Petrographic study of the Sinjar and Khurmala Formations at the Zagros and Taurus Folded Zones, in northern Iraq led to the recognition of 11 carbonate microfacies that can be grouped into seven facies associations. These facies associations deposited within outer shelf, fore-reef, reef, back-reef, lagoon, shoals/bars and channels, and tempestite subenvironments of a composite isolated carbonate platform. The digenetic imprints on the recognized microfacies are prominent and dominated by micritization, dissolution, cementation, neomorphism, dolomitization, compaction, stylolitization, and precipitation of some authigenic minerals such as pyrite, glauconite, and gypsum. Isopach and depositional facies maps of the Sinjar-Khurmala successions show three depocenters in two subbasins in the study area, two of them are elongated and coincide with the Zagroside and the Taurides trends, whereas the third accords with the trend of the Sinjar graben. The reconstruction of the history of the Sinjar and Khurmala carbonates revealed four stages of basin development within two subbasins. The first stage represents the initial deposition of the Sinjar and Khurmala Formations that was preceded by the deposition of the deep marine part of the underlying Kolosh Formation. This depositional phase is characterized by submarine fans and basinal sediments. Both subbasins were partially separated by a ridge or a series of paleohighs, which had been inherited from relieves of the Cretaceous paleosurface. During the second depositional stage, the Sinjar basin is developed by growth of another reef build-up to the southeast with a general direction from southwest near Kirkuk area to the northeast near Sulamani area. During the third depositional stage, the basin was developed through the growth of isolated carbonate platform extending from the Kirkuk to the Duhok. Such platform was drowned during the transgression that covered the northern part of the Kolosh basin and southwestern part of the Aaliji basin. The final depositional stage was represented by a still stand period, when the sea level was stilled, and led to the upgrading growth during the early Highstand system tract of the carbonate shelf . As a result, during this stage, the reef facies were prograded seaward and replaced by the back-reef facies to indicate the end of Highstand during the late regression stage.

The Paleocene-Early Eocene sequence is represented by Aliji and Umm Er Radhuma formations, while the Middle-Late Eocene sequence is represented by Jaddala and Dammam formations. The Rus Formation has been described and its basin was analyzed separately because it was deposited during the regression period (Middle Eocene), which is a transitional period between these two cycles.   This study includes analysis of the geohistory of this succession,  interpretation of the changes of the accumulation, and calculation of subsidence rates. The results were compared with the space available to explain the basin development. The study site included the boreholes of Garraf-84 and 92, Halfaya-1, Nasirya-13 and 40, and Noor-5 at the Mesopotamian Block, in addition to the  Ratawi-8, Tuba-15, Rumaila-217, Zubair-45, and West Qurna-60 at the Basra Block.      The Aliji basin was characterized by the decrease in accommodation values to the northeast direction and the increase in all the other parts of the study area. A comparison of the setting of this basin with the Umm Er Radhuma basin gives a clear evidence of the tectonic impact coming from the northeast. During the Middle Eocene stage, we notice that the basin was affected by comprehensive uplifting processes. This led to the generation of a very shallow basin (Rus basin) with the exposure of the northern part of the basin during the regression stage.      The Middle-Late Eocene basin is represented by a transgression stage with high subsidence, where the sea level had been raised and covered the northeastern and eastern parts of the studied area by deep sea deposits (Jaddala Formation). While the other parts of the study area were characterized by shallow sediments of Dammam Formation. This period ended with a clear tectonic uplift occurring in the northeastern parts and decreasing towards the southwest. This confirms the reactivation of the tectonic action from the northeast, represented by the continental collision. All these sources of evidence indicate that the study area is divided into a northern part and a southern part. Both of these parts are separated by a major tectonic lineament extending from the West Qurna oil field to the Nasiriya oil field, which confirms the presence of the tectonic boundary between the Mesopotamian block and the Basra block. In addition, there exists a secondary tectonic boundary that divides the Mesopotamian block into two parts, the first is to the east and the other is to the west. The results showed that the eastern side was most affected by the collision of the Iranian Plate with the Arabian Plate, which led to its uplift, while the western side was less affected by this tectonics evidence.

