Subsalt imaging by target-oriented wavefield least-squares migration: A 3-D field-data example

3-D field-data examples

We apply the target-oriented inversion method to a data set acquired from the Gulf of Mexico (GOM). The data set was acquired using a narrow-azimuth towed-streamer (NATS) acquisition system, and further rotated using azimuth moveout (AMO) (Biondi et al., 1998) into zero azimuth. The minimum and maximum inline offsets are $0.3$ km and $8.2$ km, respectively. The frequency content of the data set ranges between $5$ Hz and $35$ Hz. The velocity model used for migration and Hessian computation is shown in Figure 1, which is obtained using target-oriented wavefield tomography (Tang and Biondi, 2011).

We compute the migrated image using the 3-D conincal-wave migration operator, where we synthesize $101$ conical waves for each crossline and migrate $12625$ conical waves in total. The minimum and maximum inline take-off angles at the surface for the conical waves are $-30^{\circ}$ and $30^{\circ}$, respectively. The maximum frequency used for migration is $20$ Hz. The image obtained for the target area is shown in Figure 2. Note that the amplitudes of the sediment reflectors are biased; also notice the illumination shadows below the salt due to the non-unitary characteristic of the Born modeling operator.

lsm3d-target
Figure 1. Target area selected (outlined by a box) for wavefield least-squares migration. [CR]

lsm3d-imag
Figure 2. Migrated image for the selected target region. Note the illumination shadows below the salt. [CR]

Subsalt imaging by target-oriented wavefield least-squares migration: A 3-D field-data example