From the magazine, HDD

Two cities, one continuous bore

The Fossil Ridge to Arc Park (FRAP) project has the distinction of being the longest horizontal directional drilling (HDD) bore attempted in a vast natural gas deposit in project owner Chesapeake Energy Corporation’s history. The FRAP pipeline serves as a gathering and transportation route for the immense deposits of natural gas contained within the Barnett Shale, a geological formation resting underneath the state of Texas.

More than a dozen of the best site managers, engineers and safety experts in the trenchless business were on site as the project kicked off at North Park in Haltom City, Texas. After months of preparation, Chesapeake identified a path that routed the pipeline through urban surroundings to its intended destination. Although the pipeline was pulled across and under high-volume roads, as well as beneath public areas such as parks and golf courses, there was minimal interruption or inconvenience “Ó in fact, most residents and businesses along the route had no idea what was taking place some 41.2 m below.

Rock around the clock

Driver Pipeline, headquartered in Irving, Texas, completed the bore to connect a 61 cm pipeline to a main compressor station with well pads northeast of downtown Fort Worth. The Driver Pipeline crew secured their Vermeer D1000x900 Navigator drill and began the three month, 24/7 drilling project. The crew worked around the clock, safely navigating and boring. They selected a 22.2 cm rotor cone bit with mud motor, and 9.1 m sections of 12.7 cm diameter drill pipe for the
pilot bore.

With such tight tolerances (45.7 cm left to right) specified in the bore plan, there was little room for error. While the entry angle of 15 degrees, en route to an average drilling depth of 36.6 m, might be considered somewhat steep, Driver Pipeline HDD Superintendent Harold Kay explained the rationale: “Having extensive experience in and around the Fort Worth area, we were already aware of a rock ledge that exists at about 9.7 to 10.4 m below the surface,” said Mr Kay.

“If first contact with that ledge is made at less of an angle, say six to seven degrees, the drill bit is likely to deflect and skip off the top. When this happens, the radius is too small for accommodating the large-inch diameter pipe. At the 15-degree entry angle, we felt confident that when we reached the rock, the angle was sufficient for the bit to grab and hold on the first try.”

Set design

Space restrictions and limited accessibility dictated that the initial area begin small, with the spoil being removed from the bore path and hauled away via vacuum trucks and daily dump trucks used to remove large solids.

After 15 days of near-continuous drilling, the pilot bore was completed successfully and the Driver team of trenchless experts was eager to get underway with backreaming and pullback. This required three additional bores of 45.7, 66 and finally 91.4 cm, to achieve the circumference required to accommodate the 61 m X65 FBE coated steel pipe during pullback.

Staging pullback

After completing the pilot bore in 15 days, the Driver Pipeline crew was able to facilitate completion of the three reaming bores in 28 days, averaging approximately 109.7 m every 12 hours, all while preparing the pipe for its final permanent home situated some 36.6 m underground. Pullback of more than 1.6 km of steel pipe was all that remained to secure another successful installation for the cast and crew of Driver Pipeline.

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