Method of freeing pipe stuck in a well

Claim 1

IN A WELL OPERATION WHEREIN A PIPE STRING IS PLACED IN A BOREHOLE FORMED IN THE EARTH TRAVERSING A PERMEABLE FORMATION AND A CIRCULATING FLUID CONTAINING SUSPENDED FINELY DIVIDED SOLIDS IS CIRCULATED IN SAID BOREHOLE UNTIL A FILTER CAKE HAS BEEN DEPOSITED ON THE WALL OF SAID BOREHOLE TO CONTACT SAID PIPE STRING AND CAUSE SAID PIPE STRING TO BECOME DIFFERENTIALLY STUCK THEREAGAINST, THE IMPROVED METHOD OF FREEING SAID STUCK PIPE STRING WHICH COMPRISES: INJECTING A GASEOUS FLUID INTO A CIRCULATING LIQUID, CIRCULATING THE RESULTING GASIFIED LIQUID IN SAID BOREHOLE TO EFFECTIVELY REDUCE THE DIFFERENTIAL PRESSURE BETWEEN THE FLUID THEREIN AND SAID PERMEABLE FORMATION, WORKING SAID PIPE STRING IN SAID BOREHOLE WHILE CIRCULATING SAID GASIFIED LIQUID TO EFFECTIVELY FREE SAID STUCK PIPE STRING, AND MAINTAINING THE INTERIOR OF SAID DRILL PIPE STRING IN UNOBSTRUCTED FLUID COMMUNICATION WITH THE ANNULUS BETWEEN SAID PIPE STRING AND THE BOREHOLE WALL WHILE CIRCULATING GASIFIED LIQUID AND WORKING SAID PIPE STRING.