Reservoirs, seals, and trap styles
     Porous (30-40 percent) carbonates of the Natih A, C, D, and E intervals constitute the reservoirs for oils generated by Natih source rocks. Lithoclast and skeletal grainstone aprons (shoals) and rudist packstone bioherms, where fresh-water leaching has enhanced porosities, comprise many of the Natih reservoirs (Harris and Frost, 1984). In contrast, Natih field itself produces from heavily fractured, low permeability (0.5 to 10 md), chalky limestones (Whyte, 1995; Terken, 1998). Individual Natih reservoirs are sealed by the intra-formational marls and shales; a thick shale sequence of the overlying Fiqa Formation (fig. 5) forms a major regional seal for the Natih Formation. Natih oils are also found in the Shu'aiba Formation in fault-dip structures of Natih and Fahud fields. Natih oils in these fields are explained by juxtaposition against marginally mature Natih source rocks (Terken, 1998; in press). Future exploration may focus on potential reservoirs within the overlying Fiqa Formation where possible turbidite strati- graphic traps and truncation traps below Lower Fiqa shales have been recognized (Lake, 1996; Terken, 1998). 

     Most traps are structural and related to development of the foreland basin during the Late Cretaceous/Tertiary. These structures formed during two major stages of tectonics that built the Oman Mountains. Obuction and deformation during the first alpine event produced normal and strike-slip faults while the second alpine event resulted in reactivation and inversion of earlier faults near the thrust front, most of which were enhanced by halokinesis during these events (Loosvelt, 1996; Terken, 1998; in press). 

Burial history, generation, and migration
     The burial and thermal history of Natih source rocks has been discussed by Harris and Frost (1984), Terken (1998; in press) and, to a lesser degree, by Visser (1991).  Additional data, information, and diagrams on thermal maturity, as confidential reports 

     The Natih `kitchen' is defined where the extent of the organic-rich facies is present in the deepest parts of the foreland basin. The pod of active source rock was originally assigned using a series of burial history diagrams and approximated at the 2,000-meter-depth structure contour of the Natih Formation; however, subsequent modifications were made after later reports and communications with J.M.J. Terken (1998, Petroleum Development Oman). Terken (1998, in press) describes a shallower extension of active source rock of lesser thermal maturity to the east of the Fahud and Natih faults and along the Maradi Fault zone (fig. 1) which is an area of high (up to 28 °C/km) geothermal gradient. 

     The thickness of the massive Fiqa shale seal and modest folding and thrusting of the Oman Mountains forced lateral migration of Natih oils. Modeling of the Natih by Terken (1998, in press) shows that migration was initially towards the foreland bulge and Ghaba Salt Basin but was interrupted by the formation of the Fahud fault during early development of the foreland basin. The fault thus created a shadow zone preventing migration of Natih oils to reach the foreland bulge and into Yibal and Al Huwaisah fields (fig. 2). The Natih structure, however, formed during the second alpine event and subsequently deflected the hydrocarbon charge from the Fahud field. The high integrity of the massive Fiqa top seal has allowed hydrocarbons to be retained in these shallow, large-throw fault-dip structures. Only minor gas has been generated from this highly oil-prone source with some gas migration towards the Lekhwair area and Maradi Fault zone (Terken, 1998, in press). 

Natih-Fiqa Structural/Stratigraphic Assessment Unit (20160201)
     One all-inclusive assessment unit, designated as the Natih-Fiqa Structural/Stratigraphic Assessment Unit, has been assigned to the Middle Cretaceous Natih(!) TPS of the Fahud Salt Basin Province. The assessment unit boundary is defined and described by the Total Petroleum System boundary and includes all known fields and wells that produce oils, or have oil shows, that have been identified geochemically as Natih sourced (fig. 16, table 2). Thus, the Natih-Fiqa Structural/Stratigraphic assess- ment unit