Standard Wireline Data Processing
IODP logging contractor: USIO/LDEO
Hole: U1414A
Expedition: 344
Location: Costa Rica Pacific Margin (Equatorial NE Pacific Ocean)
Latitude: 8° 30.2304' N
Longitude: 84° 13.5298' W
Sea floor depth (driller's): 2469.1 m DRF
Total
penetration: 2940.7 m DRF (471.6 m DSF)
Total core
recovered: 383.95 m (
81 % of cored section)
Oldest
sediment recovered: Miocene (~15 My)
Lithologies:
Silty clay and sand, calcareous and siliceous ooze, calcareous and siliceous cemented siltstone and sandstone, 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 December 2012.
| Tool string | Run/Pass
|
Top depth (m WMSF) | Bottom depth (m WMSF) | Pipe depth (m WMSF) | Notes |
1. HRLA/UBI/GPIT/HLDS/EDTC-B/HNGS
|
Downlog
|
95 |
HLDS Caliper closed |
||
Pass 1
|
open hole |
||||
Pass 2
|
open hole |
||||
Pass 3 |
95 |
||||
2. FMS/DSI/GPIT/EDTC-B/HNGS
|
Downlog
|
95 |
Calipers closed |
||
Pass 1
|
open hole |
||||
Pass 2
|
95 |
Reference |
Hole U1414A was drilled to a depth of 2940.7 m DRF (471.6 m DSF). Since the hole had been cored and re-entered without problems, no wiper trip was carried out before starting the logging operations. Ten barrels of heavy mud were pumped at the bottom of the hole to stop backflow.
The HRLA/UBI/HLDS/EDTC-B//GPIT/HNGS tool string was run first; a downlog and three uplogs were recorded. No data could be collected below 2886 m WRF (417 m WSF), due to an impassable obstruction. The wireline heave compensator (WHC) was not used, due to malfunction. The sea state, however, was calm, with peak-to-peak heaves of less than 1 m.
The FMS/DSI/GPIT/EDTC-B/HNGS tool string was run next; one downlog and two uplog passes were recorded. The WHC was used, achieving a compensation efficiency of more than 90%, with very low peak-to-peak heave less than 0.5 m. Logs were acquired from the impassable bridge at 2886 m WRF (417 m WSF) up.
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 (- 2469 m). The sea floor depth was determined by the step in gamma ray values at 2469 m WRF on the HRLA/UBI/HLDS/EDTC-B//GPIT/HNGS. This differs by 0.1 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 from the second pass of the FMS/DSI/GPIT/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 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.
High-resolution
data. Gamma Ray data from the EDTC-B tool were 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 and upper and lower dipole on each pass. The original velocity profiles from the three passes are not fully repeatable; the velocities from pass 2, obtained from the processing of the sonic waveforms performed on shore, are of very good quality.
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.
Hole diameter was recorded by the hydraulic caliper on the HLDS tool (LCAL) and by the FMS tool (C1 and C2). The hole is very enlarged and of elliptical shape. Only below 340 m WMSF the FMS caliper readings are less than 11 inches and show a hole of circular shape (basalt interval).
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 344.
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