Multi-well energy storage and release method and system

Abstract

The invention discloses a multi-well energy storage and release method and system. The method comprises the steps that at least two wellbores which are in hydraulic communication through stratum cracks or / and rock pores are selected as energy storage or / and energy release wellbores; during energy storage, high-pressure fluid is injected into one or more of the wellbores, the wellbores are blocked, and elastic deformation of stratum rocks is kept, so that energy storage is conducted; and during energy release, the wellbore plugging pressure is reduced, so that one or more of the wellbores reversely discharge the high-pressure fluid, and energy is obtained in the reverse discharge process to generate power. The system is low in investment and maintenance cost, and is suitable for new clean power storage of various terrains.

Description

Technical Field

[0001] The present invention belongs to the technical field of underground energy storage, and in particular relates to a multi-well energy storage and release method and system. Background Art

[0002] Many renewable energy sources such as solar energy and wind energy have daily and seasonal intermittent characteristics, unstable power output, and are not suitable for providing basic load power. Therefore, it is difficult to directly enter the power grid. Solving the energy storage problem is the key to successfully expanding the scale of renewable energy production. Therefore, how to store excess clean electricity on a large scale and transmit electricity stably when the supply of sunlight and wind is insufficient is still a technical problem that all countries are working on.

[0003] At present, large-scale electricity storage methods include the use of lead-acid batteries, lithium-ion batteries, hydrogen fuel cells, compressed air energy storage, and pumped storage. Among them, lead-acid batteries, lithium-ion batteries, and hydrogen fuel cell energy storage have not been used on a large scale due to their high investment and maintenance costs; pumped storage is to pump water from a lower position to a higher position to convert electrical energy into the gravitational potential energy of water. Therefore, the pumped storage method has certain requirements for the terrain structure and cannot be applied to relatively flat plains or hilly areas; compressed air energy storage is a mature energy storage technology, but it requires abandoned mines or underground caves as gas storage media, so it can only be used in certain specific areas.

[0004] At present, geothermal energy extraction usually adopts a multi-well linkage method, with at least one injection well continuously injecting water and at least one production well continuously discharging high-temperature water (or water vapor). Injection wells usually continue to inject fluid into the formation without interruption, because interrupting the injection will make it difficult to restart the supporting equipment on the ground. If geothermal power generation exceeds the demand of the power grid, the high-temperature water (or water vapor) continuously discharged from the production well will not pass through the heat exchange and power generation equipment, but will be directly injected back into the injection well. This is a huge waste of the geothermal energy that has been mined, and there is an urgent need for a method to flexibly allocate the time of geothermal power generation.

[0005] In addition, in order to reduce parasitic loads, the fluid injection pressure in traditional geothermal extraction is usually low, and the formation pressure remains basically stable during operation. Therefore, the pressure of the high-temperature fluid discharged is usually also relatively low, and the kinetic energy of the discharged fluid cannot be recovered for power generation.

[0006] Prior art Chinese patent CN202211177295.0 discloses a multi-stratum geothermal development and energy storage system, including: a geothermal reservoir, an ordinary stratum, a tailwater reservoir, a geothermal well, an energy-using facility, a tailwater reinjection well and a tailwater reinjection device, the bottom of the geothermal well is located in the geothermal reservoir, the bottom of the tailwater reinjection well is located in the tailwater reservoir, the depth of the geothermal reservoir is greater than the tailwater reservoir, and the porosity and permeability of the geothermal reservoir and the tailwater reservoir are higher than those of the ordinary stratum; geothermal energy is stored in the geothermal reservoir, thermal fluid is extracted from the geothermal reservoir through the geothermal well, the energy-using facility uses the geothermal energy carried in the thermal fluid to work, and the tailwater generated in the process of geothermal energy utilization is reinjected into the tailwater reservoir through the tailwater reinjection well; the tailwater reinjection device uses supplementary energy to reinject the tail water stored in the tailwater reservoir into the geothermal reservoir.

[0007] The limitations of the above-mentioned existing technologies are: (1) when injecting fluid, it is necessary to switch between different formations (such as tailwater reservoirs and geothermal reservoirs); (2) only thermal energy is recovered, and fluid kinetic energy and compression potential energy are not recovered; (3) the injected fluid needs to be temporarily stored in the tailwater reservoir.

[0008] The Chinese patent application with publication number CN114016988A discloses a method and system for storing and releasing energy through formations, which generates at least one formation fracture by hydraulic fracturing in an energy storage formation without oil and gas, and then injects high-pressure fluid into the obtained formation fracture to cause elastic deformation of the formation fracture to store energy, and then releases energy by back-discharging the high-pressure fluid in the fracture to push the preset power generation equipment. The Chinese patent application with publication number CN118654399A discloses a method and system for storing and releasing energy through formation fractures and obtaining geothermal energy. The system includes a fracturing device for pumping fracturing fluid into the wellbore to generate formation fractures in the energy storage geothermal layer; an injection pipeline, to which an injection device is connected; a backflow pipeline, to which a hydroelectric power generation device, a geothermal power generation device and a heating system are connected, so that when the fluid in the formation fracture is backflowed through the backflow pipe, it can drive the hydroelectric power generation device and the geothermal power generation device to generate electricity and provide heating through the heating system; a plugging device for closing the backflow pipeline so that the fluid in the formation fracture continues to exchange heat with the energy storage geothermal layer so that the fluid temperature continues to rise. This technology uses the elastic deformation of the formation fracture to store and release energy, while using geothermal resources to generate electricity and / or provide heating.

