Standard Wireline Data Processing
IODP logging
contractor: USIO/LDEO
Hole: U1417E
Expedition:
341
Location: Gulf of Alaska (NE Pacific Ocean)
Latitude: 56° 57.5888' N
Longitude: 147° 6.5983' W
Logging date:
Sea floor
depth (driller's):
4199.5 m DRF
Sea floor
depth (logger's):
4200 m WRF
Total
penetration: 4909 m DRF (709.5 m DSF)
Total core
recovered: 146.92 m (42.1
% of 348.7 m; several drilled-down intervals)
Oldest
sediment recovered:
~5 Ma at 400 m DSF
Lithologies:
Mud, iceberg-rafted diamict, coarse-grained interval dominated by gravity flows alternate with mud, siltstone and sandstone.
The logging data
was recorded by Schlumberger in DLIS format. Data were processed at the
Borehole Research Group of the Lamont-Doherty Earth Observatory in June 2013.
| Tool string | Pass
|
Top depth (m WMSF) |
Bottom depth (m WMSF) | Pipe depth (m WMSF) | Notes |
| 1. MSS/HRLA/APS/HLDS/EDTC-B/HNGS | Downlog 1
|
80 |
|||
Downlog 2
|
recorded open hole |
Invalid APS/HLDS. Caliper closed. |
|||
Main
|
84 |
Depth reference |
|||
Repeat
|
80 |
||||
2. FMS/DSI/GPIT/EDTB-B/HNGS |
Downlog
|
80 |
Calipers closed. |
||
Pass 1
|
82 |
||||
Pass 2
|
80.5 |
||||
3. MSS/EDTC-B/HNGS |
Downlog
|
80 |
|||
Pass 1
|
80 |
||||
Pass 2
|
80 |
||||
4. VSI |
2 good stations at 211.3 and 211.9 m WSF |
Logging operations in Hole U1417E started with conditioning of the hole without wiper trip and used seawater as logging fluid. The first "triple-combo" tool string (MSS/HLDS/APS/EDTC-B/HNGS) acquired data downlog to a depth of 4824 m WRF (624 m WSF), with problems of loss of tension occurred at several tight spots or bridges. Both repeat and main logs were then recorded without problems. The second tool string (FMS/DSI/GPIT/EDTB-B/HNGS) acquired data downlog to a depth of 4778.5 m (578.5 m WSF), where an obstruction was encountered; two uplog passes were then recorded. During the third deployment, the full MSS-B tool string was used for the first time. It reached a total depth of 4404 m WRF (204 m WSF) and acquired one downlog and two uplogs. The VSI tool string was run last. It reached a total depth of 4395 m WRF (195 m WSF) and acquired only two good shots (at 1411.3 and 1411.9 m WRF) though 50 shots were fired.
The depths in the table are for the processed logs (after depth shift to the sea floor and depth matching between passes). Generally, 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, wireline and pipe stretch, tides, and the difficulty of getting an accurate sea floor from a 'bottom felt' depth in soft sediment.
The sea state was
Depth shift to sea floor and depth match. The original logs were first shifted to the sea floor (- 4200 m). The sea floor depth was determined by the step in gamma ray values at 4200 m WRF. This differs by 0.5 m from the sea floor depth given by the drillers (see above). The depth-shifted logs were then depth-matched to the gamma ray log from the main pass of the MSS/HRLA/APS/HLDS/EDTC-B/HNGS tool string.
Depth matching
is typically done in the following way. One log is chosen as reference or base
log (usually the total gamma ray log from the run with the greatest vertical
extent and no sudden changes in cable speed), and then the features in the
equivalent logs from the other runs are matched to it in turn. This matching is
performed manually. The depth adjustments that are required to bring the match
log in line with the base log are then applied to all the other logs from the
same tool string.
The drill pipe depth between the triple-combo main pass and passes from the other logging runs differs about 2-4 m, likely due to the poor hole conditions and related stick-slip motion of the tool strings.
Environmental
corrections. The HNGS
data were corrected for hole size and mud weight after the recording. The APS and
HLDS data were corrected for standoff and hole size respectively after the
recording.
High-resolution
data. Bulk density
(HLDS) and neutron porosity (APS) data were recorded with sampling rates of 2.54 and
5.08 cm, respectively, in addition to the standard sampling rate of 15.24 cm.
The enhanced bulk density curve is the result of Schlumberger enhanced
processing technique performed on the MAXIS system onboard. While in normal
processing short-spacing data are smoothed to match the long-spacing one, in
enhanced processing this is reversed. In a situation where there is good
contact between the HLDS pad and the borehole wall (low-density correction) the
results are improved, because the short spacing has better vertical resolution.
Gamma Ray data from the EDTC-B tool were recorded at sampling rates of 5.08 and 15.24
cm.
Acoustic
data. The dipole shear
sonic imager (DSI) was operated in the following modes: P&S monopole
(downlog and 2 passes) and cross-dipole (pass 1) in standard (high) frequency, upper and lower dipole (downlog and 2 passes) in high and low frequency, respectively, and
Stoneley (downlog and 2 passes). Low frequency dipole had the best slowness projection mostly below 4500 m WRF (or 300 m WSF). There were some missed picks in the compressional velocity in the upper part of the hole, as the auto picking could not distinguish between the compressional and fluid velocity. The velocities were computed from the delay times. Waveform processing is recommended to improve quality.
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, and by
correspondence between logs affected by the same formation property (e.g. the
resistivity log should show similar features to the sonic velocity log).
The data from the MSS/HRLA/APS/HLDS/EDTC-B/HNGS tool string are of variable quality. The density, resistivity, and gamma ray logs are very noisy in the uppermost 300 m of the hole section due to poor hole conditions, with some improvement below that depth. The MSS acquired good data show a clear downhole drift, possibly attributed to increase in tool temperature downhole.
A wide (>12") and/or irregular borehole affects most recordings, particularly those that require eccentralization and a good contact with the borehole wall (APS, HLDS). Hole diameter was recorded by the hydraulic caliper on the HLDS tool (LCAL) and by the FMS tool (C1 and C2). The caliper shows a very irregular borehole (4 to 18 inches), with variations of up to 13 inches in just a few meters of vertical depth. Accordingly, log data from such wash-out intervals should be used with caution.
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 and Downhole Measurements sections of the expedition reports,
Proceedings of the Integrated Drilling Program, Expedition 341.
For further questions about the logs, please contact:
Tanzhuo Liu
Phone: 845-365-8630
Fax: 845-365-3182
E-mail: Tanzhuo Liu
Cristina Broglia
Phone: 845-365-8343
Fax: 845-365-3182
E-mail: Cristina Broglia