SES-05. Distributed Acoustic Sensing (DAS): Case Study at the US Department of Energy's FORGE Site

Abstract
Distributed acoustic sensing (DAS) provides a promising new tool for seismology using fiber optic cable and an interferometer to measure light backscattered from imperfections in the fiber. By detecting seismic wave interference with the fiber, DAS can measure variations in travel times of backscattered light and calculate strain rate along segments of the fiber. The Frontier Observatory for Research in Geothermal Energy (FORGE) in western Utah provides an ideal setting to assess the capability of DAS while developing new methods for enhanced geothermal systems (EGS). The project aims to utilize DAS to image the subsurface of the FORGE site and understand the capability of DAS. In April 2022, data was collected using a 2-kilometer-long DAS array deployed only a few inches into the ground. A vibroseis survey, whereby trucks generate waves to image geologic structures in the subsurface, was conducted at FORGE during our DAS experiment allowing us to correlate with the DAS data to obtain reflections from the subsurface. We show synthetic experiments and preliminary results of real data, while on the path to demonstrating how DAS can be used for subsurface imaging. Using python and signal processing techniques, we developed a methodology to easily analyze and correlate singular channels from a DAS array we deployed at FORGE. We hope to generate a seismic imaging profile with DAS from the vibroseis signal, which should be comparable to similar seismic tools like geophones, demonstrating the capability of distributed acoustic sensing. Due to the higher density and flexibility of DAS coverage, it can even provide a higher resolution image than geophones by having meter-scale density on a kilometer-scale aperture. Paired with the abundance of fiber optic cable, DAS proves to be a valuable tool for seismology.