Retrievable bridge plug

Claim 1

IN A RETRIEVABLE BRIDGE PLUG ASSEMBLY ADAPTED TO BE LOWERED INTO A WELL CASING BY MEANS OF SETTING TOOL HAVING A TENSION MEMBER AND A COMPRESSION MEMBER, THE IMPROVEMENT COMPRISING IN COMBINATION: AN OUTER TUBULAR MANDREL, FRANGIBLE MEANS FOR CONNECTING SAID MANDREL TO THE TENSION MEMBER, A TUBULAR BODY SLIDABLY MOUNTED UPON AND ENCIRCLING A PORTION OF SAID MANDREL AND HAVING MEANS AT ONE END ENGAGEABLE TO THE COMPRESSION MEMBER, A COLLAR SLIDABLY MOUNTED ON SAID MANDREL, RELEASABLE LOCKING MEANS CONNECTING SAID COLLAR TO SAID MANDREL, MEANS INCLUDING ANNULAR DEFORMABLE PACKING RINGS ENCIRCLING SAID MANDREL AND OPERATIVELY INTERPOSED BETWEEN SAID BODY AND SAID COLLAR WHEREBY UPWARD MOVEMENT OF SAID MANDREL WITH RESPECT TO SAID BODY IS EFFECTIVE TO EXPAND SAID PACKING MEANS INTO ENGAGEMENT WITH THE CASING, RATCHET MEANS INTERPOSED BETWEEN SAID BODY AND SAID MANDREL PREVENTING UPWARD MOVEMENT OF THE BODY RELATIVE TO THE MANDREL AND MEANS INCLUDING AN AXIALLY EXTENDING ELEMENT ENGAGEABLE BY AN OVERSHOT TO MOVE SAID ELEMENT AXIALLY IN A DIRECTION TO RELEASE SAID LOCKING MEANS.