[0009] The limitation of the above two technologies is that they are only applicable to single wellbore. When there are multiple wellbores that are hydraulically connected, the fluid injected into one wellbore will flow into other wellbores. At this time, a single wellbore cannot complete the energy storage and release process independently. It is necessary to regard the hydraulically connected wellbores as a whole to coordinate the energy storage and release in time and space, and fully consider the mutual influence between the wellbores. Summary of the invention

[0010] The object of the present invention is to provide a multi-well energy storage and release method and system to partially solve or alleviate the above-mentioned deficiencies in the prior art, with low investment and maintenance costs, and a new clean electricity storage system that is adaptable to various terrains.

[0011] In order to solve the above-mentioned technical problems, the present invention specifically adopts the following technical solutions: A first aspect of the present invention is to provide a multi-well energy storage and release method, which comprises: Select at least two wellbores hydraulically connected through formation fractures and / or rock pores as wellbores for energy storage and / or energy release; When storing energy, high-pressure fluid is injected into one or more of the wellbores, so that the high-pressure fluid enters the formation cracks and / or rock pores, thereby driving the formation rock to undergo elastic deformation to accumulate elastic potential energy, and in the case where the high-pressure fluid is compressible, the high-pressure fluid generates fluid compression potential energy under the reaction force of the formation rock; at the same time, the high-pressure fluid exchanges heat with the formation rock to obtain formation thermal energy; the wellbores are blocked to maintain the elastic deformation of the formation rock to store energy; When releasing energy, the wellbore plugging pressure is reduced so that one or several wells in the wellbore can discharge high-pressure fluid, and in the process of discharge, at least one of the following is obtained: the kinetic energy of the high-pressure fluid converted from the elastic potential energy accumulated in the formation rock, the fluid compression potential energy released by the high-pressure fluid, and the thermal energy carried by the high-pressure fluid.

[0012] As an improvement, a preset power generation device is used to convert at least one of the kinetic energy of the high-pressure fluid converted from the elastic potential energy accumulated in the formation rock, the fluid compression potential energy released by the high-pressure fluid, and the thermal energy carried by the high-pressure fluid into electrical energy.

[0013] As an improvement, the power generation equipment is one or more of a hydraulic turbine, a steam turbine, a supercritical carbon dioxide turbine, an expander, a heat exchanger, and an organic Rankine cycle power generation equipment.

[0014] As an improvement, the bottom hole pressure or wellhead pressure of all wellbores is made consistent by increasing the injection rate of high-pressure fluid into wellbores with lower bottom hole pressure or / and reducing the injection rate of high-pressure fluid into wellbores with higher bottom hole pressure.

[0015] As an improvement, during energy storage, before the bottom hole pressure or / and wellhead pressure reaches a pressure threshold, the injection of high-pressure fluid into the wellbore is stopped; The pressure threshold is calculated based on one or more of the pressure levels of the injection device and the plugging device, the maximum yield strength of the wellbore casing, the closing stress of the formation fracture, the expansion pressure of the formation fracture, the maximum allowable width of the formation fracture, and the fault slip pressure in the formation.

[0016] As an improvement, when storing energy, high-pressure fluid is injected into all wellbores simultaneously; When releasing energy, high-pressure fluid is discharged through all wellbores simultaneously.

[0017] As an improvement, the wellbore into which the high-pressure fluid is injected during energy storage is different from the wellbore from which the high-pressure fluid is discharged during energy release.

[0018] As an improvement, a part of the wellbore is used as an injection wellbore for injecting high-pressure fluid; and the rest of the wellbore is used as a discharge wellbore for discharge of high-pressure fluid; When storing energy, the reverse wellbore is closed and the injection wellbore is opened, and high-pressure fluid is injected into the injection wellbore; when releasing energy, both the reverse wellbore and the injection wellbore are opened, and the flow rate of the high-pressure fluid discharged from the reverse wellbore is greater than the flow rate of the high-pressure fluid injected into the injection wellbore, so that when the energy release is completed, the injection volume of the high-pressure fluid in the injection wellbore is equal to the reverse discharge volume of the high-pressure fluid in the reverse wellbore.

[0019] As an improvement, a part of the wellbore is used as an injection wellbore for injecting high-pressure fluid; and the rest of the wellbore is used as a discharge wellbore for discharge of high-pressure fluid; When storing energy, the reverse wellbore is closed and the injection wellbore is opened, and high-pressure fluid is injected into the injection wellbore; when releasing energy, the injection wellbore is closed, the reverse wellbore is opened, and high-pressure fluid is reversed from the reverse wellbore.

[0020] As an improvement, a part of the wellbore is used as an injection wellbore for injecting high-pressure fluid; and the rest of the wellbore is used as a discharge wellbore for discharge of high-pressure fluid; When storing energy, both the injection wellbore and the reverse wellbore are opened, but the flow rate of the high-pressure fluid injected into the injection wellbore is greater than the flow rate of the high-pressure fluid discharged from the reverse wellbore; when releasing energy, the injection wellbore is closed, the reverse wellbore is opened and the high-pressure fluid is discharged from the reverse wellbore.

