--> 3-D Architecture Model of a Lower Cretaceous Carbonate Reservoir, Al Huwaisah Field, Sultanate of Oman, by V. C. Vahrenkamp and J. Grotsch; #90986 (1994).

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Abstract: 3-D Architecture Model of a Lower Cretaceous Carbonate Reservoir, Al Huwaisah Field, Sultanate of Oman

Volker C. Vahrenkamp, Jurgen Grotsch

The Al Huwaisah field in Northern Oman produces from the rudist bearing Aptian Shuaiba Formation for more than 20 years under strong water drive. Although the pool is considered a single accumulation, oil saturations and productivity are highly dependent on facies, with the best productivity in rudist facies and associated grainstones, and the poorest in lagoonal facies. infill wells suggested an uneven sweep and the possibility of significant oil being left behind in parts of the reservoir. Previous models consisted of traditional horizon maps and cross sections, which do not provide a quantified grip on volumes and location of such oil, nor guidance on where to drill future wells. This prompted the construction of a truly 3-D numerical (MONARCH) model describing the distribution of acies and reservoir properties in space.

The MONARCH model is based on six time layers, depicting the establishment of various rudist patch reefs on the pre-existing carbonate shelf carbonates, and the gradual development of a barrier separating lagoonal and back-reef from more open marine facies. The model includes correlatable and non-correlatable units. From cores and logs, eight lithofacies were described and their reservoir properties (porosity, permeability and capillary pressure) defined. This allowed a structurally constrained facies model to be translated into a hydrocarbon saturation model at virgin conditions. The resulting model allows 3-D visualization of the complex saturation distribution, assessment of volumetrics, and optimization of well planning.

The 3-D model is only as good as the data used to construct it. Model improvement requires more and better-quality subsurface data, particularly integrated core, log and production data. In addition, outcrop data is essential to provide guidance on correlation, geometries and dimensions of flow units.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994