Image-Domain Least-Squares Migration and Depth-Domain Inversion for Subsalt Sand Reservoirs

Abstract

Summary A combination of complex geology and limitations imposed by the surface seismic acquisition geometry results in seismic images contaminated by variabilities in wave propagation effects such as illumination. Consequently, imprints of variable illumination compromise the reliability of the amplitude and phase within the seismic image. Additionally, today's conventional methods of amplitude inversion assume that the seismic amplitudes are representative of the earth's acoustic and elastic properties and do not compensate for variable illumination effects. We present a subsalt case study from the Gulf of Mexico demonstrating least-squares migration in the image domain with point-spread functions (PSF) ability to simultaneously correct for illumination effects and produce a higher-resolution image of thin sand beds located in close proximity to base of salt. We discuss our approach for mitigating scattering effects present in the PSFs arising from high-contrast impedance boundaries within the earth model. Finally, we show the results from a poststack depth-domain inversion, providing true amplitude images and acoustic impedance volumes and allowing reliable assessment of the viability of previously identified drilling targets and enabling corresponding augmentation of prospect interpretation.