Standard Wireline Data Processing
Science operator: Texas A&M University
Location: Bengal Fan (equatorial N Indian Ocean)
Latitude: 8° 0.419 ' N
Longitude: 86° 47.8973' E
Logging date: March 17-18, 2015
Sea floor depth (driller's): 3690.5 m DRF
Sea floor depth (logger's): 3686 m WRF (MSS/HRLA/HLDS/EDTC-B/HNGS Main Run)
Total penetration: 3906.3 m DRF (215.7 m DSF)
Total core recovered: 164.99 m (88.4% of cored section)
Oldest sediment recovered: Pleistocene
Lithology: Sand, clay, silt, calcareous clay
The logging data
were recorded by Schlumberger in DLIS format. Data were processed at the
Borehole Research Group of the Lamont-Doherty Earth Observatory in March 2015.
|Top depth (m WMSF)
|Bottom depth (m WMSF)
|Pipe depth (m WMSF)
No nuclear source on HLDS and caliper closed. Invalid data.
No nuclear source on HLDS. Invalid data. Reference run.
Caliper closed. Invalid FMS.
In preparation for logging the drillers circulated 25 barrels of mud to clear the cuttings from the bottom of the hole, released the bit and filled the hole with weighted mud (12 ppg barite). The HRLA/MSS//HLDS/EDTC-B/HNGS tool string was run first. Like in H the previous hole, no radioactive sources were used due to concerns about potential problems in the hole. At about 2170 m DRF inside the pipe (more than 1500 m above the sea floor), the tool string began losing weight. It was inferred that it had encountered the weighted mud, so the mud was re-circulated down to the seafloor and logging resumed without incidents. Log data was collected from total depth to th sea floor and indicated good hole conditions. The FMS/DSI/GPIT/EDTC-B/HNGS tool string was run next; it acquired data downhole and uphole (two passes) from total depth.
The sea state was calm, with peak-to-peak heave of ~0.3 m. The heave compensator was used only during the MSS/HRLA/HLDS/EDTC-B/HNGS/APS/HLDS/HNGS run.
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 shift to sea floor and depth match. The original logs were first shifted to the sea floor (- 3686 m). The sea floor depth was determined by the step in gamma ray values at 3686 m WRF observed on the uplog of the MSS/HRLA/HLDS/EDTC-B/HNGS/APS/HLDS/HNGS tool string. This differs by 4.5 m from the sea floor depth given by the drillers (3690.5 m DRF). The depth-shifted logs have then been depth-matched to the gamma ray log from the main run/pass of the MSS/HRLA/HLDS/EDTC-B/HNGS/APS/HLDS/HNGS tool string. The main runs was chosen as the reference run because it was the longest one to cross the sea floor and the closest in value to the sea florr given by the drillers.
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 was corrected for hole size and the heavy mud during the recording.
High-resolution data. The gamma ray from the EDTC-B tool was recorded at sampling rates of 5.08 and 15.24 cm.
Acoustic data. The dipole shear sonic imager (DSI) was operated in P&S monopole, upper and lower dipole, and Stoneley mode during all three passes. Compressional and two shear velocities were computed from the corresponding delay times. The Stoneley data are not of good quality and have not been converted into velocity.
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 borehole was in good condition, with most diameter values less than 14 inches.
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 354. 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:
E-mail: Cristina Broglia
E-mail: Tanzhuo Liu