The Dhahaban petroleum system of Oman

The Dhahaban petroleum system, from a source rock of Cambrian age, covers s ome 50,000 km(2) and contains 1.6 x 10(9) m(3) of oil and 1000 x 10(9) m(3) of gas in place of which at least, respectively, 0.35 x 10(9) m(3) and 700 x 10(9) m(3) are recoverable. For many years, the origin of the so-called Q oil was enigmatic and defied typing to a source rock. Integration of rece nt advances in geochemistry and basin modeling has now permitted us to retr ace its source areas, model the generation and migration histories, and out line the areal and stratigraphic extent of the petroleum system. The Q oil is interpreted to have been generated by toy-salt source rocks (D hahaban Formation) of the Precambrian-Cambrian Ara Group and is mainly trap ped in younger reservoirs of the Permian Gharif and Cretaceous Shu'aiba for mations. Gas and condensate occur in deeper Paleozoic Haima reservoirs. Rel ative oil migration distances estimated from geochemical tracer molecules ( benzocarbazoles), together with migration modeling, indicate that the Q oil is derived from two different locations: a small source area along the wes tern margin of the Ghaba salt basin and a large, shallower source in the Fa hud salt basin. Burial and thermal history reconstructions indicate the oil was generated in several stages during the Paleozoic-earliest Tertiary but mainly in the Mesozoic. Initially, oil from both kitchens migrated in a so utheasterly direction toward the tilted east flank. Modeling shows that mig ration routes from the Fahud salt basin gradually shifted westward, and Q c harge only reached into southern central Oman in the last 50 m.y. Temperatu re and salinity data suggest that besides buoyant forces, hydrodynamic flui d flow contributed to this long-distance Q oil migration. With oil generation during the Mesozoic and migration during the Tertiary, remigration from deeper breached or gas-charged Haima traps most likely occ urred. Resolving the timing of charge and actual migration geometry has ide ntified new oil and gas prospects along migration pathways to known accumul ations and on spill routes from these accumulations.