Investigation of the effects of surrounding media on the distributedacoustic sensing of a helically wound fibre-optic cable with application tothe New Afton deposit, British Columbia

Fibre-optic sensing technology has recently become popular for oiland gas extraction, mining, geotechnical engineering, and hydrogeology applications.With a successful track record in many applications, distributed acousticsensing using straight fibre-optic cables has become a method of choice forseismic studies. However, distributed acoustic sensing using straight fibre-optic cables cannot detect off-axial strain at high incident angles (theangle between the ray and normal vector of the surface); hence, a helicallywound cable design was introduced to overcome this limitation. The helicallywound cable field data at the New Afton deposit in British Columbia, Canada,showed that the quality of the data is highly dependent on the incidentangle and surrounding media. A 3D finite element model developed usingCOMSOL Multiphysics quickly and efficiently assessed the effects of variousmaterials surrounding a helically wound cable for simple geometry forscenarios corresponding to a real deployment of such cable underground atthe New Afton mine. The proposed numerical modelling workflow could beapplied to more complicated scenarios (e.g., non-linear materialconstitutive behaviour and the effects of pore fluids). The results of thispaper can be used as a guideline for analyzing the impact of surroundingmedia and incident angle on the response of helically wound cable,optimizing the installation of helically wound cable in various conditions,and validating boundary conditions of 3D numerical models built foranalyzing complex scenarios.