IODP Expedition 325, Hole M0036A - Wireline Standard Data

The logging data was recorded by the University of Montpellier (Laboratoire de Tectonophysique), which is part of the European Petrophysics Consortium (EPC) in .RD format (read by the log software package WellCAD). Data were processed by the European Petrophysics Consortium.

Logging Runs

Tool string	Pass	Top depth (m WMSF)	Bottom depth (m WMSF)	Pipe depth (m WMSF)	Notes
1. ASGR 512	Uplog	0	33.3	Recorded through pipe
2. DIL45	Downlog	0	25.8	8
3. DIL45	Uplog	0	25.8	8
4. 2PSA	Uplog	7.5	16.5	8
5. ASGR 256	Uplog	0	10.7	8
6. EM51	Downlog	0	8.3	8
7. EM51	Uplog	0	7.5	8
8. 2PCA	Uplog	-	-	8	2 failed attempts

Downhole logging was conducted through an Advanced Petroleum Institute (API) hole, the diameter of which is beyond the maximum working size for the acoustic and optical borehole televiewers (ABI40 and OBI40). Therefore, a reduced logging suite was run. The first logging run was conducted through pipe using the ASGR 512 tool to a depth 136.3 m WRF (33.26 m WSF); the tool experienced a power surge on returning to the surface following logging and was no longer functional. Circulation and conditioning of the hole followed in preparation for open-hole logging, with the API pipe set at 8 m DSF. The lowering of the seabed template to the sea floor was slow, as strong currents pushed the electrical umbilical around the underside of the template. Finally, the resistivity (DIL45), sonic (2PSA), open-hole gamma (ASGR 256), and magnetic susceptibility (EM51) sondes were deployed downhole. During this period, a gradual collapse of the hole was noted and each successive tool penetrated to increasingly shallower depths. Last, the caliper tool was deployed; downhole communication problems with the tool required a second attemp with a backup tool. After this attempt also failed, logging operations were terminated.

The depths in the table are for the processed logs (after applying a depth shift to the sea floor).

Processing

Depth shift: The original logs were corrected for tool zero (ASGR512: +0.07 m, DIL45: +0.12 m, 2PSA; +0.01 m, ASGR256: +0.08 m, EM51: +0.11 m ) and shifted to the sea floor (-122.82 m). At this hole, each tool was run on an individual string with no repeated measurements between strings; the open hole (OH) gamma ray log was matched to the gamma ray log measured through pipe, and then the pipe depth kick in all other logs were matched to the pipe kick of the OH gamma log (additional small shifts were made to specific logs: deep conductivity: +0.83 m, medium conductivity: +0.72 m, magnetic susceptibility DL: +0.62 m, magnetic susceptibility UL: +0.65 m, IL DL: +1.05, IL UL: +1.07 m, FWS sonic: -0.09 m). Due to shallow water and hole depths and maintaining a fixed zero position at the top of the drill pipe, depth discrepancies between logs are minimal.

Acoustic data: The 2PSA tool was run at a frequency of 20 kHz . The data was filtered (frequency filter) in such a way that only the energy around the induced frequency (source) was analyzed. Waveform picking was done manually in the LogCrucher software package to ensure good quality data. Time picks were saved and the acoustic velocities were calculated (using the receiver spacing of 1 ft).

Quality Control

The quality of the data is assessed by checking against reasonable values for the logged lithologies and by correspondence between logs affected by the same formation property (e.g. the resistivity log should show similar features to the acoustic log).

A wide and/or irregular borehole affects most recordings, particularly those that require eccentralization and a good contact with the borehole wall. The 2PSA centralizers were undersized, so the tool would fit through the API bit; therefore, the tool was not optimally centralized in the hole and as a result errors were introduced into the measurements.

The quality of the ASGR Spectral Natural Gamma data is directly related to lithology in combination with logging speed. Despite logging speeds of 1.1 m/minute and a taking a sample every 10 cm (collecting gamma ray emissions of the formation for approximately 6 seconds for every sample) the amount of total counts obtained are still very low. This degrades the quality of the statistics that separates the raw counts into activity values of naturally occurring radioactive elements such as potassium (K), uranium (U) and thorium (Th). Negative K values are indicative of incorrect statistics. The gamma ray logs recorded through drill pipe should be used only qualitatively due to attenuation of the incoming signal.

Additional information about the drilling and logging operations can be found in the Operations section of the Site Chapter in IODP Proceedings of Expedition 325.

For any question about the data or about the LogDB database, please contact LogDB support: logdb@ldeo.columbia.edu.