System and method for mineralizing and storing CO2 by utilizing geothermal tail water

Abstract

The invention belongs to the technical field of geological storage of CO2, and particularly relates to a system and a method for mineralizing and storing CO2 by utilizing geothermal tail water. The invention discloses a system for mineralizing and sealing CO2 by utilizing geothermal tail water. The system comprises a CO2 mixing device and a geothermal water treatment device, a tail water inlet, a gas inlet and a liquid outlet are formed in the CO2 mixing device; the geothermal water treatment device is a geothermal heating or geothermal power generation device and is provided with a geothermal water inlet and a tail water outlet; the tail water inlet is communicated with the tail water outlet through a tail water conveying pipeline, the gas inlet is communicated with the CO2 gas collecting device through a gas pipeline, and the liquid outlet is communicated with the injection well through a liquid pipeline; the CO2 gas collecting device is connected with one end of a CO2 pipeline, the other end of the CO2 pipeline extends into the injection well, and a CO2 ejector is fixed in the injection well; and the geothermal water inlet is communicated with the geothermal water mining well through a pipeline. According to the system and method, geothermal resources in deep karst heat storage are exploited, and the requirement of the society for clean energy can be met.

Description

Technical Field

[0001] The present invention belongs to the technical field of CO2 geological storage, and relates to a system and method for mineralizing and storing CO2 using geothermal tail water. Background Art

[0002] In China's current energy structure, fossil energy accounts for up to 85%, of which coal accounts for nearly 70%.

[0003] The International Energy Agency (IEA) has shown that the safe storage of captured carbon dioxide will play a crucial role in the future of industry. Multiple studies have shown that it is feasible to store carbon dioxide in mafic rocks such as basalt. CO2 reacts with divalent cations (such as Ca 2+ , Mg 2+ and Fe 2+ ) dissolved from mafic rocks, resulting in the formation of various carbonate minerals and storing carbon on a geological time scale (McGrail et al., 2006). Carbonate minerals that may form include calcite (CaCO3), dolomite (Ca 0.5 Mg 0.5 CO3), magnesite (MgCO3), siderite (FeCO3), and ankerite (Ca(Fe,Mg)(CO3)2).

[0004] Carbonate rocks in China are widely distributed, and geothermal reservoir resources are rich. Carbonate rocks are formed by the supersaturation of calcium bicarbonate solution in nature and precipitation from water bodies. The mineral components of carbonate rocks are calcite and dolomite, and their main chemical components are calcium carbonate (CaCO3) or calcium magnesium carbonate (MaCa(CO3)2).

[0005] CO2 mineralization and storage is to convert CO2 into stable carbonate minerals, which can exist stably in the deep geological space of carbonate rocks for a long time and will not damage the deep karst geological environment, thus ensuring safe and permanent carbon storage and reducing greenhouse gas emissions.

[0006] How to combine the exploitation of geothermal energy from deep karst reservoirs with CO2 mineralization and storage to form an efficient energy utilization and environmental protection system is the key research direction of the present invention. Summary of the Invention

[0007] The purpose of the present invention is to provide a system and method for mineralizing and storing CO2 using geothermal tail water; this system and method can meet the social demand for clean energy by exploiting geothermal resources in deep karst reservoirs; and by injecting the captured CO2 into deep karst formations, long-term storage of CO2 can be achieved, thus mitigating the impact of global climate change.

[0008] To achieve the above purpose, the present invention provides the following technical solutions: A system for mineralizing and sequestering CO2 using geothermal tail water, comprising a CO2 mixing device and a geothermal water treatment device; the CO2 mixing device is provided with a tail water inlet, a gas inlet and a liquid outlet; the geothermal water treatment device is a geothermal heating or geothermal power generation device for converting and utilizing the high-temperature energy of geothermal water, and is provided with a geothermal water inlet and a tail water outlet; The tail water inlet is communicated with the tail water outlet through a tail water transportation pipeline, the gas inlet is communicated with a CO2 gas collection device through a gas pipeline, and the liquid outlet is communicated with an injection well through a liquid pipeline; One end of the CO2 gas collection device is connected to a CO2 pipeline, the other end of the CO2 pipeline extends into the injection well and a CO2 injector is fixed in the injection well; the geothermal water inlet is communicated with a geothermal water production well through a pipeline.

[0009] Preferably, the CO2 mixing device is a cuboid-shaped airtight reservoir, with a plurality of gas inlets opened at the bottom, and the plurality of gas inlets are arranged in a rectangular array; a tail water inlet is opened on the side.

