Standard Wireline Data Processing
Science operator: Texas A&M University
Hole: U1554F
Expedition: 395C
Location: Bjorn Drift (Central North Atlantic Ocean)
Latitude: 60° 7.5136' N
Longitude: 26° 42.1140' W
Logging date: July 8-9, 2021
Sea floor depth (driller's): 1880.8 m DRF
Sea floor depth (logger's): 1879.5 m WRF
Total penetration: 2660.7 m DRF (779.9 m DSF)
Total core recovered: 159.9 m (62.3 % of cored section)
Oldest sediment recovered: 12.7 Ma
Lithology: Carbonate-rich sediments and basalts.
The logging data were reorded by Schlumberger in DLIS format. Data were processed at the Borehole Research Group of the Lamont-Doherty Earth Observatory in July 2021.
| Tool string | Pass |
Top depth (m WMSF) |
Bottom depth (m WMSF) |
Pipe depth/casing depth (m WMSF) |
Notes |
| 1. MSS/HRLA/APS/HLDS/HNGS | Downlog | 0 | 764 | 590/603.5 | Caliper closed. Invalid APS and HLDS. |
| Repeat | 655 | 781 | Recorded open hole | ||
| Main | 0 | 781 | 590/603.5 | Reference run for depth matching. | |
| 2. FMS/DSI/GPIT/HNGS | Downlog | 0 | 782 | 590/603.5 | Caliper closed. Invalid FMS. |
| Repeat | 650.5 | 781 | Recorded open hole | ||
| Main | 0 | 781 | 590/603.5 | ||
| 3. UBI/GPIT/HNGS | Downlog | 0 | 776 | 590/603.5 | No UBI images. |
| Pass 1 | 631 | 775 | Recorded open hole | ||
| Pass 2 | 586 | 775 | Recorded open hole | ||
| Pass 3 | 0 | 584 | 590/603.5 | No UBI images. |
Following coring operations, hole U1554F was conditioned for wireline logging with a 50-barrel high-viscosity mud sweep. The MSS/HRLA/APS/HLDS/HNGS tool string was deployed first, followed by the FMS/DSI/GPIT/HNGS tool string. The first two runs acquired three passes each (downlog and 2 uplogs). The UBI/GPIT/HNGS tool string was deployed last. The UBI imager was turned off during the downlog pass and only fluid velocity data were collected. It was turned on during the uplog passes (1 and 2) to acquire acoustic images of borehole walls. No difficulty was experienced getting the tool strings inside the casing and drill pipe, which were located at 603.5 and 590 m WMSF, respectively.
The wireline heave compensator (WHC) was used in the open hole intervals to counter the 1-2 m ship heave during the logging operations.
The depths in the table are for the processed logs (after depth matching between passes and depth shift to the sea floor). 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 depth-matched to the gamma ray log from the main pass of the MSS/HRLA/APS/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 the features in the equivalent logs from the other runs are matched to it in turn. This matching is performed manually. The depth adjustments 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 were shifted to the sea floor. The sea floor depth was determined by the step in gamma ray values at 1879.5 m WRF observed on the MSS/HRLA/APS/HLDS/HNGS main pass. This value differs 1.3 m from the sea floor depth given by the drillers (see above).
Environmental corrections. The HNGS and HRLA data were corrected for hole size during the recording. The APS and HLDS data were corrected for standoff and hole size respectively during the recording.
High-resolution data. Bulk density (HLDS) and neutron porosity (APS) data were recorded at sampling rates of 2.54 and 5.08 cm, respectively, 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.
The HRLA resistivity was also acquired every 5.08 cm; in the database it was resampled at 15.24 cm, for ease of comparison with the other logs.
Acoustic data. The dipole shear sonic imager (DSI) was operated in the following modes: P&S monopole, upper and lower dipole. The sonic velocities were computed from the slownesses and they generally correlate well with the resistivity logs in the basement section.
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). Repeatability between logging runs is generally good.
Density and porosity measurements of the basement basalt were roughly 2.7-2.8 g/cm3 and 10-20% , respectively. In the sediment interval bove the basalts the density and porosity readings were 1.6-1.8 g/cm3 and 50-80%. The HRLA resistivity data ranged around 100-500 ohmm in the basalt and around 1 ohmm in the sediment.
Gamma ray logs recorded through bottom hole assembly (BHA), drill pipe, and casing should be used only qualitatively because of their attenuation of the incoming signal.
A wide (>12") and/or irregular borehole affects most recordings, particularly those that require eccentralization and a good contact with the borehole wall (APS, 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 gauge within the basement section (648-782 m WMSF) but was was markedly enlarged up to 18 in. in the sediment intervalt. As a result, density and porosity logs from 648 to 603 m WMSF should be used with caution.
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 395C.
For any question about the data or about the LogDB database, please contact LogDB support: logdb@ldeo.columbia.edu.