When Carbonate Platforms Emerge: Complicating Reservoir Heterogeneity in Natih Fm, Cretaceous, Oman
By
Peter W. Homewood1, Omar Al-Ja'Aidi2, Philippe Razin3, Anne M. Schwab4
(1) Sultan Qaboos University, Al-Khod, Oman (2) Petroleum Development Oman, Muscat, Oman (3) Bordeaux University, Bordeaux, France (4) Aberdeen University, Aberdeen, United Kingdom
The Natih formation comprises three major transgressive-regressive sequences (I-III). Higher frequency cycles, which may be correlated regionally over several hundreds of kilometers, are shown to provide best fits between stratigraphic subdivisions and reservoir flow units.
The Natih platform system emerged at the turnaround from sequence I to II, and at the top of the Natih. Complex heterogeneity developed from incisions within the upper 20 metres of the Natih E. Incision fills are made up of several genetic units, with a variety of dolomitised and carbonate facies composing smaller scale channel forms and infills or wider reaching marl-limestone cycles.
3D seismic
from North Oman shows complex channeling of the surface of the
Natih. Several hundred metres wide channels, fairly straight to slightly sinuous
in pattern but with significant depths, contrast with narrow, highly sinuous
channels showing meander loops and cutoffs. Natih E features, commonly ascribed
to pull-down artifacts from Natih A channels, have been assessed by
seismic
forward
modeling
.
The data from field exposures alone are not sufficient to allow
interpretation of channel patterns. However, the seismic
is not sufficiently
detailed to show the nature of the channel fills. The combination of
seismic
images with outcrop data, at the scale of facies and genetic units, allows
reconstruction of the heterogeneity that affects the upper 20m of the Natih E.
Understanding and predicting this heterogeneity will be crucial for the choice
of drive mechanisms (water flood or GOGD) in future EOR field development
planning.