Downhole large aperture seepage passage reconstruction method suitable for geothermal energy

Abstract

The application discloses a downhole large-aperture seepage channel reconstruction method suitable for geothermal energy, which comprises the following steps: S1: hole expansion is performed at the lowest part of a drilling channel, and rock debris is discharged after the hole expansion; the drilling channel is a straight well or a U-shaped well; fixed casings are arranged in the well walls on both sides of the straight well and the U-shaped well; a water taking pipe and a water returning pipe are arranged in the casings; and S2: a circulation channel is formed through the water returning pipe and the water taking pipe. The application has the beneficial effects that: a hole expansion channel is formed at the hole expansion part, the volume of a heat exchange area is increased, the heat exchange surface area is increased, and geothermal energy can be effectively extracted; the water returning pipe and the water taking pipe are arranged in the same drilling channel, the water returning pipe and the water taking pipe can circulate with an external heat exchange device, tail water can be timely returned, and problems such as water level drop caused by untimely return of tail water can be avoided.

Description

Technical Field

[0001] This invention relates to a new method for geothermal development, and more particularly to a method for modifying downhole large-diameter seepage channels suitable for geothermal energy. Background Technology

[0002] In recent years, geothermal energy development has made some progress, but it is still largely limited to small-scale heating, cooling, or power generation, and widespread adoption remains a long way off. Shallow, medium, and deep geothermal energy resources are relatively large-scale and have significant development potential. Currently, geothermal development through drilling relies heavily on open-hole wells for heat exchange. The small well diameter and limited heat exchange area hinder large-scale geothermal energy extraction, resulting in low energy development efficiency. In areas with abundant geothermal reserves and favorable geological conditions, and suitable site selection for geothermal resource development, increasing the heat exchange area and achieving 100% tailwater reinjection rate are crucial. Currently, tailwater reinjection wells are not connected to intake wells, relying solely on natural underground fissures for water return, leading to low return efficiency. Large-scale development of geothermal resources is particularly possible for medium- and deep geothermal resources. Therefore, increasing the downhole heat exchange area and improving the permeability of downhole heat exchange channels are the future directions for geothermal development technology.

[0003] For example, Chinese Patent Publication No. CN207247602U describes a U-shaped heat exchange structure for medium-deep geothermal energy. A fluid working medium is injected into the U-shaped heat exchange structure to exchange heat with the formation. It includes a first vertical well section, a connecting well section, and a second vertical well section connected end-to-end to form a U-shaped structure. Both the first and second vertical well sections are vertically arranged and located on opposite sides of the connecting well section. The connecting well section and the second vertical well section are horizontally connected. The upper ends of both the first and second vertical well sections have open openings. However, this design suffers from limited heat exchange area and low heat exchange efficiency. Summary of the Invention

[0004] The technical problem to be solved by this invention is: how to solve the problems of small inner diameter of wells, low heat exchange efficiency, and low tailwater reinjection efficiency.

[0005] The present invention solves the above-mentioned technical problems through the following technical means:

[0006] Methods for modifying large-diameter seepage channels in geothermal wells, applicable to geothermal energy, include:

[0007] Step S1: Enlarge the borehole at the lowest point of the drilling channel, and remove the cuttings after enlargement; the drilling channel is a vertical well or a U-shaped well; the well walls on both sides of the vertical well and the U-shaped well have fixed casings; run water intake pipes and return pipes inside the casings;

[0008] Step S2: A circulation channel is formed through the return water pipe and the intake water pipe.

[0009] This invention involves enlarging the borehole at the bottom of the drilling channel, resulting in a significantly larger diameter than the unenlarged section. After enlargement, rock cuttings are discharged, creating an enlarged channel that increases the volume and surface area of ​​the heat exchange zone, thus effectively extracting geothermal energy. Furthermore, a return water pipe and an intake water pipe are installed within the drilling channel, allowing for circulation with external heat exchange devices and timely tailwater reinjection, preventing problems such as water level drops caused by delayed tailwater reinjection.

