A method for improving underground energy recovery efficiency of compressed air energy storage in saline aquifers

Abstract

The present invention provides a method for improving the underground energy recovery efficiency of compressed air energy storage in a saline layer, comprising finding out the deep geological conditions and properties of a target site, determining the position, structure and properties of a target gas storage saline layer, a cap rock and an underlying stratum; using numerical simulation calculations to determine the design scheme of a U-shaped working well, and selecting a U-shaped working well design scheme with high recovery efficiency, wherein the U-shaped working well comprises a U-shaped well outer well and a U-shaped well inner well, the U-shaped well outer well is provided with perforations, the U-shaped well inner well is arranged in the U-shaped well outer well, and the U-shaped well inner well and the U-shaped well outer well both extend to the underlying stratum; according to the selected U-shaped well design scheme, drilling and completion construction of the site are carried out; devices of a surface energy storage system are arranged to form a complete energy storage system; and air is injected or produced. The present invention realizes that the air obtains excess underground supplementary heat to increase the outlet temperature of the air at the wellhead while ensuring that the circulating pressure remains unchanged, thereby increasing the underground energy recovery efficiency.

Description

Technical Field

[0001] The present invention belongs to the field of underground deep pore space utilization and new energy storage technology, and specifically relates to a method for improving the underground energy recovery efficiency of compressed air energy storage in saline layers. Background Art

[0002] An important technical approach to achieving the dual carbon goals is the transformation of the energy structure, from traditional fossil energy to a system dominated by clean and renewable energy. Wind and solar installed power generation has achieved a large-scale growth in the past two years, and different regions and departments are making reasonable use of the wind and solar resources that can be adapted in the region. However, the main pain point of using wind and solar grid-connected power generation is that the resources themselves are intermittent and random, making it difficult to meet the requirements of power supply safety and stability.

[0003] Large-scale energy storage technology is currently the preferred method to solve the problem of stable power supply from wind and solar power. The whole system of wind, solar and energy storage has begun to develop on a large scale both domestically and internationally. Traditional pumped storage has mature technology and an efficiency of more than 70%, accounting for the vast majority of large-scale energy storage projects in the world. However, pumped storage has certain requirements for terrain and water resources, and has a certain impact on the environment. At present, another large-scale physical energy storage technology, compressed air energy storage, has begun to develop rapidly, especially the system that uses deep underground space for gas storage, which occupies a small area and can store energy for a long time. Compared with salt cavern space, deep underground saline aquifers have been proven to be used for gas storage, and because saline aquifers are widely distributed, the energy storage space and potential are even greater, and it has become the focus of research on large-scale energy storage in the world.

[0004] The key issue in using saline aquifers for energy storage is the efficiency of underground energy recovery. At present, from the perspective of underground energy recovery efficiency, it is generally around 80-90%. How to further improve this efficiency and thus improve the applicability of the entire energy storage technology is a problem that needs to be studied. From the existing technology and research, geothermal energy deep underground has the potential to provide a certain amount of heat supplement for the energy storage process. Some studies have proposed to configure an additional geothermal mining system to heat the wellhead mining air, but this method requires additional cost of the geothermal mining system and is a loose two-system system. Alternatively, some studies have proposed to increase the surrounding heat supplement to the air by placing compressed air in a deeper reservoir, but the disadvantage of this method is that it also increases the pressure of the air circulation, which affects the overall efficiency of the compression equipment and the expander. How to develop a more compact and low-cost method that can improve the underground energy recovery efficiency without changing the circulation pressure is not yet visible. Summary of the invention

[0005] In view of the deficiencies in the prior art, the purpose of the present invention is to provide a method for improving the underground energy recovery efficiency of compressed air energy storage in saline layers. By optimizing the energy storage working well itself, the air can obtain excess underground heat to increase the outlet temperature of the air at the wellhead while ensuring the circulation pressure remains unchanged, thereby increasing the underground energy recovery efficiency without the need for an additional geothermal extraction system.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0007] A method for improving underground energy recovery efficiency of compressed air energy storage in saline aquifers, comprising the following steps:

[0008] Step S1, ascertaining the deep geological conditions and properties of the target site, and determining the location, structure and properties of the target gas storage saline layer, cap rock and underlying strata;

[0009] Step S2, using numerical simulation calculation to determine the design of the U-shaped working well, including providing a variety of U-shaped working well design schemes after exploring the deep formation conditions, using geological modeling software to perform site geological modeling and using a gas-water-heat wellbore reservoir coupling simulator to perform numerical simulation on a variety of U-shaped working well design schemes, analyzing the pressure-temperature changes in the circulation process, using an underground energy recovery formula to calculate the efficiency, and selecting a U-shaped working well design scheme with high recovery efficiency, wherein the U-shaped working well includes a U-shaped well outer well and a U-shaped well inner well, the U-shaped well outer well is provided with perforations, the U-shaped well inner well is arranged in the U-shaped well outer well and is spaced a certain distance from the U-shaped well outer well, and the U-shaped well inner well and the U-shaped well outer well both extend to the underlying formation;

