Large bore jar for a drill string

Abstract

A drill string includes a bit sub mounted to a lower end of a plurality of tubular sections, where at least one tubular section is a jar. The jar and the tubular sections have an inner diameter that is at least 4¼″ and an outer diameter that is 7″ or less. A method of drilling includes the steps of inserting the drill string into a downhole formation; causing the bit sub to drill a core sample that is received within a tubular section; and inserting a core retrieval tool through the drill string to retrieve the core sample.

1 . A drill string, comprising:
 a bit sub mounted to a lower end of a plurality of tubular sections;   at least one tubular section comprising a jar, the jar and the tubular sections having an inner diameter that is at least 4¼″ and an outer diameter that is 7″ or less; and   a coring tool having an outer diameter that is less than 4¼″.   
     
     
         2 . The drill string of  claim 1 , wherein the outer diameter is between 6¾″ and 7″. 
     
     
         3 . A jar sub for a drill string having a coring bit, comprising:
 a jar body having an inner diameter that is at least 4¼″ and an outer diameter that is 7″ or less, the inner diameter being greater than an outer diameter of a core retrieval tool.   
     
     
         4 . The jar sub of  claim 3 , wherein the outer diameter is between 6¾″ and 7″. 
     
     
         5 . A method of coring, comprising the step of:
 providing a drill string comprising a bit sub mounted to a lower end of a plurality of tubular sections, at least one tubular section comprising a jar, the jar and the tubular sections having an inner diameter that is at least 4¼″ and an outer diameter that is 7″ or less;   inserting the drill string into a downhole formation;   causing the bit sub to drill a core sample that is received within a tubular section; and   inserting a core retrieval tool through the drill string to retrieve the core sample.   
     
     
         6 . The method of  claim 5 , further comprising the step of activating the jar to free the drill string from an obstruction.