Wellbore failures and its constraints on the in-situ stress state in the Nankai Trough accretionary prism, Site C0002, IODP Expedition 348

Author(s): Sone, H.; Jurado, M. J.; Boston, B.; Yamamoto, Yuzuru; Tobin, H. J.; Saffer, Demian M.; Hirose, T.
Author Affiliation(s): Primary:
German Research Centre for Geosciences, Helmholtz Centre Potsdam, Potsdam, Germany
Instituto de Ciencias de la Tierra, Spain
University of Hawaii at Manoa, United States
Japan Agency for Marine-Earth Science and Technology, Japan
University of Wisconsin Madison, United States
Pennsylvania State University, United States
Volume Title: AGU 2014 fall meeting
Source: American Geophysical Union Fall Meeting, Vol.2014; American Geophysical Union 2014 fall meeting, San Francisco, CA, Dec. 15-19, 2014. Publisher: American Geophysical Union, Washington, DC, United States
Note: In English
Summary: The International Ocean Discovery Program (IODP) Expedition 348 extended the borehole of Site C0002, Nankai Trough, down to over 3000 meters below sea floor (mbsf) collecting core samples and in-situ geophysical data from the inner accretionary prism. In order to investigate the in-situ stress state within the prism, we characterized the occurrence and shapes of wellbore failures as observed by resistivity image logs and sonic caliper logs collected in the vertical well of Hole C0002P. Most wellbore failures were observed in the top 70 meters of Hole C0002P (2150 to 2218.5 mbsf), where resistivity images were acquired several days after the borehole was initially exposed by previous drilling and coring runs. Wide breakouts spanning up to 140 degrees are observed in the NW/SE to NNW/SSE direction suggesting that the maximum horizontal principal stress in the cored interval is in the direction generally consistent with those observed in the shallower sections of Site C0002 from earlier expeditions. In the remaining section of the borehole below, wellbore failures are much sparse and subtle in the resistivity image possibly due to the short exposure time between drilling and image acquisition (about 2 hours). Preliminary examination suggest that these features are breakouts aligned in the direction consistent with the upper section, but examination in combination with the sonic caliper data is required for further confirmation. These observations suggest that the occurrence of breakouts exhibit significant time-dependence due to processes such as pore pressure diffusion or time-dependent rock deformation. Moreover, sonic caliper data suggests that shapes and width of the wellbore failures in the studied dataset is influenced by the formation strength anisotropy (in the horizontal direction) enhanced by the steeply dipping bedding planes (60-90 degrees). Thus, constraints on in-situ stress magnitudes will be provided through comparison of wellbore failures, borehole cross section, bedding dips, downhole mud pressure records, and formation mechanical properties.
Year of Publication: 2014
Research Program: IODP Integrated Ocean Drilling Program
Key Words: 07 Marine Geology and Oceanography; Cores; IODP Site C0002; Integrated Ocean Drilling Program; Kumano Basin; Marine sediments; NanTroSEIZE; Nankai Trough; North Pacific; Northwest Pacific; Pacific Ocean; Sediments; West Pacific
Coordinates: N331800 N331801 E1363801 E1363800
Record ID: 2015065156
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