Underground Construction - June 2020 - 32

DIRECTIONAL DRILLING

Unique Intersect Bore Features Surface Tie-In
Jeff Griffin | Senior Editor

Drilling two pilot holes that meet and connect between the two
starting points always makes an interesting horizontal directional
drilling (HDD) story.
Often, intersect installations are made to cross a body of water,
and the connection is made underground, then the product pipe is
pulled through from one end of the bore hole.
A recent project in Texas took a different approach: the intersect
connection to install a 30-inch steel pipe was made on the surface
of the water in Nueces Bay, an extension of Corpus Christi Bay.
The project owner was Nustar Energy.
"The span across the bay was about 16,000 feet," said Cory
Baker, general manager of Hard Rock Directional Drilling. "We
used two rigs, each drilling 7,500 feet. Both rigs punched out in
the bay. We left about 1,000 feet in the middle for the two punch
outs to be tied in."
While drilling was underway, a trench line was dredged out of the
bottom of the bay. Crew members working from barges pulled each
section of pipe into the water, which floated because of the pipe's
buoyancy. Ends of pipe that would be placed in the dredged trench
were coated with concrete and required floats to prevent them from
sinking. Connections were made while pipes floated in the water.
"Once pipes were connected," said Baker, "we pulled back on
each end to lower the connected pipe into the dredged ditch line,
which then was backfilled. This is a short, simple description of
what was a very complex installation."
Hard Rock worked with Nustar from the conception of this
project to its completion. Marine support was provided by Orion
Marine Group.
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JUNE 2020 | UConOnline.com

Unique procedure
Making an intersect on the surface is unusual. This was, perhaps,
one of the first instances the procedure was utilized.
"In the beginning," Baker said, "we looked at doing the project
with a single drill. Running all the calculations, we found that
pulling in 15,000 feet of 30-inch pipe would be pushing the limits
of pulling capabilities and would require support of additional
equipment. In addition, it was not possible to lay out the entire
15,000 feet of pipe for a pull-in.
"We considered many options and concluded the safest and
most constructible was to do two drills into the bay and pull both
back in, allowing the connection to be made above the water. Once
the tie-in was made, we pulled back on both ends of the pipe to
lower the line into the dredged ditch in the bottom of the channel,
which was then backfilled."
Tennessee Pipeline performed the above-water welds, and Orion
backfilled the dredged trench.
A Vermeer D1000x900 drilling unit with 1 million pounds of
pullback, and maximum torque of 102,500 foot-pounds was used
on each side of the bay. Each used an 8-inch NOV mud motor
with a 12¾-inch bit and Brownlee Gyro tracking system. Support
equipment was the same for each drill rig and included a Vermeer
R9 fluid reclaimer and Tulsa Rig Iron 660 mud pump.
Baker said both pilot bores were challenging with unusual
ground conditions.
"Geotech exploration gave us a good idea of what we would
encounter under the bay," Baker explained, "but we found a larger
amount of petrified wood than expected. This was very odd and
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