A method and system for storing and releasing energy through fractures at different positions in a formation

Abstract

The present invention relates to the field of energy storage technologies. Specifically, the present invention discloses a method and system for storing and releasing energy in fractures at different positions in a formation. The method includes an integrated energy storage and release method or a split energy storage and release method that can operate independently. The integrated energy storage and release method includes: selecting at least two formation fractures at different depth positions as target energy storage fractures, and connecting the target energy storage fractures using a wellbore; injecting high-pressure fluid into the wellbore so that the high-pressure fluid can enter all the target energy storage fractures connected to the wellbore; sealing the opening of the wellbore to maintain the elastic deformation of the formation rock for energy storage; when releasing energy, reducing the wellbore sealing pressure so that the target energy storage fractures close, and using the high-pressure fluid backflowed during the closing process to generate electricity. The present invention is applicable to the energy storage and release in formation fractures at multiple different depth positions.

Description

[0001] Divisional Application

[0002] This application is a divisional application of the Chinese invention patent application [Application No.: 202411342565.8] [Title: A Method and System for Energy Storage and Release at Different Positions in the Stratum] filed on September 25, 2024. Technical Field

[0003] The present invention belongs to the field of underground energy storage, and particularly relates to a method and system for energy storage and release in fractures at different positions in the stratum. Background Art

[0004] Many renewable energy sources such as solar energy and wind energy have daily and seasonal intermittency, and their power output is unstable, making them unsuitable for providing base load power. Therefore, it is difficult to directly connect to the power grid, and solving the energy storage problem is the key to successfully expanding the production scale of renewable energy. Therefore, how to store excess clean electricity on a large scale and stably transmit electricity when both sunlight and wind power supplies are insufficient remains a technical problem that countries are working on.

[0005] Currently, large-scale power storage methods include using lead-acid batteries, lithium-ion batteries, hydrogen fuel cells, compressed air energy storage, and pumped hydro energy storage. Among them, lead-acid batteries, lithium-ion batteries, and hydrogen fuel cell energy storage have not been widely used on a large scale due to high investment and maintenance costs; pumped hydro energy storage pumps water from a lower position to a higher position to convert electrical energy into the gravitational potential energy of water. Therefore, the pumped hydro energy storage method has certain requirements for the terrain structure and cannot be applied in 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.

[0006] In view of this, there is an urgent need for a new clean power storage method with low investment and maintenance costs and adaptable to various terrains. For example, the Chinese patent application with publication number CN114016988A discloses a method and system for energy storage and release through the stratum. It generates at least one stratum fracture by performing hydraulic fracturing construction in an energy storage stratum without oil and gas, then injects high-pressure fluid into the obtained stratum fracture to make the stratum fracture undergo elastic deformation for energy storage, and then discharges the high-pressure fluid in the fracture to push a preset power generation device for energy release. However, this method is only applicable to stratum fractures at the same height position. When there are multiple stratum fractures at different positions and with different closure pressures, this method is no longer applicable because the different closure pressures of the stratum fractures make it uncontrollable for the high-pressure fluid to enter and discharge from fractures at different positions. Summary of the Invention

[0007] The object of the present invention is to provide a method and system for storing and releasing energy at different positions in a formation, partially solving or alleviating the above deficiencies in the prior art, and being applicable to storing and releasing energy in formation fractures at multiple different depth positions.

[0008] To solve the above-mentioned technical problems, the present invention specifically adopts the following technical solutions:

[0009] A method for storing and releasing energy at different positions in a formation, including an integrated energy storage and release method or a split energy storage and release method that can operate independently.

[0010] The integrated energy storage and release method includes:

[0011] Select at least two formation fractures at different depth positions as target energy storage fractures, and connect the at least two target energy storage fractures at different depth positions through a wellbore.

[0012] Inject high-pressure fluid into the wellbore so that the high-pressure fluid can enter all the target energy storage fractures connected to the wellbore, thereby driving the width of the target energy storage fractures to increase and enabling the formation rock to accumulate elastic potential energy; the pressure generated by the high-pressure fluid at each target energy storage fracture is greater than the minimum closure pressure of the corresponding target energy storage fracture and less than the maximum energy storage pressure of the corresponding target energy storage fracture.

[0013] Seal the opening of the wellbore to maintain the elastic deformation of the formation rock for energy storage.

[0014] During energy release, reduce the sealing pressure of the wellbore to cause the target energy storage fractures to close, and convert the elastic potential energy accumulated in the formation rock into the kinetic energy of the high-pressure fluid during backflow when the fractures close.

[0015] The split energy storage and release method includes:

[0016] Select at least two or two groups of formation fractures connected through a wellbore as target energy storage fractures.

[0017] Inject high-pressure fluid into the wellbore. At the same time, the high-pressure fluid can only enter one of the target energy storage fractures, thereby driving the width of the target energy storage fracture to increase and enabling the formation rock to accumulate elastic potential energy; or, group the target energy storage fractures, and at the same time, the high-pressure fluid can only enter one group of the target energy storage fractures, thereby driving the width of all the target energy storage fractures in the group to increase and enabling the formation rock to accumulate elastic potential energy; the pressure generated by the high-pressure fluid at each target energy storage fracture in the group is greater than the minimum closure pressure of the corresponding target energy storage fracture and less than the maximum energy storage pressure of the corresponding target energy storage fracture.

[0018] Seal the opening of the wellbore to maintain the elastic deformation of the formation rock for energy storage.

[0019] During energy release, reduce the wellbore plugging pressure to close the target energy storage fracture, and convert the elastic potential energy stored in the formation rock into the kinetic energy during the reverse flow of high-pressure fluid during the closing process.

[0020] As an improvement, in the integrated energy storage and release method, use the maximum energy storage pressure of the first target energy storage fracture at depth H1, the minimum closing pressure of the second target energy storage fracture at depth H2, and the depths of the first target energy storage fracture and the second target energy storage fracture from the wellhead to calculate the density range of the high-pressure fluid, where H1 < H2; specifically, it includes using the formula:

[0021] < < ;

[0022] Calculate the density range of the high-pressure fluid; where, is the maximum energy storage pressure of the first target energy storage fracture, is the density of the high-pressure fluid, is the acceleration due to gravity, H1 is the depth of the first target energy storage fracture from the wellhead, H2 is the depth of the second target energy storage fracture from the wellhead, is the minimum closing pressure of the second target energy storage fracture, and P0 is the injection pressure of the high-pressure fluid.

