Acoustic stimulation

Abstract

A downhole acoustic stimulation tool comprises: a sealed chamber containing a liquid; a pair of electrodes located in the chamber; at least one transducer arranged to generate an acoustic field between the electrodes thereby inducing cavitation in a volume of the liquid between the electrodes; and at least one capacitor configured to apply a pulse voltage across the electrodes when discharged, thereby causing the cavitating volume of liquid to form a plasma which collapses to form a shockwave. The at least one transducer constitutes a first energy source, and the at least one capacitor back and electrodes constitute a second energy source. Alternative forms and arrangements of the first and second energy sources are also disclosed.

1 . A downhole acoustic stimulation tool comprising:
 a pair of electrodes;   a feed mechanism arranged to feed a metallic conductor between the electrodes; and   a plurality of capacitor units connected in parallel, each comprising at least one capacitor.   
     
     
         2 . The downhole tool according  claim 1 , further comprising:
 a voltage control unit configured to discharge the capacitor units asynchronously to apply   a series of pulse voltages across the electrodes.   
     
     
         3 . The downhole tool according to  claim 2 , wherein a duration between successive pulse voltages is less than a charging time of each capacitor unit. 
     
     
         4 . The downhole tool according to  claim 1 , wherein the plurality of capacitors of the tool are configured so as to charge in parallel and discharge in series. 
     
     
         5 . The downhole tool according to  claim 1 , wherein each of the capacitor units comprises a plurality of capacitors connected for charging in series and discharging in parallel. 
     
     
         6 . The downhole tool according to  claim 4 , wherein the plurality of capacitors forms a Marx generator.