the first single-well concentric tube heat exchange scheme has limitations in well structure size and circulating water flow, making it difficult to meet large-scale heating demands per unit time. The second scheme, a horizontal-to-vertical well docking heat exchange scheme, presents a conflict between the heat exchange path length and the overall floor space. To obtain a sufficient heat exchange path length, a large horizontal distance is required between the horizontal and vertical wells, resulting in a large overall floor space. If the horizontal section of the horizontal well is shortened to reduce the overall floor space, insufficient heat exchange and reduced heating capacity occur; in other words, it is difficult to balance heat exchange efficiency with floor space requirements. Furthermore, in both the single-well concentric tube heat exchange scheme and the horizontal-to-vertical well docking heat exchange scheme, the fluid flows through a single heat exchange path. If a downhole accident occurs along this single heat exchange path, such as well wall collapse, casing deformation, or blockage, the entire heat exchange system will fail. Therefore, further improvements are needed. Summary of the Invention

[0005] In order to balance heat exchange efficiency with floor space and improve the reliability of the entire heat exchange system, this application provides a multi-branch horizontal docking wellbore structure to improve the heat exchange efficiency of medium-deep downhole heat exchange systems.

[0006] The above-mentioned objective of this application is achieved through the following technical solution:

[0007] A multi-branch horizontal docking wellbore structure for improving the heat exchange efficiency of a medium-deep downhole heat exchange system includes a water inlet well, which comprises a water inlet vertical well section, a water inlet displacement section, and a water inlet high-efficiency heat exchange section connected in sequence. There are at least two sets of water inlet high-efficiency heat exchange sections, and along the fluid flow path, the front end of each set of water inlet high-efficiency heat exchange sections is connected to the end region of the water inlet displacement section. A return water well also includes a return water vertical well section, a return water displacement section, and a return water high-efficiency heat exchange section connected in sequence, and along the fluid flow path, the end region of each set of water inlet high-efficiency heat exchange sections is connected to the front end region of the return water high-efficiency heat exchange section. The orientations of the water inlet displacement section and the return water displacement section are opposite to each other, such that the distance between the front end of the water inlet displacement section and the end of the return water displacement section is less than the distance between the end of the water inlet displacement section and the front end of the return water displacement section.

[0008] Preferably, the positioning direction of the inlet high-efficiency heat exchange section of each group is on the same side as the positioning direction of the return high-efficiency heat exchange section, and within the same vertical depth plane, the ends of the inlet high-efficiency heat exchange sections of each group are respectively connected to different horizontal node positions in the front end area of ​​the return high-efficiency heat exchange section.

[0009] Preferably, the angle between the wellbore centerline of the water inlet displacement section and the horizontal plane is 60°-80°; the angle between the wellbore centerline of the water return displacement section and the horizontal plane is 60°-80°.

[0010] Preferably, the high-efficiency heat exchange section for water inlet is configured as two sets, namely a first heat exchange docking section and a second heat exchange docking section; wherein, along the fluid flow path direction, the front end of the first heat exchange docking section is connected to a first drill point reserved at the end of the water inlet displacement section, the front end of the second heat exchange docking section is connected to a second drill point reserved at the side of the end of the water inlet displacement section, the end of the first heat exchange docking section is connected to a first target point reserved at the side of the front end of the high-efficiency heat exchange section for return water, and the end of the second heat exchange docking section is connected to a second target point reserved at the end of the front end of the high-efficiency heat exchange section for return water; wherein, the distance between the first drill point and the second drill point, and the distance between the first target point and the second target point are adapted to make the lengths of the first heat exchange docking section and the second heat exchange docking section compatible.

[0011] Preferably, the distance between the first drilling point and the second drilling point is 150m-250m, and the distance between the first target point and the second target point is 150m-250m.

[0012] Preferably, both the water inlet vertical well section and the water return vertical well section are provided with vertical well section casing extending from the surface to their bottom. The vertical well section casing includes multiple sets of oil casings connected in sequence by threads, and the space between the vertical well section casing and the well wall is filled with Grade G cement. Both the water inlet displacement section and the water return displacement section are provided with displacement section casing extending from their front end to their rear end. The displacement section casing includes multiple sets of oil casings connected in sequence by threads, and the space between the displacement section casing and the well wall is filled with high thermal conductivity cement. Both the water inlet high-efficiency heat exchange section and the water return high-efficiency heat exchange section are provided with high-efficiency heat exchange section casing extending from their front end to their rear end. The high-efficiency heat exchange section casing includes multiple sets of oil casings connected in sequence by threads, and the space between the high-efficiency heat exchange section casing and the well wall is filled with high thermal conductivity cement.

