Interrogation of subsea wells
Dark fibres in subsea telecommunication networks can be applied for global monitoring of seismic activity. Approaches for monitoring seismic events (earthquakes) are under development.
The OptoDAS interrogator has recorded earthquakes with DAS monitoring on subsea cables installed in the North Sea. In a cable trenched at an oil field, an earthquake at Jan Mayen (1700 km away) was recorded. The magnitude of this earthquake was 6.8. Both P and S waves were recorded within 3-5 Hz and 0.02-1 Hz, respectively.
The connectors simulator is representing the chain of wet-mate connectors to be used in subsea umbilical termination assemblies and at the subsea tree.
A typical practical subsea scenario might provide up to 5-7 dB in total loss of wet-mate connectors. With 7 dB added loss, a power loss budget as illustrated was created for this test.
Minor impact on the OptoDAS self-noise was observed with -30 dB reflections combined with the 7 dB added loss. The self-noise along the 14 km long lead-in fibre is almost constant. After the total 10 dB one-way loss, the noise level in the sensing fibre is only slightly increased compared to the noise level in the lead-in fibre.
This verifies that the OptoDAS interrogator has superior characteristics for subsea well applications. There is no need to use engineered fibre (with increased scattering) as the sensing fibre in the well. Standard type of fibres can be used.
