Abstract
The influence of hydrogen gas on Fiber Bragg Grating (FBG)-based optical fiber sensors has been validated experimentally. More in particular, the focus was on FBGs written in the so-called Butterfly Micro Structured Fiber that targets simultaneous pressure and temperature monitoring with a minimum in cross-sensitivity to be used in, for example, downhole applications for the oil and gas market. The hydrogen-induced pressure and temperature errors from this type of sensor have been quantified as a function of the partial hydrogen pressure. The induced errors can be related to the diffusion of the hydrogen into the microstructure and to refractive index changes due to the presence of the hydrogen in the micro holes and penetration of it into the fiberglass. Furthermore, we have also shown that the hydrogen-induced errors scale with the partial hydrogen pressure.
Highlights
Fiber optic sensing has demonstrated its benefits for sensing of different critical parameters in downhole applications [1,2,3,4,5]
The focus was on Fiber Bragg Grating (FBG) written in the so-called Butterfly Micro Structured Fiber that targets simultaneous pressure and temperature monitoring with a minimum in cross-sensitivity to be used in, for example, downhole applications for the oil and gas market
We have shown that the hydrogen-induced errors scale with the partial hydrogen pressure
Summary
Fiber optic sensing has demonstrated its benefits for sensing of different critical parameters in downhole applications [1,2,3,4,5]. FBG-based sensors fabricated in Micro-Structured optical fiber (MS-FBG) have been considered for sensing critical parameters in downhole applications [23,24]. The usage of FBGs written in highly-birefringent Butterfly micro-structured fibers for simultaneous measurement of pressure and temperature [29,30,31] The behavior of such specialty sensors when exposed to a hydrogen-rich environment was studied and will be reported in this document. The autoclave consists of a stainless steel cylinder with an inner cavity of 20 cm in height and 13 cm diameter It is equipped with four epoxy-based fiber feed-throughs with FC-connectors, which allow for online monitoring of samples during gas loading.
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