Method for continuous interpretation of monitoring data

Abstract

It is shown that a pressure pulse originating in a well is correlated to a pulse observed at a distant well with a characteristic time. The correlation time is directly related to the diffusion time scale arising out of the pressure diffusion equation. The relationship is affected by the source-observer or observer-observer distance but the correction is small for large distances. In practice, further corrections have to be included for finite width pulses. For these pulses, a practical scheme for continuous permeability monitoring is presented.

1 . A method for monitoring characteristics of a region of earth formation over time, comprising: 
 a. obtaining source data at at least one location in a source well;    b. obtaining observer data at at least one location in an observer well, wherein said observer data may be correlated to said source data;    c. repeating (a) and (b) one or more times;    d. developing a correlation between said source data and said observer data as a function of time; and    e. analyzing said correlation to monitor one or more characteristics of said earth formation.    
   
   
       2 . The method of  claim 1 , wherein said correlation is based on a propagation function.  
   
   
       3 . The method of  claim 1 , further comprising analyzing the shape of said correlation over time.  
   
   
       4 . The method of  claim 1 , further comprising determining the time location of the maximum value of said correlation and analyzing the decay of said maximum value over time.  
   
   
       5 . The method of  claim 4 , wherein said source data are pressure pulses, said observer data is pressure data, wherein said correlation is governed by diffusion, and wherein at least one of said one or more characteristics is permeability.  
   
   
       6 . The method of  claim 1 , wherein said source data and said observer data is differentiated pressure data.  
   
   
       7 . The method of  claim 1 , wherein said source data is flow data and said observer data is pressure data.  
   
   
       8 . The method of  claim 1 , further comprising repeating (a), (b) and (c) for more than one observer well.  
   
   
       9 . The method of  claim 1 , further comprising repeating (a), (b), and (c) for more than one source well.  
   
   
       10 . The method of  claim 5 , further comprising correcting said correlation time for storage effects at said source well.  
   
   
       11 . The method of  claim 5 , further comprising correcting said correlation time for the distance between said observer well and said source well.  
   
   
       12 . The method of  claim 5 , further comprising correcting said correlation time for the width of said pressure pulses.  
   
   
       13 . A method of monitoring permeability of a region of earth formation over time comprising: 
 a. inducing one or more pressure pulses at at least one location in at least one source well, wherein data on said induced pressure pulses is gathered;    b. measuring pressure pulse data at at least one location in at least one observer well, wherein said pressure pulse data includes pressure pulses having propagated through at least a portion of said earth formation;    c. repeating (a) and (b) one or more times;    d. developing a correlation between said induced pressure pulses and said propagated pressure pulses as a function of time; and    e. analyzing said correlation to monitor the permeability the region of earth formation.    
   
   
       14 . The method of  claim 13 , wherein said correlation is based on a propagation function.  
   
   
       15 . The method of  claim 13 , further comprising analyzing the shape of said correlation over time.  
   
   
       16 . The method of  claim 13 , further comprising determining the determining the time location of the maximum value of said correlation and analyzing the decay of said maximum value over time.  
   
   
       17 . The method of  claim 16 , wherein said correlation is governed by diffusion, and wherein at least one of said one or more characteristics is permeability.  
   
   
       18 . The method of  claim 13 , wherein said induced pressure pulse data gathered at the source well and said propagated pressure pulsed data gathered at the observer well is differentiated pressure data.  
   
   
       19 . The method of  claim 13 , wherein said induced pressure pulse data is flow data and said propagated pressure pulse is pressure data.  
   
   
       20 . The method of  claim 13 , further comprising repeating (a), (b) and (c) for more than one observer well.  
   
   
       21 . The method of  claim 13 , further comprising repeating (a), (b), and (c) for more than one source well.  
   
   
       22 . The method of  claim 18 , further comprising correcting said correlation time for storage effects at said source well.  
   
   
       23 . The method of  claim 18 , further comprising correcting said correlation time for the distance between said observer well and said source well.  
   
   
       24 . The method of  claim 18 , further comprising correcting said correlation time for the width of said induced pressure pulses.