Investigation of Time-Lapse Changes with DAS Borehole Data at the Brady Geothermal Field Using Deconvolution Interferometry

Abstract

Distributed acoustic sensing (DAS) has great potential for monitoring natural-resource reservoirs and borehole conditions. However, the large volume of data and complicated wavefield add challenges to processing and interpretation. In this study, we demonstrate that seismic interferometry based on deconvolution is a convenient tool for analyzing this complicated wavefield. We also show the limitation of this technique, in that it still requires good coupling to extract the signal of interest. We extract coherent waves from the observation of a borehole DAS system at the Brady geothermal field in Nevada. The extracted waves are cable or casing ringing that reverberate within a depth interval. These ringing phenomena are frequently observed in the vertical borehole DAS data. The deconvolution method allows us to examine the wavefield at different boundary conditions and separate the direct waves and the multiples. With these benefits, we can interpret the wavefields using a simple 1D string model and monitor its temporal changes. The velocity of this wave varies with depth, observation time, temperature, and pressure. We find the velocity is sensitive to disturbances in the borehole related to increasing operation intensity. The velocity decreases with rising temperature. The reverberation can be decomposed into distinct vibration modes in the spectrum. We find that the wave is dispersive and the fundamental mode propagates with a large velocity. This interferometry method can be useful for monitoring borehole conditions or reservoir property changes using densely-sampled DAS data.

Quantifying microseismic noise generation from coastal reflection of gravity waves recorded by seafloor DAS

“…For instance, the 27.5-32 km segment has been replaced in 2017 and the natural burial of the cable into the soft sediment is not yet sufficient to provide good coupling. Other segments are probably hanging sections (around 20 km or 34 km) that do not record Scholte waves and display cable waves (Flores et al 2021;Chang & Nakata 2022). The strain-rate of these segments is set to 0.…”

Using Dark Fiber and Distributed Acoustic Sensing to Characterize a Geothermal System in the Imperial Valley, Southern California

“…DAS has been successfully used for urban near‐surface characterization (Ajo‐Franklin et al., 2019; Dou et al., 2017; Fang et al., 2020), monitoring of unconventional reservoirs (Cheng et al., 2021; Daley et al., 2013; Jin & Roy, 2017), glacial deformation (Booth et al., 2020; Walter et al., 2020), and ocean dynamics (Cheng, Chi, et al., 2021; Lindsey et al., 2019; E. F. Williams et al., 2021; Viens et al., 2022). Recently, several DAS‐related feasibility studies have been conducted to characterize geothermal reservoirs (e.g., Chalari et al., 2019; Chang & Nakata, 2022; Feigl & Parker, 2019; Feigl & Team, 2017; Kasahara et al., 2020; Lellouch et al., 2021; Schölderle et al., 2021).…”

Feasibility of source-free DAS logging for next-generation borehole imaging

“…For example, ambient noises recorded by surface DAS systems have been studied and are widely used to derive shallow S-wave velocity structures and detect underground water 4 – 12 . However, few studies on borehole DAS ambient noise characteristics along depth have been reported 13 , 14 .…”