Gullfaks synthetic data set

B. Arntsen

July 7, 2005

Acquisition Geometry

Figure 1 shows the overall acquisition geometry of the synthetic data set. Theorigin of the coordinate system is in the upper left corner of the model, with thehorizontal axis positive towards the right and the depth axis positive downwards.

The source is moved in increments of 25m between each shot starting at theorigin. The source depth is kept constant at 6m. A total of 400 shots wererecorded.

The dataset is acquired using five different fixed receiver arrays, three hori-zontal arrays and two vertical arrays. Table 1 shows the receiver array positionsand parameters. All receiver arrays, except the streamer array, record both pres-sure, vertical and horizontal particle velocity. The streamer array only recordspressure. The receiver group interval is 12.5m for all arrays. The time samplinginterval is 4ms and the recording time for each shot is equal to 5s.

Three different subsurface models were used for the modeling, these arenamed model 1, model 2 and model 3. All models includes a 200m water layerat the top and a free surface.

Data files

The data for each model is stored in a number of files files. The files for modelmodel 1, model 2 and model 3 are summarized in tables 2-4. The data weregenerated using the Vp, Vs and density models. A simple model for the Thomsenparameters ε and δ are also included, but not used for the data generation.

Array x (m) z(m) No of receiversStreamer 0.0-9975 10.0 800Obc 1 0.0-9975 10.0 800Obc 2 0.0-9975 1650.0 800Vsp 1 3500 0.0 0-2962.5 238Vsp 2 6500 0.0 0-2962.5 238

Table 1: Receiver array parameters. x is the horizontal coordinate, while z isthe vertical coordinate

1

Vsp 1

Obc 1

-

6

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Vsp 2

Source

6 km

10 km

3.5 km 3.5km

Streameer

Obc 2

-

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Figure 1: Acquisition geometry

File name Descriptionmodel-1-vp.sgy P-wave velocity modelmodel-1-vs.sgy S-wave velocity modelmodel-1-rh.sgy Density modelmodel-1-eps.sgy Epsilon modelmodel-1-delta.sgy Delta modelmodel-1-streamer.sgy streamer array pressuremodel-1-obc1-pr.sgy Obc 1 array pressuremodel-1-obc1-vx.sgy Obc 1 array horizontal velocitymodel-1-obc1-vz.sgy Obc 1 array vertical velocitymodel-1-obc2-pr.sgy Obc 2 array pressuremodel-1-obc2-vx.sgy Obc 2 array horizontal velocitymodel-1-obc2-vz.sgy Obc 2 array vertical velocitymodel-1-vsp1-pr.sgy Vsp 1 array pressuremodel-1-vsp1-vx.sgy Vsp 1 array horizontal velocitymodel-1-vsp1-vz.sgy Vsp 1 array vertical velocitymodel-1-vsp2-pr.sgy Vsp 2 array pressuremodel-1-vsp2-vx.sgy Vsp 2 array horizontal velocitymodel-1-vsp2-vz.sgy Vsp 2 array vertical velocity

Table 2: Data file names and content for model 1

2

File name Descriptionmodel-2-vp.sgy P-wave velocity modelmodel-2-vs.sgy S-wave velocity modelmodel-2-rh.sgy Density modelmodel-2-streamer.sgy streamer array pressuremodel-2-obc1-pr.sgy Obc 1 array pressuremodel-2-obc1-vx.sgy Obc 1 array horizontal velocitymodel-2-obc1-vz.sgy Obc 1 array vertical velocitymodel-2-obc2-pr.sgy Obc 2 array pressuremodel-2-obc2-vx.sgy Obc 2 array horizontal velocitymodel-2-obc2-vz.sgy Obc 2 array vertical velocitymodel-2-vsp1-pr.sgy Vsp 1 array pressuremodel-2-vsp1-vx.sgy Vsp 1 array horizontal velocitymodel-2-vsp1-vz.sgy Vsp 1 array vertical velocitymodel-2-vsp2-pr.sgy Vsp 2 array pressuremodel-2-vsp2-vx.sgy Vsp 2 array horizontal velocitymodel-2-vsp2-vz.sgy Vsp 2 array vertical velocity

Table 3: Data file names and content for model 2

File name Descriptionmodel-3-vp.sgy P-wave velocity modelmodel-3-vs.sgy S-wave velocity modelmodel-3-rh.sgy Density modelmodel-3-streamer.sgy streamer array pressuremodel-3-obc1-pr.sgy Obc 1 array pressuremodel-3-obc1-vx.sgy Obc 1 array horizontal velocitymodel-3-obc1-vz.sgy Obc 1 array vertical velocitymodel-3-obc2-pr.sgy Obc 2 array pressuremodel-3-obc2-vx.sgy Obc 2 array horizontal velocitymodel-3-obc2-vz.sgy Obc 2 array vertical velocitymodel-3-vsp1-pr.sgy Vsp 1 array pressuremodel-3-vsp1-vx.sgy Vsp 1 array horizontal velocitymodel-3-vsp1-vz.sgy Vsp 1 array vertical velocitymodel-3-vsp2-pr.sgy Vsp 2 array pressuremodel-3-vsp2-vx.sgy Vsp 2 array horizontal velocitymodel-3-vsp2-vz.sgy Vsp 2 array vertical velocity

Table 4: Data file names and content for model 3

3

Field Byte no Description Valuetracl 1-4 Trace number 1-2001gx 81-84 Horizontal coordinate 0-10000nt 115-116 No of samples 1251dt 117-118 Horozontal and vertical sampling interval 5000 mm

Table 5: SEGY trace headers for models 1, 2 and 3

Field Byte no Description Valuetracl 1-4 Trace number 1-320000tracf 13-16 Receiver no 1-800sx 73-76 Source coordinate 0-997500gx 81-84 Receiver coordinate 0-997500nt 115-116 No of samples 1251dt 117-118 Time sampling interval 4000 µsec

Table 6: SEGY trace headers for the streamer, Obc 1 and Obc 2 arrays

Table 5 contains a summary of the SEGY trace header content for the hor-izontal models, while 6 contains trace header info for the data with horizontalreceiver arrays (streamer, obc 1 and obc 2 arrays). Table 7 contains the traceheader information for the two vertical receiver arrays (vsp 1 and vsp 2). Anyheader word not mentioned contains undefined data. The source and receivercoordinates (gx and sx fields) are recorded in meters times 100. The binarypart of the reel header contains only the time sampling interval (4ms) and theno of samples in each trace (1251). The receiver coordinate field (gx) for thevertical arrays (Vsp 1 and Vsp 2) contains the depth of the receiver instead ofthe horizontal coordinate.

Data archive

The data files have the same names as described above, except that they arecompressed with gzip and have a final file extension of “.gz”

Field Byte no Description Valuetracl 1-4 Trace number 1-95200tracf 13-16 Receiver no 1-238sx 73-76 Source coordinate 0-997500gx 81-84 Receiver coordinate 0-296250nt 115-116 No of samples 1251dt 117-118 Time sampling interval 4000 µsec

Table 7: SEGY trace headers for the Vsp 1 and Vsp 2 arrays

4