Pipeline incidents are rare, but when they do happen the industry works hard to learn from them and improve.
So, in 2016, when a Husky Midstream pipeline buckled due to ground movement, where it crossed the South slope of the North Saskatchewan River near Lloydminster, Saskatchewan, that event became the focus of considerable research.
A white paper presented at the 2022 International Pipeline Conference explained the causes and effects of the event, and the research that followed.
As some context, the river valley in question contains a near continuum of landslides that are potentially dormant or moving at extremely slow rates, and which are visually imperceptible on the ground surface. These landslides move along near horizontal pre-sheared surfaces that have developed within weak clay shale or along thin bentonite seams. The danger associated with these prairie landslides is that they are near a state of equilibrium and many of them can reactivate or accelerate with very little disturbance, creating a severe threat to pipelines and other infrastructure.
Managing ground movements
To effectively manage ground movement threats to pipelines the landslide must be identified, evaluated, and monitored with an action plan in place to ensure it does not exceed industry-accepted strain capacity limits.
To develop a full understanding of the landslide and how the pipeline will respond to ground movement, a phased approach comprising four key aspects is necessary:
- Identification of the ground movement hazard through a desktop assessment. Those with significant potential threats to the pipeline require the next phase of action.
- Site-specific non-intrusive investigation to characterize and evaluate the landslide threat to the pipeline. Those with significant potential threats to the pipeline require the next phase of action.
- Subsurface geotechnical investigation and installation of instrumentation to confirm the mechanism, magnitude and profile of ground movement supported by engineering analyses to determine if adverse effects to the pipeline result from landslide movement.
- Surveillance protocols, with established threshold criteria, to make decisions on next steps and to enact mitigation options and short- or long-term monitoring plans.
Pipeline operators have many tools and techniques available to help them identify, assess and monitor landslide movement threatening a pipeline. High fidelity fiber optic sensing (HDS), more commonly used for leak detection, is one such tool that has a significant role to play in early detection of active landslides.
HDS as a ground movement monitoring tool
After the Husky event, the operator engaged in a multi-faceted investigation to evaluate monitoring technologies for their ability to provide early warning of accelerating ground movements and climate drivers. They found that HDS is capable of detecting ground movements from a landslide as high strain events, even in the absence of ground cracking or any other visual indications of active movement at the ground surface.
Even though the HDS system could not differentiate between strain derived from an above ground source (e.g. construction), a below ground source (e.g. ground movement) or a pipeline source (e.g. pigging), it could define the location of the event, allowing the operator to review and assess.
In combination with climate data monitoring (precipitation and temperature), HDS can enhance early landslide detection through high strain and precipitation events, providing a triggering mechanism for further investigation.
“The distributed strain monitoring capability of the HDS platform presents a significant opportunity to the pipeline industry by creating an early detection mechanism for geotechnical hazards. This risk and cost reduction approach enables the operators to identify the areas of concern and implement secondary monitoring mechanisms such as strain gauges, lidar and flyovers as needed.” -Ehsan Jalilian, vice-president and CIO, HifI Engineering
The cost of landslide damage
Landslide damage is a major concern to pipeline operators across North America, for both its environmental and financial costs. The economic impact to the pipeline industry in the prairies alone is estimated to range from $40 to $60 million each year in direct damages, with up to $245 million per year in damage prevention costs.
High fidelity distributed fibre optic sensing (HDS) is a relatively new technique to the pipeline industry, but its capabilities for leak detection combined with the ability to detect geohazards such as landslides make it a valuable and cost-effective tool in the move toward zero incidents.
