IODP-MSP drilling and logging contractor: ESO

Hole: M0042A

Expedition: 325

Location: Great Barrier Reef (tropical SW Pacific)

Latitude: 19 50.63885° ' S

Longitude: 150° 26.8818' E

Logging date: March 8, 2010

Sea floor depth (driller's): 56.32 m DSL

Sea floor depth (logger's): 73.78 m WRF on ASGR; 65 m WRF on all other tools

Total penetration: 46.4 m DSF

Total core recovered:  10.94 m (23.58 % of cored section)

Lithologies: carbonate sand, corals, bioclastic sediments

 

 

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

Uplog

0

45.7

Recorded through pipe

 

2. DIL45

Downlog

0

44.6
7

 

3. DIL45

Uplog

0

44.2
7

 

4. ABI40

Uplog

7

43.20
7

 

5. ASGR

Downlog

0

39.1
7

 

6. ASGR

Uplog

0

39.2
7

 

7. EM51

Downlog

2.1

38.4
7

 

8. EM51

Uplog

1.6

38.3
7

 

9. 2PSA

Lower

32.5

38.5
7

 

10. 2PSA

Upper

7.6

32.37
7

 

11. OBI40

Uplog

8.2

39
7

 

12. 2PCA

Uplog

6.5

37.8
7

 

 

 

Downhole logging was conducted in an Advanced Petroleum Institute (API) hole, the diameter of which is beyond the maximum working size for the acoustic and optical tools (ABI40 and OBI40). However, the full tool suite of logs (with the exception of the IDRONAUT) was run downhole. Logging operations began with a through-pipe spectral gamma ray log (ASGR). The API pipe was then tripped to 7 m DSF, and conditioning of the hole started in preparation for open-hole logging. The seabed template was then lowered onto the seabed, and the dual induction logging sonde (DIL45) was deployed, followed by the acoustic borehole image (ABI40), spectral gamma (ASGR), magnetic susceptibility EM51), sonic (2PSA), optical borehole image (OBI40), and caliper (2PCA)sondes. Hole stability for open-hole logging was relatively good.

 

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 first corrected for tools zero (ASGR256: +0.03 m, DIL45: +0.16 m, ABI40: +0.14 m, ASGR256 (OH): +0.14 m, EM51: +0.18 m, 2PSA: +0.06 m, OBI40: +0.12 m, 2PCA: +0.15 m) and shifted to the sea floor (- 73.78 m for ASGR256 TP, - 65 m for all other logs). 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: -2.47 m UL, -2.58 m DL; medium conductivity: -2.68 m UL, -2.79 m DL; magnetic susceptibility: -2.89 m DL, -2.90 m UL; IL: -2.14 m DL, -2.22 m UL, FWS sonic: -8.02 m UL; ASGR256 OH: -3.86 m UL; ABI40: -2.56 m UL; OBI40: -2.596 m UL, Caliper: -2.59 m UL). 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.

 

Environmental corrections: None were applied.

 

Acoustic data: The 2PSA tool was run at a frequency of 25 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). The data are reasonably good and allow for identification of four logging units.

 

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. Gamma ray logs recorded through drill pipe should be used only qualitatively due to attenuation of the incoming signal.

 

Hole diameter was measured by the caliper tool (2PCA). While the hole was extremely large in the uppermost part (0-14 m WMSF), the caliper data show that the hole remains in gauge throughout the remaining interval.

 

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 section of the Site Chapter in IODP Proceedings of Expedition 325. For further questions about the data, please contact:

 

Dr Louise Anderson

University of Leicester

Phone: 011-44-116-252-3327

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

E-mail: IODP-UK

 

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