A U-shaped geothermal well and its construction technology

Abstract

The present invention relates to a U-shaped geothermal well and its construction process. The construction process includes: Step 1, drilling a vertical well, lowering a cementing casing, and cementing; Step 2, cavity building operation, building a cavity for the first time; selecting a butt cavity target layer at the bottom of the vertical well; drilling a cavity operation on the target layer through an expansion drill to drill out a rough blank cavity of the butt cavity; flushing, flushing the rough blank cavity, and stripping the mud skin on the peripheral wall of the rough blank cavity; Step 3, anti-leakage treatment of the peripheral wall of the rough blank cavity, injecting cement slurry into the rough blank cavity under a pressure of 2-10 MPa, so that the cement slurry penetrates into the peripheral wall of the rough blank cavity under high pressure and fills the entire rough blank cavity; the cement starts to set; secondary cavity building operation, drilling a cavity operation on the cement layer after initial setting to form a butt cavity; flushing the butt cavity; using a water seepage test to check the anti-leakage effect of the butt cavity; Step 7, completing the drilling operation of the butt well. Beneficial effects: Solve the leakage problem at the butt position of the U-shaped geothermal well.

Description

Technical Field

[0001] The present invention relates to the heat exchange technology of medium - deep geothermal closed - type, and particularly relates to a U - shaped geothermal well and its construction process. Background Technique

[0002] Geothermal resources in China are widely distributed. As a renewable energy source, they have the advantages of rich reserves, cleanliness, great development potential, and direct utilization. Geothermal energy heating can reduce large - scale coal burning and relieve the double pressures of supply guarantee and price caused by natural gas heating. Undoubtedly, it is a good solution for clean heating in winter at present.

[0003] The medium - deep geothermal closed - type down - hole heat exchange system is a heat extraction technology that does not affect underground water resources. It obtains geothermal energy through the heat exchange between the intermediate water and the geothermal reservoir without pumping groundwater, and its essential meaning is completely different from traditional medium - deep geothermal heating.

[0004] Adopting the medium - deep geothermal closed - type down - hole heat exchange system can effectively avoid problems such as sandstone heat reservoir recharge, scaling and corrosion, small water volume of geothermal wells, and dry holes.

[0005] Heat exchange principle of U - shaped butt - joint well: Drill a U - shaped butt - joint well into the rock formation, use the casing cementing process to seal the geothermal well, and establish an in - well heat exchange system. Inject cold water into the water injection well. During the flow of the low - temperature water along the vertical well section and the horizontal well section, it is heated and raised in temperature by the surrounding rock, and then flows out of the heat exchanger upward from the water production well. After the hot water returns to the ground, its heat is lifted by the heat pump unit for building heating. After cooling, the circulating water enters the underground heat exchange cycle again, bringing the heat in the surrounding rock to the surface, and cycling repeatedly without any hydraulic connection with groundwater and without damaging underground water resources.

[0006] At present, the existing U - shaped geothermal wells are prone to leakage problems at the butt - joint position. The intermediate water is easy to contact the formation, affecting underground water resources. Moreover, due to formation leakage, the water volume decreases and the pressure drops, resulting in poor operation stability of the entire Y - shaped geothermal well. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a U - shaped geothermal well and its construction process, which effectively overcomes the defects of the prior art.

[0008] The technical solution of the present invention to solve the above - mentioned technical problem is as follows:

[0009] A U-shaped geothermal well includes a vertical well and a docking well disposed underground. A docking cavity is provided at the lower end of the vertical well. An anti-leakage layer is provided on the inner wall of the docking cavity. The docking well includes a vertical well section and a horizontal well section. One end of the horizontal well section communicates with and is integrated with the lower end of the vertical well section, and the other end is connected to and communicates with the docking cavity. Cementing casings are fixedly sleeved on the inner walls of the vertical well, the vertical well section, and the horizontal well section respectively. A high thermal conductivity cementing material layer is filled between the cementing casing and the corresponding well wall.

