A coupled DAS shaped-fibre and 3D elastic finite difference wave model

Matthew Eaid, Junxiao Li, Kristopher A. H. Innanen

The interest in Distributed Acoustic Sensing (DAS) fibres, for improved geophysical acquisition, has seen substantial growth over the last half decade. The ability to drive down acquisition costs, improve repeatability, and expand the application of seismic acquisition are all attractive properties of DAS technologies. While applications of straight DAS fibres have proven successful, their well known broadside insensitivity greatly limits their application. Research efforts have recently shifted to creating fibres in more complicated shapes, such as helices, to better characterize, and recover the wavefield. These technologies show promise in negating the effects of broadside insensitivity, however, the interpretation of seismic signals recorded on helically-wound fibres is not well understood. In order to learn more about how the signal captured by shaped fibres relates to the signal captured by conventional geophones, it is imperative to develop full 3D elastic modeling tools to investigate the response of fibres of arbitrary shape, in the presence of elastic wave-fields. We begin with a discussion of the geometrical model of fibres of arbitrary shape, and how they measure the seismic wavefield. We then discuss the velocity-stress method of 3D elastic wave propagation, and how it may be extended to apply to DAS fibres. Finally, we conclude with some examples of elastic wave modeling using DAS fibres, and discuss how this technology will expand.