[0010] Step S3: According to the selected U-shaped working well design, drilling and completion of the well are carried out at the site;

[0011] Step S4, arranging the devices of the surface energy storage system to form a complete energy storage system, including a heat storage device, a compressor system and an expander system;

[0012] Step S5, during the air injection process, air enters through the inner well of the U-shaped well, flows to the bottom of the inner well of the U-shaped well, enters between the outer well of the U-shaped well and the inner well of the U-shaped well, moves upward, and finally enters the target gas storage saline layer through the perforations on the outer well of the U-shaped well; during the air production process, air enters between the outer well of the U-shaped well and the inner well of the U-shaped well from the target gas storage saline layer, moves downward to the bottom of the well, enters the inner well of the U-shaped well, and finally enters the wellhead upward along the inner well of the U-shaped well, and the air is produced.

[0013] Furthermore, in step S1, the deep geological condition detection range is 0 to 3000 meters, and the deep geological conditions and properties of the target site are determined through well logging, vertical seismic profile testing, two-dimensional or three-dimensional seismic exploration, drilling of pilot wells and coring, interference testing, formation water chemical analysis, and core displacement experiments.

[0014] Furthermore, in step S1, the target gas storage saline water layer selection principles include: reasonable matching between energy storage scale and reservoir closure structure, anticline or fault closure structure; reservoir permeability needs to be greater than 100md and reservoir thickness is required to be greater than 10m, and porosity needs to be greater than 0.1; the cap rock has good closure and integrity within a certain range, and the regional geological conditions are relatively stable; the underlying stratum has a relatively high temperature.

[0015] Furthermore, in step S2, the design principle of the U-shaped working well is as follows: the outer well of the U-shaped well is fully perforated only within the depth range of the target gas storage saline layer, allowing air and the U-shaped working well to enter and exit the reservoir during the energy storage and release process; the drilling depth of the U-shaped working well is optimized based on multiple schemes according to the actual formation drilling and completion cost and recovery efficiency, but the temperature at the depth of the bottom of the U-shaped working well must be at least greater than 80°C.

[0016] Furthermore, in step S2, the numerical simulation process is as follows: actual site geological modeling and pressure and temperature simulation of the produced gas at the wellhead during operation are required. The actual site geological modeling selects a two-dimensional radial model or a three-dimensional modeling according to the situation to simulate the pressure and temperature of the air at the outlet after the entire underground process circulates. The numerical simulation program T2WELL / EOS3 suitable for gas-water-heat wellbore-reservoir coupling needs to be used.

[0017] Further, in step S2, when calculating the underground energy recovery efficiency of each cycle process, the surface process is ignored, and only the ratio of the total energy of the air at the wellhead and the air entering the wellhead is considered. The specific enthalpy values ​​at different times can be calculated by T2WELL / EOS3. The underground energy recovery efficiency of a single cycle is calculated using the following formula;

[0018]

[0019] E efficiency =E pro / E inj (2)

[0020] Among them, E inj / pro To calculate the total energy of air injected or extracted in a single cycle, Q air is the current injection or production flow rate, h(t) is the specific enthalpy corresponding to the time; E efficiency is the underground energy recovery efficiency for a single cycle.

[0021] Furthermore, in step S2, during the design of the U-shaped working well, the diameter and extension depth of the outer well of the U-shaped well as the diameter and extension depth of the inner well of the U-shaped well need to be considered.

[0022] Furthermore, in step S3, the following aspects need to be considered during drilling: ensuring good air tightness under high temperature and high pressure conditions; reducing damage to surrounding formations during cementing; considering sand prevention between the gas storage target layer and the outer wellbore and paying attention to the corrosion effect of the gas-water mixture in the aquifer on the well pipe.

[0023] Furthermore, in step S3, a space needs to be reserved at the bottom of the U-shaped outer well and the U-shaped inner well to ensure that the friction between the inner U-shaped outer well and the U-shaped inner well is reduced during flow exchange; an insulation layer is set around the outer well of the U-shaped well within a depth range with lower background temperature.

[0024] Further, in step S4, the compressor system includes a multi-stage compressor, a heat exchanger is arranged after each stage of the compressor, the air after each stage of the compressor is cooled down, and the compression heat is stored through the heat storage device, and the expander system includes a multi-stage expander, and the compression heat stored in the heat storage device is extracted through the heat exchanger before each stage of the expander to heat the air.

[0025] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0026] (1) The present invention adopts a U-shaped working well design. While ensuring that the circulating pressure remains unchanged, it can supplement the heat of the air through heat exchange between the deep well and the formation, thereby improving the underground energy recovery efficiency, thereby increasing the benefits of the entire project and promoting it on a large scale.

