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.

What is claimed is: 
     
         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; and   when 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; and   the 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; and   when 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 H 1 , a minimum closure pressure of a second target energy storage fracture at a depth H 2 , and respective depths of the first target energy storage fracture and the second target energy storage fracture from a wellhead, with H 1 <H 2 , and specifically comprises using the following formula 
       
         
           
             
               
                 
                   
                     σ 
                     4 
                   
                   - 
                   
                     P 
                     0 
                   
                 
                 
                   g 
                   ⁢ 
                   H 
                   ⁢ 
                   2 
                 
               
               < 
               ρ 
               < 
               
                 
                   
                     σ 
                     1 
                   
                   - 
                   
                     P 
                     0 
                   
                 
                 
                   g 
                   ⁢ 
                   H 
                   ⁢ 
                   1 
                 
               
             
           
         
       
       to calculate the density range of the high-pressure fluid, wherein σ 1  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, H 1  represents the depth of the first target energy storage fracture from the wellhead, H 2  represents the depth of the second target energy storage fracture from the wellhead, σ 4  represents the minimum closure pressure of the second target energy storage fracture, and P 0  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; and   a 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; and   a 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.