Shear strength reduction method and apparatus

Abstract

A method of imposing a simple harmonic wave of bidirectional vibration on an object stuck in sand in a well bore, where vibrations are imposed in close proximity to the stuck location, and where the harmonic wave has sufficient amplitude and frequency to create soil liquefaction at the surface of the stuck object, thereby reducing the amount of overpull necessary to free the object from the sand.

1 . A method for extracting an object stuck in sand, comprising: 
 attaching a vibratory tool to a stuck object, at a well bore depth at which said stuck object is stuck by friction with sand;    generating continuous bidirectional vibration in a simple harmonic wave form with said vibratory tool; and    imparting said continuous harmonic vibration to said stuck object, at said well bore depth at which said stuck object is stuck.    
   
   
       2 . The method recited in  claim 1 , further comprising generating said continuous harmonic vibration with a sufficient amplitude to induce soil liquefaction in said sand.  
   
   
       3 . The method recited in  claim 2 , wherein said continuous harmonic vibration is generated with an amplitude of at least 1 inch.  
   
   
       4 . The method recited in  claim 1 , further comprising generating said continuous harmonic vibration with a sufficient frequency to impart mechanical energy at a rate sufficient to induce soil liquefaction in said sand.  
   
   
       5 . The method recited in  claim 4 , wherein said continuous harmonic vibration is generated with a frequency between about 10 Hz and about 20 Hz.  
   
   
       6 . The method recited in  claim 1 , further comprising generating said continuous harmonic vibration at the fundamental frequency of said stuck object.  
   
   
       7 . The method recited in  claim 1 , further comprising generating said continuous harmonic vibration at a whole number multiple of the fundamental frequency of said stuck object.  
   
   
       8 . A method for extracting an object stuck in sand in a well bore, comprising: 
 attaching a vibratory tool to a stuck object at a well bore depth at which said stuck object is stuck by friction with sand;    generating continuous bidirectional vibration in a simple harmonic wave form with said vibratory tool, said continuous harmonic vibration having sufficient amplitude and frequency to induce soil liquefaction in said sand; and    imparting said continuous harmonic vibration to said stuck object, at said well bore depth at which said stuck object is stuck.    
   
   
       9 . The method recited in  claim 8 , wherein said continuous harmonic vibration is generated with an amplitude of at least 1 inch.  
   
   
       10 . The method recited in  claim 8 , wherein said continuous harmonic vibration is generated with a frequency between about 10 Hz and about 20 Hz.  
   
   
       11 . The method recited in  claim 8 , further comprising generating said continuous harmonic vibration at the fundamental frequency of said stuck object.  
   
   
       12 . The method recited in  claim 8 , further comprising generating said continuous harmonic vibration at a whole number multiple of the fundamental frequency of said stuck object.  
   
   
       13 . An apparatus for extracting an object stuck in sand in a well bore, comprising: 
 a vibratory tool adapted to generate continuous bidirectional vibration in a simple harmonic wave form;    a mechanical connection adapted to attach said vibratory tool to a stuck object substantially at a well bore depth at which said stuck object is stuck by friction with sand, said connection being adapted to transmit said continuous harmonic vibration to said stuck object, substantially at said well bore depth at which said stuck object is stuck; and    a work string adapted to position said vibratory tool substantially at said well bore depth at which said stuck object is stuck.    
   
   
       14 . The apparatus recited in  claim 13 , wherein said vibratory tool is further adapted to generate said continuous harmonic vibration with a sufficient amplitude to induce soil liquefaction in said sand.  
   
   
       15 . The apparatus recited in  claim 14 , wherein said vibratory tool is further adapted to generate said continuous harmonic vibration with an amplitude of at least 1 inch.  
   
   
       16 . The apparatus recited in  claim 13 , wherein said vibratory tool is further adapted to generate said continuous harmonic vibration with a sufficient frequency to impart mechanical energy at a rate sufficient to induce soil liquefaction in said sand.  
   
   
       17 . The apparatus recited in  claim 16 , wherein said vibratory tool is further adapted to generate said continuous harmonic vibration with a frequency between about 10 Hz and about 20 Hz.  
   
   
       18 . The apparatus recited in  claim 13 , wherein said vibratory tool is further adapted to generate said continuous harmonic vibration at the fundamental frequency of said stuck object.  
   
   
       19 . The apparatus recited in  claim 13 , wherein said vibratory tool is further adapted to generate said continuous harmonic vibration at a whole number multiple of the fundamental frequency of said stuck object.