[0023] As an improvement, in the split-type energy storage and release method, the difference between the minimum closing pressures of the target energy storage fractures in the same group is less than the threshold.

[0024] As an improvement, in the split-type energy storage and release method, at the same time, only one target energy storage fracture or a group of target energy storage fractures are closed to convert the elastic potential energy into the kinetic energy during the reverse flow of high-pressure fluid.

[0025] As an improvement, in the split-type energy storage and release method, each or each group of the target energy storage fractures are respectively sealed in independent cavities; the cavities have channels communicating with the wellbore, and the channels can be opened and closed.

[0026] As an improvement, the target energy storage fracture is a hydraulic fracturing fracture, a natural fracture or a fault gap.

[0027] As an improvement, when injecting the high-pressure fluid, use electric energy to drive the injection equipment; during energy release, convert the kinetic energy during the reverse flow of the high-pressure fluid into electric energy through a preset generator.

[0028] As an improvement, in the split-type energy storage and release method, select any one of the target energy storage fractures or any group of target energy storage fractures with corresponding energy storage to close according to the power demand of the generator.

[0029] The present invention also provides a system for storing and releasing energy at different positions in a formation, which deploys the above-mentioned integrated energy storage and release method, including:

[0030] An injection device for injecting high-pressure fluid into the target energy storage fracture through the wellbore, so as to drive the width of the target energy storage fracture to increase and enable the formation rock to accumulate elastic potential energy; the pressure generated by the high-pressure fluid at each target energy storage fracture is greater than the minimum closure pressure of the target energy storage fracture and less than the maximum energy storage pressure of the target energy storage fracture;

[0031] A plugging device for plugging the wellbore opening to maintain the elastic deformation of the formation rock for energy storage;

[0032] A power generation device for converting the kinetic energy of the high-pressure fluid discharged during the closing process of the target energy storage fracture, which is converted from the elastic potential energy accumulated by the formation rock, into electrical energy.

[0033] The present invention also provides a system for storing and releasing energy at different positions in a formation, which deploys the above-mentioned split energy storage and release method, including:

[0034] A packer device for separately isolating each target energy storage fracture or each group of target energy storage fractures connected to the wellbore in independent cavities;

[0035] A channel opening and closing device for opening or closing the channel connecting the cavity and the wellbore;

[0036] An injection device for injecting high-pressure fluid into the target energy storage fracture through the wellbore. With the cooperation of the channel opening and closing device, the high-pressure fluid can only enter one of the target energy storage fractures connected to the wellbore at the same time, so as to drive the width of the target energy storage fracture to increase and enable the formation rock to accumulate elastic potential energy; or, at the same time, the high-pressure fluid can only enter one of the groups of target energy storage fractures, so as to drive the width of all the target energy storage fractures in the group to increase and enable the formation rock to accumulate elastic potential energy; the pressure generated by the high-pressure fluid at each of the target energy storage fractures in the group is greater than the minimum closure pressure of the corresponding target energy storage fracture and less than the maximum energy storage pressure of the corresponding target energy storage fracture;

[0037] A plugging device for plugging the wellbore opening to maintain the elastic deformation of the formation rock for energy storage;

[0038] A power generation device for converting the kinetic energy of the high-pressure fluid discharged during the closing process of the target energy storage fracture, which is converted from the elastic potential energy accumulated by the formation rock, into electrical energy.

[0039] The advantages of the present invention are as follows: The present invention is driven by electric energy and injects high-pressure fluid into fractures at different positions in the formation, so as to increase the fracture width of the formation fractures, thereby converting electric energy into elastic deformation energy of the formation rock for storage, and further realizing energy storage with low investment and low maintenance costs. Among them, the electric energy in the above steps can be derived from renewable energy such as wind power generation or solar power generation.

[0040] Further, during the gradual closing process of the formation fractures, due to the extrusion of the formation rock, the high-pressure fluid in the fractures is backflowed to the ground to drive a preset power generation device to generate electricity, that is, the elastic deformation energy of the formation fractures is converted into electric energy, thereby realizing stable power supply in the case of insufficient solar or wind energy.

[0041] The method and system of the present invention can convert the electric energy generated by sunlight or wind into elastic deformation energy of rock for storage when sunlight or wind is sufficient, and release the electric energy to the power grid when needed, which is of great significance for the grid peak regulation of wind power generation or solar power generation.

[0042] The method disclosed by the present invention also relates to the hydraulic fracturing method. As a mature technology in the field of oil and gas, the hydraulic fracturing method has been widely used, so the relevant construction supporting equipment is easy to obtain and the cost is controllable.

[0043] In addition, in some embodiments, multiple formation fractures perform integrated energy storage and energy release, with low cost and simple control.

[0044] In other embodiments, multiple formation fractures are respectively controlled for energy storage and energy release, which is more flexible and convenient to use compared with the integrated type. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for description in the embodiments or the prior art. In all the drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, the elements or parts are not necessarily drawn to actual scale. Obviously, the following-described drawings are some embodiments of the present invention, and those of ordinary skill in the art can obtain other drawings according to these drawings without creative efforts.

[0046] Figure 1 It is the flowchart of Embodiment 1;

[0047] Figure 2 It is the structural schematic diagram of Embodiment 1;

[0048] Figure 3 It is the flowchart of Embodiment 2;

[0049] Figure 4 It is a schematic structural diagram of the second embodiment;

[0050] Figure 5 It is a schematic structural diagram of the third embodiment.

[0051] Markings in the figure: 110 formation, 120 wellbore, 130 first target energy storage fracture, 140 second target energy storage fracture.

[0052] 200 injection device I, 215 third target energy storage fracture, 220 fourth target energy storage fracture, 225 fifth target energy storage fracture, 240 inner pipe I, 245 packer I, 250 packer II, 255 packer III, 260 water distributor X, 265 water distributor I, 270 water distributor II, 275 channel opening and closing device X, 280 channel opening and closing device I, 285 channel opening and closing device II.

