HDD Tackles the Mississippi
Crossing underneath the Mississippi River using horizontal directional drilling sounds like it could be something out of a driller’s fairy tale.
Pipeline owner, Boardwalk Louisiana Midstream, made that fairy tale a reality with the Westlake Brine Pipeline project: a 26-mile endeavor starting from the Bayou Choctaw Storage Terminal in Plaquemine, La., to the Westlake Chemical Facility in Geismar, La. The pipeline will transport brine from a salt dome in Bayou Choctaw on the west bank of the Mississippi River to a brand new chlor-alkali plant on the opposite east bank.
GeoEngineers, a consulting engineering firm specializing in geotechnical, geologic, hydrogeologic and environmental issues, was hired as the HDD design engineer on the project.
While using HDD to cross under the river is an accomplishment in itself, two other important aspects of the project made it slightly more impressive: The project crossed under two United States Army Corps of Engineers (USACE) levee systems and the HDD was completed using the intersect method.
Drilling Under the River
Because the length of the HDD under the Mississippi River and both levees was nearly 7,700 feet, the expected drilling fluid pressure required to remove the cuttings from the drilled hole was higher than the allowable drilling fluid pressure before reaching the exit point.
As a result, the HDD installation utilized the pilot hole intersect method of drilling, which involves drilling two 10-inch-diameter pilot holes of a mile from each side of the river to intersect under the river.
“The HDD design was completed with the understanding that the USACE would only permit the HDD installation if the risks of hydraulic fracture and creation of flow paths for under seepage and levee failure were mitigated,” says David P. Sauls, P.E., senior principal and geotechnical engineer of GeoEngineers. “This was achieved by targeting stronger soil layers at depth while installing steel casing through the softer near-surface soils.”
Ranger Field Services, a Louisiana-based drilling contractor, was elected to take on the execution of the project. They began construction of the HDD by installing casing on both the entry and exit sides. An entry side drill rig was positioned approximately 1,700-feet from the water’s edge, and on the other side of the Mississippi River, the exit rig was around 1,500-feet from the edge.
They used two Vermeer D330x500 drill rigs for the pilot hole operations, powered by 426-horsepower engines. The machines boasted 330,000 pounds of pullback and 50,000 foot-pounds of rotary torque.
Ranger jetted the pilot holes, reamed them and then rotated the casing into place using the drill rigs. The casings were installed between 65 and 70 feet below ground surface through soft clay and into dense sand. The casing on the entry side was approximately 278 feet long and the exit side around 259 feet long. Thankfully, the observed downhole annular pressures remained below the allowable drilling fluid pressures prescribed by the USACE permit.
The entry side rig was responsible for drilling 3,848 feet for the pilot hole as the exit side drill rig drilled 3,830 feet for the pilot hole. Ranger used two barges anchored in the Mississippi River to position secondary survey coil wires, which were used to locate the two pilot hole bits for the pilot hole intersect. Both pilot holes used a 97⁄8-inch roller cone mill tooth bit.
The 12-inch diameter pipeline was assembled on 137 pipe rollers in preparation for the pull back. With hard work and hole preparation, the pipe was successfully pulled in hole with a pre-installed PVC liner and a maximum pressure of 140,000 pounds. The pilot hole intersect was completed in about 50-feet of water and 115-feet below the mudline of the river.
Once it was completed, Ranger Field Services began their reaming activities, and multiple crews were utilized during reaming and swab pass activities.
One of the biggest obstacles of the project was the crossing under the two USACE levee systems. Drilling under the levees was a highly regulated engineering and construction process.
The USACE reviewed the HDD design and construction plan, including the installation of the casing and the usage of the intersect method, and required documentation of all the construction activities.
“During HDD construction, the drilling fluid pressure required to remove cuttings from the drilled hole had the potential to fracture the soil, creating a pathway for drilling fluid release to the ground surface, commonly referred to as inadvertent drilling fluid returns,” Sauls says. “If this occurs under a regulated levee, the fissure can create the potential for the water to seep from the flood side and under the levee to the protected side during a future flood.”
The result would be undermining erosion that could ultimately compromise levee stability and lead to catastrophic flooding and devastation. “A project such as this involves establishing an early and constant line of communication with the governing USACE district throughout the engineering, permitting and construction processes,” Sauls says.
Another challenge of the project was the predetermined design point of intersect under the Mississippi River. “We utilized tug boats and two 150-foot by 60-foot barges with 50-foot spuds in order to position grid wire at the intersect point,” says Boyd Simon, P.E., division manager of Ranger Field Services. As the tugs were mobilizing the barges, the tug captains were unable to move because of low visibility.
“Work was delayed two days because of the dense fog on the Mississippi River,” he says.
Weather proved to be a formidable foe, creating another problem for the crew. Due to melting snow from northern states, water levels were increasing at a steady pace.
“We were mandated by the Corps of Engineers to complete the crossing before the Mississippi River water levels rose more than 11 feet at the Carlton Gauge,” Simon says.
In order to expedite the process and meet the tough deadline, Ranger Field Services needed four different crews to work 24-hour shifts. “We weren’t prepared to have four crews on this project at one time,” Simon says. “It presented us with a lot of in-house scheduling conflicts.”
However, Ranger made it work and found a way to work around other HDD contracts and still complete the drilling on time. In fact, it was completed two days ahead of schedule, finishing the HDD in only 43 days.
“Successfully completing this HDD project under two Corps of Engineers levees reassured me of the knowledge and experience of our crew to complete these types of crossings,” Simon says.
Teamwork played a vital role throughout the project. Though GeoEngineers led the HDD design engineering and Ranger Field Services handled the actual drilling, there were a number of other participants who helped with the massive undertaking. These included: Adtech Mud Motors; DCS Fluid Solutions; Interstate Engineering; Horizontal Technology; United Pipeline; and Vermeer Corp.
The first HDD installation under the Mississippi River, though filled with its fair share of obstacles, ended successfully due to the hard work, perseverance and unwavering passion of its team. It might even be considered somewhat of a fairy tale-ending to a unique project. “And they all lived happily ever after.”