Fibre optic pressure and temperature sensor for geothermal wells

In this paper a fibre optic sensor is developed and tested to measure pressure and temperature under simulated wellbore conditions. The sensor consists of a miniature all-silica fibre optic Extrinsic Fabry-Perot Interferometer (EFPI) sensor which has a novel embedded Fibre Bragg Grating (FBG) reference sensor element to determine both pressure and temperature at the point of measurement. The sensor head is completely fabricated from fused-silica components, i.e. completely made of glass, utilizing a 200μm outer diameter silica glass fibre, a silica glass capillary and a Single-Mode FBG. All silica-glass components were spliced together using a conventional fusion splicer to obtain a robust sensor structure.