[0013] Preferably, there are overlapping sections of 50m-100m between adjacent vertical well casing sections and displacement casing sections, and between adjacent displacement casing sections and high-efficiency heat exchange casing sections, and the annular area formed by the overlapping sections is filled with cementing cement.

[0014] Preferably, the high-efficiency heat exchange section sleeve of the return water high-efficiency heat exchange section further includes a fiberglass sleeve, which is located in the docking area where the first target point and the second target point are located.

[0015] In summary, this application includes at least one of the following beneficial technical effects:

[0016] The directional relationship between the inlet and return wells, even if the wellheads of the inlet and return wells are close together and the area of ​​the well site is limited, still allows for sufficient horizontal expansion distance in the deep high-temperature strata, providing ample extension space for the high-efficiency heat exchange section. This ensures that the fluid has enough length so that it can fully absorb geothermal heat and thus improve the heat exchange effect.

[0017] The layout of a multi-branch parallel heat exchange system in the same vertical depth plane can effectively reduce the failure of the entire heat exchange system caused by downhole accidents such as wellbore collapse, casing deformation or blockage compared with the existing single heat exchange path.

[0018] By filling the annulus with high thermal conductivity cement, the stability and safety of the wellbore are ensured while improving heat exchange efficiency. The oil casing with a high thermal conductivity coating in the high-efficiency heat exchange section for water inlet and return water outlet further improves the heat exchange efficiency between the fluid and the formation. Attached Figure Description

[0019] Figure 1 This is a three-dimensional view of the overall structure of the wellbore in this application.

[0020] Figure 2 This is a schematic diagram of the fluid direction in this application.

[0021] Explanation of reference numerals in the attached diagram: 1. Water intake well; 11. Vertical water intake section; 12. Water intake displacement section; 13. High-efficiency heat exchange section; 131. First heat exchange docking section; 132. Second heat exchange docking section; 2. Return water well; 21. Vertical return water section; 22. Displacement return water section; 23. High-efficiency heat exchange section; 31. First drilling point; 32. Second drilling point; 41. First target point; 42. Second target point; 51. Casing of vertical well section; 52. Casing of displacement section; 53. Casing of high-efficiency heat exchange section; 6. Fiberglass casing; 10. Horizontal plane a; 20. Horizontal plane b. Detailed Implementation

[0022] The following is in conjunction with the appendix Figures 1 to 2 This application will be described in further detail.

[0023] This application discloses a wellbore structure for multi-branch horizontal docking well groups that improves the heat exchange efficiency of medium-deep downhole heat exchange systems.

[0024] Reference Figure 1-2 The multi-branch horizontal docking well structure for improving the heat exchange efficiency of the medium-deep downhole heat exchange system in this embodiment includes an inlet well 1 and a return well 2. The wellhead of the inlet well 1 and the wellhead of the return well 2 are located on the same horizontal plane a10 on the surface. The bottom of the inlet well 1 and the bottom of the return well 2 are both located on the same horizontal plane b20 in the deep high-temperature strata. The vertical distance between the horizontal plane a10 and the horizontal plane b20 is approximately 3000m.

[0025] The inlet well 1 is a directional well with at least two horizontal branches. Along the direction of injection of the low-temperature fluid, the inlet well 1 includes an inlet vertical well section 11, an inlet displacement section 12, and an inlet high-efficiency heat exchange section 13. There are at least two sets of inlet high-efficiency heat exchange sections 13, and the front end (i.e., the fluid inlet end) of each set of inlet high-efficiency heat exchange sections 13 is connected to the end region of the inlet displacement section 12. The return well 2 is a horizontal directional well. Along the direction of return of the high-temperature fluid (from the bottom of the well to the wellhead), the return well 2 includes a return high-efficiency heat exchange section 23, a return displacement section 22, and a return vertical well section 21. The end (i.e., the fluid outlet end) of each set of inlet high-efficiency heat exchange sections 13 is connected to the front end region of the return high-efficiency heat exchange section 23. Thus, the inlet well 1 and the return well 2 together form a closed-loop heat exchange channel from the inlet vertical well section 11, the inlet displacement section 12, each group of inlet high-efficiency heat exchange sections 13, the return high-efficiency heat exchange section 23, the return displacement section 22, and the return vertical well section 21.

