Impact of a tightly folded anisotropic layer on imaging in Papua new guinea - a modeling study
Greg Cameron, Rob Vestrum, Daniel Gillam · 2016
ABSTRACT In complex structure land environments, we often observe a sudden degradation in image quality across a seismic section. This can occur as the survey moves from the foreland into the foothills in regions such as the Zagros mountains of northern Iraq or Andes in Colombia. We have also observed this in Papua New Guinea where a more highly deformed layer comes to surface. This degradation is usually attributed to increasing complexity in near surface conditions. Reasons include poor source and receiver coupling, shallow mode conversion, and scattering. This modeling study examines the sub-surface complexity on the imaging of a deeper target. For this study we consider the near surface to be the zone that could be improved by better acquisition such as deeper shot holes or better spatial sampling along with improved statics corrections and signal processing. This is generally tens of metres below the surface. We consider the sub-surface to be a deeper zone, hundreds of meters below the surface, deep enough that better acquisition and improved signal processing cannot compensate for the complex raypaths. To improve the imaging in areas with complexity in the subsurface a realistic subsurface model is needed. Using numeric modeling, we investigate the contribution of tight folds in an anisotropic shale layer on target illumination. While near-surface weathering is often blamed for the degradation of the seismic image, this modeling study shows that deeper sub-surface complexity can have greater impact.