Method for extending a network of existing fractures

Abstract

The present invention relates to a method for extending a network of existing fractures in a subterranean formation. This method comprises pumping a first fluid into a pressurized volume to pressurize a compressible fluid in said pressurized volume to a predetermined pressure and releasing a second fluid out of the pressurized volume in a confined volume connected to the existing fractures, the second fluid being released due to a relaxation of the pressurized compressible fluid in the pressurized volume. Moreover, the release of second fluid exerts pressures in the existing fractures exceeding a fracturing threshold of the subterranean formation.

1 . A method for extending a network of existing fractures in a subterranean formation, comprising:
 /a/ pumping a first fluid into a pressurized volume to pressurize a compressible fluid in said pressurized volume to a predetermined pressure;   /b/ releasing a second fluid out of the pressurized volume in a confined volume connected to the existing fractures, the second fluid being released due to a relaxation of the pressurized compressible fluid in the pressurized volume;   
       wherein the release of second fluid exerts pressures in the existing fractures exceeding a fracturing threshold of the subterranean formation. 
     
     
         2 . The method according to  claim 1 , wherein the release is controlled by parameters in a group of comprising at least:
 a maximum pressure exerted in the existing fractures,   a duration of the release,   a pressure profile exerted in the existing fractures,   a time between two consecutive releases.   
     
     
         3 . The method according to  claim 1 , wherein the method further comprises:
 /c/ prior to the release of the second fluid, extracting a third fluid from the confined volume so as to reduce the pressure in the confined volume below a confined pressure.   
     
     
         4 . The method according to  claim 3 , wherein the confined pressure is below the predetermined pressure. 
     
     
         5 . The method according to  claim 1 , wherein the steps of the method are executed a plurality of times. 
     
     
         6 . The method according to  claim 5 , wherein the time between two consecutive releases is adjusted so that fractures don't fully close back. 
     
     
         7 . The method according to  claim 1 , wherein the first fluid and second fluid are a same fluid. 
     
     
         8 . The method according to  claim 1 , wherein the second fluid has a higher viscosity than a viscosity of the first fluid. 
     
     
         9 . The method according to  claim 1 , wherein the second fluid has a higher density than a density of the first fluid, and wherein the duration of a pulse is adapted to mitigate fingering instability formed at an interface between the first fluid and second fluid. 
     
     
         10 . The method according to  claim 1 , wherein solid particles are added with the first fluid and/or the second fluid. 
     
     
         11 . The method according to  claim 1 , wherein the predetermined pressure is below the fracturing threshold. 
     
     
         12 . A device for extending existing fractures comprising:
 an upper packer and a lower packer within a borehole, defining a confined volume with the sides of the borehole; said confined volume being adapted to be connected to the existing fractures;   a pressurized volume located in the wellbore containing a compressible fluid;   pumping means adapted to inject a first fluid in the pressurized volume so as to pressurize the compressible fluid in said pressurized volume to a predetermined pressure;   a first surface-controlled valve for controlling the first fluid circulation from the surface to the pressurized volume;   a second surface-controlled valve for controlling the second fluid circulation between the pressurized volume and the confined volume.   
     
     
         13 . The device according to  claim 12 , wherein the device further comprises:
 extracting means adapted to pump the third fluid from the confined volume so as to reduce the pressure in the confined volume below a confined pressure.