Hydraulic Jar Firing Isolation Device

Abstract

A jar device is provided with a releasable locking mechanism which secures the telescopic portions of the jar device from relative movement until released. The locking mechanism is released by a tensional force which ruptures one or more frangible members.

What is claimed is: 
     
         1 . A jar device for use in creating and applying jarring forces to a tubing string in a wellbore, the jar device comprising:
 a first telescopic portion securable to a first portion of the tubing string;   a second telescopic portion which is disposed in a nested manner within the first telescopic portion and axially moveable with respect to the first telescopic portion, the second telescopic portion securable to a second portion of the tubing string;   a jar actuation mechanism which governs axial movement of the first and second telescopic portions to cause creating of a jarring force; and   a releasable locking mechanism which secures the first and telescopic portions against relative axial movement in a safety position until released.   
     
     
         2 . The jar device of  claim 1  wherein the releasable locking mechanism comprises a frangible member which is ruptured by application of a predetermined level of shear force. 
     
     
         3 . The jar device of  claim 1  wherein the second telescopic portion further comprises a reduced diameter mandrel; and
 the mandrel sleeve radially surrounds the mandrel to protect the mandrel from exposure to debris or obstructions within the wellbore. 
 
     
     
         4 . The jar device of  claim 3  wherein:
 the mandrel sleeve is fixedly secured to the first telescopic portion; and 
 the mandrel sleeve is releasably secured to the second telescopic portion. 
 
     
     
         5 . A jar device for use in creating and applying jarring forces to a tubing string in a wellbore, the jar device comprising:
 a first telescopic portion securable to a first portion of the tubing string;   a second telescopic portion which is disposed in a nested manner within the first telescopic portion and axially moveable with respect to the first telescopic portion, the second telescopic portion securable to a second portion of the tubing string;   a jar actuation mechanism which governs axial movement of the first and second telescopic portions to cause creating of a jarring force; and   a releasable locking mechanism which secures the first and telescopic portions against relative axial movement in a safety position until released, the releasable locking mechanism being releasable by rupturing a frangible member.   
     
     
         6 . The jar device of  claim 5  wherein the second telescopic portion further comprises a reduced diameter mandrel; and
 wherein the mandrel sleeve radially surrounds the mandrel to protect the mandrel from exposure to debris or obstructions within the wellbore. 
 
     
     
         7 . The jar device of  claim 5  wherein:
 the mandrel sleeve is fixedly secured to the first telescopic portion; and 
 the mandrel sleeve is releasably secured to the second telescopic portion. 
 
     
     
         8 . A method of operating a jar device having first and second telescoping portions, the method comprising the steps of:
 disposing the jar device within a wellbore, the jar device having a releasable locking mechanism which secures the first and second telescoping portions against relative movement;   releasing the releasable locking mechanism to allow relative movement of the first and second telescopic portions; and   actuating the jar device to cause jarring impacts within the wellbore.   
     
     
         9 . The method of  claim 8  wherein the step of releasing the releasable locking mechanism further comprises rupturing a frangible member.