Standard Wireline Data Processing (Phase 2)
IODP -USIO logging contractor: LDEO-BRG
Hole: U1309D (Phase 2)
Expedition: 305
Location: Atlantis Massif - Mid Atlantic Ridge (central N Atlantic)
Latitude: 30° 10.120' N
Longitude: 42° 7.113’ W
Logging date: January 31 - February 2, 2005
Sea floor depth (driller’s): 1656 mbrf
Total penetration: 838 mbsf
Total core recovered: 631.5 m (75.36 % of cored section)
Oldest sediment cored: none
Lithologies: diabase, gabbro, oxide gabbro, troctolite
The logging data was recorded by Schlumberger in DLIS format. Data were processed at the Borehole Research Group of the Lamont-Doherty Earth Observatory.
| Tool string | Pass | Top depth (mbsf) | Bottom depth (mbsf) | Bit depth (mbsf) | Notes |
| 1. DLL/APSHLDS/GPIT/HNGS |
Main
|
150
|
829
|
170
|
|
|
Repeat
|
701
|
830
|
|
|
|
| 2. FMS/DSI/GPIT/SGT |
Pass 1
|
341
|
834
|
|
|
|
Pass 2
|
163
|
836
|
|
Reference run
|
|
| 3. WST-3 |
|
|
|
|
10 good stations
|
| 4. UBI/SGT |
Lower
|
723
|
825
|
|
|
|
Upper 1
|
466
|
713
|
|
|
|
|
Upper 2
|
504
|
705
|
|
|
|
| 5. Goettingen Magnetometer |
|
|
|
|
Third-party tool
|
Hole U1309D was drilled and logged during Expedition 304. During Expedition 305, Hole U1309D was deepened and logged in two phases. In Logging Phase 2, Hole U1309D was logged to total depth; the data are of excellent quality. No problems were encountered lowering the tools to the base of the hole, though the UBI tool required a sinker bar to increase its weight. A test of the new heave compensator was performed after FMS/GPIT/SGT/DSI Pass 2. The two lowermost WST stations recorded poor signals.
The depths in the table are for the processed logs (after depth matching between passes and depth shift to the sea floor). 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 the 'bottom felt' depth in soft sediment.
Depth match and depth shift to sea floor: The original logs were shifted to the sea floor (-1656 m), and then depth matched. Depth matching was a two-step process: first, FMS/GPIT/SGT/DSI pass 2 was matched to the reference run from the Expedition 304 logging of Hole 1309D, and second, the other passes were matched to the depth matched logs from FMS/GPIT/SGT/DSI pass 2. Because the extremely low GR values (<10 API) made matching by GR alone difficult, several logs were used for matching, including resistivity, acoustic slowness, caliper, and FMS-average.
Because the gamma ray logs did not cross the sea floor, the seafloor depth given by the drillers was used (1656 m).
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.
Sonic data: The dipole shear sonic imager (DSI) was operated in the following modes for both Pass 1 and 2: P&S monopole, cross dipole, and Stoneley mode. The data quality is very good.
High resolution data: Bulk density and neutron porosity data were recorded at a sampling rate of 2.54 and 5.08 cm, respectively. SGT gamma ray data were sampled every 5.08 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 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 on 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/APS). Hole diameter was recorded by the hydraulic caliper on the HLDS tool (LCAL) and by the FMS (C1 and C2) and UBI (radius) tools. The hole is generally in gauge (10 inches wide), but with some generally thin sections extending to about 18 inches wide (e.g. 416-421 mbsf). 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 operation can be found in the Operations section of the Site Chapter in IODP Initial Reports Volume 305. For further questions about the logs, please contact:
Cristina Broglia
Phone: 845-365-8343
Fax: 845-365-3182
E-mail: Cristina Broglia