[0021] As an improvement, during the energy storage process, the bottom hole pressure of the wellbore is less than or equal to the closing stress of the formation fracture; Alternatively, the bottom hole pressure of the wellbore is higher than the closure stress of the formation fracture, so that the width of at least one formation fracture increases; Alternatively, the bottom hole pressure of the wellbore is higher than the expansion pressure of the formation fracture.

[0022] As an improvement, the hydraulically connected portions of the wellbores are located in formations of the same formation type.

[0023] The present invention also provides a multi-well energy storage and release system, comprising: An injection device is used to inject a high-pressure fluid into one or more of the wellbores, so that the high-pressure fluid enters the formation cracks and / or rock pores, thereby driving the formation rock to undergo elastic deformation and accumulate elastic potential energy; and in the case where the high-pressure fluid is compressible, the high-pressure fluid generates fluid compression potential energy under the reaction force of the formation rock; at the same time, the high-pressure fluid exchanges heat with the formation rock to obtain formation thermal energy; A plugging device is used to plug the wellbore opening and maintain elastic deformation of the formation rock to store energy; A power generation device is used to convert at least one of the kinetic energy of high-pressure fluid converted from the elastic potential energy accumulated in the formation rock, the fluid compression potential energy released by the high-pressure fluid, and the thermal energy carried by the high-pressure fluid into electrical energy.

[0024] The present invention is beneficial in that: The present invention is driven by electric energy, and high-pressure fluid is injected into the formation through the wellbore, so that the pressure in the formation pores and / or cracks increases, so that the elastic deformation energy of the formation rock can be stored; the high-pressure fluid will also store the fluid compression potential energy as the formation pressure increases; at the same time, the formation will also exchange heat with the high-pressure fluid injected into the formation, increasing the temperature of the injected formation fluid. The electric energy in the above steps can come from renewable energy sources such as wind power generation or solar power generation.

[0025] By discharging high-pressure fluid from the wellbore to the ground, the kinetic energy, compression potential energy and heat of the high-pressure fluid can be converted back into electrical energy through ground power generation equipment, thereby achieving stable power supply when solar or wind energy is insufficient.

[0026] The method and system of the present invention can store the electric energy generated by sunlight or wind underground when there is sufficient sunlight or wind, and release the electric energy to the power grid when needed, which is of great significance for the peak load regulation of wind power generation or solar power generation.

[0027] The method and system of the present invention are applicable to formations with low permeability, such as shale formations, dense sandstone formations, mudstone formations, granite formations, hot dry rock formations, etc. Or high permeability formations that have been artificially transformed with permeability. In this way, the high-pressure fluid injected into the formation can be confined to a certain area of ​​the formation. The method and system of the present invention can also be used to transform depleted oil wells or geothermal wells into energy storage and release wells.

[0028] The method disclosed in the present invention also relates to hydraulic fracturing. As a mature technology in the field of oil and gas, hydraulic fracturing has been used on a large scale. Therefore, related construction supporting equipment is easy to obtain and the cost is controllable. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings required for use in the embodiments or the prior art descriptions are briefly introduced below. In all the drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, each element or part is not necessarily drawn according to the actual scale. Obviously, the drawings described below are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can also be obtained based on these drawings without paying creative labor.

[0030] Figure 1 It is a flow chart of the present invention.

[0031] Figure 2 It is a structural schematic diagram of the present invention.

[0032] Markings in the figure: 102 wellbore, 104 wellbore, 106 wellbore, 108 formation, 110 formation fracture, 112 injection device, 114 injection device, 116 injection device. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0034] Herein, suffixes such as "module", "component" or "unit" used to represent elements are only used to facilitate the description of the present invention, and have no specific meanings by themselves. Therefore, "module", "component" or "unit" can be used mixedly.

[0035] In this document, the terms "upper", "lower", "inner", "outer", "front", "back", "one end", "the other end" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance.

[0036] In this document, unless otherwise clearly specified and limited, the terms "installed", "provided with", "connected", etc. should be understood in a broad sense. For example, "connected" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, a direct connection, or an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0037] Herein "and / or" includes any and all combinations of one or more of the associated listed items.

[0038] Herein, "plurality" means two or more than two, ie, it includes two, three, four, five, etc.

[0039] Definition of noun: The "fluid" herein may be, but is not limited to, a gas, a liquid, an emulsion, a slurry, and a solid particle flow having flow characteristics similar to that of a liquid flow. For example, the fluid may include a water-based liquid with chemical additives; or it may be a compressible gas, such as carbon dioxide, air, nitrogen, a gas mixture, etc. The state of the fluid may be a gaseous state, a liquid state, or a supercritical state.

[0040] The term "formation" as used herein refers to a porous and permeable rock formation (e.g., shale formation, sandstone formation, carbonate formation, hot dry rock formation, etc.) underground that can act as a storage space for fluids. Typically, these fluids can be water, hydrocarbons, or gases.

[0041] "Hydraulic fracturing" or "fracture" or "fracture" in this article refers to the generation and expansion of cracks in formation rocks under the action of external forces (such as high-pressure fluid).

[0042] "Formation fractures" or "fractures" in this article are rock openings created in the formation after hydraulic fracturing or natural fractures or faults that originally exist in the formation. The terms "formation fractures" or "fractures" are interchangeable. "Fractures" can refer to a single fracture or multiple fractures or fracture swarms adjacent to the same location.

