Standard Wireline Data Processing

 

IODP logging contractor: USIO/LDEO

Hole: U1368F

Expedition: 329

Location: South Pacific Gyre (SW Pacific Ocean)

Latitude: 27° 55.0021' S

Longitude: 123° 9.6433' W

Logging date: November 17-18, 2010

Sea floor depth (driller's): 3751.9 m DRF

Sea floor depth (logger's): undetermined

Total penetration:  3867 m DRF 115.1 (m DSF)

Total core recovered: 31.74 m (27.6 % of cored section)

Oldest sediment recovered: Lower-Middle Miocene

Lithologies:  Carbonate oozes and basalts

 

Data

 

The logging data were recorded by Schlumberger in DLIS format. Data were processed at the Borehole Research Group of the Lamont-Doherty Earth Observatory in November 2010.

 

Logging Runs

Tool string
Passes
Top depth (m WMSF)

Bottom depth (m WMSF)
Pipe depth (m WMSF)
Notes
1. DIT/HLDS/GPIT/HNGS

Downlog
0
104.5
34
Invalid HLDS
Pass1
53
104.5
Open hole

Pass 2
0
104.5
34
Reference
2. FMS/GPIT/HNGS
Downlog
0
104.5
34
Invalid FMS
Pass 1
51
103
Open hole
Pass 2
0
103
34

 

 

Hole U1368F was drilled to a total depth of 115.1 m DSF and then conditioned for logging by sweeping with mud. The drill pipe was set at 34 m DSF and seawater was used for logging. The sea state was relatively high with a peak-to-peak heave of 0.4-2 m. The wireline heave compensator was used during the entire 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 (- 3751.9 m). The sea floor depth could not be determined by the step in gamma ray values on the logs. Therefore, the sea floor depth given by the drillers (see above) was used. The depth-shifted logs have then been depth-matched to the gamma ray log from pass 2 of the DIT/HLDS/GPIT/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 HLDS data were corrected for hole size during the recording.

 

High-resolution data. None recorded.

 

 

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, particularly those such as HLDS that require eccentralization and a good contact with the borehole wall. Hole diameter was recorded by the hydraulic caliper on the HLDS tool (LCAL) and by the FMS tool (C1 and C2). The caliper logs indicate that nearly the entire section of the borehole was washed out (diameter >14-19 inches) and that in the depth intervals of 38.5-40.5, 44-46, 63-64, and 86-90 m WMSF the borehole is larger than 20 inches. Thus, density logs in these depth intervals should be used with caution.

 

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 329. 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