[0010] Preferably, depending on the geological conditions, after the rock cuttings are discharged, a filler is injected into the enlarged section.

[0011] Different geological characteristics can lead to varying wellbore stability. In cases of significant geological variation and instability, ceramic particles need to be injected into the enlarged wellbore channel for support. Conversely, in favorable geological conditions such as granite or basalt, where wellbore stability is high, ceramic particles or similar materials are unnecessary. Backfilling with ceramic particles improves channel stability and permeability, facilitating tailwater reinjection. It also addresses the issue of wellbore collapse caused by erosion from the tailwater and intake water loops, and can delay heat exchange time.

[0012] The filler is one or a combination of ceramic particles and sand particles. Using ceramic particles for backfilling can improve the stability and permeability of the channel, allowing for tailwater reinjection; it also solves the problem of collapse caused by the scouring of the channel walls by the loop formed by tailwater and intake water; and it can also delay the heat exchange time.

[0013] Preferably, in step S1, the method for enlarging the vertical well is as follows: explosives are placed at the bottom of the casing of the vertical well and detonated, forming an enlarged section after the explosion.

[0014] Preferably, in step S1, the method for enlarging the vertical well is as follows: a first coiled tubing is installed inside the casing of the vertical well, explosives are placed inside the first coiled tubing, the first coiled tubing is then pulled out and the well is shut in, high-pressure gas is injected to compact the explosives, and then the well is opened; at least one packer and a safety damper are fixed at the bottom of a second coiled tubing, a second coiled tubing is installed inside the casing of the vertical well, the packer and safety damper are placed at the bottom of the casing, a cable with a detonator is delivered downhole through the second coiled tubing, the well is shut in, the cable is connected to the explosives and detonated, after the explosion, the well is slowly opened to release the pressure, and the second coiled tubing, packer, and safety damper are removed.

[0015] Explosives are used to expand the borehole underground, forming a channel with the same diameter, smooth walls, and high stability. Packers are used to separate the blasting zone from the non-blasting zone, while safety dampers are used to reduce damage to the casing and the open hole formation stability in the non-blasting zone during blasting.

[0016] Preferably, in step S1, the method for removing cuttings after the borehole enlargement in the vertical well is as follows: a third coiled tubing is installed inside the casing of the vertical well, high-pressure fluid is injected into the third coiled tubing, and the cuttings are discharged from the annular space between the casing and the third coiled tubing. After the cuttings are removed, the third coiled tubing is taken out.

[0017] Preferably, after the cuttings in the vertical well are discharged, if it is necessary to inject filler into the reaming section, the specific steps are as follows: lower the water intake pipe with the screen installed at the end to the bottom of the reaming section, lower the return water pipe to the reaming section, inject filler through the return water pipe, and discharge the fluid through the water intake pipe.

[0018] Preferably, in step S1, the method of enlarging the U-shaped well is as follows: one side of the U-shaped well is a water intake well, the other side is a water return well, and there is a horizontal well section between the water intake well and the water return well. Explosives are placed at the bottom of the casing of the water intake well or the water return well and detonated. After the explosion, the enlarged section is formed.

[0019] Preferably, the enlargement method of the U-shaped well is as follows: a first coiled tubing is laid on one side of the U-shaped well, and a second coiled tubing is laid on the other side. Only the bottom end of the first coiled tubing is connected to at least one packer and a safety damper. The packer and safety damper are placed at one end of the horizontal well section. Explosives are laid through the second coiled tubing. After the second coiled tubing is pulled out, the well is shut in. High-pressure gas is injected to compact the explosives. The well is then opened, and a third coiled tubing is laid from the same side. The bottom end of the third coiled tubing is connected to at least one packer and a safety damper. The packer and safety damper are placed at the other end of the horizontal well section. A cable with a detonator is delivered downhole through the first or third coiled tubing. The well is shut in, and the cable is connected to the explosives for detonation. After the explosion, the well is slowly opened to release the pressure, and the first coiled tubing, the third coiled tubing, the packer, and the safety damper are removed.