[0053] 300 injection device II, 305 sixth target energy storage fracture group, 310 seventh target energy storage fracture group, 315 eighth target energy storage fracture group, 320 ninth target energy storage fracture group, 325 inner pipe II, 330 packer IV, 335 packer V, 340 packer VI, 345 packer VII, 350 packer VIII, 355 water distributor III, 360 water distributor IV, 365 water distributor V, 370 water distributor VI, 375 channel opening and closing device III, 380 channel opening and closing device IV, 385 channel opening and closing device V, 390 channel opening and closing device VI. Detailed implementation manners

[0054] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some but not all of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0055] In this article, suffixes such as "module", "component" or "unit" used to represent elements are only for the convenience of explaining the present invention and have no specific meaning in themselves. Therefore, "module", "component" or "unit" can be used interchangeably.

[0056] In this text, the orientation or positional relationships indicated by terms such as "upper", "lower", "inner", "outer", "front", "rear", "one end", "the other end", etc. are based on the orientation or positional relationships shown in the drawings. These are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the devices or elements referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation on the present invention. In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance.

[0057] In this text, unless otherwise clearly specified and defined, terms such as "installed", "provided with", "connected", etc. shall 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, and can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0058] In this text, "and / or" includes any and all combinations of one or more of the listed related items.

[0059] In this text, "a plurality of" means two or more, that is, it includes two, three, four, five, etc.

[0060] Glossary of terms: The "fluid" in this text can be, but is not limited to, gas, liquid, emulsion, slurry, and solid particle flow with flow characteristics similar to that of a liquid. For example, the fluid can include water-based liquids with chemical additives or supercritical carbon dioxide. In addition, the chemical additives can include, but are not limited to, acids, gels, potassium chloride, surfactants, etc.

[0061] The "formation" in this text is a subsurface porous and permeable rock formation (e.g., shale formation, sandstone formation, carbonate rock formation, etc.), which can act as a storage space for fluids. Usually, these fluids can be water, hydrocarbons, or gas. The fluid loss into the formation from the fractures in the formation can be reduced or hindered by adding a fluid loss control agent to the fluid injected into the fractures in the formation.

[0062] The "hydraulic fracturing" or "fracturing" or "rupturing" in this text refers to the generation and propagation of fractures in formation rocks under the action of external forces (such as high-pressure fluids).

[0063] The "formation fracture" or "fracture" in this text is the rock opening gap created in the formation after hydraulic fracturing operations, or the natural fractures or fault gaps originally existing in the formation. The terms "formation fracture" and "fracture" can be used interchangeably. "Fracture" can refer to a single fracture, or multiple adjacent fractures or fracture swarms at the same location.

[0064] The "wellbore" in this article refers to a hole drilled or a conduit inserted in a formation. Generally, the wellbore is cylindrical, so the cross-section of the wellbore may be circular. Additionally, the wellbore may have any other cross-section. The wellbore can be an open hole, i.e., an open-hole wellbore, or a cased wellbore can be made by cementing a casing on the inner wall of the wellbore. The wellbore connecting the fractures can be a vertical well, a horizontal well, or an inclined well.

[0065] The "fracture closure stress" or "closure stress" in this article refers to the stress acting vertically on the fracture wall. For a horizontal fracture, the fracture closure stress is equal to the vertical stress applied to the fracture wall; for a vertical fracture, the fracture closure stress is equal to the minimum horizontal principal stress applied to the fracture wall. The fracture closure stress can be obtained through a diagnostic fracturing injection test or a rapid injection-flowback test. The fracture closure stress can also be calculated by combining well logging data and a geostress model. The terms "fracture closure stress" or "closure stress" can be interchanged. The fractures in this article can be vertical fractures or horizontal fractures.

[0066] The "fracture width" in this article refers to the relative displacement distance between the two walls in the direction perpendicular to the fracture plane of the formation.

[0067] The "target energy storage fracture" and "target fracture" in this article are both fractures selected for energy storage. The terms "target energy storage fracture" or "target fracture" can be interchanged.

[0068] Example 1

[0069] Fractures at different positions in the formation usually have different closure pressures due to different formation depths or different rock mechanical properties of the formation they are in (such as different Young's moduli or Poisson's ratios). Fractures at greater formation depths usually have greater closure pressures than those at shallower formation depths. Fractures at different positions in the formation can be created by means such as multi-stage fracturing or temporary plugging fracturing. Fractures of different geometric sizes can be created according to the preset energy storage sizes at different positions.

[0070] To apply fractures in the formation at different height positions as energy storage bodies, as Figure 1 shown, the present invention provides a method for storing and releasing energy at different positions in the formation, specifically an integrated energy storage and release method, and its specific steps include:

[0071] S101 Select formation fractures at at least two different depth positions as target energy storage fractures, and connect the target energy storage fractures with a wellbore.

[0072] In this embodiment, the selected formation fractures can be fractures formed by hydraulic fracturing, natural fractures or fault fractures, as long as they can undergo elastic deformation under the action of high-pressure fluid to accumulate elastic potential energy.

[0073] In addition, in order to facilitate the injection of high-pressure fluid and generate electricity using the backflow high-pressure fluid, multiple target energy storage fractures are connected by the same wellbore (especially a vertical well). As Figure 2 shown, in this embodiment, for the sake of simplicity of description, a simple model is used to illustrate the principle of the present invention. In this embodiment, the target energy storage fractures connected by the wellbore 120 in the formation 110 include the first target energy storage fracture at the depth H1 and the second target energy storage fracture at the depth H2. It can be foreseen that the number of target energy storage fractures can exceed 2. For example, in addition to the first target energy storage fracture and the second target energy storage fracture, there is one or more target energy storage fractures between the above-mentioned first target energy storage fracture and the second target energy storage fracture.

[0074] S102 Inject high-pressure fluid into the wellbore so that the high-pressure fluid can enter all the target energy storage fractures connected to the wellbore, thereby driving the width of the target energy storage fractures to increase and enabling the formation rock to accumulate elastic potential energy; the pressure generated by the high-pressure fluid at each target energy storage fracture is greater than the minimum closure pressure of the target energy storage fracture and less than the maximum energy storage pressure of the target energy storage fracture.

[0075] During the energy storage process, it is necessary to inject high-pressure fluid into the target energy storage fractures through the wellbore, and use the pressure of the high-pressure fluid to increase the width of the target energy storage fractures, so as to enable the formation rock to accumulate elastic potential energy.

[0076] In this embodiment, it is assumed that the maximum energy storage pressure of the first target energy storage fracture at the depth H1 is , the maximum energy storage pressure of the second target energy storage fracture at the depth H2 is , the minimum closure pressure of the first target energy storage fracture at the depth H1 is , and the minimum closure pressure of the second target energy storage fracture at the depth H2 is . Preferably, H1 < H2. Generally speaking, < , < .

