Standard Wireline Data Processing
Science operator: Texas A&M University
Hole: U1464C
Expedition: 356
Location: Roebuck Basin (Tropical SE Indian Ocean)
Latitude: 18° 3.9244' S
Longitude: 118° 37.8942' E
Logging date: September 23, 2015
Sea floor depth (driller's): 275.3 m DRF
Sea floor depth (logger's): 276 m WRF (MSS/HRLA/APS/HLDS/EDTC/HNGS downlog)
Total penetration: 1115.3 m DRF (840 m DSF)
Total core recovered: 94.03 m (17.7 % of cored section)
Oldest sediment recovered:
Lithology: Dolomitic grainstone, packstone, wackestone, mudstone.
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
|
84 |
Closed caliper. Invalid HLDS and APS. |
||
Main
|
recorded open hole |
Hole U1464C was drilled with 9 7/8" bit down to 840 m DRF (564.7 m DSF). The drill pipe was placed at ~86.7 m DSF to guide the logging tools into the open hole. The MSS/HRLA/APS/HLDS/EDTC/HNGS tool string acquired a downlog and a short uplog. The uplog was intended to be a repeat section until the string stopped due to excessive tension. After closing the caliper tool it was inferred that a hole collapse might have occurred above the tool. Recovery of the tool string and of its nuclear sources became the primary objective of the logging operation, which concluded succesfully with an undamaged tool after lowering enough pipe to clear any bridge.
The wireline heave compensator (WHC) was utilized on both MSS/HRLA/APS/HLDS/EDTC/HNGS passes. The ship's peak-to-peak heave averaged 0.6 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 (-276 m). The sea floor depth was determined by the step in gamma ray values obcserved on the MSS/HRLA/APS/HLDS/EDTC/HNGS downlog at 276 m WRF. This differs by 0.7 m from the sea floor depth of 275.3 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 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 corrected for standoff and hole size respectively during the recording.
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 1464C 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). The HLDS caliper indicatea a large hole (> 16"), which becomes increasingly rugged above 520 m WMSF as the tool string approaches the depth where it became stuck. No caliper data were acquired in the upper part of the hole after the recovery operation started.
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