[0020] Preferably, in step S1, the method for removing rock cuttings after the U-shaped well is enlarged is as follows: a fourth coiled tubing is installed in the water intake or return well, high-pressure fluid is injected into the fourth coiled tubing, the rock cuttings are discharged from the other side, and the fourth coiled tubing is removed after the cuttings are removed.

[0021] Preferably, after the rock cuttings in the U-shaped well are discharged, if it is necessary to inject filler into the enlarged section, the specific steps are as follows: a return water pipe with an isolator installed at the end is lowered into the return water well, and a water intake pipe with a screen and isolator is lowered into the intake well. Filler is injected into the enlarged section through the return water pipe, and the fluid is discharged through the intake pipe.

[0022] The advantages of this invention are:

[0023] (1) This invention enlarges the hole at the bottom of the drilling channel, and the diameter of the enlarged hole is much larger than that of the unenlarged hole. After the enlargement is completed, the rock cuttings are discharged, and an enlarged hole channel is formed at the enlarged hole, thereby increasing the volume of the heat exchange area and the heat exchange surface area, which can effectively extract geothermal energy. In addition, a return water pipe and a water intake pipe are set in the drilling channel. The return water pipe and the water intake pipe can circulate with the external heat exchange device, and timely backfilling of tailwater can avoid problems such as water level drop caused by failure to backfill tailwater in time.

[0024] (2) Vertical wells or U-shaped wells can be formed by modifying existing wells. In actual operation, if the drilling depth is not deep enough, the drilling depth is continued to reach the design depth. The cylindrical casing is installed to separate the wellbore from the formation so that the next step of operation can be carried out in the casing. It also plays a role in stabilizing the formation, preventing well wall collapse, well leakage, etc. After the casing is installed, cement is injected into the annulus between the casing and the well wall to form a cement ring and seal the formation.

[0025] (3) Explosives are used to expand the borehole in the well to form a channel with the same diameter, smooth wall and high stability; the packer is used to separate the blasting zone and the non-blasting zone, while the safety damper is used to reduce the damage to the casing and the damage to the open hole formation stability in the non-blasting zone during blasting.

[0026] (4) Using ceramic particles for backfilling can improve the stability and permeability of the channel, allowing the tailwater to be reinjected; and solve the problem of collapse caused by the scouring of the channel wall by the loop formed by the tailwater and the intake water, and can also delay the heat exchange time. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the dropping of explosives into a vertical well in Embodiment 1 of the present invention;

[0028] Figure 2 This is a schematic diagram of a vertical well enlargement in Embodiment 1 of the present invention;

[0029] Figure 3 This is a schematic diagram of cuttings removal in a vertical well according to Embodiment 1 of the present invention;

[0030] Figure 4 This is a schematic diagram of the circulation channel formed in a vertical well in Embodiment 1 of the present invention;

[0031] Figure 5 This is an explosion principle diagram in an embodiment of the present invention;

[0032] Figure 6 This is a schematic diagram of the U-shaped well for placing explosives in Embodiment 2 of the present invention;

[0033] Figure 7 This is a schematic diagram of the U-shaped well after packers and safety shock absorbers are installed on both sides in Embodiment 2 of the present invention;

[0034] Figure 8 This is a schematic diagram of the U-shaped well cuttings removal in Embodiment 2 of the present invention;

[0035] Figure 9 This is a schematic diagram of the circulation channel formed by the U-shaped well in Embodiment 2 of the present invention;

[0036] Numbering on the map:

[0037] 1. Casing; 2. Cement ring; 3. Packer; 4. Safety damper; 5a. First coiled tubing; 5b. Second coiled tubing; 5c. Third coiled tubing; 5d. Fourth coiled tubing; 6. Return water pipe; 7. Intake water pipe; 8. Centralizer. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0039] This method is applicable to the modification of large-diameter seepage channels in geothermal wells. It is suitable for both vertical and U-shaped wells. The following sections will explain the two cases separately.

