The Natih Petroleum System of North Oman

Abstract

ABSTRACT The Cretaceous Natih petroleum system is one of the smaller petroleum systems in Oman, measuring only some 20,000 square kilometers in areal extent. Resource volumes of oil initially in-place, however, are significant and amount to 1.3x109 cubic meters (equivalent to 8.2 billion barrels). Most of the recoverable oil is concentrated in two giant fields that were discovered in the early 1960s. Since that prolific time no new major discoveries have been made, except some marginally economic accumulations in the early 1980s. To evaluate the remaining hydrocarbon potential of the system, the oil kitchen was mapped and its generation and migration histories modeled and integrated with the regional setting to outline the geographical and stratigraphical extent of the petroleum system. The volume of liquid hydrocarbons generated by Natih source rocks was calculated and compared to the estimated oil-in-place to determine the generation-trapping efficiency of the petroleum system. Some 100x109 cubic meters of source rock is currently mature and produced a cumulative volume of 14x109 cubic meters (88 billion barrels) oil. Of this volume 9% has actually been discovered and 0.25x109 cubic meters (1.57 billion barrels) are currently booked as recoverable reserves, equivalent to 1.8% of the total generated volume. Both percentages classify the Natih petroleum system as the most efficient system in Oman. This extreme efficiency results from several factors, such as: (1) modest structural deformation in the foreland basin, which permits lateral migration to remain the dominant style; (2) abundant and uninterrupted access to oil charge from an active kitchen in the foreland basin; and (3) excellent intra-formational source rocks, which is retained by thick Fiqa shales. Most structural prospects have been tested in four decades of exploration. The remaining hydrocarbon potential is anticipated to exist mainly in stratigraphic traps in Fiqa turbidites in the foreland basin, and truncation traps across the northern flank of the peripheral bulge.