37 AUGUST 2023 WorldWide Drilling Resource® What to Consider Before Choosing the Right Backreamer Adapted from Information by Melfred Borzall Backreamers are the workhorse of every horizontal directional drilling (HDD) operation, which is why choosing the right backreamer for each job is crucial. At best, picking the wrong backreamer can make drilling proceed slowly and drag productivity down. At worst, the reamer can snap off in the hole, causing you to stop drilling to retrieve it or force you to abandon the hole altogether and redrill a new pilot. Use a reamer that pulls back too fast and you may cause road humping; too slow and you could either cause cratering or the reamer to drop to an undesired depth. All these scenarios eat up time and stall progress, essentially choking productivity and profitability. Broken backreamers require replacement of the original reamer and an investment in a reamer better suited for the job. Add extra for the rushed air freight to get the reamer to the jobsite as fast as possible. That’s a lot of cash you could have saved if you had the right reamer in the first place. Before deciding which reamer you need for the job, think about these factors: Ground Conditions - Know the type of material you expect to encounter before you drill the pilot hole. If you’re in sticky ground (like clay), you need a reamer with excellent mixing action and enough fluid pressure to make sure the material doesn’t ball up or leave big chunks behind in the hole. For unstable conditions like sand that face the risk of collapse, use a packing reamer with an efficient mixing action to keep the cuttings and drill fluid mixed together to support the borehole wall, and not allow the sand to collect on the bottom of the hole. Cutting Action - The type of cutting action needed also depends on your ground conditions. Shale and soft limestone require backreamers with more cutters for fracturing material, then grinding it up. Softer ground like clay or sand requires fewer cutters or you risk balling up. Harder conditions like cobble or river rocks mean you don’t need to break up baseballsized cobble as much as you just need to push it out of the way, so you need reamers with a gradual, tapered body to help push the rocks aside. This is where a solid, tapered body reamer like a basic fluted or stacked plate reamer performs best. Finally, solid rock conditions need a cutting action capable of pulverizing the rock as it’s spinning, making small rock chips which are easier to pump out of the hole. Size of Rig - Using an undersized tool (not the cutting diameter but the shaft it’s built on) with too powerful of a drill rig can damage the backreamer and stop the job. Choose a backreamer strong enough for the size of rig you’re using. If you must mix and match, it’s better to use a big rig reamer on a smaller rig than the opposite. For example, don’t use a 20,000-pound drill tool on a rig with 40 or 60,000 pounds of pullback. Volume of Drilling Fluid - Always be sure you have plenty of drill fluid flow when backreaming. Pressure isn’t as important as making sure you have enough volume passing through the shaft. If you’re not using enough fluid, you’re not going to be able to mix the soil with the drilling fluid, which allows you to remove the cuttings from the hole. Pulling back too quickly without enough fluid to carry the cuttings out of the hole can just push the material forward with the reamer, causing it to get stuck or create a speed bump. If using a reamer meant for a small rig on a big rig, the fluid holes in the reamer could be too small - not allowing enough flow to carry the cuttings out. The opposite applies, too. Using a big reamer (with big fluid holes) on a small rig means not enough pressure, causing the whole thing to ball up. HERE ARE SOME DOS AND DON’TS WHEN SELECTING A BACKREAMER DON’T Assume your OEM (original equipment manufacturer) reamer is right for every job. Hesitate to trip out and swap the reamer if ground conditions change. DO Try to get a sense of every ground type you’ll run into on each job. Ask your HDD supplier’s opinion before beginning the job. Stay open-minded; HDD tooling experts are there to help. DIR
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