[0077] When injecting high-pressure fluid into the wellbore 120, the injection pressure is P0, the fracture pressure of the first target energy storage fracture 130 is , and the fracture pressure of the second target energy storage fracture 140 is If the friction in the wellbore is ignored, the fracture pressure of the first target energy storage fracture 130 , and the fracture pressure of the second target energy storage fracture 140 , where is the density of the high-pressure fluid injected into the injection wellbore 120, is the acceleration due to gravity (approximately equal to 9.8 m / ), and H2 are the vertical distances from the wellhead to the first target energy storage fracture and the second target energy storage fracture, respectively.

[0078] For given formation rock mechanical properties (Young's modulus, Poisson's ratio, and fracture toughness) and fracture dimensions, to prevent the fracture from expanding in the length or height direction during energy storage, there is a maximum value for the fracture pressure and the volume of fluid injected into the fracture (i.e., the maximum energy storage pressure and the maximum energy storage volume). When the fracture pressure and the volume of fluid injected into the fracture reach the maximum value, the fracture reaches the maximum energy storage state. When the fracture pressure or the volume of fluid injected into the fracture is greater than the maximum value, the fracture will expand in the length or height direction.

[0079] Therefore, when injecting high-pressure fluid, both the closure pressure and the maximum energy storage pressure need to be considered. That is, the pressure generated by the high-pressure fluid at each target energy storage fracture is greater than the minimum closure pressure of the target energy storage fracture and less than the maximum energy storage pressure of the target energy storage fracture. For the upper and lower two target energy storage fractures in this embodiment, the conditions that the high-pressure fluid density needs to meet are: .

[0080] Due to the different depth positions of each target energy storage fracture, the pressure generated by the high-pressure fluid is also different. In this embodiment, the maximum energy storage pressure of the first target energy storage fracture located at depth H1, the minimum closure pressure of the second target energy storage fracture located at depth H2, and the depths of the first target energy storage fracture and the second target energy storage fracture from the wellhead are used to calculate the density range of the high-pressure fluid, H1 < H2; specifically, it includes using the formula: < < ;

[0081] Calculate the density range of the high-pressure fluid; where is the maximum energy storage pressure of the first target energy storage fracture, is the density of the high-pressure fluid, is the acceleration due to gravity, H1 is the vertical depth of the first target energy storage fracture from the wellhead, is the vertical depth of the second target energy storage fracture from the wellhead, is the minimum closure pressure of the second target energy storage fracture, and P0 is the injection pressure of the high-pressure fluid.

[0082] It should be noted that the density of the high-pressure fluid needs to be within the above range to ensure that each target energy storage fracture can be opened and will not expand. It can be understood that for embodiments with two or more target energy storage fractures, as long as the shallowest and deepest target energy storage fractures can be opened and will not expand, the target energy storage fractures in the middle position can be satisfied. That is, by controlling the density of the high-pressure fluid, the fractures at different depths can be opened and will not expand to a certain extent, that is, the controllability of the fractures at different positions can be achieved to a certain extent.

[0083] In some other embodiments, in addition to calculating the density using the simplified model in Embodiment 1 the density can also be calculated by methods such as numerical simulation .

[0084] In this embodiment, the minimum closure pressure and the maximum energy storage pressure of the target energy storage fracture can be calculated using the size of the target energy storage fracture and the formation rock mechanical properties.

[0085] S103 Seal the wellbore opening and maintain the elastic deformation of the formation rock to store energy.

[0086] When high-pressure fluid is injected into all target energy storage fractures to cause deformation, the wellbore opening can be closed so that the pressure inside the wellbore is maintained, and thus the elastic deformation of the formation rock is also maintained to achieve the purpose of energy storage.

[0087] S104 When releasing energy, reduce the wellbore sealing pressure to make the target energy storage fracture close, and convert the elastic potential energy stored in the formation rock into the kinetic energy when the high-pressure fluid flows back during the closing process.

[0088] When energy needs to be released, only the wellbore sealing pressure needs to be reduced. The target energy storage fracture will gradually close due to pressure relief, and the elastic potential energy stored in the formation rock will be converted into the kinetic energy when the high-pressure fluid flows back during the closing process. In this embodiment, a generator is preset at the wellbore outlet to convert the kinetic energy when the high-pressure fluid flows back into electrical energy again.

[0089] Based on the above method, this embodiment provides a system for storing and releasing energy at different positions in the formation, which deploys the integrated energy storage and release method disclosed in Embodiment 1, including:

[0090] An injection device for injecting high-pressure fluid into the target energy storage fracture through the wellbore to drive the width of the target energy storage fracture to increase and enable the formation rock to store elastic potential energy; the pressure generated by the high-pressure fluid at each target energy storage fracture is greater than the minimum closure pressure of the target energy storage fracture and less than the maximum energy storage pressure of the target energy storage fracture. This injection device can be driven by electrical energy.

[0091] A plugging device for plugging a wellbore opening and maintaining elastic deformation of formation rocks for energy storage.

[0092] A power generation device for converting the kinetic energy during the reverse discharge of high-pressure fluid converted from the elastic potential energy accumulated in formation rocks by a target energy storage fracture during the closing process into electrical energy.

[0093] Embodiment 2

[0094] Due to the randomness of the positions and characteristics of formation fractures, after the injection of high-pressure fluid, it is not necessarily possible to meet the requirement that the pressure generated at each target energy storage fracture is greater than the minimum closing pressure of the target energy storage fracture and less than the maximum energy storage pressure of the target energy storage fracture. This makes the energy storage for multiple formation fractures have certain limitations. To improve its universality, as Figure 3 shown, this embodiment provides a method for storing and releasing energy at different positions in a formation, specifically a split-type energy storage and release method, and its steps include:

[0095] S201 Select at least two formation fractures at different depth positions as target energy storage fractures, and the target energy storage fractures are connected by a wellbore.

[0096] In this embodiment, the selected formation fractures can be fractures formed by hydraulic fracturing, natural fractures or fault gaps, as long as they can undergo elastic deformation under the action of high-pressure fluid to accumulate elastic potential energy.

