within cavity 8 will be apparent subsequently the constraining sleeve 6 is attached to the tubular member 2 by means of one or more threaded shear pins 6d located below cavity 8 a conventional o ring seal 6b is disposed along the inner bore of carrier sleeve 6 below the cavity 8 and above the pin 6d a suitable vent hole 6c is located immediately below the seal 6b but o ring seal 6b establishes sealing integrity between the tubular member 2 and the constraining sleeve 6 below the cavity 8 thus the cavity 8 is open at its upper end to the exterior along surface 6a but sealing integrity is established below the cavity 8 by the o ring seal 6b tubular member 2 is attached at its lower end to a seal carrier sleeve or mandrel 12 by threads 2b a seal assembly 10 which will be described in detail with reference to fig3 is located between the seal carrier section 12 and the tubular member 2 the seal assembly 10 is retained within an annular cavity between the carrier 12 and the lower portion 6e of constraining sleeve 6 the cavity within which the seal assembly 10 is retained has a volume which is less than the volume of the seal assembly 10 under the conditions which will exist at a downhole location in which the packer p is located a detailed discussion of this relationship will be presented with reference to fig3 the lower portion of seal carrier 12 abuts a springloaded latching collet 16 fig1 c having latching threads 16a at its lower end.