[0010] Preferably, the setting depth of the CO2 injector is below 500 m underground.

[0011] In addition, the present invention also provides a method for mineralizing and sequestering CO2 using geothermal tail water, which adopts the above system and comprises the following steps: S1. Obtain formation data through geothermal exploration, select a carbonate rock reservoir suitable for heat storage heat extraction and well water recharge, and determine the positions and depths of the injection well and the geothermal water production well; S2. The geothermal tail water and CO2 gas generated after the exploited geothermal water is utilized by the geothermal water treatment device are fully mixed under a gas pressure of 3 MPa to obtain a CO2 aqueous solution; S3. Inject the CO2 aqueous solution obtained in step S2 into the injection well; meanwhile, the CO2 injector injects CO2 gas into the CO2 aqueous solution at a set mass flow rate, and then the CO2 aqueous solution diffuses into the carbonate rock reservoir through diffusion to complete the mineralization and sequestration of CO2.

[0012] Preferably, in step S1, the formation data includes the burial depth of the carbonate rock reservoir position, the reservoir thickness, the fracture condition of the reservoir, and the geothermal water temperature. The burial depth of the carbonate rock reservoir position exceeds 1000 m, the thickness of the carbonate rock reservoir is above 350 m, the carbonate rock reservoir has relatively developed fractures, the porosity of the fractures is greater than 0.05, the fracture probability is greater than 30%, the recharged geothermal water can be fully diffused, and the geothermal water temperature is above 50 °C.

[0013] Preferably, in step S1, the well depths and well spacings of the injection well and the geothermal water production well are determined according to the carbonate reservoir conditions. The well depths of both the injection well and the geothermal water production well are greater than 1000 m and less than or equal to 2000 m. The well diameters of the injection well and the geothermal water production well are 0.1 - 0.2 m, which can penetrate into the fractures of the carbonate reservoir. The straight-line distance between the injection well and the geothermal water production well is 400 - 1000 m.

[0014] Preferably, in step S2, the temperature of the produced geothermal water > 55 °C, and the pH value is 7 - 8. The temperature of the geothermal tail water utilized by the geothermal water treatment device > 27 °C, and the pH value is 7 - 8.

[0015] Preferably, in step S2, the temperature of the obtained CO2 aqueous solution is the temperature of the geothermal tail water, the pressure is 3 Mpa, the CO2 concentration is 30 - 40 g / kg water; the pH value is 4 - 4.5.

[0016] Preferably, in step S3, the CO2 aqueous solution obtained in step S2 is injected into the injection well at a pressure of 10 - 12 MPa and a mass flow rate of 2 - 2.5 kg / s; and / or, the CO2 ejector injects CO2 gas into the CO2 aqueous solution at a mass flow rate of 10 - 60 g / s; the pressure of the CO2 gas is 3 Mpa.

[0017] Further preferably, it also includes regularly monitoring the pH value of the geothermal water extracted by the geothermal water production well, and adjusting the mass flow rate of the CO2 ejector according to its change situation; when the pH value changes by less than 0.2, the mass flow rate of the CO2 ejector is 60 g / s; when the pH value changes by 0.2 - 0.4, the mass flow rate of the CO2 ejector is 30 g / s; when the pH value changes by more than 0.4, the mass flow rate of the CO2 ejector is 10 g / s.

[0018] Compared with the closest prior art, the technical solution provided by the present invention has the following excellent effects: (1) For the system and method for mineralization and sequestration of CO2 using geothermal tail water of the present invention, on the one hand, by exploiting the geothermal resources in the deep karst thermal reservoir, it can meet the social demand for clean energy; on the other hand, by injecting the captured CO2 into the deep karst formation, long-term sequestration of CO2 can be achieved, thereby mitigating the impact of global climate change.

[0019] (2) The system and method for mineralizing and sequestering CO2 using geothermal tail water in the present invention dissolve CO2 in an aqueous solution by utilizing the waste heat of geothermal tail water through CO2 capture and industrial CO2 transportation. By applying pressure, the CO2 aqueous solution enters the deep karst environment, and carbonate minerals are produced through mineralization reactions to sequester a large amount of CO2, which can be stably sequestered in the underground space for a long time, with good economy and strong stability. The system can operate for a long time to achieve a large amount of CO2 sequestration. At the same time, the pH value of the groundwater can be detected regularly, and the mass flow rate of the CO2 gas can be adjusted, without damaging the geological environment of the deep karst, being environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The schematic diagrams in the specification forming a part of this application are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention. Among them: Figure 1 is a schematic diagram of the system for mineralizing and sequestering CO2 using geothermal tail water in the present invention; In the figure: 1 - CO2 mixing device; 2 - geothermal water treatment device; 11 - tail water inlet; 12 - gas inlet; 13 - liquid outlet; 21 - geothermal water inlet; 22 - tail water outlet; 3 - CO2 gas collection device; 4 - injection well; 31 - CO2 pipeline; 5 - CO2 ejector; 6 - geothermal water production well.