[0040] Example 1:

[0041] This embodiment applies to vertical wells.

[0042] Step S1: Enlarge the borehole at the lowest point of the drilling channel. After enlargement, remove the cuttings. The diameter of the enlarged section should be more than twice that of the unenlarged section of the drilling channel, usually more than five times. Adjustments should be made according to the actual geological conditions of the construction.

[0043] In this embodiment, the vertical well can be drilled using conventional drilling methods to reach the designed depth, typically over 1000 meters. A vertical well is a straight borehole formed by drilling perpendicular to the ground, with the lowest point being the bottom section of the well. The well diameter can be the actual diameter used during construction. If well leakage or blowout occurs during drilling, the leakage point needs to be sealed; existing technologies can be used for this purpose.

[0044] Step S1.1: Install casing 1 in the vertical well and fix it with cement;

[0045] Conventional drilling can consist of several drilling operations. In this embodiment, the drilling is carried out in two operations. Specifically, after drilling to the designed depth with a larger drill bit in the first operation, casing 1 is run. Cement is injected between casing 1 and the well wall to cement the well. After the cement solidifies, a smaller drill bit is run in for the second operation to complete the open hole section. The inner diameter of the wellbore at casing 1 is larger than the inner diameter of the open hole section.

[0046] The casing 1 is cylindrical and separates the wellbore from the formation to facilitate the next operation inside the casing 1. It also plays a role in stabilizing the formation and preventing wellbore collapse and leakage. After the casing 1 is run in, cement is injected into the annulus between the casing 1 and the wellbore to form a cement ring 2, which seals the formation.

[0047] In actual use, the casing 1 is connected by multiple individual casing threads, which can be up to several kilometers long.

[0048] Step S1.2: Lower the explosive, install the packer 3 and safety shock absorber 4, and then detonate;

[0049] Specifically, such as Figure 1 As shown, the first coiled tubing 5a is run into the casing 1 of the vertical well to the open hole section. Explosives are placed through the first coiled tubing 5a. After the first coiled tubing 5a is pulled out, the well is shut in, high-pressure gas is injected to compact the explosives, and then the well is opened.

[0050] like Figure 2 As shown, at least one packer 3 and a safety damper 4 are fixed to the second coiled tubing 5b by threads and lowered to the top of the open hole section (the open hole section refers to the position without casing 1), and the position of the safety damper 4 is lower than the position of the packer 3; after the packer 3 and the safety damper 4 are installed in place, there are no explosives in the vertical well section above the packer 3.

[0051] Explosives are used to enlarge the borehole underground, creating a channel with a diameter larger than the open hole section, smooth walls, and high stability. Packer 3 is used to separate the blasting zone from the non-blasting zone, while safety damper 4 is used to reduce damage to the casing 1 during blasting and to minimize disruption to the open hole formation stability in the non-blasting zone. Figure 2 The circular shape inside the enlarged borehole channel represents rock cuttings.

[0052] The explosive can be an emulsion explosive with fluid properties or a high-energy powder explosive, but it needs to be made into a continuous cylindrical charge and lowered into the second continuous tubing 5b. The cylindrical charge is then compressed to ensure that the outer shell of the charge fits tightly against the wellbore wall without any gaps. Figure 5As shown, when fluid explosives or cylindrical explosives are injected into the bottom section of the well, the explosives adhere tightly to the wellbore wall. When the explosives are detonated from one end, the resulting impact pressure acts on the rock wall, creating an impact velocity V0. When the impact velocity exceeds a certain threshold, the boundary velocity V1 between the fractured and cracked zones exceeds the boundary velocity V2 between the cracked and elastic zones, causing the cracked zone to disappear. The rock fragments in the fractured zone are smaller, while the rock in the elastic zone maintains normal overall stability.

[0053] A cable with a detonator end is lowered into the second coiled tubing 5b, the well is shut in, the detonating cord at the end of the cable is connected to the explosive, and the explosion is carried out. After the explosion, the well is slowly opened to release the pressure, forming a damaged zone with a fracture zone at the bottom of the well. The second coiled tubing 5b, packer 3, and safety shock absorber 4 are then removed.