[0026] In this embodiment, the orientations of the water inlet displacement section 12 and the return water displacement section 22 are opposite to each other. Specifically, the water inlet displacement section 12 extends from its front end to its back end in a direction opposite to the wellhead of the return water well 2, while the return water displacement section 22 extends from its back end to its front end in a direction opposite to the wellhead of the water inlet well 1. This opposite orientation allows for a smaller distance between the wellheads of the water inlet well 1 and the return water well 2 on the surface. However, as the depth increases, the horizontal distance between the wellbore trajectories of the water inlet well 1 and the return water well 2 gradually increases, making the distance between the front end of the water displacement section and the back end of the return water displacement section 22 significantly smaller than the distance between the back end of the water inlet displacement section 12 and the front end of the return water displacement section 22. Therefore, even if the wellheads of the water inlet well 1 and the return water well 2 are close together and the well site area is limited, sufficient horizontal expansion distance can still be obtained in the deep high-temperature strata, providing ample extension space for the high-efficiency heat exchange section.

[0027] In this embodiment, the angle between the water inlet displacement section 12 and the wellbore centerline and the horizontal plane is 70°. In other embodiments, other values ​​within the range of 60° to 80° may also be used. The angle between the wellbore centerline and the horizontal plane of the return water displacement section 22 is 70°. In other embodiments, other values ​​within the range of 60° to 80° may also be used. The angle of 60° to 80° corresponds to a well inclination angle of 10° to 30°. This angle range has been verified by drilling engineering practice. It can not only meet the operability of directional well construction, but also achieve a large horizontal displacement increment within a limited vertical depth increment, taking into account both construction feasibility and the need for heat exchange path extension.

[0028] The orientation of each group of high-efficiency heat exchange sections 13 for water inlet and 23 for water return is on the same side, meaning that all high-efficiency heat exchange sections 13 for water inlet and 23 for water return point to the same side of the wellheads of both wells. Within the same vertical depth plane, the ends of each group of high-efficiency heat exchange sections 13 for water inlet are connected to different horizontal nodes in the front end region of the high-efficiency heat exchange section 23 for water return, thus forming a multi-branch parallel heat exchange system layout. Compared with existing single heat exchange paths, multi-branch parallel heat exchange paths can effectively reduce the failure of the entire heat exchange system caused by downhole accidents such as wellbore collapse, casing deformation, or blockage.

[0029] In this embodiment, the high-efficiency heat exchange section 13 is configured as two sets, namely the first heat exchange docking section 131 and the second heat exchange docking section 132. The front end of the first heat exchange docking section 131 is connected to the first drill point 31 reserved at the end of the water inlet displacement section 12, that is, the first heat exchange docking section 131 and the water inlet displacement section 12 continue in a straight line. The front end of the second heat exchange docking section 132 is connected to the second drill point 32 reserved on the side of the end of the water inlet displacement section 12, that is, the second heat exchange docking section 132 branches off from the near end region of the water inlet displacement section 12 by side drilling. In the above, the second drill point 32 is moved about 200m away from the end of the water inlet displacement section 12 (i.e., at the depth of the first drill point 31) along the wellbore trajectory towards the wellhead. For example, if the vertical depth of the end of the water inlet displacement section 12 is 2500m, then the vertical depth of the second drill point 32 is about 2300m.

[0030] The end of the first heat exchange docking section 131 is connected to the first target point 41 reserved on the front side of the high-efficiency heat exchange section 23, and the end of the second heat exchange docking section 132 is connected to the second target point 42 reserved at the front end of the high-efficiency heat exchange section 23. The horizontal distance between the first target point 41 and the second target point 42 is 200m. By designing the distance between the first drilling point 31 and the second drilling point 32 (along the wellbore trajectory direction) to match the distance between the first target point 41 and the second target point 42, the lengths of the first heat exchange docking section 131 and the second heat exchange docking section 132 are basically the same. The two sets of heat exchange docking sections extend in parallel in the high-temperature strata at the same depth. The total heat exchange path length of the fluid flowing underground is the sum of the lengths of each branch, thereby significantly improving the heat exchange efficiency.

