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doi:10.2204/iodp.proc.332.102.2011

SmartPlug/GeniusPlug

Instrumented retrievable casing packer (temporary monitoring system)

As part of operations in Holes C0010A and C0002G, a mechanically set retrievable packer (Baker Hughes A3 Lok-Set) equipped with a small instrument package to monitor pore pressure and temperature was installed inside a 10⅝ inch casing string during Expedition 319 (see Saffer et al., 2009). This so-called SmartPlug was set at 374 mbsf immediately above a screened casing interval within the shallow megasplay fault zone. The instrument package includes a data logger, temperature sensor within the data logger housing, a self-contained temperature sensor, and two pressure gauges: one “upward-looking” and one “downward-looking.” The pressure sensors monitor (1) below the packer seal in a screened interval that is open to the fault zone and (2) above the packer seal to serve as a hydrostatic reference open to the overlying water column. Both temperature sensors are just below the packer (Fig. F3). The SmartPlug instruments developed in 2009 can monitor formation pore pressure and temperature from the time the bridge plug is set until the instruments are retrieved at the beginning of permanent riserless observatory installation operations.

In 2010, an upgraded version of the SmartPlug, termed GeniusPlug, was developed. It relies on the SmartPlug design but replaces the end cap (the bullnose) with a second unit of the same diameter and adds 30 cm to the length of the plug (Fig. F4). The GeniusPlug hosts a continuous fluid sampler (OsmoSampler) (Jannasch et al., 2004) and a microbiological colonization experiment (flow-through osmo colonization system [FLOCS]) (Orcutt et al., 2010).

General description

The SmartPlug instruments built for Expedition 319 remain unchanged, given their robust design and uncomplicated handling, so the GeniusPlugs follow the same design. Structurally, each unit includes a hollow-bore 3.5 inch EU 8rd box-end threaded coupling at the upper end, which mates with the lower end of the Baker Hughes packer supplied by the Center for Deep Earth Exploration, and an outer O-ring sealed structural shell that is designed to withstand the loads encountered during hole reentry operations (Fig. F5). Housed inside are a high-precision pressure period counter with a 12.8 MHz real-time clock (RTC-PPC system, resolving ~10 parts per billion [ppb] of full-scale pressure, or ~0.7 Pa), a 24-bit/channel analog to digital (A/D) converter and data logger (designed and built by Bennest Enterprises, Ltd., Minerva Technologies, Ltd., and the Pacific Geoscience Centre, Geological Survey of Canada), two pressure sensors (Model 8B7000−2; Paroscientific, Inc., USA), and an independent miniature temperature logger (MTL) (Antares, Germany). Four independent temperature readings are made: (1) with the MTL, (2) with a platinum thermometer mounted on the primary data logger end cap, and (3) with each of the two pressure transducers. The inside of the structural shell is exposed to water in the cased borehole above through the internal open bore of the casing packer seal. One of the pressure sensors is connected to this volume to provide a hydrostatic reference, and the second sensor is connected to the sealed, screened borehole interval via hydraulic tubing that passes through the bottom end of the structural shell (Fig. F5). RS-422 communications with the main instrument for setting recording parameters and downloading data are conducted via a multisegment Seacon AWQ connector on the logger pressure case. Communications with the MTL are conducted through a special Antares interface and WinTemp software. The instrument frame is shock-mounted within the structural shell, and the pressure sensors are mounted with secondary shock pads within the frame (Fig. F3). Structural components are constructed with 4140 alloy steel, and pressure sensor housings and hydraulic tubing are constructed from 316 stainless steel.

The extension unit for the GeniusPlug configuration is made of the same material and further features a bulkhead to hydraulically separate the SmartPlug body from the OsmoSampler and FLOCS (Fig. F4). This way, only borehole fluid entering through the casing screens enters the lower portion of the instrument where the intakes for the OsmoSampler and FLOCS are located. These two experiments are constrained in a 7.15 inch high and 6.3 inch diameter space.

The OsmoSampler has two 2ML1 ALZET membranes that were attached to the housing with two-part epoxy (Hysol ES1902). The ends of the distilled water and saturated salt (noniodized table salt, NaCl) reservoirs are sealed with a single O-ring and held in place with a setscrew. This configuration will pump 73 mL/y at 20°C. The pump is attached to 150 m of small-bore polytetrafluoroethylene (PTFE) tubing that holds 170 mL (1.19 mm inside diameter [ID] and 2.0 mm outside diameter [OD]). The tubing was filled with 10% HCl for 5 days before it was rinsed with 18.2 MΩ water. Thus, this sampler can be deployed at 20°C for 2 y and maintain a continuous record for longer if the borehole temperature is cooler than 20°C.

