Distributed Acoustic Sensing – a new tool for seismic applications

Abstract

Distributed optical fibre sensors are established tools in the energy industry, finding many applications for production optimisation and integrity monitoring. Recently, a new class of instrument, the Distributed Acoustic Sensor (DAS), has been launched which adds seismic imaging to the list of energy industry applications. In this paper, we describe one such distributed acoustic sensor (named the iDAS) and demonstrate, through a series of lab experiments, the signal quality and performance that can be achieved. We show data which demonstrates the capability of the iDAS to measure the true acoustic signal (amplitude, frequency and phase) at all points along the sensing fibre length. We also compare the iDAS data with data collected from conventional point sensors and detail experiments which validate key performance criteria. We follow the lab experimental validation of the iDAS with a series of lab and field demonstrations. The lab demonstrations encompass localisation (ranging) of events away from the sensing fibre (for security applications) and acoustic imaging through the formation of a large acoustic camera using a single sensing fibre. The field demonstrations show comparisons of iDAS and geophone measurements in a surface seismic survey and improvements made by stacking shot records from an offshore VSP survey.