JIP2 Hole GC955-H

Chevron Gulf of Mexico Gas Hydrate JIP Drilling Program
LWD Sonic Waveforms

Drilling contractor: Chevron

Logging contractor: Schlumberger

Hole: GC955-H

Expedition: JIP2

Location: Green Canyon 955

Latitude: 27° 00' 02.0707" N (NAD27)

Longitude: 90° 25' 35.1142" W (NAD27)

Sea floor depth (step in GR log): 6718 ftbrf

Sea floor depth (drillers'): 6721 ftbrf

Total penetration: 8654 ftbrf

ACOUSTIC TOOL USED: sonicVISION

Remarks about the recording: none.

The sonicVISION data were acquired by Schlumberger/Anadrill in DLIS format and were uploaded in June 2020 using Schlumberger Techlog software. The waveform data files were output as LAS files using Techlog and were finally converted into binary files and GIF images using software written in-house. Each of the four waveforms acquired with the sonicVISION tool consists of 151 samples, at depth intervals of 2 and 6 inches. Each line of the binary files 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 case of 4 waveforms with 151 samples per waveform, this corresponds to 1 + 4x151 = 605 columns. In this hole, the specifications of the files are:

Number of columns: 605

Number of rows: 10646 (2-in sampling rate)

Number of rows: 3550 (6-in sampling rate)

The following files have been loaded:

GC955-H_2in.bin: -1 to 1773 ftbsf

GC955-H_6in.bin: -1 to 1773 ftbsf

ACOUSTIC TOOL USED: SonicScope

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

Remarks about the recording: none.

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 SonicScope data were acquired by Schlumberger/Anadrill in DLIS format and were uploaded in June 2020 using Schlumberger Techlog software. The waveform data files were output as LAS files using Techlog and were finally converted into binary files and GIF images using software written in-house.The sonic waveforms are sampled every 20 (monopole P&S monopole mode) and 40 microsec (quadrupole and low frequency monopole modes), at depth intervals of 2 and 6 inches. Each of the 12 waveforms acquired with the SonicScope tool consists of 256 samples. Each line of the binary files 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 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: 11324 (monopole and quadrupole modes, 2-in sampling rate)

Number of rows: 5017 (monopole low frequency mode, 2-in sampling rate)

Number of rows: 3776 (monopole and quadrupole modes, 6-in sampling rate)

Number of rows: 1674 (monopole low frequency mode, 6-in sampling rate)

The following files have been loaded:

GC955-H_scope_mono_2in.bin: -1 to 1886 ftbsf

GC955-H_scope_mono_6in.bin: -1 to 1886 ftbsf

GC955-H_scope_mono_lf_2in.bin: 1050.17 to 1886 ftbsf

GC955-H_scope_mono_lf_6in.bin: 1050 to 1886 ftbsf

GC955-H_scope_qp_2in.bin: -1 to 18866 ftbsf

GC955-H_scope_qp_6in.bin: -1 to 1886 ftbsf

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 (-6718 m).

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 logs, please contact:

Cristina Broglia

Phone: 845-365-8343

Fax: 845-365-3182

E-mail: chris@ldeo.columbia.edu

Gilles Guerin

Phone: 845-365-8671

Fax: 845-365-3182

E-mail: Gilles Guerin