Depth imaging of multicomponent seismic data through the application of 2D full-waveform inversion to P- and SH-wave data: SEAM II Barrett model study

We examine the value of the nine-component seismic survey by generating the Kirchhoff depth migration images of compressional wave (P-wave), converted wave (PS-wave) and horizontally polarized shear wave (SH shear wave) data simulated from the SEAM II Barrett unconventional model. We first utilize full waveform inversion to obtain a P-wave velocity model from P-wave data and an S-wave velocity model from SH-wave data. Both P-wave and SH-wave data are generated with the maximum frequency of 20 Hz while assuming that the subsurface is isotropic. To implement full waveform inversion, we use a two-dimensional time-domain finite-difference method and the L2 norm to measure the data misfit. We use both refractions and reflections in P- and SH-wave data to reconstruct the P- and S-wave velocity models from the surface to the reservoir. The inverted P- and S-wave velocities contain the main features of the model (e.g., major faults and channels) but have some difficulties in estimating high-frequency velocity variation within the first 300-m depth of the model due to the frequency constraint. We then use the inverted P- and S-wave velocities to generate Kirchhoff depth migration gathers and images from the P-, PS- and SH-wave data. The flat P- and SH-wave common-image offset gathers suggest that SH- and P-wave full waveform inversion can generate adequate S- and P-wave velocities for migration. Flat PS-wave gathers and the clear PS-wave migration image are also obtained using the inverted P- and S-wave velocities simultaneously. This result indicates that obtaining S-wave velocities from SH-wave data can aid PS-wave data processing and imaging. Moreover, the SH-wave images and S-wave images of the radial component provide better delineation of fault planes and small-scale geobodies within the reservoir since the wavelength of the S-wave is smaller compared to P-wave when similar frequency ranges are recorded. Therefore, our study shows that S-wave velocities can be successfully constructed by the two-dimensional full waveform inversion application of the SH-wave data. The subsequent imaging of multicomponent seismic data improves the delineation of certain unconventional reservoirs compared to the traditional P-wave imaging.