ABSTRACT During the Mesozoic Era, episodes of siliciclastic input onto the dominantly carbonate Arabian shelf form important elements of petroleum plays, forming proven and potential reservoirs, source rocks, and seals. This chapter examines the temporal and spatial extent of these siliciclastic episodes. It then compares them against known tectonic, climatic, and eustatic events affecting the Arabian plate that may have been acting independently or coincidently to control siliciclastic input by means of hinterland uplift, influence on denudation and run off, incision, and creation of sediment pathways and accommodation space. Particularly important phases of siliciclastic input occur in (1) the Early Triassic (Olenekian Sudair shale) coincident with major eustatic lowering, an episode of humid climate and rifting on the northern part of the Arabian plate; (2) Late Triassic (late Norian initial Minjur Sandstone) coincident with East Mediterranean rifting, a humid episode and a major eustatic sea-level fall; (3) Middle Jurassic (early Bajocian initial Dhruma Sandstone) coincident with localized uplift and a humid climate and immediately postdating a eustatic sea-level fall in the Aalenian; (4) Early Cretaceous (late Valanginian–Barremian Zubair sandstone) postdating a Valanginian eustatic lowering and coincident with humid climate and uplift in northern and western Arabia; (5) Mid-Cretaceous (latest Aptian–middle Albian Burgan Sandstone) coincident with Arabian shield uplift, humid climate, and a eustatic low. Other episodes of siliciclastic input also occur, although they tend to be more localized. Important seals are formed during the progradation of siliciclastic systems “poisoning” carbonate shelves or during transgression when distal pro-delta siliciclastic systems retreat back across the shelf, capping up-systems tract fluvial or shelfal sandstones, or when they are located above major unconformities, capping carbonate reservoirs. Siliciclastic reservoirs include the well-known and prolific fluvial and paralic sandstones that contribute, for example, to the Burgan field in Kuwait and to the Zubair and Nahr Umr reservoirs of the northern Gulf. Lowstand sands (both lowstand deltas and slope and basin gravity flow deposits) form viable, but underexplored, reservoir targets. Source rocks may be deposited in front of prograding delta systems linked to high nutrient supply and water stratification caused by freshwater overhang, leading to anoxia and preservation of organic matter. A well-known example is the Kazhdumi Formation of the Iranian Zagros. A better understanding of the fundamental controls on siliciclastic input onto the Arabian plate will enable better predictions of these key petroleum play elements and a better understanding of the subsurface risk associated with their occurrence.

ABSTRACT The mid-Cretaceous Wara Member of the Wasia Formation in the Arabian Gulf is composed of fluvio-deltaic to shallow-marine deposits. The aim of this study is, within a sequence stratigraphic framework, to characterize the facies and their distribution in terms of potential reservoir sands using core and wireline log correlations. Detailed core description, well log interpretation and correlation, sequence stratigraphy, depositional model generation, petrographic analysis, and reservoir quality assessment are integrated to gain a more comprehensive understanding of the potential reservoir quality and depositional geometries. Seven high-frequency chronostratigraphic units are identified. They are composed of up to six depositional facies associations, which include fluvial and distributary channels, shoreline and mouth-bar sand, estuarine-lagoonal deposits, delta-plain heterolithics, shelfal marine deposits, and prodelta-offshore marine shales. Lowstand to early-transgressive systems tract, fluvial and distributary channel sands are considered to be potentially the best candidate reservoir units because of the relatively high proportion of medium-grained sand with low diagenetic overprinting. Early transgressive systems tract units of shoreline sands and estuarine-lagoonal deposits are considered to be potential secondary candidates because of more pervasive diagenesis, and their finer-grained character. A west-northwest to east-northeast sand input direction has also been identified and the shoreline orientation improved.