A REVIEW OF 3D ILLUMINATION STUDIES

摘要

Illumination studies are most often applied to feasibility studies and survey design, but the concept offers a wider range of applications; e.g., during the acquisition to estimate the infill or after the acquisition to help explain acquisition-related amplitude variations or shadow zones. Conventional survey design assumes that Common Mid Point (CMP) coverage and Common Reflection Point (CRP) coverage are equivalent, but this is not the case if the investigated structure is complex. Therefore 3D model-based illumination studies are crucial, and with the increase in computer power, such studies have become a common way to deal with survey design during the last ten years. Depending on the illumination of the target surface and the quality of the data, the survey layout used for the modeling can be taken as is, adjusted, or rejected. The cost of performing an illumination study is minimal and completion time (including model building, forward modeling and illumination study) short compared to an acquisition. Therefore, not performing such study would be risky due to the high cost of a 3D seismic acquisition. There are many ways to perform illumination studies. The most common are the binning methods: after forward modeling based on ray tracing, the modeled attributes are mapped to the target surface. Binning methods are adapted when dealing with general survey design, as they give a hint of the ability of a survey layout to illuminate a whole target (shadow zones, footprint). For more specific problems, such as finding the correct layout to illuminate a shadow zone or explaining the image quality at one place (resolution), methods giving an estimate of the illumination locally are required. Different current methods for illumination studies are introduced and compared. They are classified into two categories: methods giving information over the whole target area are first reviewed (global approach), followed by methods giving information at one point at a time (local approach).