[0010] Based on the above technical solutions, the present invention can be further improved as follows.

[0011] Further, the cementing casing is a metal casing.

[0012] Further, the high thermal conductivity cementing material layer is a high thermal conductivity cementing material layer.

[0013] Further, the anti-leakage layer is an anti-leakage cement layer.

[0014] A construction process for a U-shaped geothermal well is also provided, including the following steps:

[0015] Step 1: Drill the vertical well. After drilling is completed, lower the cementing casing and perform cementing operations on the cementing casing using a high thermal conductivity cementing material layer.

[0016] Step 2: Perform cavity construction operations, specifically including:

[0017] S1. Primary cavity construction. Select a low-permeability rock formation at the bottom of the vertical well as the target layer for the docking cavity.

[0018] S2. Drill a cavity in the target layer through an expansion drill to drill out the rough cavity of the docking cavity.

[0019] S3. Flush. Flush the rough cavity to strip the mud skin on the peripheral wall of the rough cavity and keep the peripheral wall of the rough cavity clean.

[0020] Step 3: Perform anti-leakage treatment on the peripheral wall of the rough cavity, specifically including:

[0021] S4. Inject anti-leakage cement slurry into the rough cavity under a pressure of 2 - 10 MPa. The purpose is to organically combine with the peripheral wall of the rough cavity, so that the cement slurry penetrates into the peripheral wall of the rough cavity under high pressure and fills the entire rough cavity.

[0022] S5. Maintain the pump pressure at 2 - 5 MPa for 1 - 5 h until the cement starts to set to form;

[0023] Step 4: Perform secondary cavity construction operations. Drill a cavity in the cement layer after initial setting to form a docking cavity with an anti-leakage layer.

[0024] Step 5: Flush the docking cavity;

[0025] Step 6: Use a water seepage test to check the anti-leakage effect of the docking cavity;

[0026] Step 7: Complete the drilling operation of the docking well, lower the casing in the vertical well section and horizontal well section of the docking well, and use a high thermal conductivity cementing material layer to perform the cementing operation on the casing.

[0027] Further, in the above Step 6, apply a pressure greater than 2 - 10 MPa at the upper wellhead of the vertical well and maintain the pressure for 30 - 120 minutes. If the liquid level in the wellbore does not drop or does not exceed 2 mm, it passes the inspection; otherwise, it is judged as unqualified, and repeat Steps 3, 4, and 5 until the inspection passes.

[0028] Further, in the above S6, perform the cavity drilling operation on the cement layer 20 - 1000 h after the initial setting of the cement.

[0029] Further, the above anti-leakage cement slurry includes the following components in parts by mass: 5 parts of water, 10 parts of cement, and 0.3 - 0.5 parts of interfacial treatment agent.

[0030] The beneficial effect of the present invention is: solving the leakage problem at the docking position of the U-shaped geothermal well. Description of the Drawings

[0031] Figure 1 It is a schematic structural diagram of the U-shaped geothermal well of the present invention.

[0032] In the drawings, the list of components represented by each reference numeral is as follows:

[0033] 1. Vertical well; 2. Docking well; 3. Casing; 4. High thermal conductivity cementing material layer; 11. Docking cavity; 12. Anti-leakage layer; 21. Vertical well section; 22. Horizontal well section. Detailed Embodiments

[0034] The principles and features of the present invention are described below with reference to the drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0035] Embodiment: As Figure 1As shown in the figure, the U-shaped geothermal well of this embodiment includes a vertical well 1 and a docking well 2 arranged underground. A docking cavity 11 is opened at the lower end of the vertical well 1, and a leakage prevention layer 12 is provided on the inner wall of the docking cavity 11. The docking well 2 includes a vertical well section 21 and a horizontal well section 22. One end of the horizontal well section 22 communicates with the lower end of the vertical well section 21 and is integrated therewith, and the other end is connected to and communicates with the docking cavity 11. Cementing casings 3 are fixedly sleeved on the inner walls of the vertical well 1, the vertical well section 21, and the horizontal well section 22 respectively, and a high thermal conductivity cementing material layer 4 is filled between the cementing casing 3 and the corresponding well wall.

