Geometrical model for the “Croissant” multi-component DAS sensor

Carla Acosta, Kristopher A. Innanen, Kevin W. Hall

In 2023, the "Croissant" was developed and tested as a novel, low-cost, permanent, multi-component fiber for directional Distributed Acoustic Sensing (DAS), designed to capture the full strain tensor of a wavefield. The sensor was deployed at the Carbon Management Canada (CMC) Newell County Field Research Station (FRS). This research aims to analyze field data from a multi-offset and multi-azimuth source-receiver configuration and to develop a geometrical model that generates synthetic data to qualitatively predict the signals detected by the Croissant sensor. Initial field data revealed high amplitudes in the vertical components, while the horizontal components exhibited comparatively lower amplitudes. These findings suggest the potential oblique incidence of the wavefield on the sensors, with implications for refracted wave arrivals. The Croissant geometrical model required parametrization of the fiber path and consideration of previous observations, such as the second layer having a significantly higher P-wave velocity, to generate synthetic data closely resembling the field data. In conclusion, the Croissant effectively functions as a point receiver. Velocity analysis of the first break picks in the vertical component allowed for the estimation of the possible second-layer velocity, which was then used in the synthetic model. Synthetic data showed higher amplitudes in the vertical components and broadside insensitivity in the horizontal components. Accurate comparison and analysis require the use of three-component, co-located geophones.