Abstract

Qatar plays a key role in the understanding of the Phanerozoic petroleum geological history of the Arabian plate through the continuous influence of the Qatar high on the regional sedimentation patterns and deformation styles. This tectonic unit originated in the Late Pre-Cambrian, when it separated the hormuz salt, as a high, into an eastern and western basin. Ever since it has functioned as a stable area in between two differently behaving halokinetic regimes and has provided a relative high at various times in the Mesozoic. Notably, in the Jurassic and Cretaceous, it formed a shallow water carbonate platform between intra-shelf basins, which later became the focus for oil and gas migration.

Taking into account tectonic control, depositional systems, and climatic variations, the Phanerozoic history of Qatar can be subdivided into six tectono-sedimentary phases: 1) late Pre-Cambrian rifting with the development of the Qatar high surrounded by the hormuz Salt Basin; 2) Paleozoic clastic-dominated, mostly shallow marine sedimentation, interrupted by a phase of erosion and non-deposition representing the local equivalent of the Hercynian orogeny–Ice age-influenced sedimentation occurred during the Silurian and early Permian; 3) Late Permian–Triassic regional carbonate-evaporite shelf deposition; 4) Jurassic to Middle Cretaceous carbonate platforms and intra-shelf basins, controlled by local subsidence patterns, eustatic sea level fluctuations, and local siliciclastic influx; 5) latest Cretaceous to Middle Miocene Foreland Basin creation and infill by siliciclastics and carbonates; and 6) Middle Miocene to recent mostly non-deposition due to both uplift caused by the Neo-Tethys closure with continued foreland basin development and glacio-eustatic sea level lows.

Three known petroleum systems developed within this geological setting: the Paleozoic Khuff–Qusaibah system, the Mesozoic Arab-Hanifa, and the Middle Cretaceous–Hanifa systems. The crest of the Qatar high hosts both the Khuff gas reservoirs of North field, sourced by Silurian Qusaibah shales, and the stacked Middle Cretaceous oil reservoirs of the Al Shaheen field, sourced by the Jurassic hanifa shales. The Jurassic oil reservoirs of the Dukhan field are located on the northern flank of the high, whereas smaller occurrences are present in Jurassic and Cretaceous strata of salt dome structures in the Rub Al Khali Basin in the east. Oil for these was sourced from the underlying Jurassic organic-rich intra-shelf basinal deposits of the hanifa and Jubailah Formations, which matured in the oil kitchens adjacent to the Qatar high.