The Gorgon Project is developing the Gorgon and Jansz-Io gas fields through a subsea gas-gathering system feeding an onshore liquefied natural gas (LNG) plant on Barrow Island, Western Australia.
Once operational, the plant will produce 15.6 million tonnes per annum of LNG. The gas fields will also feed the domestic gas plant, with the capacity to supply 300 terajoules of gas per day to Western Australia.
LNG will be offloaded to international markets via a 2.1 km loading jetty, while the domestic gas will be piped to the Western Australian mainland.
The Jansz-Io development consists of three pipelines and a control umbilical that connects the subsea infrastructure installed at two drill centres to the LNG plant on Barrow Island.
The three pipelines are: a 30/34 inch production pipeline; an 8 inch mono ethylene glycol (MEG) pipeline; and a 6 inch utility pipeline. The two drill centres are connected to a central manifold with 4.5 km, 24 inch corrosion resistant alloy (CRA) clad infield production flowlines and associated MEG and utility pipelines.
The Jansz-Io field is located approximately 130 km northwest of Barrow Island in 1,350 m of water and will be brought on stream first. Extremes in gas flow conditions, water depth, distance and the natural environment tested the practical limits of pipeline design and construction.
Weighing up the options
Work to evaluate the range of alternatives for the joint development of the Gorgon and Jansz-Io fields commenced in 2004. When evaluating alternatives for the pipeline routes, it was critical to draw on innovative engineering solutions to ensure efficient field depletion and minimise the initial installation cost, as well as the ongoing cost of maintaining the pipelines over the estimated 50 year life of the Gorgon
This was particularly challenging when selecting the route from the Jansz-Io field. Early identification of a large area of debris adjacent to the field led to the development of two main routes – an easier but longer route heading south from the field and a shorter but more challenging northern route.
After a comprehensive decision analysis process, the northern route was selected. However, this route required crossing an underwater escarpment (scarp) at the edge of the continental shelf, where water depths vary from around 500 m down to 750 m. While this route was more cost-effective, it required the resolution of an evolving suite of significant engineering challenges, including the design and construction of a subsea pipeline with a free span of 270 m.
The first scope of the Jansz-Io development, commencing in 2010, was horizontal directional drilling (HDD) for the shore crossing on the west coast of Barrow Island, where the pipelines come ashore. The scarp crossing seabed excavation, which was undertaken to limit pipeline stresses, commenced in the first half of 2011.
Both the shore crossing and scarp seabed excavation had to be completed before the main pipelay commenced at the end of 2011 with the MEG and utility pipelines, along with the shallower sections of the production pipelines. The pipelay continued in 2013 with the deeper sections of the production pipelines across the scarp and the infield pipelines.
In 2013, work to install the three pipelines across the scarp was successfully completed, incident and injury free. This innovative solution was key to the development of the Gorgon Project and marked the end of a program that spanned nearly nine years of engineering design, site investigations, geotechnical modelling and construction activities.
“The Jansz-Io is one of the most challenging subsea developments in the world due to the combination of depth, tie back distance, pipeline routing, 50 year design life and high reliability requirements of the LNG development,”? said Gorgon Upstream Facilities Project Manager Milton Bruce.
“Typically allowable span lengths for subsea pipelines are in the order of 40 m, however the steepness of the seabed profiles at the scarp crossing resulted in pipeline free spans up to 270 m in length,”? said Mr Bruce.
Construction on a massive scale
A total of 87 different contractors and suppliers have been employed for different scopes including:
- Geotechnical, geophysical and bathymetric survey
- Subsea equipment and structures
- HDD of the shore crossing at Barrow Island
- Seabed excavation of trenches for pipelines at the scarp crossing
- Pipeline installation
- Umbilical installation
- Rock supply for stabilisation of pipelines
- Rock installation for stabilisation of pipelines.
- The engineering process has provided significant skill transfer and employment opportunities.
Many others have been engaged by consultants during the development and implementation phases, with estimates in excess of 1,000 people involved in a wide range of activities such as:
- Geotechical surveys and analysis
- Geophysical site investigations
- Seabed trenching/excavation
- Pipelay including welding, NDE and pipe measurement
- Support activities such as materials supply, logistics, catering, etc.
