TRENCHLESS | HDD
Left: Figure 8: Location of drill pipe break.
Right: Figure 9: Thruster used during pullback.
Below: Figure 10: Drill pipe rejection by method.
Partial redesign A revised design sought to maximise reuse of the existing borehole. The updated alignment shifted the exit point laterally by 5m and extended it 10m. About 457m of the initial bore from the entry rig, down to the lower belly of the profile, would be reused. New NPS 72 and NPS 84 casing were used. Pilot hole
Visual - 78.2% MPI - 9.3% UT - 8.1% EMI - 3.0%
operations for the partial re-drill used an at-bit-inclination assembly to provide at-bit steering accuracy. But the bore experienced drilling fluid losses along the upper slope and required re-work of string joints to ensure compliance with the pilot hole specifications; a bentonite-chip-based lost- circulation material (LCM) proved effective. The 30” reaming pass was started from the entry side
and advanced to 900m MD, the same elevation as the entry rig and so the farthest point with drilling fluid; the reamer was relocated to the exit side and reaming continued. A similar strategy was employed for the 42” reaming pass. Also, a 30” stabiliser was positioned directly behind the reamer to further reduce bending moments experienced within the wobble joint, although occasionally added to torque. The reaming pass took 16 days. The original drill pipe used for the crossing consisted of
standard-wall API double-white-band pipe, Grade S-135. Wobble joints were routinely removed from the drill string and replaced. Given the history of drill pipe failures on the project, heavy-wall drill pipe was used instead within the wobble joint for the remainder of the reaming phases.
Drill Pipe Breaks 3 & 4 When the contractor transitioned into the 54” reaming phase, a similar reaming strategy was planned but with adjustment to the stoppage MD locations, to minimise risk of forming a ledge within the borehole. Some elevated torque levels were observed and at 913m MD, slightly
beyond the contractor’s intended trip out point, a drill pipe failure occurred; it was about the same elevation as the previously identified ‘trouble zone’. The borehole was re-opened from the entry rig up to short of the problematic interval, which re-established bore integrity. The contractor proceeded with the 60” reaming pass
but another drill pipe failure occurred, at 420m MD. The reamer was recovered but had been damaged by the fishing attempts and had to be replaced. Reaming resumed but there were instances of elevated torque and substantial volumes of cuttings. The team enlarged the bore from the exit side, using the 54” reamer to advance beyond the problematic zone.
Pull Back with Thruster Prior to pull-in operations, a wiper and cleaning pass was performed with a 48” reamer from the exit side through to the entry side. During this pass, four sections within the 54” bore stretch exhibited higher than anticipated rotary torque, indicating localised tight zones or areas of instability within the annulus. The team used a Direct Pipe® thrusting unit to support the pull-in activities.
CONCLUSIONS From the outset, the risk profile for this HDD was recognised as extremely challenging. While early phases encountered only minor issues, the upper slope proved particularly problematic. Future HDD designs in similar geological and elevation conditions should avoid installing product pipe larger than NPS 36 where possible, as larger bore diameters with large elevation changes significantly heighten construction risk. Adaptation to the typical bore design of 60” also played a
key role. Maintaining the upper portion of the bore at a final 54”, though unconventional for an NPS 48 installation, proved to be an essential decision. Also, incorporating a Direct Pipe Thruster was critical to success as it prevented uncontrolled pipe movement that could have jeopardised safety; it also provided guidance and thrust for the pipe.
Figure 11: Product pipe successful installation.
32 | October 2026
This paper has been used with permission of the North American Society for Trenchless Technology (NASTT) and edited for space. The full paper can be found at
https://knowledgehub.nastt.org/. The authors are: Eakins, M & Coutu, B. of TC Energy; Lenderbeck, C. of CCI; Vos, B. of Blue Fox Engineering; and Funnel, J. of The Crossing Co. Copyright 2026 by NASTT. The original paper was distributed at NASTT 2026 No-Dig Show.
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