Standard Wireline Data Processing

 

IODP logging contractor: USIO/LDEO

Hole: U1353C

Expedition: 317

Location: Canterbury Basin (SW Pacific Ocean)

Latitude: 44 °46.0982' S

Longitude: 171° 40.4380 ' E

Logging date: December 27, 2009

Sea floor depth (driller's): 96 m DRF

Sea floor depth (logger's): 93.5 m WRF (triple combo main pass)

Total penetration:  625 m DRF (529 m DSF)

Total core recovered: N/A, logging-dedicated hole

 

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 December 2009.

 

Logging Runs

Tool string
Pass
Top depth (m WMSF)
Bottom depth (m WMSF)
Pipe depth (m WMSF)
Notes
1. DIT/HLDS/GPIT/HNGS
Downlog
0
528
108

No HLDS data

Main
0
528
108
Reference
Repeat
445
528
Open hole
2. FMS/DSI/GPIT/HNGS
Pass 1 Downlog
0
250
108
Calipers closed
 
Pass 1
142
250
Open hole
 
Pass 2 Downlog
133
211.5
Open hole
Calipers closed
 
Pass 2
106
209
108

 

Hole U1353C was a logging dedicated hole, drilled to a total depth of 625 m DRF. Before logging, it was conditioned by sweeping with 50 bbl of high viscosity mud and displacing with 300 bbl of heavy mud (~ 10.5 ppg, barite). Because of the expected unstable hole conditions, a modified triple combo tool string was used, which did not include the APS tool and employed the HLDS tool without radioactive source for a caliper measurement. The DIT/HLDS/GPIT/HNGS tool string was run first, followed by the FMS/DSI/GPIT/HNGS tool string, which did not reach the total depth of 625 m DRF due to hole blockage at 343 m WRF. The wireline heave compensator was operated during logging even though the peak-to-peak heave was only 0.4 - 0.6 m.

 

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 based on the logger's sea floor depth of 93.5 m WRF. This value differs 2.5 m from the driller's sea floor depth (96 m DRF). The sea floor depth was determined by the step in gamma ray values observed on the DIT/HLDS/GPIT/HNGS main pass. The depth-shifted logs were then depth-matched to those of DIT main pass (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 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 data were corrected for hole size during the recording.

 

Acoustic data. The dipole shear sonic imager (DSI) was run in upper dipole (standard frequency) and lower dipole (low frequency) modes during all FMS passes. The DSI was also run in monopole (medium frequency) mode during the downlog and uplog pass 1 and in monopole (standard frequency) mode during the downlog and uplog pass 2. Because of the slow formation, the automatic picking of wave arrivals in the sonic waveforms did not provide consistently reliable results. Reprocessing of all the original waveforms was performed to validate the original data or extract meaningful compressional and shear velocities. The most reliable shear velocity value is the one derived from the lower dipole (VS1), where the lower source frequency used generated more cohert waveforms.

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.

Hole diameter was recorded by the hydraulic caliper on the HLDS tool (LCAL) and by the FMS tool (C1 and C2). A wide (>12") and/or irregular borehole affects most recordings, particularly those that require eccentralization and a good contact with the borehole wall (HLDS). The caliper logs indicate that the lower half of the hole (> 250 m WMSF) was enlarged ( 17") and the upper half of the hole was slightly narrower, ranging from 14-17" in hole diameter.

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 317. For further questions about the logs, please contact:

 

Cristina Broglia

Phone: 845-365-8343

Fax: 845-365-3182

E-mail: Cristina Broglia

 

Tanzhuo Liu

Phone: 845-365-8630

Fax: 845-365-3182

E-mail: Tanzhuo Liu