الملخص الإنجليزي
Anzauz field is one of the major oil field in central Oman area. It is dissected by a graben fault system which developed over a release bend of a strike-slip fault system that probably was enlarged by the movement of the underlying salt. This graben separates the NE and SW accumulations. Previously, poor seismic imaging in central Oman obstructed further exploration of this prominent and undiscovered area. In 2017, new 3D seismic data was acquired across the Central Oman area, resulting in further studies in tectonostratigraphic evolution of the area. This study, tectonostratigraphic evolution of Anzauz field and it is surrounding area in Central Oman, mainly focused on the tectonic/structure and stratigraphic evolution of Anzauz field from Neoproterozoic to Cenozoic times utilizing the new 3D seismic data, well data, satellite images and geological maps.
The Anzauz field is interpreted to be formed above a deep-seated older (Neoproterozoic- Early Cambrian) fault system, strike in NW-SE direction. Older tectonic events seem to play key roles in the evolution of the Pre-Cambrian Nafun Group, which in turn influenced the subsequent deposition of the Ara Group. Mapping of the key horizons in the study area showed that the long-lived basin highs controlled greatly the position of the basin fill, including the salt deposition and thinning and thickening of the overlying stratigraphy. For example, Nimr Group (Cambrian) is thicker to the west of Anzauz high and is overlained by the Angudan unconformity. The studied area also highlighted some key challenges in the understanding of pre-Salt rocks and Haima Supergroup, including the presence of huge and clear reverse faults above Nafun Group, the growth packages within Miqrat Formation and the thickness variation within Haima formations especially above Anzauz and Suwaihat highs.
Salt movement might be the reason of this thickness variation but tectonics can not be ruled-out. During post Miqrat deposition, an extensional stress was dominating, forming pull- apart basin. Locally, Safiq Group was truncated by base Ghudun unconformity which indicates the activity of Anzauz during Ordovician time. The lack of seismic contrasts between the clastic reflectors and the absence of clear bio-stratigraphic markers within Haima and Nimr packages remain the main challenges. During post-Haima deposition, the basin fill showed a quiescent stage characteristic (no clear thickness variations), which was later truncated by base Jurassic regional unconformity affecting the Triassic and Jurassic sections. Finally, the Alpine-1 and -2 tectonic events have affected the Anzauz area, resulting in re-activation of some of the pre-existing faults.
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Overall, the Anzauz structure is interpreted as a salt-cored structure formed above a salt body and has been subjected to many phases of re-activations throughout geological times. Knowing the stages of deformations can help in exploring the full Prospectivity of Anzauz structure.