The FLOCS experiment is attached to two pumps, each identical to the ones described above for the OsmoSampler. Both pumps are attached via a T-connection to double the pump rate (146 mL/y at 20°C). Likewise, these pumps are attached to 150 m of small-bore PTFE tubing that holds 170 mL and were prepared as above. At 20°C these pumps will fill the sample coil in 14 months. The pumps will continue to work because of the amount of excess salt in the pump but will only preserve the last 14 months of fluid within the sample coil. The loss of the early portion of the record was deemed acceptable because the FLOCS is filled with about 50 mL of sterile seawater that must pass through the coils before borehole fluids are collected within the coils. As this sterile seawater enters the distilled water portion of the pump, it will decrease the pump rate but only minimally, even for a 2 y deployment. The inlet was attached to a syringe filled with 18.2 MΩ water until just before deployment.

The FLOCS experiment consists of a single unit that has four chambers. All of the parts were sterilized and materials packed with sterile tools in a hood. The chamber closest to the inlet contained two grids with autoclaved rock chips (1–2 mm thick and 5 mm × 5 mm) mounted on them facing out. These two grids were separated by autoclaved glass wool and 5 mm borosilicate glass beads. Rock chips were attached to the plastic grids using “5 min epoxy.” One grid has basalt glass in the bottom portion (AT11-20-4055-B6) and basalt above it (J2-246-R2). The other grid has basalt in the bottom portion (J2-244-R4) and olivine above it. Above the grids are three chambers filled with barite, olivine, and IODP Expedition 316 sediment (Section 316-C0004D-47R-2; ~357 mbsf), respectively. These materials were crushed from bulk rocks, sieved to <250 µm, and autoclaved. PTFE mesh screens were placed inside the cassette caps to prevent rock fragments from escaping the cassette. At sea, the FLOCS was filled with ~50 mL of sterile seawater with additional seawater added to remove air bubbles. During this process, some of the sediment from the end capsule escaped. The inlet was attached to a syringe with sterile seawater until just before deployment.

Settings

The SmartPlug instruments built in 2009 were set to begin recording data at the time they were shipped from the Pacific Geoscience Centre, Canada, to Shingu Port, Japan, on 11 April 2009, and stored in Shingu until they were transported to the Chikyu via supply boat for Expedition 319. Because one of them (Instrument 82) was not deployed during the cruise, it was shipped back to Shingu and stored in a warehouse until 2010. It was loaded onto the Chikyu during the preexpedition port call on 26 October 2010 and hence contained an 18 month record of data by the time Expedition 332 began. Logging intervals for the formation and hydrostatic pressure sensors and the internal platinum thermometer were set to 1 min; at this rate and with other operational parameters as set, battery power (provided by six Tadiran TL-5137 DD primary lithium cells) is the limiting factor for operational lifetime, which is roughly 7 y, including a de-rating factor of 75% applied to full power withdrawal. The instruments are equipped with 512 MB (low power) flash memory cards, which provide storage capacity until the year 2038 at a 1 min sampling rate. The independent MTL in Instrument 82 was set to sample temperature at 60 min intervals. The main logger clock was synchronized to Universal Time Coordinated (UTC) on 11 April 2009, and the MTL clocks were set on approximately the same date. The clock of the main logger was synchronized to UTC again on 7 August 2009 prior to deployment.

The second SmartPlug was fabricated in 2010 and followed an identical design. The main difference was the somewhat faster sampling rate of 30 s, resulting in storage capacity until the year 2033. This SmartPlug is meant to be used as a backup observatory in case operations in Hole C0002G are too slow to allow an in-time deployment of the LTBMS (see “Long-term borehole monitoring system”). All configurations and potential damage during shipping were checked prior to deployment onboard the Chikyu (Fig. F5).

The GeniusPlug extension units were set up during the first weeks of Expedition 332. The first GeniusPlug was deployed only a few days after the OsmoSampler and FLOCS units were filled. For detailed set-up procedures, refer to the above text, Figure F6, and Kopf et al. (2011).

Implementation plan

During Expedition 332, it was first planned to retrieve the bridge plug/SmartPlug observatory that was installed in August 2009 (Fig. F7). Afterward, a GeniusPlug instrument was to replace the SmartPlug and monitor pressure, temperature, microbial activity, and fluid geochemical signatures in the screened interval in the shallow megasplay fault zone (Fig. F8).

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