A method for repairing geothermal well reservoirs

Abstract

This invention relates to a method for repairing geothermal well reservoirs, belonging to the field of hydrothermal geothermal resource extraction technology. The method involves first injecting liquid carbon dioxide into the geothermal well, where it transforms from a liquid to a gaseous state, forming a gas-water-solid mixture within the well. This artificially creates a blowout, bringing solids and waste drilling fluid to the surface. Then, based on the lithology of the reservoir and the chemical properties of the plugging materials, different acids are selected to acidify the reservoir. Under high pressure, the acid penetrates the fractures, destroying and dissolving clay and carbonate plugging materials. The gas produced by the chemical reaction is then released according to regulations. A second blowout using liquid carbon dioxide removes slag, expelling a large amount of loose products or mud generated by the chemical reaction between the acid and the reservoir plugging materials. Finally, hydraulic fracturing is performed on the geothermal well reservoir to completely clear the blocked channels and fractures.

Description

Technical Field

[0001] This invention relates to a method for repairing geothermal well reservoirs, belonging to the field of hydrothermal geothermal resource extraction technology. Background Technology

[0002] Geothermal energy is a renewable thermal energy source originating from the Earth's interior. It originates from magma and the decay of radioactive materials within the Earth. This heat is continuously transferred from the lower, high-temperature rock layers to the upper, lower, low-temperature rock layers through geological conduction and tectonic convection. Geothermal reserves are vast and renewable. In recent years, the development and utilization of geothermal resources have rapidly progressed, becoming one of the key clean and renewable energy sources being developed by countries worldwide.

[0003] Currently, almost all geothermal resource development and utilization is achieved through drilling engineering. The quality of drilling engineering directly affects the stability, sustainability, and energy consumption of resource extraction. The main problem is the damage and contamination of the geothermal reservoir by drilling fluid during the drilling process. During drilling, suspended mud and broken rock cuttings in the wellbore, under the centrifugal force and high pressure (static and dynamic pressure) of the drill string rotation, fill the geothermal reservoir and form high-strength blockages. These blockages damage the geothermal reservoir, severely affecting the water ingress rate and volume, and even causing complete closure and abandonment of the reservoir. The commonly used method is conventional well washing and slag removal using submersible pumps or air compressors after well completion, which has some effect. However, conventional well washing and slag removal methods have a long cycle (the combined time for air compressor relocation and well washing exceeds 10 days), poor slag removal effect, and often fail to accurately reflect the geothermal resource volume of a single well (underestimating water output or excessive drawdown), resulting in significant deviations in the calculation results of heat and resource volume during geothermal resource evaluation and development.

[0004] Therefore, there is an urgent need to develop a geothermal well reservoir repair method with better well washing and slag removal effects. Summary of the Invention

[0005] The purpose of this invention is to provide a method for repairing geothermal well reservoirs, which can solve the problem of poor slag removal effect in current geothermal well washing methods.

[0006] To achieve the above objectives, the technical solution adopted by the geothermal well reservoir repair method of the present invention is as follows:

[0007] A method for repairing geothermal well reservoirs includes the following steps:

[0008] S1, using liquid carbon dioxide to flush the geothermal well until clean water returns from the wellhead; the method of using liquid carbon dioxide to flush the geothermal well includes the following steps: with the wellhead of the geothermal well in a closed state, injecting liquid carbon dioxide into the geothermal well, simmering the well, and then releasing the liquid through a blowout.

[0009] S2, inject acid into the geothermal reservoir of the geothermal well, and then release the flow after the well is sealed;

[0010] S3 uses liquid carbon dioxide to flush the geothermal well until clean water returns from the wellhead;

[0011] S4 is used to hydraulically fracturing the geothermal reservoir of a geothermal well.

[0012] The geothermal well reservoir repair method of the present invention first injects liquid carbon dioxide into the geothermal well. The liquid carbon dioxide changes from liquid to gas and forms a gas, water and solid mixture in the well, which artificially creates a blowout. During the high-speed blowout, on the one hand, solids and waste drilling fluid in the well are brought to the surface, and on the other hand, negative pressure is generated in the wellbore, which carries out some of the blockages in the geothermal reservoir. If the material discharged from the well after the first venting is still turbid, the above operation can be repeated until clear water returns from the wellhead. Then, based on the lithology of the geothermal reservoir and the chemical properties of the plugging filling material, different acids are selected to acidify the geothermal reservoir. Under high pressure, the acid penetrates into the fractures, destroying and dissolving clay and carbonate filling materials. The gas produced by the chemical reaction is then vented according to the regulations. Liquid carbon dioxide is then used for a second slag removal, which can remove a large amount of loose products or mud (mud-like mixture in the well) produced by the chemical reaction between the acid and the geothermal reservoir plugging material from the surface. Finally, hydraulic fracturing is performed on the geothermal reservoir to completely remove the plugging material and thoroughly unclog the plugging channels and fractures, achieving the purpose of geothermal reservoir repair and increased production.

