Towards Long-Range Distributed Acoustic Sensing in Subsea Applications

Session: Recent Development in Ultra-Dense Seismic Arrays With Nodes and Distributed Acoustic Sensing (DAS)
Type: Oral
Date: 4/30/2020
Time: 01:45 PM
Room: 110 + 140
Description: 

Distributed fiber-optic sensing (DAS) has proven to be a flexible tool in the arsenal of sensing choices for seismic and seismological applications. Intrinsic basic parameters that govern the interferometric sensing are: and gauge length among others. The interplay of effective sensing extent and required sensitivity determines the seismic signal quality that can be extracted from the basic interferometric measurement. Typical seismic applications interrogate distances on the order of a few km with signal frequencies as high as many kHz, while seismological applications interrogate 40-50 km with signal frequencies of interested in the low frequency range. A trade-off has to be made between interrogation distance and signal frequency bandwidth.

Subsea installations are often non-optimal for sensing purposes. A series of built-in losses at connectors, splices, penetrators, as well as other optical components, leads to typical light loss-budgets of 8-11 dB. These budgets are suitable for seismological applications that allow larger gauge lengths due to the lower frequency waves of interest. However, when signal frequencies of 5-500 Hz are of interest, then smaller gauge lengths and pulse widths are required, while still overcoming the light propagation losses

We acquired field test data utilizing boreholes and surface layouts, and demonstrated we can properly interrogate a 5 km section of fiber after a 30 km lossy lead-ins for typical seismic applications. The data acquisition utilized standard telecom and borehole fiber cables permanently deployed at a field site. We recorded high SNR seismic wave fields containing direct arrivals, refractions and reflections in all active sensing sections. We demonstrate the use of a state-of-the-art DAS interrogators in a practical field setting for various subsea sensing applications, such as long-reach subsea borehole-based sensing for seismic imaging purposes or opportunistic interrogation of abandoned boreholes (oil/ gas or deep scientific boreholes) allowing tie-back into a subsea infrastructure for data collection.

Presenting Author: Martin 9. Karrenbach

Authors