[0043] The term "wellbore" as used herein refers to a hole formed by drilling or inserting a conduit into the earth. Generally, a wellbore is cylindrical, so the cross-section of the wellbore may be circular. Alternatively, a wellbore may have any other cross-section. A wellbore may be an open-hole wellbore, or a cased wellbore may be formed by cementing a casing to the inner wall of the wellbore. A wellbore may be a vertical well, a horizontal well, or an inclined well.

[0044] The term "hydraulically connected" in this context refers to the situation where subsurface fluids (such as water, oil or gas) can flow and exchange between two or more wellbores. This connectivity indicates that there are pathways for fluid communication between underground structures or formations, so that changes in pressure in one wellbore can affect the behavior of fluids in another wellbore.

[0045] "Constant" or "unchanged" in this article does not mean that the absolute change of the specified item is zero, but rather that the change of the specified item is very small, and the item can be considered constant in engineering practice. It should also be recognized that the word "equal" used in this disclosure does not mean that the specified items are exactly the same, but is used to specify two items with negligible differences in engineering practice. For example, the word "equal" in this disclosure can also have the meaning of "approximately equal".

[0046] Embodiment 1: Figure 1 As shown, the present invention provides a multi-well energy storage and release method, the specific steps of which include: S1 selects at least two wellbores hydraulically connected through formation fractures and / or rock pores as wellbores for energy storage and / or energy release.

[0047] like Figure 2 The illustrated embodiment depicts a schematic diagram of a system in which wellbore 102, wellbore 104, and wellbore 106 are connected in formation 108 by formation fractures 110 and rock pores. Of course, it is understood that the number of wellbores is not limited to 3, and can be any number above 2. This embodiment takes 3 wellbores as an example to illustrate the working principle of the present invention, and other numbers of wellbores can also be deduced by analogy.

[0048] In some embodiments, the hydraulically connected portions of the wellbores 102, 104, and 106 are located in a formation 108 of the same formation type.

[0049] During S2 energy storage, high-pressure fluid is injected into one or more of the wellbores, so that the high-pressure fluid enters the formation cracks and / or rock pores, thereby driving the formation rock to undergo elastic deformation and accumulate elastic potential energy; and when the high-pressure fluid is compressible, the high-pressure fluid generates fluid compression potential energy under the reaction force of the formation rock; at the same time, the high-pressure fluid exchanges heat with the formation rock to obtain formation thermal energy; the wellbores are sealed to maintain the elastic deformation of the formation rock for energy storage.

[0050] Specifically, during the energy storage process, high-pressure fluid is injected into the wellbore 102 through an electric injection device 112 (of course, it can also be driven by other energy sources), high-pressure fluid is injected into the wellbore 104 through an injection device 114, and high-pressure fluid is injected into the wellbore 106 through an injection device 116, so that the rock pore pressure in the formation 108 and the fluid pressure in the formation fractures 110 are increased, so that the elastic deformation energy of the formation rock can be stored; for high-pressure fluids that can be compressed, such as air, nitrogen, carbon dioxide, etc., the high-pressure fluid will also store fluid compression potential energy as the formation pressure increases; of course, in some embodiments, for high-pressure fluids that cannot or are almost unable to be compressed, such as water, the fluid compression potential energy can be ignored.

[0051] At the same time, the formation will also exchange heat with the high-pressure fluid injected into the formation, increasing the temperature of the injected formation fluid.

[0052] Before the bottom hole or / and wellhead pressure reaches a preset pressure threshold, the injection of high-pressure fluid into the wellbore 102, wellbore 104, wellbore 106 is stopped and the openings of the wellbores 102, 104, 106 are blocked by a plugging device to keep the rock pore pressure and the fluid pressure in the fracture in the formation 108 unchanged, thereby starting energy storage. The pressure threshold is calculated based on one or more of the pressure levels of the injection device and the plugging device, the maximum yield strength of the wellbore casing, the closing stress of the formation fracture, the expansion pressure of the formation fracture, the maximum allowable width of the formation fracture, and the fault slip pressure in the formation.

[0053] In this embodiment, the preset threshold values ​​of the bottom hole or / and wellhead pressure depend on the constraints of the ground equipment, wellbore and formation geological conditions. For example: the pressure at the wellhead cannot exceed the pressure level of the ground injection or plugging device; the bottom hole pressure cannot exceed the maximum yield strength of the casing; the bottom hole pressure does not exceed the closing stress of the formation fracture; the bottom hole pressure cannot make the width of the formation fracture greater than the maximum allowable width (the higher the bottom hole pressure, the wider the formation fracture width), the bottom hole pressure cannot exceed the expansion pressure of the formation fracture; the bottom hole pressure does not exceed the slip pressure of the fault in the formation, etc. Using the wellbore flow model, the dynamic change relationship between the wellhead pressure and the bottom hole pressure under different injection flow rates and fluid densities can be calculated, so that the bottom hole pressure can be calculated by monitoring the wellhead pressure. The bottom hole pressure can also be monitored by a bottom hole pressure gauge.

