You just took two days to make an incredible directionally drilled pilot bore. You snaked around all the existing utilities — even the ones not marked. Kept the path right on target and at depth. And came out in the receiving pit at the perfect spot. Now comes the easy part. Right?

Throw on that big, heavy plug of a reamer that has been with you since the day the rig was delivered. It came with the drill and is what you always use. Why change now? There haven’t been that many fracouts. Plus, people are always driving through the neighborhood too fast, that speed bump needed to be there.

Sound like some familiar excuses? Directional drilling is tough enough. Why make it any harder on yourself, your equipment and the success of a job by not tooling up with the right backreamer?

What to Look For

When looking for a new backreamer, don’t expect to find a “do-it-all” reamer solution. There are some reamers that will work okay in many different conditions. But from a production standpoint, you are much better off if you can go with a reamer that is more specifically designed for the current ground conditions.

Although clay and sand seem like totally opposite types of soil conditions, the reamer you choose for both will have very similar design features. For both clay and sand, it is most important to have a reamer that has blades properly positioned to yield a super mixing action. Mixing the clay cuttings or the sand granules with your drill fluid is the key to a successful backream in these soils. Too few blades or improper position and the reamer won’t mix properly. Too many and it will ball up.

Backreaming through cobblestone conditions is just plain tough. The reamer needs to be stout enough to take the abuse of pounding through the cobbles and either crush them or force them into the wall of the borehole. A gradual taper to the reamer body and enough carbide tipped cutters for a smooth grinding action help ensure you get through the cobbles with the least amount of abuse to the drill rig. Each carbide should cut only a small amount, and overlap its coverage with the next cutter.

Steering the pilot bore through hard, compact conditions like hardpan or shale, can be very slow going and difficult. But with the right tool, the backreaming can actually go fast and easy. Similar to reaming through cobbles, you need a lot of cutters spaced along the reamer body to give a gradual, smooth cutting action. If positioned correctly, each cutter should only be removing a small amount of the borehole wall. This will greatly decrease the torque needed to ream the hole. Ideally, the reamer should also have a mixing action. Many times the properties of these hard compact soils can change once water and a cutting action is introduced. The hardpan can turn to a swelling clay and the sandstone may act like plain sand.

Backreaming through solid rock requires a totally different kind of beast called a hole opener. Hole openers are made up of several “cones” covered in tungsten carbide button inserts. Each cutter cone rotates independently. They break and crush the rock into small enough chips that they can be “floated” out of the borehole. But, you won’t get anywhere with a hole opener if you encounter soft conditions especially clay or sand. Hole openers need a certain amount of pressure or resistance to work effectively. Otherwise it’s like pulling a giant door knob through the ground.

Peter Melsheimer
is marketing director for Melfred Borzall, which is headquartered in Santa Maria, Calif.

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