Generation, Migration, and Entrapment of Precambrian Oils in the Eastern Flank Heavy Oil Province, South Oman

KONERT, GEERT, Petroleum Development Oman, Muscat, Oman, Visser, Wiekert VISSER, Koninklijke/Shell Exploratie en Produktie Labaratorium., Rijswijk, Netherlands, and HUIB A. VAN DEN BRINK, Petroleum Development Oman, Muscat, Oman

The prolific Eastern Flank Heavy Oil province east of the South Oman Salt basin is unique because of the widespread occurrence of Precambrian source rocks from which the hydrocarbons originated. Fission-track analysis and burial studies suggest that most of these

source rocks became mature and generated hydrocarbons in the Ordovician; subsequently, the source beds were uplifted and did not re-enter the oil window. Its uniqueness is also based on the all-important role played by Precambrian salt. The traps in Palaeozoic clastics were initially structured by halokinesis, and subsequently by salt dissolution. The latter process gradually removed the salt from the area and is largely responsible for the present-day structure with palaeo-withdrawal basins inverted in present-day turtles. Present-day traps are mainly post-Late Jurassic in age, significantly post-dating the time of oil generation.

Detailed field studies indicate that charge phases appear to correlate with periods of increased salt dissolution in the Late Jurassic-Early Cretaceous, Late Cretaceous, and Tertiary.

Oil was probably stored in intermediate traps below and within the salt. It was gradually released upon progressive tilting of the basin flank; it migrated updip toward the basinward retreating salt edge, and subsequently (back) spilled into the stratigraphically younger traps. Also, removal of the top seal of intra-salt and sub-salt traps by salt dissolution allowed upward remigration. It follows that charge concepts in the Eastern Flank Heavy Oil province depend on defining salt-edge-related hydrocarbon release areas, rather than on kitchen modeling.

AAPG Search and Discovery Article #91007© 1991 AAPG International Conference, London, England, September 29-October 2, 1991 (2009)