Method and system for storing and releasing energy in and from fractures at different positions of formation

Abstract

Provided are a method and system for storing and releasing energy in and from fractures at different positions of a formation. The method includes: selecting subterranean fractures at at least two different depths as target energy storage fractures, the target energy storage fractures being connected by a wellbore; injecting a high-pressure fluid into the wellbore such that the high-pressure fluid can enter all the target energy storage fractures connected with the wellbore; sealing an opening of the wellbore and maintaining elastic deformation of the formation rock so as to store energy; and when releasing energy, reducing a sealing pressure of the wellbore such that the target energy storage fractures are closed, and in the closing process, converting the elastic potential energy accumulated in the formation rock into kinetic energy for the high-pressure fluid to flow back.

Description

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of and priority to Chinese Patent Application No. 202411342565.8, filed Sep. 25, 2024, which is hereby incorporated by reference herein in its entirety.TECHNICAL FIELD

[0002] The present disclosure belongs to the field of subsurface energy storage, and particularly relates to a method and system for storing and releasing energy in and from fractures at different positions of a formation.BACKGROUND

[0003] Many renewable energy sources, such as solar energy and wind energy, exhibit daily and seasonal intermittency, with unstable power output that makes them unsuitable for providing baseload electricity. As a result, integrating them directly into the grid is challenging, and solving the energy storage problem is the key to successfully scale up renewable energy production. Therefore, how to store surplus clean electricity on a large scale and deliver electricity stably when sunlight and wind are insufficient remains a technical challenge that countries worldwide are striving to overcome.

[0004] At present, large-scale electricity storage methods include using lead-acid batteries, lithium-ion batteries, or hydrogen fuel cells, compressed air energy storage, and pumped energy storage. Among these, lead-acid batteries, lithium-ion batteries, and hydrogen fuel cells have not been employed for energy storage on a large scale due to high investment and maintenance costs. The pumped energy storage refers to pumping water from a lower elevation to a higher one, converting electrical energy into the gravitational potential energy of water. However, the pumped energy storage method has specific topographical requirements and cannot be applied in flat plains or hilly areas. Compressed air energy storage is a mature technology but relies on abandoned mines or underground caverns as gas storage media, limiting its use to certain specific areas.

[0005] In view of this, there is an urgent need for a new clean electricity storage method with lower investment and maintenance costs that can adapt to a variety of terrains. For example, the Chinese patent application No. CN114016988A discloses a method and system for storing and releasing energy with a formation. The method includes: performing hydraulic fracturing in an energy storage formation devoid of oil and gas to create at least one subterranean fracture, then injecting a high-pressure fluid into the resulting subterranean fracture such that the subterranean fracture undergoes elastic deformation to store energy, and causing the high-pressure fluid in the fracture to flow back to drive a preset power generation device to release energy. However, this method is only suitable for subterranean fractures at the same elevation. When a plurality of subterranean fractures are located at different positions with different closure pressures, this method becomes unsuitable because the different closure pressures make it uncontrollable for high-pressure fluid to enter and flow back from fractures at different positionsSUMMARY

[0006] An objective of the present disclosure is to provide a method and system for storing and releasing energy at different positions of a formation that can partially solve or alleviate the problems in the prior art as described above and can be applied to energy storage and release with subterranean fractures at a plurality of different depths.

[0007] In order to solve the above-mentioned technical problems, the present disclosure specifically adopts the following technical solutions.

[0008] A method for storing and releasing energy at different positions of a formation includes: an integrated energy storage and release method or a separate energy storage and release method, the integrated energy storage and release method and the separate energy storage and release method being independently operable,

[0009] the integrated energy storage and release method including:

[0010] selecting subterranean fractures at at least two different depths as target energy storage fractures, where the target energy storage fractures at the at least two different depths are connected by a wellbore;

[0011] injecting a high-pressure fluid into the wellbore such that the high-pressure fluid is capable of entering all the target energy storage fractures connected with the wellbore, thereby driving widths of the target energy storage fractures to increase and causing formation rock to accumulate elastic potential energy, where a pressure produced by the high-pressure fluid at each of the target energy storage fractures is greater than a minimum closure pressure of the corresponding target energy storage fracture and lower than a maximum energy storage pressure of the corresponding target energy storage fracture;

[0012] sealing an opening of the wellbore and maintaining elastic deformation of the formation rock so as to store energy; and

[0013] when releasing energy, reducing a sealing pressure of the wellbore such that the target energy storage fractures are closed, and in the closing process, converting the elastic potential energy accumulated in the formation rock into kinetic energy for the high-pressure fluid to flow back; and

[0014] the separate energy storage and release method including:

[0015] selecting at least two or two groups of subterranean fractures connected by a wellbore as target energy storage fractures;

[0016] injecting a high-pressure fluid into the wellbore, where the high-pressure fluid is only capable of entering one of the target energy storage fractures at a time, thereby driving a width of the target energy storage fracture to increase and causing formation rock to accumulate elastic potential energy; or, the target energy storage fractures are grouped, and the high-pressure fluid is only capable of entering one of the groups of target energy storage fractures at a time, thereby driving widths of all the target energy storage fractures in the group to increase and causing formation rock to accumulate elastic potential energy; and a pressure produced by the high-pressure fluid at each of the target energy storage fractures in the group is greater than a minimum closure pressure of the corresponding target energy storage fracture and lower than a maximum energy storage pressure of the corresponding target energy storage fracture;

[0017] sealing an opening of the wellbore and maintaining elastic deformation of the formation rock so as to store energy; and

[0018] when releasing energy, reducing a sealing pressure of the wellbore such that the target energy storage fractures are closed, and in the closing process, converting the elastic potential energy accumulated in the formation rock into kinetic energy for the high-pressure fluid to flow back.

[0019] As an improvement, the integrated energy storage and release method includes calculating a density range of the high-pressure fluid with a maximum energy storage pressure of a first target energy storage fracture at a depth H1, a minimum closure pressure of a second target energy storage fracture at a depth H2, and respective depths of the first target energy storage fracture and the second target energy storage fracture from a wellhead, with H1<H2, and specifically includes using the following formulaσ4-P0g⁢H2<ρ<σ1-P0g⁢H1

[0020] to calculate the density range of the high-pressure fluid, where σ1 represents the maximum energy storage pressure of the first target energy storage fracture, ρ represents a density of the high-pressure fluid, g represents a gravitational acceleration, H1 represents the depth of the first target energy storage fracture from the wellhead, H2 represents the depth of the second target energy storage fracture from the wellhead, σ4 represents the minimum closure pressure of the second target energy storage fracture, and P0 represents an injection pressure of the high-pressure fluid at the wellhead.

[0021] As an improvement, in the separate energy storage and release method, a difference between the minimum closure pressures of the target energy storage fractures in a same group is less than a threshold.

[0022] As an improvement, in the separate energy storage and release method, only one target energy storage fracture or one group of target energy storage fractures is closed at a time such that the elastic potential energy is converted to the kinetic energy for the high-pressure fluid to flow back.

[0023] As an improvement, in the separate energy storage and release method, each target energy storage fracture or each group of target energy storage fractures is isolated in an independent cavity; and the cavity has a channel that communicates with the wellbore and is capable of being opened and closed.

[0024] As an improvement, the target energy storage fracture is a hydraulic fracture, a natural fracture, or a fault fracture.

[0025] As an improvement, when the high-pressure fluid is injected, an injection device is powered by electrical energy; and when the energy is released, the kinetic energy for the high-pressure fluid to flow back is converted into electrical energy by a preset generator.

[0026] As an improvement, in the separate energy storage and release method, any one of the target energy storage fractures or any group of target energy storage fractures having corresponding stored energy is selected to be closed according to a power requirement of the generator.

[0027] The present disclosure further provides a system for storing and releasing energy at different positions of a formation, deployed with the integrated energy storage and release method described above, and including:

[0028] an injection device configured to inject, through a wellbore, a high-pressure fluid into target energy storage fractures, thereby driving widths of the target energy storage fractures to increase and causing formation rock to accumulate elastic potential energy, where a pressure produced by the high-pressure fluid at each of the target energy storage fractures is greater than a minimum closure pressure of the target energy storage fracture and lower than a maximum energy storage pressure of the target energy storage fracture;

[0029] a sealing device configured to seal an opening of the wellbore, and maintain elastic deformation of the formation rock so as to store energy; and

[0030] a power generation device configured to convert kinetic energy for the high-pressure fluid to flow back that is converted from the elastic potential energy accumulated in formation rock in a process of closing target energy storage fractures into electrical energy.

[0031] The present disclosure further provides a system for storing and releasing energy at different positions of a formation, deployed with the separate energy storage and release method described above, and including:

[0032] an isolation device configured to isolate each target energy storage fracture or each group of target energy storage fractures connected with a wellbore in an independent cavity;

[0033] a channel opening / closing device configured to open or close a channel of the cavity that communicates with the wellbore;

[0034] an injection device configured to inject, through the wellbore, a high-pressure fluid into the target energy storage fractures, where with the cooperation of the channel opening / closing device, the high-pressure fluid is only capable of entering one of the target energy storage fractures connected with the wellbore at a time, thereby driving a width of the target energy storage fracture to increase and causing formation rock to accumulate elastic potential energy; or, the high-pressure fluid is only capable of entering one group of target energy storage fractures at a time, thereby driving widths of all the target energy storage fractures in the group to increase and causing formation rock to accumulate elastic potential energy; and a pressure produced by the high-pressure fluid at each of the target energy storage fractures in the group is greater than a minimum closure pressure of the corresponding target energy storage fracture and lower than a maximum energy storage pressure of the corresponding target energy storage fracture;

[0035] a sealing device configured to seal an opening of the wellbore, and maintain elastic deformation of the formation rock so as to store energy; and

[0036] a power generation device configured to convert kinetic energy for the high-pressure fluid to flow back that is converted from the elastic potential energy accumulated in formation rock in a process of closing target energy storage fractures into electrical energy.

[0037] The present disclosure has the following beneficial effects: the present disclosure utilizes electrical energy for actuation. The high-pressure fluid is injected into the fractures at different positions of the formation such that the widths of the subterranean fractures increase, thereby converting electrical energy to elastic deformation energy of the formation rock for storage. Thus, energy storage with low investment cost and low maintenance cost is achieved. The electrical energy mentioned in the above step may come from renewable energy sources such as wind power generation or solar power generation.

[0038] Further, in the process of gradually closing the subterranean fractures, due to the squeezing action of the formation rock, the high-pressure fluid in the fractures is caused to flow back to the ground for actuating the preset power generation device to generate power. That is, the elastic deformation energy of the subterranean fractures is converted to the electrical energy. Stable power supply can thus be achieved when solar energy or wind energy is insufficient.

[0039] When sunlight or wind is sufficient, the method and system of the present disclosure can convert the electrical energy generated by the sunlight or wind to the elastic formation energy of the rock for storage, and release the electrical energy to the power grid when needed. This is of great significance for combination of wind generated power or solar generated power to the grid and peak regulation.

[0040] The method disclosed herein further involves a hydraulic fracturing method which, as a mature technique in the field of petroleum and gas, has been used on a large scale. Therefore, the related supporting construction equipment is easily available and the cost is controllable.

[0041] In addition, in some embodiments, using a plurality of subterranean fractures for integrated energy storage and release is low in cost and simple to control.

[0042] In some other embodiments, when a plurality of subterranean fractures are separately controlled for energy storage and release, compared with the integrated energy storage and release, the control is more flexible and the use is more convenient.BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate technical solutions in the embodiments of the present application or in the prior art, a brief introduction to the drawings required for the description of the embodiments or the prior art will be provided below. In all the accompanying drawings, similar elements or portions are generally identified by similar reference numerals. In the accompanying drawings, each element or portion is not necessarily drawn to the actual scale. Apparently, the accompanying drawings in the following description show merely some embodiments of the present application, and those of ordinary skill in the art may still derive other drawings from these accompanying drawings without creative efforts.

[0044] FIG. 1 is a flowchart for Embodiment 1;

[0045] FIG. 2 is a structural schematic diagram for Embodiment 1;

[0046] FIG. 3 is a flowchart for Embodiment 2;

[0047] FIG. 4 is a structural schematic diagram for Embodiment 2; and

[0048] FIG. 5 is a structural schematic diagram for Embodiment 3.LIST OF REFERENCE NUMERALS

[0049] 110—formation, 120—wellbore, 130—first target energy storage fracture, 140—second target energy storage fracture

[0050] 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—isolation device I, 250—isolation device II, 255—isolation device III, 260—fluid distributor X, 265—fluid distributor I, 270—fluid distributor II, 275—channel opening / closing device X, 280—channel opening / closing device I, 285—channel opening / closing device II

[0051] 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—isolation device IV, 335—isolation device V, 340—isolation device VI, 345—isolation device VII, 350—isolation device VIII, 355—fluid distributor III, 360—fluid distributor IV, 365—fluid distributor V, 370—fluid distributor VI, 375—channel opening / closing device III, 380—channel opening / closing device IV, 385—channel opening / closing device V, and 390—channel opening / closing device VI.DETAILED DESCRIPTION OF THE EMBODIMENTS

[0052] To make the objective, technical solutions, and advantages of the embodiments of the present disclosure clearer, the technical solutions in the embodiments of the present disclosure will be described clearly and completely below with reference to the accompanying drawings in the embodiments of the present disclosure. Apparently, the described embodiments are merely some rather than all of the embodiments of the present disclosure. All other embodiments obtained by a person of ordinary skill in the art on the basis of the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0053] As used herein, the terms such as “module”, “component”, and “unit” used to represent elements are only for convenience of description of the present disclosure, and have no specific meaning themselves. Thus, “module”, “component”, and “unit” may be used interchangeably.

