Geometric characterization of igneous intrusions: 3-D seismic insights from the Campos Basin, SE Brazil

Abstract

Abstract Igneous intrusions are important for the exploration and appraisal phases of an oilfield due to their impact on petroleum systems. Their presence can be associated with the generation, migration, accumulation, and entrapment of hydrocarbons. In particular, (1) sills with low permeability might form barriers to fluid flow and migration; (2) sills may re-use fracture networks, providing insights on fluid migration and interaction(s); (3) sills may influence source rock maturation, (4) sill-induced uplifting of overburden and faulting may generate traps, and (5) their geometric complexities enables the understanding of the interconnectedness of sill complexes, which is the focus of this study. Therefore, we provide a systematic characterization of sill geometries and their morphometric parameters. We used three-dimensional seismic data, calibrated with well logs, to interpret sills in the southern Campos Basin, Brazil. Throughout the Late Cretaceous until the Paleogene, sills intruded into the Cretaceous to the Eocene post-salt sedimentary sequence, including shallow-platform carbonates, transgressive marls, and shales. A morphometric analysis assisted by seismic attributes allowed the geometric characterization of sills, namely: (1) saucer-shaped; (2) slightly saucer-shaped; (3) climbing saucer-shaped; (4) transgressive; and (5) rough layer-parallel. The documented sills comprise a wide range of sizes (0.43–14.35 km2) that increase with depth (up to 3.18 km), extend vertically from 0.06 to 0.23 km, and vary from low (1.82–3.31°) to high dip (6.05–15.74°). The sill complex area extends over 67.35 km2. This study suggests that a thorough characterization of sill intrusions may have a substantial influence on the prediction of other igneous occurrences. The mapped sills might have implications not just on the acoustically similar shallow platform Albian carbonates of the Macae Group, but may also provide insightful geometric constraints on the Brazilian pre-salt igneous intrusions.