February 20, 2015The Mississippi River has been regarded as one of the most historic rivers in American history and has served as an inspiration for several famous authors who have used it as a backdrop for books and novels.
This historic river starts near Lake Itasca, Minn., and passes through parts of 10 states before eventually emptying into the Gulf of Mexico in southern Louisiana. During its centuries of displacing billions of gallons of water, the Mississippi has carved its way and deposited a wide array of geological sediments.
Living up to its reputation as the “mighty” Mississippi, the river evoked a mysterious aura during the early years of horizontal directional drilling (HDD) as some of the original pioneers of the industry found that attempting to cross beneath Ol’ Man River was no ordinary task. The varying degrees of geological deposits along and beneath the river at different locations proved difficult for some and virtually impossible for others as this mighty river delayed critical project schedules and claimed its share of steel in the form of stuck or lost drill tools, stem and in some cases entire segments of steel pipeline, which remained permanent fixtures beneath the river.
Forward ahead to 2014. With these inherent difficulties and mystique looming from previous crossings of the Mississippi River and the known geology for the location, it made construction planning, management and experience that much more crucial for achieving the high level of success necessary to install large-diameter, 36-in. steel pipe at an extreme record length of 9,038 ft. Some projects spanning these great lengths are already thought to be unachievable in favorable soil conditions. When a crossing includes one of the most historic and imposing rivers in North America, it made for a crossing of which legends are made.
Michels Directional Crossings completed the technically challenging crossing that stretched between the bordering states of Missouri and Illinois, and crossed under the Mississippi River and two associated levees. The installation spanned a jaw-dropping 9,038 ft, and was part of Enbridge’s 593-mile Flanagan South Pipeline.
Geological conditions can vary dramatically along the Mississippi River depending on the specific location chosen for routing of the pipeline. As the east and west portions of the pipeline had already been constructed, the critical missing link for transporting gas along the pipeline was the long-distance crossing of the Mississippi River. This crossing was originally scheduled to take place in early June as two separate drilled installations but feasibility of the two-drill scenario was affected by timing constraints that pushed initiation of construction uncomfortably close to the flooding season. To accommodate the schedule change and potential flooding threat, Enbridge won approval from the Corps of Engineers and governing Levee District to perform the crossing as a single pilot-hole intersect drill installation for 36-in. steel pipe.
While doing the work as one drill posed several challenges, including a length that had previously never been attempted with 36-in. pipe, it offered several advantages at the time of the crossing. These included:
1. Substantially reduced susceptibility to flooding which could greatly impact an already critical schedule.
2. Reduced environmental impacts by eliminating the 1.84-acre central workspace that would be required if a two drill scenario was initiated.
3. Reduced potential for inadvertent fluid releases at east and west bank levees as the single-drill option would remain at maximum vertical depth beyond the east and west bank levees without the need to day light within a central workspace that would need to be positioned within an active flood plain for a two-drill scenario.
The Michels team combined experience and ingenuity to successfully clear numerous hurdles along the way in completing this record-breaking installation.
Working near the Mississippi River presented unique challenges, including many that needed to be addressed long before equipment and crews were mobilized to the sites. Public safety and flood control were major issues for crossing under the levees. The permitting process was extensive and time-consuming causing delays in the scheduled start of the crossing. Entry was started 450 ft from the Indian Grave Levee in Illinois with the exit 450 ft from the Fabius River Levee located in Missouri. The alignment helped alleviate some impacts of flooding in the work area and avoided construction in a forested wetland or active floodplain.
In spite of those mitigative efforts, the site was far from dry, especially in the wake of two significant rainstorms that yielded several inches of rain. Mats were placed to maintain constant access to both sides of the project, allowing for efficient production and allowing for a safe access to the drill sites. In fact, a mat road on the Missouri side that served as the main access road during pullback stretched nearly two miles. The mat road on the Illinois side spanned a half-mile, and provided continuous access to the drill site which otherwise would not have been available. As on all Michels’ jobsites, safety was top priority. Tailgate safety meetings routinely addressed changing and challenging conditions, including flooded and muddy mats, which seemed to be an untimely reoccurrence. Additionally, contingency plans were developed and implemented to ensure the main work sites could sustain continuous access in event of an emergency, even if flooding left the mat roads temporarily impassable.
Several factors, including size, length and complex soil bedding, resulted in pilot hole intersect being selected as the key method of choice for drilling. Drilling began in July, just days after equipment and mats were moved and then returned following a significant rainstorm.
Gyros and steering tools were used on each of Michels’ 1.2 million-lb drill rigs to help guide steering along the alignment, which dipped to 50 ft below the deepest part of river and 80 ft below the toes of the levee.
The alignment geology consisted of clay for the first 40 to 50 ft on top of sand, which ranged from loose to dense, along with gravel, cobble and rock formations. Significant amounts of wood were also encountered in two areas, one on each side.
Michels Pipeline Construction played an integral role by performing HDD site preparation, steel pipe fabrication, X-ray, ID/OD field joint coating, hydrostatic testing and HDD pullback pipe handling. Michels Directional Crossings and Michels Pipeline Construction are divisions of Michels Corp., a Brownsville, Wis.-based utility contractor.
The pipe was assembled, welded, X-rayed and coated in one continuous string that spanned nearly two miles, which created unprecedented logistical challenges including a forced closure of a local road to accommodate the full-continuous length of pipe and a massive coordinated effort of men and equipment. That closure along with a bridge with a 12-ton weight limit turned simple tasks, like refueling, into challenging ones. Pulling back the massive pipe took a significant amount of equipment muscle. The steel pipe string weighed 282.5 lbs per foot for an astonishing total steel pipe weight of 2,551,950 lbs. Michels’ 1.2 million-lb Hercules drill rig and its 300-ton Herrenknecht Pipe Thruster were up to the challenge of pulling back this giant anaconda of a pipe string.
Drilling fluid management was critical in the environmentally sensitive area. Circulation needed to be properly maintained to allow installation while successfully avoiding inadvertent returns, which might have been impossible to access.
Controlling buoyancy was another challenge. High head and high volume pumps were staged along the pipe to allow appropriate flow of water necessary for the long pipe length.
Communication between the drill team and pipe team was critical during pullback. Many side booms were required to walk and suspend the pipe, to keep the rollers aligned and to allow buoyancy pumps to be unhooked as required. That communication was stymied by spotty cell phone service, resulting in alternate means being used. Crews worked around-the-clock during drilling and pullback to complete the installation.
Working on the project were operations manager Jeff S. Mueller and assistant operations manager Don Mueller. Project managers included: Jim McGovern, Matt Smith and Richard Zavitz; Superintendents included: Marcus Carratt, Jack Edmunds, Karl Kornkven, Paul Krings and Eric McBrair. These key leaders directed about two-dozen Directional Crossings team members who assisted in completion of this legendary project.
Greg Goral is design engineer and Jeff. S. Mueller is operations manager for Michels Directional Crossings.