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Effect of water on critical and subcritical fracture properties of Woodford shale
Author(s) -
Chen Xiaofeng,
Eichhubl Peter,
Olson Jon E.
Publication year - 2017
Publication title -
journal of geophysical research: solid earth
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.983
H-Index - 232
eISSN - 2169-9356
pISSN - 2169-9313
DOI - 10.1002/2016jb013708
Subject(s) - fracture toughness , materials science , oil shale , composite material , fracture (geology) , hydraulic fracturing , shear (geology) , mineralogy , geotechnical engineering , geology , paleontology
Subcritical fracture behavior of shales under aqueous conditions is poorly characterized despite increased relevance to oil and gas resource development and seal integrity in waste disposal and subsurface carbon sequestration. We measured subcritical fracture properties of Woodford shale in ambient air, dry CO 2 gas, and deionized water by using the double‐torsion method. Compared to tests in ambient air, the presence of water reduces fracture toughness by 50%, subcritical index by 77%, and shear modulus by 27% and increases inelastic deformation. Comparison between test specimens coated with a hydrophobic agent and uncoated specimens demonstrates that the interaction of water with the bulk rock results in the reduction of fracture toughness and enhanced plastic effects, while water‐rock interaction limited to the vicinity of the propagating fracture tip by a hydrophobic specimen coating lowers subcritical index and increases fracture velocity. The observed deviation of a rate‐dependent subcritical index from the power law K ‐ V relations for coated specimens tested in water is attributed to a time‐dependent weakening process resulting from the interaction between water and clays in the vicinity of the fracture tip.