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Title: Experimental Studies of Anisotropy on Borehole Breakouts in Mancos Shale

Journal Article · · Journal of Geophysical Research. Solid Earth
DOI:https://doi.org/10.1029/2018JB017090· OSTI ID:1515201

Abstract Measuring the size and orientation of borehole breakouts is one of the primary methods for determining the orientation and magnitudes of the in situ stresses in the subsurface. To better understand the effects of anisotropy on borehole breakouts, experiments were conducted on Mancos Shale, a finely laminated mudrock. A novel testing configuration was developed to conduct borehole breakout experiments in a standard triaxial vessel and load frame. Samples were prepared at three different orientations and deformed under 6.9 to 20.7 MPa confining pressure. The results show a variation of peak strength and breakout geometry depending on the lamination orientation. Samples deformed parallel to laminations failed at a higher maximum compressive stress than samples deformed perpendicular to laminations, which were stronger than inclined samples. These relationships are quantified by a cosine‐based failure envelope. Observed breakout shapes in perpendicular samples are V‐shaped and symmetric around the borehole, which advance as a series of fractures of increasing size into the sidewalls. In inclined samples, fractures form along weaker laminations planes and grow in an en echelon pattern towards the axial stress direction. In parallel samples, long fractures grow from the wellbore towards the axial stress direction. The observed geometries highlight potential sources of error in calculating in situ stresses from borehole breakouts.

Research Organization:
Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
Sponsoring Organization:
USDOE National Nuclear Security Administration (NNSA)
Grant/Contract Number:
AC04-94AL85000; NA0003525
OSTI ID:
1515201
Alternate ID(s):
OSTI ID: 1515791
Report Number(s):
SAND-2019-4347J; 674787
Journal Information:
Journal of Geophysical Research. Solid Earth, Vol. 124, Issue 4; ISSN 2169-9313
Publisher:
American Geophysical UnionCopyright Statement
Country of Publication:
United States
Language:
English
Citation Metrics:
Cited by: 13 works
Citation information provided by
Web of Science

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