[0054] As used herein, an orientation or positional relationship indicated by a term such as “upper”, “lower”, “inner”, “outer”, “front”, “rear”, “one end”, and “the other end” is based on the orientation or positional relationship shown in the accompanying drawings, which is only for convenience of describing the present disclosure and simplifying the description, rather than indicating or implying that the device or element referred to must have a particular orientation and be constructed and operated in a particular orientation, and therefore should not be construed as limiting the present disclosure. Moreover, terms such as “first” and “second” are merely intended for the purpose of description, and should not be construed as indicating or implying relative importance.

[0055] As used herein, unless otherwise clearly specified and limited, meanings of terms “mounting”, “be provided with”, and “connection” should be understood in a board sense. For example, the “connection” may be a fixed connection, a removable connection, or an integral connection; may be a mechanical connection or an electrical connection; may be a direct connection or an indirect connection through an intermediate medium; or may be intercommunication between two components. A person of ordinary skill in the art may understand specific meanings of the foregoing terms in the present disclosure based on a specific situation.

[0056] As used herein, “and / or” includes any of and all combinations of one or more associated items that are listed.

[0057] As used herein, “a plurality of” means two or more, i.e., including two, three, four, five, etc.Term Explanation

[0058] As used herein, “fluid” may be, but not limited to, a gas, a liquid, an emulsion, a slurry, and a solid particle flow having flow characteristics similar to liquid flow. For example, the fluid may include a water-based liquid having a chemical additive or supercritical carbon dioxide. Moreover, the chemical additive may include, but is not limited to, an acid, gel, potassium chloride, a surfactant, etc.

[0059] As used herein, “formation” refers to a subsurface porous and permeable rock formation (e.g., a shale formation, a sandstone formation, or a carbonate formation), which may serve as a fluid storage space. Typically, these fluids may be water, hydrocarbons, or gases. A fluid loss control agent may be added to a fluid injected into fractures in a formation to reduce or hinder the filtration loss of the fluid in the fractures to the formation.

[0060] As used herein, “hydraulic fracturing” or “fracturing” or “breakdown” refers to cracking of formation rock and propagation of cracks under the action of an external force (e.g., a high-pressure fluid).

[0061] As used herein, “subterranean fracture” or “fracture” refers to a rock open fissure created in a formation after hydraulic fracturing, or a natural fracture or fault fracture existing in the formation. The term “subterranean fracture” or “fracture” is interchangeable. “Fracture” may refer to a single fracture, or may refer to a plurality of adjacent fractures or a fracture swarm at a position.

[0062] As used herein, “wellbore” refers to a hole formed by drilling in a formation or inserting a conduit. Generally, the wellbore is cylindrical, and the cross section of the wellbore may be circular. In addition, the wellbore may have any other cross section. The wellbore may be an open hole, i.e., open-hole wellbore, or may be a cased wellbore formed by cementing a casing on the inner wall of the wellbore. The wellbore connected with fractures may be a straight well, or may be a horizontal well or a slant well.

[0063] As used herein, “fracture closure pressure” or “closure pressure” refers to a stress vertically acting on the fracture wall. For a horizontal fracture, the fracture closure pressure is equal to a vertical stress applied to the fracture wall. For a vertical fracture, the fracture closure pressure is equal to a minimum horizontal principal stress applied to the fracture wall. The fracture closure pressure may be obtained by a diagnostic fracturing injection test or a rapid injection-flowback test. The fracture closure pressure may also be calculated with logging data in combination with an in-situ stress model. The term “fracture closure pressure” or “closure pressure” is interchangeable. The fracture mentioned herein may be a vertical fracture or a horizontal fracture.

[0064] “Width of fracture” mentioned herein refers to a relative displacement distance of two walls in a direction perpendicular to the subterranean fracture plane.

[0065] As used herein, “target energy storage fracture” and “target fracture” are both fractures selected to store energy. The term “target energy storage fracture” or “target fracture” is interchangeable.Embodiment 1

[0066] Fractures at different positions of a formation usually have different closure pressures due to different formation depths or different mechanical properties of formation rock (e.g., different Young's moduli or Poisson's ratios). A fracture at a deeper formation depth usually has greater closure pressure than a fracture at a shallow formation depth. The fractures at different positions of the formation may be created by multi-stage fracturing or temporary-sealing fracturing, etc. Fractures of different geometric sizes may be created according to preset energy storage sizes at different positions.

[0067] In order to use subterranean fractures at different depths as energy storage bodies, as shown in FIG. 1, the present disclosure provides a method for storing and releasing energy at different positions of a formation, which is specifically an integrated energy storage and release method including the following specific steps.

[0068] In step S101, subterranean fractures at at least two different depths are selected as target energy storage fractures. The target energy storage fractures are connected by a wellbore.

[0069] In the present embodiment, the selected subterranean fracture may be a fracture formed by hydraulic fracturing or may be a natural fracture or fault fracture as long as it can undergo elastic formation under the action of a high-pressure fluid to accumulate elastic potential energy.

[0070] In addition, in order to facilitate injection of the high-pressure fluid and power generation using the high-pressure fluid that flows back, a plurality of target energy storage fractures are connected by the same wellbore (in particular a vertical well). As shown in FIG. 2, in the present embodiment, for the simplicity of description, the principles of the present disclosure are explained using a simple model. In the present embodiment, the target energy storage fractures in the formation 110 that are connected by the wellbore 120 include a first target energy storage fracture at a depth H1 and a second target energy storage fracture at a depth H2. It is foreseeable that the number of the target energy storage fractures may be more than 2. For example, in addition to the first target energy storage fracture and the second target energy storage fracture, there are one or more target energy storage fractures between the first target energy storage fracture and the second target energy storage fracture.

[0071] In step S102, a high-pressure fluid is injected into the wellbore such that the high-pressure fluid can enter all the target energy storage fractures connected with the wellbore, thereby driving the widths of the target energy storage fractures to increase and causing formation rock to accumulate elastic potential energy. A pressure produced by the high-pressure fluid at each target energy storage fracture is greater than a minimum closure pressure of the target energy storage fracture and lower than a maximum energy storage pressure of the target energy storage fracture.

[0072] In the energy storage process, it is required to inject the high-pressure fluid into the target energy storage fractures through the wellbore. With the pressure of the high-pressure fluid, the widths of the target energy storage fractures increase, thereby causing the formation rock to accumulate elastic potential energy.

[0073] In the present embodiment, the maximum energy storage pressure of the first target energy storage fracture at the depth H1 is assumed to be σ1, and the maximum energy storage pressure of the second target energy storage fracture at the depth H2 to be σ2, the minimum closure pressure of the first target energy storage fracture at the depth H1 to be σ3, and the minimum closure pressure of the second target energy storage fracture at the depth H2 to be σ4. Preferably, H1<H2. Generally, σ1<σ2, and σ3<σ4.

[0074] An injection pressure for injecting the high-pressure fluid into the wellbore 120 at the wellhead is denoted by P0, and a fracture pressure of the first target energy storage fracture 130 by Pf1, and a fracture pressure of the second target energy storage fracture 140 by Pf2. If the internal frictional resistance of the wellbore is neglected, the fracture pressure of the first target energy storage fracture 130 is Pf1=P0+ρgH1, and fracture pressure of the second target energy storage fracture 140 is Pf2=P0+ρgH2, where ρ represents a density of the high-pressure fluid injected into the wellbore 120, g represents a gravitational acceleration (approximately equal to 9.8 m / s2), and H1 and H2 represent vertical distances of the first target energy storage fracture and the second target energy storage fracture from a wellhead, respectively.

[0075] For given mechanical properties (Young's modulus, Poisson's ratio, and fracture toughness) and a fracture size of the formation rock, it is required to prevent the fracture from propagating in the length or depth direction in the energy storage process, and the fracture pressure and the volume of the fluid injected into the fracture have maximums (i.e., maximum energy storage pressure and maximum energy storage volume). When the fracture pressure and the volume of the fluid injected into the fracture reach the maximums, the fracture reaches the maximum energy storage state. When the fracture pressure or the volume of the fluid injected into the fracture is above the maximum, the fracture will propagate along the length or depth direction.

[0076] Therefore, when the high-pressure fluid is injected, both the closure pressure and the maximum energy storage pressure are taken into account. That is to say, the pressure produced 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 lower than the maximum energy storage pressure of the target energy storage fracture. For two upper and lower target energy storage fractures in the present embodiment, the density of the high-pressure fluid needs to meet the following conditions: P0+ρgH2>σ4, and P0+ρgH1<σ1.

[0077] Since the depth of each target energy storage fracture is different, the pressure produced by the high-pressure fluid is also different. In the present embodiment, a density range of the high-pressure fluid is calculated with the maximum energy storage pressure of the first target energy storage fracture at the depth H1, the minimum closure pressure of the second target energy storage fracture at the depth H2, and respective depths of the first target energy storage fracture and the second target energy storage fracture from the wellhead, with H1<H2. Specifically, the following formulaσ4-P0g⁢H2<ρ<σ1-P0g⁢H1

[0078] is used to calculate the density range of the high-pressure fluid, where σ1 represents the maximum energy storage pressure of the first target energy storage fracture, ρ represents the density of the high-pressure fluid, g represents the gravitational acceleration, H1 represents the vertical depth of the first target energy storage fracture from the wellhead, H2 represents the vertical depth of the second target energy storage fracture from the wellhead, σ4 represents the minimum closure pressure of the second target energy storage fracture, and P0 represents the injection pressure of the high-pressure fluid at the wellhead.

[0079] It needs to be noted that each target energy storage fracture can be opened and will not propagate only if the density ρ of the high-pressure fluid is within the above-mentioned range. It will be appreciated that for an embodiment where there are more than two target energy storage fractures, the target energy storage fracture in the between can be opened and will not propagate only if the shallowest target energy storage fracture and the deepest target energy storage fracture can both be opened and will not propagate. That is, by controlling the density of the high-pressure fluid, it can be controlled to a certain extent that all the fractures at different depths can be opened and will not propagate, i.e., the controllability of the fractures at different positions is realized to a certain extent.

[0080] In some other embodiments, in addition to calculating the density ρ using a simplified model as in Embodiment 1, the density ρ may also be calculated using methods such as numerical simulation.

[0081] In the present embodiment, the minimum closure pressure and the maximum energy storage pressure of the target energy storage fracture can be calculated with the size of the target energy storage fracture and the mechanical properties of the formation rock.

[0082] In step S103, an opening of the wellbore is sealed, and elastic deformation of the formation rock is maintained so as to store energy.

[0083] When all the target energy storage fractures are deformed after being injected with the high-pressure fluid, the opening of the wellbore can be sealed such that the internal pressure of the wellbore is maintained, thereby maintaining the elastic formation of the formation rock (and the potential energy of the high pressure fluid is that the fluid is compressible) and achieving the purpose of energy storage.

[0084] In step S104, when releasing energy, a sealing pressure of the wellbore is reduced such that the target energy storage fractures are closed, and in the closing process, the elastic potential energy accumulated in the formation rock is converted into kinetic energy for the high-pressure fluid to flow back.

[0085] When releasing energy is required, only the sealing pressure of the wellbore is reduced, and the target energy storage fractures are gradually closed due to pressure relief. In the closing process, the elastic potential energy accumulated in the formation rock is converted into the kinetic energy for the high-pressure fluid to flow back. In the present embodiment, a generator is preset at the outlet of the wellbore, which can convert the kinetic and / or potential energy for the high-pressure fluid to flow back into electrical energy again.

[0086] Based on the method described above, the present embodiment provides a system for storing and releasing energy in and from fractures at different positions of a formation, deployed with the integrated energy storage and release method disclosed in Embodiment 1, and including:

[0087] an injection device configured to inject, through a wellbore, a high-pressure fluid into target energy storage fractures, thereby driving widths of the target energy storage fractures to increase and causing formation rock to accumulate elastic potential energy, where a pressure produced by the high-pressure fluid at each of the target energy storage fractures is greater than a minimum closure pressure of the target energy storage fracture and lower than a maximum energy storage pressure of the target energy storage fracture; where the injection device can be powered by electrical energy;

[0088] a sealing device configured to seal an opening of the wellbore, and maintain elastic deformation of the formation rock so as to store energy; and

[0089] a power generation device configured to convert kinetic energy for the high-pressure fluid to flow back that is converted from the elastic potential energy accumulated in formation rock in a process of closing target energy storage fractures into electrical energy.Embodiment 2

[0090] Due to the randomness of positions and properties of subterranean fractures, after the high-pressure fluid is injected, the requirement that the pressure produced 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 lower than the maximum energy storage pressure of the target energy storage fracture cannot be necessarily met. Consequently, there is certain limitation to energy storage with a plurality of subterranean fractures. In order to improve the universality, as shown in FIG. 3, the present embodiment provides a method for storing and releasing energy at different positions of a formation, which is specifically a separate energy storage and release method including the following specific steps.

[0091] In step S201, subterranean fractures at at least two different depths are selected as target energy storage fractures. The target energy storage fractures are connected by a wellbore.

