Abstract: Maturation and Distribution of South Atlantic Source Rocks: Examples from Deepwater Angola
Henry, Steven - GeoLearn; Schiefelbein, Craig and Illich, Harold - GeoMark Research, Inc. and Abreu, Vitor - Rice University
Mature source rocks are the primary limiting factor in extending deepwater exploration. Deepwater and Ultra-Deepwater seismic data from Western Geophysical?s Angolan surveys will be shown to illustrate the distribution of mature source rocks in deepwater. Seismic stratigraphy, paleogeographic mapping, maturation modeling and geochemical analysis have been fundamental in establishing the seaward limit of the active petroleum systems.
The primary source rocks in the South Atlantic consist of: 1) pre-salt, syn-rift; lacustrine, 2) pre-salt, Sag basin; lacustrine, marginal marine, marine (?) and 3) post-salt, drift; marine. The pre-salt, syn-rift is known to have sourced continental shelf oil fields. In deepwater, however, they are generally buried too deeply, having passed through the oil window before many of the post-salt reservoirs were deposited. If they exist along the rifted transition zone, they are likely overmature due to high heat flow associated with the break-up. The post-salt, marine source rocks generally lack significant burial to be mature, except where they underlie thick Tertiary (Congo Fan) sedimentation.
The pre-salt, Sag basin source rocks are ideally positioned to source deepwater prospects. Oils from the Angolan (Falcao) and Brazilian (Lagoa Feia) shelves are known to have originated from source rocks deposited in Sag basins with saline lacustrine environments and having a possible marine input. In deepwater, Sag basin contain nearly a kilometer of sediments younger than the Sag basins on the shelf and likely contain marine source rocks. If marine oils are identified from cored surface seeps overlying areas where the post-salt, marine is immature, then a marine pre-salt source rock will be the likely candidate.
AAPG Search and Discovery Article #90933©1998 ABGP/AAPG International Conference and Exhibition, Rio de Janeiro, Brazil