[0027] (2) The present invention utilizes underground saline water space for gas storage. Compared with salt caverns, it has a wider distribution and applicability range. Compared with rock caves and surface gas storage tanks, it has better gas storage scale and economy. It can greatly promote the grid connection safety of large-scale wind and solar power generation, and contribute to the realization of "carbon peak and carbon neutrality". BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0029] Figure 1 It is a flow chart of the implementation process of the present invention.

[0030] Figure 2 It is a general schematic diagram of the structure of the target gas storage saline layer compressed air energy storage system in the present invention.

[0031] Figure 3 Schematic diagram of fluid movement in a traditional working well.

[0032] Figure 4 The figure is a schematic diagram of fluid movement in a U-shaped working well improved by the present invention.

[0033] Figure 5 This is a schematic diagram of fluid movement in another improved U-shaped working well of the present invention.

[0034] Figure 6 It is a comparison diagram of the wellhead pressure of the traditional working well and the U-shaped working well in the present invention.

[0035] Figure 7 It is a comparison diagram of the wellhead temperature of the traditional working well and the U-shaped working well in the present invention.

[0036] Figure 8 It is a comparison chart of underground energy recovery efficiency of the traditional working well and the U-shaped working well in the present invention.

[0037] In the figure: 1-photovoltaic power generation device; 2-wind power generation device; 3-electric motor; 4-low-pressure compressor; 5-high-pressure compressor; 6-first heat exchanger; 7-second heat exchanger; 8-high-temperature hot tank; 9-low-temperature cold tank; 10-third heat exchanger; 11-high-pressure turbine; 12-low-pressure turbine; 13-coaxial generator; 14-fourth heat exchanger; 15-first throttle valve; 16-second throttle valve; 17-working well; 18-overlying stratum; 19-cap layer; 20-target gas storage saline layer; 21-underlying stratum; 22-initial air bag space; 23-U-type working well; 24-U-type well outside the well; 25-U-type well inside the well. DETAILED DESCRIPTION

[0038] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0039] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and the like are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, features defined as "first", "second", and the like may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0040] The present invention provides a method for improving the underground energy recovery efficiency of compressed air energy storage in saline aquifers, such as Figure 1 As shown, the following steps are included:

[0041] Step S1, finding out the deep geological conditions and properties of the target site, and determining the location, structure and properties of the target gas storage saline layer 20, cap layer 19 and underlying stratum 21;

[0042] Step S2, using numerical simulation calculation to determine the design of the U-shaped working well 23, including providing a variety of U-shaped working well 23 design schemes after exploring the deep formation conditions, using geological modeling software to perform site geological modeling and using a gas-water-heat wellbore reservoir coupling simulator to perform numerical simulation on a variety of U-shaped working well 23 design schemes, analyzing the pressure-temperature changes in the circulation process, using an underground energy recovery formula to calculate the efficiency, and selecting a U-shaped working well 23 design scheme with high recovery efficiency, wherein the U-shaped working well 23 includes a U-shaped well outer well 24 and a U-shaped well inner well 25, the U-shaped well outer well 24 is provided with perforations, the U-shaped well inner well 25 is arranged in the U-shaped well outer well 24 and is separated from the U-shaped well outer well 24 by a certain distance, and the U-shaped well inner well 25 and the U-shaped well outer well 24 both extend to the underlying formation 21;

[0043] Step S3, according to the selected U-shaped working well 23 design scheme, perform well drilling and completion construction at the site;

[0044] Step S4, arranging the devices of the surface energy storage system to form a complete energy storage system, including a heat storage device, a compressor system and an expander system;

[0045] Step S5, during the air injection process, air enters through the U-shaped well inner well 25, flows to the bottom of the U-shaped well inner well 25, enters between the U-shaped well outer well 24 and the U-shaped well inner well 25, moves upward, and finally enters the target gas storage saline layer 20 through the perforations on the U-shaped well outer well 24; during the air production process, air enters between the U-shaped well outer well 24 and the U-shaped well inner well 25 from the target gas storage saline layer 20, moves downward to the bottom of the well and enters the U-shaped well inner well 25, and finally enters the wellhead upward along the U-shaped well inner well 25, and the air is produced.

[0046] In the related art, the energy storage working well 17 directly penetrates into the target gas storage saline layer 20 for air injection and air extraction. From the perspective of underground energy recovery efficiency, it is generally around 80-90%, which cannot be further improved. Existing studies have proposed to configure an additional geothermal extraction system to heat the wellhead extraction air, but this method requires additional cost for the geothermal extraction system and is a loose two-system system. Alternatively, some studies have proposed to increase the surrounding air heat supplement by placing compressed air in a deeper reservoir, but the disadvantage of this method is that it also increases the pressure of the air circulation, which affects the overall efficiency of the compression equipment and the expander.