[0097] In addition, to facilitate the injection of high-pressure fluid and generate electricity using the reverse-discharged high-pressure fluid, multiple target energy storage fractures are connected by the same wellbore (especially a vertical well). In this embodiment, a simplified model is provided for easy description as Figure 4 shown. The wellbore connects the third target energy storage fracture 215 at depth H3, the fourth target energy storage fracture 220 at depth H4, and the fifth target energy storage fracture 225 at depth H5. It can be foreseen that the number of target energy storage fractures can exceed 2.

[0098] S202 Inject high-pressure fluid into the wellbore. At the same time, the high-pressure fluid can only enter one of the target energy storage fractures connected by the wellbore, so as to drive the width of the target energy storage fracture to increase and enable the formation rocks to accumulate elastic potential energy.

[0099] As Figure 4As shown in the figure, during the energy storage process, if electrical energy is used to drive an injection device to inject high-pressure fluid into the wellbore, it is assumed that the pressure generated by the high-pressure fluid can only open the third target energy storage fracture 215 of the target energy storage. However, the fourth target energy storage fracture 220 and the fifth target energy storage fracture 225 of the target energy storage cannot receive high-pressure fluid with a pressure lower than their closure pressure, so energy storage cannot be achieved. If the pressure of the high-pressure fluid is continuously increased to exceed the minimum closure pressure of the fourth target energy storage fracture 220 and the fifth target energy storage fracture 225, it may cause the pressure to exceed the maximum energy storage pressure of the third target energy storage fracture, resulting in the expansion of the third target fracture.

[0100] To avoid the above situation, in this embodiment, when injecting high-pressure fluid to drive the target energy storage fracture to generate elastic deformation, only one target energy storage fracture is injected at the same time. At this time, the remaining target energy storage fractures are in an isolated state from this target energy storage fracture, so the pressure of the high-pressure fluid only needs to be considered for this target energy storage fracture.

[0101] During the energy storage process, only high-pressure fluid is allowed to be injected into the fractures at one position at any time. Therefore, this method is not affected by the fracture closure pressure and the energy storage sequence of fractures at different positions. To achieve this goal, in this embodiment, each target energy storage fracture is separately sealed in an independent cavity; the cavity has a channel communicating with the wellbore, and the channel can be opened and closed.

[0102] S203 Plug the wellbore opening to maintain the elastic deformation of the formation rock for energy storage.

[0103] Similar to Embodiment 1, when all target energy storage fractures are injected with high-pressure fluid to generate deformation, the wellbore opening can be closed so that the pressure inside the wellbore is maintained, and thus the elastic deformation of the formation rock is also maintained to achieve the purpose of energy storage.

[0104] S204 When releasing energy, reduce the wellbore plugging pressure to close the target energy storage fracture, and convert the elastic potential energy accumulated in the formation rock into the kinetic energy when the high-pressure fluid flows back during the closing process.

[0105] When energy needs to be released, only the wellbore plugging pressure needs to be reduced. The target energy storage fracture will gradually close due to pressure relief, and the elastic potential energy accumulated in the formation rock will be converted into the kinetic energy when the high-pressure fluid flows back during the closing process. In this embodiment, a generator is preset at the wellbore outlet to convert the kinetic energy when the high-pressure fluid flows back into electrical energy again.

[0106] It should be noted that when there is a large difference in the closure pressures of the third target energy storage fracture 215, the fourth target energy storage fracture 220, and the fifth target energy storage fracture 225, uncontrollable backflow may occur during simultaneous closure. For example, the high-pressure fluid backflowing from the fifth target energy storage fracture 225 at depth H5 may enter the third target energy storage fracture 215 at depth H3 and the fourth target energy storage fracture 220 at depth H4, rather than flowing directly back out of the wellhead.

[0107] To avoid interference between fractures at different positions due to different closure pressures during the backflow process, during the energy release process, only one target energy storage fracture at a position is allowed to close at a time, and the high-pressure fluid in the fracture at this position is backflowed to the ground to drive a preset power generation device to generate electricity. Only one fracture at a position is allowed to close at any time during the energy release process, and the high-pressure fluid in the fracture at this position is backflowed to the ground to drive a preset power generation device to generate electricity. Therefore, this method is not affected by the fracture closure pressure and the energy release sequence of fractures at different positions. That is, the energy storage and release of each fracture can be controlled independently, so as to meet different power generation requirements.

[0108] Furthermore, the target energy storage fracture with corresponding energy storage is selected to close according to the power demand of the generator. Specifically, it can be one or multiple (with a small difference in closure pressure).

[0109] As Figure 4 shown, this embodiment provides a system for storing and releasing energy at different positions in a formation, which deploys the split-type energy storage and release method disclosed in Embodiment 2, including:

[0110] A sealing device for separately sealing the target energy storage fractures connected to the wellbore in independent cavities;

[0111] A channel opening and closing device for opening or closing the channel connecting the cavity and the wellbore;

[0112] An injection device for injecting high-pressure fluid into the target energy storage fracture through the wellbore. With the cooperation of the channel opening and closing device, the high-pressure fluid can only enter one of the target energy storage fractures connected to the wellbore at the same time, so as to drive the width of the target energy storage fracture to increase and enable the formation rock to accumulate elastic potential energy;

[0113] A plugging device for plugging the wellbore opening to maintain the elastic deformation of the formation rock for energy storage;

[0114] A power generation device for converting the kinetic energy of the high-pressure fluid during the backflow of the elastic potential energy accumulated from the formation rock by the target energy storage fracture during the closing process into electrical energy.

[0115] Specifically, following Example 2, the wellbore is connected to the third target energy storage fracture 215 at depth H3, the fourth target energy storage fracture 220 at depth H4, and the fifth target energy storage fracture 225 at depth H5. It can be foreseen that the number of target energy storage fractures can exceed three.

[0116] An inner pipe is arranged in the wellbore, and the sealing devices I 245, II 250, and III 255 are arranged along the axial direction of the wellbore, so as to seal the three target energy storage fractures in three independent cavities.

[0117] The injection device I 200 is provided with three water distributors, namely water distributor X 260, water distributor I 265, and water distributor II 270, corresponding to the three target energy storage fractures respectively. Each water distributor is equipped with a channel opening and closing device, and through the channel opening and closing device, the cavity can be connected to the inner pipe, so that high-pressure fluid can enter the target energy storage fracture in the cavity.