[0013] The geothermal well reservoir repair method of this invention comprises four steps, which are interconnected and operated continuously, enabling rapid wellbore cleaning, acid dissolution, re-cleaning, and reservoir fracture propagation. This invention replaces the existing traditional single-air compressor well washing and fracturing repair method with a comprehensive physical and chemical repair method. It features simplicity, practicality, low cost, high efficiency, avoidance of secondary damage, and significant effects. Compared with traditional methods, the geothermal resource volume (single well water volume) can be increased by an average of over 200%, and the repair cost of this method is only 1 / 10 of the traditional method, with a repair rate exceeding 98%.

[0014] Preferably, when using liquid carbon dioxide to flush a geothermal well, the pressure of the liquid column in the well corresponding to the injection point of the liquid carbon dioxide is 6–8 MPa. Generally, the injection point of liquid carbon dioxide is at a water depth of 600–700 m in the wellbore, where the pressure of the liquid column in the well is typically 6–8 MPa.

[0015] Preferably, in steps S1 and S3, the number of times the geothermal well is cleaned with liquid carbon dioxide is independently more than once.

[0016] Preferably, the injection volume of liquid carbon dioxide is 600–800 L each time the geothermal well is cleaned. In practice, the injection volume can be determined based on the well depth. For example, when the geothermal well depth is less than 2000 m, the injection volume is 600–680 L; when the geothermal well depth is 2000–3000 m, the injection volume is 720–800 L.

[0017] Preferably, the injection time of liquid carbon dioxide is 10 to 15 minutes each time the geothermal well is cleaned with liquid carbon dioxide.

[0018] In this invention, the well-sinking time when using liquid carbon dioxide to clean a geothermal well is 5 to 10 minutes.

[0019] Preferably, the acid solution is mainly composed of an acidic compound, water, and a corrosion inhibitor; the acidic compound is HCl, oxalic acid, or fluoroboric acid.

[0020] Preferably, the corrosion inhibitor is an aldehyde-based corrosion inhibitor. For example, the corrosion inhibitor is formaldehyde.

[0021] Preferably, the amount of acid injected is not less than twice the wellbore volume corresponding to the target well section, which is the section from the thermal reservoir location to the bottom of the well.

[0022] Preferably, the injection pump pressure of the acid solution is 2.6 to 4 MPa.

[0023] Preferably, the simmering time in step S2 is no less than 4 hours.

[0024] Preferably, the water injection rate for hydraulic fracturing in step S4 is 10-15 L / s.

[0025] In this invention, the method for hydraulic fracturing the geothermal reservoir of a geothermal well includes the following steps: continuously injecting water into the geothermal well, with the injection time determined by pressure changes displayed on the water pump pressure gauge. When the pressure gauge suddenly drops, the pump is stopped, ending the water injection. At this point, the blockage in the geothermal reservoir has been completely cleared, achieving the repair objective. During hydraulic fracturing, water is continuously injected; once the pressure suddenly drops, the repair objective is achieved. The water injection volume and injection / discharge rate are determined based on the specific conditions of each well.

[0026] Preferably, in step S1, liquid carbon dioxide is injected through the drill pipe used for geothermal drilling; in step S2, acid is injected through the drill pipe used for geothermal drilling; in step S3, liquid carbon dioxide is injected through the drill pipe used for geothermal drilling; and in step S4, water is injected through the drill pipe used for geothermal drilling.

[0027] The geothermal well reservoir repair method of the present invention employs a repair device including a drill pipe, a wellhead sealing device, a vent pipe, a liquid carbon dioxide storage device, a liquid carbon dioxide delivery pipeline, an acid storage device, an acid delivery pipeline, a clean water storage device, a clean water delivery pipeline, and a main material delivery pipeline. The wellhead sealing device is used to seal the geothermal wellhead. The vent pipe is sealed and installed on the wellhead sealing device. The outlet of the liquid carbon dioxide storage device is connected to the inlet of the liquid carbon dioxide delivery pipeline. The outlet of the acid storage device is connected to the inlet of the acid delivery pipeline. The outlet of the clean water storage device is connected to the inlet of the clean water delivery pipeline. The outlets of the liquid carbon dioxide delivery pipeline, the acid delivery pipeline, and the clean water delivery pipeline are all connected to the main material delivery pipeline. The outlet of the main material delivery pipeline is connected to the drill pipe. The main material delivery pipeline is used to deliver liquid carbon dioxide, acid, and clean water into the drill pipe.

[0028] The geothermal well reservoir repair device of the present invention is obtained by combining on-site equipment and drill pipe, without the need for specialized large air compressors and fracturing trucks, and has the advantages of low cost and convenient operation.

