Sequence Stratigraphy, Sedimentology and Hydrocarbon Potential of the Late Permian Carbonates (Khuff Formation), Southern Arabian Gulf Basin

Abdulrahman S. Alsharhan
Middle East Geological Est., Al Ain, United Arab Emirates

The Late Permian Khuff Formation of southern Arabian Gulf basin reached up to 970 m and consists of a regressive shallow water carbonate-evaporite sequence of dolomites, limestones and dolomitic limestones with subordinate anhydrite. The formation is a second-order composite sequence (KS1 to KS7). The transgressive systems set of the Khuff starts with KS7 and ends at the maximum flooding surface of KS4. The high stand systems set starts on top of Khuff second-order maximum flooding surface (MFS4) and ends at the top of the Khuff sequence KS1 which represents the top of the Khuff Formation.

Four diagenetic settings have been identified: marine phreatic, mixed phreatic, meteoric phreatic and burial. The Khuff has both primary and secondary porosity. Most open pores are a result of interparticle, intercrystalline, or dissolution vug porosity. The diagenetic features in these sediments are mainly partial cementation, dolomitization and development of secondary anhydrite. Porosity ranges from 6-20% and permeability from less than 1 to more than 500 md. Horizontal permeability is greatly enhanced by sub-vertical partings of the open pores, common in microcrystalline dolomites. Stylolites are common but unimportant as vertical barriers. Extensive fracturing of the reservoir produced a dense network of intersecting vertical and sub-vertical fractures. These fractures have a significant impact on the enhancement of the effective porosity and permeability.

The formation has proven reserves of large volumes of gas, and there is high potential for future gas and condensate to be discovered in many part of the basin which is not well-explored yet. The reservoir is capped by the shales and dolomites of the overlying Sudair Formation (Early Triassic) and is sourced from Silurian Qusaiba shales.

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas