Standard Wireline Data Processing

 

IODP logging contractor: USIO/LDEO

Hole: U1343E

Expedition: 323

Location: Arctic Gateway (Bering Sea)

Latitude: 57° 33.4156' N

Longitude: 175° 48.9951' W

Logging date: August 12-13, 2009

Sea floor depth (driller's): 1967.5 m DRF
Sea floor depth (logger's): 1962.5 m WRF

Total penetration:  2711.3 m DRF (743.8 m DSF)

Total core recovered: 700.27 m (94 % of cored section)

Oldest sediment recovered: Early Pleistocene (~ 2-2.4 my)

Lithologies:  silt with varying amounts of clay and diatoms, and minor amounts of sand, ash, foraminifers, calcareous nannofossils, and sponge spicules.

 

 

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 August 2009.

 

Logging Runs

Tool string
Pass
 Top depth (mbsf) Bottom depth (mbsf) Pipe depth (mbsf)
Notes
1.DIT/APS/HLDS/GPIT/HNGS
Downlog
162
718.5
Open hole

Invalid HLDS
Repeat
683
746
Open hole
Main
0
746
101.5
Reference
2. FMS/DSI/GPIT/HNGS
Downhole
17
746
104
Pass 1
151
746
Open hole
Pass 2
94
746
103

 

The logging operations started with the DIT/APS/HLDS/GPIT/HNGS tool string, followed by the FMS/DSI/GPIT/HNGS tool string. The wireline heave compensator was used during the entire logging session (except during FMS pass 1), even though the sea was calm. with heave of 0.45 m or less.

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 measurement from a 'bottom felt' depth in soft sediment.

 

 

Processing

 

Depth shift to sea floor and depth match. Sea floor depth was determined by the step in the gamma ray log observed at the sea floor: - 1962.5 m WRF from the DIT/APS/HLDS/GPIT/HNGS main pass. All of the logs were first depth-shifted to the sea floor (- 1962.5 m WRF) and then depth-matched to the DIT/APS/HLDS/GPIT/HNGS main pass (used as a 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. 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 monopole mode (Pass 1 and downlog in standard frequency and pass 2 in lower frequency)), lower dipole (low frequency on all three passes), and upper dipole (standard frequency for downlog and pass 1, lower frequency for 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 (APS, HLDS). The caliper logs indicate that the upper section of the borehole (151-267 m WMSF) was washed out to the degree (>14-19") where it has adversely affected the tool response. Thus, density and porosity logs in this depth interval 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 323. 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