Standard Wireline Data Processing
ODP logging contractor: USIO/LDEO
Hole: U1309D
Expedition: 340T
Location: Atlantis Massif-Mid Atlantic Ridge (central N Atlantic ocean)
Latitude: 30° 10.120' N
Longitude: 42° 7.113' W
Logging date: February 21-26, 2012
Sea floor depth (driller's): 1656 m DRF
Total penetration (IODP expedition 305): 3071.5 m DRF (1415.5 m DSF)
Total core recovered (this expedition): none
Oldest sediment recovered: none
Lithology: diabase, gabbro, oxide gabbro, dunitic troctolite
The logging data
was recorded by Schlumberger in DLIS format. Data was processed at the
Borehole Research Group of the Lamont-Doherty Earth Observatory in February 2012.
| Deployment/Tool string | Run
|
Top depth (m WMSF) | Bottom depth (m WMSF) | Pipe depth (m WMSF) | Notes |
1. HRLA/HLDS/EDTC-B/MTT
|
Downlog
|
54 |
Invalid HLDS
|
||
Main
|
Open-hole |
||||
Repeat
|
Open-hole |
||||
2. VSI/EDTC-B |
Open-hole |
No data |
|||
3. VSI/EDTC-B |
Open-hole |
No data |
|||
4. DSI/GPIT/EDTC-B |
|
No data |
|||
5. VSI/EDTC-B |
Open-hole |
50 stations, 680 shots |
|||
| 6. DSI/GPIT/EDTC-B |
Downlog |
Open-hole |
No GPIT data |
||
Uplog
|
Open-hole |
||||
7. MSS/EDTC-B |
Downlog
|
Open-hole |
|||
Main
|
Open-hole |
||||
Repeat
|
54 |
Hole U1309D is a re-entry hole: it was drilled and logged during IODP expeditions 304 and 305.
During the first deployment of this expedition, a Kinley crimper/cutter was used to recover the stuck tool string caused by broken centralizers while entering the drill pipe. The first deployment of the DSI/GPIT/EDTC-B tool string failed to collect any data as it was not possible to lower the tool string below 2345 m DRF (689 m DSF). Asecond deployment of the DSI tool string after a successful VSP experiment, was carried out without incidents. The logging operations concluded with the recording of magnetic susceptibility data (MSS). Two passes at different logging speeds were completed in order to assess the influence of logging speed on the measurements.
The sea state was moderate to low, with a peak-to-peak heave of 1-1.5 m or less. Wireline heave compensator was not operated during the deployments of the HRLA/HLDS/EDTC-B/MTT and VSI/EDTC-B tool strings due to the jerky motion of the compensator, but was operated during the deployments of DSI/GPIT/EDTC-B and MSS/EDTC-B tool strings.
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 (- 1656 m). Since the sea floor was not logged during this or previous expeditions, the sea floor depth given by the drillers during expedition 304 was used. The depth-shifted logs from the HRLA/HLDS/EDTC-B/MTT tool string have then been depth-matched to the resistivity data (Dual Laterolog) acquired during expedition 305. The data from the DSI/GPIT/EDTC-B and the main pass of MSS/EDTC-B tool strings have been depth-matched to the gamma ray log from expedition 305. The match was difficult and not very accurate due to the low signature of the gamma ray logs (less than 10 gAPI). The acoustic data could not be used in the depth matching because no DSI was run in the lower part of the hole during expedition 305 and the DSI from expedition 304 had a small overlap with this expedition data. The MSS data from both downlog and repeat pass was then depth-matched to the MSS data from the main pass via the magnetic susceptibility logs.
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 HLDS and HRLA data were corrected for the hole size during the recording.
.
High-resolution data. Bulk density (HLDS) data were at 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.
Acoustic
data. The dipole shear
sonic imager (DSI) was operated in P&S monopole, cross-dipole, upper and lower dipole, and
Stoneley mode. The velocities were computed from the P&S monopole compressional and shear slownesses. They are
generally of good quality. Processing of the sonic waveforms is recommended for 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 data are generally of intermediate to poor quality due to the low signal level (5-10 gAPI) of the basement rocks. 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) tool. The hole is generally in gauge (10-12" wide), but with some short sections extending to 18" wide (e.g., 416-421 and 1102-1103 m WMSF). The lower down in the hole, the fewer the number of wide sections.
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 340T.
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