[0029] To ensure ease of operation, the repair device also includes a mud pump, which is installed on the main material conveying pipeline and is used to pump acid and water into the drill pipe. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the repair device used in the geothermal well reservoir repair method of Embodiment 1 of the present invention;

[0031] The attached diagram is labeled as follows: 1-Wellhead sealing device; 2-Blowout pipe; 3-Liquid carbon dioxide storage tank; 4-Mud pump; 5-Clean water storage tank; 6-Acid storage tank; 7-Main material conveying pipeline; 8-Underground drill pipe; 9-Surface drill pipe; 10-Slag discharge valve; 11-Carbon dioxide pressure gauge; 12-Carbon dioxide control valve; 13-Clean water control valve; 14-Acid control valve; 15-Liquid control valve; 16-Well casing. Detailed Implementation

[0032] The geothermal well reservoir repair method of this invention is a pioneering invention. The method involves first injecting liquid carbon dioxide into the geothermal well. The liquid carbon dioxide changes from a liquid to a gaseous state, forming a gas-water-solid mixture within the well, artificially creating a blowout. During the high-speed blowout, solid materials and waste drilling fluid are carried to the surface, and a negative pressure is generated within the wellbore, carrying away some of the blockages in the reservoir. If the material discharged from the well after the first venting is still turbid, the above operation can be repeated until clear water returns from the wellhead. Then, based on the lithology of the geothermal reservoir and the chemical properties of the plugging filling material, different acids are selected to acidify the geothermal reservoir. Under high pressure, the acid penetrates into the fractures, destroying and dissolving clay and carbonate filling materials. The gas produced by the chemical reaction is then vented according to the regulations. Next, liquid carbon dioxide is used for a second slag removal, which can remove the large amount of loose products or mud (mud-like mixture in the well) produced by the chemical reaction between the acid and the geothermal reservoir plugging material from the surface. Finally, hydraulic fracturing is performed on the geothermal reservoir to completely clear the plugging material, achieving the purpose of repair and increased production.

[0033] The geothermal well reservoir repair method of this invention comprises four steps, which are interconnected and operated continuously, enabling rapid wellbore cleaning, acid dissolution, re-cleaning, and reservoir fracture propagation. This invention replaces the existing traditional single-air compressor well washing and fracturing repair method with a comprehensive physical and chemical repair method. It features simplicity, practicality, low cost, high efficiency, avoidance of secondary damage, and significant effects. Compared with traditional methods, the average geothermal resource volume (single well water volume) can be increased by more than 200%, and the repair cost of this method is only 1 / 10 of the traditional method, with a repair rate of over 98%.

[0034] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0035] Example 1

[0036] The geothermal well reservoir repair method in this embodiment adopts, as follows: Figure 1 The repair device shown will be implemented. Before describing the repair method, the repair device will be briefly introduced.

[0037] The repair device includes drill pipe, wellhead sealing device 1, vent pipe 2, liquid carbon dioxide storage tank 3, liquid carbon dioxide delivery pipeline, mud pump 4, clean water storage tank 5, clean water delivery pipeline, acid storage tank 6, acid delivery pipeline, and main material delivery pipeline 7; the drill pipe includes underground drill pipe 8 and surface drill pipe 9; the wellhead sealing device 1 is used to seal the wellhead of the geothermal well and is located at the top of the well pipe 16; there are 3 vent pipes 2, and each of the 3 vent pipes 2 has a slag discharge valve 10 installed at its outlet; the outlet of the liquid carbon dioxide delivery pipeline is connected to the main material delivery pipeline 7, and the liquid carbon dioxide... A carbon dioxide pressure gauge 11 and a carbon dioxide control valve 12 are installed on the carbon dioxide conveying pipeline; the outlet of the clean water conveying pipeline is connected to the main material conveying pipeline 7, and a clean water control valve 13 is installed on the clean water conveying pipeline; the inlet of the main material conveying pipeline 7 is connected to the outlet of the acid conveying pipeline, and an acid control valve 14 is installed on the main material conveying pipeline 7 near its inlet; a liquid control valve 15 is also installed on the main material conveying pipeline 7; a mud pump 4 is located on the main material conveying pipeline 7 and is used to pump the liquid from the clean water storage tank 5 or the acid storage tank 6 into the geothermal well. In this embodiment, the outer diameter of the drill pipe is 89 mm, the outer diameter of the well pipe 16 is 340 mm, and the outer diameter of the blowout pipe 2 is 100 mm; the liquid carbon dioxide storage tank 3 consists of several carbon dioxide cylinders, each cylinder containing 40 L of liquid carbon dioxide, and there are 15 carbon dioxide cylinders in total.

[0038] The geothermal well reservoir repair method in this embodiment uses geothermal well A (the basic parameters of geothermal well A are as follows: depth is 1800m, reservoir lithology is igneous rock-andesite, fractures are relatively developed, and the single well water volume before repair is 9m³). 3 Taking / h) as an example, the specific steps include:

[0039] (1) Lower the drill pipe to a depth of 600m in the well. The liquid column pressure at this position is 6MPa, which is suitable for the injection of liquid carbon dioxide. Then install the wellhead sealing device 1 to keep the wellhead closed, and at the same time keep the slag discharge valve 10 closed and close the liquid control valve 15. After all the valves of the 15 carbon dioxide cylinders are opened, open the carbon dioxide control valve 12 to inject liquid carbon dioxide into the geothermal well. Let the well stand for 5 minutes, and then open the slag discharge valve 10 to release the liquid. The liquid carbon dioxide changes from liquid to gas and forms a mixture of gas, water and solid in the well, which artificially creates a blowout. During the high-speed blowout, on the one hand, it carries the solids and waste drilling fluid in the well and on the other hand, it creates a negative pressure in the wellbore, which can carry out some of the blockages in the thermal reservoir. If the discharge from the well is still turbid after the first blowout, the above operation can be repeated until clear water returns from the geothermal wellhead.

