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

Abstract

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