Impression blocks are used to determine the position and condition of the top part of fish
or junk obstructing the borehole. Impression blocks feature a steel body that’s lower end
is fitted with a block of soft material, typically lead. The tool is made up on the running string and lowered without rotation to make contact with the obstruction. The resulting contact with the obstruction leaves an impression on the block’s soft material that can be identified at surface. With this information, the appropriate fishing equipment can be deployed.