[0092] In the present embodiment, the selected subterranean fracture may be a fracture formed by hydraulic fracturing or may be a natural fracture or fault fracture as long as it can undergo elastic formation under the action of a high-pressure fluid to accumulate elastic potential energy.

[0093] In addition, in order to facilitate injection of the high-pressure fluid and power generation using the high-pressure fluid that flows back, a plurality of target energy storage fractures are connected by the same wellbore (in particular a vertical well). For the convenience of description in the present embodiment, a simplified model is provided, as shown in FIG. 4, where a wellbore is connected with a third target energy storage fracture 215 at a depth H3, a fourth target energy storage fracture 220 at a depth H4, and a fifth target energy storage fracture 225 at a depth H5. It is foreseeable that the number of the target energy storage fractures may be more than 2.

[0094] In step S202, a high-pressure fluid is injected into the wellbore. The high-pressure fluid can only enter one of the target energy storage fractures connected with the wellbore at a time, thereby driving a width of the target energy storage fracture to increase and causing formation rock to accumulate elastic potential energy.

[0095] As shown in FIG. 4, in the process of storing energy, if an injection device is powered by electrical energy to inject the high-pressure fluid into the wellbore, it is assumed that the pressure produced by the high-pressure fluid can only open the third target energy storage fracture 215. The fourth target energy storage fracture 220 and the fifth target energy storage fracture 225 have higher closure pressures and cannot receive the high-pressure fluid at a pressure below their closure pressures, and thus cannot realize energy storage. If the pressure of the high-pressure fluid is increased to exceed the minimum closure pressures of the fourth target energy storage fracture 220 and the fifth target energy storage fracture 225, it is possible for the pressure to exceed the maximum energy storage pressure of the third target energy storage fracture 215, causing the third target energy storage fracture to expand.

[0096] In order to avoid the above-mentioned case, in the present embodiment, when the high-pressure fluid is injected to drive the target energy storage fractures to elastically deform, the high-pressure fluid can only be injected to one of the target energy storage fractures at a time. At this point, the other target energy storage fractures are isolated from the target energy storage fracture, and therefore, only the target energy storage fracture needs to be taken into account in terms of the pressure of the high-pressure fluid.

[0097] In any time during the energy storage process, the high-pressure fluid is only allowed to be injected to the fracture at one position. Therefore, the method is not affected by the fracture closure pressure and the energy storage sequence of the fractures at different positions. In order to achieve this purpose, in the present embodiment, each target energy storage fracture is isolated in an independent cavity. The cavity has a channel that communicates with the wellbore and can be opened and closed.

[0098] In step S203, an opening of the wellbore is sealed, and elastic deformation of the formation rock is maintained so as to store energy.

[0099] Like Embodiment 1, when all the target energy storage fractures are deformed after being injected with the high-pressure fluid, the opening of the wellbore can be sealed such that the internal pressure of the wellbore is maintained, thereby maintaining the elastic formation of the formation rock (and the potential energy of the high pressure fluid is that the fluid is compressible) and achieving the purpose of energy storage.

[0100] In step S204, when releasing energy, a sealing pressure of the wellbore is reduced such that the target energy storage fractures are closed, and in the closing process, the elastic potential energy accumulated in the formation rock is converted into kinetic energy for the high-pressure fluid to flow back.

[0101] When releasing energy is required, only the sealing pressure of the wellbore is reduced, and the target energy storage fractures are gradually closed due to pressure relief. In the closing process, the elastic potential energy accumulated in the formation rock is converted into the kinetic energy for the high-pressure fluid to flow back. In the present embodiment, a generator is preset at the outlet of the wellbore, which can convert the kinetic and / or potential energy for the high-pressure fluid to flow back into electrical energy again.

[0102] It needs to be noted that when 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 differ greatly, flow-back may be uncontrolled when they are closed simultaneously. For example, the high-pressure fluid flowing back from the fifth target energy storage fracture 225 at the depth H5 will enter the third target energy storage fracture 215 at the depth H3 and the fourth target energy storage fracture 220 at the depth H4, rather than directly flow back out of the wellhead.

[0103] In order to avoid mutual interference of the fractures at different positions due to different closure pressures in the flow-back process, in the energy release process, only the target energy storage fracture at one position is allowed to be closed at a time, and the high-pressure fluid is caused to flow back to the ground and actuate the preset power generation device to generate power. In any time during the energy release process, only the fracture at one position is allowed to be closed, and the high-pressure fluid is caused to flow back to the ground and actuate the preset power generation device to generate power. Therefore, the method is not affected by the fracture closure pressure and the energy release sequence of the fractures at different positions. That is, the energy storage in and energy release from each fracture can be controlled separately, thereby meeting different power generation requirements.

[0104] Still further, the target energy storage fracture having corresponding stored energy is selected to be closed according to the power requirement of the generator. Specifically, one or more target energy storage fractures (with a small closure pressure difference therebetween) may be selected.

[0105] As shown in FIG. 4, the present embodiment provides a system for storing and releasing energy at different positions of a formation, deployed with the separate energy storage and release method disclosed in Embodiment 2, and including:

[0106] an isolation device configured to isolate target energy storage fractures connected with a wellbore in independent cavities, respectively;

[0107] a channel opening / closing device configured to open or close a channel of the cavity that communicates with the wellbore;

[0108] an injection device configured to inject, through the wellbore, a high-pressure fluid into the target energy storage fractures, where with the cooperation of the channel opening / closing device, the high-pressure fluid can only enter one of the target energy storage fractures connected with the wellbore at a time, thereby driving a width of the target energy storage fracture to increase and causing formation rock to accumulate elastic potential energy;

[0109] a sealing device configured to seal an opening of the wellbore, and maintain elastic deformation of the formation rock so as to store energy; and

[0110] a power generation device configured to convert kinetic energy and / or potential for the high-pressure fluid to flow back that is converted from the elastic potential energy accumulated in formation rock in a process of closing target energy storage fractures into electrical energy.

[0111] Specifically, as described in Embodiment 2, the wellbore is connected with the third target energy storage fracture 215 at the depth H3, the fourth target energy storage fracture 220 at the depth H4, and the fifth target energy storage fracture 225 at the depth H5. It is foreseeable that the number of the target energy storage fractures may be more than 3.

[0112] An inner pipe is arranged within the wellbore. Isolation device I 245, isolation device II 250, and isolation device III 255 are arranged along the axial direction of the wellbore such that three target energy storage fractures are isolated in three independent cavities.

[0113] Injection device I 200 is provided with three fluid distributors, namely fluid distributor X 260, fluid distributor I 265, and fluid distributor II 270, which correspond to the three target energy storage fractures, respectively. Each fluid distributor is equipped with the channel opening / closing device. The cavity can be connected with the inner pipe by means of the channel opening / closing device, thereby allowing the high-pressure fluid to enter into the target energy storage fracture in the cavity.

[0114] For example, in order to store energy in the third target energy storage fracture 215 at the depth H3, the channel opening / closing device X 275 needs to be opened, while the channel opening / closing device I 280 and the channel opening / closing device II 285 are closed. 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 the depth H3 through the unique outlet (i.e., the channel opening / closing device X 275). Similarly, in order to store energy in the fourth target energy storage fracture 220 at the depth H4, the channel opening / closing device I 280 needs to be opened, while the channel opening / closing device X 275 and the channel opening / closing device II 285 are closed. 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 the depth H4 through the unique outlet (i.e., the channel opening / closing device I 280). Similarly, in order to store energy in the fifth target energy storage fracture 225 at the depth H5, the channel opening / closing device II 285 needs to be opened, while the channel opening / closing device X 275 and the channel opening / closing device I 280 are closed. 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 the depth H5 through the unique outlet (i.e., the channel opening / closing device II 285).

[0115] If the channel opening / closing device X 275 is opened when energy is stored in the fifth target energy storage fracture 225 at the depth H5, the high-pressure fluid subsequently injected into the inner pipe I 240 will enter the third target energy storage fracture 215 at the depth H3 because the third target energy storage fracture 215 has a lower closure pressure. Meanwhile, the high-pressure fluid entering the fifth target energy storage fracture 225 will also flow back into the inner pipe I 240, and even can enter the third target energy storage fracture 215 at the depth H3 through the channel opening / closing device X 275. This may cause serious interference for energy storage in the fifth target energy storage fracture 225.

[0116] Thus, it can be seen that in the energy storage process, it is important to adjust a flow distribution device to allow injection of the high-pressure fluid into only one target energy storage fracture in any time while not allowing the high-pressure fluid to flow to the fractures at other positions.

[0117] With the injection device I 200 cooperating with the channel opening / closing device on the fluid distributor, in any time during the energy storage process, the high-pressure fluid is only allowed to be injected to the one target energy storage fracture. Therefore, the method is not affected by the fracture closure pressure and the energy storage sequence of the fractures at different positions. For example, in some embodiments, energy may be stored first in the third target energy storage fracture 215, then in the fourth target energy storage fracture 220, and finally in the fifth target energy storage fracture 225. In some other embodiments, energy may be stored first in the fifth target energy storage fracture 225, then in the fourth target energy storage fracture 220, and finally in the third target energy storage fracture 215. Switching energy storage in the fifth target energy storage fracture 225 to energy storage in the fourth target energy storage fracture 220 may be performed at any time in the energy storage process. Switching to energy storage in the fourth target energy storage fracture 220 may be performed without waiting for the fifth target energy storage fracture 225 reaching the maximum energy storage.

[0118] After the completion of storing energy, if there is no need for energy release, the channel opening / closing device X 275, the channel opening / closing device I 280, and the channel opening / closing device II 285 are all closed so that no high-pressure fluid flows in and out of the target energy storage fractures, and the energy storage sizes of the target energy storage fractures remain unchanged.

[0119] In the energy release process, the wellhead pressure is reduced such that the fractures are gradually closed, driving the high-pressure fluid to flow back from the fractures to the ground and actuate the preset power generation device to generate power.

[0120] In some embodiments of energy release, the channel opening / closing device X 275, the channel opening / closing device I 280, and the channel opening / closing device II 285 can all be opened. The third target energy storage fracture 215 at the depth H3 is closed, driving the internal high-pressure fluid to flow from the channel opening / closing device X 275 into the inner pipe I 240. The fourth target energy storage fracture 220 at the depth H4 is closed, driving the internal high-pressure fluid to flow from the channel opening / closing device I 280 into the inner pipe I 240. The fifth target energy storage fracture 225 at the depth H5 is closed, driving the internal high-pressure fluid to flow from the channel opening / closing device II 285 into the inner pipe I 240. Finally, the high-pressure fluid gathering in the inner pipe I 240 flows back to the ground and actuates the preset power generation device to generate power.

[0121] When the closure pressures of the three target energy storage fractures differ greatly, flow-back may be uncontrolled when the three channel opening / closing devices are opened simultaneously. For example, after the high-pressure fluid flowing back from the fifth target energy storage fracture 225 at the depth H5 enters the inner pipe I 240 from the channel opening / closing device II 285, the high-pressure fluid may enter the third target energy storage fracture 215 at the depth H3 and the fourth target energy storage fracture 220 at the depth H4 through the channel opening / closing device X 275 and the channel opening / closing device I 280, respectively, rather than directly flow back out of the wellhead.

[0122] In order to avoid mutual interference of fractures at different positions due to different closure pressures in the flow-back process, in the energy release process, only one target energy storage fracture is allowed to be closed in any time, and the high-pressure fluid is caused to flow back to the ground and actuate the preset power generation device to generate power.

[0123] For example, in order to release energy from the third target energy storage fracture 215 at the depth H3, the channel opening / closing device X 275 needs to be opened, while the channel opening / closing device I 280 and the channel opening / closing device II 285 are closed. In this way, the high-pressure fluid flowing back from the third target energy storage fracture 215 through the channel opening / closing device X 275 to the inner pipe I 240 can only flow back to the ground through the unique outlet (i.e., the wellhead) for actuating the preset power generation device to generate power. Similarly, in order to release energy from the fourth target energy storage fracture 220 at the depth H4, the channel opening / closing device I 280 needs to be opened, while the channel opening / closing device X 275 and the channel opening / closing device II 285 are closed. In this way, the high-pressure fluid flowing back from the fourth target energy storage fracture 220 through the channel opening / closing device I 280 to the inner pipe I 240 can only flow back to the ground through the unique outlet (i.e., the wellhead) for actuating the preset power generation device to generate power. Similarly, in order to release energy from the fifth target energy storage fracture 225 at the depth H5, the channel opening / closing device II 285 needs to be opened, while the channel opening / closing device X 275 and the channel opening / closing device I 280 are closed. In this way, the high-pressure fluid flowing back from the fifth target energy storage fracture 225 through the channel opening / closing device II 285 to the inner pipe I 240 can only flow back to the ground through the unique outlet (i.e., the wellhead) for actuating the preset power generation device to generate power.

[0124] Since only the fracture at one position is allowed to be closed in any time during the energy release process and the high-pressure fluid in the fracture at this position is caused to flow back to the ground and actuate the preset power generation device to generate power, the method is not affected by the fracture closure pressure and the energy release sequence of the fractures at different positions. For example, in some embodiments, energy may be released first from the third target energy storage fracture 215, then from the fourth target energy storage fracture 220, and finally from the fifth target energy storage fracture 225. In some other embodiments, energy may be released first from the fifth target energy storage fracture 225, then from the fourth target energy storage fracture 220, and finally from the third target energy storage fracture 215. Switching energy release from the fifth target energy storage fracture 225 to energy release from the fourth target energy storage fracture 220 may be performed at any time in the energy release process. Switching to energy release from the fourth target energy storage fracture 220 may be performed without waiting for the stored energy of the fifth target energy storage fracture 225 decreasing to zero.

