GSJ: Volume 8, Issue 4, April 2020 213 ISSN 2320-9186 GSJ: Volume 8, Issue 4, April 2020, Online: ISSN 2320-9186 www.globalscientificjournal.com 1. Introduction: Mosul high. The source rocks are mid The most important petroleum systems mature to late mature within the western in Iraq are the Jurassic, Cretaceous, and Mesopotamian zone and within the gas Tertiary Petroleum systems. The window in the eastern Mesopotamian Paleozoic petroleum system is important zone. In the foothill zone, the maturity in the Rutba-Jezira zone of west Iraq. increases from early mature in the SW to The known extent of the Triassic mid-mature in the east. In the high petroleum system is confined to a small folded zone, the Jurassic source is within area in Kurdistan (north Iraq) (extending the late maturity window. (Jassim and into part of north east Syria and south Al-Gailani) east Turkey). The sargelu formation contains oil in The petroleum systems are discussed in fractures in some structures in N Iraq term of their source rock richness, and in the Salman zone. The oil trapped maturation, time of maturation and in the Sargelu formation is often heavy migration, reservoirs, cap rocks and the and bituminous, because of the low possible traps that might be associated maturity of this source rock in this area with them. and the lack of a seal where the evaporites of the Gotnia formation are Middle Jurassic source rocks are very absent, allowing escape of the oil to the important source rocks throughout S, shallower Tertiary reservoirs and to the NE, and N Iraq, due to the high TOC of surface. The Sargelu reservoir contains the Sargelu and Naokelekan formations oil with a wide range of oil gravities that where deposited throughout the (13.3-42oAPI) and sulphur contents Jurassic basin, it was concluded that the (1.8-2.5%). (Jassim and Al-Gailani). most of the oil of Iraq was sourced from Jurassic source rocks. The Sargelu formation is upto 400m 2. Kurdistan Jurassic thick, with a TOC content of 1.7-7.6% Formations: wt%; the lower most 40m of the formation has the highest TOC content. Five districts in The Sargelu and Naokelekan formations Kurdistan (Northern Iraq) have in the Kirkuk embayment entered the oil been chosen to be representing window at the end of the Eocene (35 the Jurassic depositional basin, MY) and are presently in the condensate Koi Sanjak, Surdash and Sirwan- and gas generating maturation levels. Balambo districts consists of same formation as in Amadia. The calculated maturity of the Sargelu The oil rich formations in Kirkuk sourcerock indicates that it is mostly oil fields known as Kirkuk group immature to early mature within the (first pay layers), which1 is | P a g e Salman zone and early mature on the belongs to the Oligocene. Kirkuk GSJ© 2020 www.globalscientificjournal.com GSJ: Volume 8, Issue 4, April 2020 ISSN 2320-9186 214 group forms sequence of reef controlled sediments, in which three separate cycles can be distinguished, table 2. The 3. Petroleum system second payment layers thought to be from formations belong to the elements and processes: Jurassic. Accordingly, districts Petroleum system elements: north of Kirkuk to Amadia district may contain I. Source rock undiscovered oil-reservoirs. II. Reservoir rock III. Seal rock Figure (1) Shows description of Jurassic IV. Over burden rock Formations in Kurdistan (northern Iraq), (after M.mustafa). Petroleum system processes: Trap formation Generation, migration, accumulation of hydrocarbons Source rock: A rock rich in organic matter which, if heated sufficiently, will generate oil or gas. Typical source rocks, usually shales or limestones, contain about 1% organic matter and at least 0.5% total organic carbon (TOC), although a rich source rock might have as much as 10% organic matter. Rocks of marine origin tend to be oil-prone, whereas terrestrial source rocks (such as coal) tend to be gas-prone. Preservation of organic matter without degradation is critical to creating a good source rock, and necessary for a complete petroleum system. Reservoir rock: a subsurface body of rock having sufficient porosity and permeability to store and transmit fluids. Sedimentary rocks are the most common reservoir rocks because they have more porosity than most igneous and 2 | P a g e GSJ© 2020 www.globalscientificjournal.com GSJ: Volume 8, Issue 4, April 2020 ISSN 2320-9186 215 metamorphic rocks and form under (Mousl and Qaiyarah) and four centers temperature conditions at which of native sulphur deposits, related to oil hydrocarbons can be preserved. A seepage in the Fatha formation and the reservoir is a critical component of a reduction of its Suphate (gypsam and complete petroleum system. anhydrite) beds. It is estimated that one billion tons of possible sulphur reserves formed in the four mineralization centers 4- Hydrocarbon seepages: in north Iraq requiring a feedstock of about 5-10 billion barrels of oil for their Hydrocarbon