Standard Wireline Data Processing
Logging contractor: LDEO
Hole: U0080A
Expedition: 344S
Location: Baffin Bay (Labrador Sea)
Latitude: 75° 35.9015' N
Longitude: 65° 2.8928' W
Logging date: August 21-22, 2012
Sea floor depth (driller's): 234 m DRF
Sea floor depth (logger's): 231.5 m WRF (MSS/HLDS/APS/HRLA/EDTC-B main run)
Total penetration: 592.5 m DRF (358.5 m DSF)
Total core recovered: 39 % of cored section
Oldest sediment recovered: Aptian-Albian
Lithology: Claystone, carbonaceous mudstone, siltstone and sandstone, mudstone, and coal
The logging data
were recorded by Schlumberger in DLIS format. Data were processed at the
Borehole Research Group of the Lamont-Doherty Earth Observatory in August 2012.
| Tool string | Pass/Run
|
Top depth (m WMSF) | Bottom depth (m WMSF) | Pipe depth (m WMSF) | Notes |
1. HRLA/APS/HLDS/HNGS/EDTC-B
|
Downlog
|
30.5 |
|
||
Repeat
|
Recorded open hole |
||||
Main
|
30.5 |
Depth reference |
|||
2. VSIT/EDTC-B |
Uplog
|
30.5 |
7 stations, 71 shots |
||
3. FMS/GPIT/EDTC-B |
Pass 1
|
Recorded open hole |
|||
Pass 2
|
Recorded open hole |
||||
4. DSI/EDTC-B |
Downlog
|
30.5 |
Monopole, dipole and Stoneley modes |
||
Uplog
|
30.5 |
Monopole, dipole and Stoneley modes |
Hole U0080A was in very good condition, with the surrounding formation well consolidated and unlikely to collapse (no falling material was collected during coring).
The HRLA/APS/HLDS/HNGS/EDTC-B tool string was deployed first and proceeded to log three passes (downlog, main and repeat) without any problem. The caliper from the HLDS tool indicated that the hole was in excellent condition, thus the VSI deployment was scheduled next.
The VSI/EDTC-B tool string reached total depth and acquired check-shots at seven stations, spaced 50 m apart. For more detail about the VSI recording, see the VSP notes.
The Formation MicroScanner (FMS) came next. The original plan included the DSI tool, but during the tool check after rig-up, it was noted that the FMS mounted below the DSI was not responding.
Last, the DSI/EDTC-B tool string was rigged up and run in the hole for two passes, after replacing one of the bow springs on one of the centralizers, which showed signs of wearing. Both downlog and uplog passes were recorded without any incidents.
During the logging operations sea conditions remained calm (~ 0.2 m peak to peak) and the wireline heave compensator was not used.
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 shift to sea floor and depth match. The original logs were first shifted to the sea floor (- 231.5 m WRF). The sea floor depth was determined by the step in gamma ray values at 231.5 m WRF observed on the HRLA/APS/HLDS/HNGS/EDTC-B main run. This differs by 2.5 m from the sea floor depth given by the drillers (see above). The depth-shifted logs were then depth-matched to the gamma ray log from the main run of the HRLA/APS/HLDS/HNGS/EDTC-B 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 in turn matched to it. 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.
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 with 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 are smoothed to match the long-spacing one, in
enhanced processing they are 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.
Gamma Ray data from the HNGS and ETDC-B tools were recorded at sampling rates of 5.08 and 15.24
cm.
Acoustic
data. The dipole shear
sonic imager (DSI) was operated with standard frequency in the P&S monopole, lower dipole and
Stoneley modes in both passes. The upper dipole was recorded in low frequency. The velocities were computed from acoustic slownesses. They are
generally of good quality.
The quality of
the data was 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 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
(APS, HLDS). Hole diameter was recorded by the hydraulic caliper on the HLDS
tool (LCAL) and by the FMS tool (C1 and C2). Both calipers show very good hole
conditions.
A null value of
-999.25 may replace invalid log values.
Additional information about the drilling and logging operations can be found in the expedition report. The BRG and Schlumberger logging reports are also included on the log DVD. For further questions about the logs, please contact:
Tanzhuo Liu
Phone: 845-365-8630
Fax: 845-365-3182
E-mail: tanzhuo@ldeo.columbia.edu
Gilles Guérin
Phone: 845-365-8671
E-mail: guerin@ldeo.columbia.edu