IODP-MSP
drilling and logging contractor: ESO
Hole: M0080A
Expedition: 381
Location: Gulf of Corinth (Ionian Sea)
Latitude: 38° 7' 12.1467" N
Longitude: 23° 5' 10.6138" E
Logging
date: December
15 – 17, 2017
Sea floor
depth (driller's): 350.22
mbsl
Sea floor
depth (logger's): 349.2
mbsl
Total
penetration: 534.10 mbsf
(drillers)
Core
recovery: 78%
Oldest
sediment recovered: n/a at time of writing
Lithologies: mud, clay, sand, gravel,
breccia
Data
During Expedition 381, slim-hole downhole logging services managed by
the European Petrophysics Consortium (EPC) were contracted by the
University of Montpellier (France). Wireline logging data were acquired in .tdf
format and processed by the EPC with the software package WellCad (v5.2). Raw
data are provided online in DLIS format. Processed standard data are available
in ASCII format.
The wireline logs were recorded with stand-alone logging tools in
stages. Stages were defined depending on drilling information, core
descriptions and physical properties measured on cores. Bentonite (32
viscosity, 8.8 lbs/gal) was present in the hole during logging through pipe and
stages 1 and 2. Sea water was circulated during Stage 3.
Through
pipe (December 15, 2017)
Run 1: ASGR512
Stage 1 (December
15-16, 2017), Lower Section
Run 1: EM51
Run 2: 2PSA
Run 3: ASGR512
Stage 2
(December 16, 2017), Middle Section
Run 1: EM51
Run 2: 2PSA
Run 3: DIL45
Run 4: ASGR512
Stage 3 (December 17, 2017),
Upper Section
Run 1: EM51
Run 2:
2PSA
Run 3:
ASGR512
Run 4: DIL45
The logging
data presented in the following table were processed by the European
Petrophysics Consortium.
Processed
Logging Data
Tool |
Section/Interval |
Top depth (m WMSF) |
Bottom depth (m WMSF) |
Pipe depth (m WMSF) |
Remarks |
ASGR512* |
All |
0 |
534.34 |
533.4 |
Through pipe |
EM51 |
Lower |
430 |
532.1 |
430 |
Stage 1 |
2PSA |
Lower |
430 |
530.40 |
430.45 |
Stage 1 |
ASGR512 |
Lower |
430 |
440.44 |
430.04 |
Stage 1 |
EM51 |
Middle |
230 |
428.46 |
230.01 |
Stage 2 |
2PSA
|
Middle |
230 |
372.55 |
230.60 |
Stage 2 |
DIL45 |
Middle |
230 |
368.68 |
230.03 |
Stage 2 |
ASGR512 |
Middle |
230 |
368.43 |
229.93 |
Stage 2 |
EM51 |
Upper |
50 |
223.99 |
50.04 |
Stage 3 |
2PSA |
Upper |
50 |
220.60 |
50.30 |
Stage 3 |
ASGR512 |
Upper |
50 |
220.98 |
50.03 |
Stage 3 |
DIL45 |
Upper |
50 |
220.47 |
50.02 |
Stage 3 |
* 2
versions of processed through pipe ASGR512 data are available. See Spectral
gamma ray data.
The
depths in the table above are for the processed logs, after applying a depth
shift to the sea floor. Discrepancies may 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
and tides. Waves’ peak to peak was always inferior to 1 m during logging, and
heave compensation was activated. Heave compensation reduced vertical movement
to a maximum amplitude of 10 cm. Other reasons for depth discrepancies
are wireline and pipe stretch, and the difficulty of getting an accurate sea
floor depth from the 'bottom felt' depth in soft sediments.
Processing
Depth
shift and depth match. For
each run, depths corrections have been applied so the data are all referenced
to the seafloor (m WMSF). Depth corrections include:
-
Zero
logger (pipe entrance in the roster box) to zero driller (rig floor);
-
Rig floor
to sea floor;
-
Difference
between the initial and final zero of the tool;
-
Manual
shift using distinctive features, wherever necessary: gamma ray logs crossing
the sea floor or tools transitioning from the open hole to the pipe, both
giving a clear signal of features that are consistent between different runs of
a same stage.
