Abstract Since the start of the twentieth century more than 550 commercially significant oil and gas fields have been discovered in the Middle East. Most of the fields have more than one pay zone and produce from shallow-water carbonates and clastics that range in age from Infracambrian to Oligo-Miocene. A providential juxtaposition of source-reservoir-seal, migration history and trapping mechanism has lead to the entrapment of hydrocarbons throughout the Phanerozoic strata of the Middle East. Each occurrence shares some characteristics but each also has unique features. The geographic occurrence of hydrocarbons in the region reflects the original facies variations across the depositional shelf and basin and the tectonic history of basement faults and halokinetic activity. The evaluation and integration of these critical variables, together with an appreciation of the maturation, migration history and trapping mechanisms, drives the search for new fields. The continued discovery of new fields proves that the region has not yielded all its treasure and stimulates future exploration. Although evidence for orogenic deformation is lacking in the Middle East, epeirogenic warping is common. The latter is attributed to the reactivation of basement faults, and evaporite structures and flow at depth. A prominent sedimentary and erosional break, locally marked by eroded Hercynian unconformities, followed an important Late Palaeozoic epeirogenic uplift. Similarly, Mesozoic sedimentary fill is broken by a major change in tectonic and depositional regimes, and numerous unconformities thought to be primarily controlled by high-frequency fluctuations in eustatic sea level and a low uniform rate of tectonic movement. Late Cretaceous and Tertiary events followed the collision and partial subduction of the east and southeastern margin of the Arabian Plate and involved vertical epeirogenic uplift of the resulting folded and thrusted gravity features. Vast areas of the Middle East Basin have yet to be extensively drilled. Although the long-lived stability of the shelf has influenced the development of the giant oil pools, and to some extent reduced the potential for stratigraphic traps, it has not eliminated the potential for smaller structures and the exploration for new oil and gas reserves. Future exploration is expected to focus on the discovery of smaller structures and subtle traps revealed by analysis of existing geological data and special seismic processing. Exploration will involve extensive regional and local geological–sedimentological studies, 3D or 4D seismic surveys and drilling progrmmes, and proposed better petroleum system model(s) for each basin (or sub-basin).

Abstract Kuwait has proven oil reserves and production from supergiant and giant fields that include the Greater Burgan (Burgan, Ahmadi, and Maqwa), Raudhatain, Sabriya, and Minagish fields. These fields are associated with very gentle oval anticlines interpreted as drape structures over deep-seated fault scarps or as growth structures related to halokinesis. These structures are generally very simple, consisting of a series of roughly parallel, anticlinal uplifts trending NNW-SSE, with a few having a more N-S to NNE-SSW trend. Reservoir rocks are found in the Jurassic Marrat, Sargelu, and Najmah Formations (carbonates), the Lower Cretaceous Ratawi and Minagish Formations (sandstones and carbonates), and the Middle Cretaceous Burgan and Wara Formations (sandstones), as well as the Mauddud and Mishrif Formations (carbonates). Depth of reservoirs range from 3680 m (12,073 ft) in the Middle Jurassic to 2000–3650 m (6561–11,975 ft) in the Lower Cretaceous and 1000–2570 m (3281–8432 ft) in the Middle Cretaceous. The most important reservoirs are the Lower and Middle Cretaceous sandstones, which are sealed by interbedded and overlying shales. Several Jurassic and Cretaceous limestone units form additional, but subordinate, reservoirs that are generally sealed by shales. Only the Upper Jurassic Gotnia salt and the overlaying Hith Anhydrite seem to act as a regional seal for Middle Jurassic limestone reservoirs. Proven and potential source rocks with high TOC values, characterized by a mixture of marine and terrestrial sapropelic organic matter, are present in the upper-Lower and Middle Jurassic and the Lower and Middle Cretaceous. Kerogens from these rocks fall between Type II and II–III. The maturity level and quality of the kerogen in the Makhul (Sulaiy) Formation suggests that they are the most likely source rocks for the Cretaceous reservoirs, and responsible for generating part of the oil which has accumulated in present structures. Source rock characteristics for the Jurassic succession vary and range from moderate to excellent TOC values in the Sargelu and Najmah Formations. Similarly, the Middle Jurassic succession potentially represents mature oil generation. Oil generation from Jurassic source rocks began in the Late Cretaceous at the time when structural traps had already started to form. The Makhul (Sulaiy) source rock entered the oil window during the Early Tertiary, whereas oil expulsion occurred throughout Tertiary time.

Abstract Name: Arabian carbonate shelf Authors A. S. Alsharhan and A. E. M. Nairn Location: From 22° to 28° north latitude and 51 ° to 57° west longitude Geologic time interval: Early-Late Cretaceous, Barremian–Maastrichtian Tectonic-sedimentary setting: Passive margin changing to back arc basin Basin type: Epeiric shelf changing to foreland basin Paleoclimate: Generally tropical Platform type: Rimmed shelf changing to distally steepened ramp Platform geometry: At least 1700 m thick; more than 750 km wide and more than 1500 km long Facies and fossils: Fine- to coarse-grained carbonates, thin intervals of shale and sandstone; pelagic and benthic foraminifera, algae, molluscs, sponges, and corals Systems tracts: Transgressive and progradational highstand Stacking patterns: Buildups