Sensitivity requirements for fiber optic pressure and velocity sensors

Optical dynamic pressure and velocity sensors are under development for oil exploration and reservoir monitoring. The abilities of these sensors to operate in high temperature and static pressure environments, without nearby electronics, offers the potential for enhanced reliability with significant reduction in life-cycle costs. To aid in the design of these sensors, the minimum sensitivity requirements are derived in terms of the minimum detectable signals by the signal conditioning equipment and background noise levels in their operating environments. These requirements are compared with the performance achieved with commercially available electronic sensors. The results indicate that conventional moving coil geophones may have serious limitations in performing wide frequency-bandwidth measurements of seismic wave particle velocity in typical borehole noise environments. Accelerometer response, on the other hand, increases linearly with frequency, and consequently the useful bandwidth of an accelerometer generally exceeds that of the geophone.