IODP-MSP
drilling and logging contractor: ESO
Hole: M0021B
Expedition: 310
Location:
Latitude: 17° 29.3427' S
Longitude:
149° 24.1692' W
Logging
date: November 16,
2005
Sea
floor depth (driller's): 92.25 mbrf (81.70 mbsl)
Sea
floor depth (logger's): 92.25 mbrf
Total
penetration: 32.21
mbsf
Total
core recovered:
21.12 m (65.57 % of cored section)
Oldest
sediment recovered:
Pleistocene sequence
Lithologies: Reef framework, algal crusts, and
microbialite matrix
TOOL USED: 2PSA (Full Waveform Sonic Probe)
Recording mode: 10 kHz (compressional waveforms), 1
kHz ( Stoneley
waveforms).
Remarks about the recording:
The
2PSA-1000 sonic probe of
Normal modes (monopole surveys) are a result of constructive interference in the waveguides (borehole). For each normal mode, there exists a frequency below which the mode cannot be exited (cutoff frequency). The normal modes are highly dispersive, with their phase velocities approaching head wave velocities as frequency approaches the mode cutoff frequency. The optimal frequency band for producing head waves narrowly includes the cutoff frequencies for the first order compressional and shear-normal modes. In this manner, unwanted modes are not exited and received head waves are high. Shear wave arrivals do not occur in monopole surveys when the shear velocity is less than the fluid velocity because critical refractions cannot occur. In this case, shear velocity can be found from the Stoneley velocity (conducted below the cutoff frequency, so that only the Stoneley wave is received while interference from other modes is suppressed). The calibration of the tool is performed either in water (1500 m/s for P-wave) or into a steel pipe (5440 m/s), while running downhole. The precision of acoustic travel time measurements is approximately 5%.
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). All presented acoustic data is accurate. Where no clear first arrivals in the waveform were present in at least two receivers, a value of zero was entered in the database. The downhole measurement spacing interval selected was 0.05 m.
The acoustic data acquired with the tool acquisition software were
converted into ASCII format. Each of the
four waveforms generally consists of 1024 samples, each recorded every 4 microsec (10 kHz mode).
Each line consists of the entire waveform, preceded by depth.
Generally, the 2PSA tool was run at a frequency of
10 kHz in Pass 1 and 1 kHz in Pass 2 in order to calculate compressional and Stoneley velocities
respectively.
(There are 1025 columns in the output .txt files…...)
The following files have been loaded:
2PSA from the only pass (pipe/casing at 2.55
mbsf, frequency of 10 kHz)
310-M0021B_2PSA_10RX1.txt: 3.20 – 7.80 mbsf
310-M0021B_2PSA_10RX2.txt: 3.20 – 7.80 mbsf
310-M0021B_2PSA_10RX3.txt: 3.20 – 7.80 mbsf
310-M0021B_2PSA_10RX4.txt: 3.20 – 7.80 mbsf
Additional
information about the drilling and logging operations can be found in the
Operations section of the Site Chapter in IODP Proceedings of Expedition 310.
For further questions about the data, please contact:
Jennifer
Inwood
Phone:
011-44-116-252-3327
Fax:
011-44--116-252-3918
E-mail: iodp@le.ac.uk
For any
web site-related problem please contact:
E-mail: logdb@ldeo.columbia.edu