Standard Wireline Data Processing

 

Science Operator: Texas A&M University

Hole: U1498B

Expedition: 366

Location: Celestial Seamount (Tropical NW Pacific)

Latitude: 16° 27.3716' N

Longitude: 147° 10.1166' E

Logging date: January 29, 2017

Sea floor depth (driller’s): 3296 m DRF

Sea floor depth (logger's): 3297.5 m WRF (MSS/HRLA/HLDS/EDTC-B/HNGS Main Run)

Total penetration (RCB coring): 3556 m DRF (260 m DSF) .

Total core recovered: 82.82 (31.9%)

Oldest sediment recovered: n/a

Lithology: Serpentinite muds with ultramafic clasts

 

 

Data

 

The logging data were recorded by Schlumberger in DLIS format and processed at the Borehole Research Group of Lamont-Doherty Earth Observatory in January 2017.

 

Logging Runs

Tool string
Pass
Top depth (m WMSF) Bottom depth (m WMSF) Pipe depth (m WMSF)
Notes
1. MSS/HRLA/HLDS/EDTC-B/HNGS
Downlog
0
226
~50

Caliper closed. Invalid HLDS.

Repeat
106
224
recorded open hole
Invalid HLDS.
Main
0
225
~50
Depth reference. Invalid HLDS.

 

 

The logging operation was carried out using one tool string (MSS/HRLA/HLDS/EDTC-B/HNGS) only.The HLDS tool was included in the tool string with the sole purpose of acquiring hole size data with the caliper. For safety reasons, noradioactive source was mounted, therefore the density data are invalid. The HLDS Caliper was opened only during the main and repeat run. The tool string encountered a soft obstruction at a depth of 3522 m DRF and thus did not reach the total depth of 3556 m DRF. As a result, all three passes were recorded from this depth up.

.

The sea state was high with a peak-to-peak heave of ~ 2.5 m. The wireline heave compensator was used during the logging operation.

 

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.

 

Processing

 

Depth shift to sea floor and depth match. The original logs were first shifted to the sea floor (-3297.5 m). The sea floor depth was determined by the step observed at the mudline in the gamma ray value (Main Run). This differs for 1.5 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.

 

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 are 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.

 

Quality Control

 

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 (e.g. the resistivity log should show features similar to the sonic velocity log). The gamma ray signature is extremely low, therefore repeatability is not very good. The data should be used with caution. Furthermore, the gamma ray logs recorded through bottom hole assembly (BHA) and drill pipe are degraded even more, 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 (HLDS). Hole diameter was recorded by the hydraulic caliper on the HLDS tool (LCAL). The hole condition was generally good, with the lower section (225-145 m WMSF) relatively narrow (11-13") and smooth but the upper section (145-51 m WMSF) larger (14-17") and rugose.

 

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 reports, Proceedings of the Integrated Drilling Program, Expedition 366. For further questions about the logs, please contact:

 

 

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