Pitfalls in Prestack Inversion of Merged Seismic Surveys
University of Oklahoma
Modern 3D seismic surveys are often of such good quality and 3D interpretation packages so user-friendly that seismic interpretation is no longer exclusively carried out by geophysicists. This ease-of-use has also been extended to more quantitative workflows, such as 3D prestack inversion, putting it in the hands on the "non-expert" – be it geologist, engineer, or new-hire geophysicist. Indeed, given good quality input seismic data, almost any interpreter who can generate good well ties and define an accurate background model, can generate a quality prestack inversion. Here we, the two new geophysicists acted as non-experts and followed the convenient path of seismic inversion of a merged data set and fell into the inversion "pit". Specifically, we applied prestack inversion to gathers that were carefully reprocessed by a major service company. The problem was not with the processing, but with our lack of understanding of the input legacy data that formed part of a larger "megamerge" survey. Specifically, the data were migrated to accommodate the longest offsets corresponding to the most recently acquired data, while older input surveys were acquired using much shorter offsets. The replacement of acquisition offsets with prestack migration offsets formed the grass mat covering the pit, and in we fell. In this presentation I will share our initial workflow and suspicious results. In addition to presenting some QC tools useful in analyzing megamerge surveys, I will show how by limiting the offsets used in our prestack inversion that we obtain less aggressive, but still useful results.
AAPG Search and Discovery Article #90200 © AAPG Geoscience Technology Workshop, Fifth Annual AAPG-SPE Deepwater Reservoir, January 28-29, 2014, Houston, Texas