Seasoned horizontal directional drilling (HDD) crews are confident in their abilities to bore through just about any ground condition. But there’s no denying that when they encounter rock, the job is more difficult.
“The ground is so abrasive, and the margin of error is so narrow in rock. There’s not much forgiveness there,” says Chris Fontana, Vermeer lifecycle sales manager. “And anytime you are trying to run a high level of torque and then steer, it’s a very challenging environment.”
That makes tooling selection critical for a successful project. Yes, tooling is important in any HDD job, but Fontana says tooling decisions can be magnified by the challenges in rock, be it solid or broken formations, cobble or granite or shale.
Patience is a virtue
Drilling through rock is not just physical. The right mindset is also necessary, including practicing patience and showing modesty.
HDD crews accustomed to boring in ground like sand or dirt will be used to higher rates of productivity than what can typically be achieved in rock. In rock, contractors need to modify their expectations on daily footage goals, and operators should modify their steering and how they manage the established bore path.
“They go from something like dirt to rock, and it’s like going from driving a race car to moving very slowly, methodically and carefully,” Fontana says. “Unless they adjust, they very well could have significant issues.”
In fact, rock drilling is increasingly becoming a specialization within the industry. If a significant enough portion of a project is known to consist of rock, that stretch may be subbed out to a contractor with a focus on rock bores.
“It’s like a niche within the HDD market,” Fontana says.
Know the ground conditions
Still, many HDD companies undertake projects in a variety of ground conditions. For beginners and the experienced alike, there’s plenty of room for continued learning.
One thing contractors need to remember is that, just like any other underground job, it’s best to know as much as possible about the ground conditions before starting work — and really, before even bidding on a project.
“Is it solid rock? Is it a broken formation?” Fontana says. “Anything they can learn ahead of time will help them select the right tooling.”
Vermeer has a rock lab at its headquarters in Pella, Iowa, that will perform several tests on rock samples to help customers find the best solution.
Of course, surprises occur downhole frequently. If a crew unexpectedly runs into rock, Fontana suggests they gather as much information as possible and check with their local dealer and their tooling manufacturer for advice on how to proceed. Get a soil sample and take photographs of the tooling that encountered the rocky ground and have an expert take a look. Have the rock tested at an accredited lab, such as the Vermeer rock lab.
Other considerations for contractors before starting work include knowing their productivity goals and the overall cost of operation for completing the job. For instance, if a contractor is going to be drilling through granite, then traditional rock bits with carbide could help that piece of tooling last longer. Alternatively, if investigations indicate that very dense rock is a small piece of an entire bore, and the deadline is tight, then a contractor may choose to use an air hammer to quickly and efficiently get through that formation.
You often get what you pay for
When it comes to selecting tooling, Fontana sees many contractors going with cheaper options in rock because they think that rock will wear down the tooling quickly and they don’t want to replace more expensive tooling. Over time, however, choosing price over quality can end up costing more.
“They think they’re going to go through a lot of pieces of tooling anyway, so they might as well pick something cheap,” Fontana says. “Then they fall in a trap of, that second-rate tooling is causing more problems in the long run. If you’re working in aggressive conditions, quality is going to make a difference.”
He also recommends that contractors tap the expertise found at the local dealership and with the tooling and drill manufacturers. They know what tooling works best, and in the case of the dealer, they should be aware of the type of ground conditions found in their area and could offer advice on what to use.
The best dealers and manufacturers also are willing to admit when they don’t have the answers and seek help from other industry sources.
“If a doctor is willing to get a second opinion, that’s usually a good sign,” Fontana says. “That’s the same philosophy Vermeer and its dealer network have. We will do everything in our power to help a customer, and if we feel outside our comfort zone, we want to make sure we get you the answer you feel comfortable with.”
Fontana says these are the types of questions contractors should try to answer when selecting tooling, particularly bits and reamers. Keep in mind that conditions vary by project.
- What formation is underground? Is it solid rock; solid and fractured; fractured and broken; or fractured, broken and sporadic?
- What kind of rock is it — shale, granite, cobble, limestone, something else?
- What is the psi (kPa) and density of the rock?
- What is the abrasivity? This can help estimate tool wear. Abrasivity is one of the tests conducted at the Vermeer rock lab.
Tooling tips on the jobsite
During a job, crews should be aware of several signs that an error may have been made in selecting tooling, including:
- Losing tooling downhole.
- Aggressive wear on things like sub savers, drive chucks and connections. That’s a sign there may be too much pressure.
- Trouble maintaining a signal and poor signal strength.
- Excessive fuel consumption or other unusual results from performance indicators on the horizontal directional drill. The pressure gauges paint a good picture of what is going on downhole.
In terms of drilling in rock, Fontana says some of the most common tooling mistakes he sees are over-steering, not selecting a housing that will allow fluid to flow at the appropriate volume and not using enough drilling fluid.
Steering is often the biggest challenge in rock. An operator should use a bit designed to provide a clean cutting action.
Proper fluid flow through the sonde housing is necessary to reduce the chance of overheating and wear by carrying cuttings away from the housing itself. Like choosing cheap tooling, not using enough drilling fluid usually stems from a contractor trying to minimize expenses — in this case disposal costs.
Operators should refer to the machine manufacturer’s guidelines for best practices on operation.
“If it’s Vermeer, for example, we have our general operating parameters of our machines in certain ground conditions,” Fontana says. “The fluid flow, maximum steering and other recommendations.”
Dealerships are a good resource in this area, too.
In the end, tooling is meant to help an HDD contractor be efficient and productive. That’s why it’s so important to get it right in the challenge posed by rocky conditions.
“Picking the right piece of tooling is just as important as selecting the right drill for the bore,” Fontana says.
For more information about Vermeer tooling, contact your local Vermeer dealer today or visit Borestore.com to purchase the tools you need.
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