Dual cantilever beam extrinsic Fabry–Perot interferometer fiber optic accelerometer for potential application in microseismic monitoring of CO2 storage

Abstract

The long-term efficient storage of CO${}_2$ requires long-term monitoring of the integrity of the geologic body, and microseismic monitoring technology provides a method for evaluating the integrity of the geologic body. To meet the microseismic monitoring requirements for CO${}_2$ geologic sequestration, a highly sensitive dual cantilever Fabry–Perot interferometric fiber optic accelerometer is proposed. Finite element simulation shows that the strain of the dual-cantilever sensing element is twice that of a single-cantilever type, thereby doubling the sensitivity of the sensor. Experimental measurements have shown that the wavelength sensitivity of the accelerometer at 240 Hz is 28.35 nm/g, the lateral wavelength sensitivity is 0.91 nm/g, and the lateral interference is only 3.2%. The accelerometer has a resolution of $35.2\mu g$ and a resonance frequency of 735 Hz, the flat response range is 15-405 Hz. and can operate normally at 200 °C with a temperature sensitivity of 47.34 pm/${}^{\circ }$C. The experimental results are in good conformity with the theoretical analysis; the accelerometer is highly sensitive, simple in structure, and resistant to high temperature, and the sensitivity is not affected by the stiffness of the optical fiber. The excellent performance of accelerometers can realize high-quality microseismic information acquisition, and through the analysis of microseismic event sequences and diffusion conditions, the diffusion distribution of CO${}_2$ can be grasped via an assessment of the integrity of geological bodies.