Reliability of fiber Bragg grating based sensors for downhole applications

A sensor for accurate and long-term fluid pressure monitoring in oil bore-holes based on optical fiber Bragg gratings (FBGs) is presented. The sensor converts fluid pressure into optical fiber strain by means of a mechanical transducer designed to withstand downhole conditions. The sensor response is investigated as a function of pressure and temperature. Effects of shock and vibration are also considered. The expected stability and lifetime of the polyimide-coated gratings in a downhole environment are estimated by modeling and extended accelerated mechanical and thermal aging tests.