BASIN ANALYSIS AND PETROLEUM ASSESSMENT OF THE MIDDLE AND UPPER JURASSIC SUCCESSION NORTHERN IRAQ

Abstract

The Upper Jurassic succession of Northern Iraq was studied in order to analyze the basin development and to evaluate the possible source rocks for younger reservoirs. Petrographic, facies analysis, and environmental studies indicates a deposition of the Upper Jurassic succession within a ramp setting. The Najmah Formation was deposited within a restricted marine, shallow open marine, and shoal environments. The Naokelekan Formation on the other hand represents deposition within restricted secondary basins eastwards. The evaporitic Gotnia Formation was formed due to a major regression correlated with the evaporitic & restricted marine Barsarine facies to the east. The major sea level rise at the end of Upper Jurassic is represented by the deep marine and basinal Chia Gara facies. Five third order cycles were recognized, each consists of Transgressive & Highstand systems tracts, whereas the Lowstand systems tract was recognized in well Tk-3 only in the lower part of the Gotnia Formation. These cycles reflect successive episodes of Transgression & Stillstand of the relative sea level. The deviation of the relative, sea level curve from the global curve at the beginning and the end of the Upper Jurassic as well as the early Kemirdgian reflects the effect of local tectonic activities. Burial history analysis reflects a variation in basin geometry through the Upper Jurassic due to variations of local tectonic activities causing the development of several secondary basins with various subsidence rates reaching its maximum in Kirkuk, Sadam, and Demir Dagh structures. These rates were reduced towards the west reaching their minimum at Al - Jauf - Gaara - Mosul paleohigh. Three initial geothermal gradients were constructed for three depth intervals. The geochemical indices of the Sargelu, Naokelekan and Chia Gara Formation reflects their high potential source rocks as well as their thermal maturation. The quantity evaluation model showed a total of (91x109 bbl.) able to migrate for the whole studied succession providing oil to the overlying reservoir through multi - phase vertical migration as well as early lateral migration from Middle Cretaceous source rocks in Central & Eastern parts of the basin towards Iran.