Micro-structured fiber distributed acoustic sensing system for borehole seismic survey

Distributed fiber optic sensing is increasingly recognized as a viable alternative to geophone arrays for the acquisition of borehole seismic data. The ability to acquire borehole seismic data in a producing well without the need to disrupt production also offers significant benefits to the operator. A novel fiber distributed acoustic sensor (DAS) with ultra-high sensitivity is presented. Through designing and fabricating the distributed micro-structured optical fiber (DMOF) with successive longitudinal microstructures to enhance the signal-to-noise ratio (SNR) of the backscattered light, and employing the coherent optical time domain reflectometer technique (C-OTDR), the sensing performance of acoustic signal can be greatly improved. Wide frequency band from 0.1Hz to 45 kHz along the 500m long sensing fiber with ultra-high strain resolution of 0.16nε is experimentally demonstrated on the ground surface and in a shallow borehole. (paper)