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Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Potential Hydrocarbon Traps in the Detachment Folds of the Dohuk Region, Kurdistan, Northern Iraq
(1) Earth Sciences, Fault Dynamics Research Group, Egham, United Kingdom.
This paper presents a detailed picture of the petroleum systems that may occur within the detachment folds of the Dohuk region. This region is situated within the Zagros orogenic belt near the north-eastern boundary of Arabian Plate in the Kurdistan region of northern Iraq. The field data combined with remote sensing interpretations were used to define the structural characteristics of the detachment folds, to determine the 2D/3D geometries of the stratigraphic units within these folds; and to resolve the relationships between the detachment folds and their fault-fracture systems. The Dohuk region is characterized by WNW - ESE striking doubly plunging, upright symmetric to slightly asymmetric detachment folds that involve approximately 8 to 9 km of sedimentary section above the Late Precambrian basement.
Two petroleum systems may occur within the detachment folds of the Dohuk region. The fractured carbonate rocks of Late Cretaceous (Qamchuqa, Aqra - Bekhme and Shiranish formations) may locally form anticlinal traps in the detachment anticlines of the Dohuk region, such as the Tawake, Dohuk, Dahkan, Kiri Rabatki, Mangesh, Shaikhan, Shaikh Adi, Alqosh and Ain Sifni anticlines. In this major petroleum system, the impermeable shales and claystones of the Paleocene - Early Eocene Kolosh Formation probably act as effective seals preventing the vertical migration of oil and gas from the underlying Middle - Late Jurassic (Sargelu and Naokelekan formations) and Early Cretaceous (Chia Gara and Balambo formations) source rocks. The highly-fractured carbonates of Middle - Late Eocene (Avanah, Pila Spi and Jeribe formations) may also form anticlinal traps, particularly in deeply buried structures and slightly uplifted detachment anticlines, such as the Tawake anticline. The clastic sediments and evaporates of the Middle Miocene Lower Fars (Fatha) Formation probably provide significant caprocks for these traps. The mechanical failure of seals above the Late Cretaceous traps due to tectonic fracturing or reactivation of pre-existing faults possible allows upward migration of hydrocarbons from the underlying mature Mesozoic source rocks to the Middle - Late Eocene petroleum system. However, the reservoir rocks of both petroleum systems were removed from the crest of the uplifted-anticlines - e.g. Bekhair, Atrush, Khoshka, Gara and Amediya anticlines.