BOREHOLE IMAGING USING DAS AMBIENT NOISE FROM THE SAN JUAN BASIN CARBONSAFE PROJECT SITE

Imaging and monitoring formations and fractures around a borehole is essential for geologic carbon storage. We have recently developed a source-free borehole imaging technique using distributed acoustic sensing (DAS) ambient noise for geothermal energy applications. We study borehole imaging using DAS ambient noise data recorded in Well 30-045 at the San Juan Basin CarbonSAFE (Carbon Storage Assurance Facility Enterprise) project site located about 16 km Northeast of Aztec, New Mexico, USA. A Silixa distributed fiber optic sensing (DFOS) system including single-mode, multimode, and precision-engineered Constellation fiber was installed in Well 30-045 to acquire DAS ambient noise, distributed strain sensing (DSS), distributed temperature sensing (DTS), and zero-offset DAS vertical seismic profiling (DAS-VSP) data. The DAS system used to acquire DAS ambient noise and DAS-VSP data includes one Carina P13 interrogator unit along with a precision-engineered fiber and one Carina P33 interrogator unit with a standard iDAS single-mode fiber. The Constellation fiber was successfully installed to a depth of 7420 ft (2261 m) and the single mode fiber was successfully installed to a depth of 8686 ft (2647 m). The two DAS systems (P13 and P33) recorded about 21 hours of DAS ambient noise data between February 26-27, 2023. The sampling rate for the survey is 0.001 s, the gauge length is 10 m, and the spatial sampling is 1 m. We analyze the 21 hours of DAS ambient noise data and obtain ambient noise RMS (root mean square) depth profiles that show noise peaks at certain depths and quiet zones at other depths. We compare DAS ambient noise RMS profiles with the zero-offset DAS-VSP data and find that the noise peaks correlate well with upgoing reflections on the DAS-VSP data, demonstrating that these peaks are located at the interfaces of geologic formations. We also find that noise zones correlate well with formations that have loss of fluid circulation caused by man-made fractures. In addition, we compare our DAS ambient noise RMS profiles with wireline well-logging data and show their consistency.