Rigonomics: Modern HDD Contractor Tools For Drilling Rock

By Jeff Griffin, Senior Editor | June 2011 Vol. 66 No. 6

At one time or another, rock is a challenge to most contractors who do horizontal directional drilling (HDD). The degree of difficulty and the efficiency with which rock is penetrated involves many factors, including the size of the drill unit, method of drilling, downhole tools and the experience and capability of drilling crews.

Rock hardness is defined by the compressive force per square inch to crush a core sample of rock. Reports citing the hardness of rock on a project very often are based on estimates, rather than tests of samples. For directional drilling purposes, “soft” rock would be about 5,000 psi and “hard” rock 25,000 psi and higher.

Some contractors are specialists in rock drilling, called in to make difficult installations others don’t want to attempt. They take pride in doing the “impossible.”

Other drilling firms make long bores to install large-diameter pipes and have the equipment and experience to handle most rock bores they encounter, but do projects in a wide range of soil conditions, including rock.

Typically contractors in these two categories operate big, powerful HDD units with 300,000 pounds of pullback and higher that are equipped with mud motors which require fluid recycling equipment for the large volume of “mud” needed to operate the motor. Terrain conditions and depths drilled often mean wireline guidance systems and True Tracker grids must be used.

Depending on site conditions and job requirements, there are options when using mud motors. Contractors who do utility work with equipment of 100,000 pounds or less may encounter rock beyond their capabilities, but downhole bits and reamers and air tools allow 30,000 to 40,000-pound pullback machines to work through surprisingly difficult conditions.

Four contractors representing each of these categories shared rock drilling knowledge and experience for this report.

H&H Enterprises
H&H Enterprises, Andover, OH, and Bemus Point, NY, is a rock specialist working primarily in the Northeastern United States.

“Ninety-five percent of our work is in rock,” said Jason Hockran, vice-president/owner. “We seek out and complete projects in rock and other complex installations that standard HDD contractors are not interested in or are unable to complete. Rock drilling is always difficult and requires a significant amount of planning and communication to meet the project expectations. “Through years of experience in rock drilling and excellent communications with customers, H&H has successfully completed thousands of rock drills.”

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