In situ stress magnitude and rock strength in the Nankai accretionary complex: a novel approach using paired constraints from downhole data in two wells

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dc.citation.articleNumber123en_US
dc.citation.journalTitleEarth, Planets and Spaceen_US
dc.citation.volumeNumber68en_US
dc.contributor.authorHuffman, K.A.en_US
dc.contributor.authorSaffer, D.M.en_US
dc.contributor.authorDugan, B.en_US
dc.date.accessioned2017-03-07T18:24:16Zen_US
dc.date.available2017-03-07T18:24:16Zen_US
dc.date.issued2016en_US
dc.description.abstractWe present a method to simultaneously constrain both far-field horizontal stress magnitudes (S hmin and S Hmax) and in situ rock unconfined compressive strength (UCS), using geophysical logging data from two boreholes located 70 m apart that access the uppermost accretionary prism of the Nankai subduction zone . The boreholes sample the same sediments and are affected by the same tectonic stress field, but were drilled with different annular pressures, thus providing a unique opportunity to refine estimates of both in situ stress magnitudes and rock strength. We develop a forward model to predict the angular width of compressional wellbore failures (borehole breakouts), and identify combinations of S Hmax and UCS that best match breakout widths observed in resistivity images from the two boreholes. The method requires knowledge of S hmin, which is defined by leak-off tests conducted during drilling. Our results define a normal to strike-slip stress regime from 900 to 1386 m below seafloor, consistent with observations from seismic and core data. Our analysis also suggests that in situ values of UCS are generally slightly lower that commonly assumed on the basis of published empirical relations between UCS and P-wave velocity.en_US
dc.identifier.citationHuffman, K.A., Saffer, D.M. and Dugan, B.. "In situ stress magnitude and rock strength in the Nankai accretionary complex: a novel approach using paired constraints from downhole data in two wells." <i>Earth, Planets and Space,</i> 68, (2016) Springer Open: http://dx.doi.org/10.1186/s40623-016-0491-4.en_US
dc.identifier.doihttp://dx.doi.org/10.1186/s40623-016-0491-4en_US
dc.identifier.urihttps://hdl.handle.net/1911/94024en_US
dc.language.isoengen_US
dc.publisherSpringer Openen_US
dc.rightsThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.en_US
dc.rights.urihttps://creativecommons.org/licenses/by/4.0/en_US
dc.subject.keywordNankai Troughen_US
dc.subject.keywordIn situ stressen_US
dc.subject.keywordUnconfined compressive strengthen_US
dc.subject.keywordBorehole breakouten_US
dc.subject.keywordIODPen_US
dc.titleIn situ stress magnitude and rock strength in the Nankai accretionary complex: a novel approach using paired constraints from downhole data in two wellsen_US
dc.typeJournal articleen_US
dc.type.dcmiTexten_US
dc.type.publicationpublisher versionen_US
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