In a retrievable packer adapted for service under high temperature and high pressure operating conditions, improved sealing is provided by a seal element prop surface which is radially offset with respect to the seal element support surface of the packer body mandrel. At least one seal element is supported on the elevated prop surface and is subjected to a radial squeeze in the set configuration, even though the lowermost outside seal element may be subject to longitudinal separation. The split level seal element support arrangement provides an annular pocket into which the seal elements can be retracted upon release and retrieval of the packer, thereby providing clearance for unobstructed retrieval. Upon release of the packer, a retainer collar is shifted away from a metal backup shoe, thereby providing an annular pocket into which the metal backup shoe is deflected, so that it does not obstruct the drift clearance as the packer is retrieved. The upper outside seal element is reinforced by a garter spring assembly having deformation resistant reinforcing material enclosed within a helical wound coil. Preloading of the seal element assembly is provided by a cover sleeve which releases when a predetermined amount of compression has been achieved. The controlled preloading of the seal elements assists movement of the elements from the lower O.D. of the packer mandrel to the upper O.D. of the prop surface, and the seal elements are forced to expand into the annulus uniformly for preventing the formation of uneven extrusion gaps.