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The interaction of propagating opening mode fractures with preexisting discontinuities in shale
Author(s) -
Lee Hunjoo P.,
Olson Jon E.,
Holder Jon,
Gale Julia F. W.,
Myers Rodrick D.
Publication year - 2015
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 - 10.1002/2014jb011358
Subject(s) - oil shale , geology , classification of discontinuities , calcite , vein , fracture (geology) , hydraulic fracturing , fracture toughness , bedding , fracture mechanics , mineralogy , materials science , composite material , geotechnical engineering , psychology , psychiatry , horticulture , biology , mathematical analysis , paleontology , mathematics
Field observations show that hydraulic fracture growth in naturally fractured formations like shale is complex. Preexisting discontinuities in shale, including natural fractures and bedding, act as planes of weakness that divert fracture propagation. To investigate the influence of weak planes on hydraulic fracture propagation, we performed Semicircular Bend tests on Marcellus Shale core samples containing calcite‐filled natural fractures (veins). The approach angle of the induced fracture to the veins and the thickness of the veins have a strong influence on propagation. As the approach angle becomes more oblique to the induced fracture plane, and as the vein gets thicker, the induced fracture is more likely to divert into the vein. Microstructural analysis of tested samples shows that the induced fracture propagates in the middle of the vein but not at the interface between the vein and the rock matrix. Cleavage planes and fluid inclusion trails in the vein cements exert some control on the fracture path. Combining the experimental results with theoretical fracture mechanics arguments, the fracture toughness of the calcite veins was estimated to range from 0.24 MPa m 1/2 to 0.83 MPa m 1/2 , depending on the value used for the Young's modulus of the calcite vein material. Measured fracture toughness of unfractured Marcellus Shale was 0.47 MPa m 1/2 .