Centralizer Increases Production Rates, Extends Life Of Other Tools

HDD Best Practices
By Jeff Griffin, Senior Editor | June 2009 Vol. 64 No. 6

Downhole tools are critical components of the horizontal directional drilling (HDD) process—no project can be completed without them. The wrong tools for soil conditions can result in excessive equipment wear and slow production—or even make it impossible to complete a job.

Drilling heads and bits, backreamers, couplings, drill pipe and other downhole tools comprise a highly competitive market with pros and cons of various products discussed and debated. However, one sometimes overlooked is the centralizer. When added to the bottom hole assembly and used correctly, a centralizer provides several benefits that lower the overall cost per foot of an installation.

"The centralizer is a tool that is overlooked in many bottom hole assembly designs,” believes Danny Crumpton, technical sales manager for Inrock, a supplier of centralizers and other HDD products and services. "The fact is, this tool is one of the most important for keeping cost per foot at its lowest."

Crumpton said centralizers are designed specifically for HDD applications.

"Centralization in front of the hole opening assembly symmetrically aligns cutters in the center of the pilot hole against the rock face, ensuring the cutters evenly engage the pilot bore as drilling progresses, providing a smooth round bore hole," said Crumpton. "The proper use of centralizers increases hole opening production rates and extends the life of cutters and hole opener bodies."

Contractor observations

Many failures in reamer bodies such as broken legs that attach the cone to the reamer body and loss of cones in the hole, can be attributed to not properly centralizing downhole tooling, believes Keith Whitaker, president/owner of Trans America Underground Ltd., Flower Mound, TX.

"One thing that is very important," Whitaker pointed out, "is getting the correct diameter of centralizer down hole. If it is not the right size for the material being cut it can act as a wedge and build up material in front of it. Tool design will help eliminate such buildup issues."

Boyd Simon, division manager for Ranger Field Services, Broussard, LA, says his HDD crews use centralizers any time they drill in rocky conditions.

"A centralizer keeps the downhole cutting tool from wobbling or bouncing around the hole," he says. "A centralizer reduces the chance of tool damage in such conditions and keeps cones and cutters constantly cutting to create a circle shaped hole, not one that is egg shaped because the tool moves around.