[0054] During the energy release of S3, the wellbore plugging pressure is reduced so that one or several wells in the wellbore can discharge high-pressure fluid, and in the process of discharge, at least one of the following is obtained: the kinetic energy of the high-pressure fluid converted from the elastic potential energy accumulated in the formation rock, the fluid compression potential energy released by the high-pressure fluid, and the thermal energy carried by the high-pressure fluid.

[0055] Specifically, when energy release is required, high-pressure fluid is discharged from wellbore 102, wellbore 104, and wellbore 106, and the kinetic energy of the discharged high-pressure fluid, and / or the compression potential energy of the high-pressure fluid, and / or the fluid thermal energy are converted into electrical energy through ground power generation equipment. The ground power generation equipment may include, but is not limited to: a hydraulic turbine, a steam turbine, a supercritical carbon dioxide turbine, a piston expander, a turbo expander, a heat exchanger, and an organic Rankine cycle (ORC) power generation equipment.

[0056] It should be pointed out that since wellbore 102, wellbore 104, and wellbore 106 are hydraulically connected through formation fractures and / or formation rock pores, the fluid injected into a certain wellbore can flow into other wellbores from formation fractures and / or formation rock pores. When storing and releasing energy, the influence between wellbores should be fully considered. For example, if only high-pressure fluid is injected into wellbore 104, the high-pressure fluid will enter wellbores 102 and 106 through formation fractures and / or formation rock pores, and enter the fractures connected to wellbores 102 and 106, which will reduce the formation fluid pressure around wellbore 104, thereby reducing the energy storage efficiency of the backflow fluid release of wellbore 104.

[0057] In order to reduce the interference between wellbores, all wellbores can store and release energy at the same time. That is, when storing energy, high-pressure fluid is injected into all wellbores at the same time; when releasing energy, high-pressure fluid is discharged through all wellbores at the same time.

[0058] Of course, in order to further reduce the interference between wellbores, when injecting high-pressure fluid into the wellbores, it is necessary to ensure that the wellbores that are hydraulically connected have the same wellhead or bottom hole pressure. In the present invention, the bottom hole pressure or wellhead pressure of all hydraulically connected wellbores can be made consistent by increasing the injection amount of high-pressure fluid in the wellbores with lower bottom hole pressure or / and reducing the injection amount of high-pressure fluid in the wellbores with higher bottom hole pressure.

[0059] For example, when the bottom hole pressure of wellbore 104 is much higher than the bottom hole pressure of wellbore 102 and 106, the fluid injected into wellbore 104 will flow into wellbore 102 and 106 through rock pores and / or cracks, affecting the energy storage efficiency of wellbore 102 and 106. The bottom hole pressure can be adjusted by increasing the injection flow rate of wellbore 102 and 106, and / or reducing the injection flow rate of wellbore 104, so that wellbore 102, 104 and 106 have the same or similar bottom hole pressure, avoiding interference between wellbore. The relationship between injection flow rate and bottom hole pressure depends on factors such as the volume of wellbore, the compressibility of injected fluid, the density of injected fluid, the permeability of formation rock, the magnitude of ground stress, and the number of formation cracks.

[0060] When the bottoms of multiple energy storage wells are at the same depth in the formation and the bottom hole pressure is the same, they usually also have the same wellhead pressure (the friction along the wellbore can be ignored).

[0061] It is easy to monitor whether there is hydraulic communication between the wellbores by using a wellhead or bottom hole pressure gauge. For example, if only high pressure fluid is injected into wellbore 104, but pressure rise is detected at the wellhead or bottom hole of wellbore 102 and wellbore 106, it can be shown that wellbore 104, wellbore 102 and wellbore 106 are hydraulically connected.

[0062] In some embodiments, the plugging device is located inside the wellbore. In other embodiments, the plugging device is located on a ground pipeline connected to the wellbore. The specific form of the plugging device in the present invention is not limited, as long as it can plug the wellbore to maintain pressure for energy storage.

[0063] In some embodiments, the hydraulically connected portions of the multiple wellbores are located in formations of the same formation type (e.g., shale formations, tight sandstone formations, sandstone formations, mudstone formations, carbonate formations, hot dry rock formations, etc.). In other words, the hydraulically connected portions of the multiple wellbores may be located in the same formation (the formation type must be the same) or in different formations of the same formation type, thereby preventing the injected fluid from being concentrated in the formation with higher permeability and the wellbores in the formation due to large differences in formation permeability.

[0064] Embodiment 2: Different from Embodiment 1, in this embodiment, the wellbore into which the high-pressure fluid is injected during energy storage is different from the wellbore from which the high-pressure fluid is discharged during energy release.

[0065] That is to say, a part of the wellbore is used as an injection wellbore for injecting high-pressure fluid; and the rest of the wellbore is used as a discharge wellbore for discharge of high-pressure fluid.

[0066] When storing energy, the reverse wellbore is closed and the injection wellbore is opened, and high-pressure fluid is injected into the injection wellbore; when releasing energy, the injection wellbore is closed, the reverse wellbore is opened, and high-pressure fluid is reversed from the reverse wellbore.

