SIKKEMA, WYTSE, and JEAN BORGOMANO, Petroleum Development Oman LLC, Muscat, Oman

ABSTRACT: Sequence Stratigraphy and Hydrocarbon Habitat of the Natih Formation in Oman

The Natih Formation is part of the Mesozoic platform carbonate succession deposited on the southeastern Arabian peninsula and one of the main hydrocarbon producing reservoirs in Oman. It is separated from the underlying carbonates of the Shuaiba Formation by the Nahr Umr Formation and is overlain by the Fiqa Formation, both acting as regional seals. The age of the Natih Formation is late Albian to early Turonian, and its deposition was terminated by early Turonian uplift. Various lithofacies are present in the Natih Formation.

The Natih Formation is cyclic, with a succession of coarsening-upward cycles of deeper marine shales and mudstones grading to shallow marine rudistid packstones and grainstones, each terminated by an emergence surface. The cyclicity is the result of eustatic sea level changes. Two deeper marine shales rich in planktonic foraminifera and organic material are intercalated within the sequence. The cycles have been used to subdivide the Natih into members labeled a to g.

A sequence stratigraphic model has been applied to the observed cyclicity, which helps to understand (1) the distribution of shallow marine grainstones (reservoir) and deeper marine shales and mudstones (seal, source rock), and (2) where the reservoir quality may have been enhanced by emergence and leaching. The model has been tested both on a regional scale and on a field scale, e.g., on seismic lines over the Sirat Prospect area in central north Oman and in the Marmul area of south Oman.

AAPG Search and Discovery Article #90990©1993 AAPG International Conference and Exhibition, The Hague, Netherlands, October 17-20, 1993.