Global cyclostratigraphic analysis of the Seychelles Southern Shelf for potential reservoir, seal and source rocks

Abstract

As part of the assessment of the exploration potential of the Seychelles area, Global Cyclostratigraphy, a model that hindcasts stratigraphy, was used to evaluate the likely spatial and temporal occurrence of potential reservoir, seal and source rocks for the time interval between the Triassic (230 MYA) and Middle Jurassic (160 MYA). Gravity and seismic analyses indicated the presence of thick sediments on the Southern Shelf. A major trend of a gravity minimum was interpreted as a paleo-rift basin. The initial working hypothesis for the sedimentary infilling of the rift was based on the analysis of paleogeographic reconstructions, seismic lines, and well data. The synrift section was interpreted to be composed of a Triassic to Jurassic interval of lacustrine deposition followed by a Jurassic marine transgression. The Global Cyclostratigraphic evaluation focused on hindcasting the depositional characteristics of the basin as it evolved and deducing the intervals that were most likely to produce and preserve hydrocarbons. Analyses of the Seychelles area indicated that the stratigraphic potential varied significantly from the Late Triassic through the Middle Jurassic, with the most reservoir-prone units being deposited at highstand or lowstand, transgression or regression depending on the time interval in question. In Middle Jurassic time, for example, marine lowstand deposits were assessed to have the most reservoir potential, while in Early Jurassic time, transgressive systems were assessed to have the most potential. Seal and source potential were similarly ranked.