METHOD TO COMPENSATE MEASUREMENT ERROR OF FIBER BRAGG GRATING SENSOR CAUSED BY HYDROGEN DARKENING

摘要

A method is described for compensating measurement errors of fiber Bragg grating (FBG) sensors installed in fiber cables in downhole oil and gas environments due to hydrogen darkening. The method involves loading a fiber of known length and multiple FBG sensors in a hydrogen chamber with control of temperature, hydrogen concentration, pressure, and time and adjusting each of the variables through a test matrix while continuously measuring and recording the fiber transmission loss and FBG spectrum changes, then creating a correlation map of fiber transmission loss vs. Bragg wavelength shift, and using that map for compensating the wavelength shift of downhole installed fiber cables as a function of their hydrogen induced transmission loss through time.