Use of distributed fibre-optic sensing for marine seismic measurements

Abstract

Heterodyne distributed vibration sensing (hDVS) and, more generically, distributed acoustic sensing (DAS) are technologies that rely on traditional fibre-optic cables to provide inline strain measurement. In recent years, hDVS has found application in seismic monitoring; in particular vertical seismic profiling (VSP) greatly benefits from the advantage of using permanent fibres cemented behind casing (Mateeva et al., 2013). VSP measurements were also demonstrated using fibre installed on production tubing (Barberan et al., 2012) and deployed within a wireline cable (Hartog et al., 2014). Another potential application for hDVS is flow monitoring, where, owing to the fibre’s large spatial coverage, it is possible to monitor vibrations and waves along the length of the well. Baihly et al. (2015) offered an insight on this use of hDVS. Furthermore, Molteni et al. (2016) evaluated microseismic monitoring as another compelling hDVS application. This paper evaluates the viability of using hDVS for distributed dynamic pressure sensing in marine seismic acquisition while reviewing the readiness of hDVS technology for this application. An initial concept of including hDVS in a streamer was disclosed by Kragh et al. (2012). Here, a possible design of a towed streamer using hDVS was discussed along with experimental results showing the potential of the technology to acquire pressure measurements in marine seismic surveys. We show the results of using hDVS to measure the pressure wavefield in two different experiments, and the results are compared with reference data acquired with traditional hydrophones. The use of a distributed measurement in towed streamers would provide a new type of measurement. The characterization of the pressure wavefield would be continuous along the cable with a denser spatial sampling. Similarly, straight fibres deployed along the streamer could characterize the tugging noise with increased spatial resolution. Furthermore, the use of cost-effective and lightweight fibres would greatly reduce the electronics embedded in the streamer and the total weight of the cable. The use of hDVS would also have new challenges – for example in how to segment the streamer into shorter sections without the fibre-optic connectors compromising the quality of the backscattered hDVS signal.