Wireline Sonic Waveform Data

 

Science operator: Texas A&M University

Hole: U1508C

Expedition: 371

Location: Tasman Sea

Latitude: 34° 26.8905' S

Longitude: 171° 20.2558' E

Logging date: August 31, 2017

Sea floor depth (driller's): 1619.7 m DRF

Sea floor depth (logger's): 1617 m WRF (MSS/HRLA/DSI/HLDS/HNGS/EDTC-B downlog)

Total penetration: 2324 m DRF (704.3 m DSF)

Total core recovered: 163.12 m (66.5 % of cored section)

Oldest sediment recovered: Not specified

Lithology: Gray nannofossil chalk with forminifers

 

ACOUSTIC TOOL USED: DSI (Dipole Sonic Imager)

Recording mode: Monopole P&S and Upper and Lower Dipole (all passes).

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.

 

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 binary and GIF format (images) 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:  4280  (downlog)

Number of rows: 2854 (main pass)

Number of rows:  829 (repeat pass)

 

The following files have been loaded:

DSI from HRLA/MSS/DSI/HLDS/EDTC-B/HNGS (Downlog, drill pipe at  m 87.5 WMSF)

371-U1508C_ldip_d.bin: 0-660 m WSF

371-U1508C_mono_d.bin:  0-660 m WSF

371-U1508C_udip_d.bin:  0-660 m WSF

 

DSI from HRLA/MSS/DSI/HLDS/EDTC-B/HNGS (Main pass, recorded open hole)

371-U1508C_ldip_main.bin: 263-706 m WSF

371-U1508C_mono_main.bin: 263-706 m WSF

371-U1508C_udip_main.bin: 263-706 m WSF

 

DSI from HRLA/MSS/DSI/HLDS/EDTC-B/HNGS (Repeat pass, recorded open hole)

371-U1508C_dip_rep.bin: 572-706 m WSF

371-U1508C_mono_rep.bin: 572-706 m WSF

371-U1508C_udip_rep.bin: 572-706 m WSF

 

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 and depth-shifted to the seafloor (-1617 m). 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.

 

For users interested in reading and converting the data to a format more suitable for their own purpose, the fortran declaration used to open the file *.bin would be:

 

open (1, file = *.bin,access = 'direct', recl = 4*(1+nrec*nsamples))

 

where nrec is the number of receivers (8 in the case of the DSI) and nsamples the number of samples per waveforms.
If the total number of depths where waveforms were recorded is ndepth (for a 150 m interval with data every 15cm, ndepth would be 1001), a generic loop to read the data would be

do k = 1, ndepth
...
read(1, rec=1+k) depth(k), ((data(i,j,k), j=1,nsamples),i = 1,nrec))
...
enddo

 

the first record in each file is a header with some of the file specifications:
- number of depths
- number of samples /trace
- number of receivers
- tool number = 0 (DSI)
- mode (1 = Lower Dipole, 2 = Upper Dipole, 3 = Stoneley, 4 = Monopole)
- vertical sampling interval
- scaling factor for depth
- waveform sampling rate in microseconds

 

Additional information about the drilling and logging operations can be found in the Operations and Downhole Measurements sections of the expedition report, Proceedings of the International Ocean Discovery Program, Expedition . For further questions about the logs, if the hole is still under moratorium please contact the staff scientist of the expedition.


After the moratorium period you may direct your questions to:


Cristina Broglia

Phone: 845-365-8343

Fax: 845-365-3182

E-mail: Cristina Broglia

 

Tanzhuo Liu

Phone: 845-365-8630

Fax: 845-365-3182

E-mail: Tanzhuo Liu