Standard Wireline Data Processing
IODP logging
contractor: USIO/LDEO
Hole: 1256D, re-entry
Expedition:
Location: Guatemala Basin (NE equatorial Pacific)
Latitude: 6° 44.1631' N
Longitude: 91° 56.6012' W
Logging date:
Sea floor
depth (driller's):
3645 m DRF
Sea floor
depth (logger's):
3643.5 m WRF (from previous expeditions)
Total
penetration: 5165 m DRF (1520 m DSF)
Total core
recovered: not applicable (mostly cored during previous expeditions))
Oldest sediment recovered: Calcareous nannofossil ooze (Middle Miocene) at Hole 1256B during ODP Leg 206
Lithologies:
Clay-rich sediments and nannofossil ooze (sediments). Basalt and gabbro (basement).
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 June 2011.
| Tool string | Pass
|
Top depth (m WMSF) |
Bottom depth (m WMSF) |
Pipe depth (m WMSF) |
Notes |
HRLA/APS/HLDS/GPIT/EDTC-B/MTT
|
downlog
|
149 |
1433 |
221 |
Invalid APS/HLDS |
uplog
|
231 |
1516 |
Reference for downlog |
Hole 1256D was a re-entry hole, cleaned by multiple bit runs including tricone and milling bits and several types of junk baskets. The last bit run before logging was a fishing magnet that recovered only little amounts of metal, suggesting that the hole was clear of most debris. The hole was flushed with fresh water in order to decrease the resistivity contrast between the borehole fluid and the formation, and enhance the quality of the electrical images.
The downlog of the HLRA/APS/HLDS/GPIT/EDTCB/MTT tool string was initiated inside the drill pipe. It was resumed after completion of the WHC
testing, logging down at 5000 ft/hr. It was stopped at 5100 m WRF to calibrate the HRLA for the in-situ temperature. While calibrating, the tool
was lowered at 1800 ft/hr and reached the bottom of the hole without trouble.
After starting logging up at 900 ft/hr, the HLDS caliper did not open immediately and the first caliper reading was only at ~5132 m WRF. Due to the position of the caliper in the tool string, about 12 m of caliper readings are missing at the bottom of the hole. At 4850 m WRF the logging speed was increased to 3600 ft/hr in order to complete the caliper log. The MTT started showing erratic readings at the end of the uplog. During rig down, it was observed that the three bow-springs of one of the centralizers were worn out, and the three springs were replaced with new ones for the subsequent FMS/DSI/GPIT/HNGS run.
During the downlog, the FMS/DSI/GPIT/HNGS tool string couldn't pass below 3885 m WRF. With the bit at 3864 m WRF, 20 m of the tool string were outside the pipe and it was concluded that the hold was at the newly refurbished upper centralizer. After trying to pass for a number of times, including bringing the tools back to the surface for problem-fixing and lowering it down again, no progress was made and the tools could not be retrieved. The Kinley fishing tools were eventually used to recover the tool string. As a result, no FMS/DSI/GPIT/HNGS logs were acquired.
The sea state was relatively calm with a peak-to-peak heave of ~ 1.0 m. The wireline heave compensator was used during the logging operation to compensate for the heave-related downhole motion of the tool string.
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 using the sea floor depth of - 3643.5 m determined by the step in gamma ray values during Leg 206. The depth-shifted uplog was then depth-matched to the gamma ray log from the Expedition 312 DLL/APS/HLDS/HNGS/TAP main pass. The depth-shifted downlog was depth-matched to the gamma ray log from the depth-matched uplog of the current expedition.
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 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 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. Gamma Ray data from the EDTC-B tool were recorded at 5.08 and 15.24 cm sampling rates.
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 density 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 (APS, HLDS). Hole diameter was recorded by the hydraulic caliper on the HLDS tool (LCAL). The caliper logs indicate that the upper part of the borehole (245 -967 m WMSF) was largely washed out (due to a number of times of re-entries and cleaning) to the degree (>14-19") where it has adversely affected 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 335.
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