Standard Wireline Data Processing (Phase 1)
IODP-USIO logging contractor: LDEO-BRG
Hole: U1309D (Phase 1)
Expedition: 304
Location: Atlantis Massif-Mid-Atlantic Ridge (central N Atlantic)
Latitude: 30° 10.120' N
Longitude: 42° 7.113’ W
Logging date: January 2, 2005
Sea floor depth (driller's): 1656 mbrf
Total penetration: 401.3 mbsf
Total core recovered: 257 m (64 % of cored section)
Oldest sediment cored: none
Lithologies: Basalt, diabase, gabbro, oxide gabbro, peridotite, 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/APS/HLDSGPIT/HNGS |
Main
|
34
|
396
|
54
|
|
|
Repeat
|
287
|
396
|
|
|
|
| 2. FMS/DSI/GPIT/SGT |
Pass
1
|
45
|
400
|
53
|
|
|
Pass
2
|
40
|
400
|
53
|
Reference run
|
Hole U1309D was logged to the bottom of the hole, and the data are of excellent quality, particularly the FMS images. Initially, the tool strings could not pass below 38.5 mbsf, so the first attempt to log Hole U1309D was abandoned. The hole was re-entered a day later, with the pipe set beneath the obstruction. The logging operation then proceeded smoothly until after the second pass of the FMS/DSI/GPIT/SGT tool string, when tool string could not pass below 69 mbsf. The planned test of the new heave compensator was limited to testing within the pipe. A UBI tool string was cancelled, owing to the blockage in the hole and time limitations.
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 to the FMS images from Pass 2 of the FMS/DSI/GPIT/SGT tool string. The LLS resistivity log from the DLL/APS/HLDS/HNGS/GPIT tool string was depth matched to the average conductivity value of the FMS images, because the extremely low GR values (<10 API) made matching by GR alone difficult.
Because gamma ray logs did not cross the sea floor, the sea floor 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 P&S monopole, lower dipole, and Stoneley mode for both Pass 1 and 2. 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). The quality of the data at Hole U1309D is excellent.
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 tool (C1 and C2). The hole is 10 inches wide below 286 mbsf. Shallower than this depth, the hole is generally between 10-12 inches wide, but with some generally short intervals extending to about 18 inches wide (e.g. 272-273 mbsf).
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 304. For further questions about the logs, please contact:
Cristina Broglia
Phone: 845-365-8343
Fax: 845-365-3182
E-mail: Cristina Broglia