[0047] Traditional working well 17 such as Figure 3 As shown, regardless of the inner and outer wellbores, the air enters from the wellhead during the injection process and moves downward along the well to the target reservoir; when the air is produced, the air flows from the reservoir into the wellbore and flows along the wellbore to the wellhead.

[0048] like Figure 4 and Figure 5 As shown, the present invention optimizes the energy storage working well itself by designing a new U-shaped working well 23. The U-shaped working well 23 includes a U-shaped outer well 24 and a U-shaped inner well 25. The U-shaped outer well 24 is provided with a perforated part. The U-shaped inner well 25 is arranged in the U-shaped outer well 24 and is separated from the U-shaped outer well 24 by a certain distance. The U-shaped inner well 25 and the U-shaped outer well 24 both extend to the underlying stratum 21. The U-shaped inner well 25 and the U-shaped outer well 24 form a heating section in the part of the underlying stratum 21, which lengthens the heat exchange between the air and the external high-temperature stratum in the deep hot stratum and increases the temperature. The air obtains excess underground heating to increase the outlet temperature of the air at the wellhead while ensuring that the circulating pressure remains unchanged, thereby increasing the underground energy recovery efficiency without the need to add an additional geothermal mining system.

[0049] The present invention adopts the U-shaped working well 23 design to ensure that the circulating pressure remains unchanged, and can supplement the heat of the air through the heat exchange between the deep well and the formation, thereby improving the underground energy recovery efficiency, thereby increasing the benefits of the entire project and promoting it on a large scale.

[0050] This invention utilizes underground saline water space to store gas. Compared with salt caverns, it has a wider distribution and applicability range. Compared with rock caves and surface gas storage tanks, it has better gas storage scale and economy. It solves the limitation problem of further efficiency improvement in underground energy storage, improves the applicability of this type of large-scale energy storage, and can greatly promote the grid-connected safety of large-scale wind and solar power generation, which helps to achieve "carbon peak and carbon neutrality".

[0051] In the present invention, in step S1, the deep geological condition detection range is 0 to 3000 meters, and the deep geological conditions and properties of the target site are determined through well logging, vertical seismic profile testing, two-dimensional or three-dimensional seismic exploration, drilling of pilot wells and coring, interference testing, formation water chemical analysis, and core displacement experiments.

[0052] The saline water layer includes an overlying stratum 18 , a cap layer 19 , a target gas storage saline water layer 20 and an underlying stratum 21 distributed from top to bottom; the cap layer 19 and the target gas storage saline water layer 20 are provided with an initial air bag space 22 .

[0053] In the present invention, in step S1, the positions of the target gas storage saline water layer 20 and the outer diameter of the U-shaped well 24 are determined, and the selection principles of the target gas storage saline water layer 20 include: reasonable matching of energy storage scale and reservoir closure structure, anticline or fault closure structure; reservoir permeability needs to be greater than 100md and reservoir thickness is required to be greater than 10m, and porosity needs to be greater than 0.1; cap rock 19 has good sealing and integrity within a certain range, and regional geological conditions are relatively stable.

[0054] like Figure 1 As shown, in one embodiment of the present invention, during the selection of the target gas storage saline layer 20, anticline structures, high porosity and high permeability strata separated by faults, and large-volume high permeability sandstone lenses in low permeability strata are selected. The reservoir permeability and porosity are good: the permeability of the target gas storage saline layer 20 must be at least 100mD and the reservoir thickness must be greater than 10m to meet the requirements of injectability and large-scale gas production; the porosity requirement is greater than 10%. The top of the reservoir is buried at a depth of more than 600m. The regional geology is stable: the seismic activity in the region is weak, geological disasters are not frequent, and there are no large mining areas. The lithology of the cap layer 19 is mainly mudstone, with a thickness of more than 10m and a permeability of less than 0.01Md. The breakthrough pressure of the cap layer 19 is 1.5-2.0 times the hydrostatic pressure of the target gas storage saline layer 20. The cap layer 19 has a continuous thickness within 2 times the horizontal distance in the closed structure area. The cap layer 19 has no cracks and faults, and there are no potential leakage channels such as abandoned wells in the region.

[0055] In the present invention, in step S1 , the underlying stratum 21 has a relatively high temperature, thereby ensuring the efficiency of the heat exchange section and reducing the overall depth of the U-shaped working well 23 .

[0056] In one embodiment of the present invention, the heat exchange portion of the U-shaped working well 23 of the underlying stratum 21 below the target gas storage saline layer 20 is within 3000m in depth, the temperature at a depth of 3000 should generally be greater than 100°C, and there are no other available oil and coal resources in the layer.

