Drilling Fluid Properties

When HDD crews are working on the Mississippi River, they know they are in for an adventure: The river’s unpredictability and ever-changing soil conditions are just a few of the challenges they face when attempting to directionally drill under North America’s largest river system.

Add to the challenge drilling under a highly scrutinized levee system with no room for missteps and the stakes are even higher.

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One such project was recently completed near Baton Rouge, La., in which Air Liquide America wanted its bundle of a 6-in. oxygen pipeline and a 6-in. nitrogen pipeline installed via HDD under the Mississippi River to feed an ExxonMobil facility. The HDD crossing was approximately 4,900 ft and was drilled about 200 ft below the top of the levee on the exit side of the river.

Installation of this bundle across the Mississippi River was far from your routine HDD project for its designer and HDD crew.

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Crews would need to drill under the levee in West Baton Rouge Parish — resulting in an extensive and detailed permit application process through the U.S. Army Corps of Engineers (USACE). This process necessitated intricate and exact geotechnical evaluations and downhole annular pressure and drilling fluid calculations by the design engineering firm GeoEngineers Inc. — calculations that must match those taken during pilot hole and reaming operations.

Complicating the design was the limited site access on the entry and exit sides, as well as two horizontal curves at the front and back ends of the pilot hole.

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“This wasn’t your standard HDD design,” said David Sauls, P.E., with GeoEngineers.

Except, Sauls said, that it was the expected design when you consider this project involved the Mississippi River and a Louisiana levee system, which protects 200 sq miles and a population of more than 20,000.
GeoEngineers was brought into the project by owner Air Liquide for its experience with the USACE permitting process and levee projects; the firm’s inclusion was critical to the success of this project. Isaacks Directional Drilling was also sought after for its experience with drilling under the Mississippi River.

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“When you drill under the Mississippi River, it’s always unique,” said Isaacks’ rig superintendent Steve Kubala, a 28-year HDD veteran who has drilled the Mississippi River on numerous occasions. “You never know what you are going to get with the Mississippi [River]. I’ve drilled it a bunch of times and [the soil conditions] changes from one spot to another. You can be drilling in clay and go a half mile down the road and it’s gravel.”

Ground conditions for this part of the Mississippi River were alluvial deposits and some soft clay at the surface along with a dense sand layer below that. This project was in the works for more than a year but construction didn’t get under way until June 2010 due to delays associated with the permit requirements, as well as a “high river stage” in January, which raised concern for flooding at an elevated risk level and puts a stop to all construction activity. Once construction started in June, the HDD work took just 20 days to complete.

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It’s All about the Levees

In designing any construction project that involves the levee system, exactitude is the name of the game — to the USACE it’s all about the safety and stability of the levees. A most notable influence driving USACE levee protection was the catastrophic Hurricane Katrina in 2005, an epic storm that attacked the flood protection systems along Louisiana’s coastline. The aftermath of the storm brought about more stringent engineering analysis requirements for permitting pipeline levee crossing construction.

“Understandably there is a lot more scrutiny of HDD by the New Orleans [USACE] District now because of Katrina,” Sauls explained. “The New Orleans district has a much more rigorous and analytical permitting process so you can demonstrate safety.”

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For all of its concerns about levee protection, HDD has become an accepted and preferred construction method by the USACE. “The height of the levee has to be maintained for flood protection capabilities,” Sauls said. “If you have crossings that go up and over the levee, you will have a pipeline that is forever in the way of the [USACE’s] need for future maintenance and levee raising operations. The approach of the New Orleans district is that they want your line out of the way.”

USACE Permit

GeoEngineers conducted a geotechnical evaluation — including two soil borings to depths up to 220 ft below ground surface and accompanying laboratory testing — before analyzing the pilot hole’s potential for hydraulic fracture of the levee foundation soil and inadvertent returns of drilling fluids that could compromise the levee’s flood protection.

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“It’s not only understanding the soils and subsurface conditions,” said David Paul Bearden Jr. with GeoEngineers. “You have to take it a step further and understand the actual drilling installation process. You have to anticipate projected drilling fluid properties and produce calculations that must match with those produced on the actual construction side. These were calculations that were determined before the HDD contractor was brought on board.”

Monitoring downhole annular pressure and drilling fluid properties were critical to the project’s success. “Because of the restriction of the downhole annular pressure, we had to address the distance Isaacks elected to drill toward the levee critical zone [drill] before pulling back to re-establish returns in the entry pit and make adjustments to the drilling fluid properties. And then start the attempt to enter the levee critical zone with the pilot hole again,” Bearden said.

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Using an HRE (now Vermeer) 500,000-lb rig and an American Augers 300-gpm mud system, Isaacks drilled the pilot hole under these conditions in nine days. Mud engineers from DCS Fluid Solutions were onsite to monitor the drilling fluid properties, along with GeoEngineers. A downhole annular pressure tool (ParaTrack 2) from INROCK Drilling Inc. was used. The  entry and exit side spaces were fraught with congestion issues and had some restricted areas where equipment could be set up. Directly behind the rig was a fairly steep drop off, so crews had to be mindful.

The entry side was also in proximity to railroad tracks, as well as two existing lines. To avoid those existing lines, the pilot hole had to weave around them and the entry alignment with the river did not line up with the exit point on the other side of the river.

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“It was like threading a needle on the entry side to get around those existing pipelines,” Bearden said, noting the same type of weaving had to be done to hit the exit point to avoid existing pipelines on that side of the river.

“We had a 31-degree bend on the exit side and an 11-degree curve at the beginning of the drill when we got to the water’s edge,” Kubala noted. “We would trip back toward the rig until we got the [annular] pressure down. Every time we went back, we cleaned out the hole, getting rid of all the solids in the hole so when we went back in, we kept the flow returns and downhole pressure down.”

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The 9 ½-in. pilot hole was reamed in one pass to 24 in., a process (including a swab pass) that took three days. Pullback of the steel pipe took about eight hours, Kubala said, noting that a weld of the pipe was made at the midway point.

Bearden noted the significance of using the downhole annular pressure tooling on the project. “Generally there are a number of contractors who use annular pressure tooling for pilot hole operations but there aren’t many that also use it while they are reaming,” he said. “It adds a bit of complexity to the project because you now have a wireline that is downhole and larger volumes of fluid are pumping past the wire inside the drill pipe while the hole is being enlarged. There is the potential for wireline failure during a 4,900-ft crossing.”

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Sauls also noted that this project was successful due to diligence and experience of the design firm, as well as the drilling crew and mud engineers. “For a project like this, it takes having the whole team on board to understand what is required,” he said.

Sharon M. Bueno is managing editor of Trenchless Technology.

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