Standard Wireline Data Processing
IODP logging
contractor: USIO/LDEO
Hole: U1438E
Expedition:
Location: Amami-Sankaku Basin (Philipine Sea)
Latitude: 27 ° 23.0153' N
Longitude: 134° 19.0898' E
Logging date:
Sea floor
depth (driller's):
4711 m DRF
Sea floor
depth (logger's):
4711 m WRF (MSS/HRLA/HLDS//EDTC-B/HNGS uplog)
Total
penetration: 6322 m DRF (1611 m DSF)
Total core recovered: 60.6 % of cored section (casing from seafloor to 605 m DSF)
Oldest
sediment recovered: n/a
Lithologies: Mud with ash, turbidites, conglomerates, breccia, sandstone, dolerite and basalt
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 July 2014.
| Tool string | Pass
|
Top depth (m WMSF) | Bottom depth (m WMSF) | Pipe depth (m WMSF) | Notes |
MSS/HRLA/HLDS/EDTC-B/HNGS
|
Downlog
|
187 |
Caliper closed. |
||
Uplog
|
187 |
No radioactive source for HLDS. Reference Run. |
|||
GBM |
Uplog
|
187 |
Goettingen Borehole Magnetometer; 3rd party tool |
After drilling completion, only seawater was used to prepare the hole and no wiper trip was scheduled due to the bridging with the pipe at the sediment/basement interface (1189 m DSF). The drill pipe was pulled out to a depth of 187 m DSF inside the casing (casing shoe at 605 m DSF). Because the drillers encountered a lot of overpull and drag from total depth to 1100 m DSF, no radioactive source was used during the logging operations. Therefore, the HLDS tool only measured the hole size (caliper readings). Additionally, a hole finder was used at the bottom of the MSS/HRLA/HLDS/EDTC-B/HNGS tool string. The hole finder was modified from the previous version available onboard to fit all the tool strings by adding a piece of stainless pipe. The tool string reached a depth of 1589 m DSF (5900 m WRF), where an impenetrabale bridge was encountered.
Because the caliper arm measured a hole diameter of 18 inches from the bridge (1189 m DSF) to the casing shoe (605 m DSF), it was decided not to run the FMS-sonic and the VSI tool strings in order to gain extra time to log deeper in the next hole dedicated to logging. The Goettingen Borehole Magnetometer (GBM) was run next; it also reached 1589 m DSF (5900 m WRF), where a bridge prevented any deeper logging.
Ship heave was relatively low (0.6 m from peak to peak), and the wireline heave compensator was used during the logging operations.
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 (- 4711 m WRF). The sea floor depth was determined by the step in gamma ray values on the uplog at 4711 m WRF, consistent with the drillers' seafloor depth of 4711 m DRF. The depth-shifted logs have then been depth-matched to the gamma ray log from the downlog.
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 HLDS data were corrected for hole size during the
recording.
High-resolution data. No bulk density (HLDS) data were recorded due to the lack of a radioactive source on the HLDS.
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). Nearly the entire logged hole section is extremely wide (>18"), beyong the reach of the caliper arms, and thus not ideal for logging.
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 reports,
Proceedings of the Integrated Drilling Program, Expedition 351.
For further questions about the logs, please contact:
Tanzhuo Liu
Phone: 845-365-8630
Fax: 845-365-3182
E-mail: Tanzhuo Liu
Cristina Broglia
Phone: 845-365-8343
Fax: 845-365-3182
E-mail: Cristina Broglia