Abstract
Distributed fibre optic sensing (DFOS) technology is widelyemployed in the oil and gas industry for monitoringseismicity, strain andtemperature during hydraulic fracturing of unconventional reservoirs. However,it is onlyin the early stages of application in the mining industry. This paperpresents a case study on the applicationof distributed acoustic sensing (DAS)technology to monitor rock mass stress conditions in anunderground mine.
The objective of this pilot project was to assess theviability of, and challenges associated with, installing fibreoptics and theireffectiveness in monitoring rock mass response to mining activities. Anengineered fibre opticcable was deployed and grouted in a 200 m-deep boreholeto monitor seismicity and strain. The raw DASstrain rate data were divided intotwo frequency bands: a high-frequency band (above 10 Hz) formicroseismicprocessing and a 1–10 Hz frequency band for strain processing.
Microseismic events and blasts detected by the fibre wereco-located with existing geophones andaccelerometers to enhance event locationaccuracy and precision. While the existing network of geophonesprovidedaccurate event locations, the addition of DAS increased the precision of thesemeasurements.In addition to microseismic monitoring, the energy attributewithin the 1–10 Hz band of DAS strain rate datawas analysed. This analysisrevealed a clear correlation between elevated energy levels on the fibre duringraiseboreoperations and a levelling off after the completion of raiseboring. Theobserved intermittent highand low energy levels on the fibre could be used forsafety assessments during raisebore operations as theseenergy fluctuationsreflect the impact of raisebore activities on rock mass stress.
Based on this limited dataset, DAS technology has thepotential to offer valuable insights into rock massbehaviour in undergroundmining environments by monitoring stress and strain conditions duringoperationssuch as raiseboring, development and production blasts. When combinedwith existing seismic systems, DASprovides an additional data point forenhancing hazard mitigation strategies in underground miningoperations.
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