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. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Motivation, background, and overview of experimental design. . . . . . . . . . . . . . . . . . . . 1 Expedition 327 CORK holes and CORK mechanical and hydraulic features. . . . . . . . . 3 Expedition 327 CORK sensors and sampling . . 6 Configuration of Expedition 327 CORKs . . . . . 9 Status of CORKs installed before Expedition 327 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Plans for ongoing and future experiments . . 13 Acknowledgments. . . . . . . . . . . . . . . . . . . . . . 13 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Tables. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 1Fisher, A.T., Wheat, C.G., Becker, K., Cowen, J., Orcutt, B., Hulme, S., Inderbitzen, K., Haddad, A., Pettigrew, T.L., Davis, E.E., Jannasch, H., Grigar, K., Aduddell, R., Meldrum, R., Macdonald, R., and Edwards, K.J., 2011. Design, deployment, and status of borehole observatory systems used for single-hole and cross-hole experiments, IODP Expedition 327, eastern flank of Juan de Fuca Ridge. In Fisher, A.T., Tsuji, T., Petronotis, K., and the Expedition 327 Scientists, Proc. IODP, 327: Tokyo (Integrated Ocean Drilling Program Management International, Inc.). doi:10.2204/iodp.proc.327.107.2011 2Expedition 327 Scientists’ addresses. 3Mohr Engineering Division, Stress Engineering Services, Houston TX 77041, USA. 4Pacific Geoscience Centre, Geological Survey of Canada, Sidney BC V8L 4B2, Canada. 5Monterey Bay Aquarium Research Institute, Moss Landing CA 95039, USA. 6Integrated Ocean Drilling Program, Texas A&M University, College Station TX 77845, USA. 7Department of Earth Sciences and Department of Biological Sciences, University of Southern California, Los Angeles CA 90089, USA. Abstract Integrated Ocean Drilling Program (IODP) Expedition 327 installed two new subseafloor borehole observatory systems (“CORKs”) in 3.5 m.y. old upper ocean crust on the eastern flank of Juan de Fuca Ridge in Holes U1362A and U1362B. Expedition 327 participants also recovered part of an instrument string previously deployed in a CORK in Hole U1301B and deployed a short replacement string. These observatories are part of a network of six CORKs that was designed to monitor, sample, and complete multidisciplinary cross-hole experiments. We present an overview of project goals and describe the design, construction, and deployment of new CORK systems. We also provide an update on the status of preexisting CORK systems as of the start of Expedition 327. Additional CORK servicing and sampling are scheduled for summer 2011 and 2012, including a long-term free-flow perturbation experiment that will test the large-scale directional properties of the upper ocean crust around the observatories. Motivation, background, and overview of experimental design Long-term borehole observatory systems Subseafloor borehole observatory systems (“CORKs”) are designed to (1) seal one or more depth intervals of a borehole so that thermal, pressure, chemical, and microbiological conditions can equilibrate following the dissipation of drilling and other operational disturbances; (2) facilitate collection of fluid and microbiological samples and temperature and pressure data using autonomous samplers and data logging systems; and (3) serve as longterm monitoring points for large-scale crustal testing, including formation response to perturbation experiments (Becker and Davis, 2005; Davis et al., 1992a; Wheat et al.). The development of CORK systems was motivated by the desire to address a broad range of scientific objectives that have been the focus of scientific ocean drilling for decades, particularly those associated with submarine hydrogeology, lithospheric and hydrothermal fluid evoludoi:10.2204/iodp.proc.327.107.2011 A.T. Fisher, C.G. Wheat, et al. CORK design, deployment, and status tion, tectonic processes and geohazards, and the nature of the deep microbial biosphere. In many cases, CORKs provide the only available technology for collecting data and samples that are essential for developing a process-based understanding of these subseafloor systems. The CORKs developed for Integrated Ocean Drilling Program (IODP) Expedition 327 share features with systems deployed during earlier drilling expeditions, particularly Ocean Drilling Program (ODP) Leg 205 and IODP Expedition 301. However, substantial modifications were made to the Expedition 327 CORK designs on the basis of specific technical and scientific goals of planned experiments and on experience gained since Expedition 301. In this paper, we describe the design and deployment of two new CORK systems during Expedition 327. We also provide a status update on CORK systems deployed during ODP Leg 