[0040] In this embodiment, after the geothermal well was flushed once with liquid carbon dioxide, the liquid discharged from the well at the end of the venting was clear water, indicating that the carbon dioxide flushing operation had brought the solids and waste drilling fluid out of the well to the surface; in this embodiment, all the liquid carbon dioxide in the 15 carbon dioxide cylinders was injected within 15 minutes.

[0041] (2) After step (1) is completed, the hot reservoir filling material cannot be cleaned up. At this time, the drill pipe in the well is lowered into the hot reservoir position, and the slag discharge valve 10, carbon dioxide control valve 12 and water control valve 13 are closed, and the liquid control valve 15 and acid control valve 14 are opened.

[0042] Since the thermal reservoir lithology in this embodiment is igneous rock and the plugging and filling materials are mud and rock cuttings, acid is injected into the thermal reservoir location through mud pump 4. Under high pressure, the acid penetrates into the fractures, destroying and dissolving the clay-like filling materials. After the acid injection is completed, the well is shut in for 4 hours, and then the slag discharge valve 10 is opened to release the gas generated by the chemical reaction according to the procedure requirements.

[0043] In this embodiment, the acid solution is composed of an acidic compound, water, and a corrosion inhibitor. The acidic compound is HCl, and the corrosion inhibitor is formaldehyde. The mass fraction of the corrosion inhibitor in the acid solution is 2%, and the mass fraction of the acidic compound is 30%. The injection pump pressure of the acid solution is 2.6 MPa, and the injection volume of the acid solution is 1000 kg. In this embodiment, the injection volume of the acid solution is twice the wellbore volume corresponding to the target well section. The target well section is the section from the thermal reservoir location to the bottom of the well.

[0044] (3) Lower the drill pipe to a depth of 600m in the well. The liquid column pressure at this position is 6MPa, which is suitable for the injection of liquid carbon dioxide. Then install the wellhead sealing device 1 to keep the wellhead closed, and at the same time keep the slag discharge valve 10 closed and close the liquid control valve 15. After all the valves of the 15 carbon dioxide cylinders are opened, open the carbon dioxide control valve 12 to inject liquid carbon dioxide into the geothermal well. Let the well stand for 5 minutes, and then open the slag discharge valve 10 to release the liquid. The liquid carbon dioxide changes from liquid to gas and forms a mixture of gas, water and solid in the well, artificially creating a blowout. During the high-speed blowout, on the one hand, it carries the solids and waste drilling fluid in the well and on the other hand, it creates a negative pressure in the wellbore, which can carry out some of the blockages in the thermal reservoir. If the discharge from the well is still turbid after the first blowout, the above operation can be repeated until clear water returns from the geothermal wellhead.

[0045] In this embodiment, after the geothermal well was flushed once with liquid carbon dioxide, the liquid discharged from the well at the end of the venting was clear water, indicating that the carbon dioxide flushing operation had brought the solids and waste liquid in the well to the surface; in this embodiment, all the liquid carbon dioxide in the 15 carbon dioxide cylinders was injected within 15 minutes.

[0046] (4) Close the slag discharge valve 10, carbon dioxide control valve 12 and acid control valve 14, and open the clean water control valve 13 and liquid control valve 15 at the same time. Continuously inject surface clean water into the well through mud pump 4. The continuous water injection time is determined according to the pressure change of the pressure gauge of mud pump 4. When the pressure gauge pressure suddenly drops, the pump can be stopped to end the injection of clean water. At this time, it means that the blockage of the thermal reservoir has been completely cleared and the repair purpose has been achieved.

[0047] In this embodiment, the injection rate of clean water is 10 L / s. When the injection time reaches 0.3 h, the pressure gauge pressure drops from 2.6 MPa to 0.2 MPa, indicating that the blockage in the thermal reservoir has been completely cleared and the hydraulic fracturing is terminated.

[0048] Example 2

[0049] The geothermal well reservoir repair method in this embodiment is implemented using the same repair device as in Embodiment 1. The difference is that the outer diameter of the drill pipe in this embodiment is 89mm, the outer diameter of the well pipe 16 is 273mm, and the outer diameter of the blowout pipe 2 is 100mm.

[0050] The geothermal well reservoir repair method in this embodiment uses geothermal well B (the basic parameters of geothermal well B are as follows: well depth is 2000m, lithology is metamorphic rock-marble, low degree of fracture development, and single well water volume is 6m³ before repair). 3 Taking / h) as an example, the specific steps include:

[0051] (1) Lower the drill pipe to a depth of 800m in the well. The height of the liquid column at this position is 120m, and the pressure of the liquid column in the well is between 6 and 8MPa. This pressure is suitable for the injection of liquid carbon dioxide. Then install the wellhead sealing device 1 to keep the wellhead closed. At the same time, keep the slag discharge valve 10 closed and close the liquid control valve 15. After all the valves of the 15 carbon dioxide cylinders are opened, open the carbon dioxide control valve 12 to inject liquid carbon dioxide into the geothermal well. Let the well stand for 10 minutes, and then open the slag discharge valve 10 to release the liquid. The liquid carbon dioxide changes from liquid to gas and forms a mixture of gas, water and solid in the well, artificially creating a blowout. During the high-speed blowout, on the one hand, it carries the solids and waste drilling fluid in the well and on the other hand, it creates a negative pressure in the wellbore, which can carry out some of the blockages in the thermal reservoir. If the discharge from the well is still turbid after the first blowout, the above operation can be repeated until clear water returns from the geothermal wellhead.

