DAS VSP Acquisition Through Coiled Tubing Fiber-Optic Cable

Kimura, Tsunehisa; Chen, Y.; Kobayashi, Yuki; Xue, Ziqiu; Adachi, Keita

doi:10.3997/2214-4609.2019x604018

Cited by 2 publications

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“…However, tube wave properties are predictable and have a much lower apparent velocity than the desired signal, and can thus be filtered out during processing. Acquisition using fibers deployed inside active wells is also possible, albeit significantly noisier (Kimura et al., 2019; Uematsu et al., 2019). The fibers can withstand harsh temperature and pressure conditions and can thus record close to or within the reservoir (Zhidong et al., 2019).…”

Section: Introductionmentioning

confidence: 99%

Low‐Magnitude Seismicity With a Downhole Distributed Acoustic Sensing Array—Examples From the FORGE Geothermal Experiment

et al. 2020

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We show the capabilities of a downhole distributed acoustic sensing (DAS) array in detecting, locating, and characterizing low‐magnitude earthquakes occurring in the vicinity of the Frontier Observatory for Research in Geothermal Energy (FORGE) site in Utah. Continuous data for 10.5 days were acquired in a monitoring well at the FORGE geothermal site during the initial stimulation of an enhanced geothermal system in April–May 2019. Earthquake activity beneath Mineral Mountains, Utah also occurred within 10 km of the FORGE monitoring well. During the experiment, four earthquakes were cataloged by routine processing of the University of Utah Seismograph Stations. Our processing of DAS data finds 77 earthquakes during that period, of which 16 are visible on the regional network. Five additional events are found by template matching DAS data. The magnitude of completeness obtained by DAS processing is better by at least M = 0.5 than the dense surface array around the FORGE site. Depth estimation using DAS is more reliable than using a surface array. While a single vertical DAS array is limited in terms of event location due to its azimuthal ambiguity, multiple DAS wells or a combination of a downhole array with surface stations or near‐surface horizontal DAS could jointly resolve locations. All detected events probably originated from the two active source areas, located 3–5 and 8–10 km away from the FORGE site, respectively. Recorded events can be reliably clustered into several distinct families thanks to the spatial density and large number of DAS channels.

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Section: Introductionmentioning

confidence: 99%

Low‐Magnitude Seismicity With a Downhole Distributed Acoustic Sensing Array—Examples From the FORGE Geothermal Experiment

et al. 2020

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Comparison between Distributed Acoustic Sensing and Geophones: Downhole Microseismic Monitoring of the FORGE Geothermal Experiment

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Lindsey

Ellsworth

et al. 2020

Seismological Research Letters

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We compare the performance of a downhole distributed acoustic sensing (DAS) fiber-optic array with that of conventional geophones. The downhole collocated arrays are part of the Frontier Observatory for Research in Geothermal Energy (FORGE) geothermal experiment, in which stimulation of the rock volume in an enhanced geothermal system (EGS) causes microseismic events. The DAS acquisition system yields data sampled at every 1 m at 2000 samples per second for the entire length of the well, spanning to a depth of 985 m from the surface. Whereas single DAS channels are substantially noisier than geophones at the same location, their large number and spatial coherency allow for the application of effective array processing techniques. We follow a complete workflow for the fiber-optic array: velocity model building, event detection, event location, and magnitude estimation. Estimated velocity models agree well with sonic logging in a nearby well and map a granitic contact accurately. Detection performance is somewhat worse than geophones and yields magnitude completeness of −1.4 compared to −1.7 for geophones. Using a single vertical fiber array, we cannot retrieve the azimuth of the events relative to the well. However, we can very accurately estimate their depth and horizontal distance from the array. Magnitude estimation with DAS approaches geophone results to within a standard deviation of M=0.115 and negligible mean difference. The DAS processing results outperform a regional and local surface array, consolidated with a shallow borehole sensor. Although downhole geophones in the FORGE experimental layout performed better, DAS holds several critical practical benefits that were not demonstrated. Thanks to its heat resistance, it can be deployed much closer to the reservoir; fibers can be deployed along cased active wells, eliminating the need for a dedicated monitoring well; the permanently installed fiber can be used for years or decades. Therefore, we argue that DAS holds vast potential for long-term monitoring of EGS projects.

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DAS VSP Acquisition Through Coiled Tubing Fiber-Optic Cable

Cited by 2 publications

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Low‐Magnitude Seismicity With a Downhole Distributed Acoustic Sensing Array—Examples From the FORGE Geothermal Experiment

Low‐Magnitude Seismicity With a Downhole Distributed Acoustic Sensing Array—Examples From the FORGE Geothermal Experiment

Comparison between Distributed Acoustic Sensing and Geophones: Downhole Microseismic Monitoring of the FORGE Geothermal Experiment

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