Standard Wireline Data Processing
IODP logging
contractor: USIO/LDEO
Hole: U1413C
Expedition:
344
Location: Costa Rica Pacific Margin (Equatorial NE Pacific Ocean)
Latitude: 8° 44.4483' N
Longitude: 84° 6.7993' W
Logging date:
Sea floor
depth (driller's):
551.4 m DRF
Sea floor
depth (logger's):
550 m WRF
Total
penetration: 1133.6 m DRF (582.2 m DSF)
Total core
recovered: 313.94 m (78% of cored section)
Oldest
sediment recovered:
Pleistocene (~1.9 My)
Lithologies: Claystone and siltstone changing to sandstone with depth
The logging data
were recorded by Schlumberger in DLIS format. Data were processed at the
Borehole Research Group of Lamont-Doherty Earth Observatory in December 2012.
| Tool string | Pass
|
Top depth (m WMSF) | Bottom depth (m WMSF) | Pipe depth (m WMSF) | Notes |
1.DIT/HLDS/EDTC-B/HNGS
|
Downlog
|
102.5 |
Caliper closed, no HLDS source |
||
Uplog
|
102.5 |
No HLDS source. Reference. |
|||
2.UBI/GPIT/EDTC-B/HNGS
|
Downlog
|
102.5 |
Calipers closed |
||
Pass 1
|
102.5 |
||||
Pass 2
|
102.5 |
||||
3.FMS/GPIT/EDTC-B/HNGS |
Downlog
|
102.5 |
Calipers closed |
||
Pass 1
|
102.5 |
||||
Pass 2
|
93.5 |
Hole U1413C was drilled to a depth of 1133.6 m DRF (582.2 m DSF). After a wiper trip, a heavy weight sepiolite/barite mud was used to condition the hole. The sea state was calm, with peak-to-peak heaves of about 1 m.
The first logging string consisted of the DIT/HLDS/EDTC-B/HNGS tools. No radioactive source was mounted in the HLDS housing, thus the tool only measured the hole diameter. A bridge was encountered at 737 m WRF (187 m WSF); after a few unsuccessful attempts to pass the bridge, an uplog was recorded from that depth. The UBI/GPIT/EDTC-B/HNGS tool string was run next; two uplogs were recorded from the impassable bridge at 187 m WSF, with the wireline heave compensator turned off during the second pass. The image is similar to the one recorded during the first pass, though the orientation is slightly different. The FMS/GPIT/EDTC-B/HNGS tool string was run last. During the second pass the pipe was moved about 10 meters higher, which allowed to acquire additional FMS data. Like in the case of the UBI tool, the FMS images from the second pass are similar to that from the first pass, though the orientation of the tool is different (see quality control below).
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 (- 550 m). The sea floor depth was determined by the step in gamma ray values at 550 m WRF on the DIT/HLDS/EDTC-B/HNGS uplog. This differs by 1.4 m from the sea floor depth given by the drillers (see above). The depth-shifted logs have then been depth-matched to the gamma ray log (HSGR) from the uplog of the DIT/HLDS/EDTC-B/HNGS tool string.
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 in turn matched to it. 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 data were corrected for hole size during the recording.
High-resolution
data. Gamma Ray data from the EDTC-B tool were recorded at sampling rates of 5.08 and 15.24
cm.
The quality of the log data at hole U1413C was assessed by checking against reasonable values for the logged lithologies and by repeatability between different passes of the same tool string.
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.
Hole diameter was recorded by the hydraulic caliper on the HLDS tool (LCAL) and by the FMS tool (C1 and C2). The calipers show a very large hole of elliptical shape. The inversion of the FMS calipers C1 and C2 during the second pass indicates that the tool had switched orientation, though the image is similar to that recorded during pass 1.
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 Ocean Drilling Program, Expedition 344.
For further questions about the logs, please contact:
Tanzhuo Liu
Phone: 845-365-8630
Fax: 845-365-8777
E-mail: Tanzhuo Liu
Cristina Broglia
Phone: 845-365-8343
Fax: 845-365-8777
E-mail: Cristina Broglia