[0054] Step S1.3: After the borehole is enlarged, remove the rock cuttings;

[0055] Specifically, such as Figure 3 As shown, a third coiled tubing 5c ​​is installed inside casing 1 in a vertical well. A high-pressure fluid, such as a high-speed sand-carrying fluid, is injected into the third coiled tubing 5c ​​by a surface pressurization pump. The rock cuttings generated after detonation are discharged through the annular space between the third coiled tubing 5c ​​and casing 1. After the cuttings are removed, the third coiled tubing 5c ​​is taken out.

[0056] Step S1.4: Fill the geological conditions with the appropriate filling material;

[0057] Specifically, due to different geological characteristics, wellbore stability may vary. When there are significant differences in the geological strata and instability, ceramic particles need to be injected into the modified channel after borehole enlargement to provide support. If the geological conditions of the strata are good, such as granite or basalt, the wellbore stability is high, and materials such as ceramic particles are not needed for support.

[0058] Specifically, refer to Figure 4 As shown, multiple centralizers 8 are threaded onto the external surface of the intake pipe 7, which is then lowered into the casing 1 to the bottom of the reaming section. In this embodiment, the centralizer 8 is a double-hole centralizer. The return pipe 6 is then lowered into the reaming section. It can be lowered directly to the top of the reaming section, allowing the filler to fall under gravity, or it can be lowered to the bottom first, and then, as the filler is injected, the return pipe 6 is lifted until it stops at the top of the reaming section. The return pipe 6 passes through multiple centralizers 8 during its descent. The filler is injected through the return pipe 6, and the fluid is returned from the intake pipe 7.

[0059] The filler is one or a combination of ceramic particles and sand particles. Using ceramic particles for backfilling can improve the stability and permeability of the channel, allowing for tailwater reinjection; it also solves the problem of collapse caused by the scouring of the channel walls by the loop formed by tailwater and intake water; and it can also delay the heat exchange time.

[0060] Step S2: A circulation channel is formed by the water intake pipe 7 and the return pipe 6 within the drilling tunnel;

[0061] After the circulation channel is formed, water is injected through the return water pipe 6 and water is taken out through the intake water pipe 7 to test the seepage rate and water temperature of the expanded channel. The screen of the intake water pipe 7 can prevent impurities from entering the heat exchange device on the ground.

[0062] After the test is completed, water is taken through the water intake pipe 7 and exchanged with the heat exchange device on the ground. Then, the water is returned through the return water pipe 6 to achieve tailwater reinjection.

[0063] It should be noted that the first continuous tubing 5a, the second continuous tubing 5b, and the third continuous tubing 5c ​​are used to distinguish continuous tubing used in different stages of the process. In actual use, the same batch of continuous tubing can be used multiple times. For example, the first continuous tubing 5a is mainly used for dropping explosives. After dropping the explosives, packer 3 and safety damper 4 are installed, and it can then be used as the second continuous tubing 5b. After removing packer 3 and safety damper 4, the second continuous tubing 5b can be used as the third continuous tubing 5c. Of course, continuous tubing of different diameters and from different batches can also be used.

[0064] It should be noted that the term "continuous tubing" in this embodiment does not specifically refer to tubing used in the petroleum industry, but rather to tubular objects capable of completing the process of this embodiment, including but not limited to: casing, drill pipe, tubing, etc.

[0065] Alternatively, the water intake pipe 7 and the return pipe 6 can also be in the form of continuous tubing.

