LWD Sonic Waveform Data

Science operator: CDEX-JAMSTEC

Hole: C0002Q

Expedition: 358

Location: Nankai Trough (NW Pacific Ocean)

Latitude: 33° 18.050' N

Longitude: 136°38.2029 ' E

Logging-while-drilling date: November 17-December 14, 2018

Sea floor depth (as seen on logs): 1967.5 m LRF

Total penetration: 5225.38 m LRF (3257.88 m LSF)

ACOUSTIC TOOL USED: SonicScope

Recording Modes: Monopole P&S, Low Frequency, and Quadrupole.

MONOPOLE P&S: measures compressional slowness in all formations and shear slowness in fast formations.

LOW FREQUENCY MONOPOLE: for Stoneley wave analysis.

QUADRUPOLE: measures shear slowness in slow formations.

The SonicScope data were acquired by Schlumberger/Anadrill in DLIS format. The data was sent onshore to Schlumberger Information Solution for processing. Each of the twelve waveforms acquired with the SonicScope tool consists of 256 samples, each sampled every 20 (monopole P&S) and 40 microsec (quadrupole and low frequency monopole modes), at depth intervals of 5.08 cm (2 inches) and 15.24 cm (6 inches).The processed data in DLIS format were first loaded into the Techlog suite software and were depth shifted to the sea floor. The packed waveform data were run through a module that applies a gain correction and were output in LAS format. Finally, the waveforms were converted into binary format and gif images. at depth intervals of 2 and 6 inches. 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 12 waveforms with 256 samples per waveform, this corresponds to 1 + (12x256 )= 3073 columns. In hole C0002Q, the specifications of the files are:

Number of columns: 3073

Number of rows: 1555 (2-in, 5.08-cm sampling rate)

Number of rows: 519 (6-in, 15.24-cm sampling rate)

The following files have been loaded:

358-C0002Q_mono_2in.bin: 2861.49-2908.59 m LSF

358-C0002Q_mono_lf_2in.bin: 2861.49-2908.59 m LSF

358-C0002Q_qp_2in.bin: 2861.49-2908.59 m LSF

358-C0002Q_mono_6in.bin: 2861.49-2908.59 m LSF

358-C0002Q_qp_6in.bin: 2861.49-2908.59 m LSF

No sonic waveforms with 2-in (5.08-cm) sampling rate were found on the JAMSTEC web site. Gilles Guerin, one of the logging specialists on expedition 358, provided them. The dataset did not include 6-in (5.8-cm) low-frequency waveforms.

All values are stored as '32 bits IEEE float'.

Any numerical software or programing language (matlab, python,...) can import the files for further analysis of the waveforms.

The sonic waveform files were depth-shifted to the seafloor (-1967.5 m).

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 Site Expedition Report and in the Methods section, Proceedings of the International Ocean Discovery Program, Expedition 358.

For questions about the logging operations and the processing performed onboard, please contact:

Yukari Kido

E-mail: ykido@jamstec.go.jp

For database-related questions you may contact:

Cristina Broglia

Phone: 845-365-8343

Fax: 845-365-3182

E-mail: Cristina Broglia

Tanzhuo Liu

Phone: 845-365-8630

Fax: 845-365-3182

E-mail: Tanzhuo Liu