Rift and passive margins

5 important questions on Rift and passive margins

Traps in rift settings

•  Alluvial fan sandstones along main faults 
•  Syn-rift (lacustrine) turbidites 
•  Later syn-rift deltaics 
•  Late syn-rift carbonates in distal areas with little 
clastic input 

Post-Rift traps and reseervoirs

Traps 
•  Stratigraphic traps (early post-rift turbidites) 
•  Drape structures over syn-rift highs 
•  (Faulted) anticlinal traps related to flower structures 
•  Simple broad anticlines related to broad structural inversion 
•  With mobile salt or clay, traps overlying diapiric structures may develop
Reservoirs 
•  Basal post-rift sands 
•  Carbonate build-ups (early post-rift) 
•  Coastal sands along basin margins 
•  Turbidites in the deeper marine 
early post-rift 
•  Later post-rift deltaics 

Passive Margin Basin of Gabon

•  Lacustrine deposits in syn-rift 
•  With excellent lacustrine oil-prone source rocks 
•  Turbidite reservoirs as well as coarse clastics at basin margin 
•  Very local carbonates in late syn-rift 
•  Marine post-rift sequence 
•  starting with transgressive sandstones, overlain by thick salt 
•  Albian outbuilding carbonates, overlain by younger clastics 
•  Local delta development 
•  Several Cretaceous marine source rock levels (global anoxia)
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South Atlantic Rift Basins - Summary 

•  Very similar Cretaceous rift basins 
•  All basins display very similar “trajectory plots” 
•  Good lacustrine source rocks in underfilled basins, 
charging mainly syn-rift reservoirs 
•  Clastics in the more proximal settings 
•  Turbidites in the deeper sectors of the rifts 
•  Carbonates in more distal settings, locally 
•  Early post-rift salt effectively separates syn-rift from 
post-rift petroleum systems 
•  Post-rift, several good marine source rock levels (Type II) 
•  Related to global highstands and anoxia 
•  Prospectivity related to maturity (burial) of post-rift (deltas) 

Baram Delta Summary

•  An important hydrocarbon province in a river at the 
mouth of a rather small river 
•  Typical deltaic development, with a structural inversion 
phase resulting in some important high trends, with 
several billion barrel fields 
•  Multiple reservoir-seal pairs in top-set sequences 
•  Source rock levels are essentially unknown 
•  In the Seria North Flank area faults are sealing at an 
impressive scale 
•  Counter-regional faults seal best 
•  Proportion of gas increases with depth 

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