[0052] In this embodiment, after the geothermal well was flushed once with liquid carbon dioxide, the liquid discharged from the well at the end of the venting was clear water, indicating that the carbon dioxide flushing operation had brought the solids and waste drilling fluid out of the well to the surface; in this embodiment, all the liquid carbon dioxide in the 15 carbon dioxide cylinders was injected within 10 minutes.

[0053] (2) After step (1) is completed, the hot reservoir filling material cannot be cleaned up. At this time, the drill pipe in the well is lowered into the hot reservoir position, and the slag discharge valve 10, carbon dioxide control valve 12 and water control valve 13 are closed, and the liquid control valve 15 and acid control valve 14 are opened.

[0054] Since the thermal reservoir lithology in this embodiment is marble, and the plugging and filling materials are carbonate rock fragments and clay mud, acid is injected into the thermal reservoir location through mud pump 4. Under high pressure, the acid penetrates into the fractures, destroying and dissolving the clay and carbonate filling materials. After the acid injection is completed, the well is shut in for 8 hours, and then the slag discharge valve 10 is opened to release the gas generated by the chemical reaction according to the procedure.

[0055] In this embodiment, the acid solution is composed of an acidic compound, water, and a corrosion inhibitor. The acidic compound is HCl, and the corrosion inhibitor is formaldehyde. The mass fraction of the corrosion inhibitor in the acid solution is 2%, and the mass fraction of the acidic compound is 30%. The injection pump pressure of the acid solution is 3MPa, and the injection volume of the acid solution is 3000kg. In this embodiment, the injection volume of the acid solution is twice the wellbore volume corresponding to the target well section. The target well section is the section from the location of the thermal reservoir to the bottom of the well.

[0056] (3) Lower the drill pipe to a depth of 800m in the well. At this position, the liquid column height is 120m and the liquid column pressure in the well is between 6 and 8MPa. This pressure is suitable for the injection of liquid carbon dioxide. Then install the wellhead sealing device 1 to keep the wellhead closed. At the same time, keep the slag discharge valve 10 closed and close the liquid control valve 15. After all the valves of the 15 carbon dioxide cylinders are opened, open the carbon dioxide control valve 12 to inject liquid carbon dioxide into the geothermal well. Let the well sit for 10 minutes, then open the slag discharge valve 10 to release the liquid. The liquid carbon dioxide changes from liquid to gas and forms a mixture of gas, water and solid in the well, artificially creating a blowout. During the high-speed blowout, on the one hand, it carries the solids and waste drilling fluid in the well and on the other hand, it creates negative pressure in the wellbore, which can carry out some of the blockages in the thermal reservoir. If the discharge from the well is still turbid after the first blowout, the above operation can be repeated until clear water returns from the geothermal wellhead.

[0057] In this embodiment, after the geothermal well was flushed once with liquid carbon dioxide, the liquid discharged from the well at the end of the venting was clear water, indicating that the carbon dioxide flushing operation had brought the solids and waste drilling fluid out of the well to the surface; in this embodiment, all the liquid carbon dioxide in the 15 carbon dioxide cylinders was injected within 10 minutes.

[0058] (4) Close the slag discharge valve 10, carbon dioxide control valve 12 and acid control valve 14, and open the clean water control valve 13 and liquid control valve 15 at the same time. Continuously inject surface clean water into the well through mud pump 4. The continuous water injection time is determined according to the pressure change of the pressure gauge of mud pump 4. When the pressure gauge pressure suddenly drops, the pump can be stopped to end the injection of clean water. At this time, it means that the blockage of the thermal reservoir has been completely cleared and the repair purpose has been achieved.

[0059] In this embodiment, the injection rate of clean water is 15L / s. When the pressure gauge pressure drops from 3MPa to 0.6MPa, it indicates that the blockage in the thermal reservoir has been completely cleared, and the hydraulic fracturing is terminated.

[0060] Example 3

[0061] The geothermal well reservoir repair method in this embodiment is implemented using the same repair device as in Embodiment 1. The difference is that the outer diameter of the drill pipe in this embodiment is 89mm, the outer diameter of the well pipe 16 is 340mm, and the outer diameter of the blowout pipe 2 is 100mm.

