Standard Wireline Data Processing



Science operator: Texas A&M University

Hole: U1546C

Expedition: 385

Location: Guaymas Basin ((tropical NE Pacific Ocean)

Latitude: 27° 37.8724' N

Longitude: 111°52.7568' W

Logging date: October 13, 2019

Sea floor depth (driller's): 1596.6 m DRF

Sea floor depth (logger's): 1596.6 m WRF

Total penetration: 2136.8 m DRF (540.2 m DSF)

Total core recovered: 139.93 m (60.3 % of cored section)

Oldest sediment recovered: 0.44 Ma

Lithology: Clay and claystone, coarse-grained mafic igneous rocks (sill).






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 2019.


Logging Runs

Tool string
Top depth (m WMSF) Bottom depth (m WMSF) Pipe depth (m WMSF) Notes
Caliper closed. Invalid HLDS. MSS disconnected.
Recorded open hole
Depth reference.
Caliper closed. Invalid FMS.



The first tool string to be lowered in Hole U1546C consisted of MSS/HRLA/HLDS/EDTC/HNGS tools. As soon as the MSS tool was powered up it failed to communicate properly with the acquisition unit. Both attempts to restart the software and to reset the tool remotely failed, so it was decided to switch to a backup tool. Since this did not resolve the problem, it was decided to run the tool string without acquiring susceptibility data. The tool string reached the driller's total depth of  2136.8 m WRF and a repeat and main pass were recorded without difficulties.

The second tool string (FMS/DSI/GPIT/EDCT-B/HNGS) reached a maximun depth of 2121.6 m WRF with a gradual loss of tension rather than a firm landing. Upon opening the caliper, the hole size appeared to be only 4 inches, therefore the uplog was started from that depth. At about 2030 m WRF there was a sudden and unexpected increase in weight, resulting in more than 2,000-lb overpull, with the top of the tool still several meters below the bottom of the hard sill layer. The excess weight dropped after briefly closing the calipers, but because of the significant amount of infill occurrence since the first run and the continuous collapse of the hole it was deemed wise to complete just one uplog. The tools were safely pulled out of the hole without difficulty or visible damage to the equipment.

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.

The sea state was calm, with peak-to-peak average heave of 0.5 m.




Depth match and depth shift to sea floor. The original logs were first depth-matched to the gamma ray log from the main pass of the MSS/HRLA/HLDS/EDTC-B/HNGS tool string. The main pass was chosen as the 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 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.


The depth-matched logs have then been shifted to the sea floor. The sea floor depth was determined by the step in gamma ray values at 1596.6 m WRF. This coincides with 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 HLDS data were corrected for standoff and hole size respectively during the recording.


High-resolution data. The bulk density (HLDS) data were recorded 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 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. Gamma Ray data from the EDTC-B tool were recorded at sampling rates of 5.08 and 15.24 cm.  The HRLA is also acquired every 5.08 cm; in the database itis 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 dipole, and Stoneley (both passes). The velocities were computed from the delay times. The uplog data were processed onboard by Schlumberger with input from LDEO-BRG personnel. This delivered much better results that correlate well with gamma ray, resistivity, and density logs. The uplog is thus to be used for interpretation or creation of a synthetic seismogram.


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.


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 hole is quite large, with the upper part about 16 inches in diameter with smaller sections about 13 inches wide. Below 340 m WMSF the hole is getting smaller, due to the presence of infill from the collapsing formation.


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 385. 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