JIP2 Hole AC21-A

Chevron Gulf of Mexico Gas Hydrate JIP Drilling Program

LWD Sonic Waveforms

Drilling contractor: Chevron

Logging contractor: Schlumberger

Hole: AC21-A

Expedition: JIP2

Location: Alaminos Canyon 21

Latitude: 26° 55' 23.8503" N (NAD27)

Longitude: 94° 54' 00.0702" W (NAD27)

Sea floor depth (step in GR log): 4940 ftbrf

Sea floor depth (drillers'): 4940 ftbrf

Total penetration: 6700 ftbrf

ACOUSTIC TOOLS USED: sonicVISION and SonicScope

The data from both tools were acquired by Schlumberger in DLIS format, sampled at depth intervals of 2 and 6 inches. In June 2020, as part of an upgrade of the logging database (LogDB), all the sonic waveforms were uploaded and formated using SLB's Techlog software, then exported and converted into binary files and GIF images using in-house software.
All sonic waveform data were depth-shifted to the seafloor (-4940 ft).

sonicVISION data:
Each of the four waveforms acquired with the sonicVISION tool consists of 151 samples, with a 20μs sampling rate.
Each row of the binary files is composed of the entire waveform set recorded at each depth, preceded by the depth value. In the case of 4 waveforms with 151 samples per waveform, this corresponds to 1 + 4x151 = 605 columns. In this hole, the specifications of the sonicVISION files are:

Number of columns: 605

Number of rows: 9596 (2-in sampling rate)

Number of rows: 3200 (6-in sampling rate)

The following files have been created:

AC21-A_2in.bin: -1 to 1598 ftbsf

AC21-A_6in.bin: -1 to 1598 ftbsf

SonicScope data:

Recording mode: Monopole P&S, Low Frequency Monopole, Quadrupole.

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

LOW FREQUENCY MONOPOLE: for Stoneley wave analysis.

QUADRUPOLE MODE: measures shear slowness in slow formations.

The sonic waveforms are sampled every 20μs (monopole P&S mode) and 40μs (quadrupole and low frequency monopole modes). Each of the 12 waveforms consists of 256 samples.
Each row of the binary files is composed of the entire waveform set recorded at each depth, preceded by the depth value. In the case of 12 waveforms with 256 samples per waveform, this corresponds to 1 + 12x256 = 3073 columns. In this hole, the specifications of the files are:

Number of columns: 3073

Number of rows: 10355 (monopole mode, 2-in sampling rate)

Number of rows: 10574 (monopole low frequency mode, 2-in sampling rate)

Number of rows: 10358 (quadrupole mode, 2-in sampling rate)

Number of rows: 3453 (monopole modes 6-in sampling rate)

Number of rows: 3526 (monopole low frequency mode, 6-in sampling rate)

Number of rows: 3454 (quadrupole mode, 6-in sampling rate)

The following files have been created:

AC21-B_scope_mono_2in.bin: -1 to 1724.5 ftbsf

AC21-B_scope_mono_6in.bin: -1 1724.5 ftbsf

AC21-B_scope_mono_lf_2in.bin: -1 to 1761 ftbsf

AC21-B_scope_mono_lf_6in.bin: -1 to 1761 ftbsf

AC21-B_scope_qp_2in.bin: -1 to 1725 ftbsf

AC21-B_scope_qp_6in.bin: -1 to 1725 ftbsf

Data Format:

All values are stored as '32 bits IEEE floating point'.

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

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.