- Creating a culture of safety
“Like all our activities, the Jansz-Io pipeline scope focused on incident and injury free activities which resulted in a positive working environment across all levels of the contractor organisations.
“Safety is a core value and an integral part of the culture at Chevron. We believe that incidents and injuries are preventable and ensure this belief is manifested throughout our operations,”? said Mr Bruce.
“One of the key elements in the management of safety across the Gorgon Project is the commitment to an incident and injury free work culture – during concept selection and engineering design, and right through to execution. This was achieved through a cultural campaign designed to bring all personnel into alignment with Chevron value that “˜we do it safely or not at all’ and belief that “˜there is always time to do it right’.”?
Specific examples of measures undertaken to develop a strong safety culture on this scope include:
- Vessel pre-mobilisation: Chevron personnel met vessels at their point of departure to develop a cohesive and supportive team structure from the vessel leadership down through the construction and vessel crews.
- Pipe handling: A vessel with automated pipe handling technology was selected for use during pipe loading from supply vessels as well as on-board movements.
This technology led to a reduction in exposure to common pipe handling risks such as:
- Dropped pipe during crane operations
- Impacts during movement of pipe to the firing line on-board
- Reduction in the requirement for manual handling of pipe and associated equipment.
Throughout the execution of the development, Chevron maintained a focus on using local suppliers and cultivating Australian industries.
The earliest use of a local supplier was with the Engineering Procurement Contracting Management contractor, Gorgon Upstream Joint Venture, which was established in Perth and has successfully led to:
- Employment of a large number of Australian engineers and designers (more than 400 at its peak)
- Development of Australian-proven technology
- A means of transferring engineering technology and systems to Australian companies
- Participation opportunities for Australian engineers and other disciplines in overseas engineering, fabrication and manufacturing locations, including the opportunities to seek alliances and undertake skills transfers.
Execution contractors have established significant technical centres in Perth to support long term operations such as the Jandakot facility, which will support the Gorgon subsea equipment for the life of the fields.
Regional business supported major construction and procurement packages in the areas of:
- Fabrication services (spool piece fabrication and small subsea (structures)
- Support services for offshore construction vessels (e.g. victualling)
- Labour and equipment requirements for activities such as rock quarrying and haulage
- Labour, services and materials associated with supply base activities.
Australian companies and research institutions have been involved since the start of the concept select phase, through Front end Engineering and Design (FEED) and finally execution of the work.
Local contractors were involved with:
- Engineering design
- Collection and analysis of metocean data
- Geophysical and geotechnical site surveys
- Construction activities
- Environmental surveys and monitoring
- Health and safety.
Any project the size and scale of Gorgon will inevitably come with significant challenges.
The Jansz-Io pipeline scope was one area that had to overcome a series of engineering challenges through FEED, detailed design and execution phases, including:
- Large-diameter pipeline: Application of a 30 inch production pipeline at Jansz-Io water depths was at the limit of existing technology for linepipe supply and pipeline installation. Coupling this with the requirement to cross such extreme seabed terrain, exacerbated design and installation challenges made this section of pipeline unique in the world of offshore oil and gas infrastructure.
- Long design life and high reliability requirements: The reliability of the subsea pipelines is critical to ensure a design life of 50 years that was specified, to provide the gas feed to the three 5.2 MTPA LNG trains on Barrow Island. The need for very high reliability led to the provision of an instrumented pipeline fatigue monitoring system to be used during operation and assure long-term fitness-for-service.
- Severe environment: Remote deep water, geo-hazard risk, exposed site location and severe seabed slopes all significantly increased the challenges associated with site investigation, pipeline design, trench construction and pipeline installation. Integration of the geophysical, geotechnical, palaeontology and pipeline engineering disciplines to validate whether the northern route was safe with respect to geo-hazard risk, led to a complex and unique design outcome. Novel site investigation methods needed to be applied. The trench excavation methods used had never been applied in such an environment, for such a large volume to be removed in this water depth to the accuracy necessary to support the design assumptions. Unique pipeline installation contingency procedures were developed and had to be applied during installation when weather conditions deteriorated.
