Wireline Sonic Waveform Data
ODP logging contractor: LDEO-BRG
Well name: 792E
Location: Izu Bonin Forearc (NW Pacific)
Latitude: 32° 23.96' N
Longitude: 140° 22.79' E
Logging date: May, 1989
Bottom felt: 1798.2 mbrf (used for depth shift to sea floor)
Total penetration: 885.9 mbsf
Total core recovered: 361.9 m (48.2 %)
TOOL USED: SDT (Sonic Digital Tool)
Recording mode: Depth-derived, borehole compensated mode, long spacing
Remarks about the recording: the main characteristic of the sonic data during the recording was the high noise level that interfered with the signal from the formation. This noise is primarily the result of absence of adequate centralization of the sonic tool, a consequence of the small diameter of the drill pipe, which makes the use of a centralizer extremely risky, as the tool string could easily get stuck. This lack of centralization resulted in asymmetrical arrivals at the receivers and 'road noise" caused by occasional direct contact of the tool with the formation.
Like in all of the past legs, the sonic waveforms are not on depth with the other logs: in Hole 792E they show an offset of about 26 and 10 m downward in the DIT/SDT/NGT and HLDT/SDT/NGT string, respectively. This offset is very clearly visible at the base of the bottom hole assembly in both runs.
Acoustic data have been recorded in LIS format. Each of the four waveforms consists of 500 samples and is recorded at a sampling rate of 0.1524 m. The original data in LIS format has been converted into ASCII and finally binary format.
Each row of the binary file is composed of the entire waveform set recorded at each depth, preceded by the depth. In the general case of 4 waveforms with 500 samples per waveform, this corresponds to 1 + 4x500 = 2001 columns. In this hole, the specifications of the files are:
Number of columns: 2001
Number of rows: 4234 (DIT/SDT/NGT)
Number of rows: 3854 (HLDT/SDT/NGT)
All values are stored as ' IEEE floating point numbers' (= 4 bytes).
Any numerical software or programing language (matlab, python,...) can import the files for further analysis of the waveforms.
The following files were converted:
SDT from DIT/SDT/NGT (bottom hole assembly at ~ 2087 mbrf)
792E-p1.bin: 2047.49-2692.6 mbrf
SDT from HLDT/SDT/NGT (bottom hole assembly at ~ 2087 mbrf)
792E-p2.bin: 2084.37-2671.57 mbrf
The sonic waveform files are not depth shifted to a reference run or to the seafloor. For depth shift to the sea floor, please refer to the DEPTH SHIFT section in the standard log documentation file. Also, please refer to the "Remarks about the recording" note above.
NOTE: For users interested in converting the data to a format more suitable for their own purpose, a simple routine to read the binary files would include a couple of basic steps (here in old fashioned fortran 77, but would be similar in matlab or other languages):
The first step is to extract the files dimensions and specification from the header, which is the first record in each file:
open (1, file = *.bin,access = 'direct', recl = 50) <-- NB:50 is enough to real all fields
read (1, rec = 1)nz, ns, nrec, ntool, mode, dz, scale, dt
The various fields in the header are:
- number of depths
- number of samples per waveform and per receiver
- number of receivers
- tool number (0 = DSI; 1 = SonicVISION; 2 = SonicScope; 3 = Sonic Scanner; 4 = XBAT; 5 = MCS; 6 = SDT; 7 = LSS; 8 = SST; 9 = BHC; 10 = QL40; 11 = 2PSA)
- mode (1 = Lower Dipole, 2 = Upper Dipole, 3 = Stoneley, 4 = Monopole)
- vertical sampling interval *
- scaling factor for depth (1.0 = meters; 0.3048 = feet) *
- waveform sampling rate in microseconds *
All those values are stored as 4 bytes integers, except for the ones marked by an asterisk, stored as 4 bytes IEEE floating point numbers.
Then, if the number of depths, samples per waveform/receiver, and receivers are nz, ns, and nrec, respectively, a command to open the file would be:
open (1, file = *.bin, access = 'direct', recl = 4*(1 + nrec*ns))
Finally, a generic loop to read the data and store them in an array of dimension nrec × ns × nz would be:
do k = 1, nz
read (1, rec = 1+k) depth(k), ((data(i,j,k), j = 1,ns), i = 1,nrec)
For further information about the logs please contact:
E-mail: Cristina Broglia