LWD Sonic Waveform Data

IODP logging contractor: CDEX

Hole: C0002A

Expedition: 314

Location: Nankai Trough (NW Pacific Ocean)

Latitude: 33° 18.0192'

Longitude: 136° 38.1810' E

Logging-while-drilling date: October 13, 2007

Sea floor depth (as seen on logs): 1964.5 mLRF

Total penetration:  1401.5 mLSF (3366 mLRF)

TOOL USED: LWD sonicVISION

The original LWD sonic data have been translated into DLIS format by Schlumberger Drilling and Measurements. Each of the four waveforms consists of 151 samples at depth intervals of 15.24 cm (6 inches) and 5.08 cm (2 inches). The data in DLIS format is first loaded on a Sun system using GeoFrame software. The waveform data files, consisting of  4 waveforms each, are then converted into ASCII and finally binary format.

Each line of the binary files is composed of the entire waveform set recorded at each depth, preceded by the depth. In the case of 4 waveforms with 151 samples per waveform, this corresponds to 1 + 4x151 = 605 columns. In this hole, the specifications of the files are:

Number of columns: 605

Number of rows: 27595 (5.08 cm sampling rate)

Number of rows: 9199 (15.24 cm sampling rate)

All values are stored as 32 bits IEEE floating point.

Any image or signal-processing program should be able to import the files and display the data.

The following files have been loaded:

 314-C0002A_2in.bin: 0-1391.7168 mLSF

 314-C0002A_6in.bin: 0-1391.7168 mLSF

The binary files have been depth-shifted to the sea floor (- 1964.5 mLRF).

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

  close (1)

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)

  enddo

Additional information about the drilling and logging operations can be found in the Operations and Downhole Measurements sections of the expedition report, Proceedings of the Integrated Drilling Program, Expedition 314 .
For any question about the data or about the LogDB database, please contact LogDB support: logdb@ldeo.columbia.edu.