A New World Revealed With Amazing Detail: Using the Latest WAZ Seismic to Review Key Structural Elements of the Fahud Salt Basin, Oman

Abstract

Petroleum Development Oman (PDO)'s processing team continues to deliver new and better seismic products that allow the interpreters to "see" what was not "seen" before. Our objective is to take advantage of this new "view" of a subsurface of a mature basin, with thousands of wells and tens of hydrocarbon fields, and update the understanding of the structural and tectonic evolution tied to the latest surface maps, from the Oman Mountains to the West Field. Previous work provides powerful insights into the tectonostratigraphic evolution of Central North Oman. The seismic used back then predates any Wide Azimuth (WAZ) product. This work carries out detailed seismic interpretation of major events and faults, using a seismic montage of volumes in what is known as the "Megacell". The level of detail is superior and the removal of artifacts such as multiples is remarkable. We focus on certain areas such as the Maradi Fault Zone, and the West Field, within a regional context that includes areas without seismic coverage such as the Oman Mountains. A regional structural reconstruction was carried out with back-striping and decompaction to review the interpretation and challenge our understanding of the evolution of the basin. This work focuses on a regional understanding of the Fahud Salt Basin, salt tectonics and evolution, main bounding fault systems, mega-sequences, and how the tectonic history of the basin is linked to the surface geology and the Arabian Plate tectonic evolution. Remarkable seismic lines show how the footwall of the deformed Mesozoic, with tens of passively tilted normal faults, gets rotated towards the main regional thrust front that carries the obducted and emplaced Semail Ophiolite and the Hawasina sediments. We seismically analyzed the Maradi Fault Zone system and observed that the new seismic reveals details that could explain why some wells did not deliver as expected. To better understand the seismic observations, we carried one new regional reconstruction, that is restored but not balanced due to the "out of section" movements. This section is back-stripped and de-compacted allowing for a unique understanding of minor details of the basin evolution. The outcome of this work can be used for future re-assessment or tuning up of the history of hydrocarbon migration and emplacement in this very mature and prolific basin. We compare "old" and "new" and incorporate these learnings into our re-evaluation of some aspects of the tectonic evolution of the basin. The seismic images and the observations from this study are unique and a regional study of this scale hasn't been published before. The advances in geophysics and imaging allow the interpreters to better understand the evolution of the basin, potentially leading to new discoveries and re-evaluating of missed opportunities due to well misplacement in older seismic volumes. The basin is mature; therefore, we do not foresee large discoveries, but small opportunities abound.