Standard Wireline Data Processing

Science operator: Texas A&M University

Hole: U1456C

Expedition: 355

Location: Laxmi Basin (Arabian Sea)

Latitude: 16°37.293959' N

Longitude: 68°50.336604' E

Logging date: 17-18 April, 2015

Sea floor depth (driller's): 3649.2 m DRF

Sea floor depth (logger's): 3646 m WRF (FMS/DSI/GPIT/EDTC/HNGS Main run)

Total penetration: 4114.4 DRF (465.2 m DSF)

Total core recovered: 215 m (78.1 % of cored section)

Oldest sediment recovered: Late Pliocene

Lithology: Nannofossil ooze, silt, clay

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 April 2015.

Logging Runs

Tool string	Pass	Top depth (m WMSF)	Bottom depth (m WMSF)	Pipe depth (m WMSF)	Notes
1.MSS/HRLA/HLDS/EDTC/HNGS	Downlog	0	465	81	No nuclear source and closed caliper. Invalid HLDS.
	Repeat	125	465	recorded open hole	No nuclear source. Invalid HLDS.
	Main	0	465	81	No nuclear source. Invalid HLDS.
2.FMS/DSI/GPIT/EDTC/HNGS	Downlog	0	465		Closed caliper. Invalid FMS.
	Repeat	127	465	recorded open hole
	Main	0	465	80
3.APS/HLDS/EDTC/HNGS	Downlog	0	465	80	Closed caliper. Invalid HLDS.
	Pass 1	119	465	recorded open hole
	Pass 2	248	465	recorded open hole
	Pass 3	0	273.5	80

In preparation for logging, the hole was displaced with 171 barrels of 10.5 lb/gal heavy mud. The drilling of Hole U1456C proceeded without any significant problems, though sands were prevalent in many cores with poor recovery, possibly indicating the presence of loose sand throughout the drilled interval. Therefore, as a precaution, it was decided to run the first drill string without a nuclear source on the lithodensity tool, which would still provide a measurement of the hole diameter and therefore some indication of the borehole quality. The deployment of the MSS/HRLA/HLDS/EDTC/HNGS tool string proceeded without incidents and collcted a downlog and two uplogs (main and repeat). The FMS/DSI/GPIT/EDTC/HNGS tool string was deployed next and also acquired one downlog and two upward passes. Because of the lack of problems during the first two deployments and the good conditions of the borehole (as shown by the caliper logs), it was decided to run the APS/HLDS/EDTC/HNGS tool string with both nuclear sources, in order to acquire density and porosity data. A downlog and three passes were recorded. The logging operations concluded very smoothly.

The wireline heave compensator (WHC) was utilized on all logging runs: on average, the ship's heave was around 0.5-0.75 m peak-to-peak.

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 (- 3646 m). The sea floor depth was determined by the step in gamma ray values obcserved on the FMS/DSI/GPIT/EDTC/HNGS main run at 3646 m WRF. This differs by 3.2  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 the main run/pass of the FMS/DSI/GPIT/EDTC/HNGS tool string. This pass was chosen as the reference run because it was the longest recorded pass to cross the sea floor.

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 HRLA 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 at 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 are 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 the following modes: P&S monopole and Stoneley (all passes), cross-dipole (main run), and upper and lower dipole (downlog and repeat run). The velocities were computed from the delay times. They are generally of good quality, with the exception of the shear velocities acquired in the main run, which therefore have not been included in the shore-based database. Processing of the sonic waveforms is recommended in order to get better 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 overall quality of the data from Hole U1456C is good.

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.

The density and porosity data were acquired in thee separate passes, but none of them covered the entoire open hole interval. The first pass ranged from about 120 m WMSF to the bottom of the hole and is deemed to be the best one, as in subsequent passes the recording was affected by the irradiation of the formation on passes 2 and 3. As an example, though pass 3 is the only pass that recorded data up to the mudline, the porosity data are clearly degraded, showing, as expected, values that are much higher than on pass 1. In conclusion, the composite plots included online only show the density and porosity data from 120 m downward.

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). Hole diameter was recorded by the hydraulic caliper on the HLDS tool (LCAL) and by the FMS tool (C1 and C2). The hole is irregular throughout most of the drilled interval; it's enlarged way above 15" in the uppermost 204 m but it drops to 13-14" values in the lower part.

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 355. 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:

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