The Barremian succession in the present study is represented by the Zubair Formation which the most significant sandstone reservoir in Iraq.The area of study is located in the Southern part of Iraq at the Luhaisand Rachi oil fields, within the Mesopotamian basin. The thickness of the Zubair Formation is about 450 m in the studied area. It is divided into three lithofacies:-The upper unit is composed mostly of shale layers, the middle unit is consists of thick layers of sandstone rocks and the lower ones is consists mainly of Shale with less sandstone layers. These units are characterized by three types of petrophysical features according to total porosity/effective porosity: -High-moderate effective porosity rocks (type I), moderate effective porosity rocks (type II) and low-non pores rocks (type III). The upper unit of theZubair Formation at the Luhais oil field is characterized by two horizons. The first is showing high resistivity-high gamma ray which represents the upper part; while the lower ones is shown low resistivity-low gamma ray. There are two good reservoir horizones with high oil saturation (low water saturation) in this unit at the Rachi oil field and Lu-3 borehole, while at the Lu-12 is appeared as one uncontaneoushorizon. The middle is characterized by two subzones in the southwestern part of Luhais oil field . The upper one characterized by high-moderate effective porosity while the lower one characterized by moderate effective porosity because of presence a low volume of shale. This unit is dominated by low resistivity-low gamma ray with three susbended bands of high resistivity-low gamma ray, these appeared in both studied oil fields. The high percentage of water saturation in this unit caused the lack of clarity of the oil saturation, which appears in narrow bands The lower unit is represented the shaledominated member of Zubair Formation, with low to non-pores rocks. This appeared in all studied wells. There are limit presences for the high-moderate effective porosity of rock within the sand bands lithofacies appears in these wells. This unit is characterized by alternative the high resistivity-high gamma ray horizon with the low resistivity-low gamma ray horizon as four cycles. There are two good reservoir horizons with high oil saturation (low water saturation) in this unit with a distribution similar to that found in the upper part. From the reservoir geology which represent by property modelling, preparing data, construction of threedimension clump and scale up for the studied oil fields. The Rachi oil field is appeared the better hydrocarbon saturation compared to Luhais oil field, although the Luhais oil field is the best of pertophysicalproperties. This indicates that the Rachi oil field was affected by the structural position as indicated by the model, while the model did not show any structural properties in the field of Lahis. Therefore, the structural and/or stratigraphic positions have the greatest influence on the hydrocarbon accumulation, regardless of petrophysical properties.

Abstract-

The Hartha Formation is one of the important formations deposited during Late Campanian age. The present study deals with four boreholes (EB-53, 54, 55 and 56) within the East Baghdad oil field to diagnoses the microfacies and interpret the depositional environments. Six major microfacies were recognized in the succession of the Hartha Formation. Their characteristic grain types and depositional texture enabled the recognition of paleoenvironment. There are Orbitoides  wackestone-packstone , Orbitoides - miliolid wackestone, Peloidal and Pellets - echinoderm wackestone to packstone, Peloidal wackestone to packstone, Pelletal wackestone to packstone, and Planktonic foraminifera wackestone-packstone. Four associations’ facies were recognized in this succession, which are shallow open marine, deep open marine, semi-resricted, and restricted. The distribution of these associations led to the recognition of three major depositional stages in the studied succession. The first stage is represented by the semi-restricted facies within the lower part of the Hartha Formation, which is characterized by Orbitoides - miliolid wackestone to the northwest direction and developed to shallow open marine and deep marine to the southeast direction. In the second stage, the sea level was rising to deposit the deep open marine facies represented by planktonic foraminifera wackestone-packstone microfacies above the semi-restricted facies ,where the succession became characterized by Peloidal and Pellets - echinoderm wackestone to packstone microfacies of restricted association. The third stage is represented by the continuation of sea level rise. This caused the building of carbonate ramp of Shiranish Formation above the shallow open marine of Hartha Formation with conformable surface.