IODP-MSP
drilling and logging contractor: ESO
Hole: M0029A
Expedition: 313
Location:
New Jersey (NW
Atlantic)
Latitude: 39° 31.1605 N
Longitude:
73° 24.7925 W
Logging
date: July 11 - 16,
2009
Sea
floor depth (driller's): 53.41 m DRF
Sea floor
depth (logger's):
53.26 m WRF
Total
penetration: 754.55
m DSF
Total
core recovered:
454.31 m (74.55 % of cored section)
Oldest
sediment recovered:
Early Miocene
Lithologies: Clays to gravels
The logging data was
recorded by the
Tool
string
|
Run/Pass
|
Top depth (m WSF)
|
Bottom depth (m WSF)
|
Pipe depth ( m DSF)
|
Notes
|
1. VSP
|
Through pipe
|
207.83
|
753.42
|
~755
|
3.05 m interval between shots |
2. ASGR
|
Through pipe |
0.01
|
757.31
|
~755
|
|
3. DIL45
|
Lower
|
482.87
|
723.87
|
~482
|
Merged with run 11 |
4. 2PSA
|
Lower 1
|
577.00
|
719.94
|
~482
|
Merged with run 5
|
5. 2PSA
|
Lower
2
|
482.45
|
576.94
|
~482
|
Merged with run 4 |
6. EM51
|
Lower
|
482.84
|
729.28
|
~482
|
Merged with run 13. Downlog used. |
7. ABI40
|
Lower
|
483.20
|
656.53
|
~482
|
|
8. VSP
|
Through pipe
|
12.76
|
226.12
|
~482
|
|
9. ASGR
|
Upper
|
322.22
|
348.02
|
~335
|
|
10. DIL45
|
Upper
|
340.07
|
347.47
|
~335
|
|
11. DIL45
|
Middle
|
403.67
|
488.16
|
~401
|
|
12. 2PSA
|
Middle
|
404.56
|
491.05
|
~401
|
|
13. EM51
|
Middle
|
403.67
|
528.44
|
~401
|
Merged with run 6 |
The depths
given in the table are for the processed data. The raw data may contain extra
data within the pipe: this data has been removed from the processed data files. The depths
in bold refer to top and bottom depths of files before merging
(i.e. the top and bottom depth of the final merged files are not in bold).
A complete
list of tool and log acronyms is available at http://brg.ldeo.columbia.edu/data/iodp-eso/exp313/exp_documents/iodp-eso-313-acronyms.html.
The logged intervals in each borehole are described as lower, middle and upper. These do not match across boreholes either in terms of depth or sequence boundary. In any case, logging has not been carried out in more than three stages. These intervals can be seen at http://brg.ldeo.columbia.edu/data/iodp-eso/exp313/exp_documents/iodp-eso-313-ops-summary.pdf.
General Information
The suite of tools available for logging on Expedition 313 consisted of spectral gamma ray (ASGR), velocity (2PSA), conductivity (DIL45), acoustic borehole imaging (ABI40) and magnetic susceptibility (EM51) measurements. Each tool was run separately. Upon coring completion, the spectral gamma log was acquired through drill pipe. Subsequently the hole was conditioned with drill mud. The unfavorable borehole conditions required logging openhole in separate intervals. Difficulties pulling pipe and the development of bridges affected the ability to log certain sections of the boreholes (especially the upper, more unconsolidated sandy sections). The logger’s zero depth position was taken as the top of the drill pipe. Discrepancies in depths between initial zeroing and zeroing on removal of the tool were generally less than 0.5 m. The depths in the table are for the processed logs (after depth shift to the sea floor). Generally, small discrepancies exist between the sea floor depths determined from the downhole logs and those determined by the drillers from the pipe length. Typical reasons for depth discrepancies are ship heave, wireline and pipe stretch, tides, and the difficulty of getting an accurate sea floor from the 'bottom felt' depth in soft sediment. For New Jersey, logging was done from a platform and so there was no ship heave to account for.
Hole M0029A logging
Logging operations in M0029A began with the
acquisition through pipe of VSP measurements from the base of the borehole to ~ 200 m WSF, at which point a lightning storm halted
operations. Through-pipe spectral gamma ray measurements were also acquired
over the entire borehole. Open hole logging operations took place in three stages:
Lower section (482 to 757 m WSF): in this section, borehole conditions
were good and all tools except the spectral gamma were run in open hole.
However, acquisition was slowed by technical difficulties. Technical problems
with the winch began towards the end of the first run on the final section of
the uplog. On the second run the primary winch failed completely at ~577 m WSF and the sonic tool was manually pulled back onto the
deck. The winch was replaced with a backup and logging continued with
the remainder of the sonic run followed by the magnetic susceptibility sonde. The acoustic log was the last data to be acquired
following a break while a fault was fixed in the backup winch. VSP data was
acquired through pipe in the upper 200 m of the hole before the pipe was pulled
to log the next interval.
