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

TL;DR

This study evaluates various optical fibers for high-temperature distributed temperature sensing in geothermal wells, identifying polyimide-coated fibers as optimal and developing a new cable design and deployment strategy.

Contribution

It provides a comprehensive analysis of fiber performance at high temperatures and introduces a novel cable design and deployment approach for geothermal applications.

Findings

Polyimide fibers are suitable for high-temperature sensing.

A new cable design improves deployment in geothermal wells.

Operational temperature limits for fibers are established.

Abstract

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 aluminum coating and a fibre with a gold coating. To select a fibre, the relationship between attenuation, temperature, and time has been analyzed together with SEM micrographs. On the basis of these experiments, polyimide fibres have been chosen for utilisation. 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.