4D DAS fiber-coupling effects in freezing near-surface ground conditions

PreviousNext No AccessFirst International Meeting for Applied Geoscience & Energy Expanded Abstracts4D DAS fiber-coupling effects in freezing near-surface ground conditionsAuthors: Jihyun YangJeffrey ShraggeGe JinJihyun YangColorado School of MinesSearch for more papers by this author, Jeffrey ShraggeColorado School of MinesSearch for more papers by this author, and Ge JinColorado School of MinesSearch for more papers by this authorhttps://doi.org/10.1190/segam2021-3582508.1 SectionsSupplemental MaterialAboutPDF/ePub ToolsAdd to favoritesDownload CitationsTrack CitationsPermissions ShareFacebookTwitterLinked InRedditEmail AbstractDistributed acoustic sensing (DAS) increasingly is being used for permanent monitoring in completed downhole installations characterized by near-elastic fiber coupling and high data quality that, for some types of interrogator units (IUs), approaches the particle velocities recorded on single-component geophones. Surface DAS installations, though, tend to be deployed in conduits, in shallow trenches, or even directly on the surface and thus exhibit relatively poorer coupling and lower signal quality for which aggressive filtering is used to recover the usable signal. This investigation examines whether nearelastic coupling can be achieved in near-surface horizontal deployments by freezing fiber within shallow trenches thus enabling the use of native velocity acquisition format without aggressive filtering. We report the results of a time-lapse experiment where we acquired DAS data on three 35 m fiber sections deployed at depths ranging from surface to 20 cm. Over a six-hour period when the air temperature dropped from +6_C to -6_C we recorded repeat sledgehammer shot records, which clearly exhibit time-varying near-surface and coupling conditions that lead to an observed 4.5% surface-wave velocity increase at colder ground temperatures. Overall, our experiment shows that freezing provides improved - but arguably more complex - fiber-ground coupling and should motivate future cryogenic DAS experiments.Keywords: 4D, near surface, sensors, surface wave, time-lapsePermalink: https://doi.org/10.1190/segam2021-3582508.1FiguresReferencesRelatedDetails First International Meeting for Applied Geoscience & Energy Expanded AbstractsISSN (print):1052-3812 ISSN (online):1949-4645Copyright: 2021 Pages: 3561 publication data© 2021 Published in electronic format with permission by the Society of Exploration GeophysicistsPublisher:Society of Exploration Geophysicists HistoryPublished: 01 Sep 2021 CITATION INFORMATION Jihyun Yang, Jeffrey Shragge, and Ge Jin, (2021), "4D DAS fiber-coupling effects in freezing near-surface ground conditions," SEG Technical Program Expanded Abstracts : 477-482. https://doi.org/10.1190/segam2021-3582508.1 Plain-Language Summary Keywords4Dnear surfacesensorssurface wavetime-lapsePDF DownloadLoading ...