Upper section (above 401 m WSF): this section was logged after to the lower section. It suffered from the presence of several bridges, which resulted in logging only a small section with the spectral gamma and the conductivity tools (~322 to 335 in pipe and 335 to 348 m WSF in open hole).
Middle section (401 to 482 m WSF): this section was logged after
to the upper section. Reaming and hole conditioning
indicated that this interval might be open and stable enough to log. The
conductivity, sonic and magnetic susceptibility tools were successfully run
with sufficient overlap to enable a confident merge of the data between the
lower and middle sections.
The rest of the upper section could not be logged due to time constraints.
The change to the backup winch in
M0029A resulted in depths being recorded both manually by the winch and
electronically through the logging software. This gave the opportunity to check
electronic depths at roughly equally spaced intervals throughout the borehole.
All downhole wireline logs
from run 5 onwards use the backup winch and have slight adjustments applied to
the electronic depths. The near-perfect repeatability in the overlapping
interval between the middle and lower intervals allows precise merging of these
datasets.
Depth shift: The original logs were first corrected for the difference in zero tool depths and the difference between logger’s and driller’s zero points (if applicable). For hole M0028A the logger’s zero point was located beneath the driller’s zero in order to make the tool entry and exit point easier to access. See
http://brg.ldeo.columbia.edu/data/iodp-eso/exp313/exp_documents/iodp-eso-313-depth-layout.pdf . Finally, logs were depth shifted to the sea floor using the driller’s depth to seafloor (-53.41 m below rig floor). The driller’s distance to seafloor was chosen as the reference depth because for each hole this fell within the range of the depth to seafloor given by the gamma ray log. The gamma ray log through pipe was taken as the reference log (continuous) and where appropriate other logs were depth-matched to it. In hole M0028A the magnetic susceptibility log required a downwards shift (0.86 m) and the sonic log required an upwards shift in both the middle (-1.11 m) and lower (-0.42 m) sections. The log depths are therefore m WMSF.
DIL45 middle section (run 11) / lower section (run 3)
EM51 middlesection (run 13 / lower section (run 6)
2PSA middle section (run 12) / lower section-pass1 (run 4) / lower section-pass 2 (run 5).
The
acquisition of acoustic borehole images occurred in several files due to their
size (see image notes for more details).
Environmental
corrections: None.
Acoustic data: The 2PSA tool was run at a frequency of 15 kHz and resultant logs can be used to calculate compressional velocities. The data was processed in the WellCAD logging package. Waveform picking was done manually to ensure good quality data. Time picks were saved and the acoustic velocities were calculated using the receiver spacing of 1 ft. All presented acoustic data is accurate. Where no clear first arrivals in the waveform were present in two receivers, a null value was entered in the database.
Spectral gamma ray: Gamma ray logs recorded through drill pipe should be used only qualitatively due to attenuation of the incoming signal.
The quality
of the data is assessed by checking against reasonable values for the logged lithologies, by repeatability between different passes of
the same tool or down and up logged intervals, and by correspondence between
logs affected by the same formation property (e.g. the resistivity log should
show similar features to the acoustic log).
The quality of the ASGR Spectral Natural Gamma data is
directly related to lithology in combination with
logging speed. Where counts are lower the reliability of the statistical
function used to separate raw counts into values of naturally
occurring radioactive elements [potassium (K), uranium (U) and thorium
(Th)] is degraded. Negative values are indicative of incorrect statistics; when this is the case, K, U and Th values at that depth
has been replaced by a null (-999.25). Gamma ray logs recorded through drill pipe
should be used only qualitatively due to attenuation of the incoming signal.
A wide and/or
irregular borehole affects most recordings, particularly those that require eccentralization and a good contact with the borehole wall. Hole diameter was calculated from the acoustic imaging
tool (ABI40).
Whenever possible, data was acquired downlog, uplog and through the pipe. In this case the uplog is
usually the final output. The only exception si at hole M0029A, where the EM51 down log
provides a better merge with the log from the middle section. The data recorded within the pipe are usually removed from the
final log. This data has been retained in the original data files.
A null
value of -999.25 may replace invalid log values.
Additional
information about the drilling and logging operations can be found in the
Operations section of the Site Chapter in IODP Proceedings of Expedition 313.
For further questions about the data, please contact:
Jennifer
Inwood
University
of Leicester
Phone:
011-44-116-252-3327
Fax:
011-44--116-252-3918
E-mail:
IODP-UK
Johanna Lofi
University
of Montpellier 2
Phone: 033-
467-149- 309
Fax: 033- 467-
143- 244
E-mail:
IODP-UK
For any web
site-related problem please contact:
E-mail:
Database Manager