Standard Wireline Data Processing
IODP logging
contractor: USIO/LDEO
Hole: U1431E
Expedition:
Location: East Sub Basin (South China Sea)
Latitude: 15° 22.5380' N
Longitude: 116° 59.9903' E
Logging date:
Sea floor
depth (driller's):
4251.3 m DRF
Sea floor
depth (logger's):
4252 m WRF (DIT/APS/HLDS/EDTC-B/HNGS uplog)
Sea floor
depth (logger's):
4251 m WRF (FMS/DSI/GPIT/EDTC-B/HNGS pass 2)
Total
penetration (RCB coring): 5260.1 m DRF (1008.8 m DSF)
Total cored interval: 443.5 m
Total core
recovered: 243 m (54.8
% of cored section)
Oldest
sediment recovered:
Miocene
Lithologies: Sediments: clay, silty clay, silty sand and nannofossil ooze. Basement: Volcaniclastic breccia and basalt.
The logging data
were recorded by Schlumberger in DLIS format. Data were processed at the
Borehole Research Group of the Lamont-Doherty Earth Observatory in February 2014.
| Tool string | Pass |
Top depth (m WMSF) | Bottom depth (m WMSF) | Pipe depth (m WMSF) | Notes |
1.DIT/APS/HLDS/EDTC-B/HNGS
|
Downlog
|
154 |
Closed caliper, invalid APS and HLDS
|
||
Uplog
|
154 |
Depth reference |
|||
2.FMS/DSI/GPIT/EDTC-B/HNGS
|
Downlog
|
154 |
Closed caliper; invalid FMS |
||
Pass 1
|
Recorded open hole |
||||
Pass 2
|
154 |
Logging operations in Hole U1431E started with a wipe trip from 863 to 979 m DSF before the second to last core and 50 barrel sepiolite mud sweeps after most of the last cores, followed by displacing the hole from 648 m DRF upwards with 240 barrels of heavy mud (11.4 ppg, barite weighted). The logging operations went smoothly, but the tool string was unable to reach the bottom of the hole at 1008.8 m DSF, due to a bridge encountered at ~464 m DSF.
A new logging cable was used during this expedition, which had to be de-torqued and run not faster than 6000 feet/hour. This slowed the trips through the water column compared to a seasoned cable. Some of the larger-than-normal differences in depth determinations at seafloor and drill-pipe base might be attributed to the use of the new cable.
The sea state was moderate, with peak-to-peak heave of ~ 1m during the DIT/APS/HLDS/EDTC-B/HNGS run and ~ 2m during the FMS/DSI/GPIT/EDTC-B/HNGS run. The wireline heave compensator was used during the logging operations.
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 original logs were first shifted to the sea floor (- 4252 m). The sea floor depth was determined by the step in gamma ray values at 4252 m WRF on the DIT/APS/HLDS/EDTC-B/HNGS uplog (reference run). This differed by 0.7 m from the sea floor depth given by the drillers (4251.3 m DRF). The depth-shifted logs from the FMS/DSI/GPIT/EDTC-B/HNGS tool string were then depth-matched to the gamma ray log from the reference run.
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 and mud weight during the recording. The EDTC-B
and HLDS data were corrected for hole size during the
recording.
High-resolution
data. The bulk density
(HLDS) data were recorded with a sampling rate of 2.54 cm 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.
The 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 P&S monopole, upper and lower dipole modes on all three passes. The monopole transmitter was run at standard (high) frequency on the downlog, medium frequency on pass 1, and low frequency on pass 2. The lower and upper dipoles were run at low and high frequency, respectively, on all passes. The downlog yielded sonic data of low quality, with shear data with no coherence and little coherence on the compressional data. Pass 1 yielded much better compressional data and unusable shear data. This was most likely due to the large hole size and severe rugosity. The medium frequency used for the monopole on pass 2 provided better the best compressional data of the three passes. Reprocessing of the sonic waveforms is recommended to get better 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 sonic velocity 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 by the FMS tool (C1 and C2). The caliper measurements show that the hole shape was ragged and the hole size was quite large (>18") for most of the hole interval, thus resulting in overall poor quality of the density and porosity log. Because logging stopped at 464 m DSF, there is no evidence of any effect of the heavy barite drilling mud on the density data over the logged interval; the dense mud is likely to have accumulated in the lower section of the hole.
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 349.
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