[0118] For example, to store energy in the third target energy storage fracture 215 at depth H3, it is necessary to open the channel opening and closing device X 275 and close the channel opening and closing devices I 280 and II 285. In this way, the high-pressure fluid injected from the inner pipe I 240 can only enter the third target energy storage fracture 215 at depth H3 through the only outlet (i.e., the channel opening and closing device X 275). Similarly, to store energy in the fourth target energy storage fracture 220 at depth H4, it is necessary to open the channel opening and closing device I 280 and close the channel opening and closing devices X 275 and II 285. In this way, the high-pressure fluid injected from the inner pipe I 240 can only enter the fourth target energy storage fracture 220 at depth H4 through the only outlet (i.e., the channel opening and closing device I 280). Similarly, to store energy in the fifth target energy storage fracture 225 at depth H5, it is necessary to open the channel opening and closing device II 285 and close the channel opening and closing devices X 275 and I 280. In this way, the high-pressure fluid injected from the inner pipe I 240 can only enter the fifth target energy storage fracture 225 at depth H5 through the only outlet (i.e., the channel opening and closing device II 285).

[0119] If the channel opening and closing device X 275 is opened when storing energy in the fifth target energy storage fracture 225 at depth H5, then the subsequent high-pressure fluid injected into the inner pipe I 240 will enter the third target energy storage fracture 215 at position H3 because the third target energy storage fracture 215 has a smaller closure pressure. At the same time, the high-pressure fluid entering the fifth target energy storage fracture 225 will also flow back into the inner pipe I 240 and can even enter the third target energy storage fracture 215 at depth H3 through the channel opening and closing device X 275. This will cause serious interference to the energy storage of the fifth target energy storage fracture 225.

[0120] It can be seen that during the energy storage process, it is important to adjust the flow distribution device to only allow high-pressure fluid to be injected into one target energy storage fracture at any time and not allow the high-pressure fluid to flow into the fractures at other positions.

[0121] Through the cooperation of the injection device I200 and the channel opening and closing device on the water distributor, only high-pressure fluid is allowed to be injected into one target energy storage fracture at any time during the energy storage process. Therefore, this method is not affected by the fracture closure pressure and the energy storage sequence of fractures at different positions. For example, in some embodiments, the third target energy storage fracture 215 can be energized first, then the fourth target energy storage fracture 220 can be energized, and finally the fifth target energy storage fracture 225 can be energized. In other embodiments, the fifth target energy storage fracture 225 can be energized first, then the fourth target energy storage fracture 220 can be energized, and finally the third target energy storage fracture 215 can be energized. Switching from energizing the fifth target energy storage fracture 225 to energizing the fourth target energy storage fracture 220 can occur at any moment during the energy storage process, and it is not necessary to wait for the fifth target energy storage fracture 225 to reach the maximum energy storage value before switching to energizing the fourth target energy storage fracture 220.

[0122] After the energy storage is completed, if energy release is not required, the channel opening and closing device X275, the channel opening and closing device I280, and the channel opening and closing device II285 can all be closed, so that no high-pressure fluid will flow into and out of the target energy storage fracture, and the energy storage size of the target energy storage fracture remains unchanged.

[0123] During the energy release process, the wellhead pressure is reduced, causing the fracture to gradually close, driving the high-pressure fluid to flow back from the fracture to the ground and pushing the preset power generation equipment to generate electricity.

[0124] In some energy release embodiments, the channel opening and closing device X275, the channel opening and closing device I280, and the channel opening and closing device II285 can be opened simultaneously. The third target energy storage fracture 215 at depth H3 closes, driving the internal high-pressure fluid to flow into the inner pipe I240 through the channel opening and closing device X275. The fourth target energy storage fracture 220 at depth H4 closes, driving the internal high-pressure fluid to flow into the inner pipe I240 through the channel opening and closing device X280. The fifth target energy storage fracture 225 at depth H5 closes, driving the internal high-pressure fluid to flow into the inner pipe I240 through the channel opening and closing device II285. Finally, the high-pressure fluid converging in the inner pipe I240 flows back to the ground and pushes the preset power generation equipment to generate electricity.

[0125] When the closing pressures of the three target energy storage fractures vary significantly, uncontrollable backflow may occur when opening the three channel opening and closing devices simultaneously. For example, the high-pressure fluid backflowing from the fifth target energy storage fracture 225 at depth H5 enters the inner pipe I240 through the channel opening and closing device II285, and can then enter the third target energy storage fracture 215 at depth H3 and the fourth target energy storage fracture 220 at depth H4 through the channel opening and closing device X275 and the channel opening and closing device I280 respectively, rather than flowing directly back out of the wellhead.

[0126] To avoid interference between fractures at different positions due to different closing pressures during the backflow process, during the energy release process, only one target energy storage fracture is allowed to close at any given time, and the high-pressure fluid in the fracture at that position is backflowed to the ground to drive the preset power generation equipment.

[0127] For example, to release the energy of the third target energy storage fracture 215 at depth H3, it is necessary to open the channel opening and closing device X275 and close the channel opening and closing device I280 and the channel opening and closing device II285. In this way, the high-pressure fluid backflowing from the third target energy storage fracture 215 to the inner pipe I240 through the channel opening and closing device X275 can only be backflowed to the ground through the only outlet (i.e., the wellhead) to drive the preset power generation equipment. Similarly, to release the energy of the fourth target energy storage fracture 220 at depth H4, it is necessary to open the channel opening and closing device I280 and close the channel opening and closing device X275 and the channel opening and closing device II285. In this way, the high-pressure fluid backflowing from the fourth target energy storage fracture 220 to the inner pipe I240 through the channel opening and closing device I280 can only be backflowed to the ground through the only outlet (i.e., the wellhead) to drive the preset power generation equipment. Similarly, to release the energy of the fifth target energy storage fracture 225 at depth H5, it is necessary to open the channel opening and closing device II285 and close the channel opening and closing device X275 and the channel opening and closing device I280. In this way, the high-pressure fluid backflowing from the fifth target energy storage fracture 225 to the inner pipe I240 through the channel opening and closing device II285 can only be backflowed to the ground through the only outlet (i.e., the wellhead) to drive the preset power generation equipment.

