A fibre optic sensor for the in situ determination of rock physical properties

TL;DR

This paper presents a novel fibre optic sensor integrated into a high-pressure, high-temperature triaxial cell for direct in situ measurement of pore pressure and temperature in rocks, enabling better understanding of rock behavior under stress.

Contribution

Introduction of a fibre optic EFPI sensor with embedded FBG for direct in situ measurement of pore pressure and temperature in rocks under high pressure and temperature conditions.

Findings

First direct pore pressure measurement in sandstone during hydrostatic compression.

Successful integration of fibre optic sensor into high-pressure environment.

Enhanced understanding of rock behavior under changing conditions.

Abstract

To understand the behaviour of rocks under changing load or temperature conditions, the determination of physical parameters like pore pressure or temperature within the pore space is essential. Within this study, the implementation of a novel fibre optic point sensor for pressure and temperature determination into a high pressure / high temperature triaxial cell is presented. For the first time, pressure was measured directly within the pore space of a Flechtinger sandstone specimen during a hydrostatic compression test at up to 70 MPa. The sensor used within this study consists of a miniature all-silica fibre optic Extrinsic Fabry-Perot Interferometer (EFPI) sensor which has an embedded Fibre Bragg Grating (FBG) reference sensor element to determine temperature and pressure directly at the point of measurement.