Hydraulic fracturing

Abstract

Method and apparatus for monitoring growth of fracture during hydraulic fracturing treatment of a ground formation. A series of tiltmeters are positioned at spaced apart tiltmeter stations at which tilt changes due to hydraulic fracturing treatment are measurable by those tiltmeters. Tilt measurements obtained from the tiltmeters at progressive times during the fracture treatment are compared with estimated tilt changes estimated from an assumed hydraulic fracturing propagation. Useful values for initially undetermined values of parameters of the model are derived using an inverse procedure. The data analysis may be performed in real time as the hydraulic treatment progresses using differing propagation models to determine a most probable model.

1 . A method of monitoring growth of a fracture during hydraulic fracturing treatment of a ground formation comprising: 
 measuring at progressive times through an extended time interval during the treatment values of physical variables dependent on propagation of the fracture;    estimating, from an assumed hydraulic fracturing propagation model that is reliant on initially undetermined parameters, values of the variables at said progressive times through the extended time interval for differing values of said parameters; and    comparing the estimated values of said variables with the measured values to derive useful values of said parameters.    
     
     
         2 . A method as claimed in  claim 1 , comprising the further step of estimating from the assumed hydraulic fracturing propagation model and the derived useful values of said parameters future propagation dependent variables.  
     
     
         3 . A method as claimed in  claim 1 , wherein the useful values of said parameters are derived by an inverse procedure.  
     
     
         4 . A method as claimed in  claim 3 , wherein the inverse procedure is a Bayesian procedure.  
     
     
         5 . A method as claimed in  claim 1 , wherein said physical variables comprise tilt changes measurable by tiltmeters disposed at spaced apart locations in the vicinity of the fracture.  
     
     
         6 . A method as claimed in  claim 1 , wherein said physical variables comprise fracturing fluid injection pressure values.  
     
     
         7 . A method as claimed in  claim 1 , wherein said physical variables comprise acoustic emissions data.  
     
     
         8 . A method of monitoring growth of a fracture during hydraulic fracturing treatment of a ground formation comprising: 
 positioning a series of tiltmeters at spaced apart tiltmeter stations at which tilt changes caused by the hydraulic fracture growth are measurable by those tiltmeters;    estimating, from an assumed hydraulic fracturing propagation model, tilt changes at the tiltmeter stations at progressive times through an extended time interval during the treatment;    obtaining, from the tilmeters, tilt measurements at said progressive times throughout the extended time interval; and    comparing the estimated tilt changes through said time interval with the actual tilt measurements throughout that time interval.    
     
     
         9 . A method as claimed in  claim 8 , further comprising deriving from the comparison of the estimated and actual tilt changes useful values for initially undetermined values of parameters of the model.  
     
     
         10 . A method as claimed in  claim 9 , wherein the useful values of said parameters are derived using an inverse procedure.  
     
     
         11 . A method as claimed in  claim 10 , wherein the inverse procedure is a Bayesian inversion procedure.  
     
     
         12 . A method as claimed in  claim 8 , wherein the fracture orientation during said time interval is estimated from the tilt measurements.  
     
     
         13 . A method as claimed in any one of  claim 8 , wherein measurements of data other than tilt changes are used to constrain the propagation model.  
     
     
         14 . A method as claimed in  claim 13 , wherein said data include hydraulic injection pressure data.  
     
     
         15 . A method as claimed in  claim 13 , wherein said data include acoustic emissions data.  
     
     
         16 . A method as claimed in  claim 8 , wherein the comparison of estimated tilt changes with measured tilt changes is performed in real time as the hydraulic fracturing treatment progresses.  
     
     
         17 . A method as claimed in  claim 16 , wherein comparisons are made through a first time interval from a start time and sequentially through successive longer time intervals from the same start time.  
     
     
         18 . A method as claimed in  claim 8 , and comprising the steps of: 
 estimating from one or more alternative hydraulic fracturing propagation models tilt changes at the tiltmeter stations at said progressive times throughout said time interval;    comparing the estimated tilt changes estimated from the assumed and alternative propagation models with the actual tilt measurements to determine a most probable propagation model.    
     
     
         19 . Apparatus for monitoring growth of a fracture during hydraulic fracturing treatment of a ground formation comprising: 
 instruments to measure physical variables dependent on propagation of the fracture; and    a signal processing unit to receive measurement signals from the instruments at progressive times through an extended time interval during the fracturing treatment and operable to estimate, from an assumed fracturing propagation model that is reliant on initially undetermined parameters, values of said physical variables at said progressive times through the extended time interval for differing values of said parameters and by comparison of the estimated values with the measurement signals to derive useful values of said parameters.    
     
     
         20 . Apparatus as claimed in  claim 19 , wherein the signal processing unit is operable to derive the values of said parameters by an inverse procedure.  
     
     
         21 . Apparatus for monitoring growth of a fracture during hydraulic fracturing treatment of a ground formation comprising: 
 a series of tiltmeters positionable at spaced apart tiltmeter stations to measure tilt changes due to hydraulic fracturing treatment; and    a signal processing unit to receive tilt measurement signals from the tiltmeters at progressive times through an extended time interval during the fracturing treatment and operable to estimate from an assumed hydraulic fracturing propagation model tilt changes at the tiltmeter stations at progressive times through an extended time interval during the treatment and to compare the estimated tilt changes through said time interval with said tilt measurement signals.    
     
     
         22 . Apparatus as claimed in  claim 21 , wherein the data processing unit is operable to derive from the comparison of the estimated tilt changes and the tilt measurement signals useful values for initially undetermined values of parameters of the model.  
     
     
         23 . Apparatus as claimed in  claim 22 , wherein the data processing unit is operable to derive the useful values of said dependent parameters by an inverse procedure.  
     
     
         24 . Apparatus as claimed in  claim 21 , wherein the signal processing unit is operable to derive from the tilt measurements estimates of fracture orientation during said extended time interval.  
     
     
         25 . Apparatus as claimed in  claim 21 , wherein the signal processing unit is operable to compare the estimated tilt changes with the tilt measurement signals in real time as the hydraulic fracturing treatment progresses.  
     
     
         26 . Apparatus as claimed in  claim 21 , wherein the signal processing unit is operable to estimate from one or more alternative hydraulic fracturing propagation models tilt changes at the tiltmeter stations at progressive times throughout the extended time interval, and to compare the estimated tilt changes estimated from the assumed and alternative propagation models with the actual tilt measurement signals to determine a most probable propagation model.