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 (multiplied by 10 to be stored as an integer). 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.