[0125] In some embodiments, the target fracture in need of energy release is selected according to a demand on the current generated power. When the demand on the current generated power is small, the third target energy storage fracture 215 at the depth H3 may be selected for energy release because the closure pressure of the third target energy storage fracture 215 is low and the pressure of the fluid flowing back to the wellhead is also low. Accordingly, the output power for driving the power generation device is low as well. When the demand on the generated power is large, the fifth target energy storage fracture 225 at the depth H5 may be selected for energy release because the closure pressure of the fifth target energy storage fracture 225 is high and the pressure of the fluid flowing back to the wellhead is also high. Accordingly, the output power for driving the power generation device is high as well.Embodiment 3

[0126] In Embodiment 2, due to a large difference in depth between the target energy storage fractures, differences in minimum closure pressure and maximum energy storage pressure between the target energy storage fractures are also large. Therefore, it is required to separately control each target energy storage fracture as a separate energy storage and release unit. However, in the present embodiment, several target energy storage fractures having similar minimum closure pressures are put into one group as a separate energy storage and release unit to be controlled separately. Thus, the equipment cost is reduced.

[0127] For subterranean fractures at different depths that are connected by a vertical well or a slant well, their minimum closure pressures are generally different. However, for subterranean fractures very close to one another, it may also be regarded as these subterranean fractures having an approximate minimum closure pressure, which, in the present embodiment, can be taken as a group to be controlled separately. In effect, when defining the subterranean fracture herein, a plurality of adjacent fractures or a fracture swarm at a position are / is taken as a single subterranean fracture.

[0128] For subterranean fractures at different positions that are connected by a horizontal well, although these subterranean fractures are located at the same depth, the subterranean fractures at different positions may also have different closure pressures due to the heterogeneity of the formation. Therefore, when the separate energy storage and release method is applied, a plurality of adjacent fractures or a fracture swarm at a position are / is taken as a group to be controlled separately. Hence, the isolation device needs to be used for separately isolating the target energy storage fractures that are connected with the wellbore at adjacent positions and have the same or similar closure pressure in independent cavities.

[0129] Based on the grouping of the subterranean fractures, the separate energy storage and release method provided in the present embodiment includes the following steps.

[0130] In step S301, at least two subterranean fractures connected by a wellbore are selected as target energy storage fractures.

[0131] As shown in FIG. 5, the wellbore includes a vertical segment and a horizontal segment, and each of the vertical segment and the horizontal segment is connected with a plurality of subterranean fractures. Certainly, at least two groups of subterranean fractures connected by the wellbore may also be selected as the target energy storage fractures.

[0132] In step S302, a high-pressure fluid is injected into the wellbore. The high-pressure fluid can only enter one of the groups of target energy storage fractures at a time, thereby driving the widths of all the target energy storage fractures in the group to increase and causing formation rock to accumulate elastic potential energy. The pressure produced 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 lower than the maximum energy storage pressure of the corresponding target energy storage fracture.

[0133] As described in the above example, the plurality of subterranean fractures connected with the vertical segment of the wellbore are adjacent in position and similar in depth and have an approximate minimum closure pressure, and thus are grouped, in the present embodiment, as a sixth target energy storage fracture group 305 to be controlled separately. It will be appreciated that if fractures or fracture swarms are present at other depths, they may also be grouped as one or more target energy storage fracture groups depending on the similarity of their minimum closure pressures.

[0134] The plurality of subterranean fractures connected with the horizontal segment of the wellbore have different minimum closure pressures due to the heterogeneity of the formation. Thus, the fractures having similar minimum closure pressures are grouped as one target energy storage fracture group, thereby forming a seventh target energy storage fracture group 310, an eighth target energy storage fracture group 315, and a ninth target energy storage fracture group 320.

[0135] The purpose of selecting the fractures having similar minimum closure pressures as a group is to meet the condition, i.e., the pressure produced 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 lower than the maximum energy storage pressure of the corresponding target energy storage fracture. The minimum closure pressures being similar refers to, in the present embodiment, the difference between the minimum closure pressures of the target energy storage fractures in the same group being less than a threshold, e.g., less than 3 MPa.

[0136] In step S303, the opening of the wellbore is sealed, and the elastic deformation of the formation rock is maintained so as to store energy.

[0137] In step S304, when releasing energy, the sealing pressure of the wellbore is reduced such that the target energy storage fractures are closed, and in the closing process, the elastic potential energy accumulated in the formation rock is converted into the kinetic energy for the high-pressure fluid to flow back.

[0138] In order to avoid mutual interference of the fractures due to different closure pressures in the flow-back process, in the energy release process, only one group of target energy storage fractures is allowed to be closed at a time, and the high-pressure fluid in the fractures at the position is caused to flow back to the ground and actuate the preset power generation device to generate power. In any time during the energy release process, only one group of target energy storage fractures is allowed to be closed, and the high-pressure fluid in the fractures at the position is caused to flow back to the ground and actuate the preset power generation device to generate power. Therefore, the method is not affected by the fracture closure pressure and the energy release sequence of the fractures at different positions.

[0139] It will be appreciated that the system for storing and releasing energy in and from fractures at different positions of a formation deployed with the above-described separate energy storage and release method has some differences from Embodiment 2, and specifically includes an isolation device, a channel opening / closing device, an injection device, a sealing device, and a power generation device.

[0140] The isolation device is configured to isolate each group of target energy storage fractures connected with a wellbore in an independent cavity. The isolation device specifically includes isolation device IV 330 and isolation device V 335 for isolating the sixth target energy storage fracture group 305 in the independent cavity. In addition, isolation device VI 340, isolation device VII 345, and isolation device VIII 350 are further included, which are configured to isolate 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.

[0141] The channel opening / closing device is configured to open or close a channel of the cavity that communicates with the wellbore. Specifically, the channel opening / closing device in the present embodiment includes channel opening / closing device 375, channel opening / closing device 380, channel opening / closing device 385, and channel opening / closing device 390. These channel opening / closing devices are in one-to-one correspondence with 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.

[0142] The injection device II 300 is configured to inject, through the wellbore, a high-pressure fluid into the target energy storage fractures. The high-pressure fluid can only enter one group of target energy storage fractures at a time, thereby driving the widths of all the target energy storage fractures in the group to increase and causing formation rock to accumulate elastic potential energy. The pressure produced 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 lower than the maximum energy storage pressure of the corresponding target energy storage fracture.

[0143] In the present embodiment, the injection device specifically includes fluid distributor III 355, fluid distributor IV 360, fluid distributor V 365, and fluid distributor VI 370 disposed on inner pipe II 325, which correspond 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.

[0144] The sealing device is configured to seal the opening of the wellbore, and maintain the elastic deformation of the formation rock (and the potential energy of the high pressure fluid is that the fluid is compressible) so as to store energy.

[0145] The power generation device is configured to convert the kinetic energy for the high-pressure fluid to flow back that is converted from the elastic potential energy accumulated in formation rock in the process of closing target energy storage fractures into electrical energy. The power generation device may also be configured to convert the potential energy (e.g., potential energy of compressed air) for the high-pressure fluid into electrical energy.

[0146] The working principles of the above devices are as shown in Embodiment 2, which will not be described redundantly in the present embodiment.

[0147] It should be pointed out that each of the devices in the present embodiment is merely in one of numerous forms. For example, in some other embodiments, the channel opening / closing device may be a valve or a nozzle, which will not be enumerated one by one in the present embodiment.

[0148] It should be noted that terms “including”, “comprising” or any other variants thereof are intended to cover non-exclusive inclusion such that a process, method, article, or apparatus including a series of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element qualified by the phrase “including a . . . ” does not exclude the presence of an additional identical element in the process, method, article, or apparatus including the element.

[0149] The embodiments of the present disclosure have been described above with reference to the accompanying drawings, but the present disclosure is not limited to the foregoing specific implementations. The foregoing specific implementations are only illustrative and not restrictive. Under the inspiration of the present disclosure, a person of ordinary skill in the art can make many improvements without departing from the purpose of the present disclosure and the protection scope defined by the claims, and these improvements shall fall within the protection scope of the present disclosure.

Examples

embodiment 1

[0066]Fractures at different positions of a formation usually have different closure pressures due to different formation depths or different mechanical properties of formation rock (e.g., different Young's moduli or Poisson's ratios). A fracture at a deeper formation depth usually has greater closure pressure than a fracture at a shallow formation depth. The fractures at different positions of the formation may be created by multi-stage fracturing or temporary-sealing fracturing, etc. Fractures of different geometric sizes may be created according to preset energy storage sizes at different positions.

[0067]In order to use subterranean fractures at different depths as energy storage bodies, as shown in FIG. 1, the present disclosure provides a method for storing and releasing energy at different positions of a formation, which is specifically an integrated energy storage and release method including the following specific steps.

[0068]In step S101, subterranean fractures at at least ...

embodiment 2

[0090]Due to the randomness of positions and properties of subterranean fractures, after the high-pressure fluid is injected, the requirement that the pressure produced 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 lower than the maximum energy storage pressure of the target energy storage fracture cannot be necessarily met. Consequently, there is certain limitation to energy storage with a plurality of subterranean fractures. In order to improve the universality, as shown in FIG. 3, the present embodiment provides a method for storing and releasing energy at different positions of a formation, which is specifically a separate energy storage and release method including the following specific steps.

[0091]In step S201, subterranean fractures at at least two different depths are selected as target energy storage fractures. The target energy storage fractures are connected by a we...

embodiment 3

[0126]In Embodiment 2, due to a large difference in depth between the target energy storage fractures, differences in minimum closure pressure and maximum energy storage pressure between the target energy storage fractures are also large. Therefore, it is required to separately control each target energy storage fracture as a separate energy storage and release unit. However, in the present embodiment, several target energy storage fractures having similar minimum closure pressures are put into one group as a separate energy storage and release unit to be controlled separately. Thus, the equipment cost is reduced.

[0127]For subterranean fractures at different depths that are connected by a vertical well or a slant well, their minimum closure pressures are generally different. However, for subterranean fractures very close to one another, it may also be regarded as these subterranean fractures having an approximate minimum closure pressure, which, in the present embodiment, can be tak...

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of and priority to Chinese Patent Application No. 202411342565.8, filed Sep. 25, 2024, which is hereby incorporated by reference herein in its entirety.TECHNICAL FIELD

[0002] The present disclosure belongs to the field of subsurface energy storage, and particularly relates to a method and system for storing and releasing energy in and from fractures at different positions of a formation.BACKGROUND

[0003] Many renewable energy sources, such as solar energy and wind energy, exhibit daily and seasonal intermittency, with unstable power output that makes them unsuitable for providing baseload electricity. As a result, integrating them directly into the grid is challenging, and solving the energy storage problem is the key to successfully scale up renewable energy production. Therefore, how to store surplus clean electricity on a large scale and deliver electricity stably when sunlight and wind are insufficient remains a technical challenge that countries worldwide are striving to overcome.

[0004] At present, large-scale electricity storage methods include using lead-acid batteries, lithium-ion batteries, or hydrogen fuel cells, compressed air energy storage, and pumped energy storage. Among these, lead-acid batteries, lithium-ion batteries, and hydrogen fuel cells have not been employed for energy storage on a large scale due to high investment and maintenance costs. The pumped energy storage refers to pumping water from a lower elevation to a higher one, converting electrical energy into the gravitational potential energy of water. However, the pumped energy storage method has specific topographical requirements and cannot be applied in flat plains or hilly areas. Compressed air energy storage is a mature technology but relies on abandoned mines or underground caverns as gas storage media, limiting its use to certain specific areas.

[0005] In view of this, there is an urgent need for a new clean electricity storage method with lower investment and maintenance costs that can adapt to a variety of terrains. For example, the Chinese patent application No. CN114016988A discloses a method and system for storing and releasing energy with a formation. The method includes: performing hydraulic fracturing in an energy storage formation devoid of oil and gas to create at least one subterranean fracture, then injecting a high-pressure fluid into the resulting subterranean fracture such that the subterranean fracture undergoes elastic deformation to store energy, and causing the high-pressure fluid in the fracture to flow back to drive a preset power generation device to release energy. However, this method is only suitable for subterranean fractures at the same elevation. When a plurality of subterranean fractures are located at different positions with different closure pressures, this method becomes unsuitable because the different closure pressures make it uncontrollable for high-pressure fluid to enter and flow back from fractures at different positionsSUMMARY

[0006] An objective of the present disclosure is to provide a method and system for storing and releasing energy at different positions of a formation that can partially solve or alleviate the problems in the prior art as described above and can be applied to energy storage and release with subterranean fractures at a plurality of different depths.

[0007] In order to solve the above-mentioned technical problems, the present disclosure specifically adopts the following technical solutions.

