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doi:10.2204/iodp.proc.337.102.2013 Methods1Expedition 337 Scientists2IntroductionThis chapter documents the methods used for shipboard measurements and analyses during Integrated Ocean Drilling Program (IODP) Expedition 337. During Expedition 337, we conducted riser drilling from 646 to 2466 m drilling depth below seafloor (DSF) in IODP Hole C0020A, which had been suspended for six years since initial drilling during the D/V Chikyu shakedown cruise (Expedition CK06-06) in 2006. During riser drilling operations, a wide range of data and 32 sediment cores were retrieved from selected intervals of high interest. Circulating riser drilling mud was monitored routinely; gas from drilling mud was analyzed online in a newly constructed mud-gas monitoring laboratory. Cuttings were sampled for shipboard and shore-based analyses. Wireline logging and in situ fluid sampling and analysis were conducted to fill the noncored interval gaps. Reference depthsDepths of each measurement or sample are reported relative to both the drilling vessel rig floor (rotary table) and the seafloor (see Table T1). These depths are determined by drill pipe and wireline length and are correlated with each other by use of distinct reference points. Drilling engineers refer to pipe length when reporting depth and report this as drilling depth below rig floor (DRF) in meters. Core depths are based on the drilling depth below rig floor to the top of the cored interval and curated length of the recovered core. Core depths are converted to core depth below seafloor, Method B (CSF-B), in which overlapping sections are compressed when recovery is >100% (IODP Depth Scales Terminology, www.iodp.org/program-policies/). Cuttings and mud depths are reported as mud depth below rig floor (MRF), based on DRF and the calculated lag depth of the cuttings (see below for further details). In referring to wireline logging results, depths are initially reported as wireline log depth below rig floor (WRF). Wireline logging depths are corrected relative to DRF using a known reference datum, such as the seafloor (“mudline”) or the base of the casing (“casing shoe”), and relative to each logging data set down the borehole, including tool speed corrections where appropriate. These corrected depths are then reported as wireline log matched depth below seafloor (WMSF) (see “Downhole logging” for further details). The depths reported in depths below rig floor (DRF, MRF, and WRF) are converted to depths below seafloor (DSF or CSF-B, mud depth below seafloor [MSF], and WMSF, respectively) by subtracting water depth and the height of the rig floor from the sea surface, with corrections relative to DRF where appropriate (Fig. F1). These depths below seafloor (DSF, CSF-B, MSF, and WMSF) are therefore all equivalent. Seismic depths are reported in either time (s) or depth (m). For time sections, a two-way traveltime (s) scale is used below sea level. For depth sections, seismic depth below seafloor (SSF) or seismic depth below sea level (SSL) are expressed in meters. Cuttings and mud depthsDuring riser drilling, drilling mud circulates within the riser pipe and the borehole between the drillship and the bottom of the hole. As the drill bit cuts through the formation, the fragments (i.e., cuttings) are suspended in the drilling mud and carried with the formation fluid and gas back to the ship. A cuttings sample is assumed to be a representative mixture of rock fragments and sediments from a given sample interval. The time between when the formation is cut by the drill bit and when these cuttings arrive at the ship is known as the “lag time,” which is a function of drilling mud pumping rate and annular mud volume, and is used to calculate the “lag depth.” At a constant pump rate, lag time and lag depth both increase as the hole is deepened and the volume of circulating mud increases. All of the depths recorded for cuttings and mud gas at Site C0020 have been corrected for this lag. Numbering of sites, holes, cores, sections, and samplesSites drilled by the Chikyu are numbered consecutively from the first site with a prefix “C.” A site refers to one or more holes drilled while the ship is positioned within 300 m of the first hole. The first hole drilled at a given site is assigned the site number modified by the suffix “A,” the second hole takes the site number and suffix “B,” and so forth. These suffixes are assigned regardless of recovery, as long as penetration takes place. During Expedition 337, we drilled at Site C0020 and occupied Hole C0020A. The hole was drilled by reoccupying the cased Hole C9001D, which was drilled and cased during the Chikyu shakedown cruise in 2006. Cored intervals are calculated based on