Patent ID: 11933932
Assignee: VINEGAR TECHNOLOGIES LLC
Field: Measurement (Instruments)
Classification: CPC G  E | IPC E  G

Claim 20:
21. A method comprising obtaining a downhole wireline permeability log by measuring NMR diffusion-T2 (D-T2), and permeability on a selection of cores of different lithologies (i.e. rock types), then using the core-calibrated parameters with D-T2 well logs to obtain a permeability well log, the method comprising the following steps:
a. obtaining cores from a selection of depths covering different lithologies,
b. measuring D-T2 on cores to determine movable fluid porosity (ϕM), i.e. porosity above T2>T2cutoff, and restricted diffusion (D/D0), where D0 is bulk diffusion versus diffusion length, (
   
    
     L
     D
    
    =
    
     
      
       D
       0
      
      ⁢
      
       t
       Δ
      
     
    
   
  
  ,
 

 where tΔ is the diffusion encoding time) using a light hydrocarbon and a heavier hydrocarbon to cover a range of LD,
c. fitting D/D0 versus LD using Padé fit to determine pore body size (d), heterogeneity length scale (LM), and tortuosity (τ) for each core,
d. determining the cementation exponent (m) for each lithology using, τ
   =
   
    ϕ
    M
    
     1
     -
     m
    
   
  
  ,
 

e. determining the heterogeneity length-scale (LM) for each lithology,
f. measuring core permeability (k) and determining the body-throat ratio BTR for each lithology from the Carman-Kozeny equation, k
   =
   
    
     
      ϕ
      M
     
     ⁢
     
      d
      2
     
    
    
     3
     ⁢
     2
     ⁢
     τ
     ⁢
     B
     ⁢
     T
     ⁢
     
      R
      2
     
    
   
  
  ,
 

g. measuring D-T2 log to determine movable fluid porosity (ϕM, log), i.e. porosity above T2>T2cutoff, and Dlog/D0 versus T2,
h. determining tortuosity log (τlog) using, τ
    
     l
     ⁢
     o
     ⁢
     g
    
   
   =
   
    ϕ
    
     M
     ,
     log
    
    
     1
     -
     m
    
   
  
  ,
 

 where m is known for each lithology from step (d),
i. fitting Dlog/D0 versus T2 using Padé fit to determine pore-body size (dlog), with τlog known from step (h), and LM fixed for each lithology from step (e), and
j. determining downhole permeability (klog) from, k
    
     l
     ⁢
     o
     ⁢
     g
    
   
   =
   
    
     
      ϕ
      
       M
       ,
       log
      
     
     ⁢
     
      d
      log
      2
     
    
    
     3
     ⁢
     2
     ⁢
     
      τ
      log
     
     ⁢
     B
     ⁢
     T
     ⁢
     
      R
      2
     
    
   
  
  ,
 

 with BTR known for each lithology from step (f).