Standard Wireline Data Processing

 

 

Science operator: Texas A&M University

Hole: U1480G

Expedition: 362

Location: Sumatra Seismogenic Zone (Equatorial SE Indian Ocean)

Latitude: 3° 2.0550' N

Longitude: 91 ° 36.3370' E

Logging date: September 5, 2016

Sea floor depth (driller's): 4158.7 m DRF

Sea floor depth (logger's): 4158.7 m WRF (HRLA/EDTC-B/HNGS main run)

Total penetration: 5590.3 m DRF (1431.6 m DSF)

Total core recovered: 329.16 m (49 % of cored section)

Oldest sediment recovered: Miocene

Lithology: Bioturbated clay with some silt and fine sand, tuffaceous sandstone and congomerates, basalt 

 

 

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 2016.

 

Logging Runs

Tool string
Pass
Top depth (m WMSF)
Bottom depth (m WMSF)
Pipe depth (m WMSF)
Notes
1.HRLA/EDTC-B/HNGS
Downlog
0
803
757.1

 
Repeat
743
808
open hole
Main
0
808
757.1
Reference

 

 

Hole U1480G was drilled to a depth of 5590.3 m DRF (1431.6 m DSF). A 10 3/4" casing was lowered to a depth of ~ 4220.7 m DRF (62 m DSF). The original plan was to log the entire open hole interval to 5590.3 m DRF (1431.6 m (DSF). However, the hole collapsed as the drill pipe was being pulled out in preparation for logging. Therefore it was decided to deplo a modified tool string without nuclear source, consisting of HRLA/EDTC-B/HNGS. The Active Heave Compensator (AHC) was engaged as soon as the tool string approached he sa floor. A downlog was recorded to 4967.6 m WRF (808.0 m WSF) where the string encountered an obstruction. A repeat pass was conducted from that depth uphole for about 70 m. The main run was recorded from 808 m WSF to the sea floor.

 

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 (- 4158.7 m). The sea floor depth was determined by the step in gamma ray values at 4158.7 m WRF on the HRLA/EDTC-B/HNGS main run. The depth-shifted logs have then been depth-matched to the gamma ray log from the main run of the HRLA/EDTC-B/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.

 

High-resolution data. Gamma Ray data from the EDTC-B tool were recorded at sampling rates of 5.08 and 15.24 cm. 

 

 

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 similar features to the sonic velocity log). Since no acoustic or density data were acquired in Hole U1480G, the data quality assessment is based on the repeatability of each log between different passes. The HRLA resistivity was somehow spikey during the repeat pass. In order to limit these spikes during the main run, a re-calibration of the tool was carried out with the tool resting at the obstruction depth.

 

Gamma ray logs recorded through bottom hole assembly (BHA) and casing should be used only qualitatively, because of the attenuation of the incoming signal. The thick-walled casing attenuates the signal more than the thinner-walled drill pipe.

 

Hole conditions could not be assessed due to the lack of a caliper log.

 

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 . For further questions about the logs, if the hole is still under moratorium please contact the staff scientist of the expedition 362.


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