US 11,867,855 B2
Downhole fiber optic hydrophone
Sebastian Jung, Inserhagen (DE); Thomas Kruspe, Wietzendorf (DE); Gunnar Tackmann, Hannover (DE); Dominik Hoheisel, Hemmingen (DE); Lennert Rabe, Celle (DE); and Jonathan Leong, Hannover (DE)
Assigned to BAKER HUGHES OILFIELD OPERATIONS LLC, Houston, TX (US)
Filed by Baker Hughes Oilfield Operations LLC, Houston, TX (US)
Filed on Dec. 10, 2019, as Appl. No. 16/709,420.
Prior Publication US 2021/0173106 A1, Jun. 10, 2021
Int. Cl. G01V 1/22 (2006.01); G01V 1/18 (2006.01)
CPC G01V 1/226 (2013.01) [G01V 1/186 (2013.01)] 24 Claims
OG exemplary drawing
 
1. An apparatus for use in a borehole, comprising:
an acoustic sensor including a pressure transducer comprising:
an interface between a fluid reservoir and a fluid body, the interface including a flexing member attached to an optical medium, the pressure transducer configured to convert an acoustic pressure signal within a borehole pressure incident on the pressure transducer to a strain on the optical medium along an axis of the optical medium via movement of the flexing member, the acoustic pressure signal propagated via the fluid body;
a detector configured to generate acoustic measurement information responsive to received electromagnetic radiation transmitted through the optical medium along the axis, at least one optical property of the optical medium being responsive to the strain on the optical medium; and
at least one coupled oscillator included in the interface between the fluid reservoir and the fluid body displacing a volume of a fluid in the fluid reservoir responsive to the acoustic pressure signal to influence motion of the flexing member so that the optical medium attached to the flexing member experiences an amplified response to the acoustic pressure signal in a predefined frequency range and the electromagnetic radiation received by the detector represents an amplified acoustic pressure signal within the predefined frequency range;
wherein the at least one coupled oscillator and the flexing member form a coupled two mass oscillatory system including a coupling spring provided by elastic properties of the fluid in the fluid reservoir and wherein the flexing member and the at least one coupled oscillator are directly coupled by the coupling spring, wherein the predefined frequency range is determined by the elastic properties of the fluid in the fluid reservoir.