Fiber Bragg grating sensor combined with silicone compliant cylinder for orientation identification of three-component geophone.

Three-component geophone rotates randomly during oil and gas exploration, which is difficult to orient. There is a severe impact on the subsequent stratigraphic inversion. By fixing the fiber Bragg grating (FBG) sensor to the three-component geophone, the twist angle is the same. The rotation angle of the three-component geophone can be obtained by measuring the twist angle of the FBG sensor. However, the three-component geophone below the FBG sensor stretches the FBG sensor. Therefore, avoiding the effect of tensile strain on the torsional strain, requires simultaneous inversion of the twist angle and stretch length of the FBG sensor. This paper introduces an FBG sensor with simultaneous inversion of torsion angle and tensile length. The sensor consists of two FBGs embedded in the spiral groove of the compliant cylinder. Firstly, the sensing principle of the FBG sensor is analyzed, and developed FBG sensing model for tensile–torsional strain, including FBG by tilting arrangement, the extension of the tensile strain range of the FBG sensor was realized. Secondly, it describes the fabrication process of the FBG sensor, including loading the FBG with pre-stress, making the FBG sensor realize the extension of the torsion angle range. Next, the convenience of inversion is realized by averaging the calibrated strain transfer coefficients. Finally, to verify the effectiveness of this bidirectional helical fiber design and sensing technology, simultaneous torsion and tension tests were conducted on FBG sensors. The experimental results show that the sensor achieves simultaneous torsion angle and tensile length inversion. The maximum torsion angle of the inversion is 180°. The maximum stretch length of the inversion is 10 mm. • The first application of FBG sensor based on a bi-directional helix structure for identification of three-component geophone orientation, and the simultaneous inversion of FBG sensor torsion angle and tensile length is realized. • The strain range is 6000 μ ϵ for axially arranged FBG. In tilt arrangement FBG, where the helical angle is 45°, the tilted FBG strain range is 4 times higher than the axial FBG strain range, and the extension of the tensile strain range has been realized. • The twist angle measured by the four-core FBG sensor is 78° (Modes et al., 2020). By loading pre-stress, the FBG sensor based on a bi-directional helical arrangement measures a torsion angle of 180°. In contrast, an expansion of the torsional angle range has been achieved. [ABSTRACT FROM AUTHOR]