Standard Data Processing
IODP logging
contractor: CDEX-JAMSTEC
Hole: C0009A
Expedition:
319
Location: Nankai Trough (NW Pacific Ocean)
Latitude: 33° 27.4704' N
Longitude: 136° 32.1489' E
Logging date:
Sea floor
depth (driller's): 2082.3 m LRF
Sea floor
depth (logger's): 2081.1 m WRF
Total
penetration: 3686 m DRF (1603.7 m DSF)
Total core
recovered: 74.7 m
Oldest
sediment recovered:
Late Miocene
Lithologies: Silty mud and mudstone with rare sand and volcanic ash interbeds, abundant wood/lignite fragments
Data
MWD/LWD data were acquired by Schlumberger Drilling and Measurement while wireline data
was acquired by Schlumberger. The acoustic data from the Sonic Scanner were processed by Schlumberger Data and Consulting Services (DCS). Depth-shifting was performed by CDEX logging Services. Image processing was carried out at the Borehole Research Group of the Lamont-Doherty Earth Observatory in 2011.
Logging Operations Summary
Table 1 and Figure 1 show a summary of coring and logging operations at Hole C0009A. Hole C0009A was drilled with MWD (Measurement-While-Drilling) combined with APWD (Annular Pressure While Drilling) and vertical drilling tool PowerDrive for some sections (Figure 2). MWD/APWD were used to 2795 m LRF (712.7 m LSF), while only MWD was run in the lower section to 3592 m LRF (1509.7 m LSF).
Upon completion of drilling with a 12-1/4 inch bit to 3686 m
LRF (1603.7 m LSF) and a wiper trip, preparations for wireline drilling started. The passive heave compensator (see 'Methods'
chapter in Expedition Report) was set up, the first time to be used in place of the active
heave compensator, which is typically used for riserless logging operations.
Set-up and use of this system went smoothly.
The first wireline logging consisted of the EMS-HRLA-PEX-GR
tool string (Figure 3). Density, porosity, gamma ray,
caliper, laterolog resistivity, and mud properties were measured during this
run. After several attempts the tool string could not pass beyond 1585.9 m WRF, hence the hole was logged from
that depth to the casing shoe (2785 m WRF, 703.9 m WSF), 8 m above total depth. A repeat section of 101.5 m was logged from the bottom to
3521 m WRF (1493.9 m WSF). A second wireline run was conducted wth a tool string consisting of FMI, MAST, and HNGS tools. Trouble at the oscillator unit of the wireline
unit caused delay between 3581.1 m and 3696.1 WRF (1500 and 1615 m WSF, respectively), and the tool string could not be
lowered deeper than 3662.2 m WRF (1581.1 m WSF). After several failed attempts, the tool string was run from 1581.1 m WRF to the 20-inch casing shoe( 2785 m WRF), and
a repeat section was logged between 2930.6 and 2845 m WRF (849.5 and 763.9 m WSF).
A junk basket (8-1/4" gauge ring) run was carried out after casing,
followed by walk-away, circular and zero offset VSPs with VSI-16.
Processing
Depth shift to sea floor and depth match. In order to correlate wireline logs with cores and cuttings, it is necessary to depth-shift the data to a common reference datum. It was chosen to tie all the logs to the bottom of the 20-in casing shoe at 2785 m WRF (703.9 m LSF) due to its clear appearance in all three logging runs. The 20-in casing and the bottom of the 26-inch and 17-inch holes are all clearly detected by the caliper, gamma ray, and resistivity tools used during the EMS-HRLA-PEX-GR runs, and by the caliper and gamma ray tools during the FMI/HNGS/EMS/MAST/PPS/GR runs.
The depth references are shown graphically in Figure 4. The height of the rotary table (rig floor) is 28.3 m above sea level (assuming minimal variation in this parameter during drilling operations), and the water depth is reported as 2054.0 m. The depths of the wireline logs are all tied to the drillers' depth at the 20-inch casing shoe, located at 2786.2 mDRF (= 703.9 mLSF and equal to 2785.0 mWRF). Therefore 2081.1 m (2785.0 -703.9) is subtracted from the logging depth (WRF) to give the depth below sea floor of the wireline log data corrected relative to the driller's depth.
A further comparison between the logs shows an excellent correlation and no need to perform any further fine tuning between the logs. As a results, the depths are expressed in m WMSF (referring to the matching of the
individual wireline log runs to each other), which is equivalent tom DSF.
Environmental
corrections. Corrections were applied at Schlumberger' s Tokyo Data and Consulting Service (DCS). The neutron data (HGNS) were corrected for the drilling fluid salinity and standoff, which yielded lower values and spikes in most sections. The resistivity data (HRLA) were also corrected for the high salinity drilling fluid and standoff. The density data (HRMS) are usually corrected for borehole size and standoff during the recording.
High-resolution
data. The Highly Integrated Gamma Ray from the HGNS tool was recorded with sampling rates of 5.08 cm in addition to the standard sampling rate of 15.24 cm.
Acoustic
data. Immediately after
acquisition, the sonic velocity data from the SonicScanner was processed by SchlumbergerÕs Tokyo Data and Consulting Service (DCS). The processing included extracting compressional,
shear, and Stoneley velocities using BestDT, a sonic
Quality Control
The quality of the
wireline log data is mostly assessed by cross-correlating available logs and
hole shape.
Density-neutron porositydata and micro-resistivity images are the most affected by
borehole conditions, such as the salinity of the drilling fluid, the large borehole (standoff) . Resistivity and gamma data may be degraded in large or washed out holes. Deep investigation measurements
such as resistivity and sonic velocity are least sensitive to borehole
conditions. Environmental corrections for hole size and standoff are applied to the
original data immediately after data acquisition by the field
engineer. If necessary, additional corrections and data processing are
conducted at the data and consulting centers by specialists to reduce these
effects (see 'Environmental correction' section of these notes. Data quality indicators are
shown along composite logs and lithostratigraphic units in Figure 5.
Three different calipers were run for hole diameter measurements. The 6-arm caliper from EMS provides the best indication of hole shape. In addition, the wire tension data indicates that the logging tool motion was not smooth. The caliper indicates that the borehole is quite good from the top to 3366 m WRF (1284.9 m WMSF) but is rugose and washed out below this depth.
The resistivity data below
3366 m WRF (1284.9 m WMSF) have poor to medium quality, as the five resistivity curves overlie each
other; this may have resulted from a highly fractured formation or failure to
reach the formation (Figure 5). Micro-resistivity
images from FMI are also affected by the borehole shape in the lower part of
the hole.
Due
to their high sensitivity to hole shape, density and
porosity were affected significantly below
3366 m WRF (1284.9 m WMSF). There were
unusual density values at several depths, and porosity data exhibit wide
variation throughout the measured range. Environmental effects are much to
blame for the poor quality of these data. Gamma ray data exhibit a steady trend and appear to be of acceptable quality.
This report was prepared at the Borehole Research Group of the Lamont Doherty Earth Oservatory, based on the processing notes and information provided by the logging staff scientists of Expedition 319. Additional information about the drilling and logging operations can be found in the Operations and Downhole Measurements sections of the expedition reports, Proceedings of the Integrated Drilling Program, Expedition 319.
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