Fracture hydromechanical response measured by fiber optic distributed acoustic sensing at milliHertz frequencies

TitleFracture hydromechanical response measured by fiber optic distributed acoustic sensing at milliHertz frequencies
Publication TypeJournal Article
Year of Publication2017
AuthorsBecker, MW, Ciervo, C, Cole, M, Coleman, T, Mondanos, M
JournalGeophysical Research Letters
Volume44
Issue14
Pagination2017GL073931
Date Published2017/07/28/
ISBN Number1944-8007
Accession NumberHBR.2017-28
Keywords1822 Geomechanics, 1828 Groundwater hydraulics, 1835 Hydrogeophysics, 8010 Fractures and faults, 8094 Instruments and techniques, distributed acoustic sensing, distributed temperature sensing, fractures, hydromechanics, hydrualic testing, oscillatory hydraulic testing
Abstract

A new method of measuring dynamic strain in boreholes was used to record fracture displacement in response to head oscillation. Fiber optic distributed acoustic sensing (DAS) was used to measure strain at mHz frequencies, rather than the Hz to kHz frequencies typical for seismic and acoustic monitoring. Fiber optic cable was mechanically coupled to the wall of a borehole drilled into fractured crystalline bedrock. Oscillating hydraulic signals were applied at a companion borehole 30 m away. The DAS instrument measured fracture displacement at frequencies of less than 1 mHz and amplitudes of less than 1 nm, in response to fluid pressure changes of less 20 Pa (2 mm H2O). Displacement was linearly related to the log of effective stress, a relationship typically explained by the effect of self-affine fracture roughness on fracture closure. These results imply that fracture roughness affects closure even when displacement is a million times smaller than the fracture aperture.

URLhttp://onlinelibrary.wiley.com/doi/10.1002/2017GL073931/abstract
DOI10.1002/2017GL073931
StartPage

2017GL073931

Short TitleGeophys. Res. Lett.