Fiber-Optic Three-Component Accelerometer for Seismic Exploration in Oil and Gas Wells Based on Ultrashort Fiber Bragg Grating Arrays

In this paper, we propose and demonstrate a fiber three-component accelerometer based on ultra-short fiber Bragg gratings (FBGs) arrays for seismic exploration in oil and gas wells. The three-component accelerometer consists of three orthogonal sensing units, each based on a spring-mass structure and encapsulated in a cylindrical casing that is resistant to temperatures up to 155 °C and pressures of 50 MPa. Ultra-short FBGs, fabricated using femtosecond laser direct writing technology, exhibit a 3 dB bandwidth > 7.10 nm and are used as mirrors for the interferometric three-component sensor, ensuring stable operation of the accelerometer over a wide temperature range [25, 300] °C. Experimental results demonstrate that the accelerometer exhibits excellent linearity, with a sensitivity of 49.14 dB (ref rad/g) measured within the [10, 700] Hz frequency range. The accelerometer has a minimum detectable acceleration (MDA) of 122.80 ng/√Hz and outperforms standard electrical geophones used for surface seismic exploration in comparative tests. To validate the detection performance of the developed fiber-optic three-component accelerometer, it was employed in receiving tests of ground-excited seismic signals in wells and cross-well seismic exploration tests. The proposed fiber interferometric accelerometer demonstrates significant advantages for large-scale quasi-distributed multi-component oil and gas resource exploration and monitoring.