Evaluation of fracture geometries in rock formations

Abstract

A method of evaluating the geometry of a hydraulic fracture in a rock formation comprises the steps of: obtaining measured values of electric and/or magnetic fields induced by the forward or back propagation of a fracturing fluid between the fracture and the rock formation; and determining the geometry of the fracture from the measured values.

1 . A method of evaluating the geometry of a hydraulic fracture in a rock formation, comprising the steps of: 
 obtaining measured values of electric and/or magnetic fields induced by the forward or back propagation of a fracturing fluid between the fracture and the rock formation; and    determining the geometry of the fracture from the measured values.    
     
     
         2 . A method of evaluating the geometry of a hydraulic fracture in a rock formation, comprising the steps of: 
 injecting into a borehole a fracturing fluid at a pressure allowing the fluid to create a fracture in a formation surrounding the borehole and to propagate into the fracture and further into the formation through the fracture faces;    measuring downhole the values of electric and/or magnetic fields induced by the propagation of the fluid into the fracture and further into the formation; and    determining the geometry of the fracture from the measured values.    
     
     
         3 . A method of evaluating the geometry of a hydraulic fracture in a rock formation, comprising the steps of: 
 injecting into a borehole a fracturing fluid at a pressure allowing the fluid to create a fracture in a formation surrounding the borehole and to propagate into the fractures and further into the formation through the fracture faces;    lowering the pressure in the borehole such that the fluid propagates back from the formation into the fracture;    measuring downhole the values of electric and/or magnetism fields induced by the back propagation of the fluid from the formation into the fracture; and    determining the geometry of the fracture from the measured values.    
     
     
         4 . The method according to  claim 2 , wherein the step of measuring the values of the electric and/or magnetic fields is performed inside a further borehole or boreholes.  
     
     
         5 . The method according to  claim 3 , wherein the step of measuring the values of the electric and/or magnetic fields is performed inside a further borehole or boreholes.  
     
     
         6 . A method according to  claim 1 , further comprising the step of: 
 providing a model from which expected values of the electric and/or magnetic field at the positions and/or times of the measured values can be calculated for adjustable fracture geometries and injection pressures;    wherein the geometry of the fracture is determined by adjusting the model to minimize the differences between the expected and measured values.    
     
     
         7 . A method according to  claim 2 , further comprising the step of: 
 providing a model from which expected values of the electric and/or magnetic field at the positions and/or times of the measured values can be calculated for adjustable fracture geometries and injection pressures;    wherein the geometry of the fracture is determined by adjusting the model to minimize the differences between the expected and measured values.    
     
     
         8 . A method according to  claim 3 , further comprising the step of: 
 providing a model from which expected values of the electric and/or magnetic field at the positions and/or times of the measured values can be calculated for adjustable fracture geometries and injection pressures;    wherein the geometry of the fracture is determined by adjusting the model to minimize the differences between the expected and measured values.    
     
     
         9 . A computer system which is operatively configured to determine the geometry of a hydraulic fracture in a subterranean rock formation from measured values of electric and/or magnetic fields induced by the forward or back propagation of a fracturing fluid between the fracture and the rock formation.  
     
     
         10 . An apparatus for evaluating a shape of a hydraulic fracture in a rock formation, the apparatus comprising: 
 a rig for injecting a fracturing fluid into a borehole at a pressure allowing the injected fluid to create a fracture and propagate into the created fracture around the borehole;    at least one downhole tool for measuring electric and/or magnetic fields induced by the propagation of said fluid into the fracture through the fracture faces and by the propagation of this fluid back into the formation from the fracture; and    a computer system according to  claim 9 , for determining the geometry of the fracture from the measured values of the electric and/or magnetic fields.