Fiber Optic Sensing for Geomechanical Monitoring: (1)-Distributed Strain Measurements of Two Sandstones under Hydrostatic Confining and Pore Pressure Conditions

Applied Sciences

Sevket Durucan¹  Ji-Quan Shi¹  Ziqiu Xue²  Yoshiaki Yamauchi³ 

[1] Department of Earth Science and Engineering, Royal School of Mines, Imperial College London, London SW7 2AZ, UK;Geological Carbon Dioxide Storage Technology Research Association, 9-2 Kizugawadai, Kizugawa-shi, Kyoto 619-0292, Japan;Neubrex Co., Ltd. Sakaemachidori 1-1-24, Chuo-ku, Kobe, Hyogo 650-0023, Japan;

关键词: brillouin scattering;    rayleigh scattering;    frequency shift;    optic fiber;    distributed strain measurement;    sandstone;   

DOI  :  10.3390/app8112103

来源: DOAJ

【 摘 要 】

In this study distributed optic fiber has been used to measure both the Rayleigh and Brillouin frequency shift of two different sandstone core samples under controlled hydrostatic confining and pore pressure in the laboratory. The Berea sandstone core is relatively homogeneous, whereas the Tako sandstone core is visibly heterogeneous with a coarse-grain and a fine-grain region. Rayleigh frequency has been found to have a superior performance over Brillouin frequency in terms of better consistency (less scattering) in the tests carried out. The strain gauge readings reveal considerable anisotropy in the stiffness of the Berea core between perpendicular (vertical) and parallel to the bedding (hoop) directions. The strains converted from Rayleigh frequency shift measurements agree reasonably well with readings by one of the four hoop strain gauge channels under increasing confining/pore pressure. For the Tako sandstone core, the contrast in the grain-size, and thus rock elastic properties, is clearly reflected in the hoop strain measurement by both strain gauges and distributed optic fiber. The outcomes of the test have demonstrated successfully the use of a single optic fiber for measuring rock strain response at different regions of a heterogeneous core sample along a continuous trajectory.

【 授权许可】

Unknown