Standard Wireline Data Processing
IODP logging contractor: USIO/LDEO
Hole: U1347A
Expedition: 324
Location: Shatsky Rise, TAMU Massif (NW Pacific Ocean)
Latitude: 32° 30.4750' N
Longitude: 159° 38.710' E
Logging date: September 30-October 1, 2009
Sea floor depth (driller's): 3461 m DRF
Sea floor depth (logger's): could not be determined
Total penetration: 3778.5 m DRF (317.5 m DSF)
Total core recovered: 116.18 m (37 % of cored section)
Oldest sediment recovered: Berriasian
Lithology: chert, chalk, siltstone, sandstone, claystone, massive basalts.
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 2009.
| Tool string | Pass |
Top depth (m WMSF) |
Bottom depth (m WMSF) |
Pipe depth (m WMSF) |
Notes |
1.DIT/APS/HLDS/GPIT/HNGS
|
Downlog |
127.5 |
|
||
Main
|
127.5 |
Reference |
|||
2.FMS/DSI/GPIT/HNGS
|
Downlog
|
127.5 |
|||
Pass 1
|
127.5 |
||||
Pass 2 |
127.5 |
The hole was drilled to a total depth of 317 m WMSF and then conditioned for logging by performing a wiper trip and displacing with 38.5 bbl of barite mud (10.5 ppg). Though barite mud may have an heavy effect on the density and photoelectric effect measurement, it was decided that it was the best approach to keep the hole stable in view of an intensive logging program, which originally included the UBI tool as well. The 9-7/8" RCB bit was released at the bottom of the hole and the pipe was set at 127-128 m WMSF. The logging operations were started with the DIT/APS/HLDS/GPIT/HNGS tool string for two passes, then followed by the FMS/DSI/GPIT/HNGS tool string for three passes. The second DIT uplog was skipped because of a likely jammed caliper arm inside the drill pipe after the first uplog. The originally planned deployement of the UBI tool string failed as soon as rig floor checks showed lack of communication between components of the tool string. Since the replacement of the telemetry cartridge did not solve the problem, the run was cancelled. Investigation of the problem was underway at the time this processing was performwed.
The sea state was relatively calm with a peak-to-peak heave of ~ 1.0 m or less. The wireline heave compensator was used during the entire logging operation.
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 (-
3461 m DRF). The logger's sea floor depth
could not be determined by the step in gamma ray values because the signal was affected by the presence of the Free Fall Funnel, drill pipe, and drill collars. As a result, the sea floor depth given by the drillers (- 3461 m DRF) was used for depth shift. The depth-shifted logs were then depth-matched to the gamma ray log from the main
pass of the DIT/APS/HLDS?GPIT/HNGS tool string (reference).
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
data were corrected for hole size during the recording. The APS and
HLDS data were corrected for standoff and hole size respectively during the
recording.
High-resolution data. Bulk density (HLDS) and neutron porosity (APS) data were recorded at sampling rates of 2.54 and 5.08 cm, respectively, 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.
Acoustic
data. The dipole shear
sonic imager (DSI) was operated in the following modes: P&S monopole
(downlog with medium frequency; passes 1 and 2 with standard frequency), upper dipole (downlog and pass 1 with standard frequency), lower dipole (downlog with low frequency and pass 1 with standard frequency), and cross-dipole (pass 2 with standard frequency). The slowness data from DTCO, DT1, and DT2 are generally of good quality for these passes and were converted to acoustic velocities (VCO, VS1 and VS2), respectively. Reprocessing of the original sonic waveforms, to be performed at a later date, is highly recommended to obtain more reliable velocity results.
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. The slightly stronger gamma ray signals from HNGS (FMS) compared to that from HNGS (DIT) are likely due to the residual radiation of the HLDS minitron from the main pass.
Hole diameter was recorded by the hydraulic caliper on the HLDS tool (LCAL) and by the FMS tool (C1 and C2). A wide (>12") and/or irregular borehole affects most recordings, particularly those that require eccentralization and a good contact with the borehole wall (APS, HLDS). The caliper logs indicate that the upper part of the borehole (above 155 m WMSF) was washed out to the degree (>15") where it may have an adverse response on the tool response. Thus, density and porosity logs in this depth interval should be used with caution.
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 324.
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:Crisitna Broglia