The Kirkuk oil field is a 100-km long and 12-km wide anticline consisting of three domes and two saddles. It is located in the Zagros Simply Folded Zone (this term does not exclude thrusting, salt diapirs, or strike slip faults). The 1927 discovery (Baba Gurgur # 1) was located on the Baba Dome and produced from the Oligocene "Main limestone." Later drilling discovered two deeper payzones in the Cretaceous. The Paleogene shallow-marine carbonates represent a major change from the Cretaceous deep-sea (flysch) sediments of the Tethys Ocean to the purely continental sediments of the Neogene Fars Group. Majid and Veizer (AAPG Bulletin, July 1986) have described the sedimentology of the Paleogene carbonate payzones in the Kirkuk field. These rocks were deposited in near-shore (mudstone, wackstone, packstone and grainstone), fore-slope (packstone and grainstone) and basinal (mudstone and wackstone) environments. Porosity is both primary (inter-granular and inter-skeletal) and secondary (tectonic fractures and chemical dissolution). Porosity varies 4-36% and permeability ranges 50-1000 millidarcy.
The 140-feet oil gusher above the derrick of Baba Gurgur No. 1 well. On 14 October 1927 the Kirkuk oil field was discovered in Iraq. Photo: APOC
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