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HDD Helps Producer Tap Gas Reserves Under DFW Airport
“As you can imagine, there are numerous logistical challenges involved with installing such an intricate pipeline system under one of the world’s busiest airports,” said Scott Driver, vice president of operations for Driver Pipeline. “The only way this project could be completed is by using HDD since what lies on the surface is a network of runways, terminals and cargo facilities. And that just describes the surface. What lies underneath presents another set of challenges.”
From the ground up (subhed)
Geological surveys completed prior to beginning the installation showed that the ground conditions and composition of the subsurface soils varied a great deal. According to Driver, the project started out in black gumbo like dirt and moved to red clay with sandstone layers. Opposite the starting point, Driver’s crews encountered sandstone with rock ledges along with just basic sand.
“The soil conditions were very difficult,” he said. “Anytime you have a sandstone layer that’s down below the ground that you can’t see, it plays havoc with drilling equipment. It takes good equipment and a skilled operator who understands the ‘feel’ of the rig, and how it is responding to what is being encountered.”
Driver credits good employees for the company’s ability to take on large and complicated projects successfully and the use of high quality equipment to complete the work efficiently. The company is using a fleet of nine Vermeer HDD rigs, including the D100x120 Series II and D330x500 models, to complete the project.
“We use our in house survey crews to plot each bore,” Driver said. Once all utilities and related lines are located, a Vermeer vacuum excavation machine is used to uncover all the lines and do a drill profile. Then we plot each utility on the drill profile before the rig ever comes in. We have five or six vacuum excavation machines that play a very big role in the drilling project on the front end. It is an essential part of the process to ensure that we don’t damage any of the existing lines.”
The pre drill process involves running tungsten carbon inserts to start a pilot hole. The size of the hole is determined by the size of pipe to occupy the bore. For example, a 24 inch pipe requires a 24 inch pass followed by a 36 inch pass and then a mud or “swab” pass to prep the hole. These passes determine the difficulty of the penetration rate that will be encountered with the cutters. A rule of thumb for over cutting is 1.5 times the diameter of the pipe.