Previous   |   Next

doi:10.2204/iodp.pr.327.2010

Preliminary assessment of expedition achievements

Site U1362

Drilling and coring objectives were fully achieved at Site U1362; however, there were challenges, and hole conditioning occupied much more time than anticipated. Core recovery in basement (~30%) is consistent with recovery from the same area during Expedition 301 and with recovery in the uppermost few hundred meters of young crust drilled during other expeditions. The lithostratigraphy developed for Hole U1362A is somewhat different from that developed for Hole U1301B, located only 800 m to the south (Fig. F9). Compared to Hole U1301B, core from Hole U1362A contains considerably greater fractions of sheet flows and basalt flows (called "massive basalt" and "basalt lava," respectively, for Hole U1301B) and evidence for more extensive and higher temperature hydrothermal alteration. Hole U1362A also contains less hyaloclastite breccia; however, only five coherent pieces of this rock type were recovered from Hole U1301B, and it seems likely that much more of this fragile rock type was present but not recovered from the formation in both locations.

A comparison of caliper logs and apparent penetration rates from Holes U1362A, U1362B, and U1301B suggests that there is some along-strike, lateral continuity in major basement units (Fig. F14). The uppermost 100 m of basement in all holes at Sites U1301 and U1362 was drilled without coring using a 14¾ inch drill bit, and the lower parts of Holes U1362A and U1362B were drilled with a 9⅞ inch drill bit rather than a coring bit, so quantitative comparison of penetration rates in individual holes can be difficult. Tides also influence both apparent penetration rates and recovery of individual cores in basement (Fig. F15). It may take 2–6 h to cut a 9.5 m basement core, and sea level in the Expedition 327 work area can change by 1–3 m during this time. If the ship experiences a rising tide while drilling, some of the apparent penetration is a result of lowering the pipe as needed to keep weight on the bit. The opposite occurs when coring during a falling tide, making penetration appear to be less than it really is (as occurred with Core 327-U1362A-17R, which had an apparent recovery >100%; Fig. F15B). Over the length of an expedition, tidal influences generally average out, but penetration rates while coring or drilling are calculated using relatively short time intervals (minutes to hours), so tidal information is certainly mixed in with the penetration rate calculations made from rig instrumentation data. Despite these caveats, the generally positive correlation between penetration rate and hole diameter suggests that the former is a useful indicator of lithologic character. For example, the uppermost 100 m in all basement holes was drilled relatively quickly at Sites U1301 and U1362, consistent with the rubbly and oversized character of the resulting boreholes and difficulties encountered when deploying 10¾ inch casing (Fig. F14).

Packer testing in Hole U1362A was partly successful, and tests were completed at the most important setting location in open hole (the same depth at which CORK packers were set). Unfortunately, the packer element was damaged either during this initial inflation and/or prior to the start of testing when the drill string was lowered into the hole to check for fill and bridges that could impede CORK deployment. Packer data will require postcruise processing, but preliminary examination of the data suggests that the lower ~90 m of Hole U1362A is about as permeable as the lower ~100 m of Hole U1301B.

A 24 h pumping and tracer injection experiment was completed in Hole U1362B (Fig. F10), and these data also indicate generally high permeability in the formation surrounding the borehole. The pressure record will require considerable processing to account for tides and changes in fluid density associated with switching from freshwater to saltwater and with the injection of additional salts as part of the tracer experiment. Rig floor and stinger fluid samples were collected during tracer injection, and shore-based analysis will be required to develop a detailed history of injectate chemistry and particle density during the test. Pressure data and chemical samples will be collected from CORKs in this area in Summer 2011, which will provide the first information from scientific ocean drilling on hole-to-hole solute and particle velocities.

Two new CORK observatories were successfully installed at Site U1362 (Fig. F11), but no scientific information will be recovered from these systems until ROV servicing in Summer 2011. Experience during Expedition 327 confirms the benefit of having sufficient weight on the bottom of long CORK casing strings (three drill collars, ~10,000 lb) to assist with "pulling" the bottom of the CORK casing into the holes. Despite difficult hole conditions, we had no problem setting either CORK in the hole during the final stages of deployment.

