Standard Wireline Data Processing
IODP -USIO logging contractor: LDEO-BRG
Hole: U1309B
Expedition: 304
Location: Atlantis Massif - Mid Atlantic Ridge (central N Atlantic))
Latitude: 30° 10.108' N
Longitude: 42° 7.11’ W
Logging date: November 30, 2004
Sea floor depth (driller's): 1653.4 mbrf
Total penetration: 103.8 mbsf
Total core recovered: 48.7 m (46.9 % of cored section)
Oldest sediment cored: Quaternary
Lithologies: Basalt, diabase, gabbro, peridotite
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/HNGS/GPIT/HNGS |
Pass
1
|
2
|
91
|
35
|
Bad APS data
|
|
Pass
2
|
0
|
91
|
20
|
|
|
| 2. FMS/DSI/GPIT/SGT |
Pass
1
|
13
|
96
|
20
|
|
|
Pass
2
|
18
|
96
|
20
|
Reference run
|
Hole U1309B was logged to within a few m of the bottom of the hole, and the hard-rock environment enabled the pipe to be set at 20 mbsf. The data are generally very good. The hole deviation was up to 7°at the base of the hole, which contributed to the poor sonic data. One FMS arm failed to close properly on Pass 2, and was slightly damaged (bent), and the UBI tool string deployment was cancelled. The old wireline heave compensator was used to counter ship heave (quite high). Finally, tests of the new heave compensator tests were run using a tool string consisting of GPIT, SGT, and DLL spacers.
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 (-1653.4 m), and then depth-matched to the GR log and FMS images from Pass 2 of the FMS/DSI/GPIT/SGT tool string. The RHOM density log from the DLL/APS/HLDS/HNGS/GPIT tool string was depth matched to the FMS images, because the extremely low GR values (<10 API) made matching by GR alone difficult.
The sea floor depth could not be determined by the step in gamma ray values, also because of the very low values, therefore the seafloor depth given by the drillers was used (1653.4 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: P&S monopole (Pass 1) and P&S monopole, lower dipole, and Stoneley mode (Pass 2). The compressional velocities from Pass 1 seem to give reasonable values, but do not match the patterns in the other physical property logs (RHOM, FMS). Shear and Stoneley velocities seem acceptable.
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 tool (C1 and C2). The hole is generally 10 inches wide, with some 1-m-thick washouts.
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