Standard Wireline Data Processing
Science operator: Texas A&M University
Hole: U1462C
Expedition: 356
Location: Northern Carnarvon Basin (Tropical SE Indian Ocean)
Latitude: 19° 49.2764' S
Longitude: 115° 42.6186' E
Logging date: September 10-11, 2015
Sea floor depth (driller's): 98 m DRF
Sea floor depth (logger's): 97.5 m WRF (MSS/HRLA/HLDS/EDTC/HNGS uplog)
Total penetration: 1048 m DRF (950 m DSF)
Total core recovered: 398.29 m (43.4 % of cored section)
Oldest sediment recovered:
Lithology: Packstone
Data
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 September 2015.
| Tool string | Run/Pass
|
Top depth (m WMSF) |
Bottom depth (m WMSF) |
Pipe depth (m WMSF) |
Notes |
1. MSS/HRLA/APS/HLDS/EDTC/HNGS
|
Downlog
|
87.5 |
Closed caliper. Invalid HLDS. |
||
Uplog
|
88 |
||||
2. VSI |
recorded open hole |
27 stations, 245 shots. |
|||
3. FMS/DSI/GPIT/EDTC/HNGS
|
Downlog
|
88.3 |
Closed caliper. Invalid FMS. |
||
Pass 1
|
recorded open hole |
||||
Pass 2
|
88 |
Hole U1462C was drilled with 9 7/8'' bit down to 1048 m DRF (950 m DSF). The drill pipe was placed at ~88 m DSF to guide the logging tools into the open hole. The MSS/HRLA/APS/HLDS/EDTC/HNGS tool string acquired a downlog and an uplog. Due to concerns that the bottom of the hole might start to cave in, no repeat run was carried out. The VSI tool was run next; it found a bridge at 881 m WRF (783.5 m WMSF). It acquired 245 shots stacked in 27 stations set about 25 m apart between 205 m WRF (107.5 m WMSF) and 874 m WRF (776.5 m WMSF). The FMS/DSI/EDTC/HNGS tool string was run last; it acquired a downlog and two passes uphole from a depth of 866 m WRF (768.5 m WMSF).
The wireline heave compensator (WHC) was utilized on both MSS/HRLA/APS/HLDS/EDTC/HNGS and FMS/DSI/GPIT/EDTC/HNGS runs. The ship's peak-to-peak heave averaged 1.8 m during the logging operations.
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 (-97.5 m). The sea floor depth was determined by the step in gamma ray values obcserved on the MSS/HRLA/APS/HLDS/EDTC/HNGS main run at 97.5 m WRF. This differs by 0.5 m from the sea floor depth of 98 m DRF given by the drillers. The depth-shifted logs have then been depth-matched to the gamma ray log from the uplog of the MSS/HRLA/APS/HLDS/EDTC/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.
Environmental corrections. The HNGS and HRLA data were corrected for hole size during the recording. The APS and HLDS data were respectively corrected for standoff and hole size during the recording.
Acoustic
data. The dipole shear
sonic imager (DSI) was operated in P&S monopole mode (compressional only) with a speed of 1800 ft/hr. The compressional velocity was computed from the delay time and is
generally of good quality. Processing of the sonic waveforms is recommended in order to get more accurate 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. The overall quality of the data from Hole U1462C is good.
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). The HLDS caliper indicated a in hole near the bottom of the logged interval, gradually increasing to over 16'' above 620 m WMSF. During the first pass, the FMS C2 caliper became stuck at 11.5'', for some unknown reasons. While the quality of the FMS data was affected, the compressional data quality was not. No problems were encountered during the second pass.
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 356. 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