However, deploying these CORKs required considerably more time than was originally allocated for several reasons. First, we spent much more time drilling, reaming, and cleaning Holes U1362A and U1362B than planned, as was required to ensure that the CORKs could be deployed once they were made up and lowered from the ship into the hole. Additionally, when the swellable packers were uncrated (just prior to deployment), we discovered that the elements were too large to be run in the open hole. Almost a day was required during the construction of the Hole U1362A CORK to reduce the diameter of the packer elements. More time was lost when the instrument string deployed below in the Hole U1362A CORK was found to be too long (most likely because of cable stretch twice that calculated based on manufacturer specifications). Because we did not have the RS tool needed to unlatch the top plug from the CORK wellhead after it was deployed, the CORK itself had to be returned to the ship to recover, shorten, and redeploy the instrument string and lower the CORK back to the seafloor. We had additional difficulty deploying the instrument string and top plug in the Hole U1362B CORK, which might have been avoided if the top plug had been fit-tested in the CORK prior to deployment. Part of the difficulty with string deployment originated with the hammer-shear release system (the same system used during Expedition 301, when it also was problematic), which should be replaced with an electronic release for future CORK expeditions. We also had problems deploying the ROV landing platform on the Hole U1362A CORK because the protective bolt installed above the packer inflation line was too long, creating an upset for the platform delivery system. Finally, we had repeated problems with the subsea camera system, which failed during several deployments and had to be recovered for repairs.

Site U1301

We were pleased to recover five of the autonomous temperature loggers deployed in Hole U1301B during Expedition 301 and to learn that thermal conditions in Hole U1301B are recovering toward natural conditions. This indicates that the cementing effort during Expedition 321T was successful in sealing the borehole after five years of cold bottom water flowing down the casing and into basement. However, the same cementing effort apparently fouled two of the three pressure lines or gauges that monitor conditions at depth below this CORK (as determined from data downloads during Summer 2010 CORK servicing). In addition, more instruments were left in Hole U1301B than were recovered, including additional temperature loggers, OsmoSamplers, and two microbiological growth experiments. Some of these instruments might have been recovered had a weak link been used above the sinker bar at depth on the original instrument cable, although we do not know precisely where the cable was fouled at depth, and all of the OsmoSamplers and microbial experiments were deployed in unstable open hole. Lessons learned from this experience, particularly the 2009 instrument recovery attempt from the Atlantis, guided planning for Expedition 327, including the placement of all downhole instruments inside coated and perforated casing.

Site 1027

The inability to complete any of our planned research activities in Hole 1027C was the greatest disappointment of Expedition 327. Initially, we attempted to use the wrong CORK recovery tool. Because we did not have the right CORK recovery tool with us at sea, considerable additional time was spent fabricating a tool and making a second recovery attempt. This attempt was also unsuccessful, and we abandoned the CORK recovery effort and focused on the remaining high-priority objectives of Expedition 327.

An ROV servicing expedition to this area is scheduled for Summer 2011, and researchers will prepare to recover the existing data logger and retrofit the Hole 1027C CORK with a new coupler and pressure logger and gauges before beginning the 1–2 year long free-flow cross-hole experiment. However, we missed the opportunity to deepen Hole 1027C, emplace a multilevel observatory, and instrument this system with fluid and microbiological sampling experiments.

Site U1363

Primary coring, sampling, and measurement objectives were achieved during the final days of Expedition 327 at Site U1363. Five holes were cored in four locations at this site. Additional holes were drilled as needed to determine basement depths and space out cores to optimize recovery of material near the sediment/basement interface. Successful temperature measurements were made in all holes. Both coring and temperature measurements were challenging because of the unstable nature of unconsolidated sandy turbidites. Preliminary analyses of temperature data and geochemical data from sedimentary pore fluids suggest that we successfully captured variations in fluid evolution associated with recharge through Grizzly Bare outcrop and subsequent regional flow to the north.

Education and outreach

Sailing multiple educators as a team provided a unique opportunity to create innovative science communication products with a critical mass of dedicated individuals. Preliminary data show an increase of 370 JOIDES Resolution Facebook fans (highest single-expedition increase) and >590 monthly active fans, plus an additional 120 fans interacting with the French page. Facebook usage peaks can be correlated with photograph and video posts, important research activities, and live video events for schools and museums. Further analysis of the Web sites and postexpedition user surveys will be completed postcruise to provide additional quantifiable metrics of impact from Expedition 327 EOC activities.

EOC team members were asked to reflect on their experiences in written form twice during the expedition, followed by a video narrative and written evaluation during the final weeks. Team members were asked to include a scientist or ship staff member in the video to discuss their mutual learning. The videos will be viewed and analyzed first by USIO outreach personnel, who will consult and share findings with the EOC team leader.

The synthesis of new learning will also be assessed by the quality and depth of the blogs (which equate with journaling) and team member projects. We will compare and contrast this new model for collaborative shipboard teaching, learning, and outreach with School of Rock and the onboard education officer program. Finally, a follow-up survey using phone interviews will be conducted in October and November 2010 to assess scientist participation, perceptions, and learning through the collaborative EOC/science partnership.

Two abstracts focusing on Expedition 327 EOC activities were submitted during the cruise for the Fall 2010 meeting of the American Geophysical Union, and two peer-reviewed publications delineating both the extent and nature of EOC preparation, shipboard activities, and metrics of success are planned.

Top of page   |   Previous   |   Next