[0021] Figure 2 is a schematic structural diagram of the CO2 mixing device of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0022] The present invention will be described in detail below with reference to the drawings and in conjunction with the embodiments. It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other.

[0023] In the description of the present invention, the orientation or positional relationships indicated by the terms "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", etc. are based on the orientation or positional relationships shown in the drawings, and are only for the convenience of describing the present invention rather than requiring the present invention to be constructed and operated in a specific orientation, so it should not be construed as a limitation to the present invention. The terms "connected" and "coupled" used in the present invention should be understood in a broad sense. For example, it can be a fixed connection or a detachable connection; it can be directly connected or indirectly connected through an intermediate component. For those of ordinary skill in the art, the specific meanings of the above terms can be understood according to specific circumstances.

[0024] According to the first aspect of the present invention, there is provided a system for mineralizing and sequestering CO2 using geothermal tail water, as Figure 1As shown, it includes a CO2 mixing device 1 and a geothermal water treatment device 2; the CO2 mixing device 1 is provided with a tail water inlet 11, a gas inlet 12 and a liquid outlet 13; the geothermal water treatment device 2 is provided with a geothermal water inlet 21 and a tail water outlet 22; The tail water inlet 11 is communicated with the tail water outlet 22 through a tail water transportation pipeline, the gas inlet 12 is communicated with a CO2 gas collection device 3 through a gas pipeline, and the liquid outlet 13 is communicated with an injection well 4 through a liquid pipeline; One end of the CO2 gas collection device 3 is connected to a CO2 pipeline 31, the other end of the CO2 pipeline 31 extends into the injection well 4 and a CO2 injector 5 is fixed in the injection well 4; the geothermal water inlet 21 is communicated with a geothermal water production well 6 through a pipeline.

[0025] After the geothermal water is extracted from the geothermal water production well 6, it enters the geothermal water treatment device 2. The geothermal water treatment device 2 includes but is not limited to a geothermal heating or geothermal power generation device, and the geothermal water is used for heating, power generation, etc.; the geothermal tail water discharged from the geothermal water treatment device 2 is introduced into the CO2 mixing device 1. At the same time, a part of the CO2 gas collected in the CO2 gas collection device 3 is transported to the CO2 mixing device 1 through a gas pipeline. The CO2 gas collection device 3 can be a CO2 gas collection tower or CO2 gas obtained from industrial transportation, and there is no restriction on the source of the CO2 gas. The CO2 mixing device 1 can be a cuboid-shaped closed reservoir, with a plurality of gas inlets opened at the bottom, and the plurality of gas inlets are arranged in a rectangular array, as Figure 2 shown; the CO2 gas enters the CO2 mixing device 1 through these gas inlets, and is fully mixed with the geothermal tail water to obtain a CO2 aqueous solution; the CO2 aqueous solution is introduced into the injection well 4, and at the same time the CO2 injector injects CO2 gas into the CO2 aqueous solution for pressurization, so that the CO2 aqueous solution enters the deep karst environment, and carbonate minerals are produced through mineralization reactions, which can be permanently and stably sealed in the underground space, realizing a large amount of CO2 sequestration. Preferably, the installation depth of the CO2 injector 5 is below 500 m underground.

[0026] According to the second aspect of the present invention, a method for mineralizing and sequestering CO2 using geothermal tail water is provided. The method adopts the system described in the first aspect, and includes the following steps: Step 1: Obtain formation data (such as the burial depth of carbonate rock reservoir, reservoir thickness, fracture conditions of the reservoir, geothermal water temperature, etc.) through geothermal exploration information. Select carbonate rock reservoirs suitable for heat extraction from the heat reservoir and reinjection of well water, and determine the locations and depths of injection wells and geothermal water production wells. The burial depth of the carbonate rock reservoir generally exceeds 1000m, the thickness of the carbonate rock reservoir is above 350m, the geothermal water temperature is above 50°C, the fractures in the reservoir are relatively developed, the porosity of the fractures is greater than 0.05, the fracture probability is greater than 30%, and the reinjected geothermal water can diffuse sufficiently. For deep karst areas, the depths of the production well and the injection well are similar, generally greater than 1000m. The straight-line distance between the production well and the injection well is generally between 400 and 1000m. The well diameters of the injection well and the geothermal water production well are 0.1 - 0.2m, which can penetrate into the fractures of the carbonate rock reservoir. The one-production-one-injection or geothermal well group mode can be adopted. It is also possible to choose to add a new CO2 mineralization and storage system to the existing deep karst heat reservoir heat extraction system.

