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Growth of borehole breakouts with time after drilling: Implications for state of stress, NanTroSEIZE transect, SW Japan

Growth of borehole breakouts with time after drilling: Implications for state of stress, NanTroSEIZE transect, SW Japan
Growth of borehole breakouts with time after drilling: Implications for state of stress, NanTroSEIZE transect, SW Japan
Resistivity at the bit tools typically provide images of wellbore breakouts only a few minutes after the hole is drilled. In certain cases images are taken tens of minutes to days after drilling of the borehole. The sonic caliper can also image borehole geometry. We present four examples comparing imaging a few minutes after drilling to imaging from about 30 min to 3 days after drilling. In all cases the borehole breakouts widen with time. The tendency to widen with time is most pronounced within a few hundred meters below the seafloor (mbsf), but may occur at depths greater than 600 mbsf. In one example the widening may be due to reduced borehole fluid pressure that would enhance borehole failure. In the three other cases, significant decreases in fluid pressure during temporal evolution of breakouts are unlikely. The latter examples may be explained by time-dependent failure of porous sediments that are in an overconsolidated state due to drilling of the borehole. This time-dependent failure could be a consequence of dilational deformation, decrease of pore fluid pressure, and maintenance of sediment strength until migrating pore fluids weaken shear surfaces and allow spallation into the borehole. Breakout orientations, and thus estimates of stress orientations, remain consistent during widening in all four cases. In vertical boreholes, breakouts wider than those initially estimated by resistivity imaging would result in higher estimates of horizontal stress magnitudes. Because the vertical overburden stress is fixed, higher estimated horizontal stresses would favor strike-slip or thrust faulting over normal faulting.
1525-2027
Q04D09
Moore, J. Casey
bd0b255f-729e-49eb-9be4-5ef5b74da062
Chang, Chandong
d15e3522-3b8c-4e51-98c0-0f2ff59a46d8
McNeill, Lisa
1fe6a1e0-ca1a-4b6f-8469-309d0f9de0cf
Thu, Moe Kyaw
f0b2b863-deb2-4ec9-916b-b79e87e942ae
Yamada, Yasuhiro
f2e17abc-24e6-483a-b96f-5886711e1af7
Huftile, Gary
b37d12d2-34d5-4063-bd88-4970bb4a6ca7
Moore, J. Casey
bd0b255f-729e-49eb-9be4-5ef5b74da062
Chang, Chandong
d15e3522-3b8c-4e51-98c0-0f2ff59a46d8
McNeill, Lisa
1fe6a1e0-ca1a-4b6f-8469-309d0f9de0cf
Thu, Moe Kyaw
f0b2b863-deb2-4ec9-916b-b79e87e942ae
Yamada, Yasuhiro
f2e17abc-24e6-483a-b96f-5886711e1af7
Huftile, Gary
b37d12d2-34d5-4063-bd88-4970bb4a6ca7

Moore, J. Casey, Chang, Chandong, McNeill, Lisa, Thu, Moe Kyaw, Yamada, Yasuhiro and Huftile, Gary (2011) Growth of borehole breakouts with time after drilling: Implications for state of stress, NanTroSEIZE transect, SW Japan. Geochemistry, Geophysics, Geosystems, 12, Q04D09. (doi:10.1029/2010GC003417).

Record type: Article

Abstract

Resistivity at the bit tools typically provide images of wellbore breakouts only a few minutes after the hole is drilled. In certain cases images are taken tens of minutes to days after drilling of the borehole. The sonic caliper can also image borehole geometry. We present four examples comparing imaging a few minutes after drilling to imaging from about 30 min to 3 days after drilling. In all cases the borehole breakouts widen with time. The tendency to widen with time is most pronounced within a few hundred meters below the seafloor (mbsf), but may occur at depths greater than 600 mbsf. In one example the widening may be due to reduced borehole fluid pressure that would enhance borehole failure. In the three other cases, significant decreases in fluid pressure during temporal evolution of breakouts are unlikely. The latter examples may be explained by time-dependent failure of porous sediments that are in an overconsolidated state due to drilling of the borehole. This time-dependent failure could be a consequence of dilational deformation, decrease of pore fluid pressure, and maintenance of sediment strength until migrating pore fluids weaken shear surfaces and allow spallation into the borehole. Breakout orientations, and thus estimates of stress orientations, remain consistent during widening in all four cases. In vertical boreholes, breakouts wider than those initially estimated by resistivity imaging would result in higher estimates of horizontal stress magnitudes. Because the vertical overburden stress is fixed, higher estimated horizontal stresses would favor strike-slip or thrust faulting over normal faulting.

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Published date: 2011

Identifiers

Local EPrints ID: 187597
URI: http://eprints.soton.ac.uk/id/eprint/187597
ISSN: 1525-2027
PURE UUID: 7170c198-2c0d-4421-a6e6-2acad19f4242
ORCID for Lisa McNeill: ORCID iD orcid.org/0000-0002-8689-5882

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Date deposited: 17 May 2011 12:16
Last modified: 16 Nov 2021 02:39

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Contributors

Author: J. Casey Moore
Author: Chandong Chang
Author: Lisa McNeill ORCID iD
Author: Moe Kyaw Thu
Author: Yasuhiro Yamada
Author: Gary Huftile

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