Standard Wireline Data Processing

 

IODP logging contractor: USIO/LDEO

Hole: U1337A

Expedition: 321

Location: Equatorial Pacific Sediment Mound (NE Equatorial Pacific)

Latitude: 3° 50.009 ' N

Longitude: 123°12.352 ' W

Logging date: May 23-25, 2009

Sea floor depth (driller's): 4472 m DRF

Sea floor depth (logger's): 4442.5 m WRF (DIT/HLDS/GPIT/HNGS)

Sea floor depth (logger's): 4474 m WRF (VSI/SGT)

Sea floor depth (logger's): 4467 m WRF (FMS/DSI/GPIT/HNGS)

Total penetration:  449.8 m DSF

Total core recovered: 421.39 m (94 % of cored section)

Oldest sediment recovered: Uppermost Oligocene

Lithology:  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
443
76

No valid HLDS
Pass 1
107.5
446
open hole
Pass 2
0
444
77.5
2. VSI/SGT
Downlog
0
194.91
Upper
0
147.04
Lower
168.7
374.7
3. FMS/DSI/GPIT/HNGS
Pass 1
123
442.5
open hole
Pass 2
0
445
77
Reference

 

Three tool strings were used at Hole U1337A. 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. During logging with the DIT/HLDS/GPIT/HNGS tool string, the Schlumberger engineer noted that one of the wheels in the depth measuring mechanism off the wireline winch was broken, possibly affecting the depth measurement. In fact, this resulted in the sea floor being detected by the DIT/HLDS/GPIT/HNGS tool string at a depth that is more than 15 m higher than the one detected by the remaining tool strings (see depth shifts, below). The wireline heave compensator was thoroughly tested during this run. To reduce the jitteriness observed during logging, a new version of the WHC control software was installed, which resulted in much higher values of the compensation efficiency.

Due to daylight requirements, the VSI/SGT tool string was run next. Nine stations were taken until a hose in the wireline heave compensator burst, releasing a large amount of hydraulic fluid. Due to the favorable weather conditions (1m peak-to trough waves), shooting was resumed, with repair of the WHC postponed to the rig-up of the last tool string. A total of 16 stations were acquired with the VSI; three additional shallow stations were attempted in soft sediments but failed, due to lack of coupling of the VSI to the borehole wall.

The FMS/DSI/GPIT/HNGS tool string run was uneventful, with further tests of the WHC conducted.

 

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. Due to the breakage in the depth measuring mechanism (see above), different values were used to depth shift the original logs to the sea floor. The sea floor depth was determined by the step in gamma ray values: 4442.5 m WRF for the three passes of the DIT/HLDS/GPIT/HNGS tool string. 4467 m WRF for the two passes of the FMS/DSI/GPIT/HNGS tool string and 4474 m WRF for the downlog and lower section of the VSI/SGT and 4472.5 m WRF for the upper section of the VSI/SGT tool string. These values differ differs by 2 to 29.5 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 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 P&S monopole and upper dipole modes during both passes. The velocities were computed from the DTCO (monopole mode) and DT2 (upper dipole mode) delay times. They data display good repeatability between the two passes, with good data below 235 m (WMSF).

 

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 U1337A 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 circular hole that becomes elliptical below 280 m (WMSF), with values in the 11-15 inch range. On the other hand, though similar in shape, the HLDS caliper is consistently higher, with values mostly in the 14-19 inch range. It is suggested that the higher values might be due to a calibration problem that needs further investigation.

 

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