Standard Wireline Data Processing

 

IODP logging contractor: USIO/LDEO

Hole: U1433B

Expedition: 349

Location: South-West Sub-Basin (South China Sea)

Latitude: 12° 55.1313' N

Longitude: 115° 2.8484' E

Logging date: 18-19 March, 21014

Sea floor depth (driller's): 4390.6 m DRF

Sea floor depth (logger's): 4395.5 WRF (HRLA/HLDS/EDTC-B/HNGS main)

Sea floor depth (logger's): 4392 WRF (HRLA/HLDS/EDTC-B/HNGS main)

Total penetration: 5249.1 m DRF (858.5 m DSF)

Total core recovered: m (65.9% of cored interval)

Oldest sediment recovered: Miocene

Lithologies:  Clay, silty clay, carbonate, 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 March 2014.

 

Logging Runs

Tool string
Run
 Top depth (m WMSF) Bottom depth (m WMSF) Pipe depth (m WMSF) Notes
1.HRLA/HLDS/EDTC-B/HNGS
Downlog
0
841
100

Caliper closed. Invalid HLDS.
Uplog
0
841
100
2.FMS/DSI/GPIT/HNGS
Downlog
0
841
100
Caliper closed. Invalid images.
Main
0
840
100
Repeat 1
822
840
open hole
Repeat 2
822
840
open hole

 

 

Two sepiolite mud sweeps, a wiper trip and displacement of the hole with heavy mud (barite) were conducted in preparation for logging. The goal of the heavy mud was to prevent the collapsing of the hole in intervals of poor core recovery. Ship heave was low (0.3 m form peak to peak), thus the wireline heave compensator was not used.

 

The first run consisted of the HRLA/HLDS/EDTC-B/HNGS tools and it reached 5226 m WRF, 23 m short of total deptrh, but about 35 meters into the basement. The FMS/DSI/GPIT/HNGS tools were deployed during the second run; the tool string reached 5227 m WRF, after passing some obstructions at 5190 m WRF. Two very short passes were cariied out in the basement, followed by a main pass all the way to the sea floor. During this last pass it was difficult to pull the tool string out of the basement interval and the cable had to be pulled at high tension before it came free. The calipers were closed during the entire process of freeing the tool string and were re-opened immediately afterwards.

 

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 (- 4395.5 m). The sea floor depth was determined by the step in gamma ray values at 4395.5 m WRF. This differs by 4.9  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 HRLA/HLDS/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. The HLDS data were corrected for standoff and hole size during the recording.

 

High-resolution data. Bulk density (HLDS) data were recorded with a sampling rate of 2.54 cm 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 EDTC-B tool were recorded at sampling rates of 5.08 and 15.24 cm. 

 

Acoustic data. The dipole shear sonic imager (DSI) was operated in P&S monopole and upper and lower dipole mode on all passes. The monopole transmitter was run at high (standard) frequency on the downlogs and at medium frequency on the uplogs.The sonic velocities were computed from the time slowness data of compressional and shear waves. They are generally of acceptable 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 ( HLDS). Hole diameter was recorded by the hydraulic caliper on the HLDS tool (LCAL) and by the FMS tool (C1 and C2). The borehole was wide and ragged in many intervals above the basement section, which resulted in an underestimate of the formation density.

 

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 349. 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