Standard Wireline Data Processing
Science operator: Texas A&M University
Hole: U1467E
Expedition: 359
Location: Maldives (Central Equatorial N Indian Ocean)
Latitude: 4° 51.0362' N
Longitude: 73°17.0197' E
Logging date: November 5-6, 2015
Sea floor depth (driller's): 499.5 m DRF
Sea floor depth (logger's): 499.5 m WRF (MSS/HRLA/APS/HLDS/EDTC-B/HNGS main run)
Total penetration: 1212.4 m DRF (712.9 m DSF)
Total core recovered: dedicated logging hole, no core recovered
Oldest sediment recovered:
Lithology: see Hole U1467C
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 November 2015.
| 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
|
95.5 |
Closed caliper. Invalid HLDS and APS data. |
||
Repeat
|
recorded open hole
|
APS nuclear source off. Invalid APS. |
|||
Main
|
95.5 |
Reference. |
|||
2. VSI/EDTC |
Uplog
|
recorded open hole
|
13 stations, 94 shots. | ||
3. FMS/DSI/GPIT/EDTC-B/HNGS |
Downlog
|
95.5
|
Calipers closed. Invalid FMS data. |
||
Pass 1
|
recorded open hole
|
||||
Pass 2
|
95.5 |
Hole U1467E was a logging-dedicated hole, therefore no coring was carried out. Hole conditions were expected to be good, therefore the first tool string, consisting of the MSS/HRLA/APS/HLDS/EDTC-B/HNGS tools, was rigged up with nuclear sources. The downlog proceeded without any incident to total depth. Repeat and main passes were carried out from total depth to 1085 and 490 m WRF respectively main pass was conducted from total depth to 485 m WRF. During the main pass the caliper was closed at about 630 m WRF in order to facilitate the re-entry into the drill pipe. Likewise the minitron source was switched off just after entering the drill pipe in order to ensure that no GR scattering would mask the sea floor signature on the main uplog. The second logging run consisted of a VSP experiment, which acquired 98 shots at 13 depths (stations).
The sea state was calm with an average peak-to-peak heave of 0.1 m. No Wireline Heave Compensator (WHC) was used.
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 (-
499.5 m). The sea floor depth
was determined by the step in gamma ray values at 499.5 m WRF on the MSS/HRLA/APS/HLDS/EDTC-B/HNGS main pass. This corresponds to the sea floor depth given by the drillers (see
above). The depth-shifted logs have then been 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 (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 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 P&S monopole, upper dipole, and Stoneley standard-frequency mode and in lower dipole low-frequency mode. The compressional and shear velocities were computed from the delay time and are
generally of good quality. Processing of the sonic waveforms is recommended in order to get more accurate 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). In Hole U1467E repeatability among the three passes was good.
The gamma ray logs
recorded through bottom hole assembly (BHA) and drill pipe should be used only
qualitatively due to the attenuation of the incoming signal. The
thick-walled BHA attenuates the signal more than the thinner-walled drill pipe.
Hole diameter was recorded by the caliper on the HLDS
tool (LCAL) and the FMS tool (C1 and C2).
Both calipers indicate a hole in good conditions for logging. They also show some evenly-spaced "artifacts" (washouts) in the 120-540 m WMSF interval. Because these mini washouts occur approximately every 9 m and only in the narrow part of the hole where the caliper possibly made good contact with the borehole wall, it is believed that they correspond to incisions made in the formation by the rotating thick drill pipe joints during the drilling.
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 report, Proceedings of the International Ocean Discovery Program, Expedition 359. For further questions about the logs, if the hole is still under moratorium please contact the staff scientist of the expedition.
After the moratorium period you may direct your questions to:
Cristina Broglia
Phone: 845-365-8343
Fax: 845-365-3182
E-mail: Cristina Broglia
Tanzhuo Liu
Phone: 845-365-8630
Fax: 845-365-3182
E-mail: Tanzhuo Liu