تأثير الوضعية الجيولوجية للعصر الجوراسي المتأخر-الطباشيري المبكر لمنطقة ما بين نهري الزاب الأعلى و الأسفل على الإمكانية النفطية لمكمن تكوين نجمة - شمال العراق

Abstract EN

Form the existence or the ence of the Late Jurassic sequences that included the following formations, Gotnia, Najmah, Naokelekan, and Chia Gara and the Early Cretaceous sequence, which composed of (Makhul, Karimia, Zangura and Garagu) formations, in the area between the upper and lower Zab Rivers and its surroundings areas, affected by the Neocomian uplift and erosion, it become clear that the studied area have different stratigraphical sequences and different amount of the hiatus, which reflected unstable blocks movements of the incompatible blocks that took place at the end of the Jurassic and the beginning of the Cretaceous.

Had worked on the formation of half-Grabens, whose movement varied during these ages, which grew up different depositional environments had led to the emergence of the following and in light of it, the area has been divided into three Regions: The Southern area of the Lower Zab River: This area forming the western extension of the Permanent Basin, which lies to the eastern part of Iraq.

Its stratigraphic sequence contains one gap extending from the late Tithonian into Early of Berriasian, which represents the hiatus of the Makhul formation.

The area between the Upper and Lower Zab Rivers: This area characterized by the shallow marine environments in which the Najmah formation is one of the most important reservoir formations in the region and the Gulf region, were deposited.

The stratigraphical sequence of this region have wide hiatus, which included (Late Oxfordian, Kimmeridgian and Tithonian) stages from the Late Jurassic, and the Berriasian – Valanginian stages from the early Cretaceous period.

This region characterized by the major erosional unconformities, where the area exposed to the Vadoze Zone for a period of 14.4 million years, and the cap rocks eroded.

The area to the north of the Upper Zab River: This area forming the eastern extension of the positive area, which lies to the western part of Iraq.

Its stratigraphic sequence contains two gap, the first one was representing the hiatus of Najmah formation or its equivalent from the Oxfordian, and exposing of the Sargelu formation to surface for 5 million years.

While the Gotnia and the lower part of Chia Gara formation were found.

The second hiatus recorded as wide gap between the middle of the Tithonian and the beginning of the Albian.

Where the following formations (the upper part of the composition of Chia Gara, Makhul, Karimia, Zangura, Garagu, Ratawi and Shu'aiba) was not deposite.

This gap have approximately 32 million years, forming this region as high topographical area of Mosul-Khleisia Height in the Late Jurassic Early Cretaceous Boundary.

To determine the location of the faults and the extent of their impact, a comparison made between the subsurface sections of the upper regions to determine the sites of the faults and their impact as: • The Fault Z1 is determined by the location of the upper Zab River, Fault Z2, was represents the Lower Zab River and the Fault Z3, extending northwest southeast and is located between the well sites of Zab-1 and Quwer-2.

This fault fragmented of the inter Zab rivers area into two secondary blocks, the Western sub-block and a Eastern sub-block, where this was 500 meters lower than the first one and forming a good Structural trap.

The effect of those Normal faults (1Z, 2Z, 3Z), was perfectly limited on the Late Jurassic-Early Cretaceous boundary.

Which revealed that the reservoir unit (Najmah formation), was exposed to the surface and the cap rocks have been eroded by the Neocomian uplift, and lading to escape of the light hydrocarbon components while the heavy bituminous stained the lithofacies and plugged their porosity.