Dual Conductor Barrels Keep HDD Interceptor Project On Target
A Conductor Barrel casing was rammed in place to create a path through poor soil conditions so that the drill can start in better soil conditions. Additionally, the casing helps contain drilling fluid during operations.
The use of pneumatic pipe ramming tools continues to be an important part of many directional drilling projects. Pipe ramming tools have become a common site on HDD projects either actively in use or sitting on a flatbed, just in case they are needed. The use pipe ramming HDD Assist methods has grown over time and now the methods have expanded the capabilities of directional drilling and are often critical to project success.
A recent project by utility contractor Amici Engineering Contractors, of Wesley Chapel, FL, included the installation of two telescoping conductor barrels to help facilitate an HDD intercept crossing.
According to Rick Melvin, Pipe Ramming Specialist for trenchless equipment manufacturer TT Technologies, Aurora, Ill., Conductor Barrel casings are used in areas with poor soils, often along waterways. The installation helps navigate to more desirable drill starting points and can help contain drilling fluids.
Melvin said, “The Conductor Barrel process differs slightly from the other HDD assist techniques with pneumatic pipe rammers. The focus a little different in the sense that it deals with the actual drilling portion of the project rather than pullback or recovery. The Conductor Barrel helps create a path or tunnel through poor soil conditions so that the drill can start in better soil conditions. The success of an HDD drilling operation is often times determined right at the start, right when drilling begins. If a bore does not begin in soil that is conducive to drilling, the success of the entire project can be in trouble.”
For the Amici project, the Conductor Barrels were installed to help with a 7,600-ft, 24-inch fusible polyvinyl chloride pipe (FPVC) HDD crossing for a reclaimed watermain.
The telescoping Conductor Barrel casings consisted of a 54-inch casing rammed in place. That was followed by a 48-inch diameter casing rammed inside of the 54-inch casing, followed by a series of centrailizers.
Melvin said, “This project was an HDD intercept project, where two HDD rigs drill out from either side of the install and then meet in the middle underneath the waterway. So, the ramming of these casing for the drill happened on each end of the installation. It was massive undertaking.”
Since the project was an HDD intercept project, two Conductor Barrels were installed, one on each side of the waterway to assist drilling for both sides toward the middle.
Conductor Barrel Installation
According to Melvin, Conductor Barrel casings are rammed into the ground, at a predetermined angle, until the right soil conditions for drilling are met. The casings are cleaned out with an auger or core barrel. In addition to assisting with drilling from the start, the conductor barrel can also serve as a friction-free section during pullback. But these casing do more than that.
Melvin explained, “A primary function this HDD Assist method to help mitigate the risk of hydro fracture or ‘frac out’ by creating a contained a drill hole down through a soft soil layer into better soils, more conducive for drilling. These casings can prevent drilling fluids, under pressure, from forcing their way into waterways or wetlands, by acting in a similar fashion to containment cells. Drilling contractors across the country use this technique to prevent drilling fluid frac out when drilling under wetlands.”
The specifications included ramming the casings in at a 14-degree angle to reach better soil as quickly as possible. A redesign, however, flattened out the drill path, from a 14-degree installation angle to an 11-degree angle. The goal here was to reduce friction during pullback and allow the driller to drill deeper if needed, while maintaining a proper bend radius for the fusible PVC pipe.
Melvin said, “Because a single casing wouldn’t reach length they wanted, the telescoping approach was used. Amici crews used their drill rig and an I-beam to support the casings at the right angle during ramming. A Grundoram Taurus pneumatic pipe rammer was attached and rammed in one casing at a time. The final measured angle, after installation of the casings was complete, was within a 10th of a degree and the horizontal alignment was within a foot or two, down hole. Very nicely done! Then they had to do the other side of the installation.”
Amici rammed the first 54-inch casing on the west side of the project and cleaned it out. After, a 48-inch casing was rammed inside of it to a depth of 240 feet. Once in place, the 48-inch was cleaned out and a 20-inch centralizer casing was then slid downhole and pushed to extended just beyond the 48-inch casing.
On the east side, a 48-inch casing was rammed in place, but not the 54-inch casing. Ultimately the 54-inch casing was not required for the conditions on that side because the drill set back was further away from the water’s edge. The 48-inch casing was rammed to a depth of 120 feet.
Bore centralizers were important components of the project ensure a smooth pullback and preventing hang ups on end of the casings during pullback.
Finding Your Center
To help drilling, reaming and pullback, bore centralizers were put in place. To reach the design depths of the casings, the drill rig was then used to drive and rotate in a 16-inch conductor casing inside of the 20-inch centralizer. The 16-inch conductor casing was installed to a length of 390 LF, or approximately 75 feet deeper to match the original design depth of the casings on the west side. That provided the desired depth in the formation that was more stable.
On the east side, a 20-inch centralizer casing followed, inserted the entire length of the 48-inch casing and similarly a 360 foot 16-inch casing was driven with the HDD Rig to reach the design depth on that side as well.
Melvin said, “The centralizer was an important component of the project. It helps ensure that nothing would get stuck on the end of the casing during pullback. After each ream pass, the centralizer casing had to be removed to allow for the reamer to exit the hole. The flanged centralizer was then reassembled and reinserted to help keep the reamer in a central position as each reaming pass approached the casing. But that takes place after the pilot bore intersect!”
During the intersect the drill heads approach each other. When the drill heads get within 100 feet of one another, one of the drill rigs retracts and leaves an empty borehole. The other drill rig continues advancing towards that borehole until the drill finds a path of least resistance as it falls into the borehole. The driller continues to follow the borehole as the other drill retracts until reaching the other side. A tracking system used to display progress and location of both drill heads. The intersect was successfully completed on the first attempt.
After successfully completing the intercept, Amici crews began the significant pullback. The 7,630-foot installation was divided into 4 sections and took 35 hours total to complete.
Reaming & Pullback
After completion of the pilot bore and reaming, both drill rigs were left in place to maintain drill rods in the hole and pump bentonite from both ends of the reamer. Five different reamers were used, an 18-inch reamer, then a 24-inch, 36-inch and then a 38-inch reamer, followed by a swab which was passed twice before pullback
The pullback was divided into four sections. Each section was placed on rollers while being pulled back. The pullback maxed out at 75,000 pounds of force for the entire 7,630-foot installation and took 35 hours total to complete, from start to finish.
Melvin said, “The Conductor Barrel casings with centralizers really played a big part in this project. Considering the jobsite layout and location along the waterway, they helped keep the fluid returns in check and successfully guided the pullback. It was an incredible project and a fantastic job by the Amici crew.”
