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doi:10.2204/iodp.proc.332.103.2011

Site C0010¹

Expedition 332 Scientists²

Background and objectives

Integrated Ocean Drilling Program (IODP) Site C0010, drilled during IODP Expedition 319, is located on the continental slope near the updip terminus of the megasplay fault, ~3.5 km north of previously drilled and cored IODP Site C0004 (Expedition 319 Scientists, 2010) (Figs. F1, F2). The latter was drilled with measurement while drilling and a limited suite of logging-while-drilling tools (geoVISION resistivity tool and gamma ray) to a total depth of 555 meters below seafloor (mbsf) and cased to 515 mbsf in preparation for later installation of a permanent long-term borehole monitoring system (LTBMS) (Fig. F3) (Expedition 319 Scientists, 2010). The casing included two casing screens that span the megasplay fault at ~407 mbsf, which provide hydraulic access to the fault zone for monitoring of pore fluid pressure and temperature and fluid sampling. The borehole was instrumented on 23 August 2009 by setting a Baker Hughes A3 Lok-Set retrievable casing packer seal (bridge plug) inside the casing above the screens at ~364 mbsf, with a third-party temporary instrument package (SmartPlug) deployed below the seal, in order to maximize scientific use of the borehole in the intervening time between drilling and future permanent observatory installation (Fig. F3) (Expedition 319 Scientists, 2010).

The SmartPlug measured pore pressure and temperature at the megasplay fault zone, as well as a hydrostatic reference at the seafloor. This is done by using two pressure transducers: one downward-looking sensor open to the megasplay fault through the casing screens and one upward-looking sensor open to the borehole above the bridge plug and in hydraulic communication with the ocean (Expedition 319 Scientists, 2010). Additionally, four temperature sensors, one at each pressure gauge for temperature compensation, one platinum chip sensor, and one stand-alone miniature temperature logger (MTL), provide continuous temperature measurements. The data recorder was set with a 1 min sampling interval for pore pressure and platinum chip temperature measurements. The MTL was set to a 30 min sampling interval, and clocks were synchronized between the autonomous MTL logger and the SmartPlug data logger.

The operational and scientific objectives for Site C0010 during IODP Expedition 332 were to:

• Retrieve the SmartPlug and the packer assembly and download the data recorded during their deployment. The SmartPlug is a simple, robust, and inexpensive instrument for temporary borehole monitoring that may have value for future IODP expeditions. One key goal was to assess the performance of the SmartPlug after deployment through the strong Kuroshio Current, as a “proof of concept.” Additionally, the SmartPlug represents the first observatory placement in the Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) program. Thus, the primary scientific objective is future shore-based analysis of the pore pressure and temperature data to constrain ambient conditions and to investigate transient behavior if observed. The downloaded data will also be used to assess the efficacy of hydraulic isolation of the screened interval from the overlying ocean in order to carefully plan future LTBMS installation and completion strategy at this site.

• Deploy an upgraded version of the SmartPlug, the “GeniusPlug.” The GeniusPlug is identical to the SmartPlug but also includes a 30 cm long extension containing an osmotically driven fluid sampler (OsmoSampler) to collect a time series of pore fluid samples from the megasplay fault zone for as long as 2 y (Jannasch et al., 2003) and a flow-through osmo colonization system (FLOCS) microbiology unit that consists of chambers filled with mineral and sediment substrates for examination of in situ microbial growth under controlled conditions (Orcutt et al., 2010; Wheat et al., 2011). Recovery of the GeniusPlug is planned at the time of LTBMS installation at Site C0010, as part of future NanTroSEIZE operations.

¹ Expedition 332 Scientists, 2011. Site C0010. In Kopf, A., Araki, E., Toczko, S., and the Expedition 332 Scientists, Proc. IODP, 332: Tokyo (Integrated Ocean Drilling Program Management International, Inc.). doi:10.2204/​iodp.proc.332.103.2011

² Expedition 332 Scientists’ addresses.

Publication: 11 December 2011
MS 332-103

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