Standard Wireline Data Processing

 

 

IODP logging contractor: USIO/LDEO

Hole: U1374A

Expedition: 330

Location: Louisville Sea Mount (Central S Pacific Ocean)

Latitude: 28° 35.7513' S

Longitude: 173° 22.8924 ' W

Logging date: January 21, 2011

Sea floor depth (driller's):1570 m DRF

Sea floor depth (logger's): 1570.5 m WRF (DIT/APS/HLDS/HNGS main run)

Total penetration:  2092 m DRF 522 (m DSF)

Total core recovered: 457.89 m ( 88 % of cored section)

Oldest sediment recovered: 75-76 Ma (Upper Cretaceous)

Lithologies:  Carbonate ooze, volcanic sand and breccia, olivine-phyric basalt (breccia and competent), plagioclase-phyric basalt (breccia and competent), olivine-augite-plagioclase-phyric basalt (breccia and competent), plagioclase-augite-olivine-phyric basalt (breccia and competent) and aphyric basalt (breccia and competent).

 

 

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 January, 2011.

 

Logging Runs

Tool string
Pass
 Top depth (m WMSF) Bottom depth (m WMSF) Pipe depth (m WMSF)
Notes
1.DIT/APS/HLDS/GPIT/HNGS
Downlog
0
506
126
No HLDS/APS
Main
0
517
126
Reference
Repeat
0
248
126
2. GBM
Downlog
n/a
n/a
n/a
3rd Party tool
Uplog
n/a
n/a
n/a
3rd Party tool
3.FMS/DSI/GPIT/HNGS
Downlog
50
487
126
No caliper/images
Main
0
517
127
Repeat
185
517.5
open
4. UBI/GPIT/HNGS
Downlog

0
502
125
No caliper/images
Interval 1
505
515
open
Interval 2
475
514
open
Interval 3
425
463
open
Interval 4
297
313
open
Interval 5
220
256
open
Interval 6
160
204
open
5. GBM
Downlog
n/a
n/a
n/a
3rd Party tool
Uplog
n/a
n/a
n/a
3rd Party tool

 

 

Hole U1374A was drilled with a 9 7/8" RCB coring bit from sea floor to 2092 m DRF. The hole was filled with sepiolite mud and a wiper trip was completeted prior to logging.

The first tool string to be lowered was the DIT/APS/HLDS/GPIT/HNGS. After three attempts to clear past bridges between 1679 and 1709 m WRF the tool string was rigged down at the surface and a bit and wiper trip were carried out to clean the hole of any bridges.

After a downlog, main and repeat run with the DIT/APS/HLDS/GPIT/HNGS were sucessfully completed, the Goettingen Borehole Magnetometer aquired a downlog and uplog. The GBM is a 3rd party tool and therefore the data collected are not processed by LDEO-BRG personnel.

The FMS/DSI/GPIT/HNGS tool string was run next and collected a downlog, main and repeat runs. The UBI/GPIT/HNGS tool string was the last Schlumberger tool string to be run; it acquired data over six selected intervals and during a downlog. The GBM was run again a second time and concluded the logging operations at Hole U1374A.

WHC was used during the logging operations. Ship's heave was about 1 m (peak to peak).

 

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 (- 1570.5 m). The sea floor depth was determined by the step in gamma ray values at 1570.5 m WRF on the main run of the DIT/APS/HLDS/GPIT/HNGS tool string. This differs by 0.5  m from the sea floor depth given by the drillers (see above). The depth-shifted logs have then been depth-matched to the gamma ray log from the main run of the DIT/APS/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 was corrected for hole size during the recording. The APS and HLDS data were corrected for standoff and hole size respectively during the recording.

 

High-resolution data. Bulk density (HLDS) and neutron porosity (APS) data were recorded sampling rates of 2.54 and 5.08 cm, respectively, in addition to the standard sampling rate of 15.24 cm. The enhanced bulk density curve is the result of Schlumberger enhanced processing technique performed on the MAXIS system onboard. While in normal processing short-spacing data is smoothed to match the long-spacing one, in enhanced processing this is reversed. In a situation where there is good contact between the HLDS pad and the borehole wall (low-density correction) the results are improved, because the short spacing has better vertical resolution. Gamma Ray data from the SGT tool were recorded at sampling rates of 5.08 and 15.24 cm. 

 

Acoustic data. The dipole shear sonic imager (DSI) was operated in the following modes: P&S monopole and upper dipole (standard frequency) in all three runs, and Stoneley mode (standard frequency) in the main run. The velocities were computed from the DTCO (compressional), DTSM (shear) and DTST (Stoneley) logs. They are generally of good quality.

 

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 that require eccentralization and a good contact with the borehole wall (APS, HLDS). Hole diameter was recorded by the hydraulic caliper on the HLDS tool (LCAL) and by the FMS tool (C1 and C2). The HLDS caliper shows that the hole is generally less than 12 inches, with the exception of the intervals at 275-298 and 360-380 m WMSF.

 

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 330. 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