Standard Wireline Data Processing


IODP operator and logging contractor: LDEO-BRG

Hole: U1320A

Expedition: 308

Location: Brazos-Trinity Basin IV (Gulf of Mexico)

Latitude: 27° 18.0809'N

Longitude: 94° 23.2537'W

Logging date: June 9-10, 2005

Sea floor depth (driller's): 1480.4 mbrf

Sea floor depth (logger's): 1478 mbrf

Total penetration: 299.6 mbsf

Total core recovered:  83.7 %

Oldest sediment recovered: Pleistocene to Holocene

Lithologies: turbiditic muds and debris flows.



The logging data was recorded by Schlumberger in DLIS format. Data were processed at the Borehole Research Group of the Lamont-Doherty Earth Observatory.


Logging Runs


Tool string Pass Top depth (mbsf) Bottom depth (mbsf) Bit depth (mbsf) Notes
Pass 1
Through pipe
Pass 2
3. WST
14 stations


Hole U1320A was successfully logged down to total depth, though both the DIT/HLDS/APS//HNGS and the WST encountered a ledge at ~176 mbsf. The lockable flapper valve had to be pumped in order to get the tool strings into and out of the pipe. The wireline heave compensator was used to counter minor ship heave.


The depths in the table are for the processed logs (after depth matching between passes and depth shift to the sea floor). 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 the 'bottom felt' depth in soft sediment.




Depth shift: The original logs were depth matched to the ECGR and DTCO logs from Pass 2 of the DSI/FMS/GPIT/SGT tool string and were then shifted to the sea floor (-1478 m). The sea floor depth was determined from the step in gamma radiation values at the sediment-water interface. For Hole U1320A, the sea-floor depth differs by 2.4 m from the "bottom felt" depth given by the drillers (see above).


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 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 SGT data were corrected for hole size during the recording. The APS and HLDS have been corrected for standoff and hole diameter respectively during the recording.


High-resolution data: Bulk density and neutron porosity data were recorded at a sampling rate of 2.54 and 5.08 cm, respectively. 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. SGT gamma ray was recorded at 15.24 and 5.08 cm sampling rates.


Acoustic data: The dipole shear sonic imager (DSI) was run in P&S mode on the first pass and P&S, cross dipole, and Stonely modes on the second pass.



Quality Control


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 on 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/APS). Hole diameter was not determined on the DSI/FMS/GPIT/SGT tool string. In this hole, the borehole diameter is generally around 10 inches, but with some washed out (>16 inches) layers, for example between 107-110 and 171-176 mbsf.


A null value of -999.25 may replace invalid log values.


Additional information about the drilling and logging operation can be found in the Operations section of the Site Chapter in IODP Expedition Reports Volume 308. For further questions about the logs, please contact:


Cristina Broglia

Phone: 845-365-8343

Fax: 845-365-3182

E-mail: Cristina Broglia