Microseismic Applications using DAS

Distributed Acoustic Sensing (DAS) is a rapidly maturing fibre optic technology with many applications for wellbore monitoring and geophysical surveillance. DAS transforms a fibre optic cable into a distributed array of acoustic sensors. Shell is developing DAS technology in partnership with OptaSense, a subsidiary of QinetiQ U.K. DAS has been proven to work for VSP applications (Mateeva et al., 2012). The technology has been improved through numerous field trials and it has been tested in a variety of installations, where it has been compared to geophones and sonic logs as a check-shot tool, and as an imaging tool for walk away VSP data. Signal to noise ratio, directionality and repeatability among other aspects have also been studied through these field trials and laboratory experiments. The performance of DAS for micro-seismic monitoring applications is still under evaluation. Although DAS offers the advantage of recording along the whole well at once, significantly increasing the number of receivers, it has several challenges with respect to geophone arrays: the current DAS system records data with a higher noise floor and with a more constrained angular sensitivity since it behaves as a doublet of one-component geophones. In this paper we report the current status of this technology regarding micro-seismic monitoring. A field trial specifically designed to test this application in a micro-seismically active area is described. The trial was jointly carried out with Petroleum Development Oman (PDO) in a field in Oman.