Standard Wireline Data Processing
Science operator: Texas A&M University
Hole: U1459C
Expedition: 356
Location: Perth Basin (Tropical SE Indian Ocean)
Latitude: 28° 40.2398' S
Longitude: 113° 33.5365' E
Logging date: August 12, 2015
Sea floor depth (driller's): 203 m DRF
Sea floor depth (logger's): 205 m WRF (MSS/HLDS/EDTC/HNGS Main run)
Total penetration: 603 m DRF (400 m DSF)
Total core recovered: 22.60 m (11.6 % of cored section)
Oldest sediment recovered:
Lithology: Glauconite-rich grainstone, grainstone with dolomite, dolostone with sand, unlithified, fine grained, very well sorted sand and gravel size grainstone. Chert in the lower part of the hole.
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
|
Top depth (m WMSF) | Bottom depth (m WMSF) | Pipe depth (m WMSF) | Notes |
1. MSS/HLDS/EDTC/HNGS
|
Downlog
|
68 |
No nuclear source and closed caliper. Invalid HLDS. |
||
Repeat
|
recorded open hole |
No nuclear source. Invalid HLDS.
|
|||
Main
|
68 |
No nuclear source. Invalid HLDS. Spliced from two passes. |
|||
2. FMS/DSI/HNGS/HNGS
|
Downlog
|
68 |
Closed caliper. Invalid FMS. |
||
Pass 1
|
recorded open hole |
||||
Pass 2
|
68 |
Hole U1459C was drilled with 9 7/8” bit down to 603 m DRF (400 m DSF). The drill pipe was placed at 68 m WMSF to guide the logging tools into the open hole. In preparation for logging, the hole was first swept with 30 barrels of high viscosity mud and then displaced with 120 barrels of 11+ ppg mud. Significant hole problems such as stuck pipe were reported regularly during the drilling. In anticipation of possible problems during logging, a modified tool string (MSS/HLDS/EDTC/HNGS) was deployed, which did not include any radioactive sources (the HLDS tool measured only the hole size)), followed by the FMS/DSI/EDTC/HNGS tool string. The original plan to run the seismic tool VSI was eventually cancelled due to the rough sea conditions.
No incidents were encountered during the MSS/HLDS/EDTC/HNGS run, except for a problem with the caliper during the first uplog of the main pass; the caliper arm would not move beyond 10" for about 75 m. It finally released, but another pass was taken to acquire a better caliper response. The two passes were later spliced splice at 500 m upWRF.
The wireline heave compensator (WHC) was utilized on both MSS/HLDS/EDTC/HNGS and FMS/DSI/EDTC/HNGS runs. The ship's heave averaged 2.4 m, with peaks up to 3.5 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 (-205 m). The sea floor depth was determined by the step in gamma ray values obcserved on the MSS/HLDS/EDTC/HNGS main run at 205 m WRF. This differs by 2 m from the sea floor depth of 203 m DRF given by the drillers. The depth-shifted logs have then been depth-matched to the gamma ray log from the main run/pass of the MSS/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 data were corrected for 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 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 U1459C 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.
Hole diameter was recorded by the hydraulic caliper on the HLDS tool (LCAL) and by the FMS tool (C1 and C2). The hole is enlarged above 15" in most of the hole above 250 m WMSF but it drops to 13-14" values in the lower part. Therefore, the log data for the larger section of the hole 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 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