The Relationship between Eustasy and the Geometry of the Stratigraphic Sequences that form the Mesozoic Carbonate Facies of the Reservoirs, Seals and Associated Source Rocks of the Middle East

A.S. Alsharhan¹ and C.G.St.C. Kendall^2
1Middle East Geological Establishment, Al-Ain, United Arab Emirates
²South Carolina University, Columbia, SC

Recent studies of the abundant subsurface data collected from Mesozoic carbonate reservoirs of Middle Eastern sedimentary basins, particularly those of the Arabian Gulf, suggest a strong relationship to eustasy of these shelf carbonates, evaporites and their associated minor clastics. It has been established that the accommodation of these basins was in part controlled by gentle tectonic subsidence punctuated by variations in eustasy, but that the character of the local major hydrocarbon fields was directly related to sea-level behavior during the deposition of the reservoir sections and their early diagenesis.
This paper classifies exploration plays and reservoir models on the basis of the geometry of the stratigraphic sequences that form them. It establishes that the sediments of most of these carbonate reservoirs, including those associated with the Araej, Arab, Shuaiba and Mishrif Formations, accumulated in the milieu of the highstand system tract and include:
a) Keep-up reservoirs with sheet-like geometry formed during sea-level stillstands and rises b) Give-up and catch-up reservoirs with lens-like geometry formed during sea-level rises and stillstands, and c) Prograded reservoirs with discontinuous clinoform geometry formed during sea-level stillstands and rises.
The source rocks for these carbonate reservoirs form widespread sheets of organic rich argillaceous limestones, marls and shales that accumulated during rapid sea-level rises and include the Hanifa-Diyab Formation and the Shilaif Formation. The similarly widespread reservoir seals are a mix of transgressive shales of the Nahr Umr Formation, dense transgressive limestones of the Thamama, and/or highstand evaporites of the Hith Anhydrite.

AAPG Search and Discovery Article #90072 © 2007 AAPG and AAPG European Region Conference, Athens, Greece