[0027] Step 2: The geothermal tail water and CO2 gas generated after the exploited geothermal water is utilized by the geothermal water treatment device are fully mixed under a gas pressure of 3MPa to obtain a CO2 aqueous solution. The temperature of the exploited geothermal water > 55°C, the pH value is 7 - 8, the temperature of the geothermal tail water generated after being utilized by the geothermal water treatment device > 27°C, and the pH value is 7 - 8; the concentration of the CO2 aqueous solution is 30 - 40g / kg water; the pH value is 4 - 4.5. CO2 dissolves in water and releases hydrogen ions. The reaction formula is as follows: CO2 + H2O → H2CO3 → HCO3 - + H + → CO3 2− + 2H + 。

[0028] Step 3: Inject the CO2 aqueous solution obtained in Step 2 into the injection well at a certain pressure and mass flow rate; meanwhile, the CO2 ejector injects CO2 gas into the CO2 aqueous solution at a set mass flow rate. Subsequently, the CO2 aqueous solution enters the carbonate rock reservoir to complete the mineralization and storage of CO2. The ejected CO2 gas is always under a water pressure of more than 10Mpa and less than or equal to 12Mpa. Since the depth of the injection well is generally higher than 1000m, the CO2 gas can be fully dissolved in the aqueous solution before leaving the injection well, and then a mineralization reaction occurs in the deep karst environment, converting into stable carbonate minerals and being stored in this environment. When the CO2 aqueous solution enters the carbonate rock reservoir, the carbonate rock undergoes dissolution and mineralization and reprecipitation.

[0029] Among them, the reaction formula for the dissolution of carbonate minerals is: CaCO3 + CO3 2- + 2H + ↔ Ca 2+ + 2HCO3- This reaction is a reversible reaction, and the reaction direction is affected by the carbonate concentration. After the reaction reaches equilibrium, karst water rich in CO2 is generated and migrates in the karst aquifer medium, spreading throughout the groundwater system.

[0030] The reaction formula for CO2 mineralization precipitation is: Ca 2+ + CO3 2- →CaCO3; The clay minerals that may exist in carbonate rocks can also react rapidly with carbonic acid. The diffused CO2 aqueous solution reacts with other components in the reservoir and is mineralized again to produce carbonate mineral precipitation. The reaction formula is as follows: Decomposition of silicate minerals releases divalent cations: (Fe,Mg)2SiO4 + 4H + →2(Fe,Mg) 2+ + SiO2 (solution) + 2H2O or CaAl2SiO8 + 8H + →Ca 2+ + 2Al 3+ + 2SiO2 (solution) + 4H2O Carbonate mineral precipitation: (Fe,Ca,Mg) 2+ + CO3 2− →(Fe,Ca,Mg)CO3.

[0031] In the above method for mineralizing and sequestering CO2 using geothermal tail water, as a preferred implementation method, in step three, the CO2 aqueous solution obtained in step two is injected into the injection well at a pressure of 10 - 12 MPa and a mass flow rate of 2 - 2.5 kg / s. Optionally, the CO2 ejector injects CO2 gas into the CO2 aqueous solution at a mass flow rate of 10 - 60 g / s; the pressure of the CO2 gas is 3 Mpa.