seepages and seepage- formation. related features occur in two main belts. The Abu Jir seepage zone is situated on One belt is located along the western the norh-south trending Abu Jir fault, boundary of the Mesopotamian zone straddling the Abu Jir basement high. It (Euphrates boundary fault), often at is dominated by large bitumen seepages intersection with transversal faults; it forming crater lakes more than 2km extends further north along the Abu Jir wide or small conduits; the most famous Fault and along the Tigris river in north of which are at Abu Jir, Ain Jabha, Ain Iraq. The location of these seepages is Hit and Ata_it. Thick bitumen beds are clearly tectonically controlled but it is interbedded with the marls and also apparently related to the western carbonates of the Fatha formation. limit of the upper Jurassic Gotnia Travertine sfinters of Miocene age are anhydrite cap rock. The two important common to the south and north of Hit areas of seeps are the Tigris in north Iraq town. Saliferous water springs occur and the Abu Jir Fault in west central along this fault zone especially near Iraq. Shithatha. Seepage activity clearly began The other belt of seepages is related to in the middle Miocene. A substantial some along anticlinal structures in the volume of oil has probably been lost in foothill zone, for example the Kirkuk, this seepage belt. Much of the oil Gilabat, and Hemrin anticlines in the expelled from Jurassic and lower Kirkuk embayment. These anticlines cretaceous source rocks in the area to the have a detachment level at the base of east may have been dissipated along this the Fatha formation. The (eternal fires) line of seeps. of Kirkuk structure and the numerous Sulphur deposits occur locally in some bitumen seepages and fused rocks large karsts in the southern desert (Ain produced by gas combustion in Hemrin Kibritia) and are probably related to the south structure are prominent seepage sulphate reduction of the lower Eocene phenomena. evaporites of the Rus formation possibly Seepage activity along the Tigris in the in the presence of hydrocarbons which Mosul area includes bitumen seepages had migrated through faults from deeper 3 | P a g e GSJ© 2020 www.globalscientificjournal.com GSJ: Volume 8, Issue 4, April 2020 ISSN 2320-9186 216 (probably Jurassic or older) source majority of oil generated from Jurassic rocks. source rocks. The oil generation potential of Jurassic source-rocks was modeled using kinetics for Type II-S kerogen. Fluid-flow and thermal parameters used in the model were calibrated with reservoir pressure and temperature data. Calculated present-day geothermal gradients vary locally averaging 22 C/km in the basin and 25 C/km in the fold belt. These modeled gradients match measured gradients assuming a present day heat flux of 43 and 48 mW/m2, respectively. Calculated vitrinite reflectance profiles are in agreement with measured Ro values, indicating that heat flow has been relatively uniform since the Cretaceous. Peak oil generation and expulsion Figure (2) Shows oil springs (seepage) in occurred during Oligocene time in the Twek village, photo Sanist, geological basin and during the late Miocene in the society of Kurdistan. fold belt. Hydrocarbon flow-path simulations show that structural traps in 5- Characterization of the close proximity to modeled migration Jurassic Petroleum System pathways that diverged from (local) of Iraq generally, and intra-platform basins were filled earliest. Prediction of Petroleum Other structures were charged later as Migration Pathways: flow pathways focused toward these features. The location of undrilled Multiphase-flow modeling of the structures in relation to predicted Jurassic Petroleum System in Iraq migration pathways should be provides an integrated analysis of the considered when evaluating these stratigraphic, thermal maturation, and structures for their hydrocarbon hydrocarbon migration histories of the potential. It follows that structures close Zagros basin and Zagros fold belt. The to modeled migration paths have lower model incorporates the essential exploration risk than those structures geologic elements and processes more distant from fluid-flow required for the accumulation of pathways.(Douglas et, al). petroleum in the region. Upper Mesozoic and Cenozoic reservoirs host the 4 | P a g e GSJ© 2020 www.globalscientificjournal.com GSJ: Volume 8, Issue 4, April 2020 ISSN 2320-9186 217 6- An example on reservoir rocks in Iraq (Kirkuk group The Kirkuk group is a reservoir unit in -Oligocene epoch): the Khurmala, Avanah, and Baba domes The Kirkuk group is represented by a of the Kirkuk structure, and in the complex of backreef/reef/forereef and Judaida, Khabaz, Bai Hassan, Ajeel and basinal units. In many fields the whole Hemrin fields in N iraq. In S Iraq it is a of the Oligocene Kirkuk group and the reservoir in the Jabal Fauqi, Halfaia, and overlying Euphrates and Jeribe Buzurgan fields.