Petroleum systems in the Middle East

Abstract

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).