Standard Wireline Data Processing




Science operator: Texas A&M University

Hole: U1545A

Expedition: 385

Location: Guaymas Basin (tropical NE Pacific Ocean)

Latitude: 27° 39.2315' N

Longitude: 111°53.339' W

Logging date: September 30, 2019

Sea floor depth (driller's): 1604.4 m DRF

Sea floor depth (logger's): 1604 m WRF (MSS/HRLA/HLDS/EDTC-B/HNGS Downlog)

Total penetration:  2107.7 m DRF (503.3 m DSF)

Total core recovered: 389 m (77.3 % of cored section)

Oldest sediment recovered: Mid Pleistocene (< 0.29 Ma)

Lithology: Laminated diatom ooze interbedded with carbonate layers





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
~ 73
Depth reference. Caliper closed, invalid HLDS.
~ 72.5
Spliced reoeat and upper logs.
recorded open hole
Caliper closed, invalid images.
Pass 1
recorded open hole
Pass 2
~ 73



The first run started with a downlog that reached a total depth of 2097 m WRF before losing all tool weight. Since the total penetration depth in hole U1485A was 2107.7 m, it was inferred that the very bottom part of the hole had collapsed and was occupied with infill. A repeat pass was started from 2097 m WRF to about 1990 m WRF; at this point several attempts were made to close the caliper before heading back down for a main run uphole, but they all failed, possibly due to the debris from the collapsed lower part of the hole. Therefore logging continued from 1990 m WRF up to the sea floor. Re-entering the pipe with the caliper still open was difficult and required an extra pull of about 2000 lbs to close it. Then it was decided to proceed with the second tool string (FMS/DSI/GPIT/EDTC-B/HNGS) rather than running a backup MSS/HRLA/APS/HLDS/EDTC-B/HNGS tool string and risking further collapse of the hole before being able to acquire any image data. During the recording of the FMS it was observed that a number of buttons on three of the four FMS pads were dead. The software was adjusted to bypass the dead buttons and new files were produced for both first and second FMS passes.


The wireline heave compensator was used during logging operations. The average heave was about 2 m.


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.




Depth match and depth shift to sea floor. The original logs were first depth-matched to the gamma ray log from the downlog of the MSS/HRLA/HLDS/EDTC-B/HNGS tool string. The downlogwas chosen as the reference run because it was the longest pass. 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 1604 m WRF on the downlog of the MSS/HRLA/HLDS/EDTC-B/HNGS tool string. This depth differed 0.4 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 HLDS data were corrected for standoff and hole size respectively during the recording.


High-resolution data. Bulk density (HLDS) data were recorded 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. The gamma ray data from the EDTC-B tool were acquired with sampling rates of 5.08 and 15.24 cm.  The HRLA was also acquired every 5.08 cm; in the database it is 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 mode (all passes). The velocities were computed from the delay times. Due to some technical issues the velocities derived from the raw sonic dataof the downlog are of poor quality. However, those calculated from the sonic data of pass 1 and 2 reprocessed by Schlumberger onboard are of good quality and should thus be used for interpretation.


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).

Because the original repeat section was eventually spliced with the upper section in order to obtain a continuous uplog, there is an interval where the primary curves are invalid, depending on the position of the tool in the tool string. The density, photoelectric effect, and caliper are invalid from about 1969 to 1990 m WRF (365 and 386 m WMSF), the resistivity is invalid from 1979 and 1990 m WRF (375 to 386 m WMSF), and the magnetic susceptibility is invalid from 1986 to 1990 m WRF (382 to 386 m WMSF).


The 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 HLDS caliper shows values ranging from 10 to about 16.5 inches; the caliper shows a narrowing of the hole to bit size values starting at about 420 m WMSF downward, possibly due to the accumulated infill from the collapsing hole.


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