[0062] The geothermal well reservoir repair method in this embodiment uses geothermal well C (the basic parameters of geothermal well C are as follows: well depth is 2000m, lithology is sedimentary rock-Cambrian limestone, fractures are not well developed, and the single well water volume before repair is 4m³). 3 Taking / h) as an example, the specific steps include:

[0063] (1) Lower the drill pipe into the well to a position where the liquid column pressure is between 6 and 8 MPa, which is suitable for the injection of liquid carbon dioxide. Then install the wellhead sealing device 1 to keep the wellhead closed, and at the same time keep the slag discharge valve 10 closed and close the liquid control valve 15. After all the valves of the 15 carbon dioxide cylinders are opened, open the carbon dioxide control valve 12 to inject liquid carbon dioxide into the geothermal well. Let the well sit for 7 minutes, and then open the slag discharge valve 10 to release the liquid. The liquid carbon dioxide changes from liquid to gas and forms a mixture of gas, water and solid in the well, artificially creating a blowout. During the high-speed blowout, on the one hand, it carries the solids and waste drilling fluid from the well and the bottom of the well to the surface, and on the other hand, it creates a negative pressure in the wellbore, which can carry out some of the blockages in the thermal reservoir. If the discharge from the well is still turbid after the first blowout, the above operation can be repeated until clear water returns from the geothermal wellhead.

[0064] In this embodiment, after the geothermal well was flushed once with liquid carbon dioxide, the liquid discharged from the well at the end of the venting was clear water, indicating that the carbon dioxide flushing operation had brought the solids and waste drilling fluid out of the well to the surface; in this embodiment, all the liquid carbon dioxide in the 15 carbon dioxide cylinders was injected within 15 minutes.

[0065] (2) After step (1) is completed, the hot reservoir filling material cannot be cleaned up. At this time, the drill pipe in the well is lowered into the hot reservoir position, and the slag discharge valve 10, carbon dioxide control valve 12 and water control valve 13 are closed, and the liquid control valve 15 and acid control valve 14 are opened.

[0066] Since the thermal reservoir lithology in this embodiment is marble, and the plugging and filling materials are carbonate rock fragments and clay mud, acid is injected into the thermal reservoir location through mud pump 4. Under high pressure, the acid penetrates into the fractures, destroying and dissolving the clay and carbonate filling materials. After the acid injection is completed, the well is shut in for 6 hours, and then the slag discharge valve 10 is opened to release the gas generated by the chemical reaction according to the procedure.

[0067] In this embodiment, the acid solution is composed of an acidic compound, water, and a corrosion inhibitor. The acidic compound is HCl, and the corrosion inhibitor is formaldehyde. The mass fraction of the corrosion inhibitor in the acid solution is 2%, and the mass fraction of the acidic compound is 30%. The injection pump pressure of the acid solution is 4 MPa. In this embodiment, the injection volume of the acid solution is twice the wellbore volume corresponding to the target well section. The target well section is the section from the thermal reservoir location to the bottom of the well.

[0068] (3) Lower the drill pipe to a position in the well where the liquid column pressure is between 6 and 8 MPa, which is suitable for the injection of liquid carbon dioxide. Then install the wellhead sealing device 1 to keep the wellhead closed, and at the same time keep the slag discharge valve 10 closed and close the liquid control valve 15. After all the valves of the 15 carbon dioxide cylinders are opened, open the carbon dioxide control valve 12 to inject liquid carbon dioxide into the geothermal well. Let the well sit for 7 minutes, and then open the slag discharge valve 10 to release the liquid. The liquid carbon dioxide changes from liquid to gas and forms a mixture of gas, water and solid in the well, artificially creating a blowout. During the high-speed blowout, on the one hand, it carries solids and waste drilling fluid from the well and the bottom of the well to the surface, and on the other hand, it creates negative pressure in the wellbore, which can carry out some of the blockages in the thermal reservoir. If the discharge from the well is still turbid after the first blowout, the above operation can be repeated until clear water returns from the geothermal wellhead.

[0069] In this embodiment, after the geothermal well was flushed once with liquid carbon dioxide, the liquid discharged from the well at the end of the venting was clear water, indicating that the carbon dioxide flushing operation had brought the solids and waste drilling fluid out of the well to the surface; in this embodiment, all the liquid carbon dioxide in the 15 carbon dioxide cylinders was injected within 15 minutes.

[0070] (4) Close the slag discharge valve 10, carbon dioxide control valve 12 and acid control valve 14, and open the clean water control valve 13 and liquid control valve 15 at the same time. Continuously inject surface clean water into the well through mud pump 4. The continuous water injection time is determined according to the pressure change of the pressure gauge of mud pump 4. When the pressure gauge pressure suddenly drops, the pump can be stopped to end the injection of clean water. At this time, it means that the blockage of the thermal reservoir has been completely cleared and the repair purpose has been achieved.

[0071] In this embodiment, the injection rate of clean water is 10L / s. When the pressure gauge pressure drops from 9MPa to 1.8MPa, it indicates that the blockage in the thermal reservoir has been completely cleared, and the hydraulic fracturing is terminated.

[0072] Example 4

[0073] The geothermal well reservoir repair method in this embodiment is implemented using the same repair device as in Embodiment 1. The difference is that the outer diameter of the drill pipe in this embodiment is 89mm, the outer diameter of the well pipe 16 is 340mm, and the outer diameter of the blowout pipe 2 is 100mm.

