Patent ID: 11970940
Assignee: CHONGQING HUADI RESOURCES ENVIRONMENT TECHNOLOGY CO., LTD
Field: Measurement (Instruments)
Classification: CPC E  G  Y | IPC E  G

Claim 0:
1. An induced earthquake evaluation method for hydraulic fracturing activated faults, comprising:
step S1, obtaining an induced earthquake evaluation unit for hydraulic fracturing activated faults according to a geological structure type, a fault distribution, a fault size, a work area size, an injection well distribution, a production well distribution, injection and production formations;
wherein the geological structure type is one selected from anticline, syncline and a fault structure among a medium structure and following structure types; the fault distribution is obtained in relation to a relative location of hydraulic fracturing injection wells and production wells; the fault size is obtained by fault grade; the induced earthquake evaluation unit is not larger than an area of a working area, and is distributed in second and third grade faults of the working area; more than 90% of hydraulic fracturing fluid injection and production wells are located in the working area and the induced earthquake evaluation unit; the injection and production formations are the same or adjacent connected formation;
step S2, obtaining a cumulative injection equivalent energy W of hydraulic fracturing fluid according to an injection method, an injection form, an injection rate and a cumulative injection amount of hydraulic fracturing fluid; wherein a formula for calculating the cumulative injection equivalent energy W is as follows:, W
  =
  
   
    ∑
    
     W
     i
    
   
   =
   
    
     ∑
     
      (
      
       
        W
        ik
       
       +
       
        W
        ip
       
      
      )
     
    
    =
    
     ∑
     
      
       1
       2
      
      [
      
       
        
         (
         
          m
          i
         
         )
        
        ⁢
        
         
          (
          
           
            ∂
            y
           
           
            ∂
            t
           
          
          )
         
         2
        
       
       +
       
        
         
          k
          i
         
         (
         
          
           ∂
           y
          
          
           ∂
           x
          
         
         )
        
        2
       
      
      ]
     
    
   
  
 

where W is the cumulative injection equivalent energy, Wik is a kinetic energy of an i injected fluid, Wip is an elastic potential energy of the i injected fluid, mi is a mass of the i injected fluid, ki is an elastic potential energy coefficient of the i injected fluid;
wherein a cumulative injected equivalent energy for continuous injection is multiplied by a factor A, and a cumulative injected equivalent energy for simultaneous injection of multiple wells is multiplied by a factor B; and formulas for calculating the factors A and B are as follows:, {
  
   
    
     
      A
      =
      
       d
       
        2
        ⁢
        
         ln
         
          d
          +
          1
         
        
       
      
     
    
   
   
    
     
      B
      =
      
       n
       
        ln
        
         3
         ⁢
         n
        
       
      
     
    
   
  
 

where d is a number of continuous injection days and n is a number of wells injected simultaneously;
step S3, obtaining an induced earthquake probability P1 caused by fault type factors according to a fault type; and obtaining an induced earthquake probability P2 according to a distance between hydraulic fracturing well and fault;
step S4, obtaining a diffusion capacity D of hydraulic fracturing fluid in a fractured formation according to rock porosity, a comprehensive permeability and a fracture development degree of hydraulic fracturing formation; and a formula for obtaining the diffusion capacity D is as follows:, D
  =
  
   
    M
    ·
    
     P
     d
    
    ·
    K
   
   
    
     μ
     1
    
    (
    
     
      P
      d
     
     +
     
      
       a
       2
      
      ⁢
      M
     
    
    )
   
  
 

where, α
   =
   
    1
    -
    
     
      K
      d
     
     
      K
      q
     
    
   
  
  ,
  
   
    P
    d
   
   =
   
    
     K
     d
    
    +
    
     4
     
      3
      ⁢
      
       μ
       d
      
     
    
   
  
  ,
  
   M
   =
   
    1
    
     (
     
      
       ϕ
       
        K
        f
       
      
      +
      
       
        α
        -
        ϕ
       
       
        K
        g
       
      
     
     )
    
   
  
  ,, D is the diffusion capacity, Kf is injected fluid volume modulus, Kg is rock skeleton volume modulus, Kd is rock mineral particle volume modulus, K is a formation rock permeability, ϕ is formation rock porosity, μd is formation rock skeleton shear modulus, μ1 is injected fluid viscosity;
step S5, obtaining an effective stress τ according to a fluid pressure and mechanical characteristics of faults; wherein hydraulic fracturing fluid diffuses over faults, weakening an effective stress on the faults; and the effective stress τ is obtained by the following formula:

τ=μ(σn−P)+τ0 

where μ is an internal friction factor of the faults, σn is an vertical pressure of the faults, P is a fluid pressure at the faults, and τ0 is a fault polymerization strength;
step S6, taking the induced earthquake evaluation unit as a whole, obtaining an average fluid pressure during injection and an original formation pressure before injection of all hydraulic fracturing injection wells, and obtaining a change rate ε of formation fluid pressure;
step S7, in the induced earthquake evaluation unit, obtaining a cumulative released equivalent energy E by hydraulic fracturing according to cumulative fluid production time, a production method and a production well distribution after hydraulic fracturing; and a formula for calculating the cumulative released equivalent energy E is as follows:, E
  =
  
   
    ∑
    
     E
     i
    
   
   =
   
    ∑
    
     
      C
      1
     
     ·
     
      C
      2
     
     ·
     
      C
      3
     
     ·
     
      ∫
      
       
        (
        
         
          T
          ⁢
          
           η
           
            K
            T
           
          
         
         -
         P
        
        )
       
       ⁢
       d
       ⁢
       V
      
     
    
   
  
 

where C1 is a production mode correction coefficient, C2 is a production speed correction coefficient, C3 is a production location correction coefficient, η is a volume expansion coefficient, KT is an isothermal compression coefficient, T is a temperature, P is the fluid pressure;
step S8, in the induced earthquake evaluation unit, obtaining an induced earthquake probability P according to the accumulative injection equivalent energy W, the induced earthquake probability P1 by the fault type, the induced earthquake probability P2 by the fault distance, the diffusion capacity D of hydraulic fracturing fluid, the effective stress τ, the change rate ε of formation fluid pressure, and the accumulative released equivalent energy E; wherein the induced earthquake probability P is obtained from the following formula:

P=f1(P1,P2,ε)·f2(W−E,D,τ)

where, f
     1
    
    (
    
     
      P
      1
     
     ,
     
      P
      2
     
     ,
     ε
    
    )
   
   =
   
    ε
    ·
    
     (
     
      
       P
       1
      
      +
      
       P
       2
      
      +
      
       
        P
        1
       
       ·
       
        P
        2
       
      
     
     )
    
   
  
  ,
  
   
    
     f
     2
    
    (
    
     
      W
      -
      E
     
     ,
     D
     ,
     τ
    
    )
   
   =
   
    
     
      
       A
       2
      
      ⁢
      D
     
     τ
    
    ⁢
    
     e
     
      
       A
       1
      
      (
      
       W
       -
       E
      
      )
     
    
   
  
  ,, A1 is an equivalent energy correction coefficient, A2 is a hydraulic fracturing fluid diffusion energy correction coefficient in a formation rock.