[0036] The beneficial effects of the entire U-shaped geothermal well are as follows:

[0037] 1) The leakage problem at the docking position is solved, thereby preventing the intermediate water from contacting the formation and protecting the underground water resources.

[0038] 2) The situation where the water volume decreases and the pressure drops in the circulating system due to formation leakage during the operation of the downhole heat exchange system of the U-shaped geothermal well is solved.

[0039] 3) The stability of the operation of the U-shaped closed docking well is ensured.

[0040] 4) Simple operation, low cost, and good effect.

[0041] Preferably, the cementing casing 3 is a metal casing. Specifically, a metal casing with good thermal conductivity, high structural strength, and not easily deformed is selected.

[0042] Preferably, the high thermal conductivity cementing material layer 4 is a high thermal conductivity cementing material layer, which can ensure good and stable underground heat exchange.

[0043] In this embodiment, the construction process of the U-shaped geothermal well includes the following steps:

[0044] Step 1: Drill the vertical well 1. After drilling is completed, lower the cementing casing 3 and perform cementing operation on the cementing casing 3 using the high thermal conductivity cementing material layer 4.

[0045] Among them, the depth of the vertical well 1 is 2500 m, the drilling diameter is Φ311.10 mm, the cementing casing 3 is Φ245.48 mm, and the wall thickness is 10.03 mm.

[0046] Step 2: Cavity construction operation, which specifically includes:

[0047] S1. Primary cavity construction, select a low-permeability rock formation at the bottom of the vertical well 1 as the target layer of the docking cavity 11.

[0048] S2. Drill a cavity operation on the target layer through an underreamer to drill out the rough cavity of the docking cavity 11.

[0049] Among them, for the cavity expansion drill, a drill bit with cutting blades (KYG125 type cavity expansion drill bit) is selected to operate at the bottom of the vertical well to create a cylindrical rough cavity with a diameter of Φ600mm and a height of 6m. The operation sequence of the cavity expansion drill bit is as follows: send the cavity expansion drill bit with cutting blades to the bottom of the vertical well, pump drilling fluid to generate pressure through the throttling nozzle - push the control rod downward - push the cutting blades to expand outward - rotate the drill string for cutting - calculate the position of the cavity bottom by measuring the drill string - lower the drill string to achieve the first cavity expansion - stop the pump and the return spring drives the control rod to move upward - drive the cutting blades to reset;

[0050] Operation requirements: During the implementation process, the drilling pressure is 5 - 20KN, the rotational speed is 30 - 70RPM, the pump pressure is 5 - 10MPa, and reaming is carried out every 1 - 2m of advancement. In the early stage, apply light pressure and slow rotation to expand the cutting blades to the specified amplitude, and then apply pressure for reaming to ensure that the diameter and depth of the cavity meet the requirements for secondary cavity construction;

[0051] S3. Flush the rough cavity to strip the mud cake on the peripheral wall of the rough cavity and keep the peripheral wall of the rough cavity clean;

[0052] Specifically, when the cavity meets the design requirements, lift the drill string, stop the pump after circulating for one week, lower the drill string to the bottom of the cavity, and flush the cavity with clean water to strip the mud cake on the rough cavity and keep the rough cavity clean;

[0053] Step Three. Conduct anti-seepage treatment on the peripheral wall of the rough cavity, which specifically includes:

[0054] S4. Inject anti-seepage cement slurry into the rough cavity under a pressure of 2 - 10MPa. The purpose is to organically combine with the peripheral wall of the rough cavity, so that the cement slurry penetrates into the peripheral wall of the rough cavity under high pressure and fills the entire rough cavity;