[0031] In other embodiments, the distance between the first drilling point 31 and the second drilling point 32, and the distance between the first target point 41 and the second target point 42, may also be other values ​​in the range of 150m to 250m.

[0032] In this embodiment, the water inlet well 1 includes a water inlet vertical well section 11, a water inlet displacement section 12, and a water inlet high-efficiency heat exchange section 13 in sequence, and there are at least two sets of water inlet high-efficiency heat exchange sections 13.

[0033] The water-entry vertical well section 11 extends from the ground surface to its bottom, and a vertical well section casing 51 is installed from the ground surface to the bottom of the water-entry vertical well section 11; the vertical well section casing 51 is composed of multiple oil casings connected sequentially by threads, with an outer diameter of 339.7 mm, a wall thickness of 9.65 mm, and a steel grade of J55; the annulus area between the vertical well section casing 51 and the well wall is filled with G-grade oil well cementing cement, and the cement slurry is returned to the ground surface from the bottom of the well in one go to complete the cementing and isolation of this section.

[0034] The water entry displacement section 12 is a directional drilling section. The front end of the water entry displacement section 12 connects to the bottom of the water entry vertical well section 11, and a displacement section casing 52 is installed from top to bottom of the water entry displacement section 12. The displacement section casing 52 is composed of multiple oil casings connected sequentially by threads, with an outer diameter of 244.5 mm, a wall thickness of 10.03 mm, and a steel grade of J55. There is an overlap section between the top of the displacement section casing 52 and the bottom of the vertical well section casing 51, with the overlap section having a length of 50 m to 10 m. Any value between 0m and 0m, within the overlapping section, the displacement section casing 52 is embedded inside the vertical well section casing 51, and the annular area between the two casings is filled and sealed with cement, which serves as a seal and pressure-bearing function; the annular area between the displacement section casing 52 and the well wall is filled with high thermal conductivity cement, which has a thermal conductivity significantly higher than that of ordinary G-grade oil well cement, which is conducive to efficiently transferring formation heat to the fluid inside the casing through the cement sheath, thereby starting to preheat the fluid in the displacement section.

[0035] The first heat exchange docking section 131 and the second heat exchange docking section 132 of the high-efficiency heat exchange section 13 are each equipped with a high-efficiency heat exchange section casing 53 from their front end to their end. The high-efficiency heat exchange section casing 53 is composed of multiple oil casings connected sequentially by threads, with an outer diameter of 139.7 mm, a wall thickness of 7.72 mm, and a steel grade of N80. The top of the high-efficiency heat exchange section casing 53 and the bottom of the displacement section casing 52 also have an overlapping section with a length of 50 m to 100 m. The annular area formed by the overlapping section is filled with high thermal conductivity cementing cement. The annular area between the remaining part of the high-efficiency heat exchange section casing 53 and the well wall is also filled with high thermal conductivity cementing cement.

[0036] In this embodiment, the return water well 2 includes, in sequence, a high-efficiency heat exchange section 23, a return water displacement section 22, and a vertical return water section 21;

[0037] The return water vertical well section 21 extends from the ground to its bottom. The return water vertical well section 21 is equipped with a vertical well section casing 51 from the ground to the bottom. Its specifications and cementing method are the same as those of the water intake vertical well section 11: the casing outer diameter is 339.7mm, the wall thickness is 9.65mm, the steel grade is J55, and the annulus is filled with G-grade oil well cementing cement.

