The impression packer is designed to make an impression of the sides of a borehole wall on a wax-covered paper. This provides the information needed to determine the location of discontinuities in the strata at different depths.
The impression packer consists of a split steel tube with the same diameter as the borehole itself. The two halves of this tube are pressed against the sides of the borehole by expansion of a pneumatic packer in the centre of the assembly. A thin layer of compressible rubber covers the outer surface of each half of the split steel tube. This provides a backing for the wax-paper which is attached by adhesive tape or rubber bands.
After taking an impression the packer is deflated and reverts to its original diameter and the split steel tube closes by the action of a spring. The assembly can then be easily removed or re-positioned inside the hole.
These packers are manufactured to order. Designs exist for borehole diameters of 76 mm and above.
Waxed impression paper - called "parafilm" - is supplied in standard rolls 500 mm wide by 15 metres long. This can be cut into strips of the appropriate size.
See also:
Core Orientation Core Barrels
