Standard Wireline Data Processing
Science operator: Texas A&M University
Hole: U1567A
Expedition: 396
Location: North Modgunn (North Eastern Atlantic Ocean)
Latitude: 65° 21.8514' N
Longitude: 3° 3.2562' E
Logging date: August 22, 2021
Sea floor depth (driller's): 1714.5 m DRF
Sea floor depth (logger's): 1713 m WRF
Total penetration: 1910.4 m DRF (195.9 m DSF)
Total core recovered: 181.55 m (95.6 % of cored section)
Oldest sediment recovered:
Lithology: Clay, sand and silt.
The logging data
was recorded by Schlumberger in DLIS format. Data were processed at the
Borehole Research Group of the Lamont-Doherty Earth Observatory in August 2021.
| Tool string | Pass
|
Top depth (m WMSF) | Bottom depth (m WMSF) | Pipe depth (m WMSF) | Notes |
1. MSS/HRLA/HLDS/HNGS
|
|
84 |
Caliper closed. Invalid HLDS. |
||
Recorded open hole |
|||||
84 |
Depth reference. |
||||
2. FMS/DSI/GPIT/HNGS
|
|
85 |
Caliper closed. Invalid FMS. |
||
Recorded open hole |
|||||
75.5 |
After coring in Hole U1567A was completed, a viscosity mud sweep was conducted, followed by displacement of the hole with 10.5 ppg mud. The MSS/HRLA/HLDS/HNGS tool string was run first. As per shipboard's party request, no porosity tool (APS) was included. The tool string reached total depth without any problems, then acquired a repeat and a main pass. The FMS/DSI/GPIT/HNGS was rigged up next and again it reached total depth without difficulty. It acquired a repeat and a main pass. The wireline heave compensator (WHC) was run whenever the tools were in open hole.
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 match and depth shift to sea floor. The original logs were first depth-matched to the gamma ray log from the main pass of the MSS/HRLA/HLDS/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.
The depth-matched logs have then been shifted to the sea floor.
Environmental
corrections. The HNGS
and HRLA data were corrected for hole size during the recording. The
HLDS data were corrected for hole size during the
recording.
High-resolution
data. Bulk density
(HLDS) data were recorded with a sampling rate of 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 the following modes: P&S monopole, upper and lower dipole, and
Stoneley (all passes). The velocities were computed from the delay timess. They are
generally of good quality, though sonic waveform processing is recommended to improve the 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).
A good correlation exist between the the density, resistivity, and compressional velocities.
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) and by the FMS tool (C1 and C2). The hole was in very good condition, with most of the values in the 11-12 inch range.
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 396. 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