Landmass movement poses a significant threat to oil and gas pipelines, especially when the lines cross through hilly or mountainous terrain. Landslides, rockfalls, subsidence, and avalanches can cause catastrophic damage, particularly to pipelines.
Additionally, engineers and operators need to be aware of slower landmass movement, referred to as soil creep. Monitoring as many types of slope movement as possible allows operators to assess risk and develop regional response plans.
“Being able to monitor slope movement allows operators to assess risk and develop changes to regional response plans.”
On the ground, engineers are making use of geotechnical instruments such as tiltmeters, inclinometers, extensometers, strain gages, piezometers and even GPS to measure displacement. Such instruments can be connected to multiplexer’s to gather many different data sets, and can be remotely accessed by operators. This is especially useful if the location of a pipeline isn’t easily accessible by personnel and/or the area needs long-term monitoring.
Operators are also making use of another, far-reaching technique to measure slope movement. InSAR, or interferometric synthetic aperture radar, provides a more complete picture of landmass movement. Not only does InSAR give a better overall image, it can be precise down to measurements in centimeter increments.
What does InSAR do?
InSAR has only been used relatively recently. The USGS noted the imaging technique first gained recognition after being used to create images of ground displacement during a 7.3 magnitude earthquake that hit eastern California in 1992. The radar images of the 1992 California earthquake were captured from the European Space Agency’s ERS satellite. The satellite sends radar waves that cover about a 60-mile wide area at any given time.
With this technique, radar energy is emitted from an orbiting satellite toward Earth. After it reaches the surface and returns to the satellite, the amplitude and phase of the radar waves are recorded. The USGS stated that factors affecting the amplitude and phase of the return signal include ground slope and the size of the object the signal hits. A different signal is returned if the radar hits a massive boulder as opposed to soft, flat terrain. The other piece of information that scientists can gather from radar imaging is the distance the signal travels. With this ability, InSAR creates topographical images and elevation maps.
For comparison’s sake
What is so valuable to scientists is that images can be taken using the same location but at different times and compared to each other to calculate movement.
When the satellite makes a successive pass over the desired location, another dataset can be recorded over the precise location as the previous dataset. The two datasets can then be compared (producing an interferogram) for any movement. If the images aren’t identical, then operators know there has been some movement. They can then take measurements to determine where the ground has moved and how much it has moved.
The technique has been useful in registering major ground movement during earthquakes and volcanic areas. Because InSAR is so precise, it can detect even the most subtle of movements. It’s also being used to detect ground movement due to subsidence. Subsidence is the movement of the earth that is defined as a gradual settling or sudden sinking. Potential subsidence of pipelines needs to be monitored during long –wall mining for coal or other natural resources.
“InSAR has been useful in registering major ground movement during earthquakes.”
Going beyond other techniques’ limitations
While using other types of geotechnical instrumentation may work adequately in many situations, there are exceptions in which InSAR can be used to substitute.
GPS can be used to measure slope movement along certain monument points. However, according to the USGS, the image may lack specificity.
Inclinometers are capable of providing even greater results. Installing an inclinometer requires boring a hole in the plane of the slope, inserting a pipe and lowering the instrument inside the pipe. The instrument then measures deflection of the pipe. The difficulty with this method, noted the USGS, is that drilling or ground boring may not be safe for personnel in risky areas.
InSAR can be used in such a situation to provide accurate results and it doesn’t subject crews on the ground to potentially hazardous conditions. InSAR has had many breakthroughs since the earthquake of 1992. InSAR has become a valuable Geohazard Management tool in assessing the integrity and conditions of slopes containing pipelines and other infrastructure.
One company, Applus+ RTD Geohazard management’s team has extensive experience with performing pipeline analysis and pipeline monitoring, including geohazard assessment. InSAR and geotechnical instrumentation are some tools used to monitor slope and pipeline conditions, which reduce the risk to operators, owners and the environment.