[0067] Likewise Figure 2As shown, during the energy storage process, high-pressure fluid is injected into the wellbore 104 through the injection device 114, and the openings of the wellbores 102 and 106 are blocked by the plugging device. The high-pressure fluid will increase the fluid pressure in the pores and cracks of the formation rock around the wellbore 104. With the continuous injection of the high-pressure fluid, the high-pressure fluid will diffuse outward through the cracks and rock pores in the formation 108, and eventually increase the pore pressure of the formation rock around the wellbore 102 and the wellbore 106 and the fluid pressure in the cracks connected to the wellbore 102 and 106. The rock pore pressure in the formation 108 and the fluid pressure in the cracks are increased, and the formation rock undergoes elastic deformation energy for storage; the high-pressure fluid will also store the fluid compression potential energy as the formation pressure increases; at the same time, the formation will also exchange heat with the high-pressure fluid injected into the formation, increasing the temperature of the injected formation fluid.

[0068] Since wellbores 102 , 104 , and 106 are hydraulically connected through formation fractures and / or formation rock pores, injecting high-pressure fluid into wellbores 104 will eventually increase the bottomhole and wellhead pressures of wellbores 102 and 106 .

[0069] When energy storage is finished, the injection of high-pressure fluid into the wellbore 104 is stopped and the opening of the wellbore 104 is sealed with a sealing device to keep the rock pore pressure in the formation 108 and the fluid pressure in the fractures unchanged, thereby storing energy.

[0070] When energy release is required, high-pressure fluid is discharged from wellbore 102 and / or wellbore 106, and the kinetic energy of the discharged high-pressure fluid, and / or the compression potential energy of the high-pressure fluid, and / or the heat of the fluid are converted back into electrical energy through ground power generation equipment.

[0071] Embodiment 3: In existing geothermal exploitation, injection wells usually continue to inject fluid into the formation without interruption, because interrupting the injection will make it difficult to restart the supporting equipment on the ground.

[0072] In order to solve the above problems in the prior art, different from the first embodiment, in this embodiment, a part of the wellbore is used as an injection wellbore for injecting high-pressure fluid; the rest of the wellbore is used as a discharge wellbore for discharging high-pressure fluid; When storing energy, the reverse wellbore is closed and the injection wellbore is opened, and high-pressure fluid is injected into the injection wellbore; when releasing energy, both the reverse wellbore and the injection wellbore are opened, and the flow rate of the reverse high-pressure fluid discharged from the reverse wellbore is greater than the flow rate of the high-pressure fluid injected into the injection wellbore, so that when the energy release is completed (neither storing energy nor releasing energy), the amount of high-pressure fluid injected into the injection wellbore is equal to the amount of high-pressure fluid discharged from the reverse wellbore. That is to say, in this embodiment, energy storage and energy release do not need to be carried out continuously, but the time of energy release can be freely selected according to demand.

[0073] This implementation will Figure 2 Considered as a geothermal production system consisting of three wellbores. When the system is working normally, by injecting high-pressure fluid into wellbore 104, the fluid diffuses outward through the cracks and rock pores in the formation 108 and heats up with the formation rock, and the high-pressure fluid eventually reaches wellbore 106 and wellbore 102, and is discharged back to the ground to generate electricity through the organic Rankine cycle (ORC) power generation equipment. Usually, when the geothermal production system reaches a steady state, the sum of the fluid flow rates discharged from wellbore 106 and wellbore 102 is equal to the fluid flow rate injected into wellbore 104 (excluding part of the high-pressure fluid remaining in the wellbore and a small amount of fluid lost to the formation).

[0074] More specifically, during the energy storage process, the high-pressure fluid is continuously injected into the wellbore 104 through the injection device 114, and the openings of the wellbores 102 and 106 are blocked by the plugging device. As the original outlet channel of the fluid is blocked, the formation pressure that was originally in a stable state increases, so that the rock pore pressure and the fluid pressure in the cracks in the formation 108 increase, and the formation rock undergoes elastic deformation energy for storage; the high-pressure fluid will also store the fluid compression potential energy as the formation pressure increases; at the same time, the formation will also exchange heat with the high-pressure fluid injected into the formation, increasing the temperature of the injected formation fluid.

[0075] When energy release is required, high-pressure fluid is discharged from wellbore 102 and wellbore 106, and the kinetic energy of the discharged high-pressure fluid, the compression potential energy of the high-pressure fluid, and the heat of the fluid are converted back into electrical energy through the ground power generation equipment. In the early stage of energy release, the sum of the flow rates of the fluids discharged from wellbore 102 and wellbore 106 will be greater than the flow rate of the fluids injected from wellbore 104, that is, the energy released from the formation is greater than the energy injected from the wellbore. As the formation pressure decays, the flow rates of the fluids discharged from wellbore 102 and wellbore 106 will gradually decrease. Finally, when the energy of the formation reservoir is completely released, the sum of the flow rates of the fluids discharged from wellbore 102 and wellbore 106 will be equal to the flow rate of the fluids injected from wellbore 104 again.

[0076] In some embodiments, during the energy storage process, both the injection wellbore and the reverse flow wellbore are opened, and the flow rate of high-pressure fluid injected into wellbore 104 is less than the flow rate of high-pressure fluid reversed from wellbores 102 and 106, so that the formation pressure continues to increase.

[0077] In some embodiments, during the energy release process, the injection of high-pressure fluid into the injection wellbore 104 is stopped (the injection wellbore 104 is closed), and only the high-pressure fluid is discharged from the reverse wellbore 102 and the reverse wellbore 106 (the reverse wellbore 102 and the reverse wellbore 106 are opened), so that the formation pressure continues to decrease.

