Wireline Sonic Waveform Data
Science operator: BP Exploration( Alaska), Inc.
Hole: Mt. Elbert-01
Location: Milne Point, North Slope (Alaska)
Latitude: 70° 27' 20.304" N
Longitude: 149° 24' 38.8434" W
Logging date: February, 2007
Total penetration: 914 m (from kelly bushing)
Permafrost depth: 595 m
Casing depth: 595 m (24.4 cm)
Kelly bushing: 16.8 m above sea level. Depth reference for all logs.
Ground elevation: 6.5 m above sea level.
Gas hydrate zones: 649.8-666.3 m (Unit C), 614.4-627.9 m (Unit D)
Lithologies: Clay, silty clay, sand, silty sand, and interbedded pebbles.
ACOUSTIC TOOL USED: DSI (Dipole Sonic Imager)
Recording mode: Monopole P&S and Upper and Lower Dipole, Cross-Dipole and Stoneley mode.
Remarks about the recording: none.
MONOPOLE P&S MODE: measures compressional and hard-rock 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.
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 converted 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: 2107 (main)
Number of rows: 2107 (repeat)
The following files have been loaded:
DSI from OBMI/DSI/GPIT/EDTC (Pass 1, casing at 595 m)
mtelbert-01_cd_ldip_cl_p1.bin: 582.8-895 m
mtelbert-01_cd_ldip_il_p1.bin: 582.8-895 m
mtelbert-01_cd_udip_cl_p1.bin: 582.8-895 m
mtelbert-01_cd_udip_il_p1.bin: 582.8-895 m
mtelbert-01_ldip_p1.bin: 582.8-895 m
mtelbert-01_mono_p1.bin: 582.8-895 m
mtelbert-01_st_p1.bin: 582.8-895 m
mtelbert-01_udip_p1.bin: 582.8-895 m
DSI from DSI/GPIT/HNGS (Pass 2, casing at 595 m)
mtelbert-01_cd_ldip_cl_p2.bin: 581.9-807 m
mtelbert-01_cd_ldip_il_p2.bin: 581.9-807 m
mtelbert-01_cd_udip_cl_p2.bin: 581.9-807 m
mtelbert-01_cd_udip_il_p2.bin: 581.9-807 m
mtelbert-01_ldip_p2.bin: 581.9-807 m
mtelbert-01_mono_p2.bin: 581.9-807 m
mtelbert-01_st_p2.bin: 581.9-807 m
mtelbert-01_udip_p2.bin: 581.9-807 m
All logs depths are referred to the kelly bushing, which is 5.6 m above sea level.
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 are depth-matched to the reference run. Please refer to the 'depth_matches' folder in the hole index page for the depth-matching values and 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
Additional information about the drilling and logging operations can be found in the Geological Survey of Canada Bulletin 601 (https://doi.org/10.4095/291751).