Preliminary evaluation of a high-pressure, high-temperature downhole optical sensor

This paper reports on the evaluation of a high-pressure high-temperature (HPHT) sensor prototype for permanent monitoring of pressure and temperature in oil wells. A Fabry-Perot (FP) pressure transducer was built using a metal capillary, metal reflecting wire and metal coated fiber which were brazed with a silver-based brazing paste using a specially designed induction heating system. The prototype sensor was tested for two outermost temperatures of the operating range of 20–350°C for which wavelength-pressure response characteristics were recorded for incremental pressure changes from 0 to 10,000psi. The results show that the sensor response to pressure was linear, with the nonlinearity error below 1%.