[0078] In some embodiments, proppants are present inside the formation fractures, which enhance the ability of fluids to migrate within the fractures.

[0079] In some embodiments, during the energy storage process, the formation fluid pressure generated after the high-pressure fluid enters the formation causes the bottom hole pressure of the wellbore to always be maintained at less than or equal to the formation fracture closure stress (usually equal to the minimum principal stress of the formation). Even if the formation fracture is closed, there are still gaps on the fracture surface due to the roughness of the fracture surface or the support of the proppant. The increase in fluid pressure in the gap can also make the gap larger.

[0080] In some embodiments, during the energy storage process, the formation fluid pressure generated after the high-pressure fluid enters the formation causes the bottom hole pressure of the wellbore to be higher than the formation fracture closure stress, thereby increasing the width of the formation fracture.

[0081] In some embodiments, during the energy storage process, the formation fluid pressure generated after the high-pressure fluid enters the formation causes the bottom hole pressure of the wellbore to be higher than the formation fracture closure stress and lower than the formation fracture expansion pressure, so that the formation fracture width increases while the formation fracture does not expand.

[0082] In some embodiments, during the energy storage process, the formation fluid pressure generated after the high-pressure fluid enters the formation causes the bottom hole pressure of the wellbore to be higher than the formation fracture expansion pressure, causing the formation fractures to expand, allowing the formation fluid to migrate to a farther place for storage.

[0083] In some embodiments, during the energy storage process, when there are multiple fractures in the formation with different closure stresses, the formation fluid pressure generated after the high-pressure fluid enters the formation causes the bottom hole pressure of the wellbore to be higher than the minimum closure stress of the multiple formation fractures, thereby increasing the width of at least one of the formation fractures.

[0084] Embodiment 4: Figure 2 As shown, the present invention also provides a multi-well energy storage and release system, comprising: The injection device is used to inject high-pressure fluid into one or more of the wellbores, so that the high-pressure fluid enters the formation cracks and / or rock pores, thereby driving the formation rock to undergo elastic deformation and accumulate elastic potential energy, and in the case where the high-pressure fluid is compressible, the high-pressure fluid generates fluid compression potential energy under the reaction force of the formation rock; at the same time, the high-pressure fluid exchanges heat with the formation rock to obtain formation thermal energy. For example, the injection device 112, the injection device 114, and the injection device 116 in the figure are used to inject high-pressure fluid into the wellbore 102, the wellbore 104, and the wellbore 106, respectively.

[0085] A plugging device is used to plug the wellbore opening and maintain elastic deformation of the formation rock to store energy; A power generation device is used to convert at least one of the kinetic energy of high-pressure fluid converted from the elastic potential energy accumulated in the formation rock, the fluid compression potential energy released by the high-pressure fluid, and the thermal energy carried by the high-pressure fluid into electrical energy.

[0086] It should be noted that, in this article, the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the sentence "comprises a ..." does not exclude the existence of other identical elements in the process, method, article or device including the element.

[0087] Through the description of the above implementation methods, those skilled in the art can clearly understand that the above-mentioned embodiment methods can be implemented by means of software plus a necessary general hardware platform, and of course by hardware, but in many cases the former is a better implementation method. Based on such an understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, can be embodied in the form of a software product, which is stored in a storage medium (such as ROM / RAM, a magnetic disk, or an optical disk), and includes a number of instructions for a computer terminal (which can be a mobile phone, a computer, a server, or a network device, etc.) to execute the methods described in each embodiment of the present invention.

[0088] The embodiments of the present invention are described above in conjunction with the accompanying drawings, but the present invention is not limited to the above-mentioned specific implementation modes, which are merely illustrative rather than restrictive. Under the guidance of the present invention, ordinary technicians in this field can also make many forms without departing from the scope of protection of the present invention and the claims, all of which are within the protection of the present invention.

Claims

1. A multi-well energy storage and release method, characterized in that include: Select at least two wellbores hydraulically connected through formation fractures and / or rock pores as wellbores for energy storage and / or energy release; When storing energy, high-pressure fluid is injected into one or more of the wellbores, so that the high-pressure fluid enters the formation cracks and / or rock pores, thereby driving the formation rock to undergo elastic deformation and accumulate elastic potential energy; and when the high-pressure fluid is compressible, the high-pressure fluid generates fluid compression potential energy under the reaction force of the formation rock; at the same time, the high-pressure fluid exchanges heat with the formation rock to obtain formation thermal energy; the wellbores are blocked to maintain the elastic deformation of the formation rock to store energy; When releasing energy, the wellbore plugging pressure is reduced so that one or several wells in the wellbore can discharge high-pressure fluid, and in the process of discharge, at least one of the following is obtained: the kinetic energy of the high-pressure fluid converted from the elastic potential energy accumulated in the formation rock, the fluid compression potential energy released by the high-pressure fluid, and the thermal energy carried by the high-pressure fluid.

2. A multi-well energy storage and release method according to claim 1, characterized in that: The preset power generation equipment is used to convert at least one of the kinetic energy of the high-pressure fluid converted from the elastic potential energy accumulated in the formation rock, the fluid compression potential energy released by the high-pressure fluid, and the thermal energy carried by the high-pressure fluid into electrical energy.

