Standard Wireline Data Processing
IODP logging
contractor: USIO/LDEO
Hole: U1438F
Expedition:
Location: Amami-Sankaku Basin (Philippine Sea)
Latitude: 27° 23.0167' N
Longitude: 134° 19.0905' E
Logging date:
Sea floor
depth (driller's):
4711 m DRF
Sea floor
depth (logger's):
4711 m WRF (MSS/HRLA/HLDS/EDTC-B/HNGS uplog)
Total
penetration: 5411 m DRF (700 m DSF)
Total core recovered: none, this hole was dedicated to logging
Lithologies: Mud with ash, turbidites, conglomerates, breccia, and sandstone were drilled at hole U1438D
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 July 2014.
| Tool string | Run
|
Top depth (m WMSF) | Bottom depth (m WMSF) | Pipe depth (m WMSF) | Notes |
MSS/APS/HRLA/HLDS/EDTC-B/SP/HNGS
|
Downlog
|
93 |
|
||
Uplog
|
93 |
Reference run |
|||
| VSI/EDTC-B/HNGS | Uplog |
525.5 |
563 |
Open hole |
Recorded open hole |
FMS/S/DSI/EDTC-B
|
Downlog
|
93 |
Closed caliper; invalid FMS |
||
Uplog
|
93 |
This is a dedicated logging hole with excellent condition. After drilling completion, only seawater was used to prepare the hole and a wiper trip was scheduled due to the bridging encountered at the depth of 300 m DSF. Ship heave was low (0.3 m from peak to peak) and 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 (-4711 m). The sea floor depth was determined by the step in gamma ray values on the uplog at 4711 m WRF, which is consistent with the drillers' seafloor depth of 4711 m DRF. The depth-shifted logs have then been depth-matched to the gamma ray log from the downlog.
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
and HRLA data were corrected for hole size during the recording. The APS and
HLDS data were corrected for standoff and hole size respectively during the
recording.
High-resolution data. Bulk density (HLDS) and neutron porosity (APS) 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 are smoothed to match the long-spacing ones, 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 operated in P&S monopole, Stoneley, upper and lower dipole mode during the uplog and in monopole mode during the downlog. The monopole and upper dipole were run at standard frequency and the lower dipole at low frequency. All sonic modes provided excellent data but the standard frequency upper dipole shear was generally better than the low frequency lower dipole shear. Stoneley and compressional data were excellent through most of the logging interval. Velocity has been calculated from DTCO, DT1, DT2 and DTST.
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 (APS, HLDS). Hole diameter was recorded by the hydraulic caliper on the HLDS tool (LCAL). Since this is a dedicated logging hole with excellent condition, the hole size was largely ideal for logging and the quality of the density and porosity logs was excellent.
The SP measurement was surprisingly good; historically the SP has always been very elusive in obtaining any good deflections in ODP/IODP holes. The SP logs correlate well with resistivity and density/porosity.
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 351.
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