Wireline Sonic Waveform Data Processing
Operator and logging contractor: LDEO-BRG
Hole: 10D (proposed site GD-3-1)
Expedition: NGHP-1
Location: Krishna-Godavari Basin, Eastern India (Bay of Bengal)
Latitude: 15° 51.86' N
Longitude: 81° 50.08' E
Logging date: June 20-21, 2006
Sea floor depth (drillers'): 1050.4 mbrf
Sea floor depth (loggers'): 1047.5 mbrf
Total penetration: 1254.2 mbrf (203.8 mbsf)
Total core recovered: 128.3 m
(62.9 % of cored section)
Oldest sediment cored: n/a
Lithology: Carbonatic
and nannofossil-rich clay
ACOUSTIC TOOL USED: DSI (Dipole Sonic Imager)
Recording mode: Monopole P&S, Upper and Lower Dipole, Stoneley mode (Pass 1), Monopole P&S, Cross Dipole, and Stoneley mode (Pass 2)
Remarks about the recording: The DSI tool started experiencing problems at the beginning of Pass 3 and was unable to record meaningful waveforms.
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: 720 (Pass 1)
Number of rows: 1003 (Pass 2)
The following files have been
loaded:
DSI from FMS/GPIT/DSI/SGT (Pass 1,
open hole)
10D-mono_p1.bin: 46.43-155.85
mbsf
10D-ldip_p1.bin: 46.43-155.85
mbsf
10D-udip_p1.bin: 46.43-155.85
mbsf
10D-st_p1.bin: 46.43-155.85
mbsf
DSI from FMS/GPIT/DSI/SGT (Pass 2,
open hole)
10D-mono_p2.bin: 3.3-155.85
mbsf
10D-st_p2.bin: 3.3-155.85 mbsf
10D-cd_ldip_il_p2.bin:
3.3-155.85 mbsf
10D-cd_ldip_cl_p2.bin:
3.3-155.85 mbsf
10D-cd_udip_il_p2.bin:
3.3-155.85 mbsf
10D-cd_udip_cl_p2.bin:
3.3-155.85 mbsf
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 (-1047.5 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 further questions about the
processing, please contact:
Cristina Broglia
Phone: 845-365-8343
Fax: 845-365-3182
E-mail: Cristina Broglia
Gilles Guerin
Phone: 845-365-8671
Fax: 845-365-3182
E-mail: Gilles Guerin