Tool |
Section/Interval |
Zero logger – Sea Level (m) |
Sea Level – Sea Floor (m) |
Zero Tool In (m) |
Zero Tool Out (m) |
ASGR512 |
All |
21.84 |
348.8 |
1.24 |
4.03 |
EM51 |
Lower |
19.82 |
348.8 |
1.9 |
1.32 |
2PSA |
Lower |
19.82 |
348.8 |
3.4 |
3.64 |
ASGR512 |
Lower |
19.82 |
348.8 |
1.24 |
1.01 |
EM51 |
Middle |
19.17 |
348.8 |
1.9 |
1.42 |
2PSA |
Middle |
19.17 |
348.8 |
3.4 |
3.51 |
DIL45 |
Middle |
19.17 |
348.8 |
2.27 |
1.97 |
ASGR512 |
Middle |
19.17 |
348.8 |
1.24 |
0.71 |
EM51 |
Upper |
17.04 |
348.8 |
1.9 |
1.57 |
2PSA |
Upper |
17.04 |
348.8 |
3.4 |
3.27 |
ASGR512 |
Upper |
17.04 |
348.8 |
1.24 |
0.99 |
DIL45 |
Upper |
17.04 |
348.8 |
2.27 |
2.24 |
Environmental
correction. Environmental corrections are designed to remove any
effect from the borehole (size, roughness, temperature, and tool standoff) or
the drilling fluid (bentonite) that may partially mask or disrupt the log
response from the formation. No post-acquisition corrections were applied at
this hole.
Sonic
data. The 2PSA
data were acquired at 10 and 15 kHz frequency in the upper and lower sections respectively. The sonic data were processed in WellCad to calculate the compressional velocity. Due to
the limited quality of the waveform, first arrivals picking was done manually.
Time picks were saved and the acoustic velocities were calculated using the R1
and R2 receivers (spacing = 1ft).
Spectral
gamma ray data. The
gamma ray logs recorded through drill pipe should be used qualitatively only
due to attenuation of the incoming signal. Further attenuation is noted at the
joint between two pipes (drop in values every ~9-10 m) because the joints have
a thicker metallic wall than the pipes. Two versions of the through pipe gamma
ray logs are provided: one without any cleaning of the data, and one where data
recorded though joints have been removed (values replaced by -999.25). The
bottom ~95 m of the drill string have a thicker wall that further attenuate the
signal received from the formation.
Conductivity
data> After using the DLL3 in Hole M0079A, it was decided to use the DIL45 to collect
deep and shallow conductivity data because the way the tool works (induction)
and the measurement range were more adapted to the type of formation
encountered. The DIL45 and EM51 are both induction tools and perform well in conductive
formations. There is a good match in trends and range of values for the wo
datasets.
Quality Control
Borehole
conditions can greatly influence log data quality. The lack of downhole images
or caliper data in Hole M0080A do not allow for an assessment of the quality of
the borehole and how it could affect collected data. The frequent problems
encountered when sending the tools down during the expedition, with difficulty
to progress further down the hole, point at possible swellings (upper 200 m of
cores recovered tended to expand too) and instability (sands, gravels) of the
formation.
The sonic
tools are ideally run with centralizers. Use of centralizers implies
bow-springs able to compress to pass through the drill bit (inner diameter = 95
mm) and then to open more than double that diameter in open hole (outer
diameter of the drill bit = 216 mm) to keep the tool centralized. No such
bow-springs were available for the tool 2PSA, this the tool string was
operated without centralizers. This most likely affected the quality of the sonic data.
The spectral
and total gamma ray acquired through pipe should be used with care as the
signal emitted by the formation was attenuated by the drill pipe wall and the
drill collars before reaching the tool.
For
further questions about the logging data, please contact:
Erwan Le
Ber
School of
Geography, Geology and the Environment
University
of Leicester
University Road
Leicester
LE1 7RH
United
Kingdom
Phone: 0116
252 3327
E-mail: elb51@le.ac.uk
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web site-related problem please contact:
E-mail: logdb@ldeo.columbia.edu