Customer: Port Kembla Port Corporation
Contract: Design and Construct
Location: Port Kembla, New South Wales
In a first for the Southern Hemisphere, McConnell Dowell used horizontal directional drilling to construct a shore crossing of bundled oil and gas pipelines under the surf zone. The project, at Seaspray on Australia’s treacherous Bass Strait coast was also the first time concrete coated pipe had been pulled the entire length of a crossing.
The offshore pipelines comprised 1,350m of DN300 oil transmission pipeline and 1,350m of high pressure DN100 gas lift line. 700m of the pipeline would pass through / remain in the drilled bore, with the additional 650m laid on the sea bed to be later extended to the oil platforms (by others). The land end of the pipelines was then connected to 19km of land based pipeline also installed by McConnell Dowell linking the offshore oil platforms to the onshore processing facility at Longford.
The DN300 pipeline is to transfer the oil/water/gas mix from the Perch and Dolphin oil platforms towards shore and the DN100 to supply gas lift gas from the Longford processing facility to the oil platforms to maintain oil flow through the pipeline.
The shore approach section required 1,350 metres of bundled 300 NB and 100 NB gas pipelines to be installed within an environmentally sensitive dune and beach setting.
The key was to establish a pilot hole to set the correct profile and alignment. Wash pipe of 700 metres length was then pushed through the hole before divers (based from the lay barge) fitted a 34” diameter reamer into the cut pipe at the exit hole. Once back on the seabed the reamer was pulled to the shore increasing the bore size of the wash pipe hole.
Rough seas with regular 4m swells, severe tidal currents, surf zone breaks, together with poor weather added quite some additional installation challenges.
The bundled pipe string, together with HDPE buoyancy units, was preassembled / welded onshore before being pulled out to sea on rollers until the inshore end was just beyond the exit of the reamed hole. This required the offshore end of the pipe bundle to be pulled a distance of 2,050m offshore using a bottom pull method from the dumb barge with a powerful winch.
The wash pipe was then connected to the pipestring and, using the onshore drilling rig, the bundled pipestring was successfully pulled land-wise through the hole.
The shore approach section was completed in 4 months, less than 25% of the time normally required (18 months) for construction of a similar size-length pipeline using conventional methods.
The land based pipeline section was completed a few months later to meet client’s staging plans.
The project earned McConnell Dowell a commendation award from the Victorian Division of Engineers Australia for Excellence.
Key to Sucess
Prior to construction, a comprehensive study of the surrounding environment was undertaken to develop a profile of the area and a number of environmental challenges were identified, such as dredging in heavy materials, installing silk curtains, ensuring water quality and maintaining correct pH levels.