Well cleaning apparatus

Abstract

An apparatus for cleaning calcites and other extraneous matter from the perforated casing of a sub-terrainian water well comprises a plurality of elongate explosive members 14 for lowering into the well, detonators 16 for detonating each member 14 to produce an explosion which propagates longitudinally of the well, and a plurality of short tubular attenuators 19 circumscribing the explosive members 14 at intervals along the length thereof. Each tubular attenuator 19 comprises a steel tube 20 and an annular ring 21 extending around the tube at a point along the length thereof. The tensile strength of the tube 20 is arranged to be less than that of the force produced by the explosion, whereas the tensile strength of the ring 21 is arranged to be greater than that of the force produced by the explosion. The rings 21 thus serve to attenuate the pressure wave substantially more than tubes 20 , thereby helping to produce a more pronounced attenuation. Furthermore, the shape and direction of the pressure wave of the explosion can be altered according to the relative positioning of the ring 21 on the tubes 20.

We claim:  
     
         1 . A well cleaning apparatus comprising an elongate explosive member for mounting longitudinally in a well, means for detonating said member to produce an explosion which propagates longitudinally thereof, and a plurality of short tubular attenuators circumscribing the explosive member at intervals along the length thereof, each tubular attenuator having a first and second circumferentially extending zones, arranged longitudinally with respect to the explosive member, the first zone having a tensile strength which is substantially greater than that of the second zone.  
     
     
         2 . A well cleaning apparatus as claimed in  claim 1 , in which the first zone has a tensile strength which is greater than the force produced by the explosion.  
     
     
         3 . A well cleaning apparatus as claimed in  claim 1 , in which the tensile strength of the second zone is less than the force produced by the explosion.  
     
     
         4 . A well cleaning apparatus as claimed in  claim 1 , in which the second zone is provided at the axial end of the attenuator facing against the direction in which the explosion propagates.  
     
     
         5 . A well cleaning apparatus as claimed in  claim 1 , in which the first zone preferably extends around the axial end of the attenuator which faces in the direction in which the explosion propagates.  
     
     
         6 . A well cleaning apparatus as claimed in  claim 1 , in which each attenuator comprises a metal tube and an annular ring extending around the tube.  
     
     
         7 . A well cleaning apparatus as claimed in  claim 6 , in which the wall of the ring is circular in cross-section.  
     
     
         8 . A well cleaning apparatus as claimed in  claim 6 , in which the tubes are formed of carbon steel.  
     
     
         9 . A well cleaning apparatus as claimed in  claim 6 , in which the tubes comprise a wall thickness of substantially 1.65 mm.  
     
     
         10 . A well cleaning apparatus as claimed in  claim 1 , comprising a detonator is disposed at one end of the explosive member.  
     
     
         11 . A well cleaning apparatus as claimed in  claim 1 , in which the distal end of the apparatus comprises a circular-section collection device arranged to be a close fit within the well casing.  
     
     
         12 . A well cleaning apparatus as claimed in  claim 11 , in which the collection device is perforated.  
     
     
         13 . A well cleaning apparatus as claimed in  claim 11 , in which the explosive member comprises a plurality of separate sections arranged longitudinally of each other, each section comprising a detonator which can be programmed to ignite at a predetermined variable time after a common detonation signal is applied to the apparatus.  
     
     
         14 . A well cleaning apparatus as claimed in  claim 11 , in which the explosive strength of the elongate explosive member increases towards one end thereof.