Standard Wireline Data Processing
Science operator: Texas A&M University
Hole: U1461D
Expedition: 356
Location: Northern Carnarvon Basin (Tropical SE Indian Ocean)
Latitude: 20°12.8325' S
Longitude: 115° 3.9389' E
Logging date: August 29-30, 2015
Sea floor depth (driller's): 138.3 m DRF
Sea floor depth (logger's): 141 m WRF (MSS/HRLA/APS/HLDS/EDTC/HNGS Downlog)
Total penetration: 1233.6 m DRF (1095.3 m DSF)
Total core recovered: 325.51 m (58.2 % of cored section)
Oldest sediment recovered:
Lithology: Wackestone, packstone, sand, mud
.
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 August 2015.
| Tool string | Run/Pass
|
Top depth (m WMSF) | Bottom depth (m WMSF) | Pipe depth (m WMSF) | Notes |
1. HRLA/MSS/APS/HLDS/EDTC/HNGS
|
Downlog
|
73.5 |
Closed caliper. Invalid HLDS. Reference run. |
||
Lower
|
recorded open hole |
||||
Upper
|
73.5 |
||||
2. FMS/DSI/GPIT/HNGS/HNGS
|
Downlog
|
73.5 |
Closed caliper. Invalid FMS. |
||
Pass 1
|
recorded open hole |
||||
Pass 2
|
73.5 |
The drilling of Hole U1461D with 9 7/8” bit proceeded uneventfully and reached down to 1095.3 m DSF m (1233.6 m DRF). The drill pipe was positioned at 79 m DSF prior to logging (73.5 m WMSF according to the processed wireline logs) to guide the logging tools into the open hole.
The HRLA/MSS/APS/HLDS/EDTC/HNGS tool string was run first; two sections were logged (lower and upper), with no overlap, as the the second pass (upper) could not descend below 999 m WMSF (1140 m WRF). During the recording of the upper section, the cable tension was 4000-7000 lbs above the values normally expected, with a peak of 9300 lbs at 559 m WMSF (700 m WRF). The tension returned to normal values at about 209 m WMSF (350 m WRF). In addition, the caliper arm did not open beyon 14" from 421 to 338 m WMSF (562 to 479 m WRF); only after applying additional current it opened to reach the maximum value of 17" up to 264 m WMSF (305 m WRF). It was later found out that heavy clay caused the caliper arm to stick. Seawater was pumped down the drill pipe to clean the tools prior to re-entry into the drill pipe. This allowed safe retrieval of the tools without further incidents.
The FMS/DSI/GPIT/EDTC/HNGS tool string was run next; a bridge was encountered at 190 m WMSF (331 m WRF), which prevented the tool string from reaching the total depth. A downlog and two uplog passes were recoderd from that depth.
The wireline heave compensator (WHC) was utilized on both runs. The ship's heave averaged 1.2 m.
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 (-141 m). The sea floor depth was determined by the step in gamma ray values obcserved on the HRLA/MSS/APS/HLDS/EDTC/HNGS downlog at 141 m WRF. This differs by 2.7 m from the sea floor depth of 138.3 m DRF given by the drillers. The depth-shifted logs have then been depth-matched to the gamma ray log from the downlog of the HRLA/MSS/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 corrected for standoff and hole size respectively during the recording.
Acoustic
data. The dipole shear
sonic imager (DSI) was operated in P&S monopole mode (compressional only) with a speed of 1800ft/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 U1461D 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. Since the caliper from the HLDS tool did not open properly between 421 and 338 m WMSF (562 to 479 m WRF), caution is recommended in using the HLDS density data, as no proper correction could be applied.
Hole diameter was recorded by the hydraulic caliper on the HLDS tool (LCAL) and by the FMS tool (C1 and C2). Due to the sticking problem mentioned above, the caliper readings from the HLDS tool are suspicious in the depth interval between 421 and 338 m WMSF.
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:
Tanzhuo Liu
Phone: 845-365-8630
Fax: 845-365-3182
E-mail: Tanzhuo Liu
Cristina Broglia
Phone: 845-365-8343
Fax: 845-365-3182
E-mail: Cristina Broglia