[0128] Since only one position of the crack is allowed to close during the energy release process at any time, the high-pressure fluid in the crack at this position is discharged to the ground in the reverse direction and drives the preset power generation equipment to generate electricity. Therefore, this method is not affected by the crack closing pressure and the energy release sequence of cracks at different positions. For example, in some embodiments, the energy of the target third energy storage crack 215 can be released first, then the energy of the target fourth energy storage crack 220 can be released, and finally the energy of the target fifth energy storage crack 225 can be released. In other embodiments, the energy of the target fifth energy storage crack 225 can be released first, then the energy of the target fourth energy storage crack 220 can be released, and finally the energy of the target third energy storage crack 215 can be released. Switching from releasing the energy of the target fifth energy storage crack 225 to releasing the energy of the target fourth energy storage crack 220 can occur at any moment during the energy release process, and it is not necessary to wait until the energy storage of the target fifth energy storage crack 225 drops to zero before switching to releasing the energy of the target fourth energy storage crack 220.

[0129] In some embodiments, the target crack for which energy is to be released can be selected according to the current power generation power requirement. For example, when the power generation power requirement is small, the energy of the target third energy storage crack 215 located at depth H3 can be selected for release because the closing pressure of the target third energy storage crack 215 is low, and the fluid pressure discharged to the wellhead is also low. Therefore, the output power of the driving power generation equipment is also low. When the power generation power requirement is large, the energy of the target fifth energy storage crack 225 located at depth H5 can be selected for release because the closing pressure of the target fifth energy storage crack 225 is high, and the fluid pressure discharged to the wellhead is also high. Therefore, the output power of the driving power generation equipment is also high.

[0130] Embodiment III

[0131] In Embodiment II, since the depth difference between each target energy storage crack is large, the difference between the minimum closing pressure and the maximum energy storage pressure between the target energy storage cracks is also large. Therefore, each target energy storage crack needs to be used as an independent energy storage and release unit for separate control. In this embodiment, several target energy storage cracks with similar minimum closing pressures are grouped as an independent energy storage and release unit for separate control, thereby reducing the equipment cost.

[0132] For cracks in different depth formations connected by vertical wells or inclined wells, the minimum closing pressure is generally different. However, for formation cracks that are very close to each other, it can also be considered that they have approximately the same minimum closing pressure and can be controlled separately as a group in this embodiment. In fact, when defining the formation cracks in the present invention, multiple adjacent cracks or crack groups at the same position are also considered as the same formation crack.

[0133] For the formation fractures at different positions connected by horizontal wells, although they are at the same depth, due to the heterogeneity of the formation, the closing pressures of the formation fractures at different positions will also be different. Therefore, when applying the split-type energy storage and release method, multiple adjacent fractures or fracture groups at the same position are used as a group for separate control, so a packer device is required to separately isolate the target energy storage fractures at adjacent positions connected to the wellbore and with the same or similar closing pressures in independent cavities.

[0134] Based on the above grouping of formation fractures, the split-type energy storage and release method provided in this embodiment includes:

[0135] S301 Select at least two formation fractures connected by a wellbore as target energy storage fractures.

[0136] As Figure 5 shown, the wellbore includes a vertical section and a horizontal section, and multiple formation fractures are connected to both the vertical section and the horizontal section. Of course, at least two groups of formation fractures connected by a wellbore can also be selected as target energy storage fractures.

[0137] S302 Inject high-pressure fluid into the wellbore. At the same time, the high-pressure fluid can only enter one group of target energy storage fractures, so as to drive the widths of all the target energy storage fractures in this group to increase and enable the formation rock to accumulate elastic potential energy; the pressure generated by the high-pressure fluid at each of the target energy storage fractures in this group is greater than the minimum closing pressure of the corresponding target energy storage fracture and less than the maximum energy storage pressure of the corresponding target energy storage fracture.

[0138] Continuing with the above example, the multiple formation fractures connected to the vertical section of the wellbore are adjacent in position and similar in depth, and have approximately the same minimum closing pressure. Therefore, in this embodiment, they are grouped as the sixth target energy storage fracture group 305 and controlled separately. It can be understood that if there are other fractures or fracture groups at other depths in the vertical section, they can also be grouped into one or more target energy storage fracture groups according to the similarity of their minimum closing pressures.

[0139] Due to the non-uniform relationship of the formation, the minimum closing pressures of the multiple formation fractures connected to the horizontal section of the wellbore are different. Therefore, fractures with similar minimum closing pressures are grouped into a target energy storage fracture group, thus forming the seventh target energy storage fracture group 310, the eighth target energy storage fracture group 315, and the ninth target energy storage fracture group 320.

[0140] The purpose of selecting cracks with similar minimum closure pressures as a group is to meet the condition that "the pressure generated by the high-pressure fluid at each of the target energy storage cracks in the group is greater than the minimum closure pressure of the corresponding target energy storage crack and less than the maximum energy storage pressure of the corresponding target energy storage crack". And the so-called similar minimum closure pressures means that in this embodiment, the difference between the minimum closure pressures of the target energy storage cracks in the same group is less than a threshold value, for example, less than 3 Mp.

[0141] S303 Plug the wellbore opening and maintain the elastic deformation of the formation rock to store energy.

[0142] During energy release in S304, reduce the wellbore plugging pressure to close the target energy storage cracks, and convert the elastic potential energy stored in the formation rock into the kinetic energy of the high-pressure fluid during backflow when the cracks are closing.

[0143] To avoid mutual interference caused by cracks with different closure pressures during the backflow process, during the energy release process, only one group of target energy storage cracks is allowed to close at the same time, and the high-pressure fluid in the cracks at this position is backflowed to the ground to drive a preset power generation device to generate electricity. Only one group of target energy storage cracks is allowed to close at any time during the energy release process, and the high-pressure fluid in the cracks at this position is backflowed to the ground to drive a preset power generation device to generate electricity. Therefore, this method is not affected by the crack closure pressure and the energy release sequence of cracks at different positions.

[0144] It can be understood that the system for storing and releasing energy at different positions in the formation by deploying the above-mentioned split-type energy storage and release method is also slightly different from that in Embodiment 2, and specifically includes:

[0145] A sealing device for separately sealing each group of target energy storage cracks connected to the wellbore in independent cavities; specifically including sealing device IV330 and sealing device V335 for sealing the sixth target energy storage crack group 305 in an independent cavity. Additionally, it also includes sealing device VI340, sealing device VII345, and sealing device VIII350 for separately sealing the seventh target energy storage crack group 310, the eighth target energy storage crack group 315, and the ninth target energy storage crack group 320.