3. A multi-well energy storage and release method according to claim 2, characterized in that: The power generation equipment is one or more of a hydraulic turbine, a steam turbine, a supercritical carbon dioxide turbine, an expander, a heat exchanger, and an organic Rankine cycle power generation equipment.

4. A multi-well energy storage and release method according to claim 1, characterized in that: The bottom hole pressure or wellhead pressure of all wellbores is made consistent by increasing the injection rate of high-pressure fluid into the wellbore with lower bottom hole pressure or / and reducing the injection rate of high-pressure fluid into the wellbore with higher bottom hole pressure.

5. A multi-well energy storage and release method according to claim 1, characterized in that: When storing energy, the injection of high-pressure fluid into the wellbore is stopped before the bottom hole or / and wellhead pressure reaches a pressure threshold; the pressure threshold is calculated based on one or more of the pressure levels of the injection device and the plugging device, the maximum yield strength of the wellbore casing, the closing stress of the formation fracture, the expansion pressure of the formation fracture, the maximum allowable width of the formation fracture, and the fault slip pressure in the formation.

6. A multi-well energy storage and release method according to claim 1, characterized in that: When storing energy, high-pressure fluid is injected into all wellbores at the same time; when releasing energy, high-pressure fluid is discharged back through all wellbores at the same time; or, The wellbore into which high-pressure fluid is injected when storing energy is different from the wellbore into which high-pressure fluid is discharged when releasing energy.

7. A multi-well energy storage and release method according to claim 1, characterized in that: A portion of the wellbore is used as an injection wellbore for injecting high-pressure fluid; the rest of the wellbore is used as a reverse wellbore for reversely discharging high-pressure fluid; when storing energy, the reverse wellbore is closed and the injection wellbore is opened, and high-pressure fluid is injected into the injection wellbore; when releasing energy, both the reverse wellbore and the injection wellbore are opened, and the flow rate of the reverse high-pressure fluid discharged from the reverse wellbore is greater than the flow rate of the high-pressure fluid injected into the injection wellbore, so that when the energy release is completed, the injection amount of the high-pressure fluid in the injection wellbore is equal to the reverse discharge amount of the high-pressure fluid in the reverse wellbore; Alternatively, a portion of the wellbore is used as an injection wellbore for injecting high-pressure fluid; the rest of the wellbore is used as a reverse wellbore for reversely discharging high-pressure fluid; when storing energy, the reverse wellbore is closed and the injection wellbore is opened, and high-pressure fluid is injected into the injection wellbore; when releasing energy, the injection wellbore is closed, the reverse wellbore is opened, and the high-pressure fluid is reversed from the reverse wellbore; Alternatively, a portion of the wellbore is used as an injection wellbore for injecting high-pressure fluid; the rest of the wellbore is used as a reverse wellbore for reversely discharging high-pressure fluid; when storing energy, both the injection wellbore and the reverse wellbore are opened, but the flow rate of the high-pressure fluid injected into the injection wellbore is greater than the flow rate of the high-pressure fluid discharged from the reverse wellbore; when releasing energy, both the reverse wellbore and the injection wellbore are opened, and the flow rate of the high-pressure fluid discharged from the reverse wellbore is greater than the flow rate of the high-pressure fluid injected into the injection wellbore, so that when the energy release is completed, the amount of high-pressure fluid injected into the injection wellbore is equal to the amount of high-pressure fluid discharged from the reverse wellbore; Alternatively, a portion of the wellbore is used as an injection wellbore for injecting high-pressure fluid; the remaining portion of the wellbore is used as a discharge wellbore for discharging high-pressure fluid; when storing energy, both the injection wellbore and the discharge wellbore are opened, but the flow rate of the high-pressure fluid injected into the injection wellbore is greater than the flow rate of the high-pressure fluid discharged from the discharge wellbore; when releasing energy, the injection wellbore is closed, the discharge wellbore is opened, and the high-pressure fluid is discharged from the discharge wellbore.

8. A multi-well energy storage and release method according to claim 1, characterized in that: During the energy storage process, the bottom hole pressure of the wellbore is less than or equal to the closing stress of the formation fracture; Alternatively, the bottom hole pressure of the wellbore is higher than the closure stress of the formation fracture, so that the width of at least one formation fracture increases; Alternatively, the bottom hole pressure of the wellbore is higher than the expansion pressure of the formation fracture.

9. A multi-well energy storage and release method according to claim 1, characterized in that: The hydraulically connected portions of the wellbores are located in formations of the same formation type.

10. A multi-well energy storage and release system, characterized in that include: An injection device is used to inject a high-pressure fluid into one or more of the wellbores, so that the high-pressure fluid enters the formation cracks and / or rock pores, thereby driving the formation rock to undergo elastic deformation and accumulate elastic potential energy; and in the case where the high-pressure fluid is compressible, the high-pressure fluid generates fluid compression potential energy under the reaction force of the formation rock; at the same time, the high-pressure fluid exchanges heat with the formation rock to obtain formation thermal energy; A plugging device is used to plug the wellbore opening and maintain elastic deformation of the formation rock to store energy; A power generation device is used to convert at least one of the kinetic energy of high-pressure fluid converted from the elastic potential energy accumulated in the formation rock, the fluid compression potential energy released by the high-pressure fluid, and the thermal energy carried by the high-pressure fluid into electrical energy.

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