Standard Wireline Data Processing

 

IODP logging contractor: USIO/LDEO

Hole: U1399C

Expedition: 340

Location: Lesser Antilles, off Martinique (Caribbean Sea)

Latitude: 14° 23.2593' N

Longitude: 61° 42.6665' W

Logging date: April 2, 2012

Sea floor depth (driller's): 2912.4 m DRF

Sea floor depth (logger's): 2910 m WRF (HRLA/HLDS/MSS/EDTC-B main)

Total penetration:  240 m DSF (3160 m DRF)

Total core recovered: 0 m (logging-dedicated hole)

Oldest sediment recovered: < 410 ka (?)

Lithologies: Alternating layers of hemipelagic mud, volcaniclastic fine sand and tephra

 

 

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 April 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
Downlog
0
239
79
Invalid caliper
Main
0
239

79
Reference
Repeat
118
239
recorded open hole
2. VSI/EDTC-B
recorded open holee
8 stations, 127 shots
3. FMS/DSI/HNGS/GPIT/EDTC-B
Downlog
0
182
79
Invalid caliper
Pass 1
121
209

recorded open hole
Invalid caliper
Pass 2
118
209

recorded open hole
 
Pass 3
0
210

79

 

 

Hole U1399C was prepared for logging by first sweeping with high viscosity mud and then displacing with heavy 10.5 lb/gal barite mud. Owing to hole stability issues the HLDS 137Cs source was not used for the HRLA/HLDS/MSS/EDTC-B 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 0.3 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 of (- 2910 m). This sea floor depth differs by 2.4 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 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.

 

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

 

Acoustic data. The dipole sonic imager (DSI) was operated in the modes of P&S monopole and upper and lower dipole modes. Standard frequency was used in P&S monopole and upper dipole modes, low frequency in lower dipoleode m. The velocities were computed from the P&S monopole compressional and upper and lower dipole shear slownesses. Both compressional and shear velocity logs from the upper dipole are generally of poor quality, but the shear velocity log from lower dipole is largely of good quality. 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 indicated that the hole was relatively in-gauge, increasing from 10" at the bottom of the hole to 14" at ~ 90 m WMSF. There were three wash-out zones (114-115, 129-133, 138-140 m WMSF) where hole diameter was >18"; log data from from those wash-out intervals should be used with caution. Furthermore, no valid caliper data were acquired during the FMS pass 1 as the caliper arms did not open.

 

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