The Peace River horizontal directional drilling (HDD) called for a 1,110 metre horizontal directional drill opened to a final ream diameter of 54 inches to allow for the installation of the 42 inch pipeline pullback section. The principal challenges faced by the crossing project were a limited construction season due to the need for frozen access roads and deep surface gravels at the crossing location.

The general contractor was Louisburg Pipeline while Engineering Technology Inc. (Entec) provided engineering services and Direct Horizontal Drilling was the HDD contractor on the crossing.

Engineering design and geotechnical investigation

During the design phase of the project, existing geophysical and geotechnical information was examined that showed surface gravels to a depth of approximately 12–15 metres. The gravels were deposited above claystone, shale and sandstone bedrock, which was expected to provide a good path for the HDD. This information had been gathered for a previous project which was over 100 metres away from the chosen crossing route. Additional geotechnical boreholes were then planned to confirm these results while preliminary designs were prepared.

Due to the presence of gravels on both the entry and exit side, a pilot hole intersect was proposed to allow the installation of surface casing on both sides of the crossing. Given the consistency of the bedrock materials, determination of the intersect location was left up to the drilling contractor. Since an intersect was required to complete the crossing, drilling contractors with successful pilot hole drilling intersect experience were selected as potential bidders for the project.

The preliminary design called for entry and exit angles of twelve degrees to balance the need for keeping the exit side casing as short as possible with the need to reduce the pipe lifting requirements for pullback. Due to the diameter of the pipeline a minimum 60 inch diameter surface casing was required. The large diameter, when combined with the length of the casing, required planning to install the casing in two telescoped stages. Ultimately a final diameter of 76 inch casing being placed through a shorter length of 84 inch diameter casing was selected to allow the casing to reach a target length of

78 metres. The target depth was selected to allow the casing to seat into bedrock at a vertical depth of 12–15 metres with some extra length for contingency. A final diameter of 76 inches was proposed to allow a smaller casing to be used as contingency against failure to reach the target depth.

Due to the long lead time for large diameter casing pipe, the materials had to be ordered prior to the completion of the new geotechnical boreholes. Unfortunately results from the geotechnical boreholes drilled at the actual crossing location showed gravel to a depth of 19 metres. Due to this change in design constraints the exit angle of the crossing needed to be increased to 15 degrees to allow the use of the previously ordered materials at the expense of greater pipe lifting requirements for pullback. Given the new exit angle of 15 degrees and a target depth of 19 metres the exit side surface casing needed to isolate 76 linear metres of the drill path from unconsolidated sand, gravel and cobbles.

The entry side gravel thicknesses were confirmed by the new geotech and the entry casing was left at its original angle of 12 degrees and proposed length of 53 metres.

Entec was concerned that the large buoyant forces exerted by the 42 inch pipeline during pullback could damage the pipe coating as it passed through the long steel exit and entry casings. To address this concern, a buoyancy control plan was designed to ensure the pipeline passed through the casings and the borehole with near neutral buoyancy, minimising the risk of coating damage.

Also of concern was the possibility that the pipeline coating could be damaged by a misalignment between the pipeline pull section and the exit casing during pullback. A misalignment could result in binding between the pipeline and casing. For this reason a detailed lifting plan was prepared to ensure the position and heights of the lifting equipment allowed the pipeline to precisely match the exit angle without placing excessive stresses on the pipeline during installation.

The final design consideration was the possibility that the surface casing might not be extracted or could damage the pipeline during extraction and could accelerate corrosion of the pipeline. To mitigate against this risk, casing insulators were to be installed in the event the casing could not be removed after pipe pullback.

Surface casing and pilot hole construction

Entry side surface casing was installed in November 2008 and reached refusal at 24 metres in length or 5 metres vertical depth. This was well in advance of the 53 metres of casing expected to be installed according to the geotechnical investigation that found bedrock at 9 metres vertical depth. Subsequent excavation to confirm the bedrock depth revealed the bedrock to be at five metres below ground surface and the casing was re-seated into bedrock.

Exit side surface casing installation began once frozen conditions were present in early December. Installation began with the excavation of a launch pit and hammering of the 84 inch surface casing. The 84 inch casing reached refusal at 41 metres. The 84 inch casing was then augered clean and the 76 inch casing installation was started. The

76 inch surface casing reached refusal at a final depth of 74 metres but was not yet seated into the bedrock needed for the HDD drilling and reaming operations. Successful contingency planning allowed the installation of 60 inch diameter casing that was installed to a final length of 88 metres and firmly sealed into bedrock at 22 vertical metres.

While the final metres of exit side casing were being installed the pilot hole was started on the entry side of the crossing using Direct Horizontal’s American Augers DD1100 drilling rig which reached a final drilled depth of 980 metres where it waited for the exit side pilot hole to begin.

The casing installation faced several challenges including long welding times, slow penetration rates and extreme cold, but the exit side HDD rig finally started drilling the remaining 130 metres of the pilot hole in early February. The pilot hole intersect was successfully completed on 14 February 2009. A slight correction to the steering in the pilot hole was successfully performed prior to the start of reaming.

The reaming operations preceded smoothly using two drilling rigs in tandem to complete the 30 inch, 42 inch and

54 inch reams within two months. Recycling the drilling fluid and pumping the high volumes required to clean the large borehole was accomplished by the use of two drilling mud pumps and an upgraded fluid cleaning system.

Pipe pullback

The 1,110 metre section of the pipeline destined to be pulled under the river was welded and pre-tested on the exit side of the crossing before the completion of reaming. The 42 inch pipe was successfully lifted to match the exit angle of 15 degrees and pulled back to the entry side rig without incident on

12 April 2009. The peak lifting height for pullback was over 19 metres. The lifting program was successfully implemented by Northern Crane Services. Due to the successfully implemented buoyancy control plan, the pull forces did not exceed 200,000 pounds and no coating damage was noted.

With the arrival of spring temperatures and the subsequent deterioration of access roads, the surface casing was unable to be completely extracted before the equipment needed to be demobilised. However, pipe insulators had been installed on the pipeline during pullback as planned and the pipeline remained isolated from the remaining 50 metres of 76 inch casing, protecting the pipeline from increased corrosion potential.

TransCanada’s successful 1,110 metre crossing of the Peace River is believed to be the longest 42 inch diameter gas pipeline installed by HDD in Canada to date. All of the project team members were pleased to have the pipeline installed and were impressed by the scale of the planning and construction effort needed to complete the crossing.

Project update

Update February 2010 – TransCanada Pipelines successfully completed a 630 metre pullback of 42 inch pipeline as part of its North Central Corridor Project. The crossing of the Loon River in northern Alberta was the third and final HDD crossing for the project. Entec completed the crossing design and lifting plan and congratulates the entire project team on achieving this milestone.