[0008] A method for storing and releasing energy at different positions of a formation includes: an integrated energy storage and release method or a separate energy storage and release method, the integrated energy storage and release method and the separate energy storage and release method being independently operable,

[0009] the integrated energy storage and release method including:

[0010] selecting subterranean fractures at at least two different depths as target energy storage fractures, where the target energy storage fractures at the at least two different depths are connected by a wellbore;

[0011] injecting a high-pressure fluid into the wellbore such that the high-pressure fluid is capable of entering all the target energy storage fractures connected with the wellbore, thereby driving widths of the target energy storage fractures to increase and causing formation rock to accumulate elastic potential energy, where a pressure produced by the high-pressure fluid at each of the target energy storage fractures is greater than a minimum closure pressure of the corresponding target energy storage fracture and lower than a maximum energy storage pressure of the corresponding target energy storage fracture;

[0012] sealing an opening of the wellbore and maintaining elastic deformation of the formation rock so as to store energy; and

[0013] when releasing energy, reducing a sealing pressure of the wellbore such that the target energy storage fractures are closed, and in the closing process, converting the elastic potential energy accumulated in the formation rock into kinetic energy for the high-pressure fluid to flow back; and

[0014] the separate energy storage and release method including:

[0015] selecting at least two or two groups of subterranean fractures connected by a wellbore as target energy storage fractures;

[0016] injecting a high-pressure fluid into the wellbore, where the high-pressure fluid is only capable of entering one of the target energy storage fractures at a time, thereby driving a width of the target energy storage fracture to increase and causing formation rock to accumulate elastic potential energy; or, the target energy storage fractures are grouped, and the high-pressure fluid is only capable of entering one of the groups of target energy storage fractures at a time, thereby driving widths of all the target energy storage fractures in the group to increase and causing formation rock to accumulate elastic potential energy; and a pressure produced by the high-pressure fluid at each of the target energy storage fractures in the group is greater than a minimum closure pressure of the corresponding target energy storage fracture and lower than a maximum energy storage pressure of the corresponding target energy storage fracture;

[0017] sealing an opening of the wellbore and maintaining elastic deformation of the formation rock so as to store energy; and

[0018] when releasing energy, reducing a sealing pressure of the wellbore such that the target energy storage fractures are closed, and in the closing process, converting the elastic potential energy accumulated in the formation rock into kinetic energy for the high-pressure fluid to flow back.

[0019] As an improvement, the integrated energy storage and release method includes calculating a density range of the high-pressure fluid with a maximum energy storage pressure of a first target energy storage fracture at a depth H1, a minimum closure pressure of a second target energy storage fracture at a depth H2, and respective depths of the first target energy storage fracture and the second target energy storage fracture from a wellhead, with H1<H2, and specifically includes using the following formulaσ4-P0g⁢H2<ρ<σ1-P0g⁢H1

[0020] to calculate the density range of the high-pressure fluid, where σ1 represents the maximum energy storage pressure of the first target energy storage fracture, ρ represents a density of the high-pressure fluid, g represents a gravitational acceleration, H1 represents the depth of the first target energy storage fracture from the wellhead, H2 represents the depth of the second target energy storage fracture from the wellhead, σ4 represents the minimum closure pressure of the second target energy storage fracture, and P0 represents an injection pressure of the high-pressure fluid at the wellhead.

[0021] As an improvement, in the separate energy storage and release method, a difference between the minimum closure pressures of the target energy storage fractures in a same group is less than a threshold.

[0022] As an improvement, in the separate energy storage and release method, only one target energy storage fracture or one group of target energy storage fractures is closed at a time such that the elastic potential energy is converted to the kinetic energy for the high-pressure fluid to flow back.

[0023] As an improvement, in the separate energy storage and release method, each target energy storage fracture or each group of target energy storage fractures is isolated in an independent cavity; and the cavity has a channel that communicates with the wellbore and is capable of being opened and closed.

[0024] As an improvement, the target energy storage fracture is a hydraulic fracture, a natural fracture, or a fault fracture.

[0025] As an improvement, when the high-pressure fluid is injected, an injection device is powered by electrical energy; and when the energy is released, the kinetic energy for the high-pressure fluid to flow back is converted into electrical energy by a preset generator.

[0026] As an improvement, in the separate energy storage and release method, any one of the target energy storage fractures or any group of target energy storage fractures having corresponding stored energy is selected to be closed according to a power requirement of the generator.

[0027] The present disclosure further provides a system for storing and releasing energy at different positions of a formation, deployed with the integrated energy storage and release method described above, and including:

[0028] an injection device configured to inject, through a wellbore, a high-pressure fluid into target energy storage fractures, thereby driving widths of the target energy storage fractures to increase and causing formation rock to accumulate elastic potential energy, where a pressure produced by the high-pressure fluid at each of the target energy storage fractures is greater than a minimum closure pressure of the target energy storage fracture and lower than a maximum energy storage pressure of the target energy storage fracture;

[0029] a sealing device configured to seal an opening of the wellbore, and maintain elastic deformation of the formation rock so as to store energy; and

[0030] a power generation device configured to convert kinetic energy for the high-pressure fluid to flow back that is converted from the elastic potential energy accumulated in formation rock in a process of closing target energy storage fractures into electrical energy.

[0031] The present disclosure further provides a system for storing and releasing energy at different positions of a formation, deployed with the separate energy storage and release method described above, and including:

[0032] an isolation device configured to isolate each target energy storage fracture or each group of target energy storage fractures connected with a wellbore in an independent cavity;

[0033] a channel opening / closing device configured to open or close a channel of the cavity that communicates with the wellbore;

[0034] an injection device configured to inject, through the wellbore, a high-pressure fluid into the target energy storage fractures, where with the cooperation of the channel opening / closing device, the high-pressure fluid is only capable of entering one of the target energy storage fractures connected with the wellbore at a time, thereby driving a width of the target energy storage fracture to increase and causing formation rock to accumulate elastic potential energy; or, the high-pressure fluid is only capable of entering one group of target energy storage fractures at a time, thereby driving widths of all the target energy storage fractures in the group to increase and causing formation rock to accumulate elastic potential energy; and a pressure produced by the high-pressure fluid at each of the target energy storage fractures in the group is greater than a minimum closure pressure of the corresponding target energy storage fracture and lower than a maximum energy storage pressure of the corresponding target energy storage fracture;

[0035] a sealing device configured to seal an opening of the wellbore, and maintain elastic deformation of the formation rock so as to store energy; and

[0036] a power generation device configured to convert kinetic energy for the high-pressure fluid to flow back that is converted from the elastic potential energy accumulated in formation rock in a process of closing target energy storage fractures into electrical energy.

[0037] The present disclosure has the following beneficial effects: the present disclosure utilizes electrical energy for actuation. The high-pressure fluid is injected into the fractures at different positions of the formation such that the widths of the subterranean fractures increase, thereby converting electrical energy to elastic deformation energy of the formation rock for storage. Thus, energy storage with low investment cost and low maintenance cost is achieved. The electrical energy mentioned in the above step may come from renewable energy sources such as wind power generation or solar power generation.

[0038] Further, in the process of gradually closing the subterranean fractures, due to the squeezing action of the formation rock, the high-pressure fluid in the fractures is caused to flow back to the ground for actuating the preset power generation device to generate power. That is, the elastic deformation energy of the subterranean fractures is converted to the electrical energy. Stable power supply can thus be achieved when solar energy or wind energy is insufficient.

[0039] When sunlight or wind is sufficient, the method and system of the present disclosure can convert the electrical energy generated by the sunlight or wind to the elastic formation energy of the rock for storage, and release the electrical energy to the power grid when needed. This is of great significance for combination of wind generated power or solar generated power to the grid and peak regulation.

[0040] The method disclosed herein further involves a hydraulic fracturing method which, as a mature technique in the field of petroleum and gas, has been used on a large scale. Therefore, the related supporting construction equipment is easily available and the cost is controllable.

[0041] In addition, in some embodiments, using a plurality of subterranean fractures for integrated energy storage and release is low in cost and simple to control.

[0042] In some other embodiments, when a plurality of subterranean fractures are separately controlled for energy storage and release, compared with the integrated energy storage and release, the control is more flexible and the use is more convenient.BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate technical solutions in the embodiments of the present application or in the prior art, a brief introduction to the drawings required for the description of the embodiments or the prior art will be provided below. In all the accompanying drawings, similar elements or portions are generally identified by similar reference numerals. In the accompanying drawings, each element or portion is not necessarily drawn to the actual scale. Apparently, the accompanying drawings in the following description show merely some embodiments of the present application, and those of ordinary skill in the art may still derive other drawings from these accompanying drawings without creative efforts.

[0044] FIG. 1 is a flowchart for Embodiment 1;

[0045] FIG. 2 is a structural schematic diagram for Embodiment 1;

[0046] FIG. 3 is a flowchart for Embodiment 2;

[0047] FIG. 4 is a structural schematic diagram for Embodiment 2; and

[0048] FIG. 5 is a structural schematic diagram for Embodiment 3.LIST OF REFERENCE NUMERALS

[0049] 110—formation, 120—wellbore, 130—first target energy storage fracture, 140—second target energy storage fracture

[0050] 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—isolation device I, 250—isolation device II, 255—isolation device III, 260—fluid distributor X, 265—fluid distributor I, 270—fluid distributor II, 275—channel opening / closing device X, 280—channel opening / closing device I, 285—channel opening / closing device II

[0051] 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—isolation device IV, 335—isolation device V, 340—isolation device VI, 345—isolation device VII, 350—isolation device VIII, 355—fluid distributor III, 360—fluid distributor IV, 365—fluid distributor V, 370—fluid distributor VI, 375—channel opening / closing device III, 380—channel opening / closing device IV, 385—channel opening / closing device V, and 390—channel opening / closing device VI.DETAILED DESCRIPTION OF THE EMBODIMENTS

[0052] To make the objective, technical solutions, and advantages of the embodiments of the present disclosure clearer, the technical solutions in the embodiments of the present disclosure will be described clearly and completely below with reference to the accompanying drawings in the embodiments of the present disclosure. Apparently, the described embodiments are merely some rather than all of the embodiments of the present disclosure. All other embodiments obtained by a person of ordinary skill in the art on the basis of the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0053] As used herein, the terms such as “module”, “component”, and “unit” used to represent elements are only for convenience of description of the present disclosure, and have no specific meaning themselves. Thus, “module”, “component”, and “unit” may be used interchangeably.

[0054] As used herein, an orientation or positional relationship indicated by a term such as “upper”, “lower”, “inner”, “outer”, “front”, “rear”, “one end”, and “the other end” is based on the orientation or positional relationship shown in the accompanying drawings, which is only for convenience of describing the present disclosure and simplifying the description, rather than indicating or implying that the device or element referred to must have a particular orientation and be constructed and operated in a particular orientation, and therefore should not be construed as limiting the present disclosure. Moreover, terms such as “first” and “second” are merely intended for the purpose of description, and should not be construed as indicating or implying relative importance.

[0055] As used herein, unless otherwise clearly specified and limited, meanings of terms “mounting”, “be provided with”, and “connection” should be understood in a board sense. For example, the “connection” may be a fixed connection, a removable connection, or an integral connection; may be a mechanical connection or an electrical connection; may be a direct connection or an indirect connection through an intermediate medium; or may be intercommunication between two components. A person of ordinary skill in the art may understand specific meanings of the foregoing terms in the present disclosure based on a specific situation.

[0056] As used herein, “and / or” includes any of and all combinations of one or more associated items that are listed.

[0057] As used herein, “a plurality of” means two or more, i.e., including two, three, four, five, etc.Term Explanation

[0058] As used herein, “fluid” may be, but not limited to, a gas, a liquid, an emulsion, a slurry, and a solid particle flow having flow characteristics similar to liquid flow. For example, the fluid may include a water-based liquid having a chemical additive or supercritical carbon dioxide. Moreover, the chemical additive may include, but is not limited to, an acid, gel, potassium chloride, a surfactant, etc.

[0059] As used herein, “formation” refers to a subsurface porous and permeable rock formation (e.g., a shale formation, a sandstone formation, or a carbonate formation), which may serve as a fluid storage space. Typically, these fluids may be water, hydrocarbons, or gases. A fluid loss control agent may be added to a fluid injected into fractures in a formation to reduce or hinder the filtration loss of the fluid in the fractures to the formation.

[0060] As used herein, “hydraulic fracturing” or “fracturing” or “breakdown” refers to cracking of formation rock and propagation of cracks under the action of an external force (e.g., a high-pressure fluid).

[0061] As used herein, “subterranean fracture” or “fracture” refers to a rock open fissure created in a formation after hydraulic fracturing, or a natural fracture or fault fracture existing in the formation. The term “subterranean fracture” or “fracture” is interchangeable. “Fracture” may refer to a single fracture, or may refer to a plurality of adjacent fractures or a fracture swarm at a position.

[0062] As used herein, “wellbore” refers to a hole formed by drilling in a formation or inserting a conduit. Generally, the wellbore is cylindrical, and the cross section of the wellbore may be circular. In addition, the wellbore may have any other cross section. The wellbore may be an open hole, i.e., open-hole wellbore, or may be a cased wellbore formed by cementing a casing on the inner wall of the wellbore. The wellbore connected with fractures may be a straight well, or may be a horizontal well or a slant well.

[0063] As used herein, “fracture closure pressure” or “closure pressure” refers to a stress vertically acting on the fracture wall. For a horizontal fracture, the fracture closure pressure is equal to a vertical stress applied to the fracture wall. For a vertical fracture, the fracture closure pressure is equal to a minimum horizontal principal stress applied to the fracture wall. The fracture closure pressure may be obtained by a diagnostic fracturing injection test or a rapid injection-flowback test. The fracture closure pressure may also be calculated with logging data in combination with an in-situ stress model. The term “fracture closure pressure” or “closure pressure” is interchangeable. The fracture mentioned herein may be a vertical fracture or a horizontal fracture.

