Low-Frequency Strain Testbed for DAS Performance Characterization

Abstract

Distributed acoustic sensing (DAS) systems were originally developed to measure high-frequency dynamic strain signals induced by sound and vibration. Recently, however, their potential for low-frequency applications has received considerable attention. In the petroleum industry, efforts are underway, led by SEAFOM, to establish recommended practices for characterizing DAS strain responses in oil and gas environments. This includes the development of a consistent methodology for evaluating DAS performance. This letter presents a mechanical approach to characterize the low-frequency strain measurement performance of DAS. The setup uses pulleys and a microstepper motor to apply controlled mechanical strain to optical fibers at varying velocities and intensities, resulting in high levels of strain at very low frequencies. Experimental results demonstrate the generation of cyclic ramp strain stimuli with amplitudes up to 4 mϵ over a 33-min cycle, which can be easily extended. DAS measurements revealed nonuniform strain distributions along the fiber, primarily influenced by friction and slip effects associated with the fiber coating and pulley bearing characteristics. These findings improve the reliability and interpretability of low-frequency DAS measurements in complex offshore environments.