During the extraction phase of an oil and gas project, pipelines are used to transport hydrocarbons from the wellhead to processing and export facilities.
Pipelines must be able to withstand adverse environmental conditions to ensure safe and reliable distribution, however, incidents of pipeline failure can (and have been known to) result in serious harm to ecosystems, public health and extreme financial loss.
Advanced detection of pipeline leaks
One of the most troublesome problems for oil and gas operators is pipeline leakage, as it can cause both loss of product and serious environmental pollution.
Over the last few years, numerous methods and systems for detecting pipeline leakage have been developed by researchers and companies.
Several sensing techniques are currently being used to detect pipeline faults. These include fibre optic sensing, wireless sensor networks and acoustic methods. Among these, fibre optic sensors have emerged as the most appropriate for long-distance pipelines with no potential safety hazard compared with traditional electrical gauges.
Algorithms can also be used to detect pipeline leakages.
Usually they are applied in conjunction with signal processing techniques and mathematic analysis.
Up until recently, no solution for leakage detection has combined both advantages of the fibre sensor and algorithms.
In 2018, researchers in China endeavoured to change this by developing a novel fibre Bragg grating (FBG)-based hoop strain sensor to measure pipeline leaks. The sensor provides a non-destructive testing method for pipeline leakage detection and localisation by installing multiple sensors along the pipeline.
In addition to the sensing method, information can also be extracted to describe the leak characteristics at different leak points or with different leak rates – which provides another opportunity to locate the leak point.
Ensuring the safe and reliable operation of pipelines
Aside from leaks, offshore pipelines are also susceptible to buckling and progressive axial movement (walking) in response to operating temperature cycles and can be destabilised by waves and currents – particularly during cyclones. Buckling, walking and on-bottom stability must be predicted and controlled to ensure the safe and reliable operation of pipelines.
This is what researchers at the University of Western Australia (UWA) set out to achieve.
The UWA pipeline engineering program comprises two major Joint Industry Projects (JIP) – SAFEBUCK and STABLEPIPE. It is a 10-year collaboration between the university and the local and international oil and gas sector.
Typically, pipelines are anchored and reinforced to provide extra stability and reduced thermal expansion. This design creates increased rigidity and resistance to natural movement, as well as increased costs associated with the physical anchors and reinforcement.
The central design principle underlying STABLEPIPE is that the seabed is less stable than the pipeline. As the sea bed shifts with normal wave action, sand transport, and extreme weather events, the pipe is usually buried through scour and sediment transport and thus ‘self-stabilises’.
On the other hand, the SAFEBUCK JIP has promoted a radical solution to the thermal expansions of pipelines, in which the pipe is permitted to buckle and displace across the seabed to relieve, rather than resist the loading.
During this work, it was found that the friction between pipelines and the seabed rises over the operating life, something that was validated by physical modelling and numerical studies undertaken at UWA. The results are more cost-effective designs with a reduced requirement for anchoring and ancillary structures.
The research has transformed how the seabed is characterised and how pipeline-seabed interactions are assessed, ultimately leading to new design methods that have been adopted by a number of industry end-users globally. The new design methods have led to increased efficiency and also to significant cost savings.
Oil and gas companies have sponsored the research, steered the activities, reviewed the outputs and adopted the outcomes (design methods, calculation approaches, software etc) in their business practices to reduce the cost of pipeline design and improve business performance.
The most recent phase of the SAFEBUCK JIP involved 20 participants, including eight major oil and gas operators and a significant number of offshore engineering contractors and resulted in the authorship of the SAFEBUCK Guideline design code.
These guidelines have become the global industry standard for the design of High Pressure High Temperature offshore pipelines and have been used by the JIP industry partners Woodside, Chevron, Det Norske Veritas and Wood Group Kenny, and their contractors, on their Australian offshore projects.
ICHTHYS LNG project pipeline
The Ichthys LNG Project is a joint venture between INPEX group companies, major partner Total, CPC Corporation Taiwan and the Australian subsidiaries of Tokyo Gas, Osaka Gas, Kansai Electric Power, JERA and Toho Gas.
Gas and condensate from the Ichthys Field is exported to onshore facilities at Bladin Point (near Darwin) via an 890 kilometre gas export pipeline (GEP) – one of the longest subsea pipelines ever built. The GEP is a 42-inch outer diameter, steel pipeline, installed with concrete weight and asphalt enamel external coating. The concrete coating provides a degree of protection for the GEP’s integrity against potential impacts, such as from dropped objects or fishing gear.
The GEP has been installed with five hot-tap-tees and one midline dummy spool, all with ‘over-trawl’ covers installed.
According to INPEX, the pipeline required approximately 700,000 tonnes of steel and was coated with roughly 550,000 tonnes of concrete.
Approximately 793 kilometres of the pipeline is located within Commonwealth waters, with water depths ranging from approximately 30 to 250 metres. Therefore, a number of measures are required to ensure the GEP operates as intended.
According to an Environment Plan Summary submitted to the National Offshore Petroleum Safety and Environmental Management Authority, inspections provide assurance that infrastructure is performing according to design. These inspections also proactively identify maintenance and/or repair activities that may be required to protect the GEP. Inspection activities include remotely operated underwater vehicles or autonomous underwater vehicle inspections and marine acoustic surveys.
If maintenance and repair activities are required, this may involve measures such as seabed intervention (e.g. jetting, mass flow excavation, installing grout bags, rock placement or concrete mattress installation), marine growth removal or ‘pigging’ to recover the integrity of, or isolate, the GEP in the event of a repair.
The Ichthys LNG Project is a large-scale LNG project by global standards, and is expected to be operational over a period of 40 years. Production from the project commenced in July 2018.
Sources: Recent Advances in Pipeline Monitoring and Oil LeakageDetection Technologies: Principles and Approaches, Mutiu Adesina Adegboye et al.; Pipeline Leak Localization Based on FBG Hoop Strain Sensors Combined with BP Neural Network, Ziguang Jia et al.; 2016 Ichthys LNG Project brochure, INPEX; Ichthys Project Gas Export Pipeline (Operation) Environment Plan Summary, INPEX