168 and IODP Expedition 301, reporting on how they were configured as of the start of Expedition 327. Finally, we describe plans for using these systems over the next several years during a series of multidisciplinary experiments. We begin with a brief overview of the motivation for Expedition 327 and related (earlier) drilling and nondrilling expeditions and experiments. ODP Leg 168 and IODP Expeditions 301 and 327 and related experiments During ODP Leg 168 a transect of eight sites was drilled across 0.9–3.6 m.y. old seafloor east of Juan de Fuca Ridge to collect sediment, rock, and fluid samples; determine thermal, geochemical, and hydrogeologic conditions in basement; and install four CORK observatories in the upper crust (Davis, Fisher, Firth, et al., 1997). Two of these CORKs were placed in 3.5–3.6 m.y. old volcanic oceanic crust near the eastern end of the drilling transect in Holes 1026B and 1027C (Fig. F1). Expedition 301 returned to this area, drilled deeper into basement at Site U1301 (Fig. F1), and conducted single-hole experiments; sampled sediment, basalt, and microbiological materials; replaced the observatory in Hole 1026B; and established two multilevel observatories in Holes U1301A and U1301B for use in long-term cross-hole experiments (Fisher et al., 2005). The primary goals of Expedition 327 were to (1) drill two new basement holes at Site U1362 (Fig. F1), core and wireline log one of these holes across a depth range of 100–360 meters subbasement (msb), conduct a 24 h pumping test, initiate a tracer-injection experiment, and install multilevel CORKs; (2) recover the existing CORK installed in Hole 1027C, deepen the hole by 40 m, and install a new multilevel CORK with instrumentation; and (3) recover and replace the instruProc. IODP | Volume 327 ment string deployed in the CORK in Hole U1301B. Work in Hole 1027C could not be completed during Expedition 327, but other primary and secondary objectives were achieved (see the “Expedition 327 summary” chapter). Considerable time and resources were applied between Expeditions 301 and 327 to service the CORK observatories in Holes 1026B, 1027C, U1301A, and U1301B. The samplers and loggers deployed in the Expedition 301 CORKs had operational life spans of 4–6 y; all of the seafloor and subseafloor instruments originally installed in these systems had to be replaced prior to the start of Expedition 327 so that these systems could be used to monitor singleand cross-hole response for several years following drillship operations. In addition, the CORKs installed in Holes U1301A and U1301B during Expedition 301 were not sealed as intended (Fisher et al., 2005), and data and samples collected during subsequent remotely operated vehicle (ROV) and submersible servicing operations showed that both observatory systems were leaking (Davis et al., 2010; Fisher et al., 2008). Several attempts were made to seal these systems using cement delivered initially with a submersible, and eventually with the R/V JOIDES Resolution during IODP Expedition 321T (Fisher and IODP Expedition 321T Scientific Party, 2010). Experimental borehole configurations During Leg 168, Hole 1026B was drilled to 295 meters below seafloor (mbsf), cased across the sediment/basement interface, and extended to 48 msb (Shipboard Scientific Party, 1997). Upper basement was unstable in this location, and it was necessary to deploy an old piece of drill pipe as a liner across uppermost basement to help keep the hole open for subsequent monitoring and fluid sampling. The original CORK installed in Hole 1026B included a data logger, pressure sensors, thermistors at multiple depths, and a fluid sampler; all were recovered in 1999 except for the fluid sampler and sinker bar, which were stuck in the hole. Prior to the initial CORK installation in 1996, the hole produced water at a rate of ~100 L/min (Fisher et al., 1997); after the CORK installation, flow persisted at ~3 L/min until a 1⁄2 inch valve was opened for microbiological sampling in 1997, at which time flow increased to ~8 L/min (Davis and Becker, 2002). When the original data logger was removed in 1999, warm (~64°C) altered basement fluid flowed rapidly (at an unknown rate) up through the 4 inch inside diameter (ID) logger landing seat until the full CORK body was replaced during Expedition 301 in summer 2004. The instrument string deployed in the new Hole 1026B CORK was recovered and replaced with a new thermistor string, fluid samplers, and microbio-

proceedings of the integrated ocean drilling program. expedition reports/proceedings of the integrated ocean drilling program

Design, deployment, and status of borehole observatory systems used for single-hole and cross-hole experiments, IODP Expedition 327, eastern flank of Juan de Fuca Ridge