Standard Wireline Data Processing

Science operator: Texas A&M University

Hole: U1583F

Expedition: 393

Location: Mid-Atlantic Ridge (S Atlantic Ocean)

Latitude: 30° 42.6175' S

Longitude: 20° 26.0336' W

Logging date: July 17, 2022

Sea floor depth (driller's): 4221.5 m DRF

Sea floor depth (logger's): 4222.5 m WRF

Total penetration: 4461 m DRF (239.5 m DSF)

Total core recovered: 45.79 m (33.1% of cored section)

Oldest sediment recovered: ~30.6 Ma

Lithology: Clayey nannofossil ooze and aphyric to moderately plagioclase-olivine-(augite) phyric pillow lavas

Data

The logging data were recorded by Schlumberger in DLIS format. Data were processed at the Borehole Research Group of Lamont-Doherty Earth Observatory in July 2022.

Logging Runs

Tool string	Pass	Top depth (m WMSF)	Bottom depth (m WMSF)	Pipe depth (m WMSF)	Notes
1. HRLA/APS/HLDS/HNGS/EDTC-B	Downlog	0	201	98	Caliper closed. Invalid HLDS and APS
	Repeat	144	234	Recorded open hole	No radioactive source. Invalid HLDS
	Main	0	179	98	No radioactive source. Invalid HLDS
2. FMS/DSI/HNGS	Downlog	0	151.5	98	Caliper closed. Invalid FMS
	Uplog	105	176	Recorded open hole

After the completion of coring operations, the HRLA/APS/HLDS/HNGS/EDTC-B tool string was deployed for logging, followed by the FMS/DSI/HNGS tool string. The first downlog of the triple combo was run with the caliper closed. The radioactive source of the HLDS sonde was not used during the logging operation due to poor hole conditions, and no density logs were acquired for this hole as a result.

The Wireline Heave Compensator (WHC) was used in the open hole interval to counter the ship heave while logging. Sea condition was high with ship heave in the 2-3 m range.

The depths in the table are for the processed logs (after depth matching between passes and depth shift to the sea floor). 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 the 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 match and depth shift to sea floor. The original logs were first depth-matched to the gamma ray log from the triple combo downlog (reference run). 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 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.

The depth-matched logs were then depth-shifted to the sea floor. The sea floor depth was determined by the step in gamma ray values at 4222.5 m WRF observed on the reference run. This differs by 1 m from the sea floor depth given by the drillers (see above).

Environmental corrections. The HNGS and HRLA data were corrected for hole size during the recording. The APS data were corrected for hole size and standoff during the recording.

High-resolution data. Gamma ray data from the EDTC-B and porosity data from the APS tools were recorded at sampling rates of 15.24 and 5.08 cm. The HRLA data were acquired every 5.08 cm; in the database they were resampled at 15.24 cm, for ease of comparison with the other logs.

Acoustic data. The dipole shear sonic imager (DSI) was operated in the following modes: P&S monopole, upper and lower dipoles, and stoneley. The sonic velocities were computed from the slownesses data.

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). For hole U1583F, repeatability is generally poor among passes of gamma ray logs and also among passes of resistivity logs, which make it extremely difficult to depth-match logs for this hole.

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. For hole U1583F, the caliper was near bit size of 9 7/8" for most of the logged open hole interval. Washouts exist at the depth interval of 145-150 m WMSF and also at about 1-2 m below the drill pipe, which may have impaired the quality of the log data.

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 report, Proceedings of the International Ocean Discovery Program, Expedition 393. For further questions about the logs, if the hole is still under moratorium please contact the staff scientist of the expedition.

After the moratorium period you may direct your questions to:

Tanzhuo Liu

Phone: 845-365-8630

Fax: 845-365-3182

E-mail: Tanzhuo Liu