Well tool and method of using same

Claim 1

A METHOD OF PRODUCING WELL FLUID THROUGH A TUBING IN A WELL CASING, WHEREIN THE ANNULUS BETWEEN THE TUBING AND THE CASING IS PACKED OFF WITH A PACKER AND WHEREIN THE TUBING HAS A LATERAL OPENING ABOVE THE PACKER, COMPRISING THE STEPS OF: (A) CLOSING OFF FLUID FLOW DOWNWARDLY THROUGH THE TUBING BELOW THE LATERAL OPENING, (B) CIRCULATING A FLUID DOWN THE CASING ANNULUS AND THROUGH SAID LATERAL OPENING FOR FLOW UPWARDLY IN SAID TUBING TO THEREBY DISPLACE THE FLUID PREVIOUSLY IN THE ANNULUS AND TUBING WITH A LIGHTER DENSITY FLUID, (C) DEVELOPING A PREDETERMINED FLUID PRESSURE DIFFERENTIAL ACROSS THE CLOSED OFF PORTION OF THE TUBING SUFFICIENT TO EFFECT AN OPENING OF THE TUBING, AND (D) CLOSING SAID LATERAL OPENING IN RESPONSE TO SAID FLUID PRESSURE DIFFERENTAIL TO DISCONTINUE CIRCULATION FROM THE ANNULUS TO THE TUBING WHILE ENABLING WELL FLUID TO BE PRODUCED THROUGH THE TUBING.