Investigating the impact of acquisition design on the problem of imaging below shallow gas

Summary

The problem of shallow, highly absorptive zones negatively affecting the quality of the seismic image at target depth is widespread across the Malay Basin. Whilst developments in processing regimes have lead to considerable improvements in the compensation of amplitudes below these areas of high absorption, the issue of improving the seismic image, and subsequently, our confidence in exploration decisions within affected fields remains a key challenge for operators in this region.

This study investigates the impact that acquisition geometry and design can have on the problem of imaging below shallow gas. Using advanced ray-based modeling techniques, we take a detailed look at the improvements in sub-gas amplitudes afforded by adopting nonconventional acquisition geometries; including, but not limited to, the large-offset (approx. 14 km), full-azimuth, dual coil shooting approach recently used in the Gulf of Mexico and broad-bandwidth acquisition techniques.

In addition to the illumination and amplitude characteristics associated with each design, we also investigate the improvements in resolution by simulating 3D prestack depth migration (PSDM) cubes at key areas of interest to try to understand the additional benefits afforded by adopting a non-conventional approach to acquisition.

Through the use of forward modeling, we provide a comprehensive insight into whether non-conventional acquisition techniques have a role to play in addressing the problem of imaging below zones of high absorption located in the overburden.

Key words::

• Shallow gas
• seismic acquisition
• forward modelling
• illumination studies
• survey evaluation and design