- Complex pipeline loading regime: The predicted multi-phase pipeline flow regime, including fines and liquid slugging with significant inclined flow, together with external vortex induced vibration and complex pipeline-soil interaction issues, drove the requirement to develop a state-of-the-art pipeline finite element structural response model. This model is unique in the manner that slug loads are formulated and in the way pipe-soil interaction has been calibrated to match actual as-built data.
- Linepipe and weld design: The requirement for Steel Catenary Riser quality fatigue performance resulted in the first ever S-lay installed pipeline section meeting BS7608 Class C/2 weld quality requirements for this pipe diameter and wall thickness. Key elements supporting this achievement included manufacture of linepipe with very tight (< 2 mm) out-of-roundness specification, development and qualification of welding procedures suited to the offshore construction environment, and development and qualification of Non-Destructive Examination (NDE) methods pushing the boundary of current technologies including development of an internal weld inspection tool capable of high-accuracy measurement of the internal weld profile.
Innovation at sea
The contractors, in collaboration with the Gorgon Upstream team, have faced several key challenges and made a large contribution to the Jansz-Io development success by developing solutions including:
- Engineering contractor development of Free Span Design: After confirming the geotechnical stability of the route, focus shifted to addressing the steepness of the seabed profile at the preferred scarp crossing location. This required both flow assurance and pipeline structural engineering focus to provide assurance that well fluids could be reliably transported through the scarp route section and that pipeline free spans up to 270 m in length could be engineered.
- Static structural design of the very long pipeline-free spans addressed pipeline bending control and the requirement for seabed excavation to generate suitable pipeline profiles, for both installation and operational conditions. Fatigue design addressed liquid-slug induced pipeline motions and vortex induced vibration due to seabed currents, including consideration of multiple pipelines interacting in close proximity. The free span design process was complex with multiple interactions. The major assurance item for pipeline span integrity was fatigue design.
Scarp trenching by seabed excavation contractor
In order to limit pipeline stresses at the edge of the scarp, it was proposed that a trench with a specific seabed profile was prepared. An excavation in 650 m water depth, with extremely severe seabed slopes and within such tight tolerances, had never been executed before, according to Chevron.
One of the primary drivers was that the edge of the scarp, if left unmodified, would pose a sharp transition for the span of the pipeline, causing point loads and potentially local buckling of the pipelines. The construction of the trench focused on creating a profile replicating the curvature of the stinger on a pipelay vessel.
Weld procedure development by pipeline installation contractor
A weld procedure development and proof testing plan was initiated by the project and performed by the pipeline installation contractor. Multiple weld procedures were developed and small scale tests performed to understand the feasibility of achieving the required design fatigue performance.
Actual pipe joints and production welds were tested at The Welding Institute in Cambridge, United Kingdom, and demonstrated required fatigue performance, a significant achievement for this pipe diameter and wall thickness.
The fatigue performance of the welds was critical to the success of the project. Through the course of the project a total of 30 full scale fatigue tests were performed between initial proof testing and final verification testing. The magnitude of the testing was significantly greater than the industry bench mark of 6-12 welds, typically tested for verification of fatigue performance.
An award-winning feat
The Jansz-Io pipeline was recently awarded the national Australian Engineering Excellence Award by Engineers Australia.
The awards celebrate engineering excellence, including environmental innovation, critical social infrastructure and major resource projects. Selected out of more than 35 entries, the award recognises the Gorgon Project’s Jansz-lo subsea pipeline and scarp crossing, which required a high level of innovation, design and technological advancements to resolve a host of engineering challenges.
The Gorgon Project is operated by Chevron. It is a joint venture of the Australian subsidiaries of Chevron (approximately 47.3 per cent), ExxonMobil (25 per cent), Shell (25 per cent), Osaka Gas (1.25 per cent), Tokyo Gas (1 percent) and Chubu Electric Power (0.417 percent).