Distributed Acoustic Sensing for Geophysical Measurement, Monitoring and Verification

Barbara Cox, Peter Wills, Denis Kiyashchenko, Jeff Mestayer, and Jorge Lopez 1

Stephen Bourne, Rob Lupton, Gabriel Solano, and Nicholas Henderson 2

David Hill and Jim Roy 3

1 Shell International Exploration and Production;

2 Shell Upstream Americas;

3 OptaSense

CSEG RECORDER February 2012

Abstract

Distributed Acoustic Sensing (DAS) is a rapidly maturing fiber-optic technology with numerous applications in geophysical and in-well monitoring, and is being developed in a partnership between Shell and Optasense. DAS transforms nearly any fiber-optic cable into a distributed array of acoustic sensors. Recording data requires a special “Interrogator Unit”, which is connected to the fiber optic infrastructure. Fiber optic cables may be installed in any kind of borehole. Previously the cost, inconvenience, and risk of well intervention associated with conventional downhole geophones made in-well geophysical monitoring expensive and often unfeasible. Permanently installed down-hole fiberoptic cables are ideal for low-cost nonintrusive geophysical monitoring. Once the cable is installed, no further well intervention is required. In order to test this DAS technology, Shell/OptaSense have executed field trials in several locations around the world. One of these locations is the Quest Carbon Capture and Storage (CCS) project in Alberta, Canada. In the Quest field trials Zero-Offset and Walk-Away VSP data were acquired to assess feasibility of monitoring CO2 containment and tracking the CO2 injection plume. The trials show that, for these applications DAS data can be substituted for geophone data: the Zero-Offset VSP using DAS is capable of deriving good quality checkshot velocity profiles and the Walk-Away VSP DAS image is similar to the corresponding geophone image. After imaging, the DAS Walk-Away VSP images are quite repeatable (NRMS=15%), a requirement for a successful time-lapse survey. In summary, this work demonstrates that it is feasible to use VSPs data recorded with DAS for geophysical measurement, monitoring, and verification.