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Abstract: A Model for Migration and Accumulation of Hydrocarbons in the Thamama and Arab Reservoirs in Abu Dhabi, U.A.E.

M. F. Hawas, H. Takezaki

The distribution of hydrocarbons in the Lower Cretaceous Thamama Group and Upper Jurassic Arab Formation in Abu Dhabi is influenced by the development of the intervening Hith anhydrites. The geochemical analysis of Thamama and Arab hydrocarbons indicate that they were generated from a common source rock: the Upper Jurassic Diyab Formation.

Studies carried out on the Miocene sabkha anhydrites in the coastal flat west of Abu Dhabi supported a model for vertical migration through the Hith anhydrites under certain conditions. The establish model implies that the Diyab oil and gas had migrated essentially vertically and individually which means that the oil migrated prior to the gas and their distribution is controlled by the differential sealing potential of the anhydrites at each migration phase: a Hith anhydrite bed of more than 30 feet (ft.) thick was a perfect seal for hydrocarbon migration into the Arab reservoirs. In this case, oils could not break through to the overlying Thamama group. But where the anhydrite bed thicknesses dropped below 30 ft. thick, this permitted oil migration through to the overlying Thamama re ervoirs during the oil generation phase in the Turonian time. At a later stage, with additional depth of burial and progressive diagenesis anhydrite beds as thin as 8 ft. thick became effective seals. These controlled the distribution of the gas during the gas generation phase in the Eocene time.

AAPG Search and Discovery Article #90956©1995 AAPG International Convention and Exposition Meeting, Nice, France