[0057] In step S2, the design principle of the U-shaped working well 23 is as follows: the U-shaped well outer well 24 is fully perforated only within the depth range of the target gas storage saline layer 20, allowing air and the U-shaped working well 23 to enter and exit the reservoir during the energy storage and release process; the drilling depth of the U-shaped working well 23 is optimized according to a variety of schemes based on the actual formation drilling and completion costs and recovery efficiency, but the temperature at the depth of the bottom of the U-shaped working well 23 must be at least greater than 80°C.

[0058] In step S2, ensure that the pressure fluctuation of the injected and extracted air is the same as that of the conventional working well 17 to prevent excessive pressure from reducing the overall efficiency; by enhancing underground heat supplementation, the temperature of the air at the extraction end is increased, thereby improving the underground energy recovery efficiency.

[0059] During the drilling process, it is necessary to use the perforation technology to open a certain range of holes on the U-shaped wellbore 24, so that the fluid in the U-shaped wellbore 24 can maintain communication with the target gas storage saline water layer 20. Complete perforation means that within the depth range of the target gas storage saline water layer 20, the U-shaped wellbore 24 of the target gas storage saline water layer 20 is opened through the perforation technology, so that the compressed air can be connected with this section of the reservoir and can enter and exit freely. In the unperforated U-shaped wellbore 24, the air cannot exchange substances with the target gas storage saline water layer 20, but heat exchange can be carried out.

[0060] In step S2, the U-shaped well 25 is set as a vertical well or a spiral well in the underlying stratum 21 below the depth range of the target gas storage saline water layer 20 for heat exchange, such as Figure 4 As shown in FIG. 1 , it is a schematic diagram of fluid movement in a U-shaped working well after the present invention is improved. The well 25 in the U-shaped well is set as a vertical well in the underlying stratum 21 below the depth range of the target gas storage saline layer 20 for heat exchange. Figure 5 As shown, it is a schematic diagram of fluid movement in another improved U-shaped working well of the present invention. The well 25 in the U-shaped well is arranged in a spiral shape in the underlying stratum 21 below the depth range of the target gas storage saline water layer 20 for heat exchange. Specifically, the well 25 in the U-shaped well is arranged in a vertical well in the overlying stratum 18 and the target gas storage saline water layer 20. The well 25 in the U-shaped well is arranged in a spiral shape in the underlying stratum 21, which can increase the heat exchange area and the fluid flow time, and is beneficial to the air heating. The well 25 in the U-shaped well is arranged in a vertical well in the overlying stratum 18 and the target gas storage saline water layer 20, and the engineering construction difficulty is small. Compared with the spiral well, the heat exchange area is small and the fluid flow time is short, but the heat loss is less.

[0061] In step S2, the numerical simulation process is as follows: actual site geological modeling and pressure and temperature simulation of wellhead produced gas during operation are required. The actual site geological modeling selects a two-dimensional radial model or a three-dimensional modeling according to the situation to simulate the pressure and temperature of the air outlet after the entire underground process circulates. The numerical simulation program T2WELL / EOS3 suitable for gas-water-heat wellbore-reservoir coupling needs to be used.

[0062] Specifically, the modeling tool for the two-dimensional radial model or the three-dimensional modeling adopts GOCAD or MVIEW.

[0063] In the present invention, in step S2, when calculating the underground energy recovery efficiency of each cycle process, the surface process is ignored, and only the ratio of the total energy of the air at the wellhead and the air entering the wellhead is considered. The specific enthalpy values ​​at different times can be calculated by T2WELL / EOS3. The underground energy recovery efficiency of a single cycle is calculated using the following formula:

[0064]

[0065] E efficiency =E pro / E inj (2)

[0066] Among them, E inj / pro To calculate the total energy of air injected or extracted in a single cycle, Q air is the current injection or production flow rate, h(t) is the specific enthalpy corresponding to the time; E efficiency is the underground energy recovery efficiency for a single cycle.

[0067] In the present invention, in step S2, during the design process of the U-shaped working well 23, it is necessary to consider the diameter and extension depth of the U-shaped well outer well 24 and the diameter and extension depth of the U-shaped well inner well 25, calculate the efficiency according to the underground energy recovery formula, select the U-shaped working well 23 design scheme with high recovery efficiency, and then select the appropriate U-shaped well outer well 24, extension depth and diameter and extension depth of the U-shaped well inner well 25.

[0068] In the present invention, in step S3, the following considerations need to be taken into account when drilling: ensuring good air tightness under high temperature and high pressure conditions; reducing damage to surrounding formations during cementing; and considering sand prevention between the target gas storage saline layer 20 and the U-shaped well outer well 24 and paying attention to the corrosion effect of the gas-water mixture in the aquifer on the U-shaped well outer well 24.

[0069] In the present invention, in step S3, a space needs to be reserved at the bottom of the U-shaped well outer well 24 and the U-shaped well inner well 25 to ensure that the friction between the inner U-shaped well outer well 24 and the U-shaped well inner well 25 is reduced during flow exchange; an insulation layer is set around the U-shaped well outer well 24 within a depth range where the background temperature is relatively low to reduce the heat dissipation of high-temperature air during the upward flow process.

[0070] In the present invention, Figure 2 As shown, in step S4, the compressor system includes a multi-stage compressor, a heat exchanger is arranged after each stage of the compressor, the air after each stage of the compressor is cooled, and the compression heat is stored through the heat storage device, and the expander system includes a multi-stage expander, and the compression heat stored in the heat storage device is extracted through the heat exchanger before each stage of the expander to heat the air.

[0071] The multi-stage compressors of the present invention are respectively a low-pressure compressor 4 and a high-pressure compressor 5, and the multi-stage expanders are respectively a high-pressure turbine 11 and a low-pressure turbine 12.

[0072] In the present invention, in step S4, before the multi-stage expander system enters the surface to generate electricity again, it is necessary to use the compression heat to warm the air and store the cold energy in a cold storage device.

[0073] In the present invention, in step S4, the compressor system includes an electric motor 3, a power generation system, a low-pressure compressor 4, a high-pressure compressor 5, a first heat exchanger 6 and a second heat exchanger 7, wherein the inlet part of the low-pressure compressor 4 enters the filtered clean air at normal temperature and pressure, and the air is compressed by the low-pressure compressor 4 and then passes through the first heat exchanger 6 to cool the compressed air, and then enters the high-pressure compressor 5, and the air is compressed by the high-pressure compressor 5 and then passes through the second heat exchanger 7 to cool the air, and the cooled high-pressure air is injected into the working well 17 through the pipeline and the first throttle valve 15.

[0074] The power generation system includes a wind power generation device 2 and a photovoltaic power generation device 1. The electric energy generated by the wind power generation device 2 and the photovoltaic power generation device 1 drives the motor 3 to operate and provide power.

[0075] In the present invention, in step S4, the expander system includes a multi-stage expander, and the expander system includes a third heat exchanger 10, a fourth heat exchanger 14, a high-pressure turbine 11, a low-pressure turbine 12 and a coaxial generator 13. After the mined air is flow- and pressure-controlled by the second throttle valve 16, it first enters the third heat exchanger 10 to further heat the high-pressure air to form high-temperature and high-pressure air. The high-temperature and high-pressure air enters the high-pressure turbine 11 to generate electricity through the coaxial generator 13. After the low-pressure air is formed, it is heated by the fourth heat exchanger 14. Then the low-pressure air enters the low-pressure turbine 12 to generate electricity again through the coaxial generator 13, and then the air is discharged into the atmosphere.

[0076] In the present invention, in step S4, the heat storage device includes a high-temperature hot tank 8 and a low-temperature cold tank 9. The high-temperature hot tank 8 is used to collect the compression heat during the air compression process of the low-pressure compressor 4 and the high-pressure compressor 5 in the compressor system, and the low-temperature cold tank 9 is used to collect the cold energy after heat exchange before the mined air enters the high-pressure turbine 11, and they are connected to the heat exchangers respectively.

[0077] In one embodiment of the present invention, Figure 2 As shown, it is a general schematic diagram of the structure of the compressed air energy storage system of the target gas storage saltwater layer 20 in the present invention. The off-peak electricity in the photovoltaic power generation device 1 and the wind power generation device 2 drives the motor 3 to drive the low-pressure compressor 4 and the high-pressure compressor 5 to work. The pure air at normal temperature and pressure (20-25°C, 0.1Mpa) first passes through the low-pressure compressor 4 and is compressed to 0.1-4.0MPa. The compressed air enters the first heat exchanger 6 and is cooled by the cold energy provided by the low-temperature cold tank 9, and the compression heat is stored in the high-temperature hot tank 8. The cooled compressed air enters the high-pressure compressor 5 for compression and is compressed to 8-15Mpa. The compressed high-temperature and high-pressure air enters the second heat exchanger 7 for heat exchange. The low-temperature cold tank 9 provides cold energy, and the compression heat is stored in the high-temperature hot tank 8. The high-pressure air coming out of the second heat exchanger 7 is Gas (25-40°C) is injected into the target gas storage saline layer 20 through the working well 17, wherein the injection flow rate is controlled by the first throttle valve 15; during the gas production and power generation process, the flow rate and pressure of the produced gas are controlled by the second throttle valve 16, the produced high-pressure air enters the third heat exchanger 10 for heating, the heat energy is provided by the high-temperature hot tank 8, and the cold energy after heat exchange is stored in the low-temperature cold tank 9, the high-temperature and high-pressure air at the outlet of the third heat exchanger 10 enters the high-pressure turbine 11, and generates electricity through the coaxial generator 13, the low-pressure air (0.1-4Mpa) at the outlet of the high-pressure turbine 11 passes through the fourth heat exchanger 14, the heat energy is provided by the high-temperature hot tank 8, the low-temperature cold tank 9 recovers the cold energy, and enters the low-pressure turbine 12 to generate electricity for the second time through the generator 13, and the exhaust gas discharged by the low-pressure turbine 12 can be directly discharged into the environment or the waste heat can be recovered.

