Volume rendering of enigmatic high-amplitude anomalies in southeast Brazil: A workflow to distinguish lithologic features from fluid accumulations

Abstract

High-quality 3D seismic data are used to extract and isolate high-amplitude anomalies so that fluid-related features, magmatic intrusions, and mass-transport deposits can be interpreted. The use of advanced seismic interpretation tools such as volume rendering and attribute extraction replaces the “traditional” horizon mapping of high-amplitude anomalies. In this work we show that the geometry of anomalies is better constrained when seismic attributes can be imaged and interpreted in three dimensions. Volume-rendering techniques are less laborious, reduce interpretation time, and to a large extent remove interpretation biases. To demonstrate the advantages of our approach, we analyze three types of anomalies in southeast Brazil. In the study area, unconformable “soft-on-hard” anomalies are related to fluid accumulations, whereas igneous sills show signature tabular and concave geometries. We also question the existence of sill-to-sill junctions in the study area, otherwise interpreted by conventional interpretation methods, based on the 3D rendering techniques described. Hence, we theorize that the appearance of the junctions on seismic data from other basins can be a consequence of overlapping sill tips, resulting in the constructive interference of their seismic signals.