A high-sensitivity FBG accelerometer and application for flow monitoring in oil wells

• Designing two fiber supports improve traditional cantilever FBG accelerometers. • Establishing accuracy mechanical model uses elasticity theory approach. • Accelerometer with high figure of merit, low cross-sensitivity, small size. • Accelerometers apply in downhole non-invasive flow measurement. In this study, a cantilever beam-based fibre Bragg grating (FBG) accelerometer is presented. Two fibre supports are arranged at both ends of a cantilever beam; therefore, the FBG can be stretched longitudinally by both displacement and rotation of the free end. The principle of this sensor is analysed by the elasticity theory approach and the accuracy of the theoretical model is verified by the ANSYS modal simulation. Furthermore, the influence of key structural parameters on the sensor characteristics is analysed by Mathematica for structural optimisation. Hence, the accelerometer exhibits a resonant frequency of approximately 76 Hz, an average sensitivity of 59.3 dB re pm/g for a 1–60 Hz flat response interval and a cross-sensitivity of less than –24.43 dB (<6.1 %), which is capable of low frequency and precision vibration measurements. Finally, a flow-monitoring test is presented and the results show that it is feasible to use FBG accelerometers for flow monitoring in oil wells.