Premium
Fracture hydromechanical response measured by fiber optic distributed acoustic sensing at milliHertz frequencies
Author(s) -
Becker M. W.,
Ciervo C.,
Cole M.,
Coleman T.,
Mondanos M.
Publication year - 2017
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1002/2017gl073931
Subject(s) - displacement (psychology) , fracture (geology) , borehole , materials science , acoustics , geology , distributed acoustic sensing , optical fiber , oscillation (cell signaling) , fiber optic sensor , optics , composite material , geotechnical engineering , fiber , physics , psychology , biology , psychotherapist , genetics
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 H 2 O). 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.