Online Barnacle Cleaning
Barnacles thrive wherever hard surfaces meet seawater, including ships hulls and moorings. Whales accumulate them on their heads. These prolific crustaceans have posed a problem for seismic equipment since marine seismic measurement began. PGS has a range of techniques to minimize barnacle growth as their presence can generate noise that affects the quality of the recorded signals.
Barnacles look like little rocks, but they’re actually crustaceans - close relatives of crabs and shrimp. They affix themselves to any hard surface and filter food from the seawater that surrounds them.
They are more widespread in warm and temperate waters and have been posing a problem for seismic in-sea equipment since the beginning of marine seismic measurements.
PGS has developed a range of techniques to minimize barnacle growth on the seismic streamer cables, as their presence can slow down acquisition and may generate noise that is detrimental to the quality of the recorded seismic signals.
In the past, manual cleaning and scraping were often the only effective measures to mitigate barnacle related problems. Today PGS employs automated streamer cleaning units (SCU), permitting continuous proactive barnacle removal during acquisition.
The SCU cleaning units are deployed at the front of the streamer and retrieved at the tail. These devices are powered by the movement of the sea relative to the streamers and pass over navigation devices without human interaction. Cleaning while seismic data recording is ongoing increases acquisition efficiency.
Automated in-sea Streamer Cleaning Units (SCU) have been engineered to allow for continuous proactive barnacle removal during ongoing operation
Onboard processing QC workflows monitor both the noise levels of hydrophone recordings and also the quality of the particle motion data and data deliverables like the upgoing wavefields of wavefield-separated, deghosted data.
For shallow tow hydrophone-only streamer acquisition, the weather is the most important source of unwanted noise. Lines affected by strong weather noise are rejected (or accepted) based on noise level criteria. For dual-sensor acquisition, noise levels are predominantly influenced by the towing noise, streamer peripherals, and barnacle growth, as well as the speed of the vessel relative to the water.
Modern real-time quality control systems implemented over the past few years on all PGS vessels enable the seismic crew to monitor noise levels together with the actual production speed of the vessel. Robust line acceptance procedures for barnacle noise have been developed that usually involve the testing of processing-based noise removal techniques on both modelled noise and real measured noise.
After the data have been acquired, noise removal algorithms and the wavefield separation process itself can eliminate noise from the raw dual-sensor data and from the ghost-free up-going wavefield (P-UP).
The other problem associated with barnacles relates to HSEQ. The build up of barnacles increases drag, which slows down operations, increases fuel use and can be a safety concern, as it adds unnecessary strain on the towing and acquisition equipment.