The Sydney Primary Loop (SPL) is a 30 km pipeline linking Liverpool in Sydney’s southwest to Marrickville. The pipeline is being built in a bid to improve security of gas supply and increase the capacity for long-term growth in both the eastern and the southwestern regions of Sydney.

The contract included crossings of Salt Pan Creek at Padstow, the Cooks River at Tempe and two crossings of the Georges River at Casula and Hammondville.

In total just over 2,074 m of DN 500 X42 Trilaminate Coated pipeline was installed as follows:

* Salt Pan Creek - 382 m * Cooks River - 528 m * Georges River Hammondville - 816 m * Georges River Casula - 348 m

The contract scope of works executed by Coe included the stringing, welding, joint coating, NDT, hydrostatic testing and drying of the installed mains. The nature of the project and the limited available space for constructing such HDD crossings in Metropolitan Sydney meant that each crossing was installed in multiple strings including a four-string pullback under the Cooks River at Mackey Park Marrickville.

With the tight construction schedule Coe Drilling chose to use three of its rigs to complete the works within the required schedule. For the Salt Pan Creek section, Coe Drill 180 was used; for Cooks River, Coe Drill 550 was used; for Georges River Hammondville; Coe Drill 680 was used; and for Georges River Casula, Coe Drill 680 was used.

Geology within the Sydney Basin is underlain by Hawkesbury Sandstone and Ashfield Shale, which required the use of 6¾ and 8 inch Wenzel mud motors and both 12¼ inch PDC and tungsten carbide drill bits and hole openers in order to open up boreholes to 711 mm diameter in the rock conditions. Mud return pipelines were also installed across three of the waterways using the services of local divers to secure their position. All returns pipelines were pressure tested prior to use to ensure no spillage occurred during drilling fluid transfer.

The selection of the HDD methodology helped the designers overcome many of the obstacles and difficulties in laying a pipeline where such rivers and creeks need crossing without disturbance to the natural environment. In many of the crossing locations the areas where also found to contain old disused garbage tips which had posed its own difficulties when planning the project and during the execution particularly during the coated pipeline installation.

Environmental concerns were also a high priority and HDD selection allowed construction to precede in areas where significant environmental importance existed. These areas featured endangered bushland communities, threatened flora, and habitat for native fauna and items of Aboriginal heritage significance. For example, pockets of threatened Downy Wattle and Cumberland Plain Land Snails, and a tree scarred by the original inhabitants of the area were found near the proposed HDD entry point for the Georges River in Deepwater Park. Significant areas representative of Cumberland plains woodland and dry forest also needed to be negotiated.

The urban environment also provided its fair share of obstacles. The Cooks River Crossing at Tempe, which included compound curve geometry, required the HDD alignment to cross close beneath the existing secondary gas mains and the jet fuel supply line to Sydney Airport as it approached the HDD exit at Mackey Park. With the use of a Vector Magnetics P2 enhanced Paratrack Guidance System, the downhole steering was carried out with a high level of confidence and the separation distance could be verified to the operators prior to drilling past the live assets.

Similarly the Paratrack system was invaluable while crossing the Georges River at Casula where the site was located 20 m from the busy M5 Freeway, which provided its own share of magnetic interference during the pilot hole drilling operation.

To add to this, the crossing passed beneath rail lines with overhead wires and the HDD exit was designed to be 1.2 m off the existing live 550 mm gas mains and 3 m beneath the existing 200 mm secondary mains, all within a 3 m wide easement where the SPL pipeline would tie-in. Precision with regards to downhole steering was essential and the P2 Paratrack system using a AC guide wire worked very well in these conditions and the target was achieved. The busy rail corridor was under constant monitoring during the works to ensure no settlement occurred during the course of the HDD activities with a baseline survey carried out prior to works commencing and daily monitoring to ensure compliance. The crossing was completed during the Australian Barefoot Skiing Championships, which provided some lively entertainment for the drilling crews.

At the peak of the HDD activities three HDD crews were operating with the support of one welding crew, one hydrostatic testing crew and one restorations crew. In total 35,000 man-hours were consumed on the HDD works.

The success of the SPL project demonstrates the ability of Coe Drilling to offer clients such as Alinta turnkey HDD solutions on multi-crossing projects with up to four HDD rigs available. The SPL project adds to the recent successful completion of two 1,500 m hard rock oil pipeline installations at the Port of Brisbane last year for Caltex Refineries (Qld) Pty Ltd. The 610 mm and 273 mm installations were also completed under a turnkey HDD contract where Coe Drilling completed the welding, installation and hydrostatic testing.