Temperature-dependent characterization of optical fibres for distributed temperature sensing in hot geothermal wells

This study was performed in order to select a proper fibre for the application of a distributed temperature sensing system within a hot geothermal well in Iceland. Commercially available high temperature graded index fibres have been tested under in situ temperature conditions. Experiments have been performed with four different polyimide-coated fibres, a fibre with an aluminium coating and a fibre with a gold coating. To select a fibre, the relationship between attenuation, temperature and time has been analysed together with SEM micrographs. Based on these experiments, polyimide fibres have been chosen for utilization. Further tests in ambient and inert atmosphere have been conducted with two polyimide-coated fibres to set an operating temperature limit for these fibres. SEM micrographs, together with coating colour changes have been used to characterize the high temperature performance of the fibres. A novel cable design has been developed, a deployment strategy has been worked out, and a suitable well for deployment has been selected.