[0038] The return water displacement section 22 is a directional drilling section, and its directional orientation is opposite to that of the water inlet displacement section 12. A displacement section casing 52 is installed from top to bottom of the return water displacement section 22. The casing has an outer diameter of 244.5 mm, a wall thickness of 10.03 mm, and is made of J55 steel. There is a 50 m to 100 m overlap between the top of the displacement section casing 52 and the bottom of the vertical well casing 51. A heat-insulating casing is also installed from the upper part of the return water displacement section casing to the wellhead area. The heat-insulating casing is made of materials with low thermal conductivity and good heat insulation performance, such as composite casing with vacuum insulation layer or heat insulation coating. It is used to reduce the heat loss of the wellbore to the surrounding formation during the process of high temperature fluid returning along the return water well 2 and to stabilize the wellhead water temperature. The annulus area between the lower casing of the return water displacement section 22 and the well wall is filled with high thermal conductivity cement. The annulus area between the end of the return water displacement section 22 and the well wall and the vertical well section casing 51 is filled with G-grade oil well cement.

[0039] The high-efficiency heat exchange section 23 for return water is equipped with a high-efficiency heat exchange section casing 53 from its front end to its rear end. The casing 53 has the same specifications as the high-efficiency heat exchange section casing 53 for water inlet well 1, with an outer diameter of 139.7 mm, a wall thickness of 7.72 mm, and a steel grade of N80. There is an overlap of 50 m to 100 m between the top of the casing and the bottom of the casing for return water displacement section 22. The annulus is filled with high thermal conductivity cementing cement.

[0040] In this embodiment, the high-efficiency heat exchange section 23 casing also includes a fiberglass casing 6 located in the docking area where the first target point 41 and the second target point 42 are located. The length of the fiberglass casing 6 covers at least the entire target area, with one end closed and the other end connected to the high-efficiency heat exchange section casing 53 by threads. By using the fiberglass casing 6, the shear strength of the fiberglass material is lower than that of the steel casing, making it easier to be drilled through by a smaller drill bit during subsequent penetration operations. Moreover, fiberglass itself is a non-magnetic material and is not affected by the geomagnetic field or the magnetization of downhole metal components. During the docking and connection construction, a target guidance instrument that receives magnetic signals can be lowered into the fiberglass casing 6 to receive the rotating magnetic signal generated by the magnetic signal generator joint at the drill bit without shielding, thereby achieving precise docking guidance.

[0041] The outer surfaces of both the 13 casing of the high-efficiency heat exchange section for water inlet and the 23 casing of the high-efficiency heat exchange section for water return are coated with a high thermal conductivity coating. This coating forms a high thermal conductivity interface between the casing and the cement sheath, further reducing the contact thermal resistance between the casing wall and the cement sheath and improving the efficiency of heat transfer from the formation to the fluid inside the casing.

[0042] In the actual docking and connection process, after drilling to the designed depth, the first heat exchange docking section 131 and the second heat exchange docking section 132 of the water inlet high-efficiency heat exchange section 13 first gradually reach the well inclination angle of 90° by increasing the inclination, that is, the horizontal attitude. Then, by three-dimensional horizontal section torsion orientation, the end of each heat exchange docking section is accurately pointed to the target position corresponding to the front end of the return water high-efficiency heat exchange section 23.

[0043] The specific docking process is as follows: When the target point (first target point 41 or second target point 42) of the return water well 2 is about 100m away, the target guidance instrument is lowered into the fiberglass casing 6 at the corresponding target point through the channel inside the casing of the return water well 2 by means of drill pipe pumping; at the same time, a magnetic signal generating connector is connected between the drill bit and the screw drill on the side of the water intake well 1, and the drill is lowered back to the bottom of the well; during the rotary drilling process, the magnetic signal generating connector generates a rotating magnetic field signal, and the target guidance instrument receives the signal without shielding inside the fiberglass casing 6, measures the position and distance of the drill bit relative to the target point in real time, and guides the drill bit to drill accurately towards the target point until the target point is drilled through and docking is completed.

[0044] After docking is completed, a small drill bit is inserted into the fiberglass casing 6 of the high-efficiency heat exchange section 23 of the return water to drill through the cementing cement and casing in the high-efficiency heat exchange section 13 of the water intake at each target point, and the cement debris and metal drill cuttings in the well barrel are cleaned to ensure that the circulation channels between the high-efficiency heat exchange section 13 of the water intake and the high-efficiency heat exchange section 23 of the return water at each target point are unobstructed.

[0045] As an optional configuration, the annulus between the displacement casing 52 and the wellbore can also be filled with G-grade cement for use in some application scenarios where heat exchange efficiency requirements are not high but cost control is a priority.