[0064] “Width of fracture” mentioned herein refers to a relative displacement distance of two walls in a direction perpendicular to the subterranean fracture plane.

[0065] As used herein, “target energy storage fracture” and “target fracture” are both fractures selected to store energy. The term “target energy storage fracture” or “target fracture” is interchangeable.Embodiment 1

[0066] Fractures at different positions of a formation usually have different closure pressures due to different formation depths or different mechanical properties of formation rock (e.g., different Young's moduli or Poisson's ratios). A fracture at a deeper formation depth usually has greater closure pressure than a fracture at a shallow formation depth. The fractures at different positions of the formation may be created by multi-stage fracturing or temporary-sealing fracturing, etc. Fractures of different geometric sizes may be created according to preset energy storage sizes at different positions.

[0067] In order to use subterranean fractures at different depths as energy storage bodies, as shown in FIG. 1, the present disclosure provides a method for storing and releasing energy at different positions of a formation, which is specifically an integrated energy storage and release method including the following specific steps.

[0068] In step S101, subterranean fractures at at least two different depths are selected as target energy storage fractures. The target energy storage fractures are connected by a wellbore.

[0069] In the present embodiment, the selected subterranean fracture may be a fracture formed by hydraulic fracturing or may be a natural fracture or fault fracture as long as it can undergo elastic formation under the action of a high-pressure fluid to accumulate elastic potential energy.

[0070] In addition, in order to facilitate injection of the high-pressure fluid and power generation using the high-pressure fluid that flows back, a plurality of target energy storage fractures are connected by the same wellbore (in particular a vertical well). As shown in FIG. 2, in the present embodiment, for the simplicity of description, the principles of the present disclosure are explained using a simple model. In the present embodiment, the target energy storage fractures in the formation 110 that are connected by the wellbore 120 include a first target energy storage fracture at a depth H1 and a second target energy storage fracture at a depth H2. It is foreseeable that the number of the target energy storage fractures may be more than 2. For example, in addition to the first target energy storage fracture and the second target energy storage fracture, there are one or more target energy storage fractures between the first target energy storage fracture and the second target energy storage fracture.

[0071] In step S102, a high-pressure fluid is injected into the wellbore such that the high-pressure fluid can enter all the target energy storage fractures connected with the wellbore, thereby driving the widths of the target energy storage fractures to increase and causing formation rock to accumulate elastic potential energy. A pressure produced by the high-pressure fluid at each target energy storage fracture is greater than a minimum closure pressure of the target energy storage fracture and lower than a maximum energy storage pressure of the target energy storage fracture.

[0072] In the energy storage process, it is required to inject the high-pressure fluid into the target energy storage fractures through the wellbore. With the pressure of the high-pressure fluid, the widths of the target energy storage fractures increase, thereby causing the formation rock to accumulate elastic potential energy.

[0073] In the present embodiment, the maximum energy storage pressure of the first target energy storage fracture at the depth H1 is assumed to be σ1, and the maximum energy storage pressure of the second target energy storage fracture at the depth H2 to be σ2, the minimum closure pressure of the first target energy storage fracture at the depth H1 to be σ3, and the minimum closure pressure of the second target energy storage fracture at the depth H2 to be σ4. Preferably, H1<H2. Generally, σ1<σ2, and σ3<σ4.

[0074] An injection pressure for injecting the high-pressure fluid into the wellbore 120 at the wellhead is denoted by P0, and a fracture pressure of the first target energy storage fracture 130 by Pf1, and a fracture pressure of the second target energy storage fracture 140 by Pf2. If the internal frictional resistance of the wellbore is neglected, the fracture pressure of the first target energy storage fracture 130 is Pf1=P0+ρgH1, and fracture pressure of the second target energy storage fracture 140 is Pf2=P0+ρgH2, where ρ represents a density of the high-pressure fluid injected into the wellbore 120, g represents a gravitational acceleration (approximately equal to 9.8 m / s2), and H1 and H2 represent vertical distances of the first target energy storage fracture and the second target energy storage fracture from a wellhead, respectively.

[0075] For given mechanical properties (Young's modulus, Poisson's ratio, and fracture toughness) and a fracture size of the formation rock, it is required to prevent the fracture from propagating in the length or depth direction in the energy storage process, and the fracture pressure and the volume of the fluid injected into the fracture have maximums (i.e., maximum energy storage pressure and maximum energy storage volume). When the fracture pressure and the volume of the fluid injected into the fracture reach the maximums, the fracture reaches the maximum energy storage state. When the fracture pressure or the volume of the fluid injected into the fracture is above the maximum, the fracture will propagate along the length or depth direction.

[0076] Therefore, when the high-pressure fluid is injected, both the closure pressure and the maximum energy storage pressure are taken into account. That is to say, the pressure produced 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 lower than the maximum energy storage pressure of the target energy storage fracture. For two upper and lower target energy storage fractures in the present embodiment, the density of the high-pressure fluid needs to meet the following conditions: P0+ρgH2>σ4, and P0+ρgH1<σ1.

[0077] Since the depth of each target energy storage fracture is different, the pressure produced by the high-pressure fluid is also different. In the present embodiment, a density range of the high-pressure fluid is calculated with the maximum energy storage pressure of the first target energy storage fracture at the depth H1, the minimum closure pressure of the second target energy storage fracture at the depth H2, and respective depths of the first target energy storage fracture and the second target energy storage fracture from the wellhead, with H1<H2. Specifically, the following formulaσ4-P0g⁢H2<ρ<σ1-P0g⁢H1

[0078] is used to calculate the density range of the high-pressure fluid, where σ1 represents the maximum energy storage pressure of the first target energy storage fracture, ρ represents the density of the high-pressure fluid, g represents the gravitational acceleration, H1 represents the vertical depth of the first target energy storage fracture from the wellhead, H2 represents the vertical depth of the second target energy storage fracture from the wellhead, σ4 represents the minimum closure pressure of the second target energy storage fracture, and P0 represents the injection pressure of the high-pressure fluid at the wellhead.

[0079] It needs to be noted that each target energy storage fracture can be opened and will not propagate only if the density ρ of the high-pressure fluid is within the above-mentioned range. It will be appreciated that for an embodiment where there are more than two target energy storage fractures, the target energy storage fracture in the between can be opened and will not propagate only if the shallowest target energy storage fracture and the deepest target energy storage fracture can both be opened and will not propagate. That is, by controlling the density of the high-pressure fluid, it can be controlled to a certain extent that all the fractures at different depths can be opened and will not propagate, i.e., the controllability of the fractures at different positions is realized to a certain extent.

[0080] In some other embodiments, in addition to calculating the density ρ using a simplified model as in Embodiment 1, the density ρ may also be calculated using methods such as numerical simulation.

[0081] In the present embodiment, the minimum closure pressure and the maximum energy storage pressure of the target energy storage fracture can be calculated with the size of the target energy storage fracture and the mechanical properties of the formation rock.

[0082] In step S103, an opening of the wellbore is sealed, and elastic deformation of the formation rock is maintained so as to store energy.

[0083] When all the target energy storage fractures are deformed after being injected with the high-pressure fluid, the opening of the wellbore can be sealed such that the internal pressure of the wellbore is maintained, thereby maintaining the elastic formation of the formation rock (and the potential energy of the high pressure fluid is that the fluid is compressible) and achieving the purpose of energy storage.

[0084] In step S104, when releasing energy, a sealing pressure of the wellbore is reduced such that the target energy storage fractures are closed, and in the closing process, the elastic potential energy accumulated in the formation rock is converted into kinetic energy for the high-pressure fluid to flow back.

[0085] When releasing energy is required, only the sealing pressure of the wellbore is reduced, and the target energy storage fractures are gradually closed due to pressure relief. In the closing process, the elastic potential energy accumulated in the formation rock is converted into the kinetic energy for the high-pressure fluid to flow back. In the present embodiment, a generator is preset at the outlet of the wellbore, which can convert the kinetic and / or potential energy for the high-pressure fluid to flow back into electrical energy again.

[0086] Based on the method described above, the present embodiment provides a system for storing and releasing energy in and from fractures at different positions of a formation, deployed with the integrated energy storage and release method disclosed in Embodiment 1, and including:

[0087] an injection device configured to inject, through a wellbore, a high-pressure fluid into target energy storage fractures, thereby driving widths of the target energy storage fractures to increase and causing formation rock to accumulate elastic potential energy, where a pressure produced by the high-pressure fluid at each of the target energy storage fractures is greater than a minimum closure pressure of the target energy storage fracture and lower than a maximum energy storage pressure of the target energy storage fracture; where the injection device can be powered by electrical energy;

[0088] a sealing device configured to seal an opening of the wellbore, and maintain elastic deformation of the formation rock so as to store energy; and

[0089] a power generation device configured to convert kinetic energy for the high-pressure fluid to flow back that is converted from the elastic potential energy accumulated in formation rock in a process of closing target energy storage fractures into electrical energy.Embodiment 2

[0090] Due to the randomness of positions and properties of subterranean fractures, after the high-pressure fluid is injected, the requirement that the pressure produced 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 lower than the maximum energy storage pressure of the target energy storage fracture cannot be necessarily met. Consequently, there is certain limitation to energy storage with a plurality of subterranean fractures. In order to improve the universality, as shown in FIG. 3, the present embodiment provides a method for storing and releasing energy at different positions of a formation, which is specifically a separate energy storage and release method including the following specific steps.

[0091] In step S201, subterranean fractures at at least two different depths are selected as target energy storage fractures. The target energy storage fractures are connected by a wellbore.

[0092] In the present embodiment, the selected subterranean fracture may be a fracture formed by hydraulic fracturing or may be a natural fracture or fault fracture as long as it can undergo elastic formation under the action of a high-pressure fluid to accumulate elastic potential energy.

[0093] In addition, in order to facilitate injection of the high-pressure fluid and power generation using the high-pressure fluid that flows back, a plurality of target energy storage fractures are connected by the same wellbore (in particular a vertical well). For the convenience of description in the present embodiment, a simplified model is provided, as shown in FIG. 4, where a wellbore is connected with a third target energy storage fracture 215 at a depth H3, a fourth target energy storage fracture 220 at a depth H4, and a fifth target energy storage fracture 225 at a depth H5. It is foreseeable that the number of the target energy storage fractures may be more than 2.

[0094] In step S202, a high-pressure fluid is injected into the wellbore. The high-pressure fluid can only enter one of the target energy storage fractures connected with the wellbore at a time, thereby driving a width of the target energy storage fracture to increase and causing formation rock to accumulate elastic potential energy.

[0095] As shown in FIG. 4, in the process of storing energy, if an injection device is powered by electrical energy to inject the high-pressure fluid into the wellbore, it is assumed that the pressure produced by the high-pressure fluid can only open the third target energy storage fracture 215. The fourth target energy storage fracture 220 and the fifth target energy storage fracture 225 have higher closure pressures and cannot receive the high-pressure fluid at a pressure below their closure pressures, and thus cannot realize energy storage. If the pressure of the high-pressure fluid is increased to exceed the minimum closure pressures of the fourth target energy storage fracture 220 and the fifth target energy storage fracture 225, it is possible for the pressure to exceed the maximum energy storage pressure of the third target energy storage fracture 215, causing the third target energy storage fracture to expand.

[0096] In order to avoid the above-mentioned case, in the present embodiment, when the high-pressure fluid is injected to drive the target energy storage fractures to elastically deform, the high-pressure fluid can only be injected to one of the target energy storage fractures at a time. At this point, the other target energy storage fractures are isolated from the target energy storage fracture, and therefore, only the target energy storage fracture needs to be taken into account in terms of the pressure of the high-pressure fluid.

[0097] In any time during the energy storage process, the high-pressure fluid is only allowed to be injected to the fracture at one position. Therefore, the method is not affected by the fracture closure pressure and the energy storage sequence of the fractures at different positions. In order to achieve this purpose, in the present embodiment, each target energy storage fracture is isolated in an independent cavity. The cavity has a channel that communicates with the wellbore and can be opened and closed.

[0098] In step S203, an opening of the wellbore is sealed, and elastic deformation of the formation rock is maintained so as to store energy.

[0099] Like Embodiment 1, when all the target energy storage fractures are deformed after being injected with the high-pressure fluid, the opening of the wellbore can be sealed such that the internal pressure of the wellbore is maintained, thereby maintaining the elastic formation of the formation rock (and the potential energy of the high pressure fluid is that the fluid is compressible) and achieving the purpose of energy storage.

[0100] In step S204, when releasing energy, a sealing pressure of the wellbore is reduced such that the target energy storage fractures are closed, and in the closing process, the elastic potential energy accumulated in the formation rock is converted into kinetic energy for the high-pressure fluid to flow back.

[0101] When releasing energy is required, only the sealing pressure of the wellbore is reduced, and the target energy storage fractures are gradually closed due to pressure relief. In the closing process, the elastic potential energy accumulated in the formation rock is converted into the kinetic energy for the high-pressure fluid to flow back. In the present embodiment, a generator is preset at the outlet of the wellbore, which can convert the kinetic and / or potential energy for the high-pressure fluid to flow back into electrical energy again.