[0066] This embodiment utilizes a vertical well to develop geothermal energy, forming a loop with an external heat exchange device via coiled tubing. Hot water from the formation is extracted directly, and the tailwater after surface heat exchange is reinjected underground through return pipe 6. Since current geothermal wells have very small boreholes, rarely exceeding 200mm, directly using the drilled open-hole for heat exchange presents the problem of limited heat exchange area, hindering large-scale geothermal energy extraction. This embodiment addresses this by enlarging the borehole at the bottom, reaching or exceeding 500mm at the heat exchange stage. This increases the volume and surface area of ​​the heat exchange zone, enabling effective geothermal energy extraction. Furthermore, by installing a return water pipe 6 and an intake water pipe 7 within the same drilling channel, tailwater can be reinjected in a timely manner. Tailwater reinjection is simple and avoids problems such as water level drop caused by untimely tailwater reinjection. Secondly, the use of ceramic particles for backfilling can improve the stability and permeability of the channel. This not only solves the problems of tailwater reinjection difficulties and collapse caused by the scouring of the channel wall by the loop formed by water intake, but also delays the heat exchange time.

[0067] The method of this embodiment can be widely applied in shallow and medium-deep geothermal development, and has great economic benefits. The hole enlargement method of this embodiment is more suitable for small-diameter and deep wells.

[0068] Example 2:

[0069] like Figure 6 As shown, this embodiment applies to U-shaped wells. The two vertical wells on either side of the U-shaped well serve as the intake well (left side) and return well (right side), with a horizontal section between them. The lowest point of the U-shaped well is the horizontal section. The length of the horizontal section can be designed according to the required heat volume; for longer horizontal sections, two opposing horizontal wells can be used. The horizontal section should be far from the intake and return wells to prevent damage to the casing 1' and cement ring 2' within the intake and return wells from the impact of the explosive detonation.

[0070] Step S1: Enlarge the borehole in the horizontal section of the drilling channel. After enlargement, remove the cuttings. The diameter of the enlarged section is more than twice that of the unenlarged section of the drilling channel, usually more than five times. Adjustments should be made according to the actual geological conditions of the construction.

[0071] In this embodiment, the U-shaped well can utilize a conventional U-shaped drilling method, with one side serving as a water intake well and the other as a return water well. The well diameter can be the actual diameter used during construction.

[0072] Step S1.1: Install casing 1' in both the intake well and the return well and fix it with cement;

[0073] Specifically, both the intake and return wells are drilled twice. The first drilling, using a larger drill bit, reaches the designed depth, followed by casing installation and cementing. After the cement hardens, a smaller drill bit is installed for the second drilling, connecting the intake and return wells and completing the open-hole section. Cement is injected into the annulus between casing 1' and the wellbore to form a cement sheath 2', sealing the formation. Casing 1' is cylindrical, separating the wellbore from the formation to facilitate subsequent operations within casing 1', and also serves to stabilize the formation and prevent wellbore collapse and leakage.

[0074] Step S1.2: As Figure 6 As shown, the explosives are lowered, and after the packer 3 and safety shock absorber 4 are installed, they are detonated.

[0075] Specifically, in a U-shaped well, a first coiled tubing 5a' is run down one side and a second coiled tubing 5b' is run down the other side. Only the bottom end of the first coiled tubing 5a' is connected to at least one packer 3' and a safety damper 4'. The packer 3' and safety damper 4' are positioned at one end of the horizontal well section. Explosives are placed inside the second coiled tubing 5b', then the second coiled tubing 5b' is pulled out and the well is shut in (both sides are closed). High-pressure gas is injected to compact the explosives, and then the well is opened. Figure 7 As shown, a third coiled tubing 5c' is installed on this side, with at least one packer 3' and a safety damper 4' connected to its bottom end. The packer 3' and safety damper 4' are positioned on the other side of the horizontal well section. A cable with a detonator is supplied downhole through the third coiled tubing 5c' (or the first coiled tubing 5a'). The well is shut in, the cable is connected to the explosive, and detonation is performed. After the explosion, the well is slowly opened to release pressure, and the first coiled tubing 5a', the third coiled tubing 5c', the packer 3', and the safety damper 4' are all removed.

[0076] The explosive can be an emulsion explosive with fluid properties or a high-energy powder explosive, but it needs to be made into a continuous cylindrical explosive charge and lowered into the second continuous tubing 5b'. The cylindrical explosive charge is then squeezed to make the outer shell of the explosive charge fit tightly against the outer wall of the wellbore without any gaps.

