Sonic Waveform Data - NGHP 01 Hole 16A

Wireline Sonic Waveform Data Processing

Operator and logging contractor: LDEO-BRG

Hole: 16A (step-out site from Holes 7A/D)

Expedition: NGHP-1

Location: Krishna-Godavari Basin, Eastern India (Bay of Bengal)

Latitude: 16° 35.5986' N

Longitude: 82° 41.0070' E

Logging date: July 16-17, 2006

Sea floor depth (drillers'): 1264.5 mbrf

Sea floor depth (loggers'): 1266 mbrf

Total penetration: 1481.5 mbrf (217 mbsf)

Total core recovered: 165.39 m (72.2 % of cored section)

Oldest sediment cored: n/a

Lithology: Mostly nannofossil and foraminifer-bearing clays with some sandy intervals (from Hole 7D)

ACOUSTIC TOOL USED: DSI (Dipole Sonic Imager)

Recording mode: Monopole P&S, Upper and Lower Dipole, Stoneley mode (Pass 1), Monopole P&S and Cross Dipole (Pass 2).

Remarks about the recording: none.

MONOPOLE P&S MODE: measures compressional and shear slowness. The monopole transmitter is excited by a high-frequency pulse, which reproduces conditions similar to previous sonic tools.

UPPER DIPOLE MODE: measures shear wave slowness using firings of the upper dipole transmitter.

LOWER DIPOLE MODE: measures shear wave slowness using firings of the lower dipole transmitter.

CROSS-DIPOLE MODE: uses alternate firings of upper and lower dipole transmitter, thus allowing acquisition of orthogonally polarized data for anisotropy studies.

transmitter, driven by a low-frequency pulse, generates the Stoneley wave.

STONELEY MODE: measures low-frequency Stoneley wave slowness. The monopole transmitter, driven by a low-frequency pulse, generates the Stoneley wave.

Acoustic data are recorded in DLIS format. Each of the eight waveforms geerally consists of 512 samples, each recorded every 10 (monopole P&S) and 40 microsec (dipolemodes), at depth intervals of 15.24 cm (6 inches).The original waveforms in DLIS format are first loaded on a virtual PC machine using Schlumberger's Techlog log analysis package. The packed waveform data files are run through a module that applies a gain correction. After they are exported from Techlog in LAS format they are converted into binaryand GIF format (images) are cconverted using in-house software. Each line is composed of the entire waveform set recorded at each depth, preceded by the depth value. In the general case of 8 waveforms with 512 samples per waveform, this corresponds to 1 + 8x512 = 4097 columns. In this hole, the specifications of the files are:

Number of columns: 4097

Number of rows: 821 (Pass 1)

Number of rows: 453 (Pass 2)

The following files have been loaded:

DSI from FMS/DSI/GPIT/SGT (Pass 1, open hole)

16A-mono_p1.bin: 86.24-211.06 mbsf

16A-ldip_p1.bin: 86.24-211.06 mbsf

16A-udip_p1.bin: 86.24-211.06 mbsf

16A-st_p1.bin: 86.24-211.06 mbsf

DSI from DSI/SGT (Pass 2, open hole)

16A-mono_p2.bin: 49.06-117.79 mbsf

16A-cd_ldip_il_p2.bin: 49.06-117.79 mbsf

16A-cd_ldip_cl_p2.bin: 49.06-117.79 mbsf

16A-cd_udip_il_p2.bin: 49.06-117.79 mbsf

16A-cd_udip_cl_p2.bin: 49.06-117.79 mbsf

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

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

The sonic waveform files were depth-shifted to the seafloor (-1266 m) but they were not depth-matched to the reference run. Please refer to the "DEPTH SHIFT" section in the standard processing notes for further information.

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

For any question about the data or about the LogDB database, please contact LogDB support: logdb@ldeo.columbia.edu.