[0102] It needs to be noted that when 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 differ greatly, flow-back may be uncontrolled when they are closed simultaneously. For example, the high-pressure fluid flowing back from the fifth target energy storage fracture 225 at the depth H5 will enter the third target energy storage fracture 215 at the depth H3 and the fourth target energy storage fracture 220 at the depth H4, rather than directly flow back out of the wellhead.

[0103] In order to avoid mutual interference of the fractures at different positions due to different closure pressures in the flow-back process, in the energy release process, only the target energy storage fracture at one position is allowed to be closed at a time, and the high-pressure fluid is caused to flow back to the ground and actuate the preset power generation device to generate power. In any time during the energy release process, only the fracture at one position is allowed to be closed, and the high-pressure fluid is caused to flow back to the ground and actuate the preset power generation device to generate power. Therefore, the method is not affected by the fracture closure pressure and the energy release sequence of the fractures at different positions. That is, the energy storage in and energy release from each fracture can be controlled separately, thereby meeting different power generation requirements.

[0104] Still further, the target energy storage fracture having corresponding stored energy is selected to be closed according to the power requirement of the generator. Specifically, one or more target energy storage fractures (with a small closure pressure difference therebetween) may be selected.

[0105] As shown in FIG. 4, the present embodiment provides a system for storing and releasing energy at different positions of a formation, deployed with the separate energy storage and release method disclosed in Embodiment 2, and including:

[0106] an isolation device configured to isolate target energy storage fractures connected with a wellbore in independent cavities, respectively;

[0107] a channel opening / closing device configured to open or close a channel of the cavity that communicates with the wellbore;

[0108] an injection device configured to inject, through the wellbore, a high-pressure fluid into the target energy storage fractures, where with the cooperation of the channel opening / closing device, the high-pressure fluid can only enter one of the target energy storage fractures connected with the wellbore at a time, thereby driving a width of the target energy storage fracture to increase and causing formation rock to accumulate elastic potential energy;

[0109] a sealing device configured to seal an opening of the wellbore, and maintain elastic deformation of the formation rock so as to store energy; and

[0110] a power generation device configured to convert kinetic energy and / or potential for the high-pressure fluid to flow back that is converted from the elastic potential energy accumulated in formation rock in a process of closing target energy storage fractures into electrical energy.

[0111] Specifically, as described in Embodiment 2, the wellbore is connected with the third target energy storage fracture 215 at the depth H3, the fourth target energy storage fracture 220 at the depth H4, and the fifth target energy storage fracture 225 at the depth H5. It is foreseeable that the number of the target energy storage fractures may be more than 3.

[0112] An inner pipe is arranged within the wellbore. Isolation device I 245, isolation device II 250, and isolation device III 255 are arranged along the axial direction of the wellbore such that three target energy storage fractures are isolated in three independent cavities.

[0113] Injection device I 200 is provided with three fluid distributors, namely fluid distributor X 260, fluid distributor I 265, and fluid distributor II 270, which correspond to the three target energy storage fractures, respectively. Each fluid distributor is equipped with the channel opening / closing device. The cavity can be connected with the inner pipe by means of the channel opening / closing device, thereby allowing the high-pressure fluid to enter into the target energy storage fracture in the cavity.

[0114] For example, in order to store energy in the third target energy storage fracture 215 at the depth H3, the channel opening / closing device X 275 needs to be opened, while the channel opening / closing device I 280 and the channel opening / closing device II 285 are closed. 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 the depth H3 through the unique outlet (i.e., the channel opening / closing device X 275). Similarly, in order to store energy in the fourth target energy storage fracture 220 at the depth H4, the channel opening / closing device I 280 needs to be opened, while the channel opening / closing device X 275 and the channel opening / closing device II 285 are closed. 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 the depth H4 through the unique outlet (i.e., the channel opening / closing device I 280). Similarly, in order to store energy in the fifth target energy storage fracture 225 at the depth H5, the channel opening / closing device II 285 needs to be opened, while the channel opening / closing device X 275 and the channel opening / closing device I 280 are closed. 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 the depth H5 through the unique outlet (i.e., the channel opening / closing device II 285).

[0115] If the channel opening / closing device X 275 is opened when energy is stored in the fifth target energy storage fracture 225 at the depth H5, the high-pressure fluid subsequently injected into the inner pipe I 240 will enter the third target energy storage fracture 215 at the depth H3 because the third target energy storage fracture 215 has a lower closure pressure. Meanwhile, the high-pressure fluid entering the fifth target energy storage fracture 225 will also flow back into the inner pipe I 240, and even can enter the third target energy storage fracture 215 at the depth H3 through the channel opening / closing device X 275. This may cause serious interference for energy storage in the fifth target energy storage fracture 225.

[0116] Thus, it can be seen that in the energy storage process, it is important to adjust a flow distribution device to allow injection of the high-pressure fluid into only one target energy storage fracture in any time while not allowing the high-pressure fluid to flow to the fractures at other positions.

[0117] With the injection device I 200 cooperating with the channel opening / closing device on the fluid distributor, in any time during the energy storage process, the high-pressure fluid is only allowed to be injected to the one target energy storage fracture. Therefore, the method is not affected by the fracture closure pressure and the energy storage sequence of the fractures at different positions. For example, in some embodiments, energy may be stored first in the third target energy storage fracture 215, then in the fourth target energy storage fracture 220, and finally in the fifth target energy storage fracture 225. In some other embodiments, energy may be stored first in the fifth target energy storage fracture 225, then in the fourth target energy storage fracture 220, and finally in the third target energy storage fracture 215. Switching energy storage in the fifth target energy storage fracture 225 to energy storage in the fourth target energy storage fracture 220 may be performed at any time in the energy storage process. Switching to energy storage in the fourth target energy storage fracture 220 may be performed without waiting for the fifth target energy storage fracture 225 reaching the maximum energy storage.

[0118] After the completion of storing energy, if there is no need for energy release, the channel opening / closing device X 275, the channel opening / closing device I 280, and the channel opening / closing device II 285 are all closed so that no high-pressure fluid flows in and out of the target energy storage fractures, and the energy storage sizes of the target energy storage fractures remain unchanged.

[0119] In the energy release process, the wellhead pressure is reduced such that the fractures are gradually closed, driving the high-pressure fluid to flow back from the fractures to the ground and actuate the preset power generation device to generate power.

[0120] In some embodiments of energy release, the channel opening / closing device X 275, the channel opening / closing device I 280, and the channel opening / closing device II 285 can all be opened. The third target energy storage fracture 215 at the depth H3 is closed, driving the internal high-pressure fluid to flow from the channel opening / closing device X 275 into the inner pipe I 240. The fourth target energy storage fracture 220 at the depth H4 is closed, driving the internal high-pressure fluid to flow from the channel opening / closing device I 280 into the inner pipe I 240. The fifth target energy storage fracture 225 at the depth H5 is closed, driving the internal high-pressure fluid to flow from the channel opening / closing device II 285 into the inner pipe I 240. Finally, the high-pressure fluid gathering in the inner pipe I 240 flows back to the ground and actuates the preset power generation device to generate power.

[0121] When the closure pressures of the three target energy storage fractures differ greatly, flow-back may be uncontrolled when the three channel opening / closing devices are opened simultaneously. For example, after the high-pressure fluid flowing back from the fifth target energy storage fracture 225 at the depth H5 enters the inner pipe I 240 from the channel opening / closing device II 285, the high-pressure fluid may enter the third target energy storage fracture 215 at the depth H3 and the fourth target energy storage fracture 220 at the depth H4 through the channel opening / closing device X 275 and the channel opening / closing device I 280, respectively, rather than directly flow back out of the wellhead.

[0122] In order to avoid mutual interference of fractures at different positions due to different closure pressures in the flow-back process, in the energy release process, only one target energy storage fracture is allowed to be closed in any time, and the high-pressure fluid is caused to flow back to the ground and actuate the preset power generation device to generate power.

[0123] For example, in order to release energy from the third target energy storage fracture 215 at the depth H3, the channel opening / closing device X 275 needs to be opened, while the channel opening / closing device I 280 and the channel opening / closing device II 285 are closed. In this way, the high-pressure fluid flowing back from the third target energy storage fracture 215 through the channel opening / closing device X 275 to the inner pipe I 240 can only flow back to the ground through the unique outlet (i.e., the wellhead) for actuating the preset power generation device to generate power. Similarly, in order to release energy from the fourth target energy storage fracture 220 at the depth H4, the channel opening / closing device I 280 needs to be opened, while the channel opening / closing device X 275 and the channel opening / closing device II 285 are closed. In this way, the high-pressure fluid flowing back from the fourth target energy storage fracture 220 through the channel opening / closing device I 280 to the inner pipe I 240 can only flow back to the ground through the unique outlet (i.e., the wellhead) for actuating the preset power generation device to generate power. Similarly, in order to release energy from the fifth target energy storage fracture 225 at the depth H5, the channel opening / closing device II 285 needs to be opened, while the channel opening / closing device X 275 and the channel opening / closing device I 280 are closed. In this way, the high-pressure fluid flowing back from the fifth target energy storage fracture 225 through the channel opening / closing device II 285 to the inner pipe I 240 can only flow back to the ground through the unique outlet (i.e., the wellhead) for actuating the preset power generation device to generate power.

[0124] Since only the fracture at one position is allowed to be closed in any time during the energy release process and the high-pressure fluid in the fracture at this position is caused to flow back to the ground and actuate the preset power generation device to generate power, the method is not affected by the fracture closure pressure and the energy release sequence of the fractures at different positions. For example, in some embodiments, energy may be released first from the third target energy storage fracture 215, then from the fourth target energy storage fracture 220, and finally from the fifth target energy storage fracture 225. In some other embodiments, energy may be released first from the fifth target energy storage fracture 225, then from the fourth target energy storage fracture 220, and finally from the third target energy storage fracture 215. Switching energy release from the fifth target energy storage fracture 225 to energy release from the fourth target energy storage fracture 220 may be performed at any time in the energy release process. Switching to energy release from the fourth target energy storage fracture 220 may be performed without waiting for the stored energy of the fifth target energy storage fracture 225 decreasing to zero.

[0125] In some embodiments, the target fracture in need of energy release is selected according to a demand on the current generated power. When the demand on the current generated power is small, the third target energy storage fracture 215 at the depth H3 may be selected for energy release because the closure pressure of the third target energy storage fracture 215 is low and the pressure of the fluid flowing back to the wellhead is also low. Accordingly, the output power for driving the power generation device is low as well. When the demand on the generated power is large, the fifth target energy storage fracture 225 at the depth H5 may be selected for energy release because the closure pressure of the fifth target energy storage fracture 225 is high and the pressure of the fluid flowing back to the wellhead is also high. Accordingly, the output power for driving the power generation device is high as well.Embodiment 3

[0126] In Embodiment 2, due to a large difference in depth between the target energy storage fractures, differences in minimum closure pressure and maximum energy storage pressure between the target energy storage fractures are also large. Therefore, it is required to separately control each target energy storage fracture as a separate energy storage and release unit. However, in the present embodiment, several target energy storage fractures having similar minimum closure pressures are put into one group as a separate energy storage and release unit to be controlled separately. Thus, the equipment cost is reduced.

[0127] For subterranean fractures at different depths that are connected by a vertical well or a slant well, their minimum closure pressures are generally different. However, for subterranean fractures very close to one another, it may also be regarded as these subterranean fractures having an approximate minimum closure pressure, which, in the present embodiment, can be taken as a group to be controlled separately. In effect, when defining the subterranean fracture herein, a plurality of adjacent fractures or a fracture swarm at a position are / is taken as a single subterranean fracture.

[0128] For subterranean fractures at different positions that are connected by a horizontal well, although these subterranean fractures are located at the same depth, the subterranean fractures at different positions may also have different closure pressures due to the heterogeneity of the formation. Therefore, when the separate energy storage and release method is applied, a plurality of adjacent fractures or a fracture swarm at a position are / is taken as a group to be controlled separately. Hence, the isolation device needs to be used for separately isolating the target energy storage fractures that are connected with the wellbore at adjacent positions and have the same or similar closure pressure in independent cavities.

[0129] Based on the grouping of the subterranean fractures, the separate energy storage and release method provided in the present embodiment includes the following steps.

[0130] In step S301, at least two subterranean fractures connected by a wellbore are selected as target energy storage fractures.

[0131] As shown in FIG. 5, the wellbore includes a vertical segment and a horizontal segment, and each of the vertical segment and the horizontal segment is connected with a plurality of subterranean fractures. Certainly, at least two groups of subterranean fractures connected by the wellbore may also be selected as the target energy storage fractures.

[0132] In step S302, a high-pressure fluid is injected into the wellbore. The high-pressure fluid can only enter one of the groups of target energy storage fractures at a time, thereby driving the widths of all the target energy storage fractures in the group to increase and causing formation rock to accumulate elastic potential energy. The pressure produced 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 lower than the maximum energy storage pressure of the corresponding target energy storage fracture.

[0133] As described in the above example, the plurality of subterranean fractures connected with the vertical segment of the wellbore are adjacent in position and similar in depth and have an approximate minimum closure pressure, and thus are grouped, in the present embodiment, as a sixth target energy storage fracture group 305 to be controlled separately. It will be appreciated that if fractures or fracture swarms are present at other depths, they may also be grouped as one or more target energy storage fracture groups depending on the similarity of their minimum closure pressures.

