Standard Wireline Data Processing

 

IODP logging contractor: USIO/LDEO

Hole: U1338B

Expedition: 321

Location: Equatorial Pacific Sediment Mound (NE Equatorial Pacific)

Latitude: 2° 30.4692 ' N

Longitude: 117° 58.1736 ' W

Logging date: June 9-11, 2009

Sea floor depth (driller's): 4209.9 m DRF

Sea floor depth (logger's): 4207.5 m WRF (DIT/HLDS/GPIT/HNGS downlog)

Sea floor depth (logger's): 4207.5 m WRF (VSI/SGT uplog)

Sea floor depth (logger's): 4208.7 m WRF (FMS/DSI/GPIT/HNGS pass 2)

Total penetration:  416.1 m DSF

Total core recovered: 417.34 m (101 % of cored section)

Oldest sediment recovered: Lower Miocene

Lithologies: Carbonate muds, nannofossil oozes, diatom oozes, laminated and bioturbated muds.

 

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 May 2009.

 

Logging Runs

Tool string Pass Top depth (mbsf) Bottom depth (mbsf) Pipe depth (mbsf) Notes
1.DIT/HLDS/GPIT/HNGS
Downlog
0
413
85

No valid HLDS
Repeat
343
413
open hole
Main
0
413
84
2. FMS/DSI/GPIT/HNGS
Downlog
0
387
144
Pass 1
197.5
413
open hole
Pass 2
0
413
149
Reference
3. VSI/SGT
Downlog
0
412
142.5
Main
0
164
141

 

Three tool strings were used at Hole U1338B. Prior to logging, the hole was swept with ~9 ppg sepiolite/attapulgite mud, followed by a wiper trip. After pumping a go-devil through the drill string to open the lockable flapper valve, the hole was displaced with ~10 ppg barite/attapulgite mud. A downlog, main and repeat pass were acquired with the DIT/HLDS/GPIT/HNGS tool string, with the repeat pass recorded befor the main one. During the main pass uphole, the tool got stuck at about 4340 m WRF, due to a borehole restriction. The tool eventually got free but the density and resistivity data acquired from 4342 m WRF (base of the obstruction) to the bottom of the pipe (4289 m WRF) are of very questionable quality and should not be used (see below).

In order to avoid getting stuck again at the obstruction depth, it was decided to lower the pipe below the base of the obstruction for the subsequent logging runs. Three passes of the FMS/GPIT/DSI/HNGS tool string were acquired next without incidents.

The VSI/SGT tool string was run last, with a total of 14 stations acquired overall.

 

The Wireline Heave Compensator was used throughout the logging operations, with more efficiency tests performed.

 

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 sea floor depth was determined by the step in gamma ray values: 4207 abd 4206.2 m WRF for the DIT/HLDS/GPIT/HNGS downlog nd main pass, respectively; 4208.7 m and 4209.7 WRF for the FMS/DSI/GPIT/HNGS downlog and pass 2, respectively; 4209 and 4207.5 m WRF for the VSI/SGT downlog and main pass, repspectively. These values all differ slightly from the sea floor depth given by the drillers 4209.9 m WRF). The depth-shifted logs have then been depth-matched to the gamma ray log from Pass 2 of the FMS/DSI/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 and SGT data were corrected for hole size during the recording. The HLDS data were corrected for hole size during the recording.

 

High-resolution data. Bulk density (HLDS) data were recorded with 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. No high resolution data were recorded with the SGT tool. 

 

Acoustic data. The dipole shear sonic imager (DSI) was operated in the following modes: P&S monopole (standard frequency) and lower dipole (low frequency, even receivers) during pass 1; P&S monopole (low frequency) and upper dipole (standard frequency, odd receivers) during pass 2; P&S monopole and upper dipole (both standard frequency) during the downlog. The velocities were computed from the DTCO (monopole mode), DT1 (lower dipole) and DT2 (upper dipole mode) delay times. The current data is preliminary and should be used with caution. While the compressional velocity log is locally of acceptable quality, reprocessing from the original waveforms, to be performed at a later date, is highly recommended to obtain more reliable 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). The logs from hole U1338B are of very good quality, with excellent repeatibility between passes.

 

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 FMS caliper from the two passes shows remarkable repeatibility, in a hole that looks mostly elliptical, with values in the 11-15 inch range. A comparison of the HLDS caliper with the FMS caliper shows good correlation, though the HLDS caliper tends to align along the longer axis of the hole. The HLDS caliper readings are in thein the 14-19 inch range.

 

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 321. 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