[0078] In order to better illustrate the present invention and reflect its advantages in efficiency, the embodiments provided by the present invention are selected as follows Figure 3 The wellhead pressure, temperature and underground energy recovery efficiency are compared between the existing conventional working well system and the U-shaped working well 23 of the present invention.

[0079] Through geological survey, the geological conditions in this embodiment are as follows: the overburden 19 on the target gas storage saline layer 20 has an extremely low permeability of 5.0×10 -19 m 2 The structure of the target gas storage saline layer 20 is a straight aquifer, and the closed structure is a very low permeability boundary 40m away from the working well 17; the reservoir depth range is 650m-800m, and the permeability of the gas storage space of the saline layer is 5.0×10-13 m 2 (500md), porosity is 0.2, formation thermal conductivity is 2.51W / (m·K); the formation background geothermal gradient is 31.25℃ / km, and the initial surface temperature is 15℃.

[0080] The design parameters of the U-shaped working well 23 are: the bottom depth of the well is 3000m. According to the geothermal gradient, the background formation temperature at the bottom of the well is 108.75℃. The perforation range of the U-shaped outer well 24 is the target reservoir range of 650-800m. The diameter of the U-shaped inner well 25 is 0.5m, the diameter of the U-shaped outer well 24 is 1.5m, and the roughness coefficient in the well is 45×10-6m. In contrast, the traditional working well 17 has a bottom depth of 800m and a well diameter of 0.5m.

[0081] The underground injection and production cycle working system is: daily cycle, with an initial 12-hour injection at a rate of 54 kg / s, a 4.5-hour stop injection, a 3-hour extraction at a rate of 216 kg / s, and a final 4.5-hour stop injection. The injection air temperature is 40°C.

[0082] MVIEW was used as the modeling software to establish a two-dimensional radially symmetric model, and T2WELL / EOS3 was used as the computational simulation program. The total simulation time was 200 cycles, or 200 days.

[0083] Figure 6 The comparison diagram of the wellhead pressure of the conventional working well 17 and the U-shaped working well 23 in the present invention shows that the pressure changes at the wellhead during the circulation process are basically the same. The pressure of the conventional well in the injection and extraction stages is slightly higher than that of the U-shaped working well 23, but the maximum difference does not exceed 0.25MPa. Figure 7 The wellhead temperature comparison diagram of the conventional working well 17 and the U-shaped working well 23 in the present invention shows that the air pressure in the extraction stage of the U-shaped working well 23 is significantly improved compared with the original system. The outlet pressure in the U-shaped extraction stage can reach 46°C, even exceeding the 40°C of the injected air, indicating that the U-shaped working well 23 provided by the present invention can increase the outlet temperature to a large extent through heat exchange between the underlying stratum 21 and the U-shaped working well 23; Figure 8 This is a comparison chart of underground energy recovery efficiency between the traditional working well 17 and the U-shaped working well 23 in the present invention. The U-shaped working well 23 provided by the present invention can enhance efficiency to a great extent. Compared with the traditional method, it can be increased by up to 6% under the conditions of this embodiment, and a part of the formation heat can be well utilized in the energy storage process.

[0084] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A method for improving the underground energy recovery efficiency of compressed air energy storage in saline layers, characterized in that: The following steps are involved: Step S1, ascertaining the deep geological conditions and properties of the target site, and determining the location, structure and properties of the target gas storage saline layer, cap rock and underlying strata; Step S2, using numerical simulation calculation to determine the design of the U-shaped working well, including providing a variety of U-shaped working well design schemes after exploring the deep formation conditions, using geological modeling software to perform site geological modeling and using a gas-water-heat wellbore reservoir coupling simulator to perform numerical simulation on a variety of U-shaped working well design schemes, analyzing the pressure-temperature changes in the circulation process, using an underground energy recovery formula to calculate the efficiency, and selecting a U-shaped working well design scheme with high recovery efficiency, wherein the U-shaped working well includes a U-shaped well outer well and a U-shaped well inner well, the U-shaped well outer well is provided with perforations, the U-shaped well inner well is arranged in the U-shaped well outer well and is spaced a certain distance from the U-shaped well outer well, and the U-shaped well inner well and the U-shaped well outer well both extend to the underlying formation; Step S3: According to the selected U-shaped working well design, drilling and completion of the well are carried out at the site; Step S4, arranging the devices of the surface energy storage system to form a complete energy storage system, including a heat storage device, a compressor system and an expander system; Step S5, during the air injection process, air enters through the inner well of the U-shaped well, flows to the bottom of the inner well of the U-shaped well, enters between the outer well of the U-shaped well and the inner well of the U-shaped well, moves upward, and finally enters the target gas storage saline layer through the perforations on the outer well of the U-shaped well; during the air production process, air enters between the outer well of the U-shaped well and the inner well of the U-shaped well from the target gas storage saline layer, moves downward to the bottom of the well, enters the inner well of the U-shaped well, and finally enters the wellhead upward along the inner well of the U-shaped well, and the air is produced.