[0077] Step S1.3: After the borehole is enlarged, remove the rock cuttings;

[0078] Specifically, such as Figure 8 As shown, a fourth coiled tubing 5d is installed on one side. High-pressure fluid is pumped into the fourth coiled tubing 5d by a surface pressurization pump. Rock cuttings generated after detonation are discharged from the other side. After the cuttings are discharged, the fourth coiled tubing 5d is removed.

[0079] Step S1.4: Fill in the filler material according to the geological conditions;

[0080] After the rock cuttings in the U-shaped well are discharged, a return water pipe 6' with a packer 3” installed at the end is lowered into the return water well, and a water intake pipe 7' with a screen and a packer 3” is lowered into the intake well. Multiple single-hole centralizers are threaded onto both the return water pipe 6' and the intake pipe 7'.

[0081] The filler is injected into the enlarged well section through the return water pipe 6', and the fluid is discharged through the intake water pipe 7'. Specifically, matched grade ceramic particles are carried by the sand-carrying fluid through the return water pipe 6' to the horizontal well section, where a breaker fluid is injected. The breaker fluid degrades the sand-carrying fluid, and a displacement fluid is used to displace the fluid in the horizontal well section. Because the sand-carrying fluid contains colloids, failure to remove them will affect subsequent recycling.

[0082] Fluids refer to the liquid within the expanded borehole section, as well as the sand-carrying fluid and gel-breaking fluid injected during the injection of filler.

[0083] Packer 3” is used to prevent filler flow; if no filler is being filled, packer 3 is not required.

[0084] Step S2: As Figure 9 As shown, the return water pipe 6' and the intake water pipe 7' form a circulation channel.

[0085] Water was returned through the return pipe 6' and taken through the intake pipe 7' to test the seepage rate and intake temperature of the enlarged channel.

[0086] After the test is completed, water is taken through the water intake pipe 7' and exchanged with the heat exchange device on the ground, and then returned through the water return pipe 6'.

[0087] It should be noted that the first continuous tubing 5a', the second continuous tubing 5b', the third continuous tubing 5c', and the fourth continuous tubing 5d are used to distinguish continuous tubing used in different stages of deployment. In actual use, the same batch of continuous tubing can be used multiple times. For example, the second continuous tubing 5b' is mainly used for deploying explosives. After the explosives are deployed, the packer 3' and safety damper 4' are installed, and it can then be used as the third continuous tubing 5c'. After the third continuous tubing 5c' is withdrawn and the packer 3' and safety damper 4' are removed, it can be used as the fourth continuous tubing 5d. Of course, continuous tubing of different diameters and from different batches can also be used.

[0088] It should be noted that the term "continuous tubing" in this embodiment does not specifically refer to tubing used in the petroleum industry, but rather to tubular objects capable of completing the process of this embodiment, including but not limited to: casing, drill pipe, tubing, etc.

[0089] This embodiment applies to U-shaped wells, utilizing horizontal well sections to develop geothermal energy. The U-shaped loop consists of an intake well, a return well, and the horizontal well section. The return well injects tailwater from the circulating cold or hot water into the formation. In the horizontal well section, the high temperature of the formation heats the circulating water, and the heated water is extracted through the intake well, forming a complete circulation system with the surface heat exchange system. This embodiment involves enlarging the wellbore in the open-hole section of the horizontal well to increase the heat exchange area and surface area, thus effectively extracting geothermal energy. However, excessively large enlarged channels can cause wellbore instability and potential collapse. Furthermore, excessively large open channels can lead to uneven water flow velocity, potentially resulting in insufficient heat exchange. Therefore, the enlarged channels need to be backfilled with ceramic particles or mixed sand and gravel particles to support the channels, slow the flow velocity, and extend the heat exchange time.

