Once the pilot bore is completed, the drill head is removed and a back reamer is attached to the drill string.

Back reamers, also known as expanders or hole openers, have two major functions. The first and most obvious is to enlarge the hole to a size large enough to allow room for the installation of the well.

The other function is to mix the cuttings with the drilling fluids to create a slurry down hole, thus creating a better environment for installing the product line.

There are numerous styles and sizes of back reamers.

Enlarging the bore hole is mostly applied step by step. For example, to reach the 600 mm diameter, firstly is used 300 mm then secondly 450 mm and lastly 600 mm diameter reamers.

Choosing the proper back reamer is dependent on the size of well being installed and the specific soil conditions.