Live online monitoring of pigs and ILI smart tools using DAS technology with fiber optical

Background:

For a long time, scrapers and PIGs of different types have been used in the Oil & Gas industry as devices for internal mechanical cleaning of pipelines. Furthermore, in recent years the use of ILI (In Line Inspection) technologies through intelligent tools or instrumented scrapers has spread globally. The objective of the latter is to determine the level of general and particular integrity of the pipelines based on direct and indirect measurements of the defects present in them.

In all cases, the monitoring, detection and eventual positioning of the tools has been and is a very important task. This activity makes it possible to identify the passage of the tool through a certain point, to know approximately its speed, in order to ensure entry into the receiving traps and, finally, to identify approximately where the scraper is located in case of jamming.

To carry out tool monitoring activity, mechanical passage detectors (flag type or electric) or magnetic type AGMs (Above Ground Markers) in the case of MFL tools are normally used. On the other hand, for tool location, tracking systems are used, placing a signal emitting device in the PIG and, in the possession of the surface technician, a receiver and proximity indicator.

The Solution:

Morken Group, based on the use of DAS (Distributed Acoustic Sensing) technology with optical fiber used for the detection of leaks and intrusions and prevention of damage to third parties, has managed to carry out live online monitoring of an intelligent MFL-type tool, having 1-meter precision and instant speed and positioning information.

In this particular case, the monitoring was carried out on an important transportation gas pipeline with a perimeter route to the Metropolitan Area of Buenos Aires, Argentina. The system is basically made up of two parts: the optical fiber and the terminal computer equipment which contains the optical unit and the processing hardware. The technology used is called DAS (Distributed Acoustic Sensor).

The operation is as follows: One of the fibers of the fiber optic cable is connected to the terminal equipment (in general, a standard cable has 12 fibers). The optical unit that the equipment has emits a beam of laser light at one end of the fiber optic cable. This beam is projected along the thread, within it, and throughout its extension. Now, if the fiber thread is crossed by an acoustic wave (mechanical wave produced by the sound generated, for example, by the passage of a cleaning or smart tool) in some part of its length, it is altered, compressing and decompressing transversally. This abnormal movement of the thread causes the light beam traveling within it to suffer backscatter. The DAS equipment is capable of detecting the aforementioned physical event and, in addition, processing it from a computer system. Finally, through an operating system and an its appropriate interface, the user is allowed to view an acoustic profile, in real time, of the entire length of the pipeline. This allows to detect any event that produces vibrations in the pipeline or in the area surrounding it. In one of the available interfaces of the technology, the live acoustic profile of the gas pipeline can be observed.

Fiber optic operation diagram

Tracking screen

Characteristics:

• A dynamic graph of space versus time (waterfall type) is displayed.
• On the abscissa axis (horizontal), the length (space) is found. There, the different features along the entire pipeline are identified, such as stations, roads, streams, valves, traps, etc.
• On the ordinate axis (vertical), there is time, which advances as it is a dynamic graph (waterfall type).
• The colors indicate the magnitude of the acoustic signals detected. Blue indicates “silence”, while red indicates presence of sounds. The larger the red signal on the graph, the higher the magnitude of the sound.
• The operator can zoom in on any part of the graph they want and also scroll through it. To do this, you must click on the “magnifying glass” type symbol and then “shade” the area you want to enlarge.
• In the upper sector, the so-called “events” identified by the system are shown. These events are identified with characteristic images (for example, a backhoe).
• On the right of the screen, there is a panel that indicates the characteristics of the point where the cursor is (fiber length, zone, etc.)

This same interface is what allows live monitoring of the MFL equipment, not only allowing its instantaneous location, but also getting its speed, a main factor to verify magnetization level.

Results and benefits:

By using the technology described, Morken was able to track the PIG, giving additional support and confidence to the user by being able to know at all times exactly where the MFL equipment was located.

Other advantages and features:

• Online real-time tracking of cleaning tools and ILI.
• Instant tool positioning.
• Location accuracy of 1m.
• Instant device speed.
• Possibility of making decisions on operational and flow variables based on the analysis of the PIG speed.
• Possibility of scheduling tasks and optimizing resources by knowing the exact speed and position.
• Elimination of uncertainty in the location of the PIG in the event of a potential jam.