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Slug Detection

Dealing with water slugs
The oil industry has defined slug detection as an important area. Slugging represents a growing problem in upstream processing plants. The challenge is to get early warnings about slugs to be able to contribute to the control of a slugging flow regime.

The traditional method to detect slugging is through pressure transmitters which are good at detecting gas slugs. Water slugs will however be difficult to detect since the difference in pressure build up is very small between oil and water. This is bad news because water slugs - not gas slugs - are the most damaging type of slugs upstream for the processing plant. Without a good method that detects water slugs operators today reduce the flow rate to compensate for the problem. An early warning that gives reliable information about the slugging will enable the operator to adjust the flow when the slug occurs. Operators can then utilise the full capacity of the plant when the flow is stable.

Water slugs become increasingly important since the production and drilling technology reach new levels, the production time and volume for each installation is prolonged. This increases the water cut for each well. Good, stable instrumentation will be a necessity to control difficult flow environments. The SeCaP™ technology offers exactly that, early warning that gives reliable information about the slugging.

Technical description
Slug detection using Sentech's SeCaP™ technology is basically implemented with two Water Cut Meters installed on the same pipe and with a well defined, short distance between them. Recognising flow profile and having real time speed of the readings of the measurement data from the SeCaP™ technology, makes the detection of slugging possible. Even with a very fast slug, propagating through the piping at say 20 m/s, Sentech’s technology will produce minimum ten to 20 readings of measurement data. On the basis of this data both the size (length) and speed of the slug can be calculated, greatly assisting the operator's flow control.