Standard Wireline Data Processing

 

IODP logging contractor: USIO/LDEO

Hole: U1397B

Expedition: 340

Location: Lesser Antilles, off Martinique (Caribbean Sea)

Latitude: 14° 54.4075' N

Longitude: 61° 25.3421' W

Logging date: March 23, 2012

Sea floor depth (driller's): 2492.9 m DRF

Sea floor depth (logger's): 2490 m WRF (HRLA/HLDS/MSS/EDTC-B/HNGS main)

Total penetration:  253.5 m DSF (2746.4 m DRF)

Total core recovered: 131.46 m (53.3 % of cored section)

Oldest sediment recovered: > 610 ka (forams)

Lithologies: Turbidites and volcaniclastic turbidites.  Lots of sand and gravel.  Hemipelagic sediments.  Poor recovery below ~110 m DRF

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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 March 2012.

 

Logging Runs

 

Tool string
Pass
 Top depth (m WMSF) Bottom depth (m WMSF) Pipe depth (m WMSF)
Notes
1. HRLA/HLDS/MSS/EDTC-B/HNGS
Downlog
0
219
80
Invalid caliper
Main
0
223

80
Reference
Repeat
116
223
recorded open hole
2. FMS/DSI/GPIT/EDTC-B
Downlog
0
212
80
Invalid caliper
Main
0
208

80
Repeat
113
214
recorded open hole

 

 

Hole U1397B was prepared for logging with a seawater/sepiolite mud. Owing to hole stability issues the HLDS 137Cs source was not used during the HRLA/HLDS/MSS/EDTC-B/HNGS logging run; while no density data were acquired, caliper measurements are available for the main and repeat runs. 

 

The sea state was low, with a peak-to-peak heave of 0.6 m or less. 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 (- 2490 m). This sea floor depth differs by 2.9 m from that given by the drillers (see above). The depth-shifted logs were then depth-matched to the gamma ray log from the HRLA/HLDS/MSS/EDTC-B/HNGS main run(reference).

 

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 in turn matched to it. 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. Due to the large and irregular borehole (see Quality Control below), the gamma ray logs acquired at this hole show poor repeatability between passes, This leads to some uncertainties in depth matching.

High-resolution data. The HNGS data were corrected for hole size during the recording.

 

Acoustic data. The dipole sonic imager (DSI) was operated in P&S monopole and upper and lower dipole modes. Standard frequency was used in P&S monopole and upper dipole modes and low frequency was used in lower dipole mode. The velocities were computed from the P&S monopole compressional and upper and lower dipole shear slownesses. Both compressional and shear velocity data from three passes are of poor quality, except for the shear velocity data from the lower dipole mode. Reprocessing of the sonic waveforms is recommended for better results.

 

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).

 

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.

 

A wide (>12") and/or irregular borehole affects most recordings. Hole diameter was recorded by the hydraulic caliper on the HLDS tool (LCAL). The caliper logs indicate an extremely large hole (>18') for the entire open hole section, resulting in an overall poor quality of the log data.

 

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 340. 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