[0074] The geothermal well reservoir repair method in this embodiment uses geothermal well D (the basic parameters of geothermal well D are as follows: well depth is 2200m, lithology is sedimentary rock - Guantao Formation sandstone, with relatively developed pores, and the single well water volume before repair is 60m³). 3 Taking / h) as an example, the specific steps include:

[0075] (1) Lower the drill pipe into the well to a position where the liquid column pressure is between 6 and 8 MPa, which is suitable for the injection of liquid carbon dioxide. Then install the wellhead sealing device 1 to keep the wellhead closed, and at the same time keep the slag discharge valve 10 closed and close the liquid control valve 15. After all the valves of the 15 carbon dioxide cylinders are opened, open the carbon dioxide control valve 12 to inject liquid carbon dioxide into the geothermal well. Let the well sit for 9 minutes, and then open the slag discharge valve 10 to release the liquid. The liquid carbon dioxide changes from liquid to gas and forms a mixture of gas, water and solid in the well, artificially creating a blowout. During the high-speed blowout, on the one hand, it carries solids and waste drilling fluid from the well and the bottom of the well to the surface, and on the other hand, it creates negative pressure in the wellbore, which can carry out some of the blockages in the thermal reservoir. If the discharge from the well is still turbid after the first blowout, the above operation can be repeated until clear water returns from the geothermal wellhead.

[0076] In this embodiment, after the geothermal well was flushed once with liquid carbon dioxide, the liquid discharged from the well at the end of the venting was clear water, indicating that the carbon dioxide flushing operation had brought the solids and waste drilling fluid out of the well to the surface; in this embodiment, all the liquid carbon dioxide in the 15 carbon dioxide cylinders was injected within 15 minutes.

[0077] (2) After step (1) is completed, the hot reservoir filling material cannot be cleaned up. At this time, the drill pipe in the well is lowered into the hot reservoir position, and the slag discharge valve 10, carbon dioxide control valve 12 and water control valve 13 are closed, and the liquid control valve 15 and acid control valve 14 are opened.

[0078] Since the thermal reservoir lithology in this embodiment is marble, and the plugging and filling materials are carbonate rock fragments and clay mud, acid is injected into the thermal reservoir location through mud pump 4. Under high pressure, the acid penetrates into the fractures, destroying and dissolving the clay and carbonate filling materials. After the acid injection is completed, the well is shut in for 6 hours, and then the slag discharge valve 10 is opened to release the gas generated by the chemical reaction according to the procedure.

[0079] In this embodiment, the acid solution is composed of an acidic compound, water, and a corrosion inhibitor. The acidic compound is HCl, and the corrosion inhibitor is formaldehyde. The mass fraction of the corrosion inhibitor in the acid solution is 2%, and the mass fraction of the acidic compound is 30%. The injection pump pressure of the acid solution is 4 MPa. In this embodiment, the injection volume of the acid solution is twice the wellbore volume corresponding to the target well section. The target well section is the section from the thermal reservoir location to the bottom of the well.

[0080] (3) Lower the drill pipe into the well to a position where the liquid column pressure is between 6 and 8 MPa, which is suitable for the injection of liquid carbon dioxide. Then install the wellhead sealing device 1 to keep the wellhead closed, and at the same time keep the slag discharge valve 10 closed and close the liquid control valve 15. After all the valves of the 15 carbon dioxide cylinders are opened, open the carbon dioxide control valve 12 to inject liquid carbon dioxide into the geothermal well. Let the well sit for 9 minutes, and then open the slag discharge valve 10 to release the liquid. The liquid carbon dioxide changes from liquid to gas and forms a mixture of gas, water and solid in the well, artificially creating a blowout. During the high-speed blowout, on the one hand, it carries the solids and waste drilling fluid from the well and the bottom of the well to the surface, and on the other hand, it creates a negative pressure in the wellbore, which can carry out some of the blockages in the thermal reservoir. If the discharge from the well is still turbid after the first blowout, the above operation can be repeated until clear water returns from the geothermal wellhead.

[0081] In this embodiment, after the geothermal well was flushed once with liquid carbon dioxide, the liquid discharged from the well at the end of the venting was clear water, indicating that the carbon dioxide flushing operation had brought the solids and waste drilling fluid out of the well to the surface; in this embodiment, all the liquid carbon dioxide in the 15 carbon dioxide cylinders was injected within 15 minutes.

[0082] (4) Close the slag discharge valve 10, carbon dioxide control valve 12 and acid control valve 14, and open the clean water control valve 13 and liquid control valve 15 at the same time. Continuously inject surface clean water into the well through mud pump 4. The continuous water injection time is determined according to the pressure change of the pressure gauge of mud pump 4. When the pressure gauge pressure suddenly drops, the pump can be stopped to end the injection of clean water. At this time, it means that the blockage of the thermal reservoir has been completely cleared and the repair purpose has been achieved.

[0083] In this embodiment, the injection rate of clean water is 13 L / s. When the pressure gauge pressure drops from 7.8 MPa to 0.7 MPa, it indicates that the blockage in the thermal reservoir has been completely cleared, and the hydraulic fracturing is terminated.