[0090] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for modifying large-diameter seepage channels in geothermal wells, characterized in that, include: Step S1: Ream the borehole at the lowest point of the drilling channel, and remove the cuttings after reaming; depending on the geological conditions, inject filler into the reamed section after the cuttings are removed; the drilling channel is a vertical well or a U-shaped well; the well walls on both sides of the vertical well and the U-shaped well have fixed casings; run water intake pipes and return pipes inside the casings; The method for enlarging a vertical well is as follows: explosives are placed at the bottom of the casing of the vertical well and detonated, forming an enlarged section after the explosion; Furthermore, the enlargement method for vertical wells is as follows: a first coiled tubing is installed inside the casing of the vertical well. Explosives are placed inside the first coiled tubing. After the first coiled tubing is pulled out, the well is shut in. High-pressure gas is injected to compact the explosives, and then the well is opened. At least one packer and a safety damper are fixed at the bottom of a second coiled tubing. A second coiled tubing is installed inside the casing of the vertical well. The packer and safety damper are placed at the bottom of the casing. A cable with a detonator is delivered downhole through the second coiled tubing. The well is shut in. The cable is connected to the explosives and detonated. After the explosion, the well is slowly opened to release the pressure, and the second coiled tubing, packer, and safety damper are removed. The method for removing cuttings after enlarging the vertical well is as follows: Run a third coiled tubing inside the casing of the vertical well, inject high-pressure fluid into the third coiled tubing, and the cuttings are discharged from the annular space between the casing and the third coiled tubing. After the cuttings are removed, take out the third coiled tubing. Step S2: A circulation channel is formed through the return water pipe and the intake water pipe.

2. The method for modifying large-diameter seepage channels in geothermal wells according to claim 1, characterized in that, After the cuttings in the vertical well are removed, if it is necessary to inject filler into the reaming section, the specific steps are as follows: lower the water intake pipe with the screen installed at the end to the bottom of the reaming section, lower the return water pipe to the reaming section, inject filler through the return water pipe, and discharge the fluid through the water intake pipe.

3. The method for modifying large-diameter seepage channels in geothermal wells according to claim 1, characterized in that, In step S1, the enlargement method of the U-shaped well is as follows: one side of the U-shaped well is a water intake well, and the other side is a return water well. A horizontal well section exists between the water intake well and the return water well. Explosives are placed at the bottom of the casing of either the water intake well or the return water well and detonated, forming an enlarged section after the explosion. Further, the enlargement method of the U-shaped well is as follows: a first coiled tubing is laid on one side of the U-shaped well, and a second coiled tubing is laid on the other side. Only the bottom end of the first coiled tubing is connected to at least one packer and a safety damper. The packer and safety damper are arranged at one end of the horizontal well section. The second coiled tubing... Explosives are placed inside the tubing. After the second coiled tubing is pulled out, the well is shut in. High-pressure gas is injected to compact the explosives. The well is then opened, and a third coiled tubing is run from the other side of the U-shaped well. At least one packer and a safety damper are connected to the bottom of the third coiled tubing. The packer and safety damper are placed at the other end of the horizontal well section. A cable with a detonator is delivered downhole through the first or third coiled tubing. The well is shut in, and the cable is connected to the explosives for detonation. After the explosion, the well is slowly opened to release the pressure, and the first and third coiled tubing, as well as the packer and safety damper, are removed.

4. The method for modifying large-diameter seepage channels in geothermal wells according to claim 1, characterized in that, In step S1, the method for removing cuttings after the U-shaped well is enlarged is as follows: a fourth coiled tubing is installed in the water intake or return well, high-pressure fluid is injected into the fourth coiled tubing, and the cuttings are discharged from the other side. After the cuttings are removed, the fourth coiled tubing is taken out.

5. The method for modifying large-diameter seepage channels in geothermal wells according to claim 1, characterized in that, After the cuttings in the U-shaped well are removed, if it is necessary to inject filler into the enlarged section, the specific steps are as follows: lower a return water pipe with an isolator installed at the end into the return water well, lower a water intake pipe with a screen and isolator into the intake well, inject filler into the enlarged section through the return water pipe, and discharge the fluid through the intake pipe.

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