Pre-reaming is a method used to ensure that a finished bored hole has optimal integrity. Pre-reaming is especially useful in horizontal directional drilling (HDD) to create large holes in stages. Some holes and materials require multiple passes of increasingly larger reamers. Pre-reaming is performed after drilling the initial bore but before the pipe is installed during the pullback stage.
Trenchlesspedia Explains Pre-Ream
The amount of material left in the hole before pipe installation (pullback) plays a crucial role in the ease and quality of pipe installation. Although time consuming, pre-reaming offers a variety of benefits. A properly sized pre-ream will lower pullback pressure when the pipe is installed, reducing the torque loads and wear on the HDD equipment. Widening the hole in stages reduces the chances of drilling fluid appearing at the surface as well as surface heaving and distortion. Pre-reaming also maximizes the integrity of the hole by reducing subsurface voids.
In order to ensure a straight ream, pre-reamers are attached to a drill string and pulled either toward or away from the exit point by the drill rig, aided by drilling fluid.