Standard Wireline Data Processing
Science operator: Texas A&M University/CDEX
Hole: U1547B
Expedition: 385
Location: Guaymas Basin ((tropical NE Pacific Ocean)
Latitude: 27° 30.4128' N
Longitude: 111° 40.7340 ' W
Logging date: October 19, 2019
Sea floor depth (driller's): 1743.3 m DRF
Sea floor depth (logger's): 1743.3 m WRF
Total penetration: 1948.5 m DRF (205.2 m DSF)
Total core recovered: 157.91 m (77 % of cored section)
Oldest sediment recovered:
Lithology: Siliceous claystone
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.
Tool string | Pass
|
Top depth (m WMSF) | Bottom depth (m WMSF) | Pipe depth (m WMSF) | Notes |
1.HRLA/HLDS/EDTC-B/HNGS
|
|
~69.7 |
|
||
~68.7 |
Depth reference |
Upon request by the co-chief scientists, a shorter version of the tool string usually employed for the first run was assembled. It did not include the magnetic susceptibility toool (MSS) and the HNGS was moved from the top to the bottom of the string. The co-chiefs were advised that this move might result in higher GR counts due to activation from the HLDS source, but on the other hand the HNGS would be able to acquire data at the very bottom of the logged interval. Because of difficulties drilling the lower part of the hole it was agreed that the wireline tools would reach as deep as the deepest point cleared during the wiper trip preceding logging operations. A depth of 1945 m DRF was thus set as maximum logging depth.
The tool string descent stopped at 1912 m WRF, where it hung up, firmly sitting down on a ledge. Any attempt to pass the obstruction was useless and the uplog started from that depth. Just before entering the pipe an overpull of more than 2,000 lb occurred. This eventually cleared but the caliper readings showed that while the tool was still static the caliper was being pushed close, allowed to open, and then pushed closed again while the winch remained stopped. It was inferred that there was material falling from the collapsing hole above, which was sliding past the tool. This prompted a quick retrieval of the tool string before getting stuck in the hole. Due to the hole conditons, plans for further passes or subsequent runs were cancelled.
The sea state was calm.
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 downlog was first depth-matched to the gamma ray log from the uplogof the HRLA/HLDS/EDTC-B/HNGStool string. The uplog was 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.
Environmental
corrections. The HNGS
and HRLA data were corrected for hole size during the recording. The HLDS data was corrected for standoff and hole size respectively during the
recording.
High-resolution
data. Bulk density
(HLDS) 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.
Gamma Ray data from the EDTC-B tool were recorded at sampling rates of 5.08 and 15.24
cm.
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). The uppermost and lowermost sections of the open-hole logged interval show that the caliper reached its maximum reading of over 16 inches. The interval from 85 to123 WMSF shows an irregular borehole with variable readings from 13 to 16 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 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