Standard Wireline Data Processing

 

IODP logging contractor: USIO/LDEO

Hole: U1348A

Expedition: 324

Location: Shatsky Rise, TAMU Massif (NW Pacific Ocean)

Latitude: 34 24.9396' N

Longitude: 159 22.9074' E

Logging date: October 5-6, 2009

Sea floor depth (driller's): 3275 m DRF

Sea floor depth (logger's): 3267 m WRF

Total penetration:  3599.1 m DRF (324.1 m DSF)

Total core recovered: 81.01 m (25 % of cored section)

Oldest sediment recovered: Aptian to Albian (early Cretaceous)

Lithology: Nannofossil ooze, chert, sandstones, carbonates, mudstones, breccias

 

 

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 October 2009.

 

Logging Runs

 

Tool string
Pass

Top depth (m WMSF)

Bottom depth (m WMSF)

Pipe depth (m WMSF)

Notes
1. DIT/HLDS/HNGS
Downlog
0
323
101
Invalid HLDS
Pass 1
62
328
101
Pass 2
0
324
101
Reference
2. FMS/DSI/GPIT/HNGS
Downlog
0
324
101
Caliper closed
Pass 1
65
328
101

 

 

The hole was drilled to a total depth of 3599.1 m DRF and then conditioned for logging by performing a wiper trip and displacing 86 bbl of barite mud (10.5 ppg). The 9-7/8" RCB bit was released at the bottom of the hole and the pipe was set at 3372.7 m DRF. The logging operations started with the DIT/HLDS/HNGS tool string (three runs), followed by the FMS/DSI/GPIT/HNGS tool string (three runs). During the second FMS uplog the tool string got stuck inside the pipe and the wireline had to be severed with a Kinley cutter at ~ 3400 m WRF. Because only limited data was recovered from this pass, no processing has been performed.

No GPIT tool was used in the DIT/HLDS/HNGS tool string because of the initial GPIT-related powering-up problem during the rig up of the tool string.

The sea was relatively calm with a peak-to-peak heave of ~ 1.0 m or less. The wireline heave compensator was used during the entire logging operations.

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 - 3267 m WRF. This depth differs 8 m from the driller's bottom-felt depth. The depth-shifted logs were then depth-matched to those of DIT/HLDS/HNGS pass 2 (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 and HLDS data were corrected for hole size during the recording.

 

High-resolution data. Bulk density (HLDS) data were recorded at sampling rates 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.

 

Acoustic data. The dipole shear sonic imager (DSI) was operated in the following modes: P&S monopole and upper dipole for both downlog and pass 1 (all with standard frequency). The slowness data from DTCO and DT2 are generally of good quality for these passes and thus converted to acoustic velocities (VCO and VS2), respectively. Reprocessing of the original sonic waveforms, to be performed at a later date, is highly recommended to obtain more reliable velocity results.

 

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 upper part of the borehole (above 150 m WMSF) was washed out to the degree (>14-19") where it can adversely affect 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 324. 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:Crisitna Broglia