[0134] The plurality of subterranean fractures connected with the horizontal segment of the wellbore have different minimum closure pressures due to the heterogeneity of the formation. Thus, the fractures having similar minimum closure pressures are grouped as one target energy storage fracture group, thereby forming a seventh target energy storage fracture group 310, an eighth target energy storage fracture group 315, and a ninth target energy storage fracture group 320.

[0135] The purpose of selecting the fractures having similar minimum closure pressures as a group is to meet the condition, i.e., the pressure produced 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 lower than the maximum energy storage pressure of the corresponding target energy storage fracture. The minimum closure pressures being similar refers to, in the present embodiment, the difference between the minimum closure pressures of the target energy storage fractures in the same group being less than a threshold, e.g., less than 3 MPa.

[0136] In step S303, the opening of the wellbore is sealed, and the elastic deformation of the formation rock is maintained so as to store energy.

[0137] In step S304, when releasing energy, the sealing pressure of the wellbore is reduced such that the target energy storage fractures are closed, and in the closing process, the elastic potential energy accumulated in the formation rock is converted into the kinetic energy for the high-pressure fluid to flow back.

[0138] In order to avoid mutual interference of the fractures due to different closure pressures in the flow-back process, in the energy release process, only one group of target energy storage fractures is allowed to be closed at a time, and the high-pressure fluid in the fractures at the position is caused to flow back to the ground and actuate the preset power generation device to generate power. In any time during the energy release process, only one group of target energy storage fractures is allowed to be closed, and the high-pressure fluid in the fractures at the position is caused to flow back to the ground and actuate the preset power generation device to generate power. Therefore, the method is not affected by the fracture closure pressure and the energy release sequence of the fractures at different positions.

[0139] It will be appreciated that the system for storing and releasing energy in and from fractures at different positions of a formation deployed with the above-described separate energy storage and release method has some differences from Embodiment 2, and specifically includes an isolation device, a channel opening / closing device, an injection device, a sealing device, and a power generation device.

[0140] The isolation device is configured to isolate each group of target energy storage fractures connected with a wellbore in an independent cavity. The isolation device specifically includes isolation device IV 330 and isolation device V 335 for isolating the sixth target energy storage fracture group 305 in the independent cavity. In addition, isolation device VI 340, isolation device VII 345, and isolation device VIII 350 are further included, which are configured to isolate 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.

[0141] The channel opening / closing device is configured to open or close a channel of the cavity that communicates with the wellbore. Specifically, the channel opening / closing device in the present embodiment includes channel opening / closing device 375, channel opening / closing device 380, channel opening / closing device 385, and channel opening / closing device 390. These channel opening / closing devices are in one-to-one correspondence with 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.

[0142] The injection device II 300 is configured to inject, through the wellbore, a high-pressure fluid into the target energy storage fractures. The high-pressure fluid can only enter one group of target energy storage fractures at a time, thereby driving the widths of all the target energy storage fractures in the group to increase and causing formation rock to accumulate elastic potential energy. The pressure produced 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 lower than the maximum energy storage pressure of the corresponding target energy storage fracture.

[0143] In the present embodiment, the injection device specifically includes fluid distributor III 355, fluid distributor IV 360, fluid distributor V 365, and fluid distributor VI 370 disposed on inner pipe II 325, which correspond 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.

[0144] The sealing device is configured to seal the opening of the wellbore, and maintain the elastic deformation of the formation rock (and the potential energy of the high pressure fluid is that the fluid is compressible) so as to store energy.

[0145] The power generation device is configured to convert the kinetic energy for the high-pressure fluid to flow back that is converted from the elastic potential energy accumulated in formation rock in the process of closing target energy storage fractures into electrical energy. The power generation device may also be configured to convert the potential energy (e.g., potential energy of compressed air) for the high-pressure fluid into electrical energy.

[0146] The working principles of the above devices are as shown in Embodiment 2, which will not be described redundantly in the present embodiment.

[0147] It should be pointed out that each of the devices in the present embodiment is merely in one of numerous forms. For example, in some other embodiments, the channel opening / closing device may be a valve or a nozzle, which will not be enumerated one by one in the present embodiment.

[0148] It should be noted that terms “including”, “comprising” or any other variants thereof are intended to cover non-exclusive inclusion such that a process, method, article, or apparatus including a series of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element qualified by the phrase “including a . . . ” does not exclude the presence of an additional identical element in the process, method, article, or apparatus including the element.

[0149] The embodiments of the present disclosure have been described above with reference to the accompanying drawings, but the present disclosure is not limited to the foregoing specific implementations. The foregoing specific implementations are only illustrative and not restrictive. Under the inspiration of the present disclosure, a person of ordinary skill in the art can make many improvements without departing from the purpose of the present disclosure and the protection scope defined by the claims, and these improvements shall fall within the protection scope of the present disclosure.

Examples

embodiment 1

[0066]Fractures at different positions of a formation usually have different closure pressures due to different formation depths or different mechanical properties of formation rock (e.g., different Young's moduli or Poisson's ratios). A fracture at a deeper formation depth usually has greater closure pressure than a fracture at a shallow formation depth. The fractures at different positions of the formation may be created by multi-stage fracturing or temporary-sealing fracturing, etc. Fractures of different geometric sizes may be created according to preset energy storage sizes at different positions.

[0067]In order to use subterranean fractures at different depths as energy storage bodies, as shown in FIG. 1, the present disclosure provides a method for storing and releasing energy at different positions of a formation, which is specifically an integrated energy storage and release method including the following specific steps.

[0068]In step S101, subterranean fractures at at least ...

embodiment 2

[0090]Due to the randomness of positions and properties of subterranean fractures, after the high-pressure fluid is injected, the requirement that the pressure produced 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 lower than the maximum energy storage pressure of the target energy storage fracture cannot be necessarily met. Consequently, there is certain limitation to energy storage with a plurality of subterranean fractures. In order to improve the universality, as shown in FIG. 3, the present embodiment provides a method for storing and releasing energy at different positions of a formation, which is specifically a separate energy storage and release method including the following specific steps.

[0091]In step S201, subterranean fractures at at least two different depths are selected as target energy storage fractures. The target energy storage fractures are connected by a we...

embodiment 3

[0126]In Embodiment 2, due to a large difference in depth between the target energy storage fractures, differences in minimum closure pressure and maximum energy storage pressure between the target energy storage fractures are also large. Therefore, it is required to separately control each target energy storage fracture as a separate energy storage and release unit. However, in the present embodiment, several target energy storage fractures having similar minimum closure pressures are put into one group as a separate energy storage and release unit to be controlled separately. Thus, the equipment cost is reduced.

[0127]For subterranean fractures at different depths that are connected by a vertical well or a slant well, their minimum closure pressures are generally different. However, for subterranean fractures very close to one another, it may also be regarded as these subterranean fractures having an approximate minimum closure pressure, which, in the present embodiment, can be tak...

Claims

1. A method for storing and releasing energy in and from fractures at different positions of a formation, comprising: an integrated energy storage and release method or a separate energy storage and release method, the integrated energy storage and release method and the separate energy storage and release method being independently operable,the integrated energy storage and release method comprising:selecting subterranean fractures at at least two different depths as target energy storage fractures, wherein the target energy storage fractures at the at least two different depths are connected by a wellbore;injecting a high-pressure fluid into the wellbore such that the high-pressure fluid is capable of entering the target energy storage fractures connected with the wellbore, thereby driving widths of the target energy storage fractures to increase and causing formation rock to accumulate elastic potential energy, wherein a pressure produced by the high-pressure fluid at each of the target energy storage fractures is greater than a minimum closure pressure of the corresponding target energy storage fracture and lower than a maximum energy storage pressure of the corresponding target energy storage fracture;sealing an opening of the wellbore and maintaining elastic deformation of the formation rock so as to store energy; andwhen releasing energy, reducing a sealing pressure of the wellbore such that the target energy storage fractures are closed, and generating power using the high-pressure fluid that flows back in the closing process; andthe separate energy storage and release method comprising:selecting at least two or two groups of subterranean fractures connected by a wellbore as target energy storage fractures;injecting a high-pressure fluid into the wellbore, wherein the high-pressure fluid is only capable of entering one of the target energy storage fractures at a time, thereby driving a width of the target energy storage fracture to increase and causing formation rock to accumulate elastic potential energy; or, the high-pressure fluid is only capable of entering one of the groups of target energy storage fractures at a time, thereby driving widths of the target energy storage fractures in a same group to increase and causing formation rock to accumulate elastic potential energy; and a pressure produced by the high-pressure fluid at each of the target energy storage fractures in the same group is greater than a minimum closure pressure of the corresponding target energy storage fracture and lower than a maximum energy storage pressure of the corresponding target energy storage fracture;sealing an opening of the wellbore and maintaining elastic deformation of the formation rock so as to store energy; andwhen releasing energy, reducing a sealing pressure of the wellbore such that the target energy storage fractures are closed, and generating power using the high-pressure fluid that flows back in the closing process;wherein in the integrated energy storage and release method or the separate energy storage and release method, the target energy storage fracture is a hydraulic fracture, a natural fracture, or a fault fracture.

2. The method for storing and releasing energy in and from fractures at different positions of a formation according to claim 1, wherein the integrated energy storage and release method comprises calculating a density range of the high-pressure fluid with a maximum energy storage pressure of a first target energy storage fracture at a depth H1, a minimum closure pressure of a second target energy storage fracture at a depth H2, and respective depths of the first target energy storage fracture and the second target energy storage fracture from a wellhead, with H1<H2, and specifically comprises using the following formulaσ4-P0g⁢H⁢2<ρ<σ1-P0g⁢H⁢1to calculate the density range of the high-pressure fluid, wherein σ1 represents the maximum energy storage pressure of the first target energy storage fracture, ρ represents a density of the high-pressure fluid, g represents a gravitational acceleration, H1 represents the depth of the first target energy storage fracture from the wellhead, H2 represents the depth of the second target energy storage fracture from the wellhead, σ4 represents the minimum closure pressure of the second target energy storage fracture, and P0 represents an injection pressure of the high-pressure fluid at the wellhead.

3. The method for storing and releasing energy in and from fractures at different positions of a formation according to claim 1, wherein in the separate energy storage and release method, a difference between the minimum closure pressures of the target energy storage fractures in a same group is less than a threshold.

4. The method for storing and releasing energy in and from fractures at different positions of a formation according to claim 1, wherein in the separate energy storage and release method, only one target energy storage fracture or one group of target energy storage fractures is closed at a time such that the high-pressure fluid in the target energy storage fracture is caused to flow back to the ground and actuate a preset power generation device to generate power.

5. The method for storing and releasing energy in and from fractures at different positions of a formation according to claim 1, wherein in the separate energy storage and release method, each target energy storage fracture or each group of target energy storage fractures is isolated in an independent cavity; and the cavity has a channel that communicates with the wellbore and is capable of being opened and closed.

6. The method for storing and releasing energy in and from fractures at different positions of a formation according to claim 1, wherein when the high-pressure fluid is injected, an injection device is powered by electrical energy; and when the energy is released, the kinetic and / or potential energy for the high-pressure fluid to flow back is converted into electrical energy by a preset generator.

7. The method for storing and releasing energy in and from fractures at different positions of a formation according to claim 6, wherein in the separate energy storage and release method, any one of the target energy storage fractures or any group of target energy storage fractures having corresponding stored energy is selected to be closed according to a power requirement of the generator.

8. A system for storing and releasing energy in and from fractures at different positions of a formation, deployed with the integrated energy storage and release method of claim 1, and comprising:an injection device configured to inject, through a wellbore, a high-pressure fluid into target energy storage fractures communicating with the wellbore, thereby driving widths of the target energy storage fractures to increase and causing formation rock to accumulate elastic potential energy, wherein a pressure produced by the high-pressure fluid at each of the target energy storage fractures is greater than a minimum closure pressure of the target energy storage fracture and lower than a maximum energy storage pressure of the target energy storage fracture;a sealing device configured to seal an opening of the wellbore, and maintain elastic deformation of the formation rock so as to store energy; anda power generation device configured to generate power using the high-pressure fluid that flows back in a process of closing the target energy storage fractures.

9. A system for storing and releasing energy in and from fractures at different positions of a formation, deployed with the separate energy storage and release method of claim 1, and comprising:an isolation device configured to isolate each target energy storage fracture or each group of target energy storage fractures connected with a wellbore in an independent cavity, wherein the target energy storage fracture is a hydraulic fracture, a natural fracture, or a fault fracture;a channel opening / closing device configured to open or close a channel of the cavity that communicates with the wellbore;an injection device configured to inject, through the wellbore, a high-pressure fluid into the target energy storage fractures, wherein with the cooperation of the channel opening / closing device, the high-pressure fluid is only capable of entering one of the target energy storage fractures connected with the wellbore at a time, thereby driving a width of the target energy storage fracture to increase and causing formation rock to accumulate elastic potential energy; or, the high-pressure fluid is only capable of entering one group of target energy storage fractures at a time, thereby driving widths of the target energy storage fractures in the group to increase and causing formation rock to accumulate elastic potential energy; and a pressure produced by the high-pressure fluid at each of the target energy storage fractures in the group is greater than a minimum closure pressure of the corresponding target energy storage fracture and lower than a maximum energy storage pressure of the corresponding target energy storage fracture;a sealing device configured to seal an opening of the wellbore, and maintain elastic deformation of the formation rock so as to store energy; anda power generation device configured to generate power using the high-pressure fluid that flows back in a process of closing the target energy storage fractures.

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