Reported proven hydrocarbon reserves of the Arabian plate region at the start of 1991 totaled 663.2 billion barrels (B bbl) of oil and 1,325.4 trillion cubic feet (tcf) of gas (66.4% and 31.5% of the world's oil and gas reserves, respectively). More than 98% of these are concentrated in the northeast margin region between northwest Iraq and Central Oman and lie in reservoirs ranging in age from late Paleozoic to early Neogene. Additional reserves, however, increasingly are being established along the other Arabian plate margins and in intra-plate basins. Occurrence of reserves, age and distribution of the sediments that generated or preserved them, and the formation of the mainly large structural (and other) traps are linked intimately to differing histories of plate marg n evolution. The proper understanding of these histories could lead to additional reserves being established. The Arabian plate margins evolved at different times, the first being the northeast passive margin. This permitted the almost uninterrupted accumulation of thick sediments over a vast area including areally extensive organic-rich source rock deposits as well as good reservoir and seal units. The north/northeast margin(s) became a collisional boundary and a new Levant margin became a transform boundary in the Neogene.

Consolidation of the Afro-Arabian craton in the latest Proterozoic and Early Cambrian created a prominent north-south basement "grain" and a northwest-southeast (Najd) shear fracture system. Rejuvenations (affecting structures/sediment patterns) occurred in later periods and have controlled major hydrocarbon occurrences.

From latest Proterozoic to late Paleozoic time, the present north/northeast Arabian plate margin region, Anatolia, central Iran and the Afghan and Indian plates formed part of the long and very wide northern passive margin of Gondwana. This region was intermittently covered by shallow epeiric seas and bordering lowlands.

The present northeast margin formed as a result of Late Permian extension, rifting, and drifting away of former Gondwanan margin blocks and opening of the neo-Tethys. The oceanic domain was propagated further westward to form the northern passive margin by the Early Cretaceous. The southeast margin (Oman) had both a rift and a transform history from the (?Late) Jurassic. Ocean plate formation in the eastern Mediterranean (Early to Middle or ? Late Jurassic) and the Afro-Indian rift (Late Jurassic/Early Cretaceous) formed the northwest transform and the southeast passive margins of the Levant and Dhofar/Somalia. The Red Sea (western) and Gulf of Aden (southwest) passive margins were created as a result of Neogene extension, rifting, and propagation of the Indian Ocean spreading ridge w stwards, separating Arabia from Africa and rotating and propelling the Arabian plate northeast to underthrust and suture with Eurasia. These motions created the new and current Levant ("Dead Sea") transform on the northwest plate margin of Arabia.

The northeast Arabian Mesozoic passive margin is characterized by the extraordinary width of its pre-erosional, carbonate and evaporite dominated, depositional shelf; reaching one and perhaps even two thousand kilometers. Across this broad shelf were interspersed intra-platform basins and swells; the latter either shed detrital material that intertongued as reservoir sediments with "basinal" source sediments or was deposited as neritic carbonate environments resulting in reservoir-quality strata. This paleogeography ensured an areally extensive distribution of multiple source/reservoir/seal units in the proper sequential order and optimum juxtapositional relationships for very efficient drainage of wide hydrocarbon kitchens into large, gentle, mainly structural closures. Leakage from hese structures was minimized by the presence of effective regional seals. The Mesozoic depositional shelf along the northwestern and northern margins was relatively narrower with poorer areal distribution of source/reservoir deposits, further complicated by considerable deep removal of sedimentary section during Late

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Jurassic/Early Cretaceous block movements. By contrast, the southeast margin remained relatively positive throughout most of the Mesozoic with the thin sedimentary cover leaving its Infracambrian/early Paleozoic source sediments at relatively shallow depths and consequently well within the liquid oil window.

The hydrocarbon potential/plays for each margin and for intra-plate basins differ according to their individual evolution history. The southeast margin is principally an Infracambrian-source/Paleozoic reservoir province with possibilities of subordinate Mesozoic or Tertiary plays in offshore basins that to date have yielded no discoveries. The northeastern margin is proven to be a large Mesozoic-sourced Mesozoic and Tertiary reservoir province. However, it has further potential for substantial new reserves generated from Silurian source rocks and trapped in Permian-Carboniferous sand (e.g. Central Saudi Arabia) and Late Permian carbonate reservoirs (Gulf region, Oman). In addition, the possibility of extensive Infracambrian source rocks charging Mesozoic (or younger) reservoirs though multistage migration via one or several paleotraps should not be ruled out, with the likelihood of older but less deeply buried Paleozoic reservoirs still containing oil.

The potential and play concepts of the northern/northwestern margins are less straightforward to categorize. In within-plate basins (aulacogens, grabens, intracratonic sags) Triassic and Late Cretaceous hydrocarbon sources are in the oil window and are increasingly found to have generated light oil/gas condensate. Toward the margin edge, and as a consequence of complexities in distribution due to Late Jurassic/Early Cretaceous deep erosion and Late Cretaceous and Miocene-Pliocene collisions, late Mesozoic source rocks preserved in troughs have either generated heavy sulphurous oil because of marginal maturity, or meteoric water flushing has been responsible for biodegradation. Silurian shales, however, both in margin-edge areas and within-plate basins of the northwest/northern regions where preserved, will prove increasingly to have generated hydrocarbons. However, future discoveries (e.g. as in southeastern Turkey, Syria, and Jordan) will require a better understanding of the Silurian subcrop distribution.

For the passive margins formed during the Neogene in the west (Red Sea) and south (Gulf of Aden), only minor discoveries have been made to date. Play targets for the former are the Neogene with good source/reservoirs/seals, and possible Jurassic objectives in the southern end of the margin. In the south the Paleogene with subordinate Neogene and Jurassic objectives appear to be viable plays. Organically rich, but immature Eocene source rocks are widely exposed on the Gulf of Aden rift shoulders, but can reach maturity offshore as a consequence of rapid subsidence and rift- related high heat flow. Within-plate grabens adjacent to the southwestern margin already have important Jurassic reserves and production (Ma'rib-Shabwa), and other grabens currently are being explored.

Arabian within-plate structural basins include failed rifts, half grabens, intracratonic sags, and strike-slip pull-apart/compressional belts. Arabian margin basin structuring includes epicratonic basins and overthrust belts. The Palmyride belt (Syria), the Ma'rib-Shabwa grabens (Yemen), the Risha basin (northeast Jordan/Iraq), the Rub al Khali basin (Arabia) and the thrust belts of the Taurus, Zagros and Oman mountain fronts show varied exploration promise and are proving to have additional hydrocarbon reserves. The Dead Sea-Levant Fracture basin(s) potential remains unassessed but locally appears promising.