an initial 9.5 m length, which is the standard core barrel length for each coring system. In addition, we specified the collection of shorter coring intervals in areas of poor recovery or slow rate of penetration (ROP) and longer coring intervals for large-diameter coring (LDC). Expansion of cores and gaps related to unrecovered material result in recovery percentages greater or less than 100%, respectively. Depth intervals are assigned starting from the depth below seafloor at which coring started (IODP coring depth scale calculated using Method A [CSF-A]; see IODP Depth Scales Terminology at www.iodp.org/program-policies/). Short cores (incomplete recovery) are all assumed to start from that initial depth by convention. Core expansion is corrected during final processing of core measurements by subtracting void spaces, subtracting exotic material, and accounting for expansion (CSF-B). A recovered core is typically divided into 1.4 m long sections that are numbered sequentially from 1 beginning at the top. During Expedition 337, whole-round core (WRC) samples were removed for time-sensitive interstitial water sampling and assigned their own section number in order to allow for rapid X-ray computed tomography (CT) scanning of time-sensitive samples. Material recovered from the core catcher was assigned to a separate section, labeled core catcher (CC), and placed at the bottom of the lowermost section of the recovered core. The LDC core was cut into 1.0 m sections on the rig floor. A full identification number for a sample from a core section consists of the following information: expedition, site, hole, core number, core type, section number, and top to bottom interval in centimeters measured from the top of the section. For example, a sample identification of “337-C0020A-2R-1, 80–85 cm,” represents a sample removed from the interval between 80 and 85 cm below the top of Section 1 of the second rotary core barrel (RCB) core from Hole C0020A, during Expedition 337 (Fig. F1). Sampling and classification of material transported by drilling mudSolid (cuttings), fluid, and gas samples were collected during riser drilling of Expedition 337. Cuttings were taken at every 10 m depth interval (DRF) from the shale shakers. Drilling mud and mud gases were also sampled from the mud circulation line. Cuttings, fluid, and mud gas were classified by drill site and hole using a sequential material number followed by an abbreviation describing the type of material. The material type identifiers are as follows:
For example, “337-C0020A-123-SMW” represents the 123rd cuttings sample recovered from Hole C0020A during Expedition 337. Identifiers of other sample material types include the following:
Cuttings handlingEvery 10 m, we routinely collected >2000 cm3 of cuttings material from the shale shaker for shipboard analysis, long-term archiving, and personal samples for shore-based postexpedition research (Fig. F2). The unwashed cuttings samples were divided as follows:
The remainder of each cuttings sample was washed gently with seawater using a sieve (250 µm opening) at the core cutting area. During sieving, a hand magnet was used to remove iron contaminants originating from drilling tools and casing. The use of the hand magnet was cancelled after magnetic minerals were abundantly observed at 1256.6 m MSF. At this point, the following samples were taken:
Lithology samples were washed with freshwater in 1 and 4 mm mesh. Samples from the 1–4 mm fraction were used for lithology description and were then sent to vacuum drying and grinding for X-ray diffraction (XRD) and X-ray fluorescence (XRF). Moisture and density (MAD) measurements used sieved samples in addition to bulk samples. The remaining portion was rinsed with freshwater. At this point a 50 cm3 sample was collected for biomarker analysis. The remaining washed samples were rinsed again with Elix water and dried at 40°C. Approximately 400 cm3 of samples, when available, was archived and sent to the core repository for future use. Sampling frequency for headspace gas analysis, community microbiology samples, and biomarker analysis was every 50 m. At each step of washing, personal samples were taken upon request. Drilling mud handlingDrilling mud samples were collected at two locations: the mud tanks and the mud ditch. Sampling at the mud tanks was carried out once a day once drilling mud was ready for use. The addition of a chemical tracer (perfluorocarbon [PFC] tracer) was also conducted at the mud tank, typically at the active tank in use for mud circulation. Samples of drilling mud that returned from the borehole were taken at the mud ditch twice a day. Both samples were used to monitor PFC tracer and hydrocarbon concentration (see “Microbiology”). Mud gas handlingMud gas was extracted from drilling mud immediately after the mud returned from the borehole. A degasser with an agitator was installed on the bypass mud flow line, and the gas extracted in the degasser chamber was pumped to the mud-gas monitoring laboratory via a polyvinyl chloride (PVC) tube. Analysis in the unit is described in “Organic geochemistry.” In situ fluid sample handlingFormation fluid samples were collected by the Schlumberger Quicksilver probe and In Situ Fluid Analyzer (IFA) installed in the wireline downhole tool (see “Downhole logging”). The fluid samples were collected in a single-phase multisample chamber (SPMC) at depth and were then transferred shipboard to Single-Phase Sample Bottles (SSBs) using Schlumberger’s sample transfer system. The SSBs were transferred to the laboratory, and the sample fluid was extracted to a glass vacuum bottle. Dissolved gas was collected in a separate sample bottle during the fluid transfer. Details of the Quicksilver probe are described in “Downhole logging.” Core handlingTwo types of coring tools were used: standard IODP (RCB) core with a plastic liner 6.6 cm in diameter and an industry-type (LDC) core with an aluminum liner 10 cm in diameter. In this report, the former is referred to as IODP core and the latter as LDC core. IODP and LDC cores were usually cut into 1.4 m sections at the core cutting area and 1.0 m sections at the drill floor, respectively. Figure F3 shows the basic flow chart of core processing. A small volume (~5 cm3) of sample was taken for micropaleontology from the core catcher section. Some syringe samples were taken at freshly cut section ends for headspace gas analysis. Considering the time, temperature, and redox sensitivity of analyses, the WRC samples were fast-tracked to the core cutting area and immediately transferred to the laboratory. These included
The sections were examined by X-ray CT scan and processed as WRC samples. The community WRC sample was divided into subsamples for contamination tests using PFC tracer; cell count; DNA analysis; biomarker analysis; MAD; carbon, sulfur, and nitrogen content; inorganic carbon; and Rock-Eval analysis. A part of the community whole round was subsampled for shore-based microbiological and biogeochemical analyses. All other sections were sealed with end caps with a slit and brought to the core processing deck. The sections were first placed in air-barrier ESCAL bags (Mitsubishi Gas Chemicals, Co., Japan) and vacuum-sealed with 3× N2 flush. The anaerobically packed core sections were stored at room temperature (~23°C) prior to subsequent nondestructive measurement and WRC sampling. Based on the temperature gradient of 22.5°C/km in this area (Osawa et al., 2002), in situ temperature of coring depths is similar to or higher than that of the core processing deck. Flushing the samples with N2 is very important for maintaining the activity of strictly anaerobic microbial components (e.g., methanogens). After the anaerobic packing of cored sections, the cored materials were examined by X-ray CT scan and whole-round multisensor core logger (MSCL-W). WRC samples were then cut out in the quality assurance/quality control (QA/QC) laboratory and stored under appropriate conditions or used for shipboard analyses. After WRC sampling, the core sections were split into working and archive halves. Digital images of archive-half sections were taken with the photo image logger (MSCL-I) before visual core description by sedimentologists and color reflectance measurement was carried out by the color spectroscopy logger (MSCL-C). Thermal conductivity measurements were performed on a sample from each core using the half-space method. Discrete cubes for P-wave velocity and impedance analysis were sampled from the working halves. Additional samples were taken for MAD, XRD, and XRF analyses. All half-round core sections were again vacuum-sealed in ESCAL bags with 3× N2 flush and transferred to cold storage. After the expedition, all cores were transported under cool temperature for archiving at the Kochi Core Center (KCC) in Kochi, Japan. LDC core sections were capped with rubber end caps and brought to the laboratory. In most sections, core material could be pushed out from the aluminum core liner and transferred to a plastic tray. The core material on the tray was immediately vacuum-wrapped in an ESCAL bag after N2 flush. Core material of two sections, however, was stuck in the aluminum core liner. In those cases, two sides of aluminum liner were cut lengthwise using the rotary saw of the core splitter to transfer the core material. After wrapping in an ESCAL bag, LDC cores were handled in a work flow identical to the standard IODP cores. |
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