[0055] S5. Keep the pump pressure at 2 - 5MPa for 1 - 5h until the cement starts to set, and then release the pressure after setting;

[0056] Step Four. Conduct secondary cavity construction operation. Drill a cavity in the cement layer after setting to form a docking cavity 11 with an anti-seepage layer 12;

[0057] Among them, 24 hours after the cement layer in S5 starts to set and the pressure is released until the cement finally sets, conduct the second cavity expansion and reduce the blades of the cavity expansion drill bit to ensure that the diameter of the docking cavity is 500m and the thickness of the cement anti-seepage layer ≥50mm. ), the operation sequence of the cavity expansion drill bit is as follows: send the cavity expansion drill bit with cutting blades to the top of the cement plug, pump drilling fluid to generate pressure through the throttling nozzle (control the expansion amplitude of the cutting blades by calculating the pressure) - push the control rod downward - push the cutting blades to expand outward (the expansion amplitude needs to ensure the thickness of the cement anti-seepage layer 4) - rotate the drill string for cutting - judge the position of the drill bit by measuring the drill string - lower the drill string to achieve the second cavity construction - stop the pump and the return spring drives the control rod to move upward - drive the cutting blades to reset.

[0058] Operation and technical requirements: During the implementation process, to prevent the cement in the chamber from falling off during the secondary cavity expansion, keep light pressure and slow drilling during the secondary cavity expansion (drilling pressure 5 - 10 KN, rotational speed 30 - 50 r / min, pump pressure 4 - 7 MPa), ream the hole once every 1 - 2 m of advancement. To ensure the success of the docking cavity, turn slowly with light pressure to expand the cutter blades to the specified amplitude, and ensure that the cement anti-seepage coat 4 meets the requirements such as a thickness of 50 - 500 mm, compressive strength ≥ 10 MPa, and anti-seepage grade ≥ P4;

[0059] Step Five: Flush the docking cavity 11;

[0060] Step Six: Use a water seepage test to check the anti-seepage effect of the docking cavity 11;

[0061] Step Seven: Complete the drilling operation of the docking well 2, lower the casing string 3 into the vertical well section 21 and the horizontal well section 22 of the docking well 2, and use the high - thermal - conductivity cementing material layer 4 to perform the cementing operation on the casing string 3.

[0062] In the above Step Six, apply a pressure greater than 2 - 10 MPa at the upper wellhead of the vertical well 1 and maintain the pressure for 30 - 120 min. If the liquid level in the wellbore does not drop or drops by no more than 2 mm, it passes the inspection; otherwise, it is judged as unqualified, and repeat Steps Three, Four, and Five until the inspection passes.

[0063] In the above S6, perform the cavity drilling operation on the cement layer 20 - 1000 h after the initial setting of the cement.

[0064] It should be supplementary explained that: The casing string 3 in the above vertical well 1 extends downward to a position close to the bottom of the vertical well 1 (that is, the peripheral wall part at the bottom of the vertical well 1 is not sleeved with the casing string 3). When the anti - seepage cement slurry is injected into the rough - blank cavity, the injection height should cover the part of the bottom of the vertical well 1 that is not sleeved with the casing string 3 and be connected to the lower end of the casing string 3.

[0065] The above high - thermal - conductivity cementing material layer is obtained by pouring and solidifying cement slurry. Specifically, the materials involved in this high - thermal - conductivity cementing material layer are prior art, such as the cementing materials described in the patent with the application number 201910669431X.

[0066] Preferably, the above anti - seepage layer 12 is an anti - seepage cement layer, which can ensure that the docking cavity 11 has good anti - seepage performance.

[0067] The above anti - seepage layer 12 is obtained by pouring and solidifying special cement slurry. Specifically, the cement slurry includes the following components in parts by mass: 5 parts of water, 10 parts of cement, and 0.3 - 0.5 parts of interfacial treatment agent. This anti - seepage cement slurry has multiple functions such as anti - seepage, waterproofing, pollution - free, corrosion - resistant, plugging pore cracks, and enhancing adhesion.

