Standard Wireline Data Processing
IODP logging
contractor: USIO/LDEO
Hole: U1383C
Expedition: 336
Location: Mid Atlantic Ridge (central tropical N Atlantic)
Latitude: 22° 48.1241' N
Longitude: 46° 3.1662' W
Logging date:
Sea floor
depth (driller's):
4425.2 m DRF
Sea floor
depth (logger's):
4421.5 m WRF (DEBI-T/HLDS/EDTC-B/HNGS Pass 2 Uplog)
Total
penetration: 4756.2 m DRF (331 m DSF)
Total core
recovered: 50.31 m (19 % of cored section)
Oldest
sediment recovered:
Miocene
Lithologies: Limestone, hyaloclastite, phyric and aphyric basalt
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 November 2011.
| Tool string | Pass
|
Top depth (m WMSF) | Bottom depth (m WMSF) | Pipe depth (m WMSF) | Notes |
1. DEBI-T/HLDS/EDTC-B/HNGS
|
Pass 1 Downlog
|
52.5 |
Invalid HLDS
|
||
Pass 1 Uplog
|
|
||||
Pass 2 Downlog
|
52.5 |
Invalid HLDS |
|||
Pass 2 Uplog
|
52.5 |
Depth match reference |
|||
2. FMS/DSI/GPIT/HNGS
|
Downlog
|
52.5 |
|||
Pass 1
|
|||||
Pass 2
|
52.5 |
Hole U1383C was executed as a CORK hole with the upper section being cased to a depth of ~ 60 m DSF. The hole was prepared with two wiper trips before logging. The resistivity tool (HRLA) was not used as planned due to some technical failures.The wireline heave compensator was used during the logging operations in order to compensate for a peak-to-peak heave of ~ 2 m.
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.
Depth shift to sea floor and depth match. The sea floor depth was determined by the step in gamma ray values at 4421.5 m WRF. This differs by 3.7 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 Pass 2 Uplog of the DEBI-T/HLDS/EDTC-B/HNGS tool string (reference).
Depth matching
is typically done in the following way. One log is chosen as reference (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 were 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.
Environmental
corrections. The HNGS
data were corrected for hole size during the recording. The
HLDS data were corrected for standoff and hole size respectively during the
recording.
High-resolution data. Bulk density (HLDS) and EDTC-B data were recorded at 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 is 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.
Acoustic data. The dipole shear sonic imager (DSI) was run in Monopole P&S (with standard frequency) and Stoneley modes. The slowness data are of good quality and were converted to acoustic velocities. Reprocessing of the original sonic waveforms is highlyrecommended to obtain more reliable velocity results.
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 density log).
Gamma ray logs
recorded through bottom hole assembly (BHA) and drill pipe should be used only
qualitatively, because of the attenuation of the incoming signal. The
thick-walled BHA attenuates the signal more than the thinner-walled drill pipe.
A wide (>12") and/or irregular borehole affects most recordings, particularly those that require eccentralization and a good contact with the borehole wall (HLDS). Hole diameter was recorded by the hydraulic caliper on the HLDS tool (LCAL) and also on the FMS tool (C1 and C2). The caliper logs indicate that in the sections at 152-166 m and above 132 m WMSF the borehole was largely washed out to the degree (>15-19") where they have adversely affected the tool response. Thus, density logs in these depth intervals should be used with caution. Furthermore, due to the malfunction of HLDS caliper arm, the caliper log from Pass 2 Uplog of the DEBI-T tool string contains invalid data that significantly underestimate the actual size of the borehole and hence should not be used for any purpose.
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 336.
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