Shale is a layered mudrock that runs in ribbons through the earth. Though softer than many other types of rock, shale presents its own challenges during drilling. If you approach the shale at too shallow of an angle or use the wrong bit during a pilot shot, the drill is likely to glance off the surface and not penetrate the shale at all. During backreaming, the wrong choices can open up a whole new can of worms that can dramatically slow drilling progress or bring it to a halt. During our decades of providing HDD solutions for drillers working in every type of material, we’ve seen the strategies and tools that work for shale — and those that result in frustration and work stoppage. Here are a few proven tips to increase your speed and efficiency when backreaming through shale.
Every HDD job brings plenty of unknowns. The more attention you pay during your pilot shot, the more likely you are to be successful and productive during your backream. After shooting out the borehole, check the drill bit. Clumped-up material will give a sense of the shale’s softness and if you’ll need to use a reamer that can handle clay. Additionally, pay close attention to the material that is slurried out of the borehole. Clay will appear chunky or lumpy, instead of a nice, smooth texture that resembles soft serve ice cream or thinner. In cases where operators see clay, they should make sure to use a reamer that performs well in sticky conditions. If the shale stays hard during piloting, check the size of the cuttings. If they’re too big, further drilling will cause the reamer to struggle when slurring the chunks out of the hole. Cuttings will settle on the bottom of the hole then grab onto the backreamer, which can cause you to get stuck.