[0084] Comparative Example 1

[0085] The difference between the geothermal well reservoir repair method in this comparative example and the geothermal well reservoir repair method in Example 1 is that this comparative example repairs geothermal well E (geothermal well E is the adjacent well of geothermal well A in Example 1, and the parameters of geothermal well E and geothermal well A are similar), and when repairing geothermal well E, step (1) is omitted, and the amount of liquid carbon dioxide injected in step (3) of this comparative example is equal to the sum of the amount of liquid carbon dioxide injected in steps (1) and (3) of Example 1.

[0086] Comparative Example 2

[0087] The only difference between the geothermal well reservoir repair method in this comparative example and the geothermal well reservoir repair method in Example 2 is that this comparative example repairs geothermal well F (geothermal well F is the adjacent well of geothermal well B in Example 2, and the parameters of geothermal well F and geothermal well B are similar), and when repairing geothermal well F, step (3) is omitted, and the amount of liquid carbon dioxide injected in step (1) of this comparative example is equal to the sum of the amount of liquid carbon dioxide injected in steps (1) and (3) of Example 2.

[0088] Experimental Example

[0089] To evaluate the repair effect of the geothermal well reservoir repair methods in each embodiment, the water volume of each geothermal well before and after repair, as well as the well depth and reservoir lithology of each well, are listed in Table 1.

[0090] Table 1 shows the single-well water volume before and after repair of geothermal wells in each embodiment.

[0091]

Claims

1. A method for repairing geothermal well reservoirs, characterized in that, Includes the following steps: S1, using liquid carbon dioxide to flush the geothermal well until clean water returns from the wellhead; The method of using liquid carbon dioxide to clean geothermal wells includes the following steps: with the wellhead of the geothermal well in a closed state, liquid carbon dioxide is injected into the geothermal well, and after the well is sealed, the liquid is released and drained. S2, inject acid into the geothermal reservoir of the geothermal well, and then release the flow after the well is sealed; S3 uses liquid carbon dioxide to flush the geothermal well until clean water returns from the wellhead; S4 is used to hydraulically fracturing the geothermal reservoir of a geothermal well.

2. The geothermal well reservoir repair method as described in claim 1, characterized in that, When using liquid carbon dioxide to clean geothermal wells, the pressure of the liquid column in the well corresponding to the injection point of the liquid carbon dioxide is 6 to 8 MPa.

3. The geothermal well reservoir repair method as described in claim 1 or 2, characterized in that, In steps S1 and S3, the number of times the geothermal well is cleaned with liquid carbon dioxide is independently more than once.

4. The geothermal well reservoir repair method as described in claim 3, characterized in that, Each time liquid carbon dioxide is used to clean a geothermal well, the amount of liquid carbon dioxide injected is 600-800L.

5. The geothermal well reservoir repair method as described in claim 4, characterized in that, Each time liquid carbon dioxide is used to clean a geothermal well, the injection time is 10 to 15 minutes.

6. The geothermal well reservoir repair method as described in claim 1 or 2, characterized in that, When using liquid carbon dioxide to clean geothermal wells, the simmering time is 5 to 10 minutes.

7. The geothermal well reservoir repair method as described in claim 1, characterized in that, The acid solution is composed of an acidic compound, water, and a corrosion inhibitor; the acidic compound is HCl, oxalic acid, or fluoroboric acid; and the corrosion inhibitor is an aldehyde corrosion inhibitor.

8. The geothermal well reservoir repair method as described in claim 1 or 7, characterized in that, The amount of acid injected shall be no less than twice the wellbore volume corresponding to the target well section, which is the section from the thermal reservoir to the bottom of the well; the injection pump pressure of the acid shall be 2.6 to 4 MPa; the well simmering time in step S2 shall be no less than 4 hours.

9. The geothermal well reservoir repair method as described in claim 1, characterized in that, In step S4, the water injection rate for hydraulic fracturing is 10–15 L / s.

10. The geothermal well reservoir repair method as described in claim 1 or 2, characterized in that, The geothermal well reservoir repair method employs a repair device including drill pipe, wellhead sealing device, vent pipe, liquid carbon dioxide storage device, liquid carbon dioxide delivery pipeline, acid storage device, acid delivery pipeline, clean water storage device, clean water delivery pipeline, and main material delivery pipeline. The wellhead sealing device is used to seal the geothermal wellhead. The vent pipe is sealed through the wellhead sealing device. The outlet of the liquid carbon dioxide storage device is connected to the inlet of the liquid carbon dioxide delivery pipeline. The outlet of the acid storage device is connected to the inlet of the acid delivery pipeline. The outlet of the clean water storage device is connected to the inlet of the clean water delivery pipeline. The outlets of the liquid carbon dioxide delivery pipeline, the acid delivery pipeline, and the clean water delivery pipeline are all connected to the main material delivery pipeline. The outlet of the main material delivery pipeline is connected to the drill pipe. The main material delivery pipeline is used to deliver liquid carbon dioxide, acid, and clean water into the drill pipe.

Images