Data

The logging data was recorded by the University of Montpellier (Geosciences Montpellier) who are 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 (EPC). VSP data was recorded and procesed by the University of Alberta who were contracted by EPC.

Logging Runs

Tool string	Run/Pass	Top depth (m WSF)	Bottom depth (m WSF)	Pipe depth ( m DSF)	Notes
1. ASGR	Thru pipe	0	603.38	~631
2. DIL45	Lower	418.77	623.57	~421
3. EM51	Lower	418.69	623.84	~421
4. 2PSA	Lower	417.68	621.68	~421
5. ABI40	Lower	419.94	575.30	~421
6. ASGR	Lower	409.97	620.77	~421
7. DIL45	Middle	193.24	343.09	~195
8. EM51	Middle	192.95	338.55	~195
9. ASGR	Middle	188.13	337.43	~195
10. 2PSA	Middle	191.98	327.28	~195
11. ABI40	Middle	194.25	328.15	~195
12. VSP	Middle	204.00	328.72	~195	Interval spacing 0.91 m
13. VSP	Through pipe	0.45	204.00	~195	Interval spacing 0.91 m

The depths given in the table are for the processed data. The raw data may contain extra data within the pipe which has been removed from the processed data files. The depths in italics refer to top and bottom depths of files which have then been merged (i.e. the top and bottom depth of the final merged file are those depths that are not in italics).

A complete list of tool and log acronyms is available at http://brg.ldeo.columbia.edu/data/iodp-eso/exp313/exp_documents/iodp-eso-313-acronyms.html.

Logging Nomenclature

The logged intervals in each borehole are described as lower, middle and upper. These do not match across boreholes either in terms of depth or sequence boundary. In any case, logging has not been carried out in more than three stages. These intervals can be seen at

http://brg.ldeo.columbia.edu/data/iodp-eso/exp313/exp_documents/iodp-eso-313-ops-summary.pdf

General Information

The suite of tools available for logging on Expedition 313 consisted of spectral gamma ray (ASGR), velocity (2PSA), conductivity (DIL45), acoustic borehole imaging (ABI40) and magnetic susceptibility (EM51) measurements. Each tool was run separately. Upon coring completion, the spectral gamma log was acquired through drill pipe. Subsequently the hole was conditioned with drill mud. The unfavorable borehole conditions required logging openhole in three separate intervals. Difficulties pulling pipe and the development of bridges affected the ability to log certain sections of the boreholes (especially the upper, more unconsolidated sandy sections). The logger’s zero depth position was taken as the top of the drill pipe. Discrepancies in depths between initial zeroing and zeroing on removal of the tool were generally less than 0.5 m. The depths in the table are for the processed logs (after depth shift to the sea floor). Generally, small discrepancies 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. For New Jersey, logging was done from a platform and so there was no ship heave to account for.

Hole M0027A logging

Through-pipe gamma ray measurements were acquired over almost the entire borehole. VSP measurements were acquired in the middle section in open hole and through pipe in the upper section. Open hole logging operations can be described in three stages:

Lower section (623 to 418 m WSF): in this section, borehole conditions were extremely good. The lowest part of the hole was infilled by 8 m of sediment after pipe pulling. All the tools were deployed, including open hole ASGR measurements to allow calibration of the through-pipe data.

Middle section (343 to 192 m WSF): despite poor logging conditions due to borehole instability, all tools were deployed. Open hole ASGR measurements were acquired to allow the through pipe measurements to be calibrated. The lower part of the middle section has not been logged due to borehole collapse and progressive upward bridge progression during the logging operations. At the bottom of this section, acoustic images affected by cloudy borehole water attest of borehole instability and the acoustic caliper indicates an increasingly narrow hole towards the base of the logged interval.

Upper section (above 192 m WSF): this section of the hole was not logged due to difficulties in pulling the pipe up.

Processing

Depth shift: The original logs were first corrected for the difference in zero tool depths and the difference between logger’s and driller’s zero points (if applicable). For M0027A the logger’s zero was the same as the driller’s zero. See http://brg.ldeo.columbia.edu/data/iodp-eso/exp313/exp_documents/iodp-eso-313-depth-layout.pdf . Finally, logs were depth shifted to the sea floor using the driller’s depth to seafloor (-50.15 m DRF). The driller’s distance to seafloor was chosen as the reference depth because for each hole this fell within the range of the depth to seafloor given by the gamma ray log. The gamma ray log through pipe was taken as the reference log (continuous) and where appropriate other logs were depth-matched to it. For M0027A, no depth matching was required and so all processed log depths are in m WSF.

Environmental corrections: None.

Data merges: the acquisition of acoustic borehole images occurred in several files due to their size (see image notes for more details).

Acoustic data: The 2PSA tool was run at a frequency of 15 kHz and resultant logs can be used to calculate compressional velocities. The data was processed in the WellCAD logging package. Waveform picking was done manually to ensure good quality data. Time picks were saved and the acoustic velocities were calculated (using the receiver spacing of 1 ft). All presented acoustic data is accurate. Where no clear first arrivals in the waveform were present in two receivers, a null value was entered in the database.

Spectral gamma ray: Gamma ray logs recorded through drill pipe should be used only qualitatively due to attenuation of the incoming signal. Open hole repeat sections in M0027A allowed for data calibration. A fault on the down log required a restart, which resulted in an offset +22 m at the conclusion of the log. However, upon applying this correction the sea floor detected on the logs differs less than a 0.5 m from that given by the drillers.

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 or down and up logged intervals, and by correspondence between logs affected by the same formation property (e.g. the resistivity log should show similar features to the acoustic log).

The quality of the ASGR Spectral Natural Gamma data is directly related to lithology in combination with logging speed. Where counts are lower the reliability of the statistical function used to separate raw counts into values of naturally occurring radioactive elements [potassium (K), uranium (U) and thorium (Th)] is degraded. Negative values are indicative of incorrect statistics; when this is the case, K, U and Th values at that depth has been replaced by a null (-999.25). Gamma ray logs recorded through drill pipe should be used only qualitatively due to attenuation of the incoming signal.

A wide and/or irregular borehole affects most recordings, particularly those that require eccentralization and a good contact with the borehole wall. Hole diameter was calculated from the acoustic imaging tool (ABI40).

Whenever possible, data was acquired downlog, uplog and through the pipe. In this case the uplog is usually the final output. The data recorded within the pipe are usually removed from the final log. This data has been retained in the original data files.

Jennifer Inwood

University of Leicester

Phone: 011-44-116-252-3327

Fax: 011-44--116-252-3918

E-mail: iodp@le.ac.uk

Johanna Lofi

University of Montpellier 2

Phone: 033- 467-149- 309

Fax: 033- 467- 143- 244

E-mail: iodp@le.ac.uk

For any web site-related problem please contact:

E-mail: logdb@ldeo.columbia.edu