Distributed fiber-optic interferometric sensor for the detection of pressure fluctuations in reservoirs

A fiber-optic interferometric sensor for the detection of the resonant modes of reservoirs is reported. Study of the characteristics of fiber-optic hydrophones identified the ratio ΔL/Δp, i.e., the differential fiber-optic elongation due to pressure change, as the critical parameter to be enhanced in order to improve the sensor sensitivity. A model of the sensor, suitable for detecting the very-low-frequency and long-wavelength pressure changes characteristic of reservoir resonances, is proposed. The sensor is designed as a straight length of optical fiber with small masses attached at regular intervals. The dynamical analysis shows a sensitivity two orders of magnitude larger than that of the unmodified optical fiber. Use of the sensor as a resonant device is discussed. Experiments performed using the first prototype in a resonant tank are described and agree well with theoretical predictions, confirming the validity of the approach