[0046] As another optional configuration, the number of high-efficiency heat exchange sections 13 can be set to more than two sets. Correspondingly, multiple side drilling points can be arranged at the end of the water inlet displacement section 12, and multiple target points can be arranged at the front end of the high-efficiency heat exchange section 23, thereby realizing the parallel operation of three or more sets of heat exchange docking sections and further increasing the total heat exchange path length of the fluid in the deep high-temperature strata.

[0047] The construction steps for multi-branch horizontal docking well groups are summarized as follows:

[0048] Step 1: Drill vertical well sections for water intake well 1 and return well 2 at the well site, run in vertical well section casing 51, φ339.7mm×9.65mm, J55 steel grade, and inject G grade oil well cement to complete the first well cementing.

[0049] Step 2: Perform two-stage directional drilling from the bottom of the vertical well section of each well downwards. The directional orientations of the water inlet displacement section 12 and the water return displacement section 22 are opposite to each other. Control the well inclination angle within the range of 10° to 30°, that is, the angle between the displacement section and the horizontal plane is 60° to 80°, and drill to the designed depth.

[0050] Step 3: Run the displacement section casing 52 into the return water displacement section 22. Install a heat-insulating casing at the top and a regular displacement section casing 52 at the bottom. The top of the casing overlaps with the bottom of the vertical well section casing 51 by 50m to 100m. Inject cement into the annulus, using Grade G cement at the top and high thermal conductivity cement at the bottom. Run the displacement section casing 52 into the water inlet displacement section 12. Overlap with the vertical well section casing 51 by 50m to 100m. Inject high thermal conductivity cement into the annulus.

[0051] Step 4: Drill three sections from the end of the water inlet displacement section 12 to drill out the first heat exchange docking section 131, which extends in a straight line; at the side drilling point near the end of the water inlet displacement section 12, move 150m to 250m upward along the trajectory from the end to drill a side drilling branch to drill out the second heat exchange docking section 132; drill three sections from the bottom of the return water displacement section 22 to drill out the return water high-efficiency heat exchange section 23.

[0052] Step 5: Install fiberglass casing 6 in the target area of ​​the high-efficiency heat exchange section 23 of the return water, and install high-efficiency heat exchange section casing 53 with a high thermal conductivity coating on the outer surface in the remaining areas. The casing is φ139.7mm×7.72mm and made of N80 steel. The top of each casing section overlaps with the bottom of the previous casing section by 50m to 100m. Inject high thermal conductivity cementing into the annulus.

[0053] Step 6: After drilling each heat exchange docking section of the water inlet well 1 to the designed depth, increase the inclination to a horizontal attitude with a well inclination angle of 90°, and align the first target point 41 and the second target point 42 at the front end of the high-efficiency heat exchange section 23 of the return water by three-dimensional horizontal section torsion orientation.

[0054] Step 7: Perform magnetic signal docking. Pump the target guidance instrument to the target position inside the fiberglass casing 6 of the return water well 2. Connect the magnetic signal generator after the drill bit of the water well 1. During the rotary drilling process, the target guidance instrument will guide the drilling in real time until the target point is drilled through and docking is completed.

[0055] Step 8: Insert a small drill bit into the casing of the high-efficiency heat exchange section 23 of the return water section, and drill through the cementing cement and casing of the high-efficiency heat exchange section 13 of the return water section at each target point in sequence. Clean up the wellbore debris and ensure that the two wells are connected in circulation at all docking target points.

Claims

1. A wellbore structure for a multi-branch horizontal docking well group to improve the heat exchange efficiency of a medium-deep downhole heat exchange system, characterized in that: include The water inlet well (1) includes a water inlet vertical well section (11), a water inlet displacement section (12) and a water inlet high-efficiency heat exchange section (13) connected in sequence. The water inlet high-efficiency heat exchange section (13) consists of at least two sets, and along the fluid flow path, the front end of each set of water inlet high-efficiency heat exchange section (13) is connected to the end region of the water inlet displacement section (12). The return water well (2) includes a return water vertical well section (21), a return water displacement section (22) and a return water high-efficiency heat exchange section (23) connected in sequence. Along the fluid flow path, the end of each group of water inlet high-efficiency heat exchange sections (13) is connected to the front end area of ​​the return water high-efficiency heat exchange section (23). The orientations of the water inlet displacement segment (12) and the water return displacement segment (22) are opposite to each other, so that the distance between the front end of the water inlet displacement segment (12) and the end of the water return displacement segment (22) is less than the distance between the end of the water inlet displacement segment (12) and the front end of the water return displacement segment (22).

