Pulse fracturing device and method

Abstract

A method of inducing fracture in at least a portion of a geologic structure includes inducing acoustic waves into a fluid medium present in a borehole extending at least partially into the structure. Embodiments may include preheating or pressurizing the fluid medium prior to inducing the acoustic wave therein. A device for fracturing at least a portion of a geologic structure includes electrodes for producing a spark to generate ordinary acoustic waves in the fluid medium. Embodiments may include structures for preheating or pressurizing the fluid medium prior to inducing the acoustic wave therein.

1 . A device for inducing fractures in at least a portion of a geologic structure adjacent a borehole, comprising:
 an upper packer and a lower packer, which, when placed within the borehole, together with the sides of the borehole, define a confined volume;   a pair of electrodes, disposed between the upper and lower packer and defining a spark gap between the pair of electrodes;   a power supply, in electrical communication with the electrodes and configured and arranged to generate a spark in the spark gap;   a pump, communicable to the confined volume and configured and arranged to generate a pressure in the confined volume when the device is in use; and   a heater, configured and arranged to heat a fluid present in the confined volume when the device is in use.   
     
     
         2 . A device as in  claim 1 , wherein at least one of the electrodes further comprises an actuator, configured and arranged to controllably feed electrode material to control a length of the spark gap. 
     
     
         3 . A device as in  claim 2 , wherein the actuator is configured to be actuatable in response to an output of a sensor configured and arranged to measure the length of the spark gap. 
     
     
         4 . A device as in  claim 1 , wherein the power supply comprises a primary electrical system comprising:
 a high voltage DC circuit;   an energy storage component, configured and arranged to store energy produced by the high voltage DC circuit; and   a high voltage switch, configured and arranged to discharge the energy storage component.   
     
     
         5 . A device as in  claim 4 , wherein the energy storage component comprises one or more capacitors. 
     
     
         6 . A device as in  claim 4 , wherein the power supply further comprises a secondary electrical system comprising:
 a pulse generator, configured and arranged to generate pulses of high voltage electrical energy synchronized with the discharge of the energy storage component to initiate generation of the spark in the spark gap.   
     
     
         7 . A device as in  claim 1 , further comprising a chemical additive injection system comprising:
 a storage tank, configured and arranged to store a chemical additive;   a pump, configured and arranged to inject the chemical additive into the confined volume, when the device is in use.   
     
     
         8 . A device as in  claim 1 , wherein the heater comprises a hot fluid source and a delivery conduit, the delivery conduit having an opening proximate the electrodes such that, in operation, hot fluid from the hot fluid source can be delivered to a region of the electrodes to create a thermal gradient in the spark gap. 
     
     
         9 . A device as in  claim 8  wherein the delivery conduit extends through one or both of the electrodes. 
     
     
         10 . A method for inducing a fracture in at least a portion of a geologic structure, the method comprising:
 positioning an upper packer and a lower packer within a borehole of a geologic structure to define a confined volume;   pumping a fluid to pressurize the confined volume to a predetermined pressure;   heating the fluid in the confined volume to a predetermined temperature; and   forming a pressure pulse in the fluid to induce a fracture in the geologic structure by generating a spark within the confined volume.   
     
     
         11 . The method of  claim 10 , further comprising injecting a chemical additive into the confined volume to enhance the pressure pulse. 
     
     
         12 . The method of  claim 10 , wherein the spark is generated using a pair of electrodes. 
     
     
         13 . The method of  claim 12 , further comprising:
 sensing a separation distance between the pair of electrodes; and   adjusting the separation distance between the pair of electrodes responsive to the sensed separation distance.   
     
     
         14 . The method of  claim 10 , further comprising pressurizing a fluid column outside the confined volume to a pressure less than the pressurized fluid in the confined volume. 
     
     
         15 . The method of  claim 10 , further comprising circulating the fluid out of the confined volume by injecting heated pressured fluid. 
     
     
         16 . The method of  claim 10 , further comprising repeating the forming the pressure pulse at a frequency generally below 10 Hz. 
     
     
         17 . The method of  claim 10 , wherein the predetermined pressure is a pressure below the threshold pressure above which the geologic structure would fracture. 
     
     
         18 . The method of  claim 17 , wherein the predetermined pressure is within about 10% of the threshold pressure. 
     
     
         19 . The method of  claim 10 , wherein the predetermined temperature is a temperature within about 95% to 99% of the boiling point of the fluid. 
     
     
         20 . The method of  claim 10 , wherein the pressure pulse comprises an expanding gas bubble that exerts pressure on the fluid, which generates an acoustic wave.