[0068] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A U-shaped geothermal well, characterized in that: It includes a vertical well (1) and a docking well (2) arranged underground. A docking cavity (11) is provided at the lower end of the vertical well (1). An anti-seepage layer (12) is provided on the inner wall of the docking cavity (11). The docking well (2) includes a vertical well section (21) and a horizontal well section (22). One end of the horizontal well section (22) communicates with and is integrated with the lower end of the vertical well section (21), and the other end is connected to and communicates with the docking cavity (11). Solid casing pipes (3) are fixedly sleeved on the inner walls of the vertical well (1), the vertical well section (21), and the horizontal well section (22) respectively. A high thermal conductivity cementing material layer (4) is filled between the solid casing pipe (3) and the corresponding well wall. The construction process of this U-shaped geothermal well includes the following steps: Step 1: Drill the vertical well (1). After drilling is completed, lower the solid casing pipe (3) and perform cementing operations on the solid casing pipe (3) using the high thermal conductivity cementing material layer (4). Step 2: Cavity construction operations, specifically including: S1. For the first cavity construction, select a low-permeability rock formation at the bottom of the vertical well (1) as the target layer of the docking cavity (11). S2. Drill a cavity in the target layer through an underreamer to drill out the rough blank cavity of the docking cavity (11). S3. Flush, flush the rough blank cavity, strip the mud skin on the peripheral wall of the rough blank cavity, and keep the peripheral wall of the rough blank cavity clean. Step 3: Anti-seepage treatment of the peripheral wall of the rough blank cavity, specifically including: S4. Inject anti-seepage cement slurry into the rough blank cavity under a pressure of 2 - 10 MPa. The purpose is to organically combine with the peripheral wall of the rough blank cavity, so that the cement slurry penetrates into the peripheral wall of the rough blank cavity under high pressure and fills the entire rough blank cavity. S5. Keep the pump pressure at 2 - 5 MPa for 1 - 5 h until the cement starts to set. Step 4: Second cavity construction operation, perform drilling operations on the cement layer after initial setting to form a docking cavity (11) with an anti-seepage layer (12). Step 5: Flush the docking cavity (11). Step 6: Use a water seepage test to check the anti-seepage effect of the docking cavity (11). Step 7: Complete the drilling operation of the docking well (2), lower the solid casing pipe (3) into the vertical well section (21) and the horizontal well section (22) of the docking well (2), and perform cementing operations on the solid casing pipe (3) using the high thermal conductivity cementing material layer (4).

2. The U-shaped geothermal well according to claim 1, characterized in that: The solid casing pipe (3) is a metal casing pipe.

3. A U-shaped geothermal well according to claim 1, characterized in that: The high thermal conductivity cementing material layer (4) is a high thermal conductivity cementing material layer.

4. A U-shaped geothermal well according to any one of claims 1 to 3, characterized in that: The anti-seepage layer (12) is an anti-seepage cement layer.

5. A U-shaped geothermal well according to any one of claims 1 to 3, characterized in that: In step 6, apply a pressure greater than 2 - 10 MPa at the upper wellhead of the vertical well (1) and maintain the pressure for 30 - 120 min. If the liquid level in the wellbore does not drop or does not exceed 2 mm, it passes the inspection; otherwise, it is judged as unqualified, and repeat steps three, four, and five until the inspection passes.

6. A U-shaped geothermal well according to any one of claims 1 to 3, characterized in that: In step 4, perform drilling operations on the cement layer 20 - 1000 h after the cement starts to set.

7. A U-shaped geothermal well according to any one of claims 1 to 3, characterized in that: The anti-seepage cement slurry includes the following components in parts by mass: 5 parts of water, 10 parts of cement, and 0.3 - 0.5 parts of an interfacial treatment agent.

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