2. The method for improving underground energy recovery efficiency of compressed air energy storage in saline layers according to claim 1, characterized in that: In step S1, the deep geological condition detection range is 0 to 3000 meters, and the deep geological conditions and properties of the target site are ascertained through well logging, vertical seismic profile testing, two-dimensional or three-dimensional seismic exploration, drilling of pilot wells and coring, interference testing, formation water chemical analysis, and core displacement experiments.

3. The method for improving underground energy recovery efficiency of compressed air energy storage in saline layers according to claim 1, characterized in that: In step S1, the target gas storage saline water layer selection principles include: reasonable matching between energy storage scale and reservoir closure structure, anticline or fault closure structure; reservoir permeability needs to be greater than 100md and reservoir thickness is required to be greater than 10m, and porosity needs to be greater than 0.

1.

4. The method for improving underground energy recovery efficiency of compressed air energy storage in saline layers according to claim 1, characterized in that: In step S2, the design principle of the U-shaped working well is as follows: the outer well of the U-shaped well is fully perforated only within the depth range of the target gas storage saline water layer, allowing air and the U-shaped working well to enter and exit the target gas storage saline water layer during the energy storage and release process; the drilling depth of the U-shaped working well is optimized according to multiple schemes based on the actual formation drilling and completion cost and recovery efficiency, but the temperature at the depth of the bottom of the U-shaped working well must be at least greater than 80°C.

5. The method for improving underground energy recovery efficiency of compressed air energy storage in saline layers according to claim 1, characterized in that: In step S2, the numerical simulation process is as follows: actual site geological modeling and pressure and temperature simulation of wellhead produced gas during operation are required. The actual site geological modeling selects a two-dimensional radial model or a three-dimensional modeling according to the situation to simulate the pressure and temperature of the air outlet after the entire underground process circulates. The numerical simulation program T2WELL / EOS3 suitable for gas-water-heat wellbore-reservoir coupling needs to be used.

6. The method for improving underground energy recovery efficiency of compressed air energy storage in saline aquifers according to claim 5, characterized in that: In step S2, when calculating the underground energy recovery efficiency of each cycle process, the surface process is ignored, and only the ratio of the total energy of the air at the wellhead and the air entering the wellhead is considered. The specific enthalpy values ​​at different times can be calculated by T2WELL / EOS3. The underground energy recovery efficiency of a single cycle is calculated using the following formula; AND efficiency =And pro / AND inj (2) Among them, E inj / pro To calculate the total energy of air injected or extracted in a single cycle, Q air is the current injection or production flow rate, h(t) is the specific enthalpy corresponding to the time; E efficiency is the underground energy recovery efficiency for a single cycle.

7. The method for improving underground energy recovery efficiency of compressed air energy storage in saline layers according to claim 1, characterized in that: In step S2, during the design of the U-shaped working well, the diameter and extension depth of the outer well of the U-shaped well as the diameter and extension depth of the inner well of the U-shaped well need to be considered.

8. The method for improving underground energy recovery efficiency of compressed air energy storage in saline layers according to claim 1, characterized in that: In step S3, the following considerations need to be taken into account when drilling: ensuring good air tightness under high temperature and high pressure conditions; reducing damage to surrounding formations during cementing; considering sand prevention between the target gas storage saline layer and the wellbore outside the U-shaped well, and paying attention to the corrosion effect of the gas-water mixture in the aquifer on the wellbore.

9. The method for improving underground energy recovery efficiency of compressed air energy storage in saline layers according to claim 1, characterized in that: In step S3, a space needs to be reserved at the bottom of the U-shaped outer well and the U-shaped inner well to ensure that the friction between the U-shaped outer well and the U-shaped inner well is reduced during flow exchange.

10. The method for improving underground energy recovery efficiency of compressed air energy storage in saline aquifers according to claim 1, characterized in that: In step S4, the compressor system includes a multi-stage compressor, a heat exchanger is arranged after each stage of the compressor, the air after each stage of the compressor is cooled down, and the compression heat is stored through the heat storage device. The expander system includes a multi-stage expander, and the compression heat stored in the heat storage device is extracted through the heat exchanger before each stage of the expander to heat the air.

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