Abstract

With estimated reserves of ~5.5 billion bbls of oil and 30 trillion cubic feet (TCF) of gas, the Sultanate of Oman ranks among the smaller hydrocarbon producers in the Middle East. However, the petroleum systems associated with these hydrocarbon accumulations are some of the most fascinating in the world as they are dominated by Pre-Cambrian source rocks.

The Sultanate of Oman is located on the eastern margin of the Arabian plate and is bounded on the north by the Eurasian collision zone, on the east by a transform fault with the Indian plate, and on the south by the Gulf of Aden spreading center. This part of the Arabian plate experienced more frequent and intense tectonic deformation than the interior parts of the plate, which is recorded in its stratigraphy.

Pre-Cambrian source rocks form the main petroleum systems, while a Cretaceous petroleum system is of only minor importance in the northwest of the country. The classical petroleum systems of the Middle East, formed by Jurassic and Silurian source rocks, are not found to be active due to non-deposition/erosion.

Hydrocarbon reservoirs range in age from Pre-Cambrian to middle Cretaceous and encompass a wide range of lithologies, ranging from tropical carbonates, shallow marine, and continental siliciclastics to glacial meltwater deposits. The main oil reservoirs are middle Cretaceous carbonates and Permo-Carboniferous clastics, while the main gas accumulations are hosted by Cambro-Ordovician sandstones.

A crucial ingredient for the Pre-Cambrian petroleum system was the development of a number of salt basins at the Pre-Cambrian–Cambrian boundary. As the main source rocks are located within and below the salt package, the location of salt edges and windows had a major control on hydrocarbon migration. It has been suggested that most of the hydrocarbon generation from Pre-Cambrian source rocks occurred before present-day reservoirs and traps were formed. The km-thick salt layers within these basins may have trapped hydrocarbons until later tectonic tilting, salt movement, and dissolution allowed hydrocarbon migration to shallower levels. The salt was also a key ingredient for present-day trap formation, as many traps are related to salt pillows, diapirs, or dissolution.

A complex migration history, a wide range in lithology and age of reservoirs, and a strong structural overprint makes the exploration and development of hydrocarbons in the Sultanate of Oman a technically challenging but fascinating task.