[0146] A channel opening and closing device for opening or closing the channel connecting the cavity and the wellbore. Specifically, the channel opening and closing devices in this embodiment include channel opening and closing device 375, channel opening and closing device 380, channel opening and closing device 385, and channel opening and closing device 390, and the above channel opening and closing devices correspond one-to-one to the sixth target energy storage crack group 305, the seventh target energy storage crack group 310, the eighth target energy storage crack group 315, and the ninth target energy storage crack group 320.

[0147] An injection device II300 is used to inject high-pressure fluid into target energy storage fractures through a wellbore. At the same time, the high-pressure fluid can only enter one group of target energy storage fractures, so as to drive the width of all target energy storage fractures in this group to increase, enabling the formation rock to accumulate elastic potential energy. The pressure generated by the high-pressure fluid at each of the target energy storage fractures in this group is greater than the minimum closure pressure of the corresponding target energy storage fracture and less than the maximum energy storage pressure of the corresponding target energy storage fracture.

[0148] In this embodiment, the specific injection device includes water distributors III355, IV360, V365, and VI370 provided on the inner pipe II325, corresponding to the sixth target energy storage fracture group 305, the seventh target energy storage fracture group 310, the eighth target energy storage fracture group 315, and the ninth target energy storage fracture group 320 respectively.

[0149] A plugging device is used to plug the wellbore opening to maintain the elastic deformation of the formation rock for energy storage.

[0150] A power generation device is used to convert the kinetic energy of the high-pressure fluid discharged when the elastic potential energy accumulated from the formation rock by the target energy storage fractures during the closing process into electrical energy.

[0151] For the working principle of the above device, refer to Embodiment 2, which will not be elaborated in this embodiment.

[0152] It should be noted that each device in this embodiment is only one of its many forms. For example, in some other embodiments, the channel opening and closing device can be a valve or a nozzle, which will not be listed one by one in this embodiment.

[0153] It should be noted that in this article, the term "including", "comprising" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "including one..." does not exclude the existence of another identical element in the process, method, article or device including the element.

[0154] The embodiments of the present invention have been described above in conjunction with the accompanying drawings. However, the present invention is not limited to the above specific embodiments. The above specific embodiments are merely illustrative and not restrictive. Under the inspiration of the present invention, those of ordinary skill in the art can also make many forms without departing from the purpose of the present invention and the scope protected by the claims, and these all belong to the protection scope of the present invention.

Claims

1. A method for storing and releasing energy in fractures at different positions in a formation, characterized in that: Including an integrated energy storage and release method or a split energy storage and release method that can operate independently; The integrated energy storage and release method includes: Selecting formation fractures at at least two different depth positions as target energy storage fractures, and connecting the target energy storage fractures at at least two different depth positions through a wellbore; Injecting high-pressure fluid into the wellbore so that the high-pressure fluid can enter all the target energy storage fractures connected to the wellbore, thereby driving the width of the target energy storage fractures to increase, and further enabling the formation rock to accumulate elastic potential energy; the pressure generated by the high-pressure fluid at each target energy storage fracture is greater than the minimum closing pressure of the corresponding target energy storage fracture and less than the maximum energy storage pressure of the corresponding target energy storage fracture; Sealing the opening of the wellbore to maintain the elastic deformation of the formation rock for energy storage; During energy release, reducing the wellbore sealing pressure to cause the target energy storage fractures to close, and using the reverse-flow high-pressure fluid to generate electricity during the closing process; The split energy storage and release method includes: Selecting at least two or two groups of formation fractures connected through a wellbore as target energy storage fractures; Injecting high-pressure fluid into the wellbore, and at the same time, the high-pressure fluid can only enter one of the target energy storage fractures, thereby driving the width of the target energy storage fracture to increase and enabling the formation rock to accumulate elastic potential energy; or, at the same time, the high-pressure fluid can only enter one of the groups of target energy storage fractures, thereby driving the width of all the target energy storage fractures in the same group to increase and enabling the formation rock to accumulate elastic potential energy; the pressure generated by the high-pressure fluid at each target energy storage fracture in the same group is greater than the minimum closing pressure of the corresponding target energy storage fracture and less than the maximum energy storage pressure of the corresponding target energy storage fracture; Sealing the opening of the wellbore to maintain the elastic deformation of the formation rock for energy storage; During energy release, reducing the wellbore sealing pressure to cause the target energy storage fractures to close, and using the reverse-flow high-pressure fluid to generate electricity during the closing process; and at the same time, only one target energy storage fracture or one group of target energy storage fractures closes, and the high-pressure fluid in the target energy storage fracture is reverse-flowed to the ground to drive a preset power generation device to generate electricity; In the integrated energy storage and release method or the split energy storage and release method, the target energy storage fractures are hydraulic fracturing fractures, natural fractures or fault gaps; In the integrated energy storage and release method, the density range of the high-pressure fluid is calculated using the maximum energy storage pressure of the first target energy storage fracture at depth H1, the minimum closing pressure of the second target energy storage fracture at depth H2, and the depths of the first target energy storage fracture and the second target energy storage fracture from the wellhead respectively, where H1 < H2; specifically, it includes using the formula: ； Calculate the density range of the high-pressure fluid; wherein, is the maximum energy storage pressure of the first target energy storage fracture, is the density of the high-pressure fluid, is the acceleration due to gravity, H1 is the depth of the first target energy storage fracture from the wellhead, and H2 is the depth of the second target energy storage fracture from the wellhead, is the minimum closure pressure of the second target energy storage fracture, and P0 is the injection pressure of the high-pressure fluid.

2. A method for storing and releasing energy through fractures at different positions in a formation according to claim 1, characterized in that: In the split energy storage and release method, the difference between the minimum closing pressures of the target energy storage fractures in the same group is less than a threshold value.

3. A method for storing and releasing energy through fractures at different positions in a formation according to claim 1, characterized in that: In the split energy storage and release method, each or each group of the target energy storage fractures is separately sealed in an independent cavity; the cavity has a channel communicating with the wellbore, and the channel can be opened and closed.

4. A method for storing and releasing energy in fractures at different positions in a formation according to claim 1, characterized in that: When injecting the high-pressure fluid, using electric energy to drive the injection equipment; during energy release, converting the kinetic energy of the reverse-flow of the high-pressure fluid into electric energy through a preset generator.

5. A method for storing and releasing energy through fractures at different positions in a formation according to claim 4, characterized in that: In the split energy storage and release method, any one of the target energy storage cracks or any group of target energy storage cracks with corresponding energy storage is selected to close according to the power demand of the generator.

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