2. The multi-lateral docking well group wellbore structure for improving the heat exchange efficiency of a downhole heat exchange system in a medium-deep well according to claim 1, characterized in that: The positioning direction of the inlet high-efficiency heat exchange section (13) of each group is the same as that of the return high-efficiency heat exchange section (23), and within the same vertical depth plane, the ends of the inlet high-efficiency heat exchange section (13) of each group are respectively connected to different horizontal node positions in the front end area of ​​the return high-efficiency heat exchange section (23).

3. The multi-lateral docking well group wellbore structure of Claim 2, wherein: The angle between the wellbore centerline of the water inlet displacement section (12) and the horizontal plane is 60°-80°; the angle between the wellbore centerline of the water return displacement section (22) and the horizontal plane is 60°-80°.

4. The multi-lateral docking well group wellbore structure of Claim 2, wherein: The high-efficiency heat exchange section (13) for water inlet is configured in two groups, namely a first heat exchange docking section (131) and a second heat exchange docking section (132); wherein, along the fluid flow path direction, the front end of the first heat exchange docking section (131) is connected to the first drill point (31) reserved at the end of the water inlet displacement section (12), the front end of the second heat exchange docking section (132) is connected to the second drill point (32) reserved on the side of the end of the water inlet displacement section (12), and the end of the first heat exchange docking section (131) is connected to the second drill point (32) reserved on the side of the end of the water inlet displacement section (12). The first target point (41) is pre-reserved at the front end of the high-efficiency heat exchange section (23) of the return water, and the second target point (42) is pre-reserved at the front end of the high-efficiency heat exchange section (23) of the return water. The distance between the first drill point (31) and the second drill point (32) and the distance between the first target point (41) and the second target point (42) are adapted to make the lengths of the first heat exchange docking section (131) and the second heat exchange docking section (132) compatible.

5. The multi-lateral docking well group wellbore structure of Claim 4, wherein: The distance between the first drilling point (31) and the second drilling point (32) is 150m-250m, and the distance between the first target point (41) and the second target point (42) is 150m-250m.

6. The multi-lateral docking well group wellbore structure of Claim 2, wherein: Both the water inlet vertical well section (11) and the water return vertical well section (21) are equipped with vertical well section casing (51) extending from the ground surface to their bottom. The vertical well section casing (51) includes multiple sets of oil casings connected in sequence by threads, and the space between the vertical well section casing (51) and the well wall is filled with Grade G cement. Both the water inlet displacement section (12) and the water return displacement section (22) are equipped with displacement section casing (52) extending from their front end to their rear end. The displacement section casing (52) includes... The well includes multiple sets of oil casings that are connected in sequence by threads. The displacement section casing (52) is filled with high thermal conductivity cement between itself and the well wall. The water inlet high efficiency heat exchange section (13) and the water return high efficiency heat exchange section (23) are each provided with a high efficiency heat exchange section casing (53) from its front end to its end. The high efficiency heat exchange section casing (53) includes multiple sets of oil casings that are connected in sequence by threads. The high efficiency heat exchange section casing (53) is filled with high thermal conductivity cement between itself and the well wall.

7. The well structure of the multi-lateral docking horizontal well group for improving the heat exchange efficiency of the downhole heat exchange system in the medium-deep well according to claim 6, characterized in that: There are overlapping sections of 50m-100m between adjacent vertical well casing (51) and displacement casing (52), and between adjacent displacement casing (52) and high-efficiency heat exchange casing (53), and the annular area formed by the overlapping sections is filled with cementing cement.

8. The multi-lateral docking well group wellbore structure of Claim 6, wherein: The high-efficiency heat exchange section sleeve (53) of the return water high-efficiency heat exchange section (23) also includes a fiberglass sleeve (6), which is located in the docking area where the first target point (41) and the second target point (42) are located.

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