Reservoir Character of Carbonate/evaporite Oil Fields of the Middle East: A Response to Depositional Setting and Accommodation Space

Kendall, Christopher G.; Alsharhan, Abdulrahman S.

Most of the Arabian Gulf major oil and gas fields are from the Permian through Tertiary are sequestered in carbonates and sealed by evaporites formed under arid to semiarid conditions. The field style can be classified on the basis of a sequence stratigraphy framework, depositional setting and facies hierarchies. This framework of erosional and flooding surfaces was formed by base-level change driven by epeirogenetic tectonic movement and eustatic history. This template is populated by a diversity of depositional systems, and facies geometric architecture but interestingly these reservoirs are commonly within wide spread continuous sheets that tend to shoal up on carbonate shelves. These range from grain to muddy carbonates. Reservoir character ranges from depositional fabrics to diagenetic, the latter often related to dolomitization. The porosity may be interparticlal and intercrystalline and/or leached often over 25% with permeability's of over 100md related to preserved primary fabrics and early secondary porosity. The seal is nearly always evaporite (eg: Hith and Lower Fars) or tightly cemented dolomite and limestone, all of which provide a regional caprock on major fields.

Examples include reservoir in fields of Permian, Triassic, Jurassic, and Tertiary of Iraq, Syria, Iran, Kuwait, Saudi Arabia, Bahrain, Qatar, UAE, Oman and Yemen. For instance Kirkuk (bioherm & foreslope), Jambur (shallow marine), Gachsaran (shelf wackestones and packstone), Wafra (shallow water carbonate), Ghawar, Awali, Umm Shaif, Zakum, Yibal, Dukhan, North Field, and South Pars (wackestones, to grainstones often dolomitized), and several others.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013