[0032] In the above method for mineralizing and sequestering CO2 using geothermal tail water, as a preferred embodiment, it further includes regularly monitoring the pH value of the geothermal water extracted by the geothermal water production well, and adjusting the mass flow rate of the CO2 ejector according to its change; when the pH value changes by less than 0.2, the mass flow rate of the CO2 ejector is 60 g / s; when the pH value changes between 0.2 and 0.4, the mass flow rate of the CO2 ejector is 30 g / s; when the pH value changes by more than 0.4, the mass flow rate of the CO2 ejector is 10 g / s. When the pH value changes by less than 0.2, the reinjected geothermal water has not fully diffused, and the carbonate rock reservoir has a large mineralization basis. A mass flow rate of 60 g / s for the CO2 ejector can increase the concentration of CO2, which is beneficial to a more complete mineralization reaction. When the pH value changes between 0.2 and 0.4, at this time, the mineralization reaction in the carbonate rock reservoir enters a stable stage, and the mass flow rate of the CO2 ejector is 30 g / s, and the system can operate stably for a long time. When the pH value changes by more than 0.4, the geothermal water in the carbonate rock reservoir changes greatly, which may affect the deep karst geothermal environment. The mass flow rate of the CO2 ejector should be reduced to 10 g / s to ensure the stable operation of the system.

[0033] During the injection process, the CO2 gas in the solution and the CO2 gas released by the carbon dioxide ejector will escape in the deep high-temperature environment. In this application, high-pressure injection plus well depth limitation can ensure that the gas will not escape from the injection well. The ejected CO2 gas is always under a water pressure of more than 10 Mpa. Since the depth of the injection well is generally higher than 1000 m, the CO2 gas can be fully dissolved in the aqueous solution before leaving the injection well, and then a mineralization reaction occurs in the deep karst environment, transforming into stable carbonate minerals and being stored in this environment.

[0034] The radioactive isotope labeling method is used to quantitatively monitor and detect the dissolved and chemically transformed CO2. A low level of radioactive carbon-14 is used as a tracer to label the injected CO2. Among them, the ratio of carbon-14 to carbon-12 is 2×10 -11 , and the ratio of carbon-14 to carbon-12 is regularly detected through the production well to determine the proportion of CO2 retained and mineralized in the reservoir. Through detection, it can be obtained that the carbon-14 reaction appears on the 35th day, and the CO2 aqueous solution gradually diffuses in the reservoir, reaching the peak concentration after 318 days. Subsequently, with the progress of the mineralization reaction, the carbon-14 concentration gradually decreases. After 2 years, the ratio of carbon-14 to carbon-12 is 2.273×10 -12 , and the proportion of CO2 retained and mineralized in the reservoir is 88.64%.

[0035] Through calculation, it can be obtained that calculated by recharging 20,000 tons per year, the annual CO2 storage volume through geothermal water recharge is more than 600 tons, the annual CO2 storage volume through the CO2 ejector is more than 300 tons, and the annual CO2 storage volume using this system can reach more than 900 tons. Recharging the geothermal tail water into the original carbonate rock reservoir can prevent the chemical components of the geothermal tail water from polluting the ground environment, and the geothermal tail water does not need to be temperature-treated anymore, saving the cost of the heating process.

[0036] If industrial water is recharged and heated without using geothermal water, the annual recharging water volume is about 20,000 tons, the heating temperature is 20 °C, it is estimated that the industrial water is about 2 yuan per ton, and the heating cost is about 15.8 yuan per ton. Then, the annual recharging will cost 20,000×(2 + 15.8) = 356,000 yuan more.

[0037] In summary, the present invention captures CO2 and transports industrial CO2, dissolves CO2 in an aqueous solution, makes the CO2 aqueous solution enter the deep karst environment through pressurization, and generates carbonate minerals through mineralization reactions, which can be stably sealed in the underground space for a long time, with good economy and strong stability. The system can operate for a long time to achieve a large amount of CO2 storage. Through measurement, it can be obtained that the CO2 storage rate can reach more than 85% within 2 years, and the storage effect is obvious. And the carbonate rock reservoir has been stably existing in the deep environment for more than thousands of years. Therefore, the mineralized carbonate rock reservoir can stably exist for thousands of years, with excellent stability. At the same time, the pH value change of the groundwater can be detected regularly, and the mass flow rate of the CO2 gas can be adjusted, which can effectively control the pH value of the geothermal water, ensure that the geothermal water remains weakly alkaline, and the deep karst environment will not be adversely affected by the slight change of the geothermal water, and will not damage the geological environment of the deep karst, which is beneficial to maintaining the long-term stable operation of the system and is environmentally friendly. The annual CO2 storage volume using this system can reach 600 - 1100 tons. Recharging the geothermal tail water into the original carbonate rock reservoir can prevent the chemical components of the geothermal tail water from polluting the ground environment, and the geothermal tail water does not need to be temperature-treated anymore, saving the cost of the heating process.

[0038] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, 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 system for storing CO2 by mineralization of geothermal tail water, characterized in that: It comprises a CO2 mixing device and a geothermal water treatment device; the CO2 mixing device is provided with a tail water inlet, a gas inlet and a liquid outlet; the geothermal water treatment device is a geothermal heating or geothermal power generation device, which is provided with a geothermal water inlet and a tail water outlet; The tail water inlet is connected to the tail water outlet through a tail water transport pipeline, the gas inlet is connected to the CO2 gas collection device through a gas pipeline, and the liquid outlet is connected to the injection well through a liquid pipeline; The CO2 gas collection device is connected to one end of the CO2 pipeline, the other end of the CO2 pipeline extends into the injection well and a CO2 injector is fixed in the injection well; the geothermal water inlet is connected to the geothermal water extraction well through a pipeline.

2. The system for storing CO2 by mineralization of geothermal tail water according to claim 1, characterized in that: The CO2 mixing device is a rectangular closed water storage tank, with a plurality of gas inlets opened at the bottom, and the plurality of gas inlets are arranged in a rectangular array; and a tail water inlet is opened on the side.

3. The system for storing CO2 by mineralization of geothermal tail water according to claim 1, characterized in that: The CO2 injector is installed at a depth of less than 500m underground.

4. A method for storing CO2 by mineralization of geothermal tail water, characterized in that: The system according to any one of claims 1 to 3 is used, comprising the following steps: S1. Obtain formation data through geothermal exploration, select carbonate reservoirs suitable for heat storage and well water reinjection, and determine the location and depth of injection wells and geothermal water extraction wells; S2. The geothermal tail water and CO2 gas generated after the exploited geothermal water is used by the geothermal water treatment device are fully mixed at a gas pressure of 3MPa to obtain a CO2 aqueous solution; S3. Inject the CO2 aqueous solution obtained in step S2 into the injection well; at the same time, the CO2 injector injects CO2 gas into the CO2 aqueous solution at a set mass flow rate, and then the CO2 aqueous solution diffuses into the carbonate reservoir to complete the mineralization and storage of CO2.

5. The method for storing CO2 by mineralization of geothermal tail water according to claim 4, characterized in that: In step S1, the formation data includes the burial depth of the carbonate reservoir location, the reservoir thickness, the reservoir fracture conditions, and the geothermal water temperature. The burial depth of the carbonate reservoir location exceeds 1000m, the thickness of the carbonate reservoir is above 350m, and the geothermal water temperature is above 50°C.

6. The method for storing CO2 by mineralization of geothermal tail water according to claim 4, characterized in that: In step S1, the depth and spacing of the injection well and the geothermal water extraction well are determined according to the carbonate reservoir conditions. The depths of the injection well and the geothermal water extraction well are both greater than 1000m and less than or equal to 2000m. The diameters of the injection well and the geothermal water extraction well are 0.1-0.2m, which can penetrate deep into the fractures of the carbonate reservoir. The straight-line distance between the injection well and the geothermal water extraction well is 400-1000m.

7. The method for storing CO2 by mineralization of geothermal tail water according to claim 4, characterized in that: In step S2, the temperature of the mined geothermal water is greater than 55°C, and the pH value is 7-8. The temperature of the geothermal tail water produced by the geothermal water treatment device is greater than 27°C, and the pH value is 7-8.

8. The method for storing CO2 by mineralization of geothermal tail water according to claim 4, characterized in that: In step S2, the temperature of the obtained CO2 aqueous solution is the geothermal tail water temperature, the pressure is 3Mpa, the CO2 concentration is 30-40g / kg water; and the pH value is 4-4.

5.

9. The method for storing CO2 by mineralization of geothermal tail water according to claim 4, characterized in that: In step S3, the CO2 aqueous solution obtained in step S2 is injected into the injection well at a pressure of 10 to 12 MPa and a mass flow rate of 2 to 2.5 kg / s; And / or, the CO2 injector injects CO2 gas into the CO2 aqueous solution at a mass flow rate of 10 to 60 g / s; the CO2 gas pressure is 3 MPa.

10. The method for storing CO2 by mineralization of geothermal tail water according to claim 9, characterized in that: It also includes regular monitoring of the pH value of geothermal water extracted from geothermal water extraction wells, and adjusting the mass flow rate of the CO2 injector according to its changes; when the pH value changes below 0.2, the mass flow rate of the CO2 injector is 60g / s; when the pH value changes between 0.2 and 0.4, the mass flow rate of the CO2 injector is 30g / s; when the pH value changes above 0.4, the mass flow rate of the CO2 injector is 10g / s.

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