Fibre-Optic sensing is being actively used nowadays in various exploration and monitoring applications. Distributed Temperature Sensing (DTS) is used for measurements and monitoring of the temperature. Distributed Acoustic Sensing (DAS) is used to register seismic vibrations along a fibre optic cable. The low frequency DAS signal can be affected by temperature variations. Studying the effects of temperature change on DAS measurements is crucial for the time-lapse seismic and passive monitoring with DAS because it helps to eliminate or even avoid temperature-related noise. To estimate temperature effects on DAS measurements we conducted a series of experiments in the Curtin/NGL research facility and Curtin University Rock-Physics Laboratory. Two different fibres were tested in the laboratory and one cable (installed in the Curtin/NGL well) was examined at the site. Obtained results show that DAS is sensitive to temperature changes and its response is proportional to a time derivative of temperature. Our study demonstrates that by using DAS and DTS (temperature logs) together, it is possible to estimate strain - temperature change dependency (thermal coefficients - microstrain/C) for a particular fibre-optical cable. Estimated coefficients indicate that cable type/design can affect low-frequency DAS response to temperature changes.

Open-Access Online Publication: March 03, 2023