Double‐Tubing Encapsulated Fiber Optic Temperature Sensor

Increasing the efficiency of oil production operations requires improved sensors to supply critical information such as mixed‐phase fluid flow, pressure and temperature measurements within the down‐hole oil environment. In order to provide robust and reliable fiber optic temperature sensors capable of operating in the harsh down‐hole oil environment, where temperatures might exceed 250 °C and pressures might reach 20,000 psi (140 Mpa), a novel type of fiber optic temperature sensor has been developed. This temperature sensor functions as an EFPI (extrinsic Fabry‐Perot interferometric) sensor. One unique contribution of this work is that the glass tubing used is a borosilicate glass with a relatively high coefficient of thermal expansion (CTE) and long gauge length, allowing a much higher sensitivity to be achieved, without hysteresis. The sensor structure utilizes a dual tubing design (tubing within a tubing) to allow pressure isolation. An LED light beam is used as the signal interrogation source to remo...